Glutathione metabolic enzyme activities in diabetic platelets as a function of glycemic control

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.

Attenuation of oxidative stress and cardioprotective effects of zinc supplementation in experimental diabetic rats

Oxidative stress plays a major role in the pathogenesis of diabetes mellitus, which further exacerbates damage of cardiac, hepatic and other tissues. We have recently reported that Zn supplementation beneficially modulates hyperglycaemia and hypoinsulinaemia, with attendant reduction of associated metabolic abnormalities in diabetic rats. The present study assessed the potential of Zn supplementation in modulating oxidative stress and cardioprotective effects in diabetic rats. Diabetes was induced in Wistar rats with streptozotocin, and groups of diabetic rats were treated with 5- and 10-fold dietary Zn interventions (0·19 and 0·38 g Zn/kg diet) for 6 weeks. The markers of oxidative stress, antioxidant enzyme activities and concentrations of antioxidant molecules, lipid profile, and expressions of fibrosis and pro-apoptotic factors in the cardiac tissue were particularly assessed. Supplemental Zn showed significant attenuation of diabetes-induced oxidative stress in terms of altered antioxidant enzyme activities and increased the concentrations of antioxidant molecules. Hypercholesterolaemia and hyperlipidaemia were also significantly countered by Zn supplementation. Along with attenuated oxidative stress, Zn supplementation also showed significant cardioprotective effects by altering the mRNA expressions of fibrosis and pro-apoptotic factors (by >50 %). The expression of lipid oxidative marker 4-hydroxy-2-nonenal (4-HNE) protein in cardiac tissue of diabetic animals was rectified (68 %) by Zn supplementation. Elevated cardiac and hepatic markers in circulation and pathological abnormalities in cardiac and hepatic tissue architecture of diabetic animals were ameliorated by dietary Zn intervention. The present study indicates that Zn supplementation can attenuate diabetes-induced oxidative stress in circulation as well as in cardiac and hepatic tissues.

Argan oil prevents prothrombotic complications by lowering lipid levels and platelet aggregation, enhancing oxidative status in dyslipidemic patients from the area of Rabat (Morocco)

Background

It is now established that patients with hyperlipidemia have a high risk of atherosclerosis and thrombotic complications, which are two important events responsible for the onset and progression of cardiovascular disease. In the context of managing dyslipidemia by means of dietary advice based on the consumption of argan oil, we wanted to investigate the effect of virgin argan oil on plasma lipids, and for the first time, on the platelet hyperactivation and oxidative status associated with dyslipidemia. This study concerns patients recruited in the area of Rabat in Morocco.

Methods

39 dyslipidemic (79% women) patients were recruited for our study in the area of Rabat in Morocco. They were randomly assigned to the two following groups: the argan group, in which the subjects consumed 25 mL/day of argan oil at breakfast for 3 weeks, and the control group in which argan oil was replaced by butter.

Results

After a 3-week consumption period, blood total cholesterol was significantly lower in the argan oil group, as was LDL cholesterol (23.8% and 25.6% lower, respectively). However, the HDL cholesterol level had increased by 26% at the end of the intervention period compared to baseline. Interestingly, in the argan oil group thrombin-induced platelet aggregation was lower, and oxidative status was enhanced as a result of lower platelet MDA and higher GPx activity, respectively.

Conclusions

In conclusion, our results, even if it is not representative of the Moroccan population, show that argan oil can prevent the prothrombotic complications associated with dyslipidemia, which are a major risk factor for cardiovascular disease.

Balneotherapy in medicine: A review

Bathing in water (balneotherapy or spa therapy) has been frequently and widely used in classical medicine as a cure for diseases. This paper reviews the present literature on the use of balneotherapy in dermatologic, chronic musculoskeletal (inflammatory and non-inflammatory), metabolic and psychological conditions.We performed a systematic review on related papers appearing in the Medline and Cochrane Library database from 1966 to 2003 that included randomized controlled and non-randomized clinical trials using balneotherapy. We also determined to reflect where possible the chemical compositions of spas.The major dermatologic and musculoskeletal diseases that are frequently treated by balneotherapy with a remarkable rate of success are atopic dermatitis, psoriasis, rheumatoid arthritis (RA), ankylosing spondylitis, osteoarthritis and low back pain. Moreover, the effects of spa therapy on several metabolic conditions are discussed. The mechanisms by which broad spectrums of diseases respond to spa therapy probably incorporate chemical, thermal and mechanical effects.The importance of balneotherapy either alone or as complement to other therapies should be considered after, or accompanying, orthodox medical treatments.

Type 1 diabetes mellitus and major depressive disorder: evidence for a biological link

AIMS/HYPOTHESIS

A growing body of research suggests that the prevalence of major depressive disorder (MDD) in children and youth with type 1 diabetes mellitus is significantly higher than that of youth without type 1 diabetes and is associated with increased illness severity. The objective of this article is to review the current literature on the pathophysiology of these two common diseases with respect to potential areas of overlapping biological dysfunction.

METHODS

A search of English language articles published between 1966 and 2010 was conducted and augmented with manual review of reference lists from the identified publications.

RESULTS

The evidence suggests plausible mechanisms whereby a biological relationship between type 1 diabetes and MDD may exist. These include the effects of circulating cytokines associated with autoimmune diabetes, the direct impact of insulin deficiency on neurogenesis/neurotransmitter metabolism, the effects of the chronic hyperglycaemic state, occurrence of iatrogenic hypoglycaemia and the impact of basal hyperactivity of the hypothalamic-pituitary-adrenal axis.

CONCLUSIONS/INTERPRETATION

Shared biological vulnerabilities may be implicated in the comorbidity of type 1 diabetes and MDD. Further research is warranted to determine the magnitude of associations and confirm their observation in clinical populations.

Evaluation of the antioxidant properties of N-acetylcysteine in human platelets: prerequisite for bioconversion to glutathione for antioxidant and antiplatelet activity

N-Acetylcysteine (NAC) is a frequently used "antioxidant" in vitro, but the concentrations applied rarely correlate with those encountered with oral dosing in vivo. Here, we investigated the in vitro antioxidant and antiplatelet properties of NAC at concentrations (10-100 microM) that are achievable in plasma with tolerable oral dosing. The impact of NAC pretreatment (2 hours) on aggregation of platelets from healthy volunteers in response to thrombin and adenosine diphosphate and on platelet-derived nitric oxide (NO) was examined. NAC was found to be a weak reducing agent and a poor antioxidant compared with glutathione (reduced form) (GSH). However, platelets treated with NAC showed enhanced antioxidant activity and depression of reactive oxygen species generation associated with increases in intraplatelet GSH levels. An approximately 2-fold increase in NO synthase-derived nitrite was observed with 10 microM NAC treatment, but the effect was not concentration dependent. Finally, NAC significantly reduced both thrombin-induced and adenosine diphosphate-induced platelet aggregation. NAC should be considered a weak antioxidant that requires prior conversion to GSH to convey antioxidant and antithrombotic benefit at therapeutically relevant concentrations. Our results suggest that NAC might be an effective antiplatelet agent in conditions where increased oxidative stress contributes to heightened risk of thrombosis but only if the intraplatelet machinery to convert it to GSH is functional.

Lipid peroxidation of membrane phospholipids generates hydroxy-alkenals and oxidized phospholipids active in physiological and/or pathological conditions

Polyunsaturated fatty acids (PUFAs) and their metabolites have a variety of physiological roles including: energy provision, membrane structure, cell signaling and regulation of gene expression. Lipids containing polyunsaturated fatty acids are susceptible to free radical-initiated oxidation and can participate in chain reactions that increase damage to biomolecules. Lipid peroxidation, which leads to lipid hydroperoxide formation often, occurs in response to oxidative stress. Hydroperoxides are usually reduced to their corresponding alcohols by glutathione peroxidases. However, these enzymes are decreased in certain diseases resulting in a temporary increase of lipid hydroperoxides that favors their degradation into several compounds, including hydroxy-alkenals. The best known of these are: 4-hydroxy-2-nonenal (4-HNE) and 4-hydroxy-2-hexenal (4-HHE), which derive from lipid peroxidation of n-6 and n-3 fatty acids, respectively. Compared to free radicals, these aldehydes are relatively stable and can diffuse within or even escape from the cell and attack targets far from the site of the original event. These aldehydes exhibit great reactivity with biomolecules, such as proteins, DNA, and phospholipids, generating a variety of intra and intermolecular covalent adducts. At the membrane level, proteins and amino lipids can be covalently modified by lipid peroxidation products (hydoxy-alkenals). These aldehydes can also act as bioactive molecules in physiological and/or pathological conditions. In addition this review is intended to provide an appropriate synopsis of identified effects of hydroxy-alkenals and oxidized phospholipids on cell signaling, from their intracellular production, to their action as intracellular messenger, up to their influence on transcription factors and gene expression.

High-dose folate may improve platelet function in acute coronary syndrome and other pathologies associated with increased platelet oxidative stress

Although nitric oxide of endothelial origin plays a major role in warding off inappropriate thrombus formation, platelets also express the "constitutive" isoform of nitric oxide synthase (cNOS). Activation of this enzyme by calcium influx during platelet aggregation provides an important feedback signal that dampens platelet recruitment. Platelets also express a membrane-bound NAD(P)H oxidase complex, activated by collagen receptors, that produces superoxide. Superoxide can directly quench NO; moreover, by giving rise to peroxynitrite, it can oxidize the cNOS cofactor tetrahydrobiopterin (BH4), thereby suppressing cNOS activity and converting it to superoxide generator. In a canine model of acute coronary syndrome, infusion of BH4 has been shown to prevent thrombus formation. Platelets from patients with acute coronary syndrome produce markedly less NO than do control platelets. A reasonable explanation for these findings is that episodic contact with collagen boosts platelet superoxide production, oxidizing BH4. Since 5-methyltetrahydrofolate can reduce oxidized BH4, or otherwise compensate for its deficiency, supplementation with its precursor folic acid may improve platelet function in acute coronary syndrome and possibly reduce risk for coronary thrombosis in other at-risk patients. Other research demonstrates that superoxide production is increased, and nitric oxide production diminished, in platelets of diabetics; the ability of glutathione--a peroxynitrite scavenger--to largely ameliorate these abnormalities, is consistent with a prominent role for BH4 deficiency in diabetic platelet malfunction. Reports that platelet NO production is decreased, and/or superoxide production increased, in patients with disorders associated with insulin resistance syndrome, suggest that BH4 deficiency--potentially remediable with high-dose folate--may likewise contribute to the platelet hyperreactivity noted in these disorders. Supplemental vitamin C and arginine also have the potential to boost platelet production of NO Increased intakes of taurine, magnesium, gamma-tocopherol, fish oil, and garlic may help to stabilize platelets by additional mechanisms. As a complement to the proven benefits of low-dose aspirin, a supplemental regimen emphasizing these nutrients in appropriate doses may act directly on platelets to further diminish risk for thrombotic episodes.

The molecular biology of chronic wounds and delayed healing in diabetes

Wound healing is a complicated and integrated process. Although there is some tolerance in terms of redundancy and interrelated control mechanisms, pushing beyond such limits may contribute to delayed wound healing, and in extreme cases lead to chronic wounds/ulcers and thus potentially to lower extremity amputation. Diabetes is associated with such disruption in wound healing. Research in humans and in animal models has identified a large number of changes associated with diabetes at the molecular level in delayed wound healing and to a lesser extent in chronic diabetic ulcers. Better overall understanding of these changes and how they are interrelated would allow for specifically targeted treatment, thus ensuring improved quality of life for patients and providing savings to the high costs that are associated with all aspects of chronic diabetic ulcers. This review examines the work done at the molecular level on chronic diabetic ulcers, as well as considering changes seen in diabetes in general, both in humans and animal models, that may in turn contribute to ulcer formation.

Alterations of glomerular and extracellular levels of glutathione peroxidase in patients and experimental rats with diabetic nephropathy

To investigate the status and role of glutathione peroxidase (GPX) in diabetic nephropathy, we measured GPX in the plasma and urine of 14 patients with diabetic glomerulosclerosis (DGS) and measured glomerular GPX immunostaining in these patients and in rats with streptozotocin-induced diabetes of varying duration. Plasma GPX levels were significantly lower in DGS patients than in diabetic patients without nephropathy (P < .05) or normal controls (P < .01). Urinary GPX concentrations were also significantly lower in DGS patients than in diabetic patients without nephropathy or normal controls (both P < .05). Immunostaining of glomerular GPX was significantly less in DGS patients than in normal controls (P < .05) and was negatively correlated with the glomerular sclerosis score and the index of mesangial expansion. Serial examination of glomerular GPX in diabetic rats showed that immunostaining scores for glomerular GPX in rats were significantly lower than those in normal control rats after 1 and 3 months' duration of diabetes, and staining scores were also significantly lower in rats killed after 3 months of diabetes than in those killed after 1 week. In conclusion, our study demonstrates that GPX concentrations in plasma, urine, and glomeruli are decreased in individuals with DGS and that the immunostaining of glomerular GPX decreases progressively.

Diabetic patients without vascular complications display enhanced basal platelet activation and decreased antioxidant status

Vascular complications are the leading causes of morbidity and mortality in diabetic patients. The contribution of platelets to thromboembolic complications is well documented, but their involvement in the initiation of the atherosclerotic process is of rising interest. Thus, the aim of the present study was to evaluate basal arachidonic acid metabolism in relation to the redox status of platelets in both type 1 and type 2 diabetic patients, in the absence of vascular complications, as compared with respective control subjects. For the first time, we show that basal thromboxane B(2), the stable catabolite of thromboxane A(2), significantly increased in resting platelets from both type 1 and type 2 diabetic patients (58 and 88%, respectively), whereas platelet malondialdehyde level was only higher in platelets from type 2 diabetic subjects (67%). On the other hand, both vitamin E levels and cytosolic glutathione peroxidase activities were significantly lower in platelets from diabetic patients as compared with respective control subjects. We conclude that platelet hyperactivation was detectable in well-controlled diabetic patients without complications. This abnormality was associated with increased oxidative stress and impaired antioxidant defense in particular in type 2 diabetic patients. These alterations contribute to the increased risk for occurrence of vascular diseases in such patients.

Activation of p38 mitogen-activated protein kinase/cytosolic phospholipase A2 cascade in hydroperoxide-stressed platelets

12-Hydroperoxy-eicosatetraenoic acid (12-HpETE), the main hydroperoxide formed in platelets from arachidonic acid (AA) by 12-lipoxygenase, has been shown to increase the sensitivity of platelets to agonists resulting in increased aggregation. The aim of the present study was to determine the direct effect of low concentrations of 12-HpETE on the signaling pathways leading to AA release from membrane phospholipids and thromboxane A2 (TxA2) formation. Exogenous 12-HpETE activated platelet p38 mitogen-activated protein kinase (p38 MAPK), as assessed by its phosphorylation, at a concentration as low as 100 nM and was much more potent than hydrogen peroxide. Moreover, the incubation of platelets with 100 nM 12-HpETE for 2 min led to the phosphorylation of cytosolic phospholipase A2 (cPLA2). It was associated with a significant decrease in the concentration of AA esterified in phospholipids and an increased concentration of thromboxane B2, the stable catabolite of TxA2. Additionally, decreasing glutathione peroxidase activity pharmacologically favored endogenous 12-HpETE formation and led to an increase in phosphorylated p38 MAPK, while a thiol-reducing agent such as N-acetyl-cysteine fully prevented it. Finally, significant activation of p38 MAPK was also observed in platelets from type 2 diabetic patients with mild hyperglycemia. In conclusion, our data provide a new insight into the mechanism of 12-HpETE-induced platelet priming, suggesting that hydroperoxide-induced p38 MAPK activation could play a relevant role in the exacerbated platelet activation associated with oxidative stress as found in diabetes.

DNA damage and antioxidant defense in peripheral leukocytes of patients with Type I diabetes mellitus

We determined relationship among DNA damage, nitric oxide (NO) and antioxidant defense in leukocytes of patients with Type 1 DM. DNA damage was evaluated as strand breakage and formamidopyrimidine DNA glycosylase (Fpg)-sensitive sites by the comet assay in DNA from leukocytes of the subjects. Nitrite level, as a product of NO, superoxide dismutase (SOD) activity and glutathione peroxidase (G-Px) activity of the leukocytes were measured by spectrophotometric kits. Serum glucose level and glycosylated haemoglobin (HbA(1c)) were higher in the patients, as expected. Differences in measured parameters between controls and patients were assessed in men and women separately. There was no significant difference between patient and control groups in neither men nor women for nitrite level. Strand breakage and Fpg-sensitive sites were found to be increased, SOD and G-Px activities of the leukocytes were found to be decreased in both men and women of patient group as compared to their respective controls. Significant correlations were determined between strand breakage and HbA(1c) (r = 0.37, P<0.05); Fpg-sensitive sites and HbA(1c) (r = 0.59, P<0.01); Fpg-sensitive sites and glucose (r = 0.45, P<0.02); Fpg-sensitive sites and SOD (r = -0.48, P<0.02); HbA(1c) and SOD (r = -0.50, P<0.02). In conclusion, impaired antioxidant defense in leukocytes of patients with Type 1 DM may be one of the responsible mechanisms for increased DNA damage in those patients.

Covalent binding of hydroxy-alkenals 4-HDDE, 4-HHE, and 4-HNE to ethanolamine phospholipid subclasses

Lipid oxidation is implicated in a wide range of pathophysiogical disorders, and leads to reactive compounds such as fatty aldehydes, of which the most well known is 4-hydroxy-2E-nonenal (4-HNE) issued from 15-hydroperoxyeicosatetraenoic acid (15-HpETE), an arachidonic acid (AA) product. In addition to 15-HpETE, 12(S)-HpETE is synthesized by 12-lipoxygenation of platelet AA. We first show that 12-HpETE can be degraded in vitro into 4-hydroxydodeca-(2E,6Z)-dienal (4-HDDE), a specific aldehyde homologous to 4-HNE. Moreover, 4-HDDE can be detected in human plasma. Second, we compare the ability of 4-HNE, 4-HDDE, and 4-hydroxy-2E-hexenal (4-HHE) from n-3 fatty acids to covalently modify different ethanolamine phospholipids (PEs) chosen for their biological relevance, namely AA- (20: 4n-6) or docosahexaenoic acid- (22:6n-3) containing diacyl-glycerophosphoethanolamine (diacyl-GPE) and alkenylacyl-glycerophosphoethanolamine (alkenylacyl-GPE) molecular species. The most hydrophobic aldehyde used, 4-HDDE, generates more adducts with the PE subclasses than does 4-HNE, which itself appears more reactive than 4-HHE. Moreover, the aldehydes show higher reactivity toward alkenylacyl-GPE compared with diacyl-GPE, because the docosahexaenoyl-containing species are more reactive than those containing arachidonoyl. We conclude that the different PE species are differently targeted by fatty aldehydes: the higher their hydrophobicity, the higher the amount of adducts made. In addition to their antioxidant potential, alkenylacyl-GPEs may efficiently scavenge fatty aldehydes.

Pathophysiologic role of redox status in blood platelet activation. Influence of docosahexaenoic acid

Decrease of platelet glutathione peroxidase activity results in increased life span of lipid hydroperoxides, especially the 12-lipoxygenase product of arachidonic acid, 12-HpETE. Phospholipase A2 activity is subsequently enhanced with the release of arachidonic acid, which results in higher thromboxane formation and platelet function. Docosahexaenoic acid may either potentiate platelet lipid peroxidation or lower it when used at high or low concentrations, respectively. In the case of slowing down lipid peroxidation, docosahexaenoic acid was specifically incorporated in plasmalogen ethanolamine phospholipids. This could have a relevant pathophysiologic role in atherothrombosis.

Pro- and antioxidant activities of docosahexaenoic acid on human blood platelets

n - 3 polyunsaturated fatty acids may protect against vascular diseases, however, their high accumulation in membranes may increase lipid peroxidation and subsequently induce deleterious effects in patients suffering from oxidative stress. This led us to investigate in vitro the dose-dependent effect of docosahexaenoic acid (DHA) on the redox status of human platelets. We have compared the effect of different DHA concentrations (0.5, 5 and 50 micro mol L(-1)) corresponding to DHA/albumin ratios of 0.01, 0.1 and 1. At the highest concentration, DHA elicited a marked oxidative stress, as evidenced by high malondialdehyde and low vitamin E levels whereas the lowest DHA concentration significantly decreased the malondialdehyde formation, with no change in vitamin E. The proportion of DHA was only increased in plasmalogen phosphatidylethanolamine at low concentration to rise in all phosphatidyl-choline and -ethanolamine subclasses at high concentration. Thus, the results show a biphasic effect of DHA with antioxidant and prooxidant effects at low and high concentrations, respectively, with a possible relationship with the phospholipid subclass in which it accumulates.

Enhanced menadione cytotoxicity in platelets isolated from streptozotocin-induced diabetic rats

To study whether chemically induced cytotoxicity occurs in diabetic platelets, platelets isolated from rats made hyperglycemic (diabetic) by a prior intravenous administration of streptozotocin were incubated with menadione and the cytotoxicity was assessed by the amount of lactate dehydrogenase (LDH) released from the menadione exposed platelets as a function of time. Platelets isolated from diabetic rats released greater amount of LDH in response to menadione than those from normal rats. Consistent with this finding, induction of menadione cytotoxicity was not dependent on glutathione depletion, but on greater generation of free radicals in diabetic platelets. Greater sensitivity of diabetic platelets to the menadione-induced cytotoxicity was accompanied by release of serotonin from dense granules, suggesting that this mechanism contributes to cardiovascular diseases in diabetic subjects.

Assessment of DNA base oxidation and glutathione level in patients with type 2 diabetes

The first aim of the present study was to examine the relationship between reduced glutathione (GSH) level, a powerful cellular antioxidant, and oxidative damage to DNA; and secondly, to see the effect of glycemic control on oxidative DNA damage in type 2 diabetics. We determined GSH level and, using the comet assay, formamidopyrimidine DNA glycosylase (Fpg)-sensitive sites which indicates oxidised guanine in freshly isolated blood from age-matched type 2 diabetics and controls. We found significant differences between men and women in the control group for both GSH and Fpg-sensitive sites. Therefore, we compared the controls and type 2 diabetics separately in men and women. GSH level of whole blood was found to be lower, Fpg-sensitive sites in leukocytes was found to be higher in the both type 2 diabetic men and women, as compared with their respective controls. When the diabetic group was divided into two groups as well-controlled diabetics and poorly-controlled diabetics with respect to glycosylated haemoglobine levels, it was found that Fpg-sensitive sites was significantly higher in the poorly-controlled diabetics than in the well-controlled diabetics in both the men and women. GSH level was lower in the poorly-controlled diabetics but not significantly. Fpg-sensitive sites were found to be moderately correlated with both glycosylated haemoglobine and GSH, and weakly correlated with glucose. Data indicate that decreased GSH level may be a contributory factor for enhanced oxidative DNA damage in type 2 diabetics; and chronic hyperglycemia derived from poorly-controlled diabetic conditions may induce oxidative DNA damage in these patients.

Susceptibility of glutatione and glutathione-related antioxidant activity to hydrogen peroxide in patients with type 2 diabetes: effect of glycemic control

OBJECTIVES

The aim of the present study was to examine the susceptibility of glutathione (GSH) and glutathione related antioxidant enzymes to oxidation in type 2 diabetic patients with and without glycemic control.

DESIGN AND METHODS

Erythrocyte glutathione level and activities of glutathione peroxidase (G-Px), glutathione reductase (G-Red) and glutathione S-transferase (GST) in controls, well controlled and poorly controlled type 2 diabetics were measured by spectrophotometric assays before and after the incubation in vitro with H2O2.

RESULTS

GSH level, G-Px and G-Red activities decreased but GST activity increased in the erythrocytes from all the groups after the incubation with H2O2. Percentage of decrease in GSH was independent from glycemic control, whereas the percentage of decreases in G-Px and G-Red was related to glycemic control. The percentage of increase in GST was found to be independent from diabetes.

CONCLUSIONS

GSH and GSH-related antioxidant enzymes in human erythrocytes are susceptible to oxidation, particularly, G-Px and G-Red which were found to be more susceptible to oxidation in erythrocytes from poorly controlled type 2 diabetic patients.

Relationship between metabolic glycaemic control and platelet content of glutathione and its related enzymes, in insulin-dependent diabetes mellitus

The relationship between glycaemic metabolic control and intracellular concentration of reduced glutathione (GSH) and related enzymes GSH-peroxidase (GSH-Px), GSH-reductase (GSH-Red), GSH-transferase (GSH-Tr), glucose-6-P-dehydrogenase (G6PDH), and thioltransferase (TT) in patients with insulin-dependent diabetes mellitus (IDDM) is controversial. Choosing platelets as cell model (as commonly done in previous studies), the aim of this study was to relate the platelet content of GSH and related enzymes to glycaemic metabolic control, expressed as glycated haemoglobin (HbA1c), as well as to presence of retinopathy and nephropathy in 114 IDDM patients. As compared to controls, both GSH and GSH-Red (geometric means (95% CI)) were significantly increased in platelets of diabetic patients: 3.3 (0.7-9.6) vs. 2.4 (0.8-7.6) mmol 10(-9) platelets; P=0.01 for GSH, and 30.6 (14.7-61.6) vs. 22.2 (8.7-52.2) mU 10(-9) platelets, P=0.0002 for GSH-Red, and TT activity was marginally decreased in the IDDM group (P=0.06). While no clear relationship was present between GSH-related enzymes and HbA1c, a trend was present toward a non-linear relation between HbA1c and GSH, being significantly related by a parabolic curve (P=0.002). As compared to patients with normoalbuminuria (n=88), diabetic patients with increased urinary albumin excretion rate (n=26) had a significant decrease in platelet TT concentration (3.2 (0.9-6.7) vs. 5.1 (1.9-18.7) mU 10(-9) platelets; P=0.0002), whereas retinopathy was not associated to modifications in GSH or in the enzymatic pattern. In summary: (a) platelet GSH and GSH-Red are increased in IDDM, while other enzymes are unmodified; (b) GSH seems to be related to metabolic control according to non-linear parabolic curve; (c) presence of increased albuminuria is associated to a selective decrease in platelet TT content.

N-dansyl-S-nitrosohomocysteine a fluorescent probe for intracellular thiols and S-nitrosothiols

The fluorescence emission spectrum of N-dansyl-S-nitrosohomocysteine was enhanced approximately 8-fold upon removal of the NO group either by photolysis or by transnitrosation with free thiols like glutathione. The fluorescence enhancement was reversible in that it could be quenched in the presence of excess S-nitrosoglutathione. Attempts were then made to utilize N-dansyl-S-nitrosohomocysteine as an intracellular probe of thiols/S-nitrosothiols. Fluorescence microscopy of fibroblasts in culture indicated that intracellular N-dansyl-S-nitrosohomocysteine levels reached a maximum within 5 min. N-Dansyl-S-nitrosohomocysteine fluorescence was directly proportional to intracellular GSH levels, directly determined with HPLC. N-Dansyl-S-nitrosohomocysteine preloaded cells were also sensitive to S-nitrosoglutathione uptake as the intracellular fluorescence decreased as a function of time upon exposure to extracellular S-nitrosoglutathione.

Diabetes-induced alterations in platelet metabolism

OBJECTIVES

This review summarizes the recent findings on some aspects of platelet metabolism that appear to be affected as a consequence of diabetes mellitus. The metabolites include glutathione, L-Arginine/nitric oxide, as well as the ATP-dependent exchange of Na+/K+ and Ca2+.

CONCLUSIONS

Several aspects of platelet metabolism are altered in diabetics. These metabolic events give rise to a platelet that has less antioxidants, and higher levels of peroxides. The direct consequence of this is the overproduction platelet agonists. In addition, there is evidence for altered Ca2+ and Na+ transport across the plasma membrane. Recent evidence indicates that plasma ATPases in diabetic platelets are not damaged instead their activities are likely to be modulated by oxidized LDL. Finally, platelet inhibitory mechanisms regulated by NO appear to be perturbed in the diabetes disease-state. The combined production of NO and superoxide by NOS isoforms in the platelet could be a major contributory factor to platelet pathogenesis in diabetes mellitus.

Involvement of lipid peroxidation in platelet signalling

A well-known signalling pathway in blood platelets consists in the release of arachidonic acid (AA) from membrane phospholipids and its specific oxygenation into bioactive derivatives. In particular, cyclic prostaglandin endoperoxides and thromboxane A2 are potent inducers of platelet functions and are produced in greater amounts when the level of lipid hydroperoxides is higher than normal, as 'physiological concentrations' of such peroxides activate the cyclooxygenation of AA. In this context, a lower activity of platelet glutathione peroxidase (GPx), the key-enzyme for the degradation of lipid hydroperoxides, has been reported in aging, which will ensure a longer life span to those peroxides. Accordingly, the biosynthesis of pro-aggregatory prostanoids is elevated in platelets from the elderly. On the other hand, fatty acids from marine origin have been recognized as inhibitors of platelet functions, and they may alter the redox status of cells. They may for instance increase the platelet GPx activity, an effect that can be prevented by antioxidants. Overall, these data point out the relevance of the redox status in platelet functions.

Effects of fatty acids on human platelet glutathione peroxidase: possible role of oxidative stress

Highly polyunsaturated fatty acids of the n-3 family are known to be inhibitors of platelet functions, but these fatty acids (FA) may alter the platelet antioxidant status, depending on their concentrations. The present study was aimed to investigate the effect of various FA on glutathione-dependent peroxidase (GPx), the required antioxidant enzyme for degrading FA hydroperoxides. Human platelets were enriched in vitro with either n-3 (18:3, 20.5, or 22.6), n-6 (18:2 or 18:3) FA, 18:1 n-9 or 16:0, and the GPx activity was then measured. It was found that n-3 FA enhanced the GPx activity whereas the others did not affect the enzyme activity. The increased GPx activity was associated with an increased amount of the enzyme measured by Western blotting. The enhanced activity and amount of GPx induced by 22:6n-3, the most potent activator among the n-3 FA, was completely abolished in the presence of cycloheximide at a concentration known to inhibit platelet protein synthesis. Because platelets are devoid of nucleus, which rules out the involvement of transcriptional factors, this suggests that 22:6n-3 might act at a translational level. On the other hand, 22:6n-3 treatment increased the malondialdehyde formation and decreased the vitamin E level in platelets, both events that could be prevented by the antioxidant epicatechin. Because epicatechin also suppressed the enhancement of both the activity and amount of GPx induced by 22:6n-3, we conclude that the increased GPx activity (possibly via protein synthesis) might be associated with an oxidative stress induced by 22:6n-3 and/or 20:4n-6 released from the platelet endogenous pool in the course of the 22:6n-3 enrichment.

In vitro and in vivo effects of selenium and selenium with vitamin E on platelet functions in diabetic rats relationship to platelet sorbitol and fatty acid distribution

In vitro 30 min of incubation with selenomethionine (Sm) + vitamin E multiplied by about five platelet selenium (Se) decreased significantly platelet thrombin and ADP-induced aggregation decrease. Four groups of streptozotocin-induced diabetic rats were fed with a supplemented purified diet with an Se-rich yeast (Selenion): DSel, Sm: DSm, Sm alpha-tocopherol: DSmE or unsupplemented diet: D. After 24 wk of supplementation, only a decrease in thrombin-induced aggregation in group DSel compared to DSm and DSmE and D was observed. However, after 24 wk of diet compared to 14 wk, in group D and DSm, a significant increase in thrombin-induced aggregation occurred (p < 0.0001), whereas a significant decrease in groups DSel and DSmE (p < 0.0001, p < 0.03) was noted. After 21 wk of diet, in DSmE, platelet adhesion to fibronectin was significantly decreased compared to group D (p < 0.05). These changes in DSmE were associated with a significant decrease in platelet sorbitol (p < 0.02) and a very significant increase in platelet Se (p < 0.0005). Sm associated with vitamin E would appear more efficient to prevent oxidative damage of diabetic platelet membrane and thus to modulate its hyperactivity.

Balneotherapy and platelet glutathione metabolism in type II diabetic patients

Effects of balneotherapy on platelet glutathione metabolism were investigated in 12 type II (non-insulin-dependent) diabetic patients. Levels of the reduced form of glutathione (GSH) on admission were well correlated with those of fasting plasma glucose (FPG; r = 0.692, P < 0.02). After 4 weeks of balneotherapy, the mean level of GSH showed no changes; however, in well-controlled patients (FPG < 150 mg/dl), the level increased (P < 0.01) and in poorly controlled patients (FPG > 150 mg/dl), the value decreased (P < 0.05). There was a negative correlation between glutathione peroxidase (GPX) activities and the levels of FPG (r = -0.430, P < 0.05). After balneotherapy, the activity increased in 5 patients, decreased in 3 patients and showed no changes (alteration within +/- 3%) in all the other patients. From these findings in diabetic patients we concluded: (1) platelet GSH synthesis appeared to be induced in response to oxidative stress; (2) lowered GPX activities indicated that the antioxidative defense system was impaired; and (3) platelet glutathione metabolism was partially improved by 4 weeks balneotherapy, an effect thought to be dependent on the control status of plasma glucose levels. It is suggested that balneotherapy is beneficial for patients whose platelet antioxidative defense system is damaged, such as those with diabetes mellitus and coronary heart disease.

Glutathione, glutathione utilizing enzymes and thioltransferase in platelets of insulin-dependent diabetic patients: relation with platelet aggregation and with microangiopatic complications

Reduced glutathione (GSH) and activity of GSH related enzymes play a key role in defence against oxygen free radicals, whose production is, as known, raised in patients affected by diabetes mellitus, and at the same time they may contribute to the process of platelet aggregation. The purpose of this study was to evaluate GSH levels and activity of glutathione peroxidase (GSH-Px), glutathione reductase (GSSG-Red), glutathione transferase (GSH-Tr), glucose-6-phosphate-dehydrogenase (G6PDH), and thioltransferase (TT) in platelets of insulin-dependent diabetic patients in fair metabolic control (mean glycated haemoglobin: 6.5%), as related to presence of retinopathy, neuropathy or nephropathy and to platelet aggregation by arachidonic acid (AA) in vitro. Mean effective dose (ED50) of AA was on average significantly lower in the group of insulin-dependent diabetic patients (0.41 +/- 0.02 mM (SEM), n = 46) as compared with that of control subjects strictly matched for age, sex and weight (0.77 +/- 0.02, n = 51; P = 0.0001). Mean platelet GSH as well as the activity of GSH related enzymes expressed as geometric mean (95% confidence intervals) were similar in diabetic patients and in controls, except for GSSG-Red whose activity was significantly higher in diabetic subjects (28.5 (14.4-57.5) mU 10(-9) platelets vs. 20.3 (8.7-56) mU 10(-9) platelets; P = 0.01). In the diabetic group TT was reduced when compared with healthy controls (3.8 (0.9-12.2) mU 10(-9) platelets vs. 6 (1.6-26.1) mU 10(-9) platelets; P = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Hematologic complications of diabetes mellitus

In summary, hematologic abnormalities in diabetes affect the function, morphology, and metabolism of blood cells, and the coagulation system. These complications can contribute to the development of anemia, infection, and hypercoagulability in diabetic dogs and cats. Some hematologic changes, such as glycosylated hemoglobin and fructosamine, play an important role as markers of glycemic control. Hematologic changes also serve as important models for changes occurring in other tissues, such as cataract formation and nephropathy. Further study of blood alterations will enhance our knowledge of the biochemistry and pathophysiology of diabetes and diabetic complications and stimulate the development of effective preventative and therapeutic measures.

Platelet glutathione transport: characteristics and evidence for regulation by intraplatelet thiol status

The present study demonstrates the carrier-mediated uptake of intact glutathione (GSH) by human platelets. Platelet GSH uptake was characterized as being Na+ independent and saturable. The KM, apparent and Vmax, apparent for GSH uptake in platelet plasma membrane vesicles were 28.0 +/- 8.4 microM and 263.5 +/- 28.5 pmol/min per mg protein, respectively. The transport was inhibited by GSH analogs and enhanced by KCl-induced membrane depolarization. GSH transport may be regulated by the intracellular thiol status, since the depletion of intraplatelet GSH with 100 microM 1-chloro-2,4-dinitrobenzene (CDNB) increased GSH uptake by approximately 40%. The KM, apparent and Vmax, apparent for GSH uptake in intact platelets changed from 99.5 +/- 15 microM and 42 +/- 7.5 pmol/min per 10(9) platelets, respectively, to 33.7 +/- 6.7 microM and 21.5 +/- 6.9 pmol/min per 10(9) platelets, respectively, on reducing intraplatelet GSH with 100 microM CDNB.

Identification of the site of non-enzymatic glycation of glutathione peroxidase: rationalization of the glycation-related catalytic alterations on the basis of three-dimensional protein structure

Bovine erythrocyte glutathione peroxidase has been glycated in vitro by incubation in 0.05 M glucose at pH 7.4. Upon glycation the estimated KM for t-butylhydroperoxide reduction increased by approx. 3-fold in comparison to non-glycated glutathione peroxidase. The glycated protein fraction was stabilized by NaBH4 reduction and subjected to tryptic cleavage. Affinity chromatography of the tryptic digest on m-aminophenylboronate-Agarose resulted in the isolation of a single glycated peptide. The peptide was identified as T94-K117 by amino-acid composition comparison to the published amino-acid sequence for this enzyme. The glycation site has been identified as the epsilon-NH2 group of K110. Examination of the three-dimensional structure of bovine erythrocyte glutathione peroxidase indicates that K110 lies on the surface of the protein approximately 15 A away from the active site selenocysteine (SEC 45). Modeling studies indicate that K110 can communicate via H-bonded interactions with the alpha-helix containing the active site residues (SEC-45 and R50). The observed elevation of KM upon glycation of bovine glutathione peroxidase is discussed in terms of the disruption of the long range H-bonded interaction.

ELISA for in vivo assessment of nonenzymatically glycated platelet glutathione peroxidase

Using a combination of boronate affinity chromatography and ELISA methodology, a simple procedure was devised to selectively determine the in vivo glycated state of the platelet glutathione peroxidase (GSH-Px) from normal and diabetic subjects. The mean total GSH-Px levels in the normal (n = 14) and diabetic (n = 18) platelets were 1167 +/- 97 and 1007 +/- 73 ng/mg protein, respectively. The mean percentage glycated GSH-Px in the normal and diabetic platelets were 5.79 +/- 0.72% and 11.68 +/- 0.95%, respectively. When the percentage glycated GSH-Px was compared with the fructosamine values, a correlation coefficient of 0.71 was obtained. This indicates that the glycation status of platelet GSH-Px can be utilized as a sensitive, short-term index of plasma glucose levels.

Purification and characterization of glutathione peroxidase from human blood platelets. Age-related changes in the enzyme

Platelet glutathione peroxidase (GPx) is known to play a pivotal role in controlling the level of lipid hydroperoxides, especially those resulting from the 12-lipoxygenase activity. GPx was purified from the cell cytosol by more than 700-fold using an exchange chromatography, FPLP, gel filtration and covalent fixation. Isoelectric focusing revealed a peak activity at pH 5.1. The molecular mass of the enzyme was found between 90 and 100 kDa by gel filtration, and was approximating at 23 kDa by SDS-PAGE. A polyclonal antibody raised against commercial bovine erythrocyte GPx recognized the human platelet enzyme. It is concluded that human platelet GPx is likely a homotetramer of 92 kDa as described for most other sources. We have also found that the decreased platelet GPx activity observed in platelets from elderly people is associated with a lower content of the immunoreactive enzyme.