Conjugated linoleic acids alter bone fatty acid composition and reduce ex vivo prostaglandin E2 biosynthesis in rats fed n-6 or n-3 fatty acids

This study evaluated the effects of conjugated linoleic acids (CLA) on tissue fatty acid composition and ex vivo prostaglandin E₂ (PGE₂) production in rats given diets varying in n-6 and n-3 fatty acids. Four groups of rats were given a basal semipurified diet (AIN-93G) containing 70 g/kg of added fat for 42 d. The fat treatments were formulated to contain CLA (0 vs. 10 g/kg of diet) and n-6 (soybean oil having an n-6/n-3 ratio of 7.3) and n-3 fatty acids (menhaden oil+safflower oil having an n-6/n-3 ratio of 1.8) in different ratios in a 2×2 factorial design. Fatty acids in liver, serum, muscle, heart, brain, spleen, and bone (cortical, marrow, and periosteum) were analyzed by capillary gas-liquid chromatography. The various dietary lipid treatments did not affect growth; however, CLA improved feed efficiency. The CLA isomers were found in all rat tissues analyzed although their concentrations varied. Dietary CLA decreased the concentrations of 16∶1n−7, 18∶1, total monounsaturates and n−6 fatty acids, but increased the concentrations of n−3 fatty acids (22∶5n−3 and 22∶6n−3), and saturates in the tissues analyzed. Ex vivo PGE₂ production in bone organ culture was decreased by n−3 fatty acids and CLA. We speculate that CLA reduced the concentration of 18∶1 fatty acids by inhibiting liver Δ9-desaturase activity. The fact that CLA lowered ex vivo PGE₂ production in bone organ culture suggests that these conjugated fatty acids have the potential to influence bone formation and resorption.     

Effects of essential fatty acid deficiency on prostaglandin synthesis and fatty acid composition in rat renal medulla

Studies are reported on the capacity of isolated rat renal papilla (inner medulla) to synthesize and release prostaglandin (PG) E from endogenous and exogenous precursor(s) during development of an essential fatty acid (EFA) deficiency in the rat. Weanling (21-day-old) male Sprague-Dawley rats were fed a fat-free diet supplemented with either 5% hydrogenated coconut oil (HCO) or 5% safflower oil (SO). At approximately 3, 6 and 7 weeks (6, 9 and 10 weeks of age), groups of animals fed each diet were killed for studies of PGE synthesis in the renal papillae. Differences in the fatty acid composition of the papillae lipids of the animals of each group were also determined. The in vitro production of PGE from endogenous precursor(s) was significantly reduced in the papillae from the 6-week-old rats fed the HCO diet compared to the control (SO) rats, and appeared to be near maximally depressed in the 10-week-old animals compared to that of animals fed an EFA deficient diet for over a year in an accessory experiment. Analyses of the fatty acids of the papillae lipids of the HCO groups showed that the levels of 18∶2 and 20∶4 were markedly reduced, and those of 16∶1, 18∶1 and 20∶3 were elevated compared to the controls even in the 6-week-old animals, typical of an EFA deficiency. The papillae lipids of the animals fed the HCO diet were also depleted of their stores of 22∶4ω6. A fatty acid believed to be derived by chain elongation of 20∶3ω9, 22∶3, was found in large concentrations in the papillae triglycerides of the EFA deficient rats. Incubations of exogenous arachidonic acid (20∶4) in homogenates and tissue slices of the papillae of the HCO dietary groups showed that the PG synthetase was not impaired by an EFA deficiency. The rate of PGE synthesis in the papillae of the EFA deficient animals was generally enhanced when exogenous 20∶4 was added, indicating that the concentration of available precursor(s) is a primary factor in the control of PGE synthesis in the papilla of the rat.     

Polyunsaturated fatty acids regulate cytokine and prostaglandin E2 production by respiratory cells in response to mast cell mediators

A protective association between breastfeeding and the development of bronchial asthma has been demonstrated. However, a mechanism remains unclear. FA present in human milk but rare in infant formula have been associated with marked immunological modulation as well as some indications of protection from asthma development. We examined the effect of in vitro manipulation of membrane phospholipid on the production of cytokines and prostaglandin (PG)E₂ by respiratory epithelial cells (A549) in response to stimulation by mast cell mediators of allergic disease [histamine, tumor necrosis factor (TNF)-α, interleukin (IL)-4 and IL-5]. DHA and CLA significantly decreased the production of IL-8 in response to stimulation by TNF-α [2907±970 (DHA) and 6471±1203 (CLA) vs. 12,287±2309 (control) pg/ml; P≤0.05, mean±SEM], whereas both EPA and DHA reduced histamine-stimulated RANTES (regulation on activation, T cell-expressed and-secreted) production [2314±861 (EPA) and 877±326 (DHA) vs. 8526±1118 (control) pg/ml; P≤0.03]. PGE₂ released in response to histamine was decreased by n−3 [1305±399 (α-linolenic acid), 406±73 (EPA), and 265±32 (DHA) vs. 9324±3672 (control) pg/mL; P≤0.05] and increased by n−6 [18,843±4439 (arachidonic acid) vs. 9324±3672 (control) pg/mL; P=0.02], with CLA producing a decrease of the same magnitude as DHA [553±126 (CLA) vs. 9324±3672 (control) pg/mL; P=0.03]. This study demonstrates the potential for immunological manipulation of the respiratory epithelium by FA in situ during allergic responses and suggests that further investigation into FA intervention in infants via human milk or supplemented infant formula, to prevent the development of allergic disease, may be worthwhile.     

The effects of dietary 9-trans,12-rans-octadecadienoate on composition and fatty acids of rat lungs

Dietarytrans,trans-linoleate (trans 18∶2), when fed to rats in increasing amounts, caused a reduction in lung weights, particularly at very high dietary concentrations. The fatty acids of the phospholipids and triglycerides were altered. The percentage of oleic and arachidonic acid decreased as dietarytrans 18∶2 was increased. Eicosatrienoic acid (20∶3) appeared in the phospholipids of lungs from rats receiving 100% dietarytrans 18∶2, but its concentration was much lower than in lungs from rats on an essential fatty acid deficient diet, indicating thattrans 18∶2 inhibited the enzymes synthesizing 20∶3.     

Effect of vitamin E deficiency on the lipid class and fatty acid composition of rat brain gray and white matter

Three-week old male Sprague-Dawley rats were placed on a control or vitamin E-deficient diet for 9 months. The total lipid and cholesterol contents of brain gray and white matter areas in the vitamin E-deficient group did not differ from controls. The concentration of cerebrosides was lower in white matter but higher in gray matter of deficient animals. However, sulfatide was significantly (P<0.001) higher in white and gray matter of deficient animals compared with controls. Lysolecithin was not found in vitamin E-deficient gray matter but was present in control gray matter lipids. No marked differences were found in the concentrations or relative amounts of sphinogomyelin, phosphatidyl choline, phospholipids of gray or white matter of vitamin E-deficient rats as compared to controls. In addition no remarkable differences were found in the fatty acid composition of total lipid extracts of gray or white matter from vitamin E-deficient rats when compared with controls. Presented in part at the Biochemistry/Biophysics Meeting, Minneapolis, 1974, and the Sixth Meeting of the American Society for Neurochemistry, Mexico City, 1975.     

Arachidonic acid,prostaglandin E2 and leukotriene C4 levels in gingiva and submandibular salivary glands of rats fed diets containing n−3 fatty acids

The effect of dietary n−3 fatty acids on prostaglandin E₂ (PGE₂) and leukotriene C₄ (LTC₄) levels in rat salivary glands and gingiva was examined in two separate nutritional studies. In the first set of experiments, two groups of male weanling Sprague-Dawley rats were fed semipurified diets containing 10% corn oil (control group) or 10% menhaden oil (experimental group). Rats were killed after 8 wk on the diets; the fatty acid composition of total phospholipids and the concentrations of PGE₂ and its precursor, arachidonic acid, were measured in gingiva and submandibular salivary glands (SMSG). Dietary n−3 fatty acids were incorporated into the tissue phospholipids. Arachidonic acid levels were reduced by 56% in gingiva and SMSG of rats fed menhaden oil compared with the control rats fed the diet containing corn oil. The concentrations of PGE₂ in SMSG and gingiva of rats fed the diet containing menhaden oil were reduced by 74% and 83%, respectively. In a subsequent nutritional study, we tested whether the diet-induced reduction in tissue arachidonic acid levels would also result in a corresponding decrease in LTC₄ production. Three groups of rats were fed diets containing 5% corn oil (group 1), 4% ethyl ester concentrate of n−3 fatty acids plus 1% corn oil (group 2), or 5% ethyl ester concentrate of n−3 fatty acids (group 3). After 6 wk of feeding, gingiva and SMSG were analyzed for arachidonic acid content andin vitro production of LTC₄. Arachidonic acid content of total phospholipids was about 60% lower in gingiva and 69% lower in SMSG of rats fed the ethyl ester concentrate of n−3 fatty acids (groups 2 and 3) than those of the control group fed the corn oil diet (group 1). Upon incubation with calcium ionophore, gingiva and SMSG from rats fed the n−3 fatty acids rich diet produced significantly less TLC₄ than those from rats of the control group. Because PGE₂ and LTC₄ are believed to be important biochemical mediators of periodontal disease, one may speculate that a diet-induced reduction in their levels may have a beneficial effect upon the course of the disease. The function of salivary glands may also be altered because of the role of these eicosanoids in salivary secretions. Presented in part for the Hatton Award Competition at the American Association for Dental Research Meeting, San Francisco, California, March 15–19, 1989, and at the International Association for Dental Research Meeting, Acapulco, Mexico, April 17–21, 1991.     

The effects of dietary protein on the fatty acid composition and Δ6 desaturase activity of rat hepatic microsomes

Recently, significant differences between rats fed a casein diet and rats fed a soybean protein diet have been observed in hepatic phospholipid fatty acid patterns (Sjöblom, L., and Eklund, A.,Biochim. Biophys. Acta 1004, 187–192, 1990). The influence of these two diets on the Δ6 desaturase activity was investigated in the present study because the hepatic desaturase system is a source of unsaturated fatty acids. The rats fed a casein diet showed higher desaturase activity than those fed soybean protein when using either linoleic acid (P<0.005) or oleic acid (P<0.05) as substrates. The phosphatidylcholine fraction of hepatic microsomes showed increases in oleic acid (P<0.005) and 20∶3ω9 (P<0.001) levels as well as decreases in stearic acid (P<0.001), linoleic acid (P<0.005) and arachidonic acid (P<0.005) levels in rats which were fed casein rather than soybean protein. Similar differences between the two groups were also observed in the phosphatidylethanolamine and phosphatidylinositol fractions. These data indicate that the qualitative properties of the dietary protein source may influence the fatty acid pattern of rat hepatic microsomes by interfering with Δ6 desaturase activity.     

The effect of a fish oil diet on the fatty acid composition of individual phospholipids and eicosanoid production by rat platelets

When rats were fed a diet containing chow or fish oil for six weeks, the platelet phospholipid content and percent distribution were similar. In the fish oil fed animals there was a 54, 40, 41, and 24% reduction, respectively, in the levels of 20∶4(n−6) in the choline-, ethanolamine-, inositol-and serine-containing glycerophospholipids. Dietary fish oil increased the total (n−3) polyunsaturated fatty acid content in all lipids. This effect was most pronounced in the ethanolamine glycerophospholipids which now contained 26, 11, and 4 nmols of 20∶5(n−3), 22∶5(n−3), and 22∶6(n−3) in 10⁹ cells. Ionophore A23187 stimulation of platelets from the chow fed rats resulted in the synthesis of 7, 64, and 3.5 nmols of 12-hydroxy-5,8,10-heptadecatrienoic acid, 12-hydroxy-5,8,10,14-eicosatetraenoic acid and 12-hydroxy-5,8,10,14,17-eicosapentaenoic acid, respectively, from 1×10⁹ cells. The values from animals fed fish oil were 4, 18, and 27 nmol/10⁹ platelets. It was not possible to detect any lipoxygenase products from 22∶5(n−3) or 22∶6(n−3), even though both acids are readily metabolized by lipoxygenase when added directly to platelets. These findings suggest that 22-carbon (n−3) fatty acids are not liberated when phospholipases are activated by calcium mobilization.