Leveraging quantitative systems pharmacology and artificial intelligence to advance treatment of chronic kidney disease mineral bone disorder.

Chronic kidney disease mineral bone disorder (CKD-MBD) is a complex clinical syndrome responsible for the accelerated cardiovascular mortality seen in individuals afflicted with CKD. Current approaches to therapy have failed to improve clinical outcomes adequately, likely due to targeting surrogate biochemical parameters as articulated by the guideline developer, Kidney Disease: Improving Global Outcomes (KDIGO). We hypothesized that using a Systems Biology Approach combining machine learning with mathematical modeling, we could test a novel approach to therapy targeting the abnormal movement of mineral out of bone and into soft tissue that is characteristic of CKD-MBD. The mathematical model describes the movement of calcium and phosphate between body compartments in response to standard therapeutic agents. The machine-learning technique we applied is reinforcement learning (RL). We compared calcium, phosphate, parathyroid hormone (PTH), and mineral movement out of bone and into soft tissue under four scenarios: standard approach (KDIGO), achievement of KDIGO guidelines using RL (RLKDIGO), targeting abnormal mineral flux (RLFLUX), and combining achievement of KDIGO guidelines with minimization of abnormal mineral flux (RLKDIGOFLUX). We demonstrate through simulations that explicitly targeting abnormal mineral flux significantly decreases abnormal mineral movement compared with standard approach while achieving acceptable biochemical outcomes. These investigations highlight the limitations of current therapeutic targets, primarily secondary hyperparathyroidism, and emphasize the central role of deranged phosphate homeostasis in the genesis of the CKD-MBD syndrome.NEW & NOTEWORTHY Artificial intelligence is a powerful tool for exploration of complex processes but application to clinical syndromes is challenging. Using a mathematical model describing the movement of calcium and phosphate between body compartments combined with machine learning, we show the feasibility of testing alternative goals of therapy for Chronic Kidney Disease Mineral Bone Disorder while maintaining acceptable biochemical outcomes. These simulations demonstrate the potential for using this platform to generate and test hypotheses in silico rapidly, inexpensively, and safely.

Generalized Propensity Score Methods to Assess CKD-Associated Physiologic Factors and Risk of Kidney Failure in the Chronic Renal Insufficiency Cohort (CRIC) Study.

Epidemiologic studies have identified many biochemical risk factors for chronic kidney disease (CKD) progression that are correlates of kidney function, termed here 'CKD-associated physiologic factors'. Uncertainty remains if these factors are risk factors or risk markers accounting for aspects of kidney function not otherwise captured. We aimed to use flexible machine learning, a dynamic covariate history including kidney function informative markers, and generalized propensity score (GPS) weighting, to better control confounding for such exposures. We studied 3,052 adults with CKD in the Chronic Renal Insufficiency Cohort Study. We established a 2-year run-in period and assembled 90 variables that characterize variability and trends of selected CKD-associated physiologic factors and confounders. Using SuperLearner, we created a GPS for each CKD-associated physiologic factor and performed GPS-weighted Cox regressions. For context, we also evaluated results from traditional multivariable Cox proportional hazards models as in prior studies. Similar to traditional approaches, bicarbonate, calcium, potassium, hemoglobin, and PTH were each associated with risk of kidney failure using GPS weighting. The GPS approach detected non-linear associations in many factors, some of which were not detected with traditional models. We conclude that many associations between CKD-associated physiologic factors and kidney outcomes remain strong after GPS weighting.

Comparative Effectiveness of Alternative Treatment Approaches to Secondary Hyperparathyroidism in Patients Receiving Maintenance Hemodialysis: An Observational Trial Emulation.

RATIONALE & OBJECTIVE: Optimal approaches to treat secondary hyperparathyroidism (SHPT) in patients on maintenance hemodialysis (HD) have yet to be established in randomized controlled trials (RCTs). STUDY DESIGN: Two observational clinical trial emulations. SETTING & PARTICIPANTS: Both emulations included adults receiving in-center HD from a national dialysis organization. The patients who had SHPT in the period between 2009 and 2014, were insured for≥180 days by Medicare as primary payer, and did not have contraindications or poor health status limiting theoretical trial participation. EXPOSURE: The parathyroid hormone (PTH) Target Trial emulation included patients with new-onset SHPT (first PTH 300-600pg/mL), with 2 arms defined as up-titration of either vitamin D sterols or cinacalcet within 30 days (lower target) or no up-titration (higher target). The Agent Trial emulation included patients with a PTH≥300 pg/mL while on≥6µg weekly of vitamin D sterol (paricalcitol equivalent dose) and no prior history of cinacalcet. The 2 arms were defined by the first dose or agent change within 30 days (vitamin D-favoring [vitamin-D was up-titrated] vs cinacalcet-favoring [cinacalcet was added] vs nondefined [neither applies]). Multiple trials per patient were allowed in trial 2. OUTCOME: The primary outcome was all-cause death over 24 months; secondary outcomes included cardiovascular (CV) hospitalization or the composite of CV hospitalization or death. ANALYTICAL APPROACH: Pooled logistic regression. RESULTS: There were 1,152 patients in the PTH Target Trial (635 lower target and 517 higher target). There were 2,726 unique patients with 6,727 patient trials in the Agent Trial (6,268 vitamin D-favoring trials and 459 cinacalcet-favoring trials). The lower PTH target approach was associated with reduced adjusted hazard of death (HR, 0.71 [95% CI, 0.52-0.93]), CV hospitalization (HR, 0.78 [95% CI, 0.63-0.98]), and their composite (HR, 0.74 [95% CI, 0.61-0.89]). The cinacalcet-favoring approach demonstrated lower adjusted hazard of death compared to the vitamin D-favoring approach (HR, 0.79 [95% CI, 0.62-0.99]), but not of CV hospitalization or the composite outcome. LIMITATIONS: Potential for residual confounding; low use of cinacalcet with low power. CONCLUSIONS: SHPT management that is focused on lower PTH targets may lower mortality and CV disease in patients receiving HD. These findings should be confirmed in a pragmatic randomized trial. PLAIN-LANGUAGE SUMMARY: Optimal approaches to treat secondary hyperparathyroidism (SHPT) have not been established in randomized controlled trials. Data from a national dialysis organization was used to identify patients with SHPT in whom escalated treatment may be indicated. The approach to treatment was defined based on observed upward titration of SHPT-controlling medications: earlier titration (lower target) versus delayed titration (higher target); and the choice of medication (cinacalcet vs vitamin D sterols). In the first trial emulation, we estimated a 29% lower rate of death and 26% lower rate of cardiovascular disease or death for patients managed with a lower versus higher target approach. Cinacalcet versus vitamin D-favoring approaches were not consistently associated with outcomes in the second trial emulation. This observational study suggests the need for additional clinical trials of SHPT treatment intensity.

Klotho and Clinical Outcomes in CKD: Findings From the Chronic Renal Insufficiency Cohort (CRIC) Study.

RATIONALE & OBJECTIVE: Klotho deficiency may affect clinical outcomes in chronic kidney disease (CKD) through fibroblast growth factor-23 (FGF23)-dependent and -independent pathways. However, the association between circulating Klotho and clinical outcomes in CKD remains unresolved and was the focus of this study. STUDY DESIGN: Prospective observational study. SETTING & PARTICIPANTS: 1,088 participants in the Chronic Renal Insufficiency Cohort (CRIC) Study with an estimated glomerular filtration rate (eGFR) of 20-70mL/min/1.73m2. EXPOSURE: Plasma Klotho level at the year-1 study visit. OUTCOMES: 5-year risks of all-cause mortality, heart failure hospitalization, atherosclerotic cardiovascular events, and a composite kidney end point that comprised a sustained 50% decrease in eGFR, dialysis, kidney transplant, or eGFR<15mL/min/1.73m2. ANALYTICAL APPROACH: We divided Klotho into 6 groups to account for its nonnormal distribution. We used Cox proportional hazards regression and subdistribution hazards models to compare survival and clinical outcomes, respectively, between Klotho groups. We sequentially adjusted for demographic characteristics, kidney function, cardiovascular risk factors, sample age, and FGF23. RESULTS: Mean eGFR was 42mL/min/1.73m2, and median Klotho concentration was 0.31ng/mL (IQR, 0.10-3.27ng/mL). When compared with the lowest Klotho group, survival (HR, 0.77; 95% CI, 0.32-1.89), heart failure hospitalization (HR, 1.10; 95% CI, 0.38-3.17), atherosclerotic cardiovascular events (HR, 1.19; 95% CI, 0.57-2.52), and CKD progression (HR, 1.05; 95% CI, 0.58-1.91) did not differ in the high Klotho group. In contrast, FGF23 was significantly associated with mortality and heart failure hospitalization independent of Klotho levels. LIMITATIONS: Despite adjustments, we cannot exclude the potential influence of residual confounding or sample storage on the results. A single measurement of plasma Klotho concentration may not capture Klotho patterns over time. CONCLUSIONS: In a large, diverse, well-characterized CKD cohort, Klotho was not associated with clinical outcomes, and Klotho deficiency did not confound the association of FGF23 with mortality or heart failure hospitalization. PLAIN-LANGUAGE SUMMARY: Klotho is a protein that is vital to mineral metabolism and aging and may protect against cardiovascular disease. Klotho levels decrease in chronic kidney disease (CKD), but the association between Klotho and clinical outcomes in CKD remains uncertain. In a prospective cohort study of more than 1,000 people with CKD, circulating Klotho levels were not associated with kidney disease progression, cardiovascular outcomes, or mortality. These results suggest that the decrease in circulating Klotho levels in CKD does not play a prominent role in the development of poor clinical outcomes.

Identifying Gut Microbiome Features that Predict Responsiveness Toward a Prebiotic Capable of Increasing Calcium Absorption: A Pilot Study.

Previously, we demonstrated that prebiotics may provide a complementary strategy for increasing calcium (Ca) absorption in adolescents which may improve long-term bone health. However, not all children responded to prebiotic intervention. We determine if certain baseline characteristics of gut microbiome composition predict prebiotic responsiveness. In this secondary analysis, we compared differences in relative microbiota taxa abundance between responders (greater than or equal to 3% increase in Ca absorption) and non-responders (less than 3% increase). Dual stable isotope methodologies were used to assess fractional Ca absorption at the end of crossover treatments with placebo, 10, and 20 g/day of soluble corn fiber (SCF). Microbial DNA was obtained from stool samples collected before and after each intervention. Sequencing of the 16S rRNA gene was used to taxonomically characterize the gut microbiome. Machine learning techniques were used to build a predictive model for identifying responders based on baseline relative taxa abundances. Model output was used to infer which features contributed most to prediction accuracy. We identified 19 microbial features out of the 221 observed that predicted responsiveness with 96.0% average accuracy. The results suggest a simplified prescreening can be performed to determine if a subject's bone health may benefit from a prebiotic. Additionally, the findings provide insight and prompt further investigation into the metabolic and genetic underpinnings affecting calcium absorption during pubertal bone development.

Calcineurin inhibitor effects on kidney electrolyte handling and blood pressure: tacrolimus versus voclosporin.

BACKGROUND AND HYPOTHESIS: Calcineurin inhibitors affect kidney electrolyte handling and blood pressure through an effect on the distal tubule. The second generation calcineurin inhibitor voclosporin causes hypomagnesemia and hypercalciuria less often than tacrolimus. This suggests different effects on the distal tubule, but this has not yet been investigated experimentally. METHODS: Rats were treated with voclosporin, tacrolimus or vehicle for 28 days. Dosing was based on a pilot experiment to achieve clinically therapeutic concentrations. Drug effects were assessed by electrolyte handling at day 18 and 28, thiazide testing at day 20, telemetric blood pressure recordings, and analysis of mRNA and protein levels of distal tubular transporters at day 28. RESULTS: Compared to vehicle, tacrolimus but not voclosporin significantly increased the fractional excretions of calcium (>4-fold), magnesium and chloride (both 1.5-fold) and caused hypomagnesemia. Tacrolimus but not voclosporin significantly reduced distal tubular transporters at mRNA and/or protein level, including the sodium-chloride cotransporter, transient receptor melastatin 6, transient receptor potential vanilloid 5, cyclin M2, sodium-calcium exchanger and calbindin-D28K. Tacrolimus but not voclosporin reduced the mRNA level and urinary excretion of epidermal growth factor. The saluretic response to hydrochlorothiazide at day 20 was similar in the voclosporin and vehicle groups, whereas it was lower in the tacrolimus group. The phosphorylated form of the sodium-chloride cotransporter was significantly higher at day 28 in rats treated with voclosporin than in those treated with tacrolimus. Tacrolimus transiently increased blood pressure, whereas voclosporin caused a gradual but persistent increase in blood pressure which was further characterized by high renin, normal aldosterone, and low endothelin-1. CONCLUSIONS: In contrast to tacrolimus, voclosporin does not cause hypercalciuria and hypomagnesemia, but similarly causes hypertension. Our data reveal differences between the distal tubular effects of tacrolimus and voclosporin and provide a pathophysiological basis for the clinically observed differences between the two calcineurin inhibitors.

Pre-Transplant Hyperparathyroidism and Graft or Patient Outcomes After Kidney Transplantation.

The impact of pre-transplant parathyroid hormone (PTH) levels on early or long-term kidney function after kidney transplantation is subject of debate. We assessed whether severe hyperparathyroidism is associated with delayed graft function (DGF), death-censored graft failure (DCGF), or all-cause mortality. In this single-center cohort study, we studied the relationship between PTH and other parameters related to bone and mineral metabolism, including serum alkaline phosphatase (ALP) at time of transplantation with the subsequent risk of DGF, DCGF and all-cause mortality using multivariable logistic and Cox regression analyses. In 1,576 kidney transplant recipients (51.6 ± 14.0 years, 57.3% male), severe hyperparathyroidism characterized by pre-transplant PTH ≥771 pg/mL (>9 times the upper limit) was present in 121 patients. During 5.2 [0.2-30.0] years follow-up, 278 (15.7%) patients developed DGF, 150 (9.9%) DCGF and 432 (28.6%) died. A higher pre-transplant PTH was not associated with DGF (HR 1.06 [0.90-1.25]), DCGF (HR 0.98 [0.87-1.13]), or all-cause mortality (HR 1.02 [0.93-1.11]). Results were consistent in sensitivity analyses. The same applied to other parameters related to bone and mineral metabolism, including ALP. Severe pre-transplant hyperparathyroidism was not associated with an increased risk of DGF, DCGF or all-cause mortality, not supporting the need of correction before kidney transplantation to improve graft or patient survival.

Parathyroidectomy and Cinacalcet Use in Medicare-Insured Kidney Transplant Recipients.

RATIONALE & OBJECTIVE: Posttransplant hyperparathyroidism is common, and treatment practices are poorly characterized. The goal of this study was to examine the incidence, associations, and outcomes of posttransplant parathyroidectomy and calcimimetic use in a cohort of Medicare-insured US kidney transplant recipients. STUDY DESIGN: Retrospective observational cohort study. SETTING & PARTICIPANTS: We used the US Renal Data System to extract demographic, clinical, and prescription data from Medicare Parts A, B, and D-insured patients who received their first kidney transplant in 2007-2013. We excluded patients with pretransplant parathyroidectomy. PREDICTORS: Calendar year of transplantation and pretransplant patient characteristics. OUTCOME: (1) Incidence of and secular trends in parathyroidectomy and cinacalcet use in the 3 years after transplant; (2) 90-day outcomes after posttransplant parathyroidectomy and cinacalcet initiation. ANALYTICAL APPROACH: Temporal trends and pretransplant correlates of parathyroidectomy and cinacalcet use were assessed using proportional hazards models and multivariable Poisson regression, respectively. RESULTS: The inclusion criteria were met by 30,127 patients, of whom 10,707 used cinacalcet before transplant, 551 underwent posttransplant parathyroidectomy, and 5,413 filled≥1 prescription for cinacalcet. The rate of posttransplant parathyroidectomy was stable over time. By contrast, cinacalcet use increased during the period studied. Long dialysis vintage and pretransplant cinacalcet use were strongly associated with posttransplant parathyroidectomy and cinacalcet use. Roughly 1 in 4 patients were hospitalized within 90 days of posttransplant parathyroidectomy, with hypocalcemia-related diagnoses being the most common complication. Parathyroidectomy (vs cinacalcet initiation) was not associated with an increase in acute kidney injury. LIMITATIONS: We lacked access to laboratory data to help assess the severity of secondary/tertiary hyperparathyroidism. The cohort was limited to Medicare beneficiaries. CONCLUSIONS: Almost one-fifth of our study cohort was treated with parathyroidectomy and/or cinacalcet. Further studies are needed to establish the optimal treatment for posttransplant hyperparathyroidism.

Tolvaptan treatment is associated with altered mineral metabolism parameters and increased bone mineral density in ADPKD patients.

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is characterized by a unique bone and mineral phenotype. The impact of tolvaptan treatment on mineral metabolism and bone mineral density (BMD) is unknown. METHODS: We conducted an analysis in the Bern ADPKD Registry, a prospective observational cohort study. Mineral metabolism parameters were measured at baseline and every 12 months thereafter. BMD was determined by dual-energy X-ray absorptiometry at baseline and after 3 years. Multivariable mixed-effects regression models were applied to assess changes in mineral metabolism parameters and BMD associated with tolvaptan treatment. RESULTS: A total of 189 participants (122 without and 67 with subsequent tolvaptan treatment) were included in the analysis. During follow-up, tolvaptan treatment was associated with increased BMD at the femoral neck {ß = 0.092 [95% confidence interval (CI) 0.001-0.183], P = .047}. In addition, tolvaptan treatment was associated with higher plasma magnesium [ß = 0.019 (95% CI 0.001-0.037), P = .037], bicarbonate [ß = 0.972 (95% CI 0.242-1.702), P = .009] and urine pH [ß = 0.214 (95% CI 0.056-0.372), P = .008] and lower parathyroid hormone [ß = -0.191 (95% CI -0.328 to -0.053), P = .006], 1,25(OH)D3 [ß = -0.126 (95% CI -0.235 to -0.164), P = .024] and fractional urinary magnesium excretion [ß = -0.473 (95% CI -0.622 to -0.324), P < .001]. CONCLUSIONS: Chronic tolvaptan treatment is associated with increased femoral BMD and significant changes in both mineral metabolism and acid-base parameters in ADPKD patients.

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.

A national cross-sectional analysis of dietary copper intake and abdominal aortic calcification in the US adults: NHANES 2013-2014.

BACKGROUND AND AIMS: Copper is an essential dietary element with a crucial role in physiological regulation. However, the relationship between dietary copper intake and abdominal aortic calcification (AAC) remains uncertain. METHODS AND RESULTS: This study encompassed a cohort of 2535 adults aged over 40 years, derived from the National Health and Nutrition Examination Survey 2013-2014. Dietary copper intake from both food sources and supplements was assessed through two 24-h dietary recall interviews. AAC was measured by dual-energy X-ray absorptiometry and classified into 3 groups using the Kauppila score system. Multivariable logistic regression models were constructed to evaluate the association between dietary copper intake and AAC. Among the participants, a total of 771 individuals (30.4%) were diagnosed with AAC, of which 239 (9.4%) exhibited severe AAC. Higher dietary copper intake was significantly associated with a lower incidence of severe AAC. Specifically, for each 1 mg/day increase in dietary copper intake, the incidence of severe AAC decreased by 38% (odds ratios [OR] 0.62, 95% confidence intervals [CI] 0.39-0.98) after adjustment for relevant covariates. Moreover, individuals in the third tertile of copper intake had a 37% lower incidence of AAC compared to those in the first tertile [OR 0.63, 95% CI (0.43-0.95)]. However, no significant associations were found between supplemental copper intake or serum copper levels and AAC. CONCLUSIONS: This study demonstrates that lower dietary copper intake, rather than serum copper levels or supplement copper intake, is significantly associated with a higher prevalence of AAC in adults ≥40 years old in the United States.

Nutrition in Children With Chronic Kidney Disease: How to Thrive?

The nutritional status and management of children with chronic kidney disease (CKD) are complex and require a combined pediatric nephrology team work approach with physicians, nutritionists, nurses, and physical/occupational therapists. Prospective observational studies such as Children with CKD in the US, the 4C study in Europe and the International Pediatric Peritoneal Dialysis Network have advanced the field. However, most recommendations and guidelines from international task forces such as Kidney Diseases Improving Global Outcomes and Pediatric Renal Nutrition Taskforce are opinion-based rather than evidence-based. There is exciting ongoing research to improve nutrition in children with CKD to help them thrive.

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.

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.

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.

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.

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.

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.

[A case of severe hyperparathyroidism in clinical practice. Case report].

Disorders of the mineral balance often determine the symptoms, the severity of the course and the prognosis of many diseases. Primary hyperparathyroidism (PHPT) is a common endocrine disease caused by increased secretion of parathyroid hormone as a result of primary damage to the parathyroid glands. Diagnosis of PHPT is often difficult. Clinical signs of PHPT appear months or years after the onset of the disease, however, the presence of hypercalcemia serves as an early indication of the disease of the thyroid gland. Often, patients are observed for a long time by related specialists (rheumatologists, traumatologists-orthopedists, oncologists), which gives rise to a lot of problems consisting in the lack of adequate treatment and its result, the progression of the disease, disability, and a decrease in the quality of life. Often, patients are observed for a long time by related specialists (rheumatologists, orthopedic traumatologists, oncologists) under the "masks" of various pathologies (osteoporosis, recurrent urolithiasis, etc.), which gives rise to a lot of problems, consisting in an erroneous diagnosis, lack of adequate treatment and its result, progression of the disease, disability, and a decrease in the quality of life. Late diagnosis of PHPT leads to the development of severe complications (osteoporetic fractures, renal failure) and an increased risk of premature death. A clinical case of late diagnosis of PHPT at the stage of pronounced bone complications of the disease, which proceeded under the guise of osteoarthritis, is considered. According to the results of laboratory and instrumental studies, the following were revealed: hypercalcemia, a significant increase in the concentration of PTH, adenoma of the left lower parathyroid gland, hyperparathyroid osteodystrophy, and a decrease in bone mineral density. Surgical treatment was performed - selective parathyroidectomy with the development of hypocalcemia in the early postoperative period, which was stopped by taking calcium supplements and active vitamin D metabolites and is designed to help practitioners of various specialties to understand the issues of diagnosis of PHPT and effective care for patients.

Effects of acid on bone.

The homeostatic regulation of a stable systemic pH is of critical importance for mammalian survival. During metabolic acidosis (a reduction in systemic pH caused by a primary decrease in serum bicarbonate concentration), as seen in clinical disorders such as the later stages of chronic kidney disease, renal tubular acidosis, or chronic diarrhea, bone buffers the accumulated acid; however, this homeostatic function of the skeleton occurs at the expense of the bone mineral content and leads to decreased bone quality. During short-term studies to model acute metabolic acidosis, there is initial physiochemical bone mineral dissolution, releasing carbonate and phosphate proton buffers into the extracellular fluid. In addition, there is net proton influx into the mineral with release of bone sodium and potassium. During long-term studies to model chronic metabolic acidosis, there is also inhibition of osteoblast activity, resulting in reduced bone formation, and an increase in osteoclast activity, resulting in increased bone resorption and release of calcium and anionic proton buffers. These physicochemical and cell-mediated bone responses to metabolic acidosis, in addition to an acidosis-induced increased urine calcium excretion, without a corresponding increase in intestinal calcium absorption, induce a net loss of body calcium that is almost certainly derived from the mineral stores of bone.