BACKGROUND: HSCT conditioning regimens cause massive lysis of hematopoietic cells with release of toxic intracellular molecules into the circulation.

OBJECTIVES: To describe the response to oxidative stress early after hemopoietic stem cell transplantation (HSCT) and assess the association of early oxidative stress with later transplant outcomes.

STUDY DESIGN: Key components of in the body's physiological response to oxidative stress were studied in a cohort of 122 consecutive pediatric allogeneic HSCT recipients. Glutathione reductase (GSR), glutathione peroxidase (GPX) and glutathione synthetase protein expression was measured using ELISA and reduced and oxidized glutathione (GSH and GSSG) levels were quantified using mass spectrometry.

RESULTS: GSR is an inducible enzyme which catalyzes the regeneration of reduced glutathione (GSH). Levels of GSR increased by more than five-fold between start of conditioning chemotherapy and day 0 (median 87ng/mL to 459ng/mL, p<0.0001). GPX catalyzes removal of toxic reactive oxygen species (ROS) by oxidation of GSH. GPX4 levels fell briskly by day 0 (median 20.3 ng/mL prior to HSCT to 7.4ng/mL at day 0, p<0.0001), likely indicating consumption of the enzyme as cell lysis and subsequent oxidative stress occurred. Levels of the antioxidant substrate reduced glutathione stayed stable from pre-HSCT through day 14, likely maintained by increased glutathione synthesis by the enzyme glutathione synthetase, whose median levels increased from 38.8ng/mL before conditioning to 54ng/mL at day 21 (p=0.02). GSR levels were associated with patient outcomes. Median GSR levels were significantly elevated through days 0-21 in those who died in the first year after HSCT compared to those who survived. Similarly, patients who developed high risk transplant-associated thrombotic microangiopathy (TA-TMA) and grade 2 and above graft vs host disease (GVHD) also had significantly higher GSR levels early after HSCT.

CONCLUSION(S): Our data suggest that the body is for the most part able to mount a brisk and effective response to the oxidative stress associated with lysis of the hematopoietic cell system before HSCT. Our data also suggest that early events in the first 21 days of HSCT may set the scene for later clinical events in the first year after HSCT. It is plausible that patients who are unable to effectively overcome this early period of significant oxidative stress may have increased endothelial injury and activation of complement. Potential therapeutics to augment and optimize the body's response to oxidative stress may improve outcomes.