Gamma-linolenic acid (GLA) is cytotoxic to 36B10 malignant rat astrocytoma cells but not to 'normal' rat astrocytes

Cell-type specific anti-cancerous effects of nitro-oleic acid and its combination with gamma irradiation

Nitro-fatty acids (NFAs) are endogenous lipid mediators capable of post-translational modifications of selected regulatory proteins. Here, we investigated the anti-cancerous effects of nitro-oleic acid (NO2OA) and its combination with gamma irradiation on different cancer cell lines. The effects of NO2OA on cell death, cell cycle distribution, or expression of p21 and cyclin D1 proteins were analyzed in cancer (A-549, HT-29 and FaDu) or normal cell lines (HGF, HFF-1). Dose enhancement ratio at 50 % survival fraction (DERIC50) was calculated for samples pre-treated with NO2OA followed by gamma irradiation. NO2OA suppressed viability and induced apoptotic cell death. These effects were cell line specific but not in general selective for cancer cells. HT-29 cell line exerted higher sensitivity toward NO2OA treatment among cancer cell lines tested: induction of cell cycle arrest in the G2/M phase was associated with an increase in p21 and a decrease in cyclin D1 expression. Pre-treatment of HT-29 cells with NO2OA prior irradiation showed a significantly increased DERIC50, demonstrating radiosensitizing effects. In conclusion, NO2OA exhibited potential for combined chemoradiotherapy. Our results encourage the development of new NFAs with improved features for cancer chemoradiation.

Disentangling the environmental processes responsible for the world's largest farmed fish-killing harmful algal bloom: Chile, 2016

The dictyochophyte microalga Pseudochattonella verruculosa was responsible for the largest farmed fish mortality ever recorded in the world, with losses for the Chilean salmon industry amounting to US$ 800 M in austral summer 2016. Super-scale climatic anomalies resulted in strong vertical water column stratification that stimulated development of a dynamic P. verruculosa thin layer (up to 38 μg chl a L^-1) for several weeks in Reloncaví Sound. Hydrodynamic modeling (MIKE 3D) indicated that the Sound had extremely low flushing rates (between 121 and 200 days) in summer 2016. Reported algal cell densities of 7000-20,000 cells mL^-1 generated respiratory distress in fish that was unlikely due to low dissolved oxygen (permanently >4 mg L^-1). Histological examination of salmon showed that gills were the most affected organ with significant tissue damage and circulatory disorders. It is possible that some of this damage was due to a diatom bloom that preceded the Pseudochattonella event, thereby rendering the fish more susceptible to Pseudochattonella. No correlation between magnitude of fish mortality and algal cell abundance nor fish age was evident. Algal cultures revealed rapid growth rates and high cell densities (up to 600,000 cells mL^-1), as well as highly complex life cycle stages that can be easily overlooked in monitoring programs. In cell-based bioassays, Chilean P. verruculosa was only toxic to the RTgill-W1 cell line following exposures to high cell densities of lysed cells (>100,000 cells mL^-1). Fatty acid profiles of a cultured strain showed elevated concentrations of potentially ichthyotoxic, long-chain polyunsaturated fatty acids (PUFAs) (69.7% ± 1.8%)- stearidonic (SDA, 18:4ω3-28.9%), and docosahexaenoic acid (DHA, 22:6ω3-22.3%), suggesting that lipid peroxidation may help to explain the mortalities, though superoxide production by Pseudochattonella was low (< 0.21 ± 0.19 pmol O₂^- cell^-1 h^-1). It therefore remains unknown what the mechanisms of salmon mortality were during the Pseudochattonella bloom. Multiple mitigation strategies were used by salmon farmers during the event, with only delayed seeding of juvenile fish into the cages and towing of cages to sanctuary sites being effective. Airlift pumping, used effectively against other fish-killing HABs in the US and Canada was not effective, perhaps because it brought subsurface layers of Pseudochattonella to the surface, or and it also may have lysed the fragile cells, rendering them more lethal. The present study highlights knowledge gaps and inefficiency of contingency plans by the fish farming industry to overcome future fish-killing algal blooms under future climate change scenarios. The use of new technologies based on molecular methods for species detection, good farm practices by fish farms, and possible mitigation strategies are discussed.

Anticancer activities of fatty acids and their heterocyclic derivatives

Traditional chemotherapy relies on the premise that rapidly proliferating cancer cells are more likely to be killed by a cytotoxic agent, but in reality, the long-standing problem of chemotherapy is the lack of tumor-specific treatments. Apart from the impact on tumor cells, the drugs' major limitation is their severe adverse side effects on normal cells and tissues. Nutritional and epidemiological studies have indicated that cancer progression is correlated with the consumption of fatty acids, but the exact mechanisms still remain unknown. In the first part of our review, we discussed the beneficial effects of free fatty acids (saturated and unsaturated) on the progress of carcinogenesis in different tumor cell lines. We presented various mechanisms proposed in the literature, which explain the possible impact on the cells metabolism. The second part describes modifications of different fatty acids with existing anticancer drugs and heterocyclic moieties by condensation reactions. Such conjugations increased the tissue selectivity and made chemotherapy potentially more effective and less toxic in in vivo and in vitro studies. This fatty acid modifications, which change the activity of compounds, their uptake selectivity and alter drug delivery methods, may be the key to unlocking true medical potential of fatty acids.

Bioactive lipids as modulators of immune check point inhibitors

It is proposed that arachidonic acid (AA, 20:4 n-6) and other polyunsaturated fatty acids (PUFAs) in combination with immune check point inhibitors and tumor infiltrating lymphocytes (TILs) enhances the activity of T and NK cells and macrophages and thus, aids in the elimination of tumor cells and suppresses inflammatory side effects due to immune check point inhibitors.

Differential action of polyunsaturated fatty acids and eicosanoids on bleomycin-induced cytotoxicity to neuroblastoma cells and lymphocytes

INTRODUCTION

This study was conducted to examine whether bleomycin-induced growth inhibitory action on human neuroblastoma cells (IMR-32) is influenced by anti-inflammatory metabolites of polyunsaturated fatty acids (PUFAs): lipoxin A4 (LXA4), resolvin D1 and protectin D1 in vitro.

MATERIAL AND METHODS

The in vitro study was conducted using monolayer cultures of exponentially growing IMR-32 cells. The effects of various PUFAs and eicosanoids and anti-inflammatory metabolites of PUFAs such as lipoxin A4 (LXA4), resolvin D1 and protectin D1 on the growth of IMR-32 cells and human lymphocytes in vitro were investigated. The potential of PUFAs, eicosanoids and LXA4, resolvin D1 and protectin D1 to modify the growth inhibitory effects of bleomycin was also studied in IMR-32 cells and human lymphocytes.

RESULTS

PUFAs inhibited the growth of IMR-32 cells (EPA > DHA = AA > GLA = ALA > DGLA = LA) significantly (p < 0.001) while prostaglandins were found to be not effective. Bleomycin-induced growth inhibitory action on IMR-32 cells was augmented by PUFAs and its metabolites (p < 0.05). PUFAs and LXA4 did not inhibit the growth of human lymphocytes and bleomycin-induced growth inhibitory action was also not enhanced by these bioactive lipids.

CONCLUSIONS

Bioactive lipids have differential action on normal human lymphocytes and tumor cells in vitro. The apparent lack of effect of PUFAs in combination with bleomycin on the growth of human lymphocytes in comparison to their growth inhibitory action on IMR-32 cells suggests that PUFAs can be used in combination with bleomycin to target tumor cells with little concern over this combination's effect on the growth of human lymphocytes. Further studies are warranted to evaluate these differential effects under in vivo conditions.

Lipidomic analysis reveals a radiosensitizing role of gamma-linolenic acid in glioma cells

Previous studies have demonstrated that gamma-linolenic acid (GLA) is effective against glioma cells under both in vitro and in vivo conditions. In the present study we determined how GLA alone or in combination with irradiation alters the fatty acid (FA) and lipid profiles, the lipid droplet (LD) content, the lipid biosynthetic gene expression and the apoptosis of glioma cells. In GLA-treated cells direct correlations were found between the levels of various FAs and the expression of the corresponding FA biosynthetic genes. The total levels of saturated and monosaturated FAs decreased in concert with the down-regulation of FASN and SCD1 gene expression. Similarly, decreased FADS1 gene expression was paralleled by lowered arachidonic acid (20:4 n-6) and eicosapentaenoic acid (20:5 n-3) contents, while the down-regulation of FADS2 expression was accompanied by a diminished docosahexaenoic acid (22:6 n-3) content. Detailed mass spectrometric analyses revealed that individual treatments gave rise to distinct lipidomic fingerprints. Following uptake, GLA was subjected to elongation, resulting in dihomo-gamma-linolenic acid (20:3 n-6, DGLA), which was used for the synthesis of the LD constituent triacylglycerols and cholesteryl esters. Accordingly, an increased number of LDs were observed in response to GLA administration after irradiation. GLA increased the radioresponsiveness of U87 MG cells, as demonstrated by an increase in the number of apoptotic cells determined by FACS analysis. In conclusion, treatment with GLA increased the apoptosis of irradiated glioma cells, and GLA might therefore increase the therapeutic efficacy of irradiation in the treatment of gliomas.

Anti-cancer activities of ω-6 polyunsaturated fatty acids

The ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) are two major families of PUFAs present as essential cellular components which possess diverse bioactivities. The ω-3s, mainly found in seafood, are associated with many beneficial effects on human health, while the ω-6s are more abundant in our daily diet and could be implicated in many pathological processes including cancer development. Increasing evidence suggests that the adverse effects of ω-6s may be largely attributed to arachidonic acid (AA, a downstream ω-6) and the metabolite prostaglandin E2 (PGE2) that stems from its cyclooxygenase (COX)-catalyzed lipid peroxidation. On the other hand, two of AA's upstream ω-6s, γ-linolenic acid (GLA) and dihomo-γ-linolenic acid (DGLA), are shown to possess certain anti-cancer activities, including inducing cell apoptosis and inhibiting cell proliferation. In this paper, we review the documented anti-cancer activities of ω-6 PUFAs, including the recent findings regarding the anti-cancer effects of free radical-mediated DGLA peroxidation. The possible mechanisms and applications of DGLA (and other ω-6s) in inducing anti-cancer activity are also discussed. Considering the wide availability of ω-6s in our daily diet, the study of the potential beneficial effect of ω-6 PUFAs may guide us to develop an ω-6-based diet care strategy for cancer prevention and treatment.

Effect of polyunsaturated fatty acids and their metabolites on bleomycin-induced cytotoxic action on human neuroblastoma cells in vitro

In the present study, we noted that bleomycin induced growth inhibitory action was augmented by all the polyunsaturated fatty acids (PUFAs) tested on human neuroblastoma IMR-32 (0.5 × 10(4) cells/100 µl of IMR) cells (EPA > DHA > ALA = GLA = AA > DGLA = LA: ∼ 60, 40, 30, 10-20% respectively) at the maximum doses used. Of all the prostaglandins (PGE1, PGE2, PGF2α, and PGI2) and leukotrienes (LTD4 and LTE4) tested; PGE1, PGE2 and LTD4 inhibited the growth of IMR-32 cells to a significant degree at the highest doses used. Lipoxin A4 (LXA4), 19,20-dihydroxydocosapentaenoate (19, 20 DiHDPA) and 10(S),17(S)-dihydroxy-4Z,7Z,11E,13Z,15E,19Z-docosahexaenoic acid (protectin: 10(S),17(S)DiHDoHE), metabolites of DHA, significantly inhibited the growth of IMR-32 cells. Pre-treatment with AA, GLA, DGLA and EPA and simultaneous treatment with all PUFAs used in the study augmented growth inhibitory action of bleomycin. Surprisingly, both indomethacin and nordihydroguaiaretic acid (NDGA) at 60 and 20 µg/ml respectively enhanced the growth of IMR-32 cells even in the presence of bleomycin. AA enhanced oxidant stress in IMR-32 cells as evidenced by an increase in lipid peroxides, superoxide dismutase levels and glutathione peroxidase activity. These results suggest that PUFAs suppress growth of human neuroblastoma cells, augment growth inhibitory action of bleomycin by enhancing formation of lipid peroxides and altering the status of anti-oxidants and, in all probability, increase the formation of lipoxins, resolvins and protectins from their respective precursors that possess growth inhibitory actions.

Combination of unsaturated fatty acids and ionizing radiation on human glioma cells: cellular, biochemical and gene expression analysis

Background

Based on previous observations a potential resort in the therapy of the particularly radioresistant glioma would be its treatment with unsaturated fatty acids (UFAs) combined with irradiation.

Methods

We evaluated the effect of different UFAs (arachidonic acid (AA), docosahexaenoic acid (DHA), gamma-linolenic acid (GLA), eicosapentaenoic acid (EPA) and oleic acid (OA)) on human U87 MG glioma cell line by classical biochemical end-point assays, impedance-based, real-time cellular and holographic microscopic analysis. We further analyzed AA, DHA, and GLA at morphological, gene and miRNA expression level.

Results

Corresponding to LDH-, MTS assays and real-time cytoxicity profiles AA, DHA, and GLA enhanced the radio sensitivity of glioma cells. The collective application of polyunsaturated fatty acids (PUFAs) and irradiation significantly changed the expression of EGR1, TNF-α, NOTCH1, c-MYC, TP53, HMOX1, AKR1C1, NQO1, while up-regulation of GADD45A, EGR1, GRP78, DDIT3, c-MYC, FOSL1 were recorded both in response to PUFA treatment or irradiation alone. Among the analyzed miRNAs miR-146 and miR-181a were induced by DHA treatment. Overexpression of miR-146 was also detected by combined treatment of GLA and irradiation.

Conclusions

Because PUFAs increased the radio responsiveness of glioma cells as assessed by biochemical and cellular assays, they might increase the therapeutic efficacy of radiation in treatment of gliomas. We demonstrated that treatment with DHA, AA and GLA as adjunct to irradiation up-regulated the expression of oxidative-stress and endoplasmic reticulum stress related genes, and affected NOTCH1 expression, which could explain their additive effects.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-511X-13-142) contains supplementary material, which is available to authorized users.

Polyunsaturated fatty acids and gliomas: a critical review of experimental, clinical, and epidemiologic data

Certain polyunsaturated fatty acids (PUFAs) called essential fatty acids (EFAs) cannot be biosynthesized by the body and hence, need to be obtained from diet. These PUFAs and their metabolites have multiple physiological functions that are altered in tumor cells due to a decreased expression of Δdelta-6-desaturase, which is an essential step in their metabolism. As a result, tumor cells would be protected from the toxic effect caused by free radicals, one product of EFA metabolism. EFAs have been proposed to have therapeutic potential in the treatment of glioblastoma. Gliomas are the most common primary tumors of the central nervous system in children and adults. High-grade gliomas remain a therapeutic challenge in neuro-oncology because there is no treatment that achieves a significant improvement in survival. Novel therapeutic strategies that use PUFAs for the treatment of gliomas have been assessed in cell cultures, rodent glioma models, and humans, with encouraging results. Here we review the latest progress made in the field.

Differential sensitivity to 4-hydroxynonenal for normal and malignant mesenchymal cells

Normal and malignant cells of various origin differ in their sensitivity to oxidative stress. Therefore, we used normal and malignant mesenchymal cells--human osteosarcoma cells (HOS and 143B), human fibroblasts (WI38) and two primary cultures of normal human osteoblasts to test sensitivity to reactive aldehyde 4-hydroxynonenal (HNE), known as a second messenger of free radicals and a signaling molecule. Upon HNE-treatment, decrease in cell viability (by Trypan-blue), apoptosis induction (by TiterTACS TUNEL assay), HNE-protein binding (by HNE-His ELISA) were higher in malignant than in normal cells, while glutathione content was higher in normal cells. These results indicate that HNE affects the growth of malignant mesenchymal cells more than normal and that this effect was mainly related to lower glutathione concentration and higher binding of HNE to the cellular proteins. We thus assume that HNE and GSH homeostasis play an important role in the growth regulation of normal and malignant mesenchymal cells.

Differential activation of catalase expression and activity by PPAR agonists: implications for astrocyte protection in anti-glioma therapy

Glioma survival is dismal, in part, due to an imbalance in antioxidant expression and activity. Peroxisome proliferator-activated receptor (PPAR) agonists have antineoplastic properties which present new redox-dependent targets for glioma anticancer therapies. Herein, we demonstrate that treatment of primary cultures of normal rat astrocytes with PPAR agonists increased the expression of catalase mRNA protein, and enzymatic activity. In contrast, these same agonists had no effect on catalase expression and activity in malignant rat glioma cells. The increase in steady-state catalase mRNA observed in normal rat astrocytes was due, in part, to de novo mRNA synthesis as opposed to increased catalase mRNA stability. Moreover, pioglitazone-mediated induction of catalase activity in normal rat astrocytes was completely blocked by transfection with a PPARγ-dominant negative plasmid. These data suggest that defects in PPAR-mediated signaling and gene expression may represent a block to normal catalase expression and induction in malignant glioma. The ability of PPAR agonists to differentially increase catalase expression and activity in normal astrocytes but not glioma cells suggests that these compounds might represent novel adjuvant therapeutic agents for the treatment of gliomas.

Modulation of glioma risk and progression by dietary nutrients and antiinflammatory agents

Gliomas are tumors of glial origin formed in the central nervous system and exhibit profound morphological and genetic heterogeneity. The etiology of this heterogeneity involves an interaction between genetic alterations and environmental risk factors. Scientific evidence suggests that certain natural dietary components, such as phytoestrogens, flavonoids, polyunsaturated fatty acids, and vitamins, may exert a protective effect against gliomas by changing the nature of the interaction between genetics and environment. Similarly, certain antiinflammatory drugs and dietary modifications, such as methionine restriction and the adoption of low-calorie or ketogenic diets, may take advantage of glioma and normal glial cells' differential requirements for glucose, methionine, and ketone bodies and may, therefore, be effective as part of preventive or treatment strategies for gliomas. Treatment trials of glioma patients and chemoprevention trials of individuals with a known genetic predisposition to glioma using the most promising of these agents, such as the antiinflammatory drugs curcumin and gamma-linolenic acid, are needed to validate or refute these agents' putative role in gliomas.

Antineoplastic effects of gamma linolenic Acid on hepatocellular carcinoma cell lines

The aim of this study was to investigate the effect and the mechanism of gamma linolenic acid (GLA) treatment on human hepatocellular (HCC) cell lines. The human HCC cell line HuH7 was exposed to GLA. Cell proliferation and reactive oxygen species (ROS) generation including lipid peroxidation and apoptosis were compared. We then used a cDNA microarray analysis to investigate the molecular changes induced by GLA. GLA treatment significantly reduced cell proliferation, generated ROS, and induced apoptosis. After 24 h exposure of Huh7 cells to GLA, we identified several genes encoding the antioxidant proteins to be upregulated: heme oxygenase-1 (HO-1), aldo-keto reductase 1 family C1 (AKR1C1), C4 (AKR1C4), and thioredoxin (Trx). The HO-1 protein levels were overexpressed in Huh7 cells after GLA exposure using a Western blot analysis. Furthermore, chromium mesoporphyrin (CrMP), an inhibitor of HO activity, significantly potentiated GLA cytotoxicity. GLA treatment has induced cell growth inhibition, ROS generation including lipid peroxidation, and HO-1 production for antioxidant protection against oxidative stress caused by GLA in Huh7 cells. GLA treatment should be considered as a therapeutic modality in patients with advanced HCC.

Lipids, mitochondria and cell death: implications in neuro-oncology

Polyunsaturated fatty acids (PUFAs) are known to inhibit cell proliferation of many tumour types both in vitro and in vivo. Their capacity to interfere with cell proliferation has been linked to their induction of reactive oxygen species (ROS) production in tumour tissues leading to cell death through apoptosis. However, the exact mechanisms of action of PUFAs are far from clear, particularly in brain tumours. The loss of bound hexokinase from the mitochondrial voltage-dependent anion channel has been directly related to loss of protection from apoptosis, and PUFAs can induce this loss of bound hexokinase in tumour cells. Tumour cells overexpressing Akt activity, including gliomas, are sensitised to ROS damage by the Akt protein and may be good targets for chemotherapeutic agents, which produce ROS, such as PUFAs. Cardiolipin peroxidation may be an initial event in the release of cytochrome c from the mitochondria, and enriching cardiolipin with PUFA acyl chains may lead to increased peroxidation and therefore an increase in apoptosis. A better understanding of the metabolism of fatty acids and eicosanoids in primary brain tumours such as gliomas and their influence on energy balance will be fundamental to the possible targeting of mitochondria in tumour treatment.

Cytotoxicity of unsaturated fatty acids in fresh human tumor explants: concentration thresholds and implications for clinical efficacy

Background

Unsaturated fatty acids (UFAs) exhibit in vitro cytotoxicity against many malignant cell lines and yield decreased cancer incidence and reduced tumor growth in animal models. But clinical and animal studies to date have achieved response using only localized delivery methods such as intratumoral infusion. To explore possibilities for enhanced clinical efficacy, fresh surgical explants of tumors from 22 patients with five malignancies were exposed to γ-linolenic acid (GLA) and α-linolenic acid (ALA) and analyzed with an in vitro chemosensitivity testing system, the Fluorescent Cytoprint Assay (FCA). A total of 282 micro-organ cultures derived from these malignant tumors were exposed to GLA and ALA at different concentrations.

Results

GLA and ALA exhibited greater than 90% cytotoxicity at a sharp concentration threshold between 500 μM and 1 mM against all but two malignant micro-organ cultures tested in 5-10% serum. In tests using 30-40% serum, GLA and ALA killed tumor at concentrations of 2 mM and above.

Conclusions

The concentration threshold of 500 μM to 2 mM exhibited for antitumor activity by GLA and ALA is much higher than that observed in most previously reported cell culture studies but consistent with physiological concentrations found to kill tumor clinically and in animals. A mechanism of antitumor activity by unsaturated fatty acids through selective destabilization of the malignant plasma membrane is considered. An oral regimen is proposed for phase I clinical testing that could push the area under the curve for serum concentration of unbound unsaturated fatty acids over time to much higher levels than previously achieved for systemic administration and into the range that could yield antitumor response.

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.

LC/ESR/MS study of spin trapped carbon-centred radicals formed from in vitro lipoxygenase-catalysed peroxidation of gamma-linolenic acid

Gamma-linolenic acid (GLA) has been reported as a potential anti-cancer and anti-inflammatory agent and has received substantial attention in cancer care research. One of the many proposed mechanisms for GLA biological activity is free radical-mediated lipid peroxidation. However, no direct evidence has been obtained for the formation of GLA-derived radicals. In this study, a combination of LC/ESR and LC/MS was used with alpha-[4-pyridyl-1-oxide]-N-tert-butyl nitrone (POBN) to profile the carbon-centred radicals that are generated in lipoxygenase-catalysed GLA peroxidation. A total of four classes of GLA-derived radicals were characterized including GLA-alkyl, epoxyallylic, dihydroxyallylic radicals and a variety of carbon-centred radicals stemming from the beta-scissions of GLA-alkoxyl radicals. By means of an internal standard in LC/MS, one also quantified each radical adduct in all its redox forms, including an ESR-active form and two ESR-silent forms. The results provided a good starting point for ongoing research in defining the possible biological effects of radicals generated from GLA peroxidation.

Fatty acid synthase: a novel target for antiglioma therapy

High levels of fatty acid synthase (FAS) expression have been observed in several cancers, including breast, prostate, colon and lung carcinoma, compared with their respective normal tissue. We present data that show high levels of FAS protein in human and rat glioma cell lines and human glioma tissue samples, as compared to normal rat astrocytes and normal human brain. Incubating glioma cells with the FAS inhibitor cerulenin decreased endogenous fatty acid synthesis by approximately 50%. Cell cycle analysis demonstrated a time- and dose-dependent increase in S-phase cell arrest following cerulenin treatment for 24 h. Further, treatment with cerulenin resulted in time- and dose-dependent decreases in glioma cell viability, as well as reduced clonogenic survival. Increased apoptotic cell death and PARP cleavage were observed in U251 and SNB-19 cells treated with cerulenin, which was independent of the death receptor pathway. Overexpressing Bcl-2 inhibited cerulenin-mediated cell death. In contrast, primary rat astrocytes appeared unaffected. Finally, RNAi-mediated knockdown of FAS leading to reduced FAS enzymatic activity was associated with decreased glioma cell viability. These findings suggest that FAS might be a novel target for antiglioma therapy.

Induction of apoptosis in K562/ADM cells by gamma-linolenic acid involves lipid peroxidation and activation of caspase-3

Numerous studies have revealed that gamma-linolenic acid (GLA) possesses effective tumoricidal properties while not inducing damage to normal cells or creating harmful systemic side effects. It can exert anti-tumor efficacy against a variety of cancers including leukemia. However, little is known about the effects of GLA on leukemia resistant to chemotherapy, emerging as a serious clinical problem. The present study tested GLA-induced apoptosis in K562/ADM multidrug-resistant (MDR) leukemic cells and investigated its possible mechanisms. Using cell viability, fluorescent staining of nuclei, flow cytometric Annexin V/PI double staining and lactate dehydrogenase (LDH) release, we found that GLA could inhibit cell growth and induce apoptosis and secondary necrosis. The results showed that incubation with GLA concentrations of 10-60 microg/ml caused a dose- and time-dependent decrease of K562/ADM cell viability, and the IC50 value was 50.5 microg/ml at 24 h and 31.5 microg/ml at 48 h. Flow cytometry using Annexin V/PI double staining assessed apoptosis, necrosis and viability. Typical apoptotic nuclei were shown by staining of K562/ADM cells with DNA-binding fluorochrome Hoechst 33342, characterized by chromatin condensation and nuclear fragmentation. On the other hand, after treated K562/ADM cells with 20 microg/ml GLA for 48 h and with 40 microg/ml GLA for 12 h, the LDH release significantly increased, indicated losses of plasma membrane integrity and presence of necrosis. Further, the inhibition of GLA-induced apoptosis by a pan-caspase inhibitor (z-VAD-fmk) suggested the involvement of caspases. The increase of caspase-3 activity with GLA concentration confirmed its role in the process. The results also showed that the malondialdehyde (MDA) content was also significantly elevated, and antioxidant BHT could block GLA cytotoxity, indicating the cytotoxity induced by GLA may be due to lipid peroxidation.

Closely related colon cancer cell lines display different sensitivity to polyunsaturated fatty acids, accumulate different lipid classes and downregulate sterol regulatory element-binding protein 1

N-6 polyunsaturated fatty acids (PUFAs) may be associated with increased risk of colon cancer, whereas n-3 PUFAs may have a protective effect. We examined the effects of docosahexaenoic acid (DHA), eicosapentaenoic acid and arachidonic acid on the colon carcinoma cell lines SW480 derived from a primary tumour, and SW620 derived from a metastasis of the same tumour. DHA had the strongest growth-inhibitory effect on both cell lines. SW620 was relatively more growth-inhibited than SW480, but SW620 also had the highest growth rate in the absence of PUFAs. Flow cytometry revealed an increase in the fraction of cells in the G2/M phase of the cell cycle, particularly for SW620 cells. Growth inhibition was apparently not caused by increased lipid peroxidation, reduced glutathione or low activity of glutathione peroxidase. Transmission electron microscopy revealed formation of cytoplasmic lipid droplets after DHA treatment. In SW620 cells an eightfold increase in total cholesteryl esters and a 190-fold increase in DHA-containing cholesteryl esters were observed after DHA treatment. In contrast, SW480 cells accumulated DHA-enriched triglycerides. Arachidonic acid accumulated in a similar manner, whereas the nontoxic oleic acid was mainly incorporated in triglycerides in both cell lines. Interestingly, nuclear sterol regulatory element-binding protein 1 (nSREBP1), recently associated with cell growth regulation, was downregulated after DHA treatment in both cell lines. Our results demonstrate cell-specific mechanisms for the processing and storage of cytotoxic PUFAs in closely related cell lines, and suggest downregulation of nSREBP1 as a possible contributor to the growth inhibitory effect of DHA.

PPARgamma-dependent effects of conjugated linoleic acid on the human glioblastoma cell line (ADF)

Conjugated linoleic acid (CLA) has been shown to exert beneficial effects against carcinogenesis, atherosclerosis and diabetes. It has been demonstrated that CLA modulates lipid metabolism through the activation of peroxisome proliferator-activated receptors (PPARs). The PPAR family comprises 3 closely related gene products, PPAR alpha, beta/delta and gamma, differing for tissue distribution, developmental expression and ligand specificity. It has also been demonstrated that activated PPARgamma results in growth inhibition and differentiation of transformed cells. These observations stimulated a great interest toward PPARgamma ligands as potential anticancer drugs to be used in a differentiation therapy. Glioblastomas are the most commonly diagnosed primary tumors of the brain in humans. The prognosis of patients with high-grade gliomas is poor and only marginally improved by chemotherapy. The aim of this work was to study the effects of CLA and of a specific synthetic PPARgamma ligand on cell growth, differentiation and death of a human glioblastoma cell line as well as on parameters responsible for the metastatic behavior of this tumor. We demonstrate here that CLA and PPARgamma agonist strongly inhibit cell growth and proliferation rate and induce apoptosis. Moreover, both treatments decrease cell migration and invasiveness. The results obtained show that CLA acts, directly or indirectly, as a PPARgamma activator, strongly suggesting that this naturally occurring fatty acid may be used as brain antitumor drug and as a chemopreventive agent. Moreover, the gamma-agonist, once experimented and validated on man, may represent a useful coadjuvant in glioblastoma therapy and in the prevention of recurrences.

From bench to the clinic: gamma-linolenic acid therapy of human gliomas

Malignant gliomas are among the most devastating of cancers and are a major cause of mortality in a young population with a median survival time of 9 months following cytoreductive surgery, radiotherapy and chemotherapy. Recent studies showed that polyunsaturated fatty acids especially gamma-linolenic acid (GLA) have selective tumoricidal action especially against malignant glioma cells both in vitro and in vivo. Limited open label clinical studies showed that intratumoral injection/infusion of GLA is safe and effective against malignant gliomas. In view of this, large-scale, double blind studies are needed to establish the usefulness of GLA in the treatment of malignant brain tumors.

Enhanced radiosensitivity of rat autochthonous mammary tumors by dietary docosahexaenoic acid

Dietary docosahexaenoic acid (DHA), which integrates into tumor cell membranes, has been reported to enhance the efficacy against tumors of cytotoxic drugs that induce reactive oxygen species (ROS). Because ionizing radiation also generate ROS, we initiated a study to determine whether dietary DHA might sensitize mammary tumors to irradiation. Mammary tumors were induced by N-methylnitrosourea (NMU) in Sprague-Dawley rats. The optimal dose of radiation to examine the effect of DHA on tumor response to irradiation was determined to be 18 grays (Gy) using a 4-6 MeV electron beam (according to the depth of the target volume) delivered in a single fraction from a linear accelerator. Two groups of rats were fed a basal diet containing 7% of a mixture of peanut and rapeseed oils enriched with 8% of an oil containing either a low (palm oil) or high (DHASCO oil containing 40% DHA) DHA content. DHA group was equally subdivided into 2 groups without or with addition of vitamin E (100 IU/kg diet). Irradiation was carried out when the first tumor in each rat reached 1.5 cm2 and subsequent change in tumor size was documented over time. DHA level in adipose tissue, taken as a biomarker, was higher in the DHA supplemented group compared to the control group. Vitamin E level in liver, the best storage for this compound, was higher in the vitamin E supplemented DHA group compared to the DHA group. Tumor size decreased by 60% at 12 days after irradiation in the DHA group vs. 31% in the control group (p = 0.03) and 36% in the DHA plus vitamin E group. Therefore, dietary DHA sensitized mammary tumors to radiation. The addition of vitamin E inhibited the beneficial effect of DHA, suggesting that this effect might be mediated by oxidative damage to the peroxidizable lipids.

The eicosanoid cascade: possible role in gliomas and meningiomas

Eicosanoids constitute a large family of biologically active lipid mediators that are produced by two enzyme classes, cyclooxygenases (COX-1 and COX-2) and lipoxygenases (5-LO, 12-LO, and 15-LO). Increasing evidence suggests that in addition to a variety of epithelial malignancies, the two most common types of human brain tumour, gliomas and meningiomas, aberrantly overexpress eicosanoid producing enzymes and release a spectrum of eicosanoids that may promote tumorigenesis and the development of peritumorous brain oedema. Glioma and meningioma cells are killed in vitro and in animal models when exposed to COX-2 and 5-LO inhibitors, and their effectiveness is under investigation in clinical trials for treatment of patients with malignant brain tumours. However, despite research into the role of the eicosanoid cascade in the tumorigenesis of human brain tumours, many important questions remain unanswered. Current and newer agents that specifically target key players of the eicosanoid cascade could change the approach to treating brain tumours, because their benefits may lie in their synergism with conventional cytotoxic treatments and/or with other novel agents targeted against other procarcinogenic pathways.

A nucleotide insertion in the transcriptional regulatory region of FADS2 gives rise to human fatty acid delta-6-desaturase deficiency

Fatty acid delta-6-desaturase (FADS2) is the rate-limiting enzyme in mammalian synthesis of long-chain polyunsaturated fatty acids. We investigated the molecular mechanism of FADS2 deficiency in skin fibroblasts from a patient deficient in this enzyme. Expression analyses demonstrated an 80% to 90% decrease in the steady-state level of FADS2 mRNA in patient-derived cells compared with normal controls that was consistent with previous metabolic biochemical studies. In vitro transcription assays indicated an 80% decrease in the rate of transcriptional initiation in patient-derived cells, thus implicating transcriptional regulation as the mechanism for the decreased transcript levels. Sequence analysis of the 5' end of the gene revealed the insertion of a thymidine between positions -941 and -942 upstream of the translation start site in patient-derived cells compared with normal cells and published sequences. Promoter-reporter assays demonstrated a 6-fold decrease in promoter activity in the polymorphic variant FADS2 regulatory region compared with the normal gene, confirming the functional relevance of the insertion mutation to the decreased expression of the gene in the patient-derived cells. These findings indicate that fatty acid delta-6-desaturase deficiency and decreased FADS2 transcription are caused by a nucleotide insertion in the transcriptional regulatory region of the human FADS2 gene.

Protective role of glucose-6-phosphate dehydrogenase activity in the metabolic response of C6 rat glioma cells to polyunsaturated fatty acid exposure

Polyunsaturated fatty acids (PUFAs) can influence tumor growth and migration, both in vitro and in vivo. The PUFA gamma-linolenic acid (GLA) has been reported to improve the poor prognosis associated with human gliomas, although its effects at sublethal concentrations on residual cells postsurgery are poorly understood. The study investigated the effects sublethal PUFA doses (90 or 150 microM) may have on rat C6 glioma cell energy metabolism, since an adequate energy supply is essential for cell proliferation, migration, and apoptosis. Of note was the identification of mitochondrial heterogeneity in relation to the mitochondrial membrane potential (MMP), which has been suggested but unproven in previous studies. GLA and eicosapentaenoic acid (EPA) caused significant changes in cellular fatty acid composition and increased the percentage of cells with a low MMP after a 96-h exposure period. The presence of PUFAs inhibited C6 cell proliferation and migration, although apoptosis was not induced. The protein expression and activity of glucose-6-phosphate dehydrogenase was increased after 96-h incubation with 90 microM GLA and EPA and would allow redox regulation through increased NADPH production, permitting the maintenance of adequate intracellular reduced glutathione concentrations and limiting rates of lipid peroxidation and reactive oxygen species generation. Neither NADP(+)-isocitrate dehydrogenase nor NADP(+)-malate dehydrogenase activity responded to PUFAs, suggesting it is glucose-6-phosphate dehydrogenase that is the principal source of NADPH in C6 cells. These data compliment studies showing that higher concentrations of GLA induced glioma cell death and tumor regression and suggest that GLA treatment could be useful for the inhibition of residual cell proliferation and migration after surgical removal of the tumor mass.

Docosahexaenoic acid enhances arsenic trioxide-mediated apoptosis in arsenic trioxide-resistant HL-60 cells

Recent reports indicate a broad spectrum of antileukemic activity for arsenic trioxide (As(2)O(3)) due to its ability to induce apoptosis via intracellular production of reactive oxygen species (ROS). Despite its potent apoptotic mechanism, As(2)O(3) is not equally effective in all leukemic cells, which has prompted a search for agents enhancing As(2)O(3) efficacy. Recently, evidence has been gathered that the polyunsaturated fatty acid docosahexaenoic acid (DHA) may sensitize tumor cells to ROS-inducing anticancer agents. The aim of our investigation was to evaluate whether DHA enhances As(2)O(3)-mediated apoptosis in As(2)O(3)-resistant HL-60 cells. While 1 microM As(2)O(3) or 25 microM DHA reduced cell viability to 85.8% +/- 2.9% and 69.2% +/- 3.6%, combined treatment with As(2)O(3) and DHA reduced viability to 13.0% +/- 9.9% with a concomitant increase of apoptosis. Apoptotic cell death was preceded by collapse of the mitochondrial membrane potential, increased expression of proapoptotic B-cell lymphoma protein-2-associated X protein (Bax), and caspase-3 activation. Importantly, the combined effect of As(2)O(3) and DHA was associated with increased production of intracellular ROS and toxic lipid peroxidation products and was abolished by the antioxidant vitamin E or when oleic acid (a nonperoxidizable fatty acid) was used in place of DHA. Intracellular ROS and toxic lipid peroxidation products most likely constitute the key mediators contributing to the combined effect of As(2)O(3) and DHA. Our data provide the first evidence that DHA may help to extend the therapeutic spectrum of As(2)O(3) and suggest that the combination of As(2)O(3) and DHA could be more broadly applied in leukemia therapy.

Gamma-linolenic acid therapy of human gliomas

OBJECTIVES

We investigated the effect of intratumoral administration of gamma-linolenic acid (GLA) in human gliomas.

METHODS

We evaluated the effect of the administration of 1 mg of GLA for 7 d via a cerebral reservoir placed into the tumor bed or by direct intratumoral delivery in nine patients who had grade 4 disease and recurrent glioma after surgery, radiation, or chemotherapy.

RESULTS

There was some, but not dramatic, improvement in patients' survival. No significant prolongation of life span was expected considering the advanced nature of the disease. Nevertheless, it was encouraging that GLA produced no significant side effects in any patient. Regression of the cerebral gliomas was visualized on computed tomography and magnetic resonance imaging.

CONCLUSIONS

Based on results of the present and previous studies, we believe that GLA is a safe antitumor agent and that higher doses of GLA should be investigated in future studies.

In vitro studies on the relationship between polyunsaturated fatty acids and cancer: tumour or tissue specific effects?

In vitro cell culture experiments have lead to the consensus in the literature that certain PUFAs have a selective cytotoxic or anti-proliferative effect on tumour cells and a minimal, or no effect on normal cells. Re-examination of key publications showed that when normal cells were used for comparison, they were generally not from the same cell, tissue, or species type as the tumour cells. Recently, investigations have included more appropriate normal control cells, and though tumour specific cytotoxic/anti-proliferative PUFA effects are found in some cell types, in others the normal cells are more sensitive. Cell type differences were found in the relative ability of individual PUFAs to act. However, within a cell type differences in susceptibility were influenced by grade and stage of tumour, immortalisation and tumourigenic status, cell culture media and cell plating density. Together these results suggest that the consensus is not valid, and that susceptibility to PUFA is cell type specific, and alters during neoplastic progression. Furthermore, the cytotoxic/anti-proliferative effect induced by both n-3 and n-6 PUFAs on a wide variety of cell types, associated with an increase in lipid peroxidation in vitro, cannot account for the in vivo data on the relationship between dietary fat and certain cancers. However, the effects of PUFAs and their metabolites on cell signalling pathways may explain the in vivo data.

Synergistic interaction between vinorelbine and gamma-linolenic acid in breast cancer cells

It has been suggested that exogenous unsaturated fatty acids (UFAs) may increase the cytotoxic activity of cancer chemotherapeutic agents. We examined how y-linolenic acid (GLA; 18: 3n-6), the most promising UFA in the treatment of human tumors, affects the effectiveness of the lipophilic drug vinorelbine (VNR) on human breast carcinoma cell lines. Cells were exposed simultaneously to VNR and GLA or sequentially to GLA followed by VNR. Cell viability was determined by MTT assay. The increase in VNR-induced cell growth inhibition was measured by dividing the IC50 and IC70 values (50 and 70% inhibitory concentrations, respectively) that were obtained when the cells were exposed to VNR alone with those with VNR plus GLA. We found that GLA enhanced in a dose-dependent manner the cell growth inhibitory activity of VNR on MCF-7 cells (up to 9-fold). As GLA by itself showed anti-proliferative effects, possible GLA-VNR interactions at the cellular level were assessed employing the isobologram analysis and the combination index (CI) method of Chou-Talalay. Both methods showed an overall synergism between GLA and VNR in MCF-7 cells. At a high level of cell kill, the synergism was greater when a 24 h GLA pre-exposure or co-exposures were tested. Synergy was likewise observed with the GLA-VNR combination in MDA-MB-231, T47D, and SK-Br3 breast cancer cells. In all cell lines, the synergism was independent of the treatment schedule and the exposure time. Under conditions inhibiting lipid peroxidation using Vitamin E (dl-alpha-tocopherol), the enhancing effect of GLA (an easily oxidizable UFA) on VNR activity was partially abolished. However, when Vitamin E was used in combination, a similar synergistic increase in growth inhibition was obtained. These latter observations strongly implies that the synergistic effects of GLA with VNR are not mediated through a mechanism involving a generation of lipoperoxides. For comparison, the effects of other UFAs were examined on VNR chemosensitivity: GLA was the most potent at enhancing VNR activity, followed by docosahexaenoic acid (22: 6n-3), eicosapentaenoic acid (20: 5n-3) and alpha-linolenic acid (18: 3n-3), whereas linoleic acid (18: 2n-6) and arachidonic acid (20: 4n-6) did not increase VNR chemosensitivity. Very high concentrations of oleic acid (OA; 18:1 n-9), an UFA inversely correlated with breast cancer risk, also enhanced VNR effectiveness. Thus, various types of UFAs were not equivalent with respect to their actions on VNR effectiveness. In conclusion, our results give experimental support to the hypothesis that some UFAs can be used as modulators of tumor cell chemosensitivity and provide the rationale for in vivo preclinical investigation.

Repression of cellular anaplerosis as the hypothesized mechanism of gamma-linolenic acid-induced toxicity to tumor cells

In in vitro cultures, the cell is virtually isolated and can no longer rely on mechanisms for physiological regulation of substrate availability found in tissues. More emphasis is laid on utilization of preponderant substrate in a proposed reciprocal relationship between glycolysis and free fatty acid (FFA) oxidation for energy. Supraphysiological concentrations of gamma-linolenic acid and some other polyunsaturated fatty acids (PUFAs) therefore suppress glycolysis but also inhibit FFA oxidation initiated through a cytochrome P450-mediated epoxidation of PUFA to inhibit fatty acid synthase (FAS) activity. FAS inhibition accumulates malonyl CoA which inhibits carnitine palmitoyl transferase I and prevents FFA oxidation. The cell is starved of energy and anabolic intermediates, leading to decreased proliferation or death for tumor cells. Tumor cells are more vulnerable to this induced toxicity due to possession of specific phenotypes of elevated expression for FAS and pyruvate kinase, type M2, both factors inducing tumor cell apoptosis on inhibition.

Peroxisome proliferator-activated receptor- gamma expression in human malignant and normal brain, breast and prostate-derived cells

The constitutive and gamma -linolenic acid (GLA)-induced expression of peroxisome proliferator-activated receptor gamma (PPAR gamma) immunoreactive protein in a panel of human malignant brain (U87MG, T98G); breast (MCF-7, MB MDA-231, MB MDA 435) and prostate (ALVA, DU-145, LNCaP, PC3) cell lines have been compared with those for their normal cell counterparts, the human normal astrocyte (NHA), mammary epithelial (HMEC) and prostate epithelial (PrEC) cells, respectively. Constitutive levels of expression for PPAR gamma protein were significantly higher in the malignant cell lines relative to their normal cells. GLA supplementation did not affect the protein expression in malignant cells but caused 6- and 3-fold increases in normal breast and prostate cells, respectively. Since activation of PPAR gamma protein in some human malignant cell lines has been demonstrated to induce tumour cell death, these findings signal the need to exploit the significantly elevated expression of this protein in the therapy of human cancer.

Cytotoxicity of combined essential fatty acids on a human prostate cancer cell line

In this study the effect of single and concomitantly added n-6 or n-3 polyunsaturated fatty acids (PUFAs) was investigated on human prostate cells. Data obtained from the single fatty acids (FAs) experiments showed that except for oleic acid (OA), arachidonic (AA) and linoleic acid (LA), which had very little (less than 10% cells dead) effect on the cells, an increase in dead cells was observed at physiological concentrations of, eicosapentaenoic acid (EPA), gamma-linolenic acid (GLA) and alpha-linolenic acid (ALA). However, this was not the case when combining these acids at physiological concentrations. A slight increase in cell death was only obtained with three combinations of ALA, namely with AA, OA, or GLA. Other combinations with ALA, such as with LA or EPA, had respectively no effect on cell number or increased the cell number by causing less cells to die. Other PUFAs combinations tested, did not show the three groups mentioned with ALA, but only the last two types, namely, no effect, or a decrease in the amount of cell death. The latter might mean that the FA combination had stimulated the cells, since a decrease in the amount of dead cells was observed. Therefore, it is concluded that the characteristics of combined FAs may differ from single FAs, which may explain some controversies in the literature and in response to treatments.

Role of peroxisomal oxidation in the conversion of arachidonic acid to eicosatrienoic acid in human skin fibroblasts

Human skin fibroblasts converted [5,6,8,9,11,12,14,15-3H]arachidonic acid ([3H]20:4) to eicosatrienoic acid (20:3), but appreciable amounts of radiolabeled 20:3 were not detected in corresponding incubations with [1-(14)C]20:4. This indicates that the main pathway for synthesizing 20:3 from arachidonic acid in the fibroblast involves oxidative removal of the carboxyl group of arachidonic acid. Fibroblasts deficient in long-chain acyl coenzyme A dehydrogenase (LCAD) converted [3H]20:4 to [3H]20:3. However, Zellweger fibroblasts that are deficient in peroxisomal fatty acid oxidation did not, indicating that the oxidative removal of the carboxyl group occurs in the peroxisomes. [3H]Hexadecatrienoic acid (16:3) was the main product that accumulated when [3H]20:4 was incubated with normal, LCAD deficient, and very long-chain acyl coenzyme A dehydrogenase (VLCAD) deficient fibroblasts, but Zellweger fibroblasts did not form this product. Normal fibroblasts converted [3H]16:3 to radiolabeled 20:3 and arachidonic acid. These findings suggest that some of the 16:3 produced from arachidonic acid by peroxisomal beta-oxidation can be recycled and that this recycling process constitutes a novel pathway for the conversion of arachidonic acid to 20:3 in human fibroblasts.

Inhibition of the expression of VE-cadherin/catenin complex by gamma linolenic acid in human vascular endothelial cells, and its impact on angiogenesis

Gamma linolenic acid (GLA) has been recently shown to inhibit tumour-induced angiogenesis. The present study investigated the effects of GLA on the HUVEC-specific adhesion. After treatment with GLA, HUVECs decreased the amounts of Triton soluble and insoluble VE-cadherin and beta-catenin and reduced tube formation in matrix in a concentration-dependent manner. An anti-VE-cadherin antibody dissociated HUVECs' colonies and exerted similar inhibitory effects on tube formation of HUVECs. These data indicate that the VE-cadherin/catenins complex is essential for formation and maintenance of new capillaries. It is concluded, therefore, that GLA inhibits tumour-induced angiogenesis partly via the decrease in the expression of VE-cadherin and beta-catenin.

n-3 polyunsaturated fatty acids and cancer

n-3 Polyunsaturated fatty acids are promising molecules in cancer prevention and the potentiation of cancer treatment. Recent studies have highlighted the importance of their interactions with other food components. Their effects on tumor growth depend upon background levels of n-6 polyunsaturated fatty acids and antioxidants, and this could account for previously inconsistent results in experimental carcinogenesis. Recognition of the role of lipoperoxidation in the anti-tumor effects of polyunsaturated fatty acids, which is apparent in a variety of in-vitro or in-vivo systems, has been a major advance in the field. Consequently, n-3 polyunsaturated fatty acids appear to be excellent substrates for lipid peroxidation in situations where an oxidative stress is involved, such as in the action of several cytotoxic agents in the treatment of cancer.