PREP (Prolyl Endopeptidase): PREP is an enzyme that reflects the activity of a serine protease involved in breaking down proline-containing peptides. It plays an important role in the metabolism of neuropeptides and peptide hormones, contributing to cognitive processes and the inflammatory response. Changes in PREP activity have been associated with neurological disorders, including Alzheimer's disease, highlighting its role in neurodegeneration and cognitive function.