Stacking-Dependent Spin Interactions in Pd/Fe Bilayers on Re(0001)

Using spin-polarized scanning tunneling microscopy and density functional theory, we have studied the magnetic properties of Pd/Fe atomic bilayers on Re(0001). Two kinds of magnetic ground states are discovered due to different types of stacking of the Pd adlayer on Fe/Re(0001). For fcc stacking of Pd on Fe/Re(0001), it is a spin spiral propagating along the close-packed (ΓK[over ¯]) direction with a period of about 0.9 nm, driven by frustrated exchange and Dzyaloshinskii-Moriya interactions. For the hcp stacking, the four-site four-spin interaction stabilizes an up-up-down-down state propagating perpendicular to the close-packed direction (along ΓM[over ¯]) with a period of about 1.0 nm. Our work shows how higher-order exchange interactions can be tuned at interfaces.

Stability of single skyrmionic bits

The switching between topologically distinct skyrmionic and ferromagnetic states has been proposed as a bit operation for information storage. While long lifetimes of the bits are required for data storage devices, the lifetimes of skyrmions have not been addressed so far. Here we show by means of atomistic Monte Carlo simulations that the field-dependent mean lifetimes of the skyrmionic and ferromagnetic states have a high asymmetry with respect to the critical magnetic field, at which these lifetimes are identical. According to our calculations, the main reason for the enhanced stability of skyrmions is a different field dependence of skyrmionic and ferromagnetic activation energies and a lower attempt frequency of skyrmions rather than the height of energy barriers. We use this knowledge to propose a procedure for the determination of effective material parameters and the quantification of the Monte Carlo timescale from the comparison of theoretical and experimental data.

Magnetic skyrmions are swirling magnetization textures which are topologically stabilized in helical magnets under an applied magnetic field. Here, the authors use Monte Carlo simulations to explore the stability of skyrmions against a ferromagnetic phase and their potential as single bits.

Enhanced atomic-scale spin contrast due to spin friction

Atom manipulation with the magnetic tip of a scanning tunneling microscope is a versatile technique to construct and investigate well-defined atomic spin arrangements. Here we explore the possibility of using a magnetic adatom as a local probe to image surface spin textures. As a model system we choose a Néel state with 120° between neighboring magnetic moments. Close to the threshold of manipulation, the adatom resides in the threefold, magnetically frustrated hollow sites, and consequently no magnetic signal is detected in manipulation images. At smaller tip-adatom distances, however, the adatom is moved towards the magnetically active bridge sites and due to the exchange force of the tip the manipulation process becomes spin dependent. In this way the adatom can be used as an amplifying probe for the surface spin texture.

Conical spin-spiral state in an ultrathin film driven by higher-order spin interactions

We report a transverse conical spin spiral as the magnetic ground state of a double-layer Mn on a W(110) surface. Using spin-polarized scanning tunneling microscopy, we find a long-range modulation along the [001] direction with a periodicity of 2.4 nm coexisting with a local row-wise antiferromagnetic contrast. First-principles calculations reveal a transverse conical spin-spiral ground state of this system which explains the observed magnetic contrast. The canting of the spins is induced by higher-order exchange interactions, while the spiraling along the [001] direction is due to frustrated Heisenberg exchange and Dzyaloshinskii-Moriya interaction.

The plant sterol brassicasterol as additional CSF biomarker in Alzheimer's disease

OBJECTIVE

Plant sterols (sitosterol, campesterol, stigmasterol and brassicasterol) are solely dietary-derivable sterols that are structurally very similar to cholesterol. In contrast to peripheral cholesterol, plant sterols can cross the blood-brain barrier and accumulate within mammalian brain. As an impaired function of the cerebrospinal fluid (CSF)-blood barrier is linked to neurodegenerative disorders, i.e. Alzheimer's disease (AD), we investigated whether this results in altered plant sterol concentrations in CSF.

METHOD

Applying gas chromatography/mass spectrometry analysis, plant sterol concentrations were measured in plasma and CSF of patients with AD (n = 67) and controls (n = 29). Age, gender, plasma-to-CSF albumin ratio, CSF Aβ(42) , CSF pTau, APOE4 genotype, and serum creatinine were applied as covariates in the statistical analysis for individual plant sterols in order to compare plasma and CSF plant sterol concentrations between patients with AD and controls.

RESULTS

Albumin quotient was a consistent predictor in CSF for cholesterol and methyl plant sterols campesterol and brassicasterol. Comparison of lipid parameters per diagnosis based on relevant predictors revealed significantly lower concentrations of brassicasterol (P < 0.001) in CSF of patients with AD. Binary logistic regression analysis revealed that brassicasterol improved the predictive value when added to pTau and Aβ42 in a biomarker model.

CONCLUSION

Brassicasterol might be a relevant additional biomarker in AD.

Long-term efficacy and safety of ezetimibe 10 mg in patients with homozygous sitosterolemia: a 2-year, open-label extension study

OBJECTIVE

To assess the long-term efficacy and safety profile of ezetimibe 10 mg/day in patients with homozygous sitosterolemia.

METHODS

This was an extension of a multi-centre, randomised, double-blind, placebo-controlled base study in which patients with homozygous sitosterolemia and plasma sitosterol concentrations > 5 mg/dl were randomised 4 : 1 to ezetimibe 10 mg/day (n = 30) or placebo (n = 7) for 8 weeks. Patients who successfully completed the base study with > 80% compliance to study medication were eligible to enter two, successive, 1-year extension studies in which ezetimibe 10 mg/day was administered in an open-label manner. Patients remained on their current treatment regimen (e.g. bile salt-binding resins, statins and low-sterol diet) during the base and extension studies. Patients had to be off ezetimibe therapy for > or = 4 weeks prior to entering the first extension. Efficacy and safety/tolerability parameters were evaluated every 12 and 26 weeks in the first and second years respectively. The primary efficacy end-point was mean percentage change in plasma sitosterol from baseline to study end for the cohort of patients (n = 21) who successfully completed the second extension study.

RESULTS

Treatment with ezetimibe 10 mg/day led to significant mean percentage reductions from baseline in plasma concentrations of sitosterol (-43.9%; p < 0.001), campesterol (-50.8%; p < 0.001), low-density lipoprotein (LDL) sterols (-13.1%; p < 0.050), total sterols (-10.3%; p < 0.050) and apolipoprotein (apo) B (-10.1%; p < 0.050). No significant changes from baseline were observed for lathosterol, high-density lipoprotein sterol, triglycerides or apo A-1. Maximal reductions in sitosterol and campesterol occurred within the first 52 weeks of treatment and were sustained for the duration of the study. For LDL sterol, total sterols and apo B, maximal reductions were achieved early (by weeks 4 or 16) and waned slightly through the remainder of the study. Overall ezetimibe 10 mg was well tolerated.

CONCLUSION

In patients with homozygous sitoserolemia, long-term treatment with ezetimibe 10 mg/day for 2 years was effective in reducing plasma plant sterol concentrations with an overall favourable safety and tolerability profile.

Atomic-scale spin spiral with a unique rotational sense: Mn monolayer on W(001)

Using spin-polarized scanning tunneling microscopy we show that the magnetic order of 1 monolayer Mn on W(001) is a spin spiral propagating along 110 crystallographic directions. The spiral arises on the atomic scale with a period of about 2.2 nm, equivalent to only 10 atomic rows. Ab initio calculations identify the spin spiral as a left-handed cycloid stabilized by the Dzyaloshinskii-Moriya interaction, imposed by spin-orbit coupling, in the presence of softened ferromagnetic exchange coupling. Monte Carlo simulations explain the formation of a nanoscale labyrinth pattern, originating from the coexistence of the two possible rotational domains, that is intrinsic to the system.

Efficacy and safety of ezetimibe 40 mg vs. ezetimibe 10 mg in the treatment of patients with homozygous sitosterolaemia

OBJECTIVE

To assess the effect of ezetimibe (EZE) 40 mg/day on non-cholesterol sterol plasma concentrations in patients with homozygous sitosterolaemia (HoS).

METHODS

This was a multi-centre, randomised, double-blind, placebo-controlled parallel group study. Twenty-seven patients (> or = 18 years) with HoS and plasma sitosterol levels > 5 mg/dl who had been taking EZE 10 mg/day for > or = 6 months prior to enrolment received open-label EZE 10 mg/day for the duration of the study and were randomised 1 : 1 to blinded EZE 30 mg/day (4 x EZE 10 mg tablets; n = 13) or placebo (1 x EZE 10 mg tablet and 3 x matching placebo tablets; n = 14) for 26 weeks. Patients were permitted to remain on other ongoing treatments (e.g. bile salt-binding resin, statin and/or low sterol diet). End-points included median per cent between-group changes from baseline in plasma sitosterol, campesterol, lathosterol, low-density lipoprotein (LDL) sterols, LDL cholesterol (LDL-C) measured by gas-liquid chromatography, and Achilles tendon thickness size measured radiographically.

RESULTS

Ezetimibe 40 mg/day resulted in median per cent changes from baseline in plasma sitosterol levels of 3.3% vs. -10% in the EZE 10 mg/day group, in plasma campesterol of -0.5% vs. -9.7% in the EZE 10 mg/day group, and in plasma lathosterol of 0.8% vs. 1.1% in the EZE 10 mg/day group (p = ns for all between-group differences). Median per cent changes in the EZE 40 mg/day and EZE 10 mg/day groups, respectively, were 1.3% and 0% for LDL sterols and 2.5% and 4.4% for LDL-C (p = ns for both between-group differences). At study end-point, Achilles tendon thickness remained unchanged in the EZE 40 mg/day group and increased slightly in the EZE 10 mg/day group (2.2%), yielding a non-significant between-group difference of -2.2%. EZE 40 mg/day was generally well tolerated.

CONCLUSIONS

In patients with HoS, treatment with EZE 40 mg/day for 26 weeks was no more effective at reducing plasma plant sterol concentrations vs. EZE 10 mg/day. EZE 40 mg/day had a safety and tolerability profile similar to EZE 10 mg/day.

Effects of high-dose itraconazole treatment on lipoproteins in men

OBJECTIVE

Epidemiological studies have convincingly demonstrated a positive association between LDL-cholesterol (LDL-C) and coronary artery disease but, in the case of HDL-C, there is an inverse association. Administration of high doses of the antifungal agent ketoconazole (800 mg/d) reduces serum concentrations of total cholesterol and LDL-C and there is a tendency for an increase in HDL-C. Our goal was to examine whether high-dose itraconazole raises HDL-C in subjects with normal levels of cholesterol.

PATIENTS AND METHODS

8 male patients with onychomycosis received 2 one-week cycles of treatment with itraconazole at a dose of 400 mg once daily in an open, prospective exploratory trial. Serum levels of itraconazole and its active metabolite hydroxyitraconazole were determined using high-performance liquid chromatography at the end of each treatment cycle. Fasting levels of serum lipoproteins and triglycerides were measured twice using routine enzymatic assays at the beginning and end of each cycle. The effects of itraconazole and hydroxyitraconazole on HDL-C metabolism were assessed in vitro using a human Caco-2 cell line and analyzing apoA-I levels with an enzyme-linked immunosorbent assay.

RESULTS

During itraconazole treatment total cholesterol and LDL-C decreased on average by 12% (p < 0.001) and 17% (p < 0.001), respectively, whereas HDL-C increased by 21% (p < 0.001). The ratio LDL: HDL-C, an index of atherogenic risk, decreased by 30% (p < 0.001). Incubation of Caco-2 cells in the presence of itraconazole and hydroxyitraconazole for 3 hours resulted in a significant increase in apoA-I concentration in the medium (913 and 412%, respectively) compared with control.

CONCLUSION

In addition to its inhibitory effect on cholesterol synthesis, high-dose itraconazole (400 mg/d) causes a significant decrease in serum LDL-C and, in contrast to ketoconazole, a significant increase in HDL-C. In vitro studies with Caco-2 cells indicate that the latter observation might be caused by an increase in apoA-I levels.

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.

Atomic spin structure of antiferromagnetic domain walls

The search for uncompensated magnetic moments on antiferromagnetic surfaces is of great technological importance as they are responsible for the exchange-bias effect that is widely used in state-of-the-art magnetic storage devices. We have studied the atomic spin structure of phase domain walls in the antiferromagnetic Fe monolayer on W(001) by means of spin-polarized scanning tunnelling microscopy and Monte Carlo simulations. The domain wall width only amounts to 6-8 atomic rows. Although walls oriented along <100> directions are found to be fully compensated, detailed analysis of <110>-oriented walls reveals an uncompensated perpendicular magnetic moment. Our result represents a major advance in the field of antiferromagnetism, and may lead to a better understanding of the magnetic interaction between ferromagnetic and antiferromagnetic materials.

Observation of a complex nanoscale magnetic structure in a hexagonal Fe monolayer

We have observed a novel magnetic structure in the pseudomorphic Fe monolayer on Ir(111). Using spin-polarized scanning tunneling microscopy we find a nanometer-sized two-dimensional magnetic unit cell. A collinear magnetic structure is proposed consisting of 15 Fe atoms per unit cell with 7 magnetic moments pointing in one and 8 moments in the opposite direction. First-principles calculations verify that such an unusual magnetic state is indeed lower in energy than all solutions of the classical Heisenberg model. We demonstrate that the complex magnetic structure is induced by the strong Fe-Ir hybridization.

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 beta-amyloid (Abeta)(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.

Ratio of lathosterol to campesterol in serum predicts the cholesterol-lowering effect of sitostanol-supplemented margarine

OBJECTIVE

Plant sterol/stanol margarines are recommended as a lipid-lowering dietary supplement in the treatment of hypercholesterolemia. Parameters predicting the individual cholesterol-lowering effect have not been elucidated so far. Therefore, we investigated the responsiveness to sitostanol-supplemented margarine in a specially selected population.

METHODS AND RESULTS

From a total number of 137 male subjects with hypercholesterolemia, eight subjects with the lowest and eight subjects with the highest ratios of lathosterol to campesterol in serum were included in the study. They received 1 g sitostanol-supplemented margarine b.i.d. for four weeks. Serum lipoproteins, the cholesterol precursor lathosterol, the plant sterols campesterol and sitosterol were measured. Subjects with a low ratio of lathosterol to campesterol had a significant decrease of serum total cholesterol (-14.2%; p < 0.01) and LDL cholesterol (-13.8%; p < 0.01; responder). In subjects with a high ratio there was no significant change in total cholesterol and LDL cholesterol (2.2 and 4.3%; non-responder).

CONCLUSION

The ratio of serum lathosterol to campesterol predicts the reduction of total cholesterol and LDL cholesterol during administration of sitostanol-supplemented margarine in patients with mild hypercholesterolemia.

Polymorphism in neuropeptide Y influences CSF cholesterol levels but is no major risk factor of Alzheimer's disease

Neuropeptide Y (NPY) is a neurotransmitter expressed in the central nervous system and involved in learning and memory. The NPY L7P polymorphism has been associated with altered cholesterol levels in obese patients. Since altered cholesterol metabolism is also involved in Alzheimer's disease (AD), the effects of two NPY polymorphisms (L7P and IVS1-100 T/G) on CSF and plasma cholesterol and 24S-hydroxycholesterol were investigated in AD patients and non-demented controls. Furtheremore, the effect of both NPY polymorphisms on the risk of AD was studied. The NPY IVS1-100 T/G polymorphism influenced CSF levels of cholesterol, whereas CSF and plasma levels of 24S-hydroxycholesterol and plasma cholesterol were not altered by genotype. NPY L7P polymorphism did not influence CSF or plasma cholesterol or 24S-hydroxycholesterol. Both NPY polymorphisms did not influence the risk of AD. Our data support the observation, that NPY polymorphisms might influence cholesterol metabolism, but might not act as major risk factor in AD.

Revealing antiferromagnetic order of the Fe monolayer on W(001): spin-polarized scanning tunneling microscopy and first-principles calculations

We prove that the magnetic ground state of a single monolayer Fe on W(001) is c(2x2) antiferromagnetic, i.e., a checkerboard arrangement of antiparallel magnetic moments. Real space images of this magnetic structure have been obtained with spin-polarized scanning tunneling microscopy. An out-of-plane easy magnetization axis is concluded from measurements in an external magnetic field. The magnetic ground state and anisotropy axis are explained based on first-principles calculations.

Normalisation of serum cholestanol concentration in a patient with cerebrotendinous xanthomatosis by combined treatment with chenodeoxycholic acid, simvastatin and LDL apheresis

The concentrations of serum cholesterol, cholestanol and non-cholesterol sterols were measured in a patient with cerebrotendinous xanthomatosis under different therapeutic regimens. During treatment with chenodeoxycholic acid (CDCA) (750 mg/day) plus simvastatin (20 mg/day) for two years cholesterol and cholestanol concentrations averaged 188+/-10 mg/dl and 0.54+/-0.03 mg/dl. Thereafter treatment with simvastatin was discontinued. During treatment with low-density lipoprotein (LDL)-apheresis plus CDCA for 33 weeks, cholestanol concentrations reached almost normal levels (0.48+/-0.03 mg/dl immediately before and 0.32+/-0.02 mg/dl directly after LDL-apheresis, n=6). A further reduction of cholesterol and cholestanol was achieved by addition of simvastatin (20 mg/day). Cholesterol and cholestanol concentrations before and after LDL-apheresis during this treatment period averaged 122+/-4 mg/dl and 55+/-10 mg/dl, and 0.42+/-0.02 mg/dl and 0.18+/-0.06 mg/dl, respectively. Despite the consistent reduction of cholestanol to normal or even subnormal levels, a definite improvement of clinical symptoms was not noted. Our results suggest caution in the recourse to an aggressive cholestanol lowering therapy.

Altered levels of plasma 24S- and 27-hydroxycholesterol in demented patients

Alterations in brain cholesterol metabolism and reduced 24S-hydroxycholesterol plasma levels have been described in Alzheimer's disease (AD) and vascular dementia (VD). We hypothesize that changes in peripheral cholesterol metabolism, such as alterations in the plasma levels of 27-hydroxycholesterol, might also be involved. Plasma levels of 24S-hydroxycholesterol and 27-hydroxycholesterol in patients suffering from dementing disorders such as AD, VD, and mild cognitive impairment (MCI) were compared to those in age- and cholesterol matched non-demented and depressed subjects. Cholesterol corrected concentrations of plasma 24S-hydroxycholesterol and 27-hydroxycholesterol were significantly reduced in patients with dementing disorders compared to non-demented subjects and depressed patients. A strong positive correlation between plasma 24S-hydroxycholesterol and 27-hydroxycholesterol levels was observed. The ratios of plasma 24S-hydroxycholesterol to 27-hydroxycholesterol were higher in patients with dementing disorders compared to non-demented subjects. Our results support the observation, that cholesterol metabolism is altered in dementing disorders, indicated by different plasma concentrations of brain specific and peripherally produced oxysterols.

Influence of peroxisome proliferator-activated receptor γ gene polymorphism on 24S-hydroxycholesterol levels in Alzheimer’s patients

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear hormone receptor, that is involved in lipid and glucose metabolism, which both seem to influence the risk of Alzheimer's disease (AD). 24S-Hydroxycholesterol is the major cholesterol elimination product of the brain and plasma and CSF 24S-hydroxycholesterol levels are altered in patients with neurodegenerative diseases. We investigated the effect of the common Pro12Ala variant of the PPARgamma gene on plasma cholesterol levels and 24S-hydroxycholesterol/ cholesterol ratios in 124 AD patients and 77 healthy controls. Furthermore, the influence of PPARgamma polymorphism on the risk of AD in 247 AD patients and 324 healthy controls was investigated. We found that PPARgamma Pro12Ala polymorphism influenced plasma 24S-hydroxycholesterol/ cholesterol ratios in AD patients in that carriers of the Ala allele presented with higher ratios than homozygote carriers of the Pro-allele. PPARgamma polymorphism did not influence the risk of AD. These results might point to an influence of PPARgamma Pro12Ala polymorphism on the elimination of 24S-hydroxycholesterol.

Polymorphisms in glutathione S-transferase omega-1 and AD, vascular dementia, and stroke

BACKGROUND

Glutathione S-transferase omega-1 (GSTO1) protects from oxidative stress, a risk factor for Alzheimer disease (AD), vascular dementia (VaD), and stroke. Polymorphisms in GSTO1 might influence the function of the protein and thus the risk of AD, VaD, and stroke.

METHODS

The GSTO1 gene was screened for variations. The effect of the detected polymorphisms on the risk of AD, VaD, and stroke was evaluated. CSF levels of cholesterol and plasma homocysteine levels were compared according to the GSTO1 genotype.

RESULTS

Two missense polymorphisms in exon 4 of GSTO1 (Ala140Asp and Glu155DeltaGlu) were detected and tested for their association with AD, VaD, and stroke. The Asp/Asp and Ala/Asp genotypes increased the risk of stroke (p = 0.003, OR = 2.1), and the Asp/Asp genotype increased the risk of VaD (p = 0.02, OR = 2.2). GSTO1 polymorphisms did not influence the risk of AD, but the Asp allele influenced the age at onset (p = 0.05). In nondemented probands CSF levels of cholesterol were increased in carriers of the Asp/Asp genotype (p = 0.004); however, in patients with manifest dementia the authors found decreased CSF levels of cholesterol in carriers of the Asp/Asp genotype (p = 0.028). Serum homocysteine levels in stroke patients were higher in carriers of at least one Asp allele (p = 0.011).

CONCLUSION

The GSTO1 Asp allele may be a genetic risk factor for cerebrovascular diseases, and might influence the course of Alzheimer disease, even though effects vary in different studies.

Sitosterolemia—a rare disease

Elevated plasma plant sterol concentrations, xanthomatosis, and accelerated-often fatal-atherosclerosis at young age are the major findings in patients with homozygous sitosterolemia. A defect in the ABCG5 or ABCG8 co-transporter gene locus (STSL) causes an increased intestinal absorption and a decreased biliary elimination of all sterols, plant sterols as well as cholesterol, leading to a 50 to 200-fold increase in plasma plant sterol concentrations. A few recent publications indicate that even moderately elevated plasma plant sterol levels might be associated with an increased risk of atherosclerosis. This raises the question whether plant sterols themselves might be atherogenic or whether elevated plasma levels are a marker for a decreased ABCG5/G8 transporter activity which itself causes an increased risk for atherosclerosis. However, current data are too few to conclude that elevated plant sterol concentrations in plasma are an additional risk factor for coronary heart disease. But especially young patients suffering from xanthomatosis and/or atherosclerotic diseases with only mildly or moderately elevated plasma cholesterol should be screened for sitosterolemia by measurement of plasma plant sterol levels.

Influence of rifampin on serum markers of cholesterol and bile acid synthesis in men

OBJECTIVE

It has been demonstrated in preliminary studies that rifampin, a semisynthetic antibiotic and known inducer of hepatic cytochrome P450 3A4, reduces serum concentrations of total bile acids only in individuals with liver disease and elevated serum bile acid levels.

METHODS

We studied the effect of rifampin on concentrations of surrogate serum markers of cholesterol and bile acid synthesis as well as of cholesterol absorption in 10 male subjects before and after administration of rifampin (600 mg/day) for 6 days. Cholesterol and its precursors were analyzed by gas-liquid chromatography (GLC), bile acid intermediates and individual bile acids by isotope-dilution methods using GLC-mass spectrometry (MS) or by high-performance liquid chromatography (HPLC).

RESULTS

Treatment with rifampin resulted in a 70% increase (p = 0.008) of the serum concentration of the bile acid precursor 7alpha-hydroxy-4-cholesten-3-one, which is a marker for bile acid production. Serum total cholesterol was not altered, however, treatment with rifampin elevated the ratio of lathosterol to cholesterol, an indicator of cholesterol synthesis, by 23% (p = 0.037). Interestingly, serum concentration of total bile acids decreased slightly by 29% (p = 0.022), mainly due to a lowering of the secondary bile acid, deoxycholic acid (-60%; p = 0.005).

CONCLUSION

A 6-day treatment with rifampin induces a reduction of deoxycholic serum concentrations in healthy men associated with a moderate increase of serum markers of bile acid and endogenous cholesterol synthesis.

Ezetimibe effectively reduces plasma plant sterols in patients with sitosterolemia

BACKGROUND

Sitosterolemia is a recessively inherited disorder that results from mutations in either ABCG5 or G8 proteins, with hyperabsorption of dietary sterols and decreased hepatic excretion of plant sterols and cholesterol. As a consequence of markedly elevated plasma and tissue sitosterol and campesterol levels, premature atherosclerosis develops.

METHODS AND RESULTS

In this multicenter, double-blind, randomized, placebo-controlled study, we examined whether treatment with ezetimibe, an inhibitor of cholesterol absorption, reduces plant sterol levels in patients with sitosterolemia. After a 3-week placebo run-in, 37 patients were randomized to receive placebo (n=7) or ezetimibe 10 mg/d (n=30) for 8 weeks. Sitosterol concentrations decreased by 21% (P<0.001) in patients treated with ezetimibe compared with a nonsignificant 4% rise in those on placebo (between-group P<0.001). The reduction in sitosterol from baseline was progressive, with further decline observed at each subsequent biweekly visit. Campesterol also progressively declined, with a mean decrease after 8 weeks of 24% with ezetimibe and a mean increase of 3% with placebo treatment (between-group P<0.001). Reductions in plant sterol concentrations were similar irrespective of whether patients were undergoing concomitant treatment with resin or statin. Reductions in total sterols and apolipoprotein B were also observed. Ezetimibe was well tolerated, with no serious treatment-related adverse events or discontinuations due to adverse events being reported.

CONCLUSIONS

Ezetimibe produced significant and progressive reductions in plasma plant sterol concentrations in patients with sitosterolemia, consistent with the hypothesis that ezetimibe inhibits the intestinal absorption of plant sterols as well as cholesterol, leading to reductions in plasma concentrations.

Serum Lipid Analysis Confirms the Diagnosis of X-Linked Dominant Chondrodysplasia Punctata - Conradi-Hünermann-Happle Syndrome

We present the morphological and biochemical findings in a twelve month old girl with chondrodysplasia punctata X2 - Conradi-Hünermann-Happle syndrome. This disease is characterized by limb length discrepancies, growth retardation, ichthyosis, cataracts, and punctate calcification. The diagnosis could finally be confirmed by increased concentrations of cholesterol precursors as recently found in the plasma and tissues of affected patients.

Domain wall orientation in magnetic nanowires

Scanning tunneling microscopy reveals that domain walls in ultrathin Fe nanowires are oriented along a certain crystallographic direction, regardless of the orientation of the wires. Monte Carlo simulations on a discrete lattice are in accordance with the experiment if the film relaxation is taken into account. We demonstrate that the wall orientation is determined by the atomic lattice and the resulting strength of an effective exchange interaction. The magnetic anisotropy and the magnetostatic energy play a minor role for the wall orientation in that system.

Spin-polarized electron scattering at single oxygen adsorbates on a magnetic surface

Scanning tunneling spectroscopy (STS) on the system of isolated oxygen atoms adsorbed on the double layer of Fe on W(110) shows highly anisotropic spatial oscillations in the local density of states in the vicinity of the adsorbates. We explain this in terms of a single-particle model as electron waves being scattered by the potential induced by the presence of the oxygen atoms. Analysis of the wavelength of the standing electron waves and comparison with ab initio spin-resolved electronic structure calculations reveal that minority-spin bands of d-like symmetry are involved in the scattering process. By applying spin-polarized STS, we observe this standing wave pattern on one particular type of magnetic domain of Fe on W(110) only, thereby proving that the standing electron waves are highly spin polarized.

24S-hydroxycholesterol: a marker of brain cholesterol metabolism

The enzymatic conversion of CNS cholesterol to 24S-hydroxycholesterol, which readily crosses the blood-brain barrier, is the major pathway for brain cholesterol elimination and brain cholesterol homeostasis maintenance. The enzyme mediating this conversion has been characterized at the molecular level (CYP46) and is mainly located in neurons. Like other oxysterols, 24S-hydroxycholesterol is efficiently converted into normal bile acids or excreted in bile in its sulfated and glucuronidated form. Levels of 24S-hydroxycholesterol in the circulation decrease with age in infants and children. In adults, however, the levels appear to be stable. There is accumulating evidence pointing toward a potentially important link between cholesterol, beta-amyloid, and Alzheimer's disease. Concentrations of 24S-hydroxycholesterol in plasma and cerebrospinal fluid (CSF) are significantly higher in Alzheimer's disease and vascular demented patients at early stages of the disease compared to healthy subjects. Variations in genetic background, time of disease onset, and severity of dementia are potential sources of variance. Inhibitors of cholesterol biosynthesis, also termed statins, seem to have a reductive influence on the generation of the amyloid precursor protein, the neuronal secretion of beta-amyloid, and on de novo cholesterol synthesis. Recent epidemiological studies indicate that the prevalence of diagnosed AD and vascular dementia is reduced among people taking statins for a longer period of time. High-dose simvastatin treatment (80 mg/day) in patients with hypercholesterolemia leads to a significant decrease in brain-specific serum 24S-hydroxycholesterol concentrations and indicates a diminished cholesterol metabolism in the brain. CSF levels of cholesterol and lathosterol, a cholesterol precursor considered to be an indicator for cholesterol neogenesis, were significantly decreased in statin-treated subjects compared to non-treated normo- and hypercholesterolemic subjects. Also, CSF concentrations of 24S-hydroxycholesterol were significantly lower in statin-treated patients compared to normocholesterolemic subjects. Treatment with high-dose simvastatin in normocholesterolemic Alzheimer patients for 26 weeks at early stages of the disease results in a significant decrease in Abeta-levels in cerebrospinal fluid. This decrease correlates with the reduction of 24S-hydroxycholesterol.

Combination of serum markers related to several mechanisms in Alzheimer's disease

Alzheimer's disease (AD) probably involves several pathobiochemical mechanisms and this may be reflected by changes in different serum components. The present study investigated whether the combined analysis of serum molecules related to different mechanisms improves the discrimination of AD patients from healthy controls. Serum of patients with AD was analyzed for a broad spectrum of marker molecules, including 11 inflammatory proteins, 12 sterol intermediates and phytosterols, 2 brain-specific proteins and 4 constituents involved in homocysteine homeostasis. The serum molecule concentrations were combined in a logistic regression model, using a forward stepwise inclusion mode. The results showed that the combination of interleukin-6 (IL-6) receptor, protein alpha1 fraction, cysteine and cholesterol concentrations improved the discrimination between AD patients and healthy controls compared to the single markers. In conclusion, the results of this study have shown that the complex pathology in AD is reflected in a pattern of altered serum concentrations of several marker molecules related to several pathobiochemical mechanisms.

The role of 24S-hydroxycholesterol in Alzheimer's disease

Studies on Alzheimer's disease (AD) revealed that cholesterol metabolism might be involved in the pathogenesis of this neurodegenerative disorder. The apolipoprotein E4 genotype is a known risk factor in AD. Elevated serum cholesterol concentrations are detected in patients with AD and two recent epidemiological studies have indicated that treatment with inhibitors of cholesterol synthesis (statins) decrease the incidence of AD. 24R- and 24S-hydroxycholesterol, the major cholesterol elimination product of the brain, possess neurotoxic effects in vitro, and increased concentrations of 24S-hydroxycholesterol have been detected in patients from our department, suggesting a role for this oxysterol in the pathogenesis of AD. This review will give a brief overview on the relevance of 24S-hydroxycholesterol as a possible risk factor and diagnostic state marker for AD.

Decreased levels of the brain specific 24S-hydroxycholesterol and cholesterol precursors in serum of multiple sclerosis patients

The serum concentration of 24S-hydroxycholesterol reflecting brain cholesterol turnover may be a possible marker for neurodegeneration and demyelination in multiple sclerosis. Serum was analyzed for cholesterol precursors and oxysterols in multiple sclerosis patients of different clinical subtypes (n=20 each subtype) and in 37 healthy controls. Serum 24S-hydroxycholesterol levels were lower in primary progressive and in older relapsing remitting multiple sclerosis patients. Furthermore, serum levels of lathosterol were decreased in all clinical subtypes. The results are important given recent interest in statin treatment in multiple sclerosis, which will further decrease the cholesterol precursor and oxysterol levels. The decreased levels of brain specific and peripheral sterols indicate a role for cholesterol homeostasis in relation to the pathology of multiple sclerosis, at least in the primary progressive clinical subtype.

Genetic association of acyl-coenzyme A: cholesterol acyltransferase with cerebrospinal fluid cholesterol levels, brain amyloid load, and risk for Alzheimer's disease

A common polymorphism of the gene encoding acyl-coenzyme A: cholesterol acyltransferase 1 (SOAT1), which is involved in the regulation of beta-amyloid peptide generation, is associated with low brain amyloid load (P=0.03) and with low cerebrospinal fluid levels of cholesterol (P=0.005). This polymorphism of SOAT1 is also associated with reduced risk for Alzheimer's disease in ethnically distinct populations (P=0.0001, odds ratio: 0.6, 95% confidence interval 0.4-0.8).

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

Cholesterol and 24S-hydroxycholesterol are involved in the pathogenesis of Alzheimer's 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.

[Serum markers in relation to cognitive functioning in an aging population: results of the Maastricht Aging Study (MAAS)]

Little is known of the biochemical processes of cognitive decline during 'healthy' aging. Biological markers in body fluids, such as blood, could provide insight in those processes. In the present studies serum concentrations of different markers have been correlated to cognitive functioning of cognitively healthy aging individuals over a period of six years (mean age 57 years, SD 11, n = 93). Markers were related to mechanisms known to be involved in Alzheimer's disease, including inflammation, cholesterol homeostasis and homocysteine homeostasis. Domains of cognitive function addressed were cognitive speed (Letter-Digit Coding test), attention and information processing (Stroop test), and memory (Word Learning test: Total Words and Delayed Recall). Baseline concentrations of haptoglobine, homocysteine, lathosterol and lanosterol were negatively correlated with cognitive functioning on the Stroop test over the whole follow-up period of six years. Concentrations of all markers, i.e. haptoglobine, C-reactive protein, homocysteine, lathosterol and lanosterol, were also negatively correlated with functioning on the Word Learning test (Delayed Recall and for some markers also with the Total Words) over the whole six-years follow-up period. In conclusion, concentrations of serum markers related to inflammation, homocysteine and cholesterol homeostasis are not only associated with Alzheimer's disease, but also with cognitive functioning in the cognitively healthy aging population.

Serum cholesterol, precursors and metabolites and cognitive performance in an aging population

The present study investigated if a causal relation exists between serum concentrations of precursors and metabolites of cholesterol and cognitive performance in a healthy aging population. Cognitive function addressing four domains of 144 individuals (30-80 years) was tested at baseline and after 6 years of follow-up. Serum concentrations of different sterols related to cholesterol were measured. Serum levels of lathosterol and lanosterol correlated negatively with cognitive performance on the Word Learning tests for verbal learning and memory. This was observed at baseline and follow-up and was independent of age, sex and educational level. Furthermore, the levels of lathosterol and lanosterol at baseline correlated with performance on the Stroop test and Word Learning tests over the 6-year follow-up period. Serum levels of 27-hydroxycholesterol and 24S-hydroxycholesterol showed inconsistent correlations, while cholesterol, desmosterol, sitosterol and campesterol were not related to cognitive performance.Thus, relative high serum ratios of the cholesterol precursors lanosterol and lathosterol, indicative for a high rate of endogenous cholesterol synthesis, are associated with relatively low memory performance in this aging population.

Comparison of the hepatic clearances of campesterol, sitosterol, and cholesterol in healthy subjects suggests that efflux transporters controlling intestinal sterol absorption also regulate biliary secretion

BACKGROUND

Recently identified ABCG5/8 transporters are responsible in part for the different absorption rates of campesterol, sitosterol, and cholesterol. These transporters are also expressed in the liver and might regulate biliary sterol secretion.

AIMS

This study was therefore conducted to determine the biliary secretion rates and hepatic clearances of campesterol, sitosterol, and cholesterol.

SUBJECTS

Six healthy, male volunteers.

METHODS

Deuterium labelled sitosterol and campesterol, and unlabelled sitostanol were constantly infused together with a liquid formula using a duodenal perfusion technique. Biliary secretion and hepatic clearance rates were calculated from hourly bile and plasma samples.

RESULTS

Plasma concentrations of cholesterol, campesterol, and sitosterol averaged 167.5 (50) mg/dl (SD), 0.50 (0.22) mg/dl, and 0.30 (0.10) mg/dl, respectively. Sitosterol showed a significantly higher biliary secretion rate (1.23 (0.87) mg/h) than campesterol (0.76 (0.54) mg/h, p=0.0321), but both plant sterols had significantly lower biliary secretion rates compared with cholesterol (47.7 (17.5) mg/h; p=0.001 for both). Hepatic clearance of cholesterol (0.31 (0.18) dl/h) was significantly lower compared with campesterol (2.11 (2.51) dl/h) and sitosterol (4.97 (4.70) dl/h; p=0.028 for both), and the clearance of campesterol was significant lower compared with sitosterol (p=0.028).

CONCLUSION

The observed inverse relation between hepatic clearance and known intestinal absorption of cholesterol, campesterol, and sitosterol supports the hypothesis that the ABCG5/8 transporters regulating intestinal sterol absorption might also be involved in biliary sterol excretion.

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 Alzheimer's 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.

Oxidized plant sterols in human serum and lipid infusions as measured by combined gas-liquid chromatography-mass spectrometry

Some oxidized forms of cholesterol (oxysterols) are thought to be atherogenic and cytotoxic. Because plant sterols are structurally related to cholesterol, we examined whether oxidized plant sterols (oxyphytosterols) could be identified in human serum and soy-based lipid emulsions. We first prepared both deuterated and nondeuterated reference compounds. We then analyzed by gas-liquid chromatography-mass spectrometry the oxyphytosterol concentrations in serum from patients with phytosterolemia or cerebrotendinous xanthomatosis, in a pool serum and in two lipid emulsions. 7-Ketositosterol, 7 beta-hydroxysitosterol, 5 alpha, 6 alpha-epoxysitosterol, 3 beta,5 alpha,6 beta-sitostanetriol, and probably also 7 alpha-hydroxysitosterol were present in markedly elevated concentrations in serum from phytosterolemic patients only. Also, campesterol oxidation products such as 7 alpha-hydroxycampesterol and 7 beta-hydroxycampesterol were found. Interestingly, sitosterol was oxidized for approximately 1.4% in phytosterolemic serum, which is rather high compared with the approximate 0.01% oxidatively modified cholesterol normally seen in human serum. The same oxyphytosterols were also found in two lipid emulsions in which the ratio of oxidized sitosterol to sitosterol varied between 0.038 and 0.041. In conclusion, we have shown that oxidized forms of plant sterols are present in serum from phytosterolemic patients and two frequently used soy-based lipid emulsions. Currently, it is unknown whether oxyphytosterols affect health, as has been suggested for oxysterols. However, 7 beta-hydroxycholesterol may be one of the more harmful oxysterols, and both sitosterol and campesterol were oxidized into 7 beta-hydroxysitosterol and 7 beta-hydroxycampesterol. The relevance of these findings therefore deserves further exploration.

Concentrations of different sterols in the striatum and serum of 3-nitropropionic acid-treated Wistar and Lewis rats

In the present study, we examined the long-term effect of oxidative stress induced neurodegeneration on sterol concentrations in striatum and serum of Wistar and Lewis rats. Three weeks after treatment with 3-nitropropionic acid, no differences in 24S-hydroxycholesterol concentrations were observed in striatal homogenates and serum. Ratios of striatal campesterol to cholesterol were higher after 3-nitropropionic acid treatment as compared to controls of both rat strains suggesting an increased passage of this exogenous plant sterol across the blood-brain-barrier. Ratios of lathosterol to cholesterol in serum and striatum were lower in treated rats as compared with controls of both rat strains. Absolute concentrations of serum and striatal cholesterol precursors and plant sterols differed between the controls of both rat strains. It was concluded that the changes observed in sterol concentrations in the striatum and serum indicate that cholesterol homeostasis may be affected during neurodegenerative processes associated with blood-brain-barrier damage.

Total plasma homocysteine and related amino acids in end-stage renal disease (ESRD) patients measured by gas chromatography-mass spectrometry--comparison with the Abbott IMx homocysteine assay and the HPLC method

Increased concentrations of homocysteine probably contribute to the high cardiovascular morbidity and mortality in hemodialysed end-stage renal disease (ESRD) patients and are determined by a variety of factors such as age, residual renal function, and vitamin status. Fasting plasma concentrations of total homocysteine, methionine, cysteine, and cystathionine were determined by gas chromatography-mass spectrometry (GC-MS) in 131 ESRD patients receiving daily oral folate (160-320 microg) and vitamin B6 (10-20 mg) supplements. Concentrations of homocysteine determined by GC-MS were compared with those measured by high-performance liquid chromatography (HPLC) and an immunofluorescence method (IMx analyzer) using Passing-Bablok regression analysis. Mean plasma concentration of total homocysteine determined by GC-MS (28.7+/-11.9 micromol/l [mean+/-SD]) was significantly lower than that determined by HPLC (34.0+/-14.5 micromol/l; p<0.001) or IMx (32.4+/-13.9 micromol/l; p<0.001). A close correlation existed between GC-MS and HPLC (r=0.931; y=1.203 x+0.279) and GC-MS and IMx (r=0.896; y=1.105 x+0.766). Linear regression analysis showed positive correlations between plasma concentrations of homocysteine and cysteine (r=0.434; p<0.001) and homocysteine and cystathionine (r=0.187; p=0.032). Plasma concentrations of homocysteine correlated negatively with folate (r=-0.281; p=0.001) and vitamin B12 (r=-0.229; p=0.009). GC-MS proved to be a sensitive and reliable method for the determination of total plasma homocysteine and related amino acids. Despite vitamin supplementation, ESRD patients requiring chronic maintenance hemodialysis, have high plasma concentrations of homocyst(e)ine which seems to be metabolized mainly within the transsulfuration pathway, while remethylation to methionine seems to be disturbed.

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

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.

Neutral sterols of rat epididymis. High concentrations of dehydrocholesterols in rat caput epididymidis

Phospholipids and sterols are known to have multiple functions in reproductive tissue of mammals. High concentrations of the cholesterol precursor desmosterol have been described in testis, epididymis, and spermatozoa of various species. These findings and the recent discovery of some cholesterol precursors as meiosis-activating sterols suggest important functions of cholesterol precursors in fertility. Many sterol intermediates appear from the 19-step conversion of lanosterol, the first sterol synthesized in the cascade of cholesterol synthesis, to cholesterol. The biochemical basis of the genetically inherited Smith-Lemli-Opitz syndrome has been described as a defective conversion of 7-dehydrocholesterol to cholesterol. Since this discovery, interest has focused on this special cholesterol precursor. Here, we report high concentrations of 7- and 8-dehydrocholesterol in caput epididymidis and spermatozoa derived from caput epididymidis of Sprague-Dawley and Wistar rats, which comprised up to 30% of total sterols. In contrast to caput epididymidis, 7- and 8-dehydrocholesterol were barely detected in cauda epididymidis or testis. Desmosterol increased several times from caput to cauda epididymidis. This is the first report of the natural appearance of high concentrations of dehydrocholesterols in mammalian tissue, and it underlines the putative importance of cholesterol precursors in reproductive tissue.