Native amniotic fluid promotes barrier-associated maturation of the neonatal intestine under physiological conditions

The neonatal intestine undergoes dynamic maturation after birth, during which an effective epithelial barrier is essential for intestinal adaptation and function. Amniotic fluid (AF) contains diverse bioactive components that may contribute to intestinal development. This study aimed to investigate whether native AF supports barrier-associated maturation of the neonatal intestine under physiological, non-injury conditions.

In vitro models using Caco-2 and IEC-6 cells and an in vivo neonatal rat model were used to assess the effects of 25% and 50% native AF. Tight junction protein expression, including Claudin-1, Claudin-8, and Occludin, was measured by Western blotting. Barrier-related properties were evaluated using transepithelial electrical resistance (TEER) and fluorescein isothiocyanate-conjugated inulin permeability assays.

Native AF at 25% and 50% increased tight junction protein expression, with the strongest response observed in the 50% AF group (P<0.01). TEER values increased in Caco-2 and IEC-6 monolayers (P<0.001 for 50% AF) and in neonatal rat intestinal tissues, particularly on day 14 (P<0.01 for 50% AF). Permeability to fluorescein isothiocyanate-conjugated inulin decreased significantly in both AF-treated monolayer groups (P<0.001). Intestinal morphology remained unchanged across treatment groups.

Native AF increased tight junction protein expression, improved barrier-related properties in epithelial monolayers, and produced early ex vivo TEER changes in neonatal rat intestinal tissues without altering intestinal morphology. These findings suggest that AF may support physiological postnatal barrier-associated maturation, although direct in vivo permeability effects require further investigation.