Effects of structural changes of fatty acids on lipid accumulation in adipocytes and primary hepatocytes

Metabolic regulation of fatty acid esterification and effects of conjugated linoleic acid on glucose homeostasis in pig hepatocytes

Conjugated linoleic acids (CLAs) are geometric and positional isomers of linoleic acid (LA) that promote growth, alter glucose metabolism and decrease body fat in growing animals, although the mechanisms are poorly understood. A study was conducted to elucidate the effects of CLA on glucose metabolism, triglyceride (TG) synthesis and IGF-1 synthesis in primary culture of porcine hepatocytes. In addition, hormonal regulation of TG and IGF-1 synthesis was addressed. Hepatocytes were isolated from piglets (n = 5, 16.0 ± 1.98 kg average body weight) by collagenase perfusion and seeded into collagen-coated T-25 flasks. Hepatocytes were cultured in William's E containing dexamethasone (10-8 and 10-7 M), insulin (10 and 100 ng/ml), glucagon (0 and 100 ng/ml) and CLA (1 : 1 mixture of cis-9, trans-11 and trans-10, cis-12 CLA, 0.05 and 0.10 mM) or LA (0.05 and 0.10 mM). Addition of CLA decreased gluconeogenesis (P < 0.05), whereas glycogen synthesis and degradation, TG synthesis and IGF-1 synthesis were not affected compared with LA. Increased concentration of fatty acids in the media decreased IGF-1 production (P < 0.001) and glycogen synthesis (P < 0.01), and increased gluconeogenesis (P < 0.001) and TG synthesis (P < 0.001). IGF-1 synthesis increased (P < 0.001) and TG synthesis decreased (P < 0.001) as dexamethasone concentration in the media rose. High insulin/glucagon increased TG synthesis. These results indicate that TG synthesis in porcine hepatocytes is hormonally regulated so that dexamethasone decreases and insulin/glucagon increases it. In addition, CLA decreases hepatic glucose production through decreased gluconeogenesis.

A rapid method for determining arachidonic:eicosapentaenoic acid ratios in whole blood lipids: correlation with erythrocyte membrane ratios and validation in a large Italian population of various ages and pathologies

Background

Omega-3 and -6 polyunsaturated fatty acids (LCPUFA), are important for good health conditions. They are present in membrane phospholipids.

The ratio of total n-6:n-3 LCPUFA and arachidonic acid:eicosapentaenoic acid (AA and EPA), should not exceed 5:1. Increased intake of n-6 and decreased consumption of n-3 has resulted in much higher, ca 10/15:1 ratio in RBC fatty acids with the possible appearance of a pathological "scenario". The determination of RBC phospholipid LCPUFA contents and ratios is the method of choice for assessing fatty acid status but it is labour intensive and time consuming.

Aims of the study

[i] To describe and validate a rapid method, suitable for large scale population studies, for total blood fatty acid assay; [ii] to verify a possible correlation between total n-6:n-3 ratio and AA:EPA ratios in RBC phospholipids and in whole-blood total lipids, [iii] to assess usefulness of these ratio as biomarkers of LCPUFA status.

Methods

[1] Healthy volunteers and patients with various pathologies were recruited.

[2] Fatty acid analyses by GC of methyl esters from directly derivatized whole blood total lipids and from RBC phospholipids were performed on fasting blood samples from 1432 subjects categorised according to their age, sex and any existing pathologies.

AA:EPA ratio and the total n-6:n-3 ratio were determined.

Results

AA:EPA ratio is a more sensitive and reliable index for determining changes in total blood fatty acid and it is correlated with the ratio derived from extracted RBC phospholipids.

Conclusions

The described AA:EPA ratio is a simple, rapid and reliable method for determining n-3 fatty acid status.

Are fish oil omega-3 long-chain fatty acids and their derivatives peroxisome proliferator-activated receptor agonists?

Background

Peroxisome proliferator-activated receptors (PPARα, PPARγ, and PPARδ) are physiological sensors for glucose and lipid homeostasis. They are also the targets of synthetic drugs; such as fibrates as PPARα agonists which lower lipid level, and glitazones as PPARγ agonists which lower glucose level. As diabetes and metabolic diseases are often associated with high blood glucose and lipid levels, drugs that activate both PPARα/γ would be a logical approach. But synthetically developed PPARα/γ dual agonists and glitazones are showing side effects such as weight gain and edema. Therefore, natural compounds and their close derivatives are focused as future drugs against metabolic diseases.

Presentation of hypothesis

Docosahexaenoic acid and eicosapentaenoic acid, which are the fatty acids abundant in fish oil, are traditionally used against metabolic diseases. These fatty acids act as PPAR agonists that transcript the genes involved in glucose and lipid homeostasis. Present hypothesis suggests that the derivatives of these fatty acids are stronger PPAR agonists than the parent compounds. X-ray structures of PPARs indicate that α or β derivatives of fatty acids would fit into PPARα/γ binding cavity. Therefore, the derivatives will exhibit stronger affinities and activities than the parent compounds.

Testing of the hypothesis

Ligand binding assays and gene transactivation assays should be performed to test the hypothesis. Fluorescence-based methods are advantageous in binding assays, because they were found more suitable for fatty acid binding assays. In transactivation assays, care should be taken to remove contaminants from recombinant proteins.

Implications of the hypothesis

Present hypothesis is framed on the basis of molecular structure of natural PPAR agonists. Small structural changes in the molecular structure of fatty acids have a great influence on activating different PPARs. Therefore, this hypothesis bridges the concept of natural PPAR agonists and the use of structural information in designing new drugs against diabetes and metabolic syndrome. The derivatives may also be used as anti-inflammatory and anticancer agents.

Effect of conjugated linoleic acid type, treatment period, and dosage on differentiation of 3T3 cells

This study was conducted to determine effect of CLA and linoleic acid (LA) on cell differentiation, cellular glycerol-3-phosphate dehydrogenase (GPDH) activity, and FA accumulation in differentiating 3T3-L1 cells (3 isomers x 3 treatment periods x 4 doses). The cells were cultured in 24-well plates for proliferation until confluence. Then they were treated with media containing 0, 10, 35, or 70 mg/L (0, 35, 125, or 250 mmol/L, respectively) of LA, cis9,trans11- or trans10,cis12-CLA during early (day 0-2), intermediate and late (day 3-8), or overall (day 0-8) differentiation periods. Dexamethasone, methyl-isobutylxanthine, and insulin were supplemented to the media only for the early period to induce the differentiation. On day 8 of postconfluence the cells were harvested for Oil Red O staining, analysis of GPDH activity, and determination of the FA Concentration. Cellular LA or CLA was found to accumulate in a dose-response manner, mainly during the intermediate/late period. Treatment with trans10,cis12-CLA lowered (P < 0.05) GPDH activity and the concentration of FA including palmitic acid (16:0) and palmitoleic acid (16:1), especially during the intermediate/late and overall periods, or whenever a high dose of 70 mg/L was applied. This also resulted in a higher (P < 0.05) ratio of saturated FA to monounsaturated FA. Treatment with LA or cis9,trans11-CLA lowered cellular FA only when they applied during the early period at a dose of 70 mg/L. The results demonstrated that the inhibitory effects of CLA on differentiation, GPDH activity, and FA accumulation of 3T3-L1 cells are dependent on the isomer type, treatment period, and dose.

Conjugated linoleic acid and human health: a critical evaluation of the evidence

PURPOSE OF REVIEW

This review critically evaluates studies investigating the effects of conjugated linoleic acid on human health, including effects on body composition, blood lipids, liver metabolism, insulin sensitivity and immune function. It focuses mainly on human intervention studies, but includes some reference to animal and cellular studies which provide insight into potential molecular mechanisms of action of conjugated linoleic acid.

RECENT FINDINGS

Human studies continue to report inconsistent effects of conjugated linoleic acid on human health. Some of these reports are based on overinterpretation of marginal effects of supplementation. Recent data suggest that the effects of the substance may be isomer dependent and that cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acids have opposing effects on blood lipids and on metabolism in adipocytes and hepatic cells.

SUMMARY

Claims that conjugated linoleic acid is beneficial for health remain as yet unconvincing. Human studies investigating the effects of conjugated linoleic acid supplements have tended to use mixtures of isomers and have been inconsistent. More recent studies have attempted to use relatively pure preparations of single isomers and these studies suggest that the effects of conjugated linoleic acid may be isomer-specific. These recent data suggest a relative detrimental effect of trans-10,cis-12 conjugated linoleic acid on blood lipids. There appears to be little effect of conjugated linoleic acid on immune function and the effects on insulin sensitivity remain unclear.

Sulfur-substituted and alpha-methylated fatty acids as peroxisome proliferator-activated receptor activators

FA with varying chain lengths and an alpha-methyl group and/or a sulfur in the beta-position were tested as peroxisome proliferator-activated receptor (PPAR)alpha, -delta(beta), and -gamma ligands by transient transfection in COS-1 cells using chimeric receptor expression plasmids, containing cDNAs encoding the ligand-binding domain of PPARalpha, -delta, and -gamma. For PPARalpha, an increasing activation was found with increasing chain length of the sulfur-substituted FA up to C14-S acetic acid (tetradecylthioacetic acid = TTA). The derivatives were poor, and nonsignificant, activators of PPARdelta. For PPARgamma, activation increased with increasing chain length up to C16-S acetic acid. A methyl group was introduced in the alpha-position of palmitic acid, TTA, EPA, DHA, cis9,trans11 CLA, and trans10,cis12 CLA. An increased activation of PPARalpha was obtained for the alpha-methyl derivatives compared with the unmethylated FA. This increase also resulted in increased expression of the two PPARalpha target genes acyl-CoA oxidase and liver FA-binding protein for alpha-methyl TTA, alpha-methyl EPA, and alpha-methyl DHA. Decreased or altered metabolism of these derivatives in the cells cannot be excluded. In conclusion, saturated FA with sulfur in the beta-position and increasing carbon chain length from C9-S acetic acid to C14-S acetic acid have increasing effects as activators of PPARalpha and -gamma in transfection assays. Furthermore, alpha-methyl FA derivatives of a saturated natural FA (palmitic acid), a sulfur-substituted FA (TTA), and PUFA (EPA, DHA, c9,t11 CLA, and t10,c12 CLA) are stronger PPARalpha activators than the unmethylated compounds.

Effect of abomasal infusions of geometric isomers of 10,12 conjugated linoleic acid on milk fat synthesis in dairy cows

The trans-10,cis-12 isomer of conjugated linoleic acid (CLA) decreases TAG accumulation in 3T3-L1 adipocytes, reduces lipid accretion in growing animals, and inhibits milk fat synthesis in lactating mammals. However, there is evidence to suggest that other FA may also exert antilipogenic effects. In the current experiment, the effects of geometric isomers of 10,12 CLA on milk fat synthesis were examined using four Holstein-British Friesian cows in a 4 x 4 Latin Square experiment with 14-d periods. Treatments consisted of abomasal infusions of skim milk, or skim milk containing trans-10,cis-12 CLA (T1), trans-10,trans-12 CLA (T2), or a mixture of predominantly 10,12 isomers containing (g/l00 g) trans-10,cis-12 (35.0), cis-10,trans-12 (23.2), trans-10,trans-12 (14.9), and cis-10,cis-12 (5.1). CLA supplements were prepared from purified ethyl linoleate and infused as nonesterified FA. Infusions were conducted over a 4-d period with a 10-d interval between treatments and targeted to deliver 4.5 g/d of 10,12 CLA isomers. Compared with the control, trans-10, trans-12 CLA had no effect (P> 0.05) on milk fat yield, whereas treatments T1 and T3 depressed (P < 0.05) milk fat content (19.8 and 22.9%, respectively) and decreased milk fat output (20.8 and 21.3%, respectively). Comparable reductions in milk fat synthesis to 4.14 and 1.80 g trans-10,cis-12/d supplied by treatments T1 and T3 indicate that other 10,12 geometric isomers of CLA have the potential to exert antilipogenic effects. The relative abundance of cis-10,trans-12 CLA in treatment T3 and the low transfer efficiency of this isomer into milk suggest that cis-10,trans-12 CLA was the active component..