All animal experiments were performed in compliance with the ARRIVE guidelines. The study was approved by the Ethics Review Committee of Sichuan Scientist Biotechnology Co., Ltd. (IACUC ISSUE SYST-2024-011). A detailed experimental timeline summarizing the study design is provided in Supplementary Figure 1.
Animal preparation and treatment
Mice were deeply anesthetized with 2% isoflurane inhalation. Under deep anesthesia, blood was collected via retro-orbital enucleation. Immediately after blood collection, eyeballs were enucleated for retinal tissue harvest. Subsequently, cervical dislocation was performed under deep anesthesia to ensure euthanasia. Colon tissues were then dissected immediately. Animals exhibiting adverse events were promptly removed from the study and received appropriate veterinary care.
Randomization and blinding
Male C57BL/6 mice, aged 5 weeks and weighing between 20 and 30 grams, were accommodated under strictly regulated conditions, including temperature and humidity. After one week of acclimatization, C57BL/6 mice were randomly assigned to three groups (blank, model, and intervention groups) using a computer-generated random number sequence. The randomization sequence was generated by an investigator not involved in animal handling or outcome assessment.
To ensure blinding, all animal care, drug administration, and data collection were performed by investigators unaware of group allocation. The coded group assignments were revealed only after the completion of all experiments and statistical analyses. The blinding applied to: the technician performing oral gavage; the pathologist evaluating retinal histology; and the analyst quantifying Western blot (WB) bands.
Sample size calculation
The sample size was determined based on a preliminary experiment evaluating retinal ganglion cell (RGC) counts under the same experimental conditions. Assuming a two-sided significance level (α) of 0.05 and a statistical power (1-β) of 0.80, a minimum of 5 mice per group was required to detect a clinically relevant difference in RGC counts between the model and intervention groups. Considering a potential dropout rate of approximately 20%, each group was set to include 6 mice.
Establishment of diabetic animals
The blank group received a standard diet, whereas the intervention and model groups were administered a high-fat, high-sugar diet (HFHSD) for a duration of four weeks. Following this dietary period, the intervention and model groups underwent intraperitoneal injection with a 1% Streptozotocin (STZ) solution at a dosage of 35 mg/kg17,18,19,20. After seventy-two hours of injection, mice exhibiting non-fasting blood glucose levels exceeding 16.7 mmol/L were considered to have successfully induced a DM model and were selected for further experimentation. The DM animals continued with the high-fat, high-sugar diet for an additional four months, whereas the blank group maintained their standard diet.
Taxonomic validation and quality assessment
The eight ingredients in QMG were taxonomically validated using the Modernized Plant Names Search (MPNS, http://mpns.kew.org/mpns-portal/). The quality of composition reporting for the QMG was evaluated using the ConPhYMP tool.
Administration methods
In the intervention group, the animals were orally administered QMG. QMG was purchased from Zhejiang Sansheng Mandi Pharmaceutical Co., Ltd. (Chinese National Drug Approval No. Z20090036). The QMG suspension was prepared by uniformly mixing QMG with distilled water. Mice in the intervention group were administered the suspension via oral gavage at an equivalent volume to the model and blank groups. The dosage was calculated based on the clinical single therapeutic dose of 4.5 g per 60 kg adult (the standard unit dose of the marketed formulation) using the body surface area (BSA) normalization method recommended by the FDA and Reagan-Shaw21. The conversion factor between adult humans (Km = 37) and mice (Km = 3) was 12.33, resulting in a mouse dose of 0.9 g/kg body weight. The model group and the blank group received an equivalent volume of saline via oral gavage. The administration was conducted daily between 9 AM and 11 AM for a consecutive period of 3 months.
Observation and testing indicators
General vital signs monitoring
The general vital signs and physiological indicators, including body weight, blood glucose levels, water and food consumption, urine output, activity levels and behavior, body temperature, as well as fur and skin condition, were systematically observed and recorded to comprehensively assess therapeutic interventions and detect potential complications.
Observation of morphological changes in the retina by HE staining analysis
All specimens were processed through an automatic dehydrator using a series of ethanol and xylene solutions after fixation, followed by embedding in paraffin. Subsequently, 4 µm paraffin sections were cut and stained with HE and then mounted with neutral gum. Retinal images were scanned using a 3DHISTECH Pannoramic SCAN scanner. Image analysis and data measurement were performed by Image-Pro Plus.
Detection of serum IL-6, TNF-α, and IL-1β by ELISA analysis
Blood samples were collected via retro‑orbital enucleation. Serum was separated by centrifugation at 1,000 × g for 15 min at 4 °C and stored at -80 °C until analysis. Serum levels of IL‑1β, IL‑6, and TNF‑α were measured according to standard procedures, including reagent equilibration, sample addition, incubation, washing, conjugate and substrate addition, reaction termination, optical density measurement, and concentration calculation based on a standard curve. The optical density was read at 450 nm using a microplate reader, and cytokine concentrations were calculated against standard curves.
Detection of the key regulatory proteins in retina and colon by WB analysis
Three independent biological replicates were conducted on a single membrane and sequentially probed for target proteins. All replicates were derived from a single cohort of animals sacrificed concurrently. When the molecular weight of a target protein was too close to that of GAPDH (<5 kDa difference), they were analyzed on independent membranes to prevent signal overlap. Each membrane was probed exclusively for either the target protein or GAPDH to ensure accurate quantification. The following primary antibodies were used: GAPDH polyclonal antibody (1:5000), CMKLR1 polyclonal antibody (1:1000), Wnt5a polyclonal antibody (1:1000), TP53 polyclonal antibody (1:1000), AP-1 monoclonal antibody (1:5000), and PPAR gamma (PPAR-γ) polyclonal antibody (1:1000). Total proteins were obtained by cell lysis followed by centrifugation. Protein concentrations were determined using the BCA assay. The extracted proteins were resolved by SDS-PAGE using a 12% separating gel and subsequently transferred onto membranes. The membranes were blocked in TBST containing 5% non-fat milk and incubated with the appropriate primary antibodies overnight at 4 °C. Following washing, the membranes were incubated with HRP-conjugated anti-rabbit or anti-mouse secondary antibodies at a dilution of 1:10,000. Finally, the protein bands were visualized and analyzed through chemiluminescence imaging. During visualization and data processing, blots were cropped horizontally to remove irrelevant molecular weight regions, and all sample lanes were retained without removal of inter-lane areas. Slight edge distortion may occur during cropping to remove irrelevant gel regions.
Detection of gut microbiota by 16S rDNA sequencing analysis
Fresh fecal samples were collected from each mouse prior to terminal procedures. Mice were placed individually in sterile cages for 10–15 min to allow spontaneous defecation. Fecal pellets were immediately collected with sterile forceps, transferred to sterile 1.5 mL tubes, snap-frozen in liquid nitrogen, and stored at -80 °C until DNA extraction. All procedures were performed under sterile conditions to minimize cross-contamination. The interval between defecation and freezing was maintained within 10 min to ensure microbial integrity. The fecal genomic DNA (gDNA) samples were purified using the Fecal gDNA extraction kit, followed by full-length 16S rDNA gene amplification via polymerase chain reaction (PCR) with universal primers 8F (5’-AGAGTTTGATCATGGCTCAG-3’) and 1492R (5’-CGGTTACCTTGTTACGACTT-3’). The PCR products were subsequently analyzed by agarose gel electrophoresis, purified, and quantified for downstream applications. High-throughput sequencing was conducted on the Nanopore GridION sequencer. The data analysis process included basecalling, data quality control, species annotation, phylogenetic tree construction, community analysis, Alpha and Beta diversity analysis, and differentially abundant species analysis and community function prediction. Various tools and databases, such as NanoFilt, Usearch, the R programming language, Python, and the SILVA database, were utilized during the analysis.
Correlation analysis of the gut–retina axis with systemic inflammation and multi-level gut Microbiota
To explore the potential associations between multi-level gut microbiota with serum inflammatory cytokines and key regulatory proteins, correlation analysis was performed by using the Luoning Bio-Cloud platform. Initially, the species abundance data at the Kingdom, Phylum, Class, Order, Family, Genus, and Species levels were extracted from the sequencing results. Physicochemical factors, including serum inflammatory cytokines and protein expression levels, were compiled into an environmental factor file. To ensure the reliability and visualization of the correlations, the data underwent normalization to eliminate the scale differences between microbial abundance and clinical measurement units. The correlation coefficients (R-values) and corresponding significance levels (P-values) were calculated. The results were visualized using a correlation heatmap, where color gradients indicate the strength and direction of the correlation (red representing positive correlation, blue representing negative correlation), and asterisks (**) denote statistical significance (P < 0.01).
Statistical methods
All statistical analyses and visualization were performed using GraphPad Prism. The t-test to compare means was employed for data that adhered to normal distribution. In cases where data deviated from normality, the Kruskal-Wallis test was used. Spearman's or Pearson's correlation was conducted for variable relationships. All statistical tests were conducted as two-tailed, with statistical significance set at 0.05.