Modulation of intracellular second messengers by dietary fat during colonic tumor development

Autism as a disorder of deficiency of brain-derived neurotrophic factor and altered metabolism of polyunsaturated fatty acids

Autism has a strong genetic and environmental basis in which inflammatory markers and factors concerned with synapse formation, nerve transmission, and information processing such as brain-derived neurotrophic factor (BDNF), polyunsaturated fatty acids (PUFAs): arachidonic (AA), eicosapentaenoic (EPA), and docosahexaenoic acids (DHA) and their products and neurotransmitters: dopamine, serotonin, acetylcholine, γ-aminobutyric acid, and catecholamines and cytokines are altered. Antioxidants, vitamins, minerals, and trace elements are needed for the normal metabolism of neurotrophic factors, eicosanoids, and neurotransmitters, supporting reports of their alterations in autism. But, the exact relationship among these factors and their interaction with genes and proteins concerned with brain development and growth is not clear. It is suggested that maternal infections and inflammation and adverse events during intrauterine growth of the fetus could lead to alterations in the gene expression profile and proteomics that results in dysfunction of the neuronal function and neurotransmitters, alteration(s) in the metabolism of PUFAs and their metabolites resulting in excess production of proinflammatory eicosanoids and cytokines and a deficiency of anti-inflammatory cytokines and bioactive lipids that ultimately results in the development of autism. Based on these evidences, it is proposed that selective delivery of BDNF and methods designed to augment the production of anti-inflammatory cytokines and eicosanoids and PUFAs may prevent, arrest, or reverse the autism disease process.

Effect of orlistat on fecal fat, fecal biliary acids, and colonic cell proliferation in obese subjects

BACKGROUND & AIMS

Orlistat is a weight management agent that selectively inhibits gastrointestinal lipase activity. Because of orlistat's mode of action, increased fecal fat is presented to the colonic mucosa, and fecal bile acid and free fatty acid composition may be altered during treatment. Our aim was to assess the effect of treatment of obese subjects with orlistat 120 mg 3 times a day for 6 weeks on fecal lipid and bile acid parameters and colonic mucosal cell proliferation.

METHODS

Twenty-four obese (body mass index, 30-40 kg/m2) but otherwise healthy male and female subjects were enrolled in a single-center, randomized, double-blind, placebo-controlled, parallel-group study. Participants were hospitalized during days 1-3 and 33-42 of treatment and were treated as outpatients for the remaining days.

RESULTS

Treatment with orlistat for 6 weeks resulted in significantly greater increases in fecal weight, total fecal fat, and fecal free fatty acids than placebo. Total fecal bile acid amounts decreased slightly with orlistat, and increased significantly with placebo treatment (P < .05 between-group difference). Orlistat did not alter colonic cell proliferation as assessed by the 3 proliferative indices (5-bromo-2-deoxyuridine, whole crypt mitotic count, and proliferating cell nuclear antigen).

CONCLUSIONS

Biochemical changes in fecal composition related to the pharmacodynamic mode of action of orlistat are not accompanied by altered colonic cell proliferation, a putative biomarker of colon cancer risk.

Can memory be improved? A discussion on the role of ras, GABA, acetylcholine, NO, insulin, TNF-alpha, and long-chain polyunsaturated fatty acids in memory formation and consolidation

It is proposed that long-chain polyunsaturated fatty acids when given from the perinatal period will ensure proper development and growth of the brain and maintain the activity and/or concentrations of ras, nitric oxide, insulin, and various neurotransmitters and cytokines at physiological level and thus, improve memory and prevent learning deficits.

The role of dietary long-chain n-3 fatty acids in anti-cancer immune defense and R3230AC mammary tumor growth in rats: influence of diet fat composition

We determined if long-chain n-3 fatty acids fed as part of a: (1) high polyunsaturated fat diet (currently recommended by several health agencies) or (2) low polyunsaturated fat diet (representative of that consumed by a large segment of the North American population) improved antitumor immune defense and inhibited tumor growth. Rats were fed one of four semi-purified diets (20% w/w fat) for 21 days pre- and 17 days post- R3230AC mammary tumor implantation. The polyunsaturated to saturated fatty acid (P/S) ratio was either 1 (high P/S diet) or 0.35 (low P/S diet). At each P/S ratio, diets provided long-chain n-3 fatty acids at 0 or 5% w/w of total fat. Long-chain n-3 fatty acids fed in a high P/S diet did not affect tumor growth or host immune responses. In contrast, feeding long-chain n-3 fatty acids in a low P/S diet increased natural killer cell cytotoxicity, splenocyte nitric oxide and interleukin-2 production, and the proportion of activated (CD25+) CD8+ and CD28+ cells, but did not significantly inhibit tumor growth. For both P/S diets, tumor cells from rats fed long-chain n-3 fatty acids had a higher n-3 content and n-3/n-6 ratio in phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol. Furthermore, the magnitude of increase in n-3 fatty acid incorporation into tumor phospholipids was greater when fed in a low P/S diet. We demonstrated that the dietary P/S ratio significantly influences the effect of long-chain n-3 fatty acids on host immune responses and n-3 fatty acid incorporation into tumor cells. These findings warrant further consideration when designing dietary recommendations.

Essential fatty acids as possible mediators of the actions of statins

Statins and polyunsaturated fatty acids have similar actions: both enhance endothelial nitric oxide synthesis, inhibit the production of pro-inflammatory cytokines, lower cholesterol levels, prevent atherosclerosis and are of benefit in coronary heart disease, stroke and osteoporosis. Statins enhance the conversion of linoleic acid and eicosapentaenoic acid to their long chain derivatives. Animals with essential fatty acid deficiency show an increase in HMG-CoA reductase activity, which reverts to normalcy following topical application of linoleic acid. Similarly to statins, polyunsaturated fatty acids also inhibit HMG-CoA reductase activity. In view of the similarity in their actions and as statins influence essential fatty acid metabolism, it is suggested that essential fatty acids and their metabolites may serve as second messengers of the actions of statins.

Biological mechanisms in breast cancer invasiveness: relevance to preventive interventions

Migration studies suggest that the high incidence of postmenopausal breast cancer in Western women is related mainly to epigenetic factors. Progression from ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC) also appears to involve environmental rather than genetic factors, and a role has been postulated for metabolic-endocrine changes related to the Western lifestyle. Protein kinase C (PKC) is important in cell signal transduction, and laboratory studies show that PKC stimulates the activities of urokinase plasminogen activator, matrix metalloproteinases and cell adhesion molecules, all of which are known to increase invasiveness in human mammary cancer cell lines. In rodents, the activity of PKC in tissue cells is enhanced by insulin, and PKC isoenzymes have been shown to stimulate the development of hyperinsulinaemic insulin resistance in rodents. Clinically, hyperinsulinaemia and the concomitant increase in circulating levels of free oestradiol and bioactive insulin-like growth factor 1 (IGF1) are each confirmed markers of high risk for breast cancer in women. Lesions of DCIS show evidence of regression with mammary involution, but it is postulated that this may be opposed by the concomitants of hyperinsulinaemic insulin resistance. The prevalence of the latter is increasing in Western populations, and a combination of high IGF1 and low IGF-binding protein 3 concentrations has been associated with the presence of DCIS lesions in premenopausal women. Measures that enhance insulin sensitivity in such women may reduce the risk of progression in DCIS lesions, and a clinical trial is proposed to test the hypothesis.

Essential fatty acids, lipid peroxidation and apoptosis

Essential fatty acids (EFAs) and their metabolites, especially gamma-linolenic acid, arachidonic acid, eicosapentaenoic acid and decosahexaenoic acid are known to induce apoptotic death of tumour cells. But the exact mechanism by which these fatty acids are able to induce apoptosis is not clear. Recent studies suggest that these fatty acids are able to induce apoptosis in cells over expressing cytochrome P450 following depletion of cellular glutathione and inhibition of carnitine palmitoyl transferase I (CPTI) activity. On the other hand, BCL-2 prevented apoptosis induced by these long-chain fatty acids, where as n-3 fatty acids suppressed ras expression leading to suppression of development of overt neoplasia. Phosphorylation of BCL-2 inhibits its ability to interfere with apoptosis and enhances lipid peroxidation leading to the occurrence of apoptosis. Tumour cells treated with long-chain fatty acids show increase in lipid peroxidation process, depletion of antioxidants and phosphorylation of proteins. Based on these results, it is suggested that long-chain fatty acids induce apoptosis by enhancing lipid peroxidation, suppressing BCL-2 expression possibly by phosphorylation and augmentation of P450 activity. Thus, these long-chain fatty acids may, infact act at the level of gene/oncogene expression in producing their cytotoxic action on tumour cells.

Peroxisome proliferator-activated receptors: a critical link among fatty acids, gene expression and carcinogenesis

It has been known for many years that long-chain fatty acids derived from endogenous metabolism and/or nutrition can act as second messengers and regulators of cell signaling pathways. For example, fatty acids regulate the activity of protein kinase C (PKC) in a mechanism distinct from activation by diacylglycerol. Like PKC activators such as phorbol esters, essential fatty acids activate PKC and in doing so modulate the activity of growth factor receptors such as epidermal growth factor receptor (EGFR). Unsaturated fatty acids can inhibit GTPase activating protein, thereby quenching signals from p21-ras. These studies have shown that fatty acids can influence numerous signaling pathways and that these small lipophilic substances may be ancient second messengers. Fatty acids are also known modulators of the carcinogenic process, showing distinct tissue-specific pro- or anticancer effects. However, the reason for such a dichotomous effect on cellular processes has not been adequately described. In this article, the inclusion of a steroid hormone receptor-signaling pathway in mediating fatty acids' effects will be summarized. This signaling molecule has been deemed the peroxisome proliferator-activated receptor (PPAR) and has been extensively examined in regard to its response to xenobiotic, fatty acid-like chemicals (peroxisome proliferators, PP). PP, like fatty acids, activate PPAR and modulate tissue-specific responses. The goal of this review is to describe a potential role for PPAR in mediating the effects of fatty acids on gene expression, cell growth, differentiation and apoptosis.