Liquid chromatography determination of alpha-tocopherol in erythrocytes

A longitudinal study of antioxidant status in phenylketonuric patients

OBJECTIVES

To investigate the implications of the three main factors of the antioxidant system reported in relation to oxidative damage in phenylketonuric patients: selenium, ubiquinone-10 (Q10) and antioxidant enzymes over 3 years of metabolic follow-up.

DESIGN AND METHODS

Longitudinal study of 46 phenylketonuric patients (age range: 6 months-34 years). Antioxidants were measured by atomic absorption spectrophotometric, chromatographic and spectrophotometric procedures.

RESULTS

Plasma selenium concentrations in phenylketonuria (PKU) were not different from those of a healthy population. Decreased plasma Q10 concentrations were mainly related to the dietary control and the age of patients. Erythrocyte catalase activity was significantly decreased in PKU while the other enzyme activities were not different from those of a healthy population.

CONCLUSION

Selenium status is not impaired in phenylketonuric patients under dietary treatment. Q10 values tend to decrease with increased patient age. Catalase activity was negatively associated with plasma phenylalanine values.

Development and validation of HPLC method for the determination of alpha-tocopherol in human erythrocytes for clinical applications

In this work, a simple isocratic reversed-phase HPLC method for determination of alpha-tocopherol in human erythrocytes has been developed and validated. After separation of plasma the erythrocytes were washed three times with 0.9% sodium chloride containing 0.01% butylated hydroxytoluene (BHT) as antioxidant and then were diluted 1:1 (v/v) with the same solution. In the liquid-liquid extraction (LLE) procedure, 2500 microL of n-hexane was added to 500 microL of erythrocytes. After 2 min this mixture was deproteinized by addition of cool ethanol (500 microL, 5 min) denatured with 5% methanol containing alpha-tocopherol acetate (20 micromol L(-1)), as internal standard, and then extracted for 5 min by vortex mixing. After centrifugation (10 min, 1600xg) an aliquot (2000 microL) of the clean extract was separated and evaporated under nitrogen. The residue was dissolved in 400 microL methanol and analysed by reversed-phase HPLC on a 4.6 mmx150 mm, 5 microm Pecosphere C18 column; the mobile phase was 100% methanol, flow rate 1.2 mL min(-1). The volume injected was 100 microL and detection was by diode-array detector at a wavelength of 295 nm. The extraction recovery of alpha-tocopherol from human erythrocytes was 100.0+/-2.0%. The detection limit was 0.1 micromol L(-1) and a linear calibration plot was obtained in the concentration range 0.5-20.0 micromol L(-1). Within determination precision was 5.2% RSD (n=10), between determination precision was 6.1% RSD (n=10). The method was applied successfully in a clinical study of patients with acute pancreatitis and for determination of the reference values in the healthy Czech population.

Lipophilic antioxidants in patients with phenylketonuria

BACKGROUND

Low serum ubiquinone-10 concentrations have been described in phenylketonuric patients fed natural-protein-restricted diets. Such low concentrations may be related to increased free radical damage.

OBJECTIVE

We evaluated the relation between low serum ubiquinone-10 concentrations and other lipophilic antioxidants (tocopherol and retinol), selenium, glutathione peroxidase activity, and malondialdehyde concentrations as a marker of lipid peroxidation.

DESIGN

This was a cross-sectional study of 58 patients with phenylketonuria (aged 2-36 y; median: 13 y) under dietary treatment, 58 age-matched control subjects, and 30 children with moderate hyperphenylalaninemia fed unrestricted diets (aged 3-17 y; median: 7.5 y). Serum ubiquinone-10 concentrations were analyzed by HPLC with electrochemical detection. Serum retinol, serum tocopherol, and plasma malondialdehyde were analyzed by HPLC with ultraviolet detection.

RESULTS

A significant positive correlation was observed between ubiquinone-10 and tocopherol (r = 0.510, P < 0.001) in the patients with phenylketonuria. After the patients were stratified into 2 groups according to ubiquinone-10 values, significantly lower concentrations of tocopherol were observed in group 1 (low ubiquinone values) than in group 2 (normal ubiquinone values), the hyperphenylalaninemic children, and the control group. Plasma malondialdehyde concentrations were significantly higher in group 1 than in the other groups. No significant differences between groups 1 and 2 were observed in daily intakes of selenium, ascorbate, tocopherol, or retinol.

CONCLUSIONS

Plasma lipid peroxidation seems to be increased in phenylketonuria. Low concentrations of ubiquinone-10 could be associated with either excessive tocopherol consumption or high malondialdehyde concentrations in patients with phenylketonuria.

Coenzyme Q10 in plasma and erythrocytes: comparison of antioxidant levels in healthy probands after oral supplementation and in patients suffering from sickle cell anemia

BACKGROUND

The membrane-associated antioxidant coenzyme Q10 (CoQ10) or ubiquinone-10 is frequently measured in serum or plasma. However, little is known about the total contents or redox status of CoQ10 in blood cells.

METHODS

We have developed a method for determination of CoQ10 in erythrocytes. Total CoQ10 in erythrocytes was compared to the amounts of ubiquinone-10 and ubihydroquinone-10 in plasma using high-pressure liquid chromatography (HPLC) with electrochemical detection and internal standardisation (ubiquinone-9, ubihydroquinone-9).

RESULTS

Investigations in 10 healthy probands showed that oral intake of CoQ10 (3 mg/kg/day) led to a short-term (after 5 h, 1.57+/-0.55 pmol/microl plasma) and long-term (after 14 days, 4.00+/-1.88 pmol/microl plasma, p<0.05 vs. -1 h, 1.11+/-0.24 pmol/microl plasma) increase in plasma concentrations while decreasing the redox status of CoQ10 (after 14 days, 5.37+/-1.31% in plasma, p<0.05 vs. -1 h, 6.74+/-0.86% in plasma). However, in these healthy probands, CoQ10 content in red blood cells remained unchanged despite excessive supplementation. In addition, plasma and erythrocyte concentrations of CoQ10 were measured in five patients suffering from sickle cell anemia, a genetic anemia characterised by an overall accelerated production of reactive oxygen species. While these patients showed normal or decreased plasma levels of CoQ10 with a shifting of the redox state in favour of the oxidised part (10.8-27.2% in plasma), the erythrocyte concentrations of CoQ10 were dramatically elevated (280-1,093 pmol/10(9) ERY vs. 22.20+/-6.17 pmol/10(9) ERY).

CONCLUSIONS

We conclude that normal red blood cells may regulate their CoQ10 content independently from environmental supplementation, but dramatic changes may be expected under pathological conditions.

Homocysteine and lipid peroxidation in haemodialysis: role of folinic acid and vitamin E

BACKGROUND

Cardiovascular diseases are the leading cause of death in haemodialysis patients. Hyperhomocysteinaemia is an independent risk factor. Basic research has provided strong evidence that oxidation of low-density lipoprotein (LDL) plays an important role in the pathogenesis of atherosclerosis. Oxidative stress, lipid metabolism alterations, and hyperhomocysteinaemia observed in haemodialysis patients could induce increases in LDL oxidation. This study was designed to determine the effect of folinic acid on hyperhomocysteinaemia and to assess the antioxidant efficacy of folinic acid. The antioxidant effect of folinic acid was compared with that of vitamin E.

METHODS

Sixteen stable patients (11 men, five women; mean age 54.3+/-6.32 years) on standard haemodialysis received 400 mg of vitamin E, orally, at the end of each haemodialysis session for 3 months. After a 1-month wash-out, they received 10 mg of folinic acid, intravenously, at the end of each haemodialysis session for an additional 3 months. Blood samples were drawn in the morning after an overnight fast and before dialysis. Plasma vitamin E was analysed by high-pressure liquid chromatography. Malondialdehyde (MDA) was determined using a fluorimetric method and plasma copper oxidized anti-LDL antibodies (Ab-LDLox) were measured with an ELISA method using native LDL and oxLDL as antigens. Plasma homocysteine was determined by an FPIA method.

RESULTS

Folinic acid supplements significantly reduced hyperhomocysteinaemia (-44%), MDA concentrations (-40%), and IgG-LDLox titres (-13%).

CONCLUSIONS

Treatment with folinic acid lowers plasma homocysteine levels and, like vitamin E, affords antioxidant protection, which prevents lipid peroxidation. This lowering of lipid peroxidation may reduce the risk of atherosclerosis and prevent or delay cardiovascular complications in HD patients.

The reduction of nitroblue tetrazolium by red blood cells: a measure of Red Cell membrane antioxidant capacity and hemoglobin-membrane binding sites

The reduction of nitroblue tetrazolium (NBT) with intact Red Blood Cells (RBCs) is biphasic with an initial rapid reduction followed by a slower second phase. This biphasic kinetics has been explained with the initial rapid phase attributed to antioxidants in the red cell which reduce membrane bound NBT and the slower phase associated with the reaction of NBT with membrane bound hemoglobin. This model has been confirmed by a utilization of a number of red cell modifications which either increase the red cell antioxidants (vitamin C and vitamin E) or damage the red cell membrane (cumene hydroperoxide and N-ethylmaleimide). The utilization of this assay for human blood samples was investigated by studying a series of 20 human subjects ranging between 34 and 87 years of age. It was possible to fit all of these samples with two adjustable parameters which reflect the red cell membrane antioxidant capacity (x) and the hemoglobin membrane interactions (m). The antioxidant capacity shows a significant (p < .002; R = -.67) decrease with age. This finding is consistent with a decrease in the level of antioxidants in aged subjects. In addition, the number of hemoglobin membrane sites are negatively correlated with the antioxidant capacity (p < .02; R = -.52) suggesting that the oxidative stress associated with reduced antioxidants results in increased hemoglobin-membrane interactions.

Vitamin E supplementation in hyperlipidaemic patients: effect of increasing doses on in vitro and in vivo low-density lipoprotein oxidation

BACKGROUND

Vitamin E supplementation is associated with a reduced risk of developing atherosclerotic events; probably because it inhibits low-density lipoprotein (LDL) oxidation, an initial step in atherosclerosis. Metal ion-dependent LDL oxidation is a commonly used method to estimate oxidizability of LDL, but the effect of antioxidant supplementation on the levels of autoantibodies to oxidised LDL (ox-LDL), an in vivo indicator of LDL oxidation, is unknown.

DESIGN

This double-blind, placebo-controlled study investigated the susceptibility of LDL to copper induced oxidation and malondialdehyde (MDA) derivatized-LDL (MDA-LDL) in hyperlipidaemic patients on supplements of vitamin E. The vitamin E group (n = 20) took vitamin E 100 IU daily and the dose was doubled at six-weekly intervals to 1600 IU daily. The control group (n = 17) received placebo in the same fashion. Blood samples were obtained at baseline and each subsequent visit to measure vitamin E status and oxidation of LDL.

RESULTS

A significant increase in both alpha-tocopherol levels and the lengths of lag phase was seen in the vitamin E group after first week of supplementation (100 IU day-1). This continued to rise in a dose-dependent fashion with a doubling of the lag phase on 1600 IU daily. However, the titre of antibodies to MDA-LDL was not altered.

CONCLUSIONS

The results suggest that although regarded as an in vivo marker of LDL oxidation, antibodies to MDA-LDL may not be a suitable measure to evaluate the effect of short-term antioxidant supplementation. The failure of autoantibody titres to fall despite reduced oxidizability of LDL may possibly be attributable to a long half-life of the antibody or, once initiated, a continuous immunological response to ox-LDL contained in atherosclerotic lesions of the arterial wall.

Lipid peroxidation of isolated chylomicrons and oxidative status in plasma after intake of highly purified eicosapentaenoic or docosahexaenoic acids

Fourteen healthy male volunteers were given two separate high-saturated-fat meals with and without the addition of 4 g highly purified ethyl esters of either eicosapentaenoic acid (EPA) (95% pure, n = 7) or docosahexaenoic acid (DHA) (90% pure, n = 7) supplied as 1-g capsules each containing 3.4 mg vitamin E. The chylomicrons were isolated 6 h after the meals, at peak concentrations of n-3 fatty acids (FA). Addition of n-3 FA with the meal caused a 10.4-fold increase in the concentration of n-3 FA in chylomicrons compared to the saturated fat meal without addition of n-3 FA. After the saturated-fat meal, the concentration of thiobarbituric acid-reactive substances (TBARS) was 327.6 +/- 34.6 nmol/mmol triacylglycerol (TAG), which increased to 1015.8 +/- 212.0 nmol/mmol TAG (P < 0.0001, n = 14) after EPA and DHA were added to the meal. There was no significant correlation between the concentrations of TBARS and vitamin E in the chylomicrons collected 6 h after the test meal. The present findings demonstrate an immediate increase in chylomicron peroxidation ex vivo provided by intake of highly purified n-3 FA. The capsular content of vitamin E was absorbed into chylomicrons, but the amount of vitamin E was apparently not sufficient to protect chylomicrons against lipid peroxidation ex vivo. Daily intake of 4 g n-3 FA either as EPA or DHA for 5 wk did not change the plasma concentration of TBARS. Although not significantly different between groups, DHA supplementation decreased total glutathione in plasma (P < 0.05) and EPA supplementation increased plasma concentration of vitamin E (P < 0.05). The other lipid-soluble and polar antioxidants in plasma remained unchanged during 5 wk of intervention with highly purified n-3 FA.

Antioxidant status in hyperphenylalaninemia

Abnormal oxidative stress was observed in some inborn errors of metabolism owing to the accumulation of toxic metabolites leading to excessive free radical production and to the influence of restricted diets on the antioxidant status. Erythrocyte antioxidant enzymes activities and tocopherol concentrations were measured in a group of phenylketonuric (n = 42) and mild-hyperphenylalaninemic (n = 28) patients compared with 45 age-matched controls. We also determined plasma selenium levels in these groups. We also evaluated the possible relationship between antioxidant status and neuropsychological disorders. Erythrocyte glutathione peroxidase (GSH-Px) activity was significantly lower (P < 0.001) in both phenylketonuric and mild-hyperphenylalaninemic patients compared with the control group, but no differences were observed between the two groups of patients. Neuropsychological disturbances were more frequent in the group of PKU patients with low GSH-Px activity than in PKU patients with normal GSH-Px. Low GSH-Px activity might be explained in phenylketonuria as a result of a selenium deficiency caused by a poor selenium intake or absorption, but not in mild hyperphenylalaninemic patients with free diet. Selenium levels were normal in both groups of patients, so low glutathione peroxidase activity in both phenylketonuric and hyperphenylalaninemic groups might be influenced by other factors, such as the consequences of an unbalanced amino acid profile, common to both conditions.

Antioxidant enzymes and fatty acid status in erythrocytes of Down syndrome patients

The excess of genetic information in patients with Down syndrome (DS) produces an increase in the catalytic activity of superoxide dismutase (SOD1), an antioxidant enzyme coded on chromosome 21. It has been suggested that an increase in oxidative stress in DS patients may cause adverse effects in the cell membranes through the oxidation of polyunsaturated fatty acids (PUFAs). The aim of this study was to evaluate the cellular antioxidant system by determining the catalytic activity of the SOD1, glutathione peroxidase (GPx), catalase (CAT), and glutathione reductase (GR) enzymes and the concentrations of α-tocopherol in red blood cells (RBCs) in a group of 72 DS patients. The profile of fatty acids in the phospholipids of RBC membranes was also evaluated. The activity of the erythrocyte antioxidant enzymes is significantly higher in the DS group than in the control group (SOD1, 635 ± 70 U/g Hb vs 476 ± 67 U/g Hb; CAT, 1843 ± 250 U/g Hb vs 1482 ± 250 U/g Hb; GPx, 23.2 ± 5.3 U/g Hb vs 21.5 ± 3.6 U/g Hb; and GR, 9.32 ± 1.4 U/g Hb vs 6.9 ± 1.3 U/g Hb, respectively). No differences were observed in RBC α-tocopherol concentrations between the two groups studied. Long-chain n6 PUFA (C20:3n6, C20:4n6) concentrations were increased in DS patients, suggesting enhanced Δ-6-desaturase activity. The long-chain n3 PUFA (docosahexenoic acid) does not appear to be affected by increased oxidative stress, probably because of the existence of compensatory antioxidant mechanisms.

Effects of Simvastatin and omega-3 fatty acids on plasma lipoproteins and lipid peroxidation in patients with combined hyperlipidaemia

OBJECTIVES

Patients with combined hyperlipidemia are at increased risk for development of coronary heart disease. The purpose of this study was to evaluate the efficiency and the safety of treatment with Simvastatin and omega-3 fatty acids in patients with this lipid disorder.

DESIGN

A double-blind placebo controlled, randomized study evaluating the effects of Simvastatin separately and in combination with omega-3 fatty acids in 41 healthy patients with defined hyperlipidemia. After a 16 weeks dietary run-in period the patients were treated in periods of 5 weeks.

RESULTS

As expected Simvastatin (20 mg day[-1]) reduced serum total cholesterol, triacylglycerols, apolipoproteins B and E and increased HDL-cholesterol and apolipoprotein A1. Addition of omega-3 fatty acids (4 g day[-1]) further decreased serum triacylglycerols (P = 0.007), total cholesterol (P = 0.052) and apolipoprotein E (P = 0.035). No significant changes attributable to supplementation of polyunsaturated fatty acids on the content of lipid peroxides in plasma and in the various lipoprotein fractions were observed.

CONCLUSIONS

The combined treatment of Simvastatin and omega-3 fatty acids seems to be an efficient and safe alternative for patients with combined hyperlipidemia.

Tocopherol in inborn errors of intermediary metabolism

Red blood cell tocopherol was measured in a group of 92 children with inborn errors of intermediary metabolism to evaluate the peroxidative damage in different mitochondrial and cytosolic defects, and to consider the need for treatment or vitamin supplementation. Tocopherol was determined by HPLC with UV detection. Results were expressed in nanomoles red blood cell tocopherol per gram protein. Significant differences (Mann-Whitney; P < 0.001) were found between tocopherol levels in untreated patients: 19 with mitochondrial defects versus 23 with cytosolic enzyme or transport defects, and versus 58 age-matched reference values. In conclusion, mitochondrial enzyme deficiencies, either amino and organic acidurias or defects of energy metabolism, seem to produce an excess of free radicals with the consequent utilization of tocopherol as antioxidant. This is not apparent in the cytosolic enzyme defects studied, whose tocopherol levels are in the normal range. Treatment with tocopherol completely corrects the deficient antioxidant status.

The effect of hormone replacement therapy on vitamin E status in postmenopausal women

OBJECTIVES

Vitamin E (alpha-tocopherol) is the most important dietary antioxidant found in lipids and cell membranes and its intake is inversely related to the incidence of atherosclerotic cardiovascular disease. Oestrogen-containing oral contraceptives may decrease plasma vitamin E level in young women. We investigated if oestrogen-containing hormone replacement therapy (HRT) may have the same effect on vitamin E status in postmenopausal women

METHODS

Eighteen healthy postmenopausal women took a combination of oestrogen/progestogen (Harmogen Provera) therapy and another ten acted as a control group. Blood samples were taken at baseline and repeated after 3 and 6 months in both groups. Vitamin E in plasma, red cells and isolated low-density lipoprotein (LDL) was measured as alpha-tocopherol by high-performance liquid chromatography.

RESULTS

Vitamin E status showed no change in either group after 3 and 6 months in comparison to its baseline value.

CONCLUSION

Combined oestrogen/progestogen HRT for 6 months in healthy postmenopausal women did not alter vitamin E. status in vivo.

Lipid peroxidation and antioxidant vitamins C and E in hypertensive patients

Lipid peroxidation is a free radical process which is implicated in the formation of atherosclerosis. Vitamins C and E are important natural antioxidants which inhibit lipid peroxidation and a high intake of these vitamins, particularly vitamin E, is related to a reduced incidence of ischaemic heart disease. Hypertension is an independent risk factor for atherosclerosis and its relationship to antioxidant status is undetermined. In this study, we investigated free radical activity by measuring plasma malondialdehyde (MDA) using high-performance liquid chromatography (HPLC), vitamin C status measured as plasma ascorbic acid and vitamin E status measured as plasma lipid standardized alpha-tocopherol and erythrocyte alpha-tocopherol. We compared 28 patients with essential hypertension to 31 healthy subjects. Results showed that in comparison with the healthy subjects, the hypertensive patients had significantly higher plasma MDA levels (0.95 +/- 0.28 vs 0.69 +/- 0.21 mumol/l, mean +/- SD, p < 0.001) and significantly lower levels of plasma ascorbic acid (34.83 +/- 12.88 vs 51.76 +/- 13.34 mumol/L, p < 0.01). In addition, erythrocyte alpha-tocopherol concentration, which may reflect vitamin E protection in cell membranes, was significantly lower in hypertensive patients when compared with the normotensive controls (3.87 +/- 0.53 vs 4.82 +/- 1.01 mumol/l, p < 0.001), although plasma alpha-tocopherol levels were similar in the two groups (25.07 +/- 10.45 vs 23.96 +/- 6.07 mumol/l). Our results suggest that hypertensive patients may have increased lipid peroxidation and reduced protection from vitamins C and E. This may contribute to the propensity in such patients to develop atherosclerosis.

Determination of alpha-tocopherol in plasma and erythrocytes by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method for the determination of alpha-tocopherol in plasma or erythrocytes with photodiode-array detection is described. Using this detector, information about the spectrum, absorption maxima and purity of the peak is obtained. Tocopherol was separated on a 5-microns Spherisorb ODS-2 column with methanol as element at a flow-rate of 1.0 ml/min. As little as 100 microliters of plasma or 150 microliters of erythrocytes can be used for accurate analysis with direct extraction without saponification. The speed, specificity, sensitivity and reproducibility of this technique make it particularly suitable for the routine determination of alpha-tocopherol in plasma or erythrocytes.

Determination of plasma tocopherols by high-performance liquid chromatography with coulometric detection

An HPLC procedure has been developed for tocopherol determination with coulometric detection in human serum samples. Eluent optimization and foreign peak identification (bilirubin) by mass spectrometry are described. An extraction procedure gave yields around 98% with 1.3% coefficient of variation, and the calibration ranged from 0.1 to 200 mg/l with a correlation coefficient of 0.999. The detection limit achieved for vitamin E was 60 pg (3 ng/ml).