Differential response of porcine osteoblasts and chondrocytes in cell or tissue culture after 5-aminolevulinic acid-based photodynamic therapy.
OBJECTIVE
Outcome in osteochondral allografting is limited by the immunological incompatibility of the grafted tissue. Based on a resistance of chondrocytes to photodynamic therapy in cell culture it is proposed that 5-aminolevulinic acid-based photodynamic therapy (5-ALA-PDT) might be used to inactivate bone while maintaining viability of chondrocytes and thus immunomodulate bone selectively.


METHODS
Chondrocytes and osteoblasts from porcine humeral heads were either isolated (cell culture) or treated in situ (tissue culture). To quantify cytotoxic effects of 5-ALA-PDT (0-20 J/cm(2), 100 mW/cm(2)) an (3-(4,5-dimethylthiazol-2-yl)-2,5-di-phenyltetrazolium bromide) (MTT)-assay was used in cell culture and in situ hybridization in tissue culture to assess metabolic active cells (functional osteoblasts: col alpha(1)(I) mRNA, functional chondrocytes: col alpha(1)(II) mRNA).


RESULTS
In cell culture, survival after 5-ALA-PDT was significantly higher for chondrocytes (5 J/cm(2): 87+/-12% compared to untreated cells) than for osteoblasts (5J/cm(2): 12+/-11%). In tissue culture, the percentage of functional chondrocytes in cartilage showed a decrease after 5-ALA-PDT (direct fixation: 92+/-2%, 20 J/cm(2): 35+/-15%; P<0.0001). A significant decrease in the percentage of bone surfaces covered by functional osteoblasts was observed in freshly harvested (31+/-3%) compared to untreated tissues maintained in culture (11+/-4%, P<0.0001), with no further decrease after 5-ALA-PDT.


CONCLUSIONS
Chondrocytes were more resistant to 5-ALA-PDT than osteoblasts in cell culture, while in tissue culture a loss of functional chondrocytes was observed after 5-ALA-PDT. Since osteoblasts - but not chondrocytes - were sensitive to the tissue culture conditions, devitalized bone with functional cartilage might already be achieved by applying specific tissue culture conditions even without 5-ALA-PDT.
Department of Clinical Research, Group for Bone Biology and Orthopaedic Research, University of Bern, Switzerland. johannesbastian@gmx.de
J D
JD
Bastian
R J
RJ
Egli
R
R
Ganz
W
W
Hofstetter
M
M
Leunig
D000622:Aminolevulinic Acid / Q000494:pharmacology*; D000818:Animals; D002358:Cartilage, Articular / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects* / Q000528:radiation effects; D005240:Feasibility Studies; D010006:Osteoblasts / Q000187:drug effects* / Q000528:radiation effects; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology*; D034421:Sus scrofa; D046509:Tissue Culture Techniques
D017319:Photosensitizing Agents; D000622:Aminolevulinic Acid