Ammonia impairs tight junction barriers by inducing mitochondrial dysfunction in Caco-2 cells

Area of Science:

• Gastroenterology
• Cell Biology
• Microbiology

Background:

• Ammonia is a key gut microbial metabolite, but its precise role in intestinal homeostasis remains unclear.
• Intestinal barrier function, regulated by tight junctions (TJs), is crucial for gut health.
• Understanding ammonia's impact on TJs is vital for deciphering host-microbe interactions.

Purpose of the Study:

• To investigate how ammonia affects intestinal tight junction proteins and barrier function.
• To elucidate the mechanisms underlying ammonia's impact on intestinal cells.
• To explore potential protective strategies against ammonia-induced intestinal damage.

Main Methods:

• Utilized human intestinal Caco-2 cells to model the intestinal barrier.
• Assessed cell permeability using transepithelial electrical resistance and dextran flux.
• Analyzed tight junction protein localization via immunoblot and immunofluorescence.
• Investigated cellular mechanisms including oxidative stress markers, mitochondrial function, and gene expression via DNA microarray.

Main Results:

• Ammonia significantly increased intestinal cell permeability in a dose-dependent manner.
• Ammonia reduced the membrane localization of key tight junction proteins (ZO1, ZO2, occludin, claudins).
• Ammonia induced oxidative stress, mitochondrial dysfunction, and impaired cellular energy metabolism.
• N-acetyl cysteine treatment partially reversed ammonia-induced TJ permeability and structural damage.

Conclusions:

• Ammonia compromises intestinal barrier integrity primarily through oxidative stress induction in intestinal cells.
• Mitochondrial dysfunction may precede or contribute to ammonia-induced oxidative stress.
• These findings highlight a potential mechanism linking gut microbial metabolites to intestinal barrier dysfunction.