Phytochemical Composition, Safety and Hypoglycemic Activity of Purple tea and Guava Extracts in a Mouse Model of Diabetes Mellitus

Abstract

Diabetes mellitus is a metabolic disorder presenting with hyperglycemia and affects 382 million people worldwide. It is managed by insulin and oral hypoglycemic drugs, exercise and diet. Oral hypoglycemic drugs and insulin are very costly, unavailable and have severe side effects like hypoglycemia. Medicinal plants have been used for the management of diabetes and many other diseases. This is because of their reported efficacy, affordability and accessibility. However, antidiabetic activity and safety of medicinal plants extracts are not well documented. Tea (Camellia sinensis) and Guava (Psidium quajava) are commonly used in traditional medicine in Kenya and elsewhere with increased acclaimed efficacy against diabetes mellitus. Therefore, this study is aimed at determining the safety and anti-diabetic activity of leave extracts of newly bred Kenyan purple tea and guava. Activity guided extraction was done using aqueous, ethanol, acetone, ethyl acetate and chloroform solvents. The dose levels of plant extracts tested was 300mg/kg body weight on alloxan induced diabetic mice treated for a period of 14 days. The standard drug Glibenclamide (Daonil®) 5mg/kg was used as positive control. Biochemical indicators including Alanine transaminase (ALT) and Blood Urea Nitrogen (BUN) were evaluated to assay any toxic effect of the plant extracts on the liver and kidneys. Histological examinations of liver, kidney and pancreas were analyzed for in vivo toxicity. The results were analyzed using one way ANOVA with Tukey’s post hoc analysis and comparison between groups considered significant at P<0.05 level. The data was expressed as mean ± S.E.M (standard Error of mean) using SPSS version 16. Results of phytochemical screening of purple tea and guava leave extracts showed the presence of alkaloids, flavonoids, phenols, tannins, saponins, steroids and terpenoids. The acute oral toxicity test did not reveal any significant toxic effect resulting from purple tea and guava leave extracts. ALT and BUN levels in mice treated with the two plant extracts did not xvii have any significant changes compared to the mice in the control group. There were no major histopathological changes in the liver, kidneys and the pancreas and most features compared well with the control mice. Camellia sinensis (purple tea) and Psidium guajava (guava) leaf extracts showed significant (P<0.05) blood glucose lowering ability compared to the diabetic control group treated with normal saline. In addition, the assay of purple tea indicated that ethanolic and aqueous leaf extract (300mg/kg) were effective in lowering blood glucose from the 4th hour and 6th hour respectively after administration. Acetone extract of purple tea at a dose of 300mg/kg significantly (P<0.05) reduced blood glucose after 8th hour only. Both aqueous and ethanolic extracts of Psidium guajava at 300mg/kg were effective from the 6th hour post administration. Acetyl acetate extract of Psidium guajava at a dose of 300mg/kg, significantly (P<0.05) reduced blood glucose after 4th and 6th hour after administration. Long term reduction of blood glucose up to 14 days was demonstrated by aqueous and ethanolic leave extracts of the two plants. This was achieved by daily oral administration of the leave extracts to the mice and blood glucose assessed on day 7 and day 14 after overnight fasting. The standard drug Glibenclamide significantly (P<0.05) reduced blood glucose from the 4th hour upon oral administration to diabetic mice. In conclusion, purple tea and guava leaves extracts are safe and significantly reduced blood glucose in diabetic mice. Isolation of bioactive compounds responsible for the anti-diabetic activity and studying hypoglycemic activity using higher doses of the extracts is recommended.