E. Ferguson et al., Characterization of the adduct formed from the reaction between homocysteine thiolactone and low-density lipoprotein: Antioxidant implications, FREE RAD B, 26(7-8), 1999, pp. 968-977
Homocysteine thiolactone is a cyclic thioester that is implicated in the de
velopment of atherosclerosis. This molecule will readily acylate primary am
ines, forming a homocystamide adduct, which contains a primary amine and a
thiol. Here, we have characterized and evaluated the antioxidant potential
of the homocystamide-low-density lipoprotein (LDL) adduct, a product of the
reaction between homocysteine thiolactone and LDL, Treatment of LDL with h
omocysteine thiolactone resulted in a time-dependent increase in LDL-bound
thiols that reached approximately 250 nmol thiol /mg LDL protein. The thiol
groups of the homocystamide-LDL adduct were labeled with the thiol-reactiv
e nitroxide, methanethiosulfonate spin label. Using paramagnetic relaxing a
gents and the electron spin resonance spin labeling technique, we determine
d that the homocystamide adducts were predominately exposed to the aqueous
phase. The homocystamide-LDL adduct was resistant to myoglobin- and Cu2+-me
diated oxidation (with respect to native LDL), as measured by the formation
of conjugated dienes and thiobarbituric acid reactive substances, and the
depletion of vitamin E. This antioxidant effect was due to increased thiol
content, as the effect was abolished with N-ethylmaleamide pre-treatment. W
e conclude that the reaction between homocysteine thiolactone and LDL gener
ates an LDL molecule that is more resistant to oxidative modification than
native LDL. The potential relationship between the homocystamide-LDL adduct
and the development of atherosclerosis is discussed. (C) 1999 Elsevier Sci
ence Inc.