The Behavioral and Neurochemical Effects of a Novel d-Amino Acid Oxidase Inhibitor Compound 8 [4H-Thieno [3,2-b]pyrrole-5-carboxylic Acid] and d-Serine

Abstract

Multiple studies indicate that N-methyl-D-aspartate (NMDA) receptor hypofunction underlies some of the deficits associated with schizophrenia. One approach for improving NMDA receptor function is to enhance occupancy of the glycine modulatory site on the NMDA receptor by increasing the availability of the endogenous coagonists D-serine. Here, we characterized a novel D-amino acid oxidase (DAAO) inhibitor, compound 8 [4H-thieno [3,2-b]pyrrole-5-carboxylic acid] and compared it with D-serine. Compound 8 is a moderately potent inhibitor of human (IC 50 , 145 nM) and rat (IC 50 , 114 nM) DAAO in vitro. In rats, compound 8 (200 mg/kg) decreased kidney DAAO activity by ϳ96% and brain DAAO activity by ϳ80%. This marked decrease in DAAO activity resulted in a significant (p Ͻ 0.001) elevation in both plasma (220% of control) and cerebrospinal fluid (CSF; 175% of control) D-serine concentration. However, compound 8 failed to significantly influence amphetamine-induced psychomotor activity, nucleus accumbens dopamine release, or an MK-801 (dizocilpine maleate)-induced deficit in novel object recognition in rats. In contrast, high doses of D-serine attenuated both amphetamine-induced psychomotor activity and dopamine release and also improved performance in novel object recognition. Behaviorally efficacious doses of D-serine (1280 mg/kg) increased CSF levels of D-serine 40-fold above that achieved by the maximal dose of compound 8. These findings demonstrate that pharmacological inhibition of DAAO significantly increases D-serine concentration in the periphery and central nervous system. However, acute inhibition of DAAO appears not to be sufficient to increase D-serine to concentrations required to produce antipsychotic and cognitive enhancing effects similar to those observed after administration of high doses of exogenous D-serine.

Effects of D-Amino Acid Oxidase Inhibitor on the Extracellular D-Alanine Levels and the Efficacy of D-Alanine on Dizocilpine-Induced Prepulse Inhibition Deficits in Mice

“…Adage's group reported a slight increase in D-serine levels in rat brain following intravenous administration of a pyrazole-3-carboxylate based DAAO inhibitor (AS057278) alone [39], indicating that this effect may be due to its ability to penetrate the blood-brain barrier. Furthermore, Smith et al [40] have developed the novel DAAO inhibitor 4H-thieno[3,2-b]pyrrole-5-carboxylic acid (IC 50 =145 nM for human, IC 50 =114 nM for rat). This compound failed to significantly influence amphetamine-induced psychomotor activity, nucleus accumbens dopamine release, or (+)-MK-801 (dizocilpine)-induced deficit in novel object recognition in rats, suggesting that acute inhibition of DAAO by this compound appears not to be sufficient to increase D-serine to concentrations required to produce antipsychotic and cognitive enhancing effects similar to those observed after administration of high doses of D-serine [40].…”

“…Furthermore, Smith et al [40] have developed the novel DAAO inhibitor 4H-thieno[3,2-b]pyrrole-5-carboxylic acid (IC 50 =145 nM for human, IC 50 =114 nM for rat). This compound failed to significantly influence amphetamine-induced psychomotor activity, nucleus accumbens dopamine release, or (+)-MK-801 (dizocilpine)-induced deficit in novel object recognition in rats, suggesting that acute inhibition of DAAO by this compound appears not to be sufficient to increase D-serine to concentrations required to produce antipsychotic and cognitive enhancing effects similar to those observed after administration of high doses of D-serine [40]. In contrast, there is no correlation between the distribution of DAAO and NMDA receptors in the brain [41,42].…”

Fluorimetric assay for D-amino acid oxidase activity in rat brain homogenate by using D-kynurenine as a substrate

“…Both MPC and Compound 8 (each 100 μM) could completely attenuate the DAAO activity ( Figure 6). It has been reported that the IC 50 value of Compound 8 is 114 nM (17), while that of MPC is 0.91 μM (12), indicating that Compound 8 is a more potent inhibitor of DAAO activity. However, the results from this study ( Figure 6) indicated that both specific inhibitors (100 μM) appropriately inhibited the DAAO activity.…”

“…To assess DAAO activity in rat brain tissues, the brain tissue homogenates were centrifuged as previously described (15,17), and the pellet fraction was then used as an enzyme source for the proposed assay. Increasing concentrations of D-KYN were added to the reactions to determine its optimum concentration as a substrate, which was set at the plateau level of 7.0 mM (Figure 2).…”

“…DAAO activity in a tissue homogenate is usually assessed by measuring the H 2 O 2 (11)(12)(13)(14) or α-keto acid that is generated after addition of a substrate, D-alanine, or D-proline (10,(15)(16)(17). Using the increased H 2 O 2 , an oxidative reaction that generates a colorimetric or fluorescent compound in the presence of a peroxidase is performed.…”