Introduction

Mechanisms of toxicity refer to the biological processes by which toxic substances cause adverse effects in living organisms. Understanding these mechanisms is crucial for toxicology studies, as it provides insights into the potential risks associated with exposure to specific chemicals or compounds. In this article, we will discuss the main mechanisms of toxicity and the types of toxicology studies that are designed to evaluate these mechanisms according to the OECD guidelines and equivalent guidelines from other regulatory organizations.

1. Interaction with biomolecules

One of the primary mechanisms of toxicity involves the interaction of toxic substances with essential biomolecules, such as proteins, lipids, and nucleic acids. This interaction can lead to the formation of adducts, the inhibition or activation of enzymes, the disruption of cellular processes, and, ultimately, cell injury or death. Toxicology studies aimed at understanding these interactions include genotoxicity testing (OECD TG 471, 473, and 487) and protein binding assays.

2. Reactive oxygen species (ROS) generation

Toxic substances can cause the production of reactive oxygen species, leading to oxidative stress and damage to cellular components, such as lipids, proteins, and DNA. This mechanism of toxicity is often associated with inflammation, neurodegeneration, and cancer. Toxicology studies that assess the potential for ROS generation include in vitro and in vivo oxidative stress assays, as well as general toxicity studies that evaluate histopathological changes associated with oxidative damage (OECD TG 408, 409, and 453).

3. Disruption of cellular signaling pathways

Toxic substances can interfere with cellular signaling pathways, leading to altered gene expression, disrupted cellular processes, and cell injury or death. These effects can result from direct interactions with signaling molecules or through indirect mechanisms, such as the generation of ROS or changes in cellular metabolism. Toxicology studies that investigate the impact of toxic substances on cellular signaling pathways include in vitro assays (e.g., reporter gene assays) and in vivo studies evaluating molecular and cellular endpoints (OECD TG 451, 452, and 453).

4. Disruption of membrane function

Toxic substances can interfere with the function of cellular membranes, leading to changes in membrane permeability, ion transport, and the activity of membrane-bound enzymes. This can result in cellular dysfunction, injury, or death. Toxicology studies that assess the effects of toxic substances on membrane function include in vitro assays measuring membrane integrity and in vivo studies evaluating histopathological changes associated with membrane damage (OECD TG 408, 409, and 453).

5. Immune system modulation

Toxic substances can modulate the immune system, leading to immunosuppression, hypersensitivity, or autoimmune reactions. This can result in increased susceptibility to infections, allergic reactions, or the development of autoimmune diseases. Toxicology studies that investigate the effects of toxic substances on the immune system include immunotoxicity testing (OECD TG 407 and 443) and allergenicity testing (OECD TG 429, 430, and 431).

Conclusion

Understanding the mechanisms of toxicity is essential for toxicology studies, as it helps to predict the potential risks associated with exposure to specific chemicals or compounds. By using various toxicology tests in accordance with OECD guidelines and equivalent guidelines from other regulatory organizations, researchers can gain valuable insights into the potential hazards posed by toxic substances and inform the development of safety measures and regulations to protect human health and the environment.