Effect of Curcumin on the Production of Nitric Oxide by Cultured Rat Mammary Gland

Abstract

We have hypothesized that one aspect of the antitumor activity of curcumin (diferuloylmethane) during the promotion stage of mammary gland tumorigenesis may be linked to reduction of free radicals (Inano et al., Carcinogenesis, 20: 1011–1018, 1999). Nitric oxide (NO) has been found to inflict damage on important biomolecules, and the overproduction of NO in diseases may be implicated in carcinogenesis and tumor progression. We have reported that the presence of three isoforms of nitric oxide synthases (NOS) and NO generation in the mammary gland correlate with the mammary gland development and mammary carcinogenesis. We, therefore, investigated the inhibitory activity of curcumin for the production of NO in rat mammary glands by using an organ culture system to validate the effectiveness and usefulness of curcumin in the pathophysiology of the mammary gland. A diced mammary gland (approximately 3 mm cubes) from the inguinal part of a female Wistar-MS rat treated with estradiol and progesterone was cultured with 2 ml of 5% FCS/DMEM in the presence or absence of LPS (0.5 μg/ml) for 2–3 days. Curcumin (∼100 μM) was added at the same time to the LPS-treated cultures. In some experiments, curcumin was added to the culture after the LPS had been washed out. The NO production was significantly increased (by almost 20-fold compared to the control) by the addition of LPS to the culture system. This enhancement of NO production by LPS was reduced to 76 and to 56% by addition of 30 and 100 μM curcumin, respectively, to the culture. When LPS was eliminated from the culture after prestimulation for 1 day, the production of NO by the mammary gland dropped off, although some NO was still detectable. Curcumin did not further inhibit the production of NO by the prestimulated mammary gland after the elimination of LPS from the culture. The inducible nitric oxide synthase (iNOS, 122 kDa) and endothelial nitric oxide synthase (eNOS, 152 kDa) isoforms were detected in the mammary gland extracts at the end of the organ culture. The quantity of iNOS was apparently increased in the gland treated with LPS, while the eNOS expression was clearly diminished. Curcumin (100 μM) obviously suppressed the iNOS expression in the mammary glands cultured with LPS, and a recovery in the eNOS expression was observed. On the other hand, curcumin exhibited scavenging activity for the NO released from N-ethyl-2-(1-ethyl-2-hydroxy-2-nitrosohydrazino)-ethanamine (NOC 12), a NO donor compound, in the coincubation mixture. These results indicate that curcumin has the ability to inhibit iNOS induction by LPS in the mammary gland and to scavenge NO radicals, which might explain, at least partly, its therapeutic properties in inflammation of the mammary gland.