Non-Transferrin-Bound Iron During Autologous Stem Cell Transplantation and Conventional Intensive Chemotherapy.
Authors: Sahlstedt Leila , von Bonsdorff Leni , Ebeling Freja , Parkkinen Jaakko , Juvonen Eeva , Ruutu Tapani 
Published: October 2019

Abstract
Abstract 4310

Introduction
Intensive chemotherapy causes cessation of iron utilization by the bone marrow, leads to release of iron from the liver through hepatocellular injury, and disturbs transferrin production. These effects may lead to full transferrin saturation and the appearance of free, non-transferrin-bound iron (NTBI) in the serum. Hydroxyl radicals catalyzed by NTBI can cause cellular damage and contribute to therapy-related complications. The present study was designed to demonstrate the appearance and timing of NTBI during autologous stem cell transplantation and conventional intensive chemotherapy.

Patients and Methods
Twenty-four adult patients were enrolled. Sixteen patients with multiple myeloma or lymphoma were conditioned with an intensive cytotoxic regimen prior to autologous stem cell transplantation (aSCT). The conditioning for multiple myeloma was either melphalan monotherapy (Mel) or melphalan combined with fractionated total body irradiation (Mel/TBI), and for lymphoma a combination chemotherapy regimen (BEAC). Eight patients had acute leukemia and were treated with various cytopenia-inducing chemotherapies (Chemo). Serum samples were collected coinciding with routine sampling, before the initiation of the chemotherapy and during the first 20 days after the onset of the chemotherapy. The median number of samples per patient was 18.5 (range 16-21) in the aSCT group and 15.5 (7-21) in the Chemo group. TfSat was calculated using the formula: serum iron (mmol/l)/ serum transferrin (g/l) x 3.98 without a cutoff at 100 %. NTBI in serum was determined by the bleomycin assay modified for small serum volumes. The samples were analyzed for NTBI only when the respective TfSat was above 80 %, based on our previous observation that NTBI was not detectable below that cutoff level.

Results
A steep rise of the mean transferrin saturation was seen in all study groups during the first days after starting the chemotherapy, reaching the maximum levels of 76 to 93 per cent at four to six days. Among the aSCT groups, the TfSat levels were significantly lower in the Mel group compared to BEAC (P= 0.0002). In the Chemo group the levels stayed high significantly longer than in the aSCT groups (P < 0.0001). In the Chemo group the mean transferrin concentration was below the reference range during the whole study period, whereas in all the aSCT groups the initially normal mean transferrin levels decreased below the reference range during the study. None of the aSCT patients were NTBI-positive at baseline, and three of the aSCT patients (1 Mel, 2 Mel/TBI) also remained NTBI-negative throughout the study period. In all other patients NTBI was detected variably, for an average duration of 15.6 days from the first positive sample to the last positive one in the Chemo group, and for 6.1 days, respectively, in the aSCT group. The proportion of the NTBI-positive samples was higher among the Chemo patients (59 %) compared to the aSCT patients (22 %) (P< 0.001). Among the aSCT patients the proportion of NTBI-positive samples was lower in the Mel group compared to the Mel/TBI and BEAC groups (P= 0.04 and 0.01, respectively). In the aSCT patients the disappearance or marked reduction of NTBI-positive samples coincided with the recovery of the bone marrow function, as demonstrated by the leukocyte counts. In the Chemo group there was no leukocyte recovery during the study period and the proportion of NTBI-positive samples remained high throughout the whole period.

Conclusions
NTBI was detectable in the majority (21/24) of patients receiving conditioning for autologous transplantation or intensive chemotherapy for acute leukemia. The presence of NTBI coincided with bone marrow suppression, and NTBI largely disappeared at the recovery of the bone marrow function. The treatment that caused the longest bone marrow suppression (Chemo) was associated with the most prolonged presence of NTBI. The timing of the presence of NTBI accords with the presence of the most important non-infectious complication of intensive chemotherapy and autologous transplantation, mucosal injury, and free iron is likely to contribute to this and probably other complications of the intensive treatments.

Disclosures:
No relevant conflicts of interest to declare.