Chi Hoa Pham

Evaluation of the toxic impact of silver nanoparticles on Japanese medaka (Oryzias latipes).

The increased use of nano-sized metallic materials is likely to result in the release of these particles into the environment. It is, however, unclear if these materials are harmful to aquatic animals. Furthermore, because the dissolution of such nanomaterials will occur, it is probable that some of the adverse effects resulting will result from the dissolved metal species. In this study, therefore, we investigated the health and environmental impact of silver nanoparticles (Ag-NPs) on Japanese Medaka by studying changes in the expression of stress-related genes using real time RT-PCR analysis and compared these results with those of Medaka exposed to soluble silver ions. The stress-related genes selected here were metallothionein, HSP 70, GST, p53, CYP 1A and the transferrin gene. The expression levels of each gene were determined using two different Ag-NPs dosages and were quantified by measuring the mRNA concentrations in liver extracts with the Taqman-based Real-Time PCR method. The results suggest that these two silver forms have distinguishable toxic fingerprints between them. While the Ag-NPs led to cellular and DNA damage, as well as carcinogenic and oxidative stresses, genes related with metal detoxification/metabolism regulation and radical scavenging action were also induced. In contrast, the ionic silver led to an induction of inflammatory response and metallic detoxification processes in the liver of the exposed fish, but resulted in a lower overall stress response when compared with the Ag-NPs.

Biomarker gene response in male Medaka (Oryzias latipes) chronically exposed to silver nanoparticle

The chronic toxicity test has been conducted for twenty-eight days to characterize the hepatic expression levels of eight stress-related genes after exposing Medaka to two doses of silver nitrate or a silver nanoparticle (Ag-NP) using real time RT-PCR analysis. This extends our previously published work to include three additional biomarkers and three later time points. In comparing with the control, the significant induction of MT and GST genes in livers of the fish exposed to 1 μg/l Ag-NPs was observed at various time points during the test period. The Orla C3-1 (Medaka) gene was slightly induced only with 1 μg/l Ag-NPs at 7-day exposure while the suppression of p53 and HSP70 was recorded in all exposures at the end of the test. The gene encoding transferrin was repressed at day 21 by both silver types and at every exposure dosage. These results revealed that the Ag-NPs increase metal detoxification, oxidative and inflammatory stress, and finally stimulate immune responses in Medaka. The conspicuous induction of choriogenin L and vitellogenin 1 in male fish exposed to Ag-NPs, especially at 7- and 21-day, compared with the exposures of AgNO(3) or control was the first attempt to examine estrogenic effects of Ag-NPs.

Construction and characterization of Japanese medaka (Oryzias latipes) hepatic cDNA library and its implementation to biomarker screening in aquatic toxicology

To strengthen the toxicogenomic study, we constructed a library of hepatic cDNA from Japanese medaka under influence of specific chemical mediated stress responses. Gene expression profile analysis of the cDNA microarrays followed by real time RT-PCR assay were conducted to screen particular biomarkers for 17-beta estradiol (E2), nonylphenol (NP) and 2-chlorophenol (2CP). Information of 1509 high-quality ESTs including 260 new ESTs was added onto GenBank and dbEST. The ESTs were clustered and assembled into 159 contigs and 372 singletons. Among them, 128 contigs and 163 singletons (54.8%) were functionally characterized and 13 UniESTs (2.5%) were hypothetical proteins. Ontology analysis resulting in 282 UniESTs which involved with 2102 GOs and 93 sequences associated with 116 enzyme codes. For each test chemical, two specific biomarkers were selected from the gene expression profiling of microarrays. The expression patterns of the marker genes in real time PCR analysis were consistent with the regulated gene expression patterns in microarrays. The tentative biomarkers showed unique gene expression patterns depending on chemical concentration(s) and exposure duration in real time RT-PCR analysis. The analysis accomplished of the hepatic cDNA library and its information added to genetic and genomic resources could be sufficiently valuable specifically for aquatic toxicity studies.