Lucie Frémont

Essential fatty acids in trout serum lipoproteins, vitellogenin and egg lipids

This paper describes evidence of (n−3) and particularly of 22∶6 (n−3) fatty acid enrichment in trout lipoproteins as well as in vitellogenin, egg lipovitellin and oil globule. Among the lipoproteins, HDL and LDL were the main forms of blood lipid transport, whereas phospholipids and cholesteryl esters are the preferential chemical carriers for (n−3) fatty acid transport. However, cholesteryl esters were less important as esterified fatty acid carriers than in man. Taken together with the data obtained in mammals, our results suggest that there may be a relationship between EFA activity and the distribution of the EFA among the lipoprotein lipid fractions in vertebrates, irrespective of the EFA series. Administration of an (n−3) fatty acid deficient diet for three months prior to trout spawning produced a significant increase in egg lipid content, primarily as a result of the increase of the oil globule composed almost exclusively of triacylglycerols. This diet decreased the 22∶6 (n−3), as well as the (n−3) fatty acid contents of lipoproteins, lipovitellin, vitellogenin and the oil globule. In contrast, the (n−3) fatty acid level was always higher in lipoproteins and lipovitellin than in the vitellogenin and the oil globule. Moreover, the relative levels of 22∶6 (n−3) and total (n−3) fatty acids were quite similar in lipoproteins and lipovitellin on the one hand, and in vitellogenin and the oil globule on the other. These findings suggest a direct relationship between the two forms of plasma lipid transport and the two egg compartments. During ovogenesis, dietary lipids seemed to be diverted from the adipose tissue and essentially deposited in the egg.

Effect of dietary fatty acids differing by chain lengths and ω series on the growth and lipid composition of turbot Scophthalmus maximus L.

1. A previous paper (Gatesoupe et al., 1977) showed that turbot had a specific requirement for omega 3HPUFA since equivalent dietary amounts of 18:3 omega 3 or omega 3HPUFA (0.55% of the diet) did not lead to the same growth performances. 2. In the present paper, we demonstrated that fish given a high level of dietary 18:3 omega 3 (3.7% of the diet), without omega 3HPUFA, presented better growth than those offered a lower level of 18:3 omega 3, and almost the same performances as fish receiving 0.57% omega 3HPUFA. 3. This suggested that turbot, like trout, might be able to use the 18:3 omega 3 as a precursor of the omega 3 series. Furthermore, according to the present relatively short-term experiment, elongation-desaturation reactions of the omega 3FA did not appear to be reduced with low dietary omega 3FA levels. 4. On the other hand, these types of reactions seemed to be totally missing with the 18:2 omega 6. Thus, it may be assumed that there was no direct relationship between growth and omega 3 elongating-desaturating activities, and that omega 3 lowering fish body content was not the cause, or at least not the only cause, of poor growth in long-term experiments.

Effects of a (n−3) polyunsaturated fatty acid-deficient diet on profiles of serum vitellogenin and lipoprotein in vitellogenic trout (Salmo gairdneri)

During the 6 months of vitellogenesis, 3-year-old female trout (Salmo gairdneri) were fed either an enriched (E) or an (n−3) polyunsaturated fatty acid (PUFA)-deficient (D) diet; serum vitellogenin (VG) and lipoproteins (d<1.21 g/ml) were analyzed at the third month of vitellogenesis (September) and at ovulation (December). The serum content of high density lipoproteins (HDL), the major protein class, maintained a mean value of 1500 mg/dl at both stages and with both diets. On the contrary, very low density lipoproteins (VLDL) were 90% higher during vitellogenesis than at spawning time, whereas excess vitellogenin circulated at this period (6580 mg/dl serum with diet E). The diet deficient in (n−3) lowered serum vitellogenin content by 16% in September and by 26% in December. The degree of (n−3) PUFA incorporation moderately decreased in low density lipoproteins (LDL) and in HDL with the (n−3)-deficient diet. The effect was more pronounced for 20∶5. On the other hand, essential 22∶6 was incorporated into vitellogenin at the same rate in September as in December with diet E (23% and 25%, respectively), whereas after a 3-month deficiency, the percentage fell to 12%; this percentage rose again to 19% at spawning time. These findings show that, although stored (n−3) PUFA were not exhausted after a 6-month dietary deficiency, the incorporation of essential fatty acids (EFA) into vitellogenin during the early stages of oogenesis was low, suggesting changes in egg composition that may influence hatching.

Fatty acid composition of lipids in the trout—I. Influence of dietary fatty acids on the triglyceride fatty acid desaturation in serum, adipose tissue, liver, white and red muscle

Abstract 1. 1. The present study examined the influence of 6 and 10% lipid-diets on the fatty acid composition of triglyceride body compartments and the influence of two diets differing by their n-6 and n- 3 HPUFA content on the bioconversion of 18:2 n- 6 and 18:3 n- 3 . 2. 2. A 6% fat diet caused a high level of 18:1 n- 9 as previously reported in fish and mammals for low fat diets. 3. 3. The lipid content of trout serum was very high (about 2000 mg/100 ml) but the apolar (triglycerides + cholesteryl esters) and more polar (phospholipids + free cholesterol) components in trout serum were balanced as in man. 4. 4. A useful index [P + Σ(n−x)]/P , where P is the precursor of the n − x series, allows us to determine the relative importance of the Δ9, or Δ6, desaturation. 5. 5. The n-3 HPUFA seem to present a feedback effect on the n-x and n-6 FA bioconversions as reported by some authors whereas the Δ6 desaturation of 18:1 n-9 was blocked. 6. 6. The general decreasing importance of the Δ6-desaturation in the compartments is as followed: liver, serum, intestine and muscle, adipose tissue.

A comparison of the lipoprotein profiles in male trout (Salmo gairdneri) before maturity and during spermiation

1. The distribution and concentration of blood lipoproteins were determined in three groups of male rainbow trout (Salmo gairdneri) each, fed the same diet and reared at a temperature of 17-18 degrees C. 2. The three groups (A, B and C) differed as to age (A and B were 1 yr old, while C was 3 yr old) and to degree of sexual maturity (A was sexually immature, while B and C were in spermiation). 3. Total serum lipoprotein levels reached high values in A, B and C (1900, 2400 and 1500 mg/100 ml. respectively) but their distribution depended largely on the degree of sexual maturity of the fish. 4. Very low density lipoproteins (VLDL) and low density lipoproteins (LDL) were predominant in juvenile trout, whereas high density lipoproteins (HDL) accounted for more than 50% of the total lipoproteins in spermiating trout. 5. In the latter class of lipoproteins, the phospholipid comprised 70% of the total lipid. 6. Essential 22:6 (n-3) was the main polyunsaturated fatty acid in all the lipid fractions of each of the lipoprotein classes; it was found in higher percentages in structural lipid, phospholipid and cholesterol ester, comprising between 35 and 40% of the total fatty acids. 7. These findings support the hypothesis that the production and utilization of lipoproteins in trout are related to the annual formation of gonadal tissue. The lipoproteins might be vehicles for cholesterol and essential fatty acid 22:6 (n-3), incorporated into gonadal tissue during gametogenesis.

Fatty acid composition of lipids in the trout—II. Fractionation and analysis of plasma lipoproteins

Abstract 1. 1. Blood level of lipoproteins was studied in adult male trout. Blood samples were collected in April, i.e. 3–4 months after the spawning period. 2. 2. Samples from 15 fish were pooled for analysis. The main classes of lipoproteins: chylomicrons, VLDL, LDL, HDL were present, but their electrophoretic mobility was different from that of human lipoproteins. 3. 3. The proportions of VLDL, LDL, HDL were respectively 26, 51 and 23% of total lipoproteins. The eventual correlation of the predominance of LDL and the annual reproductive cycle has not been elucidated yet. 4. 4. The major lipids in the different classes of lipoproteins were TG in VLDL and PL in LDL and HDL. The level of total cholesterol was 235 mg/100 ml plasma; about half of it was unesterified in all classes of lipoproteins. The NEFA contents of the plasma fractions d 1.21 g/ml were negligible as compared to those of the esterified forms of fatty acids. 5. 5. The level of essential fatty acid 22:6 n- 3 in all classes of lipoproteins was much higher than in the dietary lipids. It is suggested that a part of the dietary 18:3 n- 3 was elongated and desaturated in the intestinal epithelium and incorporated into chylomicrons and VLDL.

Response of plasma lipids to dietary cholesterol and wine polyphenols in rats fed polyunsaturated fat diets.

This experiment was designed to evaluate the effects of dietary red wine phenolic compounds (WP) and cholesterol on lipid oxidation and transport in rats. For 5 wk, weanling rats were fed polyunsaturated fat diets (n−6/n−3=6.4) supplemented or not supplemented with either 3 g/kg diet of cholesterol, 5 g/kg diet of WP, or both. The concentrations of triacylglycerols (TAG, P<0.01) and cholesterol (P<0.0002) were reduced in fasting plasma of rats fed cholesterol despite the cholesterol enrichment of very low density lipoprotein + low density lipoprotein (VLDL+LDL). The response was due to the much lower plasma concentration of high density lipoprotein (HDL) (−35%, P<0.0001). In contrast, TAG and cholesteryl ester (CE) accumulated in liver (+120 and +450%, respectively, P<0.0001). However, the cholesterol content of liver microsomes was not affected. Dietary cholesterol altered the distribution of fatty acids mainly by reducing the ratio of arachidonic acid to linoleic acid (P<0.0001) in plasma VLDL+LDL (−35%) and HDL (−42%) and in liver TAG (−42%), CE (−78%), and phospholipids (−28%). Dietary WP had little or no effect on these variables. On the other hand, dietary cholesterol lowered the α-tocopherol concentration in VLDL+LDL (−40%, P<0.003) and in microsomes (−60%, P<0.0001). In contrast, dietary WP increased the concentration in microsomes (+21%, P<0.0001), but had no effect on the concentration in VLDL+LDL. Cholesterol feeding decreased (P<0.006) whereas WP feeding increased (P<0.0001) the resistance of VLDL+LDL to copper-induced oxidation. The production of conjugated dienes after 25 h of oxidation ranged between 650 (WP without cholesterol) and 2,560 (cholesterol without WP) μmol/g VLDL+LDL protein. These findings show that dietary WP were absorbed at sufficient levels to contribute to the protection of polyunsaturated fatty acids in plasma and membranes. They could also reduce the consumption of α-tocopherol and endogenous antioxidants. The responses suggest that, in humans, these substances may be beneficial by reducing the deleterious effects of a dietary overload of cholesterol.

Dietary sunflower oil reduces plasma and liver triacylglycerols in fasting rats and is associated with decreased liver microsomal phosphatidate phosphohydrolase activity

Plasma and liver lipids were studied in male weanling rats fed diets containing moderate levels of fat (6% by weight) as sunflower oil (SF diet, rich in linoleic acid), salmon oil (SM diet, rich in long-chain n-3 fatty acids), or a blend of peanut and rapeseed oil (PR diet, rich in oleic acid). After nine weeks of feeding, the fasting plasma cholesterol concentrations were 49 and 24% lower in groups SM and SF, respectively, as compared to group PR. Both dietary salmon oil and sunflower oil lowered the tricylglycerol concentration of plasma and liver but, unexpectedly, the response was higher with sunflower oil. Indeed, in group SM the values were 15 and 30% lower in plasma and liver, whereas in group SF, they were 24 and 53% lower, respectively. As compared to group PR, liver triacylglycerols and microsomes contained 2.5- and 2.3-fold less oleic acid, respectively, in group SF, and they were 9.2- and 3.2-fold enriched in n-3 fatty acids, respectively, in group SM. The liver triacylglycerol concentrations were correlated with changes in the microsomal Mg2+-dependent phosphatidate phosphohydrolase activity (r=0.47,P<0.01). As oleic acid, unlike long-chain n-3 fatty acids, is considered to promote the triacylglycerol synthesis and secretion, our findings suggest that changes in the membrane fatty acid composition could affect the triacylglycerol content of liver and plasma. Moreover, the availability within the liver, of oleic acid, predominantly incorporated into triacylglycerols, might limit the triacylglycerol production in SF-fed rats.

Serum vitellogenin and yolk proteolipid complex composition in relation to ovarian growth in rainbow trout Salmo gairdneri (rich.)

Abstract 1. 1. Ovarian growth in rainbow trout was estimated by the measurement of the gonadosomatic index, the oocyte diameter, and the proportion of the yolk proteolipid complex. 2. 2. These parameters were related to the levels of the serum yolk precursor, vitellogenin. 3. 3. An extensive oocyte enlargement occurs during the first 3 months of the exogenous vitellogenesis. 4. 4. After this period, the proportion of yolk proteolipid complex in the oocyte decreased relative to the weight of the oocyte whereas an excess of vitellogenin was present in the serum. 5. 5. An increase of the very low density lipoproteins level was also observed in the serum. 6. 6. Chemical composition of the serum vitellogenin was unchanged while that of the yolk proteolipid complex showed some variations throughout the reproductive cycle.

Effect of essential fatty acid deficiency on lipid composition of basolateral plasma membrane of pig intestinal mucosal cells

The effect of essential fatty acid (EFA) deficiency on the lipid composition of basolateral plasma membranes (BPM) from intestinal mucosal cells was investigated in weaning pigs fed control or EFA-deficient diets for 12 weeks. The phospholipid and cholesterol contents relative to protein were similar in both groups, showing a cholesterol/phospholipid molar ratio of 0.6. The distribution of phospholipid classes was also unaffected by the diet. In contrast, fatty acid profiles of the two phospholipid main classes, phosphatidylcholine and phosphatidylethanolamine were altered by EFA deficiency. Linoleic acid (18∶2n−6) was largely reduced, whereas arachidonic acid (20∶4n−6) only slightly decreased in EFA-deficient pigs. The unsaturation index was essentially maintained by high levels of oleic acid (18∶1n−9) and by conversion of oleic acid to 5,8,11-eicosatrienoic acid (20∶3n−9). Finally, during the period of EFA deficiency, the lipid composition of BPM of the intestinal mucosal cells was little affected, suggesting a preferential uptake of 20∶4n−6 and (or) precursor mobilized from other tissues. However, an effect of dietary treatment on the function of membrane-associated proteins cannot be ruled out.