Influence of the parathyroid glands on bone metabolism

Transcriptome and metabolome analysis of osteoblasts identifies disrupted purine metabolism and parathyroid hormone associated pathway induced by P. gingivalis infection

Porphyromonas gingivalis (P. gingivalis), a major pathogenic bacterium of chronic periodontitis and central player in the onset and subsequent progression of periodontitis, can cause alveolar bone resorption. The osteoblast dysfunction induced by P. gingivalis infection is a crucial pathological process causing bone loss. However, the comprehensive responses of osteoblasts, especially metabolism processes involved in osteoblast dysfunction under P. gingivalis invasion are largely unknown. In the present study, to profile the molecules switched in osteoblast dysfunction caused by P. gingivalis infection, the effect of P. gingivalis invasion on osteoblast differentiation was assessed and investigated through transcriptomics and metabolomics approaches. We found that P. gingivalis infection dramatically impaired osteoblast function. P. gingivalis invasion disrupted homeostasis of phosphorus (Pi)/calcium (Ca2+) and induced robust oxidative stress, cell apoptosis and massive activation of inflammatory response in osteoblasts. Notably, the exposure to P. gingivalis induced the inactivation of endocrines pathways, involved in bone formation, which is characterized by downregulated genes and less accumulated metabolites in "Parathyroid hormone synthesis, secretion and action", its downstream "Wnt signaling pathway" and related Pi/Ca2+ transport. Furthermore, we found that disrupted purine metabolism produced less ATP in P. gingivalis-infected osteoblasts and the reduced ATP may directly inhibit phosphorus transport. Collectively, these results provide a new insight into the molecular changes in P. gingivalis-infected osteoblasts in a comprehensive way.

Bone development in fetuses with intrauterine growth restriction caused by maternal endocrine-metabolic dysfunctions

Intrauterine growth restriction (IUGR) affects a large proportion of infants, particularly in underdeveloped countries. Among the main causes of IUGR, maternal endocrine-metabolic dysfunction is highlighted, either due to its high incidence or due to the severity of the immediate and mediated changes that these dysfunctions cause in the fetus and the mother. Although the effects of endocrine and metabolic disorders have been widely researched, there are still no reviews that bring together and summarize the effects of these conditions on bone development in cases of IUGR. Therefore, the present literature review was conducted with the aim of discussing bone changes observed in fetuses with IUGR caused by maternal endocrine-metabolic dysfunction. The main endocrine dysfunctions that occur with IUGR include maternal hyperthyroidism, hypothyroidism, and hypoparathyroidism. Diabetes mellitus, hypertensive disorders, and obesity are the most important maternal metabolic dysfunctions that compromise fetal growth. The bone changes reported in the fetus are, for the most part, due to damage to cell proliferation and differentiation, as well as failures in the synthesis and mineralization of the extracellular matrix, which results in shortening and fragility of the bones. Some maternal dysfunctions, such as hyperthyroidism, have been widely studied, whereas conditions such as hypoparathyroidism and gestational hypertensive disorders require further study regarding the mechanisms underlying the development of bone changes. Similarly, there is a gap in the literature regarding changes related to intramembranous ossification, as most published articles only describe changes in endochondral bone formation associated with IUGR. Furthermore, there is a need for more research aimed at elucidating the late postnatal changes that occur in the skeletons of individuals affected by IUGR and their possible relationships with adult diseases, such as osteoarthritis and osteoporosis.

Melatonin inhibits RANKL‑induced osteoclastogenesis through the miR‑882/Rev‑erbα axis in Raw264.7 cells

Melatonin, secreted in a typical diurnal rhythm pattern, has been reported to prevent osteoporosis; however, its role in osteoclastogenesis remains unclear. In the present study, the ability of melatonin to inhibit receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis and the associated mechanism were investigated. Raw264.7 cells were cultured with RANKL (100 ng/ml) and macrophage colony-stimulating factor (M-CSF; 30 ng/ml) for 7 days, and tartrate-resistant acid phosphatase (TRAP) staining was used to detect osteoclastogenesis following treatment with melatonin. In addition, the effect of melatonin on cathepsin K and microRNA (miR)-882 expression was investigated via western blotting and reverse transcription-quantitative PCR. Melatonin significantly inhibited RANKL-induced osteoclastogenesis in Raw264.7 cells. From bioinformatics analysis, it was inferred that nuclear receptor subfamily 1 group D member 1 (NR1D1/Rev-erbα) may be a target of miR-882. In vitro, melatonin upregulated Rev-erbα expression and downregulated miR-882 expression in the osteoclastogenesis model. Rev-erbα overexpression boosted the anti-osteoclastogenesis effects of melatonin, whereas miR-882 partially diminished these effects. The present results indicated that the miR-882/Rev-erbα axis may serve a vital role in inhibiting osteoclastogenesis following RANKL and M-CSF treatment, indicating that Rev-erbα agonism or miR-882 inhibition may represent mechanisms through which melatonin prevents osteoporosis.

Parathyroid Hormone Fragments: New Targets for the Diagnosis and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder

As a common disorder, chronic kidney disease (CKD) poses a great threat to human health. Chronic kidney disease-mineral and bone disorder (CKD-MBD) is a complication of CKD characterized by disturbances in the levels of calcium, phosphorus, parathyroid hormone (PTH), and vitamin D; abnormal bone formation affecting the mineralization and linear growth of bone; and vascular and soft tissue calcification. PTH reflects the function of the parathyroid gland and also takes part in the metabolism of minerals. The accurate measurement of PTH plays a vital role in the clinical diagnosis, treatment, and prognosis of patients with secondary hyperparathyroidism (SHPT). Previous studies have shown that there are different fragments of PTH in the body's circulation, causing antagonistic effects on bone and the kidney. Here we review the metabolism of PTH fragments; the progress being made in PTH measurement assays; the effects of PTH fragments on bone, kidney, and the cardiovascular system in CKD; and the predictive value of PTH measurement in assessing the effectiveness of parathyroidectomy (PTX). We hope that this review will help to clarify the value of accurate PTH measurements in CKD-MBD and promote the further development of multidisciplinary diagnosis and treatment.

Effects of Ethyl Acetate Extract of Poncirus trifoliata Fruit for Glucocorticoid-Induced Osteoporosis

Poncirus trifoliata fruit (PTF) affects the digestive and cardiovascular systems, and kidney function. The authors studied the effects of ethyl acetate (EtOAc) extract of PTF on the activities of osteoblasts and in an animal model. The main compounds of the EtOAc extract, naringin and poncirin have been confi rmed by HPLC and NMR analysis. Effects of osteoblastic differentiation were mea-sured by alkaline phosphatase (ALP) activity, osteopontin (OPN) protein expression and osteoprotegerin (OPG) mRNA expression in MC3T3-E1 cells. Also, osteoclast differentiation was measured by multinucleated cells (MNCs) formation through tartrate resistance acid phosphatase (TRAP)-positive staining. Bone mineral density (BMD) was measured before and after treatment with EtOAc extract of PTF in prednisolone-induced osteoporotic mice. Dexamethasone (DEX) decreased OPN and OPG expression level in MC3T3-E1 cells and ALP activity was decreased by DEX dose-dependently. EtOAc extract of PTF recovered the levels of ALP activity, and the expression of OPN and OPG in MC3T3-E1 cells treated with DEX. In osteoclast differentiation, multinucleated TRAP-positive cell formation was significantly suppressed by the EtOAc extract of PTF. Total body BMD was restored by EtOAc extract of PTF in prednisolone-induced osteoporotic mice. In conclusion, EtOAc extract of PTF recovered DEX-mediated deteriorations in osteoblastic and osteoclastic functions, and increased BMD in glucocorticoid-induced osteoporosis.

Renal complications in multiple myeloma and related disorders: survivorship care plan of the International Myeloma Foundation Nurse Leadership Board

Kidney dysfunction is a common clinical feature of symptomatic multiple myeloma. Some degree of renal insufficiency or renal failure is present at diagnosis or will occur during the course of the disease and, if not reversed, will adversely affect overall survival and quality of life. Chronic insults to the kidneys from other illnesses, treatment, or multiple myeloma itself can further damage renal function and increase the risk for additional complications, such as anemia. Patients with multiple myeloma who have light chain (Bence Jones protein) proteinuria may experience renal failure or progress to end-stage renal disease (ESRD) and require dialysis because of light chain cast nephropathy. Kidney failure in patients with presumed multiple myeloma also may result from amyloidosis, light chain deposition disease, or acute tubular necrosis caused by nephrotoxic agents; therefore, identification of patients at risk for kidney damage is essential. The International Myeloma Foundation's Nurse Leadership Board has developed practice recommendations for screening renal function, identifying positive and negative contributing risk and environmental factors, selecting appropriate therapies and supportive care measures to decrease progression to ESRD, and enacting dialysis to reduce and manage renal complications in patients with multiple myeloma.

Review: The diabetic bone: a cellular and molecular perspective

With the increasing worldwide prevalence of diabetes the resulting complications, their consequences and treatment will lead to a greater social and financial burden on society. One of the many organs to be affected is bone. Loss of bone is observed in type 1 diabetes, in extreme cases mirroring osteoporosis, thus a greater risk of fracture. In the case of type 2 diabetes, both a loss and an increase of bone has been observed, although in both cases the quality of the bone overall was poorer, again leading to a greater risk of fracture. Once a fracture has occurred, healing is delayed in diabetes, including nonunion. The reasons leading to such changes in the state of the bone and fracture healing in diabetes is under investigation, including at the cellular and the molecular levels. In comparison with our knowledge of events in normal bone homeostasis and fracture healing, that for diabetes is much more limited, particularly in patients. However, progress is being made, especially with the use of animal models for both diabetes types. Identifying the molecular and cellular changes in the bone in diabetes and understanding how they arise will allow for targeted intervention to improve diabetic bone, thus helping to counter conditions such as Charcot foot as well as preventing fracture and accelerating healing when a fracture does occur.

Calcitonin-secreting pancreatic endocrine tumors: systematic analysis of a rare tumor entity

OBJECTIVE

Pancreatic endocrine tumors (PETs) are characterized by the presence of hormone syndromes. Reports focusing on calcitonin-secreting PET (CTsPETs) are very rare. This study aimed to define a CTsPET-associated syndrome in regard to chemical, anatomical, and developmental aspects.

METHODS

A computerized MEDLINE search was conducted under the search items: "pancreatic endocrine tumor," "calcitonin," "neuroendocrine pancreatic tumor," and "pancreas." Results of clinical, histopathological, immunohistochemical, and biochemical assessments of all patients identified with CTsPET were registered and statistically analyzed.

RESULTS

Thirty-seven patients with CTsPET were identified. Mean serum calcitonin was elevated to the 89.2-fold of the upper reference value. Main symptoms were watery diarrhea (51.4%) and abdominal pain (35.1%). Most patients (59.5%) presented with metastatic spread at the time of diagnosis. Of all patients, 66.7% were alive after a mean follow-up of 28.9 months. Survival was higher in patients who underwent more aggressive surgical therapies independent from tumor sizes and in those with no metastases at the time of diagnosis.

CONCLUSIONS

High calcitonin levels should always raise suspicion of medullary thyroid carcinomas. However, when thyroid examination remains without pathological findings, a CTsPET should be excluded. An aggressive surgical approach even in cases with large primary tumor sizes may lead to a longer survival.

Sclerostin and Dickkopf-1 in renal osteodystrophy

BACKGROUND AND OBJECTIVES

The serum proteins sclerostin and Dickkopf-1 (Dkk-1) are soluble inhibitors of canonical wnt signaling and were recently identified as components of parathyroid hormone (PTH) signal transduction. This study investigated the associations between sclerostin and Dkk-1 with histomorphometric parameters of bone turnover, mineralization, and volume in stage 5 chronic kidney disease patients on dialysis (CKD-5D).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a cross-sectional study, 60 CKD-5D patients underwent bone biopsies followed by histomorphometry. Levels of sclerostin, Dkk-1, and intact PTH (iPTH) were determined in blood.

RESULTS

Serum levels of sclerostin and iPTH correlated negatively. In unadjusted analyses, sclerostin correlated negatively with histomorphometric parameters of turnover, osteoblastic number, and function. In adjusted analyses, sclerostin remained a strong predictor of parameters of bone turnover and osteoblast number. An observed correlation between sclerostin and cancellous bone volume was lost in regression analyses. Sclerostin was superior to iPTH for the positive prediction of high bone turnover and number of osteoblasts. In contrast, iPTH was superior to sclerostin for the negative prediction for high bone turnover and had similar predictive values than sclerostin for the number of osteoblasts. Serum levels of Dkk-1 did not correlate with iPTH or with any histomorphometric parameter.

CONCLUSIONS

Our data describe a promising role for serum measurements of sclerostin in addition to iPTH in the diagnosis of high bone turnover in CKD-5D patients, whereas measurements of Dkk-1 do not seem to be useful for this purpose.

Short-term exposure to low-carbohydrate, high-fat diets induces low bone mineral density and reduces bone formation in rats

Low-carbohydrate, high-fat (LC-HF) diets are popular for inducing weight loss in adults and are also used as part of a treatment for children with epilepsy. However, potential risks and side effects remain controversial. We investigated effects of LC-HF diets on growth, bone mineral density (BMD), and turnover in growing rats fed for 4 weeks either normal chow (CH, 9% fat, 33% protein, and 58% carbohydrates), LC-HF-1 (66% fat, 33% protein, and 1% carbohydrates), or LC-HF-2 (94.5% fat, 4.2% protein, and 1.3% carbohydrates). Rats fed LC-HF diets accumulated significantly more visceral and bone marrow fat and showed increased leptin but decreased insulin-like growth-factor 1 (IGF-1). Both LC-HF diets significantly decreased body length (nose to rump), but lengths of humerus, tibia, and femur were significantly reduced with LC-HF-2 only. Peripheral quantitative computed tomography (pQCT) and micro-CT (microCT) independently revealed significant reductions in BMD of tibiae in both LC-HF groups, and tibial maximum load was impaired. Bone-formation marker N-terminal propeptide of type I procollagen was reduced in sera of LC-HF groups, whereas bone resorption marker CrossLaps remained unchanged. Real-time PCR analysis revealed significant reductions by 70% to 80% of transcription factors influencing osteoblastogenesis (Runx2, osterix, and C/EBPbeta) in bone marrow of rats fed LC-HF diets. In conclusion, both LC-HF diets impaired longitudinal growth, BMD, and mechanical properties, possibly mediated by reductions in circulating IGF-1. Serum bone-formation markers as well as expression of transcription factors influencing osteoblastogenesis were reduced. This might indicate a lower rate of mesenchymal stem cells differentiating into osteoblasts, thus explaining reduced bone formation with LC-HF diets.

Effect of teriparatide on early bone loss after kidney transplantation

Kidney transplantation is associated with bone loss and a high risk of fractures. Prophylactic treatment of bone is therefore recommended in the early posttransplant period. As a large number of transplant recipients develop adynamic renal osteodystrophy, recombinant parathyroid hormone (rPTH) could be a promising therapeutic option. In a 6-month double-blind, randomized trial, 26 kidney transplant recipients were treated with daily subcutaneous injections of 20 microg teriparatide (PTH 1-34) or placebo. Bone mineral density (BMD) of the femoral neck, lumbar spine and radial bone was measured at transplantation and after 6 months. Paired bone biopsies for histomorphometric analysis were obtained in six, and for measurement of bone matrix mineralization in five patients of each group. Serologic bone markers were measured at baseline and every 3 months. A total of 24 out of 26 patients completed the study. Femoral neck BMD was stable in the teriparatide group, but decreased significantly in the placebo group. Lumbar spine and radial BMD, histomorphometric bone volume and bone matrix mineralization status remained unchanged in both groups. Serologic bone markers were similarly reduced in both groups throughout the study. We conclude that teriparatide does not improve BMD early after kidney transplantation. Neither histological analysis nor bone markers provide evidence of improved bone turnover or mineralization.

Uraemic hyperparathyroidism causes a reversible inflammatory process of aortic valve calcification in rats

AIMS

Renal failure is associated with aortic valve calcification (AVC). Our aim was to develop an animal model for exploring the pathophysiology and reversibility of AVC, utilizing rats with diet-induced kidney disease.

METHODS AND RESULTS

Sprague-Dawley rats (n = 23) were fed a phosphate-enriched, uraemia-inducing diet for 7 weeks followed by a normal diet for 2 weeks ('diet group'). These rats were compared with normal controls (n = 10) and with uraemic controls fed with phosphate-depleted diet ('low-phosphate group', n = 10). Clinical investigations included serum creatinine, phosphate and parathyroid hormone (PTH) levels, echocardiography, and multislice computed tomography. Pathological examinations of the valves included histological characterization, Von Kossa staining, and antigen and gene expression analyses. Eight diet group rats were further assessed for reversibility of valve calcification following normalization of their kidney function. At 4 weeks, all diet group rats developed renal failure and hyperparathyroidism. At week 9, renal failure resolved with improvement in the hyperparathyroid state. Echocardiography demonstrated valve calcifications only in diet group rats. Tomographic calcium scores were significantly higher in the diet group compared with controls. Von Kossa stain in diet group valves revealed calcium deposits, positive staining for osteopontin, and CD68. Gene expression analyses revealed overexpression of osteoblast genes and nuclear factor kappaB activation. Valve calcification resolved after diet cessation in parallel with normalization of PTH levels. Resolution was associated with down-regulation of inflammation and osteoblastic features. Low-phosphate group rats developed kidney dysfunction similar to that of the diet group but with normal levels of PTH. Calcium scores and histology showed only minimal valve calcification.

CONCLUSION

We developed an animal model for AVC. The process is related to disturbed mineral metabolism. It is associated with inflammation and osteoblastic features. Furthermore, the process is reversible upon normalization of the mineral homeostasis. Thus, our model constitutes a convenient platform for studying AVC and potential remedies.

Vitamin D and its implications for musculoskeletal health in women: an update

Vitamin D is a hormone that controls phosphorus, calcium, and bone metabolism and neuromuscular function. Vitamin D synthesis is a process in which the skin, liver, and kidney are sequentially involved. The vitamin D pool is completed by the amount taken with food and supplements. Vitamin D deficiency causes osteopenia, precipitates and exacerbates osteoporosis, causes a painful disease, osteomalacia, and increases muscle weakness, which worsens the risk of falls and fractures. A high prevalence of vitamin D insufficiency exists in the apparently healthy population, osteoporotic patients, and patients with prior fractures. Factors contributing to low vitamin D levels include low sunlight exposure, decreased skin synthesis and intestinal absorption, and inadequate diet. The simplest way to correct hypovitaminosis is adequate nutrition and supplements. However, few patients with osteoporosis and/or fractures, receive adequate supplements. Vitamin D insufficiency may alter the regulatory mechanisms of parathyroid hormone and may induce a secondary hyperparathyroidism that increases the risk of osteoporosis and fractures, although the necessary degree of this is not established. Monitoring of serum 25-hydroxyvitamin D levels is the only way to assess vitamin D status. The ideal healthy blood levels of 25-hydroxyvitamin D are controversial, although a range from 30 to 60ng/mL is widely accepted. The role of vitamin D supplementation is to provide humans with the nutrient in an amount closer to the biological norm for our species. This amount of vitamin D results in optimal function of many aspects of health, including balance and muscle strength, thus reducing the risk of fracture beyond what is possible via the quality and quantity of bone itself.