Background and aims

Cluster of differentiation 36 (CD36) is a key scavenger receptor in the control of macrophage uptake of oxidised low-density lipoproteins (oxLDL). CD36 expression levels are not down regulated by intracellular cholesterol but are upregulated by oxidised low density lipoprotein (oxLDL) leading to the formation of lipid loaded foam cells, a major constituent of atherosclerotic plaques. We have previous shown that CD36 is down regulated by 7,8-dihydroneopterin, an antioxidant generated by γ-interferon activated macrophages. How CD36 down regulation affects oxLDL induced cytotoxicity, CD36 oxLDL upregulation and foam cell formation is examined using human monocyte like U937 cell line as a model system of human macrophages.

Methods

Low density lipoprotein (LDL) was prepared by ultracentrifugation from human plasma and oxidised in copper chloride. CD36 levels in U937 cells were measured by western blot analysis. and lipid accumulation was measured by oil red-O staining and 7-ketocholesterol accumulation by high performance liquid chromatography. Cell viability was measured by flow cytometry analysis after propidium iodide staining.

Results

7,8-dihydroneopterin concentrations above 100 μM caused a concentration and time dependent decrease in cellular CD36 levels to 20 % of the untreated cells after 24 h. Upregulation of CD36 by oxLDL was inhibited by 7,8-dihydroneopterin treatment. The CD36 down regulation was associated with decrease in foam cell formation but not a reduction on oxLDL cytotoxicity.

Conclusions

7,8-dihydroneopterin down regulated CD36 in U937 cells, inhibiting foam cell formation but not oxLDL mediated cell death. 7,8-dihydroneopterin may modulate foam cell formation in atherosclerotic plaques.

中文翻译：

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巨噬细胞抗氧化剂 7,8-二氢蝶呤对 CD36 的下调抑制泡沫细胞形成，但不抑制 oxLDL 细胞毒性

背景和目标

分化簇 36 (CD36) 是控制巨噬细胞摄取氧化低密度脂蛋白 (oxLDL) 的关键清道夫受体。CD36 表达水平不会被细胞内胆固醇下调，而是被氧化低密度脂蛋白 (oxLDL) 上调，导致脂质泡沫细胞的形成，这是动脉粥样硬化斑块的主要成分。我们之前已经表明 CD36 被 7,8-二氢蝶呤下调，7,8-二氢蝶呤是一种由 γ-干扰素激活的巨噬细胞产生的抗氧化剂。CD36 下调如何影响 oxLDL 诱导的细胞毒性、CD36 oxLDL 上调和泡沫细胞形成，使用人类单核细胞如 U937 细胞系作为人类巨噬细胞的模型系统进行检查。

方法

低密度脂蛋白 (LDL) 通过超速离心从人血浆中制备并在氯化铜中氧化。通过蛋白质印迹分析测量 U937 细胞中的 CD36 水平。通过油红-O染色和高效液相色谱法测量7-酮胆固醇积累来测量脂质积累。在碘化丙啶染色后通过流式细胞术分析测量细胞活力。

结果

7,8-二氢蝶呤浓度高于 100 μM 导致细胞 CD36 水平在 24 小时后浓度和时间依赖性降低至未处理细胞的 20%。oxLDL 对 CD36 的上调受到 7,8-二氢蝶呤处理的抑制。CD36 下调与泡沫细胞形成的减少有关，但与 oxLDL 细胞毒性的降低无关。

结论

7,8-二氢蝶呤下调 U937 细胞中的 CD36，抑制泡沫细胞形成，但不抑制 oxLDL 介导的细胞死亡。7,8-二氢蝶呤可调节动脉粥样硬化斑块中的泡沫细胞形成。