Early destruction of tryptophan residues of apolipoprotein B is a vitamin E-independent process during copper-mediated oxidation of LDL

Antioxidant activity of aminoethylcysteine ketimine decarboxylated dimer on copper‐induced LDL oxidation

“…In The TBARS assay was used to assess the degree of lipid peroxidation. The decrease in tryptophan fluorescence was used to monitor the kinetics of coppermediated LDL oxidation at the protein level [18,19]. As reported by Giessauf et al [18] in the early stages of this kind of oxidation, a certain number of Trp residues of Apo-B-100 are …”

“…The biological relevance of this study is supported by the recent finding of this sulfur-containing aminoacid in human urine [7], bovine cerebellum [8] and human plasma (unpublished data) at concentrations comparable to those used for these experiments. Moreover, the use of copper as a catalyst to test LDL resistance to oxidative modifications in the presence of antioxidants is significant due to the actions of this ion in the promotion of the oxidation of lipoproteins in two main ways: namely 1) at the protein moiety level (it has been reported that the destruction of Trp residues of Apo B 100 is an early event in copper-mediated LDL oxidation [18]); 2) at the lipid moiety level by decomposing preexisting lipid hydroperoxides to give peroxyl and alkoxyl radicals which initiate further lipid peroxidation [4,[21][22][23]. Redox-active copper has also been detected in human atherosclerotic lesions [24] suggesting that copper may act as an in vivo prooxidant and atherogenic agent.…”

“…All fluorescence measurements were performed with a Jasco FP-770 fluorimeter. The decrease of the LDL-Trp fluorescence of a solution of 50 ~tg LDL/rnl PBS after addition of 3 IxM CuCI2 (final concentration) was measured, in the presence or absence of AECK-DD, at an emission wavelenght of 331 nm, with excitation set to 282 nm [18,19]. The dimer did not interfere in the fluorescence measurements.…”

Kinetic study of low density lipoprotein oxidation by copper

“…Approximately 80% of total copper ions are likely to be bound to the apo-B 100 protein, possibly to ligands in close vicinity to the LDL lipids (18). Aside from histidine and / or cysteine which are known to readily from copper complexes, preferred binding sites have been identified at or near tryptophan residues (19). The early oxidation of apo-B 100 tryptophan residues and the formation of kynurenine and formylkynurenine suggest a localized formation of protein radicals by copper at specific apo-B 100 complexes (20).…”

Caracterização de lipoproteína de baixa densidade (LDL) por meios espectroscópicos

“…Desses resíduos de sete a oito estão localizados na superfície da apoB-100, e os vinte e oito à vinte nove resíduos estão localizados no interior da região da apoB-100 [28], [29].…”