Major depressive disorder: a possible typisation according to serotonin, inflammation, and metabolic syndrome

Abstract

Objective: Major depressive disorder (MDD) is closely related to obesity, inflammation, and insulin resistance, all together being etiologically linked to metabolic syndrome development. The depressive disorder has a neuroendocrinological component, co-influencing the metabolic syndrome, while metabolic syndrome (MetS) is characterized by increased cytokine levels, which are known to cause a depressed mood. This study aimed to establish biological subtypes of the depressive disorder based on researched clinical, laboratory, and anthropometric variables. Methods: We performed a cross-sectional study on a sample of 293 subjects (145 suffering from a depressive disorder and 148 healthy controls). Results were analyzed with multivariate statistical methods as well as with cluster and discriminant analysis. In order to classify depressive disorder on the grounds of laboratory, anthropometric, and clinical parameters, we performed cluster analysis, which resulted in three clusters. Results: The first cluster is characterized by low platelet serotonin, high cortisol levels, high blood glucose levels, high triglycerides levels, high HAMD score, increased waist circumference, high CRP values, and a high number of previous depressive episodes, was named Combined (Metabolic) depression. The inflammatory depression cluster is defined with average platelet serotonin values, normal cortisol, and all other parameter levels, except for increased IL-6 levels. The serotoninergic depression cluster is characterized by markedly low platelet serotonin, and all other parameters are within the normal range. Conclusions: From a biological point of view, depressive disorder is not uniform, and as such, these findings suggest potential clinically useful and generalizable biological subtypes of depressive disorder.