Inhibition of Glutathione S-Transferases (GSTs) from Parasitic Nematodes by Extracts from Traditional Nigerian Medicinal Plants B. B. Fakae 1 , A. M. Campbell 2 , J. Barrett 2 , I. M. Scott 2 , P. H. Teesdale-Spittle 2 , E. Liebau 3 and P. M. Brophy 2 * 1 Department of Veterinary Parasitology and Entomology, University of Nigeria, Nsukka, Nigeria 2 Institute of Biological Sciences, University of Wales, Aberystwyth SY23 3DA, UK 3 Department of Biochemical Parasitology, Bernhard Nocht Institute for Tropical Medicine, Bernhard-Nocht-Str. 74, D-20359, Hamburg, Germany Piliostigma thonningii, Ocimum gratissimum, Nauclea latifolia and Alstonia boonei are used in Nigerian traditional medicines against gastrointestinal helminths of animals and man. Proanthocyanidins were detected in Piliostigma 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 Alsto- nia), the Nauclea LD 50 being similar to the anthelmintic drug piperazine. Extracts were also toxic to the parasitic nematode 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 mg/mL respectively for Ascaris GST and 4, 8, 28 mg/mL respectively for Oncho- cerca GST. We suggest that the inhibitory properties of some of these Nigerian plant extracts against GST may contribute to the pharmacological basis of their efficacy against helminths in traditional herbal use. Copyright # 2000 John Wiley & Sons, Ltd. Keywords: nematode; Piliostigma thonningii; glutathione S-transferase; proanthrocyanidin; anthelmintic. INTRODUCTION Gastrointestinal helminths, especially nematodes, are a continuing serious problem to the health of domesticated animals and man in the tropics. In the absence of reserves for rotational grazing, control in animals is dependent on, as in humans, the availability of cheap and effective treatment. Unfortunately, in many parts of the world, the prevalence of anthelmintic resistance in economically important helminths has increased dramatically (Sang- ster, 1999). Furthermore, several alternative therapeutics remain too expensive for purchase by rural populations (Fakae, 1990). The development of a new generation of cost-effective anthelmintic agents is vital to the future of control of helminth diseases in the tropics and therefore ethno-veterinary medicine is receiving renewed interest (Schillhorn van Veen, 1997). Rural communities in Nigeria have continued to exploit natural products from plants as vermifuges. Preliminary studies on extracts of these medicinal plants have indicated bioactivity in vitro and in vivo, against stages of gastrointestinal helminths (Asuzu and Onu 1993, 1994; Njoku et al., 1996). Mechanisms of action of these extracts are not yet fully known (Njoku et al., 1997). Leads from these empirical screenings, however, justify progression to rational screening of these plant extracts. Glutathione S-transferases (GSTs) have been identified as potential vaccine candidates in cestode and digenean parasites (Brophy and Barrett, 1990: Brophy and Pritchard 1994). Biological roles of helminth GSTs have been proposed to include general detoxification and ligand binding functions. The ability of helminth GSTs to effectively neutralize known cytotoxic products arising from reactive oxygen species attack on cell membranes provides evidence that GSTs have the potential to protect the parasite against the host immune response (Brophy et al., 1989). Our research on parasitic nematodes (includ- ing Ascaris suum, Onchocerca volvulus and Haemonchus contortus) highlights the importance of GST in establish- ing chronic infection (Brophy et al., 1994; Brophy and Pritchard, 1994). The structural divergence of the parasitic helminth GST detoxification system from that of the host may constitute an ‘Achilles heel’, if potent and selective inhibitors of helminth GST can be identified in drug discovery programmes. We have previously shown that substituted phenol- based anthelmintics inhibit all native and recombinant helminth GSTs so far analysed (Papadopoulos et al., 1989; Brophy et al., 1990). The present study investi- gated inhibitory effects of extracts from Nigerian medicinal plants on two recombinant nematode GSTs, and in nematode and brine shrimp bioassays. As a role for PHYTOTHERAPY RESEARCH Phytother. Res. 14, 630–634 (2000) Copyright # 2000 John Wiley & Sons, Ltd. * Correspondence to: P. M. Brophy, Institute of Biological Sciences, University of Wales, Aberystwyth SY23 3DA, UK. E-mail: pmb@aber.ac.uk Contract/grant sponsor: The Royal Society. Contract/grant sponsor: The Wellcome Trust; Contract/grant number: 055136/ Z/98/Z. Contract/grant sponsor: UNDP/WORLD BANK/WHO Special Programme for Research in Tropical Diseases; Contract/grant number: TDR 960011. Received 6 December 1999 Accepted 27 June 2000