Summary: Background and objectives: The serum proteins sclerostin and Dickkopf-1 (Dkk-1) are soluble inhibitors of canonical wnt signaling and were recently identified as components of parathyroid hormone (PTH) signal transduction. This study investigated the associations between sclerostin and Dkk-1 with histomorphometric parameters of bone turnover, mineralization, and volume in stage 5 chronic kidney disease patients on dialysis (CKD-5D).Design, setting, participants, & measurements: In a cross-sectional study, 60 CKD-5D patients underwent bone biopsies followed by histomorphometry. Levels of sclerostin, Dkk-1, and intact PTH (iPTH) were determined in blood.Results: Serum levels of sclerostin and iPTH correlated negatively. In unadjusted analyses, sclerostin correlated negatively with histomorphometric parameters of turnover, osteoblastic number, and function. In adjusted analyses, sclerostin remained a strong predictor of parameters of bone turnover and osteoblast number. An observed correlation between sclerostin and cancellous bone volume was lost in regression analyses. Sclerostin was superior to iPTH for the positive prediction of high bone turnover and number of osteoblasts. In contrast, iPTH was superior to sclerostin for the negative prediction for high bone turnover and had similar predictive values than sclerostin for the number of osteoblasts. Serum levels of Dkk-1 did not correlate with iPTH or with any histomorphometric parameter.Conclusions: Our data describe a promising role for serum measurements of sclerostin in addition to iPTH in the diagnosis of high bone turnover in CKD-5D patients, whereas measurements of Dkk-1 do not seem to be useful for this purpose.

Objective: Activation of the mammalian target of rapamycin (mTOR) pathway is important for immune cell activation and bone metabolism. To date, the contribution of mTOR signaling to joint inflammation and structural bone and cartilage damage is unknown. The aim of this study was to investigate the potential of inhibiting mTOR as a treatment of inflammatory arthritis.Methods: Human tumor necrosis factor–transgenic mice in which inflammatory arthritis was developing were treated with 2 different mTOR inhibitors, sirolimus or everolimus. The effects of treatment on clinical disease activity, inflammation, and localized joint and cartilage destruction were studied. In addition, the effects of mTOR inhibition on osteoclast survival and expression of key molecules of osteoclast function were analyzed in vitro. Moreover, synovial tissue from patients with rheumatoid arthritis (RA) was assessed for activation of the mTOR pathway.Results: Inhibition of mTOR by sirolimus or everolimus reduced synovial osteoclast formation and protected against local bone erosions and cartilage loss. Clinical signs of arthritis improved after mTOR inhibition, and histologic evaluation showed a decrease in synovitis. In vitro, mTOR inhibition down‐regulated the expression of digestive enzymes and led to osteoclast apoptosis. Moreover, mTOR signaling was shown to be active in the synovial membrane of patients with RA, particularly in synovial osteoclasts.Conclusion: Signaling through mTOR is an important link between synovitis and structural damage in inflammatory arthritis. Current pharmacologic inhibitors of mTOR could be effective in protecting joints against structural damage.

Sclerostin is a soluble inhibitor of osteoblast function. Sclerostin is downregulated by the parathyroid hormone (PTH). Here, it was investigated whether sclerostin levels are influenced by intact (i) PTH and whether sclerostin is associated with bone turnover, microarchitecture and mass in dialysis patients. Seventy-six haemodialysis patients and 45 healthy controls were included in this cross-sectional study. Sclerostin, Dickkopf-1 (DKK-1), intact parathyroid hormone (iPTH), vitamin D and markers of bone turnover were analysed. A subset of 37 dialysis patients had measurements of bone mineral density (BMD) using dual-energy X-ray absorptiometry and bone microarchitecture using high-resolution peripheral quantitative computed tomography. Dialysis patients had significantly higher sclerostin levels than controls (1257 pg/mL versus 415 pg/mL, P < 0.001). Significant correlations were found between sclerostin and gender (R = 0.41), iPTH (R = -0.28), 25-hydroxy-cholecalciferol (R = 0.27) and calcium (R = 0.25). Gender and iPTH remained significantly associated with sclerostin in a multivariate analysis. Sclerostin serum levels were positively associated with BMD at the lumbar spine (R = 0.46), femoral neck (R = 0.36) and distal radius (R = 0.42) and correlated positively mainly with trabecular structures such as trabecular density and number at the radius and tibia in dialysis patients. DKK-1 was related neither to bone measures nor to serologic parameters. Considering that sclerostin is an inhibitor of bone formation, the observed positive correlations of serum sclerostin with BMD and bone volume were unexpected. Whether its increase in dialysis patients has direct pathogenetic relevance or is only a secondary phenomenon remains to be seen.

Background. Because mammalian target of rapamycin (mTOR) inhibitors combine anticancer and immunosuppressive properties we investigated: 1) the activation status and prognostic significance of the mTOR pathway in hepatocellular carcinoma (HCC) tissues of patients undergoing orthotopic liver transplantation (OLT) for HCC, and 2) the single and combinatorial efficacy of RAD001 in HCC cells. Methods. PTEN, p-AKT, p-mTOR, p-p70S6K, and p-4EBP-1 were analyzed by immunohistochemistry in explanted HCCs of 166 patients undergoing OLT. Efficacy of RAD001 as mono- and combination therapy with doxorubicin was tested in Hep3B and SNU398 cells. Results. The mTOR pathway is activated in about 40% of patients undergoing OLT for HCC but no direct correlation between up- and downstream proteins was observed. We found no influence of mTOR pathway protein expression on disease free survival (DFS) or overall survival (OS). There was a marked single agent and chemo-sensitizing effect of RAD001 against HCC cells in vitro. Conclusion. The mTOR pathway is active in 40% of patients with HCC undergoing OLT, but has no influence of DFS or OS. No direct correlation was observed between up- and downstream proteins limiting the use of upstream proteins to predict mTOR activity. Prospective clinical trials are needed to test whether the activation status of the mTOR pathway in HCCs predicts the antitumor effect of rapamycin derivative in the posttransplantation course.

Sclerostin serum levels are increased in patients with chronic kidney disease (CKD). Osteoporosis and CKD often occur simultaneously. Currently antisclerostin antibodies are in clinical development for the treatment of osteoporosis. The objective of this study was to study the renal handling of sclerostin. This was a cross-sectional study. The study was conducted at a university hospital and outpatient renal clinic. One hundred twenty men and women with CKD stage 1-5 participated in the study. Measurements of sclerostin in urine and serum (ELISA), renal function [estimated glomerular filtration rate (eGFR)], electrolytes, α1-microglobulin, PTH, vitamin D, and markers of bone turnover were conducted. Eight human kidney biopsies were stained for sclerostin using immunohistochemistry. Urinary excretion of sclerostin was measured. Urinary sclerostin excretion increased with declining eGFR (R=-0.75, P<.001), from 10.4 (±12.7) pmol/L in patients with eGFR greater than 90 mL/min per 1.73 m2 (CKD stage 1) to 117.9 (±65.4) pmol/L in patients with eGFR less than 15 mL/min per 1.73 m2 (CKD stage 5, P<.001). Fractional excretion of sclerostin increased with declining eGFR (R=-0.83, P<.001) from 0.45% (±0.6%) in CKD 1 to 26.3% (±17.6%) in CKD 5 (P<.001). Fractional excretion of sclerostin correlated with fractional excretion of α1-microglobulin (R=0.82, P<.001). No association between serum sclerostin and fractional excretion of phosphorus was found in a multivariate analysis. Sclerostin was detected in proximal tubular cells, showing a diffuse cytoplasmic staining pattern. Increased sclerostin serum levels in CKD patients are not due to decreased renal elimination. On the contrary, renal elimination increases with declining kidney function. Whether this has consequences on antisclerostin antibody dosing, efficacy, or safety in patients with CKD remains to be determined.