Melanin in Fonsecaea pedrosoi: a trap for oxidative radicals
1 Instituto de Biofísica Carlos Chagas Filho (IBCCF), Centro de Ciências da Saúde (CCS), Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, RJ, Brazil
2 Laboratório de Tecnologia em Bioquímica e Microscopia, Centro Universitário da Zona Oeste (UEZO), Rio de Janeiro, Brazil
3 Instituto de Ciências Exatas, Departamento de Química, Universidade Federal Rural do Rio de Janeiro, RJ, Brazil
4 Instituto de Física, Universidade Federal do Rio de Janeiro, RJ, Brazil
BMC Microbiology 2010, 10:80 doi:10.1186/1471-2180-10-80Published: 16 March 2010
The pathogenic fungus Fonsecaea pedrosoi constitutively produces the pigment melanin, an important virulence factor in fungi. Melanin is incorporated in the cell wall structure and provides chemical and physical protection for the fungus.
We evaluated the production of nitric oxide (NO) in macrophages, the oxidative burst and the inducible nitric oxide synthase (i-NOS) activity in interactions between activated murine macrophages and F. pedrosoi. Experiments were carried out with or without tricyclazole (TC) treatment, a selective inhibitor of the dihydroxynaphthalene (DHN)-melanin biosynthesis pathway in F. pedrosoi. The paramagnetisms of melanin and the TC-melanin were analysed by electron spin resonance. The fungal growth responses to H2O2 and to S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide donor, were also evaluated.
Melanised F. pedrosoi cells were more resistant to both H2O2 and NO. Nitrite was not detected in the supernatant of macrophages incubated with melanised fungal cells. However, i-NOS expression was unaffected by the presence of either untreated control F. pedrosoi or TC-treated F. pedrosoi. In addition, the inhibition of the DHN-melanin pathway by TC improved the oxidative burst capability of the macrophages.
The NO-trapping ability of F. pedrosoi melanin is an important mechanism to escape the oxidative burst of macrophages.