TNF alpha processing enzyme inhibitors prevent aspirin-induced TNF alpha release and protect against gastric mucosal injury in rats.

Background: Although previous studies indicate that prevention of tumour necrosis factor alpha (TNF alpha) release protects against NSAID-induced gastric mucosal injury, intracellular pathways by which aspirin causes TNF alpha release are unknown, TNF alpha is synthesized as a precursor which is proteolytically cleaved by a specific converting enzyme, TACE, to release the mature cytokine. TACE inhibitors prevent TNF alpha release and protect against TNF alpha-mediated disease, Aim: To investigate: (i) molecular events that regulate TNF alpha secretion in response to aspirin in vivo and in vitro; (ii) whether TNF alpha secretion inhibitors prevent aspirin-induced TNF alpha release and protect against gastric mucosal damage; and (iii) whether TNF alpha exerts a direct cytotoxic effect on gastric epithelial cells. Methods: In vitro studies were carried out on mouse macrophages and rat gastric mucosal cells, Gastric mucosal damage was induced in rats by oral administration of 300 mg/kg aspirin. TNF alpha cytotoxicity on gastric mucosal cells was examined by treating rats with lipopolysaccharide to release TNF alpha or by incubating dispersed gastric mucosal cells with increasing concentrations of TNF alpha. Results: Aspirin increases intracellular calcium (Ca2+) levels and causes a time and concentration dependent increase in macrophage TNF alpha mRNA accumulation and cytokine release. Agents that cause Ca2+ mobilization with a receptor-independent mechanism, such as ionomycin and thapsigargin, stimulate TNFa release. Incubating the macrophages in a Ca2+ free medium inhibited TNF alpha secretion, Agents that prevent TNF alpha mRNA transcription, e.g, lisophylline, PGE(2), interleukin-10 and 8-BrcAMP, or TACE inhibitors, e.g. EDTA, TAPI-2 and BB-3103, inhibit TNF alpha release and protect rats against gastric mucosal injury induced by oral administration of aspirin, TNF alpha exerts a direct cytotoxic effect on gastric epithelial cells as demonstrated by the reduced viability observed in gastric mucosal cells prepared from rats treated with lipopolysaccharide, or directly incubated with increasing concentrations of TNF alpha, Conclusions: (i) Aspirin directly stimulates TNF alpha gene transcription; (ii) TACE inhibitors protect against aspirin-induced gastric mucosal injury; and (iii) TNF alpha exerts a direct cytotoxic effect on gastric epithelial cells.