Available evidence suggests that Syzygium spp ethyl acetate solubles (EAS) contain triterpene mixtures (oleanolic/ursolic acid and methyl maslinate/methyl corosolate) with hypoglycaemic properties in streptozotocin (STZ)-induced diabetic rats. Accordingly, maslinic acid (MA) was isolated from S. aromaticum. Air-dried powdered flower buds of S. aromaticum were sequentially extracted thrice at 24 h intervals with 3 litres on each occasion of hexane, dichloromethane, ethyl acetate and methanol. The stereostructure of MA obtained following recrystallization with chloroform and methanol was elucidated by 1 h- and 13C-NMR spectroscopy (1D and 2D) on chemical and physicochemical evidence. Oral glucose tolerance (OGT) responses to various doses of MA (20, 40 and 80 mg.kg-1, p.o.) were monitored in 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 after 6 h in animals treated with MA twice daily by means of a bulbed steel tube for a period of 5 weeks while, food and water intake as well as body weight were monitored 24 hours after treatment every third day. All results are presented as mean± standard error means where P<0.05 denotes statistical significance. All doses of MA significantly decreased blood glucose of non-diabetic and STZ-induced diabetic rats throughout the experimental period. Comparisons of the blood glucose lowering effects of the MA doses at each time appeared to be dose-dependent in STZ-induced diabetic rats. MA administration reduced the body weight loss of STZ-induced diabetic rats without altering food intake. The results suggest that MA, like metformin, contains blood glucose lowering properties suggesting that it is a potential drug for the management of type 1 diabetes mellitus.
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.