Specific binding of 15 HETE to lymphocytes. Effects on the fluidity of plasmatic membranes

Trans-10,cis-12-conjugated linoleic acid increases phagocytosis of porcine peripheral blood polymorphonuclear cellsin vitro

Trans-10,cis-12-conjugated linoleic acid (t10c12-CLA) has been shown to alter immune function. PPARγ has been shown to potentially play an important role in regulating inflammatory and immune responses by modulating the activity of monocytes and macrophages. Previous studies have indicated that the phagocytic capacity of porcine peripheral blood polymorphonuclear cells (PMN) was enhanced by the culture supernatant fraction from t10c12-CLA-stimulated porcine peripheral blood mononuclear cells (PBMC) but not by t10c12-CLA itself. In the present study, we examined the effects of t10c12-CLA on PPARγ and TNF-α expression of porcine PBMC and the phagocytic capacity of PMN. t10c12-CLA increased TNF-α mRNA expression and production by PBMC. The phagocytic capacity of porcine PMN was enhanced by either culture supernatant fraction from PBMC treated with t10c12-CLA or recombinant porcine (rp) TNF-α. Anti-rpTNF-α polyclonal antibody inhibited the enhancement of PMN phagocytic capacity. t10c12-CLA also up regulated PPARγ mRNA expression in porcine PBMC. Bisphenol A diglycidyl ether, a PPARγ antagonist, not only completely negated the t10c12-CLA-stimulating effects on TNF-α expression and production by porcine PBMC, but also decreased the enhancement of PMN phagocytic capacity by the t10c12-CLA-stimulated porcine PBMC culture supernatant fraction. These results suggest that t10c12-CLA has an immunostimulating effect on porcine PMN phagocytic capacity, which is mediated by TNF-α from PBMC via a PPARγ-dependent pathway.

Dietary conjugated linoleic acid modulates phenotype and effector functions of porcine CD8(+) lymphocytes

In vivo vaccination and challenge studies have demonstrated that CD8(+) lymphocytes are essential for the development of cell-mediated protection against intracellular pathogens and neoplastic cells. Depletion of peripheral blood CD8(+) cells interferes with clearance of viruses and intracellular fungi, induction of delayed type hypersensitivity responses and antitumoral activity. In contrast to humans or mice, porcine peripheral CD8(+) lymphocytes are characterized by a heterogeneous expression pattern (i.e., CD8alphabeta and CD8alphaalpha) that facilitates the study of distinctive traits among minor CD8(+) cell subsets. A factorial (2 x 2) arrangement within a split-plot design, with 16 blocks of two littermate pigs as the experimental units for immunization treatment (i.e., unvaccinated or vaccinated with a proteinase-digested Brachyspira hyodysenteriae bacterin) and pig within block as the experimental unit for dietary treatment (soybean oil or conjugated linoleic acid) were used to investigate the phenotypic and functional regulation of CD8(+) cells by dietary conjugated linoleic acid (CLA). Dietary CLA supplementation induced in vivo expansion of porcine CD8(+) cells involving T-cell receptor (TCR)gammadeltaCD8alphaalpha T lymphocytes, CD3(-)CD16(+)CD8alphaalpha (a porcine natural killer cell subset), TCRalphabetaCD8alphabeta T lymphocytes and enhanced specific CD8(+)-mediated effector functions (e.g., granzyme activity). Expansion of peripheral blood TCRalphabetaCD8alphabeta cells was positively correlated (r = 0.89, P < 0.01) with increased percentages of CD8alphabeta(+) thymocytes. Functionally, CLA enhanced the cytotoxic potential of peripheral blood lymphocytes and proliferation of TCRgammadeltaCD8alphaalpha cells. Collectively, these results indicate that dietary CLA enhances cellular immunity by modulating phenotype and effector functions of CD8(+) cells involved in both adaptive and innate immunity.

Phospholipase A(2)s and lipid peroxidation

Lipid peroxidation of membrane phospholipids can proceed both enzymatically via the mammalian 15-lipoxygenase-1 or the NADPH-cytochrome P-450 reductase system and non-enzymatically. In some cells, such as reticulocytes, this process is biologically programmed, whereas in the majority of biological systems lipid peroxidation is a deleterious process that has to be repaired via a deacylation-reacylation cycle of phospholipid metabolism. Several reports in the literature pinpoint a stimulation by lipid peroxidation of the activity of secretory phospholipase A(2)s (mainly pancreatic and snake venom enzymes) which was originally interpreted as a repair function. However, recent experiments from our laboratory have demonstrated that in mixtures of lipoxygenated and native phospholipids the former are not preferably cleaved by either secretory or cytosolic phospholipase A(2)s. We propose that the platelet activating factor (PAF) acetylhydrolases of type II, which cleave preferentially peroxidised or lipoxygenated phospholipids, are competent for the phospholipid repair, irrespective of their role in PAF metabolism. A corresponding role of Ca(2+)-independent phospholipase A(2), which has been proposed to be involved in phospholipid remodelling in biomembranes, has not been addressed so far. Direct and indirect 15-lipoxygenation of phospholipids in biomembranes modulates cell signalling by several ways. The stimulation of phospholipase A(2)-mediated arachidonic acid release may constitute an alternative route of the arachidonic acid cascade. Thus, 15-lipoxygenase-mediated oxygenation of membrane phospholipids and its interaction with phospholipase A(2)s may play a crucial role in the pathogenesis of diseases, such as bronchial asthma and atherosclerosis.

Dual metabolic pathways of 12-HETE in rat aortic smooth muscle cells

12(S)-HETE, a major lipoxygenase-derived compound from arachidonic acid is incorporated and metabolized by vascular smooth muscle cells via beta-oxidation. We have now identified for the first time in this cell type 12(S)-HETE metabolites formed by a combination of reductase and oxidation pathways. HPLC and GC-MS analysis of time-course experiments allow us to characterize two different metabolic pathways: a direct peroxisomal beta-oxidation of 12(S)-HETE leading to the formation of 16:3 (8-OH) which accumulates first and a reduction of one of the conjugated double bonds of 12(S)-HETE giving the dihydro-intermediate 20:3(12-OH) that transiently accumulates before being converted itself by peroxisomal beta-oxidation to 16:2(8-OH). Taken together these results may suggest that the transient accumulation of 20:3(12-OH) through transcellular metabolism of 12(S)-HETE may represent a part of the modulatory effect of 12(S)-HETE on vascular function.

Bioactions of 5-hydroxyicosatetraenoate and its interaction with platelet-activating factor

In a variety of stimulated cells, platelet-activating factor (PAF) and numerous arachidonate derivatives are co-products that form as a consequence of receptor-mediated phospholipid mobilization. These lipid co-products produce a plethora of biological effects in a wide variety of cell systems. Furthermore, they often have a fascinating although less widely appreciated, interaction. 5-HETE, at submicromolar concentrations, exerts relatively few direct bioactions. It does, however, potently (16-160 nM) raise cytosolic free calcium [Ca2+]i and augment PAF-induced responses in human polymorphonuclear neutrophils (PMN) by as much as 100- to 1000-fold. 5-HETE acts on PMN by a structurally specific, stereospecific and pertussis toxin-inhibitable mechanism. In addition, PMN exposed to 5-HETE exhibit homologous but not heterologous desensitization. These findings suggest that 5-HETE, like PAF, may bind to its own specific plasmalemmal receptors to exert its unique set of bioactions. However, further investigation is required to demonstrate any putative 5-HETE receptors. Other potential mechanisms of 5-HETE-induced bioactions together with the possible effects of 5-HETE on PAF transduction mechanisms are also discussed.

Effect of arachidonic acid metabolites on thymocyte proliferation

The influences of prostaglandin E2 (PGE2), 15-hydroxyeicosatetraenoic acid (15-HETE) and leukotrienes (LT) on the proliferative response of mature (PNA-) and immature (PNA+) mouse thymocytes was investigated. Both PNA+ and PNA- thymocytes proliferated when cultured with concanavalin A plus interleukin-2. PGE2 in concentrations of 10(-6) to 10(-9) M caused significant inhibition of proliferation of both PNA+ and PNA- thymocytes in these cultures. In contrast, the lipoxygenase products 15-HETE, LTB4, LTC4 and LTD4 caused marked increases in proliferation of PNA+ thymocytes while having no effect on PNA- cells. Therefore, the effect of leukotrienes on thymocyte proliferation depends upon the level of cell maturation and mainly affects immature PNA+ thymocytes.

Evidence for specific binding of 15 hydroxyeicosatetraenoic acid to pituitary rat cells

Specific receptors for [3H]-15 HETE have been identified on GH3 cells, a cloned strain of rat pituitary cells. With incremental inputs of radioligand and a constant cell number, specific [3H]-15 HETE binding reached a plateau indicative of saturable binding sites. Ligand analysis of the Scatchard plot demonstrated a single class of high affinity binding sites with a dissociation constant (Kd) of 0.75 nM. 12 HETE competed with radiolabeled 15 HETE (IC50 = 1 x 10(-6) +/- 0.8 M). In contrast, arachidonic acid, leukotriene B4, prostaglandins E2 and F2 alpha did not compete with [3H]-15 HETE.

15-HETE "modulates" expression of C3b receptor (CR1) antigen on peripheral blood B-lymphocytes

We have studied the effect of the lipoxygenase metabolite, 15-HETE, on the expression of the human C3b receptor (CR1) by a B-lymphocyte enriched population of human peripheral blood leukocytes. The number of CR1 antigenic sites expressed by B-lymphocytes isolated from HLA typed donors was determined by equilibrium binding studies using an 125 I-labelled mouse monoclonal anti CR1 antibody before and after 16 hrs incubation in RPMI alone or containing 10(-6)M, 10(-7)M or 10(-8)M final concentration of 15-HETE. In B44- subjects CR1 expression on B cells increased 63% after incubation in RPMI alone. This increase was inhibited in the presence of 10(-6)M and 10(-7)M 15-HETE (23% and 30% increase respectively). In contrast, B44+ individuals showed a smaller increase in CR1 numbers when incubated in RPMI alone. In the presence of 15-HETE CR1 antigenic sites continued to increase. When B44+ subjects were classified as A29+ or A29-, donors that were A29+ B44+ accounted for the augmentation observed while A29- B44+ individuals did not differ from individuals that were A29- B44-.

Structural requirements in hydroxyeicosanoids for the activation of the 5-lipoxygenase in PT-18 mast/basophil cells

We have previously reported that 15-hydroxyeicosatetraenoic acid (15-HETE) stimulated the 5-lipoxygenase in the murine PT-18 mast/basophil cell line to produce leukotriene B4 and 5-HETE from exogenously added arachidonic acid. In order to determine the structural requirements in the HETE molecule that are necessary for the activation of this 5-lipoxygenase, various isomeric HETEs, derivatives and analogs were prepared, purified and tested. The order of stimulatory potencies was: 15-HETE acetate greater than 15-HETE = 15-hydroperoxyeicosatetraenoic acid (15-HPETE) greater than 5-HPETE = 12-HPETE greater than 5-HETE. 15-HETE methyl ester, 12-HETE and prostaglandin E2 were ineffective over the concentration range tested. Several diHETEs were also tested. 5S,15S-DiHETE was somewhat less potent than 15-HETE, whereas both 8S,15S-diHETE and leukotriene B4 were inactive. The calcium ionophore A23187 was much less effective than 15-HETE. These structure-activity studies indicate the importance of the nature, position and location of the various functional groups in the HETE molecule and suggest that a specific recognition site is involved in the activation of the 5-lipoxygenase in PT-18 cells.