Preventive Effect of Small Molecular Fraction of Irpex lacteus (Agaricomycetes) Fruiting Body against Chronic Nephritis in Mice and Identification of Active Compounds.

Previous study found that the fruit body of Irpex lacteus has an effect on the prevention and treatment of chronic nephritis. In this study, we systematically investigated the preventive effect of small molecular fraction (SMF) of the fungal fruit body against chronic nephritis. In addition, we analyzed, isolated, and identified the chemical constituents of SMF, and screened the activity of three small peptides isolated in vitro. The results showed SMF significantly reduced amounts of urine protein (UP), the content of urea (BUN), creatinine (Cr), tumor necrosis factor-α (TNF-α), and maleic dialdehyde (MDA) in serum, and significantly increased superoxide dismutase (SOD) level in renal tissue homogenate (P < 0.05). Moreover, the results of hematoxylin and eosin (H&E) and Masson staining of renal tissues indicated that SMF has protective effects on renal tissues and prevents renal interstitial from fibrosis. The peptide sequences isolated from SMF were identified as WSMGPAPDSVH (SP1), QCTGNASCSPPC (SP2), and HYCCTAKYA (SP3), which were active compounds for the prevention of nephritis, and these new peptides were isolated for the first time. The cell proliferation assay showed that 10 µg/L transforming growth factor-ß1 (TGF-ß1) significantly induced the proliferation of human renal tubular epithelial cells (HK-2), compared with the control group, and the difference was statistically significant (P < 0.01). However, when combined with three small peptides, respectively, the cell proliferation was significantly inhibited (P < 0.05). These results suggest that isolated peptides can maintain the morphological stability of HK-2 cells, inhibit cell proliferation induced by TGF-ß1 to some extent, and prevent cell fibrosis.