A Partial Convergence in Action of Methylene Blue and Artemisinins: Antagonism with Chloroquine, a Reversal with Verapamil, and an Insight into the Antimalarial Activity of Chloroquine

Abstract

Artemisinins rapidly oxidize leucomethylene blue (LMB) to methylene blue (MB); they also oxidize dihydroflavins such as the reduced conjugates RFH₂ of riboflavin (RF), and FADH₂ of the cofactor flavin adenine dinucleotide (FAD), to the corresponding flavins. Like the artemisinins, MB oxidizes FADH₂, but unlike artemisinins, it also oxidizes NAD(P)H. Like MB, artemisinins are implicated in the perturbation of redox balance in the malaria parasite by interfering with parasite flavoenzyme disulfide reductases. The oxidation of LMB by artemisinin is inhibited by chloroquine (CQ), an inhibition that is abruptly reversed by verapamil (VP). CQ also inhibits artemisinin-mediated oxidation of RFH₂ generated from N-benzyl-1,4-dihydronicotinamide (BNAH)-RF, or FADH₂ generated from NADPH or NADPH-Fre, an effect that is also modulated by verapamil. The inhibition likely proceeds by the association of LMB or dihydroflavin with CQ, possibly involving donor-acceptor or π complexes that hinder oxidation by artemisinin. VP competitively associates with CQ, liberating LMB or dihydroflavin from their respective CQ complexes. The observations explain the antagonism between CQ-MB and CQ-artemisinins in vitro, and are reconcilable with CQ perturbing intraparasitic redox homeostasis. They further suggest that a VP-CQ complex is a means by which VP reverses CQ resistance, wherein such a complex is not accessible to the putative CQ-resistance transporter (PfCRT).

Novel Peroxides as Promising Anticancer Agents with Unexpected Depressed Antimalarial Activity

“…falciparum and in tumor cells are still under debate. [24] In our previous studies, [9,25,26] we described that artemisinin and semisynthetic peroxide analogues acted in malaria parasites by oxidizing dihydroflavin cofactorso fr edox-activef lavoenzyme. Perturbationo fr edox homeostasis coupled with the generation of reactive oxygen species (ROS) contributed to the death of the parasites.O nt he basis of this discovery, our current study measured the oxidative capacities of three classes of compounds, and for the first time, the correlation between the oxidative properties and antimalarial activity among these compounds was examined.…”

Mechanisms of hematin crystallization and inhibition by the antimalarial drug chloroquine

“…The traditional Western treatment for malaria, quinine, and its synthetic homologs (chloroquine, mefloquine, and others) (8)(9)(10)(11) putatively works by blocking hematin crystallization (12). Available evidence suggests that artemisinin, another antimalarial drug, binds to heme (2,13). The sequestration of heme into hemozoin is a suitable target for new antimalarials.…”

Efficacy of Proveblue (Methylene Blue) in an Experimental Cerebral Malaria Murine Model

“…However, the efficacy of the combination may be due to the efficacy of Proveblue and not to synergism of the two compounds (no significant difference between Proveblue alone and the combination of Proveblue and dihydroartemisinin efficacy; P ϭ 0.732). Artemisinin should have a synergistic interaction with methylene blue; artemisinin reoxidizes leucomethylene blue, which is produced by the reduction of methylene blue in parasites by the NADPH-flavin reductase system, from methylene blue, and together they oxidize FADH 2 (17). However, methylthioninium chloride (Proveblue) is a drug with a short terminal elimination half time of 18.5 h, and dihydroartemisinin has also a short elimination half time (0.5 to 2 h).…”