Circulating endocannabinoids and genetic polymorphisms as predictors of posttraumatic stress disorder symptom severity : heterogeneity in a community-based cohort

Terri A. deRoon-Cassini, Carisa L. Bergner, Samantha A. Chesney, Nicholas R. Schumann, Tara Sander Lee, Karen J. Brasel and Cecilia J. Hillard

Translational Psychiatry, 2022, 12, 48, 1-12.

Doi : 10.1038/s41398-022-01808-1

 

The endocannabinoid signaling system (ECSS) regulates fear and anxiety. While ECSS hypoactivity can contribute to symptoms of established post-traumatic stress disorder (PTSD), the role of the ECSS in PTSD development following trauma is unknown. A prospective, longitudinal cohort study of 170 individuals (47% non-Hispanic Caucasian and 70% male) treated at a level 1 trauma center for traumatic injury was carried out. PTSD symptom assessments and blood were obtained during hospitalization and at follow-up (6–8 months post injury). Serum concentrations of the endocannabinoids N-arachidonoyl-ethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) were determined at both time points and selected genetic polymorphisms in endocannabinoid genes, including rs324420 in fatty acid amide hydrolase, were assessed. For the entire sample, serum concentrations of AEA at hospitalization were significantly higher in those diagnosed with PTSD at follow-up (p = 0.030). Serum concentrations of 2-AG were significantly, positively correlated with PTSD symptom severity at follow-up only in minorities (p = 0.014). Minority participants (mostly Black/African American) also demonstrated significant, negative correlations between serum AEA concentrations and PTSD symptom severity both measured at hospitalization (p = 0.015). The A/A genotype at rs324420 was associated with significantly higher PTSD symptom severity (p = 0.025) and occurred exclusively in the Black participants. Collectively, these results are contrary to our hypothesis and find positive associations between circulating endocannabinoids and risk for PTSD. Minority status is an important modulator of the association between endocannabinoids and risk for PTSD, suggesting that the ECSS contributes to risk most significantly in these individuals and the contextual factors related to these findings should be further explored.

 

INTRODUCTION

Each year, approximately 2.5 million people in the United States are involved in a traumatic event that requires emergent care at a trauma center [1, 2]. Epidemiological studies indicate that over 10% of the general population has a diagnosis of post-traumatic stress disorder (PTSD) [3], and those who have experienced a traumatic injury are at greater risk for the disorder than the general population [4]. PTSD following injury is negatively related to the physical and mental quality of life after trauma and occurs
in 25–40% of those traumatically injured [5]. Given these data, understanding factors that predict risk for the ultimate development of PTSD will inform better clinical approaches to the treatment of trauma that prevent PTSD.

Considerable evidence indicates that the endocannabinoid signaling system (ECSS) is stress-responsive and contributes to the regulation of anxiety and fear [6]. The ECSS includes the CB1 cannabinoid receptor (CB1R) and two endogenous ligands, Narachidonoylethanolamine (AEA) and 2-arachidonoyl-glycerol (2-AG) [7]. CB1Rs are highly expressed throughout the brain, including regions involved in the processing of fear and formation of memories [8]. Brain ECSS subserves activity-dependent, retrograde
synaptic signaling, thus plays a vital role in moment-tomoment synaptic activity [9]. Importantly, glucocorticoids [10, 11] and corticotropin-releasing factor [12] regulate brain concentrations of 2-AG and AEA, respectively; and many preclinical studies demonstrate that the ECSS is an important link between stress exposure and changes in synaptic activity, particularly in limbic brain regions [13].

Preclinical studies demonstrate that hypoactivity of the ECSS produces effects that are similar to symptoms of PTSD, including increased anxiety-related behaviors [14], deficient extinction of aversive memories [15], and sleep dysregulation [16]. On the other hand, the elevation of AEA-mediated CB1R activation through inhibition of fatty acid amide hydrolase (FAAH) is anxiolytic under aversive conditions [14]; promotes fear extinction, a component of coping and adaptation following traumatic stress [17]; and normalizes PTSD-like symptoms in a rat model [18]. In a clinical sample exposed to the 9/11 World Trade Center attacks 4–6 years prior, diagnosis of non-remitting PTSD was significantly related to reduced concentrations of circulating 2-AG compared to traumaexposed non-PTSD individuals [19]. Taken together, these studies support the hypothesis that hypoactive ECSS could exacerbate
while increased ECSS activity could alleviate PTSD symptoms.

Polymorphisms in human genes for proteins of the ECSS have been identified that support a role for the ECSS in emotional regulation [20]. In particular, polymorphisms in the CB1R gene (CNR1) are associated with anhedonia in individuals exposed to childhood abuse [21] and could interact with other genes to contribute to anxiety phenotypes [22]. A genetic polymorphism in FAAH (rs324420) influences amygdalar reactivity in response to threatening, fearful, and angry faces in healthy subjects [17, 23].
Carriers of the A allele at this locus exhibit quicker habituation of amygdala reactivity to threat and low scores on a personality trait of stress-reactivity [17] but, in individuals with anxiety disorders, A
allele carriers are more prone to anxiety [24, 25].

Thus, there is emerging evidence that the state of activation of the ECSS could contribute to the symptoms of established PTSD. However, what is not known is the relationship of the ECSS to the
risk for the development of PTSD. To address this gap, we assessed serum 2-AG and AEA concentrations soon after trauma in traumatically injured individuals and examined their correlations with PTSD diagnosis and symptom burden 6–8 months later, particularly for ethnic/racial minority patients and women, who have been shown to be at greatest risk for PTSD following trauma [26]. Our central hypothesis, based upon the preclinical literature, proposed that elevated serum concentrations of 2-AG and AEA at the time of trauma would be associated with reduced PTSD symptoms 6–8 months later. Similarly, we predicted that individuals with the minor allele at rs324420 would exhibit less
PTSD symptom severity. Given that several polymorphisms in the gene for the CB1R have been associated with altered risk for the development of psychopathology [13], we carried out exploratory
studies of CNR1 polymorphisms at rs1049353, rs806371, and rs2180619 in association with risk for PTSD without a priori hypotheses.

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