Reduced antidiabetic effect of metformin and down-regulation of hepatic Oct1 in rats with ethynylestradiol-induced cholestasis

Drug disposition in cholestasis: An important concern

Cholestasis, a chronic liver condition, disrupts bile acid homeostasis and complicates drug disposition, posing significant challenges in medicating cholestatic patients. Drug metabolism enzymes and transporters (DMETs) are pivotal in drug clearance. Research indicates that cholestasis leads to alterations in both hepatic and extrahepatic DMETs, with changes in expression and function documented in rodents and humans. This review synthesizes the modifications in key drug disposition components within cholestasis, focusing on cytochrome P450 (CYP450), drug transporters, and their substrates. Additionally, we briefly discuss certain drugs that have demonstrated efficacy in restoring DMET expression in cholestatic conditions. Ultimately, these insights necessitate a reevaluation of drug selection and dosing guidelines for patients with cholestasis.

Renal Pharmacokinetic Adaptation to Cholestasis Causes Increased Nephrotoxic Drug Accumulation by Mrp6 Downregulation in Mice

In hepatic dysfunction, renal pharmacokinetic adaptation can be observed, although information on the changes in drug exposure and the interorgan regulation of membrane transporters in kidney in liver diseases is limited. This study aimed to clarify the effects of renal exposure to nephrotoxic drugs during cholestasis induced by bile duct ligation (BDL). Among the 11 nephrotoxic drugs examined, the tissue accumulation of imatinib and cisplatin in kidney slices obtained from mice 2 weeks after BDL operation was higher than that in sham-operated mice. The uptake of imatinib in the kidney slices of BDL mice was slightly higher, whereas its efflux from the slices was largely decreased compared to that in sham-operated mice. Proteomic analysis revealed a reduction in renal expression of the efflux transporter multidrug resistance-associated protein 6 (Mrp6/Abcc6) in BDL mice, and both imatinib and cisplatin were identified as Mrp6 substrates. Survival probability after cisplatin administration was reduced in BDL mice. In conclusion, the present study demonstrated that BDL-induced cholestasis leads to the downregulation of the renal basolateral efflux transporter Mrp6, resulting in drug accumulation in renal cells and promoting drug-induced renal injury.

Renal tubular transporter-mediated interactions between mirogabalin and cimetidine in rats

Cimetidine at a clinical dosage decreased the renal clearance (CLr) of mirogabalin in humans by inhibition of renal secretion. Mirogabalin is a substrate of human OAT1/3, OCT2, MATE1 and/or MATE2-K. To clarify the mechanism behind the above interaction, it was investigated whether cimetidine inhibits the process of mirogabalin uptake at the basolateral side or the process of its efflux at the apical side in rat kidney in vivo.Cimetidine was administered to rats by a constant infusion to achieve an unbound plasma concentration of 7.0 μM and examine its effect on the renal disposition of [¹⁴C]metformin, [³H]p-aminohippuric acid (PAH), and [¹⁴C]mirogabalin.Cimetidine significantly induced the intrarenal accumulation of radioactivity (Kp, kidney) and decreased the renal clearance (CLr) of [¹⁴C]mirogabalin. These effects resulted in significantly decreased total clearance (CLt). Kp, kidney, and CLr of [¹⁴C]metformin, except CLt, were also affected, but no parameters of [³H]PAH were affected by cimetidine.These findings clarified that an unbound plasma concentration of cimetidine of 7.0 μM inhibited the apical efflux not the basolateral uptake of [¹⁴C]mirogabalin in rat kidney, suggesting that mirogabalin/cimetidine interaction was caused by inhibiting the apical efflux transporter, human MATE1 and/or MATE2-K, not the basolateral uptake transporter, human OCT2, in the kidney.

Bile duct ligation differently regulates protein expressions of organic cation transporters in intestine, liver and kidney of rats through activation of farnesoid X receptor by cholate and bilirubin

Body is equipped with organic cation transporters (OCTs). These OCTs mediate drug transport and are also involved in some disease process. We aimed to investigate whether liver failure alters intestinal, hepatic and renal Oct expressions using bile duct ligation (BDL) rats. Pharmacokinetic analysis demonstrates that BDL decreases plasma metformin exposure, associated with decreased intestinal absorption and increased urinary excretion. Western blot shows that BDL significantly downregulates intestinal Oct2 and hepatic Oct1 but upregulates renal and hepatic Oct2. In vitro cell experiments show that chenodeoxycholic acid (CDCA), bilirubin and farnesoid X receptor (FXR) agonist GW4064 increase OCT2/Oct2 but decrease OCT1/Oct1, which are remarkably attenuated by glycine-β-muricholic acid and silencing FXR. Significantly lowered intestinal CDCA and increased plasma bilirubin levels contribute to different Octs regulation by BDL, which are confirmed using CDCA-treated and bilirubin-treated rats. A disease-based physiologically based pharmacokinetic model characterizing intestinal, hepatic and renal Octs was successfully developed to predict metformin pharmacokinetics in rats. In conclusion, BDL remarkably downregulates expressions of intestinal Oct2 and hepatic Oct1 protein while upregulates expressions of renal and hepatic Oct2 protein in rats, finally, decreasing plasma exposure and impairing hypoglycemic effects of metformin. BDL differently regulates Oct expressions via Fxr activation by CDCA and bilirubin.

Metabolic Action of Metformin

Metformin, a cheap and safe biguanide derivative, due to its ability to influence metabolism, is widely used as a first-line drug for type 2 diabetes (T2DM) treatment. Therefore, the aim of this review was to present the updated biochemical and molecular effects exerted by the drug. It has been well explored that metformin suppresses hepatic glucose production in both AMPK-independent and AMPK-dependent manners. Substantial scientific evidence also revealed that its action is related to decreased secretion of lipids from intestinal epithelial cells, as well as strengthened oxidation of fatty acids in adipose tissue and muscles. It was recognized that metformin’s supra-therapeutic doses suppress mitochondrial respiration in intestinal epithelial cells, whereas its therapeutic doses elevate cellular respiration in the liver. The drug is also suggested to improve systemic insulin sensitivity as a result of alteration in gut microbiota composition, maintenance of intestinal barrier integrity, and alleviation of low-grade inflammation.

Drugs repurposed: An advanced step towards the treatment of breast cancer and associated challenges

Breast cancer (BC) is mostly observed in women and is responsible for huge mortality in women subjects globally. Due to the continued development of drug resistance and other contributing factors, the scientific community needs to look for new alternatives, and drug repurposing is one of the best opportunities. Here we light upon the drug repurposing with a major focus on breast cancer. BC is a division of cancer known as the leading cause of death of 2.3 million women globally, with 685,000 fatalities. This number is steadily rising, necessitating the development of a treatment that can extend survival time. All available treatments for BC are very costly as well as show side effects. This unfulfilled requirement of the anti-cancer drugs ignited an enthusiasm for drug repositioning, which means finding out the anti-cancer use of already marketed drugs for other complications. With the advancement in proteomics, genomics, and computational approaches, the drug repurposing process hastens. So many drugs are repurposed for the BC, including alkylating agents, antimetabolite, anthracyclines, an aromatase inhibitor, mTOR, and many more. The drug resistance in breast cancer is rising, so reviewing how the challenges in breast cancer can be combated with drug repurposing. This paper provides the updated information on all the repurposed drugs candidates for breast cancer with the molecular mechanism responsible for their anti-tumor activity. Additionally, all the challenges that occur during the repurposing of the drugs are discussed.

Changes of Transporters and Drug-metabolizing Enzymes in Nephrotic Syndrome

BACKGROUND

Drug-metabolizing enzymes and transporters play key roles in drug disposition and drug interactions. The alterations of their expression will influence drug pharmacokinetics and pharmacodynamics. However, the changes in the expression of enzymes and transporters in the disease state are still unclear.

OBJECTIVE

Our study was to investigate the changes in the expression of main enzymes and drug transporters distributed in Adriamycin nephropathy rat liver, kidney, and intestine.

METHODS

An intravenous injection with a single dose of Adriamycin (6mg/kg) was made to establish Adriamycin nephropathy (AN) model and normal groups were injected with normal saline. Serum was collected for lipid metabolism, renal, and hepatic function measurement. The real-time PCR and western blot were applied to determine the mRNA and protein expression of drug enzymes and transporters.

RESULTS

In the kidney, a greater expression of Mdr1, Mrp2, Mrp4 Oat2 and Oct2 mRNA was found in AN rats as compared with control rats. In the liver, the expression of Bcrp mRNA was more doubled or tripled than control groups and downregulation of Mdr1, Mrp2, Mrp4 and Bsep gene expression was found in AN rats. Besides, we observed a downward trend of Cyp1a2, Cyp3a4 and Cyp2c9 mRNA levels in AN groups. In the duodenum, the expression of Mdr1 and Mrp3 mRNA level was decreased, while Bcrp and Mrp2 mRNA were increased.

CONCLUSION

The changes in drug-metabolizing enzymes and transporters expression in AN rats were clarified, which may be beneficial for understanding the altered pharmacokinetics and pharmacodynamics of clinical drugs and reduce unexpected clinical findings for nephropathy patients.

Organic Cation Transporters in Human Physiology, Pharmacology, and Toxicology

Individual cells and epithelia control the chemical exchange with the surrounding environment by the fine-tuned expression, localization, and function of an array of transmembrane proteins that dictate the selective permeability of the lipid bilayer to small molecules, as actual gatekeepers to the interface with the extracellular space. Among the variety of channels, transporters, and pumps that localize to cell membrane, organic cation transporters (OCTs) are considered to be extremely relevant in the transport across the plasma membrane of the majority of the endogenous substances and drugs that are positively charged near or at physiological pH. In humans, the following six organic cation transporters have been characterized in regards to their respective substrates, all belonging to the solute carrier 22 (SLC22) family: the organic cation transporters 1, 2, and 3 (OCT1–3); the organic cation/carnitine transporter novel 1 and 2 (OCTN1 and N2); and the organic cation transporter 6 (OCT6). OCTs are highly expressed on the plasma membrane of polarized epithelia, thus, playing a key role in intestinal absorption and renal reabsorption of nutrients (e.g., choline and carnitine), in the elimination of waste products (e.g., trimethylamine and trimethylamine N-oxide), and in the kinetic profile and therapeutic index of several drugs (e.g., metformin and platinum derivatives). As part of the Special Issue Physiology, Biochemistry, and Pharmacology of Transporters for Organic Cations, this article critically presents the physio-pathological, pharmacological, and toxicological roles of OCTs in the tissues in which they are primarily expressed.

Anti-inflammatory Property of AMP-activated Protein Kinase

BACKGROUND

One of the many debated topics in inflammation research is whether this scenario is really an accelerated form of human wound healing and immunityboosting or a push towards autoimmune diseases. The answer requires a better understanding of the normal inflammatory process, including the molecular pathology underlying the possible outcomes. Exciting recent investigations regarding severe human inflammatory disorders and autoimmune conditions have implicated molecular changes that are also linked to normal immunity, such as triggering factors, switching on and off, the influence of other diseases and faulty stem cell homeostasis, in disease progression and development.

METHODS

We gathered around and collected recent online researches on immunity, inflammation, inflammatory disorders and AMPK. We basically searched PubMed, Scopus and Google Scholar to assemble the studies which were published since 2010.

RESULTS

Our findings suggested that inflammation and related disorders are on the verge and interfere in the treatment of other diseases. AMPK serves as a key component that prevents various kinds of inflammatory signaling. In addition, our table and hypothetical figures may open a new door in inflammation research, which could be a greater therapeutic target for controlling diabetes, obesity, insulin resistance and preventing autoimmune diseases.

CONCLUSION

The relationship between immunity and inflammation becomes easily apparent. Yet, the essence of inflammation turns out to be so startling that the theory may not be instantly established and many possible arguments are raised for its clearance. However, this study might be able to reveal some possible approaches where AMPK can reduce or prevent inflammatory disorders.

Enhanced Intestinal Permeability and Plasma Concentration of Metformin in Rats by the Repeated Administration of Red Ginseng Extract

We aimed to assess the potential herb-drug interactions between Korean red ginseng extract (RGE) and metformin in rats in terms of the modulation of metformin transporters, such as organic cation transporter (Oct), multiple toxin and extrusion protein (Mate), and plasma membrane monoamine transporter (Pmat). Single treatment of RGE did not inhibit the in vitro transport activity of OCT1/2 up to 500 µg/mL and inhibited MATE1/2-K with high IC₅₀ value (more than 147.8 µg/mL), suggesting that concomitant used of RGE did not directly inhibit OCT- and MATE-mediated metformin uptake. However, 1-week repeated administration of RGE (1.5 g/kg/day) (1WRA) to rats showed different alterations in mRNA levels of Oct1 depending on the tissue type. RGE increased intestinal Oct1 but decreased hepatic Oct1. However, neither renal Oct1/Oct2 nor Mate1/Pmat expression in duodenum, jejunum, ileum, liver, and kidney were changed in 1WRA rats. RGE repeated dose also increased the intestinal permeability of metformin; however, the permeability of 3-O-methyl-d-glucose and Lucifer yellow was not changed in 1WRA rats, suggesting that the increased permeability of metformin by multiple doses of RGE is substrate-specific. On pharmacokinetic analysis, plasma metformin concentrations following intravenous injection were not changed in 1WRA, consistent with no significant change in renal Oct1, Oct2, and mate1. Repeated doses of RGE for 1 week significantly increased the plasma concentration of metformin, with increased half-life and urinary excretion of metformin following oral administration of metformin (50 mg/kg), which could be attributed to the increased absorption of metformin. In conclusion, repeated administration of RGE showed in vivo pharmacokinetic herb-drug interaction with metformin, with regard to its plasma exposure and increased absorption in rats. These results were consistent with increased intestinal Oct1 and its functional consequence, therefore, the combined therapeutic efficacy needs further evaluation before the combination and repeated administration of RGE and metformin, an Oct1 substrate drug.

Ursodeoxycholate Restores Biliary Excretion of Methotrexate in Rats with Ethinyl Estradiol Induced-Cholestasis by Restoring Canalicular Mrp2 Expression

The in vivo relevance of ursodeoxycholate (UDCA) treatment (100 mg/kg/day, per oral tid for 5 days before cholestasis induction followed by the same dosing for 5 days) on hepatic function was investigated in rats with 17α-ethinylestradiol (EE, 10 mg/kg, subcutaneous for 5 days)-induced experimental cholestasis. The bile flow rate and the expression level of hepatic multidrug resistance-associated protein 2 (Mrp 2) that were decreased in cholestasis were restored after UDCA treatment. Consistent with this, the biliary excretion clearance (CL_exc,bile) of a representative Mrp2 substrate—methotrexate (MTX)—was decreased in cholestatic rats but was restored after UDCA treatment. Consequently, the plasma concentrations of MTX, which were increased by cholestasis, were decreased to control levels by UDCA treatment. Thus, the restoration of CL_exc,bile appears to be associated with the increase in Mrp2 expression on the canalicular membrane by UDCA treatment followed by Mrp2-mediated biliary excretion of MTX. On the other hand, the hepatic uptake clearance (CL_up,liver) of MTX was unchanged by cholestasis or UDCA treatment, suggestive of the absence of any association between the uptake process and the overall biliary excretion of MTX. Since UDCA has been known to induce the expression of canalicular MRP2 in humans, UDCA treatment might be effective in humans to maintain or accelerate the hepatobiliary elimination of xenobiotics or metabolic conjugates that are MRP2 substrates.

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.

肝脏转运体表达和功能的变化对肝疾病的影响

转运体是药物吸收、分布、代谢和排泄的重要决定因素, 在肝脏表达尤为广泛. 肝脏转运体可以摄取大多数内源性物质、营养物质和外源性物质进入肝脏, 在肝脏内经过一系列的代谢转化, 最终将其外排入胆汁, 并由胆汁排到肝外. 越来越多的证据表明, 肝脏疾病状态下转运体的表达和功能会发生改变, 影响药物在体内的处置过程, 进而增加药物相互作用的可能性, 同时加大了疾病药物治疗的难度. 本文从肝脏摄取型和外排型转运体两方面出发, 针对肝脏转运体表达和功能的变化对肝疾病的影响作一综述.

Effect of Liver Disease on Hepatic Transporter Expression and Function

Liver disease can alter the disposition of xenobiotics and endogenous substances. Regulatory agencies such as the Food and Drug Administration and the European Medicines Evaluation Agency recommend, if possible, studying the effect of liver disease on drugs under development to guide specific dose recommendations in these patients. Although extensive research has been conducted to characterize the effect of liver disease on drug-metabolizing enzymes, emerging data have implicated that the expression and function of hepatobiliary transport proteins also are altered in liver disease. This review summarizes recent developments in the field, which may have implications for understanding altered disposition, safety, and efficacy of new and existing drugs. A brief review of liver physiology and hepatic transporter localization/function is provided. Then, the expression and function of hepatic transporters in cholestasis, hepatitis C infection, hepatocellular carcinoma, human immunodeficiency virus infection, nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, and primary biliary cirrhosis are reviewed. In the absence of clinical data, nonclinical information in animal models is presented. This review aims to advance the understanding of altered expression and function of hepatic transporters in liver disease and the implications of such changes on drug disposition.

Altered Expression of Transporters, its Potential Mechanisms and Influences in the Liver of Rodent Models Associated with Diabetes Mellitus and Obesity

Diabetes mellitus is becoming an increasingly prevalent disease that concerns patients and healthcare professionals worldwide. Among many anti-diabetic agents in clinical uses, numerous reports are available on their altered pharmacokinetics because of changes in the expression of drug transporters and metabolic enzymes under diabetic states. These changes may affect the safety and efficacy of therapeutic agents and/or drug-drug interaction with co-administered agents. Therefore, the changes in transporter expression should be identified, and the underlying mechanisms should be clarified. This review summarizes the progress of recent studies on the alterations in important uptake and efflux transporters in liver of diabetic animals and their regulatory pathways.

Metformin action: concentrations matter

Metformin has been used for nearly a century and is now the most widely prescribed oral anti-diabetic agent worldwide. Yet how metformin acts remains only partially understood and controversial. One key reason may be that almost all previous studies were conducted with supra-pharmacological concentrations (doses) of metformin, 10-100 times higher than maximally achievable therapeutic concentrations found in patients with type 2 diabetes mellitus.

Hepatic expression of detoxification enzymes is decreased in human obstructive cholestasis due to gallstone biliary obstruction

BACKGROUND & AIMS

Levels of bile acid metabolic enzymes and membrane transporters have been reported to change in cholestasis. These alterations (e.g. CYP7A1 repression and MRP4 induction) are thought to be adaptive responses that attenuate cholestatic liver injury. However, the molecular mechanisms of these adaptive responses in human obstructive cholestasis due to gallstone biliary obstruction remain unclear.

METHODS

We collected liver samples from cholestatic patients with biliary obstruction due to gallstones and from control patients without liver disease (n = 22 per group). The expression levels of bile acid synthetic and detoxification enzymes, membrane transporters, and the related nuclear receptors and transcriptional factors were measured.

RESULTS

The levels of bile acid synthetic enzymes, CYP7B1 and CYP8B1, and the detoxification enzyme CYP2B6 were increased in cholestatic livers by 2.4-fold, 2.8-fold, and 1.9-fold, respectively (p<0.05). Conversely, the expression levels of liver detoxification enzymes, UGT2B4/7, SULT2A1, GSTA1-4, and GSTM1-4, were reduced by approximately 50% (p<0.05) in human obstructive cholestasis. The levels of membrane transporters, OSTβ and OCT1, were increased 10.4-fold and 1.8-fold, respectively, (p<0.05), whereas those of OSTα, ABCG2 and ABCG8 were all decreased by approximately 40%, (p<0.05) in human cholestatic livers. Hepatic nuclear receptors, VDR, HNF4α, RXRα and RARα, were induced (approximately 2.0-fold, (p<0.05) whereas FXR levels were markedly reduced to 44% of control, (p<0.05) in human obstructive cholestasis. There was a significantly positive correlation between the reduction in FXR mRNA and UGT2B4/7, SULT2A1, GSTA1, ABCG2/8 mRNA levels in livers of obstructive cholestatic patients (p<0.05).

CONCLUSIONS

The levels of hepatic detoxification enzymes were significantly decreased in human obstructive cholestasis, and these decreases were positively associated with a marked reduction of FXR levels. These findings are consistent with impaired detoxification ability in human obstructive cholestasis.

Effects of 1α,25-dihydroxyvitamin D3 , the natural vitamin D receptor ligand, on the pharmacokinetics of cefdinir and cefadroxil, organic anion transporter substrates, in rat

Evidence in the literature suggests that 1α,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ], the vitamin D receptor ligand, down-regulated the expression of the rat renal organic anion (renal organic anion transporter, rOAT) and oligopeptide (rPEPT) transporters, but increased intestinal rPEPT1 expression. We investigated, in rats, the intravenous and oral pharmacokinetics of 2 mg/kg cefdinir and cefadroxil, two cephalosporins that are eliminated via renal OAT1/OAT3 and are substrates of PEPT1/PEPT2, with and without 1,25(OH)2 D3 treatment. The area under the plasma concentration-time curve (AUC) of cefdinir or cefadroxil after 1,25(OH)2 D3 treatment was increased significantly because of decreased clearance (CL). Both kidney uptake and cumulative urinary recovery were significantly decreased, whereas liver uptake and fecal recovery remained unchanged in 1,25(OH)2 D3 -treated rats. Similar changes in AUC and CL were observed for both drugs upon coadministration of probenecid, the OAT inhibitor. Oral availability of cefdinir and cefadroxil remained unchanged with 1,25(OH)2 D3 treatment, suggesting lack of a role for intestinal rPEPT1. Rather, reduction of rOAT1/rOAT3 mRNA expression in kidney with 1,25(OH)2 D3 -treatment was observed, confirmed by decreased function in MDCKII cells overexpressing human OAT1 and OAT3. These composite results suggest that 1,25(OH)2 D3 treatment reduces cefdinir and cefadroxil clearances by diminution of renal OAT1/OAT3 expression, implicating a role for 1,25(OH)2 D3 in eliciting transporter-based drug interactions.

Small molecule adenosine 5'-monophosphate activated protein kinase (AMPK) modulators and human diseases

Adenosine 5'-monophosphate activated protein kinase (AMPK) is a master sensor of cellular energy status that plays a key role in the regulation of whole-body energy homeostasis. AMPK is a serine/threonine kinase that is activated by upstream kinases LKB1, CaMKKβ, and Tak1, among others. AMPK exists as αβγ trimeric complexes that are allosterically regulated by AMP, ADP, and ATP. Dysregulation of AMPK has been implicated in a number of metabolic diseases including type 2 diabetes mellitus and obesity. Recent studies have associated roles of AMPK with the development of cancer and neurological disorders, making it a potential therapeutic target to treat human diseases. This review focuses on the structure and function of AMPK, its role in human diseases, and its direct substrates and provides a brief synopsis of key AMPK modulators and their relevance in human diseases.

Drug disposition alterations in liver disease: extrahepatic effects in cholestasis and nonalcoholic steatohepatitis

INTRODUCTION

The pharmacokinetics (PK) of drugs and xenobiotics, namely pharmaceuticals, is influenced by a host of factors that include genetics, physiological factors and environmental stressors. The importance of disease on the disposition of xenobiotics has been increasingly recognized among medical professionals for alterations in key enzymes and membrane transporters that influence drug disposition and contribute to the development of adverse drug reactions.

AREAS COVERED

This review will survey pertinent literature of how liver disease alters the PKs of drugs and other xenobiotics. The focus will be on nonalcoholic steatohepatitis as well as cholestatic liver diseases. A review of basic pharmacokinetic principles, with a special emphasis on xenobiotic metabolizing enzymes and membrane transporters, will be provided. Specifically, examples of how genetic alterations affect metabolism and excretion, respectively, will be highlighted. Lastly, the idea of 'extrahepatic' regulation will be explored, citing examples of how disease manifestation in the liver may affect drug disposition in distal sites, such as the kidney.

EXPERT OPINION

An expert opinion will be provided highlighting the definite need for data in understanding extrahepatic regulation of membrane transporters in the presence of liver disease and its potential to dramatically alter the PK and toxicokinetic profile of numerous drugs and xenobiotics.

Role of age-related decrease of renal organic cation transporter 2 in the effect of atenolol on renal excretion of metformin in rats

Many diabetes patients, especially the elder ones, suffered from hypertension simultaneously. Therefore, it is very likely that a large number of diabetes patients receiving metformin hydrochloride may simultaneously be given beta-blockers. Knowing that both metformin and atenolol are eliminated by organic cation transporter 2 (OCT2/SLC22A2) expressed in the renal basolateral membrane, it is not clear whether there is a competitive effect on the renal excretion of metformin and/or atenolol when metformin and atenolol were co-administered, and whether age was involved in this drug-drug interaction. In this present study, both young rats (aged 3 months) and aged rats (aged 12 months) were used, rats were divided into metformin-treated group and metformin and atenolol co-administrated group, respectively. Either metformin (2.5 mg/kg) alone or metformin (2.5 mg/kg) in combination with atenolol (8 mg/kg) was administered to rats by tail vein injection. Then, urine was collected and the metformin concentration in urine was determined by HPLC. The localization and expression of rOCT2 in kidney were also investigated by Western blotting and immunohistochemistry. Significant differences of t 1/2, K e, CLtot and the accumulated metformin excretion in urine were founded in aged rats, but not in young rats, between metformin-treated group (2.002 ± 0.51 h, 0.346 ± 0.07/h, 57.161 ± 18.59 %, 4,287.087 ± 458.08 μg) and metformin plus atenolol-treated group (3.03 ± 0.67 h, 0.228 ± 0.05/h, 43.199 ± 10.28 %, 3,239.972 ± 446.61 μg). Moreover, a significant age-related decrease in rOCT2 protein expression was observed in the aged rats (P < 0.01), which may be responsible for the effect of atenolol on the renal excretion of metformin in the aged rats. In conclusion, there is a drug-drug interaction between atenolol and metformin, and more attention should be paid when atenolol and metformin were co-administered to the aged people inclinical.

Genetic polymorphisms of OCT-1 confer susceptibility to severe progression of primary biliary cirrhosis in Japanese patients

BACKGROUND

To identify the genetic factors involved in the pathogenesis of primary biliary cirrhosis (PBC), we focused on the organic cation transporter 1 (OCT1/SLC22A1), which is closely associated with phosphatidylcholine synthesis in hepatocytes.

METHODS

We selected four (rs683369, rs2282143, rs622342 and rs1443844) OCT-1 single nucleotide polymorphisms (SNPs), and genotyped these SNPs using the TaqMan probe method in 275 Japanese PBC patients and 194 gender-matched, healthy volunteers as controls.

RESULTS

The Chi-square test revealed that the rs683369 variant allele (G) was associated with insusceptibility to PBC development [P = 0.009, odds ratio (OR) 0.60, 95 % confidence interval (CI) 0.40-0.88] in an allele model, and that the rs683369 variant allele (G) was associated with jaundice-type progression in a minor allele dominant genotype model (P = 0.032, OR 3.10, 95 % CI 1.05-9.14). The OCT-1 rs2282143 variant (T) and rs622342 variant (C) were also associated with jaundice-type progression in a minor allele recessive genotype model (P = 0.0002, OR 10.58, 95 % CI 2.36-47.54, and P = 0.006, OR 7.84, 95 % CI 1.39-44.36, respectively). Furthermore, the association of OCT-1 rs683369 and rs622342 with susceptibility to jaundice-type progression was confirmed by a replication study with a distinct set of PBC patients who underwent liver transplantation.

CONCLUSIONS

The present study is the first report on the association of OCT-1 genetic polymorphisms with the overall development and jaundice-type progression of PBC.

New perspective for an old antidiabetic drug: metformin as anticancer agent

Metformin, an inexpensive, well-tolerated oral agent that is commonly used in the first-line treatment for type 2 diabetes, has become the focus of intense research as a potential anticancer agent. This research reflects a convergence of epidemiologic, clinical, and preclinical evidence, suggesting that metformin may lower cancer risk in diabetics and improve outcomes of many common cancers. Notably, metformin mediates an approximately 30 % reduction in the lifetime risk of cancer in diabetic patients. There is growing recognition that metformin may act (1) directly on cancer cells, primarily by impacting mitochondrial respiration leading to the activation of the AMP-activated protein kinase (AMPK), which controls energy homeostasis in cells, but also through other mechanisms or (2) indirectly on the host metabolism, largely through AMPK-mediated reduction in hepatic gluconeogenesis, leading to reduced circulating insulin levels and decreased insulin/IGF-1 receptor-mediated activation of the PI3K pathway. Support for this comes from the observation that metformin inhibits cancer cell growth in vitro and delays the onset of tobacco carcinogen-induced lung cancer in mice and that metformin and its analog phenformin delay spontaneous tumor development cancer-prone transgenic mice. The potential for both direct antitumor effects and indirect host-mediated effects has sparked enormous interest, but has led to added challenges in translating preclinical findings to the clinical setting. Nonetheless, the accumulation of evidence has been sufficient to justify initiation of clinical trials of metformin as an anticancer agent in the clinical setting, including a large-scale adjuvant study in breast cancer, with additional studies planned.

Altered pharmacokinetics of cimetidine caused by down-regulation of renal rat organic cation transporter 2 (rOCT2) after liver ischemia-reperfusion injury

The renal tubular secretion of cationic drugs is dominated by basolateral organic cation transporter 2 (rOCT2/SLC22A2) and luminal multidrug and toxin extrusion 1 (rMATE1/SLC47A1). Little is known about the variation in the expression of these renal transporters after liver ischemia-reperfusion (I/R) injury. Here, we examined the pharmacokinetics of a cationic drug, cimetidine, and renal rOCT2 and rMATE1 levels as well as their regulation after liver I/R. Rats were subjected to 60 min of liver ischemia followed by 12 h of reperfusion. The antioxidant Trolox was administered intravenously 5 min before reperfusion. The systemic and tubular secretory clearances of cimetidine (78% and 55%) as well as renal rOCT2 and rMATE1 levels (67% and 61%) in I/R rats were decreased compared with those in sham-operated rats, respectively. However, the renal tissue-to-plasma concentration ratio but not the renal tissue-to-urine clearance ratio of cimetidine was decreased after liver I/R. Moreover, Trolox prevented the decreases in renal rOCT2 levels and systemic clearance of cimetidine after liver I/R. These results demonstrate that liver I/R decreases the tubular secretion of cimetidine, mainly because of the decreased rOCT2 level in the kidney, and that oxidative stress should be responsible in part for decreased renal rOCT2 after liver I/R injury.

Effects of 17α-ethynylestradiol-induced cholestasis on the pharmacokinetics of doxorubicin in rats: reduced biliary excretion and hepatic metabolism of doxorubicin

1. Since the prevalent hormonal combination therapy with estrogen analogues in cancer patients has frequency and possibility to induce the cholestasis, the frequent combination therapy with 17α-ethynylestradiol (EE, an oral contraceptive) and doxorubicin (an anticancer drug) might be monitored in aspect of efficacy and safety. Doxorubicin is mainly excreted into the bile via P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (Mrp2) in hepatobiliary route and metabolized via cytochrome P450 (CYP) 3A subfamily. Also the hepatic Mrp2 (not P-gp) and CYP3A subfamily levels were reduced in EE-induced cholestatic (EEC) rats. Thus, we herein report the pharmacokinetic changes of doxorubicin with respect to the changes in its biliary excretion and hepatic metabolism in EEC rats. 2. The pharmacokinetic study of doxorubicin after intravenous administration of its hydrochloride was conducted along with the investigation of bile flow rate and hepatobiliary excretion of doxorubicin in control and EEC rats. 3. The significantly greater AUC (58.7% increase) of doxorubicin in EEC rats was due to the slower CL (32.9% decrease). The slower CL was due to the reduction of hepatic biliary excretion (67.0% decrease) and hepatic CYP3A subfamily-mediated metabolism (21.9% decrease) of doxorubicin. These results might have broader implications to understand the altered pharmacokinetics and/or pharmacologic effects of doxorubicin via biliary excretion and hepatic metabolism in experimental and clinical estrogen-induced cholestasis.

Renal uptake of substrates for organic anion transporters Oat1 and Oat3 and organic cation transporters Oct1 and Oct2 is altered in rats with adenine-induced chronic renal failure

Chronic renal failure (CRF) leads to decreased drug renal clearance and glomerular filtration rate. However, little is known about renal tubular excretion and reabsorption in CRF. We examined transport activity of renal transporters using rats with adenine-induced CRF. We examined the effect of adenine-induced CRF on mRNA level, protein expression of transporters expressed in kidney by real-time polymerase chain reaction, and western blotting. In vivo kidney uptake clearances of benzylpenicillin and metformin, which are typical substrates for renal organic anion transporters Oat1 and Oat3 and organic cation transporters Oct1 and Oct2, respectively, were evaluated. Protein and mRNA expression levels of Oat1, Oat 3, Oct1, and Oct2 were significantly decreased in adenine-induced CRF rats. On the contrary, levels of P-glycoprotein and Mdr1b mRNA were significantly increased in adenine-induced CRF rats. The mRNA expression levels of Oatp4c1, Mate1, Urat1, Octn2, and Pept1 were significantly decreased. Kidney uptake clearance of benzylpenicillin and that of metformin were significantly decreased in adenine-induced CRF rats. Also, serum from CRF rats did not affect Oat1, Oat3, Oct1, and Oct2 function. In conclusion, our results indicate that adenine-induced CRF affects renal tubular handling of drugs, especially substrates of Oat1, Oat3, Oct1, and Oct2.

Endocrine and metabolic regulation of renal drug transporters

Renal xenobiotic transporters are important determinants of urinary secretion and reabsorption of chemicals. In addition to glomerular filtration, these processes are key to the overall renal clearance of a diverse array of drugs and toxins. Alterations in kidney transporter levels and function can influence the efficacy and toxicity of chemicals. Studies in experimental animals have revealed distinct patterns of renal transporter expression in response to sex hormones, pregnancy, and growth hormone. Likewise, a number of disease states including diabetes, obesity, and cholestasis alter the expression of kidney transporters. The goal of this review is to provide an overview of the major xenobiotic transporters expressed in the kidneys and an understanding of metabolic conditions and hormonal factors that regulate their expression and function.

Effects of metformin on learning and memory behaviors and brain mitochondrial functions in high fat diet induced insulin resistant rats

AIM

Metformin is a first line drug for the treatment of type 2 diabetes mellitus (T2DM). Our previous study reported that high-fat diet (HFD) consumption caused not only peripheral and neuronal insulin resistance, but also induced brain mitochondrial dysfunction as well as learning impairment. However, the effects of metformin on learning behavior and brain mitochondrial functions in HFD-induced insulin resistant rats have never been investigated.

MAIN METHODS

Thirty-two male Wistar rats were divided into two groups to receive either a normal diet (ND) or a high-fat diet (HFD) for 12weeks. Then, rats in each group were divided into two treatment groups to receive either vehicle or metformin (15mg/kg BW twice daily) for 21days. All rats were tested for cognitive behaviors using the Morris water maze (MWM) test, and blood samples were collected for the determination of glucose, insulin, and malondialdehyde. At the end of the study, animals were euthanized and the brain was removed for studying brain mitochondrial function and brain oxidative stress.

KEY FINDINGS

We found that in the HFD group, metformin significantly attenuated the insulin resistant condition by improving metabolic parameters, decreasing peripheral and brain oxidative stress levels, and improving learning behavior, compared to the vehicle-treated group. Furthermore, metformin completely prevented brain mitochondrial dysfunction caused by long-term HFD consumption.

SIGNIFICANCE

Our findings suggest that metformin effectively improves peripheral insulin sensitivity, prevents brain mitochondrial dysfunction, and completely restores learning behavior, which were all impaired by long-term HFD consumption.

Cardioprotective effects of metformin and vildagliptin in adult rats with insulin resistance induced by a high-fat diet

Insulin resistance has been shown to be associated with cardiac sympathovagal imbalance, myocardial dysfunction, and cardiac mitochondrial dysfunction. Whereas metformin is a widely used antidiabetic drug to improve insulin resistance, vildagliptin is a novel oral antidiabetic drug in a group of dipeptidyl peptidase-4 inhibitors in which its cardiac effect is unclear. This study aimed to determine the cardiovascular effects of metformin and vildagliptin in rats with insulin resistance induced by high-fat diet. Male Wistar rats were fed with either a normal diet or high-fat diet (n =24 each) for 12 wk. Rats in each group were divided into three subgroups to receive the vehicle, metformin (30 mg/kg, twice daily), or vildagliptin (3 mg/kg, once daily) for another 21 d. Heart rate variability (HRV), cardiac function, and cardiac mitochondrial function were determined and compared among these treatment groups. Rats exposed to a high-fat diet developed increased body weight, visceral fat, plasma insulin, cholesterol, oxidative stress, depressed HRV, and cardiac mitochondrial dysfunction. Metformin and vildagliptin did not alter body weight and plasma glucose levels but decreased the plasma insulin, total cholesterol, and oxidative stress levels. Although both metformin and vildagliptin attenuated the depressed HRV, cardiac dysfunction, and cardiac mitochondrial dysfunction, vildagliptin was more effective in this prevention. Furthermore, only vildagliptin prevented cardiac mitochondrial membrane depolarization caused by consumption of a high-fat diet. We concluded that vildagliptin is more effective in preventing cardiac sympathovagal imbalance and cardiac dysfunction, as well as cardiac mitochondrial dysfunction, than metformin in rats with insulin resistance induced by high-fat diet.

AMP-activated protein kinase: an emerging drug target to regulate imbalances in lipid and carbohydrate metabolism to treat cardio-metabolic diseases

The adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor of energy metabolism at the cellular as well as whole-body level. It is activated by low energy status that triggers a switch from ATP-consuming anabolic pathways to ATP-producing catabolic pathways. AMPK is involved in a wide range of biological activities that normalizes lipid, glucose, and energy imbalances. These pathways are dysregulated in patients with metabolic syndrome (MetS), which represents a clustering of major cardiovascular risk factors including diabetes, lipid abnormalities, and energy imbalances. Clearly, there is an unmet medical need to find a molecule to treat alarming number of patients with MetS. AMPK, with multifaceted activities in various tissues, has emerged as an attractive drug target to manage lipid and glucose abnormalities and maintain energy homeostasis. A number of AMPK activators have been tested in preclinical models, but many of them have yet to reach to the clinic. This review focuses on the structure-function and role of AMPK in lipid, carbohydrate, and energy metabolism. The mode of action of AMPK activators, mechanism of anti-inflammatory activities, and preclinical and clinical findings as well as future prospects of AMPK as a drug target in treating cardio-metabolic disease are discussed.

Metformin in cancer: translational challenges

The anti-diabetic drug metformin is rapidly emerging as a potential anti-cancer agent. Metformin, effective in treating type 2 diabetes and the insulin resistance syndromes, improves insulin resistance by reducing hepatic gluconeogenesis and by enhancing glucose uptake by skeletal muscle. Epidemiological studies have consistently associated metformin use with decreased cancer incidence and cancer-related mortality. Furthermore, numerous preclinical and clinical studies have demonstrated anti-cancer effects of metformin, leading to an explosion of interest in evaluating this agent in human cancer. The effects of metformin on circulating insulin levels indicate a potential efficacy towards cancers associated with hyperinsulinaemia; however, metformin may also directly inhibit tumour growth. In this review, we describe the mechanism of action of metformin and summarise the epidemiological, clinical and preclinical evidence supporting a role for metformin in the treatment of cancer. In addition, the challenges associated with translating preclinical results into therapeutic benefit in the clinical setting will be discussed.

Increased expression of hepatic organic cation transporter 1 and hepatic distribution of metformin in high-fat diet-induced obese mice

Although the effect of obesity on drug disposition remains an important issue for clinicians, little is known about the effects of obesity on organic cation transporter 1 (OCT1) expression and activity. Here, we show that hepatic OCT1 expression was higher in mice fed a high-fat (HF) diet for 19 weeks compared with mice fed a control diet. Since HF diet-induced obese mice exhibited elevation of plasma proinflammatory cytokines, leptin, and insulin levels, we evaluated the effect of leptin, insulin, and tumor necrosis factor-alpha (TNF-alpha) on OCT1 mRNA expression in HepG2 cells. Both leptin and insulin significantly increased OCT1 mRNA expression in HepG2 cells, but TNF-alpha did not. This finding was consistent with in vivo results. Using the OCT1 substrate metformin, we further measured the extent of hepatic uptake of metformin in obese and lean mice using the ratio of hepatic concentration to plasma concentration of metformin at 1 h after administration. The hepatic uptake of metformin was significantly higher in mice fed a HF diet compared with lean mice. In conclusion, our results suggest, at least in part, that obesity might have an effect on the absorption or distribution pharmacokinetics of metformin through an increase in hepatic OCT1 expression.

Elevated systemic elimination of cimetidine in rats with acute biliary obstruction: the role of renal organic cation transporter OCT2

Renal tubular secretion of cationic drugs is dominated by two classes of organic cation transporters, OCT2/SLC22A2 and MATE1/SLC47A1, localized to the basolateral and brush-border membranes of the renal tubular epithelial cells, respectively. However, little is known about the expression and function of these transporters in acute cholestasis. Systemic clearance of cimetidine was significantly higher in rats with bile duct ligation (BDL) for 24 hours than in sham-operated rats, with no significant changes in the volume of distribution between the groups. In addition, net tubular secretory clearance of cimetidine was significantly higher in the BDL rats compared with the sham rats, with no significant changes in the glomerular filtration rate. Moreover, the renal tissue-to-plasma concentration ratio of cimetidine was elevated in BDL rats, although the renal tissue-to-urine clearance ratio of cimetidine was not different between the two groups. The expression level of basolateral organic cation transporter rOCT2 protein in the kidney cortex was markedly higher in BDL rats than that in the sham rats, but that of H+/organic cation antiporter rMATE1 protein in the brush-border membranes was not significantly different between the two groups. These results demonstrate that the renal tubular secretion of cimetidine was increased by acute cholestasis, and this increase was attributable to elevated expression levels of rOCT2 but not of rMATE1 in the rat.

Sitagliptin attenuates metformin-mediated AMPK phosphorylation through inhibition of organic cation transporters

To assess potential interactions between sitagliptin and metformin, we sought to characterize the in vitro inhibitory potency of sitagliptin on the uptake of MPP(+) and metformin, representative substrates for OCTs, and to evaluate the pharmacological pathways that may be affected by the combination of metformin and sitagliptin. Among the OATs and OCTs screened, OAT3-mediated salicylate uptake and OCT1- and OCT2-mediated MPP(+) uptake were inhibited by sitagliptin. The K(i) values of sitagliptin for OCT1- and OCT2-mediated metformin uptake were 34.9 and 40.8 μM, respectively. As OCT1 is the gate protein for metformin action in the liver, we investigated whether sitagliptin-mediated OCT1 inhibition affected metformin-induced activation of AMPK signalling. Treatment with sitagliptin in MDCK-OCT1 and HepG2 cells resulted in a reduced level of phosphorylated AMPK, with K(i) values of 38.8 and 43.3 μM, respectively. These results suggest that the inhibitory potential of sitagliptin on OCT1 may attenuate the first step of metformin action, that is, the phosphorylation of AMPK. Nevertheless, the likelihood of a drug-drug interaction between sitagliptin and metformin is believed to be remote in usual clinical setting.

Expression of organic cation transporters OCT1 (SLC22A1) and OCT3 (SLC22A3) is affected by genetic factors and cholestasis in human liver

An important function of hepatocytes is the biotransformation and elimination of various drugs, many of which are organic cations and are taken up by organic cation transporters (OCTs) of the solute carrier family 22 (SLC22). Because interindividual variability of OCT expression may affect response to cationic drugs such as metformin, we systematically investigated genetic and nongenetic factors of OCT1/SLC22A1 and OCT3/SLC22A3 expression in human liver. OCT1 and OCT3 expression (messenger RNA [mRNA], protein) was analyzed in liver tissue samples from 150 Caucasian subjects. Hepatic OCTs were localized by way of immunofluorescence microscopy. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and genome-wide single-nucleotide polymorphism microarray technology served to genotype 92 variants in the SLC22A1-A3/OCT1-3 gene cluster. Transport of metformin by recombinant human OCT1 and OCT3 was compared using transfected cells. OCT1 mRNA and protein expression varied 113- and 83-fold, respectively; OCT3 mRNA expression varied 27-fold. OCT1 transcript levels were on average 15-fold higher compared with OCT3. We localized the OCT3 protein to the basolateral hepatocyte membrane and identified metformin as an OCT3 substrate. OCT1 and OCT3 expression are independent of age and sex but were significantly reduced in liver donors diagnosed as cholestatic (P < or = 0.01). Several haplotypes for OCT1 and OCT3 were identified. Multivariate analysis adjusted for multiple testing showed that only the OCT1-Arg61Cys variant (rs12208357) strongly correlated with decreased OCT1 protein expression (P < 0.0001), and four variants in OCT3 (rs2292334, rs2048327, rs1810126, rs3088442) were associated with reduced OCT3 mRNA levels (P = 0.03).

CONCLUSION

We identified cholestasis and genetic variants as critical determinants for considerable interindividual variability of hepatic OCT1 and OCT3 expression. This indicates consequences for hepatic elimination of and response to OCT substrates such as metformin.