Evaluation of renal biomarkers, including symmetric dimethylarginine, following gentamicin-induced proximal tubular injury in the rat

Symmetric dimethylarginine (SDMA) is an excretory renal function biomarker shown to correlate well with glomerular filtration rate in dogs, cats, humans, and rats. The objectives of this study were to determine utility of serum SDMA as a renal biomarker in a rat model of gentamicin-induced renal injury and provide validation of a commercially available SDMA immunoassay for rat serum. Rats were randomly assigned to one of three dose levels of gentamicin (20, 50, or 100 mg/kg) or a vehicle control group and dosed once daily by subcutaneous injection for either four or ten days. Serum and urine renal biomarker evaluation including serum SDMA, hematologic and serum biochemical analysis, urinalysis, and histologic examination of kidney were performed. Prior to biologic validation, analytic validation of the SDMA immunoassay for rat serum was performed including assessment of assay accuracy, precision, analytical sensitivity, linearity, analyte stability, and interference testing. Among markers of excretory renal function SDMA and serum creatinine increased earliest and at the lowest gentamicin concentrations and were significantly increased in both the 50 mg/kg and the 100 mg/kg dosage levels in the 4 and 10-dose treatment groups compared to controls. Time- and dose-dependent increases were noted for all urinary biomarkers investigated in this study, with µALB being most responsive and OPN least responsive for detection of gentamicin-induced injury across dose levels and schedules investigated. The SDMA immunoassay met all set quality requirements assessed in analytical validation. This study is the first to investigate performance of serum SDMA as compared to other excretory renal function markers in a rat gentamicin acute toxicity model. In this study serum SDMA was an earlier biomarker for detection of gentamicin-induced toxicity than serum cystatin C, BUN, and creatinine clearance. The SDMA immunoassay provides a reliable commercially available assay for future renal investigations in rat models.

Increased Endocytosis of Cadmium-Metallothionein through the 24p3 Receptor in an In Vivo Model with Reduced Proximal Tubular Activity

Background: The proximal tubule (PT) is the major target of cadmium (Cd2+) nephrotoxicity. Current dogma postulates that Cd2+ complexed to metallothionein (MT) (CdMT) is taken up through receptor-mediated endocytosis (RME) via the PT receptor megalin:cubilin, which is the predominant pathway for reuptake of filtered proteins in the kidney. Nevertheless, there is evidence that the distal parts of the nephron are also sensitive to damage induced by Cd2+. In rodent kidneys, another receptor for protein endocytosis, the 24p3 receptor (24p3R), is exclusively expressed in the apical membranes of distal tubules (DT) and collecting ducts (CD). Cell culture studies have demonstrated that RME and toxicity of CdMT and other (metal ion)–protein complexes in DT and CD cells is mediated by 24p3R. In this study, we evaluated the uptake of labeled CdMT complex through 24p3R after acute kidney injury (AKI) induced by gentamicin (GM) administration that disrupts PT function. Subcutaneous administration of GM at 10 mg/kg/day for seven days did not alter the structural and functional integrity of the kidney’s filtration barrier. However, because of PT injury, the concentration of the renal biomarker Kim-1 increased. When CdMT complex coupled to FITC was administered intravenously, both uptake of the CdMT complex and 24p3R expression in DT increased and also colocalized after PT injury induced by GM. Although megalin decreased in PT after GM administration, urinary protein excretion was not changed, which suggests that the increased levels of 24p3R in the distal nephron could be acting as a compensatory mechanism for protein uptake. Altogether, these results suggest that PT damage increases the uptake of the CdMT complex through 24p3R in DT (and possibly CD) and compensate for protein losses associated with AKI.

Consensus-based technical recommendations for clinical translation of renal BOLD MRI

Harmonization of acquisition and analysis protocols is an important step in the validation of BOLD MRI as a renal biomarker. This harmonization initiative provides technical recommendations based on a consensus report with the aim to move towards standardized protocols that facilitate clinical translation and comparison of data across sites. We used a recently published systematic review paper, which included a detailed summary of renal BOLD MRI technical parameters and areas of investigation in its supplementary material, as the starting point in developing the survey questionnaires for seeking consensus. Survey data were collected via the Delphi consensus process from 24 researchers on renal BOLD MRI exam preparation, data acquisition, data analysis, and interpretation. Consensus was defined as ≥ 75% unanimity in response. Among 31 survey questions, 14 achieved consensus resolution, 12 showed clear respondent preference (65–74% agreement), and 5 showed equal (50/50%) split in opinion among respondents. Recommendations for subject preparation, data acquisition, processing and reporting are given based on the survey results and review of the literature. These technical recommendations are aimed towards increased inter-site harmonization, a first step towards standardization of renal BOLD MRI protocols across sites. We expect this to be an iterative process updated dynamically based on progress in the field.

1962. Renal Outcomes for Participants Taking F/TAF vs. F/TDF for HIV PrEP in the DISCOVER Trial

Background In the DISCOVER PrEP trial, emtricitabine/tenofovir alafenamide (F/TAF) was noninferior to emtricitabine/tenofovir disoproxil fumarate (F/TDF) for HIV prevention. Here, we report on the renal outcomes of F/TAF and F/TDF among all DISCOVER participants and in those on baseline F/TDF PrEP who were randomized to F/TAF. Methods In total, 5387 men who have sex with men (MSM) and transgender women (TGW) at risk for HIV were randomized 1:1 to receive blinded F/TDF or F/TAF taken once daily (full cohort). Of these, 905 were on F/TDF PrEP at enrollment; of whom, 465 were randomized to F/TAF. Renal function and safety assessments included urinalysis (UA), estimated glomerular filtration rate (eGFRCG), urine protein:creatinine (Cr) ratio (UPCR), markers of proximal tubular function (β2-microglobulin:Cr ratio [β2M:Cr] and retinol-binding protein:Cr ratio [RBP:Cr]) and investigator-reported renal adverse events (AEs). Week 48 data are presented. Results In the full cohort, F/TAF was associated with more favorable changes in eGFRCG, β2M:Cr, and RBP:Cr compared with F/TDF (Table 1). Treatment-emergent proteinuria by UA was more common with F/TDF than F/TAF (24.3% vs. 21.3% P = 0.009), as were treatment-emergent elevations in UPCR >200 mg/g (35 [1.5%] vs. 16 [0.7%], P = 0.005). Compared with F/TDF, participants taking F/TAF had numerically fewer study drug-related renal AEs, severe study drug-related renal AEs, and discontinuations due to renal AEs (Table 2). Proximal renal tubulopathy (Fanconi syndrome) was reported in one participant in the F/TDF arm and none in the F/TAF arm. In participants on F/TDF PrEP at enrollment who were randomized to F/TAF, statistically significant increases in eGFRCG were apparent as early as week 4 (Table 1 and Figure 1), as were decreases in tubular proteinuria (Table 1). Renal biomarker changes in PrEP-naïve participants mirrored those in the full cohort. Conclusion Through 48 weeks, MSM and TGW taking F/TAF for PrEP had significantly better measures of renal function and fewer study-drug-related renal AEs compared with those taking F/TDF; switching from F/TDF to F/TAF was associated with improvements in eGFRCG and tubular function biomarkers. F/TAF for PrEP is effective and has a superior renal safety profile compared with F/TDF. Disclosures All Authors: No reported Disclosures.

Normal Anatomy, Histology, and Spontaneous Pathology of the Kidney, and Selected Renal Biomarker Reference Ranges in the Cynomolgus Monkey

To further our understanding of the nonhuman primate kidney anatomy, histology, and incidences of spontaneous pathology, we retrospectively examined kidneys from a total of 505 control Cynomolgus monkeys ( Macaca fascicularis; 264 male and 241 females) aged 2 to 6 years, from toxicity studies. Kidney weights, urinalysis, and kidney-related clinical biochemistry parameters were also evaluated. Although the functional anatomy of the monkey kidney is relatively similar to that of other laboratory animals and humans, a few differences and species-specific peculiarities exist. Unlike humans, the macaque kidney is unipapillate, with a relatively underdeveloped papilla, scarce long loops of Henle, and a near-equivalent cortical to medullary ratio. The most common spontaneous microscopic findings were interstitial infiltrates or interstitial nephritis and other tubular lesions, but several forms of glomerulopathy that may be interpreted as drug-induced were occasionally observed. Common incidental findings of little pathological significance included: papillary mineralization, epithelial pigment, multinucleate cells, cuboidal metaplasia of the Bowman’s capsule, and urothelial inclusions. Kidney weights, and some clinical chemistry parameters, showed age- and sex-related variations. Taken together, these data will aid the toxicologic pathologist to better evaluate the nonhuman primate kidney and assess the species’ suitability as a model for identifying and characterizing drug-induced injury.