Carrie Burdinski MS, an anatomy and physiology professor at Delta College, has an excellent 2 hour Youtube video on everything you need to know to understand the role of the autonomic nervous system in postural orthostatic tachycardia syndrome (POTS). Ms Burdinski does an excellent job of describing the physiology of non tachycardia symptoms of POTS like “brain fog” and loss of temperature control, both symptoms of Long Covid.
Ms Burdinski gave an interesting overview of different ways that genetics and epigenetics influence the regulation of the norepinephrine (noradrenaline) transporter that clears “used” noradrenaline from the the synaptic cleft. A quick title search of PubMed reveals the following
- Mutations in the NET gene that result in a single amino acid substitution in the translated protein that affect the efficiency of noradrenaline / norepinephrine uptake.
- Epigenetic methylation of the promoter of the NET gene that prevents translation of the gene into messenger RNA (mRNA)
- Epigenetic micro RNA binding to the NET mRNA that prevents it from being translated into a protein.
Once the NET mRNA is translated into a protein, there are numerous “post translational” modifications that can regulate protein function. (Mandela and Ordway 2006)
Examples of regulating NET
These examples from the Mandela and Ordway review are pretty typical of protein regulation. We need to remember that the adrenergic receptors are also subject to regulation at the protein level.
- Phosphates may be added to amino acids serine, threonine, and tyrosine by protein kinase C, casein kinase II, Ca2+ calmodulin kinase, and cAMP dependent protein kinase. The latter is particularly interesting because many heterotrimeric G proteins, of which the adrenergic receptors are a few of many, signal through an enzyme that makes cAMP.
- A large number of neurotransmitters that bind to heterotrimeric G protein receptors
- Protein phosphatases remove phosphates from serine, threonine, and tyrosine.
- Insulin is known to decrease NET mRNA expression in locus coeruleus neurons of the rat
- Atrial natriuretic factor (ANF) increases production of NET
- Nerve growth factor decreases NET mRNA levels.
- Nitric oxide may regulate NET by thiol nitrosation and/or cGMP dependent protein kinase.
We will not get into the dozens, if not hundreds, of pharmaceuticals that can regulate norepinephrine/noradrenaline release, reuptake, and binding to its many receptors. Ms Burdinsky was obviously frustrated with the myriad of pharmaceuticals not only to regulate these proteins up to mitigate the side effects.
Ms Burdinski went over the physiology behind each and every bullet point on this screen shot and why she thought these dietary interventions help POTS patients. The reasons behind copper were
- Copper is needed for proper handling that we have covered in the ceruloplasmin post.
- Ms Burdinski postulated that if the presynaptic neuron is that recycling used noradrenaline because of impaired reuptake by NET, it needs more copper for dopamine hydrolase, the enzyme that synthesizes noradrenaline from dopamine. If noradrenaline is not recycled, it just diffuses away from the synaptic cleft. Therefore the neuron needs to make more
Copper deficiency and autonomic dysfunction
This 1988 study came from the United States Department of Agriculture, Agriculture Human Nutrition Research Center in Grand Forks, North Dakota. Lukaski and coworkers explored this link in female volunteers. This study seemed to start as a simple baroreceptor reflex investigation. When we are at rest, our brains get adequate blood flow. Upon standing gravity decreases the blood volume in our brains. This causes our blood vessels to contract.
Eight women, 18-36 years old, were monitored on four separate diets for a total of 135 days
- basal, low diet copper 0.65 mg d -1 and adequate in ascorbic acid (90 mg d-l) 42 days
- basal low copper + 1.5 g acid d -1 ascorbic acid for 42 days
- basal + 0.8 mg d -1 copper, control normal copper, 14 days
- basal +2 mg d –1 copper for 37 days, repletion.
Copper retention or chemical balance
- Retention was calculated as the difference between intake and excretion in urine and feces. Menstrual and sweat loses were not considered.
- At the end of each dietary period, fasting venous blood samples were obtained to determine biochemical indices of copper status.
- Total plasma copper was determined by atomic absorption spectroscopy .
- Ceruloplasmin enzymatic activity was assayed as a colorimetric p-phenylenediamine oxidase assay.
- Ceruloplasmin content was measured by the radial immuno diffusion assay.
- Autonomic cardiovascular function was assessed at the end of each dietary period.
- Volunteers were tested in the post absorptive state after a 30-minute rest during which they were supine on a bed in a quiet room.
- Variation in resting supine heart rate was determine over a three-minute period using the mean square successive differences of R-R intervals .
- Orthostatic responses, upon arising form supine position and standing, were measured for heart rate and blood pressure.
- Heart rate response was defined as the ratio of the R-R interval of the 30th to the 15th beat after standing.
- Blood pressure was measured as each volunteer was supine and resting quietly and after one minute upon standing.
The hand grip exercise
- Standing heart rate and blood pressure responses were determined before and during five minutes of sustained hand grip exercise with the dominant arm at 30% maximal voluntary contraction using a calibrated handgrip dynamometer.
- Maximal voluntary contraction was determined at the end of each diet period.
- Heart rate was recorded continuously using a multichannel electrocardiograph and standard limb leads.
- Blood pressure was determined by auscultation on the inactive arm with diastolic pressure defined as the fourth phase Korotkov sound.
Most copper is excreted in the feces
Note that the copper supplemented diet has almost 5x the copper as the low copper diet. A remarkable observation in this study is that whether the copper is low or high, most of it is excreted in the feces. Virtually the same amount of copper is excreted in the urine. Retention of copper is higher in the copper supplemented arm of this study. Ascorbic acid (AA) had no influence on copper retention. What is not clear is if the large excretion of copper is due to failure to absorb it in the first place.
Dietary increases in copper and ceruloplasmin
The following graphs were reproduced from table 2 to emphasize the similarities and differences. Treatments different from the normal copper control at p<0.05 are indicated by “*”. Variations of copper in these short term diets had no influence on plasma copper. All eight women spent some time in each group.
Concentrations of ceruloplasmin, as measured by radial immune diffusion, are in units of mg per liter of plasma. We can only assume that the authors used standards to calibrate the diffusion values. A ceruloplasmin reference range is 200-350 mg per liter. The low copper diet, with or without ascorbic acid (AA) decreased ceruloplasmin activity without decreasing the amount of protein. In fact, AA slightly increased the amount of ceruloplasmin protein in the plasma.
Ceruloplasmin enzymatic activity, in units of mg per liter, dropped (p<0.05) when the participants were on low copper diets with or without ascorbic acid (AA) supplementation. Copper supplementation to 2.65 mg per day did not increase the enzyme activity above what was observed when the participants over on 1.45 mg copper per day (Cu).
POTS spoiler, slight detour
The spoiler alert, the authors reported no differences in the blood pressure responses from going to a supine position to standing. At the time of the study, the scientific community was becoming aware of the cardiovascular response to exercise. A short publication by Qumar and Read (1987) documented a decrease of blood flow to the mesenteric circulation to the small intestine in response to exercise. Many readers were told as children, “Don’t swim right after you eat lunch or you will get a stomach ache!”
If we are running from a dangerous situation, we’d want the blood flow (Q) to our gastrointestinal to decrease somewhat to allow more flow to our legs. When a vessel relaxes, the radius (r) becomes larger and flow increases. When the pressure gradient increases, flow increases. If all vessels were to simultaneously relax, blood flow have to drastically increase to keep the tissues oxygenated. Restricting the flow through some and increasing the flow through those arteries that supply muscles that are exercising means the cardiac output (flow) only has to increase a little bit.
The mean arterial pressure (MAP)
MAP may be estimated as the DP + 1/3 (SP-DP) where SP and DP are the systolic and diastolic blood pressures. It approximates the average pressure during the cardiac cycle. MAP is affected by factors such as:
- Volume of blood pumped by the heart per minute (cardiac output, flow, Q)
- Heart rate (beats per minute)
- Blood pressure
- Resistance to blood flow in the vessels
An increase or decrease in any of these factors can proportionately affect mean arterial pressure and bring corresponding consequences to the perfusion of major organs like the brain and kidneys.
The heart rate was not different before the hand grip exercise started at time 0. The heart rate gradually increased during the 5 minutes of the exercise. The amount of copper in the diet made no difference.
When the subjects were on low copper diets, their diastolic blood pressures increased more within 2 minutes (P<0.05) of hand grip exercise. (P<0.001) When the subjects were on low copper diets, their systolic blood pressures increased more within 3 minutes (P<0.05) of hand grip exercise.
Mean arterial pressure was noticeably elevated in the copper deficient subjects after only 1 minute of the hand grip exercise. Recall from Poiseuille’s Law that it is the pressure differential, ∆P, and resistance that drives flow.
Lukaski and coworkers discussed the possibility of vascular tone being altered by the impaired collagen cross linking enzyme lysyl oxidase. This group were experts in Cu/Zn superoxide dismutase 3 and angiotenin II activation of super oxide generator NADPH oxidase.
Ceruloplasmin loading of copper predicts MAP in response to exercise
A summary figure related the mean arterial pressure to the hand grip test to the “ceruloplasmin ratio.” This ratio is the enzymatic activity to the amount of the protein as measured by radial immune-diffusion. Each symbol represents an individual participant.
The authors discussed the locus ceruleus as an integrator of afferent input with efferent output that control adrenergic cardiovascular reflexes (locus ceruleus-noradrenergic system or LC-NA system). This locus was also noted as being a copper enriched region of the brain. Blood pressure control during isometric hand grip exercise involves sympathetic (noradrenergic) afferent from skeletal muscle neurons. Lukaski and coworkers (1988) concluded that the involvement of copper required further study.
POTS and Long Covid?
The big question here is if POTS patients and those with Long Covid autonomic dysfunction are copper deficient. David Goldstein of the NIH has reviewed possible causes of POTS in Long Covid. Dr Goldstein gives a more in depth overview of some aspects of the ANS than covered in this post. He mentions autoimmunity. We have covered our research on NMDA repceptor suto antibodies in Long Covid in another post. Blitshteyn and Brook (2017) described a female patient who had received the HPV Cervavix vaccine who later developed POTS. This patient tested positive for anti-NMDA receptor antibodies, responded positively to immunomodulatory therapy, and had her symptoms come back when the therapy was discontinued. The CDC has addressed this association.
POTS and gluten sensitivity?
Copper deficiency in celiac disease has been addressed elsewhere. Are POTS patients more likely to have self reported gluten intolerance or bonefid celiac disease? Hugo Penny and coworkers (2016) of the Royal Hallamshire Hospital in Sheffield, UK surveyed 100 POTS patients. Four of the 100 POTS patients had serologically and biopsy proven celiac disease. Gluten sensitivity was reported in 42% of these 100 POTS patients versus 19% of the control population.
- Blitshteyn S, Brook J. (2017) Postural tachycardia syndrome (POTS) with anti-NMDA receptor antibodies after human papillomavirus vaccination. Immunol Res. 2017 Feb;65(1):282-284.
- Goldstein D. S. (2021). The possible association between COVID-19 and postural tachycardia syndrome. Heart rhythm, 18(4), 508–509.
- Hoggard N, Hadjivassiliou M, West JN, Sanders DS. Is there a relationship between gluten sensitivity and postural tachycardia syndrome? Eur J Gastroenterol Hepatol. 2016 Dec;28(12):1383-1387
- Lukaski HC, Klevay LM, Milne DB.(1988) Effects of dietary copper on human autonomic cardiovascular function. Eur J Appl Physiol Occup Physiol. 58(1-2):74-80.
- Mandela P, Ordway GA. (2006) The norepinephrine transporter and its regulation. J Neurochem. 2006 Apr;97(2):310-33. doi: 10.1111/j.1471-4159.2006.03717.x. Epub 2006 Mar 15. PMID: 16539676 Free article.
- Neselioglu S, Ergin M, Erel O. (2017) A New Kinetic, Automated Assay to Determine the Ferroxidase Activity of Ceruloplasmin. Anal Sci.33(12):1339-1344.
- Qamar MI, Read AE.(1987)Effects of exercise on mesenteric blood flow in man. Gut. 28(5):583-7.