In vivo and in vitro regulation of syndecan 1 in prostate cells by n-3 polyunsaturated fatty acids

Natural compounds targeting nuclear receptors for effective cancer therapy

Human nuclear receptors (NRs) are a family of forty-eight transcription factors that modulate gene expression both spatially and temporally. Numerous biochemical, physiological, and pathological processes including cell survival, proliferation, differentiation, metabolism, immune modulation, development, reproduction, and aging are extensively orchestrated by different NRs. The involvement of dysregulated NRs and NR-mediated signaling pathways in driving cancer cell hallmarks has been thoroughly investigated. Targeting NRs has been one of the major focuses of drug development strategies for cancer interventions. Interestingly, rapid progress in molecular biology and drug screening reveals that the naturally occurring compounds are promising modern oncology drugs which are free of potentially inevitable repercussions that are associated with synthetic compounds. Therefore, the purpose of this review is to draw our attention to the potential therapeutic effects of various classes of natural compounds that target NRs such as phytochemicals, dietary components, venom constituents, royal jelly-derived compounds, and microbial derivatives in the establishment of novel and safe medications for cancer treatment. This review also emphasizes molecular mechanisms and signaling pathways that are leveraged to promote the anti-cancer effects of these natural compounds. We have also critically reviewed and assessed the advantages and limitations of current preclinical and clinical studies on this subject for cancer prophylaxis. This might subsequently pave the way for new paradigms in the discovery of drugs that target specific cancer types.

The Involvement of Polyunsaturated Fatty Acids in Apoptosis Mechanisms and Their Implications in Cancer

Cancer is a significant global public health issue and, despite advancements in detection and treatment, the prognosis remains poor. Cancer is a complex disease characterized by various hallmarks, including dysregulation in apoptotic cell death pathways. Apoptosis is a programmed cell death process that efficiently eliminates damaged cells. Several studies have indicated the involvement of polyunsaturated fatty acids (PUFAs) in apoptosis, including omega-3 PUFAs such as alpha-linolenic acid, docosahexaenoic acid, and eicosapentaenoic acid. However, the role of omega-6 PUFAs, such as linoleic acid, gamma-linolenic acid, and arachidonic acid, in apoptosis is controversial, with some studies supporting their activation of apoptosis and others suggesting inhibition. These PUFAs are essential fatty acids, and Western populations today have a high consumption rate of omega-6 to omega-3 PUFAs. This review focuses on presenting the diverse molecular mechanisms evidence in both in vitro and in vivo models, to help clarify the controversial involvement of omega-3 and omega-6 PUFAs in apoptosis mechanisms in cancer.

Peroxisome Proliferator-Activated Receptors and the Hallmarks of Cancer

Peroxisome proliferator-activated receptors (PPARs) function as nuclear transcription factors upon the binding of physiological or pharmacological ligands and heterodimerization with retinoic X receptors. Physiological ligands include fatty acids and fatty-acid-derived compounds with low specificity for the different PPAR subtypes (alpha, beta/delta, and gamma). For each of the PPAR subtypes, specific pharmacological agonists and antagonists, as well as pan-agonists, are available. In agreement with their natural ligands, PPARs are mainly focused on as targets for the treatment of metabolic syndrome and its associated complications. Nevertheless, many publications are available that implicate PPARs in malignancies. In several instances, they are controversial for very similar models. Thus, to better predict the potential use of PPAR modulators for personalized medicine in therapies against malignancies, it seems necessary and timely to review the three PPARs in relation to the didactic concept of cancer hallmark capabilities. We previously described the functions of PPAR beta/delta with respect to the cancer hallmarks and reviewed the implications of all PPARs in angiogenesis. Thus, the current review updates our knowledge on PPAR beta and the hallmarks of cancer and extends the concept to PPAR alpha and PPAR gamma.

Plasma Metabolomics Analysis of Polyvinyl Chloride Workers Identifies Altered Processes and Candidate Biomarkers for Hepatic Hemangiosarcoma and Its Development

BACKGROUND

High-level occupational vinyl chloride (VC) exposures have been associated with hepatic hemangiosarcoma, which typically develops following a long latency period. Although VC is genotoxic, a more comprehensive mode of action has not been determined and diagnostic biomarkers have not been established. The purpose of this study is to address these knowledge gaps through plasma metabolomics.

METHODS

Plasma samples from polyvinyl chloride polymerization workers who developed hemangiosarcoma (cases, n = 15) and VC exposure-matched controls (n = 17) underwent metabolomic analysis. Random forest and bioinformatic analyses were performed.

RESULTS

Cases and controls had similar demographics and routine liver biochemistries. Mass spectroscopy identified 606 known metabolites. Random forest analysis had an 82% predictive accuracy for group classification. 60 metabolites were significantly increased and 44 were decreased vs. controls. Taurocholate, bradykinin and fibrin degradation product 2 were up-regulated by greater than 80-fold. The naturally occurring anti-angiogenic phenol, 4-hydroxybenzyl alcohol, was down-regulated 5-fold. Top affected ontologies involved: (i) metabolism of bile acids, taurine, cholesterol, fatty acids and amino acids; (ii) inflammation and oxidative stress; and (iii) nicotinic cholinergic signaling.

CONCLUSIONS

The plasma metabolome was differentially regulated in polyvinyl chloride workers who developed hepatic hemangiosarcoma. Ontologies potentially involved in hemangiosarcoma pathogenesis and candidate biomarkers were identified.

A Pilot Study Assessing the Impact of rs174537 on Circulating Polyunsaturated Fatty Acids and the Inflammatory Response in Patients with Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of death and disability in persons under age 45. The hallmark secondary injury profile after TBI involves dynamic interactions between inflammatory and metabolic pathways including fatty acids. Omega-3 polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) have been shown to provide neuroprotective benefits by minimizing neuroinflammation in rodents. These effects have been less conclusive in humans, however. We postulate genetic variants influencing PUFA metabolism in humans could contribute to these disparate findings. Therefore, we sought to (1) characterize the circulating PUFA response and (2) evaluate the impact of rs174537 on inflammation after TBI. A prospective, single-center, observational pilot study was conducted to collect blood samples from Level-1 trauma patients (N = 130) on admission and 24 h post-admission. Plasma was used to quantify PUFA levels and inflammatory cytokines. Deoxyribonucleic acid was extracted and genotyped at rs174537. Associations between PUFAs and inflammatory cytokines were analyzed for all trauma cases and stratified by race (Caucasians only), TBI (TBI: N = 47; non-TBI = 83) and rs174537 genotype (GG: N = 33, GT/TT: N = 44). Patients with TBI had higher plasma DHA levels compared with non-TBI at 24 h post-injury (p = 0.013). The SNP rs174537 was associated with both PUFA levels and inflammatory cytokines (p < 0.05). Specifically, TBI patients with GG genotype exhibited the highest plasma levels of DHA (1.33%) and interleukin-8 (121.5 ± 43.3 pg/mL), which were in turn associated with poorer outcomes. These data illustrate the impact of rs174537 on the post-TBI response. Further work is needed to ascertain how this genetic variant directly influences inflammation after trauma.

The Combination of Omega-3 Stearidonic Acid and Docetaxel Enhances Cell Death over Docetaxel Alone in Human Prostate Cancer Cells

Background: Docetaxel (DOC), or Taxotere, is an anthracycline antibiotic used to treat multiple types of cancer. It is a first-line chemotherapy treatment for patients with metastasized, hormone-resistant prostate cancer (PCa) or for patients with high-risk, localized PCa that could benefit from early chemotherapy treatment. Previously, we showed that stearidonic acid (SDA), an omega-3 fatty acid, enhances the cytotoxicity of doxorubicin (DOX) in human PCa cells. This observation suggests that PCa therapies using SDA and chemotherapeutic drugs in combination offer attractive possibilities for developing treatments that ameliorate toxic side effects of some commonly used chemotherapy drugs.

Objectives: We used androgen-resistant PC3 and DU 145 cells derived from human prostate cancer to quantify the effects of combined SDA and DOC on proliferation/viability and on the production of pro-apoptotic caspases 9 and 3. We also compared the effects of SDA with those of BAY, a pharmacological inhibitor of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-ĸB), in androgen-sensitive LNCaP cells. Finally, we qualitatively and quantitatively assessed the drug combination on androgen receptor (AR) and peroxisome proliferator-activated receptor gamma (PPARγ) expression in LNCaP and PC3 cells, respectively.

Methods: The half maximal inhibitory concentration (IC50) and combination indices of SDA and DOC in PC3 and DU 145 cells were determined using the MTT cell viability assay. To quantify the effects of SDA and BAY on NF-ĸB activity, we used luciferase reporter assays in LNCaP cells that were stably transduced with lentiviral vectors carrying NF-ĸB response element sequence upstream of the luciferase gene sequence. AR and PPARγ expression were assessed by western blotting and immunocytochemistry. We considered caspase 9 and 3 cleavage to be apoptosis markers and determined the drug combination effect on the extent of that cleavage by western blot analysis.

Results: The cytotoxic effects of DOC were synergistically enhanced by SDA when the two were added to DU145 and PC3 cell cultures. Combination index (CI) analyses based on the Chou-Talalay method and mass action law showed synergistic interaction with CI <1. SDA suppressed TNFα-induced NF-κB activity similarly to BAY. The SDA/DOC combination down regulated testosterone (T)-induced AR and troglitazone-induced PPARγ protein expression when compared to using the drugs singly. Similarly, the SDA/DOC combination induced caspase 9 and 3 production and cleavage suggesting apoptosis induction. Like our DOX studies, this work provides proof-of-concept for using SDA and DOC in combination to reduce the dose, and therefore the toxicity, of DOC and possibly increasing the survival benefit in DOC clinical translation studies.

Involvement of apoptotic pathways in docosahexaenoic acid-induced benefit in prostate cancer: Pathway-focused gene expression analysis using RT2 Profile PCR Array System

Background

Present study aimed to better understand the potential apoptotic pathways that involved in docosahexaenoic acid (DHA)-induced apoptosis of prostate cancer cells.

Methods

Human prostate cancer DU145 cells were treated with different concentrations of fish oil, omega-3 PUFA (DHA, and Eicosapentaenoic acid, EPA), or omega-6 PUFA (Arachidonic acid, AA). Cell viability and apoptosis were evaluated by MTT assay and Hoechst staining. Pathway-focused gene expression profiling of DU145 cells was analyzed with the RT² Profile PCR Array System. The results were verified by real time quantitative polymerase chain reaction (RT-qPCR).

Results

AA exposure showed no obvious effect on viability of DU145 cells. However, exposure with fish oil, EPA, or DHA for 24 h significantly affected cell viability. The growth inhibition of DHA was more pronounced than that of EPA and showed a time-dependent increase. DHA exposure caused typical apoptotic characteristics. Ten genes were more expressed, while 5 genes were less expressed following DHA exposure. RT-qPCR confirmed the time dependent effect of DHA on the expression of these differentially expressed genes. KEGG pathway analysis showed that DHA may induce the apoptosis of cancer cells preferentially through mediating P53, MAPK, TNF, PI3K/AKT, and NF-κB signaling pathways.

Conclusion

Our study demonstrated the beneficial action of DHA on human prostate carcinoma cell line DU145. The pro-apoptotic effect of DHA on DU145 cells may involve mediation various pathways, especially P53, MAPK, TNF, PI3K/AKT, and NF-κB signaling pathways. Molecular mechanisms of DHA on apoptosis of cancer cells still need to be further clarified.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-017-0442-5) contains supplementary material, which is available to authorized users.

Fish-Derived Omega-3 Fatty Acids and Prostate Cancer: A Systematic Review

BACKGROUND

The use of natural health products in prostate cancer (PrCa) is high despite a lack of evidence with respect to safety and efficacy. Fish-derived omega-3 fatty acids possess anti-inflammatory effects and preclinical data suggest a protective effect on PrCa incidence and progression; however, human studies have yielded conflicting results.

METHODS

A search of OVID MEDLINE, Pre-MEDLINE, Embase, and the Allied and Complementary Medicine Database (AMED) was completed for human interventional or observational data assessing the safety and efficacy of fish-derived omega-3 fatty acids in the incidence and progression of PrCa.

RESULTS

Of 1776 citations screened, 54 publications reporting on 44 studies were included for review and analysis: 4 reports of 3 randomized controlled trials, 1 nonrandomized clinical trial, 20 reports of 14 cohort studies, 26 reports of 23 case-control studies, and 3 case-cohort studies. The interventional studies using fish oil supplements in patients with PrCa showed no impact on prostate-specific antigen levels; however, 2 studies showed a decrease in inflammatory or other cancer markers. A small number of mild adverse events were reported and interactions with other interventions were not assessed. Cohort and case-control studies assessing the relationship between dietary fish intake and the risk of PrCa were equivocal. Cohort studies assessing the risk of PrCa mortality suggested an association between higher intake of fish and decreased risk of prostate cancer-related death.

CONCLUSIONS

Current evidence is insufficient to suggest a relationship between fish-derived omega-3 fatty acid and risk of PrCa. An association between higher omega-3 intake and decreased PrCa mortality may be present but more research is needed. More intervention trials or observational studies with precisely measured exposure are needed to assess the impact of fish oil supplements and dietary fish-derived omega-3 fatty acid intake on safety, PrCa incidence, treatment, and progression.

Endogenous omega-3 long-chain fatty acid biosynthesis from alpha-linolenic acid is affected by substrate levels, gene expression, and product inhibition

Previous studies have suggested that dietary alpha-linolenic acid (ALA) increases the levels of omega-3 long-chain polyunsaturated fatty acids (ω-3 LC-PUFAs)in vivo, but the conversion procedure and the genes involved remain poorly understood.

Omega-3 Fatty Acids and Cancer Cell Cytotoxicity: Implications for Multi-Targeted Cancer Therapy

Cancer is a major disease worldwide. Despite progress in cancer therapy, conventional cytotoxic therapies lead to unsatisfactory long-term survival, mainly related to development of drug resistance by tumor cells and toxicity towards normal cells. n-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), can exert anti-neoplastic activity by inducing apoptotic cell death in human cancer cells either alone or in combination with conventional therapies. Indeed, n-3 PUFAs potentially increase the sensitivity of tumor cells to conventional therapies, possibly improving their efficacy especially against cancers resistant to treatment. Moreover, in contrast to traditional therapies, n-3 PUFAs appear to cause selective cytotoxicity towards cancer cells with little or no toxicity on normal cells. This review focuses on studies investigating the cytotoxic activity of n-3 PUFAs against cancer cells via apoptosis, analyzing the molecular mechanisms underlying this effective and selective activity. Here, we highlight the multiple molecules potentially targeted by n-3 PUFAs to trigger cancer cell apoptosis. This analysis can allow a better comprehension of the potential cytotoxic therapeutic role of n-3 PUFAs against cancer, providing specific information and support to design future pre-clinical and clinical studies for a better use of n-3 PUFAs in cancer therapy, mainly combinational therapy.

n-3 Polyunsaturated Fatty Acids and their Role in Cancer Chemoprevention

Polyunsaturated fatty acids (PUFAs), including omega-3 (n-3) and omega-6 (n-6) PUFAs, are essential for human health. Recent research shows n-3 PUFAs and their mediators can inhibit inflammation, angiogenesis and cancer via multiple mechanisms, including reduced release of n-6 fatty acid arachidonic acid from cell membranes, inhibition of enzymatic activities, and direct competition with arachidonic acid for enzymatic conversions. In this review, we discuss inflammation-related cancer, anti-inflammatory effects of n-3 PUFA lipid mediators, antineoplastic activities of n-3 PUFA in vitro and in vivo, and present an update on recent human trials.

The therapeutic effects of docosahexaenoic acid on oestrogen/androgen-induced benign prostatic hyperplasia in rats

Benign prostatic hyperplasia (BPH) is one of the major disorders of the urinary system in elderly men. Docosahexaenoic acid (DHA) is the main component of n-3 polyunsaturated fatty acids (n-3 PUFAs) and has nerve protective, anti-inflammatory and tumour-growth inhibitory effects. Here, the therapeutic potential of DHA in treating BPH was investigated. Seal oil effectively prevented the development of prostatic hyperplasia induced by oestradiol/testosterone in a rat model by suppressing the increase of the prostatic index (PI), reducing the thickness of the peri-glandular smooth muscle layer, inhibiting the proliferation of both prostate epithelial and stromal cells, and downregulating the expression of androgen receptor (AR) and oestrogen receptor α (ERα). An in vitro study showed that DHA inhibited the growth of the human prostate stromal cell line WPMY-1 and the epithelial cell line RWPE-1 in a dose- and time-dependent manner. In both cell lines, the DHA arrested the cell cycle in the G2/M phase. In addition, DHA also reduced the expression of ERα and AR in the WPMY-1 and RWPE-1 cells. These results indicate that DHA inhibits the multiplication of prostate stromal and epithelial cells through a mechanism that may involve cell cycle arrest and the downregulation of ERα and AR expression.

Effects of eicosapentaenoic acid and docosahexaenoic acid on prostate cancer cell migration and invasion induced by tumor-associated macrophages

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the major n-3 polyunsaturated fatty acids (PUFAs) in fish oil that decrease the risk of prostate cancer. Tumor-associated macrophages (TAMs) are the main leukocytes of intratumoral infiltration, and increased TAMs correlates with poor prostate cancer prognosis. However, the mechanism of n-3 PUFAs on prostate cancer cell progression induced by TAMs is not well understood. In this study, we investigated the effects of EPA and DHA on modulating of migration and invasion of prostate cancer cells induced by TAMs-like M2-type macrophages. PC-3 prostate cancer cells were pretreated with EPA, DHA, or the peroxisome proliferator-activated receptor (PPAR)-γ antagonist, GW9662, before exposure to conditioned medium (CM). CM was derived from M2-polarized THP-1 macrophages. The migratory and invasive abilities of PC-3 cells were evaluated using a coculture system of M2-type macrophages and PC-3 cells. EPA/DHA administration decreased migration and invasion of PC-3 cells. The PPAR-γ DNA-binding activity and cytosolic inhibitory factor κBα (IκBα) protein expression increased while the nuclear factor (NF)-κB p65 transcriptional activity and nuclear NF-κB p65 protein level decreased in PC-3 cells incubated with CM in the presence of EPA/DHA. Further, EPA/DHA downregulated mRNA expressions of matrix metalloproteinase-9, cyclooxygenase-2, vascular endothelial growth factor, and macrophage colony-stimulating factor. Pretreatment with GW9662 abolished the favorable effects of EPA/DHA on PC-3 cells. These results indicate that EPA/DHA administration reduced migration, invasion and macrophage chemotaxis of PC-3 cells induced by TAM-like M2-type macrophages, which may partly be explained by activation of PPAR-γ and decreased NF-κB p65 transcriptional activity.

The omega-3 polyunsaturated fatty acid DHA induces simultaneous apoptosis and autophagy via mitochondrial ROS-mediated Akt-mTOR signaling in prostate cancer cells expressing mutant p53

Docosahexaenoic acid (DHA) induces autophagy-associated apoptotic cell death in wild-type p53 cancer cells via regulation of p53. The present study investigated the effects of DHA on PC3 and DU145 prostate cancer cell lines harboring mutant p53. Results show that, in addition to apoptosis, DHA increased the expression levels of lipidated form LC3B and potently stimulated the autophagic flux, suggesting that DHA induces both autophagy and apoptosis in cancer cells expressing mutant p53. DHA led to the generation of mitochondrial reactive oxygen species (ROS), as shown by the mitochondrial ROS-specific probe mitoSOX. Similarly, pretreatment with the antioxidant N-acetyl-cysteine (NAC) markedly inhibited both the autophagy and the apoptosis triggered by DHA, indicating that mitochondrial ROS mediate the cytotoxicity of DHA in mutant p53 cells. Further, DHA reduced the levels of phospho-Akt and phospho-mTOR in a concentration-dependent manner, while NAC almost completely blocked that effect. Collectively, these findings present a novel mechanism of ROS-regulated apoptosis and autophagy that involves Akt-mTOR signaling in prostate cancer cells with mutant p53 exposed to DHA.

Mechanisms of omega-3 polyunsaturated fatty acids in prostate cancer prevention

This review focuses on several key areas where progress has been made recently to highlight the role of omega-3 polyunsaturated fatty acid in prostate cancer prevention.

15-Lipoxygenase-1-mediated metabolism of docosahexaenoic acid is required for syndecan-1 signaling and apoptosis in prostate cancer cells

Fatty acid metabolism impacts multiple intracellular signaling pathways in many cell types, but its role in prostate cancer cells is still unclear. Our previous studies have shown that the n-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) induces apoptosis in human prostate cancer cells by a syndecan-1 (SDC-1)-dependent mechanism. Here, we examined the contribution of lipoxygenase (LOX)- and cyclooxygenase (COX)-mediated DHA metabolism to this effect. Pan-LOX inhibitor (nordihydroguaiaretic acid), 15-LOX inhibitor (luteolin) or 15/12-LOX inhibitor (baicalein) blocked the induced effect of DHA on SDC-1 expression and apoptosis in human prostate cancer cells, whereas 5-LOX inhibitor, AA861, was ineffective. Human prostate cancer cells lines (PC3, LNCaP and DU145 cells) expressed two 15-LOX isoforms, 15-LOX-1 and 15-LOX-2, with higher 15-LOX-1 and lower 15-LOX-2 expressions compared with human epithelial prostate cells. Knockdown of 15-LOX-1 blocked the effect of DHA on SDC-1 expression and caspase-3 activity, whereas silencing 15-LOX-2, 5-LOX, COX-1, COX-2 or 12-LOX had no effect. Moreover, the ability of DHA to inhibit the activity of the PDK/Akt (T308) signaling pathway was abrogated by silencing 15-LOX-1. These findings demonstrate that 15-LOX-1-mediated metabolism of DHA is required for it to upregulate SDC-1 and trigger the signaling pathway that elicits apoptosis in prostate cancer cells.

15-lipoxygenase metabolites of docosahexaenoic acid inhibit prostate cancer cell proliferation and survival

A 15-LOX, it is proposed, suppresses the growth of prostate cancer in part by converting arachidonic, eicosatrienoic, and/or eicosapentaenoic acids to n-6 hydroxy metabolites. These metabolites inhibit the proliferation of PC3, LNCaP, and DU145 prostate cancer cells but only at ≥1-10 µM. We show here that the 15-LOX metabolites of docosahexaenoic acid (DHA), 17-hydroperoxy-, 17-hydroxy-, 10,17-dihydroxy-, and 7,17-dihydroxy-DHA inhibit the proliferation of these cells at ≥0.001, 0.01, 1, and 1 µM, respectively. By comparison, the corresponding 15-hydroperoxy, 15-hydroxy, 8,15-dihydroxy, and 5,15-dihydroxy metabolites of arachidonic acid as well as DHA itself require ≥10-100 µM to do this. Like DHA, the DHA metabolites a) induce PC3 cells to activate a peroxisome proliferator-activated receptor-γ (PPARγ) reporter, express syndecan-1, and become apoptotic and b) are blocked from slowing cell proliferation by pharmacological inhibition or knockdown of PPARγ or syndecan-1. The DHA metabolites thus slow prostate cancer cell proliferation by engaging the PPARγ/syndecan-1 pathway of apoptosis and thereby may contribute to the prostate cancer-suppressing effects of not only 15-LOX but also dietary DHA.

Polyunsaturated fatty acid metabolism in prostate cancer

Polyunsaturated fatty acids (PUFA) play important roles in the normal physiology and in pathological states including inflammation and cancer. While much is known about the biosynthesis and biological activities of eicosanoids derived from ω6 PUFA, our understanding of the corresponding ω3 series lipid mediators is still rudimentary. The purpose of this review is not to offer a comprehensive summary of the literature on fatty acids in prostate cancer but rather to highlight some of the areas where key questions remain to be addressed. These include substrate preference and polymorphic variants of enzymes involved in the metabolism of PUFA, the relationship between de novo lipid synthesis and dietary lipid metabolism pathways, the contribution of cyclooxygenases and lipoxygenases as well as terminal synthases and prostanoid receptors in prostate cancer, and the potential role of PUFA in angiogenesis and cell surface receptor signaling.

Omega-3 fatty acids induce apoptosis in human breast cancer cells and mouse mammary tissue through syndecan-1 inhibition of the MEK-Erk pathway

Human epidemiological studies have shown that diets enriched in n-3 polyunsaturated fatty acids (n-3 PUFA) are associated with a lower incidence of cancers including breast cancer. Our previous studies showed that the n-3 PUFA, docosahexaenoic acid (DHA), upregulated syndecan-1 (SDC-1) expression to induce apoptosis in the human breast cancer cell line MCF-7. We now present evidence of a signaling pathway that is impacted by SDC-1 in these cells and in mouse mammary tissues to result in apoptosis. In MCF-7 cells and SK-BR-3 cells, DHA and a SDC-1 ectodomain impaired signaling of the p44/42 mitogen-activated protein kinase (MAPK) pathway by inhibiting the phosphorylation of MAPK/Erk (MEK)/extracellular signal-regulated kinase (Erk) and Bad to induce apoptosis. SDC-1 siRNA significantly enhanced phosphorylation of these signal molecules and blocked the inhibitory effects of DHA on their phosphorylation. SDC-1 siRNA diminished apoptosis of MCF-7 cells, an effect that was markedly blocked by MEK inhibitor, PD98059. In vivo studies used (i) Fat-1 mice, a genetic model able to convert n-6 to n-3 PUFA to result in higher SDC-1 levels in Fat-1 mammary tissue compared with that of wild-type (wt) mice. Phosphorylation of MEK, Erk and Bad was lower in the Fat-1 versus wt tissue and (ii) SDC-1(-/-) mice that demonstrated markedly higher levels of phosphorylated MEK, Erk and Bad in mammary gland tissue compared with those of SDC(+/+) mice. These data elucidate a pathway whereby SDC-1, upregulated by DHA, induces apoptosis in breast cancer cells through inhibition of MEK/Erk/Bad signaling.

Omega-3 Fatty Acids and PPARgamma in Cancer

Omega-3 (or n-3) polyunsaturated fatty acids (PUFAs) and their metabolites are natural ligands for peroxisome proliferator receptor activator (PPAR)gamma and, due to the effects of PPARgamma on cell proliferation, survival, and differentiation, are potential anticancer agents. Dietary intake of omega-3 PUFAs has been associated with a reduced risk of certain cancers in human populations and in animal models. In vitro studies have shown that omega-3 PUFAs inhibit cell proliferation and induce apoptosis in cancer cells through various pathways but one of which involves PPARgamma activation. The differential activation of PPARgamma and PPARgamma-regulated genes by specific dietary fatty acids may be central to their distinct roles in cancer. This review summarizes studies relating PUFAs to PPARgamma and cancer and offers a new paradigm relating an n-3 PUFA through PPARgamma to the expression of the cell surface proteoglycan, syndecan-1, and to the death of cancer cells.

Endogenous synthesis of n-3 polyunsaturated fatty acids in Fat-1 mice is associated with increased mammary gland and liver syndecan-1

Long chain n-3 PUFA have been shown to have chemopreventive properties against breast cancer through various mechanisms. One pathway, studied in human breast cancer cell lines, involves upregulation of the proteoglycan, syndecan-1 (SDC-1) by n-3 PUFA-enriched LDL. Using Fat-1 mice that are able to convert n-6 to n-3 PUFA, we tested whether SDC-1 level in vivo is elevated in mammary glands due to endogenously synthesized rather than LDL-derived n-3 PUFA. Female Fat-1 and wild type (wt) mice were fed an n-6 PUFA- enriched diet for 7 weeks. Fatty acid analysis of plasma lipoproteins showed that total n-6 PUFA reflected dietary intake similarly in both genotypes (VLDL, 36.2±2.2 and 40.9±3.9; LDL, 49.0±3.3 and 48.1±2.0; HDL, 54.6±1.2 and 58.2±1.3, mean ± SEM percent of total fatty acids for Fat-1 and wt animals respectively). Lipoprotein percent n-3 PUFA was also similar between groups. However, phospholipids and triglycerides extracted from mammary and liver tissues demonstrated significantly higher n-3 PUFA and a corresponding decrease in the ratio n-6/n-3 PUFA in Fat-1 compared to wt mice. This was accompanied by higher SDC-1 in mammary glands and livers of Fat-1 mice, thus demonstrating that endogenously synthesized n-3 PUFA may upregulate SDC-1 in the presence of high dietary n-6 PUFA.

Effects of n-3 PUFAs on breast cancer cells through their incorporation in plasma membrane

Background

PUFAs are important molecules for membrane order and function; they can modify inflammation-inducible cytokines production, eicosanoid production, plasma triacylglycerol synthesis and gene expression. Recent studies suggest that n-3 PUFAs can be cancer chemopreventive, chemosuppressive and auxiliary agents for cancer therapy. N-3 PUFAs could alter cancer growth influencing cell replication, cell cycle, and cell death. The question that remains to be answered is how n-3 PUFAs can affect so many physiological processes. We hypothesize that n-3 PUFAs alter membrane stability, modifying cellular signalling in breast cancer cells.

Methods

Two lines of human breast cancer cells characterized by different expression of ER and EGFR receptors were treated with AA, EPA or DHA. We have used the MTT viability test and expression of apoptotic markers to evaluate the effect of PUFAs on cancer growth. Phospholipids were analysed by HPLC/GC, to assess n-3 incorporation into the cell membrane.

Results

We have observed that EPA and DHA induce cell apoptosis, a reduction of cell viability and the expression of Bcl2 and procaspase-8. Moreover, DHA slightly reduces the concentration of EGFR but EPA has no effect. Both EPA and DHA reduce the activation of EGFR.

N-3 fatty acids are partially metabolized in both cell lines; AA is integrated without being further metabolized. We have analysed the fatty acid pattern in membrane phospholipids where they are incorporated with different degrees of specificity. N-3 PUFAs influence the n-6 content and vice versa.

Conclusions

Our results indicate that n-3 PUFA feeding might induce modifications of breast cancer membrane structure that increases the degree of fatty acid unsaturation. This paper underlines the importance of nutritional factors on health maintenance and on disease prevention.

Syndecan-1-dependent suppression of PDK1/Akt/bad signaling by docosahexaenoic acid induces apoptosis in prostate cancer

Evidence indicates that diets enriched in n-3 polyunsaturated fatty acids (n-3 PUFAs) reduce the risk of prostate cancer, but biochemical mechanisms are unclear. Syndecan-1 (SDC-1), a transmembrane heparan sulfate proteoglycan, supports the integrity of the epithelial compartment. In tumor cells of epithelial lineage, SDC-1 is generally downregulated. This may result in perturbation of homeostasis and lead to progression of malignancy. Our studies have shown that the n-3 PUFA species, docosahexaenoic acid (DHA), increases SDC-1 expression in prostate tissues of Pten knockout (Pten(P-/-)) mice/cells and human prostate cancer cells. We have now determined that DHA-mediated up-regulation of SDC-1 induces apoptosis. Bovine serum albumin-bound DHA and exogenous human recombinant SDC-1 ecotodomain were delivered to PC3 and LNCaP cells in the presence or absence of SDC-1 small interfering (si)RNA. In the presence of control siRNA, both DHA and SDC-1 ectodomain induced apoptosis, whereas SDC-1 silencing blocked DHA-induced but not SDC-1 ectodomain-induced apoptosis. Downstream effectors of SDC-1 signaling linked to n-3 PUFA-induced apoptosis involved the 3'-phosphoinositide-dependent kinase 1 (PDK1)/Akt/Bad integrating network. A diet enriched in n-3 PUFA decreased phosphorylation of PDK1, Akt (T308), and Bad in prostates of Pten(P-/-) mice. Similar results were observed in human prostate cancer cells in response to DHA and SDC-1 ectodomain. The effect of DHA on PDK1/Akt/Bad signaling was abrogated by SDC-1 siRNA. These findings define a mechanism by which SDC-1-dependent suppression of phosphorylation of PDK1/Akt/Bad mediates n-3 PUFA-induced apoptosis in prostate cancer.

Hepatic heparan sulfate proteoglycans and endocytic clearance of triglyceride-rich lipoproteins

Hypertriglyceridemia, characterized by the accumulation of triglyceride-rich lipoproteins in the blood, affects 10-20% of the population in western countries and increases the risk of atherosclerosis, coronary artery disease, and pancreatitis. The etiology of hypertriglyceridemia is complex, and much interest exists in identifying and characterizing the biological and environmental factors that affect the synthesis and turnover of plasma triglycerides. Genetic studies in mice have recently identified that heparan sulfate proteoglycans are a class of receptors that mediate the clearance of triglyceride-rich lipoproteins in the liver. Heparan sulfate proteoglycans are expressed by endothelial cells that line the hepatic sinusoids and the underlying hepatocytes, and are present in the perisinusoidal space (space of Disse). This chapter discusses the dependence of lipoprotein binding on heparan sulfate structure and the identification of hepatocyte syndecan-1 as the primary proteoglycan that mediates triglyceride-rich lipoprotein clearance.