Shin Young Ahn

Dipeptidyl peptidase IV inhibitor attenuates kidney injury in rat remnant kidney

BackgroundThe inhibition of dipeptidyl peptidase (DPP) IV shows protective effects on tissue injury of the heart, lung, and kidney. Forkhead box O (FoxO) transcriptional factors regulate cellular differentiation, growth, survival, the cell cycle, metabolism, and oxidative stress. The aims of this study were to investigate whether the DPP IV inhibitor sitagliptin could attenuate kidney injury and to evaluate the status of FoxO3a signaling in the rat remnant kidney model.MethodsRats were received two-step surgery of 5/6 renal mass reduction and fed on an oral dose of 200 mg/kg/day sitagliptin for 8 weeks. Before and after the administration of sitagliptin, physiologic parameters were measured. After 8 weeks of treatment, the kidneys were harvested.ResultsThe sitagliptin treatment attenuated renal dysfunction. A histological evaluation revealed that glomerulosclerosis and tubulointerstitial injury were significantly decreased by sitagliptin. Sitagliptin decreased DPP IV activity and increased the renal expression of glucagon-like peptide-1 receptor (GLP-1R). The subtotal nephrectomy led to the activation of phosphatidylinositol 3-kinase (PI3K)-Akt and FoxO3a phosphorylation, whereas sitagliptin treatment reversed these changes, resulting in PI3K-Akt pathway inactivation and FoxO3a dephosphorylation. The renal expression of catalase was increased and the phosphorylation of c-Jun N-terminal kinase (JNK) was decreased by sitagliptin. Sitagliptin treatment reduced apoptosis by decreasing cleaved caspase-3 and −9 and Bax levels and decreased macrophage infiltration.ConclusionsIn rat remnant kidneys, DPP IV inhibitor attenuated renal dysfunction and structural damage. A reduction of apoptosis, inflammation and an increase of antioxidant could be suggested as a renoprotective mechanism together with the activation of FoxO3a signaling. Therefore, DPP IV inhibitors might provide a promising approach for treating CKD, but their application in clinical practice remains to be investigated.

Hypoxia-Inducible Factor Activation Protects the Kidney from Gentamicin-Induced Acute Injury

Gentamicin nephrotoxicity is one of the most common causes of acute kidney injury (AKI). Hypoxia-inducible factor (HIF) is effective in protecting the kidney from ischemic and toxic injury. Increased expression of HIF-1α mRNA has been reported in rats with gentamicin-induced renal injury. We hypothesizd that we could study the role of HIF in gentamicin-induced AKI by modulating HIF activity. In this study, we investigated whether HIF activation had protective effects on gentamicin-induced renal tubule cell injury. Gentamicin-induced AKI was established in male Sprague-Dawley rats. Cobalt was continuously infused into the rats to activate HIF. HK-2 cells were pre-treated with cobalt or dimethyloxalylglycine (DMOG) to activate HIF and were then exposed to gentamicin. Cobalt or DMOG significantly increased HIF-1α expression in rat kidneys and HK-2 cells. In HK-2 cells, HIF inhibited gentamicin-induced reactive oxygen species (ROS) formation. HIF also protected these cells from apoptosis by reducing caspase-3 activity and the amount of cleaved caspase-3, and -9 proteins. Increased expression of HIF-1α reduced the number of gentamicin-induced apoptotic cells in rat kidneys and HK-2 cells. HIF activation improved the creatinine clearance and proteinuria in gentamicin-induced AKI. HIF activation also ameliorated the extent of histologic injury and reduced macrophage infiltration into the tubulointerstitium. In gentamicin-induced AKI, the activation of HIF by cobalt or DMOG attenuated renal dysfunction, proteinuria, and structural damage through a reduction of oxidative stress, inflammation, and apoptosis in renal tubular epithelial cells.

The Occurrence of Warfarin-Related Nephropathy and Effects on Renal and Patient Outcomes in Korean Patients

Background Warfarin-related nephropathy (WRN) is a recently described disease entity, in which excessive warfarinization (international normalized ratio (INR) >3.0) causes acute kidney injury. Previous reports regarding WRN included few Asian patients who might have differed from the western WRN patients in terms of genetic and environmental factors. Methods During the period of March 2003 to December 2011, the data about a total of 1297 patients who had serum creatinine (sCr) level measured within 1 week after INR >3.0 and within 6 months before INR >3.0 was analyzed through the retrospective review of electronic medical records of a single tertiary hospital in Korea. Result WRN developed in 19.3% of patients having excessive warfarinization. The incidence was higher in the chronic kidney disease (CKD) group than the non-CKD group. The risk of WRN increased as the basal serum albumin level decreased and was strongly associated with highest quartile serum AST level at post INR elevation and the presence of congestive heart failure. But the presence of atrial fibrillation was protective against the development of WRN. Neither the presence of CKD nor basal estimated glomerular filtration rate (eGFR) was an independent risk factor for WRN. Despite no difference in the basal sCr level, the sCr level was higher in patients with WRN than those without WRN after follow-up. The mortality rates were also higher in patients with WRN. Conclusions WRN developed in 19.3% of patients having excessive warfarinization. A lower basal serum albumin, highest quartile serum AST level at post INR elevation, and congestive heart failure were associated with the occurrence of WRN. The development of WRN adversely affected renal and patient outcomes.

Incident Chronic Kidney Disease and Newly Developed Complications Related to Renal Dysfunction in an Elderly Population during 5 Years: A Community-Based Elderly Population Cohort Study

Background Few studies have evaluated the association between incident chronic kidney disease (CKD) and related complications, especially in elderly population. We attempted to verify the association between GFR and concurrent CKD complications and elucidate the temporal relationship between incident CKD and new CKD complications in a community-based prospective elderly cohort. Method We analyzed the available data from 984 participants in the Korean Longitudinal Study on Health and Aging. Participants were categorized into 6 groups according to eGFR at baseline examination (≥90, 75–89, 60–74, 45–59, 30–44, and <30 ml/min/1.73 m2). Result The mean age of study population was 76 ± 9.1 years and mean eGFR was 72.3 ± 17.0 ml/min/1.73 m2. Compared to eGFR group 1, the odds ratio (OR) for hypertension was 2.363 (95% CI, 1.299-4.298) in group 4, 5.191 (2.074-12.995) in group 5, and 13.675 (1.611-115.806) in group 6; for anemia, 7.842 (2.265-27.153) in group 5 and 13.019 (2.920-58.047) in group 6; for acidosis, 69.580 (6.770-715.147) in group 6; and for hyperkalemia, 19.177 (1.798-204.474) in group 6. Over a 5-year observational period, CKD developed in 34 (9.6%) among 354 participants with GFR ≥ 60 ml/min/1.73 m2 at basal examination. The estimated mean number of new complications according to analysis of co-variance was 0.52 (95% CI, 0.35–0.68) in subjects with incident CKD and 0.24 (0.19–0.29) in subjects without CKD (p = 0.002). Subjects with incident CKD had a 2.792-fold higher risk of developing new CKD complications. A GFR level of 52.4 ml/min/1.73 m2 (p = 0.032) predicted the development of a new CKD complication with a 90% sensitivity. Conclusion In an elderly prospective cohort, CKD diagnosed by current criteria is related to an increase in the number of concurrent CKD complications and the development of new CKD complications.

Outcomes of Predialysis Nephrology Care in Elderly Patients Beginning to Undergo Dialysis

Background The proportion of elderly patients beginning to undergo dialysis is increasing globally. Whether early referral (ER) of elderly patients is associated with favorable outcomes remains under debate. We investigated the influence of referral timing on the mortality of elderly patients. Methods We retrospectively assessed mortality in 820 patients aged ≥70 years with end-stage renal disease (ESRD) who initiated hemodialysis at a tertiary university hospital between 2000 and 2010. Mortality data was obtained from the time of dialysis initiation until December 2010. We assigned patients to one of two groups according to the time of their first encounters with nephrologists: ER (≥ 3 months) and late referral (LR; < 3 months). Results During a mean follow-up period of 25.1 months, the ER group showed a 24% reduced risk of long-term mortality relative to the LR group (HR = 0.760, P = 0.009). Rate of reduction in 90-day mortality for ER patients was 58% (HR = 0.422, P=0.012). However, the statistical significance of the difference in mortality rates between ER and LR group was not observed across age groups after 90 days. Old age, LR, central venous catheter, high white blood cell count and corrected Ca level, and lower levels of albumin, creatinine, hemoglobin, and sodium were significantly associated with increased risk of mortality. Conclusions Timely referral was also associated with reduced mortality in elderly ESRD patients who initiated hemodialysis. In particular, the initial 90-day mortality reduction in ER patients contributed to mortality differences during the follow-up period.

Estimating 24-Hour Urine Sodium Level with Spot Urine Sodium and Creatinine

The 24-hr urine sodium excretion level was estimated based on the spot urine sodium, and the efficacy of the formula was validated to determine the status of low salt intake <100 mEq Na/day. The 24-hr urine samples were collected from 400 patients. The 24-hr urine creatinine level was estimated with the use of three formulas: a newly derived Korean equation (E24UCR_K), and Tanaka (E24UCR_T) and Cockcroft-Gault (E24UCR_CG) equations. The correlation coefficients between the estimated and measured 24-hr urine creatinine for these three equations were 0.863, 0.846, and 0.896, respectively (All P<0.001). After estimating the 24-hr urine sodium levels, the correlation coefficients between the estimated and measured 24-hr urine sodium levels were 0.466, 0.490, and 0.516, respectively (All P<0.001). The sensitivity of three formulas to estimate the measured 24-hr urine sodium≥100 mEq/day using the estimated amount≥100 mEq/day was 84.3%, 87.6%, and 84.8%, respectively. In conclusion, the three equations used to estimate the 24-hr urine sodium content were useful to determine the status of low salt intake. Graphical Abstract

Decreased estimated glomerular filtration rate is not directly related to increased insulin resistance

AIMS Insulin resistance (IR) is associated with chronic kidney disease (CKD) but little is known about the possible causal relationship and differences in IR based on estimated glomerular filtration rate (eGFR) groups. The objective of this study was to identify a possible association between the level of renal dysfunction and IR. METHODS We measured eGFR and calculated the Homeostasis Model Assessment IR (HOMA-IR) index value. The study included 17,157 subjects ≥20years old without diabetes who underwent voluntary health check-ups. We classified subjects into four groups according to eGFR: Group 1, eGFR ≥90; Group 2, eGFR 75-89; Group 3, eGFR 60-74; Group 4, eGFR <60mL/min/1.73m(2). RESULTS While HOMA-IR index values were higher in lower eGFR groups compared with higher eGFR groups (P<0.001), multivariate analysis revealed that the relationship was not significant. HOMA-IR index values in eGFR groups estimated by analysis of covariance (ANCOVA) adjusted for related factors were not significantly higher in lower eGFR groups. When we stratified the subjects by the number of MS components, there were no meaningful differences in HOMA-IR values according to eGFR group. The frequency of high HOMA-IR index (≥2.5) among eGFR groups stratified with number of MS components was not significantly different. CONCLUSION Decreased kidney function is not associated with IR.

Risk Factors for Acute Kidney Injury and In-Hospital Mortality in Patients Receiving Extracorporeal Membrane Oxygenation.

Background and Objectives Although acute kidney injury (AKI) is the most frequent complication in patients receiving extracorporeal membrane oxygenation (ECMO), few studies have been conducted on the risk factors of AKI. We performed this study to identify the risk factors of AKI associated with in-hospital mortality. Methods Data from 322 adult patients receiving ECMO were analyzed. AKI and its stages were defined according to Kidney Disease Improving Global Outcomes (KDIGO) classifications. Variables within 24 h before ECMO insertion were collected and analyzed for the associations with AKI and in-hospital mortality. Results Stage 3 AKI was associated with in-hospital mortality, with a hazard ratio (HR) (95% CI) of 2.690 (1.472–4.915) compared to non-AKI (p = 0.001). The simplified acute physiology score 2 (SAPS2) and serum sodium level were also associated with in-hospital mortality, with HRs of 1.02 (1.004–1.035) per 1 score increase (p = 0.01) and 1.042 (1.014–1.070) per 1 mmol/L increase (p = 0.003). The initial pump speed of ECMO was significantly related to in-hospital mortality with a HR of 1.333 (1.020–1.742) per 1,000 rpm increase (p = 0.04). The pump speed was also associated with AKI (p = 0.02) and stage 3 AKI (p = 0.03) with ORs (95% CI) of 2.018 (1.129–3.609) and 1.576 (1.058–2.348), respectively. We also found that the red cell distribution width (RDW) above 14.1% was significantly related to stage 3 AKI. Conclusion The initial pump speed of ECMO was a significant risk factor of in-hospital mortality and AKI in patients receiving ECMO. The RDW was a risk factor of stage 3 AKI.

Effects of acute kidney injury and chronic kidney disease on long-term mortality after coronary artery bypass grafting

BACKGROUND Both acute kidney injury (AKI) and chronic kidney disease (CKD) are important issues in patients undergoing coronary artery bypass grafting (CABG), particularly with regard to mortality. However, their synergistic or discrete effects on long-term mortality remain unresolved. METHODS A total of 1,899 patients undergoing CABG were retrospectively analyzed. The adjusted hazard ratios for all-cause mortality were calculated after stratifying the timeframes. To evaluate the synergistic effects between AKI and CKD, the relative excess risk due to interaction was applied. RESULTS The presence of AKI, CKD, or both increased the hazard ratios for mortality, compared with the absence of both: AKI alone, 1.84 (1.464-2.319); CKD alone, 2.46 (1.735-3.478); and AKI and CKD together, 3.21 (2.301-4.488). However, the relationships with mortality were different between AKI and CKD, according to the timeframes: AKI primarily affected early mortality, particularly within 3 years, whereas CKD had a relatively constant effect on both the early and late periods. When the parameters from the relative excess risk due to interaction were obtained, there was a synergistic additive effect on early mortality between AKI and CKD. CONCLUSIONS The relationships with mortality after CABG were different between AKI and CKD. However, their effects were not exclusive but synergistic.

Relationship between changes in body fat and a decline of renal function in the elderly.

Obesity is a risk factor for chronic kidney disease, and its prevalence among the elderly is increasing. We investigated the effects of changes in body fat percentage (BFP) on the longitudinal changes in the estimated glomerular filtration rate (eGFR) in the elderly. This prospective cohort study included 390 participants aged >65 years who underwent bioelectrical impedance analysis at baseline and follow-up as a part of the Korean Longitudinal Study on Health and Aging. After a median follow-up period of 5.3 years, BFP was significantly higher than that at the start point (P<0.05). Participants who had the largest increase in BFP had the highest BMI and waist circumference (WC) (P<0.001). The highest tertile had the highest white blood cell count and erythrocyte sedimentation rate, incidence of rapid progression, and decline in eGFR >25% (P≤0.017, P = 0.025, P = 0.005, respectively). The lowest tertile had the lowest triglyceride and highest high-density lipoprotein levels (P<0.05). The adjusted decline rate in eGFR was correlated with a change in BFP (P = 0.039), but not with that in BMI or WC. The highest tertile had a 4.875-fold increase in the risk for rapid progression to a decline in eGFR (95% CI: 1.366–17.397) and a 4.931-fold decrease in the risk to a decline in eGFR>25% (95% CI: 1.617–15.037), when compared with the lowest tertile. In subgroup analysis, the incidence of renal outcomes was significantly increased according to the increase in BFP in patients with lower eGFR (P≤0.010). A change in BFP may be associated with inflammation and dyslipidemia development, and longitudinal changes in body fat are related to a decrease in eGFR in the elderly.