Sex differences in pharmacokinetics of cilostazol in rats.

The pharmacokinetics of cilostazol was investigated after oral and intravenous administration in both male and female rats. After oral administration, area under serum concentration-time curve (AUC) was about 35-fold higher in female rats than in male rats, and absolute bioavailability was about 5.8-fold higher in female rats than in male rats. Total body clearance (CL(total)) for female rats was around one-sixth of that for male rats. In vivo hepatic clearance (CL(h)) calculated based on isolated liver perfusion studies was even higher than or around 90% of the in vivo CL(total) of cilostazol for female and male rats, respectively, indicating that cilostazol is mainly eliminated by the liver in both male and female rats. In vitro metabolism studies utilizing hepatic microsomes and recombinant cytochrome (CYP) isoforms clearly indicated that major metabolites of cilostazol were generated extensively with hepatic microsomes of male rats and that male-predominant CYP3A2 and male-specific CYP2C11 were mainly responsible for the hepatic metabolism of cilostazol. Therefore, the great sex differences in the pharmacokinetics of cilostazol were mainly attributed to the large difference in hepatic metabolism. Our experimental results also suggested that the substantial metabolism of cilostazol in the small intestine and its possible saturation would be responsible for dose-dependent bioavailability in both male and female rats.

Manserin, a secretogranin II-derived peptide, distributes in the rat endocrine pancreas colocalized with islet-cell specific manner.

Manserin is a recently characterized 40-amino acid neuropeptide derived from secretogranin II, a protein belonging to the chromogranin family. Although the physiological roles of manserin have not been elucidated to date, manserin has been shown to distribute in not only the brain but also the endocrine system such as the pituitary and adrenal glands, suggesting its role in the endocrine system. The present study aimed to explore the occurrence and distribution of manserin in the rat pancreas using an immunohistochemical technique with a polyclonal antibody against rat manserin. Immunoreactivity for manserin was readily detected in almost whole islets of Langerhans whereas not at all in the exocrine pancreas. Manserin-expressing cells were not colocalized with the glucagon-secreting cells (alpha cells), whereas they colocalized with insulin-secreting cells (beta cells) and somatostatin-secreting cells (delta cells), although their intracellular distribution was different. These results indicate that manserin, occurring in the endocrine pancreas, may have a potential role in the endocrine system.

Co-administration of tacrolimus suppresses pharmacokinetic modulation of multiple subcutaneously administered human interferon-alpha in Beagle dogs.

Specific antibody production is an important issue in crossover pharmacokinetic (PK) studies of protein-based formulations. We recently reported that intravenous co-administration of tacrolimus with multiple human interferon-alpha (h-IFN) administrations successfully suppressed the production of anti-h-IFN antibodies in rats. Since crossover PK studies are preferentially carried out using larger animals such as dogs or monkeys that are capable of accepting the same dosage formulations as those for clinical use, we extended our study of co-administration of tacrolimus with multiple h-IFN administrations to beagle dogs in the present study. Beagle dogs were subcutaneously administered 0.5 million IU/kg of h-IFN once a week for 4 weeks. In some experiments, tacrolimus at 0.01 or 0.1 mg/kg was intravenously co-administered at the same time as the h-IFN administration. Co-administration of the lower dose of tacrolimus (0.01 mg/kg) failed to suppress the anti-h-IFN IgG responses, while co-administration of the higher dose (0.1 mg/kg) successfully suppressed these responses. Moreover, co-administration of tacrolimus had little effect on the serum creatinine concentrations, suggesting that multiple administrations of tacrolimus at the concentrations examined did not cause severe renal disorders. Taken together, the present data confirm that co-administration of tacrolimus is a promising way to assess crossover PK studies of human or humanized proteinic formulations in beagle dogs.

Nonexploratory movement and behavioral alterations in a thalidomide or valproic acid-induced autism model rat.

Autism is a behaviorally characterized disorder with impairments in social interactions, as well as stereotyped, repetitive patterns of behaviors and interests. Exposure of rat fetuses to thalidomide (THAL) or valproic acid (VPA) on the ninth day of gestation has been reported as a useful model for human autism. We have shown that early serotonergic neural development is disrupted in these rats. In the current study, we used a radial maze and open field experimental paradigm to investigate whether these rats present behavioral and/or learning aberrations. THAL (500mg/kg), VPA (800mg/kg), or vehicle was administered orally to E9 pregnant rats at 7-10 weeks of age. Although the mean number of correct and incorrect arm choices in the initial eight arm choices did not differ between control and teratogen-exposed groups, achievement of learning (seven or eight consecutive correct choices for 3 consecutive days for individual rats) seemed to be impaired in teratogen-exposed groups. Interestingly, average time to explore the maze task was shorter in the teratogen-exposed groups, indicating that correct choice might be due to mere coincidence (i.e., nonexploratory movement). Unexpectedly, no significant differences were observed in social interaction in these rats. These results indicate that prenatal exposure to THAL and VPA might alter behavior in a manner that is, in part, consistent with human autism.

In vitro-in vivo correlation for wet-milled tablet of poorly water-soluble cilostazol.

The purpose of the present study was to investigate oral bioavailability of an immediate release tablet containing wet-milled crystals of a poorly water-soluble drug, cilostazol, and to establish in vitro-in vivo correlation. Sub-micron sized cilostazol (median diameter: 0.26 microm) was successfully prepared using a beads-mill in water in the presence of a hydrophilic polymer and an anionic surfactant. The milled suspension was solidified with a sugar alcohol as a water-soluble carrier by spray-drying method. The co-precipitate was compressed into an immediate release tablet with common excipients. Oral bioavailability of the wet-milled cilostazol tablet in male beagle dogs was 13-fold higher than the hammer-milled commercial tablet in fasted condition. Food did not increase the oral bioavailability of the wet-milled tablet, while 4-fold increase was found for the commercial tablet. Irrespective to the bioavailability enhancement, in vitro dissolution rate of the wet-milled tablet was even slower than the commercial tablet by the compendial method (USP Apparatus 2). On the other hand, a good correlation was found between the dissolution profiles obtained by a flow-through cell method (USP Apparatus 4, closed-loop system without outlet filter) using a large volume of water and sodium lauryl sulfate (SLS) solution at the concentration lower than the critical micellar concentration (cmc) as dissolution media corresponding to the fasted and fed conditions, respectively.

Optimization of suppository preparation containing sodium laurate and taurine that can safely improve rectal absorption of rebamipide.

We previously reported that the fatty base suppository containing sodium laurate (C12) and taurine (Tau) (C12-Tau suppository) could enhance the colonic absorption of rebamipide, a poorly water-soluble and poorly absorbable drug, without any serious mucosal damages in rats. In the preset study, in order to make C12-Tau suppositories available for practical use, the scaling-up studies of animal and formulation size were performed, compared with the suppositories containing sodium caprate (C10) (C10 suppository) at the same amounts as those contained in the commercial products. Twenty-mg C12 improved the dissolution of rebamipide from suppository remarkably and the addition of 30-mg Tau only slightly decreased the dissolution rate. The absorption of rebamipide from rabbit rectum was more markedly improved by suppositories containing C12 than C10 suppositories. Although Tau tended to attenuate the absorption-enhancing effect of C12, several C12-Tau suppositories kept high bioavailability values, which were much higher than control. Histopathological studies showed that Tau exerted the cytoprotective action and that C12-Tau suppositories were better than C10 suppositories in safety. Considering the balance between efficacy and safety, the suppository containing 10- or 20-mg C12 with 30-mg Tau is better than C10 suppositories as commercial products and could be promising for practical use in human.

Effect of particle size reduction on dissolution and oral absorption of a poorly water-soluble drug, cilostazol, in beagle dogs.

The purpose of the present study was to investigate the effects of particle size on the dissolution and oral absorption of cilostazol. Three types of suspensions having different particle size distributions were prepared of the hammer-milled, the jet-milled cilostazol crystals and the NanoCrystal spray-dried powder of cilostazol. In vitro dissolution rate of cilostazol was significantly increased by reducing the particle size. The dissolution curves of the cilostazol suspensions were in good agreement with the simulation based on the Noyes-Whitney equation. The bioavailability of cilostazol after oral administration to dogs was increased with reducing the particle size. While positive food effect on the absorption was observed for the suspensions made of the hammer-milled and the jet-milled crystals, no significant food effect was found for the suspension made of the NanoCrystal cilostazol spray-dried powder. These results could be qualitatively predicted from the in vitro dissolution data using the bio-relevant media, FaSSIF and FeSSIF. In conclusion, the NanoCrystal technology is found to be efficient to improve the oral bioavailability of cilostazol and to avoid the food effect on the absorption.

Carrageenans can regulate the pulmonary absorption of antiasthmatic drugs and their retention in the rat lung tissues without any membrane damage.

Effects of various viscous vehicles on pulmonary absorption of antiasthmatic drugs were examined by an in situ pulmonary absorption experiment. Theophylline and fluticasone propionate were used as antiasthmatic drugs. The serum concentration-time profile of theophylline without viscous vehicles was similar to that following the intravenous injection, indicating that pulmonary absorption of theophylline was rapid and absolute. The serum concentration of theophylline was not controlled in the presence of 5% gelatin or 2% sodium alginate. However, 1% iota-carrageenan could control and regulate the serum concentration of theophylline. In the pharmacokinetic analysis, the C(max) values of theophylline significantly decreased, and its T(max) values increased in the presence of 1% and 2% iota-carrageenan, 1% kappa-carrageenan, and 2% sodium alginate compared with the control. The MRT and MAT values of theophylline with 1% iota-carrageenan were significantly higher than those without viscous vehicles. The local concentration of theophylline in the lung at 1h after intratracheal administration increased five-fold with 1% iota-carrageenan compared with the control. On the other hand, the pulmonary absorption of fluticasone propionate was controlled and regulated in the presence of 0.5% kappa-carrageenan. Additionally, the pulmonary inflammation after the exposure of carrageenans administered to the lung was evaluated in rats. Iota- and kappa-carrageenans did not cause local serious damage and inflammation to the pulmonary tissue. Therefore, these findings indicated that the carrageenans were effective to regulate the absorption rate of antiasthmatic drugs including theophylline and fluticasone propionate.

Development of suppository formulation safely improving rectal absorption of rebamipide, a poorly absorbable drug, by utilizing sodium laurate and taurine.

To develop the safe formulation that can safely improve bioavailability of poorly absorbable drugs and that is practically available, we prepared the suppositories of rebamipide, a poorly soluble and poorly absorbable antiulcer drug, by employing the combinatorial use of sodium laurate (C12), an absorption enhancer, with taurine (Tau) or L-glutamine (L-Gln), an adjuvant exerting the cytoprotective action. Although the dissolution of rebamipide from fatty base (FB) suppository prepared using Witepsol H-15 was very slow, it was remarkably improved by the addition of C12 and L-Gln or Tau into the suppository. On the other hand, the dissolution of rebamipide from water-soluble base (WB) suppository prepared using polyethylene glycol was very rapid and the addition of adjuvants did not influence its dissolution so much. Rectal absorption of rebamipide examined in rats was remarkably improved by FB suppository containing C12 or both C12 and Tau, while the enhancing effect of C12 was relatively small in the case of WB suppositories. Biochemical and histopathological studies have confirmed that FB suppository containing both C12 and Tau or L-Gln did not cause any serious local damage, while FB suppository containing C12 only caused the erosion and shrinkage for a lot of rectal epithelial cells. In conclusion, FB suppository employing the combinatorial use of C12 with Tau could be a promising formulation that is effective and safe enough for poorly absorbable drugs to be practically administered.