half life
The time it takes for a measurable quantity, such as a drug concentration, to decrease by half of its initial value and is expressed in units of time, e.g. hours.
hepatic
Pertaining to the liver.
Hepatitis
A viral infection of the liver, which may be called by hepatitis A, B or C.
hepatocytes
The main cell type in the liver (parenchymal cell). Hepatocytes can be used to study the metabolism of drug candidates and their ability to induce (up-regulate) or suppress (down-regulate) CYP enzyme expression. Freshly isolated (primary culture) or cryopreserved hepatocytes are used for drug metabolism studies; whereas, primary cultures of hepatocytes are used for enzyme induction studies.
HIV
Human Immunodeficiency Virus; the cause of Acquired Immunodeficiency Syndrome (AIDS).
homogenate
Material that has been homogenized. A liver homogenate is prepared by mechanical disruption of the cells resulting in the release of organelles (subcellular fractions).
homogeneous
Of uniform structure or composition throughout.
homogenize
A process that, in our application, involves breaking apart cells from tissue such as liver, releasing organelles and cytoplasm.
hormone
A substance originating in an organ or gland that is conveyed through the blood to another part of the body, stimulating it by chemical action to regulate functional activity or to increase secretion of another hormone. Many steroid hormones are substrates for drug-metabolizing enzymes.
HPLC
High performance liquid chromatography. (Also known as, high pressure liquid chromatography.)
hydrophilic
Literally: “water-loving.” Fat-soluble (lipophilic) xenobiotics are generally biotransformed to water soluble (hydrophilic) metabolites.
hydrophobic
Literally: “fear of water.” Synonymous with lipophilic. Can be used to describe substances that are not water soluble. Most drugs are hydrophobic(lipophilic), and are converted to water-soluble hydrophilic metabolites by biotransforming enzymes.