Acid Composition Of Microsomal Lipids Research Articles

Lipid Modifications of Microsomes Isolated from Villus and Crypt Zones of Bovine Intestinal Mucosa: Relationship with Fatty Acid Binding Protein

The present studies were conducted to examine the fatty acid composition of microsomal lipids of bovine small intestine. Microsomes and cytosol were isolated from mucosal scrapings enriched with villus and cryts cells, and the following studies were conducted to: 1) analyse fatty acids from microsomal lipids; 2) incorporate 1–14C oleic acid to microsomal lipids; and 3) bind 1–14C oleic acid to cytosolic proteins of villus and crypt zone. The results of these studies demonstrated that: (1) the major unsaturated fatty acids of microsomes were oleic (C18:1 n–9), linoleic (C18:2 n–6) and arachidonic acids (C20:4 n–6), which increased from crypt to villus tip of the bovine intestinal mucosa; (2) gel filtration chromatography indicated that the low-molecular weight cytosolic proteins obtained from superficial mucosal scrapings contained the greatest oleic acid binding activity; (3) the incorporation of 1–14C oleic acid to microsomes was higher in phospholipids, triglycerides and cholesterol esters from villus than in crypts zones; (4) the protein content of cytosol and microsomes was longer in villus zones than in crypts zones; (5) the peroxidizability index showed the highest value in villus microsomes.

Effect of polyunsaturated fatty acid deficiency on dipole relaxation in the membrane interface of rat liver microsomes

The influence of a fat-free diet on the lipid dynamics of rat liver microsomes and liposomes of microsomal lipids was studied by using different fluorescence methods. Lifetime distribution and rotational diffusion of probes with different localization in the lipid bilayer were measured using multifrequency fluorometry. Lateral mobility was studied by measuring excimer formation of pyrenedodecanoic acid. Dipolar relaxation in the interfacial region was studied using 2-dimethylamino-6-lauroylnaphthalene (Laurdan). In spite of large changes in the fatty acid composition of microsomal lipids, polyunsaturated fatty acid deficiency showed no effect on the lifetime distribution and rotational mobility of 1,6-diphenyl-1,3,5-hexatriene (DPH), 1-(4-(trimethylamino)phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH), 2-, 7- and 12-(9-anthroiloxy)stearic acids. The treatment did not change the lateral diffusion of pyrenedodecanoic acid, either. However, generalized polarization of Laurdan fluorescence was higher in polyunsaturated fatty acid deficient microsomes as compared to the polyunsaturated fatty acid sufficient ones. This effect was also observed in liposomes of the total microsomal lipids, indicating that the changes in fatty acid composition resulting from polyunsaturated fatty acid deficiency produced a small but significant decrease in the rate of dipolar relaxation in the region of the lipid polar groups of the bilayer. The absence of lipid gel phase domains in rat liver microsomes was also indicated by Laurdan fluorescence features.

Modulation of Lipid Chylomicron-Synthesizing Enzymes in Rats by the Dietary (n-6):(n-3) Fatty Acid Ratio

The effect of diets with various (n-6):(n-3) polyunsaturated fatty acid (PUFA) ratios and a constant polyunsaturated: saturated fatty acid ratio on the basal activity of chylomicron lipid synthesizing enzymes was investigated in rat intestinal microsomes. Enzymes studied were: acyl-CoA:cholesterol acyltransferase (ACAT); acyl-CoA:lysophosphatidylcholine acyltransferase (MGAT) and acyl-CoA:1,2-diacylglycerol acyltransferase (DGAT). Results showed that after a 4-wk feeding period, ACAT, ACLAT and DGAT basal activities were significantly enhanced by the dietary fatty acids of the (n-3) series, whereas MGAT activity was not affected. When the highest (n-6):(n-3) ratio (51.0) was compared with the lowest (0.8), the increase attained was about 58, 76 and 73% for ACAT, ACLAT and DGAT, respectively. Fatty acid composition of microsomal lipids was drastically altered by the diets because (n-3) PUFA replaced the (n-6) series as the dietary (n-6):(n-3) ratio was lowered. These compositional changes could explain the observed modification in the membrane-bound enzyme activities. We suggest that (n-3) PUFA ingestion leads to an enhanced velocity of chylomicron synthesis in rats.

The effect of toluene on rat lung benzo[ a]pyrene metabolism and microsomal membrane lipids

Toluene (1 g/kg, i.p., 1 and 4 h) was shown to decrease total cytochrome P-450 (P450) content in rat lung. At both timepoints, reduction in pulmonary P450 content was associated with a decrease in aryl hydrocarbon hydroxylase (AHH) activity, a detoxication pathway for benzo[ a]pyrene (BaP). At 4 h, toluene increased the toxication/detoxication ratios of BaP metabolites in pulmonary microsomes, primarily via inhibition of hydroxy metabolite formation. The structurally analogous solvents p- and m-xylene have been previously shown to produce a similar pattern of MFO changes in rat lung; the inhibition of BaP metabolism was found to be related to alterations in pulmonary microsomal lipids following administration of p- but not m-xylene. In the present study, toluene-induced alterations in MFO parameters were not found to be associated with changes in microsomal lipids. Toluene did not affect either total phospholipid or cholesterol content at either timepoint. Similarly, no changes in speciated phospholipids were observed. Membrane integrity, expressed as conjugated diene formation, also remained unchanged following toluene administration. Toluene did, however, decrease microsomal inner-core membrane fluidity at 4 h but had no effect on membrane leaflet fluidity at either timepoint. These data suggest that the fatty acid composition of microsomal lipids may play a role in the metabolic alterations observed in pulmonary microsomes following toluene administration.

Influence of neonatal age on changes in fatty acid composition of microsomal lipids induced by long-term and short-term cholesterol feeding

Changes observed as a function of chick age in fatty acid composition of lipids from liver microsomes were considerably small, while the unsaturation index increased throughout postnatal development. Supplementation of the diet with 2% cholesterol from hatching produced a significant decrease in the levels of palmitic acid and a clear increase in those of polyunsaturated fatty acids. Maximum effects were attained on day 19 of treatment. Alterations in the fatty acid composition were more pronounced after short-term (48 h) cholesterol feeding. Administration for 48 h of a standard diet to chicks fed a cholesterol diet for 10 days from hatching restored the levels of fatty acids to those of the controls. However, when cholesterol feeding was prolonged for 24 days from hatching, no effect was found after the same treatment. Suppression of the cholesterol diet for 48 h in animals cholesterol fed for 48 h had no effect in 12-day-old chicks while the change to a standard diet produced a reversion of the effect of cholesterol feeding in 26-day-old animals.

Activities of fatty acid desaturases and fatty acid composition of liver microsomes in rats fed β-carotene and 13- cis-retinoic acid

The fatty acid composition of microsomal lipids and the activities of Δ9- and Δ6-desaturases in liver microsomes of rats fed diets supplemented with β-carotene and two levels of 13- cis-retinoic acid were studied. Four groups of male, weanling rats were fed semipurified diets containing 0 or 100 mg β-carotene per kg diet, and 20 or 100 mg 13- cis-retinoic acid per kg diet. After 11 weeks of feeding, the rats were killed, liver microsomes were prepared and assayed for Δ9-desaturase and Δ6-desaturase activities. The activity of Δ9-desaturase was lower in liver microsomes of rats fed β-carotene-supplemented diet or the diet supplemented with the higher level of 13- cis-retinoic acid. Microsomal Δ6-desaturase activity was, however, higher in liver of rats fed 13- cis-retinoic acid; there was no effect of β-carotene on Δ6-desaturase activity. The fatty acid compositional data on total lipids of liver microsomes were consistent with the diet-induced changes in fatty acid desaturases. Phospholipid composition of liver microsomes was also altered as a result of feeding β-carotene or 13- cis-retinoic acid-containing diets. The proportions of phosphatidylethanolamine were generally higher, whereas those of phosphatidylcholine were lower in the experimental groups as compared with the control.

Effect of dietary fatty acid composition on the biosynthesis of unsaturated fatty acids in rat liver microsomes.

AbstractA study was made of the influence of semisynthetic diets of low and high unsaturation on the fatty acid composition and desaturation‐chain elongation enzymatic activity of the liver microsomal fractions of male Sprague‐Dawley rats of different ages. Groups of rats were fed 5 or 20% coconut oil (CO), or a 5 or 20% mixture of corn and menhaden oils (3∶7) (CME) from weaning to 100 wk of age. Growth rate and food consumption were measured during this period in which animals were sacrificed at 36, 57, 77 and 100 wk of age. Both the level and composition of the dietary fat supplements produced marked effects on the fatty acid composition of the liver microsomal lipids. In general, the fatty acid composition of the microsomal fractions reflected that of the dietary fat and was more unsaturated with the higher level of fat fed. The rate of conversion of linoleic to arachidonic acid in assays performed in vitro with liver microsomal preparations from animals of the different groups also showed marked differences. The 6‐desaturase‐chain elongation activity was higher in the 5% than 20% group and corresponded to the essential fatty acid (EFA) status of the animals in these groups as represented by the triene‐tetraene ratio of the microsomal lipid. The relationship of the 6‐desaturase activity to fatty acid composition of the microsomal lipid indicated that if varied directly with the level of 20∶3ω9, 18∶1 and 16∶1 and was inhibited by arachidonic acid. The activity of the 6‐desaturase enzyme system was lowest in the liver microsomal fraction obtained from the animals fed the CME diets and appeared to be suppressed by the high levels of 20∶5 and 22∶6 that accumulated in the microsomal lipid. Accordingly, the levels of arachidonic acid were lower in the microsomal lipid of these groups than those of the corresponding CO groups in spite of a greater abundance of linoleic acid in the diet. The data suggest that the activity of the 6‐desaturase‐chain elongation system is regulated by the fatty acid composition of the microsomal lipid as influenced by the composition of the dietary fat.

Regulation by Dietary Fats of 3-Hydroxy-3-Methylglutaryl-Coenzyme a Reductase in Rat Liver

The effects of various dietary fats on the activity of 3-hydroxy-3-methylglutaryl-Coenzyme A (HMG-CoA) reductase in rat liver microsomes, the rate-limiting enzyme in cholesterogenesis, were examined. A series of experiments demonstrated the dependency of the HMG-CoA reductase activity on the nature of dietary fats. When saturated fats with chain length of 12 to 18 were the dietary sources and were fed at the 10% level for 19 days, feeding fats with shorter chain fatty acids caused a lower enzyme activity compared to those with longer chain fatty acids. The activity was also regulated by the degree of unsaturation of dietary fats; when safflower oil, camellia oil or tristearin were fed at the 10% level for 18 days, the higher the unsaturation, the lower the activity. When trimyristin or tripalmitin were fed at the 10% level for 14 days, addition of essential fatty acid, at the level of minimum daily requirement (1% was replaced by safflower oil), did not affect the enzyme activity. Through the rate of incorporation of mevalonate into cholesterol in the 12,500 x g supernatant fraction of the liver was also found to be influenced by the types of dietary fats, the extent of the response appeared much smaller than that of HMG-CoA reductase. No consistent correlation between the HMG-CoA reductase activity and the content of microsomal cholesterol or cholesteryl ester and the fatty acid composition of microsomal lipids was observed.

Effect of "drugs for liver disease" on hepatotoxic action of carbon tetrachloride. IV. Relationship between fatty acid composition of phospholipids and drug monooxygenation activity in rat liver microsomes and role of phosphorylcholine.

To clarify a correlation between the fatty acid composition and the drug-metabolizing enzyme activity in liver microsomes and the action of drug for liver disease, phosphorylcholine (PC), the fatty acid composition of microsomal lipids and aminopyrine N-demethylase activity were measured during PC administration to carbon tetrachloride (CCl4)-poisoned rats. A dose of CCl4 for 2 days produced a clear per cent decrease in stearic and arachidonic acids and an increase of palmitic and oleic acids of microsomal phospholipids. The phosphatidylcholine in the poisoned rats consisted of less arachidonic and stearic acids and more linoleic acid. Administration of PC resulted in the restoration of the fatty acid content to the control levels at relatively early stage. It was found that there was a good correlation between the arachidonic acid content of the phospholipids, especially phosphatidylcholine, and the aminopyrine N-demethylase activity. Electron transfer between endogenous P-450 and NADPH added significantly dropped and the percentage of P-450 reduced with NADPH added was much smaller in CCl4-poisoned rats. These results suggest that the fatty acid composition of the phospholipids may regulate the structure of the endoplasmic membrane and phospholipids of specific structure may play an essential and functional role in oxidative demethylation in the particles.