FIG 4.

Inhibition of fibrogenesis by silymarin correlates with decreased IL-13 serum amounts and reduced IL-13-induced collagen I production by fibroblasts. (A) Analysis of the correlation between IL-13 serum amounts and hepatic hydroxyproline contents in infected nontreated or treated mice. Samples examined for hydroxyproline and IL-13 came from the same pool of mice. The Pearson analysis resulted in an r value of 0.93 (significant linear correlation, P < 0.0001). (B) Quantification of collagen I production by L929 cells treated with rIL-13 (50 ng/ml), SIL (50 μM), or rIL-13+SIL for a week. (C) Experiment similar to that described for panel B, except that NAC (10 mM) was used instead of SIL. Collagen I immunofluorescence staining was analyzed as described in Materials and Methods. *, P < 0.05 compared to vehicle (Veh) in panel B or untreated (−) in panel C; #, P < 0.05, compared to rIL-13. (D) Illustrative confluent cell cultures as in panel C assessed for collagen I production by immunofluorescence microscopy. Insets represent collagen I and DAPI (4′,6-diamidino-2-phenylindole) simultaneously stained cell cultures. Skin was used as a specific labeling control (left). (E) Based on our results, we postulate that SIL acts pleiotropically to inhibit fibrogenesis by decreasing IL-13 levels, fibroblast proliferation, and IL-13-dependent and basal (possibly ROS-dependent) collagen I production.