Androgen receptor is responsible for rat organic cation transporter 2 gene regulation but not for rOCT1 and rOCT3

Regulation of renal organic cation transporters

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

Is metformin a possible treatment for diabetic neuropathy?

Metformin is a hypoglycemic drug widely used in the treatment of type 2 diabetes. It has been proven to have analgesic and neuroprotective effects. Metformin can reverse pain in rodents, such as diabetic neuropathic pain, neuropathic pain caused by chemotherapy drugs, inflammatory pain and pain caused by surgical incision. In clinical use, however, metformin is associated with reduced plasma vitamin B12 levels, which can further neuropathy. In rodent diabetes models, metformin plays a neuroprotective and analgesic role by activating adenosine monophosphate-activated protein kinase, clearing methylgloxal, reducing insulin resistance, and neuroinflammation. This paper also summarized the neurological adverse reactions of metformin in diabetic patients. In addition, whether metformin has sexual dimorphism needs further study.

The Role of NF-kB in the Downregulation of Organic Cation Transporter 2 Expression and Renal Cation Secretion in Kidney Disease

Organic cation transporter 2 (OCT2), encoded by the SLC22A2 gene, is the main cation transporter on the basolateral membrane of proximal tubular cells. OCT2 facilitates the entry step of the vectorial transport of most cations from the peritubular space into the urine. OCT2 downregulation in kidney disease models is apparent, yet not clear from a mechanistic vantage point. The aim of this study was to explore the role of inflammation, a common thread in kidney disease, and NF-kB in OCT2 modulation and tubular secretion. Among the OCTs, OCT2 was found consistently downregulated in the kidney of rats with chronic kidney disease (CKD) or acute kidney injury (AKI) and in patients diagnosed with CKD, and it was associated with the upregulation of TNFα renal expression. Exposure to TNFα reduced the expression and function of OCT2 in primary renal proximal tubule epithelial cells (RPTEC). Silencing or pharmacological inhibition of NF-kB rescued the expression of OCT2 in the presence of TNFα, indicating that OCT2 repression was NF-kB-dependent. In silico prediction coupled to gene reporter assay demonstrated the presence of at least one functional NF-kB cis-element upstream the transcription starting site of the SLC22A2 gene. Acute inflammation triggered by lipopolysaccharide injection induced TNFα expression and the downregulation of OCT2 in rat kidney. The inflammation did reduce the active secretion of the cation Rhodamine 123, with no impairment of the glomerular filtration. In conclusion, the NF-kB pathway plays a major role in the transcriptional regulation of OCT2 and, in turn, in the overall renal secretory capacity.

Evaluation of sex differences in the pharmacokinetics of oral sumatriptan in healthy Korean subjects using population pharmacokinetic modeling

Sumatriptan was introduced in 1983, as the first of the triptans, selective 5‐hydroxytryptamine (5‐HT_1B/1D) receptor agonists, to treat moderate to severe migraine. Migraine predominates in females. Although there have been reports of sex differences in migraine‐associated features and pharmacokinetics (PKs) of some triptans, sex differences in the PKs of oral sumatriptan have never been evaluated in Korean. We conducted this study of oral sumatriptan to assess the sex differences in Korean population. Thirty‐eight healthy Korean subjects who participated in two separate clinical studies receiving a single oral dose of 50 mg sumatriptan with the same protocols were included in this analysis. A total of 532 sumatriptan concentration observations were used for a population PK modeling. Validation of final population PK model of sumatriptan was performed using bootstrap and visual predictive check. The PK profile of oral sumatriptan was adequately described by a one‐compartmental model with combined transit compartment model and a first‐order absorption. The covariate analysis showed that the clearance of oral sumatriptan was significantly higher in males than in females (male: 444 L/h, female: 281 L/h). Our results showed that there were sex differences in the clearance of oral sumatriptan. These results encourage further studies to establish the sumatriptan pharmacokinetic–pharmacodynamic model considering sex‐related PK differences, which may help to determine optimal dosing regimens for effective treatment of migraine in males and females. Clinical trial registration: CRIS Registration No. KCT0001784.

Effects of 1α,25-Dihydroxyvitamin D3 on the Pharmacokinetics of Procainamide and Its Metabolite N-Acetylprocainamide, Organic Cation Transporter Substrates, in Rats with PBPK Modeling Approach

In this study, possible changes in the expression of rat organic cationic transporters (rOCTs) and rat multidrug and toxin extrusion proteins (rMATEs) following treatment with 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) were investigated. Rats received intraperitoneal administrations of 1,25(OH)₂D₃ for four consecutive days, and the tissues of interest were collected. The mRNA expression of rOCT1 in the kidneys was significantly increased in 1,25(OH)₂D₃-treated rats compared with the control rats, while the mRNA expressions of rOCT2 and rMATE1 in the kidneys, rOCT1 and N-acetyltransferase-II (NAT-II) in the liver, and rOCT3 in the heart were significantly decreased. Changes in the protein expression of hepatic rOCT1 and renal rOCT2 and rMATE1 were confirmed by western blot analysis. We further evaluated the pharmacokinetics of procainamide (PA) hydrochloride and its major metabolite N-acetyl procainamide (NAPA) in the presence of 1,25(OH)₂D₃. When PA hydrochloride was administered intravenously at a dose 10 mg/kg to 1,25(OH)₂D₃-treated rats, a significant decrease in renal and/or non-renal clearance of PA and NAPA was observed. A physiological model for the pharmacokinetics of PA and NAPA in rats was useful for linking changes in the transcriptional and translational expressions of rOCTs and rMATE1 transporters to the altered pharmacokinetics of the drugs.

Metformin reduces androgen receptor and upregulates homeobox A10 expression in uterine endometrium in women with polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) causes anovulation and is associated with a reduced clinical pregnancy rate. Metformin, which is widely used for treating PCOS, can lead to successful pregnancy by restoring the ovulation cycle and possibly improving endometrial abnormality during the implantation period. However, the mechanism by which metformin improves endometrial abnormality remains unknown. Women with PCOS have an aberrant expression of steroid hormone receptors and homeobox A10 (HOXA10), which is essential for embryo implantation in the endometrium.

METHODS

In this study, we examined whether metformin affects androgen receptor (AR) and HOXA10 expression in PCOS endometrium in vivo and in human endometrial cell lines in vitro. Expression of AR and HOXA10 was evaluated by immunohistochemistry, fluorescent immunocytochemistry, and western blot analysis.

RESULTS

AR expression was localized in both epithelial and stromal cells; however, HOXA10 expression was limited to only stromal cells in this study. In women with PCOS, 3 months after metformin treatment, the expression of AR was reduced in epithelial and stromal cells in comparison to their levels before treatment. In contrast, HOXA10 expression in the stromal cells with metformin treatment increased in comparison to its level before treatment. Further, we showed that metformin counteracted the testosterone-induced AR expression in both Ishikawa cells and human endometrial stromal cells (HESCs); whereas, metformin partly restored the testosterone-reduced HOXA10 expression in HESCs in vitro.

CONCLUSIONS

Our results suggest that metformin may have a direct effect on the abnormal endometrial environment of androgen excess in women with PCOS.

TRIAL REGISTRATION

The study was approved by the Ethical Committee of Fukushima Medical University (approval no. 504, approval date. July 6, 2006), and written informed consent was obtained from all patients. https://www.fmu.ac.jp/univ/sangaku/rinri.html.

Effects of Androgen Receptor Inhibition on Kanamycin-Induced Hearing Loss in Rats

Megalin has been proposed as an endocytic receptor for aminoglycosides as well as estrogen and androgen. We aimed to investigate the otoprotective effects of antiandrogens (flutamide, FM) on kanamycin (KM)-induced hearing loss in rats. Rats were divided into four groups. The KM group was administered KM (20 mg/kg/day) for 5 days, while the FM group received FM (15 mg/kg/day) for 10 days. In the KM + FM group, KM and FM (15 mg/kg/day) were simultaneously injected for 5 days and then FM was injected for 5 days. Auditory brainstem responses were measured. Western blotting and/or quantitative reverse transcriptase-polymerase chain reaction were performed for megalin, cytochrome P450 1A1 (Cyp1a1), Cyp1b1, metallothionein 1A (MT1A), MT2A, tumor necrosis factor (TNF)-α, caspase 3, and cleaved caspase 3. The FM + KM group showed attenuated auditory thresholds when compared with the KM group at 4, 8, 16, and 32 kHz (all p < 0.05). The KM + FM group showed lower megalin and Cyp1b1 levels than the KM group (all p < 0.05). The KM + FM group revealed lower MT1A, TNFα, and caspase 3 protein levels, compared with those in the KM group (all p < 0.05). Androgen receptor inhibition protects against cochlear injuries in KM-induced hearing loss rats by attenuating megalin expression, revealing anti-inflammatory and anti-apoptotic effects.

Farnesoid X Receptor Activation Stimulates Organic Cations Transport in Human Renal Proximal Tubular Cells

Farnesoid X receptor (FXR) is a ligand-activated transcription factor highly expressed in the liver and kidneys. Activation of FXR decreases organic cation transporter (OCT) 1-mediated clearance of organic cation compounds in hepatocytes. The present study investigated FXR regulation of renal clearance of organic cations by OCT2 modulation and multidrug and toxin extrusion proteins (MATEs). The role of FXR in OCT2 and MATEs functions was investigated by monitoring the flux of ³H-MPP⁺, a substrate of OCT2 and MATEs. FXR agonists chenodeoxycholic acid (CDCA) and GW4064 stimulated OCT2-mediated ³H-MPP⁺ uptake in human renal proximal tubular cells (RPTEC/TERT1 cells) and OCT2-CHO-K1 cells. The stimulatory effect of CDCA (20 µM) was abolished by an FXR antagonist, Z-guggulsterone, indicating an FXR-dependent mechanism. CDCA increased OCT2 transport activity via an increased maximal transport rate of MPP⁺. Additionally, 24 h CDCA treatment increased MATEs-mediated ³H-MPP⁺ uptake. Moreover, CDCA treatment increased the expression of OCT2, MATE1, and MATE2-K mRNA compared with that of the control. OCT2 protein expression was also increased following CDCA treatment. FXR activation stimulates renal OCT2- and MATE1/2-K-mediated cation transports in proximal tubules, demonstrating that FXR plays a role in the regulation of OCT2 and MATEs in renal proximal tubular cells.

Metformin and gut microbiota: their interactions and their impact on diabetes

The ratio of human to bacterial cells in the human body (microbiota) is around 1:1. As a result of co-evolution of the host mucosal immune system and the microbiota, both have developed multiple mechanisms to maintain homeostasis. However, dissociations between the composition of the gut microbiota and the human host may play a crucial role in the development of type 2 diabetes. Metformin, the most frequently administered medication to treat patients with type 2 diabetes, has only recently been suggested to alter gut microbiota composition through the increase in mucin-degrading Akkermansia muciniphila, as well as several SCFA-producing (short-chain fatty acid) microbiota. The gut microbiota of participants on metformin has exerted alterations in gut metabolomics with increased ability to produce butyrate and propionate, substances involved in glucose homeostasis. Thus, metformin appears to affect the microbiome, and an individual's metformin tolerance or intolerance may be influenced by their microbiome. In this review, we will focus on the effects of metformin in gut microbiota among patients with T2DM.

The antidiabetic drug metformin prevents and reverses neuropathic pain and spinal cord microglial activation in male but not female mice

Metformin is a widely prescribed drug used in the treatment of type II diabetes. While the drug has many mechanisms of action, most of these converge on AMP activated protein kinase (AMPK), which metformin activates. AMPK is a multifunctional kinase that is a negative regulator of mechanistic target of rapamycin (mTOR) and mitogen activated protein kinase (MAPK) signaling. Activation of AMPK decreases the excitability of dorsal root ganglion neurons and AMPK activators are effective in reducing chronic pain in inflammatory, post-surgical and neuropathic rodent models. We have previously shown that metformin leads to an enduring resolution of neuropathic pain in the spared nerve injury (SNI) model in male mice and rats. The precise mechanism underlying this long-lasting effect is not known. We conducted experiments to investigate the effects of metformin on SNI-induced microglial activation, a process implicated in the maintenance of neuropathic pain that has recently been shown to be sexually dimorphic. We find that metformin is effective at inhibiting development of neuropathic pain when treatment is given around the time of injury and that metformin is likewise effective at reversing neuropathic mechanical hypersensitivity when treatment is initiation weeks after injury. This effect is linked to decreased Iba-1 staining in the dorsal horn, a marker of microglial activation. Importantly, these positive behavioral and microglia effects of metformin were only observed in male mice. We conclude that the neuropathic pain modifying effects of metformin are sex-specific supporting a differential role for microglial activation in male and female mice.

Effects of chronic aspartame consumption on MPTP-induced Parkinsonism in male and female mice

BACKGROUND

Parkinson's disease is a progressive neurodegenerative disorder. Aspartame (l-aspartyl-l-phenylalanine methyl ester), a low calorie sweetener used in foods and beverages.

OBJECTIVES

This study investigated the effect of chronic aspartame intake on Parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

METHOD

Forty-eight mice (24 males and 24 females): control, aspartame, MPTP, and aspartame + MPTP groups tested by Y-maze, stepping, forced swimming and olfactory preference tests. Brain tissues examined for dopamine content, tyrosine hydroxylase, inducible nitric oxide synthase (iNOS), glutathione peroxidase, phosphorylated tau and α-synuclein protein. Histopathological evaluation of brain sections at the level of basal ganglia was done.

RESULTS

Decreased dopamine content, tyrosine hydroxylase expression, glutathione peroxidase expression and increased iNOS, tau and α-synuclein expression in groups received aspartame, MPTP or both agents simultaneously in both males and females group.

CONCLUSIONS

Increased dopaminergic degeneration and complications with chronic aspartame consumption and more injury in male groups.

Atorvastatin modulates drug transporters and ameliorates nicotine-induced testicular toxicity

We studied the changes in mRNA expressions of influx and efflux transporters, blood-testis-barrier proteins (BTB) and key apoptotic genes in the testis of rats coadministered with nicotine and atorvastatin. Rats were divided into four groups: (i) control, (ii) atorvastatin (10 mg/kg b.wt), (iii) nicotine (0.6 mg/kg b.wt) and (iv) atorvastatin (10 mg/kg b.wt) + nicotine (0.6 mg/kg b.wt). Atorvastatin was given by oral intubation and nicotine by intraperitoneal injection. After 60 days of treatment, expressions of key apoptotic genes involved in both intrinsic and extrinsic pathways; solute carrier influx transporters SLCOB1, SLC22A1 and efflux transporter ABCB1 associated with transport of atorvastatin and nicotine, and proteins of BTB were assayed. Nicotine administration activated apoptosis and downregulated SLCOB1, which transport atorvastatin. Atorvastatin administration suppressed apoptotic pathway and downregulated SLC22A1, transporter of nicotine. Coadministration of atorvastatin with nicotine downregulated expressions of apoptotic genes. The combined administration of atorvastatin and nicotine reduced the influx of both atorvastatin and nicotine and enhanced the efflux of these drugs thereby altering the microenvironment of testis and improving testicular function. We conclude that atorvastatin-mediated alterations of BTB and drug transporters might have played a significant role in ameliorating nicotine-induced testicular toxicity.

Different effect of testosterone and oestrogen on urinary excretion of metformin via regulating OCTs and MATEs expression in the kidney of mice

The aim of this study was to investigate the effect of testosterone and oestrogen on regulating organic cation transporters (Octs) and multidrug and toxin extrusions (Mates) expression in the kidney of mice and urinary excretion of metformin. 8 week‐old male db/db mice were treated with estradiol (5 mg/kg), testosterone (50 mg/kg) or olive oil with same volume. Metformin (150 mg/kg) was injected in daily for successive 7 days. Plasma, urine and tissue concentrations of metformin were determined by liquid chromatography‐tandem mass spectrometry (LCMS) assay. Western blotting and Real‐time PCR analysis were successively used to evaluate the renal protein and mRNA expression of Octs and MATEs. After treatment, the protein expression of Mate1 and Oct2 in testosterone group was significantly increased than those in control group (both P < 0.05). The protein expression of Mate1 and Oct2 in estradiol group was significantly reduced by 29.4% and 43.3%, respectively, compared to those in control group (all P < 0.05). These data showed a good agreement with the change in mRNA level (all P < 0.05). The plasma metformin concentration (ng/ml) in mice treated with estradiol was significantly higher than control and testosterone group (677.56 ± 72.49 versus 293.92 ± 83.27 and 261.46 ± 79.45; P < 0.01). Moreover, testosterone increased the metformin urine excretion of mice while estradiol decreasing (both P < 0.01). Spearman correlation analysis showed that gonadal hormone was closely associated with Mate1 and Oct2 expression and metformin urine excretion in db/db mice (all P < 0.05). Testosterone and oestrogen exerted reverse effect on metformin urinary excretion via regulating Octs and Mates expression in the kidney of mice.

Sex-differences in renal expression of selected transporters and transcription factors in lean and obese Zucker spontaneously hypertensive fatty rats

The aim of this study was to identify sex-dependent expression of renal transporter mRNA in lean and obese Zucker spontaneously hypertensive fatty (ZSF1) rats and to investigate the interaction of the most altered transporter, organic anion transporter 2 (Oat2), with diabetes-relevant metabolites and drugs. Higher incidence of glomerulosclerosis, tubulointerstitial fibrosis, and protein casts in Bowman's space and tubular lumen was detected by PAS staining in obese male compared to female ZSF1 rats. Real-time PCR on RNA isolated from kidney cortex revealed that Sglt1-2, Oat1-3, and Oct1 were higher expressed in kidneys of lean females. Oct2 and Mrp2 were higher expressed in obese males. Renal mRNA levels of transporters were reduced with diabetic nephropathy in females and the expression of transcription factors Hnf1β and Hnf4α in both sexes. The highest difference between lean and obese ZSF1 rats was found for Oat2. Therefore, we have tested the interaction of human OAT2 with various substances using tritium-labeled cGMP. Human OAT2 showed no interaction with diabetes-related metabolites, diabetic drugs, and ACE-inhibitors. However, OAT2-dependent uptake of cGMP was inhibited by furosemide. The strongly decreased expression of Oat2 and other transporters in female diabetic ZSF1 rats could possibly impair renal drug excretion, for example, of furosemide.

Renal transport of organic anions and cations

Organic anions and cations (OAs and OCs, respectively) comprise an extraordinarily diverse array of compounds of physiological, pharmacological, and toxicological importance. The kidney, primarily the renal proximal tubule, plays a critical role in regulating the plasma concentrations of these organic electrolytes and in clearing the body of potentially toxic xenobiotics agents, a process that involves active, transepithelial secretion. This transepithelial transport involves separate entry and exit steps at the basolateral and luminal aspects of renal tubular cells. Basolateral and luminal OA and OC transport reflects the concerted activity of a suite of separate proteins arranged in parallel in each pole of proximal tubule cells. The cloning of multiple members of several distinct transport families, the subsequent characterization of their activity, and their subcellular localization within distinct regions of the kidney, now allows the development of models describing the molecular basis of the renal secretion of OAs and OCs. New information on naturally occurring genetic variation of many of these processes provides insight into the basis of observed variability of drug efficacy and unwanted drug-drug interactions in human populations. The present review examines recent work on these issues.

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.

The gonadal hormone regulates the plasma lactate levels in type 2 diabetes treated with and without metformin

OBJECTIVE

Our previous study showed there was a gender difference in plasma lactate concentrations in subjects with type 2 diabetes. This study investigated the effect of sex hormone levels on plasma lactic acid (LA) levels in type 2 diabetes with and without metformin therapy.

SUBJECTS AND METHODS

Fasting whole blood specimens of 392 type 2 diabetes patients treated with metformin (n=199) or not (n=193) were collected. LA was measured with an enzyme-electrode assay. Levels of sex hormones, including testosterone (T) and estradiol (E(2)), were measured with a chemiluminescence microparticle immunoassay. Spearman's or Pearson's correlation and logistic regression analysis were performed for the factors associated with LA.

RESULTS

The LA level in the metformin group was significantly higher than that in the non-metformin group (1.26±0.43 vs. 1.14±0.49 mmol/L, P<0.001), and LA levels of females were significantly higher than those of males (P<0.001). LA concentrations were positively correlated with E(2) level but negatively correlated with metformin and T levels (P<0.01). The logistic regression analysis showed that gender, creatinine, E(2), metformin, and T were independent factors influencing lactate levels. Analysis of subgroups demonstrated that the LA concentrations increased with the elevation of E(2) level (P<0.05) but decreased with the rising of T level (P<0.05).

CONCLUSIONS

Sex hormones play an important role on regulating plasma lactate levels in diabetes patients treated with metformin. E(2) up-regulates but T tend to down-regulate lactate levels.

Male-dominant activation of rat renal organic anion transporter 1 (Oat1) and 3 (Oat3) expression by transcription factor BCL6

Background

Organic anion transporters 1 (Oat1) and 3 (Oat3) mediate the transport of organic anions, including frequently prescribed drugs, across cell membranes in kidney proximal tubule cells. In rats, these transporters are known to be male-dominant and testosterone-dependently expressed. The molecular mechanisms that are involved in the sex-dependent expression are unknown. Our aim was to identify genes that show a sex-dependent expression and could be involved in male-dominant regulation of Oat1 and Oat3.

Methodology/Principal Findings

Promoter activities of Oat1 and Oat3 were analyzed using luciferase assays. Expression profiling was done using a SurePrint G3 rat GE 8×60K microarray. RNA was isolated from renal cortical slices of four adult rats per sex. To filter the achieved microarray data for genes expressed in proximal tubule cells, transcription database alignment was carried out. We demonstrate that predicted androgen response elements in the promoters of Oat1 and Oat3 are not functional when the promoters were expressed in OK cells. Using microarray analyses we analyzed 17,406 different genes. Out of these genes, 56 exhibit a sex-dependent expression in rat proximal tubule cells. As genes potentially involved in the regulation of Oat1 and Oat3 expression, we identified, amongst others, the male-dominant hydroxysteroid (17-beta) dehydrogenase 1 (Hsd17b1), B-cell CLL/lymphoma 6 (BCL6), and polymerase (RNA) III (DNA directed) polypeptide G (Polr3g). Moreover, our results revealed that the transcription factor BCL6 activates promoter constructs of Oat1 and Oat3.

Conclusion

The results indicate that the male-dominant expression of both transporters, Oat1 and Oat3, is possibly not directly regulated by the classical androgen receptor mediated transcriptional pathway but appears to be regulated by the transcription factor BCL6.

LAPTM4A interacts with hOCT2 and regulates its endocytotic recruitment

Human organic cation transporter 2 (hOCT2) is involved in the transport of endogenous and exogenous organic cations mainly in cells of the kidney and the brain. Here, we focus on the regulation of hOCT2 by direct protein-protein interaction. Screening within a mating-based split-ubiquitin-yeast-two-hybrid system (mBSUS) revealed the lysosomal-associated protein transmembrane 4 alpha (LAPTM4A) as a potential interacting protein. Interaction of LAPTM4A and hOCT2 was confirmed by pulldown assays, FRET microscopy analysis and immunofluorescence microscopy. Functionally, overexpression of LAPTM4A significantly decreased ASP(+) uptake in HEK293 cells stably transfected with hOCT2, suggesting a negative regulation of hOCT2-mediated transport. Furthermore, overexpression of LAPTM4A leads to a significantly decreased hOCT2 plasma membrane expression in surface biotinylation experiments. In addition, significant expression of LAPTM4A in human kidney was demonstrated by immunoblotting and immunofluorescence.In this work, LAPTM4A has been identified as interaction partner of hOCT2. LAPTM4A regulates the function of hOCT2 by influencing its trafficking to/from the cell membrane and processing it via the intracellular sorting machinery.

Sex- and diet-specific changes of imprinted gene expression and DNA methylation in mouse placenta under a high-fat diet

BACKGROUND

Changes in imprinted gene dosage in the placenta may compromise the prenatal control of nutritional resources. Indeed monoallelic behaviour and sensitivity to changes in regional epigenetic state render imprinted genes both vulnerable and adaptable.

METHODS AND FINDINGS

We investigated whether a high-fat diet (HFD) during pregnancy modified the expression of imprinted genes and local and global DNA methylation patterns in the placenta. Pregnant mice were fed a HFD or a control diet (CD) during the first 15 days of gestation. We compared gene expression patterns in total placenta homogenates, for male and female offspring, by the RT-qPCR analysis of 20 imprinted genes. Sexual dimorphism and sensitivity to diet were observed for nine genes from four clusters on chromosomes 6, 7, 12 and 17. As assessed by in situ hybridization, these changes were not due to variation in the proportions of the placental layers. Bisulphite-sequencing analysis of 30 CpGs within the differentially methylated region (DMR) of the chromosome 17 cluster revealed sex- and diet-specific differential methylation of individual CpGs in two conspicuous subregions. Bioinformatic analysis suggested that these differentially methylated CpGs might lie within recognition elements or binding sites for transcription factors or factors involved in chromatin remodelling. Placental global DNA methylation, as assessed by the LUMA technique, was also sexually dimorphic on the CD, with lower methylation levels in male than in female placentae. The HFD led to global DNA hypomethylation only in female placenta. Bisulphite pyrosequencing showed that neither B1 nor LINE repetitive elements could account for these differences in DNA methylation.

CONCLUSIONS

A HFD during gestation triggers sex-specific epigenetic alterations within CpG and throughout the genome, together with the deregulation of clusters of imprinted genes important in the control of many cellular, metabolic and physiological functions potentially involved in adaptation and/or evolution. These findings highlight the importance of studying both sexes in epidemiological protocols and dietary interventions.

Emerging role for drug transporters at the blood-testis barrier

Drug transporters are integral membrane proteins that transport a broad range of substrates into and out of cells, usually against a concentration gradient. Studies have shown that efflux pumps such as P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) localize at the blood-testis barrier (BTB), where they protect the testis from drugs and xenobiotics that are detrimental to spermatogenesis. At the same time, efflux pumps might also preclude entry of non-hormonal contraceptives to the testis. In more recent studies, P-gp function was correlated with BTB integrity. In this review, we discuss findings that have made a significant impact on our understanding of efflux pumps in the testis. Modulation of efflux pump function via specific inhibitors could help to deliver contraceptives to the testis in the future.

SLC22A2 gene 808 G/T variant is related to plasma lactate concentration in Chinese type 2 diabetics treated with metformin

AIM

To investigate the potential relationship between the SLC22A2 gene polymorphism and blood lactate concentration in Shanghai Hans suffering from type 2 diabetes mellitus (T2DM).

METHODS

The SLC22A2 single nucleotide polymorphism (SNP) 808G/T was genotyped in 400 T2DM patients, including a metformin-treated group (n=200) and a non-metformin-treated group (n=200). Fasting plasma lactic acid levels were measured with an enzyme-electrode assay. Biochemical indexes, including plasma alanine aminotransferase (ALT), creatinine (Cr), and glycolated hemoglobin (HbA1c), were also measured.

RESULTS

The fasting plasma lactate concentration in the metformin-treated group was significantly higher than that in the non-metformin-treated group (1.29+/-0.45 mmol/L vs 1.18+/-0.44 mmol/L, P=0.015). Additionally, the ratio of patients with hyperlactacidemia was 8% (16/200) for the metformin-treated group and 5.5% (11/200) for the non-metformin-treated group, with no lactic acidosis found in either group. The frequency of the SLC22A2 808G/T T allele was 12.9%. Patients with the mutant genotype (TT) had a higher blood lactate concentration in the metformin-treated group than those in the non-metformin-treated group (t=2.492, P=0.013). This trend was not observed in the GG and GT genotypes when compared with metformin-treated and non-metformin-treated groups. Patients with the mutant genotype (TT) in the metformin-treated group also had a higher incidence of hyperlactacidemia compared with the GG genotype (40.0% vs 6.9%, P=0.050) in the metformin-treated group and the GG (6.0%, P=0.042) or GT (4.3%, P=0.043) genotypes in the non-metformin-treated group. In the metformin-treated group, there were significant gender differences in lactate concentrations in the TT (2.18+/-0.15 vs 1.04+/-0.27 mmol/L, P=0.008) and GG genotypes (1.40+/-0.51 vs 1.19+/-0.35 mmol/L, P=0.004). The lactate levels of women with the TT genotype were the highest in the metformin-treated group, but differences in lactate levels among the genotypes were not observed in the non-metformin-treated group.

CONCLUSION

There is an 808G/T polymorphism in the SLC22A2 gene in Chinese Hans with T2DM. The 808G>T variance in the SLC22A2 gene can affect the plasma lactate level and the incidence of hyperlactacidemia in T2DM patients undergoing metformin therapy. Additionally, the female patients carrying the TT genotype are prone to lactatemia.

Enhanced renal accumulation of cisplatin via renal organic cation transporter deteriorates acute kidney injury in hypomagnesemic rats

BACKGROUND

This study aimed to explore the effects of hypomagnesemia on cisplatin (CDDP)-induced acute kidney injury (AKI) in rats and the relation of hypomagnesemia to the regulation of organic cation transporters and renal accumulation of CDDP.

METHODS

Sprague-Dawley rats were given an Mg-deficient diet starting 7 days before treatment with CDDP. CDDP was administered intravenously to rats in the normal Mg-diet group and Mg-deficient-diet group at 3 mg/kg via the left jugular vein. At the specified periods after injection of CDDP, the amount of platinum in blood and organ samples was determined using inductively coupled plasma-mass spectrometry. Protein expression levels of renal organic cation transporters were determined. Uptake of tetraethylammonium (TEA) bromide in renal slices of rats was measured.

RESULTS

Rats fed a Mg-deficient diet showed a significant body weight decrease and a marked decrease in serum Mg levels compared with control rats fed an adequate Mg diet. Serum blood urea nitrogen and creatinine levels were unaltered after CDDP treatment in control rats, whereas these levels were markedly elevated in hypomagnesemic rats. Immunoblotting revealed up-regulation of the organic cation transporter rOCT2 in hypomagnesemic rats before CDDP administration, but not of rOCT1 or rat multidrug and toxin-extrusion 1. TEA uptake by renal slices from hypomagnesemic rats was significantly higher compared with that of control rats. Renal accumulation of CDDP was markedly increased in hypomagnesemic rats.

CONCLUSION

These results suggest that hypomagnesemia could cause dehydration and up-regulation of rOCT2, enhancing renal accumulation of CDDP and the deterioration of AKI.

Regulatory role of testosterone in organic cation transport: in vivo and in vitro studies

The renal proximal tubule (RPT) plays a crucial role in organic cation (OC) secretion and has a major impact on pharmacokinetics of OC drugs. Secretory transport is vectorial. Thus, it involves transporters located at both basolateral and apical membranes. Although sex hormones have been shown to regulate OC transport, there is little data on the effect of testosterone on OC secretion in a whole animal. Therefore, we determined the clearance of tetraethylammonium (TEA), a model OC substrate, in intact and castrated male mice. Castration significantly decreased renal TEA secretion by 30%, and testosterone supplementation returned TEA secretion to control levels in castrated mice. The mechanism of this effect was further examined in isolated mouse renal proximal tubules (mRPT). TEA uptake in isolated mRPT from castrated mice was reduced by 36%. This effect was reversed in tubules from castrated mice supplemented with testosterone. Kinetic analysis of [(3)H]-TEA uptake in isolated mRPT showed a decreased V(max) with no change in K(m), implying that the decrease in transport rate was caused by lowering in the number of transporters in castrated mice rather than a change in transporter affinity. Quantitative real time polymerase chain reaction (real time PCR) revealed that organic cation transporter (OCT)2 is the major TEA transporter in male mice. Moreover, OCT2 mRNA level was significantly reduced after castration. Castrated mice also showed a modest increase in organic cation/carnitine transporter 1 (OCTN1) mRNA level, indicating that testosterone may also regulate apical OCTN1 expression. These data suggest that testosterone regulates transepithelial transport of OC through modulation of OCT2 expression in male mice.

Testosterone-independent down-regulation of Oct2 in the kidney medulla from a uranyl nitrate-induced rat model of acute renal failure: effects on distribution of a model organic cation, tetraethylammonium

Although acute renal failure (ARF) has been an area of extensive research in recent decades, our understanding of ARF is far from complete. Organic cations (OCs) are primarily excreted via vectorial transport by various renal organic cation transporters (OCTs). It is reasonable to assume that ARF may alter the expression profiles of these transporters. In a rat ARF model, induction of ARF by uranyl nitrate (UN) treatment significantly decreased the levels of Oct2 (slc22a2) mRNA and protein in the kidney medulla. mRNA expression of the other OCTs was not appreciably altered. The plasma level of testosterone, a well-known regulator of Oct2, was not changed, suggesting that the Oct2 down-regulation is testosterone-independent. The effect of reduced Oct2 expression on the distribution of a model OC, tetraethylammonium (TEA), in various rat tissues including kidney cortex and kidney medulla was investigated during steady state plasma TEA concentrations. The steady state tissue-to-plasma (T/P) TEA ratio was decreased in the kidney medulla (approximately 15-fold) during ARF. These results indicate that, in a rat model of ARF, reduced Oct2 expression in the kidney medulla results in decreased distribution of TEA to the kidney medulla, thereby reducing renal clearance of TEA in UN-ARF rats.

Regulation of basal core promoter activity of human organic cation transporter 1 (OCT1/SLC22A1)

Human organic cation transporter 1 (OCT1/SLC22A1) plays important roles in the hepatic uptake of cationic drugs. The functional characteristics of this transporter have been well evaluated, but molecular information regarding transcriptional regulation is limited. In the present study, therefore, we examined the gene regulation of OCT1 gene focusing on basal core expression. An approximately 2.5-kb fragment of the OCT1 promoter region was isolated, and promoter activity was measured by luciferase assay in the human liver cell lines Huh7 and HepG2. Deletion analysis suggested that the region spanning -141/-69 was essential for the basal core transcriptional activity and that this region contained the sequence of a cognate E-box (CACGTG). The E-box is known to be bound by the basal transcription factors, upstream stimulating factors (USFs), and the functional involvements of USF1 and USF2 were confirmed by a transactivation effect, a mutational analysis of the E-box, and an electrophoretic mobility shift assay. The transactivation effect of USFs on the OCT1 promoter was further stimulated by hepatocyte nuclear factor 4alpha, a liver-enriched transcription factor. There were no polymorphisms in the proximal promoter region (about 400 bp) of OCT1 gene (n = 109). These findings indicated that both USF1 and USF2 bind to an E-box sequence located in the OCT1 core promoter region and are required for the basal gene expression of this transporter.

Organic cation transporters

1. Organic cation transporters (OCTs) translocate endogenous (e.g. dopamine) and exogenous (e.g. drugs) substances of cationic nature and, therefore, play an important role in the detoxification of exogenous compounds. This review aims to furnish essential information on OCTs, with an emphasis on pharmacological aspects. 2. Analysis of the literature on OCTs makes clear that there is a species- and organ-specific distribution of the different isoforms, which can also be differentially regulated. OCTs are responsible for the excretion and/or distribution of many drugs and also for serious tissue-specific side-effects such as cisplatin-induced nephrotoxicity. The presence of single nucleotide polymorphisms in these transporters significantly influences the response of patients to medication, as demonstrated for the antidiabetic drug metformin. 3. A substantial amount of research has to be undertaken to clarify further the OCT structure-function relationships specifically to define the role of oligomerization on their activity and regulation, to identify intracellular interaction partners of OCTs, and to characterize their pharmacogenetic aspects.

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

PURPOSE

To investigate the effect of 17alpha-ethynylestradiol (EE)-induced cholestasis on the expression of organic cation transporters (Octs) in the liver and kidney, as well as the pharmacokinetics and pharmacodynamics of metformin in rats.

METHODS

Octs mRNA and protein expression were determined. The pharmacokinetics and tissue uptake clearance of metformin were determined following iv administration (5 mg/kg). Uptake of metformin, glucagon-mediated glucose production, and AMP-activated protein kinase (AMPK) activation were measured in isolated hepatocytes. The effect of metformin (30 mg/kg) on blood glucose levels was tested using the iv glucose tolerance test (IVGTT).

RESULTS

The mRNAs of hepatic Oct1, renal Oct1, and Oct2 were decreased by 71.1%, 37.6%, and 94.5%, respectively, by EE cholestasis. The hepatic Oct1 and renal Oct2 proteins were decreased by 30.6% and 60.2%, respectively. The systemic and renal clearance of metformin were decreased. The in vitro hepatocyte uptake of metformin was decreased by 86.4% for V (max). Suppression of glucagon-stimulated glucose production and stimulation of AMPK activation in hepatocytes by metformin were diminished. In addition, metformin did not demonstrate a glucose-lowering effect during IVGTT in EE cholestasis.

CONCLUSION

The antidiabetic effect of metformin may be diminished in diabetic patients with EE cholestasis, due to impaired hepatic uptake of the drug via OCT1.

Kidney-specific expression of human organic cation transporter 2 (OCT2/SLC22A2) is regulated by DNA methylation

Human organic cation transporter 2 (OCT2/SLC22A2), which is specifically expressed in the kidney, plays critical roles in the renal secretion of cationic compounds. Tissue expression and membrane localization of OCT2 are closely related to the tissue distribution, pharmacological effects, and/or adverse effects of its substrate drugs. However, the molecular mechanisms underlying the kidney-specific expression of OCT2 have not been elucidated. In the present study, therefore, we examined the contribution of DNA methylation of the promoter region for the OCT2 gene to its tissue-specific expression using human tissue samples. In vivo methylation status of the proximal promoter region of OCT2 and that of OCT1, a liver-specific organic cation transporter, were investigated by bisulfite sequencing using human genomic DNA extracted from the kidney and liver. All CpG sites in the OCT2 proximal promoter were hypermethylated in the liver, while hypomethylated in the kidney. On the other hand, the promoter region of OCT1 was hypermethylated in both the kidney and liver. The level of methylation of the OCT2 promoter was especially low at the CpG site in the E-box, the binding site of the basal transcription factor upstream stimulating factor (USF) 1. In vitro methylation of the OCT2 proximal promoter dramatically reduced the transcriptional activity, and an electrophoretic mobility shift assay showed that methylation at the E-box inhibited the binding of USF1. These results indicate that kidney-specific expression of human OCT2 is regulated by methylation of the proximal promoter region, interfering with the transactivation by USF1.

Physiological and pharmacokinetic roles of H+/organic cation antiporters (MATE/SLC47A)

Vectorial secretion of cationic compounds across tubular epithelial cells is an important function of the kidney. This uni-directed transport is mediated by two cooperative functions, which are membrane potential-dependent organic cation transporters at the basolateral membranes and H+/organic cation antiporters at the brush-border membranes. More than 10 years ago, the basolateral organic cation transporters (OCT1-3/SLC22A1-3) were isolated, and molecular understandings for the basolateral entry of cationic drugs have been greatly advanced. However, the molecular nature of H+/organic cation antiport systems remains unclear. Recently, mammalian orthologues of the multidrug and toxin extrusion (MATE) family of bacteria have been isolated and clarified to function as H+/organic cation antiporters. In this commentary, the molecular characteristics and pharmacokinetic roles of mammalian MATEs are critically overviewed focusing on the renal secretion of cationic drugs.

Critical roles of Sp1 in gene expression of human and rat H+/organic cation antiporter MATE1

A H+/organic cation antiporter (multidrug and toxin extrusion 1: MATE1/SLC47A1) plays important roles in the tubular secretion of various clinically important cationic drugs such as cimetidine. We have recently found that the regulation of this transporter greatly affects the pharmacokinetic properties of cationic drugs in vivo. No information is available about the regulatory mechanisms for the MATE1 gene. In the present study, therefore, we examined the gene regulation of human (h) and rat (r) MATE1, focusing on basal expression. A deletion analysis suggested that the regions spanning -65/-25 and -146/-38 were essential for the basal transcriptional activity of the hMATE1 and rMATE1 promoter, respectively, and that both regions contained putative Sp1-binding sites. Functional involvement of Sp1 was confirmed by Sp1 overexpression, a mutational analysis of Sp1-binding sites, mithramycin A treatment, and an electrophoretic mobility shift assay. Furthermore, we found a single nucleotide polymorphism (SNP) in the promoter region of hMATE1 (G-32A), which belongs to a Sp1-binding site. The allelic frequency of this rSNP was 3.7%, and Sp1-binding and promoter activity were significantly decreased. This is the first study to clarify the transcriptional mechanisms of the MATE1 gene and to identify a SNP affecting the promoter activity of hMATE1.

Influence of estrogen and xenoestrogens on basolateral uptake of tetraethylammonium by opossum kidney cells in culture

The sex steroid hormone estrogen down-regulates renal organic cation (OC) transport in animals, and it may contribute to sex-related differences in xenobiotic accumulation and excretion. Also, the presence of various endocrine-disrupting chemicals, i.e., environmental chemicals that possess estrogenic activity (e.g., xenoestrogens) may down-regulate various transporters involved in renal accumulation and excretion of xenobiotics. The present study characterizes the mechanism by which long-term (6-day) incubation with physiological concentrations of 17beta-estradiol (E(2)) or the xenoestrogens diethylstilbestrol (DES) and bisphenol A (BPA) regulates the basolateral membrane transport of the OC tetraethylammonium (TEA) in opossum kidney (OK) cell renal cultures. Both 17beta-E(2) and the xenoestrogen DES produced a dose- and time-dependent inhibition of basolateral TEA uptake in OK cell cultures, whereas the weakly estrogenic BPA had no effect on TEA uptake. Treatment for 6 days with either 1 nM 17beta-E(2) or DES reduced TEA uptake by approximately 30 and 40%, respectively. These effects were blocked completely by the estrogen receptor antagonist ICI 182780 (Faslodex, fulvestrant), suggesting that these estrogens regulate OC transport through the estrogen receptor, which was detected (estrogen receptor alpha) in OK cell cultures by reverse transcription-polymerase chain reaction. The J(max) value for TEA uptake in 17beta-E(2)- and DES-treated OK cell cultures was approximately 40 to 50% lower than for ethanol-treated cultures, whereas K(t) was unaffected. This reduction in transport capacity was correlated with a reduction in OC transporter OCT1 protein expression following treatment with both agents.

Gender differences in kidney function

Sex hormones influence the development of female (F) and male (M) specific traits and primarily affect the structure and function of gender-specific organs. Recent studies also indicated their important roles in regulating structure and/or function of nearly every tissue and organ in the mammalian body, including the kidneys, causing gender differences in a variety of characteristics. Clinical observations in humans and studies in experimental animals in vivo and in models in vitro have shown that renal structure and functions under various physiological, pharmacological, and toxicological conditions are different in M and F, and that these differences may be related to the sex-hormone-regulated expression and action of transporters in the apical and basolateral membrane of nephron epithelial cells. In this review we have collected published data on gender differences in renal functions, transporters and other related parameters, and present our own microarray data on messenger RNA expression for various transporters in the kidney cortex of M and F rats. With these data we would like to emphasize the importance of sex hormones in regulation of a variety of renal transport functions and to initiate further studies of gender-related differences in kidney structure and functions, which would enable us to better understand occurrence and development of various renal diseases, pharmacotherapy, and drug-induced nephrotoxicity in humans and animals.

Polyspecific organic cation transporters: structure, function, physiological roles, and biopharmaceutical implications

The body is equipped with broad-specificity transporters for the excretion and distribution of endogeneous organic cations and for the uptake, elimination and distribution of cationic drugs, toxins and environmental waste products. This group of transporters consists of the electrogenic cation transporters OCT1-3 (SLC22A1-3), the cation and carnitine transporters OCTN1 (SLC22A4), OCTN2 (SLC22A5) and OCT6 (SLC22A16), and the proton/cation antiporters MATE1, MATE2-K and MATE2-B. The transporters show broadly overlapping sites of expression in many tissues such as small intestine, liver, kidney, heart, skeletal muscle, placenta, lung, brain, cells of the immune system, and tumors. In epithelial cells they may be located in the basolateral or luminal membranes. Transcellular cation movement in small intestine, kidney and liver is mediated by the combined action of electrogenic OCT-type uptake systems and MATE-type efflux transporters that operate as cation/proton antiporters. Recent data showed that OCT-type transporters participate in the regulation of extracellular concentrations of neurotransmitters in brain, mediate the release of acetylcholine in non-neuronal cholinergic reactions, and are critically involved in the regulation of histamine release from basophils. The recent identification of polymorphisms in human OCTs and OCTNs allows the identification of patients with an increased risk for adverse drug reactions. Transport studies with expressed OCTs will help to optimize pharmacokinetics during development of new drugs.

Polyspecific organic cation transporters: structure, function, physiological roles, and biopharmaceutical implications

The body is equipped with broad-specificity transporters for the excretion and distribution of endogeneous organic cations and for the uptake, elimination and distribution of cationic drugs, toxins and environmental waste products. This group of transporters consists of the electrogenic cation transporters OCT1-3 (SLC22A1-3), the cation and carnitine transporters OCTN1 (SLC22A4), OCTN2 (SLC22A5) and OCT6 (SLC22A16), and the proton/cation antiporters MATE1, MATE2-K and MATE2-B. The transporters show broadly overlapping sites of expression in many tissues such as small intestine, liver, kidney, heart, skeletal muscle, placenta, lung, brain, cells of the immune system, and tumors. In epithelial cells they may be located in the basolateral or luminal membranes. Transcellular cation movement in small intestine, kidney and liver is mediated by the combined action of electrogenic OCT-type uptake systems and MATE-type efflux transporters that operate as cation/proton antiporters. Recent data showed that OCT-type transporters participate in the regulation of extracellular concentrations of neurotransmitters in brain, mediate the release of acetylcholine in non-neuronal cholinergic reactions, and are critically involved in the regulation of histamine release from basophils. The recent identification of polymorphisms in human OCTs and OCTNs allows the identification of patients with an increased risk for adverse drug reactions. Transport studies with expressed OCTs will help to optimize pharmacokinetics during development of new drugs.

Characterization of the Basal promoter element of human organic cation transporter 2 gene

Human organic cation transporter 2 (hOCT2; SLC22A2) is abundantly expressed in the kidney, and it plays important roles in the renal tubular secretion of cationic drugs. Although the transport characteristics of hOCT2 have been studied extensively, there is no information available for the transcriptional regulation of hOCT2. The present study was undertaken to identify the cis-element and trans-factor for basal expression of hOCT2. The transcription start site was located 385 nucleotides above the translation start site by using 5'-rapid amplification of cDNA ends. An approximately 4-kilobase fragment of the hOCT2 promoter region was isolated and the promoter activities were measured in the renal epithelial cell line LLC-PK1. A deletion analysis suggested that the region spanning -91 to -58 base pairs was essential for basal transcriptional activity. This region lacked a TATA-box but contained a CCAAT box and an E-box. Electrophoretic mobility shift assays showed that specific DNA/protein complexes were present in the E-box but not in the CCAAT box, and supershift assays revealed that upstream stimulatory factor 1 (USF-1), which belongs to the basic helix-loop-helix-leucine zipper family of transcription factors, bound to the E-box. Mutation of the E-box resulted in a decrease in hOCT2 promoter activity, and overexpression of USF-1 enhanced the hOCT2 promoter activity in a dose-dependent manner. This article reports the first characterization of the hOCT2 promoter and shows that USF-1 functions as a basal transcriptional regulator of the hOCT2 gene via the E-box.

Gene expression and regulation of drug transporters in the intestine and kidney

Intestinal absorption and renal secretion of ionic drugs are controlled by a number of drug transporters expressed at the brush-border and basolateral membranes of epithelial cells. Over the last several years, considerable progress has been made regarding the molecular identification and functional characterization of drug transporters. Under some physiological and pathophysiological conditions, the expression and transport activity of drug transporters are changed, affecting the pharmacokinetics of substrate drugs. The regulation of transport activity in response to endogenous and exogenous signals can occur at various levels such as transcription, mRNA stability, translation, and posttranslational modification. Transcriptional regulation is of particular interest, because changes in transport activity are dynamically regulated by increases or decreases in levels of mRNA expression. The tissue-specific expression of drug transporters is also under transcriptional control, and recent studies using clinical samples from human tissues have revealed the expression profiles of drug transporters in the human body. The purpose of this research updates is to review the recent progress in the study of the gene expression and regulation of intestinal and renal drug transporters.