SCINTIGRAPHIC EVALUATION OF EXPERIMENTAL COLITIS IN RABBITS

Scintigraphic techniques are frequently used for evaluation of inflamm atory bower disease. The radiopharmaceutical of choice is labeled leuk ocytes. In this study, two new agents, In-111-labeled polyethylene gly col-coated liposomes and In-111-labeled human nonspecific gamma globul in (immunoglobulin G; IgG), were compared with In-111-leukocytes in a rabbit model of colitis. Methods: In rabbits, acute colitis was induce d by colonic instillation of trinitrobenzene sulfonic acid at 25 cm fr om the anal sphincter. After 24 hr, 15 MBq of the radiopharmaceuticals was injected intravenously in groups of four rabbits. Twenty-four hou rs after injection, the animals were killed and macroscopic abnormalit ies were scored in seven consecutive affected colonic segments of 5 cm each (0 = normal, 1 = inflammation, 2 = ulcers). The ex vivo uptake w as measured in the normal ascending colon and the affected colonic seg ments. The colitis index (CI, affected-to-normal colon-uptake ratio) w as calculated. Results: Histologically, an acute, patchy, transmural c olitis was observed at the site of instillation and the distal colon. The CI of all agents in colitis lesions correlated with the severity o f the abnormalities. With increasing severity, the CI for liposomes wa s 1.86 +/- 0.24, 4.88 +/- 0.42 and 7.42 +/- 0.54 (r(2) = 0.68, p < 0.0 01); for leukocytes 1.77 +/- 0.32, 3.10 +/- 0.58 and 5.54 +/- 0.83 (r( 2) = 0.31, p < 0.01); for IgG 1.60 +/- 0.29, 2.81 +/- 0.21 and 2.65 +/ - 0.21 (r(2) = 0.29, p < 0.02). Conclusion: Indium-111-labeled-leukocy tes, -IgG and -liposomes all show increased uptake in inflamed colonic tissue. Indium-111-liposomes showed the highest CI, which correlates best with the morphological abnormalities. Indium-111-leukocytes and I n-111-liposomes are superior to In-111-IgG for this indication.