Mitochondria: A subcellular target to prevent non-steroidal anti-inflammatory drug (NSAID) -induced gastric ulcer
Non-steroidal anti-inflammatory drugs (NSAIDs) develop gastropathy, the cause for the induction of gastropathy is not yet clear. We have investigated the role of mitochondria on the development of indomethacin (a non-steroidal anti-inflammatory drug)-induced gastropathy in rat. Indomethacin, develops gastropathy by inducing mitochondrial pathology and reactive oxygen species (ROS) generation. Indomethacin damages mitochondrial ultrastructure and causes mitochondrial dysfunction as documented by transmission electron microscopic studies, decreased stage-3 respiration, dehydrogenase activity and transmembrane potential (Dym). Upregulation of proapoptotic Bax, Bak and downregulation of antiapoptotic Bcl-2, BclxL are found to occur in NSAID-induced gastric mucosal apoptosis, which favors mitochondrial translocation of Bax to open mitochondrial permeability transition pores (MPTP). Opening of MPTP releases apoptosis promoting factor, cytochrome c, which then activates caspase-9 and active caspase-9 further activates caspase-3. Mitochondrial pathology is associated with increased generation of intramitochondrial ROS, such as O2·-, H2O2 and ·OH leading to oxidative stress. O2·- is the most effective to damage mitochondrial aconitase, leading to the release of iron from its iron-sulfur cluster. Immunoprecipitation of mitochondrial aconitase and subsequent westernimmunoblotting indicate carbonylation of aconitase along with the loss of activity in vivo after indomethacin treatment. The release of iron has been documented by fluorescence imaging of mucosal cells by using Phen Green SK, a specific probe for chelatable iron. Interestingly, intra-mitochondrial ·OH generation is crucial for the development of mitochondrial pathology and activation of mitochondrial death pathway by indomethacin. Scavenging of ·OH by dimethyl sulfoxide or α-phenyl-n-tert-butyl-nitrone, a spin-trap, prevents indomethacin-induced mitochondrial ultrastructural changes, oxidative stress, collapse of Dym, and mitochondrial dysfunction. Scavenging of ·OH also prevents the activation of NSAID-induced gastric mucosal cell death and gastropathy.