Tryptophan/kynurenine metabolism in human leukocytes is independent of superoxide and is fully maintained in chronic granulomatous disease

Abstract

In chronic granulomatous disease (CGD), defective phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity causes reduced superoxide anion (O2.-) radical production leading to frequent infections as well as granulomas and impaired wound healing indicative of excessive inflammation. Based on recent mouse studies, the lack of O 2.--dependent interferon γ (IFNγ)-induced synthesis of kynurenine (kyn), an anti-inflammatory tryptophan metabolite produced by indolamine 2,3 deoxygenase (IDO), was proposed as a cause of hyperinflammation in CGD and this pathway has been considered for clinical intervention. Here, we show that IFNγ induces normal levels of kynurenine in cultures of O2.--deficient monocytes, dendritic cells, and polymorphonuclear leukocytes from gp91PHOX- or p47 PHOX-deficient human CGDdonors. Kynurenine accumulation was dose- and time-dependent as was that of a downstream metabolite, anthranilic acid. Furthermore, urinary and serum levels of kynurenine and a variety of other tryptophan metabolites were elevated rather than suppressed in CGD donors. Although we did not specifically evaluate kyn metabolism in local tissue or inflamed sites in humans, our data demonstrates that O2.- anion is dispensable for the rate-limiting step in tryptophan degradation, and CGD patients do not appear to have either hematopoietic cell or systemic deficits in the production of the anti-inflammatory kynurenine molecule.