Ascorbic acid requirement for optimal flexor tendon repair in vitro.

Numerous studies from our laboratory have defined aspects of the repair process in a lacerated flexor tendon model, both in vivo and in vitro. Inherent in the development of a viable tissue or cell culture model system is the definition of the optimal media environment. Since our laboratory investigations of in vitro flexor tendon repair encompass the formation of numerous extracellular matrix proteins, we have defined the optimal level of ascorbic acid with which to study the tendon wound healing process. The ascorbic acid requirement for proline and lysine hydroxylase activity during collagen biosynthesis is well known, and the importance of this vitamin for matrix proteoglycan synthesis more recently has been appreciated. This report describes the effect of several levels of ascorbic acid on 3H-thymidine incorporation, collagen and noncollagen protein synthesis, and glucose utilization and lactate production. Profundus flexor tendon segments were obtained from young adult New Zealand white rabbits and maintained in organ culture for periods of 1, 2, or 3 weeks. Ascorbic acid concentrations ranged from 50 to 300 micrograms/ml and were added fresh at each 48-h media change. Tendon protein synthesis, glucose metabolism, and cell permeability/viability were significantly correlated with the level of ascorbic acid in the culture medium. The results suggest that ascorbic acid levels in excess of the traditional 50 micrograms/ml are necessary to optimally maintain flexor tendons from adult animals in organ culture with 48-h media and ascorbate changes. Additionally, it may be necessary to determine the precise ascorbic acid requirement for individual tissues, since the specific tissue/cell and species requirement for ascorbate may vary.