Purine pathway enzymes in a cyst forming strain of Toxoplasma gondii

The activities of purine salvage enzymes in tachyzoites from a cyst-forming strain of Toxoplasma gondii were determined using HPLC. Six enzymes were a ssayed both in vitro and in vivo : adenosine deaminase, guanine deaminase, purine nucleoside phosphorylase, xanthine oxidase, hypoxanthine-guanine pho sphoribosyltransferase and adenine phosphoribosyltransferase. In vitro, the tachyzoites were cultured in the human myelomonocytic cell line THP-1, for 24 h to 96 h. Neither guanine deaminase nor hypoxanthine-guanine phosphori bosyltransferase activity was detected in 24 and 96 h cultures. In vivo, in controls and infected animals, the purine nucleoside phosphorylase and ade nosine deaminase activities were the most important activities both in sera and cerebral tissue in comparison with the other activities. It was also n oted that the infection modified the enzymatic activities of this purine sa lvage pathway, in particular, the guanine deaminase cerebral activity of in fected mice was 20-fold lower than the value of controls. The treatment of mice with 2',3'-dideoxyinosine, a purine analog, at the dose of 100 mg.kg(- 1).d for 30 days, induced an important increase of all enzymatic activities in the brains in comparison with control animals. These data suggest that one target of 2',3'-dideoxyinosine is the purine metabolism.