Eszopiclone facilitation of the antidepressant efficacy of fluoxetine using a social defeat stress model

NSC689857, an inhibitor of Skp2, produces antidepressant-like effects in mice

We have previously reported that two inhibitors of an E3 ligase S-phase kinase-associated protein 2 (Skp2), SMIP004 and C1, have an antidepressant-like effect in non-stressed and chronically stressed mice. This prompted us to ask whether other Skp2 inhibitors could also have an antidepressant effect. Here, we used NSC689857, another Skp2 inhibitor, to investigate this hypothesis. The results showed that administration of NSC689857 (5 mg/kg) produced an antidepressant-like effect in a time-dependent manner in non-stressed male mice, which started 8 days after drug administration. Dose-dependent analysis showed that administration of 5 and 10 mg/kg, but not 1 mg/kg, of NSC689857 produced antidepressant-like effects in both non-stressed male and female mice. Administration of NSC689857 (5 mg/kg) also induced antidepressant-like effects in non-stressed male mice when administered three times within 24 h (24, 5, and 1 h before testing) but not when administered acutely (1 h before testing). In addition, NSC689857 and fluoxetine coadministration produced additive antidepressant-like effects in non-stressed male mice. These effects of NSC689857 were not associated with the changes in locomotor activity. Administration of NSC689857 (5 mg/kg) also attenuated depression-like behaviors in male mice induced by chronic social defeat stress, suggesting therapeutic potential of NSC689857 in depression. Overall, these results suggest that NSC689857 is capable of exerting antidepressant-like effects in both non-stressed and chronically stressed mice.

Identification of the antidepressive properties of C1, a specific inhibitor of Skp2, in mice

We have reported that SMIP004, an inhibitor of S-phase kinase-associated protein 2 (Skp2), displays antidepressant-like activities in stress-naïve and chronically stressed mice. Here, we investigated the antidepressant-like effect of C1, another inhibitor of Skp2, in mouse models following acute or chronic drug administration at different doses and treatment times by using the tail suspension test (TST), forced swimming test (FST), and social interaction test (SIT). The time- and dose-dependent results showed that the antidepressant-like effect of C1 occurred 8 days after the drug treatment, and C1 produced antidepressant-like activities at the dose of 5 and 10 but not 1 mg/kg in male or female mice. C1 administration (5 mg/kg) also induced antidepressant-like effects in stress-naïve mice in a three-times administration mode within 24 h (24, 5, and 1 h before the test) but not in an acute administration mode (1 h before the test). The C1 and fluoxetine co-administration produced additive effect on depression-like behaviors in stress-naïve mice. The antidepressant-like effect of C1 was not associated with the change in locomotor activity, as no increased locomotor activity was observed in different treatment modes. Furthermore, the long-term C1 treatment (5 mg/kg) was found to ameliorate the depression-like behaviors in chronic social defeat stress-exposed mice, suggesting that C1 can produce antidepressant-like actions in stress conditions. Since C1 is a specific inhibitor of Skp2, our results demonstrate that inhibition of Skp2 might be a potential strategy for the treatment of depression, and Skp2 may be potential target for the development of novel antidepressants.

Chronic social defeat stress differentially regulates the expression of BDNF transcripts and epigenetic modifying enzymes in susceptible and resilient mice

Objectives: Although stress is considered a primary risk factor for neuropsychiatric disorders, a majority of individuals are resilient to the effects of stress exposure and successfully adapt to adverse life events, while others, the so-called susceptible individuals, may have problems to properly adapt to environmental changes. However, the mechanisms underlying these different responses to stress exposure are poorly understood.Methods: Adult male C57BL/6J mice were exposed to chronic social defeat stress protocol and levels of brain derived neurotrophic factor (BDNF) transcripts and epigenetic modifying enzymes were analysed by real-time PCR in the hippocampus (HPC) and prefrontal cortex (PFC) of susceptible and resilient mice.Results: We found a selective reduction of BDNF-6 transcript in the HPC and an increase of BDNF-4 transcript in the PFC of susceptible mice. Moreover, susceptible mice showed a selective reduction of the g9a mRNA levels in the HPC, while HDAC-5 and DNMT3a mRNA levels were specifically reduced in the PFC.Conclusions: Overall, our results, showing a different expression of BDNF transcripts and epigenetic modifying enzymes in susceptible and resilient mice, suggest that stress resilience is not simply a lack of activation of stress-related pathways, but is related to the activation of additional different specific mechanisms.

Antidepressant-Like Actions of Inhibitors of Poly(ADP-Ribose) Polymerase in Rodent Models

BACKGROUND

Many patients suffering from depressive disorders are refractory to treatment with currently available antidepressant medications, while many more exhibit only a partial response. These factors drive research to discover new pharmacological approaches to treat depression. Numerous studies demonstrate evidence of inflammation and elevated oxidative stress in major depression. Recently, major depression has been shown to be associated with elevated levels of DNA oxidation in brain cells, accompanied by increased gene expression of the nuclear base excision repair enzyme, poly(ADP-ribose) polymerase-1. Given these findings and evidence that drugs that inhibit poly(ADP-ribose) polymerase-1 activity have antiinflammatory and neuroprotective properties, the present study was undertaken to examine the potential antidepressant properties of poly(ADP-ribose) polymerase inhibitors.

METHODS

Two rodent models, the Porsolt swim test and repeated exposure to psychological stressors, were used to test the poly(ADP-ribose) polymerase inhibitor, 3-aminobenzamide, for potential antidepressant activity. Another poly(ADP-ribose) polymerase inhibitor, 5-aminoisoquinolinone, was also tested.

RESULTS

Poly(ADP-ribose) polymerase inhibitors produced antidepressant-like effects in the Porsolt swim test, decreasing immobility time, and increasing latency to immobility, similar to the effects of fluoxetine. In addition, 3-aminobenzamide treatment increased sucrose preference and social interaction times relative to vehicle-treated control rats following repeated exposure to combined social defeat and unpredictable stress, mediating effects similar to fluoxetine treatment.

CONCLUSIONS

The poly(ADP-ribose) polymerase inhibitors 3-aminobenzamide and 5-aminoisoquinolinone exhibit antidepressant-like activity in 2 rodent stress models and uncover poly(ADP-ribose) polymerase as a unique molecular target for the potential development of a novel class of antidepressants.

Effect of agomelatine on memory deficits and hippocampal gene expression induced by chronic social defeat stress in mice

Chronic stress is known to induce not only anxiety and depressive-like phenotypes in mice but also cognitive impairments, for which the action of classical antidepressant compounds remains unsatisfactory. In this context, we investigated the effects of chronic social defeat stress (CSDS) on anxiety-, social- and cognitive-related behaviors, as well as hippocampal Bdnf, synaptic plasticity markers (PSD-95, Synaptophysin, Spinophilin, Synapsin I and MAP-2), and epigenetic modifying enzymes (MYST2, HDAC2, HDAC6, MLL3, KDM5B, DNMT3B, GADD45B) gene expression in C57BL/6J mice. CSDS for 10 days provoked long-lasting anxious-like phenotype in the open field and episodic memory deficits in the novel object recognition test. While total Bdnf mRNA level was unchanged, Bdnf exon IV, MAP-2, HDAC2, HDAC6 and MLL3 gene expression was significantly decreased in the CSDS mouse hippocampus. In CSDS mice treated 3 weeks with 50 mg/kg/d agomelatine, an antidepressant with melatonergic receptor agonist and 5-HT_2C receptor antagonist properties, the anxious-like phenotype was not reversed, but the treatment successfully prevented the cognitive impairments and hippocampal gene expression modifications. Altogether, these data evidenced that, in mice, agomelatine was effective in alleviating stress-induced altered cognitive functions, possibly through a mechanism involving BDNF signaling, synaptic plasticity and epigenetic remodeling.

Elevated DNA Oxidation and DNA Repair Enzyme Expression in Brain White Matter in Major Depressive Disorder

BACKGROUND

Pathology of white matter in brains of patients with major depressive disorder (MDD) is well-documented, but the cellular and molecular basis of this pathology are poorly understood.

METHODS

Levels of DNA oxidation and gene expression of DNA damage repair enzymes were measured in Brodmann area 10 (BA10) and/or amygdala (uncinate fasciculus) white matter tissue from brains of MDD (n=10) and psychiatrically normal control donors (n=13). DNA oxidation was also measured in BA10 white matter of schizophrenia donors (n=10) and in prefrontal cortical white matter from control rats (n=8) and rats with repeated stress-induced anhedonia (n=8).

RESULTS

DNA oxidation in BA10 white matter was robustly elevated in MDD as compared to control donors, with a smaller elevation occurring in schizophrenia donors. DNA oxidation levels in psychiatrically affected donors that died by suicide did not significantly differ from DNA oxidation levels in psychiatrically affected donors dying by other causes (non-suicide). Gene expression levels of two base excision repair enzymes, PARP1 and OGG1, were robustly elevated in oligodendrocytes laser captured from BA10 and amygdala white matter of MDD donors, with smaller but significant elevations of these gene expressions in astrocytes. In rats, repeated stress-induced anhedonia, as measured by a reduction in sucrose preference, was associated with increased DNA oxidation in white, but not gray, matter.

CONCLUSIONS

Cellular residents of brain white matter demonstrate markers of oxidative damage in MDD. Medications that interfere with oxidative damage or pathways activated by oxidative damage have potential to improve treatment for MDD.

GABAA receptor subtypes: Therapeutic potential in Down syndrome, affective disorders, schizophrenia, and autism

The γ-aminobutyric acid (GABA) system plays a pivotal role in orchestrating the synchronicity of local networks and the functional coupling of different brain regions. Here we review the impact of the GABAA receptor subtypes on cognitive and emotional behavior, paying particular attention to five disease states: cognitive dysfunction and Down syndrome, anxiety disorders, depression, schizophrenia, and autism. Through the bidirectional modulation of tonic inhibition, α5-subunit-containing GABAA receptors permit the bidirectional modulation of cognitive processes, and a partial inverse agonist acting at the α5-subunit-containing GABAA receptor is in a clinical trial in individuals with Down syndrome. With regard to anxiety disorders, the viability of nonsedative anxiolytics based on the modulation of α2- and α3-subunit-containing GABAA receptors has been established in clinical proof-of-concept trials. Regarding the remaining three disease states, the GABA hypothesis of depression offers new options for antidepressant drug development; cognitive symptoms in schizophrenia are attributed to a cortical GABAergic deficit, and dysfunctional GABAergic inhibition is increasingly understood to contribute to the pathophysiology of autism spectrum disorders.