title: The proliferative potential of human cardiac stem cells was unaffected after a long-term cryopreservation of tissue blocks.
abstract: BACKGROUND
  Human c-kit-positive cardiac stem cells (CSCs) have been used to treat patients suffering from ischemic cardiomyopathy. This study aimed to investigate whether a long-term storage of cardiac tissues would influence the growth potential of the subsequently isolated CSCs.
  
  
  METHODS
  A total of 34 fresh samples were obtained from various cardiac regions [right atrium (RA), left atrium (LA), and/or left ventricle (LV)] of 21 patients. From 12 of these patients, 18 samples kept frozen for ~2 years were employed to prepare and characterize the CSCs. After confirming the specificity of the cell sorting by c-kit immunolabeling, the growth rate (number of doublings per day), BrdU positivity, and colony forming unit (CFU) were measured in each CSC population; the values were compared among distinct cardiac regions as well as between fresh and frozen tissues from which CSCs were derived.
  
  
  RESULTS
  Among independent measurements indicating growth potential, the growth rate and BrdU positivity remarkably correlated in freshly prepared CSCs. The cells obtained from every examined region displayed a high proliferative capacity with the growth rate of 0.48±0.19 and the BrdU positivity of 15.0%±7.6%. The right atrial CSCs tended to show a greater growth than those in the other two areas. Similarly, the CSCs were isolated from tissue blocks, cryopreserved for ~2 years, and compared with CSCs derived from the fresh specimens of the same patients. Importantly, we were able to obtain and culture CSCs from every frozen material, and their proliferative potential, represented by the growth rate of 0.47±0.22 and the BrdU positivity of 13.7%±7.9%, was not inferior to that of the freshly prepared cells.
  
  
  CONCLUSIONS
  The long-term cryopreservation of cardiac tissues did not affect the growth potential of the derivative CSCs. Our findings should expand the therapeutic applications of these cells over a longer time span.
authors.affiliation: Tokai University Institute of Innovative Science and Technology, Kanagawa, Japan;; Department of Cardiology, Sakakibara Heart Institute, Tokyo, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Hosoda
authors.affiliation: Department of Cardiology, Sakakibara Heart Institute, Tokyo, Japan.
authors.forename: Nobuo
authors.initials: N
authors.lastname: Iguchi
authors.affiliation: Department of Cardiovascular Surgery, Tokai University School of Medicine, Kanagawa, Japan.
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Cho
authors.affiliation: Tokai University Institute of Innovative Science and Technology, Kanagawa, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Inoue
authors.affiliation: Department of Cardiology, Tokai University School of Medicine, Kanagawa, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Murakami
authors.affiliation: Department of Cardiovascular Surgery, Tokyo Bay Urayasu Ichikawa Medical Center, Chiba, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Tabata
authors.affiliation: Department of Cardiovascular Surgery, Sakakibara Heart Institute, Tokyo, Japan.
authors.forename: Shuichiro
authors.initials: S
authors.lastname: Takanashi
authors.affiliation: Department of Cardiology, Sakakibara Heart Institute, Tokyo, Japan.
authors.forename: Hitonobu
authors.initials: H
authors.lastname: Tomoike
keywords: Adult stem cells; c-kit receptor; cell proliferation; cryopreservation; heart