The potential of gliclazide, a sulphonylurea to influence the oxidative processes within the pathogenesis of diabetic vascular disease

A BRIEF COMMUNICATION

Gliclazide, a sulfonylurea widely used for treatment of diabetes mellitus, is known to scavenge reactive oxygen species. To clarify whether its antioxidative ability interferes with the glycation processes, we incubated bovine serum albumin (BSA) with 1 M glucose or 1 m M methylglyoxal, in the presence or absence of gliclazide, and observed the formation of advanced glycation end products (AGEs). AGE production was assessed by AGE-specific fluorescence, an enzyme-linked immunosorbent assay (ELISA), and Western blotting. The fluorescence at excitation/emission wavelengths of 320/383 nm and 335/385 nm was definitely increased by incubating BSA with 1 M glucose or 1 m M methylglyoxal, and 1 m M gliclazide significantly blunted the fluorescent augmentation, in both wavelengths, in a dose-dependent fashion. Gliclazide almost equaled to aminoguanidine, a putative antiglycation agent, in the inhibitory effect on the glucose-induced fluorescence, while the methylglyoxal-derived fluorescent formation was less suppressed by gliclazide than by aminoguanidine. The AGE concentrations determined by ELISA showed similar results. Incubation of BSA with 1 M glucose or 1 m M methylglyoxal yielded an apparent increase in carboxymethyllysine or argpyrimidine. Both AGEs were significantly lowered by 1 m M gliclazide and a reduction of glucose-derived carboxymethyllysine was comparable to that caused by aminoguanidine. The results of Western blotting supported the findings in ELISA. To our knowledge, the present study provides the first evidence of the antiglycation effect of gliclazide on in vitro AGE formation from glucose and methylglyoxal.

Gliclazide treatment lowers serum ICAM-1 levels in poorly controlled type 2 diabetic patients

OBJECTIVE

To investigate the potential effect of gliclazide on serum ICAM-1 (intercellular adhesion molecule-1) and VCAM-1 (vascular cell adhesion molecule-1) levels in poorly controlled type 2 diabetic patients.

PATIENTS AND METHODS

The study included 104 patients, randomly divided into two groups. Group A comprised 53 patients (26 men) treated with gliclazide with a mean age of 67.5+/-9.9 years, a mean diabetes duration of 13.4+/-5.4 years and a mean HbA1c of 8.6+/-1.1%. Group B comprised 51 patients (25 men) treated with glibenclamide with a mean age of 66.4+/-10.9 years, a mean diabetes duration of 13.2+/-6.1 years and a mean HbA1c of 8.4+/-1.3%. A third group of 30 healthy controls (15 men) with a mean age of 63.3+/-10.4 years was also included. Serum levels of ICAM-1 and VCAM-1 were measured at the beginning of the study and after six months of treatment.

RESULTS

Pretreatment serum ICAM-1 and VCAM-1 levels did not differ between groups A and B, while they were significantly higher (P=0.0001) than in healthy controls. No significant difference in HbA1c, body mass index, blood pressure control and lipid profile between the two groups was observed after the sixth month of treatment. In group A, serum ICAM-1 levels after six months of treatment were significantly reduced from 623.12+/-61.17 ng/ml to 370.14+/-49.92 ng/ml (P=0,01), while no reduction was found in VCAM-1 levels. In group B, no reduction was found in serum ICAM-1 and VCAM-1 levels after the end of the study.

CONCLUSIONS

Our results suggest that gliclazide treatment reduces serum ICAM-1 levels in poorly controlled type 2 diabetic patients. This reduction is independent of the hypoglycaemic action of gliclazide.

Lymphocyte ecto-5'-nucleotidase in obese type 2 diabetic patients treated with gliclazide

OBJECTIVE

Lymphocyte 5'-nucleotidase is sensitive to superoxide anion, and is an indicator of oxidative stress in humans. The aim of this study was to assess the effect of the sulfonylurea drugs gliclazide and glibenclamide on lymphocyte ecto-5'-nucleotidase of type 2 diabetic patients.

METHODS

Thirty obese type 2 diabetic patients were treated for three months after randomisation either with gliclazide or glibenclamide. Basic laboratory parameters (glycaemia, fructosamine, C-peptide), plasma malondialdehyde levels (MDA) as well as lymphocyte 5'-nucleotidase activity were determined, for all patients and 16 healthy controls, before and after the treatment.

RESULTS

5'-nucleotidase activity in diabetic patients before treatment with gliclazide was 1.61 +/- 0.16 nmol/min/10(6) lymphocytes, and was significantly (P < 0.01) increased compared with the level in healthy controls. After three months of gliclazide treatment, ecto-5'-nucleotidase activity fell significantly by 47.39% and 36% in unstimulated Con A- and PMA-stimulated lymphocytes, respectively. Glibenclamide treatment had no effect on ecto-5'-nucleo-tidase of type 2 diabetic patients. Glycoregulation was improved, as plasma fructosamine decreased from 53.4 to 42.1 and from 50.5 to 43.4 U/g proteins after gliclazide and glibenclamide treatment, respectively. Plasma MDA levels markedly decreased after gliclazide but not glibenclamide treatment.

CONCLUSION

These results show that gliclazide treatment inhibits the activity of lymphocyte ecto-5'-nucleotidase and presumably de-creases the concentration of adenosine at the cell surface. A decrease in 5'-nucleotidase activity and attenuation of adenosine production may be a factor in the protection of tissue injury in type 2 diabetic patients.

Platelet activation in type 2 diabetes mellitus

The abnormal metabolic state that accompanies diabetes renders arteries susceptible to atherosclerosis, being capable of altering the functional properties of multiple cell types, including endothelium and platelets. In particular, an altered platelet metabolism and changes in intraplatelet signaling pathways may contribute to the pathogenesis of atherothrombotic complications of diabetes. A variety of mechanisms may be responsible for enhanced platelet aggregation. Among them, hyperglycemia may represent a causal factor for in vivo platelet activation, and may be responsible for nonenzymatic glycation of platelet glycoproteins, causing changes in their structure and conformation, as well as alterations of membrane lipid dynamics. Furthermore, hyperglycemia-induced oxidative stress is responsible for enhanced peroxidation of arachidonic acid to form biologically active isoprostanes, which represents an important biochemical link between impaired glycemic control and persistent platelet activation. Finally, increased oxidative stress is responsible for activation of transcription factors and expression of redox-sensitive genes leading to a phenotypic switch of endothelium toward an adhesive, pro-thrombotic condition, initial platelet activation, adhesion and subsequent platelet aggregate formation. All this evidence is strengthened by the results of clinical trials documenting the beneficial effects of metabolic control on platelet function, and by the finding that aspirin treatment may even be more beneficial in diabetic than in high-risk non-diabetic patients. Attention to appropriate medical management of diabetic patients will have great impact on long-term outcome in this high-risk population.

Neurovascular disease, antioxidants and glycation in diabetes

People with diabetes are ten to fifteen times more likely to have a lower limb amputation (LLA) than non-diabetic individuals. Fifteen percent of people with diabetes will develop a foot ulcer during their lifetime, the rate of major amputation amongst diabetic individuals continues to rise, foot problems remain the commonest reason for diabetes-related hospitalisation and recurrence rates in patients with previous foot ulcers are 50% or more. Hyperglycaemia-induced oxidative stress has been shown to result in decreased nerve conduction velocity, and decreased endoneural blood flow-both precursors for neuropathy. Vitamin antioxidants have been shown to be effective therapy in experimental models in reducing free radical species and inhibiting the oxidative process in diabetes subjects. Little work has been published, however, regarding the dietary use of antioxidants from foods, and their specific effects on neurovascular disease and glycation within the diabetes population. Aetiological and prevention studies with dietary antioxidants from foods aimed at the complex nature of foot problems in diabetes are needed.

Effects of aminoguanidine and desferrioxamine on some vascular and biochemical changes associated with streptozotocin-induced hyperglycaemia in rats

The effects of aminoguanidine (AG; 100 mg x kg(-1)) and desferrioxamine (DFO; 50 mg x kg(-1)) on some vascular and biochemical changes associated with streptozotocin (STZ; 65 mg x kg(-1); i.p.)-induced hyperglycaemia were investigated in rats. Both AG and DFO were administered i.p., once daily, for 14 consecutive days to normal and hyperglycaemic animals. The responsiveness of the isolated aortic rings to phenylephrine (PE) was tested. In addition, biochemical markers for oxidative stress such as plasma levels of lipid peroxides and total thiols, as well as the activities of erythrocytic superoxide dismutase (SOD) and whole blood glutathione peroxidase (GSH-Px) were assessed. Results of the present study indicated that induction of hyperglycaemia was associated with increased aortic ring responsiveness to PE, loss in body weight, increase in urine volume, elevation of plasma total thiols and lipid peroxide levels and elevated SOD and GSH-Px enzymatic activities. Treatment of normal rats with AG reduced the response of their aortae to PE. Furthermore, a profound increase in body weight without any significant change in the measured biochemical parameters was observed. In hyperglycaemic animals, AG tended to normalize the enhanced aortic response to PE and modulated STZ-induced biochemical changes without affecting the elevated plasma glucose level. Treatment of normal rats with DFO reduced the response of their aortae to PE and decreased their body weight without altering any of the chosen biochemical parameters. In hyperglycaemic animals, DFO attenuated the responsiveness of their aortae to PE and at the same time, did not affect the loss in body weight and the elevation of plasma glucose level observed in the hyperglycaemic group. Additionally, DFO normalized the elevated plasma level of total thiols and exerted a modulatory influence on the enhanced activities of SOD and GSH-Px as well as on the increased levels of lipid peroxides. Our data lend further credence for the contribution of oxidative stress in the vascular and biochemical changes associated with STZ-induced hyperglycaemia. It is also apparent that advanced glycosylation end products and nitric oxide might be involved. Until clinical studies prove the efficacy and safety of these drugs, specific agents which could scavenge free radicals and block protein glycosylation seem beneficial as a helpful adjunct to the therapy of diabetes.

Diabetes mellitus in older patients. Is tight blood glucose control warranted?

Diabetes mellitus is a major health problem in the older population, where it is mainly of the non-insulin-dependent type [i.e. non-insulin-dependent diabetes mellitus (NIDDM)]. Epidemiological evidence and extrapolation of trial data from patients with insulin-dependent diabetes mellitus (IDDM) suggests that improving glycaemic control reduces the risk of developing microvascular complications (i.e. retinopathy, nephropathy and neuropathy) and also slows the rate of progression of these complications in patients with early disease. Macrovascular morbidity and mortality is, however, more common than microvascular disease in the older population and the evidence that improved glycaemic control significantly reduces the impact of macrovascular disease is weak. Thus, the overall benefits of tight glycaemic control are less well defined in older patients, who tend to have NIDDM, than in younger patients with IDDM. There are small but significant risks associated with tight glycaemic control in the older patient, including potentially fatal hypoglycaemia with sulphonyl-ureas and/or insulin, and fatal metformin-induced lactic acidosis. Patients at especially high risk of these complications can, however, be identified and inappropriate pharmacological intervention can be avoided.