Automation and Miniaturization of the Bioluminescent UGT-Glo Assay for Screening of UDP-Glucuronosyltransferase Inhibition by Various Compounds

Exploring the Chemical Space of Proluciferins as Probe Substrates for Human Cytochrome P450 Enzymes

We report the synthesis of 21 new proluciferin compounds that bear a small aliphatic ether group connected to the 6' hydroxy function of firefly luciferin and either contain an acid or methyl ester function at the dihydrothiazole ring. Each of these compounds was found to be a substrate for some members of the human CYP1 and CYP3 families; a total of 92 new enzyme-substrate pairs were identified. In a screen of the whole human P450 complement (CYPome) with three selected proluciferin acid substrates, another 13 enzyme-substrate pairs were detected, which involve enzymes belonging to the CYP2, CYP4, CYP7, CYP21, and CYP27 families. All in all, we identified new probe substrates for members of seven out of 18 human CYP families.

Evaluating Chemicals for Thyroid Disruption: Opportunities and Challenges with in Vitro Testing and Adverse Outcome Pathway Approaches

BACKGROUND

Extensive clinical and experimental research documents the potential for chemical disruption of thyroid hormone (TH) signaling through multiple molecular targets. Perturbation of TH signaling can lead to abnormal brain development, cognitive impairments, and other adverse outcomes in humans and wildlife. To increase chemical safety screening efficiency and reduce vertebrate animal testing, in vitro assays that identify chemical interactions with molecular targets of the thyroid system have been developed and implemented.

OBJECTIVES

We present an adverse outcome pathway (AOP) network to link data derived from in vitro assays that measure chemical interactions with thyroid molecular targets to downstream events and adverse outcomes traditionally derived from in vivo testing. We examine the role of new in vitro technologies, in the context of the AOP network, in facilitating consideration of several important regulatory and biological challenges in characterizing chemicals that exert effects through a thyroid mechanism.

DISCUSSION

There is a substantial body of knowledge describing chemical effects on molecular and physiological regulation of TH signaling and associated adverse outcomes. Until recently, few alternative nonanimal assays were available to interrogate chemical effects on TH signaling. With the development of these new tools, screening large libraries of chemicals for interactions with molecular targets of the thyroid is now possible. Measuring early chemical interactions with targets in the thyroid pathway provides a means of linking adverse outcomes, which may be influenced by many biological processes, to a thyroid mechanism. However, the use of in vitro assays beyond chemical screening is complicated by continuing limits in our knowledge of TH signaling in important life stages and tissues, such as during fetal brain development. Nonetheless, the thyroid AOP network provides an ideal tool for defining causal linkages of a chemical exerting thyroid-dependent effects and identifying research needs to quantify these effects in support of regulatory decision making. https://doi.org/10.1289/EHP5297.

The Effect of Piperine Pro-Nano Lipospheres on Direct Intestinal Phase II Metabolism: The Raloxifene Paradigm of Enhanced Oral Bioavailability

Phase II biotransformation reactions have been gaining more attention due to their acknowledged significance in drug bioavailability, drug development, and drug-drug interactions. However, the predominant role of phase I metabolism has always overshadowed phase II metabolism, resulting in insufficient data regarding its mechanisms. In this paper, we investigate the effect of an advanced lipid based formulation on the phase II metabolism process of glucuronidation, occuring in the enterocytes monolayer. The investigated formulation is a self-emulsifying drug delivery system, termed pro-nano lipospheres, which contains the natural absorption enhancer piperine. To evaluate the effect of this formulation on direct glucuronidation we chose the model molecule raloxifene. First, glucuronidation is the main clearance pathway of this compound without involvement of preceding mechanisms. Second, raloxifene's extensive glucuronidation site is primarily at the intestine. Raloxifene's oral bioavailability was determined in a series of pharmacokinetic experiments using the freely moving rat model. In order to test the effect of the formulation on the relevant UGT enzymes reported in the clinic, we used the in vitro method of UGT-Glo Assay. Coadministration of raloxifene and piperine pro-nano lipospheres to rats resulted in a 2-fold increase in the relative oral bioavailability of raloxifene. However, coadministration of raloxifene with blank pro-nano lipospheres had no effect on its oral bioavailability. In contrast to the difference found in vivo between the two vehicles, both formulations extended an inhibitory effect on UGT enzymes in vitro. Ultimately, these findings prove the ability of the formulation to diminish intestinal direct phase II metabolism which serves as an absorption obstacle for many of today's marketed drugs. Pro-nano lipospheres is a formulation that serves as a platform for the simultaneous delivery of the absorption enhancer and a required drug. The discrepancy found between the in vivo and in vitro models demonstrates that the in vitro method may not be sensitive enough to distinguish the difference between the formulations.

Screening of six UGT enzyme activities in human liver microsomes using liquid chromatography/triple quadrupole mass spectrometry

RATIONALE

Uridine 5'-diphosphoglucuronosyltransferase (UGT) enzymes are essential for the clearance of many drugs; however, altered UGT activity is a potential cause of adverse drug-drug interactions (DDI). The early detection of potential DDI is an important aspect of drug discovery that has led to the development of new screening methods for drug interactions. We developed a screening method for the simultaneous evaluation of six human liver UGT enzyme activites using in vitro cocktail incubation and tandem mass spectrometry.

METHODS

The two in vitro cocktail doses were developed to minimize drug interactions among substrates. The method is based on liquid chromatography/tandem mass spectrometry (LC/MS/MS). Electrospray ionization (ESI) in both positive and negative modes was used to quantify the metabolites and the diagnostic loss of the glucuronosyl moiety to form the aglycone product was estimated using the selected reaction monitoring (SRM) mode.

RESULTS

The method was validated by comparing inhibition data obtained from the incubation of each individual probe substrate alone with data from the cocktail method. The intra- and inter-day accuracy and precision data for the six UGT metabolites ranged from 92.2 to 100.3% and less than 15.2%, respectively. The IC(50) values showed no significant differences between individual and cocktail incubations.

CONCLUSIONS

As a screening technique for inhibitory interactions of these six human liver UGT enzymes, this method will be useful for advancing mechanistic understanding of drug interactions.