Trans-10, cis-12 conjugated linoleic acid decreases de novo lipid synthesis in human adipocytes

Improving and Streamlining Gene Editing in Yarrowia lipolytica via Integration of Engineered Cas9 Protein

The oleaginous yeast Yarrowia lipolytica is a prominent subject of biorefinery research due to its exceptional performance in oil production, exogenous protein secretion, and utilization of various inexpensive carbon sources. Many CRISPR/Cas9 genome-editing systems have been developed for Y. lipolytica to meet the high demand for metabolic engineering studies. However, these systems often necessitate an additional outgrowth step to achieve high gene editing efficiency. In this study, we introduced the eSpCas9 protein, derived from the Streptococcus pyogenes Cas9(SpCas9) protein, into the Y. lipolytica genome to enhance gene editing efficiency and fidelity, and subsequently explored the optimal expression level of eSpCas9 gene by utilizing different promoters and selecting various growth periods for yeast transformation. The results demonstrated that the integrated eSpCas9 gene editing system significantly enhanced gene editing efficiency, increasing from 16.61% to 86.09% on TRP1 and from 33.61% to 95.19% on LIP2, all without the need for a time-consuming outgrowth step. Furthermore, growth curves and dilution assays indicated that the consistent expression of eSpCas9 protein slightly suppressed the growth of Y. lipolytica, revealing that strong inducible promoters may be a potential avenue for future research. This work simplifies the gene editing process in Y. lipolytica, thus advancing its potential as a natural product synthesis chassis and providing valuable insights for other comparable microorganisms.

Conjugated linoleic acid (CLA) as a functional food: Is it beneficial or not?

Conjugated linoleic acid (CLA) has attracted great attention in recent years as a popular class of functional food that is broadly used. It refers to a group of geometric and positional isomers of linoleic acid (LA) with a conjugated double bond. The main natural sources of CLA are dairy products, beef and lamb, whereas only trace amounts occur naturally in plant lipids. CLA has been shown to improve various health issues, having effects on obesity, inflammatory, anti-carcinogenicity, atherogenicity, immunomodulation, and osteosynthesis. Also, compared to studies on humans, many animal researches reveal more positive benefits on health. CLA represents a nutritional avenue to improve lifestyle diseases and metabolic syndrome. Most of these effects are attributed to the two major CLA isomers [conjugated linoleic acid cis-9,trans-11 isomer (c9,t11), and conjugated linoleic acid trans-10,cis-12 isomer (t10,c12)], and their mixture (CLA mix). In contrast, adverse effects of CLA have been also reported, such as glucose homeostasis, insulin resistance, hepatic steatosis and induction of colon carcinogenesis in humans, as well as milk fat inhibition in ruminants, lowering chicken productivity, influencing egg quality and altering growth performance in fish. This review article aims to discuss the health benefits of CLA as a nutraceutical supplement and highlight the possible mechanisms of action that may contribute to its outcome. It also outlines the feasible adverse effects of CLA besides summarizing the recent peer-reviewed publications on CLA to ensure its efficacy and safety for proper application in humans.

Changes in the Lipid Metabolism of the Longissimus thoracis Muscle in Bulls When Using Different Feeding Strategies during the Growing and Finishing Phases

The objective was to evaluate the supplementation strategy's effect on beef cattle during the growing phase and two systems during the finishing phase. One hundred and twenty young bulls were randomly divided in a 2 × 2 factorial design to receive either mineral (ad libitum) or protein + energy (3 g/kg body weight (BW)/day) during the growing phase and pasture plus concentrate supplementation (20 g/kg BW/day) or feedlot (25:75% corn silage:concentrate) during the finishing phase. Feedlot-fed bulls had meat (Longissimus thoracis-LT) with a higher content of lipids and saturated and monounsaturated fatty acids and a greater upregulation of stearoyl-CoA desaturase and sterol regulatory element-binding protein-1c than animals that fed on pasture (p < 0.05). On the other hand, pasture-fed bulls had meat with a higher content of α-linoleic acid, linolenic acid, and n6 and a greater n6:n3 ratio compared to the feedlot-fed group (p < 0.05). In addition, meat from pasture-fed bulls during the finishing phase had 17.6% more isocitrate dehydrogenase enzyme concentration than the feedlot group (p = 0.02). Mineral-fed and pasture-finished bulls showed down-regulation of peroxisome proliferator-activated receptor gamma (p < 0.05), while the bulls fed protein + energy and finished in the feedlot had higher carnitine palmitoyltransferase 2 expression (p ≤ 0.013). In conclusion, mineral or protein + energy supplementation in the growing does not affect the fatty acid composition of intramuscular fat of LT muscle. In the finishing phase, feeding bulls in the feedlot upregulates the lipogenic genes and consequently improves the intramuscular fat content in the meat.

Emodin attenuates high lipid-induced liver metastasis through the AKT and ERK pathways in vitro in breast cancer cells and in a mouse xenograft model

Emodin, a natural anthraquinone derivative, can inhibit lipid synthesis and breast cancer cell proliferation. We previously found that emodin decreased breast cancer liver metastasis via epithelial-to-mesenchymal transition (EMT) inhibition. However, the mechanism through which emodin affects breast cancer liver metastasis in high-fat diet-induced obese and hyperlipidemic mice has not been elucidated. Bioinformatics analysis was used to reveal the potential targets and pathways of emodin. The mouse model of liver metastasis was established by injecting breast cancer cells into the left ventricle in high-fat diet-induced obese mice. The effect of emodin on inhibiting liver metastasis of breast cancer was evaluated by animal experiments. The mechanisms through which emodin inhibits liver metastasis of breast cancer were studied by cell and molecular biological methods. Emodin reduced lipid synthesis by inhibiting the expression of triglyceride (TG) synthesis-related genes, such as fatty acid synthase (Fasn), glycerol-3-phosphate acyltransferase 1 (Gpat1), and stearoyl-CoA desaturase (Scd1), and ultimately reduced liver metastasis in breast cancer. In addition, emodin inhibited breast cancer cell proliferation and invasion through the serine/threonine kinase (AKT) signaling and extracellular-regulated protein kinase (ERK) pathways by interacting with CSNK2A1, ESR1, ESR2, PIM1 and PTP4A3. Our results indicate that emodin may have therapeutic potential in the prevention or treatment of breast cancer liver metastasis.

Main regulatory factors of marbling level in beef cattle

The content of intramuscular fat (IMF), that determines marbling levels is considered as one of the vital factors influencing beef sensory quality including tenderness, juiciness, flavour and colour. The IMF formation in cattle commences around six months after conception, and continuously grows throughout the life of the animal. The accumulation of marbling is remarkably affected by genetic, sexual, nutritional and management factors. In this review, the adipogenesis and lipogenesis process regulated by various factors and genes during fetal and growing stages is briefly presented. We also discuss the findings of recent studies on the effects of breed, gene, heritability and gender on the marbling accumulation. Various research reported that feeding during pregnancy, concentrate to roughage ratios and the supplementation or restriction of vitamin A, C, and D are crucial nutritional factors affecting the formation and development of IMF. Castration and early weaning combined with high energy feeding are effective management strategies for improving the accumulation of IMF. Furthermore, age and weight at slaughter are also reviewed because they have significant effects on marbling levels. The combination of several factors could positively affect the improvement of the IMF deposition. Therefore, advanced strategies that simultaneously apply genetic, sexual, nutritional and management factors to achieve desired IMF content without detrimental impacts on feed efficiency in high-marbling beef production are essential.

Dermal white adipose tissue: Much more than a metabolic, lipid-storage organ?

The role of dermal white adipose tissue (dWAT) has emerged in the biomedical science as an ancillary fat district in the derma without a defined and distinct function respect to the subcutaneous adipose tissue (sWAT). Despite some evidence describing dWAT as an immune-competent compartment, particularly engaged in wound repair, very few reports dealing with dWAT has elucidated its major modulatory role within the skin biology. Whereas an increasing bulk of evidence allows researcher to describe the main activity of sWAT, in humans dWAT is not properly a separated fat compartment and therefore scarcely considered in the scientific debate. Due to its strategic position between epidermis and sWAT, dermal fat might play a much more intriguing role than expected. This review tries to shed light on this issue, by expanding the debate about a possible role of dWAT in skin physiology.

The Study of the Response of Fat Metabolism to Long-Term Energy Stress Based on Serum, Fatty Acid and Transcriptome Profiles in Yaks

Simple Summary

The serum, fatty acid and transcriptome profiles in the subcutaneous fat of yaks were measured to explore the effect of long-term energy stress (ES) on fat metabolism during the cold season. The study indicated that under long-term ES during the cold season, the amount of fat in yaks was less, and fat mobilization was one of the main ways by which energy was obtained in yaks. Yaks regulated fat metabolism in subcutaneous fat primarily through adenosine 5′-monophosphate-activated protein kinase (AMPK) signaling. Glucose (GLU) intake, fat catabolism, fatty acid synthesis and fatty acid oxidation in the subcutaneous fat of yaks were all inhibited, which resulted in the fat mobilization of yaks slowing as much as possible under long-term ES. In addition, the energy expenditures in fat cells were inhibited by regulating phosphatidylinositol 3’ -kinase (PI3K)-serine/threonine-protein kinase (Akt) andmammalian target of rapamycin (mTOR) signaling, and the limited energy obtained from GLU and fat was consumed by muscle and organs as much as possible. These factors led to an energy balance in yaks under long-term ES. The fat stored in yaks can be expended for as long as possible, and yaks can survive for as long as necessary under long-term ES.

Abstract

Long-term energy stress (ES) during the cold season is a serious problem for the breeding of yaks. In this paper, the response of fat metabolism in yaks to long-term ES during the cold season was studied. Gas chromatography (GC) analysis showed that the percentage of saturated fatty acids (SFAs) in the subcutaneous fat of the yaks in the ES group was 42.7%, which was less than the 56.6% in the CO group (p < 0.01) and the percentage of polyunsaturated unsaturated fatty acids (PUFAs) in the subcutaneous fat of the yaks in the ES group was 38.3%, which was more than the 26.0% in the CO group (p < 0.01). The serum analysis showed that fatty acid oxidation in yaks was increased under long-term ES. In the subcutaneous fat of yaks under long-term ES, the gene expression levels of glycerol-3-phosphate acyltransferase 4 (GPAT4), hormone-sensitive lipase (HSL), patatin-like phospholipase domain-containing protein 2 (PNPLA2), acyl-CoA dehydrogenase (ACAD), acyl-coenzyme A thioesterase 8 (ACOT8), facilitated glucose transporter (GLUT4), 3-oxoacyl-[acyl-carrier-protein] synthase (OXSM), oestradiol 17-beta-dehydrogenase 8 (HSD17B8) and malonate-Co-A ligase ACSF3 (ACSF3) were downregulated (q < 0.05), whereas the gene expression levels of aquaporin-7 (AQP7), long-chain-fatty-acid-CoA ligase (ACSL), elongation of very long chain fatty acids protein (ELOVL) and fatty acid desaturase 1 (FADS1) were upregulated (q < 0.05), indicating the inhibition of fat catabolism, fat anabolism, fatty acid oxidation, glucose (GLU) intake and SFA synthesis and the promotion of glycerinum (GLY) transportation and PUFA synthesis. Additional findings showed that the gene expression levels of leptin (LEP), adenosine 5′-monophosphate-activated protein kinase (AMPK) and phosphatidylinositol 3-kinase (PI3K) were upregulated (q < 0.05), whereas the gene expression levels of malonyl-CoA decarboxylase (MCD), sterol regulatory element-binding protein 1 (SREBF1), mammalian target of rapamycin (mTOR) and serine/threonine-protein kinase (AKT) were downregulated (q < 0.05), indicating that fat metabolism in the subcutaneous fat of yaks under ES was mainly regulated by AMPK signaling and mTOR and PI3K-AKT signaling were also involved. Energy consumption was inhibited in the subcutaneous fat itself. This study can provide a theoretical basis for the healthy breeding and genetic breeding of yaks.

Oxidative Stress, Nutrition and Cancer: Friends or Foes?

The relationship between cancer and nutrition, as well as nutrition and oxidative stress, shares puzzling aspects that current research is investigating as the possible components of an intriguing regulating mechanism involving the complex interplay between adipose tissue and other compartments. Along the very recent biological evolution, humans underwent a rapid change in their lifestyles and henceforth the role of the adipocytes earned a much more complex task in the fine tuning of the tissue microenvironment. A lipidic signaling language probably evolved in association with the signaling role of reactive oxygen species, which gained a fundamental part in the regulation of cell stem and plasticity. The possible relationship with cancer onset might have some causative mechanism in the impairment of this complex task, usually deregulated by drastic changes in one's own lifestyle and dietary habit. This review tries to address this issue.

Maternal conjugated linoleic acid alters hepatic lipid metabolism via the AMPK signaling pathway in chick embryos

The effects of maternal conjugated linoleic acid (CLA) on embryonic development and hepatic lipid metabolism were investigated in chick embryos. A total of 180 Arbor Acres female broiler breeders (36 wk old) were randomly divided into the following 3 dietary treatment groups: a basic diet (control), a basic diet containing 0.5% CLA (CLA1), and a basic diet containing 1.0% CLA (CLA2). The females were fed for 8 wk, and the eggs from each group were collected and hatched during the last 2 wk. The results showed that the addition of dietary CLA increased the broken egg rate and reduced the fertilization rate and the egg hatchability (P < 0.05). CLA enrichment decreased the polyunsaturated and monounsaturated fatty acids and increased the saturated fatty acids in the yolk sac (P < 0.05). The yolk sac weight, body weight, and body length had a linear decrease with CLA supplementation (P < 0.05). In the developing chick embryo (at E14) and newly hatched chick (D0), the serum triglyceride concentration decreased with maternal CLA supplementation and was accompanied by a reduction in subcutaneous adipose tissue deposition. In addition, maternal CLA supplementation mediated the hepatic lipid metabolism by decreasing the mRNA expression of sterol regulatory element-binding proteins-1c (SREBP-1c), fatty acid synthase and acetyl-CoA carboxylase, and increasing the mRNA expression of adenosine 5'-monophosphate-activated protein kinase α (AMPKα), peroxisome proliferator-activated receptors α (PPARα), liver fatty acid-binding protein, adipose triglyceride lipase and carnitine palmitoyltransferase in embryonic chick livers (P < 0.05). A drop in SREBP-1c protein expression and an increase in the protein expression of p-AMPKα and PPARα were also observed in the liver of chick embryo (P < 0.05). In conclusion, maternal CLA supplementation regulated the fatty acid composition in the yolk sac, and mediated embryonic chick development and hepatic lipometabolism, and these effects may be related to the AMPK pathway. These findings suggest the potential ability of maternal CLA supplementation to reduce fat deposition in chick embryos.

Probiotics: How Effective Are They in the Fight against Obesity?

Obesity has been associated with structural and functional changes in the gut microbiota. The abundance in, and diversity of, certain bacteria may favor energy harvest and metabolic pathways leading to obesity. Therefore, gut microbiota has become a potential target that can be manipulated to obtain optimal health. Probiotics have been shown to influence the composition of the gut microbiota, improve gut integrity, and restore the microbial shifts characteristic of obesity. Based on physical and biochemical parameters, metabolic and inflammatory markers, and alterations in gut microbe diversity, animal studies revealed beneficial results in obese models whereas the results in humans are sparse and inconsistent. Thus, the purpose of this review is to present evidence from animal studies and human clinical trials demonstrating the effects of various probiotic strains and their potential efficacy in improving obesity and associated metabolic dysfunctions. Furthermore, the review discusses current gaps in our understanding of how probiotics modulate gut microflora to protect against obesity. Finally, we propose future studies and methodological approaches that may shed light on the challenges facing the scientific community in deciphering the host–bacteria interaction in obesity.

Review: Nutrigenomics of marbling and fatty acid profile in ruminant meat

The present review will present the recent published results and discuss the main effects of nutrients, mainly fatty acids, on the expression of genes involved in lipid metabolism. In this sense, the review focuses in two phases: prenatal life and finishing phase, showing how nutrients can modulate gene expression affecting marbling and fatty acid profile in meat from ruminants. Adiposity in ruminants starts to be affected by nutrients during prenatal life when maternal nutrition affects the differentiation and proliferation of adipose cells enhancing the marbling potential. Therefore, several fetal programming studies were carried out in the last two decades in order to better understand how nutrients affect long-term expression of genes involved in adipogenesis and lipogenesis. In addition, during the finishing phase, marbling becomes largely dependent on starch digestion and glucose metabolism, being important to create alternatives to increase these metabolic processes, and modulates gene expression. Different lipid sources and their fatty acids may also influence the expression of genes responsible to encode enzymes involved in fat tissue deposition, influencing meat quality. In conclusion, the knowledge shows that gene expression is a metabolic factor affecting marbling and fatty acid profile in ruminant meat and diets and their nutrients have direct effect on how these genes are expressed.

Nutrient Regulation: Conjugated Linoleic Acid's Inflammatory and Browning Properties in Adipose Tissue

Obesity is the most widespread nutritional disease in the United States. Developing effective and safe strategies to manage excess body weight is therefore of paramount importance. One potential strategy to reduce obesity is to consume conjugated linoleic acid (CLA) supplements containing isomers cis-9, trans-11 and trans-10, cis-12, or trans-10, cis-12 alone. Proposed antiobesity mechanisms of CLA include regulation of (a) adipogenesis, (b) lipid metabolism, (c) inflammation, (d) adipocyte apoptosis, (e) browning or beiging of adipose tissue, and (f) energy metabolism. However, causality of CLA-mediated responses to body fat loss, particularly the linkage between inflammation, thermogenesis, and energy metabolism, is unclear. This review examines whether CLA's antiobesity properties are due to inflammatory signaling and considers CLA's linkage with lipogenesis, lipolysis, thermogenesis, and browning of white and brown adipose tissue. We propose a series of questions and studies to interrogate the role of the sympathetic nervous system in mediating CLA's antiobesity properties.

Subspecies and diet affect the expression of genes involved in lipid metabolism and chemical composition of muscle in beef cattle

Fourteen Nellore and 14 Angus young bulls with BW of 381±11.8kg were randomly assigned into 2 feeding groups (whole shelled corn without forage (WSC) or corn silage and ground corn (GC)) to evaluate chemical composition and expression of genes involved in lipid metabolism in the longissimus thoracis (LT). We hypothesized that bulls fed the WSC diet have greater amounts of intramuscular fat and Angus have higher expression levels of PPAR and SREBF. Meat from Angus bulls had greater ether extract compared to Nellore (P<0.05). Muscle from bulls fed the WSC diet had greater expression of PPARA (P<0.05) and lower levels of SREBF1 expression (P<0.01). The LT of Nellore fed GC had greater expression of FABP4, ACACA and SCD genes (P<0.01). In conclusion, the greater concentration of starch in the WSC diet did not increase marbling in the beef of bulls fed this diet due to the reduced expression of SREBF1.

Nutrigenomics and Beef Quality: A Review about Lipogenesis

The objective of the present review is to discuss the results of published studies that show how nutrition affects the expression of genes involved in lipid metabolism and how diet manipulation might change marbling and composition of fat in beef. Several key points in the synthesis of fat in cattle take place at the molecular level, and the association of nutritional factors with the modulation of this metabolism is one of the recent targets of nutrigenomic research. Within this context, special attention has been paid to the study of nuclear receptors associated with fatty acid metabolism. Among the transcription factors involved in lipid metabolism, the peroxisome proliferator-activated receptors (PPARs) and sterol regulatory element-binding proteins (SREBPs) stand out. The mRNA synthesis of these transcription factors is regulated by nutrients, and their metabolic action might be potentiated by diet components and change lipogenesis in muscle. Among the options for dietary manipulation with the objective to modulate lipogenesis, the use of different sources of polyunsaturated fatty acids, starch concentrations, forage ratios and vitamins stand out. Therefore, special care must be exercised in feedlot feed management, mainly when the goal is to produce high marbling beef.

Incorporation and effects of punicic acid on muscle and adipose tissues of rats

BACKGROUND

This study evaluated the effect of pomegranate seed oil (PSO) supplementation, rich in punicic acid (55 %/C18:3-9c,11 t,13c/CLNA), on the lipid profile and on the biochemical and oxidative parameters in the gastrocnemius muscle and adipose tissues of healthy rats. Linseed oil (LO), rich in linolenic acid (52 %/C18:3-9c12c15c/LNA) was used for comparison.

METHODS

Male Wistar rats (n = 56) were distributed in seven groups: control (water); LNA 1 %, 2 % and 4 % (treated with LO); CLNA 1 %, 2 % and 4 % (treated with PSO), po for 40 days. The percentages were compared to the daily feed intake. Fatty acid profile were performed by gas chromatography, antioxidant enzymes activity by spectrophotometer and the adipocytes were isolated by collagenase tissue digestion. Analysis of variance (ANOVA) was applied to check for differences between the groups (control, LNAs and CLNAs) and principal component analysis (PCA) was used to project the groups in the factor-place (PC1 vs PC2) based on the biochemical responses assessed in the study.

RESULTS

The fatty acids profile of tissues showed that the LNA percentages were higher in the animals that were fed LO. However, PA was only detected in the adipose tissues. Conjugated linoleic acid (CLA) was present in all the tissues of the animals supplemented with PSO, in a dose dependent manner, and 9c11t-CLA was the predominant isomer. Nevertheless there were no changes in the total weight gain of the animals, the weights of the tissues, and the oxidative stress parameters in the muscle. In addition, there was an increase in the size of the epididymal fat cells in the groups treated with PSO. Principal component analysis (PCA) showed that the CLNAs groups were arranged separately with a cumulative variance of 68.47 %.

CONCLUSIONS

The results show that PSO can be used as a source of CLAs but that it does not cause changes in body modulation and does not interfere in the antioxidant activity of healthy rats.

Sphingolipids are required for efficient triacylglycerol loss in conjugated linoleic Acid treated adipocytes

Conjugated linoleic acid (CLA) reduces adiposity in human and mouse adipocytes. This outcome is achieved through a variety of biological responses including increased energy expenditure and fatty acid oxidation, increased inflammation, repression of fatty acid biosynthesis, attenuated glucose transport, and apoptosis. In the current study, profiling of 261 metabolites was conducted to gain new insights into the biological pathways responding to CLA in 3T3-L1 adipocytes. Sphinganine and sphingosine levels were observed to be highly elevated in CLA treated adipocytes. Exogenous chemicals that increased endogenous ceramide levels decreased lipid levels in adipocytes, and activated AMP-activated protein kinase (AMPK) as well as NF-κB, both of which are typically activated in CLA treated adipocytes. Concurrent inhibition of ceramide de novo biosynthesis and recycling from existing sphingolipid pools attenuated the lipid lowering effect normally associated with responses to CLA, implicating ceramides as an important component of the lipid lowering response in CLA treated adipocytes.

Low level of trans-10, cis-12 conjugated linoleic acid decreases adiposity and increases browning independent of inflammatory signaling in overweight Sv129 mice

The objective of this study was to determine the extent to which a low level of trans-10, cis-12 (10,12) conjugated linoleic acid (CLA) decreases adiposity and increases browning in overweight mice, its dependence on inflammatory signaling and potential synergistic effects of daily exercise. Young, Sv129 male mice were fed a high-fat diet for 5 weeks to make them fat and glucose intolerant and then switch them to a low-fat diet with or without 0.1% 10,12 CLA, sodium salicylate or exercise for another 7 weeks. 10,12 CLA decreased white adipose tissue (WAT) and brown adipose tissue mass, and increased the messenger RNA and protein levels, and activities of enzymes associated with thermogenesis or fatty acid oxidation in WAT. Mice fed 10,12 CLA had lower body temperatures compared to controls during cold exposure, which coincided with decreased adiposity. Although sodium salicylate decreased 10,12 CLA-mediated increases in markers of inflammation in WAT, it did not affect other outcomes. Exercise had no further effect on the outcomes measured. Collectively, these data indicate that 10,12 CLA-mediated reduction of adiposity is independent of inflammatory signaling, and possibly due to up-regulation of fatty acid oxidation and heat production in order to regulate body temperature. Although this low level of 10,12 CLA reduced adiposity in overweight mice, hepatomegaly and inflammation are major health concerns.

Modulation of peroxisome proliferator-activated receptor gamma (PPAR γ) by conjugated fatty acid in obesity and inflammatory bowel disease

Conjugated fatty acids including conjugated linoleic acid (CLA) and conjugated linolenic acid (CLNA) have drawn significant attention for their variety of biologically beneficial effects. Evidence suggested that CLA and CLNA could play physiological roles by regulating the expression and activity of PPAR γ. This review summarizes the current understanding of evidence of the role of CLA (cis-9,trans-11 CLA and trans-10,cis-12 CLA) and CLNA (punicic acid and α-eleostearic acid) in modulating the expression or activity of PPAR γ that could in turn be employed as complementary treatment for obesity and inflammatory bowel disease.

10E,12Z-conjugated linoleic acid impairs adipocyte triglyceride storage by enhancing fatty acid oxidation, lipolysis, and mitochondrial reactive oxygen species

Conjugated linoleic acid (CLA) is a naturally occurring dietary trans fatty acid found in food from ruminant sources. One specific CLA isomer, 10E,12Z-CLA, has been associated with health benefits, such as reduced adiposity, while simultaneously promoting deleterious effects, such as systemic inflammation, insulin resistance, and dyslipidemia. The precise mechanisms by which 10E,12Z-CLA exerts these effects remain unknown. Despite potential health consequences, CLA continues to be advertised as a natural weight loss supplement, warranting further studies on its effects on lipid metabolism. We hypothesized that 10E,12Z-CLA impairs lipid storage in adipose tissue by altering the lipid metabolism of white adipocytes. We demonstrate that 10E,12Z-CLA reduced triglyceride storage due to enhanced fatty acid oxidation and lipolysis, coupled with diminished glucose uptake and utilization in cultured adipocytes. This switch to lipid utilization was accompanied by a potent proinflammatory response, including the generation of cytokines, monocyte chemotactic factors, and mitochondrial superoxide. Disrupting fatty acid oxidation restored glucose utilization and attenuated the inflammatory response to 10E,12Z-CLA, suggesting that fatty acid oxidation is critical in promoting this phenotype. With further investigation into the biochemical pathways involved in adipocyte responses to 10E,12Z-CLA, we can discern more information about its safety and efficacy in promoting weight loss.

The phospholipase C inhibitor U73122 attenuates trans-10, cis-12 conjugated linoleic acid-mediated inflammatory signaling and insulin resistance in human adipocytes

We have demonstrated that trans-10, cis-12 conjugated linoleic acid (18:2t10,c12)-mediated delipidation of human adipocytes was dependent on increased intracellular calcium and activation of inflammatory signaling in human primary adipocytes. These data are consistent with the actions of diacylglycerol and inositol triphosphate derived from phospholipase C (PLC)-dependent cell signaling. To test the hypothesis that PLC was an upstream activator of these cellular responses to 18:2t10,c12, primary cultures of human adipocytes were pretreated with 1-[6-((17β-3-methoxyestra-1,3,5 (10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione (U73122), a universal PLC inhibitor, followed by 18:2t10,c12 treatment. U73122 attenuated 18:2t10,c12-mediated insulin resistance within 48 h and suppression of the mRNA levels of peroxisome proliferator-activated receptor (PPAR)γ, insulin-stimulated glucose transporter-4, acetyl-CoA carboxylase-1, and stearoyl-CoA desaturase-1, and the protein levels of PPARγ within 18-24 h. U73122 inhibited 18:2t10,c12-mediated induction of the inflammatory-related genes calcium/calmodulin-dependent protein kinase-β, cyclooxygenase-2, monocyte chemoattractant protein-1, interleukin (IL)-6, and IL-8, secretion of IL-6 and IL-8, and the activation of extracellular signal-related kinase, c-Jun N-terminal kinase, and c-Jun within 18-24 h. Moreover, 18:2t10,c12 increased the mRNA levels of heat shock proteins within 6-24 h and intracellular calcium concentrations within 3 min, which were inhibited by U73122. Lastly, 18:2t10,c12 increased the abundance of PLCγ1 in the plasma membrane within 3 min. Taken together, these data suggest that PLC plays an important role in 18:2t10,c12-mediated activation of intracellular calcium accumulation, inflammatory signaling, delipidation, and insulin resistance in human primary adipocytes.

Current issues surrounding the definition of trans-fatty acids: implications for health, industry and food labels

The definition of trans-fatty acids (TFA) was established by the Codex Alimentarius to guide nutritional and legislative regulations to reduce TFA consumption. Currently, conjugated linoleic acid (CLA) is excluded from the TFA definition based on evidence (primarily preclinical studies) implying health benefits on weight management and cancer prevention. While the efficacy of CLA supplements remains inconsistent in randomised clinical trials, evidence has emerged to associate supplemental CLA with negative health outcomes, including increased subclinical inflammation and oxidative stress (particularly at high doses). This has resulted in concerns regarding the correctness of excluding CLA from the TFA definition. Here we review recent clinical and preclinical literature on health implications of CLA and ruminant TFA, and highlight several issues surrounding the current Codex definition of TFA and how it may influence interpretation for public health. We find that CLA derived from ruminant foods differ from commercial CLA supplements in their isomer composition/distribution, consumption level and bioactivity. We conclude that health concerns associated with the use of supplemental CLA do not repudiate the exclusion of all forms of CLA from the Codex TFA definition, particularly when using the definition for food-related purposes. Given the emerging differential bioactivity of TFA from industrial v. ruminant sources, we advocate that regional nutrition guidelines/policies should focus on eliminating industrial forms of trans-fat from processed foods as opposed to all TFA per se.

Cross regulation of sirtuin 1, AMPK, and PPARγ in conjugated linoleic acid treated adipocytes

Trans-10, cis-12 conjugated linoleic acid (t10c12 CLA) reduces triglyceride (TG) levels in adipocytes through multiple pathways, with AMP-activated protein kinase (AMPK) generally facilitating, and peroxisome proliferator-activated receptor γ (PPARγ) generally opposing these reductions. Sirtuin 1 (SIRT1), a histone/protein deacetylase that affects energy homeostasis, often functions coordinately with AMPK, and is capable of binding to PPARγ, thereby inhibiting its activity. This study investigated the role of SIRT1 in the response of 3T3-L1 adipocytes to t10c12 CLA by testing the following hypotheses: 1) SIRT1 is functionally required for robust TG reduction; and 2) SIRT1, AMPK, and PPARγ cross regulate each other. These experiments were performed by using activators, inhibitors, or siRNA knockdowns that affected these pathways in t10c12 CLA-treated 3T3-L1 adipocytes. Inhibition of SIRT1 amounts or activity using siRNA, sirtinol, nicotinamide, or etomoxir attenuated the amount of TG loss, while SIRT1 activator SRT1720 increased the TG loss. SRT1720 increased AMPK activity while sirtuin-specific inhibitors decreased AMPK activity. Reciprocally, an AMPK inhibitor reduced SIRT1 activity. Treatment with t10c12 CLA increased PPARγ phosphorylation in an AMPK-dependent manner and increased the amount of PPARγ bound to SIRT1. Reciprocally, a PPARγ agonist attenuated AMPK and SIRT1 activity levels. These results indicated SIRT1 increased TG loss and that cross regulation between SIRT1, AMPK, and PPARγ occurred in 3T3-L1 adipocytes treated with t10c12 CLA.

Oleic acid attenuates trans-10,cis-12 conjugated linoleic acid-mediated inflammatory gene expression in human adipocytes

The weight loss supplement conjugated linoleic acid (CLA) consists of an equal mixture of trans-10,cis-12 (10,12) and cis-9,trans-11 (9,11) isomers. However, high levels of mixed CLA isomers, or the 10,12 isomer, causes chronic inflammation, lipodystrophy, or insulin resistance. We previously demonstrated that 10,12 CLA decreases de novo lipid synthesis along with the abundance and activity of stearoyl-CoA desaturase (SCD)-1, a δ-9 desaturase essential for the synthesis of monounsaturated fatty acids (MUFA). Thus, we hypothesized that the 10,12 CLA-mediated decrease in SCD-1, with the subsequent decrease in MUFA, was responsible for the observed effects. To test this hypothesis, 10,12 CLA-treated human adipocytes were supplemented with oleic acid for 12 h to 7 days, and inflammatory gene expression, insulin-stimulated glucose uptake, and lipid content were measured. Oleic acid reduced inflammatory gene expression in a dose-dependent manner, and restored the lipid content of 10,12 CLA-treated adipocytes without improving insulin-stimulated glucose uptake. In contrast, supplementation with stearic acid, a substrate for SCD-1, or 9,11 CLA did not prevent inflammatory gene expression by 10,12 CLA. Notably, 10,12 CLA impacted the expression of several G-protein coupled receptors that was attenuated by oleic acid. Collectively, these data show that oleic acid attenuates 10,12 CLA-induced inflammatory gene expression and lipid content, possibly by alleviating cell stress caused by the inhibition of MUFA needed for phospholipid and neutral lipid synthesis.