Autoantibodies Against Oxidised Low-Density Lipoprotein in Patients w ith Obstructive Sleep Apnoea Clin Chem Lab M ed 1999; 37(5):517–520 © 1999 by Walter de Gruyter · Berlin · New York Seppo Saarelainen 1 , Terho Lehtimäki 2,3 , Olli Jaak- kola 2,3 , Tuija Poussa, Matti Nikkilä 4 , Tiina Solakivi 2,3 , and M arkku M . Nieminen 1 1 Department of Pulmonary Diseases and 2 Research Laboratory for Atherosclerosis, Department of Clinical Chemistry, Tampere University Hospital, 3 Department of Medical Biochemistry, Medical School, University of Tampere 4 Department of Internal Medicine, Tampere City Hospital, Tampere, Finland Autoantibodies against oxidised low -density lipopro- tein (OxLDL-Abs) have been proposed to be an indica- tor of endothelial dysfunction and a novel tool for find- ing individuals with a high cardiovascular risk. In a cross-sectional study, OxLDL-Abs were measured in 297 patients w ith obstructive sleep apnoea (OSA) and 54 controls using an enzyme-linked immunosorbent assay. The autoantibodies w ere increased in patients w ith OSA when compared to controls (age, body mass in- dex (BMI) and gender adjusted, p = 0.001). However, w ithin the OSA patients, OxLDL-Abs w ere not related to smoking, hypertension or BM I, and there w as a w eak negative correlation (r = –0.16, P = 0.007) between age and levels of OxLDL-Abs. In conclusion, at present the measurement OxLDL-Abs still remains a method for basic research and is not applicable for screening of at-risk patients w ith OSA. Key words: Atherosclerosis; LDL cholesterol; Autoanti- bodies; Obstructive sleep apnoea. Introduction Obstructive sleep apnoea (OSA) and snoring are asso- ciated with the male gender, age, central obesity and smoking – all well-known risk factors for atherosclero- sis (1).OSA causes pulsatile hypertension during sleep, but the possible causal relationship to daytime hyper- tension is still unproven (2) and there is no evidence that OSA in its own right is a cause of atherosclerosis. However, in animal models, two typical events in the apnoea cycle, hypoxaemia (3) and sympathetic activa- tion (4), have been atherogenic. Intimal macrophages absorb oxidised and acety- lated low-density lipoprotein (LDL) through the scaven- ger receptor pathway when they become foam cells (5). Deposited LDL found in the foam cells is usually modified by free radical-mediated oxidation (6). Dean and Wilcox (7)have hypothesised that repeated noctur- nal hypoxia followed by reperfusion in OSA may gen- erate a flux of free radicals, induce endothelin expres- sion, suppress nitric oxide generation and induce local vasoconstriction and changes in vascular permeability. Autoantibodies against oxidised LDL (OxLDL-Abs) are an indicator of endothelial dysfunction in systemic (8) and coronary (9) arteries and, according to a recent report, also predict myocardial infarction (10). We con- ducted a study to evaluate OxLDL-Abs in a middle- aged population with several cardiovascular risk fac- tors including OSA. Patients and M ethods Patients and Controls A total of 297 (27 female) consecutive patients with OSA (apnoea index ≥ 5 events/h) were recruited. Patients with a neurological or cerebrovascular disease were excluded. The controls (n = 54, including 17 female) wereorthopaedic outpa- tients and hospital employees. The control subjects fulfilled a structured questionnaire including all current medical condi- tions and medication before blood samples were taken and blood pressure and weight were measured. Individuals taking antihypertensives or having a seated blood pressure of ≥ 160/95 mmHg at least twice were classified as hypertensives. All those having a smoking history of at least five pack-years (a pack-year defined as smoking 20 cigarettes per day for a year) were classified as smokers. The study was approved by the Ethical Committee of Tampere University Hospital, and all par- ticipating subjects gave their informed consent. Sleep studies Sleep recordings were performed on 111 patients with an Alice 3 ® digital polysomnograph (Healthdyne, Belgium) and on 186 patients with a partial polygraphy including the Static Charge Sensitive Bed (SCSB, Biomatt ® , Biorec, Finland) for respiratory and body movements, a thermistor for air-flow and a position detector. Nocturnal oxygen saturation was measured during both recordings with a Biox III ® oximeter (Ohmeda, USA) with a finger probe. The recordings were scored manually before assessed by a sleep physician. Assay for OxLDL-Abs Serum was stored at –20 °C until analysed. Autoantibodies against copper-oxidised LDL were determined by enzyme- linked immunosorbent assay as previously described (8). In short, antigens for this assay included native LDL (natLDL) prepared from the pooled plasma of ten donors and protected against oxidation by 0.27 mmol/l EDTA and 20 μmol/l buty- lated hydroxytoluene (BHT) in phosphate buffered saline (PBS), and OxLDL obtained after 24-h oxidation of the natLDL with 2μmol/l CuSO 4 . For enzyme-linked immunosorbent assay, half of the wells on a polystyrene plate (Nunc, Roskilde, Denmark) were coated with 50 μl of natLDL and the other half with 50 μl copper-oxi-