# Glucose-Dependent Insulinotropic Polypeptide Inhibits AGE-Induced NADPH Oxidase-Derived Oxidative Stress Generation and Foam Cell Formation in Macrophages Partly via AMPK Activation

## TL;DR

This study shows that GIP reduces oxidative stress and foam cell formation in macrophages caused by AGEs, partly through AMPK activation.

## Contribution

The study reveals a novel mechanism by which GIP inhibits AGE-induced oxidative stress and foam cell formation via AMPK activation.

## Key findings

- AGEs increase ROS and gene expressions in macrophages, which are blocked by [D-Ala2]GIP(1–42) or NADPH oxidase inhibitors.
- AMPK inhibition reduces the protective effects of [D-Ala2]GIP(1–42), while AMPK activation mimics its effects.
- GIP suppresses foam cell formation by reducing the Cdk5-CD36 pathway via AMPK activation.

## Abstract

Glucose-dependent insulinotropic polypeptide (GIP) of the incretin group has been shown to exert pleiotropic actions. There is growing evidence that advanced glycation end products (AGEs), senescent macromolecules formed at an accelerated rate under chronic hyperglycemic conditions, play a role in the pathogenesis of atherosclerotic cardiovascular disease in diabetes. However, whether and how GIP could inhibit the AGE-induced foam cell formation of macrophages, an initial step of atherosclerosis remains to be elucidated. In this study, we address these issues. We found that AGEs increased oxidized low-density-lipoprotein uptake into reactive oxygen species (ROS) generation and Cdk5 and CD36 gene expressions in human U937 macrophages, all of which were significantly blocked by [D-Ala2]GIP(1–42) or an inhibitor of NADPH oxidase activity. An inhibitor of AMP-activated protein kinase (AMPK) attenuated all of the beneficial effects of [D-Ala2]GIP(1–42) on AGE-exposed U937 macrophages, whereas an activator of AMPK mimicked the effects of [D-Ala2]GIP(1–42) on foam cell formation, ROS generation, and Cdk5 and CD36 gene expressions in macrophages. The present study suggests that [D-Ala2]GIP(1–42) could inhibit the AGE-RAGE-induced, NADPH oxidase-derived oxidative stress generation in U937 macrophages via AMPK activation and subsequently suppress macrophage foam cell formation by reducing the Cdk5-CD36 pathway.