123Iodine-labelled anti-VCAM-1 antibody scintigraphy in the assessment of experimental colitis.

Objectives To evaluate the usefulness of 123 I-labelled anti-vascular cell adhesion molecule-1 (VCAM-1) monoclonal antibody (MAb) scintigraphy in the assessment of colonic inflammatory damage. Design Colitis was induced by intracolonic administration of 30 mg trinitrobenzenesulphonic acid in 0.5 ml of 50% (v/v) ethanol. Rats injected with vehicle served as controls. Animals were studied at day 7 after induction of colitis. Methods Scintigraphy was performed in control and trinitrobenzenesulphonic acid-induced colitic rats 2, 4 and 24 h after intravenous administration of 123 I-anti-VCAM-1 MAb. Scintigraphic uptake was quantified in selected areas on scintigraphs. Animals were killed, tissue 1231 radioactivity accumulation was measured, and accumulation of anti-VCAM-1 MAb in each organ was calculated. 99m Tc-hexamethyl propylene amine oxime-labelled leucocyte scintigraphy was performed in additional groups of animals for comparison. Results Colonic tracer uptake was visible in scans of colitic, but not control animals. Quantification of scintigraphic uptake in the colon was significantly higher in colitic rats than in control animals (P < 0.0001). The specificity of the increase was demonstrated by lack of 123 I-labelled non-binding MAb uptake in the colon, and by displacement of 123 I-anti-VCAM-1 MAb colonic uptake by pre-treatment with unlabelled MAb. Accumulation of anti-VCAM-1 MAb in the colon of colitic rats was eightfold higher than in control animals. Strong correlations were found between quantification of scintigraphic uptake, anti-VCAM-1 MAb accumulation, histological damage and myeloperoxidase activity in the colon. Conclusion 123 I-labelled anti-VCAM-1 MAb scintigraphy allows an accurate evaluation of colonic inflammatory damage in trinitrobenzenesulphonic acid-induced colitis, suggesting a potential role for this imaging technique in the assessment of human IBD.