Polyunsaturated fatty acids (PUFA) and eicosanoids in human health and pathologies

Formation and antiproliferative effect of prostaglandin E(3) from eicosapentaenoic acid in human lung cancer cells

We investigated the formation and pharmacology of prostaglandin E(3) (PGE(3)) derived from fish oil eicosapentaenoic acid (EPA) in human lung cancer A549 cells. Exposure of A549 cells to EPA resulted in the rapid formation and export of PGE(3.) The extracellular ratio of PGE(3) to PGE(2) increased from 0.08 in control cells to 0.8 in cells exposed to EPA within 48 h. Incubation of EPA with cloned ovine or human recombinant cyclooxygenase 2 (COX-2) resulted in 13- and 18-fold greater formation of PGE(3), respectively, than that produced by COX-1. Exposure of A549 cells to 1 microM PGE(3) inhibited cell proliferation by 37.1% (P < 0.05). Exposure of normal human bronchial epithelial (NHBE) cells to PGE(3), however, had no effect. When A549 cells were exposed to EPA (25 microM) or a combination of EPA and celecoxib (a selective COX-2 inhibitor), the inhibitory effect of EPA on the growth of A549 cells was reversed by the presence of celecoxib (at both 5 and 10 microM). This effect appears to be associated with a 50% reduction of PGE(3) formation in cells treated with a combination of EPA and celecoxib compared with cells exposed to EPA alone. These data indicate that exposure of lung cancer cells to EPA results in a decrease in the COX-2-mediated formation of PGE(2), an increase in the level of PGE(3), and PGE(3)-mediated inhibition of tumor cell proliferation.

Polyunsaturated fatty acids and gene expression

PURPOSE OF REVIEW

This review focuses on the effect(s) of n-3 polyunsaturated fatty acids on gene transcription as determined by data generated using cDNA microarrays. Introduced within the past decade, this methodology allows detection of the expression of thousands of genes simultaneously and, hence, is a potentially powerful tool for studying the regulation of physiological mechanisms that are triggered or inhibited by nutrients.

RECENT FINDINGS

Recent data generated with cDNA microarrays not only confirm the effects of n-3 polyunsaturated fatty acids on regulation of lipolytic and lipogenic gene expression as determined by more traditional methods but also emphasize the tissue specificity of this regulation. cDNA microarray experiments also have expanded our understanding of the role of n-3 polyunsaturated fatty acids in regulation of expression of genes involved in many other pathways. These include: oxidative stress response and antioxidant capacity; cell proliferation; cell growth and apoptosis; cell signaling and cell transduction.

SUMMARY

The cDNA microarray studies published to date show clearly that n-3 polyunsaturated fatty acids, usually provided as fish oil, modulate expression of a number of genes with such broad functions as DNA binding, transcriptional regulation, transport, cell adhesion, cell proliferation, and membrane localization. These effects, in turn, may significantly modify cell function, development and/or maturation.

Cancer cachexia and tumor growth reduction in Walker 256 tumor-bearing rats supplemented with N-3 polyunsaturated fatty acids for one generation

In this study we investigated the effect of lifelong supplementation of the diet with coconut oil (CO, rich in saturated fatty acids) or fish oil (FO, rich in n-3 polyunsaturated fatty acids, PUFAs) on tumor growth, animal survival, and metabolic indicators of cachexia in adult rats. Female Wistar rats were supplemented with CO or FO prior to mating and then throughout pregnancy and gestation, and then the male offspring were supplemented from weaning until 90 days of age. Then they were inoculated subcutaneously with Walker 256 tumor cells. Tumor weight at 14 days in control rats (those fed standard chow) was approximately 20 g. These animals displayed cancer cachexia, which was characterized by loss of weight, hypoglycemia, hyperlacticidemia, hypertriacylglycerolemia, and depletion of glycogen stores. Supplementation of the diet with CO did not change these parameters, except that there was a smaller decrease in serum triacylglycerol concentration. Supplementation of the diet with FO significantly decreased tumor growth (by approximately 60%), increased survival (50% at 30 days postinoculation vs. 30% in the controls and 13.5% in the CO group), and prevented the fall in body weight. Furthermore, FO supplementation partly abolished the fall in serum glucose, totally prevented the elevation in serum lactate concentrations, partly prevented the hypertriacylgylcerolemia, and preserved tissue glycogen stores. Lifelong consumption of FO, rich in n-3 PUFAs, protects against tumor growth and cancer cachexia and improves survival.

Nutritional-pharmacological combinations--a novel approach to reducing colon cancer incidence

BACKGROUND

Recent studies have suggested that n-9 fatty acids in olive oil prevent colon carcinogenesis while n-6 PUFA seems to activate this process.

AIMS

To evaluate the effects of nutritional-pharmacological combinations made up of olive or soy oil-based diets and the drug sulindac, on colon cancer incidence in a chemically induced (1,2-dimethylhydrazine, DMH) rat cancer model.

METHODS

Male rats were assigned to two different dietary regimes based on a standard murine defined diet (AIN-76A) containing either a low (4%) or high (15 %) concentration of olive or soy oil. Some groups also received sulindac in their food (80 mg/kg food) starting from the ninth week following the first DMH or vehicle administration.

RESULTS

Oleic and linoleic acid reached higher levels in plasma and liver lipids when rats were fed high concentrations of olive or soy oil, respectively. Rats fed a low or high soy oil-based diet showed no significant difference in the number of aberrant crypt foci (ACF) in proximal or distal colon specimens. In contrast, rats fed a higher olive oil-based diet developed a significantly lower number of ACF than rats fed a low concentration of olive oil. Addition of sulindac reduced the number of ACF in rats fed the 4%, but not the 15%, soy oil diet. In contrast, the effect of sulindac was significant when combined with both the low and high concentrations of olive oil. High soy oil-based diet or DMH treatment upregulated colon expression of Bcl-2, but not that of cyclooxygenase-2 (COX-2). In contrast, olive oil dose-dependently downregulated the expression of both Bcl-2 and COX-2 in colonic mucosa and also abrogated the upregulation of Bcl-2 by DMH. Olive oil/sulindac combinations were effective in downregulating colonic mucosa Bcl-2 expression (with the 4% oil diet) and COX-2 expression (with the 15% oil diet). These effects were not observed in rats fed the soy oil/sulindac combinations. Caspase-3 activity in colonic mucosa was unaffected by soy oil or soy oil/sulindac combinations. The addition of olive oil, on the other hand, significantly enhanced colonic caspase-3 activity.

CONCLUSIONS

Diets containing high levels of olive oil exert a significant protective effect from tumor development that is additive with the inhibitory effect of sulindac. These inhibitory effects are mediated by regulating the expression and activity of key proteins involved in prostaglandin-biosynthesis and apoptosis-induction pathways. It may be concluded that appropriate dietary-pharmacological combination can improve anti-tumor efficacy over either dietary or pharmacological intervention alone.

The natural activities of cells, the role of reactive oxygen species, and their relation to antioxidants, nutraceuticals, botanicals, and other biologic therapies

There have been remarkable advances in molecular and cell biology that define the mechanisms of how various supplements function in and around cells. Current evidence strongly supports the probability that cellular functions and cellular responses that pertain to inflammation, disease, and life and death activity can be modulated with supplementation; however, the complexity of each individual's reaction and the vast differences in physiologic influences makes clinical research difficult in regard to clinical studies using antioxidant and biologic therapies. Not enough is known specifically about each supplement and its interactions with cells, nor is enough understood about how the body compensates or reacts to such applications. What works well in one individual or species might work differently in another. In addition, not all antioxidants are created equally, and discrepancies in purity and absorption can occur. It must also be determined whether or not less than optimum levels or infrequent usage will produce the same physiological effects. Not everyone--nor every species of animal--responds in the same manner to supplements, which might account for the variations in clinical research. The cellular effects of antioxidants and other supplements are well defined and meaningful, and their clinical application looks promising despite individual variations. Combinations of antioxidants are synergistic and support cellular functions, effects that are often not apparent with individual agents. Such combinations offer a variety of mechanisms for reducing oxygen metabolites in tissues, altering signaling pathways, and modulating transcription factors, and they might play key roles in reducing the damage afforded by ROS. It is the author's opinion that combinations of antioxidants are best suited for clinical application in modulating disease and reducing premature aging when caused by excessive free radical accumulation. Clinicians should approach clinical application of these supplements based on the best available scientific research and species-specific information available.

Effects of polyunsaturated fatty acids on prostaglandin synthesis and cyclooxygenase-mediated DNA adduct formation by heterocyclic aromatic amines in human adenocarcinoma colon cells

Dietary heterocyclic aromatic amines (HCA) and polyunsaturated fatty acids (PUFA) are both believed to play a role in colon carcinogenesis, and are both substrate for the enzyme cyclooxygenase (COX). In HCA-7 cells, highly expressing isoform COX-2, we investigated the effects of PUFA on prostaglandin synthesis and DNA adduct formation by the HCA 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). Furthermore, we studied the role of COX, COX-2 in particular, and cytochrome P4501A2 (CYP1A2) by using the enzyme inhibitors indomethacin (IM), NS-398, and phenethyl isothiocyanate (PEITC), respectively. COX-mediated formation of prostaglandin E2 (PGE2) from linoleic acid (LA) showed that HCA-7 cells can convert LA into arachidonic acid (AA). Alternatively, eicosapentaenoic acid (EPA) was found to compete with AA for COX. Strongly decreased PGE2 levels by addition of IM demonstrated involvement of COX in PUFA metabolism. Both IM and NS-398 inhibited adduct formation by HCA to nearly the same extent, indicating involvement of COX-2 rather than COX-1, while CYP1A2 activity in HCA-7 cells was demonstrated by addition of PEITC. Overall, inhibiting effects were stronger for PhIP than for IQ. HCA-DNA adduct formation was stimulated by addition of PUFA, although high PUFA concentrations partly reduced this stimulating effect. Finally, similar effects for n-3 and n-6 fatty acids suggested that adduct formation may not be the crucial mechanism behind the differential effects of PUFA on colon carcinogenesis that have been described. These results show that COX, and COX-2 in particular, can play a substantial role in HCA activation, especially in extrahepatic tissues like the colon. Furthermore, the obvious interactions between PUFA and HCA in COX-2 expressing cancer cells may be important in modulating colorectal cancer risk.

Phospholipase A2 expression in tumours: a target for therapeutic intervention?

Phospholipase A(2) (PLA(2)) enzymes are involved in lipid metabolism and, as such, are central to several cellular processes. The different PLA(2)s identified to date can be classified into three groups: secreted PLA(2) (sPLA(2)), calcium-independent PLA(2) (iPLA(2)) and calcium-dependent cytosolic PLA(2) (cPLA(2)). In addition to their role in cellular signalling, PLA(2)s have been implicated in diverse pathological conditions, including inflammation, tissue repair and cancer. Elevated levels of sPLA(2) and cPLA(2) have been reported in several tumour types. Here, we summarize the current views on the PLA(2)s, and look at their expression, role in human malignancy and potential as targets for anticancer drug development.

PPARγ pathway activation results in apoptosis and COX-2 inhibition in HepG2 cells

AIM: To investigate whether troglitazone (TGZ), the peroxisome proliferator-activated receptor (PPAR) gamma ligand, can induce apoptosis and inhibit cell proliferation in human liver cancer cell line HepG2 and to explore the molecular mechanisms.

METHODS: [3-(4, 5)-dimethylthiazol-2-yl]-2, 5-diphenyl tetrazolium bromide (MTT), [³H] Thymidine incorporation, Hochest33258 staining, DNA ladder, enzyme-linked immunosorbent assay (ELISA), RT-PCR, Northern and Western blotting analyses were employed to investigate the effect of TGZ on HepG2 cells and related molecular mechanisms.

RESULTS: TGZ was found to inhibit the growth of HepG2 cells and to induce apoptosis. During the process, the expression of COX-2 mRNA and protein and Bcl-2 protein was down-regulated, while that of Bax and Bak proteins was up-regulated, and the activity of caspase-3 was elevated. Furthermore, the level of PGE₂ was decreased transiently after 12 h of treatment with 30 μM troglitazone.

CONCLUSION: TGZ inhibits cell proliferation and induces apoptosis in HepG2 cells, which may be associated with the activation of caspase-3-like proteases, down-regulation of the expression of COX-2 mRNA and protein, Bcl-2 protein, the elevation of PGE₂ levels, and up-regulation of the expressions of Bax and Bak proteins.