Cytotoxicity In Mice Research Articles

Genotoxicity of Titanium Dioxide Nanoparticles using the Mouse Bone Marrow Micronucleus and Sperm Morphology Assays

Titanium dioxide nanoparticles (TiO2-NPs) have recently been of public health and scientific concern due to their widespread use in industrial and household applications. However, there is limited information concerning its in vivo cytogenotoxicity. In this study, the cytogenotoxic effects of TiO2-NPs on the somatic tissue using the mouse bone marrow micronucleus (MN) assay and on reproductive tissue using the mouse sperm morphology assay and testicular histopathology were investigated. Five concentrations of 9.38, 18.75, 37.50, 75.00 and 150.00 mg/kg bwt were administered intraperitoneally at 0.5 mL/mouse to mice for five and ten consecutive days in the MN assay; and for five consecutive days in the sperm morphology assay. Double distilled water and cyclophosphamide (20 mg/kg bwt) served as negative and positive controls, respectively. A significant (p<0.05) increase in MN was observed in bone marrow cells of treated mice at 37.50 mg/kg bwt concentration in the 5-day exposure and at all concentrations in the 10-day exposure. The sperm cells examined 5 and 10 weeks from the first day of exposure showed significant increase (p<0.05) in abnormal sperm cells at tested concentrations. Histopathologically, TiO2-NPs disrupted the normal cellular architecture of testicular tissues in exposed mice; as it caused severe lesions such as congestion of the interstitium oedema, vacuolation and necrosis. These suggest that the bone marrow and testicular cells may be potential targets for TiO2-NPs induced DNA damage and cytotoxicity in mice. This is of public health importance considering increasing exposure to TiO2-NPs in consumer products.

Influence of polystyrene nanoparticles in inducing cytotoxicity in mice co-injected anti-inflammatory agent, tetracycline or sodium valproate

Influence of polystyrene nanoparticles in inducing cytotoxicity in mice co-injected anti-inflammatory agent, tetracycline or sodium valproate

Discovery of Highly Potent Tyrosinase Inhibitor, T1, with Significant Anti-Melanogenesis Ability by zebrafish in vivo Assay and Computational Molecular Modeling

Tyrosinase is involved in melanin biosynthesis and the abnormal accumulation of melanin pigments leading to hyperpigmentation disorders that can be treated with depigmenting agents. A natural product T1, bis(4-hydroxybenzyl)sulfide, isolated from the Chinese herbal plant, Gastrodia elata, is a strong competitive inhibitor against mushroom tyrosinase (IC50 = 0.53 μM, Ki = 58 ± 6 nM), outperforms than kojic acid. The cell viability and melanin quantification assay demonstrate that 50 μM of T1 apparently attenuates 20% melanin content of human normal melanocytes without significant cell toxicity. Moreover, the zebrafish in vivo assay reveals that T1 effectively reduces melanogenesis with no adverse side effects. The acute oral toxicity study evidently confirms that T1 molecule is free of discernable cytotoxicity in mice. Furthermore, the molecular modeling demonstrates that the sulfur atom of T1 coordinating with the copper ions in the active site of tyrosinase is essential for mushroom tyrosinase inhibition and the ability of diminishing the human melanin synthesis. These results evident that T1 isolated from Gastrodia elata is a promising candidate in developing pharmacological and cosmetic agents of great potency in skin-whitening.

MTOR: A gate to NK cell maturation and activation

mTOR: A gate to NK cell maturation and activation

Comparative pulmonary toxicity of two ceria nanoparticles with the same primary size.

Ceria nanoparticles (nano-ceria) have recently gained a wide range of applications, which might pose unwanted risks to both the environment and human health. The greatest potential for the environmental discharge of nano-ceria appears to be in their use as a diesel fuel additive. The present study was designed to explore the pulmonary toxicity of nano-ceria in mice after a single exposure via intratracheal instillation. Two types of nano-ceria with the same distribution of a primary size (3–5 nm), but different redox activity, were used: Ceria-p, synthesized by a precipitation route, and Ceria-h, synthesized by a hydrothermal route. Both Ceria-p and Ceria-h induced oxidative stress, inflammatory responses and cytotoxicity in mice, but their toxicological profiles were quite different. The mean size of Ceria-p agglomerates was much smaller compared to Ceria-h, thereby causing a more potent acute inflammation, due to their higher number concentration of agglomerates and higher deposition rate in the deep lung. Ceria-h had a higher reactivity to catalyzing the generation of reactive oxygen species (ROS), and caused two waves of lung injury: bronchoalveolar lavage (BAL) inflammation and cytotoxicity in the early stage and redox-activity-evoked lipid peroxidation and pro-inflammation in the latter stage. Therefore, the size distribution of ceria-containing agglomerates in the exhaust, as well as their surface chemistry are essential characteristics to assess the potential risks of using nano-ceria as a fuel additive.

The Effect of Mushroom Beta-Glucans from Solid Culture of Ganoderma lucidum on Inhibition of the Primary Tumor Metastasis.

This study evaluates the effect of mushroom beta-glucans (MBGS) derived from solid culture of Ganoderma lucidum on tumor inhibition by examining size of the primary tumor and rate of metastasis in Lewis lung carcinoma (LLC) bearing mice (C57BL/6), given oral administration of MBGS with radiation therapy. A previous result showed that MBGS enhances NK cell-mediated cytotoxicity in mice without LLC bearing in advance. Furthermore, applications of MBGS in conjunction with radiation therapy were effective in controlling tumor growth, and rate of metastasis, life threatening, and can potentially serve as a protective factor for wounds and hair loss that resulted from the overgrowth of primary tumor in LLC bearing mice.

HPV16 CTL Epitope Peptide-activated Dendritic Cell and Natural Killer Co-culture for Therapy of Cervical Cancer in an Animal Model

There is increasing evidence that natural killer (NK) cells play an important role in antitumor immunity following dendritic cell (DC) vaccination. Little is known, however, about the optimal stimulation of DCs by epitopes and NK interactions for cytotoxicity in tumors. In this study, DC cells activated by the HPV16E7.49-57 epitope and LPS were co-cultured with NK cells in vitro, and then used ot immunize mice to study CTL activity of TC-1, which constitutively expresses HPV16E6E7, with an LDH release assay. Cytotoxicity in mice immunized with DC loaded with epitope HPVE7.49-57 vaccine co-cultured with NK was enhanced significantly (p<0.01). In conclusion, talk-across between DC and NK cells enhances their functions, also improving cytotoxicity againsttumor cells, suggesting that activated DC-NK by epitopes has potential application for cancer-specific immuno-cellular therapy.

Enhancing Production and Cytotoxic Activity of Polymeric Soluble FasL-Based Chimeric Proteins by Concomitant Expression of Soluble FasL

Membrane FasL is the natural trigger of Fas-mediated apoptosis. A soluble homotrimeric counterpart (sFasL) also exists which is very weakly active, and needs oligomerization beyond its trimeric state to induce apoptosis. We recently generated a soluble FasL chimera by fusing the immunoglobulin-like domain of the leukemia inhibitory factor receptor gp190 to the extracellular region of human FasL, which enabled spontaneous dodecameric homotypic polymerization of FasL. This polymeric soluble human FasL (pFasL) displayed anti-tumoral activity in vitro and in vivo without systemic cytotoxicity in mouse. In the present work, we focused on the improvement of pFasL, with two complementary objectives. First, we developed more complex pFasL-based chimeras that contained a cell-targeting module. Secondly, we attempted to improve the production and/or the specific activity of pFasL and of the cell-targeting chimeras. We designed two chimeras by fusing to pFasL the extracellular portions of the HLA-A2 molecule or of a human gamma-delta TCR, and analyzed the consequences of co-expressing these molecules or pFasL together with sFasL on their heterotopic cell production. This strategy significantly enhanced the production of pFasL and of the two chimeras, as well as the cytotoxic activity of the two chimeras but not of pFasL. These results provide the proof of concept for an optimization of FasL-based chimeric proteins for a therapeutic use.

Influence of nano-polystyrene particles in inducing cytotoxicity in mice co-injected with carbon tetrachloride, cisplatin, or paraquat

Influence of nano-polystyrene particles in inducing cytotoxicity in mice co-injected with carbon tetrachloride, cisplatin, or paraquat

The Rac activator DOCK2 regulates natural killer cell–mediated cytotoxicity in mice through the lytic synapse formation

AbstractNatural killer (NK) cells play an important role in protective immunity against viral infection and tumor progression, but they also contribute to rejection of bone marrow grafts via contact-dependent cytotoxicity. Ligation of activating NK receptors with their ligands expressed on target cells induces receptor clustering and actin reorganization at the interface and triggers polarized movement of lytic granules to the contact site. Although activation of the small GTPase Rac has been implicated in NK cell–mediated cytotoxicity, its precise role and the upstream regulator remain elusive. Here, we show that DOCK2, an atypical guanine nucleotide exchange factor for Rac, plays a key role in NK cell–mediated cytotoxicity. We found that although DOCK2 deficiency in NK cells did not affect conjugate formation with target cells, DOCK2-deficienct NK cells failed to effectively kill leukemia cells in vitro and major histocompatibility complex class I–deficient bone marrow cells in vivo, regardless of the sorts of activating receptors. In DOCK2-deficient NK cells, NKG2D-mediated Rac activation was almost completely lost, resulting in a severe defect in the lytic synapse formation. Similar results were obtained when the Rac guanine nucleotide exchange factor activity of DOCK2 was selectively abrogated. These results indicate that DOCK2-Rac axis controls NK cell–mediated cytotoxicity through the lytic synapse formation.

Construction and immunogenicity of a ∆apxIC/ompP2 mutant of &lt;i&gt;Actinobacillus pleuropneumoniae&lt;/i&gt; and &lt;i&gt;Haemophilus parasuis&lt;/i&gt;

The apxIC genes of the Actinobacillus pleuropneumoniae serovar 5 (SC-1), encoding the ApxIactivating proteins, was deleted by a method involving sucrose counter-selection. In this study, a mutant strain of A. pleuropneumoniae (SC-1) was constructed and named DapxIC/ ompP2. The mutant strain contained foreign DNA in the deletion site of ompP2 gene of Haemophilus parasuis. It showed no haemolytic activity and lower virulence of cytotoxicity in mice compared with the parent strain, and its safety and immunogenicity were also evaluated in mice. The LD50 data shown that the mutant strain was attenuated 30-fold, compared with the parent strain (LD50 of the mutant strain and parent strain in mice were determined to be 1.0 × 10(7) CFU and 3.5 × 10(5) CFU respectively). The mutant strain that was attenuated could secrete inactivated ApxIA RTX toxins with complete antigenicity and could be used as a candidate live vaccine strain against infections of A. pleuropneumoniae and H. parasuis.

Protective effect of adipocytes fatty acid binding protein inhibitor on pancreas islet cell against macrophage-mediated cytotoxicity of mice in vitro

To investigate the potential role of adipocytes fatty acid binding protein (A-FABP)inhibitor to prevent pancreatic islet cells from cytotoxic injury by inflammatory cytokines released from macrophage. Co-culture system for RAW264.7 macrophage and MIN6 insulinoma cells was established through transwell combined with A-FABP inhibitor BMS309403 treatment for 48 h. Meanwhile, cultured RAW264.7 and MIN6 respectively were set up as controls. In the inhibitor group, BMS309403 preprocessing (5 µmol/L) was performed 2 h before co-culture. The expression of toll-like receptors(TLR)4 and A-FABP in RAW264.7 macrophages was detected by RT-PCR and Western blotting, interleukin (IL)-1β and tumor necrosis factor(TNF)-α levels in the supernatant were detected by ELISA, Glucose-stimulated insulin level was detected by insulin radioimmuno-assay kits for the function of islets. (1) The mRNA and protein levels of both TLR4 and A-FABP in RAW264.7 macrophages as well as the concentrations of IL-1β and TNF-α in the supernatant were significantly higher in co-culture group than in macrophages control group (P < 0.05). (2) Insulin secretion stimulated by high glucose was obviously decreased in co-culture group when compared with insulinoma cells control group [(16.0 ± 2.2) vs (41.1 ± 6.6) ng/ml, P < 0.05]. After the treatment with A-FABP inhibitor, the mRNA and protein levels of both TLR4 and A-FABP as well as the concentrations of IL-1β and TNF-α in the supernatant were significantly lower than in co-culture control (P < 0.05). However, insulin secretion stimulated by high glucose was significantly enhanced when compared with insulinoma cells control group [(31.4 ± 3.3) vs (16.0 ± 2.2) ng/ml, P < 0.05]. This study demonstrated that co-culture of macrophage and islet cells can activate inflammation pathway, stimulate inflammatory cytokine release and decrease insulin secretion from islet cells. A-FABP inhibitor can protect islet cells from macrophage-mediated cytotoxicity and preserve its insulin secretory function.

Attenuation of p-dimethylaminoazobenzene initiated genotoxicity and cytotoxicity in mice by the combined treatment of a traditional homeopathic remedy Chelidonium Majus 200C and vitamin-C

The homeopathic remedy Chelidonium majus 200C (Chel-200) is traditionally used by homeopathic practitioners in liver ailments arising out of hepatotoxicity. The present investigation was aimed at examining whether vitamin C (L-ascorbic acid or AA), used in both traditional and orthodox medicines, can show better effects when used in combination with Chel-200, in favorably modifying the toxicological effects induced by the chronic feeding of p-dimethylaminoazobenzene (p-DAB, initiator) and phenobarbital (PB, promoter) in mice for 7 days through 120 days to induce hepatotoxicity and liver tumors. Mice were euthanized at 7, 15, 30, 60, 90, and 120 days of carcinogen feeding to assess various cytogenetical, biochemical and histological changes occurring in them. In a placebo controlled study, Chel-200 or the respective placebo (Alcohol-200C or Alc, “vehicle” of homeopathic drug), was orally administered to toxicant-fed mice. Sub-groups of the mice receiving Chel-200 were also fed either AA or an Alc placebo and their individual and conjoint effects were studied against the respective controls, to evaluate if the combination therapy of Chel-200 with AA can be of additional help in the amelioration of the toxicities generated by the toxicants. The combined feeding of Chel- 200 and AA appeared to reduce the cytotoxic and genotoxic effects significantly, when compared to either only the Chel-200 or AA fed group. A similar trend was also obtained in the results of scanning and transmission electron microscopic studies of the livers. Experiments in other mammalian models are warranted to confirm if these drugs in combination could be used in palliative care of human patients with liver diseases including cancer.

In VivoPhosphoantigen Levels in Bisphosphonate-Treated Human Breast Tumors Trigger Vγ9Vδ2 T-cell Antitumor Cytotoxicity through ICAM-1 Engagement

Nitrogen-containing bisphosphonates (N-BP) such as zoledronate and risedronate exhibit antitumor effects. They block the activity of farnesyl pyrophosphate synthase (FPPS) in the mevalonate pathway, leading to intracellular accumulation of mevalonate metabolites (IPP/ApppI), which are recognized as tumor phosphoantigens by Vγ9Vδ2 T cells. However, mechanisms responsible for Vγ9Vδ2 T-cell recognition of N-BP-treated tumors producing IPP/ApppI remain unclear. The effects of N-BPs on Vγ9Vδ2 T-cell expansion and anticancer activity were evaluated in vitro and in animal models of human breast cancers. The modalities of recognition of breast tumors by Vγ9Vδ2 T cells in N-BP-treated animals were also examined. We found a strong correlation between Vγ9Vδ2 T-cell anticancer activity and intracellular accumulation of IPP/ApppI in risedronate-treated breast cancer cells in vitro. In addition, following risedronate treatment of immunodeficient mice bearing human breast tumors, human Vγ9Vδ2 T cells infiltrated and inhibited growth of tumors that produced high IPP/ApppI levels but not those expressing low IPP/ApppI levels. The combination of doxorubicin with a N-BP improved, however, Vγ9Vδ2 T-cell cytotoxicity against breast tumors expressing low IPP/ApppI levels. Moreover, Vγ9Vδ2 T-cell cytotoxicity in mice treated with risedronate or zoledronate did not only depend on IPP/ApppI accumulation in tumors but also on expression of tumor cell surface receptor intercellular adhesion molecule-1 (ICAM-1), which triggered the recognition of N-BP-treated breast cancer cells by Vγ9Vδ2 T cells in vivo. These findings suggest that N-BPs can have an adjuvant role in cancer therapy by activating Vγ9Vδ2 T-cell cytotoxicity in patients with breast cancer that produces high IPP/ApppI levels after N-BP treatment.

Ptaquiloside-induced immunotoxic effects are reversed by selenium supplementation (87.21)

Abstract Pteridium aquilinum (Pa) is a poisonous plant and its ingestion has been closely associated with human and animal cancers. Our earlier studies have shown that Pa reduces white pulp of spleen and NK cell cytotoxicity in mice. In addition, we observed that selenium (Se) reversed Pa-induced spleen damage. In this study the aim was evaluate if ptaquiloside (Ptq), the main toxic principle found in Pa, is responsible for its immunotoxic effects and if Se would reverse these effects. For in vivo study, mice were separated into 4 groups: control, Ptq, Ptq+Se, and Se. Mice were treated by gavage for 14 days with Ptq (5.3mg/kg BW) and/or Se (1.3mg/kg BW). Mice were killed and it was prepared a non-adherent splenic cells suspensions to perform NK cell activity assay against YAC cell line. For in vitro study, cultures of non-adherent splenic cells were performed for each mouse as follows: untreated, Se 0.1mM, RPMI extract of Pa (RE) 4mg/ml, RE 4mg/ml+Se 0.1mM (co-incubation), and RE 4mg/ml+Se 0.1mM (RE/1h wash and then Se/1h). After treatment, the cells were washed to proceed both NK cell activity assay and MTT assay. We observed that Ptq reduced NK cytotoxicity, which permits to suppose that Ptq is the principle responsible by immunotoxic effects. Moreover, NK cell activity was completely recovered after Se supplementation in vivo and in vitro. These results showed for the first time that Pa-induced immunotoxic effects are caused by Ptq and that these effects are fully recovered by Se.

Effects of Pteridium aquilinum on mice are not associated with the elicitation stage in delayed-type hypersensitivity response

Species: OtherPteridium aquilinum (Pa) is one of the five most common plants on the planet and is known to cause cancer in animals and humans. Our earlier studies have shown that Pa causes injury in lymphoid organs, decreases bone marrow cellularity, reduces delayed-type hypersensitivity (DTH) response and NK cytotoxicity in mice. In this study, we have evaluated the activity of T lymphocytes of spleen and peritoneal macrophages in order to see whether there is any correlation of these effects with reduction in DTH response. For T lymphocytes proliferation assay, nine C57BL/6 male mice were used per group and treated by gavage up to 14 days as follows: control (Co)0.0, Pa (P)30.0 gPa/kg BW. At sacrifice, the spleen was removed to prepare cell suspension. From the cells obtained in each mouse, 1×107 cells/mL were incubated with 1 L of CFSE for 20min in the dark. After this, cells were washed and suspended at 2×106 cells/mL in RPMI and 100 L aliquots were added to a 96-well microtiter plate. Untreated and PHA (10 L/well) treated were set up in triplicates and incubated for 96h at 37 ◦C in a humidified atmosphere at 5% CO2. The samples were analysed by flow cytometry. In another study, for the analysis of macrophages, eight C57BL/6 male mice were used per group and the same protocol was utilized for treatment, but on 10th day all mice were injected i.p. with 1mL of thioglycollate 10%. At sacrifice, the peritonealmacrophages were collected with PBS. For the oxidative burst analysis, from the cells obtained in each mouse, 1x106 cells/tube were incubated during 30min at 37 ◦C with either DCFHDA or DCFH-DA and PMA or DCFH-DA and Staphylococcus aureus conjugated with propidium iodide (SAPI). For the phagocytosis analysis, from the cells obtained in each mouse, 1×106 cells/tube were incubated 30min at 37 ◦C with either SAPI or DCFH-DA and SAPI. The samples were analysed by flow cytometry. No change in the proliferation of T lymphocytes and macrophage activities was observed after Pa treatment, suggesting that the reduction in DTH response is probably due to inefficiency on the sensitization stage (activation and expansion of antigenspecific memory Th1 cells) and not on the elicitation stage (Th1 and macrophage activation). Further experiunopathology 128 (2009) 211–347

Low dose streptozotocin causes stimulation of the immune system and of anti-islet cytotoxicity in mice.

Multiple low doses of streptozotocin are known to induce immune-mediated insulin deficient diabetes and depression of immune reactivity. We show here that immune depression by streptozotocin is not general but that some parts of the immune system are stimulated. Spleen cells from streptozotocin-treated mice showed enhanced cytotoxicity against syngeneic islet cells and various tumour cells including insulinoma cells. Several cell types served as effector cells, including macrophages, asialo GM1+ and Lyt-2+ lymphocytes. The increased cytotoxic activity towards islet cells was mostly due to macrophages and to non-asialo GM1+ and non-Lyt-2+ lymphocytes. A higher activation state of macrophages in low dose streptozotocin-treated mice was demonstrated by measurements of superoxide anion release. We conclude that multiple low doses of streptozotocin stimulate 'natural cytotoxicity', i.e. the non-MHC restricted cytotoxic activity of macrophages, T cells and natural killer lymphocytes.

Mesenchymal Stem Cells Over-expressing Hepatocyte Growth Factor Improve Small-for-size Liver Grafts Regeneration

Ischemia-reperfusion (I/R) associated with small-for-size liver transplantation (SFSLT) impairs liver graft regeneration. Mesenchymal stem cells (MSCs) have the capability, under specific conditions, of differentiating into hepatocytes. Hepatocyte growth factor (HGF) has potent anti-apoptotic and mitogenic effects on hepatocytes during liver injury, and has been utilized in many experimental and clinical applications. In this study, we implanted HGF-expressing MSCs into liver grafts via the portal vein, using a 30% small-for-size rat liver transplantation model. HGF, c-met expression, hepatic injury and liver regeneration were assessed after liver transplantation. Our study demonstrated that MSCs over-expressing HGF prevented liver failure and reduced mortality in rats after SFSLT. These animals also exhibited improved liver function and liver weight recovery during the early post-transplantation period. Using green fluorescent protein (GFP) gene as a marker, we demonstrated that the engrafted cells and their progeny incorporated into remnant livers and produced albumin. These findings suggest that MSCs genetically modified to over-express HGF and implanted in the liver graft, may offer a novel approach to promoting liver regeneration after small-for-size transplantations.

Cartap-induced cytotoxicity in mouse C 2C 12 myoblast cell line and the roles of calcium ion and oxidative stress on the toxic effects

Our previous study has demonstrated that instead of neuromuscular blockage cartap, an organonitrogen insecticide, could cause a marked irreversible Ca 2+-dependent contracture in both isolated mouse and rabbit phrenic nerve-diaphragms. We further examined the potential of direct myocytotoxicity of cartap and the possible roles of calcium ion and oxidative stress on cartap-induced muscle cell injury using the mouse myoblast cell line, C 2C 12. Cartap exerted a dose- and time-dependent cytotoxic effect in C 2C 12 cells measured by MTT colorimetric assay and trypan blue dye exclusion. The extracellular activities of both creatine kinase (CK) and lactate dehydrogenase (LDH) were elevated in the cartap-treated groups at or greater than 100 μM. The isoenzymatic profiles showed that the elevations were mainly due to CK-3, LDH-3, and LDH-4. Following the addition of 0.5–2.5 mM EGTA, a Ca 2+ chelator, or 30–100 μM verapamil, an L-type Ca 2+ channel blocker, the cartap-induced reduction in MTT metabolic rate of C 2C 12 cells was significantly restored in a dose-dependent manner in both EGTA and verapamil-treated cells. Furthermore, EGTA could significantly reduce the cartap-induced elevation in the levels of total extracellular CK and LDH activities. Additionally, cartap significantly increased the level of endogenous reactive oxygen species (ROS) in C 2C 12 cells in a dose- and time-dependent manner. The cartap-induced ROS generation could be significantly inhibited by antioxidants, including Vitamins C and E, catalase, and superoxide dismutase, with catalase the most effective. EGTA could significantly inhibit cartap-induced ROS generation in a dose-dependent manner. The results suggested that cartap could induce ROS generation in C 2C 12 cells via a Ca 2+-dependent mechanism resulting in subsequent cytotoxicity, at least partially, to C 2C 12 cells. It is speculated that both Ca 2+ and Ca 2+-induced ROS may also play the central role on the myogenic contracture and myofiber injury of the diaphragm leading to respiratory failure and subsequent death in rabbits exposed ocularly to cartap.

Pulmonary Bronchiolar Cytotoxicity and Formation of Dichloroacetyl Lysine Protein Adducts in Mice Treated with Trichloroethylene

This study was undertaken to test the hypothesis that bronchiolar damage induced by trichloroethylene (TCE) is associated with bioactivation within the Clara cells with the involvement of CYP2E1 and CYP2F2. Histopathology confirmed dose-dependent Clara cell injury and disintegration of the bronchiolar epithelium in CD-1 mice treated with TCE doses of 500 to 1000 mg/kg i.p. Immunohistochemical studies, using an antibody that recognizes dichloroacetyl lysine adducts, revealed dose-dependent formation of adducts in the bronchiolar epithelium. Localization of dichloroacetyl adducts in the Clara cells coincided with damage to this cell type in TCE-treated mice. Pretreatment of CD-1 mice with diallyl sulfone, an inhibitor of CYP2E1 and CYP2F2, abrogated the formation of the dichloroacetyl adducts and protected against TCE-induced bronchiolar cytotoxicity. Treatment of wild-type and CYP2E1-null mice with TCE (750 mg/kg i.p.) also elicited bronchiolar damage that correlated with the formation of adducts in the Clara cells. Immunoblotting, using lung microsomes from TCE-treated CD-1 mice, showed dose-dependent production of dichloroacetyl adducts that comigrated with CYP2E1 and CYP2F2. However, TCE treatment resulted in a loss of immunoreactive CYP2E1 and CYP2F2 proteins and p-nitrophenol hydroxylation, a catalytic activity associated with both cytochrome P450 enzymes. The TCE metabolite, chloral hydrate, was formed in incubations of TCE with lung microsomes from CD-1, wild-type, and CYP2E1-null mice. The levels were higher in CD-1 than in either wild-type or CYP2E1-null mice, although levels were higher in CYP2E1-null than in wild-type mice. These findings supported the contention that TCE bioactivation within the Clara cells, predominantly involving CYP2F2, correlated with bronchiolar cytotoxicity in mice.