Characterization of Changes in Gene Expression and Biochemical Pathways at Low Levels of Benzene Exposure

Benzene, a ubiquitous environmental pollutant, causes acute myeloid leukemia (AML). Recently, through transcriptome profiling of peripheral blood mononuclear cells (PBMC), we reported dose-dependent effects of benzene exposure on gene expression and biochemical pathways in 83 workers exposed across four airborne concentration ranges (from 10 ppm) compared with 42 subjects with non-workplace ambient exposure levels. Here, we further characterize these dose-dependent effects with continuous benzene exposure in all 125 study subjects. We estimated air benzene exposure levels in the 42 environmentally-exposed subjects from their unmetabolized urinary benzene levels. We used a novel non-parametric, data-adaptive model selection method to estimate the change with dose in the expression of each gene. We describe non-parametric approaches to model pathway responses and used these to estimate the dose responses of the AML pathway and 4 other pathways of interest. The response patterns of majority of genes as captured by mean estimates of the first and second principal components of the dose-response for the five pathways and the profiles of 6 AML pathway response-representative genes (identified by clustering) exhibited similar apparent supra-linear responses. Responses at or below 0.1 ppm benzene were observed for altered expression of AML pathway genes and CYP2E1. Together, these data show that benzene alters disease-relevant pathways and genes in a dose-dependent manner, with effects apparent at doses as low as 100 ppb in air. Studies with extensive exposure assessment of subjects exposed in the low-dose range between 10 ppb and 1 ppm are needed to confirm these findings.苯作为一种广泛存在的环境污染物，可诱发急性髓系白血病（acute myeloid leukemia, AML）。近期，本团队通过对外周血单个核细胞（peripheral blood mononuclear cells, PBMC）开展转录组谱分析，针对83名暴露于四个空气苯浓度梯度（最低暴露水平为10 ppm）的工人与42名处于非工作场所环境苯暴露水平的受试者，报道了苯暴露对基因表达及生化通路的剂量依赖性效应。本研究针对全部125名研究对象，基于连续苯暴露数据进一步解析上述剂量依赖性效应：通过42名环境暴露受试者的未代谢尿苯水平，估算其空气苯暴露浓度；采用一种新型非参数数据自适应模型选择方法，估算每个基因的表达随剂量的变化情况。本研究还提出了用于建模通路响应的非参数方法，并利用该方法估算了AML通路及另外4条关注通路的剂量响应曲线。通过五条通路剂量响应的前两个主成分均值所捕捉到的多数基因响应模式，以及经聚类鉴定出的6个AML通路响应代表性基因的表达谱，均呈现出相似的显著超线性响应特征。在苯暴露浓度≤0.1 ppm时，即可观测到AML通路基因及细胞色素P450 2E1（cytochrome P450 2E1, CYP2E1）的表达改变。综上，本研究数据表明苯可通过剂量依赖性方式改变疾病相关通路及基因的表达，且在空气苯暴露浓度低至100 ppb时即可观测到相关效应。未来需针对10 ppb至1 ppm低剂量暴露范围的受试者开展全面暴露评估的研究，以验证本研究发现。