PEPTIDES AND PEPTIDASES AS TARGETS FOR THERAPEUTIC INTERVENTION Dr R A Skidgel BIOLOGICALLY ACTIVE PEPTIDES ACTH 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 AndrogenStimulating Hormone Casomorphins Cerebellin Cholecystokinin Chromostatin CLIP Contraceptive Tetrapeptide Corticotropin Inhibiting Peptide Corticostatin Corticotropin Releasing Factor Cytokines Delta Sleep Inducing Peptide Dermorphin Dermaseptin Diabetes Associated Peptide Diazepam Binding Inhibitor Dynorphins Endorphin Endothelins Met Enkephalin Leu Enkephalin Epidermal Mitosis Inhibiting Pentapeptide Erythropoietin Follicle Stimulating Hormone Galanin Gastrin Gliadorphin Granuliberin R Glucagon Growth Factors Growth Hormone Growth Hormone Releasing Hormone Inhibin Insulin Interleukins Kallidin Kyotorphin Lactorphin Leucokinins Lipotropin Luteinizing Hormone LH LH Releasing Hormone Magainins Mastoparan Melanin Concentrating Hormo ne Melanocyte Stimulating Hormone Melanostatin Page 1 of 15 Morphine Modulating Neuropeptide Motilin Neoendorphin Neoendorphin Neurokinin A Neurokinin B Neuromedin N Neuropeptide Y Neuropeptide P Neuroprotectin Neurotensin Neutrophil Defensins Oxytocin PACAP Pituitary Adenylate Cyclase Activating Peptide Pancreastatin Pancreatic Polypeptide Parathyroid Hormone Peptide Histidine Isoleucine Peptide YY Prolactin Proctolin Rigin Secretin Somatostatin Substance P Systemin Thymosin Thyrotropin Thyrotropin Releasing Hormone Tuftsin Vasopressin ADH VIP Vasoactive Intestinal Peptide GENERATION OF MULTIPLE PROTEINS FROM ONE GENE VIA RNA SPLICING This scheme illustrates the transcription of DNA into a primary RNA transcript that contains intervening sequences introns which are not present in the mature RNA The primary RNA transcript is spliced to remove the introns giving the mature RNA containing only exons The mature RNA contains untranslated regions at both ends and a contiguous sequence in the middle which is translated into protein In some cases alternative splicing of the RNA can lead to more than one type of mRNA resulting in the synthesis of multiple proteins from one gene Page 2 of 15 Page 3 of 15 GENERAL SCHEME OF PEPTIDE HORMONE PROCESSING AND METABOLISM Peptide hormones are initially synthesized as part of a larger prohormone In most cases the prohormone is cleaved at paired basic residues Arg Lys Lys Arg Arg Arg or Lys Lys by an endoprotease 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 a carboxypeptidase to generate the active peptide After interaction with a specific receptor the peptide is cleaved by one or more peptidases into inactive fragments or in certain cases into a fragment which may have altered activity and receptor specificity Page 4 of 15 Page 5 of 15 GENERAL 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 only one 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 can potentially cleave many different peptides Page 6 of 15 EXAMPLE 1 ANGIOTENSIN I CONVERTING ENZYME EXAMPLE 2 NEUTRAL ENDOPEPTIDASE 24 11 Page 7 of 15 3 THE FUNCTION S OF A PEPTIDASE WILL DEPEND ON ITS LOCALIZATION AND THE PEPTIDE HORMONES AVAILABLE TO IT IN THAT LOCATION IN A PARTICULAR PHYSIOLOGICAL OR PATHOLOGICAL SITUATION EXAMPLE NEUTRAL ENDOPEPTIDASE 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 PEPTIDE HORMONE ACTION 1 MIMIC THE ACTION OF A PEPTIDE HORMONE Administer the Peptide Advantages see above Disadvantages see above Stimulate Endogenous Synthesis of the Peptide Advantage Level of the peptide can be specifically increased at its normal site of action Disadvantage Control of synthesis of most peptide hormones is poorly understood Page 8 of 15 Block the Degradation by Peptidase s 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 Disadvantages Blocking one peptidase may interfere with the metabolism of more than one peptide Inhibition of more than one peptidase may be needed to block the degradation of a peptide Enhancing general levels of a peptide with multiple actions may produce side effects 2 BLOCK THE ACTION OF A PEPTIDE A Use a Receptor Antagonist 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 Disadvantages Many peptide receptor antagonists are themselves peptides and suffer from the disadvantages listed above Peptide antagonists by competitively inhibiting peptidase s could increase the concentration of the natural peptide B Block the Synthesis Processing of the Peptide Advantages All actions of the peptide can be blocked Page 9 of 15 Enzyme inhibitors can be synthesized with high affinity specificity and bioavailability 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 Exogenous Enzyme Advantage Potential for de toxifying deleterious peptides released in pathological conditions Disadvantages Probably not possible to activate peptidases as most are present in their fully active form Activation or administration of a peptidase would likely enhance the degradation of many peptides Delivery of
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