Glutathione and glutathione-metabolizing enzymes in the erythrocytes of healthy children and in children with insulin-dependent diabetes mellitus, juvenile rheumatoid arthritis, coeliac disease and acute lymphoblastic leukaemia

Improved glycemic control either alone, or combined with antioxidant supplementation, fails to restore blood glutathione or markers of oxidative stress in adolescents with poorly controlled type 1 diabetes

In earlier studies, we showed that adolescents with type 1 diabetes mellitus (T1DM) have significant glutathione (GSH) depletion and that GSH is reciprocally related to glycemic control. In both the general population and in those with diabetes, the use of over-the-counter antioxidant supplements is widespread. We hypothesized that improved glycemic control, alone or in combination with dietary antioxidants, would restore blood GSH pool. The study included 41 participants who were 15.8 ± 2.4 years of age (mean ± standard deviation) and with poorly controlled T1DM (hemoglobin A1c [HbA1c] 8.2 ± 0.6%). Erythrocyte GSH, and 3-nitrotyrosine, F2-isoprostane, and 8-hydroxy-2'-deoxy-guanosine (as markers of protein, lipid, and DNA oxidative stress, respectively) were determined in the postabsorptive state after blood glucose was maintained overnight near euglycemia. Participants were then randomized to a mix of antioxidants (vitamin C, selenium, zinc, vitamin E, β-carotene) or placebo for 3 to 6 months, and diabetes management was intensified using CSII (n = 30) or multiple daily injections (n = 11) coupled with CDE phone calls and visits with a Nutritionist. A second, identical study was performed when/if a drop in HbA1c ≥0.5% was achieved. HbA1c levels dropped similarly in both groups (from 8.9 ± 1.0% to 7.9 ± 0.9% and 8.5 ± 0.6% to 7.7 ± 0.7% in placebo and antioxidant group, respectively). Neither total nor reduced GSH was altered by improved metabolic control. Markers of protein, lipid, and DNA oxidation remained unaltered. We conclude that, in youngsters with T1DM, neither a significant improvement in diabetes control over a 3-month period nor the regimen of dietary antioxidant supplied in the current study can mitigate oxidative stress. These findings suggest that, in adolescents with T1DM, (1) more sustained improvement of diabetes control may be needed to alleviate oxidative stress and (2) the putative benefit of antioxidant supplements remains to be proven.

Oxidative stress as a biomarker for monitoring treated celiac disease

INTRODUCTION

High levels of reactive oxygen species (ROS) and impaired antioxidant defense systems lead to oxidative stress (OxS) and tissue injury in different intestinal and extra intestinal conditions, including celiac disease (CD). The aim of the present study was to investigate the role and potential use of ROS and other biomarkers of OxS in the clinical management of CD.

METHODS

We collected duodenal specimens and blood samples from naïve patients (N-CD), patients on a gluten free diet (GFD) including responders (CD-GFD) and non-responders (NRCD). We measured plasmatic ROS production (electron paramagnetic resonance, EPR), lipid peroxidation (thiobarbituric acid-reactive substances, TBARS), protein oxidation (protein carbonyl, PC), total antioxidant capacity (TAC), nitric oxides and glutathione (GSH) in erythrocytes.

RESULTS

Fifty-four patients affected by CD were enrolled (17 N-CD, 18 CD-GFD and 19 NRCD; 44 F; age 44 ± 13 years). A significant increase of plasmatic OxS biomarkers (ROS, peroxidated lipids, oxidized proteins, and nitrate concentrations) and decrease of antioxidant species (TAC and GSH levels) were found in NRCD and N-CD compared to CD-GFD. Comparably, a significant direct relationship between the severity of duodenal atrophy, ROS production rates and TBARS was found; conversely, TAC and GSH presented an inverse correlation.

DISCUSSION

OxS is involved in CD tissue damage and correlates with the degree of duodenal atrophy. These findings suggest the possible role of OxS biomarkers as indicators of CD activity during the clinical follow-up.

Glutathione redox cycle in small intestinal mucosa and peripheral blood of pediatric celiac disease patients

The celiac disease is an autoimmune gastrointestinal disorder caused by gluten from wheat, rye or barley. In genetically predisposed persons, gluten induces the immune-mediated inflammation of small intestinal mucosa. Histological lesions include intraepithelial lymphocytosis, crypt hypertrophy and villous atrophy, resulting in malabsorption of micro- and macronutrients. The only treatment for celiac patients is a permanent gluten-free diet (GFD). Reactive oxygen species (ROS) and oxidative stress are strongly associated with the celiac disease. Glutathione (GSH) is a main detoxifier of endogenous and exogenous ROS in the intestine. In order to explain the role of glutathione redox cycle in celiac patients, we examined the activities of GSH-related antioxidant (AO) enzymes glutathione peroxidase (GPx) and glutathione reductase (GR), as well as the concentration of GSH in small intestinal biopsies and peripheral blood of children affected by the celiac disease. The concentration of lipid hydroperoxides (LOOH) as markers of oxidative damage was measured in the same samples. The results clearly demonstrate a significant malfunction of GSH redox cycle with a concomitant decrease in the capacity to regenerate GSH and detoxify LOOH in celiac patients, even after several years of GFD. The oral administration of GSH and a diet rich in natural antioxidants, as well as appropriate dietary supplements, could be of great benefit to the patients.

Radicals and oxidative stress in diabetes

Recent evidence is reviewed indicating increased oxidative damage in Type 1 and Type 2 diabetes mellitus as well as deficits in antioxidant defence enzymes and vitamins. Mechanisms are considered whereby hyperglycaemia can increase oxidative stress, and change the redox potential of glutathione and whereby reactive oxygen species can cause hyperglycaemia. It is argued that oxygen, antioxidant defences, and cellular redox status should now be regarded as central players in diabetes and the metabolic syndrome.

Alterations in enzymatic antioxidant defence in diabetes mellitus--a rational approach

Defence against the reactive oxidants produced during aerobic metabolism is a complex process and is provided by a system of enzymes and antioxidant compounds capable of preventing excess radical production, neutralising free radicals and repairing the damage caused by them. Regulation of the antioxidant system must provide sufficient, properly located, antioxidant compounds and enzymes. Damage to this system has been proved to play a role in various disorders. Long-term complications of diabetes mellitus are supposed to be partially mediated by oxidative stress. The authors summarise experimental and clinical investigations in this field and analyse the possible importance of the changes in the antioxidant system in the development of diabetic vascular complications.

Inactivation of glutathione reductase by 4-hydroxynonenal and other endogenous aldehydes

4-Hydroxynonenal, a product of oxidative degradation of unsaturated lipids, is an endogenous reactive alpha,beta-unsaturated aldehyde with numerous biological activities. 4-Hydroxynonenal rapidly inactivated glutathione reductase in an NADPH-dependent reaction. Inactivation appears to involve the initial formation of an enzyme-inactivator complex, K(D) = 0.5 microM, followed by the inactivation reaction, k = 1.3 x 10(-2) min(-1). alpha,beta-Unsaturated aldehydes such as acrolein, crotonaldehyde, and cinnamaldehyde also inactivated glutathione reductase, although rates varied widely. Inactivation of glutathione reductase by alpha,beta-unsaturated aldehydes was followed by slower NADPH-independent reactions that led to formation of nonfluorescent cross-linked products, accompanied by loss of lysine and histidine residues. Other reactive endogenous aldehydes such as methylglyoxal, 3-deoxyglucosone, and xylosone inactivated glutathione reductase by an NADPH-independent mechanism, with methylglyoxal being the most reactive. However, 2-oxoaldehydes were much less effective than 4-hydroxynonenal. Inactivation of glutathione reductase by these 2-oxoaldehydes was followed by slower reactions that led to the formation of fluorescent cross-linked products over a period of several weeks. These changes were accompanied by loss of arginine residues. Thus, the sequence of events is different for inactivation and modification of glutathione reductase by alpha,beta-unsaturated aldehydes compared with 2-oxoaldehydes with respect to kinetics, NADPH requirements, fluorescence changes, and loss of amino acid residues. The ability of 4-hydroxynonenal at low concentrations to inactivate glutathione reductase, a central antioxidant enzyme, suggests that oxidative degradation of unsaturated lipids may initiate a positive feedback loop that enhances the potential for oxidative damage.

Glycation (non-enzymic glycosylation) inactivates glutathione reductase

Non-enzymic binding of sugars to proteins (glycation) is a common biological phenomenon that is increased in diabetes. Most work has been directed towards structural proteins which may be present for many years and would continue to accumulate sugar residues. As glycation is a non-specific reaction, other proteins such as enzymes will also be susceptible to glycation and could well display altered activity. We investigated the effect of various sugars whose concentrations increase in diabetes in insulin-independent tissues on glutathione reductase, an enzyme that maintains the GSH level in cells. Glucose, glucose 6-phosphate and fructose all displayed a time-dependent inhibition of glutathione reductase activity, suggesting that these sugars glycate this enzyme. Aspirin gave some protection against the loss of activity induced by glucose.