Low density lipoprotein oxidation by ferritin at lysosomal pH

Abstract

Oxidation of low density lipoprotein (LDL) has been proposed to be involved in the pathogenesis of atherosclerosis. We have previously shown that LDL can be oxidised by iron in lysosomes. As the iron-storage protein ferritin might enter lysosomes by autophagy, we have investigated the ability of ferritin to catalyse LDL oxidation at lysosomal pH. LDL was incubated with ferritin at 37 o C and pH 4.5 and its oxidation monitored spectrophotometrically at 234 nm by the formation of conjugated dienes and by measuring oxidised lipids by HPLC or a tri-iodide assay. Iron released from ferritin was measured using the ferrous iron chelator bathophenanthroline and by ultrafiltration followed by atomic absorption spectroscopy. LDL was oxidised effectively by ferritin (0.05 -0.2 µM). The oxidation at lysosomal pH (pH 4.5) was much faster than at pH 7.4. Ferritin increased cholesteryl linoleate hydroperoxide, total lipid hydroperoxides and 7-ketocholesterol. Iron was released from ferritin at acidic pH. The iron chelators, diethylenetriaminepentaacetate and EDTA, and antioxidant N,N‫-׳‬diphenyl-p-phenylenediamine inhibited the oxidation considerably, but not entirely. The antioxidant tempol did not inhibit the initial oxidation of LDL, but inhibited its later oxidation.Cysteamine, a lysosomotropic antioxidant, inhibited the initial oxidation of LDL in a concentrationdependent manner, however, the lower concentrations exhibited a pro-oxidant effect at later times, which was diminished and then abolished as the concentration increased. These results suggest that ferritin might play a role in lysosomal LDL oxidation and that antioxidants that accumulate in lysosomes might be a novel therapy for atherosclerosis.

Lysosome (Dys)function in Atherosclerosis—A Big Weight on the Shoulders of a Small Organelle

“…Indeed, the lysosomal acidic environment increases the solubility of iron facilitating oxidation (Satchell and Leake, 2012). Furthermore, it has been demonstrated that LDL can be oxidized within the lysosomes of macrophages (Lamb and Leake, 1994;Ojo and Leake, 2018;Ahmad and Leake, 2019). In contrast, when LDL are incubated with copper at acidic pH its oxidation is delayed (Morgan and Leake, 1995), indicating that LDL oxidation by copper within lysosomes is unlikely to occur.…”

Effect of vitamin E on low density lipoprotein oxidation at lysosomal pH

“…the large clinical trials of a-tocopherol were ineffective. It would be desirable to conduct clinical trials of antioxidants that accumulate in lysosomes and inhibit the oxidation of LDL at acidic pH, such as cysteamine [22][23][24][25].…”

“…We have shown previously that LDL can be oxidised by iron in the lysosomes of macrophages [21] and that this causes the secretion of inflammatory cytokines [22]. The antioxidant cysteamine, which accumulates in lysosomes, inhibits the lysosomal oxidation of LDL [22][23][24][25] and decreases atherosclerosis in LDL receptor-deficient mice [25]. The oxidation of LDL by ferrous ion at lysosomal pH (pH 4.5) was not effectively inhibited by a-tocopherol [26].…”

An Overview of Cupping Treatment

“…56 Bilindiği üzere, canlıda majör oksidan molekül olan demir, ROS üretimini indükleyerek doku hasarına neden olmasının yanı sıra; endojen antioksidanlarda azalma, lipid peroksidasyon hasarı ve okside LDL üretiminden sorumludur. 57,58 Ayrıca hacamatın, olan demirin birikimini azalttığı bilinmektedir ve bu etkisinin büyük oranda demir ekskresyonunun artışına bağlı olduğu tahmin edilmektedir. 59 Bu bağlamda yapılan çalışmalardan bazıları örnek olarak aşağıda sunulmuştur:…”