INTERLEUKIN-1-BETA IS A POTENT GROWTH INHIBITOR OF ADULT-RAT HEPATOCYTES IN PRIMARY CULTURE

Interleukin-1.beta. (IL-1.beta.) strongly inhibited DNA synthesis of adult rat hepatocytes in primary culture stimulated by insulin and epidermal growth factor (EGF). Its effect was dose-dependent and was maximal at 2 ng/ml. IL-1.beta. had no cytotoxic effect but changed the cells from a flat to a spindle shape as shown by phase-contrast microscopy. The inhibition of DNA synthesis by IL-1.beta. was closely correlated with a decrease in the labeling index. This inhibitory effect was observed only when IL-1.beta. was added for 10 h to cultured hepatocytes in the G1 phase within 12 h after addition of insulin and EGF; it was not observed in the S phase, which starts about 24 h after addition of the mitogens. Exposure of the hepatocytes to IL-1.beta. for two 1-h periods, one at an early stage (0-6 h) and one at a late stage (6-12 h) of the G1 phase, resulted in the same marked inhibition of DNA synthesis as exposure to IL-1.beta. for 10 h in the G1 phase. This requirement of IL-1.beta. at two stages in the G1 phase for inhibition of DNA synthesis of hepatocytes is different from that with transforming growth factor-.beta., which is required for only 1 h in the early G1 phase for a similar inhibition. These findings suggest that IL-1.beta. acts at two distinct stages in the G1 phase and that its cooperative actions are necessary to inhibit growth of adult rat hepatocytes in primary culture. Other cytokines, such as IL-6/B-cell stimulating factor-2, were less potent, but caused significant inhibition of DNA synthesis of adult rat hepatocytes at 2 ng/ml, whereas IL-2 and tumor necrosis factor did not affect hepatocyte growth. From hepatocyte growth. From these results it is suggested that Kupffer cells in liver lobules and macrophages in the blood may play important roles, mainly via IL-1, in repair of liver damage and regeneration.