Increased diene conjugates in diabetic subjects with microangiopathy

Effect of Olea europaea leaves extract on streptozotocin induced diabetes in male albino rats

The present study was aimed to evaluate the effect of olive (Olea europaea) leaves extract on streptozotocin (STZ)-induced diabetic male rats. The experimental rats were divided into six groups. Rats of the first group were served as normal controls. Rats of the second group were diabetic control. The third and fourth groups were diabetic rats, treated with olive leaves extract at low and high doses respectively. The fifth and sixth groups were non diabetic rats, subjected to olive leaves extract at the same doses given to the third and fourth groups respectively. The minimum of body weigh gain was noted in diabetic rats of the second group. the levels of serum glucose, insulin, total protein, albumin, triglycerides, cholesterol, low density lipoprotein cholesterol (LDL-C), very low density lipoprotein cholesterol (VLDL-C), creatine kinase (CK), lactate dehydrogenase (LDH) and malondialdehyde (MDA) were significantly increased, while the levels of high density lipoprotein cholesterol (HDL-C), superoxide dismutase, (SOD) glutathione (GSH) and catalase (CAT) were statistically decreased in diabetic rats of the second group. The levels of liver insulin receptor substrate 1 (IRS1) and insulin receptor A (IRA) were significantly declined in diabetic rats of the second group. The diabetic pancreatic sections from diabetic rats of the second group showed several histopathological changes. Administration of low and high doses of olive leaves extract improved the observed physiological, molecular and histopathological alterations. Collectively, the obtained results confirmed that the protective effects of olive leaves extract are attributed to the antioxidant activities of olive leaves extract and its active constituents.

Dietary intake of natural antioxidants: vitamins and polyphenols

Oxidative stress is a condition in which oxidant metabolites exert their toxic effect because of an increased production or an altered cellular mechanism of protection; oxidative stress is rapidly gaining recognition as a key phenomenon in chronic diseases. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions by being oxidized themselves. Endogenous defence mechanisms are inadequate for the complete prevention of oxidative damage, and different sources of dietary antioxidants may be especially important. This article calls attention to the dietary antioxidants, such as vitamins A, C, and E and polyphenols. Compelling evidence has led to the conclusion that diet is a key environmental factor and a potential tool for the control of chronic diseases. More specifically, fruits and vegetables have been shown to exert a protective effect. The high content of minerals and natural antioxidant as vitamins A, C, and E and polyphenols in fruits and vegetables may be a main factor responsible for these effects.

Endothelial dysfunction and oxidative stress in type 1 and type 2 diabetic patients without clinical macrovascular complications

AIMS

To evaluate the relationship between oxidative stress and endothelial dysfunction (ED) in diabetic patients without clinical macrovascular complications.

METHODS

In 27 type 1, 56 type 2 diabetic patients and 35 healthy controls the redox state (GSH, GSSG; enzymatic method), endothelin-1 (ET-1; ELISA) and von Willebrand factor (vWF; ELISA) plasma levels, urinary vascular endothelial growth factor (VEGF; ELISA) were measured.

RESULTS

Decreased GSH levels (p<0.05, type 1 and type 2), GSH/GSSG ratio (p<0.05 type 1, p<0.001 type 2) and elevated vWF levels (p<0.001, type 1 and type 2) were observed in diabetic patients in comparison with controls. A negative correlation between GSH and vWF (p<0.02 and p<0.001, in type 1 and type 2, respectively) and GSH and BMI (p<0.02 in type 1 and type 2) was observed. ET-1 was positively correlated to age (p<0.05) and diabetes duration (p<0.03) in type 1, while vWF was correlated to systolic blood pressure (p<0.05) in type 2 diabetic patients. Urinary VEGF was higher in type 2 (p<0.05) in comparison with type 1 diabetic patients and was correlated to glycemia (p<0.05) and systolic blood pressure (p<0.05).

CONCLUSIONS

These data might indicate that markers of oxidative stress and ED are altered in diabetic patients without clinical macrovascular complications.

Effect of alpha-tocopherol and beta-carotene supplementation on the incidence of type 2 diabetes

AIMS/HYPOTHESIS

Type 2 diabetes is associated with reduced antioxidant defence. Only a few human studies have investigated the role of antioxidants in the pathogenesis of diabetes. This study aimed to examine whether alpha-tocopherol or beta-carotene affected the occurrence of type 2 diabetes.

METHODS

In the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study, a double-blind, controlled trial, 29,133 male smokers aged 50-69 years were randomised to receive either alpha-tocopherol (50 mg/day) or beta-carotene (20 mg/day) or both agents or placebo daily for 5-8 years (median 6.1 years). Baseline serum samples were analysed for alpha-tocopherol and beta-carotene using HPLC. Cases of diabetes were identified from a nationwide Finnish registry of patients receiving drug reimbursement for diabetes. Of 27,379 men without diabetes at baseline, 705 men were diagnosed with diabetes during the follow-up of up to 12.5 years.

RESULTS

Baseline serum levels of alpha-tocopherol and beta-carotene were not associated with the risk of diabetes in the placebo group: the relative risk (RR) between the highest and lowest quintiles of alpha-tocopherol was 1.59 (95% CI 0.89-2.84) and that for beta-carotene was 0.66 (95% CI 0.40-1.10). Neither supplementation significantly affected the incidence of diabetes: the RR was 0.92 (95% CI 0.79-1.07) for participants receiving alpha-tocopherol compared with non-recipients and 0.99 (95% CI 0.85-1.15) for participants receiving beta-carotene compared with non-recipients.

CONCLUSIONS/INTERPRETATION

Neither alpha-tocopherol nor beta-carotene supplementation prevented type 2 diabetes in male smokers. Serum levels of alpha-tocopherol and beta-carotene were not associated with the risk of type 2 diabetes.

Embryonic oxidative stress as a mechanism of teratogenesis with special emphasis on diabetic embryopathy

Reactive oxygen species (ROS) are involved in the etiology of numerous diseases including cardio-vascular diseases and diabetes mellitus. There is evidence that several teratogens affect the developing embryo by increasing its oxidative stress and, because of its relatively weak antioxidant defense, especially at the early stages of organogenesis, result in severe embryonic damage. This mechanism seems to operate in diabetes-induced embryonic damage as well as in the mechanism of teratogenicity caused by ionizing radiation, hypoxia, alcohol and cocaine use and cigarette smoking. We studied the role of oxidative stress in diabetic induced embryopathy, both in vivo and in vitro. Under diabetic condition there was a significant decrease in the activity of endogenous antioxidant enzymes and of vitamins C and E in the embryos and their yolk sacs. The lowest activity was observed in the malformed experimental embryos when compared to experimental embryos without anomalies. Similar results were obtained in the Cohen diabetic rats, where the diabetic prone (CDs) rats were unable to increase their antioxidant enzyme activity in spite of the diabetes. Studies performed by other investigators show similar results. Human and animal studies show that the main mechanism of fetal damage induced by high levels of ionizing irradiation, cocaine and alcohol abuse, hypoxia and cigarette smoking is also by increased embryonic oxidative stress. Similarly, several drugs exert their teratogenic activity via embryonic oxidative stress. Abnormal placentation may also cause enhanced placental oxidative stress, resulting in embryonic death, preeclampsia or congenital anomalies. Inability of the developing embryo to cope with that stress may result in embryonic death and/or congenital anomalies. Animal studies also show that a variety of antioxidants are effective in decreasing the damaging effects of heightened oxidative stress induced by teratogens. Effective antioxidants, which might also be of clinical use, include vitamins C and E, carotenoids, folic acid, as well as synthetic products. Appropriate clinical studies with antioxidants in pregnancies of high risk to develop oxidative stress are needed, since non-toxic antioxidants might prove an efficient and inexpensive way to reduce the rate of some serious and sometimes fatal congenital anomalies.

Diphenyl diselenide reduces temporarily hyperglycemia: Possible relationship with oxidative stress

This study was designed to determine the effect of diphenyl diselenide and ebselen, synthetic organoselenium compounds with antioxidant properties, in diabetic rats. Diabetes was induced by the administration of streptozotocin (STZ) (45mg/kg, intravenous). In experimental trials, diphenyl diselenide, but not ebselen, caused a significant reduction in blood glucose levels of STZ-treated rats. This effect of diphenyl diselenide was accompanied by a reduction in the levels of glycated proteins. Diphenyl diselenide ameliorate superoxide dismutase activity (liver and erythrocytes) and Vitamin C levels (liver, kidney and blood), which were decreased in STZ-treated rats. In normal rats, diphenyl diselenide caused per se an increase in hepatic, renal and blood GSH levels. Similarly, treatment with diphenyl diselenide restored hepatic and renal GSH levels in STZ-treated rats. TBARS and protein carbonyl levels were not modified by STZ and/or diphenyl diselenide and ebselen treatments. Our findings suggest that diphenyl diselenide can be considered an anti-diabetogenic agent by exhibiting anti-hyperglycemic and antioxidant properties.

Defective metabolism of oxidized phospholipid by HDL from people with type 2 diabetes

HDL protects against atherosclerosis development. Defective functioning of HDL in type 2 diabetes may be one cause of increased cardiovascular disease associated with type 2 diabetes. HDL modulates LDL oxidation through the action of paraoxonase-1 (PON1), which is one of the major mechanisms by which HDL is antiatherogenic. We have compared the ability of HDL from people with type 2 diabetes (n = 36) with no coronary heart disease (CHD) to metabolize oxidized palmitoyl arachidonyl phosphatidylcholine (ox-PAPC), a major product of LDL oxidation and a PON1 substrate, with that of HDL isolated from healthy control subjects (n = 19) and people with CHD but no diabetes (n = 37). HDL from people with type 2 diabetes metabolized 11% less ox-PAPC, and HDL from people with CHD metabolized 6% less, compared with HDL from control subjects (both P < 0.01). The ability of HDL from control and type 2 diabetic subjects containing the PON1-192RR alloform to metabolize ox-PAPC was significantly reduced compared with PON1-192QQ or QR genotypes (P < 0.05). The defective ability of HDL to metabolize ox-PAPC was reflected in a significant increase in circulating plasma oxidized LDL concentration in the two patient groups (37 +/- 5, 53 +/- 7, and 65 +/- 7 mmol/l for control, CHD, and type 2 diabetic subjects, respectively; P < 0.001), with PON1-192RR genotype carriers having the highest concentrations. In the control group, there was a significant negative correlation between serum PON1 activity and oxidized LDL concentration (r = 0.856, P < 0.001); however, this correlation was not evident in the patient groups. HDL from type 2 diabetic subjects without CHD had a decreased ability to metabolize oxidized phospholipids, which could lead to increased susceptibility to develop cardiovascular disease.

Diabetic neuropathy and oxidative stress

This review will focus on the impact of hyperglycemia-induced oxidative stress in the development of diabetes-related neural dysfunction. Oxidative stress occurs when the balance between the production of reactive oxygen species (ROS) and the ability of cells or tissues to detoxify the free radicals produced during metabolic activity is tilted in the favor of the former. Although hyperglycemia plays a key role in inducing oxidative stress in the diabetic nerve, the contribution of other factors, such as endoneurial hypoxia, transition metal imbalances, and hyperlipidemia have been also suggested. The possible sources for the overproduction of ROS in diabetes are widespread and include enzymatic pathways, auto-oxidation of glucose, and mitochondrial superoxide production. Increase in oxidative stress has clearly been shown to contribute to the pathology of neural and vascular dysfunction in diabetes. Potential therapies for preventing increased oxidative stress in diabetic nerve dysfunction will be discussed.

Insulin decreases intracellular oxidative stress in patients with type 2 diabetes mellitus

Patients affected by diabetes mellitus have oxidative stress with an impaired glutathione (GSH) redox state. The objective of this study was to determine the influence of insulin on oxidative stress, defined as a reduced intracellular GSH/GSH disulfide (GSSG) ratio and lipid peroxidation by plasma thiobarbituric acid reactive substances (TBARSs) in patients with type 2 diabetes. Two experimental interventions were used: (1) measurement of GSH/GSSG ratio after insulin incubation in erythrocytes from 10 type 2 diabetic patients, and (2) measurement of intraerythrocytic GSH/GSSG ratio and plasma TBARS in 14 type 2 diabetic patients during an in vivo hyperinsulinemic condition obtained from a euglycemic hyperinsulinemic clamp study. We confirmed that our patients underwent oxidative stress as shown by the significant difference in intracellular GSH/GSSG ratio in diabetic patients as compared to controls (13.56+/-3.84 vs 27.89+/-8.37, P<.0001). We found a significant elevation in the GSH/GSSG ratio after 2 hours of incubation with insulin in erythrocytes from diabetic patients (11.56+/-1.98 to 15.61+/-2.62, P<.001). During the clamp studies, GSH/GSSG ratio had already increased after 60 minutes and even more after 120 minutes (baseline, 15.04+/-4.19; at 60 minutes, 19.74+/-6.33; at 120 minutes, 25.33+/-11.15; P<.0001). On the contrary, no significant changes were observed in plasma TBARS (3.59+/-0.77 to 3.56+/-0.83, NS). We conclude that insulin in patients with type 2 diabetes mellitus can reduce intracellular oxidative stress through increased GSH/GSSG ratio.

Dietary soy prevents brain Na+, K(+)-ATPase reduction in streptozotocin diabetic rats

The aim of this study was to investigate Na+, K(+)-ATPase activity in cerebral cortex, hippocampus and hypothalamus of diabetic rats. The action of dietary soy protein on the effect produced by diabetes on this activity was also tested. Forty-nine-day-old Wistar were divided into two groups: diabetes streptozotocin (50 mg/kg body weight) and control (citrate solution). Rats were sacrificed 56 days later. In other set of experiments, rats received a dietary with casein (control) from day 21 to the 49 of postnatal-age and were subjected to diabetes or received citrate (control). One week later, rats received a special dietary with soy protein with isoflavones or casein (control) from day 56 to the 105 of postnatal-age. Results showed that diabetic rats presented a reduction ( approximately 40%) of Na+, K(+)-ATPase activity in all structures studied. Pretreatment with soy protein prevented the inhibitory effects of diabetes on the enzyme activity. Assuming the possibility that these effects might also occur in the human condition, our findings may be relevant to explain, at least in part, the neurologic dysfunction associated with diabetes and might support a novel therapeutic strategy (soy protein) to slow the progression of neurodegeneration in this disorder.

Dysregulation of hepatic superoxide dismutase, catalase and glutathione peroxidase in diabetes: response to insulin and antioxidant therapies

Recent evidence suggests that impaired antioxidant status is involved in oxidative stress associated with diabetes. The main antioxidant enzymes include superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX). The aim of the present investigation was to evaluate the activities and protein expression of these antioxidant enzymes in streptozotocin-induced diabetes. Furthermore, the effects of insulin and antioxidant therapy alone and in combination were studied. Male Sprague-Dawley rats were rendered diabetic by streptozotocin administration and randomly assigned to untreated, insulin-treated, antioxidant (vitamin E and C)-treated and insulin plus antioxidant-treated groups. Normal rats fed either a regular diet or the antioxidant (vitamin E and C)-rich diet served as controls. The animals were observed for 4 weeks. Diabetic animals showed marked weight loss, decreased activities of Cu Zn SOD and CAT and normal GPX activity. Additionally, the expression of all antioxidant enzyme proteins was decreased in the diabetic rats compared to the untreated controls. Insulin therapy prevented weight loss and normalized the activities and protein expression of all antioxidant enzymes. Antioxidant therapy in the diabetic rats normalized Cu Zn SOD and GPX protein expression. Combined therapy with insulin and antioxidants normalized all measured antioxidant enzyme protein expression and activities. Thus diabetes-associated reductions in antioxidant enzymes can be ameliorated by insulin and/or antioxidant therapy.

Relationship between malondialdehyde level and glutathione peroxidase activity in diabetic rats

BACKGROUND

This investigation describes the relationship between glutathione peroxidase activities, an antioxidant enzyme, and the oxidative status in diabetic rat blood.

METHODS

Malondialdehyde level and glutathione peroxidase activity were measured by spectrophotometric techniques.

RESULTS AND CONCLUSIONS

Malondialdehyde content in the diabetic rats group was increased compared to that in the controls [3.08+/-0.32 (mean+/-S.E.) vs. 1.15+/-0.29 mM/g hemoglobin, P>0.01]. Glutathione peroxidase activity in the diabetic rats group was increased compared to that in the control [10.27+/-1.39 (mean+/-S.E.) vs. 3.14+/-0.38 micromol NADPH/min/g hemoglobin, P>0.01]. Our results show a positive correlation between serum glutathione peroxidase and malondialdehyde concentration in diabetic rats.

Modulatory Effect of Gymnema montanum Leaf Extract on Brain Antioxidant Status and Lipid Peroxidation in Diabetic Rats

The effects of leaf extract from Gymnema montanum, an endangered and endemic plant, were examined on brain lipid peroxidation in experimental diabetic rats. Ethanolic extract of G. montanum leaves was administered orally (50, 100, and 200 mg/kg of body weight) for 3 weeks, and changes in blood glucose, plasma insulin, and lipid peroxidation markers such as thiobarbituric acid-reactive substances (TBARS), hydroperoxides, and levels of antioxidants, namely, superoxide dismutase, catalase, glutathione peroxidase, reduced glutathione, and glutathione-S-transferase, were examined in the brain of alloxan-induced diabetic rats. Glibenclamide was used as a standard reference drug. A significant increase in the activities of antioxidants was observed in brain on treatment with G. montanum leaf extract and glibenclamide for 3 weeks. Both the treated groups showed significant decreases in formation of TBARS and hydroperoxides in brain, suggesting a role in protective action against lipid peroxidation-mediated membrane damage. Our findings indicate that G. montanum leaf extract possesses antiperoxidative and antioxidant effects in addition to its antidiabetic activity. This report helps to create awareness on the need for conservation of medicinal plants, and G. montanum is one such plant that needs to be conserved through various propagation trials.

Activity of pancreatic antioxidative enzymes and malondialdehyde concentrations in rats with hyperglycemia caused by fluoride intoxication

The aim of this work was to examine the effect of fluoride ions on antioxidative enzyme activity in the pancreas of rats exposed during 4 months to NaF in drinking water. The study was carried out in 30 four-week-old male Wistar FL rats, that were randomly assigned to three equal groups and given distilled water ad libitum for three weeks. Subsequently, two examined groups of animals were exposed to NaF in drinking water: group 1 (10 rats) at 50 mg F(-)/L (2.63 mmol/L), group 2 (10 rats) at 100 mg F(-)/L (5.26 mmol/L). The control group (10 rats) received distilled water. After 4 months the animals were anesthetized with ether prior to collection of pancreas and cardiac blood. Serum concentrations of glucose and fluoride, as well as activities of the cytoplasmic (CuZn-SOD) and the mitochondrial (Mn-SOD) superoxide dismutase, glutathione peroxidase (GSH-Px) and concentrations of malondialdehyde (MDA) in the homogenized pancreas were measured. The activity of CuZn-SOD was reduced by 50% and a tendency to lower activities of Mn-SOD was observed. No changes were noted in the activity of GSH-Px or concentrations of MDA. We conclude that: 1) the fluoride caused hyperglycemia in rats in this study is not accompanied by an activation of the free radical production in the pancreas; 2) the hyperglycemia in the exposed rats cannot be attributed to pancreatic damage caused by fluoride ions (the cause in this case appears to be extrapancreatic); 3) the inhibition of pancreatic CuZn-SOD is probably due to the direct action of fluoride on the enzyme.

Dietary glutathione protects rats from diabetic nephropathy and neuropathy

Recently, much attention has focused on the role of oxidative stress in the various forms of tissue damage in patients with diabetes. The aim of this study was to examine the involvement of oxidative stress in the progression of kidney dysfunction and neuropathy in diabetes and to evaluate the potential usefulness of glutathione (GSH) in diabetes. We examined the effect that treatment of streptozotocin (STZ)-induced diabetic rats with GSH has on the renal and neural functions. Diabetic rats were treated with 1 g/100 g GSH as a dietary supplement. GSH significantly suppressed the diabetes-induced increase in urinary 8-hydroxy-2'-deoxyguanosine, one of the markers of oxidative stress. It also prevented the diabetes-induced increases in albumin and creatinine in urine. The diabetes-induced increase in the tail flick reaction time to thermal stimuli also was normalized by treatment with dietary GSH. In conclusion, GSH treatment can beneficially affect STZ-induced diabetic rats, with preservation of in vivo renal and neural function. This suggests a potential usefulness of dietary GSH treatment to reduce diabetic complications.

Ageing and diabetes: implications for brain function

Diabetes mellitus is associated with moderate cognitive deficits and neurophysiological and structural changes in the brain, a condition that may be referred to as diabetic encephalopathy. Diabetes increases the risk of dementia, particularly in the elderly. The emerging view is that the diabetic brain features many symptoms that are best described as "accelerated brain ageing." The clinical characteristics of diabetic encephalopathy are discussed, as well as behavioural (e.g. spatial learning) and neurophysiological (e.g. hippocampal synaptic plasticity) findings in animal models. Animal models can make a substantial contribution to our understanding of the pathogenesis, which shares many features with the mechanisms underlying brain ageing. By unravelling the pathogenesis, targets for pharmacotherapy can be identified. This may allow treatment or prevention of this diabetic complication in the future. We discuss changes in glutamate receptor subtypes, in second-messenger systems and in protein kinases that may account for the alterations in synaptic plasticity. In addition, the possible role of cerebrovascular changes, oxidative stress, nonenzymatic protein glycation, insulin and alterations in neuronal calcium homeostasis are addressed.

The role of oxidative stress in the onset and progression of diabetes and its complications: a summary of a Congress Series sponsored by UNESCO-MCBN, the American Diabetes Association and the German Diabetes Society

This review summarises the results and discussions of an UNESCO-MCBN supported symposium on oxidative stress and its role in the onset and progression of diabetes. There is convincing experimental and clinical evidence that the generation of reactive oxygen species (ROI) is increased in both types of diabetes and that the onset of diabetes is closely associated with oxidative stress. Nevertheless there is controversy about which markers of oxidative stress are most reliable and suitable for clinical practice. There are various mechanisms that contribute to the formation of ROI. It is generally accepted that vascular cells and especially the endothelium become one major source of ROI. An important role of oxidative stress for the development of vascular and neurological complications is suggested by experimental and clinical studies. The precise mechanisms by which oxidative stress may accelerate the development of complications in diabetes are only partly known. There is however evidence for a role of protein kinase C, advanced glycation end products (AGE) and activation of transcription factors such as NF kappa B, but the exact signalling pathways and the interactions with ROI remain a matter of discussion. Additionally, results of very recent studies suggest a role for ROI in the development of insulin resistance. ROI interfere with insulin signalling at various levels and are able to inhibit the translocation of GLUT4 in the plasma membrane. Evidence for a protective effect of antioxidants has been presented in experimental studies, but conclusive evidence from patient studies is missing. Large-scale clinical trials such as the DCCT Study or the UKPDS Study are needed to evaluate the long-term effects of antioxidants in diabetic patients and their potential to reduce the medical and socio-economic burden of diabetes and its complications.

Lipid hydroperoxide and markers of renal disease susceptibility in African-Caribbean and Caucasian patients with Type 2 diabetes mellitus

AIMS

The reasons for the increased incidence of diabetic nephropathy in African-Caribbean compared with Caucasian subjects are poorly understood. Increased oxidative stress is linked to the development of endothelial dysfunction and histological abnormalities associated with diabetic renal disease. Therefore, it was assessed whether a marker of oxidative stress, lipid hydroperoxide (LOOH) and endothelial damage, von Willebrand factor (vWF) varied according to ethnic origin in the presence or absence of early diabetic nephropathy.

METHODS

Eighty-eight patients with Type 2 diabetes mellitus of African-Caribbean or Caucasian origin without a history of cardiovascular disease or clinical proteinuria were studied. Patients were classified as having microalbuminuria or normal albumin excretion. Fasting plasma vWF and LOOH were measured by an inhouse enzyme-linked immunoassay and ferrous oxidation with xylenol orange (FOX) assay, respectively. The relationship of LOOH to urinary albumin status, the metabolic disturbances of diabetes, blood pressure and ethnic origin were assessed using multivariate analysis.

RESULTS

Compared with Caucasian patients those of African-Caribbean origin had higher systolic blood pressure and HDL-cholesterol (157.8 +/- 17.0 vs. 147.8 +/- 24.4, P = 0.041 and 1.6 +/- 0.4 vs. 1.3 +/- 0.5, P = 0.018) but lower total triglycerides (1.3 +/- 0.8 vs. 1.9 +/- 1.1, P = 0.008). LOOH was significantly higher in the African-Caribbean patients compared with Caucasians (5.98 +/- 2.49 vs. 4.49 +/- 2.19, P = 0.006). vWF tended to be higher in microalbuminuric patients but showed no variation with ethnicity. In logistic regression analysis, LOOH was the only independent predictor of a raised albumin excretion rate (P = 0.008). In multiple regression analysis, African-Caribbean ethnicity (P = 0.020) HDL-cholesterol (P = 0.036), total triglycerides (P = 0.002) and a raised albumin excretion rate (P = 0.002) were independent predictors of LOOH.

CONCLUSIONS

In this group of Type 2 diabetic patients an increase in LOOH is associated with abnormal urinary albumin excretion. African-Caribbean origin was a determinant of LOOH independently of microalbuminuria. It is postulated that increased oxidative stress is of pathophysiological significance in accelerating the development of renal disease in African-Caribbean patients.

Plasma ferritin and type 2 diabetes mellitus: a critical review

Multiple factors appear to be involved in the pathogenesis of type 2 (non insulin dependent) diabetes mellitus (DM). One of these factors may be iron overload. This critical review summarizes the major studies on the link between type 2 DM, insulin resistance, glycemic control, diabetic complications and hyperferritinemia. Although some studies suggested that plasma ferritin concentration is positively correlated with insulin resistance and with the risk of acquiring type 2 DM, substantial iron overload is not a typical feature of DM. There is no correlation between plasma ferritin level and glycemic control or diabetic microangiopathic complications.

Antioxidant Activity of Secoisolariciresinol Diglucoside-derived Metabolites, Secoisolariciresinol, Enterodiol, and Enterolactone

Secoisolariciresinol diglucoside (SDG), an antioxidant isolated from flaxseed, is metabolized to secoisolariciresinol (SECO), enterodiol (ED), and enterolactone (EL) in the body. The effectiveness of SDG in hypercholesterolemic atherosclerosis, diabetes, and endotoxic shock could be due to these metabolites. These metabolites may have antioxidant activity. However, the antioxidant activity of these metabolites is not known. The antioxidant activity of SECO, ED, and EL was investigated using chemiluminescence (CL) of zymosan-activated polymorphonuclear leukocytes (PMNLs) [PMNL-CL]. Other antioxidants (SDG and vitamin E) were also used for comparison. SDG, SECO, ED, EL, and vitamin E, each in the concentration of 0.5, 1.0, 2.5, 5.0 and 10.0 mg/ml, produced a concentration-dependent reduction in zymosan-activated PMNL-CL. SDG, SECO, ED, EL, and vitamin E, in the concentration of 2.5 mg/ml, produced a reduction of zymosan-activated PMNL-CL by 23.8%, 91.2%, 94.2%, 81.6% and 18.7%, respectively. Activated PMNLs produce reactive oxygen species and luminol-dependent CL reflects the amount of oxygen species generated from activated PMNLs. The reduction of PMNL-CL, therefore, reflects the antioxidant activity of the compounds studied. These results suggest that the metabolites of SDG have antioxidant activity. The antioxidant activity was highest with SECO and ED and lowest with vitamin E. The antioxidant potency of SECO, ED, EL, and SDG was 4.86, 5.02, 4.35, and 1.27 respectively, as compared to vitamin E. SECO, ED and EL are respectively 3.82, 3.95, and 3.43 more potent than SDG.

The role of oxidative stress in diabetic retinopathy

PURPOSE

To investigate the role of oxidative stress in the development of diabetic retinopathy.

METHODS

This study included 25 patients with diabetic retinopathy (group I), 34 patients with non-insulin-dependent diabetes mellitus without any angiopathy complications (group II) and 26 healthy subjects (group III). The serum malondialdehyde (MDA)-like metabolite levels as an index of lipid peroxidation, the erythrocyte glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and serum vitamin C levels of the patients and healthy subjects were measured.

RESULTS

The mean serum concentration of MDA-like metabolites of patients in group I was 4.38 +/- 1.31 nmol/ml, in group II was 3.38 +/- 0.95 nmol/ml and in group III was 2.61 +/- 0.85 nmol/ml. There were significant differences between the groups (p = 0.001 for group I compared with group II, p = 0.0001 for group I compared with group III and p = 0.002 for group II compared with group III). There was a significant correlation between the serum lipid peroxidation concentrations and duration of the disease (r = 0.36, p = 0.047). The mean erythrocyte GSH-Px and SOD levels of group I were respectively 68.97 +/- 18.04 and 1597.78 +/- 296.46 U/g Hb, of group II were 64.30 +/- 19.26 and 1581.33 +/- 278.08 U/g Hb, and of group III were 65.52 +/- 17.58 and 1587.44 +/- 281.17 U/g Hb. There were no significant differences among the antioxidant enzyme levels in the three groups (p > 0.05). The mean serum vitamin C level in group I was 42.72 +/- 8.90 mumol/l, in group II was 49.26 +/- 11.52 mumol/l and in group III was 58.57 +/- 9.75 mumol/l. There were significant differences among the mean serum vitamin C levels of the three groups (p = 0.02 for group I versus group II p = 0.001 for group I versus group III and p = 0.002 for group II versus group III).

CONCLUSIONS

Free radicals forming in diabetes mellitus and increasing over time may play a role in the development of diabetic retinopathy, which is an important complication of the disease.

Oxidative stress as a mechanism of diabetes in diabetic BB prone rats: effect of secoisolariciresinol diglucoside (SDG)

Secoisolariciresinol diglucoside (SDG) isolated from flaxseed has antioxidant activity and has been shown to prevent hypercholesterolemic atherosclerosis. An investigation was made of the effects of SDG on the development of diabetes in diabetic prone BioBreeding rats (BBdp rats), a model of human type I diabetes [insulin dependent diabetes mellitus (IDDM)] to determine if this type of diabetes is due to oxidative stress and if SDG can prevent the incidence of diabetes. The rats were divided into three groups: Group I, BioBreeding normal rats (BBn rats) (n = 10); group II, BBdp untreated (n = 11); and group III, BBdp treated with SDG 22 mg/kg body wt, orally) (n = 14). Oxidative stress was determined by measuring lipid peroxidation product malondialdehyde (MDA) an index of level of reactive oxygen species in blood and pancreas; and pancreatic chemiluminescence (Pancreatic-CL), a measure of antioxidant reserve. Incidence of diabetes was 72.7% in untreated and 21.4% in SDG-treated group as determined by glycosuria and hyperglycemia. SDG prevented the development of diabetes by approximately 71%. Development of diabetes was associated with an increase in serum and pancreatic MDA and a decrease in antioxidant reserve. Prevention in development of diabetes by SDG was associated with a decrease in serum and pancreatic-MDA and an increase in antioxidant reserve. These results suggest that IDDM is mediated through oxidative stress and that SDG prevents the development of diabetes.

Increased nitrotyrosine staining in kidneys from patients with diabetic nephropathy

BACKGROUND

Proximal tubular cells produce nitric oxide (NO.). We have shown that under hyperglycemic conditions, cultured proximal tubular cells express cytochrome P450 2E1, which is capable of producing superoxide (O2.). NO. and O2. react to form peroxynitrite (ONOO.), a powerful oxidant. ONOO. nitrosylates tyrosine moieties on proteins causing tissue damage. Our hypothesis is that ONOO. plays a role in early diabetic tubular damage and perhaps disease progression.

METHODS

Renal biopsies from patients with diabetic nephropathy (DM), acute allograft rejection (AAR), acute allograft tubular necrosis (ATN), and glomerulonephritis (GN) were obtained. Normal kidney specimens were taken from nephrectomy samples (N = 10 for each group). The tissues were examined for the presence of nitrotyrosine using an immunoperoxidase technique with a polyclonal antibody. Samples were then arbitrarily scored, and the results analyzed (analysis of variance and Student's t-test for unpaired data). The number of apoptotic cells in a sample of tubules in each biopsy was also assessed.

RESULTS

The DM biopsies showed increased staining for nitrotyrosine in proximal tubules (P = 0.0001) and in the thin limb of the loop of Henle (P = 0.0006) compared with all other groups. There was increased staining in the ascending and distal tubules in GN as compared to DM and ATN (P = 0.01). Nitrotyrosine was also found in all distal tubules and collecting ducts, including normals. There was no difference in the number of apoptotic tubular cells in diabetics compared with controls.

CONCLUSION

To our knowledge, these data provide the first evidence for the presence of nitrotyrosine in both normal and diseased kidneys. The significance of the findings in normals is unclear, but could be due to activation of constitutive NOS. However, the study clearly demonstrates increased production of ONOO. in proximal tubules of patients with DM, and suggests that oxidant injury of the proximal tubules plays an important part in the pathogenesis of DM.

The effects of glycation/glycoxidation on the liberation of 8-epi-PGF2alpha from low density lipoprotein during its in vitro oxidation

In individuals suffering from diabetes mellitus, low-density lipoprotein (LDL) can undergo glycoxidation, both the surface protein and the unsaturated fatty acids in the particle core experiencing oxidative damage. In these patients, plasma levels of glycated(g)/glycoxidated(go) low-density lipoprotein and of 8-epi-PGF2alpha (8-IP), a relatively stable peroxidation product of arachidonic acid, are increased. This study reports on the modified oxidation of gLDL and goLDL by human umbilical vein endothelial cells or by copper cations in the absence of cells. In both systems, glycated LDL was found to be more easily oxidized than either nLDL or goLDL. In addition, liberation of 8-IP from glycoxidated LDL is significantly reduced, because a large amount of 8-IP is already formed during long-term glycation of LDL in the absence of metal chelators, i.e. during glycoxidation. From these in vitro results we conclude, that 1) gLDL is more prone to cell-mediated oxidation than native or goLDL and 2) the increased in vivo plasma levels of 8-IP observed in diabetes mellitus could be due to prolonged LDL-glycoxidation liberating continuously significant amounts of 8-IP.

Clinical relevance of the oxidative stress concept

Subjects with type 2 diabetes have markedly increased rates of coronary heart disease (CHD) that are only partly explained by the increased levels of conventional cardiovascular risk factors such as total cholesterol, hypertension, and smoking. Although an increasing number of studies have suggested a role for glycemia in cardiovascular disease, considerable controversy remains. This issue may be resolved when the results of the UK Prospective Diabetes Study (UKPDS) are presented. One possible promising relatively new risk factor that may explain high levels of CHD in diabetic subjects is increased oxidative stress. Type 2 diabetic subjects have an increased preponderance of small dense low-density lipoprotein (LDL), which predisposes to the oxidation of LDL. Almost all studies show that diabetic subjects have increased oxidative stress. In addition, they may have lower levels of alpha-tocopherol. In most studies, increased oxidative stress has been associated with cardiovascular disease, although prospective data are lacking. If levels of oxidative stress are increased, what are the best levels to reduce it to? Improved glycemic control has been associated with decreased oxidative stress. Antioxidant replacement such as alpha-tocopherol may also be beneficial. Interestingly, some special properties of hypoglycemic agents have been described. Gliclazide has been reported to favorably affect both free radicals and platelet reactivity. Gliclazide may have a more favorable effect on tissue plasminogen activator (tPA) than tolbutamide. In conclusion, increased levels of oxidative stress may underlie some of the increased risk of cardiovascular disease in diabetic subjects. Interventions to decrease levels of oxidative stress by methods such as improved glycemic control, antioxidant therapy (ie, alpha-tocopherol), and gliclazide are indicated.

Gliclazide scavenges hydroxyl and superoxide radicals: an electron spin resonance study

The role of reactive oxygen species in diabetes and its complications are well known. Two therapeutic agents commonly used in the treatment of diabetes are the sulfonylureas gliclazide and glibenclamide. These drugs effectively reduce blood sugar in non-insulin-dependent diabetes mellitus, by augmenting insulin release. Gliclazide is known to be a general free radical scavenger as shown by its inhibition of o-dianisidine photo-oxidation. In this study, the effects of gliclazide and glibenclamide on free radicals were examined in vitro, using electron spin resonance spectroscopy. Superoxide radical (O2*-) generated from the hypoxanthine-xanthine oxidase system or hydroxyl radical (OH*) generated via the Fenton reaction were analyzed as spin adducts of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Gliclazide scavenged O2*- and OH* in a dose-dependent manner whereas glibenclamide was without effect. These findings suggest that gliclazide is not only effective in reducing blood sugar, but may also be beneficial as a result of inhibition of lipid and protein denaturation, which is believed to lead to the development of diabetic complications.

Abnormal markers of endothelial cell activation and oxidative stress in children, adolescents and young adults with type 1 diabetes with no clinical vascular disease

BACKGROUND

Endothelial cell dysfunction is an early feature of vascular disease and oxidative stress may be involved in its pathogenesis.

METHODS

Fifty-one children, adolescents and young people with Type 1 diabetes with no clinical diabetic angiopathy, mean age+/-SD of 16+/-4 years, diabetes duration of 8+/-5 years, and HbA(1c) of 8.5+/-1.6%, and 29 age, sex matched normal controls had blood samples assayed for E-selectin, intercellular cell adhesion molecule-1, von Willebrand Factor, red cell superoxide dismutase, plasma thiol and red cell glutathione.

RESULTS

E-selectin and ICAM-1 levels were significantly higher in the diabetic patients at 72+/-24 ng/ml and 287+/-57 ng/ml, respectively vs 43+/-16 ng/ml and 248+/-71 ng/ml in the normal controls (p<0.0002 and p<0.013). Von Willebrand Factor levels were not different between the two groups. Superoxide dismutase activity was significantly higher in the diabetic group at 220+/-58 micro/ml vs 175+/-24 micro/ml in the normal controls p<0.001, and those of plasma thiol and red cell glutathione were significantly lower in the diabetic group, at 1267+/-202 micromol/l and 458+/-38 micromol/l, respectively vs 1403+/-278 micromol/l and 487+/-70 micromol/l in the controls p<0.02 and p<0.03. Levels of superoxide dismutase correlated negatively with plasma thiol, age and diabetes duration r=-0.318, p<0.02; r=-0. 328, p<0.02; and r=-0.286, p<0.05, respectively.

CONCLUSION

These results confirm evidence of endothelial perturbation in young people with diabetes mellitus, and they also suggest that free radical generation may contribute to this dysfunction. This supports the hypothesis that vascular disease starts early in the course of childhood diabetes, akin to the situation in adults with diabetes.

alpha-Lipoic acid decreases oxidative stress even in diabetic patients with poor glycemic control and albuminuria

In the present cross-sectional study, the influence of alpha-lipoic acid on markers of oxidative stress, assessed by measurement of plasma lipid hydroperoxides (ROOHs), and on the balance between oxidative stress and antioxidant defence, determined by the ratio ROOH/(alpha-tocopherol/cholesterol), was examined in 107 patients with diabetes mellitus. Patients receiving alpha-lipoic acid (600 mg/day for > 3 months) had significant lower ROOHs and a lower ROOH/(alpha-tocopherol/cholesterol) ratio than those without alpha-lipoic acid treatment [ROOH: 4.76 +/- 2.49 vs. 7.16 +/- 3.22 mumol/l; p < .0001] and [ROOH/(alpha-tocopherol/cholesterol): 1.37 +/- 0.72 vs. 2.16 +/- 1.17; p < 0.0001]. In addition, the influence of glycemic control and albuminuria on ROOHs and on the ratio of ROOH/(alpha-tocopherol/cholesterol) was examined in the presence and absence of alpha-lipoic acid treatment. Patients were subdivided into three groups based on (1) their HbA1 levels (< 7.5, 7.5-9.5, and > 9.5%) and (2) their urinary albumin concentrations (< 20, 20-200, and > 200 mg/l). Neither poor glycemic control, nor the presence of micro- or macroalbuminuria prevented the antioxidant effect of alpha-lipoic acid. Using stepwise multiple regression analysis, alpha-lipoic acid was found to be the only factor significantly predicting low ROOHs and a low ratio of ROOH/(alpha-tocopherol/cholesterol). These data provide evidence that treatment with alpha-lipoic acid improves significantly the imbalance between increased oxidative stress and depleted antioxidant defence even in patients with poor glycemic control and albuminuria.

Susceptibility of low- and high-density lipoproteins from diabetic subjects to in vitro oxidative modification

AIMS

To investigate the hypothesis that lipid peroxidation of both low-density lipoproteins (LDL) and high-density lipoproteins (HDL) is important in the development of atherosclerosis.

METHODS

We have investigated whether LDL and HDL from patients with Type 1 diabetes mellitus (DM, n = 16) and Type 2 DM (n = 15) is more susceptible to Cu2+ -induced lipid peroxidation than LDL and HDL from a similar number of nondiabetic controls matched for age, gender and serum cholesterol.

RESULTS

The vitamin E content of LDL and HDL from both groups of diabetic patients was not significantly different from controls. The LDL from Type 2 diabetic patients and HDL from both diabetic groups were significantly richer in triglyceride than controls. Phospholipid was decreased in LDL from Type 2 diabetic patients and protein was decreased in HDL in Type 1 DM, but otherwise the composition of LDL and HDL in diabetic subjects was similar to controls. No significant differences were observed in the generation of conjugated dienes or lipid peroxides in either LDL or HDL when the two groups were compared with each other or with their respective controls.

CONCLUSIONS

Increased lipid peroxidation occurring in vivo in diabetes is unlikely to be the result of increased susceptibility of lipoproteins to lipid peroxidation, but rather to increased generation of free radicals, to oxidation of lipids other than those present in serum lipoproteins or to decreases in antioxidant systems other than the fat-soluble antioxidants present in lipoproteins.

Early endothelial alterations in non-insulin-dependent diabetes mellitus

The high incidence of cardiovascular morbidity and mortality in non-insulin-dependent diabetes mellitus with albuminuria cannot be fully explained by the presence of standard cardiovascular risk factors. We assessed some pathogenic factors of diabetic vascular atherosclerotic damage in 72 non-insulin-dependent diabetes mellitus patients controlled by diet alone and 60 healthy controls. Our study aim was to assess the early onset of these alterations and to correlate them with the presence of microalbuminuria. We determined their incidence in two carefully selected groups of diabetic patients without clinical signs of cardiovascular risk and complications, where diet alone achieved glycometabolic balance. Microalbuminuric patients had an alterated oxide-reductive balance and elevated values of plasminogen activator inhibitor, tissue plasminogen activator, von Willebrand factor, endothelin-1 and betathromboglobulin compared with the normoalbuminuric diabetics and controls. Our findings support the hypothesis that a state of endothelial dysfunction characterized by altered oxide-reductive balance, modified hemostasis and changes in the endothelial barrier properties occurs much earlier in non-insulin-dependent diabetic patient especially in diabetics with microalbuminuria. In addition, alterations in the oxide-reductive balance, and hemostasis occur early and may be an underlying cause of microangiopathic complications in microalbuminuric diabetics.

Influence of reduced glutathione infusion on glucose metabolism in patients with non-insulin-dependent diabetes mellitus

To evaluate the relationship between oxidative stress and glucose metabolism, insulin sensitivity and intraerythrocytic reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio were measured in 10 non-insulin-dependent diabetes mellitus (NIDDM) patients and 10 healthy subjects before and after the intravenous administration of GSH. In particular, after baseline insulin sensitivity was assessed by a 2-hour euglycemic hyperinsulinemic clamp, either glutathione (1.35 g x m2 x min(-1)) or placebo (saline) were infused over a period of 1 hour. The same protocol was repeated at a 1-week interval, in cross-over, according to a randomized, single-blind design. In healthy subjects, baseline intraerythrocytic GSH/GSSG ratio (P < .0005) and total glucose uptake (P < .005) were significantly higher than in NIDDM patients. In the same subjects, GSH infusion significantly increased total glucose uptake (from 37.1 +/- 6.7 micromol kg(-1) x min(-1) to 39.5 +/- 7.7 micromol x kg(-1) x min(-1), P < .05), whereas saline infusion was completely ineffective. In addition, the mean intraerythrocytic GSH/GSSG ratio significantly increased after GSH infusion (from 21.0 +/- 0.9 to 24.7 +/- 1.3, P < .05). Similar findings were found in diabetic patients, in whom GSH infusion significantly increased both total glucose uptake (from 25.3 +/- 9.0 micromol x kg(-1) x min(-1) to 31.4 +/- 10.0 micromol x kg(-1) x min(-1), P < .001) and intraerythrocytic GSH/GSSG ratio (from 14.8 +/- 4.1 to 21.7 +/- 6.7, P < .01). Pooling diabetic patients and controls, significant correlations were found between intraerythrocytic GSH/GSSG ratio and total glucose uptake (r = .425, P < .05), as well as between increments of the same variables after GSH infusion (r = .518, P < .05). In conclusion, our data support the hypothesis that abnormal intracellular GSH redox status plays an important role in reducing insulin sensitivity in NIDDM patients. Accordingly, intravenous GSH infusion significantly increased both intraerythrocytic GSH/GSSG ratio and total glucose uptake in the same patients.

Elevation of plasma lipid peroxides in non-insulin dependent diabetics with multiple lacunar infarcts

Our purpose was to determine whether lipid peroxides are elevated in the plasma of patients with non-insulin dependent diabetes with multiple lacunar infarcts as detected by magnetic resonance imaging (MRI), and to confirm whether peroxide levels correlate with glycemic controls and blood lipid levels. The level of lipid peroxide (measured as thiobarbituric acid reactive substances (TBARS)) was measured in 23 healthy controls and 28 diabetics showing normal MRI findings and 22 diabetics with multiple lacunar infarcts. These groups were age-matched. In patients with multiple lacunar infarcts, systolic blood pressure, diastolic blood pressure and TBARS levels were significantly higher than in diabetics without such infarcts (p < 0.05). When the diabetic patients were divided into two groups according to the presence or absence of hypertriglyceridemia or hyperglycemia, in both groups plasma TBARS levels in patients with multiple lacunar infarcts were significantly higher than in patients without such infarcts. Multivariate analysis showed systolic blood pressure and plasma TBARS levels to be independent predictors of multiple lacunar infarcts. Among diabetics, total plasma TBARS levels were positively correlated with fasting blood glucose, HbA1c and triglyceride levels, but not with total cholesterol levels and age. In conclusion plasma lipid peroxides were elevated in diabetics with multiple lacunar lesions, and are related to the metabolic imbalance of plasma glucose and lipids.

Deamination of methylamine and angiopathy; toxicity of formaldehyde, oxidative stress and relevance to protein glycoxidation in diabetes

Semicarbazide-sensitive amine oxidase (SSAO) is located in the vascular smooth muscles, retina, kidney and the cartilage tissues, and it circulates in the blood. The enzyme activity has been found to be significantly increased in blood and tissues in diabetic patients and animals. Methylamine and aminoacetone are endogenous substrates for SSAO. The deaminated products are formaldehyde and methylglyoxal respectively, as well as H2O2 and ammonia, which are all potentially cytotoxic. Formaldehyde and methylglyoxal are cytotoxic towards endothelial cells. Excessive SSAO-mediated deamination may directly initiate endothelial injury and plaque formation, increase oxidative stress, which can potentiate oxidative glycation, and/or LDL oxidation and damage vascular systems. Formaldehyde is also capable of exacerbating advanced glycation, and thus increase the complexity of protein cross-linking. Uncontrolled SSAO-mediated deamination may be involved in the acceleration of the clinical complications in diabetes.

Clinical and biochemical determinants of plasma lipid peroxide levels in type 2 diabetes

The enhanced risk and increased severity of atheroma in diabetes is well recognized but, as yet, incompletely explained. A cross-sectional study of vascular disease risk factors in a group of type 2 diabetic patients from South West Scotland has revealed an association between glycaemic control, assessed by HbAl level and plasma lipid peroxides measured by a specific high-performance liquid chromatography method. Duration of diabetes appeared to be a subsidiary contributor to lipid peroxidation. We suggest this evidence supports the importance of glycaemic control in modulating glyco-oxidative mechanisms probably crucial to production of diabetic complications. Atherosclerosis prevention in diabetes may hinge on exemplary simultaneous control of both hyperglycaemia and hyperlipidaemia.

Glutathione levels are reduced in diabetic rat retina but are not influenced by ischemia followed by recirculation

Free radicals have recently been proposed to play a role in the development of diabetic retinopathy. The aim of the present study was to examine whether the abnormal metabolism caused by diabetes and by ischemia followed by recirculation interferes with a free radical enzyme defense system in the retina, ie, glutathione. Diabetes mellitus was induced by injecting streptozotocin ([STZ] 60 mg/kg body weight [BW] intraperitoneally). After 2 and 6 months, respectively, glutathione levels were measured in the retina and compared against those of age-matched normal control rats. Retinal ischemia was induced by careful ligation of the vessels and the accompanying optic nerve behind the left eye bulb. The right eye served as a control. After 90 minutes of ischemia, retinal circulation was reestablished by removing the ligature. Two-month-old diabetic rats were kept for an additional 3 days and normal rats for 5 minutes, 15 minutes, or 3 days before they were killed for measurement of glutathione. Retinal levels of glutathione were significantly lower in 6-month diabetic compared with 2-month diabetic rats (16.6 +/- 2.9 v 19.0 +/- 2.2 nmol/mg protein, P < .05) and 6-month normal control rats (16.6 +/- 2.9 v 21.0 +/- 2.1 nmol/mg protein, P < .001). Ischemia followed by recirculation did not influence the total tissue level of glutathione either in 2-month-old diabetic rats or in normal rats. The present study indicates that the abnormal metabolism caused by diabetes, rather than by changes in retinal circulation, results in an impaired defense mechanism against free radicals, a factor that may be of importance for the development of diabetic retinopathy. However, since glutathione levels in the present study were measured in the whole retina, it cannot be excluded that particular cell types, such as vascular cells, show an alteration in glutathione that is masked by the glutathione levels in the other nonvascular cells of the retina. Studies using other techniques are needed to further explore this subject.

Free radical scavenging enzymes in fetal dysmorphogenesis among offspring of diabetic rats

Recent studies have suggested that the fetal dysmorphogenesis in diabetic pregnancies is associated with an increase in embryonic oxygen-free radicals. This excess of oxygen-free radicals may result from either overproduction or decreased clearance by the enzymatic scavenging mechanism. However, there are no in vivo data on the activity of embryonic oxygen-free radical scavenging enzymes. The purpose of the current study is to investigate whether this increase in embryonic oxygen-free radicals is the result of a change in the activity of the fetal oxygen-free radical scavenging/antioxidant enzymes during pregnancy complicated by maternal diabetes in an in vivo rat model. Thirty-six Sprague-Dawley rats were randomly assigned to one of two study groups: nondiabetic control and an untreated diabetic group. On day 12, fetuses were examined for crown-rump lengths, somite numbers, and external anomalies. The activity of fetal oxygen-free radical scavenging enzymes, including superoxide dismutase (SOD), glutathione peroxidase (GPX), and catalase (CAT), were determined. The untreated diabetic group of rats had a significantly higher mean blood glucose level than that of the nondiabetic controls and also a significantly lower weight gain, higher resorption rate, smaller embryonic size with lower total protein content, and a approximately 6-fold increase in the rate of fetal neural tube defects compared to the nondiabetic controls. Superoxide dismutase activity was significantly reduced in the embryos with neural tube defects regardless of maternal diabetic status (2.25 +/- 0.83 vs. 1.17 +/- 0.04 u/mg protein; P < 0.05). Glutathione peroxidase and catalase activity were significantly reduced in malformed versus normal-formed embryos of nondiabetic mothers (GPX-2.68 +/- 1.15 vs. 4.46 +/- 1.12 mu/mg protein, CAT -1.67 +/- 0.53 vs 2.49 +/- 0.61 u/mg protein respectively; P < 0.01). However, overall catalase activity was increased in embryos of diabetic mothers as compared to controls. Two-way analysis of variance identified fetal malformations as the variance associated with reduced fetal SOD activity, whereas maternal diabetes was associated with the increase in fetal catalase activity. Neither neural tube defect nor maternal diabetes was found to be the variable affecting fetal GPX activity, Fetal oxygen-free radical scavenging enzymes respond differently to the adverse environment created by maternal diabetes during pregnancy. Defects in embryonic SOD and catalase activity, regardless of maternal diabetic status, may reduce the ability of the fetus to clear free oxygen radicals, thereby exposing it to an increased oxidative load that may cause fetal dysmorphogenesis. The diabetic state of the mothers did not decrease embryonic activity of any of the scavenging enzymes. Therefore, although excess oxidative load, as observed in diabetes, may cause tissue injury and embryopathy, the mechanism does not appear to be a diabetes-induced reduction in the action of the scavenging enzymes.

Aminoguanidine inhibits semicarbazide-sensitive amine oxidase activity: implications for advanced glycation and diabetic complications

Aminoguanidine, a nucleophilic hydrazine, has been shown to be capable of blocking the formation of advanced glycation end products. It reduces the development of atherosclerotic plaques and prevents experimental diabetic nephropathy. We have found that aminoguanidine is also quite potent at inhibiting semicarbazide-sensitive amine oxidase (SSAO) both in vitro and in vivo. The inhibition is irreversible. This enzyme catalyses the deamination of methylamine and aminoacetone, which leads to the production of cytotoxic formaldehyde and methylglyoxal, respectively. Serum SSAO activity was reported to be increased in diabetic patients and positively correlated with the amount of plasma glycated haemoglobin. Increased SSAO has also been demonstrated in diabetic animal models. Urinary excretion of methylamine is substantially increased in the rats following acute or chronic treatment with aminoguanidine. Urinary methylamine levels were substantially increased in streptozotocin (STZ)-induced diabetic rats following administration of aminoguanidine. The non-hydrazine SSAO inhibitor (E)-2-(4-fluorophenethyl)-3-fluoroallylamine hydrochloride (MDL-72974A) has been shown to reduce urinary excretion of lactate dehydrogenase (an indicator of nephropathy) in STZ-induced diabetic rats. Formaldehyde not only induces protein crosslinking, but also enhances the advanced glycation of proteins in vitro. The results support the hypothesis that increased SSAO-mediated deamination may be involved in structural modification of proteins and contribute to advanced glycation in diabetes. The clinical implications for the use of aminoguanidine to prevent glycoxidation have been discussed.

Effect of streptozotocin-induced hyperglycemia on lipid profiles, formation of advanced glycation endproducts in lesions, and extent of atherosclerosis in LDL receptor-deficient mice

Investigations into the mechanisms by which diabetes accelerates atherosclerosis have been hampered by the lack of suitable animal models. We hypothesized that streptozotocin-treated LDL receptor-deficient mice would be a good model of diabetic atherosclerosis because streptozotocin causes diabetes in the parent C57BL/6 strain and because in these mice diet-induced hypercholesterolemia leads to the formation of advanced atherosclerotic lesions throughout the aorta. Diabetes was induced in 18 mice by intraperitoneal injection of streptozotocin. Low-dose insulin was given subcutaneously to prevent excessive mortality and extreme elevations in triglyceride levels. The control group was subjected to sham injections. Both groups were fed a diet containing .075% cholesterol for six months. Average blood glucose was higher in the diabetic group than in the control group (257 +/- 67 mg/dL versus 111 +/- 7 mg/dL, P < 0.05). Although plasma cholesterol was similar (966 +/- 399 versus 1002 +/- 180 mg/dL) in both groups, VLDL cholesterol was higher whereas LDL cholesterol was lower in the diabetic group. Immunocytochemical analysis demonstrated significantly more advanced glycation end-product (AGE) epitopes in the artery wall of the diabetic group, whereas staining for oxidation-specific epitopes was similar in both groups. Sera of diabetic mice also contained significantly more IgG autoantibodies that bound to several AGE epitopes than did sera from control mice. Despite the presence of hyperglycemia, diabetic dyslipidemia, and enhanced AGE formation in the diabetic mice, both groups had a similar extent of atherosclerosis (diabetic, 17.3 +/- 5.2; control, 16.5 +/- 6.6% of the aortic surface). These data suggest that, at least under conditions of marked hypercholesterolemia; hyperglycemia and enhanced AGE formation do not contribute significantly to atherogenesis in LDL-/- mice.

Lipid peroxidation in type 2 normolipidemic diabetic patients

Vascular complications, as a consequence of atherosclerosis, are the main causes of morbidity and mortality in diabetes. Low density lipoprotein (LDL) oxidation is accepted as a relevant pathogenic mechanism in atherogenesis. The aim of this work was to study the relationship between lipid peroxidation (LPO) and metabolic control. LPO was evaluated in 40 type 2 normolipidemic diabetic patients by measuring thiobarbituric acid reactive substances (TBARS), in the plasma, using malondialdehyde (MDA), end product of the oxidation of polyunsaturated fatty acids, as a standard. Fast blood glucose (FBG), serum total cholesterol (TC) and serum triglycerides (TG) were evaluated by routine methods. Fructosamine (FR) was measured by the nitroblue tetrazolium (NBT) colorimetric test. An elevated level of lipid peroxides (P < 0.001) was observed in the plasma of diabetic patients (4.51 +/- 1.29 nmol/ml) as compared to normal subjects (3.54 +/- 1.00 nmol/ml). Lipid peroxides did not correlate with the FR levels, nor with FBG, TC and TG. These results show an increase of LPO in type 2 normolipidemic diabetic patients. Probably the mechanism for higher lipid peroxide levels in diabetes is multifactorial. Our study supports the hypothesis of a role of oxidative stress in diabetes independently of the lipid serum content.

7-ketocholesterol, a specific indicator of lipoprotein oxidation, and malondialdehyde in non-insulin dependent diabetes and peripheral vascular disease

Increased free radical-mediated lipoprotein oxidation may contribute to the increased prevalence of atherosclerosis in non-insulin dependent diabetes. We have determined levels of malondialdehyde (MDA) and 7-ketocholesterol, a specific indicator of free radical-mediated oxidation of lipoprotein cholesterol, in serum in very low density lipoprotein, intermediate density lipoprotein, low density lipoprotein (LDL) and high density lipoprotein fractions of serum separated by sequential flotation ultracentrifugation. Four groups of male subjects were studied: normal controls, diabetic patients with no evidence of microvascular complications or macrovascular disease, diabetic and non-diabetic patients with peripheral vascular disease (PVD). MDA was increased in vascular disease patients (diabetic 4.5 (3.7-5.8), non-diabetic 4.4 (3.2-5.7) mumol/l, median (2.5-97.5 percentiles)) than controls (3.6 (2.9-5.0) mumol/l) (P < 0.01), but was not increased in uncomplicated diabetic patients (3.8 (3.0-4.8) mumol/l). There were no significant differences in 7-ketocholesterol concentration in LDL, but calculated total 17-ketocholesterol was lower in non-diabetic vascular patients than controls (P < 0.01). Vitamin C concentration was reduced in diabetic and non-diabetic patients with vascular disease. No significant difference in concentration of vitamin E or A was found. In six normal subjects the concentration of MDA was low in lipoproteins separated by ultracentrifugation but high in the residue following lipoprotein fractionation (70-80% total serum MDA). In conclusion, the concentration of MDA by the thiobarbituric acid assay in untreated serum may not reflect free radical damage to lipoproteins. There was no evidence of increased lipoprotein oxidation using 7-ketocholesterol in NIDDM or PVD.