Adipose tissue mass and location affect circulating adiponectin levels.

AIMS/HYPOTHESIS: Plasma levels of adiponectin are inversely associated with body mass. We hypothesised that adipose tissue distribution and body composition influences adiponectin levels. METHODS: We assessed plasma adiponectin concentrations and dual-energy X-ray absorptiometry (DEXA) measurements of body composition among 2,820 participants from the Dallas Heart Study. RESULTS: Among both women and men, adiponectin levels were higher in whites than in either Hispanics or African-Americans (for women: median 9.99 µg/ml [25th,75th percentile 7.11, 13.77] vs 7.56 µg/ml [5.05, 9.98] vs 6.39 µg/ml [4.37, 9.41], respectively, p < 0.0001; for men: 6.43 µg/ml [4.66, 9.19] vs 5.55 µg/ml [3.64, 7.50] vs 5.03 µg/ml [3.39, 7.28], p < 0.0001). In univariate analysis, each individual component of body mass was inversely associated with adiponectin. After multivariate analysis, adiponectin levels were found to be positively associated with lower extremity fat, whether expressed in absolute mass (for women: ß = 0.055, p < 0.0001; for men: ß = 0.061, p < 0.0001), or as a relative proportion (for women: ß = 0.035, p < 0.0001; for men: ß = 0.034, p < 0.0001). This association was consistent across ethnicities. Conversely, adiponectin was negatively correlated with truncal fat, both in absolute (for women: ß = -0.039, p < 0.0001; for men: ß = -0.044, p < 0.0001) and relative terms (for women: ß = -0.027, p < 0.0001; for men ß = -0.033, p < 0.0001). At the extreme of body mass, higher degrees of lower extremity and truncal adiposity were associated with higher levels of adiponectin. CONCLUSIONS/INTERPRETATION: These data suggest that the location of adipose depots differentially influences circulating adiponectin concentrations-a finding observed across ethnicity and sex. Gross measures of body mass alone do not adequately account for adiponectin levels. This supports a role of adiponectin as a mediator of the positive effects of lower extremity adiposity on improvements in insulin sensitivity.

The influence of age and body mass index on the metabolic syndrome and its components.

OBJECTIVE: The aim of this study was to evaluate the influence of ageing and body mass index (BMI) on the revised National Cholesterol Education Program (NCEP)-defined metabolic syndrome, its components, diabetes and coronary heart disease prevalence using the Third National Health and Nutrition Examination Survey. METHODS: Data from adults aged 20 and older who received morning physical examinations after a fast of at least 9 h (n = 7959), representing 196.8 million Americans were used in this analysis. The population was stratified by age deciles and BMI categories using standard definitions of overweight and obesity. Due to small sample size, those few individuals with BMI <18.5 were excluded. RESULTS: Fasting glucose, diabetes and systolic blood pressure (SBP) seem to have a linear relationship with age and BMI, that is, increasing BMI seems to linearly reduce the age decile when the mean exceeds the NCEP cutpoint. Regardless of BMI, the prevalence of diabetes and hypertension increases with age. Triglyceride levels and prevalence of metabolic syndrome follow a pattern that is less linear. Fasting insulin and C-reactive protein (CRP) levels correlate better with BMI than age. Diastolic BP and HDL cholesterol for men and women (analysed separately) did not correlate with either age or BMI. CONCLUSION: For each component of the metabolic syndrome and associated factors, there is a complex interaction between ageing and obesity. Some components are associated with obesity but not ageing (e.g. CRP), while others are associated with both obesity and ageing (e.g. glucose). Even when the association exists, the specific relationship can appear to be more (e.g. SBP) or less (e.g. triglycerides) linear.

Expression of anti-Müllerian hormone (AMH) in the equine testis.

Anti-Müllerian hormone (AMH) induces regression of Müllerian ducts during male fetal development; in the human male, it is expressed in Sertoli cells during fetal development (and through puberty). The objective was to characterize expression of AMH in the fetal, neonatal, prepubertal, and adult equine testis, as well as in equine cryptorchid testes, in select testicular neoplasms, and in intersex gonads, based upon immunohistochemistry (IHC). Testes were removed from equine fetuses at 5.5, 10, and 11 months of gestation, at 12 months of age, and from adult stallions. In addition, cryptorchid testes, testis tumors (teratomas, seminomas, Sertoli cell tumors), and male intersex gonads were examined by IHC for expression of AMH using a goat polyclonal primary antibody (alpha-AMH) directed against a C-terminal peptide antigen from human AMH. Immunolabeling with alpha-AMH was localized to Sertoli cells within the developing seminiferous tubules of fetal, neonatal and prepubertal equine testes, with no expression detected in Sertoli cells from normal adult equine testes. Furthermore, expression was detected in cryptorchid testes (in animals up to 3-4 years of age) and in Sertoli cell tumors and male intersex gonads. In conclusion, AMH was strongly expressed by Sertoli cells in fetal, neonatal and prepubertal equine testes, but not in normal adult testes. That AMH was expressed in cryptorchid testes may provide a useful biomarker for detection of cryptorchid testes, as well as for immunohistochemical characterization of testicular tumors and intersex gonads in the horse.

Expression of anti-Müllerian hormone (AMH) in equine granulosa-cell tumors and in normal equine ovaries.

Anti-Müllerian hormone (AMH), also known as Müllerian inhibiting substance (MIS), is expressed by granulosa cells in females of many mammalian species, and circulating AMH concentrations have been used to monitor granulosa-cell tumors (GCT) in women. The objective was to characterize expression of AMH in equine GCT, and in normal equine ovaries, based upon immunohistochemistry (IHC), using a polyclonal primary antibody directed against human AMH. Equine GCT (n=27) and normal equine ovaries (n=10) were examined by IHC. In addition, sera from four mares with GCT were characterized for AMH bioactivity, based upon suppression of Müllerian duct development in the fetal rat. Immunolabeling with alpha-AMH was localized to granulosa cells in equine GCT, as well as within antral follicles in normal ovaries. Expression of AMH first appeared in granulosa cells of small growing follicles and was most intense in small antral follicles; large antral or atretic follicles had reduced immunolabeling. Omission of the primary antibody or incubation of the primary antibody with the corresponding blocking peptide eliminated immunolabeling of granulosa cells in GCT and in normal antral follicles, confirming the specificity of the immunolabel. Sera from mares with GCT had increased AMH bioactivity compared to control sera. In conclusion, AMH was strongly expressed by granulosa cells in equine GCT and in normal antral follicles. Therefore, anti-Müllerian hormone may be a useful biomarker for detection of GCT in the horse.

Effects of polyunsaturated fats on lipid metabolism in patients with hypertriglyceridemia.

Studies were carried out on the effects of polyunsaturated fats on lipid metabolism in 11 patients with hypertriglyceridemia. During cholesterol balance studies performed in eight patients, the feeding of polyunsaturated fats, as compared with saturated fats, caused an increased excretion of endogenous neutral steroids, acidic steroids, or both in most patients. Increases in steroid excretions were marked in some patients and generally exceeded the decrement of cholesterol in the plasma compartment. The finding of a greater excretion of fecal steroids on polyunsaturated fats in hypertriglyceridemic patients contrasts to the lack of change in sterol balance previously reported for patients with familial hypercholesterolemia; however, other workers have found that polyunsaturated fats also enhance steroid excretion in normal subjects. In most of the patients, simultaneous studies were carried out on biliary lipid composition, hourly outputs of biliary lipids, and pool sizes of bile acids. In several but not all patients, fasting gallbladder bile became more lithogenic after institution of polyunsaturated fats. This increased lithogenicity was not due to a decrease in bile acid pools; in no case was the pool decreased by polyunsaturated fats. On the other hand, two patients showed an increased output of biliary cholesterol, and frequently there was an increase in fecal neutral steroids that were derived from cholesterol; thus, polyunsaturated fats may increase bile lithogenicity in some patients through mobilization of cholesterol into bile. Reductions in plasma cholesterol during the feeding of polyunsaturated fats was seen in most patients, and these changes were usually associated with a decrease in concentration of plasma triglycerides. In fact, the degree of cholesterol lowering was closely correlated with the extent of triglyceride reduction. Therefore, in hypertriglyceridimec patients polyunsaturated fats may contribute to cholesterol reduction by changing the metabolism of triglycerides or very low density lipoproteins. The findings of changes in the metabolism of cholesterol, bile acids, and triglycerides in the patients of this study suggests that polyunsaturated fats may cause a lowering of cholesterol through multiple mechanisms, and it seems unlikely that a single action can explain all the effects of these fats on the plasma lipids.

Effects of obesity and caloric intake on biliary lipid metabolism in man.

The effects of obesity and caloric intake on biliary lipid metabolism were investigated in a series of related studies. The degree of saturation of gallbladder bile with cholesterol was found to be significantly higher in a group of 23 obese healthy subjects than in a group of 23 nonobese controls matched for age, sex, and race. Bile was also significantly more saturated in 11 obese subjects before than after weight reduction. To determine whether supersaturated bile in obesity is due to excessive secretion of cholesterol or to deficient secretion of bile acids and phospholipids, the hepatic outputs of these three lipids were measured during constant duodenal infusion of formula in the same 11 subjects before and after weight reduction. Weight reduction resulted in significant reduction of cholesterol output but not of bile acid or phospholipid output. Moreover, very obese subjects were found to have cholesterol secretion rates markedly higher than less obese subjects previously studied by the same method. In obese subjects, bile was supersaturated with cholesterol despite increased bile acid pool sizes and increased secretion rates of bile acids and phospholipids. Supersaturated bile in the obese could therefore be attributed to a single defect in lipid secretion, namely, an excessive output of cholesterol. To determine whether the rate of caloric intake can account for the effects of obesity on biliary lipid composition and secretion, nine obese white men were studied on a weight maintenance diet and then during weight reduction on a 1,000 cal diet. As compared to weight maintenance, chronic caloric restriction resulted in reduced outputs of cholesterol, bile acids, and phospholipids, reduced bile acid pool size, and reduced synthesis and fecal excretion of cholesterol. Saturation of bile with cholesterol did not decrease during weight reduction, evidently because of the mobilization of cholesterol from adipose stores and the marked reduction in bile acid and phospholipid output observed during chronic caloric restriction. Acute alterations in caloric infusion rates did not fully reproduce the effects of chronic administration of high and low calorie diets. Likewise, chronic intake of hypercaloric diets by nonobese subjects did not reproduce the cholesterol hypersecretion characteristic of the obese. Thus, increased cholesterol secretion in obese subjects could not be fully explained by the amount of calories they ingested to maintain stable weight. It is concluded that obesity is characterized by excessive hepatic secretion of cholesterol which results in supersaturated bile.

Preservation of the endogenous antioxidants in low density lipoprotein by ascorbate but not probucol during oxidative modification.

Several lines of evidence indicate that the oxidative modification of low density lipoproteins (LDL) may provide an important link between plasma LDL and the genesis of the atherosclerotic lesion. Ascorbate is an important water-soluble, chain-breaking antioxidant in humans. Probucol, a lipid-soluble antioxidant drug has been shown to retard the progression of atherosclerosis. The aim of the present study was to compare the effects of probucol and physiologic levels of ascorbate on the oxidative modification of LDL in both a cell-free (2.5 microM Cu++ in phosphate-buffered saline) and cellular system (human monocyte macrophages in Ham's F-10 medium). Both ascorbate and probucol inhibited the oxidative modification of LDL in both systems to a similar degree as evidenced by the thiobarbituric acid-reacting substance activity, electrophoretic mobility, and degradation by macrophages. However, whereas co-incubation with physiologic levels of ascorbate resulted in a substantial preservation of the alpha-tocopherol, gamma-tocopherol, and beta-carotene of the LDL, probucol in concentrations ranging from 10 to 80 microM failed to protect these antioxidants. Thus, in addition to being as potent as probucol in inhibiting the oxidation of LDL, ascorbate in contrast preserves the endogenous antioxidants in the LDL.

Significance of low density lipoprotein production in the regulations of plasma cholesterol level in man.

To determine whether production or catabolism of low density lipoprotein (LDL) is the major factor controlling LDL concentrations in subjects with plasma cholesterol levels from low-normal to mildly elevated, measurements of apoprotein of LDL (apoLDL) turnover were performed in 16 patients with various plasma cholesterol concentrations. Cholesterol balance studies were done simultaneously in 13 of these patients. Plasma concentrations of apoLDL and LDL-cholesterol were positively correlated with synthetic rates of apoLDL (r = 0.74, P less than 0.001; r = 0.50, P less than 0.05, respectively). No correlation was noted between the fractional catabolic rate for apoLDL and apoLDL levels (or LDL-cholesterol). For further analysis, the patients were divided into three groups with stepwise increases in apoLDL concentrations. When apoLDL levels rose significantly, from 83 +/- 5 SEM to 122 +/- 2 to 149 +/- 5 mg/dl, synthetic rates for apoLDL also increased significantly from 11.6 +/- 12. to 17.0 +/- 0.9 to 23.8 +/- 1.8 mg/d/kg ideal weight. In contrast, the fractional catabolic rate of apoLDL was not different among the three groups (0.32 +/- 0.03 vs. 0.29 +/- 0.02 vs. 0.33 +/- 0.03/d). No relation was noted between synthesis of total body cholesterol (or bile acids) and concentrations, production rates, or removal of apoLDL. Thus, concentrations of apoLDL and LDL-cholesterol in these subjects with plasma cholesterol levels from low-normal to mildly elevated were regulated mainly by synthetic rates of apoLDL and not by LDL catabolism.

In vivo evidence for reduced binding of low density lipoproteins to receptors as a cause of primary moderate hypercholesterolemia.

The causes of primary moderate hypercholesterolemia are not understood, but some patients have reduced fractional clearance rates (FCRs) for low density lipoproteins (LDL). This could be due to either decreased activity of LDL receptors or to a defect in structure (or composition) of LDL that reduces its affinity for receptors. To distinguish between these causes, simultaneous turnover rates of autologous and normal homologous LDL were determined in 15 patients with primary moderate hypercholesterolemia. In 10, turnover rates of both types of LDL were indistinguishable, which indicated that autologous LDL was cleared as efficiently as normal homologous LDL. In five others, FCRs for autologous LDL were significantly lower than for homologous LDL. Two of the latter five were treated with mevinolin, and although FCRs for both types of LDL rose during treatment, differences in FCRs between the two types of LDL persisted. In these five patients, autologous LDL appeared to be a poor ligand for LDL receptors.

The metabolism of cholestanol, cholesterol, and bile acids in cerebrotendinous xanthomatosis.

The metabolism of cholesterol and its 5-dihydro derivative, cholestanol, was investigated by means of sterol balance and isotope kinetic techniques in 3 subjects with cerebrotendinous xanthomatosis (CTX) and 11 other individuals. All subjects were hospitalized on a metabolic ward and were fed diets practically free of cholesterol and cholestanol. After the intravenous administration of [1,2-(3)H]cholestanol, the radioactive sterol was transported and esterified in plasma lipoproteins in an identical manner to cholesterol. In these short-term experiments, the specific activity-time curves of plasma cholestanol conformed to two-pool models in both the CTX and control groups. However, cholestanol plasma concentrations, total body miscible pools, and daily synthesis rates were two to five times greater in the CTX than control individuals. The short-term specific activity decay curves of plasma [4-(14)C]cholesterol also conformed to two-pool models in both groups. However, in the CTX subjects the decay was more rapid, and daily cholesterol synthesis was nearly double that of the control subjects. Plasma concentrations and the sizes of the rapidly turning over pool of exchangeable cholesterol were apparently small in the CTX subjects, and these measurements did not correlate with the large cholesterol deposits found in tendon and tuberous xanthomas. Despite active cholesterol synthesis, bile acid formation was subnormal in the CTX subjects. However, bile acid sequestration was accompanied by a rise in plasma cholestanol levels and greatly augmented fecal cholestanol outputs. In contrast, the administration of clofibrate lowered plasma cholesterol levels 50% and presumably reduced synthesis in the CTX subjects. Plasma cholesterol concentrations and fecal steroid excretion did not change significantly during this therapy. These findings indicate that the excessive tissue deposits of cholesterol and cholestanol that characterize CTX were associated with hyperactive neutral sterol synthesis. The demonstration of subnormal bile acid formation suggests that defective bile acid synthesis may predispose to the neutral sterol abnormalities.

The effects of unsaturated dietary fats on absorption, excretion, synthesis, and distribution of cholesterol in man.

Cholesterol balance studies were carried out in 11 patients with various types of hyperlipoproteinemia to determine the mechanism by which unsaturated fats lower plasma cholesterol. Unsaturated fats produced no increase in fecal endogenous neutral steroids in 10 of 11 patients and no decrease in absorption of exogenous cholesterol in 5 patients who received cholesterol in the diet. In 8 of 11 patients no changes occurred in excretion of bile acids during the period on unsaturated fat when plasma cholesterol was declining. However, in 3 of 11 patients small but significant increases in bile acid excretion were found during this transitional period; in 2 others increases also occurred after plasma cholesterol had become constant at lower levels on unsaturated fat.Since the majority of patients showed no change in cholesterol or bile acid excretions during the transitional period, we propose that when excretion changes did occur they were probably not the cause of the plasma cholesterol change. Furthermore, turnover data and specific activity curves suggested that cholesterol synthesis was not influenced by exchange of dietary fats. Thus, excluding changes in excretion and synthesis, we conclude that it is most likely that unsaturated fats cause plasma cholesterol to be redistributed into tissue pools. We have also examined the possibility that cholesterol which is redistributed into tissues could be secondarily excreted as neutral steroids or bile acids. In at least 5 of 11 patients excretion patterns were consistent with this explanation. However, we cannot rule out that excretion changes may have been due to alterations in transit time, to changes in bacterial flora, or to transitory changes in absorption or synthesis of cholesterol or bile acids. Our conclusion that unsaturated fats cause a redistribution of cholesterol between plasma and tissue pools points to the necessity in future to explore where cholesterol is stored, to what extent stored cholesterol can be mobilized, and to define the factors governing these fluxes.

Metabolic studies in familial hypercholesterolemia. Evidence for a gene-dosage effect in vivo.

To investigate the gene-dosage effect in familial hypercholesterolemia (FH), metabolic studies were conducted in a group of well-characterized patients with either heterozygous (n = 7) or homozygous (n = 7) FH and the results were compared to those obtained in normal subjects (n = 6). The turnover of (125)I-labeled low-density lipoprotein (LDL) was measured in all of the normals, all but one of the FH heterozygotes, and in all of the homozygotes. Chemical cholesterol balance was performed simultaneously with the (125)I-LDL turnover in all seven of the homozygotes. With regard to (125)I-LDL turnover, FH homozygotes, who possess two doses of the mutant FH gene, exhibited a threefold increase in the rate of apoLDL synthesis while the fractional catabolic rate (FCR) for the apoprotein was only about one-third of normal. Heterozygotes, who have only one dose of the mutant FH gene, exhibited intermediate values for both parameters; that is, the FCR was two-thirds of normal and the apoLDL synthetic rate was 1.7-fold greater than normal. THE DATA INDICATE THAT THE SINGLE GENE DEFECT IN FH PRODUCES TWO DISTINCT ABNORMALITIES OF LDL METABOLISM: (a) an increase in the synthetic rate for apoLDL and (b) a decrease in the efficiency of apoLDL catabolism. Both defects are more severe in FH homozygotes than in heterozygotes. The FCR for apoLDL in the homozygotes appeared to be fixed at congruent with 17%/d whereas the plasma LDL level varied about twofold. These findings suggest that the twofold variation in plasma LDL levels observed in these seven patients is caused by variation in the plasma apoLDL synthetic rates. Consistent with this conclusion was the finding that the correlation between the plasma LDL level and the apoLDL synthetic rates in the seven FH homozygotes was 0.943. The rate of total body cholesterol synthesis determined by chemical cholesterol balance did not appear to clearly differ between normals and patients with either one or two mutant FH genes. Two of the youngest FH homozygotes exhibited cholesterol overproduction but the other five did not. No consistent abnormality of bile acid metabolism was observed in these patients. Because the daily plasma flux of cholesterol on LDL is about threefold greater than the amount of cholesterol produced per day, a significant amount of the cholesterol liberated from LDL degradation must be reused.

Comparisons of metabolism of apolipoprotein B in normal subjects, obese patients, and patients with coronary heart disease.

This study was designed to examine the integrated metabolism of apolipoprotein B (apo B) in very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), and low density lipoproteins (LDL) in normal subjects, obese patients, and a group of patients with coronary heart disease (CHD). Turnover rates of 131I-VLDL-B, 131I-IDL-B, 125I-LDL-B, and [3H]VLDL-triglycerides (TG) were determined by the multicompartmental analysis that used the model described in the preceding article (Beltz, W.F., et al. 1985. J. Clin. Invest. 76: 575-585). Compared with five normal subjects, four obese subjects had increased synthesis rates of both VLDL-B and VLDL-TG. Production of LDL-B was inconsistently raised in these same patients. Five patients with CHD had enhanced production of both VLDL-B and LDL-B, but secretion rates of VLDL-TG were not increased. Thus, in patients with obesity and in those with CHD, synthesis rates of VLDL particles may be abnormally high. In the obese patients, the VLDL appeared to be of normal composition, but in patients with CHD, the VLDL were relatively poor in TG. The study also showed that a significant fraction of VLDL-B is removed directly from the circulation and never reaches LDL regardless of the type of patients. The fraction that does reach LDL is one factor that determines LDL concentrations.

The effects of chenodiol on biliary lipids and their association with gallstone dissolution in the National Cooperative Gallstone Study (NCGS).

The National Cooperative Gallstone Study was a double-masked trial conducted to determine the efficacy and safety of chenodeoxycholic acid (chenodiol) for dissolution of cholesterol gallstones. Patients with radiolucent gallstones were randomly allocated to either a high dose (750 mg/d, n = 305) or low dose (375 mg/d, n = 306) of chenodiol or placebo (n = 305) administered for 2 yr. Specimens of gallbladder bile were obtained for biliary lipid analysis on 50% of all white obtained for biliary lipid analysis on 50% of all white patients at base line and after 3-mo therapy, on 45% at 12 mo, and on 36% at 24 mo. Among these specimens, 20% were inadequate for analysis. For analysis of data, available values during therapy were averaged up to time of dissolution, study exit, or study termination. In the high-dose group, percent chenodiol (molar percent of all bile acids) increased markedly and remained high during the 2 yr of follow-up. Also, molar percent cholesterol decreased significantly and remained low during the 2 yr of follow-up. In the low-dose group, percent chenodiol increased and remained significantly increased. Percent cholesterol saturation decreased at 3 mo, but at 24 mo it was not different from that in the placebo group, suggesting a physiological adaptation to the low dose by 2 yr. 79% of patients on high dose had greater than 70% chenodiol. Among these, half showed unsaturated bile (less than 100% cholesterol saturation) while the remainder were supersaturated; in the former group with unsaturated bile, 23% had complete dissolution and 51% had partial (greater than 50% reduction in stone size) or complete dissolution. In contrast, those with over 70% chenodiol and supersaturated bile had only 5% complete dissolution. Thus, development of unsaturated bile was a major factor associated with gallstone dissolution. The data also indicate that values for percent cholesterol saturation were a better predictor of gallstone dissolution than molar percent chenodiol, although a high percent chenodiol usually was required to obtain unsaturation.

Cholesterol distribution in the bulk tissues of man: variation with age.

Lacking reliable data on cholesterol concentrations in muscle, adipose tissue, skin, and connective tissues (i.e., the "bulk tissues") in "normal" man, we have completed these analyses in 21 men and 8 women who died suddenly and unexpectedly; their ages ranged from 23 to 78 yr. In 11 of these subjects aged 20-40 yr, the mean cholesterol concentrations ranged from 180-440 mg/100 g dry tissue. In contrast, in 13 subjects aged 60-80 yr the values were 23-28% higher in muscle, adipose, and skin, while in dura mater, biceps, and psoas tendons the concentrations were 130, 260, and 460% higher (respectively). Esterified cholesterol in these connective tissues was found to be the major contributor, increasing 5- to 10-fold in the older group as opposed to a less than 5-fold rise in free cholesterol. In view of the large proportion of total body weight represented by these tissues, it is clear that large amounts of cholesterol can be accumulated there over a lifetime; indeed, the dense connective tissues appear to act uniquely as a trap for cholesterol, especially in the esterified form. Whether analyses of tendinous tissues in man, accessible during life, mirror the pattern of cholesterol deposition in arterial connective tissue remains to be determined.

Mechanisms of lithogenic bile formation in American Indian women with cholesterol gallstones.

Hepatic secretions of biliary lipids were estimated in 43 patients with and without cholesterol gallstones. Studies were carried out by a marker dilution technique employing duodenal intubation with a three-lumen tube. Hourly secretion rates of cholesterol, bile acids, and phospholipids were determined during constant infusion with liquid formula. In 17 American Indian women with gallstones, hourly outputs of biliary bile acids were significantly less than those in 7 Indian men and 12 Caucasian women without gallstones. These findings suggest that a decreased hepatic secretion of bile acids contributes significantly to the production of a lithogenic bile in Indian women. However, in Indian women with gallstones, secretion of biliary cholesterol was also significantly increased, as compared with Caucasian women without stones. Therefore, lithogenic bile in Indian women was, in most cases, due to a combined decrease in bile acid output and increase in cholesterol secretion. In an attempt to determine the mechanisms for these abnormalities, cholesterol balance studies were done in Indian women with gallstones and normal Indian men. Balance data were compared with results reported previously in non-Indian patients studied by the same techniques, and in general, Indian women showed a slight increase in fecal excretion of bile acids. Since bile acids in the enterohepatic circulation were relatively depleted in Indian women, these patients had a reduced fractional reabsorption. However, previous studies have shown that Caucasians can rapidly replenish bile acid pools in the presence of much greater intestinal losses, and it is suggested that among Indian women with gallstones, reduced secretion rates of bile acids are primarily the result of defective homeostatic regulation of bile acid synthesis. In Indian women with gallstones, at least two factors may have contributed to an increased availability of cholesterol in the liver for secretion into bile. First, cholesterol was inadequately converted into bile acids, and secondly, an increased amount of cholesterol was synthesized, as shown by the balance technique. This enhanced production of cholesterol can partially be explained by obesity, but other factors may also play a role.

Metabolism of beta-sitosterol in man.

The metabolism of beta-sitosterol was compared to that of cholesterol in 12 patients. Sterol balance methods were supplemented by radiosterol studies, with the following results. (a) Plasma concentrations of beta-sitosterol ranged from 0.30 to 1.02 mg/100 ml plasma in patients on intakes of beta-sitosterol typical of the American diet. Plasma levels were raised little when intakes were increased greatly, and on fixed intakes they were constant from week to week. On diets devoid of plant sterols, the plasma and feces rapidly became free of beta-sitosterol. (b) The percentage of esterified beta-sitosterol in the plasma was the same as for cholesterol. However, the rate of esterification of beta-sitosterol was slower than that for cholesterol. (c) Specific activity-time curves after simultaneous pulse labeling with beta-sitosterol-(3)H and cholesterol-(14)C conformed to two-pool models. The two exponential half-lives of beta-sitosterol were much shorter than for cholesterol, and pool sizes were much smaller. Values of turnover for beta-sitosterol obtained by the sterol balance method agreed closely with those derived by use of the two-pool model. There was no endogenous synthesis of beta-sitosterol in the patients studied; hence, daily turnover of beta-sitosterol equaled its daily absorption. Absorption of beta-sitosterol was 5% (or less) of daily intake, while cholesterol absorption ranged from 45 to 54% of intake. (d) About 20% of the absorbed beta-sitosterol was converted to cholic and chenodeoxycholic acids. The remainder was excreted in bile as free sterol; this excretion was more rapid than that of cholesterol. (e) The employment of beta-sitosterol as an internal standard to correct for losses of cholesterol in sterol balance studies is further validated by the results presented here.

Reduction in cholesterol and low density lipoprotein synthesis after portacaval shunt surgery in a patient with homozygous familial hypercholesterolemia.

The turnover of 125I-labeled low density lipoprotein (LDL) and the total body balance of cholestrol were studied in a 6-yr-old girl with the homozygous form of familial hypercholesterolemia (FH) before and after the surgical creation of an end-to-side portacaval shunt. The results were compared with those of similar studies simultaneously performed in untreated patients with the heterozygous form of FH and with the results of earlier studies performed on normolipidemic subjects. Before shunt surgery, the rate of synthesis of LDL in the FH homozygote (mg/kg per day) was fourfold higher than in normolipidemic subjects and twofold higher than in her heterozygous mother. The fractional catabolic rate for LDL in the homozygote was decreased to 33% of normal control values. The rate of cholesterol synthesis, estimated by chemical sterol balance, was higher in the FH homozygote than in two FH heterozygotes of similar age studied simultaneously. When considered in relation to the markedly elevated level of plasma cholesterol, the observed rate of cholesterol synthesis in the FH homozygote was inappropriately elevated. Bile acid production was normal in all three children. 5 mo after shunt surgery, the rate of LDL synthesis in the homozygote had declined by 48% as compared with the preoperative value, and this caused a 39% drop in the plasma LDL cholesterol level despite a 17% reduction in the fractional catabolic rate of the lipoprotein. The rate of cholesterol synthesis fell by 62% as compared with the preoperative value. The findings of an inappropriately elevated rate of production of both cholesterol and LDL as well as a reduced fractional catabolic rate for the lipoprotein in the untreated FH homozygote are consistent with results of studies in cultured fibroblasts indicating that the primary genetic defect in FH involves a deficiency in a cell-surface receptor for LDL that regulates both cholesterol synthesis and LDL degradation. Although the mechanism for the decline in production of cholesterol and LDL after portacaval shunt surgery is unknown, it was observed that these changes were associated with marked increases in the plasma concentrations of bile acids and glucagon.

Elevated cholesterol and bile acid synthesis in a young patient with homozygous familial hypercholesterolemia.

Cholesterol balance studies were carried out twice in a young male patient with homozygous familial hypercholesterolemia. At 13 mo, cholesterol balance in this patient averaged 31.3 mg/kg per d, and bile acid excretion was 12.0 mg/kg per d; at 3 yr, results were similar, 27.3 and 15.5 mg/kg per d for cholesterol balance and bile acids, respectively. A normal boy of 3 yr was also studied for comparison with the second study in our patient. Cholesterol balance and bile acid outputs in the normal child were 11.5 and 3.3 mg/kg per d, respectively. Thus, in comparison with the normal child, the patient with homozygous familial hypercholesterolemia had a marked increase in synthesis of cholesterol and bile acids. Although synthesis of bile acids was high in this patient, the fraction of newly synthesized cholesterol converted into bile acids (40-56%) was in the normal range; this suggests that the enhanced output of bile acids was secondary to an increased synthesis of cholesterol and not to malabsorption of bile acids, which likely would have produced a higher fractional conversion. Although our patient has been studied at a younger age than any reported in the literature, two similar children 5 and 6 yr of age were also observed to have elevated cholesterol synthesis. This finding contrasts with those in older children with the homozygous as well as heterozygous forms of this disease who appear to have normal synthesis of cholesterol and bile acids. Therefore, increased synthesis of cholesterol seems to be characteristic of early homozygous familial hypercholesterolemia, and may be a manifestation of a loss of feedback inhibition of cholesterol synthesis secondary to an absence of specific cell-surface receptors for low density lipoproteins. However, as children with this disease grow older, other mechanisms may come into play to restore cholesterol synthesis to normal levels.

Kinetic model for production and metabolism of very low density lipoprotein triglycerides. Evidence for a slow production pathway and results for normolipidemic subjects.

A model for the synthesis and degradation of very low density lipoprotein triglyceride (VLDL-TG) in man is proposed to explain plasma VLDL-TG radioactivity data from studies conducted over a 48-h interval after injection of glycerol labeled with 14C, 3H, or both. The curve describing the radioactivity of plasma VLDL triglycerides reaches a maximum at about 2 h, after which the decay is biphasic in all cases; the late curvature becoming evident only after 8--12 h. To fit the complex curve, it was necessary to postulate two pathways for the incorporation of plasma glycerol into VLDL-TG, one much slower than the other. A process of stepwise delipidation of VLDL in the plasma compartment, previously proposed for VLDL apoprotein models, was also necessary. Predicted VLDL-TG synthesis rates calculated with this model can differ significantly from those based on experiments of shorter duration in which the slow VLDL-TG component is not apparent. The results of these studies strongly support the interpretation that the late, slow component of the VLDL-TG activity curve is predominantly due to the slowly turning-over precursor compartment in the conversion pathway and is not due either to a slow compartment in the labeled precursor, plasma free glycerol, or to an exchange of plasma VLDL-TG with an extravascular compartment. It also cannot, in these studies, be attributed to a slowly turning-over VLDL-TG moiety in the plasma. The model was tested with data from 59 studies including normal subjects and patients with obesity and(or) various forms of hyperlipoproteinemia. Good fits were obtained in all cases, and the estimated parameter values and their uncertainties for 13 normolipemic nonobese subjects are presented. Sensitivty testing was carried out to determine how critical various parameter estimations are to the assumptions introduced in the modeling.