A Sensitive and Specific Liquid Chromatography-Tandem Mass Spectrometry Assay for Simultaneous Quantification of Salivary Melatonin and Cortisol: Development and Comparison With Immunoassays

An LC-MS/MS-based method for the simultaneous quantification of melatonin, cortisol and cortisone in saliva

Disturbances in the diurnal pattern are associated with several clinical and psychological conditions, including depression and fatigue. Salivary sampling for melatonin, cortisol and cortisone provides a non-invasive method for frequent sampling and obtaining biochemical insight into the diurnal pattern of individuals. Therefore, a new liquid chromatography-tandem mass spectrometry-based method for the measurement of salivary melatonin, cortisol and cortisone was developed and validated. The method required 250 μl saliva, used isotope dilution methodology and was based on a liquid-liquid extraction for sample preparation, reversed-phase chromatography and multiple reaction monitoring on a mass spectrometer for quantitation. The lower limits of quantification obtained were 0.010 nmol/L for melatonin, 0.5 nmol/L for cortisol and 1.00 nmol/L for cortisone and the limits of detection were 0.003 nmol/L, 0.15 nmol/L and 0.1 nmol/L respectively. The method imprecision was ≤14% for all measurands, and the method comparison showed highly comparable results with high correlation coefficients (all ≥0.964). Potential interference of cortisol and cortisone by prednisolone was observed and could be detected by chromatogram review. Typical diurnal patterns for melatonin, cortisol and cortisone were observed in the saliva of 20 cancer survivors who collected saliva throughout the day.

Comparative analysis of salivary cortisol measurements using different assay methods in relation to serum-free cortisol measurement

Objectives

Salivary cortisol reflects the biologically active form of serum cortisol, offering a noninvasive evaluation method for the diurnal rhythm of the hypothalamic-pituitary-adrenal (HPA) axis. While liquid chromatography-tandem mass spectrometry (LC-MS/MS) is known for its specificity, immunoassays (IA) are commonly used because of their simplicity. This study aimed to assess the performance of salivary cortisol measurement using both IA and LC-MS/MS in comparison to serum-free cortisol measurement.

Methods

Assay results for 188 saliva and 94 serum samples from 47 participants were analyzed. Salivary samples collected at different time points were analyzed using IA and LC-MS/MS. Serum samples were analyzed for cortisol, cortisol-binding globulin, and free cortisol. The statistical analyses included correlations and method comparisons.

Results

The diurnal salivary cortisol profiles exhibited a comparable circadian rhythm pattern; however, the concentrations measured using IA were consistently higher than those measured using LC-MS/MS. The correlation analysis revealed robust associations among salivary cortisol (IA), salivary cortisol (LC-MS/MS), and serum-free cortisol levels (LC-MS/MS). However, the method comparison revealed a systematic bias between IA and LC-MS/MS in salivary cortisol measurement.

Conclusions

This study contributes to the ongoing debate on assay techniques by affirming the suitability of IA and LC-MS/MS for salivary cortisol measurement to assess dynamic changes in HPA axis activity. The identified systematic bias emphasizes the importance of selecting methods based on specific research or clinical requirements.

Ratiometric fluorescent sensing of melatonin based on inner filter effect and smartphone established detection

Melatonin (MLT) is a crucial neurohormone having inhibitory effects over various types of cancer. In this work, 3,6-Diaminocarbazole (DAC), a fluorescent probe is utilized to detect MLT in a highly sensitive, selective and facile way. The unique feature of present work is that MLT is sensed by ratiometric fluorescent technique based on the inner filter effect (IFE) using DAC at an emission wavelength of 310 nm. As a result, a noticeable change in color from red to cyan is observed and the quantitative analysis of fluorescence signals at these wavelengths are used to detect MLT observing a linear relationship between the ratio of emission intensities and the concentration of MLT over a linear range of 0 to 78 μM. DAC can accurately measure the detailed quantity of MLT with a limit of detection of 30 nM and has proved to be an efficient sensing probe due to its excellent molar absorptivity and high photoluminescence quantum yield (PLQY). Sensing characterization was carried out UV-Vis, steady-state, and time- resolved fluorescence spectroscopic techniques. The smartphone app "RGB colour detector" value has been successfully linked with the considerable detectable color changes of DAC on addition of MLT. HOMO-LUMO have been calculated using DFT with B3LYP/6-31G(d,p) level and band gaps of 3.77 eV and 4.91 eV were found for DAC and MLT, respectively. Electrons are not allowed energetically to transfer from MLT to DAC, as is evident from their band gaps. Therefore, IFE can be considered the foremost method in fluorescence quenching of present investigation. The developed sensor was verified by spiking of MLT in human serum.

Development and Validation of an Ultrasensitive LC-MS/MS Method for the Quantification of Melatonin in Human Saliva

A growing body of literature describes the potential effects of circadian disruption on human health. Indeed, psychiatric diseases, metabolic syndrome, and cancers may be linked to disturbance of the circadian rhythm. Currently, the best practice to assess circadian rhythm is the measurement of melatonin levels. Our goal was thus to develop and validate a highly sensitive LC-MS/MS method to follow salivary melatonin levels throughout the day and night. Our method reached a lower limit of the measuring interval (LLMI) of 0.8 pg/mL. To our knowledge, it is the most sensitive method allowing quantitation of melatonin in saliva. Saliva, obtained from passive drooling or salivette, was extracted by an efficient and quick liquid-liquid extraction with no further cleanup needed. The method was validated according to the European Medicines Agency (EMA) guidelines and provided excellent results regarding accuracy, precision, linearity, selectivity, and specificity. Comparison between radioimmunoassay and our method was performed and showed differences at low levels, most likely due to cross-reactivity with other indols. To assess daytime melatonin levels in humans, salivary melatonin levels of ten volunteers were monitored throughout the day and showed lower daytime levels than reported in previous studies.

High-throughput quantitation of trace level melatonin in human milk by on-line enrichment liquid chromatography-tandem mass spectrometry

The level of melatonin in human milk might be closely related to infant development and the building up of their circadian rhythms. The large population investigation on this topic would provide insights for the prevention and treatment of diseases related to early development and circadian rhythms. However, it has not been well studied. Trace level endogenous melatonin and difficulties in sample collection are among the challenges limiting the progress. High throughput analytical method with high specificity and sensitivity to determine the endogenous melatonin concentration is highly desired. A newly developed easily operated and high-throughput sensitive on-line enrichment liquid chromatography-tandem mass spectrometry (LC-MS/MS) method would be reported in this paper. Melatonin-d₃ (MEL-d₃) was used as a surrogate standard for the calibration curve and melatonin-d₄ (MEL-d₄) was used as an internal standard. Sample preparation was simply performed in 96-well plate by protein precipitation using acetonitrile (ACN). The supernatant was injected directly into the easily configured LC-MS/MS system with an enlarged sample loop and a mixer. Positive mode multiple reaction monitoring (MRM) was adopted for the measurement of melatonin in milk. 100 μL sample was used for analysis and the calibration curve linear range was 1-1000 pg mL^-1. In three validation batches, the accuracy was within 11.0% deviation from the relative nominal concentration, whereas the intra- and inter-assay precision was ≤4.1% and ≤6.8% relative standard deviation (RSD), respectively. Although matrix effect was observed in the validation experiments, the stable isotope labeled internal standard (MEL-d₄) could correct it and the overall relative matrix effect of MEL-d₃/MEL-d₄ was close to 100%. The overall spike recovery of the method was 101.7% with 5.1% RSD. Compared to currently reported methods, it could reach 1 pg mL^-1 lower limit of quantification (LLOQ) with a smaller sample volume, sample preparation could be easily performed by automated liquid handling system and was more suitable for large population cohort studies on trace level endogenous melatonin determination.