Mitochondrial quality control and its emerging role in the pathogenesis of diabetic kidney disease

Most eukaryotic cells have mitochondrial networks that can change in shape, distribution, and size depending on cellular metabolic demands and environments. Mitochondrial quality control is critical for various mitochondrial functions including energy production, redox homeostasis, intracellular calcium handling, cell differentiation, proliferation, and cell death. Quality control mechanisms within mitochondria consist of antioxidant defenses, protein quality control, DNA damage repair systems, mitochondrial fusion and fission, mitophagy, and mitochondrial biogenesis. Defects in mitochondrial quality control and disruption of mitochondrial homeostasis are common characteristics of various kidney cell types under hyperglycemic conditions. Such defects contribute to diabetes-induced pathologies in renal tubular cells, podocytes, endothelial cells, and immune cells. In this review, we focus on the roles of mitochondrial quality control in diabetic kidney disease pathogenesis and discuss current research evidence and future directions.

Effects of online hemodiafiltration on anemia and nutritional status in chronic hemodialysis patients

Background@#Online hemodiafiltration (OL-HDF) offers considerable advantages in clearance of molecules of various sizes. However, evidence of clinical effects of OL-HDF is scarce in Korea. In this study, we investigated changes in laboratory values over more than 12 months after switching to OL-HDF. @*Methods@#Adult patients with end-stage renal disease undergoing hemodialysis (HD) were prospectively enrolled in a K-cohort (CRIS no. KCT0003281) from 6 tertiary hospitals in South Korea. We recruited 435 patients, 339 of whom were on HD at enrollment. One hundred eighty-two patients were followed for more than 24 months. Among them, 44 were switched to OL-HDF for more than 12 months without conversion to HD. We used a paired t test to compare baseline and 24-month follow-up results. @*Results@#The mean age of the subjects was 61.2 ± 12.2 years, and 62.6% were male. The baseline hemoglobin level was not significantly different between HD and OL-HDF group (10.61 ± 1.15 vs. 10.46 ± 1.03 g/dL, P = 0.437). However, the baseline serum protein and albumin levels were significantly lower in the OL-HDF group (6.82 ± 0.49 vs. 6.59 ± 0.48 g/dL, P = 0.006; 3.93 ± 0.28 vs. 3.73 ± 0.29 g/dL, P < 0.001). In patients switched to OL-HDF, levels of hemoglobin and serum albumin significantly increased (10.46 ± 1.03 vs. 11.08 ± 0.82 g/dL, P = 0.001; 3.73 ± 0.29 vs.

Beneficial Effect of Chloroquine and Amodiaquine on Type 1 Diabetic Tubulopathy by Attenuating Mitochondrial Nox4 and Endoplasmic Reticulum Stress

Background@#Oxidative stress induced by chronic hyperglycemia is recognized as a significant mechanistic contributor to the development of diabetic kidney disease (DKD).Nonphagocytic nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) is a major source of reactive oxygen species (ROS) in many cell types and in the kidney tissue of diabetic animals. We designed this study to explore the therapeutic potential of chloroquine (CQ) and amodiaquine (AQ) for inhibiting mitochondrial Nox4 and diabetic tubular injury. @*Methods@#Human renal proximal tubular epithelial cells (hRPTCs) were cultured in highglucose media (30 mM D-glucose), and diabetes was induced with streptozotocin (STZ, 50 mg/kg i.p. for 5 days) in male C57BL/6J mice. CQ and AQ were administered to the mice via intraperitoneal injection for 14 weeks. @*Results@#CQ and AQ inhibited mitochondrial Nox4 and increased mitochondrial mass in hRPTCs under high-glucose conditions. Reduced mitochondrial ROS production after treatment with the drugs resulted in decreased endoplasmic reticulum (ER) stress, suppressed inflammatory protein expression and reduced cell apoptosis in hRPTCs under high-glucose conditions. Notably, CQ and AQ treatment diminished Nox4 activation and ER stress in the kidneys of STZ-induced diabetic mice. In addition, we observed attenuated inflammatory protein expression and albuminuria in STZ-induced diabetic mice after CQ and AQ treatment. @*Conclusion@#We substantiated the protective actions of CQ and AQ in diabetic tubulopathy associated with reduced mitochondrial Nox4 activation and ER stress alleviation. Further studies exploring the roles of mitochondrial Nox4 in the pathogenesis of DKD could suggest new therapeutic targets for patients with DKD.

Validation Study of an Operational Tolerance Signature in Korean Kidney Transplant Recipients

Operational tolerance (OT), defined as maintaining stable graft function without immunosuppression after transplant surgery, is an ideal goal for kidney transplant recipients (KTRs). Recent investigations have demonstrated the distinctive features of B cells, T cells, and dendritic cell-related gene signatures and the distributions of circulating lymphocytes in these patients; nonetheless, substantial heterogeneities exist across studies. This study was conducted to determine whether previously reported candidate gene biomarkers and the profiles of lymphocyte subsets of OT could be applied in Korean KTRs. Peripheral blood samples were collected from 153 patients, including 7 operationally tolerant patients. Quantitative real-time PCR and flow cytometry were performed to evaluate gene expression and lymphocyte subsets, respectively. Patients with OT showed significantly higher levels of B cell-related gene signatures (IGKV1D-13 and IGKV4-1), while T cell-related genes (TOAG-1) and dendritic cell-related genes (BNC2, KLF6, and CYP1B1) were not differentially expressed across groups. Lymphocyte subset analyses also revealed a higher proportion of immature B cells in this group. In contrast, the distributions of CD4⁺ T cells, CD8⁺ T cells, mature B cells, and memory B cells showed no differences across diagnostic groups. An OT signature, generated by the integration of IGKV1D-13, IGKV4-1, and immature B cells, effectively discriminated patients with OT from those in other diagnostic groups. Finally, the OT signature was observed among 5.6% of patients who had stable graft function for more than 10 years while on immunosuppression. In conclusion, we validated an association of B cells and their related signature with OT in Korean KTRs.

Update of aristolochic acid nephropathy in Korea

BACKGROUND/AIMS: The true incidence of aristolochic acid nephropathy (AAN) is thought to be underestimated because numerous ingredients known or suspected to contain aristolochic acid (AA) are used in traditional medicine in Korea. METHODS: We collected data on cases of AAN since 1996 via a database in Korea. We evaluated the year of AAN development, route to obtaining AA-containing herbal medicine, gender, reason for taking AA-containing herbal medicine, clinical manifestations, histological findings, phytochemical analysis, and prognosis of patients with AAN. RESULTS: Data on 16 cases of AAN were collected. Thirteen cases developed AAN before and three cases after the prohibition of AA-containing herbal medicine by the Korea Food and Drug Administration. Patients were prescribed AA-containing herbal medicine from oriental clinics or had purchased it from traditional markets. AAN was distributed in all age groups. Young females were most commonly exposed to AA-containing herbal medicine for slimming purposes and postpartum health promotion, while older adults took AA-containing compounds for the treatment of chronic diseases. The most common symptoms presented at hospitalization were nausea and vomiting, and acute kidney injury was accompanied by Fanconi syndrome in almost half of the patients. Phytochemical analysis of AA in herbal medicine was available in six cases. Progression to end stage renal disease (ESRD) was observed in seven patients (43.8%), and five patients (31.3%) had progressed to ESRD within 6 months of diagnosis. CONCLUSIONS: Our report shows that patients were still exposed to AA-containing herbal medicine and that there is a possibility of underdiagnosis of AAN in Korea. A stronger national supervision system of herbal ingredients and remedies in oriental medicine is needed to prevent AAN.

Estimating the urinary sodium excretion in patients with chronic kidney disease is not useful in monitoring the effects of a low-salt diet

BACKGROUND: Several epidemiologic studies have suggested that the urine sodium excretion (USE) can be estimated in lieu of performing 24-hour urine collection. However, this method has not been verified in patients with chronic kidney disease (CKD) or in an interventional study. The purpose of this study was to evaluate the usefulness of estimating USE in a prospective low-salt diet education cohort (ESPECIAL). METHODS: A new formula was developed on the basis of morning fasting urine samples from 228 CKD patients in the ESPECIAL cohort. This formula was compared to the previous four formulas in the prediction of 24-hour USE after treatment with olmesartan and low-salt diet education. RESULTS: Most previously reported formulas had low predictability of the measured USE based on the ESPECIAL cohort. Only the Tanaka formula showed a small but significant bias (9.8 mEq/day, P < 0.05) with a low correlation (r = 0.34). In contrast, a new formula showed improved bias (−0.1 mEq/day) and correlation (r = 0.569) at baseline. This formula demonstrated no significant bias (−1.2 mEq/day) with the same correlation (r = 0.571) after 8 weeks of treatment with olmesartan. Intensive low-salt diet education elicited a significant decrease in the measured USE. However, none of the formulas predicted this change in the measured urine sodium after diet adjustment. CONCLUSION: We developed a more reliable formula for estimating the USE in CKD patients. Although estimating USE is applicable in an interventional study, it may be unsuitable for estimating the change of individual sodium intake in a low-salt intervention study.

Evaluation of Digital PCR as a Technique for Monitoring Acute Rejection in Kidney Transplantation

Early detection and proper management of kidney rejection are crucial for the long-term health of a transplant recipient. Recipients are normally monitored by serum creatinine measurement and sometimes with graft biopsies. Donor-derived cell-free deoxyribonucleic acid (cfDNA) in the recipient's plasma and/or urine may be a better indicator of acute rejection. We evaluated digital PCR (dPCR) as a system for monitoring graft status using single nucleotide polymorphism (SNP)-based detection of donor DNA in plasma or urine. We compared the detection abilities of the QX200, RainDrop, and QuantStudio 3D dPCR systems. The QX200 was the most accurate and sensitive. Plasma and/or urine samples were isolated from 34 kidney recipients at multiple time points after transplantation, and analyzed by dPCR using the QX200. We found that donor DNA was almost undetectable in plasma DNA samples, whereas a high percentage of donor DNA was measured in urine DNA samples, indicating that urine is a good source of cfDNA for patient monitoring. We found that at least 24% of the highly polymorphic SNPs used to identify individuals could also identify donor cfDNA in transplant patient samples. Our results further showed that autosomal, sex-specific, and mitochondrial SNPs were suitable markers for identifying donor cfDNA. Finally, we found that donor-derived cfDNA measurement by dPCR was not sufficient to predict a patient's clinical condition. Our results indicate that donor-derived cfDNA is not an accurate predictor of kidney status in kidney transplant patients.

Fatal Invasive Pulmonary Aspergillosis after Combined Induction with Rituximab and Antithymocyte Globulin for Kidney Transplantation in a Sensitized Recipient, and Early Rejection Therapy with Plasmapheresis and Low-dose Immunoglobulin / 대한이식학회지

A high degree of sensitization to human leukocyte antigen requires more intensive induction therapy; however, this increases vulnerability to opportunistic infections following kidney transplantation. Although recent studies have suggested that combined induction therapy with antithymocyte globulin and rituximab would be more effective in highly sensitized kidney recipients, we experienced a case of near-fatal invasive pulmonary aspergillosis 2 months after combined induction and early rejection therapy for graft dysfunction. Fortunately, the patient recovered with intensive antifungal treatment and lung lobectomy for a necrotic cavity. Antifungal prophylaxis should be considered in cases undergoing intensive induction therapy.

Plasma endocan level and prognosis of immunoglobulin A nephropathy

BACKGROUND: Endocan, previously called endothelial cell–specific molecule-1, is a soluble proteoglycan that is secreted from vascular endothelial cells. Elevated plasma endocan levels were shown to be associated with poor cardiovascular outcomes in patients with chronic kidney disease (CKD). We investigated the clinical relevance of plasma and urine endocan levels in patients with immunoglobulin A nephropathy (IgAN). METHODS: Sixty-four patients with IgAN and 20 healthy controls were enrolled in this study. Plasma and urine endocan levels were measured. Clinical parameters, pathologic grades, and renal outcomes were compared among subgroups with different plasma and urine endocan levels. RESULTS: Both plasma and urine endocan levels were significantly higher in patients with IgAN than in controls. Elevated serum phosphorus and C-reactive protein were independent determinants for plasma endocan, and elevated C-reactive protein was also an independent determinant for urine endocan levels in multivariate analysis. Plasma endocan level was not significantly different across CKD stages, but patients with higher plasma endocan levels showed adverse renal outcome. Urine endocan levels were also elevated in patients with poor renal function. Cox proportional hazard models showed that high plasma endocan was an independent risk factor for CKD progression after adjusting for the well-known predictors of outcome in patients with IgAN. CONCLUSION: This study suggested that plasma endocan might be useful as a prognostic factor in patients with IgAN.

Genetic Variations of Tyrosine Hydroxylase in the Pathogenesis of Hypertension

One of the major pathophysiological features of primary hypertension is an inappropriate activation of the sympathetic nervous system, which is mediated by excessive synthesis and secretion of catecholamine into the blood. Tyrosine hydroxylase (TH), a rate-limiting enzyme in the synthesis of catecholamine, has been highlighted because genetic variations of TH could alter the activity of the sympathetic nervous system activity and subsequently contribute to the pathogenesis of hypertension. Here, we discuss the role of TH as a regulator of sympathetic activity and review several studies that investigated the relationship between genetic variations of TH and hypertension.

Metabolomics Research in Kidney Transplantation / 대한이식학회지

Acute and chronic immune injury, drug toxicity, and cardiovascular complications remain a critical challenge following kidney transplantation. Success from these hurdles is closely associated with the ability to monitor patients and responsively adjust their medication. Metabolic and biochemical profiling (metabolomics) may enable detection of early changes in cell signal transduction regulation and biochemistry with high sensitivity and specificity. However, metabolomics have not been studied extensively in the field of kidney transplantation. This review describes the basic principles of metabolomics, summarizes recent studies, and suggests future perspectives.

Effect of blood pressure and glycemic control on the plasma cell-free DNA in hemodialysis patients

BACKGROUND: The plasma levels of cell-free DNA (cfDNA) are known to be elevated under inflammatory or apoptotic conditions. Increased cfDNA levels have been reported in hemodialysis (HD) patients. The aim of this study was to investigate the clinical significance of cfDNA in HD patients. METHODS: A total of 95 patients on HD were enrolled. We measured their predialysis cfDNA levels using real-time EIF2C1 gene sequence amplification and analyzed its association with certain clinical parameters. RESULTS: The mean plasma cfDNA level in the HD patients was 3,884 +/- 407 GE/mL, and the mean plasma cfDNA level in the control group was 1,420 +/- 121 GE/mL (P < 0.05). Diabetic patients showed higher plasma cfDNA levels compared with nondiabetic patients (P < 0.01). Patients with cardiovascular complications also showed higher plasma cfDNA levels compared with those without cardiovascular complication (P < 0.05). In univariable analysis, the cfDNA level was associated with 3-month mean systolic blood pressure (SBP), white blood cell, serum albumin, creatinine (Cr), normalized protein catabolic rate in HD patients. In diabetic patients, it was significantly correlated with SBP, hemoglobin A1c, and serum albumin. In multivariate analysis, SBP was the independent determinant for the cfDNA level. In diabetic patients, cfDNA level was independently associated with hemoglobin A1c and SBP. CONCLUSIONS: In patients with HD, cfDNA is elevated in diabetic patients and patients with cardiovascular diseases. Uncontrolled hypertension and poor glycemic control are independent determinants for the elevated cfDNA. Our data suggest that cfDNA might be a marker of vascular injury rather than proinflammatory condition in HD patients.

A case of Ramsay Hunt syndrome diagnosed after kidney transplantation

We report the first case of Ramsay Hunt syndrome (RHS) diagnosed after kidney transplantation in Korea. RHS is a disease caused by latent varicella-zoster characterized to involve geniculate ganglion of the seventh cranial nerve. Patients who have undergone kidney transplantation can be easily affected by viral infections because of their immune-compromised status. A 35-year-old man with hypertensive end-stage renal disease underwent kidney transplantation. Two months after surgery, the recipient was diagnosed with RHS and treated with antivirals and steroids. However, after using the antiviral agents for the recommended duration, facial paralysis occurred as a new presentation and he required further treatment. Otalgia and periauricular vesicles improved, but the facial palsy remained.

Prediction of Helicobacter pylori Infection Status via Close Observation of Gastric Mucosal Pattern by Standard Endoscopy

BACKGROUND/AIMS: Common endoscopic findings in stomachs with Helicobacter pylori infections include antral nodularity, thickened gastric folds, and visible submucosal vessels. These findings are suggestive but not diagnostic of H. pylori infection. Magnifying endoscopy can reveal more precisely the abnormal mucosal patterns in an H. pylori-infected stomach; however, it requires more training, expertise, and time. We aimed to establish a new classification for predicting H. pylori-infected stomachs by non-magnifying standard endoscopy alone. MATERIALS AND METHODS: A total of 617 participants who underwent gastroscopy were prospectively enrolled from August 2011 to January 2012. We performed a careful close examination of the corpus at the greater curvature maintaining a distance < or =10 mm between the endoscope tip and the mucosal surface. We classified gastric mucosal patterns into four categories: normal regular arrangement of collecting venules (numerous minute red dots), mosaic-like appearance (type A; swollen areae gastricae or snakeskin appearance), diffuse homogenous redness (type B), and mixed pattern (type C; irregular redness with groove) to predict H. pylori infection status. RESULTS: The frequencies of H. pylori infection in patients with a normal regular arrangement of collecting venules pattern and types A, B, and C patterns were 9.4%, 87.7%, 98.1%, and 90.9%, respectively. The sensitivity, specificity, and positive and negative predictive values of all abnormal patterns for prediction of H. pylori infection were 93.3%, 89.1%, 92.3%, and 90.6%, respectively. The overall accuracy was 91.6%. CONCLUSIONS: Careful close observation of the gastric mucosal pattern with standard endoscopy can predict H. pylori infection status.

Clinicopathological role of kidney injury molecule-1 in immunoglobulin A nephropathy

BACKGROUND: Urinary kidney injury molecule-1 (KIM-1) is an early and sensitive biomarker of acute kidney injury, but it is unclear if it is a biomarker of chronic glomerulonephritis. We evaluated whether urinary KIM-1 levels in patients with immunoglobulin A (IgA) nephropathy can be a marker to reflect clinicopathological severity and predict the prognosis. METHODS: We measured urinary KIM-1 levels in 40 patients (15 males; mean age 36.67+/-12.9 years) with IgA nephropathy and 10 healthy people (5 males; mean age 37.37+/-9.6 years) as controls. The correlation of urinary KIM-1 levels with patients' clinical parameters, histological grades, and follow-up data were analyzed using the modified H. S. Lee grading system and tubulointerstitial change scores. RESULTS: Urinary KIM-1 levels were higher in patients with IgA nephropathy than healthy controls (P=0.001). Univariate and multivariate regression analyses showed that urinary KIM-1 levels had a direct correlation with H. S. Lee grade and tubulointerstitial inflammation (P=0.004 and P=0.011, respectively). CONCLUSION: In patients with IgA nephropathy, urinary KIM-1 has a significant correlation with histopathologic severity.

A Case of Colon Cancer Associated with Streptococcus gallolyticus Subspecies pasteurianus Bacteremia / 대한내과학회지

Streptococcus Gallolyticus subspecies pasteurianus is a biotype II/2 of Streptococcus bovis. Although there is a clear correlation between Streptococcus bovis bacteremia and the risk of developing colon cancer, the relationship between Streptococcus gallolyticus subspecies pasteurianus bacteremia and colon cancer is not clear. We report a 53-year-old female who initially presented with fever and low back pain. Streptococcus gallolyticus subspecies pasteurianus was isolated in blood cultures, so we performed a colonoscopy and discovered colon cancer.