Journal of lipid mediators最新文献

Immune and inflammatory responses involve a whole array of cells and cell products which interact and mutually regulate each other. Many of these interactions are mediated by cytokines acting through specific receptors. Furthermore, lipid mediators such as PAF and the arachidonic acid metabolites LTB4 and PGE2 are known to affect several of the mechanisms involved in the regulation of the immune and inflammatory responses. In this paper, we review recent data from our laboratory illustrating the differential regulation of IL-6 and TNF alpha production and IL-2 receptor alpha and beta expression by these lipid mediators. We show that the regulation of these genes is both transcriptional and post-transcriptional, and that LT and PG can also be involved as second messengers in these regulatory processes.

We investigated the effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) on the 5-lipoxygenase (5-LO) component of the leukotriene (LT) biosynthetic pathway of human neutrophils, in order to better understand the mechanism whereby the cytokine primes for LT synthesis. We found that GM-CSF increased 5-LO activation elicited by platelet-activating factor (PAF), N-formyl-methionyl-leucyl-phenylalanine (fMLP), C5a, LTB4, IL-8 and calcium ionophore A23187, as determined by using an exogenous substrate. A close correlation was observed between the priming kinetics of GM-CSF on 5-LO activation and on LT synthesis; moreover, the effects of the cytokine on both 5-LO activation and LT synthesis were inhibited when the cells had been exposed to either the protein synthesis inhibitor, cycloheximide (CX), or the transcription inhibitor, actinomycin D (AD), prior to incubation with GM-CSF. These results raise the possibility that the priming by GM-CSF of LT synthesis may involve an effect of the cytokine on 5-LO protein synthesis and gene expression.

Leukotriene (LT) A4 hydrolase (EC 3.3.2.6) is a bifunctional zinc metalloenzyme that possesses both an epoxide hydrolase activity, i.e., the well-known conversion of LTA4 into the proinflammatory substance LTB4, and a recently discovered peptidase activity. We have employed biochemical/kinetic analyses of native enzyme as well as site directed mutagenesis towards a recombinant enzyme to explore structural and functional properties of the enzyme active center. Thus, we have found that the peptidase activity is selectively stimulated by chloride ions, in a manner that suggests the presence of an anion binding site. Furthermore, a number of mutated enzymes have been constructed, expressed in E. coli, and purified to homogeneity to allow enzyme activity determinations and zinc analyses. The catalytic properties and zinc contents of these mutated enzymes establish the three zinc binding ligands of the protein and identify Glu-296 as a catalytic amino acid, directly involved in the peptidase, but not in the epoxide hydrolase reaction. In conclusion, our data provide strong evidence that the two catalytic activities of LTA4 hydrolase are exerted via non-identical but overlapping active sites.

Arachidonate 15-lipoxygenase (15-lipoxygenase) is a lipid-peroxidizing enzyme associated with specific inflammatory cells seen in asthma and atherosclerosis. In atherosclerosis, 15-lipoxygenase is induced in the macrophages of human and rabbit lesions and has been implicated in foam cell formation. In human lung, 15-lipoxygenase is preferentially expressed in airway epithelial cells and eosinophils. Our studies have focused both on the regulation of expression and on the structure-function relationships of the enzyme. To determine factors that could regulate expression, peripheral blood monocytes were purified and cultured with combinations of 18 factors. Only interleukin-4 (60 pM) induced 15-lipoxygenase mRNA, protein and enzymatic activity. Interferon-gamma (100 pM) inhibited the interleukin-4 dependent induction of 15-lipoxygenase. Results with cultured human airway cells were similar. These data suggest that expression of 15-lipoxygenase is regulated by interleukin-4, and that 15-lipoxygenase is a potential downstream effector molecule for this potent cytokine. In parallel studies, we have investigated determinants of positional specificity using site-directed mutagenesis and bacterial expression of human 15-lipoxygenase. Hypotheses for mutagenesis were derived from an analysis of conserved differences among multiple lipoxygenase sequences. Switching four amino acids in 15-lipoxygenase to their counterparts in 12-lipoxygenase resulted in a variant enzyme that produced equal 12- and 15-lipoxygenation. Further analysis has identified two amino acids that completely control the positional specificity of 15-lipoxygenase. These data have led to a preliminary model of the enzyme's active site region.

We investigated the age-related changes of renal cytochrome P450-dependent arachidonic acid metabolism in 3-, 5-, 7-, 9-, 11-, 13- and 20-week-old male Dahl salt-sensitive (DS) and -resistant (DR) rats on a low sodium diet (0.3% NaCl). NADPH-dependent arachidonic acid metabolism was separated and measured by a radio-HPLC system. The formation of 19-hydroxyeicosatetraenoic acid (HETE), 20 HETE, 1,20-dioic acid, epoxyeicosatrienoic acids (EETs), and dihydroxyeicosatrienoic acid (DHET) was age dependent in both DS and DR rats. omega-Hydroxylase (20-HETE and 1,20-dioic acid formation) and (omega-1)-hydroxylase (19-HETE formation) were increased from 3 to 5 weeks age, then decreased with aging in DR rats. Whilst omega/(omega-1)-hydroxylase activities were increased from 3- to 9-week-old rats, they decreased with aging in DS rats. omega/(omega-1)-Hydroxylase activities were higher in 3-5-week-old DR than DS rats. Epoxygenase activities (EETs and DHET formations) were highest in 3-week-old DS and DR rats, and showed no significant differences between two strains of rats at any ages tested. Renal cytochrome P450-dependent arachidonic acid metabolites have a wide and contrasting spectrum of biological and renal effects, and their relative rates of production may influence not only renal hemodynamics but also pro- and antihypertensive mechanisms of hypertension in Dahl rats.