Assessment of the possible adverse effects of oils enriched with n-3 fatty acids in rats: peroxisomal proliferation, mitochondrial dysfunctions and apoplexy

High resistance to lipid peroxidation of bird heart mitochondria and microsomes: Effects of mass and maximum lifespan

The aim of this investigation was to study the connection between body size, fatty acid composition and sensitivity to lipid peroxidation of heart mitochondria and microsomes isolated from different size bird species: manon (Lonchura striata), quail (Coturnix coturnix var japonica), pigeon (Columba livia), duck (Cairina moschata) and goose (Anser anser), representing a 372-fold range of body mass. Fatty acids of total lipids were determined using gas chromatography and lipid peroxidation was evaluated with a chemiluminescence assay. The fatty acids present in heart organelles of the different bird species analyzed showed a small number of significant allometric trends. In mitochondria, from the individual fatty acid data, palmitoleic acid (C16:1 n7) increased allometrically (r=0.878), while stearic acid (C18:0) was negatively related to body mass (r=-0.903). Interestingly, none of the calculated fatty acid variables, the average fatty acid saturated, monounsaturated, polyunsaturated (PUFA) and the unsaturation index (UI) was established to show significant body size-related variations. In heart microsomes, the content of C18:0 was significantly smaller (r=-0.970) in the birds of greater size. A significant allometric increase in linoleic acid (C18:2 n6) (r=0.986), polyunsaturated (r=0.990) and UI (r=0.904) was observed in the larger birds. The total n6 fatty acids of heart mitochondria did not show significant differences when it was correlated to body mass of the birds. Moreover, positive allometric relationships were shown for microsomes. The total n3 fatty acids of heart mitochondria and microsomes indicated no significant correlations to body mass of birds. The C16:1 n7, C18:0 in mitochondria and C18:0, C18:2 n6, PUFA, UI and PUFA n6 in microsomes showed significant differences when they were correlated to maximum life span (MLSP) of birds. As light emission=chemiluminescence originated from heart organelles was not statistically significant, a lack of correlation between the sensitivity to lipid peroxidation and body size or maximum life span was obtained. These results indicate that the high resistance of bird hearts to the attack by free radicals is body size-independent and would be related to the preservation of cardiac function.

Double bond content of phospholipids and lipid peroxidation negatively correlate with maximum longevity in the heart of mammals

Free radical damage is currently considered a main determinant of the rate of aging. Unsaturated fatty acids are the tissue macromolecules most sensitive to oxidative damage. Therefore, the presence of relatively low degrees of fatty acid unsaturation is expected in the tissues of longevous animals. In agreement with this prediction, fatty acid analyses of heart phospholipids in eight mammals ranging in maximum life span (MLSP) from 3.5 to 46 years showed that their total number of double bonds is negatively correlated with MLSP (r = -0.78, P < 0.02). The low double content of longevous mammals was not due to a low polyunsaturated fatty acid content. Instead, it was mainly due to a redistribution between types of polyunsaturated fatty acids from the highly unsaturated docosahexaenoic acid (22:6n-3) to the less unsaturated linoleic acid (18:2n-6) in longevous animals (r = -0.89, P < 0.003 for 22:6n-3 and r = 0.91, P < 0.002 for 18:2n-6 versus MLSP), where n = number of different animals in each species. This redistribution suggests that one of the mechanisms responsible for the low number of fatty acid double bonds is the presence of low desaturase activities in longevous animals, although other causing factors must be involved. In agreement with the low degree of fatty acid unsaturation of longevous mammals, the sensitivity to lipid peroxidation (r = -0.87; P < 0.005) and the in vivo lipid peroxidation (r = -0.86, P < 0.005) in the heart were also negatively correlated with MLSP across species. These results, together with previous ones obtained in rodents, birds, and humans, suggest that the low degree of tissue fatty acid unsaturation of longevous homeothermic animals could have been selected during evolution to protect the tissues against oxidative damage.

Extraperoxisomal targets of peroxisome proliferators: mitochondrial, microsomal, and cytosolic effects. Implications for health and disease

Peroxisome proliferators are a structurally diverse group of compounds that include the fibrate hypolipidemic drugs, the phthalate ester industrial plasticizers, the phenoxy acid herbicides, and the anti-wetting corrosion inhibitors perfluorinated straight-chain monocarboxylic fatty acids. Administration of these chemicals to rodents results in a number of effects, the most prominent being hepatomegaly and induction of peroxisomal enzyme activities. Several of these compounds have also been associated with the production of liver tumors in rodents and are classified as nongenotoxic hepatocarcinogens. Experimental evidence suggests that humans are not susceptible to these effects following exposure to peroxisome-proliferating compounds. This has led to the proposal that an "actual threat to humans" from exposure to one of these compounds seems "rather unlikely". Indeed, recent reports suggest that peroxisome proliferators may prove valuable as antitumor agents in humans. However, this assessment is preliminary given that peroxisome proliferators also produce a myriad of extraperoxisomal effects in livers and other tissues of experimental animals. Such effects include both stimulation and inhibition of mitochondrial and microsomal metabolism and alteration of the activities of various cytosolic enzymes. These responses may be directly or indirectly related to the effects on peroxisomes or may be totally independent of these events. Whether the extraperoxisomal effects of these compounds occur in humans is not known and their potential impact on human health remains to be investigated.

Docosahexaenoic acid-rich fish oil does not enhance the elevation of serum transaminase and liver triacylglycerol induced by carbon tetrachloride in mice

Carbon tetrachloride (CCl4) is metabolized to trichloromethyl radical and induces liver injury with elevated serum transaminase and increased hepatic triacylglycerols (TG). To answer the question whether dietary polyunsaturated fatty acids (PUFA) enhance free radical-mediated liver injury, a docosahexaenoic acid (DHA)-rich fish oil (FO) or a saturated and monounsaturated fatty acid-rich beef tallow diet was fed to mice for 4 wk and then CCl4 was administered. When thiobarbituric acid-reactive substances (TBARS) were measured in the absence of antioxidant the FO diet and CCl4 treatment markedly increased liver TBARS values synergistically, apparently supporting the interpretation that the highly autoxidizable DHA accelerates lipid peroxidation induced by CCl4. However,no such marked interaction was observed between diet and CCl4 treatment in liver TBARS values measured in the presence of an antioxidant in the assay mixtures as well as in conjugated diene contents. Furthermore, the FO diet did not enhance CCl4-induced elevation of serum transaminase but lowered liver TG levels. The proportion of DHA,the most easily autoxidizable among common PUFA, was increased but those of eicosanoid precursors were decreased in liver phospholipids by CCl4 treatment, possibly reflecting the inflammation-related mobilization of eicosanoid precursors but not lipid peroxidation. These results indicate that dietary enrichment with DHA does not enhance CCl4-induced liver injury through the so-called free radical-mediated propagative autoxidation of DHA in mice.

Effects of dietary docosahexaenoic acid on survival time and stroke-related behavior in stroke-prone spontaneously hypertensive rats

1. Dietary docosahexaenoic acid (DHA) suppressed the age-dependent increase in systolic blood pressure and prolonged the average survival time of stroke-prone spontaneously hypertensive rats (SHRSP). 2. Dietary DHA (1% and 5% in diets) altered the circadian rhythm of SHRSP, causing significant increases in ambulatory activity during the dark period. At the onset of stroke, desynchronization with light and dark phases and new biological rhythms were noted in all of the control SHRSP (DHA 0%). DHA treated SHRSP did not show such behavioral changes. 3. These effects were accompanied by the increase of DHA and the decrease of AA levels in plasma and brain cortex. 4. It was concluded that dietary DHA suppresses the development of hypertension and stroke-related behavioral changes, resulting in prolongation of the SHRSP's life span.

Unusual effects of some vegetable oils on the survival time of stroke-prone spontaneously hypertensive rats

Preliminary experiments have shown that a diet containing 10% rapeseed oil (low-erucic acid) markedly shortens the survival time of stroke-prone spontaneously hypertensive (SHRSP) rats under 1% NaCl loading as compared with diets containing perilla oil or soybean oil. High-oleate safflower oil and high-oleate sunflower oil were found to have survival time-shortening activities comparable to that of rapeseed oil; olive oil had slightly less activity. A mixture was made of soybean oil, perilla oil, and triolein partially purified from high-oleate sunflower oil to adjust the fatty acid composition to that of rapeseed oil. The survival time of this triolein/mixed oil group was between those of the rapeseed oil and soybean oil groups. When 1% NaCl was replaced with tap water, the survival time was prolonged by approximately 80%. Under these conditions, the rapeseed oil and evening primrose oil shortened the survival time by approximately 40% as compared with n-3 fatty acid-rich perilla and fish oil; lard, soybean oil, and safflower oil with relatively high n-6/n-3 ratios shortened the survival time by roughly 10%. The observed unusual survival time-shortening activities of some vegetable oils (rapeseed, high-oleate safflower, high-oleate sunflower, olive, and evening primrose oil) may not be due to their unique fatty acid compositions, but these results suggest that these vegetable oils contain factor(s) which are detrimental to SHRSP rats.