Bioassay-Guided Isolation, GC–MS And FT-IR Characterisation Of Antidiabetic Fractions From Portulaca Lutea Aerial Parts

Abstract

Portulaca lutea (Portulacaceae) is an indigenous purslane used in folk practice for wounds and inflammatory skin conditions, yet its antidiabetic potential has not been systematically investigated. The present work reports successive extraction, phytochemical screening, acute toxicity, antidiabetic activity and in-vitro antioxidant evaluation of the aerial parts, followed by bioassay-guided isolation, GC–MS characterisation and FT-IR fingerprinting of the most active methanol fraction. Powdered aerial parts were extracted by Soxhlet with petroleum ether, chloroform, methanol and water in turn. Acute toxicity was assessed in mice and antidiabetic activity was examined at 200 mg/kg in Wistar rats using normoglycaemic, oral glucose tolerance, alloxan-induced (acute and 14-day) and streptozotocin-induced (acute and 14-day) models, with glibenclamide (10 mg/kg) as reference. Antioxidant activity of the methanol and aqueous extracts was measured by DPPH and superoxide scavenging and Folin–Ciocalteu total phenolics. The methanol extract (13.16 % w/w yield) contained alkaloids, glycosides, saponins, flavonoids, steroids/triterpenoids and tannins, and was non-toxic up to 2000 mg/kg. In alloxan-diabetic rats the methanol extract lowered blood glucose by 38.0 % at 8 h (single dose) and by 54.04 % on day 14 (multi-dose); in streptozotocin-diabetic rats the corresponding reductions were 37.83 % and 54.74 %. The methanol extract scavenged DPPH (IC50 19.20 µg/ml) and superoxide (IC50 34.41 µg/ml) and contained 65.33 mg GAE/g total phenolics. Column chromatography of the methanol extract on silica gel yielded four fractions (PL-M-01 to PL-M-04); GC–MS of PL-M-01 revealed triterpenoids and fatty acid esters, of PL-M-02 triterpenoids, of PL-M-03 flavonoids (luteolin, quercetin, kaempferol, apigenin, genistein), and of PL-M-04 alkaloids and catecholamines (dopamine, noradrenalin, oleraceins A–D). PL-M-01 and PL-M-03 at 50 mg/kg lowered blood glucose by 69 % and 62 % in alloxan rats and by 56 % and 54 % in STZ rats, respectively. FT-IR fingerprinting of PL-M-01 and PL-M-03 confirmed the functional groups assigned by GC–MS. The findings identify P. lutea methanol extract as a promising source of antidiabetic phenolics and triterpenoids suitable for further preclinical development.