Effect of probenecid on blood levels and renal elimination of furosemide and endogenous compounds in rats: Discovery of putative organic anion transporter biomarkers

Molecular insights into P2X signalling cascades in acute kidney injury

Acute kidney injury (AKI) is a critical health issue with high mortality and morbidity rates in hospitalized individuals. The complex pathophysiology and underlying health conditions further complicate AKI management. Growing evidence suggests the pivotal role of ion channels in AKI progression, through promoting tubular cell death and altering immune cell functions. Among these channels, P2X purinergic receptors emerge as key players in AKI pathophysiology. P2X receptors gated by adenosine triphosphate (ATP), exhibit increased extracellular levels of ATP during AKI episodes. More importantly, certain P2X receptor subtypes upon activation exacerbate the situation by promoting the release of extracellular ATP. While therapeutic investigations have primarily focused on P2X4 and P2X7 subtypes in the context of AKI, while understanding about other subtypes still remains limited. Whilst some P2X antagonists show promising results against different types of kidney diseases, their role in managing AKI remains unexplored. Henceforth, understanding the intricate interplay between P2X receptors and AKI is crucial for developing targeted interventions. This review elucidates the functional alterations of all P2X receptors during normal kidney function and AKI, offering insights into their involvement in AKI. Notably, we have highlighted the current knowledge of P2X receptor antagonists and the possibilities to use them against AKI in the future. Furthermore, the review delves into the pathways influenced by activated P2X receptors during AKI, presenting potential targets for future therapeutic interventions against this critical condition.

Effect of Cimetidine on Metformin Pharmacokinetics and Endogenous Metabolite Levels in Rats

Tubular secretion is a primary mechanism along with glomerular filtration for renal elimination of drugs and toxicants into urine. Organic cation transporters (OCTs) and multidrug and toxic extrusion (MATE) transporters facilitate the active secretion of cationic substrates, including drugs such as metformin and endogenous cations. We hypothesized that administration of cimetidine, an Oct/Mate inhibitor, will result in increased plasma levels and decreased renal clearance of metformin and endogenous Oct/Mate substrates in rats. A paired rat pharmacokinetic study was carried out in which metformin (5 mg/kg, intravenous) was administered as an exogenous substrate of Oct/Mate transporters to six Sprague-Dawley rats with and without cimetidine (100 mg/kg, intraperitoneal). When co-administered with cimetidine, metformin area under the curve increased significantly by 3.2-fold, and its renal clearance reduced significantly by 73%. Untargeted metabolomics was performed to investigate the effect of cimetidine on endogenous metabolome in the blood and urine samples. Over 8,000 features (metabolites) were detected in the blood, which were shortlisted using optimized criteria, i.e., a significant increase (P value < 0.05) in metabolite peak intensity in the cimetidine-treated group, reproducible retention time, and quality of chromatogram peak. The metabolite hits were classified into three groups that can potentially distinguish inhibition of i) extra-renal uptake transport or catabolism, ii) renal Octs, and iii) renal efflux transporters or metabolite formation. The metabolomics approach identified novel putative endogenous substrates of cationic transporters that could be tested as potential biomarkers to predict Oct/Mate transporter mediated drug-drug interactions in the preclinical stages. SIGNIFICANCE STATEMENT: Endogenous substrates of renal transporters in animal models could be used as potential biomarkers to predict renal drug-drug interactions in early drug development. Here we demonstrated that cimetidine, an inhibitor of organic cation transporters (Oct/Mate), could alter the pharmacokinetics of metformin and endogenous cationic substrates in rats. Several putative endogenous metabolites of Oct/Mate transporters were identified using metabolomics approach, which could be tested as potential transporter biomarkers to predict renal drug-drug interaction of Oct/Mate substrates.