Inhibition of α-amylase, α-glucosidase and pancreatic lipase by phenolic compounds of Rumex maderensis (Madeira sorrel). Influence of simulated gastrointestinal digestion on hyperglycaemia-related damage linked with aldose reductase activity and protein glycation

In this work, we report the in vitro inhibitory potential of Rumex maderensis rnethanolic extracts (leaves, flowers, and stems) towards key digestive enzymes linked to type-2 diabetes and obesity (alpha-amylase, alpha-glucosidase, pancreatic lipase). The inhibitory activity towards aldose reductase and glycation of bovine serum albumin (BSA) is also reported; in these latter assays, the effect of simulated digestion on the bioactivities was evaluated. The inhibitory activities of R. maderensis extracts were statistically compared with the inhibition produced by reference compounds for each assay. The analysed extracts exhibited significant inhibitory activities, which decreased after the gastrointestinal digestion, possibly due to some loss of phenolics that took place during the digestion process. The most important results were observed during the BSA-glycation assay, in which the analysed extracts presented higher potency than a reference compound: aminoguanidine (AMC). This research is the first showing the potential anti-diabetic activity of R. maderensis.