Manipulation of the acute inflammatory response by dietary polyunsaturated fatty acid modulation.

Dietary polyunsaturated fatty acid modulation has been used as an anti-inflammatory strategy in experimental models of disease as well as in clinical trials. To elucidate the mechanisms underlying the anti-inflammatory effects of manipulating dietary polyunsaturated fatty acids, the in vivo effects of essential fatty acid (EFA) deficiency and (n-3) fatty acid supplementation were contrasted using a model of acute inflammation induced by the i.p. injection of zymosan into mice. Both diets led to a substantial decrease in tissue (n-6) fatty acid content. EFA deficiency was also characterized by the accumulation of (n-9) fatty acids, particularly 20:3 (n-9), the fatty acid that uniquely characterizes the deficiency state. Dietary (n-3) fatty acid supplementation led instead to marked increases in (n-3) fatty acids, especially 20:5 (n-3). With respect to the antiinflammatory effects of the two diets, EFA deficiency, but not (n-3) fatty acid supplementation, depleted levels of resident peritoneal macrophages. EFA deficiency was also more effective than (n-3) fatty acid supplementation in inhibiting the influx of polymorphonuclear neutrophils in response to zymosan. The effect of the two diets on the in vivo generation of leukotriene(LT)B also differed markedly. EFA deficiency completely inhibited the synthesis of LTB. Dietary (n-3) fatty acid supplementation, in contrast, reduced the production of LTB4 by only 50%. With (n-3) fatty acid supplementation LTB5 was produced. The more modest effect of (n-3) fatty acid supplementation in decreasing LTB4 generation was not due to blockade of the cyclooxygenase pathway. EFA deficiency, but not (n-3) fatty acid supplementation, was associated with the decreased synthesis of thromboxane. Although dietary fatty acid modulation has been shown to diminish platelet activating factor (PAF) synthesis, studies using the PAF receptor blocker, L659989, established that PAF was not a significant factor in the elicitation of leukocytes in this model of inflammation. In summary, the anti-inflammatory effect of EFA deficiency was more marked that that of dietary (n-3) fatty acid supplementation in acute inflammation. This difference in anti-inflammatory potential appeared to be due to either the greater effect of EFA deficiency in decreasing levels of resident peritoneal macrophages or in suppressing the in vivo generation of LTB4.

Glycogen repletion and exercise endurance in rats adapted to a high fat diet.

It is well accepted that exercise endurance is directly related to the amount of carbohydrate stored in muscle and that a low carbohydrate diet reduces glycogen storage and exercise performance. However, more recent evidence has shown that when the organism adapts to a high fat diet endurance is not hindered. The present study was designed to test that claim and to further determine if animals adapted to a high fat diet could recover from exhausting exercise and exercise again in spite of carbohydrate deprivation. Fat-adapted (3 to 4 weeks, 78% fat, 1% carbohydrates) rats (FAT) ran (28 m/min, 10% grade) as long as carbohydrate-fed (69% carbohydrates) animals (CHO) (115 v 109 minutes, respectively) in spite of lower pre-exercise glycogen levels in red vastus muscle (36 v 54 mumols/g) and liver (164 v 313 mumols/g) in the FAT group. Following 72 hours of recovery on the FAT diet, glycogen in muscle had replenished to 42 mumols/g (v 52 for CHO) and liver glycogen to 238 mumols/g (v 335 for CHO). The animals were run to exhaustion a second time and run times were again similar (122 v 132 minutes FAT v CHO). When diets were switched after run 1, FAT-adapted animals, which received carbohydrates for 72 hours, restored muscle and liver glycogen (48 and 343 mumols/g, respectively) and then ran longer (144 minutes) than CHO-adapted animals (104 minutes) that ate fat for 72 hours and that had reduced glycogen repletion. We conclude that, in contrast to the classic CHO loading studies in humans that involved acute (72 hours) fat feedings and subsequently reduced endurance, rats adapted to a high fat diet do not have a decrease in endurance capacity even after recovery from previous exhausting work bouts. Part of this adaptation may involve the increased storage and utilization of intramuscular triglycerides (TG) as observed in the present experiment.

Role of cholecystokinin and the cholinergic system in intestinal stimulation of gallbladder contraction in man.

To determine the role of cholecystokinin and the cholinergic system in intestinal stimulation of gallbladder contraction, we studied the effects of atropine on plasma cholecystokinin and gallbladder contraction in six healthy volunteers (four men and two women aged 20 to 27 yr). Effects were noted after intraduodenal fat instillation and after dosage with exogenous cholecystokinin inducing plasma cholecystokinin concentrations similar to those after intraduodenal fat instillation. At regular intervals before and after administration of each stimulus, plasma cholecystokinin concentrations and gallbladder volumes were measured by radioimmunoassay and real-time ultrasonography, respectively. Intraduodenal infusion of 250 ml 20% Intralipid induced a peak plasma cholecystokinin increment of 10.2 +/- 1.6 pmol/L compared with 10.7 +/- 0.7 pmol/L during infusion of 1 Ivy dog unit per kilogram per hour of cholecystokinin. The increases in plasma cholecystokinin after fat and exogenous cholecystokinin administration were accompanied by similar decreases in gallbladder volume. Integrated gallbladder contraction after fat instillation was 3,939% +/- 288%.min compared with 3,301% +/- 359%.min during cholecystokinin infusion (NS). Atropine (0.015 mg/kg as bolus followed by 0.005 mg/kg/hr) did not change plasma cholecystokinin concentrations but induced similar inhibition of gallbladder contraction to 2,296% +/- 511%.min (p less than 0.05) after intraduodenal fat instillation and to 1,756% +/- 456%.min (p less than 0.05) during cholecystokinin infusion. We conclude that cholecystokinin is of major importance in intestinal stimulation of gallbladder contraction. Atropine inhibits the gallbladder response to intraduodenal fat. This inhibition is not due to a reduction in cholecystokinin secretion but to a diminished gallbladder response to cholecystokinin.

Selective opioid receptor antagonist effects upon intake of a high-fat diet in rats.

Short-term (2 h) intake of a high-fat diet in rats was significantly inhibited by intravenous (0.1-10 mg/kg: 39-67%) and central (1-5 micrograms, i.c.v.: 51%) naloxone. The irreversible mu opioid antagonist, beta-funaltrexamine (10 micrograms, i.c.v.: 37%), but not the irreversible mu 1 antagonist, naloxonazine (10 mg/kg, i.v.) inhibited intake, suggesting mu 2 receptor mediation. The delta antagonist, ICI 174864 (1-10 micrograms, i.c.v.: 41%) inhibited high-fat diet intake only at doses that also produced motor dysfunction.

Protein and carbohydrate selection respond to changes in dietary saturated fatty acids but not to changes in essential fatty acids.

We previously reported differences in protein and carbohydrate selection patterns in post-weanling rats fed beef tallow or soybean oil-based diets. Two experiments were designed to determine the characteristic of the dietary fat which mediates the selection behavior. For each experiment, dietary fat was 20% (w/w) of diets and fatty acid profiles were obtained by blending fat sources. Rats were randomly assigned to diets (24% protein, 40% carbohydrate) which varied only in fatty acid composition. After 2 weeks, rats selected from 2 diets with the fat composition previously fed, but varying in their protein and carbohydrate composition (55% protein, 4% carbohydrate and 5% protein, 61% carbohydrate). Experiment 1 was designed to test the effect of relative (omega 6: omega 3 ratios of 1 and 20) and absolute (15% or 4% omega 6, 0.7% or 0.2% omega 3) differences in essential fatty acids on macronutrient selection patterns. Differences in dietary essential fatty acids had no effect on energy intake or the proportion of energy consumed as protein and carbohydrate. Experiment 2 examined the effect of differences in the level of saturated fat (3-10% diet (w/w] on protein and carbohydrate selection. Animals selecting from diets with higher levels of saturated fat consumed more energy as protein and less as carbohydrate than rats selecting from diets with lower levels of saturated fat (p less than 0.0001). Regression analysis was used to examine the relationship between percent protein or carbohydrate energy and classes of dietary fat. The strongest relationship existed between percent dietary saturated fat and percent protein or carbohydrate energy (p less than 0.0001). Polyunsaturated:saturated fat ratio was also weakly associated with percent protein and carbohydrate energy (p less than 0.05). Polyunsaturated, monounsaturated, omega 6 and omega 3 fatty acids were not significantly related to percent protein or carbohydrate energy. These results indicated that protein and carbohydrate selection patterns are altered in response to qualitatively different dietary fatty acids, and that the amount of saturated fat in the diet is the important characteristic of dietary fat mediating the behavioral alteration.

Adaptation of the exocrine pancreas to diet.

Pancreatic adaptation represents dietary regulation of gene expression; dietary substrates alter the synthesis and mRNA levels of their respective digestive enzymes. The mechanisms whereby mRNA levels change are not understood, but they must be elucidated. Although the changes in synthesis of proteases, amylase, and lipase parallel the changes in their mRNA levels in response to respective substrates, the concomitant changes in the synthesis of the other enzymes can be discordant with mRNA levels. The evidence supports a pretranslational mechanism of the adaptation of proteases, amylase, and lipase to their respective substrates and suggests potential translational mechanisms of other enzymes in these adaptations. Changes in synthesis occur within hours after a dietary change, but whether mRNA levels also change so early is unknown. Rapid, adaptive changes may occur by a different mechanism from later adaptation, possibly by translational control or nuclear transport. The differential effects of acute and chronic caerulein administration support the possibility of multiple mechanisms of regulation by a single effector. The mediators of pancreatic adaptations have not yet been identified, except for adaptation to dietary protein. CCK appears to mediate protease adaptation through the feedback regulation of its release by dietary protein. Available evidence supports a role of insulin and glucose in the adaptation to carbohydrate and a role of secretin and ketones in the adaptation to dietary fat. Elucidation of the mediators of pancreatic adaptation to carbohydrate and fat and their mechanisms is needed.

Hypotheses for the etiology of colorectal cancer--an overview.

Colorectal cancer is the second most common cancer in the United States. Various dietary, colonic, and fecal components have been implicated as causative factors. Although numerous studies have been conducted to test them, so far no one factor has stood out as the most likely cause of colorectal cancer. This review presents the evidence for and against the major factors and concludes that bile acids are the most strongly implicated factors in the etiology of colorectal cancer.

Essential fatty acids and immune response.

The implication that essential fatty acids (EFA) can affect immune response was based on the observation that EFA deficiency can accentuate or improve symptoms of certain autoimmune diseases in animals, and that supplementation of linoleic acid to animals reversed such effects. Furthermore, treatment of animals with cyclooxygenase inhibitors abrogated the effect of linoleic acid. Administration of cyclooxygenase inhibitors to animals enhanced both cell-mediated and humoral immune responses. In vitro studies have shown that prostaglandin E (PGE) group inhibits both T and B lymphocyte functions; it is suggested that effects of EFA on immune response are, in part, mediated through eicosanoids. Growing evidence now suggests that the PGE group of prostaglandins can serve as a negative feedback modulator of immune response. However, in vitro effects of other cyclooxygenase-derived products, such as PGI2 and thromboxane A2 (TXA2) have not been well established, perhaps because of their instability in aqueous media. Unlike the PGE group, some of lipoxygenase-derived products of arachidonic acid have shown immunostimulatory effects, as assessed by lymphokine production in vitro. Whether such effects can be seen in vivo remains to be determined. Some lipoxygenase-derived products with strong chemotactic action may indirectly influence immune response by modulating the population of antigen-presenting macrophages in tissues. Thus, the net effect of eicosanoids synthesized in macrophages on modulating immune response may depend on relative amounts of cyclooxygenase-derived products as compared with lipoxygenase-derived products. Macrophages are the major source of eicosanoids among immunocompetent cells. The profile of eicosanoids, produced in vitro by macrophages, varies with type of stimuli and anatomical sites. It can also be affected by the fatty acid composition of tissue lipids, which in turn can be modified by the composition of dietary EFA. Whether manipulating dietary EFA can modulate immune response in normal humans and animals needs to be determined.

The effect of dietary n-6 and n-3 polyunsaturated fatty acids on blood pressure and tissue fatty acid composition in spontaneously hypertensive rats.

Effects of dietary n-6 and n-3 fatty acids (FAs) on blood pressure (BP) and tissue phospholipid (PL) FA composition in spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats were compared. Male weanling SHR and WKY were fed a fat-free semisynthetic diet supplemented with 10% (w/w) fats containing (a) 78% 18:2n-6 (LA-rich), (b) 20% LA and 55% 18:3n-3 (LN-rich), or (c) 11% LA and 3% LN (CON) for seven weeks. Dietary fats did not affect the BP elevation, but significantly altered the FA composition of brain, adrenal gland, renal medulla and cortex PL in SHR. The LA-rich diet increased n-6 FA while it reduced n-3 FA levels. The levels of 20:4n-6 were not significantly different between animals fed the LA-rich and the CON diets. LN-rich diet increased the levels of n-3 FAs, while it reduced those of n-6 FAs. However, the extent of change was significantly less in SHR than in WKY. In all dietary groups, SHR, as compared to WKY, had a relatively higher level of the 2 series prostaglandin (PG) precursor, 20:4n-6, and a relatively lower level of the 1 and 3 series PG precursors, 20:3n-6 and 20:5n-3. The possibility that the unbalanced eicosanoid FA precursor levels might contribute to the development of hypertension in this animal model is discussed.

Effects of dietary linoleic acid on beta-adrenergic responsiveness of the guinea pig respiratory system.

Respiratory autonomic beta-adrenergic receptor function was investigated in isolated tracheal spirals of guinea pigs receiving different diets. Comparison was made between control and Haemophilus influenzae treated animals; this latter group serving as animal model for atopy. The different semi-synthetic diets (35 energy%) varying in their linoleic acid contents (5.85, 11.25 and 22.05 en%), exerted profound effects on membrane fatty acid composition. No influence of these diets on either food intake or growth could be detected. Isoprenaline induced relaxation of guinea pig tracheal spirals was maximal in the dietary group receiving moderate linoleic acid (11.25 en%). Both the addition and the withdrawal of linoleic acid to this diet resulted in a significant impairment of beta-adrenergic receptor function, to the same extent as can be induced by Haemophilus influenzae. The results are discussed in view of current concepts for atopy.

Interaction of dietary cholesterol and triglycerides in the regulation of hepatic low density lipoprotein transport in the hamster.

These studies report the effects of dietary cholesterol and triglyceride on rates of receptor-dependent and receptor-independent LDL transport in the liver of the hamster. In animals fed diets enriched with 0.1, 0.25, or 1% cholesterol for 1 mo, receptor-dependent LDL transport in the liver was suppressed by 43, 63, and 77%, respectively, and there were reciprocal changes in plasma LDL-cholesterol concentrations. In addition, dietary triglycerides modified the effect of dietary cholesterol on hepatic LDL transport and plasma LDL concentrations so that at each level of cholesterol intake, polyunsaturated triglycerides diminished and saturated triglycerides accentuated the effect of dietary cholesterol. When animals were raised from weaning on diets containing small amounts of cholesterol, the decline in receptor-dependent LDL transport was nearly abolished by the addition of polyunsaturated or monounsaturated triglycerides, but was markedly augmented by the addition of saturated lipids. When animals raised on diets containing cholesterol and saturated triglycerides were returned to the low cholesterol, low triglyceride control diet, hepatic receptor-dependent LDL transport and plasma LDL-cholesterol concentrations returned essentially to normal within 2 wk. Neither receptor-independent LDL transport nor the receptor-dependent uptake of asialofetuin was significantly altered by dietary cholesterol or triglyceride suggesting that the effect of these lipids on hepatic LDL receptor activity was specific and not due to a generalized alteration in the physiochemical properties of hepatic membranes. These studies demonstrate the important role of saturated triglycerides in augmenting the effect of cholesterol in suppressing hepatic LDL receptor activity and elevating LDL-cholesterol levels.

Chronic ethanol feeding inhibits plasma levels of insulin-like growth factor-1.

The purpose of this study was to determine whether the generalized catabolic effects of chronic ethanol may be associated with a decline in plasma levels of insulin-like growth factor-1 (IGF-1). Male Sprague-Dawley rats were fed a liquid diet containing 5% ethanol or pair-fed a diet made isocaloric with maltose-dextrin. Animals were maintained on this diet for either 12 days or 4.5 months. Another group of animals were fed control diet ad libitum for 2 weeks. After 12 days of feeding, plasma concentrations of IGF-1 in ad libitum fed rats were 771 +/- 41 ng/ml which was greater than concentrations in either pair-fed (595 +/- 23 ng/ml) or ethanol-fed (680 +/- 40 ng/ml) rats (P less than 0.05). After 4.5 months of feeding, plasma levels of IGF-1 in ad libitum and pair-fed rats were similar to the 12 day study (736 +/- 56 and 607 +/- 26 ng/ml, respectively). However, a significant decrease in plasma levels of IGF-1 was observed in ethanol-fed animals over the 4.5 month period (551 +/- 28 ng/ml, P less than 0.05). Results of a similar study in rats fed a high-fat diet for 4.5 months were similar to those found with the low-fat diet. These results indicate that 1) dietary restriction of the type routinely used in this pair-feeding regimen decreases plasma levels of IGF-1, 2) chronic ethanol feeding further decreases plasma IGF-1 levels compared to pair-fed rats, 3) the effects of ethanol on IGF-1 concentrations are not modified by dietary fat, and 4) the effects on IGF-1 are not directly dependent on elevated plasma ethanol concentrations. Our results suggest that IGF-1 secreting cells in the liver may be progressively damaged by chronic ethanol feeding.

Membrane fatty acid composition and radiation response of Bp8 sarcoma ascites tumour cells.

The radiation response of Bp8 sarcoma ascites tumour cells with differences in membrane fatty acid composition was studied. The cells were grown i.p. in NMRI mice and their membrane composition was changed in response to different dietary regimes provided to the host animals. Three diets that differed only with regard to the source of fatty acids, i.e. sunflower seed oil, coconut oil, hydrogenated lard and a fourth commercially available standard laboratory diet, were given to the mice for different lengths of time, before implantation of the tumour cells. The time course for the dietary regimes to induce different levels of changes in membrane fatty acid composition of the ascites cells was established. The evaluation of the radiosensitivity of cells with different membrane fatty acid composition was done in vitro. Cell survival, expressed by D0, varied only insignificantly between the four dietary groups, while their repair capacity (Dq and n) differed significantly. Increased repair capacity was observed for ascites cells grown in animals on diets enriched in sunflower seed oil and coconut oil, compared with cells from mice fed the hydrogenated lard diet or from cells from the control animals. The membrane fatty acid composition of the cells from the two dietary groups with increased levels of repair capacity differed extensively, and in general there was no correlation observed between radiation response and the membrane fatty acid composition of the four dietary groups studied. For two of the dietary groups, coconut oil and control, with marked differences in membrane fatty acid composition, the effects of irradiation on ascites tumour growth rate and cell cycle distribution were followed in vivo. For none of these parameters was an effect of membrane fatty acid composition on radiation response observed.

A fish oil diet inhibits amyloid P component (AP) acute phase responses in arthritis susceptible mice.

Amyloid P component (AP) bears close homology with C-reactive protein and behaves as an acute phase reactant in the plasma of mice but not in man. Our aim was to determine whether AP is influenced by diet, gender, and arthritis severity in a murine model of arthritis. B10.RIII mice were segregated according to gender and diet at 8 wk of age: the source of fat was either corn oil, fish oil, or beef tallow (5% by weight). Four weeks later, each mouse was immunized with 100 micrograms fetal bovine type II collagen, and the incidence and severity of arthritis was noted at weekly intervals. AP was measured by competitive ELISA in plasma taken 5 wk and 15 wk after immunization. AP levels were less in fish oil fed males and females. Under all conditions tested AP levels of females were greater than in males. There was a negative correlation between AP levels and the severity of arthritis. We conclude from these data that although AP levels cannot be used as indices of arthritis severity, there are significant dietary and gender effects on AP concentrations as long as 15 wk after immunization with type II collagen.

Low prevalences of coronary heart disease (CHD), psoriasis, asthma and rheumatoid arthritis in Eskimos: are they caused by high dietary intake of eicosapentaenoic acid (EPA), a genetic variation of essential fatty acid (EFA) metabolism or a combination of both?

The low prevalences of CHD, psoriasis, asthma and rheumatoid arthritis in Eskimos have been attribute to the high dietary intake of EPA from fish and marine mammals. However, even on a Western diet, Eskimos have plasma arachidonic acid (AA) levels far below those seen in Europeans while dihomogammalinolenic acid (DGLA) levels are higher in Eskimos. These low AA and high DGLA levels seem to be due to a genetic abnormality in EFA desaturation since they are found even when EPA intakes are low. Since AA is known to be important in the pathogenesis of CHD, asthma, psoriasis and arthritis, while DGLA has properties which make it of likely therapeutic value in these conditions, the genetically high DGLA and low AA are likely to be as important as dietary EPA in determining Eskimo disease patterns.

Effects of dietary additions of 1,3-butanediol or lard for sows on survival of neonatal pigs.

In nine trials, 278 late-term gravid sows were fed isocaloric amounts (8,500 kcal metabolizable energy (ME)/d) of a fortified, corn-soybean meal based diet in which 20% of their daily ME intake was supplied by corn starch, 1,3-butanediol or lard from about d 106 of gestation to parturition. After parturition, the sow's daily ME intake was increased to 18,000 kcal. Sows fed starch and lard remained on their respective diets for the duration of a 28-d lactation; whereas, those initially fed butanediol were switched to the starch diet after parturition. Number of pigs born per litter, average pig birth weight and incidence of stillbirths were not influenced (P greater than .30) by the prepartum diet of the sow. However, the inclusion of isocaloric levels of butanediol for starch in the preparatum diet and lard for starch in the pre- and postpartum diets increased the number of pigs weaned per litter by .45 (P less than .13) and .16 pigs (8.25, 7.96 vs 7.80) and improved the survival rate of pigs from birth to weaning by 4.3 (P less than .13) and 2.7 percentage units (84.5, 82.8 vs 80.1%), respectively. Average pig weights at 28 d of age for litters of sows fed butanediol prepartally were similar to those of sows fed starch, but were less (P less than .01) than those of sows fed lard throughout lactation.

Dietary protein, enhancement of N-nitrosomethylurea-induced mammary carcinogenesis, and their effect on hormone regulation in rats.

The effect of supplemental dietary protein (casein) fed with high fat diets was investigated using the N-nitrosomethylurea-induced mammary tumor model. Isocaloric diets containing casein and corn oil at 19 and 15% (normal protein-high fat) or 33 and 15% (high protein-high fat) were fed ad libitum to Sprague-Dawley mother rats. Female offspring continued on the diet. Food consumption and growth curves were similar over the entire growth period. N-Nitrosomethylurea (50 mg/kg body weight) or saline was administered at 7 and 8 weeks of age via the tail vein. Dietary protein had no effect on serum prolactin or growth hormone throughout the estrous cycle: Prior to carcinogen administration, at 7 weeks old, proestrus at 5 p.m., serum prolactin was 231.6 +/- 141.0 (SE) ng/ml (12 rats) versus 292.2 +/- 141.0 (13 rats) for normal versus high protein diet groups, respectively. No difference was noted after carcinogen injection at 9, 13, 28, and 33 weeks of age. Similarly no effect was noted on serum growth hormone activity. Tumor latency was 7 weeks and incidence was 100% in normal protein (24 rats) and high protein (39 rats) groups 28 weeks after carcinogen treatment. The number of tumors per rat (4.38 +/- 0.37 versus 2.87 +/- 0.35, P less than 0.002) and average tumor weight (17.97 +/- 2.63 versus 9.94 +/- 2.92 g) were significantly greater in the high protein group. Study indicates that diet or carcinogen treatment did not alter hormone regulation during the estrous cycle. However, supplemental dietary protein increased the effect of high fat diets enhancing the mammary tumor burden.

Learning is improved by a soybean oil diet in rats.

A semi-synthetic diet containing 20% polyunsaturated fat (soybean) oil was fed to young male hooded rats for 21 days. These animals exhibited improved performance on an environmentally-cued testing paradigm which is thought to reflect cognitive learning skills (i.e., Place Navigation Water Task). Other rats fed the same base diet but containing 20% saturated fat (lard) showed no such improvement compared to chow-fed (4.5% mixed fat) controls. The animals fed soybean oil also exhibited a transient resistance to extinguish this learning. This improved learning could not be explained by changes in general motor activity, basal body temperature, energy consumption, body weight, or in the brain activity of choline acetyltransferase, the marker enzyme for cholinergic neurons. These findings constitute the first evidence that short-term variations in the quality of dietary fat can enhance mammalian learning.