Mechanism of pi-induced vascular calcification

Autonomous cortisol secretion promotes vascular calcification in vivo and in vitro under hyperaldosteronism

Autonomous cortisol secretion (ACS) is not uncommon in patients with primary aldosteronism (PA). However, the cardiovascular burden of ACS due to its dysregulated cortisol secretion remains poorly understood. Thus, we examined the effects of ACS on vascular calcification in a hyperaldosteronism environment in vitro and in vivo. A total of 339 patients with PA with adrenal incidentaloma and low-dose dexamethasone suppression test data (cutoff level: cortisol > 1.8 μg/dL) from a prospectively maintained database were enrolled; abdominal aortic calcification (AAC) scores were quantitatively estimated. Human aortic smooth muscle cells (HAOSMCs) were used as in vitro model of vascular calcification. In this study, 65 of the 339 patients with PA had ACS; 274 did not. Patients with PA/ACS had a higher AAC score (1171.0 ± 2434.0 vs. 489.5 ± 1085.3, P = 0.012) than patients without ACS. ACS was independently associated with AAC score (β = 0.139, P = 0.004) in multivariate analysis, and post-suppression cortisol level was significantly correlated with the AAC score (P = 0.004). In the HAOSMC model, co-treatment with cortisol synergistically stimulated alkaline phosphatase activity and calcium deposition in a hyperaldosteronism environment. The stimulatory effect of cortisol was abolished by the mineralocorticoid receptor (MR) antagonist eplerenone, but not glucocorticoid receptor antagonist mifepristone, indicating a MR-dependent mechanism. In conclusion, the presence of ACS is associated with heavier vascular calcification in patients with PA. Aldosterone and cortisol synergistically activate HAOSMC calcification via MR signaling, via a process that can be attenuated by eplerenone.

Panax quinquefolius saponin inhibits vascular smooth muscle cell calcification via activation of nuclear factor-erythroid 2-related factor 2

BACKGROUND

Panax quinquefolius saponin (PQS) is the main active component of Panax quinquefolius. Emerging evidence suggests that PQS exerts beneficial effects against cardiovascular diseases. However, the role and mechanism of PQS in vascular calcification are not unclear. The present study investigated the effects of PQS on the calcification of vascular smooth muscle cell (VSMCs).

METHODS

The present study used calcification medium containing 3 mM inorganic phosphate (Pi) to induce rat VSMCs calcification. We investigated the effects of PQS on VSMCs calcification using alizarin red staining and alkaline phosphatase (ALP) activity assays. The intracellular reactive oxygen species (ROS) levels and the transcriptional activity of nuclear factor-erythroid 2-related factor 2 (Nrf2) were determined. The mRNA and protein expression levels of Nrf2, the antioxidant gene heme oxygenase-1 (HO-1), osteogenic markers, including runt-related transcription factor 2 (Runx2) and bone morphogenetic protein 2 (BMP2), and Kelch-like ECH-associated protein 1 (Keap1) were also measured.

RESULTS

Treatment with Pi significantly increased intracellular calcium deposition and ALP activity, which were suppressed by PQS in a concentration-dependent manner. During VSMCs calcification, PQS inhibited the mRNA and protein expression of Runx2 and BMP2. PQS treatment reduced intracellular ROS production and significantly upregulated Nrf2 transcriptional activity and the expression of Nrf2 and its target antioxidant gene HO-1. PQS suppressed the Pi-induced protein expression of Keap1, which is an endogenous inhibitor of Nrf2. Keap1 siRNA treatment induced Nrf2 expression and downregulated Runx2 expression in the presence of Pi and PQS.

CONCLUSION

Taken together, these findings suggest that PQS could effectively inhibit VSMCs calcification by ameliorating oxidative stress and regulating osteogenic genes via the promotion of Nrf2 expression.

Mitochondria and vascular calcification in chronic kidney disease: Lessons learned from the past to improve future therapy

Chronic kidney disease-mineral and bone disorders (CKD-MBD) is a common complication of CKD Stages 3-5. Hyperphosphatemia is one of the major metabolic components of CKD-MBD, frequently resulting in vascular calcification (VC) in advanced-stage patients. Also, a long duration of renal replacement therapy can cause the worsening of VC, leading to increased cardiovascular morbidity and mortality. Vascular smooth muscle cells play an important role in the development of VC through osteochondrogenic transformation and the apoptotic process. It has been shown that mitochondrial dysfunction is involved with CKD progression, and excessive oxidative stress can aggravate osteoblastic transformation and VC. Currently, novel interventions targeting mitochondrial function and dynamics, in addition to mitochondrial antioxidants, have been studied with the aim of attenuating VC. This review aims to comprehensively summarize and discuss the experimental and clinical reports concerning mitochondrial studies, along with the purpose of interventions that can improve the outcomes of VC among CKD patients.

Effect of Bushen Huoxue decoction on inhibiting osteogenic differentiation of vascular smooth cells by regulating OPG/RANK/RANKL system in vascular calcification

BACKGROUND

To investigate the effects of Bushen Huoxue Decoction (BSHXD) and its underlying molecular mechanisms on inhibiting osteogenic differentiation of vascular smooth muscle cells (VSMCs) in vascular calcification via regulating the mRNA expression of osteoprotegerin (OPG) and the receptor activator of the nuclear factor-kappa B ligand (RANKL).

METHODS

VSMCs from the aortas of rats were cultured in vitro. Osteogenic differentiation of VSMCs was induced by high levels of an inorganic phosphate medium (2.4 mM). BSHXD-containing serum was prepared using the serum-pharmacological method. VSMCs were plated using 6-well plates at an approximate density of 4.0×104 cells/mL and cultured for 10 days. This was followed by the application of different concentrations of BSHXD-containing serum. The percentage of concentrations of BSHXD-containing serum in high, middle and low dosage group was 20%, 10% and 5%, respectively. Calcium nodules were evaluated by alizarin red S staining, and alkaline phosphatase (ALP) activity and calcium deposition were both examined as per the instruction of the test kits on the 3rd, 6th, and 10th days. Protein expression level of ALP and α-smooth muscle actin (α-SMA) were detected by Western blot on the 3rd, 6th, and 10th days. The mRNA expression of the OPG and RANKL were also detected by real-time PCR on the 3rd, 6th, and 10th days.

RESULTS

Compared with the control group, BSHXD significantly attenuated the calcium nodules that were examined by alizarin red-S staining. Protein expression levels of α-SMA were up-regulated and ALP were down-regulated on the BSHXD group (P<0.05). BSHXD also attenuated the ALP activity and calcium deposition of the VSMCs (P<0.05). These changes were associated with the effect of BSHXD on up-regulating the expression of OPG mRNA and down-regulating the expression of RANKL mRNA in the process of osteogenic differentiation of VSMCs.

CONCLUSIONS

BSHXD has a beneficial effect on inhibiting osteogenic differentiation of VSMCs induced by high levels of phosphate. The underlying mechanism appears to be related to the modulation of expressions of OPG mRNA and RANKL mRNA in the VSMCs, thereby preventing the phenotypic changes of VSMCs to an osteogenic phenotype.

Vitamin K‑dependent proteins involved in bone and cardiovascular health (Review)

In postmenopausal women and elderly men, bone density decreases with age and vascular calcification is aggravated. This condition is closely associated with vitamin K2 deficiency. A total of 17 different vitamin K-dependent proteins have been identified to date. Vitamin K-dependent proteins are located within the bone, heart and blood vessels. For instance, carboxylated osteocalcin is beneficial for bone and aids the deposition of calcium into the bone matrix. Carboxylated matrix Gla protein effectively protects blood vessels and may prevent calcification within the vascular wall. Furthermore, carboxylated Gla-rich protein has been reported to act as an inhibitor in the calcification of the cardiovascular system, while growth arrest-specific protein-6 protects endothelial cells and vascular smooth muscle cells, resists apoptosis and inhibits the calcification of blood vessels by inhibiting the apoptosis of vascular smooth muscle cells. In addition, periostin may promote the differentiation, aggregation, adhesion and proliferation of osteoblasts. Periostin also occurs in the heart and may be associated with the reconstruction of heart function. These vitamin K-dependent proteins may exert their functions following γ-carboxylation with vitamin K, and different vitamin K-dependent proteins may exhibit synergistic effects or antagonistic effects on each other. In the cardiovascular system with vitamin K antagonist supplement or vitamin K deficiency, calcification occurs in the endothelium of blood vessels and vascular smooth muscle cells are transformed into osteoblast-like cells, a phenomenon that resembles bone growth. Both the bone and cardiovascular system are closely associated during embryonic development. Thus, the present study hypothesized that embryonic developmental position and tissue calcification may have a certain association for the bone and the cardiovascular system. This review describes and briefly discusses several important vitamin K-dependent proteins that serve an important role in bone and the cardiovascular system. The results of the review suggest that the vascular calcification and osteogenic differentiation of vascular smooth muscle cells may be associated with the location of the bone and cardiovascular system during embryonic development.

Serum levels of Growth Arrest-Specific 6 protein and soluble AXL in patients with ST-segment elevation myocardial infarction

BACKGROUND

Serum soluble AXL (sAXL) and its ligand, Growth Arrest-Specific 6 protein (GAS6), intervene in tissue repair processes. AXL is increased in end-stage heart failure, but the role of GAS6 and sAXL in ST-segment elevation myocardial infarction (STEMI) is unknown.

OBJECTIVES

To study the association of sAXL and GAS6 acutely and six months following STEMI with heart failure and left ventricular remodelling.

METHODS

GAS6 and sAXL were measured by enzyme-linked immunosorbent assay at one day, seven days and six months in 227 STEMI patients and 20 controls. Contrast-enhanced magnetic resonance was performed during admission and at six months to measure infarct size and left ventricular function.

RESULTS

GAS6, but not sAXL, levels during admission were significantly lower in STEMI than in controls. AXL increased progressively over time (p<0.01), while GAS6 increased only from day 7. GAS6 or sAXL did not correlate with brain natriuretic peptide or infarct size. However, patients with heart failure (Killip >1) had higher values of sAXL at day 1 (48.9±11.9 vs. 44.0±10.7 ng/ml; p<0.05) and at six months (63.3±15.4 vs. 55.9±13.7 ng/ml; p<0.05). GAS6 levels were not different among subjects with heart failure or left ventricular remodelling. By multivariate analysis including infarct size, Killip class and sAXL at seven days, only the last two were independent predictors of left ventricular remodelling (odds ratio 2.24 (95% confidence interval: 1.08-4.63) and odds ratio 1.04 (95% confidence interval: 1.00-1.08) respectively).

CONCLUSION

sAXL levels increased following STEMI. Patients with heart failure and left ventricular remodelling have higher sAXL levels acutely and at six month follow-up. These findings suggest a potential role of the GAS6-AXL system in the pathophysiology of left ventricular remodelling following STEMI.

Effects of extracellular acid stimulation on rat vascular smooth muscle cell in Gas6/Axl or PI3K/Akt signaling pathway

Recent studies have indicated that extracellular acid stimulation inhibited the calcification of vascular smooth muscle cells (VSMCs). Cell apoptosis played an important role in the occurrence and development of vascular calcification. We further explored the effects of Gas6/Axl or PI3K/Akt signaling pathway on the inhibition of rat VSMCs calcification in response to extracellular acid stimulation. Our study demonstrated that a high concentration of phosphorus induced apoptosis and calcification of VSMCs, decreased expression of Axl, and reduced phosphorylation of Akt. Stimulation of extracellular acid counteracted the effects as above by increasing the expression of Axl and Akt phosphorylation and decreasing the expression of activated Caspase3, which thereby decreased cell apoptosis and calcification. Moreover, the effects can be attenuated by PI3K inhibitor. Our study proved that extracellular acid stimulation played a vital role in the inhibition of rat VSMCs calcification and apoptosis in Gas6/Axl or PI3K/Akt signaling pathway.

A novel role for the mineralocorticoid receptor in glucocorticoid driven vascular calcification

Vascular calcification, which is common in the elderly and in patients with atherosclerosis, diabetes and chronic renal disease, increases the risk of cardiovascular morbidity and mortality. It is a complex, active and highly regulated cellular process that resembles physiological bone formation. It has previously been established that pharmacological doses of glucocorticoids facilitate arterial calcification. However, the consequences for vascular calcification of endogenous glucocorticoid elevation have yet to be established. Glucocorticoids (cortisol, corticosterone) are released from the adrenal gland, but can also be generated within cells from 11-keto metabolites of glucocorticoids (cortisone, 11-dehydrocorticosterone [11-DHC]) by the enzyme, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). In the current study we hypothesized that endogenous glucocorticoids facilitate vascular smooth muscle cell (VSMC) calcification and investigated the receptor-mediated mechanism underpinning this process.

In vitro studies revealed increased phosphate-induced calcification in mouse VSMCs following treatment for 7 days with corticosterone (100 nM; 7.98 fold; P < 0.01), 11-DHC (100 nM; 7.14 fold; P < 0.05) and dexamethasone (10 nM; 7.16 fold; P < 0.05), a synthetic glucocorticoid used as a positive control. Inhibition of 11β-HSD isoenzymes by 10 μM carbenoxolone reduced the calcification induced by 11-DHC (0.37 fold compared to treatment with 11-DHC alone; P < 0.05). The glucocorticoid receptor (GR) antagonist mifepristone (10 μM) had no effect on VSMC calcification in response to corticosterone or 11-DHC. In contrast, the mineralocorticoid receptor (MR) antagonist eplerenone (10 μM) significantly decreased corticosterone- (0.81 fold compared to treatment with corticosterone alone; P < 0.01) and 11-DHC-driven (0.64 fold compared to treatment with 11-DHC alone; P < 0.01) VSMC calcification, suggesting this glucocorticoid effect is MR-driven and not GR-driven. Neither corticosterone nor 11-DHC altered the mRNA levels of the osteogenic markers PiT-1, Osx and Bmp2. However, DAPI staining of pyknotic nuclei and flow cytometry analysis of surface Annexin V expression showed that corticosterone induced apoptosis in VSMCs.

This study suggests that in mouse VSMCs, corticosterone acts through the MR to induce pro-calcification effects, and identifies 11β-HSD-inhibition as a novel potential treatment for vascular calcification.

Use of vitamin D receptor activator, incident cardiovascular disease and death in a cohort of hemodialysis patients

The use of vitamin D receptor activators (VDRAs) is an independent predictor of a lower risk of death from cardiovascular disease (CVD) in patients with chronic kidney disease (CKD). We examined whether the use of VDRAs and other CKD-mineral bone disorder (MBD)-related factors are associated with incident CVD or death after CVD in hemodialysis patients. This is a historical cohort study of 37 690 prevalent hemodialysis patients without previous history of CVD at the end of 2004 extracted from a nationwide registry in Japan. The key exposure was the use of VDRAs, and the outcomes were incident CVD (myocardial infarction, cerebral infarction, cerebral hemorrhage, and sudden death) and death after CVD during the 1-year follow-up. VDRAs were used in 57% of the subjects at baseline. We identified 2433 patients with incident CVD and 397 deaths after the events. In multivariate logistic regression models, independent predictors of incident CVD were non-use of VDRA, higher intact PTH, non-use of calcium-based phosphate-binder, and non-use of non-calcium-based phosphate binder. Risk of death after CVD was not significantly associated with VDRA, whereas it was lower in those with lower corrected calcium, and the risk was higher in those with higher phosphate and in non-users of calcium-based phosphate binders. The use of VDRAs was associated with a lower risk of incident CVD but not with death after CVD in this large cohort of hemodialysis patients. The CKD-MBD-related predictors of poor outcomes are associated with the risk of incident CVD, the risk of death after CVD, or both.

Quantitative analysis of abdominal aortic calcification in CKD patients without dialysis therapy by use of the Agatston score

BACKGROUND/AIM

The aim of the present study was to quantitatively examine factors associated with aortic calcification in non-dialysis CKD patients.

METHODS

We quantitatively investigated aortic calcification from the renal artery to the bifurcation in 149 non-dialysis CKD patients (58±16 years; 96 males and 53 females, 48 diabetics; eGFR 40.3 ± 29.3 ml/min), and measured Agatston scores using multi-slice computed tomography.

RESULT

Of 149 patients, aortic calcification was present in 117. In patients with aortic calcification, age (p<0.001), C-reactive protein (p<0.001), and intact-PTH (p < 0.001) were significantly higher, estimated glomerular filtration rate (eGFR) was significantly lower (p<0.001), and diabetes was observed more often (p<0.05). In regards to the degree of aortic calcification, the Agatston scores correlated significantly and positively with age (ρ=0.438, p<0.001) and serum phosphate (ρ=0.208, p=0.024), and correlated significantly but negatively with e-GFR (ρ=-0.353, p<0.001). In multiple regression analysis, eGFR was associated significantly and independently with the log [Agatston score] (β=-0.346, p<0.01), after adjustment for several confounders including serum phosphate and the presence of diabetes.

CONCLUSIONS

Hyperphospatemia, chronic inflammation, diabetes, and decreased GFR are associated significantly with the presence of aortic calcification in non-dialysis CKD patients. Decreased eGFR was associated significantly and independently with the quantitative degree of aortic calcification.

Magnesium inhibits Wnt/β-catenin activity and reverses the osteogenic transformation of vascular smooth muscle cells

Magnesium reduces vascular smooth muscle cell (VSMC) calcification in vitro but the mechanism has not been revealed so far. This work used only slightly increased magnesium levels and aimed at determining: a) whether inhibition of magnesium transport into the cell influences VSMC calcification, b) whether Wnt/β-catenin signaling, a key mediator of osteogenic differentiation, is modified by magnesium and c) whether magnesium can influence already established vascular calcification. Human VSMC incubated with high phosphate (3.3 mM) and moderately elevated magnesium (1.4 mM) significantly reduced VSMC calcification and expression of the osteogenic transcription factors Cbfa-1 and osterix, and up-regulated expression of the natural calcification inhibitors matrix Gla protein (MGP) and osteoprotegerin (OPG). The protective effects of magnesium on calcification and expression of osteogenic markers were no longer observed in VSMC cultured with an inhibitor of cellular magnesium transport (2-aminoethoxy-diphenylborate [2-APB]). High phosphate induced activation of Wnt/β-catenin pathway as demonstrated by the translocation of β-catenin into the nucleus, increased expression of the frizzled-3 gene, and downregulation of Dkk-1 gene, a specific antagonist of the Wnt/β-catenin signaling pathway. The addition of magnesium however inhibited phosphate-induced activation of Wnt/β-catenin signaling pathway. Furthermore, TRPM7 silencing using siRNA resulted in activation of Wnt/β-catenin signaling pathway. Additional experiments were performed to test the ability of magnesium to halt the progression of already established VSMC calcification in vitro. The delayed addition of magnesium decreased calcium content, down-regulated Cbfa-1 and osterix and up-regulated MGP and OPG, when compared with a control group. This effect was not observed when 2-APB was added. In conclusion, magnesium transport through the cell membrane is important to inhibit VSMC calcification in vitro. Inhibition of Wnt/β-catenin by magnesium is one potential intracellular mechanism by which this anti-calcifying effect is achieved.

Phosphate-induced rat vascular smooth muscle cell calcification and the implication of zinc deficiency in a7r5 cell viability

The calcification of vascular smooth muscle cells (VSMCs) is considered one of the major contributors for vascular disease. Phosphate is known as the inducer for VSMC calcification. In this study, we assessed whether phosphate affected cell viability and fetuin-A, a calcification inhibitor protein, both which are related to VSMC calcification. Also, VSMC viability by zinc level was assessed. The results showed that phosphate increased Ca and P deposition in VSMCs (A7r5 cell line, rat aorta origin). This phosphate-induced Ca and P deposition was consistent with the decreased A7r5 cell viability (P<0.05), which implies phosphate-induced calcification in A7r5 cells might be due to the decreased VSMC cell viability. As phosphate increased, the protein expression of fetuin-A protein was up-regulated. A7r5 cell viability decreased as the addition of cellular zinc level was decreased (P<0.05). The results suggested that zinc deficiency causes the decreased cell viability and it would be the future study to clarify how zinc does act for VSMC cell viability. The results suggest that the decreased VSMC viability by high P or low Zn in VSMCs may be the risk factor for vascular disease.

5-aza-2'-Deoxycytidine, a DNA methyltransferase inhibitor, facilitates the inorganic phosphorus-induced mineralization of vascular smooth muscle cells

AIM

Vascular calcification, an independent risk factor for cardiovascular disease in patients with chronic kidney disease(CKD), refers to the mineralization of vascular smooth muscle cells(VSMCs) caused by phenotypic changes toward osteoblast-like cells. DNA methylation, mediated by DNA methyltransferases(DNMTs), plays an important role in the differentiation of osteoblasts. We herein assessed the effects of a DNMT inhibitor on phenotypic changes in VSMCs and the development of vascular calcification.

METHODS

The effects of 5-aza-2'-deoxycytidine(5-aza-dC), a DNMT inhibitor, on human aortic smooth muscle cells(HASMCs) were evaluated. The expression and DNA methylation status of osteogenic genes were determined using RT-qPCR and bisulfite sequencing, respectively. Mineralization of HASMCs was induced by high concentrations of inorganic phosphate(Pi), as confirmed by quantitation of the calcium levels and von Kossa staining. Moreover, we examined the effects of the suppression of DNMT1 and/or alkaline phosphatase(ALP) on the mineralization of HASMCs.

RESULTS

5-aza-dC increased the expression and activity of ALP and reduced the DNA methylation levels of the ALP promoter region in the HASMCs. In addition, both treatment with 5-aza-dC and downregulation of the DNMT1 expression promoted the Pi-induced mineralization of HASMCs. Moreover, both treatment with phosphonoformic acid(PFA), a sodium-dependent phosphate transporter inhibitor, and suppression of the ALP expression inhibited the 5-aza-dC-promoted mineralization of HASMCs.

CONCLUSIONS

The present study showed that DNMT inhibitors facilitate the Pi-induced development of vascular calcification via the upregulation of the ALP expression along with a reduction in the DNA methylation level of the ALP promoter region.

Trichostatin A, an HDAC class I/II inhibitor, promotes Pi-induced vascular calcification via up-regulation of the expression of alkaline phosphatase

AIM

Vascular calcification, a major complication of chronic kidney disease (CKD), refers to the mineralization of vascular smooth muscle cells (VSMCs), resulting from a phenotypic change towards osteoblast-like cells. Histone deacetylase inhibitors (HDIs), potential therapeutic agents for CKD, are known to promote the differentiation and mineralization of osteoblasts. In this study, we aimed to determine the effects of an HDI on the phenotypic change of VSMCs and the development of vascular calcification.

METHODS

The effect of trichostatin A (TSA), an HDI, on human aortic smooth muscle cells (HASMCs) was determined. The mineralization of HASMCs was induced by inorganic phosphorus (Pi), and was confirmed by quantitation of Ca levels and by von Kossa staining. Furthermore, we examined the effect of alkaline phosphatase (ALP) suppression using siRNA on Pi-induced vascular calcification in the presence or absence of TSA.

RESULTS

TSA increased the expression and activity of ALP in HASMCs at a concentration which showed an inhibitory effect of histone deacetylase (HDAC) activity but not on cell viability. Moreover, TSA promoted the Pi-induced mineralization of HASMCs. In addition, both phosphonoformic acid (PFA), which is a sodium-dependent phosphate transporter inhibitor, and suppression of ALP expression by siRNA markedly inhibited the TSA-promoted mineralization of HASMCs.

CONCLUSION

These data show that inhibition of HDAC activity promotes Pi-induced vascular calcification via the up-regulation of ALP expression. Taken together, HDIs may increase the risk of vascular calcification in CKD patients.

Statin use and calcific uremic arteriolopathy: a matched case-control study

BACKGROUND

Calcific uremic arteriolopathy (CUA), also known as calciphylaxis, is characterized by vascular calcification, thrombosis and intense inflammation. Prior research has shown that statins have anticalcification, antithrombotic and antiinflammatory properties; however, the association between statin use and CUA has not been investigated.

METHODS

This matched case-control study included 62 adult maintenance hemodialysis (HD) patients with biopsy-confirmed CUA diagnosed between the years 2002 and 2011 (cases). All cases were hospitalized at the time of diagnosis. Controls (n = 124) were hospitalized maintenance HD patients without CUA (matched to cases by gender and timing of hospitalization). Univariate and multivariable logistic regression models were applied to compute odds ratio (OR) and 95% confidence intervals (CI) for CUA in statin users, and also to examine previously described associations.

RESULTS

The mean age of cases was 58 years. Most were females (68%), and of white race (64%). Statin use was more common in controls than in cases (39 vs. 19%, p < 0.01). Statin use was associated with lower odds of CUA in unadjusted (OR 0.38, 95% CI 0.18-0.79) and adjusted (OR 0.20, 95% CI 0.05-0.88) analyses. Hypercalcemia (OR 2.25, 95% CI 1.14-4.43), hypoalbuminemia (OR 5.73, 95% CI 2.79-11.77), calcitriol use (OR 5.69, 95% CI 1.02-31.77) and warfarin use (OR 4.30, 95% CI 1.57-11.74) were positively associated with CUA in adjusted analyses whereas paricalcitol and doxercalciferol were not (OR 1.33, 95% CI 0.54-3.27).

CONCLUSION

Statin use may be negatively associated with odds of CUA. Further large prospective studies with attention to potential confounders are needed to confirm these findings.

High expression of the Pi-transporter SLC20A1/Pit1 in calcific aortic valve disease promotes mineralization through regulation of Akt-1

The regulation of phosphate (Pi) handling is crucial during calcification of the aortic valve. Gene profiling of Pi transporters revealed that VIC culture expresses SLC201A1/Pit1 and SLC20A2/Pit2. On exposure to a mineralizing medium (2 mM Pi), the expression of Pi transporters in VIC culture is increased several folds, with the highest magnitude for SLC20A1. By using siRNAs, we established that silencing SLC20A1 significantly reduced Pi-induced mineralization of VICs. In human pathological specimens, we found that the expression of SCL20A1 was increased in CAVD tissues compared to control non-mineralized aortic valves. Treatment of VIC culture with Pi promoted the loss of mitochondrial membrane potential (ΔΨm) and cytochrome c release within the cytosol, leading to apoptosis. Inhibition of Pi transporters with phosphonoformic acid (PFA) prevented Pi-mediated apoptosis of VICs. Moreover, we discovered that the level of the Akt-1 transcript is diminished in CAVD tissues compared with control valves. Accordingly, treatment with Pi caused a reduction of the Akt-1 transcript in VIC culture, and treatment with PFA or siRNA against SLC20A1 restored the level of Akt-1. Overexpression of Akt-1 (pCMVAkt-1) prevented both Pi-induced apoptosis and mineralization of VIC culture. These results strongly suggest that overexpression of SLC20A1 promotes apoptosis and mineralization by altering the level of Akt-1.

α-Lipoic acid attenuates vascular calcification via reversal of mitochondrial function and restoration of Gas6/Axl/Akt survival pathway

Vascular calcification is prevalent in patients with chronic kidney disease and leads to increased cardiovascular morbidity and mortality. Although several reports have implicated mitochondrial dysfunction in cardiovascular disease and chronic kidney disease, little is known about the potential role of mitochondrial dysfunction in the process of vascular calcification. This study investigated the effect of α-lipoic acid (ALA), a naturally occurring antioxidant that improves mitochondrial function, on vascular calcification in vitro and in vivo. Calcifying vascular smooth muscle cells (VSMCs) treated with inorganic phosphate (Pi) exhibited mitochondrial dysfunction, as demonstrated by decreased mitochondrial membrane potential and ATP production, the disruption of mitochondrial structural integrity and concurrently increased production of reactive oxygen species. These Pi-induced functional and structural mitochondrial defects were accompanied by mitochondria-dependent apoptotic events, including release of cytochrome c from the mitochondria into the cytosol, subsequent activation of caspase-9 and -3, and chromosomal DNA fragmentation. Intriguingly, ALA blocked the Pi-induced VSMC apoptosis and calcification by recovery of mitochondrial function and intracellular redox status. Moreover, ALA inhibited Pi-induced down-regulation of cell survival signals through the binding of growth arrest-specific gene 6 (Gas6) to its cognate receptor Axl and subsequent Akt activation, resulting in increased survival and decreased apoptosis. Finally, ALA significantly ameliorated vitamin D(3) -induced aortic calcification and mitochondrial damage in mice. Collectively, the findings suggest ALA attenuates vascular calcification by inhibiting VSMC apoptosis through two distinct mechanisms; preservation of mitochondrial function via its antioxidant potential and restoration of the Gas6/Axl/Akt survival pathway.

Serum fibroblast growth factor-23 levels and progression of aortic arch calcification in non-diabetic patients on chronic hemodialysis

AIM

Vascular calcification is a cause of cardiovascular death in hemodialysis (HD) patients. The aim of the present study was to evaluate the relationship between the progression of aortic arch calcification (AoAC) and serum fibroblast growth factor (FGF)-23.

METHODS

The enrolled study subjects were 127 (83 men and 44 women) HD patients. Calcification of the aortic arch was semiquantitatively estimated with a score (AoACS) on plain chest radiology. Change in AoACS (ΔAoACS) was obtained by subtracting the baseline AoACS value from the follow-up AoACS value. The second assessment was performed from 5 years after the first determination.

RESULTS

The percentage of male gender in non-progressors (58.5%) was lesser than in regressors (60.0%) and progressors (74.6%). In addition, the dialysis duration in regressors (14.1±5.1 years) was shorter than in non-progressors (19.5±7.0 years) and progressors (16.8±7.5 years). Interestingly, the serum FGF-23 level in regressors (39225.5±9247.9 pg/mL) was significantly higher than in non-progressors (12896.5±26323.5 pg/mL) and progressors (14062.4±18456.8 pg/mL). Multi-ple regression analyses showed male gender (β value=0.969, F=5.092, p=0.0192), serum levels of albumin (β value=-1.395, F=4.541, p=0.0296) and log FGF-23 (β value=-0.001, F=7.273, p=0.0115) to be significant independent determinants of ΔAoACS.

CONCLUSION

Changes in AoAC evaluated by using a simple chest radiograph are associated with serum FGF-23 levels. Excess accumulation of FGF-23 in serum may enable to inhibit the calcification process in vessel walls in chronic HD patients.

High-phosphate-induced calcification is related to SM22α promoter methylation in vascular smooth muscle cells

Hyperphosphatemia is closely related to vascular calcification in patients with chronic kidney disease. Vascular smooth muscle cells (VSMCs) exposed to high phosphate concentrations in vitro undergo phenotypic transition to osteoblast-like cells. Mechanisms underlying this transdifferentiation are not clear. In this study we used two in vitro models, human aortic smooth muscle cells and rat aortic rings, to investigate the phenotypic transition of VSMCs induced by high phosphate. We found that high phosphate concentration (3.3 mmol/L) in the medium was associated with increased DNA methyltransferase activity and methylation of the promoter region of SM22α. This was accompanied by loss of the smooth muscle cell-specific protein SM22α, gain of the osteoblast transcription factor Cbfa1, and increased alkaline phosphatase activity with the subsequent in vitro calcification. The addition of a demethylating agent (procaine) to the high-phosphate medium reduced DNA methyltransferase activity and prevented methylation of the SM22α promoter, which was accompanied by an increase in SM22α expression and less calcification. Additionally, downregulation of SM22α, either by siRNA or by a methyl group donor (S-adenosyl methionine), resulted in overexpression of Cbfa1. In conclusion, we demonstrate that methylation of SM22α promoter is an important event in vascular smooth muscle cell calcification and that high phosphate induces this epigenetic modification. These findings uncover a new insight into mechanisms by which high phosphate concentration promotes vascular calcification.

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.

Validity and usefulness of aortic arch calcification in chest X-ray

BACKGROUND

Arterial calcification is associated with cardiovascular (CV) disease, to be leading to vessel wall stiffness and causing the management of hemodynamics in the elderly more difficult. Here, we compared the extent of calcification in the aortic arch by reviewing chest X-rays to that in the abdominal aorta as assessed by more detailed examinations. In addition, the validity of the grading and the relationship of this useful grading to clinical risk factors were evaluated.

METHODS AND RESULTS

The extent of aortic arch calcification (AAC) on a postero-anterior plain chest X-ray was divided into four grades (0 to 3). First, AAC grade was assessed in patients who underwent two quantitative examinations for abdominal aortic calcification; lateral radiograph of lumbar spine and/or computer tomography, and was positively correlated with the abdominal aortic calcification level. Subsequently, AAC grade in 239 out-patients (115 men; mean age, 61.9 years) was also evaluated, and was 0, 1, 2, and 3 in 46%, 22%, 29%, and 4% of the population, respectively, was significantly associated with pulse pressure and intima-media thickness. AAC grade in patients with diabetes or renal dysfunction was significantly higher than in those without each risk, but there was no association with other risk factors. In addition, AAC grade was positively correlated with risk factor clustering.

CONCLUSION

Assessment of AAC detectable on a chest X-ray is very useful and its grade reflects the magnitude of calcified change in the whole aorta. In addition, AAC evaluation may provide supportive information for atherosclerotic risk stratification.