Drug Metab. Pharmacokinet. 21 (1): 1–18 (2006). Review Multiplicity of Mammalian Reductases for Xenobiotic Carbonyl Compounds Toshiyuki MATSUNAGA, Shinichi SHINTANI and Akira HARA* Laboratory of Biochemistry, Gifu Pharmaceutical University, Gifu, Japan Full text of this paper is available at http://www.jstage.jst.go.jp/browse/dmpk Summary: A variety of carbonyl compounds are present in foods, environmental pollutants, and drugs. These xenobiotic carbonyl compounds are metabolized into the corresponding alcohols by many mammalian NAD(P)H-dependent reductases, which belong to the short-chain dehydrogenaseWreductase (SDR) and aldo-keto reductase superfamilies. Recent genomic analysis, cDNA isolation and characteriza- tion of the recombinant enzymes suggested that, in humans, the six members of each of the two superfamilies, i.e., total of 12 enzymes, are involved in the reductive metabolism of xenobiotic carbonyl compounds. They comprise three types of carbonyl reductase, dehydrogenaseWreductase (SDR family) member 4, 11b-hydroxysteroid dehydrogenase type 1, L-xylulose reductase, two types of a‰atoxin B1 aldehyde reductase, 20a-hydroxysteroid dehydrogenase, and three types of 3a-hydroxysteroid dehydrogenase. Accumulating data on the human enzymes provide new insights into their roles in cellular and molecular reactions including xenobiotic metabolism. On the other hand, mice and rats lack the gene for a protein corresponding to human 3a-hydroxysteroid dehydrogenase type 3, but instead possess additional ˆve or six genes encoding proteins that are structurally related to human hydroxy- steroid dehydrogenases. Characterization of the additional enzymes suggested their involvement in species-speciˆc biological events and species diŠerences in the metabolism of xenobiotic carbonyl compounds. Key words: Carbonyl reduction; short-chain dehydrogenaseWreductase superfamily; aldo-keto reductase superfamily; carbonyl reductase; hydroxysteroid dehydrogenase; species diŠerence alcohols by NADPH-dependent reductases with broad Introduction substrate speciˆcity. Some NADPH-dependent reduc- Aldehydes, ketones and quinones are present in a tases reduce quinones through two-electron transfer to diverse range of natural and synthetic compounds to the corresponding hydroqinones, which is also mediated which living organisms are exposed. In addition, car- by NA(D)PH:quinone reductase. This group of reduc- bonyl compounds are formed through biological tases with broad substrate speciˆcity for xenobiotic transformation of endogenous components and carbonyl compounds was originally called `aldo-keto xenobiotics that are ingested. Aldehydes are chemically reductases'1) andWor `carbonyl reductases'.2) Subse- reactive and interact with the nucleophilic centers of quently, according to the accumulated knowledge on nucleic acids and proteins. a-Dicarbonyl compounds, the functions and structures of the reductases, most such as methyl glyoxal and diacetyl, are more reactive. carbonyl-reducing enzymes have been grouped into two Ketones are less reactive, and many drugs contain keto distinct protein families, the short-chain dehydrogenase group(s). Quinones have a toxic eŠect, i.e., quinone- (SDR)3) and aldo-keto reductase (AKR)4) superfamilies. induced oxidative stress, when they are reduced through There had been three excellent reviews on the single-electron transfer to the corresponding semiqui- carbonyl-reducing enzymes by 2000.5–7) Over the recent nones. Organisms have evolved several enzyme systems ˆve years, several new enzymes that may reduce for detoxifying reactive carbonyl compounds. Such well xenobiotic carbonyl compounds have been found on established pathways include the oxidation of aldehydes genomic analysis, and thus the enzyme names have been to the corresponding carboxylic acids by aldehyde changed. For example, well-known carbonyl reductase dehydrogenases and aldehyde oxidases, and the reduc- (CBR), a member of the SDR superfamily, is now tion of aldehydes and ketones into the corresponding named CBR1 according to the Human Gene Nomencla- Received; September 30, 2005, Accepted; October 24, 2005 *To whom correspondence should be addressed:AkiraHARA, Laboratory of Biochemistry, Gifu Pharmaceutical University, Mitahora-higashi, Gifu, Gifu 502-8585, Japan. Tel. & Fax. ＋81-58-237-8586, E-mail: hara＠gifu-pu.ac.jp 1 2 Toshiyuki MATSUNAGA et al. Table 1. Human enzymes involved in the reduction of xenobiotic carbonyl compounds. Gene name Subcellular Accession Enzymes (location) Other names Endogenous substrates localization numbera) SDR family CBR1 CBR1 Carbonyl reductase, PG 9-ketoreductase PG, isatin, (21q22.13) ketosteroids Cytoplasm P16152 CBR3 CBR3 Unknown Cytoplasm O75828 (21q22.2) 11bHSD 1 HSD11B1 Corticosteroid 11b-dehydrogenase isozyme 1 11-Ketoglucocorticoids Microsomes P28845 (1q32-q41) DHRS4 Dhrs4 Peroxisomal short-chain alcohol dehydrogenase, Retinal Peroxisomes Q9BTZ2 (14q11.2) NADPH-dependent retinol dehydrogenaseWreductase (NDRD) L-Xylulose DXCR DicarbonylWL-xylulose reductase, diacetyl L-Xylulose, diacetyl Cytoplasm Q7Z4W1 reductase (17q25.3) reductase AKR family AKR7A2 AKR7A2 A‰atoxin B1 aldehyde reductase member 2, Succinic semialdehyde Golgi O43488 (1p35.1-p36.23) AFAR2 AKR7A3 AKR7A3 A‰atoxin B1 aldehyde reductase member 3, Unknown Cytoplasm O95154 (1p35.1-p36.23) AFAR1 AKR1C1 AKR1C1 20a-HSD, 3(20)a-HSD, DD1 3- and 20-ketosteroids Cytoplasm Q04828 (10 q15-q14) AKR1C2 AKR1C2 3a-HSD type 3, DD2, bile acid-binding protein 3-Ketosteroids Cytoplasm P52895 (10 q15-q14) AKR1C3 AKR1C3 3a-HSD type 2, 17b-HSD type 5, PGF synthase, 3-, 17- and 20-keto- Cytoplasm P42330 (10 q15-q14) DDX steroids, PGD2 AKR1C4 AKR1C4 3a-HSD type 1, DD4, chlordecone reductase 3-ketosteroids Cytoplasm P17516 (10 q15-q14) a)The structural and functional information is available under the accession numbers of UniprotKBWSwiss-Prot (http:WWkr.expasy.orgWsprotW). ture Committee (HGNC), because of the occurrence of reductase exhibit broad substrate speciˆcities for four types of CBR. Several mammalian enzymes that xenobiotic carbonyl compounds (Tables 1 and 2). CBRs were regarded as CBRs in the previous reviews are now are classiˆed into four types, CBR1, CBR2, CBR3 and classiˆed into CBR1-CBR3 or have been identiˆed as CBR4 (Table 3). members of the AKR superfamily. The enzymes that 1. Carbonyl reductases (CBRs, EC 1.1.1.181) belong to the AKR superfamily have also been named CBR1: The cDNA for the human enzyme was ˆrst according to the nomenclature for this superfamily. In cloned by Wermuth et al.,8) who also characterized its addition, novel physiological roles of several enzymes properties using the enzyme puriˆed from the brain, and have been reported. Therefore, we have reviewed the proposed its identity with xenobiotic ketone reductase literature on mammalian carbonyl-reducing enzymes and prostaglandin (PG) 9-ketoreductase.9) The enzyme using the new nomenclature in order to clarify their is ubiquitously distributed in human tissues.10) The gene relationship with the previously known enzymes. is mapped to chromosome 21q22.12, very close to the superoxide dismutase 1 locus at position 21q22.11.11) Carbonyl-reducing Enzymes in the SDR Superfamily The mRNA expression in MCF-7 cells is induced 3- or The SDR superfamily includes about 3,000 primary 4-fold in 24 hours by 2,(3)-t-butyl-4-hydroxyanisole, structures of functionally heterogeneous proteins, and b-naphtho‰avone, or Sudan 1.12) Human CBR1 is a becomes one of the largest protein families to date.3) 30 kDa-monomer comprising 277 amino acids, and The sequence identity of the members of this family is belongs to the SDR family. Recently, Tanaka et al.13) low, but the three-dimensional structures of many solved the crystal structure of the enzyme-NADP＋- members exhibit highly similar aWb folding patterns inhibitor complex, which has provided important in- with a central b-sheet, typical of the Rossmann-fold that sights as to the substrate binding site and the design of participates in cofactor binding. The catalytic tetrad of potent inhibitors of the enzyme, although its tertiary Asn-Ser-Tyr-Lys is conserved in the members of this structure is highly similar to that of porcine CBR1.14) superfamiy. Among the members, CBRs, 11b-hydro- Human CBR1 catalyzes the NADPH-dependent xysteroid dehydrogenase (HSD) type 1, dehydrogenaseW reduction of various carbonyl compounds, the best sub- reductase (SDR family) member 4 and L-xylulose strates being p-ando-quinones derived from polycyclic Mammalian Carbonyl-Reducing Enzymes 3 Table 2. Typical xenobiotic substrates of human reductases. Enzyme Drugs Others CBR1 Daunorubicin, doxorubicin, haloperidol, Quinones, aromatic aldehydes, aromatic ketones, NNK bromperidol, metyrapone, loxoprofen, wortmannin, dolasetron CBR3 Menadione 11bHSD 1 Ketoprofen, metyrapone, insecticidal metyrapone NNK, menadione, aromatic aldehydes and ketones, 7-ketocholesterol analogues, oracin DHRS4 Dicarbonyl compounds with aromatic rings, alkyl phenyl ketones, some aromatic aldehydes and ketones L-Xylulose Dicarbonyl compounds, some aromatic aldehydes and ketones reductase AKR7A2 Daunorubicin, ethacrynic acid A‰atoxin B1 dialdehyde, dicarbonyl compounds, aromatic aldehydes AKR7A3 A‰atoxin B1 dialdehyde, 9,10-phenanthrenequinone,4-nitrobenzaldehyde AKR1C1 Dolasetron, naloxone, naltrexone, oxycodone, oracin, Aromatic aldehydes and ketones, quinones, dicarbonyl compounds, befunolol, ketotifen, 10-oxonortriptyline, haloperidol, NNK, trans-dihydrodiols of aromatic hydrocarbons, alicyclic alcohols loxoprofen,