Intestinal absorption of hawthorn flavonoids--in vitro, in situ and in vivo correlations

Our previous studies identified hyperoside (HP), isoquercitrin (IQ) and epicatechin (EC) to be the major active flavonoid components of the hawthorn phenolic extract from hawthorn fruits demonstrating inhibitory effect on in vitro Cu(+2)-mediated low density lipoproteins oxidation. Among these three hawthorn flavonoids, EC was the only one detectable in plasma after the oral administration of hawthorn phenolic extract to rats. The present study aims to investigate the intestinal absorption mechanisms of these three hawthorn flavonoids by in vitro Caco-2 monolayer model, rat in situ intestinal perfusion model and in vivo pharmacokinetics studies in rats. In addition, in order to investigate the effect of the co-occurring components in hawthorn phenolic extract on the intestinal absorption of these three major hawthorn flavonoids, intestinal absorption transport profiles of HP, IQ and EC in forms of individual pure compound, mixture of pure compounds and hawthorn phenolic extract were studied and compared. The observations from in vitro Caco-2 monolayer model and in situ intestinal perfusion model indicated that all three studied hawthorn flavonoids have quite limited permeabilities. EC and IQ demonstrated more extensive metabolism in the rat in situ intestinal perfusion model and in vivo study than in Caco-2 monolayer model. Moreover, results from the Caco-2 monolayer model, rat in situ intestinal perfusion model as well as the in vivo pharmacokinetics studies in rats consistently showed that the co-occurring components in hawthorn phenolic extract might not have significant effect on the intestinal absorption of the three major hawthorn flavonoids studied.     

Nonlinear stereoselective pharmacokinetics of ketoconazole in rat after administration of racemate

The stereoselective pharmacokinetics of ketoconazole (KTZ) enantiomers were studied in rat after i.v. and oral administration of (+/-)-KTZ. Sprague-Dawley rats were administered racemic KTZ as 10 mg/kg i.v. or orally over the range 10-80 mg/kg as single doses. Serial blood samples were collected over a 24-h period via surgically placed jugular vein cannulae. Plasma was assayed for KTZ enantiomer concentrations using stereospecific HPLC. Enantiomeric plasma protein binding was determined using an erythrocyte partitioning method at racemic concentrations of 10 and 40 mg/L. Stereoselective metabolism was tested by incubating the racemate (0.5-250 microM) with rat liver microsomes. In all rats, (+)-KTZ plasma concentrations were higher (up to 2.5-fold) than (-)-KTZ. The clearance and volume of distribution of the (-) enantiomer were approximately twofold higher than antipode. Half-life did not differ between the enantiomers. After oral doses the t(max) was not stereoselective. For both enantiomers with higher doses the respective half-life were found to increase. The mean unbound fraction of the (-) enantiomer was found to be up to threefold higher than that of the (+) enantiomer. At higher concentrations nonlinearity in plasma protein binding was observed for both enantiomers. There was no evidence of stereoselective metabolism by liver microsomes. Stereoselectivity in KTZ pharmacokinetics is attributable to plasma protein binding, although other processes such as transport or intestinal metabolism may also contribute.     

Prediction of pharmacokinetic properties using experimental approaches during early drug discovery

There has been a significant increase in the number of compounds synthesized in early drug-discovery programs with the advances in combinatorial chemistry and high-throughput biological screening efforts. Various in silico, in vitro and in situ approaches have been described in literature that achieve higher throughput pharmacokinetic screening. In silico methodologies have mainly attempted to quantify the prospects of oral absorption of compounds based upon their physico-chemical properties. There is a greater availability of in vitro and in situ approaches to screen compounds for intestinal permeability (as a surrogate for absorption) and metabolic stability (as a surrogate for clearance). More recent modifications of the in vitro and in situ approaches to assess the potential of absorption and metabolism have enabled a higher throughput and an ability to correlate better with in vivo pharmacokinetics of compounds.     

Effects of DFA IV in rats: calcium absorption and metabolism of DFA IV by intestinal microorganisms.

Di-D-fructose-2,6':6,2'-dianhydride (DFA IV) is a disaccharide consisting of two fructose residues that can be prepared from levan by levan fructotransferase from Arthrobacter nicotinovorans GS-9, and it can be expected to have novel physiological functions from its unique structure. In this study, the effects of DFA IV on calcium absorption and the metabolism of DFA IV by intestinal microorganisms were studied in rats to examine the physiological functions of DFA IV. The apparent calcium absorption in rats fed with DFA IV was significantly higher than that in the control rats, and it seems that calcium absorption had almost been completed at the end of the small intestine. DFA IV also increased the calcium absorption in in vitro experiments, using everted jejunal and ileal sacs, and this result supports the finding obtained in the in vivo experiments. These results indicate that DFA IV may have a function for increasing the calcium absorption in the small intestine of rats. However, the effect in the large intestine could not be clearly observed because of the lack of calcium that reached there. The results of analyses of organic acids in the cecal and colonic contents and of DFA IV in the fecal, cecal, and colonic contents showed that the metabolism of DFA IV by microorganisms in the large intestine progressed gradually, and that DFA IV was converted mainly to acetate, butyrate, and lactate.     

Route-dependent stereoselective pharmacokinetics of tramadol and its active O-demethylated metabolite in rats

The effects of route of administration on the stereoselective pharmacokinetics of tramadol (T) and its active metabolite (M1) were studied in rats. A single 20 mg/kg dose of racemic T was administered through intravenous, intraperitoneal, or oral route to different groups of rats, and blood and urine samples were collected. Samples were analyzed using chiral chromatography, and pharmacokinetic parameters (mean +/- SD) were estimated by noncompartmental methods. Following intravenous injection, there was no stereoselectivity in the pharmacokinetics of T. Both enantiomers showed clearance values (62.5 +/- 27.2 and 64.4 +/- 39.0 ml/min/kg for (+)- and (-)-T, respectively) that were equal or higher than the reported liver blood flow in rats. Similar to T, the area under the plasma concentration-time curves (AUCs) of M1 did not exhibit stereoselectivity after intravenous administration of the parent drug. However, the systemic availability of (+)-T was significantly (P < 0.05) higher than that of its antipode following intraperitoneal (0.527 +/- 0.240 vs. 0.373 +/- 0.189) and oral (0.307 +/- 0.136 vs. 0.159 +/- 0.115) administrations. The AUC of the M1 enantiomers, on the other hand, remained mostly nonstereoselective regardless of the route of administration. Pharmacokinetic analysis indicated that the stereoselectivity in the pharmacokinetics of oral T is due to stereoselective first pass metabolism in the liver and, possibly, in the gastrointestinal tract. The direction and extent of stereoselectivity in the pharmacokinetics of T and M1 in rats were in agreement with those previously reported in humans, suggesting that the rat may be a suitable model for enantioselective studies of T pharmacokinetics.     

Stereoselective metabolism of fenoxaprop‐ethyl and its chiral metabolite fenoxaprop in rabbits

The stereoselective metabolism of the enantiomers of fenoxaprop‐ethyl (FE) and its primary chiral metabolite fenoxaprop (FA) in rabbits in vivo and in vitro was studied based on a validated chiral high‐performance liquid chromatography method. The information of in vivo metabolism was obtained by intravenous administration of racemic FE, racemic FA, and optically pure (−)‐(S)‐FE and (+)‐(R)‐FE separately. The results showed that FE degraded very fast to the metabolite FA, which was then metabolized in a stereoselective way in vivo: (−)‐(S)‐FA degraded faster in plasma, heart, lung, liver, kidney, and bile than its antipode. Moreover, a conversion of (−)‐(S)‐FA to (+)‐(R)‐FA in plasma was found after injection of optically pure (−)‐(S)‐ and (+)‐(R)‐FE separately. Either enantiomers were not detected in brain, spleen, muscle, and fat. Plasma concentration–time curves were best described by an open three‐compartment model, and the toxicokinetic parameters of the two enantiomers were significantly different. Different metabolism behaviors were observed in the degradations of FE and FA in the plasma and liver microsomes in vitro, which were helpful for understanding the stereoselective mechanism. This work suggested the stereoselective behaviors of chiral pollutants, and their chiral metabolites in environment should be taken into account for an accurate risk assessment. Chirality, 2011. © 2011 Wiley‐Liss, Inc.     

Influence of the route of administration on the pharmacokinetics of pirprofen enantiomers in the rat

The pharmacokinetics of the enantiomers of the non-steroidal anti-inflammatory drug pirprofen were studied in male Sprague-Dawley rats after oral and intravenous (iv) doses of the racemate. No significant differences were detected between the enantiomers after oral or iv dosing in t_½, Vd, or ∑Xu. However, the R:S area under the plasma concentration (AUC) ratio after oral doses (0.92 ± 0.13) was slightly but significantly lower than after matching iv doses (1.05 ± 0.036). The absolute bioavailability of the active S-enantiomer (78.5%) after oral doses was higher than the inactive R-enantiomer (69.3%). The plasma protein binding of both enantiomers was saturable over a fivefold range of plasma concentrations. At higher plasma concentrations, the S-enantiomer was less bound than the R-enantiomer. In an in vitro experiment using everted rat jejunum, no chiral inversion was discernible. The dependency of the AUC ratio of the enantiomers on the route of administration may be due to stereoselective first-pass metabolism. © 1993 Wiley-Liss, Inc.     

Stereoselective regulations of P-glycoprotein by ginsenoside Rh2 epimers and the potential mechanisms from the view of pharmacokinetics

Chirality is an interesting topic and it is meaningful to explore the interactions between chiral small molecules and stereoselective biomacromolecules, with pre-clinical and clinical significances. We have previously demonstrated that 20(S)-ginsenoside Rh2 is an effective P-glycoprotein (P-gp) inhibitor in vitro and in vivo. Considering the stereochemistry of ginsenoside Rh2, in our present study, the regulatory effects of 20(R)-Rh2 on P-gp were assayed in vivo, and the differential regulations of P-gp by ginsenoside Rh2 epimers in vivo were compared and studied. Results showed that 20(S)-Rh2 enhanced the oral absorption of digoxin in rats in a dose-dependent manner; 20(R)-Rh2 at low dosage increased the oral absorption of digoxin, but this effect diminished with elevated dosage of 20(R)-Rh2. Further studies indicated stereoselective pharmacokinetic profiles and intestinal biotransformations of Rh2 epimers. In vitro studies showed that Rh2 epimers and their corresponding deglycosylation metabolites protopanaxadiol (Ppd) epimers all exhibited stereoselective regulations of P-gp. In conclusion, in view of the in vitro and in vivo dispositions of Rh2 and the regulations of P-gp by Rh2 and Ppd, it is suggested that the P-gp regulatory effect of Rh2 in vivo actually is a double actions of both Rh2 and Ppd, and the net effect is determined by the relative balance between Rh2 and Ppd with the same configuration. Our study provides new evidence of the chiral characteristics of P-gp, and is helpful to elucidate the stereoselective P-gp regulation mechanisms of ginsenoside Rh2 epimers in vivo from a pharmacokinetic view.     

The uptake of oleic acid by rat small intestine: a comparison of methodologies

The interaction between long-chain and medium-chain lipids during intestinal absorption was examined using several model systems. A decrease in steady-state triolein (LCT) output in thoracic duct lymph after addition of trioctanoin (MCT) to the duodenal infusion confirmed previous studies in unanesthetized rats which demonstrated inhibition of steady-state LCT uptake from the small intestinal lumen by MCT. In slices of everted rat jejunum octanoic acid reduced incorporation into triglyceride and initial uptake of (14)C-labeled oleic acid from micellar solutions. Inhibition of uptake did not occur at 0 degrees C, when triglyceride synthesis was blocked. Incubation of slices at low pH (5.8) or in the presence of dimethyl sulfoxide also reduced uptake of oleic acid and its incorporation into triglyceride. However, when everted sacs of jejunum were similarly incubated, octanoate, dimethyl sulfoxide, or low pH caused no inhibition of oleic acid uptake or esterification. The results indicate that the significance of kinetic data describing intestinal fatty acid absorption which were obtained from experiments conducted in vitro is highly questionable, and that suitable models for in vivo uptake kinetics have yet to be developed. However, analysis of the in vitro kinetic data suggests that the intestinal mucosal membrane does not function as a simple lipid interface with respect to fatty acid absorption.     

Estimation of oral drug absorption in man based on intestine permeability in rats

Predicting the fraction of an oral dose absorbed in humans is of considerable interest at an early stage of a research program in the pharmaceutical industry. Models described in the literature to predict the oral absorption in man include: the permeability in Caco-2 cells, absorption from a perfused segment of rat intestinal lumen and uptake into everted rings. The present study used an isolated and vascularly perfused rat small intestine to determine the permeability values of eleven compounds across the intestinal epithelium. A good correlation was obtained between the permeability values determined in this model and the proportion of an oral dose absorbed in humans. Compared to the other models, the present one could allow the appearance in the artificial bloodstream and the intestinal metabolism of a compound to be studied simultaneously.     

The stereoselective metabolism of halofantrine to desbutylhalofantrine in the rat: evidence of tissue-specific enantioselectivity in microsomal metabolism

The pharmacokinetics of the antimalarial drug (+/-)-halofantrine are stereoselective in humans and rats. To better understand the stereoselective metabolism of the drug to its primary metabolite, desbutylhalofantrine (DHF), a series of in vitro and in vivo experiments were undertaken in the rat. Formation of (-)-DHF exceeded that of (+)-DHF in liver microsomes [(-):(+) ratio of intrinsic formation clearances = 1.4]. In contrast, in intestinal microsomes no significant stereoselectivity was noted in the formation of the DHF enantiomers. Intestinal microsomes were also less efficient at producing the DHF enantiomers than were liver microsomes. Based on kinetic analysis of the DHF formation, there appeared to be more than one enzyme involved in the biotransformation. (+/-)-Ketoconazole (KTZ) effectively inhibited the formation of both DHF enantiomers by both liver and intestinal microsomes, although the reduction was more marked in liver microsomes. Through a combination of the use of CYP antibodies and recombinant CYP isoenzymes, the involvement of CYP 2B1/2, 3A1, 3A2, 1A1, 2C11, 2C6, 2D1, and 2D2 were implicated in the metabolism of halofantrine to DHF. Of these, CYP3A1/2 and CYP2C11 appeared to be the primary isoenzymes involved, although CYP2C11 showed greater (+)-DHF than (-)-DHF formation, whereas for CYP3A1 it was similar to the isolated rat liver microsomes. In vivo, oral (+/-)-KTZ caused significant increases in plasma halofantrine and decreases in DHF enantiomer plasma concentrations.     

Stereoselective pharmacokinetics of ornidazole after intravenous administration of individual enantiomers and the racemate

The pharmacokinetics of ornidazole (ONZ) were investigated following i.v. administration of racemic mixture and individual enantiomers in beagle dogs. Plasma concentrations of ONZ enantiomers were analyzed by chiral high-performance liquid chromatography (HPLC) on a Chiralcel OB-H column with quantification by UV at 310 nm. Notably, the mean plasma levels of (-)-ONZ were higher in the elimination phase than those of (+)-ONZ. (-)-ONZ also exhibited greater t1/2, MRT, AUC(0-t) and smaller CL, than those of its antipode. The area under the plasma concentration-time curve (AUC(0-t)) of (-)-ONZ was about 1.2 times as high as that of (+)-ONZ. (+)-ONZ total body clearance (CL) was 1.4 times than its optical antipode. When given separately, there were significant differences in the values of AUC(0-infinity) and CL between ONZ enantiomers (P < 0.05), indicating that elimination of (+)-ONZ was more rapid than that of (-)-ONZ. No significant differences were found between the estimates of the pharmacokinetic parameters of (+)-ONZ or (-)-ONZ, obtained following administration as the individual and as a racemic mixture. This study demonstrates that the elimination of ONZ enantiomers is stereoselective and chiral inversion and enantiomer/enantiomer interaction do not occur when the enantiomers are given separately and as racemic mixture.     

Effect of somatostatin on intestinal absorption of nutrients the rat

Effects of somatostatin on absorption of D-glucose, L-leucine and triacylglycerols by the small intestine were studied in rats after treatment with the peptide in vivo and in everted jejunal segments in vitro.Absorption of glucose was not affected in vitro by somatostatin or the analogue [D-Trp⁸, D-Cys¹⁴]somatostatin at concentrations up to 0.006 mM. Addition of various peptidase inhibitors had no influence, suggesting that failure of somatostatins to inhibit absorption was not due to inactivation by peptidases. Glucose absorption in vitro by jejunum from rats treated with high doses of somatostatin in vivo was not different from that of untreated rats. The biguanide phenformin inhibited glucose absorption, whether added in vitro (IC₅₀ ≈ 1 mM) of after treatment in vivo (3–100 mg/kg per os). The blood glucose increase following oral glucose administration in fasted rats was not affected by somatostatin, but significantly suppressed by phenformin.Absorption of leucine in vitro was not affected by somatostatin (up to 0.03 mM) or [D-Trp⁸, D-Cys¹⁴]somatostatin (0.01 mM), but inhibited by phenformin (IC₅₀ = 2 mM).Absorption of acylglycerols (glycerol tri[1-¹⁴C]oleate) administered orally was significantly inhibited by somatostatin (twice 5 mg/kg subcutaneously) and phenformin (100 mg/kg per os).In rats — apparently in contrast to man — somatostatin does not decrease role of somatostatin in carbohydrate absorption remains controversial. Investigations in healthy [9] and diabetic [20] human subjects suggest that the peptide inhibits (directly or indirectly) the intestinal absorption of glucose in man. On the other hand, our results and those of others obtained in experiments in rats [4,11,21] and Rhesus monkeys [7] clearly do not support such a role in these species. Further studies are therefore needed to resolve this problem.     

Pharmacokinetic data of propranolol enantiomers in a comparative human study with (S)- and (R,S)-propranolol

The pharmacokinetics of (S)-propranolol were compared after the oral administration of a 40 mg dose of the pure enantiomer and an 80 mg dose of a racemic mixture of (R,S)-propranolol. The results of this study indicate that the bioavailability of (S)-propranolol, as expressed by the mean area under the concentration-time curve (AUC) and maximum serum concentration, is lower after 40 mg of the optically pure drug than after the racemic drug.     

Intestinal absorption of vitamin E in experimental renal failure

We studied intestinal absorption of vitamin E in rats with experimental renal failure (RF) and in sham-operated normal and pair-fed controls using in vivo perfusion and in vitro everted sacs. The in vivo absorption rates per unit of intestine length were significantly reduced in RF and pair-fed groups. Expression of data per unit of intestine weight gave normal values in the pair-fed but depressed values in the RF animals. Vitamin E uptake in vitro was significantly increased in RF animals, suggesting enhanced permeability. We conclude: (i) vitamin E absorption in vivo is impaired in experimental RF; (ii) this is in part due to reduced nutrient intake; and (iii) disparity between in vivo and in vitro results suggests the presence of some inhibitory influence(s) in intact animals with RF.     

Enantioselective metabolism of (R)- and (S)-4-hydroxy-2-nonenal in rat

4-Hydroxy-2-nonenal (HNE) is an endogenous product of lipid peroxidation, which is believed to play a biological role in the pathogenesis of various diseases. HNE is formed as a racemic mixture of (R)- and (S)- enantiomers. These enantiomers differ in their biological properties. The aim of this study was to investigate separately the in vivo metabolism of the two HNE enantiomers in male rats after intravenous administration of the corresponding radiolabeled compounds and to compare the results with those obtained with the racemic mixture. Although the difference in the excretion rates was not statistically significant, the HPLC profiles of urinary metabolites showed qualitative and quantitative differences between the two enantiomers. The level of 3-mercapturic acid-1,4-dihydroxynonane, which is considered as the major urinary metabolite of HNE, was significantly lower in the case of (S)-HNE injected rats. In vitro studies using rat liver cytosolic incubations and HNE-glutathione conjugate as substrate were performed to clarify the intermediate pathways involved in their metabolism. Large differences were obtained in the reduction and retro-Michael conversion steps of the metabolism between the conjugates originating from the two enantiomers.     

Stereopharmacology of carnitine

L-Carnitine (L-beta-hydroxy-gamma-N,N,N-trimethylaminobutyric acid) plays an essential role in fatty acid transport in the mitochondrion. Conditions that appear to benefit from exogenous supplementation of L-carnitine include anorexia, chronic fatigue, cardiovascular disease, hypoglycemia, male infertility, muscular myopathies, renal failure and dialysis. D-Carnitine is not biologically active and might interfere with the proper utilization of the L isomer, and so there are claims that the racemic mixture (DL-carnitine) should be avoided. Despite the fact that it is known about the systemic manifestations of oral intake of this compound, oral supplementation with DL-carnitine for treatment of primary and secondary carnitine deficiency syndromes has been used in Russia for 25 years. The purpose of the present review was to contrast the differences in pharmacokinetics, phannacodynamics, biochemistry, and toxicity between treatments of L- and DL-carnitine. There is some evidence that L-carnitine and D-carnitine compete for uptake in small intestine and tubular re-absorption in kidneys. After intestinal absorption, L- and D-carnitine is transferred to organs whose metabolism is dependent on fatty acid oxidation, such as heart and skeletal muscle, and D-carnitine competitively depletes muscle level of L-carnitine. Whereas L-carnitine is found to be essential for the oxidation of fatty acids, D-carnitine causes a depletion of L-carnitine, and hindered fatty acid oxidation and energy formation. Pharmacological effects of carnitine are stereospecific, since L-carnitine was effective in various animals and clinical studies, while D- and DL-carnitine was found to be ineffective or toxic, for example, to muscle cells and to the myocardium. DL-Carnitine causes symptoms of myasthenia and cardiac arrhythmias, which disappeared after L-carnitine administration. Clinically toxic effect of D-carnitine was described in patients with renal failure on long-term haemodialysis, in adriamycin (doxorubicin) cardiotoxicity and in stable angina pectoris.     

Differential stereoselective pharmacokinetics of pantoprazole,a proton pump inhibitor in extensive and poor metabolizers of pantoprazole—a preliminary study

Pantoprazole (PAN) is a proton pump inhibitor that is administered as a racemic mixture. The pharmacokinetics of PAN enantiomers were investigated in extensive metabolizers (EMs) and apparent poor metabolizers (PMs) of PAN who received a single 40, 60, or 80 mg oral dose of racemic PAN as enteric-coated formulation. In the EMs, the serum concentrations of (−)-PAN were slightly higher than those of (+)-PAN at each dose level. The (+)/(−) ratios for the area under the concentration-time curve (AUC) and the half-life were 0.58–0.89 and 0.62–0.88, respectively. In the PMs, the serum concentrations of both enantiomers were much higher than those in the EMs at each dose level and significant differences in pharmacokinetics of (+)- and (−)-PAN were observed. The half-lives for (+)-PAN were 2.67–3.77 times longer than those for (−)-PAN. The AUCs for (+)-PAN were 2.65–3.45 times greater than those for (−)-PAN. Therefore, the metabolism of (+)-PAN is impaired to a greater extent than (−)-PAN in the PMs, which resulted in the stereoselective disposition of PAN in the PMs. It has been suggested that the EMs and the PMs of PAN could be differentiated by determining the (+)/(−) enantiomer ratio in serum at one time point, possibly 2–6 h after oral dosing, because the (+)/(−) enantiomer ratios in the PMs were opposite those in the EM subjects. Chirality 9:17–21, 1997 © 1997 Wiley-Liss, Inc.     

Development of in vitro pharmacokinetic screens using Caco-2, human hepatocyte, and Caco-2/human hepatocyte hybrid systems for the prediction of oral bioavailability in humans

In this study, in vitro systems were used to build 2 pharmacokinetic models that predict human oral bioavailability: the Caco-2/hepatocyte combination model and the Caco-2/hepatocyte hybrid model. Data obtained in vitro on Caco-2 cell permeability and hepatocyte clearance are routinely used to predict the fraction of absorption after oral administration and the extent of first-pass metabolism, respectively. In the Caco-2/hepatocyte combination model, results from a Caco-2 cell permeability assay and a hepatocyte clearance assay were combined to project oral bioavailability. Comparison of oral bioavailabilities predicted by the combination model and reported oral bioavailabilities in humans for 30 marketed compounds resulted in a modest correlation (r(2) = 0.66). The Caco-2/hepatocyte hybrid model, as previously reported, joins the Caco-2 and hepatocyte clearance systems into 1 assay. Improvements to the previous model were made by incorporating an elimination phase into the Caco-2/hepatocyte hybrid model. In the new hybrid model, the compound was added to a Caco-2-containing donor compartment and allowed to permeate for 2 h to a hepatocyte-containing receiver compartment. Subsequently, to mimic an elimination phase, the donor compartment was removed, and permeated compound was incubated with hepatocytes alone for an additional 3 h. The area under the concentration versus time curve (AUC) was determined for each of the same 30 marketed compounds assessed by the combination model. A linear regression analysis comparing the in vitro AUCs and reported oral bioavailabilities in humans showed a reasonable correlation (r(2) = 0.73). This study demonstrates that the Caco-2/hepatocyte hybrid model is more favorable and further proves the potential and feasibility of using in vitro screenings for the prediction of in vivo pharmacokinetics in humans.     

Chiral HPLC determination and stereoselective pharmacokinetics of tetrahydroberberine enantiomers in rats

Tetrahydroberberine (THB), a racemic mixture of (+)‐ and (?)‐enantiomer, is a biologically active ingredient isolated from a traditional Chinese herb Rhizoma corydalis (yanhusuo). A chiral high performance liquid chromatography method has been developed for the determination of THB enantiomers in rat plasma. The enantioseparation was carried out on a Chiral®‐AD column using methanol:ethanol (80:20, v/v) as the mobile phase at the flow rate 0.4 ml/min. The ultraviolet detection was set at 230 nm. The calibration curves were linear over the range of 0.01–2.5 μg/ml for (+)‐THB and 0.01‐5.0 μg/ml for (?)‐THB, respectively. The lower limit of quantification was 0.01 μg/ml for both (+)‐THB and (?)‐THB. The stereoselective pharmacokinetics of THB enantiomers in rats was studied after oral and intravenous administration at a dose of 50 and 10 mg/kg racemic THB (rac‐THB). The mean plasma levels of (?)‐THB were higher at almost all time points than those of (+)‐THB. (?)‐THB also exhibited greater C_max, and AUC_0–∞, smaller CL and V_d, than its antipode. The (?)/(+)‐enantiomer ratio of AUC_0–∞ after oral and intravenous administration were 2.17 and 1.43, respectively. These results indicated substantial stereoselectivity in the pharmacokinetics of THB enantiomers in rats. Chirality, 2012. © 2012 Wiley Periodicals, Inc.