Effect of dibutyryl cyclic AMP on phagocytosis and production of nitric oxide and tumor necrosis factor- α in cultured rat Kupffer cells

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Dibutyryl cyclic AMP (DBcAMP) is an analogue of cAMP. DBcAMP has many effects on hepatocellular carcinoma, liver cirrhosis, ischemic liver failure and endotoxin-induced inflammatory liver injury. However, little is known about the mechanism of DBcAMP action in Kupffer cells. We examined the effects of DBcAMP on phagocytic activity and production of nitric oxide (NO) and tumor necrosis factor- α (TNF- α) in cultured rat Kupffer cells treated with lipopolysaccharide (LPS). NO concentrations in culture supernatants were measured using an NO analyzer and TNF- α levels were measured with ELISA. Immunofluorescent staining for nuclear factor- κ B (NF- κ B) was visualized using an anti-NF- κ B p65 antibody. DBcAMP premedication had no effect on LPS-stimulated phagocytic activity of Kupffer cells but increased NO production and inhibited TNF- α production in a dose-dependent manner. Genistein did not block, but H-89 did block, the inhibitory effect of DBcAMP on LPS-stimulated TNF- α production in Kupffer cells. We conclude that DBcAMP inhibits LPS-stimulated TNF- α production by activating cyclic AMP-dependent protein kinase. Using immunofluorescent staining for NF- κ B, we demonstrate that the effect of DBcAMP does not involve signal transduction through NF- κ B.