t10c12-CLA maintains higher bone mineral density during aging by modulating osteoclastogenesis and bone marrow adiposity

Conjugated linoleic acid (CLA) has been shown to positively influence calcium and bone metabolism. Earlier, we showed that CLA (equal mixture of c9t11-CLA and t10c12-CLA) could protect age-associated bone loss by modulating inflammatory markers and osteoclastogenesis. Since, c9t11-CLA and t10c12-CLA isomers differentially regulate functional parameters and gene expression in different cell types, we examined the efficacy of individual CLA isomers against age-associated bone loss using 12 months old C57BL/6 female mice fed for 6 months with 10% corn oil (CO), 9.5% CO + 0.5% c9t11-CLA, 9.5% CO + 0.5% t10c12-CLA or 9.5% CO + 0.25% c9t11-CLA + 0.25% t10c12-CLA. Mice fed a t10c12-CLA diet maintained a significantly higher bone mineral density (BMD) in femoral, tibial and lumbar regions than those fed CO and c9t11-CLA diets as measured by dual-energy-X-ray absorptiometry (DXA). The increased BMD was accompanied by a decreased production of osteoclastogenic factors, that is, RANKL, TRAP5b, TNF-alpha and IL-6 in serum. Moreover, a significant reduction of high fat diet-induced bone marrow adiposity was observed in t10c12-CLA fed mice as compared to that of CO and c9t11-CLA fed mice, as measured by Oil-Red-O staining of bone marrow sections. In addition, a significant reduction of osteoclast differentiation and bone resorbing pit formation was observed in t10c12-CLA treated RAW 264.7 cell culture stimulated with RANKL as compared to that of c9t11-CLA and linoleic acid treated cultures. In conclusion, these findings suggest that t10c12-CLA is the most potent CLA isomer and it exerts its anti-osteoporotic effect by modulating osteoclastogenesis and bone marrow adiposity.     

Fatty acid composition and conjugated linoleic acid content of different tissues in rats fed individual conjugated linoleic acid isomers given as triacylglycerols small star,filled

HEAT TREATMENT OF VEGETABLE OILS GAVE RISE TO FOUR MAIN CONJUGATED LINOLEIC ACID (CLA) ISOMERS : the 9c,11t, 9t,11t, 10t,12c and 10t,12t. The diet of male Wistar rats was supplemented with 150 mg/day either 9c,11t-, 9t,11t-, 10t,12c- or 10t,12t CLA isomers for 6 days and their effects on lipid composition were investigated in liver, heart, skeletal muscle Gastrocnemius, kidneys, brain and adipose tissue. The incorporation of all isomers was low (< 1.4%) and the level was as follows : adipose tissue > Gastrocnemius > liver, kidneys > brain. The main changes in the overall lipid composition were observed in skeletal muscle (Gastrocnemius) and in heart and were associated with feeding the 10t,12c and 10t,12t isomers. The diet enriched in 10t,12t CLA decreased the total long chain polyunsaturated fatty acid proportion in Gastrocnemius (from 18.4% to 14.4%) and increased that of 20:4 n-6 in heart (from 16.9 to 19.3%). The diet enriched in 10t,12c CLA decreased the monounsaturated fatty acid proportion in Gastrocnemius (from 32.0 to 26.1%) and produced an effect similar to the 10t,12t in heart. By contrast, the 9c,11t and 9t,11t isomers did not affect fatty acid composition in all tissues and organs. We concluded that ingestion of 10t,12c and 10t,12t CLA present in oils and in CLA mixtures could change muscle lipid composition.     

Dietary conjugated linoleic acid in the cis-9, trans-11 isoform reduces parathyroid hormone in male, but not female, rats

Previously, a mixture of conjugated linoleic acid (CLA) isoforms reduced parathyroid hormone (PTH) in male rats over 8 weeks. The objective herein was to determine which isoform caused the reduction in PTH; whether the effect was sex specific; and whether CLA-induced reductions in PTH were sustained. Male and female weanling rats (n=48) were randomized to a control diet or one made with 0.5% of the diet as cis-9, trans-11 (c9,t11) CLA, 0.5% of the diet as trans-10, cis-12 (t10,c12) CLA or these CLA in a mixture. Measurements made after 4, 8 and 16 weeks were body weight, bioactive PTH, ionized Ca, whole-body and regional bone mineral density (BMD) using dual-energy X-ray absorptiometry. With the use of a factorial design, a sexxc9,t11 CLA interaction was observed that reduced PTH (139.5+/-63.9 vs. 95.8+/-42.4 pg/ml, P=.02) in male rats only. No other effects of c9,t11 CLA were observed. Regarding t10,c12 CLA, no interaction effects were observed, but a main effect was observed to reduce lumbar spine BMD (0.265+/-0.044 vs. 0.255+/-0.044 g/cm(2), P<.01) along with reduced retention of Ca and P at Week 4. No other dietary effects were observed. In summary, the c9,t11 CLA isoform is responsible for reduced PTH and this effect is sex specific; this was true whether fed as a pure isomer or mixed with an equal amount of t10,c12 CLA. Whether such reductions in PTH might be observed in females lacking sex hormones such as ovariectomized rats and also in humans is required to expand health implications of dietary CLA.     

Inter-organ proteomic analysis reveals insights into the molecular mechanisms underlying the anti-diabetic effects of cis-9, trans-11-conjugated linoleic acid in ob/ob mice

cis‐9, trans‐11‐Conjugated linoleic acid (c9 t11 CLA) exerts anti‐diabetic effects by improving systemic insulin sensitivity and inflammation. Levels of CLA in beef can be increased by feeding cattle on pasture. This study aimed to explore the efficacy of a CLA‐rich diet (0.6% w/w c9 t11 CLA), presented as beef enriched with CLA or beef supplemented with synthetic CLA (c9 t11 CLA), for 28 days on molecular biomarkers of the metabolic syndrome, and adipose, hepatic, and skeletal muscle proteome in male ob/ob mice. Despite equal weight gain, CLA‐fed mice had lower plasma glucose, insulin, non‐esterified fatty acid, triacylglycerol and interleukin‐6, and higher adiponectin concentrations than controls. c9 t11 CLA induced differential regulation of redox status across all tissues, and decreased hepatic and muscle endoplasmic reticulum stress. CLA also modulated mechanistic links between the actin cytoskeleton, insulin signalling, glucose transport and inflammation in the adipose tissue. In the liver and muscle, c9 t11 CLA improved metabolic flexibility through co‐ordination between carbohydrate and energy metabolism. c9 t11 CLA may ameliorate systemic insulin sensitivity in obesity‐induced diabetes by altering cellular stress and redox status, and modulating nutrient handling in key insulin‐sensitive tissues through complex biochemical interplay among representative proteomic signatures.     

Differential incorporation of dietary conjugated linolenic and linoleic acids into milk lipids and liver phospholipids in lactating and suckling rats

Interest in health benefits of conjugated fatty acids is growing. The present study compared the incorporation pattern of dietary conjugated linolenic acids (CLnA) into milk with that of conjugated linoleic acids (CLA). Lactating Sprague-Dawley rats (Day 1) were divided into five groups fed the control diet (n=4) or one of four experimental diets supplemented with 1–2% CLA or CLnA mixture (n=8 each). Supplementation of 1% and 2% CLA led to enrichment of 4.17% and 8.57% CLA, respectively, while supplementation of 1% and 2% CLnA resulted in enrichment of only 0.98% and 1.71% CLnA in the milk lipids, demonstrating the transfer of CLnA from maternal diet to milk was discriminated. When the lactating rats were given a diet containing a CLnA mixture of 9t,11t,13t-, 9c,11t,13t- and 9c,11t,13c-CLnA isomers, two CLA isomers, namely, 9t,11t (0.59–0.90%) and 9c,11t (1.21–1.96%), were found in the milk, suggesting that three CLnA isomers were Δ-13 saturated. Dietary CLnA at 1–2% had no effect on liver phospholipid (PL) fatty acid composition of both maternal and suckling rats, whereas dietary CLA increased docosahexaenoic acid (4c,7c,10c,13c,16c,19c-22:6) and palmitic acid (16:0) proportionally in the PL of maternal rats, but it suppressed 16:0 in the PL of suckling rats. It is concluded that maternal rats incorporate CLnA isomers into milk differently from that of CLA isomers. Most interesting is that maternal rats can metabolically convert CLnA to CLA.     

Effects of Two Conjugated Linoleic Acid Isomers on Body Fat Mass in Overweight Humans

Objective: To examine the effects of two different conjugated linoleic acid (CLA) isomers at two different intakes on body composition in overweight humans. Research Methods and Procedures: Eighty‐one middle‐aged, overweight, healthy men and women participated in this bicentric, placebo‐controlled, double‐blind, randomized study. For 6 weeks (run‐in period), all subjects consumed daily a drinkable dairy product containing 3 g of high oleic acid sunflower oil. Volunteers were then randomized over five groups receiving daily either 3 g of high oleic acid sunflower oil, 1.5 g of cis‐9, trans‐11 (c9t11) CLA, 3 g of c9t11 CLA, 1.5 g of trans‐10, cis‐12 (t10c12) CLA, or 3 g of t10c12 CLA administrated as triacylglycerol in a drinkable dairy product for 18 weeks. Percentage body fat mass and fat and lean body mass were assessed at the end of the run‐in and experimental periods by DXA. Dietary intake was also recorded. Results: Body fat mass changes averaged 0.1 ± 0.9 kg (mean ± SD) in the placebo group and ?0.3 ± 1.4, ?0.8 ± 2.1, 0.0 ± 2.3, and ?0.9 ± 1.7 kg in the 1.5‐g c9t11, 3‐g c9t11, 1.5‐g t10c12, and 3‐g t10c12 groups, respectively. Changes among the groups were not significantly different (p = 0.444). Also, lean body mass and dietary intake were not significantly different among the treatments. Discussion: A daily consumption of a drinkable dairy product containing up to 3 g of CLA isomers for 18 weeks had no statistically significant effect on body composition in overweight, middle‐aged men and women.     

The effect of conjugated linoleic acid on the viability and metabolism of human osteoblast-like cells

Studies in experimental animals and murine osteoblast cells in culture have produced conflicting findings on the effect of conjugated linoleic acid (CLA) on bone formation. The present study investigated the influence of CLA on viability and metabolism of two human osteoblast-like cell lines (SaOS2 and MG63). Both cell lines were exposed to increasing concentrations (0-50 microM) of CLA either as pure cis (c) 9: trans (t) 11 and t10:c12 CLA isomers or a blend of isomers, or linoleic acid (C18:2). Cell cytotoxicity and degree of DNA fragmentation were unaffected by any fatty acid treatment. PGE2 biosynthesis by both cell lines was variably reduced by CLA isomer blend and t10:c12 CLA, but not c9:t11 CLA. Alkaline phosphatase activity was variably increased by all CLA treatments. These results suggest a lack of cytotoxic effect of CLA on human osteoblast-like cells and tentatively suggest a possible beneficial effect on bone formation in humans.     

Effect of diets supplemented with different conjugated linoleic acid (CLA) isomers on protein expression in C57/BL6 mice

Background

The individual genetic variations, as a response to diet, have recently caught the attention of several researchers. In addition, there is also a trend to assume food containing beneficial substances, or to supplement food with specific compounds. Among these, there is the conjugated linoleic acid (CLA), which has been demonstrated to reduce fat mass and to increase lean mass, even though its mechanism of action is still not known. We investigated the effect of CLA isomers (CLA c9,t11 and CLA t10,c12) on the proteomic profile of liver, adipose tissue, and muscle of mouse, with the aim of verifying the presence of a modification in fat and lean mass, and to explore the mechanism of action.

Methods

C57/BL6 mice were fed for 2 months with different diets: (1) standard chow, (2) CLA c9,t11 diet, (3) CLA t10,c11 diet, (4) CLA isomers mixture diet, and (5) linoleic acid diet. The proteomic profile of liver, white adipose tissue, and muscle was investigated. Statistical significance of the spots with an intensity higher than twofold in expression compared to the control was tested using student’s t test (two-tail).

Results

We found that both isomers modulate the proteomic profiles of liver, adipose tissue, and muscle by different mechanisms of action. Liver steatosis is mostly due to the isomer CLA t10,c12, since it alters the expression of lipogenetic proteins; it acts also reducing the adipose tissue and increasing fatty acid oxidation in muscle. Conversely, CLA c9,t11 has no relevant effects on liver and adipose tissue, but acts mostly on muscle, where it enhances muscular cell differentiation.

Conclusions

Administration of CLA in humans has to be carefully personalized, since even considering the presence of a species-specific effect, adverse effects might occur on long-term supplementation. Here we demonstrated that, in mouse, CLA is effective in reducing fat mass, but it also induces liver steatosis. The increase of lean mass is linked to an induction of cell proliferation, which, on long-term supplementation, might also lead to adverse effects.

     

Distribution of conjugated linoleic acid and metabolites in different lipid fractions in the rat liver.

Conjugated linoleic acid (CLA) is known to provide certain health benefits in experimental animal models. The major CLA isomer in food is c 9,t11-CLA. A primary objective of this study was to investigate the uptake of c 9,t11-CLA and its downstream metabolites into various lipid fractions in the liver of rats fed either a high or low CLA diet (containing 0.1 or 0.8 g CLA/100 g diet, respectively). As expected, the levels of all conjugated diene (CD) fatty acids (CD 18:2 + CD 18:3 + CD 20:3 + CD 20:4) were elevated about 8-fold in the high CLA diet group. However, there was no change in the distribution of CLA and CLA metabolites into various lipid fractions due to CLA intake. Unlike linoleic acid or gamma-linolenic acid, which were distributed mainly in phospholipids, CD 18:2, CD 18:3, and CD 20:3 were incorporated primarily in neutral lipid. Furthermore, the incorporation of all nonconjugated unsaturated fatty acids was not perturbed by CLA. Regardless of the level of CLA in the diet, CD 20:4 was predominantly enriched in phosphatidylserine and phosphatidylinositol. In contrast, arachidonic acid was primarily enriched in phosphatidylcholine and less so in phosphatidylethanolamine. The above findings may have potential implication regarding the role of CLA in modulating eicosanoid metabolism.     

Dietary conjugated linoleic acid does not adversely affect bone mass in obese fa/fa or lean Zucker rats

Conjugated linoleic acid (CLA) elevates body ash in healthy animals. The objective of the present study was to determine if single or mixed CLA isomers improve bone mass in an obese and hyperinsulinemic state. Male (n = 120) lean and obese fa/fa Zucker rats (age, 6 weeks) were randomized to 8 weeks on a control diet or to 0.4% (w/w) cis-9, trans-11 CLA (Group 1); 0.4% (w/w) trans-10, cis-12 CLA (Group 2); 0.4% (w/w) cis-9, trans-11 CLA and 0.4% (w/w) trans-10, cis-12 CLA (Group 3); 0.4% (w/w) cis-9, trans-11 CLA, 0.4% (w/w) trans-10, cis-12 CLA, and traces of other CLA isomers (Group 4); and 0.4% (w/w) cis-9, trans-11 CLA, 0.4% (w/w) trans-10, cis-12 CLA, and 0.3% (w/w) other CLA isomers (Group 5). Bone area (BA), bone mineral content (BMC), and bone mineral density (BMD) of the whole body, spine, and femur were measured at baseline (6 weeks) and at 14 weeks of age. Effects of genotype, diet, and genotype x diet interactions were assessed using factorial analysis of variance. At 6 and 14 weeks, whole-body BA and BMC were lower in lean rats compared with fa/fa rats. Similarly, at 14 weeks, fa/fa rats had a higher spine and femur BMD despite a lower femur weight. The fa/fa rats in Groups 4 and 5 had higher adjusted whole-body BMC compared with Group 3, but not with Group 1, Group 2, or the control. In lean rats, Group 3 had a greater adjusted whole-body BMC than Groups 1 and 2, but not Group 4, Group 5, or the control. Thus, commercially available CLA mixtures and single CLA isomers do not affect bone mass in a hyperinsulinemic, obese state.     

Modulation of proliferation and differentiation of C2C12 skeletal muscle cells by fatty acids

AimsThis study was performed to elucidate whether mitogen-activated protein kinases (MAPKs) are involved in the modulation of the proliferation and differentiation of skeletal muscle cells by fatty acids.Main methodsC2C12 myoblasts were cultured in differentiation medium containing 2% horse serum for 3 days, and treated with each fatty acid. Phosphorylation levels of MAPKs were examined by immunoblot analysis.Key findingsThe mono-unsaturated fatty acids (MUFAs), oleic acid (OA) and n?6 polyunsaturated fatty acids (n?6 PUFAs), linoleic acid (LA), γ-linoleic acid (GLA), and arachidonic acid (AA) increased the proliferation of C2C12 cells. On the other hand, n?3 polyunsaturated fatty acids (n?3 PUFAs) and saturated fatty acids (SFs) did not affect the proliferation of C2C12 cells. In addition, the treatment of cis-9, trans-11 conjugated linoleic acid (c9,t11 CLA) showed an increased cell proliferation. However, trans-10, cis-12 conjugated linoleic acid (t10,c12 CLA) significantly inhibited cell proliferation. Treatment of C2C12 cells with LA, OA, and c9,t11 CLA increased phosphorylation levels of ERK1/2 and JNK during proliferation. During cell differentiation, OA, LA, and c9,t11 CLA stimulated differentiation of C2C12 cells, whereas t10,c12 CLA inhibited differentiation. We also found that OA, LA, and c9, t11 CLA increased phosphorylation level of ERK1/2, but not JNK during differentiation.SignificanceThese results suggest that fatty acids are able to modulate the proliferation and differentiation of skeletal muscle and MAPKs may be involved in the modulation of the proliferation and differentiation of skeletal muscle cells by fatty acids.     

Differential effects of conjugated linoleic acid isomers on macrophage glycerophospholipid metabolism

Conjugated linoleic acids (CLA) are dietary fatty acids. Whereas cis-9,trans-11-(c9,t11)-CLA can be found in meat and dairy products, trans-9,trans-11-(t9,t11)-CLA is a constituent of vegetable oils. Previous studies showed that these two isomers activate different nuclear receptors and, thus, expression of genes related to lipid metabolism. Here we show that these CLA isomers are differentially elongated and desaturated in primary monocyte-derived macrophages isolated from healthy volunteers by using gas chromatography-mass spectrometry (GC-MS). We further demonstrate that c9,t11-CLA incorporates in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) species and activates de novo glycerophospholipid synthesis by quantitative electrospray ionization-tandem mass spectrometry (ESI-MS/MS). c9,t11-CLA leads to strong shifts of the species profiles to PC 18:2/18:2 and PE 18:2/18:2, which are due to de novo synthesis and fatty acid remodeling. In contrast, t9,t11-CLA is preferentially bound to neutral lipids, including triglycerides and cholesterol esters. Taken together our results show that c9,t11-CLA and t9,t11-CLA have differential effects on PC and PE metabolism. Moreover, these data demonstrate that the structure of fatty acids not only determines their incorporation into lipid classes but also modulates the kinetics of lipid metabolism, particularly PC synthesis.     

cis-9,trans-11 conjugated linoleic acid stimulates expression of angiopoietin like-4 in the placental extravillous trophoblast cells

A number of studies have been carried out to examine the biological function of conjugated linoleic acid (CLA) and its potential health benefits. However, not much is known about how CLA isomers mediate their effect on angiogenesis and vascularization during early placentation. In this paper we demonstrate that cis-9,trans-11(c9,t11)-CLA stimulated the expression of angiopoietin like-4 (ANGPTL4) mRNA and protein accompanied by tube formation in first trimester placental trophoblast cells, HTR8/SVneo whereas the other CLA isomer, trans-10,cis-12 (t10,c12)-CLA had no such effects. c9,t11-CLA however did not stimulate expression of the most potent angiogenic factor, vascular endothelial growth factor (VEGF) in these cells. Silencing ANGPTL4 in these cells significantly reduced the stimulatory effect of c9,t11-CLA on tube formation, indicating the involvement of ANGPTL4. In addition, c9,t11-CLA increased the mRNA expression of several pro-angiogenic factors such as fatty acid binding protein-4 (FABP4), cyclooxygenase-2 (COX-2) and adipose differentiation-related protein (ADRP) in HTR8/SVneo cells. c9,t11-CLA also induced the uptake of docosahexaenoic acid, 22:6n − 3 (DHA), a stimulator of tube formation in these cells. Triacsin C, an acylCoA synthetase inhibitor, attenuated c9,t11-CLA induced DHA uptake, tube formation and cellular proliferation in HTR8/SVneo cells.     

Abnormal immune responses in fa/fa Zucker rats and effects of feeding conjugated linoleic acid

Objective: The objective of this study was to characterize immune function in the fa/fa Zucker rat, and to determine the effects of feeding conjugated linoleic acid (CLA) isomers on immune function. Methods and Procedures: Lean and fa/fa Zucker rats were fed for 8 weeks nutritionally complete diets with different CLA isomers (%wt/wt): control (0%), c9t11 (0.4%), t10c12 (0.4%), or MIX (0.4% c9t11 + 0.4% t10c12). Isolated splenocytes were used to determine phospholipid (PL) fatty acid composition and cell phenotypes, or stimulated with mitogen to determine their ability to produce cytokines, immunoglobulins (Ig), and nitric oxide (NO). Results: Splenocyte PL of fa/fa rats had a higher proportion of total monounsaturated fatty acids and n ?3 polyunsaturated fatty acids (PUFA), and lower n ?6 PUFA and n ?6‐to‐n ?3 PUFA ratio (P < 0.05). Feeding CLA increased the content of CLA isomers into PL, but there were lower proportions of each CLA isomer in fa/fa rats. Splenocytes of fa/fa rats produced more amounts of IgA, IgG, and IgM, NO, and interleukin‐1β (IL‐1β), IL‐6, and tumor necrosis factor‐α (TNF‐α) (P < 0.05). Obese rats fed the t10c12 diet produced less TNF‐α and IL‐1β (lippopolysaccharide (LPS), P < 0.05). Splenocytes of fa/fa rats produced less concanavalin A (ConA)‐stimulated IL‐2 (P < 0.0001) than lean rats, except fa/fa rats fed the c9t11 diet (P < 0.05). Discussion: The c9t11 and t10c12 CLA isomers were incorporated into the membrane PL of the fa/fa Zucker rat, but to a lesser extent than lean rats. Splenocytes of obese rats responded in a proinflammatory manner and had reduced T‐cell function and feeding the t10c12 and c9t11 CLA isomers may improve some of these abnormalities by distinct methods.     

Effect of conjugated linoleic acid isomers on lipoproteins and atherosclerosis in the Syrian Golden hamster

Conjugated linoleic acid (CLA) is a group of positional and geometric isomers of linoleic acid (LA, C18:2 cis-9, cis-12) that are reported to have important biological activities, including protection against atherosclerosis. In this study, the potential role of the individual cis-9, trans-11 and trans-10, cis-12 isomers of CLA in atherogenesis were compared with LA in the Syrian Golden hamster. Supplementation of a high-fat, high-cholesterol diet (HFHC) with 1% (w/w) cis-9, trans-11 CLA or trans-10, cis-12 CLA did not significantly affect plasma cholesterol levels compared to supplementation with 1% (w/w) LA. Very low density lipoprotein cholesterol (VLDL-C) was lower and plasma triglycerides (TG) were higher in diets where C18:2 fatty acid was added to the HFHC diet, but neither the cis-9, trans-11 CLA group nor trans-10, cis-12 CLA group was significantly different from the LA control group. CLA supplementation did not significantly affect low density lipoprotein cholesterol (LDL-C). Trans-10, cis-12 CLA increased high density lipoprotein cholesterol (HDL-C) levels compared to LA or cis-9, trans-11 CLA (P<0.02), and although the ratio of non-HDL-C:HDL-C in the cis-9, trans-11 CLA group (1.11+/-0.54) and the trans-10, cis-12 CLA group (1.11+/-0.21) was lower than the LA group (1.29+/-0.45), the reduction did not reach statistical significance. Atherosclerosis was assessed in the ascending aorta by measuring the number of aortic cross-sections containing Oil Red O-stained intimal lesions. Compared to the LA group (60+/-11%), both the cis-9, trans-11 CLA group (38+/-8%) and the trans-10, cis-12 CLA group (28+/-7%) had fewer sections displaying a fatty streak lesion, although the differences did not reach statistical significance. These results suggest that individual CLA isomers may reduce atherosclerotic lesion development in the hamster, but when compared to LA, the apparent atheroprotective effects do not correlate with beneficial changes in lipoprotein profile.     

Conversion of t11t13 CLA into c9t11 CLA in Caco-2 cells and inhibition by sterculic oil

Background

Conjugated linoleic acids (CLA), and principally c9t11 CLA, are suspected to have numerous preventive properties regarding non-infectious pathologies such as inflammatory diseases, atherosclerosis and several types of cancer. C9t11 CLA is produced in the rumen during biohydrogenation of linoleic acid, but can also be synthesized in mammalian tissues from trans-vaccenic acid (C18:1 t11) through the action of delta-9 desaturase (D9D). For several years, it is also known that c9t11 CLA can be synthesized from conjugated linolenic acids (CLnA), i.e. c9t11c13 CLnA and c9t11t13 CLnA. This study aimed at investigating to which extent and by which route c9t11 CLA can be produced from another isomer of CLA, the t11t13 CLA that is structurally very similar to c9t11t13 CLnA, in Caco-2 cells.

Methodology/Principal Findings

Caco-2 cells were incubated for 24 h with 20 µmol/l of t11t13 CLA in the absence or presence of sterculic oil used as an inhibitor of D9D. Caco-2 cells were able to convert t11t13 CLA into c9t11 CLA, and c9t11t13 CLnA was formed as an intermediate compound. In the presence of sterculic oil, the production of this intermediate was decreased by 46% and the formation of c9t11 CLA was decreased by 26%. No other metabolite was detected.

Conclusions/Significance

These results not only highlight the conversion of t11t13 CLA into c9t11 CLA but demonstrate also that this conversion involves first a desaturation step catalysed by D9D to produce c9t11t13 CLnA and then the action of another enzyme reducing the double bond on the Δ13 position.     

The effects of t10,c12 CLA isomer compared with c9,t11 CLA isomer on lipid metabolism and body composition in hamsters

The objective of the present study was to examine the effects of two different isomers of conjugated linoleic acid (CLA), c9,t11 CLA and t10,c12 CLA, compared with linoleic acid (LA) used as control, on body composition, lipoprotein profile, hepatic lipids and fecal fat content in hamsters. Animals were assigned to the three diet groups (n=15) during 28 days. The diet was composed of 2% of the experimental fat, and throughout the experimental protocol, the hamsters experienced similar food intake. No significant differences were noted in body weight gain among the three diet groups. However, the t10,c12 CLA-fed animals showed higher low-density lipoprotein cholesterol (LDL-C) concentrations (0.9+/-0.1 mmol/L) than those who ingested either LA (0.6+/-0.1 mmol/L) or c9,t11 CLA isomer (0.7+/-0.1 mmol/L), although the t10,c12 CLA consumption decreased hepatic cholesterol and triglycerides and increased fecal fat content compared with the other two groups. Under the present experimental conditions, the dietary c9,t11 CLA isomer showed no positive beneficial effect on plasma lipids. Furthermore, the t10,c12 CLA isomer induced undesirable higher LDL-C, although it reduced hepatic lipids and fat digestibility in hamsters.     

Influence of conjugated linoleic acid isomers on the metastasis of colon cancer cells in vitro and in vivo

This study investigated the isomer-specific effects of cis-9,trans-11 (c9,t11) and trans-10,cis-12 (t10,c12) conjugated linoleic acid (CLA) on the metastasis of colon cancer cells in vitro and in vivo. Cell migration was examined by a Boyden chamber assay in SW480 cells. MMP-9 activity was monitored by gelatin zymography, and MMP-9 protein and mRNA levels were determined by Western blot and RT-PCR analysis, respectively, in SW480 cells. For the experimental metastasis, BALB/c mice were injected intravenously with CT-26 cells in the tail vein. Mice were fed a diet containing either no CLA or 0.1% c9,t11 or t10,c12 CLA for 4 weeks. In experimental metastasis, the numbers of pulmonary nodules were significantly lower in mice fed CLA isomers than in mice fed a control diet (P<.05). Results from the Boyden chamber assay revealed that c9,t11 CLA significantly inhibited cell migration (P<.05), whereas t10,c12 CLA had no effect on cell migration. The activity of MMP-9 was significantly inhibited by c9,t11 CLA (P<.05) but not by t10,c12 CLA. However, neither MMP-9 protein nor mRNA levels were altered by either of these CLA isomers. We have demonstrated that diets containing 0.1% c9,t11 and t10,c12 CLA were equally effective in inhibiting colon cancer cell metastasis in vivo. However, in vitro, only c9,t11 but not t10,c12 inhibited colon cancer cell migration and MMP-9 activity.     

The effect of conjugated linoleic acid on calcium absorption and bone metabolism and composition in adult ovariectomised rats

The effect of conjugated linoleic acid (CLA) on postmenopausal bone metabolism has not been investigated. Therefore, forty-three adult ovariectomised (OVX) rats (8-9 rats per group) were fed either a control diet containing 40 g/kg soyabean oil (SBO diet) or the SBO diet with 0 (control OVX), 2.5, 5 or 10 g/kg of CLA (replacing soybean oil) for 9 weeks. A group of sham-operated (SH) rats were fed the SBO diet. OVX rats had significantly (P<0.05) lower femoral bone mineral density and macromineral concentration, and intestinal Ca absorption compared to SH rats. CLA supplementation had no effect on these parameters. Ex vivo PGE(2) biosynthesis by bone and urinary Pyr and Dpyr (markers of bone resorption) were significantly higher (P<0.001) in control OVX rats compared with SH rats, and were significantly (P<0.001) lowered by CLA supplementation with 5 and 10, but not 2.5 g/kg diet in OVX rats. In conclusion, CLA supplementation appeared to reduce the rate of bone resorption in adult OVX rats.