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Acetaminophen overdose is the most often cause of acute liver injury. The toxic mechanism is linked to formation of an active metabolite that reacts with glutathione generating acetaminophen-glutathione conjugate (APAP-SG). This compound has been recognized to be non-toxic generally. Our preliminary results showed, however, that APAP-SG could possess a toxic effect too. Therefore, the aim of our study was to prepare, purify and to test possible toxicity of APAP-SG. We prepared APAP-SG using organic synthesis. The conjugate was purified by preparative HPLC and its structure was confirmed using mass spectrometry. Final purity of APAP-SG was >98 %. We estimated a toxic effect of APAP-SG in isolated rat liver mitochondria using a fluorescent ROS probe. We assessed ROS production in presence of complex I or complex II substrates. The increase of ROS-dependent fluorescence in presence of glutamate/malate was 104 ± 13 % and 130 ± 10 % in 1 mM and 5 mM APAP-SG, respectively, in comparison with controls. ROS production related to presence of complex II substrate was enhanced 4-times in APAP-SG (5 mM) treated mitochondria (compared to controls). We conclude, we proved our hypothesis that APAP-SG conjugate is able to induce a mitochondrial impairment leading to enhanced ROS production.

The aim of the present work was to investigate a new mechanism likely contributing to the toxic action of acetaminophen, especially to explore the possible inhibition of glutathione reductase through an acetaminophen-glutathione conjugate (APAP-SG). APAP-SG conjugate was synthesized by organic synthesis and purified by column chromatography. The inhibitory effect of the conjugate on two types of glutathione reductase (from yeasts and rat hepatocytes) was tested spectro-photometrically. We found that the enzyme activity was reduced similarly after the treatment with 2.96 mM acetaminophen-glutathione conjugate in both yeast and hepatocyte glutathione reductases (GR); the enzyme activity was inhibited to 52.7+/-1.5 % (2.4+/-0.3 mU/ml) in yeast GR (control activity was 5.6+/-0.3 mU/ml) and to 48.1+/-8.8 % (2.2+/-0.2 mU/ml) in rat hepatocytes lysate GR (control activity was 5.2+/-0.2 mU/ml). In addition, the enzyme activity (from hepatocytes lysate) was decreased to 79+/-7 %, 67+/-2 % and 39+/-7 %, in 0.37, 1.48 and 3.7 mM concentration of the conjugate, respectively. We found that glutathione reductase, the essential enzyme of the antioxidant system, was dose-dependently inhibited by the product of acetaminophen metabolism - the conjugate of acetaminophen and glutathione.