EFFECTS OF THE PROMISING SIRTUIN-1 ACTIVATOR PYRABENTIN ON A RAT MODEL OF PREDIABETES

Abstract

Introduction. It is known that part of the therapeutic effects of the first-line antidiabetic drug metformin are associated with the regulatory pathway of one of the energy sensors – adenosine monophosphate-activated protein kinase. In addition, among the subtle signaling mechanisms of metformin action, there are effects mediated by the activation of another energy sensor, sirtuin-1, which is also one of the key elements in the regulation of epigenetic processes and inhibits the work of a number of genes that were activated by hyperglycemia and oxidative stress. In turn, sirtuin-1 activity is suppressed under conditions of insulin resistance.

Among the array of substituted pyrrolinones, imidazoles, 1,2,4-triazoles, and azepines, a promising sirtuin-1 activator compound was discovered under the conditional name pyrabentin (pat. 121946 UA).

The aim of the study was to evaluate the effects of pyrabentin compared to metformin on parameters of carbohydrate metabolism and oxidative status in rats in a prediabetes model.

Materials and methods. A prediabetes model was reproduced in sexually mature white outbred male rats (n=24) by a combination of a high-fructose diet (free access to fructose solution, 200 g/L, 8 weeks) and subcutaneous administration of dexamethasone (0.125 mg/kg body weight, on the 7th and 8th weeks, 5 days per week, once a day). The control group of animals (n=6) of the corresponding sex and age consumed a standard diet (proteins – 15.0%, fats – 5.0%, carbohydrates – 80.0% of total calories). After the model was formed, the compounds were administered to three groups of animals (n=6) for 4 weeks: placebo (3-5% aqueous emulsion of Tween-80 per os); metformin 50 mg/kg body weight in 3-5% aqueous emulsion of Tween-80 per os by gavage; pyrabentin 100 mg/kg body weight in 3-5% aqueous emulsion of Tween-80 per os by gavage. The control group received placebo according to a similar scheme.

Body weight and naso-anal distance were assessed in dynamics and body mass index (BMI) was calculated. Intraperitoneal glucose tolerance test (IGT) (3 g/kg body weight, 0 min; 30 min; 60 min and 120 min) and short insulin test (1 U/kg body weight, 0 min; 15 min, 30 min and 60 min) were performed using the glucose oxidase method (Eksan-Gm, Lithuania), and integral glycemia was calculated. The oxidative status of experimental animals was characterized spectrophotometrically by lipid peroxidation products – diene conjugates and active compounds that react with thiobarbituric acid (TBA) in blood serum and 10% liver homogenate. Blood levels of reduced glutathione and the activities of glutathione peroxidase (GP) (EC 1.11.1.9) and glutathione-S-transferase (EC 2.5.1.18.) in 10% liver homogenate were measured. Thiol antioxidant protection was assessed by the content of free SH-groups in blood serum. Statistical evaluation was performed using one-way analysis of variance at a significance level of P≤0.05.

Results. The selected model led to the development of abdominal obesity in experimental animals, namely, to an increase in BMI (P=0.043) and abdominal fat mass (P=0.020). Administration of active compounds for 4 weeks resulted in normalization of BMI relative to the placebo group, but total abdominal fat remained higher than in control animals (P=0.001 and P=0.010, respectively). In experimental rats, there was no statistically significant increase in basal glycemia during the formation of the model compared to the control group, but impaired glucose tolerance and the development of insulin resistance were noted. It was found that both metformin and pyrabentin significantly affected glucose tolerance in animals with prediabetes, as evidenced by a decrease in integral glycemia during IGT compared to the placebo group (22.73±0.22 mmol/L and 23.01±0.59 mmol/L vs. 25.29±0.69 mmol/L, respectively, P<0.01). In addition, both active compounds equally improved sensitivity to exogenous insulin, but did not restore it to normal values.

The development of prediabetes was accompanied by an increase in the intensity of lipoperoxidation processes (TBA-active compounds in blood serum: 0.89±0.08 µmol/L versus 0.70±0.07 µmol/L, 0.05<P≤0.1; TBA-active compounds in liver homogenate: 45.63±1.32 µmol/g versus 29.49±0.88 µmol/g, P<0.05). Pyrabenthin statistically significantly improved the estimated lipid peroxidation indices at the level of the reference drug.

Changes in the content of reduced glutathione and the activity of antioxidant defense enzymes under simulated conditions did not reach statistical significance; only a trend towards a decrease in GP activity was observed in the liver of all animals with prediabetes and a trend towards an increase in the level of reduced glutathione in the circulation in the pyrabentin group rats. It should be noted that pyrabentin, unlike metformin, had a positive effect on the level of thiols (SH-groups: 1.66±0.05 µmol/L and 1.43±0.19 µmol/L, respectively, versus 1.22±0.06 µmol/L in the placebo group, P<0.001 relative to the pyrabentin group).

Conclusion. In a model of prediabetes in sexually mature rats, which corresponds to the common problem of abdominal obesity in the human population in middle age, the ability of a promising sirtuin-1 activator compound, pyrabentin, to influence glucose intolerance, insulin sensitivity, lipoperoxidation, antioxidant protection, and obesity indicators at the level of the comparator drug has been demonstrated after 4 weeks of oral administration, which justifies further in-depth study of other metabolic antidiabetic effects of the above-mentioned substance.