Inhibition of inducible nitric oxide synthase by β-lapachone in rat alveolar macrophages and aorta

Abstract

1. β-Lapachone, a plant product, has been shown to be a novel inhibitor of DNA topoisomerase. In this study, we performed experiments to examine the effects of β-lapachone on lipopolysaccharide (LPS)-induced inducible nitric oxide (NO) synthase (iNOS) in rat alveolar macrophages and aortic rings. 2. In alveolar macrophages, incubation with LPS (10 μg ml-1) for various time intervals resulted in a significant increase in nitrite production and iNOS protein synthesis, that was inhibited by co-incubation with β-lapachone (1-4.5 μM) without any cytotoxic effects. However, addition of β-lapachone after induction of NO synthase by LPS failed to affect the nitrite production. 3. Treatment with LPS (10 μg ml-1) for 6 h resulted in significant expression of mRNA for iNOS which was significantly inhibited in the presence of β-lapachone (3 μM) in alveolar macrophages. 4. In endothelium-intact rings of thoracic aorta, β-lapachone (1 and 3 μM) markedly inhibited the hypocontractility to phenylephrine in aortic rings treated with LPS (10 μg ml-1) for 4 h. When β-lapachone was added 3 h after LPS into the medium, the contractions evoked by phenylephrine were not significantly different in the presence or absence of β-lapachone. 5. Treatment with LPS (10 μg ml-1) for 4 h resulted in a significant increase in iNOS protein synthesis which was inhibited in the presence of β-lapachone (3 μM), but did not affect the constitutive (endothelial and neuronal) NOS forms in aortic rings. 6. These results indicate that β-lapachone is capable of inhibiting expression and function of iNOS in rat alveolar macrophages and aortic rings. It is considered that β-lapachone can be developed as a potential anti-inflammatory agent in the future.