Evidence for an Interaction Between the β-Blocker Pafenolol and Bile Salts in the Intestinal Lumen of the Rat Leading to Dose-Dependent Oral Absorption and Double Peaks in the Plasma Concentration–Time Profile

Pafenolol is a -blocker with unusual oral absorption properties. The blood concentration–time profile exhibits two peaks, and the bioavailability is low and dose dependent because of incomplete and nonlinear intestinal uptake. We addressed the question whether the intestinal absorption of pafenolol was affected by bile depletion in the gut lumen of rats. Further, the hypothesis that variable gastric emptying accounts for double peaks in blood was tested by duodenal administration of pafenolol. Following intraduodenal administration to rats with intact bile secretion, double peaks were observed in the blood concentration–time curve. The bioavailability was 6.8 ± 0.7% for the low dose (1 µmol/kg) and increased significantly to 28 ± 10% following the high duodenal dose (25 µmol/kg). These blood concentration–time profiles exclude interrupted gastric emptying as cause of the twin peaks. In bile duct-cannulated rats the intestinal absorption of the low dose (1 µmol/kg) was still poor (F = 10.7 ± 5.5%) and the blood concentration–time profile contained two peaks. Following administration of a high duodenal dose (25 µmol/kg) to rats with an almost bile-free small intestine, the absorption rate increased and the double-peak phenomenon disappeared in five of seven rats, while the bioavailability increased significantly, to 62 ± 27%. These results suggest that the low bioavailability of pafenolol is due to a complexation between bile and pafenolol in the gut lumen, preventing intestinal uptake in the major part of the small intestine. Further, such complex formation in the intestinal lumen may be the underlying mechanism of the double peaks observed in the blood concentration–time profile.     

Appearance of Double Peaks in Plasma Concentration–time Profile after Oral Administration Depends on Gastric Emptying Profile and Weight Function

Purpose Mechanism for double-peak occurrence in plasma concentration profile after oral administration of drugs is controversial, although irregular gastric emptying would be an important factor. The objective of this study was to assess the effect of gastric emptying and a weight function, i.e. pharmacokinetics after reaching the systemic circulation, on the double-peak appearance in plasma concentration profiles. Materials and Methods Alprazolam, which generates irregular gastric emptying, was orally co-administered with theophylline to rats, and the plasma concentration profiles or absorption rates were compared between the two drugs. Both drugs are highly absorbable, but alprazolam is rapidly eliminated from plasma, while the elimination of theophylline is very slow. Results Oral administration of alprazolam generated the irregular gastric emptying profiles, resulting in multiple peaks in the absorption rate profiles of both drugs. The double peaks in the absorption rate profiles led to the double peaks in plasma concentration profiles for alprazolam, but not necessarily for theophylline. Simulation study clearly indicated that the slower elimination from plasma made the first peak less recognizable. Conclusions The irregular gastric emptying could be a main reason for the double peaks in plasma concentration profiles. However, the frequency of double-peak occurrence depends on the weight function, particularly the elimination rate, of each drug.     

Modelling Response Time Profiles in the Absence of Drug Concentrations: Definition and Performance Evaluation of the K–PD Model

The plasma concentration–time profile of a drug is essential to explain the relationship between the administered dose and the kinetics of drug action. However, in some cases such as in pre-clinical pharmacology or phase-III clinical studies where it is not always possible to collect all the required PK information, this relationship can be difficult to establish. In these circumstances several authors have proposed simple models that can analyse and simulate the kinetics of the drug action in the absence of PK data. The present work further develops and evaluates the performance of such an approach. A virtual compartment representing the biophase in which the concentration is in equilibrium with the observed effect is used to extract the (pharmaco)kinetic component from the pharmacodynamic data alone. Parameters of this model are the elimination rate constant from the virtual compartment (KDE), which describes the equilibrium between the rate of dose administration and the observed effect, and the second parameter, named EDK₅₀ which is the apparent in vivo potency of the drug at steady state, analogous to the product of EC₅₀, the pharmacodynamic potency, and clearance, the PK “potency” at steady state. Using population simulation and subsequent (blinded) analysis to evaluate this approach, it is demonstrated that the proposed model usually performs well and can be used for predictive simulations in drug development. However, there are several important limitations to this approach. For example, the investigated doses should extend from those producing responses well below the EC₅₀ to those producing ones close to the maximum response, optimally reach steady state response and followed until the response returns to baseline. It is shown that large inter-individual variability on PK–PD parameters will produce biases as well as large imprecision on parameter estimates. It is also clear that extrapolations to dosage routes or schedules other than those used to estimate the parameters should be undertaken with great caution (e.g., in case of non-linearity or complex drug distribution). Consequently, it is advised to apply this approach only when the underlying structural PD and PK are well understood. In any case, K–PD model should definitively not be substituted for the gold standard PK–PD model when correct full model can and should be identified.     

Suitability of Various Noninfinity Area Under the Plasma Concentration–Time Curve (AUC) Estimates for Use in Bioequivalence Determinations: Relationship to AUC from Zero to Time Infinity (AUCO–INF)

The influence of random error and elimination rate on estimates of the area under the curve from zero to time infinity (AUC0–INF) was determined in a simulation study using noninfinity measured AUC values (i.e., AUCTM, area to a measured common sampling time, and AUC0-LAST, area to the last measured sampling time). Further, the extent of absorption of generic danazol, baclofen, and oxazepam was determined using measured methods of estimating area under the curve in bioequivalence studies. The noninfinity AUC estimates and their 90% confidence intervals for the difference in product means were compared for each individual drug. Products chosen fulfilled one of the following three criteria: (1) a high apparent intrasubject variability and a half-life greater than 8 hr (danazol); (2) a low apparent intrasubject variability and a half-life less than 4 hr (baclofen); and (3) products exhibiting a low apparent intrasubject variability and a half-life greater than 8 hr (oxazepam). For the simulated data, AUCTM performed best when subjects had similar half-lives (i.e., low variability), which results in AUCTM = AUC0–LAST. On the other hand, AUC0–LAST worked best with a high fractional standard deviation (fsd) and a short elimination half-life (i.e., less than 4 hr). The noninfinity 90% confidence intervals for danazol and oxazepam were inconsistent with those observed at AUC0–INF. However, baclofen, which has a short elimination half-life, exhibited good agreement between the noninfinity and the AUC0–INF 90% confidence intervals. However, across all three drug groups, the comparison based upon the area calculated from time zero to the last quantifiable concentration, AUC0–LAST, consistently provided the best approximation of AUC0–INF.     

Aerosolized Montelukast Polymeric Particles—An Alternative to Oral Montelukast–Alleviate Symptoms of Asthma in a Rodent Model

Purpose

Cysteinyl leukotrienes (CysLTs) propagate inflammatory reactions that result from allergen exposure in asthma. Montelukast, a CysLT type-1 receptor antagonist, disrupts mediator–receptor interactions and minimizes inflammatory response. In this study, we have evaluated anti-asthmatic efficacy of inhalable montelukast-loaded large porous particulate formulations in ovalbumin-induced rat airway inflammation model that mimics asthma.

Methods

The anti-inflammatory effects of a montelukast-loaded formulation were investigated in rats by measuring the total protein content, levels of injury markers and number of inflammatory cells in the bronchoalveolar lavage fluid (BALF). The histopathological studies assessed the morphological and structural changes that occur in asthmatic lungs. Animals were also challenged with methacholine to examine the airway hyper-reactivity.

Results

Compared with healthy animals, asthmatic animals showed a 3.8- and 4.77-fold increase in the protein content and number of inflammatory cells in BALF, respectively. Intratracheal montelukast particles reduced the protein content by 3.3-fold and the number of inflammatory cells by 2.62-fold. Also, montelukast particles reduced the lactate dehydrogenase (LDH) and myeloperoxidase (MPO) levels by a 4.87- and 6.8-fold in BALF, respectively. Montelukast particles reduced the airway wall thickness by 2.5-fold compared with untreated asthmatic lungs. Further, particulate formulation protected the lungs against methacholine-induced bronchial provocation (p?Conclusions Respirable large porous particles containing montelukast alleviated allergen-induced inflammatory response in an animal model and prevented histological changes associated with asthma. Thus montelukast-loaded large porous polylactic acid (PLA) particles could be an aerosolized delivery approach for administration of currently available oral montelukast.     

Development of a Novel Simplified PBPK Absorption Model to Explain the Higher Relative Bioavailability of the OROS® Formulation of Oxybutynin

A new minimal Segmented Transit and Absorption model (mSAT) model has been recently proposed and combined with intrinsic intestinal effective permeability (P _eff,int ) to predict the regional gastrointestinal (GI) absorption (f _abs ) of several drugs. Herein, this model was extended and applied for the prediction of oral bioavailability and pharmacokinetics of oxybutynin and its enantiomers to provide a mechanistic explanation of the higher relative bioavailability observed for oxybutynin’s modified-release OROS® formulation compared to its immediate-release (IR) counterpart. The expansion of the model involved the incorporation of mechanistic equations for the prediction of release, transit, dissolution, permeation and first-pass metabolism. The predicted pharmacokinetics of oxybutynin enantiomers after oral administration for both the IR and OROS® formulations were in close agreement with the observed data. The predicted absolute bioavailability for the IR formulation was within 5% of the observed value, and the model adequately predicted the higher relative bioavailability observed for the OROS® formulation vs. the IR counterpart. From the model predictions, it can be noticed that the higher bioavailability observed for the OROS® formulation was mainly attributable to differences in the intestinal availability (F _G ) rather than due to a higher colonic f _abs , thus confirming previous hypotheses. The predicted f _abs was almost 70% lower for the OROS® formulation compared to the IR formulation, whereas the F _G was almost eightfold higher than in the IR formulation. These results provide further support to the hypothesis of an increased F _G as the main factor responsible for the higher bioavailability of oxybutynin’s OROS® formulation vs. the IR.     

Pharmacokinetic–Pharmacodynamic Modeling of the Hydroxy Lerisetron Metabolite L6-OH in Rats: An Integrated Parent–Metabolite Model

Purpose The twofold aim of this study was to characterize in vivo in rats the pharmacokinetics (PK) and pharmacodynamics (PD) of L6-OH, a metabolite of lerisetron with in vitro pharmacological activity, and evaluate the extent to which L6-OH contributes to the overall effect. Methods The PK of L6-OH was determined directly postmetabolite i.v. dose (PK-1), and also simultaneously for L (lerisetron concentration) and for generated L6-OH after lerisetron dose (200 μg kg⁻¹, i.v.), using Nonlinear Mixed Effects Modeling with an integrated parent–metabolite PK model (PK-2). Surrogate effect was measured by inhibition of serotonin-induced bradycardia. Protein binding was assayed via ultrafiltration and all quantification was performed via liquid chromatography-electrospray ionization-mass spectrometry. Results L6-OH showed elevated plasma and renal clearances, and volume of distribution (PK-1). The in vivo potency (PD) of L6-OH was high (EC₅₀ = 0.098 ng mL⁻¹ and EC_50unbound = 0.040 ng mL⁻¹). Total clearance for L (PK-2) in the presence of generated L6-OH (CL_L = CL_→L6-OH + CL_n) was 0.0139 L min⁻¹. Most of this clearance was L6-OH formation (F_c = 99.6%), but only an 8.6% fraction of L6-OH was released into the bloodstream. The remainder undergoes biliar and fecal elimination. The parameters estimated from PK-2 were used to predict concentrations of L6-OH (Cp_L6) generated after a lerisetron therapeutic dose (10 μg kg⁻¹) in the rat. These concentrations are needed for the PD model and are below the quantification limit. Cp_L6max was less than the EC₅₀ of L6-OH. Conclusions We conclude that after lerisetron administration, L6-OH is extensively formed in the rat but it is quickly eliminated; therefore, besides being equipotent with the parent drug, the L6-OH metabolite does not influence the effect of lerisetron.     

Methodological Aspects of the Use of a Calibrator in In Vivo Microdialysis–Further Development of the Retrodialysis Method

Purpose. To investigate the performance of two alternative retrodialysis recovery methods and to describe the influence of different recoveries on the reliability in estimating unbound extracellular concentrations of morphine. Methods. Unbound concentrations of morphine in striatum and in blood were determined by microdialysis after a 10 min i.v. infusion in freely moving rats. In vivo recovery of morphine was determined by morphine itself, retrodialysis by drug, and by the calibrator nalorphine, retrodialysis by calibrator. Results. The low calibrator recovery in striatum (8.6%) resulted in large variability in the estimation of unbound extracellular concentrations when retrodialysis by calibrator was used. In blood, where the recovery was higher (36%), the variability was smaller. Also, when retrodialysis by drug was used, the variability remained low. This difference is caused by the propagation of errors in the way retrodialysis recovery is determined. Therefore, calibrator recovery values 20% are preferable in concentration estimations using retrodialysis by calibrator. Conclusions. When no time-dependent change in recovery is observed, retrodialysis by drug determined before the systemic administration is the best method. The calibrator is valuable as a quality control during the experiment.     

Assessment of Drug–drug Interaction and Optimization in Capecitabine and Irinotecan Combination Regimen using a Physiologically Based Pharmacokinetic Model

Capecitabine and irinotecan (CPT-11) combination regimen (XELIRI) is used for colorectal cancer treatment. Capecitabine is metabolized to 5-fluorouracil (5-FU) by three enzymes, including carboxylesterase (CES). CES can also convert CPT-11 to 7-ethyl-10-hydroxycamptotecin (SN-38). CES is involved in the metabolic activation of both capecitabine and CPT-11, and it is possible that drug–drug interactions occur in XELIRI. Here, a physiologically based pharmacokinetic (PBPK) model was developed to evaluate drug–drug interactions. Capecitabine (180 mg/kg) and CPT-11 (180 mg/m²) were administered to rats, and blood (250 μL) was collected from the jugular vein nine times after administration. Metabolic enzyme activities and K_i values were calculated through in vitro experiments. The plasma concentration of 5-FU in XELIRI was significantly decreased compared to capecitabine monotherapy, and metabolism of capecitabine by CES was inhibited by CPT-11. A PBPK model was developed based on the in vivo and in vitro results. Furthermore, a PBPK model-based simulation was performed with the capecitabin dose ranging from 0 to 1000mol/kg in XELIRI, and it was found that an approximately 1.7-fold dosage of capecitabine was required in XELIRI for comparable 5-FU exposure with capecitabine monotherapy. PBPK model-based simulation will contribute to the optimization of colorectal cancer chemotherapy using XELIRI.     

Pharmacokinetic–pharmacodynamic model of fimasartan applied to predict the influence of a high fat diet on its blood pressure-lowering effect in healthy subjects

Purpose

Fimasartan is a non-peptide angiotensin II receptor antagonist which selectively blocks the AT₁ receptor. The aim of our study was to perform a population pharmacokinetic–pharmacodynamic (PK–PD) analysis of fimasartan to evaluate the effect of food on the mechanistic PK–PD relationship.

Methods

This was a food–drug interaction single-center study involving 24 healthy subjects that was designed as a randomized, open-label, single-dosing, two-way crossover trial. Extensive PK data was obtained on blood samples collected at 0, 0.5, 1, 2, 2.5, 3, 4, 6, 8, 12, and 24 h post-dosing and five systolic/diastolic blood pressure (BP) measurements made at 0, 4, 8, 12 and 24 h post-dosing and used to construct a mixed effect model (NONMEM, ver. 6.2).

Results

A two-compartment linear PK model with zero-order (fasted) or Weibull (fed with high-fat diet) absorption best described the PK of fimasartan. Relative bioavailability decreased by 37 % when the subjects were given a high-fat diet.

Conclusions

The turnover PK–PD model combined with pre-defined cosine function for circadian rhythm described the BP changes measured within 24 h after dosing better than the effect compartment or transduction models. To predict the influence of a high-fat diet on the blood pressure-lowering effect of fimasartan in healthy subjects, we simulated changes in BP when fimasartan was given daily for 30 days. The overlapping pattern of simulated BP curves in the fasted versus fed group demonstrated that a high-fat diet would not cause a clinically significant reduction in the BP-lowering effect of fimasartan, despite a significant reduction in bioavailability.     

Pharmacokinetic–Pharmacodynamic Modeling of Tolmetin Antinociceptive Effect in the Rat Using an Indirect Response Model: A Population Approach

The relationship between the pharmacokinetics and the antinociceptive effect of tolmetin was characterized by an indirect model using a population approach. Animals received an intra-articular injection of uric acid in the right hindlimb to induce its dysfunction. Once dysfunction was complete, rats received an oral tolmetin dose of 1, 3.2, 10, 31.6, 56.2, or 100mg/kg and antinociceptive effect and blood tolmetin concentration were simultaneously evaluated. Tolmetin produced a dose-dependent recovery of functionality, which was not directly related to blood concentration. An inhibitory indirect response model was used based on these response patterns and the fact that tolmetin reduced nociception by inhibiting prostaglandin synthesis. Pharmacokinetic (PK) and pharmacodynamic (PD) data were simultaneously fitted using nonlinear mixed effects modeling (NONMEM) to the one-compartment model and indirect response model. The individual time courses of the response were described using Bayesian analysis with population parameters as a priori estimates. There was good agreement between the predicted and observed data. Population analysis yielded a maximal inhibition of the nociceptive response of 76% and an IC₅₀ of 9.22 g/ml. This IC₅₀ is similar to that for tolmetin-induced prostaglandin synthesis inhibition in vitro (3.0 g/ml). The present results demonstrate that mechanism-based PK-PD analysis using a population approach is useful for quantitating individual responses as well as reflecting the actual mechanism of action of a given drug in vivo.     

Application of the Tissue Composition–Based Model to Minipig for Predicting the Volume of Distribution at Steady State and Dermis-to-Plasma Partition Coefficients of Drugs Used in the Physiologically Based Pharmacokinetics Model in Dermatology

The minipig continues to build a reputation as a viable alternative large animal model to predict humans in dermatology and toxicology studies. Therefore, it is essential to describe and predict the pharmacokinetics in that species to speed up the clinical candidate selection. Essential input parameters in whole-body physiologically based pharmacokinetic models are the tissue-to-plasma partition coefficients and the resulting volume of distribution at steady-state (V_ss). Mechanistic in vitro– and in silico–based models used for predicting these parameters of tissue distribution of drugs refer to the tissue composition–based model (TCM). Robust TCMs were initially developed for some preclinical species (e.g., rat and dog) and human; however, there is currently no model available for the minipig. Therefore, the objective of this present study was to develop a TCM for the minipig and to estimate the corresponding tissue composition data. Drug partitioning into the tissues was predominantly governed by lipid and protein binding effects in addition to drug solubilization and pH gradient effects in the aqueous phase on both sides of the biological membranes; however, some more complex tissue distribution processes such as drug binding to the collagen-laminin material in dermis and a restricted drug partitioning into membranes of tissues for compounds that are amphiphilic and contain sulfur atom(s) were also challenged. The model was validated by predicting V_ss and the dermis-to-plasma partition coefficients (K_p-dermis) of 68 drugs. The prediction of K_p-dermis was extended to humans for comparison with the minipig. The results indicate that the extended TCM provided generally good agreements with observations in the minipig showing that it is also applicable to this preclinical species. In general, up to 86% and 100% of the predicted V_ss values are respectively within 2-fold and 3-fold errors compared to the experimentally determined values, whereas these numbers are 78% and 94% for K_p-dermis when the anticipated outlier compounds are not included. Binding data to dermis are comparable between minipigs and humans. Overall, this study is a first step toward developing a mechanistic TCM for the minipig, with the aim of increasing the use of physiologically based pharmacokinetic models of drugs for that species in addition to rats, dogs, and humans because such models are used in preclinical and clinical transdermal studies.     

Acute Nose-Only Exposure of Rats to Phosgene. Part II. Concentration × Time Dependence of Changes in Bronchoalveolar Lavage During a Follow-Up Period of 3 Months

Groups of young adult male Wistar rats were acutely exposed to phosgene gas for either 30 or 240 min using a directed-flow nose-only mode of exposure. In 30-min exposed rats the concentrations were 0.94, 2.02, 3.89, 7.35, and 15.36 mg/m³, which relate to C × t products of 28.2, 60.6, 116.7, 220.5, and 460.8 mg/m³ × min. In 240-min exposed rats the concentrations were 0.96, 0.387, 0.786, 1.567, and 4.2 mg/m³, which relate C × t products of 47.0, 92.9, 188.6, 376, and 1008 mg/m³ × min. Six rats/group were sacrificed on postexposure days 1, 3, 7, 14, and 84, while the rats of the 1008 mg/m³ × min group where sacrificed on postexposure days 1, 7, 14, and 28. The focus of measurements was directed toward indicators of inflammatory response and increased transmucosal permeability in bronchoalveolar lavage (BAL), including lung weights. Lungs from rats sacrificed at the end of the postexposure period were additionally examined by histopathology. Mortality did not occur at any C × t product. The most pronounced changes were related to C × t-dependent increases in the following markers in BAL: protein, soluble collagen, polymorphonuclear leukocytes (PMN) counts, and alveolar macrophages with foamy appearance. These indicators were maximal on the first postexposure day, while total cell counts and alveolar macrophages containing increased phospholipids reached their climax around post-exposure day 3. At 1008 mg/m³ × min the most sensitive indicators in BAL, that is, protein, PMN, and collagen, resolved within 2 wk, whereas at lower C × t products they reached the level of the control by postexposure day 7. At 1008 mg/m³ × min (day 28), histopathology revealed a minimal to slight hypercellularity in terminal bronchioles with focal peribronchiolar inflammatory infiltrates and focal septal thickening. At lower C × t products (day 84) the rats from all groups were indistinguishable and Sirius red-stained lungs did not provide evidence of late-onset sequelae, such as fibrotic changes or collagen deposition. At similar C × t products the changes in BAL were slightly less pronounced using 30-min exposure periods when compared to 240-min exposure periods. In summary, the phosgene-induced transmucosal permeability caused a C × t-dependent increase of several BAL indicators, of which those of protein, PMN, and soluble collagen were most pronounced. Exposure intensities up to 116.7 mg/m³ × min did not cause changes different from those observed in controls, while at 188.6 mg/m³ × min distinct differences to the control existed. Despite the extensively increased airway permeability, histopathology did not provide evidence of lung tissue remodeling or irreversible sequelae.     

Application of a Combined “Effect Compartment/Indirect Response Model” to the Central Nervous System Effects of Tiagabine in the Rat

Pharmacological inhibition of GABA uptake transporters provides a mechanism for increasing GABAergic transmission, which may be useful in the treatment of various neurological disorders. The purpose of our investigations was to develop an integrated pharmacokinetic–pharmacodynamic (PK/PD) model for the characterization of the pharmacological effect of tiagabine, R-N-(4,4-di-(3-methylthien-2-yl)but-3-enyl)nipecotic acid, in individual rats in vivo. The tiagabine-induced increase in the amplitude of the EEG 11.5–30 Hz frequency band (), was used as pharmacodynamic endpoint. Chronically instrumented male Wistar rats were randomly allocated to four groups which received an infusion of 3, 10, or 30 mg kg ^–1 ml min ^-1 kg^–1, 1.50.1 L kg^–1 and 200.2 min.A time delay was observed between the occurrence of maximum plasma drug concentrations and maximal response. A physiological PK/PD model has been used to account for this time delay, in which a biophase was postulated to account for tiagabine available to the GABA uptake carriers in the synaptic cleft and the increase in EEG effect was considered an indirect response due to inhibition of GABA uptake carriers. The population values for the pharmacodynamic parameters characterizing the delay in pharmacological response relative to plasma concentrations were k_eo=0.030 min ^–1 and k_out=81 min^–1, respectively. Because of the large difference in these values the PK/PD model was simplified to the effect compartment model. Population estimates were E₀=155 6 V, E_max=100 5 V, EC₅₀=287 7 ng ml^–1, Hill factor=1.8 0.2 and k_eo=0.030 0.002 min ^–1. The results of this analysis show that for tiagabine the combined effect compartment-indirect response model can be simplified to the classical effect compartment model.     

Modeling of Human Corticosteroid Binding Globulin. Use of Structure–Activity Relations in Soft Steroid Binding to Refine the Structure

Purpose We propose a model for human corticosteroid binding globulin that is capable of explaining at the molecular level the experimentally observed binding affinities of four ligands. A new method of analyzing data from docking studies is proposed. Methods Displacement of radioactive ligand by competitive binding gives the experimentally determined binding affinities of the competitors. A theoretical model, based on homology with crystallographically determined structures, was studied in an automated docking procedure for the determination of theoretical affinities. The docking runs were analyzed by a hybrid principal component-clustering analysis. Results Of the two binding sites considered, only one—that in the vicinity of Cys 60—can reproduce the experimentally observed order of binding affinities although the lowest energies are found at the site in the vicinity of Cys 228. Conclusions Models proposed for proteins should be always conditioned to take into account experimentally observed results. In the current work, we have shown that an informed analysis of theoretical docking studies can lead to a more logical model of the protein, one that can explain and give a deeper understanding of the stereochemical requirements of binding. A preliminary account of this work was presented at the 5th Retrometabolism Based Drug Design and Targeting Conference, Kowaki-En, Japan, May 8–11, 2005.     

Oral Delivery of Highly Lipophilic,Poorly Water-Soluble Drugs: Self-Emulsifying Drug Delivery Systems to Improve Oral Absorption and Enable High-Dose Toxicology Studies of a Cholesteryl Ester Transfer Protein Inhibitor in Preclinical Species

BMS-A is an inhibitor of cholesteryl ester transfer protein and is a highly lipophilic compound (clogP 10.5) with poor aqueous solubility (<0.0001 mg/mL at pH 6.5). The compound exhibits low oral exposure when dosed as cosolvent solution formulations. The purpose of this study was to evaluate lipid-based formulations for enabling high-dose toxicology studies and enhancing toxicology margins of BMS-A in preclinical studies in nonrodent species. The solubility of BMS-A was screened in lipid and cosolvent/surfactant excipients, and prototype formulations were developed. In vitro tests showed that fine/microemulsions were formed after aqueous dilution of lipid formulations, and BMS-A was transferred from oil phase to aqueous phase with enhanced solubility following lipid digestion. When dosed in dogs at 200 mg/kg, a Gelucire-based formulation exhibited more than 10-fold higher exposure compared to the solution formulation and was thus selected for toxicology studies in dogs. For monkeys, an olive oil formulation was developed, and the exposure was about 7-fold higher than that from the solution. In summary, lipid-based drug delivery could be applied in early stages of drug discovery to enhance oral exposure and enable preclinical toxicology studies of highly lipophilic compounds, while facilitating the candidate selection of a molecule which is more specifically designed for bioperformance in a lipid-based drug delivery strategy.     

Protective Effects of Diallyl Sulfide, a Garlic Constituent, on the Warm Hepatic Ischemia–Reperfusion Injury in a Rat Model

PURPOSE: The aim of this study is to evaluate the effects of diallyl sulfide (DAS) on the warm hepatic ischemia-reperfusion (IR) injury in a rat model. METHODS: Rats (n = 8-10/group) were subjected to sham operation or warm ischemia (1 h)-reperfusion (3 h) preceded by a single intraperitoneal dose (1.75 mmol/kg) of DAS or vehicle, and relevant biochemical parameters were monitored. RESULTS: Warm IR injury caused a significant increase in the plasma markers of liver injury, which was attenuated by DAS. The hepatoprotective effects of DAS were associated with significant reductions in lipid peroxidation markers and in situ generation of superoxide in the liver and increases in the glutathione levels of the liver and bile, suggestive of an antioxidant effect for DAS. Additionally, DAS caused an almost twofold increase in the protein expression of the liver heme oxygenase-1, an enzyme that confers cytoprotection against oxidative stress. Whereas the total cytochrome P450 remained unchanged, the protein levels and activity of CYP2E1, which plays an important role in the generation of reactive oxygen species, significantly decreased by DAS pretreatment. CONCLUSIONS: DAS protects the liver from warm IR injury by reducing oxidative stress through, at least in part, induction of heme oxygenase-1 and inhibition of CYP2E1.