Inhibition of glutathione S-transferases (GSTs) from parasitic nematodes by extracts from traditional Nigerian medicinal plants

Piliostigma thonningii, Ocimum gratissimum, Nauclea latifolia and Alstonia boonei are used in Nigerian traditional medicines against gastrointestinal helminths of animals and man. Proantbocyanidins were detected in Piliostigm a and Nauclea, but not Alstonia or Ocimum. Extracts of these plants killed 50% of brine shrimp nauplii at <10 ppm (Nauclea), 100 ppm (Piliostigma) and <1000 ppm (Ocimum and Alstonia), the Nauclea LD50 being similar to the ant helmintic drug piperazine, Extracts were also toxic to the parasitic nemato de Haemonchus infective L3 stage. Nematode glutathione-S-transferases (GSTs ) are potential drug targets. Apart from Alstonia all the medicinal plants contained heat-stable inhibitory activities against recombinant Ascaris and Onchocerca GSTs in vitro. Piliostigma, Ocimum and Nauclea had IC(50)s Of 2 , 10 and 15 mug/mL respectively for Ascaris GST and 4, 8, 28 mug/mL respect ively for Onchocerca GST. We suggest that the inhibitory properties of some of these Nigerian plant extracts against GST may contribute to the pharmac ological basis of their efficacy against helminths in traditional herbal us e. Copyright (C) 2000 John Whey & Sons, Ltd.