Structural, mechanistic and clinical aspects of MRP1

The cDNA encoding ATP-binding cassette (ABC) multidrug resistance protein MRP1 was originally cloned from a drug-selected lung cancer cell line resistant to multiple natural product chemotherapeutic agents. MRP1 is the founder of a branch of the ABC superfamily whose members (from species as diverse as plants and yeast to mammals) share several distinguishing structural features that may contribute to functional and mechanistic similarities among this subgroup of transport proteins. In addition to its role in resistance to natural product drugs, MRP1 (and related proteins) functions as a primary active transporter of structurally diverse organic anions, many of which are formed by the biotransformation of various endo- and xenobiotics by Phase II conjugating enzymes, such as the glutathione S-transferases. MRP1 is involved in a number of glutathione-related cellular processes. Glutathione also appears to play a key role in MRP1-mediated drug resistance. This article reviews the discovery of MRP1 and its relationships with other ABC superfamily members, and summarizes current knowledge of the structure, transport functions and relevance of this protein to in vitro and clinical multidrug resistance.     

Regulation of mucin expression: mechanistic aspects and implications for cancer and inflammatory diseases

Mucins are large multifunctional glycoproteins whose primary functions are to protect and lubricate the surfaces of epithelial tissues lining ducts and lumens within the human body. Several lines of evidence also support the involvement of mucins in more complex biological processes such as epithelial cell renewal and differentiation, cell signaling, and cell adhesion. Recent studies have uncovered the role of select mucins in the pathogenesis of cancer, underscoring the importance of a detailed knowledge about mucin biology. Under normal physiological conditions, the production of mucins is optimally maintained by a host of elaborate and coordinated regulatory mechanisms, thereby affording a well-defined pattern of tissue-, time-, and developmental state-specific distribution. However, mucin homeostasis may be disrupted by the action of environmental and/or intrinsic factors that affect cellular integrity. This results in an altered cell behavior that often culminates into a variety of pathological conditions. Deregulated mucin production has indeed been associated with numerous types of cancers and inflammatory disorders. It is, therefore, crucial to comprehend the underlying basis of molecular mechanisms controlling mucin production in order to design and implement adequate therapeutic strategies for combating these diseases. Herein, we discuss some physiologically relevant regulatory aspects of mucin production, with a particular emphasis on aberrations that pertain to pathological situations. Our views of the achievements, the conceptual and technical limitations, as well as the future challenges associated with studies of mucin regulation are exposed.     

Enzyme promiscuity: evolutionary and mechanistic aspects

The past few years have seen significant advances in research related to the 'latent skills' of enzymes - namely, their capacity to promiscuously catalyze reactions other than the ones they evolved for. These advances regard (i) the mechanism of catalytic promiscuity - how enzymes, that generally exert exquisite specificity, promiscuously catalyze other, and sometimes barely related, reactions; (ii) the evolvability of promiscuous functions - namely, how latent activities evolve further, and in particular, how promiscuous activities can firstly evolve without severely compromising the original activity. These findings have interesting implications on our understanding of how new enzymes evolve. They support the key role of catalytic promiscuity in the natural history of enzymes, and suggest that today's enzymes diverged from ancestral proteins catalyzing a whole range of activities at low levels, to create families and superfamilies of potent and highly specialized enzymes.     

Hemorrhagic fever with renal syndrome: clinical aspects

Hemorrhagic fever with renal syndrome (HFRS) is an acute viral fever which typically progresses through five stages: an acute grippe, followed by hemorrhage and shock, acute renal insufficiency from tubulo-interstitial nephritis, and recovery. Death from circulatory or renal failure occurs in 5%-15% of cases. In mild or abortive forms of the disease, associated with viral strains enzootic in Scandinavia the illness is milder. Hemorrhage and shock occur with lower frequency and the fatality rate is less than 1%. Pathologic examination of HFRS cases from Asia discloses generalized congestion, hyperemia, and hemorrhage, with scattered foci of necrosis in numerous organs. Congestion and hemorrhage are most evident in the kidney medulla. Widespread microscopic evidence of capillary and vascular dysfunction is found, with endothelial cell swelling, perivascular edema, diapadesis of erythrocytes and mononuclear cell infiltration. Hemorrhage and inflammation in the renal interstitium and tubular epithelial degeneration characterize the kidney pathology. Limited data indicate pathogenic roles for cell destruction from viral infection as well as immune mediated mechanisms. No specific therapy is available.     

Halogenation of aromatic compounds: thermodynamic, mechanistic and ecological aspects

Biological halogenation of aromatic compounds implies the generation of reducing equivalents in the form of e.g. NADH. Thermodynamic calculations show that coupling the halogenation step to a step in which the reducing equivalents are oxidized with a potent oxidant such as O₂ or N₂O makes the halogenation reaction thermodynamically feasible without the input of additional energy in the form of e.g. NADH. In a current model on the halogenation of tryptophan to 7-chloro-l-tryptophan NADH and O₂ are proposed as co-substrates in a reaction in which the aromatic compound is oxidized via an epoxide as intermediate. The thermodynamic calculations thus indicate that such a route hinges on mechanistic insights but has no thermodynamic necessity. Furthermore the calculations suggest that halogenation of tryptophan and other aromatic compounds should be possible with N₂O, and possibly even with nitrate replacing O₂ as the oxidant.     

Alcohol consumption, genetic variants in alcohol deydrogenases, and risk of cardiovascular diseases: a prospective study and meta-analysis

Objective

First, to investigate and compare associations between alcohol consumption and variants in alcohol dehydrogenase (ADH) genes with incidence of cardiovascular diseases (CVD) in a large German cohort. Second, to quantitatively summarize available evidence of prospective studies on polymorphisms in ADH1B and ADH1C and CVD-risk.

Methods

We conducted a case-cohort study nested within the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam cohort including a randomly drawn subcohort (n = 2175) and incident cases of myocardial infarction (MI; n = 230) or stroke (n = 208). Mean follow-up time was 8.2±2.2 years. The association between alcohol consumption, ADH1B or ADH1C genotypes, and CVD-risk was assessed using Cox proportional hazards regression. Additionally, we report results on associations of variants in ADH1B and ADH1C with ischemic heart disease and stroke in the context of a meta-analysis of previously published prospective studies published up to November 2011.

Results

Compared to individuals who drank >0 to 6 g alcohol/d, we observed a reduced risk of MI among females consuming >12 g alcohol/d (HR = 0.31; 95% CI: 0.10–0.97) and among males consuming >24 to 60 g/d (HR = 0.57; 95% CI: 0.33–0.98) or >60 g alcohol/d (HR = 0.30; 95% CI: 0.12–0.78). Stroke risk was not significantly related to alcohol consumption >6 g/d, but we observed an increased risk of stroke in men reporting no alcohol consumption. Individuals with the slow-coding ADH1B*1/1 genotype reported higher median alcohol consumption. Yet, polymorphisms in ADH1B or ADH1C were not significantly associated with risk of CVD in our data and after pooling results of eligible prospective studies [ADH1B*1/1: RR = 1.35 (95% CI: 0.98–1.88; p for heterogeneity: 0.364); ADH1C*2/2: RR = 1.07 (95% CI: 0.90–1.27; p for heterogeneity: 0.098)].

Conclusion

The well described association between alcohol consumption and CVD-risk is not reflected by ADH polymorphisms, which modify the rate of ethanol oxidation.     

Tetrahydrobiopterin and nitric oxide: mechanistic and pharmacological aspects

In previous minireviews in this journal, we discussed work on induction of tetrahydrobiopterin biosynthesis by cytokines and its significance for nitric oxide (NO) production of intact cells as well as functions of H4-biopterin identified at this time for NO synthases (Proc Soc Exp Biol Med 203: 1-12, 1993; Proc Soc Exp Biol Med 219: 171-182, 1998). Meanwhile, the recognition of the importance of tetrahydrobiopterin for NO formation has led to new insights into complex biological processes and revealed possible novel pharmacological strategies to intervene in certain pathological conditions. Recent work could also establish that tetrahydrobiopterin, in addition to its allosteric effects, is redox-active in the NO synthase reaction. In this review, we summarize the current view of how tetrahydrobiopterin functions in the generation of NO and focus on pharmacological aspects of tetrahydrobiopterin availability with emphasis on endothelial function.     

A note on cardiovascular diseases and physical aspects of the environment

This paper presents a biometeorological study of ischaemic heart diseases and a thermal load index combining meteorological factors, clothing insulation and metabolic rate. The study is based on records of weather and of hospital admissions. The data were grouped into four seasonal periods approximating the four major climate seasons experienced at Toronto, Canada. Statistical analysis of the seasonal data for five years (1976–1980) shows a good association between the deviations from group averages of the thermal load index and corresponding deviations of the number of patients admitted to hospitals at Toronto due to cardiovascular diseases if two out of nineteen data points are excluded from the analysis. In the authors' view, recognizing the nature of climate and other records, there is good reason to believe that this association is meaningful. The results indicate that at a given activity level and clothing insulation there is a higher incidence of coronorary diseases when the thermal sensation is to the cold side of the neutral comfort condition. Probable causes are advanced for the fact that 12% of the data appear anomalous.     

Prions and prion diseases: fundamentals and mechanistic details

Prion diseases, often called transmissible spongiform encephalopathies (TSEs), are infectious diseases that accompany neurological dysfunctions in many mammalian hosts. Prion diseases include Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy (BSE, "mad cow disease") in cattle, scrapie in sheep, and chronic wasting disease (CWD) in deer and elks. The cause of these fatal diseases is a proteinaceous pathogen termed prion that lacks functional nucleic acids. As demonstrated in the BSE outbreak and its transmission to humans, the onset of disease is not limited to a certain species but can be transmissible from one host species to another. Such a striking nature ofprions has generated huge concerns in public health and attracted serious attention in the scientific communities. To date, the potential transmission ofprions to humans via foodbome infectiorn and iatrogenic routes has not been alleviated. Rather, the possible transmission of human to human or cervids to human aggravates the terrifying situation across the globe. In this review, basic features about prion diseases including clinical and pathological characteristics, etiology, and transmission of diseases are described. Based on recently accumulated evidences, the molecular and biochemical aspects of prions, with an emphasis on the molecular interactions involved in prion conversion that is critical during prion replication and pathogenesis, are also addressed.     

Cerebral vascular diseases; certain clinical and electroencephalographic aspects

In a preliminary study of 52 patients with cerebral vascular disease, clinical and electroencephalographic evaluations were compared. Most of the patients were in the sixth and seventh decade of life and had had symptoms of cerebral vascular disease for over a year. Seventeen of the patients had clinical evidence of intermittent cerebral ischemia. When routine electroencephalographic techniques were used, 47 per cent of the records were within normal limits. Twenty patients with cerebral vascular disease, eight of whom had clinical cerebral vascular insufficiency, were studied during posturally induced hypotension. No activation was detected in any of these 20 patients. It would appear that other methods of activation, including tilt-table studies, and serial recordings should be further explored and evaluated in these disorders if more clinically useful information is to be gained.     

Dendritic cells as killers: mechanistic aspects and potential roles

Dendritic cells (DC) are professional APC endowed with the unique capacity to activate naive T cells. DC also have important effector functions during the innate immune response, such as pathogen recognition and cytokine production. In fact, DC represent the crucial link between innate and adaptive immune responses. However, DC are quite heterogeneous and various subsets endowed with specific pathogen recognition mechanisms, locations, phenotypes, and functions have been described both in rodents and in humans. A series of studies indicated that rodent as well as human DC could also mediate another important innate function, i.e., cell-mediated cytotoxicity, mostly toward tumor cells. In this article, we will review the phenotypes of these so-called killer DC, their killing mechanism, and putative implication in the immune response.     

Radiation protection by Terminalia chebula: Some mechanistic aspects

Radioprotective ability of the aqueous extract of the fruit of Terminalia chebula (TCE) was evaluated for its antioxidant and radioprotective abilities. TCE (50 μg) was able to neutralise 1,1-diphenyl-2-picrylhydrazyl, a stable free radical by 92.9%. The free radical neutralizing ability of TCE was comparable to that of ascorbate (100 μM) 93.5% and gallic acid (100 μM) 91.5% and was higher than that of the diethyldithiocarbamate (200 μM) 55.4%, suggesting the free radical activity of TCE. TCE protected the plasmid DNA pBR322 from undergoing the radiation-induced strand breaks. Radiation damage converts the supercoiled form (ccc) of plasmid to open circular form (oc); the presence of TCE during radiation exposure protected the plasmid from undergoing these damages. The administration of TCE (80 mg/kg body weight, i.p.) prior to whole body irradiation of mice (4 Gy) resulted in a reduction of peroxidation of membrane lipids in the mice liver as well as a decrease in radiation-induced damage to DNA, as assayed by single-cell gel electrophoresis (comet assay). TCE also protected the human lymphocytes from undergoing the gamma radiation-induced damage to DNA exposed in vitro to 2 Gy gamma-radiation. These results suggest the radioprotective ability of TCE.