Lactoferrin, endotoxin, and nitric oxide metabolism in pulmonary alveolar macrophages

Background. Lactoferrin (LF) and its effects on airway macrophages (M phi) are poorly characterized. Since LF binds lipopolysaccharide (LPS), and nitric oxide (NO) production by M phi is induced with LPS, M phi-related responses to both molecules were studied. Methods. Rat lung M phi were treated with LF and/or LPS for 24 h, and thereafter the NO metabolite nitrite was measured in culture supernatants. At 24 h, M phi-related expression of inducible NO synthase (iNOS) was determined by Northern analysis. To understand how LF might alter iNOS expression, nuclear factor kappa B (NF-kappa B) activation was studied in M phi. Results. LF did not stimulate M phi-related nitrite production at concentrations present in bronchial mucus. An excess of LF increased M phi-related nitrite production, but NO generation was less than that initiated by LPS. The LPS-binding peptide, polymyxin B, reduced LF and LPS responses to basal levels. After 24 h, mRNA expression of iNOS was lower in M phi treated with LF or LF + LPS vs. LPS alone. M phi had markedly increased NF-kappa B activation when treated with LPS or LPS + LF, while LF minimally increased NF-kappa B nuclear binding compared to untreated cells. Conclusions. M phi responses to LF may be induced by the LF-LPS complex rather than LF alone. Molecular responses of M phi to LPS differ from those of M phi stimulated by LF or the LF-LPS complex. These findings are likely important in the control of lung inflammation and injury.