Background and aims ApoM is an anti-atherogenic and vasculoprotective 25 kDa apolipoprotein suggested to play a role in keeping endothelial barrier integrity. The aims of the current study were to determine the impact of SLE disease activity on apoM levels and investigate if apoM levels reflect endothelial function in SLE.

Methods Plasma concentrations of apoM were measured with ELISA in two SLE cohorts, all patients fulfilling ≥4 American College of Rheumatology (ACR) classification criteria for SLE, and 100 healthy controls (HC). Patients in cohort I had active disease as evaluated with SLEDAI scores. In cohort II endothelial function was measured by EndoPAT 2000 and correlated to apoM levels. A low Reactive Hyperemia Index (RHI) value indicates endothelial dysfunction.

Results In cohort I, the plasma levels of apoM were found to be significantly decreased in SLE (p<0.0001), and the apoM concentrations correlated inversely to disease activity (SLEDAI, r=−0.29, p=0.0063). ApoM was also significantly lower in patients with active nephritis, leukopenia, anti-DNA antibodies or rash compared to patients without these manifestations.

In cohort II, using linear regression analysis, there was a positive correlation between apoM levels and the RHI value, indicating endothelial dysfunction, in the younger SLE patients: β=0.94 CI 95% 0.22,1.65 r=0.32 p=0.011.

Conclusions SLE related inflammation may have an impact on lower plasma apoM, which may affect the endothelium and the process towards cardiovascular disease.