(P26-020-25) Not All Saturated Fatty Acids Are Equal – The Case of Cyclopropane Fatty Acid Xenolipids

Objectives: The human gut harbors numerous metabolites derived from food and microbial metabolism. One example of non-self “xeno”-metabolites is the unique class of saturated fatty acids (SFAs) called cyclopropane fatty acids (CpFAs), lipids with bacterial origins. While our work and that of others suggests that CpFAs are members of the human lipidome, their bioactivities remain largely unknown. Their cyclopropane ring in CpFAs induces a structural bend resembling that of monounsaturated fatty acids (MUFAs), leading us to hypothesize that CpFAs can bind PPARα, PPARδ, and PPARγ nuclear receptors, which play key roles in metabolic gene regulation in liver, adipose, and other tissues.

Methods: This study integrated large-scale in silico docking and molecular dynamics simulations (Schrödinger) to compare the binding characteristics of all possible CpFAs, MUFAs, and SFAs across all three PPARs. Experimental validation was conducted using LanthaScreen TR-FRET coactivator binding assays for a subset of lipids. Functional effects were assessed in 3T3-L1 preadipocytes treated with increasing concentrations of the same lipids, along with PPAR agonists and antagonists, measuring changes in PPAR target gene expression via RT-qPCR.

Results: The modeling analyses revealed isoform-specific binding patterns, with CpFAs showing strong predicted affinities for PPARα and PPARδ (ranging from -30 to -70 kcal/mol), influenced by chain length and ring position. Biochemical assays confirmed CpFA binding to PPARα and δ, with average EC₅₀ of 8 µM and 25 µM, respectively. Functional studies showed that CpFAs, particularly those with chain lengths over 15, dose-dependently upregulated Angptl4 expression in 3T3-L1 cells, surpassing related MUFAs and SFAs. Pre-treatment with PPAR antagonists blunted these effects, confirming CpFA interactions with PPAR pathways.

Conclusions: CpFAs effectively modulate PPARs pathways, especially PPARα and δ, and outperform both related MUFAs and SFAs. These findings challenge the notion that all SFAs are equivalent, highlighting the need for a more nuanced analysis of lipid categories in evaluating dietary patterns and health outcomes. They also suggest that xenolipids derived from food and gut microbes may influence local and systemic bioactivities.

Funding Sources: This work was funded by NIH-NIDDK and the UC Davis Department of Surgery.