Pharmacokinetics of ¹²⁵I-GST-TatdMt, a recombinant fusion protein possessing potent anti-obesity activity, after intravenous, nasal, oral, and subcutaneous administration

This study first reports the absorption kinetics of GST-TatdMt, a recombinant Tat protein possessing potent anti-obesity activity, in rats after nasal, s.c., and p.o. administration. GST-TatdMt was over-expressed in E. coli, purified, and radioiodinated using the IODO-GEN method. The radioiodinated ¹²⁵I-GST-TatdMt was administered to rats by nasal, s.c., and oral routes at doses of 7.3 μg (420.7 nCi), 146.5 μg (8413.8 nCi), and 146.5 μg (8413.8 nCi), respectively. For the determination of absolute bioavailability, ¹²⁵I-GST-TatdMt was also given to rats by i.v. injection (73.2 μg, 4206.9 nCi). Following administration by extravascular routes, the systemic absorption of radioactivity was prolonged, with C_max being attained within 4.2-8.0 h. The absolute bioavailability calculated as dose-normalized AUC_{extravascular}/AUC_i.v. was 98.0, 75.8, and 87.1% after nasal, s.c., and oral administration, respectively. The majority of administered radioactivity was excreted in urine (57.5-64.7%), with fecal excretion being less (2.5-12.7%). The distribution of ¹²⁵I-GST-TatdMt to various tissues was also determined at 4 and 72 h after s.c. injection. The findings of this study suggest that this protein may be absorbed into the systemic circulation when given by extravascular administration.