Cytochrome P450 Isozymes Involved in Aromatic Hydroxylation and Side-Chain N-Desisopropylation of Alprenolol in Rat Liver Microsomes.
作者:Shizuo NARIMATSU、Masaya TACHIBANA、Yasuhiro MASUBUCHI、Susumu IMAOKA、Yoshihiko FUNAE、Tokuji SUZUKI
DOI:10.1248/bpb.18.1060
日期:——
Alprenolol 4-hydroxylation and N-desisopropylation in liver microsomes from male Wistar rats were kinetically analyzed to be biphasic. In the 4-hydroxylation at a low substrate concentration (5μM), significant strain [Wistar>Dark Agouti (DA)] and sex (male>female) differences were observed, and the differences decreased at a high substrate concentration (1mM). In the N-desisopropylation, only a strain difference (Wistar>DA) was observed at the low substrate concentration. Cytochrome P450BTL (P450BTL, corresponding to CYP2D2) in a reconstituted system with 5μM alprenolol had high 4-hydroxylase activity, which was about 10 times that of P450ml corresponding to CYP2C11, and N-desisopropylase activity at a similar extent to P450ml. The two microsomal activities at 5μM alprenolol were efficiently decreased by antibodies against P450BTL and by sparteine, a typical substrate of the CYP2D subfamily. Polyclonal antibodies against P450ml and P450PB-1 (corresponding to CYP3A2) partially suppressed only N-desalkylation at 5μM, whereas they reduced the two activities at 1mM. P450ml showed a high N-desisopropylase activity at a substrate concentration of 1mM, where the sex difference was not observed. Furthermore, P450PB-2 corresponding to CYP2C6, which is one of the major P450 isozymes in female rats, also had 4-hydroxylase and N-desalkylase activities. These results suggest that a CYP2D isozyme(s) is the primary enzyme in alprenolol 4-hydroxylation and N-desisopropylation in a lower substrate concentration range, and that the involvement of some male-specific P450 isozyme(s) other than CYP2C11 or CYP3A2 may cause the sex difference in the 4-hydroxylation. In a higher substrate concentration range, CYP2C11 is thought to play a major role particularly in N-desisopropylation in male rats. In female rats, some major constitutive P450 isozyme(s) with a relatively high Km value (e.g., CYP2C6) may be involved in the metabolism of alprenolol, resulting in the disappearance of the sex difference.
经动力学分析,雄性 Wistar 大鼠肝脏微粒体中的阿普洛尔 4-羟基化和 N-去甲丙基化是双相的。在低底物浓度(5μM)的 4-羟基化过程中,观察到显著的品系[Wistar>Dark Agouti (DA)]和性别(雄性>雌性)差异,在高底物浓度(1mM)时差异减小。在 N-异丙基化过程中,仅在低底物浓度下观察到菌株差异(Wistar>DA)。细胞色素 P450BTL(P450BTL,对应于 CYP2D2)在 5μM 阿普洛尔的重组系统中具有较高的 4-羟化酶活性,约为对应于 CYP2C11 的 P450ml 的 10 倍,N-脱羟丙基酶活性与 P450ml 相似。针对 P450BTL 的抗体和 CYP2D 亚家族的典型底物斯巴替因能有效降低这两种微粒体在 5μM 阿普洛尔浓度下的活性。针对 P450ml 和 P450PB-1(对应于 CYP3A2)的多克隆抗体在 5μM 时仅部分抑制了 N-脱烷基化,而在 1mM 时则降低了这两种活性。P450ml 在底物浓度为 1mM 时显示出较高的 N-去烷基化酶活性,在这种情况下没有观察到性别差异。此外,与 CYP2C6 相对应的 P450PB-2(雌性大鼠的主要 P450 同工酶之一)也具有 4-羟化酶和 N-脱烷基酶活性。这些结果表明,在较低的底物浓度范围内,CYP2D 同工酶是阿普洛尔 4-羟基化和 N-脱烷基化的主要酶,除 CYP2C11 或 CYP3A2 外,一些雄性特异性 P450 同工酶的参与可能导致 4-羟基化的性别差异。在较高的底物浓度范围内,CYP2C11 被认为在雄性大鼠的 N-异丙基化过程中发挥主要作用。在雌性大鼠中,一些 Km 值相对较高的主要组成型 P450 同工酶(如 CYP2C6)可能参与了阿普洛尔的代谢,从而导致性别差异消失。