Morse D C, Stein A P, Thomas P E, Lowndes H E
Department of Pharmacology and Toxicology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA.
Toxicol Appl Pharmacol. 1998 Sep;152(1):232-9. doi: 10.1006/taap.1998.8477.
Cytochromes P450 1A1 and 1A2 are involved in the oxidation of a wide spectrum of endogenous compounds and xenobiotics. Although their presence has been repeatedly confirmed in brain tissue, reports regarding their distribution in the brain are often contradictory. In the present study the possibility was examined that CYP1A1 and CYP1A2 are localized and inducible in the brain-CSF barrier and regions with a leaky blood brain barrier, where they may serve as a protective metabolic barrier. CYP1A1 and CYP1A2 levels were determined in subcellular fractions of multiple brain regions, as well as tissue homogenates of circumventricular organs, and the meninges by Western blotting and catalytic activity in control male rats and rats treated with the inducer beta-naphthoflavone (BNF). In control animals CYP1A1 immunoreactive protein was undetectable in regional brain microsomes or whole tissue homogenates of the arachnoid, dura mater, choroid plexus, pineal gland, median eminence, and pituitary. However, low levels of ethoxyresorufin O-deethylase (EROD) activity were observed in homogenates of the arachnoid, dura mater, choroid plexus, pineal gland, and pituitary. Western blotting revealed only low levels of CYP1A2 immunoreactive protein in brain microsomes from the cortex, cerebellum, brainstem, thalamus, hippocampus, and striatum from control animals. Following BNF treatment, EROD activity was induced 12-42-fold in the arachnoid, choroid plexus, dura mater, pineal gland, pituitary, and median eminence. Western blot analysis revealed CYP1A1 to be induced in the arachnoid, dura mater, choroid plexus, pineal gland, and pituitary, while CYP1A2 was undetectable. No induction of CYP1A1 or CYP1A2 protein was observed in brain microsomes from the olfactory bulb, cortex, striatum, hippocampus, cerebellum, or brainstem following BNF treatment, providing that the arachnoid membranes and choroid plexus had been carefully removed prior to brain dissection. Neither CYP1A1, 1A2 protein, nor EROD activity were detected in purified brain mitochondria, regardless of treatment or region. In conclusion, catalytically active CYP1A1 is located in the meninges as well as certain circumventricular organs, is inducible by BNF, and appears to be absent or expressed constitutively at very low levels in the majority of the brain parenchyma. The localization of CYP1A1 in the blood-CSF barrier and circumventricular tissues likely plays a role in protecting the brain from xenobiotics.
细胞色素P450 1A1和1A2参与多种内源性化合物和外源性物质的氧化过程。尽管它们在脑组织中的存在已被反复证实，但关于它们在脑中分布的报道往往相互矛盾。在本研究中，我们探讨了CYP1A1和CYP1A2在脑-脑脊液屏障以及血脑屏障渗漏区域定位并可被诱导的可能性，在这些区域它们可能作为一种保护性代谢屏障。通过蛋白质免疫印迹法测定了对照雄性大鼠以及用诱导剂β-萘黄酮（BNF）处理的大鼠多个脑区的亚细胞组分、室周器官组织匀浆和脑膜中CYP1A1和CYP1A2的水平，并检测了其催化活性。在对照动物中，在脑区微粒体或蛛网膜、硬脑膜、脉络丛、松果体、正中隆起和垂体的全组织匀浆中未检测到CYP1A1免疫反应性蛋白。然而，在蛛网膜、硬脑膜、脉络丛、松果体和垂体的匀浆中观察到低水平的乙氧异吩恶唑酮-O-脱乙基酶（EROD）活性。蛋白质免疫印迹法显示，对照动物大脑皮层、小脑、脑干、丘脑、海马体和纹状体的脑微粒体中仅存在低水平的CYP1A2免疫反应性蛋白。BNF处理后，蛛网膜、脉络丛、硬脑膜、松果体、垂体和正中隆起的EROD活性被诱导提高了12至42倍。蛋白质免疫印迹分析显示，蛛网膜、硬脑膜、脉络丛、松果体和垂体中CYP1A1被诱导表达，而未检测到CYP1A2。在BNF处理后，若在脑解剖前仔细去除蛛网膜和脉络丛，则嗅球、大脑皮层、纹状体、海马体、小脑或脑干的脑微粒体中未观察到CYP1A1或CYP1A2蛋白的诱导表达。无论处理方式或脑区如何，纯化的脑线粒体中均未检测到CYP1A1、1A2蛋白或EROD活性。总之，具有催化活性的CYP1A1位于脑膜以及某些室周器官中，可被BNF诱导，并且在大多数脑实质中似乎不存在或仅以极低水平组成性表达。CYP1A1在血-脑脊液屏障和室周组织中的定位可能在保护大脑免受外源性物质影响方面发挥作用。
