Insulysin

Abstract: The steady-state level of amyloid β-peptide (Aβ) represents a balance between its biosynthesis from the amyloid precursor protein (APP) through the action of the β- and γ-secretases and its catabolism by a variety of proteolytic enzymes Recent attention has focused on members of the neprilysin (NEP) family of zinc metalloproteinases in amyloid metabolism NEP itself degrades both Aβ1−40 and Aβ1−42in vitro and in vivo, and this metabolism is prevented by NEP inhibitors Other NEP family members, for example endothelin-converting enzyme, may contribute to amyloid catabolism and may also play a role in neuroprotection Another metalloproteinase, insulysin (insulin-degrading enzyme) has also been advocated as an amyloid-degrading enzyme and may contribute more generally to metabolism of amyloid-forming peptides Other candidate enzymes proposed include angiotensin-converting enzyme, some matrix metalloproteinases, plasmin and, indirectly, thimet oligopeptidase (endopeptidase-2415) This review critically evaluates the evidence relating to proteinases implicated in amyloid catabolism Therapeutic strategies aimed at promoting Aβ degradation may provide a novel approach to the therapy of Alzheimer's disease

Abstract: The steady state concentration of the Alzheimer's amyloid-beta peptide in the brain represents a balance between its biosynthesis from the transmembrane amyloid precursor protein (APP), its oligomerisation into neurotoxic and stable species and its degradation by a variety of amyloid-degrading enzymes, principally metallopeptidases. These include, among others, neprilysin (NEP) and its homologue endothelin-converting enzyme (ECE), insulysin (IDE), angiotensin-converting enzyme (ACE) and matrix metalloproteinase-9 (MMP-9). In addition, the serine proteinase, plasmin, may participate in extracellular metabolism of the amyloid peptide under regulation of the plasminogen-activator inhibitor. These various amyloid-degrading enzymes have distinct subcellular localizations, and differential responses to aging, oxidative stress and pharmacological agents and their upregulation may provide a novel and viable therapeutic strategy for prevention and treatment of Alzheimer's disease. Potential approaches to manipulate expression levels of the key amyloid-degrading enzymes are highlighted.

Abstract: Insulysin (EC. 3.4.22.11) has been implicated in the clearance of beta amyloid peptides through hydrolytic cleavage. To further study the action of insulysin on Abeta peptides recombinant rat insulysin was used. Cleavage of both Abeta(1-40) and Abeta(1-42) by the recombinant enzyme was shown to initially occur at the His(13)-His(14), His(14)-Gln(15), and Phe(19)-Phe(20) bonds. This was followed by a slower cleavage at the Lys(28)-Gly(29), Val(18)-Phe(19), and Phe(20)-Ala(21) positions. None of the products appeared to be further metabolized by insulysin. Using a rat cortical cell system, the action of insulysin on Abeta(1-40) and Abeta(1-42) was shown to eliminate the neurotoxic effects of these peptides. Insulysin was further shown to prevent the deposition of Abeta(1-40) onto a synthetic amyloid. Taken together these results suggest that the use of insulysin to hydrolyze Abeta peptides represents an alternative gene therapeutic approach to the treatment of Alzheimer's disease.

Abstract: Insulysin (IDE) and neprilysin (NEP) were found to be inactivated by oxidation with hydrogen peroxide, an iron−ascorbate oxidation system, and by treatment with 2,2‘-azobis(2-amidinopropane) dihydrochloride (AAPH). In each case reaction led to the introduction of protein carbonyl groups as judged by reaction with 2,4-dintrophenylhydrazine. IDE was inactivated by reaction with 4-hydroxy-2-nonenal (HNE) with the concomitant formation of protein adducts. NEP was not inactivated to a significant extent by HNE, but some HNE-adduct formation did occur. Prior reaction with hydrogen peroxide or AAPH led to enhanced formation of HNE adducts. Treatment of IDE with AAHP or hydrogen peroxide increased its susceptibility to proteolysis, while treatment of NEP with iron/ascorbate or hydrogen peroxide increased its susceptibility to proteolysis. Since IDE and NEP play a prominent role in the clearance of amyloid β peptides, their oxidative inactivation and enhanced proteolysis can contribute to the onset and/or progress...