Insulin resistance in systemic lupus erythematosus patients: contributing factors and relationship with subclinical atherosclerosis.

OBJECTIVES Insulin resistance (IR) plays a role in the increased cardiovascular risk of systemic lupus erythematosus (SLE) patients. This study aimed to determine the potential association of IR with disease activity, drug exposure and subclinical atherosclerosis in patients with SLE. METHODS This cross-sectional study encompassed 87 non-diabetic SLE patients and 82 sex-matched controls. Insulin and C-peptide serum levels, IR indexes by homeostatic model assessment (HOMA2) (both insulin-based: HOMA2-IR, and with C-peptide: HOMA2-IR-C-peptide) and lipid profiles were assessed in patients and controls. Activity (SLEDAI), severity (Katz) and damage (SLICC) index scores, as well as carotid intima-media thickness (cIMT) and carotid plaques, were determined in SLE patients. A multivariable regression analysis, adjusted for classic IR related factors, was performed to evaluate the differences in IR indexes between patients and controls and how IR is associated with disease-related characteristics, including carotid ultrasound results, in SLE patients. RESULTS SLE patients had higher C-peptide serum levels (2.61±1.51 vs. 1.34±0.62 ng/ml, p=0.00) and elevated HOMA2-IRC-peptide index (1.90±1.12 vs. 0.97±0.45, p=0.00) than controls. These differences remained statistically significant after adjusting for classic cardiovascular risk factors and prednisone intake. Traditional IR-related factors, such as body mass index, waist circumference or hypertension, and prednisone intake were significantly associated with HOMA2-IR and HOMA2-IRC-peptide in SLE patients. SLICC damage index was independently associated with HOMA2-IR-C-peptide. The presence of carotid plaques and cIMT values were associated with IR indexes in SLE patients only in the univariate analysis. CONCLUSIONS C-peptide serum levels are independently up-regulated in SLE patients. Although classic IR factors and prednisone are associated with IR, SLE damage over time also contributes to IR in an independent way.