Evaluation of Haricot Bean Retrograded Resistant Starch as a Film Forming Excipient in Oral ColonTargeted Delivery of Mesalamine

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Addis Abeba University


The colon has been evaluated intensively for about three decades as a site of drug delivery, not only for local colonic pathologies but also for systemic delivery of small therapeutic molecules, protein and peptide drugs. As a site for drug delivery, colon offers a near neutral pH, reduced digestive enzymatic activity, a long transit time and an increased responsiveness to absorption enhancers. Targeting drugs to the colon has two major implications in colonic disorders, explicitly reduced systemic toxicity and increased local therapeutic efficacy. The main objective of this study is to prepare haricot bean retrograded resistant starch and evaluate its potential as film forming excipient in tablet formulation for oral colon-targeted delivery of mesalamine. To prepare retrograded resistant starch, haricot bean starch was dispersed in distilled water in the ratio of 1:4 and autoclaved (121 °C) for about 1 h until complete disruption of starch granules and then the gelatinized starch de-branched using pullulanase enzyme. The product obtained was autoclaved (121 °C) for about 1 h, cooled to room temperature and then stored in a refrigerator for 24 h at 3 °C. This step was repeated 10 times. The slurry obtained in the previous stage was treated with heat stable alpha amylase, amyloglucosidase and then with pepsin to obtain enzyme resistant starch type 3 (RS3). The product obtained was washed four times with plenty of hot water (90 °C) and the residue was left to dry in an oven overnight. Gravimetric method was used to determine the RS3yield.In-vitro methods, dissolution and fermentation studies were used to determine the release profiles of mesalamine in the GI tract. The yields of haricot bean RS3 were in the range of 74.7- 78.0% per dry mass of haricot bean starch. The inherent nature of haricot bean and extrinsic factors (processing conditions) may have contributed for such high yield. Haricot bean native starch had showed CA-type starch polymorphism. The in-vitro mesalamine cumulative percentage releases of all coating formulations, which differ either in RS3: EC (Ethyl cellulose) ratio or in their film thickness, in simulated gastrointestinal fluids were less than 4% during the 7 h study period. The cumulative percentage releases of mesalamine of the different coating formulations in the fermentation study were in the range of 57-82% in 12 h of the study period. The results indicate that haricot bean resistant starch has a good potential to be used as a film forming excipient in oral colon-targeted delivery of drugs.



Colon-targeted delivery, Haricot bean, Resistant starch, Meslamine, Fermentation study