Molecular role of ascorbate in enhancement of NO production in activated macrophage-like cell line, J774.1.

Ascorbate-enhanced nitric oxide (NO) production in lipopolysaccharide (LPS)- and interferon-gamma (IFN-gamma)-activated macrophage J774.1 cells through the inducible nitric oxide synthase (iNOS) pathway. The iNOS gene was synergistically induced by LPS and IFN-gamma. The inductive mechanism of ascorbate on the iNOS gene was studied by examining the degradation of I kappa B alpha by Western blotting, activation of the nuclear factor kappa B (NF-kappa B) by gel shift assays, and protein levels of interferon regulatory factor 1 (IRF-1) in LPS- and IFN-gamma-activated cells. Ascorbate had no effect on the onset of either I kappa B alpha degradation or the nuclear translocation of NF-kappa B, but it delayed the recovery of I kappa B alpha. The prolonged degradation of I kappa B alpha caused by ascorbate in LPS- and IFN-gamma-activated cells paralleled elevated NF-kappa B binding to DNA, which led to an increase in the iNOS protein level. Ascorbate alone did not induce I kappa B alpha degradation or NF-kappa B activation. Furthermore, ascorbate exerted no effect on the expression of I kappa B alpha and ubiquitin genes in the activated cells. Ascorbate could modulate NF-kappa B DNA binding activity in response to combined LPS and IFN-gamma activation, which increases NO production in activated macrophages.