Effect of Continuous Intravenous Calcium Loading on Fibroblast Growth Factor 23 in Normal and Uremic Rats

Association between serum fibroblast growth factor-23 concentrations and blood calcium levels in chronic kidney disease cats with upper urolithiasis

OBJECTIVES

This study investigated whether serum fibroblast growth factor (FGF)-23 concentrations are associated with serum total calcium (tCa) and blood ionised calcium (iCa) concentrations in cats with chronic kidney disease (CKD) and upper urolithiasis.

METHODS

Serum samples and the medical records of cats with CKD with nephroliths, ureteroliths or both were investigated retrospectively. Cats with a serum creatinine concentration >250 μmol/l and/or a serum phosphorus concentration ⩾1.50 mmol/l were excluded. Based on cut-offs for serum tCa (2.70 mmol/l) or blood iCa (1.40 mmol/l), cats were divided into the following groups: total hypercalcaemia (H-tCa) (>2.70 mmol/l) and total normocalcaemia (N-tCa) (⩽2.70 mmol/l) groups, or ionised hypercalcaemia (H-iCa) (>1.40 mmol/l) and ionised normocalcaemia (N-iCa) (⩽1.40 mmol/l) groups, respectively. Serum FGF-23 concentrations were compared between groups and correlation analysis was performed.

RESULTS

Thirty-two cats with CKD and upper urolithiasis were included. Serum FGF-23 concentrations in the H-tCa group (median 573 pg/ml [range 125-3888]; n = 12) were significantly higher compared with the N-tCa group (median 245 pg/ml [range 94-627]; n = 20) (P = 0.001). Serum FGF-23 concentrations in the H-iCa group (median 1479 pg/ml [range 509-3888]; n = 6) increased significantly compared with the N-iCa group (median 245 pg/ml [range 94-637]; n = 26) (P <0.001). Serum FGF-23 concentrations significantly correlated with serum tCa (r = 0.511, P = 0.003) and blood iCa concentrations (r = 0.425, P = 0.015) but not serum creatinine (r = 0.279, P = 0.122) or phosphorus concentrations (r = 0.208, P = 0.253).Conclusions and relevance Increased serum FGF-23 concentrations were associated with hypercalcaemia independently of creatinine and phosphate status in cats with CKD and upper urolithiasis.

Serum alkaline phosphatase and infection-related mortality in hemodialysis patients: ten-year outcomes of the Q-cohort study

BACKGROUND

High serum alkaline phosphatase (ALP) levels are associated with excess all-cause and cardiovascular mortality in patients undergoing hemodialysis (HD). However, the long-term relationship between serum ALP levels and infection-related mortality remains unclear.

METHODS

A total of 3502 maintenance HD patients were registered in the Q-Cohort Study, an observational cohort study in Japan. The primary outcome was infection-related mortality during a 10-year follow-up period. The covariate of interest was serum ALP levels at baseline. The association between serum ALP levels and infection-related mortality was calculated using a Cox proportional hazards model and a Fine-Gray subdistribution hazards model with non-infection-related death as a competing risk.

RESULTS

During the follow-up period, 446 patients died of infection. According to their baseline serum ALP levels, the patients were categorized into sex-specific quartiles (Q1-Q4). Compared with patients in the lowest serum ALP quartile (Q1), those in the highest quartile (Q4) had a significantly higher multivariable-adjusted hazard ratio (HR) of 1.70 [95% confidence interval (CI) 1.24-2.32] for infection-related mortality. Furthermore, the HR for every 50 U/L increase in serum ALP levels was 1.24 (95% CI 1.12-1.36) for infection-related mortality. These associations remained consistent in the competing risk model: subdistribution HR, 1.47; 95% CI 1.07-2.03 for Q4 compared with Q1.

CONCLUSION

Higher serum ALP levels were significantly associated with a higher risk of infection-related mortality in patients undergoing HD.

Serum fibroblast growth factor-23 concentrations in young and mature adult cats with chronic kidney disease

OBJECTIVES

The aim of this study was to investigate serum fibroblast growth factor (FGF)-23 concentrations in young and mature adult cats with chronic kidney disease (CKD).

METHODS

The present study retrospectively investigated the serum samples and medical records of 1-8-year-old clinically healthy cats (control group, n = 7) and cats with CKD (n = 54). Cats with CKD were divided into four stages based on serum creatinine concentrations, according to the International Renal Interest Society (IRIS) CKD guidelines. Serum FGF-23 concentrations were compared between cats in the control group, IRIS stages 1, 2 and 3-4 CKD. Continuous variables were analysed using correlations and multiple linear regression.

RESULTS

Serum FGF-23 concentrations were significantly higher in cats with IRIS stages 1, 2 and 3-4 CKD, compared with those in the control group (P = 0.02, P = 0.002 and P = 0.002, respectively). Additionally, serum FGF-23 concentrations in cats with IRIS stages 3-4 CKD had higher serum FGF-23 concentrations than those with IRIS stages 1 and 2 CKD (P = 0.04 and P = 0.02, respectively). In the multiple linear regression analysis, serum urea nitrogen concentration, serum phosphorus concentration and blood ionised calcium concentration were independent variables predicting serum FGF-23 concentration.

CONCLUSIONS AND RELEVANCE

Serum FGF-23 concentrations in younger cats with CKD increased in early-stage CKD and were associated with mineral metabolic markers, as also occurs in geriatric cats.

Shedding Light on the Complex Regulation of FGF23

Early research has suggested a rather straightforward relation between phosphate exposure, increased serum FGF23 (Fibroblast Growth Factor 23) concentrations and clinical endpoints. Unsurprisingly, however, subsequent studies have revealed a much more complex interplay between autocrine and paracrine factors locally in bone like PHEX and DMP1, concentrations of minerals in particular calcium and phosphate, calciprotein particles, and endocrine systems like parathyroid hormone PTH and the vitamin D system. In addition to these physiological regulators, an expanding list of disease states are shown to influence FGF23 levels, usually increasing it, and as such increase the burden of disease. While some of these physiological or pathological factors, like inflammatory cytokines, may partially confound the association of FGF23 and clinical endpoints, others are in the same causal path, are targetable and hence hold the promise of future treatment options to alleviate FGF23-driven toxicity, for instance in chronic kidney disease, the FGF23-associated disease with the highest prevalence by far. These factors will be reviewed here and their relative importance described, thereby possibly opening potential means for future therapeutic strategies.

Increased Risk of Infection-Related and All-Cause Death in Hypercalcemic Patients Receiving Hemodialysis: The Q-Cohort Study

Although hypercalcemia is a risk factor for all-cause mortality in hemodialysis patients, it remains unknown whether hypercalcemia increases the risk of infection-related death. A total of 2869 hemodialysis patients registered in the Q-Cohort Study, a multicenter, prospective cohort study of hemodialysis patients, were analyzed. The predictor was albumin-corrected serum calcium level at baseline. The main outcome was infection-related death. Death risk were estimated by multivariable-adjusted Cox proportional hazard risk models and competing risk models. During the follow-up period of 4 years, 107 patients died of infection and 473 died of any cause. The patients were divided into four groups by the serum calcium level at baseline (G1, 5.7-8.9 mg/dL; G2, 9.0-9.4 mg/dL; G3, 9.5-9.9 mg/L; G4 10.0-16.5 mg/dL). In the multivariable-adjusted model, the incidence of infection-related death was significantly higher in the highest serum calcium group (G4) compared with the lowest serum calcium group (G1): hazard ratio [95% confidence interval], 2.34 [1.35-4.04], P = 0.002. Furthermore, higher serum calcium level was significantly associated with increased risk of all-cause death. In conclusion, our data suggest that a higher serum calcium level may be a risk factor for infection-related and all-cause death in hemodialysis patients.

Memo1 gene expression in kidney and bone is unaffected by dietary mineral load and calciotropic hormones

Mediator of cell motility 1 (MEMO1) is a ubiquitously expressed modulator of cellular responses to growth factors including FGF23 signaling, and Memo1-deficient mice share some phenotypic traits with Fgf23- or Klotho-deficient mouse models. Here, we tested whether Memo1 gene expression is regulated by calciotropic hormones or by changing the dietary mineral load. MLO-Y4 osteocyte-like cells were cultured and treated with 1,25(OH)2 -vitamin D3 . Wild-type C57BL/6N mice underwent treatments with 1,25(OH)2 -vitamin D3 , parathyroid hormone, 17β-estradiol or vehicle. Other cohorts of C57BL/6N mice were fed diets varying in calcium or phosphate content. Expression of Memo1 and control genes was assessed by qPCR. 1,25(OH)2 -vitamin D3 caused an acute decrease in Memo1 transcript levels in vitro, but not in vivo. None of the hormones tested had an influence on Memo1 transcripts, whereas the assessed control genes reacted the expected way. Dietary interventions with calcium and phosphate did not affect Memo1 transcripts but altered the chosen control genes' expression. We observed that Memo1 was not regulated by calciotropic hormones or change in mineral load, suggesting major differences between the regulation and physiological roles of Klotho, Fgf23, and Memo1.

Short- and Long-term Effects of Dialysate Calcium Concentrations on Mineral and Bone Metabolism in Hemodialysis Patients: The K4 Study

RATIONALE & OBJECTIVE

The short- and long-term impact of conversion of dialysate calcium concentration from either 2.5 or 3.0 mEq/L to 2.75 mEq/L on mineral and bone metabolism remains unknown in hemodialysis patients.

STUDY DESIGN

Nonrandomized intervention study.

SETTING & POPULATION

12 hemodialysis patients treated at baseline with a 2.5-mEq/L dialysate calcium concentration and another 12 hemodialysis patients treated with a 3.0-mEq/L dialysate calcium concentration.

INTERVENTION

Use of 2.75-mEq/L dialysate calcium concentration.

OUTCOMES

Changes in intradialytic calcium and phosphate clearance and changes in predialysis and intradialytic serum and ionized mineral and biochemical parameters over the 24 weeks following dialysate calcium conversion.

RESULTS

Conversion of dialysate calcium concentration from 2.5 to 2.75 mEq/L increased intradialytic calcium loading and serum total and ionized calcium levels, whereas conversion of dialysate calcium from 3.0 to 2.75 mEq/L decreased intradialytic calcium loading and serum total and ionized calcium levels. Dialysate calcium concentration conversion did not affect intradialytic serum parathyroid hormone level, intradialytic phosphate elimination, or predialysis serum calcium, phosphate, parathyroid hormone, and fibroblast growth factor 23 levels. Intradialytic calcium influx was determined by dialysate calcium concentration and predialysis serum calcium levels, whereas intradialytic phosphate elimination was determined by predialysis serum phosphate levels.

LIMITATIONS

Small sample size and no control groups treated with 2.5- and 3.0-mEq/L dialysate calcium concentrations during the 24 weeks of the observation period.

CONCLUSIONS

Conversion of dialysate calcium concentration from either 3.0 or 2.5 to 2.75 mEq/L results in expected changes in calcium loading based on predialysis calcium concentration. The dialysate calcium concentration should be personalized based on clinical factors.

FUNDING

None.

TRIAL REGISTRATION

University Hospital Medical Information Network, www.umin.ac.jp/english/, R000040105, UMIN000035184.

Regulation of fibroblast growth factor 23 (FGF23) in health and disease

Fibroblast growth factor 23 (FGF23) is mainly produced in the bone and, upon secretion, forms a complex with a FGF receptor and coreceptor αKlotho. FGF23 can exert several endocrine functions, such as inhibiting renal phosphate reabsorption and 1,25-dihydroxyvitamin D3 production. Moreover, it has paracrine activities on several cell types, including neutrophils and hepatocytes. Klotho and Fgf23 deficiencies result in pathologies otherwise encountered in age-associated diseases, mainly as a result of hyperphosphataemia-dependent calcification. FGF23 levels are also perturbed in the plasma of patients with several disorders, including kidney or cardiovascular diseases. Here, we review mechanisms controlling FGF23 production and discuss how FGF23 regulation is perturbed in disease.