The seaweed-derived oxysterol, saringosterol, was recently identified as an agonist of the liver-X-receptor β (LXRβ). LXRβ is a transcription factor that plays a crucial role in lipid metabolism, specifically in cholesterol homeostasis and a variety of chronic inflammatory diseases. However, its impact on aortic valve stenosis is unknown.

 

In the present study, we investigated the effects of saringosterol-containing seaweed extracts in a murine aortic valve stenosis model. After wire-induced injury of the aortic valve, animals were fed with either saringosterol-containing extract- (229.4 µg/d) or vehicle enriched chow. Haemodynamic changes were assessed using echocardiography. Hepatic and plasma concentrations of saringosterol were measured using gas chromatography-mass spectrometry with selected ion-monitoring. Histological sections through the aortic valves were stained to assess the cell types and extracellular matrix. Human aortic valve interstitial cells (VIC) were used to study the underlying molecular mechanisms of saringosterol treatment. Finally, stenotic human aortic valves were assessed by mRNA sequencing and subsequent qPCR.

Treatment with saringosterol resulted in significant accumulation of saringosterol in liver tissue (saringosterol vs. vehicle: 31.82 ± 5.03 ng/mg vs. 1.86 ± 0.04 ng/mg; n = 10–11; p < 0.0001). Correspondingly, an upregulation of downstream-targets of LXR was observed. Six weeks after wire-injury, aortic valve peak velocity increased. This effect was attenuated in mice receiving saringosterol (saringosterol vs. vehicle: 1348 ± 112.6 mm/s vs. 1712 ± 118.1 mm/s; n = 10–11; p < 0.05). This finding was accompanied by a reduction in valve area by H.E.-staining (saringosterol vs. vehicle: 0.119 ± 0.013 mm² vs. 0.163 ± 0.011 mm²; n = 10–11; p < 0.05). In vitro, saringosterol dose-dependently increased the transcription of ABCA1 and ABCG1 in VIC. This effect was completely abolished by pharmacological inhibition of the LXR receptor with its antagonist GSK2033. Furthermore, saringosterol reduced the expression of RUNX-2 and ACTA-2 in procalcifing medium, suggesting less differentiation into osteoblastic and myofibroblastic phenotypes, respectively. Finally, mRNA sequencing revealed LXR-associated pathways to be significantly upregulated in human aortic valve stenosis. 

 

To our knowledge, the present study is the first to describe LXRβ to be causally involved in both human and experimental aortic valve stenosis. Oral application of seaweed-derived saringosterol attenuated aortic stenosis in vivo. LXRβ activation prevented adverse cell differentiation in vitro and thus decreased the aortic stenosis phenotype. Upregulation of LXRβ-associated pathways in human aortic valve stenosis may represent an escape mechanism and shows the therapeutic potential of saringosterol.