J. Dairy Sci. 89:3826-3832
© American Dairy Science Association, 2006.
Conjugated Linoleic Acid Reduces Phorbol Ester-Induced Prostaglandin F2
Production by Bovine Endometrial Cells1
C. Rodriguez-Sallaberry,
C. Caldari-Torres,
E. S. Greene and
L. Badinga2
Department of Animal Sciences University of Florida, Gainesville 32611
2 Corresponding author: Badinga{at}animal.ufl.edu
 |
ABSTRACT
|
|---|
Recent interest in conjugated linoleic acid (CLA) research stems from the well-documented anticarcinogenic, antiatherogenic, antidiabetic, and antiobesity properties of CLA in animal models. The objective of this study was to examine the effects of 2 CLA isomers (cis-9,trans-11 and trans-10,cis-12) on phorbol 12,13-dibutyrate (PDBu)-induced PGF2
production in cultured bovine endometrial (BEND) cells. Confluent BEND cells were incubated in the absence (control) or presence of 100 µM each of linoleic acid, cis-9,trans-11 CLA, or trans-10,cis-12 CLA for 24 h. After incubation, cells were rinsed and then stimulated with PDBu (100 ng/mL) for 6 h. Compared with untreated cells, PDBu stimulated PGF2 secretion (+25-fold) within 6 h. The increases in PGF2 secretion were paralleled by signifi-cant induction of prostaglandin endoperoxide synthase-2 (PGHS-2) mRNA (+63-fold) and protein (+1.6-fold) expression. In spite of stimulatory effects on PGHS-2 and peroxisome proliferator-activated receptor 
(PPAR) mRNA responses, CLA greatly decreased PGF2 production by PDBu-stimulated BEND cells. There was no evidence for PDBu or CLA modulation of PPAR protein synthesis in cultured BEND cells. Results indicated that CLA modulation of PGF2 production by BEND cells was not mediated through PGHS-2 or PPAR gene repression.
Key Words: conjugated linoleic acid • uterus • prostaglandin F2 • cow
|
INTRODUCTION
|
|---|
Prostaglandin endoperoxide synthase (PGHS) is a rate-limiting enzyme that catalyzes the initial step of prostaglandin (PG) biosynthesis from arachidonic acid (Dubois et al., 1993; Herschman, 1996). This enzyme is encoded by 2 separate genes, PGHS-1 and PGHS-2, both of which participate in the formation of a variety of eicosanoids, including PGD2, PGE2, PGF2, PGI2, and thromboxane A. Prostaglandin endoperoxide synthase-1 is expressed constitutively, whereas PGHS-2 is an inducible early gene that is upregulated by various stimuli, including cytokines, growth factors, and tumor promoters (Kujubu et al., 1991; Dubois et al., 1994; Arslan and Zingg, 1996). Prostaglandin endoperoxide synthase-2 is readily expressed in bovine endometrial (BEND) cells and is thought to mediate phorbol 12,13-dibutyrate (PDBu)-induced PG synthesis in endometrial cells (Binelli et al., 2000; Badinga et al., 2002; Mattos et al., 2003). The BEND cells possess characteristics typical of uterine epithelial cells, with a cobblestone appearance and expression of cytokeratin, and therefore constitute an excellent model for examining dietary regulation of PGF2 production in reproductive tissues.
Conjugated linoleic acid (CLA) is a collective term describing a mixture of positional and geometric dienoic isomers of linoleic acid (LA; 18:2). To date, up to 17 CLA isomers have been described, with double bonds ranging in position from carbons 6 and 8 to carbons 12 and 14 (Dhiman et al., 2005). Unlike naturally occurring unsaturated fatty acids, the double bonds in CLA occur on adjacent carbons and are not separated by a methylene group. Essentially all cis- and trans-isomeric conformations of CLA have been identified in food. However, the predominant CLA in ruminant fats is the cis-9,trans-11 (c9,t11) isomer, which accounts for more than 80% of total CLA isomers in dairy products and 75% of those in beef fats (Chin et al., 1992). This isomer originates from CLA produced by rumen bacteria as an intermediate in the biohydrogenation of LA or from tissue synthesis of CLA by 
9-desaturase conversion of trans-11 18:1 fatty acid (vaccenic acid; Dhiman et al., 2005). Although available evidence indicates that CLA attenuates PG production in mammalian species (Harris et al., 2001; Urquhart et al., 2002), the mechanism by which CLA alters endometrial PG biosynthesis is not fully understood.
Peroxisome proliferator-activated receptors (PPAR) are ligand-activated transcription factors that regulate multiple physiological processes, including inflammation, development, and lipid metabolism (Escher and Wahli, 2000). Tissue distribution of PPAR and PPAR
gene transcripts indicates that they play roles in fatty acid catabolism and adipogenesis, respectively (Braissant et al., 1996). Much less is known about the function and regulation of PPAR, although it is highly expressed in the brain, colon, and skin (Braissant et al., 1996). We recently detected an inverse relationship between PPAR and uterine expression of bovine estrogen receptor and PGHS-2 genes (Balaguer et al., 2005), suggesting that this nuclear receptor subtype may play an important role in the control of reproductive processes in domestic mammals.
Given the lack of information relating uterine components of the PG cascade and supplemental CLA, the objectives of this study were 1) to examine the effects of 2 CLA isomers on PDBu-induced PGF2 production and 2) to determine the relationships between supplemental CLA and endometrial expression of PGHS-2 and PPAR genes.
|
MATERIALS AND METHODS
|
|---|
Materials
Polystyrene tissue culture dishes (100 x 20 mm) were purchased from Corning (Corning Glass Works, Corning, NY). The Hams F-12 medium, antibiotic/antimycotic, PDBu, horse serum, D-valine, insulin, fatty acid-free BSA, aprotinin, leupeptin, and pepstatin were from Sigma Chemical Co. (St. Louis, MO). The minimum essential medium and fetal bovine serum were from US Biologicals (Swampscott, MA) and Atlanta Biologicals (Norcross, GA), respectively. Linoleic acid, c9,t11 CLA, trans-10,cis-12 (t10,c12) CLA, PGHS-2 antibody, and PGF2 standard were from Cayman Chemicals (Ann Arbor, MI). The PPAR and secondary antirabbit IgG antibodies were from Santa Cruz Biotechnology (Santa Cruz, CA). The enhanced chemiluminescence kit was purchased from PerkinElmer (Boston, MA). Hanks’ balanced salt solution (HBSS) and TriZol reagent were from Gibco BRL (Carlsbad, CA). Isotopically-labeled PGF2 (5,6,8,9,11,12,14,15[n-3H]PGF2; 208 Ci/mmol) was from Amershan Biosciences (Piscataway, NJ). The anti-PGF2 antibody was purchased from Oxford Biomedicals (Oxford, MI). BioTrans nylon membrane and [-32P]deoxycitidine triphosphate (SA 3,000 Ci/nmol) were from MP Biomedicals (Atlanta, GA). The PGHS-2 cDNA probe was cloned from an ovarian follicular cDNA library (Liu and Belury, 1998), whereas the PPAR probe was generated from bovine endometrial RNA (Balaguer et al., 2005).
Cell Culture and Treatment
Immortalized BEND cells (American Type Culture Collection # CRL-2398, Manassas, VA) were suspended (0.5 x 106 cells/mL) in growth medium (40% Hams F-12, 40% minimum essential medium, 1% antibiotic/ antimycotic, 200 U/L of insulin, 0.343 g/L of D-valine, 10% heat-inactivated fetal bovine serum, and 10% horse serum) and incubated at 37°C in a 95% air–5% CO2 environment. Each culture was replenished with fresh medium on the second and fourth day after seeding, and cells reached confluence after 4 to 5 d of culture.
To examine the effects of supplemental CLA on uterine PGF2 production, BEND cells were treated with PDBu alone (100 ng/mL) or PDBu in combination with 100 µM of LA, c9,t11 CLA, or t10,c12 CLA (Figure 1
). Fatty acids were complexed with BSA (1:3 ratio) for 2 h, and then treatments were applied to cells for a 24-h period. After the 24-h exposure to fatty acids, cells were rinsed with HBSS and challenged with PDBu for another 6 h. Cell-conditioned media were collected and stored at –20°C for subsequent PGF2 radioimmunoassay. The remaining cell monolayer was rinsed with HBSS, lysed in TriZol reagent, and stored at –80°C for subsequent mRNA analysis.
PGF2 Radioimmunoassay
The PGF2 concentration in cell-conditioned media was measured in duplicate as described by Binelli et al. (2000). Assay sensitivity was 0.1 ng/mL and intra-and interassay coefficients of variation were 8.2 and 15.8%, respectively. Final PGF2 concentrations were expressed as picograms per milliliter of media because the total cell numbers did not vary among Petri dishes (Caldari-Torres et al., 2006).
RNA Isolation and Analysis
Total cellular RNA was isolated from control and treated BEND cell cultures using TriZol reagent according to the manufacturer’s instructions. Ten micrograms of RNA was fractionated in 1.0% agarose–formaldehyde gel and blotted to a BioTrans nylon membrane by capillary action. The RNA was cross-linked to the membrane by UV irradiation and baked at 80°C for 1 h. The RNA filters were hybridized consecutively with random primer-labeled PGHS-2 and PPAR cDNA probes. The PGHS-2 cDNA probe was a gift from Jean Sirois (Université de Montreal, St-Hyacinthe, Canada), whereas the cDNA probe for PPAR was generated using a set of primers (forward: 5'-CACTCTCACTGCTG GACAA-3'; reverse: 5'-TGCGGTTCTTCTTCTGGATT-3') designed from the bovine gene sequence (GenBank accession number: AF 229357). The size (216 bp) and identity of the PCR product were further verified by DNA sequencing before its use in Northern blot analyses. After hybridization, RNA filters were washed for 20 min in 50 mL of 2x saline sodium citrate–0.1% SDS at room temperature, followed by two 15-min washes in 0.1x saline sodium citrate–0.1% SDS at 42°C. The filters were blotted dry and exposed to X-ray films for 6 to 24 h at –80°C. Hybridization signals for each target gene were quantified by densitometric analysis and are reported as ratios of target gene values over the corresponding 18S rRNA values.
Western Blot Analysis of PGHS-2 and PPAR
For Western blot analyses, whole cell lysates were prepared as described by Binelli et al. (2000). Briefly, 500 µL of ice-cold whole cell extract buffer (50 mM Tris, pH 8.0; 300 mM NaCl; 20 mM NaF; 1 mM Na3VO4; 1 mM Na4P2O7; 1 mM EDTA; 1 mM ethylene glycolbis 2 aminoethylether-N,N,N',N'-tetraacetic acid; 1 mM dithiothreitol; 0.5 mM phenylmethanesulfonyl fluoride; 10% vol/vol glycerol, 0.5% vol/vol Nonidet P-40, and 10 µg/mL each of aprotinin, leupeptin, and pepstatin) were added to each dish and cells were collected in 1.5-mL microcentrifuge tubes and incubated for 30 min at 4°C. Cell lysates were centrifuged at 4°C for 2 min (13,000 x g) to remove cell debris. Protein concentration in the supernatant was determined by the method of Lowry et al. (1951). Protein (25 µg) from each dish was resolved on a 7.5% SDS-PAGE, and electrophoretically transferred to a nitrocellulose membrane. The membrane was blocked for 2 h in 5% (wt/vol) nonfat dried milk in Tris-buffered saline (TBS) containing 0.1% Tween-20 (pH 7.4), rinsed with TBS containing 0.1% Tween-20, and hybridized with antibodies against either PGHS-2 or PPAR diluted (1:500) in TBS containing 5% nonfat dried milk. Target proteins were detected by enhanced chemiluminescence and the relative abundance of each protein was quantified by densitometric analysis (Kodak EDAS 290; Kodak, Rochester, NY).
Statistical Analyses
Prostaglandin F2, mRNA, and protein responses were analyzed using the GLM procedure in the SAS software package (SAS Institute Inc., Cary, NC). For PGF2 concentration, the sources of variation included experiment, treatment, experiment x treatment interaction, and dish (experiment x treatment). The dish nested within experiment and treatment was considered a random variable; therefore, the dish variance was used as an error term to test the effects of experiment, treatment, and experiment x treatment interaction. For PGHS-2 and PPAR mRNA responses, the statistical models included experiment, treatment, and experiment x treatment interaction. Densitometric values for each target gene were expressed as ratios over the values for 18S ribosomal RNA. For Western blot analysis, the statistical model included only the main effect of treatment. For all responses, when treatment effects were detected (P < 0.05), means were separated using preplanned orthogonal contrasts.
|
RESULTS
|
|---|
Stimulation of BEND cells with PDBu increased (P < 0.01) PGF2 production by 23-fold (Figure 2A). The increase in PGF2 production coincided with marked induction (P < 0.01) of PGHS-2 mRNA (Figure 2B) and PGHS-2 protein (Figure 2C) expression. Conversely, treatment with PDBu had no detectable effect on PPAR mRNA (Figure 3A) or PPAR protein (Figure 3B) concentrations in cultured BEND cells.
View larger version (34K):
[in this window]
[in a new window]
|
Figure 2. Effect of phorbol 12,13-dibutyrate (PDBu) on PGF2 (A), prostaglandin endoperoxide synthase-2 (PGHS-2) mRNA (B), and PGHS-2 protein (C) concentrations in cultured bovine endometrial cells. For Northern and Western blot analyses, the top panel shows a representative Northern or Western blot, whereas the bottom panel represents means ± SEM calculated over 2 experiments (n = 4 for each treatment). Asterisks above histograms indicate differences between treatments (P < 0.01).
|
|
Preincubation of BEND cells with CLA, and not LA, reduced (P < 0.01) the PGF2 response to PDBu by 24% (Figure 4). The 2 CLA isomers were equally potent in decreasing the PGF2 response to PDBu (Figure 4). The concentration of PGHS-2 mRNA transcript was greater (P < 0.01) in BEND cells cotreated with PDBu and the 3 fatty acids than in the cells treated with PDBu alone (Figure 5A). The fatty acid treatment had a negligible effect on PGHS-2 protein response to PDBu (Figure 5B). The relative abundance of PPAR mRNA transcript was greater (P < 0.01) in BEND cells coincubated with PDBu and fatty acids than in those treated with PDBu alone (Figure 6A). None of the fatty acids studied had detectable effects on the PPAR protein concentration in PDBu-stimulated BEND cells (Figure 6B).
View larger version (27K):
[in this window]
[in a new window]
|
Figure 4. Effect of linoleic acid (LA) and conjugated linoleic acid (CLA) isomers [cis-9,trans-11 (c9,t11) and trans-10,cis-12 (t10,c12)] on PGF2 response to phorbol 12,13-dibutyrate (PDBu) in cultured bovine endometrial cells. Treatment means were compared using preplanned orthogonal contrasts. Contrast 1: PDBu vs. (LA + c9,t11 + t10,c12), P < 0.01. Contrast 2: LA vs. CLA (c9,t11 + t10,c12), P < 0.01. Contrast 3: c9,t11 CLA vs. t10,c12 CLA, P = 0.4.
|
|
View larger version (46K):
[in this window]
[in a new window]
|
Figure 5. Effects of linoleic acid (LA) and conjugated linoleic acid (CLA) on prostaglandin endoperoxide synthase-2 (PGHS-2) mRNA (A) and PGHS-2 protein (B) responses to phorbol 12,13-dibutyrate (PDBu) in bovine endometrial cells. For each response, the top panel shows a representative Northern or Western blot, whereas the bottom panel represents means ± SEM calculated over 2 experiments (n = 4 for each treatment). Treatment means were compared using pre-planned orthogonal contrasts. For PGHS-2 mRNA, contrast 1: PDBu vs. [LA + cis-9,trans-11 CLA (c9,t11) + trans-10,cis-12 CLA (t10,c12)], P < 0.01. Contrast 2: LA vs. CLA (c9,t11 + t10,c12), P < 0.01. Contrast 3: c9,t11 CLA vs. t10,c12 CLA, P < 0.01. For PGHS-2 protein, contrast 1: PDBu vs. (LA + c9,t11 CLA + t10,c12 CLA), P = 0.2. Contrast 2: LA vs. CLA (c9,t11 + t10,c12), P = 0.2. Contrast 3: c9,t11 CLA vs. t10,c12 CLA, P = 0.3.
|
|
View larger version (46K):
[in this window]
[in a new window]
|
Figure 6. Effects of linoleic acid (LA) and conjugated linoleic acid (CLA) on peroxisome proliferator-activated receptor (PPAR) mRNA (A) and PPAR protein (B) responses to phorbol 12,13-dibutyrate (PDBu) in bovine endometrial cells. For each response, the top panel shows a representative Northern or Western blot, whereas the bottom panel represents means ± SEM calculated over 2 experiments (n = 4 for each treatment). Treatment means were compared using pre-planned orthogonal contrasts. For PPAR mRNA, contrast 1: PDBu vs. [LA + cis-9,trans-11 CLA (c9,t11) + trans-10,cis-12 CLA (t10,c12)], P < 0.01. Contrast 2: LA vs. CLA (c9,t11 + t10,c12), P < 0.05. Contrast 3: c9,t11 CLA vs. t10,c12 CLA, P < 0.01. For PPAR protein, PDBu vs. (LA + c9,t11 CLA + t10,c12 CLA), P = 0.4. Contrast 2: LA vs. CLA (c9,t11 + t10,c12), P = 0.2. Contrast 3: c9,t11 CLA vs. t10,c12 CLA, P = 0.2.
|
|
|
DISCUSSION
|
|---|
Conjugated linoleic acid is a collective term describing a mixture of positional and geometric isomers of LA. They occur naturally in ruminant fats and dairy products and have been shown to reduce the incidence of tumors, activate the immune function, reduce body fat deposition, and increase feed efficiency and growth in animal models (Pariza et al., 2001). Results of this study extend previous observations that supplemental CLA reduces eicosanoid production in mammalian models (Whigham et al., 2002; Ogborn et al., 2003; Cheng et al., 2003). The effect was CLA-specific because LA, the parent molecule of CLA, had no detectable effect on PGF2 response to PDBu.
The mechanism underlying CLA inhibition of PG production is not fully understood and may involve more than one pathway. Banni et al. (1999) reported that CLA supplementation of rat mammary tissue increased the accumulation of CLA metabolites at the expense of LA metabolites in the tissue. Because CLA metabolites are potent inhibitors of PGHS-2 and lipoxygenase enzymes (Nugteren and Christ-Hazelhof, 1987), it has been suggested that supplemental CLA may reduce PG production, in part by inhibiting PGHS-2 enzyme activity in cultured mammalian cells. In addition, polyunsaturated fatty acids do not alter phospholipase A2 protein levels in BEND cells (Mattos et al., 2003), suggesting that CLA may compete with arachidonic acid for interaction with PGHS-2. Other studies have indicated that supplemental CLA may compete with LA in elongation and desaturation steps in the synthesis of arachidonic acid, the major precursor of PGE2 and PGF2 (Thompson et al., 1997; Liu and Belury, 1998). In support of this hypothesis, incubation of murine keratinocytes with CLA reduced the content of arachidonic acid in cells, whereas LA increased the arachidonic acid content. The decreased arachidonic acid content in CLA-treated cells was associated with a marked decrease in PGE2 production, whereas LA enhanced PGE2 production (Liu and Belury, 1998).
In addition to decreasing the arachidonic acid content in the cell, CLA may have effects at the level of gene expression. Consistent with this hypothesis, Iwakiri et al. (2002) showed that CLA supplementation greatly reduced mRNA abundance of PGHS-2 and inducible nitric oxide synthase in activated macrophages. The authors postulated that CLA may inhibit cellular PGHS-2 gene expression through inactivation of nuclear factor 
ß. It is unlikely that this mechanism of gene repression is functional in BEND cells, because CLA failed to attenuate PGHS-2 mRNA response in PDBu-stimulated BEND cells. The observation that CLA up-regulated PGHS-2 gene expression in BEND cells is consistent with a previous report (Nakanishi et al., 2003), and suggests that, in this cell type, CLA modulation of PG production may involve posttranscriptional modification of PGHS-2 activity. This hypothesis does not rule out the possibility that the substrate availability for PG biosynthesis may also be limiting in CLA-treated BEND cells.
Our laboratory recently reported an inverse relationship between PPAR and estrogen receptor and PGHS-2 mRNA concentrations in bovine endometrial tissues collected from d 3 and 7 cyclic Holstein cows (Balaguer et al., 2005). Therefore, we sought to examine whether CLA-induced attenuation of PGF2 production by BEND cells may be associated with altered PPAR mRNA or protein synthesis. Priming of BEND cells with c9,t11 and t10,c12 CLA isomers enhanced PPAR mRNA response to PDBu, but had no detectable effect on the PPAR protein concentration. There was no apparent relationship between PPAR mRNA content and PGF2 concentration in control or PDBu-treated cells. These findings suggest that PPAR is probably not the major mediating factor in CLA-mediated reduction of uterine eicosanoid production in cattle.
|
CONCLUSIONS
|
|---|
Priming of BEND cells with c9,t11 and t10,c12 CLA isomers greatly decreased the PGF2 response to PDBu. This inhibitory effect was CLA specific, because LA, the parent molecule of CLA, had a negligible effect on the endometrial PGF2 response to PDBu. Coincubation with both CLA isomers enhanced PGHS-2 and PPAR mRNA responses to PDBu, suggesting that these fatty acids alter PGF2 production through a mechanism that does not involve PGHS-2 or PPAR gene repression. Further studies are needed to test whether CLA isomers affect the activity of various enzymes and transcription factors involved in the PG biosynthetic cascade.
|
FOOTNOTES
|
|---|
1 This manuscript is published as part of the Journal Series of the University of Florida Agriculture Experiment Station. 
Received for publication February 26, 2006.
Accepted for publication April 24, 2006.
|
REFERENCES
|
|---|
Arslan, A., and H. H. Zingg. 1996. Regulation of COX-2 gene expression in rat uterus in vivo and in vitro. Prostaglandins 52:217–219.
Badinga, L., A. Guzeloglu, and W. W. Thatcher. 2002. Bovine somatotropin attenuates phorbol ester-induced prostaglandin F2 production in bovine endometrial cells. J. Dairy Sci. 85:537–543.[Abstract]
Balaguer, S. A., R. A. Pershing, C. Rodriguez-Sallaberry, W. W. Thatcher, and L. Badinga. 2005. Effects of bovine somatotropin on uterine genes related to the prostaglandin cascade in lactating dairy cows. J. Dairy Sci. 88:543–552.[Abstract/Free Full Text]
Banni, S., E. Angioni, V. Casu, M. P. Melis, G. Carta, F. P. Corongiu, H. Thompson, and C. Ip. 1999. Decrease in linoleic acid metabolites as a potential mechanism in cancer risk reduction by conjugated linoleic acid. Carcinogenesis 20:1019–1024.[Abstract/Free Full Text]
Binelli, M., A. Guzeloglu, L. Badinga, D. R. Arnold, J. Sirois, T. R. Hansen, and W. W. Thatcher. 2000. Interferon-
modulates phorbol ester-induced production of prostaglandin and expression of cyclooxygenase-2 and phospholipase-A2 from bovine endometrial cells. Biol. Reprod. 63:417–424.[Abstract/Free Full Text]
Braissant, O., F. Foufelle, C. Scotto, M. Dauca, and W. Wahli. 1996. Differential expression of peroxisome proliferator-activated receptors (PPARs): Tissue distribution of PPAR-, -ß, and - in the adult rat. Endocrinology 137:354–366.[Abstract]
Caldari-Torres, C., C. Rodriguez-Sallaberry, E. S. Greene, and L. Badinga. 2006. Differential effects of omega-3 and omega-6 fatty acids on prostaglandin F2 production by bovine endometrial cells. J. Dairy Sci. 89:971–977.[Abstract/Free Full Text]
Cheng, Z., M. Elmes, D. R. E. Abayasekara, and D. C. Wathes. 2003. Effects of conjugated linoleic acid on prostaglandins produced by isolated cells from maternal intercotyledonary endometrium, fetal allantochorion and amnion in late pregnant ewes. Biochim. Biophys. Acta 1633:170–178.[Medline]
Chin, S. F., J. M. Storkson, Y. L. Ha, and M. Pariza. 1992. Dietary sources of conjugated dienoic isomers of linoleic acid, a newly recognized class of anticarcinogens. J. Food Compost. Anal. 5:185–197.
Dhiman, T. R., S.-H. Nam, and A. L. Ure. 2005. Factors affecting conjugated linoleic acid content in milk and meat. Crit. Rev. Food Sci. Nutr. 45:463–482.[Medline]
Dubois, R. N., S. B. Abramson, and L. Crofford. 1993. Cyclooxygenase in biology and disease. FASEB J. 12:1063–1073.
Dubois, R. N., J. Award, J. Morrow, L. J. Roberts, and P. R. Bishop. 1994. Regulation of eicosanoid production and mitogenesis in rat intestinal epithelial cells by transforming growth factor- and phorbol ester. J. Clin. Invest. 93:493–498.[Medline]
Escher, P., and W. Wahli. 2000. Peroxisome proliferators-activated receptors: Insight into multiple cellular functions. Mutat. Res. 448:121–138.[Medline]
Harris, M. A., R. A. Hansen, P. Vidsudhiphan, J. L. Kolso, J. B. Thomas, B. A. Watkins, and K. G. D. Allen. 2001. Effects of conjugated linoleic acids and docosahexaenoic acid on rat liver and reproductive tissue fatty acids, prostaglandins and matrix metalloproteinase production. Prostaglandins Leukot. Essent. Fatty Acids 65:23–29.[Medline]
Herschman, H. R. 1996. Prostaglandin synthase 2. Biochim. Biophys. Acta 1299:125–140.[Medline]
Iwakiri, Y., D. A. Sampson, and K. G. D. Allen. 2002. Suppression of cyclooxygenase-2 and inducible nitric oxide synthase expression by conjugated linoleic acid in murine macrophages. Prostaglandins Leukot. Essent. Fatty Acids 67:435–443.[Medline]
Kujubu, D. A., B. S. Fletcher, B. C. Warnum, R. W. Lim, and H. R. Herschman. 1991. TIS10, a phorbol ester tumor promoter-inducible mRNA from Swiss 3T3 cells, encodes a novel prostaglandin synthase/cyclooxygenase homologue. J. Biol. Chem. 266:12866–12872.[Abstract/Free Full Text]
Liu, K. L., and M. A. Belury. 1998. Conjugated linoleic acid reduces arachidonic acid content and PGE2 synthesis in murine keranocytes. Cancer Lett. 127:15–22.[Medline]
Lowry, O. H., N. H. Rosebrough, A. L. Farr, and R. J. Randall. 1951. Protein measurement with the Folin phenol reagent. J. Biol. Chem. 193:265–270.[Free Full Text]
Mattos, R., A. Guzeloglu, L. Badinga, C. R. Staples, and W. W. Thatcher. 2003. Polyunsaturated fatty acids and bovine interferon- modify phorbol ester-induced secretion of prostaglandin F2 and expression of prostaglandin endoperoxide synthase-2 and phospholipase-A2 in bovine endometrial cells. Biol. Reprod. 69:780–787.[Abstract/Free Full Text]
Nakanishi, T., T. Koutoku, S. Kawahara, A. Murai, and M. Furuse. 2003. Dietary conjugated linoleic acid reduces cerebral prostaglandin E2 in mice. Neurosci. Lett. 341:135–138.[Medline]
Nugteren, D. H., and E. Christ-Hazelhof. 1987. Naturally occurring conjugated octadecatrienoic acid are strong inhibitors of prostaglandin biosynthesis. Prostaglandins 33:403–417.[Medline]
Ogborn, M. R., E. Nitschmann, N. Bankovic-Calic, H. A. Weiler, S. Fitzpatrick-Wong, and H. M. Aukema. 2003. Dietary conjugated linoleic acid reduces PGE2 release and interstitial injury in rat polycystic kidney disease. Kidney Int. 64:1214–1221.[Medline]
Pariza, M. W., Y. Park, and M. E. Cook. 2001. The biologically active isomers of conjugated linoleic acid. Prog. Lipid Res. 40:283–298.[Medline]
Thompson, H., Z. Zhu, S. Banni, K. Darcy, T. Loftus, and C. Ip. 1997. Morphological and biochemical status of the mammary gland as influenced by conjugated linoleic acid: Implication for a reduction in mammary cancer risk. Cancer Res. 57:5067–5072.[Abstract/Free Full Text]
Urquhart, P., S. M. Parkin, J. S. Rogers, J. A. Bosley, and A. Nicolaou. 2002. The effect of conjugated linoleic acid on arachidonic acid metabolism and eicosanoid production in human saphenous vein endothelial cells. Biochim. Biophys. Acta 1580:150–160.[Medline]
Whigham, L. D., A. Higbee, D. E. Bjorling, Y. Park, M. W. Pariza, and M. E. Cook. 2002. Decreased antigen-induced eicosanoid release in conjugated linoleic acid-fed guinea pigs. Am. J. Physiol. Regul. Integr. Comp. Physiol. 282:R1104–R1112.[Abstract/Free Full Text]
This article has been cited by other articles:
|
|
|
|
 
E. Castaneda-Gutierrez, B. C. Benefield, M. J. de Veth, N. R. Santos, R. O. Gilbert, W. R. Butler, and D. E. Bauman
Evaluation of the Mechanism of Action of Conjugated Linoleic Acid Isomers on Reproduction in Dairy Cows
J Dairy Sci,
September 1, 2007;
90(9):
4253 - 4264.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
