Cytotoxic and genotoxic effects of tert-butyl hydroperoxide on Chinese hamster B14 cells

In vivo mutagenicity assessment of orally treated tert-butyl hydroperoxide in the liver and glandular stomach of MutaMouse

BACKGROUND

tert-Butyl hydroperoxide (TBHP; CAS 75-91-2), a hydroperoxide, is mainly used as a polymerization initiator to produce polyethylene, polyvinyl chloride, and unsaturated polyester. It is a high-production chemical, widely used in industrial countries, including Japan. TBHP is also used as an additive for the manufacturing of food utensils, containers, and packaging (UCP). Therefore, there could be consumer exposure through oral intake of TBHP eluted from UCPs. TBHP was investigated in various in vitro and in vivo genotoxicity assays. In Ames tests, some positive results were reported with and/or without metabolic activation. As for the mouse lymphoma assay, the positive result was reported, regardless of the presence or absence of metabolic activation enzymes. The results of some chromosomal aberrations test and comet assay in vitro also demonstrated the genotoxic positive results. On the other hand, in in vivo tests, there are negative results in the bone marrow micronucleus test of TBHP-administered mice by single intravenous injection and the bone marrow chromosomal aberration test using rats exposed to TBHP for 5 days by inhalation. Also, about dominant lethal tests, the genotoxic positive results appeared. In contrast, there is little information about in vivo mutagenicity and no information about carcinogenicity by oral exposure.

RESULTS

We conducted in vivo gene mutation assay using MutaMice according to the OECD Guidelines for the Testing of Chemicals No. 488 to investigate in vivo mutagenicity of TBHP through oral exposure. After repeated dosing for 28 days, there were no significant differences in the mutant frequencies (MFs) of the liver and glandular stomach up to 300 mg/kg/day (close to the maximum tolerable dose (MTD)). The positive and negative controls produced the expected responses.

CONCLUSIONS

These findings show that orally administrated TBHP is not mutagenic in the mouse liver and glandular stomach under these experimental conditions.

Hybrid DNA-Carbon Dot-Poly(vinylpyrrolidone) Hydrogel with Self-Healing and Shape Memory Properties for Simultaneous Trackable Drug Delivery and Visible-Light-Induced Antimicrobial Photodynamic Inactivation

A two-step methodology for simultaneous conjugation of DNA and poly(vinylpyrrolidone) (PVP) polymer to a single carbon quantum dot (CD) is demonstrated for the first time to fabricate a pH-responsive DNA-CD-PVP hybrid hydrogel. Cross-linking in the hydrogel was achieved using CD as the common nucleus through the formation of DNA I-motif conformation at neutral to acidic pH and noncovalent interaction of PVP that infuse self-healing and shape memory properties in the hydrogel. The hydrogel is capable of loading and sustained delivery of drugs for more than 2 weeks as demonstrated using a model drug, Hemin. The quenching of fluorescence of CD by Hemin was trackable even through simple visual monitoring, which showed that Hemin can diffuse from the loaded part to the unloaded part of the hydrogel during the self-healing process. Most significantly, the chosen CD generates reactive oxygen species (ROS) upon visible light irradiation, armoring the hydrogel with worthy antimicrobial activity. Biocompatibility of the DNA-CD-PVP hydrogel was established on human fibroblast cells, indicating their potential use in biomedical area pertaining to wound healing.

Targeting breast cancer metabolism with a novel inhibitor of mitochondrial ATP synthesis

Inhibitors of mitochondrial respiration and ATP synthesis may promote the selective killing of respiration-competent cancer cells that are critical for tumor progression. We previously reported that CADD522, a small molecule inhibitor of the RUNX2 transcription factor, has potential for breast cancer treatment. In the current study, we show that CADD522 inhibits mitochondrial oxidative phosphorylation by decreasing the mitochondrial oxygen consumption rate (OCR) and ATP production in human breast cancer cells in a RUNX2-independent manner. The enzyme activity of mitochondrial ATP synthase was inhibited by CADD522 treatment. Importantly, results from cellular thermal shift assays that detect drug-induced protein stabilization revealed that CADD522 interacts with both α and β subunits of the F1-ATP synthase complex. Differential scanning fluorimetry also demonstrated interaction of α subunits of the F1-ATP synthase to CADD522. These results suggest that CADD522 might target the enzymatic F1 subunits in the ATP synthase complex. CADD522 increased the levels of intracellular reactive oxygen species (ROS), which was prevented by MitoQ, a mitochondria-targeted antioxidant, suggesting that cancer cells exposed to CADD522 may elevate ROS from mitochondria. CADD522-increased mitochondrial ROS levels were enhanced by exogenously added pro-oxidants such as hydrogen peroxide or tert-butyl hydroperoxide. Conversely, CADD522-mediated cell growth inhibition was blocked by N-acetyl-l-cysteine, a general ROS scavenger. Therefore, CADD522 may exert its antitumor activity by increasing mitochondrial driven cellular ROS levels. Collectively, our data suggest in vitro proof-of-concept that supports inhibition of mitochondrial ATP synthase and ROS generation as contributors to the effectiveness of CADD522 in suppression of tumor growth.

Validating interfacial behaviour of surface-active ionic liquids (SAILs) with computational study integrated with biocidal and cytotoxic assessment

Surface-active ionic liquids (SAILs) belonging to the series of N-alkylmethylimidazolium halides [C₈mimX] (X = Br, Cl, and BF₄) and [C_nmimBr] (n = 10, 12, 14, and 16) were employed to understand the influence of hydrophobicity of alkyl chain length and the chaotropicity of counter-ions of SAILs on the micellization, antimicrobial action and cytotoxicity properties. The micellization phenomenon of SAILs in an aqueous environment was examined employing tensiometry and steady-state fluorescence spectrophotometry. The corresponding interfacial parameters viz., critical micelle concentration (CMC), effectiveness (γ_CMC), surface pressure (П_CMC), maximum surface excess concentration (Г_max), and the minimum area engaged per molecule (A_min) at the air-water interface were evaluated at 303.15 K. These experimental findings were monitored and geometrically optimized theoretically using Gaussian software to highlight the recent advances in this field of theoretical calculations for putative structure. The simulation descriptors correlated the micellization behavior as a function of hydrophobicity which may contribute to obtaining awareness on their ecological behavior and fate. In addition, the biological screening of all the examined SAILs was undertaken with a combined experimental and theoretical (optimized) method against bacteria and fungus. Results revealed that SAILs with the alkyl chain-length greater than C₈- act as a fair antimicrobial agent against the selected microbial strain which is attributed to the enhanced degree of SAILs hydrophobicity. The cytotoxicity of these imidazolium-based SAILs was also assessed on the cervical human cell line (HeLa) using the MTT cell viability assay and the data thus obtained were subjected to statistical analysis.

The role of low molecular weight thiols in Mycobacterium tuberculosis

Low molecular weight (LMW) thiols are molecules with a functional sulfhydryl group that enable them to detoxify reactive oxygen species, reactive nitrogen species and other free radicals. Their roles range from their ability to modulate the immune system to their ability to prevent damage of biological molecules such as DNA and proteins by protecting against oxidative, nitrosative and acidic stress. LMW thiols are synthesized and found in both eukaryotes and prokaryotes. Due to their beneficial role to both eukaryotes and prokaryotes, their specific functions need to be elucidated, most especially in pathogenic prokaryotes such as Mycobacterium tuberculosis (M.tb), in order to provide a rationale for targeting their biosynthesis for drug development. Ergothioneine (ERG), mycothiol (MSH) and gamma-glutamylcysteine (GGC) are LMW thiols that have been shown to interplay to protect M.tb against cellular stress. Though ERG, MSH and GGC seem to have overlapping functions, studies are gradually revealing their unique physiological roles. Understanding their unique physiological role during the course of tuberculosis (TB) infection, would pave the way for the development of drugs that target their biosynthetic pathway. This review identifies the knowledge gap in the unique physiological roles of LMW thiols and proposes their mechanistic roles based on previous studies. In addition, it gives an update on identified inhibitors of their biosynthetic enzymes.

The effect of Msh2 knockdown on toxicity induced by tert-butyl-hydroperoxide, potassium bromate, and hydrogen peroxide in base excision repair proficient and deficient cells

The DNA mismatch repair (MMR) and base excision repair (BER) systems are important determinants of cellular toxicity following exposure to agents that cause oxidative DNA damage. To examine the interactions between these different repair systems, we examined whether toxicity, induced by t-BOOH and KBrO₃, differs in BER proficient (Mpg^+/+, Nth1^+/+) and deficient (Mpg^−/−, Nth1^−/−) mouse embryonic fibroblasts (MEFs) following Msh2 knockdown of between 79 and 88% using an shRNA expression vector. Msh2 knockdown in Nth1^+/+ cells had no effect on t-BOOH and KBrO₃ induced toxicity as assessed by an MTT assay; knockdown in Nth1^−/− cells resulted in increased resistance to t-BOOH and KBrO₃, a result consistent with Nth1 removing oxidised pyrimidines. Msh2 knockdown in Mpg^+/+ cells had no effect on t-BOOH toxicity but increased resistance to KBrO₃; in Mpg^−/− cells, Msh2 knockdown increased cellular sensitivity to KBrO₃ but increased resistance to t-BOOH, suggesting a role for Mpg in removing DNA damage induced by these agents. MSH2 dependent and independent pathways then determine cellular toxicity induced by oxidising agents. A complex interaction between MMR and BER repair systems, that is, exposure dependent, also exists to determine cellular toxicity.

The effect of oxidative stress upon the intestinal uptake of folic acid: in vitro studies with Caco-2 cells

Folic acid (FA) is a vitamin essential for normal cellular functions, growth, and development. Because humans cannot synthesize this micronutrient, it must be obtained from dietary sources through intestinal absorption. The intestinal tract is a major target for oxidative stress. Our aim was to investigate the effect of oxidative stress upon the uptake of FA by Caco-2 cells. Oxidative stress was induced by exposure of the cells to tert-butyl hydroperoxide (TBH) for 1 h. TBH (3,000 μM) induced an increase in biomarkers of oxidative stress, while maintaining cell viability and proliferation. In relation to the apical uptake of (3)H-FA, TBH (3,000 μM) reduced the cellular accumulation of (3)H-FA (10 nM), although the characteristics (kinetics, pH dependence, and inhibitory profile) of (3)H-FA uptake were not changed. This effect was associated with a decrease in the mRNA steady-state levels of proton-coupled folate transporter and folate receptor alpha and of the efflux transporter multidrug resistance protein 2. Moreover, TBH (3,000 μM) did not affect the noncarrier-mediated apical uptake of (3)H-FA. Finally, the effect of TBH upon (3)H-FA apical uptake was not dependent on protein kinase A, protein kinase C, mitogen-activated protein kinases, phosphoinositide 3-kinase, nuclear factor kappa B, and protein tyrosine kinases, but was completely prevented by dietary polyphenols (resveratrol, quercetin, and EGCG). These results suggest that oxidative stress at the intestinal level may result in a reduction in the intestinal absorption of dietary FA and that polyphenolic dietary components may offer protection against oxidative stress-induced inhibition of intestinal FA absorption.

The methyl xanthine caffeine inhibits DNA damage signaling and reactive species and reduces atherosclerosis in ApoE(-/-) mice

OBJECTIVE

Caffeine remains one of the most widely consumed drugs in the world. Caffeine has multiple actions, including inhibition of the DNA damage response, and its metabolites, 1-methylxanthine and 1-methyluric acid, are potent antioxidants. Combined, these properties can exert direct effects on cell proliferation, cell death, inflammation, and DNA repair, all important processes that occur in atherosclerosis.

METHODS AND RESULTS

We first examined the effects of caffeine on mouse vascular smooth muscle cells. Caffeine inhibited activation of the DNA damage response regulator ataxia telangiectasia mutated protein and its downstream targets. Caffeine delayed DNA repair, had a concentration-dependent effect on cell proliferation, and protected against apoptosis. In vitro caffeine reduced oxygen consumption and decreased generation of reactive oxygen species. In vivo caffeine reduced DDR activation in vascular and nonvascular tissues, reduced reactive nitrogen species and serum levels of the DNA adduct 8-oxo-guanine, and inhibited atherogenesis in fat-fed ApoE(-/-) mice. Reduction in atherosclerosis was independent of the effects on blood pressure and serum lipids but associated with reduced cell proliferation and ataxia telangiectasia mutated protein activation.

CONCLUSIONS

The Methyl Xanthine caffeine inhibits the DNA damage response in vitro and in vivo, regulates both cell proliferation and apoptosis after DNA damage, inhibits reactive species, and reduces atherogenesis in ApoE(-/-) mice.

Inactivation of YAP1 enhances sensitivity of the yeast RNR3-lacZ genotoxicity testing system to a broad range of DNA-damaging agents

Despite the great advances by using microorganism-based genotoxicity testing systems to assess environmental genotoxic compounds, most of them respond poorly, particularly to oxidative agents. In this study, we systematically examined the RNR3-lacZ reporter gene expression in Saccharomyces cerevisiae mutant strains defective in the protection against reactive oxygen species and found that only YAP1 deletion resulted in a significant enhancement in the detection of oxidative damage. To our surprise, YAP1 deletion also caused an increased cellular sensitivity to a variety of DNA damage. This altered sensitivity appears to be independent of oxidative damage because under conditions in which vitamin C treatment rescued oxidative damage, it failed to reverse the phenotypes caused by other types of DNA damage. Furthermore, although inactivation of cell permeability genes enhanced the RNR3-lacZ detection sensitivity particularly to large molecular weight compounds, their effects on small molecular oxidative agents are minimal. Taken together, this study helps to create a hypersensitive genotoxicity testing system to a broad range of DNA-damaging agents by deleting a single yeast gene.

Ischemia/reperfusion in rat: antioxidative effects of enoant on EEG, oxidative stress and inflammation

PRIMARY OBJECTIVE

The present study was undertaken to evaluate whether enoant, which is rich in polyphenols, has any effect on electroencephalogram (EEG), oxidative stress and inflammation in ischemia/reperfusion (I/R) injury.

METHODS

Ischemia was induced by 2-hour occlusion of bilateral common carotid artery. Animals orally received enoant. Group 1 was the ischemic control group. Group 2 was treated with enoant of 1.25 g kg⁻¹ per day for 15 days after I/R. Group 3 received the same concentration of enoant as in group 2 for 15 days before and after I/R. Group 4 was the sham operation group. EEG activities were recorded and the levels of TNF-α, IL-1β and IL-6, TBARS and GSH were measured in the whole brain homogenate.

RESULTS

There were significant changes in EEG activity in groups treated with enoant either before or after ischemia when compared with their basal EEG values. TNF-α, IL-6 and IL-1β levels were significantly increased after I/R. GSH levels in group 3 treated with enoant in both pre- and post-ischemic periods were significantly increased and TBARS concentration was decreased compared with the ischemic group.

CONCLUSION

The findings support that both pre-ischemic and post-ischemic administrations of enoant might produce neuroprotective action against cerebral ischemia.

Mechanisms participating in oxidative damage of isolated rat hepatocytes

The aim of the study was to evaluate time course and dose dependence of peroxidative damage induced by tert-butyl hydroperoxide (tBHP) in rat hepatocytes cultured in suspension and in monolayer. At the lowest (0.1 mM) concentration, decrease of cytosolic glutathione and discharge of mitochondrial membrane potential (MMP) could be detected. Significant increases in leakage of lactate dehydrogenase and in malondialdehyde concentrations together with decrease of pyruvate-dependent respiration were detected at higher tBHP concentrations (above 0.5 mM) and after longer periods of incubation. Changes in plasma membrane integrity were observed at 1 mM concentration of tBHP. Succinate-dependent oxidation was most resistant to peroxidative damages. Opening of the mitochondrial permeability transition pore was responsible for the discharge of mitochondria membrane potential. In the presence of cyclosporine A and succinate, the membrane potential could be restored. Our data showed that the most sensitive indicators of the peroxidative damage are changes of cytosolic glutathione concentration and MMP.

Effects of 17beta-estradiol, and its metabolite, 4-hydroxyestradiol on fertilization, embryo development and oxidative DNA damage in sand dollar (Dendraster excentricus) sperm

Oxidative compounds have been demonstrated to decrease the fertilization capability and viability of offspring of treated spermatozoa. As estrogen and its hydroxylated metabolites readily undergo redox cycling, this study was undertaken to determine if estrogens and other oxidants could damage DNA and impair sperm function. Sperm was preexposed to either 17beta-estradiol (E2), 4-hydroxyestradiol (4OHE2) or the oxidant t-butyl hydroperoxide (t-BOOH), and allowed to fertilize untreated eggs. The fertilization rates and development of the larvae were assessed, as well as the amount of 8-oxodeoxyguanosine (8-oxodG) as an indication of oxidative DNA damage. All compounds caused significant decreases in fertilization and increases in pathological abnormalities in offspring, with 4OHE2 being the most toxic. Treatment with 4OHE2 caused a significant increase of 8-oxodG, but E2 failed to show any effect. Pathological abnormalities were significantly correlated (r(2)=0.44, p< or =0.05) with 8-oxodG levels in sperm treated with t-BOOH and 4OHE2, but not E2. 8-OxodG levels also were somewhat weakly correlated with impaired fertilization in 4OHE2-treated sperm (r(2)=0.33, p< or =0.05). The results indicate that biotransformation of E2 to 4OHE2 enhances oxidative damage of DNA in sperm, which can reduce fertilization and impair embryonic development, but other mechanisms of action may also contribute to these effects.

Quercus infectoria galls possess antioxidant activity and abrogates oxidative stress-induced functional alterations in murine macrophages

The present study reports the antioxidant activity of ethanolic extract of Quercus infectoria galls. The antioxidant potency of galls was investigated employing several established in vitro model systems. Their protective efficacy on oxidative modulation of murine macrophages was also explored. Gall extract was found to contain a large amount of polyphenols and possess a potent reducing power. HPTLC analysis of the extract suggested it to contain 19.925% tannic acid (TA) and 8.75% gallic acid (GA). The extract potently scavenged free radicals including DPPH (IC(50)~0.5 microg/ml), ABTS (IC(50)~1 microg/ml), hydrogen peroxide (H(2)O(2)) (IC(50)~2.6 microg/ml) and hydroxyl (*OH) radicals (IC(50)~6 microg/ml). Gall extract also chelated metal ions and inhibited Fe(3+) -ascorbate-induced oxidation of protein and peroxidation of lipids. Exposure of rat peritoneal macrophages to tertiary butyl hydroperoxide (tBOOH) induced oxidative stress in them and altered their phagocytic functions. These macrophages showed elevated secretion of lysosomal hydrolases, and attenuated phagocytosis and respiratory burst. Activity of macrophage mannose receptor (MR) also diminished following oxidant exposure. Pretreatment of macrophages with gall extract preserved antioxidant armory near to control values and significantly protected against all the investigated functional mutilations. MTT assay revealed gall extract to enhance percent survival of tBOOH exposed macrophages. These results indicate that Q. infectoria galls possess potent antioxidant activity, when tested both in chemical as well as biological models.

Purification and characterization of antioxidant peptide from hoki (Johnius belengerii) frame protein by gastrointestinal digestion

To extract antioxidant peptide from hoki frame protein hydrolysate (APHPH), we employed six proteases (pepsin, trypsin, papain, alpha-chymotrypsin, Alcalase and Neutrase) for enzymatic hydrolysis, and the antioxidant activities of their hydrolysates were investigated using both lipid peroxidation inhibition assay and free radical scavenging assay by electron spin resonance spin-trapping technique. Among hydrolysates, peptic hydrolysate, having the highest antioxidant activity, further separated into four groups using ultrafiltration membranes and purified consecutive chromatographic methods. Finally, the purified peptide had a molecular mass of 1801 Da, and amino acid sequence was identified as Glu-Ser-Thr-Val-Pro-Glu-Arg-Thr-His-Pro-Ala-Cys-Pro-Asp-Phe-Asn. APHPH inhibited lipid peroxidation higher than that of alpha-tocopherol as positive control and efficiently quenched different sources of free radical: 1,1-diphenyl-2-pycryl-hydrazyl (IC(50)=41.37 microM), hydroxyl (IC(50)=17.77 microM), peroxyl (IC(50)=18.99 microM) and superoxide radicals (IC(50)=172.10 microM). Furthermore, APHPH decreased t-butylhydroperoxide-induced cytotoxicity on human embryonic lung fibroblasts and efficiently protected free-radical-induced DNA damage.