title: Parasite killing in Plasmodium vivax malaria by nitric oxide: implication of aspartic protease inhibition.
abstract: Nitric oxide (NO) is known to possess antiparasitic activity towards Plasmodium species. Parasite proteases are currently considered to be promising targets for antimalarial chemotherapy. In the present study, we have studied the inhibitory effect of NO on the activity of plasmepsin in Plasmodium vivax, the pepsin-like aspartic protease which is believed to be involved in the cleavage during hemoglobin degradation in Plasmodium falciparum. NO donors (+/-) (E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR-3), S-nitrosoglutathione (GSNO), and sodium nitroprusside (SNP) were found to inhibit this plasmepsin activity in a dose-dependent manner in purified P. vivax aspartic protease enzyme extracts. This inhibitory effect may be attributable to the nitrosylation of the cysteine residue at the catalytic site. However, an inhibitor of aspartic protease activity, namely pepstatin, was also found to inhibit (IC50 3 microM ) the enzyme activity, which we have used as a positive control. Our results therefore provide novel insights into the pathophysiological mechanisms, and will be useful for designing strategies for selectively upregulating NO production in P. vivax infections for antimalarial chemotherapy and also biochemical adaptations of the malaria parasite for survival in the host erythrocytes with a better understanding of the protease substrate interactions.
authors.affiliation: Malaria Research Centre, 22 Sham Nath Marg, Delhi-110 054, India. sharmaaru20032003@yahoo.co.in
authors.forename: Arun
authors.initials: A
authors.lastname: Sharma
authors.forename: Alex
authors.initials: A
authors.lastname: Eapen
authors.forename: Sarala K
authors.initials: SK
authors.lastname: Subbarao
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry / Q000378:metabolism; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D020134:Catalytic Domain; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000737:chemistry; D004229:Dithiothreitol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004912:Erythrocytes / Q000166:cytology / Q000378:metabolism; D005780:Gelatin / Q000378:metabolism; D018086:Glutamate Dehydrogenase (NADP+) / Q000737:chemistry; D005978:Glutathione; D006863:Hydrogen-Ion Concentration; D020128:Inhibitory Concentration 50; D016780:Malaria, Vivax / Q000378:metabolism / Q000628:therapy*; D008981:Molsidomine / Q000031:analogs & derivatives* / Q000378:metabolism; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism*; D020030:Nitric Oxide Donors; D009599:Nitroprusside / Q000737:chemistry / Q000494:pharmacology; D010434:Pepsin A / Q000737:chemistry; D010436:Pepstatins / Q000737:chemistry / Q000494:pharmacology; D010961:Plasmodium / Q000378:metabolism; D010966:Plasmodium vivax / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D026361:Reactive Nitrogen Species; D026422:S-Nitrosoglutathione / Q000737:chemistry; D013997:Time Factors; D015854:Up-Regulation
chemical_list: D020030:Nitric Oxide Donors; D010436:Pepstatins; D011480:Protease Inhibitors; D026361:Reactive Nitrogen Species; D009599:Nitroprusside; D001224:Aspartic Acid; D009569:Nitric Oxide; D026422:S-Nitrosoglutathione; C002385:linsidomine; D005780:Gelatin; D008981:Molsidomine; D002374:Catalase; D018086:Glutamate Dehydrogenase (NADP+); D016282:Aspartic Acid Endopeptidases; D010434:Pepsin A; C089643:plasmepsin; D005978:Glutathione; D003545:Cysteine; D004229:Dithiothreitol; C031375:pepstatin