Aging and brain free cholesterol concentration on amyloid-ß peptide accumulation in guinea pigs.

Alzheimer's disease is a complex multifactorial neurodegenerative disorder wherein age is a major risk factor. The appropriateness of the Hartley guinea pig (GP), which displays high sequence homologies of its amyloid-ß (Aß40 and Aß42) peptides, Mdr1 and APP (amyloid precursor protein) and similarity in lipid handling to humans, was appraised among 9-40 weeks old guinea pigs. Protein expression levels of P-gp (Abcb1) and Cyp46a1 (24(S)-hydroxylase) for Aß40, and Aß42 efflux and cholesterol metabolism, respectively, were decreased with age, whereas those for Lrp1 (low-density lipoprotein receptor related protein 1), Rage (receptor for advanced glycation endproducts) for Aß efflux and influx, respectively, and Abca1 (the ATP binding cassette subfamily A member 1) for cholesterol efflux, were unchanged among the ages examined. There was a strong, negative correlation of the brain Aß peptide concentrations and Abca1 protein expression levels with free cholesterol. The correlation of Aß peptide concentrations with Cyp46a1 was, however, not significant, and concentrations of the 24(S)-hydroxycholesterol metabolite revealed a decreasing trend from 20 weeks old toward 40 weeks old guinea pigs. The composite data suggest a role for free cholesterol on brain Aß accumulation. The decreases in P-gp and Lrp1 protein levels should further exacerbate the accumulation of Aß peptides in guinea pig brain.

Pharmacokinetics of collagen dipeptides (Gly-Pro and Pro-Hyp) and tripeptides (Gly-Pro-Hyp) in rats.

Although systemic exposure to peptides, such as Gly-Pro-Hyp, Pro-Hyp, and Gly-Pro, has been reported following administration of collagen hydrolysates from fish scale and porcine skin in vivo, the individual peptide pharmacokinetics remain unknown. We administered the three peptides individually to rats via the intravenous (5 mg/kg) and intragastric (100 mg/kg) routes and then monitored systemic exposure and urinary excretion. The peptides in biological samples were analyzed via liquid chromatography/tandem mass spectrometry. Gly-Pro-Hyp tended to exhibit higher first-pass metabolism than Pro-Hyp; the absolute oral bioavailabilities of Gly-Pro-Hyp and Pro-Hyp were 4.4% and 19.3%, respectively. Gly-Pro levels were very low in the systemic circulation. Pro-Hyp biotransformed from Gly-Pro-Hyp behaved similarly to Pro-Hyp alone when administered orally. Flip-flop kinetics (elimination rate ≫ absorption rate) were evident, probably reflecting transporter-mediated slow absorption. A double-peak phenomenon was observed for Gly-Pro-Hyp and Pro-Hyp when administered orally, and 5.9% ± 2.6% and 1.9% ± 0.3% of each dose were excreted in urine after intravenous administration, respectively. Urinary recovery of Gly-Pro was limited to 0.4% ± 0.5% of the intravenous dose. This work represents the first individual pharmacokinetics of Gly-Pro-Hyp, Pro-Hyp, and Gly-Pro in vivo.

Optimizing transcardial perfusion of small molecules and biologics for brain penetration and biodistribution studies in rodents.

Efficiently removing blood from the brain vasculature is critical to evaluate accurately the brain penetration and biodistribution of drug candidates, especially for biologics as their blood concentrations are substantially higher than the brain concentrations. Transcardial perfusion has been used widely to remove residual blood in the brain; however, the perfusion conditions (such as the perfusion rate and time) reported in the literature are quite varied, and the performance of these methods on blood removal has not been investigated thoroughly. In this study, the effectiveness of the perfusion conditions was assessed by measuring brain hemoglobin levels. Sodium nitrite (NaNO2 ) as an additive in the perfusate was evaluated at different concentrations. Blood removal was significantly improved with 2% NaNO2 over a 20 min perfusion in mouse without disrupting the integrity of the blood-brain barrier (BBB). In mice, the optimized perfusion method significantly lowered the measured brain-to-plasma ratio (Kp,brain ) for monoclonal antibodies due to the removal of blood contamination and small molecules with a moderate-to-high BBB permeability and with a high brain-unbound-fraction (fu,brain ) presumably due to flux out of the brain during perfusion. Perfusion with or without NaNO2 clearly removed the residual blood in rat brain but with no difference observed in Kp,brain between the perfusion groups with or without 2% NaNO2 . In conclusion, a perfusion method was successfully developed to evaluate the brain penetration of small molecules and biologics in rodents for the first time. The transcardial perfusion with 2% NaNO2 effectively removed the residual blood in the brain and significantly improved the assessment of brain penetration of biologics. For small molecules, however, transcardial perfusion may not be performed, as small molecule compounds could be washed away from the brain by the perfusion procedure.

Significance of the Vitamin D Receptor on Crosstalk with Nuclear Receptors and Regulation of Enzymes and Transporters.

The vitamin D receptor (VDR), in addition to other nuclear receptors, the pregnane X receptor (PXR) and constitutive androstane receptor (CAR), is involved in the regulation of enzymes, transporters and receptors, and therefore intimately affects drug disposition, tissue health, and the handling of endogenous and exogenous compounds. This review examines the role of 1α,25-dihydroxyvitamin D3 or calcitriol, the natural VDR ligand, on activation of the VDR and its crosstalk with other nuclear receptors towards the regulation of enzymes and transporters, notably many of the cytochrome P450s including CYP3A4 and sulfotransferase 2A1 (SULT2A1) as well as cholesterol 7α-hydroxylase (CYP7A1). Moreover, the VDR upregulates the intestinal channel, TRPV6, for calcium absorption, LDL receptor-related protein 1 (LRP1) and receptor for advanced glycation end products (RAGE) in brain for ß-amyloid peptide efflux and influx, the sodium phosphate transporters (NaPi), the apical sodium-dependent bile acid transporter (ASBT) and organic solute transporters (OSTα-OSTß) for bile acid absorption and efflux, respectively, the renal organic anion transporter 3 (OAT3) and several of the ATP-binding cassette protein transporters-the multidrug resistance protein 1 (MDR1) and the multidrug resistance-associated proteins (MRPs). Hence, the role of the VDR is increasingly being recognized for its therapeutic potential and pharmacologic activity, giving rise to drug-drug interactions (DDI). Therapeutically, ligand-activated VDR shows anti-inflammatory effects towards the suppression of inflammatory mediators, improves cognition by upregulating amyloid-beta (Aß) peptide clearance in brain, and maintains phosphate, calcium, and parathyroid hormone (PTH) balance and kidney function and bone health, demonstrating the crucial roles of the VDR in disease progression and treatment of diseases.

Absolute oral and subcutaneous bioavailability of ortho-topolin riboside in mice.

Among essential phytohormones playing a pivotal role in regulating growth and development, ortho-topolin riboside (oTR) exerts the most substantial anti-tumor potency in various cancer cell lines. This study was designed to establish a quantitative determination method for oTR in mouse plasma using high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS), to validate the analytical method including stability, and to characterise its pharmacokinetic behaviour in mice. After simple protein precipitation with acetonitrile including kinetin riboside (internal standard), oTR was eluted on a reversed-phase column using a mobile phase of water and acetonitrile (3:7 v/v, including 0.1% formic acid). The protonated precursor ion [M+H]+ and major fragment ion were confirmed at m/z 374.06 and 241.99 for oTR, and 348.23 and 216.06 for the IS, respectively. oTR was stable under bench and storage conditions. The analytical method met the criteria of FDA-validated bioanalytical methods and was successfully applied to a pharmacokinetic study for the first time following oral, subcutaneous, and intravenous administrations. While oTR was merely absorbed by an oral route, 90% of the absolute subcutaneous bioavailability was observed.

A sensitive analytical method for the determination of SG-SP1 in rat plasma by HPLC-MS/MS and its application to a pharmacokinetic study.

SG-SP1, a newly synthesised gallic acid derivative, blocks histamine release by reducing calcium influx in mast cells and inhibits inflammatory cytokine expression. This derivative has promising anti-allergic potential. Our research was designed to establish a quantitative determination method for SG-SP1 in rat plasma using high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS), to validate the analytical method including stability and to characterise its pharmacokinetic behaviour in rats. After simple protein precipitation with acetonitrile including an internal standard, SG-SP1 was eluted on a reversed-phase column using a mobile phase of water and acetonitrile (2:8 v/v, including 0.1 % formic acid). The protonated precursor ion [M+H]+ and major fragment ion were confirmed at m/z 588.2 and 180.1, respectively. The substance was stable under bench and storage conditions. The analytical method met the criteria of FDA-validated bioanalytical methods and was successfully applied to a pharmacokinetic study for the first time. SG-SP1 decayed in a biphasic pattern with terminal half-life of 5.1 h and clearance of about 3.2 L/h/kg. Double peaks were observed following oral administration, and the absolute oral bioavailability was ∼1 %.

Pharmacokinetics of panduratin A following oral administration of a Boesenbergia pandurata extract to rats.

Boesenbergia pandurata and its major active ingredient, panduratin A (PAN), exhibit antibacterial, anti-oxidant, anti-inflammatory, and anti-obesity effects. We explored the time course of the plasma and tissue (in the major organs, gums and skin) concentrations of PAN after oral administration of a B. pandurata extract to rats. Model-dependent analysis was used to quantify the skin distribution of PAN after systemic exposure. The PAN level peaked at 1.12 ± 0.22 µg/mL after 3 h, and then biexponentially decayed with a terminal half-life of 9 h. The mean clearance (Cl/F) was 2.33 ± 0.68 L/h/kg. The PAN levels in organs were in the following order (highest first): skin, lung, heart, gum, liver, spleen, kidney, and brain. For the first time, the time course of PAN levels in plasma and organs was investigated after oral administration of a BPE. This study helps to explain the pharmacological activities of PAN in the skin and gums. The pharmacokinetic model provided data in the plasma and skin concentrations of PAN, which are of fundamental importance to evaluate its efficacy.

Use of Intravenous Infusion Study Design to Simultaneously Determine Brain Penetration and Systemic Pharmacokinetic Parameters in Rats.

In drug discovery, the extent of brain penetration as measured by free brain/plasma concentration ratio (Kp,uu) is normally determined from one experiment after constant intravenous infusion, and pharmacokinetics (PK) parameters, including clearance (CL), volume of distribution at steady state (Vss), and effective half-life (t 1/2 ,eff) are determined from another experiment after a single intravenous bolus injection. The objective of the present study was to develop and verify a method to simultaneously determine Kp,uu and PK parameters from a single intravenous infusion experiment. In this study, nine compounds (atenolol, loperamide, minoxidil, N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl]sarcosine, sulpiride, and four proprietary compounds) were intravenously infused for 4 hours at 1 mg/kg or 24 hours at 1 or 6 mg/kg or bolus injected at 1 mg/kg. Plasma samples were serially collected, and brain and cerebrospinal fluid samples were collected at the end of infusion. The PK parameters were obtained using noncompartmental analysis (NCA) and compartmental analysis. The Kp,uu,brain values of those compounds increased up to 2.86-fold from 4 to 24 hours. The CL calculated from infusion rate over steady-state concentration from the 24-hour infusion studies was more consistent with the CL from the intravenous bolus studies than that from 4-hour infusion studies (CL avg. fold of difference 1.19-1.44 vs. 2.10). The compartmental analysis using one- and two-compartment models demonstrated better performance than NCA regardless of study design. In addition, volume of distribution at steady state and t 1/2,eff could be accurately obtained by one-compartment analysis within 2-fold difference. In conclusion, both unbound brain-to-plasma ratio and PK parameters can be successfully estimated from a 24-hour intravenous infusion study design. SIGNIFICANCE STATEMENT: We demonstrated that the extent of brain penetration and pharmacokinetic parameters (such as clearance, Vss, and effective t 1/2) can be determined from a single constant intravenous infusion study in rats.

Pharmacokinetics of Shikimic Acid Following Intragastric and Intravenous Administrations in Rats.

Shikimic acid, a critical starting material for the semi-total synthesis of oseltamivir to treat and prevent influenza, exerts many pharmacological effects. However, the optimal bioanalytical method has not been adequately defined. We used liquid chromatography-tandem mass spectrometry to quantitate shikimic acid in rat plasma and studied its pharmacokinetics after intragastric and intravenous administration. Plasma was spiked with an internal standard, and the proteins were precipitated with acetonitrile, followed by solvent evaporation and reconstitution of the mobile phase. Shikimic acid was separated on a hydrophilic reverse-phase column and showed a mass transition ([M-H]-) at m/z 173.4→136.6. Shikimic acid exhibited bi-exponential decay after intravenous dosing, with a rapid distribution (5.57 h-1) up to 1 h followed by slow elimination (0.78 h-1). The steady state distribution and clearance volumes were 5.17 and 1.79 L/h/kg, respectively. After intragastric administration, the shikimic acid level peaked at about 3 h, and the material then disappeared mono-exponentially with a half-life of 1.3 h. A double peak phenomenon was observed. The absolute oral bioavailability was about 10% in rats. We explored the relationship between the pharmacokinetics and pharmacodynamics of shikimic acid.

Human Amyloid-ß40 Kinetics after Intravenous and Intracerebroventricular Injections and Calcitriol Treatment in Rats In Vivo.

Amyloid-ß peptides of 40 and 42 amino acid lengths, which are synthesized in neurons and degraded in the brain and liver, have the potential to aggregate and form neuritic plaques in Alzheimer disease. The kinetics of human amyloid-ß (hAß) 40 were examined in the rat pursuant to intravenous and intracerebroventricular administration after pretreatment with calcitriol, the active vitamin D receptor ligand (6.4 nmol·kg-1 in 0.3 ml corn oil every other day for four intraperitoneal doses) to induce P-glycoprotein (P-gp) and enhance hAß40 brain efflux. The interference of hAß40 by media matrix that suppressed absorbance readings in the ELISA assay was circumvented with use of different calibration curves prepared in Standard Dilution Buffer, undiluted, 10-10,000 or 5-fold diluted plasma, or artificial cerebrospinal fluid. Simultaneous fitting of hAß40 plasma and cerebrospinal fluid (CSF) data after intravenous and intracerebroventricular administration were described by catenary-mammillary models comprising of a central and two peripheral compartments, the brain, and one to four CSF compartments. The model with only one CSF compartment (model I) best fitted the intravenous data that showed a faster plasma decay t1/2 and slower equilibration between plasma and brain/CSF. Calcitriol induction increased the brain efflux rate constant, k41 (1.8-fold), at the blood-brain barrier when compared with the control group, as confirmed by the 2-fold (P < 0.05) increase in brain P-gp relative protein expression. SIGNIFICANCE STATEMENT: An accurate description of the kinetic behavior of human amyloid-ß (hAß) 40 is needed in defining the toxic peptide as a biomarker of Alzheimer disease. Modeling of hAß40 data after intravenous and intracerebroventricular administration to the rat revealed an initially faster plasma half-life that reflected faster peripheral distribution but slower equilibration between plasma and brain/cerebrospinal fluid even with calcitriol pretreatment that increased P-glycoprotein protein expression and enhanced efflux clearance from brain.

Characterization of CGK012 in rat plasma by high performance liquid chromatography and mass spectrometry (HPLC-MS/MS): Application to a pharmacokinetic study.

CGK012 is a newly synthesized pyranocoumarin substance suppressing the activation and transcription of ß-catenin related to Wnt3a-CM. A bioanalytical method for CGK012 was developed and validated in rat plasma, and the method was applied to determine the plasma concentrations after intravenous administration. Plasma was cleaned-up by protein precipitation by acetonitrile including an internal standard. The substances were separated on a reversed-phase column, and the mobile phase was a mixture of water and acetonitrile (3:7, v/v; 0.1 % formic acid). The mass transition occurred at m/z 358.2→229.2 for CGK012 [M+H]+. CGK012 was stable in the various conditions, and the present assay met the criteria of bioanalytical method validation. CGK012 bi-exponentially decayed with the half-life of 4.0 h at the terminal phase. Mean Vd and clearance were 0.69 L/kg and 1.31 L/h/kg, respectively. This is the first bioanalytical method developed for quantification of CGK012 in rat plasma using LC-MS/MS, which would be useful to examine pharmacokinetic study of the substance.

Noteworthy idiosyncrasies of 1α,25-dihydroxyvitamin D3 kinetics for extrapolation from mouse to man: Commentary.

Calcitriol or 1,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ] is the active ligand of the vitamin D receptor (VDR) that plays a vital role in health and disease. Vitamin D is converted to the relatively inactive metabolite, 25-hydroxyvitamin D3 [25(OH)D3 ], by CYP27A1 and CYP2R1 in the liver, then to 1,25(OH)2 D3 by a specific, mitochondrial enzyme, CYP27B1 (1α-hydroxylase) that is present primarily in the kidney. The degradation of both metabolites is mostly carried out by the more ubiquitous mitochondrial enzyme, CYP24A1. Despite the fact that calcitriol inhibits its formation and degradation, allometric scaling revealed strong interspecies correlation of the net calcitriol clearance (CL estimated from dose/AUC∞ ), production rate (PR), and basal, plasma calcitriol concentration with body weight (BW). PBPK-PD (physiologically based pharmacokinetic-pharmacodynamic) modeling confirmed the dynamic interactions between calcitriol and Cyp27b1/Cyp24a1 on the decrease in the PR and increase in CL in mice. Close scrutiny of the literature revealed that basal levels of calcitriol had not been taken into consideration for estimating the correct AUC∞ and CL after exogenous calcitriol dosing in both animals and humans, leading to an overestimation of AUC∞ and underestimation of the plasma CL. In humans, CL was decreased in chronic kidney disease but increased in cancer. Collectively, careful pharmacokinetic data analysis and improved definition are achieved with PBPK-PD modeling, which embellishes the complexity of dose, enzyme regulation, and disease conditions. Allometric scaling and PBPK-PD modeling were applied successfully to extend the PBPK model to predict calcitriol kinetics in cancer patients.

The Segregated Intestinal Flow Model (SFM) for Drug Absorption and Drug Metabolism: Implications on Intestinal and Liver Metabolism and Drug-Drug Interactions.

The properties of the segregated flow model (SFM), which considers split intestinal flow patterns perfusing an active enterocyte region that houses enzymes and transporters (<20% of the total intestinal blood flow) and an inactive serosal region (>80%), were compared to those of the traditional model (TM), wherein 100% of the flow perfuses the non-segregated intestine tissue. The appropriateness of the SFM model is important in terms of drug absorption and intestinal and liver drug metabolism. Model behaviors were examined with respect to intestinally (M1) versus hepatically (M2) formed metabolites and the availabilities in the intestine (FI) and liver (FH) and the route of drug administration. The %contribution of the intestine to total first-pass metabolism bears a reciprocal relation to that for the liver, since the intestine, a gateway tissue, regulates the flow of substrate to the liver. The SFM predicts the highest and lowest M1 formed with oral (po) and intravenous (iv) dosing, respectively, whereas the extent of M1 formation is similar for the drug administered po or iv according to the TM, and these values sit intermediate those of the SFM. The SFM is significant, as this drug metabolism model explains route-dependent intestinal metabolism, describing a higher extent of intestinal metabolism with po versus the much reduced or absence of intestinal metabolism with iv dosing. A similar pattern exists for drug-drug interactions (DDIs). The inhibitor or inducer exerts its greatest effect on victim drugs when both inhibitor/inducer and drug are given po. With po dosing, more drug or inhibitor/inducer is brought into the intestine for DDIs. The bypass of flow and drug to the enterocyte region of the intestine after intravenous administration adds complications to in vitro-in vivo extrapolations (IVIVE).

Application of an Inter-Species Extrapolation Method for the Prediction of Drug Interactions between Propolis and Duloxetine in Humans.

Duloxetine (DLX) is a potent drug investigated for the treatment of depression and urinary incontinence. DLX is extensively metabolized in the liver by two P450 isozymes, CYP2D6 and CYP1A2. Propolis (PPL) is one of the popular functional foods known to have effects on activities of CYPs, including CYP1A2. Due to the high probability of using DLX and PPL simultaneously, the present study was designed to investigate the potent effect of PPL on pharmacokinetics (PKs) of DLX after co-administration in humans. A PK study was first conducted in 18 rats (n = 6/group), in which the plasma concentration of DLX and its major metabolite 4-hydroxy duloxetine (4-HD) with or without administration of PPL was recorded. Population PKs and potential effects of PPL were then analyzed using NONMEM software. Lastly, these results were extrapolated from rats to humans using the allometric scaling and the liver blood flow method. PPL (15,000 mg/day) exerts a statistically significant increase in DLX exposures at steady state, with a 20.2% and 24.6% increase in DLX C m a x , s s and the same 28.0% increase in DLX A U C s s when DLX (40 or 60 mg) was administered once or twice daily, respectively. In conclusion, safety issues are required to be attended to when individuals simultaneously use DLX and PPL at high doses, and the possibility of interactions between DLX and PPL might be noted.

Discovery and Biological Evaluations of Halogenated 2,4-Diphenyl Indeno[1,2-b]pyridinol Derivatives as Potent Topoisomerase IIα-Targeted Chemotherapeutic Agents for Breast Cancer.

With the aim of developing new effective topoisomerase IIα-targeted anticancer agents, we synthesized a series of hydroxy- and halogenated 2,4-diphenyl indeno[1,2-b]pyridinols using a microwave-assisted single step synthetic method and investigated structure-activity relationships. The majority of compounds with chlorophenyl group at 2-position and phenol group at the 4-position of indeno[1,2-b]pyridinols exhibited potent antiproliferative activity and topoisomerase IIα-selective inhibition. Of the 172 compounds tested, 89 showed highly potent and selective topoisomerase IIα inhibition and antiproliferative activity in the nanomolar range against human T47D breast (2.6 nM) cancer cell lines. In addition, mechanistic studies revealed compound 89 is a nonintercalative topoisomerase II poison, and in vitro studies showed it had promising cytotoxic effects in diverse breast cancer cell lines and was particularly effective at inducing apoptosis in T47D cells. Furthermore, in vivo administration of compound 89 had significant antitumor effects in orthotopic mouse model of breast cancer.

Hepatic clearance concepts and misconceptions: Why the well-stirred model is still used even though it is not physiologic reality?

The liver is the most important drug metabolizing organ, endowed with a plethora of metabolizing enzymes and transporters to facilitate drug entry and removal via metabolism and/or biliary excretion. For this reason, much focus surrounds the development of clearance concepts, which are based on normalizing the rate of removal to the input or arterial concentration. By so doing, some authors have recently claimed that it implies one specific model of hepatic elimination, namely, the widely used well-stirred or venous equilibration model (WSM). This commentary challenges this claim and aims to provide a comprehensive discussion of not only the WSM but other currently applied hepatic clearance models - the parallel tube model (PTM), the dispersion model (DM), the zonal liver model (ZLM), and the heterogeneous capillary transit time model of Goresky and co-workers (GM). The WSM, PTM, and DM differ in the patterns of internal blood flow, assuming bulk, plug, and dispersive flows, respectively, which render different degrees of mixing within the liver that are characterized by the magnitudes of the dispersion number (DN), resulting in different implications concerning the (unbound) substrate concentration in liver (CuH). Early models assumed perfusion rate-limited distribution, which have since been modified to include membrane-limited transport. The recent developments associated with the misconceptions and the sensitivity of the models are hereby addressed. Since the WSM has been and will likely remain widely used, the pros and cons of this model relative to physiological reality are further discussed.

Identification of DNA and glutathione adducts in male Sprague-Dawley rats exposed to 1-bromopropane.

Occupational exposure of workers to 1-bromopropane (1-BP) has raised concerns in industry for many years. Despite the known toxicity of this chemical, molecular events attributed to exposure to 1-BP have not been extensively studied. The aim of the present study was to examine the effects of 1-BP exposure on adduct formation with DNA and glutathione (GSH) in male Sprague-Dawley rats in an attempt to determine the early stages of toxicity. Following 6 h after either single or daily exposure to 1-BP for 3 days, N7-propyl guanine and S-propyl GSH were quantified in several organs by using liquid chromatography-mass spectrometry (LC-MS/MS). The results showed that N7-propyl guanine was maximally formed in liver followed by spleen, testes, and lung in both dose- and time-dependent manners. However, DNA adduct was not detected in cardiac tissue. In the case of S-propyl GSH, this compound was formed in the following order in various organs: liver > testes > spleen > kidney > lung > heart. In a subsequent in vitro study, formation of N7-propyl guanine initiated by 1-BP in calf thymus DNA was not markedly affected by addition of liver homogenates, which indicated that this chemical may be acting as a direct alkylating agent. In contrast, an in vitro study with free GSH demonstrated that 1-BP reduced GSH and elevated production of S-propyl GSH, and that the production of this adduct was significantly higher in the presence of active liver homogenates. Data indicated that formation of GSH adducts initiated by 1-BP might be associated with an enzyme-driven process. Although further characterization is necessary, it would appear that N7-propyl guanine and S-propyl GSH might serve as useful markers in cases of exposure assessment of 1-BP.

Theoretical consideration of the properties of intestinal flow models on route-dependent drug removal: Segregated Flow (SFM) vs. Traditional (TM).

The intestine is endowed with a plethora of enzymes and transporters and regulates the flow of substrate to the liver. Physiologically-based pharmacokinetic models have surfaced to describe intestinal removal. The traditional model (TM) describes the intestinal flow as a whole perfusing the entire tissue that contains the intestinal transporters and enzymes. The segregated flow model (SFM) describes that only a fraction (fQ  < 0.2) of the intestinal blood flow perfuses the enterocyte region where the intestinal enzymes and transporters are housed, rendering a lower drug distribution/intestinal clearance when drug enters via the circulation than from the gut lumen. As shown by simulations, a higher intestinal clearance and extraction ratio (EI,iv ) exists for the TM than for SFM after iv dosing. By contrast, the EI,po after po dosing is higher for the SFM, due to the smaller volume of distribution for the enterocyte region and a lower flow rate that result in increased mean residence time and higher drug extraction. Under MBI (mechanism-based inhibition), the AUCR,po after oral bolus is the highest for drug when inhibitor is given orally, with SFM > TM. Competitive inhibition of intestinal enzymes leads to higher liver metabolism; again, when both drug and inhibitor are given orally, changes in the SFM > TM. However, less definitive patterns result with inhibition of both intestinal and liver enzymes. In conclusion, differences exist for EI and drug-drug interaction (DDI) between the TM and SFM. The fractional intestinal blood flow (fQ ) is a key factor affecting different extents of intestinal/liver metabolism of the drug after oral as well as intravenous administration.

Stereo-Selective Pharmacokinetics of Ilimaquinone Epimers Extracted from a Marine Sponge in Rats.

An ilimquinone (IQ) mixture isolated from Hippiospongia metachromia, consisting of IQ and epi-ilimaquinone (epi-IQ), exerts anti-HIV, anti-microbial, anti-inflammatory, and anti-cancer effects. An HPLC-MS/MS method was developed for simultaneous determination of the two epimers in rat plasma, separating them using a biphenyl column. Ascorbic acid is added during the sample preparation to ensure the stability of both isomers. The plasma concentrations of the isomers were monitored following intravenous and oral administration of the IQ mixture in rats as well as the individual epimers that were separately orally administered. Compare to IQ, epi-IQ was much more stable in rat plasma, likely due to its configurations of decalin. Both substances decayed in more than bi-exponential pattern, with an elimination rate constant of 1.2 h-1 for IQ and 1.7 h-1 for epi-IQ. The epi-IQ was distributed more widely than IQ by about two-fold. Consequently, the clearance of epi-IQ was greater than that of IQ by about three-fold. The oral absolute bioavailability for IQ was 38%, and, that for epi-IQ, was 13%. Although the systemic exposure of IQ was greater than that of epi-IQ by ~8.7-fold, the clearance of each isomer was similar when administered either orally or intravenously, when normalized for bioavailability. The stereo-specific behavior of the isomers appears to originate from differences in both their tissue distribution and gastrointestinal permeability.

Effects of Verapamil and Diltiazem on the Pharmacokinetics and Pharmacodynamics of Rivaroxaban.

Concomitant use of rivaroxaban with non-dihydropyridine calcium channel blockers (non-DHPs) might lead to an increase of systemic rivaroxaban exposure and anticoagulant effects in relation to the inhibition of metabolic enzymes and/or transporters by non-DHPs. This study was designed to evaluate the effects of verapamil and diltiazem on the pharmacokinetics and the prolongation of prothrombin time of rivaroxaban in rats. The data were analyzed using a pharmacokinetic/pharmacodynamics (PK/PD) modeling approach to quantify the influence of verapamil. Verapamil increased the systemic exposure of rivaroxaban by 2.8-fold (p <0.001) which was probably due to the inhibition of efflux transportation rather than metabolism. Prothrombin time was also prolonged in a proportional manner; diltiazem did not show any significant effects, however. A transit PK model in the absorption process comprehensively describes the double-peaks of rivaroxaban plasma concentrations and the corresponding change of prothrombin time with a simple linear relationship. The slope of prothrombin time vs. rivaroxaban plasma concentration in rats was retrospectively found to be insensitive by about 5.4-fold compared to than in humans. More than a 67% dose reduction in rivaroxaban is suggested in terms of both a pharmacokinetic point of view, and the sensitivity differences on the prolongation of prothrombin time when used concomitantly with verapamil.