A high intake of conjugated linoleic acid does not affect liver and kidney function tests in healthy human subjects

Effects of dibutyl phthalate on lipid metabolism in liver and hepatocytes based on PPARα/SREBP-1c/FAS/GPAT/AMPK signal pathway

Phateacid esters (PAEs), such as dibutyl phthalate (DBP), have been widely used and human exposure results into serious toxic effects; such as the development of fatty liver disease. In the present study, SD rat models for in vivo study (normal and fatty liver model group) and hepatocytes for in vitro study (normal and abnormal lipid metabolism model group) were established to determine the effects of DBP on liver function and discover the possible mechanisms. Meanwhile, the peroxisome proliferator activated receptor (PPARα) blocker, GW6471, with the Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activator, AICAR, were applied in vitro study to clarify the role of PPARα/SREBP-1c/FAS/GPAT/AMPK signal pathway in the process. Results suggested that DBP could activate PPARα signaling pathway and affected the protein expression of SREBP, FAS and GPAT to cause hyperlipidemia and abnormal liver function. DBP also could inhibit the phosphorylation and activation of AMPK to inhibit the decomposition and metabolism of lipids. Interestingly, the effects of DBP could be alleviated by GW6471 and AICAR. Our experimental results provide reliable evidence that DBP exposure could further induce liver lipid metabolism disorder and other hepatic toxicity through PPARα/SREBP-1c/FAS/GPAT/AMPK signal pathway.

Conjugated Linoleic Acid and Brain Metabolism: A Possible Anti-Neuroinflammatory Role Mediated by PPARα Activation

Fatty acids play a crucial role in the brain as specific receptor ligands and as precursors of bioactive metabolites. Conjugated linoleic acid (CLA), a group of positional and geometric isomers of linoleic acid (LA, 18:2 n-6) present in meat and dairy products of ruminants and synthesized endogenously in non-ruminants and humans, has been shown to possess different nutritional properties associated with health benefits. Its ability to bind to peroxisome proliferator-activated receptor (PPAR) α, a nuclear receptor key regulator of fatty acid metabolism and inflammatory responses, partly mediates these beneficial effects. CLA is incorporated and metabolized into brain tissue where induces the biosynthesis of endogenous PPARα ligands palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), likely through a positive feedback mechanism where PPARα activation sustains its own cellular effects through ligand biosynthesis. In addition to PPARα, PEA and OEA may as well bind to other receptors such as TRPV1, further extending CLA own anti-neuroinflammatory actions. Future studies are needed to investigate whether dietary CLA may exert anti-inflammatory activity, particularly in the setting of neurodegenerative diseases and neuropsychiatric disorders with a neuroinflammatory basis.

Impact of Conjugated Linoleic Acid (CLA) on Skeletal Muscle Metabolism

Conjugated linoleic acid (CLA) has garnered special attention as a food bioactive compound that prevents and attenuates obesity. Although most studies on the effects of CLA on obesity have focused on the reduction of body fat, a number of studies have demonstrated that CLA also increases lean body mass and enhances physical performances. It has been suggested that these effects may be due in part to physiological changes in the skeletal muscle, such as changes in the muscle fiber type transformation, alteration of the intracellular signaling pathways in muscle metabolism, or energy metabolism. However, the mode of action for CLA in muscle metabolism is not completely understood. The purpose of this review is to summarize the current knowledge of the effects of CLA on skeletal muscle metabolism. Given that CLA not only reduces body fat, but also improves lean mass, there is great potential for the use of CLA to improve muscle metabolism, which would have a significant health impact.

Pros and cons of CLA consumption: an insight from clinical evidences

This comprehensive review critically evaluates whether supposed health benefits propounded upon human consumption of conjugated linoleic acids (CLAs) are clinically proven or not. With a general introduction on the chemistry of CLA, major clinical evidences pertaining to intervention strategies, body composition, cardio-vascular health, immunity, asthma, cancer and diabetes are evaluated. Supposed adverse effects such as oxidative stress, insulin resistance, irritation of intestinal tract and milk fat depression are also examined. It seems that no consistent result was observed even in similar studies conducted at different laboratories, this may be due to variations in age, gender, racial and geographical disparities, coupled with type and dose of CLA supplemented. Thus, supposed promising results reported in mechanistic and pre-clinical studies cannot be extrapolated with humans, mainly due to the lack of inconsistency in analyses, prolonged intervention studies, follow-up studies and international co-ordination of concerted studies. Briefly, clinical evidences accumulated thus far show that CLA is not eliciting significantly promising and consistent health effects so as to uphold it as neither a functional nor a medical food.

Dairy foods and dairy protein consumption is inversely related to markers of adiposity in obese men and women

A number of intervention studies have reported that the prevalence of obesity may be in part inversely related to dairy food consumption while others report no association. We sought to examine relationships between energy, protein and calcium consumption from dairy foods (milk, yoghurt, cheese, dairy spreads, ice-cream) and adiposity including body mass index (BMI), waist (WC) and hip circumference (HC), and direct measures of body composition using dual energy X-ray absorptiometry (% body fat and abdominal fat) in an opportunistic sample of 720 overweight/obese Australian men and women. Mean (SD) age, weight and BMI of the population were 51 ± 10 year, 94 ± 18 kg and 32.4 ± 5.7 kg/m², respectively. Reduced fat milk was the most commonly consumed dairy product (235 ± 200 g/day), followed by whole milk (63 ± 128 g/day) and yoghurt (53 ± 66 g/day). Overall dairy food consumption (g/day) was inversely associated with BMI, % body fat and WC (all p < 0.05). Dairy protein and dairy calcium (g/day) were both inversely associated with all adiposity measures (all p < 0.05). Yoghurt consumption (g/day) was inversely associated with % body fat, abdominal fat, WC and HC (all p < 0.05), while reduced fat milk consumption was inversely associated with BMI, WC, HC and % body fat (all p < 0.05). Within a sample of obese adults, consumption of dairy products, dairy protein, and calcium was associated with more favourable body composition.

Hepatic lipid metabolic pathways modified by resveratrol in rats fed an obesogenic diet

OBJECTIVE

The scientific community is on the look-out for safe biomolecules useful in the prevention of obesity and related aberrations such as fatty liver. This study analyzed the influence of resveratrol on hepatic triacylglycerol metabolism.

METHODS

Male Sprague-Dawley rats were divided into control and resveratrol-treated groups (30 mg/kg of body weight per day) and fed a commercial obesogenic diet for 6 wk. Liver triacylglycerol content and the activity of carnitine palmitoyl transferase-Ia (CPT-Ia), acyl-coenzyme A oxydase (ACO), fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (ME), acetyl-coenzyme A carboxylase (ACC), adenosine monophosphate-activated protein kinase (AMPK), and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) activation were measured. Mitochondrial protein cytochrome C oxidase subunit 2 (COXII), mitochondrial transcription factor A (TFAM), sterol regulatory element-binding protein-1c (SREBP-1c), peroxisome proliferator-activated receptor-α (PPAR-α), sirtuin-1 (SIRT1), hepatocyte nuclear factor receptor-4α (HNF-4α), and PGC-1α mRNA levels were also analyzed. Serum insulin was quantified.

RESULTS

Resveratrol decreased liver fat accumulation, increased CPT-Ia and ACO, and decreased ACC activities. Other lipogenic enzymes, FAS, ME, and G6PDH were not modified. The polyphenol activated AMPK and PGC-1α. The expression of SRBP-1c, PPAR-α, SIRT1, PGC-1α, HNF-4α, TFAM, and COXII was not modified. No changes in serum insulin levels were observed.

CONCLUSION

Resveratrol partly prevents the increase in liver fat accumulation induced by high-fat high-sucrose feeding by increasing fatty acid oxidation and decreasing lipogenesis. These effects are mediated by the activation of the AMPK/SIRT1 axis.

Implication of conjugated linoleic acid (CLA) in human health

Conjugated linoleic acid (CLA) has drawn significant attention in the last two decades for its variety of biologically beneficial effects. CLA reduces body fat, cardiovascular diseases and cancer, and modulates immune and inflammatory responses as well as improves bone mass. It has been suggested that the overall effects of CLA are the results of interactions between two major isomers, cis-9,trans-11 and trans-10,cis-12. This review will primarily focus on current CLA publications involving humans, which are also summarized in the tables. Along with a number of beneficial effects of CLA, there are safety considerations for CLA supplementation in humans, which include effects on liver functions, milk fat depression, glucose metabolism, and oxidative stresses.

Effect of a high intake of conjugated linoleic acid on lipoprotein levels in healthy human subjects

BACKGROUND

Trans fatty acids are produced either by industrial hydrogenation or by biohydrogenation in the rumens of cows and sheep. Industrial trans fatty acids lower high-density lipoprotein (HDL) cholesterol, raise low-density lipoprotein (LDL) cholesterol, and increase the risk of coronary heart disease. The effects of trans fatty acids from ruminants are less clear. We investigated the effect on blood lipids of cis-9, trans-11 conjugated linoleic acid (CLA), a trans fatty acid largely restricted to ruminant fats.

METHODOLOGY/PRINCIPAL FINDINGS

Sixty-one healthy women and men were sequentially fed each of three diets for three weeks, in random order, for a total of nine weeks. Diets were identical except for 7% of energy (approximately 20 g/day), which was provided either by oleic acid, by industrial trans fatty acids, or by a mixture of 80% cis-9, trans-11 and 20% trans-10, cis-12 CLA. After the oleic acid diet, mean (+/- SD) serum LDL cholesterol was 2.68+/-0.62 mmol/L compared to 3.00+/-0.66 mmol/L after industrial trans fatty acids (p<0.001), and 2.92+/-0.70 mmol/L after CLA (p<0.001). Compared to oleic acid, HDL-cholesterol was 0.05+/-0.12 mmol/L lower after industrial trans fatty acids (p = 0.001) and 0.06+/-0.10 mmol/L lower after CLA (p<0.001). The total-to-HDL cholesterol ratio was 11.6% higher after industrial trans fatty acids (p<0.001) and 10.0% higher after CLA (p<0.001) relative to the oleic acid diet.

CONCLUSIONS/SIGNIFICANCE

High intakes of an 80:20 mixture of cis-9, trans-11 and trans-10, cis-12 CLA raise the total to HDL cholesterol ratio in healthy volunteers. The effect of CLA may be somewhat less than that of industrial trans fatty acids.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00529828.