Fumihiko Koiwa

Clinical practice guideline for the management of chronic kidney disease-mineral and bone disorder

Masafumi Fukagawa, Keitaro Yokoyama, Fumihiko Koiwa, Masatomo Taniguchi, Tetsuo Shoji, Junichiro James Kazama, Hirotaka Komaba, Ryoichi Ando, Takatoshi Kakuta, Hideki Fujii, Msasaaki Nakayama, Yugo Shibagaki, Seiji Fukumoto, Naohiko Fujii, Motoshi Hattori, Akira Ashida, Kunitoshi Iseki, Takashi Shigematsu, Yusuke Tsukamoto, Yoshiharu Tsubakihara, Tadashi Tomo, Hideki Hirakata, and Tadao Akizawa for CKD-MBD Guideline Working Group, Japanese Society for Dialysis Therapy

Sevelamer hydrochloride and calcium bicarbonate reduce serum fibroblast growth factor 23 levels in dialysis patients.

Abstract:  Fibroblast growth factor 23 (FGF23) is a member of the fibroblast growth factor superfamily which displays a strong phosphaturic action and an inhibition of vitamin D 1‐α hydroxylase activity. Fourty‐six patients undergoing maintenance hemodialysis therapy participated in the study. They were randomly divided into 2 groups, and treated with either 3 g sevelamer hydrochloride + 3 g of calcium bicarbonate (CaCO3), or 3 g of CaCO3 alone. Serum FGF23 levels were determined by a sandwich enzyme‐linked immunosorbent assay (ELISA) system that detects the intact form of FGF23 molecules. Although the serum inorganic phosphate (Pi) levels were comparable before treatment, the levels were significantly lower in the patients treated with sevelamer hydrochloride + CaCO3 than those with CaCO3 alone after 4 weeks of treatment (P < 0.05). Serum FGF23 levels significantly decreased after 4 weeks of the treatment with sevelamer hydrochloride + CaCO3 from the pretreatment levels (P < 0.05), while no changes were found in the patients treated with CaCO3 alone. Thus, the use of sevelamer hydrochloride and CaCO3 reduced serum FGF23 levels in dialysis patients presumably through inhibiting phosphate load into the intestine.

Activation of calcium-sensing receptor accelerates apoptosis in hyperplastic parathyroid cells

Calcimimetic compounds inhibit not only parathyroid hormone (PTH) synthesis and secretion, but also parathyroid cell proliferation. The aim of this investigation is to examine the effect of the calcimimetic compound NPS R-568 (R-568) on parathyroid cell death in uremic rats. Hyperplastic parathyroid glands were obtained from uremic rats (subtotal nephrectomy and high-phosphorus diet), and incubated in the media only or the media which contained high concentration of R-568 (10(-4)M), or 10% cyclodextrin, for 6h. R-568 treatment significantly suppressed medium PTH concentration compared with that of the other two groups. R-568 treatment not only increased the number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay-positive cells, but also induced the morphologic changes of cell death determined by light or electron microscopy. These results suggest that CaR activation by R-568 accelerates parathyroid cell death, probably through an apoptotic mechanism in uremic rats in vitro.

Involvement of alpha-klotho and fibroblast growth factor receptor in the development of secondary hyperparathyroidism.

Background/Aims: Fibroblast growth factor 23 (FGF23) has been shown to suppress parathyroid hormone (PTH) secretion. α-Klotho has been demonstrated to function as a fibroblast growth factor receptor (FGFR) cofactor for FGF23. Thus, both α-Klotho and FGFR may play roles in PTH synthesis and/or secretion. Functions of α-Klotho and FGFR in secondary hyperparathyroidism (SHPT) remain to be studied. The present studies explore the role of α-Klotho and FGFR in SHPT. Methods: Hyperplastic parathyroid glands (n = 44) were obtained from patients with SHPT. Results: Immunohistochemical study showed that both α-Klotho and FGFR1c expression in hyperplastic glands was significantly decreased compared with that in normal glands (Klotho p < 0.01, and FGFR1c p < 0.05). A significant positive correlation was observed between α-Klotho and FGFR1c (r2 = 0.375, p < 0.01) indicating a cooperative system. Both α-Klotho (r2 = 0.235, p < 0.05) and FGFR1c (r2 = 0.181, p < 0.05) correlated positively with the calcium-sensing receptor (CaR), which plays an important role in the development of SHPT. In addition, expression of α-Klotho correlated negatively with parathyroid cell proliferation, as confirmed by Ki67 staining (r2 = 0.148, p < 0.05). Conclusion: Decreased expression of α-Klotho and FGFR1c in parallel with CaR expression and parathyroid cell growth may be involved in the pathogenesis of SHPT.

Prospective randomized multicenter trial of sevelamer hydrochloride and calcium carbonate for the treatment of hyperphosphatemia in hemodialysis patients in Japan.

Abstract:  A prospective, randomized open‐label trial of sevelamer hydrochloride with or without calcium carbonate (CC) involved 86 hemodialysis patients in Japan. The dosage of CC was fixed at 3.0 g/day for the 12‐week study. After the first 4 weeks all subjects were changed from CC to sevelamer 3.0 g/day for another 4 weeks, then allocated randomly to three groups for the final 4 weeks: group A, sevelamer 6.0 g/day; group B, sevelamer 3.0 g/day and CC 3.0 g/day; group C, CC 3.0 g/day. The target serum phosphorous concentration (P) = 5.5 mg/dL and the corrected calcium concentration (Ca) was 9.0–10.0 mg/dL. Of the 86 patients, 62 finished the study without a change of dosage and their data were analyzed (group A, N = 16; group B, N = 26; group C, N = 20). At week 8 compared with week 4, the concentration of P increased from 5.7 ± 1.4 to 6.4 ± 1.7 mg/dL in group A, and decreased significantly in groups B and C, and in group B compared with groups A and C; groups A and C had similar concentrations at week 8. The Ca concentration decreased significantly from 9.7 ± 1.0 to 9.1 ± 0.7 mg/dL after the change to sevelamer. At week 8 Ca was not significantly changed in group A, whereas a significant increase occurred in groups B and C. Side‐effects with sevelamer administration occurred in 34 of the 86 patients and 24 dropped out of the study, with a high frequency in group A (13/29; 44.8%). In conclusion, there was an additive effect of sevelamer for the treatment of hyperphosphatemia with CC. The combination therapy was better tolerated and showed higher patient compliance than CC or sevelamer monotherapy.

Vitamin D receptor activators inhibit vascular smooth muscle cell mineralization induced by phosphate and TNF-α

BACKGROUND Vascular calcification is a highly regulated process. Tumor necrosis factor-α (TNF-α) has been shown to accelerate the highly regulated osteogenic process in vascular smooth muscle cells (VSMCs). Vitamin D receptor activators (VDRAs) have been associated with beneficial cardiovascular outcomes in patients with chronic kidney disease. We examined whether maxacalcitol, a vitamin D(3) analog, exhibits a suppressive effect on VSMC mineralization induced by phosphate and TNF-α. METHODS Human VSMCs were treated with either vehicle, maxacalcitol (10(-9) to 10(-7) M), or calcitriol (10(-9) to 10(-7) M) in 2.5 mM of phosphate media with TNF-α (1 ng/mL) for 9 days. VSMC mineralization was determined and expression of genes associated with the osteogenic process was examined by real-time reverse transcription-polymerase chain reaction. Expression of matrix metalloproteinase-2 (MMP-2) messenger RNA (mRNA) in VSMCs and MMP-2 protein in media was also analyzed. RESULTS Vehicle-treated VSMCs exhibited massive mineralization, which was inhibited by maxacalcitol in a concentration-dependent manner. Calcitriol also inhibited the mineralization. While vehicle-treated VSMCs exhibited increased mRNA expression of genes associated with the osteogenic process (Cbfa1/Runx2 and osteocalcin) compared with VSMCs grown in normal media without TNF-α (control), maxacalcitol and calcitriol suppressed the increase in mRNA species. Furthermore, vehicle-treated VSMCs exhibited increased MMP-2 mRNA and protein in the media that were suppressed notably by maxacalcitol. CONCLUSIONS Both the VDRAs abrogated the acceleration of the osteogenic process induced by phosphate and TNF-α in VSMCs, which was linked to inhibition of mineralization in VSMCs. MMP-2 blockade by VDRAs may contribute to an inhibitory effect on vascular calcification.

Vitamin D and vascular calcification in chronic kidney disease

Vascular calcification is frequently observed and is closely associated with cardiovascular mortality in patients with chronic kidney disease (CKD). Vascular calcification is largely divided into two types. One is atherosclerotic intimal layer calcification and the other is medial layer calcification (Monckebergs calcification). The latter is more common in patients with CKD than in general population. Evidence is growing that vascular calcification is a regulated active process as well as a passive process resulting from elevated serum phosphate (P) and an increase in the calcium phosphate (Ca x P) product leading to oversaturated plasma. Proving the active process, in vitro studies have demonstrated that the transformation of vascular smooth muscle cells (VSMCs) into osteoblast-like cells is a crucial mechanism in the progression of vascular calcification. Reduction of the activity of systemic and local inhibitors has also been recognized to be important. The link between vitamin D and vascular calcification is complex. Experimental and clinical researches have revealed that both vitamin D excess and vitamin D deficiency have been shown to be associated with vascular calcification in uremic milieu. On the other hand, although there are some biases, recent large observational studies have demonstrated that vitamin D has beneficial effects on the mortality of patients with CKD independent of serum Ca, P, and parathyroid hormone levels, likely due to its activation of the vitamin D receptor in vasculature and cardiac myocytes. Further prospective studies are necessary to evaluate the direct effect of vitamin D on vascular calcification in order to improve the cardiovascular health of patients with CKD.

Comparison between Whole and Intact Parathyroid Hormone Assays

The standard measurement of parathyroid hormone (PTH) is the intact PTH (iPTH) assay, which is used for approximately 90% of Japanese dialysis patients. The iPTH assay reacts not only with 1–84 PTH, but also with large truncated fragments of non‐1–84 PTH, including 7–84 PTH. On the other hand, the whole PTH assay is specific for 1–84 PTH. The aim of the current study was to define the validity of both whole and intact PTH assays. A total of 738 hemodialysis patients were enrolled from twelve dialysis services. The serum PTH level was evaluated by both intact and whole PTH assays simultaneously. Non‐1–84 PTH was determined by subtracting the whole PTH value from that of the intact PTH assay. The median level of whole PTH was 121 pg/mL, and that of iPTH was 210 pg/mL. The whole PTH assay had a very high correlation with the iPTH assay (r = 0.870, P < 0.001). For 43 out of 738 patients (5.8%) the value for intact PTH—whole PTH was <0. Both assays significantly correlated with non‐1–84 PTH (P < 0.001), while the iPTH assay, particularly, had a very high correlation with non‐1–84 PTH (r = 0.791). As a whole, 18% of the total population was misclassified into a different Japanese guideline category. Stratified by Japanese guideline classifications, 28% of patients within an iPTH target range were misclassified. Using Bland–Altman plot analysis, as the serum PTH level increased, there was a large difference between two assays. Both PTH assays correlate strongly, although the whole PTH assay may be more useful for precise evaluation of PTH function than the iPTH assay.

Reversible posterior leukoencephalopathy syndrome after blood transfusion in a patient with end-stage renal disease

A 42-year-old female end-stage renal disease (ESRD) patient with reversible posterior leukoencephalopathy syndrome (RPLS) post-transfusion during initiation of hemodialysis is reported. Eleven days after the onset of illness, we diagnosed encephalopathy as a grand mal seizure resulting from diffuse cerebral edema. One reason for the delayed diagnosis was that her symptom, a throbbing headache that occurred during her first dialysis, indicated dialysis disequilibrium syndrome. We must bear in mind that a small amount of transfusion could cause RPLS even during the first dialysis. To our knowledge, this is the first case report on RPLS after blood transfusion in an ESRD patient.

Detection of Peripheral Artery Disease by Duplex Ultrasonography among Hemodialysis Patients

BACKGROUND AND OBJECTIVES Peripheral arterial disease (PAD) is a known predictor of cardiovascular morbidity and mortality among hemodialysis patients. Although ankle-brachial BP index (ABI) is a simple and reliable test for PAD screening, its sensitivity has been suggested to decrease among dialysis patients. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS We performed a cross-sectional outpatient cohort study to examine prevalence of PAD among hemodialysis patients using duplex ultrasonography of the lower extremity artery. We also evaluate the influence of increased arterial stiffness on impaired accuracy of ABI for PAD screening. RESULTS Of 315 total patients, 23.8% had PAD. PAD was associated with younger age, diabetes, current smoking, atherosclerotic comorbidities, increased total cholesterol levels, increased triglyceride levels, and lower Kt/V. The receiver operating characteristic analysis (area under the receiver operating characteristic curve = 0.846) showed that sensitivity and specificity of ABI values for PAD were 49.0 and 94.8%, respectively. An ABI cut-off value of 1.05 resulted in the best sensitivity (74.5%) and specificity (84.4%). There was a significant difference in sensitivity of ABI levels <0.9 for detecting PAD among patients in different brachial-ankle pulse wave velocity quartiles. In patients with the highest brachial-ankle pulse wave velocity quartile, PAD was most prevalent (46.5%), and ABI had the highest accuracy in detecting PAD (area under the curve, 0.933). CONCLUSIONS These results suggest that duplex ultrasonography was a useful tool for screening asymptomatic PAD among hemodialysis patients and that the diagnostic value of ABI for PAD was affected by various factors.