Siphonaxanthin, a carotenoid from green algae, suppresses advanced glycation end product-induced inflammatory responses.

Advanced glycation end products (AGEs) induce inflammation and contribute to the pathogenesis of atherosclerosis. Although many studies have demonstrated the protective effects of carotenoids against atherosclerosis, the effects of carotenoids on AGE-induced inflammation have not been characterized. As such, we aimed to identify carotenoids that provided protection against AGE-elicited inflammation. AGE-stimulated RAW264 macrophages were first evaluated for NO generation. Among 17 carotenoids tested, only siphonaxanthin significantly suppressed it. Next, mRNA expression levels were measured in RAW264 macrophages and human umbilical vascular endothelial cells following siphonaxanthin and AGE treatment. Siphonaxanthin significantly suppressed AGE-induced mRNA expression of interleukin-6 and cellular adhesion molecules, which are known to be important for the pathogenesis of atherosclerosis. Siphonaxanthin also significantly suppressed endoplasmic reticulum (ER) stress marker genes. A reporter gene assay revealed that siphonaxanthin, as well as an ER stress inhibitor, significantly inhibited AGE-induced nuclear factor-κB (NF-κB) activation. Altogether, mitigation of ER stress and subsequent NF-κB activation is one of the molecular mechanisms by which siphonaxanthin suppressed AGE-elicited inflammation. Siphonaxanthin is a carotenoid commonly found in standard diets and is considered relatively safe for human consumption, and hence, dietary intake of siphonaxanthin or siphonaxanthin-containing green algae could be beneficial in lowering the risk of developing atherosclerosis.