Mathematical modelling of the automated FADU assay for the quantification of DNA strand breaks and their repair in human peripheral mononuclear blood cells

Culture medium-dependent isoproterenol stability and its impact on DNA strand breaks formation and repair

In vitro mechanistic research is mostly performed without taking into consideration the potential influence of cell culture media and/or their supplements and therefore, interactions between compounds of interest and medium ingredients may be overlooked. Isoproterenol (isoprenaline) is a synthetic catecholamine used as sympathomimetic drug that stimulates β-adrenergic receptors and is widely used in biomedical research. Clinical studies have shown that isoproterenol is rapidly metabolized in the human body with a plasma half-life of about 2-5 min. However, despite its use in many in vitro and ex vivo studies, the stability of isoproterenol in cell culture media has not been characterized. Our results show a decrease of isoproterenol concentration in RPMI medium but high stability of the compound in TexMACS medium. The isoproterenol oxidation product isoprenochrome forms during treatment in both media. However, isoprenochrome formation is significantly lower in TexMACS medium. The effective level of isoproterenol and the formation of oxidation products might explain the discrepancies observed in isoproterenol-induced genotoxicity and cytotoxicity.

The Radioprotective Effect of Procaine and Procaine-Derived Product Gerovital H3 in Lymphocytes from Young and Aged Individuals

Ionizing radiation induces genomic instability in living organisms, and several studies reported an ageing-dependent radiosensitivity. Chemical compounds, such as scavengers, radioprotectors, and modifiers, contribute to reducing the radiation-associated toxicity. These compounds are often antioxidants, and therefore, in order to be effective, they must be present before or during exposure to radiation. However, not all antioxidants provide radioprotection. In this study, we investigated the effects of procaine and of a procaine-based product Gerovital H3 (GH3) on the formation of endogenous and X-ray-induced DNA strand breaks in peripheral blood mononuclear cells (PBMCs) isolated from young and elderly individuals. Interestingly, GH3 showed the strongest radioprotective effects in PBMCs from young subjects, while procaine reduced the endogenous amount of DNA strand breaks more pronounced in aged individuals. Both procaine and GH3 inhibited lipid peroxidation, but procaine was more effective in inhibiting mitochondria free radicals' generation, while GH3 showed a higher antioxidant action on macrophage-induced low-density lipoprotein oxidation. Our findings provide new insights into the mechanisms underlying the distinct effects of procaine and GH3 on DNA damage.

Influence of Acute Exercise on DNA Repair and PARP Activity before and after Irradiation in Lymphocytes from Trained and Untrained Individuals

Several studies indicate that acute exercise induces DNA damage, whereas regular exercise increases DNA repair kinetics. Although the molecular mechanisms are not completely understood, the induction of endogenous reactive oxygen species (ROS) during acute exhaustive exercise due to metabolic processes might be responsible for the observed DNA damage, while an adaptive increase in antioxidant capacity due to regular physical activity seems to play an important protective role. However, the protective effect of physical activity on exogenously induced DNA damage in human immune cells has been poorly investigated. We asked the question whether individuals with a high aerobic capacity would have an enhanced response to radiation-induced DNA damage. Immune cells are highly sensitive to radiation and exercise affects lymphocyte dynamics and immune function. Therefore, we measured endogenous and radiation-induced DNA strand breaks and poly (ADP-ribose) polymerase-1 (PARP1) activity in peripheral blood mononuclear cells (PBMCs) from endurance-trained (maximum rate of oxygen consumption measured during incremental exercise V'O2max > 55 mL/min/kg) and untrained (V'O2max < 45 mL/min/kg) young healthy male volunteers before and after exhaustive exercise. Our results indicate that: (i) acute exercise induces DNA strand breaks in lymphocytes only in untrained individuals, (ii) following acute exercise, trained individuals repaired radiation-induced DNA strand breaks faster than untrained individuals, and (iii) trained subjects retained a higher level of radiation-induced PARP1 activity after acute exercise. The results of the present study indicate that increased aerobic fitness can protect immune cells against radiation-induced DNA strand breaks.

Synergistic Effects of Weightlessness, Isoproterenol, and Radiation on DNA Damage Response and Cytokine Production in Immune Cells

The implementation of rotating-wall vessels (RWVs) for studying the effect of lack of gravity has attracted attention, especially in the fields of stem cells, tissue regeneration, and cancer research. Immune cells incubated in RWVs exhibit several features of immunosuppression including impaired leukocyte proliferation, cytokine responses, and antibody production. Interestingly, stress hormones influence cellular immune pathways affected by microgravity, such as cell proliferation, apoptosis, DNA repair, and T cell activation. These pathways are crucial defense mechanisms that protect the cell from toxins, pathogens, and radiation. Despite the importance of the adrenergic receptor in regulating the immune system, the effect of microgravity on the adrenergic system has been poorly studied. Thus, we elected to investigate the synergistic effects of isoproterenol (a sympathomimetic drug), radiation, and microgravity in nonstimulated immune cells. Peripheral blood mononuclear cells were treated with the sympathomimetic drug isoproterenol, exposed to 0.8 or 2 Gy γ-radiation, and incubated in RWVs. Mixed model regression analyses showed significant synergistic effects on the expression of the β2-adrenergic receptor gene (ADRB2). Radiation alone increased ADRB2 expression, and cells incubated in microgravity had more DNA strand breaks than cells incubated in normal gravity. We observed radiation-induced cytokine production only in microgravity. Prior treatment with isoproterenol clearly prevents most of the microgravity-mediated effects. RWVs may be a useful tool to provide insight into novel regulatory pathways, providing benefit not only to astronauts but also to patients suffering from immune disorders or undergoing radiotherapy.

Impaired PARP activity in response to the β-adrenergic receptor agonist isoproterenol

Psychological stress has been associated with DNA damage, thus increasing the risk of numerous diseases including cancer. Here, we investigate the effect of acute and chronic stress on poly(ADP-ribose) polymerase-1 (PARP-1), a sensor of DNA damage and DNA repair initiator. In order to mimic the chronic release of epinephrine, human peripheral blood mononuclear cells (PBMCs) were treated repeatedly with the sympathomimetic drug isoproterenol. We found significant induction of DNA strand breaks that remained unrepaired 24 h after ex vivo incubation. Isoproterenol-induced DNA strand breaks could be partially prevented by pre-treatment with the β-adrenergic receptor antagonist propranolol. Furthermore, the level of PARP-1 protein and PARP activity decreased and the levels of the PARP substrate nicotinamide adenine dinucleotide (NAD⁺) and of adenosine triphosphate (ATP), necessary to replenish NAD⁺ pools, were lowered by isoproterenol treatment. In conclusion our data provide novel insights into the mechanisms of isoproterenol-induced genotoxicity linking β-adrenergic stimulation and PARP-1.

Preclinical Biokinetic Modelling of Tc-99m Radiophamaceuticals Obtained from Semi-Automatic Image Processing

The aim of this study was to develop a semi automatic image processing algorithm (AIPA) based on the simultaneous information provided by X-ray and radioisotopic images to determine the biokinetic models of Tc-99m radiopharmaceuticals from quantification of image radiation activity in murine models. These radioisotopic images were obtained by a CCD (charge couple device) camera coupled to an ultrathin phosphorous screen in a preclinical multimodal imaging system (Xtreme, Bruker). The AIPA consisted of different image processing methods for background, scattering and attenuation correction on the activity quantification. A set of parametric identification algorithms was used to obtain the biokinetic models that characterize the interaction between different tissues and the radiopharmaceuticals considered in the study. The set of biokinetic models corresponded to the Tc-99m biodistribution observed in different ex vivo studies. This fact confirmed the contribution of the semi-automatic image processing technique developed in this study.

Effects of pyrogallic acid on Microcystis aeruginosa: oxidative stress related toxicity

Pyrogallic acid (PA) is used in various industrial and consumer products. The molecular mechanisms underlying PA's toxicity was not fully understood. In this study, toxicity of PA on Microcystis aeruginosa with reactive oxygen species (ROS) generation as an end point was investigated. The results showed an increase in the percentage of cells with loss of membrane integrity and enhanced intracellular ROS production. Exposure to 50mgL(-1) PA for 48h caused the highest percentage of loss of membrane integrity (56.7%), and a 2.54-fold higher intracellular ROS level compared to control. Further investigation revealed that PA caused a dose-dependent increase in DNA strand breaks (DSB) of M. aeruginosa at exposure concentration from 2 to 50mgL(-1). The incubation of cells with ROS scavengers ascorbic acid, N-acetyl-l-cysteine (NAC) and tocopherol markedly alleviated the level of PA-induced DSB. Analysis of PA autoxidized products in culture solution showed that PA was quickly converted to purpurogallin (PG), and PG was further autoxidized to other polyphenolic compounds. PA and PG might participate a futile redox cycle, which mediated ROS production in M. aeruginosa. These results suggested DNA strands and cell membrane were two targets of ROS induced by PA, and oxidative damage was an important mechanism for the toxicity of PA against M. aeruginosa.

Emerging metrology for high-throughput nanomaterial genotoxicology

The rapid development of the engineered nanomaterial (ENM) manufacturing industry has accelerated the incorporation of ENMs into a wide variety of consumer products across the globe. Unintentionally or not, some of these ENMs may be introduced into the environment or come into contact with humans or other organisms resulting in unexpected biological effects. It is thus prudent to have rapid and robust analytical metrology in place that can be used to critically assess and/or predict the cytotoxicity, as well as the potential genotoxicity of these ENMs. Many of the traditional genotoxicity test methods [e.g. unscheduled DNA synthesis assay, bacterial reverse mutation (Ames) test, etc.,] for determining the DNA damaging potential of chemical and biological compounds are not suitable for the evaluation of ENMs, due to a variety of methodological issues ranging from potential assay interferences to problems centered on low sample throughput. Recently, a number of sensitive, high-throughput genotoxicity assays/platforms (CometChip assay, flow cytometry/micronucleus assay, flow cytometry/γ-H2AX assay, automated 'Fluorimetric Detection of Alkaline DNA Unwinding' (FADU) assay, ToxTracker reporter assay) have been developed, based on substantial modifications and enhancements of traditional genotoxicity assays. These new assays have been used for the rapid measurement of DNA damage (strand breaks), chromosomal damage (micronuclei) and for detecting upregulated DNA damage signalling pathways resulting from ENM exposures. In this critical review, we describe and discuss the fundamental measurement principles and measurement endpoints of these new assays, as well as the modes of operation, analytical metrics and potential interferences, as applicable to ENM exposures. An unbiased discussion of the major technical advantages and limitations of each assay for evaluating and predicting the genotoxic potential of ENMs is also provided.