Pharmacokinetics, Biodistribution, and Biosafety of PEGylated Gold Nanoparticles In Vivo

Despite the obvious advantages of gold nanoparticles for biomedical applications, controversial and incomplete toxicological data hamper their widespread use. Here, we present the results from an in vivo toxicity study using gold nanoparticles coated with polyethylene glycol (PEG-AuNPs). The pharmacokinetics and biodistribution of PEG-AuNPs were examined in the rat’s liver, lung, spleen, and kidney after a single i.v. injection (0.7 mg/kg) at different time intervals. PEG-AuNPs had a relatively long blood circulation time and accumulated primarily in the liver and spleen, where they remained for up to 28 days after administration. Increased cytoplasmic vacuolation in hepatocytes 24 h and 7 days after PEG-AuNPs exposure and apoptotic-like cells in white splenic pulp 24 h after administration has been detected, however, 28 days post-exposure were no longer observed. In contrast, at this time point, we identified significant changes in lipid metabolism, altered levels of liver injury markers, and elevated monocyte count, but without marked biological relevance. In blood cells, no DNA damage was present in any of the studied time intervals, with the exception of DNA breakage transiently detected in primary kidney cells 4 h post-injection. Our results indicate that the tissue accumulation of PEG-AuNPs might result in late toxic effects.

Multiple recent sex chromosome fusions in Drosophila virilis associated with elevated satellite DNA abundance

Repetitive satellite DNA is highly variable both within and between species, and is often located near centromeres. However, the abundance or array length of satellite DNA may be constrained or have maximum limits. Drosophila virilis contains among the highest relative satellite abundances, with almost half its genome composed of three related 7 bp satellites. We discovered a strain of D. virilis that has 15% more pericentromeric satellite DNA compared to other strains, and also underwent two independent centromere-to-centromere sex chromosome fusion events. These fusions are presumably caused by DNA breakage near the pericentromeric satellites followed by repair using similar repetitive regions of nonhomologous chromosomes. We hypothesized that excess satellite DNA might increase the risk of DNA breaks and genome instability when stressed, which would be consistent with the apparent high rate of fusions we found in this strain. To directly quantify DNA breakage levels between strains with different satellite DNA abundances, we performed the comet assay after feeding flies gemcitabine and administering low-dose gamma radiation. We found a positive correlation between the rate of DNA breakage and satellite DNA abundance. This was further supported by a significant decrease in DNA breakage in an otherwise genetically identical substrain that lost the chromosome fusion and several megabases of satellite DNA. We find that the centromere-to-centromere fusions resulted in up to a 21% nondisjunction rate between the X and Y chromosomes in males, adding a fitness cost. Finally, we propose a model consistent with our data that implicates genome instability as a critical evolutionary constraint to satellite abundance.

The Chemical Basis of Intracerebral Hemorrhage and Cell Toxicity With Contributions From Eryptosis and Ferroptosis

Intracerebral hemorrhage (ICH) is a particularly devastating event both because of the direct injury from space-occupying blood to the sequelae of the brain exposed to free blood components from which it is normally protected. Not surprisingly, the usual metabolic and energy pathways are overwhelmed in this situation. In this review article, we detail the complexity of red blood cell degradation, the contribution of eryptosis leading to hemoglobin breakdown into its constituents, the participants in that process, and the points at which injury can be propagated such as elaboration of toxic radicals through the metabolism of the breakdown products. Two prominent products of this breakdown sequence, hemin, and iron, induce a variety of pathologies including free radical damage and DNA breakage, which appear to include events independent from typical oxidative DNA injury. As a result of this confluence of damaging elements, multiple pathways of injury, cell death, and survival are likely engaged including ferroptosis (which may be the same as oxytosis but viewed from a different perspective) and senescence, suggesting that targeting any single cause will likely not be a sufficient strategy to maximally improve outcome. Combination therapies in addition to safe methods to reduce blood burden should be pursued.

Do TUNEL and Other Apoptosis Assays Detect Cell Death in Preclinical Studies?

The terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay detects DNA breakage by labeling the free 3ʹ-hydroxyl termini. Given that genomic DNA breaks arise during early and late stages of apoptosis, TUNEL staining continues to be widely used as a measure of apoptotic cell death. The advantages of the assay include its relative ease of performance and the broad availability of TUNEL assay kits for various applications, such as single-cell analysis of apoptosis in cell cultures and tissue samples. However, as briefly discussed herein, aside from some concerns relating to the specificity of the TUNEL assay itself, it was demonstrated some twenty years ago that the early stages of apoptosis, detected by TUNEL, can be reversed. More recently, compelling evidence from different biological systems has revealed that cells can recover from even late stage apoptosis through a process called anastasis. Specifically, such recovery has been observed in cells exhibiting caspase activation, genomic DNA breakage, phosphatidylserine externalization, and formation of apoptotic bodies. Furthermore, there is solid evidence demonstrating that apoptotic cells can promote neighboring tumor cell repopulation (e.g., through caspase-3-mediated secretion of prostaglandin E2) and confer resistance to anticancer therapy. Accordingly, caution should be exercised in the interpretation of results obtained by the TUNEL and other apoptosis assays (e.g., caspase activation) in terms of apoptotic cell demise.

Toxicologic Evaluation for Amorphous Silica Nanoparticles: Genotoxic and Non-Genotoxic Tumor-Promoting Potential

Amorphous silica nanoparticles (SiO2NPs) have been widely used in medicine including targeted drug/DNA delivery, cancer therapy, and enzyme immobilization. Nevertheless, SiO2NPs should be used with caution due to safety concerns associated with unique physical and chemical characteristics. The objective of this study was to determine the effects of SiO2NPs on genotoxic and non-genotoxic mechanisms associated with abnormal gap junctional intercellular communication (GJIC) in multistage carcinogenesis. The SiO2NPs exhibited negative responses in standard genotoxicity tests including the Ames test, chromosome aberration assay, and micronucleus assay. In contrast, the SiO2NPs significantly induced DNA breakage in comet assay. Meanwhile, SiO2NPs inhibited GJIC based on the results of scrape/loading dye transfer assay for the identification of non-genotoxic tumor-promoting potential. The reduction in expression and plasma membrane localization of Cx43 was detected following SiO2NP treatment. Particularly, SiO2NP treatment increased Cx43 phosphorylation state, which was significantly attenuated by inhibitors of extracellular signal-regulated kinases 1/2 (ERK1/2) and threonine and tyrosine kinase (MEK), but not by protein kinase C (PKC) inhibitor. Taken together, in addition to a significant increase in DNA breakage, SiO2NP treatment resulted in GJIC dysregulation involved in Cx43 phosphorylation through the activation of mitogen-activated protein kinase (MAPK) signaling. Overall findings of the genotoxic and non-genotoxic carcinogenic potential of SiO2NPs provide useful toxicological information for clinical application at an appropriate dose.

Dengue virus sustains viability of infected cells by counteracting apoptosis-mediated DNA breakage

Dengue is the most important arboviral disease inflicting mankind. This mosquito-borne Flavivirus causes mild to severe dengue fever which in some cases leads to life-threatening conditions namely, dengue haemorrhagic fever and dengue shock syndrome. Annual infection is estimated at 390 million globally with 96 million manifesting clinically. So, ≥80% infections are asymptomatic and self-limiting. Dengue virus (DV) non-structural protein 1 (NS1) is a proven virotoxin abundantly present in the victim’s blood. We found that DV-infected or only NS1-expressing cells both can induce Cleaved Caspase3, due to antiviral response of host cells. NS1-transfected cells also showed nuclear damage and significant levels of DNA breaks suggestive of ensuing apoptosis. So, it was established that NS1 alone is capable of causing apoptosis. Surprisingly, despite secreting similar amount of soluble NS1, the DV-infected cells showed intact nuclear morphology and background levels of DNA nicks. These observations suggested that DV downregulates apoptosis of infected cells, which is a viral strategy against host defence. Furthermore, DV-infected cells counteracted Camptothecin-induced apoptotic DNA break. DV-infection was also found to keep the infected cells metabolically more active than only NS1 expressing cells. So, DV bypasses cellular defence against virus i.e. apoptosis by counteracting cellular DNA break and keeps the infected cells metabolically active to support virus replication for longer period which eventually results in high virus titer in circulation. Our findings reveal another level of intricacy involving dengue virus-host interactions and perhaps explain why ≥80% DV infections are asymptomatic/self-limiting despite the presence of NS1 virotoxin in infected cells.Author SummaryNS1, a virotoxin, abundantly present in Dengue patients blood, is a major player behind disease patho-biogenesis including plasma leakage. Despite the presence of NS1 in blood, Dengue is asymptomatic and self-limiting in more than 80% dengue virus (DV) infected people. We investigated this observation and found that plasmid-mediated NS1 expression and secretion in cells are sufficient to cause programmed cell death (apoptosis) and associated cellular DNA breakage. However, cells infected with dengue virus and secreting equivalent amounts of NS1 didn’t exhibit apoptotic DNA breakage. Consequently, DV-infected cells showed better survival than cells in which only NS1 was transiently expressed by transfection with expression plasmid. We also found that DV can even prevent chemical induced apoptotic DNA damage in infected host cells. So, DV bypasses host antiviral defence i.e. apoptosis by counteracting cellular DNA breakages and keeps the infected cells metabolically active to prolong virus replication.

A Review on: “Recent Updates on Poly-Adp-Ribosylation (Parylation) in Physiology and Pathology”

One of the most common cellular responses to DNA breakage is the covalent post-translational modification of the nuclear proteins with poly ADP ribose from the NAD+ as a precursor, which is mostly catalyzed by the poly-ADP-ribose polymerase1(PARP1).