The Roles and Associated Mechanisms of Adipokines in Development of Metabolic Syndrome.

Metabolic syndrome is a cluster of metabolic indicators that increase the risk of diabetes and cardiovascular diseases. Visceral obesity and factors derived from altered adipose tissue, adipokines, play critical roles in the development of metabolic syndrome. Although the adipokines leptin and adiponectin improve insulin sensitivity, others contribute to the development of glucose intolerance, including visfatin, fetuin-A, resistin, and plasminogen activator inhibitor-1 (PAI-1). Leptin and adiponectin increase fatty acid oxidation, prevent foam cell formation, and improve lipid metabolism, while visfatin, fetuin-A, PAI-1, and resistin have pro-atherogenic properties. In this review, we briefly summarize the role of various adipokines in the development of metabolic syndrome, focusing on glucose homeostasis and lipid metabolism.

Long-term Prognosis of Anti-Neutrophil Cytoplasmic Antibody-Negative Renal Vasculitis: Cohort Study in Korea.

Few studies have reported on the long-term prognosis of anti-neutrophil cytoplasmic antibody (ANCA)-negative renal vasculitis. Between April 2003 and December 2013, 48 patients were diagnosed with renal vasculitis. Their ANCA status was tested using indirect immunofluorescence and enzyme-linked immunosorbent assays. During a median (interquartile range) follow-up duration of 933.5 (257.5-2,079.0) days, 41.7% of patients progressed to end stage renal disease (ESRD) and 43.8% died from any cause. Of 48 patients, 6 and 42 were ANCA-negative and positive, respectively. The rate of ESRD within 3 months was higher in ANCA-negative patients than in ANCA-positive patients (P = 0.038). In Kaplan-Meier survival analysis, ANCA-negative patients showed shorter renal survival than did ANCA-positive patients (log-rank P = 0.033). In univariate Cox-proportional hazard regression analysis, ANCA-negative patients showed increased risk of ESRD, with a hazard ratio 3.190 (95% confidence interval, 1.028-9.895, P = 0.045). However, the effect of ANCA status on renal survival was not statistically significant in multivariate analysis. Finally, ANCA status did not significantly affect patient survival. In conclusion, long-term patient and renal survival of ANCA-negative renal vasculitis patients did not differ from those of ANCA-positive renal vasculitis patients. Therefore, different treatment strategy depending on ANCA status might be unnecessary.

Bilirubin activates transcription of HIF-1α in human proximal tubular cells cultured in the physiologic oxygen content.

The expression of hypoxia-inducible factor (HIF) is influenced by reactive oxygen species (ROS). Effect of bilirubin on HIF-1 expression in proximal tubular cells was investigated under physiological oxygen concentration, which is relative hypoxic condition mimicking oxygen content in the medulla of renal tissue. The human kidney (HK2) cells were cultured in 5% oxygen with or without bilirubin. HIF-1α protein expression was increased by bilirubin treatment at 0.01-0.2 mg/dL concentration. The messenger RNA expression of HIF-1α was increased by 1.69±0.05 folds in the cells cultured with 0.1 mg/dL bilirubin, compared to the control cells. The inhibitors of PI3K/mTOR, PI3K/AKT, and ERK 1/2 pathways did not attenuate increased HIF-1α expression by bilirubin. HIF-1α expression decreased by 10 µM exogenous hydrogen peroxide (H2O2); scavenger of ROS with or without bilirubin in the HK2 cells increased HIF-1α concentration more than that in the cells without bilirubin. Exogenous H2O2 decreased the phosphorylation of P70S6 kinase, which was completely reversed by bilirubin treatment. Knockdown of NOX4 gene by small interfering RNA (siRNA) increased HIF-1α mRNA expression. In coonclusion, bilirubin enhances HIF-1α transcription as well as the up-regulation of HIF-1α protein translation through the attenuation of ROS and subunits of NADPH oxidase.

Effect of bilirubin on triglyceride synthesis in streptozotocin-induced diabetic nephropathy.

We aimed to elucidate the effect of bilirubin on dyslipidemia and nephropathy in a diabetes mellitus (DM) type I animal model. Sprague-Dawley rats were separated into control, DM, and bilirubin-treated DM (Bil) groups. The Bil group was injected intraperitoneally with 60 mg/kg bilirubin 3 times per week and hepatoma cells were cultured with bilirubin at a concentration of 0.3 mg/dL. The Bil group showed lower serum creatinine levels 5 weeks after diabetes onset. Bilirubin treatment also decreased the amount of mesangial matrix, lowered the expression of renal collagen IV and transforming growth factor (TGF)-ß1, and reduced the level of apoptosis in the kidney, compared to the DM group. These changes were accompanied by decreased tissue levels of hydrogen superoxide and NADPH oxidase subunit proteins. Bilirubin decreased serum total cholesterol, high-density lipoprotein cholesterol (HDL-C), free fatty acids, and triglycerides (TGs), as well as the TG content in the liver tissues. Bilirubin suppressed protein expression of LXRα, SREBP-1, SCD-1, and FAS, factors involved in TG synthesis that were elevated in the livers of DM rats and hepatoma cells under high-glucose conditions. In conclusion, bilirubin attenuates renal dysfunction and dyslipidemia in diabetes by suppressing LXRα and SREBP-1 expression and oxidative stress.

Urinary sodium excretion has positive correlation with activation of urinary renin angiotensin system and reactive oxygen species in hypertensive chronic kidney disease.

It is not well described the pathophysiology of renal injuries caused by a high salt intake in humans. The authors analyzed the relationship between the 24-hr urine sodium-to-creatinine ratio (24HUna/cr) and renal injury parameters such as urine angiotensinogen (uAGT/cr), monocyte chemoattractant peptide-1 (uMCP1/cr), and malondialdehyde-to-creatinine ratio (uMDA/cr) by using the data derived from 226 hypertensive chronic kidney disease patients. At baseline, the 24HUna/cr group or levels had a positive correlation with uAGT/cr and uMDA/cr adjusted for related factors (P<0.001 for each analysis). When we estimated uAGT/cr in the 24HUna/cr groups by ANCOVA, the uAGT/cr in patients with ≥200 mEq/g cr was higher than in patients with <100 mEq/g cr (708 [95% CI, 448-967] vs. 334 [95% CI, 184-483] pg/mg cr, P=0.014). Similarly, uMDA/cr was estimated as 0.17 (95% CI, 0.14-0.21) pM/mg cr in patients with <100 mEq/g cr and 0.27 (95% CI, 0.20-0.33) pM/mg cr in patients with ≥200 mEq/g cr (P=0.016). During the 16-week follow-up period, an increase in urinary sodium excretion predicted an increase in urinary angiotensinogen excretion. In conclusion, high salt intake increases renal renin-angiotensin-system (RAS) activation, primarily, and directly or indirectly affects the production of reactive oxygen species through renal RAS activation.

Association between circulating ECM-associated molecules and cardiovascular outcomes in hemodialysis patients: a multicenter prospective cohort study.

Hemodialysis patients are susceptible to cardiovascular remodeling, which increases the risk of cardiovascular morbidity and mortality. Circulating extracellular matrix (ECM)-associated molecules increase during cardiovascular remodeling and can be potential biomarkers of adverse cardiovascular outcomes. However, their clinical significance in patients undergoing hemodialysis remain unclear. This study aimed to elucidate the association between circulating ECM-associated molecules and cardiovascular outcomes in patients undergoing hemodialysis. To this end, we measured levels of plasma matrix metalloproteinase (MMP)-2, MMP-9, tenascin-C, and thrombospondin-2 in 372 patients with hemodialysis. Plasma MMP-2 levels were significantly higher in patients with future cardiovascular events than in those without future cardiovascular events (P = 0.004). All measured molecules had significant correlations with amino-terminal pro-brain natriuretic peptide levels, but the correlation coefficient was the strongest for plasma MMP-2 (rho = 0.317, P < 0.001). High plasma MMP-2 levels were predictive of left ventricular (LV) diastolic dysfunction (adjusted odds ratio per a standard deviation increase = 1.48, 95% confidence interval [CI] = 1.05-2.08) and were independently associated with an increased risk of composite cardiovascular events (adjusted hazard ratio per a standard deviation increase = 1.30, 95% CI = 1.04-1.63). In conclusion, high plasma MMP-2 levels are associated with LV diastolic dysfunction and an increased risk of adverse cardiovascular outcomes in hemodialysis patients.

Dipeptidyl peptidase IV inhibitor attenuates kidney injury in rat remnant kidney.

BACKGROUND: The 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. METHODS: Rats 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. RESULTS: The 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. CONCLUSIONS: In 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.

The Effect of DNA Methylation in the Development and Progression of Chronic Kidney Disease in the General Population: An Epigenome-Wide Association Study Using the Korean Genome and Epidemiology Study Database.

BACKGROUND: Although knowledge of the genetic factors influencing kidney disease is increasing, epigenetic profiles, which are associated with chronic kidney disease (CKD), have not been fully elucidated. We sought to identify the DNA methylation status of CpG sites associated with reduced kidney function and examine whether the identified CpG sites are associated with CKD development. METHOD: We analyzed DNA methylation patterns of 440 participants in the Korean Genome and Epidemiology Study (KoGES) with estimated glomerular filtration rates (eGFRs) ≥ 60 mL/min/1.73 m2 at baseline. CKD development was defined as a decrease in the eGFR of <60 at any time during an 8-year follow-up period ("CKD prediction" analysis). In addition, among the 440 participants, 49 participants who underwent a second methylation profiling were assessed for an association between a decline in kidney function and changes in the degree of methylation of CpG sites during the 8 years ("kidney function slope" analysis). RESULTS: In the CKD prediction analysis, methylation profiles of a total of 403,129 CpG sites were evaluated at baseline in 440 participants, and increased and decreased methylation of 268 and 189 CpG sites, respectively, were significantly correlated with the development of CKD in multivariable logistic regression. During kidney function slope analysis using follow-up methylation profiles of 49 participants, the percent methylation changes in 913 CpG sites showed a linear relationship with the percent change in eGFR during 8 years. During functional enrichment analyses for significant CpG sites found in the CKD prediction and kidney function slope analyses, we found that those CpG sites represented MAPK, PI3K/Akt, and Rap1 pathways. In addition, three CpG sites from three genes, NPHS2, CHCHD4, and AHR, were found to be significant in the CKD prediction analysis and related to a decline in kidney function. CONCLUSION: It is suggested that DNA methylation on specific genes is associated with the development of CKD and the deterioration of kidney function.

Plasma Interleukin-6 Level Predicts the Risk of Arteriovenous Fistula Dysfunction in Patients Undergoing Maintenance Hemodialysis.

Systemic inflammation has been proposed as a relevant factor of vascular remodeling and dysfunction. We aimed to identify circulating inflammatory biomarkers that could predict future arteriovenous fistula (AVF) dysfunction in patients undergoing hemodialysis. A total of 282 hemodialysis patients were enrolled in this prospective multicenter cohort study. Plasma cytokine levels were measured at the time of data collection. The primary outcome was the occurrence of AVF stenosis and/or thrombosis requiring percutaneous transluminal angioplasty or surgery within the first year of enrollment. AVF dysfunction occurred in 38 (13.5%) patients during the study period. Plasma interleukin-6 (IL-6) levels were significantly higher in patients with AVF dysfunction than those without. Diabetes mellitus, low systolic blood pressure, and statin use were also associated with AVF dysfunction. The cumulative event rate of AVF dysfunction was the highest in IL-6 tertile 3 (p = 0.05), and patients in tertile 3 were independently associated with an increased risk of AVF dysfunction after multivariable adjustments (adjusted hazard ratio = 3.06, p = 0.015). In conclusion, circulating IL-6 levels are positively associated with the occurrence of incident AVF dysfunction in hemodialysis patients. Our data suggest that IL-6 may help clinicians identify those at high risk of impending AVF failure.

The low number of red blood cells is an important risk factor for all-cause mortality in the general population.

Patients with advanced chronic kidney disease (CKD) show decreased hemoglobin levels. We aimed to verify the changes of red blood cell (RBC) number according to glomerular filtration rate (GFR) levels and its influence on the clinical outcome. With the data from routine health checkups of 114,496 adults, we grouped the subjects according to quartile levels of RBC number in each gender. Mortality data were from the National Statistical Office. RBC number was increased with decreasing GFR and/or the presence of a component of metabolic syndrome (MS) in subjects with GFR ≥ 50 ml/min/1.73 m². The estimated mean RBC number of subjects with GFR 89-50 ml/min/1.73 m² was higher compared to those with GFR ≥ 100 ml/min/1.73 m² by ANCOVA. In men, the death rate was the highest in the 1st quartile group (1Q) of RBC number (1.22%), followed by the 2nd quartile group (2Q, 0.42%), the 3rd quartile group (3Q, 0.39%), and the 4th quartile group (4Q, 0.29%) (p < 0.001). The hazard ratio (HR) of death in 2Q, 3Q and 4Q was 0.446, 0.580, and 0.440, respectively, compared to 1Q (p < 0.001). Among men in 1Q group, subjects with hemoglobin < 14.0 g/dL showed higher mortality rate than those with hemoglobin 14.0-14.9 g/dL or ≥ 15.0 g/dL (2.3% : 0.8% : 1.1%, respectively, p < 0.001). In conclusion, the RBC number was increased according to declines of GFR in the range of GFR ≥ 50 ml/min/1.73 m² and was an important risk factor for mortality.

Urine and Serum Electrolytes and Biochemical Values Associated with Osteoporosis in Premenopausal and Postmenopausal Women: A Longitudinal and Cross-Sectional Study Using Korean Genome and Epidemiology Study (KoGES) Cohort.

Osteoporosis is a major public health concern, especially in women. This study aims to identify early biomarkers from biochemical measurements of serum and urine for recognizing the development of osteoporosis and osteopenia in premenopausal and postmenopausal women. From the Korean Genome and Epidemiology Study (KoGES) cohort, longitudinal study participants with normal bone density were enrolled and assessed for the association of baseline clinical and biochemical factors with osteoporosis development over 4 years. In addition, a cross-sectional study between normal bone density and osteopenia/osteoporosis was conducted to validate the risk factors found in the longitudinal cohort. Of the 5272 female participants in the KoGES cohort, 813 women (501 premenopausal and 312 menopausal) who had normal bone density at baseline were included in the longitudinal study. During the 4 years of follow-up, 64 patients developed osteoporosis and 354 developed osteopenia. In a multivariate logistic regression analysis, serum calcium and urine uric acid levels were significantly associated with elevated osteoporosis risk in premenopausal and postmenopausal women, respectively (risk of osteoporosis by serum calcium levels in premenopausal women: 4.03 (1.09-14.93), p = 0.037; risk of osteoporosis by urine uric acid levels in postmenopausal women: 24.08 (1.79-323.69), p = 0.016). For the cross-sectional study, serum and urine parameters were compared between women with osteopenia or osteoporosis at baseline and those with normal bone density. Urine uric acid levels were found to be significantly higher in both premenopausal and postmenopausal women with bone loss than in women with normal bone density (p < 0.001 and p = 0.004, respectively). Uric acid level in urine may be an early marker for the development of osteoporosis in women, especially after menopause.

Glomerular Immune Deposits Are Predictive of Poor Long-Term Outcome in Patients with Adult Biopsy-Proven Minimal Change Disease: A Cohort Study in Korea.

BACKGROUND AND OBJECTIVES: There has been little published information on risk factors for poor long-term outcome in adult biopsy-proven minimal change disease (MCD). METHODS: Data from sixty-three adult, biopsy-proven primary MCD patients treated at a tertiary university hospital between 2003 and 2013 were analyzed. Baseline clinical and pathologic factors were assessed for the associations with composite outcome of creatinine doubling, end stage renal disease, or all-cause mortality. RESULTS: During a median (interquartile) 5.0 (2.8-5.0) years, the composite outcome occurred in 11.1% (7/63) of patients. The rate of glomerular immune deposits was 23.8% (15/63). Patients with glomerular immune deposits showed a significantly lower urine protein creatinine ratio than those without deposits (P = 0.033). The rate of non-responders was significantly higher in patients with glomerular immune deposits than in those without deposits (P = 0.033). In patients with deposits, 26.7% (4/15) developed the composite outcome, while only 6.3% (3/48) developed the composite outcome among those without deposits (P = 0.049). In multivariate Cox proportional hazards regression analysis, the presence of glomerular immune deposits was the only factor associated with development of the composite outcome (hazard ratio: 2.310, 95% confidence interval: 1.031-98.579, P = 0.047). CONCLUSION: Glomerular immune deposits were associated with increased risk of a composite outcome in adult MCD patients. The higher rate of non-responders in patients with deposits might be related to the poor outcome. Future study is needed.

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.