In vitro and in vivo acute antihyperglycemic effects of five selected indigenous plants from Jordan used in traditional medicine

Ethnopharmacological relevance: Achillea santolina L., Pistacia atlantica Desf, Rheum ribes L., Sarcopoterium spinosum (L.) Spach and Teucrium polium L. have traditionally been used as herbal antidiabetic medicines. However their alleged benefits and mechanisms remain elusive. Aim of the study: This study aimed to evaluate the effect of water extracts of these plants in in vitro and in vivo experiments. Materials and methods: In vitro enzymatic starch digestion with aqueous extracts from plants at concentrations of 1, 5, 10, 12.5, 25, 50 and 100 mg/ml was assayed using alpha-amylase and alpha-amyloglucosidase. Acarbose was used as control and glucose liberation was determined by glucose oxidase method. Oral starch tolerance test (OSTT) and oral glucose tolerance test (OGTT) were determined for the plant extracts at concentrations 125, 250 and 500 mg/kg b.wt. on Sprague-Dawley rats. Blood glucose levels in rats treated with plant extracts and drugs (acarbose or metformin and glipizide) were measured at 30, 0, 45, 90 and 135 min. Results: Compared to acarbose (IC50 = 1.2 mu g/ml), water extracts of Pistacia atlantica, Rheum ribes and Sarcopoterium spinosum exerted significant dose dependent dual inhibition of alpha-amylase and alpha-glucosidase in in vitro enzymatic starch digestion bioassay, with IC(50)s; 46.98, 58.9 and 49.9 mg/ml, respectively. Comparable in vivo results were obtained for starch-fed rats, exhibiting significant acute postprandial antihyperglycemic efficacies. While Achillea santolina and Teucrium polium extracts lacked any favourable in vitro anti-alpha-amylase and anti-alpha-glucosidase effect, other modes of action can possibly explain their substantial acute antihyperglycemic activities in starch-treated rats. Except for Pistacia atlantica extracts, none of the investigated extracts qualified for improving the glucose intolerance in fasted rats on glucose loading. Conclusions: Pistacia atlantica, Rheum ribes and Sarcopoterium spinosum can be considered as potential candidates for amelioration/management of type 2 diabetes. (C) 2010 Elsevier Ireland Ltd. All rights reserved.