Mineral and bone disorder and longterm survival in a chronic kidney disease grade 3b-4cohort

Mineral and bone disorder biomarkers ‘normal ranges’ are controversial. The aim of the study was to evaluate the association between serum calcium (Ca), phosphate (P), intact parathyroid hormone (iPTH), and 25(OH) vitamin D levels and mortality risk, in a chronic kidney disease (CKD) grade (G) 3b-4 cohort. The Uruguayan National Renal Healthcare Program (NRHP-UY) CKD patients’ cohort, included between 1 October 2004 and 1 March 2020 and followed-up until 1 March 2021, was analyzed with the Ethics Committee approval. A total of 6473 patients were analyzed: 56% men, median age 73 (65–79) years, 55% on CKD G3b. At the end of the follow-up, 2459 (37.7%) patients had died (6.4/100 patient–year). There were iPTH data on 2013 patients (younger, with lower estimated glomerular filtration rate (eGFR) and lesser comorbidities). By bivariate Cox analysis the lowest death risk was observed with mean Ca between 9.01 and 10.25 mg/dl, P between 2.76 and 4.0 mg/dl, iPTH ≤ 105 pg/ml, and 25(OH) vitamin D >10 ng/ml. The multivariate Cox regression mortality risk adjusted to age, sex, CKD etiology, diabetes, smoking, cardiovascular comorbidity, blood pressure, proteinuria, eGFR, renin-angiotensin system blockers and vitamin D treatments, serum Ca, P, iPTH, and 25(OH) vitamin D (n = 964) showed that a higher mortality risk was associated with p > 4.00 mg/dl (HR 1.668, CI 95%: 1.201–2.317), iPTH >105 pg/ml (HR 1.386, CI 95%: 1.012–1.989), and 25(OH) vitamin D ≤ 10 ng/ml (HR 1.958, CI 95%: 1.238–3.098) and a lower mortality risk with 1,25(OH)₂ vitamin D treatment (HR 0.639, CI 95%: 0.451–0.906). These data may contribute to the precise G3b-4 CKD-MBD biomarkers levels definition.

Comparison of measured vs kinetic-model predicted phosphate removal during hemodialysis and hemodiafiltration

BACKGROUND

To what extent hemodiafiltration (HDF) improves management of hyperphosphatemia over hemodialysis (HD) is a subject of ongoing investigation.

METHODS

We modified a previously described phosphate kinetic model to include incorporation of EUDIAL recommended equations for hemodiafiltration (HDF) clearance. We used the model to predict the recovery of phosphate from spent dialysate/hemofiltrate and compared this with averaged data from five published studies. Mean study average predialysis serum phosphate was 1.81 ± 0.20 mmol/L. Session length was close to 240 min per treatment. All HDF was done postdilution, at an average rate of 65 ± 24 mL/min.

RESULTS

Measured mean phosphate removal was 1039 ± 136 mg (33.5 ± 4.41 mmol, slightly lower than the model-predicted mean value of 1092 ± 127 mg (35.3 ± 4.09 mmol). The measured ratio of phosphate removal with HDF compared with HD averaged 1.15 ± 0.22, ranging from 1.01 to 1.44. Using mean study input parameters for patient size and treatment characteristics, the predicted ratio of phosphate removal with HDF compared with HD averaged 1.095 ± 0.029, ranging from 1.05 to 1.13.

CONCLUSIONS

Addition of EUDIAL-recommended convective clearance equations to a phosphate kinetic model predicts a 10% or greater benefit in terms of phosphate removal for HDF compared with HD at typical dialysis and hemodiafiltration treatment settings. These predictions are similar to the HDF advantage reported in the literature in studies where phosphate removal has been measured in spent dialysate.

Bone, fat, and muscle interactions in health and disease

Energy metabolism is a point of integration among the various organs and tissues of the human body, not only in terms of consumption of energy substrates but also because it concentrates a wide interconnected network controlled by endocrine factors. Thus, not only do tissues consume substrates, but they also participate in modulating energy metabolism. Soft mesenchymal tissues, in particular, play a key role in this process. The recognition that high energy consumption is involved in bone remodeling has been accompanied by evidence showing that osteoblasts and osteocytes produce factors that influence, for example, insulin sensitivity and appetite. Additionally, there are significant interactions between muscle, adipose, and bone tissues to control mutual tissue trophism. Not by chance, trophic and functional changes in these tissues go hand in hand from the beginning of an individual's development until aging. Likewise, metabolic and nutritional diseases deeply affect the musculoskeletal system and adipose tissue. The present narrative review highlights the importance of the interaction of the mesenchymal tissues for bone development and maintenance and the impact on bone from diseases marked by functional and trophic disorders of adipose and muscle tissues.

Differences in Phosphate and Parathyroid Hormone Concentrations over the Day among Patients on Hemodialysis

BACKGROUND

Elevated serum phosphate and parathyroid hormone (PTH) concentrations are associated with cardiovascular events, bone disease, and mortality in patients on maintenance hemodialysis. Although circadian changes are known in people with CKD, it is unknown whether differences occur in these parameters over the course of a day in people receiving hemodialysis.

METHODS

We used clinical data from Fresenius Medical Care US dialysis clinics to determine how the time of day when measurements were collected (hemodialysis treatment start time) may be associated with serum phosphate and PTH concentrations. We used harmonic regression to assess these associations while accounting for demographic data and treatment parameters.

RESULTS

A total of 96,319 patients receiving maintenance hemodialysis were included in this analysis. Patients had a mean age of 64±14 years, 43% were women, and dialysis start times ranged from 3:00 am to 7:59 pm. The mean serum phosphate concentration was 5.2±1.5 mg/dl, and the median PTH was 351 pg/ml (interquartile range [IQR], 214-547). In fully adjusted models, serum phosphate had a nadir at 11:00 am of 4.97 (IQR, 4.94-5.01) mg/dl and a peak at 7:00 pm of 5.56 (IQR, 5.50-5.62) mg/dl. Serum PTH had a nadir at 9:00 am of 385 (IQR, 375-395) pg/ml and a peak at 7:00 pm of 530 (IQR, 516-547) pg/ml.

CONCLUSIONS

Among patients receiving maintenance hemodialysis, concentrations of PTH and phosphate before a dialysis session vary with the time of day that these values are measured. Consideration of whether these values were obtained at peak or nadir times of the day may be important in treatment decisions.

Management of fracture risk in CKD-traditional and novel approaches

The coexistence of osteoporosis and chronic kidney disease (CKD) is an evolving healthcare challenge in the face of increasingly aging populations. Globally, accelerating fracture incidence causes disability, impaired quality of life and increased mortality. Consequently, several novel diagnostic and therapeutic tools have been introduced for treatment and prevention of fragility fractures. Despite an especially high fracture risk in CKD, these patients are commonly excluded from interventional trials and clinical guidelines. While management of fracture risk in CKD has been discussed in recent opinion-based reviews and consensus papers in the nephrology literature, many patients with CKD stages 3-5D and osteoporosis are still underdiagnosed and untreated. The current review addresses this potential treatment nihilism by discussing established and novel approaches to diagnosis and prevention of fracture risk in patients with CKD stages 3-5D. Skeletal disorders are common in CKD. A wide variety of underlying pathophysiological processes have been identified, including premature aging, chronic wasting, and disturbances in vitamin D and mineral metabolism, which may impact bone fragility beyond established osteoporosis. We discuss current and emerging concepts of CKD-mineral and bone disorders (CKD-MBD) and integrate management of osteoporosis in CKD with current recommendations for management of CKD-MBD. While many diagnostic and therapeutic approaches to osteoporosis can be applied to patients with CKD, some limitations and caveats need to be considered. Consequently, clinical trials are needed that specifically study fracture prevention strategies in patients with CKD stages 3-5D.

Secondary hyperparathyroidism (CKD-MBD) treatment and the risk of dementia

BACKGROUND

Elevated parathyroid hormone (PTH) levels have been reported as a potential risk factor for cognitive impairment. Compared with the general population, older adults with end-stage renal disease (ESRD) who are frequently affected by secondary hyperparathyroidism (SHPT) are at increased risk of developing dementia. The main objective of our study was to evaluate if the risk of dementia in older (age ≥66 years) ESRD patients differed if they were treated for SHPT.

METHODS

Using the United States Renal Data System and Medicare claims, we identified 189 433 older adults without a diagnosis of dementia, who initiated dialysis between 2006 and 2016. SHPT treatment was defined as the use of vitamin D analogs, phosphate binders, calcimimetics or parathyroidectomy. We quantified the association between treated SHPT and incident dementia during dialysis using a multivariable Cox proportional hazards model with inverse probability weighting, considering SHPT treatment as a time-varying exposure.

RESULTS

Of 189 433 older ESRD adults, 92% had a claims diagnosis code of SHPT and 123 388 (65%) were treated for SHPT. The rate of incident dementia was 6 cases per 100 person-years among SHPT treated patients compared with 11 cases per 100 person-years among untreated patients. Compared with untreated SHPT patients, the risk of dementia was 42% lower [adjusted hazard ratio (aHR) = 0.58, 95% confidence interval (CI): 0.56-0.59] among SHPT treated patients. The magnitude of the beneficial effect of SHPT treatment differed by sex (Pinteraction = .02) and race (Pinteraction ≤ .01), with females (aHR = 0.56, 95% CI: 0.54-0.58) and those of Asian (aHR = 0.51, 95% CI: 0.46-0.57) or Black race (aHR = 0.51, 95% CI: 0.48-0.53) having a greatest reduction in dementia risk.

CONCLUSION

Receiving treatment for SHPT was associated with a lower risk of incident dementia among older patients with ESRD. This work provides additional support for the treatment of SHPT in older ESRD patients.

Critical Role of Osteopontin in Maintaining Urinary Phosphate Solubility in CKD

Background

Nephron loss dramatically increases tubular phosphate to concentrations that exceed supersaturation. Osteopontin (OPN) is a matricellular protein that enhances mineral solubility in solution; however, the role of OPN in maintaining urinary phosphate solubility in CKD remains undefined.

Methods

Here, we examined (1) the expression patterns and timing of kidney/urine OPN changes in CKD mice, (2) if tubular injury is necessary for kidney OPN expression in CKD, (3) how OPN deletion alters kidney mineral deposition in CKD mice, (4) how neutralization of the mineral-binding (ASARM) motif of OPN alters kidney mineral deposition in phosphaturic mice, and (5) the in vitro effect of phosphate-based nanocrystals on tubular epithelial cell OPN expression.

Results

Tubular OPN expression was dramatically increased in all studied CKD murine models. Kidney OPN gene expression and urinary OPN/Cr ratios increased before changes in traditional biochemical markers of kidney function. Moreover, a reduction of nephron numbers alone (by unilateral nephrectomy) was sufficient to induce OPN expression in residual nephrons and induction of CKD in OPN-null mice fed excess phosphate resulted in severe nephrocalcinosis. Neutralization of the ASARM motif of OPN in phosphaturic mice resulted in severe nephrocalcinosis that mimicked OPN-null CKD mice. Lastly, in vitro experiments revealed calcium-phosphate nanocrystals to induce OPN expression by tubular epithelial cells directly.

Conclusions

Kidney OPN expression increases in early CKD and serves a critical role in maintaining tubular mineral solubility when tubular phosphate concentrations are exceedingly high, as in late-stage CKD. Calcium-phosphate nanocrystals may be a proximal stimulus for tubular OPN production.

Strategies to lower fibroblast growth factor 23 bioactivity

Fibroblast growth factor 23 (FGF23) is a circulating hormone derived from the bone whose release is controlled by many factors and exerts a multitude of systemic actions. There are congenital and acquired disorders of increased and decreased FGF23 levels. In chronic kidney disease (CKD), elevations of FGF23 levels can be 1000-fold above the upper physiological limit. It is still debated whether this high FGF23 in CKD is a biomarker or causally related to morbidity and mortality. Data from human association studies support pathogenicity, while experimental data are less robust. Knowledge of the biology and pathobiology of FGF23 has generated a plethora of means to reduce FGF23 bioactivity at many levels that will be useful for therapeutic translations. This article summarizes these approaches and addresses several critical questions that still need to be answered.

Kidney Failure Alters Parathyroid Pin1 Phosphorylation and Parathyroid Hormone mRNA-Binding Proteins, Leading to Secondary Hyperparathyroidism

BACKGROUND

Secondary hyperparathyroidism (SHP) is a common complication of CKD that increases morbidity and mortality. In experimental SHP, increased parathyroid hormone (PTH) expression is due to enhanced PTH mRNA stability, mediated by changes in its interaction with stabilizing AUF1 and destabilizing KSRP. The isomerase Pin1 leads to KSRP dephosphorylation, but in SHP parathyroid Pin1 activity is decreased and hence phosphorylated KSRP fails to bind PTH mRNA, resulting in high PTH mRNA stability and levels. The up- and downstream mechanisms by which CKD stimulates the parathyroid glands remain elusive.

METHODS

Adenine-rich high-phosphate diets induced CKD in rats and mice. Parathyroid organ cultures and transfected cells were incubated with Pin1 inhibitors for their effect on PTH expression. Mass spectrometry was performed on both parathyroid and PTH mRNA pulled-down proteins.

RESULTS

CKD led to changes in rat parathyroid proteome and phosphoproteome profiles, including KSRP phosphorylation at Pin1 target sites. Furthermore, both acute and chronic kidney failure led to parathyroid-specific Pin1 Ser16 and Ser71 phosphorylation, which disrupts Pin1 activity. Pharmacologic Pin1 inhibition, which mimics the decreased Pin1 activity in SHP, increased PTH expression ex vivo in parathyroid glands in culture and in transfected cells through the PTH mRNA-protein interaction element and KSRP phosphorylation.

CONCLUSIONS

Kidney failure leads to loss of parathyroid Pin1 activity by inducing Pin1 phosphorylation. This predisposes parathyroids to increase PTH production through impaired PTH mRNA decay that is dependent on KSRP phosphorylation at Pin1-target motifs. Pin1 and KSRP phosphorylation and the Pin1-KSRP-PTH mRNA axis thus drive SHP.

Genetic Variants Associated With Mineral Metabolism Traits in Chronic Kidney Disease

CONTEXT

Chronic kidney disease (CKD) causes multiple interrelated disturbances in mineral metabolism. Genetic studies in the general population have identified common genetic variants associated with circulating phosphate, calcium, parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF23).

OBJECTIVE

In this study we aimed to discover genetic variants associated with circulating mineral markers in CKD.

METHODS

We conducted candidate single-nucleotide variation (SNV) analysis in 3027 participants in the multiethnic Chronic Renal Insufficiency Cohort (CRIC) to determine the associations between SNVs and circulating levels of mineral markers.

RESULTS

SNVs adjacent to or within genes encoding the regulator of G protein-coupled signaling 14 (RGS14) and the calcium-sensing receptor (CASR) were associated with levels of mineral metabolites. The strongest associations (P < .001) were at rs4074995 (RGS14) for phosphate (0.09 mg/dL lower per minor allele) and FGF23 (8.6% lower), and at rs1801725 (CASR) for calcium (0.12 mg/dL higher). In addition, the prevalence of hyperparathyroidism differed by rs4074995 (RGS14) genotype (chi-square P < .0001). Differential inheritance by race was noted for the minor allele of RGS14. Expression quantitative loci (eQTL) analysis showed that rs4074995 was associated with lower RGS14 gene expression in glomeruli (P = 1.03 × 10-11) and tubules (P = 4.0 × 10-4).

CONCLUSION

We evaluated genetic variants associated with mineral metabolism markers in a CKD population. Participants with CKD and the minor allele of rs4074995 (RGS14) had lower phosphorus, lower plasma FGF23, and lower prevalence of hyperparathyroidism. The minor allele of RGS14 was also associated with lower gene expression in the kidney. Further studies are needed to elucidate the effect of rs4074995 on the pathogenesis of disordered mineral metabolism in CKD.

Diastolic Pressure and ACR Are Modifiable Risk Factors of Arterial Stiffness in T2DM Without Cardiovascular Disease

AIM

To evaluate early, before the onset of cardiovascular events and of chronic renal insufficiency, the association between chronic kidney disease (CKD)-mineral bone disorder (MBD) biomarkers and vascular stiffness [Cardio Ankle Vascular Index (CAVI)] in the course of type 2 diabetes (T2DM).

METHOD

We evaluated 174 T2DM patients [median age 56 years; male/female (M/F) 100/74] with diabetes duration < 10 years and without decreased estimated glomerular filtration rate (eGFR; ≥60 mL/min/1.73 m2) or macrovascular complications. Thirty-four age-matched healthy subjects [M/F 13/21; age 53.5 (50.0-57.7) years; eGFR 107.5 (97.0-119.7) mL/ min1.73 m2] served as local reference control for CAVI (pathological: ≥8) and the novel CKD-MBD biomarkers.

RESULTS

Albumin-to-creatinine ratio (ACR) averaged 8.5 mg/g (5.6-17.2) with 12.6% of the patients showing pathologic values, indicative of incipient diabetic nephropathy. Serum parathyroid hormone, fibroblast growth factor 23, and sclerostin were higher while 1,25-dihydroxyvitamin D and Klotho were lower than a control group. CAVI was normal (<8) in only 54% and correlated positively with age (P < 0.001), hemoglobin 1A1c (P = 0.036), and systolic (P = 0.021) and diastolic blood pressure (DBP) (P = 0.001) and negatively correlated with 25-hydroxyvitamin D (P = 0.046). In multivariate analysis, age, DBP, ACR, and serum Klotho were independent positive predictors of CAVI.

CONCLUSION

In the absence of overt cardiovascular disease and of chronic renal insufficiency, CAVI is frequently pathologic in T2DM. DBP and ACR are modifiable risk factors of vascular stiffness in T2DM, thus warranting optimal assessment.

High-Resolution Mass Spectrometry for the Measurement of PTH and PTH Fragments: Insights into PTH Physiology and Bioactivity

Full-length parathyroid hormone (PTH 1-84) is crucial for the regulation of calcium and phosphate homeostasis and bone remodeling. PTH 1-84 is metabolized into various PTH fragments, which are measured with varying levels of efficiency by PTH immunoassays. These PTH fragments, which increase in serum as CKD progresses, could potentially modulate the effects of PTH 1-84 and contribute to CKD-associated bone disorders. To obtain a true biologic representation of total PTH bioactivity, it is necessary to measure not only PTH 1-84 but also PTH fragments that are present in circulation. Traditional second-generation PTH immunoassays collectively measure PTH 1-84, PTH fragments, and post-translationally modified PTH 1-84, making it difficult to accurately predict the character of underlying renal osteodystrophy. This review highlights current advances in methods available for PTH measurement and the clinical relevance of PTH fragments in CKD. We emphasize the usefulness of mass spectrometry as a potential reference method for PTH measurement.

Association of Genetically Predicted Fibroblast Growth Factor-23 with Heart Failure: A Mendelian Randomization Study

BACKGROUND AND OBJECTIVES

Elevated fibroblast growth factor-23 (FGF23) has been consistently associated with heart failure, particularly heart failure with preserved ejection fraction, among patients with CKD and in the general population. FGF23 may directly induce cardiac remodeling and heart failure. However, biases affecting observational studies impede robust causal inferences. Mendelian randomization leverages genetic determinants of a risk factor to examine causality. We performed a two-sample Mendelian randomization to assess causal associations between FGF23 and heart failure.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Genetic instruments were genome-wide significant genetic variants associated with FGF23, including variants near PIP5K1B, RGS14, LINC01229, and CYP24A1. We analyzed data from the Heart Failure Molecular Epidemiology for Therapeutic Targets and BioVU biobanks to examine associations of the four variants with overall heart failure, heart failure with preserved ejection fraction, and heart failure with reduced and mid-range ejection fraction. We developed an eGFR polygenic risk score using summary statistics from the Chronic Kidney Disease Genetics Consortium (CKDGen) genome-wide association study of eGFR in >1 million individuals and performed stratified analyses across eGFR polygenic risk score strata.

RESULTS

Genetically determined FGF23 was not associated with overall heart failure in the Heart Failure Molecular Epidemiology for Therapeutic Targets consortium (odds ratio, 1.13; 95% confidence interval, 0.89 to 1.42 per unit higher genetically predicted log FGF23) and the full BioVU sample (odds ratio, 1.32; 95% confidence interval, 0.95 to 1.84). In stratified analyses in BioVU, higher FGF23 was associated with overall heart failure (odds ratio, 3.09; 95% confidence interval, 1.38 to 6.91) among individuals with low eGFR-polygenic risk score (<1 SD below the mean), but not those with high eGFR-polygenic risk score (P interaction = 0.02). Higher FGF23 was also associated with heart failure with preserved ejection fraction among all BioVU participants (odds ratio, 1.47; 95% confidence interval, 1.01 to 2.14) and individuals with low eGFR-polygenic risk score (odds ratio, 7.20; 95% confidence interval, 2.80 to 18.49), but not those high eGFR-polygenic risk score (P interaction = 2.25 × 10^-4). No significant associations were observed with heart failure with reduced and midrange ejection fraction.

CONCLUSION

We found no association between genetically predicted FGF23 and heart failure in the Heart Failure Molecular Epidemiology for Therapeutic Targets consortium. In BioVU, genetically elevated FGF23 was associated with higher heart failure risk, specifically heart failure with preserved ejection fraction, particularly among individuals with low genetically predicted eGFR.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2022_07_28_CJN00960122.mp3.

Effect of Bis(maltolato)oxovanadium(IV) on Zinc, Copper, and Manganese Homeostasis and DMT1 mRNA Expression in Streptozotocin-Induced Hyperglycemic Rats

Our aim was to examine whether vanadium (IV) corrects alterations in zinc, copper and manganese homeostasis, observed in streptozotocin-induced hyperglycemic rats, and whether such changes are related to divalent metal transporter 1 (DMT1) mRNA expression, and antioxidant and proinflammatory parameters. Four groups of Wistar rats were examined: control; hyperglycemic (H); hyperglycemic treated with 1 mg V/day (HV); and hyperglycemic treated with 3 mg V/day (HVH). Vanadium was supplied in drinking water as bis(maltolato)oxovanadium(IV) for five weeks. Zinc, copper and manganese were measured in food, excreta, serum and tissues. DMT1 mRNA expression was quantified in the liver. Hyperglycemic rats showed increased Zn and Cu absorption and content in the liver, serum, kidneys and femurs; DMT1 expression also increased (p < 0.05 in all cases). HV rats showed no changes compared to H rats other than decreased DMT1 expression (p < 0.05). In the HVH group, decreased absorption and tissular content of studied elements (p < 0.05 in all cases) and DMT1 expression compared to H (p < 0.05) were observed. Liver zinc, copper and manganese content correlated positively with glutathione peroxidase activity and negatively with catalase activity (p < 0.05 in both cases). In conclusion, treatment with 3 mg V/d reverted the alterations in zinc and copper homeostasis caused by hyperglycemia, possibly facilitated by decreased DMT1 expression.

Impaired Mineral Ion Metabolism in a Mouse Model of Targeted Calcium-Sensing Receptor (CaSR) Deletion from Vascular Smooth Muscle Cells

BACKGROUND

Impaired mineral ion metabolism is a hallmark of CKD-metabolic bone disorder. It can lead to pathologic vascular calcification and is associated with an increased risk of cardiovascular mortality. Loss of calcium-sensing receptor (CaSR) expression in vascular smooth muscle cells exacerbates vascular calcification in vitro. Conversely, vascular calcification can be reduced by calcimimetics, which function as allosteric activators of CaSR.

METHODS

To determine the role of the CaSR in vascular calcification, we characterized mice with targeted Casr gene knockout in vascular smooth muscle cells ( ^SM22α CaSR ^{Δflox/Δflox} ).

RESULTS

Vascular smooth muscle cells cultured from the knockout (KO) mice calcified more readily than those from control (wild-type) mice in vitro. However, mice did not show ectopic calcifications in vivo but they did display a profound mineral ion imbalance. Specifically, KO mice exhibited hypercalcemia, hypercalciuria, hyperphosphaturia, and osteopenia, with elevated circulating fibroblast growth factor 23 (FGF23), calcitriol (1,25-D₃), and parathyroid hormone levels. Renal tubular α-Klotho protein expression was increased in KO mice but vascular α-Klotho protein expression was not. Altered CaSR expression in the kidney or the parathyroid glands could not account for the observed phenotype of the KO mice.

CONCLUSIONS

These results suggest that, in addition to CaSR's established role in the parathyroid-kidney-bone axis, expression of CaSR in vascular smooth muscle cells directly contributes to total body mineral ion homeostasis.

Bone phenotypes in multiple endocrine neoplasia type 1: survey on the MEN1 Florentine database

Multiple endocrine neoplasia type 1 (MEN1) is a rare, inherited cancer syndrome characterized by the development of multiple endocrine and non-endocrine tumors. MEN1 patients show a reduction of bone mass and a higher prevalence of early onset osteoporosis, compared to healthy population of the same age, gender, and ethnicity. During the monitoring and follow-up of MEN1 patients, the attention of clinicians is primarily focused on the diagnosis and therapy of tumors, while the assessment of bone health and mineral metabolism is, in many cases, marginally considered. In this study, we retrospectively analyzed bone and mineral metabolism features in a series of MEN1 patients from the MEN1 Florentine database. Biochemical markers of bone and mineral metabolism and densitometric parameters of bone mass were retrieved from the database and were analyzed based on age ranges and genders of patients and presence/absence of the three main MEN1-related endocrine tumor types. Our evaluation confirmed that patients with a MEN1 diagnosis have a high prevalence of earlyonset osteopenia and osteoporosis, in association with levels of serum and urinary markers of bone turnover higher than the normal reference values, regardless of their different MEN1 tumors. Fifty percent of patients younger than 26 years manifested osteopenia and 8.3% had osteoporosis, in at least one of the measured bone sites. These data suggest the importance of including biochemical and instrumental monitoring of bone metabolism and bone mass in the routine medical evaluation and follow-up of MEN1 patients and MEN1 carriers as important clinical aspects in the management of the syndrome.

Natural History of Bone Disease following Kidney Transplantation

BACKGROUND

Knowledge of the effect of kidney transplantation on bone is limited and fragmentary. The aim of this study was to characterize the evolution of bone disease in the first post-transplant year.

METHODS

We performed a prospective, observational cohort study in patients referred for kidney transplantation under a steroid-sparing immunosuppressive protocol. Bone phenotyping was done before, or at the time of, kidney transplantation, and repeated at 12 months post-transplant. The phenotyping included bone histomorphometry, bone densitometry by dual-energy x-ray absorptiometry, and biochemical parameters of bone and mineral metabolism.

RESULTS

Paired data were obtained for 97 patients (median age 55 years; 72% male; 21% of patients had diabetes). Bone turnover remained normal or improved in the majority of patients (65%). Bone histomorphometry revealed decreases in bone resorption (eroded perimeter, mean 4.6% pre- to 2.3% post-transplant; P<0.001) and disordered bone formation (fibrosis, 27% pre- versus 2% post-transplant; P<0.001). Whereas bone mineralization was normal in all but one patient pretransplant, delayed mineralization was seen in 15% of patients at 1 year post-transplant. Hypophosphatemia was associated with deterioration in histomorphometric parameters of bone mineralization. Changes in bone mineral density were highly variable, ranging from -18% to +17% per year. Cumulative steroid dose was related to bone loss at the hip, whereas resolution of hyperparathyroidism was related to bone gain at both spine and hip.

CONCLUSIONS

Changes in bone turnover, mineralization, and volume post-transplant are related both to steroid exposure and ongoing disturbances of mineral metabolism. Optimal control of mineral metabolism may be key to improving bone quality in kidney transplant recipients.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Evolution of Bone Histomorphometry and Vascular Calcification Before and After Renal Transplantation, NCT01886950.

Effect of lanthanum carbonate on serum calciprotein particles in patients with stage 3-4 CKD-results from a placebo-controlled randomized trial

BACKGROUND

Calciprotein particles (CPP) are colloidal aggregates of calcium phosphate and the mineral-binding protein fetuin-A, and are potential mediators of cardiovascular disease in chronic kidney disease (CKD). Emerging evidence suggests non-calcium-containing phosphate binders may reduce serum CPP in patients with kidney failure who require dialysis; however, it is unclear whether similar interventions are effective in patients with earlier stages of CKD.

METHODS

The IMpact of Phosphate Reduction On Vascular End-points in CKD (IMPROVE-CKD) was a multi-centre, placebo-controlled, randomized trial of lanthanum carbonate on cardiovascular markers in 278 participants with stage 3b/4 CKD. In this pre-specified exploratory analysis, primary (CPP-I) and secondary CPP (CPP-II) were measured in a sub-cohort of participants over 96 weeks. Treatment groups were compared using linear mixed-effects models and the relationship between serum CPP and pulse wave velocity (PWV) and abdominal aortic calcification (AAC) was examined.

RESULTS

A total of 253 participants had CPP data for baseline and at least one follow-up timepoint and were included in this analysis. The mean age was 62.4 ± 12.6 years, 32.0% were female and the mean estimated glomerular filtration rate (eGFR) was 26.6 ± 8.3 mL/min/1.73 m2. Baseline median serum CPP-I was 14.9 × 104 particles/mL [interquartile range (IQR) 4.6-49.3] and median CPP-II was 3.3 × 103 particles/mL (IQR 1.4-5.4). There was no significant difference between treatment groups at 96 weeks in CPP-I [22.8% (95% confidence interval -39.2, 36.4), P = 0.65] or CPP-II [-18.3% (95% confidence interval -40.0, 11.2), P = 0.20] compared with a placebo. Serum CPP were not correlated with baseline PWV or AAC, or with the progression of either marker.

CONCLUSIONS

Lanthanum carbonate was not associated with a reduction of CPP at 96 weeks when compared with a placebo in a CKD cohort.

Prevalence, progression and implications of breast artery calcification in patients with chronic kidney disease

Breast arterial calcification (BAC) is increasingly recognized as a specific marker of medial calcification. The present retrospective observational cohort study aimed to define the prevalence, progression rate, risk factors and clinical implications of BAC in chronic kidney disease (CKD) patients across stages of disease. The presence and extent of BAC were determined on mammograms in 310 females (58.7 ± 10.8 years, Caucasian) with CKD across various stages of disease [CKD G2-5D n = 132; transplant (Tx) recipients n = 178]. In a subset of 88 patients, repeat mammography was performed, allowing us to calculate the annualized BAC rate. Overall, BAC was observed in 34.7% of the patients. BAC prevalence (P = 0.02) and BAC score (P = 0.05) increased along the progression of CKD. In the overall cohort, patients with BAC were characterized by older age, more cardiovascular disease, more inflammation, higher pulse pressure and borderline higher prevalence of diabetes and were more often treated with a vitamin K antagonist (VKA). The BAC progression rate was significantly lower in Tx patients as compared with CKD G5D. Progressors were characterized by more inflammation, worse kidney function, higher BAC score and higher serum phosphate level (Tx only) at baseline and were more often treated with a VKA. Major adverse cardiovascular event-free survival was significantly worse in Tx patients with BAC. In conclusion, BAC is common among CKD patients, progresses at a slower pace in Tx patients as compared with CKD 5D and associates with dismal cardiovascular outcomes. BAC score, kidney function, serum phosphate at baseline and VKA usage seem to be important determinants of progression.

Bone and Mineral Disease in Kidney Transplant Recipients

After kidney transplantation, mineral and bone disorders are associated with higher risk of fractures and consequent morbidity and mortality. Disorders of calcium and phosphorus, vitamin D deficiency, and hyperparathyroidism are also common. The epidemiology of bone disease has evolved over the past several decades due to changes in immunosuppressive regimens, mainly glucocorticoid minimization or avoidance. The assessment of bone disease in kidney transplant recipients relies on risk factor recognition and bone mineral density assessment. Several drugs have been trialed for the treatment of post-transplant mineral and bone disorders. This review will focus on the epidemiology, effect, and treatment of metabolic and skeletal derangements in the transplant recipient.

Systematic Review and Meta-Analyses of the Effects of Phosphate-Lowering Agents in Nondialysis CKD

BACKGROUND

Benefits of phosphate-lowering interventions on clinical outcomes in patients with CKD are unclear; systematic reviews have predominantly involved patients on dialysis. This study aimed to summarize evidence from randomized controlled trials (RCTs) concerning benefits and risks of noncalcium-based phosphate-lowering treatment in nondialysis CKD.

METHODS

We conducted a systematic review and meta-analyses of RCTs involving noncalcium-based phosphate-lowering therapy compared with placebo, calcium-based binders, or no study medication, in adults with CKD not on dialysis or post-transplant. RCTs had ≥3 months follow-up and outcomes included biomarkers of mineral metabolism, cardiovascular parameters, and adverse events. Outcomes were meta-analyzed using the Sidik-Jonkman method for random effects. Unstandardized mean differences were used as effect sizes for continuous outcomes with common measurement units and Hedge's g standardized mean differences (SMD) otherwise. Odds ratios were used for binary outcomes. Cochrane risk of bias and GRADE assessment determined the certainty of evidence.

RESULTS

In total, 20 trials involving 2498 participants (median sample size 120, median follow-up 9 months) were eligible for inclusion. Overall, risk of bias was low. Compared with placebo, noncalcium-based phosphate binders reduced serum phosphate (12 trials, weighted mean difference -0.37; 95% CI, -0.58 to -0.15 mg/dl, low certainty evidence) and urinary phosphate excretion (eight trials, SMD -0.61; 95% CI, -0.90 to -0.31, low certainty evidence), but resulted in increased constipation (nine trials, log odds ratio [OR] 0.93; 95% CI, 0.02 to 1.83, low certainty evidence) and greater vascular calcification score (three trials, SMD, 0.47; 95% CI, 0.17 to 0.77, very low certainty evidence). Data for effects of phosphate-lowering therapy on cardiovascular events (log OR, 0.51; 95% CI, -0.51 to 1.17) and death were scant.

CONCLUSIONS

Noncalcium-based phosphate-lowering therapy reduced serum phosphate and urinary phosphate excretion, but there was an unclear effect on clinical outcomes and intermediate cardiovascular end points. Adequately powered RCTs are required to evaluate benefits and risks of phosphate-lowering therapy on patient-centered outcomes.

Assessment of the measurement of canine and feline serum fibroblast growth factor-23 concentrations by automated chemiluminescence immunoassay

This study compared canine and feline fibroblast growth factor (FGF)-23 concentration measurements between automated chemiluminescence assay (CLEIA) and enzyme-linked immunosorbent assay (ELISA). Seventy serum samples each from dogs and cats were evaluated. FGF-23 measurements by CLEIA significantly correlated with those of ELISA in both dogs and cats. The Bland–Altman test showed that FGF-23 between CLEIA and ELISA had fixed and proportional biases, respectively, in both dogs and cats. Measurements by CLEIA were lower than those of ELISA, especially in higher serum FGF-23 concentrations. This study showed that FGF-23 concentrations in dogs and cats can be evaluated by automated CLEIA. However, FGF-23 cannot be directly compared between CLEIA and ELISA.

Abnormalities in Cardiac Structure and Function among Individuals with CKD: The COMBINE Trial

Background

Individuals with CKD have a high burden of cardiovascular disease (CVD). Abnormalities in cardiac structure and function represent subclinical CVD and can be assessed by cardiac magnetic resonance imaging (cMRI).

Methods

We investigated differences in cMRI parameters in 140 individuals with CKD stages 3b-4 who participated in the CKD Optimal Management with BInders and NicotinamidE (COMBINE) trial and in 24 age- and sex-matched healthy volunteers. Among COMBINE participants, we examined the associations of eGFR, urine albumin-creatinine ratio (UACR), phosphate, fibroblast growth factor 23 (FGF23), and parathyroid hormone (PTH) with baseline (N=140) and 12-month change (N=112) in cMRI parameters.

Results

Mean (SD) ages of the COMBINE participants and healthy volunteers were 64.9 (11.9) and 60.4 (7.3) years, respectively. The mean (SD) baseline eGFR values in COMBINE participants were 32.1 (8.0) and 85.9 (16.0) ml/min per 1.73 m² in healthy volunteers. The median (interquartile range [IQR]) UACR in COMBINE participants was 154 (20.3-540.0) mg/g. Individuals with CKD had lower mitral valve E/A ratio compared with healthy volunteers (for CKD versus non-CKD, β estimate, -0.13; 95% CI, -0.24 to -0.012). Among COMBINE participants, multivariable linear regression analyses showed that higher UACR was significantly associated with lower mitral valve E/A ratio (β estimate per 1 unit increase in natural-log UACR, -0.06; 95% CI, -0.09 to -0.03). This finding was preserved among individuals without baseline CVD. UACR was not associated with 12-month change in any cMRI parameter. eGFR, phosphate, FGF23, and PTH were not associated with any cMRI parameter in cross-sectional or change analyses.

Conclusions

Individuals with CKD stages 3b-4 have evidence of cMRI abnormalities. Albuminuria was independently associated with diastolic dysfunction, as assessed by mitral valve E/A ratio, in individuals with CKD with and without clinical CVD. Albuminuria was not associated with change in any cMRI parameter.