Investigating the effects of gossypetin on glucose homeostasis and selected complications of diet-induced prediabetes in male Sprague Dawley rats.

Abstract

Background. Prediabetes is an intermediate glycaemic state between normoglycaemia and chronic hyperglycaemia. This condition has become increasingly prevalent worldwide due to the consumption of high-calorie diets and a sedentary lifestyle. Prediabetes is characterised by abnormal glucose metabolism and is associated with complications such as non-alcoholic fatty liver disease (NAFLD), cardiovascular and renal dysfunctions, similar to that observed in type 2 diabetes mellitus. The current management strategy for prediabetes involves a combination of dietary and pharmacological interventions. However, patient adherence to dietary intervention is often low, leading to reduced pharmacological effectiveness. Therefore, anti-diabetic agents that are effective even without dietary intervention are needed. Gossypetin (GTIN), a hexahydroxylated flavonoid, has shown potent antioxidant and anti-inflammatory properties. This study sought to investigate the effects of GTIN on glucose homeostasis and selected markers of cardiovascular, hepatic and renal dysfunction in a prediabetic rat model, both with and without dietary intervention. Materials and Methods. Thirty-six male Sprague Dawley rats (150–180 g) were divided into Group 1 (n=6) and Group 2 (n=30). Prediabetes was induced by feeding Group 2 a high-fat, high-carbohydrate (HFHC) diet for 20 weeks, while Group 1 received a normal diet (ND). Prediabetes was confirmed by fasting blood glucose (FBG) and 2-hour oral glucose tolerance tests (OGTT) according to the American Diabetes Association criteria. The prediabetic rats (n = 30) were subdivided into five groups (n = 6 per group): one group received no therapeutic intervention, while the remaining four groups were treated with either GTIN (15 mg/kg) or metformin (MET, 500 mg/kg), with or without dietary intervention, for 12 weeks. Body mass index (BMI), waist circumference (WC), blood pressure, heart rate, caloric intake, fluid intake and urine output were monitored every four weeks during the treatment period. After treatment, animals were sacrificed; blood and tissues (skeletal muscle, heart, liver, kidney) were collected and stored for biochemical analysis. The thesis comprised four studies evaluating the effects of GTIN on glucose homeostasis, cardiovascular function, hepatic function and renal function in a diet-induced prediabetic rat model. Results. In the first study, animals in the untreated pre-diabetic (PD) control group exhibited significantly higher fasting and postprandial blood glucose levels, as well as elevated plasma insulin concentrations and increased homeostatic model assessment for insulin resistance (HOMA2-IR) index, relative to the non-prediabetic (NPD) group. Similarly, increased caloric intake, body weight and plasma ghrelin levels were observed in the PD control group. Notably, these parameters were significantly reduced in the PD animals receiving GTIN treatment. Additionally, glycogen levels in the liver and skeletal muscle, which was disturbed in the PD control group, showed significant improvement following GTIN treatment , both with and without dietary intervention. In the second study, the PD control group exhibited dyslipidaemia characterized by significantly higher plasma triglyceride, total cholesterol, low-density lipoprotein and very low-density lipoprotein levels, along with decreased high-density lipoprotein (HDL) levels compared with the NPD group. This was accompanied by cardiovascular dysfunction, as evidenced by significantly higher mean arterial pressure (MAP), body mass index (BMI), waist circumference (WC) and plasma endothelial nitric oxide synthase (eNOS) levels in the PD control. Additionally, there were increased heart malondialdehyde levels, reduced heart superoxide dismutase and glutathione peroxidase activity as well as increased plasma interleukin-6, tumour necrosis factor alpha and C-reactive protein levels, indicating enhanced oxidative stress and systemic inflammation. Notably, both GTIN-treated groups showed significantly reduced plasma lipid levels and increased HDL, as well as decreases in MAP, BMI, WC and eNOS levels compared with the PD control. Additionally, GTIN significantly decreased heart lipid peroxidation, enhanced antioxidant activity and decreased plasma inflammation markers. In the third study, the PD group exhibited hepatic steatosis and liver dysfunction evidenced by significantly higher liver triglyceride (TAG) content, liver weights, sterol regulatory element-binding protein-1c (SREBP-1c), malondialdehyde (MDA) levels, and liver injury enzyme levels, along with decreased liver superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, and plasma bilirubin levels in comparison to NPD. Histologically, there was increased lipid droplet accumulation and structural disarray in the PD group. GTIN treatment significantly reduced liver TAGs, liver weights and plasma SREBP-1c levels, as well as improved liver SOD and GPx activity while decreasing liver MDA levels and liver injury enzymes in comparison to the PD control. Notably, GTIN treatment increased plasma bilirubin levels. Liver histology in the GTIN-treated groups revealed decreased lipid droplet accumulation and improved tissue integrity. In the fourth study, GTIN significantly reduced fluid intake, urine output and kidney weights in both the presence and absence of dietary intervention compared with the PD group, indicating improved renal function. Additionally, GTIN administration improved glomerular filtration rate, and normalized creatinine, albumin, urea and uric acid levels. It also improved electrolyte homeostasis by restoring renal sodium and potassium handling along with reduced plasma aldosterone levels. GTIN attenuated renal oxidative stress as evidenced by lower kidney MDA, interleukin-6, tumour necrosis factor-α and higher total antioxidant status levels. Additionally, GTIN reduced kidney injury markers including plasma KIM-1 and urinary podocin mRNA expression. Conclusion. This study demonstrated that chronic consumption of high-calorie diets led to the development of prediabetes. This was associated with impairments in glucose homeostasis as well as cardiovascular, liver and kidney functions. However, treatment with GTIN regardless of dietary intervention may ameliorate disturbed glucose homeostasis as well as cardiovascular, liver and renal dysfunction during prediabetes. These findings suggest that GTIN may represent a promising therapeutic alternative for the management of prediabetes, particularly where adherence to dietary intervention is difficult to maintain. This may help delay the progression from PD to T2DM and reduce the burden of T2DM-associated complications.