Exposure of Rats to Permethrin, Pyridostigmine or Diethyl‐M‐Toluamide (DEET) Attenuates Skeletal Muscle Function.

Background Gulf War Illness (GWI) is a chronic multi-symptom disorder experienced by as many as a third of the veterans of the 1991 Gulf War. GWI mainly affects nervous and skeletal muscle (SkM) systems yielding cognitive deficit, depression, muscle pain, weakness, intolerance to exercise and fatigue. Military personnel was exposed to toxic substances such as insecticides and repellents like permetrim (PM), N;N-diethyl-m-toluamide (DEET), and pyridostigmine (PB) provided as a prophylactic for a nerve gas attack. Methods Three months old male Wistar rats were used for all experiments (n=50). Control group (n=10) were provided water (oral), 70% ethanol (applied to back skin). The PB group (n=10) were given pyridostigmine 1.3 mg/kg/day by oral gavage. The PM group (n=10) were dosed at 0.13 mg/kg/day (back of shaved skin in 70% ethanol). The DEET group (n=10) were dosed at 40 mg/kg/day (back skin in ethanol). A physically restrained group (n=10) was also included with animals being restrained for 5 min/day (in rat plexiglass holders). Treatments were provided daily for 3 weeks. At 6 weeks, animals were subjected to treadmill and front limb strength testing followed by euthanasia and SkM (gastrocnemius) muscles collected for histological and biochemical analysis. Results Animals exposed to chemicals did not evidence changes in body weight or food intake. The front limb strength of the animals was recorded weekly. Significant strength increases were recorded in control, PM, DEET and restricted groups. However, in the PB group strength increases were not detected showing ~ 35% decrease vs. contros. At the end of the treatment phase, overall physical endurance was evaluated on a treadmill. This evaluation demonstrated that the groups administered with the different chemical agents (PM, PB and DEET) significantly blunted the fatigue resistance time (on average 12 minutes) vs. controls (18 min). The gastrocnemius mass (weight) of animals exposed to PB, PM and DEET were significantly decreased by ~15% vs. controls. Gastrocnemius myofiber cross area measurements (CSA) were measured and results demonstrate that in the PB, PM and DEET groups it is significantly decreased by ~13% vs. controls. Oxidative stress levels were assessed in muscles and we observed that groups administered with DEET, PM and PB increased carbonyl protein content (average >40 nmol/ml) vs. controls (25 nmol/ml). The plasma levels of the pro-inflammatory cytokines IL-1b, TNF-a, and IFN-g were elevated only in the PB group (vs. controls) with no differences noted with the other chemical agents. Conclusions Exposure of rodents to equivalent human doses of associated GWI chemicals leads to a loss of muscle mass and strength and/or function. These effects are likely related to increases in oxidative stress and/or pro-inflammatory cytokines.