Aripiprazole: in major depressive disorder

Design, Synthesis, and Pharmacology of New Triazole-Containing Quinolinones as CNS Active Agents

Epilepsy and major depressive disorder are the two of the most common central nervous system (CNS) diseases. Clinicians and patients call for new antidepressants, antiseizure medicines, and in particular drugs for depression and epilepsy comorbidities. In this work, a dozen new triazole-quinolinones were designed, synthesized, and investigated as CNS active agents. All compounds reduced the immobility time significantly during the forced swim test (FST) in mice at the dosage of 50 mg/kg. Compounds 3f-3j gave superior performance over fluoxetine in the FST with more reductions of the immobility time. Compound 3g also reduced immobility time significantly in a tail suspension test (TST) at the dosage of 50 mg/kg, though its anti-immobility activity was inferior to that of fluoxetine. An open field test was carried out and it eliminated the false-positive possibility of 3g in the FST and TST, which complementarily supported the antidepressant activity of 3g. We also found that almost all compounds except 3k exhibited antiseizure activity in the maximal electroshock seizure (MES) model at 100 or 300 mg/kg. Compounds 3c, 3f, and 3g displayed the ED₅₀ of 63.4, 78.9, and 84.9 mg/kg, and TD₅₀ of 264.1, 253.5, and 439.9 mg/kg, respectively. ELISA assays proved that the mechanism for the antiseizure and antidepressant activities of compound 3g was via affecting the concentration of GABA in mice brain. The molecular docking study showed a good interaction between 3g and the amino acid residue of the GABA_A receptor. Excellent drug-like properties and pharmacokinetic properties of compound 3a-l were also predicted by Discovery Studio. These findings provided a new skeleton to develop agents for the treatment of epilepsy and depression comorbidities.

Recent advances in understanding depressive disorder: Possible relevance to brain stimulation therapies

Recent research has provided novel insights into the major depressive disorder (MDD) and identified certain biomarkers of this disease. There are four main mechanisms playing a key role in the related pathophysiology, namely (1) monoamine systems dysfunction, (2) stress response, (3) neuroinflammation, and (4) neurotrophic factors alteration. Robust evidence on the decreased homovanillic acid in the cerebrospinal fluid (CSF) of patients with MDD supports a rationale for therapeutic stimulation of the medial forebrain bundle activating the dopamine reward system. Both activation and suppression of the hypothalamic-pituitary-adrenal (HPA) axis in MDD and related conditions indicate usefulness of its evaluation for the disease subtyping. Elevated proinflammatory cytokines (specifically, interleukin-6) in CSF imply the role of neuroinflammation resulting in activation of the tryptophan-kynurenine pathway. Finally, neuroplasticity and trophic effects of the brain-derived neurotrophic factor (BDNF) may be related to both structural abnormalities of the brain in MDD and the underlying mechanisms of various therapies. In addition, the gut-brain interaction is pivotal, since lack of beneficial microbes confer the risk of MDD through negative effects on the dopamine system, HPA axis, and vagal nerve. All these factors may be highly relevant to treatment of MDD with contemporary brain stimulation therapies.

Inflammation and depression: a causal or coincidental link to the pathophysiology?

This review summarises the evidence that chronic low grade inflammation triggers changes that contribute to the mental and physical ill health of patients with major depression. Inflammation, and the activation of the hypothalamic pituitary axis by stress, are normal components of the stress response but when stress is prolonged and the endocrine and immune system become chronic resulting in the activation of the peripheral macrophages, the central microglia and hypercortisolemia, the neuronal networks are damaged and become dysfunctional. The proinflammatory cytokines, in addition to activating the hypothalamic-pituitary-adrenal axis and thereby increasing cortisol synthesis, also activate the tryptophan-kynurenine pathway. This results in the synthesis of the neurotoxic N-methyl-d-aspartate (NMDA) glutamate agonist quinolinic acid and 3-hydroxykynurenine thereby enhancing oxidative stress and contributes to neurodegeneration which characterise major depression particularly in late life.While antidepressants attenuate some of the endocrine and immune changes caused by inflammation, not all therapeutically effective antidepressants do so. This suggests that drugs which specifically target the immune, endocrine and neurotransmitter systems may be more effective antidepressants.The preliminary clinical evidence that some non-steroidal anti-inflammatory drugs, such as the cyclooxygenase 2 inhibitor celecoxib, can enhance the response to standard antidepressant treatment is therefore considered and a critical assessment made of the possible limitations of such an approach to novel antidepressant development.

Biochemical markers subtyping major depressive disorder

The pathophysiology of major depressive disorder (MDD) remains elusive, and there is no established biochemical marker used in the daily clinical setting. This situation may result in part from the heterogeneity of MDD, which might include heterogeneous subgroups with different biological mechanisms. In this review, we discuss three promising biological systems/markers to potentially subtype MDD: the dopamine system, the hypothalamic-pituitary-adrenal axis, and chronic inflammatory markers. Several lines of evidence suggest that a facet of MDD is a dopamine agonist-responsive subtype. Focusing on the hypothalamic-pituitary-adrenal axis, depressive spectrum disorders show hypercortisolism to hypocortisolism, which could be detected by hormonal challenge tests, such as the dexamethasone/corticotrophin-releasing hormone test. Finally, accumulating evidence suggests that at least some MDD patients show characteristics similar to those of chronic inflammatory diseases, including neuroinflammatory markers and reduced tryptophan due to the increased activation of the tryptophan-kynurenine pathway. Future studies should examine the inter-relations between these systems/markers to subtype and integrate the pathophysiology of MDD.

Impact of inflammation on neurotransmitter changes in major depression: an insight into the action of antidepressants

This review summarises the evidence that chronic low grade inflammation plays an important role in the pathology of depression. Evidence is provided that pro-inflammatory cytokines, together with dysfunctional endocrine and neurotransmitter systems, provide a network of changes that underlie depression and may ultimately contribute to the neurodegenerative changes that characterise depression in the elderly. Antidepressants attenuate the inflammatory changes and hypercortisolaemia by reducing the release of the pro-inflammatory cytokines from activated microglia, and by sensitizing the glucocorticoids receptors in the HPA axis. These effects correlate with an improvement in monoamine neurotransmitter function. The possible mechanisms whereby this cascade of changes occurs are outlined. In conclusion, the mechanisms whereby antidepressants act should now consider the involvement of the immune and endocrine systems in addition to the central neurotransmitters. This may open up possibilities for a new generation of antidepressants in the future.

Aripiprazole: a dopamine modulator that mimics methylphenidate in producing faster antidepressant effects

Up to 60% of depressed patients do not respond to two months of pharmacotherapy, and late treatment responses are often correlated with poor outcomes and may be characterized as treatment-resistant depression (TRD). Previous studies have noted that the addition of a psychostimulant such as methylphenidate to the therapeutic regimen of patients with TRD or those depressed patients with comorbid fatigue, advanced age, or a major medical illness showed significant improvement within two weeks. One explanation for the benefit of methylphenidate in treating TRD is that it enhances the level of dopamine in the brain. Adjunctive low dose aripiprazole in patients with TRD has also become a common intervention. Several studies have focused on aripiprazole's pharmacodynamic and pharmacokinetic profiles, but no definitive comments on its antidepressant effects. We hypothesize that a low dose of aripiprazole might play a role as a dopamine agonist similar to that of methylphenidate due to its partial dopamine D2 agonist and 30% intrinsic dopaminergic activity. In addition to its use in patients with TRD, adjunctive aripiprazole might work like methylphenidate in those depressed patients with fatigue, advanced age, or major illnesses. A new drug invention which combined an antidepressant with an adequate dose of aripiprazole should be considered. The neurobiological basis for this combination in treating TRD awaits further study.

Aripiprazole augmentation strategy in clomipramine-resistant depressive patients: an open preliminary study

Recent evidence supports the use of second generation antipsychotics in drug resistant depression. The aim of the present open-label study was to evaluate the effect of aripiprazole as an add-on medication in drug-resistant depressed patients who had not responded to clomipramine. Thirty-five patients with major depressive disorder (MDD) were included in the study. All patients had not responded to a previous adequate treatment with an SSRI and had been receiving clomipramine (daily doses ranging from 100 to 300 mg) for 113.9 ± 18.9 days without getting significant clinical improvement. Aripiprazole was added at the fixed dose of 5mg/day and clinical status as well as clomipramine plasma levels were monitored before and after 4, 8, and 24 weeks of combined treatment. Hamilton depression rating scale scores significantly decreased over the follow-up period with 91.4% and 34.3% of patients getting a response or a remission, respectively, after 24 weeks of combined treatment. No worsening of clomipramine-related side effects nor new side effects were observed. The clinical improvement was accompanied by a progressive and significant increase in clomipramine plasma levels. With the limitation of an open-label design, these data suggest for the first time the putative efficacy and safety of aripiprazole in combination with a tricyclic medication in drug resistant depressed patients. The role of the observed pharmacokinetic interaction in the mechanism of aripiprazole antidepressant activity remains to be proved.

Aripiprazole inhibits superoxide generation from phorbol-myristate-acetate (PMA)-stimulated microglia in vitro: implication for antioxidative psychotropic actions via microglia

Altered antioxidant status has been implicated in schizophrenia. Microglia, major sources of free radicals such as superoxide (•O(2)(-)), play crucial roles in various brain pathologies. Recent postmortem and imaging studies have indicated microglial activation in the brain of schizophrenic patients. We previously demonstrated that atypical antipsychotics including aripiprazole significantly inhibited the release of nitric oxide and proinflammatory cytokines from interferon-γ-stimulated microglia in vitro. Antioxidative effects of antipsychotics via modulating microglial superoxide generation have never been reported. Therefore, we herein investigated the effects of antipsychotics on the •O(2)(-) generation from phorbol-myristate-acetate (PMA)-stimulated rodent microglia by the electron spin resonance (ESR) spectroscopy and also examined the intracellular mechanism by intracellular Ca(2+) imaging and immunostaining. Neuronal damage induced by microglial activation was also investigated by the co-culture experiment. Among various antipsychotics, only aripiprazole inhibited the •O(2)(-) generation from PMA-stimulated microglia. Aripiprazole proved to inhibit the •O(2)(-) generation through the cascade of protein kinase C (PKC) activation, intracellular Ca(2+) regulation and NADPH oxidase activation via cytosolic p47(phox) translocation to the plasma/phagosomal membranes. Formation of neuritic beading, induced by PMA-stimulated microglia, was attenuated by pretreatment of aripiprazole. D2R antagonism has long been considered as the primary therapeutic action for schizophrenia. Aripiprazole with D2R partial agonism is effective like other antipsychotics with fewer side effects, while aripiprazole's therapeutic mechanism itself remains unclear. Our results imply that aripiprazole may have psychotropic effects by reducing the microglial oxidative reactions and following neuronal reactions, which puts forward a novel therapeutic hypothesis in schizophrenia research.

Inhibitory effects of SSRIs on IFN-γ induced microglial activation through the regulation of intracellular calcium

Microglia, which are a major glial component of the central nervous system (CNS), have recently been suggested to mediate neuroinflammation through the release of pro-inflammatory cytokines and nitric oxide (NO). Microglia are also known to play a critical role as resident immunocompetent and phagocytic cells in the CNS. Immunological dysfunction has recently been demonstrated to be associated with the pathophysiology of depression. However, to date there have only been a few studies on the relationship between microglia and depression. We therefore investigated if antidepressants can inhibit microglial activation in vitro. Our results showed that the selective serotonin reuptake inhibitors (SSRIs) paroxetine and sertraline significantly inhibited the generation of NO and tumor necrosis factor (TNF)-α from interferon (IFN)-γ-activated 6-3 microglia. We further investigated the intracellular signaling mechanism underlying NO and TNF-α release from IFN-γ-activated 6-3 microglia. Our results suggest that paroxetine and sertraline may inhibit microglial activation through inhibition of IFN-γ-induced elevation of intracellular Ca(2+). Our results suggest that the inhibitory effect of paroxetine and sertraline on microglial activation may not be a prerequisite for antidepressant function, but an additional beneficial effect.

Getting the balance right: Established and emerging therapies for major depressive disorders

Major depressive disorder (MDD) is a common and serious illness of our times, associated with monoamine deficiency in the brain. Moreover, increased levels of cortisol, possibly caused by stress, may be related to depression. In the treatment of MDD, the use of older antidepressants such as monoamine oxidase inhibitors and tricyclic antidepressants is decreasing rapidly, mainly due to their adverse effect profiles. In contrast, the use of serotonin reuptake inhibitors and newer antidepressants, which have dual modes of action such as inhibition of the serotonin and noradrenaline or dopamine reuptake, is increasing. Novel antidepressants have additive modes of action such as agomelatine, a potent agonist of melatonin receptors. Drugs in development for treatment of MDD include triple reuptake inhibitors, dual-acting serotonin reuptake inhibitors and histamine antagonists, and many more. Newer antidepressants have similar efficacy and in general good tolerability profiles. Nevertheless, compliance with treatment for MDD is poor and may contribute to treatment failure. Despite the broad spectrum of available antidepressants, there are still at least 30% of depressive patients who do not benefit from treatment. Therefore, new approaches in drug development are necessary and, according to current research developments, the future of antidepressant treatment may be promising.