Effect of Excipients on the Stability and Transport of Recombinant Human Epidermal Growth Factor (rhEGF) across Caco-2 Cell Monolayers

The effect of sixteen excipients on the transport of recombinant human epidermal growth factor (rhEGF) across Caco-2 cell monolayers was examined at $37^{\circ}C$. The apparent apical to basolateral (A-B) permeability ($P_{app}$) of 30 $\mu$ M rhEGF was $8.15\times 10^{-7}$ cm/sec, indicative of a poor level of absorption in the GI tract. The Papp was 1.7- and 6.3-fold greater than the $P_{app}$ in the basolateral to apical (B-A) direction and the A-B permeability of mannitol, respectively, and decreased dramatically to a negligible level at $4^{\circ}C$, consistent with a receptor mediated transcytosis of rhEGF. The stability of rhEGF was very poor, undergoing more than 85% degradation in 2 h in the transport medium at $37^{\circ}C$. A significant increase in the $P_{app}$ could be achieved by the addition of certain excipients, as exemplified by 23, 21, 20 and 16-fold increases, in the presence of sodium taurochenodeoxycholate (NaTCDC), sodium taurodeoxycholate (NaTDC), sodium glycodeoxycholate (NaGDC) and sodium laurylsulfate (SLS) (all at a concentration of 1 % w/v), respectively. A significant increase in stability could also be achieved by the addition of some of the excipients, as represented by 1 % SLS, which nearly completely stabilized the rhEGF. Unfortunately, however, an increase in the $P_{app}$ of rhEGF could not be achieved without a simultaneous and extensive decrease in the integrity of the cell membranes. Thus, more efficient excipients, that specifically enhance the permeation of rhEGF and do not alter the membrane integrity, should be pursued in order to safely enhance the permeation of rhEGF.