K. von Bergmann

Comparison of intestinal absorption of cholesterol with different plant sterols in man

Abstract. Intestinal absorption of cholesterol, campes‐terol, campestanol, stigmasterol and sitosterol were measured in 10 healthy subjects by an intestinal perfusion technique over a 50 cm segment of the upper jejunum using sitostanol as non‐absorbable marker. Cholesterol absorption was highest and averaged 33%, whereas the absorption rate of sitosterol averaged 4.2% and of stigmasterol 4.8%. Higher absorption rates were found for campesterol (9.6%). Canipestanol, the 5a saturated derivative of campesterol, showed the highest absorption rate (12.5%) of all plant sterols. A positive correlation between the absorption rate of cholesterol and campesterol was established. In addition, there was a negative correlation between the ratio of sitosterol to cholesterol and the mass of cholesterol absorption. These results are in agreement with previous observations in animal studies, namely, that increasing the length of the side‐chain of cholesterol decreases the absorbability of the sterol. Surprisingly, campestanol, the 5α saturated derivate of campesterol, was shown to have higher absorbability compared with its unsaturated compound. This finding is in contrast to previous assumptions, that hydrogenisa‐tion of the nucleus double bond of a sterol causes a decrease of absorbability, as has been demonstrated for cholesterol/cholestanol and sitosterol/sitostanol.

Chiral magnetic order at surfaces driven by inversion asymmetry

Chirality is a fascinating phenomenon that can manifest itself in subtle ways, for example in biochemistry (in the observed single-handedness of biomolecules) and in particle physics (in the charge-parity violation of electroweak interactions). In condensed matter, magnetic materials can also display single-handed, or homochiral, spin structures. This may be caused by the Dzyaloshinskii–Moriya interaction, which arises from spin–orbit scattering of electrons in an inversion-asymmetric crystal field. This effect is typically irrelevant in bulk metals as their crystals are inversion symmetric. However, low-dimensional systems lack structural inversion symmetry, so that homochiral spin structures may occur. Here we report the observation of magnetic order of a specific chirality in a single atomic layer of manganese on a tungsten (110) substrate. Spin-polarized scanning tunnelling microscopy reveals that adjacent spins are not perfectly antiferromagnetic but slightly canted, resulting in a spin spiral structure with a period of about 12 nm. We show by quantitative theory that this chiral order is caused by the Dzyaloshinskii–Moriya interaction and leads to a left-rotating spin cycloid. Our findings confirm the significance of this interaction for magnets in reduced dimensions. Chirality in nanoscale magnets may play a crucial role in spintronic devices, where the spin rather than the charge of an electron is used for data transmission and manipulation. For instance, a spin-polarized current flowing through chiral magnetic structures will exert a spin-torque on the magnetic structure, causing a variety of excitations or manipulations of the magnetization and giving rise to microwave emission, magnetization switching, or magnetic motors.

Treatment of severe familial hypercholesterolemia in childhood with sitosterol and sitostanol

This study was undertaken to compare the ability of two plant sterols to reduce serum levels of lipids and to compare their mechanism of action in nine children with severe familial hypercholesterolemia (total and low-density lipoprotein cholesterol concentrations averaged 9.57 mmol/L (370 mg/dl) and 7.87 mmol/L (301 mg/dl)). After a 3-month strict diet, the children were given sitosterol pastils (2 gm three times a day) for 3 months, followed by a 7-month course of sitostanol (0.5 gm three times a day). Serum lipoprotein levels and serum concentrations of campesterol and sitosterol were determined in all nine children, and the fecal excretion of neutral and acidic sterols were determined in seven children at the end of each therapeutic regimen. Sitosterol reduced low-density lipoprotein cholesterol levels by 20% (p < 0.01); sitostanol reduced low-density lipoprotein cholesterol levels by 33% after 3 months and 29% after 7 months (p < 0.01 compared with diet; p < 0.05 compared with sitosterol). Although sitosterol did not alter serum concentrations of campesterol and sitosterol, a significant reduction did occur during sitostanol therapy (-47% and -51%, respectively; p < 0.01). Fecal excretion of neutral sterols increased from 6.7 mg/kg per day during the control period to 9.7 mg/kg per day during sitosterol administration (p < 0.05), and to 12.6 mg/kg per day during sitostanol administration (p < 0.05 compared with diet and sitosterol periods), indicating an increase in the inhibition of intestinal cholesterol absorption. All children completed the study and no obvious side effects occurred. The data indicate that sitostanol, even with a dose four-fold lower than that of sitosterol, was significantly more effective in reducing elevated levels of low-density lipoprotein cholesterol, and the reduction in serum lipid levels was of the same magnitude as that observed with systemic lipid-lowering drugs. These results suggest that sitostanol, a nonabsorbable plant sterol, could be the drug of choice for treating familial hypercholesterolemia in childhood.

24S-hydroxycholesterol in cerebrospinal fluid is elevated in early stages of dementia

The brain is the most cholesterol-rich organ in the human body. Accumulation of excess cholesterol in hippocampal neurons promotes the cleavage of the amyloid precursor protein (APP) into amyloidogenic components with the consequence of the acceleration of neuronal degeneration. Conversion of cholesterol to 24S-hydroxycholesterol mediated by cholesterol 24S-hydroxylase (CYP46) is the major pathway for the elimination of brain cholesterol and the maintenance of brain cholesterol homeostasis. We examined whether cerebrospinal fluid (CSF) 24S-hydroxycholesterol levels differ between patients with dementia, patients with mild cognitive impairment (MCI), and cognitively intact control subjects. Plasma and CSF concentrations of 24S-hydroxycholesterol and cholesterol in 32 patients with Alzheimers disease (AD), 11 patients with vascular dementia, seven patients with MCI, and seven cognitively intact control subjects were measured by combined gas-chromatography/mass spectrometry. We show elevated concentrations of 24S-hydroxycholesterol in the CSF of AD patients and we interpret this finding as a consequence of increased cholesterol turnover in the central nervous system during neurodegeneration. The observed influence of the apolipoprotein E epsilon4 (APOE4) allele on CSF 24S-hydroxycholesterol concentrations with a gene-dosage effect suggests the existence of a link between the AD risk factor APOE4 and CNS cholesterol metabolism. The elevation of CSF 24S-hydroxycholesterol appears to occur early in the disease process, since patients with mild cognitive impairment had also increased CSF concentrations of this compound. We believe that the CSF concentration of 24S-hydroxycholesterol is altered in AD-related neurodegeneration and thus, CSF 24S-hydroxycholesterol may be a marker for monitoring the onset and progression of the disease.

Mechanisms of action of plant sterols on inhibition of cholesterol absorption. Comparison of sitosterol and sitostanol.

SummaryThe effects of two different plant sterols on intestinal cholesterol absorption were compared in normal volunteers by an intestinal perfusion study during a control period followed by high dose infusion of sitosterol or sitostanol (3.6 μmol/min), to which subjects were allocated in a randomized manner. Cholesterol absorption during the control period was similar in the two groups, averaging 0.88 ± 0.48 μmol/min (32 ± 11%) for group I (sitosterol) and 0.68 ± 0.33 μmol/min (29 ± 9%) for group II (sitostanol). The infusion of a high dose of sitosterol resulted in a significant reduction of cholesterol absorption to 0.47 μmol/min (16%). Following the same dose of sitostanol, cholesterol absorption diminished significantly to 0.15 ± 0.11 μmol/min (5.1 ± 2.9%). Overall cholesterol absorption declined during sitosterol infusion by almost 50%, whereas sitostanol infusion caused a reduction of cholesterol absorption by almost 85%. These findings of a more effective inhibition of cholesterol absorption by sitostanol might confirm the observation recorded by others that an increase in hydrophobicity of a plant sterol results in a higher affinity but lower capacity to mixed micells. This may cause an effective displacement of cholesterol from micellar binding and therefore diminished cholesterol absorption.

Effect of low-dose sitostanol on serum cholesterol in patients with hypercholesterolemia

Sitostanol (24-ethyl-5 alpha-cholestan-3 beta-ol), a hydrogenated derivative of sitosterol, was administered in a low dose (1.5 g/day) for 4 weeks to 6 patients with hypercholesterolemia. Total cholesterol was reduced significantly after 3 and 4 weeks by 10 and 15%, respectively. The reduction of total cholesterol was entirely due to a fall in LDL cholesterol. Total triglycerides and HDL cholesterol were not altered. Two weeks after cessation of sitostanol administration serum cholesterol returned to pretreatment levels. No significant amounts of sitostanol could be detected in plasma during therapy. These results suggest that low-dose sitostanol might be a useful hypolipidemic agent for the treatment of mild hypercholesterolemia.

Metabolism and drug interactions of 3-hydroxy-3-methylglutaryl coenzyme A-reductase inhibitors (statins)

Abstract. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA)-reductase inhibitors (statins) are mainly considered for long-term use and often constitute part of a multiple-drug regime. Besides common adverse drug effects, such as nausea, abdominal discomfort and headaches, all statins harbour the risk of myopathy and fatal rhabdomyolysis. Usually, the frequency of myopathy is low but the incidence increases during concomitant drug therapy. Statins do not differ in their pharmacodynamic property. Therefore, the differences in their pharmacokinetic profiles, i.e. affinity for metabolising enzymes, constitute the rationale for choosing a specific statin especially for combination therapy. In order to point out harmful combinations of therapeutics, this review summarises the pharmacokinetic data of six clinically used statins (atorvastatin, cerivastatin, fluvastatin, lovastatin, pravastatin and simvastatin) with special regard to metabolism and drug interactions. In summary, statins that lack a significant hepatic metabolism, i.e. pravastatin, or that are metabolised by more than one cytochrome P450 isoenzyme, i.e. fluvastatin, or whose metabolism is taken over by other cytochrome P450 isoenzymes in case of blockage of the main metabolising enzyme, i.e. cerivastatin, are the least prone to drug interactions. Nevertheless, in case of a specific concomitant drug therapy known to be associated with a higher risk of adverse events, i.e. cyclosporin A and statin, clinical symptoms of myopathy and biochemical data, such as increasing serum creatine phosphokinase, should be monitored carefully.

Polymorphism in the cholesterol 24S-hydroxylase gene is associated with Alzheimer's disease

Cholesterol and 24S-hydroxycholesterol are involved in the pathogenesis of Alzheimers disease (AD). Increased serum cholesterol concentrations have been detected in patients with AD. 24S-Hydroxycholesterol is the primary cholesterol elimination product of the brain and possesses neurotoxic properties in vitro. The enzyme catalyzing the conversion of cholesterol to 24S-hydroxycholesterol, cholesterol 24S-hydroxylase (CYP46), is mainly expressed in neurons. Concentrations of 24S-hydroxycholesterol in cerebrospinal fluid (CSF) and serum differ significantly between AD patients and non-demented subjects. To test the hypothesis if polymorphisms in the CYP46 gene might influence the function of the respective enzyme and thus cholesterol metabolism in the human brain, we screened for polymorphisms in 114 AD patients and 144 healthy controls. Two intronic single nucleotide polymorphisms were observed and their allelic distribution was investigated. In our study sample, carriers of the C allele of the IVS3+43C → T polymorphism were more prevalent in the group of AD patients than in healthy controls, while another IVS2-150A → G polymorphism did not show a significant association with AD. The CC genotype of the IVS3+43C → T polymorphism was associated with an increased 24S-hydroxycholesterol/cholesterol ratio in the CSF of AD patients. Our results indicate that the CYP46 gene locus may predispose to AD by increasing the 24S-hydroxycholesterol/cholesterol ratio in the brain.

Plasma 24s-hydroxycholesterol: a peripheral indicator of neuronal degeneration and potential state marker for Alzheimer's disease

The conversion of brain cholesterol into 24S-hydroxycholesterol and its subsequent release into the periphery is probably an important step for the maintenance of brain cholesterol homeostasis. Recent findings suggest that plasma 24S-hydro-xycholesterol may be elevated in Alzheimers disease (AD) and vascular dementia at least at some stage of the disease, suggesting increased brain cholesterol turnover during neuro-degeneration. We investigated whether plasma 24S-hydroxy-cholesterol concentrations depend on the severity of AD and on the apolipoprotein E (apoE) genotype. Severity of AD and inheritance of the apoE4 allele were independently associated with reduced plasma 24S-hydroxycholesterol/cholesterol ratios. The results suggest that the decrease of plasma 24S-hydroxycholesterol/cholesterol in severely affected AD patients is a peripheral marker for loss of cholesterol 24S-hydroxylase in the CNS. Inheritance of the apoE4 allele may be associated with increased apoE-mediated transport of brain cholesterol to the periphery or with decreased activity of the 24S-hydroxylase. Longitudinal studies will assess the validity of the ratio plasma 24S-hydroxycholesterol/cholesterol as a state marker for AD.

The effect of simvastatin treatment on the amyloid precursor protein and brain cholesterol metabolism in patients with Alzheimer's disease.

During the last years, several clinical studies have been published trying to elucidate the effect of statin treatment on amyloid precursor protein (APP) processing and metabolism of brain cholesterol in Alzheimer’s disease (AD) in humans. We present an open biochemical study where 19 patients with AD have been treated with simvastatin (20 mg/day) for 12 months. The aim was to further investigate the effect of simvastatin treatment on cerebrospinal fluid (CSF) biomarkers of APP processing, AD biomarkers as total tau and tau phosphorylated at threonine 181, brain cholesterol metabolism as well as on cognitive decline in patients with AD. Despite biochemical data suggesting that treatment with 20 mg/day of simvastatin for 12 months does affect the brain cholesterol metabolism, we did not find any change in CSF or plasma levels of β-amyloid (Aβ)1–42. However, by analysis of APP isoforms, we found that statin treatment may favor the nonamyloidogenic pathway of APP processing. The relevance and mechanism between statin treatment and AD has to be further elucidated by using statins of different lipophility in different dosages over a longer period of time.