Effects of reduced dietary linoleic acid intake, alone or combined with an algal source of docosahexaenoic acid, on MDA-MB-231 breast cancer cell growth and apoptosis in nude mice

Effects of dietary linseed, evening primrose or fish oils on fatty acid and prostaglandin E2 contents in the rat livers and 7,12-dimethylbenz[a]anthracene-induced tumours

We examined the influence of diets supplemented with fish and vegetable oils on fatty acid and prostaglandin E2 (PGE2) contents in livers of non-7,12-dimethylbenz[a]anthracene (DMBA)- and DMBA-treated rats, and in DMBA-induced tumours. Decreased concentrations of saturated fatty acids and increased unsaturated fatty acid levels were observed in liver phospholipids of rats fed these oils. There was a marked difference in the concentrations of fatty acids found in the tumours and those present in liver lipids. Oleic acid was the main unsaturated fatty acid found in the tumour tissue. Both liver and tumour PGE2 contents were clearly correlated to the diet. The PGE2 concentrations were decreased in livers and tumours of rats fed fish (FO) and linseed oils (LO).

Cell-cycle arrest in Jurkat leukaemic cells: a possible role for docosahexaenoic acid

Docosahexaenoic acid (DHA) is known to have anti-cancer activities by mechanisms that are not well understood. In the present study, we test one possible pathway for DHA action in Jurkat leukaemic cells. Low doses of DHA (10 microM) are shown to induce cell-cycle arrest, whereas higher doses are cytotoxic. However, when cells that were pre-treated with 10 microM DHA are given an additional 10 microM DHA dose, cell viability rapidly decreases. Immunoblotting reveals that repeated low doses of DHA results in activation of caspase 3, implying induction of apoptosis. DHA (10 microM) is shown to increase ceramide levels after 6 h of incubation and, after 24 h, the cells appear to be arrested in S phase. With DHA, the amount of phosphorylated retinoblastoma protein (pRb) decreases significantly. Western blot analysis also shows that DHA greatly reduces the level of cyclin A, while increasing the level of p21 WAF1, a cellular inhibitor of cyclin A/cyclin-dependent kinase 2 (cdk2) activity. Furthermore, the observed DHA-induced doubling of the ratio of hypophosphorylated pRb (hypo-pRb) to total pRb is inhibited by tautomycin and phosphatidic acid (PA), known inhibitors of protein phosphatase 1 (PP1), and by the PP2 inhibitor okadaic acid. The present study demonstrates one possible connected pathway for DHA action. By this pathway, low doses of DHA increase ceramide levels, which leads to inhibition of cdk2 activity and stimulation of PP1 and PP2A. The net effect of cdk2 inhibition and protein phosphatase activation is an inhibition of pRb phosphorylation, consequently arresting Jurkat cell growth.

Influence of omega-3 fatty acids on the growth of human colon carcinoma in nude mice

The present study investigated the influence of dietary omega-3 fatty acid supplementation on the growth of human colon carcinoma xenograft in athymic nude mice. Four diets were fed to evaluate the effect of levels and types of fat on colon tumor growth. Animals were maintained on a standard diet modified by addition of fats containing omega-3 and omega-6 fatty acids to represent high and low fat intakes for 53 days. The final mean estimated tumor weight for the high fat corn oil (24%) fed group was 2,302 mg, whereas the low fat (8% corn oil) group was 1,681 mg. The final mean tumor weight of the high fat menhaden oil fed group was 782 mg representing a 66% decrease in growth compared to the high fat corn oil group and a decrease of 54% compared to the low corn oil fed group. The high fat golden algae oil fed group resulted in a mean final tumor weight of 223 mg representing a 90% inhibition of tumor growth relative to the high fat corn oil fed group and 87% inhibition of growth compared to the low fat corn oil fed group. These findings indicate that dietary omega-3 fatty acids possess significant tumor suppressing properties and that the primary tumor suppressing fatty acid is docosahexaenoic acid. Histopathologic examination of control and treated tumors and expression array analyses (human cytokine and apoptosis arrays) support the tumor growth inhibition data and provide evidence for discussion of possible mechanisms for the observed growth inhibition.

Prevention of docosahexaenoic acid-induced cytotoxicity by phosphatidic acid in Jurkat leukemic cells: the role of protein phosphatase-1

The present investigation explores the role of phosphatidic acid (PA), a specific protein phosphatase-1 (PP1) inhibitor, in cytotoxicity induced by docosahexaenoic acid (DHA). The cytotoxicity of DHA was assayed by quantifying cell survival using the trypan blue exclusion method. A dose-response effect demonstrated that 5 or 10 microM DHA has no effect on Jurkat cell survival; however, 15 microM DHA rapidly decreased cell survival to 40% within 2 h of treatment. Cytotoxicity of 15 microM DHA was prevented by PA. Structurally similar phospholipids (lysophosphatidic acid, sphingosine 1-phosphate, sphingosine, and sphingosine phosphocholine) or metabolites of PA (lyso-PA and diacylglycerol) did not prevent DHA-induced cytotoxicity. PA did not produce micelles alone or in combination with DHA as examined spectrophotometrically, indicating that PA did not entrap DHA and therefore did not affect the amount of DHA available to the cells. Supporting this observation, the uptake or incorporation of [1-14C]DHA in Jurkat cells was not affected by the presence of PA. However, PA treatment reduced the amount of DHA-induced inorganic phosphate released from Jurkat leukemic cells and also inhibited DHA-induced dephosphorylation of cellular proteins. These observations indicate that PA has exerted its anti-cytotoxic effects by causing inhibition of protein phosphatase activities. Cytotoxicity of DHA on Jurkat cells was also blocked by the use of a highly specific caspase-3 inhibitor (N-acetyl-ala-ala-val-ala-leu-leu-pro-ala-val-leu-leu-ala-leu-leu-ala-pro-asp-glu-val-asp-CHO), indicating that the cytotoxic effects of DHA were due to the induction of apoptosis though activation of caspase-3. Consistent with these data, proteolytic activation of procaspase-3 was also evident when examined by immunoblotting. PA prevented procaspase-3 degradation in DHA-treated cells, indicating that PA causes inhibition of DHA-induced apoptosis in Jurkat leukemic cells. Since DHA-induced apoptosis can be inhibited by PA, we conclude that the process is mediated through activation of PP1.

The Mediterranean diets: What is so special about the diet of Greece? The scientific evidence

The term "Mediterranean diet," implying that all Mediterranean people have the same diet, is a misnomer. The countries around the Mediterranean basin have different diets, religions and cultures. Their diets differ in the amount of total fat, olive oil, type of meat and wine intake; milk vs. cheese; fruits and vegetables; and the rates of coronary heart disease and cancer, with the lower death rates and longer life expectancy occurring in Greece. Extensive studies on the traditional diet of Greece (the diet before 1960) indicate that the dietary pattern of Greeks consists of a high intake of fruits, vegetables (particularly wild plants), nuts and cereals mostly in the form of sourdough bread rather than pasta; more olive oil and olives; less milk but more cheese; more fish; less meat; and moderate amounts of wine, more so than other Mediterranean countries. Analyses of the dietary pattern of the diet of Crete shows a number of protective substances, such as selenium, glutathione, a balanced ratio of (n-6):(n-3) essential fatty acids (EFA), high amounts of fiber, antioxidants (especially resveratrol from wine and polyphenols from olive oil), vitamins E and C, some of which have been shown to be associated with lower risk of cancer, including cancer of the breast. These findings should serve as a strong incentive for the initiation of intervention trials that will test the effect of specific dietary patterns in the prevention and management of patients with cancer.

Regulation of tumor angiogenesis by dietary fatty acids and eicosanoids

Angiogenesis is a prerequisite for tumor growth and metastasis. Vascular endothelial cell proliferation, migration, and capillary formation are stimulated by angiogenic growth factors, which include the proteins vascular endothelial growth factor, basic fibroblast growth factor, and transforming growth factor-beta, and eicosanoids synthesized from n-6 fatty acids. Clinical studies have shown that angiogenesis in solid tumors relates to a poor prognosis and, in premalignant lesions, indicates potential for cancerous transformation. High-fat, n-6 fatty acid-rich diets were associated with a relatively poor prognosis in breast cancer patients; in a nude mouse model the same diet enhanced breast cancer progression, whereas n-3 fatty acids exerted suppressive effects that were associated with impaired angiogenesis. Lipoxygenase and cyclooxygenase products of n-6 fatty acid metabolism are angiogenic in in vitro assays. This activity is blocked by pharmacological inhibitors of eicosanoid biosynthesis, and one, indomethacin, suppressed n-6 fatty acid-stimulated murine mammary carcinoma growth and metastasis and tumor vascularization. Review of the experimental data suggests that selective inhibitors of eicosanoid-synthesizing enzymes and dietary intervention with n-3 fatty acids merit clinical evaluation as adjuvant therapy and chemopreventive agents.

Partial chemical/structural elucidation of anti-mutagenic compounds from corn

In this study, corn fractions obtained from an isolation process of anti-mutagenic factors in our previous research work (Burgos-Hernández et al., 2001), were subjected to several analyses for chemical/structural elucidation. The anti-mutagenic activity of these fractions was tested against aflatoxin B(1) (AFB(1)) and 1-methyl-3-nitro-1-nitrosoguanidine (MNNG), a mutagen that does not require bioactivation. Two concentrations of this agent in the corn fractions were tested for anti-mutagenicity in the Salmonella/microsomal mutagenicity assay, using tester strain TA100 with no metabolic activation. Corn fractions tested showed evidence of anti-mutagenic activity by producing a dose-response type of relationship between a constant amount of MNNG and several concentrations of tested corn fraction. Five different varieties of yellow corn were tested in order to determine if the anti-mutagenic factors were intrinsic to corn. Variety of the corn did not show an effect on the reduction of the mutagenic potential of AFB(1) suggesting that anti-mutagenic compounds are intrinsic to corn. Four corn fractions, previously obtained after the isolation process were analyzed by MALDI-MS and GC-MS. MALDI-MS showed the presence of two groups of molecules or molecular fragments. The molecular mass of one group ranged from 250 to 370 m/z, the other ranged from 540 to 640 m/z. GC-MS identified linoleic acid as one of the compounds responsible for the anti-mutagenic activity present in corn.

Docosahexaenoic acid induces apoptosis in Jurkat cells by a protein phosphatase-mediated process

Docosahexaenoic acid (DHA) is an omega-3 fatty acid under intense investigation for its ability to modulate cancer cell growth and survival. This research was performed to study the cellular and molecular effects of DHA. Our experiments indicated that the treatment of Jurkat cells with DHA inhibited their survival, whereas similar concentrations (60 and 90 microM) of arachidonic acid and oleic acid had little effect. To explore the mechanism of inhibition, we used several measures of apoptosis to determine whether this process was involved in DHA-induced cell death in Jurkat cells. Caspase-3, an important cytosolic downstream regulator of apoptosis, is activated by death signals through proteolytic cleavage. Incubation of Jurkat cells with 60 and 90 microM DHA caused proteolysis of caspase-3 within 48 and 24 h, respectively. DHA treatment also caused the degradation of poly-ADP-ribose polymerase and DNA fragmentation as assayed by flow cytometric TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) assay. These results indicate that DHA induces apoptosis in Jurkat leukemic cells. DHA-induced apoptosis was effectively inhibited by tautomycin and cypermethrin at concentrations that affect protein phosphatase 1 (PP1) and protein phosphatase 2B (PP2B) activities, respectively, implying a role for these phosphatases in the apoptotic pathway. Okadaic acid, an inhibitor of protein phosphatase 2A, had no effect on DHA-induced apoptosis. These results suggest that one mechanism through which DHA may control cancer cell growth is through apoptosis involving PP1/PP2B protein phosphatase activities.