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.
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