Screening for phosphodiesterase inhibitory activity of Thai medicinal plants

INTRODUCTION: Phosphodiesterases (PDEs) are a group of enzymes that have powerful effects on cellular signaling because they regulate the second messenger, cAMP or cGMP. PDE inhibitors have been used for treatment of many indications such as cardiovascular diseases, chronic obstructive pulmonary diseases, erectile dysfunction and pulmonary hypertension. THE AIM OF THE STUDY: The aim of the study was to search for sources of PDE inhibitors from Thai biodiversity. MATERIALS AND METHODS: Some Thai medicinal plants used as aphrodisiac and neurotonic agents together with plants from Leguminosae collected from the North of Thailand were screened for PDE inhibitory activity using a radioassay. RESULTS: Seven from nineteen aphrodisiac and neurotonic plants as well as three from twelve Leguminosae plants showed potent PDEs inhibitory activity. The concentrations that could inhibit 50% PDE activity (IC(50)) of the active extracts were determined in comparison to the standard inhibitor, 3-isobutyl-1-methylxanthine (IBMX). Betula alnoides, Hiptage benghalensis, Leea indica and Senna surrattensis showed IC(50) values in the range of microgram per milliliter while IBMX standard showed an IC(50) value of 0.68+/-0.13 microg/ml. CONCLUSION: Thai biodiversity was the great sources of PDE inhibitors.