Minocycline, schizophrenia and GluR1 glutamate receptors

Microglia Activation and Schizophrenia: Lessons From the Effects of Minocycline on Postnatal Neurogenesis, Neuronal Survival and Synaptic Pruning

The implication of neuroinflammation in schizophrenia, sustained by recent genetic evidence, represents one of the most exciting topics in schizophrenia research. Drugs which inhibit microglia activation, especially the classical tetracycline antibiotic minocycline are currently under investigation as alternative antipsychotics. However, recent studies demonstrated that microglia activation is not only a hallmark of neuroinflammation, but plays important roles during brain development. Inhibition of microglia activation by minocycline was shown to induce extensive neuronal cell death and to impair subventricular zone (SVZ) neurogenesis and synaptic pruning in the early postnatal and adolescent rodent brain, respectively. These deleterious effects contrast with the neuroprotective actions of minocycline at adult stages. They are of potential importance for schizophrenia, since minocycline triggers similar pro-apoptotic effects in the developing brain as NMDA receptor (NMDAR) antagonists, known to induce long-term schizophrenia-like abnormalities. Moreover, altered postnatal neurogenesis, recently described in the human striatum, was proposed to induce striatal dopamine dysregulation associated with schizophrenia. Finally, the effect of minocycline on synapse remodeling is of interest considering the recently reported strong genetic association of the pruning-regulating complement factor gene C4A with schizophrenia. This raises the exciting possibility that in conditions of hyperactive synaptic pruning, as supposed in schizophrenia, the inhibitory action of minocycline turns into a beneficial effect, with relevance for early therapeutic interventions. Altogether, these data support a differential view on microglia activation and its inhibition. Further studies are needed to clarify the relevance of these results for the pathogenesis of schizophrenia and the use of minocycline as antipsychotic drug.

Minocycline exacerbates apoptotic neurodegeneration induced by the NMDA receptor antagonist MK-801 in the early postnatal mouse brain

NMDA receptor (NMDAR) antagonists induce in perinatal rodent cortical apoptosis and protracted schizophrenia-like alterations ameliorated by antipsychotic treatment. The broad-spectrum antibiotic minocycline elicits antipsychotic and neuroprotective effects. Here we tested, if minocycline protects also against apoptosis triggered by the NMDAR antagonist MK-801 at postnatal day 7. Surprisingly, minocycline induced widespread cortical apoptosis and exacerbated MK-801-triggered cell death. In some areas such as the subiculum, the pro-apoptotic effect of minocycline was even more pronounced than that elicited by MK-801. These data reveal among antipsychotics unique pro-apoptotic properties of minocycline, raising concerns regarding consequences for brain development and the use in children.

Adjunctive Minocycline in Clozapine-Treated Schizophrenia Patients With Persistent Symptoms

OBJECTIVE

Clozapine is the most effective antipsychotic for treatment refractory people with schizophrenia, yet many patients only partially respond. Accumulating preclinical and clinical data suggest benefits with minocycline. We tested adjunct minocycline to clozapine in a 10-week, double-blind, placebo-controlled trial. Primary outcomes tested were positive, and cognitive symptoms, while avolition, anxiety/depression, and negative symptoms were secondary outcomes.

METHODS

Schizophrenia and schizoaffective participants (n = 52) with persistent positive symptoms were randomized to receive adjunct minocycline (100 mg oral capsule twice daily; n = 29) or placebo (n = 23).

RESULTS

Brief Psychiatric Rating Scale (BPRS) psychosis factor (P = 0.098; effect size [ES], 0.39) and BPRS total score (P = 0.075; ES, 0.55) were not significant. A change in total BPRS symptoms of more than or equal to 30% was observed in 7 (25%) of 28 among minocycline and 1 (4%) of 23 among placebo participants, respectively (P = 0.044). Global cognitive function (MATRICS Consensus Cognitive Battery) did not differ, although there was a significant variation in size of treatment effects among cognitive domains (P = 0.03), with significant improvement in working memory favoring minocycline (P = 0.023; ES, 0.41). The Scale for the Assessment of Negative Symptoms total score did not differ, but significant improvement in avolition with minocycline was noted (P = 0.012; ES, 0.34). Significant improvement in the BPRS anxiety/depression factor was observed with minocycline (P = 0.028; ES, 0.49). Minocycline was well tolerated with significantly fewer headaches and constipation compared with placebo.

CONCLUSIONS

Minocycline's effect on the MATRICS Consensus Cognitive Battery composite score and positive symptoms were not statistically significant. Significant improvements with minocycline were seen in working memory, avolition, and anxiety/depressive symptoms in a chronic population with persistent symptoms. Larger studies are needed to validate these findings.

Evidence for a dysregulated immune system in the etiology of psychiatric disorders

There is extensive bi-directional communication between the brain and the immune system in both health and disease. In recent years, the role of an altered immune system in the etiology of major psychiatric disorders has become more apparent. Studies have demonstrated that some patients with major psychiatric disorders exhibit characteristic signs of immune dysregulation and that this may be a common pathophysiological mechanism that underlies the development and progression of these disorders. Furthermore, many psychiatric disorders are also often accompanied by chronic medical conditions related to immune dysfunction such as autoimmune diseases, diabetes and atherosclerosis. One of the major psychiatric disorders that has been associated with an altered immune system is schizophrenia, with approximately one third of patients with this disorder showing immunological abnormalities such as an altered cytokine profile in serum and cerebrospinal fluid. An altered cytokine profile is also found in a proportion of patients with major depressive disorder and is thought to be potentially related to the pathophysiology of this disorder. Emerging evidence suggests that altered immune parameters may also be implicated in the neurobiological etiology of autism spectrum disorders. Further support for a role of immune dysregulation in the pathophysiology of these psychiatric disorders comes from studies showing the immunomodulating effects of antipsychotics and antidepressants, and the mood altering effects of anti-inflammatory therapies. This review will not attempt to discuss all of the psychiatric disorders that have been associated with an augmented immune system, but will instead focus on several key disorders where dysregulation of this system has been implicated in their pathophysiology including depression, schizophrenia and autism spectrum disorder.

Oligodendroglial alterations and the role of microglia in white matter injury: relevance to schizophrenia

Schizophrenia is a chronic and debilitating mental illness characterized by a broad range of abnormal behaviors, including delusions and hallucinations, impaired cognitive function, as well as mood disturbances and social withdrawal. Due to the heterogeneous nature of the disease, the causes of schizophrenia are very complex; its etiology is believed to involve multiple brain regions and the connections between them, and includes alterations in both gray and white matter regions. The onset of symptoms varies with age and severity, and there is some debate over a degenerative or developmental etiology. Longitudinal magnetic resonance imaging studies have detected progressive gray matter loss in the first years of disease, suggesting neurodegeneration; but there is also increasing recognition of a temporal association between clinical complications at birth and disease onset that supports a neurodevelopmental origin. Presently, neuronal abnormalities in schizophrenia are better understood than alterations in myelin-producing cells of the brain, the oligodendrocytes, which are the predominant constituents of white matter structures. Proper white matter development and its structural integrity critically impacts brain connectivity, which affects sensorimotor coordination and cognitive ability. Evidence of defective white matter growth and compromised white matter integrity has been found in individuals at high risk of psychosis, and decreased numbers of mature oligodendrocytes are detected in schizophrenia patients. Inflammatory markers, including proinflammatory cytokines and chemokines, are also associated with psychosis. A relationship between risk of psychosis, white matter defects and prenatal inflammation is being established. Animal models of perinatal brain injury are successful in producing white matter damage in the brain, typified by hypomyelination and/or dysmyelination, impaired motor coordination and prepulse inhibition of the acoustic startle reflex, recapitulating structural and functional characteristics observed in schizophrenia. In addition, elevated expression of inflammation-related genes in brain tissue and increased production of cytokines by blood cells from patients with schizophrenia indicate immunological dysfunction and abnormal inflammatory responses, which are also important underlying features in experimental models. Microglia, resident immune defenders of the central nervous system, play important roles in the development and protection of neural cells, but can contribute to injury under pathological conditions. This article discusses oligodendroglial changes in schizophrenia and focuses on microglial activity in the context of the disease, in neonatal brain injury and in various experimental models of white matter damage. These include disorders associated with premature birth, and animal models of perinatal bacterial and viral infection, oxygen deprivation (hypoxia) and excess (hyperoxia), and elevated systemic proinflammatory cytokine levels. We briefly review the effects of treatment with antipsychotic and anti-inflammatory agents in models of perinatal brain injury, and comment on the therapeutic potential of these strategies. By understanding the neurobiological basis of oligodendroglial abnormalities in schizophrenia, it is hoped that patients will benefit from the availability of targeted and more efficacious treatment options.

What is behind the non-antibiotic properties of minocycline?

Minocycline is a second-generation, semi-synthetic tetracycline that has been in use in therapy for over 30 years for its antibiotic properties against both Gram-positive and Gram-negative bacteria. It displays antibiotic activity due to its ability to bind to the 30S ribosomal subunit of bacteria and thus inhibit protein synthesis. More recently, it has been described to exert a variety of biological actions beyond its antimicrobial activity, including anti-inflammatory and anti-apoptotic activities, inhibition of proteolysis, as well as suppression of angiogenesis and tumor metastasis, which have been confirmed in different experimental models of non-infectious diseases. There are also many studies that have focused on the mechanisms involved in these non-antibiotic properties of minocycline, including anti-oxidant activity, inhibition of several enzyme activities, inhibition of apoptosis and regulation of immune cell activation and proliferation. This review summarizes the current findings in this topic, mainly focusing on the mechanisms underlying the immunomodulatory and anti-inflammatory activities of minocycline.

Significance of NMDA receptor-related glutamatergic amino acid levels in peripheral blood of patients with schizophrenia

Hypo-function of N-methyl d-aspartate (NMDA) receptors is strongly involved in the brain pathophysiology of schizophrenia. Several excitatory amino acids, such as endogenous glutamate, glycine, serine and alanine, which are involved in glutamate neurotransmission via NMDA receptors, were studied to further understand the pathophysiology of schizophrenia and to find a biological marker for this disease, particularly in peripheral blood. In this literature review, we connect several earlier clinical studies and several studies of excitatory amino acid levels in peripheral blood in a historical context. Finally, we join these results and our previous studies, the Juntendo University Schizophrenia Projects (JUSP), which investigated plasma glutamatergic amino acid levels in detail, and considered whether these amino acid levels may be diagnostic, therapeutic, or symptomatic biological markers. This review concludes that peripheral blood levels of endogenous glycine and alanine could be a symptomatic marker in schizophrenia, while peripheral blood levels of exogenous glycine and alanine in augmentation therapies could be therapeutic markers. Noteworthy peripheral blood levels of endogenous d-serine could reflect its brain levels, and may prove to be a useful diagnostic and therapeutic marker in schizophrenia. In addition, measurements of new endogenous molecules, such as glutathione, are promising. Finally, for future therapies with glutamatergic agents still being examined in animal studies, the results of these biological marker studies may lay the foundation for the development of next-generation antipsychotics.

Emerging role of glutamate in the pathophysiology of major depressive disorder

Major depressive disorder (MDD) is a common, chronic, recurrent mental illness that affects millions of individuals worldwide. To date, the monoaminergic systems (serotonin, norepinephrine, and dopamine) have received the most attention in the neurobiology of MDD, and all classes of antidepressants target these monoaminergic systems. Accumulating evidence suggests that the glutamatergic system plays an important role in the neurobiology and treatment of this disease. Some clinical studies have demonstrated that the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist ketamine has rapid antidepressant effects in treatment-resistant patients with MDD. Here, the author reviews the recent findings on the role of the glutamatergic system in the neurobiology of MDD and in new potential therapeutic targets (NMDA receptors, AMPA receptors, metabotropic glutamate receptors, ceftriaxone, minocycline, N-acetyl-L-cysteine) for MDD.

Minocycline affects cocaine sensitization in mice

Growing evidence has pointed to an interaction between the tetracycline antibiotic minocycline and drugs with abuse liability such as opioids and amphetamines. In this work, we tested the hypothesis that similar to its effects on methamphetamine-induced locomotor sensitization, minocycline may influence the behavioral effects of cocaine. Experiments were performed in male C57BL/6J mice using an automated system to measure locomotor activity. We found that 80 mg/kg minocycline significantly reduced locomotor activity when administered either alone or injected 30 min prior to cocaine, which increased locomotor activity. To investigate whether minocycline selectively affects the development of locomotor sensitization induced by four daily injections of 10mg/kg cocaine, we sought a schedule of minocycline administration that does not per se affect locomotor activity. Thus, we selected 40 mg/kg minocycline administered 3h prior to cocaine; minocycline did not affect cocaine-stimulated locomotor activity on the first day of administration but prevented the development of cocaine sensitization. We also tested whether minocycline would affect an already established cocaine sensitization. After establishing the sensitization effect by four daily injections, cocaine treatment was discontinued and mice were treated with minocycline daily (days 5-11) or on day 11 only. There was no effect of minocycline treatment on the response of cocaine-sensitized mice to the challenge dose of cocaine on day 11. The mechanisms by which minocycline interferes with the development of cocaine sensitization need to be characterized.