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The orally bioavailable alpha form of the naturally-occurring fat-soluble vitamin E, with potent antioxidant and cytoprotective activities. Upon administration, alpha-tocopherol neutralizes free radicals, thereby protecting tissues and organs from oxidative damage. Alpha-tocopherol gets incorporated into biological membranes, prevents protein oxidation and inhibits lipid peroxidation, thereby maintaining cell membrane integrity and protecting the cell against damage. In addition, alpha-tocopherol inhibits the activity of protein kinase C (PKC) and PKC-mediated pathways. Alpha-tocopherol also modulates the expression of various genes, plays a key role in neurological function, inhibits platelet aggregation and enhances vasodilation. Compared with other forms of tocopherol, alpha-tocopherol is the most biologically active form and is the form that is preferentially absorbed and retained in the body.
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A naturally occurring allotropic pnictogen and metalloid trace element with atomic symbol As, atomic number 33, and atomic weight 74.92 that is found in water, air, food, and soil, and has a role as a micronutrient. Arsenic, which is highly toxic with acute or chronic exposure to moderate or high levels through an unknown mechanism of action, is used in many industrial processes, as well as in pharmaceuticals, feed additives, and pesticides. It is characterized as a white, yellow, gray metallic, or black solid that is odorless. Exposure occurs by inhalation, ingestion, or contact.
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A non-essential amino acid. In hepatocytes, L-citrulline is synthesized in the urea cycle by the addition of carbon dioxide and ammonia to ornithine. L-citrulline is converted into L-arginine by the enzymes argininosuccinate synthetase and argininosuccinate lyase in the presence of L-aspartate and ATP. Subsequently, L-arginine is converted to nitric oxide by nitric oxide synthase and L-citrulline is regenerated as a by-product.
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The most potent form of the naturally occurring steroid sex hormone in humans, produced by ovary, placenta, testis, and in small amount by adrenal cortex. Estradiol binds to a specific intracellular estrogen receptor located in female organs, breasts, hypothalamus and pituitary. The receptor-ligand complex promotes gene expression necessary for the maintenance of fertility and secondary sexual characteristics in females. In addition, estradiol exhibits mild anabolic and metabolic properties, and increases blood coagulability. Estradiol, the principal intracellular human estrogen, is substantially more active at the cellular level than its metabolites, estrone and estriol.
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A collective term for pteroylglutamic acids and their oligoglutamic acid conjugates. As a natural water-soluble substance, folic acid is involved in carbon transfer reactions of amino acid metabolism, in addition to purine and pyrimidine synthesis, and is essential for hematopoiesis and red blood cell production. (NCI05)
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An amino acid derivative and homolog of cysteine containing an additional methylene bridge. Homocysteine is a product of methionine metabolism and elevated plasma levels are associated with cardiovascular disease, Alzheimer disease and several metabolic diseases.
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An immunoglobulin isotype (subclass). This isotype has the unique ability to bind with high affinity to IgE receptors (FceRI) on mast cells and basophils and induce degranulation and cytokine production by these cells when they are crosslinked by antigen. In addition to a central role in atopy and allergic responses, it has been speculated that IgE-mediated mast cell degranulation, by its release of mediators that increase vascular permeability, has an important role in the initiation of immune response in general.
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A long-acting barbituric acid derivative with antipsychotic property. Phenobarbital binds to and activates the gamma-aminobutyric acid (GABA)-A receptor, thereby mimicking the inhibitory actions of GABA in the brain. The activation effects of the phenobarbital-receptor-ionophore complex include increased frequency of chloride channel openings, membrane hyperpolarization and ultimately synaptic inhibition and decreased neuronal excitability. In addition, this agent inhibits glutamate induced depolarization.
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A hydantoin derivative and a non-sedative antiepileptic agent with anticonvulsant activity. Phenytoin potentially acts by promoting sodium efflux from neurons located in the motor cortex reducing post-tetanic potentiation at synapses. The reduction of potentiation prevents cortical seizure foci spreading to adjacent areas, stabilizing the threshold against hyperexcitability. In addition, this agent appears to reduce sensitivity of muscle spindles to stretch causing muscle relaxation.
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An aminoglycoside antibiotic derived from Streptomyces tenebrarius with bacteriostatic activity. Following active transport into the cell, tobramycin binds irreversibly to a specific aminoglycoside receptor on the bacterial 30S ribosomal subunit and interferes with the initiation complex between messenger RNA and the 30S subunit, thereby inhibiting initiation of protein synthesis, consequently leading to bacterial cell death. In addition, tobramycin induces misreading of the mRNA template causing incorrect amino acids to be incorporated into the growing polypeptide chain, consequently interfering with protein elongation.
