Do we need another inflammation marker in cardiac surgery?

Objectives: The inflammatory status following cardiac surgery is triggered by the release of vasodilating effector molecules such as kynurenine (KYN), which is formed from the amino acid tryptophan mediated by the enzyme indolamine-2,3-dioxygenase (IDO). KYN blood levels indicate IDO activity and can be quantified by a simple colorimetric test. In contrast, commonly used proinflammatory cytokines must be determined using ELISA technique. We investigated the time course of KYN during and after cardiac bypass surgery to evaluate it as an early marker of inflammation in comparison to established inflammatory markers.

Methods: This pilot study included 12 patients undergoing coronary bypass surgery with conventional extracorporeal circulation. Blood samples were taken 24 h before surgery, at the beginning of anaesthesia, seven times during surgery, at the arrival on ICU, and 12, 24, and 48 h after arrival. Leukocytes, CRP, ICAM-1, P-selectin, TNF-alpha and KYN were measured at all points of time. All blood values were normalised to haematocrit.

Results: KYN concentrations were significantly increased at 12, 24, and 48 h after arrival on ICU compared to preoperative values (p < 0.001). In 4/12 patients KYN levels increased transiently after releasing the cross-clamp. Of the traditional markers leukocytes peaked earliest at 3 h after onset of anaesthesia (p < 0.001) followed by TNF-alpha at ICU arrival (p < 0.001). CRP and ICAM-1 rose significantly above baseline (p < 0.001) starting at 12 and 24 h after ICU arrival, respectively. P-selectin levels showed no statistically relevant changes.

Conclusion: Serum levels of kynurenine indicating IDO activity can be used as a new inflammation marker following cardiac surgery. Individual early response to intraprocedural maneuvers in a subset of patients, which was not seen in established markers, needs to be clarified. Knowing KYN time course, next step would be testing its kinetics under different perfusion conditions. Quantification of KYN is cheaper and faster than conventional ELISA-based assays of inflammation markers and may thus be preferable to established markers.