TABLE 3.

The contribution of selected serum inflammation biomarker and cytokine concentrations as independent predictors of tryptophan, its metabolites, and pyridoxal 5′-phosphate in a subset of healthy young adults from the TSS¹

	Neopterin		IL-10		TNF-α		MCP-1		CRP
Dependent variable	Estimate2	P	Estimate2	P	Estimate2	P	Estimate2	P	Estimate2	P
Kynurenine-to-tryptophan ratio	0.26	<0.0001	0.11	0.003	0.07	0.047	−0.05	0.22	0.06	0.12
Tryptophan	−0.10	0.012	0.01	0.72	−0.12	<0.001	0.11	0.003	−0.05	0.21
Kynurenine	0.17	<0.0001	0.13	0.0002	−0.04	0.31	0.06	0.09	0.02	0.63
3-Hydroxykynurenine	0.10	0.026	0.10	0.012	0.05	0.25	−0.01	0.76	0.08	0.08
Kynurenic acid	0.07	0.08	0.00	0.92	−0.05	0.18	0.08	0.031	−0.06	0.15
Xanthurenic acid	−0.05	0.25	0.02	0.61	−0.03	0.46	0.06	0.13	0.01	0.73
Anthranilic acid	0.11	0.004	0.05	0.17	−0.06	0.11	0.04	0.23	−0.03	0.49
3-Hydroxyanthranilic acid	−0.01	0.78	0.08	0.043	0.00	0.91	0.04	0.33	0.09	0.039
Pyridoxal 5′-phosphate	−0.16	<0.0001	−0.03	0.46	−0.03	0.39	0.00	0.96	−0.11	0.005

¹The TSS included 2508 participants. Subjects included in the current study were from a random subset of 800 TSS participants on whom cytokine analysis was performed. Subjects with CRP >10 mg/L or neopterin >10 nmol/L or with multiple (>2) cytokines >7 times the IQR were excluded as having possible subclinical inflammation, leaving a final set of 737 subjects for data analysis. CRP, C-reactive protein; MCP-1, monocyte chemoattractant protein 1; TSS, Trinity Student Study.

²For regression analysis, all tryptophan metabolites and cytokines were normalized by inverse normal-rank transformations. Pyridoxal 5′-phosphate and each of the tryptophan metabolites were treated as dependent variables in separate multinomial regression models, in which they were regressed on the measured cytokines for independent association and adjusted for sex, BMI, smoking, alcohol intake and oral contraceptive use. Statistical significance was set at P < 0.05.