A comparison of measured and estimated glomerular filtration rate in successfully treated HIV-patients with preserved renal function.

BACKGROUND: Monitoring of renal function becomes increasingly important in the aging population of HIV-1 infected patients. We compared Cockroft & Gault (C&G), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), Modification of Diet in Renal Disease (MDRD), Cystatin C- and 24 h urine-based estimated GFR (eGFR) with the gold standard, measured GFR (mGFR) using [125I]-iothalamate. METHODS: Substudy within a randomized, multinational trial comparing continuing zidovudine/ lamivudine with switching to tenofovir/ emtricitabine in patients with suppressed HIV-1 infection. Accuracy (defined as the mean difference between eGFR and mGFR) and precision (defined as standard deviation (SD) of the mean difference between eGFR and mGFR) of the eGFRs were calculated using linear regression and Bland & Altman analysis. RESULTS: We included 19 patients, 18 men, 15 Caucasian, mean (SD) age 46.0 y (± 8.9) and BMI 23.9 kg/m2 (± 3.0). Mean (SD) mGFR was 102 ml/min/1.73 m2 (± 19), 4 patients had mild renal dysfunction. All eGFRs tended to underestimate true GFR, with best accuracy for C&G (-1 ml/min/1.73 m2), CKD-EPI (-1 ml/min/1.73 m2), 24 hcreatinine clearance (-2 ml/min/1.73 m2) and MDRD-6 (0 ml/min/1.73 m2), and worst for cystatin C-based (-9 ml/min/1.73 m2) and MDRD-4 estimations (-10 ml/min/1.73 m2). Accuracy worsened at higher mGFR, but was not significantly influenced by age. C&G tended to overestimate at higher BMI. Precision was comparable for all GFR estimations. CONCLUSIONS: In this limited number of patients with preserved renal function and suppressed HIV-infection C&G and CKD-EPI appeared to be the best reflection of real GFR and most practical tool for monitoring GFR.

Postprandial changes in the phospholipid composition of circulating microparticles are not associated with coagulation activation.

INTRODUCTION: Evidence is present that the phospholipid composition of circulating cell-derived microparticles (MP) affects coagulation in vivo, and that postprandial metabolic alterations may be associated with hypercoagulable state. Our objective was to investigate whether postprandial metabolic responses affect the phospholipid composition of MP, and whether such changes are associated with coagulation activation. MATERIALS AND METHODS: Twelve healthy males were studied twice and randomly received two consecutive meals or remained fasted. Blood was collected before and at 2, 4, 6 and 8h following breakfast. Plasma concentrations of prothrombin-F(1+2) and thrombin-antithrombin-complexes were measured. Numbers and cellular origin of MP were determined by flowcytometry. The phospholipid composition of MP was determined by hpTLC. In vitro procoagulant activity of MP was studied by fibrin generation. RESULTS: During the meal visit, plasma glucose, triglyceride and insulin levels increased, compared to baseline and the fasting visit (all P<0.05). Postprandially, the total numbers of MP increased in time compared to the fasting visit (P<0.05). Erythrocyte-derived MP increased (6-fold) during the meal visit, but remained constant on the fasting day (P<0.001). On the meal versus fasting day circulating MP contained increased phosphatidylcholine (P<0.05) and decreased sphingomyelin (P<0.05) amounts. The amount of phosphatidylserine did not change. Concentrations of plasma F(1+2) and thrombin-antithrombin were similar on both days, as was the ability of MP to generate fibrin in vitro. CONCLUSION: Although numbers, cellular origin and phospholipid composition of MP alter during exposure to two consecutive meals in healthy subjects, this does not lead to changes in the coagulation activation in vivo.

Persistent decline in estimated but not measured glomerular filtration rate on tenofovir may reflect tubular rather than glomerular toxicity.

BACKGROUND: Tenofovir disoproxil fumarate (TDF) has been associated with proximal renal tubulopathy and reduction in estimated glomerular filtration rate (eGFR), without accounting for the tubular secretion of creatinine. METHODS: A substudy was performed among 19 participants of a randomized 48-week trial, comparing continuing first-line zidovudine/lamivudine (ZDV/3TC) with switching to TDF/emtricitabine (FTC). GFR was measured with [(125)I]-iothalamate (mGFR) and effective renal plasma flow (ERPF) with [(131)I]-hippuran. eGFR and tubular effects were assessed using plasma and urine samples. RESULTS: Of the 19 patients, 18 were men, 15 whites, mean (SD) age 46.0 (8.9) years, plasma HIV-1 RNA less than 50 copies/ml in all. After 48 weeks, eGFR using Cockcroft-Gault equation and ERPF, but not mGFR, had significantly decreased, and urinary α1-microglobulin/creatinine and microalbumin/creatinine significantly increased in patients on TDF. Although phosphate metabolism on TDF was affected at week 4, differences between groups disappeared during follow-up. CONCLUSION: Replacing ZDV/3TC with TDF/FTC in this limited sample of virologically suppressed HIV-1-infected adults was associated with mild persistent tubular but not glomerular dysfunction over 48 weeks. The observed persistent decrease in Cockcroft-Gault-based eGFR, but not mGFR, rather than being indicative of glomerular dysfunction may be explained by TDF inhibiting tubular creatinine excretion.

Human apolipoprotein C-I expression in mice impairs learning and memory functions.

The H2 allele of APOC1, giving rise to increased gene expression of apolipoprotein C-I (apoC-I), is in genetic disequilibrium with the APOE4 allele and may provide a major risk factor for Alzheimer's disease (AD). We found that apoC-I protein is present in astrocytes and endothelial cells within hippocampal regions in both human control and AD brains. Interestingly, apoC-I colocalized with beta-amyloid (Abeta) in plaques in AD brains, and in vitro experiments revealed that aggregation of Abeta was delayed in the presence of apoC-I. Moreover, apoC-I was found to exacerbate the soluble Abeta oligomer-induced neuronal death. To establish a potential role for apoC-I in cognitive functions, we used human (h) APOC1(+/0) transgenic mice that express APOC1 mRNA throughout their brains and apoC-I protein in astrocytes and endothelial cells. The hAPOC1(+/0) mice displayed impaired hippocampal-dependent learning and memory functions compared with their wild-type littermates, as judged from their performance in the object recognition task (P = 0.012) and in the Morris water maze task (P = 0.010). ApoC-I may affect learning as a result of its inhibitory properties toward apoE-dependent lipid metabolism. However, no differences in brain mRNA or protein levels of endogenous apoE were detected between transgenic and wild-type mice. In conclusion, human apoC-I expression impairs cognitive functions in mice independent of apoE expression, which supports the potential of a modulatory role for apoC-I during the development of AD.

Alterations in lipoprotein homeostasis during human experimental endotoxemia and clinical sepsis.

Cell wall constituents of bacteria are potent endotoxins initiating inflammatory responses which may cause dramatic changes in lipid metabolism during the acute phase response. In this study, the sequential changes in lipoprotein composition and lipid transfer and binding proteins during clinical sepsis and during low-dose experimental endotoxemia were followed. In addition, the effect on (phospho)lipid homeostasis by administration of reconstituted HDL (rHDL) prior to low-dose LPS administration was investigated. Changes in (apo)lipoprotein concentrations typical of the acute phase response were observed during clinical sepsis and experimental endotoxemia with and without the rHDL intervention. During clinical sepsis negative correlations between the acute phase marker C-reactive protein (CRP) and lecithin:cholesterol acyltransferase (LCAT) and cholesterylester transfer protein (CETP) activities were seen, whereas positive correlations between plasma phospholipid transfer protein (PLTP) activity and acute phase markers such as CRP and LPS binding protein were observed. Plasma lipid changes upon rHDL/LPS infusion were comparable with the control group (low-dose LPS only). PLTP activity decreased upon LPS infusion and transiently increased during rHDL infusion, whereas LCAT activity slightly decreased upon both LPS infusion and LPS/rHDL infusion. However, long-lasting increases of circulating HDL cholesterol, apo A-I and a high initial processing of both phosphatidylcholine (PC) and lyso-PC, were indicative for extensive rHDL and LDL remodelling. Both sepsis and experimental endotoxemia lead to a disbalance of lipid homeostasis. Depending on the magnitude of the inflammatory stimulus, LCAT and PLTP activities reacted in divergent ways. rHDL infusion did not prevent the lipid alterations seen during the acute phase response. However profound changes in both HDL and LDL phospholipid composition occurred upon rHDL infusion. This may be explained, at least in part, by the fact that PLTP as a positive acute phase protein, can accelerate the alterations in (phospho)lipid homeostasis thereby playing a role in the attenuation of the acute phase response.

Estimation of residual glomerular filtration rate in dialysis patients from the plasma cystatin C level.

BACKGROUND: Residual renal function influences morbidity, mortality and quality of life of chronic dialysis patients. Residual glomerular filtration rate (rGFR) is therefore an important parameter in the follow-up of these patients. Because rGFR is measured as the mean of creatinine and urea clearance, a complete 24 h urine collection is essential, but often very difficult to manage for these patients. METHODS: We investigated if plasma cystatin C (cysC) could give a good estimate of rGFR in dialysis patients and compared it to the measured rGFR, as well as to the rGFR estimate obtained with the Modification of Diet in Renal Disease (MDRD) formula. A total of 465 patients were included in this study. CysC levels of 215 haemodialysis (HD) and 95 chronic ambulatory peritoneal dialysis (PD) patients were used to derive a formula for rGFR. This formula was tested in the validation group of 107 HD and 48 PD patients. RESULTS: The cysC formula derived in the modelling group was rGFR = -0.70 + 22 x (1/cysC). The mean estimated rGFR obtained with this formula in the validation group was not significantly different from the mean measured rGFR: difference 0.19 ml/min/1.73 m(2), 95% confidence interval (CI) -2.37 to 2.75 ml/min/1.73 m(2). The MDRD formula gave a larger difference from the mean measured rGFR (3.13 ml/min/1.73 m(2)) and a much wider 95% CI (-1.29 to 7.55 ml/min/1.73 m(2)). A separate model for HD and PD patients did not improve the estimation of rGFR. CONCLUSIONS: The cysC formula showed better accuracy and precision than the MDRD formula. Therefore the cysC formula and not the MDRD formula should be used to calculate rGFR in dialysis patients when no 24 h urine sample is available.

Cystatin C in critically ill patients treated with continuous venovenous hemofiltration.

Assessment of residual renal function in critically ill patients with acute renal failure (ARF) treated with continuous venovenous hemofiltration (CVVH) is difficult. Cystatin C (CysC) is a low-molecular-weight protein (13.3 kDa) removed from the body by glomerular filtration. Its serum concentration has been advocated for assessment of renal function in patients with kidney disease. To investigate whether the removal of CysC by CVVH is likely to influence its serum concentration, concentrations of CysC were measured in 3 consecutive samples in 18 patients with oliguric ARF treated with CVVH (2 L/hr). Samples were taken from the afferent and efferent blood lines and from the ultrafiltrate line. Concentrations of CysC did not change during the time interval studied. The mean serum concentrations of CysC were 2.25+/-0.45 mg/L in the afferent and 2.19+/-0.56 mg/L in the efferent samples (NS); ultrafiltrate concentrations of CysC were 1.01+/-0.45 mg/L. The sieving coefficient of CysC was 0.52+/-0.20; the clearance of CysC was 17.3+/-6.6 mL/min; and the quantity of CysC removed averaged 2.13 mg/hr. During CVVH (2 L/hr), the quantity of CysC removed is less than 30% of its production and no rapid changes in its serum concentration are observed. Therefore, CVVH (2 L/hr) is unlikely to influence serum concentrations of CysC significantly, which suggests that it can be used to monitor residual renal function during CVVH.

Atp8b1 deficiency in mice reduces resistance of the canalicular membrane to hydrophobic bile salts and impairs bile salt transport.

Progressive familial intrahepatic cholestasis type 1 (PFIC1, Byler disease, OMIM 211600) is a severe inherited liver disease caused by mutations in ATP8B1. ATP8B1 is a member of the type 4 subfamily of P-type ATPases, which are phospholipid flippases. PFIC1 patients generally develop end-stage liver disease before the second decade of life. The disease is characterized by impaired biliary bile salt excretion, but the mechanism whereby impaired ATP8B1 function results in cholestasis is unclear. In a mouse model for PFIC1, we observed decreased resistance of the hepatocanalicular membrane to hydrophobic bile salts as evidenced by enhanced biliary recovery of phosphatidylserine, cholesterol, and ectoenzymes. In liver specimens from PFIC1 patients, but not in those from control subjects, ectoenzyme expression at the canalicular membrane was markedly deficient. In isolated mouse livers Atp8b1 deficiency impaired the transport of hydrophobic bile salts into bile. In conclusion, our study shows that Atp8b1 deficiency causes loss of canalicular phospholipid membrane asymmetry that in turn renders the canalicular membrane less resistant toward hydrophobic bile salts. The loss of phospholipid asymmetry may subsequently impair bile salt transport and cause cholestasis.

A pilot study into measurements of markers of atherosclerosis in periodontitis.

BACKGROUND: Periodontitis may be a possible risk factor for atherosclerosis. The current pilot study explored arterial wall thickness and other variables associated with atherosclerosis in healthy subjects with and without periodontitis. METHODS: Patients with moderate (N = 34) and severe periodontitis (N = 15) and controls (N = 14) were recruited. Intima media thickness (IMT) of the common carotid arteries (CCA), internal carotid arteries (ICA), and bifurcations of carotid arteries (BCA) was estimated bilaterally using B-mode ultrasound. An overall IMT was calculated as the mean of these six measurements. C reactive protein (CRP), fibrinogen, and von Willebrand factor (vWf) were measured in plasma as indicators of systemic inflammation and atherosclerotic disease. Microalbuminuria was determined as a marker of endothelial cell dysfunction. RESULTS: IMT for CCA were 0.64, 0.68, and 0.69 mm for control, moderate, and severe periodontitis, respectively (not significant). IMT for BCA did not vary among groups. IMT of ICA was largest for severe periodontitis (0.81 mm); corresponding values for controls and moderate periodontitis were 0.58 and 0.55 mm, respectively (P= 0.023). Severe periodontitis patients had an overall IMT of 0.76 mm, while moderate periodontitis patients and controls had lower values (0.64 and 0.65 mm, respectively; P= 0.153). After adjusting for potential confounding factors, the increased IMT for ICA in severe periodontitis was also significant (Padj = 0.040). CRP (P= 0.020, Padj = 0.050) and vWf (P= 0.019, Padj = 0.013) were higher in periodontitis than controls; microalbuminuria was not different between groups. Power calculations suggest that a 4-fold expansion of the severe patient and control groups will result in a high chance (power level 80%) that a clinically significant association between the overall IMT and periodontitis will be observed. CONCLUSION: The present pilot study indicates that a full study investigating the relationship between periodontitis and atherosclerosis is warranted.

A comparison between cystatin C, plasma creatinine and the Cockcroft and Gault formula for the estimation of glomerular filtration rate.

BACKGROUND: In clinical practice, the glomerular filtration rate (GFR) is often estimated from plasma creatinine. Several studies have shown cystatin C (cys C) to be a better parameter for the diagnosis of impaired renal function. No data are available, however, on the performance of cys C in follow-up of patients, compared with creatinine. Also, comparisons of cys C with the Cockcroft and Gault (C&G) formula for estimation of GFR are few. METHODS: Plasma samples were obtained from 93 consecutive patients seen for GFR determination and from 30 patients with diabetes mellitus type 2, of whom 23 were investigated a second time after 2 years. GFR was determined with [125I]iothalamate. Plasma creatinine was determined enzymatically and the creatinine clearance calculated according to C&G. Cys C was measured with a particle-enhanced immunonephelometric method. RESULTS: GFR correlated with 1/cys C (r = 0.873) as well as with C&G (r = 0.876). The area under the curve (AUC) of the receiver operating curves (ROCs), a measure of diagnostic accuracy, for cys C (0.931) and C&G (0.938) were equal (P = 0.815) and both better than the creatinine AUC (0.848; P = 0.006). Bland and Altman analysis showed that the simple formula GFR = -4.32 + 80.35 x 1/cys C, derived from our data, gave more accurate (P < 0.0001) and more precise (P = 0.024) GFR estimates than obtained with the C&G formula. The day-to-day variation (biological +analytical) for cys C was small (3.1%, SD 2.51%) in diabetic patients. In the follow-up study in diabetic patients, cys C was the parameter which had the best correlation (r = 0.66) with changes in GFR. CONCLUSIONS: Cys C shows a high correlation with GFR. With a very simple formula, cys C gives a good estimate of GFR, more accurate and precise than C&G. Because biological variation is low, cys C gives also a good assessment of GFR changes during follow-up. Cys C is the preferred endogenous parameter for GFR.

Pitfalls in gastrointestinal permeability measurement in ICU patients with multiple organ failure using differential sugar absorption.

OBJECTIVE: To assess whether gastrointestinal permeability (GIP) at intensive care unit (ICU) admission, measured by differential sugar absorption, is related to severity of disease and multiple organ failure (MOF). Post hoc, to analyse the relation between the urinary sugar recovery and renal function. DESIGN: Prospective observational cohort study. SETTING: Eighteen-bed general ICU of a teaching hospital. PATIENTS: Sixty-four ventilated patients admitted with MOF. INTERVENTIONS: GIP was assessed within 24 h using cellobiose (C), sucrose (S) and mannitol (M) absorption. MEASUREMENTS AND RESULTS: Severity of disease: APACHE II and III, SAPS II and MPM II systems. Organ failure: SOFA, MODS and Goris score. The median urinary recovery of C was 0.147% (range 0.004-2.145%), of S 0.249% (0.001-3.656%) and of M 10.7% (0.6-270%). In 16 patients, M recovery was over 100% of the oral dose. They received red blood cell transfusion (RBC). In the non-transfused, the median cellobiose/mannitol (CM) ratio was 0.015 (0.0004-0.550). CM ratio was not related to severity of disease and inversely related to the SOFA score ( r=-0.30, p=0.04). Post hoc regression analysis showed that recoveries of C, S and M were positively related to urinary volume. Recoveries of C and S, but not of M, were positively related to creatinine clearance. The CM ratio corrected for diuresis, but was inversely related to creatinine clearance. CONCLUSIONS: Differential C, S and M absorption testing is unreliable after RBC transfusion, since bank blood contains mannitol. The excretion of C and S, but not of M, is limited by renal dysfunction. Differential sugar absorption is not reliable to test GIP in MOF patients, since non-permeability related factors act as confounders.