Mass spectrometry-based imaging to investigate the distribution of metabolites in the retina of diabetic rats improved by Panax notoginseng

Based on mass spectrometry imaging method, we investigated the effects of Panax notoginseng in improving diabetic retinopathy (DR) and interfering with corneal, vitreous and retinal metabolites, to reveal the mechanism of Panax notoginseng's action in improving DR. All animal experiments were approved by the Experimental Animal Ethics Committee of Beijing University of Chinese Medicine (Approval No.: BUCM-2023052204-2117). Streptozotocin (STZ)-induced diabetes mellitus (DM) rat model was used, and fasting blood glucose (FBG) and glucosylated serum protein (GSP) levels were measured in each group of rats. Occludin and zonula occludens-1 (ZO-1) were detected by immunofluorescence staining; air flow-assisted desorption electrospray ionization mass spectrometry imaging (AFADESI-MSI) was used to detect endogenous metabolites in the cornea, vitreous, and retinal microregions of the eyes of rats in the DM group and Panax notoginseng group. Endogenous metabolites were detected in the cornea, vitreous, and retinal microregions of the DM and Panax notoginseng groups, and the DM and Panax notoginseng groups were screened for different metabolites by principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA). Differential metabolites were screened in the DM and Panax notoginseng groups, the in situ spatial information of differential metabolites in each microregion was analyzed, and the related metabolic pathways were analyzed by the Kyoto encyclopedia of genes and genomes (KEGG) database. The results showed that compared with the DM group, diabetic rats in the Panax notoginseng group showed a decreasing trend in both FBG and GSP, and an increase in the expression of ZO-1 and occludin in the retina (P < 0.001); AFADESI-MSI analysis showed that there were a total of 34 differential metabolites in the cornea, vitreous body, and retinal microregion in the Panax notoginseng group, of which Panax notoginseng called back 13 differential metabolites. In the retinal microregion, Panax notoginseng significantly regulated lysophosphatidylserine (18∶0), phosphatidylethanolamine (34∶2) and phosphatidylserine (40∶7/42∶7). The metabolic pathway enrichment results indicated that Panax notoginseng mainly regulated glycerophospholipid metabolism, glycosylphosphatidylinositol synthesis, niacin and nicotinamide metabolism as well as glycerol ester metabolic pathways. In conclusion, Panax notoginseng improves the blood-retinal barrier (BRB) in diabetic rats, and its mechanism of action may be closely related to glycerophospholipid metabolism. This study provides scientific evidence for the mechanism of action of Panax notoginseng in improving DR, and demonstrates the potential of mass spectrometry imaging technology applied to the study of pharmacological mechanisms.