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.

Assessment of DNA repair efficiency in the inbred BTBR T+tf/J autism spectrum disorder mouse model exposed to gamma rays and treated with JNJ7777120.

Information regarding DNA repair in autism is limited to a few studies, which have reported inconsistent results. Therefore, we designed a study to determine whether DNA repair efficiency is altered in autism and to investigate whether the H4 ligand JNJ7777120 can enhance DNA repair efficiency in BTBR T+tf/J (BTBR) mice; we also attempted to elucidate the mechanism(s) underlying this amelioration. Evaluation of DNA damage using the comet assay on bone marrow cells showed increased levels of DNA damage in BTBR mice compared with age-matched control C57BL/6J mice. Conversely, BTBR animals pretreated with 20 mg/kg JNJ7777120 for five days exhibited significant decreases in DNA damage compared with that of control BTBR mice. Our results also indicated higher sensitivity of BTBR mice exposed to gamma rays to DNA damage generation. A marked difference was observed between BTBR and C57BL/6J mice at different sampling times after irradiation, with BTBR mice showing a higher percentage of DNA damage and slower repair rate than that of C57BL/6J mice. JNJ7777120 led to enhanced repair of the DNA damage induced by radiation when administered to BTBR mice five days prior to radiation. Additionally, oxidative stress in BTBR mice was significantly elevated with a reduced GSH/GSSG ratio; significant amelioration was subsequently observed in JNJ7777120-pretreated BTBR mice. Furthermore, repetitive behaviors were also attenuated in BTBR mice by JNJ7777120 treatment without altering locomotor activity. Our results suggest that JNJ7777120 can be developed for use as a therapeutic agent to enhance DNA repair efficiency in autism spectrum disorder.

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.

Impact of dexrazoxane on doxorubicin-induced aneuploidy in somatic and germinal cells of male mice.

PURPOSE: Despite dexrazoxane's increasing use in mitigating doxorubicin-induced cardiotoxicity, no data are available in the literature on the potential aneugenicity of drug combination. Therefore, detailed evaluation of aneugenic potential of this combination is essential to provide more insights into aneuploidy induction that may play a role in the development of secondary malignancies and reproductive toxicity after treatment with doxorubicin. Thus, our aim was to determine whether dexrazoxane has influence on the aneuploidy induced by doxorubicin in germinal and somatic cells of male mice. METHODS: Sperm BrdU-incorporation assay, sperm FISH assay and the bone marrow micronucleus test complemented by FISH assay were used to determine aneuoploidy. Moreover, the formation of 8-OHdG, one of the oxidative DNA damage by-products, has been evaluated. RESULTS: Dexrazoxane was not aneugenic at the doses tested. Pre-treatment of mice with dexrazoxane significantly reduced doxorubicin-induced aneuploidy in a dose-dependent manner. Doxorubicin induced marked biochemical alterations characteristic of oxidative DNA damage, and prior administration of dexrazoxane before doxorubicin challenge ameliorated this biochemical marker. CONCLUSION: This study provides evidence that dexrazoxane has a protective role in the abatement of doxorubicin-induced aneuploidy. This activity resides, at least in part, in its radical scavenger activity. Thus, dexrazoxane can avert secondary malignancies and abnormal reproductive outcomes in cured cancer patients exposed to doxorubicin.

Dominant lethal effects of nocodazole in germ cells of male mice.

The ability of the anticancer drug, nocodazole, to induce dominant lethal mutations in male germ cells was investigated by the in vivo dominant lethal test. Mice were treated with single doses of 15, 30 and 60 mg/kg nocodazole. These males were mated at weekly intervals to virgin females for 6 weeks. Nocodazole clearly induced dominant lethal mutations in the early spermatid stage with the highest tested dose. Mice treated with 60 mg/kg nocodazole showed an additional peak of dominant lethal induction in mature spermatozoa during the first week matings after treatment. The percentage sperm count and sperm motility were significantly decreased after treatment of males with 30 and 60 mg/kg nocodazole. Moreover, the middle and highest doses of nocodazole significantly increased the percentage of abnormal sperm. Our study provides evidence that nocodazole is a germ cell mutagen. Marked alteration in the spermiogram analysis after nocodazole treatment possibly confirms that nocodazole has a significant effect on sperm maturation and development during storage and transit. The demonstrated mutagenicity profile of nocodazole may support further development of effective chemotherapy with less mutagenicity. Moreover, the cancer patients and medical personnel exposed to this drug chemotherapy may stand a higher risk for abnormal reproductive outcomes.

Genotoxic evaluation of chloroacetonitrile in murine marrow cells and effects on DNA damage repair gene expressions.

Although chloroacetonitrile (CAN), a disinfection by-product of chlorination of drinking water, is considered a rodent carcinogen that induces lung adenomas in mice, previous studies on its genotoxicity have yielded inconclusive results. Thus, its cancer mode of action has not been clearly defined. We evaluated CAN-induced genotoxicity in mice using mouse bone marrow micronucleus test, comet assays and expression of genes associated with DNA damage repair. Mice exposed to CAN at 8.75, 17.5, 35 and 52.5mg/kg for 7 days did not exhibit any significant increases in the incidence of micronuclei formation at 24 and 48h after last exposure. However, CAN caused significant suppressions of erythroblast proliferation at the highest dose. In the alkaline comet assay, there was a significant increase in the incidence of DNA strand breaks in mice killed after 3h of last treatment with 35 and 52.5mg/kg/day CAN, while no significant difference in the DNA strand breaks was found in mice killed after 24h of the last treatment. However, slight (but significant) CAN-induced oxidative DNA damage was detected following Fpg digestion at 3-h sampling time, digestion with EndoIII resulted in considerable increases in oxidative DNA damage at 3 and 24h after the last exposure to 35 and 52.5mg/kg/day CAN as detected by oxidative comet assays. The expression of DNA repair genes OGG1 , Apex1, PARP1 and p53 were up-regulated in mice given 35mg/kg/day CAN at 3h but not in 24h after the last treatment except OGG1 . However, the significant up-regulation of OGG1 at 24h after the last treatment further indicates the occurrence of oxidative DNA damage. Overall, CAN exposure is associated with up-regulation of DNA repair gene expression and the induction of oxidative DNA damage, which may be at least partially responsible for CAN-induced genotoxicity and eventually cause carcinogenicity.

Germ cell mutagenicity of topoisomerase I inhibitor topotecan detected in the male mouse-dominant lethal study.

To investigate the ability of topotecan, a topoisomerase I-targeting anticancer drug, to induce dominant lethal mutations in male mouse germ cells, males were treated with single doses of 3, 6 and 12 mg/kg topotecan. Each male was mated at 4-day intervals to virgin females for a total of nine 4-day mating intervals. The two highest doses of topotecan are shown to be mutagenic in post-meiotic cells. The greatest effect occurred in those cells which were in the early-spermatid stage at the time of exposure. Mice treated with 12 mg/kg topotecan showed an additional peak of dominant lethal induction in mature sperm during the first 4-day matings after treatment. The mutagenic effects were directly correlated with free radicals accumulation as an obvious increase in the generation reactive oxygen species and 8-hydroxydeoxyguanosine was noted in animals treated with 6 and 12 mg/kg topotecan. Treatment of male mice with N-acetylcysteine, a free radical scavenger, significantly protected mice from topotecan-induce dominant lethality. Moreover, N-acetylcysteine had no antagonizing effect on topotecan-induce topoisomerase-I inhibition. Our study provides evidence that topotecan is a germ cell mutagen and its effect is more pronounced during the post-meiotic stages through a mechanism that may involves increases in DNA oxidative stress.

Salubrious effects of dexrazoxane against teniposide-induced DNA damage and programmed cell death in murine marrow cells.

The intention of the present study was to answer the question whether the catalytic topoisomerase-II inhibitor, dexrazoxane, can be used as a modulator of teniposide-induced DNA damage and programmed cell death (apoptosis) in the bone marrow cells in vivo. The alkaline single cell gel electrophoresis, scoring of chromosomal aberrations, micronuclei and mitotic activity were undertaken in the current study as markers of DNA damage. Apoptosis was analysed by the occurrence of a hypodiploid DNA peak and caspase-3 activity. Oxidative stress marker such as intracellular reactive oxygen species production, lipid peroxidation, reduced and oxidised glutathione were assessed in bone marrow as a possible mechanism underlying this amelioration. Dexrazoxane was neither genotoxic nor apoptogenic in mice at the tested dose. Moreover, for the first time, it has been shown that dexrazoxane affords significant protection against teniposide-induced DNA damage and apoptosis in the bone marrow cells in vivo and effectively suppresses the apoptotic signalling triggered by teniposide. Teniposide induced marked biochemical alterations characteristic of oxidative stress including accumulation of intracellular reactive oxygen species, enhanced lipid peroxidation, accumulation of oxidised glutathione and reduction in the reduced glutathione level. Prior administration of dexrazoxane ahead of teniposide challenge ameliorated these biochemical alterations. It is thus concluded that pretreatment with dexrazoxane attenuates teniposide-induced oxidative stress and subsequent DNA damage and apoptosis in bone marrow cells. Based on our data presented, strategies can be developed to decrease the teniposide-induced DNA damage in normal cells using dexrazoxane. Therefore, dexrazoxane can be a good candidate to decrease the deleterious effects of teniposide in the bone marrow cells of cancer patients treated with teniposide.

Effect of metformin on clastogenic and biochemical changes induced by adriamycin in Swiss albino mice.

Diabetes mellitus (DM) is a chronic disease that is characterized by deteriorating glycemic control. The disease is known to be caused by imbalance between reactive oxygen species (ROS) and antioxidant defense systems. Hyperglycemia is commonly observed in a wide variety of diseases, including cancer. Although, therapy against glycemic control, is used in all these diseases, the diabetic cancer patients are on additional therapy with anticancer drugs. The objective of present study was to study if Glucophage (metformin), a very popular antidiabetic agent can avert the mutagenicity and lipid peroxidation caused by adriamycin (ADR), which is a commonly used cytotoxic drug. The experimental protocol included oral treatment of mice with different doses (62.5, 125 and 250 mg/kg day) of metformin for 7 days. Some mice in each group were injected i.p. with ADR (15 mg/kg). In each case animals were killed, 30 or 24, 48 and 72 h after the last treatment and femurs were excised for cytological studies by micronucleus test. Additional experiments on estimation of glutathione (GSH) and malondialdehyde (MDA) were undertaken in blood and serum, respectively. Twenty-four hour after the treatment, blood from each mouse was collected from heart and preserved for analysis. The results obtained revealed that pretreatment with metformin: (i) reduced the ADR-induced frequency of micronuclei without any alteration in its cytotoxicity and (ii) protected against the ADR-induced increase and decrease of MDA and GSH, respectively. The exact mechanism of action is not known, however, the inhibition of ADR-induced clastogenicity and lipid peroxidation by metformin may be attributed to the antioxidant action of the latter. Our results demonstrate that metformin might be useful to avert secondary tumor risk by decreasing the accumulation of free radicals and inhibition of mutagenicity.

Increased toxicity of methamphetamine in morphine-dependent mice.

1. The effect of methamphetamine on morphine-dependent mice was investigated by calculating the LD50 (i.p.), measuring motor activity, anorectic actions, and body temperature. 2. Methamphetamine was more toxic in morphine-dependent mice (LD50 = 20.6 mg/kg) than in normal mice (LD50 = 43.2 mg/kg). 3. Methamphetamine-induced locomotor activity was greater in morphinized than in nonmorphinized mice at doses of 2.5 and 5 mg/kg i.p. 4. Methamphetamine also increased the body temperature of morphinized mice more than that of normal mice (P < 0.05). 5. These findings suggest that methamphetamine is more toxic in morphine-dependent than in nondependent mice.