Immune modulation by altered nutrient metabolism: nutritional control of immune-induced growth depression

The effects of conjugated linoleic acid supplementation on immune function in healthy volunteers

OBJECTIVE

To assess the effects of dietary supplementation using two isomeric blends of conjugated linoleic acid (CLA) on immune function in healthy human volunteers.

DESIGN

Double-blind, randomised, placebo-controlled intervention trial.

SUBJECTS AND INTERVENTION

A total of 55 healthy volunteers (n=20 males, n=35 females) were randomised into one of three study groups who received 3 g/day of a fatty acid blend containing a 50:50 cis-9, trans-11: trans-10, cis-12 CLA isomer blend (2 g CLA), and 80:20 cis-9, trans-11: trans-10, cis-12 (80:20) CLA isomer blend (1.76 g CLA) or linoleic acid (control, 2 g linoleic acid) for 8 weeks.

RESULTS

Supplementation with the 80:20 CLA isomer blend significantly (P< or =0.05) enhanced PHA-induced lymphocyte proliferation. CLA decreased basal interleukin (IL)-2 secretion (P< or =0.01) and increased PHA-induced IL-2 and tumor necrosis factor alpha (TNF(alpha)) production (P< or =0.01). However, these effects were not solely attributable to CLA as similar results were observed with linoleic acid. CLA supplementation had no significant effect on peripheral blood mononuclear cells IL-4 production, or on serum-soluble intercellular adhesion molecule-1 (sICAM-1) or plasma prostaglandin E2 (PGE2) or leukotreine B4 (LTB4) concentrations.

CONCLUSIONS

This study shows that CLA supplementation had a minimal effect on the markers of human immune function. Furthermore, supplementation with CLA had no immunological benefit compared with linoleic acid.

Supplementation with conjugated linoleic acid for 24 months is well tolerated by and reduces body fat mass in healthy, overweight humans

After 12 mo in a randomized, double-blind, placebo-controlled trial of conjugated linoleic acid (CLA) supplementation (2 groups received CLA as part of a triglyceride or as the free fatty acid, and 1 group received olive oil as placebo), 134 of the 157 participants who concluded the study were included in an open study for another 12 mo. The goals of the extension study were to evaluate the safety [with clinical chemistry analyses and reported adverse events (AEs)] and assess the effects of CLA on body composition [body fat mass (BFM), lean body mass (LBM), bone mineral mass (BMM)], body weight, and BMI. All subjects were supplemented with 3.4g CLA/d in the triglyceride form. Circulating lipoprotein(a) and thrombocytes increased in all groups. There was no change in fasting blood glucose. Aspartate amino transferase, but not alanine amino transferase, increased significantly. Plasma total cholesterol and LDL cholesterol were reduced, whereas HDL cholesterol and triglycerides were unchanged. The AE rate decreased compared with the first 12 mo of the study. Body weight and BFM were reduced in the subjects administered the placebo during the initial 12 mo study (-1.6 +/- 3.2 and -1.7 +/- 2.8 kg, respectively). No fat or body weight changes occurred in the 2 groups given CLA during the initial 12 mo. LBM and BMM were not affected in any of the groups. Changes in body composition were not related to diet and/or training. In conclusion, this study shows that CLA supplementation for 24 mo in healthy, overweight adults was well tolerated. It confirms also that CLA decreases BFM in overweight humans, and may help maintain initial reductions in BFM and weight in the long term.

Consumption of conjugated linoleic acid (CLA) from CLA-enriched cheese does not alter milk fat or immunity in lactating women

Isomers of conjugated linoleic acid (CLA) decreased milk fat, altered immunity, and reduced the risk for cardiovascular disease (CVD) in some animals. The major form of CLA in the human diet is c9,t11-18:2 (rumenic acid; RA). We studied the effects of high RA consumption on plasma and milk RA concentration, milk composition, immunity, and CVD risk factors in lactating women (n = 36) assigned to 1 of 3 treatments: control, low CLA cheese (LCLA; 160 mg RA/d), or high CLA cheese (HCLA; 346 mg RA/d). The increase in plasma RA concentration between baseline and 8 wk in women consuming HCLA cheese was significantly greater than that of controls. At study completion (8 wk), milk RA concentration among women consuming HCLA cheese was greater (P < 0.05) than that of controls (0.37 vs. 0.26% of fatty acids). Treatment did not affect milk fat, protein, or lactose concentrations, immune indices (e.g., plasma T-helper cells and interleukin-2), or measured risk factors for CVD (e.g., plasma triacylglyceride and cholesterol). In summary, consumption of a RA-enriched cheese modestly increased plasma and milk RA concentrations without affecting total milk fat, plasma and milk indices of immunity, or selected risk factors for CVD.

Hydrogenation for Low Trans and High Conjugated Fatty Acids

Hydrogenated vegetable oils contain of trans fatty acids. Because of the increased health concern about trans fatty acids, new hydrogenations have been studied to seek ways for substantial reduction of the trans fatty acids in the hydrogenated vegetable oils. This paper reviews new hydrogenation processes such as electrocatalytic hydrogenation, precious catalyst hydrogenation, and supercritical fluid state hydrogen, which have shown promising results for the reduction of trans fatty acids below the level of 8%. This paper also reviews the recently introduced hydeogenation technique for high accumulation of conjugated linoleic acids, beneficiary functional components. The hydrogenated vegetable oils with high quantity conjugated linoleic acid might provide the possibility for the utilization of hydrogenated oils as health-prompting food ingredients.

Effects of cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid on immune cell function in healthy humans

BACKGROUND

Animal studies have suggested that conjugated linoleic acid (CLA), a natural component of ruminant meat and dairy products, may confer beneficial effects on health. However, little information on the effects of CLA on immune function is available, especially in humans. Furthermore, the effects of individual isomers of CLA have not been adequately investigated.

OBJECTIVE

This study investigated the effects of supplementing the diet with 3 doses of highly enriched cis-9,trans-11 CLA (0.59, 1.19, and 2.38 g/d) or trans-10,cis-12 CLA (0.63, 1.26, and 2.52 g/d) on immune outcomes in healthy humans.

DESIGN

The study had a randomized, double-blind, crossover design. Healthy men consumed 1, 2, and 4 capsules sequentially that contained 80% of either cis-9,trans-11 CLA or trans-10,cis-12 CLA for consecutive 8-wk periods. This regimen was followed by a 6-wk washout and a crossover to the other isomer.

RESULTS

Both CLA isomers decreased mitogen-induced T lymphocyte activation in a dose-dependent manner. There was a significant negative correlation between mitogen-induced T lymphocyte activation and the proportions of both cis-9,trans-11 CLA and trans-10,cis-12 CLA in peripheral blood mononuclear cell lipids. However, CLA did not affect lymphocyte subpopulations or serum concentrations of C-reactive protein and did not have any consistent effects on ex vivo cytokine production.

CONCLUSION

CLA supplementation results in a dose-dependent reduction in the mitogen-induced activation of T lymphocytes. The effects of cis-9,trans-11 CLA and trans-10,cis-12 CLA were similar, and there was a negative correlation between mitogen-induced T lymphocyte activation and the cis-9,trans-11 CLA and trans-10,cis-12 CLA contents of mononuclear cells.

The effect of dietary conjugated linoleic acid on egg yolk fatty acids and hatchability in Japanese quail

Conjugated linoleic acid (CLA) increased the ratio of saturated fatty acids to monounsaturated fatty acids in yolk and caused embryo mortality. Our preliminary studies showed that CLA had less of an effect on hatchability of quail than chickens. Hence, the objective was to determine the effects of dietary CLA on quail egg fatty acid content and hatchability. Eight male-female Japanese quail pairs per group were randomly assigned to diets containing 0 (canola oil; CO), 0.25, 0.5, 1, 2, or 3% CLA for 8 wk. Eggs were collected, held at 15 degrees C for 24 h, and then incubated. Three eggs from each group were collected for fatty acid analysis on the 45th day. At the end of the 8 wk, all quail were euthanized. Liver samples from female quail were obtained for fatty acid analysis. Diet containing 3, 2, or 1% CLA caused 100% embryo mortality after 6, 10, or 12 d of feeding, whereas overall hatchabilities in groups 0, 0.25, and 0.5 were 84, 86, and 64%, respectively. As the dietary CLA increased, egg and hepatic CLA increased, C16:0 increased and C16:1(n-7) and C18:1(n-9) decreased, whereas C18:0 remained unchanged. Diets containing 1, 2, or 3% CLA decreased the C20:4(n-6) levels in yolk (significantly) and liver (inconsistently) lipids. Yolk CLA levels from 0, 0.25, 0.5, 1, 2, and 3% CLA were 0.31, 0.90, 1.48, 2.44, 5.88, and 11.2%, respectively. The ratios of C16:0/C16:1(n-7) in yolks from groups fed 0, 0.25, 0.5, 1, 2, or 3% CLA were 8.2, 16.3, 20.4, 24.6, 26.1, and 28.6, respectively. The ratios of C18:0/C18:1(n-9) in yolks from hens fed 0, 0.25, 0.5, 1, 2, or 3% CLA were 0.28, 0.40, 0.48, 0.49, 0.69, and 0.83, respectively. Quail fed 0.25% CLA had increased egg size, whereas quail fed 2 or 3% had reduced egg size compared with those fed CO. Liver sizes (%) in all of the groups were increased, except for the group fed 0.25% CLA. These data suggest that CLA may affect hatchability possibly by changing the fatty acid composition of the yolk.

The effects of water supplementation with vitamin E and sodium salicylate (Uni-Sol) on the resistance of turkeys to Escherichia coli respiratory infection

The objective of this study was to determine the prophylactic efficacy of two commercial products, soluble vitamin E and soluble sodium salicylate (Uni-Sol), in an Escherichia coli respiratory challenge. The drinking water of male turkey poults was nonsupplemented or supplemented with either vitamin E or Uni-Sol or a combination of both at dosages recommended by the manufacturer. There were 110 birds in each of the four treatments, housed in four floor pens per treatment. At 5 wk of age, birds in half of the pens were challenged with an air sac inoculation of approximately 50 colony-forming units of E. coli. Water treatment commenced 5 days before challenge and continued for 2 wk after challenge, when birds were necropsied. All water treatments prevented the decrease in body weight due to E. coli challenge; however, either vitamin E or Uni-Sol alone, but not the combination of the two, decreased body weight in nonchallenged controls. Either vitamin E or Uni-Sol treatment alone, but not the combination of the two, significantly decreased mortality and air sacculitis scores of challenged birds, and all treatments decreased the isolation rates of E. coli from the liver. All treatments protected liver, spleen, and bursa weights (relative to body weight) from the effects of E. coli challenge, and Uni-Sol alone or vitamin E with Uni-Sol protected relative heart weights from the effect of challenge. Uni-Sol treatment alone increased the main effect mean total leukocyte counts and the number and percent of lymphocytes. Uni-Sol in combination with vitamin E increased the number of lymphocytes of challenged birds. Uni-Sol alone decreased the main effect mean heterophil/lymphocyte ratio (H/L) ratio, whereas vitamin E alone increased the H/L ratio of challenged birds. These results indicate that treatment of turkey poults with vitamin E or Uni-Sol prior to and during the stressful events that can lead to colisepticema may decrease disease incidence and mortality.

Conjugated linoleic acid: health implications and effects on body composition

Conjugated linoleic acid (CLA) is attracting interest because of its purported effects on body composition, specifically a reduction in body fat mass and an increase in lean body mass. Other reported beneficial health-related effects of CLA include anticarcinogenic, antiatherogenic, antidiabetogenic, and immune modulating properties. Because research on CLA has been almost exclusively in animals and the mechanism(s) by which CLA exerts its effects remain largely unknown, scientists are extremely cautious about making definitive statements about CLA. Despite the limited research on CLA in human subjects, numerous Internet websites and health food stores sell CLA supplements or CLA-containing products as weight loss or ergogenic aids. The increasing popularity of CLA as a dietary supplement makes it important that dietitians and health professionals are aware of CLA and are able to provide the public with science-based information regarding CLA.

Conjugated linoleic acid supplementation for 1 y reduces body fat mass in healthy overweight humans

BACKGROUND

Short-term trials showed that conjugated linoleic acid (CLA) may reduce body fat mass (BFM) and increase lean body mass (LBM), but the long-term effect of CLA was not examined.

OBJECTIVE

The objective of the study was to ascertain the 1-y effect of CLA on body composition and safety in healthy overweight adults consuming an ad libitum diet.

DESIGN

Male and female volunteers (n = 180) with body mass indexes (in kg/m(2)) of 25-30 were included in a double-blind, placebo-controlled study. Subjects were randomly assigned to 3 groups: CLA-free fatty acid (FFA), CLA-triacylglycerol, or placebo (olive oil). Change in BFM, as measured by dual-energy X-ray absorptiometry, was the primary outcome. Secondary outcomes included the effects of CLA on LBM, adverse events, and safety variables.

RESULTS

Mean (+/- SD) BFM in the CLA-triacylglycerol and CLA-FFA groups was 8.7 +/- 9.1% and 6.9 +/- 9.1%, respectively, lower than that in the placebo group (P < 0.001). Subjects receiving CLA-FFA had 1.8 +/- 4.3% greater LBM than did subjects receiving placebo (P = 0.002). These changes were not associated with diet or exercise. LDL increased in the CLA-FFA group (P = 0.008), HDL decreased in the CLA-triacylglycerol group (P = 0.003), and lipoprotein(a) increased in both CLA groups (P < 0.001) compared with month 0. Fasting blood glucose concentrations remained unchanged in all 3 groups. Glycated hemoglobin rose in all groups from month 0 concentrations, but there was no significant difference between groups. Adverse events did not differ significantly between groups.

CONCLUSION

Long-term supplementation with CLA-FFA or CLA-triacylglycerol reduces BFM in healthy overweight adults.

Immunomodulatory properties of conjugated linoleic acid

In vitro studies of the use of immune cells and animal models demonstrate that conjugated linoleic acid (CLA), a lipid, modulates immune function. In addition, recent publications demonstrate that 2 active CLA isomers (ie, cis-9,trans-11 CLA and trans-10,cis-12 CLA) modulate immune function in humans. Aspects of both the innate and adaptive immune responses are affected by dietary CLA supplementation. CLA consists of a mixture of isomers, which reduced immune-induced wasting and enhanced ex vivo lymphocyte proliferation in broilers and decreased tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) production in rat models. In mice, ex vivo lymphocyte proliferation and IL-2 production were increased. Furthermore, evidence suggests that the cis-9,trans-11 and trans-10,cis-12 CLA isomers exert distinct effects on immune function. Specifically, these 2 isomers have differential effects on specific T cell populations and immunoglobulin subclasses in animal and human studies. Herein, a systematic review of the literature and relevant new data are presented with an aim to compare data and to present an overview covering the innate and adaptive components of the immune response that are regulated by CLA. In addition, potential mechanisms of action are discussed and the need for future studies on the immunomodulatory properties of CLA are outlined in detail. The understanding of the mechanism(s) by which CLA increases immune function will aid in the development of nutritionally based therapeutic applications to augment host resistance against infectious diseases and to treat immune imbalances, which result in inflammatory disorders, allergic reactions, or both.

Perspective on the safety and effectiveness of conjugated linoleic acid

The amount of scientific literature on conjugated linoleic acid (CLA) is growing at a phenomenal rate. Animal studies and clinical trials indicate the possibility that CLA could be useful in improving human health in a number of areas, eg, controlling body fat gain and enhancing immunity while also reducing inflammation and other adverse effects typically associated with immune enhancement. The background of this growing research field and mechanistic insights from animal and cell culture experiments are briefly reviewed. Experimental and clinical data relating to the safety and effectiveness of CLA in humans are presented and discussed.

Detection of conjugated C16 PUFAs in rat tissues as possible partial beta-oxidation products of naturally occurring conjugated linoleic acid and its metabolites

In a previous paper, we showed that naturally occurring conjugated linoleic acid (CLA) from butter fat is metabolized in vivo to higher metabolites such as conjugated diene (CD) 18:3, CD 20:3 and CD 20:4, all the while retaining the conjugated diene structure. In this paper, we describe the detection of two more metabolites with characteristic conjugated diene UV spectra. HPLC retention times, UV and MS spectra identified the CLA metabolites as CD 16:2 and CD 16:3. The accumulation of CD 16:2 was significantly higher than that of CD 16:3 in all tissues examined. Tissue distributions of CD 16:2 and CD 16:3 were similar, with plasma and adipose tissue showing the highest levels, while kidney had the lowest and the liver an intermediate level. CD 16 fatty acids accounted for about 20% of the total CLA metabolites. The kidney, however, was an exception where CD 16 fatty acids accounted for only 11% of total metabolites. Analyses of liver lipid classes showed that CD 16:2 and CD 16:3 were preferentially incorporated into neutral lipids. This preferential incorporation was very similar to CLA as shown previously. We hypothesize that CD 16:2 and CD 16:3 may be derived from partial beta-oxidation of CLA and CD 20:4, respectively, even though we cannot rule out that CD 16:3 may also be derived from CD 18:3 and CD 20:3. Incubation of skin human fibroblasts from X-linked adrenoleukodystrophy (ALD) patients with c9,t11 CLA showed that CD 16:2 formation in ALD cells was about 50% lower than control cells. This result may tempt to hypothesize that, at least in part, CD 16:2 is beta-oxidized in peroxisomes.

Evidence for potential mechanisms for the effect of conjugated linoleic acid on tumor metabolism and immune function: lessons from n-3 fatty acids

Conjugated linoleic acid (CLA) and the long-chain polyunsaturated n-3 fatty acids have been shown in vivo and in vitro to reduce tumor growth. Tumor growth could occur by slowing or stopping cell replication (by interfering with transition through the cell cycle), increasing cell death (via necrosis and/or apoptosis), or both. The anticancer effects of fatty acids, shown in vivo, could also be mediated by effects on the host's immune system. Although it is widely recognized that n-3 fatty acids can alter immune and inflammatory responses, considerably less is known about CLA. For n-3 fatty acids, several candidate mechanisms have been proposed for their immune effects, including changes in 1) membrane structure and composition, 2) membrane-mediated functions and signals (eg, proteins, eicosanoids), 3) gene expression, and 4) immune development. Considerable work has been done that shows the potential importance of CLA as an anticancer treatment; however, many questions remain as to how this effect occurs. This review summarizes the CLA and cancer literature and then uses the evidence for the anticancer immune and tumor properties of the long-chain n-3 fatty acids docosahexaenoic and eicosapentaenoic acids to suggest future research directions for mechanistic studies on CLA and cancer.

Evidence that the anti-obesity effect of conjugated linoleic acid is independent of effects on stearoyl-CoA desaturase1 expression and enzyme activity

The trans-10,cis-12 isomer of conjugated linoleic acid (CLA) reduces body fat gain in animals and inhibits stearoyl-CoA desaturase (SCD) activity in 3T3-L1 adipocytes. To test whether CLA's body fat reduction is mediated by SCD1, wild-type and SCD1-null mice were fed diet supplemented with 0.2% trans-10,cis-12 (t10c12) CLA for 4 weeks. The t10c12 CLA-supplemented diet significantly reduced body fat mass in both wild type and SCD1-null mice. Similarly, t10c12 CLA diet decreased blood triglyceride and free fatty acid levels regardless of SCD1 genotypes. Mice fed t10c12 CLA exhibited increased mRNA expression of fatty acid synthase and uncoupling protein 2 in both genotypes. Taken together, the effects of t10c12 CLA on reduction of body fat gain, blood parameters, and mRNA expression in both SCD1-null mice and wild-type mice were similar, indicating that the anti-obesity effect of t10c12 CLA may be independent of the effects of this CLA isomer on SCD1 gene expression and enzyme activity.

Effects of dietary conjugated linoleic acid on haematological and humoral responses in the grower pig

The effects of conjugated linoleic acid (CLA) on the levels of total serum leucocytes, granulocytes including neutrophils, basophils, and eosinophils, as well as on monocytes and leucocytes were measured in pigs selected from a clean (minimal disease) herd. Thirty pigs were fed different rates of dietary CLA (0, 1.25, 2.5, 5.0, 7.5, and 10.0 g CLA-55/kg diet) for 8 weeks. Blood samples were collected at the end of the study for assessment of haematological and humoral responses to CLA supplementation. No difference in total white blood cells including the neutrophil, monocyte, and lymphocyte counts was observed among different dietary groups. A dose-dependent reduction (P = 0.02) in eosinophil concentrations suggests that CLA exerts anti-inflammatory activities. A 2-fold increase in the level of basophils was recorded in pigs fed lower levels of CLA (1.25 and 2.5 g CLA/kg diet) but the levels decreased gradually (P = 0.05) and were below the detection limit at the highest rate (10 g/kg) of CLA supplementation. The level of IgG was reduced by over 50% in CLA-fed pigs (P < 0.001), although the response was quadratic in nature (P < 0.001). T-cell population analysis showed that CD4+ cells tended (P = 0.06) to be reduced linearly with increasing inclusion of CLA in the diet. Our results suggest that dietary CLA modulates haematological and humoral responses in a dose-dependent manner.

Production and Metabolic Responses of Periparturient Holstein Cows to Dietary Conjugated Linoleic Acid and trans-Octadecenoic Acids

Thirty-eight multiparous Holstein cows were utilized in a completely randomized design to examine the effect of feeding calcium salts of conjugated linoleic acid (CLA) and trans-octadecenoic acids (trans-C18:1) on animal performance and lipid and glucose metabolism during the transition to lactation. Dietary treatments were initiated approximately 28 d prior to expected calving dates and continued through d 49 postpartum. Prepartum treatments consisted of 1) a basal diet (Control), 2) basal diet + 150 g/d of CLA mix (CLA), and 3) basal diet + 150 g/d of trans-C18:1 mix (TRANS). Amounts of calcium salts of CLA and trans-C18:1 mixes were adjusted to 225 g/d during the 49-d postpartum treatment period. All diets were offered as a total mixed ration. Prepartum fat supplementation had no detectable effects on dry matter intake, body weight, or body condition score. After parturition, cows in the TRANS group consumed less dry matter at wk 4, 5, and 6 of lactation than did cows in the control group. Cows fed the trans-C18:1 supplement were in a more severe negative energy balance than those fed the control diet at 1 wk of lactation. Periparturient fat supplementation had no detectable effects on milk yield during wk 1 to 7 of lactation. Milk fat was not affected during wk 1 to 4, but was reduced after wk 4 of lactation by dietary CLA. Feeding calcium salts of CLA decreased short- to medium-chain fatty acid (C4 to C14) concentrations and increased both linoleic and linolenic acid concentrations in milk fat. Concentrations of nonesterified fatty acids and beta-hydroxybutyric acid in blood were greater in cows fed the CLA-supplemented diet than in those fed the control diet at 1 wk of lactation. In spite of small numerical tendencies, hepatic lipid and triacylglycerol concentrations did not vary significantly among dietary treatments. Periparturient fat supplementation had no detectable effects on plasma glucose and insulin concentrations. Steady-state concentrations of hepatic mRNA encoding pyruvate carboxylase and phosphoenolpyruvate carboxykinase were greater for the TRANS treatment group than the control and CLA groups. Results indicate that dietary CLA and trans-C18:1 fatty acids may affect lipid and glucose metabolism in early postpartum Holstein cows through distinct mechanisms.

Hepatic lipid characteristics and histopathology of laying hens fed CLA or n−3 fatty acids

The effect of dietary CLA and n-3 PUFA on hepatic TAG accumulation, histopathology, and FA incorporation in lipid classes by laying chickens was investigated. One hundred twenty 30-wk-old single comb white leghorn laying hens were distributed randomly to four treatments (3 replications of 10 birds) and were fed diets containing CLA and animal fat (Diet I), 18:3n-3 (Diet II), or long-chain n-3 FA (Diet III). A sunflower oil (n-6 FA)-based diet vvas the control. Feeding Diet I resulted in an increase in hepatic total lipids (P < 0.05). The liver TAG content was 32.2, 18.9, 29.4, and 18.7 mg/g for hens fed Diet I, Diet II, Diet III, and the control diet, respectively (P< 0.05). The serum TAG was lowest in birds fed Diet II (P < 0.05). Diet I resulted in an increase in the total number of fat vacuoles and lipid infiltration in hepatocytes (P < 0.05). The number of cells with 75% or higher lipid vacuolation was observed only in birds fed Diet I. Feeding diets containing CLA resulted in an increase in the content of the c9,t11 CLA isomer in liver TAG and PC (P < 0.05). No difference was observed in the CLA concentration of hepatic PE fractions. The content of DHA (22:6n-3) was higher in the TAG, PC, and PE of hens fed Diet II and Diet III than Diet I and the control (P < 0.05). Feeding CLA resulted in an increase in total saturated FA in the TAG and PC fractions (P < 0.05). Long-term feeding of CLA in laying birds leads to an increase in liver TAG and may predispose birds to fatty liver hemorrhagic syndrome.

Dose Response of Milk Fat to Intravenous Administration of the trans-10, cis-12 Isomer of Conjugated Linoleic Acid

Intravenous infusion of conjugated linoleic acid (CLA) was evaluated as a simpler method than abomasal infusion and the feeding of calcium salts to examine milk fat depression. The objectives were to determine the dose-dependent response of milk fat and plasma metabolites to intravenous administration of the trans-10, cis-12 isomer of CLA, an isomer identified to possess an inhibitory effect on milk fat synthesis. Four multiparous Holstein cows averaging 123 +/- 30 d in milk were randomly assigned to treatments in a 4 x 4 Latin square design. Catheters were inserted into the jugular vein for infusions and blood sampling. Treatments consisted of intravenous infusions of 0, 2, 4, and 6 g/d CLA (> 95% trans-10, cis-12 CLA). Infusates contained 72 g/d of a parenteral solution, saline, and CLA to 90 ml. Periods were of 5 d duration with a 7 d wash out. Milk was sampled at each milking and analyzed for fat, protein, and fatty acids. Blood samples were obtained on the last day of each period. Dry matter intake (22.4 +/- 2.4 kg/d), milk yield (28.5 +/- 3.3 kg/d), and protein percent (3.26 +/- 0.08%) of cows were not affected by treatment. However, milk fat percentage was reduced linearly with increasing doses of CLA. Milk fat percentage was 4.17, 3.53, 3.29, and 2.92% on d 5 for treatments 0, 2, 4, and 6 g/d CLA, respectively. Concentrations (4.2 mg/g of fat) of cis-9, trans-11 CLA in milk fat were not affected by treatment. However, an increase in the trans-10, cis-12 CLA content of milk fat was observed. Milk fat contained 0.00, 0.02, 0.06, and 0.10 mg of trans-10, cis-12 CLA per g of fat (SEM = 0.065) for treatments 0, 2, 4, and 6 g/d CLA, respectively. Plasma NEFA concentration increased linearly with the dose of the trans-10, cis-12 CLA. Intravenous infusion of the trans-10, cis-12 isomer of CLA depressed milk fat in a linear manner over the range of infusion studied and, therefore, is an alternative to abomasal infusion.

Effect of conjugated linoleic acid on meat quality, lipid metabolism, and sensory characteristics of dry-cured hams from heavy pigs

We investigated conjugated linoleic acid (CLA) supplementation administered to heavy pigs, assessing carcass characteristics, meat quality, and sensory characteristics of dry-cured (Parma) ham. Thirty-six pigs, averaging 97 kg BW, were assigned randomly to three feeding groups in which diets were supplemented with either 0, 0.25, or 0.5% (as-fed basis) of a CLA preparation containing 65% CLA isomers. All pigs were slaughtered at 172 kg BW. No (P > 0.05) differences were observed in dressing percentage, loin and ham weight, or pH and color of longissimus and semimembranosus muscle. Tenth-rib backfat thickness tended to be lower (P < 0.10) in carcasses from CLA-fed pigs. The oxidative stability of longissimus muscle was greater (P < 0.05) in pigs fed CLA than control, but only at the longer (300 min) oxidation time. Acetyl-CoA carboxylase activity in adipose tissue of CLA-fed pigs was less (P < 0.05) than that of pigs fed diets devoid of supplemental CLA. Composition of ham fat was markedly affected (P < 0.01) by dietary CLA, with higher saturated fatty acids, lower monounsaturated fatty acids, and higher CLA in the fat of CLA-fed pigs regardless of supplementation level. Although melting quality was improved (P < 0.05), most sensory characteristics and the chemical composition of dry-cured hams were not (P > 0.05) affected by incorporation of CLA. Results indicated that dietary CLA alters lipid metabolism, producing lower concentrations of monounsaturated fatty acids and increased concentrations of CLA isomers in the fat of heavy pigs. Moreover, supplementing diets with CLA produced only minimal improvements in Parma ham sensory traits and had no appreciable effects on fresh pork quality.

Conjugated linoleic acid isomers and mammary cancer prevention

There is increasing evidence that individual isomers of conjugated linoleic acid (CLA) may have unique biological or biochemical effects. A primary objective of this study was to determine whether there might be differences in the anticancer activity of 9,11-CLA and 10,12-CLA. This was achieved by evaluating the reduction in premalignant lesions and carcinomas in the mammary gland of rats that had been treated with a single dose of methylnitrosourea and given 0.5% of either highly purified CLA isomer in the diet. Our results showed that the anticancer efficacies of the two isomers were very similar. At 6 wk after carcinogen administration, the total number of premalignant lesions was reduced by 33-36%. At 24 wk, the total number of mammary carcinomas was reduced by 35-40%. The concentration of each CLA isomer and its respective metabolites was analyzed in the mammary fat pad. Tissue level of 10,12-CLA was much lower than that of 9,11-CLA. The pool of metabolites from each isomer was very similar between the two groups and represented only a small fraction of total conjugated diene fatty acids. Feeding of 9,11-CLA resulted in minimal changes in other unsaturated fatty acids. In contrast, feeding of 10,12-CLA produced a wider spectrum of perturbations. Small but significant increases in 16:1 and 16:2 were detected; these were accompanied by decreases in 20:2, 20:3, 20:4, 22:4, and 22:6. The above observation suggests that 10,12-CLA might be more potent than 9,11-CLA in interfering with elongation and desaturation of linoleic and linolenic acids. In summary, our study showed that, at the 0.5% dose level, the anticancer activity of 9,11-CLA and 10,12-CLA was very similar, even though accumulation of 10,12-CLA in the mammary tissue was considerably less than that of 9,11-CLA. These confounding changes of the other unsaturated fatty acids in contributing to the effect of 10,12-CLA need to be clarified.

Production of free conjugated linoleic acid by Lactobacillus acidophilus and Lactobacillus casei of human intestinal origin

A gas chromatographic procedure was used for analysis of conjugated linoleic acid (CLA) isomers cis-9, trans-11-octadecadienoic; trans-10, cis-12 octadecadienoic; and trans-9, trans-11-octadecadienoic (c9t11, t10c12, t9t11) produced by lactobacilli. Four different cultures, two strains each of Lactobacillus acidophilus and Lactobacillus casei were tested for their ability to produce CLA from free linoleic acid in MRS broth supplemented with linoleic acid. Different concentrations of linoleic acid (0, 0.05, 0.1, 0.2 and 0.5 mg/ml) were added to MRS broth, inoculated with the lactobacilli, and incubated at 37 degrees C. Viable counts and amounts of individual isomers of CLA (c9t11, t10c12, t9t11) were measured at 0, 24, 48, and 72 h. All the cultures were able to produce free CLA in media supplemented with linoleic acid. Maximum production of CLA (80.14 to 131.63 microg/ml) was observed at 24 h of incubation in broth containing 0.02% of free linoleic acid. No significant (P > 0.05) increases in total CLA levels were observed after 24 h of incubation. The ability of the cultures to produce CLA in skim milk supplemented with 0.02% free linoleic acid also was studied. In this medium, the total amounts of free CLA after 24 h of incubation ranged from 54.31 to 116.53 microg/ml. The use of lactic acid bacteria able to form free CLA in cultured dairy products may have potential health or nutritional benefits. Free CLA in the products likely would be more readily available for absorption from the digestive tract than if it were incorporated into the cells of the starter culture.

Protective action of CLA against oxidative inactivation of paraoxonase 1, an antioxidant enzyme

The effect of CLA on paraoxonase 1 (PON1), one of the antioxidant proteins associated with HDL, was investigated for its protective action against oxidative inactivation as well as its stabilization activity. When cis-9 (c9),trans-11 (t11)-CLA and t10,c12-CLA were examined for their protective activity against ascorbate/Cu(2+)-induced inactivation of PON1 in the presence of Ca2+, two CLA isomers exhibited a remarkable protection (Emax, 71-74%) in a concentration-dependent manner (50% effective concentration, 3-4 microM), characterized by a saturation pattern. Such a protective action was also reproduced with oleic acid, but not linoleic acid. Rather, linoleic acid antagonized the protective action of CLA isomers in a noncompetitive fashion. Additionally, the two CLA isomers also protected PON1 from oxidative inactivation by H2O2 or cumene hydroperoxide. The concentration-dependent protective action of CLA against various oxidative inactivation systems suggests that the protective action of CLA isomers may be mediated through their selective binding to a specific binding site in a PON1 molecule. Separately, the inactivation of PON1 by p-hydroxymercuribenzoate (PHMB), a modifier of the cysteine residue, was also prevented by CLA isomers, suggesting the possible existence of the cysteine residue in the binding site of CLA. The c9,t11-CLA isomer seems to be somewhat more effective than t10,c12-CLA in protecting against the inactivation of PON1 by either peroxides or PHMB, in contrast to the similar efficacy of these two CLA isomers in preventing ascorbate/Cu(2+)-induced inactivation of PON1. Separately, CLA isomers successfully stabilized PON1, but not linoleic acid. These data suggest that the two CLA isomers may play a beneficial role in protecting PON1 from oxidative inactivation as well as in its stabilization.

Effect of a mixture of conjugated linoleic acid isomers on growth performance and antibody production in broiler chicks

The effect of dietary conjugated linoleic acid (CLA) isomers mixture on antibody titres against sheep blood erythrocytes (SRBC) and immunoglobulin (Ig) G concentration in plasma was studied in broiler chickens. In experiment 1, male and female broiler chicks (11 d of age, Cobb strain) were fed a diet supplemented with 10 g CLA or 10 g safflower-seed oil/kg diet for 2 weeks. An SRBC suspension (5:100, v/v) in a phosphate buffer was intravenously injected at 18 d of age and a blood sample was taken from the wing vein at 25 d of age. Chicks fed the CLA-supplemented diet had enhanced first antibody titres in plasma to SRBC as compared with those fed the safflower-seed oil-supplemented diet, irrespective of sex differences. In experiment 2, male broiler chicks (8 d of age, Ross strain) were fed a basal diet or a diet containing 10 g CLA/kg diet for 3 weeks. CLA in the CLA diet partially replaced the soyabean oil in the basal diet. The SRBC suspension was intravenously injected at 15 and 25 d of age and a blood sample was obtained at 21 and 29 d of age. The first antibody titres against SRBC were higher in chicks fed the CLA diet than those in chicks fed the basal diet, but the second titres were not. Plasma IgG concentrations in chicks fed the CLA diet were higher than those in chicks fed the basal diet on both sampling days. The results showed that dietary CLA enhanced antibody production in broiler chickens.

trans-10,cis-12 CLA inhibits differentiation of 3T3-L1 adipocytes and decreases PPAR gamma expression

The trans-10,cis-12 isomer of conjugated linoleic acid (CLA) has been shown to reduce body fat gain in mice. However, the underlying molecular mechanism is not well characterized. Here we report evidence that trans-10,cis-12 (t10c12) CLA inhibits preadipocyte differentiation. Treating differentiating 3T3-L1 preadipocytes with t10c12 CLA and conjugated nonadecadienoic acid (CNA, a 19-carbon CLA cognate) resulted in decreased intracellular triglyceride accumulation and mRNA levels of the adipogenic gene fatty acid synthase and adipocyte lipid binding protein. T10c12 CLA and CNA also reduced protein levels of adipocyte transcription factors, peroxisome proliferator-activated receptor gamma and CCAAT/enhancer binding protein alpha. Similarly, CLA reduced body fat gain and significantly inhibited the expression of PPAR gamma and its downstream target lipoprotein lipase in mouse adipose tissue. These observations indicate that CLA decreases body fat gain in part by inhibiting the differentiation of preadipocytes.

Effects of cis-9, trans-11 and trans-10, cis-12 conjugated linoleic acid (CLA) isomers on immune function in healthy men

OBJECTIVES

To study the effects of two different mixtures of the main conjugated linoleic acid (CLA) isomers cis-9, trans-11 CLA and trans-10, cis-12 CLA on human immune function.

DESIGN

Double-blind, randomized, parallel, reference-controlled intervention study.

SUBJECTS AND INTERVENTION

Seventy-one healthy males aged 31-69 y received one of the following treatments: (1). mixture of 50% c9,t11 CLA and 50% t10,c12 CLA isomers (CLA 50:50); (2). mixture of 80% c9,t11 CLA and 20% t10,c12 CLA isomers (CLA 80:20); and (3). sunflower oil fatty acids (reference). The treatments were given as supplements in softgel capsules providing a total of 1.7 g (c9,t11+t10,c12) CLA fatty acids (50:50) or 1.6 g (c9,t11+t10,c12) CLA glycerides (80:20) per day in treatment groups for 12 weeks.

RESULTS

Almost twice as many subjects reached protective antibody levels to hepatitis B when consuming CLA 50:50 fatty acids (15/24, 62%) compared with subjects consuming the reference substance (7/21, 33%, P=0.075). In subjects consuming CLA 80:20 glycerides this was 8/22 (36%). Other aspects of immune function, ie DTH responses, NK cell activity, lymphocyte proliferation and production of TNF-alpha, IL1-beta, IL6, IFN-gamma, IL2, IL4, and PGE(2), were not affected.

CONCLUSION

This is the first study that suggests that CLA may beneficially affect the initiation of a specific response to a hepatitis B vaccination. This was seen in the CLA 50:50, but not in the CLA 80:20 group.

Modulation of body composition and immune cell functions by conjugated linoleic acid in humans and animal models: benefits vs. risks

We have reviewed the published literature regarding the effects of CLA on body composition and immune cell functions in humans and in animal models. Results from studies in mice, hamsters, rats, and pigs generally support the notion that CLA reduced depot fat in the normal or lean strains. However, in obese rats, it increased body fat or decreased it less than in the corresponding lean controls. These studies also indicate that t10,c12-CLA was the isomer that reduced adipose fat; however, it also increased the fat content of several other tissues and increased circulating insulin and the saturated FA content of adipose tissue and muscle. Four of the eight published human studies found small but significant reductions in body fat with CLA supplementation; however, the reductions were smaller than the prediction errors for the methods used. The other four human studies found no change in body fat with CLA supplementation. These studies also report that CLA supplementation increased the risk factors for diabetes and cardiovascular disease including increased blood glucose, insulin, insulin resistance, VLDL, C-reactive protein, lipid peroxidation, and decreased HDL. Most studies regarding the effects of CLA on immune cell functions have been conducted with a mixture of isomers, and the results have been variable. One study conducted in mice with the purified c9,t11-CLA and t10,c12-CLA isomers indicated that the two isomers have similar effects on immune cell functions. Some of the reasons for the discrepancies between the effects of CLA in published reports are discussed. Although significant benefit to humans from CLA supplementation is questionable, it may create several health risks in both humans and animals. On the basis of the published data, CLA supplementation of adult human diets to improve body composition or enhance immune functions cannot be recommended at this time.

Assessing the cost of mounting an immune response

The evolution of parasite resistance has often been assumed to be governed by antagonistic selection pressures. Defense against pathogens, by mounting an immune response, confers evident benefits but may also incur costs, so that the optimal level of defense is expected to depend on the balance between benefits and costs. Although the benefits of immune surveillance are well known, estimates of costs are still equivocal. Here we studied the behavioral and physiological modifications associated with exposure to a nonreplicating antigen (lipopolysaccharide [LPS] of Escherichia coli) in a passerine species, the house sparrow (Passer domesticus). We further investigated whether the behavioral and physiological changes provoked by LPS induced measurable repercussions on life-history traits, such as the breeding effort and reproductive success. Finally, we tested whether the trade-off between immune activation and breeding effort was modulated by the workload required to feed the brood. Exposure to LPS reduced activity and increased body mass loss of captive individuals; similarly, LPS injection induced a dramatic drop in feeding rate and reproductive success of breeding females. However, this reduction depended on brood size, suggesting that the strength of the trade-off between immune activation and reproduction was affected by the workload required to feed the brood. Overall, this study stresses the magnitude of costs associated with mounting immune responses and the ecological and evolutionary consequences for natural populations.

Immunoglobulin and cytokine production from spleen lymphocytes is modulated in C57BL/6J mice by dietary cis-9, trans-11 and trans-10, cis-12 conjugated linoleic acid

We evaluated the effect of cis-9, trans-11 (9c,11t) and trans-10, cis-12 (10t,12c) conjugated linoleic acid (CLA) on the immune system in C57BL/6J mice. Mice were fed experimental diets containing 0% CLA (controls), 1% 9c,11t-CLA, 1% 10t,12c-CLA or a 1:1 mixture (0.5% + 0.5%) of these two CLA isomers for 3 wk. Relative spleen weights of all CLA fed mice were greater than the controls. Spleen lymphocytes isolated from the mice fed 10t,12c-CLA produced more immunoglobulin (Ig)A and IgM but not IgG when stimulated with concanavalin A (ConA) compared with controls. IgA production from unstimulated spleen lymphocytes was greater in the 10t, 12c-CLA group than in controls. Conversely, 9c,11t-CLA did not affect the production of any of the Ig subclasses. Lymphocytes isolated from 9c,11t-CLA fed mice produced more tumor necrosis factor-alpha than the control group. The proportion of B cells in the spleen lymphocyte population was significantly lower in the 9c,11t-CLA group, and higher in the 10t,12c-CLA group than in the controls. Compared with the control group, the percentage of CD4(+) T cells was lower in the 10t,12c-CLA group, and the percentage of CD8(+) T cells was higher in the 9c,11t-CLA group. Furthermore, the percentage of CD8(+) T cells was higher in the 1:1 mixture group than in controls. The CD4(+)/CD8(+) ratio was lower in the 1:1 mixture group than in controls. These results suggest that 9c,11t and 10t,12c-CLA can stimulate different immunological effects and that the simultaneous intake of the two isomers can change the T cell population.

Dietary CLA decreased weight loss and extended survival following the onset of kidney failure in NZB/W F1 mice

In an earlier study, we showed that feeding CLA immediately after weaning prolonged survival of NZB/W F1 mice after onset of proteinuria. In the present study, the feeding of CLA was delayed until mice had developed proteinuria. Thirty NZB/W F1 mice were fed a regular rodent chow after weaning. Urine samples were collected to detect proteinuria. Once a mouse was proteinuria positive, it was then randomly assigned to a 0.5% CLA supplement semipurified diet or a control diet (supplement 0.5% corn oil). The next proteinuria positive mouse was then assigned to the opposite diet to which the first mouse was assigned. Mice fed the control diet lost 25% more body weight (13.0 g) than mice fed the CLA diet (9.7 g). Moreover, CLA-fed mice survived an average 1.7-fold longer (148 d) than mice fed the control diet (89 d) after the onset of proteinuria. This follow-up study confirmed that dietary CLA had a beneficial effect in the autoimmune NZB/W F1 mouse. In summary, the cachectic symptom of systemic lupus erythematosus was decreased by dietary CLA and survival days were increased over control group.

The impact of fortification with conjugated linoleic acid (CLA) on the quality of fluid milk

The effects of added conjugated linoleic acid (CLA) on the sensory, chemical, and physical characteristics of 2% total fat (wt/wt) fluid milk were studied. Milks with 2% (wt/wt) total fat (2% CLA, 1% CLA 1% milkfat, 2% milkfat) were made by the addition of cream or CLA triglyceride oil into skim milk followed by HTST pasteurization and homogenization. The effects of adding vitamin E (200 ppm) and rosemary extract (0.1% wt/wt based on fat content) were investigated to prevent lipid oxidation. HTST pasteurization resulted in a significant decrease of the cis-9/trans-11 isomer and other minor CLA isomers. The cis-9/trans-11 isomer concentration remained stable through 2 wk of refrigerated storage. A significant loss of both the cis-9/trans-11 and the cis-10/trans-12 isomers occurred after 3 wk of refrigerated storage. The loss was attributed to lipase activity from excessive microbial growth. No differences were found in hexanal or other common indicators of lipid oxidation between milks with or without added CLA (P > 0.05). Descriptive sensory analysis revealed that milks with 1 or 2% CLA exhibited low intensities of a "grassy/vegetable oil" flavor, not present in control milks. The antioxidant treatments were deemed to be ineffective, under the storage conditions of this study, and did not produce significant differences from the control samples (P > 0.05). CLA-Fortified milk had significantly lower L* and b* values compared with 2% milkfat milk. No significant differences existed in viscosity. Consumer acceptability scores (n = 100) were lower (P < 0.05) for CLA-fortified milks compared to control milks, but the addition of chocolate flavor increased acceptability (P < 0.05).

Dietary conjugated linoleic acid alters hepatic lipid content and fatty acid composition in broiler chickens

We examined the effect of dietary conjugated linoleic acid (CLA) on growth performance and liver composition in broiler chickens. Day-old male broiler chicks were assigned to receive a diet supplemented with corn oil (5%; n = 48) or CLA (5%; n = 48) for 21 d. Broilers fed CLA weighed less and grew at slower rates than broilers fed corn oil. Feed intake and feed conversion were higher for the corn-oil group than for the CLA dietary group. Hepatic lipid and triacylglycerol concentrations were significantly reduced by dietary CLA. The proportions of saturated fatty acids (SFA) in liver lipids increased, whereas those of monounsaturated fatty acids (MUFA) decreased with CLA supplementation. Although the total concentration of polyunsaturated fatty acids (PUFA) did not change with dietary treatment, the concentration of linoleic acid as a percentage of total methylated fatty acids decreased, and that of linolenic add increased in broilers fed CLA. The concentration of CLA isomers in liver lipids increased substantially with CLA feeding. The relative proportion of the c9,t11 CLA isomer in hepatic lipids was much higher than that of the t10,c12 or t9,t11 CLA isomers. These studies provide evidence that feeding CLA to broilers results in substantial reduction in liver fat accumulation and promotes CLA incorporation into hepatic lipid pools.

ISOMERS OF CONJUGATED LINOLEIC ACID MODULATE HUMAN PREADIPOCYTE DIFFERENTIATION

Conjugated linoleic acids (CLAs) reduce fat deposition in several mammalian species. Among the proposed mechanisms for this effect are reduced preadipocyte proliferation and differentiation. We measured proliferation and differentiation of cultured human preadipocytes treated with CLAs. Preadipocytes were differentiated with insulin, hydrocortisone, transferrin, and 10% fetal bovine serum, with isobutyl-methylxanthine included for the first 2 d. The differentiation medium contained 200 microM oleic acid (C18:1), 50 microM cis-9,trans-11-CLA (9,11-CLA), or 50 microM trans-10,cis-12-CLA (10,12-CLA); the negative control medium contained no added fatty acid, and the cells did not differentiate. Cell number increased three to four times during the 17 d of differentiation, but was 30-35% lower in the CLA-treated cells than in the negative control cells. Compared with the negative control cells, differentiation was increased in the cells treated with C18:1 (increased Oil Red O-stained material [OROSM], triacylglycerol, glycerol 3-phosphate dehydrogenase activity [GPDH], peroxisome proliferator-activated receptor-gamma [PPAR gamma] messenger ribonucleic acid [mRNA], and lipoprotein lipase [LPL] mRNA). In effect, the C18:1-treated cells act as a positive control to demonstrate the differentiation capacity of each cell lot. Both 9,11-CLA- and 10,12-CLA-treated cells had increased differentiation (increased OROSM, triacylglycerol, GPDH, PPAR gamma, and LPL) compared with the negative control cells. The data suggest that early in differentiation when de novo fatty acid (FA) synthesis is limited and competition for FAs by membrane and triacylglycerol synthetic pathways is great, human preadipocytes do not differentiate unless a PPAR gamma ligand is added. Either CLA isomer or C18:1 can provide such a ligand.

Dietary conjugated linoleic acid decreased cachexia, macrophage tumor necrosis factor-alpha production, and modifies splenocyte cytokines production

The effect of conjugated linoleic acid (CLA) on macrophage functions were studied in vitro, in vivo, and ex vivo. In RAW macrophage cell line, CLA (mixed isomers) was shown to inhibit lipopolysaccharide (LPS)-stimulated tumor necrosis factor-alpha (TNF-alpha) production. Two CLA isomers, c9,t11 and t10,c12, were tested on RAW cells and it was found that the c9,t11 was the isomer responsible for the inhibition of LPS-induced TNF-alpha production. BALB/c mice were used to determine the effect of dietary CLA on body weight wasting and feed intake after LPS injection. CLA was protective against LPS-induced body weight wasting and anorexia. Plasma TNF-alpha levels after LPS injection were lower in the CLA group compared with the corn oil-fed control group 2 hr post-LPS injection. In a separate experiment, 30 mice were fed a CLA-supplemented diet or a corn oil-supplemented diet for 6 weeks and peritoneal resident macrophages were obtained for measuring TNF-alpha and nitric oxide production after in vitro exposure to interferon-gamma (IFN-gamma) and/or LPS. TNF-alpha production was not found to be different in peritoneal macrophages from mice fed the dietary treatments, but less nitric oxide was produced in macrophages from CLA-fed mice upon stimulation when compared with macrophages from control-fed mice. Splenocytes were also collected from the mice fed the dietary treatments and stimulated to produce cytokines in culture. Supernatant was used to run cytokine enzyme-linked immunoabsorbant assays. Interleukin-4 (IL-4) was decreased in CLA-fed mice when splenocytes were stimulated with concanavalin A (Con A) for 44 hr; however, IL-2 and the IL-2-to-IL-4 ratio were elevated.

Effects of conjugated linoleic acid (CLA) on immune responses, body composition and stearoyl-CoA desaturase

Conjugated linoleic acid (CLA) has shown a wide range of biologically beneficial effects; reduction of incidence and severity of animal carcinogenesis, reduction of the adverse effects of immune stimulation, reduction of severity of atherosclerosis, growth promotion in young rats, and modulation of stearoyl-CoA desaturase (SCD). One of the most interesting aspects of CLA is its ability to reduce body fat while enhancing lean body mass which is associated with the trans-10,cis-12 isomer of CLA. The effects of CLA are unique characteristics that have not been observed with other polyunsaturated fatty acids. In this review, we will focus on the effects of CLA on immune responses, body compositional changes and stearoyl-CoA desaturase.

Effects of conjugated linoleic acid on anaphylaxis and allergic pruritus

The effects of conjugated linoleic acid (CLA) against anaphylaxis and allergic pruritus were investigated using a in vivo assay. Inhibitory effects of CLA were observed on the immediate (type 1) hypersensitivity reaction, with CLA significantly suppressing the decrease in blood pressure (BP) and blood flow (BF) induced by the hen egg-white lysozyme (HEL)-anaphylactic reaction in ddY mice. After oral administration, CLA showed antipruritic activity, with significant inhibition of scratching behavior induced by compound 48/80 (COM), a histamine-release agent. When painted onto the skin, CLA also inhibited COM, platelet-activating factor, and protease-induced scratching behavior, and COM-induced vasodilation of the skin. CLA offers promise as a drug for the treatment of allergic and inflammatory pruritus not only as an oral but also a topical agent. The present findings demonstrate that CLA can be effective for the prevention and treatment of allergic disease with severe pruritus.

Dietary conjugated linoleic acid in health: physiological effects and mechanisms of action

Conjugated linoleic acid (CLA) is a group of polyunsaturated fatty acids found in beef, lamb, and dairy products that exist as positional and stereo-isomers of octadecadienoate (18:2). Over the past two decades numerous health benefits have been attributed to CLA in experimental animal models including actions to reduce carcinogenesis, atherosclerosis, onset of diabetes, and body fat mass. The accumulation of CLA isomers and several elongated/desaturated and beta-oxidation metabolites have been found in tissues of animals fed diets with CLA. Molecular mechanisms of action appear to include modulation of eicosanoid formation as well as regulation of the expression of genes coding for enzymes known to modulate macronutrient metabolism. This review focuses on health benefits, metabolism, and potential mechanisms of action of CLA and postulates the implications regarding dietary CLA for human health.

Dietary conjugated linoleic acid reduces body fat mass and affects gene expression of proteins regulating energy metabolism in mice

ICR and C57BL/6J mice were fed experimental diets containing either a 2% fatty acid preparation rich in conjugated linoleic acid (CLA) or a preparation rich in linoleic acid and free of CLA for 21 days. CLA greatly decreased weights of white adipose tissue and interscapular brown adipose tissue in the two strains. CLA reduced mRNA levels of glucose transporter 4 (Glut 4) in white and brown adipose tissue of both strains. A CLA-dependent decrease in mRNA levels of peroxisome proliferator activated receptor (PPAR) gamma was seen in interscapular brown adipose tissue of both strains and in white adipose tissue of C57BL/6J but not ICR mice. Dietary CLA was found to cause a decrease in the mRNA levels of uncoupling protein (UCP) 1 in brown adipose tissue when the value was corrected for the expression of a house-keeping gene (beta-actin) in the two strains. Uncorrected values were, however, indistinguishable between the animals fed the CLA diet and CLA-free diet. UCP 3 expression in brown adipose tissue was much lower in mice fed the CLA diet than in those fed the control diet in both strains. In contrast, CLA greatly up-regulated the gene expression of UCP 2 in brown adipose tissue. Dietary CLA also increased UCP 2 mRNA level in skeletal muscle. It is apparent that dietary CLA decreases white and brown adipose tissue mass, accompanying changes in the gene expression of proteins regulating energy metabolism in white and brown adipose tissues, and skeletal muscle of mice.

Clinical trial results support a preference for using CLA preparations enriched with two isomers rather than four isomers in human studies

CLA mixtures are now commercially available. They differ from each other with respect to their content of CLA isomers and their degree of purification. As a group of natural FA, CLA have been widely assumed to be safe. However, the suspected presence of both impurities and particular isomers might induce undesirable side effects. Despite this potential health risk, only a few CLA preparations have been tested under rigorous conditions for clinical efficacy and safety. Based on the limited results available, it is possible to suggest that preparations enriched in c9,t11 and t10,c12 isomers are preferable for human consumption compared to preparations containing four isomers, in terms both of safety and efficacy.

Production of conjugated linoleic acid by intestinal bacteria in dogs and cats

Production of conjugated linoleic acid (CLA) by the intestinal bacteria of dogs and cats was demonstrated by incubating their feces with linoleic acid (LA). CLA accumulated once, and then decreased with time. The numbers of LA-hydrogenating bacteria in the intestines appeared to decrease greatly with the ages of dogs and cats. As a major product of LA biohydrogenation, trans-vaccenic acid (t-VA) was identified. Most CLA and t-VA were readily solubilized by shaking the incubation mixture with bovine serum albumin, which strongly supports the presumption that CLA and t-VA are mostly formed on the outer surface of cell membrane, or excreted to the outer cell surface. This result suggests that CLA and t-VA can readily be absorbed through the large intestines. Triacylglycerol and phospholipid were shown to be hydrolyzed to free fatty acids by fecal bacteria, which is critical for biohydrogenation to occur, because esterified LA is not hydrogenated. However, since the ability of intestinal bacteria to produce CLA is probably low, it is desirable to augment CLA production.