Polyphenol-rich extract and fractions of Terminalia phaeocarpa Eichler possess hypoglycemic effect, reduce the release of cytokines, and inhibit lipase, α-glucosidase, and α-amilase enzymes.

ETHNOPHARMACOLOGICAL RELEVANCE: species of Terminalia (Combretaceae) are used to treat diabetes and metabolic disorders in Asia, Africa, and America. Terminalia phaeocarpa Eichler is an endemic tree from Brazil, popularly known as capitão. This species is closely related to Terminalia argentea Mart., also vulgarly known as capitão, a native but not endemic tree. Due to their phenotype similarity, these species might eventually prove inseparable and they are indistinctly used by locals to treat diabetes, among other diseases. The potential antidiabetic effect of T. argentea has been previously reported, whereas the biological effects and chemical composition of T. phaeocarpa have never been addressed so far.

AIM OF THE STUDY: investigate the hypoglycaemic effect of an ethanol extract (EE) of T. phaeocarpa leaves and its ethyl acetate (FrEtOAc) and hydromethanolic (FrMEOH) fractions, in addition to their activity on the release of pro-inflammatory mediators and inhibition of lipase, α-amylase, and α-glucosidase enzymes. Additionally, it aimed to characterize the chemical composition of the extract and fractions, seeking to identify the compounds related to the biological activities.

MATERIALS AND METHODS: The effect on the release of TNF-α, IL-1β, and CCL-2 was evaluated in LPS-stimulated THP-1 cells (ATCC TIB-202). The inhibition of lipase, α-amylase, and α-glucosidase was tested in vitro, whereas the hypoglycemic effect was assayed in the oral starch tolerance test. The chemical composition was investigated by extensive UHPLC-DAD-ESI-MS/MS analyses.

RESULTS: The extract and derived fractions reduced TNF-α (EE pIC50 = 4.58 ± 0.01; FrEtOAc pIC50 = 4.69 ± 0.01; FrMeOH pIC50 = 4.54 ± 0.02) and IL-1β (EE pIC50 = 4.86 ± 0.02; FrEtOAc pIC50 = 4.86 ± 0.02; FrMeOH pIC50 = 4.75 ± 0.01) release by LPS-stimulated THP-1 cells in a concentration-dependent manner, whereas the inhibitory effect on CCL-2 release did not reach a clear linear relationship for the tested concentrations. The extract and fractions also inhibited in vitro the activity of lipase (EE pIC50 = 3.97 ± 0.12; FrEtOAc pIC50 = 3.87 ± 0.04; FrMeOH pIC50 = 3.67 ± 0.14), α-amylase (EE pIC50 = 4.46 ± 0.27; FrEtOAc pIC50 = 5.47 ± 0.27; FrMeOH pIC50 = 4.26 ± 0.22), and α-glucosidase (EE pIC50 = 5.46 ± 0.05; FrEtOAc pIC50 = 5.79 ± 0.11; FrMeOH pIC50 = 5.74 ± 0.05). The pIC50 values of the test samples were lower than those obtained with orlistat (7.59 ± 0.08) and acarbose (6.04 ± 0.37 and 7.63 ± 0.04) employed as the positive controls respectively in the lipase, α-amylase, and α-glucosidase assays. When assayed in the oral starch tolerance test, the extract and fractions also reduced animal glycaemia. UHPLC-DAD-ESI-MS/MS analyses of the extract and fractions led to the identification of 38 phenolic compounds, mainly phenolic acids, ellagitannins and flavonoids, among others, all of them first-time described for the species.

CONCLUSION: Based on our findings, T. phaeocarpa has hypoglycaemic activity and polyphenols are the probable bioactive compounds, which support the ethnomedical use of the species.