Keiko Uchida

The progression of vascular calcification and serum osteoprotegerin levels in patients on long-term hemodialysis

BACKGROUND The aortic calcification index (ACI), estimated on abdominal computed tomographic scans, has been associated with the extent of arteriosclerosis in hemodialysis patients. However, the contribution of biochemical markers to the progression of vascular calcification in patients undergoing hemodialysis is not fully understood. METHODS We examined the relationship between coronary risk factors; metabolic factors, including serum osteoprotegerin (OPG) concentration; and progression of vascular calcification in 26 dialysis patients. RESULTS Mean patient age was 52.6 +/- 8.7 (SD) years, and mean duration of dialysis therapy was 7.7 +/- 5.8 years. ACI was measured twice in each patient, and the mean interscan period was 4.9 +/- 0.3 years. Mean ACI changed from 22.2 +/- 24.2 to 33.9 +/- 28.8 overall, and mean change in ACI (DeltaACI) was 12.0 +/- 9.9. Patients were divided into 2 groups: slow progressors, with DeltaACI of 4.1 +/- 3.2 (n = 13), and rapid progressors, with DeltaACI of 19.8 +/- 7.9 (n = 13). Serum fasting glucose and CRP levels of rapid progressors were high, and their serum albumin and intact parathyroid hormone levels were low. Multiple regression analyses showed that serum OPG levels were independently associated with vascular calcification in the hemodialysis patients studied. CONCLUSION Rapid progression of vascular calcification was associated with dose of calcium carbonate prescribed and serum OPG concentration. The clinical significance of these observations remains to be determined.

Pathogenesis and treatment of autosomal-dominant nephrogenic diabetes insipidus caused by an aquaporin 2 mutation

Frame-shift mutations within the C terminus of aquaporin 2 (AQP2) cause autosomal-dominant nephrogenic diabetes insipidus (AD-NDI). To identify the molecular mechanism(s) of this disease in vivo and to test possible therapeutic strategies, we generated a mutant AQP2 (763–772 del) knockin mouse. Heterozygous knockin mice showed a severely impaired urine-concentrating ability. However, they were able to slightly increase urine osmolality after dehydration. This milder phenotype, when compared with autosomal-recessive NDI, is a feature of AD-NDI in humans, thus suggesting successful establishment of an AD-NDI mouse model. Immunofluorescence of collecting duct cells in the AD-NDI mouse revealed that the mutant AQP2 was missorted to the basolateral instead of apical plasma membrane. Furthermore, the mutant AQP2 formed a heterooligomer with wild-type AQP2 and showed a dominant-negative effect on the normal apical sorting of wild-type AQP2 even under dehydration. Using this knockin mouse, we tested several drugs for treatment of AD-NDI and found that rolipram, a phosphodiesterase 4 inhibitor, was able to increase urine osmolality. Phosphodiesterase inhibitors may thus be useful drugs for the treatment of AD-NDI. This animal model demonstrates that a mutant monomer gains a dominant-negative effect that reverses the normal polarized sorting of multimers.

The importance of low blood urea nitrogen levels in pregnant patients undergoing hemodialysis to optimize birth weight and gestational age

Most published reports indicate that intensified hemodialysis results in better pregnancy outcomes. Here we studied clinical characteristics and the outcomes of 28 pregnant women receiving hemodialysis. We found an association between maternal blood data and birth weight, and gestational age and outcomes. There were 18 surviving infants who were followed up for one year. In the others there were 4 spontaneous abortions, 1 stillbirth, 3 neonatal deaths and 2 deaths after birth. Analysis of blood chemistry for 20 pregnancies from 12 weeks of gestation until delivery showed that the average hemoglobin level was significantly higher in the group that successfully delivered than in the unsuccessful group. There were significant negative relationships between the blood urea nitrogen (BUN) level and the birth weight or gestational age in the latter cohort. A birth weight equal to or greater than 1500 g or a gestational age equal to or exceeding 32 weeks corresponded to BUN levels of 48-49 mg/dl or less. Whether the low BUN is the direct cause of the improved outcome remains to be examined.

Decreased tyrosine phosphorylation of nephrin in rat and human nephrosis.

Phosphorylation of tyrosine residue (Y1204) of rat nephrin by Fyn kinase allows Nck adaptor protein binding to nephrin motifs, which include the phosphorylated tyrosine. This phosphorylation-dependent switch induces actin polymerization in a cell culture system. Here, we generated an antibody recognizing phosphorylated nephrin at the Nck binding sites pY1204 and pY1228 to determine the phosphorylation status of nephrin using a rat model of puromycin aminonucleoside-induced nephrosis. Changes in globular actin (G-actin) and filamentous actin (F-actin) contents in isolated glomeruli were measured by western blot. Before experimental nephrosis, both Y1204 and Y1228 were phosphorylated, and most of the actin was filamentous. Before the onset of overt proteinuria, however, phosphorylation of both Y1204 and Y1228 rapidly decreased and became almost undetectable. During this period, the amount of F-actin in glomeruli began to decrease, whereas G-actin increased. Phosphorylation of nephrin at Y1228 in glomeruli of patients with minimal change nephrosis was significantly decreased compared with that in normal glomeruli. Our study suggests that tyrosine phosphorylation of nephrin by regulating F-actin formation may be important for the maintenance of normal podocyte morphology and function.

Association between Single-Nucleotide Polymorphisms in Selectin Genes and Immunoglobulin A Nephropathy

Although intensive efforts have been undertaken to elucidate the genetic background of immunoglobulin A nephropathy (IgAN), genetic factors associated with the pathogenesis of this disease are still not well understood. We designed a case-control association study that was based on linkage disequilibrium among single-nucleotide polymorphisms (SNPs) in the selectin gene cluster on chromosome 1q24-25, and we found two SNPs in the E-selectin gene (SELE8 and SELE13) and six SNPs in the L-selectin gene (SELL1, SELL4, SELL5, SELL6, SELL10, and SELL11) that were significantly associated with IgAN in Japanese patients. All eight SNPs were in almost complete linkage disequilibrium. SELE8 and SELL10 caused amino acid substitutions from His to Tyr and from Pro to Ser (chi2=9.02, P=.0026, odds ratio = 2.73 [95% confidence interval [CI] 1.38--5.38] for His-to-Tyr substitutions; chi2=17.4, P=.000031, odds ratio = 3.61 [95% CI 1.91--6.83] for Pro-to-Ser substitutions), and SELL1 could affect promoter activity of the L-selectin gene (chi2=19.5, P=.000010, odds ratio = 3.77 [95% CI 2.02--7.05]). The TGT haplotype at these three loci was associated significantly with IgAN (chi2=18.67, P=.000016, odds ratio = 1.88 [95% CI 1.41--2.51]). Our results suggest that these eight SNPs in selectin genes may be useful for screening populations susceptible to the IgAN phenotype that involves interstitial infiltration.

Association of single-nucleotide polymorphisms in the polymeric immunoglobulin receptor gene with immunoglobulin A nephropathy (IgAN) in Japanese patients

AbstractImmunoglobulin A nephropathy (IgAN) is a primary glomerulonephritis of common incidence world-wide whose etiology and pathogenesis remain unresolved, although genetic factors are assumed to be involved in the development and progression of this disease. To identify genetic variations that might confer susceptibility to IgAN, we performed a case-control association study involving 389 Japanese IgAN patients and 465 controls. Genome-wide analysis of approximately 80,000 single-nucleotide polymorphisms (SNPs) identified a significant association between IgAN and six SNPs located in the PIGR (polymeric immuoglobulin receptor) gene at chromosome 1q31-q41. One of them, PIGR-17, caused an amino-acid substitution from alanine to valine at codon 580 (χ2=13.05, P=0.0003, odds ratio [OR] =1.59, 95% confidence interval [95% CI] =1.24–2.05); the OR of minor homozygotes to others was 2.71 (95% CI = 1.31–5.61). Another SNP, PIGR-2, could affect promoter activity (χ2 = 11.95, P=0.00055, OR=1.60, 95% CI=1.22–2.08); the OR of minor homozygotes to others was 2.08 (95% CI=0.94–4.60). Pairwise analyses demonstrated that all six SNPs were in almost complete linkage disequilibrium. Biopsy specimens from IgAN patients were positively stained by antibody against the secretory component of PIGR, but corresponding tissues from non-IgAN patients were not. Our results suggest that a gene associated with susceptibility to IgAN lies within or close to the PIGR gene locus on chromosome 1q in the Japanese population.

Effects of Sevelamer on the Progression of Vascular Calcification in Patients on Chronic Haemodialysis

Background/Aim: Vascular calcification is thought to be associated with a high cardiovascular mortality rate in patients with end-stage renal disease. Control of hyperphosphataemia is important for the treatment of the vascular calcification. The aim of the present study was to evaluate the effects of sevelamer hydrochloride on the progression of aortic calcification in haemodialysis (HD) patients. Methods: 42 HD patients were studied in this study and divided into two groups (sevelamer vs. calcium). Sevelamer was added and titrated up to achieve serum P control for 6 months. The estimations of aortic calcification index (ACI) by abdominal computed tomography scans were performed twice in each patient. We compared the changes in serum calcium, phosphorus, intact parathyroid hormone, and lipids in two groups. Results: Serum phosphorus levels decreased significantly from 6.7 ± 0.7 to 6.2 ± 0.5 mg/dl with no changes in serum intact parathyroid hormone levels in the sevelamer group (p < 0.01), and increased from 6.5 ± 1.0 to 6.7 ± 1.1 mg/dl in the calcium group (p < 0.05). Serum calcium levels did not change in the sevelamer group and calcium group. The serum levels of total cholesterol decreased significantly from 158.5 ± 20.7 to 146.2 ± 24.1 mg/dl (p = 0.024) and the low-density lipoprotein cholesterol level from 65.3 ± 14.4 to 54.7 ± 11.6 mg/dl (p = 0.014) in the sevelamer group. Serum C-reactive protein decreased significantly from 0.14 ± 0.13 to 0.08 ± 0.11 mg/dl in the sevelamer group (p = 0.038) and significantly increased (0.18 ± 0.09 vs. 0.22 ± 0.12 mg/dl) in the calcium group (p = 0.042). The mean changes in ACI (ΔACI) were 3.6 ± 1.5% in the sevelamer group and 8.2 ± 3.1% in the calcium group. Conclusions: Sevelamer allows a better serum phosphorus control compared with calcium-based phosphate binder and suppresses the progression of aortic calcification in HD patients.

Glomerular expression of cell-cycle-regulatory proteins in human crescentic glomerulonephritis

Abstract To elucidate the mechanism underlying crescentic formation, we assessed the phenotypic characterization and cell-cycle protein expression in human crescentic glomerulonephritis (CRGN). Kidney tissue specimens taken from CRGN patients (10 patients with pauci-immune type rapidly progressive glomerulonephritis (RPGN), 2 patients with Henoch-Schönlein purpura nephritis, and 1 patient with IgA nephropathy) were examined immunohistochemically. Most of the cellular components of the crescents expressed cytokeratin, whereas few cells expressed PHM-5. CD68-positive cells were minor components of cellular crescents, indicating that the major principal cellular component of the crescents is made up of cells with the parietal glomerular epithelial cell (PEC) phenotype. Additionally, serial section analysis revealed that Ki-67-positive cells in the crescents were frequently cyclin-A positive and Bcl-2 positive, but seldom cyclin-B1 positive. Moreover, the expression of cyclin-dependent kinase inhibitor p27Kip1 was low in the cellular crescents, despite being exclusively positive in podocytes within the same section. We concluded that the major component of the cellular crescents is made up of PECs and that apparent expression of cyclins and Bcl-2 and restrained expression of p27Kip1 may be synergistically associated with the development of cellular crescents in human CRGN.

Soluble Osteopontin and Vascular Calcification in Hemodialysis Patients

Background: Vascular calcification often occurs in patients with uremia. As osteopontin (OPN) is not only involved in the physiological but also the pathological calcification of tissues, OPN may be associated with the pathogenesis of aortic calcification in hemodialysis (HD) patients. Methods: We examined the expression of OPN in atherosclerotic aortas of HD patients. In addition, we performed a prospective longitudinal study by using CT scans to detect aortic calcifications and by measuring the plasma OPN concentration by ELISA in HD patients (20 men, 16 women; mean age 55.2 ± 21.3 years) and in healthy volunteers (18 men, 17 women; mean age 54.0 ± 13.2 years). Results: By immunohistochemical staining, OPN was abundantly localized in atherosclerotic plaques of HD patients. The macrophages surrounding the atheromatous plaques were identified as the OPN-expressing cells. We furthermore found that the concentration of soluble plasma OPN was significantly higher in HD patients as compared with the concentrations in age-matched healthy volunteers (837.3 ± 443.2 vs. 315.1 ± 117.4 ng/ml, p < 0.01). The OPN concentration was positively correlated with the aortic calcification index in HD patients (r = 0.749, p < 0.01). Conclusion: These data suggest that OPN, secreted by macrophages, plays a role in the calcification of atheromatous plaques in HD patients.

Effects of long-term treatment with mizoribine in patients with proliferative lupus nephritis.

AIM Mizoribine (MZR) is a purine antimetabolic immunosuppressant agent that has few little severe adverse events. We studied whether maintenance therapy with MZR and prednisolone (PSL) in severe proliferative lupus nephritis patients could improve immunity, reduce proteinuria, prevent renal relapse, and reduce steroid dose. METHOD Long-term maintenance therapy with MZR and PSL was evaluated in ten patients with biopsy-proven proliferative lupus nephritis. Patients with severe lupus nephritis, who had proteinuria of 0.5 g or more even after treatments with plasma exchange and/or pulse methyl prednisolone, were recruited. MZR at an average dose of 140 +/- 10 (100 - 200) mg was administered two to three times/day in combination with PSL. The average period for the MZR maintenance therapy was 89.7 +/- 5.5 (70 - 126) months. Urine protein excretion, serum hemolytic complement activity (CH50), C3, serum creatinine, general and biochemical blood examinations, anti-ds-DNA antibody were collected at each monthly medical examination. RESULTS All patients were females, mean age 43.0 +/- 3.3 years. A significant decrease in proteinuria was noted two years after the combination therapy (p = 0.0016). Five patients experienced lupus nephritis relapse. Patients who did not experience relapses had their MZR combination therapy initiated earlier (p = 0.037) when compared with the patients who experienced relapses. Serum creatinine levels remained unchanged in all patients throughout treatment and follow-up, even during renal relapses. Levels of C3 and CH50 normalized as proteinuria decreased. None of the patients developed serious side effects during MZR treatment. A significant steroid-sparing effect was observed three years after initiating MZR (p = 0.0025). CONCLUSION From our long-term observation, maintenance therapy with low-dose PSL combined with MZR can eliminate proteinuria and have steroid-sparing effect. Early initiation of the therapy can protect against renal relapses among severe proliferative lupus nephritis patients without serious side effects.