Intestinal Absorption of Acyclovir [beta]-Glucoside: Comparative Study with Acyclovir, Guanosine, and Kinetin [beta]-Glucoside

To characterize the intestinal absorption of a beta-glucose conjugate of acyclovir (9-[(2-hydroxyethoxy) methyl] guanine, ACV) and compare it to ACV and its analogues in terms of stability and transport by Na+/glucose cotransporter (SGLTI). ACVbeta(glc) was enzymatically synthesized using cellulase. Intestinal absorption experiments were performed with rat everted small intestine. Conformation of the glucose moiety was analyzed by NMR spectroscopy. The ACVbeta(glc) was stable on the mucosal side, and was transported to the serosal side in all regions of the small intestine. However, significant contribution of SGLTI to the transport of ACVbetaglc was not observed. NMR spectroscopic analysis indicated that the glucose conformation of ACVbeta(glc) was the 4C1 chair form, identical to beta-glucose or SGLT1-transportable beta-glucosides reported previously. Therefore, other factors such as molecular size and charge due to aglycone may cause no transport of ACVbeta(glc) by SGLT1. On the other hand, the hydrophilicity of ACVbeta(glc) was much higher than of ACV, suggesting water solubility-derived improvement of intestinal absorption of ACV. ACVbeta(glc) is stable and absorbable, but it is not transported by SGLT1. No involvement of SGLT1 in the ACVbeta(glc) transport is not due to glucose conformation.