Simultaneous quantification of tizoxanide and tizoxanide glucuronide in mouse plasma by liquid chromatography-tandem mass spectrometry

Glucuronidation of tizoxanide, an active metabolite of nitazoxanide, in liver and small intestine: Species differences in humans, monkeys, dogs, rats, and mice and responsible UDP-glucuronosyltransferase isoforms in humans

Tizoxanide (TZX) is an active metabolite of nitazoxanide (NTZ) originally developed as an antiparasitic agent, and is predominantly metabolized into TZX glucuronide. In the present study, TZX glucuronidation by the liver and intestinal microsomes of humans, monkeys, dogs, rats, and mice, and recombinant human UDP-glucuronosyltransferase (UGT) were examined. The kinetics of TZX glucuronidation by the liver and intestinal microsomes followed the Michaelis-Menten or biphasic model, with species-specific variations in the intrinsic clearance (CLint). Rats and mice exhibited the highest CLint values for liver microsomes, while mice and rats were the highest for intestinal microsomes. Among human UGTs, UGT1A1 and UGT1A8 demonstrated significant glucuronidation activity. Estradiol and emodin inhibited TZX glucuronidation activities in the human liver and intestinal microsomes in a dose-dependent manner, with emodin showing stronger inhibition in the intestinal microsomes. These results suggest that the roles of UGT enzymes in TZX glucuronidation in the liver and small intestine differ extensively across species and that UGT1A1 and/or UGT1A8 mainly contribute to the metabolism and elimination of TZX in humans. This study presents the relevant and novel-appreciative report on TZX metabolism catalyzed by UGT enzymes, which may aid in the assessment of the antiparasitic, antibacterial, and antiviral activities of NTZ for the treatment of various infections.

Quantitation of tizoxanide in multiple matrices to support cell culture, animal and human research

Currently nitazoxanide is being assessed as a candidate therapeutic for SARS-CoV-2. Nitazoxanide is rapidly broken down to its active metabolite tizoxanide upon administration. Unlike many other candidates being investigated, tizoxanide plasma concentrations achieve antiviral levels after administration of the approved dose, although higher doses are expected to be needed to maintain these concentrations across the dosing interval in the majority of patients. Here an LC-MS/MS assay is described that has been validated in accordance with Food and Drug Administration (FDA) guidelines. Fundamental parameters have been evaluated, and these included accuracy, precision and sensitivity. The assay was validated for human plasma, mouse plasma and Dulbecco's Modified Eagles Medium (DMEM) containing varying concentrations of Foetal Bovine Serum (FBS). Matrix effects are a well-documented source of concern for chromatographic analysis, with the potential to impact various stages of the analytical process, including suppression or enhancement of ionisation. Herein a validated LC-MS/MS analytical method is presented capable of quantifying tizoxanide in multiple matrices with minimal impact of matrix effects. The validated assay presented here was linear from 15.6 ng/mL to 1000 ng/mL. The presented assay here has applications in both pre-clinical and clinical research and may be used to facilitate further investigations into the application of nitazoxanide against SARS-CoV-2.

Analysis of tizoxanide, active metabolite of nitazoxanide, in rat brain tissue and plasma by UHPLC-MS/MS

Tizoxanide, the active metabolite of nitazoxanide, has recently been reported as an effective agent for the treatment of glioma. As there had been no report about the analysis of tizoxanide in brain tissue, we established extraction and UHPLC-MS/MS methods to quantify tizoxanide in rat brain and plasma to evaluate the brain-to-plasma ratio of tizoxanide. The biological samples were mainly prepared by acetonitrile and the separation was performed on a Waters XBridge® BEH C₁₈ column. The mobile phase was composed of water mixed with 10 mm ammonium formate (pH 3.0) and acetonitrile according a gradient volume. Tizoxanide and topiramate (internal standard) were monitored utilizing negative electron spray ionization in multiple reaction monitoring mode. The methods were validated to be precise and accurate within the dynamic range of 5-1000 ng/mL and 0.2-50 ng/g for plasma and brain tissue samples, respectively. The lower limit of quantitation of the method was 0.2 ng/g, which was far more sensitive than all existing methods to quantify tizoxanide in biological samples. Application performed on rats exhibited that the brain-to-plasma ratio of tizoxanide ranged from 3.16 to 26.86% in 1 h after administration of 10 mg/kg nitazoxanide.