Increased hepatic apoptosis during short-term caloric restriction is not associated with an enhancement in caspase levels. Exp. Gerontol

Abstract Long-term caloric restriction extends lifespan, probably through a reduction in radical production and attenuation of oxidative stress. In addition, caloric restriction is associated with a reduction and incidence in tumor pathology, probably, in part, via an enhanced rate of apoptosis. We examined whether short-term (2-month) caloric restriction (40% reduction compared to ad libitum controls) increased hepatic apoptosis and if this was associated by an enhancement in various proteolytic caspase (-3, -7, -9, -12) levels and/or a decrease in two potential inhibitors of apoptosis (the x-linked inhibitor of apoptosis protein XIAP and heat shock protein 70). Short-term caloric restriction resulted in a significant decline, compared to ad libitum controls, in both body mass (30%) and liver mass (46%). While hepatic apoptosis (DNA fragmentation) was significantly higher in the caloric restricted rats, this was not associated with any increase in caspase (-3, -7, -9, -12) levels in the liver. Indeed, the levels of caspase-3, -7 and -12 were significantly lower in the caloric restricted group compared to the ad libitum controls and no differences were observed between groups in either XIAP or HSP70 levels. These findings suggest that enhanced hepatic apoptosis observed after 2-months of caloric restriction is not a result of elevated caspase levels at this time, thereby suggesting that an alternative, caspase-independent pathway may be involved.

Doxorubicin treatment in vivo activates caspase-12 mediated cardiac apoptosis in both male and female rats

We investigated in vivo the chemotherapeutic anthracycline agents doxorubicin and its ability to activate mitochondrial-mediated, receptor-mediated and endoplasmic/sarcoplasmic reticulum-mediated apoptosis transduction pathways in cardiac tissue from male and female rats. We administered a single low dose of doxorubicin (10 mg/kg of body weight, i.p.) and then isolated mitochondrial and cytosolic proteins one and four days later from the heart. Caspase-3 protein content and caspase-3 activity were significantly increased after day four of doxorubicin treatment in both male and female rats. However, while males had DNA fragmentation at day one but not day four following doxorubicin administration, females showed no significant increase in DNA fragmentation at either time. Caspase-12, localized in the SR, is considered a central caspase, and its activation by cleavage via calpain indicates activation of the SR-mediated pathway of apoptosis. Cleaved caspase-12 content and calpain activity significantly increased after day four of doxorubicin treatment in both sexes. In the mitochondrial-mediated pathway, there were no significant treatment effects observed in cytosolic cytochrome c and cleaved (active) caspase-9 in either sex. In control rats (saline injection), glutathione peroxidase (GPX) activity and hydrogen peroxide (H2O2) production were lower in females compared to males. Doxorubicin treatment did not significantly affect H2O2, GPX activity or ATP production in isolated mitochondria in either sex. Female rats produced significantly lower levels of H2O2 production one day after doxorubicin treatment, whereas male rats produced significantly less mitochondrial H2O2 four days after doxorubicin treatment. The receptor-mediated pathway (caspase-8 and c-FLIP) showed no evidence of being significantly activated by doxorubicin treatment. Hence, doxorubicin-induced apoptosis in vivo is mediated by the SR to a greater extent than other apoptotic pathways and should therefore be considered for targeted therapeutic interventions. Moreover, no major sex differences exist in apoptosis signaling transduction cascade due to doxorubicin treatment