Jean Paul Blond

Effect of low levels of dietary fish oil on fatty acid desaturation and tissue fatty acids in obese and lean rats

The effect of very low levels of dietary long-chain n−3 fatty acids on Δ6 desaturation of linoleic acid (18∶2n−6) and α-linolenic acid (18∶3n−3), and on Δ5 desaturation of dihomo-γ-linolenic acid (20∶3n−6), in liver microsomes and its influence on tissue fatty acids were examined in obese and lean Zucker rats and in Wistar rats. Animals fed for 12 wk a balanced diet containing ca. 200 mg of long-chain polyunsaturated n−3 fatty acids per 100 g of diet were compared to those fed the same amount of α-linoleic acid. Low amounts of long-chain n−3 fatty acids greatly inhibited Δ6 desaturation of 18∶2n−6 and Δ5 desaturation of 20∶3n−6, while Δ6 desaturation of 18∶3n−3 was not inhibited in Zucker rats and was even stimulated in Wistar rats. Inhibition of the biosynthesis of long-chain n−6 fatty acids was reflected in a decrease in arachidonic acid (20∶4n−6) content of serum lipids when fasting, and also in the phospholipid fatty acids of liver microsomes. On the contrary, heart and kidney phospholipids did not develop any decrease in 20∶4n−6 during fish oil ingestion. Docosahexaenoic acid (22∶6n−3), present in the dietary fish oil, was increased in serum lipids and in liver microsome, heart, and kidney phospholipids.

Δ5-desaturation of dihomogammalinolenic acid (20:3(n−6)) into arachidonic acid (20 : 4(n−6)) by rat liver microsomes and incorporation of fatty acids in microsome phospholipids

Liver microsomes of rats fed an essential fatty acid (EFA)-deficient diet or a commercial balanced diet were used to study the effect of incubation time on the delta 5-desaturation of [14C]dihomogammalinolenic acid (20:3(n-6)) into arachidonic acid (20:4(n-6)) and incorporation of the two acids into microsomal phospholipids. The EFA-deficient diet highly increased the desaturation rate of 20:3(n-6). Incorporation of the formed 20:4(n-6) into microsomal phospholipids was also increased but at saturating concentration of substrate only. At early times of incubation, the precursor 20:3(n-6) was rapidly incorporated into phospholipids. Formation and incorporation of 20:4(n-6) into phospholipids proceeded more progressively. Data suggest that desaturation of 20:3(n-6) and incorporation of both 20:3(n-6) and 20:4(n-6) into phospholipids occur concomitantly and independently.

Elongation and desaturation of arachidonic and eicosapentaenoic acids in rat liver. Effect of clofibrate feeding

The fatty acid elongation-desaturation ability of 5,8,11,14-eicosatetraenoic (20:4(n-6)) and 5,8,11,14,17-eicosapentaenoic (20:5(n-3)) acids was determined in both liver microsomal and light mitochondrial (rich in peroxisomes) fractions of untreated and clofibrate treated rats. The elongation and the subsequent desaturation steps were performed in the corresponding favorable media. 20:5(n-3) elongation was about 2-times more extensive than that of 20:4(n-6). Clofibrate feeding for 10 days resulted in a marked decrease in the elongation rate with the two substrates, while the delta 4 desaturation rate was increased. There were small differences in the elongation rate between the microsomal and light mitochondrial fractions, however, the relative delta 4 desaturation rate was higher in the light mitochondrial fraction than microsomes.

Incorporation of Δ6- and Δ5-desaturation fatty acids in liver microsomal lipid classes of obese Zucker rats fed n − 6 or n − 3 fatty acids

The aim of this work was to study the effect of dietary n − 6 (as borage oil) and of n − 3 (as fish oil) fatty acids on the incorporation — in liver microsomal lipid classes — of fatty acids involved in Δ6- and Δ5-desaturations in obese Zucker rat compared with their lean littermates and with Wistar control rats. We observed that body and liver weights were decreased when obese Zucker rats were fed the fish oil diet. The major part of the radioactivity was recovered, in the obese Zucker rats, into the neutral lipids and especially into the triacylglycerols, while it was recovered into the phospholipid classes, especially into phosphatidylcholine, in the two other strains. Results show, in all phenotypes, an increased α-linolenic acid Δ6-desaturation in PL classes when the rats were fed the fish oil diet. However, a decreased linoleic acid Δ6- and Δ5-desaturation was observed in obese Zucker rats fed the fish oil diet. The fish oil diet favours the n − 3 fatty acid biosynthesis and incorporation into liver microsomal lipid classes to the prejudice of the n − 6 fatty acid series. The fatty acid incorporation is simultaneously regulated by the genetical phenotype and dietary fatty acids.

Influence of cyclopropene fatty acids (Baobab seed oil) feeding on the in vitro Δ9 desaturation of stearic acid in rat liver microsomes

Abstract Δ9 desaturation of [1−14C] stearic acid to oleic acid was studied in liver microsomes of rats fed either fresh Baobab seed oil, containing cyclopropene fatty acids (malvalic acid and sterculic acids), or heated Baobab oil, containing only minor amounts of these acids. This was compared with rats fed a control oil mixture or a fat-free diet. Up to 50 nmol of substrate, Δ9 desaturation rate was the same in rats fed the three fat diets. From 50 to 150 nmol, the desaturation rates were practically constant in rats fed fresh Baobab seed oil. It increased in heated oil-fed rats at the same rate as in the control group, but more slowly than in the fat-free diet group. Fatty acid composition of liver microsomal lipids did not reflect the in vitro observed desanturation rate because monounsaturated fatty acids were in the same percentages in fresh and heated Baobab seed oil-fed rats. Moreover, the proportion of arachidonic acid was lower, and that of linoleic acid higher for both diets, in comparison with controls, suggesting a decreased Δ6 and/or Δ5 desaturation rate.

Incorporation into liver microsomal lipids of linoleic and stearic acids and of their respective products of Δ6 and Δ9 desaturation, γ-linolenic and oleic acids: effect of age and of blackcurrant seed oil

The incorporation of [1-14C]linoleic and [1-14C]stearic acid and of their Δ6 and Δ9 desaturation products (γ-linolenic and oleic acids, respectively) into different classes of lipids was studied in liver microsomes of rats in function of the diet (blackcurrant seed oil diet, containing γ-linolenic acid, versus control diet) and in function of age (3, 6 and 9 months). After Δ6 desaturation, total radioactivity was distributed between phospholipids, especially phosphatidylcholine, and neutral lipids. The desaturation product, γ-linolenic acid, was totally recovered in the phospholipid fraction. Blackcurrant seed oil, which decreased the rate of Δ6 desaturation in 6- and 9-month-old rats, also decreased the incorporation of radioactivity in total phospholipids, especially in phosphatidylcholine. At 6 months of age, after Δ9 desaturation, the majority of radioactivity was recovered in neutral lipids principally as oleic acid, the desaturation product. The precursor, stearic acid, was highly incorporated into phospholipids, especially in rats on a diet of blackcurrant seed oil.

Intestinal conversion of linoleic acid to arachidonic acid in the rat

Abstract The arachidonic acid (C20:4, n-6) appearing in intestinal lymph during linoleic acid (C18:2, n-6) absorption may originate from enterocyte synthesis or from the liver either after secretion in biliary phospholipids at the same time dietary linoleic acid absorption occurs or via plasma. The radioactivity measured in the total bile collected during the 6 hours of linoleic acid absorption is too small to explain hepatic origin of the C20:4 detected by high performance liquid chromatography analysis of labeled fatty acids recovered in the lymph, in the intestinal mucosa, and the intestinal wall at the peak of linoleic acid intestinal absorption. This study confirms the probability that under in vivo conditions, during the absorption processes, rat intestine is able to convert dietary linoleic acid independent of liver desaturases and elongase activities.