Elucidation of plasma protein binding, blood partitioning, permeability, CYP phenotyping and CYP inhibition studies of Withanone using validated UPLC method: An active constituent of neuroprotective herb Ashwagandha

ETHNOPHARMACOLOGICAL RELEVANCE

Withanone (WN), an active constituent of Withania somnifera commonly called Ashwagandha has remarkable pharmacological responses along with neurological activities. However, for a better understanding of the pharmacokinetic and pharmacodynamic behavior of WN, a comprehensive in-vitro ADME (absorption, distribution, metabolism, and excretion) studies are necessary.

AIM OF THE STUDY

A precise, accurate, and sensitive reverse-phase ultra-performance liquid chromatographic method of WN was developed and validated in rat plasma for the first time. The developed method was successfully applied to the in-vitro ADME investigation of WN.

MATERIAL AND METHODS

The passive permeability of WN was assayed using PAMPA plates and the plasma protein binding (PPB) was performed using the equilibrium dialysis method. Pooled liver microsomes of rat (RLM) and human (HLM) were used for the microsomal stability, CYP phenotyping, and inhibition studies. CYP phenotyping was evaluated using the specific inhibitors. CYP inhibition study was performed using specific probe substrates along with WN or specific inhibitors.

RESULTS

WN was found to be stable in the simulated gastric and intestinal environment and has a high passive permeability at pH 4.0 and 7.0 in PAMPA assay. The PPB of WN at 5 and 20 μg/mL concentrations were found to be high i.e. 82.01 ± 1.44 and 88.02 ± 1.15%, respectively. The in vitro half-life of WN in RLM and HLM was found to be 59.63 ± 2.50 and 68.42 ± 2.19 min, respectively. CYP phenotyping results showed that WN was extensively metabolized by CYP 3A4 and1A2 enzymes in RLM and HLM. However, the results of CYP Inhibition studies showed that none of the CYP isoenzymes were potentially inhibited by WN in RLM and HLM.

CONCLUSION

The in vitro results of pH-dependent stability, plasma stability, permeability, PPB, blood partitioning, microsomal stability, CYP phenotyping, and CYP inhibition studies demonstrated that WN could be a better phytochemical for neurological disorders.

Use of hepatocytes isolated from a liver-humanized mouse for studies on the metabolism of drugs: application to the metabolism of fentanyl and acetylfentanyl

Purpose

The usefulness of hepatocytes isolated from a liver-humanized mouse (PXB-cells) as a model in vitro system for the prediction of the in vivo metabolism of new drugs of abuse was evaluated.

Methods

For the drug metabolism study, fentanyl, a powerful synthetic opioid, and acetylfentanyl, an N-acetyl analog of fentanyl, were selected as model drugs. PXB-cells were cultured with the drug for 24–48 h and then the media were collected and analyzed by liquid chromatography/mass spectrometry after deproteinization with acetonitrile.

Results

The main metabolite formed from fentanyl by PXB-cells was the desphenethylated metabolite (nor-fentanyl), and the other major metabolites formed were 4′-hydroxy-fentanyl, β-hydroxy-fentanyl and (ω-1)-hydroxy-fentanyl. ω-Hydroxy-fentanyl and 4′-hydroxy-3′-methoxy-fentanyl were the minor metabolites. Similar results were obtained for acetylfentanyl. The metabolite profile of fentanyl in PXB-cells was consistent with the in vivo metabolite profile of fentanyl reported previously. Most of the 4′-hydroxy- and 4′-hydroxy-3′-methoxy-metabolites of fentanyl and acetylfentanyl were conjugated in PXB-cells, indicating that PXB-cells had high conjugation enzyme activities. From experiments using human liver microsomes and anti-CYP antibodies, it was revealed that CYP3A4 was involved in the production of nor-fentanyl, β-hydroxy-fentanyl and (ω-1)-hydroxy-fentanyl, while CYP2D6 was partially involved in the production of 4′-hydroxy-fentanyl.

Conclusions

Our results indicated that PXB-cells have high activities of phase I and phase II drug-metabolizing-enzymes, can be stably supplied, and are easy to use; thus, PXB-cells are highly useful for the prediction of the in vivo metabolism of drugs of abuse.