Angiotensin I-Converting Enzyme Inhibitor Activity of Some Plants Used in Thai Indigenous Medicine

The inhibition of angiotensin-converting enzyme (ACE) to lower angiotensin is important in the treatment of hypertension (HT). ACE inhibitory activity is rarely documented in Thai traditional and indigenous medicine. Here, we evaluated the angiotensin I-converting enzyme inhibitory (ACEi) activity through bio-screening of selected medicinal plant species traditionally used for HT treatment by ethnic communities in northern Thailand, including Blumea balsamifera (L.) DC., Clerodendrum chinense (Osbeck) Mabb., Rotheca serrata (L.) Steane & Mabb., and Zingiber purpureum Roscoe. Using an in vitro assay, ethanolic extracts were evaluated for ACE inhibitory activity. Among the four extracts tested, the ethanolic leaf extract of Blumea balsamifera was the most effective by reducing ACE activity by 29, 36, and 64% at concentrations of 0.4, 2.0, and 10.0 mg/mL, respectively. The rhizome extract of Zingiber purpureum showed the second highest activity, with inhibition rates of 34%, 39%, and 40% at the corresponding concentrations. Cytotoxicity testing in HEK293T kidney cells was conducted to underscore the detectable toxicity under the tested conditions. Interestingly, intercultural and cross-cultural comparisons revealed a degree of agreement in the use of medicinal plants for hypertension treatment. Plant species traditionally used across multiple cultures tended to show higher levels of ACE inhibitory activity, suggesting their potential as candidates for the development of novel anti-hypertensive agents. To our knowledge, this is the first report describing the ACE inhibitory activity of medicinal plant species used for hypertension treatment by ethnic communities in northern Thailand.