Alan Chait

Human atherosclerotic intima and blood of patients with established coronary artery disease contain high density lipoprotein damaged by reactive nitrogen species

High density lipoprotein (HDL) is the major carrier of lipid hydroperoxides in plasma, but it is not yet established whether HDL proteins are damaged by reactive nitrogen species in the circulation or artery wall. One pathway that generates such species involves myeloperoxidase (MPO), a major constituent of artery wall macrophages. Another pathway involves peroxynitrite, a potent oxidant generated in the reaction of nitric oxide with superoxide. Both MPO and peroxynitrite produce 3-nitrotyrosine in vitro. To investigate the involvement of reactive nitrogen species in atherogenesis, we quantified 3-nitrotyrosine levels in HDL in vivo. The mean level of 3-nitrotyrosine in HDL isolated from human aortic atherosclerotic intima was 6-fold higher (619 ± 178 μmol/mol Tyr) than that in circulating HDL (104 ± 11 μmol/mol Tyr; p < 0.01). Immunohistochemical studies demonstrated striking colocalization of MPO with epitopes reactive with an antibody to 3-nitrotyrosine. However, there was no significant correlation between the levels of 3-chlorotyrosine, a specific product of MPO, and those of 3-nitrotyrosine in lesion HDL. We also detected 3-nitrotyrosine in circulating HDL, and linear regression analysis demonstrated a strong correlation between the levels of 3-chlorotyrosine and levels of 3-nitrotyrosine. These observations suggest that MPO promotes the formation of 3-chlorotyrosine and 3-nitrotyrosine in circulating HDL but that other pathways also produce 3-nitrotyrosine in atherosclerotic tissue. Levels of HDL isolated from plasma of patients with established coronary artery disease contained twice as much 3-nitrotyrosine as HDL from plasma of healthy subjects, suggesting that nitrated HDL might be a marker for clinically significant vascular disease. The detection of 3-nitrotyrosine in HDL raises the possibility that reactive nitrogen species derived from nitric oxide might promote atherogenesis. Thus, nitrated HDL might represent a previously unsuspected link between nitrosative stress, atherosclerosis, and inflammation.

Comparison of Methods of Plasma Triglyceride Turnover

Over the past several years, a kinetic approach has been widely used in an attempt to determine whether either overproduction or impaired removal of very low-density lipoproteins (VLDL) is the fundamental mechanism underlying the elevated triglyceride (TG) levels seen in many primary and secondary hyperlipidentic states. No method of measuring TG or VLDL turnover has gained universal acceptance since none has been adequately validated. Therefore, a comparison of data between studies is often difficult, and conflicting conclusions have been claimed as to the prime mechanism of the TG elevation in endogenous hypertriglyceridemia (Farguhar et al., 1965; Bierman et al., 1970; Boberg et al., 1972; Havel et al., 1970). In addition to methodologic considerations, differences in results and conclusions may partly be accounted for by marked differences in patient selection and heterogeneity of subjects studied.