Arginase I: a limiting factor for nitric oxide and polyamine synthesis by activated macrophages?

Because arginase hydrolyzes arginine to produce ornithine and urea, it has the potential to regulate nitric oxide (NO) and polyamine synthesis. We tes ted whether expression of the cytosolic isoform of arginase (arginase I) wa s limiting for NO or polyamine production by activated RAW 264.7 macrophage cells. RAW 264.7 cells, stably transfected to overexpress arginase I or be ta -galactosidase, were treated with interferon-gamma to induce type 2 NO s ynthase or with lipopolysaccharide or 8-bromo-cAMP (8-BrcAMP) to induce orn ithine decarboxylase. Overexpression of arginase I had no effect on NO synt hesis. In contrast, cells overexpressing arginase I produced twice as much putrescine after activation than did cells expressing beta -galactosidase. Cells overexpressing arginase I also produced more spermidine after treatme nt with 8-BrcAMP than did cells expressing beta -galactosidase. Thus endoge nous levels of arginase I are limiting for polyamine synthesis, but not for NO synthesis, by activated macrophage cells. This study also demonstrates that it is possible to alter arginase I levels sufficiently to affect polya mine synthesis without affecting induced NO synthesis.