R. Neil Dalton

Increasing dimethylarginine levels are associated with adverse clinical outcome in severe alcoholic hepatitis

Previous studies suggest reduced hepatic endothelial nitric oxide synthase activity contributes to increased intrahepatic resistance. Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, undergoes hepatic metabolism via dimethylarginine‐dimethylamino‐hydrolase, and is derived by the action of protein‐arginine‐methyltransferases. Our study assessed whether ADMA, and its stereo‐isomer symmetric dimethylarginine (SDMA), are increased in alcoholic hepatitis patients, and determined any relationship with severity of portal hypertension (hepatic venous pressure gradient measurement) and outcome. Fifty‐two patients with decompensated alcoholic cirrhosis were studied, 27 with acute alcoholic hepatitis and cirrhosis, in whom hepatic venous pressure gradient was higher (P = 0.001) than cirrhosis alone, and correlated with ADMA measurement. Plasma ADMA and SDMA were significantly higher in alcoholic hepatitis patients and in nonsurvivors. Dimethylarginine‐dimethylamino‐hydrolase protein expression was reduced and protein‐arginine‐methyltransferase‐1 increased in alcoholic hepatitis livers. ADMA, SDMA and their combined sum, which we termed a dimethylarginine score, were better predictors of outcome compared with Pugh score, MELD and Maddreys discriminant‐function. Conclusion: Alcoholic hepatitis patients have higher portal pressures associated with increased ADMA, which may result from both decreased breakdown (decreased hepatic dimethylarginine‐dimethylamino‐hydrolase) and/or increased production. Elevated dimethylarginines may serve as important biological markers of deleterious outcome in alcoholic hepatitis. (HEPATOLOGY 2007;45:62–71.)

Susceptibility of glomerular filtration rate estimations to variations in creatinine methodology: a study in older patients

Background: It is recommended that measurement of serum creatinine should be supplemented with a creatinine-based estimation of glomerular filtration rate (GFR). The influence of creatinine methodology on these estimates is not always appreciated. We have studied differences in creatinine methods and their influence on GFR estimation specifically in older people. Methods: In all, 46 older patients (mean age 80 y, range 69-92 y) with predominantly mild or moderate kidney disease were studied. Serum creatinine was measured using a rate Jaffe method and two different enzymatic methods. Isotope dilution mass spectrometry served as the reference creatinine method. GFR was estimated using both the Modification of Diet in Renal Disease (MDRD) and Cockcroft and Gault formulae: a 51Cr-EDTA GFR estimation served as the reference GFR method. Results: Both enzymatic methods produced creatinine results that were significantly different (P < 0.001) from the reference method. The Jaffe method over- and underestimated creatinine at low and high concentrations, respectively. The most likely explanation for these differences relates to standardization of the assays. Irrespective of creatinine method, the Cockroft and Gault formula tended to underestimate GFR, and the MDRD formula to overestimate GFR. Use of the differing creatinine methods to estimate GFR produced predictable biases of the estimate, with mean GFR estimates varying by 14% across the creatinine methods. Conclusion: Estimates of GFR depend critically upon the accuracy and precision of the creatinine measurement used in their calculation.

Effect of Fenofibrate on Kidney Function: A 6-Week Randomized Crossover Trial in Healthy People

BACKGROUNDnFenofibrate was associated with increases in serum creatinine concentrations. The effect of short-term fenofibrate treatment on kidney function was investigated in subjects with normal kidney function.nnnSTUDY DESIGNnDouble-blind, crossover, placebo-controlled.nnnSETTING AND PARTICIPANTSn24 middle-aged subjects with normal kidney function (estimated creatinine clearance > or = 80 mL/min).nnnINTERVENTIONnSubjects were treated with fenofibrate (160-mg/d tablet) and placebo in two 6-week periods separated by a washout.nnnOUTCOMES AND MEASUREMENTSnThe primary outcome measure was glomerular filtration rate measured by means of inulin clearance, with a test of noninferiority to rule out a change in the 95% confidence interval (CI) greater than 20%. Secondary outcomes included effective renal plasma flow measured by means of para-aminohippurate (PAH) clearance, creatinine clearance, creatinine secretion (ratio of creatinine to inulin clearance), serum cystatin C and uric acid, and urinary excretion of creatinine. Glomerular and tubular damage was evaluated by using albumin and retinol-binding protein levels and N-acetyl-beta-d-glucosaminidase activity.nnnRESULTSnInulin clearance was unchanged after fenofibrate (change [Delta] between treatments on 6-week values, 0.8 mL/min; 95% CI, -10.5 to 12.2; P = 0.9), but PAH clearance decreased (Delta, -33; 95% CI, -66 to -1; P = 0.05). Changes in inulin and PAH clearances were not greater than 20%. Plasma creatinine level increased (Delta, 0.11 mg/dL; 95% CI, 0.05 to 0.18; P < 0.05), and creatinine clearance decreased (Delta, -9.5 mL/min; 95% CI, -14.4 to -4.7; P < 0.001). Creatinine secretion and urinary creatinine excretion were unchanged (Delta, -0.05; 95% CI, -0.11 to 0.02; P = 0.2; Delta, 0.37 g/24 h; 95% CI, -0.13 to 0.88; P = 0.1, respectively). Plasma cystatin C level increased (Delta, 0.18 mg/L; 95% CI, 0.03 to 0.34; P = 0.02) and serum uric acid level decreased (Delta, -0.7 mg/dL; 95% CI, -1.2 to -0.3; P = 0.1). Urinary albumin and retinol-binding protein levels were unchanged, but urinary N-acetyl-beta-d-glucosaminidase activity increased (Delta, 20.0 mumol/h/mmol creatinine; 95% CI, 9.3 to 30.7; P = 0.001).nnnLIMITATIONSnShort treatment duration and inclusion of healthy subjects precludes conclusions about effects of longer term use in patients with kidney disease. Small changes in glomerular filtration rate may be difficult to detect by using clearance methods. Interference with the creatinine assay cannot be excluded.nnnCONCLUSIONnShort-term fenofibrate treatment did not alter glomerular filtration rate by more than 20% in subjects with normal kidney function, but a smaller decrease cannot be ruled out. Increased serum creatinine levels may be caused by decreased creatinine clearance. The explanation for decreased creatinine clearance and increased serum creatinine levels in this study is not clear.

Adolescent Type 1 Diabetes cardio-renal Intervention Trial (AdDIT): Urinary screening and baseline biochemical and cardiovascular assessments

OBJECTIVE We assessed the association between early increases in albumin excretion and cardiovascular (CV) and renal markers in a large cohort of young people with type 1 diabetes. RESEARCH DESIGN AND METHODS As part of preliminary screening for a multicenter, randomized controlled trial of statins/ACE inhibitors, we measured albumin–creatinine ratio (ACR) in six early morning urine samples from 3,353 adolescents (10–16 years of age) and calculated tertiles based on an established algorithm. From those subjects deemed to be at higher risk (upper ACR tertile), we recruited 400 into the intervention study (trial cohort). From those subjects deemed to be at lower risk (middle–lower ACR tertiles), we recruited 329 to the observation cohort. At baseline, vascular measurements (carotid intima-media thickness, pulse wave velocity [PWV], flow-mediated dilatation, digital pulse amplitude tonometry), renal markers (symmetric dimethylarginine, cystatin C, creatinine), and CV disease markers (lipids and apolipoproteins [Apo] A-1 and B, C-reactive protein, asymmetric dimethylarginine) were assessed. RESULTS Age- and sex-adjusted PWV was higher in the trial than in the observational cohort (5.00 ± 0.84 vs. 4.86 ± 0.70 m/s; P = 0.021). Similarly, non-HDL cholesterol (2.95 ± 0.83 vs. 2.81 ± 0.78 mmol/L; P = 0.02) and ApoB–ApoA-1 ratio (0.50 ± 0.14 vs. 0.47 ± 0.11; P = 0.04) were higher in the trial cohort. Cystatin C and creatinine were decreased (0.88 ± 0.13 vs. 0.90 ± 0.13 mg/L, P = 0.04; 51.81 ± 10.45 vs. 55.35 ± 11.05 μmol/L, P < 0.001; respectively) and estimated glomerular filtration rate (137.05 ± 23.89 vs. 129.31 ± 22.41 mL/min/1.73 m2; P < 0.001) increased in the trial compared with the observational cohort. CONCLUSIONS Our data demonstrate that in adolescents with type 1 diabetes, the group with the highest tertile of albumin excretion showed more evidence of early renal and CV disease than those in the lower tertiles.

Inflammation is an important determinant of levels of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) in acute liver failure.

Acute liver failure (ALF) is characterized by rapid progressive organ failure and poor outcome. The pathophysiology of multiorgan dysfunction in ALF remains unclear but increased systemic inflammatory response is believed to be an important determining factor. Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, results from proteolysis and the liver is a major site for its metabolism. ADMA has been shown to independently predict outcome in multiorgan failure associated with severe liver dysfunction. In this study, we tested the hypothesis that proinflammatory cytokine driven responses are important in modulating ADMA levels in patients with acetaminophen‐induced ALF. Blood samples were collected from 10 ALF patients (grade IV encephalopathy) from admission until the time of transplantation or death, and assayed for cytokines and ADMA. A total of 8 patients required treatment for raised intracranial pressure and all patients were managed with standard of care, including full mechanical ventilation and veno‐venous hemofiltration. ADMA levels were markedly higher in ALF patients compared to age‐matched controls (P < 0.001) and correlated with the levels of proinflammatory cytokines. In pretransplantation patients undergoing hepatic venous catheterization, we demonstrated no significant uptake of ADMA across the failing liver. However, following liver transplantation, ADMA levels reduced acutely. A timed study of ADMA levels during transplantation demonstrated a slight increase during the anhepatic phase but a marked and sustained reduction in ADMA following liver reperfusion. In conclusion, our data show a significant correlation between ADMA levels and proinflammatory cytokines, supporting a hypothesis that proinflammatory cytokines may regulate ADMA metabolism in ALF. Liver Transpl 13:400–405, 2007.

Differential excretion of urinary proteins in children with vesicoureteric reflux and reflux nephropathy.

We studied 40 children with a history of vesicoureteric reflux (VUR) without evidence of renal scarring, 93 children with a history of VUR and renal scarring and 10 children with previous urinary tract infections in whom the urinary tract was radiologically normal. Urine retinol-binding protein (RBP), albumin andN-acetyl-β-d-glucosaminidase (NAG) were measured in each child. All were free from infection at the time of the analysis. Urinary RBP and NAG levels were significantly elevated (P<0.001) in the group of children with renal scarring. Elevated RBP levels were detected in 51% of children with bilateral renal scarring compared with 7% of children with unilateral scarring. Urine RBP excretion increased progressively according to the type of scarring, best determined by the type of scarring of the less affected kidney. In children with renal scarring, elevated NAG levels were seen mostly in the 65 children with bilateral scarring and severe reflux. Urine albumin excretion was elevated in 10 children, 9 with bilateral scarring, all of whom had elevated RBP excretion. Urine protein excretion was unaffected by the presence or absence of persisting VUR. There was a strong negative correlation between glomerular filtration rate and RBP excretion (r=−0.69). We conclude that evidence of tubular dysfunction is common in children with bilateral renal scarring and usually precedes any glomerular protein leak. Tubular dysfunction may be the consequence of relative nephron hyperperfusion in the presence of bilateral scarring.

Glomerular and tubular function in glycogen storage disease.

Urinary protein and calcium excretion were assessed in 77 patients with the hepatic glycogen storage diseases (GSD): 30 with GSD-I (median age 12.4 years, range 3.2–32.9 years), 25 with GSD-III (median age 10.5 years, range 4.2–31.3 years) and 22 with GSD-IX (median age 11.8 years, range 1.2–35.4 years). Inulin (Cinulin) and para-aminohippuric acid (CPAH) clearances were also measured in 33 of these patients. Those with GSD-I had significantly greater albumin (F=15.07,P<0.001), retinolbinding protein (RBP) (F=14.66,P<0.001),N-acetyl-β-d glucosaminidase (NAG) (F=9.41,P<0.001) and calcium (F=7.41,P=0.001) excretion than those with GSD-III and GSD-IX. GSD-I patients (n=18) also had significantly higherCinulin (F=5.57,P=0.009), butCPAH did not differ (F=0.77, NS). Renal function was normal in GSD-III and GSD-IX patients. In GSD-I,Cinulin (r=−0.51,P=0.03) and NAG excretion (r=−0.40,P=0.03) were inversely correlated with age, whereas albumin excretion was positively correlated with age (r=+0.41,P=0.03). RBP and calcium excretion were generally high throughout all age groups. Hyperfiltration in GSD-I is associated with renal tubular proteinuria that occurs before the onset of significant albuminuria. Deficiency of glucose-6-phosphatase within the proximal renal tubule may primarily cause tubular dysfunction, glomerular hyperfiltration being a secondary phenomenon.

Measurement of β2-microglobulin, retinol-binding protein, α1-microglobulin and urine protein 1 in healthy children using enzyme-linked immunosorbent assay

Enzyme-linked immunosorbent assays (ELISA) have been developed for the measurement of β2-microglobulin (B2M), retinol-binding protein (RBP), α1-microglobulin (A1M) and urine protein 1 (UP1) in children. Results from random urine samples in 43 children (31 for B2M) are, when corrected for urine creatinine (geometric mean (range)): B2M 9.8 (6.0–40.7) μg/mmol, RBP 8.1 (< 1–24.5) μg/mmol, A1M 0.4 (0.1–2.2) mg/mmol and UP1 17.8 (< 2–309.4) μg/mmol. Fractional excretions (FE) in 23 children (14 for B2M) are (geometric mean (range)): FEB2M 0.04% (0.02–0.10%) and FEUP1 0.10% (0.01–1.21%). Results in overnight urine collections are also presented. Our results extend existing data for normal ranges in adults to include children and provide data on UP1 concentrations.

Newborn screening for medium chain acyl-CoA dehydrogenase deficiency in England: prevalence, predictive value and test validity based on 1.5 million screened babies

Background Medium chain acyl-CoA dehydrogenase deficiency (MCADD) is a rare, life-threatening condition. Early diagnosis by screening asymptomatic newborns may improve outcome, but the benefit to newborns identified with variants not encountered clinically is uncertain. Objective To estimate, overall and by ethnic group: screen-positive prevalence and predictive value (PPV); MCADD prevalence; proportion MCADD variants detected of predicted definite or uncertain clinical importance. Setting All births in areas of high ethnic minority prevalence in England. Methods Prospective multicentre pilot screening service; testing at age five to eight days; standardized screening, diagnostic and management protocols; independent expert review of screen-positive cases to assign MCADD diagnosis and predicted clinical importance (definite or uncertain). Results Approximately 1.5 million babies (79% white; 10% Asian) were screened. MCADD was confirmed in 147 of 190 babies with a positive screening result (screen-positive prevalence: 1.20 per 10,000; MCADD prevalence: 0.94 per 10,000; PPV 77% [95% CI 71–83]), comprising 103 (70%) with MCADD variants of definite clinical importance (95 white [95%]; 2 Asian [2%]) and 44 (30%) with variants of uncertain clinical importance (29 white [67%]; 12 Asian [28%]). Conclusion One baby in every 10,000 born in England is diagnosed with MCADD by newborn screening; around 60 babies each year. While the majority of MCADD variants detected are predicted to be of definite clinical importance, this varies according to ethnic group, with variants of uncertain importance most commonly found in Asian babies. These findings provide support for MCADD screening but highlight the need to take account of the ethnic diversity of the population tested at implementation.

Cardiac Autonomic Dysfunction Is Associated With High-Risk Albumin-to-Creatinine Ratio in Young Adolescents With Type 1 Diabetes in AdDIT (Adolescent Type 1 Diabetes Cardio-Renal Interventional Trial)

OBJECTIVE This study examined the association between cardiac autonomic dysfunction and high albumin-to-creatinine ratio (ACR) in adolescents with type 1 diabetes. RESEARCH DESIGN AND METHODS Adolescents recruited as part of a multicenter screening study (n = 445, 49% female, aged 10–17 years, mean duration 6.9 years; mean HbA1c 8.4%, 68 mmol/mol) underwent a 10-min continuous electrocardiogram recording for heart rate variability analysis. Time-domain heart rate variability measures included baseline heart rate, SD of the R-R interval (SDNN), and root mean squared difference of successive R-R intervals (RMSSD). Spectral analysis included sympathetic (low-frequency) and parasympathetic (high-frequency) components. Standardized ACR were calculated from six early morning urine collections using an established algorithm, reflecting age, sex, and duration, and stratified into ACR tertiles, where the upper tertile reflects higher nephropathy risk. RESULTS The upper-tertile ACR group had a faster heart rate (76 vs. 73 bpm; P < 0.01) and less heart rate variability (SDNN 68 vs. 76 ms, P = 0.02; RMSSD 63 vs. 71 ms, P = 0.04). HbA1c was 8.5% (69 mmol/mmol) in the upper tertile vs. 8.3% (67 mmol/mol) in the lower tertiles (P = 0.07). In multivariable analysis, upper-tertile ACR was associated with faster heart rate (β = 2.5, 95% CI 0.2–4.8, P = 0.03) and lower RMSSD (β = −9.5, 95% CI −18.2 to −0.8, P = 0.03), independent of age and HbA1c. CONCLUSIONS Adolescents at potentially higher risk for nephropathy show an adverse cardiac autonomic profile, indicating sympathetic overdrive, compared with the lower-risk group. Longitudinal follow-up of this cohort will further characterize the relationship between autonomic and renal dysfunction and the effect of interventions in this population.