D-serine Augmentation of Neuroplasticity

Schizophrenia (Sz) is a major public health problem associated with core cognitive deficits that are amongst the strongest predictors of impaired functional outcome. In addition, Sz patients show reduced cortical neuroplasticity, defined as reduced learning during training on exercises that place implicit, increasing demands on early auditory information processing. As improved auditory processing can facilitate gains in those cognitive processes that are more proximal to daily functioning (e.g., verbal memory, executive functioning), enhancing neuroplasticity for better auditory processing represents an unmet clinical need and a rate-limiting first step prior to remediating cognition and overall function. As supported by recently published data and review, the study proposes that localized N-methyl-D-aspartate-type glutamate receptor (NMDAR) dysfunction leads to impaired auditory neuroplasticity, which in turn leads to impaired cognition. Over recent years, NMDAR glycine site agonists have increasingly been shown to facilitate neuroplasticity in both Sz and healthy volunteers. D-serine is a NMDAR modulator that when combined with neuroplasticity-based auditory remediation, leads to highly significant, acute improvement in both auditory plasticity and the early auditory processing measures mismatch negativity (MMN) and theta intertrial coherence (theta). Both MMN and theta-ITC are sensitive measures of functional target engagement of both NMDAR agonism and auditory remediation. In a preliminary study, plasticity correlated with reading and working memory, suggesting plasticity improvements are predictive of functionally relevant outcomes. While D-serine appears to be efficacious for neuroplasticity enhancement and target engagement in a dose dependent manner, the optimal dose remains an open question, as does the ability of combined D-serine + neuroplasticity-based auditory remediation to produce sustained, functional improvement. This study utilizes the Early Stage Testing of Pharmacologic or Device-based Interventions for the Treatment of Mental Disorders (R61/R33): RFA-MH-17-702. The ultimate goal of this study is to enhance efficacy and efficiency of auditory cognitive remediation by augmenting with D-serine. This study will confirm target engagement, pharmacodynamics, functional relationships and the optimal dose (80 vs.100 vs. 120 mg/kg, IND: 122821) of D-serine treatment combined with 3 sessions of our auditory remediation program. As previously, D-serine will be given 30 minutes before sessions, allowing for auditory remediation during peak serum levels and a pharmacodynamic assessment. Successful completion is defined by ≥moderate effect size change in auditory plasticity, MMN and theta, plus a moderate effect size correlation with functionally relevant cognitive measures ("auditory cognition") without safety issues. Successful completion of this study will pave the way for a larger, definitive study pairing D-serine with auditory remediation or testing alternative dose intervals (1x vs. 2x week). In addition to testing a potentially viable treatment, this project will stimulate industry to utilize this methodology to assess the efficacy of novel NMDAR modulators, using D-serine as a "gold-standard."