sRANKL/OPG IN CHILDREN WITH IDIOPATHIC HYPERCALCIURIA Pavlou M, Siomou E, Cholevas V, Siamopoulou A, Challa A Child Health Department, Division of Pediatric Nephrology, Medical School, University of Ioannina, Ioannina, Greece Materials and Methods • Twenty four children of median age 6.5 yrs (range 2.3-16.4) with IH (5 had urolithiasis & 2 nephrocalcinosis) were examined at the time of diagnosis and after 3 months of salt free and adequate Ca diet. The diagnosis of hypercalciuria was assigned for patients with 24hr urinary calcium excretion >4mg/Kg/day and/or with a spot urine calcium to creatinine ratio > 0.22 for over 2 years of age • Clinically healthy children (n=46) matched for age, sex, season and with normal Ca excretion, were used as controls (median 8.0 yrs; range 1.8-16.3 ) • Serum sRANKL (total), OPG, 25(OH)D, 1,25(OH) 2 D, intact PTH, Ca, Pi, osteocalcin (N-MID OC), ALP, CTX-crosslaps and urine Ca, creatinine, oxalate and citrate were determined • Body mass index (BMI) z-score was also assessed Conclusions  No evident changes in the serum cytokines OPG and sRANKL were noted in children with IH, while Gomes et al have reported higher bone expression of both RANKL and OPG in adult patients with IH than in controls 10  Hence an autocrine role of the above cytokines cannot be excluded  Also bone metabolism in the children of the present study seems to have been affected by increased bone resorption, as indicated by the higher levels of serum CTX-Crosslaps and unaffected formation, since osteocalcin was not found different from controls References 1. Moore ES, Coe FL, McMann BJ, Favus MJ (1978) Idiopathic hypercalciuria in children: prevalence and metabolic characteristics. J Pediatr 92:906–910 2. Gillespie RS, Stapleton FB (2004) Nephrolithiasis in children. Pediatr Rev 25:131–139 3. Schwaderer AL, Cronin R, Mahan JD, Bates CM (2008) Low bone density in children with hypercalciuria and/or nephrolithiasis. Pediatr Nephrol 23: 2209-2214 4. Zerwekh JE (2010). Bone disease and hypercalciuria in children. Pediatr Nephrol 25: 395-401 5. Tsuda E, Goto M, Mochizuki S, et al (1997). Isolation of a novel cytokinefrom human fibroblats that specifically inhibits osteoclastogenesis. Biochem Biophys Res Commun 234: 137-142 6. Blair JM, Zheng Y, Dunstan CR (2007) RANK ligand Int. J Biochem Cell Biol 39: 1077-1081 7. Lacey DL, Timms E, Tan HL, et al (1998) Osteoprotegerin ligand is a cytokine that regulates osteoclast differentiation and activation. Cell 93: 165-176 8. Yun TJ,Tallquist MD, Aicher A, et al (2001) Osteoprotegerin, a crucial regulatorr of bone metabolism, also regulates B cell developmentand function. J Immunol 166: 1482-1491 9. Tat SK, Padrines M, Theoleyre S, et al (2006) OPG/membranous-RANKL complex is internalise via clathrin pathway before a lysosomal and a proteasomal degradation. Bone 39: 706-715 10. Gomes SA, Machado dos Reis L, Noronha IL, Jorgetti V, Heilberg IP (2008). RANKL is a mediator of bone resorption in idiopathic hypercalciuria. Clin J Am Soc Nephrol 3: 1446–1452 • The receptor activator of nuclear factor kB ligand (RANKL) plays a central role in osteoclast differentiation.  Experimental studies have shown that OPG is a decoy receptor for RANKL, by preventing RANK activation, since it binds to RANKL prior to the receptor interaction. Thus, inhibiting osteoclast differentiation and bone resorption 7,8  It is also a modulator of RANKL half-life 9  To date, no studies have been published evaluating the RANKL/OPG circulating levels in children with ΙΗ Introduction • The prevalence of Idiopathic hypercalciuria (IH) in the children of the Western world is reported to range between 2.2 and 6.4% and is the most common cause of paediatric nephrolithiasis 1,2 • Decreased bone mineral density (BMD) has been associated with hypercalciuria in paediatric populations 3,4 . Some studies have shown increased bone resorption or turnover as the probable mechanism of bone loss, but the causes are not firmly established 4 • Investigations in bone biology identified the RANKL/RANK/OPG system, the set of cytokines or cytokine receptors belonging to the tumor necrosis factor (TNF) family, that are required for control of bone modelling and remodelling 5,6 . Objective To determine any relationship of serum concentrations of OPG, RANKL and OPG/RANKL ratio with IH in children Results  The BMI z-score was lower in patients (-0.425 ± 0.641) than controls (+0.06 ± 1.0, p=0.016), but height did not differ significantly.  Although urinary Ca excretion (24hCa & UCa/UCr) decreased at 3mo (24hUCa: p=0.06; UCa/UCr: p=0.014), on average it had not reached control values and was still higher (p<0.0001 & p<0.001)  Ucitrate/UCr and UCa/UCitrate did not differ in patients before and after diet or compared to controls, while 24h oxalate excretion was lower in the patients at diagnosis  No significant differences were found for serum Ca, Pi, 25OHD, 1,25(OH) 2 D, PTH, N-MID OC, ALP, OPG and sRANKL or for the sRANKL/OPG ratio  Only serum concentrations of CTX-Crosslaps were significantly higher in both patient samples than controls (p<0.02 & p<0.05) TABLE 1. Serum sRANKL and OPG levels in children with IH and controls Serum Patients (M±SD) Patients after 3mo diet (M±SD) Controls (M±SD) p 25OHD (ng/ml) 30.4 ± 17.2 35.7 ± 23.9 35.6 ± 21.2 NS 1,25 (OH) 2 D (pg/ml) 19.3 ± 12.3 17.6 ± 11.9 20.4 ± 15.8 NS iPTH (pg/ml) 22.7 ± 13.0 26.6 ± 16.0 28.0 ± 15.5 NS Ca (mg/dl) 10.3 ± 0.4 10.3 ± 0.4 10.3 ± 0.4 NS Pi (mg/dl) 4.92 ± 0.46 4.85 ± 0.5 4.86 ± 0.51 NS ALP (IU/L) 214 ± 128 202 ± 50 189 ± 65 NS N-MID OC (ng/ml) 64.2 ± 44.1 - 63.7 ± 24.6 NS Crosslaps (CTX) (ng/ml) 1.63 ± 0.67 1.56 ± 0.45 1.24 ± 0.56 <0.02, <0.05 TABLE 2. Serum biochemical findings of the patients on diagnosis, after 3 month diet and of controls a: p=0.06, b: p=0.014 between the two patient groups Median age (range) sRANKL (pmol/L) M±SD OPG (pmol/L) M±SD sRANKL/OPG ratio M±SD Patients (n=24) 6.5 yrs (2.3-16.4) 39.9 ± 21.8 p = NS 3.03 ± 1.17 p = NS 15.2 ± 1 0.8 p = NS Patients 3 mo after diet 6.7 (2.5-17.0) 41.1 ± 22.9 p = NS 2.92 ± 0.85 p = NS 15.6 ± 10.1 p = NS Controls (n=46) 8.0 yrs (1.8-16.3) 42.6 ± 27.1 2.58 ± 1.27 20.1 ± 18.2 Urine Patients (M±SD) Patients after 3 mo diet (M±SD) Controls (M±SD) p Ca (mg/Kg/24h) 6.29 ± 2.0 5.19 ± 2.3 a 2.14 ± 1.1 <0.0001 UCa/UCr (mg/mg) 0.30 ± 0.19 0.21 ± 0.12 b 0.10 ± 0.06 <0.0001, <0.001 24 h UCitr/UCr (mg/g) 94.4 ± 53.4 91.0 ± 73.9 59.5 ± 63.2 NS 24 UCa/UCitr (mg/mg) 6.2 ± 3.2 6.0 ± 3.8 6.9 ± 6.4 NS 24h U Oxal (mg/1.73m 2 ) 21.3 ± 8.3 27.4 ± 11.8 a 26.8 ± 7.5 P<0.05 TABLE 3. Excretion of Ca, citrate and oxalate in children with IH and controls p: between patients and controls Disclosure: None of the authors have any potential conflict of interest