Arsenite decreases CYP3A4 and RXRα in primary human hepatocytes
Arsenite decreases CYP3A4 and RXRα in primary human hepatocytes
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DOI：
10.1124/dmd.105.003954
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发表时间：
2005-07-01
影响因子：
3.9
通讯作者：
Sinclair, JF
中科院分区：
文献类型：
--
作者：
Noreault, TL;Kostrubsky, VE;Sinclair, JF
砷是一种自然存在的、世界范围内的污染物，与人类的许多病理状况有关，包括癌症和几种形式的肝脏疾病。造成这些疾病的因素之一可能是砷改变细胞色素P450 （P450）水平。p450参与氧化代谢和许多有毒化学物质的消除。CYP3A4是人类主要的P450蛋白，参与了目前使用的一半药物的代谢。急性暴露于亚砷酸盐降低了培养的人肝细胞中CYP1A1/2蛋白的诱导和活性，以及培养的大鼠肝细胞中CYP3A23的诱导。这里，在人肝细胞的原代培养中，我们评估了急性亚砷酸盐暴露对CYP3A4和参与CYP3A4表达的几种转录因子的影响。这些研究中使用的亚砷酸盐浓度对肝细胞无毒，也没有引起氧化反应。在存在CYP3A4诱导剂利福平（Rif）或苯巴比妥的情况下，用亚砷酸盐治疗导致CYP3A4 mRNA、蛋白和活性显著降低。此外，未经处理的细胞中CYP3A4水平在亚砷酸盐处理后下降。CYP3A4基因的转录主要受类视黄醇X受体α (RXR α)和孕烷X受体（PXR）的异源二聚体调控。我们发现亚砷酸盐没有影响PXR或转录因子Sp1的表达，但导致PXR对Rif的响应性显著降低。亚砷酸盐引起核RXR α蛋白的大量减少，RXR α mRNA的减少程度较小。这些结果表明，亚砷酸盐通过降低PXR的活性以及核受体RXR α的表达来抑制未处理和诱导的人肝细胞中CYP3A4的转录。
Arsenic is a naturally occurring, worldwide contaminant implicated in numerous pathological conditions in humans, including cancer and several forms of liver disease. One of the contributing factors to these disorders may be the alteration of cytochrome P450 ( P450) levels by arsenic. P450s are involved in the oxidative metabolism and elimination of numerous toxic chemicals. CYP3A4, a major P450 in humans, is involved in the metabolism of half of all currently used drugs. Acute exposure to arsenite decreases the induction of CYP1A1/2 proteins and activities in cultured human hepatocytes, as well as CYP3A23 in cultured rat hepatocytes. Here, in primary cultures of human hepatocytes, we assessed the effects of acute arsenite exposure on CYP3A4 and several transcription factors involved in CYP3A4 expression. The concentrations of arsenite used in these studies were nontoxic to the hepatocytes and failed to elicit an oxidative response. Treatment with arsenite in the presence of CYP3A4 inducers, rifampicin (Rif) or phenobarbital, caused major decreases in CYP3A4 mRNA, protein, and activity. In addition, the levels of CYP3A4 in untreated cells were decreased following arsenite treatment. Transcription of the CYP3A4 gene is primarily regulated by heterodimers of the retinoid X receptor alpha (RXR alpha) and the pregnane X receptor (PXR). We found that arsenite failed to affect expression of PXR or the transcription factor Sp1, yet caused a significant decrease in PXR responsiveness to Rif. Arsenite caused a large decrease in nuclear RXR alpha protein and, to a lesser extent, RXR alpha mRNA. These results suggest that arsenite inhibits both untreated and induced CYP3A4 transcription in primary human hepatocytes by decreasing the activity of PXR, as well as expression of the nuclear receptor RXR alpha.