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Mitochondrial versus microsomal bioactivation of paracetamol by human liver and kidney tissues

Ege Arzuk1, Mehmet Tokdemir2, Hilmi Orhan1

  • 1Department of Pharmaceutical Toxicology, Faculty of Pharmacy, Ege University, İzmir, Turkey.

Toxicology Letters
|May 20, 2022
PubMed

Insights

Paracetamol (PAR) toxicity targets mitochondria. This study found that mitochondria can generate the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI), suggesting a direct role in paracetamol-induced liver injury.

Area of Science:

  • Biochemistry
  • Toxicology
  • Cell Biology

Background:

  • Mitochondria are a primary target in paracetamol (PAR)-induced liver toxicity.
  • Microsomal cytochrome P450 enzymes (CYPs) are known to bioactivate PAR to N-acetyl-p-benzoquinone imine (NAPQI), which alkylates mitochondrial proteins.
  • The translocation of NAPQI from microsomes to mitochondria is a proposed mechanism for PAR hepatotoxicity.

Purpose of the Study:

  • To investigate the hypothesis that NAPQI is formed locally within mitochondria, catalyzed by mitochondrial CYPs.
  • To compare the metabolic capacities of liver and kidney mitochondria in generating NAPQI.
  • To explore the role of mitochondrial CYP2E1 and CYP3A4 in paracetamol metabolism and toxicity.

Main Methods:

  • Isolation of cellular fractions from human liver and kidney.
  • Assessment of mitochondrial CYP2E1 and CYP3A4 activities.
  • Measurement of NAPQI formation in mitochondrial fractions.
  • Evaluation of paracetamol-induced mitochondrial permeability transition pore (mPTP) opening.

Main Results:

  • Human liver and kidney mitochondria are capable of generating NAPQI.
  • Mitochondrial CYP2E1 and CYP3A4 activities were comparable to their microsomal counterparts in both organs.
  • Higher mitochondrial CYP2E1 activity in male kidneys mirrored previously reported microsomal findings.
  • No correlation was observed between kidney CYP2E1 activity and NAPQI formation, nor was mPTP opening induced by PAR in kidney mitochondria.

Conclusions:

  • Mitochondria can directly generate NAPQI, supporting a role in paracetamol-induced hepatotoxicity.
  • While mitochondrial CYPs contribute to NAPQI formation, the lack of PAR-induced mPTP opening in kidney mitochondria suggests alternative toxicity pathways in this organ.
  • Further research is needed to elucidate the specific mechanisms of paracetamol toxicity in the kidney.
Keywords:
BioactivationHepatotoxicityHumanMitochondriaNephrotoxicityParacetamol

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