Delivering Transcutaneous Auricular Neurostimulation to Regulate Platelet Activity in Healthy Human Subjects
Authors: Blanc Lionel , Huston Jared , Bravo-Iñiguez Carlos , Papoin Julien , Ahmad Maaryj , Mirro Isabella , Benner Caroline , Le Brooke , McWade Melanie , Czura Christopher J , Covalin Alejandro , Khodaparast Navid 
Published: December 2024

Background: Implantable cervical vagus nerve stimulation (VNS) is an accepted therapy for the treatment of refractory epilepsy, depression, inflammation, and stroke. Recent studies have demonstrated that VNS reduces bleeding times and shed blood volumes by ~45% in animal models of soft tissue injury. These results have recently been confirmed in mice, including hemophilia mice deficient in FVIII, without evidence of systemic clotting, changes in global blood pressure, bradycardia, or hypotension. VNS induces a statistically significant upregulation of thrombin/antithrombin (TAT) complex formation in blood shed from a wound, but not in the circulation, suggesting enhanced localized, but not systemic, thrombin production and clot formation. Mechanistic studies demonstrate that VNS triggers release of acetylcholine in the spleen, which induces platelet calcium uptake through the alpha 7 subunit of nicotinic acetylcholine receptor (α7 nAChR). This efferent function of the vagus nerve to “prime” platelets has been termed the “neural tourniquet.” Ex vivo challenge of primed platelets with thrombin leads to increased surface expression of P selectin. While these preclinical data indicate that VNS can reduce bleeding time and shed blood volume, no studies to date have been conducted to determine if these approaches can modulate hemostasis in humans.

Transcutaneous auricular vagus nerve stimulation (taVNS) is an emerging non-invasive alternative to cervical VNS and has been applied for headache, migraine, heart failure, asthma, tinnitus, and other conditions. Transcutaneous auricular neurostimulation (tAN) is an FDA-cleared technology (Sparrow Ascent System, K230796) that stimulates branches of the vagus and trigeminal nerves on and around the ear. tAN stimulates the release of central nervous system endorphins, shifts circulating monocytes to an anti-inflammatory phenotype, inhibits pro-inflammatory cytokine release, and has sustained antinociceptive effects. tAN is currently being tested in a healthy human population to determine whether it can alter platelet phenotype. This first-in-human trial will determine whether the neural tourniquet pathway exists in humans, and whether it can be accessed transcutaneously.

Study design and Treatment: This study is designed as a randomized, double-blind, sham-controlled, single-center research study in which healthy adults will be randomized 1:1 into one of two experimental groups, to receive taVNS or tAN. Participants will receive 30 min of sham stimulation (taVNS or tAN), followed by 30 min of active stimulation (taVNS or tAN). Blood will be collected before and after sham stimulation and at several timepoints after stimulation. Samples will be analyzed by flow cytometry to assess platelet phenotype and thromboelastography to assess coagulation characteristics.

Eligibility Criteria: Inclusion criteria are participants between 18-65 years of age. Exclusion criteria include a history of thrombocytopenia, coagulopathy, abnormal bleeding or blood disorder, or conditions that can cause coagulopathic conditions (e.g., atrial fibrillation, heart valve surgery or replacement, hip or knee replacement); or use of coagulation- or platelet-modifying therapies.

Statistical Methods: Data will be collected at multiple timepoints and compared using two-way ANOVA Graphpad Prism.

Endpoints: Platelet surface marker expression of P selectin, activated glycoprotein IIb/IIIaThromboelastography

At the time of abstract submission, 23 subjects have completed the study, and two are in process. Enrollment is expected to conclude by October 2024.