Examining the Role of Ascorbic Acid in Prevention of Heterotopic Ossification

Abstract

Heterotopic ossification (HO) is a condition in which mature bone forms in a non-osseous tissue following extreme trauma such as injury or surgery (1]. It is thought that a particular cell type known as mesenchymal stem cells (MSCs) are the main contributor to this condition. Here we identify muscle precursor cells (MPCs), a population of multipotent stem cells, as an alternative source of HO. The present study confirms this potential of MPCs to be induced into an osteogenic lineage, demonstrating significant increases in alkaline phosphatase (ALP) activity when MPCs were treated with 100ng/ml bone-morphogenetic protein-2 (BMP-2), (p$0.05). These findings were used to develop the model for this study. The main objective of this study was to examine the efficacy of vitamin C (ascorbic acid) as a potential new prophylactic treatment for HO. Current prophylactic treatments include radiation therapy and the use of non-steroidal anti-inflammatory drugs (NSAIDs). Radiation therapy works based on the production of reactive oxygen species (ROS) which cause oxidative stress in the individual, thereby disrupting the mechanisms associated with HO. These preventative treatments however are either expensive and/or may result in non­ union of normal bone or other harmful side-effects. As such, a new preventative treatment is needed for this condition. This study demonstrates that at doses of 200µM ascorbic acid functions as a pro-oxidant by producing a type of ROS; superoxide. When cells were treated with 200µM ascorbic acid in combination with 100ng/ml BMP-2, ALP activity did not increase. This suggests that ascorbic acid is able to block BMP-2-induced osteogenesis of MPCs. When cells were treated further with an antioxidant, 1mM TEMPOL, in combination with 1OOng/m l BM P -2 and 200µM ascorbic acid, alkaline phosphatase activity significantly increased. These data suggest that ascorbic acid can act as a pro-oxidant to create oxidative stress and prevent osteogenesis in MPCs. If administered at the appropriate dose, this treatment may function in a similar way to radiation therapy, by disrupting mechanisms involvedwith HO via oxidative stress, without the negative side-effectsor harmful risks. The results of this study indicate that ascorbic acid should be further explored in animal models and clinical trials as a potential prophylactic treatment for HO.