Sidhu J S, Omiecinski C J
Department of Environmental Health, University of Washington, Seattle, USA.
J Pharmacol Exp Ther. 1996 Jan;276(1):238-45.
Previously, we demonstrated that elevated levels of cyclic AMP (cAMP) repressed phenobarbital (PB)-inducible cytochrome P450 (CYP)2B gene expression in primary rat hepatocyte cultures. Although CYP3A1 induction by PB was similarly repressed by most of the cAMP-enhancing strategies, forskolin additions in particular resulted in marked stimulation of CYP3A1 expression. Here we examined whether this effect was due to forskolin's ability to activate adenylate cyclase. By using a specific ELISA for assessment of intracellular cAMP levels, we determined that forskolin and a water-soluble analog (L858051; 7 beta-desacetyl-7 beta-(N-methylpiperazine)) were equipotent in stimulating adenylate cyclase activity. However, only forskolin and its inactive 1,9-dideoxy analog were active as inducers of CYP3A1. In comparative studies, both dexamethasone and PB were ineffective in stimulating production of intracellular cAMP. Furthermore, treatment of hepatocytes with glucagon, dibutyryl-cAMP, or N6O2'-dibutyryl-cyclic GMP, resulted in no detectable enhancement of CYP3A1 gene expression. These results demonstrated that CYP3A1 induction by forskolin is independent of cAMP, and instead is likely to involve a direct chemical effect of forskolin on the CYP3A1 activation pathway.
此前，我们证明，在原代大鼠肝细胞培养物中，环磷酸腺苷（cAMP）水平升高会抑制苯巴比妥（PB）诱导的细胞色素P450（CYP）2B基因表达。虽然大多数增强cAMP的策略同样会抑制PB对CYP3A1的诱导作用，但添加福司可林尤其会显著刺激CYP3A1的表达。在此，我们研究了这种效应是否归因于福司可林激活腺苷酸环化酶的能力。通过使用特异性酶联免疫吸附测定（ELISA）评估细胞内cAMP水平，我们确定福司可林和一种水溶性类似物（L858051；7β-去乙酰基-7β-（N-甲基哌嗪））在刺激腺苷酸环化酶活性方面具有同等效力。然而，只有福司可林及其无活性的1,9-二脱氧类似物作为CYP3A1的诱导剂具有活性。在比较研究中，地塞米松和PB均无法有效刺激细胞内cAMP的产生。此外，用胰高血糖素、二丁酰-cAMP或N6O2'-二丁酰环鸟苷酸处理肝细胞，未检测到CYP3A1基因表达的增强。这些结果表明，福司可林对CYP3A1的诱导作用独立于cAMP，相反，可能涉及福司可林对CYP3A1激活途径的直接化学作用。
