Curcumin Modulates NOX Gene Expression and ROS Production via P-Smad3C in TGF-β-Activated Hepatic Stellate Cells

Background: Liver fibrosis, associated with HSCs, occurs when a healthy liver sustains damage, thereby impairing its function. NADPH oxidases (NOXs), specifically isoforms 1, 2, and 4, play a role in reactive oxygen species (ROS) production during hepatic injuries, resulting in fibrosis. Curcumin has shown strong potential in mitigating liver fibrosis. Our research aimed to investigate the effects of curcumin on lowering NOX and ROS levels. This compound was also studied for its effects on NOXs, ROS concentrations through the inhibition of Smad3 phosphorylation in transforming growth factor beta (TGF-β)-activated human HSCs. Methods: MTT assay investigated the cytotoxic effects of curcumin on HSCs. The cells were activated by exposure to TGF-β (2 ng/mL) for 24 hours. After activating, the cells were treated with curcumin at 25-150 μM concentrations. After administering curcumin to the cells, we employed RT-PCR and Western blot techniques to evaluate the related gene and protein expression levels. This evaluation was primarily focused on the mRNA expression levels of NOX1, NOX2, NOX4 and phosphorylated Smad3C. Results: The mRNA expression level of aforesaid NOXs as well as α-smooth muscle actin (α-SMA), collagen1-α, and ROS levels were significantly reduced following 100 μM curcumin treatment. Furthermore, curcumin significantly decreased the p-Smad3C protein level in TGF-β-activated cells, with fold changes of 3 and 2 observed at 75 and 100 μM, respectively. Conclusions: Curcumin decreased the levels of ROS and NOX, as well as the expression of α-SMA and collagen1-α. The primary mechanism for this reduction could be linked to the level of p-Smad3C. Hence, curcumin could serve as an effective therapeutic agent for liver fibrosis.