Docosahexaenoic Acid (DHA), a Primary Tumor Suppressive Omega-3 Fatty Acid, Inhibits Growth of Colorectal Cancer Independent of p53 Mutational Status

Nutrition modulation of gastrointestinal toxicity related to cancer chemotherapy: from preclinical findings to clinical strategy

Chemotherapy-induced gut toxicity is a major dose-limiting toxicity for many anticancer drugs. Gastrointestinal (GI) complications compromise the efficacy of chemotherapy, promote overall malnutrition, aggravate cancer cachexia, and may contribute to worsened prognosis. The GI tract is an attractive target for nutrition modulation, owing to its direct exposure to the diet, participation in uptake and metabolism of nutrients, high rate of cell turnover, and plasticity to nutrition stimuli. Glutamine, ω-3 polyunsaturated fatty acids, and probiotics/prebiotics are therapeutic factors that potentially modulate GI toxicity related to cancer treatments. Preclinical and clinical evidence are reviewed to critically define plausible benefits of these factors and their potential development into adjuncts to cancer chemotherapy. Mechanisms underlying the action of these nutrients are being unraveled in the laboratory. Optimal strategies to translate these findings into clinical care still remain to be elucidated. Key questions that remain to be answered include the following: which nutrient or combination of nutrients is selected for which patient and chemotherapy regimen? What mechanisms are responsible for modulation, and how are nutrient(s) administered in a clinically optimal manner? Research exploring interactions between different nutrients in GI protection is ongoing and demands further understanding. How nutrition preparations given to chemotherapy-treated patients are formulated in terms of component selection and dose optimization should be carefully studied and justified.

Differential roles of internal and terminal double bonds in docosahexaenoic acid: Comparative study of cytotoxicity of polyunsaturated fatty acids to HT-29 human colorectal tumor cell line

The role of the double bonds in docosahexaenoic acid (22:6(Δ4,7,10,13,16,19); DHA) in cytotoxic lipid peroxidation was studied in a superoxide dismutase-defective human colorectal tumor cell line, HT-29. In a conventional culture, DHA and other polyunsaturated fatty acids (PUFAs) were found to induce acute lipid peroxidation and subsequent cell death. PUFAs that lack one or both the terminal double bonds (Δ19 and Δ4) but share Δ7,10,13,16 such as 22:5(Δ7,10,13,16,19), 22:5(Δ4,7,10,13,16), and 22:4(Δ7,10,13,16) were more effective than DHA. Lipid peroxidation and cell death were completely inhibited, except by 22:4(Δ7,10,13,16) when radical-mediated reactions were suppressed by culturing cells in 2% O(2) in the presence of vitamin E. DHA and C22:5 PUFAs but not 22:4(Δ7,10,13,16) were efficiently incorporated in phosphatidylinositol, regardless of the culturing conditions. These and other results suggested that the internal unsaturations Δ7,10,13,16 were sensitive to lipid peroxidation, whereas the terminal ones Δ19 and Δ4 appeared to be involved in assimilation into phospholipids.

Molecular mechanisms for chemoprevention of colorectal cancer by natural dietary compounds

Colorectal cancer is one of the major causes of cancer-related mortality in both men and women worldwide. This review focuses on preventing the initiation and promotion of neoplastic growth in colorectal cancer, particularly with natural dietary compounds. Chemoprevention is defined as the use of natural dietary compounds and/or synthetic substances that can delay, prevent, or even reverse the development of adenomas, as well as the progression from adenoma to carcinoma. The molecular mechanisms of their chemopreventive action are associated with the modulation of signaling cascades, gene expressions involved in the regulation of cell proliferation, differentiation, and apoptosis and the suppression of chronic inflammation, metastasis, and angiogenesis. Here, we summarize the currently known targets and signaling pathways whereby natural dietary compounds interfere with the development of colorectal cancer, and thus providing evidence for these substances in colonic cancer chemopreventive action.

Reactive oxygen species abrogate the anticarcinogenic effect of eicosapentaenoic acid in Atm-deficient mice

Recent studies have demonstrated that n-3 polyunsaturated fatty acids such as eicosapentaenoic acid (EPA) are able to suppress cell proliferation and inhibit tumor growth. The objective of our study was to investigate the influence of a high dose EPA on the development of the tumor phenotype in ataxia-telangiectasia mutated (Atm)-deficient mice, a genetic cancer model that is associated with increased levels of oxidative stress. We analyzed toxicity, proliferation, cell-cycle progression, and apoptosis of EPA in vitro and latency to tumorigenesis in vivo. Because of the impact of reactive oxygen species (ROS) on the tumor incidence in ataxia telangiectasia (AT), we further analyzed the effect of EPA on the generation of ROS and oxidative DNA damage (ODD). EPA effectively inhibited proliferation, altered cell-cycle progression, and induced apoptosis of tumor cells (AT-4). EPA showed no effect on the latency to tumorigenesis in Atm-deficient mice. EPA treatment was accompanied by a significant increase of ROS and ODD. Our results demonstrate the antiproliferative effect of EPA on tumor cells by alteration of cell-cycle progression and induction of apoptosis in vitro. On the other hand, EPA treatment of Atm-deficient mice led to the formation of ROS and accumulation of ODD that might have abrogated the anticarcinogenic effect caused by EPA.

DHA alters expression of target proteins of cancer therapy in chemotherapy resistant SW620 colon cancer cells

Diets rich in n-3 polyunsaturated fatty acids (PUFAs) have been associated with a reduced risk of several types of cancer. Recent reports have suggested that these PUFAs enhance the cytotoxic effect of cancer chemoradiotherapy. The effect of docosahexaenoic acid (DHA) on key cell cycle regulators and target proteins of cancer therapy was investigated in the human malign colon cancer cell line SW620. Cell cycle check point proteins such as p21 and stratifin (14-3-3 sigma) increased at mRNA and protein level, whereas cell cycle progression proteins such as cell division cycle 25 homolog and cyclin-dependent kinase 1 decreased after DHA treatment. Protein levels of inhibitors of apoptosis family members associated with chemotherapy resistance and cancer malignancy, survivin and livin, decreased after the same treatment: likewise the expression of NF-kappaB. Levels of the proapoptotic proteins phosphorylated p38 MAPK and growth arrest-inducible and DNA damage-inducible gene 153/C/EBP-homologous protein (CHOP) increased. The results indicate that DHA treatment causes simultaneous cell cycle arrest in both the G1 and G2 phase. In conclusion, DHA affects several target proteins of chemotherapy in a favorable way. This may explain the observed enhanced chemosensitivity in cancer cells supplemented with n-3 PUFAs and encourage further studies investigating the role of n-3 PUFAs as adjuvant to chemotherapy and radiotherapy in vivo.

Docosahexaenoic acid induces dose dependent cell death in an early undifferentiated subtype of acute myeloid leukemia cell line

Acute myeloid leukemia (AML) is the most frequently diagnosed adulthood leukemia, yet current therapies offer a cure rate of less than 30%. This may be due in part to the fact that the leukemia-initiating cells in AML reside within the rare and highly primitive CD34(+)CD38(-) hematopoietic stem/progenitor cell (HSC) population that are often resistant to chemotherapy. Docosahexanoic acid (DHA), a major component of fish oil, has previously been shown to inhibit the induction and progression of breast, prostate and colon cancer, and increase the therapeutic effects of numerous chemotherapeutics, often by enhancing apoptosis. In the present studies, we investigated DHA's effect on the primitive and undifferentiated AML cell line KG1a, to explore the potential of this fatty acid to serve as adjuvant therapy for AML. Treatment of KG1a cells with DHA for 96 hours did not lead to maturation or cell cycle modification when compared to an untreated KG1a control (n = 4). However, DHA treatment of KG1a cells resulted in a progressive loss of viability, DNA fragmentation, and an increase in Annexin V expression, demonstrating DHA-induced apoptosis (n = 4). Moreover, expression of the pro-apoptotic protein Bax was increased, with resultant skewing in the Bax/bcl-2 ratio, providing a mechanistic explanation for the observed DHA-induced increase in apoptosis. Since we also show that DHA does not have a detrimental effect on normal hematopoiesis our results suggest that DHA could potentially serve as an well-tolerated adjuvant in the treatment of AML patients.

The influence of feeding linoleic, gamma-linolenic and docosahexaenoic acid rich oils on rat brain tumor fatty acids composition and fatty acid binding protein 7 mRNA expression

Background

Experimental studies indicate that gamma linolenic acid (GLA) and docosahexaenoic acid (DHA) may inhibit glioma cells growth but effects of oral consumption of these fatty acids on brain tumor fatty acid composition have not been determined in vivo.

Methods

GLA oil (GLAO; 72% GLA), DHA oil (DHAO; 73% DHA) were fed to adult wistar rats (1 mL/rat/day) starting one week prior to C6 glioma cells implantation and continued for two weeks after implantation. Control group were fed same amount of high linoleic acid safflower oil (74–77% linoleic acid). Fatty acid composition of tumor samples was determined in a set of 8–12 animals in each group and serum fatty acid in 6 animals per each group. Gene expression of tumor fatty acid binding protein 7 (FABP7), epidermal growth factor receptor (EGFR), peroxisome proliferator activated receptor γ (PPAR-γ) and retinoid × receptor-α (RXR-α) were determined in a set of 18 animals per group.

Results

DHAO feeding increased EPA of brain tumors and decreased ratio of n-6/n-3 fatty acids. Serum levels of EPA were also increased in DHAO group. A similar trend in serum and tumor levels of DHA were observed in DHAO group but it did not achieve statistical significance. GLAO increased serum concentration of GLA but had no significant effect on tumor GLA or dihomo-gamma linolenic acid (DGLA) concentrations. Gene expression of FABP7 was up-regulated in tumors of DHAO group but no other significant effects were observed on EGFR, PPAR-γ or RXR-α expression, and expression of these genes in tumors of GLAO were not different from SFO group.

Conclusion

Dietary supplementation of DHA containing oil could be an effective way to increase levels of long chain n-3 fatty acids in brain tumors and this increase may be mediated partly by up-regulation of FABP7 expression.