Iohexol Clearance Research Articles

Estimated Glomerular Filtration Rate (eGFR) based on cystatin C was associated with increased risk of hip and proximal humerus fractures in women and decreased risk of hip fracture in men, whereas eGFR based on creatinine was not associated with fracture risk in both sexes: The Tromsø Study.

Patients with end-stage kidney disease have an increased fracture risk. Whether mild to moderate reductions in kidney function is associated with increased fracture risk is uncertain. Results from previous studies may be confounded by muscle mass because of the use of creatinine-based estimates of the glomerular filtration rate (eGFRcre). We tested the hypothesis that lower eGFR within the normal range of kidney function based on serum cystatin C (eGFRcys) or both cystatin C and creatinine (eGFRcrecys) predict fractures better than eGFR based on creatinine (eGFRcre). In the Tromsø Study 1994-95, a cohort of 3016 women and 2836 men aged 50-84years had eGFRcre, eGFRcys and eGFRcrecys estimated using the Chronic Kidney Disease Epidemiology Collaboration equations. Hazard ratios (HRs) (95% confidence intervals) for fracture were calculated in Cox's proportional hazards models and adjusted for age, height, body mass index, bone mineral density, diastolic blood pressure, smoking, physical activity, previous fracture, diabetes and cardiovascular disease. During a median of 14.6years follow-up, 232, 135 and 394 women and 118, 35 and 65 men suffered incident hip, proximal humerus and wrist fractures. In women, lower eGFRcre did not predict fracture, but the risk for hip and proximal humerus fracture increased per standard deviation (SD) lower eGFRcys (HRs 1.36 (1.16-1.60) and 1.33 (1.08-1.63)) and per SD lower eGFRcrecys (HRs 1.25 (1.08-1.45) and 1.30 (1.07-1.57)). In men, none of the eGFR estimates were related to increased fracture risk. In contrast, eGFRcys and eGFRcrecys were inversely associated with hip fracture risk (HRs 0.85 (0.73-0.99) and 0.82 (0.68-0.98)). In women, each SD lower eGFRcys and eGFRcrecys increased the risk of hip and proximal humerus fracture by 25-36%, whereas eGFRcre did not. In men, none of the estimates of eGFR were related to increased fracture risk, and each SD lower eGFRcys and eGFRcrecys decreased the risk of hip fracture by 15-18%. The findings particularly apply to a cohort of generally healthy individuals with a normal kidney function. In future studies, the association of measured GFR using the gold standard method of iohexol clearance with fractures risk should be examined for causal inference. More clinical research is needed before robust clinical inferences can be made.

Evaluation of glomerular filtration rate using iohexol plasma clearance in critically ill patients with augmented renal creatinine clearance: A single-centre retrospective study.

Augmented renal creatinine clearance (ARC) (≥130 ml min-1 1.73 m-2) is frequent in intensive care unit (ICU) patients and may impact patient outcome. To compare glomerular filtration rate (GFR) measured with iohexol plasma clearance and creatinine clearance in critically ill patients with augmented renal clearance. Single-centre, retrospective study. French University Hospital ICU from November 2016 to May 2019. Adult patients with augmented renal clearance who had a measurement of iohexol plasma clearance. Agreement between 6 h creatinine clearance (6 h CrCl) and iohexol plasma clearance (GFRio). Twenty-nine patients were included. The median 6 h creatinine clearance was 195 [interquartile range (IQR) 162 to 251] ml min-1 1.73 m-2 and iohexol clearance was 133 [117 to 153] ml min-1 1.73 m-2. Sixteen patients (55%) had hyperfiltration (clearance >130 ml min-1 1.73 m-2) measured with iohexol clearance. Mean bias between iohexol and creatinine clearance was -80 [limits of agreement (LoA) -216 to 56 ml min-1 1.73 m-2]. For Cockcroft and Gault Modification of Diet in Renal Disease equation (MDRD), Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI) formulae, mean biases were, respectively -27 (LoA -99 to 45), -14 (LoA -86 to 59) and 15 (LoA -33 to 64) ml min-1 1.73 m-2. In the present study, we found that in patients with augmented renal creatinine clearance, half of the patients do not have hyperfiltration using iohexol clearance measurements. We observed an important bias between 6 h CrCl and GFRio with large LoA. In critically patients with ARC, 6 h CrCl does not reliably estimate GFR and 6 h CrCl nearly systematically overestimates renal function. Comparison of creatinine-based GFR estimations and GFRio show acceptable bias but wide LoA.

Kinetic Glomerular Filtration Rate Equations in Patients With Shock: Comparison With the Iohexol-Based Gold-Standard Method.

Static glomerular filtration rate formulas are not suitable for critically ill patients because of nonsteady state glomerular filtration rate and variation in the volume of distribution. Kinetic glomerular filtration rate formulas remain to be evaluated against a gold standard. We assessed the most accurate kinetic glomerular filtration rate formula as compared to iohexol clearance among patients with shock. Retrospective multicentric study. Three French ICUs in tertiary teaching hospitals. Fifty-seven patients within the first 12 hours of shock. On day 1, we compared kinetic glomerular filtration rate formulas with iohexol clearance, with or without creatinine concentration correction according to changes in volume of distribution and ideal body weight. We analyzed three static glomerular filtration rate formulas (Cockcroft and Gault, modification of diet in renal disease, and Chronic Kidney Disease-Epidemiology Collaboration), urinary creatinine clearance, and seven kinetic glomerular filtration rate formulas (Jelliffe, Chen, Chiou and Hsu, Moran and Myers, Yashiro, Seelhammer, and Brater). We evaluated 33 variants of these formulas after applying corrective factors. The bias ranged from 12 to 47 mL/min/1.73 m2. Only the Yashiro equation had a lower bias than urinary creatinine clearance before applying corrective factors (15 vs 20 mL/min/1.73 m2). The corrected Moran and Myers formula had the best mean bias, 12 mL/min/1.73 m2, but wide limits of agreement (-50 to 73). The corrected Moran and Myers value was within 30% of iohexol-clearance-measured glomerular filtration rate for 27 patients (47.4%) and was within 10% for nine patients (15.8%); other formulas showed even worse accuracy. Kinetic glomerular filtration rate equations are not accurate enough for glomerular filtration rate estimation in the first hours of shock, when glomerular filtration rate is greatly decreased. They can both under- or overestimate glomerular filtration rate, with a trend to overestimation. Applying corrective factors to creatinine concentration or volume of distribution did not improve accuracy sufficiently to make these formulas reliable. Clinicians should not use kinetic glomerular filtration rate equations to estimate glomerular filtration rate in patients with shock.

Iohexol plasma clearance simplified by Dried Blood Spot (DBS) sampling to measure renal function in conscious mice

There is no simple method to measure glomerular filtration rate (GFR) in mice, which limits the use of mice in models of renal diseases. We aimed at simplifying the plasma clearance of iohexol in mice, using dried blood spot (DBS) sampling in order to reduce the amount of blood taken for analysis. GFR was measured simultaneously by a reference method in total blood—as described before—and tested method using DBS in fifteen male and six female C57BL/6J mice. Total blood extraction was 50 μL for the reference methods and 25μL for the tested methods, distributed in 5 samples. The agreement of GFR values between both methods was analyzed with the concordance correlation coefficient (CCC), total deviation index (TDI) and coverage probability (CP). The agreement between both methods was excellent, showing a TDI = 8.1%, which indicates that 90% of the GFR values obtained with DBS showed an error ranging from − 8 to + 8% of the reference method; a CCC of 0.996 (CI: 0.992), reflecting high precision and accuracy and a CP of 94 (CI: 83), indicating that 6% of the GFR values obtained with DBS had an error greater than 10% of the method in blood. So, both methods are interchangeable. DBS represent a major simplification of GFR measurement in mice. Also, DBS improves animal welfare by reducing the total blood required and refining the procedure.

Kidney function and markers of renal damage after renal denervation. Does method of measurement matter? The Reshape CV‐Risk Study

Data suggest that renal denervation (RDN) in treatment‐resistant hypertension (TRHT) is safe in terms of renal function. However, most studies report kidney function as creatinine‐based estimated glomerular filtration rate (eGFR), which may be biased by non‐renal factors. Damage markers other than albuminuria have never been evaluated after RDN. In this non‐randomized RDN trial, we studied changes in kidney function, assessed as measured GFR (mGFR) and various GFR estimates, six months and two years after RDN. We also examined changes in albuminuria and a biomarker of tubular dysfunction. Adult non‐diabetic patients with TRHT and eGFR ≥45 ml/min/1.73 m2 were recruited from hypertension clinics. Before bilateral RDN, mGFR was measured by iohexol clearance. We estimated eGFR from serum creatinine and cystatin C (eGFRcrea, eGFRcys, and eGFRcreacys), and albumin‐creatinine ratio (ACR) and N‐acetyl‐β‐D‐glucosaminidase (NAG)‐creatinine ratio (NAG‐CR) were measured in spot urines. All measurements were repeated after six and twenty‐four months.Twenty patients, mean age 54 (±9) years and baseline mGFR 83 (±20) ml/min/1.73 m2 underwent RDN. After six months, mGFR fell, eGFRcrea remained unchanged, whereas eGFRcys and eGFRcreacys increased. At 2 years’ follow‐up, eGFRcreacys was significantly lower than at baseline. mGFR was 78 (±28) ml/min/1.73 m2. Change in ambulatory systolic BP predicted change in eGFRcrea. Urinary NAG‐CR, but not ACR, increased during follow‐up.Different GFR assessments gave diverging results after RDN. Therefore, care should be taken to method when evaluating kidney function after RDN. Increases in a tubular dysfunction biomarker suggest that kidney damage may occur. Long‐term renal follow‐up is needed after RDN.

Unraveling the Contribution of Fluid Therapy to the Development of Augmented Renal Clearance in a Piglet Model.

Augmented renal clearance (ARC) observed in the critically ill pediatric population has received an increased attention over the last years due to its major impact on the disposition and pharmacokinetics of mainly renally excreted drugs. Apart from an important inflammatory trigger, fluid administration has been suggested to contribute to the development of ARC. Therefore, the primary objective of this study was to evaluate the effect of continuous intravenous fluid administration on renal function using a conventional piglet animal model and to quantify the impact of fluid administration on the pharmacokinetics of renally excreted drugs. At baseline, twenty-four piglets (12 treatment/12 control; 7 weeks old, all ♂) received the marker drugs iohexol (64.7 mg/kg body weight (BW)) and para-aminohippuric acid (10 mg/kg BW) to quantify glomerular filtration rate and effective renal plasma flow, respectively. In addition, the hydrophilic antibiotic amikacin (7.5 mg/kg BW) was administered. Following this baseline measurement, the treatment group received fluid therapy as a constant rate infusion of 0.9% saline at 6 mL/kg/h over 36 h. After 24 h of fluid administration, the marker drugs and amikacin were administered again. When comparing both groups, a significant effect of fluid administration on the total body clearances of iohexol (p = 0.032) and amikacin (p = 0.0014) was observed. Clearances of iohexol and amikacin increased with on average 15 and 14%, although large interindividual variability was observed. This led to decreased systemic exposure to amikacin, which was manifested as decrease in area under the plasma concentration-time curve from time 0 h to infinity from 34,807 to 30,804 ng.h/mL. These results suggest that fluid therapy is a key factor involved in the development of ARC and should be taken into account when administering mainly renally excreted drugs. However, further research is necessary to confirm these results in children.

Renoprotective role of bariatric surgery in patients with established chronic kidney disease.

BackgroundBariatric surgery (BS) has been postulated as the most effective measure for weight reduction. Weight loss improves metabolic parameters and exerts changes in renal function that lead to the amelioration of absolute or relative glomerular hyperfiltration, a condition that may be renoprotective in the long term. However, few studies have demonstrated the influence of BS in patients with severe obesity and chronic kidney disease (CKD). Our objective was to analyse the evolution of renal function, adipose tissue–derived molecules and inflammatory parameters in patients with CKD after BS.MethodsThis is an observational and prospective study. Thirty patients were screened and 12 were included between January 2016 and January 2018 with a 24-month follow-up. Glomerular filtration rate (GFR) was determined by plasma iohexol clearance. Adipokines, cytokines, circulating hormones and fibrotic parameters were evaluated before and 12 months after BS using the Bioplex system.ResultsThe mean age was 50.6 years and 58.3% were males. Seven patients had a body mass index >40 kg/m2 and 66.7% were diabetic. Twenty-four months following BS there was a significant decrease in body weight (36.4%). Proteinuria decreased by 63.7 ± 28.2%. Measured GFR significantly diminished from before surgery to Month 24 after surgery (94 ± 44 to 79 ± 44 mL/min, P = 0.03). There was a significant decrease in adipocyte-derived molecules (leptin and vifastin) as well as in pro-inflammatory cytokines [interleukin (IL)-1β, tumour necrosis factor α, IL-6 and monocyte chemoattractant protein-1] and other circulating factors (vascular endothelial growth factor and transforming growth factor β isoforms).ConclusionsBS is an effective option to prevent kidney damage in obese subjects with CKD due to the improvement of glomerular hyperfiltration, adipocyte cytokines metabolic and inflammatory parameters.

Low birthweight is associated with lower glomerular filtration rate in middle-aged mainly healthy women.

BackgroundLow birthweight (LBW) has been shown to increase the risk of severe kidney disease. Studies have also shown associations between LBW and lower estimated glomerular filtration rate (GFR) in young adults. In this study we investigated whether LBW associates with measured GFR (mGFR) in middle-aged mainly healthy adults.MethodsWe invited individuals with LBW (1100–2300 g) and individuals with normal BW (NBW; 3500–4000 g) ages 41–52 years. GFR was measured using plasma clearance of iohexol. BW and BW for gestational age (BWGA) were obtained from the Medical Birth Registry of Norway and tested as main predictors. GFR was the main outcome.ResultsWe included 105 individuals (57 LBW and 48 NBW). The mean GFR was 95 ± 14 mL/min/1.73 m2 in the LBW group and 100 ± 13 mL/min/1.73 m2 in the NBW group (P = 0.04). There was a significant sex difference: in women the mean GFR was 90 ± 12 versus 101 ± 14 mL/min/1.73 m2 in the LBW and NBW groups, respectively (P = 0.006), whereas corresponding values for men were 101 ± 15 versus 100 ± 11 mL/min/1.73 m2 (P = 0.7). Using linear regression, we found the GFR was 4.5 mL/min/1.73 m2 higher per 1 kg higher BW for women (P = 0.02), with a non-significant 1.2 mL/min/1.73 m2 lower GFR for men (P = 0.6). In analyses of BWGA, there was also a significant association for women, but not for men.ConclusionsMiddle-aged mainly healthy women with LBW had lower mGFR as compared with women with NBW. No such difference was found for men.

A New Panel-Estimated GFR, Including β2-Microglobulin and β-Trace Protein and Not Including Race, Developed in a Diverse Population

Glomerular filtration rate (GFR) estimation based on creatinine and cystatin C (eGFRcr-cys) is more accurate than estimated GFR (eGFR) based on creatinine or cystatin C alone (eGFRcr or eGFRcys, respectively), but the inclusion of creatinine in eGFRcr-cys requires specification of a person's race. β2-Microglobulin (B2M) and β-trace protein (BTP) are alternative filtration markers that appear to be less influenced by race than creatinine is. Study of diagnostic test accuracy. Development in a pooled population of 7 studies with 5,017 participants with and without chronic kidney disease. External validation in a pooled population of 7 other studies with 2,245 participants. Panel eGFR using B2M and BTP in addition to cystatin C (3-marker panel) or creatinine and cystatin C (4-marker panel) with and without age and sex or race. GFR measured as the urinary clearance of iothalamate, plasma clearance of iohexol, or plasma clearance of [51Cr]EDTA. Mean measured GFRs were 58.1 and 83.2 mL/min/1.73 m2, and the proportions of Black participants were 38.6% and 24.0%, in the development and validation populations, respectively. Indevelopment, addition of age and sex improved the performance of all equations compared with equations without age and sex, but addition of race did not further improve the performance. In validation, the 4-marker panels were more accurate than the 3-marker panels (P< 0.001). The 3-marker panel without race was more accurate than eGFRcys (percentage of estimates greater than 30% different from measured GFR [1 - P30] of 15.6% vs 17.4%; P= 0.01), and the 4-marker panel without race was as accurate as eGFRcr-cys (1 - P30 of 8.6% vs 9.4%; P= 0.2). Results were generally consistent across subgroups. No representation of participants with severe comorbid illness and from geographic areas outside of North America and Europe. The 4-marker panel eGFR is as accurate as eGFRcr-cys without requiring specification of race. A more accurate race-free eGFR could be an important advance.

Prediction of Kidney Drug Clearance: A Comparison of Tubular Secretory Clearance and Glomerular Filtration Rate.

Although proximal tubular secretion is the primary mechanism of kidney drug elimination, current kidney drug dosing strategies are on the basis of eGFR. In a dedicated pharmacokinetic study to compare GFR with tubular secretory clearance for predicting kidney drug elimination, we evaluated stable outpatients with eGFRs ranging from 21 to 140 ml/min per 1.73 m2. After administering single doses of furosemide and famciclovir (metabolized to penciclovir), we calculated their kidney clearances on the basis of sequential plasma and timed urine measurements. Concomitantly, we quantified eight endogenous secretory solutes in plasma and urine using liquid chromatography-tandem mass spectrometry and measured GFR by iohexol clearance (iGFR). We computed a summary secretion score as the scaled average of the secretory solute clearances. Median iGFR of the 54 participants was 73 ml/min per 1.73 m2. The kidney furosemide clearance correlated with iGFR (r=0.84) and the summary secretion score (r=0.86). The mean proportionate error (MPE) between iGFR-predicted and measured furosemide clearance was 30.0%. The lowest MPE was observed for the summary secretion score (24.1%); MPEs for individual secretory solutes ranged from 27.3% to 48.0%. These predictive errors were statistically indistinguishable. Penciclovir kidney clearance was correlated with iGFR (r=0.83) and with the summary secretion score (r=0.91), with similar predictive accuracy of iGFR and secretory clearances. Combining iGFR with the summary secretion score yielded only modest improvements in the prediction of the kidney clearance of furosemide and penciclovir. Secretory solute clearance measurements can predict kidney drug clearances. However, tight linkage between GFR and proximal tubular secretory clearance in stable outpatients provides some reassurance that GFR, even when estimated, is a useful surrogate for predicting secretory drug clearances in such patients.

Comparison of iohexol plasma clearance formulas vs. inulin urinary clearance for measuring glomerular filtration rate.

The one-compartment iohexol plasma clearance has been proposed as a reliable alternative to renal inulin clearance. However, this method's performance depends on the formula used to calculate glomerular filtration rate (GFR). This study reports on performance comparisons between various mathematical formulas proposed for iohexol plasma clearance vs. inulin urinary clearance. GFR was simultaneously determined by inulin and iohexol clearance in 144 participants (age: 10-84years; glomerular filtration rate: 15-169mL/min/1.73m2). A retrospective cross-sectional study evaluated the performance of four formulas proposed to calculate plasma iohexol clearance (Brøchner-Mortensen, Fleming etal., Jødal-Brøchner-Mortensen, and Ng-Schwartz-Munoz). The performance of each formula was assessed using bias, precision (standard deviation of the bias), accuracy (percentage iohexol within 5, 10, and 15%), root mean square error, and concordance correlation coefficient vs. renal inulin clearance as reference. Regarding accuracy, there was no difference in root mean square error (RMSE), P5, P10, or P15 between the four formulas. The four concordance correlation coefficients (CCC) between the value from each formula and in-GFR were high and not significantly different. At in-GFR≥90mL/min/1.73m2, Ng-Schwartz-Munoz formula performed slightly better than other formulas regarding median bias (-0.5; 95% CI [-3.0 to 2.0] and accuracy P15 (95.0; 95% CI [88.0-100.0]). The studied formulas were found equivalent in terms of precision and accuracy, but the Ng-Schwartz-Munoz formula improved the accuracy at higher levels of in-GFR.

Urinary excretion of epidermal growth factor and rapid loss of kidney function.

Lower urinary excretion of the kidney tubule-specific biomarker epidermal growth factor (uEGF) is associated with increased risk of renal function [glomerular filtration rate (GFR)] loss in diabetes and in patients with established chronic kidney disease (CKD). We investigated whether uEGF is associated with rapid GFR decline or incident CKD in the general population. Subjects without CKD or diabetes were recruited from the general population in Tromso, Norway [Renal Iohexol Clearance Survey (RENIS); N = 1249] and Groningen, the Netherlands [Prevention of REnal and Vascular END-stage disease (PREVEND); N = 4534], with a median follow-up of 5.6 and 7.4 years, respectively. GFR was measured by iohexol clearance in the RENIS and estimated using the CKD Epidemiology Collaboration creatinine-cystatin C equation in the PREVEND study. Rapid GFR decline was defined as an annual GFR loss >3.0 mL/min/1.73 m2 and in sensitivity analyses as subjects with the 10% steepest GFR slope within each cohort. Lower baseline uEGF excretion was associated with rapid GFR loss in both cohorts {RENIS, odds ratio [OR] per 1 μg/mmol lower uEGF 1.42 [95% confidence interval (CI) 1.06-1.91], P = 0.02; PREVEND, OR 1.29 [95% CI 1.10-1.53], P < 0.01}, adjusted for baseline GFR, albumin:creatinine ratio and conventional CKD risk factors. Similar results were obtained using the outcome of the 10% steepest GFR slope in each cohort. Lower uEGF levels were associated with incident CKD in the combined analysis of both cohorts. Lower uEGF levels are associated with increased risk of rapid GFR loss and incident CKD in the general population. This finding, together with previous findings in CKD and high-risk populations, supports that uEGF may serve as a broadly applicable biomarker representing the tubular component of the current glomerulus-centric clinical risk assessment system.

Two Toxic Lipid Aldehydes, 4-hydroxy-2-hexenal (4-HHE) and 4-hydroxy-2-nonenal (4-HNE), Accumulate in Patients with Chronic Kidney Disease.

Lipid aldehydes originating from the peroxidation of n-3 and n-6 polyunsaturated fatty acids are increased in hemodialysis (HD) patients, a process already known to promote oxidative stress. However, data are lacking for patients with chronic kidney disease (CKD) before the initiation of HD. We prospectively evaluated the changes of plasma concentrations of two major lipid aldehydes, 4-HHE and 4-HNE, according to the decrease of glomerular filtration rate (GFR) in 40 CKD and 13 non-CKD participants. GFR was measured by inulin or iohexol clearance. Thus, 4-hydroxy-2-nonenal (4-HNE) and 4-hydroxy-2-hexenal (4-HHE) were quantitated in plasma by gas chromatography coupled with mass spectrometry and their covalent adducts on proteins were quantified by immunoblotting. On the one hand, 4-HHE plasma concentration increased from CKD stage I–II to CKD stage IV–V compared to non-CKD patients (4.5-fold higher in CKD IV–V, p < 0.005). On the other hand, 4-HNE concentration only increased in CKD stage IV–V patients (6.2-fold, p < 0.005). The amount of covalent adducts of 4-HHE on plasma protein was 9.5-fold higher in CKD patients than in controls (p < 0.005), while no difference was observed for 4-HNE protein adducts. Plasma concentrations of 4-HNE and 4-HHE are increased in CKD IV–V patients before the initiation of hemodialysis.

A Simplified Iohexol-Based Method to Measure Renal Function in Sheep Models of Renal Disease.

Sheep are highly adequate models for human renal diseases because of their many similarities in the histology and physiology of kidney and pathogenesis of kidney diseases. However, the lack of a simple method to measure glomerular filtration rate (GFR) limits its use as a model of renal diseases. Hence, we aimed to develop a simple method to measure GFR based on the plasma clearance of iohexol by assessing different pharmacokinetic models: (a) CL2: two-compartment (samples from 15 to 420 min; reference method); (b) CL1: one-compartment (samples from 60 to 420 min); (c) CLlf: CL1 adjusted by a correction formula and (d) SM: simplified CL2 (15 to 300 min). Specific statistics of agreement were used to test the models against CL2. The agreement between CL1 and CL2 was low, but both CL1f and SM showed excellent agreement with CL2, as indicated by a total deviation index of ~5–6%, a concordance correlation of 0.98–0.99% and a coverage probability of 99–100%, respectively. Hence, the SM approach is preferable due to a reduced number of samples and shorter duration of the procedure; two points that improve animal management and welfare.

Abstract 3015: Tucatinib inhibits creatinine and metformin renal tubule secretion but has no effect on renal function (GFR)

Abstract Background: Tucatinib (TUC) is a potent, highly selective investigational HER2 tyrosine kinase inhibitor in development for treatment of patients with HER2+ metastatic breast cancer (MBC). In HER2CLIMB (H2C), a pivotal study of patients with HER2+ MBC, a modest transient, reversible increase in serum creatinine (SCr) levels was observed in patients who received TUC. Similarly, in a study with healthy volunteers, SCr increased after 300 mg BID TUC and returned to baseline levels after TUC discontinuation. Clinically, SCr is used as a biomarker for glomerular filtration rate (GFR) and is routinely measured to monitor for potential renal injury. However, SCr renal elimination also depends on the kidney transporters OCT2 (uptake), MATE1 (efflux) and MATE2-K (efflux). Inhibition of OCT2 and MATE1/2-K has been associated with SCr increases in the absence of kidney damage (e.g., abemaciclib). In vitro assessments and a clinical study were performed to assess the impact of TUC on OCT2 and MATE1/2-K-mediated transport. Methods: Inhibition of OCT2, MATE1, and MATE2-K-mediated transport by TUC was estimated in transfected MDCK-II cells using creatinine and metformin (MF), a sensitive OCT2 and MATE1/2-K substrate used to quantify transport inhibition in vivo, as probe substrates. Subsequently, a single-arm drug-drug interaction study was performed in 17 healthy volunteers to evaluate the effects of TUC on MF PK. MF (850 mg, PO) was administered in the absence and presence of TUC (300 mg BID, PO). Iohexol was administered to calculate actual GFR (aGFR) in the absence and presence of TUC. Plasma (iohexol, MF and TUC) and urine (MF) samples were collected for PK analysis; drug concentrations were measured using validated LC-MS/MS methods. Serum and urine creatinine levels were also measured. Results: In MDCK II cells, TUC inhibited creatinine transport by OCT2 (IC50 = 0.107 µM) and MATE1 (IC50 = 0.086 µM) and MF transport by MATE1 (IC50 = 0.340 µM) and MATE2-K (IC50 = 0.135 µM), but not by OCT2 (IC50 = 14.7 µM). Using these IC50 values, physiologically-based pharmacokinetic (PBPK) model simulations predicted a 1.16 to 1.35-fold increase of MF exposure in the presence of TUC. Consistent with the PBPK prediction, in healthy volunteers MF exposure (AUCinf) increased ~1.4-fold and renal clearance decreased from 29.99 L/h to 17.64 L/h in the presence of TUC with no effect on MF Cmax. Iohexol clearance was unaffected in the presence of TUC indicating no change in aGFR. SCr increased in the presence of TUC and returned to baseline 8 days after TUC discontinuation. Conclusions: Together, these data demonstrate that the observed SCr increase in clinical studies with TUC is due to inhibition of tubular secretion of creatinine via OCT2 and MATE1 and not due to an effect on kidney function. An alternative, non-creatinine-based measure of renal function should be considered for tucatinib. Citation Format: Ariel R. Topletz-Erickson, Anthony Lee, JoAl Mayor, Evelyn Rustia, Layth Abdulrasool, Luke Walker, Christopher J. Endres. Tucatinib inhibits creatinine and metformin renal tubule secretion but has no effect on renal function (GFR) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3015.

Simultaneous glomerular filtration rate determination using inulin, iohexol, and 99mTc-DTPA demonstrates the need for customized measurement protocols

Urinary inulin clearance is considered the gold standard of glomerular filtration rate (GFR) measurement but plasma clearance of less expensive and more accessible tracers is more commonly performed. Many plasma sampling protocols exist but little is known about their accuracy. Here, the study objectives were to compare plasma iohexol and 99mTc-DTPA GFR with varying sampling strategies to the GFR measured by urinary inulin and to identify protocols with the greatest accuracy according to clinical characteristics. GFR was measured simultaneously using urinary inulin, plasma iohexol, and plasma 99mTc DTPA clearance. Blood was sampled from 2 to 10 hours after injection. For each method, bias, precision, and accuracy (P30 and mean absolute error) were calculated for the entire cohort and for eGFR-EPI creatinine subgroups (<30, 30-59, and≥60 ml/min/1.73m2) and the edema stage using urinary inulin clearance as the gold standard. The mean inulin GFR of the 77 participants was 33 ml/min/1.73m2. Delay of both the initial and the final samples in plasma iohexol protocols yielded the highest accuracy in the setting of low GFR (<30 ml/min/1.73m2). Early initial and final samples yielded the highest accuracy in the setting of high GFRs (≥60 ml/min/1.73m2). No sampling strategy was accurate in edematous patients. Thus, our study demonstrates that customization of GFR protocols according to the anticipated level of GFR are required to optimize protocol accuracy.

Relative Hypoxia and Early Diabetic Kidney Disease in Type 1 Diabetes.

The objective of this study was to compare the ratio of renal oxygen availability (RO2) to glomerular filtration rate (GFR), a measure of relative renal hypoxia, in adolescents with and without type 1 diabetes (T1D) and relate the ratio to albuminuria, renal plasma flow (RPF), fat mass, and insulin sensitivity (M/I). RO2 was estimated by blood oxygen level-dependent MRI; fat mass was estimated by DXA; GFR and RPF were estimated by iohexol and p-aminohippurate clearance; albuminuria was estimated by urine albumin-to-creatinine ratio (UACR); and M/I was estimated from steady-state glucose infusion rate/insulin (mg/kg/min) by hyperglycemic clamp in 50 adolescents with T1D (age 16.1 ± 3.0 years, HbA1c 8.6 ± 1.2%) and 20 control patients of similar BMI (age 16.1 ± 2.9 years, HbA1c 5.2 ± 0.2%). The RO2:GFR (ms/mL/min) was calculated as RO2 (T2*, ms) divided by GFR (mL/min). Whole-kidney RO2:GFR was 25% lower in adolescents with T1D versus control patients (P < 0.0001). In adolescents with T1D, lower whole-kidney RO2:GFR was associated with higher UACR (r = -0.31, P = 0.03), RPF (r = -0.52, P = 0.0009), and fat mass (r = -0.33, P = 0.02). Lower medullary RO2:GFR was associated with lower M/I (r = 0.31, P = 0.03). In conclusion, adolescents with T1D exhibited relative renal hypoxia that was associated with albuminuria and with increased RPF, fat mass, and insulin resistance. These data suggest a potential role of renal hypoxia in the development of diabetic kidney disease.

Cystatin C and Urine Albumin to Creatinine Ratio Predict 5-Year Mortality and Cardiovascular Events in People Living With HIV.

Identifying people with HIV (PWH) at risk for chronic kidney disease, cardiovascular events, and death is crucial. We evaluated biomarkers to predict all-cause mortality and cardiovascular events, and measured glomerular filtration rate (mGFR) slope. Biomarkers were measured at enrollment. Baseline and 5-year mGFR were measured by plasma iohexol clearance. Outcomes were a composite criterion of all-cause mortality and/or cardiovascular events, and mGFR slope. Of 168 subjects, 146 (87.4%) had undetectable HIV load. Median follow-up was 59.1 months (interquartile range, 56.2-62.1). At baseline, mean age was 49.5 years (± 9.8) and mean mGFR 98.9 mL/min/1.73m2 (± 20.6). Seventeen deaths and 10 cardiovascular events occurred during 5-year follow-up. Baseline mGFR was not associated with mortality/cardiovascular events. In multivariable analysis, cystatin C (hazard ratio [HR], 5.978; 95% confidence interval [CI], 2.774-12.88; P < .0001) and urine albumin to creatinine ratio (uACR) at inclusion (HR, 1.002; 95% CI, 1.001-1.004; P < .001) were associated with mortality/cardiovascular events. Area under receiver operating curve of cystatin C was 0.67 (95% CI, .55-.79) for mortality/cardiovascular event prediction. Biomarkers were not associated with GFR slope. uACR and cystatin C predict all-cause mortality and/or cardiovascular events in PWH independently of mGFR.

Quantitation of iohexol, a glomerular filtration marker, in human plasma by LC–MS/MS

We developed a high-performance liquid chromatography mass spectrometry method for quantitating iohexol in 50 μL human plasma. After acetonitrile protein precipitation, chromatographic separation was achieved with a Shodex Asahipak NH2P-50 2D (5 μm, 2 × 150 mm) column and a gradient of 0.1 % formic acid in acetonitrile and 0.1 % formic acid in water over a 10 min run time. Mass spectrometric detection was performed on a Micromass Quatromicro triple-stage bench-top mass spectrometer with electrospray, positive-mode ionization. The assay was linear from 1 to 500 μg/mL for iohexol, proved to be accurate (101.3–102.1 %) and precise (<3.4 %CV), and fulfilled Food and Drug Administration (FDA) criteria for bioanalytical method validation. Recovery from plasma was 53.1–64.2 % and matrix effect was trivial (−3.4 to −1.3 %). Plasma freeze thaw stability (97.4–99.4 %), stability for 5 months at −80 °C (95.5–103.3 %), and stability for 4 h at room temperature (100.6–103.3 %) were all acceptable. This validated assay using a deuterated internal standard will be an important tool in measuring iohexol clearance and determining glomerular filtration rate (GFR) in patients.

Effects of the SGLT2 inhibitor dapagliflozin on proteinuria in non-diabetic patients with chronic kidney disease (DIAMOND): a randomised, double-blind, crossover trial

SGLT2 inhibition decreases albuminuria and reduces the risk of kidney disease progression in patients with type 2 diabetes. These benefits are unlikely to be mediated by improvements in glycaemic control alone. Therefore, we aimed to examine the kidney effects of the SGLT2 inhibitor dapagliflozin in patients with proteinuric kidney disease without diabetes. DIAMOND was a randomised, double-blind, placebo-controlled crossover trial done at six hospitals in Canada, Malaysia, and the Netherlands. Eligible participants were adult patients (aged 18-75 years) with chronic kidney disease, without a diagnosis of diabetes, with a 24-h urinary protein excretion greater than 500 mg and less than or equal to 3500 mg and an estimated glomerular filtration rate (eGFR) of at least 25 mL/min per 1·73 m2, and who were on stable renin-angiotensin system blockade. Participants were randomly assigned (1:1) to receive placebo and then dapagliflozin 10 mg per day or vice versa. Each treatment period lasted 6 weeks with a 6-week washout period in between. Participants, investigators, and study personnel were masked to assignment throughout the trial and analysis. The primary outcome was percentage change from baseline in 24-h proteinuria during dapagliflozin treatment relative to placebo. Secondary outcomes were changes in measured GFR (mGFR; via iohexol clearance), bodyweight, blood pressure, and concentrations of neurohormonal biomarkers. Analyses were done in accordance with the intention-to-treat principle. This study is registered with ClinicalTrials.gov, NCT03190694. Between Nov 22, 2017, and April 5, 2019, 58 patients were screened, of whom 53 (mean age 51 years [SD 13]; 32% women) were randomly assigned (27 received dapagliflozin then placebo and 26 received placebo then dapagliflozin). One patient discontinued during the first treatment period. All patients were included in the analysis. Mean baseline mGFR was 58·3 mL/min per 1·73 m2 (SD 23), median proteinuria was 1110 mg per 24 h (IQR 730-1560), and mean HbA1c was 5·6% (SD 0·4). The difference in mean proteinuria change from baseline between dapagliflozin and placebo was 0·9% (95% CI -16·6 to 22·1; p=0·93). Compared with placebo, mGFR was changed with dapagliflozin treatment by -6·6 mL/min per 1·73 m2 (-9·0 to -4·2; p<0·0001) at week 6. This reduction was fully reversible within 6 weeks after dapagliflozin discontinuation. Compared with placebo, bodyweight was reduced by 1·5 kg (0·03-3·0; p=0·046) with dapagliflozin; changes in systolic and diastolic blood pressure and concentrations of neurohormonal biomarkers did not differ significantly between dapagliflozin and placebo treatment. The numbers of patients who had one or more adverse events during dapagliflozin treatment (17 [32%] of 53) and during placebo treatment (13 [25%] of 52) were similar. No hypoglycaemic events were reported and no deaths occurred. 6-week treatment with dapagliflozin did not affect proteinuria in patients with chronic kidney disease without diabetes, but did induce an acute and reversible decline in mGFR and a reduction in bodyweight. Long-term clinical trials are underway to determine whether SGLT2 inhibitors can safely reduce the rate of major clinical kidney outcomes in patients with chronic kidney disease with and without diabetes. AstraZeneca.