Targeting mitochondrial bioenergetics: the "Achilles' heel" of Leishmania

The parasite Leishmania is the causative agent of leishmaniasis and relies on a single "mitochondrion" as its "powerhouse". It also has a compromised antioxidant defense system. Consequently, potential therapeutic strategies include triggering mitochondrial dysfunction along with subversion of host metabolic bioenergetics; however, such information remains poorly defined. The focus of this study was to delineate the impact of antileishmanials amphotericin B (Ampho B) and miltefosine (hexadecylphosphocholine [HePC]) on the metabolic bioenergetics of Leishmania parasites vis-à-vis mammalian macrophages.

In promastigotes, the redox status was evaluated by flow cytometry; levels of ATP were measured by chemiluminescence; and oxygen consumption rate (OCR), extracellular acidification rate (ECAR), and substrate utilization were assessed by XFp Analyzer. In Leishmania donovani (L. donovani)-infected macrophages, expression of metabolic bioenergetics related regulatory molecules was assessed by droplet digital polymerase chain reaction (ddPCR) and immunoblotting.

In promastigotes, at their respective 50% and 90% inhibitory concentrations (IC₅₀ and IC₉₀), Ampho B and HePC disrupted redox homeostasis, enhanced generation of mitochondrial superoxide, depleted OCR and ATP, and caused a greater degree of mitochondrial inhibition with HePC than with Ampho B. The L. donovani promastigotes sourced acetyl CoA primarily from the fatty acid oxidation pathway for mitochondrial tricarboxylic acid cycle, and inhibition of the mitochondrial fatty acid oxidation was higher with Ampho B. In L. donovani-infected macrophages, there was significantly increased expression of the Ampk axis (Ampk-Lkb1-Sirt1), mitochondrial biogenesis marker Pgc1α, and markers of oxidative phosphorylation (Cox IV, Atp synthase). The rate-limiting enzymes of glycolysis, namely  HkII, Pfk, Pkm2, and glucose transporter (Glut1), were enhanced, but expression of Mtor was decreased. All markers of the Ampk axis and oxidative phosphorylation were significantly curtailed by both antileishmanials in favor of parasite clearance, whereas glycolytic markers remained unchanged; overall, the dampening of metabolic bioenergetics by HePC was greater than that caused by Ampho B.

Targeting the "mitochondrion" and metabolic reprogramming are effective leishmanicidal strategies adopted by HePC and Ampho B, with the degree of inhibition by HePC exceeding that of Ampho B. Accordingly, screening for compounds capable of mediating metabolic reprogramming could augment the limited armamentarium of antileishmanials.