Drug uptake systems in liver and kidney: a historic perspective. Clin Pharmacol Ther. 2010;87:39-47. [PMID: 19924123 DOI: 10.1038/clpt.2009.235]

Renal interstitial permeability changes induced by microbubble-enhanced diagnostic ultrasound

Ultrasound-targeted microbubble (MB) destruction (UTMD) has been shown to increase the glomerular permeability, providing a potential novel therapeutic approach in targeted drug release for kidney diseases. Therefore, we investigated the impact of UTMD on renal interstitial permeability using MB-mediated diagnostic ultrasound (DUS). The left kidney of Sprague-Dawley (SD) rat was insonated by UTMD with either continuous or intermittent mode for 5 min. Evans blue (EB) revealed that both modes induced renal vascular permeability increase after DUS but recovered after 24 h. Intermittent insonation caused more severe injury than continuous mode. Red blood cells leaked out of the capillaries into interstitium without glomerular capillary hemorrhage (GCH) by hematoxylin and eosin (HE) staining. Electronic microscopy revealed the disruption of focal capillary wall in interstitial tissues. Morphological results confirmed capillary wall recovered in 24 h post-treatment. Results from fluorescence-labeled MBs showed that MBs were mainly localized in the interstitial portion of the tubular region and retained at 24 h. Intriguingly, urinalysis showed no clinical proteinuria after treatment. Our results indicated that MB plus DUS specifically and reversibly enhanced the interstitial permeability without affecting glomerulus, which may be developed into a therapeutic approach for targeting drug release to individual renal compartments.

Gene expression variability in human hepatic drug metabolizing enzymes and transporters

Interindividual variability in the expression of drug-metabolizing enzymes and transporters (DMETs) in human liver may contribute to interindividual differences in drug efficacy and adverse reactions. Published studies that analyzed variability in the expression of DMET genes were limited by sample sizes and the number of genes profiled. We systematically analyzed the expression of 374 DMETs from a microarray data set consisting of gene expression profiles derived from 427 human liver samples. The standard deviation of interindividual expression for DMET genes was much higher than that for non-DMET genes. The 20 DMET genes with the largest variability in the expression provided examples of the interindividual variation. Gene expression data were also analyzed using network analysis methods, which delineates the similarities of biological functionalities and regulation mechanisms for these highly variable DMET genes. Expression variability of human hepatic DMET genes may affect drug-gene interactions and disease susceptibility, with concomitant clinical implications.

Gene expression profiling of transporters in the solute carrier and ATP-binding cassette superfamilies in human eye substructures

The barrier epithelia of the cornea and retina control drug and nutrient access to various compartments of the human eye. While ocular transporters are likely to play a critical role in homeostasis and drug delivery, little is known about their expression, localization and function. In this study, the mRNA expression levels of 445 transporters, metabolic enzymes, transcription factors and nuclear receptors were profiled in five regions of the human eye: cornea, iris, ciliary body, choroid and retina. Through RNA expression profiling and immunohistochemistry, several transporters were identified as putative targets for drug transport in ocular tissues. Our analysis identified SLC22A7 (OAT2), a carrier for the antiviral drug acyclovir, in the corneal epithelium, in addition to ABCG2 (BCRP), an important xenobiotic efflux pump, in retinal nerve fibers and the retinal pigment epithelium. Collectively, our results provide an understanding of the transporters that serve to maintain ocular homeostasis and which may be potential targets for drug delivery to deep compartments of the eye.

The promiscuous binding of pharmaceutical drugs and their transporter-mediated uptake into cells: what we (need to) know and how we can do so

A recent paper in this journal sought to counter evidence for the role of transport proteins in effecting drug uptake into cells, and questions that transporters can recognize drug molecules in addition to their endogenous substrates. However, there is abundant evidence that both drugs and proteins are highly promiscuous. Most proteins bind to many drugs and most drugs bind to multiple proteins (on average more than six), including transporters (mutations in these can determine resistance); most drugs are known to recognise at least one transporter. In this response, we alert readers to the relevant evidence that exists or is required. This needs to be acquired in cells that contain the relevant proteins, and we highlight an experimental system for simultaneous genome-wide assessment of carrier-mediated uptake in a eukaryotic cell (yeast).

Expression and function of renal and hepatic organic anion transporters in extrahepatic cholestasis

Obstructive jaundice occurs in patients suffering from cholelithiasis and from neoplasms affecting the pancreas and the common bile duct. The absorption, distribution and elimination of drugs are impaired during this pathology. Prolonged cholestasis may alter both liver and kidney function. Lactam antibiotics, diuretics, non-steroidal anti-inflammatory drugs, several antiviral drugs as well as endogenous compounds are classified as organic anions. The hepatic and renal organic anion transport pathways play a key role in the pharmacokinetics of these compounds. It has been demonstrated that acute extrahepatic cholestasis is associated with increased renal elimination of organic anions. The present work describes the molecular mechanisms involved in the regulation of the expression and function of the renal and hepatic organic anion transporters in extrahepatic cholestasis, such as multidrug resistance-associated protein 2, organic anion transporting polypeptide 1, organic anion transporter 3, bilitranslocase, bromosulfophthalein/bilirubin binding protein, organic anion transporter 1 and sodium dependent bile salt transporter. The modulation in the expression of renal organic anion transporters constitutes a compensatory mechanism to overcome the hepatic dysfunction in the elimination of organic anions.

Patulin in apple juice and its risk assessments on albino mice

The contamination of apple juice with patulin mycotoxin is a major risk factor in food safety. This study focuses to assess the biochemical and histopathological effects of patulin in apple juice samples collected from different outlets retailing in Jeddah, Kingdom of Saudi Arabia. On the basis of the selected dose level, 152.5 ppb patulin/ml was administered daily orally for up to 6 weeks to male albino mice. The exposure to contaminated samples revealed significant elevation of all the studied blood parameters (alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase activities as well as creatinine, urea and uric acid contents). On the other hand, and with regard to the accumulated neuronal toxicity of the tested dose level, the toxic signs were recorded as significant increase in the aggressive and locomotor behavioral changes. In addition, the brain areas monoamines concentration revealed variable increased changes. The potential maximal changes in norepinephrine, dopamine and serotonin5-hydroxytryptamine levels attained in cortex, hypothalamus, striatum, hippocampus, midbrain and pons and medulla were assessed. Moreover, the histological examination revealed degeneration and necrosis in liver tissues and degenerated glomeruli and hemorrhage between the tubules of the cortical region in kidney tissues. The study declared that patulin-contaminated (152.5 ppb) apple juice exhibited liver, kidney and neurotoxicological effects in 6 weeks orally administered mice.

A perspective on efflux transport proteins in the liver

Detailed knowledge regarding the influence of hepatic transport proteins on drug disposition has advanced at a rapid pace over the past decade. Efflux transport proteins located in the basolateral and apical (canalicular) membranes of hepatocytes play an important role in the hepatic elimination of many endogenous and exogenous compounds, including drugs and metabolites. This review focuses on the role of these efflux transporters in hepatic drug excretion. The impact of these proteins as underlying factors for disease is highlighted, and the importance of hepatic efflux proteins in the efficacy and toxicity of drugs is discussed. In addition, a brief overview of methodology to evaluate the function of hepatic efflux transport proteins is provided. Current challenges in predicting the impact of altered efflux protein function on systemic, intestinal, and hepatocyte exposure to drugs and metabolites are highlighted.

Current understanding of hepatic and intestinal OATP-mediated drug-drug interactions

At present, many patients are medicated with various drugs, which are, at the same time, associated with an increased risk of drug-drug interactions (DDIs). Detailed analysis of mechanisms underlying DDIs is the basis of a better prediction of adverse drug events caused by drug interactions. In the last few decades, an involvement of transporters in such processes has been more and more recognized. Indeed, uptake transporters belonging to the organic anion-transporting polypeptide (OATP) family have been shown to interact with a variety of drugs in clinical use. Particularly, the subfamily of OATP1B transporters has been extensively studied, identifying several clinical significant DDIs based on those hepatic uptake transporters. By contrast, the role of OATP2B1 in this context is rather underestimated. Therefore, in addition to known interactions based on OATP1B transporters, we have focused on DDIs probably based on OATP2B1 inhibition in the liver and those possibly owing to the inhibition of OATP2B1-mediated drug absorption in the intestine.

Tissue distribution and phenobarbital induction of target SLC- and ABC- transporters in cattle

In veterinary pharmaco-toxicological sciences, few data about uptake and efflux drug transporters (DTs) expression and regulation phenomena have been published. In this study, the tissue distribution and transcriptional modulation of solute carrier (SLC) and ATP-binding cassette (ABC) DTs were investigated in cattle orally administered with phenobarbital (PB) by using a quantitative real-time RT-PCR approach. The criterion for target gene selection was the PB-responsiveness in human and rodent model species. All target DTs were expressed in the liver. Only two of the seven PB-responsive target DTs (SLCO1B3 and SLC10A1) were not constitutively expressed in cattle extra-hepatic tissues. The greatest number of DTs (SLCO2B1, ABCB1, ABCC2, ABCG2) were expressed in intestine and testis, followed by, adrenal gland (SLCO2B1, ABCB1, ABCG2), lung (ABCB1, ABCG2), kidney, and skeletal muscle (ABCG2). PB administration never altered DTs mRNA levels, except for an increase in hepatic ABCC2 mRNA and a down-regulation of renal ABCG2. Altogether, these results confirm only to some extent data obtained in humans and laboratory species; clearly, they should be considered a preliminary step for further molecular investigations about species-differences in DT gene expression and regulation as well as in DT expression and function.

In vivo biodistribution and small animal PET of (64)Cu-labeled antimicrobial peptoids

Peptoids are a rapidly developing class of biomimetic polymers based on oligo-N-substituted glycine backbones, designed to mimic peptides and proteins. Inspired by natural antimicrobial peptides, a group of cationic amphipathic peptoids has been successfully discovered with potent, broad-spectrum activity against pathogenic bacteria; however, there are limited studies to address the in vivo pharmacokinetics of the peptoids. Herein, (64)Cu-labeled DOTA conjugates of three different peptoids and two control peptides were synthesized and assayed in vivo by both biodistribution studies and small animal positron emission tomography (PET). The study was designed in a way to assess how structural differences of the peptidomimetics affect in vivo pharmacokinetics. As amphipathic molecules, major uptake of the peptoids occurred in the liver. Increased kidney uptake was observed by deleting one hydrophobic residue in the peptoid, and (64)Cu-3 achieved the highest kidney uptake of all the conjugates tested in this study. In comparison to peptides, our data indicated that peptoids had general in vivo properties of higher tissue accumulation, slower elimination, and higher in vivo stability. Different administration routes (intravenous, intraperitoneal, and oral) were investigated with peptoids. When administered orally, the peptoids showed poor bioavailability, reminiscent of that of peptide. However, remarkably longer passage through the gastrointestinal (GI) tract without rapid digestion was observed for peptoids. These unique in vivo properties of peptoids were rationalized by efficient cellular membrane permeability and protease resistance of peptoids. The results observed in the biodistribution studies could be confirmed by PET imaging, which provides a reliable way to evaluate in vivo pharmacokinetic properties of peptoids noninvasively and in real time. The pharmacokinetic data presented here can provide insight for further development of the antimicrobial peptoids as pharmaceuticals.

Nuclear receptors in the multidrug resistance through the regulation of drug-metabolizing enzymes and drug transporters

Chemotherapy is one of the three most common treatment modalities for cancer. However, its efficacy is limited by multidrug resistant cancer cells. Drug metabolizing enzymes (DMEs) and efflux transporters promote the metabolism, elimination, and detoxification of chemotherapeutic agents. Consequently, elevated levels of DMEs and efflux transporters reduce the therapeutic effectiveness of chemotherapeutics and, often, lead to treatment failure. Nuclear receptors, especially pregnane X receptor (PXR, NR1I2) and constitutive androstane activated receptor (CAR, NR1I3), are increasingly recognized for their role in xenobiotic metabolism and clearance as well as their role in the development of multidrug resistance (MDR) during chemotherapy. Promiscuous xenobiotic receptors, including PXR and CAR, govern the inducible expressions of a broad spectrum of target genes that encode phase I DMEs, phase II DMEs, and efflux transporters. Recent studies conducted by a number of groups, including ours, have revealed that PXR and CAR play pivotal roles in the development of MDR in various human carcinomas, including prostate, colon, ovarian, and esophageal squamous cell carcinomas. Accordingly, PXR/CAR expression levels and/or activation statuses may predict prognosis and identify the risk of drug resistance in patients subjected to chemotherapy. Further, PXR/CAR antagonists, when used in combination with existing chemotherapeutics that activate PXR/CAR, are feasible and promising options that could be utilized to overcome or, at least, attenuate MDR in cancer cells.

Contribution of tumoral and host solute carriers to clinical drug response

Members of the solute carrier family of transporters are responsible for the cellular uptake of a broad range of endogenous compounds and xenobiotics in multiple tissues. Several of these solute carriers are known to be expressed in cancer cells or cancer cell lines, and decreased cellular uptake of drugs potentially contributes to the development of resistance. As result, the expression levels of these proteins in humans have important consequences for an individual's susceptibility to certain drug-induced side effects, interactions, and treatment efficacy. In this review article, we provide an update of this rapidly emerging field, with specific emphasis on the direct contribution of solute carriers to anticancer drug uptake in tumors, the role of these carriers in regulation of anticancer drug disposition, and recent advances in attempts to evaluate these proteins as therapeutic targets.

Engineering of affibody molecules for therapy and diagnostics

Affibody molecules are small and robust non-immunoglobulin affinity ligands capable of binding to a wide range of protein targets. They are selected from combinatorial libraries based on a 58 amino acid, three-alpha-helical Z-domain scaffold. They share no sequence or structural homologies to antibodies and in contrast to antibodies they can be functionally produced both by peptide synthesis and by recombinant expression in Escherichia coli. Protein engineering is used to adapt Affibody molecules binding to a target of interest to the specific demands imposed by the intended application. Obviously, the optimal molecule for molecular imaging will be different from the optimal molecule for therapy. Here, we describe general strategies to optimize Affibody molecules for diagnostic imaging and therapy applications.

Pharmacokinetics of the soluble guanylate cyclase activator cinaciguat in individuals with hepatic impairment

Cinaciguat is intended for use in patients with acute decompensated heart failure. The drug is eliminated predominantly via the liver and, therefore, the potential impact of hepatic impairment on cinaciguat pharmacokinetics needs to be determined. This nonrandomized, open-label, observational study investigated the pharmacokinetics of cinaciguat in individuals with mild (Child-Pugh A; n = 8) or moderate (Child-Pugh B; n = 8) hepatic impairment and matched healthy volunteers (n = 16). An exploratory analysis of pharmacodynamic parameters was also conducted. Individuals with mild hepatic impairment and their controls received a single (4-hour) intravenous infusion of 100 µg/h cinaciguat, whereas individuals with moderate hepatic impairment and their controls received 50 µg/h. Cinaciguat was well tolerated and had a favorable safety profile. The most frequent treatment-emergent adverse events were headache (4 participants) and spontaneous penile erection (2 participants). In individuals with mild hepatic impairment, only minor increases in plasma cinaciguat concentrations and no significant differences in pharmacodynamic parameters were observed, compared with controls. Individuals with moderate hepatic impairment had a substantially higher cinaciguat exposure than controls. This higher exposure was associated with more pronounced vasodilatation. This study demonstrates that in individuals with mild hepatic impairment, individual dose adaptation may not be required.

Functions of OATP1A and 1B transporters in vivo: insights from mouse models

Organic anion-transporting polypeptides (OATPs) are a superfamily of uptake transporters that mediate the cellular uptake of a broad range of endogenous and exogenous compounds. Of these OATP transporters, members of the 1A and 1B subfamilies have broad substrate specificities. Because they are mainly expressed in liver, kidney and small intestine, OATP1A and 1B transporters can have a major impact on the pharmacokinetics of many drugs. To study their role in physiology and drug disposition, several mouse models lacking functional expression of one or more OATPs have been generated. This review discusses recent findings for these models that have led to new insights into the impact of OATP1A and 1B transporters on pharmacokinetics and toxicokinetics, and on bilirubin detoxification and bile acid handling in normal liver physiology.

Dendrimer-based macromolecular conjugate for the kidney-directed delivery of a multitargeted sunitinib analogue

The development of a macromolecular conjugate of a multitargeted tyrosine kinase inhibitor is described that can be used for renal-specific delivery into proximal tubular cells. A novel sunitinib analogue, that is, 17864, is conjugated to a NH(2) -PAMAM-G3 dendrimer via the platinum (II)-based Universal Linkage System (ULS™). The activity of 17864 is retained after coordination to the ULS linker alone or when coupled to NH(2) -PAMAM-G3. 17864-UlS-NH(2) -PAMAM-G3 is non-toxic to proximal tubular cells in vitro. After intravenous administration to mice, 17864-UlS-NH(2) -PAMAM-G3 rapidly and efficiently accumulates in the kidneys. These results are encouraging for future studies focusing on the development of novel therapeutics for the treatment of renal diseases.

Increased exposure of phosphatidylethanolamine on the surface of tumor vascular endothelium

We have previously shown that oxidative stress within the tumor microenvironment causes phosphatidylserine (PS) to redistribute from the inner to the outer membrane leaflet of the endothelial cells (EC) creating a highly specific marker for the tumor vasculature. Because the distribution of phosphatidylethanolamine (PE) and PS within the membrane is coregulated, we reasoned that PE would also be localized in the outer membrane leaflet of tumor EC. To demonstrate this, the PE-binding peptide duramycin was biotinylated and used to determine the distribution of PE on EC in vitro and in vivo. Exposure of cultured EC to hypoxia, acidity, reactive oxygen species, or irradiation resulted in the formation of membrane blebs that were intensely PE-positive. When biotinylated duramycin was intravenously injected into tumor-bearing mice, it preferentially localized to the luminal surface of the vascular endothelium. Depending on tumor type, 13% to 56% of the tumor vessels stained positive for PE. PE-positive vessels were observed in and around hypoxic regions of the tumor. With the exception of intertubular vessels of the kidney, normal vessels remained unstained. To test the potential of PE as a biomarker for imaging, duramycin was conjugated to the near-infrared fluorophore 800CW and used for optical imaging of RM-9 prostate carcinomas. The near-infrared probe was easily detected within tumors in live animals. These results show that PE, like PS, becomes exposed on tumor vascular endothelium of multiple types of tumors and holds promise as a biomarker for noninvasive imaging and drug targeting.

Transport processes of radiopharmaceuticals and -modulators

Radiotherapy and radiology have been indispensable components in cancer care for many years. The detection limit of small tumor foci as well as the development of radio-resistance and severe side effects towards normal tissues led to the development of strategies to improve radio-diagnostic and -therapeutic approaches by pharmaceuticals. The term "radiopharmaceutical" has been used for drugs labeled with radioactive tracers for therapy or diagnosis. In addition, drugs have been described to sensitize tumor cells to radiotherapy (radiosensitizers) or to protect normal tissues from detrimental effects of radiation (radioprotectors). The present review summarizes recent concepts on the transport of radiopharmaceuticals, radiosensitizers, and radioprotectors in cells and tissues, e.g. by ATP-binding cassette transporters such as P-glycoprotein. Strengths and weaknesses of current strategies to improve transport-based processes are discussed.

Substrate recognition and translocation by polyspecific organic cation transporters

Organic cation transporters (OCTs) of the SLC22 family play a pivotal role in distribution and excretion of cationic drugs. They mediate electrogenic translocation of cations in both directions. OCTs are polyspecific transporters. During substrate translocation they perform a series of conformational changes involving an outward-facing conformation, an occluded state and an inward-facing conformation. Mutagenesis of OCT1 in combination with homology modeling showed that identical amino acids form the innermost parts of the outward-open and inward-open binding clefts. In addition to low affinity substrate binding sites, OCT1 contains high affinity substrate binding sites that can mediate inhibition via non-transported compounds.

Pharmaceutical drug transport: the issues and the implications that it is essentially carrier-mediated only

All cells necessarily contain tens, if not hundreds, of carriers for nutrients and intermediary metabolites, and the human genome codes for more than 1000 carriers of various kinds. Here, we illustrate using a typical literature example the widespread but erroneous nature of the assumption that the 'background' or 'passive' permeability to drugs occurs in the absence of carriers. Comparison of the rate of drug transport in natural versus artificial membranes shows discrepancies in absolute magnitudes of 100-fold or more, with the carrier-containing cells showing the greater permeability. Expression profiling data show exactly which carriers are expressed in which tissues. The recognition that drugs necessarily require carriers for uptake into cells provides many opportunities for improving the effectiveness of the drug discovery process.

Characterization of organic anion-transporting polypeptide (Oatp) 1a1 and 1a4 null mice reveals altered transport function and urinary metabolomic profiles

Organic anion-transporting polypeptides (Oatp) 1a1 and 1a4 were deleted by homologous recombination, and mice were characterized for Oatp expression in liver and kidney, transport in isolated hepatocytes, in vivo disposition of substrates, and urinary metabolomic profiles. Oatp1a1 and Oatp1a4 proteins were undetected in liver, and both lines were viable and fertile. Hepatic constitutive messenger RNAs (mRNAs) for Oatp1a4, 1b2, or 2b1 were unchanged in Oatp1a1⁻/⁻ mice, whereas renal Oatp1a4 mRNA decreased approximately 50% (both sexes). In Oatp1a4⁻/⁻ mice, no changes in constitutive mRNAs for other Oatps were observed. Uptake of estradiol-17β-D-glucuronide and estrone-3-sulfate in primary hepatocytes decreased 95 and 75%, respectively, in Oatp1a1⁻/⁻ mice and by 60 and 30%, respectively, in Oatp1a4⁻/⁻ mice. Taurocholate uptake decreased by 20 and 50% in Oatp1a1⁻/⁻ and Oatp1a4⁻/⁻ mice, respectively, whereas digoxin was unaffected. Plasma area under the curve (AUC) for estradiol-17β-D-glucuronide increased 35 and 55% in male and female Oatp1a1⁻/⁻ mice, respectively, with a concurrent 50% reduction in liver-to-plasma ratios. In contrast, plasma AUC or tissue concentrations of estradiol-17β-D-glucuronide were unchanged in Oatp1a4⁻/⁻ mice. Plasma AUCs for dibromosulfophthalein increased nearly threefold in male Oatp1a1⁻/⁻ and Oatp1a4⁻/⁻ mice, increased by 40% in female Oatp1a4⁻/⁻ mice, and were unchanged in female Oatp1a1⁻/⁻ mice. In both lines, no changes in serum ALT, bilirubin, and cholesterol were noted. NMR analyses showed no generalized increase in urinary excretion of organic anions. However, urinary excretion of taurine decreased by 30-40% and was accompanied by increased excretion of isethionic acid, a taurine metabolite generated by intestinal bacteria, suggesting some perturbations in intestinal bacteria distribution.

In vitro and in vivo assessment of renal drug transporters in the disposition of mesna and dimesna

Mesna and its dimer, dimesna, are coadministered for mitigation of ifosfamide- and cisplatin-induced toxicities, respectively. Dimesna is selectively reduced to mesna in the kidney, producing its protective effects. In vitro screens of uptake and efflux transporters revealed saturable uptake by renal organic anion transporters OAT1, OAT3, and OAT4. Efflux transporters breast cancer resistance protein; multidrug and toxin extrusion 1 (MATE1); multidrug resistance proteins MRP1, MRP2, MRP4, and MRP5; and P-glycoprotein (Pgp) significantly reduced dimesna accumulation. Further investigation demonstrated that renal apical efflux transporters MATE1, MRP2, and Pgp were also capable of mesna efflux. Administration of OAT inhibitor probenecid to healthy subjects significantly increased combined mesna and dimesna plasma exposure (91% ± 34%) while decreasing the renal clearance due to net secretion (67.0% ± 12.7%) and steady-state volume of distribution (45.2% ± 13.4%). Thus, the kidney represents a significant sink of total mesna, whereas function of renal drug transporters facilitates clearance in excess of glomerular filtration rate and likely the presence of active mesna in the urine. Loss of renal transporter function due to genetic variability or drug-drug interactions may decrease the efficacy of chemoprotectants, increasing the risk of ifosfamide- and cisplatin-induced toxicities.

Xenobiotic metabolism, disposition, and regulation by receptors: from biochemical phenomenon to predictors of major toxicities

To commemorate the 50th anniversary of the Society of Toxicology, this special edition article reviews the history and current scope of xenobiotic metabolism and transport, with special emphasis on the discoveries and impact of selected "xenobiotic receptors." This overall research realm has witnessed dynamic development in the past 50 years, and several of the key milestone events that mark the impressive progress in these areas of toxicological sciences are highlighted. From the initial observations regarding aspects of drug metabolism dating from the mid- to late 1800's, the area of biotransformation research witnessed seminal discoveries in the mid-1900's and onward that are remarkable in retrospect, including the discovery and characterization of the phase I monooxygenases, the cytochrome P450s. Further research uncovered many aspects of the biochemistry of xenobiotic metabolism, expanding to phase II conjugation and phase III xenobiotic transport. This led to hallmark developments involving integration of genomic technologies to elucidate the basis for interindividual differences in response to xenobiotic exposures and discovery of nuclear and soluble receptor families that selectively "sense" the chemical milieu of the mammalian cell and orchestrate compensatory changes in gene expression programming to accommodate complex xenobiotic exposures. This review will briefly summarize these developments and investigate the expanding roles of xenobiotic receptor biology in the underlying basis of toxicological response to chemical agents.

Frequencies of single-nucleotide polymorphisms of SLCO1A2, SLCO1B3 and SLCO2B1 genes in a Finnish population

Organic anion transporting polypeptides 1A2, 1B3 and 2B1 (OATP1A2, OATP1B3 and OATP2B1) are expressed in tissues important for pharmacokinetics, and mediate the cellular influx of various endogenous and exogenous compounds, including drugs. The aim of the study was to investigate the frequencies of single-nucleotide polymorphisms (SNP) of SLCO1A2, SLCO1B3 and SLCO2B1 in a Finnish population. The distribution of nine non-synonymous SLCO1A2, SLCO1B3 and SLCO2B1 SNPs was determined in 552 healthy Finnish Caucasian participants by using allelic discrimination with TaqMan 5'nuclease assays. The SLCO1A2 c.38T>C (p.Ile13Thr) and c.516C>T (p.Glu172Asp) SNPs were found with variant allele frequencies of 12.9% (95% confidence interval: 11.0-15.0) and 7.2% (5.8-8.8). The variant allele frequencies of SLCO1B3 c.334T>G (p.Ser112Ala), c.699G>A (p.Met233Ile) and c.767G>C (p.Gly256Ala) were 77.0% (74.4-79.4), 76.9% (74.3-79.3) and 12.8% (10.9-14.9), respectively. None of the participants carried the SLCO1B3 c.1309G>A (p.Gly437Ser) SNP. The SLCO2B1 c.601G>A (p.Val201Met), c.935G>A (p.Arg312Gln) and c.1457C>T (p.Ser486Phe) variant allele frequencies were 2.1% (1.4-3.1), 13.6% (11.7-15.7) and 2.8% (2.0-4.0), respectively. The SLCO1B3 c.334T>G and c.699G>A SNPs were in a nearly complete linkage disequilibrium (r² = 0.99, D' = 1.00), all other SNP pairs showed only a weak correlation. In conclusion, non-synonymous sequence variations of SLCO1A2, SLCO1B3 and SLCO2B1 occur at high frequencies in the Finnish population.

Clinical pharmacology profile of raltegravir, an HIV-1 integrase strand transfer inhibitor

Raltegravir is an HIV-1 integrase inhibitor approved to treat HIV infection in adults in combination with other antiretrovirals. Data from healthy volunteers demonstrate that raltegravir is rapidly absorbed with a mean half-life of approximately 7 to 12 hours, with steady state achieved in approximately 2 days. Raltegravir is characterized by both high intra- and interindividual variabilities, although neither gender, race, age, body mass index, food intake, nor renal or hepatic insufficiency has a clinically meaningful effect on raltegravir pharmacokinetics. Raltegravir lacks activity as a perpetrator of drug-drug interactions and demonstrates a low propensity to be subject to drug-drug interactions. Raltegravir is metabolized primarily by UGT1A1 and is not affected by P450 inhibitors or inducers. Inhibitors of UGT1A1 (eg, atazanavir) can increase plasma concentrations of raltegravir, although this increase has not been found to be clinically meaningful. Likewise, inducers of UGT1A1 (eg, rifampin) can reduce plasma concentrations of raltegravir, and the clinical significance of this reduction is being investigated in ongoing clinical studies. Raltegravir demonstrates favorable clinical pharmacology and a drug interaction profile that permits administration to a wide, demographically diverse patient population and coadministration with many other therapeutic agents, including antiretroviral agents and supportive medications, without restrictions or dose adjustment.

Mechanism of polybrominated diphenyl ether uptake into the liver: PBDE congeners are substrates of human hepatic OATP transporters

Polybrominated diphenyl ethers (PBDEs) are flame-retardants that upon chronic exposure enter the liver where they are biotransformed to potentially toxic metabolites. The mechanism by which PBDEs enter the liver is not known. However, due to their large molecular weights (MWs approximately 485 to 1000 Da), they cannot enter hepatocytes by simple diffusion. Organic anion-transporting polypeptides (OATPs) are responsible for hepatic uptake of a variety of amphipathic compounds of MWs larger than 350 Da. Therefore, in the present study, Chinese hamster ovary cell lines expressing OATP1B1, OATP1B3, and OATP2B1 were used to test the hypothesis that OATPs expressed in human hepatocytes would be responsible for the uptake of PBDE congeners 47, 99, and 153. The results demonstrated that PBDE congeners inhibited OATP1B1- and OATP1B3-mediated uptake of estradiol-17-beta-glucuronide as well as OATP2B1-mediated uptake of estrone-3-sulfate in a concentration-dependent manner. Direct uptake studies confirmed that all three PBDE congeners are substrates for the three tested hepatic OATPs. Detailed kinetic analysis revealed that OATP1B1 transported 2,2',4,4'-tetrabromodiphenyl ether (BDE47) with the highest affinity (K(m) = 0.31 microM) followed by 2,2',4,4',5-pentabromodiphenyl ether (BDE99) (K(m) = 0.91 microM) and 2,2',4,4',5,5'-hexabromodiphenyl ether (BDE153) (K(m) = 1.91 microM). For OATP1B3, the order was the same (BDE47: K(m) = 0.41 microM; BDE99: K(m) = 0.70 microM; BDE153: K(m) = 1.66 microM), while OATP2B1 transported all three congeners with similar affinities (BDE47: K(m) = 0.81 microM; BDE99: K(m) = 0.87 microM; BDE153: K(m) = 0.65 microM). These results clearly suggest that uptake of PBDEs via these OATPs is a mechanism responsible for liver-specific accumulation of PBDEs.