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Proatherogenic pathways leading to vascular calcification.

Cardiovascular disease is the leading cause of morbidity and mortality in the western world and atherosclerosis is the major common underlying disease. The pathogenesis of atherosclerosis involves local vascular injury, inflammation and oxidative stress as well as vascular calcification. Vascular calcification has long been regarded as a degenerative process leading to mineral deposition in the vascular wall characteristic for late stages of atherosclerosis. However, recent studies identified vascular calcification in early stages of atherosclerosis and its occurrence has been linked to clinical events in patients with cardiovascular disease. Its degree correlates with local vascular inflammation and with the overall impact and the progression of atherosclerosis. Over the last decade, diverse and highly regulated molecular signaling cascades controlling vascular calcification have been described. Local and circulating molecules such as osteopontin, osteoprogerin, leptin and matrix Gla protein were identified as critical regulators of vascular calcification. We here review the current knowledge on molecular pathways of vascular calcification and their relevance for the progression of cardiovascular disease.

Calcinosis↗

Dexamethasone enhances In vitro vascular calcification by promoting osteoblastic differentiation of vascular smooth muscle cells.

Vascular calcification is often associated with atherosclerotic lesions. Moreover, the process of atherosclerotic calcification has several features similar to the mineralization of skeletal tissue. Therefore, we hypothesized that vascular smooth muscle cells might acquire osteoblastic characteristics during the development of atherosclerotic lesions. In the present study, we investigated the effect of dexamethasone (Dex), which is well known to be a potent stimulator of osteoblastic differentiation in vitro, on vascular calcification by using an in vitro calcification model. We demonstrated that Dex increased bovine vascular smooth muscle cell (BVSMC) calcification in a dose- and time-dependent manner. Dex also enhanced several phenotypic markers of osteoblasts, such as alkaline phosphatase activity, procollagen type I carboxy-terminal peptide production, and cAMP responses to parathyroid hormone in BVSMCs. We also examined the effects of Dex on human osteoblast-like (Saos-2) cells and compared its effects on BVSMCs and Saos-2 cells. The effects of Dex on alkaline phosphatase activity and the cAMP response to parathyroid hormone in BVSMCs were less prominent than those in Saos-2 cells. Interestingly, we detected that Osf2/Cbfa1, a key transcription factor in osteoblastic differentiation, was expressed in both BVSMCs and Saos-2 cells and that Dex increased the gene expression of both transcription factors. These findings suggest that Dex may enhance osteoblastic differentiation of BVSMCs in vitro.

Alkaline Phosphatase↗

[Preparation of vascular calcification in vivo and vascular smooth muscle cell calcification in vitro of rats].

OBJECTIVE: To investigate simple, economical, stable and efficient methods of in vivo and in vitro cardiovascular calcification models in rats. METHODS: Rats received Vitamin D(3) (300 000 U/kg, i.m.) and nicotine (25 mg/kg, 5 mL/kg in peanut oil, p.o.) at 8 a.m. on day 1. The nicotine administration was repeated at 6 p.m. Rats in control group received an injection of normal saline (i.m.) and two gavages of medium oil. All of the rats were then allowed to recover for 4 weeks and given standard rodent chow. After the measurement of cardiac function the rats were sacrificed and the calcium content in myocardium and aorta were measured. Von Kossa staining was used to detect the deposit of calcium in myocardium and aorta. Cultured smooth muscle cell(SMC) derived from rat thoracic aorta was treated with beta-glycerophosphate for 14 days, then the calcium content and deposit were measured. RESULTS: Compared with control group, the rats with cardiovascular calcification showed a lower body weight, The ratio of left heart to body weight, myocardial and aortic calcium content were increased respectively. Alkaline phosphatases activity in calcified myocardium and aorta were increased respectively, compared with the control. The values of animal mean blood pressure (MBP), heart rate (HR) and left ventricle end-distolic pressure (LVEDP) showed no significant alteration (P>0.05) in vitamin D3 plus nicotine (VDN) group. The values of +LV dp/dt(max) and -LV dp/dtmax were significantly lower in VDN group (P<0.05 and P<0.01, respectively). In calcified vascular smooth muscle cells(VSMCs), von Kossa staining for calcification, showed positive staining as black/brown areas within the main, large, nodular structures as shown in extracellular matrix and cytoplasma. The content of calcium, (45)Ca(2+) uptake and alkaline phosphatase (ALP) activity in calcified VSMCs were increased (all P<0.01), respectively, compared with that of the control. CONCLUSION: These methods can be used to produce calcification models in vivo and in vitro, which save money and time and are easy to manipulate.

Animals↗

Vitamin D and vascular calcification.

PURPOSE OF REVIEW: Vascular calcification is frequently found in patients with osteoporosis, atherosclerosis and chronic kidney disease, leading to high morbidity and mortality rates. The effects of vitamin D excess and deficiency on vascular calcification are reviewed in this article. RECENT FINDINGS: There is evidence from experimental studies that mediacalcinosis induced by vitamin D excess is an active and reversible process. Vitamin D excess, however, is rarely seen in the general human population. Experimental data also demonstrate that physiologic vitamin D actions include the inhibition of processes that are important for intimal and medial artery calcification such as pro-inflammatory cytokine release, adhesion molecule release, and proliferation and migration of vascular smooth muscle cells. In uremic rats, low levels of the vitamin D hormone calcitriol are associated with massive vascular and soft tissue calcifications. Whereas retrospective studies already indicate a beneficial effect of active vitamin D on mortality rates in chronic kidney disease, little is yet known about the effect of vitamin D deficiency on cardiovascular morbidity and mortality in the general population. SUMMARY: Available data indicate that vitamin D exerts a biphasic 'dose response' curve on vascular calcification with deleterious consequences not only of vitamin D excess but also of vitamin D deficiency.

Animals↗

Hyperphosphatemia and vascular calcification in end-stage renal disease.

Vascular calcification is a common finding in atherosclerosis and a serious problem in uremic patients. Because of the correlation of hyperphosphatemia and vascular calcification, the ability of extracellular inorganic phosphate levels to regulate human aortic smooth muscle cell (HSMC) culture mineralization in vitro was examined. HSMC cultured in media containing normal physiologic levels of inorganic phosphate (1.4 mM) did not mineralize. In contrast, HSMC cultured in media containing phosphate levels comparable with those seen in hyperphosphatemic individuals (>1.4 mM) showed dose-dependent increases in mineral deposition. Mechanistic studies showed that elevated phosphate treatment of HSMC also enhanced the expression of the osteoblastic differentiation markers osteocalcin and osf2/Cbfa-1. The effects of elevated phosphate on HSMC were mediated by a sodium-dependent phosphate cotransporter (NPC) as indicated by the ability of the specific NPC inhibitor phosphonoformic acid to dose-dependently inhibit phosphate-induced calcium deposition as well as osteocalcin and Cbfa-1 gene expression. The NPC in HSMC was identified as Pit-1, a member of the novel type III NPCs. These data suggest that elevated phosphate may directly stimulate HSMC to undergo phenotypic changes that predispose to calcification and offers a novel explanation of the phenomenon of vascular calcification under hyperphosphatemic conditions. Furthermore, we examined the factors affecting peripheral vascular calcification in 332 nondiabetic hemodialysis patients. There were 45 nondiabetic patients with vascular calcification. In multivariate logistic regression, the significant factors affecting vascular calcification were advanced age, longer duration of hemodialysis, increased phosphate concentrations, male gender, and lower predialysis diastolic pressure. Our findings suggest that an elevated phosphate level may directly stimulate HSMC to undergo phenotypic changes that predispose to calcification and offer a novel explanation of the phenomenon of vascular calcification under hyperphosphatemic conditions.

Aorta↗

N-3 fatty acids inhibit vascular calcification via the p38-mitogen-activated protein kinase and peroxisome proliferator-activated receptor-gamma pathways.

Fish oil supplementation is associated with lower risk of coronary artery disease in humans, and it has been shown to reduce ectopic calcification in an animal model. However, whether N-3 fatty acids, active ingredients of fish oil, have direct effects on calcification of vascular cells is not clear. In this report, we investigated the effects of eicosapentaenoic acid and docosahexaenoic acid (DHA) on osteoblastic differentiation and mineralization of calcifying vascular cells (CVCs), a subpopulation of bovine aortic medial cells that undergo osteoblastic differentiation and form calcified matrix in vitro. Results showed that N-3 fatty acids inhibited alkaline phosphatase (ALP) activity and mineralization of vascular cells, suggesting that they directly affect osteoblastic differentiation in vascular cells. By Western blot analysis, DHA activated p38-mitogen-activated protein kinase (MAPK) but not extracellular-regulated kinase (ERK) or Akt. An inhibitor of p38-MAPK partially reversed the inhibitory effects of DHA on osteoblastic differentiation and mineralization. Transient transfection experiments showed that DHA also activated peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Both p38-MAPK activator and PPAR-gamma agonists reproduced the inhibitory effects of DHA on CVC mineralization. Pretreatment with DHA also inhibited interleukin-6-induced ALP activity and mineralization. Together, these results suggest that N-3 fatty acids directly inhibit vascular calcification, and that the inhibitory effects are mediated by the p38-MAPK and PPAR-gamma pathways.

Animals↗

Fibronectin enhances in vitro vascular calcification by promoting osteoblastic differentiation of vascular smooth muscle cells via ERK pathway.

The process of vascular calcification presents several features similar to osteogenesis in which fibronectin (FN) acts as a regulator of osteoblastic differentiation and the ERK signal pathway is involved. In order to find whether FN promotes the osteoblastic differentiation of vascular smooth muscle cells (VSMCs) through the ERK signal pathway, we investigated the effect of FN on the calcification of VSMCs by using an in vitro cell model. VSMCs cultured in plates with FN (0-20 microg/cm2) coating were induced to calcify by 10 mM sodium beta-glycerophosphate (beta-GP). FN exacerbated VSMC calcification in a dose- and time-dependent manner, as indicated by the number of calcifying nodules per slide and the amount of calcium in the deposition. Data from RT-PCR and immunoblotting assay revealed that FN also enhanced the expression of several phenotypic markers of osteoblasts, including alkaline phosphatase (ALP) activity, osteocalcin (OC), and Osf2/Cbfa1, a key transcription factor in osteoblastic differentiation. Furthermore, a specific inhibitor for ERK, PD98059 (10 microM), significantly suppressed the effect of FN on calcification and phenotypic marker expression. These findings seem to suggest that FN enhanced vascular calcification by promoting the osteoblastic differentiation of VSMCs via ERK signal pathway.

Animals↗

Changes of heme oxygenase-carbon monoxide system in vascular calcification in rats.

The aim of the present study was to investigate the change in heme oxygenase (HO)-carbon monoxide (CO)-cyclic guanosine monophosphate (cGMP) pathway in vascular calcification. Vascular calcification model was established in rats by using vitamin D(3) and nicotine. Vascular calcium content, alkaline phosphatase (ALP) activity, HO activity, HbCO formation and content of cGMP in vessels were measured. Immunochemistry (IH) for HO 1 expression and in situ hybridization (ISH) for HO 1 mRNA were observed. Compared to those of control rats, the aortic calcium content and vascular ALP activity in rats of the calcified group (VDN group) were obviously increased, but HO 1 activity, CO concentration and cGMP content in vessels of rats in VDN group were markedly decreased. Expressions of HO-1 protein and mRNA were significantly decreased compared to control rats. Vascular calcification might induce a down regulation in vascular HO-CO-cGMP pathway.

Alkaline Phosphatase↗

[Pathogenesis and therapy for vascular calcification in patients on chronic hemodialysis].

Vascular calcification is a common complication of end-stage renal disease (ESRD) and is likely related to the high incidence of cardiovascular disease in patients with ESRD. Vascular calcification occurs both in the vascular intima and in the tunica media. Intimal calcification is disseminated and is associated with damaged endothelium and macrophage. On the contrary, medial calcification occurs in patchy distribution and the most frequent cells types found in its vicinity are smooth muscle cells (SMC). The uremic state is associated with numerous metabolic abnormalities and endocrine disturbances primarily involving calcium and phosphorus metabolism. In addition, ESRD is considered state of active inflammatory response. These dysfunctions likely contribute to the development and progression of vascular calcification. Recent reports have shown that this is a highly regulated process governed by factors that closely resemble calcium deposition in bone tissue. Vascular calcification requires changes in the phenotype of SMC and the expression of several bone-associated proteins normally involved in bone metabolism. This review is focused on the role of phosphorus in the pathogenesis of vascular calcification and the therapeutic approaches currently available to slow its progression in patients with ESRD.

Calcinosis↗

Chemical and hormonal determinants of vascular calcification in vitro.

Vascular calcification is a complex process that is dependent not only on the physicochemical effects of Ca, PO(4), and pH, but also on smooth muscle factors that may be regulated by these ions as well as by 1,25-dihydroxyvitamin D(3) (calcitriol) and parathyroid hormone (PTH). These minerals and hormones were tested in a model of medial calcification in rat aorta maintained in culture for 9 days. Calcification was quantitated as incorporation of (45)Ca, alkaline phosphatase activity was measured in aortic homogenates, and osteopontin production was measured from immunoblots of culture medium. At 1.8 mM Ca (1.46 mM free), calcification occurred at or above 2.8 mM PO(4). At 3.8 mM PO(4), calcification occurred at or above 1.10 mM free [Ca]. At a constant [Ca] x [PO(4)], calcification varied directly with [Ca] and inversely with [PO(4)]. Calcification was directly related to pH between 7.19 and 7.50 but not altered by PTH or calcitriol. Alkaline phosphatase activity and osteopontin production were increased by Ca, PO(4), calcitriol, and PTH. We conclude that calcification of rat aorta in vitro requires elevation of both [Ca] and [PO(4)], and that [Ca] rather than [PO(4)] or the product of the two is the dominant determinant. The induction of alkaline phosphatase and osteopontin indicates that Ca and PO(4) have effects in addition to simple physicochemical actions. Although PTH and calcitriol did not increase calcification in vivo, they have effects on smooth muscle that could influence calcification in vivo. Calcification is enhanced by alkalinity within the range produced during hemodialysis.

Alkaline Phosphatase↗

Mechanisms of vascular calcification in uremia.

Vascular calcification and cardiovascular disease mortality are highly correlated with increased serum phosphate levels in end-stage renal disease patients. Mechanistic studies in cultured human smooth muscle cells (SMCs) indicate that increased phosphate levels induces both calcification and phenotypic transition through a pathway requiring a sodium-dependent phosphate cotransporter. Thus, in addition to contributing to increased calcium x phosphate product (Ca x P), hyperphosphatemia may have direct effects on SMCs that predispose these cells to calcium deposition in end-stage renal disease patients.

Calcinosis↗

Advanced oxidation protein products, parathyroid hormone and vascular calcification in uremia.

Vascular calcification is a frequent complication of uremic patients. In addition to classical risk factors such as age, male gender, smoking, inflammation, hypertension, dyslipidemia, and diabetes, which also exist in the general population, patients with chronic renal failure have other risk factors such as oxidative stress, inflammation, hyperparathyroidism, hypoparathyroidism, hypercalcemia, hyperphosphatemia, and overtreatment with calcium and vitamin D. These latter risk factors may even have a better predictive value than classical risk factors for coronary heart disease in uremic patients.

Calcinosis↗

[Control of calcium and phosphate metabolism and prevention of vascular calcifications in uremic patients].

Vascular calcifications are more frequent in dialysis patients than in the general population or in patients with cardiovascular disease (CVD) and normal renal function. The reasons for this high incidence are multiple; they include traditional factors such as hypertension, diabetes, dyslipidemia, and specific factors such as sodium overload, hyperomocysteinemia, chronic inflammation and oxidative stress, as well as mineral metabolism disturbances. Specifically, hyperphosphatemia and the elevated calcium (Ca) x phosphate product have been associated with an increased risk for the development of vascular calcification and death. Treatment with Ca salts can induce hypercalcemia, increased Ca x phosphate product and Ca overload. Sevelamer substitution for Ca salts has been documented to attenuate the progression of coronary artery and aortic calcification. A possible mechanism explaining this observation could be ongoing Ca loading related to oral Ca ingestion. Treatment with Ca salts could induce Ca overload, particularly in patients dialyzed against a high dialysate Ca (>1.5 mmol/L) solution, which is known to determine a positive dialysis balance. Conversely, an overall negative Ca balance can result from low Ca dialysate use (1.25 mmol/L) when the patients do not receive Ca supplements or vitamin D metabolites. Maintaining normal Ca and phosphate balances remains a primary goal in the management of dialysis patients. Control of hyperphopshataemia should be achieved either using Ca and aluminum-free phosphate binders, such as sevelamer, or Ca salts, alone or in combination, provided that a daily oral elemental Ca intake of 1.5 g is not exceeded.

Calcinosis↗

[Vascular calcification in end stage renal disease].

Vascular calcification is thought to play a crucial role in the excessive cardiovascular mortality and morbidity in patients with end-stage renal disease (ESRD). Recent evidence suggests that uremic vascular calcification is an active cell-mediated process resembling osteogenesis in bone, rather than passive precipitation of calcium and phosphorus in the setting of deranged mineral metabolism. To date, several bone-associated proteins (osteopontin, bone sialoprotein, alkaline phosphatase, type I collagen) have been demonstrated in histological sections of vessels obtained from patients with ESRD or calcific uremic arteriolopathy. In in vitro experiments, addition of uremic serum upregulates osteopontin expression by cultured vascular smooth muscle cells. We are only beginning to understand the process by which vascular smooth muscle cells transform into osteoblast-like cells, although phosphorus may play a key role. Additional factors mediating or modulating development of vascular calcification in ESRD remain to be identified. Further understanding of the pathophysiology of uremic vascular calcification is needed to design effective therapeutic strategies to intervene with this devastating condition in ESRD population.

Journal Article↗

Uremia-related vascular calcification: more than apatite deposition.

In the present study, we characterized and compared the mineral phase deposited in the aortic wall of two different frequently used chronic renal failure rat models of vascular calcification. Vascular calcification was induced in rats by either a 4-week adenine treatment followed by a 10-week high-phosphate diet or 5/6 nephrectomy followed by 6 weeks of 0.25 microg/kg/day calcitriol treatment and a high-phosphate diet. Multi-element mapping for calcium and phosphate together with mineral identification was performed on several regions of aortic sections by means of synchrotron X-ray-mu-fluorescence and diffraction. Bulk calcium and magnesium content of the aorta was assessed using flame atomic absorption spectrometry. Based on the diffraction data the Von Kossa-positive precipitate in the aortic regions (N=38) could be classified into three groups: (1) amorphous precipitate (absence of any diffraction peak pattern, N=12); (2) apatite (N=16); (3) a combination of apatite and magnesium-containing whitlockite (N=10). The occurrence of these precipitates differed significantly between the two models. Furthermore, the combination of apatite and whitlockite was exclusively found in the calcitriol-treated animals. These data indicate that in adenine/phosphate-induced uremia-related vascular calcification, apatite is the main component of the mineral phase. The presence of magnesium-containing whitlockite found in addition to apatite in the vitamin D-treated rats, has to be seen in view of the well-known vitamin D-stimulated gastrointestinal absorption of magnesium.

Animals↗

[Disturbances of mineral metabolism and vascular calcifications in dialysis patients (review)].

Vascular calcifications are more frequent in dialysis patients than in the general population or in patients with cardiovascular disease and normal renal function. The reasons for this high incidence are multiple. They include traditional factors such as hypertension, diabetes, dyslipidaemia, and specific factors such as sodium overload, hyperomocysteinaemia, chronic inflammation, oxidative stress as well as disturbance of mineral metabolism. Specifically, hyperphosphataemia and the elevated calcium (Ca) x phosphate product have been associated with an increased risk for development of vascular calcification and death. Even though a causal relationship between the use of Ca- containing phosphate binders and the development of vascular calcifications has not been documented, treatment with Ca salts can induce hypercalcaemia, increased Ca x phosphate product, and Ca overload. A net intestinal Ca absorption of 180-500 mg has been documented in uraemic patients after a meal containing 1200 mg of Ca. Thus, treatment with Ca salts may induce Ca overload when a patient is dialyszed against a high dialysate Ca (> 1.5 mmol/L) solution, which is known to determine a positive dialysis balance. On the contrary, an overall negative Ca balance can result from the use of a low Ca dialysate (1.25 mmol/L) when the patients do not receive Ca supplements or vitamin D metabolites. Maintaining a normal Ca and phosphate balance remains one of the primary goals in the management of dialysis patients. Control of hyperphopshataemia should be obtained using either Ca and aluminium- free phosphate binders, such as sevelamer, or Ca salts, while avoiding a daily oral elemental Ca intake > 1.5 g.

Calcinosis↗

[Hormonal regulation of vascular calcification].

Recent evidence suggests that vascular calcification is a controlled process and involves the altered differentiation of mesenchymal cells. For example, vitamin D(3) was reported to enhance vascular calcification by suppressing PTHrP action that is an inhibitor of calcification. Quite recently, leptin has been shown to enhance the osteoblastic differentiation of stromal cells and calcification of vascular cells. These results suggest the intimate relationship between bone and lipid or adipose tissue.

English Abstract↗

Regulation of vascular calcification: roles of phosphate and osteopontin.

Vascular calcification is prevalent in aging as well as a number of pathological conditions, and it is now recognized as a strong predictor of cardiovascular events in the general population as well as diabetic and end-stage renal disease patients. Vascular calcification is a highly regulated process involving inductive and inhibitory mechanisms. This article focuses on two molecules, phosphate and osteopontin, that have been implicated in the induction or inhibition of vascular calcification, respectively. Elevated phosphate is of interest because hyperphosphatemia is recognized as a major nonconventional risk factor for cardiovascular disease mortality in end-stage renal disease patients. Studies to date suggest that elevated phosphate stimulates smooth muscle cell phenotypic transition and mineralization via the activity of a sodium-dependent phosphate cotransporter. Osteopontin, however, appears to block vascular calcification most likely by preventing calcium phosphate crystal growth and inducing cellular mineral resorption.

Animals↗