Study of an octadecaneuropeptide derived from diazepam binding inhibitor (DBI): biological activity and presence in rat brain.

Abstract

An endogenous brain neuropeptide with 104 amino acid residues that modulates gamma-aminobutyric acid receptor function was termed DBI because it displaces diazepam from its specific brain binding sites. Tryptic digestion of DBI generates an octadecaneuropeptide (ODN) that is more potent than the parent compound in the displacement of specifically bound beta-[3H]carboline-3-carboxylate methyl ester [( 3H]BCCM) and in proconflict action (Vogel test in thirsty rats). The proconflict action of ODN is antagonized by the imidobenzodiazepinone Ro 15-1788, which is a specific antagonist of beta-carboline and benzodiazepine recognition sites. The ODN amino acid sequence is Gln-Ala-Thr-Val-Gly-Asp-Val-Asn-Thr-Asp-Arg-Pro-Gly-Leu-Leu-Asp-Leu-Lys. The pharmacological properties associated with this sequence were confirmed by comparing the activity of ODN generated from tryptic digestion of DBI with that of ODN obtained by synthesis. Amidation of the terminal lysine of ODN produces a peptide (ODN-NH2) devoid of pharmacological activity. Three peptides containing the COOH-terminal segment of ODN were synthesized. All these peptides [Arg-Pro-Gly-Leu-Leu-Asp-Leu-Lys (octapeptide), Pro-Gly-Leu-Leu-Asp-Leu-Lys (heptapeptide), and Gly-Leu-Leu-Asp-Leu-Lys (hexapeptide)] express the displacing and proconflict actions of ODN. In primary cultures of cerebellar granule cells of rat, DBI, ODN, octapeptide, heptapeptide, and hexapeptide preferentially displace [3H]BCCM over [3H]flunitrazepam; moreover, they displace bound [3H]BCCM completely but [3H]flunitrazepam only by 50%. These data suggest that ODN includes a specific ligand for the gamma-aminobutyric acid receptor regulatory site occupied by beta-carbolines. Using rabbit antibodies directed against the NH2-terminal portion of ODN, we detected ODN-like material in rat brain homogenates. However, whether this material is identical to the ODN generated by tryptic digestion of DBI remains to be established.

Pharmacological Characterization of the Receptor Mediating the Anorexigenic Action of the Octadecaneuropeptide: Evidence for an Endozepinergic Tone Regulating Food Intake

“…It is now clearly established that ODN can interact with CBR associated with the GABA A receptor (Ferrero et al, 1986;Tonon et al, 1989;Slobodyansky et al, 1990). In addition, it has been shown that several of the effects induced by ODN are mediated via a G-proteincoupled receptor.…”

“…All endozepines characterized so far derive from diazepam-binding inhibitor (DBI), an 86 amino-acid polypeptide precursor which has the potential to generate several biologically active fragments including the triakontatetraneuropeptide DBI 17-50 (TTN) and the octadecaneuropeptide DBI [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] (ODN) (Ferrero et al, 1986). The DBI gene is widely expressed in the central nervous system (Alho et al, 1988;Tong et al, 1991;Yanase et al, 2002).…”

Diazepam-binding inhibitor-derived peptides induce intracellular calcium changes and modulate human neutrophil function

“…Proteolytic cleavage of DBI results in the production of several biologically active fragments (collectively known as endozepines [2]) that are involved in the regulation of multiple processes, such as mitochondrial steroid biosynthesis in adrenocortical and Leydig cells [3,4], glucose-induced insulin secretion from pancreatic islets [5], and ␥-aminobutyric acid (GABA)-induced inhibition on pituitary melanotrope cells [6]. The biological actions of DBI-derived peptides have been ascribed mainly to their ability to bind central-type benzodiazepine receptors (cBRs) located on the GABA A receptor complex [see ref .…”

The endozepine ODN stimulates polyphosphoinositide metabolism in rat astrocytes

“…All endozepines derive from an 86 amino acid precursor polypeptide called diazepam-binding inhibitor (DBI) which generates, through proteolytic cleavage, several biologically active fragments, including the triakontatetraneuropeptide DBI [4][5][6].…”