LXR-beta signalling is a key mediator in the pathogenesis of aortic valve stenosis and its prevention by saringosterol

Background

Cholesterol metabolism contributes as a risk factor for aortic valve stenosis (AS), but pharmacological approaches remained unsatisfying. The liver-X-receptor (LXR) is a key regulator in cholesterol metabolism, though its clinical use is limited due to unwanted side effects. The seaweed-derived oxysterol saringosterol is an agonist of the LXRβ, promising a more favourable tolerability.

Purpose

This study aimed to better understand the pathophysiology of aortic valve stenosis and to assess the potential of saringosterol as a targeted pharmacotherapy.

Methods

Tissue samples from aortic valves were collected from patients with AS or aortic valve regurgitation (AR). Transcriptomics were performed and gene ontology (GO) analysis was used to determine pathways and genes that are relevant to AS, and then validated using qPCR.

In vivo, mice received a wire-induced aortic valve stenosis and were either fed a diet supplemented with saringosterol or control diet. Haemodynamic characteristics were assessed using echocardiography. Additionally, hepatic concentrations of saringosterol, expression of LXRβ regulated genes as well as aortic valve thickness and composition were assessed.

In vitro, human aortic valve interstitial cells (VIC) were cultured in a procalcifing medium and stimulated with saringosterol to investigate the underlying molecular mechanisms.

Results

Transcriptomic analysis of AS samples revealed the regulation of several GO-terms related to cholesterol- or lipid metabolism. Many of the genes identified were regulated by LXRβ, suggesting its pathophysiological relevance in AS. We validated this assumption by performing qPCR from aortic valves for the most prominent downstream targets of LXRβ, ABCA1 and ABCG1, with both being differentially regulated.

In vivo, treatment with saringosterol for six weeks resulted in a significant accumulation of saringosterol in liver tissue as well as induction of LXRβ-regulated genes. Furthermore, treatment with saringosterol strikingly reduced the development of AS after wire injury as assessed by echocardiographic and histological measurements.

In vitro, the differentiation of VIC into osteoblastic and myofibroblastic phenotypes was abolished by saringosterol, which reduced the expression of the procalcifying mediators RUNX-2 and ACTA-2 in a dose-dependent manner.

Conclusion

We identified LXRβ-signalling as a key regulator in the pathophysiology of AS. Transcriptomic analyses revealed that cholesterol metabolism was altered in human AS, and many of the genes involved were linked to the LXRβ. In a murine model, we demonstrated that oral application of saringosterol induced LXRβ-activity and mitigated the development of AS. In vitro experiments demonstrated that saringosterol prevents adverse cell differentiation of VIC, which provides a mechanistic explanation.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): BONFOR Universität Bonn

P5625Markers for cholesterol absorption are associated with In-stent-restenosis after coronary stenting in stable coronary artery disease: An Optical Coherence Tomography study

Background

Plant sterols are suspected to exert atherosclerotic propensity. Modern drug-eluting stents are superior to bare metal stents but show a late catch up phenomenon for restenosis. Due to its superb resolution, optical coherence tomography (OCT) has the capability to identify and quantifiy very early patterns of in-stent proliferation. Studies have shown that in-stent neointimal proliferation is linked to late in-stent stenosis.

Purpose

This study aimed to analyze associations of plasma levels for markers of cholesterol homeostasis such as campesterol and sitosterol (markers for cholesterol absorption) as well as lanosterol (marker for cholesterol synthesis)and and their respective oxides with In-stent restenosis after stent deployment in stable coronary artery disease.

Methods

Plasma cholesterol was measured by gas chromatography-flame ionization detection. Plasma campesterol, sitosterol and lanosterol and their oxides were analyzed by gas chromatography-mass selective detection. In-stent proliferation (restenosis) was assessed after six months by OCT in 33 patients (21 males). A quantitative OCT algorithm was applied to each stent by steps of one mm and in-stent proliferation volumes and areas were calculated and normalized to stent length and area. In-stent proliferation can be measured by OCT as global volumes and focal areas.

Results

No clinically significant restenosis or angiographic restenosis of >30% was observed at 6-month f/u. Mean cholesterol level was 166,5±62,8 mg/dl and positively correlated with proliferation volume/cm (r=0.316, p=0.037) and absolute median proliferation area (r=0.322, p=0.029). Absolute median proliferation area and relative median proliferation area correlated positively with markers for cholesterol absorption such as campesterol-to-cholesterol (r=0.277, p=0.07 and 0.315, p=0.037) and sitosterol-to-cholesterol (r=0.237, p=0.092 and 0.322, p=0.034), whereas lanosterol (a marker for cholesterol synthesis) and its ratio to cholesterol correlated negatively with proliferation volumes and areas (p<0.05; table). Moreover, 7-beta-OH-campesterol correlated positively with proliferation volumes and areas (p<0.05, table). Also, the ratio of 7-beta-OH-campesterol-to-cholesterol correlated positively with proliferation volumes and areas (p<0.1,; table), but did not reach significance in this relatively small sample size. Morevover, there was a positive association of the sum of all plant sterol oxides with In-stent restenosis (data not shown).

Conclusions

In this hypothesis-generating study, in-stent proliferation assessed by OCT at six months follow-up was positively associated with markers for cholesterol absorption and negatively associated with markers for cholesterol synthesis. Larger studies will have to evaluate whether patients with high cholesterol absorption might benefit in particular from combined-lipid-lowering therapy with a statin and a cholesterol absorption Inhibitor.

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.

The Crystallography of Metal Halides formed within Single Walled Carbon Nanotubes

The crystal growth behaviour and crystallography of a variety of metal halides incorporated within single walled carbon nanotubes (SWNTs) as determined by high resolution electron microscopy (HRTEM) is described. Simple packed structures, such as the alkali halides, form related structures within SWNTs that are found to be integral atomic layers in terms of their thickness as a function of the encapsulating SWNT diameter. An enhanced HRTEM image restoration technique reveals precise data concerning lattice distortions present in these crystals. More complex structures, such as those derived from 3D complex, layered and chain halides form related crystal structures within SWNTs. In narrow SWNTs (i.e. with diameters less than ca. 1.6 nm), structures consisting of individual 1D polyhedral chains (1D-PHCs) were obtained that were derived from the corresponding bulk halides structures. In the case of infinite 3D network and layered halides, the 1D polyhedral chains form with lower co-ordinations than in the bulk. Molecular halides also intercalate into SWNTs but these do not readily form organised structures within SWNTs.

A composite method for the determination of the chirality of single walled carbon nanotubes

An approach to the unambiguous determination of the conformation of individual single walled nanotubes utilizing high-resolution transmission electron microscopy and digital image processing is described. The exit plane wave of single walled nanotubes restored from a focal series of images is used in a stepwise characterization procedure utilizing both the phase of the real space restoration and its Fourier transform. A combination of these complementary characterization steps yields an accurate measurement of the chiral vector for an individual nanotube.

Nocturnal plasma melatonin levels after flunitrazepam administration in healthy subjects

Polysomnographic sleep patterns and melatonin secretion were investigated in 5 young (age 25.6 +/- 1.1 years) and 5 middle-aged (age 49.4 +/- 5.4 years) healthy male subjects after intravenous administration of 1 mg flunitrazepam and placebo in a randomized, double-blind and cross-over setting. The area under the curve (AUC) of total nocturnal melatonin plasma concentration decreased 23.3 +/- 11.5% in young subjects (P < or = 0.05) and 39.3 +/- 5.2% in middle-aged subjects (P < or = 0.05) after flunitrazepam infusion compared with placebo infusion. Differences in nocturnal peak values of melatonin were 5.4 +/- 22.0% in young subjects (not significant) and 34.0 +/- 14.7% in middle-aged subjects (p < or = 0.05). Flunitrazepam significantly (P < or = 0.05) improved sleep latency and the number of sleep stage changes in the group of all subjects. These results show that, although the benzodiazepine flunitrazepam improves sleep, it reduces the nocturnal secretion of melatonin, and therefore alters the circadian rhythm of a hormone which is supposed to play a special role in circadian sleep-wake rhythmicity.