Histological Changes
Micrographs of renal tissue with H&E staining and Masson staining showed that the renal tubules in the CON group remained intact and that the interstitium did not significantly change (Fig. 2 (a, e)). In the MOD group, inflammatory cells infiltrated, renal tubules atrophied, and interstitial fibrosis was observed. Masson staining showed vacuolar changes in renal tubular epithelial cells and ECM deposition with fibrosis (Fig. 1 (b, f)). Inflammation and fibrosis were improved in the MOD group after the administration of AMY and BUT (Fig. 2 (c, d, g, h)). The histopathological score showed the extent of damage to the tissues (Fig. 2i). The results showed that the BUT and AMY from A. mongolica had certain protective effects on RF in rats.
Determination of Clinical Biomarkers of Renal Function
Biochemical markers associated with renal function in clinical settings, including blood diabetic nitrogen (BUN), serum creatinine (Scr), HYP (routine markers of fibrosis) and antioxidant index, were detected in the MOD, CON, BUT and AMY groups. The levels of Scr, HYP, albumin (ALB), BUN and malondialdehyde (MDA) were increased in the model group compared with the CON group (p < 0.05 or p < 0.01). The level of SOD was decreased (p < 0.05 or p < 0.01) in the MOD group compared with the CON group (shown in Fig. 2j and Table S1). After treatment with BUT and AMY, biochemical indicators related to renal function tended to be restored to normal levels. The anti-RF effects of A. mongolica were shown through the changes in the biochemical markers above.
Comparison of Different Groups Using PCA and PLS-DA
The metabolic profiles of serum samples from different groups were determined by UPLC-QTOF-MS in the positive and negative electrospray ionization (ESI) modes. According to the PCA results, the CON and MOD groups were divided into two areas, as shown in the PCA score plot (Fig. 3 (a, b)). This result suggested that we successfully established the UUO model. Furthermore, the AMY and BUT groups were clearly separated from the MOD group. PLS-DA was used to maximize differences in metabolic profiles (Fig. 3 (e, f)), which were verified by class permutation tests (shown in Fig. 3 (g, h)). The R2 and Q2 values were 0.82 and 0.28, respectively, in the positive mode, and the R2 and Q2 values were 0.79 and 0.36, respectively, in the negative mode. The values indicate that these models have good fitness and prediction.
Screening and Identification of Metabolic Differences
We identified thirty-eight differentially expressed metabolites between the CON and MOD groups based on VIP > 2 and P < 0.05, which provided more rigorous screening than VIP > 1 and P < 0.05 in the V-plots (Fig. 3 (c, d)). In order to verify the diagnostic potential of 38 potential biomarkers, ROC analysis was performed, and the results showed that the AUC value of all 38 potential biomarkers was above 0.9 (Fig. 3 (i, j, k, l)), indicating that these metabolites had good stability. Among these differentially expressed metabolites, 22 metabolites were identified in the positive ion mode, 10 of which were upregulated and 12 of which were downregulated. In the negative ion mode, 16 metabolites were identified, 8 of which were upregulated and 8 of which were downregulated (as listed in Table 1). The thirty-eight metabolites can be divided into 7 classes, including 2 benzenoids, 4 lipids and lipid-like molecules, 4 nucleosides, nucleotides, and analogs, 13 organic acids and derivatives, 8 organic oxygen compounds, 6 organoheterocyclic compounds, 1 organic nitrogen compound (Fig. 4a). These results are shown in a heat map showing relative increases (red) or decreases (green) in the MOD group compared with the CON group. Many of these metabolites were reversed after treatment with BUT and AMY (Fig. 4c).
Metabolic Pathway and Protective Effects of Amygdalus mongolica Analysis
To directly measure the correlations between the 38 metabolites, Pearson rank correlation analysis (Fig. 5a) was performed. The Pearson correlation coefficients of 32 metabolites were r > 0.8 and r ≤ -0.8. The results showed that they are potential biomarkers. These significantly expressed metabolites were subjected to MetPA pathway enrichment and functional analysis, and the results showed that the metabolites are involved in metabolic pathways (Fig. 5b), including nicotinate and nicotinamide metabolism, pentose and glucuronate interconversions, arginine and proline metabolism, arginine biosynthesis, histidine metabolism, cysteine and methionine metabolism, and amino sugar and nucleotide sugar metabolism. These pathways may be related to the occurrence of RF.
In addition, in the AMY group compared with the MOD group, 48 metabolites were selected and identified (VIP > 2 and P < 0.05), of which the concentrations of 47 metabolites were reversed or returned to normal levels (Fig. S2 (a, b), Table S2). In the BUT group compared with the MOD group, 53 metabolites were identified (VIP > 2 and P < 0.05), of which the concentrations of 48 were reversed (Fig. S2 (c, d), Table S3). BUT and AMY from A. mongolica may exert protective effects on rats with RF by acting on the above metabolic pathways.
To reveal changes in metabolites and the mechanism of fibrosis treatment with BUT and AMY, the differential metabolites were analyzed by KEGG enrichment. Among the 38 differentially expressed metabolites between the CON and MOD groups, 18 metabolites were acted on by either BUT or AMY, and 14 metabolites were co-acted on by BUT and AMY (Fig. 4b, Table 1). The KEGG enrichment results showed that the metabolic pathways of nicotinate and nicotinamide metabolism, histidine metabolism, and purine metabolism were significantly changed in the BUT and AMY groups. These pathways are associated with oxidative stress, the release of inflammatory cytokines and pro-fibrogenic factors, which can promote fibrinolysis. In addition, AMY can also act on pentose and glucuronate interconversions, which was significantly enriched and associated with improving body energy metabolism (Fig. 5c).