DIFFERENTIAL INDUCTION OF EICOSANOID SYNTHESIS IN MONOCYTIC CELLS TREATED WITH RETINOIC ACID AND 1,25-DIHYDROXY-VITAMIN-D3

Synthesis and release of eicosanoids is characteristic to mature monoc ytes, while in undifferentiated premonocytic cells arachidonic acid (A A) metabolism is barely detectable. Since some vitamins and cytokines induce differentiation of these cells to a more monocyte-like cell typ e, we evaluated the effect of retinoic acid (RA), 1,25(OH)2-vitamin D3 (1,25-D3) and interferon-gamma (IFN-gamma) on AA metabolism in the hu man premonocytic cell lines U937 and THP-1. In U937 cells, differentia tion with RA (1 muM) followed by stimulation with the calcium ionophor e A23187 (10 muM) or platelet activating factor (PAF, 100 nM) signific antly increased synthesis of immunoreactive 6-keto PGF1alpha, TxB2 and PGE2 5- to 6-fold. Analysis of AA metabolism in RA-differentiated cel ls prelabelled with [H-3]-AA revealed the formation of additional radi oactive compounds which coeluted with standards for PGF2alpha, PGD2 an d 12-hydroxyheptadecatrienoic acid (HHT). The structural identity of 6 -keto PGF1alpha, TxB2, PGE2 and HHT was confirmed by gas chromatograph y-mass spectrometry (GC-MS). In parallel, RA induced the expression of the monocytic surface antigen CD11b, but not CD14. Differentiation wi th 1,25-D3 (10 nM) only marginally increased stimulated eicosanoid for mation, while it more effectively induced expression of CD11b and CD14 . Pretreatment with IFN-gamma (100 IU/ml) slightly increased stimulus- dependent AA metabolism, but did not induce expression of CD11b or CD1 4. Induction of eicosanoid synthesis by RA was further confirmed in TH P-1 cells. These data indicate that RA most effectively induced cycloo xygenase activity and stimulus-dependent eicosanoid formation in U937 and THP-1 cells. Furthermore, since expression of monocytic surface an tigens differed between RA and 1,25-D3, it is suggested that induction of cyclooxygenase activity may correlate to differentiation into dist inct monocytic phenotypes.