Cedars-Sinai Medical Center, California, United States
Background/Case Studies: Extracorporeal photopheresis (ECP) uses ultraviolet radiation of 320 to 400 nm wavelength (UVA) to covalently bind methoxsalen to the DNA of white blood cells collected for processing and eventual return to a patient’s circulation. Subsequent apoptosis of these cells is thought to produce systemic immunomodulation. A 70-year-old male status post allogeneic hematopoietic stem cell transplantation for AML was undergoing ECP for chronic GVHD with bronchiolitis obliterans necessitating oxygen supplementation. After several uneventful ECP procedures it was noticed that the leukocyte collection bag had dark brown discoloration. Hemolysis and methemoglobinemia were ruled out and the discoloration attributed to the presence of eltrombopag (ELT), recently prescribed for thrombocytopenia. Dose dependent ELT plasma discoloration has been described and shown to interfere with some spectrophotometric analyses. Concern that ELT may absorb wavelengths in the UVA spectrum requiring an adjustment in the length of UVA exposure for effective ECP led us to explore this possibility.
Study
Design/Methods: Prior to the addition of methoxalen and irradiation, we obtained cell-free supernatant from the leukocyte collection bag on the day the discoloration was noted (Scan A), from another patient not on ELT (Scan B), and from this patient after cessation of ELT therapy when no visible discoloration was noted (Scan C). All samples underwent scanning spectrophotometric absorbance analysis through the 300-750 nm wavelength range. Specimens were diluted 1:10 with normal saline which functioned as the reference blank.
Results/Findings: While absolute absorbances differ between the three samples, none of the samples exhibited absorbance in the 320-390 nm range when compared to the samples’ baselines. Most of the discolored supernatant’s absorbance (Scan A) is in the 430-550 nm range of visible light. The 390-430 nm absorbance peak noted in our patient’s plasma when discolored (Scan A) and visibly clear (Scan C) are most likely due to protein-bound imine and glucuronide ELT metabolites having long serum half-lives. The amount of UVA radiation absorbed in this fraction is estimated to be less than 2% of the total and be of low energy. Conclusions: Instrument-calculated irradiation times vary according to the volume and hematocrit of the treatment bag contents, and the age of the UVA source. Our findings suggest that the serum chromogens associated with ELT and its metabolites should not interfere with substrate penetration by the high-energy UVA photons delivered during ECP nor the resultant immunomodulatory actions. Indeed, with no adjustments to the instrument calculated irradiation time our patient responded well, and no longer required oxygen supplementation well before his course of ECP was concluded.
