Inhibitors of Eicosanoid Biosynthesis Reveal that Multiple Lipid Signaling Pathways Influence Malaria Parasite Survival in Anopheles gambiae.

Kwon Kwon,Smith Smith

doi:10.3390/insects10100307

Abstract

Eicosanoids are bioactive signaling lipids derived from the oxidation of fatty acids that act as important regulators of immune homeostasis and inflammation. As a result, effective anti-inflammatory drugs have been widely used to reduce pain and inflammation which target key eicosanoid biosynthesis enzymes. Conserved from vertebrates to insects, the use of these eicosanoid pathway inhibitors offer opportunities to evaluate the roles of eicosanoids in less-characterized insect systems. In this study, we examine the potential roles of eicosanoids on malaria parasite survival in the mosquito Anopheles gambiae. Using Plasmodium oocyst numbers to evaluate parasite infection, general or specific inhibitors of eicosanoid biosynthesis pathways were evaluated. Following the administration of dexamethasone and indomethacin, respective inhibitors of phospholipid A2 (PLA2) and cyclooxygenase (COX), oocyst numbers were unaffected. However, inhibition of lipoxygenase (LOX) activity through the use of esculetin significantly increased oocyst survival. In contrast, 12-[[(tricyclo[3.3.1.13,7]dec-1-ylamino)carbonyl]amino]-dodecanoic acid (AUDA), an inhibitor of epoxide hydroxylase (EH), decreased oocyst numbers. These experiments were further validated through RNAi experiments to silence candidate genes homologous to EH in An. gambiae to confirm their contributions to Plasmodium development. Similar to the results of AUDA treatment, the silencing of EH significantly reduced oocyst numbers. These results imply that specific eicosanoids in An. gambiae can have either agonist or antagonistic roles on malaria parasite survival in the mosquito host.

Highlights

Mosquitoes are able to transmit numerous pathogens that cause high human morbidity and mortality [1,2], most notably malaria, which causes over 200 million cases and 435,000 deaths every year [3]
We examined the potential role of eicosanoids on Plasmodium infection using known eicosanoid inhibitors in An. gambiae
Prior to taking an infected blood meal, mosquitoes were primed by the injection of specific inhibitors to interrupt the conversion of arachidonic acid (AA) to prostaglandins (PGs), leukotrienes (LTs), lipoxins (LXs), or dihydroxyeicosatrienoic acid (DHETs) derivatives (Figure 1A) to determine their respective influence on malaria parasite survival

Summary

Introduction

Mosquitoes are able to transmit numerous pathogens that cause high human morbidity and mortality [1,2], most notably malaria, which causes over 200 million cases and 435,000 deaths every year [3]. Plasmodium parasites undergo severe bottlenecks in the mosquito which can be attributed to the innate immune response that limits parasite survival [4,6]. This includes multiple mechanisms of parasite killing [7,8,9,10,11,12,13] which involve the complex interplay between the mosquito midgut [14,15], immune cells known as hemocytes [12,13,16], and humoral components of the hemolymph [7,8,9]

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Conclusion