Objective: To compare chondrocyte proliferation and metabolism in three-dimensional fibrin cultures formed from polymerized autogenous fibrinogen with that of commercially manufactured fractionated fibrinogen.
Animals: Fibrinogen and chondrocytes for in vitro experimentation derived from 2 horses, ages 12 and 14 months, donated for reasons unrelated to skeletal or hematologic abnormalities.
Procedure: Fibrinogen was isolated from whole blood, using plasma cryoprecipitation and centrifugation, and fractionated fibrinogen was purchased. Each was mixed with 10 x 10(6) chondrocytes/0.5 ml of fibrinogen, and was polymerized by addition of 0.5 ml of calcium-activated thrombin. Thirty 1-ml fibrin-chondrocyte disks were formed from each fibrinogen source and cultured for 0 (n = 6), 7 (n = 12), or 14 (n = 12) days. Chondrocyte metabolism and cell proliferation in each fibrin type were objectively assessed by assays for total proteoglycan content, [35S]proteoglycan accumulation, proteoglycan monomer size, and total DNA. Cell morphology and cartilage-specific cell function was evaluated by routine histologic, alcian blue histochemical, type-II collagen immunohistochemical, and type-II collagen in situ hybridization methods.
Results: Histologic examination indicated better retention of chondrocyte morphology in autogenous composites. Autogenous fibrinogen also stimulated greater chondrocyte proliferation (DNA content increased 1.4-fold on day 14) and supported higher proteoglycan accumulation (increased 1.4-fold on day 14), compared with commercial, fractionated fibrinogen. Abundant intracellular type-II procollagen mRNA was detected in autogenous fibrin cultures by in situ hybridization, and translation was confirmed by extensive pericellular type-II collagen accumulation.
Conclusions: Autogenous fibrinogen has an inherent capacity to maintain chondrocyte phenotypic metabolism that is reduced or absent in commercially prepared fibrinogen. Enhanced, differentiated cell function may be useful for in vivo applications, but represents an added variable that may confound in vitro experiments, and should be considered when designing studies of chondrocyte function.