Conjugated linoleic acid and bone biology

Dietary conjugated linoleic acid reduces PGE2 release and interstitial injury in rat polycystic kidney disease

BACKGROUND

Conjugated linoleic acid (CLA) describes positional isomers of linoleic acid (LA). Experimental health benefits of CLA include amelioration of malignancy and inflammatory disease and reduction of adiposity. The Han:SPRD-cy rat model of polycystic kidney disease (PKD) features prominent renal interstitial inflammation and fibrosis that is amenable to dietary modification. We studied CLA supplementation in the modification of inflammatory outcomes in the Han:SPRD-cy rat.

METHODS

Male offspring of Han:SPRD-cy heterozygotes were fed diets, using corn oil or corn oil with a CLA enriched oil (1% of diet by weight as CLA). After 8 weeks, measurements included renal function and morphometry, ex vivo release of renal prostaglandin E2 (PGE2), and renal and hepatic tissue fatty acid profiles.

RESULTS

Urine creatinine was significantly higher in PKD animals fed CLA (P = 0.004), but differences in serum creatinine and creatinine clearance did not quite reach significance in PKD animals. CLA feeding reduced interstitial inflammation (P < 0.001), fibrosis (P = 0.03), and renal PGE2 release (P = 0.02). Cystic change and oxidized low-density lipoprotein (LDL) staining did not change significantly. CLA feeding produced increased renal and hepatic CLA isomers. Hepatic, but not renal, LA proportion was reduced on the CLA diet. The renal proportion of the PGE2 precursor, arachidonic acid (AA), was not changed by diet, but hepatic AA proportion increased significantly with CLA feeding (P= 0.009).

CONCLUSION

CLA reduces renal production of PGE2, without reduced availability of the precursor fatty acid, AA. Short-term feeding of CLA to Han:SPRD-cy rats also has significant renal anti-inflammatory and antifibrotic effects. As inflammation and fibrosis are important components of the progression of chronic renal injury, CLA may be a useful agent in dietary amelioration of renal disease.

Isomer-specific regulation of metabolism and PPARgamma signaling by CLA in human preadipocytes

Trans-10,cis-12 conjugated linoleic acid (CLA) has previously been shown to be the CLA isomer responsible for CLA-induced reductions in body fat in animal models, and we have shown that this isomer, but not the cis-9,trans-11 CLA isomer, specifically decreased triglyceride (TG) accumulation in primary human adipocytes in vitro. Here we investigated the mechanism behind the isomer-specific, CLA-mediated reduction in TG accumulation in differentiating human preadipocytes. Trans-10,cis-12 CLA decreased insulin-stimulated glucose uptake and oxidation, and reduced insulin-dependent glucose transporter 4 gene expression. Furthermore, trans-10,cis-12 CLA reduced oleic acid uptake and oxidation when compared with all other treatments. In parallel to CLA's effects on metabolism, trans-10,cis-12 CLA decreased, whereas cis-9,trans-11 CLA increased, the expression of peroxisome proliferator-activated receptor gamma (PPARgamma) and several of its downstream target genes when compared with vehicle controls. Transient transfections demonstrated that both CLA isomers antagonized ligand-dependent activation of PPARgamma. Collectively, trans-10,cis-12, but not cis-9, trans-11, CLA decreased glucose and lipid uptake and oxidation and preadipocyte differentiation by altering preadipocyte gene transcription in a manner that appeared to be due, in part, to decreased PPARgamma expression.

Conjugated linoleic acid decreases fat accretion in pigs: evaluation by dual-energy X-ray absorptiometry

Thirty female Large White x Landrace pigs (average weight 57.2 (sd 1.9) kg) were allocated to one of six dietary treatments containing 0, 1.25, 2.5, 5.0, 7.5 or 10.0 g 55 % conjugated linoleic acids (CLA) isomers (CLA-55)/kg diet and fed for 8 weeks. Each pig was scanned at 0, 28 and 56 d and again at post slaughter using dual-energy X-ray absorptiometry (DXA) to determine the temporal pattern of body composition responses. Values determined by DXA were adjusted using regression equations generated from validation experiments between chemically and DXA-predicted values. Overall, there was a significant linear reduction in fat content with the increasing levels of CLA in the diet (P=0.007, P=0.011, P=0.008 at week 4, week 8 and for the carcass, respectively). The greatest improvement was recorded at the early stages of CLA supplementation and for the highest dose of CLA (week 4, -19.2 % compared with week 8, -13.7 %). In the first 4 weeks of feeding CLA, pigs receiving 10 g CLA-55/kg diet deposited 93 g less fat/d than pigs fed basal diets (P=0.002) compared with only 6 g less fat than control animals in the final 4 weeks. Lean content and lean deposition rate were maximised at 5 and 2.5 g CLA-55/kg diet for the first 4 weeks (P=0.016) and the final 4 weeks of treatment respectively. DXA estimates of bone mineral content and bone mineral density were not affected by CLA supplementation throughout the experiment. These data demonstrate that dietary CLA decreases body fat in a dose-dependent manner and that the response is greatest over the initial 4 weeks of treatment.

Effects of conjugated linoleic acid on anaphylaxis and allergic pruritus

The effects of conjugated linoleic acid (CLA) against anaphylaxis and allergic pruritus were investigated using a in vivo assay. Inhibitory effects of CLA were observed on the immediate (type 1) hypersensitivity reaction, with CLA significantly suppressing the decrease in blood pressure (BP) and blood flow (BF) induced by the hen egg-white lysozyme (HEL)-anaphylactic reaction in ddY mice. After oral administration, CLA showed antipruritic activity, with significant inhibition of scratching behavior induced by compound 48/80 (COM), a histamine-release agent. When painted onto the skin, CLA also inhibited COM, platelet-activating factor, and protease-induced scratching behavior, and COM-induced vasodilation of the skin. CLA offers promise as a drug for the treatment of allergic and inflammatory pruritus not only as an oral but also a topical agent. The present findings demonstrate that CLA can be effective for the prevention and treatment of allergic disease with severe pruritus.

Conjugated linoleic acid decreases production of pro-inflammatory products in macrophages: evidence for a PPAR gamma-dependent mechanism

Conjugated linoleic acid (CLA) is a dietary fatty acid that has received considerable attention due to its unique properties in rodent models including anti-cancer, anti-atherogenic and anti-diabetic effects. The effects of CLA are similar to those seen with ligands for peroxisome proliferator-activated receptor (PPARs), most notably of the PPAR gamma subtype. With the recent observation of a role for PPAR gamma in regulation of immune responses, we suspected that CLA could affect immune function, in particular macrophage activity. The goal of our study was to examine whether this dietary fatty acid has anti-inflammatory properties similar to those reported for PPAR gamma activators such as 15-deoxy prostaglandin J(2) (PGJ(2)). In reporter assays, various CLA isomers activated PPAR gamma in RAW264.7 mouse macrophage (RAW) cells. CLA decreased the interferon-gamma (IFN gamma)-induced mRNA expression of mediators of inflammation including cyclooxygenase 2 (COX2), inducible NOS (iNOS), and tumor necrosis factor alpha (TNFalpha). Reporter assays also demonstrated reduced IFN gamma-stimulated transcriptional activity of the iNOS and COX2 promoters by CLA. Consequently, CLA decreased the production of PGE(2), TNFalpha and the inflammatory agent nitric oxide (NO) in RAW cells treated with IFN gamma. Other pro-inflammatory cytokines such as IL-1 beta and IL-6 were similarly decreased by CLA treatment of RAW cells. In addition, various CLA isomers induced HL60 cell differentiation along the monocytic lineage as assessed by measuring expression of the cell surface marker CD14. This differentiation process, as well as the regulation of iNOS and COX2 by 15dPGJ(2), is believed to involve PPAR gamma. Mutations of Leu(468) and Glu(471) to alanine in helix 12 of the ligand-binding domain of PPAR gamma resulted in a protein with strong dominant-negative activity (dnPPAR gamma). Transfecting dnPPAR gamma into RAW cells eliminated the ability of various CLA isomers to regulate the iNOS reporter construct. Taken together, these results suggest that CLA has anti-inflammatory properties that are mediated, at least in part, by the nuclear hormone receptor PPAR gamma.