Vascular calcification in peritoneal dialysis patients and its association with bone-derived molecules and bone histomorphometry

INTRODUCTION

Data regarding vascular calcification (VC) in contemporary peritoneal dialysis (PD) patients is scarce. Bone-vascular axis has been demonstrated in hemodialysis (HD). However, studies showing the link between bone disease and VC in PD patients are lacking. The role of sclerostin, dickkopf-related protein 1 (DKK-1), receptor activator for nuclear factor kB ligand and osteoprotegerin (OPG) in VC in PD remains to clarify.

MATERIALS AND METHODS

Bone biopsy was performed in 47 prevalent PD patients with histomorphometric analysis. Patients were submitted to pelvis and hands X-ray to evaluate VC using the Adragão score (AS). Relevant clinical and biochemical data was collected.

RESULTS

Thirteen patients (27.7%) had positive AS (AS≥1). Patients with VC were significantly older (58.9 vs. 50.4 years, p=0.011), had a lower dialysis dose (KT/V 2.0 vs. 2.4, p=0.025) and a higher glycosylated hemoglobin (7.2 vs. 5.4%, p=0.001). There was not any laboratorial parameter of mineral and bone disease used in clinical practice different between patients with or without VC. All diabetic patients had VC but only 8.1% of non-diabetic had VC (p<0.001). Patients with VC showed significantly higher erythrocyte sedimentation rate (ESR) (91.1 vs. 60.0mm/h, p=0.001), sclerostin (2250.0 vs. 1745.8pg/mL, p=0.035), DKK-1 (1451.6 vs. 1042.9pg/mL, p=0.041) and OPG levels (2904.9 vs. 1518.2pg/mL, p=0.002). On multivariate analysis, only ESR remained statistically significant (OR 1.07; 95% CI 1.01-1.14; p=0.022). Bone histomorphometric findings were not different in patients with VC. There was no correlation between bone formation rate and AS (r=-0.039; p=0.796).

CONCLUSION

The presence of VC was not associated with bone turnover and volume evaluated by bone histomorphometry. Inflammation and diabetes seem to play a more relevant role in VC in PD.

New mechanisms involved in the development of cardiovascular disease in chronic kidney disease

Chronic kidney disease (CKD) is a pathology with a high worldwide incidence and an upward trend affecting the elderly. When CKD is very advanced, the use of renal replacement therapies is required to prolong its life (dialysis or kidney transplantation). Although dialysis improves many complications of CKD, the disease does not reverse completely. These patients present an increase in oxidative stress, chronic inflammation and the release of extracellular vesicles (EVs), which cause endothelial damage and the development of different cardiovascular diseases (CVD). CKD patients develop premature diseases associated with advanced age, such as CVD. EVs play an essential role in developing CVD in patients with CKD since their number increases in plasma and their content is modified. The EVs of patients with CKD cause endothelial dysfunction, senescence and vascular calcification. In addition, miRNAs free or transported in EVs together with other components carried in these EVs promote endothelial dysfunction, thrombotic and vascular calcification in CKD, among other effects. This review describes the classic factors and focuses on the role of new mechanisms involved in the development of CVD associated with CKD, emphasizing the role of EVs in the development of cardiovascular pathologies in the context of CKD. Moreover, the review summarized the EVs' role as diagnostic and therapeutic tools, acting on EV release or content to avoid the development of CVD in CKD patients.

Impact of hepatitis virus infection on arterial calcification among incident hemodialysis patients

BACKGROUND

The impact of hepatitis virus infection on arterial calcification (AC) was not studied.

OBJECTIVE

To study the prevalence, severity and distribution of AC in incident hemodialysis patients with hepatitis B and C viral infection.

CASES AND METHODS

172 stage 5 CKD adults (98 male and 74 female) were included; 58 of them were seronegative for both hepatitis B and C (SN group), 48 were positive for hepatitis B virus infection (HBV group) and 66 were hepatitis C virus positive (HCV group). Beside histopathology of the obtained arterial samples, all these cases were examined for body mass index (BMI), serum calcium (Ca), phosphorus (P), alkaline phosphatase (AP), serum albumin, uric acid (UA), alanine transaminase (ALT), parathormone (PTH), fibroblast growth factor 23(FGF23), interleukin 6 (IL6), and 25 hydroxy vitamin D (25 (OH) vit D), hemoglobin concentration, and serum ferritin.

RESULTS

86 (50%) of the cases had AC; 11 of them were in SN group (19%), 9 in HBV group (18.8%) and all the 66 HCV group (100%). In SN group, 4 had intimal calcification, 5 had medial calcification, and 2 had both intimal and medial calcification. In HBV group, 9 had intimal calcification, while no cases were encountered with either medial or both site calcifications. In HCV group, 16 had intimal calcification, 31 had medial calcification, and 19 had both intimal and medial calcification. Calcification was in the form of spots in one case in SN group, and 6 cases in HBV group, a single plaque of calcification in 5 cases of SN group, 3 cases of HBV group, and 16 cases of HCV group, multiple plaques were detected in 4 cases in SN group, and 31 cases in HCV group, and diffuse calcification in one case in SN group, and 19 cases in HCV group. In HBV group, calcification was only detected in patients with high viremia, while all patients with low or moderate viremia were devoid of calcification. In HCV group, all patients with low viremia had intimal solitary plaque of calcification, all patients with moderate viremia had multiple plaques of medial calcification, while all patients with high viremia had diffuse intimal and medial calcification. Both groups of viral hepatitis were significantly different in comparison to SN group in either distribution or calcification score (P<0.001 in all). HBV group had significantly lower serum P, CaxP and PTH in comparison to SN group (4.6±0.66 vs. 5.45±0.77mg/dL, 36.4±7.2 vs. 44.1±8.69, and 348±65.4 vs. 405.9±83.2pg/mL, P<0.001, <0.001, and 0.035 respectively). On the other hand, HCV group did not show any significant difference in any of the studied parameters compared to SN group.

CONCLUSION

HCV positive patients are more prone to develop AC that is more extensive. HBV positive patients were less likely to have arterial medial calcification, probably related to lower serum phosphorus, CaxP product and PTH. HCV infection should be added as risk factor for AC among CKD patients. Further studies are needed to confirm these findings.

Osteoporosis and vascular calcification: A shared scenario

Osteoporosis is a systemic skeletal disease, characterised by low bone mass and deterioration in the micro-architecture of bone tissue, which causes increased bone fragility and consequently greater susceptibility to fractures. It is the most frequent metabolic bone disease in our population, and fractures resulting from osteoporosis are becoming more common. Furthermore, vascular calcification is a recognised risk factor of cardiovascular morbidity and mortality that historically has been considered a passive and degenerative process. However, it is currently recognised as an active process, which has histopathological characteristics, mineral composition and initiation and development mechanisms characteristic of bone formation. Paradoxically, patients with osteoporosis frequently show vascular calcifications. Traditionally, they have been considered as independent processes related to age, although more recent epidemiological studies have shown that there is a close relationship between the loss of bone mass and vascular calcification, regardless of age. In fact, both conditions share risk factors and pathophysiological mechanisms. These include the relationship between proteins of bone origin, such as osteopontin and osteoprotegerin (OPG), with vascular pathology, and the intercellular protein system RANK/RANKL/OPG and the Wnt signalling pathway. The mechanisms linked in both pathologies should be considered in clinical decisions, given that treatments for osteoporosis could have unforeseen effects on vascular calcification, and vice versa. In short, a better understanding of the relationship between both entities can help in proposing strategies to reduce the increasing prevalence of vascular calcification and osteoporosis in the aging population.

Mechanisms of vascular aging: What can we learn from Hutchinson-Gilford progeria syndrome?

Aging is the main risk factor for cardiovascular disease (CVD). The increased prevalence of CVD is partly due to the global increase in life expectancy. In this context, it is essential to identify the mechanisms by which aging induces CVD, with the ultimate aim of reducing its incidence. Both atherosclerosis and heart failure significantly contribute to age-associated CVD morbidity and mortality. Hutchinson-Gilford progeria syndrome (HGPS) is a rare genetic disorder caused by the synthesis of progerin, which is noted for accelerated aging and CVD. This mutant form of prelamin A induces generalised atherosclerosis, vascular calcification, and cardiac electrophysiological abnormalities, leading to premature aging and death, mainly due to myocardial infarction and stroke. This review discusses the main vascular structural and functional abnormalities during physiological and premature aging, as well as the mechanisms involved in the exacerbated CVD and accelerated aging induced by the accumulation of progerin and prelamin A. Both proteins are expressed in non-HGPS individuals, and physiological aging shares many features of progeria. Research into HGPS could therefore shed light on novel mechanisms involved in the physiological aging of the cardiovascular system.

Role of pyrophosphate in vascular calcification in chronic kidney disease

Vascular calcification is a pathology characterized by the deposition of calcium-phosphate in cardiovascular structures, mainly in the form of hydroxyapatite crystals, resulting in ectopic calcification. It is correlated with increased risk of cardiovascular disease and myocardial infarction in diabetic patients and in those with chronic kidney disease (CKD). Vascular smooth muscle cells are sensitive to changes in inorganic phosphate (Pi) levels. They are able to adapt and modify some of their functions and promote changes which trigger calcification. Pi is regulated by parathyroid hormone and 1,25-dihydroxyvitamin D. Changes in the transport of Pi are the primary factor responsible for the regulation of Pi homeostasis and the calcification process. Synthesis of calcification inhibitors is the main mechanism by which cells are able to prevent vascular calcification. Extracellular pyrophosphate (PPi) is a potent endogenous inhibitor of calcium-phosphate deposition both in vivo and in vitro. Patients with CKD show lower levels of PPi and increased activity of the enzyme alkaline phosphatase. Numerous enzymes implicated in the metabolism of PPi have been associated with vascular calcifications. PPi is synthesized from extracellular ATP by nucleotide pyrophosphatase/phosphodiesterase from extracellular ATP hydrolysis. PPi is hydrolyzed into Pi by tissue-nonspecific alkaline phosphatase. ATP can be hydrolyzed to Pi via the ectonucleoside triphosphate diphosphohydrolase family. All these enzymes must be in balance, thereby preventing calcifications. However, diseases like CKD or diabetes induce alterations in their levels. Administration of PPi could open up new treatment options for these patients.

Cardiovascular calcifications in chronic kidney disease: Potential therapeutic implications

Cardiovascular (CV) calcification is a highly prevalent condition at all stages of chronic kidney disease (CKD) and is directly associated with increased CV and global morbidity and mortality. In the first part of this review, we have shown that CV calcifications represent an important part of the CKD-MBD complex and are a superior predictor of clinical outcomes in our patients. However, it is also necessary to demonstrate that CV calcification is a modifiable risk factor including the possibility of decreasing (or at least not aggravating) its progression with iatrogenic manoeuvres. Although, strictly speaking, only circumstantial evidence is available, it is known that certain drugs may modify the progression of CV calcifications, even though a direct causal link with improved survival has not been demonstrated. For example, non-calcium-based phosphate binders demonstrated the ability to attenuate the progression of CV calcification compared with the liberal use of calcium-based phosphate binders in several randomised clinical trials. Moreover, although only in experimental conditions, selective activators of the vitamin D receptor seem to have a wider therapeutic margin against CV calcification. Finally, calcimimetics seem to attenuate the progression of CV calcification in dialysis patients. While new therapeutic strategies are being developed (i.e. vitamin K, SNF472, etc.), we suggest that the evaluation of CV calcifications could be a diagnostic tool used by nephrologists to personalise their therapeutic decisions.