Peptides In Pharmacological

A number of biologically active peptides are used in pharmacology. These are classified into hormones, growth regulators, immunomodulators, neurotransmitters, substrates or inhibitors of enzymes, and so forth. Among them, some of the growth regulators and immunomodulators should be classified as proteins because of their molecular weights. The most widely used peptide drug is insulin. Not only agonists but also antagonists of these biologically active peptides show interesting pharmacological effects. Fragment peptides containing binding sites for receptors sometimes exhibit interesting biological effects as well. For example, Gly-Arg-Gly-Asp-Ser and Tyr-Ile-Gly-Ser-Arg are the fragment peptides of fibronectin and laminin, respectively. These peptides have been shown to prevent the metastasis of tumors. Asp-Ser-Asp-Pro-Arg (Hamburger peptide), a fragment peptide of human immunoglobulin E, shows an antiallergic effect. Peptide T (Ala-Ser-Thr-Thr-Asn-Tyr-Thr), a fragment peptide of the envelope glycoprotein of human immunodeficiency virus, inhibits the binding of the viral envelope to the CD-4 receptor of T-lymphocytes.

Inhibitor peptides for proteases show various pharmacological effects. Inhibitors for angiotensin I-converting enzyme or renin show antihypertensive effects, the amino-peptidase inhibitor bestatin shows an immunostimulating effect, and proryl endopeptidase inhibitor shows an an-tiamnesic affect.

Peptides are also promising as safe vaccines for the prevention of microbial or viral infections. Because of the difficulty of intestinal absorption and inactivation in the digestive tract, most peptide drugs are administered by injection. By suitable chemical modification, such as the incorporation of synthetic amino acids or acylation of the a-amino group or the amidation of the a-carboxyl group, some biologically active peptides are improved in specific activity, half-life, and proteolytic resistance. Some peptides become available for use through the oral or nasal route after such chemical modification or after physical modification such as emulsification and incorporation into liposomes. Another pharmacological use of peptide is as a solubilizer or emulsifier of insoluble drugs. Hydrolysates of gelation and casein have been shown to have such a potency (6).

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