Inhibition of tissue-nonspecific alkaline phosphatase protects against medial arterial calcification and improves survival probability in the CKD-MBD mouse model.

Medial arterial calcification (MAC) is a major complication of chronic kidney disease (CKD) and an indicator of poor prognosis. Aortic overexpression of tissue-nonspecific alkaline phosphatase (TNAP) accelerates MAC formation. The present study aimed to assess whether a TNAP inhibitor, SBI-425, protects against MAC and improves survival probability in a CKD-mineral and bone disorder (MBD) mouse model. CKD-MBD mice were divided in three groups: vehicle, SBI-10, and SBI-30. They were fed a 0.2% adenine and 0.8% phosphorus diet from 14 to 20 weeks of age to induce CKD, followed by a high-phosphorus (0.2% adenine and 1.8% phosphorus) diet for another 6 weeks. At 14-20 weeks of age, mice in the SBI-10 and SBI-30 groups were given 10 and 30 mg/kg SBI-425 by gavage once a day, respectively, while vehicle-group mice were given distilled water as vehicle. Control mice were fed a standard chow (0.8% phosphorus) between the ages of 8 and 20 weeks. Computed tomography imaging, histology, and aortic tissue calcium content revealed that, compared to vehicle animals, SBI-425 nearly halted the formation of MAC. Mice in the control, SBI-10 and SBI-30 groups exhibited 100% survival, which was significantly better than vehicle-treated mice (57.1%). Aortic mRNA expression of Alpl, encoding TNAP, as well as plasma and aortic tissue TNAP activity, were suppressed by SBI-425 administration, whereas plasma pyrophosphate increased. We conclude that a TNAP inhibitor successfully protected the vasculature from MAC and improved survival rate in a mouse CKD-MBD model, without causing any adverse effects on normal skeletal formation and residual renal function. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Bone alkaline phosphatase: An important biomarker in chronic kidney disease - mineral and bone disorder.

Increased cardiovascular morbidity and mortality in chronic kidney disease (CKD) represents an emerging major health problem. Indeed, disturbances in mineral and bone metabolism occur frequently in CKD and are termed chronic kidney disease - mineral and bone disorder (CKD-MBD). These can lead to cardiovascular pathology, resulting in an increased cardiovascular risk. Bone alkaline phosphatase (BALP) is essential for biomineralization. Recent findings demonstrate a crucial role for BALP in the pathogenesis of vascular calcification and identified it as a promising predictor of mortality in CKD. In conjunction with parathyroid hormone (PTH), serum BALP has been suggested as a biomarker of bone turnover in CKD-MBD. In contrast to PTH, serum BALP demonstrates a lower variability and may thus be better suited for the diagnosis and longitudinal follow-up of bone turnover. The linear association with mortality, compared to the U-shaped curve for PTH, is an additional advantage, making BALP more suitable than PTH as a treatment target in CKD. Here we review the main characteristics of alkaline phosphatase isozymes/isoforms and the various assays currently used in clinical routine laboratories. We also discuss the role of BALP in both physiological and pathological mineralization, and the clinical benefit of BALP determination in CKD.

Alkaline Phosphatases in the Complex Chronic Kidney Disease-Mineral and Bone Disorders.

Alkaline phosphatases (APs) remove the phosphate (dephosphorylation) needed in multiple metabolic processes (from many molecules such as proteins, nucleotides, or pyrophosphate). Therefore, APs are important for bone mineralization but paradoxically they can also be deleterious for other processes, such as vascular calcification and the increasingly known cross-talk between bone and vessels. A proper balance between beneficial and harmful activities is further complicated in the context of chronic kidney disease (CKD). In this narrative review, we will briefly update the complexity of the enzyme, including its different isoforms such as the bone-specific alkaline phosphatase or the most recently discovered B1x. We will also analyze the correlations and potential discrepancies with parathyroid hormone and bone turnover and, most importantly, the valuable recent associations of AP's with cardiovascular disease and/or vascular calcification, and survival. Finally, a basic knowledge of the synthetic and degradation pathways of APs promises to open new therapeutic strategies for the treatment of the CKD-Mineral and Bone Disorder (CKD-MBD) in the near future, as well as for other processes such as sepsis, acute kidney injury, inflammation, endothelial dysfunction, metabolic syndrome or, in diabetes, cardiovascular complications. However, no studies have been done using APs as a primary therapeutic target for clinical outcomes, and therefore, AP's levels cannot yet be used alone as an isolated primary target in the treatment of CKD-MBD. Nonetheless, its diagnostic and prognostic potential should be underlined.

Serum alkaline phosphatase predicts mortality among maintenance hemodialysis patients.

Several observational studies have demonstrated that serum levels of minerals and parathyroid hormone (PTH) have U- or J-shaped associations with mortality in maintenance hemodialysis patients, but the relationship between serum alkaline phosphatase (AlkPhos) and risk for all-cause or cardiovascular death is unknown. In this study, a 3-yr cohort of 73,960 hemodialysis patients in DaVita outpatient dialysis were studied, and the hazard ratios for all-cause and cardiovascular death were higher across 20-U/L increments of AlkPhos, including within the various strata of intact PTH and serum aspartate aminotransferase. In the fully adjusted model, which accounted for demographics, comorbidity, surrogates of malnutrition and inflammation, minerals, PTH, and aspartate aminotransferase, AlkPhos > or =120 U/L was associated with a hazard ratio for death of 1.25 (95% confidence interval 1.21 to 1.29; P < 0.001). This association remained among diverse subgroups of hemodialysis patients, including those positive for hepatitis C antibody. A rise in AlkPhos by 10 U/L during the first 6 mo was incrementally associated with increased risk for death during the subsequent 2.5 yr. In summary, high levels of serum AlkPhos, especially >120 U/L, are associated with mortality among hemodialysis patients. Prospective controlled trials will be necessary to test whether serum AlkPhos measurements could be used to improve the management of renal osteodystrophy.

Glycosaminoglycan, collagen, and glycosidase changes in human osteoblasts treated with interleukin 1, and osteodystrophy.

Normal bone homeostasis involves a balance between osteoblast and osteoclast action, regulated by hormones and cytokine stimuli. Hemodialysis patients appear to have increased production of interleukin-1 (IL-1), interleukin-6 (IL-6) and glycosaminoglycans (GAG) in serum. IL-1 plays a role in the synthesis, degradation and degree of sulphatation of ECM components such as glycosaminoglycans. Also, continuous changes in the ECM involve enzymes such as beta-N-acetyl-d-glucosaminidase (beta-NAG) and beta-d-glucuronidase (beta-GLU) which act on different GAG classes and collagen fibers. We examined the effects of IL-1alpha on ECM synthesis and the related enzymes in human uremic osteoblast cultures. We also measured the levels of IL-1beta, and IL-6 and alkaline phosphatase activity. In biopsies of uremic bone there was less ECM deposition than resorption associated with changes in osteoblast morphology. In vitro osteoblast proliferation was higher (P< or =0.01), and extracellular GAG lower (P< or =0.01) than in controls. The enzyme beta-NAG was high (P< or =0.05) but there were no noteworthy changes in beta-GLU. ELISA of the medium indicated spontaneous production of IL-1beta and IL-6, which significantly increased after IL-1alpha treatment compared to controls. IL-1alpha reduced alkaline phosphatase activity (P< or =0.01) in uremic osteoblast cultures. IL-1 acts on osteoblasts with decreases in GAG synthesis and alkaline phosphatase activity, while beta-NAG increases. This lead to a reduction in the organic component in ECM and its mineralization, and to changes in the regulation of cytokine activity by GAG. The enzymatic breakdown might be facilitated by metabolic acidosis and failed osteoblast differentiation; these factors could be correlated with different degrees of osteodystrophy.

[Tartrate-resistant acid phosphatase--TRAP 5b--as a novel marker of bone resorption in patients with irreversible renal failure treated with dialysis]. / Winianooporna kwasna fosfataza--TRAP 5b--jako nowoczesny wskaznik resorpcji kosci u chorych z nieodwracalna niewydolnoscia nerek leczonych dializami.

UNLABELLED: The evaluation of renal osteodystrophy in everyday practise is based on measurements of non-invasive bone markers. TRAP 5b has been considered as a potentially useful marker of bone resorption rate. We assessed the clinical usefulness of TRAP 5b as a marker of bone resorption in renal osteodystrophy in comparison with standard marker which is intact parathormone (iPTH) level. MATERIAL AND METHODS: We studied 84 patients: 61 on hemodialysis (HD) for 43 +/- 25 months (36M, 25F aged 59 +/- 25 yr.) and 23 on continuous ambulatory peritoneal dialysis (CAPD) for 47 +/- 28 months (12M, 11F, aged 53 +/- 23 yr). The following parameters were determined in serum: TRAP 5b, iPTH, Ca, P, total acid phosphatase (AP). Serum TRAP 5b activity was measured using a solid phase immunofixed enzyme activity assay Bone TRAP (SBA Finland). Intact PTH was measured using immunoradiometric assay (Incstar USA). According to iPTH level patients were divided into 3 subgroups: A--(iPTH < 100 pg/ml); B--(iPTH 100 - 450 pg/ml); C--(iPTH > 450 pg/ml). RESULTS: We found significant correlation between iPTH and TRAP in dialysed pts. (r = 0.6764, p < 0.0001). In patients with high turnover renal osteodystrophy-group C significantly higher values of TRAP were found in comparison with patients with low turnover renal osteodystrophy-group A (7.5 +/- 1.4 vs. 2.9 +/- 1.4 p < 0.001). There was not significant correlation between values of TRAP and gender, cause of irreversible renal failure as well as method of dialysotherapy. CONCLUSION: In conclusion, highly significant correlation between level of TRAP 5b and iPTH found in our study justifies using TRAP 5b as an important marker of bone resorption rate in clinical practice.

[Bone alkaline phosphatase: characteristic and its clinical applications]. / Kostna frakcja fosfatazy alkalicznej: charakterstyka i przydatnosckliniczna jej oznaczania. doniesienie i.

Bone alkaline phosphatase (BALP) is one of the most frequently used biochemical markers of bone formation. The presented paper describes the enzyme's specificity, physiological values during normal growth and development as well as its clinical applications in various diseases. The main interest concerns the ability of BALP to predict bone loss in primary (postmenopausal and senile osteoporosis) and secondary osteoporosis associated with metabolic diseases (galactosemia, cystic fibrosis, celiac disease), renal osteodystrophy, Paget disease and others. The determination of BALP activity seems to be also helpful in diagnosis of the diseases and in monitoring of antiresorptive therapy. Further studies on BALP are needed to elucidate whether this bone formation marker reflect the therapy outcome of individual patients with primary osseus tumours and metastases.

Biochemical parameters of bone turnover in kidney transplant recipients.

Impairment of bone remodelling due to chronic renal failure persists even after successful kidney transplantation. Bone turnover was assessed in 22 kidney transplant recipients by measurement of serum bone markers: total (tALP) and bone alkaline phosphatase (bALP), osteocalcin (OC), procollagen I C-terminal propeptide (PICP), collagen I C-terminal telopeptide (ICTP), and iPTH. The patients were on dialysis 56.6 +/- 43.1 months before transplantation (mean +/- SD) and 34.2 +/- 23.0 months had elapsed after transplantation. The bone markers were within the reference range in 23% of patients for iPTH, 73% for tALP and 82% for bALP, 41% for OC, 73% for PICP and 50% for ICTP. A positive correlation was found between dialysis duration and ICTP, and iPTH and bone formation markers (OC, bALP). The obtained results indicate that bone turnover was increased after kidney transplantation, with prevailing bone resorption, which seems to be influenced by dialysis duration.

Cloning of human 25-hydroxyvitamin D-1 alpha-hydroxylase and mutations causing vitamin D-dependent rickets type 1.

The secosteroid hormone, 1,25-dihydroxyvitamin D [1,25(OH)2D], plays a crucial role in normal bone growth, calcium metabolism, and tissue differentiation. The key step in the biosynthesis of 1,25(OH)2D is its 1 alpha-hydroxylation from 25-hydroxyvitamin D (25-OHD) in the kidney. Because its expression in the kidney is very low, we cloned and sequenced cDNA for 25-OHD-1 alpha-hydroxylase (P450c1 alpha) from human keratinocytes, in which 1 alpha-hydroxylase activity and mRNA expression can be induced to be much greater. P450c1 alpha mRNA was expressed at much lower levels in human kidney, brain, and testis. Mammalian cells transfected with the cloned P450c1 alpha cDNA exhibit robust 1 alpha-hydroxylase activity. The identity of the 1,25(OH)2D3 product synthesized in transfected cells was confirmed by HPLC and gas chromatography-mass spectrometry. The gene encoding P450c1 alpha was localized to chromosome 12, where the 1 alpha-hydroxylase deficiency syndrome, vitamin D-dependent rickets type 1 (VDDR-1), has been localized. Primary cultures of human adult and neonatal keratinocytes exhibit abundant 1 alpha-hydroxylase activity, whereas those from a patient with VDDR-1 lacked detectable activity. Keratinocyte P450c1 alpha cDNA from the patient with VDDR-1 contained deletion/frameshift mutations either at codon 211 or at codon 231, indicating that the patient was a compound heterozygote for two null mutations. These findings establish the molecular genetic basis of VDDR-1, establish a novel means for its study in keratinocytes, and provide the sequence of the key enzyme in the biological activation of vitamin D.

Plasma total versus bone alkaline phosphatase as markers of bone turnover in hemodialysis patients.

Plasma total versus bone alkaline phosphatase as markers of bone turnover in hemodialysis patients. Plasma bone-specific alkaline phosphatase (bAP) has been demonstrated to be more reliable than total alkaline phosphatases (tAP) in providing information about bone turnover in patients with metabolic bone diseases. This study surveyed 42 hemodialysis patients who underwent a systematic transiliac bone biopsy for histomorphometry study. Plasma bAP was determined by using a new immunoassay (Tandem-R Ostase, Hybritech, Liège, Belgium). Plasma bAP values were compared with those of two other plasma markers of bone metabolism, namely tAP and intact parathyroid hormone (iPTH), for the correlations with bone histomorphometric parameters. Patients with high-turnover bone disease (HTBD) (N = 32) had significantly higher plasma bAP levels than patients with normal or low bone turnover (N/LTBD) (N = 10) (66.9 +/- 63.5 ng/mL versus 10.8 +/- 4.2 ng/mL, respectively). Bone formation and resorption were highly correlated in these patients, and plasma bAP levels were positively correlated with bone resorption parameters, including osteoclast surface (r = 0.39, P < 0.0001) and osteoclast number/mm2 (r = 0.36, P < 0.001), and with bone formation parameters, osteoblast surface (r = 0.50, P < 0.005), and bone formation rate (r = 0.91, P < 0.0001). The bone formation rate was better correlated with plasma bAP levels than with either plasma tAP or iPTH concentrations. Plasma bAP level equal or higher than 20 ng/mL, either alone or combined with plasma iPTH of 200 pg/mL, had the highest sensitivity, specificity, and predictability values for the diagnosis of high-turnover bone disease, and formally excluded patients with normal or LTBD. In conclusion, plasma bAP can be measured with a reliable immunoassay in hemodialysis patients. It represents a highly sensitive and specific biochemical marker of skeletal remodeling in these patients. Therefore, both serum iPTH and bAP are complementary in diagnoses of the type of renal osteodystrophy.

Bone alkaline phosphatase isoenzyme in renal osteodystrophy.

Serum total alkaline phosphatase is the most commonly used biochemical marker of bone disease in renal patients, but alkaline phosphatase originates from different organs and sometimes lacks specificity. Bone isoenzyme measurement is considered superior to total alkaline phosphatase for the assessment of bone metabolism. We have studied the value of bone isoenzyme, determined by a new. IRMA (Tandem-R-Ostase), in haemodialysis patients with secondary hyperparathyroidism and renal osteodystrophy. Fifty-six haemodialysis patients were studied. Intact parathyroid hormone (PTH), osteocalcin, total alkaline phosphatase and bone alkaline phosphatase were determined. A transiliac bone biopsy was performed in 20 of the 56 patients after double tetracycline labelling. There was a significant correlation between bone alkaline phosphatase and PTH (r = 0.79, P < 0.001) and between bone and total alkaline phosphatase (r = 0.84, P < 0.001) in all patients. The patients who underwent a bone biopsy showed osteitis fibrosa in 17, mixed lesion in one, adynamic bone disease in one and normal bone in one. Bone alkaline phosphatase showed a significant correlation with static and dynamic histomorphometric indices similar to that obtained with PTH and better than those of total alkaline phosphatase and osteocalcin. It is concluded that bone alkaline phosphatase (ostase) seems to be a useful non-invasive marker of bone metabolism in patients on haemodialysis with high turnover bone disease. More studies are necessary to know its value in low turnover bone disease.

[Loss of bone substance in long-term dialysis--the value of serochemical parameters]. / Knochensubstanzverlust bei Langzeitdialyse--Wertigkeit serochemischer Parameter.

During long-term hemodialysis therapy a loss of bone substance--an osteopenia--may occur. The diagnosis is possible by bone biopsy. We have analyzed the bone metabolism-associated serochemical parameters in patients suffering from osteopenia in comparison with patients with normal bone volume. 21 patients were analyzed: 14 females, 7 males, duration of dialysis 44 +/- 29.9 months, age 47.3 +/- 12.5 years. The serum values of calcium, anorganic phosphate, alkaline phosphatase, pH and c-terminal parathormone are determined. The histological bone examination according to the Delling classification did show following distribution: Type I--0, type II--10, type III--10 (without renal osteopenia--1). A quarter of the patients did show a reduction of the bone mass. The parathormone value was significantly reduced in these patients in comparison with patients without osteopenia. No significant changes could observed in the comparison of alkaline phosphatase, serum calcium, anorganic phosphate and pH value. Our results show that in patients with osteopenia the serum parathormone level is reduced relatively.

Osteocalcin serum levels in patients following renal transplantation.

Osteocalcin serum levels reflect bone turnover. In renal insufficiency secondary hyperparathyroidism and reduced renal clearance might be responsible for elevated serum levels of osteocalcin. Renal transplantation might improve renal osteodystrophy and therefore could influence osteocalcin serum levels. We determined the influence of renal transplantation on osteocalcin levels in 37 consecutive patients (25m/12f) by RIA. Blood samples were collected prior to, 3 days, 28 days, 6 months and 12 months after renal transplantation. Prior to renal transplantation osteocalcin levels were significantly elevated (mean +/- s: 23.4 +/- 12.8 ng/ml) compared to healthy volunteers (4.1 +/- 1.4 ng/ml). Following renal transplantation osteocalcin decreased significantly (9.4 +/- 8.9 ng ml) 3 days and (7.1 +/- 7.8 ng/ml) 28 days. However, 6 and 12 months following renal transplantation the mean osteocalcin level increased again (8.3 +/- 5.7 ng/ml, 12.1 +/- 15.4 ng/ml). At 6 months 11 and at 12 months only 6 of 37 patients had osteocalcin levels in the normal range. 12 months following renal transplantation 21 out of 37 patients with elevated osteocalcin levels had parathyroid hormone levels above the normal range. Additionally to increased osteocalcin levels patients prior to renal transplantation had elevated alkaline phosphatase. Alkaline phosphatase had following renal transplantation a similar pattern as osteocalcin with initial decrease and secondary increase 6 and 12 months after renal transplantation. Parathyroid hormone was elevated in all patients before renal transplantation. Following renal transplantation mean parathyroid hormone levels tell significantly, however remained above normal range in 57% of these 37 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Nature of mononuclear cells positive for acid phosphatase activity in bone marrow of patients with renal osteodystrophy.

Fifty two of 63 patients with renal osteodystrophy had one or more mononuclear cells positive for acid phosphatase in the marrow. These cells are also tartrate resistant and non-specific esterase negative, and are believed to be precursors to osteoclasts and other acid phosphatase positive cells resorbing bone on the trabecular surface.

Rapid suppression of plasma alkaline phosphatase activity after renal transplantation in patients with osteodystrophy.

Plasma alkaline phosphate activity is a important marker of increased skeletal turnover (both resorption and formation) and bone disease in uraemia, but its value after renal transplantation is uncertain. The rate of fall of alkaline phosphatase was compared in three groups of uraemic patients with osteodystrophy and elevated serum alkaline phosphatase undergoing either renal transplantation, parathyroidectomy or therapy with 1a hydroxylated vitamin D derivates. Alkaline phosphatase fell after transplantation, irrespective of graft function, with a half-time significantly less than the other treatments (p less than 0.001). We suggest that this represents a direct inhibitory effect of steroids on osteoblasts and that alkaline phosphatase is thus an unreliable marker of bone resorption after transplantation.

[Mid C regional parathyroid hormone in the clinical workup: diagnostic value in extrarenal (primary) and renal (secondary) hyperparathyroidism]. / Mitt-C-regionales Parathormon in der klinischen Routine: Diagnostische Wertigkeit beim extrarenalen (primären) und renalen (sekundären) Hyperparathyreodismus.

The selective determination of mid-C-regional parathyroid hormone (mid-C-PTH) in combination with other laboratory parameters is a reliable tool for diagnosis and treatment of extra-renal (primary) and renal (secondary) hyperparathyroidism. Early stages, which show either high-to-normal serum calcium and elevated mid-C-PTH or increased serum calcium but normal mid-C-PTH, can be distinguished from overt hyperparathyroidism. Alkaline phosphatase (AP) activity and mid-C-regional PTH provide biochemical confirmation of histologically classified renal osteodystrophy. Since the index AP X PTH signifies osseous changes in dialysis patients at an early stage, therapeutic regimens may be altered without additional invasive procedures. After renal transplantation mid-C-PTH normalizes and serum creatinine decreases. Increased mid-C-PTH in patients with normal renal graft function reflects autonomous PTH secretion, which requires careful monitoring to prevent PTH-induced hypercalciuria.