Exposure to fructose raises levels of specific stress markers in the intestines and liver of human cells and rodent models, and blocking the enzymes CYP2E1 or iNOS prevents this increase.
Mechanism
Synthesis from 1 study
Eating too much fructose turns on a harmful enzyme in the gut and liver that creates toxic chemicals. These chemicals break down the glue holding gut cells together, letting bacteria leak into the blood, which then scars the liver. They also disable a protective liver protein, causing fat to build...
Most probable mechanism
When too much fructose is consumed, it triggers a chain reaction in the gut and liver: a specific enzyme called CYP2E1 becomes more active, producing harmful chemicals that damage the gut lining and cause proteins that hold gut cells together to break down. This lets bacteria and their toxins leak into the bloodstream, which then reach the liver and activate cells that produce scar tissue. At the same time, these harmful chemicals also disable a protective liver protein, leading to fat buildup and more scarring.
Fructose intake increases the expression and activity of CYP2E1 in intestinal and hepatic tissues.
Elevated CYP2E1 generates reactive oxygen and nitrogen species, including nitric oxide, which induces iNOS expression and promotes widespread protein nitration.
Reactive nitrogen species cause tyrosine nitration of tight and adherent junction proteins in intestinal epithelial cells, marking them for ubiquitination and proteasomal degradation.
Loss of junctional proteins disrupts the intestinal barrier, increasing paracellular permeability and allowing bacterial endotoxins to enter systemic circulation.
Circulating endotoxins bind to TLR4 receptors on hepatic stellate cells, triggering their activation into collagen-producing myofibroblasts.
Activated hepatic stellate cells deposit extracellular matrix proteins, including collagen-1 and collagen-4, leading to fibrotic tissue remodeling.
Reactive nitrogen species also cause tyrosine nitration and ubiquitination of Sirt1 in hepatocytes, leading to its degradation and loss of function.
Loss of Sirt1 reduces deacetylation of PGC1-α and PPARα, impairing mitochondrial fatty acid oxidation and increasing lipid accumulation.
Reduced mitochondrial function and lipid overload promote further hepatic stellate cell activation and fibrosis progression.
Less supported by current evidence, but not ruled out
Fructose activates CYP2E1 in gut cells, which generates stress signals that turn on a cell death pathway, causing intestinal lining cells to die and further weaken the gut barrier.
Fructose increases CYP2E1 expression in intestinal epithelial cells.
CYP2E1-derived reactive oxygen species activate the stress kinase JNK.
Activated JNK upregulates the pro-apoptotic protein Bax and suppresses anti-apoptotic signals.
Bax triggers mitochondrial permeabilization, activating caspase-3 and initiating programmed cell death.
Apoptosis of intestinal epithelial cells reduces barrier integrity and contributes to increased permeability.
Evidence from Studies
Supporting (1)
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Fructose Promotes Leaky Gut, Endotoxemia and Liver Fibrosis through CYP2E1-Mediated Oxidative and Nitrative Stress
Contradicting (0)
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