Differential induction of eicosanoid synthesis in monocytic cells treated with retinoic acid and 1,25-dihydroxy-vitamin D3

Cyclooxygenase-1, but not -2, is upregulated in NB4 leukemic cells and human primary promyelocytic blasts during differentiation

Cyclooxygenase (COX)-1 or -2 and specific prostaglandin (PG) synthases catalyze the formation of various PGs. We investigated the expression and activity of COX-1 and -2 during granulocyte-oriented maturation induced by all-trans-retinoic acid (ATRA) of NB4 cells, originated from a human acute promyelocytic leukemia (APL), and in blasts from APL patients. The expression of COX isoenzymes or prostaglandin synthases was also investigated in circulating granulocytes and human bone marrow. COX-1 was expressed and enzymatically active in NB4 cells and primary blasts. COX-1 mRNA and protein were induced by ATRA. COX-1 protein increased approximately 2-3.5-fold by culture day 3 in NB4 cells and primary blasts, while basal COX-2 expression was very low and unaffected by ATRA. COX-1-dependent PGE(2) biosynthesis increased during differentiation approx. 5-fold. Indomethacin and the selective COX-1 inhibitor SC-560, but not selective COX-2 inhibition, impaired NB4 differentiation, reducing NADPH-oxidase activity, CD11b and CD11c expression. The immunohistochemistry of granulocytes and myeloid precursors in the bone marrow showed a large prevalence of COX-1 as compared to COX-2. In conclusion, COX-1 is induced during ATRA-dependent maturation and appears to contribute to myeloid differentiation both in vitro and ex vivo, and COX-1 activity may potentiate the differentiation of human APL.Leukemia (2004) 18, 1373-1379. doi:10.1038/sj.leu.2403407 Published online 10 June 2004

Cyclooxygenase expression is elevated in retinoic acid-differentiated U937 cells

Cyclooxygenase (COX) is the rate-limiting enzyme for the biosynthesis of prostaglandins in monocytes/macrophages. The COX-1 is constitutively expressed in most tissues and may be involved in cellular homeostasis, whereas the COX-2 is an inducible enzyme that may play an important role in inflammation and mitogenesis. When U937 monocytic cells were incubated with retinoic acid (RA) for 48 h, cell differentiation took place with concomitant increases in prostaglandin E2 (PGE2) production and COX activity. In this study, the mechanism of RA (all-trans- or 9-cis-RA)-induced enhancement of PGE2 biosynthesis in U937 cells was examined. Treatment of cells with all-trans- or 9-cis-RA up to 48 h caused an increase in PGE2 production in a time- and dose-dependent manner. Both RA isomers caused the enhancement of PGE2 production and the up-regulation of COX-1 expression at the protein and mRNA levels. The increase in COX-1 mRNA was found to precede the increase in COX-1 protein expression. Interestingly, the COX-2 protein and COX-2 mRNA were not detected in U937 cells, and their levels remained undetectable during the entire course of RA treatment. We conclude that treatment of U937 cells by RA for 48 h caused the initiation of cell differentiation, which was found to be concomitant with a significant increase in PGE2 production mediated via the up-regulation of COX-1 mRNA and protein expression.

Retinoic acid and lipopolysaccharide act synergistically to increase prostanoid concentrations in rats in vivo

Vitamin A and its active metabolite retinoic acid (RA) modulate host-pathogen interactions by interfering with the host immune and inflammatory response including prostaglandin (PG) biosynthesis. The effects of RA on phospholipase A(2) (PLA(2)) and cyclooxygenase (COX) isoforms in vitro are controversial, and few in vivo studies exist. We investigated the in vivo effects of RA on PG biosynthesis in the presence or absence of lipopolysaccharide (LPS) in rats. RA alone [10 mg/(kg. d) for 5 d] increased plasma and liver PG concentrations by increasing COX-1 protein expression (twofold that of control rats). RA acted synergistically with LPS to increase plasma (400-fold) and liver (15-fold) concentrations of prostaglandin E(2) (PGE(2)) and significantly, but to a lesser extent, other PG compared with RA rats, in the absence of major differences in PLA(2) expression or activity or COX-1 and COX-2 mRNA or protein expression. The RA + LPS-mediated increase in PGE(2) was significantly attenuated (97%) by aminoguanidine (AG), a relatively specific inhibitor of the inducible nitric oxide synthase (NOS2), consistent with the previously reported synergistic effect of RA and LPS on NOS2 expression and activity. In addition, RA and LPS induced the expression of the microsomal isoform of PGE synthase (mPGES). In conclusion, in vivo, RA and LPS increased PG and especially PGE(2) concentrations. The PGE(2) increase was associated with NOS2-mediated activation of COX and induction of mPGES. These results contribute to the characterization of the effects of vitamin A on the host inflammatory response.

Lack of direct connection between arachidonic acid release and prostanoid synthesis upon differentiation of U937 cell

The changes in AA incorporation and release as well as prostanoid synthesis upon differentiation of human premonocytic cell line, U937, induced by three functionally diverse agents--phorbol ester (TPA), dimethyl sulfoxide (DMSO), and retinoic acid (RA) have been investigated. The rate of AA incorporation into the cells remained unchanged whereas a 3- to 6-fold increase in AA release upon stimulation with Ca(2+)-ionophore A23187 as compared to undifferentiated cells was observed. While undifferentiated cells were incapable to metabolise AA via the cyclooxygenase pathway all three types of differentiated U937 cells produced TxB2 and PGE2. Only TPA-differentiated cells responded with a 6-fold increase of prostanoid synthesis after A23187 stimulation, whereas in DMSO-differentiated cells prostanoid synthesis was slightly stimulated by A23187 and in RA-differentiated cells it was not stimulated at all. Thus, agonist-induced prostanoid synthesis in differentiated cells is dependent on the nature of differentiating agent and does not correlate with AA liberation.

Activated lymphocytes increase expression of 5-lipoxygenase and its activating protein in THP-1 cells

The aim of this study was to investigate the regulation of the 5-lipoxygenase pathway of arachidonic acid metabolism by lymphocytes using the monocyte-like cell line, THP-1. When THP-1 cells were incubated over 4-7 days in 10% supernatant from lectin-activated human lymphocytes, their capacity to synthesize 5-lipoxygenase products was significantly increased. In contrast, the supernatant from nonactivated lymphocytes had no effect. The increase in capacity to synthesize 5-lipoxygenase products was mimicked by the addition of either granulocyte macrophage colony-stimulating factor (GM-CSF) or interleukin-3. These increases in synthetic capacity reflected increased enzymatic activity. Increased immunoreactive protein and mRNA for the enzymes 5-lipoxygenase and 5-lipoxygenase-activating protein were also found in cells conditioned with activated lymphocyte supernatants. Furthermore, the increase in mRNA for both enzymes was not blocked by cycloheximide, suggesting that the effect on steady-state mRNA levels does not require the synthesis of new protein. The increase in mRNA could be reproduced by GM-CSF. We conclude that lymphocytes can regulate the expression of 5-lipoxygenase in THP-1 cells over a period of days via the release of soluble factors.

1,25-Dihydroxyvitamin D3 Induces NAD(+)-Dependent 15-Hydroxyprostaglandin Dehydrogenase in Human Neonatal Monocytes

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3 ] induces the differentiation of monocytes into macrophage-like cells in vitro. To identify the genes expressed during this process, we performed differential display polymerase chain reaction on RNA extracted from cord blood monocytes (CBMs) treated with 1,25-(OH)2D3 . Treated CBMs expressed type-I 15-hydroxyprostaglandin dehydrogenase (type-I 15-PGDH), the key enzyme of prostaglandin E2 (PGE2 ) catabolism and a 15-PGDH–related mRNA (15-PGDHr). This newly described 15-PGDH–related mRNA was constitutively expressed in adult monocytes. 15-PGDH gene(s) transcription was accompanied by the appearance of the 15-PGDH activity in treated CBMs. In addition, the cyclooxygenase 2 mRNA level was decreased and PGE2 levels in the culture mediums were lowered (50%). Our results stress that 1,25-(OH)2D3 , at least in neonatal monocytes, can exert, directly or indirectly, a dual control on key enzymes of PGE2 metabolism. In conclusion, we suggest that modifications in prostaglandin metabolism, induced by the expression of type-I 15-PGDH and the downregulation of cyclooxygenase 2, could be involved in monocytic differentiation.

Intrinsic cyclooxygenase activity is not required for monocytic differentiation of U937 cells

Metabolism of arachidonic acid has been found to modulate cell growth and differentiation. Since differentiation of premonocytic U937 cells is paralleled by increase expression of cyclooxygenase and prostanoid synthesis, we assessed the role of cyclooxygenase in the differentiation of U937 cells. Treatment with retinoic acid (RA, 1 microM) or 1,250(OH)2-vitamin D3 (1,25-D3, 10 nM) increased the expression of the monocytic surface antigens CD11b plus CD11c, and CD11b, CD11c, CD14 plus CD18, respectively. Addition of the cyclooxygenase inhibitors indomethacin (10 microM) or piroxicam (20 microM) slightly increased expression of CD11b and CD18 in cells differentiated with RA, but did not alter expression of surface antigens in cells treated with 1,25-D3. Stimulus-dependent rises in the cytosolic-free calcium concentrations remained unchanged by the inhibitors, as was superoxide anion generation in cells stimulated with phorbol myristate acetate. Effective inhibition of cyclooxygenase over the 72 h of differentiation was proven by the marked decrease in A23187-stimulated prostanoid formation in differentiated cells. To assess whether prostaglandins negatively control monocytic differentiation, as suggested by the stimulatory effects of cyclooxygenase inhibitors on CD11b/CD18 expression in RA-treated cells, prostaglandin E2 (PGE2; 100 nM) was added to the differentiation with RA or 1,25-D3. However, the addition of PGE2 increased expression of CD11b and CD11b plus CD14, as well as superoxide anion generation. These data indicate that intrinsic cyclooxygenase activity is not required for monocytic differentiation of U937 cells. In addition, basal prostanoid secretion does not measurably contribute to monocytic differentiation.

Nutrition and the immune system: a review of nutrient-nutrient interactions

Although research on the role of single nutrients in immune function is extensive, this is not the case for multiple nutrients and subsequent nutrient-nutrient interactions. After presenting a brief overview of immune function, the authors consider reports that examine imbalance of more than one nutrient and interactive effects on immunocompetence. Availability of one nutrient may impair or enhance the action of another in the immune system, as reported for nutrients such as vitamin E and selenium, vitamin E and vitamin A, zinc and copper, and dietary fatty acids and vitamin A. Nutrient-nutrient interactions may negatively affect immune function. For example, excess calcium interferes with leukocyte function by displacing magnesium ions, thereby reducing cell adhesion. Because of consumer interest in supplementation to improve immune function, the potential for harm exists. Research is needed to improve knowledge in this area so that recommendations can be made with more confidence.

Differential effects of n-6 and n-3 polyunsaturated fatty acids on cell growth and early gene expression in Swiss 3T3 fibroblasts

Dietary n-3 polyunsaturated fatty acids (PUFAs) have been found to reduce accelerated cell growth. To study the underlying molecular mechanisms, we evaluated the effects of the n-3 PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) compared with the n-6 PUFA arachidonic acid (AA) on cell growth and early gene mRNA accumulation in Swiss 3T3 fibroblasts. AA significantly increased cell numbers and incorporation of [3H]-thymidine compared with cells treated with EPA and DHA, which did not stimulate cell growth. In contrast to AA and parallel to its effect on cell growth, EPA and DHA did not lead to a pronounced increase in Egr-1 and c-fosmRNA levels. When they were incubated together with AA, both DHA and EPA reduced AA-induced Egr-1 and c-fosmRNA accumulation and incorporation of [3H]-thymidine. We have recently shown that AA strongly increases Egr-1 and c-fosmRNA accumulation 3T3 fibroblasts through its metabolism to prostaglandin E2 (PGE2) and its subsequent activation of protein kinase C (Danesch et al., 1994, J. Biol. Chem., 269:27258-27263). Consistent with the notion that increased PGE2 formation is required for the AA-induced early gene mRNA accumulation, EPA and DHA reduced PGE2 formation from exogenous [14C]-AA by more than 60%, but they did not decrease mRNA levels following stimulation with PGE2. We suggest that, in 3T3 fibroblasts, EPA and DHA antagonize AA-induced early gene mRNA accumulation and cell growth by reducing PGE2 formation.

Linoleic acid esterified in low density lipoprotein serves as substrate for increased arachidonic acid synthesis in differentiating monocytic cells

The cellular metabolism of albumin- and lipoprotein-bound 18:2(n - 6) during monocytic differentiation was examined in the human premonocytic U937 and Mono Mac 6 cells. Differentiation for 72 h of U937 cells with retinoic acid (RA, 1 microM) or 1,25-(OH)2-vitamin D3 (1,25-D3, 10 nM) and of Mono Mac 6 cells with RA (1 microM) or lipopolysaccharide (LPS, 10 ng/ml) increased the desaturation and elongation of [1-14C]18:2(n - 6) to [1-14C]20:4(n - 6). In undifferentiated U937 and Mono Mac 6 cells, incubations with human LDL (100 micrograms/ml, 18 h) resulted in a 2.5-fold increase in 18:2(n - 6) levels in the cellular phospholipids. Differentiation of U937 cells with RA or or of Mono Mac 6 cells with LPS prior to LDL addition. Significantly reduced 18:2(n - 6) and elevated 20:4(n - 6) levels in cellular phospholipids. This increase in 20:4(n - 6) was likely not due to an increased incorporation of preformed 20:4(n - 6) esterified in LDL, as the receptor-specific degradation of [125I]LDL was reduced in both the RA-treated U937 and LPS-treated Mono Mac 6 cells. In U937 cells incubated with [1-14C]18:2(n - 6), the synthesis of TXB2, PGE2 and HHT could be detected after differentiation with RA. suggesting the availability of [1-14C]20:4(n - 6), derived from [1-14C]18:2(n - 6), for cyclooxygenase metabolism. Our results show that the conversion of 18:2(n - 6) to 20:4(n - 6) increases during monocyte differentiation. The 18:2(n - 6) supplied to the cells via the receptor-mediated uptake of LDL was utilized as substrate for the increased 20:4(n - 6) synthesis.

Effects of different polyunsaturated fatty acids on growth-related early gene expression and cell growth

Effects of polyunsaturated fatty acids on expression of early-response genes c-fos and Egr-1 and induction of cell growth were assessed in Swiss 3T3 fibroblasts. Stimulation with arachidonic acid increased mRNA levels of c-fos and Egr-1. This effect was inhibited by preincubation with cyclooxygenase inhibitors and restored by addition of prostaglandin E2 (PGE2), the predominant eicosanoid produced in Swiss 3T3 fibroblasts. Further signaling of PGE2, was mediated by a protein kinase C-dependent pathway, since downregulation, or inhibition, of protein kinase C reduced increases in mRNA levels. Parallel to the stimulatory effects on mRNA levels, AA and PGE2 also increased cell growth, as determined by uptake of [3H]-thymidine. In contrast to arachidonic acid, n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) did not increase c-fos and Egr-1 mRNA levels or cell growth. Furthermore, preliminary data indicate that EPA and DHA even reduce the stimulatory effect of AA, which is associated with reduced formation of PGE2. In conclusion, our data indicate that AA increases expression of growth-related early genes c-fos and Egr-1 Swiss 3T3 fibroblasts by its conversion to PGE2 and subsequent activation of protein kinase C, whereas n-3 fatty acids do not activate this signaling cascade.

Lovastatin induces differentiation of Mono Mac 6 cells

The proliferation of human monocytic Mono Mac 6 cells was significantly retarded by treatment with lovastatin (LOV, 10 microM) for 72 h. Treatment of Mono Mac 6 cells with LOV increased surface protein expression of monocyte-associated CD14 and the integrin-chain CD11b towards levels found in isolated human blood monocytes. These effects were dose-dependent and completely reversed by the isoprenoid precursor mevalonate (MVA). LOV failed to induce growth retardation and upregulation of CD11b or CD14 in the less mature premonocytic U937 cell line. While CD11b expression was comparable in Mono Mac 6 cells treated with LOV (10 microM), TNF (100 U ml-1) or LPS (10 ng ml-1), upregulation of CD14 by LOV was less pronounced. Basal CD23 expression was unaffected by LOV but markedly reduced by treatment with TNF or LPS. Moreover, LOV enhanced Mono Mac 6 adhesiveness to human umbilical vein endothelial cells to levels found in isolated human blood monocytes, probably due to the increased CD11b and CD14 expression. In conclusion, LOV can induce differentiation of monocytic cells which is reflected by the retardation of growth, expression of CD14 and CD11b, and enhanced adhesiveness.

Differential effects of polyunsaturated fatty acids on cell growth and differentiation of premonocytic U937 cells

The effect of long chain polyunsaturated fatty acids (PUFA) on cell growth and differentiation was assessed in human premonocytic U937 cells. Addition of either 10 microM arachidonic acid (AA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3) or docosahexaenoic acid (DHA, 22:6n-3) resulted in the rapid incorporation of these fatty acids into cellular phospholipids. Their uptake was greatest in the first 2 h. AA and EPA reached steady-state levels after 8 h, while levels of DHA increased steadily over 72 h. In parallel, fatty acid metabolites derived from AA and EPA, 22:4n-6, 22:5n-6 and 22:5n-3, 22:6n-3, respectively, increased continuously indicating an active fatty acid elongation and desaturation. The effects of PUFA on monocytic differentiation were examined in cells which had been enriched with AA, EPA or DHA for 8 h and subsequently treated with retinoic acid (RA), 1,25-(OH)2-vitamin D3 (1,25-D3), interferon-gamma (IFN-gamma) or their combinations for 72 h. Growth of differentiating or non-differentiating U937 cells was not affected by enrichment with PUFA. However, in cells differentiated with 1,25-D3 plus IFN-gamma, prior enrichment with all three PUFA slightly but significantly (P < 0.05) increased the expression of the monocytic surface antigens CD11b and CD14 and generation of superoxide anion. The data indicate that although n-6 and n-3 PUFA are rapidly incorporated into phospholipids, they do not affect cell growth. However, enrichment with PUFA increases monocytic differentiation of U937 cells when induced most effectively with 1,25-D3 plus IFN-gamma.