FABAD J. Pharm. Sci., 27, 231-237; 2002 SCIENTIFIC REVIEWS Prolyl Endopeptidase Enzyme Inhibitors of Plant Origin 0 İlkay ORHAN* , Gürdal ORHAN**, Bilge ŞENER* ltıhibitors Plaııt Prolyl Endopeptidase Enzyme of Origin Bitkisel Kaynaklı Prolil Endopeptidaz Enzim İnhibitörleri Summary : Prolyl endopeptidase (PEP) is a serine protease Özet : Prolil endopeptidaz (PEP), öğrenme ve hafıza sü• which is known ta play a role in degradation of proline­ recinde etkili prolin içerikli nöropeptitlerin yıkılnıasında rol containing neııropeptides involved in the processes of learn­ oynadığı bilinen bir serin proteazdır. PEP inhibitörlerinin ing and nıenıory. PEP inhibitors are expected to exert their sinirleri hasar ve hücre ölümüne karşı korıjyan, tanıma beneficial effects by increasing the brain levels of those neu­ fonksiyonlarını yeniden yapılandırıp iyileştirebilen nö• ropeptides ıvhich may improve and restore cognitive func­ ropeptitlerin beyin düzeylerini artırarak yararlı olnıaları tions and protect vulnerable nerves against damage and celi beklenir. Bugüne kadar, sentetik eşdeğerleri olduğu kadar, death. Therefore, they are considered to have therapeutic Alzheimer hastalığına karşı terapötik bir potansiyele sahip potential against Alzheimer's Disease. To date many com­ pounds have been isolated from natura! sources including PEP inhibitör aktiviteli pek çok bileşik, bitkiler, mantarlar plants, fungi and bacteria. Their synthetic counterparts have ve bakteriler de dahil olmak üzere doğal kaynaklardan izole been alsa studied. This revie1v covers PEP inhibitors iso­ edilmiştir. Bu derleme, bitkilerden elde edilen PEP in­ hibitörlerini kapsamaktadır. lated fronı plants. Key Words: Prolyl endopeptidase, Alzheimer's disease, Anahtar kelimeler: Profil endopeptidaz, Alzheinıer has­ neuropeptide, PEP inhibitory activity, plant talığı, nöropeptit, PEP inhibitör ak­ tivite, bitki Received 14.11.2002 Revised 17.01.2003 Accepted 18.02.2003 INIRODUCTION There is also some evidence that psychiatric dis­ orders, such as major depression, schizophrenia and Prolyl endopeptidase (PEP, also called prolyl olig­ post-traumatic stress disorder are associated with sig­ opeptidase) is a cytosolic endopeptidase involved in nificant alterations in the activity of some enzymes in­ the degradation of several proline-containing neuro­ cluding prolyl endopeptidase (PEP), ac­ peptides iınplicated in leaming and memory pro­ etylcholinesterase (AChE) and dipeptidyl peptidase­ cesses. ~fhese neuropeptides such as vasopressin, N (DPP-IV). Therefore, poleni, selective and perma­ substance P, thyrotropin-releasing hormone (TRH), nent inhibitors of PEP could serve as probes to assess oxytocin, neurotensin, angiotensins and opioids are the genuine contribution of !his enzyme in Alz­ affected in Parkinson Disease. Proline endopeptidase heiıner's pathology3-5 (PEP) contributes to the degradation of many of these neuropeptides, some of which are linked to a variety Formation of beta-amyloid and neurofibrillary tan­ of cognitive functions1,2 and could also control the gles in the brain due to genetic or other factors and production of the amyloidogenic peptide A-beta. marked reduction of certain brain neurnpeptide lev- * Gazi University, Department of Pharmacognosy, Faculty of Pharmacy, 0633 Ankara, Turkey. ** Numune Education and Research Hospital, 2nd Clinic-of Neurology, Ankara, Turkey. ° Correspondence 231 Orhan, Orhan, Şener els are consistent findings in patients with Alz­ proposed to be essential for the rnorphogenetic pro­ heimer's Disease, together with the deterioration of cess of imaginal discs and to participate in DNA syn­ cholinergic neurons 6-ZO. thesis in insect proliferation31,32. Currently, !here is a great demand for the develop­ Inhibitors of PEP ment of new drugs to improve memory deficits or to delay the neurodegenerative process. Up to the Since PEP can hydrolyze a number of peptide hor­ present, various studies have been focused on con­ rnones and neurotransmitters, abnorrnal increases or stituents with PEP inhibitory activity isolated from decreases in PEP activity could result in diseases re-· plants as well as their synthetic counterparts. In !his lated to rnemory and cognition33-41. Thus, PEP in­ ·review, general inforrnation is given about PEP and hibitors are expected to exert their beneficial effects plants possessing PEP inhibitory activity. by increasing the brain levels of those neuropeptides which may improve and restore cognitive functions Functions of PEP and protect vulnerable nerves against damage and celi death. Proline is unique among 20 amino acids in its cyclic structure. This property imposes many restrictions PEP inhibitors rnay have unique clinical relevance in on the structure of peptides and proteins and confers the prevention and treatrnent of a wide range of age­ _particular biological properties upon a wide range of related disorders including: physiologically important biomolecules. In order to deal with such peptides, nature has developed a -Memory deficits due to cerebro-vascular sclerosis group of enzymes !hat recognize this residue specif­ -Dementia of Alzheimer's type ically21. -Dementia and cogrtitive damage secondary to stroke, AIDS ete. Proline-specific peptidases fall into two classes. Pro­ lidase and aminopeptidase P cleave the N-terminal Specific PEP inhibitors are also expected to have anti­ amino acid from a peptide that is followed by proline amnesic effect. To date, ınany candidate compounds at the carbonyl-imino bond. Prolinase and proline­ with PEP inhibitory activity have been synthesized imino peptidase cleave proline at the N-terminal po­ for treatrnent of the neuropathological disorders men­ sition of peptides. Endoproteases !hat have specific­ tioned above42-47_ ity for proline are HIV-1 protease, prolyl endo­ peptidase and carboxypeptidase P. HIV-1 protease These studies suggest that PEP inhibitors may im­ cleaves the carbonyl-imino bond. PEP and car­ prove ınemory by blocking the metabolism of endog­ boxypeptidase P cleave the carboxyl side of the pro­ enous neuropeptides and have possible potential for line residue22. As a cytoplasmic protease, PEP has preventing rneınory deterioration. been characterized frorn several organisms (mush­ room, plant, bacteria) and in some organs of various PEP Inhibitors Isolated frorn Plants nmunals (cow, human, rabbit, pig and rat)23. PEP is composed of 705. arnino acids including a signal pep­ Recently, research has been concentrated on plan! tide of 20 residues. After cleavage of the signal pep­ constituents in order to discover novel PEP inhibitory tide, the mature protein which is composed of 685 compounds. For this purpose, sake (alcohol beverage residues is secreted. It is a serine protease of a novel in Japan, rnade frorn rice) and its by-product were type and does not present a proenzyrne form. Al­ studied. Pepsin hydrolysates of sake cake as a by­ though the three dimensional structure of PEP is un­ product and sake concentrate were subjected to some known, a structural pattern composed of several do­ chromatographic procedures. Three inhibitory pep­ 2 3 mains has been suggested 4- D. PEP has also been tides were obtained from sake cake as well as three 232 FABADJ. Plıarm. Sci., 27, 231-237, 2002 other peptides from sake. These peptides which exist heimer's disease52_ in rice glutelin inhibited PEP in vitra48. Fan et al. also studied the methanol extract of the un­ in a systematic screening far PEP inhibitors from tra­ derground porlion of Rhodolia sachalinensis for PEP ditional Chinese medicines, Fan el aJ.49 found !hat inhibitory activity. From this extract, five new mono­ the methanol extract from the underground portion terpenoids along with twenty-two known com­ of Rhodolia sacra showed significant inhibitory activ­ pounds were isolated. Among !hem, 1;2,3,6-tetra-O­ ity against PEP isolated from Flavobacterium me­ galloyl-~-D-glucose, 1,2,3,4,6,-penta-O-galloyl-_-D­ ningosepticum. Phytochemical investigation of the glucose, rhedionin, rhodiosin, 3-0-galloyl epi­ extract resulted in the isolation of nineteen known gallocatechin-(4~ --> -epigallocatechin 3-0-gallate and compounds. Six of !hem, namely protocatechuic acid, rosiridin displayed noncompetitive inhibition against gallic acid, (-)-epigallocatechin 3-0-gallate, 3-0- PEP53. galloylepigallocatechin-(4~ --> epigallocatechin 3-0- gallate, sacranoside A, arbutin and 4-0-(~-D­ in connection with their work, Fan et aJ.54,55 also glucopyranosyl)-gallic acid showed inhibitory activ­ screened PEP inhibitors from fourteen traditional ity. The kinetic study of these inhibitors indicated Kampo formulas and found that Tokaku-joki-to (Per­ that they were noncompetitive inhibitors except far sia and Rhubarb combination) showed a significant protocatechic acid which is a competitive inhibitor. inhibitory activity. E.xamination of this formula re­ sulted in the isolation of two new compounds, cis- The same researchers alsa screened forty-six water 3,5,4'-trihydroxystilbene 4'-0-~-D-(6-0-galloyl) glu­ and methaool extracts from plants selected on the ba­ copyranoside (1) .and 4-(4-hydroxyphenyl) -2- sis of traditional Chinese medicine lor PEP inhibition. butanone 4'-0-~-D-(6-0-galloyl-2-0-cinnamoyl) glu­ Among !hem, water extracts of Apocynum venetum copyranoside (2), along with twenty-five known com­ (80.4 %), Areca catechu (72.8 %), Comus offilinalis pounds. Twelve of !hem, namely compounds (1) and (85.3 %), Polygonum multiflorum (86.1 %), Salvia de­ (2), 4-(4-hydroxyphenyl)2-butanone 4'-0-~-D-(2,6-di­ serta