Methods for Measuring Cysteine <i>S</i>‐Conjugate β‐Lyase Activity

Lash, Lawrence H.

doi:10.1002/0471140856.tx0613s34

Cited by 1 publication

(1 citation statement)

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“…β-Lyase-mediated cleavage of 1123-CYS was monitored based on the method described by Lash ( 2007 ) with the following modifications. Spectrometric studies were carried out with a SpectraMax ® Plus 384 Microplate Reader (Molecular Devices, San José, USA) operating at a wavelength of 340 nm.…”

Section: Methodsmentioning

confidence: 99%

Species-differences in the in vitro biotransformation of trifluoroethene (HFO-1123)

Dekant,

Bertermann,

Serban

et al. 2023

Arch Toxicol

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Abstract1,1,2-Trifluoroethene (HFO-1123) is anticipated for use as a refrigerant with low global warming potential. Inhalation studies on HFO-1123 in rats indicated a low potential for toxicity (NOAELs ≥ 20,000 ppm). In contrast, single inhalation exposure of Goettingen® minipigs (≥ 500 ppm) and New Zealand white rabbits (≥ 1250 ppm) resulted in severe toxicity. It has been suggested that these pronounced species-differences in toxicity may be attributable to species-differences in biotransformation of HFO-1123 via the mercapturic acid pathway. Therefore, the overall objective of this study was to evaluate species-differences in glutathione (GSH) dependent in vitro metabolism of HFO-1123 in susceptible versus less susceptible species and humans as a basis for human risk assessment. Biotransformation of HFO-1123 to S-(1,1,2-trifluoroethyl)-L-glutathione (1123-GSH) and subsequent cysteine S-conjugate β-lyase-mediated cleavage of the corresponding cysteine conjugate (1123-CYS) was monitored in hepatic and renal subcellular fractions of mice, rats, minipigs, rabbits, and humans. While 1123-GSH formation occurred at higher rates in rat and rabbit liver S9 compared to minipig and human S9, increased β-lyase cleavage of 1123-CYS was observed in minipig kidney cytosol as compared to cytosolic fractions of other species. Increased β-lyase activity in minipig cytosol was accompanied by time-dependent formation of monofluoroacetic acid (MFA), a highly toxic compound that interferes with cellular energy production via inhibition of aconitase. Consistent with the significantly lower β-lyase activity in human cytosols, the intensity of the MFA signal in human cytosols was only a fraction of the signal obtained in minipig subcellular fractions. Even though the inconsistencies between GSH and β-lyase-dependent metabolism do not allow to draw a firm conclusion on the overall contribution of the mercapturic acid pathway to HFO-1123 biotransformation and toxicity in vivo, the β-lyase data suggest that humans may be less susceptible to HFO-1123 toxicity compared to minipigs.

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Section: Methodsmentioning

confidence: 99%