Rapamycin retards growth and causes marked alterations in the growth plate of young rats

Changes in bone density and microarchitecture in adolescents undergoing a first kidney transplantation: a prospective study

PURPOSE

Mineral bone disorder associated with chronic kidney disease (CKD-MBD) frequently persists after kidney transplantation (KTx), being due to pre-existing CKD-MBD, immunosuppressive therapies, and post-KTx hypophosphatemia. This study aimed to evaluate bone biomarkers and microarchitecture using high resolution peripheral quantitative computed tomography (HR-pQCT) at the time of KTx and 6 months thereafter and to compare these results with those of matched healthy controls (HC).

METHODS

This study presented the single-center subgroup of patients aged between 10 and 18 years included in the prospective "Bone Microarchitecture in the Transplant Patient" study (TRANSOS-NCT02729142). Patients undergoing a first KTx were matched (1:2) with HC from the "Vitamin D, Bones, Nutritional and Cardiovascular Status" cohort (VITADOS) on sex, pubertal stage, and age.

RESULTS

At a median (interquartile range, IQR) age of 15 [13; 16] years, 19 patients (6 girls, 7 pre-emptive KTx, 7 steroid-sparing immunosuppressive strategies) underwent a first KTx, with a median [IQR] parathyroid hormone level of 1.9 [1.4; 2.9] the upper limit of normal (ULN). Higher total and trabecular bone densities, along with superior trabecular microarchitecture, were observed at KTx compared to HC. Six months post-KTx, patients had significantly impaired trabecular parameters at the radius, while results were not significantly different at the weight-bearing tibia, neither cortical parameters at both sites. Six months post-KTx, 6 (32%) patients still present with metabolic acidosis, 10 (53%) persistent hyperparathyroidism (always < 2 ULN), and 5 (26%) elevated FGF23 levels; 11 (58%) received phosphate supplementation.

CONCLUSIONS

Bone density and microarchitecture at the time of KTx were superior compared to HC, but radial trabecular bone microarchitecture impairment observed 6 months post-KTx may reflect subtle albeit present post-KTx CKD-MBD. What is Known? • Mineral bone disorder associated with chronic kidney disease (CKD-MBD) frequently persists after kidney transplantation (KTx) and is associated with morbidity. However, biochemical parameters and dual X-ray absorptiometry (DXA) are poor predictors of the underlying bone disease. What is new? • The present study on 19 adolescent KTx recipients with adequate CKD-MBD control at the time of KTx reveals no significant bone disease compared to matched healthy controls. Microarchitecture impairment observes 6 months post-KTx may reflect subtle, albeit present, post-KTx CKD-MBD.

Supplementation with a Whey Protein Concentrate Enriched in Bovine Milk Exosomes Improves Longitudinal Growth and Supports Bone Health During Catch-Up Growth in Rats

BACKGROUND

Undernutrition impairs linear growth while restoration of nutritional provisions leads to accelerated growth patterns. However, the composition of the nutrition provided is key to facilitating effective catch-up growth without compromising bone quantity, quality, and long-term health.

METHODS

We evaluated the role of a whey protein concentrate enriched in bovine milk exosomes (BMEs) in modulating the proliferative properties of human chondrocytes in vitro and studied how these effects might impact bone quantity and quality measured as longitudinal tibia growth, bone mineral content (BMC) and density (BMD), and trabecular micro-CT parameters in stunted rats during catch-up growth.

RESULTS

BMEs promoted proliferation in C28/I2 human chondrocytes mediated by mTOR-Akt signaling. In a stunting rat model, two-week supplementation with BMEs during refeeding was associated with improved tibia BMD, trabecular microstructure (trabecular number (Tb. N.) and space (Tb. Sp.)), and a more active growth plate (higher volume, surface, and thickness) compared to non-supplemented stunted rats. Positive effects on physis translated to significantly longer tibias without compromising bone quality when extending the refeeding period for another two weeks.

CONCLUSIONS

Overall, BME supplementation positively contributed to longitudinal bone growth and improved bone quantity and quality during catch-up growth. These findings might be relevant for improving diets aimed at addressing the nutritional needs of children undergoing undernutrition during early life.

PINK1/Parkin-mediated mitophagy inhibits osteoblast apoptosis induced by advanced oxidation protein products

Osteoblast apoptosis plays an important role in age-related bone loss and osteoporosis. Our previous study revealed that advanced oxidation protein products (AOPPs) could induce nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) production, cause mitochondrial membrane potential (ΔΨm) depolarization, trigger the mitochondria-dependent intrinsic apoptosis pathway, and lead to osteoblast apoptosis and ultimately osteopenia and bone microstructural destruction. In this study, we found that AOPPs also induced mitochondrial ROS (mtROS) generation in osteoblastic MC3T3-E1 cells, which was closely related to NOX-derived ROS, and aggravated the oxidative stress condition, thereby further promoting apoptosis. Removing excessive ROS and damaged mitochondria is the key factor in reversing AOPP-induced apoptosis. Here, by in vitro studies, we showed that rapamycin further activated PINK1/Parkin-mediated mitophagy in AOPP-stimulated MC3T3-E1 cells and significantly alleviated AOPP-induced cell apoptosis by eliminating ROS and damaged mitochondria. Our in vivo studies revealed that PINK1/Parkin-mediated mitophagy could decrease the plasma AOPP concentration and inhibit AOPP-induced osteoblast apoptosis, thus ameliorating AOPP accumulation-related bone loss, bone microstructural destruction and bone mineral density (BMD) loss. Together, our study indicated that therapeutic strategies aimed at upregulating osteoblast mitophagy and preserving mitochondrial function might have potential for treating age-related osteoporosis.

PINK1/Parkin-mediated mitophagy inhibits osteoblast apoptosis induced by advanced oxidation protein products

Osteoblast apoptosis plays an important role in age-related bone loss and osteoporosis. Our previous study revealed that advanced oxidation protein products (AOPPs) could induce nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) production, cause mitochondrial membrane potential (ΔΨm) depolarization, trigger the mitochondria-dependent intrinsic apoptosis pathway, and lead to osteoblast apoptosis and ultimately osteopenia and bone microstructural destruction. In this study, we found that AOPPs also induced mitochondrial ROS (mtROS) generation in osteoblastic MC3T3-E1 cells, which was closely related to NOX-derived ROS, and aggravated the oxidative stress condition, thereby further promoting apoptosis. Removing excessive ROS and damaged mitochondria is the key factor in reversing AOPP-induced apoptosis. Here, by in vitro studies, we showed that rapamycin further activated PINK1/Parkin-mediated mitophagy in AOPP-stimulated MC3T3-E1 cells and significantly alleviated AOPP-induced cell apoptosis by eliminating ROS and damaged mitochondria. Our in vivo studies revealed that PINK1/Parkin-mediated mitophagy could decrease the plasma AOPP concentration and inhibit AOPP-induced osteoblast apoptosis, thus ameliorating AOPP accumulation-related bone loss, bone microstructural destruction and bone mineral density (BMD) loss. Together, our study indicated that therapeutic strategies aimed at upregulating osteoblast mitophagy and preserving mitochondrial function might have potential for treating age-related osteoporosis.

PINK1/Parkin-mediated mitophagy inhibits osteoblast apoptosis induced by advanced oxidation protein products

Osteoblast apoptosis plays an important role in age-related bone loss and osteoporosis. Our previous study revealed that advanced oxidation protein products (AOPPs) could induce nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) production, cause mitochondrial membrane potential (ΔΨm) depolarization, trigger the mitochondria-dependent intrinsic apoptosis pathway, and lead to osteoblast apoptosis and ultimately osteopenia and bone microstructural destruction. In this study, we found that AOPPs also induced mitochondrial ROS (mtROS) generation in osteoblastic MC3T3-E1 cells, which was closely related to NOX-derived ROS, and aggravated the oxidative stress condition, thereby further promoting apoptosis. Removing excessive ROS and damaged mitochondria is the key factor in reversing AOPP-induced apoptosis. Here, by in vitro studies, we showed that rapamycin further activated PINK1/Parkin-mediated mitophagy in AOPP-stimulated MC3T3-E1 cells and significantly alleviated AOPP-induced cell apoptosis by eliminating ROS and damaged mitochondria. Our in vivo studies revealed that PINK1/Parkin-mediated mitophagy could decrease the plasma AOPP concentration and inhibit AOPP-induced osteoblast apoptosis, thus ameliorating AOPP accumulation-related bone loss, bone microstructural destruction and bone mineral density (BMD) loss. Together, our study indicated that therapeutic strategies aimed at upregulating osteoblast mitophagy and preserving mitochondrial function might have potential for treating age-related osteoporosis.

Chronic Kidney Disease-Mineral Bone Disease biomarkers in kidney transplant patients

Background:

Chronic Kidney Disease associated with Mineral Bone Disease (CKD-MBD) is frequent in kidney transplant patients. Post-transplantation bone disease is complex, especially in patients with pre-existing metabolic bone disorders that are further affected by immunosuppressive medications and changes in renal allograft function. Main biochemical abnormalities of mineral metabolism in kidney transplantation (KTx) include hypophosphatemia, hyperparathyroidism (HPTH), insufficiency or deficiency of vitamin D, and hypercalcemia.

Objective:

This review aimed to summarize the pathophysiology and main biomarkers of CKD-MBD in KTx.

Methods:

A comprehensive and non-systematic search in PubMed was independently made with an emphasis on biomarkers in mineral bone disease in KTx.

Results:

CKD-MBD can be associated with numerous factors including secondary HPTH, metabolic dysregulations before KTx, and glucocorticoids therapy in post-transplant subjects. Fibroblast growth factor 23 (FGF23) reaches normal levels after KTx with good allograft function, while calcium, vitamin D and phosphorus, ultimately, result in hypercalcemia, persistent vitamin D insufficiency, and hypophosphatemia respectively. As for PTH levels, there is an initial tendency of a significant decrease, followed by a raise due to secondary or tertiary HPTH. In regard to sclerostin levels, there is no consensus in the literature.

Conclusion:

KTx patients should be continuously evaluated for mineral homeostasis and bone status, both cases with successful kidney transplantation and those with reduced functionality. Additional research on CKD-MBD pathophysiology, diagnosis, and management is essential to guarantee long-term graft function, better prognosis, good quality of life, and reduced mortality for KTx patients.

Induction and maintenance immunosuppression in pediatric kidney transplantation-Advances and controversies

Advances in immunosuppression have improved graft survival in pediatric kidney transplant recipients; however, treatment-related toxicities need to be balanced against the possibility of graft rejection. Several immunosuppressive agents are available for use in transplant recipients; however, the optimal combinations of agents remain unclear, resulting in variations in institutional protocols. Lymphocyte-depleting antibodies, specifically ATG, are the most common induction agent used for pediatric kidney transplantation in the US. Basiliximab may be used for induction in immunologically low-risk children; however, pediatric data are scarce. CNIs and antiproliferative agents (mostly Tac and mycophenolate in recent years) constitute the backbone of maintenance immunosuppression. Steroid-avoidance maintenance regimens remain controversial. Belatacept and mTOR inhibitors are used in children under specific circumstances such as non-adherence or CNI toxicity. This article reviews the indications, mechanism of action, efficacy, dosing, and side effect profiles of various immunosuppressive agents available for pediatric kidney transplantation.

Systemic Jak1 activation causes extrarenal calcitriol production and skeletal alterations provoking stunted growth

Mineral homeostasis is regulated by a complex network involving endocrine actions by calcitriol, parathyroid hormone (PTH), and FGF23 on several organs including kidney, intestine, and bone. Alterations of mineral homeostasis are found in chronic kidney disease and other systemic disorders. The interplay between the immune system and the skeletal system is not fully understood, but cytokines play a major role in modulating calcitriol production and function. One of the main cellular signaling pathways mediating cytokine function is the Janus kinase (JAK)--signal transducer and activator of transcription (STAT) pathway. Here, we used a mouse model (Jak1^S645P+/- ) that resembles a constitutive activating mutation of the Jak1/Stat3 signaling pathway in humans, and shows altered mineral metabolism, with higher fibroblast growth factor 23 (FGF23) levels, lower PTH levels, and higher calcitriol levels. The higher calcitriol levels are probably due to extrarenal calcitriol production. Furthermore, systemic Jak1/Stat3 activation led to growth impairment and skeletal alterations. The growth plate in long bones showed decreased chondrocyte proliferation rates and reduced height of terminal chondrocytes. Furthermore, we demonstrate that Jak1 is also involved in bone remodeling early in life. Jak1^S645P+/- animals have decreased bone and cortical volume, imbalanced bone remodeling, reduced MAP kinase signaling, and local inflammation. In conclusion, Jak1 plays a major role in bone health probably both, directly and systemically by regulating mineral homeostasis. Understanding the role of this signaling pathway will contribute to a better knowledge in bone growth and in mineral physiology, and to the development of selective Jak inhibitors as osteoprotective agents.

CKD-MBD post kidney transplantation

Complications of chronic kidney disease-associated mineral and bone disorders (CKD-MBD) are frequently observed in pediatric kidney transplant recipients and are associated with high morbidity, including growth failure, leg deformities, bone pain, fractures, osteonecrosis, and vascular calcification. Post-transplant CKD-MBD is mainly due to preexisting renal osteodystrophy and cardiovascular changes at the time of transplantation, glucocorticoid treatment, and reduced graft function. In addition, persistent elevated levels of parathyroid hormone (PTH) and fibroblast growth factor 23 may cause hypophosphatemia, resulting in impaired bone mineralization. Patient monitoring should include assessment of growth, leg deformities, and serum levels of calcium, phosphate, magnesium, alkaline phosphatase, 25-hydroxyvitamin D, and PTH. Therapy should primarily focus on regular physical activity, preservation of transplant function, and steroid-sparing immunosuppressive protocols. In addition, adequate monitoring and treatment of vitamin D and mineral metabolism including vitamin D supplementation, oral phosphate, and/or magnesium supplementation, in case of persistent hypophosphatemia/hypomagnesemia, and treatment with active vitamin D in cases of persistent secondary hyperparathyroidism. The latter should be done using the minimum PTH-suppressive dosages aiming at the recommended CKD stage-dependent PTH target range. Finally, treatment with recombinant human growth hormone should be considered in patients lacking catch-up growth within the first year after transplantation.

Prophylactic treatment of rapamycin ameliorates naturally developing and episode -induced heterotopic ossification in mice expressing human mutant ACVR1

Background

Fibrodysplasia ossificans progressiva (FOP) is a rare autosomal-dominant disease characterized by heterotopic ossification (HO) in soft tissues and caused by a mutation of the ACVR1A/ALK2 gene. Activin-A is a key molecule for initiating the process of HO via the activation of mTOR, while rapamycin, an mTOR inhibitor, effectively inhibits the Activin-A-induced HO. However, few reports have verified the effect of rapamycin on FOP in clinical perspectives.

Methods

We investigated the effect of rapamycin for different clinical situations by using mice conditionally expressing human mutant ACVR1A/ALK2 gene. We also compared the effect of rapamycin between early and episode-initiated treatments for each situation.

Results

Continuous, episode-independent administration of rapamycin reduced the incidence and severity of HO in the natural course of FOP mice. Pinch-injury induced HO not only at the injured sites, but also in the contralateral limbs and provoked a prolonged production of Activin-A in inflammatory cells. Although both early and injury-initiated treatment of rapamycin suppressed HO in the injured sites, the former was more effective at preventing HO in the contralateral limbs. Rapamycin was also effective at reducing the volume of recurrent HO after the surgical resection of injury-induced HO, for which the early treatment was more effective.

Conclusion

Our study suggested that prophylactic treatment will be a choice of method for the clinical application of rapamycin for FOP.

Local delivery of bone morphogenetic protein-2 from near infrared-responsive hydrogels for bone tissue regeneration

Achievement of spatiotemporal control of growth factors production remains a main goal in tissue engineering. In the present work, we combined inducible transgene expression and near infrared (NIR)-responsive hydrogels technologies to develop a therapeutic platform for bone regeneration. A heat-activated and dimerizer-dependent transgene expression system was incorporated into mesenchymal stem cells to conditionally control the production of bone morphogenetic protein 2 (BMP-2). Genetically engineered cells were entrapped in hydrogels based on fibrin and plasmonic gold nanoparticles that transduced incident energy of an NIR laser into heat. In the presence of dimerizer, photoinduced mild hyperthermia induced the release of bioactive BMP-2 from NIR-responsive cell constructs. A critical size bone defect, created in calvaria of immunocompetent mice, was filled with NIR-responsive hydrogels entrapping cells that expressed BMP-2 under the control of the heat-activated and dimerizer-dependent gene circuit. In animals that were treated with dimerizer, NIR irradiation of implants induced BMP-2 production in the bone lesion. Induction of NIR-responsive cell constructs conditionally expressing BMP-2 in bone defects resulted in the formation of new mineralized tissue, thus indicating the therapeutic potential of the technological platform.

Does mammalian target of rapamycin or sestrin 1 protein signaling have a role in bone fracture healing?

Background/aim

Fracture healing is a complex physiological process that involves a well-orchestrated series of biological events. The mammalian target of rapamycin (mTOR) and sestrin 1 (SESN 1) play a central role in cell metabolism, proliferation, and survival. The aim of our study is to present serum mTOR and SESN 1 levels by comparing patients with or without bone fractures. It is also a guide for further research on the roles of these proteins in fracture healing.

Materials and methods

A total of 34 patients (10 females, 24 males) with bone fractures and 32 controls (10 females, 22 males) participated in this study. After collecting serum venous blood samples, the quantitative sandwich ELISA technique was used for the determination of serum mTOR and SESN 1 levels.

Results

The mean serum mTOR level was significantly higher in the fracture group compared to the control group (P = 0.001). However, SESN 1 levels did not significantly differ between groups (P = 0.913).

Conclusion

We found that serum mTOR levels increased on the first day after fracture compared to the control group. However, we obtained no significant difference between groups in terms of SESN 1 levels. This study may guide further clinical studies investigating the potential role of mTOR signaling in the bone healing process.

Mammalian target of rapamycin as a therapeutic target in osteoporosis

The mechanistic target of rapamycin (mTOR) plays a key role in sensing and integrating large amounts of environmental cues to regulate organismal growth, homeostasis, and many major cellular processes. Recently, mounting evidences highlight its roles in regulating bone homeostasis, which sheds light on the pathogenesis of osteoporosis. The activation/inhibition of mTOR signaling is reported to positively/negatively regulate bone marrow mesenchymal stem cells (BMSCs)/osteoblasts-mediated bone formation, adipogenic differentiation, osteocytes homeostasis, and osteoclasts-mediated bone resorption, which result in the changes of bone homeostasis, thereby resulting in or protect against osteoporosis. Given the likely importance of mTOR signaling in the pathogenesis of osteoporosis, here we discuss the detailed mechanisms in mTOR machinery and its association with osteoporosis therapy.

mTORC1 Inhibits NF-κB/NFATc1 Signaling and Prevents Osteoclast Precursor Differentiation, In Vitro and In Mice

The mechanistic target of rapamycin complex 1 (mTORC1) is a critical sensor for bone homeostasis and bone formation; however, the role of mTORC1 in osteoclast development and the underlying mechanisms have not yet been fully established. Here, we found that mTORC1 activity declined during osteoclast precursors differentiation in vitro and in vivo. We further targeted deletion of Raptor (mTORC1 key component) or Tsc1 (mTORC1 negative regulator) to constitutively inhibit or activate mTORC1 in osteoclast precursors (monocytes/macrophages), using LyzM-cre mice. Osteoclastic formation was drastically increased in cultures of Raptor deficient bone marrow monocytes/macrophages (BMMs), and Raptor-deficient mice displayed osteopenia with enhanced osteoclastogenesis. Conversely, BMMs lacking Tsc1 exhibited a severe defect in osteoclast-like differentiation and absorptive function, both of which were restored following rapamycin treatment. Importantly, expression of nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), transcription factors that are essential for osteoclast differentiation was negatively regulated by mTORC1 in osteoclast lineages. These results provide evidence that mTORC1 plays as a critical role as an osteoclastic differentiation-limiting signal and suggest a potential drawback in treating bone loss-related diseases with mTOR inhibitors clinically. © 2017 American Society for Bone and Mineral Research.

Effects of growth hormone treatment on growth plate, bone, and mineral metabolism of young rats with uremia induced by adenine

BackgroundIn a model of growth retardation secondary to chronic kidney disease (CKD) induced by adenine, this study explores the effects of growth hormone (GH) therapy on growth plate and mineral metabolism.MethodsWeaning female rats receiving a 0.5% adenine diet during 21 days, untreated (AD) or treated with GH (ADGH) for 1 week, were compared with control rats receiving normal diet, either ad libitum or pair-fed with AD animals. AD and ADGH rats had similarly elevated serum concentrations of urea nitrogen, parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF23).ResultsUremia induced by adenine caused growth retardation and disturbed growth cartilage chondrocyte hypertrophy. We demonstrated marked expression of aquaporin 1 in the growth plate, but its immunohistochemical signal and the expression levels of other proteins potentially related with chondrocyte enlargement, such as Na-K-2Cl cotransporter, insulin-like growth factor 1 (IGF-1), and IGF-1 receptor, were not different among the four groups of rats. The distribution pattern of vascular endothelial growth factor was also similar. AD rats developed femur bone structure abnormalities analyzed by micro-computerized tomography.ConclusionGH treatment accelerated longitudinal growth velocity, stimulated the proliferation and enlargement of chondrocytes, and did not modify the elevated serum PTH or FGF23 concentrations or the abnormal bone structure.

Implications of the Interaction Between miRNAs and Autophagy in Osteoporosis

Imbalances between bone formation and resorption are the primary cause of osteoporosis. However, currently, a detailed molecular mechanism of osteoporosis is not available. Autophagy is the conserved process characterized by degrading and recycling aggregated proteins, intracellular pathogens, and damaged organelles. MicroRNAs (miRNAs) are novel regulatory factors that play important roles in numerous cellular processes, including autophagy, through the posttranscriptional regulation of gene expression. Conversely, autophagy plays a role in the regulation of miRNA homeostasis. Recent advances have revealed that both autophagy and miRNAs are involved in the maintenance of bone homoeostasis, whereas the role of the interaction of miRNAs with autophagy in osteoporosis remains unclear. In this paper, we review previous reports on autophagy, miRNAs, and their interaction in osteoporosis.

mTORC1 regulates PTHrP to coordinate chondrocyte growth, proliferation and differentiation

Precise coordination of cell growth, proliferation and differentiation is essential for the development of multicellular organisms. Here, we report that although the mechanistic target of rapamycin complex 1 (mTORC1) activity is required for chondrocyte growth and proliferation, its inactivation is essential for chondrocyte differentiation. Hyperactivation of mTORC1 via TSC1 gene deletion in chondrocytes causes uncoupling of the normal proliferation and differentiation programme within the growth plate, resulting in uncontrolled cell proliferation, and blockage of differentiation and chondrodysplasia in mice. Rapamycin promotes chondrocyte differentiation and restores these defects in mutant mice. Mechanistically, mTORC1 downstream kinase S6K1 interacts with and phosphorylates Gli2, and releases Gli2 from SuFu binding, resulting in nuclear translocation of Gli2 and transcription of parathyroid hormone-related peptide (PTHrP), a key regulator of bone development. Our findings demonstrate that dynamically controlled mTORC1 activity is crucial to coordinate chondrocyte proliferation and differentiation partially through regulating Gli2/PTHrP during endochondral bone development.

Regulation of Long Bone Growth in Vertebrates; It Is Time to Catch Up

The regulation of organ size is essential to human health and has fascinated biologists for centuries. Key to the growth process is the ability of most organs to integrate organ-extrinsic cues (eg, nutritional status, inflammatory processes) with organ-intrinsic information (eg, genetic programs, local signals) into a growth response that adapts to changing environmental conditions and ensures that the size of an organ is coordinated with the rest of the body. Paired organs such as the vertebrate limbs and the long bones within them are excellent models for studying this type of regulation because it is possible to manipulate one member of the pair and leave the other as an internal control. During development, growth plates at the end of each long bone produce a transient cartilage model that is progressively replaced by bone. Here, we review how proliferation and differentiation of cells within each growth plate are tightly controlled mainly by growth plate-intrinsic mechanisms that are additionally modulated by extrinsic signals. We also discuss the involvement of several signaling hubs in the integration and modulation of growth-related signals and how they could confer remarkable plasticity to the growth plate. Indeed, long bones have a significant ability for "catch-up growth" to attain normal size after a transient growth delay. We propose that the characterization of catch-up growth, in light of recent advances in physiology and cell biology, will provide long sought clues into the molecular mechanisms that underlie organ growth regulation. Importantly, catch-up growth early in life is commonly associated with metabolic disorders in adulthood, and this association is not completely understood. Further elucidation of the molecules and cellular interactions that influence organ size coordination should allow development of novel therapies for human growth disorders that are noninvasive and have minimal side effects.

Fifty shades of gray: Bone disease in renal transplantation

Kidney transplantation is the renal replacement therapy of choice for patients with end stage renal disease. Advances in technology, surgical techniques and pharmacotherapy have improved renal allograft survival. Increasingly, we are seeing long term side effects related to renal transplantation, bone disease being a major one amongst them. Renal transplant patients have a higher risk of fragility fractures even when compared to those who remain on dialysis. This is likely to be related to pre-existing underlying bone disease and the emergence of new metabolic bone problems post-transplant. Conditions such as persistent hyperparathyroidism and the use of certain immunosuppressive agents have a deleterious effect on the post renal transplant bone.

Remarkable advances in the field of metabolic bone research have been made in the last decade and newer imaging techniques, biomarkers and therapeutic options are now available for osteoporosis in the general population. Interest is being focused on attempting to extrapolate these new discoveries to the management of bone disease post renal transplant. This review will briefly describe the metabolic bone changes that occur after transplantation and will provide an update on the currently available investigative options and therapeutic strategies for the management of post renal transplant bone disease.

Current Status of Research on Osteoporosis after Solid Organ Transplantation: Pathogenesis and Management

Improved survival following organ transplantation has brought to the forefront some long-term complications, among which osteoporosis and associated fractures are the major ones that adversely affect the quality of life in recipients. The pathogenesis of osteoporosis in transplant recipients is complex and multifactorial which may be related to increased bone resorption, decreased bone formation, or both. Studies have shown that the preexisting underlying metabolic bone disorders and the use of immunosuppressive agents are the major risk factors for osteoporosis and fractures after organ transplantation. And rapid bone loss usually occurs in the first 6–12 months with a significant increase in fracture risk. This paper will provide an updated review on the possible pathogenesis of posttransplant osteoporosis and fractures, the natural history, and the current prevention and treatment strategies concerning different types of organ transplantation.

Local intra-articular injection of rapamycin delays articular cartilage degeneration in a murine model of osteoarthritis

Introduction

Recent studies have revealed that rapamycin activates autophagy in human chondrocytes preventing the development of osteoarthritis (OA) like changes in vitro, while the systemic injection of rapamycin reduces the severity of experimental osteoarthritis in a murine model of OA in vivo. Since the systemic use of rapamycin is associated with numerous side effects, the goal of the current study was to examine the beneficial effect of local intra-articular injection of rapamycin in a murine model of OA and to elucidate the mechanism of action of rapamycin on articular cartilage.

Methods

Destabilization of the medial meniscus (DMM) was performed on 10-week-old male mice to induce OA. Intra-articular injections of 10 μl of rapamycin (10 μM) were administered twice weekly for 8 weeks. Articular cartilage damage was analyzed by histology using a semi-quantitative scoring system at 8 and 12 weeks after surgery. Mammalian target of rapamycin (mTOR), light chain 3 (LC3), vascular endothelial growth factor (VEGF), collagen, type X alpha 1 (COL10A1), and matrix metallopeptidase 13 (MMP13) expressions were analyzed by immunohistochemistry. VEGF, COL10A1, and MMP13 expressions were further examined via quantitative RT-PCR (qPCR).

Results

Intra-articular injection of rapamycin significantly reduced the severity of articular cartilage degradation at 8 and 12 weeks after DMM surgery. A reduction in mTOR expression and the activation of LC3 (an autophagy marker) in the chondrocytes was observed in the rapamycin treated mice. Rapamycin treatment also reduced VEGF, COL10A1, and MMP13 expressions at 8 and 12 weeks after DMM surgery.

Conclusion

These results demonstrate that the intra-articular injection of rapamycin could reduce mTOR expression, leading to a delay in articular cartilage degradation in our OA murine model. Our observations suggest that local intra-articular injection of rapamycin could represent a potential therapeutic approach to prevent OA.

Mechanical activation of mammalian target of rapamycin pathway is required for cartilage development

Mechanical stress regulates development by modulating cell signaling and gene expression. However, the cytoplasmic components mediating mechanotransduction remain unclear. In this study, elimination of muscle contraction during chicken embryonic development resulted in a reduction in the activity of mammalian target of rapamycin (mTOR) in the cartilaginous growth plate. Inhibition of mTOR activity led to significant inhibition of chondrocyte proliferation, cartilage tissue growth, and expression of chondrogenic genes, including Indian hedgehog (Ihh), a critical mediator of mechanotransduction. Conversely, cyclic loading (1 Hz, 5% matrix deformation) of embryonic chicken growth plate chondrocytes in 3-dimensional (3D) collagen scaffolding induced sustained activation of mTOR. Mechanical activation of mTOR occurred in serum-free medium, indicating that it is independent of growth factor or nutrients. Treatment of chondrocytes with Rapa abolished mechanical activation of cell proliferation and Ihh gene expression. Cyclic loading of chondroprogenitor cells deficient in SH2-containing protein tyrosine phosphatase 2 (Shp2) further enhanced mechanical activation of mTOR, cell proliferation, and chondrogenic gene expression. This result suggests that Shp2 is an antagonist of mechanotransduction through inhibition of mTOR activity. Our data demonstrate that mechanical activation of mTOR is necessary for cell proliferation, chondrogenesis, and cartilage growth during bone development, and that mTOR is an essential mechanotransduction component modulated by Shp2 in the cytoplasm.

mTOR inhibitors in pediatric kidney transplantation

The mammalian target of the rapamycin (mTOR) inhibitors sirolimus and everolimus are increasingly being used in pediatric kidney transplantation in different combinations and doses. Several studies have shown beneficial effects of using mTOR inhibitors in children after pediatric renal transplantation. A switch to a low-dose calcineurin inhibitor (CNI) and mTOR inhibitor has been proven to stabilize the glomerular filtration rate. Additionally, de novo studies using a low-dose CNI and an mTOR inhibitor have shown good graft survival and a low number of rejections. Side effects of mTOR inhibitors, such as hyperlipidemia, wound healing problems, and proteinuria, mainly occur if high doses are given and if treatment is not combined with a CNI. Lower doses of mTOR inhibitors do not result in growth impairment or reduced testosterone levels. Treatment with mTOR inhibitors is also associated with a lower number of viral infections, especially cytomegalovirus. Due to their antiproliferative effect, mTOR inhibitors could theoretically reduce the risk of post-transplant lymphoproliferative disease. mTOR inhibitors, especially in combination with low-dose CNIs, can safely be used in children after kidney transplantation as de novo therapy or for conversion from CNI- and mycophenolate mofetil-based regimens.

Growth following solid organ transplantation in childhood

One of the ultimate goals of successful transplantation in pediatric solid organ transplant recipients is the attainment of optimal final adult height. This manuscript will discuss the attainment of height following solid organ transplantation in pediatric recipients of kidney, liver, heart, lung, and small bowel transplantation. Age is a primary factor with younger recipients exhibiting the greatest immediate catch up growth. Graft function is a significant contributory factor with a reduction in glomerular filtration rate correlating with poor growth in kidney recipients and the need for re-transplantation with impaired growth in liver recipients. The known adverse impact of steroids on growth has led to modification of steroid dosage and even to steroid withdrawal and steroid avoidance. In kidney and liver recipients, this has been associated with the development on occasion of acute rejection episodes. In infant heart transplantation, avoidance of maintenance corticosteroid immunosuppression is associated with normal growth velocity in the majority of patients. With marked improvement in patient and graft survival rates in pediatric organ graft recipients, it is timely that the quality of life issues, such as normal adult height, receive paramount attention. In general, normal growth post-transplantation should be an achievable goal that results in normal adult height for many solid organ transplantation recipients.

Optimization of Bone Health in Children before and after Renal Transplantation: Current Perspectives and Future Directions

The accrual of healthy bone during the critical period of childhood and adolescence sets the stage for lifelong skeletal health. However, in children with chronic kidney disease (CKD), disturbances in mineral metabolism and endocrine homeostasis begin early on, leading to alterations in bone turnover, mineralization, and volume, and impairing growth. Risk factors for CKD-mineral and bone disorder (CKD-MBD) include nutritional vitamin D deficiency, secondary hyperparathyroidism, increased fibroblast growth factor 23 (FGF-23), altered growth hormone and insulin-like growth factor-1 axis, delayed puberty, malnutrition, and metabolic acidosis. After kidney transplantation, nutritional vitamin D deficiency, persistent hyperparathyroidism, tertiary FGF-23 excess, hypophosphatemia, hypomagnesemia, immunosuppressive therapy, and alteration of sex hormones continue to impair bone health and growth. As function of the renal allograft declines over time, CKD-MBD associated changes are reactivated, further impairing bone health. Strategies to optimize bone health post-transplant include healthy diet, weight-bearing exercise, correction of vitamin D deficiency and acidosis, electrolyte abnormalities, steroid avoidance, and consideration of recombinant human growth hormone therapy. Other drug therapies have been used in adult transplant recipients, but there is insufficient evidence for use in the pediatric population at the present time. Future therapies to be explored include anti-FGF-23 antibodies, FGF-23 receptor blockers, and treatments targeting the colonic microbiota by reduction of generation of bacterial toxins and adsorption of toxic end products that affect bone mineralization.

Growth following solid organ transplantation in childhood

One of the ultimate goals of successful solid organ transplantation in pediatric recipients is attaining an optimal final adult height. This manuscript will discuss growth following transplantation in pediatric recipients of kidney, liver, heart, lung or small bowel transplants. Remarkably similar factors impact growth in all of these recipients. Age is a primary factor, with younger recipients exhibiting the greatest immediate catch-up growth. Graft function is a significant contributing factor, with a reduced glomerular filtration rate correlating with poor growth in kidney recipients and the need for re-transplantation with impaired growth in liver recipients. The known adverse impact of steroids on growth has led to modification of the steroid dose and even steroid withdrawal and avoidance. In kidney and liver recipients, this strategy has been associated with the development of acute rejection. In infant heart transplantation, avoiding maintenance corticosteroid immunosuppression is associated with normal growth velocity in the majority of patients. With marked improvements in patient and graft survival rates in pediatric organ recipients, quality of life issues, such as normal adult height, should now receive paramount attention. In general, normal growth following solid organ transplantation should be an achievable goal that results in normal adult height.

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.

Long-term side effects of treatment with mTOR inhibitors in children after renal transplantation

BACKGROUND

mTOR inhibitors (mTORI) have emerged as alternative and additive immunosuppressive agents in pediatric renal transplantation (pRTx). Their immunosuppressive, anti-proliferative, and anti-neoplastic mechanisms have been described to be effective, whereas some side effects are alarming. In particular, growth and pubertal development are of concern. The aim of this study was to look for long-term side effects of mTORI therapy in pRTx.

PATIENTS AND METHODS

The retrospective analysis focused on side effects, growth, and pubertal development under mTORI therapy in 31 children. Eighteen children were routinely monitored for estradiol, testosterone, LH, and FSH levels.

RESULTS

The occurrence of bacterial infections, lymphoceles, myelosuppression, and the course of overall linear growth was comparable with other pediatric renal transplant cohorts. According to the clinical puberty status, all but one patient showed normal age-related development in parallel to normal serum hormone levels. Only one patient experienced cytomegaly virus infection under mTORI, no post-transplant lymphoproliferative disorders (PTLD) occurred.

CONCLUSIONS

Long-term mTORI therapy is safe in pRTx. No negative impact on growth and pubertal development was observed.

Hypophosphatemia and growth

Over the last decade the discovery of fibroblast growth factor 23 (FGF23) and the progressive and ongoing clarification of its role in phosphate and mineral metabolism have led to expansion of the diagnostic spectrum of primary hypophosphatemic syndromes. This article focuses on the impairment of growth in these syndromes. Growth retardation is a common, but not constant, feature and it presents with large variability. As a result of the very low prevalence of other forms of primary hypophosphatemic syndromes, the description of longitudinal growth and the pathogenesis of its impairment have been mostly studied in X-linked hypophosphatemia (XLH) patients and in Hyp mice, the animal model of this disease. In general, children with XLH have short stature with greater shortness of lower limbs than trunk. Treatment with phosphate supplements and 1α vitamin D derivatives heals active lesions of rickets, but does not normalize growth of XLH patients. Patients might benefit from recombinant human growth hormone (rhGH) therapy, which may accelerate the growth rate without increasing body disproportion or correcting hypophosphatemia. These clinical data as well as research findings obtained in Hyp mice suggest that the pathogenesis of defective growth in XLH and other hypophosphatemic syndromes is not entirely dependent on the mineralization disorder and point to other effects of hypophosphatemia itself or FGF23 on the metabolism of bone and growth plate.

Rapamycin inhibits smooth muscle cell proliferation and obstructive arteriopathy attributable to elastin deficiency

OBJECTIVE

Patients with elastin deficiency attributable to gene mutation (supravalvular aortic stenosis) or chromosomal microdeletion (Williams syndrome) are characterized by obstructive arteriopathy resulting from excessive smooth muscle cell (SMC) proliferation, mural expansion, and inadequate vessel size. We investigated whether rapamycin, an inhibitor of the cell growth regulator mammalian target of rapamycin (mTOR) and effective against other SMC proliferative disorders, is of therapeutic benefit in experimental models of elastin deficiency.

APPROACH AND RESULTS

As previously reported, Eln(-/-) mice demonstrated SMC hyperplasia and severe stenosis of the aorta, whereas Eln(+/-) mice exhibited a smaller diameter aorta with more numerous but thinner elastic lamellae. Increased mTOR signaling was detected in elastin-deficient aortas of newborn pups that was inhibited by maternal administration of rapamycin. mTOR inhibition reduced SMC proliferation and aortic obstruction in Eln(-/-) pups and prevented medial hyperlamellation in Eln(+/-) weanlings without compromising aortic size. However, rapamycin did not prolong the survival of Eln(-/-) pups, and it retarded the somatic growth of juvenile Eln(+/-) and Eln(+/+) mice. In cell cultures, rapamycin inhibited prolonged mTOR activation and enhanced proliferation of SMC derived from patients with supravalvular aortic stenosis and with Williams syndrome.

CONCLUSIONS

mTOR inhibition may represent a pharmacological strategy to treat diffuse arteriopathy resulting from elastin deficiency.

Histone deacetylase 3 suppression increases PH domain and leucine-rich repeat phosphatase (Phlpp)1 expression in chondrocytes to suppress Akt signaling and matrix secretion

HDACs epigenetically regulate cellular processes by modifying chromatin and influencing gene expression. We previously reported that conditional deletion of Hdac3 in osteo-chondroprogenitor cells with Osx1-Cre caused severe osteopenia due to abnormal maturation of osteoblasts. The mice were also smaller. To address the abnormal longitudinal growth in these animals, the role of Hdac3 in chondrocyte differentiation was evaluated. We found that Hdac3 is highly expressed in resting and prehypertrophic growth plate chondrocytes, as well as in articular chondrocytes. Hdac3-deficient chondrocytes entered hypertrophy sooner and were smaller than normal chondrocytes. Extracellular matrix production was suppressed as glycosaminoglycan secretion and production of aggrecan, osteopontin, and matrix extracellular phosphoglycoprotein were reduced in Hdac3-deficient chondrocytes. These phenotypes led to the hypothesis that the Akt/mTOR pathway was repressed in these Hdac3-deficient chondrocytes because Akt promotes hypertrophy and matrix production in many tissues. The phosphorylation and activation of Akt, its substrate mTOR, and the mTOR substrate, p70 S6 kinase, were indeed reduced in Hdac3-deficient primary chondrocytes as well as in chondrocytes exposed to HDAC inhibitors. Expression of constitutively active Akt restored phosphorylation of mTOR and p70 S6K and matrix gene expression levels. Reduced phosphorylation of Akt and its substrates in Hdac3-deficient or HDAC inhibitors treated chondrocytes correlated with increased expression of the phosphatase Phlpp1. Hdac3 associated with a Phlpp1 promoter region containing Smad binding elements and was released after TGFβ was added to the culture. These data demonstrate that Hdac3 controls chondrocyte hypertrophy and matrix content by repressing Phlpp1 expression and facilitating Akt activity.

Conversion to sirolimus in pediatric renal transplant patients: a single-center experience

We studied efficacy and safety of conversion from CNI- to SRL-based immunosuppression in 92 kidney TX recipients, mainly due to CAN (69%). Median time of conversion was 31 months (r: 0.3-165); median time of follow-up: 36 months (r: 2-102). In the whole group mean eGFR increased from 53 ± 22 to 67 ± 26mL/min/1.73 m(2) at three months (p = 0.02) and did not change subsequently. Patients with grade I CAN had higher eGFR than those with grade II CAN. Patient and graft survival was 96% and 70% 10 yr after conversion. Patients with grade I CAN had better graft survival than those with grade II CAN: 89% vs. 65% at six yr (p = 0.02) post conversion. There were two episodes of BPAR. Baseline proteinuria >20 mg/kg/day (HR: 10) and baseline eGFR <50 mL/min/1.73 m(2) (HR: 8) were independent predictors of graft loss. Sixty-seven of 92 subjects had ≥1 AEs: diarrhea (n = 52), urinary tract infections (n = 35), and lower respiratory tract infections (n = 12) were the most frequent. Patients with >2 AEs had SRL blood levels >9 ng/mL at month 3 (p = 0.01). In conclusion, patients converted from CNI to SRL had good graft survival and tolerable but frequent AEs. Independent predictors of graft loss were baseline proteinuria and eGFR.

Growth cartilage expression of growth hormone/insulin-like growth factor I axis in spontaneous and growth hormone induced catch-up growth

INTRODUCTION

Catch-up growth following the cessation of a growth inhibiting cause occurs in humans and animals. Although its underlying regulatory mechanisms are not well understood, current hypothesis confer an increasing importance to local factors intrinsic to the long bones' growth plate (GP).

AIM

The present study was designed to analyze the growth-hormone (GH)-insulin-like growth factor I (IGF-I) axis in the epiphyseal cartilage of young rats exhibiting catch-up growth as well as to evaluate the effect of GH treatment on this process.

MATERIAL AND METHODS

Female Sprague-Dawley rats were randomly grouped: controls (group C), 50% diet restriction for 3 days+refeeding (group CR); 50% diet restriction for 3 days+refeeding & GH treatment (group CRGH). Analysis of GH receptor (GHR), IGF-I, IGF-I receptor (IGF-IR) and IGF binding protein 5 (IGFBP5) expressions by real-time PCR was performed in tibial growth plates extracted at the time of catch-up growth, identified by osseous front advance greater than that of C animals.

RESULTS

In the absence of GH treatment, catch-up growth was associated with increased IGF-I and IGFBP5 mRNA levels, without changes in GHR or IGF-IR. GH treatment maintained the overexpression of IGF-I mRNA and induced an important increase in IGF-IR expression.

CONCLUSIONS

Catch-up growth that happens after diet restriction might be related with a dual stimulating local effect of IGF-I in growth plate resulting from overexpression and increased bioavailability of IGF-I. GH treatment further enhanced expression of IGF-IR which likely resulted in a potentiation of local IGF-I actions. These findings point out to an important role of growth cartilage GH/IGF-I axis regulation in a rat model of catch-up growth.

Growth hormone improves growth retardation induced by rapamycin without blocking its antiproliferative and antiangiogenic effects on rat growth plate

Rapamycin, an immunosuppressant agent used in renal transplantation with antitumoral properties, has been reported to impair longitudinal growth in young individuals. As growth hormone (GH) can be used to treat growth retardation in transplanted children, we aimed this study to find out the effect of GH therapy in a model of young rat with growth retardation induced by rapamycin administration. Three groups of 4-week-old rats treated with vehicle (C), daily injections of rapamycin alone (RAPA) or in combination with GH (RGH) at pharmacological doses for 1 week were compared. GH treatment caused a 20% increase in both growth velocity and body length in RGH animals when compared with RAPA group. GH treatment did not increase circulating levels of insulin-like growth factor I, a systemic mediator of GH actions. Instead, GH promoted the maturation and hypertrophy of growth plate chondrocytes, an effect likely related to AKT and ERK1/2 mediated inactivation of GSK3β, increase of glycogen deposits and stabilization of β-catenin. Interestingly, GH did not interfere with the antiproliferative and antiangiogenic activities of rapamycin in the growth plate and did not cause changes in chondrocyte autophagy markers. In summary, these findings indicate that GH administration improves longitudinal growth in rapamycin-treated rats by specifically acting on the process of growth plate chondrocyte hypertrophy but not by counteracting the effects of rapamycin on proliferation and angiogenesis.

The skeleton: a multi-functional complex organ: new insights into osteoblasts and their role in bone formation: the central role of PI3Kinase

Studies on bone development, formation and turnover have grown exponentially over the last decade in part because of the utility of genetic models. One area that has received considerable attention has been the phosphatidylinositol 3-kinase (PI3K) signaling pathway, which has emerged as a major survival network for osteoblasts. Genetic engineering has enabled investigators to study downstream effectors of PI3K by directly overexpressing activated forms of AKT in cells of the skeletal lineage or deleting Pten that leads to a constitutively active AKT. The results from these studies have provided novel insights into bone development and remodeling, critical processes in the lifelong maintenance of skeletal health. This paper reviews those data in relation to recent advances in osteoblast biology and their potential relevance to chronic disorders of the skeleton and their treatment.

Sirolimus in pediatric renal transplantation

SRL, an mTOR inhibitor that inhibits cell cycle progression, represents an important alternative to CNIs, which are still the cornerstones of pediatric solid organ tx. Because there are still limited data on SRL use among pediatric solid organ recipients, further studies are needed to verify the efficacy and safety of SRL. It has unique pharmacokinetic characteristics concerning dosing intervals and reduction of the dose in combination with other immunosuppressants. SRL also has antineoplastic, antiviral, and antiatherogenic advantages over other immunosuppressive agents. The adverse effects of SRL including thrombocytopenia, hyperlipidemia, proteinuria, impaired wound healing, mouth ulcers, edema, male hypogonadism, TMA, and interstitial pneumonitis must be considered carefully in pediatric population. This article reviews the most recent data on SRL application in the field of pediatric renal tx.

Linear growth in pediatric renal transplant recipients receiving sirolimus

SRL is a potent macrolide immunosuppressive agent that can be used as maintenance therapy for prevention of rejection and avoidance of CNI nephrotoxicity. However, animal studies indicate that SRL may inhibit skeletal and muscle growth. We analyzed linear growth in 25 children, age 1-15 yr old, maintained on SRL to determine whether SRL is detrimental to linear growth. Height z-scores at baseline were compared with those at 24 months. We also compared linear growth in children receiving SRL to patients maintained on TAC. Height z-scores over 24 months did not significantly change in the SRL group as a whole. Z-scores improved in 13 of 25 patients (52%). Children with improved z-scores were significantly younger than patents who did not display improved growth: 6 ± 5 yr vs. 11 ± 4 yr (p < 0.05). Height z-scores in SRL and TAC-based patients were no different initially and at 24 months, and a similar number of patients in each group displayed improved height scores. Height z-scores improved in 52% of patients on SRL and occurred predominantly in younger patients for the initial 24 months of treatment. Linear growth in SRL patients was also similar to the results in TAC-based patients. Therefore, our data did not identify a significant adverse effect of SRL on growth.

Growth of kidney-transplanted pediatric patients treated with sirolimus

Experimental findings indicate that sirolimus (SRL) inhibits longitudinal growth by mechanisms potentially related to its inhibitory effects on both cell proliferation and expression of vascular endothelial growth factor (VEGF). The aim of this study was to investigate the growth pattern of kidney-transplanted children treated with SRL in a multicenter observational clinical study. Height, change in height SD (Δ height) and growth velocity of pediatric patients with renal transplant were calculated at 0, 6, 12, and 24 months after starting SRL. Controls of kidney-transplanted children not treated with SRL were matched by age, gender, renal function, and dose of corticosteroids. Sixty-eight children (34 SRL, 34 controls) were enrolled in the study. Nephrotoxicity was the most frequent indication to start therapy with SRL. SRL exerted an adverse effect on growth as demonstrated by significantly lower (p < 0.05) growth velocity (cm/year) and smaller change in height SD in the SRL group after 6 (4.08 vs. 6.56 and -0.05 vs. 0.14), 12 (4.44 vs. 6.11 and -0.03 vs. 0.28) and 24 (4.53 vs. 6.03 and -0.04 vs. 0.53) months of treatment. This study suggests that SRL therapy may interfere with growth of kidney-transplanted children. This undesirable effect needs to be taken into account when considering a switch to SRL and confirmed in further prospective trials including larger number of patients.

Five-year experience using sirolimus-based, calcineurin inhibitor-free immunosuppression in pediatric renal transplantation

From December 2003 to December 2008, we employed a protocol for withdrawing TAC and converting to SRL in a cohort of low-risk renal pediatric transplant recipients. We report our experience in these children with respect to graft survival, AR episodes, renal function, and adverse events. All patients received basiliximab induction and TAC, MMF, and prednisone. Criteria for conversion to SRL included first transplants without histologic evidence for AR on three-month surveillance biopsies. Patient exclusion criteria included AR prior to or before surveillance biopsies, polyoma (BK) virus nephropathy, a history of nephrotic syndrome, or multiple organ transplants. Fifty-one of 137 patients who received transplants from December 2003 to December 2008 met criteria for withdrawal of TAC and were converted to SRL. SRL was discontinued in 11 children because of adverse events within 12 months after conversion. Among the remaining 40 patients, actuarial graft survival was 91% at five yr. AR occurred in 13% of patients within one yr after conversion. Complications from SRL included aphthous ulcers (30%); viremia with BK virus (20%), EBV (13%), and CMV (3%); proteinuria (7%); elevated cholesterol (7%); diabetes mellitus (2%); thrombocytopenia (2%); erectile dysfunction (2%); and lymph edema (2%). SRL was discontinued in 20%, predominantly for aphthous ulcers. Our experience with SRL-based immunosuppression demonstrates that a CNI-free regimen can be successful in lower-risk patients meeting our selection criteria. Aphthous ulcers and BK virus viremia were the most prevalent adverse events.

De novo therapy with everolimus, low-dose ciclosporine A, basiliximab and steroid elimination in pediatric kidney transplantation

The number of acute rejections and infections after pediatric kidney transplantation (KTX) could not be reduced in the last years. To reduce these events, we investigated a new immunosuppressive protocol in a prospective trial. After KTX, 20 children (median age 12 years, range 1-17) were initially treated with Basiliximab, ciclosporine A (CsA) (trough-level = C0 200-250 ng/mL) and prednisolone. After 2 weeks, CsA dose was reduced to 50% (C0 75-100 ng/mL, after 6 months: 50-75 ng/mL) and everolimus (1.6 mg/m²) /day) was started (C0 3-6 ng/mL). Six months after KTX prednisolone was set to alternate dose and stopped 3 months later. All 20 protocol biopsies 6 months after KTX showed no acute rejection or borderline findings. Indication biopsies resulted in no acute rejections and two borderline findings. Mean glomerular filtration rate (GFR) 1 year after KTX was 71 ± 25 mL/min/1.73 m². Without cytomegalovirus (CMV)-prophylaxis, only two primary CMV infections were seen despite a donor/recipient-CMV-constellation pos./neg. in 10/20 children. In pediatric KTX, de novo immunosuppression with low-dose CsA, everolimus and steroid withdrawal after 9 months led to promising results according to numbers of acute rejections and infections. Further follow up is needed. Future larger trials will have to confirm our findings.

NVP-BEZ235, a dual pan class I PI3 kinase and mTOR inhibitor, promotes osteogenic differentiation in human mesenchymal stromal cells

Osteoblasts are bone-forming cells derived from mesenchymal stromal cells (MSCs) that reside within the bone marrow. In response to a variety of factors, MSCs proliferate and differentiate into mature, functional osteoblasts. Several studies have shown previously that suppression of the PI3K and mTOR signaling pathways in these cells strongly promotes osteogenic differentiation, which suggests that inhibitors of these pathways may be useful as anabolic bone agents. In this study we examined the effect of BEZ235, a newly developed dual PI3K and mTOR inhibitor currently in phase I-II clinical trials for advanced solid tumors, on osteogenic differentiation and function using primary MSC cultures. Under osteoinductive conditions, BEZ235 strongly promotes osteogenic differentiation, as evidenced by an increase in mineralized matrix production, an upregulation of genes involved in osteogenesis, including bone morphogenetic proteins (BMP2, -4, and -6) and transforming growth factor β1 (TGF-β1) superfamily members (TGFB1, TGFB2, and INHBE), and increased activation of SMAD signaling molecules. In addition, BEZ235 enhances de novo bone formation in calvarial organotypic cultures. Using pharmacologic inhibitors to delineate mechanism, our studies reveal that suppression of mTOR and, to a much lesser extent PI3K p110α, mediates the osteogenic effects of BEZ235. As confirmation, shRNA-mediated knockdown of mTOR enhances osteogenic differentiation and function in SAOS-2 osteoblast-like cells. Taken together, our findings suggest that BEZ235 may be useful in treating PI3K/mTOR-dependent tumors associated with bone loss, such as the hematologic malignancy multiple myeloma.

High phosphorus diet induces vascular calcification, a related decrease in bone mass and changes in the aortic gene expression

In chronic kidney disease, hyperphosphatemia has been associated to vascular calcifications. Moreover, the rate and progression of vascular calcification have been related with the reduction of bone mass and osteoporotic fractures, hereby suggesting a strong link between vascular calcification and bone loss. Our aim was to prospectively study the effects of high phosphorus diet on bone mass, vascular calcification and gene expression profile of the arterial wall. A rat model of 7/8 nephrectomy fed with normal (0.6%) and moderately high (0.9%) phosphorus diet was used. Biochemical parameters, bone mineral density and vascular calcifications were assessed. A microarray analysis of the aortic tissue was also performed to investigate the gene expression profile. After 20 weeks, the rats fed with a high phosphorus diet showed a significant increase in serum phosphorus, PTH, and creatinine, together with aortic calcification and a decrease in bone mass. The histological analysis of the vascular calcifications showed areas with calcified tissue and the gene expression profile of this calcified tissue showed repression of muscle-related genes and overexpression of bone-related genes, among them, the secreted frizzled related proteins, well-known inhibitors of the Wnt pathway, involved in bone formation. The study demonstrated prospectively the inverse and direct relationship between vascular calcification and bone mass. In addition, the microarrays findings provide new information on the molecular mechanisms that may link this relationship.

Growth failure associated with sirolimus: case report

An 11-year-old girl, who was a renal transplant recipient, developed linear growth failure associated in time with sirolimus (SRL) treatment. After 5 years of functional graft [creatinine clearance (CCr) 90 ml/min per 1.73 m(2) body surface area], she developed acute renal failure due to calcineurin inhibitor-related hemolytic uremic syndrome, and cyclosporine A was replaced by SRL. Before the drug change, she had been growing normally (5.5 cm/year) and had reached the 33.9 percentile (P) of height (z-height -0.41), similar to her target. Two years later, her height had decreased to P 6th (z-height -1.54), as her growth velocity had diminished to 2.2 cm/year, despite optimal renal function (CCr 68 ml/min per 1.73 m(2)). Human recombinant growth hormone was needed to promote her catch-up growth and achieve the P 49th of height (z-height -0.03). SRL may have deleterious effects on growing children due its characteristic anti-proliferative and anti-angiogenic properties. Pediatric transplant recipients' linear growth should be cautiously monitored while they are being given SRL.

Alterations of growth plate and abnormal insulin-like growth factor I metabolism in growth-retarded hypokalemic rats: effect of growth hormone treatment

Hypokalemic tubular disorders may lead to growth retardation which is resistant to growth hormone (GH) treatment. The mechanism of these alterations is unknown. Weaning female rats were grouped ( n = 10) in control, potassium-depleted (KD), KD treated with intraperitoneal GH at 3.3 mg·kg−1·day−1 during the last week (KDGH), and control pair-fed with KD (CPF). After 2 wk, KD rats were growth retarded compared with CPF rats, the osseous front advance (±SD) being 67.07 ± 10.44 and 81.56 ± 12.70 μm/day, respectively. GH treatment did not accelerate growth rate. The tibial growth plate of KD rats had marked morphological alterations: lower heights of growth cartilage (228.26 ± 23.58 μm), hypertrophic zone (123.68 ± 13.49 μm), and terminal chondrocytes (20.8 ± 2.39 μm) than normokalemic CPF (264.21 ± 21.77, 153.18 ± 15.80, and 24.21 ± 5.86 μm). GH administration normalized these changes except for the distal chondrocyte height. Quantitative PCR of insulin-like growth factor I (IGF-I), IGF-I receptor, and GH receptor genes in KD growth plates showed downregulation of IGF-I and upregulation of IGF-I receptor mRNAs, without changes in their distribution as analyzed by immunohistochemistry and in situ hybridization. GH did not further modify IGF-I mRNA expression. KD rats had normal hepatic IGF-I mRNA levels and low serum IGF-I values. GH increased liver IGF-I mRNA, but circulating IGF-I levels remained reduced. This study discloses the structural and molecular alterations induced by potassium depletion on the growth plate and shows that the lack of response to GH administration is associated with persistence of the disturbed process of chondrocyte hypertrophy and depressed mRNA expression of local IGF-I in the growth plate.

Bone growth during rapamycin therapy in young rats

BACKGROUND

Rapamycin is an effective immunosuppressant widely used to maintain the renal allograft in pediatric patients. Linear growth may be adversely affected in young children since rapamycin has potent anti-proliferative and anti-angiogenic properties.

METHODS

Weanling three week old rats were given rapamycin at 2.5 mg/kg daily by gavage for 2 or 4 weeks and compared to a Control group given equivalent amount of saline. Morphometric measurements and biochemical determinations for serum calcium, phosphate, iPTH, urea nitrogen, creatinine and insulin-growth factor I (IGF-I) were obtained. Histomorphometric analysis of the growth plate cartilage, in-situ hybridization experiments and immunohistochemical studies for various proteins were performed to evaluate for chondrocyte proliferation, chondrocyte differentiation and chondro/osteoclastic resorption.

RESULTS

At the end of the 2 weeks, body and tibia length measurements were shorter after rapamycin therapy associated with an enlargement of the hypertrophic zone in the growth plate cartilage. There was a decrease in chondrocyte proliferation assessed by histone-4 and mammalian target of rapamycin (mTOR) expression. A reduction in parathyroid hormone/parathyroid hormone related peptide (PTH/PTHrP) and an increase in Indian hedgehog (Ihh) expression may explain in part, the increase number of hypertrophic chondrocytes. The number of TRAP positive multinucleated chondro/osteoclasts declined in the chondro-osseous junction with a decrease in the receptor activator of nuclear factor kappa beta ligand (RANKL) and vascular endothelial growth factor (VEGF) expression. Although body and tibial length remained short after 4 weeks of rapamycin, changes in the expression of chondrocyte proliferation, chondrocyte differentiation and chondro/osteoclastic resorption which were significant after 2 weeks of rapamycin improved at the end of 4 weeks.

CONCLUSION

When given to young rats, 2 weeks of rapamycin significantly decreased endochondral bone growth. No catch-up growth was demonstrated at the end of 4 weeks, although markers of chondrocyte proliferation and differentiation improved. Clinical studies need to be done to evaluate these changes in growing children.