Does Taurine Supplementation Improve Vascular Function and Orthostatic Responses in Long COVID?

Millions of people have been infected by SARS-CoV-2, or COVID-19, and recent estimates suggest that up to 13% have developed Long COVID \[1\]. The World Health Organization defines Long COVID as "the continuation or development of new symptoms 3 months after the initial SARS-CoV-2 infection, with these symptoms lasting for at least 2 months with no other explanation." SARS-CoV-2 is known to use angiotensin converting enzyme 2 (ACE2) to enter cells \[2\], and ACE2 is located in endothelial cells throughout the cardiovascular system contributing to significant vascular dysfunction \[3\]. Indeed, vascular function, as measured by flow-mediated dilation (FMD) has been shown to be impaired in otherwise healthy young COVID-19 survivors just 3-4 weeks after infection \[4\] and persists for at least 6 months in patients who were hospitalized \[5\]. Recent work has shown a significant correlation between low plasma taurine levels (a naturally occurring amino acid which can help regulate cardiovascular and inflammation) and Long COVID symptoms, and the recovery of taurine levels was associated with fewer adverse events \[6\]. Notably, twelve weeks of taurine supplementation has been shown to improve blood pressure and vascular function in pre-hypertension \[7\]. These improvements could, in turn, improve orthostatic tolerance (i.e. lightheadedness while upright, a common symptom in Long COVID). Thus, the purpose of the current proposal is to compare Long COVID patients who are or who are not taking 12-wks taurine supplementation, measuring vascular and orthostatic responses. We hypothesize that those Long COVID patients taking taurine will have better vascular function and orthostatic responses. Participants: Drawing on the results of Sun et al. (2016) \[7\] to calculate a sample size, we used an expected change in FMD of 3.2±4.7% with taurine supplementation, resulting in a sample size of 19. To account for potential participant drop-out, we intend to recruit 30 Long COVID patients aged 18-65, including 15 males and 15 females. As this is a pilot project, we will re-evaluate our sample sizes/statistical power when approximately 8 males and 8 females have been completed \[8\]. Duration and type of symptoms will be recorded using the Symptom Burden Questionnaire for Long COVID. Autonomic function will be assessed with the COMPASS-31 questionnaire and people with symptoms of orthostatic intolerance and/or vasomotor impairment will be recruited. Sex and gender will be self-identified and used as covariates. Any co-morbidities and medication use will be recorded but not excluded. Study Design: This will be an observational study where half of the participants will already be taking taurine supplements and the other half will not. Each lab assessment will take approximately 60 minutes. Participants will come to York University at baseline and after 12 weeks of time has passed. During the first visit, they will be loaned a Polar heart rate monitor and instructed in its use for home data collection. 1. Vascular function: Resting brachial artery FMD will be measured with Duplex ultrasound imaging according to international guidelines \[9\]. Briefly, five minutes of forearm vascular occlusion using a blood pressure cuff will be applied while brachial artery diameter and flow are measured before, during and for 3 minutes after cuff occlusion. Peak hyperemic brachial arterial velocity will also be measured using Doppler ultrasound immediately after cuff release. Analysis of FMD will be done with edge-detection software (Quipu) to expedite the analysis and reduce measurement error \[10\]. Concurrently an EndoPAT device will also be used to measure endothelial function. 2. Orthostatic responses (during supine rest and 5-min 70o head-up tilt): Cardiovascular and respiratory measures: Heart rate will be measured by ECG, blood pressure/cardiac output will be monitored using a beat-by-beat non-invasive blood pressure device (NexFin), brain blood flow will be assessed with transcranial Doppler ultrasound, and respiratory rate will be assessed using a Respitrace. Heart Rate Variability (HRV): HRV provides an indicator of the autonomic control of heart rate (i.e. parasympathetic and sympathetic balance \[11\]) and will be analyzed using LabChart Pro 8.0 software in the supine and upright postures. Resting HRV will also be assessed using a Polar heart rate device at home, weekly. The heart rate data will be emailed to the students for analysis. Analysis plan: Each variable described above will be measured before and after the 12-wks time period. To test the study hypotheses, repeated measures analysis of variance will be used to examine differences over time (SPSS). Sex, gender, and symptom duration will be covariates.