Haptoglobin degradation product as a novel serum biomarker for hematopoietic stem cell transplant-associated thrombotic microangiopathy

BackgroundHematopoietic stem cell transplant (HSCT)-associated thrombotic microangiopathy (TA-TMA) is a well-known complication of HSCT and carries high risk of morbidity and mortality. A lack of consistent non-invasive diagnostic criteria can delay diagnosis and lead to irreversible organ damage.MethodsSerum samples of 100 patients that underwent HSCT at Cincinnati Children's Hospital were serially collected. Unbiased proteomic profiling by SELDI-TOF-MS was performed on serum from TA-TMA patients at baseline (pre-HSCT), 2weeks before TMA diagnosis (pre-TMA), and at clinical TMA diagnosis. Two proteins with mass to charge ratios of 12-13kDa were consistently elevated at the 2week pre-TMA time point by SELDI-TOF, compared to control samples. Potential peptides were isolated and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) on the Linear Trap Quadropole (LTQ). A MASCOT search identified haptoglobin fragments in the 12-17-kDa range. Western blot was performed to validate haptoglobin fragments as a potential biomarker.ResultsWestern blot of TA-TMA patients showed haptoglobin fragments at 12, 14, and 17kDa that varied between baseline, pre-TMA, and TMA time points for each patient. By densitometric analysis, the 17-kDa fragment in the pre-TMA samples differed significantly from TMA diagnosis (p<0.0001). There was no significant difference in the concentrations of the 12-kDa and 14-kDa fragments.ConclusionThe 17-kDa haptoglobin degradation product may represent a novel early serum biomarker for TA-TMA that could potentially allow for earlier diagnosis and intervention.