Targeting Mitochondrial Sphingolipids to Improve Brain Function in Gulf War Illness

Gulf War Illness (GWI) affects Veterans who were deployed in Southwest Asia during the Gulf War. GWI is multi‐symptom disease, which includes cognitive difficulties, depression, and anxiety. Meta‐analyses of epidemiological studies have causally linked these symptomatic profiles to prolonged chemical exposure to different pesticides and pyridostigmine bromide, a medication used as prophylaxis against chemical warfare attacks. Compelling evidence suggests that mitochondrial malfunction is a centerpiece of multiple converging processes implicated in GWI, including oxidative stress, altered synaptic transmission and inflammatory reactions. The focus of these studies is on the role of toxic sphingolipids and mitochondria in the pathogenesis of GWI. Sphingolipids are important structural components of cell membranes and pleiotropic messengers in intracellular signaling pathways. Mitochondria support energy production for biosynthetic reactions, maintenance of ion/metabolite gradients and muscular contractions. Our central hypothesis is that chemical exposure disrupts the lipid metabolism network leading to activation of acid sphingomyelinase (ASMase), a crucial enzyme of sphingolipid metabolism, and generation of toxic sphingolipids in mitochondria. To induce GWI, animals were administered a combination of pyridostigmine bromide and permethrin, i.e. GW agents (GWA), in a single dose daily for 10 days. Quantitative assessment of mitochondrial sphingolipidome was conducted using a state‐of‐the‐art metabolomics technique, tandem mass spectrometry. The cognitive and memory deficits were assessed by video‐recording using an EthovisionXT system (Noldus) and data analysis with EthoVision 13 software. Consistent with our hypothesis, the results of the studies demonstrate a long‐lasting post‐transcriptional activation of ASMase during the six months following animal exposure to GWA. The sphingolipidome analysis revealed significant disturbances in both structural and toxic sphingolipids in response to GWA. Importantly, we have identified several ceramide species, well‐known endogenous inhibitors of mitochondrial function, upregulated in cerebral mitochondria post‐GWA exposure. In mitochondria, ceramide could inhibit mitochondrial respiratory chain Complex III, which would result in an increased ROS production and the loss of mitochondrial integrity. The data indicate that the source of mitochondrial ceramide accumulation is the ASMase‐mediated hydrolysis of sphingomyelin which occurs in lysosomes. The data highlight the importance of the mitochondrial compartment in GWI and accentuate the novel role of ASMase in brain impairment. An inhibitor of ASMase activity, Amitriptyline, ameliorated GWA‐induced changes in mitochondrial sphingolipidome and behavioral abnormalities. The data provide experimental evidence to support the concept that blocking ASMase activity confers mitochondrial protection and improves the cognitive function in an animal model of GWI that provide a foundation for further investigation of novel treatments aimed to improve brain function in GWI patients. Support or Funding Information The studies were supported by the DOD grant W81XWH‐18‐1‐0230 (SAN) and VA grant I01BX002991 (TIG)