TGF-BETA-1 PROTECTS HIPPOCAMPAL-NEURONS AGAINST DEGENERATION CAUSED BY TRANSIENT GLOBAL-ISCHEMIA - DOSE-RESPONSE RELATIONSHIP AND POTENTIALNEUROPROTECTIVE MECHANISMS

Background and Purpose Transforming growth factor-beta 1 (TGF-beta 1) has been shown to rescue cultured neurons from excitotoxic and hypoxic cell death and to reduce infarct size after focal cerebral ischemia i n mice and rabbits. The present study investigated the effects of TGF- beta 1 in a different pathophysiological setting and the delayed neuro nal death of hippocampal pyramidal cells after transient global ischem ia in rats, and evaluated the potential mechanisms of the neuroprotect ive activity of TGF-beta 1. Methods Transient forebrain ischemia was i nduced in male adult Wistar rats with bilateral occlusion of both comm on carotid arteries combined with systemic hypotension for 10 minutes. Seven days after ischemia, brains were perfusion-fixed and stained fo r histological evaluation. TGF-beta 1 or vehicle was injected intracer ebroventricularly (ICV; 0.5, 4, and 50 ng) or intrahippocampally (4 ng ) 1 hour before ischemia. For in vitro studies, hippocampal neurons we re derived from E17 rat embryos and cultured for 10 to 14 days. Cells were exposed to (1) S-nitrosocysteine (SNOC; 30 mu mol/L) to induce ni tric oxide-induced oxidative injury and (2) staurosporine (0.03 rho mo l/L) to induce apoptotic cell death. Results Transient forebrain ische mia caused extensive degeneration of CAI hippocampal pyramidal cells i n vehicle-treated control animals. Ischemic injury was not significant ly reduced after ICV administration of 0.5 ng TGF-PI (71+/-7% damaged neurons versus 84+/-3% in vehicle-treated controls; n=9 and 11, respec tively; P=.07, Mann-Whitney U test). Administration of 4 ng TGF-PI red uced the percentage of damaged CAI pyramidal cells from 71+/-10% in co ntrols to 52+/-7% in TGF-beta 1-treated animals (n=11 and 12, respecti vely; P=.04). TGF-beta 1 (4 ng) also produced significant protection w hen injected directly into the hippocampal tissue. In contrast, ICV ad ministration of 50 ng TGF-P 1 failed to show a protective effect in tw o separate sets of experiments. In vitro, a 24-hour pretreatment of th e cultured hippocampal neurons with TGF-beta 1 (0.1 to 10 ng/mL) signi ficantly inhibited both nitric oxide and staurosporine neurotoxicity. Posttreatment with TGF-beta 1 (10 ng/mL) also inhibited staurosporine neurotoxicity but actually potentiated nitric oxide-induced neuronal i njury. Conclusions We demonstrated that TGF-beta 1 in a surprisingly l ow dose range has the capacity to reduce injury to CA1 hippocampal neu rons caused by transient global ischemia in rats. This protective acti on could well be associated with the antioxidative and antiapoptotic e ffects of TGF-beta 1 demonstrated in vitro.