The t10,c12 isomer of conjugated linoleic acid stimulates mammary tumorigenesis in transgenic mice over-expressing erbB2 in the mammary epithelium

Conjugated linoleic acid trans-10, cis-12 increases the expression of genes from cell cycle progression and cis-9, trans-11 stimulates apoptotic genes in different mammary tumor explants of female dogs

BACKGROUND

The conjugated linoleic acid (CLA) isomer cis-9, trans-11 is an anticarcinogen that inhibits cell proliferation and/or induces apoptosis of tumor cells. The objective of this study was to evaluate the expression of genes responsible for cell cycle regulation and apoptosis in tumor explants of mammary anaplastic carcinoma (AC) and mammary tubulopapillary carcinoma (TC) cultured in vitro with the CLA isomers cis-9, trans-11 and trans-10, cis-12.

METHODS

In this study we used mammary explants from two adult female dogs that revealed two types of malignant tumors: (a) anaplastic mammary carcinoma (AC) and (b) mammary tubulopapillary carcinoma (TC). The explants (n = 6 per treatment) had an average weight of 80.0 ± 2.0 mg and were cultured for 24 h in 35 mm culture plates under the following treatments: (a) Control: Culture medium + fatty acid free bovine serum albumin (BSA); (b) Culture medium + cis-9, trans-11 CLA (75 µM) diluted with fatty acid free bovine serum albumin (BSA), and; (c) Culture medium + trans-10, cis-12 CLA (75 µM) diluted with fatty acid free bovine serum albumin (BSA). After that, total RNA was extracted, complementary DNA was synthesized (cDNA), and quantitative analysis by real-time polymerase chain reaction (RT-qPCR) was conducted. Data were analyzed using the MIXED procedure of SAS.

RESULTS

Compared with the Control, the CLA trans-10, cis-12 treatment decreased expression of the gene encoding the p53 by 20% (P = 0.02), Caspase-3 by 25% (P = 0.06) and Bax by 51% (P = 0.001) in AC. The CLA cis-9, trans-11 increased the gene expression of proapoptotic protein Bax in TC by 68% (P = 0.01), but increased the expression of the antiapoptotic Bcl2 gene in AC by 72% (P = 0.006).

CONCLUSION

The CLA cis-9, trans-11 stimulates apoptotic genes in mammary tubulopapillary carcinoma, but has a contrary effect on the anaplastic carcinoma, and the CLA trans-10, cis-12 stimulates cell cycle progression genes and may have an antiapoptotic effect, mainly in mammary anaplastic carcinoma.

The Modulatory Effects of Fatty Acids on Cancer Progression

Cancer is the second leading cause of death worldwide and the global cancer burden rises rapidly. The risk factors for cancer development can often be attributed to lifestyle factors, of which an unhealthy diet is a major contributor. Dietary fat is an important macronutrient and therefore a crucial part of a well-balanced and healthy diet, but it is still unclear which specific fatty acids contribute to a healthy and well-balanced diet in the context of cancer risk and prognosis. In this review, we describe epidemiological evidence on the associations between the intake of different classes of fatty acids and the risk of developing cancer, and we provide preclinical evidence on how specific fatty acids can act on tumor cells, thereby modulating tumor progression and metastasis. Moreover, the pro- and anti-inflammatory effects of each of the different groups of fatty acids will be discussed specifically in the context of inflammation-induced cancer progression and we will highlight challenges as well as opportunities for successful application of fatty acid tailored nutritional interventions in the clinic.

In Utero Exposure to trans-10, cis-12 Conjugated Linoleic Acid Modifies Postnatal Development of the Mammary Gland and its Hormone Responsiveness

We previously showed that dietary trans-10, cis-12 conjugated linoleic acid (10,12 CLA) stimulates estrogen-independent mammary growth in young ovariectomized mice. Here we investigated the effects of in utero or postnatal exposure to cis-9, trans-11 (9,11 CLA) and 10,12 CLA on postnatal development of the mammary gland and its responsiveness to ovarian steroids. In the first experiment we fed dams different CLA prior to and during gestation, then cross fostered female pups onto control fed dams prior to assessing the histomorphology of their mammary glands. Pregnant dams in the second experiment were similarly exposed to CLA, after which their female pups were ovariectomized then treated with 17β-estradiol (E), progesterone (P) or E + P for 5 days. In a third experiment, mature female mice were fed different CLA for 28 days prior to ovariectomy, then treated with E, P or E + P. Our data indicate that 10,12 CLA modifies the responsiveness of the mammary glands to E or E + P when exposure occurs either in utero, or postnatally. These findings underline the sensitivity of the mammary glands to dietary fatty acids and reinforce the potential for maternal nutrition to impact postnatal development of the mammary glands and their risk for developing cancer.

Unsaturated fatty acids as a co-therapeutic agents in cancer treatment

Chemotherapy is standard treatments for many malignancies. However, in most cases, this method is not able to induce apoptosis and in many cases, with cancer recurrence, leads to patient death. There are several procedure to control and suppress malignant cells, but among these methods, administration of ɷ-3 fatty acids and ɷ-6 fatty due to their destructive effects on cancer cells is more prominent. Many clinical studies have shown beneficial effects of ɷ-3 and ɷ-6 fatty acids in cardiovascular disorders, asthma, rheumatoid arthritis, osteoporosis and in most cancers such as colon, breast, prostate and other malignancies. Studies showed that polyunsaturated fatty acids (PUFAs) have a toxic effect on cancer cells. However, the exact mechanism of how ɷ- fatty acids affect cancer cells is still unknown. In this review alternative issues of malignancies co-treatments agents such as PUFAs have been studied. Also, the latest known PUFAs mechanisms on malignancies have been described.

Weighing the Risk: effects of Obesity on the Mammary Gland and Breast Cancer Risk

Obesity is a preventable risk factor for breast cancer following menopause. Regardless of menopausal status, obese women who develop breast cancer have a worsened prognosis. Breast tissue is comprised of mammary epithelial cells organized into ducts and lobules and surrounded by adipose-rich connective tissue. Studies utilizing multiple in vivo models of obesity as well as human breast tissue have contributed to our understanding of how obesity alters mammary tissue. Localized changes in mammary epithelial cell populations, elevated secretion of adipokines and angiogenic mediators, inflammation within mammary adipose tissue, and remodeling of the extracellular matrix may result in an environment conducive to breast cancer growth. Despite these significant alterations caused by obesity within breast tissue, studies have suggested that some, but not all, obesity-induced changes may be mitigated with weight loss. Here, we review our current understanding regarding the impact of obesity on the breast microenvironment, how obesity-induced changes may contribute to breast tumor progression, and the impact of weight loss on the breast microenvironment.

Conjugated Linoleic Acid Effects on Cancer, Obesity, and Atherosclerosis: A Review of Pre-Clinical and Human Trials with Current Perspectives

Obesity and its comorbidities, including type 2 diabetes and cardiovascular disease, are straining our healthcare system, necessitating the development of novel strategies for weight loss. Lifestyle modifications, such as exercise and caloric restriction, have proven effective against obesity in the short term, yet obesity persists because of the high predilection for weight regain. Therefore, alternative approaches to achieve long term sustainable weight loss are urgently needed. Conjugated linoleic acid (CLA), a fatty acid found naturally in ruminant animal food products, has been identified as a potential anti-obesogenic agent, with substantial efficacy in mice, and modest efficacy in obese human populations. Originally described as an anti-carcinogenic fatty acid, in addition to its anti-obesogenic effects, CLA has now been shown to possess anti-atherosclerotic properties. This review summarizes the pre-clinical and human studies conducted using CLA to date, which collectively suggest that CLA has efficacy against cancer, obesity, and atherosclerosis. In addition, the potential mechanisms for the many integrative physiological effects of CLA supplementation will be discussed in detail, including an introduction to the gut microbiota as a potential mediator of CLA effects on obesity and atherosclerosis.

Trans10,cis12 conjugated linoleic acid inhibits proliferation and migration of ovarian cancer cells by inducing ER stress, autophagy, and modulation of Src

The goal of this study was to investigate the anti-cancer effects of Trans10,cis12 conjugated linoleic acid (t10,c12 CLA). MTT assays and QCM™ chemotaxis 96-wells were used to test the effect of t10,c12 CLA on the proliferation and migration and invasion of cancer cells. qPCR and Western Blotting were used to determine the expression of specific factors. RNA sequencing was conducted using the Illumina platform and apoptosis was measured using a flow cytometry assay. t10,c12 CLA (IC50, 7 μM) inhibited proliferation of ovarian cancer cell lines SKOV-3 and A2780. c9,t11 CLA did not attenuate the proliferation of these cells. Transcription of 165 genes was significantly repressed and 28 genes were elevated. Genes related to ER stress, ATF4, CHOP, and GADD34 were overexpressed whereas EDEM2 and Hsp90, genes required for proteasomal degradation of misfolded proteins, were downregulated upon treatment. While apoptosis was not detected, t10,c12 CLA treatment led to 9-fold increase in autophagolysosomes and higher levels of LC3-II. G1 cell cycle arrest in treated cells was correlated with phosphorylation of GSK3β and loss of β-catenin. microRNA miR184 and miR215 were upregulated. miR184 likely contributed to G1 arrest by downregulating E2F1. miR215 upregulation was correlated with increased expression of p27/Kip-1. t10,c12 CLA-mediated inhibition of invasion and migration correlated with decreased expression of PTP1b and decreased Src activation by inhibiting phosphorylation at Tyr416. Due to its ability to inhibit proliferation and migration, t10,c12 CLA should be considered for treatment of ovarian cancer.

Trans-Fatty Acid-Stimulated Mammary Gland Growth in Ovariectomized Mice is Fatty Acid Type and Isomer Specific

We previously reported that the trans-18:2 fatty acid trans-10, cis-12 conjugated linoleic acid (t10,c12-CLA) stimulates mammary gland development independent of estrogen and its receptor. Given the negative consequences of dietary trans-fatty acids on various aspects of human health, we sought to establish whether other trans-fatty acids could similarly induce ovary-independent mammary gland growth in mice. Prepubertal BALB/cJ mice were ovariectomized at 21 days of age then were fed diets enriched with cis-9, trans-11 CLA (c9,t11-CLA), or mixtures of trans-18:1 fatty acids supplied by partially hydrogenated sunflower, safflower, or linseed oil. The resultant mammary phenotype was evaluated 3 weeks later and compared to the growth response elicited by t10,c12-CLA, or the defined control diet. Whereas partially hydrogenated safflower oil increased mammary gland weight, none of the partially hydrogenated vegetable oils promoted mammary ductal growth. Similarly, the c9,t11-CLA supplemented diet was without effect on mammary development. Taken together, our data emphasize a unique effect of t10,c12-CLA in stimulating estrogen-independent mammary gland growth manifest as increased mammary ductal area and elongation that was not recapitulated by c9,t11-CLA or the partially hydrogenated vegetable oil diets.

Fatty Acids and Breast Cancer: Make Them on Site or Have Them Delivered

Brisk fatty acid (FA) production by cancer cells is accommodated by the Warburg effect. Most breast and other cancer cell types are addicted to fatty acids (FA), which they require for membrane phospholipid synthesis, signaling purposes, and energy production. Expression of the enzymes required for FA synthesis is closely linked to each of the major classes of signaling molecules that stimulate BC cell proliferation. This review focuses on the regulation of FA synthesis in BC cells, and the impact of FA, or the lack thereof, on the tumor cell phenotype. Given growing awareness of the impact of dietary fat and obesity on BC biology, we will also examine the less-frequently considered notion that, in addition to de novo FA synthesis, the lipolytic uptake of preformed FA may also be an important mechanism of lipid acquisition. Indeed, it appears that cancer cells may exist at different points along a "lipogenic-lipolytic axis," and FA uptake could thwart attempts to exploit the strict requirement for FA focused solely on inhibition of de novo FA synthesis. Strategies for clinically targeting FA metabolism will be discussed, and the current status of the medicinal chemistry in this area will be assessed. J. Cell. Physiol. 231: 2128-2141, 2016. © 2016 Wiley Periodicals, Inc.

Mammary gland development--It's not just about estrogen

The mammary gland (MG) is one of a few organs that undergoes most of its growth after birth. Much of this development occurs concurrently with specific reproductive states, such that the ultimate goal of milk synthesis and secretion is coordinated with the nutritional requirements of the neonate. Central to the reproductive-MG axis is its endocrine regulation, and pivotal to this regulation is the ovarian secretion of estrogen (E). Indeed, it is widely accepted that estrogens are essential for growth of the MG to occur, both for ductal elongation during puberty and for alveolar development during gestation. As the factors regulating MG development continually come to light from the fields of developmental biology, lactation physiology, and breast cancer research, a growing body of evidence serves as a reminder that the MG are not as exclusively dependent on estrogens as might have been thought. The objective of this review is to summarize the state of information regarding our understanding of how estrogen (E) has been implicated as the key regulator of MG development, and to highlight some of the alternative E-independent mechanisms that have been discovered. In particular, we review our findings that dietary trans-10,cis-12 conjugated linoleic acid promotes ductal elongation and that the combination of progesterone (P) and prolactin (PRL) can stimulate branching morphogenesis in the absence of E. Ultimately, these examples stand as a healthy challenge to the question of just how important estrogens are for MG development. Answers to this question, in turn, increase our understanding of MG development across all mammals and the ways in which it can affect milk production.

Phosphatidylcholine with cis-9,trans-11 and trans-10,cis-12 Conjugated Linoleic Acid Isomers: Synthesis and Cytotoxic Studies

Novel phosphatidylcholines and lysophosphatidylcholines with cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid (CLA) were synthesized in high yields (75–99 %). The in vitro cytotoxic activities of these compounds against three human cancer cell lines (HL-60, MCF-7, and HT-29) were evaluated. The results revealed that there are differences in the activity between phosphatidylcholine with cis-9,trans-11 and trans-10,cis-12 CLA acyl groups. 1,2-Di(9Z,11E)-octadecadienoyl-sn-glycero-3-phosphocholine was the most potent cytotoxic agent among all tested CLA derivatives and its IC50 (concentration of a compound that inhibits the proliferation of 50 % of the cancer cell population) was 29.4 µM against HL-60. Moreover, phosphatidylcholines with CLA acyls exhibited much lower cytotoxicity against non-cancer cells (Balb/3T3) than free CLA isomers.

Trans-10, cis-12 CLA dose-dependently inhibits milk fat synthesis without disruption of lactation in C57BL/6J mice

BACKGROUND

Trans-10, cis-12 conjugated linoleic acid (10,12 CLA) is a potent inhibitor of milk fat synthesis in mammals. In the cow, 10 g/d of 10,12 CLA specifically and reversibly inhibits mammary lipogenesis, whereas substantially higher doses are not specific and cause a generalized inhibition of milk synthesis.

OBJECTIVE

The objective of this study was to validate a lactating mouse model by establishing the dose response, specificity, and reversibility of the inhibition of milk fat synthesis by 10,12 CLA.

METHODS

Lactating mice (C57BL/6J) received daily doses of 0 (control), 7, 20, or 60 mg of 10,12 CLA for 5 d during established lactation. A second group of lactating mice was treated with 20 mg/d of 10,12 CLA for 4 d and followed post-treatment to evaluate reversibility.

RESULTS

CLA decreased pup growth with a 49% decrease occurring with 60 mg/d of CLA. Milk fat percentage was decreased 11% and 20% with the 7 and 20 mg/d dose, respectively, and all CLA treatments had a decreased concentration of de novo synthesized fatty acids (FAs) in milk fat. In agreement, 20 mg/d of 10,12 CLA decreased the lipogenic capacity of mammary tissue by 30% and mammary expression of FA synthase (Fasn), sterol response element binding protein 1 (Srebf1), and thyroid hormone responsive spot 14 (Thrsp) by 30-60%, whereas milk protein percentage and mammary expression of α-lactalbumin (Lalba) were unaltered. This dose of CLA reduced pup growth by nearly 20% and milk de novo synthesized FAs by >35%, and these effects were completely reversed 5 d after 10,12 CLA treatment was terminated.

CONCLUSION

Inhibition of mammary lipogenesis by 10,12 CLA is dose-dependent in the mouse, with a specific and reversible reduction in milk fat synthesis at the 20 mg/d dose and additional nonspecific effects on milk synthesis at higher CLA doses.

Trans-10, cis 12-Conjugated Linoleic Acid-Induced Milk Fat Depression Is Associated with Inhibition of PPARγ Signaling and Inflammation in Murine Mammary Tissue

Exogenous trans-10, cis-12-CLA (CLA) reduces lipid synthesis in murine adipose and mammary (MG) tissues. However, genomewide alterations in MG and liver (LIV) associated with dietary CLA during lactation remain unknown. We fed mice (n = 5/diet) control or control + trans-10, cis-12-CLA (37 mg/day) between d 6 and d 10 postpartum. The 35,302 annotated murine exonic evidence-based oligo (MEEBO) microarray and quantitative RT-PCR were used for transcript profiling. Milk fat concentration was 44% lower on d 10 versus d 6 due to CLA. The CLA diet resulted in differential expression of 1,496 genes. Bioinformatics analyses underscored that a major effect of CLA on MG encompassed alterations in cellular signaling pathways and phospholipid species biosynthesis. Dietary CLA induced genes related to ER stress (Xbp1), apoptosis (Bcl2), and inflammation (Orm1, Saa2, and Cp). It also induced marked inhibition of PPAR γ signaling, including downregulation of Pparg and Srebf1 and several lipogenic target genes (Scd, Fasn, and Gpam). In LIV, CLA induced hepatic steatosis probably through perturbations in the mitochondrial functions and induction of ER stress. Overall, results from this study underscored the role of PPAR γ signaling on mammary lipogenic target regulation. The proinflammatory effect due to CLA could be related to inhibition of PPAR γ signaling.

A proof of principle clinical trial to determine whether conjugated linoleic acid modulates the lipogenic pathway in human breast cancer tissue

Conjugated linoleic acid (CLA) is widely used as a "nutraceutical" for weight loss. CLA has anticancer effects in preclinical models, and we demonstrated in vitro that this can be attributed to the suppression of fatty acid (FA) synthesis. We tested the hypothesis that administration of CLA to breast cancer patients would inhibit expression of markers related to FA synthesis in tumor tissue, and that this would suppress tumor proliferation. Women with Stage I-III breast cancer were enrolled into an open label study and treated with CLA (1:1 mix of 9c,11t- and 10t,12c-CLA isomers, 7.5 g/d) for ≥ 10 days before surgery. Fasting plasma CLA concentrations measured pre- and post-CLA administration, and pre/post CLA tumor samples were examined by immunohistochemistry for Spot 14 (S14), a regulator of FA synthesis, FA synthase (FASN), an enzyme of FA synthesis, and lipoprotein lipase (LPL), the enzyme that allows FA uptake. Tumors were also analyzed for expression of Ki-67 and cleaved caspase 3. 24 women completed study treatment, and 23 tumors were evaluable for the primary endpoint. The median duration of CLA therapy was 12 days, and no significant toxicity was observed. S14 expression scores decreased (p = 0.003) after CLA administration. No significant change in FASN or LPL expression was observed. Ki-67 scores declined (p = 0.029), while cleaved caspase 3 staining was unaffected. Decrements in S14 or Ki-67 did not correlate with fasting plasma CLA concentrations at surgery. Breast tumor tissue expression of S14, but not FASN or LPL, was decreased after a short course of treatment with 7.5 g/day CLA. This was accompanied by reductions in the proliferation index. CLA consumption was well-tolerated and safe at this dose for up to 20 days. Overall, CLA may be a prototype compound to target fatty acid synthesis in breast cancers with a "lipogenic phenotype".

Alterations in mast cell frequency and relationship to angiogenesis in the rat mammary gland during windows of physiologic tissue remodeling

BACKGROUND

The mammary epithelium undergoes proliferation and regression accompanied by remodeling of the fibrocellular and vascular stroma. Mast cells are abundant in these compartments and have been implicated in remodeling during wound healing and cancer progression. The purpose of this study was to test the hypothesis that mast cell abundance correlates with physiologic mammary tissue remodeling during estrous cycling, lactogenesis (pregnancy and lactation) and involution.

RESULTS

Mast cell and capillary frequency were quantified in the stroma surrounding ducts and lobules from mammary glands of rats. During estrous cycling, periductal mast cell numbers were unchanged, but lobule-associated mast cells significantly increased in the regressive phase of diestrus II. During lactogenesis, lobular stroma mast cells peaked early in pregnancy, at D2, followed by a significant decrease throughout lactation. Involution was associated with a rapid return in mast cell numbers, similar to diestrus II. Lobular vascularization peaked during the state of metestrus, when limited secretory differentiation occurs. Lobular angiogenesis peaked at D7 of pregnancy, regressed, and then returned to high levels during lactation and early involution, when secretory differentiation is high.

CONCLUSIONS

These results suggest mast cells are predominantly associated with regressive lobular remodeling during cycling and involution, whereas angiogenesis is predominantly associated with secretory differentiation.

Diet-induced metabolic change induces estrogen-independent allometric mammary growth

Lifetime breast cancer risk reflects an unresolved combination of early life factors including diet, body mass index, metabolic syndrome, obesity, and age at first menses. In parallel, the onset of allometric growth by the mammary glands around puberty is widely held to be estrogen (E)-dependent. Here we report that several physiological changes associated with metabolic syndrome in response to a diet supplemented with the trans-10, cis-12 isomer of conjugated linoleic acid lead to ovary-independent allometric growth of the mammary ducts. The E-independence of this diet-induced growth was highlighted by the fact that it occurred both in male mice and with pharmacological inhibition of either E receptor function or E biosynthesis. Reversal of the metabolic phenotype with the peroxisome proliferator-activated receptor-γ agonist rosiglitazone abrogated diet-induced mammary growth. A role for hyperinsulinemia and increased insulin-like growth factor-I receptor (IGF-IR) expression during mammary growth induced by the trans-10, cis-12 isomer of conjugated linoleic acid was confirmed by its reversal upon pharmacological inhibition of IGF-IR function. Diet-stimulated ductal growth also increased mammary tumorigenesis in ovariectomized polyomavirus middle T-antigen mice. Our data demonstrate that diet-induced metabolic dysregulation, independently of ovarian function, stimulates allometric growth within the mammary glands via an IGF-IR-dependent mechanism.

The dietary fatty acid 10E12Z-CLA induces epiregulin expression through COX-2 dependent PGF(2α) synthesis in adipocytes

Conjugated linoleic acids (CLAs) are a group of dietary fatty acids that are widely marketed as weight loss supplements. The isomer responsible for this effect is the trans-10, cis-12 CLA (10E12Z-CLA) isomer. 10E12Z-CLA treatment during differentiation of 3T3-L1 adipocytes induces expression of prostaglandin-endoperoxide synthase-2 (Cyclooxygenase-2; COX-2). This work demonstrates that COX-2 is also induced in fully differentiated 3T3-L1 adipocytes after a single treatment of 10E12Z-CLA at both the mRNA (20-40 fold) and protein level (7 fold). Furthermore, prostaglandin (PG)F(2α), but not PGE(2), is significantly increased 10 fold. In female BALB/c mice fed 0.5% 10E12Z-CLA for 10 days, COX-2 was induced in uterine adipose (2 fold). In vitro, pharmacological COX-2 inhibition did not block the effect of 10E12Z-CLA on adipocyte-specific gene expression although PGF(2α) was dose-dependently decreased. These studies demonstrate that PGF(2α) was not by itself responsible for the reduction in adipocyte character due to 10E12Z-CLA treatment. However, PGF(2α), either exogenously or endogenously in response to 10E12Z-CLA, increased the expression of the potent mitogen and epidermal growth factor (EGF) receptor (EGFR) ligand epiregulin in 3T3-L1 adipocytes. Blocking PGF(2α) signaling with the PGF(2α) receptor (FP) antagonist AL-8810 returned epiregulin mRNA levels back to baseline. Although this pathway is not directly responsible for adipocyte dependent gene expression, these results suggest that this signaling pathway may still have broad effect on the adipocyte and surrounding cells.

Folate exacerbates the effects of ethanol on peripubertal mouse mammary gland development

Alcohol consumption is linked with increased breast cancer risk in women, even at low levels of ingestion. The proposed mechanisms whereby ethanol exerts its effects include decreased folate levels resulting in diminished DNA synthesis and repair, and/or acetaldehyde-generated DNA damage. Based on these proposed mechanisms, we hypothesized that ethanol would have increased deleterious effects during periods of rapid mammary gland epithelial proliferation, such as peripuberty, and that folate deficiency alone might mimic and/or exacerbate the effects of ethanol. To test this hypothesis, weight-matched 28-35 day old CD2F1 female mice were pair-fed liquid diets ±3.2% ethanol, ±0.1% folate for 4 weeks. Folate status was confirmed by assay of liver and kidney tissues. In folate deficient mice, no significant ethanol-induced changes to the mammary gland were observed. Folate replete mice fed ethanol had an increased number of ducts per section, due to an increased number of terminal short branches. Serum estrogen levels were increased by ethanol, but only in folate replete mice. These results demonstrate that folate deficiency alone does not mimic the effects of ethanol, and that folate deficiency in the presence of ethanol blocks proliferative effects of ethanol on the mammary ductal tree.

Human health effects of conjugated linoleic acid from milk and supplements

The primary purpose of the present review was to determine if the scientific evidence available for potential human health benefits of conjugated linoleic acid (CLA) is sufficient to support health claims on foods based on milk naturally enriched with cis-9, trans-11-CLA (c9, t11-CLA). A search of the scientific literature was conducted and showed that almost all the promising research results that have emerged in relation to cancer, heart health, obesity, diabetes and bone health have been in animal models or in vitro. Most human intervention studies have utilised synthetic CLA supplements, usually a 50:50 blend of c9, t11-CLA and trans-10, cis-12-CLA (t10, c12-CLA). Of these studies, the only evidence that is broadly consistent is an effect on body fat and weight reduction. A previous review of the relevant studies found that 3.2 g CLA/d resulted in a modest body fat loss in human subjects of about 0.09 kg/week, but this effect was attributed to the t10, c12-CLA isomer. There is no evidence of a consistent benefit of c9, t11-CLA on any health conditions; and in fact both synthetic isomers, particularly t10, c12-CLA, have been suspected of having pro-diabetic effects in individuals who are already at risk of developing diabetes. Four published intervention studies using naturally enriched CLA products were identified; however, the results were inconclusive. This may be partly due to the differences in the concentration of CLA administered in animal and human studies. In conclusion, further substantiation of the scientific evidence relating to CLA and human health benefits are required before health claims can be confirmed.

Direct effects of conjugated linoleic acid isomers on P815 mast cells in vitro

Conjugated linoleic acid (CLA) is a dietary fatty acid which causes extensive remodeling and mast cell recruitment in the mouse mammary gland. Two CLA isomers, 9,11- and 10,12-CLA, have differing effects in vivo, with only 10,12-CLA increasing mast cell number. The purpose of this project is to test the hypothesis that CLA acts directly on the mast cell. The P815 mastocytoma cell line was assayed for the effects of CLA on mast cell number, proliferation, apoptosis, and differentiation. Both CLA isomers decreased viable mast cell number, with no effect on membrane integrity, or cell cycle distribution. 10,12-CLA induced an increase in apoptosis, assessed by Annexin-FITC binding. Both isomers increased mast cell granularity, and secretion of MMP-9. The complex effects of CLA isomers on mast cells in the mammary gland are distinct from direct effects on mast cells in vitro, and may require interactions between multiple cell types present in vivo.

Synthesis and in vitro evaluation of analogues of avocado-produced toxin (+)-(R)-persin in human breast cancer cells

A structure-activity study of several new synthetic analogues of the avocado-produced toxin persin has been conducted, with compounds being evaluated for their cytostatic and pro-apoptotic effects in human breast cancer cells. A 4-pyridinyl derivative demonstrated activity comparable to that of the natural product, suggesting future directions for exploration of structure-activity relationships.

Conjugated linoleic acid-induced apoptosis in mouse mammary tumor cells is mediated by both G protein coupled receptor-dependent activation of the AMP-activated protein kinase pathway and by oxidative stress

Conjugated linoleic acid (CLA) has shown chemopreventive activity in several tumorigenesis models, in part through induction of apoptosis. We previously demonstrated that the t10,c12 isomer of CLA induced apoptosis of TM4t mouse mammary tumor cells through both mitochondrial and endoplasmic reticulum (ER) stress pathways, and that the AMP-activated protein kinase (AMPK) played a critical role in the apoptotic effect. In the current study, we focused on the upstream pathways by which AMPK was activated, and additionally evaluated the contributing role of oxidative stress to apoptosis. CLA-induced activation of AMPK and/or induction of apoptosis were inhibited by infection of TM4t cells with an adenovirus expressing a peptide which blocks the interaction between the G protein coupled receptor (GPCR) and Gα(q), by the phospholipase C (PLC) inhibitor U73122, by the inositol trisphosphate (IP(3)) receptor inhibitor 2-APB, by the calcium/calmodulin-dependent protein kinase kinase α (CaMKK) inhibitor STO-609 and by the intracellular Ca(2+) chelator BAPTA-AM. This suggests that t10,c12-CLA may exert its apoptotic effect by stimulating GPCR through Gα(q) signaling, activation of phosphatidylinositol-PLC, followed by binding of the PLC-generated IP(3) to its receptor on the ER, triggering Ca(2+) release from the ER and finally stimulating the CaMKK-AMPK pathway. t10,c12-CLA also increased oxidative stress and lipid peroxidation, and antioxidants blocked its apoptotic effect, as well as the CLA-induced activation of p38 MAPK, a downstream effector of AMPK. Together these data elucidate two major pathways by which t10,c12-CLA induces apoptosis, and suggest a point of intersection of the two pathways both upstream and downstream of AMPK.

Effects of ruminant trans fatty acids on cardiovascular disease and cancer: a comprehensive review of epidemiological, clinical, and mechanistic studies

There are 2 predominant sources of dietary trans fatty acids (TFA) in the food supply, those formed during the industrial partial hydrogenation of vegetable oils (iTFA) and those formed by biohydrogenation in ruminants (rTFA), including vaccenic acid (VA) and the naturally occurring isomer of conjugated linoleic acid, cis-9, trans-11 CLA (c9,t11-CLA). The objective of this review is to evaluate the evidence base from epidemiological and clinical studies to determine whether intake of rTFA isomers, specifically VA and c9,t11-CLA, differentially affects risk of cardiovascular disease (CVD) and cancer compared with iTFA. In addition, animal and cell culture studies are reviewed to explore potential pro- and antiatherogenic mechanisms of VA and c9,t11-CLA. Some epidemiological studies suggest that a positive association with coronary heart disease risk exists between only iTFA isomers and not rTFA isomers. Small clinical studies have been conducted to establish cause-and-effect relationships between these different sources of TFA and biomarkers or risk factors of CVD with inconclusive results. The lack of detection of treatment effects reported in some studies may be due to insufficient statistical power. Many studies have used doses of rTFA that are not realistically attainable via diet; thus, further clinical studies are warranted. Associations between iTFA intake and cancer have been inconsistent, and associations between rTFA intake and cancer have not been well studied. Clinical studies have not been conducted investigating the cause-and-effect relationship between iTFA and rTFA intake and risk for cancers. Further research is needed to determine the health effects of VA and c9,t11-CLA in humans.

Growth inhibition and apoptotic effect of alpha-eleostearic acid on human breast cancer cells

Alpha-eleostearic acid (α-ESA) is a natural and biologically active compound which possesses potent antioxidant and anti-tumor activity. The purpose of this study was to confirm the anticancer activity of α-ESA against human breast cancer cells and to further elucidate its mechanism of activity. Human breast cancer cells and normal liver cells were used for in-vitro tests of the anticancer activity of α-ESA, including cytotoxicity, colony formation inhibition, EdU incorporation, AO/EB staining of apoptotic cells, cell cycle distribution through flow cytometry, and PPARγ, p21, Bax, p53, and caspase-3 mRNA expressions through RT-PCR. After α-ESA treatment, the proliferation, colony formation, and EdU labeling indices of cancer cells decreased (p < 0.05), while the AO/EB-stained apoptotic cells increased (p < 0.05). By FCM analysis, the apoptotic indices increased (p < 0.01), and the cell population decreased in S phase (p < 0.01) and increased in G(2)/M phase (p < 0.05) in α-ESA treated cancer cells. RT-RCR showed that α-ESA significantly increased the expression levels of PPARγ, p21, Bax, p53, and caspase-3 mRNA. The findings in these studies suggested that α-ESA exhibited a potential cytotoxicity and apoptosis induction effect on human breast cancer cells, with little effect on normal cells at certain concentrations. The mechanism for such effects might be associated with the inhibition of DNA synthesis, induction of apoptosis, and cell cycle arrest of cancer cells through up-regulation of PPARγ, p21, Bax, p53, and caspase-3 expressions.

t10,c12-CLA decreases adiposity in peripubertal mice without dose-related detrimental effects on mammary development, inflammation status, and metabolism

The trans 10, cis 12-conjugated linoleic acid (10,12-CLA) isomer reduces adiposity in several animal models. In the mouse, however, this effect is associated with adipose tissue inflammation, hyperinsulinemia and hepatic lipid accumulation. Moreover, 10,12-CLA was recently shown to promote mammary ductal hyperplasia and ErbB2/Her2-driven mammary cancer in the mouse. Reasons for detrimental effects of 10,12-CLA on the mouse mammary gland could relate to its effect on the mammary fat pad (MFP), which is essential for normal development. Accordingly, we hypothesized that mammary effects of 10,12-CLA were mediated through the MFP in a dose-dependent manner. Female FVB mice were fed 10,12-CLA at doses of 0%, 0.1%, 0.2%, or 0.5% of the diet from day 24 of age, and effects on mammary development and metabolism were measured on day 49. The 0.5% dose reduced ductal elongation and caused premature alveolar budding. These effects were associated with increased expression of inflammatory markers and genes shown to alter epithelial growth (IGF binding protein-5) and alveolar budding (TNF-α and receptor of activated NF-κB ligand). The 0.5% dose also caused hyperinsulinemia and hepatic lipid accumulation. In contrast, the 0.1% 10,12-CLA dose had no adverse effects on mammary development, metabolic events, and inflammatory responses, but remained effective in decreasing adipose weights and lipogenic gene expression. These results show that a low dose of 10,12-CLA reduces adiposity in the mouse without negative effects on mammary development, inflammation, and metabolism, and suggest that previously reported detrimental effects relate to the use of excessive doses.

c9t11-Conjugated linoleic acid-rich oil fails to attenuate wasting in colon-26 tumor-induced late-stage cancer cachexia in male CD2F1 mice

SCOPE

Cancer cachexia is characterized by muscle and adipose tissue wasting caused partly by chronic, systemic inflammation. Conjugated linoleic acids (CLAs) are a group of fatty acids with various properties including anti-inflammatory cis9, trans11 (c9t11)-CLA and lipid-mobilizing trans10, cis12 (t10c12)-CLA. The purpose of this study was to test whether dietary supplementation of a c9t11-CLA-rich oil (6:1 c9t11:t10c12) could attenuate wasting of muscle and adipose tissue in colon-26 adenocarcinoma-induced cachexia in mice.

METHODS AND RESULTS

Loss of body weight, muscle and adipose tissue mass caused by tumors were not rescued by supplementation with the c9t11-CLA-rich oil. In quadriceps muscle, c9t11-CLA-rich oil exacerbated tumor-induced gene expression of inflammatory markers tumor necrosis factor-α, IL-6 receptor and the E3 ligase MuRF-1 involved in muscle proteolysis. In epididymal adipose tissue, tumor-driven delipidation and atrophy was aggravated by the c9,t11-CLA-rich oil, demonstrated by further reduced adipocyte size and lower adiponectin expression. However, expression of inflammatory cytokines and macrophage markers were not altered by tumors, or CLA supplementation.

CONCLUSION

These data suggest that addition of c9t11-CLA-rich oil (0.6% c9t11, 0.1% t10c12) in diet did not ameliorate wasting in mice with cancer cachexia. Instead, it increased expression of inflammatory markers in the muscle and increased adipose delipidation.

Pilot study on the effects of dietary conjugated linoleic acid on tumorigenesis and gene expression in PyMT transgenic mice

Conjugated linoleic acid (CLA) is a class of commercially available fatty acids that have been associated with anticancer properties in rodent models of chemical carcinogenesis. We conducted a pilot study to examine the antitumor effect of dietary CLA in a polyoma virus-middle T antigen (PyMT) mouse model of invasive breast cancer. Virgin 4-week-old PyMT mice were administered a mixed-isomer CLA diet (1% wt/wt) or control AIN-93G diet for 4 weeks (N = 6 and 5, respectively) and tumor burden was assessed at 8 weeks of age. Thoracic mammary glands were prepared as whole mounts with other glands being formalin fixed and paraffin embedded for histology and immunohistochemistry (IHC). Total RNA was prepared for microarray and real-time reverse transcription-polymerase chain reaction analysis. Western blots were performed for protein expression analysis. Tumor incidence was significantly increased in CLA-treated animals compared with controls (P = 0.009) and occurred with extensive lobular-alveolar expansion and loss of mammary adipose tissue. More than 100 genes were downregulated > or = 2-fold in the CLA-treated group compared with controls, including adipose-specific markers, as wells as cytoskeletal and adhesion-related genes. This was supported by dramatic decreases in the epithelial adherens E-cadherin and beta-catenin as demonstrated by IHC. Taken together, these results suggest that dietary CLA affects the mammary stromal environment, leading to tumor progression and cellular expansion in the PyMT mouse model. Further studies of the potential for cancer promotion are needed, especially because mixed-isomer CLA formulations are sold commercially as a nutritional supplement.

Fatty acids and breast cancer: the role of stem cells

Studies with animal models in vivo as well as with animal and human tumor cells in vitro suggest that specific fatty acids could reduce breast tumorigenesis. The most striking dietary fatty acid studies in animal models that show promise for reduction of breast cancer risk in humans are with conjugated linoleic acids (CLA) and n-3 fatty acids. Although a number of mechanisms have been proposed, the specific target of those fatty acids is not yet known. We sought to determine whether the effects of those fatty acids on terminally differentiated tumor cell seen could be due to alteration of breast cancer stem cells. The isomers, cis9, trans11-CLA and trans10, cis12-CLA, and the n-3 fatty acids, docosahexaenoic and eicosapentaenoic, reduced the proliferation of, and had increased toxicity towards, mammary tumor initiating cells. One mechanism involved in the effect of n-3 fatty acids may be due to alteration of the profile of prostaglandins. These results indicate that select fatty acids may be useful for preventing or reducing the risk of breast cancer as they may target the tumor initiating cell.

Activation of the AMP-activated protein kinase-p38 MAP kinase pathway mediates apoptosis induced by conjugated linoleic acid in p53-mutant mouse mammary tumor cells

Conjugated linoleic acid (CLA) inhibits tumorigenesis and tumor growth in most model systems, an effect mediated in part by its pro-apoptotic activity. We previously showed that trans-10,cis-12 CLA induced apoptosis of p53-mutant TM4t mouse mammary tumor cells through both mitochondrial and endoplasmic reticulum stress pathways. In the current study, we investigated the role of AMP-activated protein kinase (AMPK), a key player in fatty acid metabolism, in CLA-induced apoptosis in TM4t cells. We found that t10,c12-CLA increased phosphorylation of AMPK, and that CLA-induced apoptosis was enhanced by the AMPK agonist 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) and inhibited by the AMPK inhibitor compound C. The increased AMPK activity was not due to nutrient/energy depletion since ATP levels did not change in CLA-treated cells, and knockdown of the upstream kinase LKB1 did not affect its activity. Furthermore, our data do not demonstrate a role for the AMPK-modulated mTOR pathway in CLA-induced apoptosis. Although CLA decreased mTOR levels, activity was only modestly decreased. Moreover, rapamycin, which completely blocked the activity of mTORC1 and mTORC2, did not induce apoptosis, and attenuated rather than enhanced CLA-induced apoptosis. Instead, the data suggest that CLA-induced apoptosis is mediated by the AMPK-p38 MAPK-Bim pathway: CLA-induced phosphorylation of AMPK and p38 MAPK, and increased expression of Bim, occurred with a similar time course as apoptosis; phosphorylation of p38 MAPK was blocked by compound C; the increased Bim expression was blocked by p38 MAPK siRNA; CLA-induced apoptosis was attenuated by the p38 inhibitor SB-203580 and by siRNAs directed against p38 MAPK or Bim.

Tumor necrosis factor deficiency inhibits mammary tumorigenesis and a tumor necrosis factor neutralizing antibody decreases mammary tumor growth in neu/erbB2 transgenic mice

Tumor necrosis factor-alpha (TNF-alpha) is a pleiotropic cytokine that is synthesized and secreted by cells of the immune system, as well as by certain epithelia and stroma. Based on our previous studies demonstrating TNF-stimulated proliferation of normal and malignant mammary epithelial cells, we hypothesized that TNF might promote the growth of breast cancer in vivo. To test this, we generated bigenic mice that overexpressed activated neu/erbB2 in the mammary epithelium and whose TNF status was wild-type, heterozygous, or null. Mammary tumorigenesis was significantly decreased in TNF-/- mice (n = 30) compared with that in TNF+/+ mice (n = 27), with a palpable tumor incidence of 10.0% and 44.4%, and palpable tumors/mouse of 0.10 +/- 0.06 and 0.67 +/- 0.17, respectively. Tumorigenesis in the heterozygous group fell between that in the TNF+/+ and TNF-/- groups, but was not significantly different from either of the homozygous groups. The decreased tumor development in the TNF-/- mice was associated with a decreased proliferative index in the lobular and ductal mammary epithelium. To further investigate the role of TNF in breast cancer, mammary tumor-bearing mice whose tumors overexpressed wild-type neu/erbB2 were treated with a TNF-neutralizing antibody or a control antibody for 4 weeks (n = 20/group). Mammary tumor growth was significantly inhibited in mice treated with the anti-TNF antibody compared with the control antibody. Together, these data show a stimulatory role for TNF in the growth of breast tumors and suggest that TNF antagonists may be effective in a subset of patients with breast cancer.

Conjugated linoleic acid (CLA) inhibits expression of the Spot 14 (THRSP) and fatty acid synthase genes and impairs the growth of human breast cancer and liposarcoma cells

Spot 14 (THRSP, S14) is a nuclear protein involved in the regulation of genes required for fatty acid synthesis in normal and malignant mammary epithelial and adipose cells. Harvatine and Bauman (1) reported that conjugated linoleic acid (CLA) inhibits S14 gene expression in bovine mammary and mouse adipose tissues and reduces milk fat production in cows. We hypothesized that CLA inhibits S14 gene expression in human breast cancer and liposarcoma cells and that this will retard their growth. Exposure of T47D breast cancer cells to a mixture of CLA isomers reduced the expression of the S14 and fatty acid synthase (FAS) genes. The mixture caused a dose-related inhibition of T47D cell growth, as did pure c9, t11 and t10, c12-CLA, but not linoleic acid. Similar effects were observed in MDA-MB-231 breast cancer cells. Provision of 8 mircoM palmitate fully (CLA mix, t10, c12-CLA) or partially (c9, t11-CLA) reversed the antiproliferative effect in T47D cells. CLA likewise suppressed levels of S14 and FAS mRNAs in liposarcoma cells and caused growth inhibition that was prevented by palmitic acid. CLA did not affect the growth of nonlipogenic HeLa cells or human fibroblasts. We conclude that as in bovine mammary and mouse adipose cells, CLA suppresses S14 and FAS gene expression in human breast cancer and liposarcoma cells. Rescue from the antiproliferative effect of CLA by palmitic acid indicates that reduced tumor lipogenesis is a major mechanism for the anticancer effects of CLA.

t10c12 conjugated linoleic acid suppresses HER2 protein and enhances apoptosis in SKBr3 breast cancer cells: possible role of COX2

Background

HER2-targeted therapy with the monoclonal antibody trastuzumab (Herceptin®) has improved disease-free survival for women diagnosed with HER2-positive breast cancers; however, treatment resistance and disease progression are not uncommon. Current data suggest that resistance to treatment in HER2 cancers may be a consequence of NF-κB overexpression and increased COX2-derived prostaglandin E2 (PGE₂). Conjugated linoleic acid (CLA) has been shown to have anti-tumor properties and to inhibit NF-κB activity and COX2.

Methods

In this study, HER2-overexpressing SKBr3 breast cancer cells were treated with t10c12 CLA. Protein expression of the HER2 receptor, nuclear NF-κB p65, and total and phosphorylated IκB were examined by western blot and immunofluorescence. PGE₂ levels were determined by ELISA. Proliferation was measured by metabolism of 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT), and apoptosis was measured by FITC-conjugated Annexin V staining and flow cytometry.

Results/Conclusions

We observed a significant decrease in HER2 protein expression on western blot following treatment with 40 and 80 µM t10c12 CLA (p<0.01 and 0.001, respectively) and loss of HER2 protein in cells using immunoflourescence that was most pronounced at 80 µM. Protein levels of nuclear NF-κB p65 were also significantly reduced at the 80 µM dose. This was accompanied by a significant decrease in PGE₂ levels (p = 0.05). Pretreatment with t10c12 CLA significantly enhanced TNFα-induced apoptosis and the anti-proliferative action of trastuzumab (p = 0.05 and 0.001, respectively). These data add to previous reports of an anti-tumor effect of t10c12 CLA and suggest an effect on the HER2 oncogene that may be through CLA mediated downregulation of COX2-derived PGE₂.

Trans-10, cis-12 conjugated linoleic acid modulates phagocytic responses of canine peripheral blood polymorphonuclear neutrophilic leukocytes exposed to Clostridium difficile toxin B

Trans-10, cis-12 conjugated linoleic acid (t10c12-CLA) has been reported to enhance phagocyte function. Clostridium difficile toxin B (TcdB) has been known to inhibit Ras-homologous (Rho) guanosine triphosphatases (GTPases) which play essential roles in neutrophil immune functions. Here, we examined whether in vitro treatment with t10c12-CLA modulates the filamentous actin (F-actin) polymerization, phagocytic capacity, and oxidative burst activity (OBA) of canine peripheral blood polymorphonuclear neutrophilic leukocytes (PMNs) exposed to TcdB. Treatment with t10c12-CLA, but not linoleic acid, enhanced PMN F-actin polymerization, phagocytic capacity, and OBA, while TcdB suppressed these functions. t10c12-CLA reversed the suppressive effects of TcdB on these PMN functions. t10c12-CLA stimulated F-actin polymerization regardless of whether phagocytosis was stimulated by microspheres but only elevated OBA when microspheres were added. We asked whether the effects of t10c12-CLA were associated with changes in the activation of the Rho GTPase Cdc42. Treatment with t10c12-CLA augmented Cdc42 activity in both TcdB-treated and TcdB-naive PMNs during phagocytosis. Thus, t10c12-CLA up-regulates PMN phagocytic responses attenuated by TcdB. This effect is associated with an increase in actin polymerization and may involve the activation of Cdc42.

t10,c12-Conjugated linoleic acid stimulates mammary tumor progression in Her2/ErbB2 mice through activation of both proliferative and survival pathways

The t10,c12 isomer of conjugated linoleic acid (CLA) inhibits rat mammary carcinogenesis, metastasis from a transplantable mouse mammary tumor and angiogenesis; however, it stimulates mammary tumorigenesis in transgenic mice overexpressing ErbB2 in the mammary epithelium (ErbB2 transgenic mice). In the current study, we report that a 4-week supplementation of the diet with 0.5% trans-10, cis-12 conjugated linoleic acid (t10,c12-CLA) stimulated the growth of established ErbB2-overexpressing mammary tumors by 30% and increased the number of new tumors from 11% to 82%. Additionally, when t10,c12-CLA supplementation of ErbB2 transgenic mice was initiated at 21 weeks of age, a time just prior to tumor appearance, overall survival was decreased from 46.4 weeks in the control to 39.0 weeks in the CLA group, and survival after detection of a palpable tumor from 7.5 to 4.6 weeks. Short-term supplementation from 10 to 14 weeks or 21 to 25 weeks of age temporarily accelerated tumor development, but over the long term, there was no significant effect on mammary tumorigenesis. Long term as well as a short 4-week supplementation increased mammary epithelial hyperplasia and lobular development, and altered the mammary stroma; this was reversible in mice returned to the control diet. t10,c12-CLA altered proliferation and apoptosis of the mammary epithelium, although this differed depending on the length of administration and/or the age of the mice. The increased tumor development with t10,c12-CLA was associated with increased phosphorylation of the IGF-I/insulin receptor, as well as increased signaling through the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase and phosphatidylinositol 3-kinase/Akt pathways; however, neither phospho-ErbB2 nor ErbB2 was altered.

Apoptosis induced by t10,c12-conjugated linoleic acid is mediated by an atypical endoplasmic reticulum stress response

Conjugated linoleic acid (CLA) inhibits rat mammary carcinogenesis, in part by inducing apoptosis of preneoplastic and neoplastic mammary epithelial cells. The current study focused on the mechanism by which apoptosis is induced. In TM4t mammary tumor cells, trans-10,cis-12 (t10,c12)-CLA induced proapoptotic C/EBP-homologous protein (CHOP) concurrent with the cleavage of poly(ADP-ribose) polymerase. Knockdown of CHOP attenuated t10,c12-CLA-induced apoptosis. Furthermore, t10,c12-CLA induced the cleavage of endoplasmic reticulum (ER)-resident caspase-12, and a selective inhibitor of caspase-12 significantly alleviated t10,c12-CLA-induced apoptosis. Using electron microscopy, we observed that t10,c12-CLA treatment resulted in marked dilatation of the ER lumen. Together, these data suggest that t10,c12-CLA induces apoptosis through ER stress. To further explore the ER stress pathway, we examined the expression of the following upstream ER stress signature markers in response to CLA treatment: X-box binding protein 1 (XBP1) mRNA (unspliced and spliced), phospho-eukaryotic initiation factor (eIF) 2 alpha, activating transcription factor 4 (ATF4), and BiP proteins. We found that t10,c12-CLA induced the expression and splicing of XBP1 mRNA as well as the phosphorylation of eIF2 alpha. In contrast, ATF4 was induced modestly, but not significantly, and BiP was not altered. In summary, our data demonstrate that apoptosis induced by t10,c12-CLA is mediated, at least in part, through an atypical ER stress response that culminates in the induction of CHOP and the cleavage of caspase-12.

Conjugated linoleic acid isomers and cancer

We reviewed the literature regarding the effects of conjugated linoleic acid (CLA) preparations enriched in specific isomers, cis9, trans11-CLA (c9, t11-CLA) or trans10, cis12-CLA (t10, c12-CLA), on tumorigenesis in vivo and growth of tumor cell lines in vitro. We also examined the potential mechanisms by which CLA isomers may alter the incidence of cancer. We found no published reports that examined the effects of purified CLA isomers on human cancer in vivo. Incidence of rat mammary tumors induced by methylnitrosourea was decreased by c9, t11-CLA in all studies and by t10, c12-CLA in just a few that included it. Those 2 isomers decreased the incidence of forestomach tumors induced by benzo (a) pyrene in mice. Both isomers reduced breast and forestomach tumorigenesis. The c9, t11-CLA isomer did not affect the development of spontaneous tumors of the intestine or mammary gland, whereas t10, c12-CLA increased development of genetically induced mammary and intestinal tumors. In vitro, t10, c12-CLA inhibited the growth of mammary, colon, colorectal, gastric, prostate, and hepatoma cell lines. These 2 CLA isomers may regulate tumor growth through different mechanisms, because they have markedly different effects on lipid metabolism and regulation of oncogenes. In addition, c9, t11-CLA inhibited the cyclooxygenase-2 pathway and t10, c12-CLA inhibited the lipooxygenase pathway. The t10, c12-CLA isomer induced the expression of apoptotic genes, whereas c9, t11-CLA did not increase apoptosis in most of the studies that assessed it. Several minor isomers including t9, t11-CLA; c11, t13-CLA; c9, c11-CLA; and t7, c11-CLA were more effective than c9, t11-CLA or t10, c12-CLA in inhibiting cell growth in vitro. Additional studies with purified isomers are needed to establish the health benefit and risk ratios of each isomer in humans.

Conjugated linoleic acid induces apoptosis of murine mammary tumor cells via Bcl-2 loss

Conjugated linoleic acid (CLA) is a powerful anticancer agent in a number of tumor model systems; however, its precise mechanism of action remains elusive. Here, we report that t10,c12 CLA, a component of synthetic CLA supplements, induced apoptosis and G1 arrest of p53 mutant TM4t murine mammary tumor cells. Furthermore, t10,c12-CLA induced a time- and concentration-dependent cleavage of caspases-3 and -9, and release of cytochrome c from mitochondria to cytosol. Levels of Bcl-2 protein were decreased both in total cellular lysates and in mitochondria after t10,c12-CLA treatment; however, there was no significant change in Bax or Bak. Overexpression of Bcl-2 attenuated apoptosis in response to t10,c12-CLA treatment. These results demonstrate that t10,c12-CLA triggers apoptosis of p53 mutant murine mammary tumor cells through the mitochondrial pathway by targeting Bcl-2.