Toxicology

Toxicology is a branch of biology, chemistry, and medicine concerned with the study of the adverse effects of chemicals on living organisms. It is the study of symptoms, mechanisms, treatments and detection of poisoning, especially the poisoning of people.

The relationship between dose and its effects on the exposed organism is of high significance in toxicology. The chief criterion regarding the toxicity of a chemical is the dose, i.e. the amount of exposure to the substance. All substances are toxic under the right conditions. The term LD50 refers to the dose of a toxic substance that kills 50 percent of a test population (typically rats or other surrogates when the test concerns human toxicity). LD50 estimations in animals are no longer required for regulatory submissions as a part of pre-clinical development package.

The conventional relationship (more exposure equals higher risk) has been challenged in the study of endocrine disruptors. Toxicity is species-specific, lending cross-species analysis problematic. Newer methods are available to bypass animal-testing.

Toxicity of metabolites
Many substances regarded as poisons are toxic only indirectly. An example is “wood alcohol,” or methanol, which is chemically converted to formaldehyde and formic acid in the liver. It is the formaldehyde and formic acid that cause the toxic effects of methanol exposure. As for drugs, many small molecules are made toxic in the liver, a good example being acetaminophen (paracetamol), especially in the presence of chronic alcohol use. The genetic variability of certain liver enzymes makes the toxicity of many compounds differ between one individual and the next. Because demands placed on one liver enzyme can induce activity in another, many molecules become toxic only in combination with others. A family of activities that many toxicologists engage includes identifying which liver enzymes convert a molecule into a poison, what are the toxic products of the conversion and under what conditions and in which individuals this conversion takes place.

Subdisciplines of toxicology
There are various specialized subdisciplines within the field of toxicology that concern diverse chemical and biological aspects of this area. For example, toxicogenomics involves applying molecular profiling approaches to the study of toxicology. Other areas include Aquatic toxicology, Chemical (pharmaceutical) toxicology, Ecotoxicology Environmental toxicology, Forensic toxicology, Nanotoxicology and Medical toxicology.
Chemical (pharmaceutical) toxicology
Chemical or pharmaceutical toxicology is a scientific discipline involving the study of structure and mechanism related to the toxic effects of chemical agents, and encompasses technology advances in research related to chemical aspects of toxicology. Research in this area is strongly multidisciplinary, spanning computational chemistry andsynthetic chemistry, proteomics and metabolomics, drug discovery, drug metabolism and mechanisms of action, bioinformatics, bioanalytical chemistry, chemical biology, and molecular epidemiology.