Increased relative risk of delayed hemorrhage in patients taking anticoagulant/antiplatelet medications with concurrent aspirin therapy: implications for clinical practice based on 3-year retrospective analysis in a large health system.

PURPOSE: The incidence of delayed posttraumatic intracranial hemorrhage (DH) in patients on anticoagulant (AC) and antiplatelet (AP) medications, especially with concurrent aspirin therapy, is not well established, with studies reporting disparate results with between 1-10% risk of DH and 0-3% mortality. The purpose of this 3-year retrospective study is to evaluate the true risk of DH in patients on AP/AC medications with or without concurrent aspirin therapy. METHODS: One thousand forty-six patients taking AP and AC medications presenting to network emergency departments with head trauma who had repeat CT to evaluate for DH were included in the study. Repeat examinations were typically performed within 24 h (average follow-up time was 21 h and 99% were within 3 days). Mean time to DH was 20 h. All positive studies were reviewed by two board-certified neuroradiologists. Patients were excluded from the study if hemorrhage was retrospectively identified on the initial examination. Cases were reclassified as negative if hemorrhage on the follow-up examination was thought to be not present or artifactual. Cases were considered positive if the initial examination was negative and the follow-up examination demonstrated new hemorrhage. RESULTS: Overall, there was 1.91% incidence (20 patients) of DH and 0.3% overall mortality (3 patients). The group of patients taking warfarin or AP agents demonstrated a significantly higher rate of DH (3.2% compared to 0.9%) and higher mortality (0.9% compared to 0.0%) compared to the DOAC group (p < 0.01). The risk of DH in patients taking AC or AP agents with aspirin (13/20 cases) was significantly higher (RR 3.8, p < 0.01) than that of patients taking AC or AP alone (7/20 cases). CONCLUSION: The risk of DH was significantly higher in patients taking aspirin in addition to AC/AP medications. Repeat imaging should be obtained for trauma patients taking AC/AP agents with concurrent aspirin. The rate of DH was also significantly higher in patients taking warfarin or AP agents when compared to patients taking DOACs. Repeat examination should be strongly considered on patients taking warfarin or AP agents without aspirin. Given the relatively low risk of DH in patients taking DOACs alone, repeat imaging could be reserved for patients with external signs of trauma or dangerous mechanism of injury.

Enantiomer-specific positive allosteric modulation of CB1 signaling in autaptic hippocampal neurons.

The cannabinoid signaling system is found throughout the CNS and its involvement in several pathological processes makes it an attractive therapeutic target. Because orthosteric CB1 cannabinoid receptor ligands have undesirable adverse effects there has been great interest in the development of allosteric modulators - both negative (NAMs) and positive (PAMs) - of these receptors. NAMs of CB1 appeared first on the scene, followed more recently by PAMs. Because allosteric modulation can vary depending on the orthosteric ligand it is important to study their function in a system that employs endogenous cannabinoids. We have recently surveyed first generation NAMs using cultured autaptic hippocampal neurons. These neurons express depolarization induced suppression of excitation (DSE), a form of synaptic plasticity that is mediated by CB1 and 2-arachidonoyl glycerol (2-AG); they are therefore an excellent neuronal model of endogenous cannabinoid signaling in which to test CB1 modulators. In this study we find that while two related compounds, GAT211 and ZCZ011, each show PAM-like responses in autaptic hippocampal neurons, they also exhibit complex pharmacology. Notably we were able to separate the PAM- and agonist-like responses of GAT211 by examining the enantiomers of this racemic compound: GAT228 and GAT229. We find that GAT229 exhibits PAM-like behavior while GAT228 appears to directly activate the CB1 receptor. Both GAT229 and ZCZ011 represent the first PAMs that we have found to be effective in using this 2-AG utilizing neuronal model system. Because these compounds may exhibit both probe selectivity and biased signaling it will be important to test them with anandamide as well as other signaling pathways.

Where's my entourage? The curious case of 2-oleoylglycerol, 2-linolenoylglycerol, and 2-palmitoylglycerol.

2-Arachidonoylglycerol (2-AG) is the most abundant endogenous cannabinoid in the brain and an agonist at two cannabinoid receptors (CB1 and CB2). The synthesis, degradation and signaling of 2-AG have been investigated in detail but its relationship to other endogenous monoacylglycerols has not been fully explored. Three congeners that have been isolated from the CNS are 2-linoleoylglycerol (2-LG), 2-oleoylglycerol (2-OG), and 2-palmitoylglycerol (2-PG). These lipids do not orthosterically bind to cannabinoid receptors but are reported to potentiate the activity of 2-AG, possibly through inhibition of 2-AG degradation. This phenomenon has been dubbed the 'entourage effect' and has been proposed to regulate synaptic activity of 2-AG. To clarify the activity of these congeners of 2-AG we tested them in neuronal and cell-based signaling assays. The signaling profile for these compounds is inconsistent with an entourage effect. None of the compounds inhibited neurotransmission via CB1 in autaptic neurons. Interestingly, each failed to potentiate 2-AG-mediated depolarization-induced suppression of excitation (DSE), behaving instead as antagonists. Examining other signaling pathways we found that 2-OG interferes with agonist-induced CB1 internalization while 2-PG modestly internalizes CB1 receptors. However in tests of pERK, cAMP and arrestin recruitment, none of the acylglycerols altered CB1 signaling. Our results suggest 1) that these compounds do not serve as entourage compounds under the conditions examined, and 2) that they may instead serve as functional antagonists. Our results suggest that the relationship between 2-AG and its congeners is more nuanced than previously appreciated.

Aiming for allosterism: Evaluation of allosteric modulators of CB1 in a neuronal model.

Cannabinoid pharmacology has proven nettlesome with issues of promiscuity a common theme among both agonists and antagonists. One recourse is to develop allosteric ligands to modulate cannabinoid receptor signaling. Cannabinoids have come late to the allosteric table. The 'first-generation' negative and positive allosteric modulators (NAMs and PAMs) represent an important first effort. However, most studies have relied on synthetic agonists, often tested in over-expression systems rather than a defined neuronal model system that utilizes endogenously synthesized and released cannabinoids. We have systematically examined first-generation NAMs and a PAM on endocannabinoid modulation of synaptic transmission in cultured autaptic hippocampal neurons. These neurons exhibit CB1 and 2-arachidonoyl glycerol (2-AG)-mediated depolarization induced suppression of excitation (DSE) and therefore serve as a model to test CB1 modulators in a neuronal model of endogenous cannabinoid signaling. We find ORG27569, PSNCBAM-1, and PEPCAN12 attenuate DSE and do not directly inhibit CB1 receptors. Of these PSNCBAM-1 is the most efficacious while PEPCAN12 has the distinction of being an endogenous NAM. The reported NAMs pregnenolone and hemopressin as well as the reported PAM lipoxin A4 are without effect in this model of endocannabinoid signaling. In summary, three of the allosteric modulators evaluated function in a manner consistent with allosterism in a neuronal 2-AG-based model of endogenous cannabinoid signaling.