Cholesterol metabolism in groups of rhesus monkeys with high or low response of serum cholesterol to an atherogenic diet

Serum metabolic variables associated with impaired glucose tolerance induced by high-fat-high-cholesterol diet in Macaca mulatta

Dyslipidemia caused by 'Western-diet pattern' is a strong risk factor for the onset of diabetes. This study aimed to disclose the relationship between the serum metabolite changes induced by habitual intake of high-fat and high-cholesterol (HFHC) diet and the development of impaired glucose tolerance (IGT) and insulin resistance through animal models of Macaca mulatta. Sixteen M. mulatta (six months old) were fed a control diet or a HFHC diet for 18 months. The diet effect on serum metabolic profiles was investigated by longitudinal research. Islet function was assessed by intravenous glucose tolerance and hyperinsulinemic-euglycemic clamp test. Metabonomics were determined by (1)H proton nuclear magnetic resonance spectroscopy. Prolonged diet-dependent hyperlipidemia facilitated visceral fat accumulation in liver and skeletal muscle and disorder of glucose homeostasis in juvenile monkeys. Glucose disappearance rate (K(Glu)) and insulin response to the glucose challenge effects in HFHC monkeys were significantly lower than in control monkeys. Otherwise, serum trimethylamine-N-oxide (TMAO), lactate and leucine/isoleucine were significantly higher in HFHC monkeys. Sphingomyelin and choline were the most positively correlated with K(Glu) (R(2) = 0.778), as well as negative correlation (R(2) = 0.64) with total cholesterol. The HFHC diet induced visceral fat, abnormal lipid metabolism and IGT prior to weight gain and body fat content increase in juvenile monkeys. We suggest that increased serum metabolites, such as TMAO, lactate, branched-chain amino acids and decreased sphingomyelin and choline, may serve as possible predictors for the evaluation of IGT and insulin resistance risks in the prediabetic state.

Maintenance of the LDL cholesterol:HDL cholesterol ratio in an elderly population given a dietary cholesterol challenge

We previously evaluated the responses to dietary cholesterol in children and young adults. In this study, the effects of dietary cholesterol on plasma lipids and LDL atherogenicity were evaluated in 42 elderly subjects (29 postmenopausal women and 13 men > 60 y old). Our exclusion criteria were diabetes, heart disease, and the use of reductase inhibitors. The study followed a randomized crossover design in which subjects were assigned to consume the equivalent of 3 large eggs (EGG) daily or the same amount of a cholesterol-free, fat-free egg substitute (SUB) for a 1-mo period. After a 3-wk washout period, subjects were assigned to the alternate treatment. The concentration of plasma cholesterol after the EGG period varied among subjects. When all subjects were evaluated, there were significant increases in LDL cholesterol (LDL-C) (P < 0.05) and HDL-C (P < 0.001) for both men and women during the EGG period, resulting in no alterations in the LDL-C:HDL-C or the total cholesterol:HDL-C ratios. In addition, the LDL peak diameter was increased during the EGG period for all subjects. In contrast, the measured parameters of LDL oxidation, conjugated diene formation, and LDL lag time did not differ between the EGG and the SUB periods. We conclude from this study that dietary cholesterol provided by eggs does not increase the risk for heart disease in a healthy elderly population.

Men classified as hypo- or hyperresponders to dietary cholesterol feeding exhibit differences in lipoprotein metabolism

The purpose of this study was to evaluate the differences that occur within the plasma compartment of normolipidemic men, classified on the basis of their response to prolonged consumption of additional dietary cholesterol. Using a crossover design, 40 men aged 18-57 y were randomly allocated to an egg (640 mg/d additional dietary cholesterol) or placebo group (0 mg/d additional dietary cholesterol), for two 30-d periods, which were separated by a 3-wk washout period. Subjects were classified as hypo- [increase in plasma total cholesterol (TC) of <0.05 mmol/L for each additional 100 mg of dietary cholesterol consumed] or hyperresponders (increase in TC of > or =0.06 mmol/L for each additional 100 mg of dietary cholesterol consumed) on the basis of their plasma reaction to the additional dietary cholesterol provided. Male hyporesponders did not experience an increase in LDL cholesterol (LDL-C) or HDL cholesterol (HDL-C) during the egg period, whereas both lipoproteins were significantly (P < 0.0001 and P < 0.05, respectively) elevated in hyperresponders. Although the LDL/HDL ratio was increased in male hyperresponders after the high cholesterol period, the mean increase experienced by this population was still within National Cholesterol Education Program guidelines. Furthermore, male hyperresponders had higher lecithin cholesterol acyltransferase (P < 0.05) and cholesteryl ester transfer protein (P < 0.05) activities during the egg period, which suggests an increase in reverse cholesterol transport. These data suggest that additional dietary cholesterol does not increase the risk of developing an atherogenic lipoprotein profile in healthy men, regardless of their response classification.

Exogenous hypercholesterolemic rats, compared with their progenitor, Sprague-Dawley rats, promptly alter cholesterol metabolism in the liver and secrete cholesterol-rich particles in response to dietary cholesterol

Early responses of cholesterol metabolism to dietary cholesterol were compared between exogenous hypercholesterolemic (ExHC) and Sprague-Dawley rats. Both strains had a similar radioactivity of [14C]cholesterol in the serum half a day after the oral administration, but thereafter the radioactivity disappeared slowly in ExHC rats. ExHC rats promptly altered in response to the dietary cholesterol, activities of cholesterol 7 alpha-hydroxylase and cholesterol synthesis in the liver and fecal excretion of bile acids derived from [14C]cholesterol administered orally. Lymphatic transport for 24 hr [14C]cholesterol was similar between the strains. Triton administration resulted in a marked accumulation of cholesterol in serum d > 1.006 g/mL lipoproteins in ExHC rats; in addition, the formation of cholesteryl esters from [14C]oleic acid intravenously infused was greater in ExHC rats. These results indicate that ExHC rats increase serum cholesterol in response to exogenous cholesterol by decreasing the liver uptake and enhancing the secretion in the liver.

Effect of dietary cholesterol and fat on the expression of hepatic sterol 27-hydroxylase and other hepatic cholesterol-responsive genes in baboons (Papio species)

Our studies of baboons with low and high responses to dietary cholesterol and fat suggest that low-responding baboons increase the activity of hepatic sterol 27-hydroxylase, an important enzyme of bile acid synthesis, considerably more than do high-responding baboons when challenged with a high-cholesterol, high-fat (HCHF) diet. The present studies were conducted to determine whether hepatic sterol 27-hydroxylase mRNA levels and plasma 27-hydroxycholesterol concentrations also differed with dietary responsiveness. Sixteen adult male baboons with a wide range of VLDL cholesterol plus LDL cholesterol (VLDL+LDL cholesterol) response to an HCHF diet were selected. They were examined first while on a chow diet and then after 1, 3, 6, 10, 18, 26, 36, 52, 72, and 104 weeks on the HCHF diet. Plasma and lipoprotein cholesterol concentrations increased rapidly during the first 3 weeks and stabilized thereafter. On the basis of the response in VLDL/LDL cholesterol, we selected five low-responding, four medium-responding, and five high-responding baboons for more intensive study in more detail. In low responders, the major increase in serum cholesterol concentration was in HDL cholesterol, whereas in medium and high responders it was in both VLDL+LDL and HDL cholesterol. In low and medium responders, serum or VLDL+LDL cholesterol did not change after 3 weeks of consumption of the HCHF diet, whereas in high responders VLDL+LDL cholesterol declined between 78 and 104 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

ApoA-IV phenotype affects diet-induced plasma LDL cholesterol lowering

The National Cholesterol Education Program (NCEP) recommends that dietary total fat, saturated fat, and cholesterol intake be reduced to < or = 30% of calories, < 10% of calories, and < 300 mg/d, respectively (step 1 diet), in the general population to reduce plasma low-density lipoprotein cholesterol (LDL-C) levels and heart disease risk. We examined the LDL-C-lowering response to such a diet (26% fat, 8% saturated fat, and 201 mg/d cholesterol) compared with an average American diet (39% fat, 15% saturated fat, and 435 mg cholesterol/d) in 153 subjects using diet periods of 4 through 24 weeks for each diet phase. The mean LDL-C reduction was 13% in men (n = 93) and 7% in postmenopausal women (n = 60). The effect of apolipoprotein (apo) A-IV phenotype on responsiveness was examined. LDL-C lowering in men was significantly (P < .005) less (7%) for 17 apoA-IV (1/2) subjects than for 76 apoA-IV (1/1) subjects (16%). In women, 7% lowering was observed in both 12 apoA-IV (1/2) subjects and 48 apoA-IV (1/1) subjects. ApoA-IV phenotype had a significant effect on plasma high-density lipoprotein cholesterol levels during both dietary periods; women carrying the apoA-IV-2 allele had higher levels than those homozygous for the apoA-IV-1 allele. The opposite was true for triglyceride levels, but only during the period when the subjects consumed the high-fat, high-cholesterol diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypo- and hyperresponse of serum cholesterol level and low density lipoprotein production and degradation to dietary cholesterol in man

Serum cholesterol in man rises when cholesterol intake increases, but the extent of the elevation varies between subjects. Part of the variation between subjects is spurious and not reproducible; it is caused by random diet-independent fluctuations of serum lipid levels. Part is due to consistent metabolic differences between subjects. We have earlier found that responsiveness was associated with higher initial total and HDL cholesterol, lower habitual cholesterol consumption, and lower body mass index, and unrelated to gender, age, or apo E phenotype. We have now investigated the metabolic basis of variability by measuring turnover rates of low density lipoprotein (LDL) apolipoprotein B (apo B) on a low-cholesterol diet (140 mg/day) and a high-cholesterol diet (900 mg/day) in 8 volunteers with well-defined differences in the responsiveness of their serum cholesterol to diet. Autologous 125I-LDL was injected on day 23 of each diet period. Its fractional catabolic rate (FCR) was estimated from the ratio of 125I in urine over that in plasma, seven days after injection. FCR (mean +/- SD) increased from 0.24 +/- 0.02 pools/day on the low- to 0.31 +/- 0.20 on the high-cholesterol diet. LDL-apo B concentration rose from 49 +/- 13 to 63 +/- 12 mg/dl, and LDL-apo B production rate, calculated as FCR x concentration/body weight, from 4.8 +/- 1.2 to 8.0 +/- 1.4 mg/kg/day. The individual rise in production rate was significantly correlated with the rise in the serum concentration of LDL-apo B (r = 0.90) or LDL-cholesterol (r = 0.75), and also with the rise in total serum cholesterol measured in these same subjects in similar experiments 3-4 years earlier (r = 0.74). Degradation of LDL by freshly isolated blood mononuclear cells and by mononuclear cells incubated for 72 h in lipoprotein-deficient medium (derepressed cells) was measured on both diets in these and in additional volunteers. The rate of degradation (mean +/- SD) of standard human LDL by fresh cells was 336 +/- 166 ng LDL protein/mg cell protein per 8 h on the low-cholesterol diet, and decreased by 147 +/- 180 ng/mg per 8 h or 44% on the high-cholesterol diet (n = 23, p < 0.01). The catabolic activity of derepressed cells obtained when subjects were on the low-cholesterol diet was negatively related to the LDL cholesterol response (r = -0.57, n = 18, p < 0.05), and to the total cholesterol response in earlier experiments (r = -0.45, n = 18, p < 0.10).(ABSTRACT TRUNCATED AT 400 WORDS)

Within-individual variation in serum cholesterol levels: association with DNA polymorphisms at the apolipoprotein B and AI-CIII-AIV loci in patients with peripheral arterial disease

We have examined the association between variation at the apolipoprotein (apo) B gene and apo AI-CIII-AIV gene cluster and within-individual variation in serum cholesterol levels. Annual measurements were available over a period of 5-10 years in a group of 117 male patients with peripheral arterial disease. The overall within-individual coefficient of variation in cholesterol levels over time was 13.9%. For all patients, Restriction Fragment Length Polymorphism (RFLP) genotype at the apo B gene (XbaI and EcoRI) and apo AI-CIII-AIV gene cluster (XmnI, PstI and PvuII-CIII) had previously been determined. At the apo B locus, individuals heterozygous for either the XbaI or EcoRI RFLP showed significantly greater within-individual variability over time compared to individuals of other genotypes. At the apo AI-CIII-AIV gene cluster, individuals homozygous for the common allele of either the PstI or PvuIIA RFLPs showed the greatest within-individual variability over time but there was no difference in this estimate associated with XmnI genotype. Our observations suggest that variation at both the apo B and apo AI-CIII-AIV loci interacts with unidentified environmental factors to determine individual variability in serum cholesterol levels over time.

Isolation and characterization of plasma lipoproteins of common marmoset monkey. Comparison of effects of control and atherogenic diets

This study examines the potential of the common marmoset monkey (Callithrix jacchus) to serve as a model for human lipoprotein metabolism and atherosclerosis. The lipoproteins of animals fed a low-fat, low-cholesterol diet and a high-fat (12% wt/wt lard), high-cholesterol (0.34% wt/wt) diet were characterized by the combination of sequential ultracentrifugation and Pevikon block electrophoresis. Based on chemical and physical properties, equivalents of human very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL), including and HDL-with apolipoprotein E subclass, were demonstrated. In control animals, whose plasma cholesterol concentration was 140.1 +/- 20.2 mg/dl (means +/- SD), approximately 40% of the plasma cholesterol was transported by LDL as compared with approximately 70% in humans. The cholesterol-fed marmosets segregated into two groups: hypo- and hyper-responders. The hyper-responders had plasma cholesterol levels of 450 to 970 mg/ml. The hypercholesterolemia was associated with elevated concentrations of VLDL, intermediate density lipoproteins, and LDL; in addition, these lipoproteins were enriched in cholesteryl esters relative to lipoproteins isolated from control animals. The HDL (d greater than 1.09 g/ml) levels did not change in response to cholesterol feeding, although the HDL-with apolipoprotein E found in the d = 1.02 to 1.09 g/ml fraction increased approximately fivefold. Based on immunological characteristics and sialic acid content, the common marmoset appeared to lack a lipoprotein(a) equivalent. The results of a short-term feeding study (11 months) suggest that this monkey was susceptible to the development of diet-induced atherosclerosis. The hyper-responsive animals developed foam cell lesions and moderately proliferative intimal lesions, predominantly within the thoracic aorta. In summary, the results of our studies indicate that the common marmoset monkey potentially is a useful model for the study of both lipoprotein metabolism and diet-induced atherosclerosis.

"Variability gene" effect of cholesteryl ester transfer protein (CETP) genes

Cholesteryl ester transfer protein (CETP) may have important roles in transfer of lipids from cells to serum lipoproteins or between circulating lipoprotein particles. Restriction fragment length polymorphisms (RFLPs) in DNA at the CETP locus have been detected. In the present study we have used RFLPs detectable with the restriction enzyme TaqI to examine if CETP influences serum lipid variability (as opposed to absolute lipid levels). We have compared within-pair difference in serum lipid and apolipoprotein levels in monozygotic twin pairs of various genotypes in the B polymorphism at the CETP locus and uncovered significant differences between genotypes. We conclude that the CETP locus has "variability genes" (as opposed to "level genes") with respect to total and LDL cholesterol variability. A person's total genetic risk for coronary heart disease may depend on his or her combination of "level genes" and "variability genes". The method of analysis applied may be the best available for the study of gene - environment interaction.

Sterol balance and cholesterol absorption in inbred strains of rabbits hypo- or hyperresponsive to dietary cholesterol

In 2 inbred strains of rabbits with high or low response of plasma cholesterol to dietary cholesterol, excretion of steroids in the feces and efficiency of cholesterol absorption were determined. Rates of whole-body cholesterol synthesis, measured as fecal excretion of bile acids and neutral steroids minus cholesterol intake, were similar in hypo- and hyperresponders fed a low-cholesterol (8 mumol/100 g) diet. Transfer of the rabbits to a high-cholesterol (182 mumol/100 g) diet caused an increase in fecal bile acid excretion in hypo- but not in hyperresponders. Dietary cholesterol did not affect neutral steroid excretion in either rabbit strain. Hyperresponders tended to accumulate more cholesterol in their body than did hyporesponders. After the rabbits were switched back from the high- to the low-cholesterol diet, rates of whole-body cholesterol synthesis were significantly higher in the hypo- than in the hyperresponders. With the use of the simultaneous oral administration of [3H]cholesterol and beta-[14C]sitosterol, hyperresponders were found to absorb significantly higher percentages of cholesterol than hyporesponders. It is concluded that the differences in stimulation of bile acid excretion after cholesterol feeding and the efficiency of cholesterol absorption are important determinants of the phenomenon of hypo- and hyperresponsiveness in the 2 inbred rabbit strains.

Differences in fecal excretion of cholesterol and bacterial degradation products in high- and low-responding rhesus monkeys: implications in colon cancer

This paper reports the differences in the fecal excretion of cholesterol and its degradation products in high- and low-responding rhesus monkeys fed diets with and without extra cholesterol. The high-responding monkeys had a great increase in plasma cholesterol concentration when fed a high-cholesterol diet, whereas the low-responders had a small increase when fed the same diet. The results show that low-responding monkeys, when fed high-cholesterol diets, excrete nearly two to three times the amount of cholesterol and its bacterial degradation products in the feces than the high-responding monkeys. We suggest that these two select groups of monkeys may be useful models for the study of the role cholesterol and its bacterial degradation products play in colon cancer.

Differences in individual responsiveness of serum cholesterol to fat-modified diets in man

In the period 1963-1974, 82 monks and 48 nuns from five Dutch and Belgian Trappist monasteries each participated in two or more out of nine different trials designed to test the effect of 58 different fat-modified diets on serum cholesterol. We analysed these data to quantify the extent to which healthy, normolipaemic subjects differ in the responsiveness of their serum cholesterol to a change in dietary fatty acid composition. Statistically significant between-person variance components (SD2p) were found in the serum cholesterol responses for the whole group (SD2p = [0.20 mmol l-1]2), for the men (SD2p = [0.24 mmol l-1]2) and for those women who participated in three or more trials (SD2p = [0.14 mmol l-1]2). The between-person variation (expressed as SD) was on average only half as large as the within-person variation in response when the same subject was challenged repeatedly. It is concluded that medically significant differences in responsiveness to fat-modified diets exist in both men and women. However, few subjects fail entirely to respond to a change in dietary fatty acid composition. In addition, the large within-subject variability makes it difficult to identify hypo- and hyperresponders.

Low density lipoprotein kinetics in African Green monkeys showing variable cholesterolaemic responses to diets realistic for westernised people

African Green (vervet) monkeys were fed either an atherogenic Western diet (WD), a prudent diet (PD), or a high carbohydrate diet (HCD) for various lengths of time. Monkeys differed greatly in their response to the WD, and a strong negative correlation was observed between the fractional catabolic rates (FCR) of low density lipoprotein (LDL) and the total plasma cholesterol concentrations (r = -0.83 P = 0.0029). Similarly the individual synthetic rates (SR) of LDL plotted against the total plasma cholesterol concentrations showed a correlation coefficient of r = 0.94 P = 0.01 for WD animals. There was no correlation for PD or HCD animals for either SR or FCR and the total plasma cholesterol concentrations. The aortic lesion scores correlated with the SRs (r = 0.66 P = 0.040) but not with the FCRs. LDL turnover was also studied using 125I-labelled native LDL and methylated 131I-labelled LDL in African Green monkeys showing high or low cholesterolaemic response to an atherogenic Western diet. Measurements after 4 weeks and again after 6 months on the diet showed a decrease in both total and non-receptor mediated clearance of LDL. Receptor-mediated catabolism was significantly lowered in the hyperresponding group (P = 0.0011) and not in the hyporesponding group with a resultant significant difference between the two groups being P = 0.0355 after 6 months. Non-receptor mediated catabolism of LDL was similarly affected in that there was no significant difference between the two groups at 4 weeks but the clearance of methylated LDL was markedly lowered at 6 months, for the hyporesponding group P = 0.0003 and for the hyperresponding group P = 0.0184. Furthermore the hyperresponding group was depressed to a significantly greater extent when compared to the hyporesponding group (P = 0.0241).

Atherosclerosis of cynomolgus monkeys hyper- and hyporesponsive to dietary cholesterol. Lack of effect of vasectomy

A moderately atherogenic diet was fed to young adult cynomolgus macaque males that were observed to be either hypo- or hyperresponsive to dietary cholesterol and who were randomized into groups to be either vasectomized or sham-vasectomized. The extent of atherosclerosis was found to be considerably greater at all arterial sites studied for the monkeys that were hyperresponsive to dietary cholesterol. The differences in atherosclerosis development among the hyperresponder monkeys occurred primarily in the proximal portions of the coronary arteries, the proximal and distal portions of the common carotid arteries, and only in the most proximal portions of the femoral arteries. There were no significant effects of vasectomy or sham vasectomy on atherosclerosis extent in either the hyper- or the hyporesponding groups, although there was a suggestion of somewhat larger lesions in the left circumflex coronary artery of hyperresponder monkeys that were vasectomized and somewhat smaller atherosclerotic lesions in the left common carotid arteries of vasectomized monkeys. The data presented here do not support our first report of worsened atherosclerosis among cynomolgus monkeys fed diets high in cholesterol. The findings of the current study are consistent with recent epidemiological studies of vasectomized and nonvasectomized human males.

Studies on the mechanism of high intestinal absorption of cholesterol and campesterol in high-responding rhesus monkeys

To understand better the mechanism of higher absorption of cholesterol and campesterol in high-responding than in low-responding rhesus monkeys, we measured the concentrations of the two sterols in the micellar fraction isolated from small intestinal content, and also determined their rates of esterification by cholesterol esterase prepared from the small intestinal mucosa. The results show that the concentrations of both cholesterol and campesterol in the micellar fraction were significantly higher in the high- than in low- and intermediate-responding rhesus monkeys. Also the rates of esterification of both sterols are higher in the proximal segment of the small intestine in high-responders than the other two groups. We conclude that the two necessary steps in the process of sterol absorption, namely, the amounts of sterols solubilized in micelles and their esterification within mucosal cells which are higher in high- than in low-responders are responsible for the higher absorption of the sterols in the high-responding rhesus monkeys.

Relationships between dietary cholesterol, cholesterol absorption, cholesterol synthesis, and plasma cholesterol in rhesus monkeys

The relationships between the cholesterol content of the diet, plasma cholesterol concentration, cholesterol absorption, and cholesterol synthesis (measured indirectly by desmosterol suppression technique) are explored in groups of high- and low-responding rhesus monkeys fed diets containing 0.02, 0.15 and 0.75 mg cholesterol/kcal. The cholesterol content of the diet (expressed as mg/kcal) is positively correlated with plasma cholesterol concentration and is negatively correlated with percent cholesterol absorption in both groups. Also the cholesterol content of the diet is negatively correlated (r = -0.66) with cholesterol synthesis only in low-responders but not in high-responders. Similarly, the correlation between percent cholesterol absorption and cholesterol synthesis is significant in the low-responders (r = 0.82, P less than 0.01) but not in the high-responders (r = 0.12, P greater than 0.1). Further, a negative correlation (r = -0.61) is observed between cholesterol synthesis and plasma cholesterol concentration in the low-responders but in the high-responders, there is no relationship between the parameters. From these correlations we conclude that the higher cholesterol absorption in the high-responders than in the low-responders is one important mechanism responsible for the development of severe hypercholesterolemia in the high-responding monkeys fed cholesterol. The results also suggest that there might be a lower sensitivity in the feedback inhibition mechanism of cholesterol biosynthesis in the high-responding than in the low-responding rhesus monkeys.

Hereditary hyperlipidemia in the rabbit due to overproduction of lipoproteins. I. Biochemical studies

An inherited metabolic disorder in a strain of New Zealand White rabbits, characterized by marked hypercholesterolemia (394 +/- 100 mg/dl), with moderately elevated or normal triglyceride levels is described. Low density lipoprotein (LDL), intermediate density lipoprotein (IDL) and very low density lipoprotein (VLDL) cholesterol levels were increased. VLDL and IDL, and to a lesser extent LDL, had increased free cholesterol and esterified cholesterol content, and triglyceride content was reduced. Kinetic studies with 131I and 125I-labelled rabbit lipoproteins showed a marked increase in production rates of VLDL apo B and LDL apo B. LDL cholesterol levels were directly related to LDL apo B production rate (r = 0.938, p less than 0.001). Both in hypercholesterolemic and normal rabbits injected with labelled VLDL, the specific activity-time curves of VLDL apo B and LDL apo B did not intersect, indicating that LDL apo B was in part derived from sources other than VLDL. No defect was demonstrated in receptor-mediated catabolism of LDL by cultured skin fibroblasts from hyperlipidemic animals. The fractional catabolic rate of LDL apo B was subnormal, but increased when the expanded LDL apo B pool size was reduced by exchange transfusion; the low fractional catabolism may therefore be attributable, at least in part, to saturation of LDL receptors consequent upon the increased pool size of LDL. The hyperlipidemia in this strain of rabbits may be unique in that the underlying mechanism appears to be overproduction of VLDL and LDL.

Esterases in inbred strains of mice with differential cholesterolemic responses to a high-cholesterol diet

Specific esterase isoenzyme patterns in plasma may be associated with responsiveness of serum cholesterol to dietary cholesterol. In rabbits and rats the presence and absence of a high-mobility, anodal esterase band on electrophoresis have been shown to be associated with hypo- and hyperresponsiveness, respectively. We fed for 28 days male mice of 7 inbred strains either a low-cholesterol, commercial diet or a diet containing 2% (w/w) cholesterol, 0.5% cholic acid and 5% olive oil. Feeding the high-cholesterol diet revealed marked inter-strain differences in the responses of plasma and liver cholesterol; the increases ranged from 21 to 129% and from 10 to 80-fold, respectively. There was no association between esterase isoenzyme patterns in plasma and the sensitivity to the high-cholesterol diet. The mean baseline plasma total esterase activity tended to be positively associated with the absolute response of plasma cholesterol to the high-cholesterol diet (r = 0.56; n = 7), but the positive relationship between the baseline concentration of the ES-1 component in plasma and the cholesterolemic response was stronger (r = 0.84; n = 7; P less than 0.05). The high-cholesterol diet caused a significant increase in plasma total esterase activities in 6 out of the 7 strains. Evidence is presented that the increase in plasma total esterase activity, which was associated with an increase in the activity and concentration of the so-called ES-2 isoenzyme, is the result of an enhanced release of esterases from the intestine, rather than from the liver. A significant, positive correlation was found between the baseline intestinal esterase activity and the cholesterolemic response after cholesterol feeding (r = 0.83; n = 7; P less than 0.05).

Hypo- and hyperresponders: individual differences in the response of serum cholesterol concentration to changes in diet

The feeding of cholesterol-rich diets to random-bred animals results in marked interindividual differences in the response of serum cholesterol. Certain animals show only small responses (hyporesponders), whereas others develop high degrees of hypercholesterolemia (hyperresponders). Inbred strains of rabbits, rats, and mice differing in their sensitivity to dietary cholesterol are available. In these animals, and also in monkeys, the responsiveness to high-cholesterol diets has a strong genetic basis. The existence of hyper- and hyporesponders also holds in humans, though not as pronounced as in laboratory animals. Repeated trials with the same subjects have shown that persons exist with a consistently low or high response to increased intakes of cholesterol. However, "spontaneous," diet-independent within-person variations in the level of serum cholesterol markedly inflate the between-person variation in the response of serum cholesterol; both variations are of the same order of magnitude. Hypo- and hyperresponsiveness to dietary cholesterol extends to other hypercholesterolemic components of the diet. In humans and rabbits hyperresponsiveness to dietary cholesterol is associated with responsiveness to dietary saturated fatty acids. The mechanisms underlying hypo- and hyperresponsiveness to dietary cholesterol have not yet been unraveled. On the basis of available data, we propose that in hyperresponders, compared with hyporesponders, there is a higher hepatic efflux of cholesterol in low-density lipoproteins (LDL), or its precursors, after cholesterol consumption. This may be caused by insufficient inhibition of cholesterol biosynthesis and/or the high capacity of cholesterol absorption in the hyperresponders. The stimulation of LDL production accounts for the increase in LDL cholesterol in serum. The number of hepatic LDL receptors, which may be already decreased in hyperresponders, will decrease further through down-regulation. The receptor-mediated LDL clearance decreases, but the absolute amount of LDL cholesterol taken up by the cells via the receptor and by the receptor-independent pathway increases because of the increased level of LDL cholesterol. In this way a new equilibrium is reached in which LDL production equals LDL catabolism. The phenomenon of hypo- and hyperresponsiveness may have implications for counseling subjects who attempt to lower their serum cholesterol by diet. However, identification of true hyper- and hyporesponders is greatly hampered by within-person fluctuations of the level of serum cholesterol. No simple test is available to discriminate hypo- from hyperresponders.(ABSTRACT TRUNCATED AT 400 WORDS)

The rate of biliary cholesterol secretion in high- and low-responding rhesus monkeys

The rates of secretion of cholesterol in bile measured by an isotope ratio method were found similar in cholesterol-fed high- and low-responding rhesus monkeys. The results indicate that the failure on the part of the high-responders to increase proportionately the fecal excretion of neutral steroids to compensate for the higher absorption of cholesterol than the low-responders, as suggested earlier, is not due to a difference in the rate of biliary cholesterol secretion but must lie in some other aspect of cholesterol metabolism.

The role of individual differences in lipoprotein, artery wall, gender, and behavioral responses in the development of atherosclerosis

Striking individual differences exist in the response of animals to atherogenic diets. In this communication, we have summarized the accumulated data that relate to a better understanding of this individuality in susceptibility to atherosclerosis. Described herein, are the accumulated data concerning individual differences in the ways in which animals respond to dietary cholesterol. Also contained in this review, are beginning efforts to understand individual differences in susceptibility to coronary artery atherosclerosis at the level of the artery wall ("mesenchymal susceptibility"). We have placed special emphasis on individual differences that exist among cynomolgus macaques in certain psychosocial variables that contribute to individual differences in susceptibility. Among male cynomolgus macaques both status and social condition contribute to these individual differences. Additionally, individual differences in cardiovascular reactivity contribute to varying degrees of atherosclerosis development largely independent of plasma lipid concentrations. Among cynomolgus macaque females, stress-ovarian function relationships have a major influence on the relative degree to which these female animals are protected against diet-induced coronary artery atherosclerosis.

Effects of feeding cholesterol and mixed plant sterols on the fecal excretion of acidic steroids in rhesus monkeys

The effects of feeding diets with high or low amounts of cholesterol and with low or high levels of mixed plant sterols (sitosterol: campesterol: stigmasterol, 60:35:5) on the daily fecal excretion of acidic steroids were studied in rhesus monkeys. During periods of low dietary plant sterol, total fecal acidic steroid excretion was 43% lower (P less than 0.01) during low dietary cholesterol than during high dietary cholesterol. During periods of high dietary plant sterols the fecal acidic steroid excretion was 113% higher (P less than 0.01) with low dietary cholesterol than with high dietary cholesterol. Addition of mixed plant sterols to the low-cholesterol diet produced nearly a 2-fold increase (P less than 0.005) whereas, such an addition to the high cholesterol diet produced a significant decrease by about 53% (P less than 0.025) in the total fecal acidic steroid excretion. The results suggest that the effect of cholesterol feeding on fecal acidic steroid excretion depends on the level of plant sterols in the diet. This interaction of the effects of cholesterol and plant sterols on the fecal acidic steroid excretion is probably related to the inhibitory effect of plant sterols on cholesterol absorption.

Plasma lipoprotein profiles and arylesterase activities in two inbred strains of rabbits with high or low response of plasma cholesterol to dietary cholesterol

Cholesterol feeding for 4 weeks of female and male rabbits of two inbred strains increased plasma cholesterol concentrations by about 11 and 48 mmole/1 in the hypo- and hyperresponsive strain, respectively. On the low-cholesterol pre-experimental diet, the hyporesponsive animals had significantly higher plasma HDL (high density protein) cholesterol levels than hyperresponders. In both strains, cholesterol feeding caused elevations of cholesterol in all lipoprotein classes, the difference between the hypo- and hyperresponsive strains in essence only being observed in the VLDL (very low density lipoprotein) fraction. Basal plasma total arylesterase activity was significantly higher in the hypo- than in the hyperresponsive rabbits. Dietary cholesterol caused an increase in plasma esterase activity in both We suggest that in rabbits a low plasma arylesterase activity and a low concentration of HDL cholesterol are associated with an increased sensitivity to dietary cholesterol.

Variability in individual serum cholesterol response to change in diet

Few systematic data are available on the range of individual blood lipid responsiveness to specific diet changes. Multiple, carefully standardized total serum cholesterol (TC) measurements were made in 58 men under a variety of controlled dietary conditions. Responsiveness was defined for each individual as the change in mean TC per unit change in Diet Score based on the Keys-Minnesota equation. Only 3% were potentially "nonresponders," and even these probably evidenced some response. Of the group, 64% responded within 30% of prediction. We classed 9% as hyporesponders, while in another 9% responsiveness exceeded 1.5 times expectation. We conclude that in metabolically normal individuals the variation in short-term response to dietary change is normally distributed but that nonresponse to diet change is rare. Because metabolic, intrinsic hyporesponsiveness of TC to change in diet composition is uncommon, assessment of the real effectiveness of a dietary regimen in an individual is best based on observed dietary changes. TC changes among individuals under treatment should be based on multiple determinations and interpreted with caution.

Cholesteryl esters in pig liver during atherogenic diets and foreign serum protein infusions

Eight-month-old pigs were fed a diet supplemented with 15% lard (group II) or 15% lard plus 1.5% cholesterol (group III) for 4 months. Five of the animals fed the high fat and cholesterol diet received two i.v. infusions of foreign serum protein (group IV). One group of animals was treated with the same infusions without dietary fat or cholesterol supplement (group V). Liver lipids and serum cholesterol levels were determined. In group II the concentration and fatty acid composition of hepatic cholesteryl esters showed no marked differences from controls (group I). The same findings were present in 2 of 5 animals of group III; in the other 3 animals higher hepatic cholesteryl ester concentrations and predominantly an elevation of monoenoic acid fraction, in one case also a rise of trienoic acid fraction were obtained. These alterations were found in the liver of all animals of group IV. The reverse was observed in the animals which were given the same serum infusions but only the stock diet (group V): a reduction of hepatic cholesteryl ester concentration and no striking alteration in fatty acid pattern. In cryostat sections of all liver specimens no stainable lipid could be detected. There was no correlation between liver and serum fatty acid composition of cholesteryl esters. The total cholesterol levels in serum showed no increase in group V, a slight increase in group II, a moderate increase in group IV, and a marked, partly large increase in group III. These results are discussed in relation to the effect of cholesterol and fat feeding on cholesterol metabolism and essential fatty acid requirement.

Plasma lecithin: cholesterol acyltransferase activity in high- and low-responding rhesus monkeys

The initial rate of esterification of plasma cholesterol by lecithin: cholesterol acyltransferase (LCAT) was measured in high- and low-responding rhesus monkeys fed a moderately high cholesterol (0.15 mg/kcal) diet. The results show that the rate of esterification of cholesterol in the plasma of the high-responders was significantly (p less than 0.025) higher than that of the low-responding animals. In view of known relationships between LCAT activity and plasma lipoprotein metabolism, it is suggested that the lipoprotein metabolism in the high-responders would differ from that in the low-responders.

Genetic and physiological aspects of cholesterol accumulation in hyperresponding and hyporesponding rabbits

After a 5 week period of feeding a cholesterol-rich diet to rabbits, hyperresponders with high plasma cholesterol levels and hyporesponders with low plasma cholesterol levels could be distinguished from normal responders. The response was found to be correlated with the esterase genotype at the Est-2 locus. The increase in total body cholesterol was higher in hyper-than in hyporesponders. In both groups most of the accumulated dietary cholesterol was found in plasma and liver. Adrenal weight and plasma corticosterone levels were more increased in hyper- than in hyporesponders. The cholesterol-rich diet resulted in an augmentation of liver lipase and lipoprotein lipase activities. These lipolytic activities were more increased in hyper- than in the hyporesponders.

Diet and sire effects on serum cholesterol and cholesterol absorption in infant baboons (Papio cynocephalus)

One hundred three baboon infants, the progeny of an equal number of dams and seven sires, were breast fed or were fed prepared formulas containing 1.2, 29, or 61 mg/dl cholesterol for 14 weeks. We measured serum cholesterol and triglyceride concentrations at birth and at 3-week intervals, and cholesterol absorption at 12 weeks. Dietary cholesterol had a significant effect on serum cholesterol concentration at 12 weeks and on cholesterol absorption, but did not affect weight or serum triglyceride concentration. Sire had a significant effect on serum cholesterol concentration at birth and at 12 weeks, but the effect at birth did not predict the effect at 12 weeks. Sire did not affect cholesterol absorption, serum triglyceride concentration, or weight at 12 weeks. The sire effect on serum cholesterol concentration in infancy is not mediated by control of cholesterol absorption. Males weighed more than females at 12 weeks, but sex did not affect serum cholesterol concentration, triglyceride concentration, or cholesterol absorption.

In vitro regulation of cholesterol metabolism by low density lipoproteins in skin fibroblasts from hypo-and hyperresponding squirrel monkeys

When squirrel monkeys (Saimiri sciureus) are fed diets containing cholesterol, some individuals (hyperresponders) become hypercholesterolemic, while others (hyporesponders) are able to maintain nearly normal plasma cholesterol concentrations. Skin fibroblasts were grown from three hyperresponder and threehyporesponder squirrel monkeys, previously characterized on the basis of their plasma cholesterol response to two cholesterol-containing diets and the pheno-type of their parents. The rates of cholesterol synthesis and esterification were determined in the cultured fibroblasts incubated with low density lipoproteins isolated from normocholesterolemic squirrel monkeys or hypercholesterolemic rhesus monkeys. Both lipoprotein preparations influenced the metabolic parameters measured in a similar manner in cells from both hypo- and hyperresponder animals. Exposure of skin fibroblasts to low density lipoproteins resultd in a stimulation of cholesterol esterification and a suppression of cholesterol synthesis in cells from both hypo- and hyperresponder animals. When incubated with increasing concentrations of low density lipoprotein cholesterol, up to 50 microgram/ml, fibroblasts from both hypo-and hyperresponding animals responded with a similar maximum percentage suppression of sterol synthesis. Thus, hyperresponsiveness to dietary cholesterol in squirrel monkeys, although a heritable characteristic, is not associated with an inability of low density lipoprotein to suppress cholesterol synthesis or stimulate cholesterol esterification as occurs in familial hypercholesterolemia in man.