Drug Metab. Pharmacokinet. 27 (5): 543­547 (2012). Copyright © 2012 by the Japanese Society for the Study of Xenobiotics (JSSX) Note Developmental Changes of Aldehyde Oxidase Activity and Protein Expression in Human Liver Cytosol Yoshitaka TAYAMA1,*,KazumiSUGIHARA1,2,SeigoSANOH2, Katsushi MIYAKE1, Shigeyuki KITAMURA2,3 and Shigeru OHTA2 1Faculty of Pharmaceutical Science, Hiroshima International University, Kure, Japan 2Division of Medicinal Chemistry, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan 3Nihon Pharmaceutical University, Saitama, Japan Full text of this paper is available at http://www.jstage.jst.go.jp/browse/dmpk Summary: Aldehyde oxidase (AO) plays a role in metabolizing many drugs, such as methotrexate and 6- mercaptopurine. We previously showed that AO activity in rat liver rapidly increases from birth, reaching a plateau within 4 weeks, and is regulated at the protein expression level. However, developmental changes of AO activity and protein expression in human liver have not been reported. Here, we investigated the developmental changes and variability of AO in 16 human livers (13 children ranging from 13 days to 12 years old and 3 adults, 17, 34 and 45 years old). Young children (13 days to 4 months after birth) showed little liver AO activity, evaluated in terms of the activities for oxidation of N-1-methylnicotinamide to N-1- methyl-2-pyridone-5-carboxamide and N-1-methyl-4-pyridone-3-carboxamide in liver cytosol. However, these oxidase activities were markedly increased after 4 months, reaching the adult level by about 2 years of age. The AO band density in immunoblotting analysis waswellcorrelatedwiththeAOactivityamongall subjects (p < 0.01, r2 = 0.771). Therefore, AO activity in the liver of young children is regulated at the AO protein expression level. Thus, as in rats, the AO activity in humans rapidly increases soon after birth, and is regulated at the protein expression level. Keywords: aldehyde oxidase; developmental change; children; human; liver P450, flavin-containing monooxygenase¥ activities.16®19¥ In Introduction addition, developmental changes of several phase II drug- Aldehyde oxidase ¤AO, EC 1.2.3.1¥ mediates the oxi- metabolizing enzymes ¤glutathione S-transferase, sulfotrans- dation of aldehydes and nitrogenous heterocyclic xeno- ferase and glucuronyltransferase¥ in young children have biotics.1®5¥ It is involved in the metabolism of many drugs, been reported.20,21¥ This information is important, because including antimalarials ¤quinine¥,6¥ anticancer drugs ¤metho- of the possible influence on drug efficacy and side effects; trexate, 6-mercaptopurine and cyclophosphamide¥,7,8¥ anti- for example, in neonates who have immature glucuronyl- viral drugs ªfamciclovir and zidovudine ¤AZT¥«,9®11¥ and transferase activity, impaired metabolism of chloramphenicol antiepilepsy drugs ¤zonisamide¥.12¥ Therefore, AO activity is can result in so-called grey baby syndrome.15¥ important in clinical treatment, and developmental changes As regards AO, ontogenic changes of its activity in rat of AO in humans should be taken into account in pediatric liver have been reported.22¥ However, there is a marked medicine. species difference of AO activity between rats and humans. Developmental changes of several drug-metabolizing Therefore, in the present study, we examined the develop- enzymes have been examined in mammals,13,14¥ including mental changes of AO activity and their relationship to AO humans.15¥ For example, human liver shows ontogenic protein expression in 16 human livers covering the age range changes of phase I drug-metabolizing enzyme ¤cytochrome of 13 days to 45 years. Received October 14, 2011; Accepted March 1, 2012 J-STAGE Advance Published Date: March 27, 2012, doi:10.2133/dmpk.DMPK-11-NT-124 *To whom correspondence should be addressed: Yoshitaka TAYAMA, Ph.D., Faculty of Pharmaceutical Science, Hiroshima International University, 5-1-1 Hirokoshingai, Kure 737-0112, Japan. Tel. +81-823-73-8576, Fax. +81-823-73-8981, E-mail: [email protected] This work was supported by a Grant-in-Aid for Scientific Research (no. 18790132) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. 543 544 Yoshitaka TAYAMA, et al. means + standard deviation ¤S.D.¥. The statistical signifi- Materials and Methods cance of differences was evaluated by use of the F-test fol- Chemicals and materials: N-1-Methylnicotinamide lowed by Welchös t-test. The correlation between AO activ- ¤NMN¥ and N$-methylnicotinamide were obtained from ity and protein band density was evaluated using Pearsonös Tokyo Chemical Industry Co., Ltd. ¤Tokyo, Japan¥. N-1- correlation. A value of p g 0.05 was considered significant. Methyl-2-pyridone-5-carboxamide ¤2-PY¥ and N-1-methyl- Results 4-pyridone-3-carboxamide ¤4-PY¥ were prepared according to Pullman and Colowick,23¥ and Shibata et al., respec- Developmental changes of liver aldehyde oxidase tively.24¥ Polyvinylidene fluoride ¤PVDF¥ membranes were in young children and adults: The activity for purchased from Millipore Co., Ltd. ¤Billerica, USA¥,10® conversion of NMN to 2-PY and 4-PY was assayed as an 20% polyacrylamide gel for electrophoresis was from Atto indicator of AO activity. As shown in Figure 1, the AO Co., Ltd. ¤Tokyo, Japan¥ and anti-rat AO antibodies were activities of H0354 ¤13 days old¥ and H0282 ¤2 months old¥ from Trans Genic Inc. ¤Kumamoto, Japan¥. Horseradish were low ¤0.44 and 0.49 nmol/30 min/mg protein, respec- peroxidase-conjugated goat anti-rabbit IgG was purchased tively¥. On the other hand, the AO activities of H0057 from Nacalai Tesque Co., Ltd. ¤Kyoto, Japan¥. ¤2 years old¥ were 2.13 nmol/30 min/mg protein, being Human subjects: The S9 fractions of 16 human livers virtually identical to the level in adults. Among samples were purchased from BD-Gentest Co. ¤New Jersey, USA¥. from humans over 2 years old, H0054 ¤12 years old¥ showed The cytosolic fraction was obtained from the S9 fraction by the lowest activity ¤2.31 nmol/30 min/mg protein¥, while centrifugation at 105,000 ' g for 60 min. Protein concen- H0215 ¤6 years old¥ showed the highest activity ¤4.70 nmol/ tration was determined in duplicate by the method of Lowry 30 min/mg protein¥, indicating that inter-individual dif- et al. with bovine serum albumin as the standard protein.25¥ ferences exist. Assay of NMN oxidase activity: NMN oxidase Expression of aldehyde oxidase protein in liver activity was measured according to the method of Ohkubo of young children and adults: SDS-PAGE immuno- et al.26¥ The amounts of 4-PY and 2-PY formed were blot analysis with anti-rat AO antibodies indicated the pres- measured by HPLC. Briefly, the incubation mixture ence of AO ¤150 kDa¥ in all samples from subjects over consisted of 0.2 µmol of NMN and liver cytosol equivalent 4 months old. On the other hand, AO was not detected in to 50®100 mg wet weight of liver in a final volume of 1 ml of H0354 ¤13 days old¥ or H0282 ¤2 months old¥ clearly 0.1 M K, Na-phosphate buffer ¤pH 7.4¥. The incubation was ¤Fig. 1¥. The AO band density was well correlated with AO performed at 37ôC for 30 min. After addition of 10 µg of activity in all subjects ¤p g 0.01, r2 © 0.771¥ and in subjects N$-methylnicotinamide ¤an internal standard¥, the mixture under 2 years old ¤p g 0.05, r2 © 0.631¥¤Fig. 2¥. was extracted with five volumes of ethyl acetate and the Developmental change of aldehyde oxidase extract was evaporated to dryness. The residue was dis- characteristics: We also examined the developmental solved in 0.1 ml of methanol, and an aliquot was subjected change of AO characteristics in terms of the 2-PY/4-PY to analysis by HPLC. HPLC was performed with a Capcell metabolite ratio. The 2-PY/4-PY ratio in the samples from pak C18 UG120 column ¤25 cm ' 4.6 mm, Shiseido Co. 8 subjects under 2 years of age was 8.11 + 0.78, while that Ltd., Tokyo, Japan¥ for the separation of 2-PY and 4-PY. in 6 subjects over 2 years of age was 9.00 + 2.33, and this The mobile phase was acetonitrile-water ¤3:97, v/v¥. The difference was not significant ¤p © 0.33¥. chromatograph was operated at a flow rate of 0.8 ml/min Discussion and with a detection wavelength of 254 nm. The elution times of 4-PY, 2-PY and N$-methylnicotinamide ¤an internal AO plays an important role in metabolizing many drugs standard¥ were 8.0, 9.0 and 19.2 min, respectively. used to treat pediatric patients, so developmental changes Immunoblot analysis of aldehyde oxidase: The of AO activity could be of clinical importance, and could expression levels of AO protein were determined by potentially be a useful parameter to guide dose adjustment in immunoblot analysis of liver cytosol protein. Human cyto- young patients in order to avoid toxicity. solic proteins ¤50 µg¥ were separated by SDS-PAGE on In the present study, we evaluated the ontogenic changes 10®20% polyacrylamide gel ¤Atto Co., Ltd.¥, and trans- of AO in the human liver. Neonates and infants ¤13 days to 4 ferred to PVDF membranes by electroblotting. Membranes months old¥ showed little liver AO activity. However, AO were then blocked with 2% skimmed milk in 25 mM activity subsequently increased, reaching a plateau by 2 years Tris-buffered saline ¤pH 7.6¥®0.1% Tween 20 for 1 h of age ¤Fig. 1¥. Although a spike of AO activity appeared and probed with anti-rat AO antibodies ¤1:1,000¥ for 24 h. to exist at around 6®8 years of age in our samples, we The membranes were washed, and antibody binding was previously observed no spike of in vivo AO activity in this detected with horseradish peroxidase-conjugated goat anti- age range, and large inter-individual differences ¤up to 3.9- rabbit IgG ¤1:1,000¥, followed by development with Chemi- fold¥ were seen in samples from subjects over 2 years.27¥ Lumi One L ¤Nacalai Tesque, Inc., Kyoto, Japan¥.