Tomato juice regulates bile acid-TGR5 signaling and reverses cognitive deficit and neuroinflammation in high-fat high-cholesterol diet-induced mice

Abstract

Cognitive deficits and neuroinflammation are significant complications associated with metabolic diseases induced by a high-fat, high-cholesterol (HFHC) diet. Although tomato juice (TJ) has shown potential benefits for brain health, its specific interventional role remains unclear. This research examined the capability of TJ to mitigate HFHC-induced cognitive deficits and delineated TJ's specific mechanisms against neuroinflammation. The results demonstrated that TJ effectively ameliorated cognitive impairments triggered by HFHC diets, improving spatial working memory, novel object recognition, and reducing anxiety-like behaviors in open space and elevated maze tests. Moreover, TJ mitigated neuronal damage, decreased the activity of immune cells, and diminished the level of COX-2 and iNOS in the hippocampus. Additionally, TJ decreased serum TNF-α and lipopolysaccharide levels, reduced liver inflammation, and improved intestinal barrier markers Claudin-1 and Mucin-2 expression. Fecal metabolomics demonstrated that TJ significantly upregulated bile acid metabolism-related pathways. TJ also altered the profile of serum bile acids, elevating the levels of Takeda G protein-coupled receptor 5 (TGR5)-activating bile acids, including deoxycholic acid, ursodeoxycholic acid, and tauroursodeoxycholic acid. TJ upregulated TGR5 protein expression and inhibited the phosphorylation of protein kinase B and nuclear factor kappa B proteins in the hippocampus. Notably, the positive effects of TJ on cognition and TGR5 activation were nullified in an antibiotic-treated mouse model, underscoring the essential role of the gut-brain axis in mediating TJ's neuroprotective effects. These findings propose that bile acid-TGR5 signaling may be associated with the anti-neuroinflammatory effects of TJ, which may represent a novel approach for neurogenic disease prevention.