Critical role of Interleukin 21 and T follicular helper cells in hypertension and vascular dysfunction.

T and B cells have been implicated in hypertension, but the mechanisms by which they produce a coordinated response is unknown. T follicular helper (Tfh) cells that produce interleukin 21 (IL21) promote germinal center (GC) B cell responses leading to immunoglobulin (Ig) production. Here we investigate the role of IL21 and Tfh cells in hypertension. In response to angiotensin (Ang) II-induced hypertension, T cell IL21 production is increased, and Il21-/- mice develop blunted hypertension, attenuated vascular end-organ damage, and decreased interleukin 17A (IL17A) and interferon gamma production. Tfh-like cells and GC B cells accumulate in the aorta and plasma IgG1 is increased in hypertensive WT but not Il21-/-mice. Furthermore, Tfh cell deficient mice develop blunted hypertension and vascular hypertrophy in response to Ang II infusion. Importantly, IL21 neutralization reduces blood pressure (BP) and reverses endothelial dysfunction and vascular inflammation. Moreover, recombinant IL21 impairs endothelium-dependent relaxation ex vivo and decreases nitric oxide production from cultured endothelial cells. Finally, we show in humans that peripheral blood T cell production of IL21 correlates with systolic BP and IL17A production. These data suggest that IL21 may be a novel therapeutic target for the treatment of hypertension and its micro- and macrovascular complications.

Insulin resistance is a significant determinant of sarcopenia in advanced kidney disease.

Maintenance hemodialysis (MHD) patients display significant nutritional abnormalities. Insulin is an anabolic hormone with direct effects on skeletal muscle (SM). We examined the anabolic actions of insulin, whole-body (WB), and SM protein turnover in 33 MHD patients and 17 participants without kidney disease using hyperinsulinemic-euglycemic-euaminoacidemic (dual) clamp. Gluteal muscle biopsies were obtained before and after the dual clamp. At baseline, WB protein synthesis and breakdown rates were similar in MHD patients. During dual clamp, controls had a higher increase in WB protein synthesis and a higher suppression of WB protein breakdown compared with MHD patients, resulting in statistically significantly more positive WB protein net balance [2.02 (interquartile range [IQR]: 1.79 and 2.36) vs. 1.68 (IQR: 1.46 and 1.91) mg·kg fat-free mass-1·min-1 for controls vs. for MHD patients, respectively, P < 0.001]. At baseline, SM protein synthesis and breakdown rates were higher in MHD patients versus controls, but SM net protein balance was similar between groups. During dual clamp, SM protein synthesis increased statistically significantly more in controls compared with MHD patients ( P = 0.03), whereas SM protein breakdown decreased comparably between groups. SM net protein balance was statistically significantly more positive in controls compared with MHD patients [67.3 (IQR: 46.4 and 97.1) vs. 15.4 (IQR: -83.7 and 64.7) µg·100 ml-1·min-1 for controls and MHD patients, respectively, P = 0.03]. Human SM biopsy showed a positive correlation between glucose and leucine disposal rates, phosphorylated AKT to AKT ratio, and muscle mitochondrial markers in controls but not in MHD patients. Diminished response to anabolic actions of insulin in the stimulated setting could lead to muscle wasting in MHD patients.

Systemic inflammation is associated with exaggerated skeletal muscle protein catabolism in maintenance hemodialysis patients.

BACKGROUND: Systemic inflammation and muscle wasting are highly prevalent and coexist in patients on maintenance hemodialysis (MHD). We aimed to determine the effects of systemic inflammation on skeletal muscle protein metabolism in MHD patients. METHODS: Whole body and skeletal muscle protein turnover were assessed by stable isotope kinetic studies. We incorporated expressions of E1, E214K, E3αI, E3αII, MuRF-1, and atrogin-1 in skeletal muscle tissue from integrin ß1 gene KO CKD mice models. RESULTS: Among 129 patients with mean (± SD) age 47 ± 12 years, 74% were African American, 73% were male, and 22% had diabetes mellitus. Median high-sensitivity C-reactive protein (hs-CRP) concentration was 13 (interquartile range 0.8, 33) mg/l. There were statistically significant associations between hs-CRP and forearm skeletal muscle protein synthesis, degradation, and net forearm skeletal muscle protein balance (P < 0.001 for all). The associations remained statistically significant after adjustment for clinical and demographic confounders, as well as in sensitivity analysis, excluding patients with diabetes mellitus. In attempting to identify potential mechanisms involved in this correlation, we show increased expressions of E1, E214K, E3αI, E3αII, MuRF-1, and atrogin-1 in skeletal muscle tissue obtained from an animal model of chronic kidney disease. CONCLUSION: These data suggest that systemic inflammation is a strong and independent determinant of skeletal muscle protein homeostasis in MHD patients, providing rationale for further studies using anticytokine therapies in patients with underlying systemic inflammation. FUNDING: This study was in part supported by NIH grants R01 DK45604 and 1K24 DK62849, the Clinical Translational Science Award UL1-TR000445 from the National Center for Advancing Translational Sciences, the Veterans Administration Merit Award I01 CX000414, the SatelliteHealth Normon Coplon Extramural Grant Program, and the FDA grant 000943.

Sarcopenic Obesity Definitions by Body Composition and Mortality in the Hemodialysis Patients.

OBJECTIVE: Sarcopenic obesity (SO), a combination of low muscle mass and high fat mass, is considered as risk factor for mortality in general population. It is unclear if SO affects mortality in maintenance hemodialysis (MHD) patients. In this study, we aimed to determine whether body composition as assessed by currently available SO definitions is related to all-cause mortality in MHD subjects. We also examined the impact of applying different definitions on the prevalence of SO in our MHD database. DESIGN: Retrospective analysis. SUBJECTS: Adult patients on MHD for at least 3 months with no acute illness studied in the clinical research center between 2003 and 2011. INTERVENTION: Assessment of body composition was performed using dual energy x-ray absorptiometry. SO (appendicular skeletal mass: arm lean mass + leg lean mass and fat mass) was defined according to Baumgartner definition, Janssen criteria 1, and Janssen criteria 2. MAIN OUTCOME MEASURE: All-cause mortality and prevalence of SO. Patient deaths were ascertained from medical records and United States social security death index. RESULTS: Of 122 participants, 62% were male; mean age was 46 years (interquartile range: 40, 54) in men and 50 years (44, 61) in women. Prevalence of SO ranged from 12% to 62% in men and 2% to 74% in female according to different definitions. SO prevalence was lowest using the Baumgartner criteria (all: 8%, men 12%, women: 2%) and highest according to the Janssen criteria 2 (all: 57%, men 46%, women 74%). There were 45 deaths during a median follow-up period of 44 (20, 76) months. SO by any definition was not statistically significantly associated with mortality during follow-up. CONCLUSIONS: The current SO definitions are not applicable to predict increased risk of death in MHD patients. We found high degree of variation in the rates of SO when using different definitions. Future studies should focus on establishing MHD population-specific thresholds of muscle mass and adiposity for accurate prognostication.

Leucine disposal rate for assessment of amino acid metabolism in maintenance hemodialysis patients.

BACKGROUND: Protein energy wasting (PEW) is common in patients undergoing maintenance hemodialysis (MHD) and closely associated with poor outcomes. Insulin resistance and associated alterations in amino acid metabolism are potential pathways leading to PEW. We hypothesized that the measurement of leucine disposal during a hyperinsulinemic- euglycemic-euaminoacidemic clamp (HEAC) procedure would accurately measure the sensitivity to insulin for its actions on concomitant carbohydrate and protein metabolism in MHD patients. METHODS: We examined 35 MHD patients and 17 control subjects with normal kidney function by hyperinsulinemic-euglycemic clamp (HEGC) followed by HEAC clamp procedure to obtain leucine disposal rate (LDR) along with isotope tracer methodology to assess whole body protein turnover. RESULTS: The glucose disposal rate (GDR) by HEGC was 5.1 ± 2.1 mg/kg/min for the MHD patients compared to 6.3 ± 3.9 mg/kg/min for the controls (p = 0.38). The LDR during HEAC was 0.09 ± 0.03 mg/kg/min for the MHD patients compared to 0.11 ± 0.05 mg/kg/min for the controls (p = 0.009). The LDR level was correlated with whole body protein synthesis (r = 0.25; p = 0.08), with whole body protein breakdown (r = -0.38 p = 0.01) and net protein balance (r = 0.85; p < 0.001) in the overall study population. Correlations remained significant in subgroup analysis. The GDR derived by HEGC and LDR correlated well in the controls (r = 0.79, p < 0.001), but less so in the MHD patients (r = 0.58, p < 0.001). CONCLUSIONS: Leucine disposal rate reliably measures amino acid utilization in MHD patients and controls in response to high dose insulin.

Obesity, diabetes and survival in maintenance hemodialysis patients.

Increased body mass index (BMI) confers a survival advantage in maintenance hemodialysis (MHD) patients. Diabetic (diabetes mellitus (DM)) patients undergoing MHD have worse survival. There are limited studies examining the effect of obesity on the risk of death among MHD patients with diabetes. Ninety-eight MHD patients were studied for median follow-up time of 33 months. Patients were classified according to the presence of obesity (BMI ≥ 30 kg/m(2)) or DM. Primary outcome was all-cause mortality. Cox regression was used to evaluate the effect of obesity on time to death. Effect modification and mediation analysis were also performed. Mean age was 49 ± 13 years, 66% were male, 48% were obese and 34% were diabetic. Mortality rates (per 100 person-years) were: 3.4 for non-diabetic obese, 8.6 for non-diabetic non-obese, 14.3 for diabetic non-obese and 18.1 for diabetic obese patients. Log-rank comparing diabetic obese versus non-diabetic obese was significant (p=0.007). Diabetes was associated with an increased risk of mortality after adjustment for potential mediators. Effect modification of obesity in the mortality risk was different between patients with and without diabetes. With adjustment for adipokines, a greater effect modification by diabetes was observed; whereas, adjustment for inflammatory marker did not influence the effect modification. Diabetic obese MHD patients have increased mortality risk compared to non-diabetic obese. Obesity does not offer survival benefits in diabetic obese MHD patients and potentially may have detrimental effects. Larger studies evaluating the effect of adipokines and obesity in outcomes in the diabetic MHD population need to be undertaken.

Insulin resistance and protein metabolism in chronic hemodialysis patients.

OBJECTIVE: Loss of lean body mass (sarcopenia) is associated with increased morbidity and mortality in patients receiving chronic hemodialysis (CHD). Insulin resistance (IR), which is highly prevalent in patients receiving CHD, has been proposed to play a critical role in the development of sarcopenia. The aim of this study was to examine the effect of IR on amino acid metabolism in patients receiving CHD. DESIGN: This was a cross-sectional study. SUBJECTS: The study included 12 prevalent (i.e., patients that have been on dialysis for more than 90 days) African American patients receiving CHD. METHODS: IR was measured as glucose disposal rate (GDR) determined from hyperinsulinemic euglycemic clamp (HGEC) studies performed 3 consecutive times. Plasma amino acid (AA) concentrations were measured by real-time high-performance liquid chromatography (HPLC) throughout the clamp study. The primary outcome was percentage change in leucine concentrations during the clamp study. The main predictor was the GDR measured simultaneously during the HGEC studies. Mixed model analysis was used to account for repeated measures. RESULTS: All individual AA concentrations declined significantly in response to high-dose insulin administration (P < .001). There was a significant direct association between GDR by HECG studies and the percentage change in leucine concentration (P = .02). Although positive correlations were observed between GDR values and concentration changes from baseline for other AAs, these associations did not reach statistical significance. CONCLUSIONS: Our results suggest that the severity of IR of carbohydrate metabolism is associated with a lesser decline in plasma leucine concentrations, suggesting a similar resistance to protein anabolism. Insulin resistance represents a potential mechanism for sarcopenia commonly observed in patients receiving CHD.

Recent advances in acute kidney injury epidemiology.

PURPOSE OF REVIEW: Expanding rates of acute kidney injury (AKI) coupled with increasing awareness of its short-term and long-term sequelae have focused efforts to identify patients at risk for this disease and its complications. This review details the recent attempts to identify novel risk factors for AKI, describes further refinements in the diagnostic and prognostic approach using biological markers of injury, and highlights the features of AKI that independently predict poor long-term outcomes. RECENT FINDINGS: The presence of proteinuria predicts the development of AKI independently of estimated glomerular filtration rate. Initial results from a large prospective study of AKI biomarkers in cardiac surgery indicate lower agreement with serum creatinine as an AKI standard than observed in early studies. AKI severity and duration are important predictors of chronic kidney disease and long-term mortality. A minority of patients surviving AKI with decreased kidney function is seen by a nephrologist. SUMMARY: Although the pathophysiologic link is unclear, proteinuria is an easily measurable risk factor for AKI worth considering before anticipated procedures or medication exposures carrying nephrologic risk. Investigation extending beyond agreement with serum creatinine is needed to fully understand the diagnostic and prognostic value of AKI biomarkers. Severity and duration are components of AKI that can help risk-stratify survivors in need of monitoring or nephrology referral.