Demographic factors that influence human disc cell proliferation in vitro.

BACKGROUND CONTEXT: Although previous work has shown that greater age, greater disc degeneration, female gender, and surgical derivation of disc tissue had deleterious effects on cell proliferative potential, relatively little is known about the association between disc cell proliferation in vitro and clinical donor characteristics.

PURPOSE: To identify the relationships between donor characteristic and the in vitro proliferative potential of human disc cells from the annulus.

STUDY DESIGN/SETTING: Studies were approved by the human subjects Institutional Review Board. Donor data included donor source, ethnicity, age, gender, smoking history, height, weight, number of years of back pain, and Thompson score. Cells cultured from the annulus were tested for proliferation.

PATIENT SAMPLE: There were two study populations: 1) Comparison Group (32 control donors and 33 control surgical subjects; 60 Caucasians, 5 African-Americans). Cell proliferation, age, Thompson score, height, weight, and smoking history were statistically analyzed for control donors versus control surgical group. No significant differences were present, and these two groups were pooled to form the Comparison Group. 2) Nineteen subjects from the United Arab Emirates who underwent disc surgery.

OUTCOME MEASURES: Linear models were fit to the data to determine the best prediction of cell proliferation as the outcome variable; multiple R-squared was used to determine model goodness of fit.

METHODS: Control donor specimens were obtained from the National Cancer Institute Cooperative Human Tissue Network, and control donor surgical specimens from disc surgeries. A standardized cell proliferation assay was used to evaluate monolayer and three-dimensional agarose cell proliferation. Data were expressed as mean cpm[(3)H]-thymidine per microgram deoxyribonucleic acid+/-SEM. Standard statistical methods used the SAS system for data analysis.

RESULTS: No differences were present in the Comparison Group versus the Middle Eastern group for mean Thompson score (both averaged grade III), mean age (44.3 vs. 43.0 years, respectively), gender, height, weight, length of time with back pain (1.9 years vs. 2.1 years respectively), or smoking history. Three-dimensional proliferation in agarose was not significantly different for the two groups. Monolayer proliferation, however, was significantly different (17,434+/-2,929 vs. 6,693+/-2,103, respectively), p=.019. Linear regression models were fit to the data to determine the best prediction using proliferation as the outcome variable. In the Middle Eastern group, monolayer cell proliferation bore a significant negative correlation to age (p=.02, r=-.32), whereas the Comparison Group showed no such relationship. The following equation was derived to fit these data: Log(10) of proliferation (cpm/mug deoxyribonucleic acid)=10.915-0.7919 (Middle Eastern ethnicity)-0.0296 (Age). The r(2) for this equation is 0.203 (ie, 20.3% of the change in proliferation is explained by age and Middle Eastern ethnicity). Middle Eastern ethnicity and age were significant in this equation (p=.04 and .0003, respectively).

CONCLUSIONS: Studies have shown that familial history, age, and smoking are important risk factors for disc degeneration in Arabic pedigrees. It is interesting that our present findings also point to age and familial history as important significant factors influencing monolayer proliferation. Further research is needed to identify the cellular basis for this influence on cellular proliferative capacity.