Multiple approaches to assess the effects of F-53B, a Chinese PFOS alternative, on thyroid endocrine disruption at environmentally relevant concentrations

A Chinese perfluorooctane sulfonate (PFOS) substitute frequently detected in the environment, 6:2 chlorinated polyfluorinated ether sulfonate (F-53B), has a similar structure to PFOS and it is proposed to cause thyroid dysfunction. To further confirm this hypothesis, the effects of F-53B on the thyroid endocrine system and underlying mechanisms were investigated in vitro and in vivo using rat pituitary GH3 cells and developing zebrafish, respectively. In GH3 cells, F-53B enhanced cell proliferation in a dose-dependent manner, indicative of thyroid receptor agonistic activity. In zebrafish larvae, F-53B exposure induced significant developmental inhibition and increased thyroxine (T₄) but not 3,5,3'-triiodothyronine (T₃) levels accompanied by a decrease in thyroglobulin (TG) protein and transcript levels of most genes involved in the hypothalamic-pituitary-thyroid (HPT) axis. Interestingly, T₄ levels remained significantly increased while TG protein and gene transcription levels were markedly upregulated after depuration. Molecular docking studies revealed that F-53B binds to transthyretin (TTR) by forming hydrogen bonds with Lys123 and Lys115, thereby interfering with thyroid hormone homeostasis. Our collective in vitro, in vivo and in silico studies provide novel evidence that F-53B disrupts the thyroid endocrine system at environmentally relevant concentrations, which cannot be recovered after depuration. Given the persistence of F-53B in the environment, the long-term consequences of thyroid hormone disruption by this chemical warrant further investigation.

Validation of an in vitro screening test for predicting the tumor promoting potential of chemicals based on gene expression

Chemical carcinogenesis is a multifactorial process comprising two main stages: initiation and promotion. Tumor promoters cause the development of tumors in initiated cells and the majority of them are non-genotoxic carcinogens. The identification of tumor promoters is important for preventing cancer. We previously identified 22 specific gene markers using a global gene expression analysis of chemically induced tumor promotion and established an in vitro real-time PCR screening assay for the assessment of the tumor promoting potential of chemicals in BALB/c 3T3 cells. Our in vitro tumor promoter screening test, based on these marker genes, enables earlier assessment, and is easier to conduct than classical methods. The general applicability of these markers, however, was unknown. In this study, to evaluate the performance of a set of markers, we independently validated a separate sample set, which had various structures and properties. Independent validation of the signature of 63 test chemicals showed an accuracy, sensitivity, and specificity of the assay of 96.8%, 97.0% and 96.7%, respectively. These results indicate that the tumor promoting activity assay, based on the expression of 22 marker genes, will become a valuable tool for rapid screening of potential tumor promoters.

The emerging low-dose therapy for advanced cancers

Generally minute doses of drugs have been prescribed in biotherapies, homeopathy, immunization and vaccinations for centuries. Now the use of low doses of drugs is on the rise to combat serious diseases such as advanced cancers around the world. This new therapeutic approach to address solid tumors and other advanced diseases is a departure from the conventional use of maximum dose protocol. A small dose of the prescribed drug is frequently administered in a continuous fashion, at regular intervals, either as a standard treatment or as a maintenance therapy for a long time. However, this new treatment method lacks any standard for drug quantization, dose fractionation, repetition frequency and duration of a treatment course for an individual patient. This paper reviews literature about metronomic therapy and discusses hormesis: both phenomena occur in low dose ranges. Better mathematical models, computer simulations, process optimization and clinical trials are warranted to fully exploit the potential of low dose metronomic therapy to cure chronic and complicated diseases. New protocols to standardize metronomic dosimetry will answer the age old questions related to hormesis and homeopathy. It appears that this new low-dose metronomic therapy will have far reaching effects in curing chronic diseases throughout the world.

A perspective on the scientific, philosophical, and policy dimensions of hormesis

The hormesis concept has broad implications for biology and the biomedical sciences. This perspective on hormesis concentrates on toxicology and toxicological risk assessment and secondarily explores observations from other fields. It considers the varied manifestations of hormesis in the context of a broad family of biological stress responses. Evidence for hormesis is reviewed, and the hormesis model is contrasted with more widely accepted dose-response models in toxicology: a linear nonthreshold (LNT) model for mutagenesis and carcinogenesis, and a threshold model for most other toxicologic effects. Scientific, philosophical, and political objections to the hormesis concept are explored, and complications in the hormesis concept are analyzed. The review concludes with a perspective on the current state of hormesis and challenges that the hormesis model poses for risk assessment.

An investigation of hormesis of trichloroethylene in L-02 liver cells by differential proteomic analysis

Hormesis is the dose-response pattern of the biological responses to toxic chemicals, characterized by low-dose stimulation and high-dose inhibition. Although it is known that some cell types exhibit an adaptive response to low levels of cytotoxic agents, its molecular mechanism is still unclear and it has yet to be established whether this is a universal phenomenon that occurs in all cell types in response to exposure to every chemical. Trichloroethylene (TCE) is an organic solvent widely used and is released into the atmosphere from industrial degreasing operations. Acute (short-term) and chronic (long-term) inhalation exposure to trichloroethylene can affect the human health. In order to elucidate a cell-survival adaptive response of L-02 liver cells exposed to low dose of TCE, CCK-8 assay was used to assess cytotoxicity, and examined the possible mechanisms of hormesis by proteomics technology. We found that exposure of L-02 liver cells to low level of TCE resulted in adaptation to further exposure to higher level, about 1,000 protein-spots were obtained by two-dimensional electrophoresis (2-DE) and five protein spots were identified by matrix-assisted laser desorption/ionization mass spectrometry and tandem mass spectrometry sequencing of tryptic peptides. Our results suggest that a relationship may exist between identified proteins and TCE-induced hormesis, which are very useful for further study of the mechanism and risk assessment of TCE.