Nephropathy induced by cisplatin results from mitochondrial disruption, impaired energy metabolism, altered expression of renal transporters, and accumulation of urinary toxins

BACKGROUND

The administration of platinum-based drugs such as cisplatin and its derivatives, which are frequently used during clinical chemotherapy, is highly restricted due to the incidence of nephrotoxicity. The present study focused on investigating cisplatin-induced nephrotoxicity from the perspective of energy metabolism, renal transporter expression and urinary toxin accumulation.

METHODS

This study investigated cisplatin's toxic effects, including nephrotoxicity, cardiotoxicity, hepatotoxicity, pulmonary toxicity, and splenotoxicity. We used transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to characterize the accumulation of cisplatin in the kidney and the structure of renal mitochondria. The production of reactive oxygen species (ROS) induced by cisplatin in renal tubular epithelial cells was evaluated by in vitro experiments, and apoptosis of renal tubular epithelial cells and alterations to the renal microvasculature were assessed. Metabolites associated with the glycolytic and tricarboxylic acid pathways were measured, and renal transporters expression, autophagy, and urinary toxins (UTs) accumulation were also assessed.

RESULTS

Our results reveal that cisplatin-induced varying degrees of damage to the heart, liver, spleen, lungs, and kidneys, including inflammatory and fibrotic damage. Accumulation of cisplatin in renal mitochondria disrupted mitochondrial structure and mitochondrial function, as evidenced by decreased levels of glucose 6-phosphate and ribose 5-phosphate and elevated levels of isocitric acid. Cisplatin-induced accumulation of ROS in renal tubular epithelial cells led to apoptosis and, ultimately, constriction or loss of renal microvasculature. Furthermore, dysregulation of renal transporter expression, activation of autophagy and increased accumulation of UTs was observed.

CONCLUSION

Accumulation of cisplatin in the kidney led to damage to mitochondrial structure and function, apoptosis of renal tubular epithelial cells, constriction or loss of renal microvasculature, dysfunction of renal transporters, activation of autophagy, and accumulation of UTs.

Recent Advances on the Regulations of Organic Anion Transporters

The organic anion transporter (OAT) family of over 10 members within the solute carrier (SLC) superfamily of membrane proteins plays critical roles in facilitating the flux of negatively charged molecules in and out of cell membranes. These anionic molecules include various endogenous and exogenous compounds such as signaling molecules, nutrients, metabolites, toxins, and drugs. Therefore, OATs actively contribute to the systemic homeostasis and efficacy of therapeutics. This article provides a brief overview on recent advances in the understanding of the regulatory mechanisms that control the expression and activity of OATs in both health and diseases.

Mechanistic Study on the Effect of Renal Impairment on the Pharmacokinetics of Vildagliptin and its Carboxylic Acid Metabolite

PURPOSE

To clarify the mechanism of renal impairment leading to different degrees of increased plasma exposure to dipeptidyl peptidase 4 inhibitor vildagliptin and its major metabolite, M20.7.

METHODS

The 5/6 nephrectomized (5/6 Nx) rat model, to simulate chronic renal failure (CRF) patients, combined with kidney slices and transporter studies in vitro were used to assess this pharmacokinetic differences.

RESULTS

After intragastric administration to 5/6 Nx rats, vildagliptin showed increased plasma levels by 45.8%, and M20.7 by 7.51 times, which was similar to patients with severe renal impairment. The recovery rate of M20.7 in urine and feces increased by less than 20%, showing limited effect of renal impairment on vildagliptin metabolism. In vitro studies found M20.7 to be the substrate for organic anion transporter 3 (OAT3). However, the active uptake of M20.7 in renal slices showed no difference between the 5/6 Nx and normal rats. In OAT3 overexpressed cells, the protein-bound uremic toxins, 3-carboxy-4-methyl-5propyl-2-furanpropionate (CMPF), hippuric acid (HA) and indoxyl sulfate (IS), which accumulate in CRF patients, inhibited M20.7 uptake with IC₅₀ values of 5.75, 29.0 and 69.5 μM respectively, far lower than plasma concentrations in CRF patients, and showed a mixed inhibition type.

CONCLUSIONS

The large increase in plasma exposure of M20.7 could be attributed to the accumulation of uremic toxins in CRF patients, which inhibited OAT3 activity and blocked renal excretion of M20.7, while vildagliptin, with high permeability, showed a slight increase in plasma exposure due to reduced glomerular filtration.

The Role of Uptake and Efflux Transporters in the Disposition of Glucuronide and Sulfate Conjugates

Glucuronidation and sulfation are the most typical phase II metabolic reactions of drugs. The resulting glucuronide and sulfate conjugates are generally considered inactive and safe. They may, however, be the most prominent drug-related material in the circulation and excreta of humans. The glucuronide and sulfate metabolites of drugs typically have limited cell membrane permeability and subsequently, their distribution and excretion from the human body requires transport proteins. Uptake transporters, such as organic anion transporters (OATs and OATPs), mediate the uptake of conjugates into the liver and kidney, while efflux transporters, such as multidrug resistance proteins (MRPs) and breast cancer resistance protein (BCRP), mediate expulsion of conjugates into bile, urine and the intestinal lumen. Understanding the active transport of conjugated drug metabolites is important for predicting the fate of a drug in the body and its safety and efficacy. The aim of this review is to compile the understanding of transporter-mediated disposition of phase II conjugates. We review the literature on hepatic, intestinal and renal uptake transporters participating in the transport of glucuronide and sulfate metabolites of drugs, other xenobiotics and endobiotics. In addition, we provide an update on the involvement of efflux transporters in the disposition of glucuronide and sulfate metabolites. Finally, we discuss the interplay between uptake and efflux transport in the intestine, liver and kidneys as well as the role of transporters in glucuronide and sulfate conjugate toxicity, drug interactions, pharmacogenetics and species differences.

Drug Transporters in the Kidney: Perspectives on Species Differences, Disease Status, and Molecular Docking

The kidneys are a pair of important organs that excretes endogenous waste and exogenous biological agents from the body. Numerous transporters are involved in the excretion process. The levels of these transporters could affect the pharmacokinetics of many drugs, such as organic anion drugs, organic cationic drugs, and peptide drugs. Eleven drug transporters in the kidney (OAT1, OAT3, OATP4C1, OCT2, MDR1, BCRP, MATE1, MATE2-K, OAT4, MRP2, and MRP4) have become necessary research items in the development of innovative drugs. However, the levels of these transporters vary between different species, sex-genders, ages, and disease statuses, which may lead to different pharmacokinetics of drugs. Here, we review the differences of the important transports in the mentioned conditions, in order to help clinicians to improve clinical prescriptions for patients. To predict drug-drug interactions (DDIs) caused by renal drug transporters, the molecular docking method is used for rapid screening of substrates or inhibitors of the drug transporters. Here, we review a large number of natural products that represent potential substrates and/or inhibitors of transporters by the molecular docking method.

Sulfation predominates the pharmacokinetics, metabolism, and excretion of forsythin in humans: major enzymes and transporters identified

Forsythin extracted from Forsythiae Fructus is widely used to treat fever caused by the common cold or influenza in China, Japan and Korea. The present study aimed to analyze the pharmacokinetics, metabolism and excretion routes of forsythin in humans and determine the major enzymes and transporters involved in these processes. After a single oral administration, forsythin underwent extensive metabolism via hydrolysis and further sulfation. In total, 3 of the 13 metabolites were confirmed by comparison to reference substances, i.e., aglycone M1, M1 sulfate (M2), and M1 glucuronide (M7). Hydrolysis was the initial and main metabolic pathway of the parent compound, followed by extensive sulfation to form M2 and a reduced level of glucuronidation to form M7. In addition, the plasma exposure of M2 and M7 were 86- and 4.2-fold higher than that of forsythin. Within 48 h, ~75.1% of the administered dose was found in urine, with M2 accounting for 71.6%. Further phenotyping experiments revealed that sulfotransferase 1A1 and UDP-glucuronosyltransferase 1A8 were the most active hepatic enzymes involved in the formation of M2 and M7, respectively. The in vitro kinetic study provided direct evidence that M1 showed a preference for sulfation. Sulfated conjugate M2 was identified as a specific substrate of organic anion transporter 3, which could facilitate the renal excretion of M2. Altogether, our study demonstrated that sulfation dominated the metabolism and pharmacokinetics of forsythin, while the sulfate conjugate was excreted mainly in the urine.

Characterization and quantitative determination of henagliflozin metabolites in humans

Henagliflozin is a highly specific inhibitor of sodium-glucose co-transporter-2 (SGLT2) proposed as a more efficient medication for type 2 diabetes mellitus (T2DM). In this work, henagliflozin metabolic profile was investigated in human plasma and urine samples using a newly developed high-performance liquid chromatography coupled with time-of-flight mass spectrometry (HPLC/Q-TOF MS) method. A total of 8 metabolites were observed, while the structures of four major metabolites, including M1 (O-deethylation metabolite), M5-1 (2-O-β-glucuronide conjugate), M5-2 (6-O-β-glucuronide conjugate), and M5-3 (3-O-β-glucuronide conjugate) were confirmed in our study after comparison with the reference standards. The principal henagliflozin metabolic pathways were identified as glucuronidation and O-deethylation in humans. The principal form of henagliflozin in human plasma was parent drug, followed by M5-1; while it was M5-3 and M5-1 in urine. Subsequently, an accurate and simple LC-MS/MS method was developed for simultaneously determine M5-1, M5-2, and M5-3 in human plasma. After optimization of this method, three M5 isomers were successfully separated and quantified using chromatography. Acetonitrile-induced protein precipitation method was adapted for extracting the analytes from human plasma. Separation was conducted using Gemini C₁₈ column under gradient elution with 5 mM aqueous ammonium acetate (A) and acetonitrile (B) mobile phases. Negative electrospray ionization was conducted using a selective reaction monitoring with the same transition of m/z 629→321 for detection of three M5 isomers. The method showed good linearities for M5-1, M5-2, and M5-3 within the range of 1.00-150 ng/mL, 0.500-75.0 ng/mL, and 1.00-150 ng/mL, respectively. Conclusively, the method has been applied successfully to assess phase I henagliflozin pharmacokinetics and pharmacodynamics and providing effective safety evaluations.

Regulation of organic anion transporters: Role in physiology, pathophysiology, and drug elimination

The members of the organic anion transporter (OAT) family are mainly expressed in kidney, liver, placenta, intestine, and brain. These transporters play important roles in the disposition of clinical drugs, pesticides, signaling molecules, heavy metal conjugates, components of phytomedicines, and toxins, and therefore critical for maintaining systemic homeostasis. Alterations in the expression and function of OATs contribute to the intra- and inter-individual variability of the therapeutic efficacy and the toxicity of many drugs, and to many pathophysiological conditions. Consequently, the activity of these transporters must be highly regulated to carry out their normal functions. This review will present an update on the recent advance in understanding the cellular and molecular mechanisms underlying the regulation of renal OATs, emphasizing on the post-translational modification (PTM), the crosstalk among these PTMs, and the remote sensing and signaling network of OATs. Such knowledge will provide significant insights into the roles of these transporters in health and disease.

Kidney Transporters and Drug-Induced Injury in Drug Development

Influx and efflux kidney tubular transporters are major determinants of the disposition of xenobiotics, including pharmaceutical drugs. On the basolateral membrane of proximal tubular cells, there are influx transporters, such as organic cation transporters. On the apical membrane of proximal tubular cells, there are efflux transporters, such as multidrug and toxin extrusion proteins. The secretion process across the apical membrane into the lumen occurs via efflux transporters which plays an important role in serum creatinine (sCr) elimination in urine. The interference of a pharmaceutical drug with transporters can lead to changes in sCr with no alterations in biomarkers or light microscopic evidence indicative of renal injury. Identification of transporters that influence drug disposition, toxicity, and overall nonclinical safety assessment is important in drug discovery and development programs. This mini review describes some key aspects of kidney tubular transporters and drug-induced renal toxicities in safety risk assessment and drug development.

Effects of Tenofovir on the Single-Dose Pharmacokinetics of Intravenous Morinidazole in Healthy Chinese Subjects

The effects of multiple-dose administration of tenofovir disoproxil fumarate (TDF) on the pharmacokinetics of morinidazole (MOR) were compared in healthy subjects. MOR exposure was similar, with an area under the curve from 0 h to infinity (AUC_0-∞) treatment ratio for MOR+TDF/MOR of 1.01 (90% confidence interval, 0.97 to 1.06). No relevant differences were observed regarding plasma exposure of metabolites. Renal clearances of MOR and its metabolites were not affected by TDF. No unexpected safety or tolerability issues were observed.

Uraemic syndrome of chronic kidney disease: altered remote sensing and signalling

Uraemic syndrome (also known as uremic syndrome) in patients with advanced chronic kidney disease involves the accumulation in plasma of small-molecule uraemic solutes and uraemic toxins (also known as uremic toxins), dysfunction of multiple organs and dysbiosis of the gut microbiota. As such, uraemic syndrome can be viewed as a disease of perturbed inter-organ and inter-organism (host-microbiota) communication. Multiple biological pathways are affected, including those controlled by solute carrier (SLC) and ATP-binding cassette (ABC) transporters and drug-metabolizing enzymes, many of which are also involved in drug absorption, distribution, metabolism and elimination (ADME). The remote sensing and signalling hypothesis identifies SLC and ABC transporter-mediated communication between organs and/or between the host and gut microbiota as key to the homeostasis of metabolites, antioxidants, signalling molecules, microbiota-derived products and dietary components in body tissues and fluid compartments. Thus, this hypothesis provides a useful perspective on the pathobiology of uraemic syndrome. Pathways considered central to drug ADME might be particularly important for the body's attempts to restore homeostasis, including the correction of disturbances due to kidney injury and the accumulation of uraemic solutes and toxins. This Review discusses how the remote sensing and signalling hypothesis helps to provide a systems-level understanding of aspects of uraemia that could lead to novel approaches to its treatment.

Toxicokinetics and Metabolism of 3-Monochloropropane 1,2-Diol Dipalmitate in Sprague Dawley Rats

Fatty acid esters of 3-monochloropropane 1,2-diol (3-MCPD) are a group of processing-induced toxicants. To better clarify their possible toxicological effects and mechanisms, it is important to investigate their absorption, distribution, metabolism, and excretion. In this study, the kinetic parameters of 3-MCPD dipalmitate in Sprague Dawley (SD) rat plasma were determined using ultraperformance liquid chromatography-triple quadrupole mass spectrometry. 3-MCPD dipalmitate was absorbed in rats with a C_max of 135.00 ng/mL, a T_1/2 of 3.87 h, a T_max of 2.5 h, an MRT of 5.08 h, a CL of 3.50 L/h/g, a V_d of 21.34 L/g, and an AUC_0-∞ of 458.47 h·ng/mL. A total of 17 metabolites were identified, and 16 of them were reported for the first time. Furthermore, these metabolites were examined for their presences in the liver, kidney, testis, brain, spleen, thymus, intestine, plasma, feces, and urine samples 2, 6, 12, 24, and 48 h after oral administration of 3-MCPD dipalmitate using Metabolynx software.

Evidence for the Validity of Pyridoxic Acid (PDA) as a Plasma-Based Endogenous Probe for OAT1 and OAT3 Function in Healthy Subjects

Plasma pyridoxic acid (PDA) and homovanillic acid (HVA) were recently identified as novel endogenous biomarkers of organic anion transporter (OAT) 1/3 function in monkeys. Consequently, this clinical study assessed the dynamic changes and utility of plasma PDA and HVA as an initial evaluation of OAT1/3 inhibition in early-phase drug development. The study was designed as a single-dose randomized, three-phase, crossover study; 14 Indian healthy volunteers received probenecid (PROB) (1000 mg orally) alone, furosemide (FSM) (40 mg orally) alone, or FSM 1 hour after receiving PROB (40 and 1000 mg orally) on days 1, 8, and 15, respectively. PDA and HVA plasma concentrations remained stable over time in the prestudy and FSM groups. Administration of PROB significantly increased the area under the plasma concentration-time curve (AUC) of PDA by 3.1-fold (dosed alone; P < 0.05), and 3.2-fold (coadministered with FSM; P < 0.01), compared with the prestudy and FSM groups, respectively. The corresponding increase in HVA AUC was 1.8-fold (P > 0.05) and 2.1-fold (P < 0.05), respectively. The increases in PDA AUC are similar to those in FSM AUC, whereas those of HVA are smaller (3.1-3.2 and 1.8-2.1 vs. 3.3, respectively). PDA and HVA renal clearance (CL _R) values were decreased by PROB to smaller extents compared with FSM (0.35-0.37 and 0.67-0.73 vs. 0.23, respectively). These data demonstrate that plasma PDA is a promising endogenous biomarker for OAT1/3 function and that its plasma exposure responds in a similar fashion to FSM upon OAT1/3 inhibition by PROB. The magnitude and variability of response in PDA AUC and CL _R values between subjects is more favorable relative to HVA.

Renal organic anion transporters in drug-drug interactions and diseases

The kidney plays a vital role in maintaining systemic homeostasis. Active tubular secretion and reabsorption, which are mainly mediated by transporters, is an efficient mechanism for retaining glucose, amino acids, and other nutrients and for the clearance of endogenous waste products and xenobiotics. These substances are recognized by uptake transporters located in the basolateral and apical membranes of renal proximal tubule cells and are extracted from plasma and urine. Organic anion transporters (OATs) belong to the solute carrier (SLC) 22 superfamily and facilitate organic anions across the plasma membranes of renal proximal tubule cells. OATs are responsible for the transmembrane transport of anionic and zwitterionic organic molecules, including endogenous substances and many drugs. The alteration in OAT expression and function caused by diseases, drug-drug interactions (DDIs) or other issues can thus change the renal disposition of substrates, induce the accumulation of toxic metabolites, and lead to unexpected clinically outcome. This review summarizes the recent information regarding the expression, regulation, and substrate spectrum of OATs and discusses the roles of OATs in diseases and DDIs. These findings will enables us to have a better understanding of the related disease therapy and the potential risk of DDIs mediated by OATs.

Microbiota-derived uremic retention solutes: perpetrators of altered nonrenal drug clearance in kidney disease

INTRODUCTION

Scientific interest in the gut microbiota is increasing due to improved understanding of its implications in human health and disease. In patients with kidney disease, gut microbiota-derived uremic toxins directly contribute to altered nonrenal drug clearance. Microbial imbalances, known as dysbiosis, potentially increase formation of microbiota-derived toxins, and diminished renal clearance leads to toxin accumulation. High concentrations of microbiota-derived toxins such as indoxyl sulfate and p-cresol sulfate perpetrate interactions with drug metabolizing enzymes and transporters, which provides a mechanistic link between increases in drug-related adverse events and dysbiosis in kidney disease. Areas covered: This review summarizes the effects of microbiota-derived uremic toxins on hepatic phase I and phase II drug metabolizing enzymes and drug transporters. Research articles that tested individual toxins were included. Therapeutic strategies to target microbial toxins are also discussed. Expert commentary: Large interindividual variability in toxin concentrations may explain some differences in nonrenal clearance of medications. Advances in human microbiome research provide unique opportunities to systematically evaluate the impact of individual and combined microbial toxins on drug metabolism and transport, and to explore microbiota-derived uremic toxins as potential therapeutic targets.