Objective  To investigate the effects of Qingguang'an II Formula (QGA II) on the gut microbiota of mice with chronic high intraocular pressure (IOP) model, and explore its key microbiota for protecting the optic nerve.

Methods  A total of 10 specific pathogen free (SPF) grade female DBA/2J mice were randomly divided into model group and QGA II group (n = 5 for each group), while additional 5 SPF-grade female C57BL/6J mice were assigned to control group. Mice presented spontaneous high IOP and showed elevated approximately at the age of seven months. The high IOP was maintained until week 38, when gavage was initiated. Mice in control group underwent the same intragastric treatment, while those in QGA II group were gavaged with QGA II (9.67 g/kg), once a day for four weeks. Retinal morphology was examined using hematoxylin and eosin (HE) staining, with the number of retinal ganglion cells (RGCs) counted. The expression level of Brn3a protein, a specific marker for RGCs, was detected by immunofluorescence, with the mean optical density (OD) measured for quantitative analysis. In addition, 16S rDNA sequencing was leveraged to analyze changes in the diversity of gut microbiota, including their α-diversity (Chao1, Shannon, Pielou’s evenness, and observed species index) and β-diversity. Venn diagrams and linear discriminant analysis effect size (LEfSe) analysis was employed to investigate the number of amplicon sequence variants (ASVs), the abundance of differential gut microbiota species, and the classification of species at both the phylum and genus levels within the three groups of mice.

Results  HE staining revealed that compared with control group, model group showed significant reduction in the number of RGCs (P < 0.01), with intracellular vacuolar degeneration and nuclear pyknosis. After QGA II treatment, the number of RGCs was significantly increased compared with model group (P < 0.01), with notable improvements in intracellular vacuolar degeneration. Immunofluorescence analysis showed that the mean OD of Brn3a protein was significantly decreased in model group compared with control group (P < 0.01), while QGA II treatment significantly elevated its expression level (P < 0.01). Analysis of α-diversity showed that after QGA II intervention, the Chao1, Shannon, and Pielou’s evenness indices were significantly increased (P < 0.01), and the observed species index was elevated (P < 0.05). β-Diversity analysis demonstrated distinct clustering among the three groups, indicating relatively low similarity in bacterial community structures. ASV clustering identified a total of 14 061 ASVs across all groups, with 9 514 ASVs shared between model and QGA II groups. At the phylum level, the abundance of Bacteroidetes was significantly decreased in model group compared with control group (P < 0.01), while Firmicutes and the Firmicutes/Bacteroidetes (F/B) ratio were significantly increased (P < 0.01). QGA II treatment significantly reduced both Firmicutes abundance and the F/B ratio (P < 0.01). At the genus level, Lactobacillus was dominant across all groups, with its abundance significantly increased in model group (P < 0.01) and subsequently decreased following QGA II intervention (P < 0.05).

Conclusion QGA II restructured the gut microbiota of DBA/2J mice with chronic high IOP, bringing changes in their diversity and abundance of components. Firmicutes, Bacteroidetes, Lactobacillus, along with their associated microorganisms, are likely critical components of the gut microbiota that contribute to the optic neuroprotective effects of QGA II on chronic high IOP mice.