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

Objective: 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.

Method: 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.

Results: 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.

Conclusion: Our results indicate that for white and non-white dialysis patients different biochemical parameters are associated with depressive symptoms.