PARG inhibitor (Satya Pharma Innovations)

PARG [poly(ADP-ribose) glycohydrolase] catalyses the hydrolysis of α(1″→2′) or α(1‴→2″) O-glycosidic linkages of ADP-ribose polymers to produce free ADP-ribose. We investigated possible mechanistic similarities between PARG and glycosidases, which also cleave O-glycosidic linkages. Glycosidases typically utilize two acidic residues for catalysis, thus we targeted acidic residues within a conserved region of bovine PARG that has been shown to contain an inhibitor-binding site. The targeted glutamate and aspartate residues were changed to asparagine in order to minimize structural alterations. Mutants were purified and assayed for catalytic activity, as well as binding, to an immobilized PARG inhibitor to determine ability to recognize substrate. Our investigation revealed residues essential for PARG catalytic activity. Two adjacent glutamic acid residues are found in the conserved sequence Gln755-Glu-Glu757, and a third residue found in the conserved sequence Val737-Asp-Phe-Ala-Asn741. Our functional characterization of PARG residues, along with recent identification of an inhibitor-binding residue Tyr796 and a glycine-rich region Gly745-Gly-Gly747 important for PARG function, allowed us to define a PARG ‘signature sequence’ [vDFA-X3-GGg-X6–8-vQEEIRF-X3-PE-X14-E-X12-YTGYa], which we used to identify putative PARG sequences across a range of organisms. Sequence alignments, along with our mapping of PARG functional residues, suggest the presence of a conserved catalytic domain of approx. 185 residues which spans residues 610–795 in bovine PARG.

Although the Defensive Burying paradigm has been used as a behavioral "model" for the study of anxiety and/or antianxiety agents, the effects of chronic treatment with antidepressant agents (i.e., "antipanic" agents) have not been examined in this paradigm. The present study examined the effects of two antianxiety treatments on this behavior: 1) acute treatment (30-minute pretreatment) with the benzodiazepine anxiolytic chlordiazepoxide and 2) chronic treatment (twice daily for 7-12 weeks) with the antipanic agents imipramine (IMI), desipramine (DMI) or pargyline (PARG). Prior to testing, female Sprague-Dawley rats were placed in a 40 x 30 x 40 cm Plexiglas chamber containing clay bedding material (5 cm deep) for 30-minute periods on each of four consecutive days. On the fifth day, a wire-wrapped prod was placed at one end of the chamber. Rats were placed in the chamber individually and a 3 mA shock was delivered upon contact with the prod. Defensive Burying behavior (i.e., the moving of bedding material toward or over the prod) was recorded for 15 minutes postshock. In a dose-dependent manner, acute treatment with chlordiazepoxide reduced the frequency of occurrence of burying behavior, increased the latency to initiation of burying, and decreased the duration of burying. In contrast, chronic treatment with IMI, DMI, or PARG failed to exhibit anxiolytic-like effects on any measure of Defensive Burying. These data suggest that the Defensive Burying paradigm may not be an "animal model" for the study of panic disorder and potential antipanic agents.