Atherogenic Index of Plasma in Relation to Angiographic Coronary Artery Disease Severity, Plasma Fatty Acid Composition, and Estimated Desaturase Activity: A Cross-Sectional Study

Background/Objectives: Conventional lipid parameters incompletely reflect coronary atherosclerotic burden, particularly in the setting of metabolic heterogeneity and residual cardiovascular risk. Composite indices such as the atherogenic index of plasma (AIP) and the triglyceride–glucose (TyG) index have emerged as integrative markers. Fatty acid desaturases regulate key pathways of lipid metabolism, and estimated desaturase activity indices (SCD-16, SCD-18, D5D, and D6D) may provide complementary information on the metabolic pathways underlying AIP and the TyG index. However, the relationships among composite atherogenic indices, plasma fatty acid composition, estimated desaturase activity indices, and coronary artery disease (CAD) severity remain incompletely understood. Methods: In this cross-sectional study, 61 patients undergoing coronary angiography for suspected CAD were evaluated. Coronary atherosclerotic burden was quantified using the Gensini score. AIP and the TyG index were calculated from fasting biochemical parameters. Plasma fatty acid composition was analyzed using gas chromatography–mass spectrometry, and estimated desaturase activity indices were calculated using product-to-precursor ratios. Results: AIP was independently associated with Gensini score (β = 37.020, p < 0.001), whereas the TyG index was not independently associated after adjustment for potential confounders (p = 0.101). In correlation analyses, AIP was positively correlated with HOMA-IR (ρ = 0.352, p < 0.05). Myristic acid was positively correlated with AIP, the TyG index, and VLDL (ρ = 0.297, 0.288, and 0.325, respectively; all p < 0.05), whereas n-6 polyunsaturated fatty acids were positively correlated with LDL (ρ = 0.276, p = 0.031). Among the estimated desaturase activity indices, D6D was positively correlated with AIP, BMI, insulin, and VLDL (ρ = 0.262, 0.376, 0.340, and 0.266, respectively; all p < 0.05), whereas D5D was inversely correlated with BMI and VLDL (ρ = −0.319 and −0.266, respectively; both p < 0.05). No significant associations were observed for SCD-16 or SCD-18. Conclusions: The observed associations between AIP, angiographic CAD severity, selected fatty acid species, and estimated desaturase activity indices suggest that AIP may provide complementary information regarding metabolic alterations associated with coronary atherosclerosis. These findings provide a basis for future studies exploring the relationship between composite atherogenic indices and fatty acid metabolism.