TNF-alpha 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-alpha (TNF-alpha) in adipose tissue. TNF-alpha has be en implicated as an inducer of the synthesis of plasminogen activator inhib itor-1 (PAI-1), the primary physiological inhibitor of fibrinolysis, mediat ed by plasminogen activators in cultured adipocytes. To identify mechanism( s) through which TNF-alpha induces PAI-1, 3T3-L1 preadipocytes were differe ntiated into adipocytes and exposed to TNF-alpha for 24 h. TNF-alpha select ively increased the synthesis of PAI-1 without increasing activity of plasm inogen activators. Both superoxide (generated by xanthine oxidase plus hypo xanthine) and hydrogen peroxide were potent inducers of PAI-1, and hydroxyl radical scavengers completely abolished the TNF-alpha induction of PAI-1. Exposure of adipocytes to TNF-alpha or insulin alone over 5 days increased PAI-1 production. These agonists exert synergistic effects. Results obtaine d suggest that TNF-alpha stimulates PAI-1 production by adipocytes, an effe ct potentiated by insulin, and that adipocyte generation of reactive oxygen centered radicals mediates the induction of PAI-1 production by TNF-alpha. Because induction of PAI-1 by TNF-alpha is potentiated synergistically by insulin, both agonists appear likely to contribute to the impairment of fib rinolytic system capacity typical in obese, hyperinsulinemic patients.