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 pathogenesis of bronchial asthma. We tested whether cationic proteins interfere with the cationic amino-acid transport in alveolar macrophages (AM Phi) and tracheal epithelial cells, and whether L-arginine-dependent pathways were affected. The effect of cationic polypeptides on cellular uptake of [H-3]-L-arginine, nitrite accumulation, and the turnover of [H-3]-L-arginine by nitric 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 concentration-dependent manner (at 300 mu g/ml by 70%). Poly-L-lysine, protamine, and major basic protein teach up to 300 mu g/ml) tested in rat AM Phi inhibited [H-3]-L-arginine uptake by 35 to 50%. During 6 h incubation in amino acid-free Krebs solution, rat AM Phi, precultured in the absence or presence of LPS (1 mu g/ml), accumulated 1.4 and 3.5 nmol/10(6) cells nitrite, respectively. Addition of 100 mu M L-arginine increased nitrite accumulation by 70 and 400% in control and lipopolysaccharide-treated AM Phi, respectively. Nitrite accumulation in the presence of L-arginine was reduced by poly-L-arginine 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 accumulation already in the absence of extracellular L-arginine. Poly-L-arginine (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 inhibit 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.