Tanaka Nagako, Miyasho Taku, Shinkyo Raku, Sakaki Toshiyuki, Yokota Hiroshi
Laboratory of Veterinary Biochemistry, Graduate School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Hokkaido 069-8501, Japan.
Life Sci. 2006 Nov 25;79(26):2463-73. doi: 10.1016/j.lfs.2006.09.030. Epub 2006 Oct 5.
Deficiency of drug glucuronidation in the cat is one of the major reasons why this animal is highly sensitive to the side effects of drugs. The characterization of cytochrome P450 isoforms belonging to the CYP1A subfamily, which exhibit important drug oxidation activities such as activation of pro-carcinogens, was investigated. Two cDNAs, designated CYP1A-a and CYP1A-b, corresponding to the CYP1A subfamily were obtained from feline liver. CYP1A-a and CYP1A-b cDNAs comprise coding regions of 1554 bp and 1539 bp, and encode predicted amino acid sequences of 517 and 512 residues, respectively. These amino acid sequences contain a heme-binding cysteine and a conserved threonine. The cDNA identities, as well as the predicted amino acid sequences containing six substrate recognition sites, suggest that CYP1A-a and CYP1A-b correspond to CYP1A1 and CYP1A2, respectively. This was confirmed by the kinetic parameters of the arylhydrocarbon hydroxylase and 7-ethoxyresorufin O-deethylase activities of expressed CYPs in yeast AH22 cells and by the tissue distribution of each mRNA. However, theophylline 3-demethylation is believed to be catalyzed by CYP1A1 in cats, based on the high V(max) and low K(m) seen, in contrast to other animals. Because feline CYP1A2 had a higher K(m) for phenacetin O-deethylase activity with acetaminophen, which cannot be conjugated with glucuronic acid due to UDP-glucuronosyltransferase deficiency, it is supposed that the side effects of phenacetin as a result of toxic intermediates are severe and prolonged in cats.
猫体内药物葡萄糖醛酸化缺乏是该动物对药物副作用高度敏感的主要原因之一。对属于CYP1A亚家族的细胞色素P450同工型进行了表征研究，这些同工型具有重要的药物氧化活性，如前致癌物的激活。从猫肝脏中获得了两个与CYP1A亚家族相对应的cDNA，分别命名为CYP1A-a和CYP1A-b。CYP1A-a和CYP1A-b cDNA的编码区分别为1554 bp和1539 bp，分别编码517和512个氨基酸残基的预测氨基酸序列。这些氨基酸序列包含一个血红素结合半胱氨酸和一个保守的苏氨酸。cDNA的同一性以及包含六个底物识别位点的预测氨基酸序列表明，CYP1A-a和CYP1A-b分别对应于CYP1A1和CYP1A2。在酵母AH22细胞中表达的CYPs的芳烃羟化酶和7-乙氧基试卤灵O-脱乙基酶活性的动力学参数以及每个mRNA的组织分布证实了这一点。然而，与其他动物相比，基于所观察到的高V(max)和低K(m)，茶碱3-去甲基化被认为是由猫体内的CYP1A1催化的。由于猫的CYP1A2对非那西丁O-脱乙基酶活性与对乙酰氨基酚的K(m)较高，而对乙酰氨基酚由于UDP-葡萄糖醛酸基转移酶缺乏而不能与葡萄糖醛酸结合，因此推测非那西丁由于有毒中间体导致的副作用在猫体内严重且持续时间长。
