Available evidence suggests that Syzygium spp ethyl acetate extract solubles (EAS) contain triterpene constituents; oleanolic acid (OA), ursolic acid (UA) and methyl maslinate with hypoglycaemic properties. The effects of maslinic acid (MA) on blood glucose in type 1 diabetes mellitus are, however, unclear. Accordingly, we evaluated anti-hyperglycaemic effects of MA in streptozotocin (STZ)-induced diabetic rats, an experimental model for type 1 diabetes. Extraction and fractionation of Syzigium aromaticum flower bud EAS produced triterpene mixtures containing OA, UA and methyl maslinate/methyl corosolate from which MA was obtained following recrystallization with chloroform and methanol. The structure of MA was elucidated by spectroscopy. Oral glucose tolerance responses to various doses of MA were monitored in groups of non-diabetic and STZ-induced diabetic rats after an 18-h fast. Rats treated with deionized water or metformin acted as untreated and treated positive controls, respectively. Blood glucose concentrations were measured at 15 min intervals for the first hour, and hourly thereafter for 3 h. Short-term effects were monitored every third day after 6 h treatment with MA for 5 weeks. Food and water intake, and weight were measured every third day at 9 h00, 24 h after treatment. Acute MA administration induced dose-dependent reduction in blood glucose concentration in diabetic rats. Additionally, chronic treatment of diabetic animals with MA was associated with antihyperglycaemic effects and reduced water intake. Body weight gain was also increased throughout the experimental period although food intake was not altered. We conclude that MA could be effective in type 1 diabetes mellitus or in cases of glucose tolerance impairment; however, further studies are needed to elucidate the possible mechanism(s) involved in the hypoglycaemic effects of MA.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.