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Recent studies have demonstrated a significant role of mitochondrial DNA (mtDNA) defects in the pathogenesis of many human and some canine tumours. The aim of this study was to identify mutations in the ND2 and ND4 mitochondrial genes in canine mast cell tumours and determine their association with the process of neoplastic transformation and the phenotypic traits of dogs. In total, 136 gene sequences from 68 biological samples, including blood and neoplastic tissue samples from 34 dogs with diagnosed MCTs, were analysed. The study consisted in DNA sequencing of the ND2 and ND4 genes as well as bioinformatics and statistical analyses. For the first time, mutations in NADH-dehydrogenase genes were detected in dogs with MCTs. In total, 22 polymorphic loci and 19 mutations in the ND2 and ND4 genes were identified. The majority of the identified mutations were homoplasmic, and tumour heteroplasmy was detected in eight nucleotide positions in three dogs. Seven of the ND2 mutations and two of the ND4 mutations caused an amino acid change. The changes in non-synonymous protein-coding SNPs did not exert an adverse effect on proteins. A statistically significant correlation of the presence of mutations/polymorphisms with the sex, age, and size of the dogs and the tumour location was demonstrated. Polymorphisms and mutations in NADH-dehydrogenase genes, including mastocyte-specific changes, in canine mast cell tumours that had not been reported earlier in the literature were identified. Some of these changes may imply that these are the hotspot mutations in canine mast cell tumours. It cannot be excluded that the molecular changes are directly associated with the development of mast cell tumours, and further investigations are needed to verify whether they can become molecular markers of MCTs in the future.

Increasing numbers of oncological patients and growing drug resistance ensure that new methods of cancer treatment are intensively sought. Combining drugs for a synergistic effect is one of several possible ways to mitigate this problem. This leads to reducing the effective drug dose and the occurrence of side effects. Doxorubicin (DOX) is an antineoplastic agent that has several mechanisms of action. DOX intercalates between base pairs of DNA helix, inhibits topoisomerase II and also forms reactive oxygen species. Bortezomib (BZT) is an antitumor agent belonging to the group of proteasome inhibitors. It has been observed that BZT triggers an oxidative stress response in vitro and in vivo. Accumulation of oxidatively damaged proteins and the simultaneously blocking of the proteasome can be very damaging to the tumour cell. For this reason, the aim of the study was to assess the potentially synergistic effect of DOX and BZT on human acute lymphoblastic leukemia (ALL). In the work, the cells were treated with both agents and their combinations and the effect was evaluated on the basis of morphological assessment, MTT assay and level of reduced glutathione measurement. The study has shown that on acute lymphoblastic leukemia cells, synergistic effects came about in the combination of 1nM BZT with a wide range of concentrations of DOX. Herein, the visible, coactive effect of DOX and BZT was observed on oxidative stress levels. This phenomenon can be essential in blunting the possibility of rapid manifestation of resistance seen in BZT monotherapy. In addition, the needed very low concentrations of DOX reduce the risk of therapy side effect.

Hypoxic cancer cells are more aggressive and responsible for more efficient metastasis and recurrence. It seems worth-while, hence, to supplement current cytostatic drugs therapy (i.e. cisplatin) with hypoxia cytotoxic agents (i.e. tirapazamine), the toxicity of which is activated by hypoxia. Cisplatin and tirapazamine can change a redox equilibrium and consequently lead to changes in cell metabolism, fibrosis and apoptosis. The aim of this study was to evaluate the cisplatin/tirapazamine toxicological synergism. In doing so we tested selected kidney oxidative stress parameters, as well as nephrotoxicity markers, in plasma and urine. Once a week for 6 weeks, rats received intraperitoneally two doses of tirapazamine (5 or 10 mg/kg bw), 2 hours before cisplatin (2 mg/kg bw) was applied. Our results show that Tirapazamine (TP) had no significant adverse effect on the redox balance, oxidative stress and kidney function in rats receiving cisplatin (CP). However, TP significantly increased protein concentration in the kidneys of rats. In all tested groups, a significant decrease in NADH concentration in kidneys was recorded, which could indicate disorder in the cell metabolism. TP also was found to have prevented bacterial infection caused by CP. In summary, there was no nephrotoxic synergy of TP with CP at an unacceptable level.

One of the less known mechanisms of doxorubicin action is the effect on the functioning of the ubiquitin-proteasome degradation system (UPS). So far, the role of impaired proteasome activity in the development of anthracycline cardiomyopathy has not been clarified. It has been shown, however, that doxorubicin decreases the expression of proteins, including the expression of the calcium channel. However, it has not been established whether the observed disturbances are due to the activation of the UPS system by doxorubicin, or due to inhibition of translation or transcription. Therefore, the aim of the study was to evaluate the mRNA and protein expression of plasmalemmal (NaCaX, L-type) and sarcoplasmic reticulum (SERCA2, RyR2) channels in rat embryonic cardiomyocytes treated with doxorubicin and the proteasome inhibitor – bortezomib. The study was conducted utilizing the rat cardiomyocyte H9C2 line that was treated with doxorubicin and bortezomib in different concentrations. After 24 hours incubation, mRNA and protein expression analysis followed. The study did not show any universal mechanism of doxorubicin influence on calcium channel expression. With regard to the Na/Ca exchanger, we saw that DOX decreased the protein level in a proteasome activitydependent manner. Moreover, we noted that the SERCA2 protein expression level was regulated by degradation intensity, however at the same time, no significant effect of doxorubicin on the level of this protein was demonstrated.

The aim of the study was to identify polymorphisms and mutations in the mitochondrial ND4 gene and to analyse the associations between the occurrence of molecular changes in mtDNA and phenotypic traits in tumours in German Shepherd dogs. Fifty samples obtained from blood and tumour tissues of German Shepherd dogs with diagnosed tumours were analysed. DNA extraction, amplification, and sequencing of the mtDNA ND4 gene, and bioinformatics, statistical, and in silico protein coding SNP analyses were performed. ND4 mutations and/or polymorphisms were noted in eleven nucleotide positions in nearly half of the examined dogs. All the changes were substitution mutations. A majority of the changes identified were homoplasmic. In one dog with osteosarcoma, blood heteroplasmy was detected. In two positions of the ND4 gene, presence of non-synonymous mutations leading to amino acid changes in the ND4 protein was reported. Analyses carried out to determine the deleterious effect of mutations indicated an almost 97 and 62% probability that a single amino acid substitution (p.G239V and p.I401T, respectively) in the protein has a negative impact on its function. The results of statistical analyses indicate a significant association between the occurrence of mutations in three loci of the ND4 gene and the location of tumours. The mutations identified may be a result of cell adaptation to the changes in the environment occurring during carcinogenesis. The high frequency of mutations in the tumours may indicate genetic instability of mtDNA, which may also play a role in carcinogenesis.

The main side effects of the administration of doxorubicin, a widely used anticancer drug, is the generation of a reactive oxygen species (ROS) in normal cells. As a result, redox disorders and secondary oxidative stress are developed. Doxorubicin ROS generation is attributed to enzymes that are produced abundantly in hepatocytes. Oxidative stress has been a well-known risk factor of doxorubicin-related toxicity. However, in addition, according to the data collected in the last decade, changes in thyroxin status can propagate ROS generation, and, thus, initiate the doxorubicin hepatic effect. Moreover, both compounds have an impact on the cell metabolism. The aim of the study was to verify the thesis that thyroxin can modulate the effect of doxorubicin with regard to redox status and lipid metabolism disorders. In our work, we determined the ratio of NADP+/ NADPH and NAD+/NADH in liver homogenates, blood ketone bodies and triglycerides in the liver and blood in rats treated with doxorubicin and thyroxin. Our results indicate that thyroxin has an insignificant effect on NAD+/NADH, NADP+/NADPH ratios and on hepatic and blood triglycerides. Moreover, thyroxin administration normalized the level of blood ketone bodies that was disturbed by doxorubicin.

The redox cycle triggered by one electron reduction of doxorubicin and tirapazamine - both anticancer agents - leads to superoxide production. This superoxide production itself removes one iron atom from the [4Fe-4S] cluster, being an active center of aconitase. In addition, the incurred changes in cell redox equilibrium may affect lipid metabolism. The aim of the study was to evaluate a concomitant effect of both drugs on hepatic aconitase activity and triglycerides level. In our study, doxorubicin (1.8 mg/kg b.w.) was administered intraperitoneal (i.p.) six times, once a week, within male Wistar rats, to achieve a cumulative dose of 10.8 mg/kg b.w. Two hours before every doxorubicin administration, tirapazamine in the dose of either 5 or 10 mg/kg b.w. was also i.p. injected. A week after withdrawing drug administration, the liver was taken for biochemical analysis. Therein, an increase in aconitase activity and a decrease in triglycerides level was seen in all groups exposed to doxorubicin. Our work demonstrated that tirapazamine administration had no influence on both tested parameters, but its higher dose rate normalized aconitase activity affected by doxorubicin.

Introduction: Cytotoxicity of doxorubicin (DOX) – an anticancer drug, mostly results from reactive oxygen species (ROS) generation. Some enzymes catalyzing this process and enzymes of antioxidant defense are regulated by iodothyronine hormones. Thus, disorders in iodothyronine hormone status may affect doxorubicin-induced redox imbalance and anabolic/catabolic disorders. The aim of this study was to evaluate the influence of doxorubicin and thyroxine (T4) associated treatment on liver morphology, markers of oxidative stress and plasma lipid parameters.Materials and methods: Rats were intraperitoneally treated with doxorubicin (1.5 mg/kg) once a week for ten weeks. Thyroxine was simultaneously given in drinking water (0.2 or 2.0 mg/l) for 14 weeks.Results: There were higher hepatic level of malonyldialdehyde (MDA) of all tested groups and at the same time in rats treated with DOX plus T4 lower concentrations of total glutathione compared to controls were observed. Morphology of liver did not show any features of necrosis or steatosis but a decrease of glycogen content in T4 DOX groups compared to DOX treatment was observed. The concomitant administration of a lower dose of thyroxine and doxorubicin decreased triglycerides (TG) and increased LDL level compared to the DOX group.Discussion: Thyroxin supplementation caused redox equilibrium disorders and oxidative stress in liver of rats receiving DOX. The study revealed the normalizing influence of thyroxin on glycogen deposits that were observed after doxorubicin treatment. Apart from an adverse impact of thyroxine administration on LDL in rats treated with doxorubicin, a beneficial effect of lower dose of thyroxine on serum TG level was revealed.