Differences in the association of inflammation and tryptophan with depressive symptoms between white and non-white chronic dialysis patients.

Abstract

Possibly, different biochemical parameters are involved in the development of depressive symptoms in white and non-white dialysis patients. We examined whether the association between inflammation and depressive symptoms and between tryptophan and depressive symptoms differs between white and non-white dialysis patients and whether the association between inflammation and depressive symptoms is mediated by tryptophan degradation along the kynurenine pathway in both groups. Depressive symptoms were measured with the BDI-II. HsCRP, IL-1β, IL-6, IL-10, and TNFα and tryptophan and its degradation products kynurenine and 3-hydroxykynurenine were measured in 270 white and 220 non-white patients. The presence of depressive symptoms was significantly higher in non-white patients (51%) than in white patients (37%) (P<0.01). Among white patients, HsCRP was significantly associated with depressive symptoms (β=0.6 (95% CI: 0.1-1.2)). Among non-white patients, significant associations with depressive symptoms were found for both HsCRP (β=1.0 (95% CI: 0.1-2.0)) and IL-6 (β=2.6 (95% CI: 0.8-4.4)). Tryptophan levels were only significantly associated with depressive symptoms in non-white patients (β=-0.3 (95% CI: -0.4--0.1)). Tryptophan degradation along the kynurenine pathway did not mediate the association between inflammatory markers and depressive symptoms in either group. Our results indicate that for white and non-white dialysis patients different biochemical parameters are associated with depressive symptoms.