Objective: ​​​​​​To assess replicability of skin sebum volatile organic compound (VOC) composition 1) within the same subjects; 2) in frozen vs fresh samples, and 3) in skin swabs vs. skin-patches,  with an  aim of exploring a novel noninvasive biomarker in Parkinson’s disease (PD). ​​​​​

Background: PD patients (PDp) emit a distinctive odor detectable by those with heightened smell or using specific devices [1], [2]. Little is known on the effect of the sample collection process on VOC composition, which is an important first step in exploring this potential novel biomarker in PD.

Method: We included 15 PDp and 12 healthy controls (HC). Each participant applied a skin patch to the back area for 12h. In 12 PDp and 4 HC a skin swab was additionally collected from the back area after removing the patch. 3 PDp and 2 HC applied a patch twice, at 2 different time points. 9 HC simultaneously applied 2 patches, after collection, one was frozen at -40°C for 1 month, while one was analysed within 24h. Headspace solid-phase microextraction coupled to gas chromatography–mass spectrometry was used to obtain VOC profiles. Compound identification was performed using NIST 14 Mass Spectral Library and NIST Retention Index Library, followed by a quality control check. Using t-tests, we compared the number of 1) identified compounds (nID); 2) unidentified peaks (nNA); and 3) compounds due to material and environmental contamination (nC). For identified compounds we calculated how many were present in both samples from the same participants, obtaining % of matching compounds.

Results: 57 samples were analysed. On average 56% of compounds were matched within the same subjects (N=5). Fresh and frozen samples had 46% of matching compounds (N=9). Fresh samples had significantly more nID (p=0.033), nNA (p=0.001) and nC (p=0.013) compared to frozen.HC had significantly more nID compared to PDp (p=0.01), with no differences in nNA and nC. Skin swabs compared to skin patches had 35% of matching compounds, significantly more nID (p=0.0001) and nC (p=0.039), while there was no difference in nNA.

Conclusion: Sample collection methods strongly impact measured skin VOC composition. Sample freezing significantly decreased the number of detected compounds. We found moderate within-subject replicability, suggesting that multiple samples from the same individual should be obtained to increase robustness.

References: [1] E. Sinclair et al., ‘Validating differential volatilome profiles in Parkinson’s disease’, ACS Cent. Sci., vol. 7, no. 2, pp. 300–306, Feb. 2021, doi: 10.1021/ACSCENTSCI.0C01028/SUPPL_FILE/OC0C01028_SI_002.XLSX.
[2] D. K. Trivedi et al., ‘Discovery of Volatile Biomarkers of Parkinson’s Disease from Sebum’, 2019, doi: 10.1021/acscentsci.8b00879.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effects-of-sample-collection-methods-on-skin-sebum-volatilome-composition-in-parkinsons-disease-patients-a-methodological-pilot-study/