Hurst Christopher H, Waxman David J
Department of Biology, Division of Cell and Molecular Biology, Boston University, Boston, Massachusetts 02215, USA.
Toxicol Sci. 2003 Aug;74(2):297-308. doi: 10.1093/toxsci/kfg145. Epub 2003 Jun 12.
Phthalate esters are widely used as plasticizers in the manufacture of products made of polyvinyl chloride. Mono-(2-ethylhexyl)-phthalate (MEHP) induces rodent hepatocarcinogenesis by a mechanism that involves activation of the nuclear transcription factor peroxisome proliferator-activated receptor-alpha (PPARalpha). MEHP also activates PPAR-gamma (PPARgamma), which contributes to adipocyte differentiation and insulin sensitization. Human exposure to other phthalate monoesters, including metabolites of di-n-butyl phthalate and butyl benzyl phthalate, is substantially higher than that of MEHP, prompting this investigation of their potential for PPAR activation, assayed in COS cells and in PPAR-responsive liver (PPARalpha) and adipocyte (PPARgamma) cell lines. Monobenzyl phthalate (MBzP) and mono-sec-butyl phthalate (MBuP) both increased the COS cell transcriptional activity of mouse PPARalpha, with effective concentration for half-maximal response (EC50) values of 21 and 63 microM, respectively. MBzP also activated human PPARalpha (EC50=30 microM) and mouse and human PPARgamma (EC50=75-100 microM). MEHP was a more potent PPAR activator than MBzP or MBuP, with mouse PPARalpha more sensitive to MEHP (EC50=0.6 microM) than human PPARalpha (EC50=3.2 microM). MEHP activation of PPARgamma required somewhat higher concentrations, EC50=10.1 microM (mouse PPARgamma) and 6.2 microM (human PPARgamma). No significant PPAR activation was observed with the monomethyl, mono-n-butyl, dimethyl, or diethyl esters of phthalic acid. PPARalpha activation was verified in FAO rat liver cells stably transfected with PPARalpha, where expression of several endogenous PPARalpha target genes was induced by MBzP, MBuP, and MEHP. Similarly, activation of endogenous PPARgamma target genes was evidenced for all three phthalates by the stimulation of PPARgamma-dependent adipogenesis in the 3T3-L1 cell differentiation model. These findings demonstrate the potential of environmental phthalate monoesters for activation of rodent and human PPARs and may help to elucidate the molecular basis for the adverse health effects proposed to be associated with human phthalate exposure.
邻苯二甲酸酯被广泛用作聚氯乙烯制品生产中的增塑剂。单（2-乙基己基）邻苯二甲酸酯（MEHP）通过一种涉及激活核转录因子过氧化物酶体增殖物激活受体α（PPARα）的机制诱导啮齿动物肝癌发生。MEHP还能激活PPAR-γ（PPARγ），这有助于脂肪细胞分化和胰岛素敏感性。人类接触其他邻苯二甲酸单酯，包括邻苯二甲酸二丁酯和邻苯二甲酸丁苄酯的代谢物，比接触MEHP的程度高得多，这促使人们对它们激活PPAR的潜力进行研究，该研究在COS细胞以及PPAR反应性肝脏（PPARα）和脂肪细胞（PPARγ）细胞系中进行检测。邻苯二甲酸单苄酯（MBzP）和邻苯二甲酸单仲丁酯（MBuP）均能提高小鼠PPARα在COS细胞中的转录活性，半数最大效应浓度（EC50）值分别为21和63微摩尔。MBzP还能激活人PPARα（EC50 = 30微摩尔）以及小鼠和人PPARγ（EC50 = 75 - 100微摩尔）。MEHP是比MBzP或MBuP更强效的PPAR激活剂，小鼠PPARα对MEHP的敏感性高于人PPARα（小鼠PPARα的EC50 = 0.6微摩尔，人PPARα的EC50 = 3.2微摩尔）。MEHP激活PPARγ所需浓度略高，小鼠PPARγ的EC50 = 10.1微摩尔，人PPARγ的EC50 = 6.2微摩尔。未观察到邻苯二甲酸的单甲酯、单正丁酯、二甲酯或二乙酯对PPAR有明显激活作用。在稳定转染PPARα的FAO大鼠肝细胞中证实了PPARα的激活，其中MBzP、MBuP和MEHP诱导了几种内源性PPARα靶基因的表达。同样，在3T3-L1细胞分化模型中，通过刺激PPARγ依赖性脂肪生成，证实了这三种邻苯二甲酸酯对内源性PPARγ靶基因的激活作用。这些发现证明了环境邻苯二甲酸单酯激活啮齿动物和人类PPAR的潜力，并可能有助于阐明与人类邻苯二甲酸暴露相关的不良健康影响的分子基础。
