Do cytotoxicity and cell death cause false positive results in the in vitro comet assay?

The comet assay is used to measure DNA damage induced by chemical and physical agents. High concentrations of test agents may cause cytotoxicity or cell death, which may give rise to false positive results in the comet assay. Systematic studies on genotoxins and cytotoxins (i.e. non-genotoxic poisons) have attempted to establish a threshold of cytotoxicity or cell death by which DNA damage results measured by the comet assay could be regarded as a false positive result. Thresholds of cytotoxicity/cell death range from 20% to 50% in various publications. Curiously, a survey of the latest literature on comet assay results from cell culture studies suggests that one-third of publications did not assess cytotoxicity or cell death. We recommend that it should be mandatory to include results from at least one type of assay on cytotoxicity, cell death or cell proliferation in publications on comet assay results. A combination of cytotoxicity (or cell death) and proliferation (or colony forming efficiency assay) is preferable in actively proliferating cells because it covers more mechanisms of action. Applying a general threshold of cytotoxicity/cell death to all types of agents may not be applicable; however, 25% compared to the concurrent negative control seems to be a good starting value to avoid false positive comet assay results. Further research is needed to establish a threshold value to distinguish between true and potentially false positive genotoxic effects detected by the comet assay

Do cytotoxicity and cell death cause false positive results in the in vitro comet assay?

The comet assay is used to measure DNA damage induced by chemical and physical agents. High concentrations of test agents may cause cytotoxicity or cell death, which may give rise to false positive results in the comet assay. Systematic studies on genotoxins and cytotoxins (i.e. non-genotoxic poisons) have attempted to establish a threshold of cytotoxicity or cell death by which DNA damage results measured by the comet assay could be regarded as a false positive result. Thresholds of cytotoxicity/cell death range from 20% to 50% in various publications. Curiously, a survey of the latest literature on comet assay results from cell culture studies suggests that one-third of publications did not assess cytotoxicity or cell death. We recommend that it should be mandatory to include results from at least one type of assay on cytotoxicity, cell death or cell proliferation in publications on comet assay results. A combination of cytotoxicity (or cell death) and proliferation (or colony forming efficiency assay) is preferable in actively proliferating cells because it covers more mechanisms of action. Applying a general threshold of cytotoxicity/cell death to all types of agents may not be applicable; however, 25% compared to the concurrent negative control seems to be a good starting value to avoid false positive comet assay results. Further research is needed to establish a threshold value to distinguish between true and potentially false positive genotoxic effects detected by the comet assay

Safe-by-design gelatin-modified zinc oxide nanoparticles

We report an innovative low-cost wet precipitation synthesis method for gelatin-modified zinc oxide nanoparticles (GM ZnO NPs) at the interface between the gelatin hydrogel and aqueous electrolyte. Diffusion of ammonia through the hydrogel matrices with different gelatin contents induced precipitation of the product in contact with the surface of the aqueous solution of zinc ions. The obtained precipitate was subjected to thermal treatment to partially decompose the adsorbed gelatin in the NP structure. Physicochemical properties of obtained GM ZnO NPs were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential thermal analysis (DTA), thermogravimetry (TG), photon correlation spectroscopy (PCS), zeta potential measurements, and inductively coupled plasma-mass spectrometry (ICP-MS). The estimated mean crystallite size of GM ZnO NP powders was in the range from 5.8 to 12.1 nm. The synthesized NPs exhibited nanosheet morphology and arranged into flake-like aggregates. The toxic potential was investigated in vitro in human hepatocellular carcinoma cell line HepG2. The thiazolyl blue tetrazolium bromide (MTS) assay was used to assess cell viability, 2 ',7 '-dichlor-fluorescein-diacetate (DCFH-DA) assay to examine the formation of intracellular reactive oxygen species (ROS), and comet assay to evaluate the genotoxic response. GM ZnO NPs slightly reduced HepG2 cell viability, did not induce ROS formation, and showed low genotoxic potential at very high doses (100 mu g mL(-1)). ZnO NPs fabricated and modified using the proposed methodology deserve further study as potential candidates for antibacterial agents or dietary supplements with low overall toxicity

Poly (epsilon-caprolactone) microspheres for prolonged release of selenium nanoparticles

Poly (e-caprolactone) (PCL) microspheres as a carrier for sustained release of antibacterial agent, selenium nanoparticles (SeNPs), were developed. The obtained PCL/SeNPs microspheres were in the range 1-4 mu m with the encapsulation efficiency of about 90%. The degradation process and release behavior of SeNPs from PCL microspheres were investigated in five different degradation media: phosphate buffer solution (PBS), a solution of lipase isolated from the porcine pancreas in PBS, 0.1 M hydrochloric acid (HCl), Pseudomonas aeruginosa PAO1 cell-free extract in PBS and implant fluid (exudate) from the subcutaneously implanted sterile polyvinyl sponges which induce a foreign-body inflammatory reaction. The samples were thoroughly characterized by SEM, TEM, FTIR, XRD, PSA, DSC, confocal microscopy, and ICP-OES techniques. Under physiological conditions at neutral pH, a very slow release of SeNPs occurred (3 and 8% in the case of PBS or PBS + lipase, respectively and after 660 days), while in the acidic environment their presence was not detected. On the other hand, the release in the medium with bacterial extract was much more pronounced, even after 24 h (13%). After 7 days, the concentration of SeNPs reached a maximum of around 30%. Also, 37% of SeNPs have been released after 11 days of incubation of PCL/SeNPs in the implant exudate. These results suggest that the release of SeNPs from PCL was triggered by Pseudomonas aeruginosa PAO1 bacterium as well as by foreign body inflammatory reaction to implant. Furthermore, PCL/SeNPs microspheres were investigated in terms of their biocompatibility. For this purpose, cytotoxicity, the formation of reactive oxygen species (ROS), and genotoxicity were evaluated on HepG2 cell line. The interaction of PCL/SeNPs with phagocytic cell line (Raw 264.7 macrophages) was monitored as well. It was found that the microspheres in investigated concentration range had no acute cytotoxic effects. Finally, SeNPs, as well as PCL/SeNPs, showed a considerable antibacterial activity against Gram-positive bacteria: Staphylococcus aureus (ATCC 25923) and Staphylococcus epidermidis (ATCC 1228). These results suggest that PCL/SeNPs-based system could be an attractive platform for a prolonged prevention of infections accompanying implants

Poly (epsilon-caprolactone) microspheres for prolonged release of selenium nanoparticles

Poly (e-caprolactone) (PCL) microspheres as a carrier for sustained release of antibacterial agent, selenium nanoparticles (SeNPs), were developed. The obtained PCL/SeNPs microspheres were in the range 1-4 mu m with the encapsulation efficiency of about 90%. The degradation process and release behavior of SeNPs from PCL microspheres were investigated in five different degradation media: phosphate buffer solution (PBS), a solution of lipase isolated from the porcine pancreas in PBS, 0.1 M hydrochloric acid (HCl), Pseudomonas aeruginosa PAO1 cell-free extract in PBS and implant fluid (exudate) from the subcutaneously implanted sterile polyvinyl sponges which induce a foreign-body inflammatory reaction. The samples were thoroughly characterized by SEM, TEM, FTIR, XRD, PSA, DSC, confocal microscopy, and ICP-OES techniques. Under physiological conditions at neutral pH, a very slow release of SeNPs occurred (3 and 8% in the case of PBS or PBS + lipase, respectively and after 660 days), while in the acidic environment their presence was not detected. On the other hand, the release in the medium with bacterial extract was much more pronounced, even after 24 h (13%). After 7 days, the concentration of SeNPs reached a maximum of around 30%. Also, 37% of SeNPs have been released after 11 days of incubation of PCL/SeNPs in the implant exudate. These results suggest that the release of SeNPs from PCL was triggered by Pseudomonas aeruginosa PAO1 bacterium as well as by foreign body inflammatory reaction to implant. Furthermore, PCL/SeNPs microspheres were investigated in terms of their biocompatibility. For this purpose, cytotoxicity, the formation of reactive oxygen species (ROS), and genotoxicity were evaluated on HepG2 cell line. The interaction of PCL/SeNPs with phagocytic cell line (Raw 264.7 macrophages) was monitored as well. It was found that the microspheres in investigated concentration range had no acute cytotoxic effects. Finally, SeNPs, as well as PCL/SeNPs, showed a considerable antibacterial activity against Gram-positive bacteria: Staphylococcus aureus (ATCC 25923) and Staphylococcus epidermidis (ATCC 1228). These results suggest that PCL/SeNPs-based system could be an attractive platform for a prolonged prevention of infections accompanying implants