Impaired Antioxidant Capacity Research Articles

Biochemical and clinical correlates of hypouricemia in surgical and critically ill patients

Changes in plasma uric acid concentration (UA, mumol/L) in postoperative and critical illness have pathophysiological and clinical relevance and may alter plasma antioxidant capacity. This issue is poorly understood because UA is simultaneously affected by multiple factors with impacts that have never been definitively characterized. Data from 1050 measurements of UA and additional variables obtained in 151 patients were processed using regression analysis. The main direct correlate of UA was plasma creatinine (Cr), even in the absence of renal failure. UA was also related directly to sodium, glucose, cholesterol, albumin and other variables, and inversely to bilirubin. Postoperatively UA decreased, remaining related to preoperative UA and decreasing further with sepsis. In parenterally fed patients, UA was also inversely related to the amino acid dose. The following best fit explained three-quarters of its variability: UA=85.0(ln Cr, micromol/L)+0.6(preoperative UA)+4.3 (sodium, mmol/L)+5.4(glucose, mmol/L)-0.2(bilirubin, micromol/L)-28.9(amino acid dose, g/kg/day)-935.6; n=231, r(2)=0.74, p<0.0001. A contribution of extremely low UA to impaired plasma antioxidant capacity was suggested in severe sepsis. These data show the combined effect of several factors on UA. The results may help to evaluate changes in UA in the clinical setting and pathophysiological events related to oxidative stress, and provide evidence of impaired plasma antioxidant capacity in severe sepsis.

Low hair selenium and plasma glutathione peroxidase in children with chronic renal failure

Selenium (Se) is a trace element that incorporates into the selenoenzyme glutathione peroxidase (GSH-Px). There are conflicting results regarding the Se levels and activity of GSH-Px in adult uremic patients. The aim of this study was to determine (1) the hair Se status, (2) the possible relation between the hair Se status and the antioxidant enzyme, GSH-Px, and (3) the influence of different treatment procedures on hair Se status and GSH-Px activity in children with CRI, those treated conservatively and those on HD and on CAPD. Ninety-three patients, including 32 patients with CRI, treated conservatively, 42 PD patients, 19 HD patients and 34 healthy children were enrolled in the study. The hair Se level was measured by the atomic absorption spectrophotometer method. Plasma GSH-Px activity was determined using a Randox test combination (RANSEL). Hair Se levels were significantly lower in the CRI, CAPD, and HD groups when compared to the control group (P=0.001, P=0.001, and P=0.001, respectively). Plasma GSH-Px activity was significantly lower in the CRI, CAPD, and HD groups when compared to the control group (P=0.001, P=0.001, and P=0.001, respectively). Plasma GSH-Px activity correlated with the GFR in patients with CRI and the control group (P=0.000; r(2)=0.60). There was no correlation between plasma GSH-Px and hair Se levels in the patient and control groups. These results revealed a decreased hair Se level and impaired antioxidative capacity in children with CRI on CAPD and HD. The lack of any relation between plasma GSH-Px and hair Se suggests that plasma GSH-Px is not a good marker of Se stores.

The Role of Phospholipid Hydroperoxide Glutathione Peroxidase Isoforms in Murine Embryogenesis

Phospholipid hydroperoxide glutathione peroxidase (GPx4) is a selenocysteine-containing enzyme, and three different isoforms (cytosolic, mitochondrial, and nuclear) originate from the GPx4 gene. Homozygous GPx4-deficient mice die in utero at midgestation, since they fail to initiate gastrulation and do not develop embryonic cavities. To investigate the biological basis for embryonic lethality, we first explored expression of the GPx4 in adult murine brain and found expression of the protein in cerebral neurons. Next, we profiled mRNA expression during the time course of embryogenesis (embryonic days 6.5-17.5 (E6.5-17.5)) and detected mitochondrial and cytosolic mRNA species at high concentrations. In contrast, the nuclear isoform was only expressed in small amounts. Cytosolic GPx4 mRNA was present at constant levels (about 100 copies per 1000 copies of glyceraldehyde-3-phosphate dehydrogenase mRNA), whereas nuclear and mitochondrial isoforms were down-regulated between E14.5 and E17.5. In situ hybridization indicated expression of GPx4 isoforms in all developing germ layers during gastrulation and in the somite stage in the developing central nervous system and in the heart. When we silenced expression of GPx4 isoforms during in vitro embryogenesis using short interfering RNA technology, we observed that knockdown of mitochondrial GPx4 strongly impaired segmentation of rhombomeres 5 and 6 during hindbrain development and induced cerebral apoptosis. In contrast, silencing expression of the nuclear isoform led to retardations in atrium formation. Taken together, our data indicate specific expression of GPx4 isoforms in embryonic brain and heart and strongly suggest a role of this enzyme in organogenesis. These findings may explain in part intrauterine lethality of GPx4 knock-out mice.

Effect of aging on resistance to oxidative stress in human endothelial progenitor cells (EPCs)

The role of oxidative stress and antioxidant enzymes in the aging related dysfunction of EPCs has not been studied. We hypothesized that impaired antioxidant capacity contributes to dysfunction of EPCs. Early EPCs isolated from healthy young (24±3 year-old, n=9) and aged (71±5 year-old, n=9) males were examined. The levels of protein expression and enzymatic activity of glutathione peroxidase 1 (GPX1) were decreased significantly in the EPCs from aged individuals in compared to EPCs from young individuals (n=9, P<0.05). After 24 h of serum starvation EPC numbers in young group and aged group were 0.6±0.2 and 0.4±0.1, respectively (expressed as ratio to the cell number under normal culture conditions, n=6, P<0.05). H2O2 (1mM) treatment for 24 h significantly decreased EPC number to 37±13% in aged, compared with young individuals (67±13%, n=3, P<0.05). Furthermore, under normal culture conditions the numbers of senescent β-galactosidase (β-gal) positive EPCs were not significantly different between young and aged subjects (46.1±8.4%, and 58.3±7.6, respectively, n=3). However, H2O2 (50 μM) treatment significantly increased the β-gal positive cells in aged EPCs (73±9%), compared with young EPCs (43±11%, n=3, P<0.05). These results suggest that EPCs of older individuals are more susceptible to oxidative stress induced by H2O2 and serum starvation, resulting in decreased survival and increased senescence. Reduced expression of GPX1 may contribute to EPC dysfunction with aging.

Genetic Polymorphisms of GSTT1, GSTM1, GSTP1, MnSOD, and Catalase in Nonhereditary Chronic Pancreatitis: Evidence of Xenobiotic Stress and Impaired Antioxidant Capacity

Epidemiological studies have demonstrated a variety of potential environmental factors that may alter susceptibility to chronic pancreatitis (CP) through oxidative/xenobiotic stress; however, a direct causal and mechanistic role has not been established. We aimed (1) to determine the prevalence of functional genetic polymorphisms in the antioxidant enzymes, glutathione S-transferase GSTM-1, GSTP-1, and GSTT-1, manganese superoxide dismutase, and catalase in CP and (2) to reveal evidence of oxidative stress in patients with CP by measuring whole-blood glutathione redox status. In total, 122 patients with CP (75 alcohol-induced [A1CP], 33 idiopathic [ICP], and 13 hereditary) and 245 age- and sex-matched controls were recruited. The prevalence of the functional GSTT-1 genotype (GSTT-1*A) was significantly higher in CP (88.5%) compared to healthy controls (76%; chi2 = 7.26, P = 0.007). Stratification to disease etiology demonstrated that the GSTT-1*A genotype was also significantly more prevalent among patients with ICP (94%; P = 0.02; 95% CI, 0.04-9.16) but not in those with A1CP. In 22 patients with stable CP, the whole-blood glutathione concentration (median [IQR]: 72 micromol/L [21-181 micromol/L]) and the glutathione redox ratio (GSH/GSSG) (median [IQR]: 9 (3-77]) were significantly reduced compared to those in 20 healthy volunteers (median [IQR]: 815 micromol/L [679-1148 micromol/L], P < 0.001, and 96 [52-347], P = 0.005, respectively). We conclude that the GSTT-1 functional genotype is associated with ICP. Evidence of altered glutathione redox status suggests that this disease modification may be a consequence of oxidative stress or the bioactivation of xenobiotics.

Evaluation of Oxidative Stress after Repeated Intravenous Iron Supplementation

Parenteral iron has been recommended for the treatment of iron deficiency in the majority of maintenance hemodialyzed (HD) patients. However, iron supplementation and consequent over saturation of transferrin and high iron levels, may aggravate oxidative stress already present in these patients. This study aimed to further clarify the role of repeated intravenous iron therapy as a supplementary cause of oxidative stress in HD patients. Markers of free radical activities (carbonyl reactive derivatives, CRD, thiol groups, SH, malondialdehyde, MDA) and antioxidant enzyme activities (superoxide dismutase, SOD and glutathione peroxidase, GPX) were determined in plasma and red blood cells (RBC) of 19 hemodialysis patients given a total iron dose of 625 mg (ferrogluconat, Ferrlecit, 62.5 mg). Blood samples were taken before the first and after the last dose of iron. Twenty apparently normal subjects served as healthy controls. Before iron treatment, HD patients exhibited increased concentrations of MDA and CRD in plasma and red blood cells, accompanied with impaired antioxidant capacity. All patients responded to iron therapy with a significant increase in their serum ferritin, serum iron, hemoglobin, and red blood cells levels. However, iron treatment resulted in enhanced oxidative stress in plasma of HD patients, since significant increase in plasma MDA and CRD concentrations, together with a decrease in nonprotein SH groups levels were detected. Supplementation with iron did not significantly influence plasma SOD and GPX activities, nor did any of the red blood cell parameters tested. Our data show that, despite improvement in hematological parameters, an increase in iron stores due to supplementation could also contribute to increased free radical production in HD patients.

Changes in the intracellular homocysteine and glutathione content associated with aging

Since moderate hyperhomocysteinemia is an independent risk factor for vascular disease by mean of its oxidant effect and glutathione plays a main role as intracellular redox-regulating agent, we have studied for the first time the total intracellular content of homocysteine in aging. Plasma homocysteine concentration, total intracellular and plasma glutathione, and other related thiol compounds such as cysteine and the glutathione catabolite cysteinglycine were also studied. Forty three healthy elderly subjects and twenty seven healthy young ones were studied. The total intracellular peripheral blood mononuclear cell content was higher for homocysteine, cysteine and cysteinglycine, whereas that of the total glutathione was greatly decreased in elderly people with respect to young ones. Elderly subjects showed significantly higher levels than young ones of total plasma homocysteine and cysteinglycine, but not cysteine, whereas total plasma glutathione levels were increased. In addition, elderly subjects showed significantly decreased plasma vitamin E levels and increased concentrations of serum lipid peroxides measured as TBARS (reaction product of malondialdehyde with thiobarbituric acid). The intracellular glutathione content presented significantly negative correlation with serum TBARS, and intracellular and plasma homocysteine levels. These findings show an increase of homocysteine synthesis associated with aging, which in turn can produce an augmented oxidant effect on endothelium, and an impaired intracellular antioxidant capacity leading to an enhanced lipid peroxidation and decreased total intracellular glutathione content.

Impairment of intestinal glutathione synthesis in patients with inflammatory bowel disease

Background—Reactive oxygen species contribute to tissue injury in inflammatory bowel disease (IBD). The tripeptide glutathione (GSH) is the most important intracellular antioxidant.Aims—To investigate constituent amino acid plasma levels and the...

The apparent autoxidation rate of catechols in dopamine-rich regions of human brains increases with the degree of depigmentation of substantia nigra.

The concentrations of the 5-S-cysteinyl adducts of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylalanine (DOPA) and the levels of noradrenaline (NA), DA, DOPAC and DOPA were determined in the putamen (PUT), caudate nucleus (CN) and substantia nigra (SN) of human post mortem brains with or without depigmentation and degeneration of the SN. The levels of DA, DOPAC and DOPA decreased with the degree of depigmentation and degeneration in the three brain regions while NA levels only decreased in SN and PUT. In general, the concentrations of the 5-S-cysteinyl adducts did not differ, but the ratios of 5-S-cysteinyl-DA/DA, 5-S-cysteinyl-DOPAC/DOPAC and 5-S-cysteinyl-DOPA/DOPA were higher in patients with a more depigmentated and degenerated SN, except for the 5-S-cysteinyl-DA/DA ratio in the PUT. Higher ratios were also found in the cell body areas compared to the neuron terminal areas. Thus depigmentation and degeneration of dopaminergic SN neurons, seem to be correlated to enhanced rates of autoxidation, possibly due to an impaired antioxidant capacity.