Inhibition of Site I mitochondrial electron transport by an extract of the seeds of Millettia thonningii: a potential mechanism for the plant's molluscicidal and schistosome larvicidal activity

A dichloromethane extract of the seeds of Millettia thonningii (Leguminosae) which contains a mixture of isoflavonoids (predominately robustic acid, alpinumisoflavone and dimethylalpinumisoflavone) is known to have larvicidal activity towards the miracidia and cercariae of schistosomes and to possess significant molluscicidal activity. The present investigation has assayed the effects of this extract on the electron transport systems of isolated rat liver mitochondria. The extract was found to inhibit mitochondrial electron transport at Site I (NADH dehydrogenase) at concentrations of 30–159 mg l-1. Although the extract is not as potent an inhibitor at Site I as rotenone, a known inhibitor of NADH dehydrogenase, such observations could explain the molluscicidal and schistosomicidal activity of dichloromethane extracts of the seeds of M. thonningii.