NPPA and coronary artery disorder: According to their findings, KYN/Trp ratio was increased and Trp was decreased in CAD compared to controls (Table 4), and Trp degradation correlates with the levels of neopterin, the formation of which is stimulated by IFN-γ, suggesting that the lowering of Trp concentration is caused by the IFN-γ-induced stimulation of IDO and subsequent activation of KP.