A role for apoptosis in the toxicity and mutagenicity of bleomycin in AHH-1 tk+/- human lymphoblastoid cells

New Formulations of Polysaccharide-Based Hydrogels for Drug Release and Tissue Engineering

Polysaccharide-based hydrogels are very promising materials for a wide range of medical applications, ranging from tissue engineering to controlled drug delivery for local therapy. The most interesting property of this class of materials is the ability to be injected without any alteration of their chemical, mechanical and biological properties, by taking advantage of their thixotropic behavior. It is possible to modulate the rheological and chemical-physical properties of polysaccharide hydrogels by varying the cross-linking agents and exploiting their thixotropic behavior. We present here an overview of our synthetic strategies and applications of innovative polysaccharide-based hydrogels: hyaluronan-based hydrogel and new derivatives of carboxymethylcellulose have been used as matrices in the field of tissue engineering; while guar gum-based hydrogel and hybrid magnetic hydrogels, have been used as promising systems for targeted controlled drug release. Moreover, a new class of materials, interpenetrating hydrogels (IPH), have been obtained by mixing various native thixotropic hydrogels.

The effects of the electric fields on hydrogels to achieve antitumoral drug release

The achievement of electrochemotherapy was obtained using electrodes covered with guar gum (GG) hydrogel swollen in a sulfate bleomycin solution. The bleomycin delivery into the plasma membranes of cancer cells occurs only when field strength (V/cm) was applied, decreasing the drug contact with healthy tissues. The effect of the delivered bleomycin at different concentrations was examined on tumoral mouse fibroblast (NIH3T3) and human coronary artery endothelial cells. The GG hydrogel released the drug only when the field strength was applied and the amount depended on the electromotive force. Consequently, cellular survival depended on the field strength. Moreover in vitro results showed a bigger cellular mortality of the NIH3T3 compared with endothelial cells. The best parameters to be utilized in electrochemotherapy were ascertained.

Effects of 2.45 GHz electromagnetic fields with a wide range of SARs on bacterial and HPRT gene mutations

Present day use of mobile phones is ubiquitous. This causes some concern for human health due to exposure to high-frequency electromagnetic fields (HFEMF) from mobile phones. Consequently, we have examined the effects of 2.45 GHz electromagnetic fields on bacterial mutations and the hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene mutations. Using the Ames test, bacteria were exposed to HFEMF for 30 min at specific absorption rates (SARs) from 5 to 200 W/kg. In all strains, there was no significant difference in the frequency of revertant colonies between sham exposure and HFEMF-exposed groups. In examination of mutations of the HPRT gene, Chinese hamster ovary (CHO)-K1 cells were exposed to HFEMF for 2 h at SARs from 5 to 200 W/kg. We detected a combination effect of simultaneous exposure to HFEMF and bleomycin at the respective SARs. A statistically significant difference was observed between the cells exposed to HFEMF at the SAR of 200 W/kg. Cells treated with the combination of HFEMF at SARs from 50 to 200 W/kg and bleomycin exhibited increased HPRT mutations. As the exposure to HFEMF induced an increase in temperature, these increases of mutation frequency may be a result of activation of bleomycin by heat. We consider that the increase of mutation frequency may be due to a thermal effect.

Magnetic fields generated by an induction heating (IH) cook top do not cause genotoxicity in vitro

The use of induction heater (IH) cook tops in homes has become widespread, especially in Japan, but there are concerns about the safety of intermediate frequency (IF) electromagnetic fields associated with these cooking appliances. Since the cellular genotoxicity of IF magnetic fields has not been examined in cultured cells, we examined the effects of these fields at a magnetic flux density of 532 +/- 20 microT at 23 kHz, using an exposure unit with a built-in CO2 incubator. Exposure to the IF magnetic field at 532 microT for 2 h did not affect the growth of CHO-K1 cells and caused no mutagenic effects in bacterial mutation assays. Exposure to the IF magnetic field for 2 h induced neither single nor double DNA strand breaks in comet assays, and caused no significant change in the mutation frequency at the HPRT locus compared to sham exposure. The magnetic field used in this study is more than 80 times higher than the level recommended as safe in the International Commission on Non-ionizing Radiation Protection (ICNIRP) guidelines. From these results, we suggest that exposure to an IF magnetic field for 2 h does not cause cellular genotoxicity in bacteria and in Chinese hamster cells. However, the possibility of effects on other cellular functions remains, and further studies on the cellular effects of IF magnetic fields are required.

Molecular analysis of mitochondrial DNA mutations from bleomycin-treated rats

In our previous studies, we have shown the mutagenicity of bleomycin (BLM) at the nuclear hprt locus. In the present study we have analyzed mutagenic effects of BLM in mitochondrial DNA (mtDNA) using short extension-PCR (SE-PCR) method for detection of low-copy deletions. Fisher 344 rats were treated with a single dose of BLM and total DNA preparations from splenic lymphocytes were processed in SE-PCR assay. Spontaneous deletions were typically flanked by direct repeats (78.5%), while the in BLM-treated group, direct repeats were found in only 46.6% of breakpoints. The ratio between deletions based on direct repeats and random sequence deletions changed from 3.67 in control group to 0.87 in BLM-treated animals, which corresponds to an approximate 1.7-fold increase in the deletion mutation frequency. Furthermore, 62.5% of deletions not flanked by direct repeats in the treated group contained cleavage sites for BLM. The localization of breakpoints was not entirely random. We have found four clusters containing deletions from both groups indicative of deletion hot spots. The results indicate that BLM exposure may be associated with the induction of mtDNA mutations, and suggest the utility of SE-PCR method for evaluating drug-induced genotoxicity.

Influence of dietary antioxidants on the mutagenicity of 7,12-dimethylbenz[a]anthracene and bleomycin in female rats

Studies on agents that modulate carcinogen-induced genotoxic effects in experimental animals provide end points that can be used for assessing the antimutagenic or anticarcinogenic properties of putative chemopreventive compounds and for predicting their protective efficacy in humans. In this study, we investigated the ability of the dietary antioxidant Vitamins C, E, beta-carotene and the mineral selenium to inhibit the mutant frequency (MF) induced by treatment of rats with 7,12-dimethylbenz[a]anthracene (DMBA), a mammary carcinogen and bleomycin (BLM), an anti-tumor agent that can damage DNA by free radical mechanisms. Both chemicals have been previously shown to be mutagenic in the rat lymphocyte Hprt assay. Adult female Fischer 344 rats were given the antioxidants singly or in a combination 2 weeks prior to mutagen treatment. Antioxidant intake continued for an additional 4 weeks post-mutagen treatment. At sacrifice, spleens were aseptically removed for the isolation of lymphocytes to conduct the mutagenesis assay at the Hprt locus. The DMBA and BLM treatment induced a marked increase in MF, 52.8 x 10(-6) and 19.2 x 10(-6), respectively, over the controls. The MFs seen in the individual antioxidants alone (single or mixture) were relatively similar to the controls, with the exception of Vitamins C and E, that had 1.7- and 1.5-fold increase, respectively. The degree of inhibitory response was dependent on the type of mutagen and the particular antioxidant. BLM/antioxidant combination had inhibitions ranging from 44 to 80%, while DMBA/antioxidant system ranged from 60 to 93%, with Vitamins C and E achieving the highest inhibition in both systems. The mixture displayed low inhibitory responses, 44.6% for BLM/mix and 47% DMBA/mix. On the whole, the results indicate that the dietary constituents tested are antimutagenic; however, because of the gradations seen with the responses, the protective efficacy of these antioxidants may depend on the type of mutagen/carcinogen they encounter. Pending molecular analysis of mitochondrial DNA mutations will also indicate whether there is a shift in the mutational spectra produced by the carcinogens in the presence of antioxidants.

Evaluation of the genotoxicity of the phytoestrogen, coumestrol, in AHH-1 TK(+/-) human lymphoblastoid cells

Coumestrol, a phytoestrogen found in high levels in alfalfa and red clover, is of concern since endocrine disorders have been observed in farm animals exposed to high levels of phytoestrogens. Previous studies found that coumestrol was an effective inducer of DNA strand breaks, micronuclei, and mutations in the Hypoxanthine phosphoribosyl transferase (HPRT) gene of Chinese hamster ovary cells. In the experiments presented here, we extended the previous studies to examine the effect of coumestrol exposure on AHH-1 TK(+/-) human lymphoblastoid cells. Micronuclei were induced with the highest frequency occurring at day 2 after exposure. Flow cytometric analysis of annexin V-FITC-7-aminoactinomycin D stained cells indicated that the primary pathway of cell death was by apoptosis. Mutations were induced in the Thymidine Kinase (TK) gene and were due primarily to the induction of clones with the slow-growth phenotype. Subsequent molecular analysis revealed the loss of exon 4 in the coumestrol-induced clones, indicative of loss-of heterozygosity and consistent with a proposed inhibition of topoisomerase-II activity as a mechanism of action for coumestrol. Taken together, these results suggest that coumestrol exhibits both mutagenic and clastogenic properties in cultured human lymphoblastoid cells.

Induction of apoptosis in KB cells by pingyangmycin

Pingyangmycin (PYM; Bleomycin A(5)), an antitumour antibiotic is currently used during anticancer therapy. Previous experiments demonstrated that the therapeutic efficiency of PYM for treatment of malignant tumours is considered to be related to its ability to cause DNA strand breaks in vitro. However, very little is known about the interaction of PYM with the target cells, and it is still unclear how PYM enters the cells. In this study, cell death induced by PYM was studied in a human squamous cell carcinoma cell line (KB cells). In order to determine if cell death occurred by necrosis (reproductive cell death) or apoptosis (programmed cell death), KB cells were exposed to different concentrations of PYM and evaluated by biochemical and morphological criteria. Our results indicate that KB cells displayed an arrest in the G(2)-M phase of the cell cycle and became enlarged and polynucleated before dying at the low concentrations of PYM. In contrast, when cells were exposed to high concentrations of PYM, morphological changes identical to those usually associated with apoptosis were observed as well as internucleosomal digestion of genomic DNA. In conclusion, we demonstrate that PYM is able to induce two distinct modes of cell death depending on the doses of PYM.

Attenuation of bleomycin-induced Hprt mutant frequency in female and male rats by calorie restriction

Calorie restriction modulates spontaneous and chemically induced tumors and increases maximal life span in experimental animals; however, the mechanism by which calorie restriction exerts its ameliorating effects is not fully elucidated, although reduced levels of reactive oxygen species (ROS) by calorie restriction has generated much interest. In the present study, we have determined whether or not calorie restriction would affect the mutagenic response in rats treated with bleomycin (BLM) a radiomimetic drug that is associated with DNA damage by a free radical mechanism. Fourteen weeks after weaning, the rats were divided into two groups; ad libitum (AL)-fed and 40% calorie restriction. Both AL and calorie-restricted animals were injected with 2.5, 5.0 and 10.0 mg BLM/kg, or with phosphate-buffered saline (PBS), and they were killed 4 weeks post drug treatment. Lymphocytes from the spleens were seeded in 96-well microtiter plates to determine mutant frequency in the hypoxantine guanine phosphoribosyl transferase (Hprt) gene. The mutant frequency in the BLM-treated rats was higher in AL males (P=0.001), and AL females (P=0.0174) than in their calorie-restricted counterparts. The difference in mutagenic response relative to AL males and AL females appeared unrelated to a low percent cloning efficiency seen in the males, since the mean absolute number of Hprt mutant clones was higher in the AL males compared to the females. A reduction in animal weight by calorie restriction was significant in both sexes (P<0.001), but the dose effect appeared non-significant. The results indicate that calorie intake of 60% reduced the mutagenic response of BLM, a compound known to induce oxidative DNA damage, and suggest a possible decrease in ROS as a function of calorie restriction.

Characterization of p53 in Chinese hamster cell lines CHO-K1, CHO-WBL, and CHL: implications for genotoxicity testing

Since the p53 gene function is critical to how a cell responds to DNA damage, we investigated the p53 status in Chinese hamster cell lines commonly used in genotoxicity tests for cytogenetic damage around the world. These included: Chinese hamster ovary K1 (CHO-K1), Chinese hamster ovary WBL (CHO-WBL), and Chinese hamster lung (CHL) cells. The results of DNA sequencing, protein analysis, and cell cycle analysis demonstrate that the CHO-K1 and CHO-WBL cell lines have mutant p53 sequence [a mutation in codon 211 in exon 6 resulting in a change from Thr (ACA) to Lys (AAA)], mutant protein (high spontaneous levels that are non-inducible after X-irradiation), and mutant function (lack of G1 checkpoint). Interestingly, the CHL cell line has a completely wild-type p53 DNA sequence. However, the CHL cells have an abnormally high spontaneous level of wild-type p53 protein expression that is not inducible after X-irradiation, yet there is some evidence of G1 delay after irradiation. The protein data suggests that p53 in CHL cells is not being regulated normally, and thus is probably not functioning normally. The mechanism leading to this abnormal regulation of p53 in CHL cells clearly does not involve mutation in the p53 gene. Overall, the CHL cell line may be similar to the CHO cell lines, in that they all appear to have abnormal p53 function. Further work is needed to determine whether the presence of spontaneously high levels of wild-type p53 in CHL cells results in a difference in response to DNA damage (quantitatively or qualitatively) compared to the p53 mutant CHO cell lines.

P53 integrity in the genetically engineered mammalian cell lines AHH-1 and MCL-5

Recently, a C to T transition mutation in exon 8 of the p53 gene has been identified in a subculture of the genetically engineered human lymphoblastoid cell line AHH-1 and this mutation was proposed to cause a loss of function of the p53 suppressor protein and may limit the use of this cell culture in genotoxicology test assays. This led us to investigate early passage cultures of AHH-1 and its derivative MCL-5 to determine the distribution of the mutation. In order to characterise the presence of mutations at the p53 locus, exon 8 was analysed using restriction enzyme analysis and automated sequencing to locate possible changes of sequence. Mutations were identified at codon 282, and treatment with the Msp1 restriction enzyme led to incomplete digestion suggesting the presence of heterozygosity at the site which was confirmed by sequencing. Our results indicate that the p53 gene is heterozygous at the interface between the codons 281 and 282 in both AHH-1 and MCL-5. An Annexin V labeling study was carried out and both AHH-1 and MCL-5 cell lines were shown to undergo DNA damage induced cell death after a 1-h exposure to MNNG.

A mutation in the p53 tumor suppressor gene of AHH-1 tk+/- human lymphoblastoid cells

Loss-of-function mutations in the p53 tumor suppressor gene result in an altered response to DNA-damaging agents. Included in the mutant p53 phenotype are the loss of the G1 checkpoint and delayed apoptotic cell death, characteristics we have consistently observed in the AHH-1 tk+/- cell line following exposure to DNA-damaging agents. In order to determine the functional status of p53 in the AHH-1 tk+/- cell line, molecular analysis (single-strand conformational polymorphism [SSCP] and sequence analysis) was performed on exons 5-9 of the p53 gene. In addition, the status of the p53 gene in the closely related lymphoblast line, MCL-5, which, in our hands, has a much higher spontaneous rate of apoptosis than AHH-1 tk+/-, was also determined by molecular analysis. Initial SSCP analysis of AHH-1 tk+/- revealed an abnormal migration pattern of exon 8 when compared to a wild-type control. Subsequent sequence analysis indicated that a base-pair substitution (CGG-->TGG) mutation had occurred at codon 282, a reported "hot spot' for 5-methylcytosine mutations in the human p53 gene. Neither SSCP nor sequence analysis of exons 5-9 of MCL-5 indicated any differences from wild-type DNA. These results suggest that the lack of a G1 arrest and the delayed entrance into apoptosis observed in chemically-exposed AHH-1 tk+/- cells are, at least partially, accounted for by a loss-of-function mutation in the p53 gene.