The effect of real-ambient PM2.5 exposure on the lung and gut microbiomes and the regulation of Nrf2.

The influence of air pollution on human health has sparked widespread concerns across the world. Previously, we found that exposure to ambient fine particulate matter (PM2.5) in our "real-ambient exposure" system can result in reduced lung function. However, the mechanism of organ-specific toxicity is still not fully elucidated. The balance of the microbiome contributes to maintaining lung and gut health, but the changes in the microbiome under PM2.5 exposure are not fully understood. Recently, crosstalk between nuclear factor E2-related factor 2 (Nrf2) and the microbiome was reported. However, it is unclear whether Nrf2 affects the lung and gut microbiomes under PM2.5 exposure. In this study, wild-type (WT) and Nrf2-/- (KO) mice were exposed to filtered air (FA) and real ambient PM2.5 (PM) in the " real-ambient exposure" system to examine changes in the lung and gut microbiomes. Here, our data suggested microbiome dysbiosis in lung and gut of KO mice under PM2.5 exposure, and Nrf2 ameliorated the microbiome disorder. Our study demonstrated the detrimental impacts of PM2.5 on the lung and gut microbiome by inhaled exposure to air pollution and supported the protective role of Nrf2 in maintaining microbiome homeostasis under PM2.5 exposure.

Application of ARE-reporter systems in drug discovery and safety assessment.

The human body is continuously exposed to xenobiotics and internal or external oxidants. The health risk assessment of exogenous chemicals remains a complex and challenging issue. Alternative toxicological test methods have become an essential strategy for health risk assessment. As a core regulator of constitutive and inducible expression of antioxidant response element (ARE)-dependent genes, nuclear factor erythroid 2-related factor 2 (Nrf2) plays a critical role in maintaining cellular redox homeostasis. Consistent with the properties of Nrf2-mediated antioxidant response, Nrf2-ARE activity is a direct indicator of oxidative stress and thus has been used to identify and characterize oxidative stressors and redox modulators. To screen and distinguish chemicals or environmental insults that affect the cellular antioxidant activity and/or induce oxidative stress, various in vitro cell models expressing distinct ARE reporters with high-throughput and high-content properties have been developed. These ARE-reporter systems are currently widely applied in drug discovery and safety assessment. In the present review, we provide an overview of the basic structures and applications of various ARE-reporter systems employed for discovering Nrf2-ARE modulators and characterizing oxidative stressors.

Developmental arsenic exposure induces dysbiosis of gut microbiota and disruption of plasma metabolites in mice.

Arsenic is a notorious environmental pollutant. Of note, developmental arsenic exposure has been found to increase the risk of developing a variety of ailments later in life, but the underlying mechanism is not well understood. Many elements of host health have been connected to the gut microbiota. It is still unclear whether and how developmental arsenic exposure affects the gut microbiota. In the present study, we found that developmental arsenic exposure changed intestinal morphology and increased intestinal permeability and inflammation in mouse pups at weaning. These alterations were accompanied by a significant change in gut microbiota, as evidenced by considerably reduced gut microbial richness and diversity. In developmentally arsenic-exposed pups, the relative abundance of Muribaculaceae was significantly decreased, while the relative abundance of Akkermansia and Bacteroides was significantly enhanced at the genus level. Metabolome and pathway enrichment analyses indicated that amino acid and purine metabolism was promoted, while glycerophospholipid metabolism was inhibited. Interestingly, the relative abundance of Muribaculaceae and Akkermansia showed a strong correlation with most plasma metabolites significantly altered by developmental arsenic exposure. These data indicate that gut microbiota dysbiosis may be a critical link between developmental arsenic exposure and metabolic disorders and shed light on the mechanisms underlying increased susceptibility to diseases due to developmental arsenic exposure.

Research for type 2 diabetes mellitus in endemic arsenism areas in central China: role of low level of arsenic exposure and KEAP1 rs11545829 polymorphism.

Type 2 diabetes mellitus (T2DM) is one of the major public health problems worldwide; both genetic and environmental factors are its risk factors. Arsenic, an environmental pollutant, might be a risk factor for T2DM, but the association of low-to-moderate level arsenic exposure with the risk of T2DM is still inconsistent. Single nucleotide polymorphisms (SNPs) can affect the development of T2DM, but the study on KEAP1 rs11545829 (G>A) SNP is few. In this paper, we explored the effect of KEAP1 rs11545829 (G>A) SNP and low-to-moderate level arsenic exposure on risk of T2DM in a cross-sectional case-control study conducted in Shanxi, China. Total of 938 participants, including 318 T2DM cases and 618 controls, were enrolled. Blood glycosylated haemoglobin (HbA1c) was detected by Automatic Biochemical Analyzer, and participants with HbA1c≧6.5% were diagnosed as T2DM. Urinary total arsenic (tAs, mg/L), as the indicator of arsenic exposure, was detected by liquid chromatography-atomic fluorescence spectrometry (LC-AFS). Genomic DNA was extracted and the genotypes of KEAP1 rs11545829 SNP were examined by multiplex polymerase chain reaction (PCR). The urinary tAs concentration in recruited participants was 0.075 (0.03-0.15) mg/L, and was associated with an increased risk of T2DM (OR = 8.45, 95% CI 2.63-27.17); rs11545829 mutation homozygote AA genotype had a protective effect on risk of T2DM (OR = 0.42, 95 % CI 0.25-0.73). Although this protective effect of AA genotype was found in participants with higher urinary tAs level (>0.032 mg/L) (OR = 0.48, 95% CI 0.26-0.86), there was no interaction effect for arsenic exposure and rs11545829 SNP on risk of T2DM. In addition, BMI modified the association between rs11545829 SNP and the risk of T2DM (RERI = -1.11, 95% CI -2.18-0.04). The present study suggest that low-to-moderate level arsenic exposure may be a risk factor, while KEAP1 rs11545829 SNP mutation homozygote AA genotype may be a protective factor for risk of T2DM, especially for T2DM patients with urinary tAs level>0.032 mg/L.

Long-isoform NFE2L1 silencing inhibits acquisition of malignant phenotypes induced by arsenite in human bronchial epithelial cells.

Chronic arsenic exposure is associated with the increased risk of several types of cancer, among which, lung cancer is the most deadly one. Nuclear factor erythroid 2 like 1 (NFE2L1), a transcription factor belonging to CNC-bZIP family, regulates multiple important cellular functions in response to acute arsenite exposure. However, the role of NFE2L1 in lung cancer induced by chronic arsenite exposure is unknown. In this study, we firstly showed that chronic arsenite exposure (36 weeks) led to epithelial-mesenchymal transition (EMT) and malignant transformation in human bronchial epithelial cells (BEAS-2B). During the process of malignant transformation, the expression of long isoforms of NFE2L1 (NFE2L1-L) was elevated. Thereafter, BEAS-2B cells with NFE2L1-L stable knockdown (NFE2L1-L-KD) was chronically exposed to arsenite. As expected, silencing of NFE2L1-L gene strikingly inhibited the arsenite-induced EMT and the subsequent malignant transformation. Additionally, NFE2L1-L silencing suppressed the transcription of EMT-inducer SNAIL1 and increased the expression of E-cadherin. Conversely, NFE2L1-L overexpression increased SNAIL1 transcription but decreased E-cadherin expression. Collectively, our data suggest that NFE2L1-L promotes EMT by positively regulating SNAIL1 transcription, and is involved in malignant transformation induced by arsenite.

Metabolic reprogramming in the arsenic carcinogenesis.

Chronic exposure to arsenic has been associated with a variety of cancers with the mechanisms undefined. Arsenic exposure causes alterations in metabolites in bio-samples. Recent research progress on cancer biology suggests that metabolic reprogramming contributes to tumorigenesis. Therefore, metabolic reprogramming provides a new clue for the mechanisms of arsenic carcinogenesis. In the present manuscript, we review the latest findings in reprogramming of glucose, lipids, and amino acids in response to arsenic exposure. Most studies focused on glucose reprogramming and found that arsenic exposure enhanced glycolysis. However, in vivo studies observed "reverse Warburg effect" in some cases due to the complexity of the disease evolution and microenvironment. Arsenic exposure has been reported to disturb lipid deposition by inhibiting lipolysis, and induce serine-glycine one-carbon pathway. As a dominant mechanism for arsenic toxicity, oxidative stress is considered to link with metabolism reprogramming. Few studies analyzed the causal relationship between metabolic reprogramming and arsenic-induced cancers. Metabolic alterations may vary with exposure doses and periods. Identifying metabolic alterations common among humans and experiment models with human-relevant exposure characteristics may guide future investigations.

Pb-Induced Eryptosis May Provoke Thrombosis Prior to Hemolysis.

Lead (Pb) is a common metal, which can be toxic to the human body via the pollution of water or food, and can cause anemia and other diseases. However, what happens before hemolysis and anemia caused by Pb poisoning is unclear. Here, we demonstrated Pb can cause procoagulant activity of erythroid cells leading to thrombosis before hemolysis. In freshly isolated human erythroid cells, we observed that Pb resulted in hemolysis in both concentration- and time-dependent manners, but that no lysis occurred in Pb-exposed erythroid cells (≤20 µM for 1 h). Pb treatment did not cause shape changes at up to 0.5 h incubation but at 1 h incubation echinocyte and echino-spherocyte shape changes were observed, indicating that Pb can exaggerate a concentration- and time-dependent trend of shape changes in erythroid cells. After Pb treatment, ROS-independent eryptosis was shown with no increase of reactive oxygen species (ROS), but with an increase of [Ca2+]i and caspase 3 activity. With a thrombosis mouse model, we observed increased thrombus by Pb treatment (0 or 25 mg/kg). In brief, prior to hemolysis, we demonstrated Pb can cause ROS-independent but [Ca2+]i-dependent eryptosis, which might provoke thrombosis.

Rifampicin impairs adipogenesis by suppressing NRF2-ARE activity in mice fed a high-fat diet.

Prolonged treatment with rifampicin (RFP), a first-line antibacterial agent used in the treatment of drug-sensitive tuberculosis, may cause various side effects, including metabolic disorders. The nuclear factor (erythroid-derived 2)-like 2 (NFE2L2, also known as NRF2) plays an essential regulatory role in cellular adaptive responses to stresses via the antioxidant response element (ARE). Our previous studies discovered that NRF2 regulates the expression of CCAAT-enhancer-binding protein ß (Cebpb) and peroxisome proliferator-activated receptor gamma (Pparg) in the process of adipogenesis. Here, we found that prolonged RFP treatment in adult male mice fed a high-fat diet developed insulin resistance, but reduced fat accumulation and decreased expression of multiple adipogenic genes in white adipose tissues. In 3 T3-L1 preadipocytes, RFP reduced the induction of Cebpb, Pparg and Cebpa at mRNA and protein levels in the early and/or later stage of hormonal cocktail-induced adipogenesis. Mechanistic investigations demonstrated that RFP inhibits NRF2-ARE luciferase reporter activity and expression of NRF2 downstream genes under normal culture condition and in the early stage of adipogenesis in 3 T3-L1 preadipocytes, suggesting that RFP can disturb adipogenic differentiation via NRF2-ARE interference. Taken together, we demonstrate a potential mechanism that RFP impairs adipose function by which RFP likely inhibits NRF2-ARE pathway and thereby interrupts its downstream adipogenic transcription network.

Liver-specific Nrf2 deficiency accelerates ethanol-induced lethality and hepatic injury in vivo.

Alcoholic liver disease (ALD) is a major cause of morbidity and mortality from liver disorders. Various mechanisms, including oxidative stress and impaired lipid metabolism, have been implicated in the pathogenesis of ALD. Our previous studies showed that nuclear factor erythroid-derived 2-like 2 (Nrf2) is a master regulator of adaptive antioxidant response and lipid metabolism by using a liver-specific Nrf2 knockout (Nrf2(L)-KO) mouse model. In the current study, an ALD model was developed by a Lieber-DeCarli liquid-based ethanol diet given to this Nrf2(L)-KO mouse strain. We found that Nrf2(L)-KO mice were quite sensitive to lethality from 6.3% ethanol diet. We thus decreased the ethanol concentration to 4.2% to obtain tissues to analyze the role of hepatic Nrf2 in the development of ALD. We found that mild hepatic steatosis occurred with both liquid control and 4.2% ethanol diet feeding, which contain 35% fat. Both the fatty acid ß-oxidation marker peroxisome proliferators-activated receptor α (PPARα), and lipogenesis regulator PPARγ were reduced with ethanol feeding in Nrf2(L)-KO mice, compared to Nrf2 floxed control mice (Nrf2-LoxP). However, Nrf2(L)-KO livers showed more cell injury than the livers of Nrf2-LoxP mice. Consistent with these data, there was increased proportion of apoptotic cells in the liver of ethanol-fed Nrf2(L)-KO mice comparing Nrf2-LoxP controls. Mechanistically, Nrf2 mediated expression of ethanol detoxification enzymes, such as alcohol dehydrogenase 1 and aldehyde dehydrogenase1a1, likely contributed to the sensitivity to ethanol toxicity. In conclusion, hepatic Nrf2 is critical to the development of ALD, particularly the morbidity and liver injury.

Titanium dioxide nanoparticles enhance thrombosis through triggering the phosphatidylserine exposure and procoagulant activation of red blood cells.

BACKGROUND: Expanding biomedical application of anatase titanium dioxide (TiO2) nanoparticles (NPs) is raising the public concern on its potential health hazards. Here, we demonstrated that TiO2 NPs can increase phosphatidylserine (PS) exposure and procoagulant activity of red blood cells (RBCs), which may contribute to thrombosis. RESULTS: We conducted in vitro studies using RBCs freshly isolated from healthy male volunteers. TiO2 NPs exposure (≦ 25 µg/mL) induced PS exposure and microvesicles (MV) generation accompanied by morphological changes of RBCs. While ROS generation was not observed following the exposure to TiO2 NPs, intracellular calcium increased and caspase-3 was activated, which up-regulated scramblase activity, leading to PS exposure. RBCs exposed to TiO2 NPs could increase procoagulant activity as measured by accelerated thrombin generation, and enhancement of RBC-endothelial cells adhesion and RBC-RBC aggregation. Confirming the procoagulant activation of RBC in vitro, exposure to TiO2 NPs (2 mg/kg intravenously injection) in rats increased thrombus formation in the venous thrombosis model. CONCLUSION: Collectively, these results suggest that anatase TiO2 NPs may harbor prothrombotic risks by promoting the procoagulant activity of RBCs, which needs attention for its biomedical application.

Nrf2 deficiency aggravates the kidney injury induced by subacute cadmium exposure in mice.

Cadmium (Cd) is a heavy metal pollutant that adversely effects the kidney. Oxidative stress and inflammation are likely major mechanisms of Cd-induced kidney injury. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is crucial in regulating antioxidant and inflammatory responses. To investigate the role of Nrf2 in the development of subacute Cd-induced renal injury, we utilized Nrf2 knockout (Nrf2-KO) and control mice (Nrf2-WT) which were given cadmium chloride (CdCl2, 1 or 2 mg/kg i.p.) once daily for 7 days. While subacute CdCl2 exposure induced kidney injury in a dose-dependent manner, after the higher Cd dosage exposure, Nrf2-KO mice showed elevated blood urea nitrogen (BUN) and urinary neutrophil gelatinase-associated lipocalin (NGAL) levels compared to control. In line with the findings, the renal tubule injury caused by 2 mg Cd/kg, but not lower dosage, in Nrf2-KO mice determined by Periodic acid-Schiff staining was more serious than that in control mice. Further mechanistic studies showed that Nrf2-KO mice had more apoptotic cells and severe oxidative stress and inflammation in the renal tubules in response to Cd exposures. Although there were no significant differences in Cd contents of tissues between Cd-exposed Nrf2-WT and Nrf2-KO mice, the mRNA expression of Nrf2 downstream genes, including heme oxygenase 1 and metallothionein 1, were significantly less induced by Cd exposures in the kidney of Nrf2-KO compared with Nrf2-WT mice. In conclusion, Nrf2-deficient mice are more sensitive to kidney injury induced by subacute Cd exposure due to a muted antioxidant response, as well as a likely diminished production of specific Cd detoxification metallothioneins.

CircZNF609 is involved in the pathogenesis of focal segmental glomerulosclerosis by sponging miR-615-5p.

As a set of distinct syndromes, focal segmental glomerulosclerosis (FSGS) is the most common cause of adult nephrotic syndrome with diverse mechanisms. We recently found that expression of the circular RNA circZNF609 is increased in renal biopsies of lupus nephritis patients. In the present study, we aimed to determine whether circZNF609 participates in the pathogenesis of FSGS in mice given Adriamycin. In FSGS mice, circZNF609 was upregulated while miR-615-5p was downregulated in FSGS mice analyzed by qPCR and fluorescence in situ hybridization (FISH). Expression of podocyte proteins Wilms tumor 1 (WT1) and podocin were decreased, while expression of collagen 1 (COL1) and transforming growth factor-beta1 (TGF-ß1) were increased on Western blotting. Renal circZNF609 levels were positively correlated and miR-615-5p levels were negatively correlated with the degree of podocyte injury and renal fibrosis. Importantly, circZNF609 and miR-615-5p co-localized to glomeruli and tubules on FISH. Perfect match seeds were found between circZNF609 and miR-615-5p and COL1 mRNA, leading us to explore mechanisms of circZNF609 in bovine serum albumin (BSA) stimulating HK-2 cells, which model the toxicity of proteinuria on tubular cells. In vitro studies, circZNF609 increased and miR-615-5p decreased after BSA treatment and were negatively correlated with each other. COL1 and TGF-ß1 were both upregulated and negatively correlated with miR-615-5p. Lastly, circZNF609 expression increased in glomeruli and tubules of FSGS patient renal biopsies. We conclude that circZNF609 may play an important role in FSGS by sponging miR-615-5p.

miR-150 inhibitor ameliorates adriamycin-induced focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) is the most common cause of adult nephrotic syndrome in USA. Its mechanisms remain unclear and the effective treatment lacks. We previously reported that upregulation of microRNA (miR)-150 in human podocytes increases profibrotic proteins and decreases anti-fibrotic suppressor of cytokine signaling 1 (SOCS1). We aimed to clarify whether miR-150 inhibitor can ameliorate glomerular injury and to identify its corresponding mechanisms in adriamycin-induced FSGS mice. We found that renal miR-150 increased in adriamycin-induced FSGS mice and FAM-labeled locked nucleic acid-anti-miR-150 (LNA-anti-miR-150) was absorbed by the animal kidneys 6 h after subcutaneous injection. The administration of LNA-anti-miR-150 (2 mg/kg BW twice weekly for 6 w) inhibited renal miR-150 levels without systemic toxicity. With renal miR-150 inhibition, proteinuria, hypoalbuminemia, and hyperlipemia were ameliorated in FSGS mice compared to the scrambled LNA. Meanwhile, the elevated profibrotic proteins and proinflammatory cytokines, decreased antifibrotic SOCS1, and the filtration of T cells in FSGS mice were reverted by LNA-anti-miR-150. Finally, we found that miR-150 most located on podocytes in renal biopsies of FSGS patients. We conclude that LNA-anti-miR-150 might be a novel promising therapeutic agent for FSGS. The renal protective mechanisms might be mediated by anti-fibrosis and anti-inflammation as well as reducing infiltration of T cells in the kidney.

Long-isoform NRF1 protects against arsenic cytotoxicity in mouse bone marrow-derived mesenchymal stem cells by suppressing mitochondrial ROS and facilitating arsenic efflux.

Acute exposure to arsenic is known to cause bone marrow depression and result in anemia, in which the dusfunction of cells in the bone marrow niche such as mesenchymal stem cells (MSCs) is vital. However, the mechanism underlying response of MSCs to arsenic challange is not fully understood. In the present study, we investigated the role of nuclear factor erythroid 2-related factor (NRF) 1 (NRF1), a sister member of the well-known master regulator in antioxidative response NRF2, in arsenite-induced cytotoxicity in mouse bone marrow-derived MSCs (mBM-MSCs). We found that arsenite exposure induced significant increase in the protein level of long-isoform NRF1 (L-NRF1). Though short-isoform NRF1 (S-NRF1) was induced by arsenite at mRNA level, its protein level was not obviously altered. Silencing L-Nrf1 sensitized the cells to arsenite-induced cytotoxicity. L-Nrf1-silenced mBM-MSCs showed decreased arsenic efflux with reduced expression of arsenic transporter ATP-binding cassette subfamily C member 4 (ABCC4), as well as compromised NRF2-mediated antioxidative defense with elevated level of mitochondrial reactive oxygen species (mtROS) under arsenite-exposed conditions. A specific mtROS scavenger (Mito-quinone) alleviated cell apoptosis induced by arsenite in L-Nrf1-silenced mBM-MSCs. Taken together, these findings suggest that L-NRF1 protects mBM-MSCs from arsenite-induced cytotoxicity via suppressing mtROS in addition to facilitating cellular arsenic efflux.

Correction: Camptothecin suppresses NRF2-ARE activity and sensitises hepatocellular carcinoma cells to anticancer drugs.

The original version of this article contained an error in Figure 6A. The volumes of the tumour xenografts were incorrectly calculated. The correct figure and figure legend are provided, where the volume has been calculated using V = length × width2×π/6. The interpretation of the data and conclusions are not affected.

Nrf2 deficiency aggravates the increase in osteoclastogenesis and bone loss induced by inorganic arsenic.

Arsenic exposure increases the risk of various bone disorders. For instance, chronic exposure to low level arsenic can cause bone resorption by promoting osteoclast differentiation. Osteoclast precursor cells produce hydrogen peroxide after low level arsenic exposure and then undergo differentiation, producing cells which break down bone matrix. Nuclear factor E2-related factor 2 (Nrf2) regulates receptor activator of nuclear factor-κB dependent osteoclastogenesis by modulating intracellular reactive oxygen species (ROS) signaling via expression of cytoprotective enzymes. Here we tested the hypothesis that loss of Nrf2 will increase arsenic-induced bone loss. We treated 40 week-old Nrf2+/+ and Nrf2-/- mice with 5 ppm arsenic in the drinking water, which produces a blood arsenic level similar to humans living in areas where arsenic exposure is endemic. After 4 months, Micro-CT and dual-energy x-ray analysis revealed a drastic overall decrease in the bone volume with arsenic treatment in mice lacking Nrf2. Deficiency of Nrf2 in RAW 264.7 cells or bone marrow-derived macrophages (BMMs) promoted arsenic-induced osteoclast differentiation. Lack of Nrf2 increases arsenic-induced ROS levels and phosphorylation of p38. N-Acetyl-cysteine and SB203580 pretreatment essentially abolished arsenic-induced phosphorylation of p38 and reversed arsenic-induced increased osteoclast differentiation in Nrf2 deficiency. Taken together, our data suggest that loss of Nrf2 causes increased oxidative stress and enhanced susceptibility to arsenic-induced bone loss.

Adipocyte-specific deficiency of Nfe2l1 disrupts plasticity of white adipose tissues and metabolic homeostasis in mice.

The maintenance of healthy adipose tissues is essential for efficient regulation of energy homeostasis. Nuclear factor-erythroid 2-related factor 1 (NFE2L1, also known as Nrf1), a CNC-bZIP protein, is a master regulator of the cellular adaptive response to stresses. To investigate the role of NFE2L1 in adipocytes, we bred a line of mice with adipocyte-specific Nfe2l1 knockout (Nfe2l1(f)-KO), and found that Nfe2l1(f)-KO mice exhibited a dramatically reduced subcutaneous adipose tissue (SAT) mass, insulin resistance, adipocyte hypertrophy, and severe adipose inflammation. Mechanistic studies revealed that Nfe2l1 deficiency may disturb the expression of lipolytic genes in adipocytes, leading to adipocyte hypertrophy followed by inflammation, pyroptosis, and insulin resistance. Our findings reveal a novel role for NFE2L1 in regulating adipose tissue plasticity and energy homeostasis.

Triptolide enhances chemotherapeutic efficacy of antitumor drugs in non-small-cell lung cancer cells by inhibiting Nrf2-ARE activity.

Non-small cell lung cancer (NSCLC) has a high mortality rate worldwide. Various treatments strategies have been used against NSCLC including individualized chemotherapies, but innate or acquired cancer cell drug resistance remains a major obstacle. Recent studies revealed that the Kelch-like ECH associated protein 1/Nuclear factor erythroid 2-related factor 2 (Keap1/Nrf2) pathway is intimately involved in cancer progression and chemoresistance. Thus, antagonizing Nrf2 would seem to be a viable strategy in cancer therapy. In the present study a traditional Chinese medicine, triptolide, was identified that markedly inhibited expression and transcriptional activity of Nrf2 in various cancer cells, including NSCLC and liver cancer cells. Consequently, triptolide made cancer cells more chemosensitivity toward antitumor drugs both in vitro and in a xenograft tumor model system using lung carcinoma cells. These results suggest that triptolide blocks chemoresistance in cancer cells by targeting the Nrf2 pathway. Triptolide should be further investigated in clinical cancer trials.