A comparison of the metabolism of [3-14C]-labeled 22- and 24-carbon (n-3) and (n-6) unsaturated fatty acids by rat testes and liver

Chronic sucrose intake decreases concentrations of n6 fatty acids, but not docosahexaenoic acid in the rat brain phospholipids

We investigated the influence of high sucrose intake, administered in drinking water, on the lipid profile of the brain and on the expression of SREBP1c and Δ-desaturase genes. Adult male rats received 30% sucrose solution for 20 weeks (Sucrose group), or plain water (Control group). After the 20th week of sucrose treatment, the Sucrose group showed permanent hyperglycemia. Sucrose treatment also increased the amount of total lipids and fatty acids in the brain. The brain fatty acid profile of total lipids as well as phosphatidylethanolamine, phosphatidylcholine and cardiolipin of the Sucrose group was extensively changed. The most interesting change was a significant decrease in n6 fatty acids, including the important arachidonic acid, whereas the content of oleic and docosahexaenoic acid remained unchanged. RT-qPCR revealed an increase in Δ-5-desaturase and SREBP1c gene expression. In conclusion, high sucrose intake via drinking water extensively changes rat brain fatty acid profile by decreasing n6 fatty acids, including arachidonic acid. In contrast, the content of docosahexaenoic acid remains constant in the brain total lipids as well as in phospholipids. Changes in the brain fatty acid profile reflect changes in the lipid metabolism of the rat lipogenic tissues and concentrations in the circulation.

Lipogenesis and lipid peroxidation in rat testes after long-term treatment with sucrose and tannic acid in drinking water

We studied the influence of long-term treatment with sucrose and tannic acid in drinking water on the fatty acid profile and lipid peroxidation in rat testes. Male Wistar rats were supplemented with sucrose (30% w/v) or with sucrose and tannic acid (sucrose 30% w/v, tannic acid 0.1% w/v) in drinking water. The treatment with sucrose elevated blood glucose levels in the plasma (p < .05) and decreased the testis weight (p < .05) and testis index (p < .05) of the rats. Sucrose treatment increased monounsaturated fatty acids (MUFA) and C22:6n3, and decreased n6 fatty acids in testis tissue. Lipid peroxidation was significantly increased after sucrose administration in plasma (p < .05) and testis tissue (p < .01). The addition of tannic acid led to the decrease in lipid peroxidation in the plasma (p < .05) and testis (p < .05), a further increase in MUFA and decrease in n6 fatty acids. In conclusion, sucrose significantly altered the testis fatty acid profile with an increase in MUFA and C22:6n3, and a decrease in n6 fatty acids. Tannic acid attenuated oxidative stress and hyperglycaemia, but it did not improve pathological changes in the fatty acid composition of the testis.

Bioconversion of α-linolenic acid into n-3 long-chain polyunsaturated fatty acid in hepatocytes and ad hoc cell culture optimisation

This study aimed to establish optimal conditions for a cell culture system that would allow the measurement of 18∶3n-3 (ALA) bioconversion into n-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA), and to determine the overall pathway kinetics. Using rat hepatocytes (FaO) as model cells, it was established that a maximum 20∶5n-3 (EPA) production from 50 µM ALA initial concentration was achieved after 3 days of incubation. Next, it was established that a gradual increase in the ALA concentration from 0 up to 125µM lead to a proportional increase in EPA, without concomitant increase in further elongated or desaturated products, such as 22∶5n-3 (DPA) and 22∶6n-3 (DHA) in 3 day incubations. Of interest, ALA bioconversion products were observed in the culture medium. Therefore, in vitro experiments disregarding the medium fatty acid content are underestimating the metabolism efficiency. The novel application of the fatty acid mass balance (FAMB) method on cell culture system (cells with medium) enabled quantifying the apparent enzymatic activities for the biosynthesis of n-3 LC-PUFA. The activity of the key enzymes was estimated and showed that, under these conditions, 50% (Km) of the theoretical maximal (V_max = 3654 µmol.g⁻¹ of cell protein.hour⁻¹) Fads2 activity on ALA can be achieved with 81 µM initial ALA. Interestingly, the apparent activity of Elovl2 (20∶5n-3 elongation) was the slowest amongst other biosynthesis steps. Therefore, the possible improvement of Elovl2 activity is suggested toward a more efficient DHA production from ALA. The present study proposed and described an ad hoc optimised cell culture conditions and methodology towards achieving a reliable experimental platform, using FAMB, to assist in studying the efficiency of ALA bioconversion into n-3 LC-PUFA in vitro. The FAMB proved to be a powerful and inexpensive method to generate a detailed description of the kinetics of n-3 LC-PUFA biosynthesis enzymes activities in vitro.

Relative efficacies of alpha-tocopherol, N-acetyl-serotonin, and melatonin in reducing non-enzymatic lipid peroxidation of rat testicular microsomes and mitochondria

In this study, we examined the relative efficacies of alpha-tocopherol, N-acetyl-serotonin, and melatonin in reducing ascorbate-Fe(2+) lipid peroxidation (LPO) of rat testicular microsomes and mitochondria. Special attention was paid to the changes produced on the highly polyunsaturated fatty acids (PUFAs) C20:4 n6 and C22:5 n6. The LPO of testicular microsomes or mitochondria produced a significant decrease of C20:4 n6 and C22:5 n6. Both long-chain PUFAs were protected when the antioxidants were incorporated either in microsomes or mitochondria. By comparison of the IC50 values obtained between alpha-tocopherol and both indolamines, it was observed that alpha-tocopherol was the most efficient antioxidant against the LPO induced by ascorbate-Fe(2+) under experimental conditions in vitro, IC50 values from the inhibition of alpha-tocopherol on the chemiluminescence were higher in microsomes (0.14 mM) than in mitochondria (0.08 mM). The protective effect observed by alpha-tocopherol in rat testis mitochondria was higher compared with microsomes, associated with the higher amount of [C20:4 n6] + [C22:5 n6] in microsomes than that in mitochondria. Melatonin and N-acetyl-serotonin were more effective in inhibiting the LPO in mitochondria than that in microsomes. Thus, a concentration of 1 mM of both indolamines was sufficient to inhibit in approximately 70% of the light emission in mitochondria, whereas a greater dosage of 10 times (10 mM) was necessary to produce the same effect in microsomes. It is proposed that the vulnerability to LPO of rat testicular microsomes and mitochondria in the presence of both indolamines is different because of the different proportion of PUFAs in these organelles.

The roles of anabolic and catabolic reactions in the synthesis and recycling of polyunsaturated fatty acids

Generally the biosynthesis and degradation of compounds take place in separate subcellular compartments. The synthesis of 22 carbon acids, with their first double bond at position 4, requires anabolic enzymes in the endoplasmic reticulum as well as peroxisomal beta-oxidation enzymes. Partial degradation-resynthesis cycles, using enzymes in these two subcellular compartments, may play an important role in determining what PUFA are available for membrane lipid biosynthesis.

Peroxisomal straight-chain Acyl-CoA oxidase and D-bifunctional protein are essential for the retroconversion step in docosahexaenoic acid synthesis

Docosahexaenoic acid (DHA, C22:6n-3) is essential for normal brain and retinal development. The nature and subcellular location of the terminal steps in DHA biosynthesis have been controversial. Rather than direct Delta4-desaturation of C22:5n-3, it has been proposed that this intermediate is elongated to C24:5n-3, desaturated to C24:6n-3, and "retroconverted" to DHA via peroxisomal beta-oxidation. However, this hypothesis has recently been challenged. The goal of this study was to determine the mechanism and specific enzymes required for the retroconversion step in human skin fibroblasts. Cells from patients with deficiencies of either acyl-CoA oxidase or D-bifunctional protein, the first two enzymes of the peroxisomal straight-chain fatty acid beta-oxidation pathway, exhibited impaired (5-20% of control) conversion of either [1-14C]18:3n-3 or [1-14C]22:5n-3 to DHA as did cells from peroxisome biogenesis disorder patients comprising eight distinct genotypes. In contrast, normal DHA synthesis was observed in cells from patients with rhizomelic chondrodysplasia punctata, Refsum disease, X-linked adrenoleukodystrophy, and deficiency of mitochondrial medium- or very long-chain acyl-CoA dehydrogenase. Acyl-CoA oxidase-deficient cells accumulated 2-5 times more radiolabeled C24:6n-3 than did controls. Our data are consistent with the retroconversion hypothesis and demonstrate that peroxisomal beta-oxidation enzymes acyl-CoA oxidase and D-bifunctional protein are essential for this process in human skin fibroblasts.

The effect of alpha-tocopherol on the lipid peroxidation of mitochondria and microsomes obtained from rat liver and testis

The effect of intraperitoneal administration of alpha-tocopherol (100 mg/kg wt/24 h) on ascorbate (0.4 mM) induced lipid peroxidation of mitochondria and microsomes isolated from rat liver and testis was studied. Special attention was paid to the changes produced on the highly polyunsaturated fatty acids C20:4 n6 and C22:6 n3 in liver and C20:4 n6 and C22:5 n6 in testis. The lipid peroxidation of liver mitochondria or microsomes produced a significant decrease of C20:4 n6 and C22:6 n3 in the control group, whereas changes in the fatty acid composition of the alpha-tocopherol treated group were not observed. The light emission was significantly higher in the control than in the alpha-tocopherol treated group. The lipid peroxidation of testis microsomes isolated from the alpha-tocopherol group produced a significant decrease of C20:4 n6 , C22:5 n6 and C22:6 n3, these changes were not observed in testis mitochondria. The light emission of both groups was similar. The treatment with alpha-tocopherol at the dose and times indicated showed a protector effect on the polyunsaturated fatty acids of liver mitochondria, microsomes and testis mitochondria, whereas those fatty acids situated in testis microsomes were not protected during non enzymatic ascorbate-Fe2+ lipid peroxidation. The protector effect observed by alpha-tocopherol treatment in the fatty acid composition of rat testis mitochondria but not in microsomes could be explained if we consider that the sum of C20:4 n6 + C22:5 n6 in testis microsomes is 2-fold than that present in mitochondria.