Renal effects of the serine protease inhibitor aprotinin in healthy conscious mice

Treatment with aprotinin, a broad-spectrum serine protease inhibitor with a molecular weight of 6512 Da, was associated with acute kidney injury, which was one of the reasons for withdrawal from the market in 2007. Inhibition of renal serine proteases regulating the epithelial sodium channel ENaC could be a possible mechanism. Herein, we studied the effect of aprotinin in wild-type 129S1/SvImJ mice on sodium handling, tubular function, and integrity under a control and low-salt diet. Mice were studied in metabolic cages, and aprotinin was delivered by subcutaneously implanted sustained release pellets (2 mg/day over 10 days). Mean urinary aprotinin concentration ranged between 642 ± 135 (day 2) and 127 ± 16 (day 8) µg/mL . Aprotinin caused impaired sodium preservation under a low-salt diet while stimulating excessive hyperaldosteronism and unexpectedly, proteolytic activation of ENaC. Aprotinin inhibited proximal tubular function leading to glucosuria and proteinuria. Plasma urea and cystatin C concentration increased significantly under aprotinin treatment. Kidney tissues from aprotinin-treated mice showed accumulation of intracellular aprotinin and expression of the kidney injury molecule 1 (KIM-1). In electron microscopy, electron-dense deposits were observed. There was no evidence for kidney injury in mice treated with a lower aprotinin dose (0.5 mg/day). In conclusion, high doses of aprotinin exert nephrotoxic effects by accumulation in the tubular system of healthy mice, leading to inhibition of proximal tubular function and counterregulatory stimulation of ENaC-mediated sodium transport.

Melatonin protects against tenofovir-induced nephrotoxicity in rats by targeting multiple cellular pathways

Nephrotoxicity is a dose-limiting side effect of long-term use of tenofovir, a reverse transcriptase inhibitor that is used for the treatment of HIV infection and chronic hepatitis B infection. Identifying an agent that prevents tenofovir disoproxil fumarate (TDF)-induced renal injury can lead to its better tolerance, and a more effective treatment can be achieved. The present study is aimed at investigating whether melatonin, a potent antioxidant and anti-inflammatory agent, protects against TDF nephrotoxicity in rats and to determine its cellular targets. Rats were divided into groups and treated as follows. Group I (control): Rats in this group (n = 6) received sterile water only by gavage for 35 days. Group II: Rats (n = 6) in this group received 600 mg/kg body weight TDF in sterile water by gavage for 35 days. Group III: Rats (n = 6) in this group received once daily 20 mg/kg bodyweight melatonin i.p. 2 h before the administration of 600 mg/kg body weight TDF in sterile water by gavage for 35 days. Group IV: Rats were pretreated daily with 20 mg/kg body weight melatonin i.p. 2 h before the administration of sterile water by gavage. All the rats were sacrificed on the 36th day, after overnight fast. Melatonin pretreatment protected the rats against TDF nephrotoxicity both histologically and biochemically. Biochemically, melatonin pretreatment attenuated TDF-induced, oxidative stress, nitrosative stress, mitochondrial pathway of apoptosis, PARP overactivation and preserved proximal tubular function (p < 0.01). This suggests that melatonin may be useful in ameliorating TDF nephrotoxicity.

995. Safety and Efficacy of F/TAF and F/TDF for PrEP in DISCOVER Participants Taking F/TDF for PrEP at Baseline

Background DISCOVER is an ongoing trial comparing emtricitabine plus tenofovir alafenamide (F/TAF) or tenofovir disoproxil fumarate (F/TDF) for HIV pre-exposure prophylaxis (PrEP). DISCOVER included some participants already taking F/TDF for PrEP at baseline (BL) creating a unique opportunity to study outcomes after switching from F/TDF to F/TAF. Methods Men who have sex with men and transgender women at risk of HIV were randomized to receive blinded daily F/TAF or F/TDF and followed for at least 96 weeks; participants taking BL F/TDF for PrEP could enroll without a washout period. Laboratory assessments included estimated glomerular filtration rate (eGFR), markers of renal proximal tubular function (RBP and β2M to creatinine ratios), and fasting cholesterol levels; these were analyzed by 2-sided Wilcoxon rank sum test. Bone mineral density (BMD) was assessed in a subset of participants and analyzed by ANOVA. Results 905 of 5387 (16.8%) participants were on BL F/TDF for PrEP for a median duration of 399 days; baseline characteristics are found in Table 1. There was one HIV infection among BL PrEP users, in a participant randomized to F/TDF who had intermittent low adherence. Participants on BL PrEP randomized to F/TAF had improvements in eGFR and markers of proximal tubular function compared to F/TDF. Median change in BMD was not statistically different for BL PrEP users assigned to F/TAF vs F/TDF, however de novo F/TAF participants had improved BMD profiles compared to F/TDF. BL PrEP users in the F/TAF arm had increases in LDL cholesterol (median +6mg/dL) compared to F/TDF, while changes in HDL and total:HDL ratio were similar. Lipid-modifying agent (LMA) initiation in BL PrEP users was more frequent in the F/TAF arm, while LMA initiation in de novo PrEP participants was similar between arms (Table 2). Table 1. Characteristics of DISCOVER participants Table 2. Efficacy and safety results Conclusion HIV incidence was low in participants taking BL PrEP. Participants who switched from F/TDF to F/TAF had improvements in renal biomarkers. There was no statistical difference in BMD among BL PrEP users, although numbers were small. The observed lipid changes in BL PrEP users are consistent with the LDL and HDL suppressive effect of TDF, and the small but higher rate of LMA initiation with F/TAF is likely related to withdrawal of this effect. Disclosures Thomas Campbell, MD, Gilead Sciences Inc. (Scientific Research Study Investigator) Amanda Clarke, MD, Gilead Sciences Inc. (Consultant, Scientific Research Study Investigator, Other Financial or Material Support, Conference attendance sponsorship)Viiv Healthcare (Consultant, Other Financial or Material Support, Conference travel sponsorship) Benoit Trottier, MD, AbbVie (Grant/Research Support, Other Financial or Material Support, Personal fees)Bristol-Myers Squibb (Grant/Research Support, Other Financial or Material Support, Personal fees)Gilead Sciences Inc. (Grant/Research Support, Scientific Research Study Investigator, Other Financial or Material Support, Personal fees)Janssen (Grant/Research Support, Other Financial or Material Support, Personal fees)Merck (Grant/Research Support, Other Financial or Material Support, Personal fees)Viiv Healthcare (Grant/Research Support, Other Financial or Material Support, Personal fees) Christoph C. Carter, MD, Gilead Sciences Inc. (Employee, Shareholder) Yongwu Shao, PhD, Gilead Sciences Inc. (Employee, Shareholder) Ramin Ebrahimi, MSc, Gilead Sciences Inc. (Employee, Shareholder) Moupali Das, MD, Gilead Sciences Inc. (Employee, Shareholder) Diana M. Brainard, MD, Gilead Sciences (Employee) Jay Gladstein, MD, Gilead Sciences Inc. (Scientific Research Study Investigator)

Axial differences in endocytosis along the kidney proximal tubule

The proximal tubule (PT) reabsorbs filtered proteins via receptor-mediated endocytosis to prevent energetically inefficient wasting in the urine. Recent intravital imaging studies have suggested that protein reabsorption occurs in early (S1) segments, which have a very high capacity. In contrast, uptake of fluid phase substrates also occurs in distal (S2) segments. In this article, we will review these findings and their implications for understanding integrated proximal tubular function, patterns of damage caused by endocytosed toxins, and the origins of proteinuria. We will also discuss whether compensatory downstream increases in protein uptake might occur in disease states, and the environmental factors that could drive these changes.

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.

Approach to the patient with renal Fanconi syndrome, glycosuria, or aminoaciduria

Up to 80% of filtered salt and water is returned back into the circulation in the proximal tubule. Several solutes, such as phosphate, glucose, low-molecular weight proteins, and amino acids are exclusively reabsorbed in this segment, so their appearance in urine is a sign of proximal tubular dysfunction. An entire orchestra of specialized apical and basolateral transporters, as well as paracellular molecules, mediate this reabsorption. Defects in proximal tubular function can be isolated (e.g. isolated renal glycosuria, aminoacidurias, or hypophosphataemic rickets) or generalized. In the latter case it is called the Fanconi–Debre–de Toni syndrome, based on the initial clinical descriptions. However, in clinical practice it is usually referred to as just the ‘renal Fanconi syndrome’. Severity of proximal tubular dysfunction can vary, and may coexist with some degree of loss of glomerular filtration capacity. Causes include a wide range of insults to proximal tubular cells, including a number of genetic conditions, drugs and poisons.

Impaired Urine Dilution Capability in HIV Stable Patients

Renal disease is a well-recognized complication among patients with HIV infection. Viral infection itself and the use of some antiretroviral drugs contribute to this condition. The thick ascending limb of Henle’s loop (TALH) is the tubule segment where free water clearance is generated, determining along with glomerular filtration rate the kidney’s ability to dilute urine.Objective. We analyzed the function of the proximal tubule and TALH in patients with HIV infection receiving or not tenofovir-containing antiretroviral treatment in comparison with healthy seronegative controls, by applying a tubular physiological test, hyposaline infusion test (Chaimowitz’ test).Material & Methods. Chaimowitz’ test was performed on 20 HIV positive volunteers who had normal renal functional parameters. The control group included 10 healthy volunteers.Results. After the test, both HIV groups had a significant reduction of serum sodium and osmolarity compared with the control group. Free water clearance was lower and urine osmolarity was higher in both HIV+ groups. Proximal tubular function was normal in both studied groups.Conclusion. The present study documented that proximal tubule sodium reabsorption was preserved while free water clearance and maximal urine dilution capability were reduced in stable HIV patients treated or not with tenofovir.