Quenching of Singlet Oxygen by Pyocyanin and Related Phenazines†

Pseudomonas aeruginosa is a human pathogen, which causes infections of various organs, including lung, skin and eye, particularly in individuals who are immunocompromised. Pyocyanin (1-hydroxy-5-methylphenazine), a cytotoxic pigment secreted by the bacterium, is among the factors that contribute to virulence of this pathogen. We have previously shown that rose bengal and riboflavin photosensitize oxidation of pyocyanin to a product(s) with diminished reactivity and toxicity. Singlet oxygen was suggested as the major oxidant, based on the inhibitory effect of sodium azide. In the present study, we used the time resolved technique to investigate direct interaction of pyocyanin and related phenazines (1-hydroxyphenazine [1-OH-Phen], 1-methoxy-5-methylphenazine [1-MeO-PCN] and phenazine methosulfate [PMS]) with 1O(2). The rate constants for the 1O(2) quenching (physical + chemical) by pyocyanin and 1-OH-Phen in D2O buffer (pD similar to 7.2) have been determined to be 4.8 x 108 and 6.8 x 108 M-1 s-1, respectively. 1-MeO-PCN and PMS were markedly less efficient 1O(2) quenchers. Among the phenazines studied only phenazine methosulfate photogenerated 1O(2) (Theta(1O(2)) = 0.56 in acetonitrile). Interaction of 1O(2) with pyocyanin and other related phenazines produced by the bacteria may be important in determining the potential utility of photochemical/pharmacological approaches to eradicate P. aeruginosa from infected tissues.