Modified Zhujing pill regulates RPE cholesterol metabolism and gut microbiota in an age-related macular degeneration mouse model

Shuibin Cen¹Shiqin Xie²KHALID IBRAHIM³Michal R. Baran⁴Xing Li⁵James Reilly⁴Zhoujin Tan²Zhiming He⁵Xinhua Shu^4*

• ¹Guangdong Industry Polytechnic, Guangzhou, China
• ²Hunan University of Chinese Medicine, Changsha, China
• ³University of Zakho, Zakho, Iraq
• ⁴Glasgow Caledonian University, Glasgow, United Kingdom
• ⁵Shaoyang University, Shaoyang, China

Background: Age-related macular degeneration (AMD) is a common retinal disorder, causing blindness in aged individuals. One of the traditional Chinese medicines, modified Zhujing pill (MZP), has been widely used to treat various ocular disorders, including AMD; however, its protective mechanisms remain elusive. In this study, we explored the functional role of MZP in high-fat diet fed mice, a commonly used model for AMD. Methods: Compounds of MZP water extract were identified by high-performance liquid chromatography (HPLC)/mass spectrometry (MS)/MS. Mice were divided into three groups: group 1 mice fed with control diet (CD), group 2 mice fed with high-fat diet (HFD), group 3 mice fed with HFD for 12 weeks; groups 1 and 2 were then treated with physiological saline, while group 3 was treated with MZP for 4 weeks. Cholesterol level and expression of cholesterol homeostasis-associated genes, antioxidant genes and proinflammatory cytokines in mouse tissues were measured using biochemical approaches. Mouse cecum microbiota compositions and metabolic functions were analyzed using 16rRNA sequencing and bioinformatics approach. Results: HFD-fed mice had high levels of cholesterol in the retinal pigment epithelial (RPE) cells, liver and serum, decreased expression of cholesterol homeostasis-associated genes and antioxidant genes in the RPE and liver, and increased expression of proinflammatory cytokines. MZP treatment counteracted HFD-induced pathologic effects. Additionally, HFD altered cecum bacterial compositions and diversities, associated with individual metabolic pathways. These metabolic pathways are involved in biosynthesis of bacterial metabolites, mitochondrial function, oxidative stress and inflammation. MZP reversed most of the changes back to control characteristics. Conclusion: We postulate that the beneficial effects of MZP against AMD are possibly related to lowering cholesterol level, suppressing oxidative stress and inflammation, and modulating gut microbiota and associated functions.