The year of immunopsychiatry: A special issue that foresaw the future

Applicability, potential and limitations of TSPO PET imaging as a clinical immunopsychiatry biomarker

PURPOSE

TSPO PET imaging may hold promise as a single-step diagnostic work-up for clinical immunopsychiatry. This review paper on the clinical applicability of TSPO PET for primary psychiatric disorders discusses if and why TSPO PET imaging might become the first clinical immunopsychiatry biomarker and the investment prerequisites and scientific advancements needed to accommodate this transition from bench to bedside.

METHODS

We conducted a systematic search of the literature to identify clinical studies of TSPO PET imaging in patients with primary psychiatric disorders. We included both original case-control studies as well as longitudinal cohort studies of patients with a primary psychiatric diagnosis.

RESULTS

Thirty-one original studies met our inclusion criteria. In the field of immunopsychiatry, TSPO PET has until now mostly been studied in schizophrenia and related psychotic disorders, and to a lesser extent in mood disorders and neurodevelopmental disorders. Quantitative TSPO PET appears most promising as a predictive biomarker for the transdiagnostic identification of subgroups or disease stages that could benefit from immunological treatments, or as a prognostic biomarker forecasting patients' illness course. Current scanning protocols are still too unreliable, impractical and invasive for clinical use in symptomatic psychiatric patients.

CONCLUSION

TSPO PET imaging in its present form does not yet offer a sufficiently attractive cost-benefit ratio to become a clinical immunopsychiatry biomarker. Its translation to psychiatric clinical practice will depend on the prioritising of longitudinal research and the establishment of a uniform protocol rendering clinically meaningful TSPO uptake quantification at the shortest possible scan duration without arterial cannulation.

Back to the future of psychoneuroimmunology: Studying inflammation-induced sickness behavior

What do we know about sickness behavior? In this article, I guide you through some of the complexity of sickness behavior occurring after an immune challenge. I highlight the many features of behavioral and affective changes induced during experimental endotoxemia in humans, and describe how little we know about many of these features. I argue that we need to dismantle the components of inflammation-induced sickness behavior, and study each component in detail. I also point out the large inter-individual differences in inflammation-induced behavioral and affective changes, and the fact that psychosocial factors likely interact with inflammation to shape inflammation-induced sickness behavior. PNI clearly lacks investigations of the vulnerability and resilient factors underlying the inter-individual variability in sickness behavior. Throughout the article, I base my argument on my published articles, and provide concrete examples from my experience and the data that I have collected over the past 10 years. Given the relevance of inflammation-induced sickness behavior for inflammation-associated depression and for how people react to infections, I encourage current and future psychoneuroimmunologists to return towards basic science of sickness behavior.

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Inflammation-related sickness behavior is relevant for inflammation-associated depression

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The many features of sickness behavior should be investigated in detail

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There are large inter-individual variability in sickness behavior

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Vulnerability and resilient factors predicting sickness responses are little known

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I call for a return towards basic science of sickness behavior.

The future of immunopsychiatry: Three milestones to clinical innovation

Psychoneuroimmunology, the area of research dedicated to understanding the fundamental interactions between the central nervous system and the immune system, has given rise to the development of Immunopsychiatry, a new discipline which harnesses the immune system to produce beneficial outcomes for mental health problems. Immunopsychiatry has the potential to become a clinically relevant specialty area in psychiatric practice, but has not yet been adopted by the wider mental health community. This paper aims to map out the future trajectory of Immunopsychiatry on its road towards science-to-policy knowledge translation and clinical implementation. Three critical milestones which will need to be reached in order for Immunopsychiatry to fulfil its promise for clinical innovation are discussed: a clear definition of patients who fall within the immunopsychiatric continuum; demonstration of well-defined clinical benefit and incorporation in clinical guidelines; and convergence with other paradigms in biological psychiatry.

The Anti-Inflammatory Role of Omega-3 Polyunsaturated Fatty Acids Metabolites in Pre-Clinical Models of Psychiatric, Neurodegenerative, and Neurological Disorders

Inflammation has been identified as one of the main pathophysiological mechanisms underlying neuropsychiatric and neurodegenerative disorders. Despite the role of inflammation in those conditions, there is still a lack of effective anti-inflammatory therapeutic strategies. Omega-3 polyunsaturated fatty acids (n-3 PUFAs) can reduce depressive symptoms and exert anti-inflammatory action putatively by the production of distinct n-3 PUFA-derived metabolites, such as resolvins D (RvD) and E (RvE) series, maresins (MaR) and protectins (PD), which are collectively named specialized pro-resolving mediators (SPMs) and act as strong anti-inflammatory agents. In this review we summarize evidence showing the effects of treatment with those metabolites in pre-clinical models of psychiatric, neurodegenerative and neurological disorders. A total of 25 pre-clinical studies were identified using the PubMed database. Overall, RvD and RvE treatment improved depressive-like behaviors, whereas protectins and maresins ameliorated neurological function. On a cellular level, RvDs increased serotonin levels in a model of depression, and decreased gliosis in neurodegenerative disorders. Protectins prevented neurite and dendrite retraction and apoptosis in models of neurodegeneration, while maresins reduced cell death across all studies. In terms of mechanisms, all SPMs down-regulated pro-inflammatory cytokines. Resolvins activated mTOR and MAP/ERK signaling in models of depression, while resolvins and maresins activated the NF-κB pathway in models of neurodegeneration and neurological disorders. Our review indicates a potential promising approach for tailored therapy with n-3 PUFAs-derived metabolites in the treatment of psychiatric, neurodegenerative, and neurological conditions.

Magnocellular Vasopressin and the Mechanism of "Glucocorticoid Escape"

It is now widely accepted that magnocellular vasopressinergic neurons in the supraoptic and paraventricular nuclei participate in the control of adrenocorticotropin secretion by the anterior pituitary gland. However, it remains to be explored in further detail, when and how these multifunctional neurons are involved in the control of anterior pituitary function. This paper highlights the role of magnocellular vasopressin in the hypothalamic pituitary adrenocortical axis with special reference to escape from glucocorticoid feedback inhibition. The signaling mechanisms underlying glucocorticoid escape by pituitary corticotrope cells, as well as the wider physiologic and pathologic contexts in which escape is known to occur-namely strenuous exercise, and autoimmune inflammation will be considered. It is proposed that by inducing escape from glucocorticoid feedback inhibition at the pituitary level, magnocellular vasopressin is critically important for the anti-inflammatory, and immunosuppressant actions of endogenous corticosteroids.