Background: Despite the identification of different pathogenic mechanism in antiphospholipid syndrome (APS), a comprehensive knowledge of the disease at the pathophysiological level is still lacking. The liver plays a central role in lipid metabolism, and hepatic dysfunction in APS may represent a key link between autoimmunity and cardiovascular disease. In this sense, characterizing hepatic functional involvement in APS could provide novel insights into disease mechanisms and uncover previously unrecognized pathways contributing to cardiovascular risk. Current therapeutic strategies for APS are limited, highlighting the need for new treatment approaches. In this context, coenzyme Q10, has demonstrated beneficial effects in several cardiovascular conditions due to its antioxidant and immunomodulatory properties.

Objectives: This study aims to:

• Characterize the circulating metabolomic signature in APS patients and its association with clinical features.

• Investigate in vivo the role of hepatic involvement in the pathophysiology of APS.

• Evaluate the direct effects of antiphospholipid antibodies (aPLs) on the metabolism and molecular profiles of hepatic cells in vitro .

• Examine the short-term impact of ubiquinol (reduced CoQ ₁₀ ) supplementation both in vivo and in vitro on the disrupted liver-metabolome axis.

Methods: A total of 129 primary APS patients and 43 healthy donors (HDs) underwent clinical and molecular characterization. Serum metabolomic profiling was performed using nuclear magnetic resonance (Nightingale), quantifying over 250 metabolites, mostly lipids. Longitudinal changes in the molecular profiles were assessed in a subgroup of 15 APS patients who received ubiquinol supplementation for one month (clinical trial NCT02218476). The involvement of liver function was explored in vivo and in vitro . Correlations between circulating metabolites, liver-related biomarkers, and aPLs were carried out. In vitro , to explore the regulatory effects of aPLs on hepatic lipid metabolism, hepatic cells were treated with purified aPLs, and their functional responses were assessed using Enzyme-Linked Immunosorbent Assay (ELISA), Seahorse XF Palmitate Oxidation Stress Test Kit, Western blotting and RT-qPCR, either alone or in combination with CoQ ₁₀ .

Results: Metabolomic profiling revealed 53 significantly altered metabolites in APS patients compared to HDs, including decreased levels of atheroprotective lipids (HDL-related lipids) and elevated levels of pro-atherogenic mediators (VLDL, LDL-related lipids). These alterations were associated with arterial thrombosis, atheroma plaques, recurrent thrombotic events and higher APS risk score in these patients. Evidence for liver involvement was supported by significant and clear correlations between circulating lipid profile and the levels of liver transaminases as well as with the levels of aPLs. Additionally, the levels of antiphospholipid antibodies were significantly associated with markers of liver risk damage, such as the FIB-4 index. To further support the hypothesis of hepatic involvement and to assess the direct impact of aPLs on hepatic cells, in vitro studies were conducted. Exposure of hepatic cells to purified aPLs increased the secretion of LDL and VLDL into the supernatant and upregulated multiple markers of liver damage and lipid metabolism. Together, these findings suggest a potential contribution of antiphospholipid antibodies to impaired liver function, leading to an aberrant circulating lipidomic profile. Treatment with antiphospholipid antibodies induced a metabolic shift in hepatic cells characterized by increased signalling and expression of fatty acid oxidation–associated markers, including enhanced phosphorylation of Acetyl-CoA Carboxylase 1 (ACC1), and upregulation of Acetyl-CoA Acyltransferase 2 (ACAA2) levels. However, this apparent activation of β-oxidation was not coupled to increased mitochondrial respiration, as evidenced by unchanged palmitate-driven oxygen consumption in functional assays. This metabolic uncoupling likely results in the accumulation of β-oxidation–derived intermediates that are not efficiently utilized for oxidative phosphorylation and may promote triglyceride synthesis and facilitate the export of proatherogenic VLDL particles. Finally, in APS patients, ubiquinol supplementation partially restored the altered lipidomic profile by decreasing pro-atherogenic and increasing anti-atherogenic lipid-related markers, highlighting its potential cardioprotective benefits. Consistently, in vitro , pre-treatment of hepatocytes with CoQ ₁₀ effectively prevented the hepatic alterations induced by aPLs exposure.