A melanin pigment purified from an epidemic strain of Burkholderia cepaciaattenuates monocyte respiratory burst activity by scavenging superoxide anion

The acquisition of Burkholderia cepacia in some cystic fibrosis patients is associated with symptoms of acute pulmonary inflammation that may be life threatening. The ability of lipopolysaccharide (LPS) from B. cepacia to pri me a monocyte cell line for enhanced superoxide anion generation was invest igated and compared with the priming activities of LPSs from Pseudomonas ae ruginosa, Stenotrophomonas maltophilia, and Escherichia coli, The human mon ocyte cell line MonoMac-6 (MM6) was primed overnight with different LPSs (1 00 ng/ml), and the respiratory burst was triggered by exposure to opsonized zymosan (125 mu g/ml). Superoxide generation was detected by enhanced chem iluminescence with Lucigenin. B. cepacia LPS was found to prime MM6 cells t o produce more superoxide anion than P, aeruginosa or S. maltophilia LPS, a nd this priming response was CD14 dependent, In addition, the inhibition of respiratory burst responses in monocytes by a bacterial melanin-like pigme nt purified from an epidemic B. cepacia strain was investigated. The melani n-like pigment was isolated from tyrosine-enriched media on which B. cepaci a had been grown and was purified by gel filtration, anion ion-exchange chr omatography, and ethanol precipitation. The scavenging potential of the mel anin-like pigment for superoxide anion radical (O-.(2)-) generated during t he respiratory burst was confirmed with superoxide produced from a cell-fre e system with xanthine-xanthine oxidase and detected by electron paramagnet ic resonance spectroscopy with the spin trap 5-diethoxyphosphoryl-5-methyl- 1-pyrroline-n-oxide The addition of melanin during the LPS priming stage ha d no effect on the subsequent triggering of the respiratory burst, but mela nin inhibited O-.(2)- detection when added at the triggering stage of the r espiratory burst. We conclude that melanin-producing B. cepacia may derive protection from the free-radical-scavenging properties of this pigment.