The bacterial redox signaller pyocyanin as an antiplasmodial agent: comparisons with its thioanalog methylene blue

Abstract

The quorum sensor and signalling molecule pyocyanin (PYO) contributes significantly to the pathophysiology of Pseudomonas aeruginosa infections. Comparison to phenothiazine drugs suggests that the antimalarial compound methylene blue (MB) can be regarded as a sulfur analog of PYO. This working hypothesis would explain why the synthetic drug MB behaves as a compound shaped in biological evolution. Here we report on redox-associated biological and biochemical properties of PYO in direct comparison to its synthetic analog MB. We quantitatively describe the reactivity of both compounds toward cellular reductants, the reactivity of their reduced leuco-forms towards O2, and their interactions with FAD-containing disulfide reductases. Furthermore, the interaction of PYO with human glutathione reductase was studied in structural detail by x-ray crystallography, showing that a single PYO molecule binds to the intersubunit cavity of the enzyme. Like MB, also PYO was also found to be active against blood schizonts of the malaria parasite P. falciparum in vitro. Furthermore, both compounds were active against the disease transmitting gametocyte forms of the parasites, which was systematically studied in vitro. As shown for mice, PYO is too toxic to be used as a drug. It may, however, have antimalarial activity in numerous human patients with concomitant Pseudomonas infections. MB, in contrast to PYO, is well tolerated and represents a promising agent for MB-based combination therapies against malaria. Current and future clinical studies can be guided by the comparisons between MB and PYO reported here. Additionally, it is of interest to study if and to what extent the protection from malaria in patients with cystic fibrosis or with severe wound infections is based on PYO produced by Pseudomonas species.

The structural biology of phenazine biosynthesis

“…Because research with the Pseudomonas aeruginosa phenazine pyocyanin has shown that phenazines can also modulate host eukaryotic cells, it is to be hoped that these interactions will also be investigated in more detail in the future. The recent structure of a complex with glutathione reductase in a work aimed at understanding the anti-malarial properties of pyocyanin can be regarded as a starting point for such studies [50]. …”

Methylene Blue for Distributive Shock: A Potential New Use of an Old Antidote

“…The medicinal use of methylene blue dates back to the late 1800s as a treatment for malaria, a urinary analgesic, and in the treatment for cyanide and carbon monoxide poisoning [3][4][5][6]. Methylene blue is currently utilized as a treatment for ifosfamide neurotoxicity [7,8].…”

The Pyruvate and α-Ketoglutarate Dehydrogenase Complexes of Pseudomonas aeruginosa Catalyze Pyocyanin and Phenazine-1-carboxylic Acid Reduction via the Subunit Dihydrolipoamide Dehydrogenase

“…In stark contrast, there is a dearth of information about biologically catalyzed phenazine reduction. Although pyocyanin and PCA are known to oxidize the electron donors NAD(P)H, dihydrolipoamide, and glutathione in vitro (15,28), it is unknown whether this is relevant in vivo or whether it is enzymatically catalyzed. To address this unknown, previous work in our laboratory attempted to identify phenazine reductases by screening transposon mutants (29,30).…”