IN-VIVO FORMATION OF ELECTRON-PARAMAGNETIC RESONANCE-DETECTABLE NITRIC-OXIDE AND OF NITROTYROSINE IS NOT IMPAIRED DURING MURINE LEISHMANIASIS

Recent studies have provided evidence for a dual role of nitric oxide (NO) during murine leishmaniasis. To explore this problem, we monitore d the formation of NO and its derived oxidants during the course of Le ishmania amazonensis infection in tissues of susceptible (BALB/c) and relatively resistant (C57BL/6) mice. NO production was detected direct ly by low-temperature electron paramagnetic resonance spectra of anima l tissues, Both mouse strains presented detectable levels of hemoglobi n nitrosyl (HbNO) complexes and of heme nitrosyl and iron-dithiol-dini trosyl complexes in the blood and footpad lesions, respectively. Estim ation of the nitrosyl complex levels demonstrated that most of the NO is synthesized in the footpad lesions, In agreement, immunohistochemic al analysis of the lesions demonstrated the presence of nitrotyrosine in proteins of macrophage vacuoles and parasites. Since macrophages la ck myeloperoxidase, peroxynitrite is likely to be the nitrating NO met abolite produced during the infection. The levels of HbNO complexes in the blood reflected changes occurring during the infection such as th ose in parasite burden and lesion size. The maximum levels of HbNO com plexes detected in the blood of susceptible mice were higher than thos e of C57BL/6 mice but occurred at late stages of infection and were ac companied by the presence of bacteria in the cutaneous lesions. The re sults indicate that the local production of NO is an important mechani sm for the elimination of parasites if it occurs before the parasite b urden becomes too high, From then on, elevated production of NO and de rived oxidants aggravates the inflammatory process with the occurrence of a hypoxic environment that may favor secondary infections.