Hydrogen peroxide cytotoxicity. Low-temperature enhancement by ascorbate or reduced lipoate.

The principal mechanism of H2O2 toxicity is thought to involve the generation of hydroxyl (HO.) radicals through its interactions with Fe2+ ions by the Fenton reaction. Of particular interest has been the demonstration by Ward, Blakely & Joner [(1985) Radiat. Res. 103, 383-392] that the cytotoxicity of H2O2 is diminished at low temperature. We have now examined this phenomenon further with a mammalian epithelial cell line (CNCMI-221). Resistance of these cells to 100 microM-H2O2 added extracellularly exhibits a transition in the temperature range between 27 degrees C and 22 degrees C. We have found that the low-temperature resistance to cytotoxic concentrations of H2O2 is abolished by preincubation of cells with reductants such as ascorbate or reduced lipoic acid. This implies that the low-temperature resistance to H2O2 cytotoxicity may be due to inhibition of cellular reductive processes. The restoration of the cytotoxic action of H2O2 at 4 degrees C by ascorbate is prevented by pre-exposure of cells to desferrioxamine. This is evidence that transition-metal ions (such as iron ions) are involved in the cytotoxicity and is consistent with a mechanism of cell damage that depends on the Fenton reaction and a metal ion in the reduced state. Restoration of H2O2 cytotoxicity at low temperature by ascorbate is consistent with the artificial production of an intracellular reducing environment that at normal temperatures is sustained by cellular metabolism.     

Incomplete depletion and rapid regeneration of Foxp3+ regulatory T cells following anti-CD25 treatment in malaria-infected mice

Investigation of the role of regulatory T cells (Treg) in model systems is facilitated by their depletion using anti-CD25 Abs, but there has been considerable debate about the effectiveness of this strategy. In this study, we have compared the depletion and repopulation of CD4+CD25+Foxp3+ Treg in uninfected and malaria-infected mice using 7D4 and/or PC61 anti-CD25 Abs. We find that numbers and percentages of CD25(high) cells, but not Foxp3+ cells, are transiently reduced after 7D4 treatment, whereas treatment with PC61 alone or in combination with 7D4 (7D4 plus PC61) reduces but does not eliminate Foxp3+ cells for up to 2 wk. Importantly, all protocols fail to eliminate significant populations of CD25-Foxp3+ or CD25(low)Foxp3+ cells, which retain potent regulatory capacity. By adoptive transfer we show that repopulation of the spleen by CD25(high)Foxp3+ cells results from the re-expression of CD25 on peripheral populations of CD25-Foxp3+ but not from the conversion of peripheral Foxp3-) cells. CD25(high)Foxp3+ repopulation occurs more rapidly in 7D4-treated mice than in 7D4 plus PC61-treated mice, reflecting ongoing clearance of emergent CD25+Foxp3+ cells by persistent PC61 Ab. However, in 7D4 plus PC61-treated mice undergoing acute malaria infection, repopulation of the spleen by CD25+Foxp3+ cells occurs extremely rapidly, with malaria infection driving proliferation and CD25 expression in peripheral CD4+CD25-Foxp3+ cells and/or conversion of CD4+CD25-Foxp3- cells. Finally, we reveal an essential role for IL-2 for the re-expression of CD25 by Foxp3+ cells after anti-CD25 treatment and observe that TGF-beta is required, in the absence of CD25 and IL-2, to maintain splenic Foxp3+ cell numbers and a normal ratio of Treg:non-Treg cells.     

Pregnant women exaggerate cautious gait patterns during the transition between level and hill surfaces

Falls are the leading cause of nonfatal injury across all age groups and a common incident for pregnant women. Thus, there is a critical demand for research to evaluate if walking strategies in pregnant women change throughout pregnancy in order to effectively intervene and minimize the incidence rate. The aim of the present study was to analyze modifications in temporal–spatial parameters as well as muscle activity during hill walking transitions in pregnant women between gestational week 20 and 32. Based upon previous literature, we hypothesized that in comparison to level walking, the transition strides of pregnant women would be distinct between trimesters in order to accommodate the physical changes within twelve weeks. Thirteen pregnant women completed a series of randomly assigned walking conditions on level and hill surfaces during gestational week 20 and 32. Our results demonstrated that pregnant women modulated their gait patterns throughout pregnancy with additional joint flexion as well as muscle activity at the ankle, knee and hip. In summary, pregnant women exaggerate cautious gait patterns by walking slower and wider with greater joint flexion and muscle activity in order to safely transition between level and hill surfaces.     

Free mycolic acid accumulation in the cell wall of the mce1 operon mutant strain of Mycobacterium tuberculosis

The lipid-rich cell wall of Mycobacterium tuberculosis, the agent of tuberculosis, serves as an effective barrier against many chemotherapeutic agents and toxic host cell effector molecules, and it may contribute to the mechanism of persistence. Mycobacterium tuberculosis strains mutated in a 13-gene operon called mce1, which encodes a putative ABC lipid transporter, induce aberrant granulomatous response in mouse lungs. Because of the postulated role of the mce1 operon in lipid importation, we compared the cell wall lipid composition of wild type and mce1 operon mutant M. tuberculosis H37Rv strains. High resolution mass spectrometric analyses of the mce1 mutant lipid extracts showed unbound mycolic acids to accumulate in the cell wall. Quantitative analysis revealed a 10.7 fold greater amount of free mycolates in the mutant compared to that of the wild type strain. The free mycolates were comprised of alpha, methoxy and keto mycolates in the ratio 1:0.9:0.6, respectively. Since the mce1 operon is regulated in vivo, the free mycolates that accumulate during infection may serve as a barrier for M. tuberculosis against toxic products and contribute to the pathogen’s persistence.     

Testing small study effects in multivariate meta-analysis

Small study effects occur when smaller studies show different, often larger, treatment effects than large ones, which may threaten the validity of systematic reviews and meta-analyses. The most well-known reasons for small study effects include publication bias, outcome reporting bias, and clinical heterogeneity. Methods to account for small study effects in univariate meta-analysis have been extensively studied. However, detecting small study effects in a multivariate meta-analysis setting remains an untouched research area. One of the complications is that different types of selection processes can be involved in the reporting of multivariate outcomes. For example, some studies may be completely unpublished while others may selectively report multiple outcomes. In this paper, we propose a score test as an overall test of small study effects in multivariate meta-analysis. Two detailed case studies are given to demonstrate the advantage of the proposed test over various naive applications of univariate tests in practice. Through simulation studies, the proposed test is found to retain nominal Type I error rates with considerable power in moderate sample size settings. Finally, we also evaluate the concordance between the proposed tests with the naive application of univariate tests by evaluating 44 systematic reviews with multiple outcomes from the Cochrane Database.