SITE-SPECIFIC DEGRADATION AND TRANSPORT OF RECOMBINANT HUMAN EPIDERMAL GROWTH-FACTOR (RHEGF) IN THE RAT GASTROINTESTINAL MUCOSA

The purpose of the present study was to elucidate the site specificity of degradation of recombinant human epidermal growth factor (rhEGF) i n the gastrointestinal mucosa and to screen absorption enhancers and e nzyme inhibitors for the development of an rhEGF oral delivery system. The degradation of rhEGF after incubation with the rat mucosal sites was determined by measuring the disappearance of rhEGF as well as the appearance of metabolites by HPLC. Two degradation products of rhEGF, M-I and M-II, were detected. Comparing peak appearance order of rhEGF and its metabolites with the previous reports, M-I and M-II were estim ated to be products by oxidation at the methionine residue, and by dea midation at the asparagine residue, respectively. The rhEGF degradatio n order was duodenum > ileum, stomach > jejunum > colon. rhEGF was rap idly degraded in the duodenum and the ileum, while relatively stable i n the colon and jejunum mucosal sites. Sodium caprate slightly inhibit ed the rhEGF degradation, whereas STDHF or EDTA had no effect on its d egradation in the jejunum mucosal sites. The degradation of rhEGF was inhibited by the addition of bestatin, sodium caprate or sodium salicy late in the duodenum mucosal sites. The transport of rhEGF across the gastrointestinal mucosa was investigated using [I-125]rhEGF. Possibly due to the strong barrier function of the membrane, the transported am ount of [I-125]rhEGF across the intestinal mucosa was less than 3% up to 3 h. Moreover, the unlabeled rhEGF (16.7 or 50 mu g/ml) had no sign ificant effect on the tracer (0.29 mu Ci/ml rhEGF) penetration. Effect s of various additives on the penetration of rhEGF across the colon we re then investigated. Glyceryl palmitostearate, sodium caprate, sodium lauryl sulfate and Tween 80 had no significant effect on the [I-125]r hEGF penetration across the colon. Thus; low penetration of rhEGF with or without various additives might be responsible for the barrier fun ction of the membrane rather than the enzymatic degradation. (C) 1998 Elsevier Science B.V. All rights reserved.