Alterations in Mitochondrial Membrane in Chemopreventive Action of Fish Oil

Apoptosis mediated chemosensitization of tumor cells to 5-fluorouracil on supplementation of fish oil in experimental colon carcinoma

5-Fluorouracil has been considered as a cornerstone therapy for colorectal cancer; however, it suffers from low therapeutic response rate and severe side effects. Therefore, there is an urgent need to increase the clinical efficacy of 5-fluorouracil. Recently, fish oil rich in n-3 polyunsaturated fatty acids has been reported to chemosensitize tumor cells to anti-cancer drugs. This study is designed to understand the underlying mechanisms of synergistic effect of fish oil and 5-fluorouracil by evaluation of tumor cell-associated markers such as apoptosis and DNA damage. The colon cancer was developed by administration of N,N-dimethylhydrazine dihydrochloride and dextran sulfate sodium salt. Further these animals were treated with 5-fluorouracil, fish oil, or a combination of both. In carcinogen-treated animals, a decrease in DNA damage and apoptotic index was observed. There was also a decrease in the expression of Fas, FasL, caspase 8, and Bax, and an increase in Bcl-2. In contrast, administration of 5-fluorouracil and fish oil as an adjuvant increased both DNA damage and apoptotic index by activation of both extrinsic and intrinsic apoptotic pathways as compared to the other groups. The increased pro-apoptotic effect by synergism of 5-fluorouracil and fish oil may be attributed to the incorporation of n-3 polyunsaturated fatty acids in membrane, which alters membrane fluidity in cancer cells. In conclusion, this study highlights that the induction of apoptotic pathway by fish oil may increase the susceptibility of tumors to chemotherapeutic regimens.

Krill oil extract suppresses cell growth and induces apoptosis of human colorectal cancer cells

Background

Colorectal cancer (CRC) is the third most common cancer in the world. The current available treatments for CRC include surgery, chemotherapy and radiotherapy. However, surgery is only useful when the disease is diagnosed at the earlier stage. Chemotherapy and radiotherapy are associated with numerous side effects that decrease the patients’ quality of life. Safer, effective alternatives, such as natural compounds, to chemotherapy are desirable. This study assessed the efficacy of free fatty acid (FFA) extract of krill oil on three human CRC cells lines.

Methods

HCT-15, SW-480 and Caco-2 cells were treated with the FFA extracts of krill oil and fish oil for 48 h while treatments with the bioactive omega-3 polyunsaturated fatty acids (LC n-3 PUFA) of these marine oils, eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3) in comparison with a n-6 PUFA, arachnoid acid (AA, C20:4n-6) were up to 72 h at the concentrations of 50, 100, 150 and 200 μM. Effects of all the treatments on cell proliferation were assessed using a water-soluble tetrazolium-1 (WST-1) assay kit at 24, 48 and 72 h. Effects of FFA extract of krill oil and EPA on apoptosis and mitochondrial membrane potential were determined using commercial kits after 48 h of treatment.

Results

Krill oil extract inhibited cell proliferation of all three cell lines in the similar manner as fish oil extract. A significant cell apoptosis and increase in mitochondrial membrane potential were observed after the treatment with krill oil extract. EPA at the concentration of 200 μM reduced significantly the proliferation of HCT-15 and SW-480 at 24, 48 and 72 h. In addition, EPA treatment (100 and 200 μM) resulted in significant cell apoptosis in all three cell lines. No significant changes were observed after treatment with DHA and AA.

Conclusions

Our results indicate that the FFA extract of krill oil maybe an effective chemotherapeutic agent to suppress proliferation and induce apoptosis in CRC cells through its bioactive constitute EPA. Although the exact mechanism of the pro-apoptotic properties of krill oil extract is unclear, mitochondrial pathway seems to be implicated.

Apoptosis-Mediated Chemoprevention by Different Ratios of Fish Oil in Experimental Colon Carcinogenesis

Apoptosis plays an important role in prevention of colon cancer. In the present study, different ratios of fish oil and corn oil increased Fas expression in both phases and a decrease in FasL expression only in post initiation phase. Treatment with fish oil activated the intrinsic apoptotic pathway by increasing Bax expression and Cyt c release and decreasing Bcl-2 levels in both phases. This suggests that intrinsic pathway is upregulated by fish oil; however, Fas-FasL activity may be involved in inhibition of reversal of immune surveillance in tumor cells.

Documentation of Ultrastructural Changes in Nucleus and Microvilli by Fish Oil in Experimental Colon Carcinogenesis

Fish oil (FO) exerts a chemopreventive effect by regulating apoptosis in colon carcinogenesis. The present study reports the ultrastructural changes in various organelles on supplementation of FO in experimental colon carcinogenesis. The carcinogen treatment led to abnormal nuclear shape and alteration in microvilli number indicating cancer establishment. On the other hand, different ratios of FO and corn oil increased chromatin condensation along with an extensive loss of microvilli in a dose- and time-dependent manner which depicts an increase in apoptosis. The associated ultrastuctural alterations support the facilitation of apoptosis by FO as a mechanism for its beneficial effect in colon carcinogenesis.

Fish oil suppresses cell growth and metastatic potential by regulating PTEN and NF-κB signaling in colorectal cancer

Homeostasis in eukaryotic tissues is tightly regulated by an intricate balance of the prosurvival and antisurvival signals. The tumor suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10), a dual-specificity phosphatase, plays a functional role in cell cycle arrest and apoptosis. NF-κB and its downstream regulators (such as VEGF) play a central role in prevention of apoptosis, promotion of inflammation and tumor growth. Therefore, we thought to estimate the expression of PTEN, Poly-ADP-ribose polymerase (PARP), NF-κBp50, NF-κBp65 and VEGF to evaluate the effect of supplementation of fish oil on apoptotic and inflammatory signaling in colon carcinoma. Male wistar rats in Group I received purified diet while Group II and III received modified diet supplemented with FO∶CO(1∶1)&FO∶CO(2.5∶1) respectively. These were further subdivided into controls receiving ethylenediamine-tetra acetic-acid and treated groups received dimethylhydrazine-dihydrochloride (DMH)/week for 4 weeks. Animals sacrificed 48 hours after last injection constituted initiation phase and that sacrificed after 16 weeks constituted post-initiation phase. We have analysed expression of PTEN, NF-κBp50, NF-κBp65 by flowcytometer and nuclear localization of NF-κB by immunofluorescence. PARP and VEGF were assessed by immunohistochemistry. In the initiation phase, animals receiving DMH have shown increased % of apoptotic cells, PTEN, PARP, NF-κBp50, NF-κBp65 and VEGF however in post-initiation phase no significant alteration in apoptosis with decreased PTEN and increased PARP, NF-κBp50, NF-κBp65 and VEGF were observed as compared to control animals. On treatment with both ratios of fish oil in both the phases, augmentation in % of apoptotic cells, decreased PTEN, PARP, NF-κBp50, NF-κBp65 and VEGF were documented with respect to DMH treated animals with effect being more exerted with higher ration in post-initiation phase. Hence, fish oil activates apoptosis, diminishes DNA damage and inhibits inflammatory signalling in a dose and time dependent manner so as to inhibit progression of colon cancer.