FGF-23 and secondary hyperparathyroidism in chronic kidney disease

Young adults' circulating FGF23 and α-klotho and their relationship with habitual dietary acid load and phosphorus intake during growth

The bone-derived hormone FGF23, primarily secreted by osteocytes, is a major player in the regulation of phosphate homeostasis. It becomes upregulated by increased circulating phosphate concentration, e.g. due to elevations in phosphorus intake (P-In) or alterations in habitual dietary acid load. The present study aimed to investigate whether long-term endogenous acid production or a habitual high phosphorus intake during childhood and adolescence may be prospectively related with altered adult levels of FGF23 and the FGF23-related metabolite α-klotho. Urinary phosphate excretion (PO4-Ex), net acid excretion (NAE), and potential renal acid load (uPRAL) were analyzed in 24-h urine samples (n = 3369) collected from 343 healthy 3-17 years old participants of the DONALD Study (Dortmund, Germany) to assess, biomarker-based, P-In and habitual dietary acid load. Circulating FGF23, α-klotho, and further blood parameters were additionally examined in young adulthood. Individual means of standard-deviation-scores were calculated for 24-h urinary biomarker excretions and anthropometrics longitudinally determined between ages 3-17 years. Multivariable linear regression was used to analyze the prospective relations of pre-adulthood PO4-Ex, NAE, and uPRAL with the adulthood outcomes FGF23 and α-klotho. After adjusting for growth period-related covariates and adulthood confounders only for P-In during growth, i.e., PO4-Ex, but not for NAE and uPRAL, a significant positive association (p = 0.03) with FGF23 and an inverse trend (p = 0.10) with the FGF23-α-klotho ratio were observed. Neither PO4-Ex, nor NAE or uPRAL were associated with soluble α-klotho levels in adulthood. The prospective relationships of long-term assessed 24-h phosphaturia and habitual dietary acid load during growth with adult circulating, phosphate-adjusted FGF23 strongly suggest that children´s habitually higher P-In does unfavorably affect adult FGF23-α-klotho axis.

Functional consequences of spatial, temporal and ligand bias of G protein-coupled receptors

G protein-coupled receptors (GPCRs) regulate every aspect of kidney function by mediating the effects of various endogenous and exogenous substances. A key concept in GPCR function is biased signalling, whereby certain ligands may selectively activate specific pathways within the receptor's signalling repertoire. For example, different agonists may induce biased signalling by stabilizing distinct active receptor conformations - a concept that is supported by advances in structural biology. However, the processes underlying functional selectivity in receptor signalling are extremely complex, involving differences in subcellular compartmentalization and signalling dynamics. Importantly, the molecular mechanisms of spatiotemporal bias, particularly its connection to ligand binding kinetics, have been detailed for GPCRs critical to kidney function, such as the AT1 angiotensin receptor (AT1R), V2 vasopressin receptor (V2R) and the parathyroid hormone 1 receptor (PTH1R). This expanding insight into the multifaceted nature of biased signalling paves the way for innovative strategies for targeting GPCR functions; the development of novel biased agonists may represent advanced pharmacotherapeutic approaches to the treatment of kidney diseases and related systemic conditions, such as hypertension, diabetes and heart failure.

Short-term effects of dapagliflozin on biomarkers of bone and mineral metabolism in patients with diabetic kidney disease: A prospective observational study

BACKGROUND

There is still a lack of information regarding the impact of sodium-glucose cotransporter 2 inhibitors (SGLT2i) on bone and mineral metabolism in patients with diabetes and chronic kidney disease (CKD). Therefore, we aimed to investigate the effects of SGLT2i in a cohort of patients suffering from diabetic kidney disease (DKD).

METHODS

In this prospective observational study, patients with type 2 diabetes and biopsy-proven diabetic nephropathy or presumptive DKD with eGFR levels ≥20 ml/min/1.73m2 and 25-OH vitamin D levels ≥20 ng/dl were included. 41 used SGLT2i (study group) and 39 continued their current treatment regimens (control group). Serum FGF-23, sclerostin, osteoprotegerin (OPG), and hydroxyproline levels were measured at baseline, 1 month and 3 months after treatment.

RESULTS

Mean age of all patients was 67±9.3 years, and 48 (60%) were female. All patients in the study group used dapagliflozin. Taking into account the renal functions at the commencement of the study, the eGFR values for the study group and the control group were 51.2±15.6 and 44.6±16.9ml/min/1.73m2, respectively (p=0.01). After three months, these values were observed to be 47.4±16.7 and 44.3±18.8 ml/min/1.73m2 (p=0.43), respectively. At baseline, OPG levels were higher in the study group (p=0.025) but there were no differences between the groups in terms of FGF-23 and sclerostin levels (p=0.670 and p=0.467, respectively). Levels of OPG, FGF-23, and sclerostin significantly decreased throughout 3 months of treatment with dapagliflozin (p<0.001 for all). Hydroxyproline levels also declined but did not reach to statistical significance (p=0.075). Multiple linear regression models revealed that treatment with SGLT2i was associated with the change in levels of sclerostin (β=0.303, p=0.011) and OPG (β=0.210, p=0.010), but not with FGF-23 (β=0.089, p=0.150).

CONCLUSIONS

FGF-23, sclerostin and OPG levels significantly declined after treatment with dapagliflozin for 3 months.

Carotid intima-media thickness, fibroblast growth factor 23, and mineral bone disorder in children with chronic kidney disease

BACKGROUND

Carotid intima-media thickness (cIMT) is a measure of atherosclerotic vascular disease and a surrogate biomarker for cardiovascular risk in patients with chronic kidney disease (CKD). Mineral and bone disorders (MBD) are complications of CKD, contributing to vascular calcification and accelerated atherosclerosis. Increased fibroblast growth factor 23 (FGF23)-the earliest detectable serum abnormality associated with CKD-MBD-has been linked with cardiovascular disease in patients with CKD. This study aimed to identify factors and analyze the relationship associated with high cIMT, high FGF23, and poor MBD control in children with CKD.

METHODS

A cross-sectional study was conducted in Yogyakarta, Indonesia recruiting children with CKD. The correlations and factors between cIMT, FGF23, and MBD were explored.

RESULTS

We recruited 42 children aged 2-18 years old with CKD stages 2 to 5D. There were no significant correlations between cIMT and factors including advanced CKD, use of dialysis, body mass index, hypertension, anemia, MBD, FGF23 levels, and left ventricular mass index (LVMI). Patients with advanced CKD had poorly controlled anemia, hypertension, and higher LVMI. In multivariate analysis, CKD stages, hypertension stages, the presence of MBD, and LVMI were associated with FGF23 levels (p < 0.05).

CONCLUSIONS

FGF23 levels increased with CKD progression, and MBD was more prevalent in advanced kidney disease. Elevated FGF23 is potentially associated with increased MBD prevalence in late-stage CKD. A larger study is needed to confirm the factors affecting cIMT in children with CKD.

Determination of the reference interval for urinary klotho to creatinine ratio of healthy dogs

For several years, alpha klotho has been considered as a candidate biomarker in chronic kidney disease (CKD), progression of CKD and CKD mineral bone disorders (CKD-MBD). The evidence on the relationship between klotho and kidney function is controversial in some areas. The aim of the study was to identify the influence of age, sex and breed on urinary alpha klotho, values in the early stages of CKD within the studied population and determine a reference interval in a group of healthy dogs. Significantly higher values were measured in older dogs over 6 years old (p = 0.026, p = 0.0007) and in the breed German Shepherd than Belgian Shepherd (p = 0.0401). On the basis of sex and in small breed dogs, no significant differences were noted. In dogs with CKD stage 2, alpha klotho values were significantly lower (p = 0.0135) than in healthy dogs. Within the studied population, a reference interval for urinary klotho to creatinine ratio (UrKl/Cr) was determined in the range of 3.94-23.55 pg/gCr. Since our findings show that alpha klotho is associated with older age, we assume that this may have influenced the results in the group of dogs with CKD stage 1 due to the presence of predominantly old dogs in this group. Future studies would be needed to consider age as a factor affecting urinary alpha klotho in dogs with CKD.

Fibroblast growth factor-23 and Alpha-Klotho concentrations in dogs with canine Leishmaniasis

This study aimed to assess the concentrations of Fibroblast Growth Factor-23 (FGF-23) and α-Klotho in healthy dogs and dogs at different stages of Canine Leishmaniasis (CanL), and investigate the changes of these parameters in relation to renal function and calcium‑phosphorus metabolism. A total of 74 dogs (22 healthy and 52 with CanL) of varying ages, sexes, and medium-sized breeds were included. Dogs with CanL were categorized into different stages (Stage I-IV) based on Leishvet recommendations. In addition to routine hematological parameters, plasma FGF-23, serum α-Klotho, urea, creatinine, phosphorus, calcium, parathormone, vitamin D concentrations, and urine protein/creatinine ratio were measured. Data from healthy dogs were compared to dogs with CanL overall and by stage. Dogs with CanL exhibited higher concentrations of FGF-23 (p < 0.05), α-Klotho, and parathormone (p < 0.001), as well as lower concentrations of vitamin D and calcium (p < 0.001). FGF-23 concentration was particularly elevated in Stage IV compared to other stages. However, no significant differences in α-Klotho levels were observed among the stages. FGF-23 levels showed a weak positive correlation with urea and creatinine concentrations and a moderate positive correlation with urine protein/creatinine ratio. This study demonstrated increased levels of FGF-23 and α-Klotho in dogs with CanL for the first time. The increase in FGF-23 levels was more prominent in advanced stages of the disease and correlated with higher urea and creatinine concentrations. These findings may serve as a basis for future diagnostic and therapeutic investigations, contributing to the understanding of the pathophysiology of kidney disease in CanL.

Alveolar bone and tibia responses to hormonal and mineral abnormalities in rats with chronic kidney disease: A pilot study

OBJECTIVES

As the impact of chronic kidney disease (CKD) severity on different bone types remains unclear, we induced increasing levels of CKD severity in a rat model and investigated hormone and mineral levels as well as alveolar and tibia bone histomorphology.

METHODS

Rats were divided into sham operation (sham), 4/6 nephrectomy (4/6Nx), 5/6Nx, and 4/6Nx with hyperphosphorous (HP) diet (4/6NxHP). At week 20, BUN, FGF23, PTH, and P were estimated in plasma. Bone parameters were evaluated by microCT, and osteoclasts and osteoid areas were evaluated by TRAP and H&E stains, respectively.

RESULTS

The 4/6NxHP and 5/6Nx groups had elevated PTH, and the 4/6NxHP group alone had elevated P. Compared to the 4/6Nx group, the 4/6NxHP group demonstrated increased FGF23 and P. In the alveolar bone, the 4/6NxHP group had reduced bone volume and BMD compared to the sham and 4/6Nx groups. In the tibia cortical bone, bone surface density was higher in the 4/6NxHP group compared to the sham group. Tibia cortical bone volume was negatively correlated with FGF23 and P. Moreover, alveolar bone volume was negatively correlated with FGF23, PTH, and P.

CONCLUSIONS

Our results demonstrate that hormone and mineral levels vary with CKD severity, and alveolar bone loss strongly correlates with these hormone and mineral alterations.

The Role of Plant-Based Diets in Preventing and Mitigating Chronic Kidney Disease: More Light than Shadows

Chronic kidney disease (CKD) is a non-communicable disease that affects >10% of the general population worldwide; the number of patients affected by CKD is increasing due in part to the rise in risk factors such as obesity, hypertension, and diabetes mellitus. As many studies show, diet can be an important tool for preventing and mitigating the onset of non-communicable diseases. Plant-based diets (PBDs) are those that emphasize the consumption of plant foods and may or may not include small or moderate amounts of animal foods. Recently, these diets have received increasing interest because they have been associated with favourable effects on health and also appear to protect against the development and progression of CKD. PBDs, which are associated with protein restrictions, seem to offer adjunctive advantages in patients with chronic kidney disease, as compared to conventional low-protein diets that include animal proteins. The principal aims of this review are to provide a comprehensive overview of the existing literature regarding the role of plant-based diets and low-protein, plant-based diets in the context of chronic kidney disease. Moreover, we try to clarify the definition of plant-based diets, and then we analyse possible concerns about the use of PBDs in patients with chronic kidney disease (nutritional deficiency and hyperkalaemia risk). Finally, we offer some strategies to increase the nutritional value of plant-based low-protein diets. In the Materials and Methods section, many studies about plant-based diets and low-protein plant-based diets (e.g., the very-low-protein diet and vegan low-protein diet, LPD) in chronic kidney disease were considered. In the Results and Conclusion section, current data, most from observational studies, agree upon the protective effect of plant-based diets on kidney function. Moreover, in patients with advanced CKD, low-protein plant-based options, especially a very-low-protein diet supplemented with heteroanalogues (VLPDs), compared to a conventional LPD appear to offer adjunctive advances in terms of delaying dialysis and mitigating metabolic disturbances. However, further studies are necessary to better investigate the possible metabolic and cardiovascular advantages of plant-based LPDs versus conventional LPDs.

Intact fibroblast growth factor 23 in heart failure with reduced and mildly reduced ejection fraction

BACKGROUND

Fibroblast growth factor-23 (FGF23) has been associated to left ventricular (LV) hypertrophy and heart failure (HF) severity. We aimed to investigate the clinical correlates and prognostic value of intact FGF23 (iFGF23) in HF patients.

METHODS

Patients with stable HF and left ventricular ejection fraction (LVEF) < 50% were prospectively enrolled, managed according to current recommendations and followed over time. iFGF23 was measured at baseline with a fully automated immuno-chemiluminescent assay.

RESULTS

We enrolled 150 patients (82% males; median age 65 years). First, second, and third iFGF23 tertiles were < 35.2 pg/mL, 35.2-50.9 pg/mL, and > 50.9 pg/mL. LVEF decreased from the first iFGF23 tertile to the third tertile (p = 0.014). N-terminal pro-B-type natriuretic peptide (NT-proBNP) increased from the first to the third tertile (p = 0.001), while peak oxygen consumption decreased (p < 0.001). Thirty-five patients (23%) experienced the primary endpoint (all-cause death or HF hospitalization at 5 years), and 26 (17%) the secondary endpoint (all-cause death at 5 years). On multivariable analysis, iFGF23 independently predicted the primary endpoint on top of age, gender and LVEF (HR 4.6 [95% CI 2.1-10.3], p < 0.001), age, gender and eGFR (HR 4.1 [95% CI 1.6-10.3], p = 0.003), as well as age, gender and NT-proBNP (HR 3.6 [95% CI 1.6-8.2], p = 0.002). iFGF23 even reclassified patient risk on top of all the 3 models, with NRI values of 0.65 (95% CI 0.30-1.01), 0.55 (95% CI 0.25-0.88), and 0.60 (95% CI 0.24-0.96), respectively (both p < 0.001).

CONCLUSIONS

Circulating iFGF23 is associated with disease severity and outcome in HF patients with reduced and mildly reduced ejection fraction.

Safety of SGLT2i with regard to bone and mineral metabolism in patients with CKD

PURPOSE OF REVIEW

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) represent a relatively new class of oral glucose-lowering agents that reduce adverse cardiovascular and kidney outcomes among individuals with chronic kidney disease (CKD). Emerging evidence suggests that SGLT2i may also affect bone and mineral metabolism. This review analyzes recent evidence on the safety of SGLT2i with respect to bone and mineral metabolism in people with CKD, and discusses potential underlying mechanisms and clinical implications.

RECENT FINDINGS

Recent studies have documented the beneficial effects of SGLT2i on cardiovascular and renal outcomes among individuals with CKD. SGLT2i may alter renal tubular phosphate reabsorption and are associated with increased serum concentrations of phosphate, fibroblast growth factor-23 (FGF-23), parathyroid hormone (PTH), decreased 1,25-hydroxyvitamin D levels, as well as increased bone turnover. Clinical trials have not demonstrated an increased risk of bone fracture associated with SGLT2i use among patients with CKD with or without diabetes mellitus.

SUMMARY

Although SGLT2i are associated with abnormalities of bone and mineral metabolism, they have not been linked to a higher risk of fracture among patients with CKD. More research is needed on the association between SGLT2i and fracture risk in this population.

Relationship between serum iPTH and peritonitis episodes in patients undergoing continuous ambulatory peritoneal dialysis

Background

Peritonitis is considered as one of the most serious complications that cause hospitalization in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). There is limited evidence on the impact of the parathyroid hormone (PTH) on the first peritoneal dialysis (PD)-associated peritonitis episode. We aimed to investigate the influence of serum intact parathyroid hormone (iPTH) on peritonitis in patients undergoing PD.

Methods

This was a retrospective cohort study. Patients undergoing initial CAPD from a single center in China were enrolled. The baseline characteristics and clinical information were recorded. The primary outcome of interest was the occurrence of the first PD-associated peritonitis episode. Five Cox proportional hazard models were constructed in each group set. In group set 1, all participants were divided into three subgroups by tertiles of the serum concentration of iPTH; in group set 2, all participants were divided into three subgroups based on the serum concentration of iPTH with 150 pg/ml interval (<150, 150-300, and >300 pg/ml). Hazard ratios and 95% confidence intervals (CIs) were calculated for each model. The multivariate linear regression analysis elimination procedure assessed the association between the clinical characteristics at baseline and the iPTH levels. Restricted cubic spline models were constructed, and stratified analyses were also conducted.

Results

A total of 582 patients undergoing initial PD (40% women; mean age, 45.1 ± 11.5 years) from a single center in China were recruited. The median follow-up duration was 25.3 months. Multivariate Cox regression analysis showed that, in the fully adjusted model, a higher serum iPTH level (tertile 3, iPTH >300 pg/ml) was significantly associated with a higher risk of PD-associated peritonitis at 3 years [tertile 3: hazard ratio (HR) = 1.53, 95%CI = 1.03-2.55, p = 0.03; iPTH > 300 pg/ml: HR = 1.57, 95%CI = 1.08-2.27, p = 0.02]. The hazard ratio for every 100 pg/ml increase in serum iPTH level was 1.12 (95%CI = 1.05-1.20, p < 0.01) in the total cohort when treating iPTH as a continuous variable.

Conclusions

An elevated iPTH level was significantly associated with an increased risk of peritonitis in patients undergoing CAPD.

The Measurement and Interpretation of Fibroblast Growth Factor 23 (FGF23) Concentrations

Two decades after the discovery of the hormone FGF23, we know more about phosphate homeostasis as it turned out that FGF23 is the central hormone that regulates this. Hereditary hypophosphatemic rickets and tumor-induced osteomalacia could by then be explained, by autonomous FGF23 production, and the nephrology field was excited by this new marker as it turned out to be independently associated with mortality in people treated by hemodialysis. This led to the development of several immunoassays to be able to measure FGF23 in blood. In the past years we learned that FGF23 is a rather stable peptide, the precision of the assays is acceptable but assays are not standardized and therefore not comparable. This means that reference values and cutoff values need to be assay specific. For several assays reference values have been established and gender and age did not seem of high importance. The phosphate content of the diet, which can be culturally dependent, however, should be taken into account when interpreting results, but to what extent is not totally clear. Currently, clinical application of the immunoassays is established in the diagnosis of hereditary hypophosphatemic rickets and diagnosis and follow-up of tumor-induced osteomalacia. Definite conclusions on the usefulness of the FGF23 measurement in people with CKD either as a marker for risk prediction or a as target for treatment remains to be determined. The latter applications would require dedicated prospective clinical trials, which may take years, before providing answers. To improve the standardization of the FGF23 assays and to shed light on the biological functions that fragments might have we might aim for an LC-MS/MS-based method to quantify both intact and fragmented FGF23. In this literature review we will summarize the current knowledge on the physiological role of FGF23, its quantification, and the clinical usefulness of its determination.

Mineral bone disorder in children with chronic kidney disease: Data from the KNOW-Ped CKD (Korean cohort study for outcome in patients with pediatric chronic kidney disease) study

BACKGROUND

Children with chronic kidney disease (CKD) are at high risk of mineral bone disorder (MBD), which leads to fractures, growth retardation, and cardiovascular disease. We aimed to comprehensively understand the relationship between renal function and factors related to MBD and evaluate the prevalence and distribution characteristics of MBD, specifically among Korean patients from the KNOW-PedCKD cohort.

METHODS

From the baseline data of the KNOW-PedCKD cohort, we examined the prevalence and distribution of MBD in 431 Korean pediatric CKD patients, including the level of corrected total calcium, serum phosphate, serum alkaline phosphatase, serum intact parathyroid hormone (iPTH), fibroblast growth factor 23 (FGF-23), serum vitamin D, fractional excretion of phosphate (FEP), and bone densitometry Z-scores.

RESULTS

The median serum calcium level remained relatively normal regardless of the CKD stage. The levels of 1,25-dihydroxy vitamin D, urine calcium-to-creatinine ratio, and bone densitometry Z-score significantly decreased with advancing CKD stage, while those of serum phosphate, FGF-23, and FEP significantly increased with CKD stage. The prevalence of hyperphosphatemia (17.4%, 23.7%, and 41.2% from CKD stages 3b, 4, and 5, respectively) and hyperparathyroidism (37.3%, 57.4%, 55.3%, and 52.9% from CKD stages 3a, 3b, 4, and 5, respectively) significantly increased with the CKD stage. Prescriptions of medications, such as calcium supplements (39.1%, 42.1%, 82.4%), phosphate binders (39.1%, 43.4%, 82.4%), and active vitamin D (21.7%, 44.7%, and 64.7%) significantly increased with CKD stage 3b, 4, and 5, respectively.

CONCLUSIONS

The results demonstrated the prevalence and relationship of abnormal mineral metabolism and bone growth according to CKD stage in Korean pediatric CKD patients for the first time.

The Interplay between Dietary Phosphorous, Protein Intake, and Mortality in a Prospective Hemodialysis Cohort

(1) Background: Current dietary recommendations for dialysis patients suggest that high phosphorus diets may be associated with adverse outcomes such as hyperphosphatemia and death. However, there has been concern that excess dietary phosphorus restriction may occur at the expense of adequate dietary protein intake in this population. We hypothesized that higher dietary phosphorus intake is associated with higher mortality risk among a diverse cohort of hemodialysis patients. (2) Methods: Among 415 patients from the multi-center prospective Malnutrition, Diet, and Racial Disparities in Kidney Disease Study, we examined the associations of absolute dietary phosphorus intake (mg/day), ascertained by food frequency questionnaires, with all-cause mortality using multivariable Cox models. In the secondary analyses, we also examined the relationship between dietary phosphorus scaled to 1000 kcal of energy intake (mg/kcal) and dietary phosphorus-to-protein ratio (mg/g) with survival. (3) Results: In expanded case-mix + laboratory + nutrition adjusted analyses, the lowest tertile of dietary phosphorus intake was associated with higher mortality risk (ref: highest tertile): adjusted HR (aHR) (95% CI) 3.33 (1.75–6.33). In the analyses of dietary phosphorus scaled to 1000 kcal of energy intake, the lowest tertile of intake was associated with higher mortality risk compared to the highest tertile: aHR (95% CI) 1.74 (1.08, 2.80). Similarly, in analyses examining the association between dietary phosphorus-to-protein ratio, the lowest tertile of intake was associated with higher mortality risk compared to the highest tertile: aHR (95% CI) 1.67 (1.02–2.74). (4) Conclusions: A lower intake of dietary phosphorus was associated with higher mortality risk in a prospective hemodialysis cohort. Further studies are needed to clarify the relationship between specific sources of dietary phosphorus intake and mortality in this population.

Chronic Kidney Disease and Cancer: Inter-Relationships and Mechanisms

Chronic kidney disease (CKD) has been recognized as an increasingly serious public health problem globally over the decades. Accumulating evidence has shown that the incidence rate of cancer was relatively higher in CKD patients than that in general population, which, mechanistically, may be related to chronic inflammation, accumulation of carcinogenic compounds, oxidative stress, impairment of DNA repair, excessive parathyroid hormone and changes in intestinal microbiota, etc. And in patients with cancer, regardless of tumor types or anticancer treatment, it has been indicated that the morbidity and incidence rate of concomitant CKD was also increased, suggesting a complex inter-relationship between CKD and cancer and arousing increasing attention from both nephrologists and oncologists. This narrative review focused on the correlation between CKD and cancer, and underlying molecular mechanisms, which might provide an overview of novel interdisciplinary research interests and the potential challenges related to the screening and treatment of CKD and cancer. A better understanding of this field might be of help for both nephrologists and oncologists in the clinical practice.

Parathyroid hormone signaling in mature osteoblasts/osteocytes protects mice from age-related bone loss

Aging is accompanied by osteopenia, characterized by reduced bone formation and increased bone resorption. Osteocytes, the terminally differentiated osteoblasts, are regulators of bone homeostasis, and parathyroid hormone (PTH) receptor (PPR) signaling in mature osteoblasts/osteocytes is essential for PTH-driven anabolic and catabolic skeletal responses. However, the role of PPR signaling in those cells during aging has not been investigated. The aim of this study was to analyze the role of PTH signaling in mature osteoblasts/osteocytes during aging. Mice lacking PPR in osteocyte (Dmp1-PPRKO) display an age-dependent osteopenia characterized by a significant decrease in osteoblast activity and increase in osteoclast number and activity. At the molecular level, the absence of PPR signaling in mature osteoblasts/osteocytes is associated with an increase in serum sclerostin and a significant increase in osteocytes expressing 4-hydroxy-2-nonenals, a marker of oxidative stress. In Dmp1-PPRKO mice there was an age-dependent increase in p16Ink4a/Cdkn2a expression, whereas it was unchanged in controls. In vitro studies demonstrated that PTH protects osteocytes from oxidative stress-induced cell death. In summary, we reported that PPR signaling in osteocytes is important for protecting the skeleton from age-induced bone loss by restraining osteoclast's activity and protecting osteocytes from oxidative stresses.

Effects of active vitamin D on insulin resistance and islet β-cell function in non-diabetic chronic kidney disease patients: a randomized controlled study

Purpose

The purpose of the study is to observe the effects of active vitamin D supplementation on insulin resistance and islet β-cell function (HOMA-β) in patients with non-diabetic chronic kidney disease (NDCKD).

Methods

A total of 134 patients with NDCKD who met the inclusion criteria were enrolled in the prospective controlled study and categorized as such: 60 patients in the non-dialysis (ND) group; 36, hemodialysis (HD) group; and 38, peritoneal dialysis (PD) group. Each group was divided into two equal-numbered subgroups for vitamin D supplementation. Those in the experimental subgroups received calcitriol 0.5 ug/day orally, and were followed-up for 6 months. A total of 117 patients were followed-up, including 57 patients in the ND group; 29, HD group; and 31, PD group. Changes in the insulin resistance index (HOMA-IR) and HOMA-β index were calculated and compared at the time of enrollment and after 1, 3, and 6 months of intervention.

Results

(1) Mean HOMA-IR value: In the ND group, mean HOMA-IR value of the experimental group significantly decreased compared with that of the control group after 3 months of intervention (P = 0.02). In the HD and PD groups, there was no statistical difference between the experimental and control groups (P > 0.05). (2) Mean HOMA-β index: In the ND group, mean HOMA-β index of the experimental group was higher than that of the control group after 1 month of active vitamin D treatment (P = 0.03), and, with an extended intervention time, the index gradually increased (P < 0.001). In the HD group, mean HOMA-β index of the experimental group was higher than that of the control group after 3 months of active vitamin D treatment (P = 0.01). Among PD patients, mean HOMA-β index of the patients in the experimental group was higher than that of the control group after 6 months of active vitamin D treatment (P = 0.02).

Conclusions

Active vitamin D supplementation improved insulin resistance and HOMA-β after 6 months in ND patients, but only improved HOMA-β in the dialysis patients, with no significant effect on insulin resistance.

What's new in bone disease and fractures in HIV?

PURPOSE OF REVIEW

People living with HIV (PWH) are at greater risk of low bone mineral density (BMD) and fractures compared to the general population. This narrative review summarises recent literature in the field, including the relative contribution of antiretroviral therapy and frailty to low BMD and fractures in PWH.

RECENT FINDINGS

The body of evidence indicating less impact on BMD from the use of tenofovir alafenamide compared to tenofovir disoproxil fumarate continues to grow, although this has not yet translated into data supporting a reduction in fracture incidence. Frailty, common in PWH, is associated with both fractures and alterations in renal-bone metabolism, but is an area that is understudied in relation to interventions to reduce fracture risk in PWH.

SUMMARY

Although a maturing field, research into interventions to reduce fracture incidence in PWH is lacking in both quantity and scope. Development of core outcome datasets for clinical trials along with trials focused on reducing or reversing frailty are required to guide improvements overall bone health outcomes in PWH.

Effects of dietary phosphates from organic and inorganic sources on parameters of phosphorus homeostasis in healthy adult dogs

BACKGROUND

The impact of dietary phosphorus (P) excess, especially on renal and cardiovascular health, has been investigated in several species, but little is known in dogs.

OBJECTIVE

The aim of this study was to examine effects of different P sources on concentration and postprandial kinetics of selected parameters of P homeostasis in dogs.

METHODS

Eight beagles received one control diet (P 0.5% dry matter [DM]) and three high P diets (poultry meal, NaH2PO4, and KH2PO4; P 1.7% DM) for 18d. Urine samples were collected pre- and postprandially while faeces were collected quantitatively for 5d and analysed for minerals. On day 18, blood was sampled 1h pre- and 0.5, 1, 1.5, 2, 3, 5 and 7h postprandially.

RESULTS

Pi (KH2PO4, NaH2PO4) but not organic P caused an increased apparent P digestibility and significantly influenced kinetics of serum FGF23, parathyroid hormone, P, CrossLaps and bonespecific alkaline phosphatase, demonstrating a disrupted calcium (Ca) and P homeostasis with potential harm for renal, cardiovascular and skeletal health.

CONCLUSIONS

Results of feeding Pi to dogs indicate distinct disturbances of Ca and P metabolism, in contrast to organic sources. The use of Pi in food can therefore not be considered as safe. Further research, especially on dose and long-term effects, is warranted.

Chronic Metabolic Acidosis in Chronic Kidney Disease

BACKGROUND

Metabolic acidosis may be diagnosed as chronic (cMA) if it persists for at least 5 days, although an exact definition has not been provided by any guidelines yet. The most common cause is CKD; numerous less-known diseases can also account for cMA.

SUMMARY

In recent years, CKD-associated cMA has been proposed to induce several clinical complications. The aim of the article was to assess the current clinical evidence for complications and the respective management of CKD-associated cMA. In summary, cMA in CKD most likely promotes protein degradation and loss of bone mineral density. It aggravates CKD progression as indicated by experimental and (partly) clinical data. Therefore, cMA control must be recommended. Besides oral bicarbonate, dietary interventions potentially offer an alternative. Veverimer is a future option for cMA control; further systematic data are needed.

CONCLUSIONS

The most common cause of cMA is CKD. CKD-associated cMA most likely induces a negative protein balance; the exact role on bone metabolism remains uncertain. It presumably aggravates CKD progression. cMA control is recommendable; the serum bicarbonate target level should range around 24 mEq/L. Veverimer may be established as future option for cMA control; further systematic data are needed.

Efficacy and safety of evocalcet in treatment of secondary hyperparathyroidism in chronic kidney disease on hemodialysis patients: A protocol for a systematic review and meta-analysis

BACKGROUND

Secondary hyperparathyroidism (SHPT) have been associated with poor health outcomes in hemodialysis patients. The cinacalcet has popularized in clinic which has efficacy but more adverse events; the novel oral calcimimetic agents evocalcet has appeared in recent years. However, it is currently unknown whether evocalcet produces more beneficial effects and fewer adverse events in patients with SHPT. The aim of this systematic review is to estimate the safety and efficacy of evocacelt.

METHODS

Only randomized controlled trials (RCT) will be included in MEDLINE, EMBASE, the Cochrane Register of Controlled Trials, and PUBMED from July 2010 to July 2020. Two reviewers will screen, select studies, extract data, and assess quality independently. The methodological quality including the risk of bias of the included studies will be evaluated using a modified assessment form, which is based on Cochrane assessment tool. Review Manager 5.3 software will be used for heterogeneity assessment, generating funnel-plots, data synthesis, subgroup analysis, and sensitivity analysis. We will use GRADE system to evaluate the quality of our evidence.

RESULTS

We will provide some more practical and targeted results investigating the effect and safety of evocalcet for SHPT on hemodialysis in the current meta-analysis.

CONCLUSION

The stronger evidence about evocalcet effect and safety will be provided for clinicians and policymakers.

ETHICS AND DISSEMINATION

Ethical approval will be unnecessary because the data being included in this systematic review come from published literature and there will be no concerns regarding privacy. Findings of this research will be disseminated in a peer-reviewed journal or conference presentations.

OSF REGISTRATION NUMBER

DOI 10.17605/OSF.IO/N59RB.

Recent advances in understanding and managing secondary hyperparathyroidism in chronic kidney disease

Secondary hyperparathyroidism is a complex pathology that develops as chronic kidney disease progresses. The retention of phosphorus and the reductions in calcium and vitamin D levels stimulate the synthesis and secretion of parathyroid hormone as well as the proliferation rate of parathyroid cells. Parathyroid growth is initially diffuse but it becomes nodular as the disease progresses, making the gland less susceptible to be inhibited. Although the mechanisms underlying the pathophysiology of secondary hyperparathyroidism are well known, new evidence has shed light on unknown aspects of the deregulation of parathyroid function. Secondary hyperparathyroidism is an important feature of chronic kidney disease-mineral and bone disorder and plays an important role in the development of bone disease and vascular calcification. Thus, part of the management of chronic kidney disease relies on maintaining acceptable levels of mineral metabolism parameters in an attempt to slow down or prevent the development of secondary hyperparathyroidism. Here, we will also review the latest evidence regarding several aspects of the clinical and surgical management of secondary hyperparathyroidism.

Tubular effects of sodium-glucose cotransporter 2 inhibitors: intended and unintended consequences

PURPOSE OF REVIEW

Sodium-glucose cotransporter 2 (SGLT2) inhibitors are antihyperglycemic drugs that act by inhibiting renal sodium-glucose cotransport. Here we present new insights into 'off target', or indirect, effects of SGLT2 inhibitors.

RECENT FINDINGS

SGLT2 inhibition causes an acute increase in urinary glucose excretion. In addition to lowering blood glucose, there are several other effects that contribute to the overall beneficial renal and cardiovascular effects. Reabsorption of about 66% of sodium is accomplished in the proximal tubule and dependent on the sodium-hydrogen exchanger isoform 3 (NHE3). SGLT2 colocalizes with NHE3, and high glucose levels reduce NHE3 activity. The proximal tubule is also responsible for the majority of phosphate (Pi) reabsorption. SGLT2 inhibition is associated with increases in plasma Pi, fibroblast growth factor 23 and parathyroid hormone levels in nondiabetics and type 2 diabetes mellitus. Studies in humans identified a urate-lowering effect by SGLT2 inhibition which is possibly mediated by urate transporter 1 (URAT1) and/or glucose transporter member 9 in the proximal tubule. Of note, magnesium levels were also found to increase under SGLT2 inhibition, an effect that was preserved in nondiabetic patients with hypomagnesemia.

SUMMARY

Cardiorenal effects of SGLT2 inhibition might involve, in addition to direct effects on glucose homeostasis, effects on NHE3, phosphate, urate, and magnesium homeostasis.

Investigation on urinary and serum alpha klotho in dogs with chronic kidney disease

Background

As a co-receptor for fibroblast growth factor 23, klotho plays a pivotal role in phosphate metabolism. The kidney is known to be the main source of soluble alpha-klotho and the principal regulator of its concentration. Previous studies in human participants showed that the concentration of soluble alpha-klotho in serum and urine decreased in chronic kidney disease (CKD) patients. However, no previous study has assessed soluble alpha-klotho levels in dogs. This study aimed to measure serum and urinary alpha-klotho levels in CKD dogs and identify their associations with International Renal Interest Society (IRIS) CKD stages and other parameters known to be associated with CKD.

Results

Serum and urinary alpha klotho concentrations were measured by a commercially available canine-specific sandwich enzyme-linked immunosorbent assay kit and compared between groups by a nonparametric Kruskal–Wallis test. Spearman’s correlation coefficient was used to evaluate the relationships between variables. A stepwise multiple regression analysis was performed to estimate the effects of independent predictors on klotho concentrations. The urine klotho-to-creatinine ratio (UrKl/Cr) was significantly lower in stage 3 dogs than the control group and was significantly lower in dogs with stage 3 and 4 CKD than in those with stage 1 and 2 disease. UrKl/Cr was negatively correlated with serum symmetric dimethylarginine (sSDMA), blood urea nitrogen (BUN), creatinine, and phosphorus concentration. Serum alpha-klotho concentration in dogs with stages 2 and 3 CKD was significantly lower than those in the control group. There was no significant correlation between serum alpha-klotho and BUN, creatinine, and phosphorus concentrations. No statistically significant differences were observed in UrKl/Cr and serum alpha-klotho concentration between groups based on sex, age, urine protein-to-creatinine ratio (UPC), or blood pressure.

Conclusions

UrKl/Cr decreased in dogs with advanced CKD, and it was negatively correlated with sSDMA, BUN, creatinine, and phosphorus concentrations. Thus, klotho is associated with CKD and its clinical consequences, including CKD-mineral bone disorder, in dogs. Although serum klotho concentration was negatively correlated with sSDMA levels, it was not apparently related to IRIS CKD stage or other parameters known to be associated with CKD.

Osteocytes' expression of the PTH/PTHrP receptor has differing effects on endocortical and periosteal bone formation during adenine-induced CKD

Osteocytes play a key role in the pathophysiology of chronic kidney disease (CKD). However, the extent to which osteocytes contribute to abnormalities in bone turnover due to excessive levels of parathyroid hormone (PTH) remains poorly understood. The purpose of this study was to determine the extent to which bone formation and tissue strength during the progression of CKD is modified through osteocytes' response to PTH. Conditional knockout mice targeting osteocytes' expression of the PTH/PTH-related protein type 1 receptor (PPR) were subjected to adenine-induced CKD. After 6-weeks of treatment, adenine-induced CKD was found to reduce bone formation at the periosteal and endocortical surfaces of the tibia. The loss in bone mass corresponded with a significant decrease in structural-level mechanical properties. In knockout mice, the loss of PPR expression in osteocytes further exacerbated the loss in bone formation at the endocortical surface, but inhibited bone loss at the periosteal surface. In general, the effects of adenine-induced CKD were not as extensive in female mice. Collectively, these findings demonstrate that osteocytes' response to PTH under adenine-induced CKD has a unique impact on bone turnover that is specific to the periosteal and endocortical surfaces.

Parathyroid Hormone: A Uremic Toxin

Parathyroid hormone (PTH) has an important role in the maintenance of serum calcium levels. It activates renal 1α-hydroxylase and increases the synthesis of the active form of vitamin D (1,25[OH]₂D₃). PTH promotes calcium release from the bone and enhances tubular calcium resorption through direct action on these sites. Hallmarks of secondary hyperparathyroidism associated with chronic kidney disease (CKD) include increase in serum fibroblast growth factor 23 (FGF-23), reduction in renal 1,25[OH]₂D₃ production with a decline in its serum levels, decrease in intestinal calcium absorption, and, at later stages, hyperphosphatemia and high levels of PTH. In this paper, we aim to critically discuss severe CKD-related hyperparathyroidism, in which PTH, through calcium-dependent and -independent mechanisms, leads to harmful effects and manifestations of the uremic syndrome, such as bone loss, skin and soft tissue calcification, cardiomyopathy, immunodeficiency, impairment of erythropoiesis, increase of energy expenditure, and muscle weakness.

Limited role for fibroblast growth factor 23 in assessing prognosis in heart failure patients: data from the TIME-CHF trial

AIM

Fibroblast growth factor 23 (FGF23) is an intensively studied biomarker at the crossroads of cardiovascular disease, heart failure (HF) and chronic kidney disease. Independent associations between increasing FGF23 levels and cardiovascular events were found in many, but not all studies. By analysing data from the TIME-CHF cohort, we sought to investigate the prognostic value of FGF23 in an elderly, multimorbid HF patient cohort. We determined differences between intact (iFGF23) and C-terminal FGF23 (cFGF23) regarding their prognostic value and their levels over time in different HF subgroups according to left ventricular ejection fraction (LVEF).

METHODS AND RESULTS

In this multicentre trial of 622 patients with symptomatic HF aged ≥60 years, we determined iFGF23 and cFGF23 at baseline, 3, 6 and 12-month follow-up. In unadjusted analyses, cFGF23 significantly predicted all HF-related outcomes at all time points. The predictive value of iFGF23 was less and not statistically significant at baseline. After multivariable adjustments, the association between both cFGF23 and iFGF23 and outcome lost statistical significance apart from cFGF23 at month 3. Overall, patients with preserved and mid-range LVEF had higher levels of iFGF23 and cFGF23 than those with reduced LVEF. Levels decreased significantly during the first 3 months in mid-range and reduced LVEF patients, but did not significantly change over time in those with preserved LVEF.

CONCLUSIONS

Fibroblast growth factor 23 is of limited value regarding risk prediction in this elderly HF population. Potentially heterogeneous roles of FGF23 in different LVEF groups deserve further investigation.

Altered Mineral Metabolism and Disequilibrium Between Calcification Promoters and Inhibitors in Chronic Hemodialysis Patients

Patients undergoing long-term hemodialysis (HD) are known to have abnormal blood concentrations of antioxidant minerals; concurrent oxidative stress can contribute to increased vascular calcification. This study aims to evaluate the associations between circulating antioxidant minerals and clinical biomarkers of vascular calcification in HD patients. Blood biochemical parameters, antioxidant minerals (selenium (Se), zinc (Zn), copper (Cu), and magnesium (Mg)), and several promoters and inhibitors of calcification (matrix Gla protein (MGP), fibroblast growth factor-23 (FGF-23), matrix metalloproteinases (MMP-2 and -9), and tissue inhibitors of metalloproteinase (TIMP-1 and -2)) were determined in HD patients (n = 62) and age- and sex-matched healthy individuals (n = 30). Compared with healthy subjects, HD patients had significantly lower plasma concentrations of Se and Zn, increased Cu and Mg, and higher levels of oxidative stress and inflammatory markers (Cu/Zn ratios, malondialdehyde (MDA), advanced glycation end products (AGEs), and C-reactive protein (CRP)). We observed that HD patients had significantly lower concentrations of MGP and higher levels of FGF-23, MMP-2 and -9, TIMP-1 and -2, and MMP-2/TIMP-2 and MMP-9/TIMP-1 ratios. We also observed significant relationships between the concentrations of these minerals and calcification biomarkers in HD patients. These results suggest that changes in the homeostasis of antioxidant minerals (Se, Zn, Cu, and Mg) may contribute to the effects of oxidative stress and inflammatory status, thereby participating in the mechanism for accelerated vascular calcification in patients undergoing long-term HD.

Evolving concepts in the pathogenesis of uraemic cardiomyopathy

The term uraemic cardiomyopathy refers to the cardiac abnormalities that are seen in patients with chronic kidney disease (CKD). Historically, this term was used to describe a severe cardiomyopathy that was associated with end-stage renal disease and characterized by severe functional abnormalities that could be reversed following renal transplantation. In a modern context, uraemic cardiomyopathy describes the clinical phenotype of cardiac disease that accompanies CKD and is perhaps best characterized as diastolic dysfunction seen in conjunction with left ventricular hypertrophy and fibrosis. A multitude of factors may contribute to the pathogenesis of uraemic cardiomyopathy, and current treatments only modestly improve outcomes. In this Review, we focus on evolving concepts regarding the roles of fibroblast growth factor 23 (FGF23), inflammation and systemic oxidant stress and their interactions with more established mechanisms such as pressure and volume overload resulting from hypertension and anaemia, respectively, activation of the renin-angiotensin and sympathetic nervous systems, activation of the transforming growth factor-β (TGFβ) pathway, abnormal mineral metabolism and increased levels of endogenous cardiotonic steroids.

FGF23 at the crossroads of phosphate, iron economy and erythropoiesis

Fibroblast growth factor 23 (FGF23) was initially characterized as an important regulator of phosphate and calcium homeostasis. New research advances demonstrate that FGF23 is also linked to iron economy, inflammation and erythropoiesis. These advances have been fuelled, in part, by the serendipitous development of two distinct FGF23 assays that can substitute for invasive bone biopsies to infer the activity of the three main steps of FGF23 regulation in bone: transcription, post-translational modification and peptide cleavage. This 'liquid bone biopsy for FGF23 dynamics' enables large-scale longitudinal studies of FGF23 regulation that would otherwise be impossible in humans. The balance between FGF23 production, post-translational modification and cleavage is maintained or perturbed in different hereditary monogenic conditions and in acquired conditions that mimic these genetic disorders, including iron deficiency, inflammation, treatment with ferric carboxymaltose and chronic kidney disease. Looking ahead, a deeper understanding of the relationships between FGF23 regulation, iron homeostasis and erythropoiesis can be leveraged to devise novel therapeutic targets for treatment of anaemia and states of FGF23 excess, including chronic kidney disease.

Effect of extended hours dialysis on markers of chronic kidney disease-mineral and bone disorder in the ACTIVE Dialysis study

Background

Chronic Kidney Disease - Mineral and Bone Disorder (CKD-MBD) is a significant cause of morbidity among haemodialysis patients and is associated with pathological changes in phosphate, calcium and parathyroid hormone (PTH). In the ACTIVE Dialysis study, extended hours dialysis reduced serum phosphate but did not cause important changes in PTH or serum calcium. This secondary analysis aimed to determine if changes in associated therapies may have influenced these findings and to identify differences between patient subgroups.

Methods

The ACTIVE Dialysis study randomised 200 participants to extended hours haemodialysis (≥24 h/week) or conventional haemodialysis (≤18 h/week) for 12 months. Mean differences between treatment arms in serum phosphate, calcium and PTH; and among key subgroups (high vs. low baseline phosphate/PTH, region, time on dialysis, dialysis setting and frequency) were examined using mixed linear regression.

Results

Phosphate binder use was reduced with extended hours (− 0.83 tablets per day [95% CI -1.61, − 0.04; p = 0.04]), but no differences in type of phosphate binder, use of vitamin D, dose of cinacalcet or dialysate calcium were observed. In adjusted analysis, extended hours were associated with lower phosphate (− 0.219 mmol/L [− 0.314, − 0.124; P < 0.001]), higher calcium (0.046 mmol/L [0.007, 0.086; P = 0.021]) and no change in PTH (0.025 pmol/L [− 0.107, 0.157; P = 0.713]). The reduction in phosphate with extended hours was greater in those with higher baseline PTH and dialysing at home.

Conclusion

Extended hours haemodialysis independently reduced serum phosphate levels with minimal change in serum calcium and PTH levels. With a few exceptions, these results were consistent across patient subgroups.

Trial registration

Clinicaltrials.gov NCT00649298. Registered 1 April 2008.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1438-3) contains supplementary material, which is available to authorized users.

Parathyroid Hormone Causes Endothelial Dysfunction by Inducing Mitochondrial ROS and Specific Oxidative Signal Transduction Modifications

Vitamin D deficiency contributes to cardiovascular risk (CVR), with hyperparathyroidism advocated as a putative mechanism. Indeed, mounting evidence supports the hypothesis that parathyroid hormone (PTH) impairs endothelial function, even though mechanisms are not fully elucidated. The present study was designed to verify in vitro the ability of sustained exposure to PTH to cause endothelial dysfunction, exploring the underlying mechanisms. In bovine aortic endothelial cells (BAECs), we evaluated the effects of PTH exposure (0.1 nM–24 hours) on both endothelial response to vasodilators, such as bradykinin (Bk (30 nM)) and acetylcholine (Ach (1 μM)), and angiogenic competence. Pretreatment with PTH impaired endothelial response to Bk but not to Ach, in terms of cytosolic calcium fluxes and NO production. In order to explore the underlying mechanisms, we assessed the production of total and mitochondrial ROS (tROS and mROS, respectively) in response to PTH (at 1 and 3 hours). PTH increased ROS generation, to an extent high enough to determine oxidation of Bk receptor B2. Conversely, the oxidation levels of M1 and M3 Ach receptors were not affected by PTH. A mROS selective scavenger (MitoTEMPO (5 μM)) restored the endothelial responsiveness to Bk while the well-known antioxidant properties of vitamin D (100 nM) failed to counteract PTH-mediated oxidative stress. PTH determined mitochondrial calcium fluxes ([Ca²⁺]_mt) and the mitochondrial calcium uniporter inhibitor Ru360 (10 μM) reduced mROS production and prevented the PTH-mediated endothelial dysfunction. Angiogenic competence was evaluated as tubular formations in the endothelial Matrigel assay and showed a significant impairment in PTH-pretreated cells (0.1 nM–24 hours), despite the increase in VEGF transcriptional levels. VEGFR2 oxidation occurred in response to PTH, suggesting that even the impairment of angiogenesis was due to the ROS surge. These results indicate that PTH affects endothelial function through ROS production, driven by mitochondrial calcium overload. PTH-induced oxidative stress might act as signaling modifiers, altering specific pathways (Bk and VEGF) and preserving others (Ach).

Conservative three-quarter versus subtotal seven-eighths parathyroidectomy in secondary hyperparathyroidism

OBJECTIVE

There is at present no consensus concerning surgical techniques for secondary hyperparathyroidism (SHPT) in end-stage renal disease (ESRD). Although both subtotal and total parathyroidectomy provide low rates of recurrence, they may induce hypoparathyroidism, damaging the bone and cardiovascular systems. The aim of our study was to compare 3/4 and 7/8 parathyroidectomy in this population and to discuss the potential benefit of more conservative treatment.

STUDY DESIGN

Prospective observational study in a university teaching hospital between 2010 and 2014.

METHODS

The study included 34 consecutive ESRD patients with SHPT: 19 underwent 3/4 parathyroidectomy (group A*3/4) and 15 underwent 7/8 parathyroidectomy (group B*7/8). Serum intact 1-84 PTH levels (before and 6 months after surgery) and hospital stay were compared between the two groups.

RESULTS

Before surgery, PTH levels were similar between the two groups. At month 6 following surgery, median PTH levels were significantly higher in group A*3/4 than in group B*7/8 (109 versus 24pg/mL, respectively; P<0.0006). Hospital stay was shorter in group A*3/4 (4.79 versus 6.80 days, respectively; P=0.008). Postoperative hypoparathyroidism requiring long-term calcium and 1alpha(OH) D3 treatment was reported in 5% of patients in group A*3/4 and 26% of patients in group B*7/8 (P=0.04).

CONCLUSIONS

In this preliminary study, 3/4 conservative parathyroidectomy seemed effective and safe, with less reported morbidity than 7/8 parathyroidectomy, as assessed by lower rates of irreversible hypoparathyroidism and shorter hospital stay.

LEVEL OF EVIDENCE

3b, individual case-control study.

Vitamin D Deficiency Aggravates the Renal Features of Moderate Chronic Kidney Disease in 5/6 Nephrectomized Rats

The pathogenesis of chronic kidney disease (CKD) involves a very complex interaction between hemodynamic and inflammatory processes, leading to glomerular/vascular sclerosis, and fibrosis formation with subsequent evolution to end-stage of renal disease. Despite efforts to minimize the progression of CKD, its incidence and prevalence continue to increase. Besides cardiovascular diseases and infections, several studies demonstrate that vitamin D status could be considered as a non-traditional risk factor for the progression of CKD. Therefore, we investigated the effects of vitamin D deficiency (VDD) in the course of moderate CKD in 5/6 nephrectomized rats (Nx). Adult male Wistar rats underwent Sham surgery or Nx and were subdivided into the following four groups: Sham, receiving standard diet (Sham); Sham VDD, receiving vitamin D-free diet (VDD); Nx, receiving standard diet (Nx); and VDD+Nx, receiving vitamin D-free diet (VDD+Nx). Sham or Nx surgeries were performed 30 days after standard or vitamin D-free diets administration. After validation of vitamin D depletion, we considered only Nx and VDD+Nx groups for the following studies. Sixty days after surgeries, VDD+Nx rats exhibited hypertension, a greater decline in renal function and plasma FGF-23 levels, renal hypertrophy, as well as higher plasma levels of PTH and aldosterone. In addition, those animals presented more significant chronic tubulointerstitial changes (cortical interstitial expansion/inflammation/fibrosis), higher expression of collagen IV, fibronectin and α-smooth muscle actin, and lower expressions of JG12 and M2 macrophages. Also, VDD+Nx rats had greater infiltration of inflammatory cells (M1 macrophages and T-cells). Such changes were accompanied by higher expression of TGF-β1 and angiotensinogen and decreased expression of VDR and Klotho protein. Our observations indicate that vitamin D deficiency impairs the renal function and worsens the renovascular and morphological changes, aggravating the features of moderate CKD in 5/6 nephrectomized rats.

PRIMARY HIP ARTHROPLASTY IN PATIENTS WITH END-STAGE OF CHRONIC KIDNEY DISEASE (LITERATURE REVIEW)

The authors present a review of current national and international literature related to the specifics of primary hip joint arthroplasty in patients with end-stage of chronic kidney disease. epidemiology aspects of such pathology are covered in detail. Screening of the patients with hip joint pathology undergoing substitute renal therapy remains a significant issue. The authors present the outcomes of use of various implant types and their fixation in primary hip joint arthroplasty such as cemented, cementless and monopolar prostheses, as well as consider features and structure of complications following primary replacements in such patients. unfortunately, the national literature lacks sufficient number of publications on the present problem. In addition, the paper presents a promising area for development of specialized care to patients on hemodialysis with hip joint pathology.

Interleukin-6 contributes to the increase in fibroblast growth factor 23 expression in acute and chronic kidney disease

The high serum fibroblast growth factor 23 (FGF23) levels in patients with acute kidney injury (AKI) and chronic kidney disease (CKD) are associated with increased morbidity and mortality. Mice with folic acid-induced AKI had an increase in bone FGF23 mRNA expression together with an increase in serum FGF23 and several circulating cytokines including interleukin-6 (IL-6). Dexamethasone partially prevented the increase in IL-6 and FGF23 in the AKI mice. IL-6 knock-out mice fed an adenine diet to induce CKD failed to increase bone FGF23 mRNA and had a muted increase in serum FGF23 levels, compared with the increases in wild-type mice with CKD. Therefore, IL-6 contributes to the increase in FGF23 observed in CKD. Hydrodynamic tail injection of IL-6/soluble IL-6 receptor (sIL-6R) fusion protein hyper IL-6 (HIL-6) plasmid increased serum FGF23 levels. Circulating sIL-6R levels were increased in both CKD and AKI mice, suggesting that IL-6 increases FGF23 through sIL-6R-mediated trans-signaling. Renal IL-6 mRNA expression was increased in mice with either AKI or CKD, suggesting the kidney is the source for the increased serum IL-6 levels in the uremic state. HIL-6 also increased FGF23 mRNA in calvaria organ cultures and osteoblast-like UMR106 cells in culture, demonstrating a direct effect of IL-6 on FGF23 expression. HIL-6 increased FGF23 promoter activity through STAT3 phosphorylation and its evolutionarily conserved element in the FGF23 promoter. Thus, IL-6 increases FGF23 transcription and contributes to the high levels of serum FGF23 in both acute and chronic kidney disease.

The FGF-23/klotho axis and its relationship with phosphorus, calcium, vitamin D, PTH, aldosterone, severity of disease, and outcome in hospitalised foals

BACKGROUND

Fibroblast growth factor-23 (FGF-23) and klotho are key regulators of vitamin D and parathyroid hormone (PTH) synthesis as well as phosphorus and calcium homeostasis; however, information on the FGF-23/klotho axis in healthy and hospitalised foals is lacking.

OBJECTIVES

The aims of this study were to measure serum FGF-23 and klotho concentrations and determine their association with serum phosphorus, total calcium (TCa), vitamin D metabolite [25(OH)D, 1,25(OH)₂ D], PTH, and aldosterone concentrations, disease severity, and mortality in hospitalised foals.

STUDY DESIGN

Prospective, multicentre, cross-sectional study.

METHODS

A total of 91 foals ≤72 h old were classified as hospitalised (n = 81; 58 septic; 23 sick non-septic [SNS]) and healthy (n = 10). Blood samples were collected on admission. Hormone concentrations were determined by immunoassays.

RESULTS

Serum FGF-23, PTH, phosphorus, and aldosterone concentrations were higher while klotho, 25(OH)D, 1,25(OH)₂ D, and TCa concentrations were lower in septic and SNS compared to healthy foals (P<0.05). In hospitalised and septic foals, increased FGF-23 and aldosterone concentrations were associated with high phosphorus and PTH but not with TCa and vitamin D metabolite concentrations. Hospitalised foals with the highest FGF-23 and lowest klotho concentrations were more likely to die (odds ratio (OR): 3.3; 95% confidence interval (CI): 1.1-10.3 and OR: 3.1; CI: 1.1-8.0, respectively).

MAIN LIMITATIONS

Blood gas, ionised calcium, blood culture information not being available for many foals, and use of the sepsis score to classify hospitalised foals.

CONCLUSIONS

Imbalances in the FGF-23/klotho axis may contribute to mineral dyshomeostasis and disease progression in critically ill foals. Elevated FGF-23 and reduced klotho, together with high phosphorus and PTH concentrations suggests FGF-23 resistance. FGF-23 and klotho are good markers of disease severity and likelihood of mortality in hospitalised foals. Aldosterone may influence phosphorus and PTH dynamics in hospitalised foals. Routine measurement of phosphorus concentrations in sick foals is recommended.

Comparison of Intact PTH and Bio-Intact PTH Assays Among Non-Dialysis Dependent Chronic Kidney Disease Patients

BACKGROUND

The third-generation bio-intact parathyroid hormone (PTH) (1-84) assay was designed to overcome problems associated with the detection of C-terminal fragments by the second-generation intact PTH assay. The two assays have been compared primarily among dialysis populations. The present study evaluated the correlations and differences between these two PTH assays among patients with chronic kidney disease (CKD) stages 3 to 5 not yet on dialysis.

METHODS

Blood samples were collected from 98 patients with CKD stages 3 to 5. PTH concentrations were measured simultaneously by using the second-generation - PTH intact-STAT and third-generation bio-intact 1-84 PTH assays. Other serum biomarkers of bone mineral disorders were also assessed. CKD stage was calculated by using the CKD-Epidemiology Collaboration (EPI) formula.

RESULTS

Serum bio-intact PTH concentrations were strongly correlated but significantly lower than the intact PTH concentrations (r=0.963, P<0.0001). This finding was consistent among CKD stages 3 to 5. PTH concentrations by both assays (intact and bio-intact PTH) positively correlated with urea (r=0.523, r=0.504; P=0.002, respectively), phosphorus (r=0.532, r=0.521; P<0.0001, respectively) and negatively correlated with blood calcium (r=-0.435, r=-0.476; P<0.0001, respectively), 25(OH) vitamin D, (r=-0.319, r=-0.353; respectively, P<0.0001) and the estimated glomerular filtration rate (r=-0.717, r=-0.688; P<0.0001, respectively).

CONCLUSIONS

Among patients with CKD stages 3 to 5 not on dialysis, the bio-intact PTH assay detected significantly lower PTH concentrations compared with intact PTH assay. Additional studies that correlate the diagnosis and management of CKD mineral and bone disorders with bone histomorphometric findings are needed to determine whether bio-intact PTH assay results are better surrogate markers in these early stages of CKD.

The Effect of Vitamin D Supplementation on Bone Metabolic Markers in Chronic Kidney Disease

Use of active forms of vitamin D is advocated in patients with chronic kidney disease (CKD) for treatment of mineral bone disease because of the presumption that native forms of vitamin D would not undergo significant activation to calcitriol, the most active biological form of vitamin D. We present secondary analysis looking at bone turnover in subjects who completed the randomized, double blind, placebo-controlled trial investigating the effect of cholecalciferol supplementation on vascular function in nondiabetic CKD stage G3-G4 and vitamin D ≤20 ng/mL (Clinical Trials Registry of India: CTRI/2013/05/003648). Patients were randomized (1:1) to receive either two directly observed oral doses of 300,000 IU of cholecalciferol or matching placebo at baseline and 8 weeks. Of the 120 subjects enrolled, 58 in the cholecalciferol group and 59 in the placebo group completed the study. At 16 weeks, the serum 25(OH)D and 1,25(OH)₂ D levels increased in the cholecalciferol group but not in the placebo group (between-group difference in mean change: 23.40 ng/mL; 95% CI, 19.76 to 27.06; p < 0.001, and 14.98 pg/mL; 95% CI, 4.48 to 27.18; p = 0.007, respectively). Intact parathyroid hormone (iPTH) decreased in the cholecalciferol group (between-group difference in mean change -100.73 pg/mL (95% CI, -150.50 to -50.95; p < 0.001). Serum total and bone-specific alkaline phosphatase (SAP, BAP) and serum C-terminal cross-linked collagen type I telopeptides (CTX-1) were significantly reduced in cholecalciferol group (between group difference for change in mean: -20.25 U/L; 95% CI, -35.14 to -5.38 U/L; p = 0.008 for SAP; -12.54 U/L; 95% CI, -22.09 to -2.98 U/L; p = 0.013 for BAP; and -0.21 ng/mL; 95% CI, -0.38 to -0.05 ng/mL; p = 0.05 for CTX-1). Correlation analysis showed significant correlation of Δ25(OH)D with ΔiPTH (r = -0.409, p < 0.0001), Δ1,25(OH)₂ D (r = 0.305, p = 0.001), ΔSAP (r = -0.301, p = 0.002), ΔBAP (r = -0.264, p = 0.004), and ΔCTX-1 (r = -0.210, p = 0.0230). Cholecalciferol supplementation corrects vitamin D deficiency and is effective in lowering serum intact parathyroid hormone and bone turnover markers in early stages of CKD. © 2017 American Society for Bone and Mineral Research.

Cinacalcet versus Placebo for secondary hyperparathyroidism in chronic kidney disease patients: a meta-analysis of randomized controlled trials and trial sequential analysis

To assess the efficacy and safety of cinacalcet on secondary hyperparathyroidism in patients with chronic kidney disease, Pubmed, Embase, and the Cochrane Central Register of Controlled Trials were searched until March 2016. Trial sequential analysis (TSA) was conducted to control the risks of type I and II errors and calculate required information size (RIS). A total of 25 articles with 8481 participants were included. Compared with controls, cinacalcet administration did not reduce all-cause mortality (RR = 0.97, 95% CI = 0.89–1.05, P = 0.41, TSA-adjusted 95% CI = 0.86–1.08, RIS = 5260, n = 8386) or cardiovascular mortality (RR = 0.95, 95% CI = 0.83–1.07, P = 0.39, TSA-adjusted 95% CI = 0.70–1.26, RIS = 3780 n = 5418), but it reduced the incidence of parathyroidectomy (RR = 0.48, 95% CI = 0.40–0.50, P < 0.001, TSA-adjusted 95% CI = 0.39–0.60, RIS = 5787 n = 5488). Cinacalcet increased the risk of hypocalcemia (RR = 8.48, 95% CI = 6.37–11.29, P < 0.001, TSA-adjusted 95% CI = 5.25–13.70, RIS = 6522, n = 7785), nausea (RR = 2.12, 95% CI = 1.62–2.77, P < 0.001, TSA-adjusted 95% CI = 1.45–3.04, RIS = 4684, n = 7512), vomiting (RR = 2.00, 95% CI = 1.79–2.24, P < 0.001, TSA-adjusted 95% CI = 1.77–2.26, RIS = 1374, n = 7331) and diarrhea (RR = 1.17, 95% CI = 1.05–1.32, P = 0.006, TSA-adjusted 95% CI = 1.02–1.36, RIS = 8388, n = 6116). Cinacalcet did not significantly reduce the incidence of fractures (RR = 0.58, 95% CI = 0.21–1.59, P = 0.29, TSA-adjusted 95% CI = 0.01–35.11, RIS = 76376, n = 4053). Cinacalcet reduced the incidence of parathyroidectomy, however, it did not reduce all-cause and cardiovascular mortality, and increased the risk of adverse events including hypocalcemia and gastrointestinal disorders.

The Parathyroid Gland and Heart Disease

The parathyroid glands are critical to maintaining calcium homeostasis through actions of parathyroid hormone (PTH). Recent clinical and molecular research has shown that direct and indirect actions of PTH also affect the heart and vasculature through downstream actions of G protein-coupled receptors in the myocardium and endothelial cells. Patients with disorders of the parathyroid gland have higher incidences of hypertension, arrhythmias, left ventricular hypertrophy, heart failure, and calcific disease which translate into increased cardiac morbidity and mortality. Importantly, clinical research also suggests that early treatment of parathyroid disorders through medical or surgical management may reverse cardiovascular remodeling and mitigate cardiac risk factors.

Biochemical and Clinical Impact of Organic Uremic Retention Solutes: A Comprehensive Update

In this narrative review, the biological/biochemical impact (toxicity) of a large array of known individual uremic retention solutes and groups of solutes is summarized. We classified these compounds along their physico-chemical characteristics as small water-soluble compounds or groups, protein bound compounds and middle molecules. All but one solute (glomerulopressin) affected at least one mechanism with the potential to contribute to the uremic syndrome. In general, several mechanisms were influenced for each individual solute or group of solutes, with some impacting up to 7 different biological systems of the 11 considered. The inflammatory, cardio-vascular and fibrogenic systems were those most frequently affected and they are one by one major actors in the high morbidity and mortality of CKD but also the mechanisms that have most frequently been studied. A scoring system was built with the intention to classify the reviewed compounds according to the experimental evidence of their toxicity (number of systems affected) and overall experimental and clinical evidence. Among the highest globally scoring solutes were 3 small water-soluble compounds [asymmetric dimethylarginine (ADMA); trimethylamine-N-oxide (TMAO); uric acid], 6 protein bound compounds or groups of protein bound compounds [advanced glycation end products (AGEs); p-cresyl sulfate; indoxyl sulfate; indole acetic acid; the kynurenines; phenyl acetic acid;] and 3 middle molecules [β₂-microglobulin; ghrelin; parathyroid hormone). In general, more experimental data were provided for the protein bound molecules but for almost half of them clinical evidence was missing in spite of robust experimental data. The picture emanating is one of a complex disorder, where multiple factors contribute to a multisystem complication profile, so that it seems of not much use to pursue a decrease of concentration of a single compound.

Con: Nutritional vitamin D replacement in chronic kidney disease and end-stage renal disease

Insufficiency of 25-hydroxyvitamin D [25(OH)D] is highly prevalent among patients with chronic kidney disease (CKD) or end-stage renal disease (ESRD) and is a critical component in the pathogenesis of secondary hyperparathyroidism. Accordingly, current National Kidney Foundation-Kidney Disease Outcomes Quality Initiative and Kidney Disease: Improving Global Outcomes guidelines recommend the correction of hypovitaminosis D through nutritional vitamin D replacement as a first-step therapeutic approach targeting secondary hyperparathyroidism. In this Polar Views debate, we summarize the existing evidence, aiming to defend the position that nutritional vitamin D replacement is not evidence-based and should not be applied to patients with CKD. This position is supported by the following: (i) our meta-analysis of randomized controlled trials shows that whereas nutritional vitamin D significantly increases serum 25(OH)D levels relative to placebo, there is no evidence either in predialysis CKD or in ESRD that parathyroid hormone (PTH) is lowered; (ii) on the other hand, in randomized head-to-head comparisons, nutritional vitamin D is shown to be inferior to activated vitamin D analogs in reducing PTH levels; (iii) nutritional vitamin D is reported to exert minimal to no beneficial actions in a series of surrogate risk factors, including aortic stiffness, left ventricular mass index (LVMI), epoetin utilization and immune function among others; and (iv) there is no evidence to support a benefit of nutritional vitamin D on survival and other 'hard' clinical outcomes. Whereas nutritional vitamin D replacement may restore 25(OH)D concentration to near normal, the real target of treating vitamin D insufficiency is to treat secondary hyperparathyroidism, which is untouched by nutritional vitamin D. Furthermore, the pleotropic benefits of nutritional vitamin D remain to be proven. Thus, there is little, if any, benefit of nutritional vitamin D replacement in CKD.

Transcription factor MafB may play an important role in secondary hyperparathyroidism

The transcription factor MafB is essential for development of the parathyroid glands, the expression of which persists after morphogenesis and in adult parathyroid glands. However, the function of MafB in adult parathyroid tissue is unclear. To investigate this, we induced chronic kidney disease (CKD) in wild-type and MafB heterozygote (MafB+/-) mice by feeding them an adenine-supplemented diet, leading to secondary hyperparathyroidism. The elevated serum creatinine and blood urea nitrogen levels in heterozygous and wild-type mice fed the adenine-supplemented diet were similar. Interestingly, secondary hyperparathyroidism, characterized by serum parathyroid hormone elevation and enlargement of parathyroid glands, was suppressed in MafB+/- mice fed the adenine-supplemented diet compared to similarly fed wild-type littermates. Quantitative RT-PCR and immunohistochemical analyses showed that the increased expression of parathyroid hormone and cyclin D2 in mice with CKD was suppressed in the parathyroid glands of heterozygous CKD mice. A reporter assay indicated that MafB directly regulated parathyroid hormone and cyclin D2 expression. To exclude an effect of a developmental anomaly in MafB+/- mice, we analyzed MafB tamoxifen-induced global knockout mice. Hypocalcemia-stimulated parathyroid hormone secretion was significantly impaired in MafB knockout mice. RNA-sequencing analysis indicated PTH, Gata3 and Gcm2 depletion in the parathyroid glands of MafB knockout mice. Thus, MafB appears to play an important role in secondary hyperparathyroidism by regulation of parathyroid hormone and cyclin D2 expression. Hence, MafB may represent a new therapeutic target in secondary hyperparathyroidism.

Comparative efficacy and safety of paricalcitol versus vitamin D receptor activators for dialysis patients with secondary hyperparathyroidism: a meta-analysis of randomized controlled trials

Background

Secondary hyperparathyroidism (SHPT) is a severe complication for dialysis patients. Vitamin D receptor activators (VDRAs) are used to treat SHPT, but the comparative efficacy and safety between paricalcitol and other vitamin D receptor activators for management of SHPT in dialysis patients has been unproven.

Methods

We searched PubMed, Embase, and the Cochrane Library for the time period through June 2017 to identify randomized controlled trials that evaluated paricalcitol compared with other VDRAs for treatment of SHPT. The primary outcome was the percentage of patients with target reduction of intact parathyroid hormone (iPTH) from baseline. Secondary outcomes included incidences of hypercalcemia and hyperphosphatemia. The random-effects model was used to estimate relative risks (RRs) with 95% confidence intervals (CIs).

Results

Eight studies (N = 759) were eligible for final inclusion. Compared with other VDRAs, no significant differences were found in the percentage of patients with target reduction of intact parathyroid hormone (iPTH) from baseline for paricalcitol treatment of SHPT in dialysis patients (RR, 1.01; 95% CI, 0. 87–1.18; p = 0.85). There were no differences in the incidence of hypercalcemia (RR, 0.95; 95% CI, 0.74–1.21; p = 0. 65) and hyperphosphatemia (RR, 0.94; 95% CI, 0.77–1.16; p = 0.58).

Conclusions

The presently available evidence is insufficient to draw a conclusion regarding whether paricalcitol therapy has a comparative efficacy and safety over other VDRAs for treating dialysis patients with SHPT. Large-sample, well-conducted, high-quality RCTs with patient-level outcomes (i.e., mortality) are urgently needed.

Electronic supplementary material

The online version of this article (10.1186/s12882-017-0691-6) contains supplementary material, which is available to authorized users.

Newly Developed Rat Model of Chronic Kidney Disease-Mineral Bone Disorder

Aim: Chronic kidney disease–mineral bone disorder (CKD–MBD) is associated with all-cause and cardiovascular morbidity and mortality in patients with CKD. Thus, elucidating its pathophysiological mechanisms is essential for improving the prognosis. We evaluated characteristics of CKD–MBD in a newly developed CKD rat model.

Methods: We used male Sprague–Dawley (SD) rats and spontaneously diabetic Torii (SDT) rats, which are used as models for nonobese type 2 diabetes. CKD was induced by 5/6 nephrectomy (Nx). At 10 weeks, the rats were classified into six groups and administered with a vehicle or a low- or high-dose paricalcitol thrice a week. At 20 weeks, the rats were sacrificed; blood and urinary biochemical analyses and histological analysis of the aorta were performed.

Results: At 20 weeks, hemoglobin A1c (HbA1c) levels, blood pressure, and renal function were not significantly different among the six groups. Serum calcium and phosphate levels tended to be higher in SDT-Nx rats than in SD-Nx rats. The urinary excretion of calcium and phosphate was significantly greater in SDT-Nx rats than in SD-Nx rats. After administering paricalcitol, serum parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) levels were significantly higher in SDT-Nx rats than in SD-Nx rats. The degree of aortic calcification was significantly more severe and the aortic calcium content was significantly greater in SDT-Nx rats than in SD-Nx rats.

Conclusions: We suggest that our new CKD rat model using SDT rats represents a useful CKD–MBD model, and this model was greatly influenced by paricalcitol administration. Further studies are needed to clarify the detailed mechanisms underlying this model.

Fibroblast Growth Factor-23 Concentration in Dogs with Chronic Kidney Disease

Background

Chronic kidney disease (CKD) is associated with hyperphosphatemia, decreased vitamin D metabolite concentrations, and hyperparathyroidism. This syndrome is known as CKD‐mineral bone disorder (CKD‐MBD). Recently, it has been shown that an increase in fibroblast growth factor‐23 (FGF‐23) concentration is an early biomarker of CKD in people. It is an independent risk factor for both progression of renal disease and survival time in humans and cats with CKD. Information about FGF‐23 in healthy dogs and those with CKD is lacking.

Objectives

To measure FGF‐23 concentration in dogs with different stages of CKD and determine its association with factors involved in CKD‐MBD, including serum phosphorus and parathyroid hormone (PTH) concentrations. A secondary aim was to validate an ELISA for measurement of plasma FGF‐23 concentration in dogs.

Animals

Thirty‐two client‐owned dogs with naturally occurring CKD and 10 healthy control dogs.

Methods

Prospective cross‐sectional study. An FGF‐23 ELISA was used to measure plasma FGF‐23 concentration in dogs and their association with serum creatinine, phosphorus, calcium, and PTH concentrations.

Results

Plasma FGF‐23 concentrations increased with severity of CKD and were significantly different between IRIS stages 1 and 2 versus stages 3 and 4 (P < .0001). Increases in FGF‐23 concentrations were more frequent than hyperparathyroidism or hyperphosphatemia in this cohort. Serum creatinine and phosphorus concentrations were the strongest independent predictors of FGF‐23 concentration.

Conclusions and clinical importance

Plasma FGF‐23 concentrations increase in dogs with CKD as disease progresses. Plasma FGF‐23 concentrations appear to be useful for further study of the pathophysiology of CKD‐MBD in dogs.

Chronic Kidney Disease

The definition and classification of chronic kidney disease (CKD) have evolved over time, but current international guidelines define this condition as decreased kidney function shown by glomerular filtration rate (GFR) of less than 60 mL/min per 1·73 m², or markers of kidney damage, or both, of at least 3 months duration, regardless of the underlying cause. Diabetes and hypertension are the main causes of CKD in all high-income and middle-income countries, and also in many low-income countries. Incidence, prevalence, and progression of CKD also vary within countries by ethnicity and social determinants of health, possibly through epigenetic influence. Many people are asymptomatic or have non-specific symptoms such as lethargy, itch, or loss of appetite. Diagnosis is commonly made after chance findings from screening tests (urinary dipstick or blood tests), or when symptoms become severe. The best available indicator of overall kidney function is GFR, which is measured either via exogenous markers (eg, DTPA, iohexol), or estimated using equations. Presence of proteinuria is associated with increased risk of progression of CKD and death. Kidney biopsy samples can show definitive evidence of CKD, through common changes such as glomerular sclerosis, tubular atrophy, and interstitial fibrosis. Complications include anaemia due to reduced production of erythropoietin by the kidney; reduced red blood cell survival and iron deficiency; and mineral bone disease caused by disturbed vitamin D, calcium, and phosphate metabolism. People with CKD are five to ten times more likely to die prematurely than they are to progress to end stage kidney disease. This increased risk of death rises exponentially as kidney function worsens and is largely attributable to death from cardiovascular disease, although cancer incidence and mortality are also increased. Health-related quality of life is substantially lower for people with CKD than for the general population, and falls as GFR declines. Interventions targeting specific symptoms, or aimed at supporting educational or lifestyle considerations, make a positive difference to people living with CKD. Inequity in access to services for this disease disproportionally affects disadvantaged populations, and health service provision to incentivise early intervention over provision of care only for advanced CKD is still evolving in many countries.