Criteria for treatment-resistant depression (TRD) and partially responsive depression (PRD) as subtypes of major depressive disorder (MDD) are not unequivocally defined. In the present document we used a Delphi-method-based consensus approach to define TRD and PRD and to serve as operational criteria for future clinical studies, especially if conducted for regulatory purposes. We reviewed the literature and brought together a group of international experts (including clinicians, academics, researchers, employees of pharmaceutical companies, regulatory bodies representatives, and one person with lived experience) to evaluate the state-of-the-art and main controversies regarding the current classification. We then provided recommendations on how to design clinical trials, and on how to guide research in unmet needs and knowledge gaps. This report will feed into one of the main objectives of the EUropean Patient-cEntric clinicAl tRial pLatforms, Innovative Medicines Initiative (EU-PEARL, IMI) MDD project, to design a protocol for platform trials of new medications for TRD/PRD.

Introduction Research linking type 2 diabetes and depression mostly relied on hospital-based diagnoses or prescription data, overlooking many outpatient diagnoses. We aimed to quantify the risks of depression in individuals newly diagnosed with type 2 diabetes, and type 2 diabetes in those newly diagnosed with depression, while exploring potential risk differences depending on age, sex, and follow-up time. Research design and methods We conducted a matched cohort study using German nationwide outpatient claims data from 2012 to 2022. Participants were individuals newly diagnosed with type 2 diabetes (N=294 642) or depression (N=1 271 537) in 2015, matched in a 1:4 ratio to controls without these conditions by age, sex, and region. The bidirectional risk was evaluated over an 8-year period using mixed-effects Cox proportional hazards models, adjusting for the Charlson Comorbidity Index, urbanicity, and area-level deprivation. Results New type 2 diabetes diagnosis was associated with higher depression risk over 8 years (N=54 561 with depression, HR=1.23, 99% CI=1.21 to 1.24). Similarly, depression diagnosis was linked to an increased type 2 diabetes risk (N=71 848 with type 2 diabetes, HR=1.15, 99% CI=1.14 to 1.17). The association between depression and type 2 diabetes was stronger in younger age groups, especially under 34 years. Findings held across sex-stratified analyses. Time stratification showed a more pronounced association between type 2 diabetes and depression risk during the earlier follow-up quarters, whereas the risk of developing type 2 diabetes after depression diagnosis remained constant throughout the follow-up period. Conclusions Our findings confirm a bidirectional link between type 2 diabetes and depression, particularly in younger individuals. As type 2 diabetes and depression are frequent, future research needs to study whether preventive approaches can reduce the risk of developing this comorbidity.

The liver partakes as a sensor and effector of peripheral metabolic changes and a regulator of systemic blood and nutrient circulation. As such, abnormalities arising from liver dysfunction can influence the brain in multiple ways, owing to direct and indirect bilateral communication between the liver and the brain. Interestingly, altered bile acid composition resulting from perturbed liver cholesterol metabolism influences systemic inflammatory responses, blood-brain barrier permeability, and neuron synaptic functions. Furthermore, bile acids produced by specific bacterial species may provide a causal link between dysregulated gut flora and neurodegenerative disease pathology through the gut-brain axis. This review will cover the role of bile acids—an often-overlooked category of active metabolites—in the development of neurological disorders associated with neurodegeneration. Further studies into bile acid signaling in the brain may provide insights into novel treatments against neurological disorders.