Investigational Effect of Trans-Anethole in Diabetes along with its associated Complications and Senile Cataract

Abstract

Background: Diabetes is a metabolic disorder characterized by elevated levels of blood glucose, which leads to serious complications like cardiovascular, cerebrovascular, nephropathy, neuropathy, retinopathy, cataract and foot damage. The risk of cardiovascular disease in diabetic patient is two to three times more than non-diabetic and development of cataract is found to be five times higher as compared to non-diabetics. These complications are caused by the involvement of polyol pathway in which aldose reductase enzyme regenerate sufficient amount of NADPH and inhibit the conversion of sorbitol to glucose using polyol dehydrogenase. It leads to increase in the amount of sorbitol into the lens which is enough to produce osmotic stress and oxidative cell injury leading to diabetic complications. Though development of modern medicine resulted in the advent of modern pharmacotherapeutics including insulin, biguanides, sulfonylureas and thiazolidinediones, there is still a need to look for new drugs as no drug (except strict glycemic control with insulin) has been shown to modify the course of diabetic complications. Traditional plant medicines or herbal formulations might offer a natural key to unlock diabetic complications. Trans-anethole is a volatile oil obtained from the various dietary sources like Foeniculum vulgare (81.63% to 87.85%), Pimpinella anisum (85-96%), Nigella sativa (38.3%), Illicium verum fruit (89.5%) and Croton zehntneri (85.7%). From the study in fennel, it showed remarkably elevated antioxidant activity of trans-anethole. Purpose: To evaluate the effect of trans-anethole in diabetes and its associated complications especially cardiovascular complications and cataract.To evaluate the effect of trans-anethole in senile cataract. Materials and methods: In vivo model of diabetic complications using high fat diet and streptozotocin (HFDSTZ) induced diabetes: Healthy Sprague-Dawley rats were randomly divided into 5 groups (n=10) named Normal control, Control treated with trans-anethole, Diabetic control, Diabetic treated with trans-anethole, Diabetic treated with standard quercetin.Diabetes was induced by high fat diet containing 58% fat, 25% protein and 17% carbohydrate, as a percentage of total kcal ad libitum, for the initial period of two weeks. Following this, animals were injected with streptozotocin (35mg/kg, i.p.). After two weeks, diabetes was confirmed by measuring serum glucose levels and animals showing serum glucose levels higher than 150 mg/dl were considered diabetic. The treatment of trans-anethole (80 mg/kg) and quercetin (1 mg/kg) drugs were given for a period of 10 weeks after induction of diabetes. The development of complications was examined at the end of 10 weeks, various parameters like biochemical; cardiac, hemodynamic and lenticular parameters were assessed. In vitro hydrogen peroxide induced cataract: The Wistar rat lenses were isolated by posterior approach under sterile conditions. The lenses were cultured in 24 well plates containing 1.5 ml of medium-199 media (without phenol red) with hydrogen peroxide 0.5 mM and pretreatment with trans-anethole (80 mg/kg) was given to the lens 24 hours prior to the induction of cataract to evaluate the preventive action of the drug. The development of cataract was seen morphologically after 24 hours and several lenticular parameters were assessed. Results: In vivo model of diabetic complications using HFD-STZ induced diabetic model: After 10 weeks, animals showed characteristic signs of diabetes like weight gain, polydipsia and polyuria. These effects were controlled in the animals treated with transanethole and quercetin. Serum glucose, glycated hemoglobin, total cholesterol, triglycerides, LDL-cholesterol, VLDL were altered in the diabetic animals which were improved by the treatment. In the present study, type 1 diabetic rats exhibited significantly higher serum LDH and CK levels as compared to those of control rats. The decrease in LDH and CK levels substantiates the beneficial effects of the plant in reducing the cardiovascular complications in diabetes mellitus. The treatment was also able to alter the hemodynamic changes i.e. hypertension and decline in rate of pressure development and decay produced in the diabetic animals as compared to that of control animals. Cardiac hypertrophy was also observed in the diabetic rats evident from the increased heart weight to femur length ratio as well as left ventricular (LV) hypertrophy characterized by increased LV weight to heart weight ratio, LV weight to RV weight ratio and LV wall thickness which were improved with the treatment. Also, diabetic rats expressed significantly high amount of collagen deposition in left ventricle and chronic treatment with trans-anethole reduced this collagen deposition. This was further confirmed by histopathological examination of left and right ventricle which showed improvement in the destruction in cardiac fibers caused due to chronic diabetic condition in the animals.Moreover, the oxidative state of the ventricles was also improved in the animals as seen by improvement in the levels of glutathione (GSH), superoxide dismutase (SOD) and lipid peroxidation (MDA levels) in right and left ventricles. Visual cataract was found to be present in only some of the diabetic control rats. High levels of aldose reductase (AR) activity was found to be present in diabetic rat lens as compared to that of control animals. Reduction of glucose by AR is a major cause of diabetic cataract which involves both osmotic stress as well as oxidative stress. Treatment with trans-anethole and quercetin was able to inhibit the AR activity and hence may be helpful in delaying the development of cataract in diabetic condition. This was also supported by improvement in the antioxidant status of the lens in diabetic treated animals as compared to the diabetic control animals. In vitro hydrogen peroxide induced cataract: Complete opacity was found to be induced in lenses treated with hydrogen peroxide. The development of opacity was confirmed by stereoscopic and transparency images. Further, it also showed improvement in the antioxidant parameters as well as lenticular parameter like sulfhydryl content, lipid peroxidation levels, Ca+ ATPase activity and crystalline distribution. Conclusions Our data suggests that trans-anethole was able to control the hyperglycemic status of diabetic animals and may be beneficial in delaying the development of the cardiovascular complications and cataract. It also showed protective effect in the development of cataract in an in-vitro hydrogen peroxide model for senile cataract. The effect of trans-anethole may be attributing to the aldose reductase enzyme activity and antioxidant activity.