Comet assay: a method to evaluate genotoxicity of nano-drug delivery system

Evaluating nanobiomaterial-induced DNA strand breaks using the alkaline comet assay

Due to their unique chemical and physical properties, nanobiomaterials (NBMs) are extensively studied for applications in medicine and drug delivery. Despite these exciting properties, their small sizes also make them susceptible to toxicity. Whilst nanomaterial immunotoxicity and cytotoxicity are studied in great depth, there is still limited data on their potential genotoxicity or ability to cause DNA damage. In the past years, new medical device regulations, which came into place in 2020, were developed, which require the assessment of long-term NBM exposure; therefore, in recent years, increased attention is being paid to genotoxicity screening of these materials. In this article, and through an interlaboratory comparison (ILC) study conducted within the Horizon 2020 REFINE project, we assess five different NBM formulations, each with different uses, namely, a bio-persistent gold nanoparticle (AuNP), an IR-780 dye-loaded liposome which is used in deep tissue imaging (LipImage™815), an unloaded PACA polymeric nanoparticle used as a drug delivery system (PACA), and two loaded PACA NBMs, i.e. the cabazitaxel drug-loaded PACA (CBZ-PACA) and the NR668 dye-loaded PACA (NR668 PACA) for their potential to cause DNA strand breaks using the alkaline comet assay and discuss the current state of genotoxicity testing for nanomaterials. We have found through our interlaboratory comparison that the alkaline comet assay can be suitably applied to the pre-clinical assessment of NBMs, as a reproducible and repeatable methodology for assessing NBM-induced DNA damage.

Genotoxicity Assessment of Metal-Based Nanocomposites Applied in Drug Delivery

Nanocomposites as drug delivery systems (e.g., metal nanoparticles) are being exploited for several applications in the biomedical field, from therapeutics to diagnostics. Green nanocomposites stand for nanoparticles of biocompatible, biodegradable and non-toxic profiles. When using metal nanoparticles for drug delivery, the question of how hazardous these "virus-sized particles" can be is posed, due to their nanometer size range with enhanced reactivity compared to their respective bulk counterparts. These structures exhibit a high risk of being internalized by cells and interacting with the genetic material, with the possibility of inducing DNA damage. The Comet Assay, or Single-Cell Gel Electrophoresis (SCGE), stands out for its capacity to detect DNA strand breaks in eukaryotic cells. It has huge potential in the genotoxicity assessment of nanoparticles and respective cells' interactions. In this review, the Comet assay is described, discussing several examples of its application in the genotoxicity evaluation of nanoparticles commonly administered in a set of routes (oral, skin, inhaled, ocular and parenteral administration). In the nanoparticles boom era, where guidelines for their evaluation are still very limited, it is urgent to ensure their safety, alongside their quality and efficacy. Comet assay or SCGE can be considered an essential tool and a reliable source to achieve a better nanotoxicology assessment of metal nanoparticles used in drug delivery.

Sclareol Inhibits Hypoxia-Inducible Factor-1α Accumulation and Induces Apoptosis in Hypoxic Cancer Cells

Purpose: The hypoxia in solid tumors is associated with the resistance to chemo/radiotherapy. Hypoxia-inducible factor-1 (HIF-1) plays a key role in cell remodeling to hypoxia. Therefore, the inhibition of HIF-1 accumulation is considered a hopeful strategy for the treatment of cancer. Here, we aimed to evaluate the geno- and cytotoxicity properties of sclareol, a natural bicyclic diterpene alcohol, on A549 cells in CoCl₂-induced hypoxia.

Methods: The cytotoxicity and apoptosis-inducing properties of sclareol on the A549 cell were evaluated using MTT assay and Annexin V/PI staining, respectively in hypoxia. DAPI staining, DNA ladder, and comet assay were used to evaluate the genotoxicity. Further, the qPCR technique was employed to assess the expression of HIF-1α, HIF-1β, and downstream target genes (GluT1, and Eno1). Finally, the level of HIF-1α protein was evaluated through Western blotting in sclareol-treated cells in hypoxia.

Results: The inhibitory concentration (IC₅₀) of sclareol against A549 cells was 8 μg/mL at 48 hours in hypoxia. The genotoxicity of sclareol was confirmed in the cells treated with sclareol in hypoxia. Sclareol induced ~46% apoptosis and also necrosis in the hypoxic condition. The qPCR analyses showed an enhanced suppression of HIF-1α, HIF-1β, GluT1, and Eno1 due to the sclareol treatment in the hypoxia. Moreover, protein quantification analysis showed dose-dependently degradation of HIF-1α in hypoxia upon treatment with sclareol.

Conclusion: The results obtained here indicate that sclareol possesses dose-dependent cytotoxicity effects against A549 cells in hypoxia through inhibition of HIF-1α protein accumulation, increasing cell sensitivity to intracellular oxygen levels, and disruption of cell adaptation to hypoxia.

Physico-Chemical Properties and Biocompatibility of Thermosensitive Chitosan Lactate and Chitosan Chloride Hydrogels Developed for Tissue Engineering Application

Recently, the modification of the initial structure of biopolymers, mainly chitosan, has been gaining importance with a view to obtain functional forms with increased practicality and specific properties enabling their use in tissue engineering. Therefore, in this article, the properties (structural and biological) of thermosensitive hydrogels obtained from chitosan lactate/chloride and two types of crosslinking agents (β-glycerol phosphate disodium salt pentahydrate and uridine 5'-monophosphate disodium salt) are discussed. The aim of the research is to identify changes in the structure of the biomaterials during conditioning in water. Structural investigations were carried out by FTIR spectroscopy. The crystallinity of gels was determined by X-ray diffraction analysis. The biocompatibility (evaluation of cytotoxicity and genotoxicity) of chitosan hydrogels was investigated by contact with human colon adenocarcinoma cell line for 48 h. The cytotoxicity was verified based on the colorimetric resazurin assay, and the genotoxicity was checked by the comet assay (percentage of DNA in the comet tail). The conducted research showed that the analyzed types of chitosan hydrogels are non-cytotoxic and non-genotoxic materials. The good biocompatibility of chitosan hydrogels surfaces makes them interesting scaffolds with clinical potential in tissue regeneration engineering.

In Vitro and In Vivo Models for Evaluating the Oral Toxicity of Nanomedicines

Toxicity studies for conventional oral drug formulations are standardized and well documented, as required by the guidelines of administrative agencies such as the US Food & Drug Administration (FDA), the European Medicines Agency (EMA) or European Medicines Evaluation Agency (EMEA), and the Japanese Pharmaceuticals and Medical Devices Agency (PMDA). Researchers tend to extrapolate these standardized protocols to evaluate nanoformulations (NFs) because standard nanotoxicity protocols are still lacking in nonclinical studies for testing orally delivered NFs. However, such strategies have generated many inconsistent results because they do not account for the specific physicochemical properties of nanomedicines. Due to their tiny size, accumulated surface charge and tension, sizeable surface-area-to-volume ratio, and high chemical/structural complexity, orally delivered NFs may generate severe topical toxicities to the gastrointestinal tract and metabolic organs, including the liver and kidney. Such toxicities involve immune responses that reflect different mechanisms than those triggered by conventional formulations. Herein, we briefly analyze the potential oral toxicity mechanisms of NFs and describe recently reported in vitro and in vivo models that attempt to address the specific oral toxicity of nanomedicines. We also discuss approaches that may be used to develop nontoxic NFs for oral drug delivery.

Geno/cytotoxicty and Apoptotic Properties of Phenolic Compounds from the Seeds of Dorema Glabrum Fisch. C.A

Introduction: Dorema glabrum (Apiaceae) is a rare and monocarpic species distributed in Transcaucasia and North West of Iran. We aimed to explore anti-cancer potency of bioactive compounds from the seeds of Dorma glabrum.

Methods: Methanol extract was subjected to phytochemical investigation using normal phase Sep-pak and reversed-phase HPLC, and cytotoxic effect of isolated compounds on CAOV-4 cell line was evaluated. Furthermore, Annexin V/PI staining and comet assay were used to study genotoxicity of compounds.

Results: Diglucosyl caffeoyl ester (1), Glucopyranosylcaffeic acid (2) and skimmin (3), were identified. MTT cytotoxicity assay showed growth inhibition of CAOV-4 cells due to treatment with compunds (1), (2) and (3) with an IC₅₀ of 99.7, 87.3 and 70.03 μg/ml at 48 h, respectively. Annexin V-FITC/PI staining showed occurrence of early/late apoptosis in the (1)-treated cells, while (2)-and (3)-treated cells necrosis/late apoptosis was dominant event. Single/double strands DNA breakages were observed by comet assay in all treatments.

Conclusion: This work provides sufficient information about anti-cancer properties of the diglucosyl caffeoyl ester from the seeds of D. glabrum.

Cyto/Genotoxicity study of polyoxyethylene (20) sorbitan monolaurate (tween 20)

Polyoxyethylene (20) sorbitan monolaurate (tween 20) is a non-ionic surfactant that is widely used as an emulsifier and stabilizer in pharmaceutical formulations, food and cosmetic industries. Although a number of studies have showed its non-toxic impacts on target cells, still, it is essential to investigate its effect on target cells. Therefore, in the present study, the anti-cell proliferation and cyto/genotoxicity effects of tween 20 are reported to address the possible mechanism for induction of apoptosis. At 40%-50% confluency, A549 cells and human umbilical vein endothelial cells were exposed to tween 20 at a recommended concentration for 24 h. After 24 h, to detect apoptosis and DNA damage, the treated cells were subjected to 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, fluorescein isothiocyanate (FITC)-labeled annexin V flow cytometry, DAPI staining, comet, and DNA ladder assays. Tween 20 decreased the growth of treated cells dose and time dependently, and single-strand DNA cleavage has been confirmed by comet assay. In addition, morphological alteration of DAPI-stained cells showed clear fragmentation in the chromatin and DNA rings within the nucleus of tween 20-treated cells. In addition, flow cytometry and DNA fragmentation assays confirmed DAPI staining assay results and indicated the occurrence of a programmed cell death (apoptosis) in the treated cells. These results demonstrate that, despite consideration of tween 20 as a safe non-ionic surfactant, it can induce apoptosis in target cells.