Toshifumi Sakaguchi

Calcimimetic Compound Upregulates Decreased Calcium-Sensing Receptor Expression Level in Parathyroid Glands of Rats with Chronic Renal Insufficiency

The reduced expression level of the calcium-sensing receptor (CaR) is attributed to the hyposensitivity of parathyroid cells to extracellular calcium concentration [Ca2+]o, which plays a crucial role in the pathogenesis of secondary hyperparathyroidism (SHPT) in patients and rats with chronic renal insufficiency (CRI). Calcimimetic compounds have been demonstrated to improve the decreased sensitivity of CaR to extracellular calcium concentration and to suppress both parathyroid hormone (PTH) oversecretion and parathyroid cell proliferation. However, the effect of calcimimetics on the reduced CaR expression level in parathyroid cells in CRI remains unclarified. The aim of this investigation was to examine the effect of the calcimimetic compound NSP R-568 (R-568) on the CaR expression in the parathyroid cells of rats with experimental CRI. Subtotally nephrectomized rats were fed a high-phosphorus diet for 8 (n = 12; Nx-8 group) or 9 wk (n = 11; Nx-9 group) to induce severe SHPT. Another group of uremic rats were fed a high-phosphorus diet for 8 wk and then orally administered R-568 (100 micromol/kg body wt) once a day for 7 d (n = 11; Nx+R-568 group). Sham-operated rats that were fed a standard diet for 9 wk were used as controls (n = 8). R-568 treatment induced a significant reduction in plasma PTH level with significant decrease in serum calcium and without change in serum phosphorus concentration. Serum 1,25(OH)2D3 level was not affected by R-568 administration. CaR mRNA and protein levels in the Nx-8 and Nx-9 groups significantly decreased compared with those in the controls; however, no significant difference in these parameters was observed between the Nx-8 and Nx-9 groups. In the Nx+R-568 group, CaR mRNA and protein levels significantly increased compared with those in either the Nx-8 or Nx-9 group. R-568 was effective in reducing the number of proliferating cell nuclear antigen-positive cells along with parathyroid gland growth suppression in the Nx+R-568 group compared with that in the Nx-9 group. The results suggest that the calcimimetic compound R-568 upregulates decreased CaR expression, and the upregulation possibly has an enhancement effect on PTH secretion and parathyroid cell hyperplasia through the improved sensitivity of CaR to [Ca2+]o.

Fibroblast growth factor 23 production in bone is directly regulated by 1α,25-dihydroxyvitamin D, but not PTH

Fibroblast growth factor 23 (FGF23), which is primarily produced by osteocytes in bone, regulates renal phosphate excretion and 1α,25-dihydroxyvitamin D [1,25(OH)(2)D(3)] metabolism. Patients with chronic kidney disease (CKD) have increased levels of circulating serum FGF23, but the direct effect on circulating FGF23 levels in renal insufficiency is still unclear. To identify the major regulator of FGF23 synthesis in renal insufficiency, we compared the effect of parathyroid hormone (PTH) and 1,25(OH)(2)D(3) on FGF23 synthesis in the calvariae of normal rats with that of uremic rats in vitro. 1,25(OH)(2)D(3) treatment significantly increased the FGF23 concentration in the medium from both groups, but the degree of increase in the uremic group was markedly higher than in the control group. A significant increase in FGF23 mRNA expression occurred as early as 4 h after treatment and reached the maximum within 8 h in the uremic group, whereas in the normal group a significant increase in FGF23 mRNA expression was observed only at 8 h. In addition, the expression of vitamin D receptor (VDR) mRNA in the calvariae of uremic rats was markedly higher than in normal rats. However, in neither group did PTH treatment affect the medium FGF23 concentration or the FGF23 mRNA levels. These results suggest that FGF23 synthesis in bone is regulated by 1,25(OH)(2)D(3) directly, not by PTH, and that increased VDR mRNA expression induced the relatively swift and strong response in the uremic group.

Regulation of Fibroblast Growth Factor 23 Production in Bone in Uremic Rats

Background: Fibroblast growth factor 23 (FGF23) regulates renal phosphate reabsorption and 1α,25-dihydroxyvitamin D [1,25(OH)2D3] metabolism. Patients with chronic kidney disease (CKD) have increased levels of circulating FGF23, but the direct regulation of this elevation of FGF23 is incompletely understood. Method:We measured plasma parameters in uremic rats fed a high-phosphorus diet and then performed parathyroidectomy (PTX) to determine its effect. We also investigated FGF23 mRNA expression in various tissues to identify the major source of circulating FGF23. Result: The uremic rats displayed dramatic changes in plasma FGF23 levels, consistent with increased expression of FGF23 in bone. Elevated FGF23 was associated with phosphate and parathyroid hormone (PTH). After PTX, the elevated FGF23 had decreased, consistent with decreased expression of FGF23 in bone. Significant decreases in plasma FGF23 were associated with PTH and 1,25(OH)2D3, but not phosphate. Conclusion: Elevated plasma FGF23 levels in uremic rats reflect the increased expression of FGF23 in bone. The expression of FGF23 in bone may be regulated by a PTH-1,25(OH)2D3 axis-dependent pathway and another PTH-dependent and 1,25(OH)2D3-independent pathway in uremic rats. The pathway may be decided by the degree of renal dysfunction.

Biochemical and Cellular Effects of Direct Maxacalcitol Injection into Parathyroid Gland in Uremic Rats

The most important etiological factors of resistance to medical treatments for secondary hyperparathyroidism are the decreased contents of the vitamin D receptor (VDR) and Ca-sensing receptor (CaSR) in parathyroid cells and a severely swollen parathyroid gland (PTG) as a result of hyperplasia. The effects of direct maxacalcitol (OCT) injection into PTG in terms of these factors were investigated in this study. The PTG of Sprague-Dawley rats that were 5/6 nephrectomized and fed a high-phosphate diet were treated by a direct injection of OCT (DI-OCT) or vehicle (DI-vehicle). The changes in serum intact parathyroid hormone (PTH), Ca(2+), and phosphorus levels, in VDR and CaSR expression levels in parathyroid cells, and in Ca(2+)-PTH curves were examined. Apoptosis was analyzed by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling method and DNA electrophoresis for PTG. DI-OCT markedly decreased serum intact PTH level, and a significant difference in this level between DI-OCT and DI-vehicle was observed. However, serum Ca(2+) and phosphorus levels did not changed markedly in both groups. The upregulations of both VDR and CaSR, the clear shift to the left downward in the Ca(2+)-PTH curve, and the induction of apoptosis after DI-OCT were observed. These findings were not observed in the DI-vehicle-treated rats. Moreover, these effects of DI-OCT were confirmed by the DI-OCT into one PTG and DI-vehicle alone into another PTG in the same rat. DI-OCT may introduce simultaneous VDR and CaSR upregulations and the regression of hyperplastic PTG, and these effects may provide a strategy for strongly suppressing PTH levels in very severe secondary hyperparathyroidism.

Significance of Serum Magnesium as an Independent Correlative Factor on the Parathyroid Hormone Level in Uremic Patients

CONTEXT PTH is a critical factor in mineral homeostasis, and chronic kidney disease mineral and bone metabolism disorder is a very important problem in patients with renal failure. Abnormal levels of PTH, serum phosphate, and calcium influence chronic kidney disease mineral and bone metabolism disorder, but there is little information about the influence of magnesium (Mg) on PTH. OBJECTIVE The aim of this study was to elucidate the correlation between magnesium and PTH levels in uremic patients just prior to beginning hemodialysis (HD) for the first time. PATIENTS We enrolled 1231 patients in nine Japanese facilities who had begun HD for end-stage renal disease. We investigated their serum Mg levels and the correlation between intact PTH (iPTH) and the serum Mg levels and other clinical parameters and medications. RESULTS The mean serum Mg was 2.2 ± 0.5 mg/dL, and hypermagnesemia was found in 663 patients (53.9%). Divided into two groups according to median iPTH level, the serum Mg levels were significantly higher in patients with low iPTH (2.3 ± 0.5 vs 2.1 ± 0.5, P < .01). Furthermore, divided into two groups according to the Mg level, iPTH levels were lower in patients with high Mg than in patients with normal serum Mg levels (277.9 ± 195.9 pg/mL vs 321.9 ± 203.7 pg/mL, P < .01). In the multiple regression analysis according to the effect of iPTH level, the serum Mg level was an independent variable after adjustment for other factors. CONCLUSIONS A high serum level of Mg is frequent in uremic patients with end-stage renal disease just prior to beginning HD. In the present set of patients, there was a significant correlation between the serum Mg and iPTH levels. Furthermore, the serum Mg level was an independent factor apart from the other factors regulating iPTH. These results suggest that serum Mg may be one of the factors regulating the serum PTH level in uremic patients.

Association between the Hemoglobin Level and Cardiothoracic Ratio in Patients on Incident Dialysis

Background/Aim: The present study explores associations between hemoglobin (Hb) levels and patients with cardiac enlargement in end-stage kidney disease (ESKD) to help prevent cardiac remodeling during the predialysis phase of chronic kidney disease (CKD). Methods: This cross-sectional study included 2,249 patients with ESKD (age, 67 w 13 years; male, 67%; diabetic kidney disease, 41%) who started hemodialysis (HD) between January 2006 and October 2013 at eight participating hospitals. We examined associations between Hb levels immediately before the first HD session and cardiothoracic ratios (CTRs). Clinical factors associated with the CTR were also assessed. Results: The mean Hb level was 8.7 w 1.6 g/dl, and the mean and median CTRs were 55.0 and 54.7%, respectively. The correlation between the Hb level and the CTR was linear and negative (r = -0.129, p < 0.001). The mean CTR and the prevalence of patients with a CTR >50% obviously decreased with increasing Hb levels (both p < 0.001 for trend). Univariate logistic regression analysis revealed an approximately 20% reduction in the odds ratio for complicating CTRs >50% per 1 g/dl increase in Hb. Hb levels of <9 g/dl were significantly associated with CTRs >50%. Numerical and categorical Hb remained significantly associated with CTRs >50% after adjusting for confounding variables. Conclusions: Lower Hb levels participate in progressive CTR enlargement in patients with ESKD, and maintaining Hb levels of >9 g/dl might help prevent cardiac remodeling during the predialysis phase of CKD. i 2014 S. Karger AG, Basel

Effect of erythropoietin-stimulating agent on uremic inflammation

BackgroundThe goal of the present study was to explore the effect of medications that are commonly prescribed for CKD patients on uremic state.MethodsThis was a cross-sectional study. From January 2006 to October 2009, 1,623 patients with end-stage kidney disease (ESKD) commenced hemodialysis (HD) at the 9 participating hospitals. The criteria for exclusion from the database were 1) serum C-reactive protein (CRP) > 3 mg/dL, 2) WBC count > 9,000/mm3 or <4,000/mm3, and 3) patients with cancer, immune complex disease, or vasculitis. A total of 900 patients were entered into the final database. We explored the association of serum CRP just before the first HD session with clinical characteristics, laboratory data, and medications for CKD in the predialysis period.ResultsOn univariate analysis, age, CTR, eGFR, and WBC were significantly correlated with CRP. Systolic and diastolic blood pressure, serum albumin, LDL-C, HDL-C, Hb, Cr, and Ca were inversely associated with CRP. Use of erythropoietin-stimulating agents (ESA) using (r = −0.111, p = 0.0015), renin-angiotensin-aldosterone system inhibitors (r = −0.083, p = 0.0154), and calcium channel blockers (r = −0.1, p = 0.0039) was also negatively correlated with CRP. However, only use of ESA showed a significant negative correlation with CRP that was independent of other clinical factors and CKD medications on multiple regression analysis.ConclusionESA may strongly reduce uremic inflammation in addition to improving anemia. To confirm this potential effect, a large-scale longitudinal study would be required.

Improvement of impaired calcium and skeletal homeostasis in vitamin D receptor knockout mice by a high dose of calcitriol and maxacalcitol

Vitamin D plays a major role in mineral and skeletal homeostasis through interaction with the nuclear vitamin D receptor (VDR) of target cells. Recent reports have indicated that some cellular effects of vitamin D may occur via alternative signaling pathways, but concrete evidence for mineral homeostasis has not been shown in vivo. To investigate this issue, the actions of calcitriol (1,25D) and maxacalcitol (OCT), which were developed for treatment of uremia-induced secondary hyperparathyroidism, were analyzed in VDR knockout (VDR(-/-)) mice. The VDR(-/-) mice were fed a rescue diet immediately after weaning. 1,25D, OCT or a control solution was administered intraperitoneally to these mice three times a week for eight weeks. Biological markers and bone growth were measured and bone histomorphometric analysis of the calcein-labeled tibia was performed 24 h after the final administration. Significantly higher levels of serum Ca(2+) were observed in 1,25D- and OCT-treated mice, but the serum parathyroid hormone level was unchanged by both agents. Impaired bone growth, enlarged and distorted cartilaginous growth plates, morphological abnormalities of cancellous and cortical bones; a morbid osteoid increase, lack of calcein labeling, and thinning of cortical bone, were all significantly improved by 1,25D and OCT. The significance of these effects was confirmed by bone histomorphometrical analysis. Upregulation of the calbindin D(9k) mRNA expression level in the duodenum may explain these findings, since this protein is a major modulator of Ca transport in the small intestine. We conclude that 1,25D and OCT both at a high dose exert significant effects on Ca and skeletal homeostasis with the principal improvement of Ca status in VDR(-/-) mice, and some of these effects may occur through an alternative vitamin D signaling pathway.

The management of hyperphosphatemia by lanthanum carbonate in chronic kidney disease patients

Hyperphosphatemia has been shown to be involved not only in the onset and progression of secondary hyperparathyroidism but also in vascular calcification. In addition, it influences the clinical course of patients with chronic kidney disease. Phosphate (Pi) binder is required in the management of hyperparaphosphatemia, because dietary Pi restriction and Pi removal by hemodialysis alone are insufficient. Lanthanum carbonate, a powerful Pi binder, has a similar effect to aluminum hydroxide in reducing serum Pi levels. As it is excreted via the liver, lanthanum carbonate has an advantage in patients with renal failure. The effect of lanthanum carbonate on serum Pi levels is almost two times higher than that of calcium (Ca) carbonate, which is commonly used. Lanthanum carbonate and Ca carbonate have an additive effect. Worldwide, there is 6 years worth of clinical treatment data on lanthanum carbonate; however, we have 3 years of clinical use in Japanese patients with hyperphosphatemia. No serious side effects have been reported. However, the most important concern is bone toxicity, which has been observed with use of aluminum hydroxide. For this study, clinical research involved analysis of bone biopsies. Although osteomalacia is the most noticeable side effect, this was not observed. Both the high- and the low-turnover bone disease concentrated into a normal bone turnover state. However, as the authors have less than 10 years’ clinical experience with lanthanum carbonate, patients should be monitored carefully. In addition, it is necessary to demonstrate whether potent treatment effects on hyperphosphatemia improve the long-term outcome.

Possible prevention of dialysis-requiring congestive heart failure by angiotensin-II receptor blockers in non-dialysis Japanese patients with Stage 5 chronic kidney disease

Background: Preventive medications for dialysis-requiring congestive heart failure (CHF) in non-dialysis Japanese patients with Stage 5 chronic kidney disease (CKD) are unknown. Our aim was to explore which CKD medication was associated with a reduced prevalence of dialysis-requiring CHF in non-dialysis Japanese patients with Stage 5 CKD. Methods: The present multicenter, retrospective, cross-sectional study examined the association between CKD medications and the prevalence of dialysis-requiring CHF in non-dialysis Japanese patients with Stage 5 CKD. Results: There were 1536 Japanese Stage 5 CKD patients who satisfied our inclusion criteria. We had 309 (20.1%) patients whom had developed dialysis-requiring CHF and 940 patients (60.8%) whom had been using angiotensin-II receptor blockers (ARBs) before initiating dialysis. In our multivariate analysis, only ARB use was significantly associated with a lower risk of CHF (Odds ratio (OR): 0.680, 95% confidence interval (CI): 0.516–0.897; p = 0.0064), of the CKD treatments examined in this study. Conclusions: We found that ARB use during the pre-dialysis period is associated with a lower prevalence of CHF in the non-dialysis Japanese patients with Stage 5 CKD, suggesting a possible prevention of dialysis-requiring CHF by ARBs, in non-dialysis Japanese patients with Stage 5 CKD.