Abstract:
There is a growth in the problems relating to diabetes and obesity within the Pacific region. A recent study found that nearly 20% of the Samoan population suffer from type 2 diabetes. The same study found that rates of obesity are correspondingly high, at 53% of the male population and almost 77% of the female population. Healthcare costs are high, and so this study was initiated to focus specifically on an economical, available and socially acceptable way of introducing anti-diabetic and anti-obesity treatments. Inspired by ethnobotanical interests relating to the unknown potential of plants within the Pacific Island region, a set of five Samoan plants were selected for evaluation of their potential to provide leads for anti-diabetic or anti-obesity treatments. The work presented here was carried out in collaboration with the Scientific Research Organisation of Samoa (SROS) which collected plant samples and provided the extracts used for the present study.
This study focused on the biological activity of the five selected Samoan plant extracts; Myristica fatua, Barringtonia samoensis, Barringtonia asiatica, Annona muricata and Neisosperma oppositifolia against pancreatic lipase and α-glucosidase enzymes. The enzyme bioassays were optimised and used to validate and identify potential anti-diabetic and anti-obesity treatments from compounds isolated and identified from the samples using LC-MS/MS and NMR spectroscopy.
Two main fractions were carried forward for further fractionation and in vitro bioassay screening; one against lipase and the other against α- glucosidase. The known compound threo-dihydroguaiaretic acid was identified and isolated from Myristica fatua having the most potent lipase inhibition whereas a mixture of compounds containing alkaloids and the compound nirathin was obtained from Neisosperma oppositifolia in a fraction that exhibited the highest α-glucosidase inhibition. The kinetic modelling of both fractions were used to identify threo-dihydroguaiaretic acid having a mixed inhibition and the compound mixture inhibiting α-glucosidase competitively.
