Targeting Photoaging With Heat-Killed Escherichia coli Nissle 1917: A Novel Cellular Model and Anti-photoaging...

Ultraviolet (UV) radiation is a major contributor to skin aging, manifesting as wrinkles, pigmentation, and structural dysfunction, collectively termed photoaging. Chronic photoaging is strongly linked to an increased risk of skin cancer. Despite the growing demand for effective anti-photoaging agents, a gap remains in both understanding the molecular basis of photoaging and validating the efficacy of new therapeutic candidates. This study aimed to establish a reliable in vitro photoaging model and evaluate the potential anti-photoaging effects of heat-killed Escherichia coli Nissle 1917 (EcN).

Human dermal fibroblast (HDF) cells were exposed to UVB radiation three times at one-day intervals. Cell viability was assessed using the MTT assay. Post-irradiation, cells were treated with varying concentrations of heat-killed EcN. Effects were evaluated through live/dead staining, apoptosis assay, cell cycle analysis, and reactive oxygen species (ROS) quantification. Resveratrol (RES), a known anti-inflammatory and anti-aging compound, was used as a reference control.

UVB exposure at 0.3 J/cm² reduced HDF cell viability to approximately 50% compared to the control group. Morphological and biochemical assessments validated the photoaging model's reliability. Treatment with 10% v/v heat-killed EcN and 100 μM RES after each UVB cycle significantly restored cell viability, reduced apoptosis and cell cycle arrest, and markedly decreased intracellular ROS levels.

This study demonstrates the efficacy of heat-killed EcN and RES in alleviating UVB-induced photoaging, likely via suppression of oxidative stress and apoptosis. The developed in vitro model offers a robust platform for future investigations into molecular mechanisms of photoaging and the evaluation of emerging photoprotective agents.