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R Stocker

Publications and source records attributed to R Stocker.

At least 73 records · Page 4Linked to original sources
PubMed1999

Lipid oxidation in human low-density lipoprotein induced by metmyoglobin/H2O2: involvement of alpha-tocopheroxyl and phosphatidylcholine alkoxyl radicals.

Metmyoglobin (metMb) and H(2)O(2) can oxidize low-density lipoprotein (LDL) in vitro, and oxidized LDL may be atherogenic. The role of alpha-tocopherol (alpha-TOH) in LDL oxidation by peroxidases such as metMb is unclear. Herein, we show that during metMb/H(2)O(2)-induced oxidation of native LDL, alpha-tocopheroxyl radical (alpha-TO(*)) and hydroperoxides and alcohols of cholesteryl esters [CE-O(O)H] and phosphatidylcholine [PC-O(O)H] accumulate concomitantly with alpha-TOH consumption. The ratio of accumulating CE-O(O)H to PC-O(O)H remains constant as long as alpha-TOH is present. Accumulation of CE-O(O)H is dependent on, and correlates with, LDL's alpha-TOH content, yet does not require preformed lipid hydroperoxides or H(2)O(2). This indicates that in native LDL alpha-TOH can act as a phase-transfer agent and alpha-TO(*) as a chain-transfer agent propagating LDL lipid peroxidation via tocopherol-mediated peroxidation (TMP). After alpha-TOH depletion, CE-O(O)H continues to accumulate, albeit at a slower rate than in the presence of alpha-TOH. This second phase of LDL oxidation is accompanied by depletion of PC-OOH, a rapid increase in the CE-O(O)H/PC-O(O)H ratio, formation of lipid-derived alkoxyl radicals and phosphatidylcholine hydroxides (PC-OH), and accumulation of a second organic radical, characterized by a broad singlet EPR signal. The latter persists for several hours at 37 degrees C. We conclude that metMb/H(2)O(2)-induced peroxidation of LDL lipids occurs initially via TMP. After alpha-TOH depletion, cholesteryl esters peroxidize at higher fractional rates than surface phospholipids, and this appears to be mediated at least in part via reactions involving alkoxyl radicals derived from the peroxidatic activity of metMb on PC-OOH.

Adult↗
PubMed1999

Are reactive oxygen species involved in the pathogenesis of murine cerebral malaria?

To investigate the involvement of oxidative tissue damage in the pathogenesis of murine cerebral malaria (CM), brain levels of protein carbonyls, 3,4-dihydroxyphenylalanine (DOPA), o-tyrosine, and dityrosine were measured during Plasmodium berghei ANKA (PbA) and P. berghei K173 (PbK) infections. During PbA infection in a CM model, brain levels of the substances were similar to those in uninfected mice. The role of phagocyte-derived reactive oxygen species in the pathogenesis of CM was examined in gp91phox gene knockout mice. The course of CM in these mice was the same as in their wild type counterparts. To examine whether superoxide production in the central nervous system could have occurred via increased xanthine oxidase activity, brain concentrations of urate were measured in CM mice and in mice infected with PbK (which does not cause CM). Brain urate concentration increased significantly in both groups of mice, suggesting that purine breakdown is not specific to CM. These results indicate that reactive oxygen species probably do not contribute to the pathogenesis of murine CM.

Animals↗
PubMed1999

Glutamate and taurine are increased in ventricular cerebrospinal fluid of severely brain-injured patients.

Glutamate contributes to secondary brain damage, resulting in cell swelling and brain edema. Under in vitro conditions, increased extracellular levels of the amino acid taurine reflect glutamate-induced osmotic cell swelling. In vivo, increases in cerebrospinal fluid (CSF) taurine could, therefore, unmask glutamate-mediated cytotoxic edema formation and possibly differentiate it from vasogenic edema. To test this hypothesis, ventricular CSF glutamate and taurine levels were measured in 28 severely brain-injured patients on days 1, 5, and 14 after trauma. Posttraumatic changes in CSF amino acids were investigated in regard to extent of tissue damage and alterations in brain edema as estimated by computerized tomography. On day 1, CSF glutamate and taurine levels were significantly increased in patients with subdural or epidural hematomas (8+/-0.8/71+/-12 microM), contusions (21+/-4.1/122+/-18 microM), and generalized brain edema (13+/-3.2/80+/-15 microM) compared to lumbar control CSF (1.3+/-0.1/12+/-1 microM; p < 0.001). CSF amino acids, however, did not reflect edema formation and resolution as estimated by computerized tomography. CSF taurine correlated positively with glutamate, eventually depicting glutamate-induced cell swelling. However, parallel neuronal release of taurine with its inhibitory function cannot be excluded. Thus, the sensitivity of taurine in unmasking cytotoxic edema formation is weakened by the inability in defining its origin and function under the conditions chosen in the present study. Overall, persisting pathologic ventricular CSF glutamate and taurine levels are highly suggestive of ongoing glial and neuronal impairment in humans following severe traumatic brain injury.

Adult↗
PubMed1999

Inhibition by a coantioxidant of aortic lipoprotein lipid peroxidation and atherosclerosis in apolipoprotein E and low density lipoprotein receptor gene double knockout mice.

Antioxidants can inhibit atherosclerosis in animals, though it is not clear whether this is due to the inhibition of aortic lipoprotein lipid (per)oxidation. Coantioxidants inhibit radical-induced, tocopherol-mediated peroxidation of lipids in lipoproteins through elimination of tocopheroxyl radical. Here we tested the effect of the bisphenolic probucol metabolite and coantioxidant H 212/43 on atherogenesis in apolipoprotein E and low density lipoprotein (LDL) receptor gene double knockout (apoE-/-;LDLr-/-) mice, and how this related to aortic lipid (per)oxidation measured by specific HPLC analyses. Dietary supplementation with H 212/43 resulted in circulating drug levels of approximately 200 microM, increased plasma total cholesterol slightly and decreased plasma and aortic alpha-tocopherol significantly relative to age-matched control mice. Treatment with H 212/43 increased the antioxidant capacity of plasma, as indicated by prolonged inhibition of peroxyl radical-induced, ex vivo lipid peroxidation. Aortic tissue from control apoE-/-;LDLr-/- mice contained lipid hydro(pero)xides and substantial atherosclerotic lesions, both of which were decreased strongly by supplementation of the animals with H 212/43. The results show that a coantioxidant effectively inhibits in vivo lipid peroxidation and atherosclerosis in apoE-/-;LDLr-/- mice, consistent with though not proving a causal relationship between aortic lipoprotein lipid oxidation and atherosclerosis in this model of the disease.

Animals↗
PubMed1999

Tocopherol-mediated peroxidation of lipoproteins: implications for vitamin E as a potential antiatherogenic supplement.

The 'oxidation theory' of atherosclerosis proposes that oxidation of low density lipoprotein (LDL) contributes to atherogenesis. Although little direct evidence for a causative role of 'oxidized LDL' in atherogenesis exists, several studies show that, in vitro, oxidized LDL exhibits potentially proatherogenic activities and lipoproteins isolated from atherosclerotic lesions are oxidized. As a consequence, the molecular mechanisms of LDL oxidation and the actions of alpha-tocopherol (alpha-TOH, vitamin E), the major lipid-soluble lipoprotein antioxidant, have been studied in detail. Based on the known antioxidant action of alpha-TOH and epidemiological evidence, vitamin E is generally considered to be beneficial in coronary artery disease. However, intervention studies overall show a null effect of vitamin E on atherosclerosis. This confounding outcome can be rationalized by the recently discovered diverse role for alpha-TOH in lipoprotein oxidation; that is, alpha-TOH displays neutral, anti-, or, indeed, pro-oxidant activity under various conditions. This review describes the latter, novel action of alpha-TOH, termed tocopherol-mediated peroxidation, and discusses the benefits of vitamin E supplementation alone or together with other antioxidants that work in concert with alpha-TOH in ameliorating lipoprotein lipid peroxidation in the artery wall and, hence, atherosclerosis.

Animals↗
PubMed1999

Magnetic resonance imaging of the postoperative knee.

Due to the recent development of arthroscopic techniques in meniscal surgery and anterior cruciate ligament reconstruction, an increasing number of postoperative patients are referred for a magnetic resonance examination of the knee because of recurrent injury. Contrary to the nonoperative patient, T2-weighted sequences and, in unequivocal cases, magnetic resonance arthrography play the most important role in the evaluation of a possible meniscal retear. In patients with anterior cruciate ligament reconstruction, the changes of the magnetic resonance appearance of the anterior cruciate ligament graft during the first year after surgery must be considered in the diagnosis of retears. Recent developments in articular cartilage defect repair and the possible role of magnetic resonance imaging in the follow-up are discussed.

Anterior Cruciate Ligament↗
PubMed1999

Thiopental attenuates energetic impairment but fails to normalize cerebrospinal fluid glutamate in brain-injured patients.

OBJECTIVES: Brain-injured patients are susceptible to secondary brain damage related to decreased cerebral perfusion pressure associated with edema formation and increased intracranial pressure (ICP). Whenever conventional therapy fails to reduce elevated ICP, barbiturate coma represents an additional intervention that may control ICP. In patients suffering from severe traumatic brain injury, cerebrospinal fluid levels of glutamate, hypoxanthine, and lactate were measured during barbiturate coma and correlated to electroencephalographic recordings and ICP. DESIGN: Prospective, descriptive study. SETTING: Ten-bed surgical intensive care unit in a university hospital. PATIENTS: Twenty-one patients with severe traumatic brain injury (Glasgow Coma Scale score < or = 9); 11 required barbiturate coma because of refractory intracranial hypertension, and 10 were manageable with continuous administration of fentanyl and midazolam. INTERVENTIONS: Thiopental was administered continuously for increased ICP within the first 24 hrs after trauma and adjusted to the burst-suppression pattern (four to six bursts per minute) on continuous electroencephalographic monitoring. MEASUREMENTS AND MAIN RESULTS: Glutamate and hypoxanthine were analyzed using high-performance liquid chromatography, whereas lactate was measured enzymatically. Patients requiring thiopental presented with significantly higher ICP, glutamate, and hypoxanthine levels than patients receiving fentanyl and midazolam (p < .05). Within the first 24 hrs, thiopental significantly reduced cerebrospinal fluid glutamate and hypoxanthine levels in all patients, i.e., the burst-suppression pattern was successfully induced (p < .001). Interestingly, in five patients cerebrospinal fluid glutamate increased to initial values again despite unchanged neuronal activity. In these patients, ICP, hypoxanthine, and lactate remained significantly elevated compared with the six patients with steadily decreasing cerebrospinal fluid glutamate, hypoxanthine, lactate, and ICP values (p < .02). CONCLUSIONS: Barbiturate coma does not unequivocally preserve energetic stability despite successful suppression of neuronal activity. Despite the use of barbiturate coma in patients with refractory intracranial hypertension, persistent release or impaired uptake of glutamate may be associated with continuous anaerobic metabolism, as shown by increases in cerebrospinal fluid hypoxanthine and lactate levels.

Adolescent↗
PubMed1999

Dietary and pharmacological antioxidants in atherosclerosis.

Antioxidants that inhibit LDL oxidation are thought to be potential anti-atherogenic compounds. The results of major human randomized trials with antioxidants have, however, been disappointing, except for probucol, which consistently inhibits restenosis. Similarly, animal intervention studies show that antioxidants do not generally inhibit atherosclerosis, although some compounds provide protection. Direct evidence for the oxidation of LDL causing atherosclerosis is needed. This article summarizes results from antioxidant intervention studies, and highlights some of the key issues that need to be addressed to link biochemical changes in the arterial wall more directly to the oxidation theory of atherosclerosis.

Animals↗
PubMed1999

Coexistence of oxidized lipids and alpha-tocopherol in all lipoprotein density fractions isolated from advanced human atherosclerotic plaques.

After investigation of the contents and redox status of antioxidants and lipids in homogenates of both normal artery and atherosclerotic plaque, we now investigated them in the density fractions (very low, low, high, and protein fractions) of atherosclerotic plaque freshly obtained from carotid endarterectomy. By using the optimum extraction method (homogenization in carbonate buffer) and after density gradient ultracentrifugation, we isolated and characterized density fractions of plaque for apolipoproteins, size and contents of alpha-tocopherol (alpha-TOH), unesterified cholesterol, cholesteryl linoleate (Ch18:2), and hydroxides and hydroperoxides of Ch18:2, ie, Ch18:2-O(O)H. The distribution of apolipoproteins was more heterogeneous than that in the corresponding lipoproteins isolated from blood, and the majority of material in all plaque density fractions was present in large particles eluting in the void volume of gel-filtration columns. The content of unesterified cholesterol per unit of protein in low- and high-density fractions was 10-fold that in corresponding plasma lipoproteins. Low- and very-low-density fractions contained most of the lesion lipids and alpha-TOH. Two to five percent of lesion Ch18:2 was present as Ch18:2-O(O)H and distributed more or less equally among all density fractions, yet the content of alpha-TOH per unit of Ch18:2 was higher than that in corresponding plasma lipoproteins. These results demonstrate that alpha-TOH and oxidized lipids coexist in all lesion density fractions, further supporting the notion that large proportions of lipids in lipoproteins of advanced stages of atherosclerosis are oxidized. However, although not ruling it out, our results do not support the suggestion that advanced stages of atherosclerosis are associated with gross deficiencies in the lipoproteins' vitamin E content.

Aged↗
PubMed1999

Dissociation of atherogenesis from aortic accumulation of lipid hydro(pero)xides in Watanabe heritable hyperlipidemic rabbits.

Antioxidants can inhibit atherosclerosis, but it is unclear how inhibition of intimal lipid oxidation relates to atherogenesis. Here we tested the effect of probucol and its metabolite bisphenol on aortic lipid (per)oxidation and atherogenesis in Watanabe heritable hyperlipidemic (WHHL) rabbits. LDL and aortas from rabbits fed probucol contained bisphenol at concentrations comparable to those in bisphenol-treated animals. Bisphenol treatment increased plasma cholesterol slightly, and plasma and aortic alpha-tocopherol more substantially; these parameters were unaffected by probucol. Bisphenol and probucol treatment both enhanced the resistance of circulating LDL to peroxyl radical-induced lipid peroxidation; this was due to bisphenol, not probucol. Only probucol enhanced LDL's resistance to Cu(2+)-induced oxidation. Both bisphenol and probucol treatment strongly inhibited aortic accumulation of hydroperoxides and hydroxides of cholesteryl esters and triglycerides [LO(O)H]. Despite this, however, probucol had a modestly significant effect on the extent of lesion formation; bisphenol had no inhibitory effect. In addition, the extent of atherosclerosis did not correlate with amounts of aortic LO(O)H present, but, as expected, it did correlate with aortic alpha-tocopherol and cholesterol. Together, these results suggest that aortic accumulation of LO(O)H is not required for, nor is alpha-tocopherol depleted during, the initiation and progression of atherogenesis in WHHL rabbits.

Animals↗
PubMed1999

Antioxidant defenses in rat intestine and mesenteric lymph.

Dietary oxysterols can reach the circulation and this may contribute to atherosclerosis, where lipid oxidation is thought to be important. There is also evidence that, in rats, peroxidized lipids are absorbed and transported into lymph [Aw TY, Williams MW, Gray L. Absorption and lymphatic transport of peroxidized lipids by rat small intestine in vivo: role of mucosal GSH. Am J Physiol 1992; 262: G99-G106], although the method used to detect lipid peroxides lacked specificity. We tested whether intragastric administration of vegetable oils containing triglyceride hydroperoxides (TG-OOH) to rats resulted in detectable lipid hydroperoxides in mesenteric lymph. Using sensitive HPLC with postcolumn chemiluminescence detection, we were unable to detect hydroperoxides of triglycerides, cholesterylesters or phospholipids during the course of lipid absorption, and lymph levels of ascorbate, urate, alpha-tocopherol and ubiquinol-9 did not change significantly. By contrast, we observed a striking reducing activity judged by the efficient reduction of administered ubiquinones-9 and -10 to the corresponding ubiquinols. Exposure of rat lymph and isolated chylomicrons to aqueous peroxyl radicals revealed patterns of antioxidant consumption and lipid hydroperoxide formation similar to those described previously for human extravascular fluids and isolated lipoproteins, respectively. In particular, rates of TG-OOH formation in lymph and chylomicrons were very low to undetectable as long as ascorbate and/or ubiquinols were present, but subsequently proceeded in a chain reaction despite the presence of alpha-tocopherol. These studies demonstrate that rat intestine and mesenteric lymph possess efficient antioxidant defenses against preformed lipid hydroperoxides and (peroxyl) radical mediated lipid oxidation. We conclude that dietary lipid hydroperoxides or postprandial oxidation of lipids are not likely to contribute to these particular forms of oxidized lipids in circulation and aortic tissue.

Administration, Oral↗
PubMed1999

Redox reactions related to indoleamine 2,3-dioxygenase and tryptophan metabolism along the kynurenine pathway.

The heme enzyme indoleamine 2,3-dioxygenase (IDO) oxidizes the pyrrole moiety of L-tryptophan (Trp) and other indoleamines and represents the initial and rate-limiting enzyme of the kynurenine (Kyn) pathway. IDO is a unique enzyme in that it can utilize superoxide anion radical (O2*- ) as both a substrate and a co-factor. The latter role is due to the ability of O2*- to reduce inactive ferric-IDO to the active ferrous form. Nitrogen monoxide (*NO) and H2O2 inhibit the dioxygenase and various inter-relationships between the nitric oxide synthase- and IDO-initiated amino acid degradative pathways exist. Induction of IDO and metabolism of Trp along the Kyn pathway is implicated in a variety of physiological and pathophysiological processes, including anti-microbial and anti-tumor defense, neuropathology, immunoregulation and antioxidant activity. Antioxidant activity may arise from O2*- scavenging by IDO and formation of the potent radical scavengers and Kyn pathway metabolites, 3-hydroxyanthranilic acid and 3-hydroxykynurenine. Under certain conditions, these aminophenols and other Kyn pathway metabolites may exhibit pro-oxidant activities. This article reviews findings indicating that redox reactions are involved in the regulation of IDO and Trp metabolism along the Kyn pathway and also participate in the biological activities exhibited by Kyn pathway metabolites.

Animals↗
PubMed1999

Time-dependent changes to lipids and antioxidants in plasma and aortas of apolipoprotein E knockout mice.

Oxidation of lipoproteins is thought to be an early event in atherogenesis. To evaluate whether aortic lipoprotein lipid (per)oxidation contributes to atherosclerosis, we investigated the time-dependent changes to lipids and antioxidants in plasma and aortas of apolipoprotein E gene knockout (apoE-/-) mice receiving a high fat diet, and compared these changes with lesion development. Circulating buoyant lipoproteins and associated cholesterol (C), cholesteryl esters (CE), and alpha-tocopherol (alpha-TOH) increased within 1 month then remained largely constant up to 6 months. Coenzyme Q (CoQ) remained unchanged for the first 3 months and increased marginally after 6 months. With increasing duration of the diet, plasma lipids showed an increased propensity to undergo peroxyl radical-induced (per)oxidation. Absolute concentrations of aortic C, hydroperoxides and hydroxides of CE (CE-O(O)H) and alpha-TOH increased gradually while aortic CE increased more markedly with changes to cholesteryl linoleate being most pronounced. Aortic CoQ remained largely unchanged. Overall, the extent of aortic CE (per)oxidation remained low (</=1%) and the ratio of incremental changes of alpha-TOH to oxidizable lipid remained unchanged. Aortic biochemistry paralleled lesion formation, particularly that in the descending thoracic aorta.Together, our results show that progressing atherosclerosis in apoE-/- mice is associated with increased aortic lipid (per)oxidation as assessed by the concentrations of CE-O(O)H, measured directly by HPLC. This supports the oxidation theory. Measurement of aortic CE-O(O)H may be useful for mechanistic studies studying the relationship between inhibition of in vivo lipid (per)oxidation and atherosclerosis.

Animals↗
PubMed1998

[Respiratory problems after injuries of the cervical spine].

Respiratory failure plays a major role in morbidity and mortality after high cervical spine injury. Initially the patients are threatened by acute loss of motor function of the respiratory muscles and the development of neurogenic pulmonary edema. In the further course alterations in the mechanical properties of the respiratory system, changes in lung function, pulmonary infections and airway problems are the main reasons for life threatening respiratory failure. Early surgical stabilization, careful weaning from mechanical ventilation, meticulous search and treatment of infections, aggressive posturing and mobilization and support of impaired mechanical functions by physiotherapy, muscle training, noninvasive respiratory support and in some cases electrophrenic pacing increase survival and independency of quadriplegic patients.

Cause of Death↗
PubMed1998

Evidence for roles of radicals in protein oxidation in advanced human atherosclerotic plaque.

Oxidative damage might be important in atherogenesis. Oxidized lipids are present at significant concentrations in advanced human plaque, although tissue antioxidants are mostly present at normal concentrations. Indirect evidence of protein modification (notably derivatization of lysine) or oxidation has been obtained by immunochemical methods; the specificities of these antibodies are unclear. Here we present chemical determinations of six protein-bound oxidation products: dopa, o-tyrosine, m-tyrosine, dityrosine, hydroxyleucine and hydroxyvaline, some of which reflect particularly oxy-radical-mediated reaction pathways, which seem to involve mainly the participation of transition- metal ions. We compared the relative abundance of these oxidation products in normal intima, and in human carotid plaque samples with that observed after radiolytically generated hydroxyl radical attack on BSA in vitro. The close similarities in relative abundances in the latter two circumstances indicate that hydroxyl radical damage might occur in plaque. The relatively higher level of dityrosine in plaque than that observed after radiolysis suggests the additional involvement of HOCl-mediated reactions in advanced plaque.

Adult↗
PubMed1998

Secretory phospholipase A2 and lipoprotein lipase enhance 15-lipoxygenase-induced enzymic and nonenzymic lipid peroxidation in low-density lipoproteins.

The oxidation of low-density lipoprotein (LDL) is thought to contribute to atherogenesis. 15-Lipoxygenase (15LO) induces LDL oxidation, and phospholipase A2 enhances this process [Sparrow, C. P. , Parthasarathy, S., and Steinberg, D. (1988) J. LipidRes. 29, 745-753]. As the underlying mechanism of the enhancing effect has not been investigated previously, we here show that in the presence of soybean 15LO (SLO) or human 15LO (rhLO), the addition of lipoprotein lipase, porcine pancreatic, or human type IIa secretory phospholipase A2 (sPLA2) greatly enhanced the accumulation of hydro(pero)xides of all major classes of LDL's lipids. Hydroperoxides of free fatty acids accumulated exclusively as enzymic products with kinetics reflecting both the formation of free fatty acids and the initial 'build-up' of alpha-tocopheroxyl radical. In contrast, hydroperoxides of cholesteryl esters and phosphatidylcholine accumulated linearly over comparatively longer periods of time and, in the case of rhLO, well beyond inactivation of the oxygenase. With SLO, formation of oxidized esterified lipids occurred nonenzymically, independent of the presence of lipase and despite the oxygenase remaining active until the end of the incubation. Enhancement of rhLO-induced LDL lipid peroxidation by sPLA2 was eliminated by a neutralizing anti-sPLA2 antibody, indicating that lipolytic activity was required for this effect. LDL depleted of alpha-tocopherol was resistant to oxidation by 15LO alone, whereas lipase overcame this resistance, demonstrating that lipases enhance 15LO-induced enzymic and nonenzymic peroxidation of LDL lipids. This is likely due to provision of free fatty acid substrate, resulting in an enhanced rate of free radical formation which itself causes nonenzymic peroxidation of esterified lipids. As lipases and 15LO are present in atherosclerotic lesions, our findings could be of pathophysiological significance.

Animals↗
PubMed1998

Oxidation of high density lipoproteins. I. Formation of methionine sulfoxide in apolipoproteins AI and AII is an early event that accompanies lipid peroxidation and can be enhanced by alpha-tocopherol.

The lipids of high density lipoproteins (HDL) are initially oxidized in preference to those in low density lipoprotein when human plasma is exposed to aqueous peroxyl radicals. In this work we report on the relative susceptibility of HDL protein and lipid to oxidation and on the role HDL's alpha-tocopherol (alpha-TOH) plays in modulating protein oxidation. Exposure of isolated HDL to either low fluxes of aqueous peroxyl radicals, Cu2+ ions, or soybean lipoxygenase resulted in the oxidation of apoAI and apoAII during the earliest stages of the reaction, i.e. after consumption of ubiquinol-10 and in the presence of alpha-TOH. Hydro(pero)xides of cholesteryl esters and phospholipids initially accumulated together with specific oxidized forms of apoAI and apoAII, separated by high pressure liquid chromatography. The specific oxidized forms of apoAI were 16 and 32 mass units heavier than those of the native apolipoproteins and contained 1 and 2 methionine sulfoxide residues per protein, respectively. The third methionine residue in apoAI, as well as Trp residues, remained unoxidized during the earliest stages of HDL oxidation examined. Exposure of isolated apoAI to peroxyl radicals, Cu2+, or soybean lipoxygenase resulted in nonspecific (for peroxyl radicals) or no discernible protein oxidation (Cu2+ and soybean lipoxygenase). This indicated that the formation of the specific oxidized forms of apoAI observed with native HDL was not the result of direct reaction of these oxidants with the apolipoprotein. In vitro and in vivo enrichment of HDL with alpha-TOH resulted in a dose-dependent increase in the extent of peroxyl radical-induced formation of HDL cholesteryl ester hydroperoxides (r = 0.96) and cholesteryl ester hydroxides (r = 0. 92), as well as the loss of apoAI (r = 0.96) and apoAII (r = 0.94). alpha-TOH enrichment also enhanced HDL lipid and protein oxidation induced by Cu2+ or soybean lipoxygenase. These results indicate that the earliest stages of HDL oxidation are accompanied by the oxidation of specific methionine residues in apoAI and apoAII and that in the absence of co-antioxidants, alpha-TOH can promote this process.

Amidines↗