Inhibitory effects of nicotinamide on intercellular adhesion molecule-1 expression on cultured human thyroid cells

We investigated the effects of nicotinamide and 3-aminobenzamide (3-AB), inhibitors of poly (ADP ribose) synthetase, on phytohaemagglutinin (PHA)- or interferon-gamma (IFN-gamma)-induced intercellular adhesion molecule-1 (ICAM-1) expression on cultured thyroid cells from patients with Graves' disease. Primary cultured thyroid cells were incubated for 3 days with IFN-gamma (10-800 U/ml) or PHA (1-50 micrograms/ml) in the presence of nicotinamide, 3-AB, superoxide dismutase or catalase. The surface expression of ICAM-1 was measured by flow cytometry. Nicotinamide and 3-AB dose-dependently inhibited the induction of ICAM-1 expression by IFN-gamma or PHA on thyroid cells. Neither catalase nor superoxide dismutase, which are free-radical scavengers, inhibited the expression of ICAM-1 on thyroid cells. Our data suggest that the mechanism of the suppression of ICAM-1 expression on thyroid cells by nicotinamide is not likely to be due to the free radical scavenging. Further studies are indicated to elucidate whether the inhibition of ICAM-1 by these drugs may result in the suppression of autoimmune reaction in the thyroid gland.