Assessing the hydration status of children with chronic kidney disease and on dialysis: a comparison of techniques.

Background: Fluid balance is pivotal in the management of children with chronic kidney disease (CKD) and on dialysis. Although many techniques are available to assess fluid status, there are only a few studies for children, of which none have been comparable against cardiovascular outcome measures. Methods: We performed a longitudinal study in 30 children with CKD5-5D and 13 age-matched healthy controls (71 measurements) to determine a correlation between optimal weight by bioimpedance spectroscopy (Wt-BIS) and clinical assessment (Wt-CA). The accuracy of Wt-BIS [relative overhydration (Rel-OH)] was compared against indicators of fluid status and cardiovascular measures. Results: There was poor agreement between Wt-CA and Wt-BIS in children on dialysis (P = 0.01), but not in CKD5 or control subjects. We developed a modified chart to plot Rel-OH against systolic blood pressure (SBP) z-score for the appropriate representation of volume status and blood pressure (BP) in children. In total, 25% of measurements showed SBP >90th percentile but not with concurrent overhydration. Rel-OH correlated with peripheral pulse pressure (P = 0.03; R = 0.3), higher N-terminal pro-brain natriuretic peptide (P = 0.02; R = 0.33) and left ventricular end-diastolic diameter (P = 0.05; R = 0.38). Central aortic mean and pulse pressure significantly associated with the left ventricular end-diastolic diameter (P = 0.03; R = 0.47 and P = 0.01; R = 0.50, respectively), but not with Rel-OH. SBP was positively associated with pulse wave velocity z-score (P = 0.04). In total, 40% of children on haemodialysis and 30% on peritoneal dialysis had increased left ventricular mass index. Conclusions: BIS provides an objective method for the assessment of hydration status in children on dialysis. We noted a marked discrepancy between BP and hydration status in children on dialysis that warrants further investigation.

Kidney disease in children: latest advances and remaining challenges.

To mark World Kidney Day 2016, Nature Reviews Nephrology invited six leading researchers to highlight the key advances and challenges within their specialist field of paediatric nephrology. Here, advances and remaining challenges in the fields of prenatal patterning, acute kidney injury, renal transplantation, genetics, cardiovascular health, and growth and nutrition, are all discussed within the context of paediatric and neonatal patients with kidney disease. Our global panel of researchers describe areas in which further studies and clinical advances are needed, and suggest ways in which research in these areas should progress to optimize renal care and long-term outcomes for affected patients.

BMP-9 regulates the osteoblastic differentiation and calcification of vascular smooth muscle cells through an ALK1 mediated pathway.

The process of vascular calcification shares many similarities with that of physiological skeletal mineralization, and involves the deposition of hydroxyapatite crystals in arteries. However, the cellular mechanisms responsible have yet to be fully explained. Bone morphogenetic protein (BMP-9) has been shown to exert direct effects on both bone development and vascular function. In the present study, we have investigated the role of BMP-9 in vascular smooth muscle cell (VSMC) calcification. Vessel calcification in chronic kidney disease (CKD) begins pre-dialysis, with factors specific to the dialysis milieu triggering accelerated calcification. Intriguingly, BMP-9 was markedly elevated in serum from CKD children on dialysis. Furthermore, in vitro studies revealed that BMP-9 treatment causes a significant increase in VSMC calcium content, alkaline phosphatase (ALP) activity and mRNA expression of osteogenic markers. BMP-9-induced calcium deposition was significantly reduced following treatment with the ALP inhibitor 2,5-Dimethoxy-N-(quinolin-3-yl) benzenesulfonamide confirming the mediatory role of ALP in this process. The inhibition of ALK1 signalling using a soluble chimeric protein significantly reduced calcium deposition and ALP activity, confirming that BMP-9 is a physiological ALK1 ligand. Signal transduction studies revealed that BMP-9 induced Smad2, Smad3 and Smad1/5/8 phosphorylation. As these Smad proteins directly bind to Smad4 to activate target genes, siRNA studies were subsequently undertaken to examine the functional role of Smad4 in VSMC calcification. Smad4-siRNA transfection induced a significant reduction in ALP activity and calcium deposition. These novel data demonstrate that BMP-9 induces VSMC osteogenic differentiation and calcification via ALK1, Smad and ALP dependent mechanisms. This may identify new potential therapeutic strategies for clinical intervention.

Successful outcome of renal transplantation in a child with HIV-associated nephropathy.

Classical HIV-associated nephropathy (HIVAN) was first described before the advent of highly active antiretroviral therapy in late stages of HIV disease with high viral load and low CD4 cell count. Renal transplantation has been successful in a large series of carefully selected HIV-infected adults, with patient and renal allograft survival approaching those of non-HIV-infected patients. We report the successful outcome of living related renal transplantation in a vertically transmitted HIV-infected 8-year-old girl with end-stage kidney disease on haemodialysis due to HIVAN. The pretransplant preparations and post-transplant care, with particular emphasis on immunosuppression and avoidance of opportunistic infections, are discussed.

Circulating angiopoietin-2 is a marker for early cardiovascular disease in children on chronic dialysis.

Cardiovascular disease (CVD) is increasingly recognised as a complication of childhood chronic kidney disease (CKD) even in the absence of diabetes and hypertension. We hypothesized that an alteration in angiopoietin-1 and -2, growth factors which regulate endothelial and vascular function could be involved. We report that the endothelial survival factor, angiopoietin-1 is low in children with pre-dialysis CKD whereas the pro-inflammatory angiopoietin-2 is elevated in children on dialysis. In dialysis patients, angiopoietin-2 positively correlated with time on dialysis, systolic blood pressure, and carotid artery intima media thickness. Elevated angiopoietin-2 levels in dialysis versus pre-dialysis CKD patients were also associated with an anti-angiogenic (high soluble VEGFR-1 and low VEGF-A) and pro-inflammatory (high urate, E-selectin, P-selectin and VCAM-1) milieu. Ang-2 was immunodetected in arterial biopsy samples whilst the expression of VEGF-A was significantly downregulated in dialysis patients. Serum urate correlated with angiopoietin-2 levels in dialysis patients and addition of uric acid was able to induce rapid release of angiopoietin-2 from cultured endothelial cells. Thus, angiopoietin-2 is a marker for cardiovascular disease in children on chronic dialysis and may act as an anti-angiogenic and pro-inflammatory effector in this context. The possibility that the release of angiopoietin-2 from endothelia is mediated by urate should be explored further.

Renal complications following lung and heart-lung transplantation.

As survival improves after lung and heart-lung transplants, the long term detrimental impact of current management on renal function becomes more apparent as the number of non-renal solid organ transplant recipients on renal transplant waiting lists increases. Progressive chronic kidney disease (CKD) is a significant cause of morbidity and mortality in the transplant population. In this review we discuss the specific problems prior to lung or heart-lung transplant that predispose to CKD, as well as potential renal complications encountered during the peri- and post-transplant period. Significant acute and chronic nephrotoxicity is caused by calcineurin inhibitors (CNI). Mechanisms to decrease CNI exposure exist but have yet to be adopted in routine clinical care. Modifiable risk factors and the current screening and management approach taken at our institution are described. Pediatric nephrologists should be involved from an early stage. Future work will need to focus on identifying more accurate measures of renal function, given the limitations of current glomerular filtration rate estimation equations in a population where nutritional status may rapidly change post transplant. Multicentre studies of CNI minimisation strategies are required to guide future therapy that aims to minimise CKD development and progression in this vulnerable population.

Chronic mineral dysregulation promotes vascular smooth muscle cell adaptation and extracellular matrix calcification.

In chronic kidney disease (CKD) vascular calcification occurs in response to deranged calcium and phosphate metabolism and is characterized by vascular smooth muscle cell (VSMC) damage and attrition. To gain mechanistic insights into how calcium and phosphate mediate calcification, we used an ex vivo model of human vessel culture. Vessel rings from healthy control subjects did not accumulate calcium with long-term exposure to elevated calcium and/or phosphate. In contrast, vessel rings from patients with CKD accumulated calcium; calcium induced calcification more potently than phosphate (at equivalent calcium-phosphate product). Elevated phosphate increased alkaline phosphatase activity in CKD vessels, but inhibition of alkaline phosphatase with levamisole did not block calcification. Instead, calcification in CKD vessels most strongly associated with VSMC death resulting from calcium- and phosphate-induced apoptosis; treatment with a pan-caspase inhibitor ZVAD ameliorated calcification. Calcification in CKD vessels was also associated with increased deposition of VSMC-derived vesicles. Electron microscopy confirmed increased deposition of vesicles containing crystalline calcium and phosphate in the extracellular matrix of dialysis vessel rings. In contrast, vesicle deposition and calcification did not occur in normal vessel rings, but we observed extensive intracellular mitochondrial damage. Taken together, these data provide evidence that VSMCs undergo adaptive changes, including vesicle release, in response to dysregulated mineral metabolism. These adaptations may initially promote survival but ultimately culminate in VSMC apoptosis and overt calcification, especially with continued exposure to elevated calcium.

Phosphate binders in CKD: chalking out the differences.

Plasma phosphate levels are important in the evolution of hyperparathyroidism and ectopic calcification in chronic kidney disease (CKD). Although dietary management may be adequate to control plasma phosphate in its early stages, most patients develop hyperphosphataemia by CKD stages 3-4 and require the addition of a phosphate binder. Calcium-containing phosphate binders are the most used and cheapest binders but have fallen out of favour because of the potential for positive calcium balance and calcium toxicity. This problem may be attenuated by newer phosphate binders such as sevelamer hydrochloride and lanthanum carbonate. In this review, the role of phosphate as a uraemic toxin and the advantages and disadvantages of the currently available phosphate binders are discussed.

A phase I trial of epstein-barr virus gp350 vaccine for children with chronic kidney disease awaiting transplantation.

BACKGROUND.: Vaccination against Epstein-Barr virus (EBV), inducing an antibody response to the envelope glycoprotein gp350, might protect EBV-negative children with chronic kidney disease from lymphoproliferative disease after transplantation. METHODS.: A phase I trial recruited children with chronic kidney disease to two successive cohorts given three injections of 12.5 microg (n=6) and 25 microg (n=10) recombinant gp350/alhydrogel vaccine over 6 to 8 weeks. RESULTS.: One in each cohort acquired wild EBV before the week 28 evaluation. Both doses were similarly immunogenic, inducing an IgG response in all 13 evaluable patients. Neutralizing antibodies were detected in four recipients (1/4 in the 12.5 microg and 3/9 in the 25 microg cohort). Median time from first vaccination to transplantation was 24 weeks. Immune responses declined rapidly and were unlikely to affect posttransplant events. DISCUSSION.: The vaccine was immunogenic but a prolonged vaccine schedule up to time of transplantation or improved adjuvants are required in future trials to reduce posttransplant EBV load and risk of lymphoproliferative disease.

Dialysis accelerates medial vascular calcification in part by triggering smooth muscle cell apoptosis.

BACKGROUND: Vascular calcification is associated with increased morbidity and mortality in stage V chronic kidney disease, yet its early pathogenesis and initiating mechanisms in vivo remain poorly understood. To address this, we quantified the calcium (Ca) load in arteries from children (10 predialysis, 24 dialysis) and correlated it with clinical, biochemical, and vascular measures. METHODS AND RESULTS: Vessel Ca load was significantly elevated in both predialysis and dialysis and was correlated with the patients' mean serum Ca x phosphate product. However, only dialysis patients showed increased carotid intima-media thickness and increased aortic stiffness, and calcification on computed tomography was present in only the 2 patients with the highest Ca loads. Importantly, predialysis vessels appeared histologically intact, whereas dialysis vessels exhibited evidence of extensive vascular smooth muscle cell (VSMC) loss owing to apoptosis. Dialysis vessels also showed increased alkaline phosphatase activity and Runx2 and osterix expression, indicative of VSMC osteogenic transformation. Deposition of the vesicle membrane marker annexin VI and vesicle component mineralization inhibitors fetuin-A and matrix Gla-protein increased in dialysis vessels and preceded von Kossa positive overt calcification. Electron microscopy showed hydroxyapatite nanocrystals within vesicles released from damaged/dead VSMCs, indicative of their role in initiating calcification. CONCLUSIONS: Taken together, this study shows that Ca accumulation begins predialysis, but it is the induction of VSMC apoptosis in dialysis that is the key event in disabling VSMC defense mechanisms and leading to overt calcification, eventually with clinically detectable vascular damage. Thus the identification of factors that lead to VSMC death in dialysis will be of prime importance in preventing vascular calcification.

The circulating calcification inhibitors, fetuin-A and osteoprotegerin, but not matrix Gla protein, are associated with vascular stiffness and calcification in children on dialysis.

BACKGROUND: Vascular calcification occurs in the majority of patients with chronic kidney disease, but a subset of patients does not develop calcification despite exposure to a similar uraemic environment. Physiological inhibitors of calcification, fetuin-A, osteoprotegerin (OPG) and undercarboxylated-matrix Gla protein (uc-MGP) may play a role in preventing the development and progression of ectopic calcification, but there are scarce and conflicting data from clinical studies. METHODS: We measured fetuin-A, OPG and uc-MGP in 61 children on dialysis and studied their associations with clinical, biochemical and vascular measures. RESULTS: Fetuin-A and OPG were higher and uc-MGP lower in dialysis patients than controls. In controls, fetuin-A and OPG increased with age. Fetuin-A showed an inverse correlation with dialysis vintage (P = 0.0013), time-averaged serum phosphate (P = 0.03) and hs-CRP (P = 0.001). Aortic pulse wave velocity (PWV) and augmentation index showed a negative correlation with fetuin-A while a positive correlation was seen with PWV and OPG. Patients with calcification had lower fetuin-A and higher OPG than those without calcification. On multiple linear regression analysis Fetuin-A independently predicted aortic PWV (P = 0.004, beta = -0.45, model R(2) = 48%) and fetuin-A and OPG predicted cardiac calcification (P = 0.02, beta = -0.29 and P = 0.014, ss = 0.33, respectively, model R(2) = 32%). CONCLUSIONS: This is the first study to define normal levels of the calcification inhibitors in children and show that fetuin-A and OPG are associated with increased vascular stiffness and calcification in children on dialysis. Higher levels of fetuin-A in children suggest a possible protective upregulation of fetuin-A in the early stages of exposure to the pro-calcific and pro-inflammatory uraemic environment.

Mineral metabolism and vascular damage in children on dialysis.

Cardiovascular disease is increasingly recognized as a life-limiting problem in young patients with chronic kidney disease, but there are few studies in children that describe its determinants. We studied the association of intact parathyroid hormone (iPTH) levels and their management on vascular structure and function in 85 children, ages 5-18 years, who had received dialysis for > or =6 months. Compared to controls, dialysis patients had increased carotid intima-media thickness and pulse-wave velocity. All vascular measures positively correlated with serum phosphorus levels, while carotid intima-media thickness and cardiac calcification score also correlated with iPTH levels. Patients with mean time-integrated iPTH levels less than twice the upper limit of normal (n = 41) had vascular measures that were comparable to age-matched controls, but those with iPTH levels greater than twice the upper limit of normal (n = 44) had greater carotid intima-media thickness, stiffer vessels, and increased cardiac calcification than controls. Patients with increased carotid intima-media thickness had stiffer vessels and a greater prevalence of cardiac calcification. There was a strong dose-dependent correlation between vitamin D and all vascular measures, and calcium intake from phosphate binders weakly correlated with carotid intima-media thickness. In conclusion, both iPTH level and dosage of vitamin D are associated with vascular damage and calcification in children on dialysis.

The vascular biology of calcification.

Vascular calcification is an active, cell-mediated process that results from an imbalance between the promoters and inhibitors of mineralization. The process of vascular calcification shares many similarities with that of skeletal mineralization. However, while skeletal mineralization is a regulated process induced by complex, well-timed developmental cues, vascular calcification is a pathological process, occurring in response to dysregulated/inappropriate environmental cues. Damage inducing agents present in the uremic milieu such as a mineral imbalance, induce vascular smooth muscle cell (VSMC) apoptosis, and vesicle release resulting in mineral nucleation and the deposition of hydroxyapatite. Under normal conditions, inhibitors of soft-tissue mineralization such as matrix gamma-carboxyglutamic acid protein are expressed locally within the vessel wall while others such as fetuin-A are present in the circulation. Down-regulation or perturbation of these proteins leads to a phenotypic transformation of VSMC into osteo/chondrocytic-like cells that have the capacity to modulate the mineralization process. Many aspects of the mechanisms underlying vascular calcification have been defined through in vitro studies and molecular biological techniques; however, there are still unanswered questions, particularly with respect to the relationship between bone and vascular calcification, processes that appear to be inversely related. A better understanding of the complex mechanisms regulating tissue calcification may have therapeutic potential in reducing the cardiovascular disease-associated morbidity and mortality in patients with renal disease.