Leukemia-related chromosomal loss detected in hematopoietic progenitor cells of benzene-exposed workers

Abstract

Benzene exposure causes acute myeloid leukemia and hematotoxicity, shown as suppression of mature blood and myeloid progenitor cell numbers. As the leukemia-related aneuploidies monosomy 7 and trisomy 8 previously had been detected in the mature peripheral blood cells of exposed workers, we hypothesized that benzene could cause leukemia through the induction of these aneuploidies in hematopoietic stem and progenitor cells. We measured loss and gain of chromosomes 7 and 8 by fluorescence in situ hybridization in interphase colony-forming unit-granulocyte-macrophage (CFU-GM) cells cultured from otherwise healthy benzene-exposed (n=28) and unexposed (n=14) workers. CFU-GM monosomy 7 and 8 levels (but not trisomy) were significantly increased in subjects exposed to benzene overall, compared with levels in the control subjects (P=0.0055 and P=0.0034, respectively). Levels of monosomy 7 and 8 were significantly increased in subjects exposed to <10 p.p.m. (20%, P=0.0419 and 28%, P=0.0056, respectively) and ≥ 10 p.p.m. (48%, P=0.0045 and 32%, 0.0354) benzene, compared with controls, and significant exposure-response trends were detected (P(trend)=0.0033 and 0.0057). These data show that monosomies 7 and 8 are produced in a dose-dependent manner in the blood progenitor cells of workers exposed to benzene, and may be mechanistically relevant biomarkers of early effect for benzene and other leukemogens.

Figure 1. Monosomy 7 and 8 in CFU-GM cells of unexposed controls and subjects exposed to <10 ppm and ≥10 ppm benzene

Trends in chromosomal monosomy rates with benzene exposure and differences in monosomy rates by benzene exposure category (i.e., unexposed controls vs. workers exposed to <10 ppm and ≥10 ppm benzene) were tested by fitting appropriate negative binomial regression models. Models were adjusted for age and sex, and additionally for smoking, alcohol, recent infections and BMI if significant (Table 1). Significant p_trend values are shown. p values are indicated as * p<0.05; ** p<0.01. Levels of monosomy 7 and 8 in CFU-GM were significantly increased at <10 ppm and ≥10 ppm benzene and with increasing benzene exposure

Figure 2. Linear vs non-linear models of monsosomy 7 and 8 versus benzene exposure

Observed versus predicted monosomy 7 and 8 counts versus benzene exposure, determined using a cross-validation approach in linear and non-linear (completely unspecified smooths) models, are plotted. There is no significant difference in the relative fit of the models.

Figure 3. White blood cell (WBC) count and number of CFU-GM colonies in unexposed controls and subjects exposed to <10 ppm and ≥10 ppm benzene

Trends in WBC cell or CGU-GM colony counts with benzene level, and differences in cell or colony count by benzene exposure category, were tested by negative binomial regression (CFU-GM) and linear regression (WBC). Models were adjusted for age and sex, and additionally for smoking, alcohol, recent infections and BMI if significant (Table 1). Significant p_trend values are shown. p values are indicated as *** p<0.001, and **** p<0.0001. WBC and CFU-GM colony counts were significantly lowered in the ≥10 ppm exposed group of workers and with increasing benzene exposure.