TNF-α and insulin, alone and synergistically, induce plasminogen activator inhibitor-1 expression in adipocytes

Obesity is associated with hyperinsulinemia and elevated concentrations of tumor necrosis factor-α (TNF-α) in adipose tissue. TNF-α has been implicated as an inducer of the synthesis of plasminogen activator inhibitor-1 (PAI-1), the primary physiological inhibitor of fibrinolysis, mediated by plasminogen activators in cultured adipocytes. To identify mechanism(s) through which TNF-α induces PAI-1, 3T3-L1 preadipocytes were differentiated into adipocytes and exposed to TNF-α for 24 h. TNF-α selectively increased the synthesis of PAI-1 without increasing activity of plasminogen activators. Both superoxide (generated by xanthine oxidase plus hypoxanthine) and hydrogen peroxide were potent inducers of PAI-1, and hydroxyl radical scavengers completely abolished the TNF-α induction of PAI-1. Exposure of adipocytes to TNF-α or insulin alone over 5 days increased PAI-1 production. These agonists exert synergistic effects. Results obtained suggest that TNF-α stimulates PAI-1 production by adipocytes, an effect potentiated by insulin, and that adipocyte generation of reactive oxygen centered radicals mediates the induction of PAI-1 production by TNF-α. Because induction of PAI-1 by TNF-α is potentiated synergistically by insulin, both agonists appear likely to contribute to the impairment of fibrinolytic system capacity typical in obese, hyperinsulinemic patients.