Neurobiological Pathways between Chronic Stress and Depression: Dysregulated Adaptive Mechanisms?

Explainable stress type classification captures physiologically relevant responses in the Maastricht Acute Stress Test

Introduction

Current stress detection methods concentrate on identification of stress and non-stress states despite the existence of various stress types. The present study performs a more specific, explainable stress classification, which could provide valuable information on the physiological stress reactions.

Methods

Physiological responses were measured in the Maastricht Acute Stress Test (MAST), comprising alternating trials of cold pressor (inducing physiological stress and pain) and mental arithmetics (eliciting cognitive and social-evaluative stress). The responses in these subtasks were compared to each other and to the baseline through mixed model analysis. Subsequently, stress type detection was conducted with a comprehensive analysis of several machine learning components affecting classification. Finally, explainable artificial intelligence (XAI) methods were applied to analyze the influence of physiological features on model behavior.

Results

Most of the investigated physiological reactions were specific to the stressors, and the subtasks could be distinguished from baseline with up to 86.5% balanced accuracy. The choice of the physiological signals to measure (up to 25%-point difference in balanced accuracy) and the selection of features (up to 7%-point difference) were the two key components in classification. Reflection of the XAI analysis to mixed model results and human physiology revealed that the stress detection model concentrated on physiological features relevant for the two stressors.

Discussion

The findings confirm that multimodal machine learning classification can detect different types of stress reactions from baseline while focusing on physiologically sensible changes. Since the measured signals and feature selection affected classification performance the most, data analytic choices left limited input information uncompensated.

Psilocybin induces acute and persisting alterations in immune status in healthy volunteers: An experimental, placebo-controlled study

Patients characterized by stress-related disorders such as depression display elevated circulating concentrations of pro-inflammatory cytokines and a hyperactive HPA axis. Psychedelics are demonstrating promising results in treatment of such disorders, however the mechanisms of their therapeutic effects are still unknown. To date the evidence of acute and persisting effects of psychedelics on immune functioning, HPA axis activity in response to stress, and associated psychological outcomes is preliminary. To address this, we conducted a placebo-controlled, parallel group design comprising of 60 healthy participants who received either placebo (n = 30) or 0.17 mg/kg psilocybin (n = 30). Blood samples were taken to assess acute and persisting (7 day) changes in immune status. Seven days' post-administration, participants in each treatment group were further subdivided: 15 underwent a stress induction protocol, and 15 underwent a control protocol. Ultra-high field (7-Tesla) magnetic resonance spectroscopy was used to assess whether acute changes in glutamate or glial activity were associated with changes in immune functioning. Finally, questionnaires assessed persisting self-report changes in mood and social behavior. Psilocybin immediately reduced concentrations of the pro-inflammatory cytokine tumor necrosis factor-α (TNF-α), while other inflammatory markers (interleukin (IL)- 1β, IL-6, and C-reactive protein (CRP)) remained unchanged. Seven days later, TNF-α concentrations returned to baseline, while IL-6 and CRP concentrations were persistently reduced in the psilocybin group. Changes in the immune profile were related to acute neurometabolic activity as acute reductions in TNF-α were linked to lower concentrations of glutamate in the hippocampus. Additionally, the more of a reduction in IL-6 and CRP seven days after psilocybin, the more persisting positive mood and social effects participants reported. Regarding the stress response, after a psychosocial stressor, psilocybin did not significantly alter the stress response. Results are discussed in regards to the psychological and therapeutic effects of psilocybin demonstrated in ongoing patient trials.

Stress, a Brief Update

Stress is fundamental for health and adaptation; it is an evolutionarily conserved response that involves several systems in the organism. The study of the stress response could be traced back to the end of the nineteenth century with George Beard's or Claude Bernard's work and, from that moment on, several studies that have allowed the elucidation of its neurobiology and the consequences of suffering from it were consolidated. In this theoretical review, we discuss the most relevant researches to our knowledge on the study of stress response, from the concept of stress, its neurobiology, the hormonal response during stress, as well as its regulation, the effects of acute and chronic stress, stress from cognition, the different stress responses during life, as well as its relationship with different psychiatric disorders. Taken together, the reviewed research updates the classic perspective on stress, increasing the factors that should be considered in research to explore the effects of stress on health.

Interleukin-6 expression and its modulation by diacerein in a rat model of chronic stress induced cardiac dysfunction

People with chronic stress have higher levels of pro-inflammatory cytokines, which enhance their susceptibility to cardiovascular diseases. Diacerein has ability to modulate pro-inflammatory cytokines such as IL-1β and IL-6; however, its efficacy in chronic stress associated cardiovascular diseases is not yet assessed. In this study, we standardized a rat model of chronic unpredictable stress (CUS) demonstrating cardiovascular dysfunctions and further assessed the effect of IL-6 modulator, diacerein, on cardiovascular functions in CUS exposed rats. The CUS procedure consisted of exposing male albino Wistar rats to random stressors, everyday for 8 weeks. The binding affinity of diacerein with IL-6 was ascertained using Docking tools viz AutoDock and SwissDock. Moreover, diacerein was administered (50 mg/kg/day x 20 days P.O) post CUS exposure to rats and the serum IL-6 levels and heart functions of CUS rats were determined by ELISA and ECG-HRV analysis, respectively. 8 weeks of CUS exposure resulted in two-fold increase in serum corticosterone and IL-6 levels in rats. The ECG and HRV analysis of CUS rats showed altered sinus rhythm, elevated heart rate, systolic blood pressure and sympathetic tone. Molecular docking studies revealed diacerein high binding affinity towards IL-6 receptor. The post-treatment of diacerein in CUS rats prevented these cardiovascular dysfunctions. Our findings thus suggests that IL-6 may have a prominent role in chronic stress induced cardiovascular dysfunctions and diacerein, could be used as a preventive measure for such conditions.

Salivary Alpha-amylase Enzyme and Salivary Cortisol Level in Depression after Treatment with Fluoxetine

Hypothalamic-Pituitary-Adrenal (HPA) axis and its end product cortisol have been extensively investigated in patients with depressive disorders for many years. Recently, salivary alpha-amylase (sAA) had emerged as a new biomarker with non-invasive and more convenience protocol for measuring sympathetic activity which were also associated with depression. Selective Serotonin Reuptake Inhibitor (SSRI) is antidepressant drug extensively used to treat depression. The aim of this study was to determine whether decrease of sAA and salivary cortisol levels could be observed in subjects with depression who were treated by fluoxetine. The total subjects were 25 depressed subjects and 10 healthy controls. sAA was examined before therapy, and after 2, 4 and 6 weeks of fluoxetine administration using a portable cocorometer. Salivary cortisol was examined before therapy, after 4 and 6 weeks of fluoxetine administration with Elisa method. The therapeutic effect was assessed with Hamilton Depression Rating Scale (HDRS). Results: sAA and cortisol level were significantly decreased after fluoxetine administration (p<0.001) followed by at least 50% reduction of HDRS scores after 6 weeks of fluoxetine administration. Levels of sAA and cortisol were higher in the depression group than in the healthy control. Conclusions: Measurement of sAA levels can be used as a potential biomarker of therapeutic response in depressed patients in addition to salivary cortisol.

Chronic exposure to metal fume PM2.5 on inflammation and stress hormone cortisol in shipyard workers: A repeat measurement study

Particulate matter with an aerodynamic diameter of ≤ 2.5 µm (PM_2.5) has been linked to adverse health outcomes in welding workers. The objective of this study was to investigate associations of chronic exposure to metal fume PM_2.5 in shipyard workers with health outcomes. A longitudinal study was conducted to determine the effects of metal fume PM_2.5 on FeNO, urinary metals, urinary oxidative stress, inflammation, and stress hormones in workers. There were 20 office workers and 49 welding workers enrolled in this study who were followed-up for a second year. We observed that Fe, Zn, and Mn were abundant in PM_2.5 to which welding workers were personally exposed, whereas PM_2.5 to which office workers were personally exposed was dominated by Pb, Cu, and Zn. We observed in the first and/or second visits that urinary 8-iso-prostaglandin F2-α (PGF2α) and 8-hydroxy-2'-deoxy guanosine (8-OHdG) were significantly increased by exposure. An increase in urinary interleukin (IL)-6 and decreases in urinary serotonin and cortisol were observed in the first and/or second visits after exposure. PM_2.5 was associated with decreases in urinary 8-OHdG and cortisol among workers. Next, we observed that urinary Ni, Co, and Fe had significantly increased among workers after a year of exposure. Urinary metals were associated with decreases in urinary 8-iso-PGF2α and cortisol among workers. Urinary Ni, Cu, and Fe levels were associated with an increase in urinary IL-6 and a decrease in urinary cortisol among workers. In conclusion, chronic exposure to metal fume PM_2.5 was associated with inflammation and a cortisol deficiency in shipyard workers, which could associate with adrenal glands dysfunction.

Salivary Alpha Amylase Enzyme and Salivary Cortisol Level in Depression after Treatment with Fluoxetine

BACKGROUND: Hypothalamic-pituitary-adrenal axis and its end product cortisol have been extensively investigated in patients with depressive disorders for many years. Recently, salivary alpha-amylase (sAA) had emerged as a new biomarker with non-invasive and more convenience protocol for measuring sympathetic activity which were also associated with depression. Selective Serotonin Reuptake Inhibitor is antidepressant drug extensively used to treat depression. AIM: The aim of this study was to determine whether decrease of sAA and salivary cortisol levels could be observed in subjects with depression who were treated by fluoxetine. METHODS: The total subjects were 25 depressed subjects and ten healthy controls. sAA was examined before therapy, and after 2, 4, and 6 weeks of fluoxetine administration using a portable cocorometer. Salivary cortisol was examined before therapy, after 4 and 6 weeks of fluoxetine administration with Elisa method. The therapeutic effect was assessed with Hamilton Depression Rating Scale (HDRS). RESULTS: sAA and cortisol levels were significantly decreased after fluoxetine administration (p < 0.001), followed by at least 50% reduction of HDRS scores after 6 weeks of fluoxetine administration. Levels of sAA and cortisol were higher in the depression group than in the healthy control. CONCLUSIONS: Measurement of sAA levels can be used as a potential biomarker of therapeutic response in depressed patients in addition to salivary cortisol.