The effect of molecular weight on the absorption enhancing properties of n-trimethyl chitosan chloride

Abstract

Delivery problems have limited the uptake of many promising new peptides drugs. The co-administration of absorption enhancing agents such as H-Trimethyl chitosan chloride (TMC), a chitosan derivative, has been proven. The aim of this study is to determine the influence of molecular weight on the absorption enhancement properties of TMC. Three different molecular weights of TMC were synthesized, with molecular weight varying between 2.03 x 10 5 g/mol (low molecular weight TMC) to 3.28 x 10 5 g/mol (high molecular weight TMC). Intrinsic viscosity of the different molecular weights was determined and ranged from 3.4 ml/g (low molecular weight TMC) to 9.2 ml/g (high molecular weight TMC). The results showed that the intrinsic viscosity increased with an increase in molecular weight. 1HNMR spectra analyses were done on the different molecular weights of TMC and the degree of quaternization (DQ) were calculated with the ranges of 33.7 % (low molecular weight TMC) to 37.7 % (high molecular weight TMC). From the mucoadhesion data obtained, an increase in molecular weight had an increase in mucoadhesive strength as well as surface tension and the high molecular weight TMC exhibited the best mucoadhesive properties, which means that the high molecular weight TMC will bond best to epithelial surfaces and have a longer contact period, thus improving its absorption enhancing effect. The effects of molecular weight on transepithelial electrical resistance (TEER) and transport experiments were studied at different TMC concentrations (0.1 % and 0.5 % w/v). All different molecular weights of TMC caused immediate and pronounce reduction in TEER values as well as an increase in transport rate. At lower concentrations (0.1 %) the high molecular weight TMC had the biggest increase in transport rate while at higher TMC concentrations the low molecular weight TMC had the biggest increase. A possible conclusion for the highest effect on the TEER and transport rate by the low molecular weight at higher concentrations (0.5% w/v), is the short chain length and low viscosity of low molecular weight TMC. The compound could "move" closer to the tight junctions and have the largest influence on the tight junction. Another reason could be that at higher concentrations (0.5% w/v) the high molecular weight TMC could be clogging the tight junctions. Because of the high molecular weight TMC's high mucoadhesive property and contact sites (due to large chain), at lower concentrations the high molecular weight TMC has a bigger effect than the low molecular weight TMC. The discrepancy in TEER and transport results of the medium molecular weight can possibly be attributed to the degree of quaternization (DQ). Because DQ is a relationship of the amount of tri-methyl amino groups present on the TMC molecule, the medium molecular weight TMC with highest DQ and thus most tri-methyl amino groups, might also be clogging the tight junction openings and restricting the transport of [14C]-mannitol despite causing the tight junction to open up as seen by drop in TEER values. A transport model was derived that described the paracellular transport of [14C]-mannitol across an epithelial membrane and the effect of using an absorption enhancer. With this model, the diffusion coefficient through the membrane could be obtained, and it was found that there was an increase in the diffusion coefficient with the administration of TMC. An initial penetration period was also observed and this influenced the calculation of the diffusion coefficients, whereby experimental data after 120 minutes only could be used.