BACKGROUND: Fibroblast growth factor (FGF) 23 is one of the most recently 
discovered FGFs. This phosphaturic hormone produced in bones is a risk factor 
for cardiovascular diseases and thus mortality. Klotho is an essential 
coreceptor for FGF23 and at the same time it is known as a "longevity" hormone. 
There are no data considering FGF23 and Klotho roles in heart transplant (HT) 
recipients. The aim of this study was to assess Klotho and FGF23 serum 
concentration in heart transplant recipients depending on immunosuppressive 
therapy regimen and comorbidities.
METHODS: Eighty-four stable heart transplant recipients were enrolled in the 
study; 22 healthy volunteers served as control subjects. FGF23 and Klotho 
protein concentration, markers of renal function, such as cystatin C and 
neutrophil gelatinase-associated lipocalin (NGAL), and heart failure markers, 
such as copeptine and N-termiinal pro-B-type natriuretic peptide (NT-proBNP), 
were evaluated.
RESULTS: FGF23 concentration was significantly higher in the HT group whereas 
Klotho protein was significantly lower. FGF23 correlated with creatinine level 
(r = 0.72; P < .001), estimated glomerular filtration rate (eGFR; r = -0.32; P < 
.01), cystatin C (r = 0.36; P < .01), NGAL (r = 0.51; P < .001), hemoglobin (r = 
-0.39; P < .001), NT-proBNP (r = 0.51; P < .001), high-density lipoprotein (HDL; 
r = 0.27; P < .05), intraventricular septum thickness (r = 0.42; P < .01) and 
right ventricular systolic pressure (r = 0.34; P < .05). Klotho protein 
correlated only with age (r = -0.21; P < .05), creatinine (r = -0.21; P < .05), 
and eGFR (r = -0.31; P < .01). FGF23 concentration was significantly higher in 
patients with eGFR <60 mL/min whereas Klotho protein was significantly lower. 
FGF23 predictors were renal function (creatinine concentration; β = 0.45; P = 
.0001), HDL (β = 0.33; P = .003), intraventricular septum thickness (β = 0.38; P 
= .0003), and right ventricular systolic pressure (β = 0.34; P = .003), 
explaining 70% of FGF23 variability.
CONCLUSIONS: FGF23/Klotho system disorders in HT recipients are related to 
cardiovascular system function and kidney failure and could cause increased risk 
of cardiovascular disease.