Tsuneo Takenaka

Xeno-Klotho Inhibits Parathyroid Hormone Signaling.

Although fibroblast growth factor (FGF) 23 was recently identified as a phosphatonin that influences vitamin D metabolism, the underlying signaling mechanisms remain unclear. FGF23 elevates the renal levels of membrane-associated klotho as well as soluble klotho. Klotho is expressed on distal tubules. Upon enzymatic cleavage, soluble klotho is released into the renal interstitial space and then into the systemic circulation. The expression of 25-hydroxyvitamin D3 1α-hydroxylase (1-OH) on proximal tubular cells is controlled by parathyroid hormone (PTH). Klotho binds to various membrane proteins to alter their function. Here, the interaction between the PTH receptor and klotho was studied using various approaches, including immunoprecipitation, in vitro cell culture, and in vivo animal experiments. Immunoprecipitation studies demonstrate, for the first time, that recombinant human klotho protein interacts with human PTH receptors to inhibit the binding of human PTH. Furthermore, when applied to human proximal tubular cells, recombinant human klotho suppresses PTH-stimulated generation of inositol trisphosphate in vitro. Moreover, PTH-induced increase of cyclic AMP secretion and 1α,25-dihydroxyvitamin D3 (1,25VD) was attenuated by recombinant human klotho in vivo. In addition, recombinant human klotho inhibits the expression of 1-OH by PTH both in vitro and in vivo. These results suggest that free klotho mediates the FGF23-induced inhibition of 1,25VD synthesis.

Calcitriol supplementation improves endothelium-dependent vasodilation in rat hypertensive renal injury.

Background/Aims: Vitamin D increases renal expression of klotho in normotensive rats. Klotho reduces oxidative stress. Methods: In this study, we aimed to determine if vitamin D would suppress oxidative stress using 4 groups of hypertensive rats: uninephrectomized, stroke-prone, spontaneously hypertensive rats fed a high-salt (6%) diet (controls; C); those treated with irbesartan (I); those treated with calcitriol (V); and those treated with both irbesartan and calcitriol (I+V). Results: Systolic blood pressure was higher in the C group than in the I and I+V groups. Albuminuria was attenuated in groups I, V, and I+V. Renal angiotensin II (AngII) concentration was lower in groups I and I+V than in group C, and plasma AngII levels of groups I and V were higher and lower than those in group C, respectively. Compared with group C, renal klotho expression, 8-epi-prostaglandin F2α excretion, and acetylcholine-induced decrease in blood pressure improved in the V and I+V groups. Conclusions: The data indicate that irbesartan effectively decreases blood pressure and renal AngII levels, and improves albuminuria. Our findings indicate that vitamin D enhances klotho expression, suppressing oxidative stress and albuminuria without substantial changes in renal AngII levels. These results suggest that the amelioration of endothelium function by vitamin D involves free klotho.

Statin Improves Flow-Mediated Vasodilation in Chronic Kidney Diseases

Background. Numbers of drugs are required to manage patients with chronic kidney disease (CKD). Drug adherence is relatively poor in this population. Methods. In 36 CKD patients with hypertension and dyslipidemia, who were prescribing amlodipine 5u2009mg and atorvastatin 10u2009mg daily, the influences of exchanging to a combination drug containing equivalent doses of amlodipine and atorvastatin were observed for 6 months. Results. At the baseline, flow-mediated dilation (FMD) was reduced (2.4 ± 0.3%), and proteinuria was significantly contributed to decrements of FMD (R 2 = 0.38, F = 3.7, dfu2009(6,29), andu2009u2009P < 0.01). Six months later from exchanging to combination drug, total cholesterol (TC, 197 ± 5 to 183 ± 3u2009mg/dL,u2009u2009P < 0.01) and triglycerides (142 ± 14 to 129 ± 10u2009mg/dL, P < 0.05) were decreased, but high density lipoprotein cholesterol (53 ± 3 to 56 ± 3u2009mg/dL, P < 0.05) was increased. FMD was slightly albeit significantly improved to 2.7 ± 0.3% (P < 0.05). No serious adverse effects were seen by the combination drug. Subanalysis for the patients with considerable reductions of TC demonstrated that the combination drug decreased proteinuria and high sensitive CRP (P < 0.05 for both). Conclusion. Our data indicate that proteinuria constitutes a determinant of a reduced FMD. The present results implicate that combination drug is useful to improve adherence and suggest that atorvastatin refines endothelium function as well as lipid profiles in CKD patients.

Klotho suppresses the renin-angiotensin system in adriamycin nephropathy

BackgroundsnKlotho protein interacts with the transforming growth factor β (TGF-β) receptor and Wnt, which contribute to the progression of renal disease, inhibiting their signals. Renal and circulating klotho levels are diminished in chronic kidney disease.nnnMethodsnExperiments were performed to assess whether supplementation of klotho protein could have protective effects on the kidney. Rats were injected with adriamycin (5 mg/kg) and divided into three groups: those treated with vehicle, those treated with klotho protein and those treated with klotho plus 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD). Rats without adriamycin treatment were used as a control.nnnResultsnAdriamycin reduced the serum klotho concentration and renal expression of klotho and E-cadherin. Adriamycin also increased the renal expression of Wnt, TGF-β, and angiotensinogen, as well as the renal abundance of β-catenin and angiotensin II. Klotho supplementation suppressed adriamycin-induced elevations of β-catenin and angiotensin II with sustained Wnt expression. Combined treatment with klotho and TDZD reversed the klotho-induced improvements in the renal abundance of β-catenin and angiotensin II as well as the expression of TGF-β and angiotensinogen without affecting E-cadherin.nnnConclusionsnOur data indicate that Wnt is involved in the pathogenesis of adriamycin nephropathy. Furthermore, klotho supplementation inhibited Wnt signaling, ameliorating renal angiotensin II. Finally, klotho protein appears to suppress epithelial-mesenchymal transition by inhibiting TGF-β and Wnt signaling.

Antialbuminuric actions of calcilytics in the remnant kidney

Hyperphosphatemia accelerates the progression of chronic kidney diseases. In the present study, the effects of ronacaleret, a calcilytic agent, on renal injury were assessed in the following four groups of rats: 5/6-nephrectomized Wistar rats as a control (C group), rats treated with ronacaleret (3 mg·kg(-1)·day(-1); R group), rats treated with calcitriol (30 ng·kg(-1)·day(-1); V group), and rats treated with both ronacaleret and calcitriol (R + V group). Three months later, rats were euthanized under anesthesia, and the remnant kidneys were harvested for analysis. Albuminuria was lower in the R and V groups than in the C group (P < 0.05). Creatinine clearance was elevated in the R and V groups compared with the C group (P < 0.05). Serum Ca(2+) and renal ANG II were higher in the R + V group than in the C group (P < 0.05 for each), and serum phosphate was reduced in the R group compared with the C group (P < 0.05). Fibroblast growth factor-23 was lower in the R group and higher in the V and R + V groups than in the C group. However, parathyroid hormone did not differ significantly among the four groups. Renal klotho expression was elevated in the R and V groups compared with the C group (P < 0.05). The present data indicate that ronacaleret preserves klotho expression and renal function with reductions in serum phosphate and albuminuria in 5/6-nephrectomized rats. Our findings demonstrate that vitamin D prevents declines in klotho expression and renal function, suppressing albuminuria.

Oxidative stress increases megalin expression in the renal proximal tubules during the normoalbuminuric stage of diabetes mellitus

Megalin, an endocytic receptor expressed in proximal tubule cells, plays a critical role in renal tubular protein reabsorption and is associated with the albuminuria observed in diabetic nephropathy. We have previously reported increased oxidant production in the renal cortex during the normoalbuminuric stage of diabetes mellitus (DM); however, the relationship between oxidative stress and renal megalin expression during the normoalbuminuric stage of DM remains unclear. In the present study, we evaluated whether oxidative stress affects megalin expression in the normoalbuminuric stage of DM in a streptozotocin-induced diabetic rat model and in immortalized human proximal tubular cells (HK-2). We demonstrated that increased expression of renal megalin accompanies oxidative stress during the early stage of DM, before albuminuria development. Telmisartan treatment prevented the diabetes-induced elevation in megalin level, possibly through an oxidative stress-dependent mechanism. In HK-2 cells, hydrogen peroxide significantly increased megalin levels in a dose- and time-dependent manner; however, the elevation in megalin expression was decreased following prolonged exposure to severe oxidative stress induced by 0.4 mmol/l hydrogen peroxide. High-glucose treatment also significantly increased megalin expression in HK-2 cells. Concurrent administration of the antioxidant N-acetyl-cysteine blocked the effects of high glucose on megalin expression. Furthermore, the hydrogen peroxide-induced increase in megalin expression was blocked by treatment with phosphatidylinositol 3-kinase and Akt inhibitors. Increase of phosphorylated Akt expression was also seen in the renal cortex of diabetic rats. Taken together, our results indicate that mild oxidative stress increases renal megalin expression through the phosphatidylinositol 3-kinase-Akt pathway in the normoalbuminuric stage of DM.

Calcium channel blockers suppress daily variations of blood pressure in hypertensive patients with end-stage renal diseases.

Abstract Hypertension is a well-known cardiovascular risk. Patients with end-stage renal diseases frequently suffer hypertension. Furthermore, daily variations of blood pressure are relatively large in patients treated with hemodialysis, partly due to ultrafiltration. Twenty hypertensive patients with end-stage renal diseases whose blood pressure was controlled by a single antihypertensive agent, either angiotensin receptor antagonist (ARB) or calcium channel blocker (CCB), were enrolled into the study. Home blood pressure measurements were also performed. Average systolic and diastolic blood pressures were similar between two agents. However, variations of systolic blood pressure during ARB treatment were greater than those of CCB, and maximal differences in daily systolic blood pressure during treatment with ARB (19u2009±u20097u2009mmHg) were greater than those with CCB (14u2009±u20096u2009mmHg, pu2009<u20090.01). Systolic blood pressure measured after hemodialysis under ARB therapy (110u2009±u20096u2009mmHg) was lower than that of CCB (118u2009±u20096u2009mmHg, pu2009<u20090.05). Daily variations of diastolic blood pressure were similar between ARB and CCB periods. Our results indicate that variations of systolic blood pressure during ARB treatment are larger than CCB, and suggest that CCB is useful to obtain the better quality of blood pressure control, improving blood pressure stability by preventing substantial drops in blood pressure in hypertensive patients with end-stage renal diseases.

Lifestyle Modifications Versus Antihypertensive Medications in Reducing Cardiovascular Events in an Aging Society: A Success Rate-oriented Simulation

Objective It is difficult to compare directly the practical effects of lifestyle modifications and antihypertensive medications on reducing cardiovascular disease (CVD). The purpose of this study was to compare the hypothetical potential of lifestyle modifications with that of antihypertensive medications in reducing CVD in an aging society using a success rate-oriented simulation. Methods We constructed a simulation model for virtual Japanese subpopulations according to sex and age at 10-year intervals from 40 years of age as an example of an aging society. The fractional incidence rate of CVD was calculated as the product of the incidence rate at each systolic blood pressure (SBP) level and the proportion of the SBP frequency distribution in the fractional subpopulations of each SBP. The total incidence rate was calculated by the definite integral of the fractional incidence rate at each SBP level in the sex- and age-specific subpopulations. Results If we consider the effects of lifestyle modifications on metabolic factors and transfer them onto SBP, the reductions in the total incidence rate of CVD were competitive between lifestyle modifications and antihypertensive medications in realistic scenarios. In middle-aged women, the preventive effects of both approaches were limited due to a low incidence rate. In middle-aged men and extremely elderly subjects whose adherence to antihypertensive medications is predicted to be low, lifestyle modifications could be an alternative choice. Conclusion The success rate-oriented simulation suggests that the effectiveness of lifestyle modifications or antihypertensive medications in preventing cardiovascular events largely depends on the baseline incidence rate and sex- and age-specific behavioral factors.

Lifestyle modifications supported by regional health nurses lowered insulin resistance, oxidative stress and central blood pressure in subjects with metabolic syndrome

BACKGROUNDnThis study was attempted to investigate whether lifestyle modifications supported by regional health nurses should improve cardio-metabolic factors--including adipocytokines, oxidative stress, and arterial stiffness--in subjects with metabolic syndrome.nnnMETHODSnThirty-six subjects with metabolic syndrome were enrolled, 28 of whom completed the 6-month lifestyle modifications (male:female=19:9). Blood and urine test results were examined in relation to metabolic factors before and after 6-month nutritional and physical activity modifications. In addition, oral glucose tolerance tests were performed and arterial stiffness was measured by brachial-ankle pulse wave velocity and radial augmentation index before and after them.nnnRESULTSnSix-month lifestyle modifications significantly reduced body weight, homeostasis model assessment index, and low-density lipoprotein cholesterol (LDL-C). They significantly attenuated oxidative stress measured by the urinary 8-hydroxy-2-deoxyguanosine/creatinine ratio. They also lowered brachial and central systolic blood pressure. They tended to decrease waist circumferences and the levels of C-reactive protein. However they did not significantly change the levels of adipocytokines, including tumour necrosis factor, soluble tumour necrosis factor receptors, and interleukin 6, or arterial stiffness measured by brachial-ankle pulse wave velocity and radial augmentation index.nnnCONCLUSIONSnSix-month lifestyle modifications supported by regional health nurses lowered body weight, insulin resistance, LDL-C, oxidative stress, and peripheral and central blood pressure in subjects with metabolic syndrome.

Impacts of sodium-glucose co-transporter type 2 inhibitors on central blood pressure

Aims: To assess the effects of sodium-glucose co-transporter type 2 inhibitors on central blood pressure, an important determinant of cardiovascular events. Methods: Canagliflozin, Empagliflozin or Luseogliflozin was given for 102 type 2 diabetic patients with hypertension and nephropathy. Central blood pressure was evaluated by radial tonometry. Clinical parameters were followed for 6u2009months. Results: Three differing sodium-glucose co-transporter type 2 inhibitors similarly reduced brachial and central blood pressures, casual blood sugar, haemoglobin A1c, estimated glomerular filtration rate and albuminuria without significant changes in pulse rate and lipid profiles. Central systolic blood pressure was associated with the decreases in albuminuria by sodium-glucose co-transporter type 2 inhibitors. Conclusion: Comparable influences of various sodium-glucose co-transporter type 2 inhibitors on central blood pressure suggest class effects.