Inhibition of novel lipoprotein(a) receptor major facilitator superfamily domain containing 5 (MFSD5) reduces development of aortic valve calcification

Funding Acknowledgements

Type of funding sources: Other. Main funding source(s): Private grant from Kowa Pharmaceuticals to Brigham and Woman's Hospital

Calcific aortic valve stenosis (CAVS) is the most prevent valvular heart disease in the western world increasing exponentially with age, with an 112% increase in CAVS deaths in the last three decades; however no therapeutic treatment is currently available. Recently, lipoprotein(a) [Lp(a)] has been demonstrated to be an independent and causal risk factor for CAVS, yet the understanding of its cellular uptake and catabolism is limited thus underscoring the need for further investigation.

This study aimed to determine a target receptor, unique for Lp(a) on the surface of valvular interstitial cells (VICs) and ascertain the role of the receptor on the development of VIC calcification.

Unbiased ligand-receptor capture mass spectrometry (TriCEPS) was used to identify target receptor, with western blotting, ELISA, qPCR, alizarin red calcium staining and immunofluorescence used to validate the targets in vitro via siRNA inhibition and overexpression. Transmission electron microscopy (TEM) was used to determine uptake of Lp(a) within excised human valves. Identification of small molecule inhibitors was assessed computationally via the L1000 dataset, with the top hit candidate validated in vitro. Genotype-phenotype studies were examined using the United Kingdom Biobank (UKBB) and the Millions Veterans Program. Linear regression was used to evaluate association between aortic stenosis and plasma Lp(a) levels, and a phenotype-wide association analysis was then performed against this generated ‘genotype’.

Ligand-receptor capture mass spectrometry was used to detect novel membrane proteins with specific binding to Lp(a); MFSD5, MRC2, LDLR were identified as possible candidates. MFSD5 RNAscope demonstrated its presence in human aortic valves. Lp(a) uptake in VICs was confirmed via western blot and TEM. MFSD5 siRNA significantly reduced dil-labelled Lp(a) uptake in human VICs (p=0.003) and HEPG2 cells (p=0.0003), conversely MFSD5 overexpression increased uptake (p=0.0345, p=0.0318), whilst specificity of MFSD5 to Lp(a) alone was shown via no change in LDL uptake following MFSD5 inhibition (p=0.616, p=0.991). MFSD5 inhibition reduced RUNX2 (p=0.0124) and Osteocalcin (p<0.001) RNA expression and reduced alizarin red staining following culture in Lp(a) osteogenic media for 21 days (p<0.0033). Druggability of MFSD5 was confirmed by the L1000 database, which identified aminopurvalanol as a binding partner for MFSD5 and significantly reduced Lp(a) uptake within VICs (p=0.0091). MFSD5-loss of function within the UKBB showed no significant cardiovascular association, however 50kb +/- of the MFSD5 gene showed nominal association with hyperlipidaemia and atrial fibrillation.

The current study demonstrates the novel Lp(a) receptor MFSD5 may be responsible for uptake of Lp(a) within VICs, resulting in the development of aortic valve calcification, highlighting the need for further exploration into the role of MFSD5 in aortic valve disease.

Long-term safety and efficacy of bempedoic acid in patients at high risk of atherosclerotic cardiovascular disease: results from the CLEAR Harmony open-label extension study

Background

Bempedoic acid (BA) is an oral first-in-class, ATP-citrate lyase inhibitor that lowers low-density lipoprotein cholesterol (LDL-C) levels in adults with hypercholesterolemia. In the phase 3 CLEAR Harmony study (NCT02666664, n=2230), BA 180 mg for 52 weeks significantly lowered LDL-C at week 12 compared with placebo and was maintained for 52 weeks in hypercholesterolemic patients with atherosclerotic cardiovascular disease (ASCVD) and/or heterozygous familial hypercholesterolemia (HeFH) on stable, maximally tolerated statins.

Purpose

To report long-term safety, tolerability, and efficacy of BA from the CLEAR Harmony open-label extension (OLE) study (NCT03067441).

Methods

After completing the 52-week placebo-controlled CLEAR Harmony study, patients immediately entered the OLE and received BA for 78 weeks, followed by a 4-week washout period; the potential cumulative exposure to BA was 2.5 years. The primary endpoint was long-term safety of BA in the OLE.

Results

A total of 1462 patients enrolled in the OLE (BA n=970; placebo n=492 from CLEAR Harmony). At OLE baseline, mean (SD) age was 66.9 (8.7) years, 73.9% were male, 96.3% had ASCVD, 3.7% had HeFH with or without ASCVD, and all were receiving statins (93.5% moderate or high intensity). At baseline of CLEAR Harmony, patients had mean (SD) LDL-C of 102.9 (29.9) mg/dL (BA) and 99.0 (24.2) mg/dL (placebo). The majority of OLE patients (86.2%, n=1260) completed 78 weeks of BA treatment. At week 12 and 78 of OLE treatment, respectively, mean LDL-C lowering from CLEAR Harmony baseline was –14.9% and –14.4%. A total of 1143 patients (78.2%) reported a treatment-emergent adverse event (TEAE), and 299 (20.5%) reported a serious TEAE. TEAEs of special interest, determined by the therapeutic area or prior observations in preclinical or early clinical studies, occurred at similar rates as CLEAR Harmony (creatine kinase elevations, 1.8%; gout, 2.6%; hepatic enzyme elevations, 2.0%; hypoglycemia, 1.2%; muscular disorders, 8.5%; neurocognitive disorders, 0.9%; new onset/worsening diabetes mellitus, 5.5%; renal disorders, 2.8%) with biochemical changes that were stable over the course of the study and approached baseline levels after treatment discontinuation. Overall, 114 patients (7.8%) reported a TEAE leading to discontinuation of BA (most common: myalgia [0.6%], muscle spasm [0.5%]).

Conclusion

Durable lipid lowering was observed through 78 weeks of BA treatment and patient adherence to BA therapy was high (86.2%). Overall safety during the OLE was similar to results reported in the 52-week-long CLEAR Harmony study and the overall BA phase 3 clinical program, with no new safety findings.

Funding Acknowledgement

Type of funding source: Private company. Main funding source(s): Esperion Therapeutics, Inc., funded the research for this study and provided writing support for this abstract. Medical writing assistance was provided by Agnella Izzo Matic, PhD, CMPP, and Kelly M Cameron, PhD, CMPP, of JB Ashtin.

Lipoprotein(a) is a strong risk factor for Aortic Valve Calcium

Background

Aortic valve calcium (AVC) is an important hallmark of aortic valve stenosis, which is the most common valvular heart disease in the Western world. Studies suggesting an important role for lipoprotein(a) [Lp(a)] in the etiology of AVC are accumulating, yet population-based evidence is scarce. Therefore, we investigated the association of Lp(a) with the presence of AVC in two large cohorts.

Methods

A total of 2412 participants from the population-based Rotterdam Study (52% women, mean age=69.6±6.3), and 859 asymptomatic persons from the Amsterdam Medical Center outpatient clinic for familial premature (non-valvular) atherosclerosis (57%women, mean age=45.9±11.6) underwent blood sampling to determine serum Lp(a) and non-enhanced cardiac CT-scan to assess AVC. We combined both cohorts and investigated the association of Lp(a) with the presence and amount of AVC using logistic and linear regression models, adjusting for age, sex, smoking, body mass index, non-high density lipoprotein cholesterol and use of antihypertensive medication.

Results

Out of a total of 3271 subjects with an average age of 63.4±7.98, AVC was present in 844 (25.8%) individuals. Higher levels of Lp(a) were associated with the presence of AVC, independent of age, sex and cardiovascular risk factors [Odds ratio (OR) per 1-SD increase in Lp(a): 1.39 (95% CI:1.27; 1.51). In persons with AVC, a higher level of Lp(a) was also related to larger volume of AVC [β per 1-SD increase in Lp(a): 0.76 (95% CI:1.27; 1.51)]. All findings were similar across both cohorts.

Conclusion

Lp(a) is a prominent and independent marker of the presence and amount of AVC in the general population. Future studies investigating the effect of Lp(a) lowering on the progression of AVC are warranted.

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): NESTOR program for geriatric research, the Netherlands Heart Foundation, the Netherlands Organization for Scientific Research, the Health Research and Development Council (28-2975 and 97-1-364), and the Municipality of Rotterdam

Vasculoprotective properties of the endothelial glycocalyx: effects of fluid shear stress

The endothelial glycocalyx exerts a wide array of vasculoprotective effects via inhibition of coagulation and leucocyte adhesion, by contributing to the vascular permeability barrier and by mediating shear stress-induced NO release. In this review, we will focus on the relationship between fluid shear stress and the endothelial glycocalyx. We will address the hypothesis that modulation of glycocalyx synthesis by fluid shear stress may contribute to thinner glycocalyces, and therefore more vulnerable endothelium, at lesion-prone sites of arterial bifurcations. Finally, we will discuss the effects of known atherogenic stimuli such as hyperglycaemia on whole body glycocalyx volume in humans and its effect on endothelial function.

Folates and cardiovascular disease

It is increasingly recognized that folates may play a role in the prevention of cardiovascular disease. Over the last few years, several studies have reported beneficial effects of folates on endothelial function, a surrogate end point for cardiovascular risk. Consistently, observational studies have demonstrated an association between folate levels and cardiovascular morbidity and mortality. The exact mechanisms underlying the ameliorative effects of folates on the endothelium remain to be elucidated. Thus far, most studies have focused on the homocysteine-lowering effects of folates. However, recently, benefits of folates independent of homocysteine lowering have also been reported. Potential mechanisms include antioxidant actions, effects on cofactor availability, or direct interactions with the enzyme endothelial NO synthase. Obviously, beneficial effects of folates on cardiovascular risk would have important clinical and dietary consequences. However, for definite conclusions, the completion of ongoing randomized controlled trials will have to be awaited.

Nitric oxide production is reduced in patients with chronic renal failure

In patients with chronic renal failure (CRF), atherosclerosis is a major cause of cardiovascular morbidity and mortality. Generally, atherosclerosis has been associated with a reduced bioavailability of nitric oxide (NO). Experimental studies have indicated the presence of enhanced NO degradation by reactive oxygen species as well as decreased NO production as possible causes for this reduced NO bioavailability. So far, the question whether or not NO production is impaired in patients with CRF has never been investigated. Therefore, we measured whole body NO production in 7 patients with CRF, and in 7 matched healthy subjects. To assess the relative importance of a dysfunction of NO synthase (NOS), we compared the NO production of these patients to that of 2 other groups known to have endothelial dysfunction, ie, 7 patients with familial hypercholesterolemia (FH) who did not yet have signs of clinical cardiovascular disease (all nonsmokers), and 5 cigarette smokers. These groups were also compared with 7 nonsmoking, age-matched healthy subjects. Whole body NO production, determined as in vivo arginine-to-citrulline conversion, was assessed by giving an intravenous infusion of [15N2]-arginine as a substrate for NOS and measuring isotopic plasma enrichment of [15N]-citrulline by LC-MS. NO production in the CRF patients (0.13+/-0.02 micromol. kg-1. h-1) was significantly lower (P<0.05) than in the corresponding control group (0.23+/-0.09 micromol. kg-1. h-1). NO production also tended to be lower in the FH patients (0.16+/-0.04 micromol. kg-1. h-1), but the difference with the corresponding control group did not reach significance (0.22+/-0.06 micromol. kg-1. h-1). In the group of smokers, NO production was similar to that in nonsmokers (0. 22+/-0.09 micromol. kg-1. h-1). In conclusion, it is demonstrated for the first time that basal whole body NO production is reduced in patients with CRF. This finding implies that therapeutic interventions to endothelial dysfunction in these patients should be primarily directed toward improvement of NO production. The finding of only a tendency toward reduction of NO production in patients with FH and the absence of a reduction in cigarette smokers suggests that other mechanisms such as enhanced NO degradation may be involved in the decrease of NO bioavailability in these groups.

Origin of superoxide production by endothelial nitric oxide synthase

Using fluorescence optical and electron spin resonance spectroscopy, we have investigated the production of superoxide by bovine endothelial nitric oxide synthase (NOS). In contrast to neuronal NOS, the heme moiety is identified as the exclusive source of superoxide production by endothelial NOS. Thus, calmodulin-mediated enzyme regulation affects production of nitric oxide and superoxide simultaneously and inseparably. The balance between the nitric oxide/superoxide reaction pathways may be shifted by addition of exogenous heme-specific agents, such as tetrahydrobiopterin. Our results have direct relevance for the pathophysiology of atherosclerosis.

NO activity in familial combined hyperlipidemia: potential role of cholesterol remnants

OBJECTIVE

Patients with familial combined hyperlipidemia (FCH) have an increased cardiovascular mortality despite only moderate elevations of LDL-cholesterol. Since endothelial NO release is intimately involved in the anti-atherosclerotic effects of the endothelium, we studied the effect of short-term lipid-lowering therapy on NO-mediated vasodilatation in patients with FCH. In view of only moderate LDL elevations, we evaluated whether alterations in other lipid fractions upon therapy correlated to changes in NO-mediated vasodilatation.

METHODS

NO activity was assessed by serotonin-induced, nitric oxide-mediated increase in forearm blood flow (FBF). Measurements were performed 2 weeks off and 4 weeks on lipid-lowering therapy in 12 FCH patients using forearm venous occlusion plethysmography. Control experiments were performed in 12 healthy subjects.

RESULTS

Serotonin-induced vasodilatation was impaired in FCH patients (FBF (unit ml/100 ml forearm tissue/min) from 3.0 (0.3) to 4.8 (0.4)) compared to controls (FBF from 2.9 (0.3) to 6.5 (0.6); p < 0.05 vs. FCH). FBF response to serotonin improved significantly upon lipid-lowering therapy (from 3.0 (0.3) to 5.7 (0.5); p < 0.05 treated vs. untreated). The level of improvement in endothelial function was significantly correlated to the absolute reduction of intermediate density lipoproteins upon lipid-lowering therapy (r = -0.64; p < 0.05), whereas it did not correlate to changes in VLDL- or LDL-cholesterol, nor to Lp(a).

CONCLUSION

Patients with familial combined hyperlipidemia have impaired NO-mediated vasodilatation, that responds rapidly to lipid lowering medication, and may be related to changes in intermediate density lipoproteins.

Tetrahydrobiopterin restores endothelial function in hypercholesterolemia

In hypercholesterolemia, impaired nitric oxide activity has been associated with increased nitric oxide degradation by oxygen radicals. Deficiency of tetrahydrobiopterin, an essential cofactor of nitric oxide synthase, causes both impaired nitric oxide activity and increased oxygen radical formation. In this study we tested whether tetrahydrobiopterin deficiency contributes to the decreased nitric oxide activity observed in hypercholesterolemic patients. Therefore, L-mono-methyl-arginine to inhibit basal nitric oxide activity, serotonin to stimulate nitric oxide activity, and nitroprusside as endothelium-independent vasodilator were infused in the brachial artery of 13 patients with familial hypercholesterolemia and 13 matched controls. The infusions were repeated during coinfusion of L-arginine (200 microg/kg/min), tetrahydrobiopterin (500 microg/min), or the combination of both compounds. Forearm vasomotion was assessed using forearm venous occlusion plethysmography and expressed as ratio of blood flow between measurement and control arm (M/C ratio). Tetrahydrobiopterin infusion alone did not alter M/C ratio. Both the attenuated L-mono-methyl-arginine-induced vasoconstriction as well as the impaired serotonin-induced vasodilation were restored in patients during tetrahydrobiopterin infusion. Tetrahydrobiopterin had no effect in controls. In conclusion, this study demonstrates restoration of endothelial dysfunction by tetrahydrobiopterin suppletion in hypercholesterolemic patients.