Raman Spectroscopy Study of Skin Biopsies from Patients with Parkinson's Disease: Trends in Alpha-Synuclein Aggregation from the Amide I Region

Parkinson's disease (PD) is one of the most common neurological pathologies with a high prevalence worldwide. PD is characterized by Lewy bodies, whose major component is the aggregates of alpha-synuclein (alpha Syn) protein. Interestingly, recent works have demonstrated that skin biopsy studies are a promising diagnostic tool for evaluating alpha-synucleinopathies. In this sense, this work focuses on the detection of alpha Syn in skin biopsies employing Raman spectroscopy, using three different approaches: (i) the in vitro Raman spectrum of alpha-synuclein, (ii) the ex vivo Raman spectra of human skin biopsies from healthy and Parkinson's disease patients, and (iii) theoretical calculations of the Raman spectra obtained from different model alpha Syn fragments using density functional theory (DFT). Significant differences in the intensity and location of Raman active frequencies in the amide I region were found when comparing healthy and PD subjects related to alpha-synuclein conformational changes and variations in their aggregation behavior. In samples from healthy patients, we identified well-known Raman peaks at 1655, 1664, and 1680 cm(-1) associated with the normal state of the protein. In PD subjects, shifted Raman bands and intensity variations were found at 1650, 1670, and 1687 cm(-1) associated with aggregated forms of the protein. DFT calculations reveal that the shape of the amide I Raman peak in model alpha Syn fragments strongly depends on the degree of aggregation. Sizable frequency shifts and intensity variations are found within the highly relevant 1600-1700 cm(-1) domain, revealing the sensitivity of the amide I Raman band to the changes in the local atomic environment. Interestingly, we obtain that the presence of surrounding waters also affects the structure of the amide I band, leading to the appearance of new peaks on the low-frequency side and a notable broadening of the Raman spectra. These results strongly suggest that, through Raman spectroscopy, it is possible to infer the presence of aggregated forms of alpha Syn in skin biopsies, a result that could have important implications for understanding alpha-synuclein related diseases.

Automated summary

This study investigates the detection of aggregated alpha-synuclein in skin biopsies of Parkinson's disease patients using Raman spectroscopy. The results show significant frequency shifts and intensity variations in the Raman spectra of PD patients compared to healthy subjects, indicating changes in protein conformation and aggregation behavior. These findings suggest that Raman spectroscopy could be a valuable tool for diagnosing alpha-synuclein related diseases.