Neural systems for choice and valuation with counterfactual learning signals.

The purpose of this experiment was to test a computational model of reinforcement learning with and without fictive prediction error (FPE) signals to investigate how counterfactual consequences contribute to acquired representations of action-specific expected value, and to determine the functional neuroanatomy and neuromodulator systems that are involved. 80 male participants underwent dietary depletion of either tryptophan or tyrosine/phenylalanine to manipulate serotonin (5HT) and dopamine (DA), respectively. They completed 80 rounds (240 trials) of a strategic sequential investment task that required accepting interim losses in order to access a lucrative state and maximize long-term gains, while being scanned. We extended the standard Q-learning model by incorporating both counterfactual gains and losses into separate error signals. The FPE model explained the participants' data significantly better than a model that did not include counterfactual learning signals. Expected value from the FPE model was significantly correlated with BOLD signal change in the ventromedial prefrontal cortex (vmPFC) and posterior orbitofrontal cortex (OFC), whereas expected value from the standard model did not predict changes in neural activity. The depletion procedure revealed significantly different neural responses to expected value in the vmPFC, caudate, and dopaminergic midbrain in the vicinity of the substantia nigra (SN). Differences in neural activity were not evident in the standard Q-learning computational model. These findings demonstrate that FPE signals are an important component of valuation for decision making, and that the neural representation of expected value incorporates cortical and subcortical structures via interactions among serotonergic and dopaminergic modulator systems.

Protection from glycine at low doses in ischemia-reperfusion injury of the rat small intestine.

BACKGROUND: Glycine at high doses is known to protect the small intestine against ischemia-reperfusion (I/R) injury. Here, we studied whether glycine at low clinically applicable doses has a protective effect. METHODS: In series 1, intestinal I/R was induced in male Wistar rats by occlusion (90 min)/reopening (120 min) of the superior mesenteric artery. Glycine was intravenously infused for 30 min before ischemia (pre-ischemic infusion), and once again from 30 min before until 60 min after reperfusion. Total glycine doses applied over the 120-min infusion were 5, 10, 20, and 75 mg glycine/kg. In series 2, pre-ischemic blood plasma glycine concentrations were determined under the conditions of series 1. RESULTS: In series 1, attenuation of I/R injury was comparable at 10, 20, and 75 mg glycine/kg, but less at 5 mg/kg (as indicated by less intestinal hemorrhages and better preserved mean arterial blood pressure, among other signs). In series 2, pre-ischemic blood plasma glycine concentrations increased with increasing glycine doses from 280 to 330, 340, 380, and 680 µM, respectively. CONCLUSION: These results demonstrate that even at a dose 50 times lower than previously applied - and at only slightly elevated plasma concentrations - glycine provides full protection against I/R injury of the small intestine.

Role of leukotrienes in leukocyte adhesion following systemic administration of oxidatively modified human low density lipoprotein in hamsters.

In vitro studies indicate that oxidatively modified low density lipoprotein (oxLDL) promotes leukocyte adhesion to the vascular endothelium, a constant feature of early atherogenesis. Using intravital fluorescence microscopy in the dorsal skinfold chamber model in awake Syrian golden hamsters, we studied whether (a) oxLDL elicits leukocyte/endothelium interaction in vivo, and whether (b) leukotrienes play a mediator role in this event. Leukocyte/endothelium interaction was assessed in the time course after intravenous injection of native human LDL (4 mg/kg body wt) and of oxLDL (7.5 microM Cu++, 6 h, 37 degrees C) into control hamsters and into hamsters, pretreated with the selective leukotriene biosynthesis inhibitor MK-886 (20 mumol/kg, i.v.). While no effect was seen after injection of native LDL, oxLDL elicited an immediate induction of leukocyte adhesion to the endothelium of arterioles and postcapillary venules. Total and differential leukocyte counts suggest that all leukocyte subsets were likewise affected by oxLDL with no specific preference for monocytes. Stimulation of leukocyte adhesion was entirely prevented in inhibitor-treated animals, suggesting the important mediator role of leukotrienes in oxLDL-induced leukocyte/endothelium interaction.

Antioxidative activity of ubiquinol-10 at physiologic concentrations in human low density lipoprotein.

Ubiquinol-10 is a powerful lipid-soluble antioxidant found in cell membranes and lipoproteins in vivo. Its mechanism of action on lipid peroxidation has been determined in model and biological systems. Data concerning antioxidative activity of ubiquinol-10 in lipoproteins, however, are still controversial. The present work examines its role in the prevention of low density lipoprotein (LDL) oxidation, specifically its influence on a copper-mediated oxidative modification of human LDL in vitro. We found that ubiquinol-10 incorporated in LDL in subnormal concentrations (0.05-0.13 mol/mol LDL incorporated in comparison with 0.10-1.20 mol/mol LDL reported as normally in human LDL) slightly but not significantly decreased production of lipid peroxidation products (lipid peroxides, conjugated dienes, thiobarbituric acid-reactive substances) during the first hours of oxidation. The extent of apolipoprotein B modification (LDL fluorescence at 360/430 nm) was also decreased. Increasing the ubiquinol-10 concentration in LDL to 0.55-1.48 mol/mol LDL made it significantly more resistant to copper-mediated oxidation than native LDL. Adding the same amounts of either ubiquinone-10 or alpha-tocopherol to the LDL suspension had almost no effect on its oxidation. Ubiquinol-10 decreased alpha-tocopherol consumption during LDL oxidation and was consumed more rapidly than the latter. These results demonstrate that LDL ubiquinol-10 content is an important factor influencing LDL susceptibility to oxidation by copper and suggest that it represents the first line of defense against oxidative modification in human LDL.

Low density lipoprotein oxidizability by copper correlates to its initial ubiquinol-10 and polyunsaturated fatty acid content.

At an early stage of oxidation induced by Cu2+, the rate of oxidative modification of human low density lipoprotein (LDL) from healthy donors correlated negatively to its ubiquinol-10 (r = -0.58, P < 0.01) and positively to its polyunsaturated fatty acid (PUFA) (r = 0.53, P < 0.05) content. The PUFA/ubiquinol-10 ratio was the best predictor of LDL susceptibility to oxidation (r = 0.68, P < 0.01). No significant correlation between LDL oxidizability and its alpha-tocopherol content was found at any oxidation stage. It is suggested that ubiquinol-10 plays a central role in the early protection of LDL PUFAs against Cu(2+)-induced oxidation whereas alpha-tocopherol posesses both pro- and antioxidant activity.

Beneficial effects of alpha-lipoic acid and ascorbic acid on endothelium-dependent, nitric oxide-mediated vasodilation in diabetic patients: relation to parameters of oxidative stress.

The impairment of nitric oxide (NO)-mediated vasodilation in diabetes has been attributed to increased vascular oxidative stress. Lipoic acid has been shown to have substantial antioxidative properties. The aim of this study was to assess the effect of lipoic acid on NO-mediated vasodilation in diabetic patients in comparison with the well-recognized effect of ascorbic acid. Using venous occlusion plethysmography, we examined the effects of lipoic acid (0.2 mM) and ascorbic acid (1 and 10 mM) on forearm blood flow responses to acetylcholine, sodium nitroprusside and concomitant infusion of the NO-inhibitor, N(G)-monomethyl-L-arginine, in 39 diabetic patients and 11 control subjects. Plasma levels of antioxidants and parameters of lipid peroxidation were measured and correlated to endothelial function tests. Lipoic acid improved NO-mediated vasodilation in diabetic patients, but not in controls. NO-mediated vasodilation was improved by ascorbic acid at 10 mM, but not 1 mM. Improvements of endothelial function by ascorbic acid and lipoic acid were closely related. The beneficial effects of lipoic acid were positively related to plasma levels of malondialdehyde and inversely related to levels of ubiquinol-10. These findings support the concept that oxidative stress contributes to endothelial dysfunction and suggest a therapeutic potential of lipoic acid particularly in patients with imbalance between increased oxidative stress and depleted antioxidant defense.

Nontransferrin-bound iron in serum of patients receiving bone marrow transplants.

Nontransferrin-bound iron (NTBI) and other parameters of iron status were measured in 40 patients undergoing bone marrow transplantation (BMT) prior to conditioning therapy (between day -10 and -7), at the time of BMT (day 0), and 2 weeks later (day + 14). Serum iron and transferrin saturation values were normal before conditioning therapy. At day 0 serum iron values were high and median transferrin saturation was 98% (changes in the values of both serum iron and transferrin saturation, p < .0001). Transferrin saturation values were still elevated 2 weeks posttransplant (day +14 vs. baseline values, p = .0001). Starting at low NTBI levels pretransplant (median 0.4 micromol/l, range 0-4.2 micromol/l, controls: < or = 0.4 micromol/l), all patients revealed high levels on day 0 (median 4.0 micromol/l, range 1.9-6.9 micromol/l, p < .0001) and 2 weeks posttransplant (median 2.7 micromol/l, range 0-6.2 micromol/l, p < .0001). These observations indicate that the plasma iron pool in patients undergoing BMT increases to a level at which the normal ability to sequestrate iron becomes exhausted and considerable amounts of NTBI appear in serum. This "free" form of iron can mediate the production of reactive oxygen species and may cause organ toxicity in the early posttransplantation period.

Impaired plasma antioxidative defense and increased nontransferrin-bound iron during high-dose chemotherapy and radiochemotherapy preceding bone marrow transplantation.

To analyze the effects of radiochemotherapy on the pro-oxidative/antioxidative balance in plasma, we measured the total radical antioxidant parameter of plasma (TRAP) and single plasma antioxidants (uric acid, sulfhydryl groups, alpha-tocopherol, ubiquinone-10/total coenzyme-Q10 ratio, ascorbate, and bilirubin) every 12 h during high-dose chemotherapy and radiochemotherapy preceding bone marrow transplantation (BMT). Nontransferrin-bound iron (NTBI) was monitored as a potential pro-oxidant. Plasma levels of polyunsaturated fatty acids (PUFA) were measured as substrates, and thiobarbituric acid-reactive substances (TBARS) were measured as products of lipid peroxidation. Allantoin was analyzed as the product of uric acid oxidation. Patients receiving busulfan, VP-16, and cyclophosphamide (BU/VP/CY) (n = 8) were compared with those receiving total body irradiation in addition to VP-16 and cyclophosphamide (TBI/VP/CY) (n = 8). TRAP values were within the normal range before therapy and decreased after BU/VP/CY by 37% (p <. 02) and after TBI/VP/CY by 39% (p <.02). During TBI and after VP-16, a temporary increase in TRAP values occurred, which was not related to changes in individual antioxidants. In vitro experiments confirmed that VP-16 had an antioxidative effect. The concentration of uric acid declined in both groups and correlated with TRAP (BU/VP/CY: r =.80, p <.001; TBI/VP/CY: r =.84, p <.001). Levels of NTBI, which is normally not found in plasma, increased rapidly during conditioning therapy (p <.02 in both groups) and correlated inversely with TRAP (weighted intraindividual Spearman rank correlation coefficient for both groups: NTBI and TRAP: r = -.59, p <.001) and PUFA (in the radiochemotherapy group: r = -.67, p <.001). Whereas PUFA declined (p <.02 in both groups), TBARS increased (p <. 05 in both groups). Furthermore, an increase of allantoin and ubiquinone-10/total coenzyme-Q10 ratio in the BU/VP/CY group was found (allantoin: p <.02; ubiquinone-10/total coenzyme-Q10 ratio: p <.05). Antioxidants only partially recovered to baseline values until day 14 after BMT. Our findings indicate oxidative stress after high-dose radiochemotherapy and suggest a contribution of NTBI therein.

Ataxia with vitamin E deficiency: biochemical effects of malcompliance with vitamin E therapy.

To prevent neuronal damage, patients with ataxia with isolated vitamin E deficiency need lifelong supplementation with high doses of vitamin E. Short interruptions of therapy, such as occur in malcompliance, do not lead to clinical symptoms. However, the authors show that even short withdrawals may cause a prolonged decrease of the total radical trapping capacity of plasma; its major contributors, such as urate and sulfhydryl groups, fail to compensate for the missing vitamin E.

Plasma ubiquinol-10 is decreased in patients with hyperlipidaemia.

Ubiquinol-10, the reduced form of ubiquinone-10 (coenzyme Q10), is a potent lipophilic antioxidant present in nearly all human tissues. The exceptional oxidative lability of ubiquinol-10 implies that it may represent a sensitive index of oxidative stress. The present study was undertaken to assess the hypothesis that the level of ubiquinol-10 in human plasma can discriminate between healthy subjects and patients who are expected to be subjected to an increased oxidative stress in vivo. Using a newly developed method, we measured plasma ubiquinol-10 in 38 hyperlipidaemic patients with and without further complications, such as coronary heart disease, hypertension, or liver disease, and in 30 healthy subjects. The oxidizability of plasma samples obtained from hyperlipidaemic patients was found to be increased in comparison with control subjects, suggesting that the patients were subjected to a higher oxidative stress in vivo than the controls. Plasma ubiquinol-10, expressed as a percentage of total ubiquinol-10 + ubiquinone-10 or normalized to plasma lipids, was lower in the patients than in controls (P = 0.001 and 0.008, respectively). The proportion of ubiquinol-10 decreased in the order young controls > aged controls > hyperlipidaemic patients without complications > hyperlipidaemic patients with complications (P = 0.003). A negative correlation was found between the proportion of ubiquinol-10 and plasma triglycerides. The hyperlipidaemic patients with hypertension had a lower proportion of ubiquinol-10 than subjects without. When the study population was divided into smokers and non-smokers, plasma ubiquinol-10 was found to be reduced amongst smokers, independently of whether it was expressed as a percentage of total ubiquinol-10 + ubiquinone-10 (P = 0.006) or normalized to plasma lipids (P = 0.009). These data suggest that the level of ubiquinol-10 in human plasma may represent a sensitive index of oxidative stress in vivo especially indicative of early oxidative damage. Measuring plasma ubiquinol-10 can be proposed as a practical approach to assess oxidative stress in humans.

High-performance liquid chromatography-coulometric electrochemical detection of ubiquinol 10, ubiquinone 10, carotenoids, and tocopherols in neonatal plasma.

A micromethod for the rapid simultaneous determination of several lipophilic antioxidants in plasma from newborn infants is presented. Because only 5 microliters of plasma is required, the procedure lends itself for repetitive use in very immature infants at risk for developing so-called "oxygen radical diseases of the premature." The method allows continuous monitoring of antioxidants in such patients and can easily be combined with monitoring other parameters of interest in this context. Reuse of blood samples taken routinely for the determination of hematocrit and bilirubin concentration is possible, reducing the blood volume required to be taken for the oxygen radical-related studies to virtually zero.

Deteriorating free radical-trapping capacity and antioxidant status in plasma during bone marrow transplantation.

Organ toxicity in BMT may in part be due to free radical damage. Therefore the 'Total Radical-trapping Antioxidant Parameter of plasma' (TRAP), individual plasma antioxidants, serum iron and linoleic acid, a main substrate of lipid peroxidation, were monitored before and after BMT, and they were compared with values obtained from healthy controls. Seven patients (3 AML, 3 CML, 1 multiple myeloma) receiving 16 mg/kg busulfan, 30-45 mg VP-16 and 120 mg/kg cyclophosphamide were investigated. TRAP values declined during chemotherapy by about 40% (day -9: 1019 +/- 245 mumol/l, mean +/- s.d.; day 0: 660 +/- 164 mumol/l; P < 0.05). The concentration of uric acid, one of the main antioxidants in plasma, decreased markedly (day -9: 339 +/- 108 mumol/l, day 0: 148 +/- 61 mumol/l; P < 0.05) and paralleled TRAP values. Vitamin E and bilirubin did not change from day -9 to 0 whereas vitamin C increased (day -9: 46 +/- 16 mumol/l, day 0: 89 +/- 44 mumol/l; P < 0.05). Serum iron rapidly increased within the pre-transplantation period, reaching values normally seen only in iron overload (day -9: 11.8 +/- 5.2 mumol/l, day 0: 40.6 +/- 6.5 mumol/l; P < 0.05). Linoleic acid levels were normal at the start and decreased substantially (27.0 +/- 1.6 wt% at day -9; 15.7 +/- 4.9 wt% at day 0; P < 0.05), indicating possible lipid peroxidation during high-dose chemotherapy. In conclusion, complex monitoring of the antioxidant status before and after BMT revealed a breakdown of plasma antioxidant defence and of radical-vulnerable lipids, which was associated with high circulating levels of iron.

Time-course of oxidation of lipids in human cerebrospinal fluid in vitro.

Oxidative mechanisms play an important role in the pathogenesis of Alzheimer's disease, Parkinson's disease and other neurodegenerative diseases. To assess whether the oxidation of brain lipoproteins plays a role in the development of these pathologies, we investigated whether the lipoproteins of human cerebrospinal fluid (CSF) are susceptible to oxidative modification in vitro. We studied oxidation time-course for up to 100 h of human CSF in the absence (autooxidation) or presence of exogenous oxidants. Autooxidation of diluted CSF was found to result in a slow accumulation of lipid peroxidation products. The time-course of lipid hydroperoxide accumulation revealed three consecutive phases, lag-phase, propagation phase and plateau phase. Qualitatively similar time-course has been typically found in human plasma and plasma lipoproteins. Autooxidation of CSF was accelerated by adding exogenous oxidants, delayed by adding antioxidants and completely inhibited by adding a chelator of transition metal ions. Autooxidation of CSF also resulted in the consumption of endogenous ascorbate, alpha-tocopherol, urate and linoleic and arachidonic acids. Taking into account that (i) lipid peroxidation products measured in our study are known to be derived from fatty acids, and (ii) lipophilic antioxidants and fatty acids present in CSF are likely to be located in CSF lipoproteins, we conclude that lipoproteins of human CSF are modified in vitro during its autooxidation. This autooxidation appears to be catalyzed by transition metal ions, such as Cu(II) and Fe(III), which are present in native CSF. These data suggest that the oxidation of CSF lipoproteins might occur in vivo and play a role in the pathogenesis of neurodegenerative diseases.

How different constituents of low density lipoprotein determine its oxidizability by copper: a correlational approach.

Although low density lipoprotein (LDL) susceptibility to oxidation is expected to be primarily related to its composition, the individual contributions of different constituents to its oxidizability remain unclear. The present study was undertaken to elucidate how different constituents of isolated LDL determine its susceptibility to oxidation induced by Cu2+ under conditions close to those of well-known Cu2(+)-oxidation assay (H. Esterbauer, G. Striegl, H. Puhl and M. Rotheneder (1989) Free Radical Research Communications, 6, 67-75). We characterized antioxidant, fatty acid and total lipid composition of human LDL from healthy donors (n = 22) and compared each with LDL oxidizability by Cu2+. LDL oxidizability was evaluated as oxidizability of antioxidant-containing LDL (rate of lipid peroxidation measured before total consumption of alpha-tocopherol, the major LDL antioxidant), oxidizability of antioxidant-depleted LDL (maximal rate of lipid peroxidation and maximal production of conjugated dienes within the propagation, antioxidant-depleted phase of oxidation) and overall LDL resistance to oxidation (duration of the lag-phase before the onset of the propagation phase). We found that the oxidizability of antioxidant-containing LDL correlated negatively with LDL content of ubiquinol-10 and free cholesterol, and positively with that of n-3 polyunsaturated fatty acids (PUFAs). LDL n-3 PUFAs, ubiquinol-10 and free cholesterol were the most important determinants of the oxidizability of antioxidant-containing LDL, contributing to about 35%, 25% and 25% of its total variability, respectively. Oxidizability of antioxidant-depleted LDL was largely determined by LDL PUFA content. The overall LDL resistance to oxidation correlated weakly with LDL chemical composition. alpha-Tocopherol was found to be only a minor contributor to the oxidizability of isolated LDL under oxidative conditions used (7.5 or 14 mol Cu2+ / mol LDL). It appears that the oxidizability of antioxidant-containing LDL represents a parameter highly sensitive to changing LDL composition, whereas the overall LDL resistance to oxidation combines contributions from different LDL constituents more uniformly, being weaker sensitive to individual factors. It is suggested that PUFAs, ubiquinol-10 and free cholesterol are the most important determinants of LDL oxidizability of Cu2+.

How different constituents of human plasma and low density lipoprotein determine plasma oxidizability by copper.

Lipoprotein oxidation induced in vitro in whole plasma is expected to represent a more relevant model of the lipoprotein oxidation in the arterial wall than the in vitro oxidation of single isolated lipoproteins, e.g. low density lipoprotein (LDL). However, it remains unclear, how lipoprotein oxidation occurring in plasma is related to chemical composition and properties of the latter as well as to those of individual plasma lipoproteins. The present study was undertaken to characterize, how different constituents of human plasma contribute to the oxidizability of plasma lipoproteins oxidized directly in plasma samples. Oxidizability of plasma lipoproteins was assessed as oxidizability of whole heparin plasma and was measured spectrophotometrically as an increase in absorbance at 234 nm. To relate plasma oxidizability to its chemical composition and properties, plasma hydrophilic and lipophilic antioxidants, fatty acids, total lipids and TRAP were measured. To relate plasma oxidizability to the properties of individual lipoproteins, chemical composition and oxidizability were evaluated for LDL. We found that the oxidation kinetics of heparin plasma (diluted 150-fold and oxidized by 50 microM Cu2+) was characterized by three consecutive phases similar to the lag-, propagation and decomposition phases of LDL oxidation. Plasma oxidizability measured as different characteristics of these phases correlated negatively with plasma initial SH-groups, albumin, ascorbate, bilirubin, alpha-tocopherol, ubiquinol-10, free cholesterol, monounsaturated and saturated fatty acid content and positively with plasma initial total cholesterol, cholesterol ester and polyunsaturated fatty acid content. Plasma oxidizability measured as a rate of conjugated diene accumulation after different periods of oxidation correlated negatively with plasma initial albumin, urate, alpha-carotene and beta-carotene content. A positive correlation between oxidizabilities of whole plasma and LDL (isolated from the same plasma samples and oxidized by 14 mol Cu2+/mol LDL) was found. These data show that the oxidizability of plasma samples is critically determined by their chemical composition. They also suggest that the plasma oxidizability measured as an increase in absorbance at 234 nm may be used as a practical measure of the oxidizability of plasma lipoproteins.

Islet cell antibodies in diabetes mellitus associated with a mitochondrial tRNA(Leu(UUR)) gene mutation.

An A3243G point mutation of the mitochondrial tRNA(Leu(UUR)) gene was detected in a Caucasian family with maternal diabetes mellitus and signs of mitochondrial dysfunction such as muscular hypotonia, encephalopathy, lactic acidosis, stroke-like episodes (MELAS), neurosensory hearing loss, cardial pre-excitation, and short stature. Low levels (10 JDF) of islet cell antibodies (ICA) in insulin-treated diabetes of the mother and impaired glucose tolerance with high levels of ICA (80 JDF) in her older son indicated that mitochondrial diabetes mellitus may involve beta cell damage. Furthermore, exocrine pancreas cell damage may also occur since the stroke-like episodes of this son were combined with pancreatitis. In all family members HLA types and plasma antioxidants were determined. Normal concentrations of hydro- and lipophilic antioxidants (including ubiquinol-10) were found.

Whole plasma oxidation assay as a measure of lipoprotein oxidizability.

Lipoprotein oxidation induced in vitro in whole plasma is expected to be a more relevant model of the lipoprotein oxidation in the arterial wall than the in vitro oxidation of single isolated lipoproteins, e.g., low density lipoprotein (LDL). However, it is unclear, whether the oxidizability of whole plasma may serve as an adequate measure of the oxidizability of plasma lipoproteins. We measured the oxidizability of whole plasma diluted 150-fold as an absorbance increase at 234 nm known to reflect the level of conjugated dienes in the samples. Plasma oxidation was induced by Cu(II), 2,2'-azobis-(2-amidinopropane) hydrochloride (AAPH), lipoxygenase or myeloperoxidase+H2O2. Oxidizability of human plasma measured in the presence of Cu(II) was found to correlate with the oxidizability of LDL measured in the common Cu(II)-based LDL oxidation assay. The plasma oxidizability also correlated positively with plasma oxidizable fatty acid and negatively with plasma antioxidant content. Supplementation of human plasma with different antioxidants (albumin, urate, ascorbate, bilirubin, alpha-tocopherol and ubiquinol-10) in vitro decreased its oxidizability. Supplementation of Watanabe heritable hyperlipidaemic rabbits with different antioxidants (vitamin E, ubiquinone-10, probucol, carvedilol) in vivo lowered the oxidizability of rabbit plasma in comparison with rabbits fed standard diet. When plasma from hyperlipidaemic patients with or without coronary heart disease and from age-matched healthy controls was studied, the plasma oxidizability was found to be highest in the patients with coronary heart disease and lowest in the controls. Taken together, these data indicate that the plasma oxidation assay (i) provides information similar to that obtained using the common LDL oxidation assay, (ii) upgrades the latter, taking into account the effect of hydrophilic antioxidants on lipoprotein oxidation and characterizing the oxidizability of all plasma lipoproteins, and (iii) offers important practical advantages, such as fast and simple sample processing, low amount of plasma required and avoidance of artefactual oxidation during lipoprotein isolation. We propose the measurement of plasma oxidizability at 234 nm as an adequate practical index of the oxidizability of plasma lipoproteins.

Antiatherosclerotic effect of probucol in WHHL rabbits: are there plasma parameters to evaluate this effect?

Probucol has been used as a lipid-lowering agent for over 10 years. Lately it has been found that its antiatherogenic action is due mainly to its antioxidative capacity, in addition to its known lipid-lowering effect. To study the antioxidative capability of probucol and its influence on plaque development we used the animal model of the LDL-receptor-defective Watanabe heritable hyperlipidemic (WHHL) rabbit. In this study we measured all lipid values before and after probucol feeding and compared them with corresponding values in untreated controls. Probucol levels were determined, as were the physiological antioxidants alpha and gamma tocopherol (vitamin E). Thiobarbituric reactive substances were measured in plasma as a parameter for lipid peroxidation. In addition to the biochemical measurements the plaque area was analyzed macroscopically and microscopically to check the antiatherosclerotic effect and correlate it with the biochemical parameters. In four experiments we showed that probucol treatment in WHHL rabbits decreases the progression of atherosclerotic plaques by way of a combined lipid-lowering and antioxidative effect.

Effect of plasma alpha-tocopherol on leukotriene E4 excretion in genetic vitamin E deficiency.

Studying the biological effects of vitamin e in humans is difficult because conditions involving vitamin E deficiency are usually associated with chronic multiple pathology. Genetic vitamin E deficiency caused by a deficient alpha-tocopherol transport protein offers unique possibilities for study of vitamin E effects since the patients can be studied in good general health. In such a patient we manipulated plasma alpha-tocopherol levels in a wide range by varying oral alpha-tocopherol supplements and measured urinary leukotriene E4 (LTE4) concentrations. LTE4 excretion proved inversely correlated to plasma alpha-tocopherol levels. This strongly suggests that in genetic vitamin E deficiency, alpha-tocopherol influences formation of leukotrienes in vivo.

Urinary alpha-tocopherol metabolites in alpha-tocopherol transfer protein-deficient patients.

Patients with alpha-tocopherol transfer protein (alpha-TTP) defects experience neurological symptoms characteristic of vitamin E deficiency and depend on continuous high alpha-tocopherol supplements. We investigated the excretion of 2,5,7, 8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC), a urinary metabolite of alpha-tocopherol, as a putative marker for the alpha-tocopherol status of alpha-TTP-deficient patients and control subjects. In three patients vitamin E supplementation was stopped for short periods of time, during which plasma alpha-tocopherol concentrations and urinary alpha-CEHC excretion were measured. In the patients, plasma alpha-tocopherol decreased below normal (<5 micromol/l) but alpha-CEHC excretion remained above the range of unsupplemented control subjects (0.118-0.306 mg/day, n = 6). In healthy subjects, however, alpha-CEHC excretion was increased only after surpassing a plasma alpha-tocopherol threshold of 30-40 micromol/l. Such a threshold did not exist in patients. The general mechanism of alpha-tocopherol degradation did not appear to differ between patients and control subjects. The presumed mechanism of omega- and subsequent beta-oxidation was supported by the detection of alpha- CPHC, an alpha -CEHC homolog with a side chain longer by 3 carbon atoms, both in supplemented patients and in control subjects.