Evidence brief: Alkyl gallates disrupt Trypanosoma brucei lipid droplets

Abstract

African trypanosomiasis is a deadly disease that affects humans and animals, with treatment hindered by drug toxicity and resistance, highlighting the need for alternative therapies. Alkyl gallates, which are plant-derived phenolipids used in the food, cosmetics, and pharmaceutical industries, have been shown to have potent anti-microbial activity; however, their mechanism of action is still unclear. This study investigated the effects of selected alkyl gallates on Trypanosoma brucei. The in vitro anti-trypanosomal and cytotoxicity of the alkyl gallates were determined using the alamarBlue assay. The effects of the alkyl gallates on lipid droplet dynamics were studied using BODIPY493/503 dye and an endogenously tagged lipid droplet kinase cell line which served as a protein marker of lipid droplets. In vitro treatment with octyl and lauryl gallates resulted in rapid cell death with low IC50 of 0.7 µM and 0.04 µM respectively. Octyl gallate treatment significantly reduced lipid droplet number within 30 minutes and by 2 hours most cells lacked lipid droplets; however, lipid droplets rebounded once the drug pressure was removed. These results show that alkyl gallates rapidly disrupt lipid droplet homeostasis in Trypanosoma brucei. Thus, these gallates could serve as a useful cell biology tool to dissect lipid droplet biogenesis and function in trypanosomes.

Introduction

Trypanosoma brucei (T. brucei) is a unicellular flagellate protozoan parasite that causes African trypanosomiasis, an infectious disease affecting humans, wildlife and livestock. Over 55 million individuals are at risk from the disease, and annual losses in livestock production are estimated at $4.5 billion [1,2]. The life cycle of T. brucei alternates between the insect vector (tsetse fly) and the mammalian host in which the parasites are found in the extravascular and intravascular compartments including the adipose and the skin [3–5]. Throughout their life cycle, trypanosomes are exposed to different environmental conditions within the mammalian host and the vector such as changes in pH, nutrients and energy sources, and one of the ways they respond to these environmental changes is by adjusting their metabolism [6,7].

Lipid metabolism is an important process in most living organisms and is based on the environment they find themselves [6,8]. For example, trypanosomes found in adipose tissue alter the gene expression of lipid metabolism-related genes to use lipids/fatty acids as a carbon source [5]. Lipid droplets are one of the important components of the lipid metabolism process. They are lipid/fat storing organelles found in the cytosol of all eukaryotes and some prokaryotic cells [9,10]. Apart from serving as storage compartments, lipid droplets are also involved in energy metabolism, lipid trafficking, protection against oxidative stress, and lipotoxicity [11]. Lipid droplets are made up of a monolayer of phospholipid and cholesterol surrounding a hydrophobic core of neutral lipids like triacylglycerides and sterol esters [12]. Studies have shown that the synthesis and/or maintenance of the lipid droplet in T. brucei and Leishmania infantum requires a protein called the lipid droplet kinase, which localizes to the periphery of the lipid droplet [13,14]. To date, evidence suggests that lipid droplets are essential for the regulation of lipid metabolism in the parasite [15]; however, the tools are lacking to unravel the functional detail of these organelles.