Evaluation of Amyloid-β Aggregation by Fourier Transform Infrared Spectrophotometer (FTIR)

Significance of the Topic

Amyloid-β aggregation into fibrillar structures is a hallmark of Alzheimer’s disease and other neurodegenerative disorders. Monitoring changes in peptide secondary structure during aggregation provides critical insights into disease mechanisms and aids in the development of therapeutic strategies.

Objectives and Overview of the Study

This work aims to evaluate the time-dependent aggregation of human amyloid-β(1–40) by Fourier transform infrared (FTIR) spectrophotometry, focusing on alterations in the amide I band to distinguish antiparallel and parallel β-sheet formation.

Methodology

• Sample preparation: Amyloid-β(1–40) was dissolved to 10 μM in ultrapure water and incubated at 25 °C for 0.5, 1, 2, 3, 24, 48 and 120 h.
• ATR measurement: Sixty microliters of solution (30 μL × 2) were applied to the ATR crystal, dried under dry air, and spectra were recorded.
• Data analysis: Second derivative spectra in the 1700–1600 cm⁻¹ region identified peak positions. Lorentzian curve fitting from 1750 to 1575 cm⁻¹ quantified peak areas corresponding to specific secondary structures.

Used Instrumentation

• Shimadzu IRTracer-100 FTIR spectrophotometer
• MicromATR™ attenuated total reflectance accessory with a nine-reflection ATR crystal
• Measurement conditions: resolution 4 cm⁻¹, 100 scans, square-triangle apodization, DLATGS detector, dry-air purge

Main Results and Discussion

Spectral analysis showed a shift in the amide I maximum from 1626 cm⁻¹ at 0.5 h to 1630 cm⁻¹ at 120 h. Second derivative spectra revealed a decrease in antiparallel β-sheet signatures at 1696 and 1626 cm⁻¹ and growth of the parallel β-sheet band at 1630 cm⁻¹. Curve fitting yielded a high/low β-sheet area ratio decline from 0.2836 to 0.1860 over 120 h, confirming a structural transition from antiparallel to parallel β-sheets during fibril maturation.

Benefits and Practical Applications of the Method

The FTIR-ATR approach offers rapid, label-free assessment of peptide secondary structures with minimal sample preparation. Its high sensitivity and ease of cleaning make it suitable for kinetic studies of aggregation, screening of aggregation inhibitors, and quality control of therapeutic peptides.

Future Trends and Potential Applications

Advancements may include coupling time-resolved FTIR with microfluidics for real-time aggregation monitoring, employing machine learning for automated spectral deconvolution, extending the method to other amyloidogenic proteins, and integrating complementary techniques such as Raman spectroscopy and NMR.

Conclusion

FTIR-ATR analysis effectively tracks the conversion of amyloid-β from antiparallel to parallel β-sheet structures during aggregation. The method’s simplicity, sensitivity, and quantitative power make it a valuable tool for neurodegenerative disease research and biopharmaceutical quality control.

References

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