Effect of various n-3/n-6 fatty acid ratio contents of high fat diets on rat liver and heart peroxisomal and mitochondrial beta-oxidation.

The present work extends tissue investigations previously performed in rat gastric mucosa on lipid metabolism alterations caused by n-3 and n-6 fatty acid-enriched diets. Liver and heart tissues are here studied and demonstrated to undergo, upon exposure to high fat diets with various n-3/n-6 fatty acid ratio contents, biochemical and morphological changes which may be enumerated as follows: (1) Rat liver peroxisomal prostaglandin E2, fatty acid but not bile acid beta-oxidation rates are enhanced, especially upon the diet with the higher n-3/n-6 fatty acid ratio. Mitochondrial beta-oxidation rates are little or not affected by the high fat diets. (2) Rat liver carnitine acyltransferases are stimulated by the high fat diets, the more rich the n-3 fatty acid content, the more pronounced the stimulatory effect. (3) Rat heart peroxisomal and mitochondrial beta-oxidation rates were increased in animals receiving the n-3 fatty acid-enriched diet. At a low n-3/n-6 fatty acid ratio content of the diet, these oxidizing rate values were in control range. The carnitine acyltransferase activities were increased in rat heart to different extents, depending on the n-3/n-6 fatty acid ratio content of the diet. (4) Ultrastructural examination and morphometric determinations on hepatocytes from rats receiving the diets with the lowest and the highest n-3/n-6 fatty acid ratio contents disclose that in the latter case the numbers and fractional volumes of peroxisomes and mitochondria are significantly higher than in the former case.

Function of dietary polyunsaturated fatty acids in the nervous system.

The brain is the organ with the second greatest concentration of lipids; they are directly involved in the functioning of membranes. Brain development is genetically programmed; it is therefore necessary to ensure that nerve cells receive an adequate supply of lipids during their differentiation and multiplication. Indeed the effects of polyunsaturated fatty acid (PUFA) deficiency have been extensively studied; prolonged deficiency leads to death in animals. Linoleic acid (LA) is now universally recognized to be an essential nutrient. On the other hand, alpha-linolenic acid (ALNA) was considered non-essential until recently, and its role needs further studies. In our experiments, feeding animals with oils that have a low alpha-linolenic content results in all brain cells and organelles and various organs in reduced amounts of 22:6(n-3), compensated by an increase in 22:5(n-6). The speed of recuperation from these anomalies is extremely slow for brain cells, organelles and microvessels, in contrast with other organs. A decrease in alpha-linolenic series acids in the membranes results in a 40% reduction in the Na-K-ATPase of nerve terminals and a 20% reduction in 5'-nucleotidase. Some other enzymatic activities are not affected, although membrane fluidity is altered. A diet low in ALNA induces alterations in the electroretinogram which disappear with age: motor function and activity are little affected but learning behaviour is markedly altered. The presence of ALNA in the diet confers a greater resistance to certain neurotoxic agents, i.e. triethyl-lead. We have shown that during the period of cerebral development, there is a linear relationship between brain content of (n-3) acids and the (n-3) content of the diet up to the point where alpha-linolenic levels reach 200 mg for 100 g food intake. Beyond that level there is a plateau. For the other organs, such as the liver, the relationship is also linear up to 200 mg/100 g, but then there is merely an abrupt change in slope and not a plateau. By varying the dietary 18:2(n-6) content, it was noted that 20:4(n-6) optimum values were obtained at 150 mg/100 g for all nerve structures, at 300 mg for testicle and muscle, 800 mg for the kidney, and 1200 mg for the liver, lung and heart. A deficiency in ALNA or an excess of LA has the same main effect: an increase in 22:5(n-6) levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of dietary n-6/n-3 ratios on lipid and prostaglandin E2 metabolism in rat gastric mucosa.

The effects of increased dietary n-3 polyunsaturated fatty acids on gastric mucosal lipid metabolism were studied in rats fed for 8 weeks with different combinations of fish and corn oils. Lipid composition, ex vivo prostaglandin E2 (PGE2) production and enzymatic activities involved in phospholipid metabolism and peroxisomal oxidative catabolism of fatty acids and PGE2 were examined. With dietary n-6/n-3 compositional ratios ranging between 75 and 3.3 it was observed that: (i) the arachidonic acid-to-eicosapentaenoic acid ratio (AA/EPA) fell from infinity to 3.1 and 5.1 in phosphatidylcholines (PC) and phosphatidylethanolamines (PE), respectively; (ii) ex vivo production of PGE2 was lowered by a factor of about 2; and (iii) gastric phospholipase A2 activity was enhanced by 32%. With dietary n-6/n-3 ratio lower than 3.3, stimulation of PGE2-CoA oxidase activity was observed whilst the PGE2 level remained constant. These data suggest that the fish oil-induced decrease in ex vivo PGE2 production is more closely related to a decrease in the membrane AA level than to an enhanced oxidative catabolism of PGE2.

Structural and functional importance of dietary polyunsaturated fatty acids in the nervous system.

The nervous system is the organ with the second greatest concentration of lipids. These lipids participate directly in membrane functioning. Brain development is genetically programmed. It is therefore necessary to ensure that nerve cells receive an adequate supply of nutrients, especially of lipids, during their differentiation and multiplication, and throughout their lives. The effects of polyunsaturated fatty acid deficiency have been extensively studied; prolonged deficiency leads to death in animals. Linoleic acid is now universally recognized to be an essential nutrient. Until recently, however, alpha-linolenic acid was considered non-essential. Feeding animals with oils that have a low alpha-linolenic content results in all brain cells and organelles and various organs having reduced amounts of 22:6n-3, which is compensated for by an increase in 22:5n-6. The speed of recuperation from these anomalies is extremely slow for brain cells, organelles, and microvessels, in contrast to other organs. A decrease in alpha-linolenic series acids in the membranes results in a 40% reduction in the Na(+)-K(+)-ATPase of nerve terminals and a 20% reduction in 5'-nucleotidase. Some other enzymatic activities are not affected, although membrane fluidity is altered. A diet low in alpha-linolenic acid induces alterations in the electroretinogram which disappear with age; motor function and activity are little affected, but learning behavior is markedly altered. The presence of alpha-linolenic acid in the diet confers a greater resistance to certain neurotoxic agents (triethyl-lead). During the period of cerebral development, there is a linear relationship between brain content of n-3 acids and the n-3 content of the diet up to the point where alpha-linolenic levels reach 200 mg for 100 g of food intake. Beyond that level there is a plateau. For other organs, such as the liver, the relationship is also linear up to 200 mg/100 g, but then there is merely an abrupt change in slope and not a plateau. When dietary 18:2n-6 content was varied, it was noted that 20:4n-6 optimum values were obtained at 150 mg/100 g for all nerve structures, 300 mg for testicle and muscle, 800 mg for kidney, and 1200 mg for liver, lung and heart. A deficiency in alpha-linolenic acid and an excess of linoleic acid have the same main effect: an increase in 22:5n-6 levels.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Effect of increasing amounts of dietary fish oil on brain and liver fatty composition.

Increasing dietary fish oil in rat had the following effect on brain lipids: Arachidonic acid regularly decreased; eicosapentanenoic acid, normally nearly undetectable, was present; 22:5(n - 3), dramatically increased but remained below 1% of total fatty acids; cervonic acid was increased by 30% at high fish oil concentration. Saturated and monounsaturated fatty acids were not affected regardless of chain-length. In contrast, in the liver, nearly all fatty acids (saturated, monounsaturated and polyunsaturated) were affected by high dietary content of fish oil, but liver function was normal: serum vitamin A and E, glutathione peroxidase, alkaline phosphatase, transaminases were not affected. Serum total cholesterol, unesterified cholesterol and phosphatidylcholine were slightly affected. In contrast, triacylglycerols were dramatically reduced in proportion to the fish oil content of the diet.

Effects of dietary corn oil and salmon oil on the oxidation of fatty acids and prostaglandin E2 in rat gastric mucosa.

The investigations previously carried out by Grataroli and colleagues (1) to elucidate the relationships between dietary fatty acids, lipid composition, prostaglandin E2 production and phospholipase A2 activity in the rat gastric mucosa are, here, extended. In the present investigations, fatty acid and prostaglandin E2 catabolizing enzymes were assayed in gastric mucosa from rats fed either a low fat diet (corn oil: 4.4% w/w) (referred as control group), a corn oil-enriched diet (17%) or a salmon oil-enriched diet (12.5%) supplemented with corn oil (4.5%) (referred as groups of treated animals) for eight weeks. Peroxisomal fatty acyl-CoA beta-oxidation was induced in the treated animals whereas the activities of catalase and mitochondrial tyramine oxidase were increased and normal, respectively. Mitochondrial acyl-CoA dehydrogenations occurred at higher rates and carnitine acyltransferase activities were enhanced. In addition, the induction of peroxisomal but not mitochondrial prostaglandoyl-E2-CoA beta-oxidation could be demonstrated. Induction of peroxisomal oxidation of fatty acids and prostaglandins is suggested to contribute to the decrease of prostaglandin E2 production in the treated animals, especially those receiving the salmon oil diet, that the above mentioned authors originally reported.

Effects of fish oil, corn oil and lard diets on lipid peroxidation status and glutathione peroxidase activities in rat heart.

In this study, we investigated the effect of various types of fats on heart lipid peroxidation status and on blood lipid parameters. Rats were fed either a low-fat diet (2.2% lard plus 2.2% corn oil), a corn oil diet (17%), a salmon oil diet (12.5%) supplemented with 4.5% corn oil, or a lard diet (15%) supplemented with 2% corn oil. All diets were supplemented with 1% cholesterol. Rats were fed for eight weeks. When compared with the low-fat diet, the salmon oil-diet intake resulted in a lower blood cholesterol, triglyceride and phospholipid concentrations (-50, -56 and -30%, respectively). Corn oil only tended to lower blood lipids; this decrease was significant for triglycerides only (-40%). The hypocholesterolemic effect of salmon oil diet is even more pronounced, if blood cholesterol values are compared with those of rats fed the lard diet. Heart lipid composition was not affected by dietary manipulations. Fatty acid composition of cardiac phosphatidylcholines and phosphatidylethanolamines, however, were altered by high-fat diets. In phosphatidylcholine, salmon oil induced a twelvefold decrease in the n-6/n-3 ratio and a 26% increase in the unsaturation index. For phosphatidylethanolamine, the n-6/n-3 ratio decreased 7.7-fold and the unsaturation index increased by 13%. A 50% decrease of the n-6/n-3 ratio was observed in animals fed the lard diet. Ultramicroscopic examination of ventricles revealed that those of the salmon oil group significantly accumulated lipofuscin-like or ceroid material, whereas this accumulation was barely detectable in hearts of the other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dietary corn oil and salmon oil on lipids and prostaglandin E2 in rat gastric mucosa.

Three groups of male rats were fed either a corn oil-enriched diet (17%, w/w), a salmon oil-enriched diet (12.5%) supplemented with corn oil (4.5%) or a low-fat diet (4.4%) for eight wk to investigate the possible relationships between dietary fatty acids and lipid composition, and prostaglandin E2 level and phospholipase A2 activity in the rat gastric mucosa. High-fat diets induced no important variation in total protein, phospholipid and cholesterol contents of gastric mucosa. Compared with a low-fat diet, corn oil produced a higher n-6/n-3 ratio in mucosal lipids, whereas this ratio was markedly lowered by a fish oil diet. In comparison with the low-fat diet, the production of prostaglandin E2(PGE2) in gastric mucosa of rats fed salmon oil was significantly decreased by a factor of 2.8. In the corn oil group, PGE2 production tended to decrease, but not significantly. In comparison with the low-fat diet, both specific and total gastric mucosal phospholipase A2 activities were increased (+ 18 and 23%, respectively) in the salmon oil group; they were unchanged in the corn oil group. It is suggested that the decrease of gastric PGE2 in rats fed fish oil is not provoked by a decrease in phospholipase A2 activity but may be the result of the substitution of arachidonic acid by n-3 PUFA or activation of PGE2 catabolism.

Effect of dietary salmon oil feeding on rat heart lipid status.

For 2 mo rats were fed a salmon oil diet (12.5%, wt/wt) supplemented with 4.5% (wt/wt) corn oil, a corn oil diet (17%, wt/wt) or a low fat diet (4.4%, wt/wt). Cardiac lipids were analyzed and fatty acid composition of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was determined. Ventricular biopsies were taken for ultramicroscopic examination. Serum cholesterol, triglyceride, phospholipid and vitamin E concentrations were significantly lower in rats fed salmon oil than in those fed the other two diets, whereas serum transaminases and vitamin A were not significantly affected. Cardiac protein, phospholipid, triglyceride and cholesterol concentrations were unaffected by diet. Cardiac phospholipid composition remained unchanged and no significant changes in lyso-PC or lyso-PE levels were observed. However, the salmon oil diet produced a markedly lower n-6/n-3 ratio in both PE and PC than in the other two diets. This was the result of replacement of n-6 polyunsaturated fatty acids (PUFA), primarily 20:4n-6 with n-3 PUFA, primarily 22:6n-3. The unsaturation index of PC and PE was higher with the salmon oil diet than with the other two diets. Ventricular biopsies of rats fed salmon oil showed mild lipid accumulation associated with some lipofuscin-like material. It is suggested that, in rat heart, fish oil led to a moderate accumulation of lipids, the composition of which may include long-chain monounsaturated fatty acids and a degradative form of peroxidized lipids.

High dietary fish oil alters the brain polyunsaturated fatty acid composition.

Feeding adult rats a 17% corn-oil diet for 8 weeks did not change brain polyunsaturated fatty acids (PUFA) compared to rats fed 2.2% corn oil (with 2.2% lard added). When the corn-oil diet was supplemented with 14.5% cod liver oil or 12.5% salmon oil, the fatty acid composition of brain PUFA was significantly altered, even if alpha-tocopherol was added to the salmon-oil diet. Comparing salmon-oil- and cod-liver-oil-fed animals with corn-oil-fed animals, arachidonic acid 22:4(n-6) and 22:5(n-6) were reduced, and 20:5(n-3), 22:5(n-3) and 22:6(n-3) were increased. Liver fatty acids were also significantly altered. Thus, the brain is not protected against a large excess of very-long-chain n-3 PUFA, which increase n-3/n-6 ratio and could lead to abnormal function, and which might be difficult to reverse.

Effect of dietary lipids on the lipid composition and phospholipid deacylating enzyme activities of rat heart.

Rats were fed lard-enriched (17%) or corn oil-enriched (17%) diets and were compared with rats fed a low fat (4.5%) diet. Cardiac protein, DNA, phospholipid (PL) and fatty acid (FA) compositions were analyzed. Neutral phospholipase A, lysophospholipase and creatine kinase activities in the membrane and cytosolic compartments were also investigated. No significant modification of cardiac protein, DNA nor PL was observed among the three groups. Some alterations appeared in the FA composition. A lard-enriched diet induced a significant increase of 22:5n-3 and 22:6n-3 in heart phosphatidylcholine (PC) and phosphatidylethanolamine (PE), whereas a linoleic acid-rich diet induced a specific increase of 22:4n-6 and 22:5n-6 in these two major PL. Compared to rats fed the low fat diet, membrane-associated phospholipase A activity, measured by endogenous hydrolysis of membrane PC and PE, showed a significant increase (+45%) for both PL in rats fed corn oil. However, the activity of membrane-associated phospholipases, measured with exogenous [1-14C]dioleoyl PC, was not different among the three groups of rats. Cytoplasmic activity was decreased in rats fed corn oil, and lysophospholipase and creatine phosphate kinase activities were not significantly affected by diet. FA modification of the long chain n-6 FA induced by corn oil may be responsible for the observed increase in phospholipase activity. Physiological implications are suggested in terms of membrane degradation and prostaglandin production.

Effects of dietary fibers and cholestyramine on the activity of pancreatic lipase in vitro.

Most experiments were conducted in the presence of human gallbladder bile; colipase and pancreatic lipase were purified using porcine pancreas. The adsorption of bile salts, phospholipids and cholesterol from the bile, together with that of pancreatic lipase was measured on wheat bran, cellulose, hemicellulose (xylan), slightly methylated pectin (42%) and cholestyramine. In contrast to cholestyramine which intensively binds biliary lipids (61.7-81.7%) and pancreatic lipase (47.5%), the fibers studied only had a low adsorbent power. The direct influence of these fibers and of cholestyramine at concentrations ranging from 0-5% on lipase activity was measured at constant pH, using two conventional assay systems, long chain triglycerides and tributyrin. In the presence of human bile and colipase, a drastic reduction in triglyceride hydrolysis by lipase was observed with cholestyramine (loss of 66-82%) and wheat bran (loss of 77-94%) at 1% concentration. The other fibers did not have any marked effects on enzyme activity. The use of a radio labeled lipase made it possible to demonstrate that the inhibitory effect of bran on enzyme activity was independent of adsorption phenomena on bran. The fraction of bran that can be solubilized in the aqueous phase, in fact, induced this reduction in activity. The presence of protein inhibitor in bran may be responsible for the reduction in pancreatic lipase activity.