Study of new methodologies for cathepsin D assays in the search for inhibitors

Abstract

Cathepsin D is an aspartyl endopeptidase involved in many pathological processes when overexpressed. In addition, it is responsible for degradation of hemoglobin ingested by parasites of schistosomiasis. For these reasons cathepsin D is considered an important target for chemotherapeutic intervention. The assays commonly performed to evaluate the inhibition of this enzyme monitor reaction products generated from the cleavage of fluorogenic peptide substrates or human hemoglobin in the presence of inhibitors that may exhibit autofluorescence/absorbance at the same wavelength used. Considering this problem, this paper presents the development and application of four methodologies for cathepsin D assays. In two methodologies the assays were performed in solution, and in one of them was used isolated bovine cathepsin D, and the other employed an extract of proteins taken from Schistosoma mansoni adult worms. A third assay was developed to evaluate inhibitors by means of a CatD-IMER bioreactor coupled to a multidimensional system in which it is possible to monitor the immobilized enzyme activity directly by quantifying the product formed. Finally, the last methodology was carried out by immobilizing the substrate human hemoglobin in the quartz crystal. The hydrolysis of hemoglobin by cathepsin D was evaluated by using a quartz crystal microbalance technique, a method that monitor the enzyme activity by mass variations. For the enzymatic assays, twenty plant extracts were evaluated, which led to the isolation and identification of the alkaloid evolitrine, the compound 4-hydroxy-3-methoxycinnamaldehyde and the flavonoids orientin and isovitexina. It were also tested 31 pure compounds, among them, the substance (z)-2-(pentadec-5-enyl)benzene-1,4-diol, which showed significant activity both against the isolated enzyme as the protein extract of S. mansoni. Finally, recombinant cathepsin D from S. mansoni was cloned and expressed using E. coli system, and in vitro studies of isolated natural product compounds showed excellent results regarding the limonoid cedrelona against somules and adult worms of S. mansoni. (AU)