Hepatocellular necrosis, fibrosis and microsomal activity determine the hepatic pharmacokinetics of basic drugs in right-heart-failure-induced liver damage

How predictive are isolated perfused liver data of in vivo hepatic clearance? A meta-analysis of isolated perfused rat liver data

Isolated perfused rat liver (IPRL) experiments have been used to answer clearance-related questions, including evaluating the impact of pathological and physiological processes on hepatic clearance (CLH). However, to date, IPRL data has not been evaluated for in vivo CLH prediction accuracy.In addition to a detailed overview of available IPRL literature, we present an in-depth analysis of the performance of IPRL in CLH prediction.While the entire dataset poorly predicted CLH (GAFE = 3.2; 64% within 3-fold), IPRL conducted under optimal experimental conditions, such as in the presence of plasma proteins and with a perfusion rate within 2-fold of physiological liver blood flow and corrected for unbound fraction in the presence of red blood cells, can accurately predict rat CLH (GAFE = 2.0; 78% within 3-fold). Careful consideration of experimental conditions is needed to allow proper data analysis.Further, isolated perfused liver experiments in other species, including human livers, may allow us to address the current in vitro-in vivo disconnects of hepatic metabolic clearance and improve our methodology for CLH predictions.

Hyperoside protects against heart failure-induced liver fibrosis in rats

Heart failure (HF) is an end-stage of various serious cardiovascular diseases, which causes liver injury. Hyperoside has been reported to exert protective effect on liver injury and fibrosis. However, the role and related mechanisms of hyperoside in HF-induced liver fibrosis are still unclear. In the current study, we established a model of HF via aortocaval fistula (ACF) in rats in vivo. Hyperoside treatment in ACF rats increased cardiac output, the maximum peak rate of rise/fall in left ventricular pressure (+dP/dt, -dP/dt) and LV ejection fraction (LVEF), decreased LV end-systolic pressure (LVESP), LV end-diastolic pressure (LVEDP) and LV end-systolic volume (LVESV), and reduced heart weight/body weight ratio in a dose-dependent manner. Moreover, hyperoside could attenuate liver fibrosis and injury in ACF rats, as evidenced by reduction of fibrosis area and hydroxyproline content, amelioration of edema and degeneration of liver cell vacuoles, and inhibition of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) levels. Further, α-smooth-muscle actin (α-SMA), collagen I, profibrotic factor-connective tissue growth factor (CTGF), matrix metalloproteinase-2 (MMP2) and MMP9 levels were down-regulated in hyperoside-treated ACF rats. Additionally, hyperoside inhibited the activation of TGF-β1/Smad pathway. Finally, we confirmed that hyperoside suppressed TGF-β1-mediated hepatic stellate cell activation in vitro. Collectively, hyperoside showed a suppressive role in HF-induced liver fibrosis and injury.

Hepatic Fibrosis in Dogs

Hepatic fibrosis is commonly diagnosed in dogs, often as a sequela to chronic hepatitis (CH). The development of fibrosis is a crucial event in the progression of hepatic disease that is of prognostic value. The pathophysiology of hepatic fibrosis in human patients and rodent models has been studied extensively. Although less is known about this process in dogs, evidence suggests that fibrogenic mechanisms are similar between species and that activation of hepatic stellate cells is a key step. Diagnosis and staging of hepatic fibrosis in dogs requires histopathological examination of a liver biopsy specimen. However, performing a liver biopsy is invasive and assessment of fibrotic stage is complicated by the absence of a universally accepted staging scheme in veterinary medicine. Serum biomarkers that can discriminate among different fibrosis stages are used in human patients, but such markers must be more completely evaluated in dogs before clinical use. When successful treatment of its underlying cause is feasible, reversal of hepatic fibrosis has been shown to be possible in rodent models and human patients. Reversal of fibrosis has not been well documented in dogs, but successful treatment of CH is possible. In human medicine, better understanding of the pathomechanisms of hepatic fibrosis is leading to the development of novel treatment strategies. In time, these may be applied to dogs. This article comparatively reviews the pathogenesis of hepatic fibrosis, its diagnosis, and its treatment in dogs.

Preclinical pharmacokinetic studies of 3-deazaneplanocin A, a potent epigenetic anticancer agent, and its human pharmacokinetic prediction using GastroPlus™

DZNep is a potential epigenetic drug, and exerts potent anti-proliferative and pro-apoptotic effects on broad-spectrum carcinomas via disruption of the EZH2 pathway. Antitumor studies on DZNep have been stuck in the preclinical phase because of the lack of information about its integral pharmacokinetic (PK) properties. To circumvent this problem, we extensively investigated the disposition characteristics of the DZNep in rats. By incorporating the disposition data across species into a whole-body physiologically based pharmacokinetic (PBPK) models using the GastroPlus(TM) software, we simulated human PK properties of DZNep and determined whether DZNep could be developed for human cancer therapy. Firstly, DZNep was found to cause nephrotoxicity in a dose-dependent manner in rats and its safe dose was determined to be 10mg/kg. DZNep showed a short plasma elimination half-life (1.1h) in rats, a low protein binding in plasma (18.5%), a low partitioning to erythrocyte (0.78), and a low intrinsic hepatic clearance in rats and humans. There was extensive tissue distribution and predominant renal excretion (80.3%). The simulated rat PBPK model of DZNep was well-verified with satisfactory coefficients of determination for all the tested tissues (R(2)>0.781). The simulated human PBPK model successfully identified that intravenous administration of DZNep at appropriate dosing regimen could be further developed for human non-small cell lung carcinoma treatments. The present findings provide valuable information regarding experimental or in silico PK characteristics of DZNep in rats and humans, which is helpful to guide future studies of DZNep in both preclinical and clinical phases.

Plasma concentrations of tadalafil in children with pulmonary arterial hypertension

BACKGROUND

There is no report documenting the plasma concentrations of tadalafil in children. This study was performed to evaluate the variability in the pharmacokinetics of tadalafil in children with pulmonary arterial hypertension (PAH) treated routinely with the drug.

METHODS

Plasma samples were taken twice (post- and predose) after repetitive oral administration, and the pharmacokinetic parameters (CL/F and V/F) in individual patients were estimated by the Bayesian method using the nonlinear mixed effects model. We also determined the unbound concentration of tadalafil using ultrafiltration.

RESULTS

Tadalafil was administered to 23 children aged between 0.25 and 17.4 years, with a mean age of 3.58 years. The mean (±SD) daily dose of tadalafil was 0.97 ± 0.41 mg/kg. Sixteen of the 23 children received bosentan concomitantly. The mean CL/F and V/F values of tadalafil were 0.149 L·h-1·kg-1 and 1.87 L/kg, respectively, which were higher than those reported in adults. No effects of age, bosentan, or the estimated glomerular filtration rate were observed on the CL/F value, indicating that other residual factors might account for the interindividual variability among children with PAH. The unbound tadalafil concentrations of the postdose samples ranged from 5.9 to 146 (46.9 ± 37.1) nmol/L, higher than the reported IC50 value of this phosphodiesterase-5 drug for humans (2-4 nmol/L, corresponding to 0.8-1.6 ng/mL).

CONCLUSIONS

We demonstrated variability in the total and unbound plasma concentrations of tadalafil in children. However, all children received the empirical doses of the drug; a mean dose of 0.97 mg·kg-1·d-1 showed sufficient unbound concentrations needed for half-maximal inhibition of human phosphodiesterase-5 in vitro. These observations may provide information for the proper use of tadalafil to treat children with PAH.

Effect of chronic hypoxic hypoxia on oxidation and glucuronidation of carvedilol in rats

Heart failure is accompanied with tissue (circulatory) hypoxia, and the metabolism of several drugs has been reported to be reduced in heart failure. The aim of this study was to investigate the effect of another type of respiratory hypoxia, hypoxic hypoxia (FiO2 15 % for 24 h followed by FiO2 10 % for 9 days) on the metabolism of carvedilol enantiomers in rats. Oxidation of carvedilol in rat liver microsomes was evaluated in the presence of reduced nicotinamide adenine dinucleotide phosphate, whereas glucuronidation was evaluated in the presence of UDP-glucuronic acid. Both oxidation and glucuronidation activities for two carvedilol enantiomers in hypoxic rat liver microsomes were similar to those in control rat liver microsomes. We also performed pharmacokinetic analysis of carvedilol enantiomers following intraportal infusion in control and hypoxic rats. The mean (±S.E.) portal clearance value of R- and S-carvedilol in control rats was 72 ± 16 and 156 ± 31 ml/min/kg, respectively, whereas that of the R- and S-enantiomers in hypoxic rats was 68 ± 8 and 113 ± 14 ml/min/kg, respectively. These findings indicated that the metabolism of carvedilol enantiomers was not significantly diminished in rats with chronic hypoxic hypoxia, and that other factor(s) besides hypoxia may be responsible for the reduced drug metabolism in heart failure.

Review article: prescribing medications in patients with cirrhosis - a practical guide

BACKGROUND

Most drugs have not been well studied in cirrhosis; recommendations on safe use are based largely on experience and/or expert opinion, with dosing recommendations often based on pharmacokinetic (PK) changes.

AIM

To provide a practical approach to prescribing medications for cirrhotic patients.

METHODS

An indexed MEDLINE search was conducted using keywords cirrhosis, drug-induced liver injury, pharmacodynamics (PDs), PKs, drug disposition and adverse drug reactions. Unpublished information from the Food and Drug Administration and industry was also reviewed.

RESULTS

Most medications have not been adequately studied in cirrhosis, and specific prescribing information is often lacking. Lower doses are generally recommended based on PK changes, but data are limited in terms of correlating PD effects with the degree of liver impairment. Very few drugs have been documented to have their hepatotoxicity potential enhanced by cirrhosis; most of these involve antituberculosis or antiretroviral agents used for HIV or viral hepatitis. Paracetamol can be used safely when prescribed in relatively small doses (2-3 g or less/day) for short durations, and is recommended as first-line treatment of pain. In contrast, NSAIDs should be used cautiously (or not at all) in advanced cirrhosis. Proton pump inhibitors have been linked to an increased risk of spontaneous bacterial peritonitis (SBP) in cirrhosis and should be used with care.

CONCLUSIONS

Most drugs can be used safely in cirrhosis, including those that are potentially hepatotoxic, but lower doses or reduced dosing frequency is often recommended, due to altered PKs. Drugs that can precipitate renal failure, gastrointestinal bleeding, SBP and encephalopathy should be identified and avoided.