Plasminogen activator inhibitor-1 synthesis in the human hepatoma cell line Hep G2. Metformin inhibits the stimulating effect of insulin.

Abstract

High plasma plasminogen activator inhibitor-i (PAI-1) activity is associated with insulin resistance and is correlated with hyperinsulinemia. The cellular origin of plasma PAI-1 in insulin resistance is not known. The hepatoma cell line Hep G2 has been shown to synthesize PAI-1 in response to insulin. The aim of this study was to analyze the insulin-mediated response of PAI-1 and lipid synthesis in Hep G2 cells after producing an insulin-resistant state by decreasing insulin receptor numbers. The effect of metformin, a dimethyl-substituted biguanide, known to lower plasma insulin and PAI-I levels in vivo was concomitantly evaluated. Preincubation by an 18-h exposure of Hep G2 cells to 1i-7 M insulin aimed at reducing the number of insulin receptors, was followed by a subsequent 24-h stimulation with 10-9 M insulin. The decrease in insulin receptors was accompanied as expected, by a reduction in I14Clacetate incorporation, an index of lipid synthesis, whereas PAI-i secretion and PAI-i mRNA expression were enhanced. The addition of metformin did not modify the effect of insulin on insulin receptors or I14C acetate incorporation. In contrast, the drug (i0-4 M) inhibited insulin-mediated PAI-1 synthesis. The results indicate that PAI-1 synthesis in presence of insulin is markedly increased in down-regulated cells, and that metformin inhibits this effect by acting at the cellular level. These in vitro data are relevant with those found in vivo in insulin-resistant patients. Hep G2 cells may be a suitable model to study PAI-1 regulation in response to hyperinsulinemia. (J. Clin. Invest. 1993. 91:2185-2193 Key words: fibrinolysis* insulin * insulin resistance -metformin-plasminogen activator inhibitor 1

PAI-1 Produced Ex Vivo by Human Adipose Tissue Is Relevant to PAI-1 Blood Level

“…23,24 Then, the fact that circadian variations in plasma PAI-1 were not considered for blood sampling and the particular composition of the population studied could both contribute to the lack of correlation observed between PAI-1, insulinemia, and BMI. Furthermore, despite demonstration of an in vitro effect of insulin on PAI-1 production by some cultured cells, [25][26][27][28][29] our results do not favor the hypothesis of a direct contribution of insulin to PAI-1 level regulation. They also underline the link between PAI-1 expression and a qualitative rather than a quantitative aspect of adipose tissue.…”

Liver Fat Content Measured by Magnetic Resonance Spectroscopy at 3.0 Tesla Independently Correlates with Plasminogen Activator Inhibitor-1 and Body Mass Index in Type 2 Diabetic Subjects

“…It has already been reported that hepatocytes produce PAI-1 (Anfosso et al 1993), and plasma PAI-1 levels are more strongly related to liver steatosis than to adipose tissue accumulation (Alessi et al 2003). Our results may indicate that even a low liver fat content stimulates hepatocytes to produce PAI-1, which may be involved in cardiovascular risk (Bastard et al 2000).…”

Lipids, thrombosis and cardiovascular disease in diabetes

“…In hepatocytes, PAI-1 synthesis is increased by inducing insulin resistance (Anfossa et al 1993), a relationship which has also been noted in clinical studies Potter van Loon et al 1993). However, the interpretation of such clinical studies is made complex by the powerful interrelationships between various features of the insulin-resistance syndrome, any of which may explain the increased levels of PAI-1 in insulin resistance and in NIDDM.…”