Biosynthetic pathways of polyunsaturated fatty acids

Liver desaturase activities and FA composition in monkeys. Effect of a low-protein diet

The aim of the present study was to measure delta9-, delta6-, and delta5-desaturase activities in liver microsomes, as well as phospholipid FA composition of liver and erythrocytes in monkeys fed a control or low-protein diet during the postweaning period. Ten Saimiri sciureus boliviensis (Cebidae) of both sexes were employed; at 12 mon of age they were separated into two groups fed ad libitum on a control or a low-protein diet for 24 mon. Saimiri sciureus had active delta9, delta6, and delta5 liver desaturase enzymes, and these activities were influenced by the diet. A low-protein diet produced a significant reduction in delta5-desaturation capacity, an increase in delta9-desaturase activity, and no change in delta6-desaturase activity (P < 0.05). These changes, evoked by protein deprivation, were reflected in the liver phospholipid FA composition. Increases in the proportion of saturated FA and in monounsaturated oleic acid (18:1n-9) and a decrease in the proportion of PUFA of the n-6 and n-3 series were produced in the animals fed a low-protein diet (P < 0.0001).

Effects of altering dietary fatty acid composition on prostaglandin synthesis and fertility

Several studies over the past 20 years have demonstrated that subjects on diets composed of substances with high levels of n-3 polyunsaturated fatty acids (PUFAs) (e.g. fish) have a decreased incidence of heart disease. On this basis, a recent report from the Department of Health has advised UK consumers to decrease the proportion of saturated as opposed to unsaturated fats in their diet and to increase the ratio of n-3 to n-6 PUFAs. This could be achieved by altering the amounts of these constituents in milk and meat. n-3 Fatty acids can most easily be added to animal feed as either fish oil or linseed oil and can be increased in the blood and milk of ruminants following protection to avoid hydrogenation in the rumen. In western countries the ratio of consumption of n-6 to n-3 PUFAs is greater than 10 and current evidence tends to suggest that a ratio nearer 5 would be more desirable and compatible with cardiovascular well being. As fertility in the UK dairy herd is already poor, it is important to establish whether alterations in dietary n-3 and n-6 PUFAs affects herd fertility before widespread changes in animal diets are recommended. Therefore, this review considers the role played by PUFAs and eicosanoids in fertility, with particular reference to the implications for farm livestock production. The evidence reviewed shows that alteration of the concentration and ratio of n-6 and n-3 PUFAs in feeds can influence prostaglandin synthesis/metabolism in a number of mammalian systems. The changed patterns of prostaglandin synthesis can as a consequence, affect the diverse functions (e.g. hormone secretion) that are normally mediated via prostaglandins. Similarly, changes in prostaglandin synthesis effected through manipulation of PUFAs has a major bearing on fertility (as PGs affect many reproductive parameters, e.g. ovulation). Several studies in cattle and other mammals, show that feeding or infusing different types of fat with varying PUFA content to females can alter: the number and size of ovarian follicles, the ovulation rate, progesterone production by the corpus luteum, the timing of luteolysis and gestational length. In the male most recent work has focussed on sperm production and experiments in fowl have demonstrated clear effects of dietary PUFAs on both the sperm membrane phospholipid composition and on fertilizing ability.

Adrenic acid delta4 desaturation and fatty acid composition in the liver of marine-oil fed streptozotocin diabetic rats

The aim of the present study was to assess the effect of streptozotocin diabetes and insulin treatment on adrenic acid delta4 desaturation and fatty acid composition of liver microsomes in Wistar rats fed a fat free semi-synthetic basal diet supplemented with 10% EPA-rich marine oil. Results showed that, in liver microsomes of hyperglycemic rats, the 22:6n-3/22:5n-3 ratio in total lipids was elevated and desaturation of adrenic acid to n-6 docosapentaenoic acid was enhanced. Insulin treatment with 2.0 I.U./100 g body weight-1 twice a day for 3 days resulted in hypoglycemia and suppressed both the increased delta4 n-6 desaturation and 22:6n-3/22:5n-3 ratio. It is concluded that the delta4 desaturation enzyme system, which is activated by experimental diabetes, is regulated by mechanisms different from those regulating delta6 and delta5 desaturations.

Growth, fatty acid composition of plasma lipid classes, and plasma retinol and alpha-tocopherol concentrations in full-term infants fed formula enriched with omega-6 and omega-3 long-chain polyunsaturated fatty acids

Full-term infants fed formula without dietary long-chain polyunsaturated fatty acids (LCF) exhibit significantly lower plasma LCP values than breast-fed infants. We studied prospectively two groups of healthy full-term infants fed conventional infant formula without LCP (F, n = 10) or the same formula enriched with both omega-6 and omega-3 LCP (LCP-F, n = 12). Anthropometric data were obtained and fatty acid (FA) compositions of plasma phospholipids, triglycerides and sterol esters as well as plasma retinol and alpha-tocopherol concentrations were determined at 5 days and 1, 2, 3 and 4 months of age. Gains in weight, length and head circumference did not differ between the two groups throughout the study period. Plasma FA values did not differ at 5 days of age. Between 1 and 4 months of age, plasma phospholipids of infants fed LCP-F consistently had significantly (p < 0.05) higher percentages of arachidonic acid (1 month: 9.7 (0.8) versus 7.0 (1.3) %wt/wt, 4 months: 8.7 (0.5) versus 6.6 (1.0) %wt/wt, median (interquartile range), LCP-F versus F) and docosahexaenoic acid (1 month: 2.9 (0.5) versus 1.6 (0.3) %wt/wt; 4 months: 2.9 (0.4) versus 0.9 (0.3) %wt/wt). Plasma retinol and alpha-tocopherol concentrations did not differ between the two groups throughout the study. We conclude that this form of LCP enrichment of formula for full-term infants effectively enhances plasma LCP contents without detectable adverse effects. The potential effects on functional outcome need to be studied carefully in prospective clinical trials.

Age-related changes in linoleic acid bioconversion by isolated hepatocytes from spontaneously hypertensive and normotensive rats

This study points out the hepatocyte interconversion of the linoleic acid family during hypertension. Hepatocyte delta 6 desaturase activity was higher in 1 month-old spontaneously hypertensive rats than in normotensive controls. A similar tendency was observed in 6 month-old SHR. delta 5 desaturase activity was higher only in 1 month-old spontaneously hypertensive rats as compared to controls. Desaturase activities were particularly high at the age of 6 months. The hepatocyte fatty acid composition showed an impairment of n-6 polyunsaturated fatty acid metabolism in spontaneously hypertensive animals. Changes were greater in the young prehypertensive rats than in adults. A storage of n-3 long chain fatty acids is remarkable in adult hypertensive rats, suggesting an alteration in peroxisomal oxidation. Such modifications may be related to the prostaglandin precursors availability to peripheral tissues such as kidney.

Altered membrane fatty acids of cultured human retinal pigment epithelium persistently infected with rubella virus may affect secondary cellular function

Persistent infection with rubella virus (RV) can alter secondary functions of host cells. Previously we had documented defective phagocytosis of latex beads by cultured human retinal pigment epithelial cells (RPE), persistently infected with M-33 RV (RPE/RV). Here, examining possible mechanisms for altered function, we reported significant differences between the total esterified fatty acids (FA) of RPE and RPE/RV membranes, measured by gas liquid chromatography. RPE/RV contained an increased proportion of saturated FA, particularly palmitic acid, with a presence of unusual chromatographic FA peaks co-eluting with odd-numbered long-chain carbon atom FA not normally found in human cells. Apical membrane microvilli, structures essential to phagocytic activity of RPE and RPE/RV, observed by scanning and transmission electron microscopy, were similar in number and appearance between uninfected RPE and RPE/RV cells before and after latex bead addition. However, RPE/RV microvilli, possibly reflecting altered membrane FA composition, engaged latex beads less effectively than uninfected RPE microvilli. In addition, microvilli remained abnormally distributed on RPE/RV cell surfaces at 48 h after latex addition. Thus, RV persistent infection may affect the cellular membrane fluidity and functional activity of human cells with increased saturated FA proportions and altered FA components of membrane phospholipids. These changes may participate in the defective phagocytosis of RPE/RV.

Adrenic acid delta 4 desaturation and fatty acid composition in liver microsomes of spontaneously diabetic Wistar BB rats

We examined the delta 4 (n-6) desaturation and the fatty acid composition of liver microsomes in the insulin-dependent spontaneously diabetic Wistar Bio-Breeding (BB) rat. The desaturation of adrenic acid to n-6 docosapentaenoic acid was decreased in the normo- and hyperglycemic diabetic rats. Insulin treatment with 1.0 IU. 100 g body weight-1 twice a day for 2 days restored the reduced activity during the hypoglycemic period. The pattern of responses was similar to that of linoleic acid delta 6 and dihomo-gamma-linolenic acid delta 5 desaturases, with a non-parallel relationship between the desaturation system and the glycemia. The microsomal fatty acid composition of BB rat liver reflected only partially to the delta 4 desaturation at different states of glycemia. Factors other than impaired desaturation system are involved in the fatty acid metabolism of spontaneously diabetic rats.

Circulating cytotoxic immune components in dominant Charcot-Marie-Tooth syndrome

Activated T cells, measured repeatedly in the demyelinating peripheral neuropathy, Charcot-Marie-Tooth syndrome (CMT; hereditary motor sensory neuropathy), might participate in myelin loss by a destructive inflammatory autoimmune process. To explore this possibility, plasma proportions of hydroxyleukotrienes, their fatty acid precursor, arachidonic acid, and lymphocyte epitopes associated with immune cell activation expression were measured in 18 adults with dominant, Type I CMT. Compared to age-matched normal controls, CMT I patients showed eicosanoid-linked immunoactivation by an elevated content of 12-hydroxy-eicosatetraenoic acid (12-HETE) in parallel with a decreased plasma percentage of its fatty acid precursor, arachidonic acid. CMT patients also had increased numbers of peripheral lymphocytes expressing activation-related epitopes, CD25+, CD26+, CD4+, and CD4/CD45RO+ primed memory cells, with enhanced CD8+ cytotoxic cells and soluble CD8 protein content. Therefore, endogenously stimulated CMT I lymphocytes include functional cytotoxic cells which appear to deplete the plasma fatty acid precursor of prostenoid agents during the secretion of potentially destructive cytokines.

Microsomal desaturation-elongation of linoleic acid following parenteral feeding with lipid emulsions in the rat

The effect of total parenteral nutrition (TPN) with lipid emulsion to supply either 27.5% or 2% total calories on in vitro desaturation-elongation of 18:2(n-6) by liver microsomes was studied in the rat. The emulsion lipid contained ca. 50% 18:2(n-6) plus 8% 18:3(n-3) or 77% 18:2(n-6) plus 0.5% 18:3(n-3). The reaction rate was influenced by the in vitro substrate concentration and inhibited above 50 mumol 18:2(n-6)/mg microsomal protein. At maximum rates of desaturation-elongation, the formation of triene and tetraene (n-6) fatty acids was reduced in rats given either of the two emulsions. The rate of (n-6) pentaene formation was increased in rats given the emulsion with low 18:3(n-3) but not in rats given the emulsion with 8% 18:3(n-3). Analyses of the microsomal lipid indicated increased free cholesterol in all rats that received TPN. Esterified cholesterol was increased only in rats given 27.5% TPN calories as lipid. Microsomal total phospholipids and phospholipid class distributions were not altered by TPN. The data are consistent with reports of reduced levels of long-chain desaturation-elongation metabolites of 18:2(n-6) in tissue phospholipids following infusion of parenteral lipid. The data suggest that the mechanism may include alterations in other metabolic pathways such as cholesterol, in addition to desaturase enzyme activities, and may be influenced by both the quantity and fatty acid composition of the lipid infused.

Rapid changes in serum, plasma and erythrocyte lipid compositions, and serum transaminase levels during continuous enteral hyperalimentation by carbohydrates alone

Twelve normal men received twice their estimated basal energy requirement by a carbohydrate solution via a nasogastric catheter during 48 hours, followed by a seven-hour fast. Subsequently, in nine of them 0.5 mg epinephrine was given subcutaneously under ongoing fasting. During hyperalimentation, serum triglycerides, phospholipids, total and free cholesterol, phospholipids/free cholesterol ratio, and plasma free fatty acids decreased, whereas the percentage of free cholesterol increased. During fasting and subsequent epinephrine administration triglycerides and free fatty acids rose without reaching basal levels. Plasma and red blood cell (RBC) fatty acid composition already changed from two hours after the start of the feeding. Most markedly, a steady decrease in RBC 18:2c, omega 6, amounting to more than 17% of the basal value at the end of the observation period was found. Neither in plasma, nor in RBC a concomitant appearance of 20:3c, omega 9 was seen. In RBC, the relative amounts of the saturated fatty acids increased, whereas those of monounsaturated and polyunsaturated fatty acids decreased. RBC content of total fatty acids decreased and that of cholesterol increased. The ratios 16:1c, omega 7/16:0 and 18:3c, omega 6/18:2c, omega 6 in plasma, and 20:3c, omega 6/18:2c, omega 6 in plasma and RBC increased, whereas those of 18:1c, omega 7/16:1c, omega 7 and 20:3c, omega 6/18:3c, omega 6 in plasma decreased. After 48 hours feeding serum glutamic pyruvic transaminase and glutamic oxaloacetic transaminase levels were moderately increased and rose further during fasting. Thus, continuous enteral hyperalimentation by carbohydrates alone rapidly induces profound changes in serum-, plasma-, and RBC lipid compositions and serum parameters of hepatic function.(ABSTRACT TRUNCATED AT 250 WORDS)

[Use of solid fat in dry mixed feed for rainbow trout (Salmo gairdneri). 2. Fatty acid composition of feed and tissue lipids]

The effect of supplemental dietary fat on the fatty acid composition of some tissue lipids of rainbow trout fingerlings was studied. Data showed that dietary fatty acids were deposited nearly unchanged in the adipose tissue. The level of eicosapentaenoic acid, however, dropped significantly. Muscle showed remarkable capacity for deposition of dietary fat, while only minor changes were observed in the fatty acid composition of liver lipids. Levels of some polyenoic acid (e.g. 18: 2 omega 6, 20:4 omega 6, 20:5 omega 3, 22:6 omega 3) showed, that the fish converted lower unsaturated fatty acids to highly unsaturated fatty acids. It was observed that dietary acids had little effect on the fatty acid composition of tissue phospholipids. This result shows, that 17% fat in the diet are tolerated by trout, without alterations in the fat composition of the liver tissue. Probably the low rearing temperature (11 degrees C) had a more pronounced effect on the fatty acid composition of phospholipids than the diet.

Hepatic delta 6-desaturase activity in lean and genetically obese ob/ob mice

Hepatic delta 6-desaturase activity is primarily located in the mitochondrial fraction in mice. Both delta 6- and delta 5-desaturase activities are increased in the liver of young (6-week-old) obese mice. The increase in hepatic delta 6-desaturase activity in obese mice does not occur until weaning. Neither restriction of food intake nor hyperinsulinaemia normalize hepatic delta 6-desaturase activity of obese mice. Both cold acclimation and tri-iodothyronine (30 micrograms/day per kg) decreased hepatic delta 6-desaturase activity of obese mice to levels observed in lean mice, whereas the increase in activity in obese mice was still maintained after the induction of hypothyroidism.

Incorporation and metabolism of exogenous fatty acids by cultured normal and tumoral glial cells

We have investigated the transformation of exogenous radioactive free fatty acids by cultured glial cells and their incorporation into complex lipids. The cells were either tumor lines (C6 and NN) or primary cultures from newborn rat hemispheres. The tumor lines could undergo morphological differentiation with dibutyryl cyclic AMP or bromodeoxyuridine. The fatty acid precursors used were palmitic, stearic, oleic, linoleic and linolenic acids. Tumor cells presented a higher incorporation of the precursors in the cell lipid acyl groups than did normal cells. Tumor cells desaturated and/or elongated palmitic, stearic and oleic acid to a higher extent than did normal cells. In contrast, tumor cells transformed linoleic and linolenic acids to their polyunsaturated derivatives to a lower extent than did normal cells. In differentiated tumor cells, these patterns of metabolism were shifted toward the patterns of normal cells. Tumor cells did not exhibit delta 4-desaturase activity, but such activity was restored in the C6 line upon dibutyryl cyclic AMP-induced differentiation. Transformation of linoleic and linolenic acid is likely to proceed through initial delta 6 desaturation. Phospholipids were preferentially labelled with the radioactive fatty acids, and only a little radioactivity was found in the neutral lipid fraction, mainly in diacylglycerols. Each fatty acid precursor label was incorporated in individual phospholipids to a proportion which reflected the typical acyl group composition of glycerophospholipids; we observed high levels of incorporation of palmitic acid and its derivatives into choline glycerophospholipids, and high levels of incorporation of linolenic acid and its derivatives into ethanolamine glycerophospholipids. This pattern was more marked in tumor cells than in normal cells, and the differentiation of tumor cells partially restored the normal pattern, mainly in bromodeoxyuridine-treated NN cells. Both types of differentiation of glial cell lines can be useful as models for the understanding of membrane physiology in normal and tumor cells.

Reduction of blood pressure associated with dietary polyunsaturated fat

Evidence linking the beneficial effect of dietary polyunsaturated fat on systolic and distolic blood pressure is reported. Under controlled dietary conditions, i.e., when the polyunsaturated fat to saturate fat ratio (P/S) is maintained at about 1.0, with fat providing 25% of total energy intake, blood pressure is significantly lowered in healthy males and females in the 40- to 60-year age group. The subjects selected for these studies were either normotensive or mildly hypertensive. When the subjects resumed their usual diets, their blood pressures reverted to baseline values. Body weights of the subjects remained relatively constant in these studies, and sodium chloride intakes averaged 8 to 12 g per day. It is suggested that the lowering of blood pressure by dietary linoleic acid is mediated through prostaglandins.

Effect of diabetes and insulin replacement on the lipid properties of hepatic smooth endoplasmic reticulum

This study is a characterization of the lipid properties of the smooth and rough endoplasmic reticulum (SER, RER) of liver from streptozotocin-induced diabetic rats. A significant decrease in membrane microviscosity was observed in the SER but not the RER of diabetic rats when compared to that of normal controls. This decrease in SER membrane microviscosity correlated with a decrease in cholesterol/phospholipid ratio of these membranes that could be accounted for solely by a change in the membrane cholesterol content. Changes in phospholipid fatty acyl chain composition were also observed in the SER membranes but these changes were small when compared to the large change in cholesterol content observed. Insulin treatment for only one day did not significantly alter the microviscosity of the SER but after 2, 4 and 6 days of treatment both membrane microviscosity and membrane cholesterol content were restored to values similar to those for normal animals. No significant changes in the RER lipid composition were observed. It is well known that increases in glucose-6-Pase (G-6-Pase) activity of liver ER membranes are associated with diabetic onset. An increase in the specific activity of G-6-Pase was observed in both SER and RER membrane preparations, although the observed increase in the SER membrane is higher. The changes in the G-6-Pase activity of the SER membranes were correlated with the alterations in the microviscosity and lipid composition of these membranes. It is postulated that lipid properties of the SER membranes may contribute to the regulation of G-6-Pase activity in that membrane.

Prostaglandins and their precursors in tissues from rats fed on trans, trans-linoleate

Feeding trans,trans-9,12-linoleate to rats as 50 and 100% of the dietary fat decreased the concentrations of n-6 fatty acids, i.e. 18:2, 20:3 and 20:4, in heart, kidney, lung, adipose tissue and platelets of rats. The concentrations of prostaglandin products prostaglandins E1, E2 and F2 alpha in serum were significantly decreased in rats receiving high concentrations of dietary trans, trans-linoleate.