STUDIO DELL¿ASSOCIAZIONE TRA INQUINAMENTO ATMOSFERICO E DISTURBO DEPRESSIVO MAGGIORE: RUOLO DI MARCATORI BIOLOGICI ED EPIGENETICI

INTRODUCTION: Major Depressive Disorder (MDD) is the most common mental disorder worldwide, affecting about 13% of adults and representing the second leading cause of disability. Despite its important social impact, etiopathology of the disease is still unknown. It has been suggested that MDD is a multifactorial disease, where genetic, environmental and biological factors may play a role. Among biological changes, epigenetic, immunological, and hormonal abnormalities have been found in MDD patients. Furthermore, recent studies have investigated whether air pollution may be a potential contributor of the onset of the disease, finding positive associations. AIMS: In a sample of MDD patients: evaluate the association between exposure to air pollution and MDD severity; evaluate the relationship between MDD severity and different biological (inflammatory, epigenetic, hormonal) markers; evaluate the association between air pollution and the biological variables of interest; quantify the specific contribution of the investigated biological variables in the chain of events linking air pollution exposure to MDD severity (in the present study, we will focus on epigenetic alterations only). METHODS: Overall, 416 MDD patients accessing the psychiatry unit of the Policlinico Hospital in Milan (Italy) from September 2020 to December 2022 have been recruited. Enrolled patients answered two questionnaires to collect demographic and lifestyle information, and history and characteristics of depression; they also donated a blood sample to examine biomarkers of interest. Severity of MDD was evaluated through five severity-of-illness rating scales: Montgomery-Asberg Depression Rating Scale (MADRS); Hamilton Depression Rating Scale (HAMD); Clinical Global Impression (CGI); Global Assessment of Functioning (GAF) and Sheehan Disability Scale (SDS). Daily exposures to particulate matter with diameter less than or equal to 10 (PM10) and 2.5 μm (PM2.5), and nitrogen dioxide (NO2) were estimated as daily means through the Flexible Air quality Regional (FARM) chemical transport model of the Lombardy regional Environmental Protection Agency (ARPA Lombardia), and assigned to each subject on the basis of his/her residential address. Daily average exposure to apparent temperature was also estimated, combining daily measurements of ambient temperature, humidity, and wind speed, retrieved from ARPA weather monitoring stations closest to patients’ residential addresses. Daily estimates of both apparent temperature and air pollutants were averaged to obtain moving averages of exposure. Multivariate regression models were used to assess the associations between air pollutant concentrations and MDD severity scales, air pollutants and methylation of CLOCK (circadian locomotor output cycles protein kaput) and CLOCK-related genes, and methylation of CLOCK and CLOCK-related genes and MDD severity scales. RESULTS: Two-thirds of included patients were females and about one-third had a family history of depression. Most women had depression with symptoms of anxiety, while men had predominantly melancholic depression; they were also more likely to experience suicidal and addictive behaviors. Average exposure to NO2 in the two weeks preceding recruitment (lag0-14) was associated with a worsening of MDD severity [HAMD: β=2.09, 95% CI (0.63; 3.56); CGI: β=0.27, 95% CI (0.02; 0.51); and GAF: β=-1.96, 95% CI (-3.60; -0.33)], while particulate matter exposure (PM10, PM2.5) was associated with MDD severity only when temperatures were low or among hypersusceptible subjects. Short-term exposure to PM10 was associated with hypomethylation of CRY2 and hypermethylation of OX1R, CRY1, and ARNTL at different lags of exposure within the two weeks preceding recruitment. Long-term exposure to PM10 (average of the three- and six-months preceding recruitment) was positively associated with CRY1 and negatively associated with CRY2. Results were similar for PM2.5 exposure. When short-term exposure to NO2 was considered, we observed an increase methylation of CRY1 and a reduced methylation of CRY2. Long-term exposure to NO2 was positively associated to the methylation of CRY1 and HERVW. In the whole population, hypermethylation of CLOCK was associated with less severe scores of depression. This association was found to be stronger in the subtype of depression “with strong symptoms of anxiety”. Hypermethylation of OXTR was associated with more severe “melancholic / psychotic / no prevalent” type depression. CONCLUSIONS: Exposure to PM10 and PM2.5 did not exert a direct effect on the severity of depressive symptoms, while their influence emerged more clearly among hypersusceptible subjects. In addition, PMs had a greater significant impact on MDD severity when temperatures were very low. NO2 exposure was strongly associated with MDD severity in the whole population and showed higher effects among hypersusceptible subjects as well as with concomitant exposures to low temperatures. Short- and long-term exposure to particulate matter resulted associated with altered methylation of CLOCK and CLOCK-related genes, which can be involved in circadian rhythms, often affected by depression. The hypermethylation of CLOCK was associated with lower scores of MDD severity suggesting (conversely) that the hypomethylation of CLOCK could be associated with a worsening of depressive symptoms. A finding consistent with preliminary data from the literature (1) which have highlighted an increased expression of CLOCK in subjects affected by MDD. Taken as a whole, these findings suggest a possible role of CLOCK and CLOCK-related genes in the pathway linking air pollution exposure to the worsening of MDD severity.