Protein binding of 99Tcm-DTPA compared with other GFR tracers

Area of Science:

• Nuclear Medicine
• Radiopharmaceutical Chemistry
• Renal Physiology

Background:

• Radiopharmaceuticals for glomerular filtration rate (GFR) measurement, such as 99mTc-DTPA, are thought to exhibit varying plasma protein binding.
• Methodology significantly influences protein binding experimental outcomes, necessitating standardized methods for accurate comparisons.

Purpose of the Study:

• To compare the in vitro and in vivo plasma protein binding of 99mTc-DTPA preparations with other GFR tracers.
• To evaluate the consistency of protein binding across different 99mTc-DTPA preparations using a standardized ultrafiltration method.

Main Methods:

• Utilized ultrafiltration to assess in vitro protein binding of six 99mTc-DTPA preparations and other GFR tracers (51Cr-EDTA, 125I-iothalamate) in donor plasma.
• Investigated in vivo protein binding of 99mTc-DTPA and 51Cr-EDTA at 5 and 40 minutes post-injection in patients.
• Applied a correction for the 'Donnan effect' to account for ion distribution during ultrafiltration.

Main Results:

• Quality control confirmed high labeling efficiency (>96%) for all 99mTc-DTPA preparations.
• In vitro protein binding of 99mTc-DTPA ranged from 9.25% to 11.12%, not significantly different from 51Cr-EDTA and 125I-iothalamate.
• In vivo protein binding of 99mTc-DTPA (12.58%-13.28%) and 51Cr-EDTA (12.54%) showed no significant differences over time or between tracers.

Conclusions:

• The in vitro and in vivo protein binding of 99mTc-DTPA is approximately 10-13%.
• Plasma protein binding of 99mTc-DTPA is comparable to that of 51Cr-EDTA and 125I-iothalamate.
• These findings support the use of 99mTc-DTPA as a reliable tracer for GFR measurement with consistent protein binding characteristics.