INDUCTION OF PLASMINOGEN-ACTIVATOR INHIBITOR TYPE-1 AND TYPE-1 COLLAGEN EXPRESSION IN RAT CARDIAC MICROVASCULAR ENDOTHELIAL-CELLS BY INTERLEUKIN-1 AND ITS DEPENDENCE ON OXYGEN-CENTERED FREE-RADICALS

Background-Ischemia with or without reperfusion induces the release of diverse products from monocytes, including cytokines such as interleu kin-1 (IL-1). To determine whether these phenomena modulate fibrinolys is and potentially exacerbate impairment of the macrocirculation, micr ocirculation, or both, we characterized the effects of IL-1 on the exp ression of fibrinolytic system and matrix proteins in rat cardiac micr ovascular endothelial cells (CMECs), Methods and Results-Confluent CME Cs were exposed to IL-1 in serum-foe medium for 24 hours, and cell-con ditioned medium was assayed for plasminogen activator inhibitor type 1 (PAI-1), the primary physiological inhibitor of plasminogen activator s, and for type 1 collagen with Western blotting. IL-1 (2 ng/mL) speci fically increased the accumulation of PAI-1 (4.4+/-0.6-fold; mean+/-SD ; n=9) without affecting tissue plasminogen activator (t-PA) or urokin ase plasminogen activator (u-PA) levels, which remained unchanged. IL- 1 increased the accumulation of collagen in conditioned media by 3.5+/ -0.7-fold (n=6). Conversely, the accumulation of both PAI-1 and collag en induced by IL-1 was inhibited with an IL-1 receptor antagonist (200 ng/mL; n=6) and with cycloheximide (10 mu g/mL; n=6), implying that p rotein synthesis was a requirement for the effect. To determine whethe r the IL-1 effect was mediated by induction of oxygen-centered free ra dical production, known to be induced by IL-1, we exposed the cells to the hydroxyl radical scavenger tetramethylthiourea (10 mmol/L) and ob served abolition of the IL-1-induced increase in the expression of PAI -1 and collagen (n=6). Conversely, superoxides (generated with 10 mU/m L xanthine oxidase plus 0.6 mmol/L hypoxanthine, and 100 mu mol/L hydr ogen peroxide) induced the accumulation of PAI-1 and collagen (n=6). I L-1 (1 mu g/kg body wt) and lipopolysaccharide (50 mu g/kg body wt) ad ministered in vivo increased PAI-1 protein in rat hearts as detected w ith Western blotting and PAI-1 immunostaining of rat heart microvessel s, indicating the effects delineated in vitro were paralleled by effec ts in vivo. Conclusions-These results indicate that IL-1-induced oxyge n-centered foe radicals stimulate elaboration of PAI-1 and collagen by CMECs, Accordingly, microvascularly mediated inhibition of fibrinolys is may predispose to the persistence of microvascular thrombi, thereby contributing to impaired microcirculatory function, the no-reflow phe nomenon, and cardiac dysfunction after ischemia and reperfusion.