Stem Cell Numbers and Quality in a Group of Patients Undergoing Hip Replacement Surgery: Increasing Marrow Fat and Plasma IL-6 Concentrations with Aging.

Diseases such as anemia which increase with age may be indicative of a decline in stem cell numbers and quality. Anemia in many elderly patients is thought to be mediated by inflammatory cytokines. Interleukin-6 (IL-6) has been reported to increase with age and to have negative effects on myelopoiesis. Another change which may correlate with age and a related decline in stem cell quality is an increase in marrow fat content. The present investigation was designed to evaluate stem cell numbers and quality in a group of patients undergoing hip replacement surgery and correlate stem cell characteristics with the percentage of fat in the marrow and plasma IL-6 concentrations. Marrow stem cells were obtained from the femoral head and trochanter at surgery. Quality was assessed by measuring the proportion of cells in the lower tip of the marrow side population compared to the upper side population by flow cytometry. Fat content in the marrow was measured as a percentage of total volume after sedimentation. A sandwiched-type ELISA was used to measure plasma IL-6 concentrations (R and D Systems). A total of 30 patients were analyzed (36–87 years of age). The number of side-population cells (stem cell numbers) declined with increasing fat content of the marrow. No difference was seen in the ratio between lower and upper side populations (stem cell quality) with age or fat content. Plasma IL-6 concentrations significantly increased with age confirming prior reports (r=0.37; p=0.03). IL-6 concentrations did not correlate with fat content of the marrow. This data suggests that marrow conversion from red (low fat) to yellow (high fat) increases with age along with plasma IL-6 concentrations but these are independent processes. Other inflammatory cytokines are currently under evaluation as potential mediators of the decline in the stem cell compartment with age with particular emphasis on various adipokines since the decline appears to correlate with increased marrow fat content.