Decorporation and therapeutic efficacy of liposomal-DTPA against thorium-induced toxicity in the Wistar rat.

Purpose: This study examined the effect of liposomal encapsulation of (99m)Tc-labeled diethylenetriaminepentaacetic acid (metastable technetium labeled DTPA) on its organ distribution and therapeutic effect of optimized neutral liposomal-DTPA against thorium ((232)Th)-induced liver toxicity and its accumulation in rat animal model.

Materials And Methods: (99m)Tc-DTPA was encapsulated in neutral (dipalmitoylphosphatidylcholine:cholesterol) and positively (dipalmitoylphosphatidylcholine:cholesterol:stearylamine) charged liposomes using thin film hydration method. Comparative efficacy of liposomal and free DTPA (11.2 mg/kg) was examined in terms of its effect on (232)Th accumulation and subsequent toxicity in the liver and blood of rat administered with (232)Th-nitrate (600 μg/kg). Organ distribution of free or liposomal (99m)Tc-DTPA was determined by solid scintillation counting and (232)Th accumulation by Inductively Coupled Plasma-Atomic Emission Spectroscopy.

Results: Neutral liposomes encapsulated with (99m)Tc-DTPA showed more uptake in liver, spleen and blood than with positively charged liposomal- and free- (99m)Tc-DTPA. Administration of (232)Th-nitrate to rat significantly increased the levels of liver toxicity markers and of oxidative injury, which were found to be restored more significantly by neutral liposomal-DTPA than free-DTPA. The accumulation of (232)Th in liver and blood of contaminated mice was found to be decreased more significantly by neutral liposomal-DTPA than by free-DTPA.

Conclusions: Decorporation and consequent mitigation of (232)Th induced toxicity may be significantly improved by liposomal encapsulation of DTPA, a chelating agent.