Effect of fish oil supplementation on the excretion of the major metabolite of prostaglandin E in healthy male subjects

We investigated the effect of fish oil supplementation on the synthesis of prostaglandin E (PGE) in vivo by measuring the excretion of its catabolite, PGE-M, in 24-hr urine by gas chromatography/mass spectrometry. Forty healthy male volunteers (24-57 years of age) consumed a controlled basal diet providing 40% of energy from fat (P/S ratio about 0.8:1), 130 mg/1000 kcal cholesterol, and a minimum of 22 mg/day of alpha-tocopherol (alpha-T), for three experimental periods lasting a total of 28 weeks. During period 1 (10 weeks) the diet was supplemented with placebo (PO) capsules (15 X 1 g/day) consisting of a blend of fats approaching the fatty acid profile of the basal diet. This was followed by a second 10-week period during which the subjects received 15 X 1 g/day capsules of fish oil concentrate (FOC). During period 3 (8 weeks) they continued the 15 g/day intake of FOC but received an additional 200 mg/day of alpha-T. PO and FOC capsules contained 1 mg alpha-T/g fat as antioxidant. A 14% reduction of PGE-M excretion was observed after 10 weeks of FOC supplementation (period 2), compared to an identical period of placebo supplementation (period 1), P = 0.009. PGE-M excretion during the last week of period 3 was not significantly different from that at the end of period 2. The reduction in PGE synthesis in response to the relatively high marine oil supplementation was large in many subjects participating in this study.

Quantitative assessment of the genotoxicity of fecapentaenes

Fecapentaenes are a group of fecal mutagens of microbial origin isolated from human stools. Fecapentaene-12 (F-12) and fecapentaene-14 (F-14), differing only in two carbon atoms in the side chain, are glyceryl ethers with a highly reactive chromophoric aliphatic side chain incorporating a conjugated pentaene moiety. Although these compounds are known for their genotoxicity, no test systems have been developed to precisely assess their relative genotoxicity. In this study F-12 and F-14 were assayed for their genotoxicity using the SOS Chromotest in which the induction of beta-galactosidase in E. coli PQ37 was used as a quantitative measure of biological activity. The activity obtained with F-12 and F-14 was compared with that of 4-nitroquinoline oxide (4-NQO) as the reference standard of a direct acting mutagen. While F-14 was almost as active as 4-NQO, F-12 was only about 25% as active as F-14, the higher analog.

Dietary fat and hormonal influences on lipoprotein fluidity and composition in premenopausal women

LDL and HDL became more fluid when health, free-living, premenopausal women were fed reduced fat diets with higher proportions of polyunsaturated fatty acids. Lipoproteins were isolated from plasma of 31 female subjects fed one of two sets of diets from typical U.S.A. foods with P/S ratios of 0.3 or 1.0. All subjects were fed high-fat diets (40% of energy) for the duration of four menstrual cycles followed by low-fat diets (20% of energy) for the next four cycles. Blood samples were collected during mid-follicular and mid-luteal phases of the fourth menstrual cycle of each diet period to assess interactive dietary and hormonal control of lipoprotein fluidity. LDL was significantly more fluid, as determined by DPH fluorescence, upon reducing fat consumption from 40 to 20% of energy for subjects eating foods with P/S = 1.0 or 0.3. Generally LDL was more fluid during the follicular phase than the luteal phase of the cycles, thus indicating hormonal influences on LDL fluidity. HDL results were similar but not as pronounced as with LDL. Lipoprotein phospholipid (PL) and cholesteryl ester (CE) fatty acyl compositions were also subject to dietary and hormonal influences. Effects were noted in several fatty acids depending upon diet and hormonal state; however, generally diet fat reduction resulted in reduced linoleate and increased oleate contents. Regression analyses showed that fluidity was more dependent upon the lipoprotein cholesterol content than upon fatty acyl composition.

Influence of dietary fat on fecal mutagenicity in premenopausal women

A dietary intervention study was conducted on 31 premenopausal women (age: 20-40 years) to investigate the relationship between dietary fat and fecal mutagenicity. After a free-living period (baseline) of one menstrual cycle, the subjects were placed on a high-fat diet (40% calories from fat) for 4 menstrual cycles, followed by a low-fat diet (20% calories from fat) for 4 menstrual cycles. One-half of the subjects were randomly assigned throughout the study to a diet with a P:S ratio of 1.0 while the other half was assigned to one with a P:S ratio of 0.3; body weight by group remained constant. Three-day stool samples were collected at the mid-follicular period during the free-living phase and during the 4th menstrual cycle of each of the 2 controlled diet periods. Mutagenicity was assayed by the SOS chromotest. Reduction of dietary fat was accompanied by a significant decrease in fecal mutagenicity in both P:S groups. Combined values, i.e., both P:S groups, were 20.3 units for high-fat diets vs. 8.78 for low-fat diets.

AT32P-dependent estimation of nanomoles of fatty acids: its use in the assay of phospholipase A2 activity

A procedure for the assay of free fatty acids which has been adapted for the assay of phospholipase A2 is described. This consists of the conversion of long chain fatty acids to fatty acyl-CoA using the Mg2(+)-dependent fatty acyl-CoA synthetase, [alpha-32P]ATP and coenzyme A. In order to ensure the complete conversion of the acid to its CoA ester pyrophosphatase is also added to the incubation mixture. AM32P formed in stoichiometric amounts is separated from the remaining AT32P by polyethyleneimine-cellulose thin-layer chromatography and the fatty acid content is calculated from the specific radioactivity of AT32P. As little as 1 to 3 nmol of fatty acids hydrolyzed from any phospholipid using nanogram amounts of phospholipase A2 can be estimated with reliability. The real advantage of the method is that it combines the sensitivity of a radiochemical procedure without having to use radiolabeled substrates for the assay of phospholipases.

Dietary fat and hormonal effects on erythrocyte membrane fluidity and lipid composition in adult women

Erythrocyte ghost membrane fluidity and phospholipid linoleate were significantly increased when higher levels of polyunsaturated fats were fed to healthy, free living, premenopausal women. Fluidity was assessed by diphenylhexatriene (DPH) fluorescence polarization measurements with hypotonically lysed red blood cells from 31 female subjects fed one of two sets of diets, which were formulated from typical US foods to contain polyunsaturate to saturate ratios (P/S) of 1.0 or 0.3. Both groups of women were fed diets with 40% of energy as fat for four menstrual cycles followed by low-fat diets having 20% of energy as fat for the next four menstrual cycles. Blood was sampled during the fourth cycle of each dietary period at times estimated to correspond to maximum secretions of estrogen and progesterone to assess interactive hormonal and dietary effects on membrane composition and fluidity. Red blood cell membranes were most fluid following higher levels of linoleate intake, either by higher (40%) total fat or higher P/S levels. Membrane fluidity was directly related to the phospholipid oleate and linoleate contents and inversely related to the molar cholesterol/phospholipid ratio. Hormonal status effects on the membranes were not extensive. Membrane fluidity in cells from women fed P/S = 0.3 diets was higher at 40% than at 20% fat during the luteal phase of the fourth cycle. In contrast, women fed the P/S = 1.0 diets had more fluid red cells at 40% fat during the follicular phase of the cycle. Regression analysis showed a direct linear correlation between membrane fluidity and red cell membrane insulin binding demonstrating a relation between receptor binding and cell membrane fluidity in the human female.

Case-control study of colorectal cancer and fecal mutagenicity

Fecal mutagenicity was measured in 68 patients with colorectal cancer and in 114 controls, using Salmonella tester strains TA98 and TA100 with and without S9 activation. Samples were also tested for fecapentaenes by high-performance liquid chromatography, to permit the separation of fecapentaene and non-fecapentaene mutagenicity. Overall, no significant case-control differences in fecal mutagenicity were observed. However, when samples containing high concentrations of fecapentaenes were excluded, non-fecapentaene TA98 mutagenicity was observed in eight cases (12%) and only four controls (4%), resulting in an estimated relative risk of 4.4 (95% confidence interval = 1.0-21.1). The association of colorectal cancer risk with non-fecapentaene TA98 mutagenicity could not be explained as an artifact of diagnostic workup or gastrointestinal bleeding among the cases. Smoking could also be excluded as a source of the TA98 mutagenicity seen, but possible dietary origins are still being explored.

Hormones regulating lipid and carbohydrate metabolism in premenopausal women: modulation by dietary lipids

The effect of high- and low-fat diets with different levels of fatty acid unsaturation on plasma hormones involved in lipid metabolism was studied during different phases of the menstrual cycle in 31 premenopausal women. Subjects were divided into two groups and were fed controlled diets containing 39% fat with a ratio of polyunsaturated to saturated fatty acids (P:S) of either 0.3 or 1.0 for four menstrual cycles and then switched to a 19% fat diet with the same P:S for another four cycles. Blood samples were analyzed during both the follicular and luteal phases. A significant direct effect of level of dietary fat was observed on plasma cortisol and dehydroepiandrosterone-sulphate whereas an inverse relationship was seen for plasma insulin. Both plasma insulin and growth hormone levels were higher during the luteal compared with the follicular phase of the menstrual cycle. None of the hormones was affected by the level of unsaturation of dietary fats.

Fecapentaene concentration and mutagenicity in 718 North American stool samples

The fecapentaenes (FP) are the predominant fecal mutagens identified to date, but they have not been shown to be carcinogenic. Epidemiologists looking for other fecal mutagens that may be related to colorectal cancer must disentangle from their investigations the pervasive mutagenic effect of the fecapentaenes. As a first step to studying the epidemiology of fecal mutagenicity independent of fecapentaenes, we compared FP measurements and Salmonella mutagenicity assay results for 718 acetone-extracted stool samples collected from a variety of subjects in the Washington DC metropolitan areas. In this large group, 50% of mutagenic samples contained elevated fecapentaenes. Specifically, three-quarters of the samples mutagenic in TA100 contained high FP levels. In contrast, mutagenicity in TA98 was not generally explainable by fecapentaenes, suggesting that non-fecapentaene TA98 mutagenicity should be one focus of future efforts to uncover colorectal carcinogens of etiologic importance.

Case-control study of colorectal cancer and fecapentaene excretion

The fecapentaenes are potent mutagens found in high concentrations in the stools of some individuals. These compounds are produced in vivo by common species of the colonic microflora, from precursors of unknown origin. The fecapentaenes have been postulated to increase the risk of colorectal cancer. To test this hypothesis, we measured fecapentaene excretion in 69 patients with adenocarcinoma of the colon or rectum, newly diagnosed at three Washington, DC area hospitals. The cases were compared with 114 surgical controls, frequency matched to the cases on age, sex, and hospital. We attempted to measure fecapentaene excretion 4 times for each subject: before surgery; and at 1 mo; 3 mo; and 6 mo following surgery. Contrary to our study hypothesis, we found fecapentaene excretion during the four study periods to be similar or even lower in cases compared to controls. An indirect measurement of fecapentaene precursors also tended to be lower in cases. The case-control differences could not be explained as effects of bleeding or of the colorectal diagnostic workup, which was assessed in a separate group of 86 patients. We conclude from these data that the excretion of fecapentaenes does not increase the risk of colorectal cancer, at least when measured near the time of diagnosis.

Relation of changes in amount and type of dietary fat to fecapentaenes in premenopausal women

Correlation studies suggest that fecal mutagenicity is increased in groups eating high-fat diets, the same groups who are often found to have high colorectal cancer incidence and mortality. The fecapentaenes are the best characterized class of fecal mutagens, but the relationship of dietary fat intake to the excretion of these potent genotoxins is unknown. We studied the effect of changes in amount and type of dietary fat on fecapentaene levels in 31 premenopausal women 20-40 years of age who participated in a controlled feeding study. After a pre-diet free-living period lasting 1 menstrual cycle, women were placed on a high-fat (40% energy from fat) diet for 4 menstrual cycles and then switched to a low-fat (20% energy from fat) diet for an additional 4 menstrual cycles. One-half the subjects were maintained throughout the study at a ratio of polyunsaturated-to-saturated fatty acids (P/S ratio) of 1.0, the other half at 0.3; body weight was constant. All meals during the controlled diet periods were prepared at the Human Study Facility of the Beltsville Human Nutrition Research Center. Fecapentaene and fecapentaene precursor levels were measured in acetone extracts from 3-day pooled stool samples collected during the study. No differences in fecapentaene or precursor levels were observed between the high- and low-fat diets at either P/S ratio. Fecapentaene and precursor levels were higher while on controlled diets than during the pre-diet free-living period, and levels declined again in the post-diet free-living period. We conclude that dietary fat has no significant effect on fecapentaene or precursor levels in acetone extracts of stool in premenopausal women. The effect of other dietary or non-dietary factors on fecapentaenes remains unknown.

Role of bile acids and neutral sterols in carcinogenesis

Epidemiological evidence regarding cancer causation suggests the existence of a strong link to diet-related lifestyles. Neutral sterols and bile acids constitute a group of metabolic endproducts known to have multiple interactions both from the standpoint of being influenced by diet as well as from the standpoint of their role in cellular and molecular processes relating to carcinogenesis. Epidemiological and experimental studies on the possible role of these steroid metabolites are reviewed.

Menstrual cycle effect on plasma lipids

In a study of 31 healthy women in which dietary intake and body weight were controlled, a significantly higher mean plasma cholesterol was observed in the follicular phase of the menstrual cycle compared to the luteal phase (mean difference of 8.4% during controlled dietary periods). Higher mean plasma triglycerides (mean difference of 7.4%) and lower HDL-cholesterol (mean difference of 5.8%) were also observed in the follicular phase of the controlled dietary study, although these differences were not consistently significant.

Influence of dietary fat on menstrual cycle and menses length

Menstrual cycle and menses lengths were determined in 31 healthy premenopausal women randomized into one of two sets of weight-maintaining diets, those with a ratio of polyunsaturated to saturated fatty acids (P/S ratio) of 1.0 and those with a P/S ratio of 0.3. After a baseline interval of one menstrual cycle, both groups were fed a high fat diet (40 per cent energy from fat) for four menstrual cycles per subject, followed by a similar interval on a low fat diet (20 per cent energy from fat). There was a significant increase of 1.3 d (P = 0.02) in the average menstrual cycle length and 0.5 d (P = 0.01) in menses length on the low fat diet. Although no significant differences were evident between the P/S groups, the effect of low fat on menstrual cycle and menses length was most pronounced in the P/S = 1.0 group.

Influence of caloric contribution and saturation of dietary fat on plasma lipids in premenopausal women

Total cholesterol, HDL cholesterol, and triglycerides were measured in 31 premenopausal women randomized into one of two diet groups: one diet with a P:S ratio of 1.0 and one diet with a P:S ratio of 0.3. Both groups were fed a high-fat diet (40% of energy from fat) for four menstrual cycles per subject followed by a similar interval on a low-fat diet (20% of energy from fat). Changing from the high-fat to the low-fat diet resulted in a nonsignificant mean decrease of 7% in total cholesterol. HDL-cholesterol response to the low-fat regimen was influenced by the P:S ratio. Women in the high P:S group showed no change; mean HDL cholesterol in women in the low P:S group decreased 12%. Plasma triglycerides increased in both groups on the low-fat diet although the increase was greatest in the low P:S group.

Reaffirmation of the validity of enzymatic cleavage of lithocholic acid from N-epsilon-lithocholyl-L-lysine and N-alpha-CBZ-N-epsilon-lithocholyl-L-lysine

N-epsilon-lithocholyl-L-lysine or N-alpha-CBZ-N-epsilon-lithocholyl-L-lysine when incubated overnight at 37 degrees C with 3 K units of clostridial cholanoylaminoacid hydrolase (from Clostridium perfringens ATCC 19574) in the presence of disodium EDTA (0.1 M), beta-mercaptoethanol (0.1 M), and sodium acetate buffer, pH 5.6, released free lithocholic acid. The latter material was isolated by thin-layer chromatography and identified by combined gas-liquid chromatography-mass spectrometry in the full scan and selected-ion mode. In order to maintain its activity, the enzyme was always stored in 1.0-ml aliquots at temperatures below -20 degrees C and each aliquot when thawed was used immediately; any left over enzyme was never reused. Contrary to the observations of Yanagisawa et al. (J. Lipid Res. 1984. 25: 1263-1271) the results of this study reaffirm the validity of the original observations on the enzymatic cleavage of lithocholic acid from tissue-bound form.

Synthesis of N-epsilon-lithocholyl-L-lysine, a component of tissue-bound lithocholic acid, via lithocholyl-N-hydroxysuccinimide

N-epsilon-lithocholyl-l-lysine is a lithocholic acid modified lysine residue found in proteins from tissues. This paper describes the synthesis of this compound as well as that of the isomeric N-alpha-lithocholyl-l-lysine and the di-substituted N-alpha-epsilon-bis-lithocholyl-l-lysine. The procedure involves the initial coupling of lithocholyl-N-hydroxysuccinimide to the appropriate N-alpha- or N-epsilon-CBZ (carbobenzloxy) protected lysine derivative followed by hydrogenolysis with palladium black of the CBZ group using formic acid as the hydrogen donor.

Concordance of nutrient information obtained by different methods

Data obtained from two vegetarian and two nonvegetarian populations by 24-h diet recall, 3-day weighed diet diary, analysis of 3-day composite food samples, and measurement of certain biochemical parameters were compared. Correlations for group means (both sexes combined) for values obtained by 24-h recall versus 3-day diet diary were protein, r = 0.96 and total calories r = 0.86. For 3-day diet diary with food analysis, protein r = 0.89, fat r = 0.90 and for reported protein intake with serum prealbumin r = 0.74, with urinary urea nitrogen r = 0.87. Correlations were low for comparisons of means of male groups for most parameters. Individual correlations for reported protein intake and biochemical parameters were lower for males than for females. This suggests that male subjects may require special attention to insure accuracy of reporting and specimen collection. These findings indicate comparability of data from 24-h recall and 3-day diary, and agreement of dietary records with certain biochemical parameters. Protein and fat intake as determined from chemical analysis of a composite food sample correlated well (r = 0.89; r = 0.90) with that calculated from food tables.

Diet, nutrition intake, and metabolism in populations at high and low risk for colon cancer. Nutrient intake

A 3-day diary with portion sizes weighed by the subject and a 24-h recall were obtained on 50 sets of subjects: Seventh-day Adventist lacto-ovo-vegetarians and nonvegetarians, and general population nonvegetarians, matched on age (+/- 5 yr), sex, marital status, education, type of milk preferred, and an index of the frequency of dairy and egg product use. An additional 18 unmatched persons who follow a pure vegetarian dietary pattern (use no meat, fish, fowl, dairy, or egg products) were recruited into the study. The rational for the dietary methods used is presented and details of each of the methods used are given. The results of the nutrient analysis of the 24-h recall and 3-day diary are presented. The 3-day nutrient intake means for the four groups are compared to the sex-specific recommended daily allowance both with and without supplements. The contribution of nutritional supplements to the nutrient intake is discussed. All groups show adequate or excess intake levels of calories, protein, and fat when either the 24-h recall or the 3-day diary values are considered. The higher intake of calories noted among nonvegetarians can be explained by a higher intake of both fat and protein in these groups. A, B, and C vitamin levels (3-day dairy estimates) are adequate both with and without supplements. Calcium intake is much below recommended levels for pure vegetarian females. Iron intake is low for all females. A heme iron source does not improve the intake levels for nonvegetarian females. A comparison of these results with prior reports of nutrient intake among Seventh-day Adventists is presented.

Diet, nutrition intake, and metabolism in populations at high and low risk for colon cancer. Dietary cholesterol, beta-sitosterol, and stigmasterol

Cholesterol and fat are implicated as dietary factors enhancing the risk for colon carcinogenesis. Plant sterols such as beta-sitosterol when added to diets of experimental animals treated with colon carcinogens reduce tumor yields and counteract the proliferative changes associated with carcinogenesis. The question of whether the diet of human populations at low risk for colon cancer is mirrored in their sterol composition is addressed in this study. Four study groups consisting of 18 Seventh-day Adventist (SDA) pure vegetarians, 50 SDA lacto-ovo vegetarians, 50 SDA nonvegetarians, and 50 general population nonvegetarians were selected from the greater Los Angeles basin, and 3-day composite diets were analyzed for their sterol composition. The most significant index of dietary sterol status is the ratio, beta-sitosterol + stigmasterol/cholesterol (plant sterol/cholesterol ratio). The values for the four groups ranged from 0.49 to 16.0 (general population nonvegetarians = 0.49; SDA-nonvegetarians = 0.98; SDA lacto-ovo vegetarians = 3.26; SDA pure vegetarians = 16.0). The data also show that the absolute amounts of cholesterol consumed as a factor by itself might not be as significant as its relationship to total plant sterols in the diet.

Diet, nutrition intake, and metabolism in populations at high and low risk for colon cancer. In situ bromination for the separation of the cholesterol-cholestanol pair in human fecal extracts

Neutral sterols from human feces were fractionated by thin-layer chromatography and by gas-liquid chromatography (GLC). A simple thin-layer chromatography procedure for the separation of cholestanol from cholesterol is described. This technique, involving in situ bromination of sterols on thin-layer chromatography plates, converts cholesterol and other unsaturated sterols to the corresponding dibromides. Under these conditions, the cholestanol-cholesterol pair which is normally indistinguishable on thin-layer chromatography and gas-liquid chromatography, is separated. Final quantification of the sterols was carried out by gas-liquid chromatography.

Diet, nutrition intake, and metabolism in populations at high and low risk for colon cancer. Metabolism of bile acids

High levels of fecal bile acids have been associated with populations at high risk for developing colon cancer. In this study, 168 subjects were drawn from populations that show low and high mortality from colon cancer [pure vegetarians, lacto-ovo vegetarians, and nonvegetarians Seventh-day Adventists (SDA) and demographically comparable group from the general population]. Lyophilized aliquots of 3-day stool samples were examined for levels of primary (cholic and chenodeoxycholic acids) and secondary (deoxycholic and lithocholic acids) bile acids. Total bile acids (mg/g lyophilized stools) were statistically different among dietary groups: SDA pure vegetarians 2.16 +/- 0.32, SDA lacto-ovo vegetarians 3.66 +/- 0.41, SDA nonvegetarians 4.39 +/- 0.44, general population nonvegetarians 6.04 +/- 0.75; but were similar when stool weights, body weights, and fat intake were taken into account. The most striking difference was evident in the ratio of secondary to primary bile acids: when compared to SDA pure vegetarians, both SDA lacto-ovo vegetarians and SDA nonvegetarians had twice the ratio while values for general population nonvegetarians were five to six times. The data indicate that these differences in excretion patterns among dietary groups reveal distinctly characteristic metabolic features associated with diet and lifestyle.