Relationship between mouse liver delta 9 desaturase activity and plasma lipids

Correlation between fatty acyl composition in neutral and polar lipids and enzyme activities from various tissues of calcium-deficient rats

In this study we investigated the changes induced by feeding rats a calcium-deficient diet (0.5 g Ca/kg diet) during 65 d after weaning. Phospholipase A2, acyl-Co synthetase and FA delta9-, delta6-, and delta5-desaturase activities were also determined. Calcium deficiency evoked a general alteration in the quality and proportion of the FA chains acylated to neutral and polar lipids from liver, lungs, spleen, brain, kidneys, fat, articular cartilage, erythrocyte ghosts, and plasmas, characterized by an increment of saturated FA and a significant depletion of polyunsaturated acids derived from linoleate and alpha-linolenate. Several interlipid and lipid/protein relationships were also modified in microsomes from calcium-deprived rats, with a concomitant reduction in the rotational mobility of the probe diphenylhexatriene. Phospholipase A2 and acyl-CoA synthetase activities were also decreased and increased, respectively, in some tissues from calcium-deficient rats, whereas delta9-, delta6- and delta5-desaturases were significantly depressed. We conclude that changes in tissue fatty acyl composition evoked by calcium deprivation are due to alterations in the acylation/deacylation cycles via inhibition of the phospholipase A2. These changes were reflected in the physicochemical properties of the membranes, which in turn inhibits desaturase activities. A possible failure in the transcriptional rate for desaturase-mRNA was also discussed.

Molecular cloning and sequence analysis of stearoyl-CoA desaturase in milkfish, Chanos chanos

Stearoyl-CoA desaturase (EC 1.14.99.5) is a key enzyme in the biosynthesis of polyunsaturated fatty acids and the maintenance of the homeoviscous fluidity of biological membranes. The stearoyl-CoA desaturase cDNA in milkfish (Chanos chanos) was cloned by RT-PCR and RACE, and it was compared with the stearoyl-CoA desaturase in cold-tolerant teleosts, common carp and grass carp. Nucleotide sequence analysis revealed that the cDNA clone has a 972-bp open reading frame encoding 323 amino acid residues. Alignments of the deduced amino acid sequence showed that the milkfish stearoyl-CoA desaturase shares 79% and 75% identity with common carp and grass carp, and 63%-64% with other vertebrates such as sheep, hamsters, rats, mice, and humans. Like common carp and grass carp, the deduced amino acid sequence in milkfish well conserves three histidine cluster motifs (one HXXXXH and two HXXHH) that are essential for catalysis of stearoyl-CoA desaturase activity. However, RT-PCR analysis showed that stearoyl-CoA desaturase expression in milkfish is detected in the tissues of liver, muscle, kidney, brain, and gill, and more expression sites were found in milkfish than in common carp and grass carp. Phylogenic relationships among the deduced stearoyl-CoA desaturase amino acid sequence in milkfish and those in other vertebrates showed that the milkfish stearoyl-CoA desaturase amino acid sequence is phylogenetically closer to those of common carp and grass carp than to other higher vertebrates.

Molecular cloning of full-length cDNA encoding delta-9 desaturase through PCR strategies and its genomic organization and expression in grass carp (Ctenopharyngodon idella)

Desaturases are enzymes that catalyze double bond formation in fatty acids, which is a critical step in the synthesis of unsaturated fatty acids in organisms. Desaturase cDNA has been cloned from various species. Here we report the cloning of a full-length cDNA of Delta(9)-desaturase from grass carp (Ctenopharyngodon idella), using a combination of PCR techniques: reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The resolved cDNA encompasses 2420 bp, containing an open reading frame corresponding to 324 amino acids. The deduced amino acid sequence shares high homology with those of mammalian desaturases. Northern blot and RT-PCR analyses demonstrated a high abundance of the transcript in liver tissue but low abundance in brain tissue. Furthermore, the structure of the gene has been resolved by screening its cognate genomic DNA library. The analysis shows that this gene is composed of six exons and five introns, encompassing a region of 8.5 kb. In particular, the last exon contains a length of the 3' untranslated region as long as 1382 bp. Although the primary sequence and the genomic organization are phylogenetically conserved between fish and mammals, the regulation of the gene expression appears to be divergent among species.

Stearoyl-CoA desaturase 1 coding sequences and antisense RNA affect lipid secretion in transfected chicken LMH hepatoma cells

Hepatic stearoyl CoA desaturase (SCD) activity in chickens from a fat line is higher than that of chickens from a lean line and correlates with plasma triacylglycerol concentrations. Furthermore, in these lines, the hepatic SCD1 mRNA level is positively correlated with the adipose tissue weight. To analyze the contribution of the SCD1 gene in the regulation of adiposity in the early stages of triacylglycerol secretion, SCD1 coding sequence and antisense RNA expression vectors were transfected in LMH cells. After selection, these cells were analyzed with regard to SCD1 expression and lipid secretion. The amounts of secreted triacylglycerols and phospholipids were shown to be higher in LMH cells transfected with the SCD1 gene, but reduced in those transfected with the SCD1 antisense sequences when compared to cells transfected with the vector alone (without SCD1 sequences). These results provide direct evidence that the expression of the SCD1 gene plays a major role in the triacylglycerol and phospholipid secretion process.

Cyclic fatty acid monomers from heated oil modify the activities of lipid synthesizing and oxidizing enzymes in rat liver

Cyclic fatty acid monomers purified from a heated linseed oil were given for 2 wk to adult rats as triacylglycerol at two dose levels, i.e., 0.1 and 1 g/100 g diet, to determine their effect on some aspects of lipid metabolism. Indirect evidence of a peroxisome proliferator-like effect was observed, as determined by an elevation of some characteristic enzyme activities, such as peroxisomal acyl-CoA oxidase, and the microsomal omega- but also (omega-1)-laurate hydroxylase (CYP4A1 and CYP2E1, respectively). The dietary cyclic fatty acids induced a coordinated regulation between the activities of the lipogenic enzymes studied (Delta9-desaturase, phosphatidate phosphohydrolase) and peroxisomal oxidation, but not with mitochondrial beta-oxidation. The dose-dependent decrease of Delta9-desaturase activity (P < 0.05) with cyclic fatty acid monomer intake was accompanied by a similar decrease of the monounsaturated fatty acid level in liver. The increase in the gamma-linolenic acid level also suggested an increase in Delta6-desaturase activity with cyclic fatty acid intake (P < 0.05). In addition, our results strongly suggested that the altered liver levels of eicosapentaenoic and arachidonic acids were due to the peroxisomal retroconversion process in rats fed cyclic acids. Finally, an effect of these cyclic compounds on the carbohydrate metabolism cannot be disregarded because they decreased liver glycogen concentration. We conclude that cyclic fatty acid monomers affect different aspects of lipid metabolism, including a phenotypic peroxisome proliferator response. This provides the ground for further studies investigating the biochemical pathways that underlie the nutritional effect of such molecules.

Changes in membrane fatty acids and delta-9 desaturase in senescence accelerated (SAMP8) mouse hippocampus with aging

Senescence accelerated mice (SAMP8) exhibit age induced impairments such as loss of memory and learning disabilities by the age of 8-10 months. Analysis of hippocampus of SAMP8 mice revealed that delta 9-desaturase (delta9desaturase) activity reduced up to 44-50% with age. Correspondingly, levels of unsaturated fatty acids are also lowered in the aged animals approximately to the same levels. RNase protection assay showed that delta9specific message decreased similarly with age. As such a decrease is known to cause alterations in membrane fluidity and affect cellular signaling pathways, these results suggest that lowering of delta9gene expression may be partly involved in age induced impairments.

Conjugated linoleic acid decreases hepatic stearoyl-CoA desaturase mRNA expression

Conjugated dienoic derivatives of linoleic acid (CLA) is a collective term for positional and geometric isomers of linoleic acid that occur naturally in foods. The two predominant isomers of CLA are the c9,t11 and t10,c12. One of the effects of CLA is to modify membrane fatty acid composition by decreasing the activity of stearoyl-CoA desaturase enzyme activity. We analyzed the changes of stearoyl-CoA desaturase gene 1 (scd1) mRNA to further define the mechanism for the decrease in Scd enzyme activity by CLA. Mice fed for two weeks with either a fat-free high carbohydrate diet (CHO) or a 5.0% corn oil diet (CO), supplemented with 0.5% CLA had a 45% and 75% decrease respectively, in scd1 mRNA levels in the liver. Consistent with the effects observed in mice, 150 microM CLA suppressed the expression of scd1 mRNA in the H2.35 mouse liver cells by 60%. Further studies with enzymatically prepared c9,t11 isomer showed that the inhibitory effect of CLA on scd1 mRNA expression in H2.35 liver cells was by isomers other than the c9,t11-CLA.

Differential expression of hepatic stearoyl-CoA desaturase gene 1 in male and female mice

The expression of hepatic stearoyl-CoA desaturase (SCD1) mRNA abundance and the fatty acid profile in male and female mice were compared. The expression of the SCD1 mRNA is significantly higher in female compared to male mice and that this difference is accompanied by higher levels of palmitoleic and oleic acid in the livers of female mice.

Lipid metabolism in pigs fed beef tallow or high-oleic acid sunflower oil

The objectives of this study were to establish the effects of high-oleic sunflower oil (HOSO) and beef tallow on tissue fatty acids and stearoyl-CoA desaturase activities in swine; and to compare effects of HOSO and tallow on swine plasma triglycerides and lipoprotein-cholesterol fractions. Sixteen gilts were divided into two groups: eight fed a control diet containing 10 g/100 g beef tallow, and eight fed a diet containing 10 g/100 g HOSO. Plasma samples were obtained before feeding began and at 4 weeks and 8 weeks of dietary treatment. Samples were obtained from longissimus dorsi muscle, liver, adipose and duodenal mucosa for the measurement of fatty acid composition and stearoyl-CoA desaturase activity. The HOSO diet increased (P < 0.05) the concentrations (mumol/g wet weight of tissue) of 18:1 and 18:2 (n-6) in adipose tissue. In muscle from pigs fed the HOSO diet, concentrations of 14:0, 16:0, 16:1, 18:0, 18:1, and 18:2 (n-6) decreased (P < 0.05) relative to muscle from pigs fed the beef tallow diet; only 14:0 and 16:1 were reduced in liver by the HOSO diet. Stearoyl-CoA desaturase specific activity [(pmol 7 min-1 mg-1 microsomal protein)] was 40 percent lower, and activity expressed as pmol 7 min-1 g-1 tissue) was 20 percent lower, in adipose tissue of pigs fed HOSO (P < 0.05). No differences due to dietary treatment were observed for desaturase activity from muscle, liver or intestinal mucosa. Plasma triglycerides declined steadily in the tallow-fed pigs, possibly reflecting the lower percentages of liver 18:0 and 18:1 acids, relative to the HOSO-fed pigs. The animals responded similarly to the addition of fat (beef tallow or HOSO) to their diets with increased (P < 0.05) plasma total, LDL- and HDL-cholesterol by 4 weeks of treatment. Total cholesterol, LDL-, VLDL- or HDL-cholesterol were not different between pigs fed beef tallow or HOSO. Thus, differences in fatty acid composition of the diets were sufficient to alter tissue fatty acid composition and adipose tissue desaturase activity, but insufficient to alter plasma lipoprotein cholesterol.

Metabolism of n-6 fatty acids by NIH-3T3 cells transfected with the ras oncogene

N-6 fatty acid metabolism was compared in NIH-3T3 cells and DT cells, which differ only in the presence of the v-Ki-ras oncogene. Non-dividing cells were incubated with [1-14C]-labelled fatty acids (18:2n-6, 18:3n-6, 20:3n-6 and 20:4n-6) at different time intervals (2-24 h) and concentration (0-120 microM). In both cells lines, the uptake of different fatty acids from the medium was similar and reached a maximum at 6-8 h. All fatty acids reached the same maximum level in DT cells, whereas, the relative uptake of added fatty acids by NIH-3T3 cells was different: 20:4n-6 > 20:3n-6 > 18:2n-6 = 18:3n-6. Throughout the incubation (2-24 h), desaturation and elongation of n-6 fatty acids was more active in DT cells than in NIH-3T3 cells. However, in both cell lines, incubated with different n-6 fatty acid precursors, the levels of radiolabelled 20:4n-6 were relatively constant. In DT cells, phosphatidylcholine was found to be the major fraction labelled with n-6 fatty acids precursors and those of endogenous synthesis, whereas, in NIH-3T3 cells the neutral lipid fraction, particularly triglycerides, was also strongly labelled. In concentration dependent studies, phospholipid labelling by fatty acids was saturable. At lower concentrations, especially in DT cells, phospholipids were labelled predominantly. As the concentration increased there was an overflow into the triglyceride fraction. Since the differences in fatty acid metabolism between the two cell lines cannot be related to the growth rate, it is suggested that they were a consequence of the expression of the v-Ki-ras oncogene.

Liver delta 5 and delta 6 desaturase activity differs among laboratory rat strains

This study was designed to examine the variations among rat strains in hepatic fatty acid desaturase activities and to determine the correlations between the activities of these enzymes and the levels of each microsomal fatty acid. Wistar rats from two different sources as well as Long-Evans and Sprague-Dawley rats were selected to assess, under standard and identical experimental conditions, the liver delta 5 and delta 6 desaturase activities. Both desaturase activities were significantly reduced by 56% in Sprague-Dawley rats when compared to BB-Wistar control rats, whereas intermediate reduced values were detected in Wistar (CR) and Long-Evans strains. The activities of delta 5 and delta 6 desaturases were significantly and positively correlated with each other. However, no significant correlations were detected between either delta 5 or delta 6 desaturase activities and levels of any of their fatty acid substrates or any other of the major microsomal fatty acids. Fatty acid composition of microsomal total lipids showed strain dependency. A positive correlation was detected between the microsomal levels of the two major final products of both desaturases, namely 20:4n-6 and 22:6n-3. In general, the sum of n-3 or n-6 fatty acids but not the ratio of one to the other, varied among rat strains. The study demonstrated that delta 6 and delta 5 desaturase activities are strain-related. The data also suggested that (i) the desaturation activity should be measured and not predicted from the fatty acid composition and (ii) different rat strains should be used for lipid metabolic studies before conclusions are drawn for rats in general.