[Magnesium homeostasis and its disturbances]

Magnesium homeostasis is maintained through normal functions of the kidney, intestine, and bone. In the kidney, approximately 80% magnesium is filtered by the glomeruli. In general, 95% filtered magnesium is collectively reabsorbed in the proximal tubule (15%-20%) , thick ascending limb of Henle (TAL, 65%-75%) , and the distal convoluted tubule (DCT, 5%-10%) . In the TAL, magnesium reabsorption regulated by the paracellular pathway via claudin-16 is driven by electrochemical voltage. Chloride channel Kb and renal outer medullary potassium channels control this lumen-positive voltage. In the DCT, the transcellular pathway via transient receptor potential melastatin 6 (TRPM6) plays a fundamental role in the final 5%-10% magnesium reabsorption. The functions of TRPM6 depend on Na-Cl co-transporters and Na( + )-K( + )-ATPase. Defects in these regulatory proteins may cause inherited or drug-induced disorders of magnesium metabolism. Recently, some proteins have been confirmed to be responsible for magnesium homeostasis ; however, further research is required to elucidate the mechanisms underlying the maintenance of magnesium homeostasis.

Composition and plaque patterns of coronary culprit lesions and clinical characteristics of patients with chronic kidney disease

Coronary artery disease is a serious complication of chronic kidney disease (CKD); however, there is little information about coronary plaque morphology in these patients. Here we identified the characteristics of coronary culprit plaques and their clinical manifestations in 78 patients with CKD divided into four groups based on their estimated glomerular filtration rate. Patients were examined by Virtual Histology-Intravascular Ultrasound, a tomographic imaging method that can visualize atherosclerotic plaques in vivo using radiofrequency analysis of ultrasound backscatter signals. These ultrasound analyses showed an increase in the relative volumes of both dense calcium and necrotic core with decreasing renal function. The necrotic core/dense calcium ratio was significantly higher in patients with acute myocardial infarction compared to those with stable angina pectoris. Furthermore, the necrotic core/dense calcium ratio decreased in advanced CKD. Thus, the plaque composition of coronary culprit lesions changed from necrotic core-rich to extensively calcium-rich plaques as renal function decreased, suggesting that such coronary culprit composition was associated with stability, particularly in advanced CKD.

Systematic evaluation of vascular access by color-Doppler ultrasound decreased the incidence of emergent vascular access intervention therapy and X-ray exposure time: a single-center observational study

Arteriovenous fistula has superior patency over other accesses, but vascular access intervention therapy (VAIVT) for stenosis or thrombosis still remain major reasons for hospital admission of dialysis patients. The aim of this study was to examine the usefulness of systematic evaluation of vascular access by color-Doppler ultrasound (CDUS). This study was a single-center observational design study. We planned screening CDUS to evaluate all vascular accesses once per year, and additionally, follow-up CDUS of post-interventional patients 1 month, 3 months and 6 months after their recent VAIVT. This systematic evaluation was started from September 2009. The observational period between September 2008 and August 2009 was defined as period A. The observational period between September 2009 and August 2010 was defined as period B. We compared the incidence of emergent VAIVT and X-ray exposure time during the period A to B. 131 patients with AV fistula were assigned. 13 patients were excluded due to death, hospital transfer or re-operation of their accesses. During period A, 57 VAIVTs were carried out, and 37 cases (65%) were emergent. During period B, 42 VAIVTs were carried out, and 11 cases (25%) were emergent. The incidence of emergent intervention therapy was lower during period B than period A (P < 0.001). The amount of X-ray exposure time per patient was decreased in patients who received VAIVT during both periods (P < 0.03). Systematic evaluation of vascular access by CDUS decreased the incidence of emergent VAIVT and X-ray exposure time.

Carvedilol ameliorates low-turnover bone disease in non-obese type 2 diabetes

BACKGROUND

Diabetic bone disease is a major complication in diabetes mellitus and is characterized by low-turnover bone formation. Recent studies have demonstrated that oxidative stress could be associated with diabetic bone disease and that β-adrenergic antagonists could increase bone formation. Our study investigated the effect of carvedilol (β-blocker), possessing an antioxidant effect, on diabetic bone disease.

METHODS

We used the non-obese, type 2 diabetes model Spontaneously Diabetic Torii (SDT) rats in this study. Sprague-Dawley rats were used as controls (control, n = 6). SDT rats were divided into four groups: diabetic (DM, n = 8), DM+insulin (DM+I, n = 7), DM+carvedilol (DM+C, n = 8), and DM+N-acetylcysteine (DM+N, n = 10) at 20 weeks. The rats were sacrificed at 30 weeks, after which blood and urine samples, bone mineral density, histomorphometry, and oxidative stress were evaluated.

RESULTS

The number of 8-hydroxydeoxyguanosine-positive cells in bone tissue was significantly lower in the DM+C and DM+N groups than in the DM group. Mineral apposition rate and bone formation rate per bone surface in the DM+C and DM+N groups were significantly higher than those in the DM group, and these parameters were better in the DM+C group than in the DM+N group.

CONCLUSION

Our data suggest that carvedilol has stronger effects on diabetic low-turnover bone disease beyond that which can be attributed to its antioxidative stress mechanism.

A clinical trial protocol for second line treatment of malignant brain tumors with BNCT at University of Tsukuba

We have evaluated the efficacy and safety of boron neutron capture therapy (BNCT) for recurrent glioma and malignant brain tumor using a new protocol. One of the two patients enrolled in this trial is a man with recurrent glioblastoma and the other is a woman with anaplastic meningioma. Both are still alive and no severe adverse events have been observed. Our findings suggest that NCT will be safe as a palliative therapy for malignant brain tumors.

Boron neutron capture therapy combined with fractionated photon irradiation for glioblastoma: a recursive partitioning analysis of BNCT patients

Eight patients to received Boron Neuron Capture Therapy (BNCT) were selected from 33 newly diagnosed glioblastoma patients (NCT(+) group). Serial 42 glioblastoma patients (NCT(-) group) were treated without BNCT. The median OS of the NCT(+) group and NCT (-) group were 24.4 months and 14.9 months. In the high risk patients (RPA class V), the median OS of the NCT(+) group tended to be better than that of NCT(-) group. 50% of BNCT patients were RPA class V.

Prognostic factors in glioblastoma multiforme patients receiving high-dose particle radiotherapy or conventional radiotherapy

The aim of this study was to evaluate the influence of prognostic factors related to patient selection on survival outcomes. Survival outcomes were retrospectively analysed in a consecutive series of 67 newly diagnosed glioblastoma multiforme (GBM) patients who had received either conventional fractionated photon radiotherapy (CRT) or high-dose particle radiotherapy (HDT). In the CRT protocol, a total dose of 60.0-61.2 Gy was administered. In the HDT protocol, an average dose of approximately 30 GyE in a single session and additional fractionated photon irradiation of total dose 30 Gy were administered to patients receiving boron neutron capture therapy; and a total dose of 96.6 GyE was administered to patients receiving proton therapy. Most of the patients had received chemotherapy with nimustine hydrochloride (ACNU) alone or with ACNU, procarbazine and vincristine. The median overall survival (OS) and progression-free survival times for all patients were 17.7 months [95% confidence interval (CI), 14.6-20.9 months] and 7.8 months (95% CI, 5.7-9.9 months), respectively. The 1- and 2-year survival rates were 67.2% and 33.7%, respectively. For patients treated with HDT, the median OS was 24.4 months (95% CI, 18.2-30.5 months), compared with 14.2 months (95% CI, 10.0-18.3 months) for those treated with CRT. The Cox proportional hazards model revealed radiation modality (HDT vs CRT) and European Organisation for Research and Treatment of Cancer recursive partitioning analysis class to be the significant prognostic factors. Age, sex, pre-operative performance status, treatment with or without advanced neuroimaging, extent of surgery and regimen of chemotherapy were not statistically significant factors in predicting prognosis. The median OS was 18.5 months (95% CI, 9.9-27.1 months) in patients of 65 years and older, compared with 16.8 months (95% CI, 13.6-20.1 months) in those 64 years and younger (p=0.871). The positive effect of HDT treatment is unlikely to reflect patient selection alone. Randomised trials with strictly controlled inclusion criteria to ensure the comparable selection of patients are required to demonstrate conclusively that prolonged survival can be attributed to high-dose particle radiotherapies.

Effects of AST-120 on left ventricular mass in predialysis patients

BACKGROUND

Cardiovascular disease (CVD) is a leading cause of death in chronic kidney disease (CKD) patients. One of the proposed mechanisms assumes that accumulated uremic toxins play an important role in the progression of CVD in CKD. Recently, it has been reported that AST-120 may attenuate progression of CVD through absorption of uremic toxins. In this study, we examined the association between the use of AST-120 and cardiac abnormalities in CKD patients.

METHODS

This was a cross-sectional study of predialysis CKD patients hospitalized in our institution between April 2008 and October 2009. We divided 107 patients into two groups based on whether AST-120 had been administered for more than 6 months (AST-120 group: n = 43) or not (control group: n = 64). Echocardiography and laboratory tests were performed for all patients; we examined the relationship between clinical characteristics and cardiac abnormalities.

RESULTS

The number of patients with left ventricular (LV) concentric change was significantly smaller in the AST-120 group than in the control group. In multivariable analysis, the administration of AST-120, gender, and pulse pressure were significantly correlated with LV concentric change.

CONCLUSIONS

Our findings suggest that AST-120 prevents the development of LV concentric change in predialysis CKD patients.

The status of Tsukuba BNCT trial: BPA-based boron neutron capture therapy combined with X-ray irradiation

The phase II trial has been prepared to assess the effectiveness of BPA (250 mg/kg)-based NCT combined with X-ray irradiation and temozolomide (75 mg/m(2)) for the treatment of newly diagnosed GBM. BPA uptake is determined by (18)F-BPA-PET and/or (11)C-MET-PET, and a tumor with the lesion to normal ratio of 2 or more is indicated for BNCT. The maximum normal brain point dose prescribed was limited to 13.0 Gy or less. Primary end point is overall survival.

Role of oxidative stress and indoxyl sulfate in progression of cardiovascular disease in chronic kidney disease

Several abnormalities of the cardiovascular system are observed in most cases of chronic kidney disease (CKD). Mechanisms underlying these abnormalities are complicated, and several factors contribute to their pathogenesis. Of these factors, oxidative stress and uremic toxins are considered to play key roles in the progression of cardiovascular disease (CVD) in CKD. Oxidative stress increases significantly in CKD and accelerates proteinuria and renal dysfunction. In addition, oxidative stress has been reported to induce cardiac hypertrophy and fibrosis. Indoxyl sulfate, a uremic toxin, has recently been suggested to play a crucial role in the development of CVD. Recent in vitro data suggest that indoxyl sulfate increases oxidative stress. Some reports have shown that AST-120, which is an oral charcoal adsorbent, can reduce oxidative stress by lowering serum indoxyl sulfate levels. Recently, we have also demonstrated that indoxyl sulfate is associated with the production of oxidative stress, and that increased oxidative stress is significantly correlated with cardiac hypertrophy and fibrosis. Furthermore, results of our basic and clinical studies suggested that AST-120 can prevent progression of cardiac hypertrophy by reducing oxidative stress in CKD. Thus, one of the main targets of the management of CKD and CVD is the control of oxidative stress and uremic toxins, such as indoxyl sulfate.

New insights into the role of fibroblast growth factor 23 in chronic kidney disease

Fibroblast growth factor 23 (FGF23) is a recently identified bone-derived hormone that regulates phosphate and 1,25-dihydroxyvitamin D metabolism. FGF23 principally acts in the kidney to induce urinary phosphate excretion and suppress 1,25-dihydroxyvitamin D synthesis in the presence of FGF receptor 1 (FGFR1) and its coreceptor Klotho. FGF23 also acts in the parathyroid to decrease parathyroid hormone synthesis and secretion. In patients with chronic kidney disease (CKD), circulating FGF23 levels are progressively increased to compensate for persistent phosphate retention, but this results in reduced renal production of 1,25-dihydroxyvitamin D and leads to hypersecretion of parathyroid hormone. In patients undergoing dialysis, FGF23 levels are markedly elevated in response to hyperphosphatemia and active vitamin D therapy, but fail to suppress the secretion of parathyroid hormone, presumably due to decreased expression of the Klotho-FGFR1 complex. In these patients, FGF23 can be used as a predictor of future development of refractory hyperparathyroidism. FGF23 also plays a central role in the pathogenesis of post-transplant hypophosphatemia in kidney transplant recipients. Furthermore, recent studies suggest that FGF23 could be an independent predictor of mortality in dialysis patients, indicating its potential role as a sensitive biomarker of disordered phosphate metabolism. This brief review summarizes recent insights into the role of FGF23 in the pathogenesis of mineral and bone disorders in CKD.

Oxidative and nitrosative stress and progression of diabetic nephropathy in type 2 diabetes

BACKGROUND

The role of nitric oxide (NO) is controversial in diabetes nephropathy progression and the mechanisms remain unknown, especially in non-obese type 2 diabetes. To examine mechanisms of nephropathy progression in non-obese type 2 diabetes, we used spontaneously diabetic Torii (SDT) rats, a newly established model of non-obese type 2 diabetes.

METHODS

Fourteen male Sprague-Dawley rats were used as a control (20 weeks, n = 6; 30 weeks, n = 8), and 20-week-old male SDT rats were divided into 2 groups: diabetic (DM, n = 8) and DM + insulin (n = 8) groups. Twenty- and 36-week-old rats were sacrificed, and blood, urine, and histomorphometric analyses, mRNA expression analysis of endothelial NO synthase (eNOS) and NADPH oxidase, and blood pressure measurement were performed.

RESULTS

At 36 weeks, NO metabolites, and 8-hydroxydeoxyguanosine (8-OHdG) were significantly higher in the diabetic group than in the other 2 groups. Further renal studies showed increased glomerular volume and mesangial area, and intensified eNOS, 8-OHdG, and nitrotyrosine immunostaining in the diabetic group. Oxidative and nitrosative stress were positively associated with increased glomerular volume and mesangial area, which were mostly recovered by insulin therapy.

CONCLUSIONS

NO and oxidative stress increased in SDT rats, suggesting that these play key roles in nephropathy progression in non-obese type 2 diabetes.