Current Developments in Toxicology: Science and Industry

When examining the toxicology of a chemical substance, animal models are used via acute, sub-chronic, or chronic exposure to study undesirable alterations in the structure or function of an experimental animal such as cytotoxicity, carcinogenicity, mutagenicity and teratogenicity. During these processes, millions of animals are forced to consume harmful chemicals and have them directly applied to their eyes and lacerated skin. Concerning the goodwill of test animals, the National Institute of Health released the first set of standards for laboratory animal care in 1963 which was revised in 1985, demanding that tests be carried out in such a way that animal suffering and discomfort were minimized by the use of an aesthetic, medicines, and euthanasia.

Simultaneously, alternative test methods were pursued to provide improved prediction of adverse health effects compared to currently used methods or advantages in terms of reduced expense, time, animal use, and animal pain and distress. For the aforementioned reasons, the Director of the National Institute of Health (NIH) created the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) in 1997, and it was made permanent by the ICCVAM Authorization Act of 2000. The ICCVAM is an interagency coordinating body of the NIH that is part of the National Toxicology Program Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM). In addition, the Act established a permanent Scientific Advisory Committee for Alternative Toxicological Methods (SACATM) to advise the NICEATM and ICCVAM. The goal of the NICEATM program and the ICCVAM is to develop, validate, and acquire regulatory approval of alternative test techniques in compliance with federal agency standards.

Today, with the coordination with these agencies, scientists have created improved techniques, assays, and models to decrease animal usage and increase data predictability, and they engage in interdisciplinary working groups that influence the future of toxicology.

New developments:

1. Short term tests (STTs)

These tests focus on chromosomal damage and genetic mutations to biological materials through in vitro assays:

 The Ames test (bacterial reverse mutation assay)  DNA strand break measurements in cells  Comet assay  Alkaline unwinding and hydroxyapatite chromatography  Alkaline elution  Cytogenetic assays  Micronucleus and chromosomal aberration assays

2. In vitro tests

Methods for keeping biological materials, tissues, and cells outside of the body are used in in vitro experiments where living tissue fragments are taken from the organism and grown in vitro. The biological materials are exposed to chemicals, and any latent effects are noted. These tests can anticipate a substance’s cellular and molecular effects on a specific tissue or organ. As a current development in vitro experiments, researchers have begun to co-culture cells from several organs in order to determine how the drug could alter interconnected biological systems. Tissue cultures provide an excellent screening method and can minimize the number of animals required for preliminary experiments.

 Murine Local Lymph Node Assay (LLNA)  Corrositex®

The putative toxin is introduced in vitro to a collagen matrix barrier that acts as artificial skin in the test. The test is timed from the time the chemical is introduced until it has breached the barrier and induced a colour change in pH indicator dyes. To determine corrosivity, the response time is compared to a categorization chart.  EpiDermTM and EPISKINTM

These are species-specific methods for assessing the corrosivity of a chemical to the human skin. The test chemical is applied in to three-dimensional in vitro tissue cultures of human skin and cell death is recorded throughout a defined exposure period.

3. Cell lines

Once a viable primary culture of cells, tissues, or organs from the organism has been established, the materials can be sub-cultured and grown into a cell line. Once a viable primary culture of cells, tissues, or organs from the organism has been established, the materials can be sub-cultured and grown into a cell line. Widely used cell lines in toxicology include:

• BJ (Boreskin fibroblasts)
• CHO (Chinese hamster ovary)
• HCT-116 (Colorectal carcinoma)
• HEK-293 (Embryonic kidney cells)
• HeLa (Cervical carcinoma)
• HUV-EC-C (Vascular endothelial cells)
• MRC-5 (Lung fibroblasts)
• Mesangial (Renal glomeruli)
• ME180 (Cervical carcinoma)

Toxins are frequently more toxic to stem cells than to other cells. Stem cells are cells that do not have a definite function and can develop into practically any cell that is needed.

Sources of stem cells:  Adult stem cells (the brain, bone marrow, blood and blood vessels, skeletal muscles, skin, the liver)  Embryonic stem cells (blastocyst, zygote)  Mesenchymal stem cells (MSCs) – connective tissue or stroma  Induced pluripotent stem cells (iPS) Types of stem cells: Totipotent, pluripotent, multipotent, Oligopotent, Unipotent

4. Toxicity pathway assays

When a cellular response pathway is sufficiently disrupted, it might have negative health effects which are known as toxicity pathways (TP). This definition implies that a TP contains three crucial characteristics;

• The fundamental biology of a TP is found in the molecular and cellular domains
• A TP is essentially a type of cellular failure. Specifically, a description of the specific conditions and sequential actions required when an external stimulus causes a cellular subsystem to malfunction and fail.
• Under some settings, the manner of failure recorded by a TP and manifested as a cellular phenotype will result in detrimental health implications at the organism level.

Emerging techniques for TPs are:

• Multiplexed Assays – enable the assessment of dozens, hundreds, or even thousands of endpoints on a single sample at the same time
• High-Content Screening Assays – use microscopy or other imaging methods to perform many assessments of cell biology at the level of single cells
• Specific-Protein Assays
• Organotypic Models

5. Machine learning-based approaches

Recently, the use of machine learning methods in computational toxicology has grown critical due to the gathering of a huge quantity of data on various toxicity endpoints in databases, the rapid growth of computer power, and the development of sophisticated data processing algorithms. Because of the predicted toxicity, many drug tests (cellular, animal, and clinical) can be avoided, which ultimately reduces the cost and labour of a medication’s preclinical and clinical trials. Quantitative Structure-Activity Relationships (QSAR) based on chemical structural factors are one of the most prevalent and established toxicity prediction methods. This approach use statistics to establish a quantifiable link between a medicinal compound’s structural or physicochemical properties and its physiological actions.