Radioimmunoassay of LTB4 and 6-trans LTB4: analytical and pharmacological characterisation of immunoreactive LTB4 in ionophore stimulated human blood.

A sensitive RIA for LTB4 (which cross-reacts 60% with 6-trans LTB4) has been developed with a minimal detectable mass of 7.4 X 10(-15) mole. The properties of a second RIA more specific for 6-trans LTB4 are also described. The latter has utility in the measurement of the enzymatic and non-enzymatic transformations of LTA4 and in the characterisation of inhibitors of LTA4 epoxide hydrolase. Conditions for the direct RIA of immunoreactive LTB4 in human plasma are described. Addition of calcium ionophore, A23187, to human blood increased basal immunoreactive LTB4 levels from less than 100pg ml-1 to 259 +/- 23ng ml-1 (mean +/- SEM, n = 16). Extraction and RPHPLC confirmed that greater than 90% of immunoreactive LTB4 co-eluted with synthetic and [3H]LTB4. Pharmacological characterisation of immunoreactive eicosanoids revealed that in vitro the NSAIDs: aspirin, indomethacin, flurbiprofen and benoxaprofen did not inhibit LTB4 but inhibited TXB2, consistent with cyclo-oxygenase inhibition whereas the prototype mixed inhibitor BW755c inhibited both LTB4 and TXB2. This experimental paradigm may be used in the clinical measurement of the bio-availability of novel agents that inhibit eicosanoid biosynthesis.