Endemic Asteraceae from Madeira archipelago: A relation of hypoglycemic activity to their polyphenolic composition

Abstract

The vascular flora of Madeira archipelago is exuberant and diverse, comprising over 1220 species of which 10% are endemic [1]. In this work, nine endemic Asteraceae plant species were studied for their phenolic profile and anti-hyperglycemic effects. The interest and selection of these species are related to their use in folk medicine. Two main groups of plants were analyzed: Helichrysum subspecies (H. devium Johns, H. melaleucum Rchb. ex. Holl, H. monizii Lowe and H. obconicum DC.) and other five endemic species: Argyranthemum pinnatifidum Lowe, Artemisia argentea L'Her, Calendula maderensis DC, Cynara cardunculus L. var. ferocissima and Phagnalon lowei DC. Alcoholic extracts were evaluated for their inhibitory activity towards key enzymes linked to type 2 diabetes using in vitro assays. Six extracts showed stronger inhibitory efficacy [IC50 0.57 to 1.35 mg/mL] than commercial drug acarbose (positive control, IC50 1.62 mg/mL) towards α-glucosidase; exceptions were H. monizii, C. maderensis and C. cardunculus. All extracts were less active than the control towards α-amylase (IC50 ranging from 1.5 to 9.1 mg/mL versus 0.02 of acarbose). Phenolic profiles were obtained by HPLC-MSn and caffeoylquinic acid derivatives (esterified with several acyl groups) were found as the main compounds in all plant species under analysis, ranging from 86 (A. glandulosa leaves) to 1918 (P. lowei leaves) mg/100 g of dry plant. The anti-diabetic properties of these caffeoylquinic acid derivatives have been extensively reported [2, 3]. Four out of ten studied species (A. argentea, A. pinnatifidum, H. melaleucum and P. lowei) are potent inhibitors of α-glucosidase with moderate lipase and low α-amylase inhibition, which is ideal for preventing bacterial fermentation of excessive indigested carbohydrates in the colon.