Activation of N-methyl-D-aspartate receptor glycine site temporally ameliorates neuropsychiatric symptoms of Parkinson's disease with dementia

Glycine-gated extrasynaptic NMDARs activated during glutamate spillover drive burst firing in nigral dopamine neurons

Burst firing in substantia nigra pars compacta dopamine neurons is a critical biomarker temporally associated to movement initiation. This phasic change is generated by the tonic activation of NMDARs but the respective role of synaptic versus extrasynaptic NMDARs in the ignition of a burst and what is their level of activation remains unknown. Using ex vivo electrophysiological recordings from adolescent rats, we demonstrate that extrasynaptic NMDARs are the primary driver of burst firing. This pool of receptors is recruited during intense synaptic activity via spillover of glutamate and require the binding of NMDAR co-agonist glycine for full activation. Basal synaptic transmission activating only synaptic NMDARs with the support of D-serine is insufficient to generate a burst. Notably, both synaptic and extrasynaptic NMDARs share the same subunit composition but are regulated by distinct co-agonists. Location of NMDARs and regionalization of co-agonists but not NMDAR subunit composition underly burst generation and may serve as a guideline in understanding the physiological role of dopamine in signaling movement.

Plasma and urinary metabolomic signatures differentiate genetic and idiopathic Parkinson's disease

Parkinson's disease (PD) is marked by alpha-synuclein accumulation and progressive dopaminergic neuron loss. Using Nuclear Magnetic Resonance (NMR)-based metabolomics, we uncovered metabolic disturbances in idiopathic PD (iPD) and PD linked to LRRK2, GBA1, and PRKN variants in a Brazilian ethnically diverse cohort, free of comorbidities, in comparison to healthy, age-matched controls. In plasma, significant PD-associated metabolites included histidine, acetate, acetoacetate, glutamine, glucose, lipids and lipoproteins, N-acetyl-glycoproteins, and sarcosine. Urine samples revealed alterations in creatine, creatinine, L-asparagine, trimethylamine, 3-beta-hydroxybutyrate, isovaleric acid, glutamine, urea, glycine, choline, arginine, and cysteine in association with PD. Notably, creatine, creatinine, acetate, glucose, and histidine showed pathway influences from LRRK2, GBA1, and PRKN variants. Enrichment analyses highlighted disruptions in glyoxylate and dicarboxylate metabolism (plasma) as well as serine, threonine, and glycine metabolism (urine). Additionally, a metabolite-gene-disease interaction network identified 15 genes associated with PD that interact with key metabolites, highlighting MAPT, SNCA, RERE, and KCNN3 as key players in both plasmaandurine. NMR in saliva samples did not show significant differences between PD groups and controls. Our findings underscore PD-associated metabolites, particularly related to arginine metabolism, the urea cycle, glutamate metabolism, glucose metabolism, and gut microbiota. These pathways and gene interactions may serve as potential biomarkers for PD diagnosis and precision medicine strategies.

Metabolomic and immune alterations in long COVID patients with chronic fatigue syndrome

Introduction

A group of SARS-CoV-2 infected individuals present lingering symptoms, defined as long COVID (LC), that may last months or years post the onset of acute disease. A portion of LC patients have symptoms similar to myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS), which results in a substantial reduction in their quality of life. A better understanding of the pathophysiology of LC, in particular, ME/CFS is urgently needed.

Methods

We identified and studied metabolites and soluble biomarkers in plasma from LC individuals mainly exhibiting ME/CFS compared to age-sex-matched recovered individuals (R) without LC, acute COVID-19 patients (A), and to SARS-CoV-2 unexposed healthy individuals (HC).

Results

Through these analyses, we identified alterations in several metabolomic pathways in LC vs other groups. Plasma metabolomics analysis showed that LC differed from the R and HC groups. Of note, the R group also exhibited a different metabolomic profile than HC. Moreover, we observed a significant elevation in the plasma pro-inflammatory biomarkers (e.g. IL-1α, IL-6, TNF-α, Flt-1, and sCD14) but the reduction in ATP in LC patients. Our results demonstrate that LC patients exhibit persistent metabolomic abnormalities 12 months after the acute COVID-19 disease. Of note, such metabolomic alterations can be observed in the R group 12 months after the acute disease. Hence, the metabolomic recovery period for infected individuals with SARS-CoV-2 might be long-lasting. In particular, we found a significant reduction in sarcosine and serine concentrations in LC patients, which was inversely correlated with depression, anxiety, and cognitive dysfunction scores.

Conclusion

Our study findings provide a comprehensive metabolomic knowledge base and other soluble biomarkers for a better understanding of the pathophysiology of LC and suggests sarcosine and serine supplementations might have potential therapeutic implications in LC patients. Finally, our study reveals that LC disproportionally affects females more than males, as evidenced by nearly 70% of our LC patients being female.

Systematic review of pharmacological interventions for people with Lewy body dementia

OBJECTIVE

Lewy body dementia (LBD) is the second most common neurodegenerative dementia, and it causes earlier mortality and more morbidity than Alzheimer's disease. Reviewing current evidence on its pharmacological management is essential for developing evidence-based clinical guidelines, and for improving the quality of its clinical care. Hence, we systematically reviewed all studies that investigated the efficacy of any medication for managing various symptoms of LBD.

METHOD

We identified eligible studies by searching 15 databases comprehensively. We completed quality assessment, extracted relevant data, and performed GRADE assessment of available evidence. We conducted meta-analyses when appropriate (PROSPERO:CRD42020182166).

RESULTS

We screened 18,884 papers and included 135 studies. Our meta-analyses confirmed level-1 evidence for Donepezil's efficacy of managing cognitive symptoms of dementia with Lewy bodies (DLB) (SMD = 0.63; p < 0.001) and Parkinson's Disease Dementia (PDD) (SMD = 0.43; p < 0.01), and managing hallucinations in DLB (SMD=-0.52; p = 0.02). Rivastigmine and Memantine have level-2 evidence for managing cognitive and neuropsychiatric symptoms of DLB. Olanzapine and Yokukansan have similar evidence for managing DLB neuropsychiatric symptoms. Level-2 evidence support the efficacy of Rivastigmine and Galantamine for managing cognitive and neuropsychiatric symptoms of PDD.

CONCLUSION

We list evidence-based recommendations for the pharmacological management of DLB and PDD, and propose specific clinical guidelines for improving their clinical management.

Supplemental data for this article can be accessed online at https://doi.org/10.1080/13607863.2022.2032601 .

Race and Ethnicity in Lewy Body Dementia: A Narrative Review

Lewy body dementia is the third most common and costliest type of dementia. It is an umbrella term for dementia with Lewy bodies and Parkinson's disease dementia, both of which place a substantial burden on the person and society. Recent findings outline ethnoracial differences in dementia risk. Delayed and misdiagnosis across ethnoracial groups contribute to higher levels of burden. In this context, we aimed to summarize current knowledge, gaps, and unmet needs relating to race and ethnicity in Lewy body dementia. In this narrative review, we provide an overview of studies on Lewy body dementia focusing on differences across ethnoracial groups and outline several recommendations for future studies. The majority of the findings comparing different ethnoracial groups were from North American sites. There were no differences in clinical prevalence and progression across ethnoracial groups. Compared to people identifying as non-Hispanic White, co-pathologies were more common and clinical diagnostic accuracy was lower for people identifying as Black. Co-morbidities (e.g., diabetes, hypertension) were more common and medication use rates (e.g., antidepressants, antiparkinsonian agents) were lower for people identifying as Black or Hispanic compared to people identifying as White. More than 90% of clinical trial participants identified as non-Hispanic White. Despite increasing efforts to overcome disparities in Alzheimer's disease and related dementias, inclusion of individuals from minoritized communities in Lewy body dementia studies continues to be limited and the findings are inconclusive. Representation of diverse populations is crucial to improve the diagnostic and therapeutic efforts in Lewy body dementia.

Emerging role of psychosis in Parkinson's disease: From clinical relevance to molecular mechanisms

Parkinson's disease (PD) is the second most common neurodegenerative disease. Psychosis is one of the common psychiatric presentations in the natural course of PD. PD psychosis is an important non-motor symptom, which is strongly correlated with a poor prognosis. Increasing attention is being given to PD psychosis. In this opinion review, we summarized and analyzed the identification, screening, epidemiology, mechanisms, risk factors, and therapeutic approaches of PD psychosis based on the current clinical evidence. PD psychosis tends to have a negative effect on patients' quality of life and increases the burden of family caregiving. Screening and identification in the early stage of disease is crucial for establishing tailored therapeutic strategies and predicting the long-term outcome. Development of PD psychosis is believed to involve a combination of exogenous and endogenous mechanisms including imbalance of neurotransmitters, structural and network changes, genetic profiles, cognitive impairment, and antiparkinsonian medications. The therapeutic strategy for PD psychosis includes reducing or ceasing the use of dopaminergic drug, antipsychotics, cholinesterase inhibitors, and non-pharmacological interventions. Ongoing clinical trials are expected to provide new insights for tailoring therapy for PD psychosis. Future research based on novel biomarkers and genetic factors may help inform individualized therapeutic strategies.

Curcumin-driven reprogramming of the gut microbiota and metabolome ameliorates motor deficits and neuroinflammation in a mouse model of Parkinson's disease

Background

Parkinson's disease (PD) is a common neurodegenerative disorder, accompanied by motor deficits as well as gastrointestinal dysfunctions. Recent studies have proved that the disturbance of gut microbiota and metabolism contributes to the pathogenesis of PD; however, the mechanisms underlying these effects have yet to be elucidated. Curcumin (CUR) has been reported to provide neuroprotective effects on neurological disorders and modulate the gut flora in intestinal-related diseases. Therefore, it is of significant interest to investigate whether CUR could exert a protective effect on PD and whether the effect of CUR is dependent on the intestinal flora and subsequent changes in metabolites.

Methods

In this study, we investigated the neuroprotective effects of CUR on a mouse model of PD induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). 16S rRNA sequencing was performed to explore the profile of the gut microbiota among controls, MPTP-treated mice and CUR-treated mice. Then, antibiotic treatment (ABX) and fecal microbiota transplantation (FMT) experiments were conducted to examine the role of intestinal microbes on the protective effects of CUR in PD mice. Furthermore, ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS)-based metabolomics analysis was used to identify the landscape of the CUR-driven serum metabolome. Finally, Pearson's analysis was conducted to investigate correlations between the gut flora-metabolite axis and CUR-driven neuroprotection in PD.

Results

Our results showed that CUR intervention effectively improved motor deficits, glial cell activation, and the aggregation of α-synuclein (α-syn) in MPTP-treated mice. 16S rRNA sequencing showed elevated abundances of Muribaculaceae, Lactobacillaceae, Lachnospiraceae and Eggerthellaceae but depleted abundances of Aerococcaceae and Staphylococcaceae in CUR-treated mice when compared with MPTP mice. ABX and FMT experiments further confirmed that the gut microbiota was required for CUR-induced protection in PD mice. Serum metabolomics analysis showed that CUR notably upregulated the levels of tyrosine, methionine, sarcosine and creatine. Importantly, strong correlations were identified among crucial taxa (Aerococcaceae, Staphylococcaceae, Muribaculaceae, Lactobacillaceae, Lachnospiraceae and Eggerthellaceae), pivotal metabolites (tyrosine, methionine, sarcosine and creatine) and the motor function and pathological results of mice. CUR treatment led to a rapid increase in the brain levels of tyrosine and levodopa (dopa) these changes were related to the abundances of Lactobacillaceae and Aerococcaceae.

Conclusions

CUR exerts a protective effect on the progression of PD by modulating the gut microbiota-metabolite axis. Lactobacillaceae and Aerococcaceae, along with key metabolites such as tyrosine and dopa play a dominant role in CUR-associated neuroprotection in PD mice. Our findings offer unique insights into the pathogenesis and potential treatment of PD.

Effects of Subdiaphragmatic Vagotomy in the MPTP-induced Neurotoxicity in the Striatum and Colon of Mice

Objective

Gut—microbiota—brain axis plays a role in the pathogenesis of Parkinson’s disease (PD). The subdiaphragmatic vagus nerve serves as a major modulatory pathway between the gut microbiota and the brain. However, the role of subdiaphragmatic vagus nerve in PD pathogenesis are unknown. Here, we investigated the effects of subdiaphragmatic vagotomy (SDV) on the neurotoxicity in the mouse striatum and colon after administration of 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP).

Methods

Sham or SVD was performed. Subsequently, saline or MPTP (10 mg/kg × 3, 2-hour interval) was administered to mice. Western blot analysis of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the striatum and phosphorylated a-synuclein (p-a-Syn) in the colon was performed.

Results

Repeated administration of MPTP significantly caused reduction of TH and DAT in the striatum and increase of p-a-Syn in the colon of mice. However, SDV did not affect the reduction of TH and DAT in the striatum and increases in p-a-Syn in the colon after repeated MPTP administration.

Conclusion

These data suggest that subdiaphragmatic vagus nerve doses not play a role in the MPTP-induced neurotoxicity in the brain and colon.

Effect of N-methyl-D-aspartate receptor enhancing agents on cognition in dementia: an exploratory systematic review and meta-analysis of randomized controlled trials

Multiple N-methyl-D-aspartate (NMDA) receptor enhancing agents have had promising effects on cognition among patients with dementia. However, the results remain inconsistent. This exploratory meta-analysis investigated the effectiveness of NMDA receptor enhancing agents for cognitive function. PubMed, the Cochrane Central Register of Controlled Trials, and the Cochrane Database of Systematic Reviews were searched for randomized controlled trials (RCTs). Controlled trials assessing add-on NMDA receptor enhancing agent treatment in patients with dementia and using cognition rating scales were eligible and pooled using a random-effect model for comparisons. The standardized mean difference (SMD) was calculated in each study from the effect size; positive values indicated that NMDA receptor enhancing agent treatment improved cognitive function. Funnel plots and the I2 statistic were evaluated for statistical heterogeneity. Moderators were evaluated using meta-regression. We identified 14 RCTs with 2224 participants meeting the inclusion criteria. Add-on NMDA receptor enhancing agents had small positive significant effects on overall cognitive function among patients with dementia (SMD = 0.1002, 95% CI 0.0105-0.1900, P = 0.02860). Subgroup meta-analysis showed patients with Alzheimer's Disease and trials using the Alzheimer Disease Assessment Scale-cognitive subscale as the primary outcome had small positive significant effects (SMD = 0.1042, 95% CI 0.0076-0.2007, P = 0.03451; SMD = 0.1267, 95% CI 0.0145-0.2388, P = 0.2686). This exploratory meta-analysis showed a very small, positive, and significant effect on overall cognition function in patients with dementia. Studies with larger samples are needed to evaluate different cognitive domains and phases of dementia.

Effect of the glycine transporter 1 inhibitor ALX-5407 on dyskinesia, psychosis-like behaviours and parkinsonism in the MPTP-lesioned marmoset

Dyskinesia and psychosis are complications encountered in advanced Parkinson's disease (PD) following long-term therapy with L-3,4-dihydroxyphenylalanine (L-DOPA). Disturbances in the glutamatergic system have been associated with both dyskinesia and psychosis, making glutamatergic modulation a potential therapeutic approach for these. Treatments thus far have sought to dampen glutamatergic transmission, for example through blockade of N-methyl-D-aspartate (NMDA) receptors or modulation of metabotropic glutamate receptors 5. In contrast, activation of the glycine-binding site on NMDA receptors is required for their physiological response. Here, we investigated whether indirectly enhancing glutamatergic transmission through inhibition of glycine re-uptake would be efficacious in diminishing both dyskinesia and psychosis-like behaviours (PLBs) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. Six marmosets were rendered parkinsonian by MPTP injection. Following repeated administration of L-DOPA to induce dyskinesia and PLBs, they underwent acute challenges of the glycine transporter 1 (GlyT₁) inhibitor ALX-5407 (0.01, 0.1 and 1 mg/kg) or vehicle, in combination with L-DOPA, after which the severity of dyskinesia, PLBs and parkinsonian disability was evaluated. In combination with L-DOPA, ALX-5407 0.1 and 1 mg/kg significantly reduced the severity of dyskinesia, by 51% and 41% (both P < 0.001), when compared to vehicle. ALX-5407 0.01, 0.1 and 1 mg/kg also decreased the severity of global PLBs, by 25%, 51% and 38% (all P < 0.001), when compared to vehicle. The benefits on dyskinesia and PLBs were achieved without compromising the therapeutic effect of L-DOPA on parkinsonism. Our results suggest that GlyT₁ inhibition may be a novel strategy to attenuate dyskinesia and PLBs in PD, without interfering with L-DOPA anti-parkinsonian action.

Targeted metabolomics study of early pathological features in hippocampus of triple transgenic Alzheimer's disease male mice

Alzheimer's disease (AD) is a serious neurodegenerative disease in people of age 65 or above. The detailed etiology and pathogenesis of AD have not been elucidated yet. In this study, the hippocampi of 2- and 6-month-old triple transgenic Alzheimer's disease male mice and age-sex-matched wild-type (WT) mice were analyzed by using targeted metabolomics approach. Compared with WT mice, 24 and 60 metabolites were found with significant differences in 2- and 6-month-old AD mice. Among these, 14 metabolites were found common while 10 metabolites showed consistent variable trends in both groups. These differential metabolites are found associated with amino acid, lipid, vitamin, nucleotide-related base, neurotransmitter and energy metabolisms, and oxidative stress. The results suggest that these differential metabolites might play a critical role in AD pathophysiology, and may serve as potential biomarkers for AD. Moreover, the results highlight the involvement of abnormal purine, pyrimidine, arginine, and proline metabolism, along with glycerophospholipid metabolism in early pathology of AD. For the first time, several differential metabolites are found to be associated with AD in this study. Targeted metabolomics can be used for rapid and accurate quantitative analysis of specific target metabolites associated with AD.

Betaine supplementation is associated with the resilience in mice after chronic social defeat stress: a role of brain-gut-microbiota axis

BACKGROUND

The brain-gut-microbiota axis plays a role in the pathogenesis of stress-related psychiatric disorders; however, its role in the resilience versus susceptibility after stress remains unclear. Dietary nutrient betaine is suggested to affect the gut microbiome. Here, we examined whether betaine supplementation can affect anhedonia-like phenotype in mice subjected to chronic social defeat stress (CSDS).

METHODS

CSDS was performed during betaine supplementation. Sucrose preference test and 16S rRNA analysis of fecal samples were performed.

RESULTS

CSDS did not produce an anhedonia-like phenotype in the betaine-treated mice, but did induce an anhedonia-like phenotype in water-treated mice. Furthermore, CSDS treatment did not alter the plasma levels of interleukin-6 (IL-6) of betaine-treated mice whereas CSDS caused higher plasma levels of IL-6 in water-treated mice. Betaine supplementation ameliorated the abnormal diversity and composition of the microbiota in the host gut after CSDS. At the genus level, CSDS caused marked increases in the several bacteria of water-treated mice, but not betaine-treated mice. CSDS increased levels of short-chain fatty acids (i.e., succinic acid and acetic acid) in feces from water-treated mice, but not betaine-treated mice. Interestingly, there are positive correlations between short-chain fatty acids (i.e., succinic acid, acetic acid, butyric acid) and several bacteria among the groups.

LIMITATIONS

Specific microbiome were not determined.

CONCLUSIONS

These findings suggest that betaine supplementation contributed to resilience to anhedonia in mice subjected to CSDS through anti-inflammation action. Therefore, it is likely that betaine could be a prophylactic nutrient to prevent stress-related psychiatric disorders.

Impairments in face discrimination and emotion recognition are related to aging and cognitive dysfunctions in Parkinson's disease with dementia

Patients with Parkinson's disease (PD) suffer from motor and non-motor symptoms; 40% would develop dementia (PD-D). Impaired face and emotion processing in PD has been reported; however, the deficits of face processing in PD-D remain unclear. We investigated three essential aspects of face processing capacity in PD-D, and the associations between cognitive, neuropsychiatric assessments and task performances. Twenty-four PD-D patients (mean age: 74.0 ± 5.55) and eighteen age-matched healthy controls (HC) (mean age: 71.0 ± 6.20) received three computerized tasks, morphing-face discrimination, dynamic facial emotion recognition, and expression imitation. Compared to HC, PD-D patients had lower sensitivity (d') and greater neural internal noises in discriminating faces; responded slower and had difficulties with negative emotions; imitated some expressions but with lower strength. Correlation analyses revealed that patients with advancing age, slow mentation, and poor cognition (but not motor symptoms) showed stronger deterioration in face perception. Importantly, these correlations were absent in the age-matched HC. The present study is among the first few examined face processing in patients with PD-D, and found consistent deficits correlated with advancing age and slow mentation. We propose that face discrimination task could be included as a potential test for the early detection of dementia in PD.

Identification of a Circulating Amino Acid Signature in Frail Older Persons with Type 2 Diabetes Mellitus: Results from the Metabofrail Study

Diabetes and frailty are highly prevalent conditions that impact the health status of older adults. Perturbations in protein/amino acid metabolism are associated with both functional impairment and type 2 diabetes mellitus (T2DM). In the present study, we compared the concentrations of a panel of circulating 37 amino acids and derivatives between frail/pre-frail older adults with T2DM and robust non-diabetic controls. Sixty-six functionally impaired older persons aged 70+ with T2DM and 30 age and sex-matched controls were included in the analysis. We applied a partial least squares-discriminant analysis (PLS-DA)-based analytical strategy to characterize the metabotype of study participants. The optimal complexity of the PLS-DA model was found to be two latent variables. The proportion of correct classification was 94.1 ± 1.9% for frail/pre-frail persons with T2DM and 100% for control participants. Functionally impaired older persons with T2DM showed higher levels of 3-methyl histidine, alanine, arginine, glutamic acid, ethanolamine sarcosine, and tryptophan. Control participants had higher levels of ornithine and taurine. These findings indicate that a specific profile of amino acids and derivatives characterizes pre-frail/frail older persons with T2DM. The dissection of these pathways may provide novel insights into the metabolic perturbations involved in the disabling cascade in older persons with T2DM.

The levels of the NMDA receptor co-agonist D-serine are reduced in the substantia nigra of MPTP-lesioned macaques and in the cerebrospinal fluid of Parkinson's disease patients

Dysfunction of NMDA receptor (NMDAR)-mediated transmission is supposed to contribute to the motor and non-motor symptoms of Parkinson’s Disease (PD), and to L-DOPA-induced dyskinesia. Besides the main agonist L-glutamate, two other amino acids in the atypical D-configuration, D-serine and D-aspartate, activate NMDARs. In the present work, we investigated the effect of dopamine depletion on D-amino acids metabolism in the brain of MPTP-lesioned Macaca mulatta, and in the serum and cerebrospinal fluid of PD patients. We found that MPTP treatment increases D-aspartate and D-serine in the monkey putamen while L-DOPA rescues both D-amino acids levels. Conversely, dopaminergic denervation is associated with selective D-serine reduction in the substantia nigra. Such decrease suggests that the beneficial effect of D-serine adjuvant therapy previously reported in PD patients may derive from the normalization of endogenous D-serine levels and consequent improvement of nigrostriatal hypoglutamatergic transmission at glycine binding site. We also found reduced D-serine concentration in the cerebrospinal fluid of L-DOPA-free PD patients. These results further confirm the existence of deep interaction between dopaminergic and glutamatergic neurotransmission in PD and disclose a possible direct influence of D-amino acids variations in the changes of NMDAR transmission occurring under dopamine denervation and L-DOPA therapy.

The glycine site of NMDA receptors: A target for cognitive enhancement in psychiatric disorders

Cognitive dysfunction is a principal determinant of functional impairment in major depressive disorder (MDD) and often persists during periods of euthymia. Abnormalities in the glutamate system, particularly in N-methyl-d-aspartate receptors (NMDARs) activity, have been shown to contribute to both mood and cognitive symptoms in MDD. The current narrative review aims to evaluate the potential pro-cognitive effects of targeting the glycine site of NMDARs in the treatment of psychiatric disorders, with a special focus on how these results may apply to MDD. Literature databases were searched from inception to May 2018 for relevant pre-clinical and clinical studies evaluating antidepressant and pro-cognitive effects of NMDAR glycine site modulators in both MDD and non-MDD samples. Six glycine site modulators with pro-cognitive and antidepressant properties were identified: d-serine (co-agonist), d-cycloserine (partial agonist), d-alanine (co-agonist), glycine (agonist), sarcosine (co-agonist) and rapastinel (partial agonist). Preclinical animal studies demonstrated improved neuroplasticity and pro-cognitive effects with these agents. Numerous proof-of-concept clinical trials demonstrated pro-cognitive and antidepressant effects trans-diagnostically (e.g., in healthy participants, MDD, schizophrenia, anxiety disorders, major neurocognitive disorders). The generalizability of these clinical studies was limited by the small sample sizes and the paucity of studies directly evaluating cognitive effects in MDD samples, as most clinical trials were in non-MDD samples. Taken together, preliminary results suggest that the glycine site of NMDARs is a promising target to ameliorate symptoms of depression and cognitive dysfunction. Additional rigorously designed clinical studies are required to determine the cognitive effects of these agents in MDD.

The Role of N-Methyl-D-Aspartate Receptor Neurotransmission and Precision Medicine in Behavioral and Psychological Symptoms of Dementia

While the world's population is aging, the prevalence of dementia and the associated behavioral and psychological symptoms of dementia (BPSD) rises rapidly. BPSD are associated with worsening of cognitive function and poorer prognosis. No pharmacological treatment has been approved to be beneficial for BPSD to date. Dysfunction of the N-methyl-D-aspartate receptor (NMDAR)-related neurotransmission leads to cognitive impairment and behavioral changes, both of which are core symptoms of BPSD. Memantine, an NMDAR partial antagonist, is used to treat moderate to severe Alzheimer's disease (AD). On the other hand, a D-amino acid oxidase inhibitor improved early-phase AD. Whether to enhance or to attenuate the NMDAR may depend on the phases of dementia. It will be valuable to develop biomarkers indicating the activity of NMDAR, particularly in BPSD. In addition, recent reports suggest that gender difference exists in the treatment of dementia. Selecting subpopulations of patients with BPSD who are prone to improvement with treatment would be important. We reviewed literatures regarding the treatment of BPSD, focusing on the NMDAR-related modulation and precision medicine. Future studies examining the NMDAR modulators with the aid of potential biomarkers to tailor the treatment for individualized patients with BPSD are warranted.

Novel Treatment Opportunities Against Cognitive Impairment in Parkinson's Disease with an Emphasis on Diabetes-Related Pathways

Cognitive impairment is highly prevalent in patients with Parkinson's disease (PD) and causes adverse health outcomes. Novel procognitive therapies are needed to address this unmet need. It is now established that there is an increased risk of dementia in patients with type 2 diabetes mellitus (T2DM) and, moreover, T2DM and PD may have common underlying biological mechanisms. As such, T2DM medications are emerging as potential therapies in the context of PD dementia (PDD). In this review, we provide an update on pathophysiological mechanisms underlying cognitive impairments and PDD, focusing on diabetes-related pathways. Finally, we have conducted a review of ongoing clinical trials in PD patients with dementia, highlighting the multiple pharmacological mechanisms that are targeted to achieve cognitive enhancement.

Sarcosine Is Uniquely Modulated by Aging and Dietary Restriction in Rodents and Humans

A hallmark of aging is a decline in metabolic homeostasis, which is attenuated by dietary restriction (DR). However, the interaction of aging and DR with the metabolome is not well understood. We report that DR is a stronger modulator of the rat metabolome than age in plasma and tissues. A comparative metabolomic screen in rodents and humans identified circulating sarcosine as being similarly reduced with aging and increased by DR, while sarcosine is also elevated in long-lived Ames dwarf mice. Pathway analysis in aged sarcosine-replete rats identify this biogenic amine as an integral node in the metabolome network. Finally, we show that sarcosine can activate autophagy in cultured cells and enhances autophagic flux in vivo, suggesting a potential role in autophagy induction by DR. Thus, these data identify circulating sarcosine as a biomarker of aging and DR in mammalians and may contribute to age-related alterations in the metabolome and in proteostasis.

Medications Used for Cognitive Enhancement in Patients With Schizophrenia, Bipolar Disorder, Alzheimer's Disease, and Parkinson's Disease

BACKGROUND/AIMS

Cognitive impairment, which frequently occurs in patients with schizophrenia, bipolar disorder, Alzheimer's disease, and Parkinson's disease, has a significant impact on the daily lives of both patients and their family. Furthermore, since the medications used for cognitive enhancement have limited efficacy, the issue of cognitive enhancement still remains a clinically unsolved challenge.

SAMPLING AND METHODS

We reviewed the clinical studies (published between 2007 and 2017) that focused on the efficacy of medications used for enhancing cognition in patients with schizophrenia, bipolar disorder, Alzheimer's disease, and Parkinson's disease.

RESULTS

Acetylcholinesterase inhibitors and memantine are the standard treatments for Alzheimer's disease and Parkinson's disease. Some studies have reported selective cognitive improvement in patients with schizophrenia following galantamine treatment. Newer antipsychotics, including paliperidone, lurasidone, aripiprazole, ziprasidone, and BL-1020, have also been reported to exert cognitive benefits in patients with schizophrenia. Dopaminergic medications were found to improve language function in patients with Parkinson's disease. However, no beneficial effects on cognitive function were observed with dopamine agonists in patients with schizophrenia. The efficacies of nicotine and its receptor modulators in cognitive improvement remain controversial, with the majority of studies showing that varenicline significantly improved the cognitive function in schizophrenic patients. Several studies have reported that N-methyl-d-aspartate glutamate receptor (NMDAR) enhancers improved the cognitive function in patients with chronic schizophrenia. NMDAR enhancers might also have cognitive benefits in patients with Alzheimer's disease or Parkinson's disease. Raloxifene, a selective estrogen receptor modulator, has also been demonstrated to have beneficial effects on attention, processing speed, and memory in female patients with schizophrenia.

CONCLUSION

Clinical trials with larger sample sizes evaluating comprehensive cognitive domains are warranted to examine the efficacy of medications in cognitive enhancement in patients with schizophrenia, bipolar disorder, Alzheimer's disease, and Parkinson's disease.

Variation in Placebo Effect Sizes in Clinical Trials of Oral Interventions for Management of the Behavioral and Psychological Symptoms of Dementia (BPSD): A Systematic Review and Meta-Analysis

Increasing placebo effect sizes over time have been reported in randomized controlled trials (RCTs) for outcomes related to psychiatric symptoms. The Neuropsychiatric Inventory (NPI) is a key outcome measure in clinical trials of the behavioral and psychological symptoms of dementia (BPSD). Accurate placebo effect size estimates for NPI are needed for sample size calculations in order to adequately power future studies. This study investigated variation in placebo effect sizes for NPI in RCTs testing oral interventions for BPSD. A search of PubMed was conducted in April 2016 for two-armed, double-blinded, placebo-controlled RCTs testing any oral intervention for management of BPSD using the NPI. Meta-analysis was conducted of baseline versus end of treatment placebo group data of included studies. Twenty-five RCTs published from 2000 to 2015 were included. Substantial variation in placebo effect sizes was detected. Participants in placebo groups showed greater improvements in recent studies compared with earlier studies. Subgroup analyses indicated robustness of this finding. From 2000 to 2008 there was no significant change in total NPI scores within placebo groups (12 studies; 1,056 participants), whereas from 2009 to 2015 there was significant improvement (mean difference: -2.68; 95% confidence interval: -4.38, -0.99; z = 3.10; p = 0.002, random effects; I² = 76%; 13 studies; 1,170 participants). This increase in NPI effect sizes in placebo groups has important implications for power calculations for future clinical trials of BPSD. Effect size estimates for NPI need to be based on more recent studies.

Assessment of a glycine uptake inhibitor in animal models of effort-related choice behavior: implications for motivational dysfunctions

RATIONALE

Motivated behavior can be characterized by a substantial exertion of effort, and organisms often make effort-related decisions based upon analyses of work-related response costs and reinforcement preference. Moreover, alterations in effort-based choice can be seen in people with major depression and schizophrenia. Effort-related decision making is studied using tasks offering choices between high effort options leading to highly valued reinforces vs low effort/low reward options. Interference with dopamine (DA) transmission by administration of the DA D2 family antagonist haloperidol biases behavior towards the lower effort option that can be obtained with minimal work, and previous research has shown that DA interacts with other transmitters, including adenosine and GABA, to regulate effort-based choice.

OBJECTIVES

The present studies focused upon the ability of the glycine transport inhibitor bitopertin to attenuate haloperidol-induced shifts in effort-related choice behavior.

METHODS

Effort-based choice in rats was assessed using the concurrent fixed ratio (FR) 5/chow feeding choice task and the T-maze barrier choice procedure.

RESULTS

Haloperidol shifted effort-based choice, biasing animals towards the low effort option in each task. Co-administration of bitopertin (1.0-10.0 mg/kg) significantly attenuated haloperidol-induced shifts in choice behavior, but the same doses of bitopertin had no effect when administered alone.

CONCLUSIONS

These results indicated that elevation of extracellular glycine via inhibition of glycine uptake was able to reverse the effects of D2 antagonism. Increases in extracellular glycine, possibly through actions on the glycine allosteric site on the NMDA receptor, may be a useful strategy for treating motivational dysfunctions in humans.

Glycinergic signaling in the human nervous system: An overview of therapeutic drug targets and clinical effects

Glycine and related endogenous compounds (d-serine, d-alanine, sarcosine) serve critical roles in both excitatory and inhibitory neurotransmission and are influenced by a multitude of enzymes and transporters, including glycine transporter 1 and 2 (GlyT1 and GlyT2), d-amino acid oxidase (DAAO), serine racemase (SRR), alanine-serine-cysteine transporter 1 (Asc-1), and kynurenine aminotransferase (KAT). MEDLINE, Web of Science, and PsychINFO were searched for relevant human trials of compounds. Many studies utilizing exogenous administration of small molecule agonists of the glycineB site of n-methyl-d-aspartate receptor have been studied as have a growing number of glycine transporter type 1 (GlyT1) inhibitors. The clinical effects of these compounds are reviewed as are the potential effects of newer novel compounds.

Synthesis and Biological Evaluation of N-((1-(4-(Sulfonyl)piperazin-1-yl)cycloalkyl)methyl)benzamide Inhibitors of Glycine Transporter-1

We previously disclosed the discovery of rationally designed N-((1-(4-(propylsulfonyl)piperazin-1-yl)cycloalkyl)methyl)benzamide inhibitors of glycine transporter-1 (GlyT-1), represented by analogues 10 and 11. We describe herein further structure-activity relationship exploration of this series via an optimization strategy that primarily focused on the sulfonamide and benzamide appendages of the scaffold. These efforts led to the identification of advanced leads possessing a desirable balance of excellent in vitro GlyT-1 potency and selectivity, favorable ADME and in vitro pharmacological profiles, and suitable pharmacokinetic and safety characteristics. Representative analogue (+)-67 exhibited robust in vivo activity in the cerebral spinal fluid glycine biomarker model in both rodents and nonhuman primates. Furthermore, rodent microdialysis experiments also demonstrated that oral administration of (+)-67 significantly elevated extracellular glycine levels within the medial prefrontal cortex (mPFC).