Presence of autoantibodies against oxidatively modified low-density lipoprotein in essential hypertension: A biochemical signature of an enhanced in vivo low-density lipoprotein oxidation

Objective: We have previously reported that low-density lipoproteins (LDL) isolated from patients with essential hypertension are more susceptible to in vitro oxidation than lipoproteins isolated from normotensive control subjects. In the present study we investigated the occurrence of in vivo LDL oxidation in hypertensive patients. Design: The presence of antioxidatively mod ified LDL autoantibodies was take as a suitable index of in vivo LDL oxidation because, after oxidat ive modifications, LDL express antigenic epitopes that elicit an immune response. The antibody titres were measured in plasma from untreated patients with newly diagnosed essential hypertension. Methods: An enzyme-linked immunosorbent assay method was employed. Using native LDL, Cu²⁺-oxidized LDL and malondialdehyde-derivatized LDL {MDA-LDU as antigens. Human serum albumin and MDA human serum albumin were also used to monitor cross-reactivity with other oxidized molecules. The antibody titre was expressed as the ratio between anti-modified and anti-native antigen absolute values. Results: The patients with essential hypertens ion had an antibody ratio significantly higher than control subjects with respect to anti-Cu²⁺-oxidized LDL immunoglobulins G and M, and with respect to anti-MDA-LDL immunoglobulins G and M. A significant posit ive correlat ion was found between anti-MDA-LDL and anti-Cu²⁺-oxidized LDL antibody titres. The anti-MDA human serum albumin antibody titre was not different in the two groups of patients. An inverse correlation was detected between the anti-MDA-LDL immunoglobulin M titre and the age of the patients. Conclusions: The results obtained are con sistent with the view that, during the early phases of hyperten sion development, LDL undergo in vivo oxidation that is mirrored by the generation of autoantibodies against epitopes of oxidized LDL. The oxidation process appears specific for LDL and might be relevant both for the progression of hypertension and for the development of the atherosclerosis that often complicates hypertension itself.