Bisphosphonates induce inflammation and rupture of atherosclerotic plaques in apolipoprotein-E null mice

Vascular calcification: Molecular mechanisms and therapeutic interventions

Vascular calcification (VC) is recognized as a pathological vascular disorder associated with various diseases, such as atherosclerosis, hypertension, aortic valve stenosis, coronary artery disease, diabetes mellitus, as well as chronic kidney disease. Therefore, it is a life-threatening state for human health. There were several studies targeting mechanisms of VC that revealed the importance of vascular smooth muscle cells transdifferentiating, phosphorous and calcium milieu, as well as matrix vesicles on the progress of VC. However, the underlying molecular mechanisms of VC need to be elucidated. Though there is no acknowledged effective therapeutic strategy to reverse or cure VC clinically, recent evidence has proved that VC is not a passive irreversible comorbidity but an active process regulated by many factors. Some available approaches targeting the underlying molecular mechanism provide promising prospects for the therapy of VC. This review aims to summarize the novel findings on molecular mechanisms and therapeutic interventions of VC, including the role of inflammatory responses, endoplasmic reticulum stress, mitochondrial dysfunction, iron homeostasis, metabolic imbalance, and some related signaling pathways on VC progression. We also conclude some recent studies on controversial interventions in the clinical practice of VC, such as calcium channel blockers, renin-angiotensin system inhibitions, statins, bisphosphonates, denosumab, vitamins, and ion conditioning agents.

Bisphosphonates and atrial fibrillation: revisiting the controversy

Bisphosphonates (BPs) are widely prescribed drugs used to treat osteoporosis, commonly arising in postmenopausal women and in chronic glucocorticoid use. Their mechanism of action is through inhibiting osteoclast-induced bone remodeling, and they also possess calcium sequestering properties. Common side effects involve the gastrointestinal system and rare but serious side effects, including osteonecrosis of the jaw. However, a link between BPs and atrial fibrillation (AF) has been proposed, with early clinical trials, such as the Fracture Intervention Trial and the HORIZON Pivotal Fracture Trial, reporting that BPs are associated with increased risk of AF. Nevertheless, subsequent studies have reported contrasting results, ranging from no effect of BPs to antiarrhythmic effects of BPs. Preclinical and electrophysiological studies on any proarrhythmic effect of BPs are limited in scope and number, but suggest possible mechanisms that include antiangionesis-related myocardial remodeling, calcium handling abnormalities, and inflammatory changes. Contrastingly, some studies indicate that BPs are antiarrhythmic by inhibiting fibrotic myocardial remodeling. In order to continue established clinical prescribing of BPs within absolute margins of safety, it will be necessary to systematically rule in/rule out these mechanisms. Thus, we discuss these studies and examine in detail the potential mechanistic links, with the aim of suggesting further avenues for research.

Targeting cathepsin K diminishes prostate cancer establishment and growth in murine bone

BACKGROUND

The processes of prostate cancer (PCa) invasion and metastasis are facilitated by proteolytic cascade involving multiple proteases, such as matrix metalloproteinases, serine proteases and cysteine proteases including cathepsin K (CatK). CatK is predominantly secreted by osteoclasts and specifically degrades collagen I leading to bone destruction. PCa and breast cancer preferentially metastasize to the bone. Importantly, CatK expression level is greater in PCa bone metastatic sites compared to primary tumor and normal prostate tissues. However, the underlying mechanism of CatK during PCa metastases into the bone remains to be elucidated. We investigated the functional role of CatK during the PCa establishment and growth process in the murine bone.

METHODS

CatK mRNA expression was validated by RT-PCR, protein expression by immunoblotting in PCa LNCaP, C4-2B, and PC3 cells as well as in PCa tissues. Its protein production was measured using ELISA assay. The effect of both knockdowns via siRNA and CatK inhibitor was compared in regard to PCa cell invasion. We further studied the dose-dependent CatK inhibitor effect on conditioned media-induced bone resorption. In setting up an animal model, C4-2B cells were injected into the tibiae of SCID mice. The animals treated with either vehicle or CatK inhibitor for 8 weeks at the time of tumor cell injection (tumor establishment model; protocol I) or 4 weeks after tumor cell injection (tumor progression model; protocol II) were applied to histological and histomorphometric analyses.

RESULTS

We confirmed CatK expression in PCa LNCaP, C4-2B, and PC3 cells as well as in PCa tissues. Furthermore, we observed the inhibitory effects of a selective CatK inhibitor on PCa cell invasion. The CatK inhibitor dose-dependently inhibited PCa-conditioned media-induced bone resorption. Upon injection of C4-2B cells into the tibiae of SCID mice, the selective CatK inhibitor significantly prevented the tumor establishment in protocol I, and reduced the tumor growth in bone in protocol II. It also decreased serum PSA levels in both animal models. The inhibitory effects of the CatK inhibitor were enhanced in combination with zoledronic acid (ZA).

CONCLUSION

The selective CatK inhibitor may prevent the establishment and progression of PCa in bone, thus making it a novel therapeutic approach for advanced PCa.

Cardiovascular Outcomes of Romosozumab and Protective Role of Alendronate

Osteoporosis and cardiovascular diseases are major public health issues. Bone and cardiovascular remodeling share multiple biological markers and pathways. Medical intervention, such as using romosozumab, an antisclerostin antibody, improves the clinical outcome of osteoporosis. However, blocking sclerostin leads to Wnt (wingless/integrated) activation and participation in the cardiovascular remodeling process, which could potentially lead to adverse events. Based on the opposing roles of bisphosphonates and the Wnt pathway on endothelial dysfunction, lipid accumulation and calcification of the vessel walls, the combination of romosozumab and bisphosphonates could be a new therapeutic approach to reducing the risks of adverse cardiovascular events in romosozumab receivers. Visual Overview- An online visual overview is available for this article.

Anti-osteoporotic drugs and vascular calcification: the bidirectional calcium traffic

During the last years, numerous epidemiological studies have demonstrated a direct relationship between vascular calcification and low bone mineral density. This observation is in line with experimental data demonstrating the osteogenic characteristics of calcified arteries. Various common risk factors have been suggested to link vascular calcification and bone loss, including aging, estrogen deficiency, vitamin D and K deficiency, diabetes mellitus, renal failure, smoking, chronic inflammation and oxidative stress. Although the underlying pathogenetic mechanisms are not yet clear, current research is focusing on anti-osteoporotic agents that could potentially affect the deposition of calcium in the arterial wall and thus provide an additional therapeutic strategy in elderly osteoporotic women prone to calcific cardiovascular disease.

Defective extracellular pyrophosphate metabolism promotes vascular calcification in a mouse model of Hutchinson-Gilford progeria syndrome that is ameliorated on pyrophosphate treatment

BACKGROUND

Progerin is a mutant form of lamin A responsible for Hutchinson-Gilford progeria syndrome (HGPS), a premature aging disorder characterized by excessive atherosclerosis and vascular calcification that leads to premature death, predominantly of myocardial infarction or stroke. The goal of this study was to investigate mechanisms that cause excessive vascular calcification in HGPS.

METHODS AND RESULTS

We performed expression and functional studies in wild-type mice and knock-in Lmna(G609G/+) mice expressing progerin, which mimic the main clinical manifestations of HGPS. Lmna(G609G/+) mice showed excessive aortic calcification, and primary aortic vascular smooth muscle cells from these progeroid animals had an impaired capacity to inhibit vascular calcification. This defect in progerin-expressing vascular smooth muscle cells is associated with increased expression and activity of tissue-nonspecific alkaline phosphatase and mitochondrial dysfunction, which leads to reduced ATP synthesis. Accordingly, Lmna(G609G/+) vascular smooth muscle cells are defective for the production and extracellular accumulation of pyrophosphate, a major inhibitor of vascular calcification. We also found increased alkaline phosphatase activity and reduced ATP and pyrophosphate levels in plasma of Lmna(G609G/+) mice without changes in phosphorus and calcium. Treatment with pyrophosphate inhibited vascular calcification in progeroid mice.

CONCLUSIONS

Excessive vascular calcification in Lmna(G609G) mice is caused by reduced extracellular accumulation of pyrophosphate that results from increased tissue-nonspecific alkaline phosphatase activity and diminished ATP availability caused by mitochondrial dysfunction in vascular smooth muscle cells. Excessive calcification is ameliorated on pyrophosphate treatment. These findings reveal a previously undefined pathogenic process in HGPS that may also contribute to vascular calcification in normal aging, because progerin progressively accumulates in the vascular tissue of individuals without HGPS.

Association between atherosclerosis and osteoporosis, the role of vitamin D

The latest data support the correlation of atherosclerosis and osteoporosis, indicating the parallel progression of two tissue destruction processes with increased fatal and non-fatal coronary events, as well as higher fracture risk. Vitamin D inadequacy associated with low bone mineral density increases fall and fracture risk, leads to secondary hyperparathyroidism, calcifies coronary arteries and significantly increases cardiovascular disease. Randomized clinical trial evidence related to extraskeletal vitamin D outcomes was limited and generally uninformative. A recent recommendation on vitamin D dietary requirements for bone health is 600 IU/d for ages 1-70 years and 800 IU/d for 71 years and older, corresponding to a serum 25-hydroxyvitamin D level of at least 20 ng/ml (50 nmol/l). Further large randomized controlled trials are needed to reassess laboratory ranges for 25-hydroxyvitamin D in both diseases, in order to avoid under- and over-treatment problems, and completely clarify the relationship between atherosclerosis and osteoporosis.

Atrial fibrillation and stroke associated with intravenous bisphosphonate therapy in older patients with cancer

PURPOSE

Recent studies have linked the use of intravenous and orally administered bisphosphonates with subsequent development of atrial fibrillation. Patients with cancer who receive intravenous bisphosphonate therapy may be at particular risk for this adverse event because they receive higher doses of these drugs than do patients treated for other indications. We examined the association of intravenous bisphosphonates with atrial fibrillation, all classifications of supraventricular tachycardia (SVT), and stroke among older patients with cancer.

PATIENTS AND METHODS

Using Surveillance, Epidemiology, and End Results (SEER)-Medicare-linked data, we identified older (≥ age 65 years) patients with cancer who were treated with intravenous infusions of bisphosphonates between January 1, 1995 and December 31, 2003. We then matched 13,714 bisphosphonate nonusers to 6,857 bisphosphonate users, at a 2:1 ratio, on cancer type, age, sex, presence of bone metastases, and SEER geographic region. Patients were observed until December 31, 2003 or until they lost coverage from Medicare Parts A and B; enrolled in a health maintenance organization; received a diagnosis of atrial fibrillation, any SVT, or stroke; or died.

RESULTS

Receipt of intravenous bisphosphonates was modestly associated with an increased risk for atrial fibrillation (hazard ratio [HR] = 1.30; 95% CI, 1.18 to 1.43), all SVT (HR = 1.28; 95% CI, 1.19 to 1.38), and stroke (HR = 1.30; 95% CI, 1.09 to 1.54). The risk for all SVT increased 7% for each increase of five bisphosphonate dose equivalents (HR = 1.07; 95% CI, 1.02 to 1.12).

CONCLUSION

Clinicians who treat patients with cancer who have received intravenous bisphosphonates should be aware of the possible cardiovascular adverse events associated with this treatment.

Adverse effects of bisphosphonates

Use of bisphosphonates has been growing steadily in the last decade. This follows the introduction of simpler dosing regimes, the availability of lower-priced generics, and concerns about the safety of hormone-replacement therapy. Bisphosphonates have a relatively good safety record and are tolerated by the majority of patients, but serious adverse events have been recorded in some cases. Only the most common of adverse effects are robustly observable in clinical trials. In general, studies were not powered to detect effects that were lower in incidence than fractures. This review of adverse events in bisphosphonate-treated patients was based on published information from case reports, case series, claims databases, national databases, surveys, adverse event reporting databases, and single or pooled clinical trials. The most common acute adverse events with bisphosphonates for osteoporosis are gastrointestinal discomfort and acute influenza-like illness. Renal complications are very rare with oral bisphosphonates and rare with i.v. bisphosphonates when used appropriately. Based on our current knowledge, skeletal events in the form of osteonecrosis of the jaw and atypical fragility fractures are rare compared with the risk of osteoporotic fractures, at least in patients with the same risk of fractures as those in the phase III trials. It is biologically plausible that atypical fragility fractures could follow from suppression of bone remodeling, but high-quality studies proving causality are lacking. Physicians are advised to critically reassess BMD and risk profile after 3-5 years of therapy to avoid treatment in patients at low risk.

Lanthanum acetate inhibits vascular calcification induced by vitamin D3 plus nicotine in rats

Lanthanum, a rare earth element, has been used to decrease serum phosphorus level in patients with chronic renal disease and hyperphosphatemia. We aimed to observe the effect and mechanism of two doses of lanthanum acetate (375 and 750 mg/kg/day) on vascular calcification induced by vitamin D3 plus nicotine treatment in rats for 4 weeks. As compared with control rats, rats with calcification showed widespread calcified nodules and irregular elastic fibers in calcified aorta on von Kossa calcium staining and increased aortic calcium and phosphorus contents, alkaline phosphatase (ALP) activity and bone-related protein expressions for osteopontin (OPN) and type III sodium dependent phosphate cotransporter Pit-1 (Pit-1). After treatment with either dose of lanthanum acetate, the calcified nodules and degree of irregular elastic fibers decreased in aortas. Lanthanum acetate at 750 mg/kg/day was more effective than 375 mg/kg/day in lessening vascular calcification by significantly reducing plasma phosphorus level, calcium x phosphorus product and ALP activity, by 30.3%, 28.6%, and 68.6%, respectively; reducing aortic phosphorus and calcium contents and ALP activity, by 48%, 53.1%, and 63.5% (all P < 0.01), respectively; reducing aortic mRNA level of OPN and Pit-1, by 55.8% (P < 0.01) and 38.8% (P < 0.05) and protein level of OPN and Pit-1, by 37.2% and 27.2% (both P < 0.01), respectively; and increasing carboxylated matrix Gla-protein (MGP) protein expression by 33.7% (P < 0.05), as compared with rats treated with vitamin D3 and nicotine alone. Lanthanum acetate could effectively inhibit the pathogenesis of vascular calcification.

Atrial fibrillation in fracture patients treated with oral bisphosphonates

OBJECTIVES

To determine if patients receiving oral bisphosphonates are at excess risk of atrial fibrillation (AF), stroke and myocardial infarction.

DESIGN

Register-based restricted cohort study.

SETTING

National Hospital Discharge Register and National Prescriptions Database (1995-2005).

SUBJECTS

Fracture patients beginning bisphosphonates (n = 15 795) were matched with unexposed fracture patients of the same age, sex and fracture type (n = 31 590).

RESULTS

Incidence rates of AF were 16.5/1000 person years in untreated fracture patients and 20.6/1000 person years in bisphosphonate users. An age- and sex-adjusted hazard ratio (HR) of 1.29 (1.17-1.41) was found for probable AF by Cox proportional hazards analysis. The effect size was reduced to HR of 1.18 (1.08-1.29) by adjustment for co-medications and comorbidity. Selective prescribing was suggested by the observation that (i) risks were increased even in patients who stopped therapy after the first packet and (ii) risks were not increased by high adherence. Bisphosphonate-exposed patients were at increased risk of hospital-treated AF [adjusted HR: 1.13 (1.01-1.26)], but the risk amongst bisphosphonate users was inversely proportional to adherence. There was no increased risk of ischaemic stroke and an increased risk of myocardial infarction was not significant after adjustment for comorbidity.

CONCLUSIONS

The increased occurrence of AF in fracture patients who are users of oral bisphosphonates should be attributed to targeting of bisphosphonates to patients who are already at increased risk of cardiovascular events.

7-ketocholesterol, a major oxysterol, promotes pi-induced vascular calcification in cultured smooth muscle cells

AIM

Oxysterols are found in high concentrations in advanced atherosclerotic plaques and are considered as an important factor in the development of vascular calcification. The purpose of this study was to investigate the effect of 7-ketocholesterol (7kc), a major oxysterol in plaques, on in vitro arterial calcification.

METHODS

Bovine vascular smooth muscle cells (VSMCs) were cultured with inorganic phosphate (Pi) in the presence or absence of 7kc. Calcium deposition was determined by Calcium C-test Wako and von Kossa staining. Phenotypic change was evaluated by mRNA expression using semi-quantitative reverse transcription-polymerase chain reaction. Cell apoptosis was determined by in situ DNA fragmentation assay.

RESULTS

7kc significantly enhanced the calcium deposition, phenotypic change of VSMCs, and apoptosis in the presence of Pi. Treatment with risedronate, a bisphosphonate, or Y-27632, an Rho kinase inhibitor, completely or partially prevented the effects induced by 7kc in the presence of Pi, respectively.

CONCLUSION

These results suggest that 7kc, a major oxysterol, significantly accelerates vascular calcification in the presence of Pi via the mevalonate pathway and Rho-ROCK signaling pathway. Our present data provide beneficial information on the development of a therapeutic approach for arterial calcification, especially in patients with a mineral imbalance, including hypocalcaemia, hyperphosphatemia, and hypercholesterolemia.

The immune response is involved in atherosclerotic plaque calcification: could the RANKL/RANK/OPG system be a marker of plaque instability?

Atherogenesis is characterized by an intense inflammatory process, involving immune and vascular cells. These cells play a crucial role in all phases of atherosclerotic plaque formation and complication through cytokine, protease, and prothrombotic factor secretion. The accumulation of inflammatory cells and thus high amounts of soluble mediators are responsible for the evolution of some plaques to instable phenotype which may lead to rupture. One condition strongly associated with plaque rupture is calcification, a physiopathological process orchestrated by several soluble factors, including the receptor activator of nuclear factor (NF)κB ligand (RANKL)/receptor activator of nuclear factor (NF)κB (RANK)/osteoprotegerin (OPG) system. Although some studies showed some interesting correlations with acute ischemic events, at present, more evidences are needed to evaluate the predictive and diagnostic value of serum sRANKL and OPG levels for clinical use. The major limitation is probably the poor specificity of these factors for cardiovascular disease. The identification of tissue-specific isoforms could increase the importance of sRANKL and OPG in predicting calcified plaque rupture and the dramatic ischemic consequences in the brain and the heart.

Bone metabolism and vascular calcification

Osteoporosis and atherosclerosis are chronic degenerative diseases which have been considered to be independent and whose common characteristic is increasing incidence with age. At present, growing evidence indicates the existence of a correlation between cardiovascular disease and osteoporosis, irrespective of age. The morbidity and mortality of osteoporosis is mainly related to the occurrence of fractures. Atherosclerosis shows a high rate of morbidity and especially mortality because of its clinical repercussions such as angina pectoris, acute myocardial infarction, stroke, and peripheral vascular insufficiency. Atherosclerotic disease is characterized by the accumulation of lipid material in the arterial wall resulting from autoimmune and inflammatory mechanisms. More than 90% of these fatty plaques undergo calcification. The correlation between osteoporosis and atherosclerosis is being established by studies of the underlying physiopathological mechanisms, which seem to coincide in many biochemical pathways, and of the risk factors for vascular disease, which have also been associated with a higher incidence of low-bone mineral density. In addition, there is evidence indicating an action of antiresorptive drugs on the reduction of cardiovascular risks and the effect of statins, antihypertensives and insulin on bone mass increase. The mechanism of arterial calcification resembles the process of osteogenesis, involving various cells, proteins and cytokines that lead to tissue mineralization. The authors review the factors responsible for atherosclerotic disease that correlate with low-bone mineral density.

Murine models of vascular thrombosis (Eitzman series)

Thrombotic complications of vascular disease are the leading cause of morbidity and mortality in most industrialized countries. Despite this, safe and effective drugs targeting these complications are limited, especially in the chronic setting. This is because of the complexity of thrombosis in both arteries and veins, which is becoming increasingly evident as numerous factors are now known to affect the fate of a forming thrombus. To fully characterize thrombus formation in these settings, in vivo models are necessary to study the various components and intricate interactions that are involved. Genetic manipulations in mice are greatly facilitating the dissection of relevant pro- and antithrombotic influences. Standardized models for the study of thrombosis in mice as well as evolving techniques that allow imaging of molecular events during thrombus formation are now available. This review will highlight some of the recent developments in the field of thrombosis using mouse models and how these studies are expanding our knowledge of thrombotic disease.

Alendronate prevents bone loss and improves tendon-to-bone repair strength in a canine model

Previously we showed a loss of bone and a concomitant decrease in mechanical properties in the first 21 days after flexor tendon insertion site injury and repair in a canine model. The goal of this short-term study was to suppress bone loss after insertion site repair using alendronate in an attempt to prevent the reduction in biomechanical properties. Flexor tendons of the second and fifth digits of the right forelimbs of canines were injured and repaired. Dogs received a daily oral dose of alendronate (2 mg/kg). One digit in each dog also received a local dose of alendronate in the bone tunnel at the time of surgery. The repair was evaluated for bone mineral density (BMD) and biomechanical properties and compared to data from a previous study in which no alendronate was used. Alendronate was effective in protecting the distal phalanx from resorption during tendon-to-bone healing (BMD was 94 and 104% of control for systemic alendronate and for systemic plus local alendronate, respectively). Alendronate treatment prevented much of the decrease in ultimate load that occurs in the first 21 days. Without treatment, ultimate load was 42% of control. With systemic alendronate treatment and systemic plus local alendronate treatment, ultimate load was 78 and 69% of control, respectively. Failure mode was significantly different when comparing alendronate treatment to repair alone. A lower incidence of suture pull through was found in alendronate treated dogs, suggesting less tendon degeneration. Ultimate load can be improved in association with preventing the bone loss that normally occurs during the early period following tendon-to-bone repair. These initial short-term data demonstrate the potential for a clinical treatment that could enhance tendon-to-bone healing.

Effects of alendronate sodium therapy on carotid intima media thickness in postmenopausal women with osteoporosis

Osteoporosis and cardiovascular disease are major health problems that lead to morbidity and mortality. Bisphosphonates are among the drugs used most frequently worldwide to treat osteoporosis, especially in older women. B-mode ultrasonography has recently become a valuable tool for early diagnosis of atherosclerotic disease because of its ability to measure carotid artery intima media thickness (CIMT). The purpose of the present study was to investigate whether alendronate sodium therapy has an effect on CIMT in postmenopausal women with osteoporosis. A total of 71 postmenopausal women with osteoporosis were evaluated before and after they began taking alendronate sodium; follow-up was provided for an average of 13+/-2 mo. Osteoporosis was diagnosed with the use of dual-energy x-ray absorptiometry, and therapy with alendronate sodium was begun at a dose of 70 mg/wk. For CIMT, B-mode ultrasonography was performed on the right and left middle and distal main carotid arteries. Before alendronate sodium therapy was initiated, the average CIMT value was 0.734+/-0.121 mm; after therapy, the average CIMT was 0.712+/-0.111 mm. This difference was not confirmed to be statistically significant. Treatment of osteoporosis does not seem to have an effect on CIMT, which is an early marker of atherosclerosis.

Bisphosphonates and atherosclerosis: why?

The increasing knowledge on bone calcification processes has revealed some similarities with vascular tissue, where calcifications of arteries and cardiac valves contribute to several cardiovascular problems, such as heart failure, systolic hypertension, and myocardial and peripheral ischemic disease. Bisphosphonates have been used extensively for over two decades for the treatment of diseases associated with excessive bone resorption, i.e., osteoporosis, osteolytic bone metastasis, hypercalcemia and Paget's disease, by blocking osteoclastic function. Etidronate, pamidronate and clodronate has been shown to inhibit the development of experimental atherosclerosis, and proposed mechanisms for this action include inhibition of arterial calcification and lipid accumulation, degradation of atherogenic LDL-cholesterol and reduced foam cell formation. Bisphosphonates inhibit various enzymes involved in cholesterol biosynthesis and suppress macrophages in atheromatous lesions. The possibility of pharmacological agents that effectively treat both osteoporosis and atherosclerosis is attractive, however, current evidence is not conclusive and further research is necessary to confirm these actions in the clinical setting.

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.