title: Renal and hepatic kinetics of Tc-99m-labelled hexakis-methoxy-isobutyl Isonitrile.
abstract: OBJECTIVE
  Technetium-99m-labelled hexakis-methoxy-isobutyl isonitrile (Tc-99m-MIBI) is a substrate for P-glycoprotein (P-gp), an ATP-binding cassette (ABC) transporter protein, and can be used to image P-gp expression. The aim was to study normal kinetics of Tc-99m-MIBI in the kidney and liver to help understand physiological studies of P-gp expression in these organs.
  
  
  METHODS
  Thirty healthy kidney transplant donors received intravenous Tc-99m-MIBI followed by dynamic scintigraphy for 20 min and static imaging at 30 and 120 min. Time-activity curves were generated from parenchymal ROI. An assumed mono-exponential Tc-99m-MIBI blood clearance with rate constant of 0.3 min-1 was used to predict the Tc-99m- MIBI that would have accumulated in the organs had none left. The activities leaving were then calculated by subtraction and expressed as percentages of the predicted total accumulated activities.
  
  
  RESULTS
  Kidney time-activity curves peaked at 2-4 min then declined to a plateau from ~15-16 min equal to 31 [SD 5]% of the total activity accumulated (corresponding to 69 [5]% rapidly eliminated) (phase 1). Bladder activity followed a similar but opposite time course. Between 30 and 120 min (phase 2), activity left at 0.36 (0.13) %.min-1. Liver curves peaked at 8-10 min. Differentiation of the elimination curve revealed that a variable proportion of tracer (5-56%; mean 30 [14]%) was rapidly excreted over ~11 min. From 30 min, activity left at 1.02 (0.23) %.min-1. There was no correlation between renal and hepatic elimination rates in either phase or between early and late phase elimination rates in either organ.
  
  
  CONCLUSIONS
  Early renal elimination is predominantly via glomerular filtration and urinary excretion. The liver rapidly excretes a more variable and lower proportion of Tc-99m-MIBI than the kidney. P-gp located at the urine/tubule and bile/hepatocyte boundaries prevents Tc-99m-MIBI re-entering cells and thereby influences elimination and retention in both phases, although other ABC transporters are probably also involved.
authors.forename: Sabina
authors.initials: S
authors.lastname: Dizdarevic
authors.forename: Mark
authors.initials: M
authors.lastname: Aplin
authors.forename: Nicola
authors.initials: N
authors.lastname: Ryan
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Holt
authors.forename: Lawrence
authors.initials: L
authors.lastname: Goldberg
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Miles
authors.affiliation: Department of Nuclear Medicine, Eastern Road, Brighton BN2 5BE, UK.
authors.forename: A Michael
authors.initials: AM
authors.lastname: Peters
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D017256:Technetium Tc 99m Sestamibi / Q000493:pharmacokinetics*; D013997:Time Factors; D014018:Tissue Distribution; D014019:Tissue Donors
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D019275:Radiopharmaceuticals; D017256:Technetium Tc 99m Sestamibi