Role of CuZn superoxide dismutase in regulating lymphocyte apoptosis during sepsis

Objective: The lymphocyte is a principal mediator of the inflammatory respo nse, and lymphocyte depletion via apoptosis may be an important mechanism o f modulating inflammation. Increased oxygen consumption occurs during sepsi s and results in the generation of reactive oxygen species. Although reacti ve oxygen species initiate apoptosis in many biological systems, their role in controlling lymphocyte apoptosis during sepsis is unclear. The objectiv e of this study was to better characterize the role of oxidative stress in precipitating lymphocyte apoptosis during sepsis and to specifically define the role of the CuZn superoxide dismutase (SOD) enzyme complex, a major an tioxidant defense, in modulating this process. Design: Prospective, randomized, controlled study. Setting: Research laboratory at an academic medical center. Subjects: Mice that were either genetically normal or that were deficient i n or overexpressed the enzyme CuZn SOD. Interventions: Mice from each genetic group were randomized to no manipulat ion (control), sham surgery, or cecal ligation and puncture. Mice were kill ed 18-24 hrs after study entry, and the thymi and spleen were removed for a nalysis of apoptosis. Measurements and Main Results: Lymphocyte apoptosis was assessed by three i ndependent methods: light microscopy, fluorescent terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeIing, and DNA gel electrophoresis. Comparisons were performed using standard parametric s tatistical tests. Lymphocyte apoptosis was present in mice after CLP but no t in control mice or in mice after sham surgery (p < .05). Mice completely lacking CuZn SOD developed significantly more lymphocyte apoptosis than did either partially CuZn SOD-deficient or genetically normal mice (p < .05). This apoptosis was more pronounced in the thymus than the spleen and, withi n the thymus, more prominent in the cortex than medulla (p < .05 for all). In contrast, mice that overexpressed CuZn SOD did not differ in the amount of apoptosis after CLP compared with genetically normal mice (p = NS for al l). Conclusions: Oxidative stress occurs in sepsis and appears to be one stimul us for the development of lymphocyte apoptosis, a process that is partly re gulated by CuZn SOD. However, we were unable to demonstrate that overexpres sion of this enzyme suppressed lymphocyte apoptosis, suggesting that either other antioxidant defenses or other pathways independent of oxidative stre ss may mediate lymphocyte elimination in this syndrome.