Oxidative stress and thiols depletion impair tibia fracture healing in young men with type 2 diabetes

Diabetes mellitus is a metabolic disorder that enhances fracture risk and hinders bone formation. The aim of the present study was to evaluate the parameters of oxidative stress, metallothioneins (MTs), metabolic changes and cytotoxicity signs in blood of young men with (DTF group) and without (TF group) type 2 diabetes (T2D) mellitus who had a tibia fracture due to trauma in relation to specific markers of bone formation. The level of reactive oxygen species was determined using a ROS-sensitive fluorescent dye dihydrorhodamine, DNA fragmentation was detected with Hoescht 33342 fluorescent dye and caspase-3 was assessed in terms of acetyl-Asp-Glu-Val-Asp p-nitroanilide. All other studied indices were determined by standard spectrometric methods. Our results revealed the significant effect of T2D on the bone healing. Indeed, the indices variation in the DTF group were significantly deeper as compared to group TF. The bone fracture in both TF and DTF groups had led to a significant decrease in antioxidants activity and/or level and a consistent increase in signs of oxidative damage. The concentration of MTs was also altered by trauma, but ina group-specific manner: an increase was noted in TF patients after trauma while in diabetes group a decrease in MTs was observed. Likewise, glutathione was strongly suppressed (by -64%) in DTF group. Tibia fracture provoked cytotoxicity which was manifested by increasing lactate dehydrogenase (LDH), cholinesterase and caspase-3 activity, the key effector of apoptosis in osteoclasts. The activity of alkaline phosphatase and total calcium increased only in TF group which demonstrated adequate remodelling process. The most prominent indices for groups splitting include ROS concentration, caspase 3, glutathione transferase and LDH activities mostly conjoint to DTF group. In sum, T2D impairs bone healing under condition of severe oxidative stress and cellular thiols depletion which result in an increase in apoptosis and DNA fragmentation. Our findings establish a biochemical link between increased oxidative stress and reduced bone markers and provide a rational for further studies investigating the role of pro- and antioxidants in bone healing.