title: Time-dependent loss of radioactivity counts associated with paracellular markers in the presence of cyclodextrin.
abstract: This communication reports an unexpected phenomenon observed during the counting of radiolabeled paracellular marker solutions in the presence of 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD). The results revealed time-dependent loss of 14C-mannitol and 14C-polyethlene glycol 4000 radioactivity counts with increased percentages of HPbetaCD. However, 14C-diazepam, a transcellular marker, displayed a stable count. A hypothesis behind this phenomenon is being proposed, involving water transfer from aqueous droplets to the surfactant rich scintillation fluid. The remaining droplets, becoming more and more concentrated in cyclodextrin, entrap the hydrophilic markers and consequently exhibit an increasing quenching effect. This effect shows that careful monitoring of radiolabeled markers used in transport experiments is necessary, even with high quench resistant scintillation fluids, to prevent erroneous interpretation of the transport data.
authors.affiliation: Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri- Kansas City, 64110-2499, USA.
authors.forename: I
authors.initials: I
authors.lastname: Pezron
authors.forename: G S
authors.initials: GS
authors.lastname: Tirucherai
authors.forename: A K
authors.initials: AK
authors.lastname: Mitra
mesh_terms: D000073738:2-Hydroxypropyl-beta-cyclodextrin; D002250:Carbon Radioisotopes; D003505:Cyclodextrins; D005079:Excipients; D011851:Radioactivity; D012588:Scintillation Counting / Q000379:methods*; D013679:Technology, Radiologic; D047392:beta-Cyclodextrins
chemical_list: D002250:Carbon Radioisotopes; D003505:Cyclodextrins; D005079:Excipients; D047392:beta-Cyclodextrins; D000073738:2-Hydroxypropyl-beta-cyclodextrin