Role of pentoxifylline in preventing radiation damage to epiphyseal growth plate chondrocytes

Radiation therapy plays an important role as part of multimodality treatment for a number of childhood malignancies. The damaging effects of radiation on bone formation in children have been well documented. Recent work suggests that the postirradiation increase in cytosolic calcium is probably responsible for the deleterious effects of radiation on growth plate chondrocytes because it causes a specific suppression of the mitogen PTHrP. Using an in vitro model of avian growth plate chondrocytes, this study demonstrates that pentoxifylline is effective in increasing basal PTHrP mRNA levels and partially preventing the radiation-induced decrease in PTHrP mRNA. This effect of pentoxifylline is probably due to its ability to lower basal levels of cytosolic calcium and the radiation-induced increase in cytosolic calcium in chondrocytes. Pentoxifylline also prevented the radiation-induced decreases in [³H]thymidine uptake and BCL2 and PTHrP receptor mRNA levels in chondrocytes. The effects of pentoxifylline appear to be specific for the PTHrP signaling pathway because it did not alter basal TGFB mRNA levels or TGFB mRNA expression in irradiated chondrocytes. The results of the current study suggest that by decreasing basal cytosolic calcium levels and curtailing the radiation-induced increase in cytosolic calcium levels in chondrocytes, pentoxifylline is able to sustain PTHrP signaling in chondrocytes and maintains the proliferative signal that is necessary to prevent chondrocytes from undergoing apoptosis.