Passive Glial Cells, Fact or Artifact?

Astrocytes that are recorded in acute tissue slices of rat hippocampus using whole-cell patch-clamp, commonly exhibit voltage-activated Na⁺ and K⁺ currents. Some reports have described astrocytes that appear to lack voltage-activated currents and proposed that these cells constitute a subpopulation of electrophysiologically passive astrocytes. We show here that these cells can spontaneously change during a recording unmasking expression of previously suppressed voltage-activated currents, suggesting that such cells do not represent a subpopulation of passive astrocytes. Superfusion of a low Ca²⁺/EGTA solution was able to reversibly suppress voltage-activated K⁺ currents in cultured astrocytes. Currents were restored upon addition of normal bath Ca²⁺. These effects of Ca²⁺ on both outward and inward K⁺ currents were dose- and time-dependent, with increasing concentrations of Ca²⁺ (from 0 to 800 μm) leading to a gradual unmasking of voltage-dependent outward and inward K⁺ currents. The transition from an apparently passive cell to one exhibiting prominent voltage-activated currents was not associated with any changes in membrane capacitance or access resistance. By contrast, in cells in which low access resistance or poor seal accounted for the absence of voltage-activated currents, improvement of cell access was always accompanied by changes in series resistance and membrane capacitance. We propose that spillage of pipette solution containing low Ca²⁺/EGTA during cell approach in slice recordings and/or poor cell access, lead to a transient masking of voltage-activated currents even in astrocytes that express prominent voltage-activated currents. These cells, however, do not constitute a subpopulation of electrophysiologically passive astrocytes. Received: 22 April 1998/Revised: 8 September 1998     

Multiple ITS Haplotypes in the Genome of the Lichenized Basidiomycete Cora inversa (Hygrophoraceae): Fact or Artifact?

The internal transcribed spacer region (ITS) of the nuclear rDNA cistron represents the barcoding locus for Fungi. Intragenomic variation of this multicopy gene can interfere with accurate phylogenetic reconstruction of biological entities. We investigated the amount and nature of this variation for the lichenized fungus Cora inversa in the Hygrophoraceae (Basidiomycota: Agaricales), analyzing base call and length variation in ITS1 454 pyrosequencing data of three samples of the target mycobiont, for a total of 16,665 reads obtained from three separate repeats of the same samples under different conditions. Using multiple fixed alignment methods (PaPaRa) and maximum likelihood phylogenetic analysis (RAxML), we assessed phylogenetic relationships of the obtained reads, together with Sanger ITS sequences from the same samples. Phylogenetic analysis showed that all ITS1 reads belonged to a single species, C. inversa. Pyrosequencing data showed 266 insertion sites in addition to the 325 sites expected from Sanger sequences, for a total of 15,654 insertions (0.94 insertions per read). An additional 3,279 substitutions relative to the Sanger sequences were detected in the dataset, out of 5,461,125 bases to be called. Up to 99.3 % of the observed indels in the dataset could be interpreted as 454 pyrosequencing errors, approximately 65 % corresponding to incorrectly recovered homopolymer segments, and 35 % to carry-forward-incomplete-extension errors. Comparison of automated clustering and alignment-based phylogenetic analysis demonstrated that clustering of these reads produced a 35-fold overestimation of biological diversity in the dataset at the 95 % similarity threshold level, whereas phylogenetic analysis using a maximum likelihood approach accurately recovered a single biological entity. We conclude that variation detected in 454 pyrosequencing data must be interpreted with great care and that a combination of a sufficiently large number of reads per taxon, a set of Sanger references for the same taxon, and at least two runs under different emulsion PCR and sequencing conditions, are necessary to reliably separate biological variation from 454 sequencing errors. Our study shows that clustering methods are highly sensitive to artifactual sequence variation and inadequate to properly recover biological diversity in a dataset, if sequencing errors are substantial and not removed prior to clustering analysis.     

Hypothyroidism as A Cause of Hyponatremia: Fact or Fiction?

ObjectiveTo illustrate that severe primary hypothyroidism alone may not be enough to cause hyponatremia in the otherwise healthy ambulatory patient.Methods:A retrospective chart review was conducted using an academic health center enterprise-wide electronic health record to identify 10 patients with primary hypo thyroidism and same-day serum thyroid-stimulating hormone (TSH), sodium, creatinine, and calculated glomerular filtration rate (GFR). Same-day free triiodothyronine or free thyroxine was also recorded if tested. Patients were included in our case series if they met the following inclusion criteria: TSH level > 100 μU/mL and same-day sodium and creatinine levels. All laboratory tests were collected on an outpatient basis.ResultsThe 10 subjects (2 men and 8 women) were ages 19 to 97 years (median, 51.5 years). Median TSH was 193 μU/mL (range, 104.2 to 515.6 μU/mL; normal, 0.40 to 5.50 μU/mL) with median sodium of 138 mmol/L (range, 136 to 142 mmol/L; normal, 135 to 146 mmol/L). The lowest sodium was 136 mmol/L with concurrent TSH of 469.7 μU/mL, free triiodothyronine of 1.0 pg/mL (normal, 1.8 to 4.6 pg/mL), and free thyroxine of 0.2 ng/ dL (normal, 0.7 to 1.8 ng/dL). Median GFR was 67.5 mL/ min/1.73 m² (range, 44 to 114 mL/min/1.73 m²; normal, 90 to 120 mL/min/1.73 m²).ConclusionIn our small series of patients with extreme TSH elevations, none had a serum sodium level below normal (< 135 mmol/L), even in the presence of a reduced GFR. Hyponatremia can be a common occurrence in hospitalized and/or chronically ill patients; however, in an otherwise relatively healthy ambulatory patient, hypothyroidism, even when severely undertreated, may be a less clinically relevant cause of hyponatremia. (Endocr Pract. 2012;18:894-897)     

Freshman 15: Fact or Fiction?

Objective: The objective of this study was to investigate changes in body weight, BMI, body composition, and fat distribution among freshman women during their 1st year of college. Research Methods and Procedures: Freshman women during the 2004 to 2005 academic year were recruited to participate. The initial baseline visit occurred within the first 6 weeks of the fall 2004 semester, with the follow‐up visit occurring during the last 6 weeks of the spring 2005 semester. At each visit, height, weight, BMI, waist and hip circumferences, and body composition (by DXA) were obtained. Results: One hundred thirty‐seven participants completed both the fall and spring visits. Significant (p < 0.0001) increases between the fall and spring visits were observed for body weight (58.6 vs. 59.6 kg), BMI (21.9 vs. 22.3), percentage body fat (28.9 vs. 29.7), total fat mass (16.9 vs. 17.7 kg), fat‐free mass (38.1 vs. 38.4 kg), waist circumference (69.4 vs. 70.3 cm), and hip circumference (97.4 vs. 98.6 cm), with no significant difference observed in the waist‐to‐hip ratio (0.71 vs. 0.71; p = 0.78). Discussion: Although statistically significant, changes in body weight, body composition, and fat mass were modest for women during their freshman year of college. These results do not support the purported “freshman 15” weight gain publicized in the popular media.     

Human age reversal: Fact or fiction?

Although chronological age correlates with various age‐related diseases and conditions, it does not adequately reflect an individual''s functional capacity, well‐being, or mortality risk. In contrast, biological age provides information about overall health and indicates how rapidly or slowly a person is aging. Estimates of biological age are thought to be provided by aging clocks, which are computational models (e.g., elastic net) that use a set of inputs (e.g., DNA methylation sites) to make a prediction. In the past decade, aging clock studies have shown that several age‐related diseases, social variables, and mental health conditions associate with an increase in predicted biological age relative to chronological age. This phenomenon of age acceleration is linked to a higher risk of premature mortality. More recent research has demonstrated that predicted biological age is sensitive to specific interventions. Human trials have reported that caloric restriction, a plant‐based diet, lifestyle changes involving exercise, a drug regime including metformin, and vitamin D3 supplementation are all capable of slowing down or reversing an aging clock. Non‐interventional studies have connected high‐quality sleep, physical activity, a healthy diet, and other factors to age deceleration. Specific molecules have been associated with the reduction or reversal of predicted biological age, such as the antihypertensive drug doxazosin or the metabolite alpha‐ketoglutarate. Although rigorous clinical trials are needed to validate these initial findings, existing data suggest that aging clocks are malleable in humans. Additional research is warranted to better understand these computational models and the clinical significance of lowering or reversing their outputs.     

Maximum Residue Levels: Fact or Fiction?

Maximum residue levels (MRLs) are trading standards that represent the maximum residue that could be found if a crop protection product (CPP) is applied according to critical good agricultural practice (cGAP). Foodstuffs are monitored for MRL compliance and exceedence can have economic, social and political consequences. There is a trade-off when calculating MRLs, as low MRLs prevent misuse of CPPs and high MRLs prevent an ‘unlucky’ farmer exceeding the MRL by chance. Chance exceedence has not been previously investigated despite the high probability of exceedence due to small data sets and calculation method. In this study, MRL calculation methods were investigated and policy for using these methods to control chance exceedence was defined. The shape and parameters of the residue distribution, LOQ and number of trials all affected the accuracy and precision of the estimated MRL. The two European methods were least accurate and precise at small numbers of trials and high CVs, with up to four different MRLs possible. Eight to 16 trials gave the best estimate of the MRL, but exceedence by chance could occur in up to 45% of samples. Policy was defined for using existing methods, and involved calculation of the MRL by both methods and taking the highest.     

Pancreatic cancer stem cells: Fact or fiction?

The terms cancer-initiating or cancer stem cells have been the subject of great interest in recent years. In this review we will use pancreatic cancer as an overall theme to draw parallels with historical findings to compare to recent reports of stem-like characteristics in pancreatic cancer. We will cover such topics as label-retaining cells (side-population), ABC transporter pumps, telomerase, quiescence, cell surface stem cell markers, and epithelial–mesenchymal transitions. Finally we will integrate the available findings into a pancreatic stem cell model that also includes metastatic disease.     

The carbon-quality temperature hypothesis: Fact or artefact?

Climate warming can reduce global soil carbon stocks by enhancing microbial decomposition. However, the magnitude of this loss remains uncertain because the temperature sensitivity of the decomposition of the major fraction of soil carbon, namely resistant carbon, is not fully known. It is now believed that the resistance of soil carbon mostly depends on microbial accessibility of soil carbon with physical protection being the primary control of the decomposition of protected carbon, which is insensitive to temperature changes. However, it is still unclear whether the temperature sensitivity of the decomposition of unprotected carbon, for example, carbon that is not protected by the soil mineral matrix, may depend on the chemical recalcitrance of carbon compounds. In particular, the carbon-quality temperature (CQT) hypothesis asserts that recalcitrant low-quality carbon is more temperature-sensitive to decomposition than labile high-quality carbon. If the hypothesis is correct, climate warming could amplify the loss of unprotected, but chemically recalcitrant, carbon and the resultant CO₂ release from soils to the atmosphere. Previous research has supported this hypothesis based on reported negative relationships between temperature sensitivity and carbon quality, defined as the decomposition rate at a reference temperature. Here we show that negative relationships can arise simply from the arbitrary choice of reference temperature, inherently invalidating those tests. To avoid this artefact, we defined the carbon quality of different compounds as their uncatalysed reaction rates in the absence of enzymes. Taking the uncatalysed rate as the carbon quality index, we found that the CQT hypothesis is not supported for enzyme-catalysed reactions, which showed no relationship between carbon quality and temperature sensitivity. The lack of correlation in enzyme-catalysed reactions implies similar temperature sensitivity for microbial decomposition of soil carbon, regardless of its quality, thereby allaying concerns of acceleration of warming-induced decomposition of recalcitrant carbon.     

Schistosome resistance to praziquantel: Fact or artifact?

Praziquantel is the current drug of choice for human schistosomiasis. Recent reports from laboratory and field studies concerning reduced praziquantel efficacy against Schistosoma mansoni have generated some controversy. The prevailing question is whether the emergence of strains of schistosome resistant to praziquantel is a fact, or an artifact resulting from erroneous field or laboratory experimentation. In this article, Padraic Fallon, Liang-feng Tao, Magdi Ismail and James Bennett examine the available evidence for schistosome resistance to praziquantel. Contributory factors to the schistosomicidal activity of praziquantel, which may interfere with evaluation of drug efficacy or resistance, are also considered.     

Hormesis and ecological risk assessment: Fact or fantasy?

Hormesis is a widespread phenomenon across occurring many taxa and chemicals, and, at the single species level, issues regarding the application of hormesis to human health and ecological risk assessment are similar. However, interpreting the significance of hormesis for even a single species in an ecological risk assessment can be complicated by competition with other species, predation effects, etc. In addition, ecological risk assessments may involve communities of hundreds or thousands of species as well as a range of ecological processes. Applying hormetic adjustments to threshold effect levels for chemicals derived from sensitivity distributions for a large number of species is impractical. For ecological risks, chemical stressors are frequently of lessor concern than physical stressors (e.g., habitat alteration) or biological stressors (e.g., introduced species), but the relevance of hormesis to non‐chemical stressors is unclear. Although ecological theories such as the intermediate disturbance hypothesis offer some intriguing similarities between chemical hormesis and hormetic‐like responses resulting from physical disturbances, mechanistic explanations are lacking. While further exploration of the relevance of hormesis to ecological risk assessment is desirable, it is unlikely that hormesis is a critical factor in most ecological risk assessments, given the magnitude of other uncertainties inherent in the process.     

Entropy—enthalpy compensation: Fact or artifact?

The phenomenon of entropy–enthalpy (S‐H) compensation is widely invoked as an explanatory principle in thermodynamic analyses of proteins, ligands, and nucleic acids. It has been suggested that this compensation is an intrinsic property of either complex, fluctuating, or aqueous systems. The questions examined here are whether the observed compensation is extra‐thermodynamic (i.e., reflects anything more than the well‐known laws of statistical thermodynamics) and if so, what does it reveal about the system? Compensation is rather variably defined in the literature and different usages are discussed. The most precise and interesting one, which is considered here, is a linear relationship between ΔH and ΔS for some series of perturbations or changes in experimental variable. Some recent thermodynamic data on proteins purporting to show compensation is analyzed and shown to be better explained by other causes. A general statistical mechanical model of a complex system is analyzed to explore whether and under what conditions extra‐thermodynamic compensation can occur and what it reveals about the system. This model shows that the most likely behavior to be seen is linear S‐H compensation over a rather limited range of perturbations with a compensation temperature Tc = dΔH/dΔS within 20% of the experimental temperature. This behavior is insensitive to the details of the model, thus revealing little extra‐thermodynamic or causal information about the system. In addition, it will likely be difficult to distinguish this from more trivial forms of compensation in real experimental systems.