Discussion
Olfactory dysfunction has become one of the common symptoms associated
with many cases of corona virus 11-13. During the
response to odorants, there is a simultaneous increase in cyclic
adenosine monophosphate and calcium cations. The cyclic adenosine
monophosphate is produced by activation of adenylate cyclase and the
increase in calcium cations is due to influx via cyclic nucleotide
channels. Therefore, it is hypothesized that decreasing intranasal free
calcium cations may reduce feedback inhibition and lead to improved
receptor response and olfactory function 14.
This prospective randomized controlled trial tested the topical
application of DTPA for the treatment of anosmia post COVID-19
infection. DTPA is a chelating agent that can strongly sequester
divalent and trivalent cations and form a strong metal complex product.
DTPA wraps around a metal ion forming up to eight bonds. At pH 8, DTPA
selectively forms a calcium-DTPA complex even in the presence of sodium,
potassium or magnesium cations. This reaction mechanism leads to a
decrease in calcium cation in the nasal secretions. The described
results confirm that the reduction of calcium cations in by DTPA
improves the olfactory performance.
The ”Sniffin’ Sticks” test is a widely used olfactory performance
assessment tool consisting of three subtests: odor threshold, odor
discrimination and odor identification. It was introduced over 20 years
ago and its test-retest reliability and validity have been demonstrated.
The calculated scores of the odor test confirmed that topical
application of DTPA produces significant improvement in odor performance15,16.
Quantitative analysis of calcium cations provides an indication of the
increase or decrease in calcium cations. This approach is based on the
design of a carbon paste ion-selective electrode. Carbon paste
electrodes are considered as an important type of ion-selective
electrodes due to their advantages of chemical inertness, robustness,
stable response, no need for internal solution and suitability for a
variety of sensing and detection applications. Also, it can be used with
a small volume of nasal secretion 10. Using the
developed electrode, it was possible to determine the calcium cation
concentration before and after the described treatment. The results
obtained showed a sharp decrease in calcium cation concentration in the
patients treated with topical DTPA. This can be explained by the
chelation of the calcium cation and the formation of the calcium DTPA
complex product.
This paper introduced an evidence for a relationship between lowering
calcium cation concentration in the nasal secretions by DTPA and the
improvement in the olfactory performance.