I. N. T. de Gómez Dumm

The activating effect of dietary protein on linoleic acid desaturation

The desaturation of14C-1-linoleic acid to γ-linolenic acid and their incorporation into the microsomal lipids of rats fed on a balanced diet and a protein diet were measured in vitro. It was shown that a protein diet does not change significantly the distribution of the radioactivity among the different lipidic fractions compared to the animals fed on a balanced diet. However the microsomal desaturation of linoleic acid to γ-linolenic acid increased in the rats maintained on a protein diet. Besides, the amount and composition of the free fatty acids present in the microsomes of the animals fed on both diets were similar enough to discard the hypothesis that they may modify the desaturation of linoleic acid produced by the diet. The enzymic activity of the linoleyl desaturase of liver microsomes of animals fed on a protein diet, measured in substrate saturating conditions, is greater than in animals with balanced diet. Consequently the results support the hypothesis that a protein diet increases specifically the desaturating activity of the microsomes.

Effect of Thyroxine on Δ6 and Δ9 Desaturation Activity

Many studies have revealed that thyroid hormones markedly affect lipid metabolism in man and in several species of animals. Concerning fatty acid biosynthesis it was demonstrated that the administration of thyroxine stimulates the incorporation of l–14c acetate into fatty acids in rats and mice (Dayton et al, 1960) (Gompertz and Greenbaum, 1966) (Marchi and Mayer, 1959). According to Gompertz and Greenbaum (1966) these observations appear to be associated with an increase of stearyl-CoA desaturase activity. Moreover Myant and Iliffe (1963) found that rats treated with thyroxine showed an inhibition of acetate incorporation, but not of malonate incorporation, into fatty acids by mitochondria free, subcellular liver preparations. Other authors have shown that the thyrotoxic state was accompanied by an increased incorporation of acetyl-CoA to fatty acid and a rise in the activity of fatty acid synthetase in rat livers (Diamant et al, 1972) (Roncari and Murthy, 1975). However, in vitro studies of fatty acid synthesis in which liver supernatant of 105,000 xg and microsomal preparations were incubated with the hormone showed that thyroxine inhibits de novo synthesis of palmitate and stimulates the desaturation reactions (Faas et al, 1972).

Comparative effect of a protein diet on the desaturation, elongation and simultaneous desaturation and elongation of linoleic acid

The effect of a protein diet on the biosynthesis of polyunsaturated fatty acids of the linoleic acid family was studied by incubation of rat liver microsomes with labeled linoleic acid. The incubation was performed in desaturating, elongating and desaturating-elongating conditions. In desaturating conditions, linoleic acid was converted to γ-linolenic acid, whereas in elongating conditions it was converted to 20∶2, 22∶2 and 24∶2. In desaturating-elongating conditions, labeling was found in γ 18∶3, 20∶2, 20∶3, 20∶4 and 22∶2. A protein diet increased the oxidative desaturation of linoleic acid to γ-linolenic and arachidonic acid biosynthesis, whereas the elongating reaction was not enhanced in the experimental conditions tested. It is suggested that the main controllable step in the linoleic acid family is the oxidative desaturation of linoleic acid to γ-linolenic acid.

Effect of epinephrine and dibutyryl cyclic AMP on Δ5-desaturation activity of rat liver microsomes

The effect of epinephrine and dibutyryl cyclic AMP on the oxidative desaturation of [1-14C]-eicosatrienoic acid to arachidonic acid of rat liver microsomes has been studied. Epinephrine, at a dose of 1 mg/kg/body weight, produced a significant decrease on Δ5-desaturation activity 3 hr after the injection. This effect was maintained up to 12 hr and reached the control values 48 hr after the hormone administration. Dibutyryl cyclic AMP treatment for 24 hr (5 mg/8 hr/100 g body weight) also produced a significant decrease of the conversion of eicosatrienoic acid to arachidonic acid in rat liver microsomes. The effect of epinephrine on Δ5-desaturation activity was postulated to be evoked through an increase of the intracellular concentration of cyclic AMP.

Effect of different carbon sources on Δ5 desaturation activity of HTC cells

SummaryThe effect of different carbon sources on Δ5 desaturation activity in Minimal Deviation Hepatoma 7288 c (HTC) cells was studied. When HTC cells were incubated in the absence of carbon sources in the medium (fasted cells) the conversion of [1-14C]eicosa-8,11,14-trienoic acid to arachidonic acid increased significantly compared to those cells incubated in S-77 medium (fed cells). This activity was not modified if fasted. cells were refed with glucose. However, the activity decreased significantly by the addition of lactalbumin hydrolysate to fasted cells. This effect can not be attributed to individual aminoacids since the addition of them to an aminoacid free medium produced no changes on Δ5 desaturation activity. The incubation of HTC cells with S-77 medium supplemented with glucose, pyruvate or glucose plus pyruvate, showed similar Δ5 desaturation activity to those cells incubated in S-77 medium alone.

Biosynthesis of polyunsaturated fatty acids from the linoleic acid family in cultured cells.

HTC cells (designated HTC for hepatoma tissue culture) were derived from the ascites form of a rat-carried Morris hepatoma 7288 C (Thompson et al, 1966). Previous studies have revealed that cells of this kind are able to desaturate and elongate fatty acids. In this respect it was demonstrated that culture HTC cells preserved the ability to desaturate stearic to oleic acid (Δ9 desaturase), α-linolenic acid to octdeca-6, 9,12,15-tetraenoic acid (Δ6 desaturase), and eicosa-8,11,14-trienoic acid to arachidonic acid (Δ5 desaturase) (Alaniz et al, 1975). They are also able to convert α-linolenic acid to higher homologs with 5 and 6 double bonds by desaturation and elongation reactions. These results also proved the existence of Δ4 desaturase activity (Alaniz et al, 1975). However, it was shown that the cell cultured in Swim’s medium supplemented with serum possessed a very low capacity to convert labeled linoleic acid of the medium to arachidonic acid. Nevertheless, these tumor cells readily converted eicosa-8,11,14-trienoic acid to arachidonic acid (Alaniz et al, 1975; Gaspar et al, 1975). Therefore, the difficulty of these cells to synthesize arachidonic acid from linoleic acid may reside in a step previous to the Δ5 desaturation of eicosa-8, 11, 14-trienoic acid. This step could be a Δ6 desaturation of linoleic acid. The discrepancy between the biosynthesis of linoleic and α-linolenic acid series is difficult to explain considering that the same enzyme desaturates linoleic and ±-linolenic acids in Δ6 position (Brenner and Peluffo, 1966) (Brenner, 1971; Brenner, 1974) (Ninno et al, 1974).

Effect of cyclosporine and sirolimus on fatty acid desaturase activities in cultured HEPG2 cells.

The aim of the present work was to evaluate the influence of cyclosporine (CsA) and sirolimus (SRL) on fatty acid (FA) desaturase activities. These enzymes (named Delta9, Delta6, and Delta5 desaturases) catalyze reactions leading to the biosynthesis of n-9, n-6, and n-3 FA families. n-3 FA family, derived from alpha-linolenic acid, is involved in the prevention of vascular events, which appear after successful kidney transplantation. Five groups of HepG(2) cells in culture were treated with either CsA (1 microg/microL and 2 microg/microL) or SRL (10 ng/mL and 20 ng/mL) for 3 days, including a control group without immunosuppressive treatment. We studied the incorporation and metabolic conversion of radioactive [1-(14)C]palmitic, linoleic, and eicosatrienoic acids. We also analyzed fatty acid composition. The distribution of radioactive metabolic products after incubation of these cells with [1-(14)C]palmitic acid revealed a decrease in Delta9 desaturase activity in the presence of each immunosuppressive drug: CsA = 0.61 +/- 0.01; SRL = 0.59 +/- 0.04 versus control = 0.79 +/- 0.05 (P < .01). We observed a significant increase in Delta6 and Delta5 desaturase activities under the influence of the immunosuppressive drugs: radiolabeled linoleic acid (CsA: 0.93 +/- 0.04; SRL: 1.02 +/- 0.03 vs control 0.60 +/- 0.03; P < .01) and eicosatrienoic acid (CsA: 1.12 +/- 0.02; SRL: 1.07 +/- 0.01 vs control 0.75 +/- 0.01; P < .01). In conclusion, CsA and SRL modulated the biosynthesis of polyunsaturated FAs, decreasing Delta9 desaturase and increasing Delta6 and Delta5 desaturase activities.