The effects of fatty acyl CoA esters on the formation of prostaglandin and arachidonoyl-CoA formed from arachidonic acid in rabbit kidney medulla microsomes

Inhibitory Investigations of Acyl-CoA Derivatives against Human Lipoxygenase Isozymes

Lipid metabolism is a complex process crucial for energy production resulting in high levels of acyl-coenzyme A (acyl-CoA) molecules in the cell. Acyl-CoAs have also been implicated in inflammation, which could be possibly linked to lipoxygenase (LOX) biochemistry by the observation that an acyl-CoA was bound to human platelet 12-lipoxygenase via cryo-EM. Given that LOX isozymes play a pivotal role in inflammation, a more thorough investigation of the inhibitory effects of acyl-CoAs on lipoxygenase isozymes was judged to be warranted. Subsequently, it was determined that C18 acyl-CoA derivatives were the most potent against h12-LOX, human reticulocyte 15-LOX-1 (h15-LOX-1), and human endothelial 15-LOX-2 (h15-LOX-2), while C16 acyl-CoAs were more potent against human 5-LOX. Specifically, oleoyl-CoA (18:1) was most potent against h12-LOX (IC₅₀ = 32 μM) and h15-LOX-2 (IC₅₀ = 0.62 μM), stearoyl-CoA against h15-LOX-1 (IC₅₀ = 4.2 μM), and palmitoleoyl-CoA against h5-LOX (IC₅₀ = 2.0 μM). The inhibition of h15-LOX-2 by oleoyl-CoA was further determined to be allosteric inhibition with a K_i of 82 +/- 70 nM, an α of 3.2 +/- 1, a β of 0.30 +/- 0.07, and a β/α = 0.09. Interestingly, linoleoyl-CoA (18:2) was a weak inhibitor against h5-LOX, h12-LOX, and h15-LOX-1 but a rapid substrate for h15-LOX-1, with comparable kinetic rates to free linoleic acid (k_cat = 7.5 +/- 0.4 s^-1, k_cat/K_M = 0.62 +/- 0.1 µM^-1s^-1). Additionally, it was determined that methylated fatty acids were not substrates but rather weak inhibitors. These findings imply a greater role for acyl-CoAs in the regulation of LOX activity in the cell, either through inhibition of novel oxylipin species or as a novel source of oxylipin-CoAs.

Production of prostaglandins in transgenic Arabidopsis thaliana

Plants do not naturally produce the very-long-chain polyunsaturated fatty acids that are the precursors of prostaglandins, but in previous studies Arabidopsis thaliana had been transformed sequentially with genes encoding a Δ(9)-elongase and a Δ(8)-desaturase to produce dihomo-γ-linolenic acid (DGLA) and eicosatetraenoic acid (ETA), and subsequently with a gene encoding a Δ(5)-desaturase to produce arachidonic acid (AA) and eicosapentaenoic acid (EPA). Transformation of A. thaliana with the first two genes consolidated on a single binary vector yielded transformants producing high levels of DGLA, and these plants were further transformed with mouse prostaglandin H synthase (PGH) genes to produce prostaglandins. Mouse PGHS-1 and PGHS-2 cDNAs were amplified for expression as three isoforms: PGHS-1 (complete coding sequence with signal peptide), PGHS-1-Ma (mature PGHS-1 sequence, without signal peptide) and PGHS-2 (complete coding sequence with signal peptide). PGHS-1 transformants showed the highest activity, followed by PGHS-2 transformants, whereas removal of the signal peptide resulted in almost complete loss of PGHS-1 activity. In order to produce a physiologically active prostaglandin, the Trypanosoma brucei prostaglandin F synthase gene was combined with the mouse PGHS-1 gene and the Mortierella alpina Δ(5)-desaturase on a binary vector. Transformation of DGLA-producing A. thaliana with this construct yielded transformants that successfully produced prostaglandin F.

Stearic acid potently modulates the activity of cyclooxygenase-1, but not cyclooxygenase-2, in the form of its CoA ester

The effects of palmitic acid (PA), stearic acid (SA) and oleic acid (OA), and their respective CoA esters, PA-CoA, SA-CoA and OA-CoA, on the activities of cyclooxygenase (COX)-1 and -2 were examined. Ten units of purified COX-1 or -2 were preincubated with drugs in the presence of hematin (0.1 microM) and phenol (2 mM) as cofactors for 10 min at 37 degrees C, and then incubated with 100 microM arachidonic acid for 2 min at 37 degrees C. The amounts of prostaglandins formed were measured by HPLC. PA, SA and OA had no effect on the COX-1 and -2 activities, but their respective CoA esters, PA-CoA, SA-CoA and OA-CoA, suppressed COX-1 activity with no significant effect on COX-2 activity. The inhibitory effect of SA-CoA was much stronger than that of PA-CoA and OA-CoA. These results suggest that SA has the potential to inhibit COX-1 activity, but not COX-2 activity, in the form of their CoA ester.

Incorporation of arachidonic and stearic acids bound to L-FABP into nuclear and endonuclear lipids from rat liver cells

The incorporation of exogenous fatty acids bound to L-FABP into nuclei was studied. Rat liver cell nuclei and nuclear matrices (membrane depleted nuclei) were incubated in vitro with [1-(14)C]18:0 and 20:4n-6 either free or bound to L-FABP, ATP and CoA. FA esterification in whole nuclei and endonuclear lipids was ATP-CoA-dependent, and with specificity regarding fatty acid type and lipid class. 18:0 and 20:4n-6, free or L-FABP bound, showed the same incorporation and esterification pattern in lipids of whole nuclei. Only 20:4n-6 L-FABP bound was less incorporated into TAG with respect to free 20:4n-6. In the nuclear matrix, 18:0 free or L-FABP bound was esterified with a higher specific activity (SA) into: PtdEtn > PtdIns, PtdSer > PtdCho. 20:4n-6 free or L-FABP bound was esterified into: PtdIns > PtdEtn > PtdCho. 20:4n-6:L-FABP was esterified in endonuclear total-PL and PtdIns with a greater SA with respect to free 20:4n-6 and with a minor one as FFA. To summarize, trafficking of FA to nuclei includes esterification of 18:0 and 20:4n-6 either free or L-FABP-bound, into nuclear and endonuclear lipids by an ATP-CoA-dependent pathway. Endonuclear fatty acid esterification was more active than that in whole nuclei, and independent of the nuclear membrane. Esterification patterns of fatty acids L-FABP-bound or free into whole nuclear lipids were the same whereas in the nuclear matrix, L-FABP could play an important role in the mobilization of 20:4n-6 into specific sites of utilization such as the PtdIns pools.

15-Hydroperoxyeicosapentaenoic acid, but not eicosapentaenoic acid, shifts arachidonic acid away from cyclooxygenase pathway into acyl-CoA synthetase pathway in rabbit kidney medulla microsomes

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). In the present study, we investigated the effects of eicosapentaenoic acid (EPA) and 15-hydroperoxyeicosapentaenoic acid (15-HPEPE) on the PG and AA-CoA formations from high and low concentrations of AA (60 and 5 microM) in rabbit kidney medulla microsomes. The kidney medulla microsomes were incubated with 60 or 5 microM [(14)C]-AA in 0.1M Tris/HCl buffer (pH 8.0) containing cofactors of COX (reduced glutathione and hydroquinone) and cofactors of ACS (ATP, MgCl(2) and CoA). After incubation, PG (as total PGs), AA-CoA and residual AA were separated by selective extraction using petroleum ether and ethyl acetate. EPA reduced the PG and AA-CoA formations from both 60 and 5 microM AA. In contrast, 15-HPEPE decreased the PG formation without affecting the AA-CoA formation from 60 microM AA, and increased the AA-CoA formation at the expense of PG formation when 5 microM AA was used as substrate concentration. The experiments utilizing Fe(2+) and an electron spin resonance (ESR) revealed that 15-HPEPE elicits these effects in the form of hydroperoxy adduct. These results suggest that 15-HPEPE, but not EPA, has the potential to shift AA away from COX pathway into ACS pathway at low substrate concentration (close to the physiological concentration of AA).

The regulation of formation of prostaglandins and arachidonoyl-CoA from arachidonic acid in rabbit kidney medulla microsomes by linoleic acid hydroperoxide

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). In the present study, we investigated the effects of linoleic acid (LA) and 13-hydroperoxyoctadecadienoic acid (13-HPODE) on the PG and AA-CoA formation from high and low concentrations of AA (60 and 5 microM) in rabbit kidney medulla microsomes. The kidney medulla microsomes were incubated with 60 or 5 microM [(14)C]-AA in 0.1M Tris-HCl buffer (pH 8.0) containing cofactors of COX (reduced glutathione and hydroquinone) and cofactors of ACS (ATP, MgCl(2) and CoA). After incubation, PG (as total PGs), AA-CoA and residual AA were separated by selective extraction using petroleum ether and ethyl acetate. LA (10-50 microM) reduced only PG formation from both 60 and 5 microM AA. 13-HPODE (10-50 microM) also reduced PG formation from 60 and 5 microM AA, but the inhibitory potency was much stronger than that by LA. Furthermore, 13-HPODE had the potential to increase the AA-CoA formation with a decrease in the PG formation from 5 microM AA. These results suggest that 13-HPODE, but not LA, may shift AA away from COX pathway into ACS pathway under low substrate concentration (near physiological concentration of AA).

Effects of endocrine disruptors on the formation of prostaglandin and arachidonoyl-CoA formed from arachidonic acid in rabbit kidney medulla microsomes

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 explore the possible actions of endocrine disruptors on the metabolic fate of free AA into these two pathways, we investigated the effects of nonylphenol (NP), bisphenol A (BPA), di-n-butyl phthalate (DBP), benzyl-n-butyl phthalate (BBP) and di-2-ethylhexyl phthalate (DEHP) on the formation of PG and AA-CoA from 5 microM AA (close to the physiological concentration of the substrate) in rabbit kidney medulla microsomes. The kidney medulla microsomes were incubated with 5 microM [(14)C]-AA in 0.1 M Tris/HCl buffer (pH 8.0) containing cofactors of COX (reduced glutathione 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. NP (1-200 microM) strongly enhanced the AA-CoA formation with a coincident decrease in the PG formation. BPA, DBP, BBP and DEHP failed to show any effect on the PG and AA-CoA formation up to 200 microM. Experiments utilizing 60 microM AA as the substrate concentration indicated that, under a low concentration of AA, NP decreases PG formation by inhibiting the COX activity, and reduces the AA flow into the COX pathway through inhibition on the COX activity, increasing availability of the substrate for the ACS and leading to enhanced AA-CoA formation. These results firstly show that NP has the potential to disturb the balance of PG and AA-CoA formations under normal physiological conditions.

Involvement of fatty acid-CoA ligase 4 in hepatocellular carcinoma growth: Roles of cyclic AMP and p38 mitogen-activated protein kinase

AIM: Fatty acid-CoA ligase 4 (FACL4) is an arachidonate-preferring enzyme which has been shown to be up-regulated in human colon cancer tissues and implicated in the colon tumorigenesis. The purpose of this study was to investigate the role of FACL4 in the human hepatocellular carcinoma (HCC) tumorigenesis and the specific signal pathways involved in this process.

METHODS: We investigated the expression and regulation of FACL4 in HCC, adjacent non-tumorous liver tissues, and cell lines.

RESULTS: In HCC patients, we demonstrated that FACL4 gene expression was markedly elevated in the cancerous tissues than in the adjacent non-cancerous liver tissues. In addition, several human hepatoma cell lines, including Hep3B and HepG2, expressed high levels of FACL4. Stable overex-pression of FACL4 knockdown plasmids (small interfering RNA, siRNA) to Hep3B cells significantly decreased FACL4 expression and subsequently limited the cell proliferation. Treatment of Hep3B cells with 8-bromo-cAMP and SB203508 (p38 MAPK inhibitor) significantly suppressed the FACL4 expression.

CONCLUSION: FACL4 is involved in the HCC tumorigenesis and both cAMP and p38 MAPK pathways are associated with the regulation of FACL4 in HCC.

Lipid Metabolism in Zebrafish

Forward genetics is an unbiased methodology to discover new genes or functions of genes. At the present, the zebrafish is one of the few vertebrate systems where large-scale forward genetic studies are practical. Fluorescent lipid labeling of zebrafish larvae derived from families created from ENU-mutagenized fish enabled us to perform a large scale in vivo screen to identify mutants with perturbed lipid processing. With the aid of the zebrafish genome project, positional cloning of mutated genes with abnormal lipid metabolism can be accelerated. MO- and gripNA-based transient gene silencing is feasible in zebrafish embryos and provides a reverse genetic screening strategy to search for important lipid regulators. The advantages of using zebrafish as a vertebrate model to study lipid metabolism include its rapid external development and its optical clarity that enables the monitoring of biological processes. Large scale, high-throughput drug screening in vivo, especially for drugs that inhibit lipid absorption, can be easily achieved in this model. These zebrafish-based assays are important tools to understand aspects of lipid biology with significant clinical implications.

The effects of nitric oxide and peroxynitrite on the formation of prostaglandin and arachidonoyl-CoA formed from arachidonic acid in rabbit kidney medulla microsomes

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.