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The elderly are less able to survive burn injury than young healthy individuals. Regardless of age, burn victims often succumb to secondary infections rather than the primary injury. Since immune responses diminish with age, it is likely that aged individuals are predisposed to a poor outcome by virtue of their weak immune system. Elevated production of macrophage-derived mediators, including interleukin-6 (IL-6), may lead to post-injury immunosuppression in young adults. Healthy aged individuals produce high circulating levels of these mediators; therefore, the combination of the age and burn trauma could further suppress immune responses and contribute to the rapid demise of aged burn patients. Herein, the effects of age and burn trauma using a murine scald injury model were examined. After injury, aged mice are less likely to survive, are unable to mount immune responses, and produce more IL-6 when compared to young adult mice given the same size injuries. Enhancing our understanding of the mechanisms responsible for regulating cell-mediated immune responses after injury could lead to the development of therapies designed to treat aged burn patients.

The aim of the present study was to determine whether oxidative stress contributes to aging of the liver in a mouse model. Liver was obtained from young (3-5 months old) and aged (18-24 months old) mice. No age-induced gross changes in liver morphology were detected by light microscopy. Apoptosis was measured using the fragment end labeling of DNA for the immunohistochemical identification of the apoptotic nuclei. The total apoptotic cells represented 1% of the total cells in livers of young mice and 8% in those of aged mice. Among the total apoptotic cells in livers of aged animals, 15% were hepatocytes, 40% sinusoidal endothelial cells, and 45% bile duct cells. Hepatic lipid peroxidation, expressed as malonaldehyde levels, protein oxidation, measured by protein carbonyl content, and DNA oxidation, measured as 8-hydroxy-2'-deoxyguanosine (oxo(8)dG), were significantly increased in the livers of aged animals as compared to younger mice. The apoptotic cells presented elevated levels of oxidized DNA, detected by immunohistochemistry using an antibody directed against oxo(8)dG in serial sections. These results suggest that livers of aged animals presents evidence of increased oxidative injury and apoptosis. Because the apoptotic cells in the aged livers are mostly bile duct cells and sinusoidal endothelial cells, the cells most sensitive to oxidative stress injury, it can be hypothesized that reactive oxygen species-induced apoptosis in these cells contributes to the aging of the liver.