Paradoxical effects of a synthetic metalloproteinase inhibitor that blocks both P55 and P75 TNF receptor shedding and TNF alpha processing in RA synovial membrane cell cultures

We have previously hypothesized that the pro-inflammatory cytokine TNF alpha has a pivotal role in the pathogenesis of rheumatoid arthritis (RA). It mediates its effects by crosslinking surface p55 or p75 TNF receptors (TNF-R), which can be proteolytically cleaved to yield soluble fragments, Upon binding TNF alpha soluble TNF-R (sTNF-R) can inhibit its function, We investigated the enzymatic nature of the proteases involved in TNF-R cleavage, and found that this process is blocked by a synthetic inhibitor of matrix metalloproteinase activity (MMP), BE-2275. Inhibition of TNF-R cleavage was observed in a number of different cell types, as detected by retention of surface bound TNF receptor and by less sTNF-R released into the cell supernatant, The augmentation of surface TNF-R expression was of biological relevance as TNF alpha-mediated necrosis of human KYM.1D4 rhabdosarcoma cells was enhanced similar to 15-fold in the presence of BE-2275. The addition of BB-2275 to rheumatoid synovial membrane cell cultures totally inhibited MMP activity and also significantly reduced the levels of soluble TNF alpha (P < 0.006), p55 sTNF-R (P < 0.006), and p75 sTNF-R (P ( 0.004), Paradoxically, despite the reduction in soluble TNF alpha levels, the production of IL-1 beta, IL-6, and IL-8, cytokines whose production was previously demonstrated to be inhibited by the addition of a neutralizing anti-TNF alpha antibody were not down-regulated by BE-2275. These results raise the interesting possibility that a close relationship exists between the enzyme(s) which process membrane-bound TNF alpha, and those involved in surface TNF-R cleavage, Furthermore our observations suggest that hydroxamate inhibitors of MMP activity which block TNF alpha secretion and TNF-R cleavage may not modulate down-stream effects of TNF alpha, and as such suggest that the precise specificity of these compounds will be highly relevant to their clinical efficacy in inflammatory diseases.