Sulforaphane Induces Oxidative Stress and Death by p53-Independent Mechanism: Implication of Impaired Glutathione Recycling

Abstract

Sulforaphane (SFN) is a naturally-occurring isothiocyanate best known for its role as an indirect antioxidant. Notwithstanding, in different cancer cell lines, SFN may promote the accumulation of reactive oxygen species (ROS) and cause cell death e.g. by apoptosis. Osteosarcoma often becomes chemoresistant, and new molecular targets to prevent drug resistance are needed. Here, we aimed to determine the effect of SFN on ROS levels and to identify key biomarkers leading to ROS unbalance and apoptosis in the p53-null MG-63 osteosarcoma cell line. MG-63 cells were exposed to SFN for up to 48 h. At 10 μM concentration or higher, SFN decreased cell viability, increased the%early apoptotic cells and increased caspase 3 activity. At these higher doses, SFN increased ROS levels, which correlated with apoptotic endpoints and cell viability decline. In exposed cells, gene expression analysis revealed only partial induction of phase-2 detoxification genes. More importantly, SFN inhibited ROS-scavenging enzymes and impaired glutathione recycling, as evidenced by inhibition of glutathione reductase (GR) activity and combined inhibition of glutathione peroxidase (GPx) gene expression and enzyme activity. In conclusion, SFN induced oxidative stress and apoptosis via a p53-independent mechanism. GPx expression and activity were found associated with ROS accumulation in MG-63 cells and are potential biomarkers for the efficacy of ROS-inducing agents e.g. as co-adjuvant drugs in osteosarcoma.

Sulforaphane induces ROS mediated induction of NKG2D ligands in human cancer cell lines and enhances susceptibility to NK cell mediated lysis

“…These results thus suggest the involvement of ROS in SFN induced increase in MICA/MICB expression. This is in agreement with many reports which confirm that the ROS mediated signaling pathway is the major mediator of SFN including induction of Antioxidant Response Element (ARE) genes as well as mediating mitotic arrest or apoptosis [24,39,40]. Increase in the expression of cyclin B1 and the phosphorylation of Cdk1 on treatment with sulforaphane was also found to be reversed by NAC pretreatment confirming that ROS is the major player in mediating the effects of SFN [41].…”

Anticancer Mechanism of Sulfur-Containing Compounds

“…PEITC (15 μM) and SFN (60 μM) rapidly and selectively oxidize the mitochondrial Prx3, but not the cytosolic Prx1 and Prx2, which are not oxidized under the same conditions [1,101]. Increased levels of ROS are reported after SFN treatment (5-20 μM) of p53-null MG63 osteosarcoma cells [104] and PEITC and BITC treatment of U-2 OS cells (10 μM and 7.5 μM, respectively) [100]. Pretreatment with NAC abolished apoptosis and ROS generation [100].…”

Acute sulforaphane action exhibits hormonal and metabolic activities in the rat: in vivo and in vitro studies

“…Because SF stimulated a significant insulin secretion without any rise in blood glucose concentration, some direct SF influence on pancreas could be suggested. The ability of SF to promote ROS generation in several cell types was demonstrated by Ferreira de Oliveira et al (2014). Lately, the activation of insulin secretion by transient increase in ROS immediately following the onset of SF was proved by Fu et al (2013).…”

“…Generally, SF is recognized as an anti-inflammatory agent in pathological hyperglycemic and oxidative conditions as well as an inducer of phase 2 enzymes via the nuclear factor E2-related factor 2 (Nrf2) transcriptional activator (Shan et al 2010;Bahadoran et al 2013). Recent documentation shows that the exposure to SF can also result in a transient ROS burst, the duration and magnitude of which are both dependent on the SF concentration and exposure period (Ferreira de Oliveira et al 2014). The occurrence of oxidative stress reliant on the dose of isothiocyanates and its short-time action was recorded in our previous study (Okulicz et al 2005).…”

“…This seems to be additionally strengthened by the glutathione depletion. Conjugation of SF with glutathione (a necessary step in SF metabolism) depletes its intracellular concentration and probably lowers the oxidative stress threshold of the cells (Ferreira de Oliveira et al 2014). The key role in the regulation of energy homeostasis leading to alteration of plasma TG in chylomicrones, VLDL particles and steatosis in the liver is played by peroxisome proliferatoractivated receptors (PPARs) (Gavrilova et al 2003;Bahadoran et al 2013).…”