Biomedical subjects

Curtis D Klaassen

Publications and source records attributed to Curtis D Klaassen.

64 records · Page 4Linked to original sources

PubMed2002

Increase in rat liver UDP-glucuronosyltransferase mRNA by microsomal enzyme inducers that enhance thyroid hormone glucuronidation.

Treatment of rats with the microsomal enzyme inducers pregnenolone-16alpha-carbonitrile (PCN), 3-methylcholanthrene (3-MC), and Aroclor 1254 [PCB (polychlorinated biphenyl)] has been shown to decrease circulating levels of thyroid hormones as well as increase microsomal glucuronidation of thyroxine (T(4)). In addition, PCN increases triiodothyronine (T(3)) uridine diphosphate glucuronosyltransferase (UGT) activity. Members of the UGT1A family are believed to glucuronidate T(4), specifically UGT1A1 and UGT1A6, whereas the UGT2 family is believed to glucuronidate T(3), namely UGT2B2. The purpose of this study was to determine whether the aforementioned microsomal enzyme inducers increase the mRNAs that encode these and other UGT enzymes in rat liver. Male Sprague-Dawley rats were fed a control diet or a diet containing PCN (1000 ppm), 3-MC (250 ppm), or PCB (100 ppm) for 7 days, at which time livers were collected. Increases in mRNA were detected by QuantiGene branched DNA signal amplification. A 3-fold increase in UGT1A1 mRNA was produced by PCN in addition to increases in UGT1A2 (4-fold) and UGT1A5 (2-fold) mRNA. PCN affected neither UGT2B2 nor any other UGT2B mRNA level. 3-MC and PCB increased UGT1A6 mRNA 6- and 4-fold, respectively. 3-MC and PCB each increased UGT1A7 mRNA 4-fold but did not significantly increase any other UGT mRNAs. These findings suggest that PCN enhances T(4) UGT activity by increased expression of UGT1A1 and that 3-MC and PCB enhance T(4) UGT activity by increased expression of UGT1A6. These findings also suggest that increased T(3) UGT activity produced by PCN is due to a mechanism other than increased transcription of UGT2B2, possibly increased UGT2B2 protein or induction of another UGT enzyme.

Animals↗

PubMed2002

Postnatal expression and induction by pregnenolone-16alpha-carbonitrile of the organic anion-transporting polypeptide 2 in rat liver.

Newborn rats are more sensitive to the toxic effects of cardiac glycosides than are adult rats. This is associated with a decreased ability to remove cardiac glycosides from blood into the liver. Pregnenolone-16alpha-carbonitrile (PCN), a prototypical rodent CYP3A inducer and pregnane-X-receptor (PXR) ligand, stimulates the hepatic clearance of cardiac glycosides in newborn rats, which results in decreased toxicity of the cardiac glycosides. The mechanism responsible for this phenomenon is not clear; however, if elucidated, it would help in understanding and preventing potential drug-drug interactions. The recently cloned rat organic anion-transporting polypeptide 2 (oatp2) (Slc21a5) is a sinusoidal hepatic uptake transporter, with very high affinities for cardiac glycosides, and thus it was hypothesized that rat oatp2 increases during postnatal development and is inducible by PCN. In the present study, livers were removed from Sprague-Dawley rats from postnatal days (pnd) 0 to 45, in 5-day increments; as well as from pnd 10 to 90, in 10-day increments, after PCN (75 mg/kg i.p., for 4 days) or corn oil (vehicle for PCN) treatment. The protein and mRNA levels of rat oatp2 were determined by Western blot analysis and branched DNA signal amplification technique, respectively. Expression of rat oatp2 protein and mRNA increased gradually during postnatal development. PCN treatment increased liver to body weight ratio in both genders, and dramatically accelerated the maturation of hepatic oatp2 protein and mRNA levels. In summary, rat oatp2 undergoes age-dependent and chemical regulation during postnatal development, and is a potential target for drug-drug and age-drug interactions.

Age Factors↗

PubMed2002

Tissue distribution and chemical induction of multiple drug resistance genes in rats.

Multiple drug resistance (mdr) genes encode P-glycoprotein, which is responsible for resistance to some cancer chemotherapeutic drugs and efflux of xenobiotics of cells. Thus, mdr can protect organs from xenobiotics. In rats, there are two mdr1 genes capable of xenobiotic transport, mdr1a and mdr1b. The purpose of this study was to determine the tissue distribution of rat mdr1a and mdr1b mRNA and whether microsomal enzyme inducers that increase phase I and II drug-metabolizing enzymes coordinately regulate mdr1a and/or mdr1b. The mRNA levels of mdr1a and mdr1b were determined using branched-DNA signal amplification technology. The highest level of expression of mdr1a mRNA was observed in the gastrointestinal tract, with levels increasing, respectively, from duodenum, jejunum, and ileum to large intestine. Expression levels of mdr1a mRNA in the cerebral cortex, cerebellum, kidney, lung, and liver were less than one-tenth of that in the ileum. The tissue distribution of mdr1b mRNA was similar to mdr1a with highest expression in the gastrointestinal tract but only about 3-fold higher than in most other tissues. The induction of mdr1a and mdr1b mRNA transcripts in liver, kidney, and ileum by treatment of rats with 18 chemicals representing aryl hydrocarbon receptor ligands, constitutive androstane receptor ligands, pregnane X receptor ligands, peroxisome proliferator-activated receptor ligands, electrophile-response-element activators, and CYP4502E1 inducers was assessed. Hepatic, renal, and intestinal expression of mdr1a and mdr1b mRNA were not significantly altered by treatment of rats with any of these classes of ligands. In conclusion, the primary expression of rat mdr1 genes is in the gastrointestinal tract where they are thought to function to decrease the absorption of some xenobiotics. Rat mdr1 gene expression is not readily increased by microsomal enzyme inducers in rats through coordinate mechanisms with phase I and II drug-metabolizing enzymes.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2002

Induction profile of rat organic anion transporting polypeptide 2 (oatp2) by prototypical drug-metabolizing enzyme inducers that activate gene expression through ligand-activated transcription factor pathways.

Knowledge of regulation of transporters would aid in predicting pharmacokinetics and drug-drug interactions. Treatment of rats with pregnenolone-16alpha-carbonitrile (PCN) and phenobarbital increases hepatic uptake of cardiac glycosides. Rat organic anion transporting polypeptide 2 (oatp2; Slc21a5) transports cardiac glycosides with high affinity. Levels of rat hepatic oatp2 protein and mRNA are regulated by PCN and phenobarbital treatment; however, the effects of other microsomal enzyme inducers on oatp2 have not been investigated. Therefore, the purpose of this study was to further determine whether oatp2 is regulated by a broader scale of drug-metabolizing enzyme inducers that are ligands or activators for the aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor (PPAR), and antioxidant/electrophile response element (ARE/EpRE). Oatp2 protein levels determined by Western blot were decreased 56 to 72% by the AhR ligands, increased 84 to 132% by the CAR ligands, and increased 230 to 360% by PXR ligands. The PPAR ligands and ARE/EpRE activators generally had minimal effects on oatp2 protein levels. Oatp2 mRNA levels, determined by the bDNA technique, generally did not show a correlation with the altered oatp2 protein levels, e.g., among PXR ligands, only PCN increased oatp2 mRNA levels, but spironolactone and dexamethasone did not. Furthermore, only PCN, but not spironolactone and dexamethasone, increased the transcription of the oatp2 gene as the amount of hnRNA was increased when determined by reverse transcription-polymerase chain reaction. In conclusion, some drug-metabolizing enzyme inducers regulate oatp2 protein levels, especially the CYP3A inducers. However, there is no correlation between their ability to increase levels of oatp2 protein and mRNA, suggesting that regulation of oatp2 by drug-metabolizing enzyme inducers occurs at both the transcriptional and post-translational levels.

Animals↗

PubMed2002

Organ distribution of multidrug resistance proteins 1, 2, and 3 (Mrp1, 2, and 3) mRNA and hepatic induction of Mrp3 by constitutive androstane receptor activators in rats.

Many phase I and II microsomal enzyme inducers share common mechanisms of transcriptional activation and thus share a similar battery of genes that are coordinately regulated. Many phase II metabolites are thought to be transported out of cells by multidrug resistance proteins 1, 2, and 3 (Mrp1, 2, and 3). The purpose of this study was to determine the organ distribution of these three transporters in rat, and whether they are coordinately regulated with phase I and II drug-metabolizing enzymes. Therefore, Mrp1, 2, and 3 mRNAs were quantified using branched DNA signal amplification in multiple tissues and in tissues from rats that were treated with 18 chemicals thought to induce drug-metabolizing enzymes by six different transcription activation mechanisms [aryl-hydrocarbon receptor ligands, constitutive androstane receptor (CAR) activators, pregnane-X-receptor ligands, peroxisome proliferator activator receptor ligands, electrophile response element (EpRE) activators, and CYP2E1 inducers]. It was found that Mrp1 was expressed at a high level in kidney, lung, intestine, and brain, with low expression in liver. Mrp2 was highly expressed in liver and duodenum, and Mrp3 was highly expressed throughout the intestine but very low in liver. Microsomal enzyme inducers did not markedly increase the expression of Mrp1 or Mrp2. However, Mrp3 expression was significantly increased by each of the CAR activators and an EpRE activator in liver. Mrp3 was not similarly induced in kidney and large intestine, demonstrating that the coordinate inducibility of Mrp3 is specific to the liver. We conclude that rat hepatic Mrp3 is induced by CAR activators, thus enhancing the vectoral excretion of some phase II metabolites from the liver to the blood.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2002

Gender-specific and developmental influences on the expression of rat organic anion transporters.

Rat organic anion transporter 1 (Oat1), Oat2, and Oat3, members of the organic anion transporter family, transport some organic anions across cellular membranes. Previously, highest Oat1 and Oat3 mRNA expression was reported in kidney and Oat2 in liver. However, gender and developmental differences in Oat expression remain unknown. This study describes gender- and age-specific patterns of rat organic anion transporter expression in various tissues. Oat mRNA expression was evaluated in adult male and female Sprague-Dawley rat tissues, and developmental expression was also determined in kidneys of Sprague-Dawley rats ranging in age from days 0 through 45. Expression was quantified using branched-DNA signal amplification. Oat1 mRNA expression was primarily observed in kidney. Surprisingly, Oat2 mRNA expression was also highest in kidney rather than in liver. Moreover, considerably higher Oat2 levels were seen in female kidney as compared with male. Finally, Oat3 mRNA expression was highest in kidney of both genders, whereas a male-predominant pattern was observed in liver. At birth, all kidney Oat mRNA levels were low. Renal Oat1 expression gradually increased throughout development, approaching adult levels at 30 days of age, where at days 40 and 45 Oat1 levels were greater in males than females. Oat2 expression in kidney was minimal through day 30 but increased dramatically at day 35 in females only. Lastly, Oat3 mRNA expression in kidney matured earliest, rapidly increasing from birth through day 10. These data indicate that Oat mRNA expression is primarily localized to the kidney, and observed expression patterns may explain some previously recognized age- and gender-dependent toxicities associated with chemical exposure.

Aging↗

PubMed2002

Tissue expression, ontogeny, and inducibility of rat organic anion transporting polypeptide 4.

To date, organic anion transporting polypeptide 4 (Oatp4; Slc21a10) is known as a liver-specific and sodium-independent transporter that mediates transport of a variety of compounds. The purpose of this study was to determine whether Oatp4 mRNA expression is specific to the liver compared with Oatp1, 2, 3, or 5. In addition, the effect of gender and age was determined by assessing the expression of Oatp4 mRNA during the postnatal development of rats. Furthermore, to determine whether Oatp4 gene expression is coordinately modulated by drug-metabolizing enzyme inducers, male rats were administered chemicals known to induce the expression of drug-metabolizing enzymes through six mechanisms: the aryl hydrocarbon receptor, constitutive androstane receptor, pregnane X receptor, peroxisome proliferator-activated receptor, electrophile response element, or CYP2E1 inducers. The levels of Oatp1, 2, 3, 4, and 5 mRNA were measured using the branched DNA signal amplification technique. The tissue distribution of Oatp4 was almost exclusively expressed in liver in contrast to Oatp1, 2, 3, and 5. The hepatic expression of Oatp4 was low in newborn rats and increased gradually to the adult level with no significant difference between genders. The expression of Oatp4 was not consistently induced by any of the six groups of enzyme inducers. These findings continue to suggest that Oatp4 is expressed specifically in the liver. The preference of Oatp4 for endogenous compounds coupled with its refractory response to known drug-metabolizing enzyme inducers suggests that Oatp4 may be largely responsible for the homeostasis of endogenous rather than exogenous chemicals, including pharmaceuticals.

Age Factors↗

PubMed2002

Induction of rat organic anion transporting polypeptide 2 by pregnenolone-16alpha-carbonitrile is via interaction with pregnane X receptor.

The rat organic anion transporting polypeptide 2 (oatp2; Slc21a5) is a liver transporter that mediates the uptake of a variety of structurally diverse compounds, and has a high affinity for cardiac glycosides. Treatment of rats with pregnenolone-16alpha-carbonitrile (PCN), a ligand for the rodent pregnane X receptor (PXR), significantly enhances the rat oatp2 gene expression. To understand the molecular mechanism of oatp2 induction by PCN, rat oatp2 gene was cloned. The rat oatp2 gene consists of 16 exons; alternative splicing of the second noncoding exon gives rise to the two published rat oatp2 cDNAs. Approximately 8700 base pairs (bp) of the 5'-flanking region of the rat oatp2 gene were linked to the luciferase reporter gene and used in transient transfection assays in H4IIE cells. Treatment of PCN induced the expression of the reporter gene in a dose-dependent manner. Four potential PXR response elements (PXREs) were identified in the 5'-flanking region of the rat oatp2 gene. One element (DR3-1) is located approximately -5000 bp with three more (DR3-2, DR3-3, and DR3-4) clustered at about -8000 bp. Results from electrophoretic mobility shift assays showed that the PXR-retinoid X receptor alpha heterodimer binds to the DR3-2 with the highest affinity, to the DR3-4 and DR3-1 with a lower affinity, and weakly or not at all to the DR3-3. Furthermore, a series of partial deletions of the 5'-flanking region illustrated that both the proximal and distal clusters of PXREs are required for maximal induction of rat oatp2 by PCN. In conclusion, these data elucidate the molecular mechanism by which PCN treatment induces rat oatp2 gene expression. In addition, this study identifies rat oatp2 as a direct PXR-targeted gene and further supports the hypothesis that activation of PXR affects a network of genes that is involved in either metabolism or transport of drugs, steroids, and bile acids.

5' Untranslated Regions↗

PubMedDate not supplied

Xenobiotic transporters: another protective mechanism for chemicals.

Xenobiotic transporters are responsible for the uptake of some chemicals into cells, and extremely important for the export of chemicals out of cells. A number of families of xenobiotic transporters have been cloned the last few years. Some microsomal enzyme inducers will enhance the plasma disappearance and biliary excretion of some xenobiotics that are not biotransformed in the intact animal, as well as in isolated hepatocytes. This is due to an up-regulation of xenobiotic transporters. As a result, some microsomal enzyme inducers will enhance the elimination and decrease the toxicity of some chemicals by enhanced transport.

Animals↗

PubMedDate not supplied

Structure, function, expression, genomic organization, and single nucleotide polymorphisms of human ABCB1 (MDR1), ABCC (MRP), and ABCG2 (BCRP) efflux transporters.

The ATP-binding cassette (ABC) transporters constitute a large family of membrane proteins, which transport a variety of compounds through the membrane against a concentration gradient at the cost of ATP hydrolysis. Substrates of the ABC transporters include lipids, bile acids, xenobiotics, and peptides for antigen presentation. As they transport exogenous and endogenous compounds, they reduce the body load of potentially harmful substances. One by-product of such protective function is that they also eliminate various useful drugs from the body, causing drug resistance. This review is a brief summary of the structure, function, and expression of the important drug resistance-conferring members belonging to three subfamilies of the human ABC family; these are ABCB1 (MDR1/P-glycoprotein of subfamily ABCB), subfamily ABCC (MRPs), and ABCG2 (BCRP of subfamily ABCG), which are expressed in various organs. In the text, the transporter symbol that carries the subfamily name (such as ABCB1, ABCC1, etc.) is used interchangeably with the corresponding original names, such as MDR1P-glycoprotein, MRP1, etc., respectively. Both nomenclatures are maintained in the text because both are still used in the transporter literature. This helps readers relate various names that they encounter in the literature. It now appears that P-glycoprotein, MRP1, MRP2, and BCRP can explain the phenomenon of multidrug resistance in all cell lines analyzed thus far. Also discussed are the gene structure, regulation of expression, and various polymorphisms in these genes. Because genetic polymorphism is thought to underlie interindividual differences, including their response to drugs and other xenobiotics, the importance of polymorphism in these genes is also discussed.

ATP Binding Cassette Transporter, Subfamily B, Mem↗