Selected coffee (Coffea arabica L.) extracts inhibit intestinal α-glucosidases activities in-vitro and postprandial hyperglycemia in SD Rats

One of the therapeutic approaches for decreasing postprandial hyperglycemia is to retard absorption of glucose by the inhibition of carbohydrate hydrolyzing enzymes, α-amylase, and α-glucosidases, in the digestive organs. Coffee consumption has been reported to beneficial effects for controlling calorie and cardiovascular diseases, however, the clear efficacy and mode of action are yet to be proved well. Therefore, in this study we evaluated in- vitro rat intestinal α-glucosidases and porcine α-amylase inhibitory activities as well as in vivo (Sprague–Dawley rat model) blood glucose lowering effects of selected coffee extracts. The water extracted Sumatra coffee (SWE) showed strong α-glucosidase inhibitory activity (IC(50), 4.39 mg/mL) in a dose-dependent manner followed by Ethiopian water extract (EWE) (IC(50), 4.97) and Guatemala water extract (GWE) (IC(50), 5.19). Excepted for GWE all the coffee types significantly reduced the plasma glucose level at 0.5 h after oral intake (0.5 g/kg-body weight) in sucrose and starch-loaded SD rats. In sucrose loading test SWE (p < 0.001) and EWE (p < 0.05) had significantly postprandial blood glucose reduction effect, when compared to control. The maximum blood glucose levels (Cmax) of EWE administration group were decreased by about 18% (from 222.3 ± 16.0 to 182.5 ± 15.4, p < 0.01) and 19% (from 236.2 ± 25.1 to 191.3 ± 13.2 h·mg/dL, p < 0.01) in sucrose and starch loading tests, respectively. These results indicate that selected coffee extract may improve exaggerated postprandial spikes in blood glucose via inhibition of intestinal sucrase and thus delays carbohydrate absorption. These in vitro and in vivo studies therefore could provide the biochemical rationale for the benefit of coffee-based dietary supplement and the basis for further clinical study.