Damage of erythrocytes by activated oxygen generated in hypoxic rat liver

The Impact of Bariatric Surgery on Glutathione Synthesis in Individuals with Severe Obesity

Glycine is deficient in individuals with obesity but improves following bariatric surgery. Glycine deficiency could impair glutathione (GSH) synthesis and worsen oxidative stress. We examined the impact of obesity-associated glycine deficiency and bariatric surgery on GSH synthesis. Twenty-one participants with severe obesity and twenty-one healthy weight controls were recruited. [1,2-13C2] glycine was infused to measure the erythrocyte (RBC) GSH synthesis rate. Participants with obesity underwent bariatric surgery, and 19 were restudied six months post-surgery. Compared to healthy weight controls, individuals with obesity had significantly lower concentrations of RBC GSH (2.43 ± 0.23 vs. 2.63 ± 0.26 mmol/L, p < 0.01). However, there were no differences in GSH fractional synthesis rate [78.0 (51.4-123.7) vs. 76.9 (49.3-110.1) % pool/day, p = 0.58] or absolute synthesis rate [1.85 (1.25-3.32) vs. 1.92 (1.43-3.03) mmol/L RBC/day, p = 0.97]. Despite a post-surgery increase in glycine concentration, no statistically significant changes in RBC GSH concentration or synthesis rates were detected. Further, the significant correlation between plasma glycine and RBC GSH concentration at baseline (r = 0.46, p < 0.01) was also lost following bariatric surgery. GSH concentration was significantly lower in participants with obesity, but bariatric surgery did not significantly increase GSH concentrations or synthesis rates.

PlanHab Study: Consequences of combined normobaric hypoxia and bed rest on adenosine kinetics

Adenosine plays a role in the energy supply of cells and provokes differential, hormone-like functions in circulating cells and various tissues. Its release is importantly regulated by oxygen tension. This renders adenosine and its kinetics interesting to investigate in humans subjected to low oxygen conditions. Especially for space exploration scenarios, hypoxic conditions - together with reduced gravity - represent two foreseen living conditions when planning manned long-duration space missions or planetary habitats. The PlanHab study investigated microgravity through inactivity in bed rest and normobaric hypoxia to examine their independent or combined effect on adenosine and its kinetics. Healthy male subjects (n = 14) completed three 21-day interventions: hypoxic bed rest (HBR); hypoxic ambulatory confinement (HAMB); normoxic bed rest (NBR). The interventions were separated by 4 months. Our hypothesis of a hypoxia-triggered increase in adenosine was confirmed in HAMB but unexpectedly also in NBR. However, the highest adenosine levels were noted following HBR. Furthermore, the percentage of hemolysis was elevated in HBR whereas endothelial integrity markers stayed low in all three interventions. In summary, these data suggest that neocytolysis accounts for these effects while we could reduce evidence for microcirculatory changes.

Hemolysis is a primary ATP-release mechanism in human erythrocytes

The hypothesis that regulated ATP release from red blood cells (RBCs) contributes to nitric oxide-dependent control of local blood flow has sparked much interest in underlying release mechanisms. Several stimuli, including shear stress and hypoxia, have been found to induce significant RBC ATP release attributed to activation of ATP-conducting channels. In the present study, we first evaluated different experimental approaches investigating stimulated RBC ATP release and quantifying hemolysis. We then measured ATP and free hemoglobin in each and every RBC supernatant sample to directly assess the contribution of hemolysis to ATP release. Hypotonic shock, shear stress, and hypoxia, but not cyclic adenosine monophosphate agonists, significantly enhanced ATP release. It tightly correlated, however, with free hemoglobin in RBC supernatants, indicating that lysis was responsible for most, if not all, ATP release. Luminescence ATP imaging combined with simultaneous infrared cell imaging showed that ATP was released exclusively from lysing cells with no contribution from intact cells. In summary, with all stimuli tested, we found no evidence of regulated ATP release from intact RBCs other than by cell lysis. Such a release mechanism might be physiologically relevant in vivo, eg, during exercise and hypoxia where intravascular hemolysis, predominantly of senescent cells, is augmented.

Role of hemolysis in red cell adenosine triphosphate release in simulated exercise conditions in vitro

INTRODUCTION

Specific adenosine triphosphate (ATP) release from red blood cells has been discussed as a possible mediator controlling microcirculation in states of decreased tissue oxygen. Because intravascular hemolysis might also contribute to plasma ATP, we tested in vitro which portion of ATP release is due to hemolysis in typical exercise-induced strains to the red blood cells (shear stress, deoxygenation, and lactic acidosis).

METHODS

Human erythrocytes were suspended in dextran-containing media (hematocrit 10%) and were exposed to shear stress in a rotating Couette viscometer at 37°C. Desaturation (oxygen saturation of hemoglobin ∼20%) was achieved by tonometry with N2 before shear stress exposure. Cells not exposed to shear stress were used as controls. Na lactate (15 mM), lactic acid (15 mM, pH 7.0), and HCl (pH 7.0) were added to simulate exercise-induced lactic acidosis. After incubation, extracellular hemoglobin was measured to quantify hemolysis. ATP was measured with the luciferase assay.

RESULTS

Shear stress increased extracellular ATP in a stress-related and time-dependent manner. Hypoxia induced a ∼10-fold increase in extracellular ATP in nonsheared cells and shear stress-exposed cells. Lactic acid had no significant effect on ATP release and hemolysis. In normoxic cells, approximately 20%-50% of extracellular ATP was due to hemolysis. This proportion decreased to less than 10% in hypoxic cells.

CONCLUSIONS

Our results indicate that when exposing red blood cells to typical strains they encounter when passing through capillaries of exercising skeletal muscle, ATP release from red blood cells is caused mainly by deoxygenation and shear stress, whereas lactic acidosis had only a minor effect. Hemolysis effects were decreased when hemoglobin was deoxygenated. Together, by specific release and hemolysis, extracellular ATP reaches values that have been shown to cause local vasodilatation.

Blood glutathione redox status and global methylation of peripheral blood mononuclear cell DNA in Bangladeshi adults

Oxidative stress and DNA methylation are metabolically linked through the relationship between one-carbon metabolism and the transsulfuration pathway, but possible modulating effects of oxidative stress on DNA methylation have not been extensively studied in humans. Enzymes involved in DNA methylation, including DNA methyltransferases and histone deacetylases, may show altered activity under oxidized cellular conditions. Additionally, in vitro studies suggest that glutathione (GSH) depletion leads to global DNA hypomethylation, possibly through the depletion of S-adenosylmethionine (SAM). We tested the hypothesis that a more oxidized blood GSH redox status is associated with decreased global peripheral blood mononuclear cell (PBMC) DNA methylation in a sample of Bangladeshi adults. Global PBMC DNA methylation and whole blood GSH, glutathione disulfide (GSSG), and SAM concentrations were measured in 320 adults. DNA methylation was measured by using the [ (3)H]-methyl incorporation assay; values are inversely related to global DNA methylation. Whole blood GSH redox status (Eh) was calculated using the Nernst equation. We found that a more oxidized blood GSH Eh was associated with decreased global DNA methylation (B ± SE, 271 ± 103, p = 0.009). Blood SAM and blood GSH were associated with global DNA methylation, but these relationships did not achieve statistical significance. Our findings support the hypothesis that a more oxidized blood GSH redox status is associated with decreased global methylation of PBMC DNA. Furthermore, blood SAM does not appear to mediate this association. Future research should explore mechanisms through which cellular redox might influence global DNA methylation.

Repeated supratherapeutic doses of paracetamol in children--a literature review and suggested clinical approach

The safety of paracetamol when given in the recommended dosage is well documented. However, in recent years there have been many reports of liver failure associated with repeated exposure to supratherapeutic doses of paracetamol. This paper reviews the literature on chronic supratherapeutic paracetamol exposure in children and the different dosing guidelines. Based on which, we suggest the following approach: liver injury secondary to repeated dosing of paracetamol should be considered when a child has received more than 75 mg/kg/d for at least 2 d, or if risk factors for paracetamol toxicity have been identified. Liver transaminases, coagulation factors, and paracetamol serum concentrations should be measured in these children and in symptomatic children with vomiting, right upper quadrant abdominal pain, and jaundice who have taken paracetamol. Treatment with N-acetyl cysteine should be started regardless of paracetamol concentrations if transaminases or INR are elevated.

CONCLUSION

Liver injury secondary to repeated dosing of paracetamol is rare but may result in severe morbidity and mortality. The cumulative dose of paracetamol should not exceed 75 mg/kg/d. Children treated with higher doses for more than 2 d should be evaluated for possible liver injury and treated with N-acetyl cysteine if evidence of liver injury is found.

Glutathione, glutathione-dependent enzymes and antioxidant status in erythrocytes from children treated with high-dose paracetamol

AIM

To investigate glutathione and antioxidant status changes in erythrocytes from febrile children receiving repeated supratherapeutic paracetamol doses.

METHODS

Fifty-one children aged 2 months to 10 years participated in the study. Three groups were studied: group 1 (n = 24) included afebrile children who did not receive paracetamol; and groups 2 (n = 13) and 3 (n = 14) included children who had fever above 38.5 degrees C for more than 72 h. Patients in group 2 received paracetamol at a dose of 50 +/- 15 (30-75) mg kg(-1) day(-1) and those in group 3 received paracetamol above the recommended therapeutic dose, ie 107 28 (80-180) mg kg(-1) day(-1). A blood sample was taken for the measurement of liver transaminases, gammaglutamil transferase (GGT), reduced glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST), superoxide dismutase (SOD) and antioxidant status.

RESULTS

Aspartate aminotransferase activity in group 3 was higher than in the other groups (P = 0.027). GSH, SOD and antioxidant status were significantly lower in group 3 compared with groups 1 and 2 (mean differences: for GSH 3.41 micromol gHb(-1), 95% confidence interval (CI) 2.10-4.72, and 2.15 micromol gHb(-1), 95% CI 0.65-3.65, respectively; for SOD 856 U min(-1) gHb(-1), 95% CI 397-1316, and 556 U min(-1) gHb(-1), 95% CI 30-1082, respectively; and for antioxidant status 0.83 mmol l(-1) plasma, 95% CI 0.30-1.36, and 0.63 mmol l(-1) plasma, 95% CI 0.02-1.24, respectively). GR activity was significantly lower in groups 3 and 2 in comparison with group 1 (mean differences 3.44 U min(-1) gHb(-1), 95% CI 0.63-6.25, and 5.64 U min(-1) gHb(-1), 95% CI 2.90-8.38, respectively). Using multiple regression analysis, paracetamol dose was found to be the only independent variable affecting GR, GST and SOD activities (P = 0.007, 0.003 and 0.008, respectively).

CONCLUSIONS

In febrile children, treatment with repeated supratherapeutic doses of paracetamol is associated with reduced antioxidant status and erythrocyte glutathione concentrations. These significant changes may indicate an increased risk for hepatotoxicity and liver damage.

Uric acid and glutathione levels during short-term whole body cold exposure

Ten healthy subjects who swim regularly in ice-cold water during the winter (winter swimming), were evaluated before and after this short-term whole body exposure. A drastic decrease in plasma uric acid concentration was observed during and following the exposure to the cold stimulus. We hypothesize that the uric acid decrease can be caused by its consumption after formation of oxygen radicals. In addition, the erythrocytic level of oxidized glutathione and the ratio of oxidized glutathione/total glutathione also increased following cold exposure, which supports this hypothesis. Furthermore, the baseline concentration of reduced glutathione was increased and the concentration of oxidized glutathione was decreased in the erythrocytes of winter swimmers as compared to those of nonwinter swimmers. This can be viewed as an adaptation to repeated oxidative stress, and is postulated as mechanism for body hardening. Hardening is the exposure to a natural, e.g., thermal stimulus, resulting in an increased tolerance to stress, e.g., diseases. Exposure to repeated intensive short-term cold stimuli is often applied in hydrotherapy, which is used in physical medicine for hardening.

Radical formation in the rat small intestine during and following ischemia

Oxidative loading during the reperfusion of the proximal jejunum of rats following a one hour-period of complete ischemia was demonstrated in in vivo-experiments by the increases of the GSSG: total glutathione ratio and the concentration of TBA-RS. The pretreatment of the animals with the xanthine oxidoreductase inhibitor allopurinol diminished the accumulation of GSSG and of TBA-RS. It was concluded that the purine nucleotide degradation is an important source of oxygen reduction products in reoxygenated small intestine. The tissue concentrations of nucleotides, nucleosides and nucleobases were measured by an ion-pair reversed-phase HPLC separation. There occurred fast declines of ATP and GTP concentrations during ischaemia leading to temporary increases of nucleoside mono- and diphosphate pools. The hypoxanthine concentration is increased about twentyfold during oxygen deficiency. The ATP and GTP restoration during the reperfusion was accelerated in presence of allopurinol. The shares of the beneficial allopurinol effects are not yet clarified.