Stigmasterol isolated from the ethyl acetate fraction of Morinda citrifolia fruit inhibits [alpha]-amylase activity: In vitro and in vivo analyses

Stigmasterol, a bioactive phytosterol that is present in numerous plants, has been explored for its antidiabetic activity. The present study extracted, fractionated, isolated and characterized the isolate in the ethyl acetate fraction of Morinda citrifolia fruit and investigated its potency as an inhibitor of [alpha]-amylase. The bioactivity-guided antidiabetic assay revealed that all fractions (A-G) exhibited notable differences with the negative control. However, fraction C reduced blood sugar levels in Swiss-Webster male mice with streptozotocin-induced diabetes by 43.08%, and was further purified to obtain the isolate. The chemical structure of the isolate was determined by employing proton nuclear magnetic resonance (NMR), carbon-13 NMR, distortionless enhancement by polarization transfer and liquid chromatography-mass spectrometry, and was confirmed as stigmasterol. An in vitro assay revealed that stigmasterol exhibited potent inhibitory activity against human [alpha]-amylase activity with an I[C.sub.50] value of 10.29+0.76 [micro]g/ml, compared to that of the fruit extract and acarbose, which were 14.16+5.72 and 43.37+1.56 [micro]g/ml, respectively. On the whole, the present study demonstrates that both Morinda citrifolia fruit extract and stigmasterol isolated from the ethyl acetate fraction of the fruit may have the potential to be developed as an anti-diabetic drugs due to their inhibitory effects on [alpha]-amylase activity. However, further studies are required to guarantee its efficacy and safety for humans. Key words: diabetes mellitus, hypoglycemic activity, metabolic disease, Morinda citrifolia, noni fruit, phytosterols