Pulsed magnetic field increases the effect of ultraviolet C radiation and thermal shock in aged yeasts / El campo magnético pulsado aumenta el efecto de la radiación ultravioleta C y el choque térmico en levaduras envejecidas

The study of the effects of the magnetic field (MF) on living matter continues to be a dilemma. Until now, the interaction mechanisms of MF with living matter that explain the observed phenomena are unknown. Despite the existing literature and the multiple effects described to date, there are few published articles that study the combined effect of MF with other physical agents during the cellular aging process. In this sense, the aim of this work is to study whether low frequency and intensity pulsed and sinusoidal MF exposure produce alterations in the cell killing effect of ultraviolet C (UVC) radiation and thermal shock during the chronological aging of S. cerevisiae. Yeast cells were exposed to 2.45 mT (50 Hz) sinusoidal MF and 1.5 mT (25 Hz) pulsed MF, during 40 days of aging, in combination with UVC radiation (50 J/m2) and/or thermal shock (52°C). Cell survival was evaluated by clonogenic assay. The exposure of yeast to pulsed MF produces an acceleration of aging, which is not observed in cells exposed to sinusoidal MF. The pulsed MF modifies the cellular response to damaging agents only in aged S. cerevisiae cells. In this sense, the pulsed MF applied increases the damage induced by UVC radiation and by thermal shock. In contrast, the sinusoidal MF used has no effect.(AU)

Molecular Mechanisms of Resistance to Ionizing Radiation in S. cerevisiae and Its Relationship with Aging, Oxidative Stress, and Antioxidant Activity.

The repair of the damage produced to the genome and proteome by the action of ionizing radiation, oxidizing agents, and during aging is important to maintain cellular homeostasis. Many of the metabolic pathways influence multiple processes. In this way, this work aims to study the relationship between resistance/response to ionizing radiation, cellular aging, and the response mechanisms to oxidative stress, free radicals, reactive oxygen species (ROS), and antioxidant activity in the yeast S. cerevisiae. Systems biology allows us to use tools that reveal the molecular mechanisms common to different cellular response phenomena. The results found indicate that homologous recombination, non-homologous end joining, and base excision repair pathways are the most important common processes necessary to maintain cellular homeostasis. The metabolic routes of longevity regulation are those that jointly contribute to the three phenomena studied. This study proposes eleven common biomarkers for response/resistance to ionizing radiation and aging (EXO1, MEC1, MRE11, RAD27, RAD50, RAD51, RAD52, RAD55, RAD9, SGS1, YKU70) and two biomarkers for response/resistance to radiation and oxidative stress, free radicals, ROS, and antioxidant activity (NTG1, OGG1). In addition, it is important to highlight that the HSP104 protein could be a good biomarker common to the three phenomena studied.

Pulsed magnetic field increases the effect of ultraviolet C radiation and thermal shock in aged yeasts.

The study of the effects of the magnetic field (MF) on living matter continues to be a dilemma. Until now, the interaction mechanisms of MF with living matter that explain the observed phenomena are unknown. Despite the existing literature and the multiple effects described to date, there are few published articles that study the combined effect of MF with other physical agents during the cellular aging process. In this sense, the aim of this work is to study whether low frequency and intensity pulsed and sinusoidal MF exposure produce alterations in the cell killing effect of ultraviolet C (UVC) radiation and thermal shock during the chronological aging of S. cerevisiae. Yeast cells were exposed to 2.45 mT (50 Hz) sinusoidal MF and 1.5 mT (25 Hz) pulsed MF, during 40 days of aging, in combination with UVC radiation (50 J/m2) and/or thermal shock (52°C). Cell survival was evaluated by clonogenic assay. The exposure of yeast to pulsed MF produces an acceleration of aging, which is not observed in cells exposed to sinusoidal MF. The pulsed MF modifies the cellular response to damaging agents only in aged S. cerevisiae cells. In this sense, the pulsed MF applied increases the damage induced by UVC radiation and by thermal shock. In contrast, the sinusoidal MF used has no effect.

Improving Oral Presentation Skills for Radiology Residents through Clinical Session Meetings in the Virtual World Second Life.

BACKGROUND: The objective of this study was to conduct a clinical session meeting in the virtual world of Second Life to improve the oral presentation skills of radiology residents and to assess the perception of the attendees. METHODS: A clinical session meeting (10 two-hour sessions over four weeks), where participants presented their own clinical sessions, followed by a turn of interventions by the attendees, was designed and carried out. Attendees were asked to complete an evaluation questionnaire. Descriptive statistics were performed. RESULTS: Twenty-eight radiology residents attended the meeting, and 23 (81.2%) completed the evaluation questionnaire; 95.7-100% of them agreed that the virtual environment was attractive and suitable for holding the meeting and that the content was appropriate for their training as residents. They rated with ≥8.9 points (from 1 to 10) different aspects of the experience, highlighting the role of teachers (9.7 ± 0.6) and the usefulness of their training (9.4 ± 0.9). CONCLUSIONS: Second Life can be used effectively to train oral communication skills in public, in an environment perceived as attractive and suitable for learning, through an experience described by the attendees as interesting and useful, highlighting the advantages of social contact with their peers.

Genomic DNA damage induced by co-exposure to DNA damaging agents and pulsed magnetic field.

PURPOSE: Many articles describe the effects of extremely low-frequency magnetic fields (MFs) on DNA damage induction. However, the mechanism of MF interaction with living matter is not yet known with certainty. Some works suggest that MF could induce an increase in the efficacy of reactive oxygen species (ROS) production. This work investigates whether pulsed MF exposure produces alterations in genomic DNA damage induced by co-exposure to DNA damaging agents (bleomycin and methyl methanesulfonate (MMS)). MATERIALS AND METHODS: Genomic DNA, prepared from S. cerevisiae cultures, was exposed to pulsed MF (1.5 mT peak, 25 Hz) and MMS (0-1%) (15-60 min), and to MF and bleomycin (0-0.6 IU/mL) (24-72 h). The damage induced to DNA was evaluated by electrophoresis and image analysis. RESULTS: Pulsed MF induced an increment in the level of DNA damage produced by MMS and bleomycin in all groups at the exposure conditions assayed. CONCLUSIONS: Pulsed MF could modulate the cytotoxic action of MMS and bleomycin. The observed effect could be the result of a multifactorial process influenced by the type of agent that damages DNA, the dose, and the duration of the exposure to the pulsed MF.

Relationship between heat shock proteins and cellular resistance to drugs and ageing.

BACKGROUND AND AIMS: Ageing is a multifactorial degenerative process which causes a decrease in the cellular capacity for repair and adaptation to external stressors. In this way, it is important to maintain the proper balance of the proteome. Heat shock proteins (HSP) will intervene in this balance, which are responsible for the correct assembly, folding and translocation of other proteins when cells are subjected to stressors. This type of protein is overexpressed in human tumor cells, while its deficit, both in function and quantity, contributes to ageing processes. The present work aims to analyze the response of cells from studies carried out in normal and tumor cells that are subjected to stressors. METHODS AND RESULTS: A PubMed search was performed using the keywords "cell ageing, cell longevity, resistance, HSP, heat shock proteins, thermal shock proteins". This search generated 212 articles. Subsequently, a series of inclusion and exclusion criteria were applied to select the articles of interest to be evaluated. Normal cells subjected to external stressors at low doses increase the number of HSP, causing them to become more resistant. In addition, tumor cells expressing high levels of HSP show greater resistance to treatment and increased cell replication. HSP intervene in the cellular resistance of both normal and tumor cells. CONCLUSIONS: In the case of normal cells, the increase in HSP levels makes them respond effectively to an external stressor, increasing their resistance and not causing cell death. In the case of tumor cells, there is an increase in resistance to treatment.

Factors and molecular mechanisms of radiation resistance in cancer cells.

PURPOSE: The aim of this work is to review the published studies on radiation resistance mechanisms and molecular markers involved in different tumors. The revision has been focused in the last 5 years (2016-2021). CONCLUSIONS: Radioresistance is a cause of concern as it causes failure of radiation therapy and subsequent tumor relapse. Combination chemotherapy and radiation therapy are clinically successful in treating many types of tumors. Despite continued improvements in cancer treatment, locoregional recurrence or metastatic spread continues to occur in a high proportion of patients after being treated with radiation therapy or combination treatments. There is strong evidence that cancer stem cells contribute to radiation resistance, contributing to treatment failure. The mechanisms of radiation resistance in different tumors are not fully understood. A better understanding of cancer stem cells and the associated signaling pathways that regulate radiation resistance will open up new strategies for treating cancer by radiation therapy. Radiation can damage malignant cells mainly by the induction of DNA double-strand breaks. However, in some tumors appear resistant cells that repopulate the tumor following therapy leading over time to the failure of the treatment. Native mechanisms and induced pathways are the cause of radiation resistance. It has been described that numerous molecular markers acting through numerous mechanisms of action involved in radiation resistance, such as apoptosis resistance, alterations of cell growth, proliferation and DNA repair, hypoxia, increase in invasiveness and migration capacity, cell cycle alterations, and expression of heat shock proteins, among others. Therefore, resistance to radiation is a multifactorial phenomenon that, in different cell types, occurs through different regulatory mechanisms in which different molecules intervene. Resistance can be acquired by altering different regulatory pathways in different tumors. The knowledge of radiation resistance markers could help in the classification and treatment of patients with more aggressive tumors.

Evidences of the (400 MHz - 3 GHz) radiofrequency electromagnetic field influence on brain tumor induction.

Due to the massive increase in non-ionizing radiation emitting devices, the social concern about the possible malignancy to its exposure has increased the research interest. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) included the radiofrequency electromagnetic field (RF-EMF) of mobile phones on the category 2B as 'possibly' carcinogenic to humans. Epidemiological studies noticed a causal association between the exposure to RF-EMF and the incidence of brain neoplasm in different populations, since this is the organ with the highest specific absorption rate. The fact that so many of the ipsilateral tumors found are statistically significant with RF-EMF exposure provides weight suggesting causality. In this way, the higher the exposure (ipsilateral vs contralateral), the longer the cumulative exposure (hours of exposure) and the longer the latency (beyond 10 years); the greater the risk. In addition, considering together all of these parameters suggest a strong causality.

Exposure of S. cerevisiae to pulsed magnetic field during chronological aging could induce genomic DNA damage.

This study evaluates the DNA damage induced by pulsed magnetic field (MF) on S. cerevisiae cells exposed during chronological aging. Samples were exposed to 25 Hz pulsed MF (1.5mT, 8 h/day) while cells were aging chronologically. Clonogenic drop test was used to study cellular survival and the mutation frequency was evaluated by scoring the spontaneous revertant mutants. DNA damage analysis was performed after aging by electrophoresis and image analysis. Yeast cells aged during 40 days of exposure showing that pulsed MF exposure induced a premature aging. In addition, a gradual increase in spontaneous mutants was found in pulsed MF samples in relation to unexposed controls. An increase in DNA degradation, over the background level in relation to controls, was observed at the end of the exposure period. In conclusion, exposure of S. cerevisiae cells to pulsed MF during chronological aging could induce genomic DNA damage.

Impact of compulsory participation of medical students in a multiuser online game to learn radiological anatomy and radiological signs within the virtual world Second Life.

Competitive game-based learning within Second Life enables effective teaching of basic radiological anatomy and radiological signs to medical students, with good acceptance and results when students participate voluntarily, but unknown in a compulsory context. The objectives of this study were to reproduce a competitive online game based on self-guided presentations and multiple-choice tests in a mandatory format, to evaluate its development and student perceptions compared to a voluntary edition in 2015 (N = 90). In 2016 and 2017, respectively, 191 and 182 third-year medical students participated in the game as a mandatory course activity. The mean (±SD) score of the game was 74.7% (±19.5%) in 2015, 71.2% (±21.5%) in 2016, and 67.5% (±21.5%) in 2017 (P < 0.01). Participants valued positively the organization and educational contents but found the virtual world less attractive and the game less interesting than in the voluntary edition. The experience globally was rated with 8.2 (±1.5), 7.8 (±1.5), and 7.1 (±1.7) mean points (±SD) in a ten-point scale, in the 2015, 2016, and 2017 editions, respectively (P < 0.05). Competitive learning games within virtual worlds like Second Life have great learning potential in radiology, but the mean score in the game decreased, acceptance of virtual world technology was lower, and opinion about the game was worse with a compulsory participation, and even worse when dropouts were not allowed. Under the conditions in which this study was conducted, learning games in three-dimensional virtual environments should be voluntary to maintain adequate motivation and engagement of medical students.

Growth alteration of Allium cepa L. roots exposed to 1.5 mT, 25 Hz pulsed magnetic field.

The response of plants to magnetic fields (MF) is not fully understood. This work studies the effects of pulsed MF on the germination and growth of Allium cepa roots. Onions were exposed to 25Hz, 1.5mT, 33h. Pulsed MF was generated by a Helmholtz-type equipment that generated rectangular voltage pulses. The results showed that fewer roots grew in the specimens exposed to pulsed MF (14±6 roots on day 1 to 21±8 on day 4) than in the control groups (32±17 to 48±23) (p<0.05 Friedman). Control specimens showed a root mean length of 7±4 mm (day 1) and 24±10 mm (day 4). The specimens treated with pulsed MF showed a length of 4±2 mm (day 1), reaching 18±9 mm on day 4 (p<0.001 ANOVA). In conclusion, the exposure of Allium cepa specimens to 25Hz, 1.5mT pulsed MF during 33h produces a decrease in the germination and growth of roots.

Identification of new proteins related with cisplatin resistance in Saccharomyces cerevisiae.

The aim of this study is to select a cisplatin-resistant Saccharomyces cerevisiae strain to look for new molecular markers of resistance and the identification of mechanisms/interactions involved. A resistant strain was obtained after 80 days of cisplatin exposure. Then, total protein extraction, purification, and identification were carried out, in wild-type (wt) and resistant strains, by tandem mass spectrometry using a "nano HPLC-ESI-MS/MS" ion trap system. The increase in the exponentially modified protein abundance index (emPAI) (resistant vs wt strains) was calculated to study the increase in protein expression. "Genemania" software ( http://www.Genemania.org/ ) was used to compare the effects, functions, and protein interactions. KEGG tool was used for metabolic pathway analysis. Data are available via ProteomeXchange with identifier PXD020665. The cisplatin-resistant strain showed 2.5 times more resistance than the wt strain for the inhibitory dose 50% (ID50) value (224 µg/ml vs 89.68 µg/ml) and 2.78 times more resistant for the inhibitory dose 90% (ID90) value (735.2 µg/ml vs 264.04 µg/ml). Multiple deregulated proteins were found in the glutathione and carbon metabolism, oxidative phosphorylation, proteasome, glycolysis and gluconeogenesis, glyoxylate metabolism, fatty acid degradation pathway, citric acid cycle, and ribosome. The most overexpressed proteins in the cisplatin-resistant strain were related to growth and metabolism (QCR2, QCR1, ALDH4, ATPB, ATPA, ATPG, and PCKA), cell structure (SCW10), and thermal shock (HSP26). The results suggest that these proteins could be involved in cisplatin resistance. The resistance acquisition process is complex and involves the activation of multiple mechanisms that interact together. KEY POINTS: • Identification of new proteins/genes related to cisplatin resistance • Increased expression of QCR2/QCR1/ALDH4/ATPB/ATPA/SCW10/HSP26/ATPG and PCKA proteins • Multiple molecular mechanisms that interact together are involved in resistance.

Game-Based Learning in Virtual Worlds: A Multiuser Online Game for Medical Undergraduate Radiology Education within Second Life.

Game-based learning can have a positive impact on medical education, and virtual worlds have great potential for supporting immersive online games. It is necessary to reinforce current medical students' knowledge about radiological anatomy and radiological signs. To meet this need, the objectives of this study were: to design a competition-based game in the virtual world, Second Life and to analyze the students' perceptions of Second Life and the game, as well as to analyze the medium-term retention of knowledge and the potential impact on the final grades. Ninety out of 197 (45.6%) third-year medical students voluntarily participated in an online game based on self-guided presentations and multiple-choice tests over six 6-day stages. Participants and non-participants were invited to perform an evaluation questionnaire about the experience and a post-exposure knowledge test. Participants rated the experience with mean scores equal to or higher than 8.1 on a 10-point scale, highlighting the professor (9.5 ± 1.1; mean ± SD) and the virtual environment (8.9 ± 1.1). Participants had better results in the post-exposure test than non-participants (59.0 ± 13.5 versus 45.3 ± 11.5; P < 0.001) and a lower percentage of answers left blank (6.7 ± 8.4 versus 13.1 ± 12.9; P = 0.014). Competitive game-based learning within Second Life is an effective and well-accepted means of teaching core radiological anatomy and radiological signs content to medical students. The higher medium-term outcomes obtained by participants may indicate effective learning with the game. Additionally, valuable positive perceptions about the game, the educational contents, and the potential benefit for their education were discovered among non-participants.

Effect of low frequency magnetic field on efficiency of chromosome break repair.

DNA repair is essential to maintain genome integrity. There is scientific evidence that exposure to magnetic fields (MF) can produce alterations in DNA repair without clear conclusions. This work aims to study the cellular response to and repair of a very deleterious type of DNA damage, the DNA double strand break (DSB), in S. cerevisiae, under MF exposure. In S. cerevisiae cells, pairs of DSB were induced enzymatically by HO endonuclease by plating the cells on Galactose-containing media. The repair processes took place under exposure to a 50Hz, 2.45mT sinusoidal MF during 21 days. MF was generated by a pair of Helmholtz coils. MF induced 1.29- and 1.5-fold increase in the number of colonies grown at day 21 of exposure in relation to untreated controls for Pho91 and Rmd5 strain, respectively. In relation to the kinetics of DSB repair during MF exposure, a higher increase (55.56-fold) in DNA reparation was observed at day 15 for Rmd5 strain in relation to the slight increment (1.18-fold) found for Pho91 strain. The results suggest that long-term MF exposure could increase the DNA repair activity and there may be a relationship between the position of the DSB and the distance to the centromere.

Medical Student Education for Abdominal Radiographs in a 3D Virtual Classroom Versus Traditional Classroom: A Randomized Controlled Trial.

OBJECTIVE. The purpose of this article is to compare the effectiveness of practical radiology learning by medical students in a 3D virtual world versus the real world. SUBJECTS AND METHODS. Two hundred fifteen 3rd-year medical students were randomized into two groups to attend the same workshop on abdominal radiography interpretation in a virtual world classroom (VW group) and in real life (RL group). Pre- and post-training knowledge tests consisting of 12 multiple choice questions were performed at the beginning of the workshop and 2 months later. RESULTS. Fifty-four of 107 and five of 108 students refused to attend their respective group, resulting in the participation of 53 students (VW group) and 103 students (RL group) in this study. No significant differences were found between groups in the tests taken before (VW group, mean [± SD], 4.5 ± 1.8 points; RL group, 4.0 ± 1.3 points) and after (VW group, 6.2 ± 1.2; RL group, 6.0 ± 1.7 points) training. CONCLUSION. Radiology education in a 3D virtual classroom fosters participatory learning and results in similar acquisition of interpretive skills as a traditional face-to-face classroom. Virtual worlds allow the performance of online activities to learn interpretive skills with guaranteed success in learning similar to that of conventional activities. Additionally, the relative lack of identity in the virtual workshops makes students less afraid to speak and more participatory.

Effect of sinusoidal and pulsed magnetic field exposure on the chronological aging and cellular stability of S. cerevisiae.

Purpose: The aim of this study is to investigate the effects of low frequency and intensity sinusoidal magnetic field (SMF) and pulsed magnetic field (PMF) exposure on the chronological aging and cellular stability of Saccharomyces cerevisiae.Materials and methods: The S. cerevisiae wild type strain (WS8105-1C) was exposed to SMF (2.45 mT, 50 Hz, continuous) and PMF (1.5 mT, 25 Hz, 8 h/day). Chronological aging was evaluated during 40 days. Survival was assayed by clonogenic assay and drop test. Cellular stability was studied by spontaneous mutation count and the index of respiratory competence (IRC).Results: We found that exposure to PMF produces an acceleration of cellular chronological aging, not observed in the groups treated with SMF. A decrease in the spontaneous frequency of mitochondrial mutation during aging was observed in PMF-treated samples. However, no alterations in the IRC during aging were found for both, SMF and PMF, treatments.Conclusions: Exposure to PMF produces the acceleration of aging and an alteration in cellular stability.

Medical Students' and Family Physicians' Attitudes and Perceptions Toward Radiology Learning in the Second Life Virtual World.

OBJECTIVE. The purpose of this study was to evaluate 3rd-year medical students' attitudes and perceptions toward a radiographic interpretation course inside the virtual world Second Life during their formal training in radiology and to compare their attitudes and perceptions with those of family physicians exposed to the same course. SUBJECTS AND METHODS. Forty-eight 3rd-year medical students voluntarily participated in a 3-week course held in Second Life during a 4-month course on general radiology. The course consisted of six 2-hour synchronous sessions and four asynchronous tasks. Fourteen family physicians voluntarily participated in a specific version of the same course. Participants completed an evaluation questionnaire about the project. RESULTS. All participants rated the experience positively and found the environment attractive and the initiative, the course, and the intervention of the professor interesting, adequate, and appropriate for their medical training (mean values ≥ 4.2/5). Participants reported little previous knowledge about Second Life but were willing to participate in future similar experiences. Family physicians self-rated their own participation as less active and rated lower interaction with their peers than did the medical students (p = 0.018 and p < 0.001). CONCLUSION. The combination of synchronous sessions and asynchronous tasks to learn radiographic interpretation in Second Life was well received by undergraduate and postgraduate attendees, who had positive opinions and attitudes; the virtual sessions and tasks minimized the costs of travel for learners and teachers, making their use financially effective. Participants perceived Second Life as an interesting and useful online tool for complementary undergraduate radiology learning and postgraduate continuing medical education.

Inactivation of RAD52 and HDF1 DNA repair genes leads to premature chronological aging and cellular instability.

The present study aims to investigate the role of radiation sensitive 52 (RAD52) and high-affinity DNA binding factor 1 (HDF1) DNA repair genes on the life span of budding yeasts during chronological aging. Wild type (wt) and rad52, hdf1, and rad52 hdf1 mutant Saccharomyces cerevisiae strains were used. Chronological aging and survival assays were studied by clonogenic assay and drop test. DNA damage was analyzed by electrophoresis after phenol extraction. Mutant analysis, colony forming units and the index of respiratory competence were studied by growing on dextrose and glycerol plates as a carbon source. Rad52 and rad52 hdf1 mutants showed a gradual decrease in surviving fraction in relation to wt and hdf1 mutant during aging. Genomic DNA was spontaneously more degraded during aging, mainly in rad52 mutants. This strain showed an increased percentage of revertant colonies. Moreover, all mutants showed a decrease in the index of respiratory competence during aging. The inactivation of RAD52 leads to premature chronological aging with an increase in DNA degradation and mutation frequency. In addition, RAD52 and HDF1 contribute to maintain the metabolic state, in a different way, during chronological aging. The results obtained could have important implications in the chronobiology of aging.

Microirradiation techniques in radiobiological research.

The aim of this work is to review the uses of laser microirradiation and ion microbeam techniques within the scope of radiobiological research. Laser microirradiation techniques can be used for many different purposes. In a specific condition, through the use of pulsed lasers, cell lysis can be produced for subsequent separation of different analytes. Microsurgery allows for the identification and isolation of tissue sections, single cells and subcellular components, using different types of lasers. The generation of different types of DNA damage, via this type of microirradiation, allows for the investigation of DNA dynamics. Ion microbeams are important tools in radiobiological research. There are only a limited number of facilities worldwide where radiobiological experiments can be performed. In the beginning, research was mostly focused on the bystander effect. Nowadays, with more sophisticated molecular and cellular biological techniques, ion microirradiation is used to unravel molecular processes in the field of radiobiology. These include DNA repair protein kinetics or chromatin modifications at the site of DNA damage. With the increasing relevance of charged particles in tumour therapy and new concepts on how to generate them, ion microbeam facilities are able to address unresolved questions concerning particle tumour therapy.

Long-term exposure to a pulsed magnetic field (1.5 mT, 25 Hz) increases genomic DNA spontaneous degradation.

The aim of this work is to investigate whether long-term pulsed magnetic field (MF) has genotoxic activity by induction of DNA damage on DNA molecules in vitro, in the absence of repair mechanisms. Yeast genomic DNA prepared by phenol extraction from S. cerevisiae cultures and the commercial DNA molecular weight marker Hyperladder I (HL-I) were exposed to 1.5 mT peak, pulsed 25 Hz MF, 8 h/day, 16 days. The total content of DNA (undamaged and damaged DNA) decreased during the exposure of genomic DNA to MF. On day 16 of exposure the DNA content was 41 ± 8.1%. In addition, the undamaged DNA decreases until 6.2 ± 3.1% for unexposed control samples and until 0.3 ± 0.1% for pulsed MF-treated samples at day 16 of exposure. Therefore, the pulsed MF induced at day 16 an increase of 20.7-fold more degradation of DNA molecules >10 000 bp (undamaged DNA) than that observed for unexposed control samples. However, no effect was observed for HL-I DNA marker exposures. We conclude that long-term exposure to a pulsed MF (1.5 mT peak, 25 Hz, 8 h/day, 16 days) induces an increment in the DNA spontaneous degradation of yeast genomic DNA.