Taste of a pill: organic cation transporter-3 (OCT3) mediates metformin accumulation and secretion in salivary glands

Optimizing metformin therapy in practice: Tailoring therapy in specific patient groups to improve tolerability, efficacy and outcomes

Metformin is the first-line medication for type 2 diabetes. It is effective and safe, provided some caution is taken in specific populations. In patients with chronic kidney disease, metformin may provide long-term benefits, and it is a first-line therapy for diabetes, but the estimated glomerular filtration rate (eGFR) must be assessed regularly, to minimize the risk for metformin accumulation. When eGFR is 30-60 mL/min/1.73m2, the dose should be reconsidered, and sick-days education provided. Metformin should be discontinued when eGFR falls below 30 mL/min/1.73m2. Metformin accumulation may increase the risk for lactic acidosis if concomitant risk factors for hyperlactataemia (liver or respiratory insufficiency, sepsis, acute heart failure) are present; in these conditions, metformin is contraindicated, even although the available evidence is reassuring. Patients on metformin often complain of gastrointestinal side effects (mainly diarrhoea and nausea) during therapy initiation, but they may sometimes occur after years of stable therapy. These usually resolve if the dose is carefully titrated, or by switching to the extended-release formulation. Patients with obesity may benefit from the significant, although modest, metformin-associated weight loss and appetite reduction. During pregnancy, metformin is associated with a reduction of pregnancy complications, especially in obese women, but some concern remains, because metformin crosses the placenta, and it is associated with a significantly lower mean birth weight than insulin. In the elderly, gastrointestinal tolerability and renal function must be reassessed more often. Vitamin B-12 should be screened regularly in long-time metformin users because metformin may induce clinical vitamin B-12 deficiency.

Cardiac Uptake of the Adrenergic Imaging Agent meta-Iodobenzylguanidine (mIBG) Is Mediated by Organic Cation Transporter 3 (Oct3)

Heart failure (HF) is a chronic disease affecting 1%-2% of the global population.123I-labeled meta-iodobenzylguanidine (mIBG) is US Food and Drug Administration-approved for cardiac imaging and prognosis risk assessment in patients with HF. As a norepinephrine analog, mIBG is believed to be transported into adrenergic nerve terminals by the neuronal norepinephrine transporter (NET) and hence image sympathetic innervation of the myocardium. We previously showed that mIBG is an excellent substrate of organic cation transporter 3 (OCT3), an extraneuronal transporter expressed in cardiomyocytes. Here, we evaluated the in vivo impact of Oct3 on mIBG disposition and tissue distribution using Oct3 knockout mice. Oct3 +/+ and Oct3 -/- mice were administered with mIBG intravenously, and mIBG plasma pharmacokinetics and tissue exposures were determined. In Oct3 +/+ mice, mIBG exhibited extensive accumulation in multiple tissues (heart, salivary gland, liver, and adrenal gland). No difference was observed in overall plasma exposure between Oct3 +/+ and Oct3 -/- mice. Strikingly, cardiac mIBG was depleted in Oct3 -/- mice, resulting in 83% reduction in overall cardiac exposure (AUC0-24 h: 12.7 vs. 2.1 μg × h/g). mIBG tissue exposure (AUC0-24 h) was also reduced by 66%, 36%, and 31% in skeletal muscle, salivary gland, and lung, respectively, in Oct3 -/- mice. Our data demonstrated that Oct3 is the primary transporter responsible for cardiac mIBG uptake in vivo and suggested that cardiac mIBG imaging mainly measures OCT3 activity in cardiomyocytes but not NET-mediated uptake in adrenergic nerve endings. Our findings challenge the current paradigm in interpreting cardiac mIBG imaging results and suggest OCT3 as a potential genetic risk marker for HF prognosis. SIGNIFICANCE STATEMENT: 123I-labeled meta-iodobenzylguanidine is used for cardiac imaging and risk assessment in heart failure patients. Contrary to the current belief that meta-iodobenzylguanidine (mIBG) tracks cardiac sympathetic innervation due to its uptake by the neuronal norepinephrine transporter, the authors demonstrated that cardiac mIBG uptake is mediated by the extraneuronal transporter Oct3. Their findings warrant a re-evaluation of the scientific rationale behind cardiac mIBG scan and further suggest organic cation transporter 3 as a risk factor for disease progression in heart failure patients.

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.

Metformin and the Liver: Unlocking the Full Therapeutic Potential

Metformin is a highly effective medication for managing type 2 diabetes mellitus. Recent studies have shown that it has significant therapeutic benefits in various organ systems, particularly the liver. Although the effects of metformin on metabolic dysfunction-associated steatotic liver disease and metabolic dysfunction-associated steatohepatitis are still being debated, it has positive effects on cirrhosis and anti-tumoral properties, which can help prevent the development of hepatocellular carcinoma. Furthermore, it has been proven to improve insulin resistance and dyslipidaemia, commonly associated with liver diseases. While more studies are needed to fully determine the safety and effectiveness of metformin use in liver diseases, the results are highly promising. Indeed, metformin has a terrific potential for extending its full therapeutic properties beyond its traditional use in managing diabetes.

Developmental metformin exposure does not rescue physiological impairments derived from early exposure to altered maternal metabolic state in offspring mice

OBJECTIVE

The incidence of gestational diabetes mellitus (GDM) and metabolic disorders during pregnancy are increasing globally. This has resulted in increased use of therapeutic interventions such as metformin to aid in glycemic control during pregnancy. Even though metformin can cross the placental barrier, its impact on offspring brain development remains poorly understood. As metformin promotes AMPK signaling, which plays a key role in axonal growth during development, we hypothesized that it may have an impact on hypothalamic signaling and the formation of neuronal projections in the hypothalamus, the key regulator of energy homeostasis. We further hypothesized that this is dependent on the metabolic and nutritional status of the mother at the time of metformin intervention. Using mouse models of maternal overnutrition, we aimed to assess the effects of metformin exposure on offspring physiology and hypothalamic neuronal circuits during key periods of development.

METHODS

Female C57BL/6N mice received either a control diet or a high-fat diet (HFD) during pregnancy and lactation periods. A subset of dams was fed a HFD exclusively during the lactation. Anti-diabetic treatments were given during the first postnatal weeks. Body weights of male and female offspring were monitored daily until weaning. Circulating metabolic factors and molecular changes in the hypothalamus were assessed at postnatal day 16 using ELISA and Western Blot, respectively. Hypothalamic innervation was assessed by immunostaining at postnatal days 16 and 21.

RESULTS

We identified alterations in weight gain and circulating hormones in male and female offspring induced by anti-diabetic treatment during the early postnatal period, which were critically dependent on the maternal metabolic state. Furthermore, hypothalamic agouti-related peptide (AgRP) and proopiomelanocortin (POMC) neuronal innervation outcomes in response to anti-diabetic treatment were also modulated by maternal metabolic state. We also identified sex-specific changes in hypothalamic AMPK signaling in response to metformin exposure.

CONCLUSION

We demonstrate a unique interaction between anti-diabetic treatment and maternal metabolic state, resulting in sex-specific effects on offspring brain development and physiological outcomes. Overall, based on our findings, no positive effect of metformin intervention was observed in the offspring, despite ameliorating effects on maternal metabolic outcomes. In fact, the metabolic state of the mother drives the most dramatic differences in offspring physiology and metformin had no rescuing effect. Our results therefore highlight the need for a deeper understanding of how maternal metabolic state (excessive weight gain versus stable weight during GDM treatment) affects the developing offspring. Further, these results emphasize that the interventions to treat alterations in maternal metabolism during pregnancy need to be reassessed from the perspective of the offspring physiology.

Investigating the ability to adhere to cardiometabolic medications with different properties: a retrospective cohort study of >500 000 patients in the USA

OBJECTIVE

Poor medication adherence remains highly prevalent and adversely affects health outcomes. Patients frequently describe properties of the pills themselves, like size and shape, as barriers, but this has not been evaluated objectively. We sought to determine the extent to which oral medication properties thought to be influential translate into lower objectively-measured adherence.

DESIGN

Retrospective cohort study.

SETTING

US nationwide commercial claims database, 2016-2019.

PARTICIPANTS

Among patients initiating first-line hypertension, diabetes or hyperlipidaemia treatment based on clinical guidelines, we measured pill size, shape, colour and flavouring, number of pills/day and fixed-dose combination status as properties.

OUTCOME MEASURES

Outcomes included discontinuation after the first fill (ie, never filling again over a minimum of 1-year follow-up) and long-term non-adherence (1-year proportion of days covered <0.80). We estimated associations between each property and outcomes, by therapeutic class (eg, statins), with multivariable logistic regression.

RESULTS

Across 604 323 patients, 14.6% discontinued after filling once (ie, were non-persistent), and 54.0% were non-adherent over 1-year follow-up. Large pill size was associated with non-adherence, except for thiazides (eg, metformin adjusted OR (aOR): 1.12, 95% CI: 1.06 to 1.18). Greater pill burden was associated with a higher risk of non-adherence across all classes (eg, metformin aOR: 1.58, 95% CI: 1.53 to 1.64 for two pills/day). Taking less than one pill/day was also associated with higher risk of non-adherence and non-persistence (eg, non-persistence statin aOR: 1.29, 95% CI: 1.20 to 1.38). Pill shape, colour, flavouring and combination status were associated with mixed effects across classes.

CONCLUSIONS

Pill burden and pill size are key properties affecting adherence for almost all classes; others, like size and combination, could modestly affect medication adherence. Clinical interventions could screen patients for potential intolerance to medication and potentially implement more convenient dosing schedules.

Summarizing studies using constitutive genetic deficiency to investigate behavioural influences of uptake 2 monoamine transporters

Burgeoning literature demonstrates that monoamine transporters with high transport capacity but lower substrate affinity (i.e., uptake 2) contribute meaningfully to regulation of monoamine neurotransmitter signalling. However, studying behavioural influences of uptake 2 is hindered by an absence of selective inhibitors largely free of off-target, confounding effects. This contrasts with study of monoamine transporters with low transport capacity but high substrate affinity (i.e., uptake 1), for which there are many reasonably selective inhibitors. To circumvent this dearth of pharmacological tools for studying uptake 2, researchers have instead employed mice with constitutive genetic deficiency in three separate transporters. By studying baseline behavioural shifts, plus behavioural responses to environmental and pharmacological manipulations-the latter primarily targeting uptake 1-investigators have been creatively characterizing the behavioural, and often sex-specific, influences of uptake 2. This non-systematic mini review summarizes current uptake 2 behaviour literature, highlighting emphases on stress responsivity in organic cation transporter 2 (OCT2) work, psychostimulant responsivity in OCT3 and plasma membrane monoamine transporter (PMAT) investigations, and antidepressant responsivity in all three. Collectively, this small but growing body of work reiterates the necessity for development of selective uptake 2-inhibiting drugs, with reviewed studies suggesting that these might advance personalized treatment approaches.

Development of a novel method for the simultaneous detection of trimethylamine N-oxide and creatinine in the saliva of patients with chronic kidney disease - Its utility in saliva as an alternative to blood

Chronic kidney disease (CKD) is associated with increased levels of creatinine and other uremic toxins (UTs), which impaired kidneys cannot filtrate. Typically, CKD is diagnosed by calculating the estimated glomerular filtration rate using serum creatinine or cystatin C levels. In pursuit of more sensitive and reliable biomarkers of kidney dysfunction, scientific attention has turned towards other UTs, such as trimethylamine N-oxide (TMAO), successfully quantified in standard matrices, blood and urine. However, less invasive monitoring of kidney function can be performed using an alternative diagnostic biofluid, saliva, which has been shown to contain clinically relevant concentrations of renal function markers. Accurate quantitative estimation of serum biomarkers using saliva measurements can only be achieved provided that there is a tight saliva-serum correlation for the analyte of interest. Therefore, we aimed to verify the correlation between saliva and serum levels of TMAO in CKD patients using newly developed and validated quantitative liquid chromatography coupled to mass spectrometry (LC-MS) method for simultaneous detection of TMAO, and creatinine - the conventional marker of renal impairment. Secondly, we applied this method to quantify TMAO and creatinine levels in the resting saliva of CKD patients collected with a standardised method involving swab-based collectors. A good linear correlation was obtained between the concentration of creatinine in serum and resting saliva of CKD patients (r = 0.72, p = 0.029) and even better in the case of TMAO (r = 0.81, p = 0.008). The analysed validation criteria were fulfilled. No significant influence of the type of swab in the Salivette® device on creatinine and TMAO concentrations in saliva was detected. Our study indicates that saliva can be successfully used in the non-invasive monitoring of renal failure in CKD by measuring salivary TMAO concentrations.

Interaction of ALK Inhibitors with Polyspecific Organic Cation Transporters and the Impact of Substrate-Dependent Inhibition on the Prediction of Drug-Drug Interactions

Small molecules targeting aberrant anaplastic lymphoma kinase (ALK) are active against ALK-positive non-small-cell lung cancers and neuroblastoma. Several targeted tyrosine kinase inhibitors (TKIs) have been shown to interact with polyspecific organic cation transporters (pOCTs), raising concerns about potential drug-drug interactions (DDIs). The purpose of this study was to assess the interaction of ALK inhibitors with pOCTs and the impact of substrate-dependent inhibition on the prediction of DDIs. Inhibition assays were conducted in transporter-overexpressing cells using meta-iodobenzylguanidine (mIBG), metformin, or 1-methyl-4-phenylpyridinium (MPP+) as the substrate. The half-maximal inhibitory concentrations (IC50) of brigatinib and crizotinib for the substrates tested were used to predict their potential for in vivo transporter mediated DDIs. Here, we show that the inhibition potencies of brigatinib and crizotinib on pOCTs are isoform- and substrate-dependent. Human OCT3 (hOCT3) and multidrug and toxin extrusion protein 1 (hMATE1) were highly sensitive to inhibition by brigatinib and crizotinib for all three tested substrates. Apart from hMATE1, substrate-dependent inhibition was observed for all other transporters with varying degrees of dependency; hOCT1 inhibition showed the greatest substrate dependency, with differences in IC50 values of up to 22-fold across the tested substrates, followed by hOCT2 and hMATE2-K, with differences in IC50 values of up to 16- and 12-fold, respectively. Conversely, hOCT3 inhibition only showed a moderate substrate dependency (IC50 variance < 4.8). Among the substrates used, metformin was consistently shown to be the most sensitive substrate, followed by mIBG and MPP+. Pre-incubation of ALK inhibitors had little impact on their potencies toward hOCT2 and hMATE1. Our results underscore the complexity of the interactions between substrates and the inhibitors of pOCTs and have important implications for the clinical use of ALK inhibitors and their DDI predictions.

The development and benefits of metformin in various diseases

Metformin has been used for the treatment of type II diabetes mellitus for decades due to its safety, low cost, and outstanding hypoglycemic effect clinically. The mechanisms underlying these benefits are complex and still not fully understood. Inhibition of mitochondrial respiratory-chain complex I is the most described downstream mechanism of metformin, leading to reduced ATP production and activation of AMP-activated protein kinase (AMPK). Meanwhile, many novel targets of metformin have been gradually discovered. In recent years, multiple pre-clinical and clinical studies are committed to extend the indications of metformin in addition to diabetes. Herein, we summarized the benefits of metformin in four types of diseases, including metabolic associated diseases, cancer, aging and age-related diseases, neurological disorders. We comprehensively discussed the pharmacokinetic properties and the mechanisms of action, treatment strategies, the clinical application, the potential risk of metformin in various diseases. This review provides a brief summary of the benefits and concerns of metformin, aiming to interest scientists to consider and explore the common and specific mechanisms and guiding for the further research. Although there have been countless studies of metformin, longitudinal research in each field is still much warranted.

Determination and disposition of meta-iodobenzylguanidine in plasma and heart of transporter-deficient mice by UPLC-MS/MS

A simple LC-MS/MS method for the quantitative determination of the norepinephrine analogue meta-iodobenzyl-guanidine (mIBG) was developed and validated for mouse plasma and tissues, including salivary gland and heart. The assay procedure involved a one-step solvent extraction of mIBG and the internal standard N-(4-fluorobenzyl)-guandine from plasma or tissue homogenates with acetonitrile. An Accucore aQ column was used to separate analytes using a gradient elution with a total run time of 3.5 min. Validation studies with quality control samples processed on consecutive days revealed values for intra-day and inter-day precision of < 11.3%, with values for accuracy ranging 96.8-111%. Linear responses were observed over the entire calibration curves range (up to 100 ng/mL), and the lower limit of quantification was 0.1 ng/mL, using sample volumes of 5 µL. The developed method was successfully applied to evaluate the plasma pharmacokinetics and tissue distribution of mIBG in wild-type mice and animals lacking the organic cation transporters OCT1, OCT2, OCT3, and/or MATE1 to further understand mechanisms contributing to drug distribution and elimination and causes of inter-individual pharmacokinetic variability.

Repression of SLC22A3 by the AR-V7/YAP1/TAZ axis in enzalutamide-resistant castration-resistant prostate cancer

Metastatic castration-resistant prostate cancer (mCRPC) is an aggressive and fatal disease, with most patients succumbing within 1-2 years despite undergoing multiple treatments. Androgen-receptor (AR) inhibitors, including enzalutamide (ENZ), are used for the treatment of mCRPC; however, most patients develop resistance to ENZ. Herein, we propose that the repression of SLC22A3 by AR-V7/YAP1/TAZ conferred ENZ resistance in mCRPC. SLC22A3 expression is specifically downregulated in the ENZ-resistant C4-2B MDVR cells, and when YAP1/TAZ is hyperactivated by AR full-length or AR-V7, these proteins interact with DNMT1 to repress SLC22A3 expression. We observed low SLC22A3 expression and high levels of TAZ or YAP1 in mCRPC patient tissues harbouring AR-V7 and the opposite expression patterns in normal patient tissues. Our findings suggest a mechanism underlying ENZ resistance by providing evidence that the AR-V7/YAP1/TAZ axis represses SLC22A3, which could be a potential treatment target in prostate cancer.

Predicting disruptions to drug pharmacokinetics and the risk of adverse drug reactions in non-alcoholic steatohepatitis patients

The liver plays a central role in the pharmacokinetics of drugs through drug metabolizing enzymes and transporters. Non-alcoholic steatohepatitis (NASH) causes disease-specific alterations to the absorption, distribution, metabolism, and excretion (ADME) processes, including a decrease in protein expression of basolateral uptake transporters, an increase in efflux transporters, and modifications to enzyme activity. This can result in increased drug exposure and adverse drug reactions (ADRs). Our goal was to predict drugs that pose increased risks for ADRs in NASH patients. Bibliographic research identified 71 drugs with reported ADRs in patients with liver disease, mainly non-alcoholic fatty liver disease (NAFLD), 54 of which are known substrates of transporters and/or metabolizing enzymes. Since NASH is the progressive form of NAFLD but is most frequently undiagnosed, we identified other drugs at risk based on NASH-specific alterations to ADME processes. Here, we present another list of 71 drugs at risk of pharmacokinetic disruption in NASH, based on their transport and/or metabolism processes. It encompasses drugs from various pharmacological classes for which ADRs may occur when used in NASH patients, especially when eliminated through multiple pathways altered by the disease. Therefore, these results may inform clinicians regarding the selection of drugs for use in NASH patients.

Pharmacokinetic Basis for Using Saliva Matrine Concentrations as a Clinical Compliance Monitoring in Antitumor B Chemoprevention Trials in Humans

This study reports the first clinical evidence of significantly high secretion of matrine in a multi-component botanical (Antitumor B, ATB) into human saliva from the systemic circulation. This is of high clinical significance as matrine can be used as a monitoring tool during longitudinal clinical studies to overcome the key limitation of poor patient compliance often reported in cancer chemoprevention trials. Both matrine and dictamine were detected in the saliva and plasma samples but only matrine was quantifiable after the oral administration of ATB tablets (2400 mg) in 8 healthy volunteers. A significantly high saliva/plasma ratios for C_max (6.5 ± 2.0) and AUC_0-24 (4.8 ± 2.0) of matrine suggested an active secretion in saliva probably due to entero-salivary recycling as evident from the long half-lives (t_1/2 plasma = 10.0 ± 2.8 h, t_1/2 saliva = 13.4 ± 6.9 h). The correlation between saliva and plasma levels of matrine was established using a population compartmental pharmacokinetic co-model. Moreover, a species-relevant PBPK model was developed to adequately describe the pharmacokinetic profiles of matrine in mouse, rat, and human. In conclusion, matrine saliva concentrations can be used as an excellent marker compound for mechanistic studies of active secretion of drugs from plasma to saliva as well as monitor the patient's compliance to the treatment regimen in upcoming clinical trials of ATB.

Tumor Distribution by Quantitative Mass Spectrometry Imaging of the Inhibitor of Apoptosis Protein Antagonist Xevinapant in Patients with Resectable Squamous Cell Carcinoma of the Head and Neck (EudraCT Number: 2014-004655-31)

As tumors are very heterogeneous, investigating the penetration and concentration of an anticancer drug in different histological regions of a tumor is key to evaluate the efficacy, to improve the pharmacokinetics/pharmacodynamics (PK/PD) relationship evaluation, and to confirm the adequacy of the dose regimen. Quantitative mass spectrometry imaging (QMSI) allows for the determination of the tissue distribution of drugs, metabolites, and biomarkers to support quick and precise evaluation of drug efficacy and safety in a single experiment. QMSI was applied in a preoperative window-of-opportunity (WoO) study of the inhibitor of apoptosis protein antagonist xevinapant (Debio 1143) in patients with resectable squamous cell carcinoma of the head and neck (SCCHN). Tumors were isolated, immediately snap-frozen, and sectioned, and then, the molecular distribution of the drug was generated by matrix-assisted laser desorption ionization (MALDI) imaging. Additionally, the different histological regions (tumor, epithelium, salivary glands, muscle, nerve, and blood vessels) were identified on stained sections adjacent to the ones used for QMSI, leading to a specific quantification integrating the biological characterization of the tumor heterogeneity. This innovative approach allowed one to highlight the high affinity of xevinapant for the tumor tissues.

MATE1 Deficiency Exacerbates Dofetilide-Induced Proarrhythmia

Dofetilide is a rapid delayed rectifier potassium current inhibitor widely used to prevent the recurrence of atrial fibrillation and flutter. The clinical use of this drug is associated with increases in QTc interval, which predispose patients to ventricular cardiac arrhythmias. The mechanisms involved in the disposition of dofetilide, including its movement in and out of cardiomyocytes, remain unknown. Using a xenobiotic transporter screen, we identified MATE1 (SLC47A1) as a transporter of dofetilide and found that genetic knockout or pharmacological inhibition of MATE1 in mice was associated with enhanced retention of dofetilide in cardiomyocytes and increased QTc prolongation. The urinary excretion of dofetilide was also dependent on the MATE1 genotype, and we found that this transport mechanism provides a mechanistic basis for previously recorded drug-drug interactions of dofetilide with various contraindicated drugs, including bictegravir, cimetidine, ketoconazole, and verapamil. The translational significance of these observations was examined with a physiologically-based pharmacokinetic model that adequately predicted the drug-drug interaction liabilities in humans. These findings support the thesis that MATE1 serves a conserved cardioprotective role by restricting excessive cellular accumulation and warrant caution against the concurrent administration of potent MATE1 inhibitors and cardiotoxic substrates with a narrow therapeutic window.

The role of MicroRNA networks in tissue-specific direct and indirect effects of metformin and its application

Metformin is a first-line oral antidiabetic agent that results in clear benefits in relation to glucose metabolism and diabetes-related complications. The specific regulatory details and mechanisms underlying these benefits are still unclear and require further investigation. There is recent mounting evidence that metformin has pleiotropic effects on the target tissue development in metabolic organs, including adipose tissue, the gastrointestinal tract and the liver. The mechanism of actions of metformin are divided into direct effects on target tissues and indirect effects via non-targeted tissues. MicroRNAs (miRNAs) are a class of endogenous, noncoding, negative gene regulators that have emerged as important regulators of a number of diseases, including type 2 diabetes mellitus (T2DM). Metformin is involved in many aspects of miRNA regulation, and metformin treatment in T2DM should be associated with other miRNA targets. A large number of miRNAs regulation by metformin in target tissues with either direct or indirect effects has gradually been revealed in the context of numerous diseases and has gradually received increasing attention. This paper thoroughly reviews the current knowledge about the role of miRNA networks in the tissue-specific direct and indirect effects of metformin. Furthermore, this knowledge provides a novel theoretical basis and suggests therapeutic targets for the clinical treatment of metformin and miRNA regulators in the prevention and treatment of cancer, cardiovascular disorders, diabetes and its complications.

Impact of the clinically approved Petasites hybridus extract Ze 339 on intestinal mechanisms involved in the handling of histamine

In patients with histamine intolerance accumulated or ingested histamine causes a broad range of undesirable symptoms. Food-derived histamine is degraded by intestinal diamine oxidase (DAO) and histamine-N-methyltransferase (HNMT), while the organic cation transporter 3 (OCT3) contributes to the transcellular flux of histamine. Anecdotal evidence from patients with HIT suggests an improvement of symptoms related to histamine intolerance after intake of Ze 339, a lipophilic CO₂-extract prepared from the leaves of Petasites hybridus. Thus, it was the aim of this study to investigate the influence of Ze 339 on DAO, HNMT and OCT3 using Caco-2 and MDCKII cells. Even though Ze 339 reduced mRNA levels of HNMT and DAO, there was no change in protein expression. Ze 339 changed neither the basal release nor the enzymatic activity of DAO. Testing the interaction of Ze 339 with the transcellular histamine transport, we observed a significant increase in the basal to apical flux in presence of high Ze 339 concentrations at the early phases of the experiment. Testing the influence of Ze 339 on OCT3-mediated histamine uptake in overexpressing MDCKII cells revealed a dose-dependent inhibition with an estimated IC₅₀ of 26.9 ug/mL for the extract. In conclusion, we report an effect of Ze 339 on transcellular histamine transport, where inhibition of OCT3 may contribute.

Contribution of membrane transporters to chemotherapy-induced cardiotoxicity

Membrane transporters play a key role in determining the pharmacokinetic profile, therapeutic safety, and efficacy of many chemotherapeutic drugs by regulating cellular influx and efflux. Rapidly emerging evidence has shown that tissue-specific expression of transporters contributes to local drug accumulation and drug-drug interactions and that functional alterations in these transporters can directly influence an individual's susceptibility to drug-induced toxicity. Comprehending the complex mechanism of transporter function in regulating drug distribution in tissues, such as the heart, is necessary in order to acquire novel therapeutic strategies aimed at evading unwanted drug accumulation and toxicities and to ameliorate the safety of current therapeutic regimens. Here, we provide an overview of membrane transporters with a role in chemotherapy-induced cardiotoxicity and discuss novel strategies to improve therapeutic outcomes.

Integrated or Independent Actions of Metformin in Target Tissues Underlying Its Current Use and New Possible Applications in the Endocrine and Metabolic Disorder Area

Metformin is considered the first-choice drug for type 2 diabetes treatment. Actually, pleiotropic effects of metformin have been recognized, and there is evidence that this drug may have a favorable impact on health beyond its glucose-lowering activity. In summary, despite its long history, metformin is still an attractive research opportunity in the field of endocrine and metabolic diseases, age-related diseases, and cancer. To this end, its mode of action in distinct cell types is still in dispute. The aim of this work was to review the current knowledge and recent findings on the molecular mechanisms underlying the pharmacological effects of metformin in the field of metabolic and endocrine pathologies, including some endocrine tumors. Metformin is believed to act through multiple pathways that can be interconnected or work independently. Moreover, metformin effects on target tissues may be either direct or indirect, which means secondary to the actions on other tissues and consequent alterations at systemic level. Finally, as to the direct actions of metformin at cellular level, the intracellular milieu cooperates to cause differential responses to the drug between distinct cell types, despite the primary molecular targets may be the same within cells. Cellular bioenergetics can be regarded as the primary target of metformin action. Metformin can perturb the cytosolic and mitochondrial NAD/NADH ratio and the ATP/AMP ratio within cells, thus affecting enzymatic activities and metabolic and signaling pathways which depend on redox- and energy balance. In this context, the possible link between pyruvate metabolism and metformin actions is extensively discussed.

Targeting OCT3 attenuates doxorubicin-induced cardiac injury

Doxorubicin is a commonly used anticancer agent that can cause debilitating and irreversible cardiac injury. The initiating mechanisms contributing to this side effect remain unknown, and current preventative strategies offer only modest protection. Using stem-cell-derived cardiomyocytes from patients receiving doxorubicin, we probed the transcriptomic landscape of solute carriers and identified organic cation transporter 3 (OCT3) (SLC22A3) as a critical transporter regulating the cardiac accumulation of doxorubicin. Functional validation studies in heterologous overexpression models confirmed that doxorubicin is transported into cardiomyocytes by OCT3 and that deficiency of OCT3 protected mice from acute and chronic doxorubicin-related changes in cardiovascular function and genetic pathways associated with cardiac damage. To provide proof-of-principle and demonstrate translational relevance of this transport mechanism, we identified several pharmacological inhibitors of OCT3, including nilotinib, and found that pharmacological targeting of OCT3 can also preserve cardiovascular function following treatment with doxorubicin without affecting its plasma levels or antitumor effects in multiple models of leukemia and breast cancer. Finally, we identified a previously unrecognized, OCT3-dependent pathway of doxorubicin-induced cardiotoxicity that results in a downstream signaling cascade involving the calcium-binding proteins S100A8 and S100A9. These collective findings not only shed light on the etiology of doxorubicin-induced cardiotoxicity, but also are of potential translational relevance and provide a rationale for the implementation of a targeted intervention strategy to prevent this debilitating side effect.

Meta-Assessment of Metformin Absorption and Disposition Pharmacokinetics in Nine Species

The objective of this study was to systematically assess literature datasets and quantitatively analyze metformin PK in plasma and some tissues of nine species. The pharmacokinetic (PK) parameters and profiles of metformin in nine species were collected from the literature. Based on a simple allometric scaling, the systemic clearances (CL) of metformin in these species highly correlate with body weight (BW) (R2 = 0.85) and are comparable to renal plasma flow in most species except for rabbit and cat. Reported volumes of distribution (VSS) varied appreciably (0.32 to 10.1 L/kg) among species. Using the physiological and anatomical variables for each species, a minimal physiologically based pharmacokinetic (mPBPK) model consisting of blood and two tissue compartments (Tissues 1 and 2) was used for modeling metformin PK in the nine species. Permeability-limited distribution (low fd1 and fd2) and a single tissue-to-plasma partition coefficient (Kp) value for Tissues 1 and 2 were applied in the joint mPBPK fitting. Nonlinear regression analysis for common tissue distribution parameters along with species-specific CL values reasonably captured the plasma PK profiles of metformin across most species, except for rat and horse with later time deviations. In separate fittings of the mPBPK model to each species, Tissue 2 was considered as slowly-equilibrating compartment consisting of muscle and skin based on in silico calculations of the mean transit times through tissues. The well-fitted mPBPK model parameters for absorption and disposition PK of metformin for each species were compared with in vitro/in vivo results found in the literature with regard to the physiological details and physicochemical properties of metformin. Bioavailability and absorption rates decreased with the increased BW among the species. Tissues such as muscle dominate metformin distribution with low permeability and partitioning while actual tissue concentrations found in rats and mice show likely transporter-mediated uptake in liver, kidney, and gastrointestinal tissues. Metformin has diverse pharmacologic actions, and this assessment revealed allometric relationships in its absorption and renal clearance but considerable variability in actual and modeled tissue distribution probably caused by transporter differences.

Helicobacter Pylori Eradication Therapy: Still a Challenge

Introduction

Helicobacter pylori (H. pylori) infection is prevalent worldwide. H. pylori therapies' adverse effects can contribute to noncompliance among patients. This study aimed to assess the association between compliance to H. pylori eradication therapy and adverse effects using various drug regimens.

Method

We conducted an observational study from September 2017 to February 2020 in two tertiary care hospitals in patients with dyspeptic symptoms. H. Pylori detection was done by histopathological examination of gastric mucosa during upper gastrointestinal endoscopy or stool for H. pylori antigen. Patients with positive results were randomly assigned one of the nine different regimens consisting of a combination of proton pump inhibitors along with at least two antibiotics. The antibiotics used in different combinations were amoxicillin, clarithromycin, metronidazole, doxycycline, levofloxacin, and bismuth sulfate. The treatment groups received standard triple therapy with and without probiotics, sequential, concomitant, levofloxacin-based triple therapy, or sequential and bismuth-based quadruple treatments. All treatments were given for two weeks. At the end of the treatment period, patients were interviewed about completing treatment and any adverse effects they may have experienced during therapy. Data were analyzed using IBM Statistical Package for the Social Sciences (SPSS) Statistics for Windows, Version 22.0 (Armonk, NY: IBM Corp.).

Results

A total of 250 patients were included in the study (62% males, 38% females) with a mean age of 37 years ± 13 years (range 12-84 years). Most patients completed the treatment regimen (80.4%), and 19.6% did not complete treatment because of adverse effects (p<0.005). The levofloxacin-based, concomitant, and standard triple regimen with probiotic treatments had the highest tolerance (≥85%). Common adverse effects were abdominal and epigastric pain (11%), alteration of taste, and diarrhea (6.5%).

Conclusion

H. pylori eradication therapy is always a challenge. Patient compliance to the treatment can only be ensured by medicines with fewer adverse effects. In our study, levofloxacin-based triple, concomitant, and standard triple regimens with probiotics are maximally acceptable treatments.

Glucose metabolism-related gene polymorphisms as the risk predictors of type 2 diabetes

Type 2 diabetes mellitus (T2DM) is a complex polygenic metabolic disease characterized by elevated blood glucose. Multiple environmental and genetic factors can increase the risk of T2DM and its complications, and genetic polymorphisms are no exception. This review is mainly focused on the related genes involved in glucose metabolic, including G6PC2, GCK, GCKR and OCT3. In this review, we have summarized the results reported globally and found that the genetic variants of GCK and OCT3 genes is a risk factor for T2DM while G6PC2 and GCKR genes are controversial in different ethnic groups. Hopefully, this summary could possibly help researchers and physicians understand the mechanism of T2DM so as to diagnose and even prevent T2DM at early time.

Role of HIV and Antiretroviral Therapy on the Expression of Placental Transporters in Women with HIV

Treatment guidelines recommend continuation of combination antiretroviral therapy (cART) throughout pregnancy for all women living with human immunodeficiency virus (HIV). Many of these drugs are substrates of transporters expressed in the placenta and therefore play a role in fetal exposure. As placental transporters can be impacted by both HIV infection and drug therapy, our objective was to explore the impact of HIV infection and cART on transporter expression. Drug transporter expression was examined in human placental samples collected from women with HIV (n = 25) and from healthy HIV(-) controls (n = 23). The effect of exposure to drugs commonly used in cART during pregnancy was examined in vitro in placental villous explants obtained from healthy women. Gene expression was measured via qRT-PCR. Several ABC (ABCG2, ABCC1,2,4) and SLC (SLC21A9, SLC22A1,3,11) transporters were significantly downregulated in placentas isolated from HIV(+) women as compared with HIV(-) controls (p < 0.05-0.001), while ABCB1 and SLC21A12 were significantly upregulated (p < 0.001). Twenty-four to 48-h exposure of human placental explants to agents used in cART resulted in significant upregulation of ABCB1 and downregulation of SLC22A11. Our findings suggest that transplacental transport may be compromised during HIV infection due to altered expression of clinically important transporters. Furthermore, in vitro results indicate that cART imposes significant alterations in placental transporters but not all changes are consistent with findings in the placenta from HIV(+) women, indicating disease effects. As this may impact in utero-fetal exposure to clinically used medications, further studies are needed to determine the overall impact on maternal-fetal transfer.

Development of a Pharmacokinetic Model of Transplacental Transfer of Metformin to Predict In Vivo Fetal Exposure

Two types of systems are used in ex vivo human placental perfusion studies to predict fetal drug exposures, that is, closed systems with recirculation of the maternal and fetal buffer and open systems using a single-pass mode without recirculation. The in vivo fetal/maternal (F:M) ratio of metformin, a cationic drug that crosses the placenta, is consistent with that reported in an open system ex vivo but not with that in a closed system. In the present study, we aimed to develop a pharmacokinetic (PK) model of transplacental transfer of metformin to predict in vivo fetal exposure to metformin and to resolve the apparent inconsistency between open and closed ex vivo systems. The developed model shows that the difference between open and closed systems is due to the difference in the time required to achieve the steady state. The model-predicted F:M ratio (approx. 0.88) is consistent with reported in vivo values [mean (95% confidence interval): 1.10 (0.69-1.51)]. The model incorporates bidirectional transport via organic cation transporter 3 (OCT3) at the basal plasma membrane, and simulations indicate that the use of trimethoprim (an OCT3 inhibitor) to prevent microbial growth in the placenta ex vivo has a negligible effect on the overall maternal-to-fetal and fetal-to-maternal clearances. The model could successfully predict in vivo fetal exposure using ex vivo human placental perfusion data from both closed and open systems. This transplacental PK modeling approach is expected to be useful for evaluating human fetal exposures to other poorly permeable compounds, besides metformin. SIGNIFICANCE STATEMENT: We developed a pharmacokinetic model of transplacental transfer of metformin, used to treat gestational diabetes mellitus, in order to predict in vivo fetal exposure and resolve the discrepancy between reported findings in open and closed ex vivo perfusion systems. The discrepancy is due to a difference in the time required to reach the steady state. The model can predict in vivo fetal exposure using data from both closed and open systems.

Organic Cation Transporters in Health and Disease

The organic cation transporters (OCTs) OCT1, OCT2, OCT3, novel OCT (OCTN)1, OCTN2, multidrug and toxin exclusion (MATE)1, and MATE kidney-specific 2 are polyspecific transporters exhibiting broadly overlapping substrate selectivities. They transport organic cations, zwitterions, and some uncharged compounds and operate as facilitated diffusion systems and/or antiporters. OCTs are critically involved in intestinal absorption, hepatic uptake, and renal excretion of hydrophilic drugs. They modulate the distribution of endogenous compounds such as thiamine, L-carnitine, and neurotransmitters. Sites of expression and functions of OCTs have important impact on energy metabolism, pharmacokinetics, and toxicity of drugs, and on drug-drug interactions. In this work, an overview about the human OCTs is presented. Functional properties of human OCTs, including identified substrates and inhibitors of the individual transporters, are described. Sites of expression are compiled, and data on regulation of OCTs are presented. In addition, genetic variations of OCTs are listed, and data on their impact on transport, drug treatment, and diseases are reported. Moreover, recent data are summarized that indicate complex drug-drug interaction at OCTs, such as allosteric high-affinity inhibition of transport and substrate dependence of inhibitor efficacies. A hypothesis about the molecular mechanism of polyspecific substrate recognition by OCTs is presented that is based on functional studies and mutagenesis experiments in OCT1 and OCT2. This hypothesis provides a framework to imagine how observed complex drug-drug interactions at OCTs arise. Finally, preclinical in vitro tests that are performed by pharmaceutical companies to identify interaction of novel drugs with OCTs are discussed. Optimized experimental procedures are proposed that allow a gapless detection of inhibitory and transported drugs.

Characterization of Meta-Iodobenzylguanidine (mIBG) Transport by Polyspecific Organic Cation Transporters: Implication for mIBG Therapy

Radiolabeled meta-iodobenzylguanidine (mIBG) is an important radiopharmaceutical used in the diagnosis and treatment of neuroendocrine cancers. mIBG is known to enter tumor cells through the norepinephrine transporter. Whole-body scintigraphy has shown rapid mIBG elimination through the kidney and high accumulation in several normal tissues, but the underlying molecular mechanisms are unclear. Using transporter-expressing cell lines, we show that mIBG is an excellent substrate for human organic cation transporters 1-3 (hOCT1-3) and the multidrug and toxin extrusion proteins 1 and 2-K (hMATE1/2-K), but not for the renal organic anion transporter 1 and 3 (hOAT1/3). Kinetic analysis revealed that hOCT1, hOCT2, hOCT3, hMATE1, and hMATE2-K transport mIBG with similar apparent affinities (K _m of 19.5 ± 6.9, 17.2 ± 2.8, 14.5 ± 7.1, 17.7 ± 10.9, 12.6 ± 5.6 µM, respectively). Transwell studies in hOCT2/hMATE1 double-transfected Madin-Darby canine kidney cells showed that mIBG transport in the basal (B)-to-apical (A) direction is much greater than in the A-to-B direction. Compared with control cells, the B-to-A permeability of mIBG increased by 20-fold in hOCT2/hMATE1 double-transfected cells. Screening of 23 drugs used in the treatment of neuroblastoma identified several drugs with the potential to inhibit hOCT- or hMATE-mediated mIBG uptake. Interestingly, irinotecan selectively inhibited hOCT1, whereas crizotinib potently inhibited hOCT3-mediated mIBG uptake. Our results suggest that mIBG undergoes renal tubular secretion mediated by hOCT2 and hMATE1/2-K, and hOCT1 and hOCT3 may play important roles in mIBG uptake into normal tissues. SIGNIFICANCE STATEMENT: mIBG is eliminated by the kidney and extensively accumulates in several tissues known to express hOCT1 and hOCT3. Our results suggest that hOCT2 and human multidrug and toxin extrusion proteins 1 and 2-K are involved in mIBG renal elimination, whereas hOCT1 and hOCT3 may play important roles in mIBG uptake into normal tissues. These findings may help to predict and prevent adverse drug interaction with therapeutic [¹³¹I]mIBG and develop clinical strategies to reduce [¹³¹I]mIBG accumulation and toxicity in normal tissues and organs.

Targeting uptake transporters for cancer imaging and treatment

Cancer cells reprogram their gene expression to promote growth, survival, proliferation, and invasiveness. The unique expression of certain uptake transporters in cancers and their innate function to concentrate small molecular substrates in cells make them ideal targets for selective delivering imaging and therapeutic agents into cancer cells. In this review, we focus on several solute carrier (SLC) transporters known to be involved in transporting clinically used radiopharmaceutical agents into cancer cells, including the sodium/iodine symporter (NIS), norepinephrine transporter (NET), glucose transporter 1 (GLUT1), and monocarboxylate transporters (MCTs). The molecular and functional characteristics of these transporters are reviewed with special emphasis on their specific expressions in cancers and interaction with imaging or theranostic agents [e.g., I-123, I-131, ¹²³I-iobenguane (mIBG), ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) and ¹³C pyruvate]. Current clinical applications and research areas of these transporters in cancer diagnosis and treatment are discussed. Finally, we offer our views on emerging opportunities and challenges in targeting transporters for cancer imaging and treatment. By analyzing the few clinically successful examples, we hope much interest can be garnered in cancer research towards uptake transporters and their potential applications in cancer diagnosis and treatment.

Membrane Transporters in Human Parotid Gland-Targeted Proteomics Approach

Salivary glands provide secretory functions, including secretion of xenobiotics and among them drugs. However, there is no published information about protein abundance of drug transporters measured using reliable protein quantification methods. Therefore, mRNA expression and absolute protein content of clinically relevant ABC (n = 6) and SLC (n = 15) family member transporters in the human parotid gland, using the qRT-PCR and liquid chromatography‒tandem mass spectrometry (LC−MS/MS) method, were studied. The abundance of nearly all measured proteins ranged between 0.04 and 0.45 pmol/mg (OCT3 > MRP1 > PEPT2 > MRP4 > MATE1 > BCRP). mRNAs of ABCB1, ABCC2, ABCC3, SLC10A1, SLC10A2, SLC22A1, SLC22A5, SLC22A6, SLC22A7, SLC22A8, SLCO1A2, SLCO1B1, SLCO1B3 and SLCO2B1 were not detected. The present study provides, for the first time, information about the protein abundance of membrane transporters in the human parotid gland, which could further be used to define salivary bidirectional transport (absorption and secretion) mechanisms of endogenous compounds and xenobiotics.

Metformin: Mechanisms in Human Obesity and Weight Loss

PURPOSE OF REVIEW

Metformin has multiple benefits for health beyond its anti-hyperglycemic properties. The purpose of this manuscript is to review the mechanisms that underlie metformin's effects on obesity.

RECENT FINDINGS

Metformin is a first-line therapy for type 2 diabetes. Large cohort studies have shown weight loss benefits associated with metformin therapy. Metabolic consequences were traditionally thought to underlie this effect, including reduction in hepatic gluconeogenesis and reduction in insulin production. Emerging evidence suggests that metformin-associated weight loss is due to modulation of hypothalamic appetite regulatory centers, alteration in the gut microbiome, and reversal of consequences of aging. Metformin is also being explored in the management of obesity's sequelae such as hepatic steatosis, obstructive sleep apnea, and osteoarthritis. Multiple mechanisms underlie the weight loss-inducing and health-promoting effects of metformin. Further exploration of these pathways may be important in identifying new pharmacologic targets for obesity and other aging-associated metabolic diseases.

Reproductive evaluations in female rat offspring exposed to metformin during intrauterine and intrauterine/lactational periods

Metformin (MET) is a widely-used drug for the treatment of type 2 diabetes mellitus and gestational diabetes. It is known that metformin crosses the placenta and can to be transferred through milk. In vitro studies show that MET decreases gonadotropin-releasing hormone and gonadotropins release in rat neurons, and decreases progesterone and estradiol in rat granulosa cells and androstenedione synthesis in human theca cells. This study evaluated whether MET maternal exposure might interfere with reproductive parameters of female offspring. Wistar female rats were treated with MET 293 mg/kg/day, by gavage, from gestational day (GD) 0 to GD 21 (METG) or GD 0 until lactation day (LD) 21 (METGL). Controls groups received water. An increase in plasmatic estradiol levels was observed during the estrus stage in the METGL group. This result suggests that exposure to MET during gestational and lactational periods might be related to programming in theca and/or granulosa cells during development.

Repurposed Biguanide Drugs in Glioblastoma Exert Antiproliferative Effects via the Inhibition of Intracellular Chloride Channel 1 Activity

The lack of in-depth knowledge about the molecular determinants of glioblastoma (GBM) occurrence and progression, combined with few effective and BBB crossing-targeted compounds represents a major challenge for the discovery of novel and efficacious drugs for GBM. Among relevant molecular factors controlling the aggressive behavior of GBM, chloride intracellular channel 1 (CLIC1) represents an emerging prognostic and predictive biomarker, as well as a promising therapeutic target. CLIC1 is a metamorphic protein, co-existing as both soluble cytoplasmic and membrane-associated conformers, with the latter acting as chloride selective ion channel. CLIC1 is involved in several physiological cell functions and its abnormal expression triggers tumor development, favoring tumor cell proliferation, invasion, and metastasis. CLIC1 overexpression is associated with aggressive features of various human solid tumors, including GBM, in which its expression level is correlated with poor prognosis. Moreover, increasing evidence shows that modification of microglia ion channel activity, and CLIC1 in particular, contributes to the development of different neuropathological states and brain tumors. Intriguingly, CLIC1 is constitutively active within cancer stem cells (CSCs), while it seems less relevant for the survival of non-CSC GBM subpopulations and for normal cells. CSCs represent GBM development and progression driving force, being endowed with stem cell-like properties (self-renewal and differentiation), ability to survive therapies, to expand and differentiate, causing tumor recurrence. Downregulation of CLIC1 results in drastic inhibition of GBM CSC proliferation in vitro and in vivo, making the control of the activity this of channel a possible innovative pharmacological target. Recently, drugs belonging to the biguanide class (including metformin) were reported to selectively inhibit CLIC1 activity in CSCs, impairing their viability and invasiveness, but sparing normal stem cells, thus representing potential novel antitumor drugs with a safe toxicological profile. On these premises, we review the most recent insights into the biological role of CLIC1 as a potential selective pharmacological target in GBM. Moreover, we examine old and new drugs able to functionally target CLIC1 activity, discussing the challenges and potential development of CLIC1-targeted therapies.

OCT3 promoter haplotype is associated with metformin pharmacokinetics in Koreans

Organic cation transporter 3 (OCT3) is expressed in various organs in humans and plays an important role in the transport of organic cations and drugs including metformin. In this study, we identified genetic variations of the OCT3 promoter and functionally characterized each variant by in vitro assays. Next, the association between the functional haplotype of the OCT3 promoter and pharmacokinetics of metformin was evaluated. In our study population, 7 variations and 2 major haplotypes were identified, of which H2 haplotype yielded a significantly higher luciferase activity than did the wild type. Two variants of H2, c.-1603G > A and c.-1547T > G, yielded significantly lower luciferase activities, whereas the luciferase activity of another variant, c.-29G > A, was significantly higher. Two transcription factors, Sp1 and USF1, were involved in the regulation of OCT3 transcription. Analysis of clinical data revealed that 25 subjects, either homozygous or heterozygous for H2, showed increased AUC_inf and C_max by 17.2% and 15.9%, respectively [P = 0.016 and 0.031, GMR (90% CI) = 1.17 (1.06–1.29) and 1.17 (1.04–1.31), respectively], compared to the 20 subjects in the control group. Our study suggests that an OCT3 promoter haplotype affects the pharmacokinetics of metformin in Koreans as well as the OCT3 transcription rate.

Metformin transporter pharmacogenomics: insights into drug disposition-where are we now?

INTRODUCTION

Metformin is recommended as first-line treatment for type 2 diabetes (T2D) by all major diabetes guidelines. With appropriate usage it is safe and effective overall, but its efficacy and tolerability show considerable variation between individuals. It is a substrate for several drug transporters and polymorphisms in these transporter genes have shown effects on metformin pharmacokinetics and pharmacodynamics. Areas covered: This article provides a review of the current status of the influence of transporter pharmacogenomics on metformin efficacy and tolerability. The transporter variants identified to have an important influence on the absorption, distribution, and elimination of metformin, particularly those in organic cation transporter 1 (OCT1, gene SLC22A1), are reviewed. Expert opinion: Candidate gene studies have shown that genetic variations in SLC22A1 and other drug transporters influence the pharmacokinetics, glycemic responses, and gastrointestinal intolerance to metformin, although results are somewhat discordant. Conversely, genome-wide association studies of metformin response have identified signals in the pharmacodynamic pathways rather than the transporters involved in metformin disposition. Currently, pharmacogenomic testing to predict metformin response and tolerability may not have a clinical role, but with additional data from larger studies and availability of safe and effective alternative antidiabetic agents, this is likely to change.

Prenatal metformin exposure or organic cation transporter 3 knock-out curbs social interaction preference in male mice

Poorly managed gestational diabetes can lead to severe complications for mother and child including fetal overgrowth, neonatal hypoglycemia and increased autism risk. Use of metformin to control it is relatively new and promising. Yet safety concerns regarding gestational metformin use remain, as its long-term effects in offspring are unclear. In light of beneficial findings with metformin for adult mouse social behavior, we hypothesized gestational metformin treatment might also promote offspring sociability. To test this, metformin was administered to non-diabetic, lean C57BL/6 J female mice at mating, with treatment discontinued at birth or wean. Male offspring exposed to metformin through birth lost social interaction preference relative to controls by time in chambers, but not by sniffing measures. Further, prenatal metformin exposure appeared to enhance social novelty preference only in females. However due to unbalanced litters and lack of statistical power, firm establishment of any sex-dependency of metformin's effects on sociability was not possible. Since organic cation transporter 3 (OCT3) transports metformin and is dense in placenta, social preferences of OCT3 knock-out males were measured. Relative to wild-type, OCT3 knock-outs had reduced interaction preference. Our data indicate gestational metformin exposure under non-diabetic conditions, or lack of OCT3, can impair social behavior in male C57BL6/J mice. Since OCT3 transports serotonin and tryptophan, impaired placental OCT3 function is one common mechanism that could persistently impact central serotonin systems and social behavior. Yet no gross alterations in serotonergic function were evident by measure of serotonin transporter density in OCT3, or serotonin turnover in metformin-exposed offspring brains. Mechanisms underlying the behavioral outcomes, and if with gestational diabetes the same would occur, remain unclear. Metformin's impacts on placental transporters and serotonin metabolism or AMPK activity in fetal brain need further investigation to clarify benefits and risks to offspring sociability from use of metformin to treat gestational diabetes.

A cautionary response to SMFM statement: pharmacological treatment of gestational diabetes

Use of oral agents to treat gestational diabetes mellitus remains controversial. Recent recommendations from the Society for Maternal-Fetal Medicine assert that metformin may be a safe first-line alternative to insulin for gestational diabetes mellitus treatment and preferable to glyburide. However, several issues should give pause to the widespread adoption of metformin use during pregnancy. Fetal concentrations of metformin are equal to maternal, and metformin can inhibit growth, suppress mitochondrial respiration, have epigenetic modifications on gene expression, mimic fetal nutrient restriction, and alter postnatal gluconeogenic responses. Because both the placenta and fetus express metformin transporters and exhibit high mitochondrial activity, these properties raise important questions about developmental programming of metabolic disease in offspring. Animal studies have demonstrated that prenatal metformin exposure results in adverse long-term outcomes on body weight and metabolism. Two recent clinical randomized controlled trials in women with gestational diabetes mellitus or polycystic ovary syndrome provide evidence that metformin exposure in utero may produce a metabolic phenotype that increases childhood weight or obesity. These developmental programming effects challenge the conclusion that metformin is equivalent to insulin. Although the Society for Maternal-Fetal Medicine statement endorsed metformin over glyburide if oral agents are used, there are few studies directly comparing the 2 agents and it is not clear that metformin alone is superior to glyburide. Moreover, it should be noted that prior clinical studies have dosed glyburide in a manner inconsistent with its pharmacokinetic properties, resulting in poor glycemic control and high rates of maternal hypoglycemia. We concur with the American Diabetes Association and American Congress of Obstetricians and Gynecologists, which recommend insulin as the preferred agent, but we believe that it is premature to embrace metformin as equivalent to insulin or superior to glyburide. Due to the uncertainty of the long-term metabolic risks of either metformin or glyburide, we call for carefully controlled studies that optimize oral medication dosing according to their pharmacodynamic and pharmacokinetic properties in pregnancy, appropriately target medications based on individual patterns of hyperglycemia, and follow the offspring long-term for metabolic risk.

Improved glycemic control with minimal systemic metformin exposure: Effects of Metformin Delayed-Release (Metformin DR) targeting the lower bowel over 16 weeks in a randomized trial in subjects with type 2 diabetes

Objective

Metformin use is restricted in patients with renal impairment due to potential excess systemic accumulation. This study evaluated the glycemic effects and safety of metformin delayed-release (Metformin DR), which targets metformin delivery to the ileum to leverage its gut-based mechanisms of action while minimizing systemic exposure.

Research designs and methods

Participants (T2DM [HbA1c 7–10.5%], eGFR ≥60 mL/min/1.73m², not taking metformin for ≥2 months) were randomized to QD placebo (PBO); QD Metformin DR 600, 900, 1200, or 1500 mg; or to single-blind BID Metformin immediate-release (IR) 1000 mg. The primary endpoint was change in HbA1c for Metformin DR vs. PBO at 16 weeks in the modified intent-to-treat (mITT) population (≥ 1 post-baseline HbA1c while on study drug), using a mixed-effects repeated measures model.

Results

571 subjects were randomized (56 years, 53% male, 80% white; BMI 32.2±5.5 kg/m²; HbA1c 8.6±0.9%; 51% metformin naive); 542 were in the mITT population. Metformin DR 1200 and 1500 mg significantly reduced HbA1c (-0.49±0.13% and -0.62±0.12%, respectively, vs. PBO -0.06±0.13%; p<0.05) and FPG (C_{average Weeks 4–16}: -22.3±4.2 mg/dL and -25.1±4.1 mg/dL, respectively vs. -2.5±4.2 mg/dL p<0.05). Metformin IR elicited greater HbA1c improvement (-1.10±0.13%; p<0.01 vs. Placebo and all doses of Metformin DR) but with ~3-fold greater plasma metformin exposure. Normalizing efficacy to systemic exposure, glycemic improvements with Metformin DR were 1.5-fold (HbA1c) and 2.1-fold (FPG) greater than Metformin IR. Adverse events were primarily gastrointestinal but these were less frequent with Metformin DR (<16% incidence) vs. Metformin IR (28%), particularly nausea (1–3% vs 10%).

Conclusion

Metformin DR exhibited greater efficacy per unit plasma exposure than Metformin IR. Future studies will evaluate the effects of Metformin DR in patients with type 2 diabetes and advanced renal disease.

Trial registration

Clinicaltrials.gov NCT02526524.

Metformin targets brown adipose tissue in vivo and reduces oxygen consumption in vitro

AIMS

To test the hypothesis that brown adipose tissue (BAT) is a metformin target tissue by investigating in vivo uptake of [¹¹ C]-metformin tracer in mice and studying in vitro effects of metformin on cultured human brown adipocytes.

MATERIALS AND METHODS

Tissue-specific uptake of metformin was assessed in mice by PET/CT imaging after injection of [¹¹ C]-metformin. Human brown adipose tissue was obtained from elective neck surgery and metformin transporter expression levels in human and murine BAT were determined by qPCR. Oxygen consumption in metformin-treated human brown adipocyte cell models was assessed by Seahorse XF technology.

RESULTS

Injected [¹¹ C]-metformin showed avid uptake in the murine interscapular BAT depot. Metformin exposure in BAT was similar to hepatic exposure. Non-specific inhibition of the organic cation transporter (OCT) protein by cimetidine administration eliminated BAT exposure to metformin, demonstrating OCT-mediated uptake. Gene expression profiles of OCTs in BAT revealed ample OCT3 expression in both human and mouse BAT. Incubation of a human brown adipocyte cell models with metformin reduced cellular oxygen consumption in a dose-dependent manner.

CONCLUSION

These results support BAT as a putative metformin target.

Organic Cation Transporter 3 Facilitates Fetal Exposure to Metformin during Pregnancy

Metformin, an oral antihyperglycemic, is increasingly being prescribed to pregnant women with gestational diabetes. Metformin is a hydrophilic cation and relies on organic cation transporters to move across cell membranes. We previously demonstrated that human and mouse placentas predominantly express organic cation transporter 3 (OCT3), but the impact of this transporter on maternal and fetal disposition of metformin is unknown. Using immunofluorescence colocalization studies in term human placenta, we showed that OCT3 is localized to the basal (fetal-facing) membrane of syncytiotrophoblast cells with no expression on the apical (maternal-facing) membrane. OCT3 positive staining was also observed in fetal capillaries. To determine the in vivo role of OCT3 in maternal and fetal disposition of metformin, we determined metformin maternal pharmacokinetics and overall fetal exposure in wild-type and Oct3-null pregnant mice. After oral dosing of [¹⁴C]metformin at gestational day 19, the systemic drug exposure (AUC_0-∞) in maternal plasma was slightly reduced by ∼16% in the Oct3^-/- pregnant mice. In contrast, overall fetal AUC_0-∞ was reduced by 47% in the Oct3^-/- pregnant mice. Consistent with our previous findings in nonpregnant mice, metformin tissue distribution was respectively reduced by 70% and 52% in the salivary glands and heart in Oct3^-/- pregnant mice. Our in vivo data in mice clearly demonstrated a significant role of Oct3 in facilitating metformin fetal distribution and exposure during pregnancy. Modulation of placental OCT3 expression or activity by gestational age, genetic polymorphism, or pharmacological inhibitors may alter fetal exposure to metformin or other drugs transported by OCT3.

Disposition of Methamphetamine and Major Metabolites in Mice: Role of Organic Cation Transporter 3 in Tissue-Selective Accumulation of Para-Hydroxymethamphetamine

Methamphetamine is one of the most widely abused illicit drugs. Although human intoxication and multiple tissue toxicities frequently occur in abusers, little is known about the distribution of methamphetamine or its primary metabolites, amphetamine and para-hydroxymethamphetamine (p-OHMA), to their sites of toxicity. This study determined the pharmacokinetics, tissue exposure, and partition ratios of methamphetamine and major metabolites in various mouse tissues and investigated the impact of organic cation transporter 3 (Oct3) following i.v. injection of methamphetamine to male Oct3^+/+ and Oct3^-/- mice. Methamphetamine, amphetamine, and p-OHMA were readily detectable in plasma with Oct3^+/+ and Oct3^-/- mice displaying similar plasma pharmacokinetic profiles for all three analytes. In addition to kidney and liver, salivary glands highly accumulated methamphetamine, amphetamine, and p-OHMA with total exposure 3.3- to 9.4-fold higher than plasma area under the concentration-time curve (AUC). Consistent with being an Oct3 substrate, p-OHMA AUC in salivary glands is reduced by 50% in Oct3^-/- mice. p-OHMA AUC in skeletal muscle is also significantly reduced in Oct3^-/- mice. Our data identified salivary glands as a novel site of high accumulation of methamphetamine and metabolites, which may underlie methamphetamine toxicity in this tissue. Furthermore, our study identified Oct3 as an important determinant of tissue uptake and exposure to p-OHMA in salivary glands and skeletal muscle. Our findings suggest that local tissue accumulation of methamphetamine and/or its metabolites may play a role in several of the reported peripheral toxicities of methamphetamine, and Oct3 can significantly impact tissue exposure to its substrates without affecting systemic elimination.

Genetic Heterogeneity of SLC22 Family of Transporters in Drug Disposition

An important aspect of modern medicine is its orientation to achieve more personalized pharmacological treatments. In this context, transporters involved in drug disposition have gained well-justified attention. Owing to its broad spectrum of substrate specificity, including endogenous compounds and xenobiotics, and its strategical expression in organs accounting for drug disposition, such as intestine, liver and kidney, the SLC22 family of transporters plays an important role in physiology, pharmacology and toxicology. Among these carriers are plasma membrane transporters for organic cations (OCTs) and anions (OATs) with a marked overlap in substrate specificity. These two major clades of SLC22 proteins share a similar membrane topology but differ in their degree of genetic variability. Members of the OCT subfamily are highly polymorphic, whereas OATs have a lower number of genetic variants. Regarding drug disposition, changes in the activity of these variants affect intestinal absorption and target tissue uptake, but more frequently they modify plasma levels due to enhanced or reduced clearance by the liver and secretion by the kidney. The consequences of these changes in transport-associated function markedly affect the effectiveness and toxicity of the treatment in patients carrying the mutation. In solid tumors, changes in the expression of these transporters and the existence of genetic variants substantially determine the response to anticancer drugs. Moreover, chemoresistance usually evolves in response to pharmacological and radiological treatment. Future personalized medicine will require monitoring these changes in a dynamic way to adapt the treatment to the weaknesses shown by each tumor at each stage in each patient.

Nanoparticle-releasing nanofiber composites for enhanced in vivo vaginal retention

Current approaches for topical vaginal administration of nanoparticles result in poor retention and extensive leakage. To overcome these challenges, we developed a nanoparticle-releasing nanofiber delivery platform and evaluated its ability to improve nanoparticle retention in a murine model. We individually tailored two components of this drug delivery system for optimal interaction with mucus, designing (1) mucoadhesive fibers for better retention in the vaginal tract, and (2) PEGylated nanoparticles that diffuse quickly through mucus. We hypothesized that this novel dual-functioning (mucoadhesive/mucus-penetrating) composite material would provide enhanced retention of nanoparticles in the vaginal mucosa. Equivalent doses of fluorescent nanoparticles were vaginally administered to mice in either water (aqueous suspension) or fiber composites, and fluorescent content was quantified in cervicovaginal mucus and vaginal tissue at time points from 24 h to 7d. We also fabricated composite fibers containing etravirine-loaded nanoparticles and evaluated the pharmacokinetics over 7d. We found that our composite materials provided approximately 30-fold greater retention of nanoparticles in the reproductive tract at 24 h compared to aqueous suspensions. Compared to nanoparticles in aqueous suspension, the nanoparticles in fiber composites exhibited sustained and higher etravirine concentrations after 24 h and up to 7d, demonstrating the capabilities of this new delivery platform to sustain nanoparticle release out to 3d and drug retention out to one week after a single administration. This is the first report of nanoparticle-releasing fibers for vaginal drug delivery, as well as the first study of a single delivery system that combines two components uniquely engineered for complementary interactions with mucus.

Metformin Accelerates Glycolytic Lactate Production in Cultured Primary Cerebellar Granule Neurons

Metformin is the most frequently used drug for the treatment of type-II diabetes. As metformin has been reported to cross the blood-brain barrier, brain cells will encounter this drug. To test whether metformin may affect the metabolism of neurons, we exposed cultured rat cerebellar granule neurons to metformin. Treatment with metformin caused a time- and concentration-dependent increase in glycolytic lactate release from viable neurons as demonstrated by the three-to fivefold increase in extracellular lactate concentration determined after exposure to metformin. Half-maximal stimulation of lactate production was found after incubation of neurons for 4 h with around 2 mM or for 24 h with around 0.5 mM metformin. Neuronal cell viability was not affected by millimolar concentrations of metformin during acute incubations in the hour range nor during prolonged incubations, although alterations in cell morphology were observed during treatment with 10 mM metformin for days. The acute stimulation of neuronal lactate release by metformin was persistent upon removal of metformin from the medium and was not affected by the presence of modulators of adenosine monophosphate activated kinase activity. In contrast, rabeprazole, an inhibitor of the organic cation transporter 3, completely prevented metformin-mediated stimulation of neuronal lactate production. In summary, the data presented identify metformin as a potent stimulator of glycolytic lactate production in viable cultured neurons and suggest that organic cation transporter 3 mediates the uptake of metformin into neurons.