Seeking standardized in vitro models of AGE-RAGE signaling in the physiological perspective of glycated dietary proteins.

INTRODUCTION

Advanced Glycation End products (AGEs) are covalent protein adducts formed through the Maillard reaction. High dietary intake might harm human health, however studies on their impact remain inconclusive. A proposed mechanism is that dietary AGEs trigger inflammation by interacting with the AGEs receptor (RAGE). However, in vitro studies on dietary AGE-RAGE signaling have reported inconsistent results, probably due to methodological issues. This study aimed to seek a standardized model of dietary AGE-RAGE signaling.

METHODS

In vitro models were characterized for surface and total RAGE expression using flow cytometry. Both commercially available and in-house prepared dietary AGE preparations were analyzed for AGE levels, aggregation, and LPS content, then tested in the model with the highest surface RAGE expression.

RESULTS

All immortalized cell lines expressed intracellular RAGE, while its surface expression was marginal or even absent. Only M-CSF-differentiated M0 macrophages showed significant surface RAGE expression. Some glycated dietary proteins induced inflammation in this model, but not all. While these proteins showed RAGE affinity in a chemical assay, the inflammatory response could not be reduced by the RAGE antagonist FPS-ZM1. Interestingly, co-incubation with the LPS scavenger PMB reduced inflammation despite negligible LPS levels in the sample.

CONCLUSION

These results challenge the hypothesis that dietary AGEs cause inflammation via RAGE activation, as glycated dietary proteins alone do not seem to induce acute inflammation. To better understand the biological activity of dietary AGEs, future studies should confirm surface RAGE expression, detail glycation methods and glycated protein characteristics, and account for LPS interference.