Pulsed electric field exposure of insulin induces anti-proliferative effects on human hepatocytes

The purpose of this study was to examine the effects and the mechanism of a pulsed electric field (PEF) on insulin and its subsequent mediation of proliferative changes in human hepatocytes in vitro. The PEF, the electric field intensity coupled into the culture medium, was about 0.7 V/m with a repeating frequency of 50 Hz. Insulin solution was exposed to PEF for 20 min and added to the culture medium of human hepatocytes. Combining fluorescence spectroscopy, immunocytochemistry, microarrays, RT-PCR and MTT, several important events of the insulin signaling pathways were investigated, including ligand-receptor binding capacity, intracellular tyrosine phosphorylation level, gene transcription, and cell proliferation. PEF produced a conformational change of insulin molecule. The binding capacity of insulin to its receptors was reduced to 87% of the control level after PEF treatment, and the average intracellular tyrosine phosphorylation level decreased by 11%. The expression of 55 of 12,000 genes examined was modified, including an increase in the expression of human tyrosine phosphatase and the small GTP-binding protein. Based on these results, a mechanism is proposed to explain the bio-effects of PEF on hepatic cell proliferation through the insulin signaling pathway.