Changes in serum lipoprotein lipids and their fatty acid compositions and lipid peroxidation in growing rats fed soybean protein versus casein with or without cholesterol

OBJECTIVE: We compared the effects of diets based on soybean protein and casein supplemented or not supplemented with 0.1% cholesterol on plasma lipoprotein lipid amounts and their fatty acid compositions, lecithin:cholesterol acyl-transferase activity, and lipid peroxidation. METHODS: The composition and concentration of lipid and apolipoprotein in different lipoprotein classes, plasma LCAT activity, and lipid peroxidation were determined in rats fed 20% highly purified soybean protein or casein with or without 0.1% cholesterol for 2 mo. RESULTS: Soybean protein and casein diets with or without cholesterol had similar plasma total cholesterol concentrations. Soybean protein consumption diminished very low-density lipoprotein particle number, as measured by diminished contents of very low-density lipoprotein triacylglycerol, phospholipid, and apolipoprotein-B100. Lecithin:cholesterol acyl-transferase activity was not significantly modified by either protein. The soybean protein diet decreased the linoleate desaturation index (20:4[omega-6]/18:2[omega-6]) in liver and high-density lipoprotein fraction 2-3-phospholipids but enhanced red blood cell resistance against free radical attack. Addition of cholesterol to both protein diets decreased concentrations of high-density lipoprotein fraction 2-3 cholesterol. Lecithin:cholesterol acyl-transferase activity tended to be greater after cholesterol feeding, likely due to the enhanced high-density lipoprotein fraction 2-3 apolipoprotein-AI, a cofactor activator for lecithin:cholesterol acyl-transferase. Regardless of dietary protein source, cholesterol supplementation decreased the linoleate desaturation index in liver and plasma lipoprotein lipids and red blood cell resistance to free radical attack. CONCLUSIONS: Our results suggest that the dietary protein origin affects lipid peroxidation and polyunsaturated fatty acid biosynthesis and distribution among liver and different lipoprotein lipid classes, but plays only a minor role in the regulation of plasma and lipoprotein cholesterol concentrations. Providing dietary cholesterol (0.1%) with casein or soybean protein attenuates the effects of these proteins, with the exception of plasma cholesterol.     

Effects on the serum lipoprotein concentrations by lipid-lowering diets with different fatty acid compositions.

It has been reported that lipid-lowering diets may reduce high density lipoprotein as well as low density lipoprotein cholesterol but that the reduction of the high density lipoproteins is less pronounced with diets of lower P/S ratios. The aim of the present study was therefore to investigate whether the effects on the low density lipoproteins could be maintained, but those on the high density lipoproteins diminished, by reducing the P/S ratio from 1.3 to 0.7. Fourteen hyperlipoproteinaemic patients in a metabolic ward were given two fat-modified diets during two consecutive 3-week periods in a randomized order. The diets were identical with regard to nutrient composition but differed with regard to the P/S ratios, which were 1.3 and 0.7, respectively. The average serum lipoprotein lipid composition and the apolipoprotein concentrations were similar at the end of the two periods. However, in the group of patients (n = 7) who started on the diet with P/S ratio 1.3 the low density lipoprotein cholesterol increased significantly (p less than 0.05) by 7% and the apolipoprotein B concentration by 10% (p less than 0.001) when shifting to the diet with P/S ratio 0.7. No changes of the high density lipoprotein concentrations were seen. The relative content of saturated fatty acids, of oleic acid, and of arachidonic acid in the plasma lipid esters decreased, but the content of linoleic acid increased, when shifting from the diet with a P/S ratio of 0.7 to that of 1.3.(ABSTRACT TRUNCATED AT 250 WORDS)     

Palmitic and stearic acids similarly affect plasma lipoprotein metabolism in cynomolgus monkeys fed diets with adequate levels of linoleic acid

This study was designed to evaluate whether the exchange of specific saturated fatty acids [SFA; palmitic acid (16:0) for stearic acid (18:0)] would differentially affect plasma lipids and lipoproteins, when diets contained the currently recommended levels of total SFA, monounsaturated fatty acids and polyunsaturated fatty acids (PUFA). Ten male cynomolgus monkeys were fed one of two purified diets (using a cross-over design) enriched either in 16:0 (palmitic acid diet) or 18:0 (stearic acid diet). Both diets provided 30% of energy as fat (SFA/monounsaturated fatty acid/PUFA: 1/1/1). The palmitic acid and stearic acid diets were based on palm oil or cocoa butter (59% and 50% of the total fat, respectively). By adding different amounts of sunflower, safflower and olive oils, an effective exchange of 16:0 for 18:0 of approximately 5% of energy was achieved with all other fatty acids being held constant. Monkeys were rotated through two 10-wk feeding periods, during which time plasma lipids and in vivo lipoprotein metabolism (following the simultaneous injection of (131)I-LDL and (125)I- HDL were evaluated). Plasma triacyglycerol (0.40 +/- 0.03 vs. 0.37 +/- 0.03 mmol/L), plasma total cholesterol (3.59 +/- 0.18 vs. 3.39 +/- 0.23 mmol/L), HDL cholesterol (1.60 +/- 0.16 vs 1.53 +/- 0.16 mmol/L) and non-HDL cholesterol (2.02 +/- 0.26 vs. 1.86 +/- 0.23 mmol/L) concentrations did not differ when monkeys consumed the palmitic acid and stearic acid diets, respectively. Plasma lipoprotein compositional analyses revealed a higher cholesteryl ester content in the VLDL fraction isolated after consumption of the stearic acid diet (P < 0.10), as well as a larger VLDL particle diameter (16.3 +/- 1.7 nm vs. 13.8 +/- 3.6 nm; P < 0.05). Kinetic analyses revealed no significant differences in LDL or HDL transport parameters. These data suggest that when incorporated into diets following current guidelines, containing adequate PUFA, an exchange of 16:0 for 18:0, representing approximately 11 g/(d.10.46 mJ) [ approximately 11 g/(d.2500 kcal)] does not affect the plasma lipid profile and has minor effects on lipoprotein composition. Whether a similar effect would occur in humans under comparable dietary conditions remains to be established.     

Profile of short-chain fatty acids and rectal proliferation in rats fed sucrose or cornstarch diets.

Rats were fed high fat (231 g/kg diet), low calcium (1.3 g/kg diet), low cellulose (20 g/kg diet) diets in which carbohydrates were represented by sucrose or starch (460 g/kg diet). A subgroup of animals was treated with 1,2-dimethylhydrazine (DMH) twice, 4 and 8 d before the beginning of the dietary treatments. Animals fed the starch diet, compared with those fed the sucrose diet, had higher concentrations of cecal and fecal short-chain fatty acids and a significantly lower acetic acid:butyric acid ratio in the cecal contents at d 105. Ratios were 14.7 +/- 1.7 and 6.8 +/- 0.4 for rats fed the sucrose and starch diets, respectively (P less than 0.01). Cecal pH was significantly lower in animals fed the starch diet for 105 d. At d 105, rectal proliferation was lower in rats fed the starch diet (labeled cells/crypt were 7.89 +/- 0.56 and 3.57 +/- 0.40 for rats fed the sucrose and starch diets, respectively, P less than 0.01); at d 30 the effect of starch on proliferation was evident in controls but not in DMH-treated rats. Rectal proliferation data were negatively correlated with the concentration and percentage of butyric acid and positively correlated with the percentage of acetic acid, the acetic acid:butyric acid ratio and cecal pH. These results suggest that low rectal proliferation in animals fed a high fat, high starch diet might be associated with a lower relative concentration of butyric acid in the cecal contents.     

Effects on the serum lipoprotein concentrations by lipid-lowering diets with different fatty acid compositions

It has been reported that lipid-lowering diets may reduce high density lipoprotein as well as low density lipoprotein cholesterol but that the reduction of the high density lipoproteins is less pronounced with diets of lower P/S ratios. The aim of the present study was therefore to investigate whether the effects on the low density lipoproteins could be maintained, but those on the high density lipoproteins diminished, by reducing the P/S ratio from 1.3 to 0.7. Fourteen hyperlipoproteinaemic patients in a metabolic ward were given two fat-modified diets during two consecutive 3-week periods in a randomized order. The diets were identical with regard to nutrient composition but differed with regard to the P/S ratios, which were 1.3 and 0.7, respectively. The average serum lipoprotein lipid composition and the apolipoprotein concentrations were similar at the end of the two periods. However, in the group of patients (n = 7) who started on the diet with P/S ratio 1.3 the low density lipoprotein cholesterol increased significantly (p less than 0.05) by 7% and the apolipoprotein B concentration by 10% (p less than 0.001) when shifting to the diet with P/S ratio 0.7. No changes of the high density lipoprotein concentrations were seen. The relative content of saturated fatty acids, of oleic acid, and of arachidonic acid in the plasma lipid esters decreased, but the content of linoleic acid increased, when shifting from the diet with a P/S ratio of 0.7 to that of 1.3.(ABSTRACT TRUNCATED AT 250 WORDS)     

Organ weights and water content of rats fed protein-deficient diets

To provide the basic information needed for studies of drug toxicity in rats suffering from protein deficiency, weanling male albino rats were fed for 28 days on either laboratory chow or a synthetic diet containing 27% or 8% of casein. The low-protein diet produced a kwashiorkoric cachexia characterized by stunting, alopecia, tail dermatitis, apathy, augmented calorie intake per kg body-weight and a 20% death rate. Autopsies at weekly intervals disclosed that the synthetic normal-protein diet produced a slight loss of total body-weight, due to loss of weight in the adrenal glands and gastrointestinal tissues, and a more-or-less generalized dehydration of body organs. The body-weight of the kwashiorkoric rats was half that of the control groups, due especially to loss of weight in caecum, kidneys, liver, muscle, skin, spleen, salivary glands and thymus gland; loss of weight was less marked in other organs, particularly the stomach, heart and testes and, especially, the brain. There was further dehydration of adrenals and brain but the liver and gastrointestinal tissues tended to be hydrated. The kwashiorkoric diet had not entirely suppressed growth-stimulated relative increase in weight of muscle, skin and testes. The histology of organs was essentially normal in the survivors. Absence of oedema in organs distinguished the kwashiorkoric rats from rats with total calorie depletion.     

Intestinal lymph lipoproteins in rats fed diets enriched in specific fatty acids

Four groups of rats were fed test diets with fats providing 75% of fatty acids as palmitate, stearate, oleate or linoleate. Absorption of radiolabeled cholesterol and the specific triglyceride into intestinal lymph lipoproteins and the lipid and protein content and composition of intestinal lymph were compared. Cholesterol and triglyceride absorptions were correlated significantly and were less with the saturated fatty acid diets. The fatty acid patterns of triglyceride-rich lymph lipoproteins mirrored the diet. Exogenous cholesterol was recovered primarily in chylomicrons, except with linoleate. In contrast, radiolabeled saturated fatty acids were recovered primarily in very low density lipoproteins and unsaturated fatty acids were recovered in chylomicrons. Lymph chylomicron size and lipid content were greater with unsaturated fat diets. Triglyceride-rich intestinal lipoproteins of rats fed saturated fats were polygonal by electron microscopy, related to the cooling of lymph samples below body temperature. A-I apolipoproteins were increased in relation to C apoproteins as lipid absorption was greater. Plasma triglycerides in all groups increased compared to rats fed the stock diet. A diet enriched in one specific fatty acid has its unique effects on lymph lipoprotein formation presumably affecting some intestinal subcellular mechanisms. Diet-induced changes in plasma lipids and lipoproteins are not directly related to these as yet unknown mechanisms.     

Effects of pyridoxine deficiency on the composition of plasma and liver fatty acids in rats fed low and high fat diets.

A study was made of the effect of pyridoxine deficiency on the fatty acids of liver and plasma in rats fed diets containing 1, 10, or 20% fat. Both ad libitum-fed and pair-fed control rats were used. In pyridoxine deficiency, arachidonic acid decreased with a concomitant increase in linoleic acid. Incubation of liver slices with [1-14C]acetate showed no significant alteration of fatty acid synthesis in pyridoxine-deficient rats fed 1 or 10% fat when compared with the ad libitum-fed control rats, but revealed a marked increase in cholesterogenesis compared with either control group. Incubations with [1-14C]linoleate resulted in no differences in the synthesis of arachidonate between the experimental and the ad libitum-fed control rats. Incubations with [5,6,8,9,11,12,14,15-3H]arachidonate showed decreased incorporation of this fatty acid in total liver lipids in pyridoxine-deficient rats compared with ad libitum fed control rats. We concluded that the diminution in arachidonate observed in liver lipids of pyridoxine-deficient rats does not result from a lower conversion of linoleate into arachidonate, but possibly from an increased degradation of this fatty acid.     

Muscle fractional protein synthesis is higher in Iberian than in Landrace growing pigs fed adequate or lysine-deficient diets

Protein deposition in Iberian pigs is low and the reasons for this are unknown. We investigated differences in protein synthesis rate in tissues of 30 Iberian and Landrace gilts fed 2 diets with adequate amino acid composition containing 160 or 120 g crude protein (CP)/kg, or a lysine-deficient diet (containing 120 or 160 g CP/kg for Iberian and Landrace pigs, respectively). Pigs were infused with a flooding dose of phenylalanine (15% as [(2)H(5)]-phenylalanine). Blood samples were taken from 12 to 40 min after the start of infusion, and samples from longissimus dorsi (ld), biceps femoris (bf), and semimembranosus (sm) muscles, liver, and duodenum were taken after slaughter. Body weights (BW) were 22.9 +/- 0.37 and 27.1 +/- 0.64 kg for Iberian and Landrace pigs, respectively. Iberian pigs fed the adequate diets had higher muscle fractional protein synthesis rates (FSR, %/d) than Landrace pigs. The FSR were 7.9 +/- 0.34 vs. 6.3 +/- 0.29%/d; 8.3 +/- 0.36 vs. 6.3 +/- 0.21%/d, and 7.7 +/- 0.23 vs. 6.4 +/- 0.36%/d for ld, bf, and sm muscles in Iberian and Landrace breeds, respectively (P < 0.01). However, muscles were between 20 and 32% smaller in the Iberian pigs (P < 0.01). Dietary protein level did not affect muscle FSR or size in either breed. Lysine deficiency reduced muscle FSR (46-49%, P < 0.001). Visceral tissues had greater relative weights in Iberian pigs (P < 0.001) with no breed differences in FSR. These findings might explain the low efficiency of protein and energy utilization by Iberian pigs compared with conventional pig breeds.     

Pork fat and chicken fat similarly affect plasma lipoprotein metabolism in cynomolgus monkeys fed diets with adequate levels of linoleic acid

The effects on plasma lipoprotein metabolism of replacing pork fat (PF) with chicken fat (CF) (formulated as part of currently recommended prudent diets) was evaluated in 10 male cynomolgus monkeys. Monkeys were rotated through three dietary periods, (each of 10-wk duration), during which total cholesterol (TC), triacylglycerol (TG) and HDL-cholesterol (HDL-C) were measured (7, 8 and 9 wk) and in vivo lipoprotein metabolism evaluated (after 9 wk). Initially, all monkeys were fed a high-fat, high-cholesterol reference diet [38% of energy (en) from fat, 18%en saturated fatty acids (SFA), 10%en monounsaturated fatty acids (MUFA), 10%en polyunsaturated fatty acids (PUFA), 0.045 mg cholesterol/kJ diet]. Subsequently, monkeys were rotated through two test diets (30%en fat, SFA/MUFA/PUFA 1:1:1, 0.004-0.005 mg cholesterol/kJ diet), in which 80% of the fat was either PF or CF, with the remaining 20% derived from high-linoleic safflower oil. There was no significant difference between the two test diets for TG, TC, nonHDL-C, HDL-C or the ratio of TC/HDL-C. Lipoprotein composition, LDL apolipoprotein B pool size, fractional catabolic rate and transport rate were also not significantly different when monkeys consumed the two test diets. These data suggest that when incorporated into diets following current guidelines and containing adequate PUFA ( approximately 7-9%en), PF and CF similarly affect plasma lipids.     

Hemoglobin glycosylation and erythrocyte free fatty acid concentrations in gari fed rats

The relationship between hemoglobin glycosylation and erythrocyte free fatty acids was studied in rats fed gari diet and corn diet. In the two gari fed groups (Groups I and II) glycosylation was 5.96±1.69% in group I and 5.51±1.69% in group II. The free fatty acid concentrations were 17.63±8.72 mmol/l and 18.50±7.23 mmol/l for the two groups respectively. Regression analysis showed a highly significant negative correlation between glycosylation and free fatty acid concentration in group I rats fed gari diet at 80% by weight of gari and a relatively low negative correlation in group II rats fed gari at 65% by weight of gari. In group III rats fed corn diet at 79% by weight of corn glycosylation was 5.35±1.54 and free fatty acid concentration was 21.13±7.70 mmol/l with a very low negative correlation between the two. We propose the use of a diabetic index: Hemoglobin glycosylation (%) + erythrocyte free fatty acid concentration (mmol/l)×10 for determining the diabetogenic effect of diets and feed-stuffs.     

Food intake, energy balance and serum leptin concentrations in rats fed low-protein diets

Studies examining the effects of low-protein diets on food intake and body weight have shown varied results. Many researchers have found low dietary protein to increase food intake, while others have found no effect or even a decrease. In 63 male Sprague-Dawley rats, we examined several low levels of dietary protein (2%, 5%, 8%, 10%, 15% vs. 20% casein) to determine the dose-response relationships between low dietary protein and food intake, body composition, energy balance and serum leptin concentrations. Food intake, over the range of low dietary protein, showed a quasi bell-shaped response curve with peak intake occurring in rats fed 8-10% casein. Peak feeding occurred at or just below the estimated protein requirement of the rats (10-12.5% casein). Compared to the 20% casein controls, food intake was severely reduced in rats fed 2% casein, while it was greater in the other low-protein groups. The amount of body fat steadily increased between the 15% casein group and the 8% casein group, and sharply declined between the 5% casein group and 2% casein group. The change in body fat reflected both the change in food intake and altered energy partitioning. Serum leptin concentrations were greater in rats fed the 5 and 8% casein diets than in control rats fed 20% casein. Serum leptin concentrations were positively associated with body fat content (r(2) = 0.763, P < 0.001). Increased serum leptin concentrations in the presence of increased food intake is suggestive of a state of leptin resistance. This animal model may provide important insights into diet-induced obesity.     

Fatty acid profiles,antioxidant status,and growth of preterm infants fed diets without or with long-chain polyunsaturated fatty acids

Summary. Long-chain polyunsaturated fatty acids (LCP) are considered conditionally essential nutrients for the infant born prematurely, and attempts are being made to match fatty acid profiles of formula and breast fed infants. In this double-blind, randomized study we investigated the effects of a formula enriched with both n-6 and n-3 LCP on plasma fatty acid profiles, antioxidant status and growth of premature infants. 29 infants received either a formula devoid of LCP or a LCP supplemented formula (0.5 g/100 g fat linoleic acid metabolites, 0.8 g/100 g fat -linolenic acid metabolites). 17 breast fed infants served as a control group. At study entry as well as two and four weeks later, plasma and urine samples were collected, growth data obtained and food tolerance was documented. At the end of the four week study period, plasma docosahexaenoic acid (DHA) levels of supplemented infants were significantly higher than those of unsupplemented infants and similar to those of infants fed human milk. Plasma n-6 LCP concentrations including arachidonic acid (AA) were similar between groups. The plasma -tocopherol levels of breast fed and supplemented infants were similar and tended to be lower than in infants fed the formula devoid of LCP. Urinary malondialdehyde (MDA) excretion of formula fed infants was significantly higher compared to infants fed human milk, but did not differ between the two formula groups. Parameters of growth and milk tolerance did not differ between groups. Our results demonstrate that plasma LCP levels similar to those of breast fed infants can be achieved with the LCP supplemented formula used in this trial, without evidence of adverse effects of the LCP enrichment.AA arachidonic acid - ALA -linolenic acid - DGLA dihomo--linolenic acid - DHA docosahexaenoic acid - EPA eicosapentaenoic acid - F formula devoid of LCP - GLA -linolenic acid - HM human milk - LA linoleic acid - LCP long-chain polyunsaturated fatty acids - LCP-F formula enriched with LCP - MDA malondialdehyde - PC phosphatidylcholine - PCA postconceptional age - PE phosphatidylethanolamine - PUFA polyunsaturated fatty acid