Prostaglandins, leukotrienes, and essential fatty acids最新文献

Several years ago we hypothesized that products of lipid and lipoprotein oxidation may contribute to pathophysiology of osteoporosis (F. Parhami, Curr. Opin. Lipidol. 8 (1997) 312), and that their effects on artery wall and bone cells may explain the parallel development of osteoporosis and atherosclerosis in the same subjects (R. Boukhris, JAMA 219 (1972) 1307; M.A. Frye, Bone Miner. 19 (1992) 185). Since then, new evidence has accumulated in support of this hypothesis and its possibility is being further tested by investigators in both vascular and bone fields (A.D. Watson, J. Biol. Chem. 272 (1997) 13597). This review will summarize the evidence to date that support the role of oxidized lipids in osteoporosis, and will address some of the issues that need further examination in order to establish whether hyperlipidemia and susceptibility to lipid oxidation may serve as risk factors for osteoporosis.

This study was designed to compare the effects of dietary arachidonic acid (AA) versus prostaglandin E(2) (PGE(2)) on bone cell metabolism and bone mass. Twenty-eight piglets from 7 litters were randomized to 1 of 4 treatments for 15 days: fatty acid supplemented formula (FA: 0.8% of total fatty acids as AA and 0.1% of total fatty acids as DHA)+PGE(2) injections (0.1mg/kg/day), FA+saline injections, standard formula (STD: n-6:n-3 of 8:1) + PGE(2) injections or STD+saline injections. PGE(2) resulted in elevated osteoblast activity as indicated by plasma osteocalcin and also reduced urinary calcium excretion. Dietary FA resulted in reduced bone resorption as indicated by urinary N-telopeptide and reduced bone PGE(2). Both PGE(2) and FA treatments independently lead to elevated femur mineral content, but the combined treatment caused a reduction. Thus the mechanisms by which PGE(2) and FA lead to enhanced bone mass are distinct.

Dietary supplementation with fish oil that contains omega-3 polyunsaturated fatty acids has been shown to enhance bone density as well as duodenal calcium uptake in rats. The latter process is supported by membrane ATPases. The present in vitro study was undertaken to test the effect of omega-3 fatty acids on ATPase activity in isolated basolateral membranes from rat duodenal enterocytes. Ca-ATPase in calmodulin-stripped membranes was activated in a biphasic manner by docosahexanoic acid (DHA) (10-30 microg/ml) but not by eicosapentanoic acid (EPA). This effect was blocked partially by 0.5 microM calphostin (a protein kinase C blocker). DHA inhibited Na,K-ATPase (-49% of basal activity, [DHA]=30 microg/ml, P <0.01). This effect could be reversed partially by 50 microM genistein, a tyrosine kinase blocker. EPA also inhibited Na,K-ATPase: (-47% of basal activity, [EPA]=30 microg/ml, P <0.01), this effect was partially reversed by 100 microM indomethacin, a cyclo-oxygenase blocker. Omega-3 fatty acids are thus involved in multiple signalling effects that effect ATPases in BLM.

A patient with mantle cell lymphoma took 12g/day of ethyl-eicosapentaenoate for 16 months. Compared to reference values, eicosapentaenoic and docosapentaenoic acids were elevated in plasma, red cells and platelets but docosahexaenoic acid levels were in the normal range. Arachidonic acid levels were moderately reduced but dihomogammalinolenic acid levels remained in the normal range. In spite of a long chain n-3 fatty acid intake higher than in most Inuit populations, arachidonic acid levels remained considerably higher in this patient than in the Inuit. The implications for understanding of fatty acid metabolism in humans are discussed.

D-003 is a mixture of higher primary aliphatic saturated acids purified from sugarcane wax, with antiplatelet and antithrombotic effects experimentally demonstrated. Octacosanoic acid is the main component of D-003, followed by triacontanoic, dotriacontanoic, and tetracontanoic acids, while other acids are minor components. This work investigates the effects of combination therapy D-003+aspirin (ASA) on arachidonic acid (AA)-induced sudden death in mice and bleeding time in rats. In addition, the effects of D-003 on serum levels of two metabolites of AA: thromboxane A(2) and prostacyclin, assessed through the measurement of their stable metabolites: thromboxane B(2) (TxB(2)) and 6 keto PgF1alpha by radioimmunoassay kits, were also investigated. Combination therapy of D-003 (50mg/kg) and ASA (3mg/kg) significantly increased bleeding time in rats in a synergistic manner compared with D-003 or ASA alone. Moreover, the combined treatment of D-003 (200mg/kg) and ASA (5mg/kg) in mice protected against AA-induced sudden death (83% survivors) in a synergistic manner which was compared with each treatment alone (33% survivors). These results indicate that antiplatelet effects of D-003 are not mediated by a cyclooxygenase inhibition. D-003 and ASA monotherapies reduced serum TxB(2) levels, whereas D-003, but not ASA, significantly increased 6 keto PgF1alpha levels.

The activation of peroxisome proliferator activated receptor gamma (PPARgamma) may play a role in the control of colorectal carcinogenesis. The expression of PPARgamma was examined by Western blotting in human colorectal tumors and matched normal adjacent tissues, as well as in various colorectal carcinoma cell lines. In the tissues, the expression of PPARgamma was elevated in tumors relative to the adjacent normal tissues. Each colorectal carcinoma cell line expressed PPARgamma. The ability of various eicosanoids to bind PPARgamma in colorectal carcinoma cells was investigated using luciferase reporter assays. The well-known PPARgamma ligands, troglitazone and 15-deoxy-Delta(12,14)-prostaglandin J(2) strongly induced PPARgamma binding activity. Products of lipoxygenases displayed moderate binding activity, while other prostaglandins and fatty acids displayed little or no reporter activation. The activation of PPARgamma by 13(S)-HODE, the major metabolite of 15-lipoxygenase-1 from linoleic acid, was concentration dependent reaching maximum at 10 micro M (35-fold activation). The endogenous production of 13(S)-HODE by expression of 15-LO-1 did not activate PPARgamma. The ability of various nonsteroidal anti-inflammatory drugs (NSAIDs) to induce PPARgamma activation was also evaluated. The conventional NSAIDs that inhibit both cyclooxygenases (COX-1 and COX-2) also induced PPARgamma binding activity. In general, however, neither COX-1- nor COX-2-specific inhibitors induced the activation of PPARgamma. Taken together, the metabolites of 15-lipoxygenase and the conventional NSAIDs were confirmed as exogenous ligands for PPARgamma in colorectal carcinoma cells.

Prostaglandin F(2alpha) (PGF(2alpha)) has been reported to activate protein kinase C (PKC) through both phospholipase (PL) C and D, resulting in the proliferation of osteoblast-like cells. In addition, it has also been reported that Erk mitogen-activated protein kinase is also involved in the mechanism of PGF(2alpha)-induced proliferation of these cells. Recently, we have reported that several growth factors stimulate Na-dependent phosphate transport (Pi transport) activity of osteoblast-like cells, which has been recognized to play an important role in their mineralization. In the present study, we investigated the effect of PGF(2alpha) on Pi transport in MC3T3-E1 osteoblast-like cells. PGF(2alpha) stimulated Na-dependent Pi transport dose dependently in the range between 1nM and 10 micro M in MC3T3-E1 cells. The effect was time dependent up to 24h. Kinetic analysis revealed that PGF(2alpha) induces newly synthesized Pi transporter. Pretreatment with actinomycin D and cycloheximide suppressed PGF(2alpha)-induced enhancement of Pi transport. Combined effect of PMA and PGF(2alpha) was not additive in Pi transport. Calphostin C, a PKC inhibitor, dose-dependently suppressed Pi transport induced by PGF(2alpha). On the contrary, U0126, which inhibits an upstream kinase of Erk (MEK), did not affect PGF(2alpha)-induced enhancement of Pi transport. In conclusion, PGF(2alpha) stimulates Pi transport through activation of PKC in osteoblast-like cells.

It is generally accepted that n-3 polyunsaturated fatty acids have beneficial effects on vascular homeostasis. Among the several functions of endothelial cells, angiogenesis contributes to tumor growth, inflammation, and microangiopathy. We have already demonstrated that eicosapentaenoic acid (EPA, 20:5, n-3) suppressed angiogenesis. In this paper, we examined the effect of docosapentaenoic acid (DPA, 22:5, n-3), an elongated metabolite of EPA, on tube-forming activity in bovine aortic endothelial cells (BAE cells) incubated between type I collagen gels. The pretreatment of BAE cells with DPA suppressed tube-forming activity induced by vascular endothelial growth factor (VEGF). The effect of DPA was stronger than those of EPA and docosahexaenoic acid (22:6, n-3). The migrating activity of endothelial cells stimulated with VEGF was also suppressed by DPA pretreatment. The treatment of BAE cells with DPA caused the suppression of VEGF receptor-2 (VEGFR-2, the kinase insert domain-containing receptor, KDR) expression in both plastic dish and collagen gel cultures. These data indicate that DPA has a potent inhibitory effect on angiogenesis through the suppression of VEGFR-2 expression.

Under physiological conditions, small amounts of free arachidonic acid (AA) are released from membrane phospholipids, and cyclooxygenase (COX) and acyl-CoA synthetase (ACS) competitively act on this fatty acid to form prostaglandins (PGs) and arachidonoyl-CoA (AA-CoA). To clarify factors deciding the metabolic fate of free AA into these two pathways, we investigated the effects of a nitric oxide (NO) donor 1-hydroxyl-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene (NOC7), and peroxynitrite (ONOO(-)) on the formation of PG and AA-CoA from high and low concentrations of AA (60 and 5 micro M) in rabbit kidney medulla microsomes. The kidney medulla microsomes were incubated with 60 or 5 micro M [14C]-AA in 0.1M Tris/HCl buffer (pH 8.0) containing cofactors of COX (reduced GSH and hydroquinone) and cofactors of ACS (ATP, MgCl(2) and CoA). After incubation, PG (as total PGs) and AA-CoA were separated by selective extraction using petroleum ether and ethyl acetate. When 60 micro M AA was used as the substrate concentration, NOC7 stimulated the PG formation at 0.5 micro M, and inhibited it at 50 and 100 micro M, without affecting the AA-CoA formation. When 5 micro M AA was used as the substrate concentration, NOC7 showed no effect on the PG and AA-CoA formation up to 10 micro M or below, but enhanced the AA-CoA formation with a coincident decrease in the PG formation at 50 micro M or over. Experiments utilizing a NO antidote, carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, revealed that the observed effects of NOC7 using 60 and 5 micro M AA are caused by NO. On the other hand, ONOO(-) stimulated the PG formation from 60 micro M AA, with no alteration in the AA-CoA formation at a concentration of 100 micro M, but when 5 micro M AA was used as the substrate concentration, it was without effect on the PG and AA-CoA formation. These findings indicate that actions of NO and ONOO(-) on the PG and AA-CoA formation by the kidney medulla microsomes may change depending on the substrate concentration. The effects of NO using 5 micro M AA were reversed by the addition of the superoxide generating system (xanthine-xanthine oxidase plus catalase), indicating that superoxide is a vital modulator of the action of NO. These results suggest that NO, but not ONOO(-), can be a regulator of the PG and AA-CoA formation at low substrate concentrations (close to the physiological concentration of AA), and that superoxide may play an important role in the action of NO.

Prostaglandin (PG) E(2) is a known bone absorbing agent that acts on osteoblasts to facilitate osteoclastogenesis by increasing the secretion of RANKL. In the present study, we investigated the direct action of PGE(2) on osteoclastic progenitors that differentiate into TRAP-positive multinucleated cells. The hematopoietic stem cell obtained from murine bone marrow was purified by a Sephadex G-10 column, and cultured in the presence of CSF-1 and RANKL to facilitate cell differentiation. The introduction of low-density PGE(2) into the culture resulted in a drastic increase of TRAP-positive multinucleated cells, whereas the addition of high-density PGE(2) had the opposite effect. PCR analysis revealed increased level of EP3 mRNA in undifferentiated cells and reduced level after the development of osteoclast; EP1, EP2 and EP4 were constitutively expressed throughout the differentiation. Investigation of intracellular signaling verified that low-density PGE(2) suppressed PKA activity in undifferentiated cells, suggesting that PGE(2) acts on the osteoclastic cell lineage to facilitate cell differentiation by suppressing PKA in the presence of RANKL.