Mapping Adverse Outcome Pathways for Kidney Injury as a Basis for the Development of Mechanism-Based Animal-Sparing Approaches to Assessment of Nephrotoxicity

Resveratrol Improves Unilateral Nephrectomy/Amikacin-Induced Oxidative Injury in Rat Kidney Tissue

Chronic kidney disease (CKD) is characterized by progressive loss of kidney function and irreversible structural changes. Both kidney donation and amikacin exhibit nephrotoxic effects; however, polyphenols like resveratrol are known for their nephroprotective properties due to antioxidant capabilities. This study investigates the protective effects of resveratrol in a renal injury model involving unilateral nephrectomy and amikacin in Wistar rats. Male Wistar rats (n = 25) were divided into following five groups: (1) vehicle control, (2) resveratrol control, (3) kidney damage (unilateral nephrectomy plus amikacin), (4) resveratrol post-treatment, and (5) resveratrol pre-treatment. Renal function was assessed through serum creatinine and urea measurements. Oxidative stress was evaluated via malondialdehyde (MDA) levels, while antioxidant status was determined through total antioxidant capacity (TAC). Tissue analysis employed H&E, PAS, and Van Giesons trichrome staining. Data analysis was conducted using ANOVA and Tukeys post-hoc test for parametric data and the Kruskal-Wallis test with Dunns post-hoc for non-parametric data, with significance set at p < 0.05. Resveratrol treatment significantly improved body weight, renal compensatory growth, and several biochemical parameters. These results indicate that resveratrol may represent a promising nutritional strategy for safeguarding kidney function and architecture in renal injury contexts.

Actin Dysregulation Mediates Nephrotoxicity of Cassiae Semen Aqueous Extracts

Cassiae semen, commonly consumed as roasted tea, has been widely used for both medicinal purposes and dietary supplements. In this study, we investigated the nephrotoxic effects and underlying mechanisms of Cassiae semen aqueous extracts (CSAEs) using computational and animal models. Both male and female Sprague Dawley rats were treated with 4.73-47.30 g/kg (body weight) of CSAEs by oral gavage twice a day for 7-28 days. We found that serum and urinary biomarkers of kidney injury and kidney coefficients were increased in a dose-dependent manner, and were accompanied by morphological alterations in the kidneys of CSAEs-treated rats. Computational and molecular docking approaches predicted that the three most abundant components of CSAEs-obtusifolin, aurantio-obtusin, and obtusin-exhibited strong affinity for the binding of F-actin, ROCK1, and Rac1, and the RhoA-ROCK pathway was identified as the most likely regulatory mechanism mediating the nephrotoxicity of CSAEs. Consistently, immunofluorescence staining revealed F-actin and cytoskeleton were frequently disturbed in renal cells and brush borders at high doses of CSAEs. Results from gene expression analyses confirmed that CSAEs suppressed the key proteins in the RhoA-ROCK signaling pathway and consequently the expression of F-actin and its stabilization genes. In summary, our findings suggest that Cassiae semen can depolymerize and destabilize actin cytoskeleton by inhibition of the RhoA-ROCK pathway and/or direct binding to F-actin, leading to nephrotoxicity. The consumption of Cassiae semen as a supplement and medicine warrants attention.

Application of the Adverse Outcome Pathway Concept to In Vitro Nephrotoxicity Assessment: Kidney Injury due to Receptor-Mediated Endocytosis and Lysosomal Overload as a Case Study

Application of adverse outcome pathways (AOP) and integration of quantitative in vitro to in vivo extrapolation (QIVIVE) may support the paradigm shift in toxicity testing to move from apical endpoints in test animals to more mechanism-based in vitro assays. Here, we developed an AOP of proximal tubule injury linking a molecular initiating event (MIE) to a cascade of key events (KEs) leading to lysosomal overload and ultimately to cell death. This AOP was used as a case study to adopt the AOP concept for systemic toxicity testing and risk assessment based on in vitro data. In this AOP, nephrotoxicity is thought to result from receptor-mediated endocytosis (MIE) of the chemical stressor, disturbance of lysosomal function (KE1), and lysosomal disruption (KE2) associated with release of reactive oxygen species and cytotoxic lysosomal enzymes that induce cell death (KE3). Based on this mechanistic framework, in vitro readouts reflecting each KE were identified. Utilizing polymyxin antibiotics as chemical stressors for this AOP, the dose-response for each in vitro endpoint was recorded in proximal tubule cells from rat (NRK-52E) and human (RPTEC/TERT1) in order to (1) experimentally support the sequence of key events (KEs), to (2) establish quantitative relationships between KEs as a basis for prediction of downstream KEs based on in vitro data reflecting early KEs and to (3) derive suitable in vitro points of departure for human risk assessment. Time-resolved analysis was used to support the temporal sequence of events within this AOP. Quantitative response-response relationships between KEs established from in vitro data on polymyxin B were successfully used to predict in vitro toxicity of other polymyxin derivatives. Finally, a physiologically based kinetic (PBK) model was utilized to transform in vitro effect concentrations to a human equivalent dose for polymyxin B. The predicted in vivo effective doses were in the range of therapeutic doses known to be associated with a risk for nephrotoxicity. Taken together, these data provide proof-of-concept for the feasibility of in vitro based risk assessment through integration of mechanistic endpoints and reverse toxicokinetic modelling.