Mechanisms of vasodilation to PTH 1-84, PTH 1-34, and PTHrP 1-34 in rat bone resistance arteries

The Molecular Mechanisms Underlying the Systemic Effects Mediated by Parathormone in the Context of Chronic Kidney Disease

Chronic kidney disease (CKD) stands as a prominent non-communicable ailment, significantly impacting life expectancy. Physiopathology stands mainly upon the triangle represented by parathormone-Vitamin D-Fibroblast Growth Factor-23. Parathormone (PTH), the key hormone in mineral homeostasis, is one of the less easily modifiable parameters in CKD; however, it stands as a significant marker for assessing the risk of complications. The updated "trade-off hypothesis" reveals that levels of PTH spike out of the normal range as early as stage G2 CKD, advancing it as a possible determinant of systemic damage. The present review aims to review the effects exhibited by PTH on several organs while linking the molecular mechanisms to the observed actions in the context of CKD. From a diagnostic perspective, PTH is the most reliable and accessible biochemical marker in CKD, but its trend bears a higher significance on a patient's prognosis rather than the absolute value. Classically, PTH acts in a dichotomous manner on bone tissue, maintaining a balance between formation and resorption. Under the uremic conditions of advanced CKD, the altered intestinal microbiota majorly tips the balance towards bone lysis. Probiotic treatment has proven reliable in animal models, but in humans, data are limited. Regarding bone status, persistently high levels of PTH determine a reduction in mineral density and a concurrent increase in fracture risk. Pharmacological manipulation of serum PTH requires appropriate patient selection and monitoring since dangerously low levels of PTH may completely inhibit bone turnover. Moreover, the altered mineral balance extends to the cardiovascular system, promoting vascular calcifications. Lastly, the involvement of PTH in the Renin-Angiotensin-Aldosterone axis highlights the importance of opting for the appropriate pharmacological agent should hypertension develop.

PTH and the Regulation of Mesenchymal Cells within the Bone Marrow Niche

Parathyroid hormone (PTH) plays a pivotal role in maintaining calcium homeostasis, largely by modulating bone remodeling processes. Its effects on bone are notably dependent on the duration and frequency of exposure. Specifically, PTH can initiate both bone formation and resorption, with the outcome being influenced by the manner of PTH administration: continuous or intermittent. In continuous administration, PTH tends to promote bone resorption, possibly by regulating certain genes within bone cells. Conversely, intermittent exposure generally favors bone formation, possibly through transient gene activation. PTH's role extends to various aspects of bone cell activity. It directly influences skeletal stem cells, osteoblastic lineage cells, osteocytes, and T cells, playing a critical role in bone generation. Simultaneously, it indirectly affects osteoclast precursor cells and osteoclasts, and has a direct impact on T cells, contributing to its role in bone resorption. Despite these insights, the intricate mechanisms through which PTH acts within the bone marrow niche are not entirely understood. This article reviews the dual roles of PTH-catabolic and anabolic-on bone cells, highlighting the cellular and molecular pathways involved in these processes. The complex interplay of these factors in bone remodeling underscores the need for further investigation to fully comprehend PTH's multifaceted influence on bone health.

Abaloparatide dose-dependently increases bone mineral density in postmenopausal women with osteoporosis: a phase 2 study

INTRODUCTION

This study aimed to determine the efficacy of abaloparatide in increasing bone mineral density (BMD) and its safety in postmenopausal Japanese women with osteoporosis.

MATERIALS AND METHODS

Randomized, double-blind, placebo-controlled, dose-finding study of abaloparatide in postmenopausal Japanese women at high fracture risk. The primary endpoint was the change in lumbar spine (LS) BMD from baseline at the last visit after daily subcutaneous injections of placebo or 40 or 80 µg abaloparatide. Other endpoints included time-course changes in LS BMD at 12, 24, and 48 weeks, in total hip (TH) and femoral neck (FN) BMDs, and in bone turnover markers.

RESULTS

Increases in LS BMD with 40 and 80 µg abaloparatide were significantly higher than that with placebo (6.6% and 11.5%, respectively), with significant between-group differences for the abaloparatide groups (4.9%). TH BMD increased by 0.4%, 1.6%, and 2.9% and FN BMD increased by 0.6%, 1.5%, and 2.4% in the placebo and 40 and 80 µg abaloparatide groups, respectively. Serum PINP rapidly increased by 67.3% and 140.7% and serum CTX slowly increased by 16.4% and 34.5% in the 40 and 80 µg abaloparatide groups, respectively. Although more adverse events were observed in the abaloparatide groups, they were mild to moderate and not dose dependent.

CONCLUSION

In postmenopausal Japanese women with osteoporosis at high fracture risk, abaloparatide for 48 weeks dose-dependently increased LS, TH, and FN BMDs, supporting further investigation with 80 μg abaloparatide for the treatment of osteoporosis in this population.

TRIAL REGISTRATION NUMBER

JapicCTI-132381.

Abaloparatide Increases Lumbar Spine and Hip BMD in Japanese Patients With Osteoporosis: The Phase 3 ACTIVE-J Study

CONTEXT

Abaloparatide reduced fracture risk in postmenopausal women with osteoporosis in the Abaloparatide Comparator Trial In Vertebral Endpoints (ACTIVE). Its effect in Japanese patients remains unexamined.

OBJECTIVE

This work aimed to determine the efficacy and safety of abaloparatide in increasing bone mineral density (BMD) in Japanese patients with osteoporosis at high fracture risk.

METHODS

This was a randomized, double-blind, placebo-controlled study conducted in Japan. Postmenopausal women and men with osteoporosis with high fracture risk were given daily subcutaneous 80 µg abaloparatide or placebo for 78 weeks (18 months). The primary end point was percentage change in lumbar spine (LS) BMD from baseline at the last visit. Secondary end points included time-course changes in LS, total hip (TH), and femoral neck (FN) BMDs and bone turnover markers, and cumulative number of fractures.

RESULTS

Abaloparatide increased LS, TH, and FN BMDs (mean [95% CI]) by 12.5% (10.3%-14.8%; P < .001), 4.3% (3.3%-5.3%), and 4.3% (2.9%-5.6%), respectively, vs placebo. Serum procollagen type I N-terminal propeptide increased rapidly to ~ 140% above baseline at 6 weeks and gradually decreased but was approximately 25% higher than baseline at 78 weeks. Serum carboxy-terminal cross-linking telopeptide of type I collagen gradually increased to 50% above baseline at 24 weeks and decreased gradually to the placebo-group level from 60 weeks. Four vertebrae of 3 participants in the placebo group, but none in the abaloparatide group, developed new vertebral fractures. The safety profile was similar to that in the ACTIVE study.

CONCLUSION

In Japanese patients with postmenopausal and male osteoporosis with high fracture risk, abaloparatide for 78 weeks robustly increased LS, TH, and FN BMDs, suggesting a similar efficacy in Japanese patients vs the ACTIVE study population.

Transient Opening of the Blood-Brain Barrier by Vasoactive Peptides to Increase CNS Drug Delivery: Reality Versus Wishful Thinking?

BACKGROUND

The blood-brain barrier inhibits the central nervous system penetration of 98% of small molecule drugs and virtually all biologic agents, which has limited progress in treating neurologic disease. Vasoactive peptides have been shown in animal studies to transiently disrupt the blood-brain barrier and regadenoson is currently being studied in humans to determine if it can improve drug delivery to the brain. However, many other vasoactive peptides could potentially be used for this purpose.

METHODS

We performed a review of the literature evaluating the physiologic effects of vasoactive peptides on the vasculature of the brain and systemic organs. To assess the likelihood that a vasoactive peptide might transiently disrupt the blood-brain barrier, we devised a four-tier classification system to organize the available evidence.

RESULTS

We identified 32 vasoactive peptides with potential blood-brain barrier permeabilityaltering properties. To date, none of these are shown to open the blood-brain barrier in humans. Twelve vasoactive peptides increased blood-brain barrier permeability in rodents. The remaining 20 had favorable physiologic effects on blood vessels but lacked specific information on permeability changes to the blood-brain barrier.

CONCLUSION

Vasoactive peptides remain an understudied class of drugs with the potential to increase drug delivery and improve treatment in patients with brain tumors and other neurologic diseases. Dozens of vasoactive peptides have yet to be formally evaluated for this important clinical effect. This narrative review summarizes the available data on vasoactive peptides, highlighting agents that deserve further in vitro and in vivo investigations.

Endoplasmic reticulum stress mediates parathyroid hormone-induced apoptosis in vascular smooth muscle cells

Vascular calcification is one of the most common complications of chronic kidney disease (CKD), which is closely associated with increased mortality and morbidity rates of CKD patients. It has been reported that increased parathyroid hormone (PTH) aggravates vascular calcification in CKD patients. However, the direct role of PTH in vascular smooth muscle cells (VSMCs) is less elucidated. Here, we present evidence that PTH promotes apoptosis of VSMCs and endoplasmic reticulum (ER) stress participates in this process. Human aorta vascular smooth muscle cells (HASMCs) were treated with different concentrations of PTH for various time. HASMC apoptosis was detected by flow cytometry. Expression of phosphorylated (p)-PERK, CHOP, IRE1, p-JNK, and cleaved caspase 3 was determined by Western blotting. We found that PTH induced HASMC apoptosis and increased the expression of cleaved caspase 3. Furthermore, PTH activated PERK-CHOP and IRE1-JNK ER stress pathways. Either inhibition of JNK by SP600125 or CHOP by siRNA ameliorated PTH-induced apoptosis in HASMCs. We therefore suggest that ER stress participates in PTH-induced apoptosis of VSMCs, which may be a possible mechanism of PTH-promoted vascular calcification in CKD patients.

Parathyroid hormone and its related peptides in bone metabolism

Parathyroid hormone (PTH) is an 84-amino-acid peptide hormone that is secreted by the parathyroid gland. It has different administration modes in bone tissue through which it promotes bone formation (intermittent administration) and bone resorption (continuous administration) and has great potential for application in sbone defect repair. PTH regulates bone metabolism by binding to PTH1R. PTH plays an osteogenic role by acting directly on mesenchymal stem cells, cells with an osteoblastic lineage, osteocytes, and T cells. It also participates as an osteoclast by indirectly acting on osteoclast precursor cells and osteoclasts and directly acting on T cells. In these cells, PTH activates the Wnt signaling, cAMP/PKA, cAMP/PKC, and RANKL/RANK/OPG pathways and other signaling pathways. Although PTH(1-34), also known as teriparatide, has been used clinically, it still has some disadvantages. Developing improved PTH-related peptides is a potential solution to teriparatide's shortcomings. The action mechanism of these PTH-related peptides is not exactly the same as that of PTH. Thus, the mechanisms of PTH and PTH-related peptides in bone metabolism were reviewed in this paper.

Bone Marrow Microvasculature

The skeleton is highly vascularized due to the various roles blood vessels play in the homeostasis of bone and marrow. For example, blood vessels provide nutrients, remove metabolic by-products, deliver systemic hormones, and circulate precursor cells to bone and marrow. In addition to these roles, bone blood vessels participate in a variety of other functions. This article provides an overview of the afferent, exchange and efferent vessels in bone and marrow and presents the morphological layout of these blood vessels regarding blood flow dynamics. In addition, this article discusses how bone blood vessels participate in bone development, maintenance, and repair. Further, mechanical loading-induced bone adaptation is presented regarding interstitial fluid flow and pressure, as regulated by the vascular system. The role of the sympathetic nervous system is discussed in relation to blood vessels and bone. Finally, vascular participation in bone accrual with intermittent parathyroid hormone administration, a medication prescribed to combat age-related bone loss, is described and age- and disease-related impairments in blood vessels are discussed in relation to bone and marrow dysfunction. © 2020 American Physiological Society. Compr Physiol 10:1009-1046, 2020.

Short-term intermittent parathyroid hormone (1-34) administration increased angiogenesis and matrix metalloproteinase 9 in femora of mature and middle-aged C57BL/6 mice

NEW FINDINGS

What is the central question of this study? We sought to assess the effects of intermittent parathyroid hormone (1-34) administration on bone angiogenesis, the redistribution of bone marrow blood vessels, and matrix metalloproteinase 9 as a function of advancing age in mice. What is the main finding and its importance? Short-term (i.e. 10 days) intermittent parathyroid hormone (1-34) administration increased the number of small (≤29-µm-diameter) bone marrow blood vessels and augmented matrix metalloproteinase 9. These changes occurred before alterations in trabecular bone. Given the rapid response in bone angiogenesis, this investigation highlights the impact of intermittent parathyroid hormone (1-34) administration on the bone vascular network.

ABSTRACT

Intermittent parathyroid hormone (PTH) administration augments bone, stimulates the production of matrix metalloproteinase 9 (Mmp9) and relocates bone marrow blood vessels closer to osteoid seams. Discrepancies exist, however, regarding bone angiogenesis. Given that Mmp9 participates in cellular homing and migration, it might aid in blood vessel relocation. We examined the influence of short-term intermittent PTH administration on angiogenesis, Mmp9 secretion and the distance between blood vessels and bone. Mature (6- to 8-month-old) and middle-aged (10- to 12-month-old) male and female C57BL/6 mice were divided into three groups: control (CON), and 5 (5dPTH) and 10 days (10dPTH) of intermittent PTH administration. Mice were given PBS (50 µl day^-1 ) or PTH(1-34) (43 µg kg^-1  day^-1 ). Frontal sections (5 µm thick) of the right distal femoral metaphysis were triple-immunolabelled to identify endothelial cells (anti-CD31), vascular smooth muscle cells (anti-αSMA) and Mmp9 (anti-Mmp9). Vascular density, Mmp9 density, area and localization, and blood vessel distance from bone were analysed. Blood vessels were analysed according to diameter: 1-29, 30-100 and 101-200 µm. Trabecular bone microarchitecture and bone static and dynamic properties were assessed. No main effects of age were observed for any variable. The density of CD31-labelled blood vessels 1-29 and 30-100 µm in diameter was higher (P < 0.05) and tended (P = 0.055) to be higher, respectively, in 10dPTH versus 5dPTH and CON. Mmp9 was augmented (P < 0.05) in 10dPTH versus the other groups. Mmp9 was closer (P < 0.05) to blood vessels 1-29 µm in diameter and furthest (P < 0.05) from bone. In conclusion, bone angiogenesis occurred by day 10 of intermittent PTH administration, coinciding with augmented Mmp9 secretion near the smallest blood vessels (1-29 µm in diameter).

PTH Derivative promotes wound healing via synergistic multicellular stimulating and exosomal activities

BACKGROUND

Diabetic wounds are a disturbing and rapidly growing clinical problem. A novel peptide, parathyroid hormone related peptide (PTHrP-2), is assumed as multifunctional factor in angiogenesis, fibrogenesis and re-epithelization. This study aims to test PTHrP-2 efficiency and mechanism in wound healing.

METHODS

Through repair phenomenon in vivo some problems were detected, and further research on their mechanisms was made. In vivo therapeutic effects of PTHrP-2 were determined by HE, Masson, microfil and immunohistochemical staining. In vitro direct effects of PTHrP-2 were determined by proliferation, migration, Vascular Endothelial Grown Factor and collagen I secretion of cells and Akt/ Erk1/2 pathway change. In vitro indirect effects of PTHrP-2 was study via exosomes. Exosomes from PTHrP-2 untreated and treated HUVECs and HFF-1 cells were insolated and identified. Exosomes were co-cultured with original cells, HUVECs or HFF-1 cells, and epithelial cells. Proliferation and migration and pathway change were observed. PTHrP-2-HUVEC-Exos were added into in vivo wound to testify its hub role in PTHrP-2 indirect effects in wound healing.

RESULTS

In vivo, PTHrP-2 exerted multifunctional pro-angiogenesis, pro-firbogenesis and re-epithelization effects. In vitro, PTHrP-2 promoted proliferation and migration of endothelial and fibroblast cells, but had no effect on epithelial cells. Therefore, we tested PTHrP-2 indirect effects via exosomes. PTHrP-2 intensified intercellular communication between endothelial cells and fibroblasts and initiated endothelial-epithelial intercellular communication. PTHrP-2-HUVEC-Exos played a hub role in PTHrP-2 indirect effects in wound healing.

CONCLUSION

These findings of this study indicated that PTHrP-2, a multifunctional factor, could promote wound healing via synergistic multicellular stimulating and exosomal activities.

Parathyroid hormone independently predicts fracture, vascular events, and death in patients with stage 3 and 4 chronic kidney disease

Doctors do not know whether treatment of high parathyroid hormone levels is linked to better outcomes in their patients with kidney disease. In this study, lower parathyroid hormone levels at baseline were linked to lower risk of fracture, vascular events, and death in people with kidney disease.

PURPOSE

Chronic kidney disease (CKD) affects ~ 20% of older adults, and secondary hyperparathyroidism (HPT) is a common condition in these patients. To what degree HPT predicts fractures, vascular events, and mortality in pre-dialysis CKD patients is debated. In stage 3 and 4 CKD patients, we assessed relationships between baseline serum PTH levels and subsequent 10-year probabilities of clinical fractures, vascular events, and death.

METHODS

We used Marshfield Clinic Health System electronic health records to analyze data from adult CKD patients receiving care between 1985 and 2013, and whose PTH was measured using a second-generation assay. Covariates included PTH, age, gender, tobacco use, vascular disease, diabetes, hypertension, hyperlipidemia, obesity, GFR, and use of osteoporosis medications.

RESULTS

Five thousand one hundred eight subjects had a mean age of 68 ± 17 years, 48% were men, and mean follow-up was 23 ± 10 years. Fractures, vascular events, and death occurred in 18%, 71%, and 56% of the cohort, respectively. In univariate and multivariate models, PTH was an independent predictor of fracture, vascular events, and death. The hazards of fracture, vascular events and death were minimized at a baseline PTH of 0, 69, and 58 pg/mL, respectively.

CONCLUSIONS

We found that among individuals with stage 3 and 4 CKD, PTH was an independent predictor of fractures, vascular events, and death. Additional epidemiologic studies are needed to confirm these findings. If a target PTH range can be confirmed, then randomized placebo-controlled trials will be needed to confirm that treating HPT reduces the risk of fracture, vascular events, and death.

Inhibition of vascular endothelial growth factor in young adult mice causes low bone blood flow and bone strength with no effect on bone mass in trabecular regions

OBJECTIVE

To determine the effect of an antibody to vascular endothelial growth factor (VEGF) on bone blood flow, bone strength, and bone mass in the young adult mouse.

METHODS

Ten-week-old male BALB/cJ mice were body weight-randomized into either a rodent anti-VEGF monoclonal antibody (anti-VEGF, B20-4.1.1; 5 mg/kg 2×/wk.; n = 12) group or a vehicle (VEH; n = 12) group. After 42 days, mice were evaluated for bone blood flow at the distal femur by 18F-NaF-PET/CT and then necropsied. Samples from trabecular and cortical bone regions were evaluated for bone strength by mechanical testing, bone mass by peripheral quantitative computed tomography (pQCT), and micoarchitecture (MicroCT). Hydration of the whole femur was studied by proton nuclear magnetic resonance relaxometry (1H NMR).

RESULTS

Distal femur blood flow was 43% lower in anti-VEGF mice than in VEH mice (p = 0.009). Ultimate load in the lumbar vertebral body was 25% lower in anti-VEGF than in VEH mice (p = 0.013). Bone mineral density (BMD) in the trabecular region of the proximal humeral metaphysis by pQCT, and bone volume fraction and volumetric BMD by MicroCT were the same in the two groups. Volume fraction of bound water (BW) of the whole femur was 14% lower in anti-VEGF than in VEH mice (p = 0.003). Finally, BW, but not cortical tissue mineral density, helped section modulus explain the variance in the ultimate moment experienced by the femur in three-point bending.

CONCLUSION

Anti-VEGF caused low bone blood flow and bone strength in trabecular bone regions without influencing BMD and microarchitecture. Low bone strength was also associated with low bone hydration. These data suggest that bone blood flow is a novel bone property that affects bone quality.

Cardiovascular findings in patients with nonsurgical hypoparathyroidism and pseudohypoparathyroidism: A cohort study

OBJECTIVE

As only sparse data are available on indices of cardiovascular health among patients with nonsurgical hypoparathyroidism (Ns-HypoPT) and pseudohypoparathyroidism (PHP), we aimed to compare the cardiovascular profile between these groups of patients.

METHODS

A total of 56 patients with Ns-HypoPT and 30 with PHP were included and underwent a clinical examination including blood sampling and measurements of arterial stiffness, pulse wave velocity (PWV) and blood pressure (BP). Arterial stiffness and PWV were measured using AtCor SphygmoCor-XCEL (Atcor Medical Pty Ltd, Sydney, NSW, Australia).

RESULTS

Patients with Ns-HypoPT had an average age of 47 ± 17 years (68% females) and PHP patients 36 ± 13 years (80% females). Over 70% in both groups were genetically screened. Groups did not differ in terms of a history of cardiovascular disease, smoking status, use of calcium and vitamin D supplements or treatment with cholesterol-lowering or antihypertensive drugs. Compared with Ns-HypoPT, PHP patients had significantly lower levels of high-density lipoproteins (HDL) cholesterol and average glucose from HbA1c (P_both  = 0.01). PWV was significantly higher among patients with Ns-HypoPT (P_crude  = 0.02), even after adjustment for mean arterial pressure, body mass index, age and gender (P_adjusted  < 0.01). Heart rate was significantly higher in Ns-HypoPT compared with PHP (P = 0.03). Office BP and 24-hour ambulatory BP did not differ between groups (P > 0.05).

CONCLUSION

Patients with Ns-HypoPT have compared with PHP a higher arterial stiffness and heart rate. This has been associated with an increased risk of cardiovascular disease. Our data suggest that resistance to PTH is present in the cardiovascular system in PHP.

Short-term intermittent PTH 1-34 administration and bone marrow blood vessel ossification in Mature and Middle-Aged C57BL/6 mice

Intermittent parathyroid hormone (PTH) administration augments bone and progressive bone marrow blood vessel (BMBV) ossification occurs with advancing age. Since intermittent PTH administration augments bone, it may also serve to increase BMBV ossification. We assessed the influence of 5- and 10-days of intermittent PTH 1–34 administration on trabecular and cortical bone and BMBV ossification in mature (6–8 mon; n = 30) and middle-aged (10–12 mon; n = 30) male and female C57BL/6 mice. Mice were divided accordingly: control (CON) and 5-days (5dPTH) and 10-days (10dPTH) of PTH. Mice were given PBS (50 μl) or PTH 1–34 (43 μg/kg/d) for 5- and 10-consecutive days. Trabecular bone microarchitecture (i.e., BV/TV [%], Tb.Th [μm], Tb.N [/mm], and Tb.Sp [μm]) was assessed in the distal femoral metaphysis and cortical bone parameters (i.e., Ct.Th [μm] and CSMI [mm⁴]) at the femoral mid-shaft. BMBV ossification (i.e., ossified vessel volume [OsVV, %] and ossified vessel thickness [OsV.Th, μm]) was assessed in the medullary cavity of the femoral shaft. All parameters were determined by μCT. At this sample size, no gender-related differences were observed so female and male data were pooled. There were no main effects nor interactions for trabecular microarchitecture and Ct.Th. However, CSMI was larger (p < 0.05) in Middle-Age vs. Mature and larger (p < 0.05) in CON and 10dPTH vs. 5dPTH. OsVV tended (p = 0.057) to be higher (0.18 ± 0.04% vs. 0.09 ± 0.02%, respectively) and OsV.Th was higher (p < 0.05; 17.4 ± 1.6 μm vs. 12.1 ± 1.4 μm, respectively) in Middle-Aged vs. Mature mice. OsVV was not altered, but ossified vessels tended (p = 0.08) to be thicker in 10dPTH (17.6 ± 2.0 μm) vs. CON (12.5 ± 1.7 μm). No interactions were observed for OsVV and OsV.Th. In conclusion, this is the first report of ossified BMBV in C57BL/6 mice. The increased OsV.Th in Middle-Aged mice coincides with previous reports of increased OsVV in aged rats. The tendency of augmented OsV.Th in 10dPTH suggests that this treatment may ultimately impair the patency of bone marrow blood vessels.

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Bone marrow blood vessel (BMBV) ossification occurs in rats and humans.

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This is the first report of BMBV ossification in Mature and Middle-Aged mice.

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Intermittent PTH administration tended to thicken ossified BMBV.

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PTH treatment may ultimately impact the patency of bone marrow blood vessels.

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 parathyroidectomy on blood bone markers and heart rate variability in patients with stage 5 chronic kidney disease

PURPOSE

Decreased heart rate variability (HRV) is closely related to abnormal cardiac autonomic nervous function, especially sympathetic hyperactivity, which intensifies the risk of cardiovascular events and sudden death. HRV parameters are lower in chronic kidney disease (CKD) and parathyroidectomy (PTX) can improve these abnormalities in severe secondary hyperparathyroidism (SHPT) patients. However, few studies have evaluated correlations between circulating bone markers and HRV in CKD patients.

METHODS

We conducted a cross-sectional study including 134 stage 5 CKD patients with 100 controls and a prospective study of 29 PTX patients with follow-up. Circulating bone biomarkers included: (1) intact parathyroid hormone (iPTH) as bone remodeling regulator; (2) bone-specific alkaline phosphatase (BAP), representing bone formation; (3) tartrate-resistant acid phosphatase 5b (TRACP-5b), indicating bone resorption; and (4) bone-derived hormone, fibroblast growth factor 23 (FGF23).

RESULTS

Stage 5 CKD patients had higher circulating iPTH, BAP, TRACP-5b, and FGF23 than controls and these bone markers were significantly elevated in SHPT patients. Baseline iPTH, BAP, and lnFGF23 were independently associated with HRV in CKD patients. After PTX with a follow-up (median interval: 6.7 months), high blood iPTH, BAP, TRACP-5b, FGF23, and attenuated HRV were ameliorated. Furthermore, improved HRV indices were associated with reduced iPTH, BAP, TRACP-5b, and FGF23.

CONCLUSIONS

Circulating bone markers are correlated with HRV in CKD 5 patients and PTX can improve decreased HRV, which are associated with corrected bone markers in severe SHPT patients. Thus, we propose that PTH increases sympathetic tone and both high circulating PTH levels and sympathetic hyperactivity increase bone turnover, and that the products of bone turnover influence HRV.

Mineral and bone disorders in conventional hemodialysis: Challenges and solutions

Despite the advent of cinacalcet and noncalcium-containing phosphate binders, controlling the progression of vascular calcification (VC) is still challenging. Recent reports demonstrate that carbamylation driven by high urea concentration aggravates VC, suggesting the importance of adequate dialysis in retarding its progression. Theoretically, other promising measures include the use of iron-based phosphate binders, vitamin K, and magnesium supplements, which should be investigated in future randomized controlled trials (RCTs), ideally with hard outcomes. While incidence of hip fracture in patients on dialysis is decreasing in the United States and Japan (possibly owing to better control of PTH levels by cinacalcet) it remains much higher than that in the general population. Many drugs used in the treatment of osteoporosis, including bisphosphonate, raloxifene, denosumab, and teriparatide can, under specific conditions, increase bone mineral density (BMD), which is associated with a lower fracture rate. However, the efficacy of these drugs in reducing the fracture rate remains to be proven in hemodialysis (HD) patients, given their adverse effects such as severe hypocalcemia and resultant worsening of secondary hyperparathyroidism. Some clinical studies have shown that cinacalcet, lanthanum carbonate, and sevelamer reduce mortality in elderly patients on HD, suggesting the benefits of reducing PTH and serum phosphate levels. However, the target ranges of PTH and phosphate levels are based solely on observational studies. This is also the case when treating low PTH levels by decreasing vitamin D or calcium load. RCTs with hard clinical endpoints comparing different targets are necessary in the future.

Intermittent PTH 1-34 administration improves the marrow microenvironment and endothelium-dependent vasodilation in bone arteries of aged rats

Inflammation coincides with diminished marrow function, vasodilation of blood vessels, and bone mass. Intermittent parathyroid hormone (PTH) administration independently improves marrow and vascular function, potentially impacting bone accrual. Currently, the influence of marrow and intermittent PTH administration on aged bone blood vessels has not been examined. Vasodilation of the femoral principal nutrient artery (PNA) was assessed in the presence and absence of marrow. Furthermore, we determined the influence of PTH 1-34 on 1) endothelium-dependent vasodilation and signaling pathways [i.e., nitric oxide (NO) and prostacyclin (PGI₂)], 2) endothelium-independent vasodilation, 3) cytokine production by marrow cells, and 4) bone microarchitecture and bone static and dynamic properties. Young (4-6 mo) and old (22-24 mo) male Fischer-344 rats were treated with PTH 1-34 or a vehicle for 2 wk. In the absence and presence of marrow, femoral PNAs were given cumulative doses of acetylcholine, with and without the NO and PGI₂ blockers, and diethylamine NONOate. Marrow-derived cytokines and bone parameters in the distal femur were assessed. Exposure to marrow diminished endothelium-dependent vasodilation in young rats. Reduced bone volume and NO-mediated vasodilation occurred with old age and were partially reversed with PTH. Additionally, PTH treatment in old rats restored endothelium-dependent vasodilation in the presence of marrow and augmented IL-10, an anti-inflammatory cytokine. Endothelium-independent vasodilation was unaltered, and PTH treatment reduced osteoid surfaces in old rats. In conclusion, the marrow microenvironment reduced vascular function in young rats, and PTH treatment improved the marrow microenvironment and vasodilation with age. NEW & NOTEWORTHY This study investigated the influence of the marrow microenvironment on bone vascular function in young and old rats. An inflamed marrow microenvironment may reduce vasodilator capacity of bone blood vessels, diminishing delivery of blood flow to the skeleton. In young rats, the presence of the marrow reduced vasodilation in the femoral principal nutrient artery (PNA). However, intermittent parathyroid hormone administration (i.e., a treatment for osteoporosis) improved the marrow microenvironment and vasodilator capacity in old PNAs.

Mechanical, hormonal and metabolic influences on blood vessels, blood flow and bone

Bone tissue is highly vascularized due to the various roles bone blood vessels play in bone and bone marrow function. For example, the vascular system is critical for bone development, maintenance and repair and provides O₂, nutrients, waste elimination, systemic hormones and precursor cells for bone remodeling. Further, bone blood vessels serve as egress and ingress routes for blood and immune cells to and from the bone marrow. It is becoming increasingly clear that the vascular and skeletal systems are intimately linked in metabolic regulation and physiological and pathological processes. This review examines how agents such as mechanical loading, parathyroid hormone, estrogen, vitamin D and calcitonin, all considered anabolic for bone, have tremendous impacts on the bone vasculature. In fact, these agents influence bone blood vessels prior to influencing bone. Further, data reveal strong associations between vasodilator capacity of bone blood vessels and trabecular bone volume, and poor associations between estrogen status and uterine mass and trabecular bone volume. Additionally, this review highlights the importance of the bone microcirculation, particularly the vascular endothelium and NO-mediated signaling, in the regulation of bone blood flow, bone interstitial fluid flow and pressure and the paracrine signaling of bone cells. Finally, the vascular endothelium as a mediator of bone health and disease is considered.

Arterial Calcification in Diabetes Mellitus: Preclinical Models and Translational Implications

Diabetes mellitus increasingly afflicts our aging and dysmetabolic population. Type 2 diabetes mellitus and the antecedent metabolic syndrome represent the vast majority of the disease burden-increasingly prevalent in children and older adults. However, type 1 diabetes mellitus is also advancing in preadolescent children. As such, a crushing wave of cardiometabolic disease burden now faces our society. Arteriosclerotic calcification is increased in metabolic syndrome, type 2 diabetes mellitus, and type 1 diabetes mellitus-impairing conduit vessel compliance and function, thereby increasing the risk for dementia, stroke, heart attack, limb ischemia, renal insufficiency, and lower extremity amputation. Preclinical models of these dysmetabolic settings have provided insights into the pathobiology of arterial calcification. Osteochondrogenic morphogens in the BMP-Wnt signaling relay and transcriptional regulatory programs driven by Msx and Runx gene families are entrained to innate immune responses-responses activated by the dysmetabolic state-to direct arterial matrix deposition and mineralization. Recent studies implicate the endothelial-mesenchymal transition in contributing to the phenotypic drift of mineralizing vascular progenitors. In this brief overview, we discuss preclinical disease models that provide mechanistic insights-and point to challenges and opportunities to translate these insights into new therapeutic strategies for our patients afflicted with diabetes mellitus and its arteriosclerotic complications.