Reed James R, dela Cruz Albert Leo N, Lomnicki Slawo M, Backes Wayne L
Department of Pharmacology and Experimental Therapeutics and The Stanley S. Scott Cancer Center, Louisiana State University Health Sciences Center, 533 Bolivar St., New Orleans, LA 70112, USA.
The Department of Environmental Sciences and LSU Superfund Research Center, Louisiana State University A&M College, Baton Rouge, LA 70803, USA.
Toxicol Appl Pharmacol. 2015 Dec 1;289(2):223-30. doi: 10.1016/j.taap.2015.09.021. Epub 2015 Sep 28.
Combustion processes generate different types of particulate matter (PM) that can have deleterious effects on the pulmonary and cardiovascular systems. Environmentally persistent free radicals (EPFRs) represent a type of particulate matter that is generated after combustion of environmental wastes in the presence of redox-active metals and aromatic hydrocarbons. Cytochromes P450 (P450/CYP) are membrane-bound enzymes that are essential for the phase I metabolism of most lipophilic xenobiotics. The EPFR formed by chemisorption of 2-monochlorophenol to silica containing 5% copper oxide (MCP230) has been shown to generally inhibit the activities of different forms of P450s without affecting those of cytochrome P450 reductase and heme oxygenase-1. The mechanism of inhibition of rat liver microsomal CYP2D2 and purified rabbit CYP2B4 by MCP230 has been shown previously to be noncompetitive with respect to substrate. In this study, MCP230 was shown to competitively inhibit metabolism of 7-benzyl-4-trifluoromethylcoumarin and 7-ethoxyresorufin by the purified, reconstituted rabbit CYP1A2. MCP230 is at least 5- and 50-fold more potent as an inhibitor of CYP1A2 than silica containing 5% copper oxide and silica, respectively. Thus, even though PM generally inhibit multiple forms of P450, PM interacts differently with the forms of P450 resulting in different mechanisms of inhibition. P450s function as oligomeric complexes within the membrane. We also determined the mechanism by which PM inhibited metabolism by the mixed CYP1A2-CYP2B4 complex and found that the mechanism was purely competitive suggesting that the CYP2B4 is dramatically inhibited when bound to CYP1A2.
燃烧过程会产生不同类型的颗粒物（PM），这些颗粒物可能会对肺部和心血管系统产生有害影响。环境持久性自由基（EPFRs）是一种在氧化还原活性金属和芳烃存在下环境废物燃烧后产生的颗粒物。细胞色素P450（P450/CYP）是膜结合酶，对大多数亲脂性外源性物质的I相代谢至关重要。由2-单氯苯酚化学吸附到含5%氧化铜的二氧化硅（MCP230）上形成的EPFR已被证明通常会抑制不同形式的P450的活性，而不影响细胞色素P450还原酶和血红素加氧酶-1的活性。先前已表明，MCP230对大鼠肝微粒体CYP2D2和纯化的兔CYP2B4的抑制机制在底物方面是非竞争性的。在本研究中，MCP230被证明可竞争性抑制纯化的、重组的兔CYP1A2对7-苄基-4-三氟甲基香豆素和7-乙氧基试卤灵的代谢。MCP230作为CYP1A2抑制剂的效力分别比含5%氧化铜的二氧化硅和二氧化硅至少高5倍和50倍。因此，尽管PM通常会抑制多种形式的P450，但PM与P450的不同形式相互作用，导致不同的抑制机制。P450在膜内以寡聚体复合物的形式发挥作用。我们还确定了PM抑制混合的CYP1A2-CYP2B4复合物代谢的机制，发现该机制完全是竞争性的，这表明当CYP2B4与CYP1A2结合时会受到显著抑制。
