No abstract

The effect of minimally modified LDL (MM-LDL) on the ability of large vessel endothelial cells (EC) to interact with monocytes and neutrophils was examined. These LDL preparations, obtained by storage or by mild iron oxidation, were indistinguishable from native LDL to the LDL receptor and were not recognized by the scavenger receptor. Treatment of

Nutritional, or dietary oxidative stress denotes a disturbance of the redox state resulting from excess oxidative load or from inadequate nutrient supply favoring prooxidant reactions. Low intake or impaired availability of dietary antioxidants including vitamins E and C, carotenoids, polyphenols, and other micronutrients (e.g., selenium) weakens the antioxidant network. Postprandial oxidative stress, as a subform of nutritional oxidative stress, ensues from sustained postprandial hyperlipidemia and/or hyperglycemia and is associated with a higher risk for atherosclerosis, diabetes, and obesity. In Western societies, a significant part of the day is spent in the postprandial state. Unsaturated fatty acids incorporated into LDL and oxidized LDL are an atherogenic factor. Lipid hydroperoxides present in the diet are absorbed, contributing to the prooxidant load. In hyperlipidemic and hyperglycemic subjects, endothelium-dependent vasodilation is impaired in the postprandial state, making postprandial oxidative stress an important factor modulating cardiovascular risk. Postprandial oxidative stress is attenuated when dietary antioxidants are supplied together with a meal rich in oxidized or oxidizable lipids. Ingestion of dietary polyphenols, e.g., from wine, cocoa, or tea, improves endothelial dysfunction and lowers the susceptibility of LDL lipids to oxidation. Polyphenols affect endothelial function not solely as antioxidants but also as modulatory signaling molecules.

In order to survive in an oxygen environment, aerobic organisms have developed numerous mechanisms to protect against oxygen radicals and singlet oxygen. One such mechanism, which appears to have attained particular significance during primate evolution, is the direct scavenging of oxygen radicals, singlet oxygen, oxo-haem oxidants and hydroperoxyl radicals by uric acid. In the present paper we demonstrate that another important 'antioxidant' property of uric acid is the ability to form stable co-ordination complexes with iron ions. Formation of urate-Fe3+ complexes dramatically inhibits Fe3+-catalysed ascorbate oxidation, as well as lipid peroxidation in liposomes and rat liver microsomal fraction. In contrast with antioxidant scavenger reactions, the inhibition of ascorbate oxidation and lipid peroxidation provided by urate's ability to bind iron ions does not involve urate oxidation. Association constants (Ka) for urate-iron ion complexes were determined by fluorescence-quenching techniques. The Ka for a 1:1 urate-Fe3+ complex was found to be 2.4 X 10(5), whereas the Ka for a 1:1 urate-Fe2+ complex was determined to be 1.9 X 10(4). Our experiments also revealed that urate can form a 2:1 complex with Fe3+ with an association constant for the second urate molecule (K'a) of approx. 4.5 X 10(5). From these data we estimate an overall stability constant (Ks approximately equal to Ka X K'a) for urate-Fe3+ complexes of approx. 1.1 X 10(11). Polarographic measurements revealed that (upon binding) urate decreases the reduction potential for the Fe2+/Fe3+ half-reaction from -0.77 V to -0.67 V. Thus urate slightly diminishes the oxidizing potential of Fe3+. The present results provide a mechanistic explanation for our previous report that urate protects ascorbate from oxidation in human blood. The almost saturating concentration of urate normally found in human plasma (up to 0.6 mM) represents 5-10 times the plasma ascorbate concentration, and is orders of magnitude higher than the 'free' iron ion concentration. These considerations point to the physiological significance of our findings.

Abstract-Shear stress regulates endothelial nitric oxide and superoxide (O 2 Ϫ· ) production, implicating the role of NADPH oxidase activity. It is unknown whether shear stress regulates the sources of reactive species production, consequent low-density lipoprotein (LDL) modification, and initiation of inflammatory events. Bovine aortic endothelial cells (BAECs) in the presence of 50 g/mL of native LDL were exposed to (1) pulsatile flow with a mean shear stress ( ave ) of 25 dyne/cm 2 and (2) oscillating flow at ave of 0. After 4 hours, aliquots of culture medium were collected for high-performance liquid chromatography analyses of electronegative LDL species, described as LDL Ϫ and LDL 2Ϫ . In response to oscillatory shear stress, gp91 phox mRNA expression was upregulated by 2.9Ϯ0.3-fold, and its homologue, Nox4, by 3.9Ϯ0.9-fold (PϽ0.05, nϭ4), with a corresponding increase in O 2 Ϫ· production rate. The proportion of LDL Ϫ and LDL 2Ϫ relative to static conditions increased by 67Ϯ17% and 30Ϯ7%, respectively, with the concomitant upregulation of monocyte chemoattractant protein-1 expression and increase in monocyte/BAEC binding (PϽ0.05, nϭ5). In contrast, pulsatile flow downregulated both gp91 phox and Nox4 mRNA expression (by 1.8Ϯ0.2-fold and 3.0Ϯ0.12-fold, respectively), with an accompanying reduction in O 2 Ϫ· production, reduction in the extent of LDL modification (51Ϯ12% for LDL Ϫ and 30Ϯ7% for LDL 2Ϫ ), and monocyte/BAEC binding. The flow-dependent LDL oxidation is determined in part by the NADPH oxidase activity. The formation of modified LDL via O 2 Ϫ· production may also affect the regulation of monocyte chemoattractant protein-1 expression and monocyte/BAEC binding.