Bleomycin hydrolase activity in pulmonary cells.

The metabolism of bleomycin (BLM) A2 by BLM hydrolase in the 105,000 X g supernatant fraction of homogenates obtained from freshly isolated and cultured pulmonary cells was assayed by high-pressure liquid chromatography. BLM A2 was converted solely to the less toxic desamido metabolite by the cytosol from isolated rabbit and bovine alveolar and interstitial macrophages, cultured rabbit and bovine pulmonary fibroblasts and cultured rabbit pulmonary artery endothelial cells. The BLM hydrolase activity in the cytosol from cultured rabbit fibroblasts had an apparent Km of 700 microM and Vmax of 33 nmol/hr/mg protein. The rate of BLM dA2 formation found with the cytosol of cultured rabbit pulmonary artery endothelial cells and pulmonary fibroblasts was 3 to 5 times greater per cell than that from the cytosol of rabbit alveolar and interstitial macrophages. Freshly isolated rabbit type II pneumocytes and bovine pulmonary artery endothelial cells grown in culture had undetectable levels of this inactivating enzyme activity. The expression of BLM hydrolase activity in rabbit pulmonary fibroblasts was stable for at least five passages in culture and was not significantly different over wide cell densities in culture. These data suggest that heterogeneity in the cellular distribution of BLM hydrolase activity exists in lungs. High levels of BLM hydrolase activity in the pulmonary endothelium or fibroblasts of some species may have an important role in determining the toxicity of BLM to the lungs.