TUMOR NECROSIS FACTOR-ALPHA-INDUCED GELATINASE-B CAUSES DELAYED OPENING OF THE BLOOD-BRAIN-BARRIER - AN EXPANDED THERAPEUTIC WINDOW

Proteolytic damage is a late event in the molecular cascade initiated by brain injury. Earlier, we proposed that matrix metalloproteinases ( MMPs) and urokinase-type plasminogen activator (uPA) are important in secondary brain injury. We have shown that intracerebral injection of activated 72-kDa type IV collagenase (gelatinase A) opens the blood-br ain barrier, and that during hemorrhagic brain injury there is endogen ous production of 92-kDa type IV collagenase (gelatinase B) and uPA. T herefore, to study the functional link between proteolytic enzymes and blood-brain barrier damage, we induced MMP expression by infusing tum or necrosis factor-alpha (TNF) intracerebrally in rats. Initially, the effect on capillary permeability of increasing doses of TNF, using [C -14]sucrose uptake, was measured. Then, the time-course of the capilla ry permeability change was studied at 4, 16, 24 and 72 h. Expression o f MMP and uPA was measured by zymography at 24 h after TNF injection a nd compared to saline-injected controls. A dose-dependent increase in capillary permeability was seen 24 h after TNF injection. Maximal upta ke of [C-14]sucrose occurred at 24 h compared to saline-injected contr ols (P < 0.05). Zymography showed production of gelatinase B, which wa s significantly greater than in saline-injected controls at 24 h (P < 0.05). Batimastat, a synthetic inhibitor to metalloprotinases, reduced sucrose uptake at 24 h (P < 0.0001), and was effective even when give n 6 h after TNF (P < 0.01). Thus, gelatinase B is the intermediate sub stance linking TNF to modulation of capillary permeability. Agents tha t interfere with transcription of proteolytic enzymes or block their a ction may reduce delayed capillary injury, extending the therapeutic w indow.