Quantitative determination of low density lipoprotein oxidation by FTIR and chemometric analysis

• Published in: Lipids Vol. 39; no. 7; pp. 687 - 692
• Main Authors: Lam, H.S, Proctor, A, Nyalala, J, Morris, M.D, Smith, W.G
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer‐Verlag 01-07-2004; Springer Nature B.V
• Subjects: Calibration; Carbonyl compounds; chemometrics; Fourier transform infrared spectroscopy; Humans; Lipoproteins, LDL - chemistry; Lipoproteins, LDL - metabolism; low density lipoprotein; Male; metrology; Oxidation; Oxidation-Reduction; Protein Conformation; quantitative analysis; Regression Analysis; Reproducibility of Results; Spectroscopy, Fourier Transform Infrared - methods; Statistics as Topic
• ISSN: 0024-4201; 1558-9307
• DOI: 10.1007/s11745-004-1283-6

This study was conducted to develop a quantitative FTIR spectroscopy method to measure LDL lipid oxidation products and determine the effect of oxidation on LDL lipid and protein. In vitro LDL oxidation at 37°C for 1 h produced a range of conjugated diene (CD) (0.14–0.26 mM/mg protein) and carbonyl contents (0.9–3.8 μg/g protein) that were used to produce calibration sets. Spectra were collected from the calibration set and partial least squares regression was used to develop calibration models from spectral regions 4000‐650, 3750‐3000, 1720‐1500, and 1180‐935 cm−1 to predict CD and carbonyl contents. The optimal models were selected based on their standard error of prediction (SEP), and the selected models were performance‐tested with an additional set of LDL spectra. The best models for CD prediction were derived from spectral regions 4000‐650 and 1180‐935 cm−1 with the lowest SEP of 0.013 and 0.013 mM/mg protein, respectively. The peaks at 1745 (cholesterol and TAG ester C=O stretch), 1710 (carbonyl C‐O stretch), and 1621 cm−1 (peptide C=O stretch) positively correlated with LDL oxidation. FTIR and chemometrics revealed protein conformation changes during LDL oxidation and provided a simple technique that has potential for rapidly observing structural changes in human LDL during oxidation and for measuring primary and secondary oxidation products.