Tryptophan Metabolism in Patients With Chronic Kidney Disease Secondary to Type 2 Diabetes: Relationship to Inflammatory Markers - PubMed (original) (raw)

Tryptophan Metabolism in Patients With Chronic Kidney Disease Secondary to Type 2 Diabetes: Relationship to Inflammatory Markers

Subrata Debnath et al. Int J Tryptophan Res. 2017.

Abstract

Objective: Type 2 diabetes (T2D) is the primary case of chronic kidney disease (CKD). Inflammation is associated with metabolic dysregulation in patients with T2D and CKD. Tryptophan (TRP) metabolism may have relevance to the CKD outcomes and associated symptoms. We investigated the relationships of TRP metabolism with inflammatory markers in patients with T2D and CKD.

Methods: Data were collected from a well-characterized cohort of type 2 diabetic individuals with all stages of CKD, including patients on hemodialysis. Key TRP metabolites (kynurenine [KYN], kynurenic acid [KYNA], and quinolinic acid [QA]), proinflammatory cytokines (tumor necrosis factor-α [TNF-α] and interleukin-6 [IL-6]), and C-reactive protein were measured in plasma. The KYN/TRP ratio was utilized as a surrogate marker for indoleamine 2,3-dioxygenase 1 (IDO1) enzyme activity.

Results: There was a significant inverse association between circulating TRP level and stages of CKD (P< 0.0001). Downstream bioactive TRP metabolites KYN, KYNA, and QA were positively and robustly correlated with the severity of kidney disease (P < 0.0001). In multiple linear regression, neither TNF-α nor IL-6 was independently related to KYN/TRP ratio after adjusting for estimated glomerular filtration rate (eGFR). Only TNF-α was independently related to KYN after taking into account the effect of eGFR.

Conclusions: Chronic kidney disease secondary to T2D may be associated with accumulation of toxic TRP metabolites due to both inflammation and impaired kidney function. Future longitudinal studies to determine whether the accumulation of KYN directly contributes to CKD progression and associated symptoms in patients with T2D are warranted.

Keywords: Chronic kidney disease; indoleamine 2,3-dioxygenase 1; inflammatory cytokines; kynurenine; tryptophan; type 2 diabetes.

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Conflict of interest statement

DECLARATION OF CONFLICTING INTERESTS: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.

Figure 1.

Simplified pathway of tryptophan metabolism in mammals. Dashed arrow indicates multiple processes. Solid arrow indicates single process. IDO-1, indoleamine 2,3-dioxygenase 1; IDO-2, indoleamine 2,3-dioxygenase 2; KAT, kynurenine aminotransferase; KMO, kynurenine 3-monooxygenase; KRA, kynureninase; NAD, nicotinamide adenine dinucleotide; TDO, tryptophan 2,3-dioxygenase.

Figure 2.

Figure 2.

Relationship between kidney function and tryptophan metabolites.a aPenalized smoothing splines were used to assess the relationship between eGFR to tryptophan metabolites. eGFR indicates estimated glomerular filtration rate.

Figure 3.

Figure 3.

Kynurenine/tryptophan ratio by stages of chronic kidney disease. Data are geometric mean and 95% confidence interval. Statistical difference between stage 1 and stage 2: P = 0.03; stage 2 and stage 3: P = 0.003; stage 3 and stage 4: P = 0.43; stage 4 and stage 5: P < 0.0001.

Comment in

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