Influence of dietary fat on the promotion of diethylnitrosamine-induced hepatocarcinogenesis in female rats

The effect of varying the amount and type of dietary fat on the promotion of gamma-glutamyltranspeptidase (GGT)-positive foci and hepatocarcinomas in female rats was studied. In the first study, two-thirds of the rats were first intubated with diethylnitrosamine (DEN, 10 mg/kg) 20 hr after partial hepatectomy; 1 week later, rats were fed one of three purified diets (a low-fat diet similar to the AIN-76 diet, a high saturated fat diet, or a high polyunsaturated fat diet) with or without 0.05% phenobarbital in the diet for 10 months. Increasing the fat level of the diet did not increase the number of GGT-positive foci arising spontaneously or induced by DEN alone. When phenobarbital was present in the diet, feeding the high polyunsaturated fat diet slightly increased the number of GGT-positive foci and the incidence of tumors. The low-fat diet, however, increased the incidence of fatty liver. We therefore reexamined the effect of diet on promotion by phenobarbital, using an additional low-fat diet with cornstarch rather than sucrose as the carbohydrate source. In this experiment, both high-fat diets slightly enhanced the induction of GGT-positive foci; the carbohydrate source had no effect. The incidence of tumors was not affected by diet in this experiment, but the incidence of fatty liver was again enhanced by feeding a diet high in sucrose. We conclude that increasing the fat level of the diet does not promote the development of DEN-initiated GGT-positive foci or carcinomas in female rats. Increasing the dietary fat level, however, may enhance promotion of liver foci by phenobarbital. Finally, increasing the sucrose content of the diet increases the incidence of fatty liver.     

Comparison of Osborne-Mendel and S5B/PL Strains of Rat: Central Effects of Galanin,NPY, β-Casomorphin and CRH on Intake of High-Fat and Low-Fat Diets

The effects of central administration of galanin, neuropeptide Y (NPY), β-casomorphin_(1–7) and corticotropin releasing hormone (CRH) on intake of either a high-fat or low-fat diet have been compared in two strains of rat, the dietary fat-sensitive Osborne-Mendel (OM) rat and the dietary fat-resistant S5B/Pl rat. Injection of galanin (0.1, 0.3 nmoles) into the 3rd cerebral ventricle stimulated the intake of both a high-fat and a low-fat diet in OM rats in a dose dependent manner but the response was significantly smaller in rats fed the low-fat diet. In S5B/Pl rats, galanin had a small stimulatory effect on food intake but only at a high dose (2 nmole). β-casomor-phin_(1–7) (5 nmoles), an opioid-like peptide, increased the intake of the high-fat but not the low-fat diet in OM rats, whereas S5B/Pl rats fed either a high-fat or a low-fat diet did not respond to β-caso-morphin/j.yy Both strains showed a similar stimulatory response to NPY (0.1, 0.5 nmoles) on the intake of the high-fat or the low-fat diet, but the magnitude of the response was attenuated in S5B/Pl rats. In contrast, the anorectic effects of CRH (0.26 nmoles) on food deprived animals was similar in both strains for both diets. We speculate that the regulatory system controlling the intake of fat activated by galanin and β-casomorphin_(1–7) may be defective in S5B/Pl rats.     

Chronic Swimming Exercise Ameliorates Low-Soybean-Oil Diet-Induced Spatial Memory Impairment by Enhancing BDNF-Mediated Synaptic Potentiation in Developing Spontaneously Hypertensive Rats

Exercise and low-fat diets are common lifestyle modifications used for the treatment of hypertension besides drug therapy. However, unrestrained low-fat diets may result in deficiencies of low-unsaturated fatty acids and carry contingent risks of delaying neurodevelopment. While aerobic exercise shows positive neuroprotective effects, it is still unclear whether exercise could alleviate the impairment of neurodevelopment that may be induced by certain low-fat diets. In this research, developing spontaneously hypertensive rats (SHR) were treated with chronic swimming exercise and/or a low-soybean-oil diet for 6 weeks. We found that performance in the Morris water maze was reduced and long-term potentiation in the hippocampus was suppressed by the diet, while a combination treatment of exercise and diet alleviated the impairment induced by the specific low-fat diet. Moreover, the combination treatment effectively increased the expression of brain-derived neurotrophic factor (BDNF) and N-methyl-d-aspartic acid receptor (NMDAR), which were both down-regulated by the low-soybean-oil diet in the hippocampus of developing SHR. These findings suggest that chronic swimming exercise can ameliorate the low-soybean-oil diet-induced learning and memory impairment in developing SHR through the up-regulation of BDNF and NMDAR expression.     

The fatty acid composition of chylomicron remnants influences their binding and internalization by isolated hepatocytes.

The binding and internalization of (125)I-labelled chylomicron remnants derived from palm, olive, corn, or fish oil (rich in saturated, monounsaturated, n-6, or n-3 polyunsaturated fatty acids, respectively) by hepatocytes from rats fed a low-fat diet or a diet supplemented with the corresponding fat for 21 days was investigated. In hepatocytes from rats fed the low-fat diet, the association of radioactivity with the cells at 4 degrees C (a measure of initial binding only) was similar with all types of remnants tested, but was more rapid at 37 degrees C (a measure of binding plus internalization) when fish oil, as compared to olive, corn or palm oil remnants, was used, and similar differences in the internalization of the particles were observed. In contrast, when hepatocytes from rats fed the fat-supplemented diets were used, the rate of association at 37 degrees C of remnants with cells from rats fed palm, corn or fish oil was similar, and higher than that found with cells from animals fed olive oil, and in this case these differences were mainly due to changes in the binding of the particles to the cells at 4 degrees C. Both excess low-density lipoprotein (LDL), which inhibits remnant uptake by the LDL receptor, and lactoferrin, which blocks the LDL receptor-related protein (LRP), were found to decrease the association of the remnants with cells from rats fed the low-fat and high-fat diets. However, in hepatocytes from animals given the low-fat diet, most of the differences between the various types of particle were retained in the presence of lactoferrin, but abolished in the presence of LDL. In contrast, in cells from rats fed the high-fat diets, the differences were reduced by both lactoferrin and LDL. These findings demonstrate that the hepatic uptake of chylomicron remnants is influenced both by the fatty acid composition of the particles, and by longer-term adaptive changes in liver tissue, and suggest that the former effects are mediated mainly by the LDL receptor, while the latter may involve both the LDL receptor and the LRP.     

Antecedent intake of traditional Asian-style diets exacerbates pancreatic beta-cell function, growth and survival after Western-style diet feeding in weaning male rats

The prevalence of type 2 diabetes has been rapidly increasing in conjunction with the westernization of diet patterns in Asia. We determined whether the antecedent consumption of traditional Asian-style diets (ADs) deteriorates insulin action, insulin secretion and pancreatic beta-cell mass after subsequent imposition of the diabetogenic challenge of Western-style diets (WDs) in weaning male Sprague-Dawley rats. Rats were provided AD (a low-fat and plant protein diet), WD (a high-fat and animal protein diet) or a control diet (CD) (a low-fat and animal protein diet) for 12 weeks. After 12 weeks, the groups were divided into two subsets; one set of the groups continued to consume their previous diets of WD, AD and CD for another 12 weeks, and the second set was divided into three groups represented by a switch in their designated diets from WD to AD, AD to WD and CD to WD. Whole-body glucose disposal rates and GLUT4 contents in soleus muscles were lower in WD regardless of the antecedent protein sources. The first-phase insulin secretion was higher in the CD group than in the other groups, whereas the second phase was lowered with AD consumption as antecedent and/or present diets. Asian-style diet and AD-WD intake did not compensate for insulin resistance due to the failure of beta-cell expansion via decreased proliferation. These findings suggest that the antecedent consumption of AD possibly accelerates and augments the development of glucose dysregulation via decreased insulin secretion capacity and pancreatic beta-cell mass when the diets switch to WD.     

Dietary obesity caused by a specific circadian eating pattern

The eating pattern is altered by high-fat diet-induced obesity. To clarify whether this is dependent on the fatty acid profile of the diet, the authors conducted two studies on adult female Sprague-Dawley rats fed normal-fat chow or high-fat diets with varying fatty acid composition. Eating pattern and body weight were assessed in rats fed canola-based (low in saturated fatty acids) or lard-based (moderate in saturated fatty acids) diets for 7 days, and in animals fed chow or canola- or butter-based diets (rich in saturated fatty acids) for 43 days. These parameters were also determined when restricted amounts of low-fat canola- or butter-based diets were consumed for 25 days. Early exposure to canola or lard high-fat feeding or prolonged access to canola- or butter-based fat-rich diets (relative to chow feeding) did not alter the normal light-dark distribution of food and energy intake. All animals ingested most of their food during the dark phase. However, feeding the high-fat canola- and butter-based diets produced an altered eating pattern during the light phase characterized by a smaller number of meals, longer intermeal interval, and enhanced satiety ratio, and consumption of shorter-lasting meals than chow-fed animals. Relative to canola or chow feeding, butter-fed animals consumed a lower number of meals during the dark phase and had a higher eating rate in the light phase, but ate larger meals overall. Only butter feeding led to overeating and obesity. When given a restricted amount of low-fat canola- or butter-based diet at the start of the light phase, rats ate most of their food in that phase and diurnal rather than nocturnal feeding occurred with restriction. These findings underscore the role of saturated fatty acids and the resulting eating pattern alteration in the development of obesity.     

A liquid chromatography-quadrupole time-of-flight (LC-QTOF)-based metabolomic approach reveals new metabolic effects of catechin in rats fed high-fat diets

Unbalanced diets generate oxidative stress commonly associated with the development of diabetes, atherosclerosis, obesity and cancer. Dietary flavonoids have antioxidant properties and may limit this stress and reduce the risk of these diseases. We used a metabolomic approach to study the influence of catechin, a common flavonoid naturally occurring in various fruits, wine or chocolate, on the metabolic changes induced by hyperlipidemic diets. Male Wistar rats ( n = 8/group) were fed during 6 weeks normolipidemic (5% w/w) or hyperlipidemic (15 and 25%) diets with or without catechin supplementation (0.2% w/w). Urines were collected at days 17 and 38 and analyzed by reverse-phase liquid chromatography-mass spectrometry (LC-QTOF). Hyperlipidic diets led to a significant increase of oxidative stress in liver and aorta, upon which catechin had no effect. Multivariate analyses (PCA and PLS-DA) of the urine fingerprints allowed discrimination of the different diets. Variables were then classified according to their dependence on lipid and catechin intake (ANOVA). Nine variables were identified as catechin metabolites of tissular or microbial origin. Around 1000 variables were significantly affected by the lipid content of the diet, and 76 were fully reversed by catechin supplementation. Four variables showing an increase in urinary excretion in rats fed the high-fat diets were identified as deoxycytidine, nicotinic acid, dihydroxyquinoline and pipecolinic acid. After catechin supplementation, the excretion of nicotinic acid was fully restored to the level found in the rats fed the low-fat diet. The physiological significance of these metabolic changes is discussed.     

Effects of barley variety,dietary fiber and β-glucan content on bile acid composition in cecum of rats fed low- and high-fat diets

Diet-induced obesity and insulin resistance have been linked to changes in bile acid (BA) profiles, which in turn are highly dependent on the dietary composition and activity of the gut microbiota. The objective of the present study was to investigate whether the type and level of fiber had an effect on cecal BA composition when included in low- and high-fat diets. Groups of rats were fed two barley varieties, which resulted in three test diets containing three levels of β-glucans and two levels of dietary fiber. BAs were preconcentrated using hollow fiber liquid-phase microextraction and quantified by gas chromatography. The amount of the secondary BAs, lithocholic-, deoxycholic- and hyodexycholic acids was generally higher in groups fed high-fat diets compared with corresponding acids in groups fed low-fat diets (P<.05). In contrast, most of the primary and the secondary BAs, ursodeoxycholic acid and β- and ω-muricholic acids, were two to five times higher (P<.05) in groups fed low-fat diets than in groups fed high-fat diets. This was particularly true for groups fed the highest level of β-glucans and in some cases also the medium level. The BA profile in the gut was strongly dependent on the amount and type of dietary fiber in the diet, which may be useful in the prevention/treatment of diseases associated with changes in BA profiles.     

Differential effects of fatty acids and exercise on body weight regulation and metabolism in female Wistar rats

High-fat diets made with different fats may have distinct effects on body weight regulation and metabolism. In the present study, the metabolic effects of high-fat (HF) diets made with fish oil, palm oil, and soybean oil were compared with a low-fat diet in female Wistar rats that were either exercised (EX, swimming) or that remained sedentary as controls. Each adult rat was exposed to the same diet that their dams consumed during pregnancy and lactation. When they were 9 weeks old, rats began an EX regimen that lasted for 6 weeks. Twenty-four hours after the last EX bout, rats were sacrificed in a fasted state. It was observed that HF feeding of soybean oil induced more body weight and fat gain, as well as insulin resistance, as indicated by insulin/glucose ratios, than other oils. Female rats fed a HF diet made with fish oil had body weight and insulin sensitivity not different from that observed in low fat fed control rats. For rats fed HF diets made with soybean oil or palm oil, EX also exerted beneficial effects by reducing body fat %, blood insulin, triglyceride and leptin levels, as well as improving insulin sensitivity.     

Effect of chronic consumption of a high-fat diet on mammary metabolism

Rats have been fed semi-synthetic diets containing 4 and 20% (w/w) corn oil for periods of 9-12 weeks covering two lactations. The mean maternal and pup weights at day-14 of the second lactation on the diets were not significantly different. The milk fatty acids of the rats on the high-fat diet contained 39 mol% linoleic acid and only 20 mol% medium-chain acids compared with over 40% for the low-fat diet. With the exception of "malic" enzyme, none of five enzymes assayed in mammary supernatants was significantly altered by the diet fed. These results suggest that the synthesis of these enzymes in the mammary gland is insensitive to dietary lipid.     

Adaptation to high-fat diet reduces inhibition of gastric emptying by CCK and intestinal oleate

Rats maintained on low-fat (LF) or high-fat (HF) diets were fitted with gastric cannulas and duodenal catheters. Intraperitoneal injection of 0.250-2.0 microg/kg cholecystokinin (CCK) significantly inhibited gastric emptying of a 5-ml NaCl load in LF rats by 26.2-55. 1% compared with emptying after vehicle injection. By contrast, CCK-induced inhibition of gastric emptying was significantly less in HF rats given the same CCK doses (10.0-31.7% inhibition over the same CCK dose range). A 20-min intraduodenal infusion of oleate (0.03 or 0.06 kcal/ml) also resulted in significant inhibition of gastric emptying in LF rats (24 and 89%, respectively). Oleate-induced inhibition of gastric emptying was significantly attenuated in rats maintained on the HF diet (2 and 56%, respectively). Unlike CCK injections or oleate infusion, intraduodenal maltotriose infusion inhibited gastric emptying to a similar degree in LF and HF rats (77 and 78%, respectively). These results indicate that feeding HF diets diminishes the enterogastric inhibition of gastric emptying by intestinal oleate and diminishes the ability of CCK to inhibit gastric emptying.     

Dietary Obesity Caused by a Specific Circadian Eating Pattern

The eating pattern is altered by high-fat diet-induced obesity. To clarify whether this is dependent on the fatty acid profile of the diet, the authors conducted two studies on adult female Sprague-Dawley rats fed normal-fat chow or high-fat diets with varying fatty acid composition. Eating pattern and body weight were assessed in rats fed canola-based (low in saturated fatty acids) or lard-based (moderate in saturated fatty acids) diets for 7 days, and in animals fed chow or canola- or butter-based diets (rich in saturated fatty acids) for 43 days. These parameters were also determined when restricted amounts of low-fat canola- or butter-based diets were consumed for 25 days. Early exposure to canola or lard high-fat feeding or prolonged access to canola- or butter-based fat-rich diets (relative to chow feeding) did not alter the normal light-dark distribution of food and energy intake. All animals ingested most of their food during the dark phase. However, feeding the high-fat canola- and butter-based diets produced an altered eating pattern during the light phase characterized by a smaller number of meals, longer intermeal interval, and enhanced satiety ratio, and consumption of shorter-lasting meals than chow-fed animals. Relative to canola or chow feeding, butter-fed animals consumed a lower number of meals during the dark phase and had a higher eating rate in the light phase, but ate larger meals overall. Only butter feeding led to overeating and obesity. When given a restricted amount of low-fat canola- or butter-based diet at the start of the light phase, rats ate most of their food in that phase and diurnal rather than nocturnal feeding occurred with restriction. These findings underscore the role of saturated fatty acids and the resulting eating pattern alteration in the development of obesity. (Author correspondence: louise.thibault@mcgill.ca)     

Dietary gamma-linolenic acid in the form of borage oil causes less body fat accumulation accompanying an increase in uncoupling protein 1 mRNA level in brown adipose tissue

Rats were fed a low-fat diet containing 2% safflower oil or 20% fat diets containing either safflower oil rich in linoleic acid, borage oil containing 25% gamma (gamma)-linolenic acid or enzymatically prepared gamma-linolenic acid enriched borage oil containing 47% gamma-linolenic acid for 14 days. Energy intake and growth of animals were the same among groups. A high safflower oil diet compared with a low-fat diet caused significant increases in both epididymal and perirenal white adipose tissue weights. However, high-fat diets rich in gamma-linolenic acid failed to do so. Compared with a low-fat diet, all the high-fat diets increased mRNA levels of uncoupling protein 1 and lipoprotein lipase in brown adipose tissue. The extents of the increase were greater with high-fat diets rich in gamma-linolenic acid. Various high-fat diets, compared with a low-fat diet, decreased glucose transporter 4 mRNA in white adipose tissue to the same levels. The amount and types of dietary fat did not affect the leptin mRNA level in epididymal white adipose tissue. However, a high safflower oil diet, but not high-fat diets rich in gamma-linolenic acid relative to a low-fat diet, increased perirenal white adipose tissue leptin mRNA levels. All high-fat diets, relative to a low-fat diet, increased the hepatic mitochondrial fatty acid oxidation rate and fatty acid oxidation enzyme mRNA abundances to the same levels. High-fat diets also increased these parameters in the peroxisomal pathway, and the increases were greater with high-fat diets rich in gamma-linolenic acid. The physiological activity in increasing brown adipose tissue gene expression and peroxisomal fatty acid oxidation was similar between the two types of borage oil differing in gamma-linolenic acid content. It was suggested that dietary gamma-linolenic acid attenuates body fat accumulation through the increase in gene expressions of uncoupling protein 1 in brown adipose tissue. An increase in hepatic peroxisomal fatty acid oxidation may also contribute to the physiological activity of gamma-linolenic acid in decreasing body fat mass.     

Dissociation of Striatal GTPase and Dopamine Release Responses to Muscarinic Cholinergic Agonists in F344 Rats: Influence of Age and Dietary Manipulation

Abstract: There is evidence that dietary lipids and age both influence neuronal membrane composition and receptor G protein-linked signal transduction, but very little information is available on the interaction between these two factors. To investigate this, we obtained striata from 2, 12, and 22-month-old male F344 rats who were fed either a high-cholesterol, high-saturated fat or low-fat diet for 1 month. The striata were assayed for muscarinic agonist-stimulated low-K_m GTPase activity using 10^?3M carbachol and 10^?5M oxotremorine and for KCl-evoked dopamine release enhancement by 10^?5M oxotremorine. Membrane cholesterol and phospholipid content and phospholipid class composition were also determined. Mature animals showed significant but divergent changes in GTPase activity and dopamine release for high-cholesterol and low-fat diets: GTPase activity decreased, whereas dopamine release increased in these groups. Alterations in GTPase activity but not in dopamine release were inversely correlated with the cholesterol/phospholipid molar ratio. Old control animals showed reductions in both GTPase activity and oxotremorine-enhanced dopamine release compared with young animals. Whereas none of the experimental diets affected GTPase activity in old animals, the low-fat diet produced a marked decrease in dopamine release. In contrast to mature and old groups, young rats showed no significant change in either GTPase or dopamine release, suggesting a relative “resistance” to such dietary lipid modulation. The observed dissociation in GTPase and dopamine release responses to diet may reflect differing effects of these diets on discrete membrane lipid domains that preferentially influence different signal transduction components. The substantial age-related differences in striatal membrane response to dietary lipid modulation may represent the effects of underlying age differences in membrane lipid metabolism, structure, and/or dynamics. Our findings support the work of other groups that have shown that brain membranes are susceptible to modification by exogenous lipids. They also suggest the need for a more systematic examination of the influence of age on the response to other types of dietary lipid changes.     

Reduced lipogenesis in cafeteria-fed rats exhibiting diet-induced thermogenesis

Fatty-acid synthesis has been measured in vivo with³H₂O in cafeteria-fed rats exhibiting diet-induced thermogenesis. Synthesis was decreased in brown adipose tissue, the liver, white adipose tissue, and the carcass of the cafeteria-fed animals compared to rats fed the normal stock diet. Whole-body synthesis was also decreased in the cafeteria-fed group. Diet-induced thermogenesis, in contrast to cold-induced non-shivering thermogenesis does not lead to increased fatty-acid synthesis and this is presumably due to the inhibitory effects on lipogenesis of the high dietary fat intake characteristic of cafeteria diets. The results also indicate that the energy cost of body fat deposition in cafeteria-fed rats is lower than in animals fed a low-fat/high-carbohydrate stock diet.     

Effect of a selective OX1R antagonist on food intake and body weight in two strains of rats that differ in susceptibility to dietary-induced obesity

An orexin-1 receptor antagonist decreases food intake whereas orexin-A selectively induces hyperphagia to a high-fat diet. In the present study, we evaluated the effect of an orexin antagonist in two strains of rats that differ in their sensitivity to becoming obese while eating a high-fat diet. Male Osborne-Mendel (OM) and S5B/Pl (S5B) rats were treated acutely with an orexin-1 receptor antagonist (SB-334867), after adaptation to either a high-fat (56% fat energy) diet or a low-fat (10% fat energy) diet that were equicaloric for protein (24% energy). Ad libitum fed rats were injected intraperitoneally with SB-334867 at doses of 3, 10 or 30 mg/kg, or vehicle at the beginning of the dark cycle, and food intake and body weight were measured. Hypothalamic prepro-orexin and orexin-1 receptor mRNA expression were analyzed in OM and S5B rats fed at a high-fat or low-fat diet for two weeks. SB-334867 significantly decreased food intake in both strains of rats eating the high-fat diet but only in the OM rats eating the low fat diet. The effect was greatest at 12 and 24 h. Body weight was also reduced in OM rats 1d after injection of SB-334867 but not in the S5B rats. Prepro-orexin and orexin-1 receptor expression levels did not differ between strains or diets. These experiments demonstrate that an orexin antagonist (SB-334867) reduces food intake and has a greater effect in a rat strain that is susceptible to dietary-induced obesity, than in a resistant strain.     

Amplifying effect of dietary taurine on the induction of cytochrome P-450 and on the urinary excretion of ascorbic acid in rats fed on phenobarbital-containing diets

Dietary taurine amplified the induction of cytochrome P-450 and the urinary excretion of ascorbic acid in rats fed on phenobarbital (PB)-containing diets. These facts suggest that taurine could influence the hepatic metabolism of xenobiotics via the induction of drug-metabolizing enzymes (DME) and the ascorbic acid metabolism. Taurine might improve the function of DME exposed by some xenobiotics.     

Failure of high dietary fat to influence serum prolactin levels during the estrous cycle in female Sprague-Dawley rats

The influence of a 20% high-fat and a 4.5% control fat diet on circulating prolactin levels was determined during the estrous cycle of intact female rats, and during a progesterone-induced surge of prolactin in ovariectomized, estrogen-primed rats. An indwelling right atrial cannula was implanted into each rat to facilitate repeated blood sampling in conscious, undisturbed animals. No differences in serum prolactin levels were observed at any time during the estrous cycle or in the progesterone-induced surge of prolactin in rats fed either the high-fat or control fat diet. There also were no differences in the estrous cycles of rats on high- or low-fat diets. It is concluded that high dietary fat promotes mammary tumor development by a mechanism that does not involve alterations in circulating prolactin levels or of estrous cycles.     

Differential response to low-fat diet between low and normal HDL-cholesterol subjects

Heart attacks frequently occur in normolipidemic subjects with low concentration of high density lipoproteins (35 mg/dL). We hypothesized that as subjects with low HDL-C already have low HDL concentrations, the major decrease of HDL-C will occur in subjects with normal HDL-C when a low-fat diet is consumed. Normolipidemic male subjects consumed three diets differing in total fat and saturated fat composition (AAD: 37%, Step-1: 28%, Step-2: 24% total fat) for 6 weeks in a three-period double-blind randomized crossover design. Plasma lipids and apolipoproteins were determined and changes in distribution of HDL subpopulations were evaluated. As a result of a low-fat diet, low HDL-C individuals slightly decreased their HDL-C, but substantially decreased their LDL-C resulting in a significant improvement in the LDL-C/HDL-C ratio. However, subjects with normal HDL-C levels decreased both their LDL-C and HDL-C resulting in an unchanged LDL-C/HDL-C ratio. We also observed significant differences in response to low-fat diets in HDL-C and alpha(1) concentrations between low and normal HDL-C subjects. In the normal HDL-C group, consumption of a low-fat diet also resulted in redistribution of apoA-I-containing HDL subpopulations, indicated by a decrease in the large apoA-I-only alpha(1) subpopulation. These data demonstrate that male subjects with low HDL-C respond to a low-fat diet differently than individuals with normal HDL-C.     

Oxidation of 5,8,11,14,17-eicosapentaenoic acid by hepatic and renal microsomes

Liver and kidney microsomes were isolated from rats raised on high-fat diets. In terms of energy, the high-fat diets contained 4% vegetable and 40% fish, vegetable or coconut oils. Each microsomal preparation was fortified with 1 mM NADPH and incubated with 5,8,11,14,17-eicosapentaenoic acid (20:5(n-3]. The number of metabolites formed was assessed by reverse-phase high-performance liquid chromatography (HPLC). To identify the major metabolites, large-scale incubations were done with 20:5(n-3) and microsomes from phenobarbital-treated rats. After extracts from the phenobarbital and dietary studies were combined, individual products were isolated by reverse- and normal-phase HPLC. The metabolites were identified by mass spectrometry, by chromatographic properties, and by comparing their retention times and mass spectra with those of chemically synthesized standards. For liver microsomes, the major metabolites were: 17,18-, 14,15-, 11,12- and 8,9-dihydroxyeicosatetraenoic acids, 20-hydroxyeicosapentaenoic acid, and 19-hydroxyeicosatetraenoic acid. For renal microsomes, the major metabolites were 20-hydroxyeicosapentaenoic and 19-hydroxypentaenoic acids. Because formation of these metabolites required NADPH and was enhanced by phenobarbital pretreatment, 20:5(n-3) appears to be oxidized by cytochrome P-450 monooxygenases. Based on reverse-phase high performance liquid chromatograms, all three high-fat diets may produce the same types of monooxygenase metabolites from 20:5(n-3). It remains unknown whether fish-oil diets induce the synthesis of monooxygenases to oxidize n-3 fatty acids, because these preliminary studies involved only two animals per dietary group.