Biomarkers for Peripartum Depression : Focusing on aspects of the immune system and the metabolome

Sammanfattning: Peripartum depression is a common, multifactorial, and potentially devastating disease among new mothers. A biological marker for peripartum depression would facilitate early detection, better understanding of the pathophysiology, and identification of targets for treatment. Evidence is growing for a potential role of the immune system in depression outside the peripartum period. Major adaptations of the immune system occur during pregnancy, justifying the search for immunological markers for peripartum depression. The immune system is very complex and dynamic during pregnancy, complicating the study of associations with depression. The metabolome is also affected by pregnancy and is linked to the immune system via, e.g., the microbiota. Hence, metabolomic profiling could increase the understanding of peripartum depression. This thesis aimed to explore inflammatory markers and metabolic profiles in the peripartum period, in order to discover possible biomarkers, and to increase the understanding of the pathophysiology of peripartum depression.All studies were conducted within the Biology, Affect, Stress, Imaging, and Cognition (BASIC) study. The Edinburgh Postnatal Depression Scale and the Mini International Neuropsychiatric Interview were used to assess depressive symptoms. Multiplex Proximity Extension assays were used to analyze inflammatory markers in pregnancy and postpartum. Luminex Bio-Plex Pro Human Cytokine Assays were used to analyze cytokine levels across the peripartum period, and gas chromatography-mass spectrometry metabolomics were used for metabolic profiling. No marker was discriminative enough to be used on its own as a biomarker for peripartum depression. However, several inflammatory markers (such as STAM-BP, TRANCE, HGF, IL-18, FGF-23, and CXCL1) were identified as possible candidates for more advanced diagnostic algorithms. The results further pointed towards the importance of adaptation of the immune system during pregnancy and postpartum, where levels of cytokines such as VEGF-A might have an important role in antenatal and postpartum depression. The results even highlight the importance of examination timing. Lastly, the metabolic profiling suggested different subgroups of women with postpartum depressive symptoms, supporting theories of peripartum depression being a heterogeneous disease in need of subgroup definition.