Linoleic acid and antioxidants protect against DNA damage and apoptosis induced by palmitic acid

Polyunsaturated fats are the main target for lipid peroxidation and subsequent formation of mutagenic metabolites, but diets high in saturated fats are more strongly associated with adverse health effects. We show that the common saturated fatty acid, palmitic acid, is a potent inducer of DNA damage in an insulin-secreting cell line, and in primary human fibroblasts. Damage is not associated with upregulation of inducible nitric oxide synthase, but is prevented by two different antioxidants, alpha-lipoic acid and 3,3'-methoxysalenMn(III) (EUK134), which also partly prevent palmitic acid-induced apoptosis and growth inhibition. Since mutagenic metabolites can be formed from peroxidation of polyunsaturated fatty acids, co-administration of palmitic and a polyunsaturated fatty acid might be particularly harmful. Palmitic acid-induced DNA damage is instead prevented by linoleic acid, which is acting here as a protective agent against oxidative stress, rather than as a source of mutagenic metabolites. These results illustrate the complexity of the relationship of dietary fat intake to genotoxicity.     

Suppression of fatty acid synthase by dietary polyunsaturated fatty acids is mediated by fat itself,not by peroxidative mechanism

This study examined the effect of dietary polyunsaturated fatty acids (PUFA) that were supplemented with vitamin E on lipid peroxidation, glutathione-dependent detoxifying enzyme system activity, and lipogenic fatty acid synthase (FAS) expression in rat liver. Male Sprague-Dawley rats were fed semipurified diets containing either 1% (w/w) corn oil or 10% each of beef tallow, corn oil, perilla oil, and fish oil for 4 wk. Alpha-tocopherol was supplemented in perilla oil (0.015%) and fish oil (0.019%). Hepatic thiobarbituric acid reactive substances, an estimate of lipid peroxidation, were not significantly different among the dietary groups. The glutathione peroxidase, glutathione reductase, and glutathione S-transferase activities were all elevated by the polyunsaturated fats, especially fish oil. The activity of FAS was reduced in the polyunsaturated fat-fed groups in the order of fish oil, perilla oil, and corn oil. The mRNA contents decreased in rats that were fed the 10% fat diets, particularly polyunsaturated fats, compared with the rats that were fed the 1% corn oil diet. Similarly, the inhibitory effect was the greatest in fish oil. These results suggest that lipid peroxidation can be minimized by vitamin E; PUFA in itself has a suppressive effect on lipogenic enzyme.     

The oxidation of benzo[a]pyrene-7,8-dihydrodiol mediated by lipid peroxidation in the rat intestine and the effect of dietary lipids

This study has demonstrated that the microsomal fraction of the rat small intestinal mucosa has the capacity to catalyse the oxidation of benzo[a]pyrene(BP)-7,8-diol to BP-diol-epoxides (BPDEs) both by a mechanism involving the mixed-function oxidase system (NADPH-dependent) and as a result of the initiation of peroxidation of the membrane phospholipids by ferrous ions, ascorbate and ADP. The NADPH-dependent reaction was fastest in the proximal part of the intestine and resulted in the formation of approximately equal amounts of BPDE I and BPDE II. The lipid peroxidation-catalysed reaction favoured the production of BPDE I and was maximal in the middle region of the intestine, closely paralleling the rate of lipid peroxidation in the intestinal sections. Feeding rats on a cod liver oil diet, rich in C20:5 and C22:6, significantly increased the incorporation of these fatty acids into the microsomal fractions. This resulted in a greatly increased rate of lipid peroxidation in vitro and a significantly higher rate of lipid peroxidation-catalysed BP-7,8-diol oxidation compared to rats fed fat-free, mono-unsaturated lard or corn oil (58% C18:2) diets. Thus the rate of conversion of BP-7,8-diol to its ultimate carcinogenic forms during lipid peroxidation in the intestinal fractions of rats fed a polyunsaturated fat was quantitatively more important than the NADPH-catalysed reaction as measured in vitro.     

Detection of 4-oxo-2-hexenal, a novel mutagenic product of lipid peroxidation, in human diet and cooking vapor

Since the diet plays an important role in the development of human cancer, it is important to identify mutagens in foods. We have detected a novel mutagenic product, 4-oxo-2-hexenal (4-OHE), in a model lipid peroxidation reaction mixture [H. Kasai, M. Maekawa, K. Kawai, K. Hachisuka, Y. Takahashi, H. Nakamura, R. Sawa, S. Matsui, T. Matsuda, 4-Oxo-2-hexenal, a mutagen formed by omega-3 fat peroxidation, causes DNA adduct formation in mouse organs, Ind. Health 43 (2005) 699-701]. In the present study, the contents of 4-OHE in various food samples were determined by a GC/MS method. Commercial perilla oil (derived from the seed of Perilla frutescens var. frutescens), which is rich in linolenic acid triglyceride (TG), the edible part of broiled fish, and various fried foods contained 4-OHE in the range of 1-70 microg/g. Furthermore, from the ethyl acetate trap (extracts) of the smoke released during the broiling of fish, 4-OHE was also detected by GC/MS. These results provide a warning to humans, who may be exposed to this mutagen. The 4-OHE may be produced from omega-3 polyunsaturated fats, such as alpha-linolenic acid-, docosahexaenoic acid (DHA)- and eicosapentaenoic acid (EPA)-TG, which are more easily oxidized than omega-6 fats, such as linoleic acid-TG.     

Dietary polyunsaturated fatty acids and heme iron induce oxidative stress biomarkers and a cancer promoting environment in the colon of rats

The end products of polyunsaturated fatty acid (PUFA) peroxidation, such as malondialdehyde (MDA), 4-hydroxynonenal (HNE), and isoprostanes (8-iso-PGF_2α), are widely used as systemic lipid oxidation/oxidative stress biomarkers. However, some of these compounds have also a dietary origin. Thus, replacing dietary saturated fat by PUFAs would improve health but could also increase the formation of such compounds, especially in the case of a pro-oxidant/antioxidant imbalanced diet. Hence, the possible impact of dietary fatty acids and pro-oxidant compounds was studied in rats given diets allowing comparison of the effects of heme iron vs. ferric citrate and of ω-6- vs. ω-3-rich oil on the level of lipid peroxidation/oxidative stress biomarkers. Rats given a heme iron-rich diet without PUFA were used as controls. The results obtained have shown that MDA and the major urinary metabolite of HNE (the mercapturic acid of dihydroxynonane, DHN-MA) were highly dependent on the dietary factors tested, while 8-iso-PGF_2α was modestly but significantly affected. Intestinal inflammation and tissue fatty acid composition were checked in parallel and could only explain the differences we observed to a limited extent. Thus, the differences in biomarkers were attributed to the formation of lipid oxidation compounds in food or during digestion, their intestinal absorption, and their excretion into urine. Moreover, fecal extracts from the rats fed the heme iron or fish oil diets were highly toxic for immortalized mouse colon cells. Such toxicity can eventually lead to promotion of colorectal carcinogenesis, supporting the epidemiological findings between red meat intake and colorectal cancer risk.Therefore, the analysis of these biomarkers of lipid peroxidation/oxidative stress in urine should be used with caution when dietary factors are not well controlled, while control of their possible dietary intake is needed also because of their pro-inflammatory, toxic, and even cocarcinogenic effects.     

Assessment of mutagenic activity of repeatedly used deep-frying fats

Mutagenic activity of repeatedly used deep-frying fats was evaluated in relation to chemical characteristics. Deep-frying fat samples were collected from local restaurants and snack bars after sensory indication of abuse. A total of 20 deep-frying fat samples and 2 unused control fat samples was tested. Fat samples were fractionated into non-polar and polar compounds by column chromatography. Amounts of polar compounds obtained ranged from 2% (by weight) for unused fat to 44% for used deep-frying fat. Levels of di- and polymeric triglycerides (DPTG) were determined using gel-permeation chromatography. DPTG concentrations of 13 used deep-frying fat samples exceeded the threshold level of 10% above which fats are rejected for use. In addition thiobarbituric acid-reactive substances (TBA-RS) were measured. Amounts of TBA-RS were just above detection levels for most fat samples. Five used fat samples, however, contained relatively high concentrations of TBA-RS, ranging from 82 to 177 nmoles malondialdehyde/g. Non-polar and polar fractions were screened for mutagenic activity using the Ames mutagenicity assay. Mutagenic activity was found predominantly in polar fractions at doses higher than 1 mg/plate in strains TA97, TA100 and TA104, variously with and without metabolic activation. The highest number of mutagenic samples was detected by strain TA97, which appeared to be most sensitive. Some samples exhibited toxic effects. Chromatography blanks, consisting of solvents processed according to the same procedures as used for fat samples, were not mutagenic. Mutagenic activity was also detected in polar material obtained from unused frying fat. Non-polar fractions of unused frying fats showed no mutagenicity. A frying experiment carried out under laboratory conditions indicated that during repeated and prolonged use of deep-frying fat mutagenic polar substances were formed. Fat samples taken after 20 and 40 h of frying contained increasing amounts of polar compounds. Mutagenic activity was highest after 20 h of frying but was slightly decreased after 40 h of frying. At this stage, however, mutagens also appeared in the non-polar fraction. Mutagenic activity of polar fractions of used deep-frying fats in strain TA97 was positively correlated with levels of TBA-RS, which may indicate the involvement of lipid oxidation products in mutagenicity of used deep-frying fats. No significant correlations were found with other chemical characteristics. In the process of deep-fat frying numerous degradation products are formed, which may include mutagenic heterocyclic amines and other pyrolysates.(ABSTRACT TRUNCATED AT 400 WORDS)     

DNA damage caused by lipid peroxidation products

Lipid peroxidation is a process involving the oxidation of polyunsaturated fatty acids (PUFAs), which are basic components of biological membranes. Reactive electrophilic compounds are formed during lipid peroxidation, mainly alpha, beta-unsaturated aldehydes. These compounds yield a number of adducts with DNA. Among them, propeno and substituted propano adducts of deoxyguanosine with malondialdehyde (MDA), acrolein, crotonaldehyde and etheno adducts, resulting from the reactions of DNA bases with epoxy aldehydes, are a very important group of adducts. The epoxy aldehydes are more reactive towards DNA than the parent unsaturated aldehydes. The compounds resulting from lipid peroxidation mostly react with DNA showing both genotoxic and mutagenic action; among them, 4-hydroxynonenal is the most genotoxic, while MDA is the most mutagenic. DNA damage caused by the adducts of lipid peroxidation products with DNA can be removed by the repairing action of glycosylases. The formed adducts have been hitherto analyzed using the IPPA (Imunopurification-(32)P-postlabelling assay) method and via gas chromatography/electron capture negtive chemical ionization/mass spectrometry (GC/EC NCI/MS). A combination of liquid chromatography with electrospray tandem mass spectrometry (LC/ES-MSMS) with labelled inner standard has mainly been used in recent years.     

Polyunsaturated fat in the methionine-choline-deficient diet influences hepatic inflammation but not hepatocellular injury

Methionine-choline-deficient (MCD) diets that cause steatohepatitis in rodents are typically enriched in polyunsaturated fat. To determine whether the fat composition of the MCD formula influences the development of liver disease, we manufactured custom MCD formulas with fats ranging in PUFA content from 2% to 59% and tested them for their ability to induce steatohepatitis. All modified-fat MCD formulas caused identical degrees of hepatic steatosis and resulted in a similar distribution of fat within individual hepatic lipid compartments. The fatty acid composition of hepatic lipids, however, reflected the fat composition of the diet. Mice fed a PUFA-rich MCD formula showed extensive hepatic lipid peroxidation, induction of proinflammatory genes, and histologic inflammation. When PUFAs were substituted with more saturated fats, lipid peroxidation, proinflammatory gene induction, and hepatic inflammation all declined significantly. Despite the close relationship between PUFAs and hepatic inflammation in mice fed MCD formulas, dietary fat had no impact on MCD-mediated damage to hepatocytes. Indeed, histologic apoptosis and serum alanine aminotransferase levels were comparable in all MCD-fed mice regardless of dietary fat content. Together, these results indicate that dietary PUFAs promote hepatic inflammation but not hepatotoxicity in the MCD model of liver disease. These findings emphasize that individual dietary nutrients can make specific contributions to steatohepatitis.     

The formation of mutagenic derivatives of benzo[a]pyrene by peroxidising fatty acids

Benzo[a]pyrene (B[a]P) when incubated in the presence of peroxidising polyunsaturated fatty acids such as linoleic acid (C18:2), arachidonic acid (C20:4), eicosapentaenoic acid (C20:5) or docosahexaenoic acid (C22:6) was converted to oxidised products. Between 7% and 9% of the B[a]P was oxidised in one hour when incubated with arachidonic acid and docosahexaenoic acid. 1,6- 3,6- and 6,12-Quinone derivatives of B[a]P were identified by HPLC. The products of B[a]P oxidation were shown to be mutagenic when tested using Sister chromatid exchange (SCE) technique and the occurrence of SCEs in CHV79 cells was increased significantly. Lipid peroxides also induced SCEs in the absence of B[a]P and there was a positive correlation between the frequency of SCEs and the extent of lipid peroxidation. The results indicate that the oxidation of B[a]P mediated by the non-enzymic peroxidation of polyunsaturated fatty acids is likely to play a role in mutagenesis and, possibly, also in carcinogenesis.     

Aging-related oxidative stress depends on dietary lipid source in rat postmitotic tissues

We investigate mitochondrial-lipid peroxidation of mitotic (liver) and postmitotic (heart and skeletal muscle) tissues of rats fed lifelong on two different lipid sources: virgin olive oil (monounsaturated fatty acids) and sunflower oil (n–6 polyunsaturated fatty acids). Two groups of 80 rats each were fed over 24 months on a diet differing in the lipid source (virgin olive oil or sunflower oil). Twenty rats per group were killed at 6, 12, 18, and 24 months; liver, heart, and skeletal muscle mitochondria were isolated and the lipid profile, hydroperoxides, vitamin E, and ubiquinone as well as catalase activity measured. Lipid peroxidation was higher in postmitotic tissues, and sunflower oil led to a higher degree of polyunsaturation and peroxidation. The levels of -tocopherol adapted to oxidative stress and preferentially accumulated during aging in heart and skeletal muscle. In conclusion, the type of dietary fat should be considered in studies on aging, since oxidative stress is directly modulated by this factor. This study confirms that postmitotic tissues are more prone to oxidative stress during aging and proposes a hypothesis to explain this phenomenon.     

Increased dietary triacylglycerol markedly enhances the ability of isolated rabbit enterocytes to secrete chylomicrons: an effect related to dietary fatty acid composition.

Dietary fats are efficiently absorbed in the small intestine and transported into the blood via the lymph as chylomicrons, despite enormous variations in the amount and composition of the dietary lipid. The aim of the present study was to investigate how enterocytes respond to increased dietary fats of different composition. Rabbits were fed a low fat chow diet, and chow supplemented with sunflower oil (high n-6 polyunsaturated fatty acids), fish oil (high n-3 polyunsaturated fatty acids), or an oil mixture of a composition similar to that of the typical western diet. Feeding fat for 2 weeks markedly stimulated the ability of the isolated enterocytes to synthesize and secrete apolipoprotein B48, triacylglycerol, and cholesteryl ester (up to 18-, 50-, and 80-fold, respectively) in particles of chylomicron density. The magnitude of stimulation was sunflower oil > western diet lipid > fish oil. Single doses of lipid given 18 h prior to isolation of enterocytes stimulated chylomicron secretion by only 10% of that observed after 2 weeks of dietary supplementation. Enterocytes are replaced rapidly (half-life 1-2 days) by cells which move from the crypts to the tips of the villi, where absorption of nutrients takes place.Our observations suggest that dietary lipids modulate the function of enterocytes as they move from the crypts, so that the cells are 'turned-on' to lipid absorption. The results also show that diets of different fatty acid composition vary in their effects.     

Gene pathways associated with mitochondrial function,oxidative stress and telomere length are differentially expressed in the liver of rats fed lifelong on virgin olive,sunflower or fish oils

This study investigates the effect of lifelong intake of different fat sources rich in monounsaturated (virgin olive oil), n6 polyunsaturated (sunflower oil) or n3 polyunsaturated (fish oil) fatty acids in the aged liver. Male Wistar rats fed lifelong on diets differing in the fat source were killed at 6 and at 24 months of age. Liver histopathology, mitochondrial ultrastructure, biogenesis, oxidative stress, mitochondrial electron transport chain, relative telomere length and gene expression profiles were studied. Aging led to lipid accumulation in the liver. Virgin olive oil led to the lowest oxidation and ultrastructural alterations. Sunflower oil induced fibrosis, ultrastructural alterations and high oxidation. Fish oil intensified oxidation associated with age, lowered electron transport chain activity and enhanced the relative telomere length. Gene expression changes associated with age in animals fed virgin olive oil and fish oil were related mostly to mitochondrial function and oxidative stress pathways, followed by cell cycle and telomere length control. Sunflower oil avoided gene expression changes related to age. According to the results, virgin olive oil might be considered the dietary fat source that best preserves the liver during the aging process.     

A role for dietary lipids and antioxidants in the activation of carcinogens

The ways in which dietary polyunsaturated fats and antioxidants affect the balance between activation and detoxification of environmental precarcinogens is discussed, with particular reference to the polycyclic aromatic hydrocarbon benzo(a)pyrene. The structure and composition of membranes and their susceptibility to peroxidation is dependent on the polyunsaturated fatty acid (PUFA) content of the cell and its antioxidant status, both of which are determined to a large degree by dietary intake of these compounds. An increase in the PUFA content of membranes stimulates the oxidation of precarcinogens to reactive intermediates by affecting the configuration and induction of membrane-bound enzymes (e.g., the mixed-function oxidase system and epoxide hydratase); providing increased availability of substrates (hydroperoxides) for peroxidases that cooxidise carcinogens (e.g., prostaglandin synthetase and P-450 peroxidase); and increasing the likelihood of direct activation reactions between peroxyl radicals and precarcinogens. Antioxidants, on the other hand, protect against lipid peroxidation, scavenge oxygen-derived free radicals and reactive carcinogenic species. In addition some synthetic antioxidants exert specific effects on enzymes, which results in increased detoxification and reduced rates of activation. The balance between dietary polyunsaturated fats, antioxidants and the initiation of carcinogenesis is discussed in relation to animal models of chemical carcinogenesis and the epidemiology of human cancer.     

GPX4 at the Crossroads of Lipid Homeostasis and Ferroptosis

Oxygen is necessary for aerobic metabolism but can cause the harmful oxidation of lipids and other macromolecules. Oxidation of cholesterol and phospholipids containing polyunsaturated fatty acyl chains can lead to lipid peroxidation, membrane damage, and cell death. Lipid hydroperoxides are key intermediates in the process of lipid peroxidation. The lipid hydroperoxidase glutathione peroxidase 4 (GPX4) converts lipid hydroperoxides to lipid alcohols, and this process prevents the iron (Fe²⁺)‐dependent formation of toxic lipid reactive oxygen species (ROS). Inhibition of GPX4 function leads to lipid peroxidation and can result in the induction of ferroptosis, an iron‐dependent, non‐apoptotic form of cell death. This review describes the formation of reactive lipid species, the function of GPX4 in preventing oxidative lipid damage, and the link between GPX4 dysfunction, lipid oxidation, and the induction of ferroptosis.     

Crystallization Kinetics and Mechanical Properties of Nougat Creme Model Fats

Fat crystal networks result from a crystallization process, forming interlinked crystal aggregates of viscoelastic character. Palm oil-based fat crystal networks, such as chocolate and nougat spreads, often show liquid oil separation during storage because the fat crystal network is too weak to retain the liquid oils trapped within its structure. To explore the relationship between crystallization kinetics and subsequent mechanical properties, i) palm oil from three different geographical origins and with diverging crystallization properties, ii) mixtures of Ghanaian palm oil with gradually increasing additions of hazelnut oil, and iii) blends of Ecuadorian palm oil with palm stearin as a tripalmitin (PPP)-rich fraction were investigated. Kinetic parameters were acquired from an extended Avrami model by isothermal differential scanning calorimetry measurements, and the results combined with the elastic properties measured by oscillation rheology since studying crystallization kinetics alone insufficiently informs about the mechanical/structural properties needed to overcome liquid oil separation. Rate constants of all investigated fats followed bell-shaped curves, with curve progression strongly dependent on the lipid composition. Ameliorating crystallization properties entailed enhanced elastic properties. The higher the maximum rate constants, the higher the elastic modulus and the gel rigidity of the respective fats. However, two different linear regions of elastic modulus versus PPP or solid fat content resulted, depending on whether palm oil was diluted with hazelnut oil or blended with a PPP-rich fraction. Hazelnut oil strongly diluted crystallizable portions of the structuring fat, thereby decreasing the mechanical properties in a power-law fashion, because the fat crystal network became less connected between fat crystal aggregates.

     

Predicting duodenal flows and absorption of fatty acids from dietary characteristics in ovine and bovine species: a meta-analysis approach

Dietary and ruminal factors modify the ruminal biohydrogenation (RBH) of polyunsaturated fatty acids (FA), with duodenal FA flows being quantitatively and qualitatively different from FA intake. Using a meta-analysis approach from a database on duodenal flows of FA in ruminants, this study aimed to determine predictive equations for duodenal and absorbed flows of saturated FA, C18:1, C18:2 and C18:3 isomers, odd- and branched-chain FA (OBCFA), C20:5n-3, C22:5n-3 and C22:6n-3 and to quantify the effects of dietary and digestive factors on those equations. The database was divided into four subsets: forage, seed, vegetable oils or animal fats (oil/fat), and fish products (fish) subsets. Models of duodenal and absorbed FA flows were obtained through variance–covariance analysis. Effects of potential interfering factors (conservation mode and botanical families of forages, lipid source, technological processing of lipid supplements, diet composition and animal characteristics) were analysed. We obtained 83 models for duodenal FA flows as a function of FA intake for saturated FA (C14:0, C16:0 and C18:0), C18:1, C18:2 and C18:3 isomers and seven other models for OBCFA. For the seed/oil/fat subset, intakes of total C18:3, C18:2 and starch content increased the duodenal t11-C18:1 flow with 0.08, 0.16 and 0.005 g/kg of dry matter intake (DMI), respectively, whereas intake level [(DMI×100)/BW] decreased it. The c9c12c15-C18:3 RBH was higher for oil/fat than seed (96.7% v. 94.8%) and a protective effect of Leguminosae v. Gramineae against RBH for that FA appeared in the forage subset. The duodenal C17:0 flow increased with starch content and decreased with ruminal pH, respectively, whereas duodenal iso-C16:0 flow decreased with dietary NDF content for the seed/oil/fat subset. The duodenal C20:5n-3, C22:5n-3 and C22:6n-3 flows depended on their respective intake and the inhibitory effect of C22:6n-3 on duodenal C18:0 flow was quantified. Thirteen models of absorbed FA flows were performed depending on their respective duodenal flows. This study determined the effects of different qualitative and quantitative dietary and digestive factors, allowing for improved predictions of duodenal and absorbed FA flows.     

Surfactant protein A inhibits the non-enzymatic lipid peroxidation of porcine lung surfactant.

The ability of surfactant protein A (SP-A) to inhibit the ascorbate-Fe(2+) induced lipid peroxidation of polyunsaturated fatty acids found in porcine lung surfactant (surfacen) was assessed by measuring the light emission - chemiluminescence during a 180-min incubation period at 37 degrees C. The light emission (chemiluminescence) was concentration dependent. Changes in the fatty acid composition of surfacen were observed when the lung surfactant was incubated in an ascorbate-Fe(2+) system. The main polyunsaturated fatty acids C18:2 n6 and C20:4 n6 found in the lung surfactant decreased considerably after a 180-min lipid peroxidation process. Native SP-A isolated from pig lungs inhibited oxidation of surfactant long chain polyunsaturated fatty acids, mainly arachidonic acid, in a dose-dependent fashion that was half-maximal (60% inhibition) at a concentration of 2.0 microg/ml and almost complete (73.6% inhibition) at 4.0 microg/ml, as indicated by inhibition of light emission and fatty acid composition analysis. At the highest concentration of lung SP-A used a very good correlation between the protection of the most polyunsaturated fatty acids and inhibition of light emission was observed.     

Influence of sex and dietary fats on platelet lipid biosynthesis in rat

The platelet biosynthesis of total lipids, lipid fractions and fatty acids was determined by incorporation of [¹⁴C]acetate in normal and castrated rats of both sexes. Comparison was made between animals fed laboratory chow alone, and animals receiving, in addition, for 4 days by stomach tube a saturated (cream) or polyunsaturated (sunflower seed oil) fat. In male rats, the polyunsaturated fat increased slightly the total platelet lipid biosynthesis. The saturated fat drastically reduced it by 43% in comparison to the polyunsaturated fat-fed animals. Normal female rats did not exhibit a similar difference in the platelet lipid synthesis. However, the inhibitory effect of saturated fat on lipid synthesis could be observed in castrated females, although it was less pronounced (27% reduction) than in castrated or normal males (43%). Administration to castrated males of estradiol for 1 month almost completely inhibited the difference induced by the feeding of the different fats in the lipid platelet synthesis of male rats. This difference in the platelet lipid biosynthesis between male and female rats, normal and castrated, was observed mostly in the phospholipid (especially phosphatidylcholine), monoacylglycerol and triacylglycerol fractions and affected primarily the synthesis of the three main saturated fatty acids, 14:0, 16:0 and 18:0. Thus, it seems that, in rat, the short-term administration of a saturated fat induces drastic changes in the platelet lipid biosynthesis, but only in males. The protection observed in females appears to be essentially dependent upon estrogens.     

Lipid peroxidation in the rat-liver S9 fraction: influence of membrane lipid composition

These studies describe the influence of membrane fatty acid composition on peroxidation processes in rat-liver S9 fractions. Lipid peroxidation may be expected to affect enzyme activity and cofactors of importance for the performance of the Salmonella Mutagenicity Test, as well as to contribute to the formation of chemically reactive degradation products that are mutagenic. Lipid peroxidation products were measured as derivatives of 2-thiobarbituric acid (TBA). The amount of TBA-reactive compounds (TBA-C), formed during incubation of S9 fractions from rats fed a diet containing sunflower-seed oil, was 8 times higher than that produced in S9 fractions prepared from rats fed diets containing coconut oil or hydrogenated lard as their only sources of fat. S9 fractions from livers of Aroclor 1254 treated rats showed a marked increase in peroxidation yields for all 3 dietary groups investigated as compared to S9 fractions from non-induced animals. The coconut oil and hydrogenated lard dietary groups showed a 13-fold increase in the yield of TBA-reactive material, while a 2-fold increase was found for the sunflower-seed oil group. The variations in the glutathione (GSH) levels and the degradation of unsaturated fatty acids were also studied in response to Aroclor 1254 treatment, fatty acid composition of the diets and incubation at 37 degrees C. Pronounced variations in the GSH levels were observed in response to Aroclor 1254 treatment and incubation conditions. A positive correlation between production of TBA-reactive material and degradation of unsaturated fatty acids was verified for S9 fractions from the coconut oil and hydrogenated lard dietary groups. Furthermore, the effect of Fe2+ on lipid peroxidation was studied in all 3 dietary groups. The rate of lipid peroxidation was increased in all groups but only the coconut oil and hydrogenated lard dietary groups showed increased total yields of TBA-C upon administration of Aroclor 1254 to rats. Lipid peroxidation processes cause chemical alterations in liver homogenates. Therefore, these effects ought to be considered both in the preparation and in the use of the S9 fraction in different test systems.