Trauma to the spinal cord results in severe tissue necrosis. Since this nectrotizing reaction occurs in well-vascularized lesions, it cannot be exclusively ischemic in origin, as has been thought. We will test the hypothesis that its pathoogenesis is related to cytotoxic secretion by macrophages. Although macrophages do secrete cytotoxic factors inimical to tissue repair, they also secrete growth promoting factors beneficial to wound healing. The following experiments explore ways of reducing the necrotizing secretions of macrophages while encouraging their secretion of growth factors favorable to angiogenesis, gliogenesis and neuritogenesis. 1. Prior to their differentiation into macrophages, monocytes can be rapidly primed by daily i.v. administration of bacterial lipopolysaccharides or muramyl dipeptides. This treatment not only primes the cells for secretion of growth factors, but specifically impairs their ability to secrete cytotoxic agents. These experiments should also help us to understand the mode of action of Piromen, a lipopolysaccharide found by Windle in 1950 to promote spinal cord regeneration in cats and monkeys. 2. The cytotoxic function of macrophages depends on the prior activation of intracellular proteases; the protease activity apparently initiates metabolic oxygen responses that result in the secretion of superoxide anions and other cytotoxic agents. Both in vitro and in vivo experiments show that this oxygen response can be lessened by treatment with protease inhibitors. Of these we have selected chloroquine, leupeptin and aprotonin for evaluation because each has a different biochelmical mode of action. In the proposed experiments, we will injure the spinal cord of rats by transection, compression or concussion and treat them intravenously with aforementioned macrophage priming agents or protease inhibitors. The effects of these agents will be assessed histologically by immunocytochemical techniques which demonstrate regeneration of axons, proliferation of astrocytes, and revascularization of the lesion site. Quantitative biochemical determination of changes in these components at the lesion site will be performed using the quantitative ELISHA assay that we recently developed.
