title: Long-term culture of bovine nucleus pulposus explants in a native environment.
abstract: BACKGROUND
  Chronic low back pain is a disease with tremendous financial and social implications, and it is often caused by intervertebral disc degeneration. Regenerative therapies for disc repair are promising treatments, but they need to be tested in physiological models.
  
  
  OBJECTIVE
  To develop a physiological in vitro explant model that incorporates the native environment of the intervertebral disc, for example, hypoxia, low glucose, and high tissue osmolarity.
  
  
  METHODS
  Bovine nucleus pulposus (NP) explants were cultured for 42 days in conditions mimicking the native physiological environment. Two different approaches were used to balance the swelling pressure of the NP: raised medium osmolarity or an artificial annulus.
  
  
  METHODS
  Bovine NP explants were either cultured in media with osmolarity balanced at isotonic and hypertonic levels compared with the native tissue or cultured inside a fiber jacket used as an artificial annulus. Oxygen and glucose levels were set at either standard (21% O2 and 4.5 g/L glucose) or physiological (5% O2 and 1 g/L glucose) levels. Samples were analyzed at Day 0, 3, and 42 for tissue composition (water, sulfated glycosaminoglycans, DNA, and hydroxyproline contents and fixed charge density), tissue histology, cell viability, and cellular behavior with messenger RNA (mRNA) expression.
  
  
  RESULTS
  Both the hypertonic culture and the artificial annulus approach maintained the tissue matrix composition for 42 days. At Day 3, mRNA expressions of aggrecan, collagen Type I, and collagen Type II in both hypertonic and artificial annulus cultures were not different from Day 0; however, at Day 42, the artificial annulus preserved the mRNA expression closer to Day 0. Gene expressions of matrix metalloprotease 13, tissue inhibitor of matrix metalloprotease 1, and tissue inhibitor of matrix metalloprotease 2 were downregulated under physiological O2 and glucose levels, whereas the other parameters analyzed were not affected.
  
  
  CONCLUSIONS
  Although the hypertonic culture and the artificial annulus approach are both promising models to test regenerative therapies, the artificial annulus was better able to maintain a cellular behavior closer to the native tissue in longer term cultures.
authors: Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, GEM-Z 4.115, 5600 MB Eindhoven, The Netherlands.
authors: Bart G M
authors: BG
authors: van Dijk
authors: Esther
authors: E
authors: Potier
authors: Keita
authors: K
authors: Ito
mesh_terms: D000818:Animals; D002417:Cattle; D018929:Cell Culture Techniques / Q000379:methods*; D007403:Intervertebral Disc / Q000502:physiology*; D023421:Models, Animal