Expression of drug transporters in human kidney: impact of sex, age, and ethnicity

How PBPK Can Help to Understand Old Drugs and Inform their Dosing in Elderly: Amantadine Case Study

Amantadine, despite being on the market for 55 years, has several unknown aspects of its pharmacokinetics especially related to the influence of covariates such as age, disease, or interactions linked to amantadine's renal elimination. As amantadine is used in Parkinson's disease and is considered a potential candidate in COVID treatment and other diseases, there is an unmet need for thorough understanding of its pharmacokinetic in special populations, such as the elderly. We aimed to mechanistically describe amantadine pharmacokinetics in healthy subjects and shed some light on the differences in drug behavior between healthy volunteers (18-65 years) and an elderly/geriatric population (65-98 years) using PBPK modeling and simulation. The middle-out PBPK model includes mechanistic description of drug renal elimination, specifically an organic cation transporter (OCT)2-mediated electrogenic bidirectional transport (basolateral) and multidrug and toxic compound extrusion (MATE)1-mediated efflux (apical). The model performance was verified against plasma and urine data reported after single and multiple dose administration in healthy volunteers and elderly patients from 18 independent studies. The ratios of predicted vs. observed maximal plasma concentration and area under the concentration-time curve values were within 1.25-fold. The model illustrates that renal transporter activity is expected to decrease in healthy elderly compared to healthy volunteers, which is in line with literature proteomic data for OCT2. The model was applied to assess the potential of reaching toxicity-related plasma concentrations in different age groups of geriatric subjects.

Regulation of renal organic cation transporters

Transporters for organic cations (OCs) facilitate exchange of positively charged molecules through the plasma membrane. Substrates for these transporters encompass neurotransmitters, metabolic byproducts, drugs, and xenobiotics. Consequently, these transporters actively contribute to the regulation of neurotransmission, cellular penetration and elimination process for metabolic products, drugs, and xenobiotics. Therefore, these transporters have significant physiological, pharmacological, and toxicological implications. In cells of renal proximal tubules, the vectorial secretion pathways for OCs involve expression of organic cation transporters (OCTs) and multidrug and toxin extrusion proteins (MATEs) on basolateral and apical membrane domains, respectively. This review provides an overview of documented regulatory mechanisms governing OCTs and MATEs. Additionally, regulation of these transporters under various pathological conditions is summarized. The expression and functionality of OCTs and MATEs are subject to diverse pre- and post-translational modifications, providing insights into their regulation in various pathological conditions. Typically, in diseases, downregulation of transporter expression is observed, probably as a protective mechanism to prevent additional damage to kidney tissue. This regulation may be attributed to the intricate network of modifications these transporters undergo, shedding light on their dynamic responses in pathological contexts.

Human ABC and SLC Transporters: The Culprit Responsible for Unspecific PSMA-617 Uptake?

[177Lu]Lu-PSMA-617 has recently been successfully approved by the FDA, the MHRA, Health Canada and the EMA as Pluvicto®. However, salivary gland (SG) and kidney toxicities account for its main dose-limiting side-effects, while its corresponding uptake and retention mechanisms still remain elusive. Recently, the presence of different ATP-binding cassette (ABC) transporters, such as human breast cancer resistance proteins (BCRP), multidrug resistance proteins (MDR1), multidrug-resistance-related proteins (MRP1, MRP4) and solute cassette (SLC) transporters, such as multidrug and toxin extrusion proteins (MATE1, MATE2-K), organic anion transporters (OAT1, OAT2v1, OAT3, OAT4) and peptide transporters (PEPT2), has been verified at different abundances in human SGs and kidneys. Therefore, our aim was to assess whether [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 are substrates of these ABC and SLC transporters. For in vitro studies, the novel isotopologue ([α,β-3H]Nal)Lu-PSMA-617 was used in cell lines or vesicles expressing the aforementioned human ABC and SLC transporters for inhibition and uptake studies, respectively. The corresponding probe substrates and reference inhibitors were used as controls. Our results indicate that [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 are neither inhibitors nor substrates of the examined transporters. Therefore, our results show that human ABC and SLC transporters play no central role in the uptake and retention of [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 in the SGs and kidneys nor in the observed toxicities.

Assessing city-wide pharmaceutical emissions to wastewater via modelling and passive sampling

With increasing numbers of chemicals used in modern society, assessing human and environmental exposure to them is becoming increasingly difficult. Recent advances in wastewater-based epidemiology enable valuable insights into public exposure to data-poor compounds. However, measuring all >26,000 chemicals registered under REACH is not just technically unfeasible but would also be incredibly expensive. In this paper, we argue that estimating emissions of chemicals based on usage data could offer a more comprehensive, systematic and efficient approach than repeated monitoring. Emissions of 29 active pharmaceutical ingredients (APIs) to wastewater were estimated for a medium-sized city in the Netherlands. Usage data was collected both on national and local scale and included prescription data, usage in health-care institutions and over-the-counter sales. Different routes of administration were considered as well as the excretion and subsequent in-sewer back-transformation of conjugates into respective parent compounds. Results suggest model-based emission estimation on a city-level is feasible and in good agreement with wastewater measurements obtained via passive sampling. Results highlight the need to include excretion fractions in the conceptual framework of emission estimation but suggest that the choice of an appropriate excretion fraction has a substantial impact on the resulting model performance.

Identification of three distinct cell populations for urate excretion in human kidneys

In humans, uric acid is an end-product of purine metabolism. Urate excretion from the human kidney is tightly regulated by reabsorption and secretion. At least eleven genes have been identified as human renal urate transporters. However, it remains unclear whether all renal tubular cells express the same set of urate transporters. Here, we show renal tubular cells are divided into three distinct cell populations for urate handling. Analysis of healthy human kidneys at single-cell resolution revealed that not all tubular cells expressed the same set of urate transporters. Only 32% of tubular cells were related to both reabsorption and secretion, while the remaining tubular cells were related to either reabsorption or secretion at 5% and 63%, respectively. These results provide physiological insight into the molecular function of the transporters and renal urate handling on single-cell units. Our findings suggest that three different cell populations cooperate to regulate urate excretion from the human kidney, and our proposed framework is a step forward in broadening the view from the molecular to the cellular level of transport capacity.

Gender Disparities in Nephrology Trials: A Meta-Analysis of Enrollment Trends between 2000 and 2021

Key Points

Women are under-represented in high-impact nephrology trials. Trends remain consistent over the past 20 years and on the basis of target condition. Addressing the imbalanced enrollment of women in trials could improve disparities in care and outcomes of kidney disease.

Background

Gender disparities in the incidence and complications of kidney diseases are well described. However, analysis to elucidate gender disparities in enrollment in nephrology randomized clinical trials (RCTs) has not been performed.

Methods

We performed a systematic review and meta-analysis of high-impact nephrology RCTs published between 2000 and 2021. We included RCTs enrolling participants aged 18 years and older in the following categories: (1 ) CKD, (2 ) AKI, (3 ) GN, (4 ) maintenance dialysis, and (5 ) kidney transplantation. We summarized trial characteristics according to reporting and enrollment of participants, enrollment site, publication year, trial category, and intervention type. Outcomes of interest include the proportion of enrolled male and female participants overall and according to trial category. In addition, we compared enrollment trends in the United States and globally to estimates of kidney disease prevalence.

Results

Most qualifying trials (373/380, 98%) reported the distribution of male and female participants. Enrollment was imbalanced overall with male participants accounting for 62% (n =215,850) of the enrolled participants and female participants for just 38% (n =133,082). Male participants formed most of trial cohorts in AKI (65%), CKD (62%), dialysis (55%), and transplant trials (65%), whereas women were majority enrollees in GN trials (61%). CKD trials under-represented women in both US trials and worldwide.

Conclusions

Women are under-represented in high-impact nephrology trials with the exception of GN trials. This imbalance may contribute to disparities in outcomes and gaps in the care of women with kidney disease.

Reconsideration of the current models of estimated kidney function-based drug dose adjustment in older adults: The role of biological age

Human lifespan has increased from a median of 46.5 years in 1950 to 71.7 years in 2022. As people age, one of the inevitable consequences is a decline in kidney function and glomerular filtration rate (GFR) which can have direct or indirect effects on the pharmacokinetic and pharmacodynamic profiles of many drugs. Numerous equations have been developed to generate estimated GFR (eGFR) using the two principal biomarkers: serum creatinine and serum cystatin C. However, the trajectory of changes with aging is dissimilar in these equations. In addition, there is recognition that chronological age (lifespan) often does not reflect biological age (healthspan) as an essential parameter in kidney function equations. In the past decade, there has been an increasing interest in quantifying biological age and new commercially available assays have entered the marketplace. In this narrative review, we illustrate how dominant equations of eGFR model the fractional change in this parameter very differently across chronological age. In addition, we review various biological age indicators (aging clocks) and challenges to their application in clinical practice. Importantly, by comparing vancomycin's mean clearance as a drug with limited metabolism and unchanged elimination between two age milestones in some recent population pharmacokinetic models, we show how efforts to quantify kidney function in older adults optimally remain under-explored, particularly those at the upper end of their lifespan. We also propose considering new models that integrate biological age as a new pathway to improve precision drug dosing in older adults.

Strain differences in the drug transport capacity of intestinal glucose transporters in Sprague-Dawley versus Wistar rats, C57BL/6J versus Kunming mice

Designing oral drug delivery systems using intestinal glucose transporters (IGTs) may be one of the strategies for improving oral bioavailability of drugs. However, little is known about the biological factors affecting the drug transport capacity of IGTs. Gastrodin is a sedative drug with a structure very similar to glucose. It is a highly water-soluble phenolic glucoside. It can hardly enter the intestine through simple diffusion but exhibits good oral bioavailability of over 80%. We confirmed that gastrodin is absorbed via the intestinal glucose transport pathway. It has the highest oral bioavailability among the reported glycosides' active ingredients through this pathway. Thus, gastrodin is the most selective drug substrate of IGTs and can be used to evaluate the drug transport capacity of IGTs. Obviously, strain is one of the main biological factors affecting drug absorption. This study firstly compared the drug transport capacity of IGTs between SD rats and Wistar rats and between C57 mice and KM mice by pharmacokinetic experiments and single-pass intestinal perfusion experiments of gastrodin. Then, the sodium-dependent glucose transporter type 1 (SGLT1) and sodium-independent glucose transporters type 2 (GLUT2) in the duodenum, jejunum, ileum and colon of these animals were quantified using RT-qPCR and Western blot. The results showed that the oral bioavailability of gastrodin in Wistar rats was significantly higher than in SD rats and significantly higher in KM mice than in C57 mice. Gastrodin absorption significantly differed among different intestinal segments in SD rats, C57 mice and KM mice, except Wistar rats. RT-qPCR and Western blot demonstrated that the intestinal expression distribution of SGLT1 and GLUT2 in SD rats and C57 mice was duodenum ≈ jejunum > ileum > colon. SGLT1 expression did not differ among different intestinal segments in KM mice, whereas the intestinal expression distribution of GLUT2 was duodenum ≈ jejunum ≈ ileum > colon. However, the expression of SGLT1 and GLUT2 did not differ among different intestinal segments in Wistar rats. It was reported that the intestinal expression distribution of SGLT1 and GLUT2 in humans is duodenum > jejunum > ileum > colon. Hence, the intestinal expression distribution of SGLT1 and GLUT2 of SD rats and C57 mice was more similar to that in humans. In conclusion, the drug transport capacity of IGTs differs in different strains of rats and mice. SD rats and C57 mice are more suitable for evaluating the pharmacokinetics of glycosides' active ingredients absorbed via the intestinal glucose transport pathway.

LncRNA GABPB1-IT1 inhibits the tumorigenesis of renal cancer via the miR-21/PTEN axis

Long noncoding RNA (lncRNA) (GABPB1-IT1) has been reported to be downregulated in lung cancer, while its expression and function in other cancers are unknown. In this study, the expression levels of GABPB1-IT1 in tissue samples from 62 ccRCC patients were measured by performing RT-qPCR. Potential base pairing formed between GABPB1-IT1 and miR-21 was explored using the online program IntaRNA 2.0 and further confirmed by Dual-luciferase activity assay and RNA pulldown assay. The role of GABPB1-IT1 and miR-21 in regulating the expression of PTEN was evaluated by RT-qPCR and Western blot. The role of GABPB1-IT1, miR-21, and PTEN in regulating the proliferation of Caki-2 cells was explored by CCK-8 assay. It was observed that GABPB1-IT1 was downregulated in ccRCC and predicted poor survival. GABPB1-IT1 directly interacted with miR-21, while it did not regulate the expression of each other. Moreover, upregulation of PTEN, which is a target of miR-21, was observed in ccRCC cells with overexpression of GABPB1-IT1. Overexpression of GABPB1-IT1 and PTEN decreased the proliferation rates of ccRCC cells. In addition, overexpression of GABPB1-IT1 reduced the enhancing effects of miR-21 on cell proliferation. Therefore, GABPB1-IT1 may upregulate PTEN by sponging miR-21 in ccRCC to inhibit cancer cell proliferation. Our study characterized a novel GABPB1-IT1/miR-21/PTEN axis in ccRCC.

A Historical Misconception in Clinical Trials of Drugs for Cancer-Age Grouping

In clinical trials of cancer drugs, grouping by age is a very common grouping method, as it can allow for a visual comparison of the different pharmaceutical responses in patients at different age stages. Under the guidance of this thinking, many researchers use age grouping when studying clinical cancer drugs. However, even people at the same age may be at different stages in their lives, such as individuals who are going through puberty, menopause/andropause, or intermediate transition, as well as childhood and old age, affected by factors such as hormone levels, immune responses, ethnic groups, and regions. Every individual has different cancer symptoms and responses to drugs; therefore, the experimental effect of life stage grouping will be more obvious and clearer. Not only does this conclusion apply to cancer drugs, but it also applies to clinical trials for other diseases. In addition, this does not mean that age grouping should be completely abandoned. Life stage is a more general interval that can be further divided into life stage groups according to the age of the patients. Based on the principal law of lifespan (PLOSP), age trends in life stages also need to be updated from time to time. To date, life stage grouping has not been discussed systematically and has not been used as a grouping method for cancer patients. In this paper, life stage grouping is discussed as one of the important grouping categories in cancer clinical trials.

Sex Difference in Cisplatin-Induced Nephrotoxicity: Laboratory and Clinical Findings

Cisplatin (CP) as the most important anticancer drug has limited usage due to a lot of side effects such as nephrotoxicity. Additionally, nephrotoxicity is gender/sex-related. There is a variety of experimental studies in association with sex and CP-induced nephrotoxicity. Some studies have reported that female sex is resistant than male sex due to greater antioxidant defense and protective effects of estrogen in females. Other studies have indicated that males are less vulnerable than females due to CP high clearance. Also, various supplementations have revealed conflicting effects in males and females. It is uncovered that sex hormones have determinant roles on the conflicting effects. Some supplements could improve CP-induced nephrotoxicity, but several supplements intensified CP-induced nephrotoxicity, especially in female sex. On the other hand, major clinical studies introduced female gender as a risk factor of CP-induced nephrotoxicity. Although, rare studies evaluated the effect of various supplemental compounds on CP-induced nephrotoxicity in patients underwent CP therapy. Therefore, it requires further investigations to clarify the controversial subject of gender/sex and CP-induced nephrotoxicity in both clinic and laboratory.

The Effect of Menopause on Antipsychotic Response

Background: It has been hypothesized that, whenever estrogen levels decline, psychosis symptoms in women increase. At menopause, this can happen in two main ways: (a) the loss of estrogen (mainly estradiol) can directly affect central neurotransmission, leading to increase in schizophrenia-related symptoms, and (b) the loss of estrogen can decrease the synthesis of enzymes that metabolize antipsychotic drugs, thus weakening their efficacy. Aims and Methods: The aim of this narrative review was to investigate the second possibility by searching PubMed and ClinicalTrials.gov for studies over the last two decades that investigated the metabolism of antipsychotics and their efficacy before and after menopause in women or that studied systemic and local estrogen level effects on the pharmacokinetics and pharmacodynamics of individual antipsychotic drugs. Results: The evidence suggests that symptom level in women with schizophrenia rises after menopause for many reasons beyond hormones but, importantly, there is an estrogen-dependent loss of efficacy related to antipsychotic treatment. Conclusion: Effective clinical intervention is challenging; nevertheless, several promising routes forward are suggested.

In Vitro Characterization of Renal Drug Transporter Activity in Kidney Cancer

The activity of drug transporters is central to the secretory function of the kidneys and a defining feature of renal proximal tubule epithelial cells (RPTECs). The expression, regulation, and function of these membrane-bound proteins is well understood under normal renal physiological conditions. However, the impact of drug transporters on the pathophysiology of kidney cancer is still elusive. In the present study, we employed different renal cell carcinoma (RCC) cell lines and a prototypical non-malignant RPTEC cell line to characterize the activity, expression, and potential regulatory mechanisms of relevant renal drug transporters in RCC in vitro. An analysis of the uptake and efflux activity, the expression of drug transporters, and the evaluation of cisplatin cytotoxicity under the effects of methylation or epidermal growth factor receptor (EGFR) inhibition showed that the RCC cells retained substantial drug transport activity. In RCC cells, P-glycoprotein was localized in the nucleus and its pharmacological inhibition enhanced cisplatin toxicity in non-malignant RPTECs. On the other hand, methylation inhibition enhanced cisplatin toxicity by upregulating the organic cation uptake activity in RCC cells. Differential effects of methylation and EGFR were observed in transporter expression, showing regulatory heterogeneity in these cells. Interestingly, the non-malignant RPTEC cell line that was used lacked the machinery responsible for organic cation transport, which reiterates the functional losses that renal cells undergo in vitro.

Role of Drug Transporters in Elucidating Inter-Individual Variability in Pediatric Chemotherapy-Related Toxicities and Response

Pediatric cancer treatment has evolved significantly in recent decades. The implementation of risk stratification strategies and the selection of evidence-based chemotherapy combinations have improved survival outcomes. However, there is large interindividual variability in terms of chemotherapy-related toxicities and, sometimes, the response among this population. This variability is partly attributed to the functional variability of drug-metabolizing enzymes (DME) and drug transporters (DTS) involved in the process of absorption, distribution, metabolism and excretion (ADME). The DTS, being ubiquitous, affects drug disposition across membranes and has relevance in determining chemotherapy response in pediatric cancer patients. Among the factors affecting DTS function, ontogeny or maturation is important in the pediatric population. In this narrative review, we describe the role of drug uptake/efflux transporters in defining pediatric chemotherapy-treatment-related toxicities and responses. Developmental differences in DTS and the consequent implications are also briefly discussed for the most commonly used chemotherapeutic drugs in the pediatric population.

Important roles of transporters in the pharmacokinetics of anti-viral nucleoside/nucleotide analogs

INTRODUCTION

Nucleoside analogs are an important class of antiviral agents. Due to the high hydrophilicity and limited membrane permeability of antiviral nucleoside/nucleotide analogs (AVNAs), transporters play critical roles in AVNA pharmacokinetics. Understanding the properties of these transporters is important to accelerate translational research for AVNAs.

AREAS COVERED

The roles of key transporters in the pharmacokinetics of 25 approved AVNAs were reviewed. Clinically relevant information that can be explained by the modulation of transporter functions is also highlighted.

EXPERT OPINION

Although the roles of transporters in the intestinal absorption and renal excretion of AVNAs have been well identified, more research is warranted to understand their roles in the distribution of AVNAs, especially to immune privileged compartments where treatment of viral infection is challenging. P-gp, MRP4, BCRP, and nucleoside transporters have shown extensive impacts in the disposition of AVNAs. It is highly recommended that the role of transporters should be investigated during the development of novel AVNAs. Clinically, co-administered inhibitors and genetic polymorphism of transporters are the two most frequently reported factors altering AVNA pharmacokinetics. Physiopathology conditions also regulate transporter activities, while their effects on pharmacokinetics need further exploration. Pharmacokinetic models could be useful for elucidating these complicated factors in clinical settings.

Considerations and challenges for sex-aware drug repurposing

Sex differences are essential factors in disease etiology and manifestation in many diseases such as cardiovascular disease, cancer, and neurodegeneration [33]. The biological influence of sex differences (including genomic, epigenetic, hormonal, immunological, and metabolic differences between males and females) and the lack of biomedical studies considering sex differences in their study design has led to several policies. For example, the National Institute of Health's (NIH) sex as a biological variable (SABV) and Sex and Gender Equity in Research (SAGER) policies to motivate researchers to consider sex differences [204]. However, drug repurposing, a promising alternative to traditional drug discovery by identifying novel uses for FDA-approved drugs, lacks sex-aware methods that can improve the identification of drugs that have sex-specific responses [7, 11, 14, 33]. Sex-aware drug repurposing methods either select drug candidates that are more efficacious in one sex or deprioritize drug candidates based on if they are predicted to cause a sex-bias adverse event (SBAE), unintended therapeutic effects that are more likely to occur in one sex. Computational drug repurposing methods are encouraging approaches to develop for sex-aware drug repurposing because they can prioritize sex-specific drug candidates or SBAEs at lower cost and time than traditional drug discovery. Sex-aware methods currently exist for clinical, genomic, and transcriptomic information [1, 7, 155]. They have not expanded to other data types, such as DNA variation, which has been beneficial in other drug repurposing methods that do not consider sex [114]. Additionally, some sex-aware methods suffer from poorer performance because a disproportionate number of male and female samples are available to train computational methods [7]. However, there is development potential for several different categories (i.e., data mining, ligand binding predictions, molecular associations, and networks). Low-dimensional representations of molecular association and network approaches are also especially promising candidates for future sex-aware drug repurposing methodologies because they reduce the multiple hypothesis testing burden and capture sex-specific variation better than the other methods [151, 159]. Here we review how sex influences drug response, the current state of drug repurposing including with respect to sex-bias drug response, and how model organism study design choices influence drug repurposing validation.

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.

Regulation of Solute Carriers OCT2 and OAT1/3 in the Kidney: A Phylogenetic, Ontogenetic and Cell Dynamic Perspective

Over the course of more than 500 million years, the kidneys have undergone a remarkable evolution from primitive nephric tubes to intricate filtration-reabsorption systems that maintain homeostasis and remove metabolic end products from the body. The evolutionarily conserved solute carriers Organic Cation Transporter 2 (OCT2), and Organic Anion Transporters 1 and 3 (OAT1/3) coordinate the active secretion of a broad range of endogenous and exogenous substances, many of which accumulate in the blood of patients with kidney failure despite dialysis. Harnessing OCT2 and OAT1/3 through functional preservation or regeneration could alleviate the progression of kidney disease. Additionally, it would improve current in vitro test models that lose their expression in culture. With this review, we explore OCT2 and OAT1/3 regulation using different perspectives: phylogenetic, ontogenetic and cell dynamic. Our aim is to identify possible molecular targets to both help prevent or compensate for the loss of transport activity in patients with kidney disease, and to enable endogenous OCT2 and OAT1/3 induction in vitro in order to develop better models for drug development.

Let's talk about sex: Differences in drug therapy in males and females

Professor Henry Higgins in My Fair Lady said, 'Why can't a woman be more like a man?' Perhaps unintended, such narration extends to the reality of current drug development. A clear sex-gap exists in pharmaceutical research spanning from preclinical studies, clinical trials to post-marketing surveillance with a bias towards males. Consequently, women experience adverse drug reactions from approved drug products more often than men. Distinct differences in pharmaceutical response across drug classes and the lack of understanding of disease pathophysiology also exists between the sexes, often leading to suboptimal drug therapy in women. This review explores the influence of sex as a biological variable in drug delivery, pharmacokinetic response and overall efficacy in the context of pharmaceutical research and practice in the clinic. Prospective recommendations are provided to guide researchers towards the consideration of sex differences in methodologies and analyses. The promotion of disaggregating data according to sex to strengthen scientific rigour, encouraging innovation through the personalisation of medicines and adopting machine learning algorithms is vital for optimised drug development in the sexes and population health equity.

Real-world data-based adverse drug reactions detection from the Korea Adverse Event Reporting System databases with electronic health records-based detection algorithm

Pharmacovigilance involves monitoring of drugs and their adverse drug reactions (ADRs) and is essential for their safety post-marketing. Because of the different types and structures of medical databases, several previous surveillance studies have analyzed only one database. In the present study, we extracted potential drug-ADR pairs from electronic health record (EHR) data using the MetaNurse algorithm and analyzed them using the Korean Adverse Event Reporting System (KAERS) database for systematic validation. The Medical Dictionary for Regulatory Activities (MedDRA) and World Health Organization (WHO) Adverse Reactions Terminology (WHO-ART) were mapped for signal detection. We used the Side Effect Resource (SIDER) database to select 2663 drug-ADR pairs to investigate unknown drug-induced ADRs. The reporting odds ratio (ROR) value was calculated for the drug-exposed and non-exposed groups of drug-ADR pairs, and 19 potential pairs showed significant signals. Appropriate terminology systems and criteria are needed to handle diverse medical databases.

Sex disparities matter in cancer development and therapy

Curing cancer through precision medicine is the paramount aim of the new wave of molecular and genomic therapies. Currently, whether patients with non-reproductive cancers are male or female according to their sex chromosomes is not adequately considered in patient standard of care. This is a matter of consequence because there is growing evidence that these cancer types generally initiate earlier and are associated with higher overall incidence and rates of death in males compared with females. Gender, in contrast to sex, refers to a chosen sexual identity. Hazardous lifestyle choices (notably tobacco smoking) differ in prevalence between genders, aligned with disproportionate cancer risk. These add to underlying genetic predisposition and influences of sex steroid hormones. Together, these factors affect metabolism, immunity and inflammation, and ultimately the fidelity of the genetic code. To accurately understand how human defences against cancer erode, it is crucial to establish the influence of sex. Our Perspective highlights evidence from basic and translational research indicating that including genetic sex considerations in treatments for patients with cancer will improve outcomes. It is now time to adopt the challenge of overhauling cancer medicine based on optimized treatment strategies for females and males.

Sex- and Gender-Based Pharmacological Response to Drugs

In humans, the combination of all sex-specific genetic, epigenetic, and hormonal influences of biologic sex produces different in vivo environments for male and female cells. We dissect how these influences of sex modify the pharmacokinetics and pharmacodynamics of multiple drugs and provide examples for common drugs acting on specific organ systems. We also discuss how gender of physicians and patients may influence the therapeutic response to drugs. We aim to highlight sex as a genetic modifier of the pharmacological response to drugs, which should be considered as a necessary step toward precision medicine that will benefit men and women. SIGNIFICANCE STATEMENT: This study discusses the influences of biologic sex on the pharmacokinetics and pharmacodynamics of drugs and provides examples for common drugs acting on specific organ systems. This study also discusses how gender of physicians and patients influence the therapeutic response to drugs.

Estrogen and estrogen receptors in kidney diseases

Acute kidney injury (AKI) and chronic kidney disease (CKD) are posing great threats to global health within this century. Studies have suggested that estrogen and estrogen receptors (ERs) play important roles in many physiological processes in the kidney. For instance, they are crucial in maintaining mitochondrial homeostasis and modulating endothelin-1 (ET-1) system in the kidney. Estrogen takes part in the kidney repair and regeneration via its receptors. Estrogen also participates in the regulation of phosphorus homeostasis via its receptors in the proximal tubule. The ERα polymorphisms have been associated with the susceptibilities and outcomes of several renal diseases. As a consequence, the altered or dysregulated estrogen/ERs signaling pathways may contribute to a variety of kidney diseases, including various causes-induced AKI, diabetic kidney disease (DKD), lupus nephritis (LN), IgA nephropathy (IgAN), CKD complications, etc. Experimental and clinical studies have shown that targeting estrogen/ERs signaling pathways might have protective effects against certain renal disorders. However, many unsolved problems still exist in knowledge regarding the roles of estrogen and ERs in distinct kidney diseases. Further research is needed to shed light on this area and to enable the discovery of pathway-specific therapies for kidney diseases.

Organic Cation Transporters in the Lung-Current and Emerging (Patho)Physiological and Pharmacological Concepts

Organic cation transporters (OCT) 1, 2 and 3 and novel organic cation transporters (OCTN) 1 and 2 of the solute carrier 22 (SLC22) family are involved in the cellular transport of endogenous compounds such as neurotransmitters, l-carnitine and ergothioneine. OCT/Ns have also been implicated in the transport of xenobiotics across various biological barriers, for example biguanides and histamine receptor antagonists. In addition, several drugs used in the treatment of respiratory disorders are cations at physiological pH and potential substrates of OCT/Ns. OCT/Ns may also be associated with the development of chronic lung diseases such as allergic asthma and chronic obstructive pulmonary disease (COPD) and, thus, are possible new drug targets. As part of the Special Issue "Physiology, Biochemistry and Pharmacology of Transporters for Organic Cations", this review provides an overview of recent findings on the (patho)physiological and pharmacological functions of organic cation transporters in the lung.

Sex Differences in Urate Handling

Hyperuricemia, or elevated serum urate, causes urate kidney stones and gout and also increases the incidence of many other conditions including renal disease, cardiovascular disease, and metabolic syndrome. As we gain mechanistic insight into how urate contributes to human disease, a clear sex difference has emerged in the physiological regulation of urate homeostasis. This review summarizes our current understanding of urate as a disease risk factor and how being of the female sex appears protective. Further, we review the mechanisms of renal handling of urate and the significant contributions from powerful genome-wide association studies of serum urate. We also explore the role of sex in the regulation of specific renal urate transporters and the power of new animal models of hyperuricemia to inform on the role of sex and hyperuricemia in disease pathogenesis. Finally, we advocate the use of sex differences in urate handling as a potent tool in gaining a further understanding of physiological regulation of urate homeostasis and for presenting new avenues for treating the constellation of urate related pathologies.

Protein Abundance of Clinically Relevant Drug Transporters in The Human Kidneys

Renal drug transporters such as the organic cation transporters (OCTs), organic anion transporters (OATs) and multidrug resistance proteins (MRPs) play an important role in the tubular secretion of many drugs influencing their efficacy and safety. However, only little is known about the distinct protein abundance of these transporters in human kidneys, and about the impact of age and gender as potential factors of inter-subject variability in their expression and function. The aim of this study was to determine the protein abundance of MDR1, MRP1-4, BCRP, OAT1-3, OCT2-3, MATE1, PEPT1/2, and ORCTL2 by liquid chromatography-tandem mass spectrometry-based targeted proteomics in a set of 36 human cortex kidney samples (20 males, 16 females; median age 53 and 55 years, respectively). OAT1 and 3, OCT2 and ORCTL2 were found to be most abundant renal SLC transporters while MDR1, MRP1 and MRP4 were the dominating ABC transporters. Only the expression levels of MDR1 and ORCTL2 were significantly higher abundant in older donors. Moreover, we found several significant correlations between different transporters, which may indicate their functional interplay in renal vectorial transport processes. Our data may contribute to a better understanding of the molecular processes determining renal excretion of drugs.

Major glucuronide metabolites of testosterone are primarily transported by MRP2 and MRP3 in human liver, intestine and kidney

Testosterone glucuronide (TG), androsterone glucuronide (AG), etiocholanolone glucuronide (EtioG) and dihydrotestosterone glucuronide (DHTG) are the major metabolites of testosterone (T), which are excreted in urine and bile. Glucuronides can be deconjugated to active androgen in gut lumen after biliary excretion, which in turn can affect physiological levels of androgens. The goal of this study was to quantitatively characterize the mechanisms by which TG, AG, EtioG and DHTG are eliminated from liver, intestine, and kidney utilizing relative expression factor (REF) approach. Using vesicular transport assay with recombinant human MRP2, MRP3, MRP4, MDR1 and BCRP, we first identified that TG, AG, EtioG, and DHTG were primarily substrates of MRP2 and MRP3, although lower levels of transport were also observed with MDR1 and BCRP vesicles. The transport kinetic analyses revealed higher intrinsic clearances of TG by MRP2 and MRP3 as compared to that of DHTG, AG, and EtioG. MRP3 exhibited higher affinity for the transport of the studied glucuronides than MRP2. We next quantified the protein abundances of these efflux transporters in vesicles and compared the same with pooled total membrane fractions isolated from human tissues by quantitative LC-MS/MS proteomics. The fractional contribution of individual transporters (f_t) was estimated by proteomics-based physiological scaling factors, i.e., transporter abundance in whole tissue versus vesicles, and corrected for inside-out vesicles (determined by 5'-nucleotidase assay). The glucuronides of inactive androgens, AG and EtioG were preferentially transported by MRP3, whereas the glucuronides of active androgens, TG and DHTG were mainly transported by MRP2 in liver. Efflux by bile canalicular transport may indicate the potential role of enterohepatic recirculation in regulating the circulating active androgens after deconjugation in the gut. In intestine, MRP3 possibly contributes most to the efflux of these glucuronides. In kidney, all studied glucuronides seemed to be preferentially effluxed by MRP2 and MDR1 (for EtioG). These REF based analysis need to be confirmed with in vivo findings. Overall, characterization of the efflux mechanisms of T glucuronide metabolites is important for predicting the androgen disposition and interindividual variability, including drug-androgen interaction in humans. The mechanistic data can be extrapolated to other androgen relevant organs (e.g. prostate, testis and placenta) by integrating these data with quantitative tissue proteomics data.

Mitochondrial dysfunction in acute kidney injury and sex-specific implications

The kidney is one of the most energy-demanding organs in the human body, and the maintenance of mitochondrial homeostasis is central to kidney function. Recent advances have led to a greater appreciation of how mitochondrial dysfunction contributes to the pathogenesis of AKI, from decreased ATP production, to enhanced mitochondrial oxidative stress, cell necrosis and apoptosis. Accumulating evidence suggests sexual dimorphism in the response to AKI with males demonstrating greater risk for developing ischemia-reperfusion and sepsis-induced kidney injury. In contrast, females may be more susceptible to nephrotoxic-AKI. There are important sex-related differences in mitochondrial respiration, biogenesis and dynamics that likely contribute to the observed sexual dimorphism in AKI. Sex hormones mediate many of these differences with multiple preclinical studies demonstrating the renoprotective actions of estrogen in many rodent models of AKI. Estrogenic control of mitochondrial biogenesis, function and reactive oxygen species (ROS) generation is discussed. Furthermore, the potential role for sex chromosomes in mediating sex differences in AKI is examined. Novel animal models such as the "four core genotypes" (FCG) mouse model provide us with important tools to study sex chromosome effects in kidney health and disease. By understanding the influences of sexual dimorphism or sex hormones on mitochondrial homeostasis and disease manifestations, we may be able to identify novel therapeutic targets and improve existing treatment options for AKI.

Pharmacokinetics, Tissue Distribution, Metabolism, and Excretion of Naringin in Aged Rats

Aging is an inevitable biological process characterized by the loss of functional capacity and associated with changes in all phases of pharmacokinetic processes. Naringin, a dietary flavanone glycoside, has been proved to be beneficial for the treatment of multiple age-associated chronic diseases. To date, the pharmacokinetic processes of naringin in aged individuals are still unknown. Thus, a rapid resolution liquid chromatography tandem triple quadrupole mass spectrometry (RRLC-QQQ-MS/MS) method was established for the determination of naringin and its metabolite naringenin in rat plasma, urine, feces, and tissue homogenate. The pharmacokinetic parameters were calculated and a higher exposure of naringin and naringenin were observed in aged rats. Naringin and naringenin were mostly distributed in gastrointestinal tract, liver, kidney, lung, and trachea. Furthermore, a total of 39 flavonoid metabolites (mainly glucuronides and sulfates) and 46 microbial-derived phenolic catabolites were screened with ultra-fast liquid chromatography-quadrupole-time-of-flight tandem mass spectrometry (UFLC-Q-TOF-MS/MS). Naringenin, hippuric acid, and 3-(4'-hydroxyphenyl)propionic acid were predominated metabolites. This study systemically investigated the pharmacokinetics, tissue distribution, metabolism, and excretion of naringin in aged rats, revealing age- and gender-related changes in the in vivo behavior of naringin. These results would be helpful for the interpretation of pharmacokinetics and pharmacodynamics of naringin in aged population.

Advances in predictive in vitro models of drug-induced nephrotoxicity

In vitro screens for nephrotoxicity are currently poorly predictive of toxicity in humans. Although the functional proteins that are expressed by nephron tubules and mediate drug susceptibility are well known, current in vitro cellular models poorly replicate both the morphology and the function of kidney tubules and therefore fail to demonstrate injury responses to drugs that would be nephrotoxic in vivo. Advances in protocols to enable the directed differentiation of pluripotent stem cells into multiple renal cell types and the development of microfluidic and 3D culture systems have opened a range of potential new platforms for evaluating drug nephrotoxicity. Many of the new in vitro culture systems have been characterized by the expression and function of transporters, enzymes, and other functional proteins that are expressed by the kidney and have been implicated in drug-induced renal injury. In vitro platforms that express these proteins and exhibit molecular biomarkers that have been used as readouts of injury demonstrate improved functional maturity compared with static 2D cultures and represent an opportunity to model injury to renal cell types that have hitherto received little attention. As nephrotoxicity screening platforms become more physiologically relevant, they will facilitate the development of safer drugs and improved clinical management of nephrotoxicants.

Cisplatin Nephrotoxicity Might Have a Sex Difference. An analysis Based on Women's Sex Hormone Changes

Background: A sex difference in cisplatin-induced nephrotoxicity (CIN) has been reported in human and animal studies. We examined in humans whether it is associated with sex-hormone changes. Methods: In this retrospective nationwide cohort study, we used Taiwan's National Health Insurance Research Database (NHIRD) to identify patients with a history of malignancy and cisplatin treatment. Patients diagnosed with kidney disease before cisplatin treatment and those with sex-organ malignancies were excluded. A diagnosis of kidney disease within 90 days after the first administration of cisplatin was the study outcome. Risk factors were estimated using a Cox regression model. Subgroup analyses were performed based on different women's estrogen levels in phases of childbearing, perimenopause, and postmenopause. Results: A retrospective analysis of the records of 3973 men (mean age: 56.15 ± 12.85 years) and 1154 women (mean age: 56.31 ± 12.40 years) showed that 1468 (36.95%) men and 451 (39.08%) women had a new diagnosis of kidney disease. The risk factors were being > 55 years old, a high comorbidity score, and a history of aminoglycoside treatment. Only postmenopausal women had a significantly higher risk of kidney injury (hazard ratio: 1.28; 95% CI: 1.02-1.61) than did men. Conclusions: Perimenopausal women have a significantly higher risk of CIN than do men, which might be explained by women's higher levels of estrogen. Additional studies on the underlying mechanisms of the sex difference of CIN are needed.

Effect of Disease Pathologies on Transporter Expression and Function

Transporters are important determinants of drug absorption, distribution, and excretion. The clinical relevance of drug transporters in drug disposition and toxicology depends on their localization in liver, kidney, and brain. There has been growing evidence regarding the importance of disease status on alterations in metabolizing enzymes and transporter proteins. This review focuses on uptake and efflux transporter proteins in liver, kidney, and brain and discusses mechanisms of altered transporter expression and function secondary to disease.

Current State and Future Trends to Optimize the Care of Chronic Kidney Disease in African Americans

BACKGROUND

African Americans (AAs) suffer the widest gaps in chronic kidney disease (CKD) outcomes compared to Caucasian Americans (CAs) and this is because of the disparities that exist in both health and healthcare. In fact, the prevalence of CKD is 3.5 times higher in AAs compared to CAs. The disparities exist at all stages of CKD. Importantly, AAs are 10 times more likely to develop hypertension-related kidney failure and 3 times more likely to progress to kidney failure compared to CAs.

SUMMARY

Several factors contribute to these disparities including genetic and social determinants, late referrals, poor care coordination, medication adherence, and low recruitment in clinical trials. Key Messages: The development and implementation of CKD-related evidence-based approaches, such as clinical and social determinant assessment tools for medical interventions, more widespread outreach programs, strategies to improve medication adherence, safe and effective pharmacological treatments to control or eliminate CKD, as well as the use of health information technology, and patient-engagement programs for improved CKD outcomes may help to positively impact these disparities among AAs.

Sex-Divergent Clinical Outcomes and Precision Medicine: An Important New Role for Institutional Review Boards and Research Ethics Committees

The efforts toward individualized medicine have constantly increased in an attempt to improve treatment options. These efforts have led to the development of small molecules which target specific molecular pathways involved in cancer progression. We have reviewed preclinical studies of sunitinib that incorporate sex as a covariate to explore possible sex-based differences in pharmacokinetics and drug–drug interactions (DDI) to attempt a relationship with published clinical outputs. We observed that covariate sex is lacking in most clinical outcome reports and suggest a series of ethic-based proposals to improve research activities and identify relevant different sex outcomes. We propose a deeper integration of preclinical, clinical, and translational research addressing statistical and clinical significance jointly; to embed specific sex-divergent endpoints to evaluate possible gender differences objectively during all stages of research; to pay greater attention to sex-divergent outcomes in polypharmacy scenarios, DDI and bioequivalence studies; the clear reporting of preclinical and clinical findings regarding sex-divergent outcomes; as well as to encourage the active role of scientists and the pharmaceutical industry to foster a new scientific culture through their research programs, practice, and participation in editorial boards and Institutional Ethics Review Boards (IRBs) and Research Ethics Committees (RECs). We establish the IRB/REC as the centerpiece for the implementation of these proposals. We suggest the expansion of its competence to follow up clinical trials to ensure that sex differences are addressed and recognized; to engage in data monitoring committees to improve clinical research cooperation and ethically address those potential clinical outcome differences between male and female patients to analyze their social and clinical implications in research and healthcare policies.

Unique sex- and age-dependent effects in protective pathways in acute kidney injury

Sex and age influence susceptibility to acute kidney injury (AKI), with young females exhibiting lowest incidence. In these studies, we investigated mechanisms which may underlie the sex/age-based dissimilarities. Cisplatin (Cp)-induced AKI resulted in morphological evidence of injury in all groups. A minimal rise in plasma creatinine (PCr) was seen in Young Females, whereas in Aged Females, PCr rose precipitously. Relative to Young Males, Aged Males showed significantly, but temporally, comparably elevated PCr. Notably, Aged Females showed significantly greater mortality, whereas Young Females exhibited none. Tissue KIM-1 and plasma NGAL were significantly lower in Young Females than all others. IGFBP7 levels were modestly increased in both Young groups. IGFBP7 levels in Aged Females were significantly elevated at baseline relative to Aged Males, and increased linearly through day 3, when these levels were comparable in both Aged groups. Plasma cytokine levels similarly showed a pattern of protective effects preferentially in Young Females. Expression of the drug transporter MATE2 did not explain the sex/age distinctions. Heme oxygenase-1 (HO-1) levels (~28-kDa species) showed elevation at day 1 in all groups with highest levels seen in Young Males. Exclusively in Young Females, these levels returned to baseline on day 3, suggestive of a more efficient recovery. In aggregate, we demonstrate, for the first time, a distinctive pattern of response to AKI in Young Females relative to males which appears to be significantly altered in aging. These distinctions may offer novel targets to exploit therapeutically in both females and males in the treatment of AKI.

Identifying disease-associated pathways in one-phenotype data based on reversal gene expression orderings

Due to the invasiveness nature of tissue biopsy, it is common that investigators cannot collect sufficient normal controls for comparison with diseased samples. We developed a pathway enrichment tool, DRFunc, to detect significantly disease-disrupted pathways by incorporating normal controls from other experiments. The method was validated using both microarray and RNA-seq expression data for different cancers. The high concordant differentially ranked (DR) gene pairs were identified between cases and controls from different independent datasets. The DR gene pairs were used in the DRFunc algorithm to detect significantly disrupted pathways in one-phenotype expression data by combing controls from other studies. The DRFunc algorithm was exemplified by the detection of significant pathways in glioblastoma samples. The algorithm can also be used to detect altered pathways in the datasets with weak expression signals, as shown by the analysis on the expression data of chemotherapy-treated breast cancer samples.

Sex Differences in Human and Animal Toxicology

Sex, the states of being female or male, potentially interacts with all xenobiotic exposures, both inadvertent and deliberate, and influences their toxicokinetics (TK), toxicodynamics, and outcomes. Sex differences occur in behavior, exposure, anatomy, physiology, biochemistry, and genetics, accounting for female-male differences in responses to environmental chemicals, diet, and pharmaceuticals, including adverse drug reactions (ADRs). Often viewed as an annoying confounder, researchers have studied only one sex, adjusted for sex, or ignored it. Occupational epidemiology, the basis for understanding many toxic effects in humans, usually excluded women. Likewise, Food and Drug Administration rules excluded women of childbearing age from drug studies for many years. Aside from sex-specific organs, sex differences and sex × age interactions occur for a wide range of disease states as well as hormone-influenced conditions and drug distribution. Women have more ADRs than men; the classic sex hormone paradigm (gonadectomy and replacement) reveals significant interaction of sex and TK including absorption, distribution, metabolisms, and elimination. Studies should be designed to detect sex differences, describe the mechanisms, and interpret these in a broad social, clinical, and evolutionary context with phenomena that do not differ. Sex matters, but how much of a difference is needed to matter remains challenging.

Development of Human Membrane Transporters: Drug Disposition and Pharmacogenetics

Membrane transporters play an essential role in the transport of endogenous and exogenous compounds, and consequently they mediate the uptake, distribution, and excretion of many drugs. The clinical relevance of transporters in drug disposition and their effect in adults have been shown in drug–drug interaction and pharmacogenomic studies. Little is known, however, about the ontogeny of human membrane transporters and their roles in pediatric pharmacotherapy. As they are involved in the transport of endogenous substrates, growth and development may be important determinants of their expression and activity. This review presents an overview of our current knowledge on human membrane transporters in pediatric drug disposition and effect. Existing pharmacokinetic and pharmacogenetic data on membrane substrate drugs frequently used in children are presented and related, where possible, to existing ex vivo data, providing a basis for developmental patterns for individual human membrane transporters. As data for individual transporters are currently still scarce, there is a striking information gap regarding the role of human membrane transporters in drug therapy in children.

Transporter effects on cell permeability in drug delivery

INTRODUCTION

The role of drug transporters as one of the determinants of cellular drug permeability has become increasingly evident. Despite the lipophilicity of a drug molecule as rate-limiting factor for passive diffusion across biological membranes, carrier-mediated and active transport have gained attention over the years. A better understanding of the effects and roles of these influx transporters towards transmembrane permeability of a drug molecule need to be delineated for drug development and delivery. Areas covered: This review focuses on findings relative to role of transporters in drug absorption and bioavailability. Particularly the areas demanding further research have been emphasized. This review will also highlight various transporters expressed on vital organs and their effects on drug pharmacokinetics. Expert opinion: Significant efforts have been devoted to understand the role of transporters, their iterative interplay with metabolizing enzymes through molecular enzymology, binding and structure-activity relationship studies. A few assays such as parallel artificial membrane permeation assay (PAMPA) have been developed to analyze drug transport across phospholipid membranes. Although large web-accessible databases on tissue selective expression profiles at transcriptomic as well as proteomic are available, there is a need to collocate the scattered literature on the role of transporters in drug development and delivery.

Autophagy, Innate Immunity and Tissue Repair in Acute Kidney Injury

Kidney is a vital organ with high energy demands to actively maintain plasma hemodynamics, electrolytes and water homeostasis. Among the nephron segments, the renal tubular epithelium is endowed with high mitochondria density for their function in active transport. Acute kidney injury (AKI) is an important clinical syndrome and a global public health issue with high mortality rate and socioeconomic burden due to lack of effective therapy. AKI results in acute cell death and necrosis of renal tubule epithelial cells accompanied with leakage of tubular fluid and inflammation. The inflammatory immune response triggered by the tubular cell death, mitochondrial damage, associative oxidative stress, and the release of many tissue damage factors have been identified as key elements driving the pathophysiology of AKI. Autophagy, the cellular mechanism that removes damaged organelles via lysosome-mediated degradation, had been proposed to be renoprotective. An in-depth understanding of the intricate interplay between autophagy and innate immune response, and their roles in AKI pathology could lead to novel therapies in AKI. This review addresses the current pathophysiology of AKI in aspects of mitochondrial dysfunction, innate immunity, and molecular mechanisms of autophagy. Recent advances in renal tissue regeneration and potential therapeutic interventions are also discussed.

Handling of Drugs, Metabolites, and Uremic Toxins by Kidney Proximal Tubule Drug Transporters

The proximal tubule of the kidney plays a crucial role in the renal handling of drugs (e.g., diuretics), uremic toxins (e.g., indoxyl sulfate), environmental toxins (e.g., mercury, aristolochic acid), metabolites (e.g., uric acid), dietary compounds, and signaling molecules. This process is dependent on many multispecific transporters of the solute carrier (SLC) superfamily, including organic anion transporter (OAT) and organic cation transporter (OCT) subfamilies, and the ATP-binding cassette (ABC) superfamily. We review the basic physiology of these SLC and ABC transporters, many of which are often called drug transporters. With an emphasis on OAT1 (SLC22A6), the closely related OAT3 (SLC22A8), and OCT2 (SLC22A2), we explore the implications of recent in vitro, in vivo, and clinical data pertinent to the kidney. The analysis of murine knockouts has revealed a key role for these transporters in the renal handling not only of drugs and toxins but also of gut microbiome products, as well as liver-derived phase 1 and phase 2 metabolites, including putative uremic toxins (among other molecules of metabolic and clinical importance). Functional activity of these transporters (and polymorphisms affecting it) plays a key role in drug handling and nephrotoxicity. These transporters may also play a role in remote sensing and signaling, as part of a versatile small molecule communication network operative throughout the body in normal and diseased states, such as AKI and CKD.