Cytotoxic Effects Of Hydrogen Peroxide Research Articles

In Vitro Effect of Instrumentation Using Ultrasonication with and without Hydrogen Peroxide on the Removal of Biofilms and Spread of Viable Microorganisms in Aerosols.

To evaluate the use of hydrogen peroxide as an adjunct to ultrasonication (US) in biofilm removal and whether it can limit the spread of viable microorganisms in the aerosol. Multi-species biofilms were formed on dentin disks and titanium disks fixed on a plastic surface. After placing the specimens in a periodontal pocket model, an ultrasonic scaler was applied for 30 s, in part combined with 0.25% or 0.5% H2O2. After treatment, the remaining biofilm was analysed for bacterial counts (colony forming units [CFU]), biofilm quantity and metabolic activity. Further, the cytotoxic effect of hydrogen peroxide on periodontal ligament fibroblasts was assessed and the spread of bacteria in aerosol was quantified. Ultrasonication reduced bacterial counts in biofilm, biofilm mass and metabolic activity on both dentin and titanium disks. Adjunctive use of 0.25% and 0.5% H2O2 more effectively reduced the viable bacteria in biofilm than ultrasonication alone; this was also found on both dentin and titanium. The different concentrations of H2O2 did not lead to corresponding differences in bacterial mass and metabolic activity. The spread of bacteria through aerosols was statistically significantly reduced when adjunctive H2O2 was used. However, a certain cytotoxic effect on periodontal ligament fibroblasts by H2O2 could not be ruled out. Irrigating with H2O2 during periodontal instrumentation with an ultrasonic scaler increases the reduction of viable bacteria within biofilms. It might limit bacterial spreading via aerosols.

Investigation of Genotoxic and Cytotoxic Effects of Hydrogen Peroxide(The Importance of DNA Repair in Oxidative Stress)

Oxidative stress-induced reactive oxygen species induce DNA damages that may result in cell death and DNA mutations. In this study, a genotoxic and cytotoxic potential of hydrogen peroxide as a ROS generator, and the effect of cell repair of oxidative stress in TK6 cells were investigated by in vitro micronucleus assay. Cell repair was inhibited by using cytosine earabinoside. Cellular responses to different concentrations of hydrogen peroxide were evaluated by generating dose-response curves. The incidence of increased MN concentrations due to increased H2O2concentrations did not allow the identification of a plateau region. A similar curve pattern was also observed with the repair inhibited group. However, damage caused by H2O2was significantly higher (p<0.001) in the cells with repair inhibition. This demonstrates the importance of DNA repair in the observation of oxidative stress. Proliferative indexes did not change due to increasing H2O2 concentrations in both groups. But the curve of repair inhibited cells was significantly higher (p<0.001) than the curve of repair efficient cells. BN and multinucleate cell counts showed decreases with increasing ROS levels generated by H2O2. But these decreases were not reflected in proliferative index scores. This may be due to H2O2-induced apoptosis, which results in the overestimation of PI values in increasing H2O2concentrations.

Protective effect of leaf extract of Abutilon indicum on DNA damage and peripheral blood lymphocytes in combating the oxidative stress

The current research explores in vitro antioxidant characteristics, radiation-induced DNA damage protection and quenching effects of the oxidative stress by the ethanolic leaf extract of Abutilon indicum (EEAI) on human peripheral blood lymphocytes (PBLs). PBLs were incubated with various concentrations of EEAI accompanied by pre- and post-treatment with hydrogen peroxide. Cell viability was investigated by MTT assay. In addition, quenching of free radicals were measured in vitro using DPPH, superoxide anion, hydrogen peroxide, reducing power and nitric oxide radical scavenging assays. These activities were compared with ascorbic acid as standard antioxidants. Furthermore, inhibition of UV radiation-induced strand break formation in plasmid pBR322 DNA and anti-Fenton reactions in calf thymus DNA was evaluated. Cytotoxic effects of hydrogen peroxide on PBLs were significantly reduced with EEAI pre-treatment compared to post-treatment in a dose-dependent manner comparable with similar cytoprotective effects of ascorbic acid (p > 0.05). EEAI has shown strong antioxidant effects in the scavenging of DPPH, superoxide anion, hydrogen peroxide, and nitric oxide. EEAI also has a strong protective effect of UV-induced plasmid pBR322 DNA cleavage and Fenton-induced DNA damage. Overall, the results revealed that Abutilon indicum has a cytoprotective, potent antioxidant and DNA protective effect that provide pharmacological credence to justify its overall biological activity. Furthermore, future studies to identifying bioactive molecules and its molecular mechanisms responsible for promising therapeutic applications in the rescue of disease-induced cellular oxidative damage.

In silico, in-vitro and in vivo screening of biological activities of citral.

Citral, one of the main components of lemongrass oil (65-85%), is known to possess various medicinal properties like enhancing skin health and vision-improvement. It also acts as flavoring agent, used in perfumes and skin care products. The objective of this work was to elucidate the biological properties of citral at molecular level using an integrated in silico, in vitro and in vivo approaches. To elucidate this in silico molecular docking studies were performed with in vitro validation by DPPH scavenging activity, MTT assays, enzymatic assays and Chorio Allantoic Membrane (CAM) assay. The in silico analysis demonstrated the potential binding of citral with PPARγ ligand binding domain and vascular endothelial growth factor receptors (VEGFR-1 and VEGFR-2). Citral is already a proven anti-oxidant which is further confirmed by increased DPPH inhibition with increased citral concentration (IC50: 6.9±1.68μg/ml, p<0.05). The results demonstrated that citral protect yeast cells from cytotoxic effects of hydrogen peroxide and also increase the activities of antioxidant enzymes like GST, SOD and LPO. It was also demonstrated to be cytotoxic to cancerous HeLa cells (IC50: 3.9±0.38μM, p<0.01) and was found anti-angiogenic by CAM assay. This study highlights many important pharmaceutical properties of citral which can be explored further to increase its industrial applications.

Cytotoxic effects of hydrogen peroxide on periodontal cells

Cytotoxic effects of hydrogen peroxide on periodontal cells

Cytotoxic effects of hydrogen peroxide on periodontal cells

Cytotoxic effects of hydrogen peroxide on periodontal cells

Lycii fructus extract ameliorates hydrogen peroxide-induced cytotoxicity through indirect antioxidant action.

LFE: Lycii Fructus extract; GSH: glutathione; NQO1: NAD(P)H:quinone oxidoreductase 1; HO-1: heme oxygenase-1; GCLC: glutamate-cysteine ligase, catalytic subunit; xCT: a component of cysteine/glutamate antiporter (cystine/glutamate exchanger); CYP1A1: cytochrome P450 1A1; GSH: glutathione; AhR: aryl hydrocarbon receptor; Nrf2: nuclear factor (erythroid-derived 2)-like 2; CGA: chlorogenic acid; RT-PCR: reverse transcription-polymerase chain reaction; DTT: dithiothreitol; PMSF: phenylmethylsulfonyl fluoride; ARE: antioxidant response element; XRE: xenobiotic responsive element.

Glutaminase-1 stimulates the proliferation, migration, and survival of human endothelial cells

Glutaminase-1 (GLS1) is a mitochondrial enzyme found in endothelial cells (ECs) that metabolizes glutamine to glutamate and ammonia. Although glutaminolysis modulates the function of human umbilical vein ECs, it is not known whether these findings extend to human ECs beyond the fetal circulation. Furthermore, the molecular mechanism by which GLS1 regulates EC function is not defined. In this study, we show that the absence of glutamine in the culture media or the inhibition of GLS1 activity or expression blocked the proliferation and migration of ECs derived from the human umbilical vein, the human aorta, and the human microvasculature. GLS1 inhibition arrested ECs in the G0/G1 phase of the cell cycle and this was associated with a significant decline in cyclin A expression. Restoration of cyclin A expression via adenoviral-mediated gene transfer improved the proliferative, but not the migratory, response of GLS1-inhibited ECs. Glutamine deprivation or GLS1 inhibition also stimulated the production of reactive oxygen species and this was associated with a marked decline in heme oxygenase-1 (HO-1) expression. GLS1 inhibition also sensitized ECs to the cytotoxic effect of hydrogen peroxide and this was prevented by the overexpression of HO-1. In conclusion, the metabolism of glutamine by GLS1 promotes human EC proliferation, migration, and survival irrespective of the vascular source. While cyclin A contributes to the proliferative action of GLS1, HO-1 mediates its pro-survival effect. These results identify GLS1 as a promising therapeutic target in treating diseases associated with aberrant EC proliferation, migration, and viability.

The role of DNA polymerase ζ in translesion synthesis across bulky DNA adducts and cross-links in human cells

Translesion DNA synthesis (TLS) is a cellular defense mechanism against genotoxins. Defects or mutations in specialized DNA polymerases (Pols) involved in TLS are believed to result in hypersensitivity to various genotoxic stresses. Here, DNA polymerase ζ (Pol ζ)-deficient (KO: knockout) and Pol ζ catalytically dead (CD) human cells were established and their sensitivity towards cytotoxic activities of various genotoxins was examined. The CD cells were engineered by altering the DNA sequence encoding two amino acids essential for the catalytic activity of Pol ζ, i.e., D2781 and D2783, to alanines. Both Pol ζ KO and CD cells displayed a prolonged cell cycle and higher incidence of micronuclei formation than the wild-type (WT) cells in the absence of exogenous genotoxic treatments, and the order of abnormality was CD>KO>WT cells. Both KO and CD cells exhibited higher sensitivity towards the killing effects of benzo[a]pyrene diol epoxide, mitomycin C, potassium bromate, N-methyl-N′-nitro-N-nitrosoguanidine, and ultraviolet C irradiation than WT cells, and there were no differences between the sensitivities of KO and CD cells. Interestingly, neither KO nor CD cells were sensitive to the cytotoxic effects of hydrogen peroxide. Since KO and CD cells displayed similar sensitivities to the genotoxins, we employed only KO cells to further examine their sensitivity to other genotoxic agents. KO cells were more sensitive to the cytotoxicity of 4-nitroquinoline N-oxide, styrene oxide, cisplatin, methyl methanesulfonate, and ethyl methanesulfonate than WT cells. However, the KO cells displayed sensitivity camptothecin, etoposide, bleomycin, hydroxyurea, crotonealdehyde, and methylglyoxal in a manner similar to the WT cells. Our results suggest that Pol ζ plays an important role in the protection of human cells by carrying out TLS across bulky DNA adducts and cross-links, but has no or limited role in the protection against strand-breaks in DNA.

Heat-shock protein HSP70 protects neuroblastoma cells SK-N-SH from the neurotoxic effects hydrogen peroxide and the β-amyloid peptide

Neuronal cell death in Alzheimer's disease is associated with the development of oxidative stress caused by the reactive oxygen species (ROS), which can be generated as a result of the effect of beta-amyloid peptides. One of the sources of ROS is hydrogen peroxide, inducing the apoptosis and necrosis of neural tissue cells. The mechanism of hydrogen peroxide apoptotic action includes launching signaling pathways that involve protein kinases PI3K, p38MAPK, JNK and ERK. Oxidative stress leads to increased synthesis of heat-shock proteins in the cells including HSP70. It was shown that the exogenous HSP70 could reduce generation of ROS in cells. In this study, we determined how HSP70 affected apoptosis and necrosis in human neuroblastoma cells SK-N-SH, induced by hydrogen peroxide and β-amyloid peptide Aβ(1-42). It was shown that HSP70 reduces the cytotoxic effects of hydrogen peroxide and beta-amyloid, and protein kinases PI3K and JNK play an important role in the mechanism of HSP70 protective effect on the peroxide induced apoptosis in SK-N-SH cells.

Tucumã fruit extracts (Astrocaryum aculeatum Meyer) decrease cytotoxic effects of hydrogen peroxide on human lymphocytes

This study quantifies the bioactive molecules in and determines the in vitro protective effect of ethanolic extracts isolated from the peel and pulp of tucumã (Astrocaryum aculeatum, Mart.), an Amazonian fruit rich in carotenoids. The cytoprotective effect of tucumã was evaluated in lymphocyte cultures exposed to H2O2 using spectrophotometric, fluorimetric, and immunoassay assays. The results confirmed that tucumã pulp extract is rich in β-carotene and quercetin, as previously described in the literature. However, high levels of these compounds were also found in tucumã peel extract. The extracts also contained significant amounts rutin, gallic acid, caffeic acid, and chlorogenic acid. Despite quantitative differences in the concentration of these bioactive molecules, both extracts increased the viability of cells exposed to H2O2 in concentrations ranging from 300 to 900μg/mL. Caspases 1, 3, and 8 decreased significantly in cells concomitantly exposed to H2O2 and these extracts, indicating that tucumã cryoprotection involves apoptosis modulation.

The Critical Role of Nitric Oxide Signaling, via Protein S-Guanylation and Nitrated Cyclic GMP, in the Antioxidant Adaptive Response

A nitrated guanine nucleotide, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), is formed via nitric oxide (NO) and causes protein S-guanylation. However, intracellular 8-nitro-cGMP levels and mechanisms of formation of 8-nitro-cGMP and S-guanylation are yet to be identified. In this study, we precisely quantified NO-dependent formation of 8-nitro-cGMP in C6 glioma cells via liquid chromatography-tandem mass spectrometry. Treatment of cells with S-nitroso-N-acetylpenicillamine led to a rapid, transient increase in cGMP, after which 8-nitro-cGMP increased linearly up to a peak value comparable with that of cGMP at 24 h and declined thereafter. Markedly high levels (>40 microm) of 8-nitro-cGMP were also evident in C6 cells that had been stimulated to express inducible NO synthase with excessive NO production. The amount of 8-nitro-cGMP generated was comparable with or much higher than that of cGMP, whose production profile slightly preceded 8-nitro-cGMP formation in the activated inducible NO synthase-expressing cells. These unexpectedly large amounts of 8-nitro-cGMP suggest that GTP (a substrate of cGMP biosynthesis), rather than cGMP per se, may undergo guanine nitration. Also, 8-nitro-cGMP caused S-guanylation of KEAP1 in cells, which led to Nrf2 activation and subsequent induction of antioxidant enzymes, including heme oxygenase-1; thus, 8-nitro-cGMP protected cells against cytotoxic effects of hydrogen peroxide. Proteomic analysis for endogenously modified KEAP1 with matrix-assisted laser desorption/ionization time-of-flight-tandem mass spectrometry revealed that 8-nitro-cGMP S-guanylated the Cys(434) of KEAP1. The present report is therefore the first substantial corroboration of the biological significance of cellular 8-nitro-cGMP formation and potential roles of 8-nitro-cGMP in the Nrf2-dependent antioxidant response.

Measurement of cell death by oxidative stress in three-dimensional spheroids from trophoblast and in fragments of decidua tissue

We report a new morphometric method for measurement of the amount of cell death in three-dimensional multicellular spheroids of the trophoblast-like cell line AC1-M59 and of cultured pieces of decidua tissue (decidua spheroids) in response to a cytotoxic agent. The viability of the spheroids was assessed by adding propidium iodide to the culture medium at the end of the toxic treatment. On fluorescence and brightfield images of serial cryosections the areas of propidium iodide fluorescence and the entire corresponding spheroids were measured by applying digital image processing and ratiometrical quantification. As an example, we evaluated the cytotoxic effect of hydrogen peroxide on both types of spheroids. The relative potency of hydrogen peroxide to induce tissue damage was assessed quantitatively for determination of the minimal concentration that leads to an increase in cytotoxicity. The method presented suggests general applicability for in vitro determination of toxicity against tissues.

Chlorogenic Acid Reduces Oxidative Stress in Rpe Cells

Our purpose was to determine whether chlorogenic acid (CGA) influence the levels of antioxidant defense status by monitoring the activity of catalase (CAT), of superoxide dismutase (SOD), reduced glutathione (GSH) content and the generation of intracellular reactive oxygen species (ROS). Confluent RPE cells (D407) were preincubated with l00 µM chlorogenic acid and after phenolic acid removal, cells were oxidatively challenged with 500µM H2O2. The dose of l00µM chlorogenic acid did not induce morphological changes in RPE cells, indicating a viability of 88% comparing with control after 24h of treatment. CGA treatment has not cytotoxic effect and reduces the cytotoxic effect of hydrogen peroxide in RPE cells. Chlorogenic acid treatment (1) up regulates the antioxidant enzymes activities CAT and SOD in RPE, especially in oxidatively stressed cells; (2) determine an increase of reduced glutathione concentration and, (3) decrease intracellular ROS generation in RPE cells subjected to oxidative stress. Chlorogenic acid could be a potential antioxidant agent for RPE cells, protecting them by oxidative stress.

Time- and activation-dependency of the protective effect of microglia on astrocytes exposed to peroxide-induced oxidative stress

Microglial as well as astroglial activation (gliosis) are common phenomena of neuropathological processes in the brain. Nevertheless, the role of glial cell communication during gliosis is still not completely understood. The data we present with this work are a part of a bigger study on microglial-astroglial cell communication. The purpose of this study was to examine the impact of microglial-astroglial cell interactions on the cytotoxic effect of hydrogen peroxide (H2O2) on astrocytes and to characterize the microglia-induced astroprotective effect in detail. Therefore, purified cell cultures of microglia and astroglia from neonatal rat brains were used. Astrocytes were pre-treated with conditioned medium from lipopolysaccharides (LPS)-activated microglia and then exposed to oxidative stress induced by H2O2 under varying conditions. Activated microglia significantly reduced the cytotoxic effect of H2O2. As well in the indirect co-culture model using conditioned medium of microglia as in a direct co-culture model with different portions of microglial cells on the astroglial monolayer the astroprotective effect clearly correlated with the degree of microglial activation. The protective effect on astrocytes was induced in less than 24 h and lasted more than 4 days. Taken together, our results indicate that microglial activation might play an important role in the modulation of the oxidative stress resistance of glial tissue during gliosis.

Dihydrodiol dehydrogenases regulate the generation of reactive oxygen species and the development of cisplatin resistance in human ovarian carcinoma cells

We have previously demonstrated that overexpression of dihydrodiol dehydrogenase isoform 1 (DDH1) or DDH2 leads to the induction of drug resistance to platinum based drugs in human ovarian, lung, cervical and germ cell tumor cell lines. DDH belongs to a family of aldoketo reductases that are involved in the detoxification of several endogenous and exogenous substrates. DDH1 and DDH2 in particular have been shown to be involved in the detoxification (activation?) of polycyclic aromatic hydrocarbons (PAH). Based on the involvement of DDH in the detoxification of electrophilic PAH intermediates, the effect of DDH on the production of reactive oxygen species (ROS) in a cisplatin-sensitive and -resistant human ovarian carcinoma cell line was investigated in the current study. In addition to the overexpression of DDH1 and DDH2, increased expression of DDH3 was demonstrated in the cisplatin-resistant 2008/C13* cells, compared to the parental 2008 cells. However, as assessed by RT-PCR, neither cell line expressed DDH4. The 2008/C13* cells were eightfold resistant to cisplatin, and transfection experiments utilizing cisplatin-sensitive 2008 cells suggest that this could be mediated by overexpression of either DDH1, DDH2, or DDH3. The 2008/C13* cells had lower basal intracellular ROS level as compared to the 2008 cells and ROS production was decreased in the recombinant 2008 cells with forced, constitutive overexpression of either, DDH1, DDH2, or DDH3. Transfection of siRNA against DDH1 or DDH2 in the cisplatin-resistant 2008/C13* cells not only significantly decreased their cisplatin-resistance index (as assayed by MTT and colony formation assay) but also led to an increase in the basal levels of ROS production (although transfection of siRNA against DDH3 resulted in cell death). The 2008/C13* cells were found to be cross-resistant to the cytotoxic effects of hydrogen peroxide and tert-butyl hydroperoxide and knockdown of either DDH1 or DDH2 expression (using siRNA) resulted in sensitization of the resistant cells to these agents. These results support the conclusion that the increased levels of DDH in the 2008/C13* cells are directly responsible for the reduced production of ROS and that this may play a role in the development of cisplatin resistance.

Stress resistance and aging: Influence of genes and nutrition

Previous studies have shown that dermal fibroblast cell lines derived from young adult mice of the long-lived Snell dwarf ( d w / d w ), Ames dwarf ( df/ df) and growth hormone receptor knockout (GHR-KO) mouse stocks are resistant, in vitro, to the cytotoxic effects of hydrogen peroxide, cadmium, ultraviolet light, paraquat, and heat. Here we show that, in contrast, fibroblasts from mice on low-calorie (CR) or low methionine (Meth-R) diets are not stress resistant in culture, despite the longevity induced by both dietary regimes. A second approach, involving induction of liver cell death in live animals using acetaminophen (APAP), documented hepatotoxin resistance in the CR and Meth-R mice, but d w / d w and GHR-KO mutant mice were not resistant to this agent, and were in fact more susceptible than littermate controls to the toxic effects of APAP. These data thus suggest that while resistance to stress is a common characteristic of experimental life span extension in mice, the cell types showing resistance may differ among the various models of delayed or decelerated aging.

Antioxidant and Anti-atherogenic Activities of Olive Oil Phenolics

The aim of the current study was to investigate the antioxidant and cellular activity of the olive oil phenolics oleuropein, tyrosol, hydroxytyrosol, and homovanillic alcohol (which is also a major metabolite of hydroxytyrosol). Well-characterized chemical and biochemical assays were used to assess the antioxidant potential of the compounds. Further experiments investigated their influence in cell culture on cytotoxic effects of hydrogen peroxide and oxidized low-density lipoprotein (LDL), nitric oxide production by activated macrophages, and secretion of chemoattractant and cell adhesion molecules by the endothelium. Inhibitory influences on in vitro platelet aggregation were also measured. The antioxidant assays indicated that homovanillic alcohol was a significantly more potent antioxidant than the other phenolics, both in chemical assays and in prolonging the lag phase of LDL oxidation. Cell culture experiments suggested that the olive oil phenolics induce a significant reduction in the secretion of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 (and a trend towards a reduced secretion of monocyte chemoattractant protein-1), and protect against cytotoxic effects of hydrogen peroxide and oxidized LDL. However, no influence on nitric oxide production or platelet aggregation was evident. The data show that olive oil phenolics have biochemical and cellular actions, which, if also apparent in vivo, could exert cardioprotective effects.

Selective and non-selective cox inhibitors up-regulate heat shock protein-70 expression and protect human monocytes and macrophages from the cytotoxic effect of hydrogen peroxide

Heat shock protein 70 (HSP-70) is a molecular chaperone that protects cells against stress stimuli. The expression of HSP-70 is normally up regulated in response to stress. However, in patients with severe sepsis, HSP-70 expression is suppressed. We hypothesized that inhibitors of cyclooxygenase (COX) could up regulate the expression of HSP-70 in human macrophages and monocytes, which in turn will improve the resistance of these cells to stress. Human monocytes and macrophages were untreated or treated with aspirin, ibuprofen or NS-398, a selective COX-2 inhibitor, for 1.5 to 24 hrs. A parallel group was exposed to a 30-min heat shock at 42°C. Western blotting and real-time polymerase chain reaction quantified, respectively, time dependent changes in HSP-70 protein expression and mRNA production. To evaluate whether elevated HSP-70 expression protects the cells from stress, cell viability was determined after exposure of cells to cytotoxic concentrations of hydrogen peroxide. Changes in cell viability were monitored using propidium iodide and fluorescent microscopy. Treatment of the monocytes or macrophage cultures with either aspirin, ibuprofen or NS-398 caused a statistically significant increase (p < 0.05; n = 4) of about 2.5 fold in HSP-70 mRNA expression that peaked at 1.5 hrs. Heat shock caused a 25-fold increase in HSP-70 mRNA expression at 1.5 hrs. The COX inhibitors also triggered a statistically significant increase (p < 0.05; n = 8) of about 2-fold in HSP-70 expression within 1.5 hrs of treatment, while the heat shock triggered a 3–5 fold increase in both cell populations. The protein levels remained elevated for 24 hrs in all treated groups. Significantly, pretreatment of the cells with either the COX inhibitors or the heat shock protected the cells from the cytotoxic effect of hydrogen peroxide. These findings suggest that both selective and non-selective COX inhibitors may be as effective as a febrile response in augmenting the body’s resistance to stress.

Hydrogen peroxide induces caspase activation and programmed cell death in the amitochondrial Tritrichomonas foetus.

Tritrichomonas foetus is an amitochondrial parasite protist which lacks typical eukaryote organelles such as mitochondria and peroxisomes, but possesses the hydrogenosome, a double-membrane-bound organelle that produces ATP. The cell death of amitochondrial organisms is poorly studied. In the present work, the cytotoxic effects of hydrogen peroxide on T. foetus and its participation on cell death were analyzed. We took advantage of several microscopy techniques, including videomicroscopy, light microscopy immunocytochemistry for detection of caspase activation, and scanning and transmission electron microscopy. We report here that in T. foetus: (1) H(2)O(2) leads to loss of motility and induces cell death, (2) the dying cells exhibit some characteristics similar to those found during the death of other organisms, and (3) a caspase-like protein seems to be activated during the death process. Thus, we propose that, although T. foetus does not present mitochondria nor any known pathways of cell death, it is likely that it bears mechanisms of cell demise. T. foetus exhibits morphological and physiological alterations in response to H(2)O(2) treatment. The hydrogenosome, a unique organelle which is supposed to share a common ancestral origin with mitochondria and has an important role in oxidative responses in trichomonads, is a candidate for participating in this event.