Phospholipid profile and production of prostanoids by murine colonic epithelium: effect of dietary fat

Potential of magnetic resonance spectroscopy in assessing the effect of fatty acids on inflammatory bowel disease in an animal model

People with inflammatory bowel disease (IBD) are at risk for developing colorectal cancer, and this risk increases at a rate of 1% per year after 8-10 years of having the disease. Saturated and omega-6 polyunsaturated fatty acids (PUFAs) have been implicated in its causation. Conversely, omega-3 PUFAs may have the potential to confer therapeutic benefit. Since proton magnetic resonance spectroscopy ((1)H MRS) combined with pattern recognition methods could be a valuable adjunct to histology, the objective of this study was to analyze the potential of (1)H MRS in assessing the effect of dietary fatty acids on colonic inflammation. Forty male Sprague-Dawley rats were administered one of the following dietary regimens for 2 weeks: low-fat corn oil (omega-6), high-fat corn oil (omega-6), high-fat flaxseed oil (omega-3) or high-fat beef tallow (saturated fatty acids). Half of the animals were fed 2% carrageenan to induce colonic inflammation similar to IBD. (1)H MRS and histology were performed on ex vivo colonic samples, and the (1)H MR spectra were analyzed using a statistical classification strategy (SCS). The histological and/or MRS studies revealed that different dietary fatty acids modulate colonic inflammation differently, with high-fat corn oil being the most inflammatory and high-fat flaxseed oil the least inflammatory. (1)H MRS is capable of identifying the biochemical changes in the colonic tissue as a result of inflammation, and when combined with SCS, this technique accurately differentiated the inflamed colonic mucosa based on the severity of the inflammation. This indicates that MRS could serve as a valuable adjunct to histology in accurately assessing colonic inflammation. Our data also suggest that both the type and the amount of fatty acids in the diet are critical in modulating IBD.

High dietary levels of a conjugated linoleic acid mixture alter hepatic glycerophospholipid class profile and cholesterol-carrying serum lipoproteins of rats

To investigate the body composition, hepatic lipids, and serum lipoproteins in response to graded levels of a conjugated linoleic acid (CLA) mixture added to a high linoleate diet, adult male Sprague-Dawley rats were randomly assigned into four dietary groups of 10 rats each and fed for 5 weeks controlled amounts of diets containing 0%, 1%, 3%, or 5% of a CLA mixture in exchange for sunflower oil. The various dietary lipid treatments did not significantly influence growth and body partitioning, although there was a trend toward decreased contents of extractable lipids in carcass (whole bled body without liver and gut) with increasing CLA. When carcass lipids of CLA-treated rats were extracted, a distinct accumulation of total CLA was observed. A dietary level of 1% CLA mixture exhibited only weak effects on hepatic glycerophospholipid levels. CLA levels of 3% and 5% caused distinct changes in phospholipid subclass distribution. These changes were reduced levels of lysophosphatidylethanolamine (LPE) and ethanolamine plasmalogen (EPL) and increased levels of phosphatidylcholine (PC). Further, a 5% level of CLA increased the hepatic concentration of phosphatidylserine (PS) compared with the other treatments. The incorporation of total CLA into individual phospholipids followed a dose-responsive manner. The extent of incorporation of CLA was not the same among the glycerophospholipid species analyzed, the order being cardiolipin > phosphatidylethanolamine and PC > LPE/EPL > phosphatidylinositol > PS. Further, CLA increased the proportions of n-3 fatty acids in the individual glycerophospholipids. High CLA diets containing 3% and 5% of a CLA mixture were associated with increased activity of catalase in the peroxisome-enriched cell fraction of liver and exhibited marked reductions of cholesterol in the low and high density lipoproteins relative to rats receiving no CLA.

Phospholipid fatty acid composition and protein kinase C activity in the large intestine of rats fed on butter and coconut-oil diets

Protein kinase C (PKC) has been proposed to play an important role in the aetiology of colon cancer. Therefore, we investigated whether the amount and type of saturated fat could affect colonic PKC activity by modifying either mucosal phospholipid fatty acid composition or faecal diacylglycerol production. Male Wistar rats (n 13 per group) were fed on diets containing butter or coconut oil at energy levels of 10% and 43% for 4 weeks. The control group received a low-fat diet providing 10% of energy from sunflowerseed oil. PKC activity was higher in the distal than the proximal colon but the quantity or type of fat did not alter PKC activity in either region of the colon. Saturated fats caused moderate changes in the fatty acid composition of caecal phospholipids, which were more obvious in the phosphatidylethanolamine than in the phosphatidylcholine fraction. A significant correlation was found between fatty acid composition of phosphatidylcholine and membrane PKC activity. In particular, there was a positive correlation between the proportion of saturated 14:0 and 18:0 and increased PKC activity while unsaturated 18:2n-6, 20:4n-6 and 16:1n-7 were inversely correlated with PKC activity. No relationship was found between phosphatidylethanolamine fatty acids and PKC activity. Concentration of faecal diacylglycerol was not affected by the diet. Overall the data suggest that diets high in saturated fat may not alter colonic PKC activity to a significant extent.

Effect of dietary fat on colonic protein kinase C and induction of aberrant crypt foci

A major objective of the present study was to determine whether a high-fat diet affects early events during colon carcinogenesis. Female Sprague-Dawley rats were injected with saline or azoxymethane (20 mg/kg) and fed either a normal (5% corn oil w/w) or a high (5% corn oil and 15% beef tallow w/w) fat diet. To assess the effect of a known tumor-promoting diet on the early events of neoplastic transformation, Study 1 examined the induction and growth of aberrant crypt foci (ACF) as well as of proliferative indices. The total number of ACF were similar in both groups even after 8 wk of dietary treatment; however, ACF with accelerated growth characteristics (> or = 4 crypts/focal lesion) were more prevalent (P < or = 0.05) in the colons of animals fed the high-fat diet. Metaphase arrest cells and 5'-bromo-2'-deoxyuridine labelled cells showed no appreciable response to dietary changes. To determine whether changes in colonic signal transduction pathways represent an early response to dietary modification, Study 2 evaluated the activity of protein kinase C (PKC), proliferative indices and changes in phospholipid fatty acid profiles. In comparison to the normal fat group, the colons of high-fat fed animals exhibited higher (P < or = 0.05) membranes and lower soluble PKC activity; however, proliferation patterns of these colons were not altered. Changes in the membrane lipid composition were minor; however, an increase in the phosphatidylcholine/phosphatidylethanolamine ratio and in 20:4n-6 was noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of dietary fat and feeding period on phosphoinositide metabolism in rat colonocytes

The objective of the present study was to examine the effect of dietary fat content on phosphoinositide (PI) metabolism, fatty acid composition in colonocytes, and colonic luminal content of bile acids (BA) and free fatty acids (FFA) in rats. Male Sprague-Dawley rats weighing approximately 166 g were fed to semipurified diet containing 3% or 21.5% beef fat and 2% corn oil. The nonfat ingredients were adjusted to correct for differences in food consumption of these diets. Animals were fed these diets ad libitum for one or four weeks. The isolated colonocytes had a viability of 88.9% in all groups. PI metabolism was examined in the absence (basal) or presence of agonists, 2 mM deoxycholic acid or 10 microM A23187. Dietary fat concentration had no effect on PI metabolism, but the length of feeding had a significant effect on basal and stimulated PI metabolism. Colonocytes of animals fed the diets for four weeks were less sensitive to stimulation of PI cycle by agonists than those of animals fed for one week. Colonocyte fatty acid composition was influenced by dietary fat and feeding period. Only the relative percentage of 20:3(n-6) was significantly lower in rats fed the high-fat diet for one week; 18:0 was lower and 18:3(n-6) was higher in colonocytes of animals fed the diets for one week than in those fed for four weeks. Several colonic fatty acids, namely, 16:0, 20:3(n-6), and 22:5(n-6), also exhibited diet-by-feeding period interaction. Intracolonic luminal contents from rats fed the high-fat diet contained elevated concentrations of BA and FFA (44% and 62%, respectively). It was concluded that despite the effects of dietary fat concentration on increased colonic BA and FFA and on altered membrane fatty acid composition, dietary fat had no effect on PI metabolism in colonocytes under the conditions in the present experiment. A difference in components between the purified diet and the commercial rat chow and/or an aging effect of the rats may alter the PI cycle of colonocytes.

Effects of high corn oil diet on preneoplastic murine colons: prostanoid production and lipid composition

In the present study, the effect of normal (5% by wt) and high (23.5% by wt) corn oil diets on prostanoid production and on the lipid composition of preneoplastic colonic epithelium was investigated. CF1 mice (female, 3-4-weeks-old) were fed a normal corn oil diet ad libitum and were treated with the colon carcinogen 1,2-dimethylhydrazine (DMH, 20 mg/kg/wk) or saline (control) for 24 wk. At this stage, all animals received the AIN-76 diet (normal corn oil) ad libitum. Following the last injection, half of the animals from each treatment group were randomly allocated to a high corn oil diet for 5 to 10 wk, whereas the remaining animals continued on the normal corn oil diet. After 5 wk of feeding, the colonic mucosa of carcinogen-treated animals had a higher level of bicyclic prostaglandin E2 (PGE2) than had the animals in the control groups; prostanoid synthesis in the colonic mucosa of control animals was unaffected by the high corn oil diet. Preneoplastic colonic mucosa of animals fed the high corn oil diet had a significantly higher level of PGE2 than corresponding control colonic mucosa. The 6-keto-prostaglandin F1 alpha/thromboxane B2 ratio was significantly lower in the DMH-treated groups than in the control groups, and was unaffected by dietary treatments. After 10 wk of feeding a particular diet, the differences in the fatty acid composition between the control and DMH-treated groups were minor. Our findings demonstrate that the preneoplastic colonic epithelium differs from that of normal epithelium with respect to prostanoid synthesis.

Lipid composition, phospholipid profile and fatty acid of rat caecal mucosa

In this study, we examined the lipid composition of rat caecal mucosa, including the fatty acid composition of major phospholipid classes. Phospholipids accounted for 90% of the total lipid, with cholesterol, triacylglycerols, diacylglycerols, fatty acids and cholesterol ester making up the remainder. Therefore, a phospholipid to neutral lipid ration of 9:1 was found. Phosphatidylethanolamine was the predominant phospholipid, with phosphatidylcholine as the second most abundant phospholipid. Cardiolipin, phosphatidylserine, phosphatidylinositol and lysophosphatidylcholine were present in lesser amounts. Sphingomyelin and lysophosphatidylethanolamine were only detected in trace amounts. The major fatty acids present in both the lipid and all phospholipid fractions were palmitate, stearate, oleate, linoleate and arachidonate. Other fatty acids of chain length greater than C20 were only detected in phospholipid fraction and accounted for < 5% of the total fatty acids in this fraction. However, 11.10% of 22:6 (n-3) and 7.17% of 24:0 were detected in phosphatidylserine and lysophosphatidylcholine, respectively. The results are discussed in terms of their possible physiological significance.

Determination of phospholipid fatty acid and triacylglycerol composition of rat caecal mucosa

The lipid composition of rat caecal mucosa, including the fatty acid composition of phospholipids and triacylglycerols, has been examined by capillary gas chromatography. Thirty-seven peaks were resolved, ranging in chain length from 12 to 24 carbon atoms. Preliminary identification of fatty acids by comparison with authentic standards was confirmed by gas chromatography-mass spectrometry using electron-impact ionization. The neutral and polar components were examined. Fatty acid methyl esters were quantified in absolute amounts with respect to the percentage of total phospholipid and triacylglycerols. The results show significantly higher levels of 16:0, 18:0, 18:1(n-9), 18:1(n-7), 18:2(n-6) and 20:4(n-6) in phospholipids, and higher levels of 16:0, 18:1(n-9) and 18:2(n-6) in triacylglycerols. On the other hand, analysis of caecal triacylglycerols revealed sn-glycerol-palmitate-oleate-palmitate, sn-glycerol-palmitate-linoleate-palmitate and sn-glycerol-palmitate-linoleate-oleate as major components.

Phospholipid profiles of human colon cancer using 31P magnetic resonance spectroscopy

Phospholipids of 16 malignant and 11 non-malignant human colon specimens were analyzed using a chloroform-methanol analytical reagent in conjunction with 31P magnetic resonance spectroscopy (MRS) at 202.4 MHz. Sixteen individual generic phospholipids were identified and quantified for statistical intergroup comparisons. Statistically significant elevations in the relative concentrations of lysophosphatidylcholine and phosphatidylcholine plasmalogen were seen in malignant tissues along with significantly depressed levels of sphingomyelin and phosphatidylethanolamine plasmalogen. The malignant and non-malignant tissue groups were further differentiated by the detection of the minor phospholipids, lysophosphatidylcholine plasmalogen, lysophosphatidylethanolamine plasmalogen, lysophosphatidic acid and phosphatidylglycerol exclusively present in the malignant tissues and by significant changes in computed phospholipid metabolic indices that were dominated by choline containing lipids. The 31P MRS methods used represent an advancement over previous protocols for identifying and quantifying major and minor tissue phospholipids making this the first direct study of membrane phospholipids in human colon tissues using 31P MRS. The phospholipid profiles obtained may provide important information regarding the nature of the malignant cell's membrane system and identify markers which may be used to estimate malignant propensity, aggressiveness of disease and provide prognostic information.

Effect of dietary fat on phospholipid class distribution and fatty acid composition in rat fat cell plasma membrane

The effect of dietary fats on phospholipid class distribution and fatty acid composition was studied in rat fat cell plasma membrane. Three groups of male Wistar weanling rats were fed for 8 wk three diets differing in the amount and nature of the fats: 1.5% sunflower oil (low fat control; LFC), 10% sunflower oil (high fat, unsaturated; HFU), 1.5% sunflower oil + 8.5% cocoa butter (high fat, saturated; HFS). Plasma membranes were prepared from epididymal adipocytes. The amount and type of dietary fat significantly altered membrane phospholipid distribution. Phospholipid content was lowered with HFU as compared to LFC or HFS diets, but no changes were observed for cholesterol. Phosphatidylinositol (PI) and phosphatidylserine (PS) were less affected by dietary changes than were other phospholipid classes. Major changes were detected for phosphatidylcholine (PC), phosphatidylethanolamine (PE) and sphingomyelin (SM) contents. No large changes in PC and PE fatty acid compositions were observed between the LFC and HFS groups, but the HFU diet induced several changes. Correlations with plasma membrane 5'-nucleotidase activities are discussed.