巴拉刈 (Paraquat)在1962年首度上市販賣，是目前世界上使用最為廣泛的除草劑之一，經常因誤食而進入人體內，它會對很多器官造成致死性的傷害，尤其是肺臟。巴拉刈會造成肺泡上皮的破壞，接著發展成肺纖維化，最後由於呼吸衰竭而造成死亡。巴拉刈造成肺毒性的機制被認為在體內產生大量的superoxide，而這些活性氧化物種攻擊細胞膜產生脂質過氧化，傷害細胞膜，然後導致細胞凋亡。
近來許多研究指出第二型肺泡上皮細胞容易受到氧化性壓力 (oxidative stress)的影響，第二型肺泡上皮細胞負責製造和分泌界面活性劑 (surfactants)，維持肺泡生理機能，因此是很重要的功能性細胞，因為paraquat對第二型肺泡上皮細胞造成傷害的詳細機制仍不清楚，所以本研究的目的是要探討巴拉刈對第二型肺泡上皮細胞功能損傷與細胞凋亡之確切作用機轉。實驗結果發現：給予大鼠第二型肺泡上皮細胞暴露巴拉刈24小時後，隨著濃度的增加 (50~900μM)，細胞存活率亦顯著的減少。利用流式細胞儀 (Flow cytometry)分析發現：第二型肺泡上皮細胞在暴露巴拉刈後會增加Sub-G1細胞數。利用螢光讀盤儀分析發現：第二型肺泡上皮細胞在暴露巴拉刈後會顯著造成細胞膜脂質過氧化物 (Lipid peroxidation, LPO)堆積。並且巴拉刈會造成粒線體膜電位去極化、使凋亡誘導因子 (AIF) 和核酸內切脢 (Endo G) 從粒線體釋放到細胞質、以及引起與細胞凋亡有關之mRNA (BAX、BID、P53)、與氧化性壓力有關之mRNA (ATF4、ATF6、GRP78、CHOP)表現和半胱氨酸蛋白酶caspase-3、-7、-9表現。綜合以上研究結果，巴拉刈會造成第二型肺泡上皮細胞功能損傷與細胞凋亡，主要之作用機制是透過氧化性傷害及粒線體和內質網依賴之細胞凋亡路徑。因此，本研究有助於釐清巴拉刈造成肺部損傷的詳細機轉，並進而提供臨床上巴拉刈中毒治療之重要方針。
Paraquat (1,1’-dimethyl-4,4’-bipyridium dichloride) is an effective herbicide which is used all over the world. Paraquat induces fatal damage to multiple organs, especially lung. The proposed mechanisms of cytotoxicity of paraquat are redox cycling and intracellular oxidative stress generation. In this study, we investigated the effects and the possible mechanisms of paraquat on the rat lung alveolar epithelial cell line (L2) and mouse lung tissue. In our study, L2 cells were exposed to paraquat (50–900μM) for 24 h. These results showed that cell viability were decreased, malondialdehyde (MDA) and reactive oxygen species (ROS) levels were increased in a dose-dependent manner after paraquat exposure for 24 h. Besides, paraquat treatment increased proteins of BAX, cytosol apoptosis-inducing factor (AIF) and cytosol Endonuclease G (Endo G) expression, and enhanced mitochondrial membrane potential depolarization. Furthermore, mitochondria-related apoptotic signals of mRNAs of BAX, BID and P53 were all increased in L2 cell after exposure to paraquat. In addition, mRNAs levels of endoplasmic reticulum stress (ER stress) related apoptotic signals of ATF4, ATF6, GRP78 and CHOP were also significantly increased. These results suggest that paraquat might induce alveolar epithelial cell death through both mitochondria- and ER stress-related pathways. These observations provide evidence that paraquat is an environmental risk factor for pulmonary injury.
