Recovery From Fatigue and Injury in Rat Muscle Imbedded With Heavy Metals
Authors: Michaelson Luke , Lovering Richard M. , Kasper Christine E 
Published: November 2023

BackgroundWounds from improvised explosive devices (IEDS) are a continuing concern in current conflicts. These injuries have been associated with heavy metal deposition in the wound. Recent data indicated imbedded tungsten, nickel, and cobalt (WNiCo) alloy pellets induced rhabdomyosarcoma neoplastic malignancies in F344 adult rats. Additionally, these transition metals have been shown to produce reactive oxygen species (ROS), i.e. hydroxyl radicals (OH•) and hydrogen peroxide (H2O2).ObjectiveThe purpose of this study was to evaluate the long‐term effects of intramuscular heavy metal WNiCo fragments, which may be present in Veterans or in active duty service members wounded by IEDs. These experiments used a rat model to evaluate whether imbedded WNiCo alloy contributed to increased susceptibility to eccentric injury or fatigue potentially via ROS activation of NADPH Oxidase.HypothesesWe hypothesized 1) the imbedded metal type and imbedded duration will reduce muscle contractility. The force‐frequency data before and after eccentrically injuring or fatiguing the contralateral tibialis anterior muscle were used to assay the muscle contractility, and 2) gp91 PHOX, a subunit of NADPH Oxidase, is increased in tibialis anterior muscle from WNiCo imbedded rats.MethodsMale adult F344 rats were randomly assigned to two procedure groups; Eccentric Injury (N = 43) and Fatigue (N = 44). Each procedure group was then separated into subgroups; SHAM (procedure control), Tantalum (inert negative control), WNiCo, and Control. Four pellets (108 +/− 1.0 mg) of WNiCo or 4 pellets (92.1 +/− 2.4mg) of tantalum were aseptically inserted into a gastrocnemius muscle. After metal exposure for a short period (2 weeks) or a long period (14 weeks), an eccentric injury protocol or fatiguing protocol was induced. Force‐frequency measurements were performed before and 5 minutes after each protocol. The differences between the maximum tetanic force, twitch force, and tetanic/twitch ratios were compared. Western Blots probing for gp91 PHOX were used to semiquantitatively compare the protein within each group. A univariate one‐way analysis of variance was performed to determine differences in tetanic force, twitch force, tetanic/twitch ratios and densitometry between each group.ResultsNo significant differences were detected within the Eccentric Injury group. Within the Fatigue group, an overall difference was detected in the Pre‐Tetanic/Twitch values, F(6,40) = 4.945, p < .001. The Tukey post hoc tests indicated the SHAM Short Period, Pre‐Tetanic/Twitch mean, 4.27 (p< .05), was significantly greater than all means except those from the Control or Sham Long Period groups, 3.53, 3.23, respectively (p > .05).ConclusionsThe overall findings indicate that low dosages of WNiCo, imbedded up to 14 weeks do not produce a systemic effect, at least not to alter the contractility of other muscles. Future studies, may need to perform similar contractile experiments in rats imbedded for a longer period of time.Support or Funding InformationDepartment of Veterans Affairs, Office of Nursing Services Uniformed Services University, Daniel K. Inouye Graduate School of Nursing