Studies on oral absorption of stearic acid SLN by a novel fluorometric method

In this study, the fluorescein isothiocyanate (FITC) labeled otcadecylamine (ODA), otcadecylamine-fluorescein isothiocyanate (ODA-FITC), was synthesized and used as a fluorescence marker to be incorporated into stearic acid solid lipid nanoparticles (SLN) by solvent diffusion method. Approximately 97.9% of added ODA-FITC was incorporated into SLN. Under sink condition, approximately 7% and less than 3% of ODA-FITC leaked from SLN in 24 h, when the ODA-FITC loaded SLNs were dispersed in plasma or phosphate buffered saline (PBS, pH 6.8) containing 0.3 wt% sodium dodecyl sulfate (SDS), respectively. The ODA-FITC loaded SLNs were then subjected to the in vivo transport experiments. The results showed that the transport efficiency of SLN by oral administration was 30%. The SLN could be extensively absorbed, and indicated a linear absorption mechanism in gastrointestinal tract within certain range of concentrations. By the external diversion experiments on lymph, it showed that approximately 77.9% of absorbed SLN was transported into systematic circulation via lymph, which is a major SLN transport pathway in gastrointestinal tract. The rest of absorbed SLN was transported directly into blood, which might be through capillary vessel or intestinal epithelial cell by paracellular pathway. The further experiment demonstrated that the polyethylene glycol monostearate (PEG2000-SA)-modified SLN could also be absorbed in gastrointestinal tract and achieved a prolonged effect in vivo.