title: Effects of methylene blue stabilizer on in vitro viability and chemotaxis of 99mTc-exametazime-labeled leukocytes.
abstract: This study was conducted to evaluate the effects of methylene blue/phosphate buffer stabilizer on the labeling efficiency, cell membrane integrity, chemotaxis, and in vitro stability of leukocytes labeled with 99mTc-exametazime.
  
  
  METHODS
  Whole blood (480 mL) was obtained from each of 3 healthy donors and divided equally into eight 60-mL aliquots. Two aliquots from each of the 3 subjects were used as a control (i.e., leukocytes were not labeled with either nonstabilized or stabilized 99mTc-exametazime) in this study. The remaining 6 aliquots from each of the 3 subjects were divided equally into the following formulation groups: (a) leukocytes labeled with nonstabilized 99mTc-exametazime, (b) leukocytes labeled with stabilized 99mTc-exametazime containing 250 microg methylene blue, and (c) leukocytes labeled with stabilized 99mTc-exametazime containing 500 microg methylene blue. Duplicate samples were evaluated to confirm the repeatability of the study. Six samples were studied under each experimental condition (i.e., control, a, b, and c groups). The cell membrane integrity and chemotatic capacity of leukocytes were measured at 1 and 3 h after preparation, whereas a complete blood count was obtained at 3 h after preparation. The labeling efficiency was calculated immediately on conclusion of cell labeling, whereas the in vitro stability of the radiolabeled leukocytes was evaluated at 3 h after radiolabeling.
  
  
  RESULTS
  None of the samples showed trypan blue-stained cells. For the chemotactic index, no statistically significant differences were noted between the 3 labeling formulations at 1 h (P = 0.43) or 3 h (P = 0.10) after preparation. None of the labeling formulations differed significantly from the control values of the chemotactic index (all P > 0.25). For the complete blood count, no significant differences were observed between any of the groups, with the exception of platelet number in the control group (P = 0.004). The labeling efficiency (P = 0.10) and in vitro stability (P = 0.33) were also similar in our comparison of the 3 labeling formulations.
  
  
  CONCLUSIONS
  With no major statistically significant difference noted either between the 3 labeling formulations or between the control and the 3 labeling formulations, we concluded that the methylene blue/phosphate buffer stabilizer (250 or 500 microg methylene blue) did not affect the cell membrane integrity, chemotactic capacity, labeling efficiency, in vitro stability, or complete blood count of leukocytes labeled with stabilized 99mTc-exametazime.
authors.affiliation: Nuclear Medicine, Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA. jhung@mayo.edu
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Hung
authors.forename: Barton C
authors.initials: BC
authors.lastname: Iverson
authors.forename: Kyra A
authors.initials: KA
authors.lastname: Toulouse
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Mahoney
mesh_terms: D002462:Cell Membrane; D002470:Cell Survival / Q000187:drug effects; D002634:Chemotaxis, Leukocyte / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D007962:Leukocytes; D008751:Methylene Blue; D019275:Radiopharmaceuticals; D019690:Technetium Tc 99m Exametazime
chemical_list: D019275:Radiopharmaceuticals; D019690:Technetium Tc 99m Exametazime; D008751:Methylene Blue