Phenacetin O-deethylation in extrahepatic tissues of rats

Modulation of Rat Hepatic CYP1A and 2C Activity by Honokiol and Magnolol: Differential Effects on Phenacetin and Diclofenac Pharmacokinetics In Vivo

Honokiol (2-(4-hydroxy-3-prop-2-enyl-phenyl)-4-prop-2-enyl-phenol) and magnolol (4-Allyl-2-(5-allyl-2-hydroxy-phenyl)phenol) are the major active polyphenol constituents of Magnolia officinalis (Magnoliaceae) bark, which has been widely used in traditional Chinese medicine (Houpu Tang) for the treatment of various diseases, including anxiety, stress, gastrointestinal disorders, infection, and asthma. The aim of this study was to investigate the direct effects of honokiol and magnolol on hepatic CYP1A and 2C-mediated metabolism in vitro using rat liver microsomes and in vivo using the Sprague-Dawley rat model. Honokiol and magnolol inhibited in vitro CYP1A activity (probe substrate: phenacetin) more potently than CYP2C activity (probe substrate: diclofenac): The mean IC₅₀ values of honokiol for the metabolism of phenacetin and diclofenac were 8.59 μM and 44.7 μM, while those of magnolol were 19.0 μM and 47.3 μM, respectively. Notably, the systemic exposure (AUC and C_max) of phenacetin, but not of diclofenac, was markedly enhanced by the concurrent administration of intravenous honokiol or magnolol. The differential effects of the two phytochemicals on phenacetin and diclofenac in vivo pharmacokinetics could at least be partly attributed to their lower IC₅₀ values for the inhibition of phenacetin metabolism than for diclofenac metabolism. In addition, the systemic exposure, CL, and V_ss of honokiol and magnolol tended to be similar between the rat groups receiving phenacetin and diclofenac. These findings improve our understanding of CYP-mediated drug interactions with M. officinalis and its active constituents.

Preoperative Phenacetin Metabolism Test in the Prediction of Postoperative Liver Dysfunction of Patients with Hepatocellular Carcinoma

BACKGROUND The risk of postoperative liver dysfunction (PLD) in patients with injured livers, such as in hepatocellular carcinoma (HCC), is still not negligible. Phenacetin metabolism test can reflect hepatic functional reserve in patients with chronic hepatic damage. The aim of this study was to assess the ability of phenacetin metabolism test to predict PLD in patients with HCC receiving partial hepatectomy. MATERIAL AND METHODS Forty-nine patients with HCC undergoing partial hepatectomy between 2014 and 2016 were included at Huashan Hospital, Fudan University. The phenacetin metabolism test was used to assess the hepatic functional reserve. The ratio of total plasma paracetamol to phenacetin was collected in patients at 2 h after oral administration of 1.0 g phenacetin, recorded 5 days prior to surgery and on the fifth postoperative day. Phenacetin metabolism test, Child-Pugh classification, and Model for End-Stage Liver Disease (MELD) score were correlated with PLD. RESULTS Of 49 patients with HCC, 13 patients (26.5%) had PLD. The association between the ratio of total plasma paracetamol to phenacetin and PLD was statistically significant (p=0.0061) and the correlation coefficient was -0.647 (p=0.0082). The phenacetin metabolism test showed a larger area under the receiver operating characteristic (ROC) curve value (0.735) than Child-Pugh's classification (0.472) and MELD score (0.419). Using the calculated cutoff of 0.6, the lower ratio of total plasma paracetamol to phenacetin preoperatively was chosen to specifically identify patients with PLD. The sensitivity and specificity were 0.657 and 0.892, respectively. CONCLUSIONS Phenacetin metabolism test could be preoperatively used in predicting PLD in HCC patients receiving partial hepatectomy. It potentially provides better prediction than Child-Pugh classification and MELD score.

Predicting Drug Extraction in the Human Gut Wall: Assessing Contributions from Drug Metabolizing Enzymes and Transporter Proteins using Preclinical Models

Intestinal metabolism can limit oral bioavailability of drugs and increase the risk of drug interactions. It is therefore important to be able to predict and quantify it in drug discovery and early development. In recent years, a plethora of models-in vivo, in situ and in vitro-have been discussed in the literature. The primary objective of this review is to summarize the current knowledge in the quantitative prediction of gut-wall metabolism. As well as discussing the successes of current models for intestinal metabolism, the challenges in the establishment of good preclinical models are highlighted, including species differences in the isoforms; regional abundances and activities of drug metabolizing enzymes; the interplay of enzyme-transporter proteins; and lack of knowledge on enzyme abundances and availability of empirical scaling factors. Due to its broad specificity and high abundance in the intestine, CYP3A is the enzyme that is frequently implicated in human gut metabolism and is therefore the major focus of this review. A strategy to assess the impact of gut wall metabolism on oral bioavailability during drug discovery and early development phases is presented. Current gaps in the mechanistic understanding and the prediction of gut metabolism are highlighted, with suggestions on how they can be overcome in the future.

Phenacetin O-deethylation is a useful tool for evaluation of hepatic functional reserve in rats with CCl(4)-induced chronic liver injury

BACKGROUND

Mortality of liver resection is as high as 3.1% to 25% in patients with chronic liver disease. Evaluation of hepatic functional reserve is critical for the prediction of risk of postoperation death. Phenacetin O-deethylation is a marker reaction of cytochrome P4501A2 (CYP1A2) activity. In this study, our aim is to investigate whether phenacetin O-deethylation is a useful tool for the evaluation of hepatic functional reserve in rats with chronic liver injury.

MATERIALS AND METHODS

Rat model for chronic liver injury was established by subcutaneous administration of 50% CCl(4), 1 mL/kg twice per week for 12 wk. Hepatic CYP1A2 activity, content, and mRNA expression were determined (n = 10). Effects of 15%, 30%, and 45% hepatectomy on phenacetin O-deethylation were evaluated in the rats (n = 5 in each group). Additionally, the correlation of risk of death after 70% hepatectomy with phenacetin O-deethylation was studied in 27 rats with chronic liver injury.

RESULTS

Compared with normal controls, CYP1A2 activity, content, and mRNA expression decreased 33%, 60%, and 50% in the rats with chronic liver injury (P < 0.05), respectively. Following the increasing of liver-resected size, CYP1A2 activity decreased proportionally (r(s) = -0.877, P < 0.05). Six of 27 rats with chronic liver injury died within 7 d after 70% hepatectomy. Phenacetin metabolism was impaired more severely in 6 rats that died than in 21 living rats (P < 0.05).

CONCLUSIONS

Phenacetin O-deethylation is a useful tool for the evaluation of hepatic functional reserve in the rats with CCl(4)-induced chronic liver injury.

In-vitro and in-vivo evaluations of cytochrome P450 1A2 interactions with nuciferine

OBJECTIVES

The effects of nuciferine, a major active aporphine alkaloid from the leaves of Nelumbo nucifera Gaertn, on a cytochrome P450 1A2 (CYP1A2) probe substrate were investigated in vitro and in vivo.

METHODS

Nuciferine and recombinant human CYP1A2 were incubated together to study the impact of nuciferine on CYP1A2 in vitro. Nuciferine was administered orally to Wistar rats at a dose of 20 mg/kg to further estimate the impact of nuciferine on CYP1A2 in vivo. A probe substrate, phenacetin, was used to index the activity of CYP1A2.

KEY FINDINGS

The IC50 value for nuciferine was determined to be 2.12 mmol/l. When phenacetin was intravenously coadministered with nuciferine compared with phenacetin alone, the elimination rate constant and total body clearance of phenacetin were decreased by 24.0% (P < 0.01) and 43.0% (P < 0.05), respectively. The mean residence time, apparent elimination half-time and area under the plasma concentration-time curve were increased by 22% (P < 0.005), 26.9% (P < 0.02) and 74.6% (P < 0.05), respectively. Similarly, when phenacetin was coadministered orally with nuciferine, the apparent elimination half-time in the nuciferine pretreated group was increased by 16.7% (P < 0.05) and the elimination rate constant was decreased by 15.4% (P < 0.05).

CONCLUSIONS

The results suggest that nuciferine inhibited CYP1A2 activity in vitro and caused changes in the pharmacokinetic parameters of phenacetin in vivo.

Activity of sulfotransferase 1A1 is dramatically upregulated in patients with hepatocellular carcinoma secondary to chronic hepatitis B virus infection

The phase I metabolizing enzyme and phase II metabolizing enzyme play vital roles in carcinogenesis, but little is known about the changes of their activities in patients with hepatocellular carcinoma (HCC) secondary to chronic hepatitis B virus (HBV) infection. In this study phenacetin, a probe drug (1 g for men and 0.85 g for women orally), was applied for the detection of sulfotransferase 1A1 (SULT1A1) and cytochrome P4501A2 (CYP1A2) activities in 82 healthy participants and 148 HCC, 106 cirrhosis, and 41 chronic hepatitis B patients. In addition, a prospective cohort study for susceptibility to HCC was performed in 205 patients with cirrhosis secondary to chronic HBV infection. Compared with the healthy participants, SLUT1A1 activity increased by 9.7-fold in the HCC patients (P < 0.01). CYP1A2 activity did not significantly differ between the healthy participants and HCC patients. CYP1A2 activity decreased by 91.2% (P < 0.01) and 67.7% (P < 0.05) in the patients with cirrhosis and chronic hepatitis B, respectively; SULT1A1 activity did not increase significantly. During an approximate 2-year follow up, three of the 46 cirrhosis patients with elevated SULT1A1 activity and normal CYP1A2 activity developed HCC, but none of the 159 cirrhosis patients used as parallel controls did (P = 0.012). These results indicate that SLUT1A1 activity is dramatically upregulated in patients with HCC secondary to chronic HBV infection. The upregulation of SULT1A1 activity is not caused by the tumor itself. The interaction between SULT1A1 and CYP1A2 can play an important role in hepatocarcinogenesis in the Chinese population.

Conjugation metabolism of acetaminophen and bilirubin in extrahepatic tissues of rats

An anhepatic rat model was used to explore the extrahepatic conjugating metabolism of acetaminophen and serum bilirubin. The recovery of glucuronide- and sulfate-acetaminophen was 47.5% in normal control and 13.4% in model rats in the urine collected for 6 h after administration of acetaminophen 20 mg kg(-1). Following the increase of acetaminophen dose to 150 mg kg(-1), the recovery of urinary glucuronide-acetaminophen increased by 53.9% in normal control; but it decreased by 36.4% in model rats. In contrast to normal control, the pretreatment with phenobarbital did not affect acetaminophen and its metabolite levels in plasma and urine in model rats. After the establishment of anhepatic model the serum direct bilirubin rose dramatically. Urinary bilirubin test was positive in model rats, but not in normal control. No changes were observed in serum total bilirubin and ratio of direct/total bilirubin after the pretreatment with ranitidine or phenobarbital 50 mg kg (-1), i.p. for 5 days in model rats. The results indicate that the glucuronide- and sulfate-acetaminophen formed in the extrahepatic tissues of model rats is 28.2% of normal control, serum free bilirubin can be transformed into conjugated bilirubin in extrahepatic tissues, and the regulation mechanism of phase II conjugating enzymes is different between the hepatic and extrahepatic tissues.