Targeting human β2 adrenergic receptors (ADRB2) for modulating blood-stage infection of Plasmodium falciparum malaria

Strategies for malarial control are met with difficulties due to insufficiency of control measures and emerging parasite drug resistance. Erythrocytes, mainly their lipid rafts-protein, have been demonstrated as targets of Plasmodium parasites interaction for invasion of cells causing infection. GPCRs, viz. ADRB2 with their central role in physiological processes and intricate signaling pathways have been the targets for a range of diseases. In vitro studies have shown signaling via erythrocytic ADRB2 regulates the entry of P. falciparum. Prior studies in our laboratory demonstrated genetic variations of membrane proteins; ADRB2, ADORA2A, ADORA2B, ABCB1 were associated with malaria progression. ADRB2 protein has been extensively studied in the context of etiology and therapeutics of asthma, and its agonists are being used as reliever drugs. Since anti-asthmatics work by internalizing the receptors, well-established drugs with known pharmacokinetic properties and efficacies can be good candidates to treat malaria. Demonstration of proof-of-concept of ADRB2-mediated mechanisms of clinical relevance may provide avenues for drug-repurposing. Erythrocyte cultures were employed to test the anti-malarial activity of β2AR-agonists and antagonists in combination with antimalarials on P. falciparum-infected erythrocytes. SYBR green-I fluorescence assay was performed to study parasite inhibition, and the results analyzed for their synergistic action. Agonist-induced receptor desensitization was assayed using flow cytometry and visualized. In vitro activities of salbutamol, propranolol, and combination treatments demonstrated parasite inhibition with acceptable haemotoxicity. The receptor internalization was found to be incremental and microscopic observations validating β2AR-desensitization were obtained, providing further mechanistic insights into β2AR-mediated parasite invasion.