Comparison of Eiscosanoids Production between Rat Polymorphonuclear Leukocytes and Macrophages: Detection by High-performance Liquid Chromatography with Precolumn Fluorescence Labeling

The upstream regulation of p38 mitogen-activated protein kinase phosphorylation by arachidonic acid in rat neutrophils

The signal transduction pathways activated by arachidonic acid that lead to p38 mitogen-activated protein kinase (MAPK) activation in neutrophils remains unclear. In this study, selective inhibitors of several signalling pathways were utilized to investigate the mechanisms of activation of p38 MAPK by arachidonic acid in rat neutrophils. Stimulation of p38 MAPK phosphorylation by arachidonic acid and its trifluoromethyl ketone analogue AACOCF3 was transient, peaking at 1 min, and was concentration-dependent. Arachidonic acid-stimulated p38 MAPK phosphorylation was attenuated in cells pretreated with the Gi/o inhibitor (pertussis toxin), but not with the dual cyclooxygenase/lipoxygenase inhibitor (BW755C) or the leukotriene biosynthesis inhibitor (MK886). Tyrosine kinase inhibitor (genistein), but not the extracellular signal-regulated kinase kinase inhibitors (PD98059 and U0126), attenuated the phosphorylation of p38 MAPK by arachidonic acid. Phosphoinositide 3-kinase inhibitors (wortmannin and LY294002) did not affect the arachidonic acid-induced response. After pretreatment of the cells with protein kinase C inhibitors (Gö6976, Gö6983 and GF109203X), only Gö6976 significantly attenuated the phosphorylation of p38 MAPK by arachidonic acid. In addition, phosphorylation of p38 MAPK by arachidonic acid was greatly attenuated by the phospholipase C inhibitor (U73122) and the Ca2+ chelator BAPTA ((1,2-bis-o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid), but not altered by the nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester. Arachidonic acid did not cause an increase in cellular cyclic GMP level. This study revealed the involvement of pertussis toxin-sensitive G protein, non-receptor tyrosine kinase, phospholipase C/Ca2+, and probably Ca2+-dependent protein kinase C in arachidonic acid-stimulated p38 MAPK activation.

Identification of a cellular protein that functionally interacts with the C2 domain of cytosolic phospholipase A(2)alpha

Cytosolic phospholipase A(2) (cPLA(2)) alpha plays critical roles in lipid mediator synthesis. We performed far-Western analysis and identified a 60-kDa protein (P60) that interacted with cPLA(2)alpha in a Ca(2+)-dependent manner. Peptide microsequencing revealed that purified P60 was identical to vimentin, a major component of the intermediate filament. The interaction occurred between the C2 domain of cPLA(2)alpha and the head domain of vimentin. Immunofluorescence microscopic analysis demonstrated that cPLA(2)alpha and vimentin colocalized around the perinuclear area in cPLA(2)alpha-overexpressing human embryonic kidney 293 cells following A23187 stimulation. Forcible expression of vimentin in vimentin-deficient SW13 cells augmented A23187-induced arachidonate release. Moreover, overexpression of the vimentin head domain in rat fibroblastic 3Y1 cells exerted a dominant inhibitory effect on arachidonate metabolism, significantly reducing A23187-induced arachidonate release and attendant prostanoid generation. These results suggest that vimentin is an adaptor for cPLA(2)alpha to function properly during the eicosanoid-biosynthetic process.

Determination of 5-hydroperoxyeicosatetraenoic acid produced in rat basophilic leukemia cell line RBL-2H3 by high-performance liquid chromatography with chemiluminescence detection

A simple and sensitive method, applicable to quantification of 5-hydroperoxyeicosatetraenoic acid (5-HPETE) produced in cells has been developed using high-performance liquid chromatography on a silica gel column with chemiluminescence detection. 5-HPETE was clearly separated from other positional isomers of HPETEs and hydroxyeicosatetraenoic acids with hexane-isopropanol-acetic acid (97:3:0.01, v/v) as the mobile phase. The lower limit of detection was about 100 pg. 5-HPETE produced in 10(7) cells of RBL-2H3 cells stimulated with A23187 was determined as 480+/-30 pg. In the present study, 5-HPETE, which occurs naturally, was detected and quantitated for the first time in intact cells.

Induction of cyclooxygenase-2 causes an enhancement of writhing response in mice

Pretreatment of mice with lipopolysaccharide for 16 h enhanced the number of acetic acid-induced writhing reactions by 2 to 3-fold. In the peritoneal exudates at 10 min after acetic acid injection, 6-keto-prostaglandin F1alpha was detected as a major prostanoid, and this level increased by several-fold by the pretreatment with lipopolysaccharide. The writhing reaction and the prostaglandin formation were almost completely suppressed by indomethacin. However, the lipopolysaccharide-induced enhancement of writhing reaction and an increment of 6-keto-prostaglandin F1alpha level were diminished by the administration of cyclooxygenase-2-selective inhibitors, such as NS-398, nimesulide, or L-745337, to a level similar to the mice that did not receive lipopolysaccharide. Cyclooxygenase-2 protein in the exudates became detectable at 5-48 h after the lipopolysaccharide-pretreatment. These results suggest that the increased prostaglandin production by cyclooxygenase-2 could be responsible for enhancement of the acetic acid-induced writhing reaction by lipopolysaccharide pretreatment.

Tissue sources of cytochrome P450 4A and 20-HETE synthesis in rabbit lungs

We previously reported that 20-hydroxyeicosatetraenoic acid (20-HETE) is an endogenous cytochrome P450 (cP450) 4A metabolite of arachidonic acid (AA) in human lung tissue, and is a potent cyclooxygenase-dependent vasodilator of isolated pulmonary arteries. In the present investigations, we identified sources of cP450 4A immunospecific protein, messenger RNA (mRNA), and 20-HETE synthesis in rabbit lungs. Microsomes of peripheral lung tissue, airways, small and large vessels, and lysates of alveolar macrophages all express proteins of approximately 50 kD which cross-reacted with a primary antibody raised against rat liver cP450 4A1. Peripheral lung tissue, small and large pulmonary arteries, airways, and isolated vascular smooth muscle cells from small pulmonary arteries produced 20-HETE when incubated with AA. Expression of cP450 4A6/4A7 mRNA was readily detectable by reverse transcription-polymerase chain reaction using isoform-specific probes and 5 microg total RNA extracted from microdissected small pulmonary arteries. These data demonstrate that small pulmonary arteries express cP450 4A proteins and vascular smooth muscle cells derived from these arteries synthesize 20-HETE. Furthermore, cP450 4A appears to be widely distributed in rabbit tissue, raising the possibility that 20-HETE generated from nonvascular tissue could serve as a paracrine factor in the pulmonary circulation.

Segregated Coupling of Phospholipases A2, Cyclooxygenases, and Terminal Prostanoid Synthases in Different Phases of Prostanoid Biosynthesis in Rat Peritoneal Macrophages

We examined herein the functional linkage of enzymes regulating the initial, intermediate, and terminal steps of PG biosynthesis to provide PGs in rat peritoneal macrophages stimulated with LPS and/or A23187. Quiescent cells stimulated with A23187 produced thromboxane B2 (TXB2) in marked preference to PGE2 within 30 to 60 min (constitutive immediate response), which was mediated by preexisting cytosolic phospholipase A2 (cPLA2), cyclooxygenase-1 (COX-1), and TX synthase. Cells treated with LPS predominantly produced PGE2 during culture for 3 to 24 h (delayed response), where cPLA2 and secretory PLA2 functioned cooperatively with inducible COX-2, which was, in turn, coupled with inducible PGE2 synthase. Cells primed for 12 h with LPS and stimulated for 30 min with A23187 produced PGE2 in marked preference to TXB2 (induced immediate response), in which three inducible enzymes, cPLA2, COX-2, and PGE2 synthase, were functionally linked. Preferred coupling of the two inducible enzymes, COX-2 and PGE2 synthase, was further confirmed by the ability of LPS-treated cells to convert exogenous arachidonic acid to PGE2 optimally at a time when both enzymes were simultaneously induced. These results suggest that distinct PG biosynthetic enzymes display segregated functional coupling following different transmembrane stimulation events even when enzymes that catalyze similar reactions in vitro coexist in the same cells.

Concordant induction of prostaglandin E2 synthase with cyclooxygenase-2 leads to preferred production of prostaglandin E2 over thromboxane and prostaglandin D2 in lipopolysaccharide-stimulated rat peritoneal macrophages

Rat peritoneal macrophages were stimulated with lipopolysaccaride (LPS) for various periods and their ability to convert exogenous arachidonic acid to various prostanoids was examined. Unstimulated cells, which expressed cyclooxygenase (COX)-1 but not COX-2, produced thromboxane (TX) B2 > prostaglandin (PG) D2 > PGE2, whereas cells stimulated for 6-12 h with LPS exhibited marked increase in conversion to PGE2, which paralleled COX-2 induction, with minimal change in conversion to TXB2 and PGD2. Pharmacological studies showed that formation of PGE2 was mediated predominantly by COX-2, PGD2 by COX-1, and TXB2 by both COX-1 and COX-2 depending upon the timing of LPS stimulation. Measurement of the conversion of exogenous PGH2 to each prostanoid in cell lysates demonstrated LPS-dependent increase in PGE2 synthase activity that was degenerated by pretreatment with actinomycin D or cycloheximide. Thus, concordant induction of terminal PGE2 synthase with COX-2 leads to the preferred production of PGE2 to TXB2 and PGD2 by LPS-stimulated macrophages.