Triggering of inflammatory response by myeloperoxidase-oxidized LDL.

The oxidation theory proposes that LDL oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis in triggering inflammation. In contrast to the copper-modified LDL, there are few studies using myeloperoxidase-modified LDL (Mox-LDL) as an inflammation inducer. Our aim is to test whether Mox-LDL could constitute a specific inducer of the inflammatory response. Albumin, which is the most abundant protein in plasma and which is present to an identical concentration of LDL in the intima, was used for comparison. The secretion of IL-8 by endothelial cells (Ea.hy926) and TNF-alpha by monocytes (THP-1) was measured in the cell medium after exposure of these cells to native LDL, native albumin, Mox-LDL, or Mox-albumin. We observed that Mox-LDL induced a 1.5- and 2-fold increase (ANOVA; P < 0.001) in IL-8 production at 100 microg/mL and 200 microg/mL, respectively. The incubation of THP-1 cells with Mox-LDL (100 microg/mL) increased the production of TNF-alpha 2-fold over the control. Native LDL, albumin, and Mox-albumin showed no effect in either cellular types. The myeloperoxidase-modified LDL increase in cytokine release by endothelial and monocyte cells and by firing both local and systemic inflammation could induce atherogenesis and its development.

Captopril inhibits the oxidative modification of apolipoprotein B-100 caused by myeloperoxydase in a comparative in vitro assay of angiotensin converting enzyme inhibitors.

The oxidative modification of low-density lipoproteins (LDL) is a key event in the formation of atheromatous lesions. Indeed, oxidized derivatives accumulate in the vascular wall and promote a local inflammatory process which triggers the progression of the atheromatous plaque. Myeloperoxidase (MPO) has been mentioned as a major contributor to this oxidative process. It takes part in the oxidation both of lipids by chlorination and peroxidation and of apolipoprotein B-100. Based on recent observations with several anti-inflammatory and thiol-containing drugs, the present study was designed to test the hypothesis that anti-hypertensive agents from the angiotensin converting enzyme (ACE) inhibitors group inhibit the oxidative modifications of Apo B-100 caused by MPO. Captopril, ramipril, enalapril, lisinopril and fosinopril were assessed by measuring: their inhibiting effect on the MPO/H(2)O(2)/Cl(-) system, the accumulation of compound II, which reflects the inhibition of the synthesis of HOCl and the LDL oxidation by MPO in presence of several concentrations of ACE inhibitors. Only captopril, a thiol-containing ACE inhibitor, was able to significantly decrease the oxidative modification of LDL in a dose dependent manner and this by scavenging HOCl. This efficient anti-hypertensive drug therefore appears to also protect against the atherosclerotic process by this newly documented mechanism.

Thiol-containing molecules interact with the myeloperoxidase/H2O2/chloride system to inhibit LDL oxidation.

Oxidized low-density lipoproteins (LDL) accumulate in the vascular wall and promote a local inflammatory process contributing to the progression of atheromatous plaque. The key role of myeloperoxidase (MPO) in this process has been documented and the enzyme has been involved in the oxidative modification of apolipoprotein B-100 in the intima and at the surface of endothelial cells. As the inhibition of this last phenomenon could be of relevance in pharmacological interventions, thiol-containing molecules such as glutathione, captopril, and N-acetylcysteine (NAC) and its lysinate salt (NAL) were tested in this system and their properties were compared with those of flufenamic acid (control). This last compound already demonstrated an inhibition of the production of HOCl by MPO and a more intense inhibition of MPO activity than glutathione, NAC, NAL, and captopril. However, NAC and NAL inhibited the oxidative modification of LDL more intensively than captopril and glutathione whereas flufenamic acid had no comparable inhibiting effect. This could be related to the presence of LDL close to the catalytic site of the enzyme. NAC and NAL therefore appeared as the most efficient inhibitors probably as a consequence of their relatively small size. The relevance of such effects has to be documented by in vivo studies.