Methylglyoxal Induces Inflammation, Metabolic Modulation and Oxidative Stress in Myoblast Cells.

Uremic sarcopenia is a serious clinical problem associated with physical disability and increased morbidity and mortality. Methylglyoxal (MG) is a highly reactive, dicarbonyl uremic toxin that accumulates in the circulatory system in patients with chronic kidney disease (CKD) and is related to the pathology of uremic sarcopenia. The pathophysiology of uremic sarcopenia is multifactorial; however, the details remain unknown. We investigated the mechanisms of MG-induced muscle atrophy using mouse myoblast C2C12 cells, focusing on intracellular metabolism and mitochondrial injury. We found that one of the causative pathological mechanisms of uremic sarcopenia is metabolic flow change to fatty acid synthesis with MG-induced ATP shortage in myoblasts. Evaluation of cell viability revealed that MG showed toxic effects only in myoblast cells, but not in myotube cells. Expression of mRNA or protein analysis revealed that MG induces muscle atrophy, inflammation, fibrosis, and oxidative stress in myoblast cells. Target metabolomics revealed that MG induces metabolic alterations, such as a reduction in tricarboxylic acid cycle metabolites. In addition, MG induces mitochondrial morphological abnormalities in myoblasts. These changes resulted in the reduction of ATP derived from the mitochondria of myoblast cells. Our results indicate that MG is a pathogenic factor in sarcopenia in CKD.

Tubulointerstitial Nephritis after Using a Sodium-glucose Cotransporter 2 Inhibitor.

We herein report a case of acute kidney injury (AKI) due to tubulointerstitial nephritis (TIN) after starting empagliflozin in a diabetic patient. The patient developed stage 1 AKI with proteinuria and elevated tubulointerstitial markers. A renal biopsy showed acute TIN with lymphocytic infiltration into the interstitium. The patient's renal function improved after discontinuation of empagliflozin and steroid administration. Sodium-glucose cotransporter 2 (SGLT2) inhibitor-induced AKI has been reported, but the underlying mechanism remains unclear, potentially because few patients with SGLT2-inhibitor-induced AKI have undergone a renal biopsy. We report the present case in the hope that it will help clarify the mechanism.

Different clinical impact of hyperuricemia according to etiologies of chronic kidney disease: Gonryo Study.

BACKGROUND: Hyperuricemia is highly prevalent in chronic kidney disease (CKD) patients, but the evidence for a relationship between uric acid (UA) and clinical outcomes in CKD patients is limited and inconsistent. We hypothesized that UA has a different impact on clinical outcomes according to the underlying disease causing CKD. METHODS: This study prospectively investigated the associations between UA and renal and non-renal outcomes according to the underlying disease causing CKD in 2,797 Japanese patients under the care of nephrologists. The patients were categorized into four groups: primary renal disease (n = 1306), hypertensive nephropathy (n = 467), diabetic nephropathy (n = 275), and other nephropathy (n = 749). The renal outcome was defined as end-stage renal disease (ESRD), and the non-renal outcome was defined as a composite endpoint of cardiovascular events (CVEs) and all-cause mortality. RESULTS: During a median 4.8-year follow-up, 359 (12.8%) patients reached the renal outcome, and 260 (9.3%) reached the non-renal outcome. In the all-patient analysis, hyperuricemia was not associated with the risks for renal and non-renal outcomes, but in primary renal disease (PRD) and hypertensive renal disease (HTN) patients, hyperuricemia was significantly associated with non-renal outcomes. Per 1 mg/dl higher UA level, multivariable adjusted hazard ratio was 1.248 (95% CI: 1.003 to 1.553) for PRD, and 1.250 (1.035 to 1.510) for HTN. Allopurinol did not reduce the risks for renal and non-renal outcomes, both in all patients and in the subgroup analysis. CONCLUSIONS: The effect of hyperuricemia on clinical outcomes in CKD patients varies according to the underlying disease causing CKD. Hyperuricemia is an independent risk factor for non-renal outcomes in primary renal disease and hypertensive renal disease patients. Allopurinol did not decrease the risks for renal and non-renal outcomes.

Impact of lower body mass index on risk of all-cause mortality and infection-related death in Japanese chronic kidney disease patients.

BACKGROUND: Several studies have reported that lower body mass index (BMI) is associated with high mortality in patients with chronic kidney disease (CKD). Rate of infection-related death in CKD patients is increasing. However, the relationship between BMI and infection-related death is unclear. METHODS: Overall, 2648 CKD outpatients (estimated glomerular filtration rate < 60 mL/min and/or presenting with proteinuria) under the care of nephrologists were prospectively followed for 5 years. Patients were stratified by quartile of BMI levels. Data on all-cause mortality before progression to end-stage kidney disease (ESKD) and the cause of death were collected. RESULTS: The median follow-up time was 3.9 years (interquartile range, 1.7-5.0); 114 patients died and 308 started renal replacement therapy. The leading causes of death were as follows; cardiovascular (41%), infection-related (21%), and malignancy-related (18%). Advanced age and lower BMI were the significant risk factors for all-cause mortality before progression to ESKD. Advanced age was statistically associated with respective causes of death, while lower BMI was associated with infection-related death only. CKD stage had no significant impact on all-cause or individual mortality. CONCLUSIONS: Low BMI was associated with significant risk of all-cause mortality and infection-related death, which may indicate the novel clinical target to improve CKD outcomes.

Concurrent isolated IgG2-positive membranous nephropathy and malignant B-cell lymphoma.

A recent systematic review showed that hematological malignancy is often complicated by membranous nephropathy (MN). Histologically, the deposition of IgG subclasses other than IgG4 may imply secondary MN, such as malignancy-associated MN (M-MN). We describe a very rare case of concurrent isolated IgG2-positive MN and B-cell lymphoma. An 83-year-old woman was hospitalized at our institute for facial and lower extremity edema persisting for 2 months. Laboratory tests showed urinary protein level of 10.8 g/day, serum albumin level of 1.6 g/dl, and serum creatinine level of 2.34 mg/dl. Soon after diagnosis of nephrotic syndrome, treatment with corticosteroid was initiated, but it proved to be ineffective. Renal biopsy showed isolated IgG2-positive MN with highly infiltrated CD20-positive lymphoid cells in the kidney. Computed tomography revealed systemic lymphadenopathy, and aberrant B-cells with immunoglobulin light chain restriction were detected in peripheral blood and bone marrow, which led to the diagnosis of mature B-cell lymphoma. Although rituximab (375 mg/m2/week) was administered, the patient suddenly died from gastrointestinal bleeding on day 40 of hospitalization. It is, thus, necessary to consider hematological malignancy when a diagnosis of MN is made. Further studies are expected to elucidate the pathogenesis and to help establish the adequate treatment for this rare situation.

Impact of hemoglobin levels on renal and non-renal clinical outcomes differs by chronic kidney disease stages: the Gonryo study.

BACKGROUND: Anemia greatly affects the development of renal and cardiovascular outcomes in chronic kidney disease (CKD) patients. However, the impact based on CKD stage remains unclear. METHODS: We prospectively followed 2,602 Japanese CKD patients under the care of nephrologists. CKD was defined according to cause, estimated glomerular filtration rate <60 mL/min, and/or proteinuria. Patient outcomes [primary end-points: cardiovascular events (CVEs), all-cause mortality, and end-stage kidney disease (ESKD) requiring renal replacement therapy] were assessed in association with basal hemoglobin (Hb) levels (<10, 10-12 and ≥12 g/dL), stratified by CKD stages. RESULTS: During follow-up, 123 patients developed CVEs, 41 died, and 220 progressed to ESKD. For stages G3, G4 and G5, ESKD frequencies were 2.8, 64.4, and 544.8 person-years, while CVEs and death were 25.6, 45.6, and 76.3 person-years, respectively. The combined endpoint rate was significantly higher in patients with Hb <10 versus Hb 10-12 g/dL, but a higher risk for CVEs and death with Hb <10 g/dL was found only in G3 [hazard ratio (HR) 4.49, (95 % confidence interval (95 % CI) 2.06-9.80)]. In contrast, risk for ESKD with Hb <10 g/dL was found only in G4 [HR 3.08 (95 % CI 1.40-6.79)] and G5 [HR 1.43 (95 % CI 1.01-2.05)]. No increased risks with higher Hb levels were found. CONCLUSION: The impact of renal anemia of Hb <10 g/dL on clinical outcomes differed by CKD stage, with a significantly high risk for CVEs and all-cause mortality in G3 and progression to ESKD in G4 and G5.

Changes in circulating biomarkers during a single hemodialysis session.

The hemodialysis (HD) procedure induces an inflammatory response potentially contributing to cardiovascular disease. Here we investigated the acute impact of HD on circulating biomarkers. Circulating biomarkers (small solutes, middle molecular-sized peptides, and proteins) related to inflammation, oxidative stress, and vascular calcification (VC) were measured before and after a single session of HD in 45 clinically stable patients. Concentrations were corrected for ultrafiltration-induced hemoconcentration. Among vascular calcification-related biomarkers, osteoprotegerin and fetuin-A remained unchanged while fibroblast growth factor-23 (FGF23) decreased by -19%. Changes of FGF23 and changes of phosphate correlated (ρ = 0.61, P < 0.001). While C-reactive protein did not change, interleukin-6 (IL-6) increased by 14% and pentraxin 3 (PTX3) increased by 45%. IL-6 and PTX3 appear to be valid biomarkers of the intradialytic inflammatory response. VC-related markers were in general not affected by the single HD session; however, the observed correlation between acute changes of FGF-23 and phosphate during HD warrants further studies.

Postprandial metabolic response to a fat- and carbohydrate-rich meal in patients with chronic kidney disease.

BACKGROUND: While chronic kidney disease (CKD) is associated with dysmetabolism including a marked insulin resistance, the postprandial response has not comprehensively been studied in CKD patients. METHODS: We conducted an intervention study comparing fasting and postprandial circulating biomarkers of glucose and lipid homeostasis, incretins, anabolic hormones, inflammation and oxidative stress in nine prevalent non-diabetic hemodialysis (HD) patients and 10 matched controls assessed after a standardized meal consisting of 75 g of milk fat, 80 g of carbohydrates and 6 g of proteins/m(2) of body surface area. RESULTS: Glucose and triglyceride increased in a similar manner following the meal, while insulin, C-peptide and glucose-dependent insulinotropic polypeptide increased more in HD patients. HDL and LDL cholesterol decreased slightly with no significant difference between the groups. The elevated baseline growth hormone (GH) in patients dropped, resulting in comparable levels in both groups 240 min after the meal; however, there was no change in insulin-like growth factor 1 (IGF-1) levels. No marked changes of interleukin 6 and tumor necrosis factor-α were observed in either group. An elevation in the DNA oxidative product 8-hydroxydeoxyguanosine was observed in HD patients. CONCLUSIONS: The postprandial state in CKD is characterized by impaired insulin sensitivity with increased incretin levels, along with GH/IGF-1 axis uncoupling and an elevation in an oxidative stress marker.

Physiological significance of reactive cysteine residues of Keap1 in determining Nrf2 activity.

Keap1 and Cul3 constitute a unique ubiquitin E3 ligase that degrades Nrf2, a key activator of cytoprotective genes. Upon exposure to oxidants/electrophiles, the enzymatic activity of this ligase complex is inhibited and the complex fails to degrade Nrf2, resulting in the transcriptional activation of Nrf2 target genes. Keap1 possesses several reactive cysteine residues that covalently bond with electrophiles in vitro. To clarify the functional significance of each Keap1 cysteine residue under physiological conditions, we established a transgenic complementation rescue model. The transgenic expression of mutant Keap1(C273A) and/or Keap1(C288A) protein in Keap1 null mice failed to reverse constitutive Nrf2 activation, indicating that cysteine residues at positions 273 and 288 are essential for Keap1 to repress Nrf2 activity in vivo. In contrast, Keap1(C151S) retained repressor activity and mice expressing this molecule were viable. Mouse embryonic fibroblasts from Keap1(C151S) transgenic mice displayed decreased expression of Nrf2 target genes both before and after an electrophilic challenge, suggesting that Cys151 is important in facilitating Nrf2 activation. These results demonstrate critical roles of the cysteine residues in vivo in maintaining Keap1 function, such that Nrf2 is repressed under quiescent conditions and active in response to oxidants/electrophiles.

Molecular basis distinguishing the DNA binding profile of Nrf2-Maf heterodimer from that of Maf homodimer.

Nrf2-small Maf heterodimer activates the transcription of many cytoprotective genes through the antioxidant response element and serves as a key factor in xenobiotic and oxidative stress responses. Our surface plasmon resonance-microarray binding analysis revealed that both Nrf2-MafG heterodimer and MafG homodimer bind to the consensus Maf recognition element with high affinity but bind differentially to the suboptimal binding sequences degenerated from the consensus. We examined the molecular basis distinguishing the binding profile of Nrf2-MafG heterodimer from that of MafG homodimer and found that the Ala-502 residue in the basic region of Nrf2 is a critical determinant of its binding specificity. In Maf proteins, a tyrosine resides in the position corresponding to Ala-502 in Nrf2. We prepared a mutant Nrf2 molecule in which Ala-502 was replaced with tyrosine. In surface plasmon resonance-microarray analysis, heterodimer of Nrf2(A502Y) and MafG displayed a binding specificity similar to that of MafG homodimer. The target genes activated by mutant Nrf2(A502Y)-small Maf heterodimer were largely different, albeit with some overlap, from those activated by wild-type Nrf2-small Maf, indicating that the array of target genes regulated by Nrf2-small Maf heterodimer differs substantially from that regulated by Maf homodimer in vivo. These results suggest that the distinct DNA binding profile of Nrf2-Maf heterodimer is biologically significant for Nrf2 to function as a key regulator of cytoprotective genes. Our contention is supported that the differential DNA binding specificity between Maf homodimers and Nrf2-Maf heterodimers establishes the differential gene regulation by these dimer-forming transcription factors.