Evaluation of the antidiabetic potential of Psidium guajava L. (Myrtaceae) using assays for α-glucosidase, α-amylase, muscle glucose uptake, liver glucose production and triglyceride accumulation in adipocytes

Abstract Ethnopharmacological relevance Psidium guajava L. (Myrtaceae) leaves are used as an herbal antidiabetic remedy in several parts of the world. On Madagascar, both the bark and leaves are used for treatment of diabetes. Materials and methods Dilution series of ethanolic extracts of P. guajava leaves and bark were used for determining inhibitory activities against yeast α-glucosidase and porcine α-amylase. Skeletal muscle glucose uptake was measured using 2-deoxy-D-(1–3H)-glucose in murine C2C12 skeletal muscle cells. Hepatic glucose-6-phosphatase activity in rat hepatoma H4IIE cells and triglyceride accumulation in murine 3T3-L1 adipocyte-like cells were assessed using Wako AutoKit Glucose assays and AdipoRed reagent, respectively. Cells were incubated for 18 h with the maximal non-toxic concentrations of the plant extracts determined by the lactate dehydrogenase cytotoxicity assay. Results Ethanolic extracts of P. guajava leaf and bark inhibited α-glucosidase with IC50 values of 1.0 ± 0.3 and 0.5 ± 0.01 μg/mL, respectively. In the α-amylase inhibition assay, the ethanolic extract of bark of P. guajava showed an IC50 value of 10.6 ± 0.4 μg/mL. None of the extracts were able to reduce glucose-6-phosphatase activity in rat hepatoma H4IIE cells. In contrast, P. guajava leaf extract significantly increased 2-deoxy-D-[1–3H]-glucose uptake in C2C12 muscle cells (161.4 ± 10.1%, p = 0.0015) in comparison to the dimethyl sulfoxide (DMSO) vehicle control, as did the reference compounds metformin (144.0 ± 7.7%, p = 0.0345) and insulin (141.5 ± 13.8%, p = 0.0495). Furthermore, P. guajava leaf and bark extract, as well as the reference compound rosiglitazone, significantly enhanced triglyceride accumulation in 3T3-L1 cells (252.6 ± 14.2%, p  Conclusion The results demonstrated that P. guajava leaf and bark extracts can be used as a natural source of α-glucosidase inhibitors. In addition, the bark extract of P. guajava was an effective α-amylase inhibitor. Moreover, P. guajava leaf extract improved glucose uptake in muscle cells, while both leaf and bark extracts enhanced the triglyceride content in adipocytes in culture. P. guajava leaf and bark extracts may thus hypothetically have future applications in the treatment of type 2 diabetes.