Effects of excess dietary L-cystine on the rat plasma lipoproteins

The effects of excess dietary cystine on the cholesterol and protein contents of rat plasma lipoproteins are described. 5% L-cystine was added to a semisynthetic diet containing 23% casein and 0.05% cholesterol, to the same diet enriched with 1% cholesterol or containing tristearin instead of lard. Rats were fed the diets during 2 months. The addition of cystine led to an increase in the plasma cholesterol level of the rats fed with the basal diet (from 0.92 to 1.56 mg/ml). But it produced a reduction of this level in cholesterol-fed rats (from 1.71 to 1.49 mg/ml). These different changes in the total plasma cholesterol level are explained by the specific effects of cystine on each lipoprotein: whatever the diet, cystine supplementation reduced the chylomicron and VLDL cholesterol contents and increased that of LDL (especially LDL2: density 1.040-1.063) and HDL. This study allowed us to compare 2 conditions which lead to hypercholesterolemia but which have opposite effects on hepatic cholesterogenesis: the supplementation of the same basal diet with 1% cholesterol or 5% cystine. In cholesterol-fed rats, the major part (49%) of plasma cholesterol was found in the chylomicrons and VLDL while the LDL2 cholesterol content was low (0.07 mg/ml plasma). Conversely, cystine-fed rats had a low chylomicron and VLDL plasma content (both enriched in apoprotein E), whereas up to 33% of the plasma cholesterol were carried by LDL2. Thus the production of LDL2 in cholesterol and cystine-fed rats could be related to hepatic cholesterogenesis.     

Methionine-induced elevation of plasma homocysteine concentration is associated with an increase of plasma cholesterol in adult rats

BACKGROUND AND AIMS: Dietary methionine affects cholesterol metabolism in growing rats. Methionine effects on adult rats and mechanisms by which methionine alters the lipid metabolism are not fully elucidated. We investigated possible mechanisms by which dietary methionine acts on lipid metabolism of adult rats. METHODS: Male adult rats were divided into three groups (n=10) and were fed casein-based diets differing in methionine concentration (low-methionine diet: 0.96 g/kg; adequate-methionine diet: 2.22 g/kg, high-methionine diet: 6.82 g/kg) for 4 weeks. Concentrations of triacylglycerols and cholesterol in plasma and lipoproteins, concentration of homocysteine in plasma, concentration of cholesterol in liver, fecal lipid excretion, expression of hepatic HMG-CoA reductase, phosphatidylethanolamine N-methyltransferase 2 (PEMT-2) and of LDL receptor were measured. RESULTS: Rats fed the high-methionine diet had higher plasma homocysteine concentrations than rats fed the low-methionine diet (p<0.05). Although concentrations of cholesterol in plasma and lipoproteins were not different between the groups, there was a distinct positive correlation between circulating plasma homocysteine and plasma cholesterol (R(2)=0.55, p<0.001). The fecal excretion of cholesterol and bile acids was not altered by dietary methionine. The relative mRNA concentration of HMG-CoA reductase and of LDL receptor remained unaffected by dietary methionine. Gene expression of PEMT-2 was higher in rats fed the high-methionine diet than in rats fed the other diets (p<0.05). CONCLUSION: The results demonstrate that dietary methionine contributes to a rise in circulating homocysteine concentration which positively correlates with the concentration of plasma cholesterol. However, the effects of methionine on cholesterol metabolism of adult rats were relatively weak.     

Lipolytic activities in rats fed a sucrose-rich diet supplemented with either cystine or cholesterol: relationships with lipoprotein profiles

To study the relationships between lipolytic activities and plasma lipoprotein levels in rats, three diets were given for 8 weeks: a semipurified diet (based on sucrose, casein and lard) and this diet enriched with 5% cystine or with 1% cholesterol. Both supplemented diets induced hypercholesterolemia. Lipoprotein analysis by density gradient ultracentrifugation of plasma indicated that hypercholesterolemia of cystine-fed rats (+52%) was characterized by an increased cholesterol level in high-density lipoprotein (HDL; +131%) and low-density lipoprotein 2 (LDL2; +147%), the lipoprotein fraction containing essentially apolipoprotein-E-rich high-density lipoproteins (HDL1), and was associated with a decreased cholesterol level in triglyceride-rich lipoproteins (TRL: -69%). That obtained by cholesterol feeding (+28%) was due to a large increase in the TRL cholesterol level (+315%) whereas cholesterol was reduced in HDL (-40%) and in LDL2 (-60%). Under these dietary conditions, the activity of hepatic lipase (HL) was measured in liver homogenates and those of both HL and lipoprotein lipase were measured in plasma after heparin injection. The activity of HL (1,783 +/- 132 mU/g liver in control rats) was increased by 48% in cystine-fed rats and decreased by 40% in cholesterol-fed rats. Similar changes were observed in the activity of both lipases measured in postheparin plasma. Highly significant positive correlations linked each lipolytic activity with the level of cholesterol, phospholipids and proteins in LDL2 (HDL1-rich fraction) and in HDL. In contrast, significant negative correlations were found between all of the TRL components and the activity of the lipases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of different protein diets on the distribution of amino acids in plasma, liver and brain in the rat.

The distribution of amino acids between plasma, liver and brain was studied in adult male rats, fed a diet containing 8.7, 17 (control animals), 32 and 51% of protein during 15 days. The caloric intake was nearly equal in all groups. The highest food intake was observed in the animals on the low protein diet. Changes in plasma amino acids were variable. In contrast to the behavior of most amino acids in plasma, the branched chain amino acids were highest in the animals fed the 51% protein diet. Despite the low protein intake in the animals fed a 8.7% protein diet, the concentration of serine, glutamic acid, glutamine, glycine, alanine, methionine, isoleucine, leucine, phenylalanine and ornithine were significantly higher compared to control animals, whereas in those receiving a high protein diet, valine, leucine, tyrosine, tryptophan and histidine increased in relation to the increased protein and amino acid intake. The plasma amino acid patterns are not greatly influenced by the amino acid distribution in the food and the amount ingested. Alanine aminotransferase, aspartate aminotransferase, glutamate dehydrogenase and cholinesterase showed a two- to fivefold increased activity in the liver of animals consuming a high protein diet. In the brain, the concentration of valine, leucine, isoleucine, phenylalanine and tyrosine in animals receiving the low protein diet was higher than in controls and increased further with increasing protein content of the diet. Glutamine was increased in all dietary groups. The predicted influx of amino acids showed increasing influx rates in dependence of the plasma amino acid concentration. The entry of tyrosine and tryptophan and their brain concentration was inversely proportional to the protein content of the diet. In the present study which considers long-term adaptation to an increasing protein and amino acid intake in comparison to a balanced control protein diet, the levels of the indispensable amino acids were maintained within narrow limits in the brain and liver. The results indicate that inspite of a variable protein intake, the body tends to keep organ amino acids in relatively narrow limits favoring in this way amino acid homeostasis.     

Serum lipids and apolipoproteins in the rat refed after starving: influence of the molecular form of nitrogen (protein, peptides, or free amino acids)

Efficient treatment of deep denutrition should promote the restoration of normal intestinal villous structure and the return to a positive nitrogen balance. To determine whether the plasma measurement of lipoproteins could serve as sensitive indexes of villous architecture and/or nitrogen balance, these parameters were compared in rats starved for three days and refed three types of diets containing either whey proteins (WP), whey protein hydrolysate (WPH), or amino acids, known to differ in their capacity to promote restoration of normal villous architecture. Starvation lowered the concentration of triglycerides and phospholipids but not cholesterol. Apolipoprotein AI and AIV concentrations were also significantly lowered (30% and 40%, respectively), but ApoE was significantly increased by 40%. Upon refeeding with all three diets, plasma lipids progressively returned to control values except for triglycerides, which were significantly elevated by the protein and peptide diets. Apoprotein AI continued to decrease for 24 hours on the peptide and amino acid diets. Control levels were restored in all groups after 48 hours. ApoAIV increased progressively in parallel with the restoration of the intestinal mucosa; after 48 hours of refeeding, plasma concentrations of apo AIV were significantly correlated with jejunal villous height and protein content (P less than .01). ApoE was depressed below control levels in the WP and WPH groups at 24 and 48 hours and restored only after 96 hours. Because ApoE was affected, both in the fed state and during refeeding by the form of dietary nitrogen, it may prove to reflect nitrogen balance and/or insulin: glucagon balance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Amino acid pattern in plasma before and after jejuno-ileal shunt operation for obesity.

The amino acid pattern in plasma was studied in a reference group (n=26) and in three groups of massive obese subjects (n=9, 8, and 9 respectively) before and at intervals after jejuno-ileostomy. The obese subjects had preoperatively an amino acid pattern significantly different from that in the reference group. The concentrations of lysine, tyrosine, 1/2 cystine, and glutamic acids were higher, and aspargin, glutamine, serine, and glycine were lower than in the reference group. During the post-operative period the amino acid pattern changed significantly; thus serine, glycine, and taurine increased and valine, lysine, leucine, tryptophan, thyrosine, 1/2 cystine, and citrulline decreased. The amino acid pattern in the obese group with the longest post-operative observation time and a stable body weight differed significantly from that in the reference group only with regard to a low valine concentration and high concentration of taurine and glutamatic acid.     

Effects of fenofibrate on lipoprotein metabolism and fatty acid distribution in Zucker rats

The short term effects of fenofibrate (150 mg/kg per day), administered by gavage, on lipoprotein and fatty acid distribution have been investigated in an hypertriglyceridemic model, the Zucker rat. Lean rats were compared to control obese and treated obese rats, and control obese animals to treated obese littermates. Classically, plasma cholesterol and triacylglycerol increased by 1.8- and 7.9-fold, respectively, in control obese versus lean rats. Treatment of the Zucker obese rats with fenofibrate reduced their plasma cholesterol by 10% and raised triacylglycerol by 47% (P less than 0.001) in comparison to untreated control obese rats. These effects were accompanied by a change in the composition of all plasma lipoproteins. The cholesterol/triacylglycerol ratio in VLDL rose by 32% while that in LDL and HDL fell by 43 and 47%, respectively. Drug therapy altered the fatty acid profile in both plasma and liver; the percentage of polyunsaturated fatty acids fell while monounsaturated fatty acids increased. The increased proportion of monounsaturated fatty acids in plasma suggests that the fatty acid composition of circulating lipoproteins is modified, particularly in VLDL. This, in association with the altered lipid distribution in VLDL may reflect an abnormal metabolism of this lipoprotein. In view of these abnormalities, we conclude that this rat is not an appropriate model for the short-term study of clofibrate analogues.     

Effects of dietary fat amount and saturation on the regulation of hepatic mRNA and plasma apolipoprotein A-I in rats

The effects of the amount of dietary fat and saturation together with cholesterol both on hepatic apolipoprotein A-I gene mRNA levels and on plasma levels of this apolipoprotein were studied in male rats. To achieve these goals, seven groups of male Wistar rats were established: control group (n=5) consuming chow diet; cholesterol group (n=4) fed on a chow diet containing 0.1% (w/w) cholesterol; coco group (n=5) fed on a chow diet containing 0.1% (w/w) cholesterol and 40% coconut oil; corn group (n=5) fed on a chow diet containing 0.1% (w/w) cholesterol and 40% corn oil; and three olive groups consuming a chow diet containing 0.1% (w/w) cholesterol and percentages of 5 (n=5), 10 (n=4) and 40% (n=5), respectively, of olive oil. Animals were kept on these diets for 2 months and then sacrificed for lipoprotein, apolipoprotein and hepatic mRNA analysis. Dietary cholesterol by itself was hypercholesterolemic when compared to chow diet, an effect that was mainly due to an increase in LDL-cholesterol. Corn oil had a hypocholesterolemic action, whether compared to chow or to cholesterol diet, due to a reduction in HDL-cholesterol as well as LDL-cholesterol. HDL-cholesterol levels of 40% olive oil diet were lower than those corresponding to coconut oil and higher than those found in corn oil diet. When compared to control or cholesterol diets, plasma apoA-I concentration appeared significantly increased in coconut and 40% olive oil diets. Coconut oil or corn oil diets did not induce any significant change in apoA-I mRNA compared to control or cholesterol diets. Compared to cholesterol diet, 40 and 10% olive oil diets induced a significant increase in the expression of this message. A positive and significant (r=0.97, P<0.01) correlation between plasma apolipoprotein A-I concentration and its hepatic mRNA, was observed when the amount of dietary olive oil was 40% (w/w). A significant negative (r=-0.97, P<0.01) correlation was found in the corn oil group and no significant association was observed in the remaining groups. Based on the increased plasma levels in coconut oil and in high percentage olive oil diets, and the differences between these two diets for mRNA expression, it can be concluded that different fatty acid containing diets regulate apolipoprotein A-I through different mechanisms, and these mechanisms could be modulated by the fat intake.     

Acyl-coenzyme A:cholesterol acyltransferase inhibitor, avasimibe, stimulates bile acid synthesis and cholesterol 7alpha-hydroxylase in cultured rat hepatocytes and in vivo in the rat.

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) inhibitors are currently in clinical development as potential lipid-lowering and antiatherosclerotic agents. We investigated the effect of avasimibe (Cl- 1011), a novel ACAT inhibitor, on bile acid synthesis and cholesterol 7alpha-hydroxylase in cultured rat hepatocytes and rats fed different diets. Avasimibe dose-dependently decreased ACAT activity in rat hepatocytes in the presence and absence of beta-migrating very low-density lipoproteins (betaVLDL) (by 93% and 75% at 10 micromol/L) and reduced intracellular storage of cholesteryl esters. Avasimibe (3 micromol/L) increased bile acid synthesis (2.9-fold) after preincubation with betaVLDL and cholesterol 7alpha-hydroxylase activity (1.7- and 2.6-fold, with or without betaVLDL), the latter paralleled by a similar induction of its messenger RNA (mRNA). Hepatocytes treated with avasimibe showed a shift from storage and secretion of cholesteryl esters to conversion of cholesterol into bile acids. In rats fed diets containing different amounts of cholesterol and cholate, avasimibe reduced plasma cholesterol (by 52% to 71%) and triglyceride levels (by 28% to 62%). Avasimibe did not further increase cholesterol 7alpha-hydroxylase activity and mRNA in cholesterol-fed rats, but prevented down-regulation by cholate. Avasimibe did not affect sterol 27-hydroxylase and oxysterol 7alpha-hydroxylase, 2 enzymes in the alternative pathway in bile acid synthesis. No increase in the ratio of biliary excreted cholesterol to bile acids was found, indicating that ACAT inhibition does not result in a more lithogenic bile. Avasimibe increases bile acid synthesis in cultured hepatocytes by enhancing the supply of free cholesterol both as substrate and inducer of cholesterol 7alpha-hydroxylase. These effects may partially explain the potent cholesterol-lowering effects of avasimibe in the rat.     

Hypocholesterolemic effect of dietary psyllium in female rats

We fed cholesterol-enriched (1% cholesterol and 0.2% cholic acid) semipurified diets containing either 3% cellulose or psyllium to 2 groups of female Wistar rats for a period of 8 weeks. The feeding of the cholesterol-enriched semipurified diets resulted in a progressive increase in plasma cholesterol levels in both groups during the 8 weeks of the experiment. The rats fed psyllium, however, had significantly lower plasma cholesterol concentrations than the animals fed cellulose throughout the experimental period (at 8 weeks, 8.92 +/- 4.42 and 16.47 +/- 8 mmol/l, respectively, means +/- SD, n = 14, p < 0.01). Most of the plasma cholesterol in both groups at the end of the study was located in the very low-density lipoprotein (VLDL) fraction (91%) and differences in total plasma cholesterol concentrations were predominantly reflected in differences in VLDL cholesterol. Plasma triglyceride concentrations were not significantly different between the 2 groups. Liver cholesterol concentrations paralleled the concentrations of plasma cholesterol and were significantly lower (p < 0.001) in the psyllium-fed rats (90.31 +/- 13.81 micromol/g liver) than in the cellulose-fed rats (60.49 +/- 15.25 micromol/g liver). Substitution of psyllium for cellulose resulted in an increase in the excretion of fecal bile acids by 26%, and this increase was predominantly caused by an increased excretion of beta-muricholic acid and the bile acids derived from beta-muricholic acid (omega-muricholic acid and hyodeoxycholic acid).     

Compared effect of n-3 and n-6 dietary fatty acids on rat intestinal acyl-CoA:cholesterol acyltransferase activity

Polyunsaturated fatty acids are known to lower plasma cholesterol concentrations. We studied their effect on intestinal acyl-CoA:cholesterol acyltransferase (ACAT) activity in rats fed either salmon oil or corn oil (17% fat) with or without 1% cholesterol. After an 8-week feeding period we confirmed the hypolipidemic effect of salmon oil and we established its ability to stimulate ACAT activity in rats fed low-cholesterol diets. The most striking effect of 1% dietary cholesterol on ACAT activity was obtained in the control group (34% enhancement), whereas cholesterol supplementation had no effect on ACAT activity in the salmon oil group. The results enable us to suggest that n-3 fatty acids have an effect per se on ACAT activity; the regulation of enzyme activity by dietary cholesterol probably involves independent processes.     

Effects of insulin on hypercholesterolemia in the streptozotocin-induced diabetic rats fed a high cholesterol diet

The effect of dietary cholesterol (Ch) on plasma lipoprotein and apolipoproteins (apo) in diabetic rats was investigated. Ch-fed diabetic rats were severely hypercholesterolemic and hypertriglyceridemic. They had higher concentrations of very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and low density lipoprotein (LDL). Concentration of high density lipoprotein (HDL) was decreased. beta-VLDL increased predominantly in Ch-fed diabetic rats, whereas IDL increased in the Ch and propylthiouracil-fed control rats. According to sodium dodecyl sulfate polyacrylamide gel electrophoresis, VLDL and IDL from Ch-fed diabetic rats were unusual in that they contained more apo E, A-I and A-IV. Concentrations of plasma apo A-I and apo E were measured by radioimmunoassay. The diabetic rats fed a labo chow showed a significantly lower concentration of plasma apo E than control rats. Plasma apo E was extremely higher in the diabetic rats fed a cholesterol diet. Plasma apo A-I was significantly increased in the diabetic rats fed a labo chow and those fed a cholesterol. Insulin treatment significantly decreased the concentrations of VLDL, IDL and LDL and plasma concentration and distribution of apolipoproteins in lipoprotein subfractions changed toward normal. However, decreased HDL in the Ch-fed diabetic rats was not recovered by insulin treatment.     

Lipoprotein catabolism in rats with portacaval anastomosis on various diets

The catabolism of lipoproteins was measured in rats with a portacaval anastomosis and in intact control rats. Radioiodinated rat high density lipoproteins or human low density lipoproteins, the major cholesterol-bearing lipoproteins in rat or man respectively, were injected intravenously into rats. More than 90% of trace amounts of these lipoproteins were removed from plasma of rats with portacaval anastomosis and controls on standard chow at closely similar rates within 24 h. Also, [125I]high density lipoproteins left the plasma at comparable rates in controls and rats with portacaval anastomosis, whether fed with a cholesterol-free chow or a carbohydrate-rich lard chow. These dietary regimens were employed to avoid artifacts through a different development of the body weight in operated and control rats. A standard laboratory chow ad libitum led to weight loss in rats with portacaval anastomosis. Pair-fed with a cholesterol-free chow both groups of rats kept the same weight, but only with a carbohydrate-rich lard chow could the natural weight gain be achieved. In all rats with portacaval anastomosis liver weights were reduced and serum cholesterol decreased by 21-31% with the major change in high density lipoproteins. The findings suggest that cholesterol concentrations are not likely to be lowered in rats with portacaval anastomosis by enhanced lipoprotein catabolism.     

Amino acids and control of nucleolar size, the activity of RNA polymerase I, and DNA synthesis in liver.

The volume of nucleolar material per nucleus and the activity of RNA polymerase I (RNA nucleotidyltransferase I) become doubled in the liver cells of rats that are fed for several days a diet that lacks essential amino acids. Omission of methionine from a fully supplemented diet is equivalent to leaving out all the amino acids, and the responses to a deficiency of tryptophan are about 40% as great. Deprivation of one of the remaining essential amino acids gives either small responses or none at all. Supplementation of the methionine-free diet with cystine blocks the nucleolar enlargement and the enhancement of the polymerase activity that would otherwise take place, but the dispensable amino acid does not affect the responses to a deprivation of one of the other essential amino acids. After deprivation of all the essential amino acids or only methionine, hepatocytes make DNA when the rat is fed a meal with protein. A preparatory diet lacking in tryptophan is much less effective; a deficiency in any of the other indispensable compounds tested fails to prepare the liver for DNA synthesis. The results give hope that elucidation of the means by which methionine deprivation affects the nucleolus will also provide information on the regulation of nuclear DNA replication in liver. One attractive possibility is that the amino acid deficiency acts by producing some imbalance in protein metabolism.     

Serum lipids, lipoprotein composition and liver cholesterol in genetically obese Zucker rats fed semipurified diets containing either casein or soy protein

The effect of semipurified diets containing either casein or soy protein on serum lipids, lipoprotein composition and liver cholesterol was studied in genetically obese Zucker rats. The ingestion of a cholesterol-enriched semipurified diet containing casein resulted in elevated levels of serum cholesterol and phospholipids compared to the feeding of a soy protein diet. No differences in serum triglycerides were observed. Differences in serum cholesterol and phospholipids were mainly reflected in the very low density lipoproteins and low density lipoproteins and to a minor extent in the high density lipoproteins. Liver cholesterol paralleled the levels of cholesterol in the serum, the rats fed casein exhibited markedly higher levels of liver cholesterol than those fed soy protein. Furthermore, the rats fed casein also had enlarged livers. Thus, this study clearly shows the differential cholesterolemic effect of dietary casein and soy protein in genetically obese Zucker rats.     

Substitution of mixed amino acids resembling soy protein for mixed amino acids resembling casein in the diet reduces plasma cholesterol in slowly,but not rapidly fed nor fasted baboons

Studies of cholesterol and triglyceride metabolism were conducted under steady-state conditions in conscious restrained female baboons to ascertain (1) whether the cholesterol- and triglyceride-lowering effects of soy protein v casein in nonrodents can be explained by differences in amino acid composition between the two proteins and (2) whether the lipid-lowering effects of soy protein are influenced by fasting or the rate of feeding, ie, the nutritional state. The metabolic changes underlying the changes in serum cholesterol and triglyceride concentration were also investigated. Isocaloric diets consisting of 45% mixed amino acids (soy or casein type), 50% glucose and 5% corn oil, including all nutritional requirements, were infused intraduodenally for five days. There were no differences in lipid levels between the soy and casein diets in fasting baboons (days 4 or 5) or when the daily diet (calculated to equal 24 hours of energy utilization) was given rapidly by constant intraduodenal infusion over seven hours (day 4). During rapid feeding there was, unexpectedly, no significant change in plasma cholesterol concentration, but the estimated rate of cholesterol oxidation to bile acids fell significantly by 38 ± 6% (from 39 ± 4 to 24 ± 3 mg/d). Significant differences between the soy and casein diets were observed only in the fed state produced by the slow constant isocaloric intraduodenal infusions of the diets [5.8 mg mixed amino acids (soy or casein type) plus 7.2 mg glucose/min/kg body wt^0.75] on day 5. These diets were calculated to equal the simultaneous rate of energy utilization. During the slow (eight to ten hour) infusions the decrease in plasma cholesterol concentration was significantly greater with the soy v casein diet (25 ± 6 v 12 ± 4%, P < .02). Likewise, with the soy diet there was a reduction of serum triglycerides in 7 of 9 experiments (.05 < P < .10), which could be explained, at least in part, by a significant reduction in plasma VLDL triglyceride secretion (0.8 ± 0.2 v 1.4 ± 2 μmol TGFA/min/kg body wt^0.75, P < .005). Thus, both the nutritional status of the animals (fed or fasting) and the rate of feeding (rapidly or slowly at the calculated simultaneous rate of energy utilization) had a profound influence on the differential cholesterol- and triglyceride-lowering effects of soy protein v casein type diets. This explains the dissociation of the postprandial hypocholesterolemic effect of the soy type diet from its tendency to even elevate fasting cholesterol levels. These studies demonstrate the crucial importance of testing therapeutic diets under various nutritional conditions and of selecting an appropriate experimental model which allows for rigorous dietary control.     

Modification of two types of cholesterol atherosclerosis in rabbits by blocking lipoprotein lysine epsilon-amino groups

In previous studies, it was shown that a lysine deficient diet reduces the severity of aortic cholesterol atherosclerosis in rabbits. Feeding 1-amino-3-imino N,N' propene diacetate (AIPD) produced 2 metabolic by products with active aldehyde groups 1-amino propenal acetic acid (APA) and malonyldialdehyde (MDA) that transiently block the lysine epsilon-amino groups of all proteins and lipoproteins in vivo. This paper reports the effects of blocking the lysine free epsilon-amino groups of all lipoproteins on 2 different types of cholesterol atherosclerosis; (1) A proliferative-type cholesterol atherosclerosis containing a high proportion of spindle-shaped myogenic foam cells rich in collagen and alcian blue-stainable material produced by feeding a diet containing cholesterol, peanut oil, ethanol and butylated hydroxyanisole and (2) cholesterol atherosclerosis containing a high proportion of polyhedral-shaped nonmyogenic macrophage-type foam cells produced by feeding cholesterol and oleic acid. After 14 weeks on the diets the mean +/- SD percent of intimal aortic area covered with the myogenic-type atherosclerosis in the control peanut oil-fed group was 34 +/- 6% and this was reduced to 13 +/- 3% in the peanut oil AIPD group. In contrast, after 14 weeks in the control oleic acid group the severity of atherosclerosis was 14 +/- 4% and this was increased to 36 +/- 7% in the oleic acid AIPD group. Aortic cholesterol concentration was decreased in the AIPD peanut oil group relative to its control but was increased in the AIPD oleic acid group relative to its control group. A higher concentration of AIPD metabolites accumulated in the atherosclerotic lesions of the oleic AIPD group than in the peanut oil AIPD group indicating that a larger amount of lysine blocked lipoprotein accumulated in the macrophage-rich lesions of the oleic acid AIPD group than in the myogenic-rich lesions of the peanut oil AIPD group. Blocking lysine epsilon-amino groups in vivo by feeding AIPD did not modify DNA synthesis in the aortae of either AIPD group relative to their control groups.     

Type and amount of dietary fat affect relative concentration of cholesterol in blood and other tissues of rats

The effects of diet on tissue cholesterol disposition in the rat were studied. Growing rats were fed a nonfat dry milk supplemented with two levels of soy-bean oil (SBO) and tallow (T) such that either 30% or 50% of total dietary calories came from fat. Two of four groups of rats fed the diets with 50% of calories from fat were supplemented with 20% ground whole oats. Considering all diets, rats fed SBO had higher blood and kidney cholesterol than did rats fed T; supplementation of the diet with oats increased the plasma cholesterol of the "50%" SBO rats and , conversely, decreased plasma cholesterol of the "50%" T rats. Muscle cholesterol content was not affected by variations in dietary fat and oats. In all treatments, cholesterol concentration of epididymal fat and liver were greater in the SBO-fed than in the T-fed rats.     

Fish protein stimulated the fibrinolysis in rats

OBJECTIVE: We hypothesized that fish protein affects blood coagulation and/or fibrinolysis, and compared the activity and amounts of factors involved in blood coagulation and fibrinolysis in rats fed the fish protein, which was treated to remove water-soluble and ethanol-soluble elements, from sardine (sardine protein). METHODS: In the first experiment, rats were fed for 21 days an AIN-93G-based control diet, and diets in which the casein of the control diet was exchanged for sardine protein at 5, 10 and 20% levels. In the second experiment, rats were fed an AIN-93G control diet and diets containing 5% fish oil, 10% sardine protein or both (5% fish oil + 10% sardine protein) for 21 days. At the end of the experiments, blood coagulation time, hemostatic parameters and fibrinolysis parameters were measured. RESULTS: The activated partial thromboplastin time (APTT), which is an assay for blood coagulation time in the intrinsic blood coagulation pathway, of rats fed the 20% sardine protein diet was significantly prolonged compared to that of rats fed the control diet. The prolonged APTT by dietary sardine protein was due to a significant decrease of the activities of plasma blood coagulation factors VIII, IX, XI and XII. On the other hand, dietary sardine protein significantly increased the activity of tissue-type plasminogen activator, and the amount of plasma plasmin-alpha(2)-plasmin inhibitor complex, which are markers of activated plasmin. Moreover, we observed that the 20% sardine protein diet increased the amount of plasma D-dimer, which is a degraded product of the fibrin polymer by plasmin. In the second experiment, the APTT and PT of rats fed the F diet were prolonged compared to those of rats fed the control diet, however the concentration and amount of fibrinolytic parameters in the plasma were almost the same as those of rats fed the control diet. In contrast, the F+S diet not only prolonged APTT and PT, but also increased the concentration and amount of fibrinolytic parameters in plasma. CONCLUSIONS: We consider that the beneficial effects to health and amelioration of cardiovascular and cerebrovascular diseases by fish consumption are caused by a combination of the suppressing effect on blood coagulation of n-3 polyunsaturated fatty acids and the promoting effect on fibrinolysis of fish protein.     

Luminal and metabolic regulation of jejunal amino acid absorption in the rat

Studies were carried out to determine the role of luminal amino acids and metabolic balance in in vivo amino acid absorption. Previous in vitro studies have shown that adaptation of amino acid transport is a complex phenomenon. In the first series of experiments, parenterally nourished rats received a 7-day jejunal infusion of either 3% aspartic acid, glutamine, lysine, valine, or mixed amino acids. A single-pass perfusion was performed to determine the effects of infusates on 5 mM valine, aspartic acid, and lysine absorption. Compared with controls receiving luminal saline, prior glutamine infusion increased valine absorption; prior valine, glutamine, and aspartic acid infusion significantly increased aspartic acid absorption; and prior valine and lysine infusion significantly increased lysine absorption. The mixed amino acid solution had no effect. The effects of metabolic balance were examined by comparing fasted rats with parenterally fed and orally fed rats. Within 24 h fasting significantly increased valine and aspartic acid absorption, despite a significant decrease in intestinal mass.