Context: Eryngium creticum Lam. (Umbelliferae), Geranium graveolens L.Her.exn Ait (Geraniaceae), Paronychia argentea Lam. (Caryophyllaceae), and Varthemia iphionoides Boiss (Compositae) have traditionally been used as antidiabetic phytomedicines. However, their alleged benefits and mechanisms remain elusive.
Objectives: To evaluate the effect of these plants on in vitro and in vivo enzymatic starch digestion.
Materials and methods: In vitro enzymatic starch digestion with acarbose or (1-50 or 100 mg/ml) plants aqueous extracts was assayed using α-amylase and α-amyloglucosidase. Oral starch tolerance tests and oral glucose tolerance tests were determined for the plant extracts at concentrations 125, 250, and 500 mg/kg body weight. Blood glucose levels in rats treated with plant extracts or drugs (acarbose or metformin and glipizide) were measured at -30, 0, 45, 90, and 135 min.
Results and discussion: In vitro, acarbose, and water extracts of G. graveolens and V. iphionoides exerted significant dose-dependent dual inhibition of α-amylase and α-glucosidase, with respective IC₅₀s of 1.2 μg/ml, 84.7, and 65.2 mg/ml. Comparable in vivo acute postprandial antihyperglycemic efficacies were obtained for G. graveolens and V. iphionoides in starch-fed rats. E. creticum exhibited substantial acute antihyperglycemic activities in starch-treated rats, despite lacking any favorable in vitro effectiveness. However, P. argentea lacked any inhibitory efficacy. None of the plant extracts qualified for improving the glucose tolerance in fasted rats on glucose loading.
Conclusion: G. graveolens and V. iphionoides can be considered as potential candidates for therapeutic modulation of impaired fasting glycemia, impaired glucose tolerance, and type 2 diabetes.