The antioxidant activity of garcinol has been identified as the basis for various bioactivities in it, and the genus Garcinia is the main source for the garcinol. G. quaesita, which is endemic to Sri Lanka, is a representative member of genus Garcinia, and the dried fruit rind of G. quaesita is used practically in all curry preparations to impart a sour flavor. In our study, garcinol was isolated (yield: 3.67%) from the dried fruit rind of G. quaesita, for the first time. Further, how cooking conditions enable the ingestion of garcinol during the consumption of curries was also examined. The garcinol content released in different cooking conditions was positively correlated with the antioxidant activity in vitro. The results revealed that boiling virgin coconut oil extract of G. quaesita, simulating the common practice of oil frying during cooking, is the best method for obtaining the highest amount of garcinol into the curry medium.

Diabetes mellitus has become a global epidemic over the past few decades and is one among the major causes of death worldwide. Although various modern medicines are in the market, herbal medicines have usually maintained worldwide popularity in achieving the primary health care needs of the diabetic population because of the multiple adverse effects related to them. Herbal medicines have a prolonged history of being used as medications and sources of medication for diabetes mellitus. Some of them are enclosed within the modern therapeutic arsenal of medicine, and others are used as complementary therapy or as dietary supplements by patients with diabetes. The present review describes on traditional antidiabetic herbal medicines with an emphasis on scientific investigations conducted on antidiabetic medicinal plants, polypherbal mixtures, isolated compounds and their associated toxicities.

The dried fruit of Garcinia quaesita Pierre (Clusiaceae), is a well-known endemic spice in Sri Lanka and has been documented in traditional medicine as an antidiabetic agent. The antihyperglycemic effect of cold water, hot water, water : acetone fruit extracts of G. quaesita and its isolated compound, garcinol in streptozotocin-induced diabetic rats was studied. The percentage improvements of glucose tolerance upon total area under the oral glucose tolerance curve in cold water, hot water and water:acetone extracts of G. quaesita (1.0 g/kg) were 6.2 %, 7.4 % and 8.1 %, respectively. The isolated compound, garcinol at the three selected doses (10 mg/kg, 20 mg/kg, 30 mg/kg), showed a dose dependent, antihyperglycemic activity of 23.6 %, 26.5 %, 31.1 % respectively compared to glibenclamide (0.5 mg/kg) (36.1 %) (p<0.05). The selected extracts of G. quaesita exhibited significant antihyperglycemic activity in streptozotocin-induced diabetic rats. The isolated compound, garcinol has significantly higher antihyperglycemic activity than the respective crude extracts. Accordingly, endemic dried fruits of G. quaesita and its isolated compound garcinol are promising antihyperglycemic agents and /or drug leads that would be beneficial in the management of diabetes mellitus.

A polyherbal drug composed of leaves of Murraya koenigii L. Spreng, cloves of Allium sativum L., fruits of Garcinia quaesita Pierre, and seeds of Piper nigrum L. is a popular drug which has been used by indigenous practitioners in Sri Lanka for the treatment of diabetes mellitus and dyslipidemia. The acute toxicity assessment was conducted, following a single oral dose of 0.25–2.0 g/kg in healthy rats, and rats were observed up to 14 days. The hot water extract (1.0 g/kg) and the water : acetone extract (0.5, 1.0, and 1.5 g/kg) were administered to Wistar rats for 28 days in the subchronic study. Hypoglycemic and antihyperglycemic activities (dose response studies) of cold water, hot water, and water : acetone extracts of the polyherbal mixture were evaluated at the doses of 0.5, 1.0, and 1.5 g/kg in healthy and streptozotocin-induced diabetic rats (70 mg/kg, ip), respectively. Acute toxicity study showed that the polyherbal drug did not cause any change in animals throughout the experimental period of 14 days. The administration of the hot water extract and the water : acetone extract of the polyherbal drug for 28 days did not produce changes in the selected biochemical and hematological parameters in Wistar rats (p > 0.05). The histological assessment corroborated the biochemical findings with no significant treatment-related changes in the kidney and liver. The treatment of polyherbal drug significantly lowered the serum glucose concentration compared to the diabetic control rats (p < 0.05) while it did not lead to a severe reduction of glucose concentration in healthy rats. The hot water and water : acetone extracts of the polyherbal drug showed a statistically significant improvement on total area under the glucose tolerance curve in diabetic rats (p < 0.05), reflecting dose-dependent antihyperglycemic effects of the drug. Based on the results, we conclude that the aforementioned antidiabetic polyherbal remedy is free of toxic/adverse effects at the equivalent human therapeutic dose in healthy Wistar rats and would be a safe therapeutic agent for long-term treatments.

The tetracyclic sesquiterpene, ishwarane, was isolated from the leaves of the representative species of the genus Hortonia, H. angustifolia, H. floribunda and H. ovalifolia collected in Sri Lanka. The complete 2D NMR assignments are reported. Ishwarane exhibited antifungal activity against Cladosporium cladosporioides.

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Ethnomedicine evolved from the traditional use of plant parts for treating various ailments. Historically, most medical breakthroughs have arisen based on the plant sources showing potential for curing many diseases. Even so, the therapeutic power and scientific validation of their modes of action remains unexplored. Sri Lanka being a biodiversity hotspot due to its high endemism and diversity has inspired the search for ethnopharmacological values which may give rise to drug leads or to the discovery of new bioactive compounds. This brief review aims to highlight the global importance of the exploration of traditional medicinal plants, current status and the progress of the studies on Sri Lankan medicinal plants, and the necessity to discover the medicinal value of the Sri Lankan plants.