Metabolic profiles of coumarin in human plasma extrapolated from a rat data set with a simplified physiologically based pharmacokinetic model

A New Version of the Tissue Composition-Based Model for Improving the Mechanism-Based Prediction of Volume of Distribution at Steady-State for Neutral Drugs

In-vitro models are available in the literature for predicting the volume of distribution at steady-state (Vdss) of drugs. The mechanistic model refers to the tissue composition-based model (TCM), which includes important factors that govern Vdss such as drug physiochemistry and physiological data. The recognized TCM published by Rodgers and Rowland (TCM-RR) and a subsequent adjustment made by Simulations Plus Inc. (TCM-SP) have been shown to be generally less accurate with neutral compared to ionized drugs. Therefore, improving these models for neutral drugs becomes necessary. The objective of this study was to propose a new TCM for improving the prediction of Vdss for neutral drugs. The new TCM included two modifications of the published models (i) accentuate the effect of the blood-to-plasma ratio (BPR) that should cover permeated molecules across the biomembranes, which is lacking in these models for neutral compounds, and (ii) use a different approach to estimate the binding in tissues. The new TCM was validated with a large dataset of 202 commercial and proprietary compounds including preclinical and clinical data. All scenario datasets were predicted more accurately with the TCM-New, whereas all statistical parameters indicate that the TCM-New showed significant improvements in terms of accuracy over the TCM-RR and TCM-SP. Predictions of Vdss were frequently more accurate for the TCM-new with 83% within twofold error versus only 50% for the TCM-RR. And more than 95% of the predictions were within threefold error and patient interindividual differences can be predicted with the TCM-New, greatly exceeding the accuracy of the published models. Overall, the new TCM incorporating BPR significantly improved the Vdss predictions in animals and humans for neutral drugs, and, hence, has the potential to better support the drug discovery and facilitate the first-in-human predictions.

Combined Risk Assessment of Food-derived Coumarin with <i>in Silico</i> Approaches

Hepatotoxicity associated with food-derived coumarin occurs occasionally in humans. We have, herein, assessed the data of existing clinical and nonclinical studies as well as those of in silico models for humans in order to shed more light on this association. The average intakes of food-derived coumarin are estimated to be 1−3 mg/day, while a ten-times higher level is expected in the worst-case scenarios. These levels are close to or above the tolerable daily intake suggested by a chronic study in dogs. The human internal exposure levels were estimated by a physiologically-based pharmacokinetic model with the use of virtual doses of coumarin in the amounts expected to derive from foods. Our results suggest that: (i) coumarin can be cleared rapidly via 7-hydroxylation in humans, and (ii) the plasma levels of coumarin and of its metabolite, o-hydroxyphenylacetic acid associated with hepatotoxicity, are considerably lower than those yielding hepatotoxicity in rats. Pharmacokinetic data suggest a low or negligible concern regarding a coumarin-induced hepatotoxicity in humans exposed to an average intake from foods. Detoxification of coumarin through the 7-hydroxylation, however, might vary among individuals due to genetic polymorphisms in CYP2A6 enzyme. In addition, the CYP1A2- and CYP2E1-mediated activation of coumarin can fluctuate as a result of induction caused by environmental factors. Furthermore, the daily consumption of food-contained coumarin was implicated in the potential risk of hepatotoxicity by the drug-induced liver injury score model developed by the US Food and Drug Administration. These results support the idea of the existence of human subpopulations that are highly sensitive to coumarin; therefore, a more precise risk assessment is needed. The present study also highlights the usefulness of in silico approaches of pharmacokinetics with the liver injury score model as battery components of a risk assessment.

Plasma concentration profiles for hepatotoxic pyrrolizidine alkaloid senkirkine in humans extrapolated from rat data sets using a simplified physiologically based pharmacokinetic model

AIM

The main aim of the current study was to obtain forward dosimetry assessments of pyrrolizidine alkaloid senkirkine plasma and liver concentrations by setting up a human physiologically based pharmacokinetic (PBPK) model based on the limited information available.

BACKGROUND

The risks associated with plant-derived pyrrolizidine alkaloids as natural toxins have been assessed.

OBJECTIVE

The pyrrolizidine alkaloid senkirkine was investigated because it was analyzed in a European transcriptomics study of natural hepatotoxins and in a study of the alkaloidal constituents of traditional Japanese food plants Petasites japonicus. The in silico human plasma and liver concentrations of senkirkine were modeled using doses reported for acute-term toxicity in humans.

METHODS

Using a simplified PBPK model established using rat pharmacokinetic data, forward dosimetry was conducted. Since in vitro rat and human intrinsic hepatic clearances were similar; an allometric scaling approach was applied to rat parameters to create a human PBPK model.

RESULTS

After oral administration of 1.0 mg/kg in rats in vivo, water-soluble senkirkine was absorbed and cleared from plasma to two orders of magnitude below the maximum concentration in 8 h. Human in silico senkirkine plasma concentration curves were generated after virtual daily oral administrations of 3.0 mg/kg senkirkine (the dose involved in an acute fatal hepatotoxicity case). A high concentration of senkirkine in the culture medium caused in vitro hepatotoxicity as evidenced by lactate dehydrogenase leakage from human hepatocyte-like HepaRG cells.

CONCLUSION

Higher virtual concentrations of senkirkine in human liver and plasma than those in rat plasma were estimated using the current rat and human PBPK models. Current simulations suggest that if P. japonicus (a water-soluble pyrrolizidine alkaloid-producing plant) is ingested daily as food, hepatotoxic senkirkine could be continuously present in human plasma and liver.

Pharmacokinetics of primary metabolites 5-hydroxythalidomide and 5'-hydroxythalidomide formed after oral administration of thalidomide in the rabbit, a thalidomide-sensitive species

The teratogenicity of the chemotherapeutic drug thalidomide is species-specific and affects humans, non-human primates, and rabbits. The primary oxidation of thalidomide in previously investigated rodents predominantly resulted in the formation of deactivated 5'-hydroxythalidomide. In the current study, similar in vivo biotransformations to 5-hydroxythalidomide and 5'-hydroxythalidomide were confirmed by the analysis of blood plasma from male rabbits, a thalidomide-sensitive species, after oral administration of thalidomide (2.0 mg/kg). Similar levels of thalidomide in seminal plasma and in blood plasma were detected using liquid chromatography-tandem mass spectrometry at 4 hr and 7 hr after oral doses in male rabbits. Seminal plasma concentrations of 5-hydroxythalidomide and 5'-hydroxythalidomide were also seen in male rabbits in a roughly similar time-dependent manner to those in the blood plasma after oral doses of thalidomide (2.0 mg/kg). Furthermore, the values generated by a simplified physiologically based pharmacokinetic rabbit model were in agreement with the measured in vivo blood plasma data under metabolic ratios of 0.01 for the hepatic intrinsic clearance of thalidomide to both unconjugated 5-hydroxythalidomide and 5'-hydroxythalidomide. These results suggest that metabolic activation of thalidomide may be dependent on rabbit liver enzymes just it was for cytochrome P450 enzymes in humanized-liver mice; in contrast, rodent livers predominantly mediate biotransformation of thalidomide to 5'-hydroxythalidomide. A developmental toxicity test system with experimental animals that involves intravaginal exposures to the chemotherapeutic drug thalidomide via semen should be considered in the future.

Metabolic profiles for the pyrrolizidine alkaloid neopetasitenine and its metabolite petasitenine in humans extrapolated from rat in vivo and in vitro data sets using a simplified physiologically based pharmacokinetic model

Naturally occurring food substances may constitute safety hazards. The risks associated with plant-derived pyrrolizidine alkaloids have been extensively evaluated. Petasites japonicus (common Japanese name, fuki) is a widely consumed water-soluble pyrrolizidine alkaloid-producing plant. In this study, neopetasitenine (acetylfukinotoxin) was selected as a model food substrate (for which human pharmacokinetics were estimated) because of its high concentration in fuki, along with petasitenine (fukinotoxin), its carcinogenic deacetylated metabolite. Although neopetasitenine was rapidly absorbed and converted to petasitenine after oral administration of 1.0 mg/kg in rats, petasitenine was slowly cleared from plasma. Forward dosimetry was conducted using in silico simplified physiologically based pharmacokinetic (PBPK) modeling formulated on experimental pharmacokinetic rat data. From ~2 hr after the oral administration of neopetasitenine in rats, the plasma concentrations of petasitenine were higher than those of neopetasitenine under the present conditions. A human PBPK model was established following an allometric scaling approach applied to rat parameters (without considering interspecies factors) to estimate human intrinsic hepatic clearances from empirical rat values. Human in silico neopetasitenine and petasitenine plasma concentration curves were simulated after daily oral administrations of 3.0 and 1.3 mg/kg neopetasitenine. These doses were taken from reported acute/short-term cases of pyrrolizidine alkaloid toxicity. In vitro hepatotoxicity of neopetasitenine and petasitenine was caused by their high concentrations in the medium for human hepatocyte-like cell line HepaRG cells as an index of lactate dehydrogenase leakage. Neopetasitenine was estimated to be rapidly absorbed and converted to deacetylated carcinogenic petasitenine, even after hepatotoxic doses of 1.0 mg/kg in humans. If the water-soluble pyrrolizidine alkaloid-producing plant P. japonicus were daily consumed as food, current simulation results suggest that dangerous amounts of deacetylated petasitenine could be continuously present in human plasma.

In Silico Screening of Natural Products Isolated from Mexican Herbal Medicines against COVID-19

The COVID-19 pandemic has already taken the lives of more than 2 million people worldwide, causing several political and socio-economic disturbances in our daily life. At the time of publication, there are non-effective pharmacological treatments, and vaccine distribution represents an important challenge for all countries. In this sense, research for novel molecules becomes essential to develop treatments against the SARS-CoV-2 virus. In this context, Mexican natural products have proven to be quite useful for drug development; therefore, in the present study, we perform an in silico screening of 100 compounds isolated from the most commonly used Mexican plants, against the SARS-CoV-2 virus. As results, we identify ten compounds that meet leadlikeness criteria (emodin anthrone, kaempferol, quercetin, aesculin, cichoriin, luteolin, matricin, riolozatrione, monocaffeoyl tartaric acid, aucubin). According to the docking analysis, only three compounds target the key proteins of SARS-CoV-2 (quercetin, riolozatrione and cichoriin), but only one appears to be safe (cichoriin). ADME (absorption, distribution, metabolism and excretion) properties and the physiologically based pharmacokinetic (PBPK) model show that cichoriin reaches higher lung levels (100 mg/Kg, IV); therefore, it may be considered in developing therapeutic tools.

Metabolic activation and deactivation of dietary-derived coumarin mediated by cytochrome P450 enzymes in rat and human liver preparations

Dietary-derived coumarin is of clinical interest for its potential hepatotoxicity in humans because such toxicity is especially evident in rats. In this study, the oxidative metabolism of coumarin to active coumarin 3,4-epoxide (as judged by the formation rates of o-hydroxyphenylacetic acid) and excretable 7-hydroxycoumarin was investigated in liver fractions from rats and humans. In rat liver microsomes, the formation rate of o-hydroxyphenylacetic acid (~6 pmol/min/mg microsomal protein) from coumarin at 10 μM was dependent on the presence of liver cytosolic fractions. Rat hepatocytes mediated similar formation rates of o-hydroxyphenylacetic acid and 7-hydroxycoumarin (~0.1 nmol/hr/10⁶ cells) at 0.20-20 μM coumarin. Human hepatocytes mediated the biotransformation of coumarin to o-hydroxyphenylacetic acid at roughly similar rates to those of rat hepatocytes. In contrast, the formation rates of 7-hydroxycoumarin by human hepatocytes were around 10-fold higher at ~1 nmol/hr/10⁶ cells. In the presence of human liver cytosolic fractions, the oxidative formation rate of o-hydroxyphenylacetic acid was relatively high in cytochrome P450 (P450) 1A2-rich human liver microsomes. The inhibitory effects of furafylline/α-naphthoflavone and 8-methoxypsoralen, P450 1A2 and 2A6 inhibitors, respectively, were seen on the rates of o-hydroxyphenylacetic and 7-hydroxylation formations, respectively, in pooled human liver microsomes. Human liver microsomes selectively inactivated for P450 1A2 and 2A6 showed low rates of o-hydroxyphenylacetic acid and 7-hydroxylation formation (~20-30% of control), respectively. Among the P450 isoforms tested, recombinant human P450 1A2 predominantly mediated o-hydroxyphenylacetic formation. These results suggested that the metabolic activation and deactivation of coumarin were mediated mainly by P450 1A2 and 2A6 enzymes, respectively. The metabolic oxidation of coumarin via 3,4-epoxidation forming o-hydroxyphenylacetic acid could inform individual human risk assessments of dietary-derived coumarin, for which hepatotoxicity is especially evident in rats.