Effects of trans-10,cis-12 conjugated linoleic acid and cognates on apolipoprotein B secretion in HepG2 cells

Untargeted GC-MS metabolomics to identify and classify bioactive compounds in Combretum platypetalum subsp. oatesii (Rolfe) Exell (Combretaceae)

INTRODUCTION

Combretum platypetalum is used in traditional African healing practices against different infections. Unfortunately, no scientific knowledge of its phytochemical composition exists, except for the isolation of two compounds from the leaves. Scientific study has been limited to the leaves only, despite the applications of stems and roots in traditional medicine practice and natural product drug discovery programs.

OBJECTIVE

Omics was applied to identify and classify different volatile and semivolatile bioactive compounds in the leaf, stem, and root parts of C. platypetalum. The thermal stability of the plant constituents at 60-65°C extraction temperature by Soxhlet and maceration at room temperature on the type, class, and concentration of compounds in the leaf was further investigated.

METHOD

A GC-MS untargeted metabolomics approach, automated deconvolution by the Automated Mass Spectral Deconvolution and Identification System (AMDIS) for GC-MS data, preprocessing by Metab R, and multivariate statistical data analysis were employed in this study.

RESULTS

A total of 97 phytoconstituents, including 17 bioactive compounds belonging to the terpenoids, flavonoids, long-chain fatty acids, and other unclassified structural arrangements distributed across C. platypetalum, were identified for the first time. A correlation (r = 0.782; P = 0.000) between Soxhlet and maceration extraction methods relative to resolved chromatographic peak areas of metabolites was established.

CONCLUSION

Findings corroborate the reported bio-investigation of its leaf extracts, its traditional uses, and previous findings from the Combretum genus. The results substantiate the possible applications of C. platypetalum in natural product drug discovery and provide a guide for future investigations.

Comparison of the Effect of trans Fatty Acid Isomers on Apolipoprotein A1 and B Secretion in HepG2 Cells

Intake of trans fatty acid (TFA) is believed to change the ratio of low-density lipoprotein (LDL) to high density lipoprotein (HDL) cholesterol in blood, which leads to cardiovascular disease. In this study, thirteen types of TFA including monoene type TFA (trans-octadecenoic fatty acid isomers, t-18:1 isomers), diene type TFA (t9,t12-18:2), and triene type TFA (t-18:3) were added to cultured HepG2 cells to compare the amount of apolipoprotein A1 and B (those relating to levels of HDL and LDL cholesterol in blood, respectively) being secreted. We found that trans-5-18:1 increased the secretion of apolipoprotein B relative to oleic acid (cis-9-18:1, control). Secretion of apolipoprotein B was also increased by t-18:3; however, the amount was not significant compared with that observed in the control. The secretion amount of apolipoprotein B tended to increase with the number of double bonds in TFA among trans-9-18:1, t9,t12-18:2, and t-18:3. The secretion amount of apolipoprotein A1 after TFA treatment was also measured. No significant difference was detected among t-18:1 groups; however, t-18:3 increased the amount significantly compared to that in the control. These results suggest that the effect of TFA isomers on the ratio of LDL to HDL cholesterol in the blood follows a mechanism different from that in cultured cells.

Sources and Bioactive Properties of Conjugated Dietary Fatty Acids

The group of conjugated fatty acids known as conjugated linoleic acid (CLA) isomers have been extensively studied with regard to their bioactive potential in treating some of the most prominent human health malignancies. However, CLA isomers are not the only group of potentially bioactive conjugated fatty acids currently undergoing study. In this regard, isomers of conjugated α-linolenic acid, conjugated nonadecadienoic acid and conjugated eicosapentaenoic acid, to name but a few, have undergone experimental assessment. These studies have indicated many of these conjugated fatty acid isomers commonly possess anti-carcinogenic, anti-adipogenic, anti-inflammatory and immune modulating properties, a number of which will be discussed in this review. The mechanisms through which these bioactivities are mediated have not yet been fully elucidated. However, existing evidence indicates that these fatty acids may play a role in modulating the expression of several oncogenes, cell cycle regulators, and genes associated with energy metabolism. Despite such bioactive potential, interest in these conjugated fatty acids has remained low relative to the CLA isomers. This may be partly attributed to the relatively recent emergence of these fatty acids as bioactives, but also due to a lack of awareness regarding sources from which they can be produced. In this review, we will also highlight the common sources of these conjugated fatty acids, including plants, algae, microbes and chemosynthesis.

Conjugated fatty acids increase energy expenditure in part by increasing voluntary movement in mice

Conjugated linoleic acid (CLA) and conjugated nonadecadienoic acid (CNA) have been previously shown to effectively reduce body fat. However, it is not clear if these effects persist with extended feeding, including potential mechanisms of increased energy expenditure. Thus the current investigation was conducted to determine the influence of dietary conjugated fatty acids on non-exercise form of voluntary movement and lipid and glucose metabolisms for 4-12 week feeding of male mice. CLA and CNA significantly reduced body weight and fat mass by increasing energy expenditure, in part by increasing voluntary movement. CLA and CNA significantly reduced serum leptin and tumour necrosis factor-α, while modulating the mRNA levels of genes associated with lipid and glucose metabolisms. The current results of increased physical activity along with modulation of lipid and glucose metabolisms by conjugated fatty acids will help contribute to future applications of these toward controlling obesity.

Effects of trans-10,cis-12 conjugated linoleic acid on body composition in genetically obese mice

Conjugated linoleic acid (CLA) has shown a number of biologically beneficial effects, including prevention of obesity. The purpose of this study was to test effects of dietary supplementation of 0.5% trans-10,cis-12 CLA in a high fat diet in neuronal basic helix-loop-helix 2 knock-out animals (N2KO), which is a unique animal model representing adult-onset inactivity-related obesity. Eight wild-type (WT) and eight N2KO female mice were fed either 0.5% trans-10,cis-12 CLA-containing diet or control diet (with 20% soybean oil diet) for 12 weeks. Body weights, food intake, adipose tissue weights, body compositions, and blood parameters were analyzed. Overall, N2KO animals had greater body weights, food intake, adipose tissue weights, and body fat compared to WT animals. CLA supplementation decreased overall body weights and total fat, and the effect of dietary CLA on adipose tissue reduction was greater in N2KO than in WT mice. Serum leptin and triglyceride levels were reduced by CLA in both N2KO and WT animals compared to control animals, while there was no effect by CLA on serum cholesterol. The effect of CLA to lower fat mass, increase lean body mass, and lower serum leptin and triglycerides in sedentary mice supports the possibility of using CLA to prevent or alleviate ailments associated with obesity.

Higher immunoglobulin production in conjugated linoleic acid-supplemented rats during gestation and suckling

Conjugated linoleic acid (CLA) has been reported to exert beneficial physiological effects on body composition and the immune system. However, little information is available on the influence of CLA on immune function during early life periods. The present study evaluates the effect of feeding an 80:20 mixture of cis-9, trans-11- and trans-10, cis-12-CLA isomers during gestation and suckling on the systemic immune response of weaned Wistar rats. Pups received dietary CLA from dams through the placental barrier and during suckling by breast milk (group A) or by oral administration (group B). Pups from group C only received CLA during suckling by oral administration. Group D constituted the reference group. Milk from dams fed the CLA diet had a high content of CLA and higher IgA and IgG concentrations than rats fed the standard diet. The plasma of pups from groups A, B and C showed six, twelve and nine times higher content of the cis-9, trans-11-CLA isomer than that of the group D pups. Rats from group A exhibited higher serum IgG concentrations than rats from the rest of the groups (22.14 (SEM 2.14) v. about 5 mg/ml; P < 0.05), whereas rats from groups A and B showed approximately 2-fold higher splenocyte IgM production than rats from groups C and D. However, CLA supplementation did not influence significantly the splenocyte proliferative response or cytokine secretion. Supplementation during gestation and suckling with an 80:20 cis-9, trans-11-trans-10, cis-12 CLA mix enhances the production of the main in vivo and in vitro Ig isotypes in Wistar rats.

The effect of trans-10, cis-12 conjugated linoleic acid on gene expression profiles related to lipid metabolism in human intestinal-like Caco-2 cells

We conducted an in-depth investigation of the effects of conjugated linoleic acid (CLA) on the expression of key metabolic genes and genes of known importance in intestinal lipid metabolism using the Caco-2 cell model. Cells were treated with 80 mumol/L of linoleic acid (control), trans-10, cis-12 CLA or cis-9, trans-11 CLA. RNA was isolated from the cells, labelled and hybridized to the Affymetrix U133 2.0 Plus arrays (n = 3). Data and functional analysis were preformed using Bioconductor. Gene ontology analysis (GO) revealed a significant enrichment (P < 0.0001) for the GO term lipid metabolism with genes up-regulated by trans-10, cis-12 CLA. Trans-10, cis-12 CLA, but not cis-9, trans-11 CLA, altered the expression of a number of genes involved in lipid transport, fatty acid metabolism, lipolysis, beta-oxidation, steroid metabolism, cholesterol biosynthesis, membrane lipid metabolism, gluconeogenesis and the citrate cycle. These observations warrant further investigation to understand their potential role in the metabolic syndrome.

Effect of conjugated linoleic acid on bone formation and rheumatoid arthritis

Conjugated linoleic acid (CLA) has shown a variety of biologically beneficial effects. Dietary CLA inhibits eddosteal bone resorption, increases endocortical bone formation, and modulates the action and expression of cyclooxygenase (COX) enzyme, thereby decreasing prostaglandin-dependent bone resorption. CLA also enhances calcium absorption and may improve bone formation in animals, although results are not consistent. Since CLA can also affect inflammatory cytokines, it is hypothesized that CLA may be a good tool for prevention or reduction of rheumatoid arthritis symptoms. The possible mechanisms by which CLA prevents rheumatoid arthritis as well as other inflammatory diseases is discussed.

Effects of trans-10,cis-12 conjugated linoleic acid on cholesterol metabolism in hypercholesterolaemic hamsters

BACKGROUND

Conjugated linoleic acid (CLA) has received great attention in recent years because of its pleiotropic biological activities, but considerably fewer studies have been published addressing its role in serum lipids and atherosclerosis compared to other topics covered.

AIMS OF THE STUDY

The aim of the present study was to assess the effects of the trans-10,cis-12 isomer of CLA on cholesterolaemia and on several metabolic pathways involved in cholesterol metabolism in hamsters.

METHODS

Animals were fed atherogenic diets supplemented with 0.5% linoleic acid, 0.5% trans-10,cis-12 CLA or 1.0% trans-10,cis-12 CLA, for 6 weeks. Serum lipoproteins were separated by FPLC. Cholesterol in serum and liver, as well as triacylglycerols and phospholipids in liver were assessed by spectrophotometry. 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCoAR), acyl-coenzyme A:cholesterol acyltransferase (ACAT) and cholesteryl ester hydrolase (CEH) activities were measured by radiometry, and LDL receptors were determined by Western blot.

RESULTS

trans-10,cis-12 CLA feeding did not modify food intake nor final body weight. Although serum total cholesterol remained unchanged, when cholesterol fractions were analyzed a significant decrease in VLDL-cholesterol was observed in CLA-fed animals, without changes in HDL-cholesterol or LDL-cholesterol. trans-10,cis-12 CLA decreased cholesterol ester content and increased free cholesterol in liver. The activity of HMGCoAR was not modified. In contrast, ACAT activity was reduced by both CLA doses and CEH was increased by the high CLA dose. LDL receptors were significantly reduced by trans-10,cis-12 feeding when expressed as arbitrary units per mg of protein, however, the total receptor mass remained unchanged.

CONCLUSIONS

These results suggest that, under the present experimental conditions, trans-10,cis-12 CLA feeding reduces cholesterol esterification in liver and decreases the minority serum VLDL-cholesterol fraction, but it does not show a hypocholesterolaemic effect. A dose-response effect was not observed.

trans-10,cis-12 Conjugated linoleic acid inhibits lipoprotein lipase but increases the activity of lipogenic enzymes in adipose tissue from hamsters fed an atherogenic diet

The aim of the present work was to investigate the effects of trans-10,cis-12 conjugated linoleic acid (CLA) on the activity and expression of lipogenic enzymes and lipoprotein lipase (LPL), as well as on the expression of transcriptional factors controlling these enzymes, in adipose tissue from hamsters, and to evaluate the involvement of these changes in the body fat-reducing effect of this CLA isomer. Thirty male hamsters were divided into three groups and fed atherogenic diets supplemented with 0 (linoleic group), 5 or 10 g trans-10,cis-12 CLA/kg diet, for 6 weeks. Body and adipose tissue weights, food intake and serum insulin were measured. Total and heparin-releasable LPL and lipogenic enzyme activities (acetyl-CoA carboxylase (ACC); fatty acid synthase (FAS); glucose-6-phosphate dehydrogenase (G6PDH); and malic enzyme (ME)) were assessed. ACC, FAS, LPL, sterol regulatory element-binding proteins (SREBP-1a), SREBP-1c and PPARgamma mRNA levels were also determined by real-time PCR. CLA did not modify food intake, body weight and serum insulin level. CLA feeding reduced adipose tissue weight, LPL activity and expression, and increased lipogenic enzyme activities, despite a significant reduction in ACC and FAS mRNA levels. The expression of the three transcriptional factors analysed (SREBP-1a, SREBP-1c and PPARgamma) was also reduced. These results appear to provide a framework for partially understanding the reduction in body fat induced by CLA. Inhibition of LPL activity seems to be an important mechanism underlying body fat reduction in hamsters. Further research is needed to better characterize the effects of CLA on lipogenesis and the role of these effects in CLA action.

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.