Circulating plastic adherent mesenchymal stem cells in aged hip fracture patients.

We examined the presence of circulating plastic adherent multipotent mesenchymal stem cells (MSCs) in fracture patients. Three patient groups (n = 10-18) were evaluated, including elderly females with a femoral neck fracture treated with cemented hemiarthroplasty, an age- and sex-matched group with hip osteoarthritis (OA) treated with cemented total hip arthroplasty (THA), and younger adults with surgically treated lower extremity fractures. The presence of circulating MSCs pre- and postoperatively was compared to bone marrow (BM) MSCs from the same subjects. Criteria for identifying MSCs included cell surface markers (CD105+, CD73+, CD90+, CD45-, CD14-), proliferation through several passages as well as osteogenic, chondrogenic, and adipogenic differentiation. Plastic adherent MSCs were found in peripheral blood (PB) from 22% of hip fracture patients, 46% of younger fracture patients, and in none of 63 pre- and postmenopausal women with hip OA. When detectable, circulating MSCs appeared between 39 and 101 h after fracture. PB derived MSCs did not differ from BM derived MSCs, except for a small population (<15%) of CD34+ cells among PB derived MSCs. This initial study indicates mobilization of MSCs into the circulation in response to fracture, even in very old patients, while circulating MSCs were not detectable before or after elective THA.