P-cresol and Indoxyl Sulfate Impair Osteogenic Differentiation by Triggering Mesenchymal Stem Cell Senescence.

Chronic kidney disease (CKD) patients obtained high levels of uremic toxins progressively develop several complications including bone fractures. Protein-bound uremic toxins especially p-cresol and indoxyl sulfate are hardly eliminated due to their high molecular weight. Thus, the abnormality of bone in CKD patient could be potentially resulted from the accumulation of uremic toxins. To determine whether protein-bound uremic toxins have an impact on osteogenesis, mesenchymal stem cells were treated with either p-cresol or indoxyl sulfate under in vitro osteogenic differentiation. The effects of uremic toxins on MSC-osteoblastic differentiation were investigated by evaluation of bone phenotype. The results demonstrated that p-cresol and indoxyl sulfate down-regulated the transcriptional level of collagen type I, deceased alkaline phosphatase activity, and impaired mineralization of MSC-osteoblastic cells. Furthermore, p-cresol and indoxyl sulfate gradually increased senescence-associated beta-galactosidase positive cells while upregulated the expression of p21 which participate in senescent process. Our findings clearly revealed that the presence of uremic toxins dose-dependently influenced a gradual deterioration of osteogenesis. The effects partially mediate through the activation of senescence-associated gene lead to the impairment of osteogenesis. Therefore, the management of cellular senescence triggered by uremic toxins could be considered as an alternative therapeutic approach to prevent bone abnormality in CKD patients.

Circulating Levels of Dickkopf-Related Protein 1 Decrease as Measured GFR Declines and Are Associated with PTH Levels.

BACKGROUND: The Wnt/ß-catenin pathway has been implicated in the development of adynamic bone disease in early-stage chronic kidney disease (CKD). Dickkopf-related protein 1 (DKK1) and sclerostin are antagonists of the Wnt/ß-catenin pathway yet have not been widely used as clinical indicators of bone disease. This study characterized levels of DKK1, sclerostin, and other biomarkers of mineral metabolism in participants across a spectrum of inulin-measured glomerular filtration rate (GFR). METHODS: GFR was measured by urinary inulin clearance (mGFR) in 90 participants. Blood samples were obtained for measurement of circulating DKK1, sclerostin, fibroblast growth factor 23 (FGF-23), parathyroid hormone (PTH), calcium, phosphate, α-klotho, and vitamin D metabolites including 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3. Spearman correlations and linear regressions were used where appropriate to examine the associations between measured values. RESULTS: The median [IQR] age was 64 years [53.0-71.0], and the median [IQR] mGFR was 32.6 [21.7-60.6] mL/min. DKK1 decreased (r = 0.6, p < 0.001) and sclerostin increased (r = -0.4, p < 0.001) as kidney function declined, and both were associated with phosphate, PTH, FGF-23, and 1,25-dihydroxyvitamin D3 in the unadjusted analysis. After adjustment for age and mGFR, DKK1 remained significantly associated with PTH. CONCLUSION: The results of this study demonstrate opposing trends in Wnt/ß-catenin pathway inhibitors, DKK1 and sclerostin, as mGFR declines. Unlike sclerostin, DKK1 levels decreased significantly as mGFR declined and was independently associated with PTH. Future studies should determine whether measurement of Wnt signaling inhibitors may be useful in predicting bone histomorphometric findings and important clinical outcomes in patients with CKD.

The relationship between urinary kidney injury molecule-1 and blood bone metabolism markers in patients with chronic kidney disease
.

OBJECTIVE: The aim of this study was to evaluate the changes of urinary kidney injury molecule-1(uKIM-1) in chronic kidney disease (CKD) at different stages, and to determine the relationships between uKIM-1 and circulating bone metabolism markers. MATERIALS AND METHODS: This cross-sectional study included CKD patients (n = 121) and controls (n = 65). CKD stages were assigned to each individual according to their estimated glomerular filtration rate (eGFR), which was calculated with the modification of diet in renal disease (MDRD) equation. We evaluated the relationships of bone metabolism markers (including calcium, phosphorus, intact parathyroid hormone (iPTH), 25 hydroxy vitamin D (25(OH)D), alkaline phosphatase (ALP), fibroblast growth factor 23 (FGF23), and α-Klotho), uKIM-1, and eGFR. We also compared the levels of bone metabolism markers and uKIM-1 at different CKD stages. The uKIM-1 level was standardized with urine creatinine (uCr). RESULTS: Compared with healthy controls, CKD patients had higher levels of uKIM-1/uCr, serum creatinine, urea, phosphorus, iPTH, and plasma FGF23, whereas they had lower levels of serum calcium, α-Klotho, and plasma 25(OH)D. In CKD patients, eGFR was positively correlated with levels of serum calcium, α-Klotho, and plasma 25(OH)D, whereas it was negatively correlated with serum phosphorus, iPTH, plasma FGF23, and uKIM-1/uCr. Serum calcium and α-Klotho were significantly decreased in patients with stage 5 CKD compared to those with stage 1 CKD. Serum phosphorus, iPTH, and plasma FGF23 were significantly elevated in patients with stage 4 CKD when compared to those with stage 1 CKD. UKIM-1/uCr was significantly elevated in patients with stage 5 CKD when compared to those with stage 1 CKD. In CKD patients, uKIM-1/uCr levels were positively correlated with levels of serum phosphorus and plasma FGF23, whereas they were negatively correlated with serum calcium and plasma 25(OH)D. CONCLUSION: UKIM-1/uCr levels are increased with the deterioration of CKD stage and are correlated with the development of CKD-mineral and bone disorder (CKD-MBD).

[New biomarkers of CKD-MBD]. / I nuovi biomarcatori della CKD-MBD.

Chronic kidney failure involves abnormalities of mineral metabolism, skeletal and of cardiovascular system (so called CKD - MBD) that have a major impact on the survival of renal patient. Increasingly complex pathophysiological mechanisms have been discovered in recent years with evidence of new molecules involved in the development of CKD - MBD. Besides the classical PTH / Vitamin D axis, the most recent discovery of a new FGF23 / Klotho axis has expanded knowledge on the mechanisms of mineral homeostasis but also on the more complex mechanisms of cellular aging, vascular calcification and cardiac remodeling. The importance of bone as an endocrine organ has become even more evident following the discovery of molecules such as Sclerostin (involved in the regulation of osteoblastic proliferation and differentiation) and Sibling (a family of proteins that regulate both local and systemic mineral metabolism). The ability to characterize as biomarkers of CKD - MBD for these new molecules depends on their eventual ability to express a specific pathophysiological processes, identify patients at risk, highlight the response to a therapeutic treatment and to be easily identifiable and quantifiable on biological fluids. As of today, it seems that we can recognize FGF23 as a biomarker of CKD-MBD, while the remaining molecules as still waiting for a more definite settlement.

Factors related with the progression of chronic kidney disease.

BACKGROUND: Our aims were to determine the rate of progression of chronic kidney disease (CKD) and to identify predictors, with particular emphasis on bone and mineral metabolism. METHODS: Retrospective and observational study including 300 patients with advanced CKD (61.2% males, 33.1% diabetics; age 65.6±14 years). Mean follow-up time was 19.4±10.1 months. Baseline estimated glomerular filtration rate (eGFR) (MDRD-4) was 22.5±7.18 mL/min. To calculate the rate of decline in eGFR, we used the slope of the regression line between all determinations of eGFR and follow-up time. We calculated the mean values for proteinuria and serum phosphate, calcium, uric acid, and PTH, as well as 24-hour urinary excretion of urea nitrogen over time for each patient. Follow-up was at least 6 months and included at least 4 measurements of eGFR. RESULTS: The mean rate of decline eGFR (-1.64 mL/min/1.73 m²/year) was inversely correlated with serum phosphate levels (4.3±2.1 mg/dL, P<.001), PTH (256.3±193.7 ng/L, p<.001) and proteinuria (0.84±1.31 g/day, P=.004) and directly correlated with mean serum calcium (P<.001) and the presence of hypertension (P<.02). However, only serum phosphate, serum PTH, and proteinuria persisted as predictors in the multivariate analysis. Stable-GFR patients (positive slope) were older (P=.041) and had lower serum phosphate and PTH levels (P<.01 and P<.01 respectively) and lower proteinuria (P<.01). CONCLUSIONS: The rate of decrease in eGFR was correlated with serum phosphate and PTH levels and proteinuria. All of these factors can be modified with an adequate treatment.

Osteodistrofia renal en pacientes con isuficiencia renal crónica atendidos en el Hospital Escuela, Tegucigalpa / Renal osteodystrophy in patients with chronic renal failure attended at Hospital Escuela, Tegucigalpa

OBJETIVO: Estudiar la frecuencia de los diferentes tipos de osteodistrofia renal en una muestra de pacientes atendidos en el Hospital Escuela. MEDOTOLOGIA. Estudio realizado en los meses de agosto y septiembre del año 2004. A través de un instrumento se recolectó la información clínica y los resultados de los exámenes de gabinete de una muestra de 39 pacientes con insuficiencia renal crónica (IRC) a quienes se les efectuó pruebas de función renal medición de Paratohormona y biopsia de hueso. RESULTADOS. De los 39 pacientes estudiados, la biopsia de hueso demostró enfermedad ósea renal en 28.3%(11), mieloma múltiple en 2.6%(1) y sin alteración ósea en 36.0% (14). En los 13 casos restantes (33.1%), el resultado fue indeterminado debido a biopsia no evaluable. De los 26 pacientes con el resultado histopatológico, la frecuencia de ostrodistrofia renal fue de 42.3% (11). entre estos 11 pacientes, la enfermedad ósea adinámica fue la mas frecuente (46%), seguida de osteítis fibrosa (36%) y osteomalacia (18%). Se detectó niveles de paratohormona (PTH) mayores de 400 pg/ml en los 4 pacientes con osteítis fibrosa (enfermedad ósea de alto remodelado) y niveles menores de 125pg/ml en 5 de los 7 pacientes con enfermedad ósea de bajo remodelado (enfermedad ósea adinámica y osteomalacia).De los 14 pacientes sin osteodistrofia renal, uno demostró valores mayores de 400 pg/ml,5 demostraron valores entre 126 y 400 pg/ml, y 8 demostraron valores menores de 125 pg/ml.CONCLUSIONES:La frecuencia de ostiodistrofia renal fue de 44%, es decir que aproximadamente por cada 2 pacientes con enfermedad renal crónica atendido en el Hospital Escuela durante el período que duró el estudio, uno tenía osteodistrofia renal. La paratohormona podría ser utilizada como marcador bioquímico para detectar enfermedad ósea de alto remodelado en los pacientes con insuficiencia renal...

Osteodistrofia renal en pacientes con isuficiencia renal crónica atendidos en el Hospital Escuela, Tegucigalpa / Renal osteodystrophy in patients with chronic renal failure attended at Hospital Escuela, Tegucigalpa

OBJETIVO: Estudiar la frecuencia de los diferentes tipos de osteodistrofia renal en una muestra de pacientes atendidos en el Hospital Escuela. MEDOTOLOGIA. Estudio realizado en los meses de agosto y septiembre del año 2004. A través de un instrumento se recolectó la información clínica y los resultados de los exámenes de gabinete de una muestra de 39 pacientes con insuficiencia renal crónica (IRC) a quienes se les efectuó pruebas de función renal medición de Paratohormona y biopsia de hueso. RESULTADOS. De los 39 pacientes estudiados, la biopsia de hueso demostró enfermedad ósea renal en 28.3%(11), mieloma múltiple en 2.6%(1) y sin alteración ósea en 36.0% (14). En los 13 casos restantes (33.1%), el resultado fue indeterminado debido a biopsia no evaluable. De los 26 pacientes con el resultado histopatológico, la frecuencia de ostrodistrofia renal fue de 42.3% (11). entre estos 11 pacientes, la enfermedad ósea adinámica fue la mas frecuente (46%), seguida de osteítis fibrosa (36%) y osteomalacia (18%). Se detectó niveles de paratohormona (PTH) mayores de 400 pg/ml en los 4 pacientes con osteítis fibrosa (enfermedad ósea de alto remodelado) y niveles menores de 125pg/ml en 5 de los 7 pacientes con enfermedad ósea de bajo remodelado (enfermedad ósea adinámica y osteomalacia).De los 14 pacientes sin osteodistrofia renal, uno demostró valores mayores de 400 pg/ml,5 demostraron valores entre 126 y 400 pg/ml, y 8 demostraron valores menores de 125 pg/ml.CONCLUSIONES:La frecuencia de ostiodistrofia renal fue de 44%, es decir que aproximadamente por cada 2 pacientes con enfermedad renal crónica atendido en el Hospital Escuela durante el período que duró el estudio, uno tenía osteodistrofia renal. La paratohormona podría ser utilizada como marcador bioquímico para detectar enfermedad ósea de alto remodelado en los pacientes con insuficiencia renal...(AU)

Biochemical measurements in the prediction of histologic subtype of renal transplant bone disease in women.

Renal transplant osteodystrophy encompasses several histologic subtypes. Bone histomorphometric examination reliably distinguishes these groups but is invasive, is time-consuming, and delays diagnosis. Establishing a noninvasive method of correctly predicting histologic subtype in an individual to direct management is an attractive proposition. We identified 19 female renal transplant recipients with histologic evidence of hyperparathyroid bone disease (HPTH) and 14 with adynamic bone (ADB). We evaluated serum osteocalcin and bone-specific alkaline phosphatase as bone formation markers and urinary hydroxyproline (Hypro) and deoxypyridinoline cross-links as bone resorption markers. Mean concentrations for all markers were higher in the HPTH group, reaching significance for Hypro (HPTH, 24.8 +/- 4.2 micromol/mmol creatinine; ADB, 13.2 +/- 5.0 micromol/mmol creatinine; P = 0.01). A cutoff of 16.4 micromol/mmol creatinine for Hypro (Youden's index, 0.65) gave a sensitivity of 93% and specificity and positive predictive value (PPV) of 72% in predicting HPTH. In combination, Hypro greater than 16.4 micromol/mmol creatinine and parathyroid hormone greater than 80 pg/mL gave a specificity of 100%, sensitivity of 32%, and PPV of 100%. Conversely, for predicting ADB, Hypro less than 15.1 micromol/mmol creatinine (Youden's index, 0.45) gave a specificity of 93%, sensitivity of 53%, and PPV of 91%. Hypro less than 15.1 micromol/mmol creatinine plus osteocalcin less than 6.8 microg/L gave a specificity of 84.2%, sensitivity of 64.3%, and PPV of 75%. Significant associations between markers and histomorphometry were evident only for Hypro and osteocalcin (with osteoblast surface) and all markers (except deoxypyridinoline cross-links) with cortical volume. Markers have limited utility in identifying histologic subtype (Hypro was most effective) and, with the exception of Hypro and osteocalcin, showed little association with cell surface markers of bone cell activity.

[Bone metabolism as assessed with selected markers of bone turnover as well as densitometry analysis in patients after successful kidney transplantation]. / Metabolizm kosci u chorych po zabiegu przeszczepienia nerki w swietle wybranych markerów obrotu kostnego oraz w ocenie densytometrycznej.

The degree of advancement as well as symptoms of renal osteodystrophy improve significantly in patients after successful kidney transplantation; however bone pathology is still present even after many post-transplant years. The aim of this study was to analyze the bone densitometry in patients during different periods after kidney transplantation and to assess bone metabolism using selected biochemical markers of bone turnover in comparison to healthy controls. Study population consisted of 73 patients of mean age 41.7 +/- 12.6 years (27F, 46M) mean 34 +/- 42 months after kidney transplantation. Mean period of maintenance dialysis prior to surgery was 28.6 +/- 20.3 months. We also analyzed age- and sex-matched control group of 24 subjects. Three-point densitometry was performed with DEXA technique. Serum levels/activity of osteocalcin, C-terminal propeptide of procollagen type I (PCTP), alkaline phosphatase (AP) and its bone-specific isoform (BAP) as well as desoxypiridine (DPD) urine level were analyzed as markers of bone turnover. Serum levels/activity of all mentioned parameters were significantly increased (p < 0.001) and urine DPD--significantly decreased (p < 0.05) in patients as compared to controls. Based on DEXA technique 26% of patients were categorized as having osteoporosis, 32.9%--osteopenia and 41.1% as normal in bone densitometry. Patients with diagnosed osteoporosis spent significantly longer time with functioning graft as compared to those with normal densitometry. In addition, subjects with osteoporosis were characterized by significantly higher serum level of osteocalcin as compared to those with osteopenia and normal DEXA (42.5 +/- 19.9 vs 26.6 +/- 15 ng/ml and 42.5 +/- 19.9 vs 30.2 +/- 104 ng/ml, respectively; p < 0.05). Identical relationship was also observed for serum PTH (128 +/- 42 vs 77.2 +/- 30.4 pg/ml and 128 +/- 42 vs 81.2 +/- 232 pg/ml, respectively; p < 0.001). There was also significant difference in PCTP level in all analyzed groups (203 +/- 85, 171 +/- 69 and 137 +/- 40 ng/ml in subjects with osteoporosis, osteopenia and normal; p < 0.05 for all differences). BAP activity reduction was observed only in the latter group of patients. Results of our study led us to conclude that the prevalence of osteoporosis and osteopenia in three-point densitometry among patients with functioning graft is high. Increased serum levels/activity of osteocalcin, PCTP, AP and BAP with concomitant decrease of urine DPD elimination suggest the predominance of bone formation over the bone resorption process.

Investigations of bone turnover in renal osteopathy.

The renal bone disease which develops in chronic renal failure (CRF) is not an uniform disorder. Histomorphometry is accepted to be the best method for characterising the state of disease. The purpose of this study was to evaluate the suitability of pyridinium crosslinks in serum and urine as indicators of bone degradation processes. Patients with CRF had significantly higher Pyridinoline (Pyd) and Deoxypyridinoline (Dpyd) levels in serum and urine compared to normal controls except the urinary excretion in the subgroup of glomerulonephritis. A correlation was found between the serum levels of crosslinks and those of both creatinine and parathormone. The Pyd and Dpyd serum levels in patients under dialysis treatment were significantly higher than those of normal controls. With regard to bone turnover urinary crosslink measurements are of minor importance in CRF. In contrast, serum measurements could be helpful in revealing bone resorption both in patients with CRF and those under dialysis treatment.

Markers of bone remodelling in metabolic bone disease.

New specific markers of bone remodelling have been developed that allow the evaluation of bone formation (plasma levels of osteocalcin and bone alkaline phosphatases) or bone resorption (collagen crosslink levels in urine). These markers can be used to evaluate bone disease. Their best application is currently in renal osteodystrophy, where there is a broad spectrum of bone abnormalities. In patients with this disease, bone markers can obviate the need for bone biopsy. So far, bone alkaline phosphatase is the most sensitive and specific marker for predicting the type of bone disease and therefore for deciding treatment in dialysed patients, although it is not ideal. Bone markers have also allowed a dramatic improvement in the comprehensive approach to bone loss with aging in women. Monitoring of the marked increase in bone turnover, and its persistence, in older women after menopause may help in the design of treatment strategies for osteoporosis. There is some hope that the measurement of urinary levels of collagen crosslinks will help to predict the clinical outcome of osteoporosis with respect to fractures in postmenopausal women. Bone markers could, besides being a measurement of bone density, help to determine the optimal treatment of postmenopausal women. Bone markers could also be used to predict or ascertain the response to treatment of osteoporosis, but few data are currently available to judge the routine usefulness of these new applications.

Characteristics of biochemical markers in patients with metabolic bone disorders.

Biochemical markers of bone turnover are expected to have some different characteristics among bone metabolic disorders. We compared bone formation markers: serum total alkaline phosphatase (s-Alp), serum osteocalcin (s-OC) and serum carboxy-terminal propeptide of type I collagen (s-PICP); and bone resorption markers: serum carboxy-terminal telopeptide of type I collagen (s-ICTP), urinary pyridinoline (u-Pyr) and urinary deoxypyridinoline (u-Dpyr) to examine which marker is the most suitable and reliable to evaluate bone turnover in patients with osteoporosis (n = 29), osteomalacia (n = 10), primary hyperparathyroidism (n = 6) and renal osteodystrophy (n = 21). The value of s-Alp in the osteomalacia group was significantly higher than those in the normal control group and the osteoporosis group (p < 0.001), and T-score of s-Alp was significantly higher than those of s-OC and s-PICP in the osteomalacia group. The values of u-Pyr and u-Dpyr in the primary hyperparathyroidism group were significantly higher than those in the other groups (p < 0.001). S-PICP, which are not dependent upon renal function, was much higher in the renal osteodystrophy group than in all other groups. In the osteoporosis group, T-score of s-ICTP was significantly higher than those of s-OC. Thus, s-Alp was a good marker in osteomalacia, u-Pyr and u-Dpyr in primary hyperparathyroidism, s-PICP in renal osteodystrophy, and s-ICTP in osteoporosis.

Elevated nephrogenous cyclic adenosine monophosphate to monitor early renal osteodystrophy.

Radiographs, serum chemistries, parathyroid hormone (PTH), and nephrogenous cyclic adenosine monophosphate (cAMP) were evaluated in thirty-two children with normal serum creatinine, chronic renal insufficiency, chronic hemodialysis, and transplantation. Nephrogenous cAMP increases linearly with creatinine, and there is a good correlation (r = 0.89) between immunoreactive PTH (iPTH) and nephrogenous cAMP except for patients with severe renal insufficiency or requiring chronic hemodialysis. Elevated nephrogenous cAMP is evidence for metabolic bone disease earlier than usually recognized. Early measurements of iPTH and nephrogenous cAMP could ensure early therapeutic intervention which might alleviate renal osteodystrophy in chronic renal insufficiency and transplant patients.