Article
Reference
Fibroblast growth factor 23 and markers of mineral metabolism in individuals with preserved renal function
DHAYAT, Nasser A, et al.
Abstract
Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that regulates phosphate homeostasis. Circulating FGF23 is elevated in chronic kidney disease (CKD) and independently associated with poor renal and cardiovascular outcomes and mortality.
Because the study of FGF23 in individuals with normal renal function has received little attention, we examined in a large, population-based study of 1128 participants the associations of FGF23 with markers of mineral metabolism and renal function. The median estimated glomerular filtration rate (eGFR) of the cohort was 105 ml/min per 1.73 m(2), and the median plasma FGF23 was 78.5 RU/ml. FGF23 increased and plasma 1,25-dihydroxyvitamin D3 decreased significantly below an eGFR threshold of 102 and 99 ml/min per 1.73 m(2), respectively. In contrast, plasma parathyroid hormone increased continuously with decreasing eGFR and was first significantly elevated at an eGFR of 126 ml/min per 1.73 m(2). On multivariable analysis adjusting for sex, age, body mass index, and GFR, FGF23 was negatively associated with 1,25-dihydroxyvitamin D3, and urinary absolute and fractional calcium [...]
DHAYAT, Nasser A, et al . Fibroblast growth factor 23 and markers of mineral metabolism in individuals with preserved renal function. Kidney International , 2016, vol. 90, no. 3, p.
648-657
DOI : 10.1016/j.kint.2016.04.024 PMID : 27370409
Available at:
http://archive-ouverte.unige.ch/unige:89458
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1 / 1
see commentary on page 477
Fibroblast growth factor 23 and markers of mineral metabolism in individuals with preserved
renal function
Nasser A. Dhayat
1,10,11, Daniel Ackermann
1,11, Menno Pruijm
2, Belen Ponte
3, Georg Ehret
4, Idris Guessous
5,6, Alexander Benedikt Leichtle
7,11, Fred Paccaud
6, Markus Mohaupt
1, Georg-Martin Fiedler
7,11, Olivier Devuyst
8, Antoinette Peche`re-Bertschi
9, Michel Burnier
2,11, Pierre-Yves Martin
3, Murielle Bochud
6, Bruno Vogt
1,11and Daniel G. Fuster
1,10,111Department of Nephrology, Hypertension, and Clinical Pharmacology, Bern University Hospital, University of Bern, Bern, Switzerland;
2Nephrology Service, University Hospital of Lausanne, Lausanne, Switzerland;3Nephrology Service, Department of Specialties of Internal Medicine, University Hospital of Geneva, Geneva, Switzerland;4Cardiology Service, Department of Specialties of Internal Medicine, University Hospital of Geneva, Geneva, Switzerland;5Department of Community Medicine, Primary Care and Emergency Medicine, University Hospital of Geneva, Geneva, Switzerland;6Institute of Social and Preventive Medicine, University Hospital of Lausanne, Lausanne, Switzerland;7Department of Laboratory Medicine, Bern University Hospital, University of Bern, Bern, Switzerland;8Institute of Physiology, University of Zurich, Zurich, Switzerland;9Endocrinology Service, Department of Internal Medicine Specialties, University Hospital of Geneva, Geneva, Switzerland;10Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland; and
11Department of Clinical Research, University of Bern, Bern, Switzerland
Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that regulates phosphate homeostasis. Circulating FGF23 is elevated in chronic kidney disease (CKD) and independently associated with poor renal and
cardiovascular outcomes and mortality. Because the study of FGF23 in individuals with normal renal function has received little attention, we examined in a large, population- based study of 1128 participants the associations of FGF23 with markers of mineral metabolism and renal function. The median estimated glomerularfiltration rate (eGFR) of the cohort was 105 ml/min per 1.73 m2, and the median plasma FGF23 was 78.5 RU/ml. FGF23 increased and plasma 1,25- dihydroxyvitamin D3 decreased significantly below an eGFR threshold of 102 and 99 ml/min per 1.73 m2, respectively.
In contrast, plasma parathyroid hormone increased continuously with decreasing eGFR and wasfirst
significantly elevated at an eGFR of 126 ml/min per 1.73 m2. On multivariable analysis adjusting for sex, age, body mass index, and GFR, FGF23 was negatively associated with 1,25-dihydroxyvitamin D3, and urinary absolute and fractional calcium excretion but not with serum calcium or parathyroid hormone. We found a positive association of FGF23 with plasma phosphate, but no association with urinary absolute or fractional phosphate excretion and, unexpectedly, a positive association with tubular maximum phosphate reabsorption/GFR. Thus, in the absence of CKD, parathyroid hormone increases earlier than FGF23 when the eGFR decreases. The increase in FGF23 occurs at a higher
eGFR threshold than previously reported and is closely associated with a decrease in 1,25-dihydroxyvitamin D3. We speculate that the main demonstrable effect of FGF23 in the setting of preserved renal function is suppression of 1,25-dihydroxyvitamin D3 rather than stimulation of renal phosphate excretion.
Kidney International(2016)90,648–657;http://dx.doi.org/10.1016/
j.kint.2016.04.024
KEYWORDS: calcium; FGF23; phosphate; PTH; TmP/GFR
Copyright ª 2016, International Society of Nephrology. Published by Elsevier Inc. All rights reserved.
F
ibroblast growth factor 23 (FGF23) is a hormone secreted by osteocytes in the bone in response to dietary phosphate loading or an increase in 1,25-dihydroxyvitamin D3.1 Binding of FGF23 to its coreceptor klotho increases the affinity of FGF23 for ubiquitously expressed FGF receptors. Klotho is mainly expressed in the kidney, brain, and parathyroid gland and thus is responsible for the cellular specificity of FGF23 action. FGF23 induces phosphaturia by downregulation of proximal tubular NaPi-IIa and -IIc transporters, reduces 1,25-dihydroxyvitamin D3by downregulation of 1-a
hydroxy-lase and upregulation of 24-hydroxylase, and suppresses para- thyroid hormone (PTH) secretion.1 In healthy individuals, when phosphate intake is high and sustained, FGF23 levels rise, leading to increased phosphaturia and downregulation of calcitriol synthesis, thereby limiting phosphate absorption, with the net result of negative external phosphate balance.2In chronic kidney disease (CKD), levels of FGF23 increase, pre- sumably to maintain phosphate balance as an adaptive response in the setting of decreased klotho levels and reduced renal excretory capacity for phosphate. As the glomerularfiltration rate (GFR) decreases, levels of FGF23 rise progressively and to very high levels.3 Increased FGF23 is independently
Correspondence: D.G. Fuster, Division of Nephrology, Hypertension, and Clinical Pharmacology, Bern University Hospital, Freiburgstrasse 15, 3010 Bern, Switzerland. E-mail:Daniel.Fuster@ibmm.unibe.ch
Received 30 December 2015; revised 21 April 2016; accepted 28 April 2016; published online 28 June 2016
c l i n i c a l i n v e s t i g a t i o n w w w . k i d n e y - i n t e r n a t i o n a l . o r g
648 Kidney International(2016)90,648–657
associated with poor renal and cardiovascular outcomes, left ventricular hypertrophy, and mortality in CKD patients.3–6 The highest FGF23 levels are found in patients on dialysis. In a large prospective study following incipient dialysis patients, high FGF23 was independently associated with increased mortality.7
In contrast to CKD patients, the study of FGF23 in in- dividuals with normal renal function has received much less attention so far. Studies assessing the role of FGF23 in non- CKD patients have been restricted to specialized subgroups of individuals and/or limited by the mineral metabolism analyte phenotype available.8–11 Thus, although much has been learned about FGF23 pathophysiology by the investi- gation of CKD patients in the past years, critical questions about the physiological role of FGF23 under normal renal function remain unanswered. To obtain more insight into FGF23 physiology, we conducted a cross-sectional analysis of markers of mineral metabolism in a large, multicenter, population-based cohort in Switzerland.
RESULTS
Characteristics of the study population
From December 2009 to March 2013, 1128 participants were recruited in the SKIPOGH (Swiss Kidney Project on Genes in Hypertension) study. Inclusion and exclusion criteria and study details are provided in the Methods section.
Demographic and anthropometric characteristics of the 1010 individuals who were included in thefinal analysis are shown inTable 1. The meanSD age of the cohort was 45.516.9 years; 47.4% of participants were men. The median eGFRcr-cys (Creatinine-Cystatin C Equation CKD-EPI [2012]) was 105.1 (interquartile range, 95.1–115.2) ml/min per 1.73 m2. Only 1.2% of the study population had an
eGFR <60 ml/min per 1.73 m2, which is one widely used
definition of CKD.12–15The distribution of plasma FGF23 was right skewed with a median level of 78.5 relative units/ml (interquartile range, 62.8–103.4), which is similar to FGF23 levels reported previously in healthy individuals10 but is significantly lower than in CKD patients.16
Mineral metabolism parameters in relation to eGFR
We next stratified the cohort into groups of descending eGFRcr-cys values to assess the association of mineral meta- bolism parameters with renal function. There was a gradual increase in mean age and body mass index (BMI) with decreasing eGFR (Table 2). Consistent with previous reports, urine fractional excretion of phosphate (FEPi) increased, the ratio of tubular maximum reabsorption of phosphate (TmP) to GFR (TmP/GFR) decreased, and 24-hour urinary phos- phate excretion decreased with decreasing eGFR (Table 2).16–18 Interestingly, alterations in plasma PTH, FGF23, and 1,25- dihydroxyvitamin D3 were already evident in the normal eGFR range. In the eGFR subgroup of 110 to 119.9 ml/min per 1.73 m2, plasma PTH was already significantly increased compared with the eGFR subgroup$120 ml/min per 1.73 m2. A first increase of plasma FGF23 was evident in the
eGFR subgroup of 100 to 109.9 ml/min per 1.73 m2; plasma 1,25-dihydroxyvitamin D3wasfirst significantly reduced in the eGFR subgroup of 90 to 99.9 ml/min per 1.73 m2. A similar pattern with an earlier increase in plasma PTH than FGF23 was observed when the cohort was stratified into groups of Table 1 | Baseline characteristics of the study population
Characteristics N All participants
Male 479 47.4%
Age, yr 1010 45.516.9
Body mass index, kg/m2 1009 24.0 (21.627.1)
Current smoker 251 24.9%
Systolic blood pressure, mm Hg 925 114.714.4 Diastolic blood pressure, mm Hg 925 73.89.3
Hypertension 176 17.4%
Diabetes 38 3.8%
Assessment of renal function
Creatinine,mmol/l 1003 73.513.9
Cystatin C, mg/l 923 0.7380.126
eGFRcr, ml/min per 1.73 m2BSA 1003 98.2 (87.0109.9) eGFRcr subgroups
3880 148 14.8%
8090 157 15.7%
90100 238 23.7%
100110 211 21.0%
110120 147 14.7%
>120 102 10.2%
eGFRcr-cys, ml/min per 1.73 m2BSA 916 105.1 (95.1115.2) eGFRcr-cys subgroups
4080 69 7.5%
8090 75 8.2%
90100 189 20.6%
100110 238 26.0%
110120 226 24.7%
>120 119 13.0%
Creatinine clearance, ml/min per 1.73 m2BSA
921 114.025.6 Creatinine clearance subgroups
4680 74 8.0%
8090 84 9.1%
90100 108 11.7%
100110 156 16.9%
110120 142 15.4%
120130 113 12.3%
130140 114 12.4%
>140 130 14.1%
Blood values
FGF23, RU/ml 1010 78.5 (62.8103.4)
PTH, pg/ml 1007 36.9 (29.444.7)
25-OH-vitamin D3, nmol/l 1006 47.0 (34.062.0) 1,25-diOH-vitamin D3, pmol/l 941 91.0 (70.0116.0)
Phosphate, mmol/l 1001 1.050.17
Calcium corrected, mmol/l 1002 2.330.09 Urine values
Phosphaturia, mmol/24 hr 976 25.3 (20.332.1) Fractional excretion of phosphate, % 968 16.5 (12.920.9)
TmP/GFR, mmol/l 968 0.868 (0.7520.996)
Calciuria, mmol/24 hr 972 3.68 (2.475.23) Fractional excretion of calcium, % 967 1.76 (1.102.68) BSA, body surface area; eGFR, estimated glomerularfiltration rate; eGFRcr, creatinine Equation CKD-EPI 2009; eGFRcr-cys, creatinine-cystatin C Equation CKD-EPI 2012;
FGF23,fibroblast growth factor 23; 1,25-diOH-vitamin D3, 1,25-dihydroxyvitamin D3; 25OH-VitD3, 25-hydroxyvitamin D3; PTH, parathyroid hormone; RU, relative unit;
TmP/GFR, ratio of tubular maximum reabsorption of phosphate to glomerular filtration rate.
The number of participants is indicated for each characteristic. Categorical variables are reported as percentage and continuous variables as the meanSD or the median (25th75th percentile).
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Kidney International(2016)90,648–657 649
Table 2 | Characteristics according to eGFRcr-cys (creatinine-cystatin C equation CKD-EPI 2012) subgroups
Characteristics N
eGFR
‡120 N
eGFR
110–119.9 N
eGFR
100–109.9 N
eGFR
90–99.9 N
eGFR
80–89.9 N
eGFR
<80
Age, yr 119 25.86.9*†‡§k 226 35.710.5*†‡§ 238 45.112.8*†‡ 189 55.912.8*† 75 62.611.1* 69 67.511.8
Body mass index, kg/m2 119 22.6 (20.8–24.8)†‡§k 226 23.2 (20.9–26)†‡§ 238 23.8 (21.8–26.7)*†‡ 188 26 (22.7–29) 75 25.5 (23.5–28.2) 69 26.3 (23.8–29.7) Assessment of renal
function
eGFRcr, ml/min per 1.73 m2BSA
119 123.3 (118.9–127.7)*†‡§k 226 109.3 (104.7–113.1)*†‡§ 238 97.8 (94.2–101.4)*†‡ 189 87.3 (82–92.3)*† 75 77.5 (72.3–81.8)* 69 64.3 (58.6–70.1) eGFRcr-cys, ml/min
per 1.73 m2BSA
119 124.8 (122.4–128.6)*†‡§k 226 115 (112.2–117.5)*†‡§ 238 104.9 (102.5–107.3)*†‡ 189 95.6 (93.1–97.5)*† 75 85.9 (83.6–87.2)* 69 72.8 (65.6–75.7) Creatinine clearance
corrected, ml/min per 1.73 m2BSA
98 14024.1*†‡§k 205 12721.3*†‡§ 221 116.519.2*†‡ 178 106.517.8*† 72 93.817.3* 68 76.416.4
Blood values
FGF23, RU/ml 119 69.7 (56.8–92.7)†‡§k 226 73.6 (58.5–91.8)*†‡§ 238 77.8 (62.4–103.6)‡ 189 84 (67.8–106.5)† 75 90 (75.6–106.2) 69 100.7 (79.8–123.1) PTH, pg/ml 117 32.4 (25.8–39.9)*†‡§k 226 34.1 (27.7–42.6)†‡§ 238 35 (28.6–43.9)*‡ 188 40.1 (33.1–46.9)† 75 39.2 (30.4–46.4)* 69 46.7 (37.9–54.8) 25-OH-vitamin D3,
nmol/l
117 54 (34–64) 226 46.5 (34.3–62) 237 48 (34–65) 188 45 (33–55) 75 45 (34–59) 69 42 (33–57)
1,25-diOH-vitamin D3, pmol/l
109 95 (72–118)‡§k 209 100 (76–124)†‡§ 232 95 (74–118)*‡ 181 84 (67–101)† 71 86 (67.5–106)* 65 74 (56–96)
Phosphate, mmol/l 119 1.080.17 226 1.050.17 237 1.050.16 189 1.040.16 75 1.040.17 69 1.050.18
Calcium corrected, mmol/l
119 2.330.09 226 2.310.09 238 2.330.09 188 2.330.08 75 2.320.1 69 2.350.11
Urine values
Phosphaturia, mmol/
24 h
113 29 (23–34.9)*†‡§k 218 26.7 (20.9–32.8)†‡§ 233 25.4 (21–32.5)*†‡ 181 24.6 (19.4–29.9)† 72 23.5 (18.4–27.3) 66 22 (16.8–25.1) Fractional excretion of
phosphate, %
114 14.5 (11.9–20.1)†§k 218 15.5 (12.1–20.5)‡§ 232 16.7 (13.3–19.9)‡ 181 16.3 (12.8–20.4)† 72 17.7 (14.6–21.2)* 66 20.4 (16.3–25.8) TmP/GFR, mmol/l 114 0.89 (0.78–1.06)k 218 0.87 (0.77–1.02) 232 0.89 (0.75–1.01) 181 0.87 (0.75–0.98) 72 0.85 (0.75–0.97) 66 0.83 (0.73–0.96) Calciuria, mmol/24 h 113 4.32 (2.62–5.85)k 217 3.8 (2.61–5.17)§ 231 3.77 (2.59–5.82)‡ 181 3.75 (2.36–5.24)† 71 3.63 (2.42–4.49)* 67 2.69 (1.55–3.46) Fractional excretion of
calcium, %
113 1.28 (0.76–2.09)†‡§k 217 1.62 (0.94–2.3)*†‡§ 231 1.75 (1.16–2.75)†‡ 180 1.91 (1.1–3.09) 74 2.46 (1.41–3.24) 67 2.16 (1.38–3.32)
1,25-diOH-vitamin D3,1,25-dihydroxyvitamin D3; 25OH-VitD3, 25-hydroxyvitamin D3; ANOVA, analysis of variance; BSA, body surface area; CKD-EPI, Chronic Kidney Disease Epidemiology Collaboration; eGFRcr, estimated glomerular
filtration rate using creatinine; eGFRcr-cys, estimated glomerularfiltration rate using the combination of creatinine and cystatin C; FGF23,fibroblast growth factor 23; PTH, parathyroid hormone; GFR, glomerularfiltration rate;
h, hour; TmP/GFR, ratio of tubular maximum resorption of phosphate to glomerularfiltration rate; yr, year.
The number of individuals is indicated for each characteristic stratified by eGFRcr-cys subgroups. Continuous variables are indicated by their meanSD or by their median (25th–75th percentile). Between-group differences are
determined by 1-way ANOVA (Welch) not assuming equal variances. If null hypothesis was rejected, pairwise comparisons of the eGFRcr-cys subgroups were performed usingttests with pooled SD and alpha error adjustment by
the method of Benjamini-Hochberg.
*P<0.05 compared with eGFRcr-cys subgroup 1 level lower.
†P<0.05 compared with eGFRcr-cys subgroup 2 levels lower.
‡P<0.05 compared with eGFRcr-cys subgroup 3 levels lower.
§P<0.05 compared with eGFRcr-cys subgroup 4 levels lower.
kP<0.05 compared with eGFRcr-cys subgroup 5 levels lower.
clinicalinvestigationNADhayatetal.:FGF23inindividualswithnormalrenalfunction
650KidneyInternational(2016)90,648–657
decreasing eGFRcr (creatinine equation CKD-EPI 2009) values (Supplementary Table S1) or creatinine clearance (Supplementary Table S2).
When plotting plasma FGF23 versus eGFRcr-cys using a quadratic spline function, the increase in log-transformed plasma FGF23 became significant at an eGFR of 102.3 ml/min per 1.73 m2(Figure 1a). This threshold represents the highest eGFR at which the 95% confidence interval (CI) for log plasma FGF23 did not overlap anymore with the 95% CI of log plasma FGF23 at any higher eGFR. Using the same approach, we observed a significant decrease in plasma 1,25- dihydroxyvitamin D3at an eGFRcr-cys threshold of 99.3 ml/
min per 1.73 m2(Figure 1b) and an increase in plasma PTH at an eGFRcr-cys of 126.3 ml/min per 1.73 m2 (Figure 1c).
An increasing plasma PTH was also the earliest sign of altered mineral metabolism when GFR was estimated by eGFRcr (Supplementary Figure S1) or by creatinine clearance (Supplementary Figure S2).
Mineral metabolism parameters in relation to 25- hydroxyvitamin D3status
The 25-hydroxyvitamin D3 status was shown previously to influence relative increases in PTH and FGF23 in patients with stage 3 CKD.19 To study the impact of plasma 25- hydroxyvitamin D3 on mineral metabolism parameters in individuals with preserved renal function, we divided our cohort into quartiles of plasma 25-hydroxyvitamin D3status (Table 3). Compared with individuals in the lowest plasma 25-hydroxyvitamin D3 quartile, individuals in the highest plasma 25-hydroxyvitamin D3 quartile were younger, had a lower BMI, a lower PTH level, a higher plasma 1,25- dihydroxyvitamin D3 level, higher plasma phosphate and plasma calcium levels, and higher absolute and fractional calciuria, but did not differ in GFR, plasma FGF23, absolute or fractional phosphaturia, or TmP/GFR.
To assess the role of plasma 25-hydroxyvitamin D3on the increase in plasma FGF23 and PTH with decreasing GFR, we
rebuiltFigure 1, adjusting for plasma 25-hydroxyvitamin D3. As shown inSupplementary Figure S3, even after adjustment for plasma 25-hydroxyvitamin D3 status, plasma PTH in- creases significantly earlier than plasma FGF23.
Association analyses
We next performed univariable association analyses of plasma FGF23 by mixed-effects linear regression models, taking family, center, and day of blood sampling as random effects into account (Table 4, model 1). The strongest negative correlate of plasma FGF23 was plasma 1,25-dihydroxyvitamin D3(linear
b
:0.00312,P<0.001; quadraticb
: 2.1105, P¼0.026). In addition, plasma FGF23 correlated positively with plasma phosphate (b
: 0.32701, P<0.001) and plasma PTH (b
: 0.002768,P¼0.014) and negatively with plasma 25- hydroxyvitamin D3 (linearb
: 0.00204, P ¼ 0.0079;quadratic
b
: 3.2 105, P ¼ 0.084). As expected, renal function was strongly negatively associated with plasma FGF23: eGFRcr (linearb
:0.004281,P<0.001; quadraticb
:8.2 105, P < 0.011), eGFRcr-cys (linear
b
: 0.005687, P<0.001; quadraticb
: 7.4105,P ¼0.053), and creati- nine clearance (linearb
:0.002939,P<0.001, quadraticb
:5.0 105, P ¼ 0.001). Interestingly, we observed also an inverse association of plasma FGF23 with urinary calcium excretion (linear
b
: 0.042465, P < 0.001; quadraticb
:0.005725, P ¼ 0.0016), and fractional calcium excretion (
b
: 0.02251, P ¼ 0.059), but no association with plasma calcium (b
: 0.24939, P ¼ 0.14). There was no significant association of plasma FGF23 with 24-hour urinary phosphate excretion or FEPi, but surprisingly a positive association with TmP/eGFR (b
: 0.20217,P¼0.0091).We then conducted a multivariable analysis taking family, center, and calendar day of blood sampling as random effects into account and adjusting for sex, age, BMI, and GFR (Table 4). GFR was approximated as eGFRcr (model 2) or eGFRcr-cys (model 3) or measured creatinine clearance (model 4). After adjustment, plasma 1,25-dihydroxyvitamin
Figure 1 | Quadratic spline functions of the associations of eGFRcr-cys (creatinine-cystatin C equation CKD-EPI 2012) with log- transformed plasmafibroblast growth factor 23 (FGF23) (a), with square-root transformed plasma 1,25-dihydroxyvitamin D3(b) and log-transformed plasma parathyroid hormone (PTH) (c).The shaded areas represent 95% confidence intervals for thefitted splines. The dotted lines represent the highest estimated glomerularfiltration rate (eGFR) at which the 95% confidence intervals of thefitted splines do not overlap anymore. RU, relative unit.
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Kidney International(2016)90,648–657 651
D3 remained the factor most strongly negatively associated with plasma FGF23 in all models, followed by 24-hour uri- nary calcium excretion, fractional calcium excretion, and plasma 25-hydroxyvitamin D3. Similarly, the positive associ- ation of plasma phosphate with plasma FGF23 persisted in all models of GFR approximations. In contrast, however, plasma PTH was no longer associated with plasma FGF23 after multivariable analysis, and the association with plasma cal- cium remained nonsignificant. Again, we detected no asso- ciation of plasma FGF23 with FEPi or 24-hour urinary phosphate excretion, but the positive association of plasma FGF23 with TmP/GFR remained significant.
DISCUSSION
We performed a thorough analysis of markers of calcium and phosphate metabolism in a population-based cohort of 1128 adult individuals, with the majority of them having preserved renal function. To our knowledge, this is the largest observational study of this kind with such a detailed phenotype. Although the study partly corroborates previous work, it reveals some disparate results and several very important novelfindings. In individuals with preserved renal function, plasma FGF23 correlates strongly and inversely with plasma 1,25-dihydroxyvitamin D3 and changes in plasma FGF23 and 1,25-dihydroxyvitamin D3 occur at a much higher GFR than previously reported.11,16 Plasma
FGF23 also correlates weakly negatively with plasma 25- hydroxyvitamin D3, suggesting that FGF23 may stimulate Cyp24A1-mediated inactivation of 25-hydroxyvitamin D3to 24,25-hydroxyvitamin D3.20,21
In line with a previous study in CKD patients, we found that plasma PTH levels are also affected by plasma 25-hydroxyvitamin D3 status in individuals with preserved renal function.19In addition, our data strongly indicate that increasing plasma PTH is the earliest sign of altered mineral metabolism when GFR decreases, well before the onset of CKD and independent of plasma 25-hydroxyvitamin D3 sta- tus. This finding is in apparent contradiction to an earlier large cohort study that reported that FGF23 becomes increased earlier than PTH in the course of CKD.16However, there are significant differences between the 2 cohorts that may explain some of the discrepancies. Our cohort consists of mostly healthy individuals without CKD (only 1.2 % with an
eGFR <60 ml/min per 1.73 m2), whereas in the CRIC
(Chronic Renal Insufficiency Cohort) study, 89.5% of par- ticipants had an eGFR <60 ml/min per 1.73 m2.16,22 Signif- icant differences between the 2 cohorts also exist with respect to comorbidities and ethnicity of participants.16,22 Thus, although plasma PTH increases clearly earlier than plasma FGF23 when GFR decreases in healthy individuals of Euro- pean ancestry, additional studies are needed to assess the generalizability of ourfindings.
Table 3 | Characteristics according to 25-hydroxyvitamin D3quartiles
Characteristics N
25OH-VitD3
>62 nmol/l N
25OH-VitD3
47–62 nmol/l N
25OH-VitD3
34–47 nmol/l N
25OH-VitD3
<34 nmol/l
Age, yr 255 41.716.8*†‡ 252 45.916.3 253 46.617.5 246 48.116.5
Body mass index, kg/m2 254 22.6 (21.1–25)*†‡ 252 24.2 (21.8–27.2)† 253 24.6 (21.7–27.1)* 246 25.2 (22.4–28.9) Assessment of renal function
eGFRcr, ml/min per 1.73 m2BSA 253 100 (89.5–110.8) 252 97.9 (84.3–110.3) 252 97.7 (86–109.6) 242 97.5 (87.6–108.3) eGFRcr-cys, ml/min per 1.73 m2BSA 225 106.9 (98.5–116.4) 231 104.7 (94.8–115.5) 233 103.8 (93.2–114.8) 223 103 (94.7–114) Creatinine clearance corrected, ml/
min per 1.73 m2BSA
232 112.324.2 231 113.625 232 116.526.3 222 113.426.6
Blood values
FGF23, RU/ml 255 78.7 (62.7–102.2) 252 79.5 (65.8–101.7) 253 75.5 (59.7–99.8)* 246 82.8 (64.4–113.1) PTH, pg/ml 255 31.4 (26.3–38.1)*†‡ 252 34.6 (28.6–42.5)*† 253 39 (32–45.6)* 246 43.3 (34.1–54.8) 25-OH-Vitamin D3, nmol/l 255 73 (66.5–82)*†‡ 252 54 (50–57)*† 253 40 (37–43)* 246 24 (20–29) 1,25-diOH-Vitamin D3, pmol/l 234 100.5 (80–125.8)*†‡ 233 93 (76–117)† 240 92 (72–113.3)* 231 78 (60–101)
Phosphate, mmol/l 253 1.070.17†‡ 251 1.060.17 251 1.030.15 242 1.020.16
Calcium corrected, mmol/l 253 2.340.08‡ 251 2.330.1 252 2.320.09 242 2.320.09
Urine values
Phosphaturia, mmol/24 h 248 24.4 (19.3–32) 244 25.5 (20.6–31.5) 245 25.5 (21.1–32.2) 235 25.8 (20.1–32.1) Fractional excretion of phosphate, % 246 0.2 (0.1–0.2) 243 0.2 (0.1–0.2) 244 0.2 (0.1–0.2) 231 0.2 (0.1–0.2) TmP/GFR, mmol/l 246 0.89 (0.78–1.02) 243 0.88 (0.76–1.01) 244 0.85 (0.75–0.97) 231 0.86 (0.75–0.98) Calciuria, mmol/24 h 247 3.76 (2.58–5.55)‡ 243 3.97 (2.85–5.27)† 243 3.6 (2.3–5.12) 235 3.38 (2.12–5.09) Fractional excretion of calcium, % 245 1.91 (1.25–2.76)†‡ 243 1.8 (1.23–2.84)† 243 1.69 (1.03–2.56) 232 1.57 (0.88–2.5) 1,25-diOH-vitamin D3,1,25-dihydroxyvitamin D3; 25OH-VitD3, 25-hydroxyvitamin D3; ANOVA, analysis of variance; BSA, body surface area; CKD-EPI, Chronic Kidney Disease Epidemiology Collaboration; eGFRcr, estimated glomerularfiltration rate using creatinine; eGFRcr-cys, estimated glomerularfiltration rate using the combination of creatinine and cystatin C; FGF23,fibroblast growth factor 23; PTH, parathyroid hormone; GFR, glomerularfiltration rate; h, hour; TmP/GFR, ratio of tubular maximum resorption of phosphate to glomerularfiltration rate; yr, year.
The number of participants is indicated for each characteristic stratified by 25-hydroxyvitamin D3quartiles. Continuous variables are indicated by their meanSD or by their median (25th–75th percentile). Between-group differences are determined by 1-way ANOVA (Welch) not assuming equal variances. If null hypothesis was rejected, pairwise comparisons of the subgroups were performed usingttests with pooled SD and alpha error adjustment by the method of Benjamini-Hochberg.
*P<0.05 compared with 25-hydroxyvitamin D3subgroup 1 level lower.
†P<0.05 compared with 25-hydroxyvitamin D3subgroup 2 levels lower.
‡P<0.05 compared with 25-hydroxyvitamin D3subgroup 3 levels lower.
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652 Kidney International(2016)90,648–657
Table 4 | Associations between log-transformed plasma FGF23, as dependent variable, with basic demographic and plasma and urinary parameters of calcium phosphate metabolism as predictor variables
Predictor variable
Model 1 Model 2 Model 3 Model 4
N b 95% CI valueP N b 95% CI valueP N b 95% CI valueP N b 95% CI valueP
Age, y Linear 1010 0.00416 0.00252–
0.00583
<0.001 1002 0.00265 0.00015– 0.00534
<0.05 915 0.00007 0.00254 to 0.0028
0.96 921 0.00284 0.00089– 0.00492
<0.01
Quadratic 0.00010 0.00021 to
0.00001
0.067 0.00012 0.00023 to 0.00001
<0.05
Sex, women Linear 1010 0.07716 0.02086–
0.13264
<0.01 1002 0.06948 0.01262– 0.12562
<0.05 915 0.04779 0.01265 to 0.10753
0.12 921 0.06208 0.00307– 0.12121
<0.05
BMI, kg/m2 Linear 1009 0.00399 0.00269 to
0.01059
0.24 1002 0.00005 0.00717 to 0.00691
0.99 915 0.00085 0.00823 to 0.00637
0.82 921 0.00082 0.0064 to 0.00777
0.82 Assessment of
renal function eGFRcr, ml/min per 1.73 m2BSA
Linear 1003 0.00428 0.00591 to 0.00259
<0.001 1002 0.00210 0.00455 to 0.00056
0.104
Quadratic 0.00008 0.00002–
0.00015
<0.05 0.00013 0.00006–
0.0002
<0.001 eGFRcr-cys, ml/
min per 1.73 m2 BSA
Linear 916 0.00569 0.00771 to 0.00361
<0.001 915 0.00549 0.00859 to
0.00225
<0.001
Quadratic 0.00007 0 to 0.00015 0.053 0.00012 0.00003–
0.0002
<0.01
Creatinine clearance corrected, ml/min per 1.73 m2BSA
Linear 921 0.00294 0.00409 to 0.0017
<0.001 921 0.00180 0.00309 to
0.00037
<0.01
Quadratic 0.00005 0.00002–
0.00008
<0.001 0.00004 0.00001–
0.00007
<0.01
Blood values
PTH, pg/ml Linear 1007 0.00277 0.00059–
0.00499
<0.05 999 0.00082 0.00155 to 0.00322
0.50 912 0.00008 0.00239 to 0.00259
0.95 918 0.00089 0.00153 to 0.00335
0.47 25-OH-vitamin
D3, nmol/l
Linear 1006 0.00204 0.00353 to 0.00052
<0.01 998 0.00200 0.00351 to 0.00044
<0.05 911 0.00148 0.00288 to 0.00004
<0.05 917 0.00164 0.00305 to 0.00018
<0.05
Quadratic 0.00003 0.084 0.00003 0–0.00007 0.085
1,25-diOH vitamin D3, pmol/l
Linear 941 0.00312 0.00408 to 0.00218
<0.001 934 0.00297 0.00397 to 0.002
<0.001 866 0.00253 0.00352 to 0.0016
<0.001 858 0.00310 0.00413 to 0.00209
<0.001
Quadratic 0.00002 0–0.00004 <0.05 0.00002 0–0.00004 <0.05 0.00002 0.00001–
0.00004
<0.05
Phosphate, mmol/l
Linear 1001 0.32701 0.15639–
0.50727 <0.001 1000 0.33620 0.15815–
0.52269 <0.001 914 0.31000 0.12398–
0.50134 <0.01 919 0.35740 0.17323–
0.55234 <0.001 Calcium
corrected, mmol/l
Linear 1002 0.24939 0.0723– 0.60622
0.14 1001 0.18370 0.1372– 0.55068
0.28 914 0.07364 0.26377– 0.45544
0.68 920 0.14470 0.18285– 0.52334
0.40
Urine values Phosphaturia,
mmol/24 hr
Linear 976 0.00218 0.00518 to 0.00088
0.16 968 0.00165 0.00178 to 0.00517
0.35 882 0.00269 0.00087 to 0.00634
0.14 911 0.00406 0.00034 to 0.00836
0.07 Fractional
excretion of phosphate, %
Linear 968 0.00067 0.00578 to 0.00407
0.79 967 0.00235 0.00798 to 0.003
0.40 882 0.00357 0.00939 to 0.00205
0.22 909 0.00295 0.00877 to 0.00265
0.31
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NADhayatetal.:FGF23inindividualswithnormalrenalfunctionclinicalinvestigation
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Although there was a clear association of plasma FGF23 with plasma phosphate, we found no association of plasma FGF23 with FEPi but a positive association of plasma FGF23 with TmP/GFR. This is an unexpected and surprisingfinding for a hormone that is considered the prototype of a phos- phatonin. FEPi is less sensitive than TmP/GFR for the detection of alterations in renal phosphate handling (despite the exact same input terms), thus a weak association of plasma FGF23 with FEPi may be missed, but a bona fide phosphatonin should decrease (and not increase) TmP/GFR.
However, the observation of a positive association of FGF23 with TmP/GFR at a high GFR is not an unprecedentedfinding and has been reported by other investigators using both intact and C-terminal FGF23 assays.23–26 Plasma phosphate and tubular reabsorption of phosphate (TRP) are the 2 parame- ters used for TmP/GFR estimation. Given the strong positive association of plasma FGF23 with plasma phosphate and the lack of an association with FEPi (which is equal to 1TRP), it is evident that plasma phosphate is driving the positive association of plasma FGF23 with TmP/GFR in the calcula- tion. Elevated plasma phosphate likely triggers FGF23 release, even in the absence of CKD.27Interestingly, however, our data indicate that elevated plasma FGF23 in our cohort is associ- ated with low plasma 1,25-dihydroxyvitamin D3but not with increased renal phosphate excretion. This suggests that thresholds for inhibition of 1,25-dihydroxyvitamin D3 syn- thesis and induction of phosphaturia by FGF23 may not be the same. Such a concept of a differential FGF23 effect in the proximal tubule would be in line with experimental data in mice that revealed different pathways for the inhibition of 1,25-dihydroxyvitamin D3 synthesis and phosphate reab- sorption.28,29Thus, in the setting of preserved renal function, the induction of phosphaturia by FGF23 may require addi- tional factors or simply higher FGF23 levels.
In contrast to FEPi and 24-hour phosphate excretion, FECa and 24-hour calcium excretion were strongly and inversely associated with plasma FGF23. It is clear that the original view of FGF23 as a pure phosphaturic hormone is too limited. In mice, FGF23 was recently shown to stimulate renal calcium reabsorption via an increase in apical mem- brane abundance of transient receptor potential vanilloid-5 in the distal convoluted tubule.30Calcium intake directly influ- enced FGF23 secretion, independently of PTH and 1,25- dihydroxyvitamin D3 in mice31,32 and rats.33 In humans, in both healthy volunteers and dialysis patients, short-term changes in plasma calcium had no effect on circulating FGF23 levels.34 Chronically, however, both high dialysate calcium as well as high calcium intake were associated with higher FGF23 levels in dialysis patients.35Whether the asso- ciation of FGF23 with reduced urinary calcium excretion observed in our study is the result of a direct FGF23 effect on the kidney or secondary to the FGF23-mediated reduction in 1,25-dihydroxyvitamin D3 cannot be answered by our cross-sectional study and remains to be tested using longi- tudinal data. Taken together, however, our data suggest that in individuals with normal renal function, plasma FGF23 is Table4|(Continued) Predictorvariable
Model1Model2Model3Model4 Nb95%CIP valueNb95%CIP valueNb95%CIP valueNb95%CIP value TmP/GFR, mmol/lLinear9680.202170.05489– 0.36065<0.019670.239500.07889– 0.40986<0.018820.241700.07889– 0.40986<0.019090.241600.07721– 0.41886<0.01 Calciuria, mmol/24hrLinear9720.042470.05845to 0.0266<0.0019640.034690.05119to 0.01857<0.0018790.032550.04977to 0.01576<0.0019040.039110.05726to 0.02205<0.001 Quadratic0.005730.0022– 0.00929<0.010.005080.0016– 0.00861<0.010.004720.00111– 0.00836<0.050.006410.00225– 0.01066<0.01 Fractional excretionof calcium,%
Linear9670.022510.0466to .000540.0599660.042840.06741to 0.01976<0.0018810.046640.07223to 0.02289<0.0019080.043380.06838to 0.01968<0.001 BMI,bodymassindex;BSA,bodysurfacearea;CI,confidenceinterval;eGFRcr,creatinineequationCKD-EPI2009;eGFRcr-cys,creatinine-cystatinCequationCKD-EPI2012;FGF23,fibroblastgrowthfactor23;25-OH,25-hydroxyvitamin D3;PTH,parathyroidhormone;TmP/GFR,ratiooftubularmaximumreabsorptionofphosphatetoglomerularfiltrationrate. Associationsbetweenlog-transformedplasmaFGF23,asadependentvariable,withbasicdemographicandplasmaandurinaryparametersofcalciumphosphatemetabolismaspredictorvariables.Allmodelswerecalculatedby mixed-effectslinearregression,takingfamily,center,andcalendardayofbloodsamplingasrandomeffectsintoaccount.Univariateanalysisforthepredictorvariablewasconductedinmodel1.Models2,3,and4containthe predictorvariableadjustedforthecovariablessex,age,BMI,andkidneyfunctionasfixedeffects.Thecovariablekidneyfunctionispresentedinmodel2byeGFRcr(estimatedbyCreatinineEquationCKD-EPI2009),inmodel3by eGFRcr-cys(estimatedbythecreatinine-cystatinCequationCKD-EPI2012),andinmodel4byGFRmeasuredusing24-hourcreatinineclearance,asdescribedintheMethodssection.Thebcoefficientsandtheir95%confidence intervalsandPvaluesofthepredictorvariablesaregivenforlinearandquadraticterms.
c l i n i c a l i n v e s t i g a t i o n NA Dhayatet al.: FGF23 in individuals with normal renal function
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