Challenges in drug target discovery in bipolar disorder

The Role of Mitochondria in Mood Disorders: From Physiology to Pathophysiology and to Treatment

Mitochondria are cellular organelles involved in several biological processes, especially in energy production. Several studies have found a relationship between mitochondrial dysfunction and mood disorders, such as major depressive disorder and bipolar disorder. Impairments in energy production are found in these disorders together with higher levels of oxidative stress. Recently, many agents capable of enhancing antioxidant defenses or mitochondrial functioning have been studied for the treatment of mood disorders as adjuvant therapy to current pharmacological treatments. A better knowledge of mitochondrial physiology and pathophysiology might allow the identification of new therapeutic targets and the development and study of novel effective therapies to treat these specific mitochondrial impairments. This could be especially beneficial for treatment-resistant patients. In this article, we provide a focused narrative review of the currently available evidence supporting the involvement of mitochondrial dysfunction in mood disorders, the effects of current therapies on mitochondrial functions, and novel targeted therapies acting on mitochondrial pathways that might be useful for the treatment of mood disorders.

Microbiota abnormalities and the therapeutic potential of probiotics in the treatment of mood disorders

Major depressive disorder (MDD) and bipolar disorder (BD) are among the leading causes of burden and disability worldwide. Despite intensified research efforts to improve the treatment options and remission rates in mood disorders, no disease modifying treatment exists for these disorders. Accumulating evidence implicates the involvement of the gut microbiota in processes relevant to etiopathology of central nervous system-based disorders. The objective of this article was to critically evaluate the evidence supporting the link between gastrointestinal microbiota and mood disorders and to discuss the potential benefits of using probiotics in the treatment of MDD and BD. The concept of psychobiotics, which is bacterial-based interventions with mental health benefit, is emerging in the field. On the other hand, while probiotics might potentially represent a significant advance, specific roles of microbiota in the pathophysiology of mood disorders still need further investigation along with intervention studies.

Distinct proteomic profiles in post-mortem pituitary glands from bipolar disorder and major depressive disorder patients

Disturbances of the hypothalamic-pituitary-adrenal axis have been implicated in the pathophysiology of bipolar disorder (BD) and major depressive disorder (MDD). To examine this further, we carried out proteomic profiling of post-mortem pituitaries from 13 BD and 14 MDD patients, in comparison to 15 controls. Liquid chromatography-mass spectrometry (LC-MS(E)) analysis showed that BD patients had significantly increased levels of the major pituitary hormones pro-opiomelanocortin (POMC) and galanin. BD patients also showed changes in proteins associated with gene transcription, stress response, lipid metabolism and growth signalling. In contrast, LC-MS(E) profiling revealed that MDD patients had significantly decreased levels of the prohormone-converting enzyme carboxypeptidease E and follow-up enzymatic analysis showed decreased activity of prolyl-oligopeptidase convertase. This suggested that altered prohormone processing may occur in pituitaries of MDD patients. In addition, MDD patients had significant changes in proteins involved in intracellular transport and cytoskeletal signalling. Finally, we carried out selective reaction monitoring (SRM) mass spectrometry profiling for validation of protein changes in key biological pathways. This confirmed increased POMC levels in BD patients with no change in the levels of this prohormone in MDD. This study demonstrates that proteomic profiling analysis of the pituitary can lead to new insights into the pathophysiology of BD and MDD. Also, given that the pituitary directly releases a variety of bioactive molecules into the bloodstream, many of the proteins identified here could serve as focal points in the search for peripheral biomarkers in clinical or drug treatment studies of BD and MDD patients.

Novel routes to bipolar disorder drug discovery

INTRODUCTION

Bipolar disorder (BD) is a severe and chronic medical condition typified by episodic recurrent mania (or hypomania) in addition to major depression. BD is associated with a number of negative outcomes including premature death, reduced quality of life and can also lead to other complications including impaired cognitive function. Unfortunately, the currently available pharmacological treatments for BD are insufficient for many with the condition.

AREAS COVERED

This review focuses on known therapeutic targets of mood stabilizing drugs including: the glycogen synthase kinase-3 (GSK-3), the phosphoinositide pathway and protein kinase C (PKC), the brain-derived neurotrophic factor (BDNF), and histone deacetylases (HDACs). This article also presents new promising therapeutic targets including: the glutamatergic pathway, mitochondrial modulators, neuropeptide-converting endopeptidases, the insulin transduction pathway, the purinergic system and the melatoninergic system.

EXPERT OPINION

Challenges in improving methods and tools to generate, integrate and analyze high-dimensional data are required to allow opening novel routes to BD drug discovery. Through the application of systems biology approaches and the use of bioinformatical tools to integrate all omics data, it will be possible in the near future to gain deeper insights into pathophysiology of BD. This will in turn lead to the identification and exploitation of new potential therapeutic approaches.