Cytoprotective Effect of Curcumin in Human Proximal Tubule Epithelial Cells Exposed to Shiga Toxin

Abstract

We conducted the following experiments to determine whether curcumin, an antioxidant compound extracted from the spice tumeric, inhibits cell death induced by Shiga toxin (Stx) 1 and 2 in HK-2 cells, a human proximal tubule cell line. Cells were incubated for 24–48 h with Stx1 or Stx2, 0–100 ng/ml. Test media contained either no further additives or 10–50 μM curcumin. Exposure to Stx1 and Stx2, 100 ng/ml, reduced cell viability to approximately 25% of control values after 24 h and 20 μM curcumin restored viability to nearly 75% of control. Cell staining confirmed that Stx1 and Stx2-induced damage in HK-2 cells involved a combination of apoptosis and necrosis. Thus, Stx1 caused apoptosis and necrosis in 12.2 ± 2.2 and 12.7 ± 0.9% of HK-2 cells, respectively. Similarly, Stx2 caused apoptosis and necrosis in 13.4 ± 2.1 and 9.0 ± 0.5% of HK-2 cells, respectively. Addition of 20 μM curcumin decreased the extent of apoptosis and necrosis to 2.9 ± 2.0 and 3.8 ± 0.2%, respectively in the presence of Stx1 and to 3.0 ± 2.1 and 3.9 ± 0.3%, respectively, for Stx2 (P < 0.01). Stx-induced apoptosis and its inhibition by curcumin were confirmed by DNA gel electrophoresis and by an assay for fragmentation. The protective effect of curcumin against Stx1 and Stx2-induced injury to HK-2 was not related to its antioxidant properties. Instead, curcumin enhanced expression of heat shock protein 70 (HSP70) in HK-2 cells under control conditions and after exposure to Stx1 or Stx2. No injury was detectable after incubation of LLC-PK1 or OK cells, non-human proximal tubule cell lines, with Stx1 or Stx2. Thus, curcumin inhibits Stx-induced apoptosis and necrosis in HK-2 cells in vitro. The cytoprotective effect of curcumin against Stx-induced injury in cultured human proximal tubule epithelial cells may be a consequence of increased expression of HSP70.