Secondary hyperparathyroidism in chronic kidney disease: pathophysiology, current treatments and investigational drugs.

INTRODUCTION: Secondary hyperparathyroidism (SHPT) is a common complication of chronic kidney disease (CKD). It begins as an adaptive increase in parathyroid hormone levels to prevent calcium and phosphate derangements. Over time, this condition becomes maladaptive and is associated with increased morbidity and mortality. Current therapies encompass phosphate-lowering strategies, vitamin D analogues, calcimimetics and parathyroidectomy. These approaches harbor inherent limitations, stimulating interest in the development of new drugs for SHPT to overcome these limitations and improve survival and quality of life among CKD patients. AREAS COVERED: This review delves into the main pathophysiological mechanisms involved in SHPT, alongside the treatment options that are currently available and under active investigation. Data presented herein stem from a comprehensive search conducted across PubMed, Web of Science, ClinicalTrials.gov and International Clinical Trials Registry Platform (ICTRP) spanning from 2000 onwards. EXPERT OPINION: The advancements in investigational drugs for SHPT hold significant promise for enhancing treatment efficacy while minimizing side effects associated with conventional therapies. Although several challenges still hinder their adoption in clinical practice, ongoing research will likely continue to expand the available therapeutic options, refine treatment strategies, and tailor them to individual patient profiles.

Hyperparathyroidism and Peripheral Arterial Disease.

Primary hyperparathyroidism (PHPT) is presented in various forms, including classic PHPT, characterised by increased parathyroid hormone (PTH) secretion, normohormonal PHPT, and normocalcaemic PHPT. Secondary hyperparathyroidism is characterised by increased PTH secretion triggered by factors such as vitamin D deficiency and kidney failure. This review aims to discuss the involvement of hyperparathyroidism (HPT) in atherosclerosis, including peripheral arterial disease (PAD). The increased level of PTH is involved in developing subclinical and overt vascular diseases, encompassing endothelial dysfunction, vascular stiffness, hypertension, and coronary and peripheral arterial diseases. It has been consistently associated with an augmented risk of cardiovascular morbidity and mortality, independent of classical risk factors for atherosclerosis. Chronic hypercalcemia associated with increased levels of PTH contributes to the development of calcification of vessel walls and atherosclerotic plaques. Vascular calcification can occur in the intima or media of the arterial wall and is associated with stiffness of peripheral arteries, which the formation of atherosclerotic plaques and narrowing of the vessel lumen can follow. For treating hyperparathyroidism, particularly SHPT, calcimimetics, novel phosphorus binders and novel vitamin D receptor activators are used. However, they are ineffective in severe PHPT. Therefore, parathyroidectomy remains the primary therapeutic option of PHPT.

The Role of Diet in Bone and Mineral Metabolism and Secondary Hyperparathyroidism.

Bone disorders are a common complication of chronic kidney disease (CKD), obesity and gut malabsorption. Secondary hyperparathyroidism (SHPT) is defined as an appropriate increase in parathyroid hormone (PTH) secretion, driven by either reduced serum calcium or increased phosphate concentrations, due to an underlying condition. The available evidence on the effects of dietary advice on secondary hyperparathyroidism confirms the benefit of a diet characterized by decreased phosphate intake, avoiding low calcium and vitamin D consumption (recommended intakes 1000-1200 mg/day and 400-800 UI/day, respectively). In addition, low protein intake in CKD patients is associated with a better control of SHPT risk factors, although its strength in avoiding hyperphosphatemia and the resulting outcomes are debated, mostly for dialyzed patients. Ultimately, a consensus on the effect of dietary acid loads in the prevention of SHPT is still lacking. In conclusion, a reasonable approach for reducing the risk for secondary hyperparathyroidism is to individualize dietary manipulation based on existing risk factors and concomitant medical conditions. More studies are needed to evaluate long-term outcomes of a balanced diet on the management and prevention of secondary hyperparathyroidism in at-risk patients at.

Real-world evidence and optimization of vocal dysfunction in end-stage renal disease patients with secondary hyperparathyroidism.

Patients with end-stage renal disease (ESRD) may demonstrate secondary hyperparathyroidism (SHPT), characterized by parathyroid hormone oversecretion in response to electrolyte imbalance (e.g., hypocalcemia and hyperphosphatemia). Moreover, this electrolyte imbalance may affect vocal cord muscle contraction and lead to voice change. Here, we explored the effects of SHPT on the voices of patients with ESRD. We used data of 147,026 patients with ESRD from the registry for catastrophic illness patients, a sub-database of Taiwan National Health Insurance Research Database. We divided these patients into 2 groups based on whether they had hyperparathyroidism (HPT) and compared vocal dysfunction (VD) incidence among them. We also prospectively included 60 ESRD patients with SHPT; 45 of them underwent parathyroidectomy. Preoperatively and postoperatively, voice analysis was used to investigate changes in vocal parameters. In the real-world database analysis, the presence of HPT significantly increased VD incidence in patients with ESRD (p = 0.003): Cox regression analysis results indicated that patients with ESRD had an approximately 1.6-fold increased VD risk (p = 0.003). In the clinical analysis, the "jitter" and "shimmer" factors improved significantly after operation, whereas the aerodynamic factors remained unchanged. In conclusion, SHPT was an independent risk factor for VD in patients with ESRD, mainly affecting their acoustic factors.

Impact of parathyroidectomy on left ventricular function in end stage renal disease patients.

BACKGROUND: Secondary hyperparathyroidism (SHPT) is a common complication in end-stage renal disease (ESRD) patients, and parathyroidectomy (PTX) is an effective treatment intervention of SHPT. However, the curative impact of PTX on left ventricular function still remains incompletely understood. To evaluate the impact of parathyroidectomy on left ventricular function in ESRD patients, we conducted this retrospective study. METHODS: Between Oct 1, 2010 and Oct 1, 2016, ESRD patients presented with SHPT who underwent parathyroidectomy were enrolled. We retrospectively collected the ultrasonic cardiogram parameter pre- and 1-year post-PTX, and analyzed the influence factor for the overturn of left ventricular hypertrophy (LVH) and the improvement of ejection fraction% (EF%). RESULTS: In all the patients (135), the main ultrasonic cardiogram parameter dramatically improved after PTX. Compared with pre-PTX, the left ventricular mass (LVM) (172.82 (135.90, 212.91) g vs. 192.76 (157.56, 237.97) g, p<0.001) and the left ventricular mass index (LVMI) (107.01 (86.79, 128.42) g/m2 vs. 123.54 (105.49, 146.64) g/m2, p<0.001) significantly declined after 1 year of the PTX. Further, 43.75% patients diagnosed with LVH before the PTX have recovered from LVH. In the subgroup analysis of 35 patients with EF% ≤ 60% pre-PTX, EF% and fractional shortening% (FS%) significantly improved after 1 year of the PTX compared with pre-PTX (EF%: 64.90 ± 7.90% vs. 55.71 ± 4.78%, p<0.001; FS% 35.48 ± 6.34% vs. 29.54 ± 2.88%, p<0.001), and 82.86% patients underwent an improvement of left ventricular systolic function post 1year of the PTX. CONCLUSIONS: tPTX+AT is an effective curative intervention of secondary hyperparathyroidism and can significantly overturn the LVH and increase the left ventricular systolic function.

Osteoblastic differentiation of bone marrow mesenchymal stem cells in uremic rats.

Severe secondary hyperparathyroidism (SHPT) represents a high turnover bone disease, osteitis fibrosa, but the pathogenesis of osteitis fibrosa remains to be fully elucidated. We examined the characteristics of the differentiation of bone marrow mesenchymal stem cells (BMSCs) into osteoblasts in uremic rats. We bred 5/6 nephrectomized (Nx) rats with a high phosphorus (P) diet to induce SHPT (Nx + HP), or Nx (Nx + ND) and normal rats (Nc + ND) fed a standard diet (ND). After 8 weeks, BMSCs were isolated from the femur and serum were analyzed. BMSCs underwent flow cytometric examination for the expression patterns of cell surface markers (CD90+, CD29+, CD45-, and CD31-). Serum creatinine (Cre) levels were significantly elevated in the Nx + NP rats compared with the Nc + NP rats. Cre levels in the Nx + HP rats were levels to those in the Nx + ND rats. Serum P and PTH levels were significantly elevated in the Nx + HP rats compared with the Nx + ND rats. Bone morphometrical analysis showed increases in both osteoid volume and eroded surfaces in the Nx + HP but not in the Nx + ND rats. The populations of harvested BMSCs were similar between all three groups. Alp, Runx2, Pth1r and Cyclin D1 mRNA expression in the BMSCs from the Nx + ND rats were significantly suppressed compared with those isolated from the Nc + ND groups. Alizarin red staining tended to be similar to the expression of these mRNA. These results suggest that the BMSCs differentiation into osteoblasts was disturbed in the uremic rats.

An examination of multiple explanations for secondary hyperparathyroidism
.

AIMS: Seven theories address the evolution of secondary hyperparathyroidism (SHPT) as chronic kidney disease (CKD) progresses. The tradeoff-in-the-nephron hypothesis states that the plasma parathyroid hormone ([PTH]) concentration rises because an increased phosphate concentration in the cortical distal nephron ([P]CDN) reduces the ionized calcium concentration in that segment. In the present study, we compared this hypothesis to its predecessors. MATERIALS AND METHODS: We studied 30 patients with estimated glomerular filtration rate (eGFR) less than 60 mL/min/1.73m2 (mean 29.5). To examine historic theories, we performed regressions of [PTH] on plasma concentrations of ionized calcium, phosphorus, 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D, and fibroblast growth factor 23, and on calcium excreted per volume of filtrate (ECa/Ccr). To assess the tradeoff-in-the-nephron hypothesis, we examined regressions of [PTH] on 100/eGFR and phosphorus excreted per volume of filtrate (EP/Ccr). RESULTS: Regressions pertinent to historic theories yielded significant direct relationships between [PTH] and both ECa/Ccr and [FGF23], but neither association supported the theory to which it pertained. [PTH] varied directly with 100/eGFR and with EP/Ccr, a surrogate for [P]CDN. EP/Ccr correlated strongly with 100/eGFR. CONCLUSIONS: The only theory of SHPT that our data support is the tradeoff-in-the-nephron hypothesis. Other theories are not supported.

Role of Vitamin D in Patients with Heart Failure with Reduced Ejection Fraction.

Heart failure (HF) with reduced ejection fraction (HFrEF) presents as the severest phenotype on the spectrum of HF. Although great progress has been made with respect to its treatment over the past 3 decades, morbidity and mortality remain high, posing a big burden on human health. Recent evidence suggests vitamin D has a critical role in maintaining heart health through activation of the vitamin D receptor expressed in cardiomyocytes, and vitamin D deficiency may be implicated in the pathophysiology of HFrEF through activation of the renin-angiotensin system, impaired calcium handling, exaggerated inflammation, secondary hyperparathyroidism, pro-fibrotic properties, and proatherogenic potential. Additionally, epidemiological data disclosed that vitamin D deficiency is highly prevalent in patients with HFrEF and is associated with poor clinical outcomes. However, randomized control trials of vitamin D supplementation in HF, especially in HFrEF, have shown inconsistent results. Thus, this article aims to review the epidemiology, pathophysiology, and prognostic value of vitamin D deficiency in HF, with a special focus on randomized control trials associated with vitamin D supplementation in patients with HFrEF.

Anatomical distribution and number of parathyroid glands, and parathyroid function, after total parathyroidectomy and bilateral cervical thymectomy.

The normal distribution of parathyroid glands is well documented. However, this study aims to evaluate the efficacy of total parathyroidectomy (TPTx) and bilateral cervical thymectomy (BCTx) for the treatment of secondary hyperparathyroidism (SHPT) through identifying the location of parathyroid glands with attention to the pattern and frequency of orthotopic and ectopic glands.Between 2013 and 2018, sixty chronic hemodialysis patients with medically refractory SHPT underwent TPTx & BCTx. The adequacy of the operation was defined by the pathological confirmation of at least 4 parathyroid glands, accompanied by an intact parathormone (iPTH) value of <60 pg/mL on postoperative day 1(POD1). Based on their anatomical localizations, four distinct sites were identified for both the upper (Zone I-IV) and lower parathyroid glands (Zone V-VIII).The mean follow-up was 15.2 ±â€Š14.6 months. The mean iPTH values on POD1 were normal in 50 patients, with an average of 11.7 ±â€Š14.4 pg/mL. Ten patients (16.6%) had persistent HPT after the operation, three of whom underwent complementary parathyroidectomy. The surgical success rates after first and second operations were both 83.3%. A total of 235 parathyroid glands were detected. Ninety-two percent of the upper parathyroids were located in Zones I and II. However, almost 28% of the lower parathyroids were ectopic and located in Zones VII and VIII.At least one fourth of the lower parathyroids are ectopic; for this reason, Zones VII and VIII require careful investigation during surgery. For upper parathyroids not found in Zone I-III, total thyroidectomy on the same side is recommended.

Calcium and Vitamin D Supplementation. Myths and Realities with Regard to Cardiovascular Risk.

Vitamin D and calcium are considered crucial for the treatment of bone diseases. Both vitamin D and calcium contribute to bone homeostasis but also preserve muscle health by reducing the risk of falls and fractures. Low vitamin D concentrations result in secondary hyperparathyroidism and contribute to bone loss, although the development of secondary hyperparathyroidism varies, even in patients with severe vitamin D deficiency. Findings from observational studies have shown controversial results regarding the association between bone mineral density and vitamin D/calcium status, thus sparking a debate regarding optimum concentrations of 25-hydroxyvitamin D and calcium for the best possible skeletal health. Although most of the intervention studies reported a positive effect of supplementation with calcium and vitamin D on bone in patients with osteoporosis, this therapeutic approach has been a matter of debate regarding potential side effects on the cardiovascular (CV) system. Thus, the aim of this review is to consider the current evidence on the physiological role of vitamin D and calcium on bone and muscle health. Moreover, we provide an overview on observational and interventional studies that investigate the effect of vitamin D and calcium supplementation on bone health, also taking into account the possible CV side-effects. We also provide molecular insights on the effect of calcium plus vitamin D on the CV system.

Parathyroid Hormone and Cardiac Electrophysiology: A Review.

Calcium has long been known to be essential to cardiac electrical activity. Parathyroid hormone (PTH) is the main regulator of serum calcium and is central to calcium homeostasis. Although there are significant data linking parathyroid disease states with changes in cardiac electrophysiology, most data have focused on how PTH modulates serum calcium to produce these effects. Close scrutiny of early literature demonstrates that the relationship between PTH and electrocardiographic changes is not straightforward, and numerous studies have linked PTH to arrhythmia. Basic science research has demonstrated that there is a basis for a direct role of PTH on cardiac electrophysiology outside of its effect on serum calcium. Later studies in secondary hyperparathyroidism indicate that PTH disturbances could have important implications for broad categories of patients with cardiovascular disease. The current review summarizes the existing literature on PTH and electrophysiology based on clinical and basic science studies of various parathyroid states, providing directions for future study.

Influence of Pre-renal Transplant Secondary Hyperparathyroidism on Later Evolution After Transplantation.

Persistence of secondary hyperparathyroidism (SHPT) is common after renal transplantation. Good diagnosis and treatment are important to avoid complications. The objective of our work was to perform a retrospective analysis of the evolution of SHPT after renal transplantation. We selected patients who had received a kidney transplant at our hospital between 2000 and 2014. The biochemical variables of chronic kidney disease-metabolic bone disorders (CKD-MBD) were collected at pretransplantation and at 3, 6, 12, and 24 months post-transplantation. Treatments related to SHPT were also analyzed. Five hundred forty-three renal transplants were included. The average preoperative parathyroid hormone (PTH) was 241.14 pg/mL, 115.7 pg/mL at 3 months, and at 12 and 24 months postoperatively, PTH levels stabilized to 112 pg/mL. Treatment related to SHPT was present in 27.3% of patients during the preoperative period, 40.4% at 3 months postoperatively, 24.2% at 12 months postoperatively, and 23.2% at 24 months postoperatively. There was a significant association between requiring some type of treatment preoperatively and the rest of the postoperative periods (P < .005). The sample was later divided into 3 groups based on preoperative PTH (1: <150 pg/mL, n = 223 [41.1%]; 2: 150-300 pg/mL, n = 173 [31.9%]; 3: >300 pg/mL, n = 147 [27.1%]) and their evolutions were compared. Higher levels of postoperative PTH in group pre-PTH 3 were observed. Group 3 also presented with greater need for treatment in the postoperative periods, with significant association (P < .05). A regression analysis was performed and found that postoperative PTH were dependent on preoperative PTH adjusted by glomerular filtration. In conclusion, parameters related to CKD-MBD (mainly PTH) after kidney transplant, dependent on preoperative levels and glomerular filtration. Patients with a greater grade of SHPT presented with higher levels of postoperative PTH despite receiving more intensive treatment.

A mathematical model of parathyroid gland biology.

Altered parathyroid gland biology in patients with chronic kidney disease (CKD) is a major contributor to chronic kidney disease-mineral bone disorder (CKD-MBD). This disorder is associated with an increased risk of bone disorders, vascular calcification, and cardiovascular events. Parathyroid hormone (PTH) secretion is primarily regulated by the ionized calcium concentration as well as the phosphate concentration in the extracellular fluid and vitamin D. The metabolic disturbances in patients with CKD lead to alterations in the parathyroid gland biology. A hallmark of CKD is secondary hyperparathyroidism, characterized by an increased production and release of PTH, reduced expression of calcium-sensing and vitamin D receptors on the surface of parathyroid cells, and hyperplasia and hypertrophy of these cells. These alterations happen on different timescales and influence each other, thereby triggering a cascade of negative and positive feedback loops in a highly complex manner. Due to this complexity, mathematical models are a useful tool to break down the patterns of the multidimensional cascade of processes enabling the detailed study of subsystems. Here, we introduce a comprehensive mathematical model that includes the major adaptive mechanisms governing the production, secretion, and degradation of PTH in patients with CKD on hemodialysis. Combined with models for medications targeting the parathyroid gland, it provides a ready-to-use tool to explore treatment strategies. While the model is of particular interest for use in hemodialysis patients with secondary hyperparathyroidism, it has the potential to be applicable to other clinical scenarios such as primary hyperparathyroidism or hypo- and hypercalcemia.

A practical self-made device in parathyroid autotransplantation for patients with secondary hyperparathyroidism.

OBJECTIVE: Secondary hyperparathyroidism (sHPT) is one of the most serious complications in patients on long-term hemodialysis. These patients may suffer from metabolic bone diseases, severe atherosclerosis, and undesirable cardiovascular events. Endoscopic parathyroidectomy with autotransplantation is a treatment option for those who do not respond to clinical management. This study aimed to investigate practical use of a self-made device in parathyroid autotransplantation for patients with sHPT, and to compare this device with ordinary surgical scissors. METHODS: A total of 15 patients with sHPT were treated with endoscopic parathyroidectomy and autotransplantation. Pieces of parathyroid tissue were squeezed in our self-made device and injected into the brachioradialis muscle. Sixteen patients with sHPT who were treated with traditional parathyroid transplantation served as controls. Serum levels of parathyroid hormone, alkaline phosphatase, calcium, phosphorus and intact parathyroid hormone were measured before and after surgery. RESULTS: Preoperative symptoms were alleviated, and serum parathyroid hormone and alkaline phosphatase levels, hyperphosphatemia, and hypercalcemia were improved or normalized in all of the patients in both groups. Pathological examinations showed that parathyroid cells remained active. CONCLUSION: Application of our squeezing device is an economic, effective, and safe method in endoscopic parathyroidectomy and autotransplantation for patients with sHPT.

Association of Anabolic Effect of Calcitriol with Osteoclast-Derived Wnt 10b Secretion.

Canonical Wnt (Wingless/Integrated) signaling is crucial in bone development and the Wnt ligand can promote osteoblast differentiation from mesenchymal progenitor cells. Calcitriol, an active vitamin D3, is used clinically for treatment of secondary hyperparathyroidism (SHPT) in chronic kidney disease (CKD) patients. The bone effects of calcitriol in SHPT remains uncertain. We hypothesized that calcitriol improves bone mass by suppressing osteoclast activity, and simultaneously promoting Wnt ligand secretion. We designed a cross-sectional study in maintenance hemodialysis patients to explore the effects of calcitriol on different bone turnover markers and specifically emphasized the Wnt 10b levels. Then, we explored the source of Wnt 10b secretion by using osteoclasts and osteoblasts treated with calcitriol in cell culture studies. Finally, we explored the effects of calcitriol on bone microarchitectures in CKD mice, using the 5/6 nephrectomy CKD animal model with analysis using micro-computed tomography. Calcitriol promoted the growth of both trabecular and cortical bones in the CKD mice. Wnt 10b and Procollagen 1 N-terminal Propeptide (P1NP) significantly increased, but Tartrate-resistant acid phosphatase 5b (Trap 5b) significantly decreased in the calcitriol-treated maintenance hemodialysis patients. Calcitriol enhanced Wnt 10b secretion from osteoclasts in a dose-dependent manner. Treatment of SHPT with calcitriol improved the bone anabolism by inhibiting osteoclasts and promoting osteoblasts that might be achieved by increasing the Wnt 10b level.

Bone metabolism, density, and geometry in postmenopausal women with vitamin D insufficiency: a cross-sectional comparison of the effects of elevated parathyroid levels.

Increased levels of parathyroid hormone (PTH) may have adverse effects on bone health. In a cross-sectional design, we investigated this hypothesis among 102 postmenopausal vitamin D insufficient women. Elevated PTH was associated with altered bone geometry, decreased bone mineral density in the spine, and increased bone turnover. INTRODUCTION: In vitamin D insufficiency, elevated parathyroid hormone (PTH) levels may contribute to adverse effect on bone. We assessed effects of PTH responses to vitamin D insufficiency on bone metabolism, density, and geometry. METHODS: Using a cross-sectional design, we investigated 102 healthy postmenopausal women with low 25-hydroxy-vitamin D (< 50 nmol/L) levels, who had either secondary hyperparathyroidism with elevated PTH levels (> 6.9 pmol/L, N = 51) or normal PTH levels (N = 51). Bone mineral density (BMD) and bone geometry were assessed by Dual-Energy X-ray absorptiometry (DXA), quantitative computed tomography (QCT) and high-resolution peripheral QCT (HRpQCT) scans. Bone metabolism was assessed by biochemistry including bone turnover markers. RESULTS: Levels of 25(OH)D were 38 (IQR 31-45) nmol/L with no differences between groups. PTH levels were 8.5 (IQR 7.5-9.5) in women with SHPT and 5.2 (4.4-6.6) pmol/L in women with normal PTH (p < 0.001). BMI and eGFR did not differ between groups. SHPT was associated with lower total- and trabecular bone area, lower cortical perimeter, and increased cortical area in tibia and radius. SHPT was associated with a lower weight-adjusted BMD at the lumbar spine (p < 0.05). High compared to normal PTH levels were associated with significantly lower plasma levels of 1,25(OH)2D, phosphate, but higher levels of osteocalcin and borderline higher levels of CTx. PTH correlated to osteocalcin and CTx. CONCLUSIONS: High PTH levels are associated with altered bone geometry, increased bone turnover, and reduced BMD at the spine. Whether an increased cortical thickness with a lower trabecular volume is an effect of PTH or not needs further elucidations.

[Update 2017 of the KDIGO guidelines on Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD). What are the real changes?]

Guidelines for the assessment, diagnosis and therapy of the alterations that characterize the CKD-MBD are an important support in the clinical practice of the nephrologist. Compared to the KDIGO guidelines published in 2009, the 2017 update made changes on some topics on which there was previously no strong evidence both in terms of diagnosis and therapy. The recommendations include the diagnosis of bone anomalies in CKD-MBD and the treatment of mineral metabolism abnormalities with particular regard to hyperphosphataemia, calcium levels, secondary hyperparathyroidism and anti-resorptive therapies. The Italian Study Group on Mineral Metabolism, in reviewing the 2017 recommendations, aimed to assess the weight of the evidence that led to this update. In fact, on some topics there has not been a substantial difference on the degree of evidence compared to the previous guidelines. The Italian Study Group emphasizes the points that may still reserve critical issues, including interpretation, and invites an evaluation that is articulated and personalized for each patient.