Aortic Stenosis and Statins

Innovative technique for the direct determination of proteins in calcified aortic valves

Aortal valve mineralization very frequently causes a genesis of aortic stenosis, which is the most often surgically treated heart disease. Hydroxyapatite deposits have been identified as one of the causes leading to the loss of elasticity of the aortic valves. It is known that phosphates/calcium is accumulated in valve tissues during mineralization, but the mechanism of this process remains unclear. The work is focused mainly on the study of protein composition of mineralized aortic valves by nano-liquid chromatography electrospray ionization in a quadrupole orthogonal acceleration time-of-flight mass spectrometry. New methodological approach based on direct enzymatic digestion of proteins contained in hydroxyapatite deposits was developed for the study of pathological processes connected with osteogenesis. Our objectives were to simplify the traditional analytical protocols of sample preparation and to analyze the organic components of the explanted aortic valves for significant degenerative aortic stenosis. The study of aortic valve mineralization on the molecular level should contribute to understanding this process, which should consequently lead to effective prevention as well as to new ways of treatment of this grave disease.

A medical therapy for aortic valve sclerosis and aortic valve stenosis? Rationale of the ASSIST study (Asymptomatic aortic Sclerosis/Stenosis: Influence of STatins): a large, observational, prospective, multicenter study of the Italian Society of Cardiovascular Echography

Progression of sclerosis and stenosis is substantially unpredictable in the individual patient: in some cases it is very slow, in others it is accelerated. In addition, different patterns of progression (linear and non-linear) are possible. It has been suggested that the aortic valve lesion can be considered a form within the spectrum of the same atherosclerotic disease. In this context it seemed reasonable to hypothesize that targeted medical therapy could retard the progression of the disease. In particular HMG-CoA reductase inhibitors (statins) and angiotensin-converting enzyme inhibitors have been tested. The first experimental and clinical studies are now available, even though they are not conclusive to date. Large, prospective, randomized trials are ideally needed, but they are quite difficult, if not even impossible, to realize in practice. The ASSIST study (Asymptomatic aortic Sclerosis/Stenosis: Influence of STatins) of the Italian Society of Cardiovascular Echography aims to create a large, prospective, observational investigation, involving many centers of echocardiography and thousands of patients, in order to provide from the real clinical world at least some of the answers to this unsolved question.

Calcific Aortic Valve Stenosis in Old Hypercholesterolemic Mice

Background— Hypercholesterolemia and old age are clinical risk factors for development of aortic valve stenosis, and hypercholesterolemia is a putative therapeutic target. We tested the hypothesis that calcification and aortic valve stenosis would develop in genetically hypercholesterolemic old mice.

Methods and Results— Twenty-four low-density lipoprotein receptor–deficient apolipoprotein B-100–only ( LDLr −/− ApoB 100/100 ) mice were fed normal chow from weaning until age 20.1±0.5 months (mean±SE; range 17 to 22 months). Twenty-one age-matched (20.8±0.9 months, range 17 to 25 months) C57Bl/6 mice served as controls. Echocardiographic imaging was used to assess morphology and function of the aortic valve and left ventricle. A subset of 12 mice underwent invasive hemodynamic assessment of aortic valve function. Functionally significant aortic stenosis, with >75% reduction in valve area, occurred in 8 of 24 LDLr −/− ApoB 100/100 mice and in 0 of 21 controls ( P =0.01). In the subset that underwent catheterization, mice with echocardiographic evidence of aortic stenosis had a systolic transvalvular gradient of 57±6 mm Hg. In the group of all LDLr −/− ApoB 100/100 mice with aortic stenosis, left ventricular mass was increased by 67% ( P =0.001) and ejection fraction was decreased by 30% ( P =0.004) compared with LDLr −/− ApoB 100/100 without aortic stenosis. Von Kossa staining of the aortic valve demonstrated abundant mineralization in LDLr −/− ApoB 100/100 mice but not in control mice. Superoxide (oxyethidium fluorescence) was present in valve tissue from all 3 groups of mice and was more abundant in mice with aortic stenosis.

Conclusions— Hypercholesterolemic LDLr −/− ApoB 100/100 mice are prone to develop calcification and oxidative stress in the aortic valve, with functional valvular heart disease, mimicking the clinical syndrome. This discovery holds promise for elucidation of the pathophysiology of aortic valve disease mechanisms and for the design of effective nonsurgical treatment.

Oxidative Stress and Vascular Disease

There is compelling evidence that oxidative stress plays a key role in the pathophysiology of several major cardiovascular diseases. In atherosclerosis, hypertension, stroke, diabetes, and heart failure, expression of superoxide is increased in blood vessels, and endothelial vasomotor function is impaired, presumably caused in large part by inactivation of nitric oxide by superoxide. Endothelial dysfunction is predictive of cardiovascular risk, and probably plays a key role in the pathophysiology of atherosclerosis and its complications. In preliminary studies in hypercholesterolemic mice and in older humans, we have found high levels of superoxide in the aortic valve, as well as aorta. We speculate that superoxide, in addition to playing a key role in atherogenesis, may play a key role in signaling that leads to calcific aortic valvular stenosis. Antioxidant enzymes, especially the three isoforms of superoxide dismutase (SOD), modulate basal levels of superoxide and protect against vasomotor dysfunction. A common gene variant of extracellular SOD (ecSOD) is associated with increased risk of ischemic heart disease. We have made recombinant adenoviruses to examine cardiovascular effects of ecSOD and its heparin-binding domain. This approach might be used to study the almost 500 other proteins with a heparin-binding domain. Finally, several key unanswered questions in relation to oxidative stress and atherosclerosis are raised, and proposed as fruitful areas of research.

Osteoporosis and atherosclerosis: biological linkages and the emergence of dual-purpose therapies

Osteoporosis and atherosclerosis are both widely prevalent in an ageing population, and induce serious morbidities and death. There is growing evidence that in addition to their relationship to ageing, osteoporosis and atherosclerosis are also linked by biological associations. This article reviews their clinical interrelations, discusses the basic biology of bone and the arterial wall, and presents five examples that illustrate their biological linkages. Current therapeutic approaches emerging from these linkages, including statins, bisphosphonates, and the thiazolidinediones, have dual effects on bone and the vasculature. Additional therapies derived from experimental studies that enhance bone density and reduce atherogenesis hold further promise to diminish the morbidity and mortality of osteoporosis and atherosclerosis, with attendant benefits to society.