Plasmodium falciparum: Food vacuole localization of nitric oxide-derived species in intraerythrocytic stages of the malaria parasite

Abstract

Nitric oxide (NO) has diverse biological functions. Numerous studies have documented NO's biosynthetic pathway in a wide variety of organisms. Little is known, however, about NO production in intraerythrocytic Plasmodium falciparum. Using diaminorhodamine-4-methyl acetoxymethylester (DAR-4M AM), a fluorescent indicator, we obtained direct evidence of NO and NO-derived reactive nitrogen species (RNS) production in intraerythrocytic P. falciparum parasites, as well as in isolated food vacuoles from trophozoite stage parasites. We preliminarily identified two gene sequences that might be implicated in NO synthesis in intraerythrocytic P. falciparum. We showed localization of the protein product of one of these two genes, a molecule that is structurally similar to a plant nitrate reductase, in trophozoite food vacuole membranes. We confirmed previous reports on the antiproliferative effect of NOS (nitric oxide synthase) inhibitors in P.falciparum cultures; however, we did not obtain evidence that NOS inhibitors had the ability to inhibit RNS production or that there is an active NOS in mature forms of the parasite. We concluded that a nitrate reductase activity produce NO and NO-derived RNS in or around the food vacuole in P. falciparum parasites. The food vacuole is a critical parasitic compartment involved in hemoglobin degradation, heme detoxification and a target for antimalarial drug action. Characterization of this relatively unexplored synthetic activity could provide important clues into poorly understood metabolic processes of the malaria parasite,

Protein S-nitrosylation in Plasmodium falciparum

“…The model of denitrosylation by reduced PfTrx1 may represent a general mechanism by which reduced PfTrx1 protects the parasites from RNS/NO stress. This protective mechanism may explain, at least in part, the parasitic tolerance to nitrosative stress generated either endogenously or exogenously (30,37); however, upon extreme NO stress or along with an increase in ROS/RNS stress together with a gradual loss of the recycling of reduced PfTrx1, PfTrx1 could be S-nitrosylated at the nonactive-site cysteine (Cys43) to a significant extent, turning the overall role of PfTrx1 from denitrosylation to transnitrosylation for transducing NO stress/signaling. The transnitrosylation model of PfTrx1 is probably of more physiological relevance during parasite transmission between mosquito vectors and hosts, as the parasites are directly exposed to the host immune response in which inflammatory levels of NO are clearly involved (2,3).…”

“…It is well known that hemoglobin digestion in the parasites' food vacuole is essential for Plasmodium parasites, providing a main source of amino acids during parasite growth (16). Given that intraparasitic RNS are abundantly present around the food vacuole where many of these hemoglobinases reside (37), nitrosative stress-derived S-nitrosylation has a high likelihood of occurrence on these hemoglobinases. Indeed, the cysteine protease falcipain has been demonstrated to be substantially inactivated by 10 lM of NO donors due to S-nitrosylation of its active site cysteine (55).…”

“…By using a specific probe, RNS have been detected in ring and trophozoite stages of P. falciparum as well as in the parasite gametocyte (37). Although P. falciparum seems to lack an NOS ortholog, it has been suggested that it probably produces NO from a nitrate/nitrite reduction pathway (37,38).…”

Thiol-Based Posttranslational Modifications in Parasites

“…Recent studies have detected NO and reactive nitrogen species (RNS) within several human pathogenic parasites (126,164,197). Here, we review NO sources and protein S-nitrosylation in human parasites and discuss the role of S-nitrosylation in antiparasitic strategies.…”

Involvement of nitric oxide and its up/down stream molecules in the immunity against parasitic infections

“…Low NO bioavailability might contribute to pathologic activation of the immune system [63] and to the experimental cerebral malaria [64]. Mechanism of NO action in malaria explain the presence of its molecules in food vacuole which is a critical parasitic compartment involved in hemoglobin degradation, heme detoxification and a target for antimalarial drug action [65]. The role of other haem enzymes including iNOS is indicated in malaria infection [66].…”