Zinc supplementation selectively decreases fetal hepatocyte DNA synthesis and insulin-like growth factor II gene expression in primary culture

Abstract

Zinc is important for normal cell growth and differentiation, DNA synthesis, and gene expression. IGF-II is a fetal growth and differentiation factor whose regulation is largely unknown. To assess the effect of zinc (Zn) on fetal hepatocyte IGF-II expression and DNA synthesis, primary cultures of ovine fetal hepatocytes were studied in serum-free medium containing 1 mumol/L Zn or supplemented to 10 or 50 mumol/L Zn. Fetal hepatocyte DNA synthesis, Zn and protein content, IGF-II mRNA, and IGF binding protein production were measured. Zn concentration in medium increased slightly in unsupplemented dishes, from 1 to 1.5 mumol/L; however, Zn concentration declined by 4 and 8 mumol/L over 24 h in culture medium supplemented to contain either 10 or 50 mumol/L Zn (p < 0.05). Zn content of cell pellets increased 155 and 204% after 24 h in supplemented cultures compared with unsupplemented controls, demonstrating uptake of Zn by the liver cells. Media Zn supplementation to 10 and 50 mumol/L decreased 3H-thymidine incorporation of cells in culture by 11 and 13%, respectively, compared with 1 mumol/L Zn (p = 0.001). Addition of Zn caused a progressive 2- to 3-fold decline in the nuclear labeling index of fetal hepatocytes, whereas the labeling index of nonhepatocytes increased almost 2-fold at 50 mumol/L compared with 1 mumol/L Zn. Associated with decreased hepatocyte DNA synthesis, IGF-II mRNA abundance declined by almost 30%. IGF binding protein content of conditioned medium did not change with added Zn.(ABSTRACT TRUNCATED AT 250 WORDS)