SERUM CONCENTRATIONS OF PROTEIN REGULATORS OSTEOBLASTOGENESIS AND OSTEOCLASTOGENESIS IN PATIENTS WITH ENDOGENOUS HYPERCORTICISM

Abstract

Purpose. Endogenous Cushing’s syndrome (CS), usually affecting young and otherwise healthy patients, is a good model to validate the effects of supraphysiological levels of glucocorticoids in humans. This study evaluates circulating levels of extracellular antagonists of Wnt/ß-catenin signaling pathway (sclerostin, Dickkopf1 (Dkkl), secretedfrizzled-related protein 1 (SFRP1)) along with osteoprotegerin (OPG) and soluble receptor activator of nuclear factor kappa-beta ligand (RANKL) in patients with CS as compared to healthy individuals. Materials and methods. Forty patients with clinically and biochemically evident CS and 40 sex, age and body-mass index matched healthy individuals provided fasting serum samples (8:00-10:00AM) for measurement of sclerostin, SFRP1 and Dkkl, RANKL., OPG along with bone turnover markers. Serum samples on RANKL., OPG., Dkkl, SFRP1, sclerostin were frozen and then concurrently measured by an enzyme immunoassay (ELISA) using commercially available reagents. Serum samples on osteocalcin (OC), carboxyterminal cross-linked telopeptide of type I collagen (CTx), cortisol in serum and saliva were assayed by electrochemiluminescence (ECLIA) Cobas e601 Roche. Urinary free cortisol (24hUFC) was measured by an immunochemiluminescence assay (extraction with diethyl ether) on a Vitros ECi. All participants were questioned regarding any recent low traumatic fractures. Patients with CS underwent standard spinal radiographs in anterior-posterior and lateral positions of the vertebrae Th4-L4 (Axiom Icons R200 "Siemens"). Results. Patents with CS (30 (26-40) years old with 24hUFC 2575 (1184-4228) nmol/l (Me (Q25-Q75)) had suppressed OC and normal CTx levels as compared to healthy subjects. A significant correlation, which we observed between OC and CTx (po=0.724 (p<0.001)) among the healthy volunteers, weakened to a non-significant level (po - 0.285 (p=0.083)) when analyzing patients with CS only. 24hUFC correlated with OC po = - 0.464 p=0.003, but not with CTx po= 0.245 (p=0.132) in patients with CS. Patients with CS had higher sclerostin levels versus healthy control subjects (p=0.032). Differences in sclerostin were due to the lack of lower sclerostin values rather than an increase in protein levels above the upper-limits of the healthy control individuals. Sclerostin levels higher than 662 pg/ml were four times more frequent in patients with CS as compared to healthy subjects (OR=4,19, 95% CI 1,44-12,22), p=0,006. Dkk1, SFRP1 did not differ from the control group. Patients with CS had a significantly lower level of RANKL (0.083 (0.075 0.093) pmol/L) as compared to healthy subjects (0.106 (0.089 0.131) pmol/L) p<0.001. Conversely, no difference was found between the OPG level in patients with CS (6.65 (4.92-7.66) pmol/L) and healthy individuals (5.77 (5.00-6.40) pmol/L), p=0.14. RANKL was lower (p=0.02) and OPG was higher (p=0.04) in patients with CS and low traumatic fractures (n=19) versus patients without fractures (n=21). Conclusions. Patients with CS have higher sclerostin level as compared to healthy subjects. Hypercotisolism prevents the normal physiological suppression of sclerostin rather than raising its absolute level. Of all the tested proteins (sclerostin, Dkk1, SFRP1, RANKL., OPG) only sclerostin seems to be a promising therapeutic approach to treating osteoporosis in patients with endogenous CS.