Page 1 of 15 PEPTIDES AND PEPTIDASES AS TARGETS FOR THERAPEUTICINTERVENTIONDr. R.A. Skidgel BIOLOGICALLY ACTIVE PEPTIDESACTH ß-Amyloid(1-40) Anaphylatoxins Angiotensin II Angiotensin(1-7) Atrial Natriuretic Peptide BAM-12P, 18P & 22P Bombesin Bradykinin Brain Natriuretic Peptides Buccalin Bursin Caerulein Calcitonin Calcitonin Gene-Related Peptide Cardiodilatin Carnosine CASH (Cortical Androgen-Stimulating Hormone) Casomorphins Cerebellin Cholecystokinin Chromostatin CLIP Contraceptive Tetrapeptide Corticotropin InhibitingPeptide Corticostatin CorticotropinReleasing Factor Cytokines Delta Sleep-Inducing Peptide Dermorphin Dermaseptin Diabetes Associated Peptide Diazepam Binding Inhibitor Dynorphins ß-Endorphin Endothelins Met-Enkephalin Leu-Enkephalin Epidermal Mitosis InhibitingPentapeptide Erythropoietin Follicle Stimulating HormoneGalanin Gastrin "-Gliadorphin Granuliberin-R Glucagon Growth Factors Growth Hormone Growth Hormone-ReleasingHormone Inhibin Insulin Interleukins Kallidin Kyotorphin α- & ß-Lactorphin Leucokinins Lipotropin Luteinizing Hormone (LH) LH-Releasing Hormone Magainins Mastoparan Melanin-Concentrating Hormone α-MelanocyteStimulating Hormone Melanostatin Morphine ModulatingNeuropeptide Motilin "-Neoendorphin ß-Neoendorphin Neurokinin A Neurokinin B Neuromedin N Neuropeptide Y Neuropeptide P ß-Neuroprotectin Neurotensin Neutrophil Defensins Oxytocin PACAP (Pituitary AdenylateCyclase Activating Peptide) Pancreastatin Pancreatic Polypeptide Parathyroid Hormone Peptide Histidine Isoleucine Peptide YY Prolactin Proctolin Rigin Secretin Somatostatin Substance P Systemin Thymosin Thyrotropin ThyrotropinReleasing Hormone Tuftsin Vasopressin (ADH) VIP (Vasoactive IntestinalPeptide)Page 2 of 15 GENERATION OF MULTIPLE PROTEINS FROM ONE GENE VIA RNA SPLICING This scheme illustrates the transcription of DNA into a primary RNA transcript that containsintervening sequences (introns) which are not present in the mature RNA. The primary RNAtranscript is spliced to remove the introns giving the mature RNA containing only exons. Themature RNA contains untranslated regions at both ends and a contiguous sequence in themiddle which is translated into protein. In some cases, alternative splicing of the RNA can leadto more than one type of mRNA resulting in the synthesis of multiple proteins from one gene.Page 3 of 15Page 4 of 15GENERAL SCHEME OF PEPTIDE HORMONE PROCESSING AND METABOLISM Peptide hormones are initially synthesized as part of a larger prohormone. In most cases, theprohormone is cleaved at paired basic residues (Arg-Lys, Lys-Arg, Arg-Arg or Lys-Lys) by anendoprotease to release a peptide containing an extra C-terminal Arg or Lys. In some cases,this form of the peptide has biological activity. The C-terminal Arg or Lys is then removed by acarboxypeptidase to generate the active peptide. After interaction with a specific receptor, thepeptide is cleaved by one or more peptidases into inactive fragments or, in certain cases, intoa fragment which may have altered activity and receptor specificity.Page 5 of 15Page 6 of 15GENERAL PRINCIPLES OF METABOLISM 1. A GIVEN PEPTIDE CAN BE CLEAVED BY MORE THAN ONE PEPTIDASE. 2. A GIVEN PEPTIDASE CAN HYDROLYZE A VARIETY OF PEPTIDES. It is a common misconception that peptidases are peptide-specific, i.e., they hydrolyze onlyone particular peptide. This notion is perpetuated by the names given to some of the enzymes(e.g., Angiotensin I Converting Enzyme, Enkephalinase, Enkephalin Convertase,Anaphylatoxin Inactivator, etc.). In fact, peptidases are peptide-bond specific and canpotentially cleave many different peptides.Page 7 of 15EXAMPLE 1: ANGIOTENSIN I CONVERTING ENZYME EXAMPLE 2: NEUTRAL ENDOPEPTIDASE 24.11Page 8 of 153. THE FUNCTION(S) OF A PEPTIDASE WILL DEPEND ON ITS LOCALIZATION AND THEPEPTIDE HORMONES AVAILABLE TO IT IN THAT LOCATION IN A PARTICULARPHYSIOLOGICAL OR PATHOLOGICAL SITUATION. EXAMPLE : NEUTRALENDOPEPTIDASE 24.11 ("ENKEPHALINASE") PEPTIDES AS THERAPEUTIC AGENTS 1.ADVANTAGES a.Highly Potent Agents (Active at 10-15M to 10-7M) b.Wide Variety of Biological Activities c.Readily Synthesized 2.DISADVANTAGES a.Very Rapidly Degraded by Peptidases b.Excreted by Kidney c.Short Duration of Action (seconds to minutes) d.Poorly Absorbed from GI Tract e.Inconvenient Administration (e.g., i.v., intra-nasal) f.Do Not Cross Blood-Brain Barrier g.Expensive to Synthesize STRATEGIES FOR DEVELOPING THERAPEUTIC AGENTS TO MIMIC OR BLOCK PEPTIDEHORMONE ACTION 1. MIMIC THE ACTION OF A PEPTIDE HORMONE Administer the Peptide Ž Advantages: see above Ž Disadvantages: see above Stimulate Endogenous Synthesis of the PeptideŽ Advantage: Level of the peptide can be specifically increased at its normal site ofaction Ž Disadvantage: Control of synthesis of most peptide hormones is poorly understoodPage 9 of 15Block the Degradation by Peptidase(s) Ž Advantages:Level of the peptide can be specifically increased at its normal site(s) of action. Peptidase inhibitors can be synthesized with good stability and bioavailability. Ž Disadvantages: Blocking one peptidase may interfere with the metabolism of more than onepeptide. Inhibition of more than one peptidase may be needed to block the degradationof a peptide. Enhancing general levels of a peptide with multiple actions may produceside-effects. 2.BLOCK THE ACTION OF A PEPTIDE A. Use a Receptor Antagonist Ž Advantages: Specific actions of a peptide mediated by a single receptor type can be blocked. Potential for few unwanted side effects. Non-peptide antagonists may have good bioavailability and stability. Ž Disadvantages: Many peptide receptor antagonists are themselves peptides and suffer from thedisadvantages listed above. Peptide antagonists, by competitively inhibiting peptidase(s), could increase theconcentration of the natural peptide.B. Block the Synthesis/Processing of the Peptide Ž Advantages: All actions of the peptide can be blocked.Page 10 of 15Enzyme inhibitors can be synthesized with high affinity, specificity andbioavailability. Ž Disadvantages: Cannot block a specific action of a peptide. Intermediate forms of a peptide may have their own biological activity. Processing enzymes process many different peptide hormones. C. Enhance Degradation by Activating Peptidases or Administer ExogenousEnzyme. Ž Advantage: Potential for de-toxifying deleterious peptides
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