EN
Heme oxygenase-1 (HO-1), an inducible enzyme degrading heme to biliverdin, iron and carbon monoxide, is involved in regulation of inflammation and angiogenesis. Tin protoporphyrin (SnPPIX) and zinc protoporphyrin (ZnPPIX) are commonly used as competitive inhibitors of HO-1. We aimed to compare the effects of SnPPIX and ZnPPIX on the production of vascular endothelial growth factor (VEGF), activity of inducible nitric oxide synthase (iNOS) and cell viability. All experiments were performed on rat vascular smooth muscle cells and murine RAW264.7 macrophages treated with 3-10 ,uM protoporphyrins. Some cells were additionally stimulated with IL-1β or with lipopolysaccharide. After a 24 h incubation period SnPPIX and ZnPPIX significantly reduced the generation of VEGF in vascular smooth muscle cells and RAW264.7, both in resting and stimulated cells. The inhibitory potentials of both protoporphyrins on VEGF synthesis were very similar. In contrast, analysis of iNOS activity revealed that results obtained with different HO-1 inhibitors are discrepant.