Gut microbiota of healthy Canadian infants: profiles by mode of delivery and infant diet at 4 months

Background:

The gut microbiota is essential to human health throughout life, yet the acquisition and development of this microbial community during infancy remains poorly understood. Meanwhile, there is increasing concern over rising rates of cesarean delivery and insufficient exclusive breastfeeding of infants in developed countries. In this article, we characterize the gut microbiota of healthy Canadian infants and describe the influence of cesarean delivery and formula feeding.

Methods:

We included a subset of 24 term infants from the Canadian Healthy Infant Longitudinal Development (CHILD) birth cohort. Mode of delivery was obtained from medical records, and mothers were asked to report on infant diet and medication use. Fecal samples were collected at 4 months of age, and we characterized the microbiota composition using high-throughput DNA sequencing.

Results:

We observed high variability in the profiles of fecal microbiota among the infants. The profiles were generally dominated by Actinobacteria (mainly the genus Bifidobacterium) and Firmicutes (with diverse representation from numerous genera). Compared with breastfed infants, formula-fed infants had increased richness of species, with overrepresentation of Clostridium difficile. Escherichia–Shigella and Bacteroides species were underrepresented in infants born by cesarean delivery. Infants born by elective cesarean delivery had particularly low bacterial richness and diversity.

Interpretation:

These findings advance our understanding of the gut microbiota in healthy infants. They also provide new evidence for the effects of delivery mode and infant diet as determinants of this essential microbial community in early life.The human body harbours trillions of microbes, known collectively as the “human microbiome.” By far the highest density of commensal bacteria is found in the digestive tract, where resident microbes outnumber host cells by at least 10 to 1. Gut bacteria play a fundamental role in human health by promoting intestinal homeostasis, stimulating development of the immune system, providing protection against pathogens, and contributing to the processing of nutrients and harvesting of energy.^1,2 The disruption of the gut microbiota has been linked to an increasing number of diseases, including inflammatory bowel disease, necrotizing enterocolitis, diabetes, obesity, cancer, allergies and asthma.¹ Despite this evidence and a growing appreciation for the integral role of the gut microbiota in lifelong health, relatively little is known about the acquisition and development of this complex microbial community during infancy.³Two of the best-studied determinants of the gut microbiota during infancy are mode of delivery and exposure to breast milk.^4,5 Cesarean delivery perturbs normal colonization of the infant gut by preventing exposure to maternal microbes, whereas breastfeeding promotes a “healthy” gut microbiota by providing selective metabolic substrates for beneficial bacteria.^3,5 Despite recommendations from the World Health Organization,⁶ the rate of cesarean delivery has continued to rise in developed countries and rates of breastfeeding decrease substantially within the first few months of life.^7,8 In Canada, more than 1 in 4 newborns are born by cesarean delivery, and less than 15% of infants are exclusively breastfed for the recommended duration of 6 months.^9,10 In some parts of the world, elective cesarean deliveries are performed by maternal request, often because of apprehension about pain during childbirth, and sometimes for patient–physician convenience.¹¹The potential long-term consequences of decisions regarding mode of delivery and infant diet are not to be underestimated. Infants born by cesarean delivery are at increased risk of asthma, obesity and type 1 diabetes,¹² whereas breastfeeding is variably protective against these and other disorders.¹³ These long-term health consequences may be partially attributable to disruption of the gut microbiota.^12,14Historically, the gut microbiota has been studied with the use of culture-based methodologies to examine individual organisms. However, up to 80% of intestinal microbes cannot be grown in culture.^3,15 New technology using culture-independent DNA sequencing enables comprehensive detection of intestinal microbes and permits simultaneous characterization of entire microbial communities. Multinational consortia have been established to characterize the “normal” adult microbiome using these exciting new methods;¹⁶ however, these methods have been underused in infant studies. Because early colonization may have long-lasting effects on health, infant studies are vital.^3,4 Among the few studies of infant gut microbiota using DNA sequencing, most were conducted in restricted populations, such as infants delivered vaginally,¹⁷ infants born by cesarean delivery who were formula-fed¹⁸ or preterm infants with necrotizing enterocolitis.¹⁹Thus, the gut microbiota is essential to human health, yet the acquisition and development of this microbial community during infancy remains poorly understood.³ In the current study, we address this gap in knowledge using new sequencing technology and detailed exposure assessments²⁰ of healthy Canadian infants selected from a national birth cohort to provide representative, comprehensive profiles of gut microbiota according to mode of delivery and infant diet.     

Listening to public concerns about human life extension

The public view of life-extension technologies is more nuanced than expected and researchers must engage in discussions if they hope to promote awareness and acceptanceThere is increasing research and commercial interest in the development of novel interventions that might be able to extend human life expectancy by decelerating the ageing process. In this context, there is unabated interest in the life-extending effects of caloric restriction in mammals, and there are great hopes for drugs that could slow human ageing by mimicking its effects (Fontana et al, 2010). The multinational pharmaceutical company GlaxoSmithKline, for example, acquired Sirtris Pharmaceuticals in 2008, ostensibly for their portfolio of drugs targeting ‘diseases of ageing''. More recently, the immunosuppressant drug rapamycin has been shown to extend maximum lifespan in mice (Harrison et al, 2009). Such findings have stoked the kind of enthusiasm that has become common in media reports of life-extension and anti-ageing research, with claims that rapamycin might be “the cure for all that ails” (Hasty, 2009), or that it is an “anti-aging drug [that] could be used today” (Blagosklonny, 2007).Given the academic, commercial and media interest in prolonging human lifespan—a centuries-old dream of humanity—it is interesting to gauge what the public thinks about the possibility of living longer, healthier lives, and to ask whether they would be willing to buy and use drugs that slow the ageing process. Surveys that have addressed these questions, have given some rather surprising results, contrary to the expectations of many researchers in the field. They have also highlighted that although human life extension (HLE) and ageing are topics with enormous implications for society and individuals, scientists have not communicated efficiently with the public about their research and its possible applications.Given the academic, commercial and media interest in prolonging human lifespan […] it is interesting to gauge what the public thinks about the possibility of living longer, healthier lives…Proponents and opponents of HLE often assume that public attitudes towards ageing interventions will be strongly for or against, but until now, there has been little empirical evidence with which to test these assumptions (Lucke & Hall, 2005). We recently surveyed members of the public in Australia and found a variety of opinions, including some ambivalence towards the development and use of drugs that could slow ageing and increase lifespan. Our findings suggest that many members of the public anticipate both positive and negative outcomes from this work (Partridge 2009a, b, 2010; Underwood et al, 2009).In a community survey of public attitudes towards HLE we found that around two-thirds of a sample of 605 Australian adults supported research with the potential to increase the maximum human lifespan by slowing ageing (Partridge et al, 2010). However, only one-third expressed an interest in using an anti-ageing pill if it were developed. Half of the respondents were not interested in personally using such a pill and around one in ten were undecided.Some proponents of HLE anticipate their research being impeded by strong public antipathy (Miller, 2002, 2009). Richard Miller has claimed that opposition to the development of anti-ageing interventions often exists because of an “irrational public predisposition” to think that increased lifespans will only lead to elongation of infirmity. He has called this “gerontologiphobia”—a shared feeling among laypeople that while research to cure age-related diseases such as dementia is laudable, research that aims to intervene in ageing is a “public menace” (Miller, 2002).We found broad support for the amelioration of age-related diseases and for technologies that might preserve quality of life, but scepticism about a major promise of HLE—that it will delay the onset of age-related diseases and extend an individual''s healthy lifespan. From the people we interviewed, the most commonly cited potential negative personal outcome of HLE was that it would extend the number of years a person spent with chronic illnesses and poor quality of life (Partridge et al, 2009a). Although some members of the public envisioned more years spent in good health, almost 40% of participants were concerned that a drug to slow ageing would do more harm than good to them personally; another 13% were unsure about the benefits and costs (Partridge et al, 2010).…it might be that advocates of HLE have failed to persuade the public on this issueIt would be unwise to label such concerns as irrational, when it might be that advocates of HLE have failed to persuade the public on this issue. Have HLE researchers explained what they have discovered about ageing and what it means? Perhaps the public see the claims that have been made about HLE as ‘too good to be true‘.Results of surveys of biogerontologists suggest that they are either unaware or dismissive of public concerns about HLE. They often ignore them, dismiss them as “far-fetched”, or feel no responsibility “to respond” (Settersten Jr et al, 2008). Given this attitude, it is perhaps not surprising that the public are sceptical of their claims.Scientists are not always clear about the outcomes of their work, biogerontologists included. Although the life-extending effects of interventions in animal models are invoked as arguments for supporting anti-ageing research, it is not certain that these interventions will also extend healthy lifespans in humans. Miller (2009) reassuringly claims that the available evidence consistently suggests that quality of life is maintained in laboratory animals with extended lifespans, but he acknowledges that the evidence is “sparse” and urges more research on the topic (Miller, 2009). In the light of such ambiguity, researchers need to respond to public concerns in ways that reflect the available evidence and the potential of their work, without becoming apostles for technologies that have not yet been developed. An anti-ageing drug that extends lifespan without maintaining quality of life is clearly undesirable, but the public needs to be persuaded that such an outcome can be avoided.The public is also concerned about the possible adverse side effects of anti-ageing drugs. Many people were bemused when they discovered that members of the Caloric Restriction Society experienced a loss of libido and loss of muscle mass as a result of adhering to a low-calorie diet to extend their longevity—for many people, such side effects would not be worth the promise of some extra years of life. Adverse side effects are acknowledged as a considerable potential challenge to the development of an effective life-extending drug in humans (Fontana et al, 2010). If researchers do not discuss these possible effects, then a curious public might draw their own conclusions.Adverse side effects are acknowledged as a considerable potential challenge to the development of an effective life-extending drug in humansSome HLE advocates seem eager to tout potential anti-ageing drugs as being free from adverse side effects. For example, Blagosklonny (2007) has argued that rapamycin could be used to prevent age-related diseases in humans because it is “a non-toxic, well tolerated drug that is suitable for everyday oral administration” with its major “side-effects” being anti-tumour, bone-protecting, and mimicking caloric restriction effects. By contrast, Kaeberlein & Kennedy (2009) have advised the public against using the drug because of its immunosuppressive effects.Aubrey de Grey has called for scientists to provide more optimistic timescales for HLE on several occasions. He claims that public opposition to interventions in ageing is based on “extraordinarily transparently flawed opinions” that HLE would be unethical and unsustainable (de Grey, 2004). In his view, public opposition is driven by scepticism about whether HLE will be possible, and that concerns about extending infirmity, injustice or social harms are simply excuses to justify people''s belief that ageing is ‘not so bad'' (de Grey, 2007). He argues that this “pro-ageing trance” can only be broken by persuading the public that HLE technologies are just around the corner.Contrary to de Grey''s expectations of public pessimism, 75% of our survey participants thought that HLE technologies were likely to be developed in the near future. Furthermore, concerns about the personal, social and ethical implications of ageing interventions and HLE were not confined to those who believed that HLE is not feasible (Partridge et al, 2010).Juengst et al (2003) have rightly pointed out that any interventions that slow ageing and substantially increase human longevity might generate more social, economic, political, legal, ethical and public health issues than any other technological advance in biomedicine. Our survey supports this idea; the major ethical concerns raised by members of the public reflect the many and diverse issues that are discussed in the bioethics literature (Partridge et al, 2009b; Partridge & Hall, 2007).When pressed, even enthusiasts admit that a drastic extension of human life might be a mixed blessing. A recent review by researchers at the US National Institute on Aging pointed to several economic and social challenges that arise from longevity extension (Sierra et al, 2009). Perry (2004) suggests that the ability to slow ageing will cause “profound changes” and a “firestorm of controversy”. Even de Grey (2005) concedes that the development of an effective way to slow ageing will cause “mayhem” and “absolute pandemonium”. If even the advocates of anti-ageing and HLE anticipate widespread societal disruption, the public is right to express concerns about the prospect of these things becoming reality. It is accordingly unfair to dismiss public concerns about the social and ethical implications as “irrational”, “inane” or “breathtakingly stupid” (de Grey, 2004).The breadth of the possible implications of HLE reinforces the need for more discussion about the funding of such research and management of its outcomes ( Juengst et al, 2003). Biogerontologists need to take public concerns more seriously if they hope to foster support for their work. If there are misperceptions about the likely outcomes of intervention in ageing, then biogerontologists need to better explain their research to the public and discuss how their concerns will be addressed. It is not enough to hope that a breakthrough in human ageing research will automatically assuage public concerns about the effects of HLE on quality of life, overpopulation, economic sustainability, the environment and inequities in access to such technologies. The trajectories of other controversial research areas—such as human embryonic stem cell research and assisted reproductive technologies (Deech & Smajdor, 2007)—have shown that “listening to public concerns on research and responding appropriately” is a more effective way of fostering support than arrogant dismissal of public concerns (Anon, 2009).Biogerontologists need to take public concerns more seriously if they hope to foster support for their work? Open in a separate windowBrad PartridgeOpen in a separate windowJayne LuckeOpen in a separate windowWayne Hall     

Suicide among children and adolescents in Canada: trends and sex differences, 1980�C2008

Background:

Suicide is the second leading cause of death for young Canadians (10–19 years of age) — a disturbing trend that has shown little improvement in recent years. Our objective was to examine suicide trends among Canadian children and adolescents.

Methods:

We conducted a retrospective analysis of standardized suicide rates using Statistics Canada mortality data for the period spanning from 1980 to 2008. We analyzed the data by sex and by suicide method over time for two age groups: 10–14 year olds (children) and 15–19 year olds (adolescents). We quantified annual trends by calculating the average annual percent change (AAPC).

Results:

We found an average annual decrease of 1.0% (95% confidence interval [CI] −1.5 to −0.4) in the suicide rate for children and adolescents, but stratification by age and sex showed significant variation. We saw an increase in suicide by suffocation among female children (AAPC = 8.1%, 95% CI 6.0 to 10.4) and adolescents (AAPC = 8.0%, 95% CI 6.2 to 9.8). In addition, we noted a decrease in suicides involving poisoning and firearms during the study period.

Interpretation:

Our results show that suicide rates in Canada are increasing among female children and adolescents and decreasing among male children and adolescents. Limiting access to lethal means has some potential to mitigate risk. However, suffocation, which has become the predominant method for committing suicide for these age groups, is not amenable to this type of primary prevention.Suicide was ranked as the second leading cause of death among Canadians aged 10–34 years in 2008.¹ It is recognized that suicidal behaviour and ideation is an important public health issue among children and adolescents; disturbingly, suicide is a leading cause of Canadian childhood mortality (i.e., among youths aged 10–19 years).^2,3Between 1980 and 2008, there were substantial improvements in mortality attributable to unintentional injury among 10–19 year olds, with rates decreasing from 37.7 per 100 000 to 10.7 per 100 000; suicide rates, however, showed less improvement, with only a small reduction during the same period (from 6.2 per 100 000 in 1980 to 5.2 per 100 000 in 2008).¹Previous studies that looked at suicides among Canadian adolescents and young adults (i.e., people aged 15–25 years) have reported rates as being generally stable over time, but with a marked increase in suicides by suffocation and a decrease in those involving firearms.² There is limited literature on self-inflicted injuries among children 10–14 years of age in Canada and the United States, but there appears to be a trend toward younger children starting to self-harm.^3,4 Furthermore, the trend of suicide by suffocation moving to younger ages may be partly due to cases of the “choking game” (self-strangulation without intent to cause permanent harm) that have been misclassified as suicides.^5–7Risk factors for suicidal behaviour and ideation in young people include a psychiatric diagnosis (e.g., depression), substance abuse, past suicidal behaviour, family factors and other life stressors (e.g., relationships, bullying) that have complex interactions.⁸ A suicide attempt involves specific intent, plans and availability of lethal means, such as firearms,⁹ elevated structures¹⁰ or substances.¹¹ The existence of “pro-suicide” sites on the Internet and in social media¹² may further increase risk by providing details of various ways to commit suicide, as well as evaluations ranking these methods by effectiveness, amount of pain involved and length of time to produce death.^13–15Our primary objective was to present the patterns of suicide among children and adolescents (aged 10–19 years) in Canada.     

Of mice and men

Thomas Erren and colleagues point out that studies on light and circadian rhythmicity in humans have their own interesting pitfalls, of which all researchers should be mindful.We would like to compliment, and complement, the recent Opinion in EMBO reports by Stuart Peirson and Russell Foster (2011), which calls attention to the potential obstacles associated with linking observations on light and circadian rhythmicity made on nocturnal mice to diurnally active humans. Pitfalls to consider include that qualitative extrapolations from short-lived rodents to long-lived humans, quantitative extrapolations of very different doses (Gold et al, 1992), and the varying sensitivities of each species to experimental optical radiation as a circadian stimulus (Bullough et al, 2006) can all have a critical influence on an experiment. Thus, Peirson & Foster remind us that “humans are not big mice”. We certainly agree, but we also thought it worthwhile to point out that human studies have their own interesting pitfalls, of which all researchers should be mindful.Many investigations with humans—such as testing the effects of different light exposures on alertness, cognitive performance, well-being and depression—can suffer from what has been coined as the ‘Hawthorne effect''. The term is derived from a series of studies conducted at the Western Electric Company''s Hawthorne Works near Chicago, Illinois, between 1924 and 1932, to test whether the productivity of workers would change with changing illumination levels. One important punch line was that productivity increased with almost any change that was made at the workplaces. One prevailing interpretation of these findings is that humans who know that they are being studied—and in most investigations they cannot help but notice—might exhibit responses that have little or nothing to do with what was intended as the experiment. Those who conduct circadian biology studies in humans try hard to eliminate possible ‘Hawthorne effects'', but every so often, all they can do is to hope for the best and expect the Hawthorne effect to be insignificant.Even so, and despite the obstacles to circadian experiments with both mice and humans, the wealth of information from work in both species is indispensable. To exemplify, in the last handful of years alone, experimental research in mice has substantially contributed to our understanding of the retinal interface between visible light and circadian circuitry (Chen et al, 2011); has shown that disturbances of the circadian systems through manipulations of the light–dark cycles might accelerate carcinogenesis (Filipski et al, 2009); and has suggested that perinatal light exposure—through an imprinting of the stability of circadian systems (Ciarleglio et al, 2011)—might be related to a human''s susceptibility to mood disorders (Erren et al, 2011a) and internal cancer developments later in life (Erren et al, 2011b). Future studies in humans must now examine whether, and to what extent, what was found in mice is applicable to and relevant for humans.The bottom line is that we must be aware of, and first and foremost exploit, evolutionary legacies, such as the seemingly ubiquitous photoreceptive clockwork that marine and terrestrial vertebrates—including mammals such as mice and humans—share (Erren et al, 2008). Translating insights from studies in animals to humans (Erren et al, 2011a,b), and vice versa, into testable research can be a means to one end: to arrive at sensible answers to pressing questions about light and circadian clockworks that, no doubt, play key roles in human health and disease. Pitfalls, however, abound on either side, and we agree with Peirson & Foster that they have to be recognized and monitored.     

Amino Acid Position-specific Contributions to Amyloid ��-Protein Oligomerization

Understanding the structural and assembly dynamics of the amyloid β-protein (Aβ) has direct relevance to the development of therapeutic agents for Alzheimer disease. To elucidate these dynamics, we combined scanning amino acid substitution with a method for quantitative determination of the Aβ oligomer frequency distribution, photo-induced cross-linking of unmodified proteins (PICUP), to perform “scanning PICUP.” Tyr, a reactive group in PICUP, was substituted at position 1, 10, 20, 30, or 40 (for Aβ40) or 42 (for Aβ42). The effects of these substitutions were probed using circular dichroism spectroscopy, thioflavin T binding, electron microscopy, PICUP, and mass spectrometry. All peptides displayed a random coil → α/β → β transition, but substitution-dependent alterations in assembly kinetics and conformer complexity were observed. Tyr¹-substituted homologues of Aβ40 and Aβ42 assembled the slowest and yielded unusual patterns of oligomer bands in gel electrophoresis experiments, suggesting oligomer compaction had occurred. Consistent with this suggestion was the observation of relatively narrow [Tyr¹]Aβ40 fibrils. Substitution of Aβ40 at the C terminus decreased the population conformational complexity and substantially extended the highest order of oligomers observed. This latter effect was observed in both Aβ40 and Aβ42 as the Tyr substitution position number increased. The ability of a single substitution (Tyr¹) to alter Aβ assembly kinetics and the oligomer frequency distribution suggests that the N terminus is not a benign peptide segment, but rather that Aβ conformational dynamics and assembly are affected significantly by the competition between the N and C termini to form a stable complex with the central hydrophobic cluster.Alzheimer disease (AD)⁴ is the most common cause of late-life dementia (1) and is estimated to afflict more than 27 million people worldwide (2). An important etiologic hypothesis is that amyloid β-protein (Aβ) oligomers are the proximate neurotoxins in AD. Substantial in vivo and in vitro evidence supports this hypothesis (3–12). Neurotoxicity studies have shown that Aβ assemblies are potent neurotoxins (5, 13–20), and the toxicity of some oligomers can be greater than that of the corresponding fibrils (21). Soluble Aβ oligomers inhibit hippocampal long term potentiation (4, 5, 13, 15, 17, 18, 22) and disrupt cognitive function (23). Compounds that bind and disrupt the formation of oligomers have been shown to block the neurotoxicity of Aβ (24, 25). Importantly, recent studies in higher vertebrates (dogs) have shown that substantial reduction in amyloid deposits in the absence of decreases in oligomer concentration has little effect on recovery of neurological function (26).Recent studies of Aβ oligomers have sought to correlate oligomer size and biological activity. Oligomers in the supernatants of fibril preparations centrifuged at 100,000 × g caused sustained calcium influx in rat hippocampal neurons, leading to calpain activation and dynamin 1 degradation (27). Aβ-derived diffusible ligand-like Aβ42 oligomers induced inflammatory responses in cultured rat astrocytes (28). A 90-kDa Aβ42 oligomer (29) has been shown to activate ERK1/2 in rat hippocampal slices (30) and bind avidly to human cortical neurons (31), in both cases causing apoptotic cell death. A comparison of the time dependence of the toxic effects of the 90-kDa assembly with that of Aβ-derived diffusible ligands revealed a 5-fold difference, Aβ-derived diffusible ligands requiring more time for equivalent effects (31). A 56-kDa oligomer, “Aβ*56,” was reported to cause memory impairment in middle-aged transgenic mice expressing human amyloid precursor protein (32). A nonamer also had adverse effects. Impaired long term potentiation in rat brain slices has been attributed to Aβ trimers identified in media from cultured cells expressing human amyloid precursor protein (33). Dimers and trimers from this medium also have been found to cause progressive loss of synapses in organotypic rat hippocampal slices (10). In mice deficient in neprilysin, an enzyme that has been shown to degrade Aβ in vivo (34), impairment in neuronal plasticity and cognitive function correlated with significant increases in Aβ dimer levels and synapse-associated Aβ oligomers (35).The potent pathologic effects of Aβ oligomers provide a compelling reason for elucidating the mechanism(s) of their formation. This has been a difficult task because of the metastability and polydispersity of Aβ assemblies (36). To obviate these problems, we introduced the use of the method of photo-induced cross-linking of unmodified proteins (PICUP) to rapidly (<1 s) and covalently stabilize oligomer mixtures (for reviews see Refs. 37, 38). Oligomers thus stabilized no longer exist in equilibrium with monomers or each other, allowing determination of oligomer frequency distributions by simple techniques such as SDS-PAGE (37). Recently, to obtain population-average information on contributions to fibril formation of amino acid residues at specific sites in Aβ, we employed a scanning intrinsic fluorescence approach (39). Tyr was used because it is a relatively small fluorophore, exists natively in Aβ, and possesses the side chain most reactive in the PICUP chemistry (40). Using this approach, we found that the central hydrophobic cluster region (Leu¹⁷–Ala²¹) was particularly important in controlling fibril formation of Aβ40, whereas the C terminus was the predominant structural element controlling Aβ42 assembly (39). Here we present results of studies in which key strategic features of the two methods have been combined to enable execution of “scanning PICUP” and the consequent revelation of site-specific effects on Aβ oligomerization.     

Proinsulin and the Genetics of Diabetes Mellitus

Insulin plays a central role in the regulation of vertebrate metabolism. The hormone, the post-translational product of a single-chain precursor, is a globular protein containing two chains, A (21 residues) and B (30 residues). Recent advances in human genetics have identified dominant mutations in the insulin gene causing permanent neonatal-onset DM² (1–4). The mutations are predicted to block folding of the precursor in the ER of pancreatic β-cells. Although expression of the wild-type allele would in other circumstances be sufficient to maintain homeostasis, studies of a corresponding mouse model (5–7) suggest that the misfolded variant perturbs wild-type biosynthesis (8, 9). Impaired β-cell secretion is associated with ER stress, distorted organelle architecture, and cell death (10). These findings have renewed interest in insulin biosynthesis (11–13) and the structural basis of disulfide pairing (14–19). Protein evolution is constrained not only by structure and function but also by susceptibility to toxic misfolding.Insulin plays a central role in the regulation of vertebrate metabolism. The hormone, the post-translational product of a single-chain precursor, is a globular protein containing two chains, A (21 residues) and B (30 residues). Recent advances in human genetics have identified dominant mutations in the insulin gene causing permanent neonatal-onset DM² (1–4). The mutations are predicted to block folding of the precursor in the ER of pancreatic β-cells. Although expression of the wild-type allele would in other circumstances be sufficient to maintain homeostasis, studies of a corresponding mouse model (5–7) suggest that the misfolded variant perturbs wild-type biosynthesis (8, 9). Impaired β-cell secretion is associated with ER stress, distorted organelle architecture, and cell death (10). These findings have renewed interest in insulin biosynthesis (11–13) and the structural basis of disulfide pairing (14–19). Protein evolution is constrained not only by structure and function but also by susceptibility to toxic misfolding.     

Erythropoietin Receptor (EpoR) Agonism Is Used to Treat a Wide Range of Disease

The erythropoietin receptor (EpoR) was discovered and described in red blood cells (RBCs), stimulating its proliferation and survival. The target in humans for EpoR agonists drugs appears clear—to treat anemia. However, there is evidence of the pleitropic actions of erythropoietin (Epo). For that reason, rhEpo therapy was suggested as a reliable approach for treating a broad range of pathologies, including heart and cardiovascular diseases, neurodegenerative disorders (Parkinson’s and Alzheimer’s disease), spinal cord injury, stroke, diabetic retinopathy and rare diseases (Friedreich ataxia). Unfortunately, the side effects of rhEpo are also evident. A new generation of nonhematopoietic EpoR agonists drugs (asialoEpo, Cepo and ARA 290) have been investigated and further developed. These EpoR agonists, without the erythropoietic activity of Epo, while preserving its tissue-protective properties, will provide better outcomes in ongoing clinical trials. Nonhematopoietic EpoR agonists represent safer and more effective surrogates for the treatment of several diseases such as brain and peripheral nerve injury, diabetic complications, renal ischemia, rare diseases, myocardial infarction, chronic heart disease and others.In principle, the erythropoietin receptor (EpoR) was discovered and described in red blood cell (RBC) progenitors, stimulating its proliferation and survival. Erythropoietin (Epo) is mainly synthesized in fetal liver and adult kidneys (1–3). Therefore, it was hypothesized that Epo act exclusively on erythroid progenitor cells. Accordingly, the target in humans for EpoR agonists drugs (such as recombinant erythropoietin [rhEpo], in general, called erythropoiesis-simulating agents) appears clear (that is, to treat anemia). However, evidence of a kaleidoscope of pleitropic actions of Epo has been provided (4,5). The Epo/EpoR axis research involved an initial journey from laboratory basic research to clinical therapeutics. However, as a consequence of clinical observations, basic research on Epo/EpoR comes back to expand its clinical therapeutic applicability.Although kidney and liver have long been considered the major sources of synthesis, Epo mRNA expression has also been detected in the brain (neurons and glial cells), lung, heart, bone marrow, spleen, hair follicles, reproductive tract and osteoblasts (6–17). Accordingly, EpoR was detected in other cells, such as neurons, astrocytes, microglia, immune cells, cancer cell lines, endothelial cells, bone marrow stromal cells and cells of heart, reproductive system, gastrointestinal tract, kidney, pancreas and skeletal muscle (18–27). Conversely, Sinclair et al.(28) reported data questioning the presence or function of EpoR on nonhematopoietic cells (endothelial, neuronal and cardiac cells), suggesting that further studies are needed to confirm the diversity of EpoR. Elliott et al.(29) also showed that EpoR is virtually undetectable in human renal cells and other tissues with no detectable EpoR on cell surfaces. These results have raised doubts about the preclinical basis for studies exploring pleiotropic actions of rhEpo (30).For the above-mentioned data, a return to basic research studies has become necessary, and many studies in animal models have been initiated or have already been performed. The effect of rhEpo administration on angiogenesis, myogenesis, shift in muscle fiber types and oxidative enzyme activities in skeletal muscle (4,31), cardiac muscle mitochondrial biogenesis (32), cognitive effects (31), antiapoptotic and antiinflammatory actions (33–37) and plasma glucose concentrations (38) has been extensively studied. Neuro- and cardioprotection properties have been mainly described. Accordingly, rhEpo therapy was suggested as a reliable approach for treating a broad range of pathologies, including heart and cardiovascular diseases, neurodegenerative disorders (Parkinson’s and Alzheimer’s disease), spinal cord injury, stroke, diabetic retinopathy and rare diseases (Friedreich ataxia).Unfortunately, the side effects of rhEpo are also evident. Epo is involved in regulating tumor angiogenesis (39) and probably in the survival and growth of tumor cells (25,40,41). rhEpo administration also induces serious side effects such as hypertension, polycythemia, myocardial infarction, stroke and seizures, platelet activation and increased thromboembolic risk, and immunogenicity (42–46), with the most common being hypertension (47,48). A new generation of nonhematopoietic EpoR agonists drugs have hence been investigated and further developed in animals models. These compounds, namely asialoerythropoietin (asialoEpo) and carbamylated Epo (Cepo), were developed for preserving tissue-protective properties but reducing the erythropoietic activity of native Epo (49,50). These drugs will provide better outcome in ongoing clinical trials. The advantage of using nonhematopoietic Epo analogs is to avoid the stimulation of hematopoiesis and thereby the prevention of an increased hematocrit with a subsequent procoagulant status or increased blood pressure. In this regard, a new study by van Rijt et al. has shed new light on this topic (51). A new nonhematopoietic EpoR agonist analog named ARA 290 has been developed, promising cytoprotective capacities to prevent renal ischemia/reperfusion injury (51). ARA 290 is a short peptide that has shown no safety concerns in preclinical and human studies. In addition, ARA 290 has proven efficacious in cardiac disorders (52,53), neuropathic pain (54) and sarcoidosis-induced chronic neuropathic pain (55). Thus, ARA 290 is a novel nonhematopoietic EpoR agonist with promising therapeutic options in treating a wide range of pathologies and without increased risks of cardiovascular events.Overall, this new generation of EpoR agonists without the erythropoietic activity of Epo while preserving tissue-protective properties of Epo will provide better outcomes in ongoing clinical trials (49,50). Nonhematopoietic EpoR agonists represent safer and more effective surrogates for the treatment of several diseases, such as brain and peripheral nerve injury, diabetic complications, renal ischemia, rare diseases, myocardial infarction, chronic heart disease and others.     

A qualitative investigation of smoke-free policies on hospital property

Background:

Many hospitals have adopted smoke-free policies on their property. We examined the consequences of such polices at two Canadian tertiary acute-care hospitals.

Methods:

We conducted a qualitative study using ethnographic techniques over a six-month period. Participants (n = 186) shared their perspectives on and experiences with tobacco dependence and managing the use of tobacco, as well as their impressions of the smoke-free policy. We interviewed inpatients individually from eight wards (n = 82), key policy-makers (n = 9) and support staff (n = 14) and held 16 focus groups with health care providers and ward staff (n = 81). We also reviewed ward documents relating to tobacco dependence and looked at smoking-related activities on hospital property.

Results:

Noncompliance with the policy and exposure to secondhand smoke were ongoing concerns. Peoples’ impressions of the use of tobacco varied, including divergent opinions as to whether such use was a bad habit or an addiction. Treatment for tobacco dependence and the management of symptoms of withdrawal were offered inconsistently. Participants voiced concerns over patient safety and leaving the ward to smoke.

Interpretation:

Policies mandating smoke-free hospital property have important consequences beyond noncompliance, including concerns over patient safety and disruptions to care. Without adequately available and accessible support for withdrawal from tobacco, patients will continue to face personal risk when they leave hospital property to smoke.Canadian cities and provinces have passed smoking bans with the goal of reducing people’s exposure to secondhand smoke in workplaces, public spaces and on the property adjacent to public buildings.^1,2 In response, Canadian health authorities and hospitals began implementing policies mandating smoke-free hospital property, with the goals of reducing the exposure of workers, patients and visitors to tobacco smoke while delivering a public health message about the dangers of smoking.^2–5 An additional anticipated outcome was the reduced use of tobacco among patients and staff. The impetuses for adopting smoke-free policies include public support for such legislation and the potential for litigation for exposure to second-hand smoke.^2,4Tobacco use is a modifiable risk factor associated with a variety of cancers, cardiovascular diseases and respiratory conditions.^6–11 Patients in hospital who use tobacco tend to have more surgical complications and exacerbations of acute and chronic health conditions than patients who do not use tobacco.^6–11 Any policy aimed at reducing exposure to tobacco in hospitals is well supported by evidence, as is the integration of interventions targetting tobacco dependence.¹² Unfortunately, most of the nearly five million Canadians who smoke will receive suboptimal treatment,¹³ as the routine provision of interventions for tobacco dependence in hospital settings is not a practice norm.^14–16 In smoke-free hospitals, two studies suggest minimal support is offered for withdrawal, ^17,18 and one reports an increased use of nicotine-replacement therapy after the implementation of the smoke-free policy.¹⁹Assessments of the effectiveness of smoke-free policies for hospital property tend to focus on noncompliance and related issues of enforcement.^17,20,21 Although evidence of noncompliance and litter on hospital property^2,17,20 implies ongoing exposure to tobacco smoke, half of the participating hospital sites in one study reported less exposure to tobacco smoke within hospital buildings and on the property.¹⁸ In addition, there is evidence to suggest some decline in smoking among staff.^18,19,21,22We sought to determine the consequences of policies mandating smoke-free hospital property in two Canadian acute-care hospitals by eliciting lived experiences of the people faced with enacting the policies: patients and health care providers. In addition, we elicited stories from hospital support staff and administrators regarding the policies.     

Structural and Functional Elucidation of the Mechanism Promoting Error-prone Synthesis by Human DNA Polymerase �� Opposite the 7,8-Dihydro-8-oxo-2��-deoxyguanosine Adduct

Human polymerase kappa (hPol κ) is one of four eukaryotic Y-class DNA polymerases and may be an important element in the cellular response to polycyclic aromatic hydrocarbons such as benzo[a]pyrene, which can lead to reactive oxygenated metabolite-mediated oxidative stress. Here, we present a detailed analysis of the activity and specificity of hPol κ bypass opposite the major oxidative adduct 7,8-dihydro-8-oxo-2′-deoxyguanosine (8-oxoG). Unlike its archaeal homolog Dpo4, hPol κ bypasses this lesion in an error-prone fashion by inserting mainly dATP. Analysis of transient-state kinetics shows diminished “bursts” for dATP:8-oxoG and dCTP:8-oxoG incorporation, indicative of non-productive complex formation, but dATP:8-oxoG insertion events that do occur are 2-fold more efficient than dCTP:G insertion events. Crystal structures of ternary hPol κ complexes with adducted template-primer DNA reveal non-productive (dGTP and dATP) alignments of incoming nucleotide and 8-oxoG. Structural limitations placed upon the hPol κ by interactions between the N-clasp and finger domains combined with stabilization of the syn-oriented template 8-oxoG through the side chain of Met-135 both appear to contribute to error-prone bypass. Mutating Leu-508 in the little finger domain of hPol κ to lysine modulates the insertion opposite 8-oxoG toward more accurate bypass, similar to previous findings with Dpo4. Our structural and activity data provide insight into important mechanistic aspects of error-prone bypass of 8-oxoG by hPol κ compared with accurate and efficient bypass of the lesion by Dpo4 and polymerase η.DNA damage incurred by a multitude of endogenous and exogenous factors constitutes an inevitable challenge for the replication machinery, and various mechanisms exist to either remove the resulting lesions or bypass them in a more or less mutation-prone fashion (1). Error-prone polymerases are central to trans-lesion synthesis across sites of damaged DNA (2, 3). Four so-called Y-class DNA polymerases have been identified in humans, Pol η,⁴ Pol ι, Pol κ, and Rev1, which exhibit different activities and abilities to replicate past a flurry of individual lesions (4, 5). Homologs have also been identified and characterized in other organisms, notably DinB (Pol IV) in Escherichia coli (6–8), Dbh in Sulfolobus acidocaldarius (9, 10), and Dpo4 in Sulfolobus solfataricus (11, 12). A decade of investigations directed at the structural and functional properties of bypass polymerases have significantly improved our understanding of this class of enzymes (5, 13). A unique feature of Y-class polymerases, compared with the common right-handed arrangement of palm, thumb, and finger subdomains of high fidelity (i.e. A-class) DNA polymerases (14), is a “little finger” or “PAD” (palm-associated domain) subdomain that plays a crucial role in lesion bypass (12, 15–21). In addition to the little finger subdomain at the C-terminal end of the catalytic core, both Rev1 and Pol κ exhibit an N-terminal extension that is absent in other translesion polymerases. The N-terminal extension in the structure of the ternary (human) hPol κ·DNA·dTTP complex folds into a U-shaped tether-helix-turn-helix “clasp” that is located between the thumb and little finger domains, allowing the polymerase to completely encircle the DNA (18). Although the precise role of the clasp for lesion bypass by hPol κ remains to be established, it is clear that this entity is functionally important, because mutant enzymes with partially or completely removed clasps exhibit diminished catalytic activity compared with the full-length catalytic core (hPol κ N1–526) or a core lacking the N-terminal 19 residues (hPol κ N19–526; the construct used for crystal structure determination of the ternary complex (18)).7,8-Dihydro-8-oxo-2′-deoxyguanosine (8-oxoG), found in both lower organisms and eukaryotes, is a major lesion that is a consequence of oxidative stress. The lesion is of relevance not only because of its association with cancer (22, 23), but also in connection with aging (24), hepatitis (25), and infertility (26). It is far from clear which DNA polymerases bypass 8-oxoG most often in a cellular context, but given the ubiquitous nature of the lesion it seems likely that more than one enzyme could encounter the lesion. Replicative polymerases commonly insert dATP opposite template 8-oxoG, with the lesion adopting the preferred syn conformation (e.g. 27, 28). It was recently found that the translesion polymerase Dpo4 from S. solfataricus synthesizes efficiently past 8-oxoG, inserting ≥95% dCTP > dATP opposite the lesion (29, 30). The efficient and low error bypass of the 8-oxoG lesion by Dpo4 is associated to a large extent with an arginine residue in the little finger domain (17). In the crystal structure of the ternary Dpo4·DNA·dCTP complex, the side chain of Arg-332 forms a hydrogen bond to the 8-oxygen of 8-oxoG, thus shifting the nucleoside conformational equilibrium toward the anti state and enabling a Watson-Crick binding mode with the incoming dCTP (30). The efficient and accurate replication of templates bearing 8-oxoG by yeast Pol η (31, 32) may indicate similarities between the bypass reactions catalyzed by the archaeal and eukaryotic enzymes. In contrast, bypass synthesis opposite 8-oxoG by human Pol κ is error-prone, resulting in efficient incorporation of A (33–35). The inaccurate bypass of 8-oxoG is thought to contribute to the deleterious effects associated with the lesion. These observations indicate different behaviors of the eukaryotic trans-lesion Pol κ and its archaeal “homolog” Dpo4 vis-à-vis the major oxidative stress lesion 8-oxoG. A mechanistic understanding of human DNA polymerases that bypass 8-oxoG in an error-prone fashion, such as hPol κ, is therefore of great interest.To elucidate commonalities and differences between the trans-8-oxoG syntheses of S. solfataricus Dpo4, yeast Pol η, and hPol κ, we carried out a comprehensive analysis of the bypass activity for the latter with template·DNA containing the 8-oxoG lesion, including pre-steady-state and steady-state kinetics of primer extension opposite and beyond 8-oxoG and LC-MS/MS assays of full-length extension products. We determined crystal structures of ternary hPol κ-(8-oxoG)DNA-dGTP and hPol κ-(8-oxoG)DNA-dATP complexes, apparently the first for any complex with adducted DNA for the κ enzyme reported to date. Our work demonstrates clear distinctions between genetically related translesion polymerases and provides insights into the origins of the error-prone reactions opposite 8-oxoG catalyzed by Y-family DNA polymerases.     

Conformational Properties of ��-PrP

Prion propagation involves a conformational transition of the cellular form of prion protein (PrP^C) to a disease-specific isomer (PrP^Sc), shifting from a predominantly α-helical conformation to one dominated by β-sheet structure. This conformational transition is of critical importance in understanding the molecular basis for prion disease. Here, we elucidate the conformational properties of a disulfide-reduced fragment of human PrP spanning residues 91–231 under acidic conditions, using a combination of heteronuclear NMR, analytical ultracentrifugation, and circular dichroism. We find that this form of the protein, which similarly to PrP^Sc, is a potent inhibitor of the 26 S proteasome, assembles into soluble oligomers that have significant β-sheet content. The monomeric precursor to these oligomers exhibits many of the characteristics of a molten globule intermediate with some helical character in regions that form helices I and III in the PrP^C conformation, whereas helix II exhibits little evidence for adopting a helical conformation, suggesting that this region is a likely source of interaction within the initial phases of the transformation to a β-rich conformation. This precursor state is almost as compact as the folded PrP^C structure and, as it assembles, only residues 126–227 are immobilized within the oligomeric structure, leaving the remainder in a mobile, random-coil state.Prion diseases, such as Creutzfeldt-Jacob and Gerstmann-Sträussler-Scheinker in humans, scrapie in sheep, and bovine spongiform encephalopathy in cattle, are fatal neurological disorders associated with the deposition of an abnormally folded form of a host-encoded glycoprotein, prion (PrP)² (1). These diseases may be inherited, arise sporadically, or be acquired through the transmission of an infectious agent (2, 3). The disease-associated form of the protein, termed the scrapie form or PrP^Sc, differs from the normal cellular form (PrP^C) through a conformational change, resulting in a significant increase in the β-sheet content and protease resistance of the protein (3, 4). PrP^C, in contrast, consists of a predominantly α-helical structured domain and an unstructured N-terminal domain, which is capable of binding a number of divalent metals (5–12). A single disulfide bond links two of the main α-helices and forms an integral part of the core of the structured domain (13, 14).According to the protein-only hypothesis (15), the infectious agent is composed of a conformational isomer of PrP (16) that is able to convert other isoforms to the infectious isomer in an autocatalytic manner. Despite numerous studies, little is known about the mechanism of conversion of PrP^C to PrP^Sc. The most coherent and general model proposed thus far is that PrP^C fluctuates between the dominant native state and minor conformations, one or a set of which can self-associate in an ordered manner to produce a stable supramolecular structure composed of misfolded PrP monomers (3, 17). This stable, oligomeric species can then bind to, and stabilize, rare non-native monomer conformations that are structurally complementary. In this manner, new monomeric chains are recruited and the system can propagate.In view of the above model, considerable effort has been devoted to generating and characterizing alternative, possibly PrP^Sc-like, conformations in the hope of identifying common properties or features that facilitate the formation of amyloid oligomers. This has been accomplished either through PrP^Sc-dependent conversion reactions (18–20) or through conversion of PrP^C in the absence of a PrP^Sc template (21–25). The latter approach, using mainly disulfide-oxidized recombinant PrP, has generated a wide range of novel conformations formed under non-physiological conditions where the native state is relatively destabilized. These conformations have ranged from near-native (14, 26, 27), to those that display significant β-sheet content (21, 23, 28–33). The majority of these latter species have shown a high propensity for aggregation, although not all are on-pathway to the formation of amyloid. Many of these non-native states also display some of the characteristics of PrP^Sc, such as increased β-sheet content, protease resistance, and a propensity for oligomerization (28, 29, 31) and some have been claimed to be associated with the disease process (34).One such PrP folding intermediate, termed β-PrP, differs from the majority of studied PrP intermediate states in that it is formed by refolding the PrP molecule from the native α-helical conformation (here termed α-PrP), at acidic pH in a reduced state, with the disulfide bond broken (22, 35). Although no covalent differences between the PrP^C and PrP^Sc have been consistently identified to date, the role of the disulfide bond in prion propagation remains disputed (25, 36–39). β-PrP is rich in β-sheet structure (22, 35), and displays many of the characteristics of a PrP^Sc-like precursor molecule, such as partial resistance to proteinase K digestion, and the ability to form amyloid fibrils in the presence of physiological concentrations of salts (40).The β-PrP species previously characterized, spanning residues 91–231 of PrP, was soluble at low ionic strength buffers and monomeric, according to elution volume on gel filtration (22). NMR analysis showed that it displayed radically different spectra to those of α-PrP, with considerably fewer observable peaks and markedly reduced chemical shift dispersion. Data from circular dichroism experiments showed that fixed side chain (tertiary) interactions were lost, in contrast to the well defined β-sheet secondary structure, and thus in conjunction with the NMR data, indicated that β-PrP possessed a number of characteristics associated with a “molten globule” folding intermediate (22). Such states have been proposed to be important in amyloid and fibril formation (41). Indeed, antibodies raised against β-PrP (e.g. ICSM33) are capable of recognizing native PrP^Sc (but not PrP^C) (42–44). Subsequently, a related study examining the role of the disulfide bond in PrP folding confirmed that a monomeric molten globule-like form of PrP was formed on refolding the disulfide-reduced protein at acidic pH, but reported that, under their conditions, the circular dichroism response interpreted as β-sheet structure was associated with protein oligomerization (45). Indeed, atomic force microscopy on oligomeric full-length β-PrP (residues 23–231) shows small, round particles, showing that it is capable of formation of oligomers without forming fibrils (35). Notably, however, salt-induced oligomeric β-PrP has been shown to be a potent inhibitor of the 26 S proteasome, in a similar manner to PrP^Sc (46). Impairment of the ubiquitin-proteasome system in vivo has been linked to prion neuropathology in prion-infected mice (46).Although the global properties of several PrP intermediate states have been determined (30–32, 35), no information on their conformational properties on a sequence-specific basis has been obtained. Their conformational properties are considered important, as the elucidation of the chain conformation may provide information on the way in which these chains pack in the assembly process, and also potentially provide clues on the mechanism of amyloid assembly and the phenomenon of prion strains. As the conformational fluctuations and heterogeneity of molten globule states give rise to broad NMR spectra that preclude direct observation of their conformational properties by NMR (47–50), here we use denaturant titration experiments to determine the conformational properties of β-PrP, through the population of the unfolded state that is visible by NMR. In addition, we use circular dichroism and analytical ultracentrifugation to examine the global structural properties, and the distribution of multimeric species that are formed from β-PrP.     

Secular trends in acute dialysis after elective major surgery �� 1995 to 2009

Background:

Acute kidney injury is a serious complication of elective major surgery. Acute dialysis is used to support life in the most severe cases. We examined whether rates and outcomes of acute dialysis after elective major surgery have changed over time.

Methods:

We used data from Ontario’s universal health care databases to study all consecutive patients who had elective major surgery at 118 hospitals between 1995 and 2009. Our primary outcomes were acute dialysis within 14 days of surgery, death within 90 days of surgery and chronic dialysis for patients who did not recover kidney function.

Results:

A total of 552 672 patients underwent elective major surgery during the study period, 2231 of whom received acute dialysis. The incidence of acute dialysis increased steadily from 0.2% in 1995 (95% confidence interval [CI] 0.15–0.2) to 0.6% in 2009 (95% CI 0.6–0.7). This increase was primarily in cardiac and vascular surgeries. Among patients who received acute dialysis, 937 died within 90 days of surgery (42.0%, 95% CI 40.0–44.1), with no change in 90-day survival over time. Among the 1294 patients who received acute dialysis and survived beyond 90 days, 352 required chronic dialysis (27.2%, 95% CI 24.8–29.7), with no change over time.

Interpretation:

The use of acute dialysis after cardiac and vascular surgery has increased substantially since 1995. Studies focusing on interventions to better prevent and treat perioperative acute kidney injury are needed.More than 230 million elective major surgeries are done annually worldwide.¹ Acute kidney injury is a serious complication of major surgery. It represents a sudden loss of kidney function that affects morbidity, mortality and health care costs.² Dialysis is used for the most severe forms of acute kidney injury. In the nonsurgical setting, the incidence of acute dialysis has steadily increased over the last 15 years, and patients are now more likely to survive to discharge from hospital.^3–5 Similarly, in the surgical setting, the incidence of acute dialysis appears to be increasing over time,^6–10 with declining inhospital mortality.^8,10,11Although previous studies have improved our understanding of the epidemiology of acute dialysis in the surgical setting, several questions remain. Many previous studies were conducted at a single centre, thereby limiting their generalizability.^6,12–14 Most multicentre studies were conducted in the nonsurgical setting and used diagnostic codes for acute kidney injury not requiring dialysis; however, these codes can be inaccurate.^15,16 In contrast, a procedure such as dialysis is easily determined. The incidence of acute dialysis after elective surgery is of particular interest given the need for surgical consent, the severe nature of the event and the potential for mitigation. The need for chronic dialysis among patients who do not recover renal function after surgery has been poorly studied, yet this condition has a major affect on patient survival and quality of life.¹⁷ For these reasons, we studied secular trends in acute dialysis after elective major surgery, focusing on incidence, 90-day mortality and need for chronic dialysis.     

Loop 2 Structure in Glycine and GABAA Receptors Plays a Key Role in Determining Ethanol Sensitivity

The present study tests the hypothesis that the structure of extracellular domain Loop 2 can markedly affect ethanol sensitivity in glycine receptors (GlyRs) and γ-aminobutyric acid type A receptors (GABA_ARs). To test this, we mutated Loop 2 in the α1 subunit of GlyRs and in the γ subunit of α1β2γ2GABA_ARs and measured the sensitivity of wild type and mutant receptors expressed in Xenopus oocytes to agonist, ethanol, and other agents using two-electrode voltage clamp. Replacing Loop 2 of α1GlyR subunits with Loop 2 from the δGABA_AR (δL2), but not the γGABA_AR subunit, reduced ethanol threshold and increased the degree of ethanol potentiation without altering general receptor function. Similarly, replacing Loop 2 of the γ subunit of GABA_ARs with δL2 shifted the ethanol threshold from 50 mm in WT to 1 mm in the GABA_A γ-δL2 mutant. These findings indicate that the structure of Loop 2 can profoundly affect ethanol sensitivity in GlyRs and GABA_ARs. The δL2 mutations did not affect GlyR or GABA_AR sensitivity, respectively, to Zn²⁺ or diazepam, which suggests that these δL2-induced changes in ethanol sensitivity do not extend to all allosteric modulators and may be specific for ethanol or ethanol-like agents. To explore molecular mechanisms underlying these results, we threaded the WT and δL2 GlyR sequences onto the x-ray structure of the bacterial Gloeobacter violaceus pentameric ligand-gated ion channel homologue (GLIC). In addition to being the first GlyR model threaded on GLIC, the juxtaposition of the two structures led to a possible mechanistic explanation for the effects of ethanol on GlyR-based on changes in Loop 2 structure.Alcohol abuse and dependence are significant problems in our society, with ∼14 million people in the United States being affected (1, 2). Alcohol causes over 100,000 deaths in the United States, and alcohol-related issues are estimated to cost nearly 200 billion dollars annually (2). To address this, considerable attention has focused on the development of medications to prevent and treat alcohol-related problems (3–5). The development of such medications would be aided by a clear understanding of the molecular structures on which ethanol acts and how these structures influence receptor sensitivity to ethanol.Ligand-gated ion channels (LGICs)² have received substantial attention as putative sites of ethanol action that cause its behavioral effects (6–12). Research in this area has focused on investigating the effects of ethanol on two large superfamilies of LGICs: 1) the Cys-loop superfamily of LGICs (13, 14), whose members include nicotinic acetylcholine, 5-hydroxytryptamine₃, γ-aminobutyric acid type A (GABA_A), γ-aminobutyric acid type C, and glycine receptors (GlyRs) (10, 11, 15–20) and 2) the glutamate superfamily, including N-methyl d-aspartate, α-amino-3-hydroxyisoxazolepropionic acid, and kainate receptors (21, 22). Recent studies have also begun investigating ethanol action in the ATP-gated P2X superfamily of LGICs (23–25).A series of studies that employed chimeric and mutagenic strategies combined with sulfhydryl-specific labeling identified key regions within Cys-loop receptors that appear to be initial targets for ethanol action that also can determine the sensitivity of the receptors to ethanol (7–12, 18, 19, 26–30). This work provides several lines of evidence that position 267 and possibly other sites in the transmembrane (TM) domain of GlyRs and homologous sites in GABA_ARs are targets for ethanol action and that mutations at these sites can influence ethanol sensitivity (8, 9, 26, 31).Growing evidence from GlyRs indicates that ethanol also acts on the extracellular domain. The initial findings came from studies demonstrating that α1GlyRs are more sensitive to ethanol than are α2GlyRs despite the high (∼78%) sequence homology between α1GlyRs and α2GlyRs (32). Further work found that an alanine to serine exchange at position 52 (A52S) in Loop 2 can eliminate the difference in ethanol sensitivity between α1GlyRs and α2GlyRs (18, 20, 33). These studies also demonstrated that mutations at position 52 in α1GlyRS and the homologous position 59 in α2GlyRs controlled the sensitivity of these receptors to a novel mechanistic ethanol antagonist (20). Collectively, these studies suggest that there are multiple sites of ethanol action in α1GlyRs, with one site located in the TM domain (e.g. position 267) and another in the extracellular domain (e.g. position 52).Subsequent studies revealed that the polarity of the residue at position 52 plays a key role in determining the sensitivity of GlyRs to ethanol (20). The findings with polarity in the extracellular domain contrast with the findings at position 267 in the TM domain, where molecular volume, but not polarity, significantly affected ethanol sensitivity (9). Taken together, these findings indicate that the physical-chemical parameters of residues at positions in the extracellular and TM domains that modulate ethanol effects and/or initiate ethanol action in GlyRs are not uniform. Thus, knowledge regarding the physical-chemical properties that control agonist and ethanol sensitivity is key for understanding the relationship between the structure and the actions of ethanol in LGICs (19, 31, 34–40).GlyRs and GABA_ARs, which differ significantly in their sensitivities to ethanol, offer a potential method for identifying the structures that control ethanol sensitivity. For example, α1GlyRs do not reliably respond to ethanol concentrations less than 10 mm (32, 33, 41). Similarly, γ subunit-containing GABA_ARs (e.g. α1β2γ2), the most predominantly expressed GABA_ARs in the central nervous system, are insensitive to ethanol concentrations less than 50 mm (42, 43). In contrast, δ subunit-containing GABA_ARs (e.g. α4β3δ) have been shown to be sensitive to ethanol concentrations as low as 1–3 mm (44–51). Sequence alignment of α1GlyR, γGABA_AR, and δGABA_AR revealed differences between the Loop 2 regions of these receptor subunits. Since prior studies found that mutations of Loop 2 residues can affect ethanol sensitivity (19, 20, 39), the non-conserved residues in Loop 2 of GlyR and GABA_AR subunits could provide the physical-chemical and structural bases underlying the differences in ethanol sensitivity between these receptors.The present study tested the hypothesis that the structure of Loop 2 can markedly affect the ethanol sensitivity of GlyRs and GABA_ARs. To accomplish this, we performed multiple mutations that replaced the Loop 2 region of the α1 subunit in α1GlyRs and the Loop 2 region of the γ subunit of α1β2γ2 GABA_ARs with corresponding non-conserved residues from the δ subunit of GABA_AR and tested the sensitivity of these receptors to ethanol. As predicted, replacing Loop 2 of WT α1GlyRs with the homologous residues from the δGABA_AR subunit (δL2), but not the γGABA_AR subunit (γL2), markedly increased the sensitivity of the receptor to ethanol. Similarly, replacing the non-conserved residues of the γ subunit of α1β2γ2 GABA_ARs with δL2 also markedly increased ethanol sensitivity of GABA_ARs. These findings support the hypothesis and suggest that Loop 2 may play a role in controlling ethanol sensitivity across the Cys-loop superfamily of receptors. The findings also provide the basis for suggesting structure-function relationships in a new molecular model of the GlyR based on the bacterial Gloeobacter violaceus pentameric LGIC homologue (GLIC).