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The Journal of Nutrition Vol. 128 No. 11 November 1998,
pp. 1950-1955
Institute of Animal Nutrition and Nutrition Physiology, Justus-Liebig-University, D-35390 Giessen, Germany
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ABSTRACT |
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Abstract
Introduction
Methods
Results
Discussion
References
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The objective of this study was to determine the effects of phytic acid on free radical generation in vitro and in growing rats. Electron spin resonance spectroscopy studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap indicate a complete inhibition of hydroxyl radical formation via the iron-catalyzed Fenton reaction at molar phytic acid/iron ratios >5. However, phytic acid had no scavenging effect on superoxide radicals generated in the xanthine/xanthine oxidase reaction. For the in vivo study, male growing albino rats were fed purified diets based on casein, cornstarch and vitamin E-stripped corn oil differing in the concentration of iron (30 or 300 mg/kg), phytic acid (0 or 10 g/kg) and dl-
-tocopheryl acetate (0 or 50 mg/kg). At marginal dietary iron supply, phytic acid supplementation reduced apparent Fe absorption, thereby decreasing liver Fe concentration. Dietary iron and phytate had no effect on the level of hepatic -tocopherol, reduced glutathione, thiobarbituric acid-reactive substances and protein carbonyls. The concentration of thiobarbituric acid-reactive substances and protein carbonyls in the liver decreased as dietary vitamin E was increased from 0 to 50 mg/kg diet. The results obtained provide evidence for antioxidant properties of phytic acid under in vitro conditions. However, neither phytic acid nor iron had any significant effect on liver oxidant or antioxidant status in vivo in growing rats.
Phytic acid (PA,3 myo-inositol 1,2,3,4,5,6 hexakisdihydrogenphosphate), the main phosphorus storage of cereals, legumes and oilseeds, is known to bind essential divalent cations such as calcium, magnesium, iron, zinc and manganese, forming largely insoluble complexes, and thereby decreasing their bioavailability in humans and other monogastric animals (Zhou and Erdman 1995 ESR spin trap studies.
The spin trapping of the hydroxyl radical formed in the Fenton reaction system was undertaken by the addition of 100 µmol/L iron from FeSO4 · 7H2O to 80 mmol/L H2O2 after 3 min of incubation. The stock solution of ferrous iron (2 mmol/L) was freshly prepared before the experiments to avoid autoxidation. No free hydroxyl radical was spin trapped in the presence of 300,000 U/L catalase. The superoxide radical generating system contained 160 µmol/L xanthine, 2 mmol/L desferrioxamine mesylate and 165 U/L xanthine oxidase. The reaction was initiated by the addition of xanthine oxidase and recorded after 1 min. In both systems 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) dissolved in phosphate buffer (pH 7.4, 100 mmol/L) was used at concentrations of 100 mmol/L. Verification of superoxide trapping in the xanthine/xanthine oxidase (X/XO) reaction was done by the addition of 65,000 U/L superoxide dismutase. Stock solutions of myo-inositol (100 mmol/L) and sodium phytate (100 mmol/L) were dissolved in phosphate buffer and the reaction was carried out at pH 7.4. For enzymatic hydrolysis of phytic acid, 1.0 mmol/L sodium phytate was incubated with 10,000 U/L microbial phytase (EC 3.1.3.8) from Aspergillus niger var. van tighem (BASF AG, Ludwigshafen, Germany) in phosphate buffer at pH 5.5 over 2 h at 37°C. After phytate hydrolysis, pH was adjusted to 7.4 using 0.1 mol/L NaOH. ESR spectra of DMPO spin adducts were recorded in glass accupette pipettes at room temperature using an electron spin resonance spectrometer (Varian E-9, X-band, Karlsruhe, Germany) operating at 9.49 GHz. Spectrometer settings were as follows: microwave power, 20 mW; modulation frequency, 100 kHz; central field, 3376 G; scan range, 100 G; time constant, 0.3 s; receiver gain, 4 × 103 (Fenton reaction) or 2 × 104 (X/XO reaction); modulation amplitude, 0.5 G (Fenton reaction) or 1.25 G (X/XO reaction), and scan time 4 min (Fenton reaction) or 2 min (X/XO reaction). Spectra shown in each figure were carried out on the same day and are representative of at least three independent experiments.
Animals and diets.
Weaned male albino rats (Wistar Unilever, Harlan/Winkelmann, Paderborn, Germany) with an initial weight of 54 ± 3 g were allocated to eight groups of seven. Rats were housed individually over a 28-d period in metal-free metabolic cages under standard conditions (22°C, 55% humidity, 12-h light:dark cycle). Rats had free access to diets and bidistilled water. Food intake was measured daily and live weight was recorded weekly. All experimental procedures were approved by the Animal Care Authorities of the University of Giessen.
Sample collection and tissue preparation.
During wk 2 and 3 (d 7-21) of the experiment, the feces of each rat were collected quantitatively. On d 28 of the experiment, the rats were anesthesized in a carbon dioxide atmosphere and subsequently killed by decapitation. The liver was removed, placed in liquid nitrogen for 24 h and then stored at Determination of dietary phytic acid.
Dietary PA was analyzed by HPLC. Samples were extracted with 24 g/L HCl and purified by anion exchange chromatography (Adsorbex SAX, Merck, Darmstadt, Germany) with 0.5 mol/L KH2PO4. HPLC analysis (Merck Hitachi) was performed on a Lichrospher 100 RP-8e column (Merck) with 0.025 mol/L KH2PO4 as the mobile phase (flow rate = 1 mL/min) using refractive index detection as described previously (Rimbach et al. 1998 Determination of minerals and trace elements.
Samples were dry-ashed for 48 h in quartz dishes at 450°C in a muffle furnace and dissolved in 3 mol/L HNO3. Minerals and trace elements in diets, in freeze-dried feces and in liver were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES, Unicam 701, Kassel, Germany) with a direct on-peak measurement. The sample uptake was performed with a peristaltic pump, and samples were dispersed into the argon plasma by a Hildebrand-Grid nebulizer (Unicam, Kassel, Germany). Accuracy of the method was checked by standard addition. Furthermore, for analytical quality control, bovine liver [certified reference material (CRM) 185] and wholemeal flour (CRM 189) from the Institute of Reference Materials and Measurements (IRMM) were analyzed together with the samples. Analyzed dietary iron concentrations in diets 1-4 (30-33 mg Fe/kg diet) and diets 5-8 (293-316 mg Fe/kg diet) showed good agreement with the supplemented amounts.
Determination of tocopherol.
The diet and liver samples were extracted with methanol/dichlormethane (1:2, v/v), and the vitamin E concentration in the extracts was determined by HPLC (Merck Hitachi) on a C-18 reversed-phase column (Lichrospher 100 RP-18, Merck) using fluorescence detection (excitation: 295 nm, emission: 340 nm) according to the assay of Bieri et al. (1979) Determination of glutathione.
Liver homogenates were centrifuged at 100,000 × g for 30 min to obtain the supernatant for the assay of reduced glutathione (GSH). To 0.5 mL of the supernatant, 4.5 mL of 0.1 mol/L sodium phosphate containing 0.005 mol/L EDTA (pH 8.0) was added. GSH in the liver homogenates was determined by the method of Hissin and Hilf (1976) Determination of TBARS.
For assessment of lipid peroxidation, thiobarbituric acid-reactive substances (TBARS) were determined in whole-liver homogenates after 60 min of incubation at 37°C with 12.5 µmol/L FeSO4 (Günther et al. 1994 Determination of protein carbonyls.
Protein oxidation was determined spectrometrically (Büchi 902, Pharmacia, Biotech, Freiburg, Germany) by the carbonyl assay of Reznick and Packer (1994) Statistical analysis.
Data are expressed as means ± SD and analyzed for normality of distribution (Shapiro-Wilk test) and equality of variance (Levine test) before ANOVA. Three-way ANOVA was performed by SPSS (Statistical Package for the Social Sciences, version 6.0.1, Chicago, IL) software. The factors of interest were the two iron levels (30 or 300 mg/kg diet), the two levels of PA (0 and 10 g/kg diet), the two levels of vitamin E (0 or 50 mg/kg diet) and their interactions. Individual treatment means were compared post hoc by the Scheffé test. Differences were considered significant at P < 0.05.
In vitro study.
In the model Fenton system containing H2O2 and Fe2+, the typical ESR signal of the DMPO/ o OH radical adduct, consisting of a 1:2:2:1 quartet with splitting constants of aN = aH = 14.9 G, was observed in the presence of DMPO (Fig. 1A). Phytic acid at a concentration of 1.0 mmol/L caused a complete quenching of the ESR signal (Fig. 1B). In contrast, the addition of PA previously incubated with 10,000 U/L microbial phytase (Fig. 1C) as well as the addition of 1.0 mmol/L myo-inositol (Fig. 1D) did not quench the DMPO/ o OH signal. The effect of increasing levels of PA added to the Fenton system on DMPO/·OH spin adducts is given in Figure 2. Molar PA/Fe concentration >5 resulted in a complete inhibition of the hydroxyl radical formation. A typical ESR spectrum of DMPO/·OOH formed by the xanthine/xanthine oxidase reaction is given in Figure 3A. No free superoxide radical was detected in the presence of superoxide dismutase (Fig. 3B). Phytic acid (Fig. 3C) and myo-inositol (Fig. 3D) had no effect on the DMPO/·OOH signal.
In vivo study.
There were no effects of the dietary treatment on food intake, daily gain and feed efficiency. Three-way ANOVA indicated that dietary iron and its interaction with phytate significantly affected apparent iron absorption (Table 2). Apparent absorption (in percentage of intake) of calcium (41-47%), magnesium (26-34%), zinc (7-12%), copper (18-24%) and manganese (3-5%) remained unchanged with different dietary treatments. The intake of the diets containing 300 mg Fe/kg resulted in significantly enhanced hepatic iron concentrations compared with diets containing 30 mg Fe/kg. The ANOVA revealed a significant interaction of phytic acid and iron on liver Fe concentration, whereas the level of vitamin E in the diet had no effect on the Fe concentration of the liver. As shown in Table 2, dietary vitamin E supplementation resulted in significantly higher hepatic concentration of
We used ESR spectroscopy to study the antioxidant properties of PA in vitro because spin trapping provides an opportunity not only to detect radicals, but also to characterize partially the types of radicals formed (Reinke and McCay 1997
INTRODUCTION
Abstract
Introduction
Methods
Results
Discussion
References
). In contrast to the antinutritive effects, potential benefits of PA and myo-inositol were observed in azoxymethane- (Shamsuddin and Ullah 1989) and dimethylhydrazine- (Shamsuddin et al. 1989) induced colon cancer, pulmonary adenoma (Estensen and Wattenberg 1993) and, in the case of transplanted fibrosarcoma (Vucenik et al. 1992), in mice and rats. Furthermore, in a wide-spectrum organ carcinogenesis model, Hirose et al. (1991) showed that a supplement of 2% phytic acid inhibited development of neoplasmatic lesions in the liver and pancreas. In vitro studies clearly demonstrated that PA also reduced cell proliferation rate in different cell lines, including erythroleukemia (Shamsuddin et al. 1992) and human mammary cancer (Shamsuddin et al. 1996). The basic mechanisms of the anticarcinogenic effect of PA are still not clear. Phytic acid may exert anticarcinogenic benefits in part because of its antioxidant capability (Thompson and Zhang 1991). A function of PA as a natural antioxidant was first postulated by Graf et al. (1984). Experimental evidence indicates that in the presence of PA, iron-catalyzed generation of hydroxyl radicals may be blocked (Graf et al. 1987). Hydroxyl radical formation was measured spectrophotometrically by the formation of formaldehyde in the presence of dimethylsulfoxide (Graf et al. 1984, Hawkins et al. 1993). However, the most direct technique available for the detection of free radicals is electron spin resonance spectroscopy (ESR). Spin trapping involves the addition reaction of the free radical of interest to a dimagnetic compound (spin trap) to produce a relatively stable spin adduct. The information about the radical trapped is contained in the hyperfine splitting of the spin adducts, whereas the amplitude of the signal enables the amount of free radicals generated to be quantified (Buettner 1987). There is a lack of information on the effect of PA on hydroxyl and superoxide radical formation using ESR. To assess free radical formation directly, ESR was used in this work. Furthermore, most in vivo experiments showing anticarcinogenic effects of PA failed to consider the mineral supply and indicators of oxidative damage in the experimental animals as pointed out previously (Pallauf and Rimbach 1997, Zhou and Erdman 1995). Therefore, the purpose of this in vivo study was to determine the effect of dietary phytate added to purified diets containing different concentrations of iron and tocopherol on liver and oxidant/antioxidant status.
MATERIALS AND METHODS
Abstract
Introduction
Methods
Results
Discussion
References
-tocopheryl acetate per kg diet were supplemented. Diets were highly enriched with calcium (8 g/kg), magnesium (1 g/kg), zinc (250 mg/kg), manganese (60 mg/kg) and copper (7 mg/kg) to counteract a reduced bioavailability of these cations. Other minerals, trace elements and vitamins were supplemented to meet the level of the recommended requirements (NRC 1995).
View this table:
Table 1.
Composition of the basal diet
80°C until analysis. For determination of thiobarbituric-acid-reactive substances and glutathione, liver samples were homogenized in 10 vol of 10 mmol/L Tris buffer, pH 7.4 in a nitrogen atmosphere. Homogenizing buffer (50 mmol/L Na2HPO4, 1 mmol/L EDTA, pH 7.4) for the protein carbonyl assay contained antiproteases (40 mg/L phenylmethyl-sulfonylfluoride, 5 mg/L leupeptine, 7 mg/L pepstatin, 5 mg/L aprotinin) and 1 g/L digitonin (Reznick and Packer 1994).
). In diets 1, 2, 5 and 6, no PA was detectable. In diets 3, 4, 7 and 8, analyzed PA concentration was 9.2, 9.4, 9.2 and 9.3 g/kg diet, respectively.
. Methanol/H2O (98:2, v/v) was used as the eluting solvent at a flow rate of 2 mL/min for isocratic elution. The chromatographic peak was identified by comparison of the retention time with a pure standards of -tocopherol and dl--tocopheryl acetate (Hoffmann-La Roche, Basel, Switzerland). In diets 1, 3, 5 and 7, analyzed vitamin E concentration was <1 mg/kg diet. Analyzed dietary vitamin E concentration in the vitamin E-supplemented diets ranged between 46 and 55 mg -tocopheryl acetate/kg diet.
based on the reaction of GSH with o-phthalaldehyde (OPT) as a fluorescent reagent. The final assay mixture contained 100 µL of diluted 100,000 × g supernatant, 1.8 mL of phosphate EDTA buffer (pH 8.0) and 100 µL of 745 nmol/L OPT dissolved in methanol. Fluorescence (Perkin Elmer LS 50 B, Beaconsfield, UK) was measured with excitation and emission wavelengths of 350 and 420 nm, respectively.
). Samples were diluted 1:1 (v/v) with 5 g/L trichloracetic acid (TCA) and centrifuged for 5 min at 13,000 × g; 500 µL TBA (10 g/L) and 50 µL butylated hydroxytoluene (5 g/L) were added to the supernatant and heated for 15 min at 100°C. After cooling, TBARS were extracted in 3 mL of 1-butanol by vortexing for 30 s and centrifugation at 2000 × g for 15 min. TBARS in the butanol layer were measured fluorometrically (Perkin Elmer LS 50 B) with excitation and emission wavelengths of 532 and 553 nm, respectively. Calibration curves were prepared with 1,1,3,3-tetraexthoxypropane as an external standard.
with slight modifications. Liver homogenate (1 mL) was added to 4 mL of 2,4-dinitrophenylhydrazine (10 mmol/L) in 2 mol/L HCl and left for 1 h at room temperature in the dark. Five milliliters of 20 g/L TCA was added to the samples; the tubes were cooled in an ice bath for 10 min and then centrifuged for 5 min at 10,000 × g to collect protein precipitates. Pellets were washed once with 4 mL 10 g/L TCA and three times with 4 mL of ethanol/ethylacetate (1:1, v/v). Final pellets were disrupted mechanically with a spatula followed by centrifugation at 15,000 × g for 10 min. Precipitates were dissolved in 6 mol/L guanidine HCl (in 20 mmol/L potassium phosphate, pH 2.3) and were incubated for 10 min at 37°C. The carbonyl content was calculated from the peak absorbance (355-390 nm) using an absorption coefficient (
) of 22,000 [(mol/L)
1 · cm1]. Results are expressed as nmol carbonyls/mg protein. Protein concentrations were determined on HCl blank pellets free of 2,4-dinitrophenylhydrazine from a bovine serum albumin standard curve dissolved in guanidine HCl and read at 280 nm.
RESULTS
Abstract
Introduction
Methods
Results
Discussion
References
View larger version (20K):
[in a new window]
Fig 1.
Typical electron spin resonance spectroscopy spectra of DMPO/·OH spin adducts formed by the Fenton reaction system containing 100 µmol/L Fe2+ and 80 mmol/L H2O2 (A) in the absence of phytic acid; (B) in the presence of 1.0 mmol/L phytic acid; (C) in the presence of 1.0 mmol/L phytic acid preincubated with 10,000 U/L microbial phytase at 37°C for 2 h; and (D) in the presence of 1.0 mmol/L myo-inositol. Spectra were recorded at room temperature 3 min after the addition of iron under the conditions described in Materials and Methods.
View larger version (16K):
[in a new window]
Fig 2.
Effect of increasing levels of phytic acid on DMPO/·OH spin adducts formed by the Fenton reaction system containing 100 µmol/L Fe2+ and 80 mmol/L H2O2. The data are expressed in arbitrary units. Spectra were recorded at room temperature 3 min after the addition of iron under the conditions described in Materials and Methods.
View larger version (23K):
[in a new window]
Fig 3.
Typical ESR spectra of DMPO/·OOH spin adducts formed by the xanthine/xanthine oxidase reaction system (A) in the absence of phytic acid; (B) in the presence of 65,000 U/L superoxide dismutase; (C) in the presence of 1.0 mmol/L phytic acid; and (D) in the presence of 1.0 mmol/L myo-inositol. Spectra were recorded at room temperature 1 min after the addition of xanthine oxidase under the conditions described in Materials and Methods.
-tocopherol. Hepatic -tocopherol, TBARS and protein carbonyls were not significantly altered by dietary iron and phytate intake. However, the concentration of TBARS and protein carbonyls in the liver decreased as dietary vitamin E was increased from 0 to 50 mg/kg diet. Furthermore, the level of reduced glutathione in the liver remained unchanged by the different dietary treatments.
View this table:
Table 2.
Percentage apparent iron absorption and vitamin E, glutathione (GSH), thiobarbituric acid-reactive substances (TBARS) and protein carbonyl levels in whole-liver homogenates of growing rats fed low (30 mg/kg diet) and high iron diets (300 mg/kg diet) with or without phytic acid (0 or 10 g/kg diet) and vitamin E (0 or 50 mg/kg diet) supplementation1
DISCUSSION
Abstract
Introduction
Methods
Results
Discussion
References
). The present ESR studies clearly demonstrate that PA is a potent inhibitor of iron-catalyzed hydroxyl formation. The antiradical effect of PA occurs by chelating iron required for the generation of hydroxyl radicals via the Fenton reaction due to the phosphorus moieties of the PA molecule because phytate hydrolysis catalyzed by microbial phytase as well as the addition of myo-inositol had no effect on DMPO/·OH spin adducts. It is hypothesized that the 1, 2, 3 equatorial-axial-equatorial trisphosphate grouping in PA has a conformation that provides mainly a specific intramolecular interaction with iron to inhibit its ability to catalyze hydroxyl radical formation (Hawkins et al. 1993, Phillippy and Graf 1997). We found a complete inhibition of hydroxyl radical formation at a molar ratio PA/Fe >5, whereas in the study of Graf et al. (1984) molar PA/Fe ratios up to 0.25 using the xanthine/xanthine oxidase reaction in the presence of Fe3+ failed to produce hydroxyl radicals, which could be measured spectrophotometrically by the formation of formaldehyde in the presence of dimethylsulfoxide. Discrepancies in the inhibiting effect of the different molar PA/Fe ratios in the two studies might be related to differences in the radical generating system, the redox state of iron as well as to differences in the sensitivity of the assays. There is no doubt that the ESR spin trapping technique is the most direct method to measure the hydroxyl radical (Yamazaki and Piette 1990). Furthermore, the trapping rate is very fast being 3.4 × 109 (mol/L)1s1 DMPO/ o OH (Finkelstein et al. 1980) and the trapped spin adduct is relatively stable. The ESR assay is very sensitive and even the presence of adventitious iron at concentrations as low as 106 mol/L is able to catalyze the Fenton reaction (Reznick et al. 1992). Phytic acid as well as myo-inositol had no effect on the rate of radical production in the xanthine/xanthine oxidase reaction, widely used as a superoxide generating system. Desferrioxamine mesylate, which binds to all six coordination sites of iron, was always added to the xanthine/xanthine oxidase assay to prevent any reaction of the superoxide radical with iron, thereby affecting nitroxide spin loss (Belkin et al. 1987). DMPO/ o OOH signals were inhibited completely by the inclusion of superoxide dismutase in the system, suggesting that the xanthine/xanthine oxidase reaction in the presence of desferrioxamine mesylate generated primarily the superoxide radical. Furthermore, splitting constants for DMPO/·OOH (aN = 14.3 G, aH = 11.7 G, aH
= 1.25 G) were identical to those reported earlier by Britigan et al. (1990). It can be concluded that under the conditions investigated, neither PA nor myo-inositol may function as scavengers for superoxide radicals.
) and other monogastric animals (Thompson and Erdman 1984). Phytic acid and iron form insoluble complexes that are not available for absorption under the pH conditions of the small intestine. Inhibition of iron and zinc absorption due to dietary phytate could be partially counteracted by the addition of microbial phytase from Aspergillus niger to phytate-rich diets in rats (Pallauf and Pippig 1997) and poultry (Biehl et al. 1997). Recently, Sandberg et al. (1996) also showed a positive effect of Aspergillus phytase on iron absorption in humans. In agreement with earlier experiments, increasing dietary iron resulted in elevated liver iron concentrations (Bristow-Craig et al. 1994, Ibrahim et al. 1997, Rimbach et al. 1997). On the basis of current data, higher liver iron stores in rats receiving the diets containing 300 mg/kg Fe were not associated with an increase in hepatic lipid, protein damage and glutathione oxidation. In this study, the cellular antioxidant defense system obviously had sufficient antioxidative capacity to counteract increased exposure to the oxidant iron originating from the diet. Bristow-Craig et al. (1994) also found no significant influence of 400 mg/kg dietary Fe on hepatic radical scavenging enzymes such as superoxide dismutase, glutathione peroxidase, glutathione reductase and catalase compared with rats fed diets containing 15 mg/kg Fe. In experimental animal models, iron overload is often induced by iron injection (Dabbagh et al. 1994), application of large amounts of carbonyl iron (Wu et al. 1990) or by Fe levels of 1000 (Ibrahim et al. 1997) and 2000 mg/kg diet (Rimbach et al. 1997) in mice and rats. For weanling and adult rats, the iron requirement for growth and maintenance according to the NRC (1995) is 35 mg/kg diet. Thus, at least a 30-fold increase of dietary iron supply was necessary to induce oxidative damage in liver, evaluated in terms of lipid and protein oxidation. The incubation of isolated hepatocytes with iron often produces severe damage and cell death (Poli 1985), whereas phytic acid prevented the peroxidation of unsaturated fatty acids driven by iron in vitro (Graf et al. 1987). However it should be considered that under physiologic conditions, tissue iron is highly regulated, not only because of the potential toxicity but also because of the lower water solubility of Fe3+. Moreover, iron is transported from the gut and in the blood with a very high affinity bound to transferrin, which is normally only partially saturated (Winterbourn 1991). Thus iron reaches the liver cells in a catalytically inactive form that seems to be largely unable to stimulate free radical reactions.
-tocopheryl acetate had significantly higher hepatic levels of TBARS and protein carbonyls as described earlier (Galeano and Puntarulo 1997). The measurement of TBARS and protein carbonyls are indirect analytical methods to determine oxidative stress. However, there is experimental evidence that the ESR technique using phenyl- (Burkitt and Mason 1991) or -(4-pyridyl-1-oxide)-N-t-butylnitrone (Reinke and McCay 1997) as spin traps also provides the opportunity for the direct measurement and characterization of free radicals in vivo. Under the conditions investigated, the status of reduced glutathione in the liver remained unchanged by the different dietary treatments despite significant changes in the hepatic -tocopherol levels. Similar results have been reported by Ibrahim et al. (1997). Hepatocytes contain almost five times the amount of glutathione present in other cells. Therefore, even alterations in cell function and metabolism can occur under oxidative stress with little or at most transient GSH depletion as shown for in vivo exposure of rats to hyperoxia (Sutherland et al. 1985). Additionally, other antioxidants such as ascorbate (Meister 1994) or dihydrolipoic acid (Bast and Haenen 1988) protect against some of the effects of GSH deficiency.
). However, in this in vivo study, neither PA nor iron had a significant effect on liver oxidant or antioxidant status. It is likely that in addition to the inhibition of iron-catalyzed oxidative damage, other pathways such as the activation of immune competent cells (Baten et al. 1989), as well as the participation of inositol phosphates in signal transduction, cell division and differentiation (Shamsuddin et al. 1992, Vucenik and Shamsuddin 1994) are also responsible for beneficial effects of dietary phytate in cancer prevention.
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FOOTNOTES |
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Manuscript received 8 April 1998. Initial reviews completed 21 May 1998. Revision accepted 30 June 1998.
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LITERATURE CITED |
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Abstract
Introduction
Methods
Results
Discussion
References
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-hydroxycholecalciferol.
Poult. Sci.
1997;
76:1424-1427-tocopherol and retinol in plasma or red blood cells by high pressure liquid chromatography.
Am. J. Clin. Nutr.
1979;
30:686-690
-oryzanol, phytic acid, tannic acid and n-tririacontane-16,18-dione in a rat wide-spectrum organ carcinogenesis model.
Carcinogenesis
1991;
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