The aim of this study was to examine whether
anorexia and
bulimia nervosa are accompanied by lower serum activity of
prolyl endopeptidase (PEP;EC 3.4.21.26;
post-proline cleaving enzyme), a cytosolic
endopeptidase which cleaves
peptide bonds on the carboxyl side of
proline in
proteins of relatively small molecular mass. Substrates of PEP are, amongst others, neuroactive
peptides, such as
arginine vasopressin,
luteinizing hormone-releasing hormone,
thyrotropin releasing hormone,alpha-melanocyte secreting
hormone,
substance P,
oxytocin,
bradykinin,
neurotensin and
angiotensin (Ag) I and II. Serum PEP activity was measured in the serum of 18 normal women, 21
anorexia nervosa and 21
bulimia nervosa women by means of a fluoremetric method. The Bulimic Investigatory Test, Edinburgh (
BITE), the
Eating Disorder Inventory (EDI) and the Hamilton Depression Rating Scale (HDRS) were scored. Serum PEP activity was significantly lower in patients with
bulimia nervosa and
anorexia nervosa, irrespective of the restricted or binging subtype, than in normal controls. There were significant and inverse correlations between serum PEP activity and the HDRS and
BITE. In
anorectic patients, but not in normal or bulimic patients, there was a significant correlation between serum PEP and body mass index. In bulimic patients, but not in normal or
anorectic patients, there was a significant correlation between serum PEP and duration of illness. It is concluded that lowered serum PEP activity takes part in the pathophysiology of
anorexia and
bulimia nervosa. It is hypothesized that a combined dysregulation of PEP and neuroactive
peptides, which are substrates of PEP, could be an integral component of
eating disorders.