Relative bioactivity of dietary RRR- and all-rac-alpha-tocopheryl acetates in swine assessed with deuterium-labeled vitamin E

Wheat germ oil vitamin E cytoprotective effect and its nutrigenomics signature in human hepatocyte lipotoxicity

Wheat germ oil (WGO) is rich in α-tocopherol (vitamin E, VE), a vitamin that has long been suggested to exert hepatoprotective effects. In this study, this function of WGO-VE and its transcriptomics fingerprint were investigated in comparison with RRR-α-tocopherol and all-rac-α-tocopherol (nVE and sVE, respectively), in human liver cells treated with oleic acid (OA) to develop steatosis and lipotoxicity. Used in chemoprevention mode, all the VE formulations afforded significant reduction of the OA-induced steatosis and its consequent impact on lipotoxicity indicators, including ROS production and efflux (as H₂O₂), and apoptotic and necrotic cell death. A trend toward a better control of lipotoxicity was observed for WGO-VE and nVE compared to sVE. Gene microarray data demonstrated that these effects of VE formulations were associated with significantly different responses of the cellular transcriptome to compensate for the modifications of OA treatment, including the downregulation of cellular homeostasis genes and the induction of genes associated with defects of liver cell metabolism, fibrosis and inflammation, liver disease and cancer. Ingenuity Pathway Analysis data showed that WGO-VE modulated genes associated with liver carcinogenesis and steatosis, whereas nVE modulated genes involved in liver cell metabolism and viability biofunctions; sVE did not significantly modulate any gene dataset relevant to such biofunctions. In conclusion, WGO-VE prevents lipotoxicity in human liver cells modulating genes that differ from those affected by the natural or synthetic forms of pure VE. These differences can be captured by precision nutrition tools, reflecting the molecular complexity of this VE-rich extract and its potential in preventing specific cues of hepatocellular lipotoxicity.

Spatiotemporal biodistribution of α-tocopherol is impacted by the source of 13C-labeled α-tocopherol in mice following a single oral dose

Natural (RRR-) α-tocopherol (αT) is more bioactive than synthetic (all racemic, all rac-) αT, but not enough is known about the tissue kinetics of the 2 αT sources. We examined the time-course bioaccumulation of natural versus synthetic αT in tissues of young, marginally vitamin E-deficient mice using ¹³C-RRR-αT or ¹³C-all rac-αT tracers. In experiment 1, 3-week old male wild-type mice were fed a vitamin E-deficient diet for 0, 1, 2, or 3 weeks (n = 5/time point). Tissue αT levels were analyzed by HPLC-PDA. Feeding a vitamin E-deficient diet for up to 3 weeks decreased total αT concentrations in all analyzed tissues except the brain, which maintained its αT level. In experiment 2, a 2-week αT-depletion period was followed by administration of a single oral dose of 0.5 mg of ¹³C-RRR-αT or ¹³C-all rac-αT. At 12 hr, 1, 2, and 4 days post-dose, serum and multiple tissues were collected (n = 3/time point). αT was quantified by HPLC-PDA, and ¹³C-αT enrichment was determined by LC-MS. Both sources of ¹³C-αT reached maximum serum levels at 12 hr post-dose. ¹³C-RRR-αT levels were significantly higher than ¹³C-all rac-αT in serum at 1 d post-dose, and in heart, lungs, and kidney at 2d post-dose. In brain, ¹³C-RRR-αT concentrations were significantly higher than ¹³C-all rac-αT at 2 and 4 d post-dose. At 4 d post-dose, ¹³C-αT levels were similar between the 2 sources in examined tissues except for brain and adipose tissue where ¹³C-RRR-αT was higher. In conclusion, αT bioaccumulation over time varied substantially depending on αT source and tissue type.

Infant Rhesus Macaque Brain α-Tocopherol Stereoisomer Profile Is Differentially Impacted by the Source of α-Tocopherol in Infant Formula

BACKGROUND

α-Tocopherol (αT) in its natural form [2'R, 4'R, 8'R αT (RRR-αT)] is more bioactive than synthetic α-tocopherol (all rac-αT). All rac-αT is widely used in infant formulas, but its accretion in formula-fed infant brain is unknown.

OBJECTIVE

We sought to compare αT and stereoisomer status in infant rhesus macaques (Macaca mulatta) fed infant formula (RRR-αT or all rac-αT) with a reference group fed a mixed diet of breast milk and maternal diet.

METHODS

From 1 d after birth until 6 mo of age, infants (n = 23) were either nursery reared and exclusively fed 1 of 2 formulas by staff personnel or were community housed with their mothers and consumed a mixed reference diet of breast milk (69 mL/d at 6 mo) transitioning to monkey diet at ∼2 mo (MF; n = 8). Formulas contained either 21 μmol RRR-αT/L (NAT-F; n = 8) or 30 μmol all rac-αT/L (SYN-F; n = 7). Total αT and αT stereoisomers were analyzed in breast milk at 2, 4, and 6 mo and in monkey plasma and liver and 6 brain regions at 6 mo of age. α-Tocopherol transfer protein (α-TTP), lipoprotein αT, and urinary α-carboxyethyl-hydroxychroman (α-CEHC) were measured. One-way ANOVA with Tukey's post-hoc test was used for analysis.

RESULTS

At study termination, plasma, liver, lipoprotein, and brain total αT did not differ between groups. However, the NAT-F-fed group had higher RRR-αT than the SYN-F-fed group (P < 0.01) and the MF group (P < 0.0001) in plasma (1.7- and 2.7-fold) and brain (1.5- and 2.5-fold). Synthetic αT 2R stereoisomers (SYNTH-2R) were generally 3- and 7-fold lower in brain regions of the NAT-F group compared with those of the SYN-F and MF groups (P < 0.05). SYNTH-2R stereoisomers were 2-fold higher in MF than SYN-F (P < 0.0001). The plasma percentage of SYNTH-2R was negatively correlated with the brain percentage of RRR-αT (r = -0.99, P < 0.0001). Brain αT profiles were not explained by α-TTP mRNA or protein expression. Urine α-CEHC was 3 times higher in the NAT-F than in the MF group (P < 0.01).

CONCLUSIONS

Consumption of infant formulas with natural (NAT-F) compared with synthetic (SYN-F) αT differentially impacted brain αT stereoisomer profiles in infant rhesus macaques. Future studies should assess the functional implications of αT stereoisomer profiles on brain health.

Form of Vitamin E Supplementation Affects Oxidative and Inflammatory Response in Exercising Horses

Vitamin E is an essential antioxidant that may benefit athletes by reducing oxidative stress and influencing cytokine expression. Supplements can be derived from natural or manufactured synthetic sources. This study aimed to determine (1) if supplemental vitamin E is beneficial to exercising horses and (2) if there is a benefit of natural versus synthetic vitamin E. After 2 weeks on the control diet (vitamin E-deficient grain and hay), 18 horses were divided into three groups and fed the control diet plus (1) 1000 IU/d synthetic α-tocopherol (SYN-L), (2) 4000 IU/d synthetic α-tocopherol (SYN-H), or (3) 4000 IU/d RRR-α-tocopherol (natural source [NAT]). On day 7, horses began a 6-week training protocol, with standard exercise tests (SETs) performed before and after the 6-week protocol. Venous blood samples were collected on days 0, 7, 29, and 49. Horses fed NAT had higher α-tocopherol (P < .05) at post-SET1 through post-SET2. Plasma thiobarbituric acid-reactive substance levels were lower in NAT versus SYN-L horses after SET2 (P = .02). Serum aspartate aminotransferase was lower after exercise in NAT horses versus SYN-L and SYN-H (P = .02), and less reduction in stride duration was seen after exercise in NAT as compared with SYN-L and SYN-H (P = .02). Gene expression of tumor necrosis factor α was lower in NAT compared with SYN-H (P = .01) but not SYN-L. In conclusion, feeding higher levels of natural vitamin E source resulted in higher serum α-tocopherol levels as well as some improvement in oxidative and inflammatory response and improved functional outcomes in response to an exercise test.

Biodiscrimination of α-tocopherol stereoisomers in plasma and tissues of lambs fed different proportions of all-rac-α-tocopheryl acetate and RRR-α-tocopheryl acetate1,2

A ratio of 1.36:1 in relative bioactivity of RRR-α-tocopheryl acetate as a natural (Nat-α-T) source to all-rac-α-tocopheryl-acetate, as a synthetic (Syn-α-T) source, is generally accepted. This factor also largely reflects the difference in bioavailability. However, studies indicate that neither bioavailability of α-tocopherol stereoisomers nor relative bioavailability between them are constant, but are dose-dependent and differ between organs. However, no information is available about how different ratios between synthetic and natural α-tocopherol affect bioavailability of α-tocopherol stereoisomers. Thirty lambs were randomly assigned to diets supplied with additives containing 5 different Syn-α-T to Nat-α-T ratios, including 100:0, 75:25, 50:50, 25:75, and 0:100. The experiment lasted for 70 d after which the lambs were slaughtered. The amount of RRR-α-tocopherol generally increased in plasma and organs with increasing the proportion of Nat-α-T in the diet (P < 0.05). However, the relative bioavailability of RRR- and RRS-α-tocopherol in plasma, organs, and abdominal fat generally decreased with increasing the proportion of Nat-α-T in the diet (P < 0.05), whereas the other stereoisomers only showed minor changes with the exception of liver. However, a linear response was maintained between the ratio of stereoisomers in the feed and the ratio in plasma and organs. In conclusion, regardless of Syn-α-T to Nat-α-T ratio in the diets, amounts of α-tocopherol stereoisomers in plasma, brain, heart, lungs, and abdominal fat were in the following order: RRR > RRS, RSR, RSS > Σ2S.

Bioavailability of α-tocopherol stereoisomers in lambs depends on dietary doses of all-rac- or RRR-α-tocopheryl acetate

When supplementing lamb diets with vitamin E, an equivalence factor of 1.36 is used to discriminate between RRR-α-tocopheryl acetate and all-rac-α-tocopheryl acetate. However, more recent studies suggest a need for new equivalence factors for livestock animals. The current study aimed to determine the effect of RRR- and all-rac-α-tocopheryl acetate supplementation on α-tocopherol deposition in lamb tissues. A total of 108 Rasa Aragonesa breed lambs were fed increasing amounts of all-rac-α-tocopheryl acetate (0.25, 0.5, 1.0 and 2.0 g/kg compound feed) or RRR-α-tocopheryl acetate (0.125, 0.25, 0.5 and 1.0 g/kg compound feed) by adding them to a basal diet that contained 0.025 g/kg feed of all-rac-α-tocopheryl acetate as part of the standard vitamin and mineral mixture. The diets were fed for the last 14 days before slaughtering at 25.8±1.67 kg BW. Within 20 min after slaughter samples of muscle, heart, liver, brain and spleen were frozen at -20°C until α-tocopherol analysis. Increased supplementation of either vitamin E sources led to a significant increase (P < 0.001) in α-tocopherol concentration in all tissues studied. The tissue with the highest α-tocopherol concentration was the liver followed by spleen, heart and muscle. At similar supplementation levels (0.25, 0.50 and 1.0 g/kg compound feed), α-tocopherol content in the selected tissues was not affected by α-tocopherol source. However, the ratios between RRR- and all-rac-α-tocopheryl acetate increased with the increasing α-tocopherol supplementation (at 0.25 and 1.0 g/kg compound feed), from 1.06 to 1.16 in muscle, 1.07 to 1.15 in heart, 0.91 to 0.94 in liver and 0.98 to 1.10 in spleen. The highest relative proportion of Ʃ2S (sum of SSS-, SSR-, SRS- and SRR-α-tocopherol)-configured stereoisomers was found in the liver of lambs supplemented with all-rac-α-tocopheryl acetate accounting for up to 35 to 39% of the total α-tocopherol retained, whereas the proportion of Ʃ2S-configured stereoisomers in the other tissues accounted for <14%. Increasing all-rac-α-tocopheryl acetate supplementation was also found to affect the 2R-configured stereoisomer profile in muscle, heart and spleen with increasing proportions of RRS-, RSR- and RSS- at the cost of RRR-α-tocopherol. In all tissues, the relative proportion of all non-RRR-stereoisomers in lambs receiving RRR-α-tocopheryl acetate was lower than RRR-α-tocopherol. These results confirm that the relative bioavailability of RRR- and all-rac-α-tocopheryl acetate is dose- and tissue-dependent and that a single ratio to discriminate the two sources cannot be used.

Identification and expression analysis of alpha tocopherol transfer protein in chickens fed diets containing different concentrations of alpha-tocopherol

Among the eight forms of vitamin E, the liver preferentially releases α-tocopherol into the circulation and it is distributed to the non-liver tissues. In the hepatocytes, alpha tocopherol transfer protein (TTPA) specifically recognizes α-tocopherol with 2R-configuration and facilitates its intracellular transfer. The identification and characterization of TTPA expression have not been demonstrated in avian species. Therefore, the objectives of this study were to identify avian TTPAs, to compare the sequence conservation, phylogenetic relationship, protein interactions, and disease associations of chicken TTPA with those of human and vertebrate TTPA, and to characterize the tissue expression of the TTPA gene in chickens fed diets supplemented with different amounts of α-tocopherol. Our results suggest that the chicken TTPA was highly conserved with the human and vertebrate TTPA, and consisted of a cellular retinaldehyde binding protein and TRIO guanine exchange factor (CRAL_TRIO) domain. Feeding diets supplemented with increasing amounts of α-tocopherol (25 IU/Kg, 50 IU/Kg, or 100 IU/Kg) to broiler chickens had no effects on growth performance compared with feeding basal diets containing no supplemental α-tocopherol. The expression of TTPA gene was detected high in the liver of chickens in response to dietary α-tocopherol concentrations, whereas its expression was very low or undetectable in the non-liver tissues. In conclusion, the chicken TTPA protein sequence is highly conserved with other avian and vertebrate TTPA protein sequences. The higher expression of TTPA gene in the chicken liver in response to dietary α-tocopherol concentrations may suggest its crucial role in transporting α-tocopherol in the chicken liver.

Characteristics of lipids and their feeding value in swine diets

In livestock diets, energy is one of the most expensive nutritional components of feed formulation. Because lipids are a concentrated energy source, inclusion of lipids are known to affect growth rate and feed efficiency, but are also known to affect diet palatability, feed dustiness, and pellet quality. In reviewing the literature, the majority of research studies conducted on the subject of lipids have focused mainly on the effects of feeding presumably high quality lipids on growth performance, digestion, and metabolism in young animals. There is, however, the wide array of composition and quality differences among lipid sources available to the animal industry making it essential to understand differences in lipid composition and quality factors affecting their digestion and metabolism more fully. In addition there is often confusion in lipid nomenclature, measuring lipid content and composition, and evaluating quality factors necessary to understand the true feeding value to animals. Lastly, advances in understanding lipid digestion, post-absorption metabolism, and physiological processes (e.g., cell division and differentiation, immune function and inflammation); and in metabolic oxidative stress in the animal and lipid peroxidation, necessitates a more compressive assessment of factors affecting the value of lipid supplementation to livestock diets. The following review provides insight into lipid classification, digestion and absorption, lipid peroxidation indices, lipid quality and nutritional value, and antioxidants in growing pigs.

Effect of vitamin E supplementation and diet on fatty acid composition and on meat colour and lipid oxidation of lamb leg steaks displayed in modified atmosphere packs

Groups of 8 lambs were allocated to one of five concentrate diets supplemented with all-rac-α-tocopheryl acetate containing 30 (C30), 60 (C60), 120 (C120), 250 (C250) and 500 (C500) mg/kg dry matter. Two other groups were fed grass silage and 400 g/day concentrate with 60 (S60) or 500 (S500) mg α-tocopheryl acetate/kg dry matter. Within diet, vitamin E level did not affect growth performance or carcass characteristics. Basal diet did not affect final live weight, conformation and fatness scores. M. semimembranosus from S lambs contained more α-tocopherol than that of C lambs on the same intake and by day 6 in MAP (75%O2/25%CO2) chroma and a* were below acceptable levels in C30 lambs. TBARS were higher in C30 and C60 muscle than in other treatments (P<0.001) after 3 and 6 days display. Muscle fatty acid composition varied with basal diet but lipid oxidation depended more on vitamin E concentration with an initial concentration of 1.9 μg/g muscle preventing significant lipid oxidation.

Meta-analysis of the effects of dietary vitamin E supplementation on α-tocopherol concentration and lipid oxidation in pork

Meta-analyses have been carried out to quantify the effect of dietary vitamin E on α-tocopherol accumulation and on lipid oxidation in porcine M. longissimus. Published results of 13 (vitamin E accumulation) and 10 (lipid oxidation) experiments respectively were used for the analyses. After a number of standardization procedures, a nonlinear relationship was found between the supplementary vitamin E and the accumulation of α-tocopherol in pork which approached a maximum value of 6.4 μg/g tissue. Pork lipid oxidation levels were described in terms of Thiobarbituric Acid Reacting Substances (TBARS) values. The statistical analysis revealed significant effect of vitamin E dose, muscle α-tocopherol concentration and supplementation time on TBARS, resulting in two prediction models for lipid oxidation. Meta-analysis has proven to be a valuable tool for combining results from previous studies to quantify the effects of dietary vitamin E. Further studies, carried out with standardized experimental protocols would be beneficial for model validation and to increase the predictive power of the derived models.

A critical review of methodologies used in determination of relative bio-availability ratio of RRR-alpha-tocopheryl acetate and all-rac-alpha-tocopheryl acetate

Bio-availability of different alpha-tocopherol forms in livestock animals is measured by the increase in plasma or tissue concentrations of alpha-tocopherol after oral administration. It is generally accepted that RRR-alpha-tocopheryl acetate (natural source vitamin E derived from vegetable oil) has a higher bio-availability compared to all-rac-alpha-tocopheryl acetate (synthetic vitamin E, i.e. alpha-tocopherol produced by chemical synthesis). However, different bio-availability ratios have been reported in the literature. The major reason for conflicting results in literature studies was the inability to separate the proportion of alpha-tocopherol originating from test materials, from the proportion of alpha-tocopherol originating from basal dietary ingredients and pre-feeding. This causes significant variability. For bio-availability determination, a baseline or control treatment is essential. The estimation of bio-availability without correction for basal vitamin E status will lead to incorrect interpretation of the results. When using proper methodologies, it is possible to correct for the impact of alpha-tocopherol intake from basal ingredients and alpha-tocopherol originating from pre-feeding, therefore yielding results reflecting the true relative bio-availability of different alpha-tocopherol substances. When reviewing literature data a critical evaluation of the method used in determination of relative bio-availability is recommended.

Utilization of stereoisomers from alpha-tocopherol in livestock animals

Alpha-tocopherol derived from natural source is a single stereoisomer (i.e. RRR-alpha-tocopherol), whereas synthetic alpha-tocopherol consists of a mixture of eight stereoisomers, including RRR-, RRS-, RSR-, RSS-alpha-tocopherol (the 2R isomers, R configuration at positions 2' of the phytyl tail) and SRR-, SSR-, SRS- and SSS-alpha-tocopherol (the 2S isomers, S configuration at positions 2' of the phytyl tail). R and S are assigned by the sequence-rule procedure, i.e. the priorities of the substituents decrease in clockwise direction or anti-clockwise direction at each chiral centre. Not all these stereoisomers are equally bio-available, which can be explained by the differences in the rate of degradation, transportation and retention. Humans and livestock animals can only utilize the 2R forms, while the 2S forms have very low bio-availability or basically are not bio-available. The utilization of 2R forms differs between different animal species. For humans and livestock animals, RRR-alpha-tocopherol has the highest bio-availability compared with other stereoisomers, while other 2R forms have lower bio-availability compared with RRR-alpha-tocopherol. The relative bio-availability of RRR- and all-rac-alpha-tocopherol is related to animal species, ages of animals and assessment criteria. In general, recent literature studies have demonstrated that the relative bioavailability of RRR- and all-rac-alpha-tocopherol is 2:1, differing from the commonly used conversion factor of 1.36:1. The latter was based on rat-resorption-gestation test. Most recent studies have shown that this conversion factor of 1.36:1 is not applicable to livestock animals and based on other metabolic functions. When IU is required to express vitamin E activity, new conversion factors need to be defined for livestock animals. Quantitative determination of bio-availability of the individual alpha-tocopherol stereoisomers will give a more detailed picture of the bioavailability of natural and synthetic vitamin E forms.

Bioavailability of α-tocopherol stereoisomers in rats depends on dietary doses ofall-rac- or RRR-α-tocopheryl acetate

The biological function of the stereoisomers of α-tocopherol is believed to depend on their bioavailability. Assessment of bioavailability within the body is therefore considered to be a good and easy way to predict biological value. The separation of α-tocopherol methyl ethers by chiral column HPLC is a good and easy tool with which to study the distribution of α-tocopherol stereoisomers. The objective of this investigation was to evaluate the bioavailability and distribution of the stereoisomers of α-tocopherol in the plasma and tissue in growing rats fed 25, 50, 100 or 200mg/kg diet of either RRR- orall-rac-α-tocopheryl acetate for 10d. The ratio between the two vitamin E sources based on their α-tocopherol concentration in plasma and tissues varied in the plasma between 1·04 and 1·74 and in tissues, ratios of 0·84–1·24 for liver, 0·34–1·59 for lung and 0·75–1·50 for spleen were obtained. An increasing dietary level ofall-rac-α-tocopheryl acetate decreased the proportion of RRR-α-tocopherol, whereas the other stereoisomers were not affected. RRS-α-Tocopherol was present in the highest proportion, followed by RSR-, RSS- and RRR-α-tocopherol. In contrast to the other tissues and plasma, the liver contained the highest proportion (29–33%) of the four 2S stereoisomers of total α-tocopherol. Rats fed RRR-α-tocopheryl acetate for 10d showed a significant increase in the plasma and tissue content of RRR-α-tocopherol and a simultaneous decrease in the other three 2R isomers, whereas the absolute content of the 2S isomers was unaffected. In adipose tissue, concentrations of the three synthetic 2R isomers remained constant, whereas there was a steep increase in the content of RRR-α-tocopherol.

Alpha-tocopherol stereoisomers

Vitamin E comprises a group of compounds possessing vitamin E activity. alpha-Tocopherol is the compound demonstrating the highest vitamin E activity, which is available both in its natural form as RRR-alpha-tocopherol isolated from plant sources, but more common as synthetically manufactured all-rac-alpha-tocopherol. Synthetic all-rac-alpha-tocopherol consists of a racemic mixture of all eight possible stereoisomers. Assessing the correct biological activity in form of bioavailability and biopotency has been a great challenge during many years as it is difficult to measure clinical endpoints in larger animals than rats and poultry. Thus, the biological effects in focus are resorption of fetuses, testicular degeneration, muscle dystrophy, anemia, encephalomalacia, and in recent years the influence of vitamin E on the immune system are the most important clinical markers of interest. For humans and animals, only different biomarkers or surrogate markers of bioactivity have been measured. In studies with rats, a good consistency between the classical resorption-gestation test and the bioavailability of the individual stereoisomers in fluids and tissues has been shown. For humans and other animals, only different biomarkers or surrogate markers of bioactivity have been measured, and due to the lack of good biological markers for bioactivities, bioavailability is often used as one of the surrogate markers for bioactivities with those limitations this must give. Therefore, a relatively simple analytical method, which allows analysis of the individual stereoisomers of alpha-tocopherol, is an important tool in order to quantify relative bioavailability of the individual stereoisomers. The analytical method presented here allows the quantification of total tocopherol content and composition by normal phase HPLC and subsequent separation of the stereoisomers of alpha-tocopherol as methyl ethers by chiral HPLC. Using this method, the alpha-tocopherol stereoisomers are separated into five peaks. The first peak consists of the four 2S isomers (SSS-, SSR-, SRR-, SRS-), the second peak consists of RSS-, the third peak consists of RRS-, the fourth peak consists of RRR-, and the fifth peak consists of RSR-alpha-tocopherol. The discussion on the bioavailability of RRR- and all-rac-alpha-tocopheryl acetate has primarily been based on human and animal studies using deuterium-labeled forms, whereby a higher biopotency of 2:1 (of RRR: all-rac) has been demonstrated, differing from the accepted biopotency ratio of 1.36:1. In agreement with previous studies, the 2S-forms exert very little importance for the vitamin E activity due to their limited bioavailability. We find notable differences between animal species with regard to the biodiscrimination between the 2R-forms. Especially, cows preferentially transfer RRR- alpha-tocopherol into the milk and blood system. The distribution of the stereoisomer forms varies from tissue to tissue, and in some cases, higher levels of the synthetic 2R-forms than of the RRR-form are obtained, for example, for rats. However, the biodiscrimination of the stereoisomers forms is influenced by other factors such as age, dietary levels, and time after dosage. More focus should be given on the bioactivity of the individual 2R-forms rather than just the comparison between RRR- and all-rac-alpha-tocopheryl acetate.

Lactating sows and suckling piglets preferentially incorporate RRR- over all-rac-alpha-tocopherol into milk, plasma and tissues

Synthetic vitamin E, all-rac-alpha-tocopherol, contains eight different stereoisomers, only one of which, RRR-alpha-tocopherol, occurs naturally. The objective of this investigation was to evaluate the relative abilities of these two vitamin E forms to enrich piglet tissues when fed as alpha-tocopheryl acetates to sows during pregnancy and lactation. alpha-Tocopherol delivery to fetuses and to suckling piglets was monitored by feeding 150 mg each of d(3)-RRR-alpha- and d(6)-all-rac-alpha-tocopheryl acetate to three pregnant sows daily from 7 d before to 7 d after giving birth. Labeled and unlabeled vitamin E concentration ratios were measured in sow plasma and milk, and in piglet (n = 9) plasma and tissues at birth, 7 and 21 d. At birth, despite elevated sow plasma deuterated alpha-tocopherol concentrations, no labeled alpha-tocopherol was detected in piglet plasma or tissues. Sow plasma and milk d(3)-alpha- to d(6)-alpha-tocopherol concentrations were 2:1, leading to a 2:1 ratio in suckling piglet plasma and tissues. In piglets at d 7 compared with birth, most tissues contained a 10-fold increase in total alpha-tocopherol; the highest deuterated vitamin E concentrations were in the liver, followed by the lung, heart, kidney, muscle, intestine and brain. In conclusion, pigs discriminate between RRR- and all-rac-alpha-tocopherol with a preference for RRR-alpha-tocopherol; thus, the official bioequivalence ratio of 1.36:1 RRR- to all-rac-alpha-tocopherol is underestimated. After initiation of suckling, piglet plasma and tissues demonstrated a dramatic increase in vitamin E concentrations, emphasizing the limited placental vitamin E transfer and the importance of milk for enhancing the vitamin E status of the newborn.

Vitamin E kinetics and the function of tocopherol regulatory proteins

Plasma and tissue alpha-tocopherol concentrations are remarkably stable, which suggests that they are regulated. alpha-Tocopherol transfer protein, tocopherol-associated protein, and tocopherol-binding protein bind alpha-tocopherol. These proteins might function as tocopherol regulatory proteins, although only tocopherol transfer protein has been shown to influence plasma and tissue alpha-tocopherol concentrations. Tissue alpha-tocopherol concentrations likely depend on tocopherol regulatory protein function and tissue lipid content, vitamin E uptake and efflux, oxidative stress, and interactions between vitamin E and other antioxidants. Pharmacokinetic models often divide tissues into rapidly perfused, slowly perfused, and very slowly perfused compartments. Tissue vitamin E concentrations might equilibrate more rapidly in tissues with greater perfusion, greater vitamin E uptake, increased amounts or activities of tocopherol regulatory protein, and lower lipid contents. The rate at which tissue concentrations approach equilibrium, however, does not predict the final equilibrium concentrations because of redistribution among tissues. Redistribution of vitamin E to adipose tissue from other tissues may be significant. Intracellular trafficking of vitamin E might occur in conjunction with membrane recycling because membrane constituents rapidly recycle between the plasma membrane and intracellular endocytic compartments. Thus, tocopherol regulatory proteins may modulate rather than directly regulate vitamin E tissue distribution and intracellular trafficking.