After 50 Years of Hepatic Clearance Models, Where Should We Go from Here? Improvements and Implications for Physiologically Based Pharmacokinetic Modeling.

There is overwhelming preference for application of the unphysiologic, well-stirred model (WSM) over the parallel tube model (PTM) and dispersion model (DM) to predict hepatic drug clearance, CLH , despite that liver blood flow is dispersive and closer to the DM in nature. The reasoning is the ease in computation relating the hepatic intrinsic clearance ( CLint ), hepatic blood flow ( QH ), unbound fraction in blood ( fub ) and the transmembrane clearances ( CLin and CLef ) to CLH for the WSM. However, the WSM, being the least efficient liver model, predicts a lower EH that is associated with the in vitro CLint ( Vmax / Km ), therefore requiring scale-up to predict CLH in vivo. By contrast, the miniPTM, a three-subcompartment tank-in-series model of uniform enzymes, closely mimics the DM and yielded similar patterns for CLint versus EH , substrate concentration [S] , and KL / B , the tissue to outflow blood concentration ratio. We placed these liver models nested within physiologically based pharmacokinetic models to describe the kinetics of the flow-limited, phenolic substrate, harmol, using the WSM (single compartment) and the miniPTM and zonal liver models (ZLMs) of evenly and unevenly distributed glucuronidation and sulfation activities, respectively, to predict CLH For the same, given CLint ( Vmax and Km ), the WSM again furnished the lowest extraction ratio ( EH,WSM = 0.5) compared with the miniPTM and ZLM (>0.68). Values of EH,WSM were elevated to those for EH, PTM and EH, ZLM when the Vmax s for sulfation and glucuronidation were raised 5.7- to 1.15-fold. The miniPTM is easily manageable mathematically and should be the new normal for liver/physiologic modeling. SIGNIFICANCE STATEMENT: Selection of the proper liver clearance model impacts strongly on CLH predictions. The authors recommend use of the tank-in-series miniPTM (3 compartments mini-parallel tube model), which displays similar properties as the dispersion model (DM) in relating CLint and [ S ] to CLH as a stand-in for the DM, which best describes the liver microcirculation. The miniPTM is readily modified to accommodate enzyme and transporter zonation.

Role of ABCB1 and ABCB4 in renal and biliary excretion of perfluorooctanoic acid in mice.

BACKGROUND: Perfluorooctanoic acid (PFOA) is one of the major per- and polyfluoroalkyl substances. The role of ATP-binding cassette (ABC) transporters in PFOA toxicokinetics is unknown. METHODS: In this study, two ABC transporters, ABCB1 and ABCB4, were examined in mice with single intravenous PFOA administration (3.13 µmol/kg). To identify candidate renal PFOA transporters, we used a microarray approach to evaluate changes in gene expression of various kidney transporters in Abcb4 null mice. RESULTS: Biliary PFOA concentrations were lower in Abcb4 null mice (mean ± standard deviation: 0.25 ± 0.12 µg/mL) than in wild-type mice (0.87 ± 0.02 µg/mL). Immunohistochemically, ABCB4 expression was confirmed at the apical region of hepatocytes. However, renal clearance of PFOA was higher in Abcb4 null mice than in wild-type mice. Among 642 solute carrier and ABC transporters, 5 transporters showed significant differences in expression between wild-type and Abcb4 null mice. These candidates included two major xenobiotic transporters, multidrug resistance 1 (Abcb1) and organic anion transporter 3 (Slc22a8). Abcb1 mRNA levels were higher in Abcb4 null mice than in wild-type mice in kidney. In Abcb4 null mice, Abcb1b expression was enhanced in proximal tubules immunohistochemically, while that of Slc22a8 was not. Finally, in Abcb1a/b null mice, there was a significant decrease in the renal clearance of PFOA (0.69 ± 0.21 vs 1.1 mL ± 0.37/72 h in wild-type mice). A homology search of ABCB1 showed that several amino acids are mutated in humans compared with those in rodents and monkeys. CONCLUSIONS: These findings suggest that, in the mouse, Abcb4 and Abcb1 are excretory transporters of PFOA into bile and urine, respectively.

Novel Screening System for Biliary Excretion of Drugs Using Human Cholangiocyte Organoid Monolayers with Directional Drug Transport.

It has recently been reported that cholangiocyte organoids can be established from primary human hepatocytes. The purpose of this study was to culture the organoids in monolayers on inserts to investigate the biliary excretory capacity of drugs. Cholangiocyte organoids prepared from hepatocytes had significantly higher mRNA expression of CK19, a bile duct epithelial marker, compared to hepatocytes. The organoids also expressed mRNA for efflux transporters involved in biliary excretion of drugs, P-glycoprotein (P-gp), multidrug resistance-associated protein 2 (MRP2), and breast cancer resistance protein (BCRP). The subcellular localization of each protein was observed. These results suggest that the membrane-cultured cholangiocyte organoids are oriented with the upper side being the apical membrane side (A side, bile duct lumen side) and the lower side being the basolateral membrane side (B side, hepatocyte side), and that each efflux transporter is localized to the apical membrane side. Transport studies showed that the permeation rate from the B side to the A side was faster than from the A side to the B side for the substrates of each efflux transporter, but this directionality disappeared in the presence of inhibitor of each transporter. In conclusion, the cholangiocyte organoid monolayer system has the potential to quantitatively evaluate the biliary excretion of drugs. The results of the present study represent an unprecedented system using human cholangiocyte organoids, which may be useful as a screening model to directly quantify the contribution of biliary excretion to the clearance of drugs.

Changes in hepatic metabolic enzyme activities and biliary excretion of 4-nitrophenol in streptozotocin induced diabetic rats

Abstract Activity of hepatic metabolic enzymes of glucuronidation and sulfation of 4-nitrophenol (PNP) and biliary excretion of its glucuronide (PNP-G) and sulfate (PNP-S) conjugates have been investigated in control and streptozotocin (STZ)-induced diabetic rats. 500 µM PNP solution was luminally perfused in a cannulated jejunal loop for 90 minutes. It was found that biliary excretion of PNP-G was significantly decreased in the diabetic rats. This effect of STZ could be completely reversed by administration of rapid-acting insulin. Activity of hepatic UDP-glucuronyltransferase and ß-glucuronidase was also depressed by the STZ pretreatment. Administration of insulin antagonized the inhibitory action of STZ on UDP-glucuronyltransferase, but the reduced activity of ß-glucuronidase was not reversed. Biliary excretion of PNP-S was also depressed in the diabetic rats. Whereas, different effects of insulin administration were observed. Namely, the lower biliary excretion rate of PNP-S was not changed after administration of insulin. Activity of the sulfotransferase and the arylsulfatase enzymes was not altered either by STZ pretreatment or by insulin administration. Biliary excretion of PNP was also significantly depressed by STZ and this depression was not changed after insulin administration. The results call attention to hepatobiliary circulation of low molecular weight xenobiotics and their glucuronide and sulfate conjugates

Patients with brain metastases derived from gastrointestinal cancer: clinical characteristics and prognostic factors

Purpose. This study seeks to evaluate the natural history, outcome, and possible prognostic factors in patients with brain metastases derived from gastrointestinal cancers. Methods. The clinical features, prognostic factors, and the effects of different treatment modalities on survival were retrospectively investigated in 103 patients with brain metastases derived from gastrointestinal cancers. Results. The median time from diagnosis of primary tumor to brain metastasis was 22.00 months. The interval between diagnosis of primary tumor relapse and brain metastasis was 8.00 months. The median follow-up time was 7.80 months. The median survival time after diagnosis of brain metastases was 4.10 months for all patients and 1.17 months for patients who received only steroids (36.9 %), 3.97 months for patients who only received whole-brain radiation therapy (WBRT 31.1 %), 11.07 months for patients who received gamma-knife surgery alone or/and WBRT (20.4 %), and 13.70 months for patients who underwent surgery and radiotherapy (12 patients, 11.6 %) (P < 0.001). Multivariate analysis revealed that recursive partitioning analysis (RPA) class, extracranial metastasis, and chemotherapy were independent prognostic factors. Brain metastasis derived from gastrointestinal tract cancer is rare, and overall patient survival is poor. Conclusion. RPA class, chemotherapy after brain metastases, and treatment regimens were independent prognostic factors for the survival of patients with brain metastases derived from gastrointestinal cancers (AU)

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Bases moleculares de la función excretora de tipo hepatobiliar de la placenta / Molecular basis of excretory function placental hepatobiliary type

The liver plays an important excretory role eliminating from the body potentially toxic compounds that are xenobiotics or produced endogenously, such as bile acids and biliary pigments. This involves both transport and biotransformation processes. During intrauterine life, the inmature fetal liver cannot carry out this function. Therefore, the placenta performs a hepatobiliary-like excretory role, transferring cholephilic compounds from the fetus to the mother. The similarity of this function in the placenta and the adult liver is probably accounted for by the presence in both organs of proteins of the OATP family, involved in the uptake of organic anions across the basolateral membrane of several epithelia, and of members of the superfamily of ATP-binding cassette (ABC) proteins, which are involved in the export of substances out of many different cells. Thus, several studies have shown that, in addition to a difussional component, that may become particularly important for unconjugated bilirubin, the main mechanisms for bile acids and bilirubin transplacental transfer from the fetus to the mother are carrier-mediated transport systems, which have vectorial properties and also play an important role in the placental barrier by preventing or reducing the net flux of noxious substances from the mother to the fetus.

El hígado juega un papel determinante en la excreción de sustancias potencialmente tóxicas de origen externo o producidas por el organismo, como ácidos biliares y bilirrubina. Esta función implica tanto procesos de transporte como de biotransformación. Durante la vida intrauterina, el hígado fetal no es aún capaz de realizar esta función, por lo que es la placenta la que asume un papel excretor similar al que desempeña el sistema hepatobiliar en el adulto. La similitud entre ambas funciones se debe a la presencia en ambos órganos de proteínas transportadoras de la familia OATP, que llevan a cabo la captación de aniones orgánicos en varios epitelios, y de miembros de la superfamilia de proteínas ABC ("ATP-binding cassette"), capaces de bombear al exterior celular una gran variedad de sustancias. Estudios recientes demostraron que, además de un componente difusional, que es más relevante en el caso de la bilirrubina no conjugada, la vía mayoritaria en la transferencia placentaria de ácidos biliares y bilirrubina está mediada por sistemas de transporte que, en conjunto, presentan características de vectorialidad feto-materna, y que por ello también juegan un papel en la barrera placentaria reduciendo el flujo de sustancias nocivas desde la madre al feto.