d-Cycloserine therapy of psychosis by symptom provocation

More Than Malnutrition: A Review of the Relationship Between Food Insecurity and Tuberculosis

Despite a significant reduction in tuberculosis (TB) mortality over the past decade, TB remains a leading cause of death worldwide. Food insecurity—through pathways such as malnutrition, mental health impact, and high-risk health behaviors—affects the risk of TB disease, treatment failure, and mortality. We searched the literature for studies reporting on the links between food insecurity and TB. In contrast to the well-documented interactions between food insecurity and HIV/AIDS, we found that the association between food insecurity and TB remains largely understudied—this is especially true with regard to non-nutritional correlations. Mental health and behavioral linkages between TB and food insecurity deserve further attention. An improved understanding of the pathways through which food insecurity impacts TB is crucial to inform evidence-based integration of interventions such as psychological counseling, psychiatric care, harm reduction programs, and efforts to address social determinants of disease within current TB programs.

D-cycloserine in Schizophrenia: New Strategies for Improving Clinical Outcomes by Enhancing Plasticity

Background

Dysregulation of N-methyl D-aspartate (NMDA) receptor signaling is strongly implicated in schizophrenia. Based on the ketamine model of NMDA receptor hypoactivity, therapeutic approaches designed to maintain a sustained increase in agonist activity at the glycine site of the NMDA receptor have produced promising, although inconsistent, efficacy for negative symptoms.

Methods

A review of the published literature on D-cycloserine (DCS) pharmacology in animal models and in clinical studies was performed. Findings relevant to DCS effects on memory and plasticity and their potential clinical application to schizophrenia were summarized.

Results

Studies in animals and clinical trials in patients with anxiety disorders have demonstrated that single or intermittent dosing with DCS enhances memory consolidation. Preliminary trials in patients with schizophrenia suggest that intermittent dosing with DCS may produce persistent improvement of negative symptoms and enhance learning when combined with cognitive behavioral therapy for delusions or with cognitive remediation. The pharmacology of DCS is complex, since it acts as a “super agonist” at NMDA receptors containing GluN2C subunits and, under certain conditions, it may act as an antagonist at NMDA receptors containing GluN2B subunits.

Conclusions

There are preliminary findings that support a role for D-cycloserine in schizophrenia as a strategy to enhance neuroplasticity and memory. However, additional studies with DCS are needed to confirm these findings. In addition, clinical trials with positive and negative allosteric modulators with greater specificity for NMDA receptor subtypes are needed to identify the optimal strategy for enhancing neuroplasticity in schizophrenia.

The Therapeutic Role of d-Cycloserine in Schizophrenia

The ketamine model for schizophrenia has led to several therapeutic strategies for enhancing N-methyl d-aspartate (NMDA) receptor activity, including agonists directed at the glycine receptor site and inhibitors of glycine reuptake. Because ketamine may primarily block NMDA receptors on inhibitory interneurons, drugs that reduce glutamate release have also been investigated as a means of countering a deficit in inhibitory input. These approaches have met with some success for the treatment of negative and positive symptoms, but results have not been consistent. An emerging approach with the NMDA partial agonist, d-cycloserine (DCS), aims to enhance plasticity by intermittent treatment. Early trials have demonstrated benefit with intermittent DCS dosing for negative symptoms and memory. When combined with cognitive remediation, intermittent DCS treatment enhanced learning on a practiced auditory discrimination task and when added to cognitive behavioral therapy, DCS improved delusional severity in subjects who received DCS with the first CBT session. These studies require replication, but point toward a promising strategy for the treatment of schizophrenia and other disorders of plasticity.

Combining d-cycloserine with motor training does not result in improved general motor learning in neurologically intact people or in people with stroke

Neurological rehabilitation involving motor training has resulted in clinically meaningful improvements in function but is unable to eliminate many of the impairments associated with neurological injury. Thus there is a growing need for interventions that facilitate motor learning during rehabilitation therapy, to optimize recovery. d-Cycloserine (DCS), a partial N-methyl-d-aspartate (NMDA) receptor agonist that enhances neurotransmission throughout the central nervous system (Ressler KJ, Rothbaum BO, Tannenbaum L, Anderson P, Graap K, Zimand E, Hodges L, Davis M. Arch Gen Psychiatry 61: 1136-1144, 2004), has been shown to facilitate declarative and emotional learning. We therefore tested whether combining DCS with motor training facilitates motor learning after stroke in a series of two experiments. Forty-one healthy adults participated in experiment I, and twenty adults with stroke participated in experiment II of this two-session, double-blind study. Session one consisted of baseline assessment, subject randomization, and oral administration of DCS or placebo (250 mg). Subjects then participated in training on a balancing task, a simulated feeding task, and a cognitive task. Subjects returned 1-3 days later for posttest assessment. We found that all subjects had improved performance from pretest to posttest on the balancing task, the simulated feeding task, and the cognitive task. Subjects who were given DCS before motor training, however, did not show enhanced learning on the balancing task, the simulated feeding task, or the associative recognition task compared with subjects given placebo. Moreover, training on the balancing task did not generalize to a similar, untrained balance task. Our findings suggest that DCS does not enhance motor learning or motor skill generalization in neurologically intact adults or in adults with stroke.

Psychiatric morbidity and other factors affecting treatment adherence in pulmonary tuberculosis patients

As the overall prevalence of TB remains high among certain population groups, there is growing awareness of psychiatric comorbidity, especially depression and its role in the outcome of the disease. The paper attempts a holistic approach to the effects of psychiatric comorbidity to the natural history of tuberculosis. In order to investigate factors associated with medication nonadherence among patients suffering from tuberculosis, with emphasis on psychopathology as a major barrier to treatment adherence, we performed a systematic review of the literature on epidemiological data and past medical reviews from an historical perspective, followed by theoretical considerations upon the relationship between psychiatric disorders and tuberculosis. Studies reporting high prevalence rates of psychiatric comorbidity, especially depression, as well as specific psychological reactions and disease perceptions and reviews indicating psychiatric complications as adverse effects of anti-TB medication were included. In sum, data concerning factors affecting medication nonadherence among TB patients suggested that better management of comorbid conditions, especially depression, could improve the adherence rates, serving as a framework for the effective control of tuberculosis, but further studies are necessary to identify the optimal way to address such issues among these patients.

D-cycloserine: an evolving role in learning and neuroplasticity in schizophrenia

As a partial agonist at the glycine site of the NMDA receptor, D-cycloserine (DCS) has been viewed as lacking potency to fully test the NMDA receptor hypofunction theory of schizophrenia. However, findings of full agonist activity at a subset of NMDA receptors that may have particular relevance to schizophrenia, plus a growing body of evidence demonstrating enhancement of learning and neuroplasticity in animal models, suggest novel therapeutic strategies with DCS in schizophrenia. Preliminary studies with once-weekly administration have supported this potential new role for DCS in schizophrenia by demonstrating benefit for negative symptoms, memory consolidation, and facilitation of cognitive behavioral therapy for delusions.

Potentiation of the NMDA receptor in the treatment of schizophrenia: focused on the glycine site

N-methyl-D-aspartate receptor (NMDAR) hypo-function theory of schizophrenia proposes that impairment in NMDAR function be associated with the pathophysiology of schizophrenia and suggests that enhancement of the receptor function may produce efficacy for schizophrenia. Consistent with this theory, for the last decade, clinical trials have demonstrated that the enhancement of NMDAR function by potentiating the glycine site of the receptor is efficacious in the treatment of schizophrenia. Full agonists of the glycine site, glycine and D-serine and a glycine transporter-1 inhibitor, sarcosine, added to antipsychotic drugs, have been shown to be effective in the treatment of negative symptoms and possibly cognitive symptoms without significantly affecting the positive symptoms of schizophrenia. A partial agonist of the glycine site, D-cycloserine, added to antipsychotic drugs, can be effective for the negative symptoms at the therapeutic doses. However, these drugs have not shown clinical efficacy when added to clozapine, suggesting that the interactions of clozapine and the glycine site potentiators may be different from those of other antipsychotic drugs and the potentiators. This article suggests that the glycine site potentiators may produce efficacy for negative and cognitive symptoms by blocking apoptosis-like neuropathological processes in patients with chronic schizophrenia and thereby can deter progressive deterioration of the disorder. This article proposes a polypharmacy of glycine site potentiators augmented with antipsychotic drugs to control positive and negative symptoms in a synergistic manner and block deterioration in schizophrenia. Since the NMDAR complex consists of multiple sites modulating receptor functions, the efficacy of glycine site potentiators for schizophrenia suggests the possibility that manipulation of other modulating sites of the NMDAR can also be efficacious in the treatment of schizophrenia.

Glutamatergic drugs for schizophrenia

BACKGROUND

It has been shown that central nervous system dopamine can play a major role in the pathophysiology of schizophrenia. Brain glutamate is thought to mediate symptoms in schizophrenia due to the influence of glutamate neurons on the dopaminergic transmission in the brain. It might be possible to decrease negative symptoms and the cognitive impairment of people with schizophrenia by treatment with glutamatergic drugs.

OBJECTIVES

To determine the efficacy of glutamatergic drugs in the treatment of schizophrenia.

SEARCH STRATEGY

We searched the Cochrane Schizophrenia Group's Trials Register (May 2002 and October 2003), inspected references of all identified studies and contacted relevant authors.

SELECTION CRITERIA

We included all randomised controlled trials in which glutamatergic medication was administered to people with schizophrenia.

DATA COLLECTION AND ANALYSIS

We reliably selected studies, quality rated them and extracted data. For dichotomous data, we estimated relative risks (RR), with the 95% confidence intervals (CI). Where possible, we calculated the number needed to treat/harm statistic (NNT/H) and used intention-to-treat analysis.

MAIN RESULTS

We included eighteen short-term trials with 358 randomised participants. The single studies were small with numbers of participants ranging between six and 51. All trials were short-term trials with a maximum duration of 12 weeks. In all of these trials, glycine, D-serine, D-cycloserine, or ampakine CX516 was used to augment the effect of antipsychotic drugs. D-cycloserine, a partial agonist of NMDA receptors' glycine site, seemed ineffective towards the symptoms of schizophrenia. NMDA receptor co-agonists glycine and D-serine showed some effects in reducing the negative symptoms of schizophrenia (n=132, SMD -0.66, CI -1.0 to -0.3, p=0.0004), but the magnitude of the effect was moderate. Furthermore, when responder rates rather than mean scores of negative symptoms were analysed the data were inconsistent: There was no difference in responder rates between glycine and the control in terms of more than 20% improvement of negative symptoms (n=62, RR 0.70, CI 0.3 to 1.71) and only a borderline significant superiority in terms of more than 50% improvement (n=62, RR 0.87, CI 0.8 to 1.00). There were also some effects in favour of glycine and/or D-serine in terms of overall and general symptoms, but the results were again inconsistent and depended on the response definition applied. Available rating scale data on positive symptoms and cognitive functioning did not indicate a statistically significant effect of glycine or D-serine.

AUTHORS' CONCLUSIONS

In general, all glutamatergic drugs appeared to be ineffective in further reducing positive symptoms of the disease when added to the existing antipsychotic treatment. Glycine and D-serine may somewhat improve negative symptoms when added to regular antipsychotic medication, but the results were not fully consistent and data are too few to allow any firm conclusions. Many participants in the included trials were treatment-resistant which may have reduced treatment response. Additional research on glutamatergic mechanisms of schizophrenia is needed.

A six-month, placebo-controlled trial of D-cycloserine co-administered with conventional antipsychotics in schizophrenia patients

RATIONALE

D-Cycloserine, a partial agonist at the glycine site of the N-methyl-D-aspartate receptor, has demonstrated inconsistent efficacy for negative and cognitive symptoms of schizophrenia. The strongest evidence for efficacy has come from studies using D-cycloserine at a dose of 50 mg/day added to conventional antipsychotics in trials of 8 weeks duration or less.

OBJECTIVE

To assess the efficacy for negative symptoms and cognitive impairment of D-cycloserine augmentation of conventional antipsychotics in a 6-month trial.

METHODS

Fifty-five schizophrenia patients with prominent negative symptoms, treated with conventional antipsychotics, were randomly assigned to treatment with D-cycloserine 50 mg/day or placebo for 6 months in a double-blind, parallel group design.

RESULTS

Twenty-six subjects completed the 6-month trial; drop-out rates did not differ between treatment groups. D-Cycloserine treatment did not differ from placebo treatment on any primary outcome measure at 8 or 24 weeks, including response of negative symptoms and performance on a cognitive battery. Serum D-cycloserine concentrations did not correlate with response of negative symptoms.

CONCLUSION

D-Cycloserine did not exhibit therapeutic effects in this trial, possibly reflecting the high drop-out rate, a narrow range of therapeutic serum concentrations, a modest magnitude of therapeutic effect for the selected outcome measures, or loss of efficacy over time. Because D-cycloserine is a partial agonist with relatively low affinity for the glycine site, the magnitude of potential therapeutic effect may be smaller than that achieved by the higher-affinity full agonists, glycine and D-serine.

The N-methyl D-aspartate receptor glycine site and D-serine metabolism: an evolutionary perspective

The N-methyl D-aspartate (NMDA) type of glutamate receptor requires two distinct agonists to operate. Glycine is assumed to be the endogenous ligand for the NMDA receptor glycine site, but this notion has been challenged by the discovery of high levels of endogenous d-serine in the mammalian forebrain. I have outlined an evolutionary framework for the appearance of a glycine site in animals and the metabolic events leading to high levels of D-serine in brain. Sequence alignments of the glycine-binding regions, along with the scant experimental data available, suggest that the properties of invertebrate NMDA receptor glycine sites are probably different from those in vertebrates. The synthesis of D-serine in brain is due to a pyridoxal-5'-phosphate (B(6))-requiring serine racemase in glia. Although it remains unknown when serine racemase first evolved, data concerning the evolution of B(6) enzymes, along with the known occurrences of serine racemases in animals, point to D-serine synthesis arising around the divergence time of arthropods. D-Serine catabolism occurs via the ancient peroxisomal enzyme d-amino acid oxidase (DAO), whose ontogenetic expression in the hindbrain of mammals is delayed until the postnatal period and absent from the forebrain. The phylogeny of D-serine metabolism has relevance to our understanding of brain ontogeny, schizophrenia and neurotransmitter dynamics.

D-serine added to clozapine for the treatment of schizophrenia

OBJECTIVE

D-Serine is a full agonist at the glycine site on the N-methyl-D-aspartate (NMDA) receptor. Previous administration of D-serine to schizophrenic patients taking nonclozapine antipsychotics improved positive, negative, and cognitive symptoms, whereas the partial agonist D-cycloserine improved negative symptoms of patients taking conventional antipsychotics but worsened symptoms in clozapine-treated patients. To study the difference between full and partial agonists at the NMDA receptor glycine site, the clinical effects of adding D-serine to clozapine were assessed.

METHOD

In a 6-week double-blind trial, 20 schizophrenic patients received placebo or D-serine (30 mg/kg per day) in addition to clozapine. Clinical efficacy, side effects, and serum levels of D-serine were determined every other week.

RESULTS

The patients exhibited no improvement with D-serine, nor did their symptoms worsen, as previously reported with D-cycloserine.

CONCLUSIONS

The results suggest either that clozapine may have an agonistic effect on the NMDA system or that clozapine-treated patients do not respond to D-serine.

A.E. Bennett Research Award. Reversal of phencyclidine-induced effects by glycine and glycine transport inhibitors

BACKGROUND

Phencycline (PCP, "angel dust") and other noncompetitive antagonists of N-methyl-D-aspartate (NMDA)-type glutamatergic neurotransmission induce psychotic effects in humans that closely resemble positive, negative, and cognitive symptoms of schizophrenia. Behavioral effects of PCP in rodents are reversed by glycine (GLY) and other NMDA augmenting agents. In rodents, behavioral effects of PCP are mediated, in part, by secondary dysregulation of subcortical dopaminergic neurotransmission. This study evaluates effects of GLY and GLY transport antagonists on behavioral and neurochemical consequences of PCP administration in rodents.

METHODS

Two separate experiments were performed. In the first, effects of GLY on PCP-induced stimulation of dopaminergic neurotransmission in nucleus accumbens were evaluated using in vivo microdialysis in awake animals. In the second, effects of a series of GLY transport antagonists were evaluated for potency in inhibiting PCP-induced hyperactivity.

RESULTS

In microdialysis studies, GLY significantly inhibited PCP-induced stimulation of subcortical DA release in a dose-dependent fashion. In behavioral studies, the potency of a series of GLY transport antagonists for inhibiting PCP-induced hyperactivity in vivo correlated significantly with their potency in antagonizing GLY transport in vitro.

CONCLUSIONS

These findings suggest, first, that GLY reverses not only the behavioral, but also the neurochemical, effects of PCP in rodents. Second, the findings suggest that GLY transport antagonists may induce similar effects to GLY, and may therefore represent an appropriate site for targeted drug development.

Glutamate in schizophrenia: clinical and research implications

The excitatory amino acids, glutamate and aspartate, are of interest to schizophrenia research because of their roles in neurodevelopment, neurotoxicity and neurotransmission. Recent evidence suggests that densities of glutamatergic receptors and the ratios of subunits composing these receptors may be altered in schizophrenia, although it is unclear whether these changes are primary or compensatory. Agents acting at the phencyclidine binding site of the NMDA receptor produce symptoms of schizophrenia in normal subjects, and precipitate relapse in patients with schizophrenia. The improvement of negative symptoms with agents acting at the glycine modulatory site of the NMDA receptor, as well as preliminary evidence that clozapine may differ from conventional neuroleptic agents in its effects on glutamatergic systems, suggest that clinical implications may follow from this model. While geriatric patients may be at increased risk for glutamate-mediated neurotoxicity, very little is known about the specific relevance of this model to geriatric patients with schizophrenia.

D-cycloserine enhances social behaviour in individually-housed mice in the resident-intruder test

D-Cycloserine (DCS) has been reported to affect the central nervous system in man. To investigate whether the compound produces specific behavioural effects, DCS was administered to male mice in a resident-intruder situation and the behaviour of the interacting mice assessed using ethological analysis. Resident mice given DCS (32.0-320.0 mg/kg PO, 60 min before testing) showed dose-dependent increases in social investigation, smaller increases in sexual behaviour and decreased aggressiveness. Defensive and flight behaviour were not affected. Intruder mice showed slight increases in sexual behaviour that were not dose-dependent, and small increases in social investigation. The increases in social investigation induced by DCS (320.0 mg/kg) in resident mice were not reversible with R-HA 966 (32.0 mg/kg IP, 30 min before testing), a blocker of the strychnine-insensitive glycine modulatory site associated with the N-methyl-D-aspartate receptor, but were blocked by the GABA antagonist bicuculline (0.56 mg/kg IP, 5 min before testing). The small DCS-induced increase in sexual behaviour in residents was reversed by R-HA 966. Within the parameters of the resident-intruder situation, DCS exerts socio-sexual behaviour-enhancing effects which are dependent upon the role of the interactant, and which are mediated by an action upon multiple substrates. DCS may be regarded as another example of a sociotropic (approach-promoting) agent.

Effects of D-cycloserine and (+)-HA-966 on the locomotor stimulation induced by NMDA antagonists and clonidine in monoamine-depleted mice

We have previously observed that an N-methyl-D-aspartate (NMDA) antagonist in combination with the alpha 2-adrenoceptor agonist clonidine produces a marked locomotor stimulation in monoamine-depleted mice. In this paper we report on how the partial glycine agonists D-cycloserine (high intrinsic activity) and (+)-HA-966 [(+)-3-amino-1-hydroxypyrrolid-2-one; low intrinsic activity] affect this response; the interaction with both an uncompetitive and a competitive NMDA antagonist was investigated. (+)-HA-966 was found to counteract the locomotor stimulation produced by clonidine combined with either an uncompetitive (MK-801 = dizocilpine) or a competitive [D-CPPene = 3-(2-carboxypiperazine-4-yl)-1-propenyl-1-phosphonic acid] NMDA antagonist. D-cycloserine potentiated the locomotor stimulation produced by either NMDA antagonist combined with clonidine, although statistical significance was achieved only in the case of MK-801. If the present hyperactivity model has any relevance for psychosis the prediction based on the present results would be that d-cycloserine, contrary to current hopes, might not be so effective in schizophrenia, whereas (+)-HA-966 might be an interesting candidate.

EEG, blood level, and behavioral effects of the antidepressant mianserin (ORG GB-94)

A pharmacokinetic analysis of a new antidepressant drug, mianserin (ORG GB-94), was undertaken in 4 male volunteers, each of whom received 15 mg mianserin on two occasions. Plasma levels peak at 2 h with a median level of 11.0 ng/ml, a median beta-phase half-life of 10.0 h, and a median apparent volume of distribution of 3.3 X 10(3) 1. EEG profile analysis shows mianserin to increase frequencies below 6 Hz, decrease those from 7.5 to 15 Hz, and increase frequencies above 18 Hz, a pattern similar to amitriptyline. Peak EEG effects range from 2 to 5 h with a pattern of measured changes that parallels plasma levels with varying latency. Decreases in vigilance measures and in critical flicker-fusion frequency show a similar time course. Mianserin is a putative thymoleptic on EEG profile analysis with high cerebral penetrance.