Mechanisms Underlying Early Rapid Increases in Creatinine in Paraquat Poisoning

Background

Acute kidney injury (AKI) is common after severe paraquat poisoning and usually heralds a fatal outcome. The rapid large increases in serum creatinine (Cr) exceed that which can be explained by creatinine kinetics based on loss of glomerular filtration rate (GFR).

Methods and Findings

This prospective multi-centre study compared the kinetics of two surrogate markers of GFR, serum creatinine and serum cystatin C (CysC), following paraquat poisoning to understand and assess renal functional loss after paraquat poisoning. Sixty-six acute paraquat poisoning patients admitted to medical units of five hospitals were included. Relative changes in creatinine and CysC were monitored in serial blood and urine samples, and influences of non-renal factors were also studied.

Results

Forty-eight of 66 patients developed AKI (AKIN criteria), with 37 (56%) developing moderate to severe AKI (AKIN stage 2 or 3). The 37 patients showed rapid increases in creatinine of >100% within 24 hours, >200% within 48 hours and >300% by 72 hours and 17 of the 37 died. CysC concentration increased by 50% at 24 hours in the same 37 patients and then remained constant. The creatinine/CysC ratio increased 8 fold over 72 hours. There was a modest fall in urinary creatinine and serum/urine creatinine ratios and a moderate increase in urinary paraquat during first three days.

Conclusion

Loss of renal function contributes modestly to the large increases in creatinine following paraquat poisoning. The rapid rise in serum creatinine most probably represents increased production of creatine and creatinine to meet the energy demand following severe oxidative stress. Minor contributions include increased cyclisation of creatine to creatinine because of acidosis and competitive or non-competitive inhibition of creatinine secretion. Creatinine is not a good marker of renal functional loss after paraquat poisoning and renal injury should be evaluated using more specific biomarkers of renal injury.     

Prediction of Patient Survival in Cases of Acute Paraquat Poisoning

Paraquat concentration-time data have been used to predict the clinical outcome following ingestion. However, these studies have included only small populations, although paraquat poisoning has a very high mortality rate. The purpose of this study was to develop a simple and reliable model to predict survival according to the time interval post-ingestion in patients with acute paraquat poisoning. Data were retrospectively collected for patients who were admitted with paraquat poisoning to Soonchunhyang University Choenan Hospital between January 2005 and December 2012. Plasma paraquat levels were measured using high-performance liquid chromatography. To validate the model we developed, we used external data from 788 subjects admitted to the Presbyterian Medical Center, Jeonju, Korea, between January 2007 and December 2012. Two thousand one hundred thirty six patients were included in this study. The overall survival rate was 44% (939/2136). The probability of survival for any specified time and concentration could be predicted as (exp(logit))/(1+exp(logit)), where logit = 1.3544+[−3.4688×log10(plasma paraquat μg/M)]+[−2.3169×log10(hours since ingestion)]. The external validation study showed that our model was highly accurate for the prediction of survival (C statics 0.964; 95% CI [0.952–0.975]). We have developed a model that is effective for predicting survival after paraquat intoxication.     

血液透析对急性百草枯中毒的临床疗效分析

目的：探讨血液透析（hemodilalysis,HD）治疗急性百草枯中毒的临床疗效,为临床应用HD治疗急性百草枯中毒提供依据。方法：选择我院2003 年3 月~2012 年7 月收治的百草枯中毒患者40 例,根据患者使用是否行透析治疗分为透析组（A组17 例）和非透析组（B 组23 例）,比较分析两组患者治疗后的肝功能、肾功能、肺功能及心肌酶学指标的变化,治疗效果及存活情况。结果：两组患者入院后前3 天ALT、AST、BUN、CR、CK、CK-MB 水平均呈上升趋势,且非透析组患者以上指标的水平高于透析组患者,但差异无统计学意义（P〉0.05）,入院后第7 天,两组以上指标的比较亦无统计学差异（P〉0.05）;两组患者之间入院时和入院后72小时内最低的SPO2%、血气分析中PaO2和PaCO2水平比较无统计学意义（P〉0.05）;透析组和非透析组患者的病死率分别为70.6%和69.6%,差异无统计学意义（P〉0.05）。结论：百草枯溶液中毒的患者预后差、病死率高,血液透析治疗并不能显著提高急性百草枯中毒患者的生存率。     

Traditional Chinese Medicine Xuebijing Treatment Is Associated with Decreased Mortality Risk of Patients with Moderate Paraquat Poisoning

Paraquat poisoning causes multiple organ injury and high mortality due to severe toxicity and lack of effective treatment. Xuebijing (XBJ) injection, a traditional Chinese medicine preparation of five Chinese herbs (Radix Salviae Miltiorrhiae, Rhizoma Chuanxiong, Flos Carthami, Angelica Sinensis and Radix Paeoniae Rubra), has an anti-inflammatory effect and is widely used in the treatment of sepsis. This retrospective study was designed to evaluate the effects of XBJ combined with conventional therapy on mortality risk of patients with acute paraquat poisoning. Out of 68 patients, 27 were treated with conventional therapy (control group) and 41 were treated with intravenous administration of XBJ (100 ml, twice a day, up to 7 days) plus conventional therapy (XBJ group). Vital organ function, survival time within 28 days and adverse events during the treatment were reviewed. Results indicated that XBJ treatment significantly increased median survival time among patients ingesting 10-30 ml of paraquat (P=0.02) compared with the control group. After adjustment for covariates, XBJ treatment was associated significantly with a lower mortality risk (adjusted HR 0.242, 95% CI 0.113 to 0.516, P=0.001) compared with the control group. Additionally, compared with Day 1, on Day 3 the value of PaO₂/FiO₂ was significantly decreased, and the values of serum alanine aminotransferase, creatinine and troponin T were significantly increased in the control group (all P<0.05), but these values were significant improved in the XBJ group (all P<0.05). Only one patient had skin rash with itch within 30 minutes after injection and no severe adverse events were found in the XBJ group. In conclusion, XBJ treatment is associated with decreased mortality risk of patients with moderate paraquat poisoning, which may be attributed to improved function of vital organs with no severe adverse events.     

血清胱抑素C在百草枯中毒所致急性肾功能损伤中的早期诊断意义

目的:探讨急性百草枯中毒(acute paraquat poisoning,APP)患者血清胱抑素C(ScysC)水平对百草枯所致急性肾功能损伤(acute renal injury,AKI)早期诊断的意义和临床价值.方法:以43例急性百草枯中毒患者和20例健康体检者为研究对象,通过紫外分光光度法检测患者入院时百草枯的血药浓度,并据此将患者分为0～5mg·L-1组、5～10mg·L-1组、＞ 10mg·L-1组,检测患者入院第1天内血肌酐(SCr)、尿素氮(Urea)、ScysC的水平.结果:不同的百草枯血药浓度组SCr和Urea的水平与对照组比较均无显著性差异(P＞0.05);0～5mg· L-1组ScysC的水平与对照组比较无显著性差异(P＞0.05),但5～10mg·L-1组及＞10mg·L-1组ScysC的水平均显著高于对照组(P＜0.05),且与血药浓度呈显著正相关;入院第1天内5～10mg· L-1组及＞10mg· L-1组的ScysC异常检出率均显著高于各组SCr和Urea异常检出率(P＜0.05).结论:ScysC能更早地反映APP所致AKI,且与中毒程度呈正相关性,可能是APP发病早期一个较SCr、Urea更敏感反映患者病情的指标.     

Reduction of paraquat toxicity by superoxide dismutase

The effect of intravenously administered superoxide dismutase on paraquat-treated rats kept either in air or an atmosphere of 90%–95% oxygen was investigated. Of those rats maintained in the oxygen-enriched atmosphere, 50% died within 30 hours whereas, 50 hours elapsed before 50% mortality was observed for the superoxide dismutase-treated rats. Those animals allowed to remain in air were more responsive to superoxide dismutase treatment. Of those animals for which paraquat was fatal, untreated rats showed 50% cumulative mortality within 35 hours after paraquat administration, whereas those rats treated with superoxide dismutase showed 50% mortality after 80 hours. Sections of lung tissue examined at low magnification indicated that the extensive alveolar and vascular damage caused by paraquat was ameliorated with the administration of superoxide dismutase. These findings may have particular relevance in the treatment of paraquat intoxication in humans.     

腹腔注射百草枯构建小鼠肺纤维化模型

目的:探讨百草枯一次性腹腔注射致小鼠肺纤维化的病理改变及半数致死剂量(LD50),进而制备肺纤维化病理改变稳定的百草枯中毒小鼠肺纤维化模型。方法:60只正常雌性C57BL/6J小鼠被随机分为6组,10只/组,分别为正常对照组及百草枯给药30、40、50、60和80 mg/kg组,所有小鼠于造模后28 d处死,取其左肺用于病理观察(HE染色),并计算LD50及各组肺纤维化Ashcroft评级。结果:至观察期28 d,小鼠一次性腹腔注射百草枯溶液的LD50为55.1923 mg/kg;各染毒组均出现不同程度的肺纤维化改变,且注射剂量越高,肺纤维化病变越严重,但早期死亡率亦越高。结论:一次性腹腔注射百草枯可制备小鼠肺纤维化模型,40和50 mg/kg为较合适的造模剂量。     

不同剂量甲泼尼龙对大鼠急性百草枯中毒肾脏的影响

目的:观察不同剂量甲泼尼龙治疗大鼠百草枯中毒肾脏损伤的疗效。方法:将120只Wistar大鼠随机分为五组,空白组,染毒组和干预组(根据甲泼尼龙剂量不同分为三组),除空白组外,均予百草枯(22mg/kg)稀释后腹腔注射,2h后依照组别、体重注射甲泼尼龙,在第1、3、7天共3个时间点,按抽签法处死实验对象6只获取标本,观察肾功能和病理变化。结果:各组血尿素氮(P=0.001<0.05)和肌酐(P=0.01<0.05)差异有统计学意义,干预组中5mg/kg甲泼尼龙组同染毒组比较差异有统计学意义。不同时间点血尿素氮(P=0.007<0.05)和肌酐(P=0.016<0.05)差异有统计学意义,其中第七天明显低于第一、三天。病理评分各组(P=0.21>0.05)差异无统计学意义。讨论:早期应用糖皮质激素治疗PQ中毒大鼠,可以显著减轻PQ中毒所致的肾损伤程度,改善肾功能,尤其小剂量改善显著,传统的大剂量糖皮质激素冲击治疗不值的推崇。     

Kinetic Analysis of Resistance to Paraquat in Conyza: Evidence that Paraquat Transiently Inhibits Leaf Chloroplast Reactions in Resistant Plants

Paraquat resistance has been claimed to be due to a sequestration of the herbicide before it reaches chloroplasts. This is based on the sensitivity of photosystem I in isolated thylakoids to paraquat, and autoradiographic analyses showing label from paraquat near veins 4 hours after treatment of a resistant biotype. Conversely, the enzymes of the superoxide detoxification pathway were found to be at constitutively elevated levels in intact class A chloroplasts of the resistant biotype of Conyza bonariensis (L.) Cronq. Evidence is presented here that physiologically active levels of paraquat rapidly inhibit chloroplast function in both the resistant and sensitive biotype, before the first sequestration was visualized. This inhibition is transient (completed in 2 hours) in the resistant biotype and irreversible in the sensitive type. Intact class A chloroplasts of the resistant biotype with or without paraquat are less susceptible to photoinduced membrane damage than the sensitive biotype without paraquat, as measured by ethane evolution. These data support a hypothesis that the ability to prevent superoxide damage keeps the resistant biotype viable while paraquat or its metabolites are being sequestered.     

Using Bosentan to Treat Paraquat Poisoning-Induced Acute Lung Injury in Rats

Background

Paraquat poisoning is well known for causing multiple organ function failure (MODS) and high mortality. Acute lung injury and advanced pulmonary fibrosis are the most serious complications. Bosentan is a dual endothelin receptor antagonist. It plays an important role in treating PF. There is no related literature on the use of bosentan therapy for paraquat poisoning.

Objective

To study the use of bosentan to treat acute lung injury and pulmonary fibrosis as induced by paraquat.

Method

A total of 120 adult Wister male rats were randomly assigned to three groups: the paraquat poisoning group (rats were intragastrically administered with paraquat at 50 mg/kg body weight once at the beginning); the bosentan therapy group (rats were administered bosentan at 100 mg/kg body weight by intragastric administration half an hour after paraquat was administered, then the same dose was administered once a day); and a control group (rats were administered intragastric physiological saline). On the 3rd, 7th, 14th, and 21st days following paraquat exposure, rats were sacrificed, and samples of lung tissue and venous blood were collected. The levels of transforming growth factor-β1 (TGF-β1), endothelin-1 (ET-1), and hydroxyproline (HYP) in the plasma and lung homogenate were determined. Optical and electronic microscopes were used to examine pathological changes.

Result

The TGF-β1, ET-1, and HYP of the paraquat poisoning group were significantly higher than in the control group, and they were significantly lower in the 21st day therapy group than in the paraquat poisoning group on the same day. Under the optical and electronic microscopes, lung tissue damage was observed to be more severe but was then reduced after bosentan was administered.

Conclusion

Bosentan can reduce inflammation factor release. It has a therapeutic effect on acute lung injury as induced by paraquat.     

硫化氢在急性百草枯中毒致大鼠肺损伤中的作用

目的阐明百草枯中毒致大鼠肺损伤时机体内源性H2S的变化,探讨硫化氢在急性百草枯中毒致大鼠肺损伤中的作用。方法按时间点将50只大鼠分为5组,同时染毒;选择对应时间点50只大鼠为对照组。分组检测肺组织中内源性H2S的含量,并及时处死大鼠,行肺组织损伤病理学评分。另外取大鼠40只分为4组,即空白对照组、染毒组、染毒+外源性H2S组、外源性H2S组,于12h后,检测肺组织中内源性H2S的含量,并及时处死大鼠,行肺组织损伤病理学评分。结果百草枯中毒致大鼠肺损伤在不同时间范围内,机体内源性H2S的含量差异有显著统计学意义(P0.01);与染毒组比较,染毒组+外源性H2S组肺损伤程度评分显著降低,差异具有显著统计学意义(P0.01)。结论百草枯致大鼠肺损伤过程中,内源性H2S的含量与肺损伤程度呈负相关;外源性H2S通过增加体内肺组织H2S的含量,抑制百草枯致肺损伤。。     

The Volume Ratio of Ground Glass Opacity in Early Lung CT Predicts Mortality in Acute Paraquat Poisoning

Background

Pulmonary injury is the main cause of death in acute paraquat (PQ) poisoning. However, whether quantitative lung computed tomography (CT) can be useful in predicting the outcome of PQ poisoning remains unknown. We aimed to identify early findings of quantitative lung CT as predictors of outcome in acute PQ poisoning.

Methods

Lung CT scanning (64-slide) and quantitative CT lesions were prospectively measured for patients after PQ intoxication within 5 days. The study outcome was mortality during 90 days follow-up. Survival curves were derived by the Kaplan-Meier method, and mortality risk factors were analyzed by the forward stepwise Cox regression analysis.

Results

Of 97 patients, 41 (42.3%) died. Among the eight different types of lung CT findings which appeared in the first 5-day of PQ intoxication, four ones discriminated between survivors and non-survivors including ground glass opacity (GGO), consolidation, pneumomediastinum and “no obvious lesion”. With a cutoff value of 10.8%, sensitivity of 85.4% and specificity of 89.3%, GGO volume ratio is better than adopted outcome indicators in predicting mortality, such as estimated amount of PQ ingestion, plasma or urine PQ concentration, acute physiology and chronic health evaluation (APACHE) II and sequential organ failure assessment (SOFA) scores. GGO volume ratios above 10.8% were associated with increased mortality (hazard ratio, 5.82; 95% confidence interval, 4.77-7.09; P < 0.001).

Conclusions

The volume ratio of GGO exceeding 10.8% is a novel, reliable and independent predictors of outcome in acute PQ poisoning.     

Paraquat toxicity

Paraquat (1,1'-dimethyl-4,4'-bipyridylium dichloride) is marketed as a contact herbicide. Although it has proved safe in use there have been a number of cases of poisoning after the intentional swallowing of the commercial product. The most characteristic feature of poisoning is lung damage, which causes severe anoxia and may lead to death. The specific toxicity to the lung can be explained in part by the accumulation of paraquat into the alveolar type I and type II epithelial cells by a process that has been shown to accumulate endogenous diamines and polyamines. When accumulated, paraquat undergoes an NADPH-dependent, one-electron reduction to form its free radical, which then reacts avidly with molecular oxygen to reform the cation and produce superoxide anion, which in turn will dismutate to form H2O2. This may lead to the formation of more reactive (and hence toxic) radicals which have the potential to cause lipid peroxidation and lead to cell death. Biochemical changes provoked by paraquat in the lung suggest that it causes a rapid, pronounced and prolonged oxidation of NADPH that initiates compensatory biochemical processes in the lung. NADPH may be further depleted as it is consumed in an attempt to detoxify H2O2 or lipid hydroperoxides. Thus it is possible that with toxic levels of paraquat in the cell, compensatory biochemical processes are insufficient to maintain levels of NADPH consistent either with cell survival or with the ability to detoxify H2O2 or prevent lipid peroxidation.     

内质网应激及自噬参与百草枯中毒所致肺损伤

目的:探讨内质网应激及自噬在百草枯中毒所致大鼠肺脏损伤中的作用。方法:选取Wistar大鼠腹80只,腹腔注射百草枯(15 mg/kg)建立百草枯中毒肺脏损伤的动物模型。染毒后1、3、7、14、21 d处死动物取肺组织,采用HE染色和Van Gieson(V.G)染色观察大鼠肺脏损伤及纤维化情况,电镜观察Wistar大鼠肺脏胞浆空泡变、自噬体的形成以及肺脏损伤。Western-blot方法观察Wistar大鼠内质网应激相关蛋白(GRP94、Caspase-12和CHOP)和自噬相关蛋白(LC3-II、Beclin-1)的表达。结果:HE及V.G染色结果显示随中毒时间延长,百草枯中毒肺损伤及肺纤维化逐渐加重;电镜结果显示百草枯中毒肺脏发生胞浆空泡变、自噬体形成。与对照组比较,在百草枯中毒组内质网应激相关蛋白GRP94在3 d表达达到峰值(P0.001),7 d表达开始降低(P0.05),CHOP蛋白表达3 d开始增加(P0.001),cleaved caspase-12蛋白表达7 d开始增加(P0.001),并逐渐加强,自噬相关蛋白LC3-II和Beclin-1表达3 d开始增加(P0.001),14 d表达最高(P0.001)。结论:内质网应激以及细胞自噬共同参与百草枯中毒所致肺脏损伤。     

百草枯致急性肺损伤大鼠模型的建立

目的建立一种百草枯诱导的急性肺损伤（ALI）大鼠模型。方法将20只SD大鼠随机分为正常对照组10只、实验组10只。实验组一次性口服灌胃百草枯（PQ）80mg／kg,于给药后1天处死大鼠,观察光镜下肺组织病理改变、肺动脉血氧分压（PaO2）、支气管肺泡灌洗液（BALF）蛋白含量等。结果给予百草枯1天后肺形态学出现显著异常,PaO2及BALF蛋白含量出现显著改变。结论一次性灌胃百草枯80mg／kg成功建立急性肺损伤动物模型。     

甘草酸二铵对百草枯中毒致急性肺损伤大鼠TLR-4表达的影响

目的探讨甘草酸二铵(DG)对百草枯(PQ)中毒致急性肺损伤(ALI)大鼠的保护作用及其机制。方法选择健康SD大鼠50只,随机分为百草枯组(PQ组)、甘草酸二铵组(DG组)和正常对照组(NS组),PQ组和DG组予百草枯100mg/kg灌胃1次,DG组于灌胃后立即腹腔注射DG 50mg/kg,每日1次,对照组与PQ组注射等剂量的生理盐水。观察至48h处死大鼠,取肺组织检测肺湿干重比;肺组织HE染色评价肺组织损伤情况;采用RT-PCR法检测肺组织TLR-4mRNA和NF-κB mRNA的表达情况。另选择健康SD大鼠50只,分组及各组处置方法同上,观察其7天内死亡率。结果 PQ组与DG组肺湿干比、肺组织TLR-4mRNA和NF-κB mRNA表达较NS组明显升高(P0.01);DG组各指标明显低于PQ组(P0.01)。HE染色结果,NS组肺部结构正常,PQ组、DG组可见肺组织水肿、出血及炎性细胞浸润等肺损伤表现,DG组病变轻于PQ组。群体死亡率比较,PQ组7天死亡率为90%,DG组为40%,NS组无死亡。结论甘草酸二铵可减轻百草枯中毒致急性肺损伤大鼠肺部炎症,其机制可能与降低TLR-4、NF-κB的表达有关。     

不同剂量甲泼尼龙对大鼠急性百草枯中毒肾脏的影响

目的：观察不同剂量甲泼尼龙治疗大鼠百草枯中毒肾脏损伤的疗效。方法：将120只Wistar大鼠随机分为五组,空白组,染毒组和干预组（根据甲泼尼龙剂量不同分为三组）,除空白组外,均予百草枯（22mg／kg）稀释后腹腔注射,2h后依照组别、体重注射甲泼尼龙,在第1、3、7天共3个时间点,按抽签法处死实验对象6只获取标本,观察肾功能和病理变化。结果：各组血尿素氮（P=0．001〈0．05）和肌酐（P=0．01〈0．05）差异有统计学意义,干预组中5mg／kg甲泼尼龙组同染毒组比较差异有统计学意义。不同时间点血尿素氮（P=0．007〈0．05）和肌酐（P=0．016〈0．05）差异有统计学意义,其中第七天明显低于第一、三天。病理评分各组（P=O．21〉0．05）差异无统计学意义。讨论：早期应用糖皮质激素治疗PQ中毒大鼠,可以显著减轻PQ中毒所致的肾损伤程度,改善肾功能,尤其小剂量改善显著,传统的大剂量糖皮质激素冲击治疗不值的推崇。     

Caspase-12抑制剂对百草枯中毒大鼠肝损伤的保护作用

目的:观察caspase-12抑制剂Z-ATAD-FMK对百草枯染毒大鼠肝脏caspase-12蛋白表达和肝细胞凋亡的影响,以及通过血清SOD和MDA的检测,探讨其对百草枯中毒大鼠肝脏保护作用和对机体氧化应激反应的作用。方法:50只健康Wistar大鼠随机分三组:A组为正常对照组;B组为模型组(PQ染毒);C组抑制剂组(PQ/Z-ATAD-FMK),于3d、7d处死B组和C组各10只大鼠。取血检测ALT、TBIL、SOD和MDA;HE染色观察肝组织病理学变化;免疫组化法检测caspase-12蛋白;二苯胺法检测细胞凋亡率。SPSS18.0统计分析。结果:Z-ATAD-FMK抑制剂组ALT、TBIL、MDA值低于模型组(P0.05),SOD高于模型组(P0.05);caspase-12蛋白表达和细胞凋亡率亦低于模型组(P0.05);HE染色显示凋亡和坏死程度也较模型组轻。结论:Caspase-12抑制剂Z-ATAD-FMK能减少百草枯中毒大鼠肝脏caspase-12蛋白表达和肝细胞凋亡率,减轻肝细胞坏死,对肝脏具有保护作用,同时可以抑制百草枯中毒大鼠的氧化应激反应。     

Spontaneous lung chemiluminescence upon paraquat administration

In vivo rat lung chemiluminescence was measured at different times after a single injection of either 30 or 60 mg paraquat/kg b.w. The lungs were isolated to determine myeloperoxidase (index of polymorphonuclear leukocytes), lung wet weight (lung edema) and malondialdehyde (lipid peroxidation). The highest chemiluminescence was reached 30 hours after injection of 30 mg/kg or 6 hours after a 60 mg/kg dose. The peak chemiluminescence was coincident with the maximum concentration of myeloperoxidase and lung wet weight suggesting that most chemiluminescence was the consequence of polymorphonuclear activation after migration to the injured areas.     

Paraquat detoxicative system in the mouse liver postmitochondrial fraction

We examined the paraquat detoxicative system in mouse livers. The survival rate of mice receiving 50 mg/kg paraquat was 41% at 7 days and significantly rose to 88, 64, 69% with pretreatment with phenytoin, phenobarbital, and rifampicin, respectively. Phenytoin induced activity in NADPH-cytochrome P450 reductase, CYP3A, CYP2B, and CYP2C that was 3 to 4 times higher than that of the controls. Phenobarbital induced CYP2B and rifampicin induced CYP3A, respectively, in addition to NADPH-cytochrome P450 reductase. 3-Methylcholanthrene did not induce these enzymes and did not alter the survival rate. All the mice pretreated with CoCl(2) (a CYP synthesis inhibitor) or SKF 525-A (a CYP inhibitor) were dead after 5 days, and troleandomycin (a CYP3A-specific inhibitor) also reduced the survival rate. When cell homogenates were incubated with paraquat and NADPH, paraquat decreased and its metabolic intermediate paraquat-monopyridone was formed. Troleandomycin inhibited the decrease in paraquat and increased the monopyridone. After making a subfraction of the homogenate, monopyridone was produced in the postmicrosomal 105,000g supernatant, but not in the microsomes. The pretreatment of mice with phenytoin decreased the monopyridone in the postmitochondrial fraction, but did not affect the supernatant. These results indicated that paraquat was first metabolized in the postmicrosomal supernatant into monopyridone, and that may have been subsequently hydroxylated by the microsomes. Repeated intravenous injections of alpha-tocopherol to paraquat-loaded mice significantly reduced the paraquat mortality and when these mice were pretreated with rifampicin, 100% of them survived. These studies demonstrate that postmitochondrial fractions play an important role in paraquat detoxication metabolism, and that the combination of CYP induction and alpha-tocopherol administration is highly useful for the survival of paraquat-exposed mice.