Does aflatoxin B1 cause hepatocellular injury and elevate AST/ALT via oxidative stress and reactive metabolites?

Aflatoxin B1 (AFB1) is a highly prevalent mycotoxin produced by Aspergillus species, commonly contaminating dietary staples such as corn, peanuts, and tree nuts in warm, humid climates. This molecule acts as a potent hepatotoxin and carcinogen, particularly threatening to individuals with pre-existing hepatic vulnerabilities.

Metabolic bioactivation

• Cytochrome P450 activation: AFB1 is a pro-toxin that undergoes biotransformation in the liver. Cytochrome P450 enzymes (specifically CYP3A4, CYP1A2, and CYP2A6) metabolize AFB1 into a highly reactive and electrophilic intermediate, aflatoxin B1-8,9-exo-epoxide (AFBO).
• Adduct formation: The electrophilic AFBO covalently binds to cellular macromolecules. It reacts with DNA to form mutagenic AFB1-N7-guanine adducts and binds to proteins, altering crucial structural and enzymatic functions within hepatocytes.

Oxidative stress and antioxidant depletion

• Glutathione depletion: Conjugation with glutathione (GSH) via glutathione S-transferases (GST) is the primary detoxification pathway for AFBO. High-dose or chronic AFB1 exposure rapidly exhausts intracellular GSH pools.
• Lipid peroxidation: Depletion of GSH compromises the cellular antioxidant defense, triggering an accumulation of reactive oxygen species (ROS). ROS attack polyunsaturated fatty acids in hepatocyte membranes, causing extensive lipid peroxidation (evidenced by elevated malondialdehyde [MDA] levels) and mitochondrial membrane depolarization.

Hepatocellular injury and transaminase elevation

• Loss of membrane integrity: Sustained oxidative stress, mitochondrial damage, and protein adducts disrupt cell membrane permeability, triggering hepatocyte apoptosis and necrosis.
• Enzyme leakage: This loss of membrane integrity allows intracellular enzymes to leak into the systemic circulation. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels elevate sharply, reflecting the severity of acute hepatocellular necrosis.

Bottom line

Aflatoxin B1 is metabolically activated by hepatic cytochrome P450 enzymes into a highly reactive epoxide (AFBO) that depletes intracellular glutathione and induces profound oxidative stress. This biochemical cascade compromises cell membrane integrity, resulting in hepatocellular necrosis and a subsequent rise in serum ALT and AST levels.