増田 貴博

Objective Tolvaptan, an oral selective V2-receptor antagonist, is a water diuretic that ameliorates fluid retention with a lower risk of a worsening renal function than conventional loop diuretics. Although loop diuretics predominantly decrease extracellular water (ECW) compared with intracellular water (ICW), the effect of tolvaptan on fluid distribution remains unclear. We therefore examined how tolvaptan changes ICW and ECW in accordance with the renal function. Methods Six advanced chronic kidney disease patients (stage 4 or 5) with fluid retention were enrolled in this study. Tolvaptan (7.5 mg/day) added to conventional diuretic treatment was administered to remove fluid retention. The fluid volume was measured using a bioimpedance analysis device before (day 0) and after (day 5 or 6) tolvaptan treatment. Results Body weight decreased by 2.6%+/- 1.3% (64.4 +/- 6.5 vs. 62.8 +/- 6.3 kg, p=0.06), and urine volume increased by 54.8%+/- 23.9% (1,215 +/- 169 vs. 1,709 +/- 137 mL/day, p=0.03) between before and after tolvaptan treatment. Tolvaptan significantly decreased ICW (6.5%+/- 1.5%, p=0.01) and ECW (7.5%+/- 1.4%, p=0.02), which had similar reduction rates (p=0.32). The estimated glomerular filtration rate remained unchanged during the treatment (14.6 +/- 2.8 vs. 14.9 +/- 2.7 mL/min/1.732 m, p=0.35). Conclusion Tolvaptan ameliorates body fluid retention, and induces an equivalent reduction rate of ICW and ECW without a worsening renal function. Tolvaptan is a novel water diuretic that has a different effect on fluid distribution compared with conventional loop diuretics.

We herein present a case of relapsed sarcoidosis with a deteriorated renal function accompanied by hypercalcemia, nephrolithiasis, and a ureteral stone in a woman with a history of ocular sarcoidosis. The ocular involvement appeared to be well controlled for a long period of time with a topical ophthalmic steroid however, we believe that the absence of apparent recrudescence could have led to the delay in our diagnosis of relapse of the disease during the follow-up period. The conundrums regarding longitudinal surveillance for both evaluating the disease activity and determining the necessity of therapeutics are also discussed.

We herein present a case of relapsed sarcoidosis with a deteriorated renal function accompanied by hypercalcemia, nephrolithiasis, and a ureteral stone in a woman with a history of ocular sarcoidosis. The ocular involvement appeared to be well controlled for a long period of time with a topical ophthalmic steroid; however, we believe that the absence of apparent recrudescence could have led to the delay in our diagnosis of relapse of the disease during the follow-up period. The conundrums regarding longitudinal surveillance for both evaluating the disease activity and determining the necessity of therapeutics are also discussed.

A 48-year-old female was admitted to our hospital presenting with a chief complaint of progressive swelling because of diabetic nephrotic syndrome. Dapagliflozin seemed to play a role in accelerating the patient’s urinary sodium excretion as well as reducing gross fluid retention despite the fact that her nephrotic condition was resistant to furosemide. Our experience emphasizes a potential novel approach to overcoming loop diuretic resistance using this agent among some subsets of type 2 diabetic subjects complicated with severe volume accumulation. We believe that combination treatment consisting of dapagliflozin and furosemide may produce diuretic synergy via sequential nephron blockade. The accumulation of more experience with additional cases similar to ours requires continuous and careful attention.

In this report, we describe the case of an end-stage kidney disease patient with tetralogy of Fallot (TOF). A 33-year-old female with TOF was admitted to our hospital with complaints of general fatigue and appetite loss probably due to uremic milieu. She was ultimately treated with peritoneal dialysis (PD) with a favorable clinical course. TOF patients with chronic kidney disease are not exceptional, although the currently available information regarding the association between TOF and renal failure severe enough to require dialysis treatment is limited. We also discuss the complex processes of how and why PD was selected as a mode of chronic renal replacement therapy in this case.

Klotho is a single-pass transmembrane protein predominantly expressed in the kidney. The extracellular domain of Klotho is subject to ectodomain shedding and is released into the circulation as a soluble form. Soluble Klotho is also generated from alternative splicing of the Klotho gene. In mice, defects in Klotho expression lead to complex phenotypes resembling those observed in dialysis patients. However, the relationship between the level of serum soluble Klotho and overall survival in hemodialysis patients, who exhibit a state of Klotho deficiency, remains to be delineated. Here we prospectively followed a cohort of 63 patients with a mean duration of chronic hemodialysis of 6.7 ± 5.4 years for a median of 65 months. Serum soluble Klotho was detectable in all patients (median 371 pg/mL, interquartile range 309-449). Patients with serum soluble Klotho levels below the lower quartile (<309 pg/mL) had significantly higher cardiovascular and all-cause mortality rates. Furthermore, the higher all-cause mortality persisted even after adjustment for confounders (hazard ratio 4.14, confidence interval 1.29-13.48). We conclude that there may be a threshold for the serum soluble Klotho level associated with a higher risk of mortality.

In the kidney, the sodiumglucose cotransporters SGLT2 and SGLT1 are thought to account for &gt;90 and similar to 3% of fractional glucose reabsorption (FGR), respectively. However, euglycemic humans treated with an SGLT2 inhibitor maintain an FGR of 40-50%, mimicking values in Sglt2 knockout mice. Here, we show that oral gavage with a selective SGLT2 inhibitor (SGLT2-I) dose dependently increased urinary glucose excretion (UGE) in wild-type (WT) mice. The dose-response curve was shifted leftward and the maximum response doubled in Sglt1 knockout (Sglt1-/-) mice. Treatment in diet with the SGLT2-I for 3 wk maintained 1.5-to 2-fold higher urine glucose/creatinine ratios in Sglt1-/- vs. WT mice, associated with a temporarily greater reduction in blood glucose in Sglt1-/- vs. WT after 24 h (-33 vs. -11%). Subsequent inulin clearance studies under anesthesia revealed free plasma concentrations of the SGLT2-I (corresponding to early proximal concentration) close to the reported IC50 for SGLT2 in mice, which were associated with FGR of 64 2% in WT and 17 2% in Sglt1-/-. Additional intraperitoneal application of the SGLT2-I (maximum effective dose in metabolic cages) increased free plasma concentrations -10-fold and reduced FGR to 44 +/- 3% in WT and to -1 +/- 3% in Sglt1-/-. The absence of renal glucose reabsorption was confirmed in male and female Sglt1/Sglt2 double knockout mice. In conclusion, SGLT2 and SGLT1 account for renal glucose reabsorption in euglycemia, with 97 and 3% being reabsorbed by SGLT2 and SGLT1, respectively. When SGLT2 is fully inhibited by SGLT2-I, the increase in SGLT1-mediated glucose reabsorption explains why only 50-60% of filtered glucose is excreted.

Our previous work has shown that gene knockout of the sodiumglucose cotransporter SGLT2 modestly lowered blood glucose in streptozotocin-diabetic mice (BG; from 470 to 300 mg/dl) and prevented glomerular hyperfiltration but did not attenuate albuminuria or renal growth and inflammation. Here we determined effects of the SGLT2 inhibitor empagliflozin (300 mg/kg of diet for 15 wk; corresponding to 60-80 mg.kg(-1).day(-1)) in type 1 diabetic Akita mice that, opposite to streptozotocin-diabetes, upregulate renal SGLT2 expression. Akita diabetes, empagliflozin, and Akita + empagliflozin similarly increased renal membrane SGLT2 expression (by 38-56%) and reduced the expression of SGLT1 (by 33-37%) vs. vehicle-treated wild-type controls (WT). The diabetes-induced changes in SGLT2/SGLT1 protein expression are expected to enhance the BG-lowering potential of SGLT2 inhibition, and empagliflozin strongly lowered BG in Akita (means of 187-237 vs. 517-535 mg/dl in vehicle group; 100-140 mg/dl in WT). Empagliflozin modestly reduced GFR in WT (250 vs. 306 mu l/min) and completely prevented the diabetes-induced increase in glomerular filtration rate (GFR) (255 vs. 397 mu l/min). Empagliflozin attenuated increases in kidney weight and urinary albumin/creatinine ratio in Akita in proportion to hyperglycemia. Empagliflozin did not increase urinary glucose/creatinine ratios in Akita, indicating the reduction in filtered glucose balanced the inhibition of glucose reabsorption. Empagliflozin attenuated/prevented the increase in systolic blood pressure, glomerular size, and molecular markers of kidney growth, inflammation, and gluconeogenesis in Akita. We propose that SGLT2 inhibition can lower GFR independent of reducing BG (consistent with the tubular hypothesis of diabetic glomerular hyperfiltration), while attenuation of albuminuria, kidney growth, and inflammation in the early diabetic kidney may mostly be secondary to lower BG.

Rieg T, Gerasimova M, Murray F, Masuda T, Tang T, Rose M, Drucker DJ, Vallon V. Natriuretic effect by exendin-4, but not the DPP-4 inhibitor alogliptin, is mediated via the GLP-1 receptor and preserved in obese type 2 diabetic mice. Am J Physiol Renal Physiol 303: F963-F971, 2012. First published July 25, 2012; doi:10.1152/ajprenal.00259.2012.-Activation of the glucagon-like peptide (GLP)-1 receptor (GLP-1R) and inhibition of dipeptidyl peptidase-4 (DPP-4) are new antidiabetic strategies. The GLP-1R and DPP-4 are also expressed in the renal proximal tubular brush border, where they may regulate Na+ reabsorption. Exendin-4 (EX4) is a naturally occurring antidiabetic polypeptide (from the saliva of the lizard Heloderma suspectum) and GLP-1R agonist; however, part of its nonglucoregulatory effects are through GLP-1R-independent mechanisms. DPP-4 cleaves and inactivates GLP-1; thus the natriuretic effect of DPP-4 inhibition may be mediated by the GLP-1R. We report that parenteral application of EX4 in wild-type mice induced a diuresis and natriuresis associated with increases in glomerular filtration rate, fractional urinary fluid and Na+ excretion, and renal membrane expression of the Na+/H+ exchanger NHE3 phosphorylated at S552 and S605, established consensus sites for cAMP-dependent PKA. These effects were absent in mice lacking the GLP-1R and independent of adenylyl cyclase 6. In comparison, parenteral application of the DPP-4 inhibitor alogliptin reduced plasma DPP-4 activity by 95% and induced a diuresis and natriuresis independent of the presence of the GLP-1R or changes in phosphorylated NHE3. The inhibitory effect on renal fluid and Na+ reabsorption of EX4, but not alogliptin, was preserved in diabetic db/db mice and associated with a modest reduction in blood pressure. These results reveal mechanistic differences in how EX4 vs. DPP-4 inhibition induces diuresis and natriuresis under normal states, with preservation of GLP-1R-mediated, but not DPP-4 inhibitor-dependent, natriuretic mechanisms in a mouse model of obese type 2 diabetes.

Obstructive sleep apnea (OSA) is common in patients with renal disease, and an association between OSA and proteinuria has been proposed. However, the effect on proteinuria of OSA treatment with continuous positive airway pressure (CPAP) is unknown. We experienced a case of severe OSA, where proteinuria was clearly improved after CPAP initiation without any changes of medication or body weight. The remarkable reduction of repetitive apnea and hypopnea by CPAP might ameliorate proteinuria by lessening renal hypoxia and sympathetic nerve activation. This case suggests that CPAP is a promising option for OSA with proteinuria. © 2012 The Author. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.

Masuda T, Muto S, Fujisawa G, Iwazu Y, Kimura M, Kobayashi T, Nonaka-Sarukawa M, Sasaki N, Watanabe Y, Shinohara M, Murakami T, Shimada K, Kobayashi E, Kusano E. Heart angiotensin II-induced cardiomyocyte hypertrophy suppresses coronary angiogenesis and progresses diabetic cardiomyopathy. Am J Physiol Heart Circ Physiol 302: H1871-H1883, 2012. First published March 2, 2012; doi:10.1152/ajpheart.00663.2011.-To examine whether and how heart ANG II influences the coordination between cardiomyocyte hypertrophy and coronary angiogenesis and contributes to the pathogenesis of diabetic cardiomyopathy, we used Spontaneously Diabetic Torii (SDT) rats treated without and with olmesartan medoxomil (an ANG II receptor blocker). In SDT rats, left ventricular (LV) ANG II, but not circulating ANG II, increased at 8 and 16 wk after diabetes onset. SDT rats developed LV hypertrophy and diastolic dysfunction at 8 wk, followed by LV systolic dysfunction at 16 wk, without hypertension. The SDT rat LV exhibited cardiomyocyte hypertrophy and increased hypoxia-inducible factor-1 alpha expression at 8 wk and to a greater degree at 16 wk and interstitial fibrosis at 16 wk only. In SDT rats, coronary angiogenesis increased with enhanced capillary proliferation and upregulation of the angiogenic factor VEGF at 8 wk but decreased VEGF with enhanced capillary apoptosis and suppressed capillary proliferation despite the upregulation of VEGF at 16 wk. In SDT rats, the phosphorylation of VEGF receptor-2 increased at 8 wk alone, whereas the expression of the antiangiogenic factor thrombospondin-1 increased at 16 wk alone. All these events, except for hyperglycemia or blood pressure, were reversed by olmesartan medoxomil. These results suggest that LV ANG II in SDT rats at 8 and 16 wk induces cardiomyocyte hypertrophy without affecting hyperglycemia or blood pressure, which promotes and suppresses coronary angiogenesis, respectively, via VEGF and thrombospondin-1 produced from hypertrophied cardiomyocytes under chronic hypoxia. Thrombospondin-1 may play an important role in the progression of diabetic cardiomyopathy in this model.

Background. Sleep-disordered breathing (SDB), characterized by repetitive apnea and hypopnea during sleep, is a risk factor for cardiovascular disease. However, the links between SDB and cardiovascular events in hemodialysis (HD) patients have not been clearly evaluated. Methods. We followed the clinical outcome of 94 HD patients, who underwent overnight pulse oximetry on dialysis day. The SDB group was defined as 3% oxygen desaturation index (ODI) over five events per hour, and the others were the normal group. The primary outcome was cardiovascular events and death. We used Kaplan-Meier curve and Cox proportional hazard model for survival analyses. Results. Forty-four patients (46.8%) were classified into the SDB group. Body mass index, diabetes mellitus, 3% ODI and Epworth sleepiness scale were significantly higher, and duration of dialysis, Kt/V, normalized protein catabolism rate and hemoglobin were lower in the SDB group than in the normal group. During a median 55 months of follow-up, Kaplan-Meier analysis revealed that the SDB group had a significantly higher rate of cardiovascular events and all-cause mortality than the normal group. Age, cardiothoracic ratio, serum albumin and 3% ODI were predictors of cardiovascular events and all-cause mortality at univariate Cox regression analysis. In the adjusted analysis, SDB is an independent predictor of increased cardiovascular events (hazard ratio 3.10; 95% confidence interval (CI), 1.35-7.12; P = 0.008) and all-cause mortality (hazard ratio 2.81; 95% CI, 1.07-7.41; P = 0.037). Conclusions. SDB is an independent risk factor for cardiovascular events and mortality in HD patients. Effective and earlier treatment for these patients is needed to improve clinical outcome.

The mechanisms explaining the clinical effects of direct maxacalcitol (OCT) injection into the hyperplastic parathyroid gland (PTG) in uremic patients with advanced secondary hyperparathyroidism (SHPT) were investigated by molecular and morphological examination. PTG of uremia-induced SHPT model rats were treated by a direct injection of OCT (DI-OCT) or vehicle (DI-vehicle). The changes in serum intact parathyroid hormone (intact-PTH) level, vitamin D and Ca-sensing receptor (VDR and CaSR, respectively) expression levels in PTG, and the calcium (Ca)-PTH response curve were examined; the induction of apoptosis in parathyroid cells (PTC) was also analyzed by the TUNEL method, DNA electrophoresis, and electron microscopic examination. Serum intact-PTH level following DI-OCT significantly decreased. Upregulation of both VDR and CaSR, a clear shift to the left downward in the Ca-PTH curve, and many apoptotic PTCs were observed in the DI-OCT-treated PTGs. However, these findings were not observed in the DI-vehicle-treated PTGs. Moreover, these effects 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 upregulation and the regression of hyperplastic PTG, and these effects may provide a strategy for strongly suppressing PTH level in uremia-induced advanced SHPT.

Tubulointerstitial involvement in the kidneys is frequently found but it is a less emphasized feature of lupus nephritis (LN). Recent studies have shown increases in the urinary excretion of beta 2-microglobulin (beta 2 MG) and N-acetyl-beta-D-glucosaminidase (NAG), which are considered to indicate the presence of tubulointerstitial damage, particularly in cases of LN. However, the changes in these urinary parameters during the clinical course of LN have not yet been fully clarified. In this report, we describe the changes in the urinary excretion of beta 2MG and NAG during immunosuppressive treatment combined with double filtration plasmapheresis in a case of LN.