Types of Polyunsaturated Fatty Acids in Epididymal Adipose Tissue Are Distinguishable Using Raman Spectroscopy and Multivariate Analysis

Biological polyunsaturated fatty acids (PUFAs) are important precursors of secondary messengers that modulate inflammatory responses, cellular growth, and cholesterol metabolism. The optimal n-6/n-3 ratio is extremely important for maintaining normal homeostasis because n-3 and n-6 PUFAs are competitively metabolized. To date, a widely accepted analytical method to determine the biological n-6/n-3 ratio is gas chromatography-mass spectrometry (GC-MS) on dried whole blood samples. However, this technique has several drawbacks, including the intrusive nature of collecting blood samples, high expenses involved, and length of time required to use the GC/MS instrument. To overcome these limitations, we introduced Raman spectroscopy (RS) to distinguish PUFAs present in the epididymal adipose tissue (EAT) isolated from experimental rats that were fed three different high-fat diets (HFDs) with multivariate analysis, including principal component analysis (PCA) and linear discriminant analysis (LDA). The diets comprised HFD, HFD + perilla oil (HFD + PO [n-3 rich oil]), and HFD + corn oil (HFD + CO [n-6 rich oil]). This method allows for quantitative, label-free, noninvasive, and rapid monitoring of biochemical changes in the EAT with high sensitivity. In RS, the Raman bands of the EAT from three different diet groups (HFD, HFD + PO, and HFD + CO) detected and distinguished peaks at 1079 (C-C stretching vibration), 1300 (CH2 deformation), 1439 (CH2 deformation), 1654 (amide I), 1746 (C = O stretching vibration), and 2879 cm(-1) (-C-H stretching vibration). The PCA-LDA analysis results showed that PUFAs in the EAT of animals receiving the three different dietary interventions can be determined according to the three groups (HFD, HFD + PO, and HFD + CO). In conclusion, we investigated the possibility of determining PUFA profiles in specimens using RS.