Development of renal bone disease

Manifestations of hyperparathyroidism in the jaws: Concepts, mechanisms, and clinical aspects

Hyperparathyroidism is one of the most common endocrine disorders worldwide. In countries where routine biochemical screening is not common, symptomatic hyperparathyroidism predominates. Its manifestations include skeletal alterations, calcification of soft tissues, kidney stones, and functional alterations in other systems. Notably, jaw alterations can be the first clinical sign of hyperparathyroidism, including brown tumor, renal osteodystrophy, osteitis fibrosa, and leontiasis ossea, and knowing such conditions is of core importance for the multidisciplinary diagnosis and management of hyperparathyroidism. We aimed to perform a concise review, systematizing the concepts and mechanisms underlying hyperparathyroidism and associated gnathic alterations. In addition, a detailed description of the clinical aspects of the jaw manifestations is presented.

Evaluation of the Relationship Between Homocysteine, Parathormone, Vitamin D3, and Bone Mineral Densitometry in Recipients of Kidney Transplant

PURPOSE

In this study, we evaluated the relationship between serum homocysteine level and proteinuria, parathyroid hormone, vitamin D, and bone mineral density in kidney transplant recipients (KTR).

MATERIALS AND METHODS

A total of 117 stable KTR older than 18 years was followed in our outpatient clinic. Demographic data were recorded. Simultaneously biochemical parameters, including glucose, blood urea nitrogenous, creatinine, calcium, phosphorus, sodium, potassium, albumin, parathormone, vitamin D₃, homocysteine, vitamin B₁₂, folate, and 24-hour urine protein, and bone mineral density of the femoral neck and spine by dual-energy x-ray absorptiometry (DEXA) were measured.

RESULTS

DEXA measurements were normal, osteoporotic, and osteopenic (12.3%, 36.3%, and 51.3%, respectively). There was a relationship between the serum homocysteine and usage of rapamycin (P = .05), statins (P = .057), and beta blockers (P = .01), DEXA measurements were not related with serum homocysteine levels and immunosuppressive drugs used. Serum homocysteine levels correlated negatively with blood urea nitrogen (P = .002), creatinine (P = .001), vitamin B₁₂ (P < .001), and a positively daily proteinuria (rho = 0.203, P = .031). There was a negative relationship between proteinuria and serum level of vitamin D.

CONCLUSIONS

The bone mineral density decreased in more than 87% of our KTR. We did not find any relationship between DEXA measurements and levels of homocysteine, vitamin D, parathormone, and immunosuppressive drugs. It should be noted that some drugs used may affect serum homocysteine levels. Interestingly, there was a relationship between proteinuria and serum levels of homocysteine and vitamin D. Therefore, serum levels of homocysteine and vitamin D should be evaluated for preventing renal damage in KTR.

Influence of Parathyroidectomy on Bone Metabolism and Bone Pain in Patients with Secondary Hyperparathyroidism

BACKGROUND

After parathyroidectomy (PTX), hungry bone syndrome leads to hypocalcemia due to bone remineralization. The aim of this pilot study was to analyze changes in markers of bone metabolism in patients with secondary hyperparathyroidism (sHPT) after PTX and to correlate these markers with bone pain measured with a validated questionnaire.

MATERIALS AND METHODS

All patients who underwent PTX for sHPT between March 2010 and February 2012 at out institution were included in this prospective observational pilot study. At the day before surgery and on the 3rd day thereafter, levels of parathyroid hormone (PTH), calcium, osteocalcin, alkaline phosphatase (AP), bone-specific AP (BAP), tartrate-resistant acid phosphatase 5b (TRAP5b), osteoprotegerin (OPG), sclerostin, fibroblast growth factor 23, and Klotho were measured. Additionally, all patients were requested to answer the Brief Pain Inventory preoperatively and on the 5th postoperative day.

RESULTS

A total of 35 patients with a mean age of 49.8 years were analyzed. A significant difference between the pre- and postoperative values could be detected in PTH, calcium, BAP, TRAP5b, and sclerostin. The highest correlation of laboratory markers with bone pain was found for preoperative PTH (r = 0.3), postoperative OPG (r = 0.4), postoperative BAP (r = -0.4), and postoperative Klotho (r = -0.4).

CONCLUSIONS

The present study revealed significant perioperative changes in PTH, BAP, sclerostin, and TRAP5b after PTX. These markers may serve as laboratory markers to monitor bone metabolism in patients with sHPT. PTH, OPG, and sclerostin were the parameters with the closest correlation to bone pain. However, larger prospective trials with a longer follow-up are required to confirm these results.

Effect of aluminum on markers of bone formation resorption in chronic hemodialysis patients

Background: T`he prevalence of aluminum (Al)-related toxicity in hemodialysis (HD) patients has declined. However, some HD patients continue to receive Al-based phosphate binders, in part because of the expense of Al-free binders.

Objective: To explore the effect of Al-based binders and their discontinuation on iron status, and markers of bone formation resorption in HD patients.

Methods: Following an initial screen of serum Al levels in 37 HD patients, a second screening was performed after discontinuation of Al-based binders in a 2-year follow-up. A desferrioxamine (DFO; 5 mg/kg) test, and assessment of iron status and bone markers were conducted in the second screening.

Results: Mean serum Al level was initially 27.8 ± 10.3 μg/L. Thirteen patients had a serum Al >30 μg/L, a level considered possibly toxic. There was a positive correlation between serum Al levels, HD duration, and cumulative dose of Al-based binder. At the second screening, the mean serum Al level decreased to 12.5 ± 7.4 μg/L. The mean serum Al level increased to 26.0 ± 14.7 μg/L post-DFO, but in none of the patients did the change in serum Al exceed the 50 μg/L threshold associated with Al-induced bone disease. The decrease in serum Al level was associated with a significant increase in intact parathyroid hormone (iPTH) whereas total alkaline phosphatase did not change.

Conclusions: We recommend that if Al-based phosphate binders are used in HD patients, serum Al level, iron, and markers of bone formation resorption be closely monitored to ensure safe use of these drugs.

Is Klotho F352V Polymorphism the Missing Piece of the Bone Loss Puzzle in Renal Transplant Recipients?

BACKGROUND

Bone disorders are next to cardiovascular problems in frequency in renal transplant (RT) recipients. Reduction in 1,25-dihydroxycholecalciferol (1,25D) levels is among the reasons causing bone loss in these patients. Klotho (KL) serves as a co-receptor for fibroblast growth factor 23 (FGF23), and functions in vitamin D metabolism. KL polymorphisms have been identified in several studies, and phenylalanine to valine substitution at amino acid position 352 seemed to be important to KL function. We investigated KL F352V polymorphism and its relation with 1,25D levels in RT recipients.

METHODS

The study included 25 RT recipients (8 female, 17 male) and 26 (14 female, 12 male) healthy control subjects who were wild (FF) phenotypes in terms of KL F352V polymorphism. RT recipients with (FV, n = 11) and without (FF, n = 14) a heterozygote polymorphism were determined with high resolution DNA melting analysis of KL F352V polymorphism. Serum 1,25D levels were measured using the RIA method.

RESULTS

RT recipients with FV phenotype had significantly lower 1,25D levels (17.58 ± 18.38 pg/ml) compared to recipients with FF phenotype (44.91 ± 24.68 pg/ml) and control subjects (28.24 ± 12.13 pg/ml). 1,25D levels in RT recipients with FF phenotype were significantly higher than control subjects.

CONCLUSIONS

KL F352V polymorphism may increase the expression of FGF23 co-receptor, KL protein and thus may decrease renal expression of 1α-hydroxylase, and/or stimulate 24-hydroxylase in RT recipients. The resultant decrease 1,25D levels may participate in bone loss in these patients.

Effect of zinc supplementation on bone formation in hemodialysis patients with normal or low turnover bone

Zinc (Zn) is an essential trace element, which has been shown to stimulate osteoblastic bone formation and to inhibit osteoclastic bone resorption in vitro. In thalassemia, major patients Zn supplementation was reported to increase whole-body bone mineral content and areal bone mineral density. Therefore, we investigated the effect of Zn supplementation on bone formation in hemodialysis (HD) patients. Nine male patients with age of 66 (35-78) years indicated by median (range), HD vintage of 57 (4-97) months and serum intact parathyroid hormone (PTH) of 113 (6-310) pg/mL were supplemented with polaprezinc containing 34 mg Zn/day for 18 months. Doses of vitamin D were not changed during supplementation. Blood was collected at baseline, 3, 6, 12 and 18 months. Serum Zn increased significantly from 58 (52-65) μg/dL to 71 (57-93) μg/dL at three months and remained unchanged until 18 months. No changes were observed in serum intact PTH during supplementation. Although we found no changes in serum bone alkaline phosphatase (BAP) during Zn supplementation analyzed by Friedman test and Scheffe post hoc test, a significant trend of increase in serum BAP was verified by Jonckheere-Terpstra test (p = 0.0409). On the contrary, there was no trend in serum TRACP5b by Jonckheere-Terpstra test. Therefore, we suggested the effect of Zn supplementation on promoting bone formation, not affected by the status of PTH and vitamin D, in HD patients with normal or low turnover bone.

Musculoskeletal manifestations of endocrine disorders

Endocrine disorders can lead to disturbances in numerous systems within the body, including the musculoskeletal system. Radiological evaluation of these conditions can demonstrate typical appearances of the bones and soft tissues. Knowledge of these patterns can allow the radiologist to suggest a diagnosis that may not be clinically apparent. This review will highlight the typical musculoskeletal findings of acromegaly, hypercortisolism, hyperthyroidism, hypothyroidism, hyperparathyroidism, pseudo- and pseudopseudohypoparathyroidism, and diabetes mellitus. The radiological manifestations of each of these endocrine disorders, along with a brief discussion of the pathophysiology and clinical implications, will be discussed.

What is the impact of immunosuppressive treatment on the post-transplant renal osteopathy?

Although glucocorticoid therapy is considered to be the main pathogenic factor, a consistent body of evidence suggests that other immunosuppressants might also play an important role in the development of the post-transplant renal osteopathy (PRO) through their pleiotropic pharmacological effects. Glucocorticoids seem to induce osteoclasts' activity suppressing the osteoblasts while data regarding other immunosuppressive drugs are still controversial. Mycophenolate mofetil and azathioprine appear to be neutral regarding the bone metabolism. However, the study analyzing any independent effect of antimetabolites on bone turnover has not been conducted yet. Calcineurin inhibitors (CNIs) induce trabecular bone loss in rodent, with contradictory results in renal transplant recipients. Suppression of vitamin D receptor is probably the underlying mechanism of renal calcium wasting in renal transplant recipients receiving CNI. In spite of an increased 1,25(OH)2 vitamin D level, the kidney is not able to reserve calcium, suggesting a role of vitamin D resistance that may be related to bone loss. More efforts should be invested to determine the role of CNI in PRO. In particular, data regarding the role of mammalian target of rapamycin inhibitors (mTORi), such as sirolimus and everolimus, in the PRO development are still controversial. Rapamycin markedly decreases bone longitudinal growth as well as callus formation in experimental models, but also lowers the rate of bone resorption markers and glomerular filtration in clinical studies. Everolimus potently inhibits primary mouse and human osteoclast activity as well as the osteoclast differentiation. It also prevents the ovariectomy-induced loss of cancellous bone by 60 %, an effect predominantly associated with a decreased osteoclast-mediated bone resorption, resulting in a partial preservation of the cancellous bone. At present, there is no clinical study analyzing the effect of everolimus on bone turnover in renal transplant recipients or comparing sirolimus versus everolimus impact on bone, so only general conclusions could be drawn. Hence, the use of mTORi might be useful in patients with PRO due to their possible potential to inhibit osteoclast activity which might lead to a decreased rate of bone resorption. In addition, it should be also emphasized that they might inhibit osteoblast activity which may lead to a decreased bone formation and adynamic bone disease. Further studies are urgently needed to solve these important clinical dilemmas.

Histomorphometric measurements of bone turnover, mineralization, and volume

A recent Kidney Disease: Improving Global Outcomes report suggested that bone biopsies in patients with chronic kidney disease should be characterized by determining bone turnover, mineralization, and volume. This article focuses on the calculations and interpretation of these measurements. In most cases of renal osteodystrophy, the bone formation rate is roughly similar to the bone resorption rate; therefore, the bone formation indices can be used to describe turnover. It is important to remember that these conventions will not apply in some situations. Activation frequency should not be confused with bone formation rate or bone metabolic unit birth rate. Abnormal mineralization can be described using the osteoid volume, increased osteoid maturation time, or increased mineralization lag time. The concept of bone volume is the easiest to understand, but there is a large error from one biopsy to the next in the same person. There are some difficulties with each of the measurements, and further research in patients with chronic kidney must be done to enable a consensus to be reached about cut points to define categories within the spectrum of renal osteodystrophy and how to evaluate treatment responses.

Osteitis fibrosa is mediated by Platelet-Derived Growth Factor-A via a phosphoinositide 3-kinase-dependent signaling pathway in a rat model for chronic hyperparathyroidism

Abnormal secretion of PTH by the parathyroid glands contributes to a variety of common skeletal disorders. Prior studies implicate platelet-derived growth factor-A (PDGF-A) as an important mediator of selective PTH actions on bone. The present studies used targeted gene profiling and small-molecule antagonists directed against candidate gene products to elucidate the roles of specific PTH-regulated genes and signaling pathways. A group of 29 genes in rats continuously infused with PTH and cotreated with the PDGF receptor antagonist trapidil were differentially expressed compared with PTH treatment alone. Several of the identified genes were functionally clustered as regulators of fibroblast differentiation and extracellular matrix modeling, including the matrix cross-linking enzyme lysyl oxidase (LOX). Treatment with beta-aminopropionitrile, an irreversible inhibitor of LOX activity, dramatically reduced diffuse mineralization but had no effect on PTH-induced fibrosis. In contrast, the receptor tyrosine kinase inhibitor Gleevec and the phosphoinositide 3-kinase inhibitor wortmannin each reduced bone marrow fibrosis. In summary, the present studies support the hypotheses that PTH-induced bone marrow fibrosis is mediated by PDGF-A via a phosphoinositide 3-kinase-dependent signaling pathway and that increased LOX gene expression plays a key role in abnormal mineralization, a hallmark of chronic hyperparathyroidism.

Biomarker candidates for cardiovascular disease and bone metabolism disorders in chronic kidney disease: a systems biology perspective

Patients with chronic kidney disease (CKD) show a panel of partially de-regulated serum markers indicative for bone metabolism disorders and cardiovascular diseases (CVDs). This review provides an overview of currently reported biomarker candidates at the interface of kidney disease, bone metabolism disorders and CVDs, and gives details on their functional interplay on the level of protein–protein interaction data. We retrieved 13 publications from 1999 to 2006 reporting 31 genes associated with CVDs, and 46 genes associated with bone metabolism disorders in patients with CKD. We identified these genes to be functionally involved in signal transduction processes, cell communication, immunity and defence, as well as skeletal development. On the basis of the given set of 77 genes further 276 interacting proteins were identified using reference data on known protein interactions. Their functional interplay was estimated by linking properties reflected by gene expression data characterizing CKD, gene ontology terms as provided by the gene ontology consortium and transcription factor binding site profiles. Highly connected sub-networks of proteins associated with CKD, CVDs or bone metabolism disorders were detected involving proteins like collagens (COL1A1, COL1A2), fibronectin, transforming growth factor-β₁, or components of fibrinogen (FG-α, FG-β, FG-γ). A systems biology approach provides a methodological framework for linking singular biomarker candidates towards deriving functional dependencies among clinically interlinked diseases.

Mineral and bone disorder after renal transplantation: a review

Chronic kidney disease-mineral bone disorder is a common clinical picture encountered in patients with end-stage renal disease and is the result of additive pathophysiological processes. Renal transplantation remains the treatment of choice for these patients, especially as advances in this field have allowed for enhanced allograft survival. However, with increasing success of renal transplantation has come a greater appreciation of some of its subsequent complications, such as posttransplantation bone disease. Recently, persistent hyperparathyroidism and osteopenia-osteoporosis have been given specific attention. Traditionally, persistent hyperparathyroidism has been treated with parathyroidectomy, although the role that calcimimetics may play in the future is promising. Newer aspects to medical management of osteopenia-osteoporosis, such as the efficacy of bisphosphonate therapy and early steroid withdrawal, are becoming apparent and some of the newer drugs for the treatment of osteoporosis are yet to be investigated in this subgroup of patients.