Aflatoxin B1 Exacerbates Genomic Instability and Apoptosis in the BTBR Autism Mouse Model via Dysregulating DNA Repair Pathway

The pathophysiology of autism is influenced by a combination of environmental and genetic factors. Furthermore, individuals with autism appear to be at a higher risk of developing cancer. However, this is not fully understood. Aflatoxin B1 (AFB1) is a potent food pollutant carcinogen. The effects of AFB1 on genomic instability in autism have not yet been investigated. Hence, we have aimed to investigate whether repeated exposure to AFB1 causes alterations in genomic stability, a hallmark of cancer and apoptosis in the BTBR autism mouse model. The data revealed increased micronuclei generation, oxidative DNA strand breaks, and apoptosis in BTBR animals exposed to AFB1 when compared to unexposed animals. Lipid peroxidation in BTBR mice increased with a reduction in glutathione following AFB1 exposure, demonstrating an exacerbated redox imbalance. Furthermore, the expressions of some of DNA damage/repair- and apoptosis-related genes were also significantly dysregulated. Increases in the redox disturbance and dysregulation in the DNA damage/repair pathway are thus important determinants of susceptibility to AFB1-exacerbated genomic instability and apoptosis in BTBR mice. This investigation shows that AFB1-related genomic instability can accelerate the risk of cancer development. Moreover, approaches that ameliorate the redox balance and DNA damage/repair dysregulation may mitigate AFB1-caused genomic instability.

The small molecule Erk1/2 signaling pathway inhibitor PD98059 improves DNA repair in an experimental autoimmune encephalomyelitis SJL/J mouse model of multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disorder in which the myelin sheath covering the central nervous system axons is damaged or lost, disrupting action potential conduction and leading to various neurological complications. The pathogenesis of MS remains unclear, and no effective therapies are currently available. MS is triggered by environmental factors in genetically susceptible individuals. DNA damage and DNA repair failure have been proposed as MS genetic risk factors; however, inconsistent evidence has been found in multiple studies. Therefore, more investigations are needed to ascertain whether DNA damage/repair is altered in this disorder. In this context, therapies that prevent DNA damage or enhance DNA repair could be effective strategies for MS treatment. The overactivation of the extracellular-signal-related kinase 1 and 2 (Erk1/2) pathway can lead to DNA damage and has been linked to MS pathogenesis. In our study, we observed substantially elevated oxidative DNA damage and slower DNA repair rates in an experimentally autoimmune encephalomyelitis animal model of MS (EAE). Moreover, statistical decreases in oxidative DNA strand breaks and faster repair rates were observed in EAE animals injected with the Erk1/2 inhibitor PD98059 (PD). Moreover, the expression of several genes associated with DNA strand breaks and repair changed in EAE mice at both the mRNA and protein levels, as revealed by the RT² Profiler PCR array and verified by RT-PCR and protein analyses. The treatment with PD mitigated these changes and improved DNA repair gene expression. Our results demonstrate clear associations between Erk1/2 activation, DNA damage/repair, and MS pathology, and further suggest that PD therapy may be a promising adjuvant therapeutic strategy.

Chloroacetonitrile reduces rat prenatal bone length and induces oxidative stress, apoptosis, and DNA damage in rat fetal liver

One of the disinfection byproducts of chlorinating drinking water is chloroacetonitrile (CAN). Thirty-six female rats were used and distributed equally into four groups. The low dose treated group received CAN at a dose of 5.5 mg/kg body weight/day (1/40 LD₅₀ ) orally from the 6th to 12th day of gestation. The high dose treated group received 11 mg/kg body weight/day (1/20 LD₅₀ ) of CAN orally for the same period, the vehicle control group received 1 mL of corn oil, and the water control group received 1 mL of distilled water orally for the same period. High dose exposure to CAN significantly reduced gravid uterine weight, fetal body weights, and length, and caused obvious skeletal deformities, weak mineralization. Fetal tibial growth plates displayed histopathologic changes. Induced oxidative stress and redox imbalance in fetal liver tissues was evidenced by significantly decreased in catalase and superoxide dismutase activity, and elevated malondialdehyde levels. Histopathological, glycogen content changes, and DNA damage were observed in the fetal liver of high dose treated group. Additionally, administration of high dose of CAN induced apoptosis, evidenced by increased caspase-3 concentration in fetal liver. Thus, extensive exposure to CAN induces poor pregnancy outcomes. CAN levels in water should be monitored regularly.

Chloroacetonitrile exposure induces endoplasmic reticulum stress and affects spindle assembly in mouse oocytes

Chloroacetonitrile (CAN) is a halogenated acetonitrile often produced while disinfecting drinking water. Previous studies have shown that maternal exposure to CAN interferes with fetal development; however, the adverse effects on maternal oocytes remain unknown. In this study, in vitro exposure of mouse oocytes to CAN reduced maturation significantly. Transcriptomics analysis showed that CAN altered the expression of multiple oocyte genes, especially those associated with the protein folding process. CAN exposure induced reactive oxygen species production, accompanied by endoplasmic reticulum (ER) stress and increased glucose regulated protein 78, C/EBP homologous protein and activating transcription factor 6 expression. Moreover, our results indicated that spindle morphology was impaired after CAN exposure. CAN disrupted polo-like kinase 1, pericentrin and p-Aurora A distribution, which may be an origin inducer that disrupts spindle assemble. Furthermore, exposure to CAN in vivo impaired follicular development. Taken together, our findings indicate that CAN exposure induces ER stress and affects spindle assembly in mouse oocytes.

Haloacetonitrile stability in cell culture media used in vitro toxicological studies

Haloacetonitriles (HANs) are an emerging class of nitrogenous disinfection by-products (DBPs) formed in disinfected drinking water and have been reported to be more cyto- and genotoxic than the regulated DBPs. HANs are also known to hydrolyze under neutral pH and normal room temperature. However, the stability of HANs has not been well characterized in DBP toxicological assessments. Most toxicological assessments expose DBPs up to several days which may result in a mixture of HANs and degradation products that might have underestimated HAN toxicity. In this study, HANs stability was characterized in 1) a buffer solution in sealed vials, 2) cell culture media (CCM) in sealed vials, and 3) CCM in 96 sealed well plates with 5% CO₂. Solutions were incubated at 37 °C for 3 days. MonoHANs were found to be stable in buffer and CCM except when HANs were incubated in CCM in plates where they could possibly be affected by volatilization and photodegradation during sample handling. However, di- and tri- HANs degraded between 70 and 100% in both buffer solution and CCM. They were also found to be less stable in CCM than in buffer solution possibly from HANs reacting with nucleophiles present in CCM (i.e., amino acids). Identified degradation products include corresponding haloacetamides and haloacetic acids for buffer solutions and only haloacetic acids and an unknown brominated compound for CCM. Results of this study suggests that reported toxicity values might have been underestimated and should consider changing CCM and DBP on a daily basis for a more accurate toxicity measurement.

Identification of chlorinated products from tyrosine and tyrosyl dipeptides during chlorination: a computational study

Chlorinated amino acids and peptides, as the model modified protein structures relevant to pathogen inactivation and an emerging class of disinfection byproducts (DBPs) with potential health risks to humans, have attracted much attention. However, due to a large variety of peptides (over 600) identified in source water and most of them featuring multiple reaction sites, it is a huge challenge to identify all the chlorinated amino acids and peptides. As a good complement to the experiment, quantum chemical computation can be used to uncover the chlorination sites and chlorinated products. In this study, frequently detected tyrosine (Tyr) and tyrosine-amide (Tyr-Am) as well as N-acetyl-tyrosine (NacTyr) were chosen as the model amino acid and model dipeptides, respectively. The results indicate that the kinetic reactivity order of reactive sites with estimated apparent rate constants (k_obs-est, in M^-1 s^-1) is amino N (10^7-8) ≫ mono-chlorinated amino N (10^1-3) >/≈ phenol ortho-C (10^0-3) ≫ meta-C (10^-3), and phenol ortho-C5 (10^2-3) > ortho-C3 (10^0-2) for dipeptides, while in thermodynamics, phenol C sites are more favorable than amino N sites. Moreover, due to the smaller differences of k_obs-est values between the mono-chlorinated amino N and the phenol ortho-C sites in tyrosyl dipeptides compared to free Tyr, more kinds of C-chloro-tyrosyl dipeptides are likely to be generated. Additionally, a structure-kinetic reactivity relationship study reveals good correlations between lg k_obs-est and NPA charges and BDEs of protons released from amino/hydroxyl groups in tyrosyl compounds rather than FED² (HOMO). The results are helpful to further understand the reactivity of various reaction sites in peptides and identify chlorinated products from tyrosyl peptides during chlorination.

Multiple exposure to methylmercury aggravates DNA damage in the BTBR T + Itpr3 tf/J autistic mouse model: the role of DNA repair efficiency

Environmental and genetic factors have been recognized to play major roles in the pathogenesis of autism. Here we examined the BTBR T⁺Itpr3^tf/J (BTBR) mice's susceptibility, an autistic model, to the genotoxic effects and DNA repair dysregulation of methylmercury. Micronuclei formation and oxidative DNA damage were analyzed using the micronucleus/fluorescence in situ hybridization test and modified comet assay, respectively. The results showed higher centromeric-positive micronuclei and oxidative DNA damage in BTBR mice exposed to methylmercury than the unexposed mice, which indicates that mutagenesis aggravated in BTBR mice after methylmercury exposure. Lipid peroxides in BTBR mice were significantly elevated, with a decrease in reduced/oxidized glutathione ratio after methylmercury exposure, indicating an augmenting oxidant-antioxidant imbalance. The expression of several genes involved in DNA repair was markedly altered in BTBR mice after methylmercury exposure as evaluated via PCR array and RT-PCR analyses. Declining of the antioxidant defense and dysregulation in DNA repair process after methylmercury exposure may explain the aggravated genotoxic susceptibility of BTBR mice. Thus, autistic individuals exposed to methylmercury must be under regular medical follow-up through standard timetabled medical laboratory inquiry to allow for early recognition of any mutagenic changes. Additionally, strategies that elevate cellular antioxidants/DNA repair efficiency may counteract methylmercury-induced genotoxicity.

Monohaloacetonitriles induce cytotoxicity and exhibit different mode of action in endocrine disruption

Haloacetonitriles are emerging disinfection by-products that can be detected in various aquatic environments. They are cytotoxic, genotoxic, mutagenic, and tumorigenic in vitro and in vivo, but their endocrine-disrupting potency remains unknown. In this study, we examined the agonistic and antagonistic estrogenic and androgenic activities of haloacetonitriles, as well as their cytotoxicity, using a yeast-based reporter assay. We also investigated the interactions of haloacetonitriles with human estrogen receptor alpha (hERα) through molecular docking. We observed that iodoacetonitrile (median lethal dose: 1.96 × 10^-5 M) and bromoacetonitrile (median lethal dose: 1.97 × 10^-5 M) had similar cytotoxicities, which are higher than that of chloroacetonitrile (median lethal dose: 7.16 × 10^-5 M). We observed bromoacetonitrile and chloroacetonitrile elicited estrogenic activity with 10% effective concentrations of 3.30 × 10^-9 M and 2.36 × 10^-9 M, respectively. This finding indicates that bromoacetonitrile and chloroacetonitrile may mimic estrogen signaling through interaction with hERα. Consistent with that result, we identified bromoacetonitrile and chloroacetonitrile interacted with residues in the original estrogen recognition sites of hERα. Our results show that bromoacetonitrile and chloroacetonitrile affect the endocrine-disrupting potency mediated via estrogen receptors by using in vitro assay and molecular docking.

3-Aminobenzamide alleviates elevated DNA damage and DNA methylation in a BTBR T+Itpr3tf/J mouse model of autism by enhancing repair gene expression

Little is known about genetic and epigenetic alterations in autism spectrum disorder. Moreover, the efficiency of DNA repair in autism must be improved to correct these alterations. We examined whether 3-aminobenzamide (3-AB) could reverse these alterations. We conducted experiments to clarify the molecular mechanism underlying these ameliorations. An assessment of genetic and epigenetic alterations by a modified comet assay showed elevated levels of oxidative DNA strand breaks and DNA hypermethylation in BTBR T⁺Itpr3^tf/J (BTBR) mice used as a model of autism. Oxidative DNA strand breaks and DNA methylation were further quantified fluorometrically, and the results showed similar changes. Conversely, 3-AB treated BTBR mice showed a significant reduction in these alterations compared with untreated mice. The expressions of 43 genes involved in DNA repair were altered in BTBR mice. RT² Profiler PCR Array revealed significantly altered expression of seven genes, which was confirmed by RT-PCR analyses. 3-AB treatment relieved these disturbances and significantly improved Ogg1 and Rad1 up-regulation. Moreover, autism-like behaviors were also mitigated in BTBR animals by 3-AB treatment without alterations in locomotor activities. The simultaneous effects of reduced DNA damage and DNA methylation levels as well as the regulation of repair gene expression indicate the potential of 3-AB as a therapeutic agent to decrease the levels of DNA damage and DNA methylation in autistic patients. The current data may help in the development of therapies that ultimately provide a better quality of life for individuals suffering from autism.

Vorinostat is genotoxic and epigenotoxic in the mouse bone marrow cells at the human equivalent doses

Vorinostat was approved as the first histone deacetylase inhibitor for the management of cutaneous T cell lymphoma. However, it's in vivo genetic and epigenetic effects on non-cancerous cells remain poorly understood. As genetic and epigenetic changes play a critical role in the pathogenesis of carcinogenesis, we investigated whether vorinostat induces genetic and epigenetic alterations in mouse bone marrow cells. Bone marrow cells were isolated 24 h following the last oral administration of vorinostat at the doses of 25, 50, or 100 mg/kg/day for five days (approximately equal to the recommended human doses). The cells were then used to assess clastogenicity and aneugenicity by the micronucleus test complemented by fluorescence in situ hybridization assay; DNA strand breaks, oxidative DNA strand breaks, and DNA methylation by the modified comet assay; apoptosis by annexin V/PI staining analysis and the occurrence of the hypodiploid DNA content; and DNA damage/repair gene expression by polymerase chain reaction (PCR) Array. The expression of the mRNA transcripts were also confirmed by real-time PCR and western blot analysis. Vorinostat caused structural chromosomal damage, numerical chromosomal abnormalities, DNA strand breaks, oxidative DNA strand breaks, DNA hypomethylation, and programed cell death in a dose-dependent manner. Furthermore, the expression of numerous genes implicated in DNA damage/repair were altered after vorinostat treatment. Accordingly, the genetic/epigenetic mechanism(s) of action of vorinostat may play a role in its carcinogenicity and support the continued study and development of new compounds with lower toxicity.

The role of the enzyme-modified comet assay in in vivo studies

The in vivo comet assay is an established genotoxicity test, with an OECD test guideline, but in its standard form it measures only DNA strand breaks. Including in the assay an additional step, in which the DNA is incubated with a lesion-specific enzyme, can provide important information about the nature of the DNA damage. Formamidopyrimidine DNA glycosylase, 8-oxoguanine DNA glycosylase or endonuclease III are commonly used in the in vitro genotoxicity test and in human biomonitoring to detect oxidised bases, but in vivo applications are rarer. A systematic literature search has identified a total of 60 papers that report such in vivo experiments, testing a variety of agents. In many cases, strand breaks were not seen, but significant levels of enzyme-sensitive sites were induced - indicating a mechanism of action involving oxidative stress. Compounds such as methyl methanesulfonate (MMS) or ethyl methanesulfonate (EMS) could be used as positive controls in both the standard and the enzyme-modified in vivo comet assays.

Degradation Mechanisms and Substituent Effects of N-Chloro-α-Amino Acids: A Computational Study

N-Chloro-α-amino acids formed in the chlorination disinfection treatment of water or wastewater and in living organisms have attracted extensive attention due to the potential toxicities of themselves and their decomposition products. The degradation mechanisms of three N-chloro-α-amino acids, i.e., N-chloro-glycine, N-chloro-alanine, and N-chloro-valine, have been systematically investigated using quantum chemical computations. The results indicate that N-chloro-α-amino acid anions undergo two competitive degradation pathways: a concerted Grob fragmentation (CGF) and β-elimination (β-E). Generally, the former predominates over the latter under neutral conditions and finally generates amines and carbonyls, while the latter is preferred under base-promoted conditions and mainly produces the respective α-keto acid anions or nitriles in the end. To gain deeper insights into the substitution effects, in view of the advantages of quantum chemical computations, a number of real or designed N-chloro-α-amino acids with traditional electron-donating groups (EDG) or electron-withdrawing groups (EWG) have been studied. All of the substituted N-chloro-α-amino acids, regardless of the type and position of substituents, are kinetically more favorable than N-monochloro-glycine for degradation via the CGF pathway. Moreover, conjugated EDG substituted on the N-terminal facilitate both CGF and β-E reactions, whereas conjugated EDG and EWG on the α-carbon are only favorable for the CGF and β-E reactions, respectively. These results are expected to expand our understanding of organic N-chloramine degradation mechanisms and chlorination reaction characteristics.

Genetic and epigenetic alterations induced by the small-molecule panobinostat: A mechanistic study at the chromosome and gene levels

Increasing evidence supports the role of genetic and epigenetic alterations in a wide variety of human diseases, including cancer. Assessment of these alterations is hence essential for estimating the hazardous effects of human exposure to medications. Panobinostat received US Food and Drug Administration's approval in 2015 for treatment of certain tumors and its usefulness as part of a strategy to treat other diseases, such as human immunodeficiency virus infection, is currently investigated. Nevertheless, no data on in vivo genotoxical and epigenotoxical effects of panobinostat are available. The aim of the current study was to assess the genotoxical and epigenotoxical properties of panobinostat in murine bone marrow cells. Molecular mechanisms underlying these alterations were also evaluated. We show that mice treated with panobinostat doses recommended for human developed numerical chromosomal abnormalities, structural chromosomal damage, oxidative DNA damage, and DNA hypomethylation. These effects were dose-dependent. Further, panobinostat altered the expression of 23 genes implicated in DNA damage, as determined by RT² Profiler polymerase chain reaction (PCR) array, and confirmed by quantitative real-time PCR and western blotting. Collectively, these findings indicate that panobinostat exposure induces aneugenicity, clastogenicity, oxidative DNA damage, DNA hypomethylation, and down-regulation of repair gene expression, which may be responsible for panobinostat-induced genotoxical and epigenotoxical effects. Considering the potential toxicity of panobinostat, the medicinal use of panobinostat must be weighed against the risk of tumorigenesis and the demonstrated toxicity profile of panobinostat may support further development of chemotherapeutic treatments with reduced toxicity. Diminishing the metabolic liabilities associated with panobinostat exposure, and simultaneous use of panobinostat with DNA repair enhancers, are examples of strategies for drug design to reduce panobinostat carcinogenicity.

Investigation of belinostat-induced genomic instability by molecular cytogenetic analysis and pathway-focused gene expression profiling

Histone deacetylases (HDACs), which regulate transcription and specific functions such as tumor suppression by p53, are frequently altered in tumors and have a contentious role in carcinogenesis. HDAC inhibitors, which have a long history of use in psychiatry and neurology, have recently been tested as possible treatments for tumors. Belinostat received regulatory approval in the USA on July 3, 2014, for use against peripheral T-cell lymphoma. However, the unavailability of information on belinostat genotoxicity in normal cells and the molecular mechanisms involved in the genetic instability after exposure to belinostat encouraged us to conduct this study. Our data showed that the exposure of mice to belinostat at the recommended human doses induced chromosome breakage, whole-chromosome lagging, and oxidative DNA damage in bone marrow cells in a dose-dependent manner. The expression levels of 84 genes involved in the DNA damage signaling pathway were evaluated by using an RT² Profiler PCR array. Belinostat exposure altered the expression of 25 genes, with statistically significant changes observed in 17 genes. The array results were supported by RT-PCR and western blotting experiments. Collectively, our results showed that belinostat exposure caused oxidative DNA damage and downregulated the expression of genes involved in DNA damage repair, which may be responsible for belinostat-induced genomic instability. Thus, the clinical usage of this drug should be weighed against the hazards of carcinogenesis, and the observed genotoxicity profile of belinostat may support further development of efficient HDAC inhibitors with weaker genotoxicity.

Genotoxic and Cytotoxic Effects of Antiretroviral Combinations in Mice Bone Marrow

Commonly used guidelines for the management of human immunodeficiency virus (HIV) infection (highly active antiretroviral therapy, HAART) include drug combinations such as tenofovir disoproxil fumarate (TDF) + lamivudine (3TC) and combivir [zidovudine (AZT) + 3TC] + efavirenz (EFV). These combinations may enhance the genotoxic effects induced by such drugs individually, since the therapy requires lifelong adherence and the drugs have unknown effects during treatment. Thus, the evaluation of the benefits and risks of HAART is of great importance. In order to assess the cytotoxic and genotoxic potential of three concentrations of each of the antiretroviral combinations TDF + 3TC (800 + 400, 1600 + 800, and 3200 + 1600 mg/kg body weight, BW) and combivir + EFV (200 + 100 + 400, 400 + 200 + 800, and 800 + 400 + 1600 mg/kg BW) after two exposure periods (24 h and 48 h), in the present study the in vivo comet assay (single-cell gel electrophoresis) and the mouse bone marrow micronucleus test were used. Neither TDF + 3TC nor combivir + EFV induced DNA damage at any concentrations tested after 24 h or 48 h using the comet assay. After 24 h, both combinations increased the micronucleus frequency at all concentrations tested. After 48 h, combivir + EFV increased the micronucleated polychromatic erythrocyte (MNPCE) frequency at the two highest concentrations tested. Polychromatic erythrocytes (PCE)/normochromatic erythrocytes (NCE) ratio was high for both combinations, suggesting that they can be mitogenic. Since genotoxicity may be related to carcinogenesis, it is necessary to conduct further studies to verify the long-term mutagenic effects of these drugs.

"Omics" in pharmaceutical research: overview, applications, challenges, and future perspectives

In the post-genomic era, biological studies are characterized by the rapid development and wide application of a series of "omics" technologies, including genomics, proteomics, metabolomics, transcriptomics, lipidomics, cytomics, metallomics, ionomics, interactomics, and phenomics. These "omics" are often based on global analyses of biological samples using high through-put analytical approaches and bioinformatics and may provide new insights into biological phenomena. In this paper, the development and advances in these omics made in the past decades are reviewed, especially genomics, transcriptomics, proteomics and metabolomics; the applications of omics technologies in pharmaceutical research are then summarized in the fields of drug target discovery, toxicity evaluation, personalized medicine, and traditional Chinese medicine; and finally, the limitations of omics are discussed, along with the future challenges associated with the multi-omics data processing, dynamics omics analysis, and analytical approaches, as well as amenable solutions and future prospects.