Hepatocyte nitric oxide production is induced by Kupffer cells

To investigate the cellular communication in the liver, nitric oxide (NO) production by sinusoidal cells and hepatocytes by stimulation with cytokines and Kupffer cell-conditioned medium was quantitatively analyzed. NO production by the cells was measured by the Griess reaction, and nitric oxide synthase (iNOS) transcription level by a competitive RT-PCR assay using mutant iNOS mRNA as a standard. NO production and iNOS mRNA transcriptional levels in Kupffer cells were markedly increased by stimulation with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma), and moderately by interleukin-1beta (IL-1beta). NO production by hepatocytes was not significantly enhanced by LPS, but was markedly enhanced by IL-1beta or the combination of tumor-necrosis factor-alpha (TNF-alpha) and IFN-gamma. Hepatocyte NO production and iNOS mRNA levels were markedly enhanced by the LPS-activated Kupffer cell conditioned medium, but these effects were reduced by heat treatment or anti-TNF antibody. Although NG-monomethyl-L-arginine acetate and dexamethasone reduced NO production by the cells, the iNOS mRNA level was reduced by dexamethasone only. Gel-shift assay showed NF-kappaB activation in hepatocytes during this activation. These data reinforce the importance of cellular communication between sinusoidal cells and hepatocytes.