Increased arterial calcification in Paget's disease of bone

New Insights to the Crosstalk between Vascular and Bone Tissue in Chronic Kidney Disease-Mineral and Bone Disorder

Vasculature plays a key role in bone development and the maintenance of bone tissue throughout life. The two organ systems are not only linked in normal physiology, but also in pathophysiological conditions. The chronic kidney disease–mineral and bone disorder (CKD-MBD) is still the most serious complication to CKD, resulting in increased morbidity and mortality. Current treatment therapies aimed at the phosphate retention and parathyroid hormone disturbances fail to reduce the high cardiovascular mortality in CKD patients, underlining the importance of other factors in the complex syndrome. This review will focus on vascular disease and its interplay with bone disorders in CKD. It will present the very late data showing a direct effect of vascular calcification on bone metabolism, indicating a vascular-bone tissue crosstalk in CKD. The calcified vasculature not only suffers from the systemic effects of CKD but seems to be an active player in the CKD-MBD syndrome impairing bone metabolism and might be a novel target for treatment and prevention.

Chronic Kidney Disease-Induced Vascular Calcification Impairs Bone Metabolism

An association between lower bone mineral density (BMD) and presence of vascular calcification (VC) has been reported in several studies. Chronic kidney disease (CKD) causes detrimental disturbances in the mineral balance, bone turnover, and development of severe VC. Our group has previously demonstrated expression of Wnt inhibitors in calcified arteries of CKD rats. Therefore, we hypothesized that the CKD-induced VC via this pathway signals to bone and induces bone loss. To address this novel hypothesis, we developed a new animal model using isogenic aorta transplantation (ATx). Severely calcified aortas from uremic rats were transplanted into healthy rats (uremic ATx). Transplantation of normal aortas into healthy rats (normal ATx) and age-matched rats (control) served as control groups. Trabecular tissue mineral density, as measured by μCT, was significantly lower in uremic ATx rats compared with both control groups. Uremic ATx rats showed a significant upregulation of the mineralization inhibitors osteopontin and progressive ankylosis protein homolog in bone. In addition, we found significant changes in bone mRNA levels of several genes related to extracellular matrix, bone turnover, and Wnt signaling in uremic ATx rats, with no difference between normal ATx and control. The bone histomorphometry analysis showed significant lower osteoid area in uremic ATx compared with normal ATx along with a trend toward fewer osteoblasts as well as more osteoclasts in the erosion lacunae. Uremic ATx and normal ATx had similar trabecular number and thickness. The bone formation rate did not differ between the three groups. Plasma biochemistry, including sclerostin, kidney, and mineral parameters, were similar between all three groups. ex vivo cultures of aorta from uremic rats showed high secretion of the Wnt inhibitor sclerostin. In conclusion, the presence of VC lowers BMD, impairs bone metabolism, and affects several pathways in bone. The present results prove the existence of a vasculature to bone tissue cross-talk. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

The evaluation and treatment of Paget's disease of bone

Paget's disease of bone is a localized skeletal disorder, which is more common in England and in countries to which the English migrated. In recent decades, the prevalence in most countries has decreased. A family history of the disorder is present in approximately 15% of patients. Patients may be asymptomatic and may be diagnosed accidently as a consequence of an elevated serum alkaline phosphatase level or a finding on an x-ray or nuclear bone scan. The diagnosis is made by x-ray but nuclear bone scans define the extent of the disease. Salmon calcitonin and bisphosphonate drugs have proven effective, but by far, the most effective therapy is a single 5 mg intravenous infusion of zoledronic acid. This can normalize alkaline phosphatase levels for up to 6.5 years. A variety of gene mutations may predispose individuals to develop the disease but environmental factors such as measles virus likely play an important role.

Paget's Disease of Bone: Diagnosis and Treatment

Paget's disease of bone is a common bone disorder characterized by disorganized bone remodeling. The most likely etiology is a slow paramyxoviral infection in genetically susceptible individuals; however, the exact cause is unknown. Enhanced bone resorption due to an increased activity of osteoclasts recruits numerous osteoblasts to resorption sites, with large quantities of new bone matrix produced as a result. The accelerated bone resorption and formation are not as closely coupled as in a healthy bone; a disorganized bone tissue is formed. Many patients are asymptomatic; rising serum alkaline phosphatase or incidental finding of characteristic radiographic lesions are often the only diagnostic clues. Common clinical manifestations include bone pain, bowing of long bones, enlarged skull, and hearing loss. An elevated serum alkaline phosphatase level correlates with the disease activity. The diagnosis is confirmed by characteristic radiographic findings and by nuclear scintigraphy of the bone (the most sensitive test). Bisphosphonates, such as zoledronic acid, pamidronate, alendronate, and risedronate, are the mainstay of treatment. Patients who do not tolerate bisphosphonates can be treated with calcitonin.

The lipid theory in the pathogenesis of calcific aortic stenosis

AIMS

Biologically active phenomena, triggered by atherogenesis and inflammation, lead to aortic valve (AV) calcification. Lipids play an important role in activating the cell signaling leading to AV bone deposition. This review, based on evidence from animal and human studies, mainly focused on the involvement of lipids and atherogenic phenomena in the pathogenesis of calcific aortic stenosis (AS).

DATA SYNTHESIS

The role of elevated low density lipoproteins for the risk of both vascular atherosclerosis and AS has been elucidated. Lipid disorders act synergistically with other risk factors to increase prevalence of calcific AS. Atherosclerosis is also involved in the pathogenesis of bone demineralization, a typical hallmark of aging, which is associated with ectopic calcification at vascular and valvular levels. Animal studies have recently contributed to demonstrate that lipids play an important role in AS pathogenesis through the activation of molecular cell signalings, such as Wnt/Lrp5 and RANK/RANKL/Osteprotegerin, which induce the transition of valvular myofibroblasts toward an osteogenic phenotype with consequent valvular bone deposition. Although all these evidence strongly support the lipid theory in AS pathogenesis, lipids lowering therapies failed to demonstrate in controlled trials a significant efficacy to slow AS progression. Encouraging results from animal studies indicate that physical activity may counteract the biological processes inducing AV degeneration.

CONCLUSIONS

This review indicates a robust interplay between lipids, inflammation, and calcific AS. This new pathophysiological scenario of such an emerging valvular disease paves the way to the next challenge of cardiovascular research: "prevent and care aortic valve stenosis".

Paget's disease diagnosed on bone scintigraphy: Case report and literature review

Paget's disease of bone is a chronic bone remodeling disorder. Although most patients are asymptomatic, a variety of symptoms and complications may develop directly from bone involvement or secondarily due to compression by the expanded bone. It is usually diagnosed from radiological and biochemical abnormalities or in advanced cases it becomes clinically evident due to the expanded bone. We report a case of Paget's disease which was detected incidentally during evaluation of nephrolithiasis and polyarthritis but had normal radiographs and normal biochemical markers.

Paget's Disease of Bone: A Review of Epidemiology, Pathophysiology and Management

Paget's disease of bone is a common disorder which may affect one or many bones. Although many patients are asymptomatic, a variety of symptoms and complications may occur. Fortunately, effective pharmacologic therapy, primarily with potent bisphosphonates, is now available to treat patients with complications or symptoms. This review of Paget's disease of bone will include epidemiology and pathophysiology, complications and clinical findings, indications for treatment, and the drugs currently available to treat this condition.

Mechanisms and clinical consequences of vascular calcification

Vascular calcification has severe clinical consequences and is considered an accurate predictor of future adverse cardiovascular events, including myocardial infarction and stroke. Previously vascular calcification was thought to be a passive process which involved the deposition of calcium and phosphate in arteries and cardiac valves. However, recent studies have shown that vascular calcification is a highly regulated, cell-mediated process similar to bone formation. In this article, we outline the current understanding of key mechanisms governing vascular calcification and highlight the clinical consequences. By understanding better the molecular pathways and genetic circuitry responsible for the pathological mineralization process novel drug targets may be identified and exploited to combat and reduce the detrimental effects of vascular calcification on human health.

Medial arterial calcification in diabetes and its relationship to neuropathy

Calcification of the media of arterial walls is common in diabetes and is particularly associated with distal symmetrical neuropathy. Arterial calcification also complicates chronic kidney disease and is an independent risk factor for cardiovascular and all-cause mortality. The term calcification is not strictly accurate because the morphological changes incorporate those of new bone formation, i.e. ossification. The processes are complex, but are closely related to those involved in bone homeostasis, and it is relevant that calcification of the arterial wall and osteopenia often co-exist. One particular factor linked to the development of arterial calcification is distal symmetrical neuropathy; indeed, it has been suggested that neuropathy explains the distal distribution of arterial calcification in diabetes. It has also been suggested that the link with neuropathy results from loss of neuropeptides, such as calcitonin gene-related peptide, which are inherently protective. The association between distal symmetrical neuropathy and calcification of the arterial wall highlights the fact that neuropathy may be an independent risk factor for cardiovascular mortality.

Vascular calcification and bone disease: the calcification paradox

Vascular calcification or ectopic mineralization in blood vessels is an active, cell-regulated process, increasingly recognized as a general cardiovascular risk factor. Remarkably, ectopic artery mineralization is frequently accompanied by decreased bone mineral density or disturbed bone turnover. This contradictory association, observed mainly in osteoporosis and chronic kidney disease, is called the 'calcification paradox'. Here, we review recent advances in our understanding of the calcification paradox, including protein expression patterns governing both normal and ectopic mineralization, the conversion of vascular smooth muscle cells to bone-like cells, and the regulatory pathways involved in both bone and vessel mineralization. Further elucidation of the mechanisms underlying the calcification paradox is crucial in order to develop preventive and therapeutic strategies to deal with vascular calcification and reduce the associated cardiovascular risk.

Bone marrow-derived cells and arterial disease

This article reviews the association between bone and artery disease, with particular relevance to progenitor cells. The review was based on insight gained by analysis of previous publications and on-going work by the authors. A large number of studies have demonstrated a correlation between bone pathology, particularly osteoporosis, and atherosclerosis. In this review we highlight the particular aspect of bone marrow progenitor cells in the bone-artery link. Progenitor cells, primarily those believed to give rise to endothelial cells, have been inversely correlated with atherosclerosis severity and risk factors. Therapeutic approaches aimed at manipulating progenitor cells in revascularization and vascular repair have demonstrated some promising results. Subtypes of progenitor cells have also been linked with vascular pathology, however, and further studies are required to assess relative beneficial and pathologic effects of bone marrow-derived progenitors. Further understanding of the link between bone and artery pathophysiology is likely to be of significant value in developing new therapies for vascular disease.

Tanshinone II A attenuates atherosclerotic calcification in rat model by inhibition of oxidative stress

AIM

We have previously proved that oxidized low-density lipoprotein (oxLDL), a proatherogenic lipoprotein, plays a pivotal role in the development of atherosclerotic calcification (AC). The present study was performed to investigate whether tanshinone II A (TS II A), an anti-oxidant which has been shown to inhibit in vitro oxidation of LDL, has the effects to inhibit AC in rat model and by which, if any, mechanisms.

METHODS

Rat AC model was induced by excessive vitamin D(2) (VD) and high cholesterol diet (HCD), which was proven to be successful histopathologically and biochemically.

RESULTS

Administration of AC rats with TS II A (35, 70 mg/kg) dose-dependently attenuated the AC pathological changes, meanwhile reduced the vessel contents of lipid and calcium. However, TS II A had no effects on serum levels of lipids, calcium and 25-OH VD. Further studies revealed that TS II A decreased serum concentration of oxLDL, reduced the superoxide anion production and malondialdehyde (MDA) in vessel. In addition, TS II A increased vessel Cu/Zn SOD activity, upregulated vessel mRNA and protein expression of Cu/Zn SOD.

CONCLUSION

The results suggested that TS II A significantly attenuated the AC in rat model, which might be attributed to its inhibition of oxLDL production independent of the serum levels of lipids, calcium and 25-OH VD, and that increasing of Cu/Zn SOD activity as well as mRNA and protein expression by TS II A might protect LDL against oxidation induced by superoxide anion in vessel.

Hypercholesterolemia accelerates vascular calcification induced by excessive vitamin D via oxidative stress

Hypercholesterolemia plays an important role in the initiation and progression of atherosclerosis and has a positive correlation with cardiovascular disease. Calcification is a common feature of atherosclerotic lesions and contributes to cardiovascular dysfunctions. The present study investigated the role of hypercholesterolemia in vascular calcification and its potential mechanism. Models of vascular calcification were established by administering vitamin D2 (VD) to rats alone or combined with a high-cholesterol diet (HCD) and by treating rat aorta smooth muscle cells (RASMCs) with beta-glycerophosphate (GP) alone or combined with oxidized low-density lipoprotein (oxLDL) in vitro. In rats, the combination of VD with HCD significantly enhanced vessel calcium deposition and the activity and mRNA expression of vessel alkaline phosphatase (ALP) compared to treatment with VD alone. This combination also enhanced serum levels of total cholesterol, oxLDL, and malondialdehyde as well as vascular production of superoxide anion, while it reduced the vascular activity of superoxide dismutase. Both simvastatin, a cholesterol-lowering agent, and antioxidant vitamin E antagonized the effects of the above combination. In RASMCs, oxLDL accumulation dependently accelerated calcium deposition in cell layers initiated by GP alone. Also, oxLDL stimulated ALP activity and mRNA expression in RASMCs in a concentration-dependent manner. Taken together, these results suggest that acceleration of vascular calcification by hypercholesterolemia might be attributed to oxidative stress and such calcification may be another target of statin or antioxidant action in antiatherosclerosis.