Rat organic anion transporter 1 (Oat1), Oat2, and Oat3,

As the need for novel antibiotic classes to combat bacterial drug resistance increases, the paucity of leads resulting from targetbased antibacterial screening of pharmaceutical compound libraries is of major concern. One explanation for this lack of success is that antibacterial screening efforts have not leveraged the eukaryotic bias resulting from more extensive chemistry efforts targeting eukaryotic gene families such as G protein-coupled receptors and protein kinases. Consistent with a focus on antibacterial target space resembling these eukaryotic targets, we used whole-cell screening to identify a series of antibacterial pyridopyrimidines derived from a protein kinase inhibitor pharmacophore. In bacteria, the pyridopyrimidines target the ATP-binding site of biotin carboxylase (BC), which catalyzes the first enzymatic step of fatty acid biosynthesis. These inhibitors are effective in vitro and in vivo against fastidious Gram-negative pathogens including Haemophilus influenzae. Although the BC active site has architectural similarity to those of eukaryotic protein kinases, inhibitor binding to the BC ATP-binding site is distinct from the protein kinase-binding mode, such that the inhibitors are selective for bacterial BC. In summary, we have discovered a promising class of potent antibacterials with a previously undescribed mechanism of action. In consideration of the eukaryotic bias of pharmaceutical libraries, our findings also suggest that pursuit of a novel inhibitor leads for antibacterial targets with active-site structural similarity to known human targets will likely be more fruitful than the traditional focus on unique bacterial target space, particularly when structure-based and computational methodologies are applied to ensure bacterial selectivity.acetylcoenzyme A carboxylase ͉ biotin carboxylase ͉ crystal structure ͉ high-throughput screening ͉ fatty acid biosynthesis

ABSTRACT:Organic anion transporters (Oats) mediate the initial step of active renal excretion, specifically substrate uptake into proximal tubule cells. Despite extensive characterization of rat Oats, mouse Oat expression patterns are virtually unknown. This study was designed to identify basal expression patterns of mouse Oat1 (Slc22a6), Oat2 (Slc22a7), and Oat3 (Slc22a8) mRNA, compare these patterns with those in rat, and characterize postnatal development of mouse Oat mRNA. Tissues were collected from adult male and female 129J and C57BL/6 mice, and male and female C57BL/6 mice 0 to 40 days of age. Oat mRNA levels were determined by branched DNA signal amplification. Mouse Oat1 mRNA was primarily expressed in kidney of both strains, with male predominance. Mouse Oat2 mRNA levels were highest in kidney of both strains without gender predominance. In both strains, Oat3 mRNA was highest in kidney, and liver expression was male-predominant. However, only 129J mice had higher Oat3 mRNA levels in female kidney than in male kidney. During postnatal development, both Oat1 and Oat2 mRNA levels began to rise after 25 days of age. Oat3 mRNA levels rose gradually from birth through 40 days of age. Oat2 mRNA increased 30-fold during the first 40 days, whereas Oat1 and Oat3 increased about 2-fold. The most notable species differences in Oat mRNA expression were a lack of Oat2 female predominance in mouse kidney and a less dramatic Oat3 male predominance in mouse liver. With the exception of a significant species difference in Oat2 expression, many similarities were found between rat and mouse Oat mRNA levels.

ABSTRACT: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 drugmetabolizing enzymes.

This article is available online at http://dmd.aspetjournals.org ABSTRACT:Messenger RNA levels of rat organic anion transporter 1 (Oat1; Slc22a6) and Oat2 (Slc22a7) in kidney and Oat3 (Slc22a8) in liver are gender-predominant. Oat1 and Oat3 are male-predominant, whereas Oat2 is female-predominant. Gonadectomized and hypophysectomized (HX) rats were studied to determine whether sex steroids and/or growth hormone (GH) are responsible for these gender-divergent patterns. GH was administered to HX rats by two daily injections (simulating male secretion) or continuous infusion (simulating female secretion). Oat1 mRNA levels, normally higher in male than female kidney, were lowered by gonadectomy and HX in male rats, but not in females. Additionally, GH injections or infusion did not alter Oat1 levels in HX rats. Oat2 mRNA levels, typically much higher in female than in male kidney, were unaffected by gonadectomy. However, HX dramatically decreased Oat2 in female kidney without altering male levels. GH administered by continuous infusion increased Oat2 in kidneys of both HX male and female rats, whereas injections had no affect. Gonadectomy reduced Oat3 mRNA levels in male livers without affecting levels in female livers. In contrast, HX decreased male and elevated female Oat3 mRNA. GH injections did not significantly change Oat3 mRNA levels in HX rats, but infusion decreased Oat3 mRNA in liver. In conclusion, androgens, but not GH, are responsible for the Oat1 mRNA gender difference in kidney; the female GH secretion pattern is responsible for the Oat2 mRNA gender difference in kidney; and both androgens and the female GH secretion pattern are responsible for the Oat3 mRNA gender difference in liver.Metabolism and excretion both determine elimination of endogenous and exogenous compounds. Liver is the primary site of metabolism, and liver and kidney are important organs in the process of excretion. Increasing or decreasing metabolism or excretion can lead to a respective decrease or increase of xenobiotic half-life, thus altering disposition. Expression of phase I [e.g., cytochromes P450 (P450s 1 )] and phase II enzymes [e.g., glucuronosyltransferases and sulfotransferases (STs)] is critical to metabolic processes, whereas transport proteins are vital for excretion. Interestingly, some enzymes and transporters are expressed in a gender-specific manner.