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Boiled flowers of Nyctanthes arbor-tristis L (Family: Oleaceae; Sepalika in Sinhala; Night
Jasmin in English) has traditionally been used in Sri Lankan Ayurvedic system to manage
diabetes. Previously it has been shown that the aqueous flower extract (AFE) could produce
hypoglycemic effects in mice. However, the exact mechanisms are not known. Hence the
present study aimed to investigate the mechanisms involved using in vitro assays. Fresh
flowers were shade dried, extracted with distilled water and freeze dried. Preliminary
phytochemical screening was conducted using standard methods and confirmed using thin
layer chromatography. The total phenolic and flavonoid content was determined at 1.5 mg/ml
dose using Gallic acid and Quercetin as respective standards. Hypoglycemic activity was
studied in vitro α-amylase assay (n=6) with Acarbose as the standard using mice equivalent
doses (1.5, 3, 5 mg/ml) and glucose transport across the yeast cells was conducted at 5, 10, 25
and 50 mM glucose concentrations. Phytochemical screening revealed the presence of
flavonoids, saponins, unsaturated sterols and triterpenes and cardiac glycosides. AFE resulted
in 600 Quercetin equivalents for total flavonoids and 1.6 Gallic acid equivalents for phenols,
both of which increased in a linear mode with increasing concentrations. A significant
(p<0.05) inhibition of α-amylase enzyme was revealed with increasing doses (1.5 mg/ml-60%,
3 mg/ml-52%, 5 mg/ml) giving IC50 value of 3 mg/ml compared to the standard. Both 1.5
mg/ml and 3 mg/ml promoted glucose uptake by yeast cells with increasing glucose
concentrations. However, 5 mg/ml exhibited the maximum absorption only at 5 mM of
glucose indicating dose independent trend. The present findings confirm that N. arbor-tristis
exerts its antidiabetic activity via inhibition of α-amylase enzyme and increasing glucose
transportation across the cell membranes. Fractionation and isolation of compounds are
required for effective utilization as therapeutic agent.
