Characterization of alpha-casozepine, a tryptic peptide from bovine alpha(s1)-casein with benzodiazepine-like activity.

Abstract

Caseins are a known source of biologically active peptides. In this study, we have shown evidence of a novel anxiolytic activity in a tryptic hydrolysate of bovine α s1-casein. Injection of 3 mg/kg of this hydrolysate significantly reduced the epileptic symptoms caused by pentylenetetrazole in rats. Anxiety reduction was also observed when the hydrolysate was tested in the elevated plus-maze and in the conditioned defensive burying rat models. Peptides isolated from the hydrolysate were examined for their affinity for the γ-amino-butyric acid (GABA) type A receptor. Only one peptide, named α -casozepine, corresponding to the 91–100 fragment from bovine α s1-casein, expressed affinity for GABA A receptor. In vitro, the peptide had 10,000 less affinity for the benzodiazepine site of the GABA A than did diazepam. However, in the conditioned defensive burying paradigm it was 10-fold more efficient than diazepam. The difference observed between the in vitro and in vivo activity of α -casozepine could not been explained by an action via the peripheral-type benzodiazepine receptor; α -casozepine had no affinity for this receptor. The α -casozepine amino acid sequence could be related to the carboxyterminal sequence of the polypeptide diazepam binding inhibitor, an endogenous ligand of the central GABAA and peripheral-type benzodiazepine receptors.