Laminaria japonica fucoidan ameliorates D-galactose-induced cognitive impairment via the regulation of tryptophan metabolism along the gut-brain axis.

Abstract

Aging is a multifactorial biological process in which chronic inflammation and oxidative stress are central to the development of age-related disorders, including neurodegenerative decline. Fucoidan, a sulfated polysaccharide extracted from brown algae, has well-documented anti-inflammatory and antioxidant effects, and therefore has the potential to be a neuroprotective agent against cognitive impairment associated with aging. In the present study, the major fucoidan fraction (LJF-2) isolated from Laminaria japonica was examined for its neuroprotective properties in a D-galactose induced aging mouse model. Oral administration of LJF-2 for 8 weeks significantly improved spatial learning and memory and suppressed neuroinflammatory responses and oxidative stress while significantly reducing the activation of astrocytes and microglia. These neuroprotective effects were linked to the regulation of key proteins involved in neuronal protection and synaptic function, such as neprilysin and synapsin, by cAMP response element-binding protein signaling. Furthermore, LJF-2 significantly remodeled the gut microbiota through a reduction in the abundance of the Bacteroidota, Proteobacteria, and several putative pathogenic genera, which enhanced the intestinal barrier integrity and modified the microbial metabolite profiles, especially those associated with tryptophan metabolism. Fecal microbiota transplantation experiments further confirmed the role of the gut microbiota modulated by LJF-2 in mediating its neuroprotective effects through reduction of oxidative stress and inflammation. Collectively, these findings suggest that LJF-2 may be a promising therapeutic approach to address the aging-related cognitive decline by modulating the gut-brain axis.