Xenobiotic metabolism

Xenobiotic metabolism is the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal biochemistry, such as drugs and poisons. These pathways are a form of biotransformation present in all major groups of organisms, and are considered to be of ancient origin. These reactions often act to detoxify poisonous compounds (although in some cases, bioactivation is possible).

Overview

Xenobiotics are compounds that are foreign to a living organism. They include substances like drugs, environmental pollutants, and natural compounds from plants and microorganisms. The body has developed various mechanisms to eliminate these substances, and xenobiotic metabolism is one of them.

Phases of Xenobiotic Metabolism

Xenobiotic metabolism typically consists of three phases: Phase I reactions, Phase II reactions, and Phase III reactions.

Phase I Reactions

Phase I reactions (also termed nonsynthetic reactions) may occur by oxidation, reduction, hydrolysis, cyclization, and decyclization reactions. Oxidation involves the enzymatic addition of oxygen or removal of hydrogen, carried out by mixed function oxidases, often in the liver.

Phase II Reactions

Phase II reactions (also termed conjugation reactions) involve the enzymatic conjugation of endogenous compounds, such as glucuronic acid or sulfate, to the xenobiotic.

Phase III Reactions

Phase III reactions involve the further modification of the xenobiotic-conjugate to increase its water solubility for excretion.

Enzymes Involved

The enzymes involved in xenobiotic metabolism are primarily located in the liver, but can also be found in other parts of the body. The most important of these enzymes are the cytochrome P450 enzymes, which are responsible for the oxidation of xenobiotics.

Clinical Significance

Understanding xenobiotic metabolism is important in pharmacology and toxicology, as it can influence the efficacy and toxicity of drugs and other xenobiotics.

See Also

• Drug metabolism
• Metabolomics
• Pharmacokinetics

References

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