Time course analysis of the effect of embedded metal on skeletal muscle gene expression [Array]

As a consequence of military operations, many veterans suffer from penetrating wounds and long-term retention of military grade heavy metal fragments. Fragments vary in size and location, and complete surgical removal may not be feasible or beneficial in all cases. Increasing evidence suggests retention of heavy metal fragments may have serious biological implications, including increased risks for malignant transformation. Previous studies assessed the tumorigenic effects of metal alloys in rats, demonstrating combinations of metals are sufficient to induce tumor formation after prolonged retention in skeletal muscle tissue. In this study, we analyzed transcriptional changes in skeletal muscle tissue in response to eight different military-relevant pure metals over 12 months. We found that most transcriptional changes occur at 1 and 3 months after metal pellets are embedded in skeletal muscle and these effects resolve at 6 and 12 months. We also report significant immunogenic effects of nickel and cobalt and suppressive effects of lead and depleted uranium on gene expression. Overall, skeletal muscle exhibits a remarkable capacity to adapt to and recover from internalized metal fragments; however, the cellular response to chronic exposure may be restricted to the metal-tissue interface. This data suggests that unless affected regions are specifically captured by biopsy, it would be difficult to reliably detect changes in muscle gene expression that would be indicative of long-term adverse health outcomes. We investigated the effects of eight militarily relevant metals: tungsten (W), nickel (Ni), cobalt (Co), iron (Fe), copper (Cu), aluminum (Al), lead (Pb), and depleted uranium (DU). The control group followed all the same procedures utilizing the metal tantalum (Ta) to serve as the surgery sham, which would control for changes such as inflammatory response to surgery and embedded foreign material. Rats were randomly assigned to one of the nine metal implant groups (n=8/group) with each metal group conducted in 4 cohorts – 1, 3, 6, or 12 months post-implant surgery. A total of 288 rats (n=8 x 9 metal groups x 4 timed cohorts) were used in this study. All metal “pellets” were cylinders 1 mm in diameter x 2 mm in length.