Brain insulin resistance: A treatment target for cognitive impairment and anhedonia in depression.

Type 2 Diabetes Mellitus (T2DM) and Major Depressive Disorder (MDD) are leading causes of disability worldwide. Indeed, both are costly and burdensome diseases at both individual and socio-economic levels. Notably, there are similar pathophysiological elements, which might explain the overlap in phenotypic symptoms and the high rate of comorbidity. Brain insulin resistance is a shared metabolic abnormality amongst many individuals with T2DM and MDD. Patients with either or both diseases often exhibit disturbances in cognition and mood, as well as the presence of anhedonia-like symptoms. However, individuals with T2DM with high glycemic control have reduced cognitive and depressive symptom burden. Based on this evidence, it is possible that repurposing therapies approved for treating insulin resistance may be useful in treating cognitive and anhedonia symptoms in depression. The objective of this review is to discuss the relationship between brain insulin resistance and depression, as well as possible disease modifying therapeutic agents targeting insulin signalling.