Pharmacokinetic study of all-trans-retinoyl-beta-D-glucuronide in Sprague-Dawley rats after single and multiple intravenous administration(s)

Preclinical pharmacokinetic evaluation of resveratrol trimethyl ether in sprague-dawley rats: the impacts of aqueous solubility, dose escalation, food and repeated dosing on oral bioavailability

Resveratrol trimethyl ether (trans-3,5,4'-trimethoxystilbene, RTE) is a naturally occurring and pharmacologically active resveratrol derivative. To evaluate its suitability as a drug candidate, a pharmacokinetic study was carried out in Sprague-Dawley rats with the emphasis to identify the impact of aqueous solubility, dose escalation, food, and repeated dosing on its oral bioavailability. Upon single intravenous administration (5 mg/kg), RTE displayed moderate clearance (35.5 ± 5.3 mL/min/kg) and a fairly long terminal elimination half-life (511 ± 136 min); dose escalation (5-20 mg/kg) did not cause nonlinear pharmacokinetics. When given orally in suspension (60 mg/kg), RTE was poorly absorbed with negligible bioavailability (< 1.5%), fasting further decreased its bioavailability (<1%). However, when administered in a solution formulated with randomly methylated-β-cyclodextrin (15 mg/kg), RTE was rapidly absorbed with good bioavailability (46.5 ± 4.8%). Dose escalation resulted in increased bioavailability (64.6 ± 8.0%) at the dose of 60 mg/kg. Repeated RTE dosing (7 daily oral doses) did not alter the clearance, terminal elimination half-life and bioavailability. In summary, the aqueous solubility of RTE was a barrier to oral absorption; repeated RTE administrations did not alter its pharmacokinetic profiles; as RTE possessed appropriate pharmacokinetic profiles, further investigation on RTE as a drug candidate is warranted.

Biopharmaceutics of 13-cis-retinoic acid (isotretinoin) formulated with modified β-cyclodextrins

13-cis-Retinoic acid (13-cis-RA), also known as isotretinoin, is commonly used in the management of severe acne. Its clinical efficacy in oncology has also been documented. As a vitamin A derivative, it is not soluble in water. This solubility barrier not only affects its oral absorption but also makes parenteral delivery difficult. Recently, water-soluble formulations of 13-cis-RA have been attempted with 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and randomly methylated-beta-cyclodextrin (RM-beta-CD). In this study, the pharmacokinetic profiles of these two formulations were assessed in Sprague-Dawley rats after single intravenous or oral administration. We found that 13-cis-RA was eliminated from the body through a dose-independent process after intravenous injection of either sodium salt or the HP-beta-CD formulation within the tested dosage range (2.0-7.5mg/kg). Furthermore, HP-beta-CD did not alter the kinetic profile of 13-cis-RA after intravenous administration in comparison with 13-cis-RA sodium salt. We also found that RM-beta-CD dramatically enhanced the oral absorption of 13-cis-RA. At 10.0mg/kg, the bioavailability of 13-cis-RA formulated with RM-beta-CD was about three-fold higher than that of the control (13-cis-RA suspended in 0.5% carboxymethylcellulose (CMC)). Similarly, the oral absorption of 13-cis-RA was not saturated within our tested range (2.5-10.0mg/kg) and the bioavailability remained unchanged. These results demonstrated that HP-beta-CD and RM-beta-CD were suitable excipients for the delivery of 13-cis-RA.

Elevation of retinyl ester level in the lungs of rats following repeated intraperitoneal injections of retinoic acid or retinoyl glucuronide

Retinoic acid (RA) is involved in the development of both the conducting airway and alveolar portions of the lung. RA plays a key role in the induction of the formation of alveolar septa. Retinoyl beta-glucuronide (RAG), an endogenous retinoid, acts like RA, but is much less cytotoxic. We examined the effect of daily intraperitoneal doses of RA and RAG (1.66 micromol/kg) in dimethyl sulfoxide (DMSO) and cotton seed oil on the stores of retinol and retinyl ester (RE) in the lung of rats. In two separate experiments, one involving normal rats, and the other involving elastase-treated rats, there was up to a 9-fold increase in REs content in the lungs of rats that received RA or RAG for 12 days as compared to Control rats. The accumulation was most profound when RA was injected in DMSO and least when RAG was injected in cotton seed oil. The reason for the accumulation of REs in the lung is not clearly known.

Biopharmaceutics of β-cyclodextrin derivative-based formulations of acitretin in sprague-dawley rats

Acitretin, an active metabolite of etretinate, is as effective as etretinate in the treatment of psoriasis. Recently, we developed some water-soluble formulations of acitretin with 2-hydroxypropyl-beta-cyclodextrin (HPBCD)/randomly substituted methyl-beta-cyclodextrin (RMBCD). In this study, the biopharmaceutic properties of these formulations were tested in Sprague-Dawley rats. After single intravenous dosing (2.5, 5, or 10 mg/kg) with the HPBCD-based formulation, the area under the plasma concentration-time curve of acitretin increased proportionally with the dose and its clearance remained unchanged within the tested dose range. We also found that the RMBCD-based formulation of acitretin improved its bioavailability and decreased the variations in various pharmacokinetic parameters. The improved biopharmaceutic properties of RMBCD-based acitretin might be attributed to its enhanced aqueous solubility. The elimination of acitretin through bile excretion was also studied. Our results indicated that the major fraction of acitretin (approximately 40%) was excreted in the bile as beta-glucuronide conjugate and only trace amounts were excreted as unconjugated acitretin (approximately 0.5%). This finding further confirmed the importance of conjugated metabolism and biliary excretion in the elimination of this drug.

Inclusion of Acitretin into Cyclodextrins: Phase Solubility, Photostability, and Physicochemical Characterization

Acitretin, a retinoid for the treatment of severe psoriasis, exhibits extremely low aqueous solubility and high photosensitivity. This study investigated the effects of the complexation of acitretin with the respective hydroxypropyl-beta-cyclodextrin (HPBCD) and randomly substituted methyl-beta-cyclodextrin (RMBCD) on the aqueous solubility and photostability of the drug. Phase-Solubility studies indicated that the solubility of acitretin was dramatically improved by formation of complexes and further increased by pH adjustment. Stability constants were much higher for acitretin complexed with RMBCD than with HPBCD. Both cyclodextrins acted to decrease degradation of acitretin in solution. The physicochemical properties of solid inclusion complexes were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and X-ray diffractometry. Molecular modeling with MMFF94s force field (SYBYL V6.6) was utilized to predict the preferred orientation of acitretin in the cyclodextrin cavity and the main structural features responsible for the enhancement of its solubility and photostability.