Nana Asare

Cytotoxic and genotoxic effects of silver nanoparticles in testicular cells

Serious concerns have been expressed about potential risks of engineered nanoparticles. Regulatory health risk assessment of such particles has become mandatory for the safe use of nanomaterials in consumer products and medicines; including the potential effects on reproduction and fertility, are relevant for this risk evaluation. In this study, we examined effects of silver particles of nano- (20nm) and submicron- (200nm) size, and titanium dioxide nanoparticles (TiO(2)-NPs; 21nm), with emphasis on reproductive cellular- and genotoxicity. Ntera2 (NT2, human testicular embryonic carcinoma cell line), and primary testicular cells from C57BL6 mice of wild type (WT) and 8-oxoguanine DNA glycosylase knock-out (KO, mOgg1(-/-)) genotype were exposed to the particles. The latter mimics the repair status of human testicular cells vs oxidative damage and is thus a suitable model for human male reproductive toxicity studies. The results suggest that silver nano- and submicron-particles (AgNPs) are more cytotoxic and cytostatic compared to TiO(2)-NPs, causing apoptosis, necrosis and decreased proliferation in a concentration- and time-dependent manner. The 200nm AgNPs in particular appeared to cause a concentration-dependent increase in DNA-strand breaks in NT2 cells, whereas the latter response did not seem to occur with respect to oxidative purine base damage analysed with any of the particles tested.

Chapter Five - Toxicity of Silver Nanomaterials in Higher Eukaryotes

Abstract The rapid expansion of nanotechnology promises to have significant benefits to society, yet there is increasing concern that exposure to nanoparticles (particles typically in vitro and in vivo uptake, biodistribution, and toxicity of AgNPs. Emphasis is placed on the systematization of data over animal and cell models, organs examined, doses applied, the type of particle administration, and the time of examination.

1-Nitropyrene (1-NP) induces apoptosis and apparently a non-apoptotic programmed cell death (paraptosis) in Hepa1c1c7 cells

Mechanistic studies of nitro-PAHs (polycyclic aromatic hydrocarbons) of interest might help elucidate which chemical characteristics are most important in eliciting toxic effects. 1-Nitropyrene (1-NP) is the predominant nitrated PAH emitted in diesel exhaust. 1-NP-exposed Hepa1c1c7 cells exhibited marked changes in cellular morphology, decreased proliferation and different forms of cell death. A dramatic increase in cytoplasmic vacuolization was observed already after 6 h of exposure and the cells started to round up at 12 h. The rate of cell proliferation was markedly reduced at 24 h and apoptotic as well as propidium iodide (PI)-positive cells appeared. Electron microscopic examination revealed that the vacuolization was partly due to mitochondria swelling. The caspase inhibitor Z-VAD-FMK inhibited only the apoptotic cell death and Nec-1 (an inhibitor of necroptosis) exhibited no inhibitory effects on either cell death or vacuolization. In contrast, cycloheximide markedly reduced both the number of apoptotic and PI-positive cells as well as the cytoplasmic vacuolization, suggesting that 1-NP induced paraptotic cell death. All the MAPKs; ERK1/2, p38 and JNK, appear to be involved in the death process since marked activation was observed upon 1-NP exposure, and their inhibitors partly reduced the induced cell death. The ERK1/2 inhibitor PD 98057 completely blocked the induced vacuolization, whereas the other MAPKs inhibitors only had minor effects on this process. These findings suggest that 1-NP may cause apoptosis and paraptosis. In contrast, the corresponding amine (1-aminopyrene) elicited only minor apoptotic and necrotic cell death, and cells with characteristics typical of paraptosis were absent.

Genotoxicity and gene expression modulation of silver and titanium dioxide nanoparticles in mice.

Abstract Recently, we showed that silver nanoparticles (AgNPs) caused apoptosis, necrosis and DNA strand breaks in different cell models in vitro. These findings warranted analyses of their relevance in vivo. We investigated the genotoxic potential and gene expression profiles of silver particles of nano- (Ag20, 20 nm) and submicron- (Ag200, 200 nm) size and titanium dioxide nanoparticles (TiO2-NPs, 21 nm) in selected tissues from exposed male mice including the gonades. A single dose of 5 mg/kg bw nanoparticles was administered intravenously to male mice derived from C57BL6 (WT) and 8-oxoguanine DNA glycosylase knock-out (Ogg1−/− KO). Testis, lung and liver were harvested one and seven days post-exposure and analyzed for DNA strand breaks and oxidized purines employing the Comet assay with Formamidopyrimidine DNA glycosylase (Fpg) treatment, and sperm DNA fragmentation by the sperm chromatin structure assay (SCSA). Based on an initial screening of a panel of 21 genes, seven genes were selected and their expression levels were analyzed in all lung and testis tissues sampled from all animals (n = 6 mice/treatment group) using qPCR. AgNPs, in particular Ag200, caused significantly increased levels of DNA strand breaks and alkali labile sites in lung, seven days post-exposure. Fpg-sensitive lesions were significantly induced in both testis and lung. The transcript level of some key genes; Atm, Rad51, Sod1, Fos and Mmp3, were significantly induced compared to controls, particularly in lung samples from Ag200-exposed KO mice. We conclude that the Ag200 causes genotoxicity and distinct gene expression patterns in selected DNA damage response and repair related genes.

3-Nitrofluoranthene (3-NF) but not 3-aminofluoranthene (3-AF) elicits apoptosis as well as programmed necrosis in Hepa1c1c7 cells.

In this study, we show that the environmental pollutant, 3-nitrofluoranthene (3-NF) but not its amine form, 3-aminofluoranthene (3-AF), induces apoptosis as well as regulated necrosis with necroptotic features in Hepa1c1c7 cells. Upon exposure to 3-NF, both typical apoptotic and necrotic cells were observed. A large number of the cells exhibited a characteristic partial nuclear chromatin condensation. Cycloheximide completely attenuated 3-NF-induced cell death. Activation of caspase-8, -9, and -3 were observed. Moreover, Z-VAD-FMK decreased the apoptotic cells, whereas the number of propidium iodide (PI)-positive cells with partial chromatin condensation was reduced by Nec-1, an inhibitor of receptor interacting protein (RIP-1). Cyp1a1, but not nitric oxide synthase (NOS), appears to be involved in activation of 3-NF to reactive metabolites. Increase in the number as well as size of lysosomes, myelinosomes, and activation of autophagy were also observed. 3-NF induced phosphorylation of ERK1/2, JNK and p38 MAPKs. Interestingly, while inhibitors of ERK1/2 and JNK reduced apoptotic as well as necrotic cell death, the p38 inhibitor, SB202190 reduced only the necrotic cell death. Taken together, 3-NF elicits both apoptosis and a caspase-independent programmed cell death (PCD) with autophagic characteristics. Conversely, with 3-AF, no apparent cytotoxic effects besides a reduction in cell proliferation was observed.

Signalling pathways involved in 1-nitropyrene (1-NP)-induced and 3-nitrofluoranthene (3-NF)-induced cell death in Hepa1c1c7 cells

We previously reported that 1-nitropyrene (1-NP) and 3-nitrofluoranthene (3-NF) elicited apoptotic cell death as well as non-apoptotic programmed cell deaths (PCDs) with paraptotic and necroptotic characteristics, respectively. In the present study, we have further confirmed and extended these findings. Flow cytometric analyses of 1-NP-exposed/3NF-exposed Hepa1c1c7 cells revealed that caspase-3 was only activated in the subpopulation of cells corresponding to that with classic apoptotic morphology. Immunocytochemical analysis indicated that leucocyte elastase inhibitor-derived DNaseII (LEI/L-DNaseII), apoptosis-inducing factor (AIF) and endonuclease G (EndoG) were more clearly translocated to the nucleus following 3-NF exposure than after 1-NP. These 3-NF-induced changes in AIF and EndoG translocation were reduced by necrostatin-1, an inhibitor of necroptotic cell death. Both compounds lead to accumulation of lipid droplets and induced DNA damage. Activation of checkpoint kinase (CHK) 1 and H2AX, but not ataxia telangiectasia mutated and CHK2, were observed. Furthermore, inhibition of p53 using pifithrin-alpha reduced the cell death induced by both compounds, suggesting a role of DNA damage/CHK1/p53 pathway in the death process. 1-NP-induced cell death was in addition characterized by increased oxidative damage and intracellular accumulation of Ca(2+). These findings further support the notion that 1-NP elicited apoptotic cell death and PCD with paraptotic characteristics, while 3-NF induced apoptosis and a PCD with necroptotic features.

3-nitrofluoranthene (3-NF)-induced apoptosis and programmed necrosis.

Polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs are environmental pollutants formed during incomplete combustion of organic material. Many possess mutagenic and carcinogenic properties, but their effects on cell death are less known. We have found that rather similar PAHs cause death by quite different mechanisms including apoptosis, necrosis as well as various mixtures of the two. In this addendum to our recent publication, Toxicology 2009 (255:140–50), we report that 3-nitrofluoranthene (3-NF) induces apoptosis as well as regulated necrosis with necroptotic features. The typical necroptotic cell exhibited partial nuclear chromatin condensation combined with damaged plasma membrane. The cells were characterized by increased size as well as number of lysosomes and myelinosomes/autophagic vesicles, and also in expression of the autophagic marker, LC3B. However, the induced autophagy appears to be a parallel event rather than the cause of cell death.