Expression of Carboxylesterase Isozymes and Their Role in the Behavior of a Fexofenadine Prodrug in Rat Skin

[Evaluation of the Oral Absorption of Ester-type Prodrugs]

The first-pass hydrolysis of oral ester-type prodrugs in the liver and intestine is mediated mainly by hCE1 and hCE2 of the respective predominant carboxylesterase (CES) isozymes. In order to provide high blood concentrations of the parent drugs, it is preferable that prodrugs are absorbed as an intact ester in the intestine, then rapidly converted to active parent drugs by hCE1 in the liver. In the present study, we designed a prodrug of fexofenadine (FXD) as a model parent drug that is resistant to hCE2 but hydrolyzed by hCE1, utilizing the differences in catalytic characteristics of hCE1 and hCE2. In order to precisely predict the intestinal absorption of an FXD prodrug candidate, we developed a novel high-throughput system by modifying Caco-2 cells. Further, we evaluated species differences and aging effects in the intestinal and hepatic hydrolysis of prodrugs to improve the estimation of in vivo first-pass hydrolysis of ester-type prodrugs. Consequently, it was possible to design a hepatotropic prodrug utilizing the differences in tissue distribution and substrate specificity of CESs. In addition, we successfully established three useful in vitro systems for predicting the intestinal absorption of hCE1 substrate using Caco-2 cells. However, some factors involved in estimating the bioavailability of prodrugs in human, such as changes in recognition of drug transporters by esterification, and species differences of the first-pass hydrolysis, should be comprehensively considered in prodrug development.

Skin Penetration and Stability Enhancement of Celastrus paniculatus Seed Oil by 2-Hydroxypropyl-β-Cyclodextrin Inclusion Complex for Cosmeceutical Applications

This study aimed to encapsulate Celastrus paniculatus seed oil (CPSO) in 2-hydroxypropyl-β-cyclodextrin (HPβCD) cavities and investigate their biological activity, physicochemical stability, and skin penetration by vertical Franz diffusion cells of the CPSO-HPβCD inclusion complex formulations. For biological activity studies-including 2,2-diphenyl-1-picryhydrazyl radical (DPPH) scavenging, metal ion chelating, and inhibition of lipid and tyrosinase inhibition activities-the CPSO-HPβCD inclusion complex exhibited lower inhibition activity than free CPSO. CPSO-HPβCD dispersion, serum, and gel formulations were prepared. All formulations containing the CPSO-HPβCD inclusion complex showed no significant changes in physical characteristics after three months' storage. The percentages of oleic acid remaining in all formulations were over 80% of the initial amount during a three-month stability study. For the skin-penetration study, compared to other formulations, the CPSO-HPβCD serum formulation exhibited the highest cumulative amount of oleic acid in the whole skin and flux through receptor fluid, after six hours, of 32.75 ± 1.25 µg/cm² and 1.02 ± 0.15 µg/cm²/h, respectively. The CPSO-HPβCD serum formulation also showed the proper viscosity. Hence, the CPSO-HPβCD inclusion complex will be beneficial for the further development of cosmeceutical products.

Synthesis, Characterization, and Evaluation of Triptolide Cell-Penetrating Peptide Derivative for Transdermal Delivery of Triptolide

Triptolide (TP) has been used as one of the most common systemic treatments for various diseases since the 1960s. However, TP displays diverse side effects on various organs, which limits its clinical application. To overcome this issue, numerous C-14-hydroxyl group derivatives of TP have been synthesized. In this research, the C-14-hydroxyl group of TP is modified by a cell-penetrating peptide polyarginine (R₇). The derivative TP-disulfide-CR₇ (TP-S-S-CR₇) containing a disulfide linkage between TP and R₇ possesses less toxicity at various concentrations on the immortal human keratinocyte (HaCaT) cell line by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay compared with free TP. Treating HaCaT cells with TP (100 nM) could increase intracellular ROS (reactive oxygen species) and decrease the activity of SOD (superoxide dismutase). Meanwhile, treating HaCaT cells with equimolar concentration of TP-S-S-CR₇ did not cause both of the above TP-induced alterations. In addition, TP-S-S-CR₇ did not show significant dermal toxicity on guinea pigs and could efficiently overcome the barrier of corneum and then reach epidermis and dermis within 2 h of transdermal administration. In addition, there was a relatively lower concentration of TP in blood indicating less toxicity on organs. Such results suggest that topical therapy using polyarginine is possible by the transdermal delivery of TP.

Estimation of human percutaneous bioavailability for two novel brominated flame retardants, 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (EH-TBB) and bis(2-ethylhexyl) tetrabromophthalate (BEH-TEBP)

2-Ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB) and bis(2-ethylhexyl)tetrabromophthalate (BEH-TEBP) are novel brominated flame retardants used in consumer products. A parallelogram approach was used to predict human dermal absorption and flux for EH-TBB and BEH-TEBP. [¹⁴C]-EH-TBB or [¹⁴C]-BEH-TEBP was applied to human or rat skin at 100nmol/cm² using a flow-through system. Intact rats received analogous dermal doses. Treated skin was washed and tape-stripped to remove "unabsorbed" [¹⁴C]-radioactivity after continuous exposure (24h). "Absorbed" was quantified using dermally retained [¹⁴C]-radioactivity; "penetrated" was calculated based on [¹⁴C]-radioactivity in media (in vitro) or excreta+tissues (in vivo). Human skin absorbed EH-TBB (24±1%) while 0.2±0.1% penetrated skin. Rat skin absorbed more (51±10%) and was more permeable (2±0.5%) to EH-TBB in vitro; maximal EH-TBB flux was 11±7 and 102±24pmol-eq/cm²/h for human and rat skin, respectively. In vivo, 27±5% was absorbed and 13% reached systemic circulation after 24h (maximum flux was 464±65pmol-eq/cm²/h). BEH-TEBP in vitro penetrance was minimal (<0.01%) for rat or human skin. BEH-TEBP absorption was 12±11% for human skin and 41±3% for rat skin. In vivo, total absorption was 27±9%; 1.2% reached systemic circulation. In vitro maximal BEH-TEBP flux was 0.3±0.2 and 1±0.3pmol-eq/cm²/h for human and rat skin; in vivo maximum flux for rat skin was 16±7pmol-eq/cm²/h. EH-TBB was metabolized in rat and human skin to tetrabromobenzoic acid. BEH-TEBP-derived [¹⁴C]-radioactivity in the perfusion media could not be characterized. <1% of the dose of EH-TBB and BEH-TEHP is estimated to reach the systemic circulation following human dermal exposure under the conditions tested.

CHEMICAL COMPOUNDS STUDIED IN THIS ARTICLE

2-Ethylhexyl 2,3,4,5-tetrabromobenzoate (PubChem CID: 71316600; CAS No. 183658-27-7 FW: 549.92g/mol logP_est: 7.73-8.75 (12)) Abdallah et al., 2015a. Other published abbreviations for 2-ethylhexyl-2,3,4,5-tetrabromobenzoate are TBB EHTeBB or EHTBB Abdallah and Harrad, 2011. bis(2-ethylhexyl) tetrabromophthalate (PubChem CID: 117291; CAS No. 26040-51-7 FW: 706.14g/mol logP_est: 9.48-11.95 (12)). Other published abbreviations for bis(2-ethylhexyl)tetrabromophthalate are TeBrDEPH TBPH or BEHTBP.