Supplementation of Antipsychotic Treatment with the Amino Acid Sarcosine Influences Proton Magnetic Resonance Spectroscopy Parameters in Left Frontal White Matter in Patients with Schizophrenia

Nutrition and schizophrenia: associations worthy of continued revaluation

BACKGROUND

Accumulating evidence have shown that diet and nutrition play significant roles in mental illness, such as depression, anxiety and bipolar disorder. However, comprehensive evaluation of the relationship between nutrition and schizophrenia is lacking.

OBJECTIVE

The present review aims to synthetic elaborate the associations between nutrition and schizophrenia. Relevant studies on dietary patterns, macronutrients, micronutrients were performed through a literature search to synthesize the extracted data.

SUMMARY

Dietary interventions may help prevent the occurrence of schizophrenia, or delay symptoms: Healthy diets like nutritious plant-based foods and high-quality protein, have been linked to reducing the risk or symptoms of schizophrenia. Moreover, diet high in saturated fat and sugar is linked to more serious outcomes of schizophrenia. Additionally, when N-acetylcysteine acts as an adjuvant therapy, the overall symptoms of schizophrenia are significantly reduced. Also nascent evidence showed mental disorders may be related to intestinal microbiota dysfunction. Our study offered important insights into the dietary habits of patients with schizophrenia and the potential impact of nutritional factors on the disease. We also emphasized the need for further research, particularly in the form of large randomized double-blind controlled trials, to better understand the effects of nutrients on schizophrenia symptoms in different populations and disease types.

Development of a highly sensitive fluorescent probe using Delonix regia (Gulmohar) tree pod shell for precise sarcosine detection in human urine samples: advancing prostate cancer diagnosis

We designed a highly sensitive fluorescent sensor for the early detection of sarcosine, a potential biomarker for prostate cancer. This sensor was based on surface-cobalt-doped fluorescent carbon quantum dots (Co-CD) using a FRET-based photoluminescent sensing platform. Blue luminescent carbon quantum dots (CQD) were synthesised through a hydrothermal approach, utilizing Delonix regia tree pod shells. Cobalt was employed to functionalize the CQD, enhancing the quantum-entrapped effects and minimizing surface flaws. To optimize Co-CD preparation, we employed a Box-Behnken design (BBD), and response surface methodology (RSM) based on single-factor experiments. The Co-CD was then used as a fluorescent probe for selective Cu2+ detection, with Cu2+ quenching Co-CD fluorescence through an energy transfer process, referred to as 'turn-off'. When sarcosine was introduced, the fluorescence intensity of Co-CD was restored, creating a 'turn-on' response. The sensor exhibited a Cu2+ detection limit (LOD) of 2.4 µM with a linear range of 0 μM to 10 µM. The sarcosine detection in phosphate buffer saline (PBS, pH 7.4) resulted in an LOD of 1.54 μM and a linear range of 0 to 10 µM. Importantly, the sensor demonstrated its suitability for clinical analysis by detecting sarcosine in human urine. In summary, our rapid and highly sensitive sensor offers a novel approach for the detection of sarcosine in real samples, facilitating early prostate cancer diagnosis.Communicated by Ramaswamy H. Sarma.

Sarcosine May Induce EGF Production or Inhibit the Decline in EGF Concentrations in Patients with Chronic Schizophrenia (Results of the PULSAR Study)

Sarcosine (N-methylglycine), a glutamatergic modulator, reduces the primary negative symptoms of schizophrenia. These beneficial changes might be mediated by trophic factors such as epidermal growth factor (EGF). We assessed associations between initial serum EGF levels or changes in serum EGF levels and symptom severity during the addition of sarcosine to stable antipsychotic treatment and thereby evaluated the associations between glutamatergic modulation, clinical changes and peripheral EGF concentrations. Fifty-eight subjects with a diagnosis of chronic schizophrenia with dominant negative symptoms, stably treated with antipsychotics, completed a prospective 6-month, randomized, double-blind, placebo-controlled study. Subjects received orally 2 g of sarcosine (n = 28) or placebo (n = 30) daily. Serum EGF levels and symptom severity (using the Positive and Negative Syndrome Scale (PANSS) and the Calgary Depression Scale for Schizophrenia (CDSS)) were assessed at baseline, 6-week and 6-month follow-up. Augmentation antipsychotic treatment with sarcosine had no effect on EGF serum levels at any time points. Only the sarcosine group showed a significant improvement in negative symptoms, general psychopathology subscales and the overall PANSS score. We found a reduction in serum EGF levels in the placebo group, but levels in the sarcosine remained stable during the study. Our data indicate that improvement in negative symptoms due to sarcosine augmentation is not directly mediated by EGF, but effective treatment may induce the production or block the decrease in EGF concentrations, which indicates the neuroprotective effect of treatment and confirms the relationship between neuroprotection and EGF levels.

Randomized controlled trial of the glycine transporter 1 inhibitor PF-03463275 to enhance cognitive training and neuroplasticity in schizophrenia

N-methyl-d-aspartate glutamate receptor (NMDAR) hypofunction is implicated in the impaired neuroplasticity and cognitive impairments associated with schizophrenia (CIAS). We hypothesized that enhancing NMDAR function by inhibiting the glycine transporter-1 (GLYT1) would improve neuroplasticity and thereby augment benefits of non-pharmacological cognitive training (CT) strategies. This study examined whether co-administration of a GLYT1 inhibitor and computerized CT would have synergistic effects on CIAS. Stable outpatients with schizophrenia participated in this double-blind, placebo-controlled, within-subject, crossover augmentation study. Participants received placebo or GLYT1 inhibitor (PF-03463275) for two 5-week periods separated by 2 weeks of washout. PF-03463275 doses (40 or 60 mg twice daily) were selected to produce high GLYT1 occupancy. To limit pharmacodynamic variability, only cytochrome P450 2D6 extensive metabolizers were included. Medication adherence was confirmed daily. Participants received 4 weeks of CT in each treatment period. Cognitive performance (MATRICS Consensus Cognitive Battery) and psychotic symptoms (Positive and Negative Syndrome Scale) were assessed in each period. 71 participants were randomized. PF-03463275 in combination with CT was feasible, safe, and well-tolerated at the doses prescribed but did not produce greater improvement in CIAS compared to CT alone. PF-03463275 was not associated with improved CT learning parameters. Participation in CT was associated with improvement in MCCB scores.

Rational and Translational Implications of D-Amino Acids for Treatment-Resistant Schizophrenia: From Neurobiology to the Clinics

Schizophrenia has been conceptualized as a neurodevelopmental disorder with synaptic alterations and aberrant cortical–subcortical connections. Antipsychotics are the mainstay of schizophrenia treatment and nearly all share the common feature of dopamine D2 receptor occupancy, whereas glutamatergic abnormalities are not targeted by the presently available therapies. D-amino acids, acting as N-methyl-D-aspartate receptor (NMDAR) modulators, have emerged in the last few years as a potential augmentation strategy in those cases of schizophrenia that do not respond well to antipsychotics, a condition defined as treatment-resistant schizophrenia (TRS), affecting almost 30–40% of patients, and characterized by serious cognitive deficits and functional impairment. In the present systematic review, we address with a direct and reverse translational perspective the efficacy of D-amino acids, including D-serine, D-aspartate, and D-alanine, in poor responders. The impact of these molecules on the synaptic architecture is also considered in the light of dendritic spine changes reported in schizophrenia and antipsychotics’ effect on postsynaptic density proteins. Moreover, we describe compounds targeting D-amino acid oxidase and D-aspartate oxidase enzymes. Finally, other drugs acting at NMDAR and proxy of D-amino acids function, such as D-cycloserine, sarcosine, and glycine, are considered in the light of the clinical burden of TRS, together with other emerging molecules.

Placebo Response in Trials of Negative Symptoms in Schizophrenia: A Critical Reassessment of the Evidence

BACKGROUND

Summarizing evidence from clinical trials of patients with schizophrenia with predominant or prominent negative symptoms (NS), a prior meta-analysis reported a large placebo effect in negative symptoms (Cohen's d = 2.909). Assuming that such an effect was clinically not plausible, we performed a critical re-assessment and an update of the previous results with newly available data from add-on and monotherapy studies.

STUDY DESIGN

Random-effect meta/regression analysis of trials that focused on predominant or prominent NS; and adopted a double-blind, randomized, placebo-controlled design. The final pooled meta-analytic database, based on the available add-on and monotherapy studies combined, included 24 publications containing data on a total of 25 studies (21 add-on, 4 monotherapy).

STUDY RESULTS

The pooled overall estimate for the placebo effect from the primary analysis for all included studies had a medium effect size, with a Cohen's d value of 0.6444 (SE = 0.091). The estimates were similar in the add-on and monotherapy studies. Meta-regression indicated that the high placebo response was significantly associated with clinical trial characteristics, including the high ratio of patients assigned to active vs. placebo treatment and short trial duration.

CONCLUSIONS

These results represent a major downward correction for a current effect size estimate of the placebo response in the negative symptoms of schizophrenia. Our findings also pinpoint certain clinical trial characteristics, which may serve as important predictors of the placebo response. The knowledge of these factors can have important implications for drug development and trial design for new drugs for negative symptoms of schizophrenia.

An integrated pathological research for precise diagnosis of schizophrenia combining LC-MS/1H NMR metabolomics and transcriptomics

BACKGROUND

Lack of clinically specific biomarkers has impeded the precise diagnosis of schizophrenia, meanwhile, limited comprehending of pathogenesis for schizophrenia has restricted the effective treatment.

METHOD

An integrated multi-omic approach, combining metabolomic platform (LC-MS and ¹H NMR) and transcriptomic platform, was established to differentiate healthy subjects from schizophrenia patients. Based on filtered metabolites and genes, characteristic spectrums were further built. Then, representative metabolites and genes were screened out through Boruta algorithm. Moreover, characteristic diagnostic formulas were established via LASSO regression analysis.

RESULT

As a result, 86 differential metabolites (in line with amino acid metabolism, etc.) and 189 differential expression genes (involving in amino acid metabolic process, etc.) were obtained as potential biomarkers for schizophrenia. The latent interaction between metabolites with genes, such as HMGCLL1 with energy metabolism, etc., was further studied through the analysis of pathway-based integration. Moreover, fine predictive ability was attributed to characteristic metabolomic/transcriptomic diagnostic spectrums/formulas.

CONCLUSION

The functional relationships of filtered metabolites and genes were studied, which could elaborate the pathological process of schizophrenia more systemically, supplying more precise information on mechanism description and diagnostic evidence of schizophrenia.

Serum levels of neuropeptide Y in patients with chronic schizophrenia during treatment augmentation with sarcosine (results of the double-blind randomized controlled PULSAR study)

OBJECTIVE

Modulation of glutamatergic neurotransmission in schizophrenia by sarcosine leads to a reduction in primary negative symptoms, while its metabolic profile is safe. In order to extend research in the area, we assessed serum levels of neuropeptide Y (NPY), a hypothalamic hormone related to anxiety and depression, also involved in mechanisms inducing weight gain. Additionally, we analyzed associations between NPY concentrations and its changes with severity of symptoms and metabolic parameters.

METHODS

A prospective 6-month, randomized, double-blind placebo-controlled trial was completed by 57 subjects with chronic schizophrenia with predominant negative symptoms and stable antipsychotic treatment. The participants received 2 g of sarcosine (n = 28) or placebo (n = 29) daily. We assessed serum NPY concentrations and severity of symptoms (with the Positive and Negative Syndrome Scale [PANSS] and Calgary Depression Scale for Schizophrenia) at the beginning of the study, after 6 weeks and 6 months.

RESULTS

Sarcosine did not affect NPY levels in all time points. The highest decrease in NPY concentrations was observed in the subjects who were initially depressed, who became euthymic at the last visit. We noticed an improvement in the total PANSS score, and negative symptom and general psychopathology subscales in the sarcosine group, however, without any correlation with NPY levels.

CONCLUSION

The use of sarcosine does not change NPY levels. Peripheral NPY concentrations may be related to depressive symptoms in schizophrenia.

Sarcosine as an add-on treatment to antipsychotic medication for people with schizophrenia: a systematic review and meta-analysis of randomized controlled trials

Background: N-methyl-glycine (sarcosine) may improve symptoms of schizophrenia via NMDA-receptor modulation. We undertook a systematic review and meta-analysis to determine the short- and long-term effectiveness of sarcosine for schizophrenia.Research design and methods: The databases Medline, Scopus, EMBASE, Cochrane Library, and PsycINFO were searched. We included six independent randomized controlled trials of sarcosine as add-on treatment to current antipsychotic medication, involving 234 adult participants with schizophrenia, and reporting data on symptom severity. Standardized mean differences (SMDs) were used to assess continuous outcomes.Results: In all of the trials, sarcosine was administered orally at 2 g/day. Treatment with sarcosine did not show a significant effect size at any of the pre-established time points (2, 4, 6, or >6 weeks), due to marked quantitative heterogeneity. However, sarcosine was associated with significant reductions of symptom severity in the subgroups of people with chronic schizophrenia and no treatment resistance (namely, without added-on clozapine) in relation to the SMD after 6 weeks treatment at -0.36 and -0.31, respectively.Conclusions: People with chronic and non-refractory schizophrenia may benefit from the use of sarcosine as an add-on treatment to antipsychotic medication. Due to the good tolerability of this compound, future trials with larger sample sizes appear worthwhile.

The potential of 1H-MRS in CNS drug development

RATIONALE

Proton magnetic resonance spectroscopy (¹H-MRS) is a cross-species neuroimaging technique that can measure concentrations of several brain metabolites, including glutamate and GABA. This non-invasive method has promise in developing centrally acting drugs, as it can be performed repeatedly within-subjects and be used to translate findings from the preclinical to clinical laboratory using the same imaging biomarker.

OBJECTIVES

This review focuses on the utility of single-voxel ¹H-MRS in developing novel glutamatergic or GABAergic drugs for the treatment of psychiatric disorders and includes research performed in rodent models, healthy volunteers and patient cohorts.

RESULTS

Overall, these studies indicate that ¹H-MRS is able to detect the predicted pharmacological effects of glutamatergic or GABAergic drugs on voxel glutamate or GABA concentrations, although there is a shortage of studies examining dose-related effects. Clinical studies have applied ¹H-MRS to better understand drug therapeutic mechanisms, including the glutamatergic effects of ketamine in depression and of acamprosate in alcohol dependence. There is an emerging interest in identifying patient subgroups with 'high' or 'low' brain regional ¹H-MRS glutamate levels for more targeted drug development, which may require ancillary biomarkers to improve the accuracy of subgroup discrimination.

CONCLUSIONS

Considerations for future research include the sensitivity of single-voxel ¹H-MRS in detecting drug effects, inter-site measurement reliability and the interpretation of drug-induced changes in ¹H-MRS metabolites relative to the known pharmacological molecular mechanisms. On-going technological development, in single-voxel ¹H-MRS and in related complementary techniques, will further support applications within CNS drug discovery.

Directly and Indirectly Targeting the Glycine Modulatory Site to Modulate NMDA Receptor Function to Address Unmet Medical Needs of Patients With Schizophrenia

Schizophrenia is a severe mental illness that affects ~1% of the world's population. It is clinically characterized by positive, negative, and cognitive symptoms. Currently available antipsychotic medications are relatively ineffective in improving negative and cognitive deficits, which are related to a patient's functional outcomes and quality of life. Negative symptoms and cognitive deficits are unmet by the antipsychotic medications developed to date. In recent decades, compelling animal and clinical studies have supported the NMDA receptor (NMDAR) hypofunction hypothesis of schizophrenia and have suggested some promising therapeutic agents. Notably, several NMDAR-enhancing agents, especially those that function through the glycine modulatory site (GMS) of NMDAR, cause significant reduction in psychotic and cognitive symptoms in patients with schizophrenia. Given that the NMDAR-mediated signaling pathway has been implicated in cognitive/social functions and that GMS is a potential therapeutic target for enhancing the activation of NMDARs, there is great interest in investigating the effects of direct and indirect GMS modulators and their therapeutic potential. In this review, we focus on describing preclinical and clinical studies of direct and indirect GMS modulators in the treatment of schizophrenia, including glycine, D-cycloserine, D-serine, glycine transporter 1 (GlyT1) inhibitors, and D-amino acid oxidase (DAO or DAAO) inhibitors. We highlight some of the most promising recently developed pharmacological compounds designed to either directly or indirectly target GMS and thus augment NMDAR function to treat the cognitive and negative symptoms of schizophrenia. Overall, the current findings suggest that indirectly targeting of GMS appears to be more beneficial and leads to less adverse effects than direct targeting of GMS to modulate NMDAR functions. Indirect GMS modulators, especially GlyT1 inhibitors and DAO inhibitors, open new avenues for the treatment of unmet medical needs for patients with schizophrenia.

Treatment effects on neurometabolite levels in schizophrenia: A systematic review and meta-analysis of proton magnetic resonance spectroscopy studies

BACKGROUND

Although there is growing evidence of alterations in the neurometabolite status associated with the pathophysiology of schizophrenia, how treatments influence these metabolite levels in patients with schizophrenia remains poorly studied.

METHODS

We conducted a literature search using Embase, Medline, and PsycINFO to identify proton magnetic resonance spectroscopy studies that compared neurometabolite levels before and after treatment in patients with schizophrenia. Six neurometabolites (glutamate, glutamine, glutamate + glutamine, gamma-aminobutyric acid, N-acetylaspartate, myo-inositol) and six regions of interest (frontal cortex, temporal cortex, parieto-occipital cortex, thalamus, basal ganglia, hippocampus) were investigated.

RESULTS

Thirty-two studies (n = 773 at follow-up) were included in our meta-analysis. Our results demonstrated that the frontal glutamate + glutamine level was significantly decreased (14 groups; n = 292 at follow-up; effect size = -0.35, P = 0.0003; I² = 22%) and the thalamic N-acetylaspartate level was significantly increased (7 groups; n = 184 at follow-up; effect size = 0.47, P < 0.00001; I² = 0%) after treatment in schizophrenia patients. No significant associations were found between neurometabolite changes and age, gender, duration of illness, duration of treatment, or baseline symptom severity.

CONCLUSIONS

The current results suggest that glutamatergic neurometabolite levels in the frontal cortex and neuronal integrity in the thalamus in schizophrenia might be modified following treatment.

Efficacy and cognitive effect of sarcosine (N-methylglycine) in patients with schizophrenia: A systematic review and meta-analysis of double-blind randomised controlled trials

BACKGROUND

Sarcosine (N-methylglycine), a type 1 glycine transporter inhibitor (GlyT1), has shown therapeutic potential for treating schizophrenia; however, studies have reported conflicting results. This meta-analysis aimed to explore the efficacy and cognitive effect of sarcosine for schizophrenia.

METHODS

In this study, PubMed, Cochrane Systematic Reviews, and Cochrane Collaboration Central Register of Controlled Clinical Trials were searched electronically for double-blinded randomised controlled trials that used sarcosine for treating schizophrenia. We used the published trials up to November 2019 to investigate the efficacy of sarcosine in schizophrenia. We pooled studies by using a random-effect model for comparing sarcosine treatment effects. Patients who were diagnosed with schizophrenia according to the criteria of the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition were recruited. Clinical improvement and cognitive function scores between baseline and after sarcosine use were compared using the standardised mean difference (SMD) with 95% confidence intervals (CIs). The heterogeneity of the included trials was evaluated through visual inspection of funnel plots and through the I² statistic.

RESULTS

We identified seven trials with 326 participants with schizophrenia meeting the inclusion criteria. All these studies evaluated the overall clinical symptoms, and four of them evaluated overall cognitive functions. Sarcosine use achieved more significant effects than the use of its comparators in relieving overall clinical symptoms (SMD = 0.51, CI = 0.26-0.76, p < 0.01). Moreover, studies with the low Positive and Negative Syndrome Scale range of 70-79 showed significant effect size (ES)s of 0.67 (95% CI: 0.03-1.31, p = 0.04). In addition, trials enrolling patients with stable clinical symptoms had significant ESs: 0.53 (95% CI: 0.21-0.85, p < 0.01). Add-on sarcosine combined with first- and second-generation antipsychotics, except clozapine, had a positive effect. For overall cognitive functions, sarcosine showed a positive but insignificant effect compared with its comparators (SMD = 0.27, CI = -0.06 to 0.60, p = 0.10). The effects were correlated with increased female proportions and decreased illness duration, albeit nonsignificantly.

CONCLUSIONS

The meta-analysis suggests that sarcosine may be associated with treatment effect on overall clinical symptoms in patients with schizophrenia but not cognitive functions.

Evasion of the accelerated blood clearance phenomenon by polysarcosine coating of liposomes

Using polyethylene glycol (PEG) to functionalize liposomes improves their stealth properties and stability in blood. However, PEG is known to induce the accelerated blood clearance (ABC) phenomenon, which occurs for multiple doses owing to anti-PEG IgM being produced after the initial injection. In this study, as an alternative to PEG, polysarcosine (PSar) was selected owing to its low antigenicity and its highly dense chains with controllable lengths, similar to PEG. Furthermore, we directly evaluate the potential of PSar for avoiding the ABC phenomenon by comparing PSar with PEG on the same liposome platform, which has similar physicochemical properties such as hydrophobic region, membrane fluidity, and size. PEG- and PSar-liposomes were prepared and characterized for comparison. PSar-liposomes showed similar physicochemical properties to PEG-liposomes in terms of size control, zeta potential, membrane polarity, and fluidity; however, ELISA results showed noticeably lower levels and faster production speeds of both IgM and IgG for PSar-liposomes than for PEG-liposomes. In addition, a pharmacokinetics experiment with multiple injections showed that PSar-PE coating of liposomes may help to circumvent the ABC phenomenon.

Discovery and Development of Non-Dopaminergic Agents for the Treatment of Schizophrenia: Overview of the Preclinical and Early Clinical Studies

Schizophrenia is a chronic psychiatric disorder that affects about 1 in 100 people around the world and results in persistent emotional and cognitive impairments. Untreated schizophrenia leads to deterioration in quality of life and premature death. Although the clinical efficacy of dopamine D2 receptor antagonists against positive symptoms of schizophrenia supports the dopamine hypothesis of the disease, the resistance of negative and cognitive symptoms to these drugs implicates other systems in its pathophysiology. Many studies suggest that abnormalities in glutamate homeostasis may contribute to all three groups of schizophrenia symptoms. Scientific considerations also include disorders of gamma-aminobutyric acid-ergic and serotonergic neurotransmissions as well as the role of the immune system. The purpose of this review is to update the most recent reports on the discovery and development of non-dopaminergic agents that may reduce positive, negative, and cognitive symptoms of schizophrenia, and may be alternative to currently used antipsychotics. This review collects the chemical structures of representative compounds targeting metabotropic glutamate receptor, gamma-aminobutyric acid type A receptor, alpha 7 nicotinic acetylcholine receptor, glycine transporter type 1 and glycogen synthase kinase 3 as well as results of in vitro and in vivo studies indicating their efficacy in schizophrenia. Results of clinical trials assessing the safety and efficacy of the tested compounds have also been presented. Finally, attention has been paid to multifunctional ligands with serotonin receptor affinity or phosphodiesterase inhibitory activity as novel strategies in the search for dedicated medicines for patients with schizophrenia.

Quantitative analysis of sarcosine with special emphasis on biosensors: a review

The quantitative determination of sarcosine is of great importance in clinical chemistry, food and fermentation industries. Elevated sarcosine levels are associated with Alzheimer, dementia, prostate cancer, colorectal cancer, stomach cancer and sarcosinemia. This review summarizes the various methods for quantitative analysis of sarcosine with special emphasis on various strategies of biosensors and their analytical performance. The current bio sensing methods have overcome the drawbacks of conventional methods. Sarcosine biosensors work optimally at pH 7.0 to 8.0 in the linear range of 0.1 to 100 μM within 2 to 17 s and between 25 and 37 °C, within a limit of detection (LOD) between 0.008 and 500 mM. The formulated biosensors can be reused within a stability period of 3-180 days. Future research could be focused to modify existing sarcosine biosensors, leading to simple, reliable, and economical sensors ideally suited for point-of-care treatment. Clinical significance Elevated sarcosine levels are associated with prostate and colorectal cancer, Alzheimer, dementia, stomach cancer and sarcosinemia. Quantitative determination of sarcosine is of great importance in clinical chemistry as well as food and fermentation industries. Attempts made in development of sarcosine biosensors have been reviewed with their advantages and disadvantages, so that scientist and clinicians can improvise the methods of developing more potent sarcosine biosensor applicable in multitudinous fields. This is the first comprehensive review which compares the various immobilization methods, sensing principles, strategies used in biosensors and their analytical performance in detail.

Serum levels of TNF-alpha in patients with chronic schizophrenia during treatment augmentation with sarcosine (results of the PULSAR study)

Sarcosine, glycine transporter inhibitor, increases glycine levels around NMDA receptor, improving primary negative symptoms of schizophrenia. The aim of our study was to find a potential relationship between initial TNF-alpha level, its changes and schizophrenia symptoms severity, resulting from adding sarcosine to a stable antipsychotic treatment. Sixty subjects with stable schizophrenia were randomized to receive either 2 g of sarcosine or placebo and completed a 6-month, double blind, placebo-controlled study. Three patients on sarcosine and one taking placebo did not complete TNF-alpha tests, planned at the beginning, after 6 weeks and after 6 months. For clinical assessments we used PANSS and CDSS scales. No changes in TNF-alpha serum concentrations in both groups at any time-points was noted. The sarcosine group achieved significant improvement in negative symptoms, general psychopathology and total PANSS score group, however without any significant correlations between TNF-alpha levels and PANSS scores in all assessments. Positive correlations between TNF-alpha levels and CDSS score were found in the placebo group and total study group. Initial TNF-alpha concentrations cannot be used as a predictor of the improvement resulting from adding sarcosine. Sarcosine does not significantly affect TNF-alpha levels. TNF-alpha may be involved in mechanisms related to depressive symptomatology in schizophrenia.

Serum levels of interleukin 6 in schizophrenic patients during treatment augmentation with sarcosine (results of the PULSAR study)

OBJECTIVE

Augmentation of sarcosine, a natural inhibitor of the glycine transporter type I, normalizes glutamatergic neurotransmission, having beneficial impact on primary negative symptoms in schizophrenia and may also influence immune system and interleukin 6 (IL-6) levels.

AIM

Finding a relationship between initial IL-6 serum concentrations or its changes and severity of symptoms as a result of sarcosine addition to stable antipsychotic treatment.

METHOD

Fifity-eight individuals with schizophrenia with predominantly negative symptoms completed a 6-month randomized, double-blind placebo-controlled prospective study. Patients received 2 g of sarcosine (n = 29) or placebo (n = 30) daily per os. We measured IL-6 levels and severity of symptoms at the beginning, after 6 weeks and 6 months. As main clinical tools, we used Positive and Negative Syndrome Scale (PANSS) and Calgary depression scale for schizophrenia (CDSS).

RESULTS

Augmentation with sarcosine had no effect on IL-6 serum levels in all time points. We noted significant improvements in negative symptoms, general psychopathology, and total PANSS score in the sarcosine group. We found correlation of initial serum IL-6 with severity of positive symptoms and negative association between IL-6 levels reduction and positive symptoms reduction.

CONCLUSIONS

Sarcosine does not significantly affect IL-6 concentrations but IL-6 may be involved in mechanisms related to the presence of positive symptoms.

The GlyT1 Inhibitor Bitopertin Ameliorates Allodynia and Hyperalgesia in Animal Models of Neuropathic and Inflammatory Pain

Background: Chronic pain conditions are difficult to treat and the therapeutic outcome is frequently unsatisfactory. Changes in excitation/inhibition balance within the dorsal horn contribute to the establishment and persistence of chronic pain. Thus, facilitation of inhibitory neurotransmission is a promising approach to treat chronic pain pharmacologically. Glycine transporter 1 (GlyT1) plays an important role in regulating extracellular glycine concentrations. Aim of the present study therefore was to investigate whether the specific GlyT1 inhibitor bitopertin (RG1678; RO4917838) might constitute a novel treatment for chronic pain by facilitating glycinergic inhibition.

Methods: Mechanical allodynia and thermal hyperalgesia were induced by chronic constriction injury of the sciatic nerve or carrageenan injections into the plantar surface of the hind paw in rodents. The effect of acute and long-term bitopertin application on the reaction threshold to mechanical and thermal stimuli was determined. General activity was determined in open field experiments. The glycine concentration in cerebrospinal fluid and blood was measured by HPLC.

Results: Systemic application of bitopertin in chronic pain conditions lead to a significant increase of the reaction thresholds to mechanical and thermal stimuli in a time and dose-dependent manner. Long-term application of bitopertin effectuated stable beneficial effects over 4 weeks. Bitopertin did not alter reaction thresholds to stimuli in control animals and had no effect on general locomotor activity and anxiety but lead to an increased glycine concentration in cerebrospinal fluid.

Conclusion: These findings suggest that inhibition of the GlyT1 by bitopertin represents a promising new approach for the treatment of chronic pain.

Ultimate Translation: Developing Therapeutics Targeting on N-Methyl-d-Aspartate Receptor

N-Methyl-d-aspartate receptors (NMDARs) are broadly distributed in the central nervous system (CNS), where they mediate excitatory signaling. NMDAR-mediated neurotransmission (NMDARMN) is the molecular engine of learning, memory and cognition, which are the basis for high cortical function. NMDARMN is also critically involved in the development and plasticity of CNS. Due to its essential and critical role, either over- or under-activation of NMDARMN can contribute substantially to the development of CNS disorders. The involvement of NMDARMN has been demonstrated in a variety of CNS disorders, including schizophrenia, depression, posttraumatic stress disorder, aging, mild cognitive impairment and Alzheimer's dementia, amyotrophic lateral sclerosis, and anti-NMDAR encephalitis. Several targets to "correct" or "reset" the NMDARMN in these CNS disorders have been identified and confirmed. With analogy to aminergic treatments, these targets include the glycine/d-serine co-agonist site, channel ionophore, glycine transporter-1, and d-amino acid oxidase. It is still early days in terms of developing novel therapeutics targeting the NMDAR. However, agents modulating NMDARMN hold promise as the next generation of CNS therapeutics.

Modulating NMDA Receptor Function with D-Amino Acid Oxidase Inhibitors: Understanding Functional Activity in PCP-Treated Mouse Model

Deficits in N-methyl-D-aspartate receptor (NMDAR) function are increasingly linked to persistent negative symptoms and cognitive deficits in schizophrenia. Accordingly, clinical studies have been targeting the modulatory site of the NMDA receptor, based on the decreased function of NMDA receptor, to see whether increasing NMDA function can potentially help treat the negative and cognitive deficits seen in the disease. Glycine and D-serine are endogenous ligands to the NMDA modulatory site, but since high doses are needed to affect brain levels, related compounds are being developed, for example glycine transport (GlyT) inhibitors to potentially elevate brain glycine or targeting enzymes, such as D-amino acid oxidase (DAAO) to slow the breakdown and increase the brain level of D-serine. In the present study we further evaluated the effect of DAAO inhibitors 5-chloro-benzo[d]isoxazol-3-ol (CBIO) and sodium benzoate (NaB) in a phencyclidine (PCP) rodent mouse model to see if the inhibitors affect PCP-induced locomotor activity, alter brain D-serine level, and thereby potentially enhance D-serine responses. D-Serine dose-dependently reduced the PCP-induced locomotor activity at doses above 1000 mg/kg. Acute CBIO (30 mg/kg) did not affect PCP-induced locomotor activity, but appeared to reduce locomotor activity when given with D-serine (600 mg/kg); a dose that by itself did not have an effect. However, the effect was also present when the vehicle (Trappsol(®)) was tested with D-serine, suggesting that the reduction in locomotor activity was not related to DAAO inhibition, but possibly reflected enhanced bioavailability of D-serine across the blood brain barrier related to the vehicle. With this acute dose of CBIO, D-serine level in brain and plasma were not increased. Another weaker DAAO inhibitor NaB (400 mg/kg), and NaB plus D-serine also significantly reduced PCP-induced locomotor activity, but without affecting plasma or brain D-serine level, arguing against a DAAO-mediated effect. However, NaB reduced plasma L-serine and based on reports that NaB also elevates various plasma metabolites, for example aminoisobutyric acid (AIB), a potential effect via the System A amino acid carrier may be involved in the regulation of synaptic glycine level to modulate NMDAR function needs to be investigated. Acute ascorbic acid (300 mg/kg) also inhibited PCP-induced locomotor activity, which was further attenuated in the presence of D-serine (600 mg/kg). Ascorbic acid may have an action at the dopamine membrane carrier and/or altering redox mechanisms that modulate NMDARs, but this needs to be further investigated. The findings support an effect of D-serine on PCP-induced hyperactivity. They also offer suggestions on an interaction of NaB via an unknown mechanism, other than DAAO inhibition, perhaps through metabolomic changes, and find unexpected synergy between D-serine and ascorbic acid that supports combined NMDA glycine- and redox-site intervention. Although mechanisms of these specific agents need to be determined, overall it supports continued glutamatergic drug development.