Eiichiro Kanda

Reciprocal interaction with G-actin and tropomyosin is essential for aquaporin-2 trafficking

Trafficking of water channel aquaporin-2 (AQP2) to the apical membrane and its vasopressin and protein kinase A (PKA)–dependent regulation in renal collecting ducts is critical for body water homeostasis. We previously identified an AQP2 binding protein complex including actin and tropomyosin-5b (TM5b). We show that dynamic interactions between AQP2 and the actin cytoskeleton are critical for initiating AQP2 apical targeting. Specific binding of AQP2 to G-actin in reconstituted liposomes is negatively regulated by PKA phosphorylation. Dual color fluorescence cross-correlation spectroscopy reveals local AQP2 interaction with G-actin in live epithelial cells at single-molecule resolution. Cyclic adenosine monophosphate signaling and AQP2 phosphorylation release AQP2 from G-actin. In turn, AQP2 phosphorylation increases its affinity to TM5b, resulting in reduction of TM5b bound to F-actin, subsequently inducing F-actin destabilization. RNA interference–mediated knockdown and overexpression of TM5b confirm its inhibitory role in apical trafficking of AQP2. These findings indicate a novel mechanism of channel protein trafficking, in which the channel protein itself critically regulates local actin reorganization to initiate its movement.

Rac is activated by erythropoietin or interleukin-3 and is involved in activation of the Erk signaling pathway

Previous studies have shown that hematopoietic cytokines, including erythropoietin (Epo) and interleukin (IL)-3, activate the Ras GTPase and the downstream Raf/Erk/Elk-1 signaling pathway. Here we report that Epo or IL-3 rapidly and transiently activates Rac, a Rho family GTPase, in hematopoietic cell lines, 32D/EpoR-Wt and UT-7. The cytokine-induced activation of Rac was augmented in a 32D/EpoR-Wt clone that inducibly overexpresses the adaptor protein CrkL or the Ras guanine nucleotide exchange factor C3G, which forms a complex with CrkL. Furthermore, the Rac activation was enhanced or inhibited in cells inducibly expressing an activated Ras mutant, H-Ras61L, or a dominant negative Ras mutant, H-Ras17N, respectively. In addition, the cytokine-induced Rac activation was inhibited by a phosphatidyl-inositol 3′-kinase (PI3K) inhibitor, LY294002, which also inhibited the Erk activation. A dominant negative Rac mutant, Rac17N, also inhibited the cytokine-induced activation of Erk as well as Elk-1. On the other hand, activation of Akt downstream of PI3K was found to play an inhibitory role in cytokine activation of Erk/Elk-1. Together, these results indicate that Rac is activated by Epo or IL-3 at downstream of the Ras/PI3K pathway in parallel with Akt and plays a role in activation of the Erk/Elk-1 signaling pathway in hematopoietic cells.

Mortality, Hospitalization, and Quality of Life among Patients with Hepatitis C Infection on Hemodialysis

BACKGROUND AND OBJECTIVES Hepatitis C virus (HCV) infection is widely prevalent among patients on hemodialysis (HD), but very rarely treated. The aim of our study is to evaluate the burdens of HCV suffered by patients on HD. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS The Dialysis Outcomes and Practice Patterns Study is an international, prospective, cohort study of patients on HD. We reviewed the HCV status of 76,689 adults enrolled between 1996 and 2015. We compared HCV-positive (HCV+) with HCV-negative (HCV-) patients for risk of mortality, hospitalization, decline in hemoglobin concentration <8.5 g/dl, and red blood cell transfusion. We also compared health-related quality of life scores using the Kidney Disease Quality of Life instrument and the Center for Epidemiologic Studies Short Depression Scale. We adjusted for age, sex, race, years on dialysis, 14 comorbid conditions (including hepatitis B infection), and serum albumin, phosphorus, and creatinine concentrations. RESULTS A total of 7.5% of patients were HCV+ at enrollment. Serum concentrations of alanine aminotransferase and aspartate aminotransferase were not markedly elevated in HCV+ patients on HD; the mean concentrations were only 22.6 and 21.8 U/L, respectively. Median follow-up was 1.4 years. Case-mix adjusted hazard ratios (95% confidence intervals) for HCV+ versus HCV- patients were 1.12 (1.05 to 1.20) for all-cause mortality, 5.90 (3.67 to 9.50) for hepatic-related mortality, 1.09 (1.04 to 1.13) for all-cause hospitalization, and 4.40 (3.14 to 6.15) for hepatic-related hospitalization. Quality of life measures indicated significantly worse scores for physical function, pain, vitality, mental health, depression, pruritus, and anorexia among HCV+ patients. The adjusted hazard ratio for transfusion was 1.36 (95% CI, 1.20 to 1.55) and incidence of hemoglobin concentration <8.5 g/dl was 1.12 (95% CI, 1.03 to 1.21). Only 1.5% of HCV+ patients received antiviral medication. CONCLUSIONS HCV infection among patients on HD is associated with higher risk of death, hospitalization, and anemic complications, and worse quality of life scores. Internationally, HCV infection is almost never treated in patients on HD. Our data provide a rationale for more frequent treatment of HCV in this population.

High serum bicarbonate level within the normal range prevents the progression of chronic kidney disease in elderly chronic kidney disease patients

BackgroundMetabolic acidosis leads to chronic kidney disease (CKD) progression. The guidelines recommend a lower limit of serum bicarbonate level, but no upper limit. For serum bicarbonate level to be clinically useful as a therapeutic target marker, it is necessary to investigate the target serum bicarbonate level within the normal range to prevent CKD progression.MethodsOne hundred and thirteen elderly CKD patients, whose serum bicarbonate level was controlled within the normal range, were enrolled in this retrospective cohort study in Ibaraki, Japan. Outcome was defined as a decrease of 25% or more in estimated glomerular filtration rate (eGFR) or starting dialysis. We used Cox proportional hazard models adjusted for patients’ characteristics to examine the association between serum bicarbonate level and the outcome.ResultsFemale patients were 36.3%: average age (SD), 70.4 (6.6) years; eGFR, 25.7 (13.6) ml/min/1.73 m2; serum bicarbonate level, 27.4 (3.2) mEq/l. Patients with the lowest quartile of serum bicarbonate levels [23.4 (1.8) mEq/l] showed a high risk of CKD progression compared with patients with high serum bicarbonate levels [28.8 (2.3) mEq/l]: adjusted hazard ratio (HR), 3.511 (95% CI, 1.342-9.186). A 1 mEq/l increase in serum bicarbonate level was associated with a low risk of CKD progression: adjusted HR, 0.791 [95% confidence interval (CI), 0.684-0.914].ConclusionsIn elderly CKD patients, our findings suggest that serum bicarbonate level is independently associated with CKD progression, and that a high serum bicarbonate level is associated with a low risk of CKD progression. A high target serum bicarbonate level within the normal range may be effective for preventing CKD progression.

Uric Acid Level Has a U-Shaped Association with Loss of Kidney Function in Healthy People: A Prospective Cohort Study

Background The relationship between hyperuricemia and chronic kidney disease (CKD) has been found in various observational studies. Although hypouricemia is associated with cardiovascular events, it has not been established as a risk factor for CKD. We investigated the relationship between serum uric acid level and the loss of kidney function and incident CKD in healthy people. Materials and Methods Healthy people were enrolled in this community-based prospective cohort study, the Saitama Cardiometabolic Disease and Organ Impairment Study, Japan. The analysis was conducted on 4188 subjects followed up for at least 3 years, 3102 for 6 years and 1052 for 9 years. Their data including glomerular filtration rate (eGFR) decline were examined every three years. The outcome event was incident CKD or the decrease in eGFR by more than 25% in three years. Multivariate statistical models were adjusted for the baseline characteristics. Results The following data was obtained: mean±SD age, male, 39.6±10.4 years, female 38.4±10.8 years; eGFR, male, 81.9±16.4 ml/min/1.73m2, female, 82.1±17.5 ml/min/1.73m2; serum uric acid level, male, 5.8±1.2 mg/dl, female, 4.1±0.9 mg/dl. Both low and high serum uric acid levels were associated with the outcome and eGFR decline in males (multivariate logistic additional additive models, linear p = 0.0001, spline p = 0.043; generalized additive models, linear p = 0.0001, spline p = 0.012). In subjects with low serum uric acid levels (male, <5 mg/dl; female, <3.6 mg/dl), multivariate linear mixed models showed that low serum uric acid levels were associated with eGFR decline in a time-dependent manner (male, p = 0.0001; female, p = 0.045). Conclusion This study showed that low as well as high levels of uric acid are associated with the loss of kidney function. Hypouricemia is a candidate predictor of kidney function decline in healthy people.

Dietary Acid Intake and Kidney Disease Progression in the Elderly

Background/Aims: Non-volatile acid is produced by metabolism of organic sulfur in dietary protein, and promotes kidney damage. We investigated the role of dietary acid load, in terms of net endogenous acid production (NEAP), in chronic kidney disease (CKD) progression. Methods: 217 CKD patients on low-protein diet with a normal serum bicarbonate level were enrolled in this retrospective cohort study in Japan. The primary outcome was 25% decline in estimated glomerular filtration rate (eGFR) or start of dialysis. Their NEAP was measured every 3 months. The patients were categorized into four groups on the basis of quartiles of NEAP every 3 months. The groups were treated as time-dependent variables. Results: The average age (SD) was 70.6 (7.1) years; eGFR 23.5 (14.2) ml/min/1.73 m2. Analysis using extended Cox models for the NEAP groups adjusted for baseline characteristics (referring to group 1 showing the lowest NEAP) showed that high NEAP was associated with a high risk of CKD progression; group 2, adjusted hazard ratio (HR) 3.930 (95% confidence interval (CI) 1.914, 8.072); group 3, adjusted HR 4.740 (95% CI 2.196, 10.288); group 4, adjusted HR 4.303 (95% CI 2.103, 8.805). Logistic regression analysis adjusted for baseline characteristics showed that the occurrence of hypoalbuminemia or hyperkalemia was associated with low serum bicarbonate level and the presence of complications at baseline, but not with NEAP. Conclusion: In elderly CKD patients, our findings suggest that high NEAP is independently associated with CKD progression. The decrease in NEAP may be an effective kidney-protective therapy.

Baseline characteristics and prevalence of cardiovascular disease in newly visiting or referred chronic kidney disease patients to nephrology centers in Japan: a prospective cohort study

BackgroundAbout 39,000 patients were newly prescribed renal replacement therapy in Japan in 2011, resulting in a total of more than 300,000 patients being treated with dialysis. This high prevalence of treated end stage kidney disease (ESKD) patients is an emergent problem that requires immediate attention. We launched a prospective cohort study to evaluate population specific characteristics of the progression of chronic kidney disease (CKD). In this report, we describe the baseline characteristics and risk factors for cardiovascular disease (CVD) prevalence among this cohort.MethodsNew patients from 16 nephrology centers who were older than 20 years of age and who visited or were referred for the treatment of CKD stage 2–5, but were not on dialysis therapy, were recruited in this study. At enrollment, medical history, lifestyle behaviors, functional status and current medications were recorded, and blood and urine samples were collected. Estimated glomerular filtration rate (eGFR) was calculated by a modified three-variable equation.ResultsWe enrolled 1138 patients, 69.6% of whom were male, with a mean age of 68 years. Compared with Western cohorts, patients in this study had a lower body mass index (BMI) and higher proteinuria. The prevalence of CVD was 26.8%, which was lower than that in Western cohorts but higher than that in the general Japanese population. Multivariate analysis demonstrated the following association with CVD prevalence: hypertension (adjusted odds ratio (aOR) 3.57; 95% confidence interval (CI) 1.82-7.02); diabetes (aOR 2.45; 95% CI 1.86-3.23); hemoglobin level less than 11 g/dl (aOR 1.61; 95% CI 1.21-2.15); receiving anti-hypertensive agents (aOR 3.54; 95% CI 2.27-5.53); and statin therapy (aOR 2.73; 95% CI 2.04-3.66). The combination of decreased eGFR and increased proteinuria was also associated with a higher prevalence of CVD.ConclusionsThe participants in this cohort had a lower BMI, higher proteinuria and lower prevalence of CVD compared with Western cohorts. Lower eGFR and high proteinuria were associated with CVD prevalence. Prospective follow up of these study patients will contribute to establishment of individual population-based treatment of CKD.

A familial case of mitochondrial disease resembling Alport syndrome

A 38-year-old man with mild sensorineural hearing loss, diabetes mellitus, proteinuria, and slight renal dysfunction was admitted to our hospital for a renal biopsy to determine the cause of kidney disease. His elder sister and mother also had sensorineural hearing loss and renal failure, suggesting the existence of a common genetic disease in this family. Although the clinical features of the patient were similar to features of Alport syndrome, renal biopsy revealed no sign of Alport syndrome. We next considered a possibility of a mitochondrial kidney disease described by Jansen in 1997. Indeed, genetic analysis of mitochondrial DNA clarified the existence of A3243G mutation in the patient and his sister. This syndrome should be recognized by nephrologists as a differential diagnosis of Alport syndrome, diabetic nephropathy, and primary glomerular diseases.

Applicability of fibroblast growth factor 23 for evaluation of risk of vertebral fracture and chronic kidney disease-mineral bone disease in elderly chronic kidney disease patients

BackgroundElderly patients with chronic kidney disease (CKD) are usually at a high risk of fractures due to both osteoporosis and CKD-mineral bone disease (MBD). A new marker is needed to prevent fractures and control CKD-MBD from the early to advanced stages of CKD. In the early stage of CKD, fibroblast growth factor 23 (FGF23) level increases before parathyroid hormone (PTH) and phosphate levels increase, and steadily increases with the progression of kidney disease. It has been reported that FGF23 is related to the overall fracture risk. We investigated the usefulness of FGF23 as a marker for evaluating the risk of vertebral fracture and CKD-MBD in elderly CKD patients.MethodsOne hundred and five elderly predialysis CKD patients who had never been treated for osteoporosis and had never used calcium supplements, vitamin D supplements, or phosphate binders were enrolled in this cross-sectional study in Tokyo, Japan. We investigated the prevalence of vertebral fracture and measured serum calcium, phosphate, 1,25(OH)2 vitamin D [1,25(OH)2D], intact PTH, FGF23, alkaline phosphatase, and urinary N-terminal telopeptide levels. Then, we examined the relationship between the level of FGF23 and those of bone-metabolism-related markers and identified markers associated with vertebral fractures in elderly CKD patients.ResultsThe background features of the patients were as follows: female, 32.4%; diabetes mellitus, 39.0%; average age (standard deviation), 73.2 (7.7) years; and estimated glomerular filtration rate (eGFR), 45.7 (24.1) ml/min/1.73 m2. Adjusted multivariate regression analysis showed that the natural logarithm value of FGF23 level [ln(FGF23)] was positively associated with body mass index (p = 0.002), serum phosphate level (p = 0.0001), and negatively with eGFR (p = 0.0006). Multivariate logistic regression analysis showed that vertebral fracture was independently associated with ln(FGF23) (adjusted odds ratio, 4.44; 95% confidence interval, 1.13-17.46). A receiver-operating-characteristic curve of ln(FGF23) showed that the optimal cutoff level of FGF23 indicative of vertebral fracture was 56.8 pg/ml (sensitivity, 0.82; specificity, 0.63).ConclusionsFGF23 level was independently associated with the levels of bone-metabolism-related markers and vertebral fracture. FGF23 is a new candidate marker for detecting abnormalities of bone metabolism and vertebral fracture in elderly CKD patients.

Linagliptin improves endothelial function in patients with type 2 diabetes: A randomized study of linagliptin effectiveness on endothelial function

The present multicenter, prospective, controlled, open and randomized three‐arm parallel study was designed to compare the effects of linagliptin with those of metformin on endothelial function.