Lethal atherosclerosis associated with abnormal plasma and tissue sterol composition in sitosterolemia with xanthomatosis

Tissue sterol composition was determined in an 18-year-old male with sitosterolemia with xanthomatosis who died suddenly and whose coronary and aortic vessels showed extensive atherosclerosis and, for comparison, in an 18-year-old male with minimal atherosclerosis who died accidently. Sterols in the control tissues (plasma, erythrocytes, cardiac muscle, lung, liver, aorta, and brain) contained cholesterol with only trace amounts of cholestanol. In contrast, sterols in corresponding tissues of the sitosterolemic subject (except brain) were composed of cholesterol, increased amounts of plant sterols, campesterol and sitosterol, and 5 alpha-saturated stanols, cholestanol, 5 alpha-campestanol, and 5 alpha-sitostanol, that were deposited in approximately the same ratio as present in plasma. However, sitosterolemic brain sterol composition resembled that of the control brain with cholesterol and only trace amounts (less than 1%) of cholestanol and phytosterols. The sitosterolemic aorta was extensively atherosclerotic and contained more than twice the quantity of sterols as the control aorta (5.6 mg/g versus 2.6 mg/g) with increased amounts of cholesterol, plant sterols, and 5 alpha-saturated stanols. These results indicate that cholesterol, plant sterols, and 5 alpha-stanols are deposited prematurely and are associated with accelerated atherosclerosis in subjects with sitosterolemia with xanthomatosis.     

Increased plasma plant sterol levels in heterozygotes with sitosterolemia and xanthomatosis

Plasma sterol levels in a family of sitosterolemia and xanthomatosis were determined by a high performance liquid chromatography. Three affected siblings manifested marked xanthomatosis including subcutaneous soft tissues and generalized atherosclerosis. Two other siblings as well as children of the patients did not show such clinical symptoms and signs. Plasma levels of cholesterol, sitosterol, campesterol, and cholestanol in three affected subjects were 190 +/- 18.5, 25.9 +/- 11.6, 16.1 +/- 7.8, 1.84 +/- 0.92 mg/dl (mean +/- SD), respectively. Four daughters of the affected subjects, who should be considered as obligatory heterozygotes, showed moderately increased levels of these sterols (195 +/- 41.7, 1.33 +/- 0.44, 1.56 +/- 0.69, 0.80 +/- 0.28 mg/dl), which were significantly higher than those of normal subjects. Treatment with cholestyramine had little effect on the increased plasma plant sterol levels, but markedly decreased plasma cholestanol concentrations in two affected siblings. This report presents the clinical features of the patients with sitosterolemia and xanthomatosis and also demonstrates that heterozygotes with this disorder have increased plasma levels of plant sterols as well as cholestanol, and suggests that this rare disease might be inherited as an autosomal co-dominant trait in certain cases. The data also indicate that cholestyramine administration was not effective in this family for treatment of sitosterolemia.     

Regulation of cholesterol biosynthesis in sitosterolemia: effects of lovastatin, cholestyramine, and dietary sterol restriction.

We investigated the effects of lovastatin, cholestyramine, and dietary sterol restriction on cholesterol synthesis and low density lipoprotein receptor function in freshly isolated mononuclear leukocytes from two unrelated sitosterolemic families. Total plasma sterol concentrations were elevated in the two homozygous sitosterolemic subjects (343 and 301 vs. 185 mg/dl in controls) and contained increased amounts of plant sterols and 5 alpha-saturated stanols (20% and 8% vs. less than 1% in controls), but were not significantly different from controls in the two heterozygous subjects. The rates of conversion of acetate to cholesterol by mononuclear leukocytes were subnormal in all homozygous and heterozygous subjects and correlated with markedly reduced microsomal 3-hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA) reductase activity. In the two homozygous subjects, cholestyramine treatment decreased plasma sterols 29% and 35%, and yet was associated with a paradoxical decline in mononuclear leukocyte HMG-CoA reductase activity. In contrast, plasma sterol concentrations decreased 14% and 5%, and mononuclear leukocyte HMG-CoA reductase activities increased 13% and 46% in three control and one heterozygous subjects treated with cholestyramine, respectively. Plasma sterol concentrations in the homozygous subjects unexpectedly failed to decline during treatment with lovastatin or a low sterol diet. In distinction, plasma sterol concentrations in three control and one heterozygous subjects dropped 28% and 31%, respectively, during treatment with lovastatin. Both cholestyramine and low dietary sterols stimulated low density lipoprotein receptor function. These results demonstrate a marked abnormality in cholesterol homeostasis in patients with homozygous sitosterolemia with xanthomatosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Heritability of plasma noncholesterol sterols and relationship to DNA sequence polymorphism in ABCG5 and ABCG8

The plasma concentrations of cholesterol precursor sterols and plant sterols vary over a 5- to 10-fold range among normolipidemic individuals, and provide indices of the relative rates of cholesterol synthesis and fractional absorption. In the present study, we examined the relative contributions of genetic and environmental factors to variation in the plasma concentrations and sterol-cholesterol ratios of five noncholesterol sterols, including the 5alpha-saturated derivative of cholesterol (cholestanol), two precursors in the cholesterol biosynthesis pathway (desmosterol and lathosterol), and two phytosterols (campesterol and sitosterol). Plasma sterol concentrations were highly stable in 30 individuals measured over a 48 week period. Regression of offspring sterol levels on the parental values indicated that plasma levels of all five noncholesterol sterols were highly heritable. Analysis of monozygotic and dizygotic twin pairs also indicated strong heritability of all five sterols. Two common sequence variations (D19H and T400K) in ABCG8, an ABC half-transporter defective in sitosterolemia, were associated with lower concentrations of plant sterols in parents, and in their offspring.Taken together, these findings indicate that variation in the plasma concentrations of noncholesterol sterols is highly heritable, and that polymorphism in ABCG8 contributes to genetic variation in the plasma concentrations of plant sterols.     

High levels of plant sterols and cholesterol precursors in cerebrotendinous xanthomatosis

We measured the cholestanol, cholesterol precursor (lathosterol), and plant sterol (campesterol and sitosterol) concentrations of serum and bile in 11 patients with cerebrotendinous xanthomatosis. The mean values of serum cholestanol, lathosterol, campesterol, and sitosterol were, respectively, 8.4-, 2.5-, 2.7-, and 1.4-times higher in the patients than in normal control subjects (n = 26). Cholestanol (6.7-fold) and campesterol (3.7-fold) levels in bile (n = 4) were also elevated in the patients. There was no significant difference of serum sterol levels between patients with coronary artery disease and those without it. Chenodeoxycholic acid treatment for periods ranging from 6 months to 3 years and 4 months lowered serum lathosterol (57.7% reduction) and campesterol (57.8%) levels in parallel with cholestanol (70.8%) level, but the sitosterol level (19.7%) decreased less. Thus, increased levels of cholesterol precursor (lathosterol), plant sterols (campesterol and sitosterol), and cholestanol were found in the serum and bile in cerebrotendinous xanthomatosis. Chenodeoxycholic acid treatment effectively reduced the levels of these sterols, except for sitosterol.     

Increased sitosterol absorption, decreased removal, and expanded body pools compensate for reduced cholesterol synthesis in sitosterolemia with xanthomatosis

We measured the turnover and absorption of sitosterol and cholesterol, along with plasma sterol and lipoprotein concentrations, in one control and two subjects with sitosterolemia with xanthomatosis. All individuals consumed the same diet which contained approximately 500 mg/day of cholesterol and 250 mg/day of sitosterol. Sterol absorption was measured by the plasma dual-isotope ratio method and turnover by plasma isotope-kinetic analysis. In two sitosterolemic subjects, 28% and 63% of the sitosterol and 69% and 49% of the cholesterol were absorbed, respectively, compared to 4% of the sitosterol and 44% of the cholesterol in the control. As expected, plasma sitosterol specific activities decayed much more rapidly than cholesterol in the control subject. In contrast, plasma sitosterol and cholesterol specific activity-time curves were similar and decayed more slowly in the sitosterolemic subjects. In the control subject, the total sitotterol pool was 290 mg and was linearly related to low absorption (18 mg/day); whereas the total sitosterol pool was 17 times (4800 mg) and 13 times (3500 mg) larger, respectively, in the sitosterolemic subjects and was expanded out of proportion to increased absorption because of decreased removal. Daily cholesterol turnover and synthesis were markedly reduced in the sitosterolemic subjects. In four sitosterolemic subjects, plasma concentrations of total sterols, low density lipoproteins, and apolipoprotein B were increased, while those of high density lipoproteins and apolipoprotein A-I were low to normal. The low density lipoproteins were very similar to those of normal control subjects in density distribution, peak flotation rate, sterol-to-protein (apolipoprotein B) ratio, particle size, and morphology. These results demonstrate in patients with sitosterolemia with xanthomatosis that: 1) the absorption of sitosterol and cholesterol is enhanced; 2) tissue recognition between cholesterol and sitosterol is lost; 3) total exchangeable sitosterol pools are expanded out of proportion to absorption because of decreased excretion; 4) plasma sterol and lipoprotein concentrations favor tissue deposition; and 5) cholesterol synthesis is diminished. We postulate that the changes in sitosterol metabolism (increased absorption, loss of tissue sterol structural recognition, expanded pools, and hepatic retention) are a response to reduced cholesterol synthesis in these subject.     

Micellar distribution of cholesterol and phytosterols after duodenal plant stanol ester infusion

Properties of the intestinal digestion of the dietary phytosterols, cholesterol and cholestanol, and the mechanisms by which phytosterols inhibit the intestinal absorption of cholesterol in healthy human subjects are poorly known. We have studied the hydrolysis of dietary plant sterol and stanol esters and their subsequent micellar solubilization by determining their concentrations in micellar and oil phases of the jejunal contents. Two liquid formulas with low (formula 1) and high (formula 2) plant stanol concentrations were infused via a nasogastric tube to the descending duodenum of 8 healthy human subjects, and intestinal contents were sampled for gas-liquid chromatographic sterol analysis 60 cm more distally. During the duodenal transit, phytosterol esters were hydrolyzed. This was especially profound for sitostanol, as its esterified fraction per milligram of sitosterol decreased 80% (P < 0.001) in formula 1 and 61% (P < 0.001) in formula 2. Contrary to that, esterified fraction of cholesterol per milligram of sitosterol was increased fourfold (P < 0.001) in formula 1 and almost sixfold (P < 0.001) in formula 2, whereas that of cholestanol remained unchanged. Percentages of esterified sterols and stanols in total intestinal fluid samples were higher after the administration of formula 2 than of formula 1. Esterified cholesterol and stanols accumulated in the oil phase, and free stanols replaced cholesterol in the micellar phase. At high intestinal plant stanol concentrations, cholesterol looses its micellar solubility possibly by replacement of its free fraction in the micellar phase by hydrolyzed plant stanols, which leads to a decreased intestinal absorption of cholesterol.     

Sitosterolemia.

Sitosterolemia is a rare inherited lipid storage disease characterized chemically by the accumulation of plant sterols and 5 alpha-saturated stanols in plasma and tissues. Very low cholesterol synthesis due to a deficiency of HMG-CoA reductase associated with increased intestinal plant sterol absorption and slow hepatic sterol removal are major biochemical features. Because cholesterol synthesis cannot up-regulate, bile acid malabsorption mobilizes body sterols for bile acid synthesis and dramatically lowers plasma and monocyte sterol concentrations and may halt the progression of the atherosclerotic process.     

Selective sterol accumulation in ABCG5/ABCG8-deficient mice

The ATP binding cassette (ABC) transporters ABCG5 and ABCG8 limit intestinal absorption and promote biliary secretion of neutral sterols. Mutations in either gene cause sitosterolemia, a rare recessive disease in which plasma and tissue levels of several neutral sterols are increased to varying degrees. To determine why patients with sitosterolemia preferentially accumulate noncholesterol sterols, levels of cholesterol and the major plant sterols were compared in plasma, liver, bile, and brain of wild-type and ABCG5/ABCG8-deficient (G5G8(-/-)) mice. The total sterol content of liver and plasma was similar in G5G8(-/-) mice and wild-type animals despite an approximately 30-fold increase in noncholesterol sterol levels in the knockout animals. The relative enrichment of each sterol in the plasma and liver of G5G8(-/-) mice (stigmasterol > sitosterol = cholestanol > bassicasterol > campesterol > cholesterol) reflected its relative enrichment in the bile of wild-type mice. These results indicate that 24-alkylated, Delta22, and 5alpha-reduced sterols are preferentially secreted into bile and that preferential biliary secretion of noncholesterol sterols by ABCG5 and ABCG8 prevents the accumulation of these sterols in normal animals. The mRNA levels for 13 enzymes in the cholesterol biosynthetic pathway were reduced in the livers of the G5G8(-/-) mice, despite a 50% reduction in hepatic cholesterol level. Thus, the accumulation of sterols other than cholesterol is sensed by the cholesterol regulatory machinery.     

Chenodeoxycholic acid normalizes elevated lipoprotein secretion and catabolism in cerebrotendinous xanthomatosis

Cerebrotendinous xanthomatosis (CTX) is a rare inherited lipid storage disease caused by a defect in bile acid synthesis in which cholesterol and its product cholestanol are deposited in neurological and vascular tissue. Therapy with chenodeoxycholic acid but not with the 7 beta-epimeric ursodeoxycholic acid is usually successful. In an untreated patient, total and low density lipoprotein (LDL) cholesterol were found to be low (134 +/- 11 and 78 +/- 8 mg/dl, respectively). The production rate (PR) and fractional catabolic rate (FCR) of very low density (VLDL) apolipoprotein B (apoB) were, however, both markedly increased (34.7 mg/kg per day and 13.7 pools/day, respectively vs. 15.1 +/- 5.0 mg/kg per day and 6.2 +/- 3.8 pools/day in controls) while the PR and FCR of LDL apoB were moderately elevated (16.3 mg/kg per day and 0.65 pools/day, respectively vs. 12.9 +/- 1.2 mg/kg per day and 0.52 +/- 0.10 pools/day in controls). After 1 month of 750 mg/day of chenodeoxycholic acid, the FCR and PR of both VLDL and LDL apoB became normal while total plasma cholesterol increased significantly to 145 +/- 18 mg/dl. In a second patient who had been receiving 750 mg/day of chenodeoxycholic acid for 6 months lipoprotein kinetics were normal. These parameters did not change when the subject was switched to 750 mg/day ursodeoxycholic acid. We postulate that cholesterol biosynthesis in CTX is derepressed by a diminished hepatic pool of chenodeoxycholic acid and that the elevated secretion of apoB is a response to the increased rate of cholesterol production.     

Common sequence variations in ABCG8 are related to plant sterol metabolism in healthy volunteers

Polymorphisms in the ATP binding cassette (ABC) transporters ABCG5 and ABCG8 are related to plasma plant sterol concentrations. It is not known whether these polymorphisms are also associated with variations in serum plant sterol concentrations during interventions affecting plant sterol metabolism. We therefore decided to study changes in serum plant sterol concentrations with ABCG5/G8 polymorphisms after consumption of plant stanol esters, which decrease plasma plant sterol concentrations. Cholesterol-standardized serum campesterol and sitosterol concentrations were significantly associated with the ABCG8 T400K genotype, as were changes in serum plant sterol concentrations after consumption of plant stanols. The reduction of -57.1 +/- 38.3 10(2) x micromol/mmol cholesterol for sitosterol in TT subjects was significantly greater compared with the -36.0 +/- 18.7 reduction in subjects with the TK genotype (P = 0.021) and the -16.9 +/- 13.0 reduction in subjects with the KK genotype (P = 0.047). Changes in serum campesterol concentrations showed a comparable association. No association with serum LDL cholesterol was found. Genetic variation in ABCG8 not only explains cross-sectional differences in serum plant sterol concentrations but also determines a subject's responsiveness to changes in serum plant sterols during interventions known to affect plant sterol metabolism.     

Gastrointestinal absorption and plasma kinetics of soy Delta(5)-phytosterols and phytostanols in humans

Our objective was to measure the systemic absorption of lecithin-emulsified Delta(5)-phytosterols and phytostanols during test meals by use of dual stable isotopic tracers. Ten healthy subjects underwent two single-meal absorption tests in random order 2 wk apart, one with intravenous dideuterated Delta(5)-phytosterols and oral pentadeuterated Delta(5)-phytosterols and the other with the corresponding labeled stanols. The oral-to-intravenous tracer ratio in plasma, a reflection of absorption, was measured by a sensitive negative ion mass spectroscopic technique and became constant after 2 days. Absorption from 600 mg of Delta(5)-soy sterols given with a standard test breakfast was 0.512 +/- 0.038% for sitosterol and 1.89 +/- 0.27% for campesterol. The absorption from 600 mg of soy stanols was 0.0441 +/- 0.004% for sitostanol and 0.155 +/- 0.017% for campestanol. Reduction of the double bond at position 5 decreased absorption by 90%. Plasma t(1/2) for stanols was significantly shorter than that for Delta(5)-sterols. We conclude that the efficiency of phytosterol absorption is lower than what was reported previously and is critically dependent on the structure of both sterol nucleus and side chain.     

Pharmacological properties of plant sterols in vivo and in vitro observations

Plant sterols have been investigated as one of the safe potential alternative methods in lowering plasma cholesterol levels. Several human studies have shown that plant sterols/stanols significantly reduce plasma total and LDL cholesterol. In this article, pharmacological characteristics of plant sterols/stanols have been summarized and discussed. In particular, experimental data that demonstrate the effects of dietary phytosterols on lipid metabolism and development of atherosclerotic lesions have been critically reviewed. Despite their similar chemical structures, phytosterols and cholesterol differ markedly from each other in regard to their pharmacological characteristics including intestinal absorption and metabolic fate. Compared to cholesterol, plant sterols have poor intestinal absorption. The most and best studied effects of plant sterols are their inhibition of intestinal cholesterol absorption. Other biological activities of phytosterols such as effects on lecithin:cholesterol acyltransferase activity, bile acid synthesis, oxidation and uptake of lipoproteins, hepatic and lipoprotein lipase activities and coagulation system have been linked to their anti-atherogenic properties. Moreover, evidence for beneficial effects of plant sterols on disorders such as cutaneous xanthomatosis, colon cancer and prostate hyperplasia has been discussed. Finally, the potential adverse effects of plant sterols as well as pathophysiology of hereditary sitosterolemia are also reviewed. In conclusion, more pharmacokinetic data are needed to better understand metabolic fate of plant sterols/stanols and their fatty acid esters as well as their interactions with other nutraceutical/pharmaceutical agents.     

Simultaneous determination of plasmatic phytosterols and cholesterol precursors using gas chromatography-mass spectrometry (GC-MS) with selective ion monitoring (SIM)

Phytosterols (beta-sitosterol, cholestanol and campesterol) and cholesterol precursors (desmosterol and lathosterol), have been suggested as important biochemical markers of intestinal cholesterol absorption and liver biosynthesis, respectively, and as useful clinical parameters in the study of hypercholesterolemia, beta-sitosterolemia, atherosclerosis and cardiovascular disease, including pharmacological response to hypolipidemic agents. We developed an optimised analytical method for the simultaneous analysis of cholestanol, desmosterol, lathosterol, campesterol and beta-sitosterol in plasma using capillary gas chromatography coupled to mass spectrometry (GC-MS) with multiple selected ion monitoring (SIM). This method is based on the alkaline hydrolysis of sterol esters, extraction of free sterols and derivatization. The recovery of all sterols was in the range 76-101%. Within-day relative standard deviations (R.S.Ds.) and the between-day R.S.Ds. of cholestanol, desmosterol, lathosterol, campesterol and beta-sitosterol were less than 8%, and their plasma levels in 161 normal subjects were (mean+/-S.D.) 4.73+/-2.57, 2.37+/-1.04, 6.23+/-3.14, 3.67+/-1.95 and 5.92+/-3.62 micromol/l, respectively.     

Rifampicin-induced CYP3A4 activation in CTX patients cannot replace chenodeoxycholic acid treatment

Cerebrotendinous xanthomatosis (CTX) is a rare neurodegenerative disorder with cholestanol accumulation resulting from mutations in the sterol 27-hydroxylase gene (CYP27A). Conventional treatment includes chenodeoxycholic acid and HMG-CoA reductase inhibitors. Mice with disrupted Cyp27A (Cyp27 KO) do not show elevated cholestanol levels nor develop CTX manifestations. This phenomenon was proposed to be due to murine CYP3A overexpression leading to an alternative pathway for degradation of bile alcohols including cholestanol. Our objective was to examine the influence of CYP3A4 induction on cholestanol elimination in CTX patients. Rifampicin (600 mg/day x 7 days), known to induce the PXR, and thereby to increase CYP3A activity, was used. The degree of CYP3A4 induction was assessed by comparing midazolam pharmacokinetics before and after rifampicin treatment. Cholestanol levels and cholestanol/cholesterol ratios were assayed during the experimental period and compared to a 3 weeks period without treatment. The results show that despite 60% increase in CYP3A4 activity following rifampicin treatment, there is no significant change in cholestanol levels. We conclude that up-regulated expression of CYP3A affects cholestanol elimination in mice differently as compared to its effect in CTX patients. Therefore, CYP3A4 inducers cannot replace chenodeoxycholic acid for the treatment of CTX.     

Correlation between apolipoprotein A-IV and triglyceride concentrations in human sera

Apolipoprotein A-IV concentration was measured by a newly developed competitive enzyme immunoassay in sera from fasted human subjects (n = 105) whose triglyceride concentrations ranged from 20 to 474 mg/dl (total cholesterol below 260 mg/dl) and in which chylomicrons could not be detected. Mean (+/- SD) apolipoprotein A-IV concentration was 13.0 +/- 2.6 mg/dl in sera with triglyceride levels ranging from 20 to 100 mg/dl, 16.9 +/- 3.7 mg/dl in sera with triglyceride levels ranging from 101 to 250 mg/dl, and 22.7 +/- 6.7 mg/dl in sera with triglyceride levels ranging from 251 to 474 mg/dl. The differences among the three groups were highly significant (P less than 0.001). Moreover, variations of apolipoprotein A-IV concentrations according to the triglyceride levels were noted within the normo-triglyceridemic population. Apolipoprotein A-IV concentration was 12.8 +/- 2.1 mg/dl for triglyceride levels ranging from 20 to 75 mg/dl and 16.4 +/- 3.8 mg/dl for triglyceride levels ranging from 76 to 150 mg/dl (P less than 0.01). In the entire population that was studied there was a significant linear correlation (r = 0.61, P less than 0.001) between the concentrations of serum apolipoprotein A-IV and triglyceride. Although the hypothesis of an unknown factor independently influencing both very low density lipoproteins and apolipoprotein A-IV cannot be ruled out, and although no apolipoprotein A-IV was found in the triglyceride-rich lipoprotein fraction after separation by gel filtration, these data suggest that, in fasting subjects, the secretion of very low density lipoproteins could contribute to the plasma apolipoprotein A-IV level.     

Comparison of the intestinal uptake of cholesterol,plant sterols,and stanols in mice

The recent identification of the aberrant transport proteins ABCG5 and ABCG8 resulting in sitosterolemia suggests that intestinal uptake of cholesterol is an unselective process, and that discrimination between cholesterol and plant sterols takes place at the level of sterol efflux from the enterocyte. Although plant sterols are structurally very similar to cholesterol, differing only in their side chain length, they are absorbed from the intestine to a markedly lower extent. In order to further evaluate the process of discrimination, three different sterols (cholesterol, campesterol, sitosterol) and their corresponding 5 alpha-stanols (cholestanol, campestanol, sitostanol) were compared concerning their concentration in the proximal small intestine, in serum, and in bile after a single oral dose of deuterated compounds. The data obtained support the hypothesis that i) the uptake of sterols and stanols is an extremely rapid process, ii) discrimination probably takes place on the level of reverse transport back into the gut lumen, iii) plant stanols are taken up, but not absorbed to a measurable extent, and iv) the process of discrimination probably also exists at the level of biliary excretion. The range of structural alterations that decrease intestinal absorption and increase biliary excretion is: 1) campesterol, 2) cholestanol-sitosterol, and 3) campestanol-sitostanol.     

Hyperabsorption and retention of campestanol in a sitosterolemic homozygote: comparison with her mother and three control subjects

We measured the percent absorption, turnover, and distribution of campestanol (24-methyl-5alpha-cholestan-3beta-ol) in a sitosterolemic homozygote, her obligate heterozygous mother, and three healthy human control subjects. For reasons relating to sterol hyperabsorption, the homozygote consumed a diet low in plant sterols that contained campestanol at about 2 mg/day. The heterozygote and three control subjects were fed a diet supplemented with a spread that contained campestanol at 540 mg/day and sitostanol (24-ethyl-5alpha-cholestan-3beta-ol) at 1.9 g/day as fatty acid esters. Plasma campestanol concentrations determined by capillary gas-liquid chromatography were 0.72 +/- 0.03 mg/dl in the homozygote, 0.09 +/- 0.04 mg/dl in the heterozygote, and 0.05 +/- 0.03 mg/dl for the control mean. After simultaneous pulse labeling with [3alpha-(3)H]campestanol intravenously and [23-(14)C]campestanol orally, the maximum percent absorption measured by the plasma dual-isotope ratio method as a single time point was 80% in the homozygote, 14.3% in the heterozygote, and 5.5 +/- 4.3% as the mean for three control subjects. Turnover (pool size) values estimated by mathematical analysis of the specific activity versus time [3alpha-(3)H]campestanol decay curves were as follows: 261 mg in the homozygote, 27.3 mg in the heterozygote, and 12.8 +/- 7.6 mg in the three control subjects (homogygote vs. controls, P < 0.001). The calculated production rate (mg/24 h) equivalent to actual absorption in the presence of dietary sterols and stanols was 0.67 mg/day or 31% of intake in the homozygote, 2.1 mg/day or 0.3% of intake in the heterozygote, and 0.7 +/- 0.3 mg/day or 0.1% of intake in the three control subjects. However, the excretion constant from pool A (K(A)) was prolonged markedly in the homozygote, but was 100 times more rapid in the heterozygote and three control subjects.Thus, campestanol, like other noncholesterol sterols, is hyperabsorbed and retained in sitosterolemic homozygotes. However, campestanol absorption was only slightly increased in the sitosterolemic heterozygote and removal was as rapid as in control subjects.     

The effect of growth hormone administration on lipids and lipoproteins in growth hormone-deficient patients

Plasma lipids, lipoproteins, and lipoprotein cholesterol levels were studied in a group (n = 8) of prepubertal growth hormone-deficient patients before and after growth hormone (GH) administration. Determination of plasma lipoproteins by a sensitive agarose gel electrophoretic technique demonstrated: (a) in the patients with two prebeta bands an intensification of the fast prebeta lipoprotein fraction after growth hormone administration; and (b) in the patients with one prebeta band the appearance of a second prebeta band after growth hormone administration. The mean (+/- SD) plasma triglyceride level before GH was 86 +/- 60 mg/dl and 158 +/- 95 mg/dl after GH (P less than 0.01). Mean (+/- SD) plasma cholesterol level before GH was 196 +/- 25 mg/dl and 174 +/- 28 mg/dl after GH (P less than 0.05). High-density lipoprotein cholesterol concentrations decreased significantly (P less than 0.001) from mean (+/- SD) 55 +/- 12 mg/dl before GH to 37 +/- 10 mg/dl after GH. Very-low-density lipoprotein cholesterol concentrations increased significantly (P less than 0.05) from mean (+/- SD) 13 +/- 12 mg/dl before GH to 23 +/- 15 mg/dl after GH. Low-density lipoprotein cholesterol concentrations decreased (N.S.) from mean (+/- SD) 123 +/- 15 mg/dl before GH to 114 +/- 15 mg/dl after GH. These lipid and lipoprotein changes could be mediated through the insulin antagonism, hyperinsulinemia, and a decrease in lipoprotein lipase activity caused by growth hormone.     

Sterol/steroid metabolism and absorption in a generalist and specialist caterpillar: Effects of dietary sterol/steroid structure,mixture and ratio

Insects cannot synthesize sterols de novo, so they typically require a dietary source. Cholesterol is the dominant sterol in most insects, but because plants contain only small amounts of cholesterol, plant-feeding insects generate most of their cholesterol by metabolizing plant sterols. Plants almost always contain mixtures of different sterols, but some are not readily metabolized to cholesterol. Here we explore, in two separate experiments, how dietary phytosterols and phytosteroids, in different mixtures, ratios, and amounts, affect insect herbivore sterol/steroid metabolism and absorption; we use two caterpillars species – one a generalist (Heliothis virescens), the other a specialist (Manduca sexta). In our first experiment caterpillars were reared on two tobacco lines – one expressing a typical phystosterol profile, the other expressing high amounts/ratios of stanols and 3-ketosteroids. Caterpillars reared on the control tobacco contained mostly cholesterol, but those reared on the modified tobacco had reduced amounts of cholesterol, and lower total sterol/steroid body profiles. In our second experiment, caterpillars were reared on artificial diets containing known amounts of cholesterol, stigmasterol, cholestanol and/or cholestanone, either singly or in various combinations and ratios. Cholesterol and stigmasterol-reared moths were mostly cholesterol, while cholestanol-reared moths were mostly cholestanol. Moth tissue cholesterol concentration tended to decrease as the ratio of dietary cholestanol and/or cholestanone increased. In both moths cholestanone was metabolized into cholestanol and epicholestanol. Interestingly, M. sexta generated much more cholestanol than epicholestanol, while H. virescens did the opposite. Finally, total tissue steroid levels were significantly reduced in moths reared on diets containing very high levels of cholestanol. We discuss how dietary sterol/steroid structural differences are important with respect to sterol/steroid metabolism and uptake, including species-specific differences.