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Term Definition
LDL Short for “low density lipoprotein,” LDL cholesterol is the “bad” cholesterol, as elevated LDL levels are associated with an increased risk of coronary heart disease. See “cholesterol” entry.
L-Dopa 3,4 dihydroxyphenylalanine, the biologically active form of dopa, it is a product of the amino acids tyrosine and phenylalanine and a synthetic precursor to other catecholamines (norepinephrine) and epinephrine as well as the skin pigment, melanin. Being a precursor to the central nervous system neurotransmitter dopamine, it can be used in a specific formulation to enhance depleted dopamine stores in Parkinson disease, as dopamine itself is unable to penetrate the blood-CNS barrier. Also known as levodopa.
Leprosy Symptomatic infection with Mycobacterium leprae, it may involve the skin, peripheral nerves, anterior eye, upper respiratory tract, and other organ systems. Leprosy can slowly and progressively lead to deforming disability with most affected people dying with it rather than of it. Leprosy is also called Hansen disease.
Leptin A hormone involved in body fat regulation. Originally it was thought to trigger weight loss, but now it is thought to signal the brain as to the quantity of fat there is on the body. The interactions of leptin with other chemicals in the body remain poorly understood, and thus it has thus far made a poor pharmaceutical target.
Leukaphoresis (1) The process of separating the white blood cells, or any of their subsets, from the remainder of blood components and collecting them. (2) A machine which aids in doing this.
Leukemia One of many types of blood cell cancer cells, most often of white blood cells or their precursors. Leukemia cells usually look quite different from their normal counterparts, and do not function properly.
Leukotriene Along with prostaglandins, one of the most well-studied chemical mediators of allergic and other inflammatory reactions. Released from mast cells and basophils, leukotrienes were originally known as the slow reacting substances of anaphylaxis. Their actions are somewhat similar to those of histamine, but Leukotriene D4, for instance, is 10 times more potent than histamine. Leukotrienes have additional key roles in the allergic inflammatory response. Researchers hope that antileukotrienes will prove more effective than antihistamines in combating allergy. Leukotriene modifiers have been used to a limited extent in the treatment of asthma.
Lifetime Risk Estimated risk of getting a condition in a lifetime, typically expressed as a ratio of 1:X. "
Ligand A molecule that interacts with a receptor.
Lipase An enzyme that breaks down specific fats/glycerides.
Lipid The biochemical term for fat. Lipids play important roles in cells, especially as an ingredient of cell membranes. For gene therapy, lipids can be formed into balls (liposomes; like soap bubbles) which can carry the therapeutic genes and fuse with cell membranes in the body.
Lipid Metabolism The process by which the body processes lipids (fats).
Liposome A hollow sphere made out of lipid which can carry payload such as gene therapy.
Lithium A positively charged element similar to sodium and potassium. Its similarity to these other elements allows it to interfere with their activities inside cells and on cell surfaces. Lithium also interferes with the biological activities of other positively charged atoms such as calcium and magnesium. Pharmacologically, lithium interferes with the activity of certain neurotransmitters. It also influences tryptophan and serotonin concentrations in the brain, and increases bone marrow production of white blood cells. Lithium has been used for the treatment of mania, including that associated with bipolar disorder, since the 1950s.
Locus Ceruleus The major group of norepinephrine-utilizing neurons in the brain, it plays a role in mediating specific functions relating to memory, emotion, arousal, and attention.
L-selectin A protein expressed on white blood cells that mediates adhesion and trafficking.
Lumen A channel or cavity through which a fluid flows.
Lym-1 A monoclonal antibody that binds a class II major histocompatability complex (MHC) protein. Lym-1 is being investigated for the treatment of B cell lymphomas.
Lymph Fluid containing a high concentration of white blood cells, found inside lymphatic vessels and lymph nodes.
Lymphatic System The organ system including the spleen, lymph nodes, and lymphatic ducts that, along with blood vessels, are responsible for the circulation of white blood cells through the body. Immune reactions take place in the lymphatic system organs.
Lymphocytes White blood cells such as B cells and T cells.
Lymphocytic Leukemia A group of malignant diseases of the white blood cells known as lymphocytes, predominantly B and T cells and their precursors.
Lymphography Visualization of the lymphatic system by x-rays (or the like) following injection and distribution of a contrast agent (dye).
Lymphoma A general term for cancer originating in the lymphatic system and involving cancerous growth of lymphocytes. There are two main categories of lymphoma: Hodgkin Disease and non-Hodgkin Lymphomas.
lymphotoxin Members of the tumor necrosis factor (TNF) family, lymphotoxin a and lymphotoxin b have similar biological roles as TNFa. These cytokines have diverse functions in immune development, immune function, and other processes.
Lysis Dissolution, explosion, tearing, as in a mechanism of cell killing.
Lysosomal Storage Disease One of several single gene disorders, each characterized by a specific defective enzyme leading to the accumulation of specific metabolites. As the enzyme is present in the intracellular digestive organelle called the lysosome, the accumulation tends to occur there.
Lysosome Intracellular digestive organelle.
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