Interrelationships Between Sclerostin, Secondary Hyperparathyroidism, and Bone Metabolism in Patients on Hemodialysis.

CONTEXT: Sclerostin is an osteocyte-derived inhibitor of bone formation and is increased in kidney failure, but its role in the pathogenesis of renal bone disease remains unknown. OBJECTIVE: We aimed to explore the association of serum sclerostin with bone metabolism in patients undergoing hemodialysis, with a particular focus on parathyroid hormone (PTH)-dependent and PTH-independent pathways. METHODS: This cross-sectional and prospective cohort study included 654 patients undergoing hemodialysis at 10 facilities in Japan. We employed multivariable linear regression to explore whether sclerostin levels were associated with metacarpal bone mineral density (BMD), intact PTH, bone alkaline phosphatase (BAP), and tartrate-resistant acid phosphatase-5b (TRACP-5b). We employed mediation analyses to explore whether and to what extent the association of PTH with bone turnover markers is mediated by sclerostin. We also compared sclerostin levels between patients with and without previous or incident fractures. RESULTS: The median sclerostin level in hemodialysis patients was 3- to 4-fold higher than that in healthy individuals. Higher sclerostin levels were associated with higher metacarpal BMD and lower levels of intact PTH, BAP, and TRACP-5b. However, the relationships of sclerostin with bone turnover markers were substantially attenuated after adjustment for PTH. Mediation analysis suggested that the effects of PTH on bone turnover markers were mainly direct rather than mediated by sclerostin. Sclerostin levels were not associated with previous or incident fractures. CONCLUSION: These findings suggest that in patients undergoing dialysis, sclerostin has only a limited role in bone metabolism and may not mediate the effect of PTH on bone turnover.

Genetic Background and Clinicopathologic Features of Adult-onset Nephronophthisis.

INTRODUCTION: Recently, nephronophthisis (NPH) has been considered a monogenic cause of end-stage renal disease (ESRD) in adults. However, adult-onset NPH is difficult to accurately diagnose and has not been reported in a cohort study. In this study, we assessed the genetic background and clinicopathologic features of adult NPH. METHODS: We investigated 18 sporadic adult patients who were suspected as having NPH by renal biopsy. We analyzed 69 genes that cause hereditary cystic kidney disease and compared clinicopathologic findings between patients with and without pathogenic mutations in NPH-causing genes. RESULTS: Seven of 18 patients had pathogenic NPH-causing mutations in NPHP1, NPHP3, NPHP4, or CEP164. Compared with patients without pathogenic mutations, those with pathogenic mutations were significantly younger but did not significantly differ in the classic NPH pathologic findings, such as tubular cysts. On the other hand, the number of tubules with thick tubular basement membrane (TBM) duplication, which was defined as >10-µm thickness, was significantly higher in patients with genetically proven adult NPH than in those without pathogenic mutations. α-Smooth muscle actin (α-SMA)-positive myofibroblasts were detected inside thick TBM duplication. CONCLUSIONS: In adult patients with NPH, thick TBM duplication was the specific finding. Our analysis also suggested that older patients tended to have no pathogenic mutations, even when they were suspected to have NPH by renal biopsy. These findings could be the novel clinical clue for the diagnosis of NPH in adult patients.

Utility of glomerular Gd-IgA1 staining for indistinguishable cases of IgA nephropathy or Alport syndrome.

BACKGROUND: Pathological findings in Alport syndrome frequently show mesangial proliferation and sometimes incidental IgA deposition, in addition to unique glomerular basement membrane (GBM) changes including thin basement membrane and/or lamellation. However, similar GBM abnormalities are also often observed in IgA nephropathy. Both diseases are also known to show hematuria, proteinuria, and sometimes macrohematuria when associated with viral infection. Therefore, it can be difficult to make a differential diagnosis, even based on clinical and pathological findings. Some recent articles demonstrated that galactose-deficient IgA1 (Gd-IgA1)-specific monoclonal antibody (KM55) could potentially enable incidental IgA deposition to be distinguished from IgA nephropathy. METHODS: We performed comprehensive gene screening and glomerular Gd-IgA1 and type IV collagen α5 chain immunostaining for five cases with both IgA deposition and GBM changes to confirm that Gd-IgA1 can help to distinguish these two diseases. RESULTS: Four of the cases were genetically diagnosed with Alport syndrome (Cases 1-4) and one was IgA nephropathy with massive GBM changes, which had a negative gene test result (Case 5). In Cases 1-4, glomerular Gd-IgA1 deposition was not detected, although there was positivity for IgA in the mesangial area. In Case 5, glomerular Gd-IgA1 deposition was observed. CONCLUSION: Gd-IgA1 expression analysis could clearly differentiate these two disorders. This approach can be applied to identify these two diseases showing identical clinical and pathological findings.

Changes in Fibroblast Growth Factor 23 and Soluble Klotho Levels After Hemodialysis Initiation.

RATIONALE & OBJECTIVE: Patients with chronic kidney failure have markedly elevated fibroblast growth factor 23 (FGF-23) levels and decreased soluble Klotho levels. However, no studies have examined the effects of hemodialysis initiation on the levels of these hormones and other parameters of mineral metabolism. STUDY DESIGN: Prospective single-arm study. SETTING & PARTICIPANTS: 20 individuals with incident kidney failure initiating hemodialysis. EXPOSURE: Initiation of hemodialysis. Dose adjustments of phosphate binders and vitamin D receptor activators and use of calcimimetics, erythropoiesis-stimulating agents, and intravenous iron were prohibited. OUTCOMES: Changes in serum levels of FGF-23, soluble Klotho, and other biochemical parameters of mineral metabolism, measured before and after each hemodialysis session, for a total of 4 sessions over 5 days. ANALYTICAL APPROACH: Repeated-measures analysis of variance. RESULTS: At baseline, participants had 18-fold higher median FGF-23 levels and 1.6-fold lower mean soluble Klotho levels compared with age- and sex-matched healthy individuals. Initiation of hemodialysis led to progressive reductions in serum phosphorus, intact parathyroid hormone, and FGF-23 levels, with dialysis-related fluctuations. No reductions were observed in levels of α1-microglobulin, which has molecular weight comparable to FGF-23. The magnitude of the FGF-23 level reductions was strongly associated with concomitant changes in serum phosphorus levels but not with the changes in intact parathyroid hormone levels. Soluble Klotho levels did not change after the initiation of hemodialysis. LIMITATIONS: Single-arm design, small sample size, short follow-up period. CONCLUSIONS: Initiation of hemodialysis in patients with chronic kidney failure led to progressive reductions in FGF-23 levels in association with reductions in serum phosphorus levels. These results suggest that phosphorus is a strong inducer of FGF-23 production and that regulation of FGF-23 production is a rapid process.

Metacarpal bone mineral density by radiographic absorptiometry predicts fracture risk in patients undergoing maintenance hemodialysis.

The 2017 Kidney Disease: Improving Global Outcomes (KDIGO) guideline update suggests bone mineral density testing to assess fracture risk in patients with chronic kidney disease, but dual-energy X-ray absorptiometry is not available in most dialysis facilities. Radiographic absorptiometry is an inexpensive and quick method for evaluating bone mineral density. Therefore, we analyzed a historical cohort of 456 maintenance hemodialysis patients to determine whether metacarpal bone mineral density measured by digital image processing, a computer-assisted radiographic absorptiometry technique, predicts fracture risk. At baseline, the median metacarpal bone mineral density T-score was -2.05 (interquartile range, -3.35 to -0.99). During a mean follow-up of 5.3 years, there were 16 clinical fractures and 11 asymptomatic vertebral fractures as estimated by height loss. Metacarpal bone mineral density T-score was significantly lower in patients who sustained a clinical fracture than in those remaining event-free. Decreasing metacarpal bone mineral density T-score was significantly associated with increased risk of clinical fracture (hazard ratio, 1.41 per 1 standard deviation decrease in bone mineral density T-score [95% confidence interval, 1.09 to 1.83]; the hazard ratio for lowest versus highest tertile was 4.86 [1.03 to 22.92]. Similar associations were observed between metacarpal bone mineral density T-score and vertebral fracture or any fracture. The results were robust to different analysis strategies and were consistent across different subgroups. Thus, radiographic absorptiometry could be a useful tool for primary screening of hemodialysis patients at high risk for fracture. Additional studies are required to determine the predictive ability of radiographic absorptiometry techniques compared to dual-energy X-ray absorptiometry or other established methods.

Development of evocalcet for unmet needs among calcimimetic agents.

INTRODUCTION: The calcium-sensing receptor is an important treatment target for secondary hyperparathyroidism (SHPT) in patients undergoing dialysis. In addition to vitamin D receptor activator, cinacalcet has recently been widely used for SHPT management, and the significant suppression of parathyroid hormone (PTH) with better control of serum calcium and phosphorus has been reported. However, low adherence and insufficient dose escalation mainly due to frequent gastrointestinal adverse events, still remain as major issues. To overcome these unmet needs, we have developed a new oral calcimimetic agent evocalcet, which has recently been approved by the Pharmaceutical Affairs Act in Japan. AREAS COVERED: PubMed was searched from inception until April 2020 with the word evocalcet to summarize the development of this new calcimimetic agent, its pharmacokinetics, and the results of clinical trials, along with an overview of the differences among calcimimetic agents. This review also includes the management of SHPT with a focus on calcimimetics. EXPERT OPINION: Evocalcet evoked fewer gastrointestinal-related adverse events while suppressing PTH at a lower dose than cinacalcet. These data suggest evocalcet may contribute to better adherence and sufficient dose escalation in patients with SHPT. Whether or not evocalcet improves clinical outcomes remains to be elucidated.

Skeletal and mineral metabolic effects of risedronate in a rat model of high-turnover renal osteodystrophy.

INTRODUCTION: High-turnover bone disease is a major consequence of SHPT and may explain the high risk for fracture in patients with advanced chronic kidney disease (CKD). Bisphosphonates suppress bone turnover and improve bone strength, but their effects have not been fully characterized in advanced CKD with severe SHPT. Bisphosphonates also increase 1,25-dihydroxyvitamin D levels in normal and uremic rats, but the underlying mechanism remains to be determined. MATERIALS AND METHODS: We investigated the skeletal and mineral metabolic effects of RIS, a pyridinyl bisphosphonate, in rats with severe SHPT induced by 5/6 nephrectomy plus a high phosphate diet. RESULTS: Nephrectomized rats developed severe SHPT, along with hyperphosphatemia, low 1,25-dihydroxyvitamin D, and markedly increased FGF23. Moreover, these rats exhibited characteristic features of high-turnover renal osteodystrophy, including increased indices of trabecular bone turnover, decreased cortical bone thickness, inferior cortical biomechanical properties, and a prominent increase in peritrabecular fibrosis. RIS treatment increased bone volume and partially attenuated trabecular bone remodeling, cortical bone loss, and mechanical properties, whereas it produced a marked improvement in peritrabecular fibrosis along with a corresponding decrease in osteogenic gene markers. RIS treatment also suppressed the elevation of FGF23, which was associated with increased 1,25-dihydroxyvitamin D. CONCLUSIONS: In a rat model of severe SHPT, treatment with RIS partially attenuated histological manifestations of high-turnover bone disease. RIS treatment also suppressed the elevation of FGF23, which may explain the increased 1,25-dihydroxyvitamin D production during the treatment.

Preventive effect of early introduction of everolimus and reduced-exposure tacrolimus on renal interstitial fibrosis in de novo living-donor renal transplant recipients.

BACKGROUND: To improve the long-term outcomes following renal transplantation, prevention of renal-allograft interstitial fibrosis (IF), mainly due to calcineurin inhibitors, is an important therapeutic target. Everolimus (EVR) was reported to have antifibrotic effects. We aimed to investigate the safety, efficacy, and IF of our modified immunosuppressive regimen, which includes early introduction of EVR and reduced-exposure tacrolimus (Tac) (EVR group), and compare it with the standard-exposure tacrolimus-based regimen (Tac group) in de novo living-donor renal recipients. METHODS: In this retrospective, single-center cohort study, we compared the 2-year clinical courses between the two groups according to intention to treat. Additionally, in patients in whom biopsies were obtained at 1 h, 3 months, and 12 months post-transplant, we compared IF between the groups using imaging analysis. RESULTS: Overall, 47 patients were included (EVR group, n = 22; Tac group, n = 25). There were no significant differences in renal function and incidences of rejection and viral infections between the groups at the 2-year post-transplant follow-up. However, pathologic imaging analysis (n = 34) revealed chronological progression of IF in the Tac group during the first year post-transplant and no changes in the EVR group (fibrosis rate at 3 months: 20.8 vs. 13.6%, p < 0.001; at 12 months: 24.7 vs. 14.7%, p < 0.001, respectively). CONCLUSION: Our modified immunosuppressive regimen may have an antifibrotic effect on transplanted kidneys without loss of safety and efficacy.

Correction to: Preventive effect of early introduction of everolimus and reduced­exposure tacrolimus on renal interstitial fibrosis in de novo living­donor renal transplant recipients.

In the Original publication of the article, the co-author name has been misspelled as "Yousuke Nakagawa".

[Update on recent progress in vitamin D research. The role of vitamin D in management of CKD-MBD.]

Vitamin D was originally discovered as a substance which alleviates rickets and studies revealed that vitamin D exerts pleiotropic effects. Vitamin D has a therapeutic effect on Chronic Kidney Disease(CKD)-associated bone lesion or secondary hyperparathyroidism. On the other hand, excessive vitamin D induces calcium and phosphate overload, resulting in vascular calcification and cardiovascular events. From the data so far, not all CKD patients can get the benefit of vitamin D. It is well indicated for CKD patients with vitamin D insufficiency, secondary parathyroidism, hypocalcemia, or low-turnover bone disease on the basis of avoiding calcium over load.

Magnesium as a new player in CKD: too little is as bad as too much?

Vascular calcification is a serious complication of chronic kidney disease, but the current therapeutic strategy is insufficient for preventing its progression. Magnesium is a potent inhibitor of calcification and represents a promising therapeutic candidate. Diaz-Tocados and colleagues now demonstrate that magnesium supplementation prevents the progression of vascular calcification in a uremic rat model, independently of the phosphate-binding capacity. We should keep in mind, however, that too much magnesium could have adverse effects on bone metabolism.

Etelcalcetide for the treatment of secondary hyperparathyroidism.

INTRODUCTION: Calcium sensing receptor is an important target for the treatment of secondary hyperparathyroidism (SHPT). Etelcalcetide hydrochloride is a novel peptide calcimimetic agent that has a similar mechanism of action as cinacalcet hydrochloride. Clinical trials of etelcalcetide have been performed in the US, Europe, and Japan, and these trials demonstrated the safety and efficacy of etelcalcetide in dialysis patients. Etelcalcetide has recently been approved in Europe, the US and Japan. Areas covered: We review the development, pharmacokinetics, and clinical efficacy and safety of etelcalcetide for the treatment of SHPT in hemodialysis patients. We also summarize the clinical evidence regarding cinacalcet to forecast the potential clinical benefit of etelcalcetide. Expert opinion: Etelcalcetide is an injectable calcimimetic with a longer elimination half-life than cinacalcet. The injectable formulation improves adherence and reduces pill burden, while the frequency of gastrointestinal adverse events has been comparable between cinacalcet and etelcalcetide. The longer half-life of etelcalcetide reduces the fluctuation of biochemical markers of mineral and bone metabolism, but it remains to be determined whether such a sustained effect results in improved outcomes. Further studies are needed to determine the impact of etelcalcetide on clinical outcomes, particularly in comparison with the conventional calcimimetic cinacalcet.

[Parenteral calcimimetics for the treatment of secondary hyperparathyroidism.]

The oral calcimimetics, cinacalcet, is reported to be effective on secondary hyperparathyroidism resistant to classical treatment like phosphate binders or vitamin D receptor activator. The problem that gastrointestinal adverse events cause poor adherence, drug discontinuation, and insufficient dose escalation remains unsolved. The novel injectable calcimimetic, etelcalcetide, is recently developed and is expected to reduce such adverse events and improve the therapeutic effects on moderate to severe secondary hyperparathyroidism. Further studies are needed to demonstrate the potential benefits of etelcalcetide compared to cinacalcet.

[Pathogenesis and clinical condition of hyperphosphatemic diseases].

Phosphorus is essential mineral to life, which has the multiple roles like postural maintenance or production of energy in the cells. Phosphate overload is harmful and compensatory mechanisms exist. Phosphate is abolished through kidneys and target organ of the compensatory mechanism is also kidneys. It is necessary to evaluate renal function and source of phosphate for estimating the cause of hyperphosphatemia. Acute hyperphosphatemia may cause severe acute kidney injury and avoidance of massive phosphate overload is needed. Chronic hyperphosphatemia have an impact on prognosis because the risk of cardiovascular event increases. Adequate restriction of phosphate intake and use of phosphate absorbent is needed for improvement of prognosis of patients with chronic kidney disease.

An adult case of severe steroid-resistant Henoch-Schönlein purpura nephritis treated with intravenous cyclophosphamide and tonsillectomy.

A previously healthy 37-year-old Canadian man living in Japan visited a hospital in Thailand while traveling because of edematous legs, purpura, arthralgia, bloody stool, and fever after an insect bite. Henoch-Schönlein purpura (HSP) was suspected. His creatinine level was 5.2 mg/dL. He was treated with oral prednisolone (PSL) and oral cyclophosphamide (CPA); after treatment, his creatinine level improved to 2.4 mg/dL. Upon returning to Japan, he was admitted to the National Center for Global Health and Medicine Hospital in Tokyo. A kidney biopsy was performed, and HSP nephritis (HSPN) was diagnosed. Renal dysfunction and proteinuria persisted despite 4 administrations of steroid-pulse therapy and 3 sessions of plasma exchange. Finally, he was treated with intravenous cyclophosphamide (IVCY). His creatinine level and proteinuria markedly improved. His microscopic hematuria disappeared after he underwent tonsillectomy. There have been only a few case reports describing patients with adult-onset HSPN necessitating IVCY. We present here a rare case of steroid-resistant HSPN treated with IVCY and tonsillectomy, with reference to some recent findings.

[Case of serious HIV-associated nephropathy resulting in the introduction of hemodialysis].

A previously healthy 46-year-old black man visited the other hospital because of fever, appetite loss and nausea. Renal dysfunction, liver injury, and a highly markedly elevated LDH level were found. Abdominal CT demonstrated enlarged liver, spleen, kidney and lymph nodes. Human immunodeficiency virus (HIV) was serologically positive. His serum BUN, creatinine and potassium were 74.9 mg/dL, 11.78 mg/dL, and 5.6 mEq/L, respectively. After admission, anuria persisted and the progression of renal failure continued despite various treatment methods, necessitating the introduction of maintenance hemodialysis(HD). A kidney biopsy was performed to confirm classical HIV-associated nephropathy (HIVAN). Antiretroviral therapy (ART) was started. Although urine was transiently excreted, HD could not be discontinued. It has been reported that HIVAN is too difficult to treat and that kidney dysfunction seldom recovers. HIVAN is well-known to occur frequently in black HIV-infected patients. However, in Japan, there have been only a few reports describing patients with serious HIVAN and renal failure necessitating HD. We present here a very rare case with HIVAN, with reference to some recent findings.