Isolation and characterization of the leaves of Brachylaena discolor extract as an anti-diabetic agent

Abstract

Diabetes mellitus is a metabolic disease, which occurs as a result of insulin deficiency and/or insulin resistance and is a major cause of disability and hospitalization. There are many known therapeutic strategies for the treatment of diabetes, with conventional treatments including the reduction of the demand for insulin, stimulation of endogenous insulin secretion, enhancement of the action of insulin at the target tissues and the inhibition of degradation of oligo- and disaccharides. One group of drugs used for the management of Type 2 diabetes is represented by the inhibitors of α-glucosidase and α-amylases. These enzymes are responsible for the breakdown of oligo- and/or disaccharides to monosaccharides. The inhibition of these enzymes leads to a decrease of blood glucose level, because monosaccharides are the form of carbohydrates which are absorbed in the small intestine. The treatment of Type 2 diabetes is complicated by several factors inherent to the disease and elevated post prandial hyperglycemia (PPHG) is one of the risk factors. Therefore, it becomes necessary to identify the amylase inhibitors from natural sources having lesser side- effects. The traditional African herbal medicinal system practiced for thousands of years have reportedly used anti-diabetic plants with no known side effects. Such plants and their products have been widely prescribed for diabetic treatment by traditional healers all around the world with less known mechanistic basis of their functioning. Therefore, these natural products need to be evaluated scientifically in order to confirm claims for their anti-diabetic properties.

This focus of this study was to investigate potential phytochemicals from Brachylaena discolor as possible dietary adjuncts or therapeutics for diabetes therapy. Methanol and aqueous extracts were evaluated for their α-amylase and α-glucosidase inhibition potential, toxicity, mutagenicity and free radical scavenging capacity. The methanol extract, which showed the most positive results was used in a chemically induced diabetic rat model. Male Wistar rats were injected with streptozotocin to induce diabetes. Rats were divided into 8 groups which consisted of both induced and non-induced rats which were dosed via gavage with methanolic plant extract, metformin and 1% Tween 80 (vehicle for delivery of extract and metformin) respectively per treatment group. Blood analysis was carried out every 7 days to monitor the general health profile, which included blood glucose levels. After 28 days of treatment rats were euthanized using Fluothane and pancreatic tissue harvested for Transmission Electron Microscopy for ultrastructural analysis. The crude extract was also subjected to preparative HPLC and LCMS for compound identification.

From results obtained Brachylaena discolor extracts showed great potential as an anti- diabetic drug. The methanolic extract of Brachylaena discolor yielded superior inhibition properties when compared to its aqueous counterparts as well as a high free radical scavenging capacity. Brachylaena discolor also exhibited a proliferative effect on the cell line in the toxicity study indicating no toxicity from the extract. In the diabetic rat model the Brachylaena discolor methanolic extract induced a marked decrease in the blood glucose level of diabetic rats with less severe side-effects when compared to metformin the reference drug used. Ultrastructural analysis showed severe mitochondrial swelling and damage to the nucleus in the diabetic untreated rats when compared to diabetic rats being treated with the plant extract. From the LCMS results 2 peaks were identified in the active fraction obtained from the preparative HPLC with the chemical formula C17H38NO2 and C16H35N2O respectively. Due to the active fraction being at the tail-end of a reverse-phase fractionation, the mixture of two peaks are likely to be a collection of saturated (non-UV active) di- / sesqui or triterpenoid. The results obtained from this study show promising potential for Brachylaena discolor as a potential dietary adjunct or therapeutic for diabetes therapy.