PREP and major depressive disorder: Additionally, some polyphenols are effective inhibitors of prolyl endopeptidases (PEP) [28,34,35,36], a family of enzymes that can hydrolyze hormones such as vasopressin, thyrotropin-releasing hormone, or substance P. Some researchers have suggested that PEPs may present a viable pharmacological target for treating various neurological conditions linked to abnormally high serum PEP activity, including Alzheimer’s disease, schizophrenia, and depression, as well as other disorders like anorexia and bulimia [37].