Bone and the Gulf War

Gulf War Illness: Unifying Hypothesis for a Continuing Health Problem

An estimated 25%⁻32% of veterans of the 1991 Gulf War continue to experience multiple unexplained health problems known as Gulf War Illness (GWI). GWI encompasses chronic pain, musculoskeletal weakness, headache, fatigue, cognitive deficits, alterations in mood, and numerous multi-system complaints. Most potential exposures implicated in GWI were not well documented but included varying levels of several neurotoxicants as well as the anticholinergic drug pyridostigmine bromide (PB), which was routinely taken as prophylaxis against the nerve agent soman. While some veterans also took chloroquine as an antimalarial agent, the literature suggests an association between receipt of multiple vaccinations prior to or during the conflict (perhaps combined with other exposures), and GWI. In-theater exposures may account for any single individual veteran's ill health but many veterans of the same era who were not deployed overseas also suffer the same or similar symptoms. The features of GWI also overlap with those of fibromyalgia, chronic fatigue syndrome and multiple chemical sensitivity, in all of which liver dysfunction has been documented, suggesting a unifying hypothesis. It is proposed that multiple vaccinations, with concurrent or subsequent exposure to PB or additional chemical insults of a liver-damaging nature, plausibly explain the pathogenesis and the observed chronicity of GWI. The suggested mechanism for GWI is thus a chemically-induced impaired liver function, with the spillage of stored vitamin A compounds ("retinoids") into the circulation in toxic concentrations, resulting in an endogenous chronic form of hypervitaminosis A. Implications of the hypothesis are briefly reviewed.

The negative impact of single prolonged stress (SPS) on bone development in mice

Posttraumatic stress disorder (PTSD) disrupts hypothalamic-pituitary-adrenal (HPA) axis function. Given the established role of HPA axis hormones in regulating bone metabolism, we tested the hypothesis that traumatic stress has a negative impact on bone development. We employed a variant single prolonged stress (SPS) model in which several stressors were applied to three week old C57BL/6J mice. Compared to the controls, the stressed mice showed increased freezing behavior reminiscent of PTSD symptoms. At two weeks, bone mineral content (BMC), bone area (B area) and bone mineral density (BMD) in total body based on dual-energy X-ray absorptiometry (DXA) analysis were reduced by 10.2%, 7.0% and 3.6%, respectively. Micro-CT analysis of the metaphyseal region of the excised tibia revealed that SPS caused a deterioration of trabecular architecture with trabecular number (Tb.N), BV/TV, connectivity density (Conn-Den) decreasing 12.0%, 18.9%, 23.3% and trabecular spacing (Tb.Sp), structure model index (SMI) increasing 13.9%, 21.8%, respectively. Mechanical loading increased the cross-sectional area in the mid-shaft region of the loaded right versus unloaded left tibia by 7.6% in the controls, and 10.0% in the stressed mice. Therefore, SPS applied to pre-pubertal young mice produced strong negative impact on both bone mass acquisition and trabecular architecture. Mechanical loading can be employed to increase bone size, a parameter related to bone strength, in normal as well as stressed conditions.

Lasting consequences of traumatic events on behavioral and skeletal parameters in a mouse model for post-traumatic stress disorder (PTSD)

BACKGROUND

Post-traumatic stress disorder (PTSD) is an anxiety disorder that not only affects mental health, but may also affect bone health. However, there have been no studies to examine the direct relationship between PTSD and bone.

METHODOLOGY/PRINCIPAL FINDINGS

We employed electric shocks in mice to simulate traumatic events that cause PTSD. We also injected the anxiogenic drug FG-7142 prior to electric shocks. Electric shocks created lasting conditioned fear memory in all mice. In young mice, electric shocks elicited not only behavioral response but also skeletal response, and injection of FG-7142 appeared to increase both types of response. For example in behavioral response within the first week, mice shocked alone froze an average of 6.2 sec in 10 sec tests, and mice injected with FG-7142 froze 7.6 sec, both significantly different (P<0.05) from control mice, which only froze 1.3 sec. In skeletal response at week 2, shocks alone reduced 6% bone mineral content (BMC) in total body (P = 0.06), while shocks with FG-7142 injection reduced not only 11% BMC (P<0.05) but also 6% bone mineral density (BMD) (P<0.05). In addition, FG-7142 injection also caused significant reductions of BMC in specific bones such as femur, lumbar vertebra, and tibia at week 3. Strong negative correlations (R(2) = -0.56, P<0.05) and regression (y = 0.2527-0.0037 * x, P<0.01) between freezing behavior and total body BMC in young mice indicated that increased contextual PTSD-like behavior was associated with reduced bone mass acquisition.

CONCLUSIONS/SIGNIFICANCE

This is the first study to document evidence that traumatic events induce lasting consequences on both behavior and skeletal growth, and electric shocks coupled with injection of anxiogenic FG-7142 in young mice can be used as a model to study the effect of PTSD-like symptoms on bone development.