Long-chain fatty acyl-CoA synthetase of rat adrenal microsomes. Effect of ACTH and epinephrine

Expression and vitamin D3 regulation of long-chain fatty-acid-CoA ligase 3 in human prostate cancer cells

We found previously that long-chain fatty-acid-CoA ligase 3 (FACL3), a critical enzyme for activation of long-chain fatty acids, was upregulated by 1α, 25(OH)(2)D(3) at an mRNA and enzyme activity levels in prostate cancer cells. Our further study indicated that the FACL3 mediated 1α,25(OH)(2)D(3) inhibition of fatty acid synthase (FAS), which is associated with many cancers, including prostate cancer. In the current study, we investigated an FACL3 protein expression and its regulation by 1α, 25(OH)(2)D(3) and its synthetic analogs EB1089 and CB1093 in prostate cancer cells. The results showed that the expression of an FACL3 protein was upregulated by 1α, 25(OH)(2)D(3), EB1089 and CB1093 in LNCaP cells, consistent with their upregulation of an FACL3 mRNA expression. In addition, the FACL3 expression was found to be markedly low at both mRNA and protein levels in more transformed prostate cancer PC-3 and DU145 cells compared with less transformed LNCaP cells. The data suggest that decreased FACL3 expression might be associated with a more malignant phenotype of prostate cancer.

Acyl-CoA synthesis, lipid metabolism and lipotoxicity

Although the underlying causes of insulin resistance have not been completely delineated, in most analyses, a recurring theme is dysfunctional metabolism of fatty acids. Because the conversion of fatty acids to activated acyl-CoAs is the first and essential step in the metabolism of long-chain fatty acid metabolism, interest has grown in the synthesis of acyl-CoAs, their contribution to the formation of signaling molecules like ceramide and diacylglycerol, and their direct effects on cell function. In this review, we cover the evidence for the involvement of acyl-CoAs in what has been termed lipotoxicity, the regulation of the acyl-CoA synthetases, and the emerging functional roles of acyl-CoAs in the major tissues that contribute to insulin resistance and lipotoxicity, adipose, liver, heart and pancreas.

Acyl-CoA synthetase activity in liver microsomes from calcium-deficient rats

A study on the kinetic properties of the nonspecific acyl-coenzyme A (CoA) synthetase activity in liver microsomal vesicles from both normal and calcium-deficient Wistar rats was carried out. After a 65-d treatment, the calcium-deficient diet reflected a 75% increase in the synthetase activity with respect to control animals. The apparent Vm was significantly enhanced, while the Km remained unchanged. We also provided experimental evidence about various fatty acids of different carbon length and unsaturation which depressed the biosynthesis of palmitoyl-CoA following different behaviors in control or calcium-deprived liver microsomes. In addition, we studied in detail the inhibition reflected by stearic, alpha-linolenic, or arachidonic acids, in the biosynthesis of palmitoyl-CoA in microsomal suspensions either from control or hypocalcemic rats. In control microsomes, stearic acid produced a pure competitive effect, while the other fatty acids followed a mixed-type inhibition. The competitive effect of stearic acid was not observed in calcium-deprived microsomes. At the same time, a mixed-type inhibition produced by either alpha-linolenic or arachidonic acid was diminished in deprived microsomes due to an increase in the noncompetitive component (alphaKi). These changes observed in apparent kinetic constants (Km, Vm, Ki, and alphaKi), as determined by Lineweaver-Burks and Dixon plots, were attributed to the important alterations in the physicochemical properties of the endoplasmic reticulum membranes induced by the calcium-deficient diet. The solubilization of the enzyme activity from both types of microsomes demonstrated that the kinetic behavior of the enzyme depends on the microenvironment in the membrane, and that the calcium ion plays a crucial role in determining the alterations observed.

Metabolism of dietary alpha-linolenic acid vs. eicosapentaenoic acid in rat immune cell phospholipids during endotoxemia

Short-term (i.e., 3 d) continuous enteral feeding of diets containing eicosapentaenoic (EPA) and gamma-linolenic (GLA) polyunsaturated fatty acids (PUFA) to endotoxemic rats reduces the levels of arachidonic acid (AA) and linoleic acid (LA) in alveolar macrophage (AM) and liver Kupffer and endothelial (K&E) cell phospholipids with attendant decreases in prostaglandin formation by these cells in vitro. Diets that contain alpha-linolenic acid (LNA) as a substrate for endogenous formation of EPA may not be as effective in facilitating these immune cell modifications given the limited activity of delta6 desaturase. In the present study we compared the effectiveness of an LNA-enriched diet vs. an (EPA + GLA)-enriched diet to displace phospholipid AA from AM and liver K&E cells in vivo in endotoxemic rats fed enterally for 3 or 6 d. We determined the fatty acid composition of AM and K&E cell phospholipids by gas chromatography. We found that AM and K&E cells from rats that had received the EPA + GLA diet for 3 d had significantly (P < 0.001) higher mole percentage of EPA and the GLA metabolite, dihomoGLA, than corresponding cells from rats given the LNA diet or a control diet enriched with LA. Rats given the LNA diet had relatively low levels of stearidonic acid, EPA and other n-3 PUFA, while rats given the LA diet had low levels of GLA and dihomoGLA. We conclude that diets enriched with LNA or LA may not be as effective as those enriched with EPA + GLA for purposes of fostering incorporation of EPA or dihomoGLA into and displacement of AA from macrophage phospholipids under pathophysiologic conditions commonly found in acutely septic patients.

Long-chain fatty Acyl-CoA synthetase enzymatic activity in rat liver cell nuclei

A long-chain fatty acyl-CoA synthetase that catalyzes the activation of long-chain fatty acids as thioesters of CoA, was described in rat liver nuclei. This is the first step for further metabolization of fatty acids in the cell. Up to now, it has been shown that long-chain fatty acyl-CoA synthetase is located in the endoplasmic reticulum, in plasma membrane, in mitochondria and in peroxisomes. The nuclear long-chain fatty acyl-CoA synthetase was assayed using palmitic (16:0), linoleic (18:2n-6) and 8,11,14-eicosatrienoic (20:3n-6) acids as substrates and was stimulated linearly with nuclear protein concentration and with incubation time The higher enzymatic activity was observed with 18:2n-6 and 20:3n-6 acids as substrates. The synthesis of palmitoyl-CoA, linoleyl-CoA and 8,11,14-eicosatrienoyl-CoA followed normal Michaelis-Menten kinetics with respect to the corresponding substrate concentrations. The acyl-CoA synthetase seems to be saturated at a substrate concentration of 12.8 microM for all the acids tested. The apparent Km values decreased in the following order 20:3n-6 > 18:2n-6 > 16:0. The lowest apparent Km for palmitic acid indicates a preference for acylation of this acid in the cell nucleus.

Arachidonic acid biosynthesis in non-stimulated and adrenocorticotropin-stimulated Sertoli and Leydig cells

The biosynthesis of arachidonic acid in Sertoli and Leydig cells isolated from the testes of mature rats has been investigated. Both types of cells incorporated [2-14C]eicosatrienoic acid from the incubation medium and transformed it into arachidonic acid. The administration of adrenocorticotropin (ACTH) to the rats decreased the delta 5 desaturating activity in the isolated testicular cells, while ACTH produced no changes in the uptake of the substrate. Similar results were obtained when ACTH was added to the incubation medium of cells isolated from non-hormone treated rats. The total fatty acid composition of the Sertoli cells isolated from ACTH-treated rats showed a significant increase in the relative percentage of 18:2n-6 and a decrease in the C20 and C22 polyenes. This may indicate that ACTH exerts an inhibitory effect on delta 6, delta 5 and delta 4 desaturase activities. Addition of corticosterone to the incubation medium also produced a significant decrease in arachidonic acid biosynthesis. Because ACTH is known to stimulate the release of corticosterone in vivo, both hormones may act cumulatively in the regulation of arachidonic acid metabolism in Sertoli and Leydig cells.

Abnormal metabolism of polyunsaturated fatty acids in adrenal glands of diabetic rats

Studies carried out on the adrenal glands of experimental diabetic rats have shown an important inhibition in polyenoic fatty acid biosynthesis. This effect was demonstrated by testing the activities of long-chain fatty acyl-CoA synthetase, the delta 5- and delta 6-desaturases of the (n-6) essential fatty-acid series and the delta 6-desaturase of the (n-3) series in liver and adrenal microsomes. The depression in desaturating activity in the insulin-deprived animals was independent of that produced on acyl-CoA-thioester biosynthesis. Experiments measuring the incorporation and transformation of [1-14C]eicosa-8,11,14-trienoic acid in adrenocortical cells isolated from streptozotocin-diabetic animals demonstrated a significant inhibition of arachidonic acid biosynthesis compared to controls. Insulin injections in diabetic rats partially restored the delta 5- and delta 6-desaturase activities. This effect could result from direct action by the hormone since the restoration was reproduced when arachidonic acid biosynthesis was measured after insulin was added to the incubation medium of adrenocortical cells isolated from diabetic animals. The results of the present study provide new information about the implication of this abnormal metabolism in the adrenal gland of diabetic rats.

Biosynthesis of polyunsaturated fatty acids of (n-6) and (n-3) series in isolated adrenocortical cells of rats. Effect of ACTH

Both the capacity of isolated adrenocortical cells to incorporate and transform [1-14C]linoleic and [1-14C]alpha-linolenic acids and the effect of ACTH on the biosynthesis of polyunsaturated fatty acids from [1-14C]alpha-linolenic acid were investigated. The cells were able to incorporate both labeled precursor acids and convert them into higher homologs. This transformation increases along the incubation time tested. When linoleic acid was the precursor, the biosynthesis of higher homologs was carried out following the desaturating-elongating route. Both pathways, the desaturating-elongating and the elongating, were detected when the substrate was alpha-linolenic acid. The results proved the existence of delta 6, delta 5 and delta 4-desaturases in this type of cells. Isolated adrenocortical cells obtained from rats treated with ACTH showed an increase in the amount of [1-14C]alpha-18:3 that remained in the cells without metabolization and, consequently, a decrease in the last product formed (20:5 n-3) was evident compared to the controls. Simultaneously, the desaturation-elongation products decreased significantly. Similar results were obtained when cells isolated from untreated rats were incubated for 3 h in the presence of ACTH. In this case, the values obtained returned to normal levels 6 h after incubation. These results were mimicked by dibutyryl-cyclic AMP. It can be concluded that the effect of ACTH on the biosynthesis of polyunsaturated fatty acids from alpha-linolenic acid was mediated through an enhancement of the intracellular levels of cAMP.