**Background:** Atherosclerotic cardiovascular disease (ASCVD) is a leading cause of mortality worldwide. ATP-binding box transporter A1 (ABCA1) promotes cholesterol efflux and inhibits inflammation through the JAK2/STAT3 pathway and by indirectly suppressing TLR4 signaling. Dietary fatty acids influence atherosclerosis progression, with saturated fatty acids generally promoting and unsaturated fatty acids protecting against cardiovascular disease. Medium-chain fatty acids like caprylic acid (C8:0) have been shown to upregulate ABCA1 expression and reduce inflammation, while omega-3 polyunsaturated fatty acids like eicosapentaenoic acid (EPA) have well-established anti-inflammatory effects. This study aimed to compare the effects of C8:0 and EPA on lipids, inflammation, and the JAK2/STAT3 pathway in the absence of ABCA1.
**Methods:** Twenty 6-week-old ABCA1⁻/⁻ mice were randomly divided into four groups (n=5 each) and fed a high-fat diet (HFD), or HFD supplemented with 2% C8:0, 2% palmitic acid (C16:0), or 2% EPA for 8 weeks. Wild-type C57BL/6J mice served as additional controls. For in vitro experiments, ABCA1 knock-down (ABCA1-KD) RAW 264.7 cells were constructed using siRNA (ABCA1-1701 plasmid) and divided into five groups: control (RAW 264.7 cells), ABCA1-KD group, ABCA1-KD + LPS (100 ng/mL), ABCA1-KD + LPS + C8:0 (100 μmol/L), and ABCA1-KD + LPS + EPA (100 μmol/L). Serum lipid profiles (TG, TC, HDL-C, LDL-C) and inflammatory cytokines (IL-1β, IL-6, IL-10, TNF-α, MCP-1) were measured using commercial kits. mRNA expression of TLR4, JAK2, STAT3, NF-κBp65, and ABCA1 in mouse aorta was determined by RT-PCR. Protein expression of ABCA1, JAK2, STAT3, p-JAK2, p-STAT3, NF-κBp65, TLR4, and MYD88 was analyzed by Western blot. Statistical analysis used one-way ANOVA with Tukey–Kramer post-hoc test; significance was set at p < 0.05.
**Key Results:** In ABCA1⁻/⁻ mice, the EPA group showed significantly lower TC, LDL-C, and non-HDL-C compared to the C8:0 and C16:0 groups (p < 0.05). The C8:0 and C16:0 groups had significantly lower TG than the HFD and EPA groups (p < 0.05). For inflammatory markers, the EPA group exhibited significantly decreased serum IL-1β, IL-6, TNF-α, and MCP-1 and significantly increased IL-10 compared to all other groups (p < 0.05). The C8:0 group had significantly lower TNF-α than HFD and C16:0 groups but significantly higher MCP-1 than the HFD group (p < 0.05). In the aorta, C8:0 significantly decreased p-STAT3 and p-JAK2 mRNA expression compared to HFD (p < 0.05), while EPA significantly reduced TLR4 and NF-κBp65 mRNA compared to HFD and C16:0 groups (p < 0.05). At the protein level, the C8:0 group had significantly lower p-STAT3 and p-JAK2 expression than HFD (p < 0.05), while the EPA group had significantly lower NF-κBp65 than HFD and C16:0 groups and significantly lower TLR4 than HFD, C16:0, and C8:0 groups (p < 0.05). In ABCA1-KD RAW 264.7 cells, the EPA group showed significantly decreased TNF-α, MCP-1, IL-6, and IL-1β and significantly increased IL-10 compared to the LPS group (p < 0.05). The C8:0 group had significantly higher TNF-α than the LPS group but significantly lower MCP-1, IL-6, IL-1β, and IL-10 (p < 0.05). Both C8:0 and EPA groups had significantly higher ABCA1 and p-JAK2 protein expression and significantly lower NF-κBp65 than the ABCA1-KD + LPS group (p < 0.05). Notably, the EPA group had significantly lower NF-κBp65 protein expression than the C8:0 group (p < 0.05).
**Clinical Implications:** This study demonstrates that in the absence of ABCA1, EPA is more effective than C8:0 at improving cholesterol metabolism and reducing systemic inflammation. The differential mechanistic pathways—C8:0 acting primarily through ABCA1-mediated JAK2/STAT3 signaling and EPA acting through TLR4/NF-κBp65 signaling—suggest that these fatty acids could be targeted to specific patient populations based on their ABCA1 functional status. Patients with ABCA1 dysfunction (e.g., Tangier disease) may benefit more from EPA supplementation than from C8:0. The upregulation of ABCA1 expression by functional nutrients represents a potential therapeutic strategy for atherosclerosis prevention and treatment. However, the small sample size, lack of atherosclerotic lesion formation in the 8-week study period, and potential compensatory mechanisms in ABCA1-deficient models limit the generalizability of these findings. Further research in combined gene-deficient models and identification of C8:0 binding proteins are needed.