Modulation of the activity of enzymes of biotransformation of xenobiotics in the lethal and not-lethal murina malaria.
During the last three decades, a number of experimental and clinical studies have shown that several infections as well as aseptic inflammatory conditions modulate the expression and activity of cytochrome P450 enzymes (CYP). Along this line, a few studies have suggested that activities of CYP and kinetics of xenobiotic compounds are altered in malaria infections as well. It is not clear, however, what drug metabolizing enzymes are altered and whether or not changes occur only at a terminal stage of severe malaria. Data are also missing on the mechanisms by which malaria modulate xenobiotic metabolism. This study was undertaken as an attempt to bridge some of these research data gaps. In the first part of the study, we found that a lethal (blood stage) malaria caused by Plasmodium berghei ANKA in C57BL/6 and DBA-2 (female) mice depressed the activities of CYP1A and 2B (EROD and BROD) while induced 2A5-mediated activity (COH) in the liver. A decreased level of CYP1A apoproteins was also found in infected mice. No malaria-caused change was noted either in microsomal (UGT and GST) or in cytosolic (GST) conjugation liver enzymes. Levels of reduced glutathione (GSH), however, were depressed by infection in C57BL/6 mice. Moreover, we found that genotoxic effects (micronuclei in bone marrow cells) of cyclophosphamide (activated by CYP2B and 3A) and DMBA (activated by CYP1A) were attenuated, while effects of a direct-acting clastogen (EMS) were enhanced in P. bergheiinfected mice. In the second part, we investigated the time-course of changes of CYP1A-, 2Band 2A5-mediated activities in C57BL/6 and DBA-2 mice infected with a lethal (P. berghei) and with a non-lethal (P. chabaudi) malaria parasite. In the non-lethal malaria, depression of CYP1A and 2B (C57BL/6), and induction of CYP2A5 activities (DBA-2) were noted only on the post-infection days (5-6) of highest parasitemia rate. Taken together, results from thesetwo parts of the study indicated that both lethal and non-lethal malaria depressed the activities of CYP1A and 2B isoforms and induced the activity of CYP2A5 in the mouse liver. Since ahypothesis has been advanced suggesting that NO plays a decisive role in the down-regulation of CYP by inflammatory stimuli (e.g., LPS), we also evaluated whether malaria-causeddepression of CYP1A and 2B activities could be attributed to an elevation of nitric oxide (NO) levels. Except for a slightly higher NO concentration around the day of the highest parasitemia rate in P. chabaudi-infected mice (DBA-2 and C57BL/6), no other increase of serum levels of NO over the background range was noted during lethal and non lethal malaria infection. To verify whether hepatic NO synthase (NOS2 or iNOS) was induced by malaria, we measured (by quantitative RT-PCR) the levels of NOS2 mRNA in the liver (and also in the spleen and brain) of DBA-2 and C57BL/6 mice infected with P. berghei. Results showed that liver and spleen NOS2 were both markedly induced by malaria in DBA-2, and to a lesser extent, in C57BL/6 mice as well. Therefore, it can not be ruled out that increased NO levels are necessary for malaria-induced depression of CYP activities.
Advisor:Francisco José Roma Paumgartten
School:Faculdades Oswaldo Cruz
Source Type:Master's Thesis
Keywords:Cytochrome P-450 Enzyme System
Date of Publication:04/30/2008