Kuykendall J R, Taylor M L, Bogdanffy M S
Haskell Laboratory for Toxicology and Industrial Medicine, E. I. du Pont de Nemours and Co., Inc., Newark, Delaware 19714.
Toxicol Appl Pharmacol. 1993 Dec;123(2):283-92. doi: 10.1006/taap.1993.1247.
Vinyl acetate is used in the paint, adhesive, and paper board industries. Vinyl acetate is a nasal carcinogen in rats exposed by inhalation for 2 years to 200 and 600 ppm, but not 50 ppm. Previous studies from our laboratory suggest that rat liver microsome-activated vinyl acetate induces plasmid DNA-histone crosslinks, in vitro, through esterase-mediated metabolism. Since nasal tissues contain high levels of carboxylesterase, tumorigenesis may be related to in situ production of the hydrolysis products acetaldehyde and acetic acid. Vinyl acetate was cytotoxic to both respiratory and olfactory tissues in vitro at 50-200 mM, but not 25 mM, after 2 hr exposure. Pretreatment of rats with the carboxylesterase inhibitor, bis-(p-nitrophenyl) phosphate (BNPP), attenuated the cytotoxic effects and metabolism of vinyl acetate in both tissue types. Semicarbazide, an aldehyde scavenger, was unable to protect the tissues from vinyl acetate-induced cytotoxicity. When the metabolites were tested, acetic acid, but not acetaldehyde, was cytotoxic to both tissues. The induction of DNA-protein crosslink (DPXL) formation by acetaldehyde and vinyl acetate in rat nasal epithelial tissues was detected using a sodium dodecyl sulfate/KCl precipitation technique. Endogenous crosslink levels ranged from 0.5 to 2.0% of total DNA and were considered background. Epithelial cells isolated from both olfactory and respiratory turbinates exhibited dose- and time-dependent increases in DPXL formation when exposed to 10-150 mM acetaldehyde for 1-2 hr at 37 degrees C. Similarly, respiratory and olfactory epithelial cells exposed to 5-75 mM vinyl acetate for 1-2 hr accumulated up to 12- and 15-fold higher crosslink levels than untreated cells, respectively. However, vinyl acetate appears to induce much higher levels of DPXLs at equimolar doses than acetaldehyde. This is thought to be related to stimulation of acetaldehyde-induced DPXL formation by the pH lowering effect of acetic acid production (via vinyl acetate hydrolysis). Pretreatment of the nasal turbinates with 1 mM BNPP reduced 25 mM vinyl acetate-induced DPXL formation by over 75% in both tissues. These data support a hypothesis that carboxylesterase-mediated hydrolysis of vinyl acetate is necessary to generate the active intracellular cross-linking agent, acetaldehyde, and the cytotoxic metabolite, acetic acid.
醋酸乙烯酯用于涂料、胶粘剂和纸板行业。醋酸乙烯酯对吸入暴露2年、浓度为200 ppm和600 ppm的大鼠是鼻腔致癌物，但对50 ppm的大鼠不是。我们实验室之前的研究表明，大鼠肝微粒体激活的醋酸乙烯酯在体外通过酯酶介导的代谢诱导质粒DNA - 组蛋白交联。由于鼻腔组织含有高水平的羧酸酯酶，肿瘤发生可能与水解产物乙醛和乙酸的原位产生有关。在体外，暴露2小时后，50 - 200 mM的醋酸乙烯酯对呼吸和嗅觉组织具有细胞毒性，但25 mM时无细胞毒性。用羧酸酯酶抑制剂双（对硝基苯基）磷酸酯（BNPP）预处理大鼠，可减弱醋酸乙烯酯在两种组织类型中的细胞毒性作用和代谢。氨基脲是一种醛清除剂，无法保护组织免受醋酸乙烯酯诱导的细胞毒性。当测试代谢产物时，乙酸对两种组织具有细胞毒性，而乙醛则没有。使用十二烷基硫酸钠/氯化钾沉淀技术检测乙醛和醋酸乙烯酯在大鼠鼻上皮组织中诱导的DNA - 蛋白质交联（DPXL）形成。内源性交联水平占总DNA的0.5%至2.0%，被视为背景。从嗅觉和呼吸鼻甲分离的上皮细胞在37℃下暴露于10 - 150 mM乙醛1 - 2小时后，DPXL形成呈现剂量和时间依赖性增加。同样，暴露于5 - 75 mM醋酸乙烯酯1 - 2小时的呼吸和嗅觉上皮细胞积累的交联水平分别比未处理细胞高12倍和15倍。然而，在等摩尔剂量下，醋酸乙烯酯似乎比乙醛诱导更高水平的DPXL。这被认为与乙酸产生（通过醋酸乙烯酯水解）的pH降低效应刺激乙醛诱导的DPXL形成有关。用1 mM BNPP预处理鼻甲可使25 mM醋酸乙烯酯诱导的两种组织中的DPXL形成减少超过75%。这些数据支持这样一种假设，即羧酸酯酶介导的醋酸乙烯酯水解对于产生活性细胞内交联剂乙醛和细胞毒性代谢产物乙酸是必要的。
