A Melanin Pigment Purified from an Epidemic Strain of Burkholderia cepacia Attenuates Monocyte Respiratory Burst Activity by Scavenging Superoxide Anion

<jats:title>ABSTRACT</jats:title> <jats:p> The acquisition of <jats:italic>Burkholderia cepacia</jats:italic> in some cystic fibrosis patients is associated with symptoms of acute pulmonary inflammation that may be life threatening. The ability of lipopolysaccharide (LPS) from <jats:italic>B. cepacia</jats:italic> to prime a monocyte cell line for enhanced superoxide anion generation was investigated and compared with the priming activities of LPSs from <jats:italic>Pseudomonas aeruginosa</jats:italic> , <jats:italic>Stenotrophomonas maltophilia</jats:italic> , and <jats:italic>Escherichia coli</jats:italic> . The human monocyte cell line MonoMac-6 (MM6) was primed overnight with different LPSs (100 ng/ml), and the respiratory burst was triggered by exposure to opsonized zymosan (125 μg/ml). Superoxide generation was detected by enhanced chemiluminescence with Lucigenin. <jats:italic>B. cepacia</jats:italic> LPS was found to prime MM6 cells to produce more superoxide anion than <jats:italic>P. aeruginosa</jats:italic> or <jats:italic>S. maltophilia</jats:italic> LPS, and this priming response was CD14 dependent. In addition, the inhibition of respiratory burst responses in monocytes by a bacterial melanin-like pigment purified from an epidemic <jats:italic>B. cepacia</jats:italic> strain was investigated. The melanin-like pigment was isolated from tyrosine-enriched media on which <jats:italic>B. cepacia</jats:italic> had been grown and was purified by gel filtration, anion ion-exchange chromatography, and ethanol precipitation. The scavenging potential of the melanin-like pigment for superoxide anion radical ( <jats:sup>•</jats:sup> O <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> ) generated during the respiratory burst was confirmed with superoxide produced from a cell-free system with xanthine-xanthine oxidase and detected by electron paramagnetic resonance spectroscopy with the spin trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline- <jats:italic>n</jats:italic> -oxide. The addition of melanin during the LPS priming stage had no effect on the subsequent triggering of the respiratory burst, but melanin inhibited <jats:sup>•</jats:sup> O <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> detection when added at the triggering stage of the respiratory burst. We conclude that melanin-producing <jats:italic>B. cepacia</jats:italic> may derive protection from the free-radical-scavenging properties of this pigment. </jats:p>