Cellular cysteine generation does not contribute to the initiation of LDL oxidation.
It has been suggested that the generation of cysteine (Cys-SH) by cells may play a role in the initiation of oxidation of low density lipoprotein (LDL). Cysteine has long been considered as an antioxidant. We studied the effect of Cys-SH on the oxidation of LDL by copper. The presence of Cys-SH had a profound inhibitory effect on the formation of conjugated dienes when fresh LDL was used. However, when we used LDL samples that were subjected to pre-incubation with copper, a progressive decrease in the inhibition and an actual enhancement of oxidation by Cys-SH could be demonstrated. The oxidation of freshly prepared LDL by RAW macrophages as compared to older LDL was considerably less. The addition of Cys-SH inhibited the oxidation of LDL by cells. In contrast, the addition of cystine (Cys-S-S) enhanced the oxidation of older LDL preparations while such additions had no effect on the oxidation of freshly prepared LDL. When pre-incubated LDL was subjected to oxidation by cells an enhancement of oxidation by Cys-S-S could be noted. These results demonstrate that the role of Cys-SH generated as a result of cellular recycling of Cys-S-S in the oxidation of LDL may not relate to the initiation of oxidation reactions. However, Cys-SH may enhance the rate of oxidation of LDL that may contain peroxides.
Santanam
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N
Department of Gynecology and Obstetrics, Emory University School of Medicine, Atlanta, GA 30322, USA.
Parthasarathy
S
S
D000975:Antioxidants / Q000378:metabolism*; D002474:Cell-Free System; D002478:Cells, Cultured; D003300:Copper / Q000737:chemistry; D003545:Cysteine / Q000097:blood*; D008077:Lipoproteins, LDL / Q000097:blood*; D008264:Macrophages / Q000378:metabolism*; D010084:Oxidation-Reduction
D000975:Antioxidants; D008077:Lipoproteins, LDL; D003300:Copper; D003545:Cysteine