Age-related effects of cocultured rat nucleus pulposus cells and macrophages on nitric oxide production and cytokine imbalance

Study Design. A study of age-related effects on nitric oxide (NO) and cytokine production in cocultured rat nucleus pulposus (NP) cells and macrophages. Objective. To evaluate the effects of age on NO and cytokine production in an in vitro model of cocultured NP cells and macrophages. Summary of Background Data. It is well known that the clinical characteristics of lumbar disc herniation differ with age. The relationship between age-related differences in clinical features and immuno-chemical factors, such as NO and inflammatory cytokines, has not been established. Methods. Male Sprague Dawley rats (n = 45), including 15 animals from 3 groups (3-, 12-, and 32-weeks old), were used. NP cells and exudated peritoneal macrophages were cocultured in serum-free media. NO levels were measured at 2-, 24-, 48-, and 72 hours using the Griess method. After 7 days of culture, the production of cytokines, including tissue inhibitor metalloproteinase-1, interferon-gamma (IFN-gamma), and interleukin-10 (IL-10) were evaluated. Results. NO levels of coculture increased with age. In the coculture groups, tissue inhibitor metalloproteinase-1 and IFN-gamma level of 3 weeks old were statistically higher than 12 and 32 weeks old. IL-10 level of 3 weeks old was statistically lower than 12 and 32 weeks old. Conclusion. NO levels of cocultures increased with age that suggests inflammatory reactions increase with age. This study showed an age-related cytokine imbalance, as represented by levels of IFN-gamma and IL-10. Stress and aging are thought to affect the extracellular matrix and change the immunologic response. Younger rat NP cells had higher cell-mediated immunity activity, while the older rat had higher humoral immunity activity. These results demonstrate that age affects the immunologic response attributable to NP cells. Further studies are needed to elucidate the mechanism of this newly observed occurrence and to apply these findings clinically.