Inhibitory effect of emulsifiers in sedds on protease activity: Just an illusion?

Evaluation of inhibitory effect of emulsifiers on pancreatic trypsin and α-chymotrypsin. The inhibitory effect of Cremophor EL, Cremophor RH 40, Brij O10, Tween 20, polyethylene glycol 8000, polyethylene glycol 400, Carbitol, Pemulen TR-1, Pemulen TR-2, Carbopol Ultrez 20 and Carbopol Ultrez 21 on pancreatic trypsin and α-chymotrypsin was tested. BAEE (Nα-Benzoyl-l-arginine ethyl ester), BTEE (N-Benzoyl-l-tyrosine ethyl ester), casein and insulin were used as substrates for trypsin and α-chymotrypsin. SEDDS containing Pemulen TR-2 were developed, loaded with insulin-DMPG (dimyristoylphosphatidylglycerol) complex, characterized and tested regarding the protective effect towards the proteolytic degradation of insulin. Cremophor EL, Cremophor RH 40, Brij O10, Tween 20, polyethylene glycol 8000, polyethylene glycol 400, Carbitol did not show any inhibitory effect towards trypsin and α-chymotrypsin, whereas Pemulen TR-1, Pemulen TR-2, Carbopol Ultrez 20 and Carbopol Ultrez 21 inhibited the enzymes in a concentration dependent manner. Moreover, Pemulen and Carbopol Ultrez emulsifiers exhibited comparable inhibitory properties (p>0.05). The incorporation of 0.34% w/w of Pemulen TR-2 in SEDDS decreased the degradation rate of the loaded insulin-DMPG complex compared to the blank formulation (p<0.05). The present study revealed that commonly used emulsifiers in SEDDS do not have inhibitory properties on the proteolytic activity of trypsin and α-chymotrypsin. Moreover, it was demonstrated that the incorporation of emulsifiers with inhibitory properties towards trypsin and α-chymotrypsin in SEDDS play a minor role in the protection of embedded drugs from enzymatic degradation.