Yoshifuru Tamura

Endogenous Fructose Production and Fructokinase Activation Mediate Renal Injury in Diabetic Nephropathy

Diabetes is associated with activation of the polyol pathway, in which glucose is converted to sorbitol by aldose reductase. Previous studies focused on the role of sorbitol in mediating diabetic complications. However, in the proximal tubule, sorbitol can be converted to fructose, which is then metabolized largely by fructokinase, also known as ketohexokinase, leading to ATP depletion, proinflammatory cytokine expression, and oxidative stress. We and others recently identified a potential deleterious role of dietary fructose in the generation of tubulointerstitial injury and the acceleration of CKD. In this study, we investigated the potential role of endogenous fructose production, as opposed to dietary fructose, and its metabolism through fructokinase in the development of diabetic nephropathy. Wild-type mice with streptozotocin-induced diabetes developed proteinuria, reduced GFR, and renal glomerular and proximal tubular injury. Increased renal expression of aldose reductase; elevated levels of renal sorbitol, fructose, and uric acid; and low levels of ATP confirmed activation of the fructokinase pathway. Furthermore, renal expression of inflammatory cytokines with macrophage infiltration was prominent. In contrast, diabetic fructokinase-deficient mice demonstrated significantly less proteinuria, renal dysfunction, renal injury, and inflammation. These studies identify fructokinase as a novel mediator of diabetic nephropathy and document a novel role for endogenous fructose production, or fructoneogenesis, in driving renal disease.

Epicatechin limits renal injury by mitochondrial protection in cisplatin nephropathy

Cisplatin nephropathy can be regarded as a mitochondrial disease. Intervention to halt such deleterious injury is under investigation. Recently, the flavanol (-)-epicatechin emerges as a novel compound to protect the cardiovascular system, owing in part to mitochondrial protection. Here, we have hypothesized that epicatechin prevents the progression of cisplatin-induced kidney injury by protecting mitochondria. Epicatechin was administered 8 h after cisplatin injury was induced in the mouse kidney. Cisplatin significantly induced renal dysfunction and tubular injury along with an increase in oxidative stress. Mitochondrial damages were also evident as a decrease in loss of mitochondrial mass with a reduction in the oxidative phosphorylation complexes and low levels of MnSOD. The renal damages and mitochondrial injuries were significantly prevented by epicatechin treatment. Consistent with these observations, an in vitro study using cultured mouse proximal tubular cells demonstrated that cisplatin-induced mitochondrial injury, as revealed by a decrease in mitochondrial succinate dehydrogenase activity, an induction of cytochrome c release, mitochondrial fragmentation, and a reduction in complex IV protein, was prevented by epicatechin. Such a protective effect of epicatechin might be attributed to decreased oxidative stress and reduced ERK activity. Finally, we confirmed that epicatechin did not perturb the anticancer effect of cisplatin in HeLa cells. In conclusion, epicatechin exhibits protective effects due in part to its ability to prevent the progression of mitochondrial injury in mouse cisplatin nephropathy. Epicatechin may be a novel option to treat renal disorders associated with mitochondrial dysfunction.

Targeting Uric Acid and the Inhibition of Progression to End-Stage Renal Disease--A Propensity Score Analysis.

Background The role of uric acid (UA) in the progression of chronic kidney disease (CKD) remains controversial due to the unavoidable cause and result relationship. This study was aimed to clarify the independent impact of UA on the subsequent risk of end-stage renal disease (ESRD) by a propensity score analysis. Methods A retrospective CKD cohort was used (n = 803). Baseline 23 covariates were subjected to a multivariate binary logistic regression with the targeted time-averaged UA of 6.0, 6.5 or 7.0 mg/dL. The participants trimmed 2.5 percentile from the extreme ends of the cohort underwent propensity score analyses consisting of matching, stratification on quintile and covariate adjustment. Covariate balances after 1:1 matching without replacement were tested for by paired analysis and standardized differences. A stratified Cox regression and a Cox regression adjusted for logit of propensity scores were examined. Results After propensity score matching, the higher UA showed elevated hazard ratios (HRs) by Kaplan-Meier analysis (≥6.0 mg/dL, HR 4.53, 95%CI 1.79–11.43; ≥6.5 mg/dL, HR 3.39, 95%CI 1.55–7.42; ≥7.0 mg/dL, HR 2.19, 95%CI 1.28–3.75). The number needed to treat was 8 to 9 over 5 years. A stratified Cox regression likewise showed significant crude HRs (≥6.0 mg/dL, HR 3.63, 95%CI 1.25–10.58; ≥6.5 mg/dL, HR 3.46, 95%CI 1.56–7.68; ≥7.0 mg/dL, HR 2.05, 95%CI 1.21–3.48). Adjusted HR lost its significance at 6.0 mg/dL. The adjustment for the logit of the propensity scores showed the similar results but with worse model fittings than the stratification method. Upon further adjustment for other covariates the significance was attained at 6.5 mg/dL. Conclusions Three different methods of the propensity score analysis showed consistent results that the higher UA accelerates the progression to the subsequent ESRD. A stratified Cox regression outperforms other methods in generalizability and adjusting for residual bias. Serum UA should be targeted less than 6.5 mg/dL.

Predictors and the Subsequent Risk of End-Stage Renal Disease – Usefulness of 30% Decline in Estimated GFR over 2 Years

Background A goal of searching risk factors for chronic kidney disease (CKD) is to halt progressing to end-stage renal disease (ESRD) by potential intervention. To predict the future ESRD, 30% decline in estimated GFR over 2 years was examined in comparison with other time-dependent predictors. Methods CKD patients who had measurement of serum creatinine at baseline and 2 years were enrolled (n = 701) and followed up to 6 years. Time-dependent parameters were calculated as time-averaged values over 2 years by a trapezoidal rule. Risk factors affecting the incidence of ESRD were investigated by the extended Cox proportional hazard model with baseline dataset and 2-year time-averaged dataset. Predictive significance of 30% decline in estimated GFR over 2 years for ESRD was analyzed. Results For predicting ESRD, baseline estimated GFR and proteinuria were the most influential risk factors either with the baseline dataset or the 2-year time-averaged dataset. Using the 2-year time-averaged dataset, 30% decline in estimated GFR over 2 years by itself showed the highest HR of 31.6 for ESRD whereas addition of baseline estimated GFR, proteinuria, serum albumin and hemoglobin yielded a better model by a multivariate Cox regression model. This novel surrogate was mostly associated with time-averaged proteinuria over 2 years with the cut-off of ~1 g/g creatinine. Conclusion These results suggest that decline in estimated GFR and proteinuria are the risk factors while serum albumin and hemoglobin are the protective factors by the time-to-event analysis. Future incidence of ESRD is best predicted by 30% decline in eGFR over 2 years that can be modified by intervention to proteinuria, hemoglobin, uric acid, phosphorus, blood pressure and use of renin-angiotensin system inhibitors in the follow-up of 2 years.

Umami: the taste that drives purine intake.

Rheumatologists commonly recommend low purine diets to gouty subjects based on studies linking the purine contents of food to increased risk for gout1. However, most rheumatologists, as well as physicians in general, do not know that one of the basic 5 human tastes is for purine-rich foods, a taste known as umami (oo-mah-mee). We present evidence of this revelation and why this may have occurred. Historically, an elevation in serum urate was considered benign except for carrying an increased risk for gout. Recently, soluble urate has been found to have myriad biologic effects, including raising blood pressure, increasing hepatic fat stores, and inducing insulin resistance2,3. Indeed, the uricase mutation that occurred in the mid-Miocene likely provided a survival advantage to our ancestors during a period of famine that occurred during that time in Europe4. If uric acid has an important role in human survival, then it is logical that there should be a taste receptor that would encourage the ingestion of foods that raise serum urate. In addition to the classic tastes of sour, bitter, sweet, and salt, there is a fifth basic taste, umami. Umami is the “savory” flavor and was first identified in traditional Japanese foods such as kombu (sea kelp), where it was found to result from the presence of free glutamate. The umami receptor in the taste buds is complex, and consists of the metabotropic glutamate receptor-4, the G-protein-coupled heterodimer of taste receptor type 1 member 1 (TAS1R1), and taste receptor type 1 receptor3 … Address correspondence to Dr. R.J. Johnson, Division of Kidney Diseases and Hypertension, University of Colorado Denver, Aurora, Colorado 80045, USA. E-mail: richard.johnson{at}ucdenver.edu

Combination of ACE inhibitor with nicorandil provides further protection in chronic kidney disease.

An inhibition in the renin-angiotensin system (RAS) is one of the most widely used therapies to treat chronic kidney disease. However, its effect is occasionally not sufficient and additional treatments may be required. Recently, we reported that nicorandil exhibited renoprotective effects in a mouse model of diabetic nephropathy. Here we examined if nicorandil can provide an additive protection on enalapril in chronic kidney disease. Single treatment with either enalapril or nicorandil significantly ameliorated glomerular and tubulointerstitial injury in the rat remnant kidney while the combination of these two compounds provided additive effects. In addition, an increase in oxidative stress in remnant kidney was also blocked by either enalapril or nicorandil while the combination of the drugs was more potent. A mechanism was likely due for nicorandil to preventing manganase superoxide dismutase (MnSOD) and sirtuin (Sirt)3 from being reduced in injured kidneys. A study with cultured podocytes indicated that the antioxidative effect could be mediated through sulfonylurea receptor (SUR) in the mitochondrial KATP channel since blocking SUR with glibenclamide reduced MnSOD and Sirt3 expression in podocytes. In conclusion, nicorandil may synergize with enalapril to provide superior protection in chronic kidney disease.

Uric acid metabolism of kidney and intestine in a rat model of chronic kidney disease

ABSTRACT Uric acid (UA) is a potential risk factor of the progression of chronic kidney disease (CKD). Recently, we reported that intestinal UA excretion might be enhanced via upregulation of the ATP-binding cassette transporter G2 (Abcg2) in a 5/6 nephrectomy (Nx) rat model. In the present study, we examined the mRNA and protein expressions of UA transporters, URAT1, GLUT9/URATv1, ABCG2 and NPT4 in the kidney and ileum in the same rat model. Additionally, we investigated the Abcg2 mRNA expression of ileum in hyperuricemic rat model by orally administering oxonic acid. Male Wistar rats were randomly assigned to three groups consisting of Nx group, oxonic acid-treated (Ox) group and sham-operated control group, and sacrificed at 8 weeks. Creatinine and UA were measured and the mRNA expressions of UA transporters in the kidney and intestine were evaluated by a real time PCR. UA transporters in the kidney sections were also examined by immunohistochemistry. Serum creatinine elevated in the Nx group whereas serum UA increased in the Ox group. Both the mRNA expression and the immunohistochemistry of the UA transporters were decreased in the Nx group, suggesting a marginal role in UA elevation in decreased kidney function. In contrast, the mRNA expression of Abcg2 in the ileum significantly increased in the Ox group. These results suggest that the upregulation of Abcg2 mRNA in the ileum triggered by an elevation of serum UA may play a compensatory role in increasing intestinal UA excretion.

A low-protein diet concomitant with high calorie intake preserves renal function and structure in diabetic OLETF rats

BackgroundOtsuka Long-Evans Tokushima Fatty (OLETF) rats, a spontaneous type 2 diabetes model, were used to clarify whether and how a low-protein diet prevents progressive diabetic nephropathy, in terms of functional and structural parameters.MethodsA low-protein diet (LPD) with 11% protein content, was compared to the normal 24% protein diet (NPD) without keeping isocaloric conditions. Daily food intake, body weight, and blood and urine chemistry were serially measured in rats from 10 through 60 weeks of age, and renal clearance studies and histological evaluations were performed at 40 and 60 weeks of age.ResultsDaily calorie intake was higher in the OLETF rats fed on the LPD than in those fed on the NPD throughout the experiment. Due to this hyperphagia, fasting blood glucose and hemoglobin (Hb)A1c were dramatically increased in the LPD-fed OLETF rats at 30 weeks and thereafter, whereas urinary protein excretion was decreased by more than half after 26 weeks in the LPD group. Plasma concentrations of total cholesterol and triglyceride were decreased in the LPD-fed OLETF rats at 40 and 60 weeks. Inulin clearance in the LPD group was higher only at 60 weeks of age. The glomerular sclerosis index (GSI) and tubulointerstitial index (TII) were preserved in the LPD group. The LPD induced a decrease in tubulointerstitial macrophage infiltration as compared with the NPD at both 40 and 60 weeks of age, but glomerular macrophage infiltration was not alleviated.ConclusionsA low-protein diet, despite the worsening hyperglycemia caused by hyperphagia, not only reduced proteinuria but also ameliorated hyperlipidemia in OLETF rats, thereby preserving renal function and structure in diabetic nephropathy, probably via a macrophage-mediated mechanism.

Immunohistochemical and in situ hybridization study of urate transporters GLUT9/URATv1, ABCG2, and URAT1 in the murine brain

BackgroundUric acid (UA) is known to exert neuroprotective effects in the brain. However, the mechanism of UA regulation in the brain is not well characterized. In our previous study, we described that the mouse urate transporter URAT1 is localized to the cilia and apical surface of ventricular ependymal cells. To further strengthen the hypothesis that UA is transported transcellularly at the ependymal cells, we aimed to assess the distribution of other UA transporters in the murine brain.MethodsImmunostaining and highly-sensitive in situ hybridization was used to assess the distribution of UA transporters: GLUT9/URATv1, ABCG2, and URAT1.ResultsImmunostaining for GLUT9 was observed in ependymal cells, neurons, and brain capillaries. Immunostaining for ABCG2 was observed in the choroid plexus epithelium and brain capillaries, but not in ependymal cells. These results were validated by in situ hybridization.ConclusionsWe propose that given their specific expression patterns in ependymal, choroid plexus epithelial, and brain capillary endothelial cells in this study, UA may be transported by these UA transporters in the murine brain. This may provide a novel strategy for targeted neuroprotection.

Successful Treatment of Infectious Endocarditis Associated Glomerulonephritis Mimicking C3 Glomerulonephritis in a Case with No Previous Cardiac Disease

We report a 42-year-old man with subacute infectious endocarditis (IE) with septic pulmonary embolism, presenting rapidly progressive glomerulonephritis and positive proteinase 3-anti-neutrophil cytoplasmic antibody (PR3-ANCA). He had no previous history of heart disease. Renal histology revealed diffuse endocapillary proliferative glomerulonephritis with complement 3- (C3-) dominant staining and subendothelial electron dense deposit, mimicking C3 glomerulonephritis. Successful treatment of IE with valve plastic surgery gradually ameliorated hypocomplementemia and renal failure; thus C3 glomerulonephritis-like lesion in this case was classified as postinfectious glomerulonephritis. IE associated glomerulonephritis is relatively rare, especially in cases with no previous history of valvular disease of the heart like our case. This case also reemphasizes the broad differential diagnosis of renal involvement in IE.