Hepatic Blood Flow Rate Research Articles

Longitudinal ultrasound imaging and network modeling in rats reveal sex-dependent suppression of liver regeneration after resection in alcoholic liver disease.

Liver resection is an important surgical technique in the treatment of cancers and transplantation. We used ultrasound imaging to study the dynamics of liver regeneration following two-thirds partial hepatectomy (PHx) in male and female rats fed via Lieber-deCarli liquid diet protocol of ethanol or isocaloric control or chow for 5-7weeks. Ethanol-fed male rats did not recover liver volume to the pre-surgery levels over the course of 2weeks after surgery. By contrast, ethanol-fed female rats as well as controls of both sexes showed normal volume recovery. Contrary to expectations, transient increases in both portal and hepatic artery blood flow rates were seen in most animals, with ethanol-fed males showing higher peak portal flow than any other experimental group. A computational model of liver regeneration was used to evaluate the contribution of physiological stimuli and estimate the animal-specific parameter intervals. The results implicate lower metabolic load, over a wide range of cell death sensitivity, in matching the model simulations to experimental data of ethanol-fed male rats. However, in the ethanol-fed female rats and controls of both sexes, metabolic load was higher and in combination with cell death sensitivity matched the observed volume recovery dynamics. We conclude that adaptation to chronic ethanol intake has a sex-dependent impact on liver volume recovery following liver resection, likely mediated by differences in the physiological stimuli or cell death responses that govern the regeneration process. Immunohistochemical analysis of pre- and post-resection liver tissue validated the results of computational modeling by associating lack of sensitivity to cell death with lower rates of cell death in ethanol-fed male rats. Our results illustrate the potential for non-invasive ultrasound imaging to assess liver volume recovery towards supporting development of clinically relevant computational models of liver regeneration.

52500 Characterization of a Series of 1,4-diaryl-pyrazolo-pyridinones as Anti-Leishmanial Agents

ABSTRACT IMPACT: The first-line chemotherapies used to treat leishmaniasis are highly toxic intravenous antimonials yet drug resistance has begun to develop, causing the use of oral treatment options with high price tags; there is a strong need for new, safe, and effective chemotherapeutic agents to treat leishmaniasis. OBJECTIVES/GOALS: This study was conducted in order to identify novel chemical compounds that exhibit anti-leishmanial activity and to further characterize their efficacy and toxicity in in vitro and in vivo systems in the hopes of future chemotherapeutic developments. METHODS/STUDY POPULATION: A total of 28 unique 1,4-diaryl-pyrazolo-pyridinone (1,4-DAPP) compounds were synthesized and anti-leishmanial efficacy and host cell toxicity were determined using L. donovani mCherry-expressing amastigotes and THP-1 macrophages. Additional pharmacokinetic analyses of a potent 1,4-DAPP compound were conducted, revealing a potential metabolite structure. A select group of the novel compounds were screened in a cutaneous leishmaniasis (CL) murine model using L. major mCherry-expressing parasites and female Balb/C mice. The treatment consisted of 10 intralesional injections of compound over a period of 4 weeks, while lesion growth was monitored via fluorescence and manual measurements. RESULTS/ANTICIPATED RESULTS: Four experimental compounds had IC50 values less than 5 micromolar, providing similar anti-leishmanial activity to Miltefosine. Compound 9279817 had a clearance almost twice the rate of normal hepatic blood flow and had a relatively high volumes of distribution, indicating this compound is rapidly cleared and distributes into tissues. In vitro rat liver microsome assays suggest a rapid metabolism of 9279817 and MS/MS results suggest this metabolite is most likely formed via oxidation of the sulfur on the lower aryl ring. This sulfoxide metabolite has similar efficacy as the parent compound and does not exhibit toxicity in vitro. Three of the experimental compounds behaved similarly to the antimony positive control in the murine CL model. DISCUSSION/SIGNIFICANCE OF FINDINGS: This study revealed a novel structural class of compounds that have anti-leishmanial activity. Experiments show compounds with similar efficacy to Miltefosine while having significantly less cytotoxicity, suggesting that the 1,4-DAPP structural class could be further developed as a potential chemotherapeutic.

Investigating the glucuronidation and sulfation pathways contribution and disposition kinetics of Bisphenol S and its metabolites using LC-MS/MS-based nonenzymatic hydrolysis method

Despite showing serious health consequences and widespread exposure, the toxicokinetic information required to evaluate the health risks of BPS is insufficient. Thus, we aim to describe the comprehensive toxicokinetics of BPS and its glucuronide (BPS-G) and sulfate (BPS–S) metabolites in rats. Simultaneous quantification of BPS and its metabolites (authentic standards) was accomplished using UPLC-MS/MS method. BPS displayed rapid absorption, extensive metabolism and fast elimination after oral administration. Following intravenous administration, BPS exhibited CL (8.8 L/h/kg) higher than the rat hepatic blood flow rate suggesting the likelihood of extrahepatic clearance. The CL value differed from those reported previously (sheep and piglets) and the probable reason could be attributed to dose- and/or interspecies differences. BPS was extensively metabolized and excreted primarily through urine as BPS-G (∼56%). BPS and BPS-S exhibited a high protein binding capacity in comparison to BPS-G. In in vitro metabolic stability study, BPS was predominantly metabolized through glucuronidation. The predicted in vivo hepatic clearance of BPS suggested it to be a high and intermediate clearance chemical in rats and humans, respectively. The significant interspecies difference observed in the clearance of BPS between rats and humans indicated that toxicokinetics of BPS should be considered for health risk assessment in humans.

In Vitro ADME, Preclinical Pharmacokinetics and Prediction of Human Pharmacokinetics of RBx14255, a Novel Ketolide with Pharmacodynamics Against Multidrug-Resistant Bacterial Pathogens.

The preclinical pharmacokinetic and pharmacodynamic properties of a potent fluoroketolide RBx14255 against Streptococcus pneumoniae and Haemophilus influenzae was compared with telithromycin and human clinical dose was predicted for preclinical development. The in vitro pharmacokinetic characterization was performed for solubility, Caco-2 permeability, microsomal stability, CYP inhibition and plasma protein binding. In vivo pharmacokinetic studies were performed in Swiss albino mice, Sprague Dawley rats and Beagle dogs. The pharmacodynamic studies were carried out in mouse against S. pneumoniae in systemic infection and against S. pneumoniae and H. influenzae in rat lung infection models. RBx14255 showed superior potency and efficacy in mouse and rat infection models. RBx14255 showed pH dependent solubility (0.41 mg/mL at pH 6.8 and >1 mg/mL at pH 1.2), moderate Caco-2 permeability (A to B: 12 nm/s) with high efflux ratio. It showed high plasma protein binding (>97%) in mouse and low binding (45- 70%) in rat, dog and human. The compound is mainly metabolized through CYP3A4. Pharmacokinetic parameters and absolute bioavailability of both, RBx14255 and telithromycin are similar in mouse. Both the ketolides showed low plasma clearance (18% of the normal hepatic blood flow rate) in mouse, moderate to high clearance in rat and dog. Mean oral bioavailability was high in mouse (≥85%), moderate in rat (RBx14255: 15% and telithromycin: 51%) and high to moderate in dog (RBx14255: 98% and telithromycin: 56%). The predicted efficacious dose for a 70kg man ranges from 124 mg BID to 226 mg BID. RBx14255 displayed significantly better pharmacodynamics which correlates with the pharmacokinetic properties against S. pneumoniae and H. influenzae as compared to telithromycin. The predicted human efficacious doses are in the range of 124-226mg, making it amenable to oral dosage form drug in human. This could be a promising clinical candidate for future studies.

4040 Investigation of a Series of 1,4-diaryl-pyrazolo-pyridinones as Anti-Leishmanial Agents

OBJECTIVES/GOALS: This study was conducted in order to identify novel chemical compounds that exhibit anti-leishmanial activity and to further characterize their efficacy and toxicity in in vitro and in vivo systems in the hopes of future chemotherapeutic developments. METHODS/STUDY POPULATION: We developed a novel, target-free fluorometric high-throughput screen (HTS) to identify small molecules with anti-leishmanial activity. Screening of 10,000 small molecules from the ChemBridge DIVERset-EXP library cassette #5 yielded 210 compounds that killed 80% of parasites. One hundred nine (109) molecular scaffolds were represented within the hit compounds, including the 1,4-diaryl-pyrazolo-pyridinone (1,4-DAPP). A total of 27 novel 1,4-DAPP compounds were synthesized and anti-leishmanial efficacy and host cell toxicity was determined using L. donovani mCherry expressing amastigotes and THP-1 macrophages. Additional pharmacokinetic analyses of a potent 1,4-DAPP compound were conducted. RESULTS/ANTICIPATED RESULTS: Four experimental compounds had IC50 values less than 5μM, providing similar anti-leishmanial activity to miltefosine. Compound 9279817 had a clearance almost twice the rate of normal hepatic blood flow and had a relatively high volume of distribution, indicating this compound is rapidly cleared and distributes into tissues. in vitro rat liver microsome assays suggest a rapid metabolism of 9279817, and MS/MS results suggest this metabolite is most likely formed via oxidation of the sulfur on the lower aromatic ring. DISCUSSION/SIGNIFICANCE OF IMPACT: This study revealed a novel structural class of compounds that have anti-leishmanial activity. in vitro experiments show compounds with similar efficacy as miltefosine while having significantly less toxicity, suggesting that this class could be further developed as a potential chemotherapeutic.

Effects of Diabetes Mellitus on the Disposition of Tofacitinib, a Janus Kinase Inhibitor, in Rats.

Tofacitinib, a Janus kinase inhibitor, was developed for the treatment of rheumatoid arthritis. Recently, it has been associated with an increased change in arthritis development in patients with diabetes. Herein, we evaluated the pharmacokinetics of tofacitinib after intravenous (10 mg/kg) and oral (20 mg/kg) administration to rats with streptozotocin-induced diabetes mellitus and control rats. Following intravenous administration of tofacitinib to rats with streptozotocin-induced diabetes mellitus, area under the plasma concentration-time curve from time zero to infinity of tofacitinib was significantly smaller (33.6%) than that of control rats. This might be due to the faster hepatic intrinsic clearance (112%) caused by an increase in the hepatic cytochrome P450 (CYP) 3A1(23) and the faster hepatic blood flow rate in rats with streptozotocin-induced diabetes mellitus than in control rats. Following oral administration, area under the plasma concentration-time curve from time zero to infinity of tofacitinib was also significantly smaller (55.5%) in rats with streptozotocin-induced diabetes mellitus than that in control rats. This might be due to decreased absorption caused by the higher expression of P-glycoprotein and the faster intestinal metabolism caused by the higher expression of intestinal CYP3A1(23), which resulted in the decreased bioavailability of tofacitinib (33.0%) in rats with streptozotocin-induced diabetes mellitus. In summary, our findings indicate that diabetes mellitus affects the absorption and metabolism of tofacitinib, causing faster metabolism and decreased intestinal absorption in rats with streptozotocin-induced diabetes mellitus.

Comparative efficacy and tolerance of centrally acting muscle relaxants in elderly patients with nonspecific musculoskeletal pain

Objective: to evaluate the clinical efficacy and tolerability of the Russian drug tolperisone (calmyrex) versus tizanidine and baclofen in the therapy of acute nonspecific musculoskeletal pain (NSMSP) in the elderly. Patients and methods. Examinations were made in 135 elderly (60–75-year-old) patients with acute NSMSP. To relieve pain syndrome, all the patients were prescribed nimesulide suspension 100 mg twice a day after meals. The patients were randomized using an envelope method to three groups, each of which took a muscle relaxant as tablets for 15 days: Group 1 received the Russian drug tolperisone (calmyrex) 150 mg thrice a day; Group 2 used tizanidine 2 mg thrice a day; Group 3 had baclofen 10 mg twice a day. Pain syndrome was rated on a visual analogue scale (VAS). To measure orthostatic blood pressure, to check the coordinator system, and to record adverse events (AEs) were mandatory. Results and discussion. At 15 days, treatment substantially reversed pain syndrome according to VAS scores in all the groups: from 68 to 14 in Group 1, from 64 to 17 in Group 2, and from 62 to 18 in Group 3 (without significant differences between the groups). AEs were more common in Groups 2 and 3 patients who received tizanidine or baclofen. Orthostatic hypotension was reported in 3 patients taking baclofen. The high safety and good tolerability of a combination of a non-steroidal anti-inflammatory drug (NSAID) and a muscle relaxant were noted in the calmyrex group. Although muscle relaxants ensure clinically significant short-term pain relief in acute nonspecific back pain, it is necessary to take into account that elderly patient can develop AEs when taking the drugs, which is associated with delayed metabolic reactions, reduced hepatic blood flow and glomerular filtration rate, and a larger number of diseases and used medications. Conclusion. Therapy with NSAIDs and centrally acting muscle relaxants for acute NSMSP in elderly people calls for special precautions due to the fact that there may be AEs that are less likely to occur with calmyrex than with tizanidine and baclofen.

Predicting successful/unsuccessful extrapolation for in vivo total clearance of model compounds with a variety of hepatic intrinsic metabolism and protein bindings in humans from pharmacokinetic data using chimeric mice with humanised liver

1. Immunodeficient chimeric mice with humanised liver have been useful in predicting total clearance values of drugs in humans. However, their usefulness may currently be limited for specific compounds with interspecies differences.2. In vivo total clearance and in vitro hepatic intrinsic clearance values of 16 model compounds were determined in control/humanised-liver mice and in mouse and human hepatocytes, respectively, for extrapolating the total clearance values of compounds in humans.3. The predictability of in vivo total clearance values of 11 model compounds in humans was adequate using pharmacokinetic data from humanised-liver mice. The predictability of total clearance values using humanised-liver mice was better than conventional allometric scaling for compounds with large interspecies differences in in vitro hepatic intrinsic clearance or plasma unbound fractions.4. There were trends that total clearance values in control and humanised-liver mice were similar to or higher than reported hepatic blood flow rates in normal mice among four compounds with poor predictability. Diazepam, with the poorest predictability, showed 38-fold-higher hepatic intrinsic clearance in mice than in humans.5. These results could lead to guidelines describing that compounds may be suited or unsuited to extrapolating total clearance values in humans from pharmacokinetics in humanised-liver mice.

Comparative Analysis of Experimental Pharmacokinetics of New Neurotropic Peptides

Experimental pharmacokinetics of new pharmacologically active peptides, modified analogues of endogenous neuropeptides, has been investigated in rats and rabbits. The study icluded 3 new drugs: (i) the nootropic drug noopept (phenylacetyl-prolyl-glycine ethyl ester); (ii) dilept (N-caproyl-L-prolyl-L-tyrosine methyl ester) – the antipsychotic with positive mnemotropic action; (iii) compound GB-115 – selective anxiolytic (phenylhexanoyl-prolyl-tryptophan amide). Differences in pharmacokinetics and biotransformation of the studied drugs depended on their structural features. The ether derivatives noopept and dilept underwent intensive metabolism by rat gastrointestinal esterases and peptidases with the formation of active metabolites. Being an amide, the compound GB-115 was more resistant to the enzymatic effects of peptidases and was detected for a longer period in the blood of experimental animals. In rabbits the studied compounds were less exposed to the enzymatic action by gastrointestinal peptidases, and were detected plasma of rabbits for a longer period. The higher stability of the compounds studied in rabbits may be attributed not only to the structural features of the studied dipeptides, but also to differences in the activity of the enzymatic systems of the gastrointestinal tract participating in their metabolism, as well as differences in the rate of hepatic and renal blood flow in rats and rabbits.

Central hemodynamic and splanchnic circulation in children with meningococcal septic shock

Meningococcal infection is caused by the bacterium Neisseria meningitidis (also termed meningococcus). Invasive meningococcal disease remains a rare infectious disease not only with high mortality but also with important morbidity and remains as a leading cause of sepsis and septic shock. The pathogenic mechanisms of microcirculatory disorders in meningococcal septic shock have been subject to controversy. This article presents the results of a study of 11 paediatric patients’ (4 boys and 7 girls) with meningococcal septic shock (Group I) who were hospitalized at the Regional Children's Infectious Hospital from 2009 to 2011. The average age of the patients was 37.4 ± 8.4 mo. Septic shock was diagnosed according to International Pediatric Sepsis Consensus Conference: definitions of criteria for sepsis and organ dysfunction in paediatrics. Heart rate, respiratory rate, systolic blood pressure, diastolic blood pressure, average blood pressure, SpO2 were monitored. The cardiac output, ejection fraction, fraction shortening, stroke volume were measured by ultrasound in M-mode by Teichholz method. Blood circulation in the a. mesenterica, a. hepatica, a. lienalis, a. renal sinister, v. porta, v. lienalis, v. renal sinister was determined by impulse Doppler’s wave. Acid-base and electrolytes level in serum, nitric oxide (NO), endothelin I, creatinine, C-reactivity protein and lactate blood level were measured. The control group consisted of 21 healthy children (9 boys and 12 girls), aged 37.5 ± 5.4 mo. in average (Group II). We used t-criteria (Student’s) and correlation with R-criteria (Spearmen) for statistical analysis. The data showed a statistically significant lower fraction of ejection, fraction of shortening, stroke volume in Group I. Moreover, our data showed a statistically high level of mesenterial and portal blood flow rate and high pulse index in v. renal sinister compared to healthy children. The blood level of NO was increased in Group I as well as in Group II. Direct correlations were determined between the level of NO and mesenteric, hepatic arterial and venous blood flow rate. Statistically significant inverse correlations between the level of NO and pulse resistive index in splanchnic vessels were discovered as well as inverse correlations between the NO level and the indicator of the severity of condition on PRISM scale (r = –0.952). At the same time, we have found no correlation between splanchnic circulation value and cardiac output. Based on the results of this study, we consider that NO has organ protective effects in children with meningococcal sepsis. Future research should aim to introduce new strategies of intensive care for patients with meningococcal septic shock with early use of inotrope and NO-donor therapy in fluid restriction combination.

Pharmacokinetic changes of drugs in a rat model of liver cirrhosis induced by dimethylnitrosamine, alone and in combination with diabetes mellitus induced by streptozotocin.

Rats with liver cirrhosis induced by N-dimethylnitrosamine (LC) and rats with LC with diabetes mellitus induced by streptozotocin (LCD) have been developed as animal models for human liver cirrhosis and liver cirrhosis with diabetes mellitus, respectively. Changes in the pharmacokinetics of drugs (mainly non-renal clearance, CLNR) in LC and LCD rats reported in the literature compared with respective control rats were reviewed. This review mainly explains the changes in the CLNRs of drugs (which are mainly metabolized via hepatic microsomal cytochrome P450s, CYPs) in LC and LCD rats, in terms of the changes in in vitro hepatic intrinsic clearance (CLint; mainly due to the changes in CYPs in the disease state), free (unbound) fraction of a drug in the plasma (fp) and hepatic blood flow rate (QH) depending on the hepatic excretion ratio of the drug. Generally, changes in the CLNRs of drugs in LC and LCD rats could be well explained by the above-mentioned three factors. The mechanism of urinary excretion of drugs (such as glomerular filtration or renal active secretion or reabsorption) in LC and LCD rats is also discussed. The pharmacokinetics of the drugs reported in the LC and LCD rats were scarce in humans. Thus, the present rat data should be extrapolated carefully to humans.

Assessment of intestinal availability (FG) of substrate drugs of cytochrome p450s by analyzing changes in pharmacokinetic properties caused by drug-drug interactions.

In this study, we developed the drug-drug interaction (DDI) method as a new assessment technique of intestinal availability (F(G), the fraction of drug transferred from the intestinal enterocytes into the liver, escaping from intestinal metabolism) based on the clearance theory. This method evaluates F(G) from changes caused by DDIs in the area under the blood concentration-time curve and in the elimination half-life of victim drugs. Application of the DDI method to data from the literature revealed that the mean and S.D. of F(G) values for 20 substrate drugs of CYP3A was 0.56 ± 0.29, whereas that for 8 substrate drugs of CYP2C9, CYP2C19, and CYP2D6 was 0.86 ± 0.11. These results were consistent with the fact that intestinal metabolism is mediated predominantly by CYP3A. The DDI method showed reasonable correlations with the conventional i.v./p.o. method and the grape fruit juice (GFJ) method (coefficients of determination of 0.41 and 0.81, respectively). The i.v./p.o. method was more susceptible to fluctuations in the hepatic blood flow rate compared with the DDI and GFJ methods. The DDI method evaluates F(G) separating from the absorption ratio (F(A)) although it requires approximation of F(A). Since preciseness of approximation of F(A) does not greatly affect the evaluation of F(G) by the DDI method, we proposed a reasonable approximation method of F(A) for the evaluation of F(G) in the DDI method. The DDI method would be applicable to a broad range of situations in which various DDI data are utilizable.

Pharmacokinetics of drugs in mutant Nagase analbuminemic rats and responses to select diuretics

To report (1) the pharmacokinetics of drugs that are mainly metabolized via hepatic cytochrome P450s (CYPs) or mainly excreted via the urine and bile, (2) the mechanism for the urinary excretion of drugs (such as glomerular filtration or renal active secretion or re-absorption), and (3) the diuretic effect of some loop diuretics in mutant Nagase analbuminaemic rats (NARs), an animal model for human familial analbuminaemia based on the pharmacokinetics of drugs reported in the literatures. In NARs, the changes in the time-averaged non-renal clearances (CL(NR)s) of drugs that are mainly metabolized via CYPs were explained in terms of changes in the hepatic intrinsic clearance (mainly because of changes in CYPs), free (unbound) fractions of drugs in the plasma (fp) and hepatic blood-flow rate (QH) depending on the hepatic excretion ratios of drugs. The CL(NR) changes of drugs mainly metabolized via hepatic CYPs can be sufficiently explained by the three earlier mentioned factors. The plasma albumin (furosemide) or globulin (azosemide, bumetanide and torasemide) binding affects their diuretic effects.

Faster non-renal clearance of metoprolol in streptozotocin-induced diabetes mellitus rats

Metoprolol is a selective β1-adrenergic receptor antagonist metabolized by hepatic cytochrome P450s (CYPs). In this study, we evaluated pharmacokinetic changes following intravenous (i.v.) and oral metoprolol in rats with diabetes mellitus induced by streptozotocin (DMIS). Metoprolol has an intermediate hepatic extraction ratio in rats (0.586–0.617), and it is assumed that the liver is exclusively responsible for metoprolol metabolism. Thus, the hepatic clearance, CLH (the non-renal clearance, CLNR) of metoprolol depends on the hepatic blood flow rate (QH), the free fraction in plasma (fp), and in vitro hepatic intrinsic clearance, CLint. After i.v. administration of 1.5mg/kg metoprolol to DMIS rats, its CLNR was 40.9% faster than control animals. This could be due to a significantly faster QH because hepatic CLint and fp were comparable between the two groups of rats due to unchanged hepatic CYP2D activity. After oral administration of 1.5mg/kg metoprolol to DMIS rats, gastrointestinal absorption was >99% of the oral dose for both groups, while the area under the curve (AUC) was 27.9% smaller, which could be caused by the greater hepatic metabolism seen in the i.v. study. These findings have potential therapeutic implications, assuming that the DMIS rats qualitatively reflect similar changes in patients with diabetes.

The influence of hepatic transport on the distribution volumes and mean residence time of drug in the body and the accuracy of estimating these parameters by the traditional pharmacokinetic calculations

The influence of hepatic uptake and efflux, which includes passive diffusion and transporter-mediated component, on drug distribution volumes [steady-state volume of distribution (V(ss)) and terminal volume of distribution (V(β))], mean residence time (MRT), clearance, and terminal half-life is considered using a simplified physiologically based pharmacokinetic model. To account for hepatic uptake, liver is treated as two-compartmental unit with drug transfer from extracellular water into hepatocytes. The exactly calculated distribution volumes and MRT are compared with that obtained by the traditional equations based on the assumption of central elimination. It was found that V(ss) may increase more than 10-fold and V(β) more than 100-fold due to the contribution of transporter-mediated uptake. The terminal half-life may be substantially shortened (more than 100-fold) due to transporters. It may also decrease significantly due to the increase of intrinsic hepatic clearance (CL(int)), whereas hepatic clearance has already reached saturation (and stays close to the possible maximum value). It is shown that in case of transporter-mediated uptake of compound into hepatocytes, in the absence of efflux and passive diffusion (unidirectional uptake), hepatic clearance is independent of CL(int) and is determined by hepatic blood flow and uptake rate constant. The effects of transporter-mediated uptake are mostly pronounced for hydrophilic acidic compounds and moderately lipophilic neutral compounds. For basic compounds and lipophilic neutral compounds the change of distribution volumes due to transporters is rather unlikely. It was found that the traditional equations provide very accurate values of V(ss), V(β), and MRT in the absence of transporter action even for very low rates of passive diffusion. On the other hand, the traditional equations fail to provide the correct values of these parameters when the increase of distribution volumes due to transporters takes place, and actually yield the values substantially smaller than the true ones (up to an order of magnitude for V(ss) and MRT, and three orders of magnitude for V(β)).

Metabolism of novel anti-HIV agent 3-cyanomethyl-4-methyl-DCK by human liver microsomes and recombinant CYP enzymes

To investigate the metabolism of 3-cyanomethyl-4-methyl-DCK (CMDCK), a novel anti-HIV agent, by human liver microsomes (HLMs) and recombinant cytochrome P450 enzymes (CYPs). CMDCK was incubated with HLMs or a panel of recombinant cytochrome P450 enzymes including CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, 3A4, and 3A5. LC-ion trap mass spectrometry was used to separate and identify CMDCK metabolites. In the experiments with recombinant cytochrome P450 enzymes, specific chemical inhibitors combined with CYP antibodies were used to identify the CYP isoforms involved in CMDCK metabolism. CMDCK was rapidly and extensively metabolized by HLMs. Its intrinsic hepatic clearance estimated from the in vitro data was 19.4 mL·min(-1)·kg(-1), which was comparable to the mean human hepatic blood flow rate (20.7 mL·min(-1)·kg(-1)). The major metabolic pathway of CMDCK was oxidation, and a total of 14 metabolites were detected. CYP3A4 and 3A5 were found to be the principal CYP enzymes responsible for CMDCK metabolism. CMDCK was metabolized rapidly and extensively in human hepatic microsomes to form a number of oxidative metabolites. CYP3A4 and 3A5 were the predominant enzymes responsible for the oxidation of CMDCK.

The Involvement of Organic Anion Transporting Polypeptide in the Hepatic Uptake of Telmisartan in Rats: PET Studies with [11C]Telmisartan

Telmisartan, a selective angiotensin II receptor antagonist, is primarily excreted via hepatobiliary transport. The predominant contribution of organic anion transporting polypeptide (OATP) 1B3 in its hepatic uptake of telmisartan has been demonstrated by in vitro transport studies. In the present study, a quantitative positron emission tomography (PET) methodology was developed for in vivo kinetic assessment of hepatobiliary transport of telmisartan. Serial abdominal PET scans were performed in rats following intravenous administration of [(11)C]telmisartan as a radiotracer. PET scans revealed that [(11)C]telmisartan was localized primarily in the liver and some of the radioactivity moved to the intestine, which corresponds to biliary excretion. Radiometabolite analysis by radiometric HPLC showed that [(11)C]telmisartan was converted to its acylglucuronide, which was mainly detected in bile, but little in plasma and liver. Integration plot analysis revealed that [(11)C]telmisartan was taken up into the liver as rapidly as the hepatic blood flow rate, and the radiometabolite was subsequently excreted into the bile. When rifampicin, a typical Oatp inhibitor, was coadministered with [(11)C]telmisartan in rats, hepatic uptake clearance of [(11)C]telmisartan was significantly decreased, whereas biliary efflux clearance was not changed. Coinjection with unlabeled telmisartan (4 and 10 mg/kg) also decreased hepatic uptake clearance of [(11)C]telmisartan. On the other hand, PET imaging analysis revealed a significant increase of biliary efflux when telmisartan dose was increased to more than 4 mg/kg. These results suggested that the hepatic uptake of [(11)C]telmisartan mainly consists of a saturable process mediated by Oatps in rats, according to noninvasive real-time measurement of tissue radioactivity with the use of PET. The present study with rats is expected to provide the feasibility of PET imaging study to quantitatively estimate OATP1B3 function in humans.

Pharmacokinetics and Hepatic Uptake of Eltrombopag, a Novel Platelet-Increasing Agent

Eltrombopag (ELT) is a novel thrombopoietin receptor agonist for the treatment of idiopathic thrombocytopenic purpura. Previous reports indicate that ELT is mainly eliminated in the liver, although its pharmacokinetic profile has not yet been clarified in detail. The purpose of the present study is to investigate the overall elimination mechanism of ELT. After intravenous administration of ELT to rats, approximately 40% of unchanged ELT was excreted into the bile in 72 h, whereas less than 0.02% of the dose was excreted in urine, indicating that liver is the major elimination organ for ELT. The total clearance was much lower than the hepatic blood flow rate and comparable with hepatic uptake clearance obtained from integration plot analysis. Coadministration of rifampicin, an organic anion transporter inhibitor, reduced both total clearance and hepatic uptake clearance of ELT. These results suggest that hepatic uptake is the rate-limiting process in the overall elimination of ELT. To further characterize the uptake mechanism, uptake of ELT by freshly isolated mouse hepatocytes was examined. The ELT uptake showed concentration and energy dependence and was inhibited by various compounds, including not only organic anions but also organic cations. Hepatic uptake clearance in vivo was reduced by coadministration of an organic cation, tetrapentylammonium. Finally, uptake of ELT was observed in human embryonic kidney 293 cells transfected with human hepatic transporters organic anion-transporting polypeptide (OATP) 1B1 and OATP2B1 and organic cation transporter OCT1. These results suggest that multiple transporters, including organic anion transporters and organic cation transporters, are involved in hepatic ELT uptake.

Liver Volume, as Assessed by Four Ultrasonic Crystals Arranged to Form a Tetrahedron, Decreases During Anaphylactic Shock in Anesthetized Rats

We determined the hepatic volume change in anaphylactic hypotension by using four ultrasonic crystals in anesthetized rats. The hepatic volume was measured with four ultrasonic crystals arranged to form a tetrahedron on the liver surface. Before in vivo experiments, using isolated perfused rat liver preparations, we compared the measured liver volume changes with the whole-liver weight changes during hepatic blood flow rate changes and venoconstriction induced by norepinephrine. The measured relative change of the tetrahedron volume (V[utc]; percentage changes of the initial volume) was closely correlated with the liver weight change (W; percentage changes of the initial liver weight): V(utc) = 0.85W - 4.11 (r² = 0.67). Then, we measured the liver weight and the tetrahedron volume during hepatic anaphylaxis in isolated perfused liver excised from the rats sensitized with ovalbumin. An injection of the antigen into the perfusate caused anaphylactic venoconstriction, liver weight loss (1.1 ± 0.3 g; 9% ± 1%), and the tetrahedron volume reduction (12% ± 4%). Finally, we measured the liver volume change during anaphylactic hypotension in anesthetized ovalbumin-sensitized rats. When the antigen was i.v. injected into anesthetized rats, along with systemic hypotension and hepatic venoconstriction, the liver tetrahedron volume decreased by 6% ± 2% from baseline. In conclusion, we established a method to measure the hepatic volume by using four ultrasonic crystals forming a tetrahedron. Using this ultrasonic crystal method, we demonstrated that liver volume decreases during anaphylactic hypotension in anesthetized rats.

Identifying a long standing error in single-bolus determination of the hepatic extraction ratio for indocyanine green

For approximately 50 years, hepatic clearance of indocyanine green (ICG) has been used to assess liver function. Steady-state infusion of ICG with simultaneous measurement of arterial and hepatic venous ICG concentrations provides unambiguous measures of the extraction ratio for ICG and the hepatic blood flow rate, but also requires cannulation of a hepatic vein. Transient clearance following injection of a single bolus of ICG, which typically involves only measurement of arterial ICG concentration, is a more commonly used procedure. Since drawing blood from a hepatic vein is often impossible, and, in any event can be difficult, there has been considerable interest in the claim by Grainger et al. (Clin Sci 64:207-212, 1983) that a single-bolus, two-compartment model "enabled the hepatic extraction ratio (ER(ss)) of dye to be determined solely from the plasma disappearance curve". The principal purpose of this paper is to show that the claim by Grainger et al. is not valid because it ignores the fact that a finite fraction of ICG entering the liver passes directly into hepatic veins without being sequestered in the liver. A valid relationship between ER(ss) and parameters determined from single-bolus clearance data is derived in this paper. For individuals with normally functioning livers, the single-bolus method of Grainger et al. yields an extraction ratio approximately 20% too large, but in cirrhotic patients with extensive intrahepatic shunting, the extraction ratio evaluated using the single-bolus method of Grainger et al. may be too large by a factor of two.