Simultaneous spectrofluorimetric determination of nasal cyclic nucleotides as biochemical markers in post-COVID-19...

Olfactory dysfunction has been linked to changes in the levels of two essential second messengers involved in olfactory signal transduction: cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Herein, cAMP and cGMP in nasal secretions were determined simultaneously using a cyclodextrin-based spectrofluorimetric technique in conjunction with first-derivative synchronous fluorescence spectroscopy. Using hydroxypropyl-β-cyclodextrin, fluorescence was enhanced, resulting in reduced spectrum overlap and increased signal strength. Synchronous fluorescence scanning at a wavelength interval (Δλ) of 50 nm, followed by first-derivative manipulation, enabled selective determination of cAMP at 420 nm and cGMP at 455 nm. The method exhibited linear responses over the concentration range of 1-100 ng/mL with acceptable correlation coefficients. The limits of detection were 0.210 ng/mL for cAMP and 0.252 ng/mL for cGMP, while the limits of quantification were 0.630 ng/mL and 0.756 ng/mL, respectively. Clinical application of the developed platform revealed an observed depletion of nasal cyclic nucleotide levels in patients with post-COVID-19 olfactory loss. Concentrations of cAMP and cGMP in the patient group were markedly reduced (19.37 ± 3.18 and 9.24 ± 1.20 ng/mL, respectively) compared to healthy individuals (73.25 ± 6.20 and 39.64 ± 3.18 ng/mL). Statistical validation through ROC curve analysis yielded AUC values of 0.99 for cAMP and 0.98 for cGMP, suggesting the suitability of the developed method for the sensitive analysis of these biomarkers in complex biological matrices, which helps in understanding the biochemical changes associated with olfactory dysfunction.