Plasma Cholesterol Precursors Research Articles

Statins increase hepatic cholesterol synthesis and stimulate fecal cholesterol elimination in mice

Statins are competitive inhibitors of HMG-CoA reductase, the rate-limiting enzyme of cholesterol synthesis. Statins reduce plasma cholesterol levels, but whether this is actually caused by inhibition of de novo cholesterol synthesis has not been clearly established. Using three different statins, we investigated the effects on cholesterol metabolism in mice in detail. Surprisingly, direct measurement of whole body cholesterol synthesis revealed that cholesterol synthesis was robustly increased in statin-treated mice. Measurement of organ-specific cholesterol synthesis demonstrated that the liver is predominantly responsible for the increase in cholesterol synthesis. Excess synthesized cholesterol did not accumulate in the plasma, as plasma cholesterol decreased. However, statin treatment led to an increase in cholesterol removal via the feces. Interestingly, enhanced cholesterol excretion in response to rosuvastatin and lovastatin treatment was mainly mediated via biliary cholesterol secretion, whereas atorvastatin mainly stimulated cholesterol removal via the transintestinal cholesterol excretion pathway. Moreover, we show that plasma cholesterol precursor levels do not reflect cholesterol synthesis rates during statin treatment in mice. In conclusion, cholesterol synthesis is paradoxically increased upon statin treatment in mice. However, statins potently stimulate the excretion of cholesterol from the body, which sheds new light on possible mechanisms underlying the cholesterol-lowering effects of statins.

A Pilot Study of the Association of Markers of Cholesterol Synthesis with Disturbed Sleep in Smith-Lemli-Opitz Syndrome.

Smith-Lemli-Opitz syndrome (SLOS) is a rare genetic disorder characterized by cholesterol synthesis impairment. A host of physical, developmental, and behavioral presentations are associated with SLOS, many of which have been related with disorder severity. Sleep disturbance is commonly reported in SLOS. This study is the first to examine the association between sleep disturbance and biomarkers of cholesterol synthesis defect. Twenty youth with SLOS participated. Biomarkers of cholesterol synthesis were obtained, including plasma sterols (i.e., 7-dehydrocholesterol, 8-dehydrocholesterol, and cholesterol), mevalonic acid, and 24-S hydroxycholsterol. A ratio of plasma cholesterol precursors to cholesterol levels was used as a measure of biochemical severity. Parents reported their children's sleep problems using the Children's Sleep Habits Questionnaire. Most markers of cholesterol synthesis disruption were associated with overall sleep disturbance. Biochemical severity of SLOS was also associated with specific sleep problems (e.g., decreased sleep duration and increased sleep onset delay) and was identified as a significant predictor of these factors. This study is the first to demonstrate associative relationships between cholesterol levels and sleep disturbance in youth with SLOS. These results add to the current understanding of how cholesterol levels may contribute to the behavioral phenotype of SLOS. These findings may inform future studies related to the role cholesterol synthesis defects play in the behavioral phenotype of SLOS and, subsequently, modalities of intervention for behavioral symptoms.

Alterations in cholesterol absorption/synthesis markers characterize Framingham Offspring Study participants with CHD

Data is limited on measures influencing cholesterol homeostasis in subjects at high risk of developing cardiovascular disease (CVD) relative to established risk factors. To address this, we quantified circulating indicators of cholesterol homeostasis (plasma phytosterols and cholesterol precursor concentrations as surrogate measures of cholesterol absorption and synthesis, respectively) in Framingham Offspring Study Cycle-6 participants diagnosed with established CVD and/or >or=50% carotid stenosis not taking lipid lowering medication (cases, N = 155) and matched controls (N = 414). Cases and controls had similar plasma LDL-cholesterol; HDL-cholesterol was significantly lower in males, while triglyceride concentrations were significantly higher in female cases relative to their respective controls. Cholesterol absorption markers were significantly higher (229 +/- 7 vs. 196 +/- 4, 169 +/- 6 vs. 149 +/- 3 and 144 +/- 5 vs. 135 +/- 3 for campesterol, sitosterol, and cholestanol, respectively), whereas cholesterol synthesis markers were significantly lower (116 +/- 4 vs. 138 +/- 3, 73 +/- 3 vs. 75 +/- 2 for lathosterol and desmosterol, respectively) in cases compared with controls, irrespective of sex. After controlling for standard risk factors, campesterol (2.47 [1.71-3.56]; P < 0.0001), sitosterol (1.86 [1.38-2.50]; P < 0.0001), cholestanol (1.57 [1.09-2.27]; P = 0.02), desmosterol (0.59 [0.42-0.84]; P = 0.003), and lathosterol (0.58 [0.43-0.77]; P = 0.0002) were significantly associated with CVD (odds ratio [95% confidence interval]). These data suggest that impaired cholesterol homeostasis, reflected by lower synthesis and higher absorption marker concentrations, are highly significant independent predictors of prevalent CVD in this study population.

Composition of plasma fatty acids and non-cholesterol sterols in anorexia nervosa.

Anorexia nervosa is a model of simple starvation accompanied by secondary hyperlipoproteinemia. The pattern of plasma fatty acids influences the levels of plasma lipids and lipoproteins. The concentration of plasma lathosterol is a surrogate marker of cholesterol synthesis de novo, concentrations of campesterol and beta-sitosterol reflect resorption of exogenous cholesterol. The aim of the study was to evaluate fatty acids in plasma lipid classes and their relationship to plasma lipids, lipoproteins, cholesterol precursors and plant sterols. We examined 16 women with anorexia nervosa and 25 healthy ones. Patients with anorexia nervosa revealed increased concentrations of total cholesterol, triglycerides, HDL-cholesterol, campesterol and beta-sitosterol. Moreover, a decreased content of n-6 polyunsaturated fatty acids was found in all lipid classes. These changes were compensated by an increased content of monounsaturated fatty acids in cholesteryl esters, saturated fatty acids in triglycerides and both monounsaturated and saturated fatty acids in phosphatidylcholine. The most consistent finding in the fatty acid pattern concerned a decreased content of linoleic acid and a raised content of palmitoleic acid in all lipid classes. The changes of plasma lipids and lipoproteins in anorexia nervosa are the result of complex mechanisms including decreased catabolism of triglyceride-rich lipoproteins, normal rate of cholesterol synthesis and increased resorption of exogenous cholesterol.

Growth hormone selectively improves intestinal cholesterol absorption after jejunoileal autotransplantation in pigs

Background/Purpose Small bowel transplantation impairs enteric function and causes malabsorption of cholesterol and bile acids. Growth hormone stimulates intestinal absorptive function. The authors hypothesized that long-term growth hormone therapy could improve absorption of bile acids and cholesterol after autotransplantation of the jejunoileum. Methods Sixteen pigs with similar food, cholesterol, and fat intake underwent either sham laparotomy or a model of jejunoileal autotransplantation, including extrinsic autonomic denervation, lymphatic interruption, and in situ cold ischemia. Five randomly chosen autotransplanted animals received daily growth hormone treatment for 8 weeks. Serum lipids, absorption, and excretion of cholesterol, bile acids, and fat were determined after 8 weeks. Mucosal morphometrics, proliferation, and enzyme activities were determined. Plasma cholesterol precursors and plant sterols, respective markers of cholesterol synthesis and absorption, were measured after 2 and 8 weeks. Results After jejunoileal autotransplantation, growth hormone treatment significantly increased body weight gain, cholesterol absorption efficiency from 45.1% to 62.1%, plasma campesterol to cholesterol proportions, and biliary secretion of cholesterol. With or without growth hormone treatment, autotransplantation significantly increased fecal bile acid excretion, plasma cholesterol precursors, fecal bacterially modified neutral sterols, mucosal thickness of the ileum (but not jejunum), and intestinal transit time when compared with sham-operated animals. Crypt cell proliferation, mucosal enzyme activities, and microvilli showed no differences between the groups. Conclusions These findings suggest that growth hormone treatment selectively improves cholesterol, but not bile acid absorption, after autotransplantation of the jejunoileum.

Effects of transection and extrinsic denervation and a model of autotransplantation of the porcine jejunoileum on cholesterol biodynamics

Background/Purpose: Small bowel transplantation impairs enteric function, necessitating transection, extrinsic denervation, and ischemia-reperfusion of the small intestine. The authors investigated how each of these nonimmunologic insides of the transplantation procedure modulates biodynamics of cholesterol and absorption of lipids. Methods: Twenty-three pigs with similar food, cholesterol, and fat intake underwent sham laparotomy (group 1), transection (group 2), extrinsic jejunoileal denervation (group 3), or a model of autotransplantation, including extrinsic jejunoileal denervation with in situ ischemia-reperfusion (group 4). Serum lipids, absorption, and excretion of cholesterol, bile acids, and fat were determined after 8 weeks. Plasma cholesterol precursors and plant sterols, respective markers of cholesterol synthesis, and absorption, were measured after 2 and 8 weeks. Results: When compared with sham laparotomy and transection groups, denervation and autotransplantation significantly decreased weight gain and increased plasma cholesterol precursors and fecal excretion of bile acids. In relation to sham operated animals, transection alone modestly increased plasma plant sterols at 2 weeks and biliary secretion and mass absorption of cholesterol. The latter changes were not observed after denervation or autotransplantation, ie, fractional and total absorption of cholesterol were significantly decreased in autotransplanted pigs when compared with transected controls. As compared with all the other groups, autotransplantion significantly increased bacterial metabolites of neutral sterols in feces and net fecal elimination of cholesterol, mainly as bile acids. Conclusions: Extrinsic autonomic denervation of the jejunoileum, with or without synchronous ischemia-reperfusion, results in increased cholesterol synthesis, bile acid malabsorption, and decreased weight gain. Cholesterol malabsorption may develop gradually after intestinal autotransplantation, and even a short period of ischemia further impairs absorptive function of the denervated jejunoileum, resulting in increased fecal elimination of cholesterol mainly as bile acids.

Comparison of deuterium incorporation and mass isotopomer distribution analysis for measurement of human cholesterol biosynthesis

To compare endogenous cholesterol biosynthesis measured by deuterium incorporation (DI) and mass isotopomer distribution analysis (MIDA), cholesterol fractional and absolute synthetic rates were measured simultaneously by both techniques under identical physiological conditions. Twelve subjects (22 to 39 years of age) underwent a dual stable isotope protocol, involving oral deuterium oxide administration and measurement of incorporation of deuterium into cholesterol coincident with constant infusion of sodium [1-(13)C]acetate and measurement of the mass isotopomer distribution pattern of newly synthesized cholesterol. Synthesis was determined over 24 h with a 7-h feeding period. Both methods yielded similar measurements of fractional cholesterol synthesis (7.8 +/- 2.5% day(-)(1) for DI vs. 6.9 +/- 2.2% day(-)(1) for MIDA). Correlation of fractional synthesis across techniques was strong (r = 0.84, P = 0.0007). Absolute synthesis rates were also not different at 24 h (13.4 +/- 4.3 mg kg(-)(1) day(-)(1) for DI vs. 11.9 +/- 3.6 mg kg(-)(1) day(-)(1) for MIDA, r = 0.79, P < 0.002). We conclude that despite different assumptions and analytical requirements, deuterium incorporation and MIDA yield similar rates of cholesterogenesis in humans when measurements are made over 24 h. The decision as to which method to adopt depends on available clinical and analytical facilities

Does Increased Crypt Cell Proliferation Impair Cholesterol Absorption after Proximal Gut Resection?

Background: The effects of proximal small-bowel resection on absorption and synthesis of cholesterol are unclear. Methods: To study cholesterol absorption and synthesis after proximal gut resections of variable length, plasma plant sterols, cholestanol, and cholesterol precursors were measured 1 and 2 months after 50% and 75% proximal small-bowel resection or transection. To examine the effect of increased crypt cell proliferation and brush border development on cholesterol absorption, the results were related to the mucosal morphology, crypt cell proliferation, and disaccharidase activities of the remaining small bowel. Results: Campesterol levels in proportion to cholesterol decreased markedly more, and those of cholestanol markedly less, than would be expected simply due to the amount of proximal small intestine removed, whereas sitosterol proportions decreased in proportion to the length of gut resection. Campesterol proportions markedly (P = 0.06) increased between 1 and 2 months after 50% resection but remained unchanged after 75% resection. Crypt cell proliferation was only increased in the 75% resection group (P < 0.05). The longer the proximal gut resection, the lower was the mucosal enzyme activity. Both resection groups showed increased plasma cholesterol precursor proportions and crypt depth (P < 0.05), whereas villus height remained unchanged. After massive proximal resection campesterol and sitosterol proportions were inversely related to crypt cell proliferation (r = -0.86-0.83, P < 0.01). Conclusions: Increased crypt cell proliferation activated by massive proximal gut resection may act as a previously unrecognized factor in aggravating cholesterol malabsorption and retarding its recovery during the early postoperative period. These findings warrant further investigation.

Increased Plasma, Biliary, and Hepatic Cholesterol Precursors in Pigs with Ileal Autotransplantation-Induced Malabsorption of Cholesterol and Bile Acids

Background: Small-bowel transplantation impairs intestinal absorptive function for unknown reasons. Methods: The proportions of plasma, biliary, and hepatic cholesterol precursors to cholesterol were determined by gas-liquid chromatography after resection of the proximal 75% of the porcine jejunoileum (n = 15) and autotransplantation of the remaining ileum (n = 15) and were related to in vivo absorption and fecal excretion of cholesterol. Results: Ileal autotransplantation significantly decreased serum (18%; P < 0.05) and liver (7.6%; P < 0.05) cholesterol content, the esterification percentage of serum cholesterol (5.1%; P < 0.0001), and the total amount of cholesterol absorbed (48%; P < 0.05) and increased fecal excretion of bile acids (108%; P < 0.0001), net cholesterol elimination (53%; P < 0.001), and the proportions of plasma (207%; P < 0.0001), biliary (183%; P < 0.0001), and hepatic (114%; P < 0.0001) cholesterol precursors. The increases were most striking for the side-chain-saturated demethylated sterols, cholestenol and lathosterol, and monomethyl sterols, whose bile/liver and plasma/liver ratios were increased in the autotransplantation group. Plasma, biliary, and hepatic precursor proportions were positively related to each other and similarly correlated with fecal bile acids and the net elimination of cholesterol in feces. Conclusions: These findings suggest that ileal autotransplantation in pigs with proximal gut resection increased the levels of cholesterol precursor sterols in plasma, bile, and liver mainly due to a bile-acid-malabsorption-induced increase in hepatic synthesis of cholesterol. Enhanced secretion of cholesterol precursors from the liver into the plasma and bile may have contributed to their increased values during the increased rate of cholesterogenesis.

Influence of breast- and formula-feeding on plasma cholesterol precursor sterols throughout the first year of life

We evaluated endogenous cholesterol synthesis and plasma lipid profile longitudinally from birth to 1 year old in infants who were exclusively breast-fed ( n = 19) or formula-fed ( n = 19) for the first 4 months of life. At 1 and 4 months of age, breast-fed infants had higher plasma total and low-density lipoprotein cholesterol and apolipoprotein B levels than formula-fed infants, whereas plasma mevalonate and lanosterol levels were not different between the two study groups. (J Pediatr 1997;131:928-31)

Adaptive lipid metabolism after ileal autotransplantation in pigs with proximal gut resection

Background . Transplantation of the small intestine impairs intestinal absorptive function, but the adaptive response of a segmental graft is unknown. The aim of this study was to investigate the effects of ileal autotransplantation on the adaptive absorption and metabolism of lipids in pigs that had undergone proximal gut resection. Methods . Serum lipids, plasma vitamins A and E, absorption and excretion of cholesterol, bile acids and fat, plasma cholesterol precursor and plant sterol proportions to cholesterol (respective markers of cholesterol synthesis and absorption), enteric structure, and transit were determined 4, 8, and 14 weeks after 75% proximal resection with (n = 15) or without (n = 15) autotransplantation of the remaining ileum. Results . As compared with pigs that underwent proximal gut resection, the additional autotransplantation reduced the adaptive increase in total serum and high-density lipoprotein cholesterol, plasma plant sterol proportions and vitamin E concentrations, cholesterol and fat absorption efficiency, and villus height (p < 0.05 for all) during the 14 postoperative weeks and resulted in increases of up to 4.6, 2.7, 1.3, and 2.1 times the plasma cholesterol precursors (p < 0.005), fecal excretion of bile acids (p < 0.0005), neutral steroids (p < 0.005), and net elimination of cholesterol (p < 0.0005), respectively. Cholesterol and fat absorption and plasma plant sterols were significantly enhanced between 8 and 14 weeks after autotransplantation (p < 0.05, p < 0.005, and p < 0.05, respectively), whereas fecal elimination of cholesterol remained increased until the end of the follow-up. Conclusions . Autotransplantation of the ileum in pigs that have undergone proximal small bowel resection disturbs the adaptive absorption of cholesterol, bile acids, fat, and fat-soluble vitamins, resulting, through increased fecal elimination of cholesterol, in decreased serum cholesterol despite a marked compensatory increase in cholesterol synthesis.

Adaptation of cholesterol absorption after proximal resection of porcine small intestine.

Cholesterol absorption occurs primarily in the upper small intestine. Our aim was to assess absorption of cholesterol during ileal adaptation after proximal small intestinal resection. In vivo absorption and elimination of cholesterol, plasma cholesterol, cholesterol precursors, and plant sterols were related to intestinal morphology and transit 4 (n = 5), 8 (n = 5), and 14 (n = 5) weeks after a 75% proximal resection of porcine small intestine, and compared to preoperative (n = 5) and transected (n = 5) control animals. Fractional cholesterol absorption, the daily amount of cholesterol absorbed, plasma cholesterol, and plant sterol to cholesterol proportions were significantly (P < 0.05 or less) decreased, whereas fecal loss of cholesterol as neutral steroids, less so as bile acids, plasma cholesterol precursor proportions, and ileal mass and villus height were significantly increased (P < 0.05 or less) after 8 weeks of the resection. Cholesterol absorption efficiency, decreased by the resection, was gradually increased from 5.4 +/- 2.2 to 26.9 +/- 3.9% during the 14 postoperative weeks (P < 0.0001) simultaneously with a 46% increase in villus height compared with transection (P < 0.0001), but absorption remained still below control levels (80.4 +/- 2.5%, P < 0.0001). In resected and control animals, villus height correlated positively with cholesterol absorption efficiency (r = 0.85, P < 0.0001; r = 0.76, P = 0.01) and plasma plant sterol proportions (r = 0.94-0.95, P < 0.0001; r = 0.78-0.85, P < 0.008), respectively. In conclusion, after massive proximal small bowel resection, adaptation of intestinal cholesterol absorption efficiency occurs in the distal ileum closely parlleling villus hypertrophy.

Lipid Metabolism in Bile Acid Malabsorption

Malabsorption of bile acid increases cholesterol synthesis and activates hepatic LDL receptors which leads to enhanced elimination of cholesterol from the body. Interruption of enterohepatic circulation of bile acids may lead to a smaller bile acid pool, which, in turn, impairs cholesterol and fat absorption by reduced micellar solubilization. Together with reduced cholesterol absorption, the increased cholesterol loss as bile acids also reduces plasma cholesterol concentrations and the biliary cholesterol excretion, too. Diminished biliary cholesterol in bile acid malabsorption may contribute to the increased incidence of gallstones associated with ileal dysfunction. Malabsorption of bile acid leads to a fall in LDL-cholesterol concentration, and an increase of HDL-cholesterol concentration has been reported. VLDL-triglyceride concentrations are almost invariably raised. Enhanced cholesterol and bile acid synthesis in ileal dysfunction is reflected by raised concentrations of plasma cholesterol precursors, especially lathosterols, which can be used as an indicator of increased bile acid loss to faeces. Cholesterol absorption, in turn, correlates positively with plasma plant sterol concentrations levels and the ratio of lathosterols to campesterols can be used as a screening measurement for ileal dysfunction. Plasma fatty acid composition is also altered as a response to fat malabsorption associated with ileal dysfunction. The proportion of essential fatty acids is inversely correlated with faecal fat excretion and endogenous fatty acid synthesis is activated.

Raised plasma cholesterol precursors in patients with gut resections.

Cholesterol synthesis, faecal bile acids and neutral sterols, and plasma squalene and free and esterified cholesterol precursor sterols concentrations were studied in patients with previous ileal resection (n = 30) or jejunoileal bypass (n = 9) to elucidate the responses of different cholesterol precursors to enhanced cholesterol synthesis induced by cholesterol and bile acid malabsorption. A subgroup of seven resection patients without fat and bile acid malabsorption served as controls. Of the resection patients, eight had a pure bile acid malabsorption and 15 a combination of fat, bile acid, and modest cholesterol malabsorption. In the patients with jejunoileal bypass, cholesterol and fat absorption was greatly decreased in addition to bile acid malabsorption. The overall cholesterol synthesis was associated with proportionately increased plasma contents of free (and, less consistently, esterified) methyl sterols, the most marked increase, up to 18 times, being recorded for free and esterified lathosterols. The concentrations of the precursor sterols were similarly increased in the subjects with bile acid and cholesterol malabsorption, the two lathosterols showing the highest correlations with the overall cholesterol synthesis (r = 0.820-0.941). In the subjects with jejunoileal bypass cholesterol malabsorption effectively regulated cholesterol synthesis and the precursor levels. Gut exclusions large enough to cause cholesterol and/or bile acid malabsorption activate cholesterol synthesis leading to a proportional elevation in the plasma concentrations of cholesterol precursors, especially in those of lathosterols and free methyl sterols. Determination of the plasma concentration of total lathosterol by a single gas-chromatographic run is a suitable method for rapid screening of clinically significant cholesterol and bile acid malabsorption.

Evaluation of bile acid malabsorption by plasma cholesterol precursor sterols in familial hypercholesterolaemia patients with and without ileal exclusion.

To evaluate the value of plasma cholesterol precursor sterols in the detection of bile acid malabsorption we measured these sterols in 14 familial hypercholesterolaemia patients, seven with and seven without an ileal exclusion. In the operated subjects bile acid malabsorption had induced a 4.8-fold increase in cholesterol synthesis, accompanied by a 1.9-5.1-fold increase in the plasma content of the eight cholesterol precursor sterols studied. There was no overlap between the two groups in any of these sterols, when total and free sterols were considered, and only three of the esterified sterols overlapped. The tri- and dimethyl sterols were mostly unesterified, monomethyl sterols modestly esterified and the demethylated sterols, especially desmosterol, were mainly esterified. The plasma lathosterol content segregated most clearly the patients with bile acid malabsorption from the controls. The lowest lathosterol value of the operated patients was 2.5-fold higher than the highest value of the control patients. Because lathosterol is the most abundant of the plasma cholesterol precursor sterols and is relatively easy to quantitate, it is suggested that plasma lathosterol measurement can be used in the detection of bile acid malabsorption.