The circadian timing system controls absorption, distribution, metabolism, and elimination processes of drug pharmacokinetics over a 24-h period. Exposure of target tissues to the active form of the drug and cytotoxicity display variations depending on the chronopharmacokinetics. For anticancer drugs with narrow therapeutic ranges and dose-limiting side effects, it is particularly important to know the temporal changes in pharmacokinetics. A previous study indicated that pharmacokinetic profile of capecitabine was different depending on dosing time in rat. However, it is not known how such difference is attributed with respect to diurnal rhythm. Therefore, in this study, we evaluated capecitabine-metabolizing enzymes in a diurnal rhythm-dependent manner. To this end, C57BL/6J male mice were orally treated with 500 mg/kg capecitabine at ZT1, ZT7, ZT13, or ZT19. We then determined pharmacokinetics of capecitabine and its metabolites, 5′-deoxy-5-fluorocytidine (5′DFCR), 5′-deoxy-5-fluorouridine (5′DFUR), 5-fluorouracil (5-FU), in plasma and liver. Results revealed that plasma Cmax and AUC0-6h (area under the plasma concentration-time curve from 0 to 6 h) values of capecitabine, 5′DFUR, and 5-FU were higher during the rest phase (ZT1 and ZT7) than the activity phase (ZT13 and ZT19) ( p < 0.05). Similarly, Cmax and AUC0-6h values of 5′DFUR and 5-FU in liver were higher during the rest phase than activity phase ( p < 0.05), while there was no significant difference in liver concentrations of capecitabine and 5′DFCR. We determined the level of the enzymes responsible for the conversion of capecitabine and its metabolites at each ZT. Results indicated the levels of carboxylesterase 1 and 2, cytidine deaminase, uridine phosphorylase 2, and dihydropyrimidine dehydrogenase ( p < 0.05) are being rhythmically regulated and, in turn, attributed different pharmacokinetics profiles of capecitabine and its metabolism. This study highlights the importance of capecitabine administration time to increase the efficacy with minimum adverse effects.
Biofunctionality and biocompatibility are essential when tissue or organs are supplemented or replaced with a polymer based material. Here, we prepared stearyl methacrylate (SM) and vinylpyrrolidone (VP) based biocompatible SM-x networks with selfhealing and shape memory properties. The mole ratios were gradually changed from hydrophilic to hydrophobic units between 10 and 90% to obtain gels meeting the requirements in various potential bioapplications. In addition to having a time-dependent viscoelastic character, the mechanical properties of the gels can be controlled by the amount of SM introduced into the reaction medium. Low SM content gels cannot fully return to their initial modulus values, while the gels formed with concentrations ≥60% are completely reversible due to the dynamic hydrophobic interactions, which is also effective in the self-healing behavior. Moreover, all of the networks can completely recall their permanent shape in seconds. The viability of human skin fibroblast cells, seeded on SM-x hydrogels, closely related to the water contact angle of the structures, was found to be over 82% at all x values. In the light of the findings, the wide range of properties of SM-x gel samples may show significant potential to address needs in a variety of biomedical applications.
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