Experimental Parasitology 112 (2006) 85–91 www.elsevier.com/locate/yexpr 0014-4894/$ - see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.exppara.2005.09.006 Leishmania major and Leishmania tropica: II. EVect of an immunomodulator, S 2 complex on the enzymes of the parasites Yassir M. Al-Mulla Hummadi a , Nada M. Al-Bashir b , RaWd A. Najim a,¤ a Department of Pharmacology, College of Medicine, University of Baghdad, P.O. Box 61208, Baghdad 12114, Iraq b Leishmania Unite, Medical Research Center, Al-Nahrain University, Baghdad, Iraq Received 29 April 2005; received in revised form 21 September 2005; accepted 21 September 2005 Available online 7 November 2005 Abstract S 2 complex has been reported to have a direct antileishmanial eVect. The possibility that the direct antileishmanial eVect may be due to inhibition of key enzymes involved in glucose metabolism and/ or enzymes associated with virulence was investigated. Cell pellets were prepared from cultures of both axenic amastigotes and promastigotes of Leishmania major (MHOM/IQ/93/MRC6) and L. tropica (MHOM/IQ/93/MRC2). S 2 complex, at various concentrations, was added to the enzyme extracts prepared from the pellets. Results show that in the Embden–Meyerhof pathway, both hexokinase and glucose-phosphate isomerase but not fructophosphokinase were dose dependently inhibited. In the hexose-monophosphate shunt both glucose-6-phosphate dehydrogenase and ribose-5-phosphate isomerase were dose dependently inhibited. Malic dehydrogenase and malic enzyme from the citric-acid cycle were both dose dependently inhibited but succinate dehydrogenase from the same pathway was not inhibited. Both enzymes associated with virulence (protease and acid phos- phatase), showed activation rather than inhibition at higher doses of S 2 complex. Thus, the direct antileishmanial eVect of S 2 complex may result, partially or entirely, from the inhibition of enzymes that are necessary for the parasites’ carbohydrate metabolism.  2005 Elsevier Inc. All rights reserved. Index Descriptors and Abbreviations: Leishmania major; Leishmania tropica; Amastigotes; Promastigotes carbohydrate metabolism enzymes; Enzymes associated with virulence; S 2 complex 1. Introduction Pentavalent antimony compounds have been the main- stay of treatment of cutaneous leishmaniasis for more than 50 years. However, resistant is now emerging (Tracy and Webster, 1996) and there are only a few alternative drugs available. S 2 complex is a low molecular weight organic covalent complex of copper chloride with ascorbic acid and nicotin- amide, synthesized by the Medical Research Center “Al- Nahrain University” in the early 1990s. In a previous com- munication, S 2 complex was reported to be eVective against Leishmania major and L. tropica in vitro (Al-Mulla Hum- madi et al., 2005). However, the antileishmanial mechanism of S 2 complex is not clear. S 2 complex was shown to have an immunomodulatory eVect on macrophages engulWng leishmanial amastigotes (Al-Mulla Hummadi et al., 2005), but the mechanism of the direct antileishmanial eVect awaits elucidation. Parasite enzymes are known to be the target of some antileishmanial drugs. Thus, pentavalent antimony drugs were reported to inhibit leishmanial glycolytic pathway enzymes (Berman, 1991). Other investigational treatments have also been reported to eVect glycolytic pathways. The NO releasing molecule, S-nitroso-N-acetyl-DL-penicilla- mine (SNAP) was demonstrated to regulate the glyceralde- hyde-3-phosphate dehydrogenase activity in promastigotes through the release of NO (Bourguignon et al., 1997). In addition, S 2 complex was shown inhibit several key enzymes of both promastigotes and amastigotes of L. dono- vani (Al-Bashir, 1997). * Corresponding author. E-mail address: raWdnajim@yahoo.com (R.A. Najim).