Cationic proteins inhibit L-arginine uptake in rat alveolar macrophages and tracheal epithelial cells - Implications for nitric oxide synthesis

Eosinophil-derived cationic proteins play an essential role in the pathogen esis of bronchial asthma. We tested whether cationic proteins interfere wit h the cationic amino-acid transport in alveolar macrophages (AM Phi) and tr acheal epithelial cells, and whether L-arginine-dependent pathways were aff ected. The effect of cationic polypeptides on cellular uptake of [H-3]-L-ar ginine, nitrite accumulation, and the turnover of [H-3]-L-arginine by nitri c oxide (NO) synthase and arginase (formation of [H-3]-L-citrulline and [H- 3]-L-ornithine, respectively) were studied. Poly-L-arginine reduced [H-3]-L -arginine uptake in rat AM Phi and tracheal epithelial cells in a concentra tion-dependent manner (at 300 mu g/ml by 70%). Poly-L-lysine, protamine, an d major basic protein teach up to 300 mu g/ml) tested in rat AM Phi inhibit ed [H-3]-L-arginine uptake by 35 to 50%. During 6 h incubation in amino aci d-free Krebs solution, rat AM Phi, precultured in the absence or presence o f LPS (1 mu g/ml), accumulated 1.4 and 3.5 nmol/10(6) cells nitrite, respec tively. Addition of 100 mu M L-arginine increased nitrite accumulation by 7 0 and 400% in control and lipopolysaccharide-treated AM Phi, respectively. Nitrite accumulation in the presence of L-arginine was reduced by poly-L-ar ginine and poly-L-lysine (100 and 300 mu g/ml) by 60 to 85% acid 20 to 30%, respectively. Poly-L-arginine, but not poly-L-lysine, inhibited nitrite ac cumulation already in the absence of extracellular L-arginine. Poly-L-argin ine (300 mu g/ml) inhibited [H-3]-L-citrulline formation by AM Phi stronger than that of [H-3]-L-ornithine. We conclude that cationic proteins can inh ibit cellular transport of L-arginine and this can limit NO synthesis. Poly -L-arginine inhibits L-arginine uptake more effectively than other cationic proteins and exerts additional direct inhibitory effects on NO synthesis.