ALVEOLAR MACROPHAGES DO NOT CONTRIBUTE TO THE DEVELOPMENT OF HYPOXIC PULMONARY HYPERTENSION BY CONTRIBUTING TO RADICAL TISSUE INJURY

We have shown previously that alveolar macrophages (AM) are involved in the development of hypoxic pulmonary hypertension (HPH). Since it was demonstrated that one aspect of HPH development is an increase in radical tissue damage, and AM represent an important source of reactive oxygen species, we hypothesized that AM contribute to the development of HPH in this way. We used liposome-encapsulated clodronate (CL) to eliminate AM in male Wistar rats (200-250 g). Control groups received either pure liposome (without clodronate; L) (both Encapsula, á 300µl, 1st, 5th, 10th days intratracheally) or no medication (C). Animals were kept in normoxia (N, n=18) or exposed to 15-day isobaric hypoxia (FiO2 0.1) (H, n=19). After the end of the exposure, bronchoalveolar lavage and lung tissue were collected. Oxidative damage was tested by determining the concentration of nitrotyrosine and malondialdehyde in lung tissue extracts. Furthemore, superoxide production was measured using vanadate-dependent chemiluminescence. In all groups, exposure to hypoxia resulted in an increase in concentrations of nitrotyrosine (N: CL 20.2±1.2, L 19.8±3.0, C 18.2±1.7, H: CL 28.8±2.6 , L 27.2±0.9, C 29.9±2.0 ng/mg of protein) and malondialdehyde (N: CL 5.5±0.9, L 6.2±0.6, C 5.6±1.6, H: CL 16.7±3.8, L 15.4±0.7, C 9.4±2.3 mmol/mg of protein). However, administration of pure liposomes or liposomes containing clodronate had no effect on nitrotyrosine and malondialdehyde concentrations compared to the control group. Moreover, exposure to hypoxia attenuated superoxide production in AM (H 3.7±0.6, N 13.5±1.4 relative units per cell). We conclude that AMs are not involved in the development of HPH directly through their contribution to radical tissue damage.