Characterization of the renal tubular transport of creatinine by activity-based protein profiling and transport kinetics

Identification of a substrate of the renal tubular transporters for detecting drug-induced early acute kidney injury

Early identification of drug-induced acute kidney injury (AKI) is essential to prevent renal damage. The renal tubules are typically the first to exhibit damage, frequently accompanied by changes in renal tubular transporters. With this in mind, we have identified an endogenous substrate of the renal tubular transporters that may serve as a biomarker for early detection of drug-induced AKI. Using gentamicin- and vancomycin-induced AKI models, we found that traumatic acid (TA), an end metabolite, was rapidly increased in both AKI models. TA, a highly albumin-bound compound (96% to 100%), could not be filtered by the glomerulus and was predominantly eliminated by renal tubules via the OAT1, OAT3, OATP4C1, and P-gp transporters. Importantly, there is a correlation between elevated serum TA levels and reduced OAT1 and OAT3 levels. A clinical study showed that serum TA levels rose before an increase in serum creatinine in 13 out of 20 AKI patients in an intensive care unit setting. In addition, there was a notable rise in TA levels in the serum of individuals suffering from nephrotic syndrome, chronic renal failure, and acute renal failure. These results indicate that the decrease in renal tubular transporter expression during drug-induced AKI leads to an increase in the serum TA level, and the change in TA may serve as a monitor for renal tubular injury. Acute kidney injury (AKI) has a high clinical incidence, and if patients do not receive timely treatment and intervention, it can lead to severe consequences. During AKI, tubular damage is often the primary issue. Endogenous biomarkers of tubular damage are critical for the early diagnosis and treatment of AKI. However, there is currently a lack of reliable endogenous biomarkers for diagnosing tubular damage in clinical practice. Tubular secretion is primarily mediated by renal tubular transporters (channels), which are also impaired during tubular damage. Therefore, we aim to identify endogenous biomarkers of tubular damage from the perspective of renal tubular transporters, providing support for the early detection and intervention of AKI. TA is a substrate of multiple channels, including OAT1, OAT3, OATP4C1, and P-gp, and is primarily secreted by the renal tubules. In the early stages of rat AKI induced by GEN and VCA, serum TA levels are significantly elevated, occurring earlier than the rise in serum creatinine (SCr). Thus, TA is expected to become a potential endogenous biomarker for the early diagnosis of tubular damage.

Utilising Endogenous Biomarkers in Drug Development to Streamline the Assessment of Drug-Drug Interactions Mediated by Renal Transporters: A Pharmaceutical Industry Perspective

The renal secretion of many drugs is facilitated by membrane transporters, including organic cation transporter 2, multidrug and toxin extrusion protein 1/2-K and organic anion transporters 1 and 3. Inhibition of these transporters can reduce renal excretion of drugs and thereby pose a safety risk. Assessing the risk of inhibition of these membrane transporters by investigational drugs remains a key focus in the evaluation of drug-drug interactions (DDIs). Current methods to predict DDI risk are based on generating in vitro data followed by a clinical assessment using a recommended exogenous probe substrate for the individual drug transporter. More recently, monitoring plasma-based and urine-based endogenous biomarkers to predict transporter-mediated DDIs in early phase I studies represents a promising approach to facilitate, improve and potentially avoid conventional clinical DDI studies. This perspective reviews the evidence for use of these endogenous biomarkers in the assessment of renal transporter-mediated DDI, evaluates how endogenous biomarkers may help to expand the DDI assessment toolkit and offers some potential knowledge gaps. A conceptual framework for assessment that may complement the current paradigm of predicting the potential for renal transporter-mediated DDIs is outlined.

Triglyceride-Glucose Index and Its Correlates: Associations with Serum Creatinine and Estimated Glomerular Filtration Rate in a Cross-Sectional Study from CHARLS 2011-2015

Background: Chronic kidney disease (CKD) has emerged as a significant global public health challenge, and the estimated glomerular filtration rate (eGFR) is widely used due to its convenience, low cost, and broad clinical applicability. Concurrently, insulin resistance (IR) serves as a crucial marker of metabolic disturbance, and alternative indicators have garnered increasing attention in CKD research in recent years. Objective: This study aims to investigate the relationship between IR-related indices (TyG index, TyG-BMI index, and TyG-WC index) and serum creatinine levels, as well as the eGFR, with the intention of uncovering their potential roles in the assessment of renal function. Methods: We analyzed nationally representative cross-sectional data from a cohort of individuals aged 45 and above in China, comprising 11,608 participants. Participants were categorized into different groups based on quartiles of the TyG index, and multiple factors, including gender, age, lifestyle, and co-morbidities, were adjusted for using linear regression models. Results: By linear regression, TyG, TyG-BMI, and TyG-WC indices were significantly positively correlated with serum creatinine and significantly negatively correlated with eGFR. Results showed similar trends when TyG, TyG-BMI, and TyG-WC indices were used as categorical variables. In the fully adjusted model, the highest quartile of serum creatinine was higher than the first quartile for TyG, TyG-BMI, and TyG-WC indices, with β values of 2.673, 3.67, and 1.937 mg/dL, respectively; the highest quartile of eGFR was lower than the first quartile, with β values of -2.4, -2.955, and -1.823 mL/min/1.73 m2. P values were statistically significant. Conclusions: This study indicates a consistent correlation between the TyG index and its related indices with serum creatinine levels and eGFR among the middle aged and elderly population in China. These findings suggest the potential utility of these indices in early screening and management of the risk of chronic kidney disease.

Identification and characterization of an endogenous biomarker of the renal vectorial transport (OCT2-MATE1)

The renal tubular organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1) mediate the vectorial elimination of many drugs and toxins from the kidney, and endogenous biomarkers for vectorial transport (OCT2-MATE1) would allow more accurate drug dosing and help to characterize drug-drug interactions and toxicity. Human serum uptake in OCT2-overexpressing cells and metabolomics analysis were carried out. Potential biomarkers were verified in vitro and in vivo. The specificity of biomarkers was validated in renal transporter overexpressing cells and the sensitivity was investigated by Km . The results showed that the uptake of thiamine, histamine, and 5-hydroxytryptamine was significantly increased in OCT2-overexpressing cells. In vitro assays confirmed that thiamine, histamine, and 5-hydroxytryptamine were substrates of both OCT2 and MATE1. In vivo measurements indicated that the serum thiamine level was increased significantly in the presence of the rOCT2 inhibitor cimetidine, and the level in renal tissue was increased significantly by the rMATE1 inhibitor pyrimethamine. There were no significant changes in the uptake or efflux of thiamine in cell lines overexpressed OAT1, OAT2, OAT3, MRP4, organic anion transporting polypeptide 4C1, P-gp, peptide transporter 2, urate transporter 1, and OAT4. The Km for thiamine with OCT2 and MATE1 were 71.2 and 10.8 μM, respectively. In addition, the cumulative excretion of thiamine at 2 and 4 h was strongly correlated with metformin excretion (R2  > 0.6). Thus, thiamine is preferentially secreted by the OCT2 and MATE1 in renal tubules and can provide a reference value for evaluating the function of the renal tubular OCT2-MATE1.