The Effects of Ascorbic Acid in the Treatment of Radiation-Induced Bone Damage

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Abstract

Introduction: Radiation-associated bone loss arises from a combination of damage to osteoblasts and increase in osteoclast number and activity after radiation exposure, leading to an osteoporotic-like state. L-ascorbic acid (AA) exerts an anabolic effect on bone by promoting osteoblast differentiation and osteoclast apoptosis in vitro. Its safety profile and antioxidant properties make for an ideal therapeutic to prevent radiation-associated bone loss.

Research Problem: Does ascorbic acid 1) prevent the decrease in proliferation and differentiation of preosteoblast cells from ionizing radiation, 2) attenuate the stimulatory effect of ionizing radiation on osteoclast precursor cells via uncoupling of osteoblast-osteoclast feedback loop via the Wnt/β-catenin Pathway, and 3) maintain the morphology and biomechanical properties of bone in rats that receive a clinically translatable course of fractionated radiation therapy?

Methods: Osteoblast (MC3T3-E1) and osteoclast (RAW 264.7) precursors were cultured in conditions of increasing AA doses, then irradiated at 2-Gy after 24 hours. Cell differentiation, osteoblast mineralization, osteoclast resorption activity was quantified. An in vivo study was performed in 68 adult female Sprague-Dawley rats divided into four groups: irradiated (n=18), non-irradiated (n=15), irradiated+AA treatment (n=17), and non-irradiated+AA treatment (n=18). AA supplementation (2mg/mL) was provided in drinking water to animal subjects for the entire study duration. The right hindlimbs were irradiated and harvested four weeks after irradiation for biomechanical (four-point bend test) and micro-computed tomography (microCT) analyses.

Conclusions: Ascorbic acid attenuated the effects of radiation on mineralization, osteoclastogenesis, and bone resorption in vitro. Conversely, early prophylactic AA treatment in rats was not effective in reversing deleterious effects of radiation on trabecular bone compared to nonirradiated controls. The in vitro efficacy of AA treatment did not translate in rats receiving prophylactic AA treatment prior to hindlimb radiation.

Future Directions: Further research is needed to assess the in vivo viability of ascorbic acid as a prophylactic radioprotectant. A more efficacious mode of delivery of the ascorbic acid in animal subjects is warranted to determine if the in vitro effects found in our studies will translate to improvement in microarchitecture and biomechanical properties of bone following irradiation.

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