Characterization of arachidonic-acid-metabolizing enzymes in adult Schistisoma mansoni

Abstract

Schistosoma mansoni has previously been reported to synthesize a wide range of eicosanoids including prostaglandins, leukotrienes and hydroxyeicosatetraenoic acids (HETEs). Our analysis of arachidonic acid metabolites synthesized by microsomal and cytosolic extracts from adult S. mansoni using thin-layer chromatography and radioimmunoassay techniques indicate the presence of a soluble, enzymatically active lipoxygenase (Lox) and the absence of any cyclooxygenase (Cox) activity. The S. mansoni Lox activity catalyzed the formation of a 15-hydroxyeicosatetraenoic acid (15-HETE)-like species. This activity was calcium-independent and inhibitable by inhibitors of mammalian and plant Lox. The conversion of linoleic acid to a 13-hydroxyoctadecadienoic acid (13-HODE)-like product by S. mansoni extracts indicates that the parasite Lox-homologue is similar to mammalian 15-Lox. Immunoblot analysis of S. mansoni extracts using antisera to different mammalian lipoxygenases detects two immunoreactive proteins with molecular weights similar to plant and mammalian lipoxygenases. In addition, polymerase chain reaction (PCR) amplification of Lox-like sequences from S. mansoni genomic DNA using degenerate primers based on conserved plant and mammalian Lox sequences, generated two PCR products which hybridized to a human 15-Lox cDNA probe. While the role of eicosanoid production in the physiology of S. mansoni is not known, eicosanoids may be essential for normal physiological processes as is the case in other invertebrates. Interestingly, 15-HETE has previously been shown to have immunosuppressive effects in mammals, and this may be related to the ability of the parasite to overcome host immune responses.