Superoxide production by the mycobacterial and pseudomonad quinoid pigments phthiocol and pyocyanine in human lung cells

The quinoid pigments phthiocol, produced by Mycobacterium tuberculosis, and pyocyanine, produced by Pseudomonas aeruginosa, were examined for their effects on O-2(.-) production in cultured human lung epithelial-like A549 cells. Intracellular O-2(.-) levels were measured using the O-2(.-)-sensitive aconitase(s), and rates of O-2(.-) generation were assessed from rates of antimycin-resistant respiration. Elevated O-2(.-) was detected in cells exposed to <25 mu M phthiocol and <2 mu M pyocyanine in neutral pH medium, and both agents impaired cell growth. The O-2(.-) scavenging mangano-porphyrin, Mn(III)TMPyP, partially protected cells against pyocyanine and phthiocol-mediated growth inhibition. O-2(.-) production by phthiocol and pyocyanine was enhanced by acidification of the growth medium. Surprisingly, the dicumarol-inhibitable quinoid detoxification enzyme DT-diaphorase was a significant source of phthiocol and pyocyanine-mediated O-2(.-) generation in cells. O-2(.-) production in macrophages by the phthiocol analog, menadione, was shown to impair macrophage mitochondrial respiration and bactericidal activity toward Escherichia coli. Phthiocol and pyocyanine, by producing O-2(.-)/H2O2, and inhibiting host cell aconitase activity, energetics, and other host cell functions, may contribute to the pathogenicity of M. tuberculosis and P. aeruginosa. (C) 1996 Academic Press, Inc.