Inflammatory phenotype and T‐cell mitochondrial reactive oxygen species in young adults with major depressive disorder
Authors: Grotle Ann‐Katrin , Darling Ashley M. , Saunders Erika F. , Fadel Paul J. , Greaney Jody L. , Trott Daniel W. 
Published: May 2022

Background

Major depressive disorder (MDD) is prevalent in young adults and projected to rise further with the COVID pandemic. Notably, MDD is associated with an increased risk of cardiovascular disease (CVD) and mortality. Although the mechanisms are unclear, evidence supports chronic systemic inflammation as a major contributor to CVD risk in older adults with MDD. However, whether an inflammatory phenotype is present in young adults with MDD prior to the onset of CVD and other comorbidities is equivocal. Recent work has implicated the sympathetic nervous system and specifically norepinephrine as a potent driver of inflammation via stimulating an increase in T‐cell mitochondrial reactive oxygen species (T‐cell mitoROS). Given previous findings of elevated plasma norepinephrine and inflammation in MDD, the purpose of this study was to examine the potential for a T‐cell mitoROS pro‐inflammatory pathway in young otherwise healthy adults with MDD. We hypothesized that young adults with MDD but otherwise free of clinical disease would have augmented circulating pro‐inflammatory cytokines and T‐cell mitoROS compared to young healthy adults without MDD (HA).

Methods

All participants underwent a structured diagnostic neuropsychiatric interview to determine the presence or absence of MDD based on the DSM‐5 diagnostic criteria for MDD. Systemic pro and anti‐inflammatory cytokines and T‐cell mitoROS were measured in 14 healthy young adults with MDD of mild‐to‐moderate severity (non‐medicated; age: 23±2 years) and 11 HA (age: 22±1 years). Serum cytokines were detected using LEGENDplex Human Essential Immune Response panel and assessed by flow cytometry. Seven serum cytokines related to the norepinephrine‐T‐cell mitoROS‐inflammation pathway were measured. Immune cells were isolated from whole blood by red blood cell lysis. T‐cell mitoROS was measured by labeling with antibodies against CD3+ (total T cells) and mitoROS targeted fluorogenic dye (MitoSoxRED) and assessed by flow cytometry. All data are expressed as mean ± SE.

Results

For pro‐inflammatory cytokines, there were no differences between MDD and HA for IL‐6 (41±18 pg/mL; 92± 66 pg/mL, P=0.66), IL‐17A (7±3 pg/mL; 17±8 pg/mL, P=0.13), TNF‐α (19±9 pg/mL; 36±18 pg/mL, P=0.20), IFNγ (120±70 pg/mL; 201±137 pg/mL, P=0.34) or IL‐2 (5±2 pg/mL; 13±6 pg/mL, P=0.25), respectively. Likewise, no differences were found in anti‐inflammatory cytokines between MDD and HA for IL‐10 (18±9 pg/mL; 78±57 pg/mL, P=0.19) or IL‐4 (33±15 pg/mL; 95±46 pg/mL, P=0.13), respectively. In contrast, T‐cell mitoROS was significantly elevated in MDD (34402±13353 a.u) compared to HA (6258±2942 a.u, P<0.05).

Conclusion

These preliminary findings suggest T‐cell mitoROS but not circulating cytokine profiles are different between young adults with and without MDD. Thus, an elevated T‐cell mitoROS may represent an early marker of immune system alterations and inflammation in MDD.