Caspase inhibition causes hyperacute tumor necrosis factor–induced shock via oxidative stress and phospholipase A2

Abstract

Dysregulated apoptotic cell death contributes to many pathological conditions, including sepsis, prompting the suggestion that caspase inhibition to block apoptosis could have useful therapeutic applications. Because the cytokine tumor necrosis factor (TNF, also known as TNF-alpha) is both pro-apoptotic and pro-inflammatory and is involved in septic shock, we tested whether caspase inhibition would alleviate TNF-induced toxicity in vivo. General caspase inhibition by the protease inhibitor zVAD-fmk exacerbated TNF toxicity by enhancing oxidative stress and mitochondrial damage, resulting in hyperacute hemodynamic collapse, kidney failure and death. Thus, survival of TNF toxicity depends on caspase-dependent processes. Our results demonstrated the pathophysiological relevance of caspase-independent, ROS-mediated pathways in response to lethal TNF-induced shock in mice. In addition, survival of TNF toxicity seemed to require a caspase-dependent protective feedback on excessive reactive oxygen species (ROS) formation and phospholipase A2 activation.

Serine protease inhibitor 2A inhibits caspase‐independent cell death

“…However, we could not exclude the possibility that the suppression of PCD by Spi2A was due not only to the inhibition of lysosomal cathepsins but also the inhibition of caspases other than the ones we have tested. In this study, we observed as have others [8][9][10] that even when caspase activation was suppressed by Z-VAD.fmk, TNF-a still triggered the release of cathepsin B from the lysosomes, induced mitochondrial permeabilization and induced ROS production. Importantly, the present study clearly indicates for the first time that the abrogation of PCD by Spi2A does not require caspases as targets of inhibition.…”

“…For example, AIF and the pro-apoptotic member of the Bcl-2 family -Bax -can induce apoptosis by dissipating mitochondrial potential in a Z-VAD.fmk-insentitive manner [20]. The damage of mitochondria that occurs in the absence of caspase activity leads to the leakage of ROS [10]. In the absence of caspases it has been suggested that other proteases, such as calpains, serine proteases and cathepsins substitute as dominant executioner proteases [20].…”

Heme Oxygenase-1 Couples Activation of Mitochondrial Biogenesis to Anti-inflammatory Cytokine Expression

“…This endogenous receptor antagonist Fourth, Nfe2l2-silenced cells challenged with LPS do not generate IL-10 or IL-1Ra, but produce more TNF-␣, which increases mitochondrial injury (65), intrinsic apoptosis (66), and reactive oxygen species-induced organ damage (67). TNF-␣ is in important pathologically as shown by the efficacy of anti-TNF therapy in several human inflammatory diseases (68).…”

Butylated hydroxyanisole is more than a reactive oxygen species scavenger

“…These data are confirmed by the inhibition of both TNF-and dsRNA-induced necrotic cell death by the complex I inhibitor rotenone (Figure 2c) 10 and an in vivo study showing partial blockage of zVAD-fmk/TNF-induced hyperacute cardiovascular collapse, renal damage and death of mice after pretreatment with rotenone. 11 Besides being an inhibitor of electron transport and a radical scavenger, BHA was also reported to inhibit lipoxygenases (LOXs). 12 These constitute a family of monomeric nonheme, nonsulfur iron dioxygenases that catalyze the conversion of polyunsaturated fatty acids into conjugated hydroperoxides.…”

“…The histograms represent an average of three independent experiments with error bars indicating standard error of the mean (S.E.M) PLA 2 has also been identified as another source of ROS in a study examining TNF-induced caspase-independent cell death in vivo. 11 The ROS-scavenging capacity of BHA has often been used to argue that ROS play a role in certain signaling pathways and in necrotic cell death in particular. Our results, however, emphasize the importance of considering all properties of BHA.…”