The purpose of this investigation was to characterize the in vitro stability and in vivo disposition of paclitaxel in rats after solubilization of paclitaxel into hydrotropic polymeric micelles. The amphiphilic block copolymers consisted of micellar a shell-forming poly(ethylene glycol) (PEG) block and a core-forming poly(2-(4-vinylbenzyloxy)-N,N-diethylnicotinamide) (P(VBODENA)) block. N,N-Diethylnicotinamide (DENA) in the micellar inner core resulted in effective paclitaxel solubilization and stabilization. Solubilization of paclitaxel using polymeric micelles of poly (ethylene glycol)-b-P(D,L-lactide) (PEG-b-PLA) served as a control for the stability study. Up to 37.4 wt% paclitaxel could be loaded in PEG-b-P(VBODENA) micelles, whereas the maximum loading amount for PEG-b-PLA micelles was 27.6 wt%. Thermal analysis showed that paclitaxel in the polymeric micelles existed in the molecularly dispersed amorphous state even at loadings over 30 wt%. Paclitaxel-loaded hydrotropic polymeric micelles retained their stability in water for weeks, whereas paclitaxel-loaded PEG-b-PLA micelles precipitated in a few days. Hydrotropic polymer micelles were more effective than PEG-PLA micelle formulations in inhibiting the proliferation of human cancer cells. Paclitaxel in hydrotropic polymer micelles was administered orally (3.8 mg/kg), intravenously (2.5 mg/kg) or via the portal vein (2.5 mg/kg) to rats. The oral bioavailability was 12.4% of the intravenous administration. Our data suggest that polymeric micelles with a hydrotropic structure are superior as a carrier of paclitaxel due to a high solubilizing capacity combined with long-term stability which has not been accomplished by other existing polymeric micelle systems.

Histamine is involved in the pathophysiology of asthma, and histamine N-methyltransferase (HNMT) plays the dominant role in histamine metabolism in human bronchial epithelium. Levels of HNMT activity in human tissues are controlled, in part, by inheritance. A common C314T polymorphism within the HNMT gene results in a Thr105Ile change in encoded amino acid, and the T314 allele is associated with decreased levels of both HNMT enzymatic activity and immunoreactive protein. Therefore, presence of the T314 allele would be expected to result in reduced histamine metabolism and increased bronchoconstriction. We characterized this common, functionally significant polymorphism in DNA samples from 237 randomly selected Caucasian control subjects and 192 samples from Caucasian asthmatic patients. Allele frequencies for the T314 HNMT allele were 0.08 in the control samples and 0.14 in samples from Caucasian asthmatic patients (odds ratio = 1.9, P < 0.01), indicating a significant increase in the frequency of subjects with low HNMT activity among asthmatics. The association between a common, functionally significant genetic polymorphism for HNMT and asthma suggests that individual variation in histamine metabolism might contribute to the pathophysiology and/or response to therapy of this disease.

ABSTRACT:The purpose of this investigation was to examine the effects of surgery and anesthesia on in vivo CYP3A activity and portal venous blood flow. Midazolam, a CYP3A probe for both rats and humans, was administered orally (2.7 mg), intravenously (0.57 mg), or via the portal vein (0.57 mg) to rats 4 h after anesthesia with ketamine/ xylazine and surgery for placement of indwelling vascular and duodenal catheters´and 3 days after surgery (chronic). The systemic clearance of midazolam was 51 ؎ 4 ml/min/kg in the chronic animals, and this was significantly decreased (29 ؎ 1 ml/min/kg, P ‫؍‬ 0.024) in acute rats studied 4 to 6 h after anesthesia and surgery. The hepatic availability (F H ), directly determined from the aortic and hepatic venous concentration gradient, was significantly higher in the acute animals (0.57 ؎ 0.05) compared with the chronic animals (0.33 ؎ 0.07, P ‫؍‬ 0.001). Hepatic availability was determined using a classical approach in which F H was calculated from the area under the plasma concentration versus time curve ratio after portal venous or intravenous administration. F H was higher in the acute rats (0.48) compared with the chronic animals (0.27 ؎ 0.03). Portal venous blood flow was significantly lower in the acute animals (5.0 ؎ 0.4 ml/min/100 g body weight) compared with the chronic animals (9.1 ؎ 0.9 ml/min/100 g body weight, P ‫؍‬ 0.015). The effect of surgery and anesthesia was confirmed using the indicator dye dilution method after infusion of [ 14 C]polyethylene glycol 4000 into the superior mesenteric artery. Our data suggest that anesthesia and surgery decreases both hepatic CYP3A activity and hepatic blood flow in rats. Studies performed in rats within 3 days of surgery and anesthesia are conducted under nonphysiologic conditions and therefore provide inaccurate assessment of drug disposition, in particular, clearance and bioavailability.During drug development, in vivo drug absorption and hepatic first-pass metabolism studies commonly are performed in rats, dogs, and primates after surgical manipulation to implant vascular and gastrointestinal catheters. The absorption and bioavailability of orally administered drugs is dependent on intestinal and liver function, including metabolism. The ability to quantify the extent and variability of first-pass metabolism and the inhibition of metabolism in vivo are important for the development of oral dosage forms. To separately determine the effects of the liver on hepatic first-pass metabolism from the contribution by the gut, the area under the plasma concentration versus time curve (AUC) following drug administration via the portal vein is compared with the AUC obtained after oral and intravenous drug administration. These experiments are typically conducted using rodents and are often conducted shortly after the animal has regained its righting reflex. Consciousness and mobility, not gastrointestinal or liver function, are therefore frequently used as parameters of surgical recovery. Although studies have clearly demonstrated tha...

AimsTo confirm the identity of the major metabolites of domperidone and to characterize the cytochrome P450s (CYPs) involved in their formation. MethodsHuman liver microsomes (HLMs) were used to characterize the kinetics of domperidone metabolism and liquid chromatography-mass spectrometry to identify the products. Isoform-specific chemical inhibitors, correlation analysis and expressed human CYP genes were used to identify the CYPs involved in domperidone oxidation. ResultsIn HLMs, domperidone underwent hydroxylation to form 5-hydroxydomperidone (MIII) and N-dealkylation to form 2,3-dihydro-2-oxo-1H-benzimidazole-1-propionic acid (MI) and 5-chloro-4-piperidinyl-1,3-dihydro-benzimidazol-2-one (M II). The formation of all three metabolites (n = 4 HLMs) followed apparent Michaelis-Menten kinetics. The mean Km values for MI, MII and MIII formation were 12.4, 11.9, and 12.6 m m, respectively. In a panel of HLMs (n = 10), the rate of domperidone (5 m m and 50 m m) metabolism correlated with the activity of CYP3A (r > 0.94; P < 0.0001). Only ketoconazole (1 m m) (by 87%) and troleandomycin (50 m m) (by 64%) inhibited domperidone (5 m m) metabolism in HLMs. Domperidone (5 and 50 m m) hydroxylation and N-dealkylation was catalyzed by expressed CYP3A4 at a higher rate than the other CYPs. CYP1A2, 2B6, 2C8 and 2D6 also hydroxylated domperidone Conclusions CYP3A-catalyzed N-dealkylation and aromatic hydroxylation are the major routes for domperidone metabolism. The drug would be expected to demonstrate highly variable bioavailability due to hepatic, and possibly intestinal first-pass metabolism after oral administration. Increased risk of adverse effects might be anticipated during concomitant administration with CYP3A inhibitors, as well as decreased efficacy with inducers of this enzyme. B. A. Ward et al. 27858 :3 Br J Clin Pharmacol

The soil matrix can impact the bioavailability of soil-bound organic chemicals, and this impact is governed in part by soil properties such as organic carbon (OC) content, clay minerals, and pH. Recently, a physiologically based extraction test (PBET) was developed to predict the bioavailability of soil-bound organic chemicals. In the current study, the bioavailability of phenanthrene (PA) from laboratory-treated soils varying in OC content, clay, and pH was investigated using an in vivo rat model and an in vitro PBET. The relationship between these two approaches was also examined. In the in vivo assay, soils and corn oil containing equivalent levels of PA were administered to Sprague-Dawley rats by gavage at two dose levels: 400 and 800 mg/kg body weight. Equivalent doses were given via intravenous injection (i.v.). The areas under the blood concentration-versus-time curves (AUC) were measured, and the absolute and relative bioavailabilities of PA were determined for each soil. In the PBET tests, one g of each soil was extracted by artificial saliva, gastric juice, duodenum juice, and bile. The fraction of PA mobilized from each soil was quantified. The AUCs of PA in all soils were significantly lower than those following iv injection (p < 0.05), indicating that the soil matrix could reduce the bioavailability of PA from soil. There were obvious trends of soils with higher OC content and clay content, resulting in the lower bioavailability of PA from soil. A significant correlation (p < 0.05) was observed between the fraction of PA mobilized from soil in the PBET and its in vivo bioavailability. The data also showed that the absolute bioavailability of PA from corn oil was low: approximately 25%. These results suggest that PBET assay might be a useful alternative in predicting bioavailability of soil-bound organic chemicals. However, due to the limited soil types and use of one chemical vs. a variety of contaminants and soil properties in the environment, further efforts involving more chemicals and soil types are needed to validate this surrogate method.

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