Cognitive dysfunction in depression – pathophysiology and novel targets

Carvalho AF, Miskowiak KW, Hyphantis TN, Kohler CA, Alves GS, Bortolato B, G Sales PM, Machado-Vieira R, Berk M, McIntyre R

CNS Neurol Disord Drug Targets. 2014;13(10):1819-35.

Abstract

Major depressive disorder (MDD) is associated with cognitive dysfunction encompassing several domains, including memory, executive function, processing speed and attention. Cognitive deficits persist in a significant proportion of patients even in remission, compromising psychosocial functioning and workforce performance. While monoaminergic antidepressants may improve cognitive performance in MDD, most antidepressants have limited clinical efficacy. The overarching aims of this review were: (1) to synthesize extant literature on putative biological pathways related to cognitive dysfunction in MDD and (2) to review novel neurotherapeutic targets for cognitive enhancement in MDD. We found that reciprocal and overlapping biological pathways may contribute to cognitive dysfunction in MDD, including an hyperactive hypothalamic-pituitary-adrenal axis, an increase in oxidative and nitrosative stress, inflammation (e.g., enhanced production of pro-inflammatory cytokines), mitochondrial dysfunction, increased apoptosis as well as a diminished neurotrophic support. Several promising neurotherapeutic targets were identified such as minocycline, statins, anti-inflammatory compounds, N-acetylcysteine, omega-3 poliunsaturated fatty acids, erythropoietin, thiazolidinediones, glucagon-like peptide-1 analogues, S-adenosyl-l-methionine (SAMe), cocoa flavonols, creatine monohydrate and lithium. Erythropoietin and SAMe had pro-cognitive effects in randomized controlled trials (RCT) involving MDD patients. Despite having preclinical and/or preliminary evidences from trials suggesting possible efficacy as novel cognitive enhancing agents for MDD, no RCT to date was performed for most of the other therapeutic targets reviewed herein. In conclusion, multiple biological pathways are involved in cognitive dysfunction in MDD. RCTs testing genuinely novel pro-cognitive compounds for MDD are warranted.

‘Hot’ cognition in major depressive disorder: a systematic review

Miskowiak KW, Carvalho AF

CNS Neurol Disord Drug Targets. 2014;13(10):1787-803.

Abstract

Major depressive disorder (MDD) is associated with significant cognitive dysfunction in both ‘hot’ (i.e. emotion-laden) and ‘cold’ (non-emotional) domains. Here we review evidence pertaining to ‘hot’ cognitive changes in MDD. This systematic review searched the PubMed and PsycInfo computerized databases in May 2014 augmented by hand searches of reference lists. We included original articles in which MDD participants (or their healthy first-degree relatives) and a healthy control group were compared on standard measures of emotional processing or reward/ punishment processing as well as systematic reviews and meta-analyses. A total of 116 articles met the inclusion criteria of which 97 were original studies. Negative biases in perception, attention and memory for emotional information, and aberrant reward/punishment processing occur in MDD. Imbalanced responses to negative stimuli in a fronto-limbic network with hyper-activity in limbic and ventral prefrontal regions paired with hypo-activity of dorsal prefrontal regions subserve these abnormalities. A cross-talk of ‘hot’ and ‘cold’ cognition disturbances in MDD occurs. Disturbances in ‘hot cognition’ may also contribute to the perpetuation of negative emotional states in MDD. Limited success in the identification of susceptibility genes in MDD has led to great research interest in identifying vulnerability biomarkers or endophenotypes. Emerging evidence points to the persistence of ‘hot’ cognition dysfunction during remission and to subtle ‘hot’ cognition deficits in healthy relatives of patients with MDD. Taken together, these findings suggest that abnormalities in ‘hot’ cognition may constitute a candidate neurocognitive endophenotype for depression.