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 cross-linking surface p55 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 metallo-proteinase activity (MMP), BB-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 approximately 15-fold in the presence of BB-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 neutralizing anti-TNF alpha antibody were not down-regulated by BB-2275. These results raise the interesting possibility that a close relationship exits 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 TNA alpha, and as such suggest that the precise specificity of these compounds will be highly relevant to their clinical efficacy in inflammatory diseases.
Williams
L M
LM
Mathilda and Terence Kennedy Institute of Rheumatology, Sunley Division, Hammersmith, London, United Kingdom.
Gibbons
D L
DL
Gearing
A
A
Maini
R N
RN
Feldmann
M
M
Brennan
F M
FM
D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors*; D011480:Protease Inhibitors / Q000494:pharmacology*; D018124:Receptors, Tumor Necrosis Factor / Q000037:antagonists & inhibitors*; D012208:Rhabdomyosarcoma / Q000473:pathology; D013583:Synovial Membrane / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors* / Q000494:pharmacology
C088671:BB 2275; D006877:Hydroxamic Acids; D011480:Protease Inhibitors; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D008666:Metalloendopeptidases