Comparative Study In Vivo and In Vitro of Uniformly 14C‐Labelled and 125I‐Labelled Recombinant Fibroblast Growth Factor 2

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Abstract
Recombinant bovine fibroblast growth factor (FGF2), uniformly labelled with 14C ([14C]FGF2), was purified and showed to be highly stable and to retain full biological activity. Organ distribution of [14C]FGF2 after intravenous injection of young rats was assessed by autoradiography of whole body sections and compared with those obtained with [125I]iodinated FGF2 (125I‐FGF2). Thyroid, stomach, intestine, bladder and skin were radioactively labelled only in the case of 125I‐FGF2. This tissue‐labelling is artefactual, probably due to free iodide binding not observed when using [14C]FGF2. High‐resolution autoradiography showed a complex tissue distribution of [14C]FGF2 in kidney and adrenal organs. Incubation of frozen eye sections with [14C]FGF2 showed a specific and high‐resolution labelling pattern of ocular tissues. After cellular internalization, [14C]FGF2 was processed into five distinct polypeptides of 16, 14, 8, 7, and 5.5 kDa. The 14‐kDa and 7‐kDa polypeptides are novel catabolic fragments not detected with radioiodinated FGF2. In terms of stability, tissue distribution specificity, and autoradiographic resolution, [14C]FGF2 proved to have more advantages than 125I‐FGF2 for pharmacokinetic and catabolism studies.