Sustained elevation of serum interleukin-6 and relative insensitivity to hydrocortisone differentiates posttraumatic stress disorder with and without depression.
BACKGROUND
Elevated levels of proinflammatory cytokines, especially interleukin-6 (IL-6), can mediate the greater risk for cardiovascular disease in individuals with posttraumatic stress disorder (PTSD), particularly in those with comorbid major depressive disorder (MDD). However, IL-6 levels are not consistently elevated in either PTSD or MDD. Although PTSD is associated with supersensitivity to glucocorticoids; prior studies have not evaluated the effect of comorbid MDD.


METHODS
Serum IL-6 levels were measured hourly between 7:00 pm and 7:00 am in individuals with PTSD with comorbid MDD (PTSD + MDD) (n = 9) and compared with those with PTSD without MDD (PTSD - MDD) (n = 9) and nontraumatized healthy control subjects (n = 14). Group differences in serum IL-6, plasma adrenocorticotropic hormone (ACTH), and plasma cortisol response to 30 mg of intravenous hydrocortisone were evaluated using linear mixed models.


RESULTS
Only subjects with PTSD + MDD exhibited higher, overnight serum IL-6 levels compared with individuals with PTSD - MDD (p < .01) and healthy control subjects (p < .001). Peak overnight IL-6 levels positively correlated with severity of PTSD (r = .56, p < .01) and depressive symptoms (r = .54, p < .01). Hydrocortisone administration significantly reduced IL-6 levels in both PTSD groups; however, IL-6 levels in PTSD + MDD were higher than both PTSD - MDD (p < .05) and healthy control subjects (p < .01). Following hydrocortisone administration, there was a greater reduction in levels of ACTH in PTSD - MDD compared with control subjects (p < .01).


CONCLUSIONS
Sustained elevations of overnight IL-6 levels and relatively decreased sensitivity to hydrocortisone distinguish PTSD + MDD from PTSD - MDD. Novel strategies that decrease IL-6 levels offer a new direction in the prevention and treatment of PTSD and associated comorbid medical illnesses.
Gill
Jessica
J
National Institutes of Nursing Research, Bethesda, Maryland, USA.
Luckenbaugh
David
D
Charney
Dennis
D
Vythilingam
Meena
M
D000293:Adolescent; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000328:Adult; D019540:Area Under Curve; D003865:Major Depressive Disorder / Q000097:blood* / Q000150:complications / Q000175:diagnosis*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood / Q000494:pharmacology*; D015850:Interleukin-6 / Q000097:blood*; D008297:Male; D008875:Middle Aged; D013313:Stress Disorders, Post-Traumatic / Q000097:blood* / Q000150:complications / Q000175:diagnosis*
D015850:Interleukin-6; D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone