Enhancement of niacin availability in the ileocolonic region by microencapsulation and coating
In the recent past, the human gut microbiota has gained increasing interest as a target for the delivery of substances due to the observed interaction between the microbiome, nutrition and health. The water-soluble vitamin niacin showed first effects on the composition of the gut microbiota. In order to enhance the availability of niacin in the ileocolonic region, where most of the microorganism are located, an early systemic absorption of niacin in the stomach and small intestine must be prevented. Therefore, two active forms of niacin (nicotinic acid (NA) and nicotinamide (NAM)) were encapsulated by a protective shellac coating applied via fluidized bed coating. The modulation of the release profile of niacin was assisted by a newly designed in vitro dissolution test and verified by a human bioavailability study with 10 healthy volunteers for each group. Different intrinsic effects on the release profile such as derived from the properties of the encapsulated compound were investigated. The active substance core was produced by a one-step spray granulation and a two-step process (extrusion with subsequent spheronisation). The latter method achieved a higher particle yield and required a lower use of shellac in relation to the mass of active substance. As an alternative to shellac coated microcapsules, the incorporation of niacin into pectin-zein hydrogel beads was characterized. A precise targeted release of niacin into the ileocolonic region in vitro and in vivo was reached by using a shellac based coating with adapted intermediate subcoatings consisting of either citric acid for NAM or sodium bicarbonate of NA. The subcoatings were able to control the effect of the physico-chemical properties of the encapsulated compound and to influence the pH-dependent dissolution of the surrounding shellac coatings. The designed in vitro dissolution test for the targeting provided a precise instrument to predict the release behavior in humans.