Interference of arachidonic acid and its metabolites with TNF-alpha release by ochratoxin A from rat liver

We investigated the role of arachidonic acid and its metabolites on the ochratoxin A (OTA) provoked release of proinflammatory and apoptotic cytokine TNF-alpha from blood-free perfused rat liver. OTA induced TNF-alpha release dose- and time-dependently yielding 2600 pg TNF-alpha/ml at 2.5 micromol/l after 90 min without significant release of LDH and lactate. Aristolochic acid, 50 micromol/l, a phospholipase A2 inhibitor, and 10 micromol/l of exogenous arachidonic acid decreased TNF-alpha below normal level. Indomethacin, 10 micromol/l, a potent inhibitor of the cyclooxygenase (COX) pathway, almost doubled TNF-alpha concentrations in the perfusion solution to reach 5500 pg/ml at 90 min. On the other hand, inhibition of lipoxgenase (LPX) by 30 micromol/l nordihydroguaiaretic acid (NDGA) and the cytochrome P-450 (CYP) pathway by 100 micromol/l of metyrapone decreased TNF-alpha below normal levels as well. Concurrent administration of two blockers (COX inhibitor with LPX inhibitor, or COX inhibitor with CYP-450 inhibitor, or LPX inhibitor with CYP-450 inhibitor) blocked TNF-alpha release below normal levels. In addition, 10 micromol/l caffeic acid phenylethyl ester, a NF-(kappa)B inhibitor, blocked OTA mediated TNF-alpha release. In conclusion, arachidonic acid and its cyclooxygenase metabolites are suppressors of OTA mediated TNF-alpha release from liver, whereas LPX and CYP-450-metabolites have the opposite effect. OTA-induced TNF-alpha release is likely to occur via the NF-(kappa)B transcription factor pathway in perfused rat liver.