Long-chain carboxychromanols, metabolites of vitamin E, are potent inhibitors of cyclooxygenases. Proc Natl Acad Sci U S A. 2008;105:20464-20469. [PMID: 19074288 DOI: 10.1073/pnas.0810962106]

Enzymatic sulfation of tocopherols and tocopherol metabolites by human cytosolic sulfotransferases

Tocopherols are essential micronutrients for mammals widely known as potent lipid-soluble antioxidants that are present in cell membranes. Recent studies have demonstrated that most of the carboxychromanol (CEHC), a tocopherol metabolite, in the plasma exists primarily in sulfate- and glucuronide-conjugated forms. To gain insight into the enzymatic sulfation of tocopherols and their metabolites, a systematic investigation was performed using all 14 known human cytosolic sulfotransferases (SULTs). The results showed that the members of the SULT1 family displayed stronger sulfating activities toward tocopherols and their metabolites. These enzymes showed a substrate preference for γ-tocopherol over α-tocopherol and for γ-CEHC over other CEHCs. Using A549 human lung epithelial cells in a metabolic labeling study, a similar trend in the sulfation of tocopherols and CEHCs was observed. Collectively, the results obtained indicate that SULT-mediated enzymatic sulfation of tocopherols and their metabolites is a significant pathway for regulation of the homeostasis and physiological functions of these important compounds.

Effectiveness of antioxidants (propolis, blueberry, vitamin E) associated with verapamil in the medical management of Peyronie's disease: a study of 151 cases

A total of 151 patients (age: 24–74 years, mean: 55 ± 10.3) diagnosed with Peyronie's disease were enrolled in a non-surgical treatment. In addition to medical histories and physical examinations, all patients underwent the following tests: penile ultrasound, IIEF questionnaire and photographic documentation. The penile curvature was measured by taking a photograph during maximum erection. All 151 patients were treated at different times and with different combinations of drugs, and afterwards, they were clinically studied and divided into five different treatment groups: 1st = verapamil (injection + iontophoresis) + vitamin E + topical diclofenac + blueberries; 2nd = verapamil (injection + iontophoresis) + vitamin E + topical diclofenac + propolis; 3rd = verapamil (injection) + vitamin E + topical Diclofenac; 4th = verapamil (iontophoresis) + vitamin E + topical diclofenac; 5th = verapamil (injection + iontophoresis) + topical diclofenac + blueberries + propolis. All patients were treated for 6 months after which they underwent the same follow-up tests as performed prior to the treatment. The following was achieved: group 1 had the most reduction in plaque size (−66.4%; p = 0.000), group 2 obtained the highest rate where penile curvature disappeared (24.5%; p = 0.019); the best results with reference to decrease in curvature angle were reached by the 2nd group (−14°) and group 1 obtained −9.6° (p = 0.000).

Vitamin E forms inhibit IL-13/STAT6-induced eotaxin-3 secretion by up-regulation of PAR4, an endogenous inhibitor of atypical PKC in human lung epithelial cells

Eotaxin-3 (CCL-26), a potent chemokine for eosinophil recruitment and contributing significantly to the pathogenesis of asthma, is secreted by lung epithelial cells in response to T helper 2 cytokines including interleukin 13 (IL-13). Here we showed that vitamin E forms, but not their metabolites, differentially inhibited IL-13-stimulated generation of eotaxin-3 in human lung epithelial A549 cells. The relative inhibitory potency was γ-tocotrienol (γ-TE) (IC50 ~15 μM)>γ-tocopherol, δ-tocopherol (IC50 ~25-50 μM)>α-tocopherol. Consistent with suppression of eotaxin, γ-TE treatment impaired IL-13-induced phosphorylation of STAT6, the key transcription factor for activation of eotaxin expression, and consequently blocked IL-13-stimulated DNA-binding activity of STAT6. In search of the upstream target of γTE by using inhibitor and siRNA approaches, we discovered that the atypical protein kinase C (aPKC) signaling, instead of classical PKC, p38 MAPK, JNK or ERK, played a critical role in IL-13-stimulated eotaxin generation and STAT6 activation. While showing no obvious effect on aPKC expression or phosphorylation, γ-TE treatment resulted in increased expression of prostate-apoptosis-response 4 (PAR4), an endogenous negative regulator of aPKCs. Importantly, γ-TE treatment led to enhanced formation of aPKC/PAR4 complex that is known to reduce aPKC activity via protein-protein crosstalk. Our study demonstrated that γ-TE inhibited IL-13/STAT6-activated eotaxin secretion via up-regulation of PAR4 expression and enhancement of aPKC-PAR4 complex formation. These results support the notion that specific vitamin E forms may be useful anti-asthmatic agents.

Metabolism of tocotrienols in animals and synergistic inhibitory actions of tocotrienols with atorvastatin in cancer cells

Tocotrienols (T3s), members of the vitamin E family, exhibit potent anti-cancer, anti-oxidative, anti-inflammatory, and some other biological activities. To better understand the bioavailability and metabolism of T3s, T3s and their metabolites were identified in urine and fecal samples from mice on diet supplemented with mixed T3s using HPLC/electrochemical detection and liquid chromatography electrospray ionisation mass spectrometry (LC-ESI-MS). Whereas the short-chain metabolites carboxyethyl hydroxychromans (CEHCs) and carboxymethylbutyl hydroxychromans (CMBHCs) were the major metabolites of T3s, several new metabolites with double bonds were also identified. Similar to tocopherols, the majority of T3 metabolites were excreted as sulfate/glucuronide conjugates in mouse urine. The distribution of γ- and δ-T3 and γ-T3 metabolites were also determined in different organs as well as in urine and fecal samples from mice on diets supplemented with corresponding T3s. The synergistic anti-cancer actions of γ-T3 and atorvastatin (ATST) were studied in HT29 and HCT116 colon cancer cell lines. The combination greatly potentiated the ability of each individual agent to inhibit cancer cell growth and to induce cell cycle arrest and apoptosis. The triple combination of γ-T3, ATST, and celecoxib exhibited synergistic actions when compared with any double combination plus the third agent. Mechanistic studies revealed that the synergistic actions of γ-T3 and ATST could be attributed to their mediation of 3-hydroxy-3-methyl-glutaryl-CoA reductase, and the subsequent inhibition of protein geranylgeranylation. It remains to be determined whether such a synergy occurs in vivo.

Gamma-tocotrienol induces apoptosis and autophagy in prostate cancer cells by increasing intracellular dihydrosphingosine and dihydroceramide

Although cell-based studies have shown that γ-tocotrienol (γTE) exhibits stronger anticancer activities than other forms of vitamin E including γ-tocopherol (γT), the molecular bases underlying γTE-exerted effects remains to be elucidated. Here we showed that γTE treatment promoted apoptosis, necrosis and autophagy in human prostate PC-3 and LNCaP cancer cells. In search of potential mechanisms of γTE-provoked effects, we found that γTE treatment led to marked increase of intracellular dihydroceramide and dihydrosphingosine, the sphingolipid intermediates in de novo sphingolipid synthesis pathway but had no effects on ceramide or sphingosine. The elevation of these sphingolipids by γTE preceded or coincided with biochemical and morphological signs of cell death and was much more pronounced than that induced by γT, which accompanied with much higher cellular uptake of γTE than γT. The importance of sphingolipid accumulation in γTE-caused fatality was underscored by the observation that dihydrosphingosine and dihydroceramide potently reduced the viability of both prostate cell lines and LNCaP cells, respectively. In addition, myriosin, a specific inhibitor of de novo sphingolipid synthesis, counteracted γTE-induced cell death. In agreement with these cell-based studies, γTE inhibited LNCaP xenograft growth by 53% (p < 0.05), compared to 33% (p = 0.07) by γT, in nude mice. These findings provide a molecular basis of γTE-stimulated cancer cell death and support the notion that elevation of intracellular dihydroceramide and dihydrosphingosine is likely a novel anticancer mechanism.

Why tocotrienols work better: insights into the in vitro anti-cancer mechanism of vitamin E

The selective constraint of liver uptake and the sustained metabolism of tocotrienols (T3) demonstrate the need for a prompt detoxification of this class of lipophilic vitamers, and thus the potential for cytotoxic effects in hepatic and extra-hepatic tissues. Hypomethylated (γ and δ) forms of T3 show the highest in vitro and in vivo metabolism and are also the most potent natural xenobiotics of the entire vitamin E family of compounds. These stimulate a stress response with the induction of detoxification and antioxidant genes. Depending on the intensity of this response, these genes may confer cell protection or alternatively they stimulate a senescence-like phenotype with cell cycle inhibition or even mitochondrial toxicity and apoptosis. In cancer cells, the uptake rate and thus the cell content of these vitamers is again higher for the hypomethylated forms, and it is the critical factor that drives the dichotomy between protection and toxicity responses to different T3 forms and doses. These aspects suggest the potential for marked biological activity of hypomethylated "highly metabolized" T3 that may result in cytoprotection and cancer prevention or even chemotherapeutic effects. Cytotoxicity and metabolism of hypomethylated T3 have been extensively investigated in vitro using different cell model systems that will be discussed in this review paper as regard molecular mechanisms and possible relevance in cancer therapy.

A paraptosis-like cell death induced by δ-tocotrienol in human colon carcinoma SW620 cells is associated with the suppression of the Wnt signaling pathway

Tocotrienol is considered a beneficial effect agent on inhibition of tumor development. In this study, we focused on the effects of δ-tocotrienol and its possible mechanism on induction of death in human colon cancer SW620 cells. δ-Tocotrienol inhibited proliferation of SW620 cell in a dose-dependent manner. Our findings showed that δ-tocotrienol effectively induced paraptosis-like death in SW620 cells, correlated with the vacuolation that may be from welling and fusion of mitochondria and/or the endoplasmic reticulum (ER) as well as caspase-3 nonactivated. However, there were no changes in apoptosis based on flow cytometry analysis. Of being noted, δ-tocotrienol reduced the expression of β-catenin and wnt-1 proteins by about 50% at the highest dose (20μmol/L). δ-Tocotrienol also decreased cyclin D1, c-jun and MMP-7 protein levels in SW620 cells. Altogether, these data indicate that δ-tocotrienol induces paraptosis-like cell death, which is associated with the suppression of the Wnt signaling pathway. Thus, our findings may provide a novel application in treatment of human colon carcinoma.

At the Frontier; RXLR Effectors Crossing the Phytophthora-Host Interface

Plants are constantly beset by pathogenic organisms. To successfully infect their hosts, plant pathogens secrete effector proteins, many of which are translocated to the inside of the host cell where they manipulate normal physiological processes and undermine host defense. The way by which effectors cross the frontier to reach the inside of the host cell varies among different classes of pathogens. For oomycete plant pathogens - like the potato late blight pathogen Phytophthora infestans - it has been shown that effector translocation to the host cell cytoplasm is dependent on conserved amino acid motifs that are present in the N-terminal part of effector proteins. One of these motifs, known as the RXLR motif, has a strong resemblance with a host translocation motif found in effectors secreted by Plasmodium species. These malaria parasites, that reside inside specialized vacuoles in red blood cells, make use of a specific protein translocation complex to export effectors from the vacuole into the red blood cell. Whether or not also oomycete RXLR effectors require a translocation complex to cross the frontier is still under investigation. For one P. infestans RXLR effector named IPI-O we have found a potential host target that could play a role in establishing the first contact between this effector and the host cell. This membrane spanning lectin receptor kinase, LecRK-I.9, interacts with IPI-O via the tripeptide RGD that overlaps with the RXLR motif. In animals, RGD is a well-known cell adhesion motif; it binds to integrins, which are membrane receptors that regulate many cellular processes and which can be hijacked by pathogens for either effector translocation or pathogen entry into host cells.

Lipid antioxidants: free radical scavenging versus regulation of enzymatic lipid peroxidation

The essentiality of polyunsaturated lipids makes membranes susceptible to peroxidative modifications. One of the most contemporary examples includes selective peroxidation of cardiolipin in mitochondria of cells undergoing apoptosis. Cardiolipin peroxidation products are required for the mitochondrial membrane permeabilization, release of pro-apoptotic factors and completion of the cell death program. Therefore, search for effective inhibitors of cardiolipin peroxidation is critical to discovery and development of anti-apoptotic antioxidants. Mitochondria contain significant amounts of α-tocopherol, a well known scavenger of reactive free radicals. In the present study, we used an oxidative lipidomics approach to evaluate the effect of α-tocopherol and its homologues with different lengths of the side-chain such as 2,5,7,8,-tetramethyl-2(4-methylpentyl)-6-chromanol and 2,2,5,7,8-pentamethyl-6-chromanol, on oxidation of tetralinoleoyl cardiolipin induced by cytochrome c in the presence of hydrogen peroxide. Our data indicate that vitamin E homologues inhibit not only accumulation of tetralinoleoyl cardiolipin hydroperoxides but also hydroxy-derivatives of tetralinoleoyl cardiolipin formed in the enzymatic peroxidase half-reaction catalyzed by cytochrome c. This suggests that protective effects of vitamin E homologues against tetralinoleoyl cardiolipin peroxidation catalyzed by cytochrome c/hydrogen peroxide are realized largely due to their effects on the peroxidase activity of cytochrome c towards tetralinoleoyl cardiolipin rather than via their scavenging activity.

Natural forms of vitamin E and 13'-carboxychromanol, a long-chain vitamin E metabolite, inhibit leukotriene generation from stimulated neutrophils by blocking calcium influx and suppressing 5-lipoxygenase activity, respectively

Leukotrienes generated by 5-lipoxygenase (5-LOX)-catalyzed reaction are key regulators of inflammation. In ionophore-stimulated (A23187; 1-2.5 μM) human blood neutrophils or differentiated HL-60 cells, vitamin E forms differentially inhibited leukotriene B(4) (LTB(4)) with an IC(50) of 5-20 μM for γ-tocopherol, δ-tocopherol (δT), and γ-tocotrienol, but a much higher IC(50) for α-tocopherol. 13'-Carboxychromanol, a long-chain metabolite of δT, suppressed neutrophil- and HL-60 cell-generated LTB(4) with an IC(50) of 4-7 μM and potently inhibited human recombinant 5-LOX activity with an IC(50) of 0.5-1 μM. In contrast, vitamin E forms had no effect on human 5-LOX activity but impaired ionophore-induced intracellular calcium increase and calcium influx as well as the subsequent signaling including ERK1/2 phosphorylation and 5-LOX translocation from cytosol to the nucleus, a key event for 5-LOX activation. Further investigation showed that δT suppressed cytosolic Ca(2+) increase and/or LTB(4) formation triggered by ionophores, sphingosine 1-phosphate, and lysophosphatidic acid but not by fMLP or thapsigargin, whereas 13'-carboxychromanol decreased cellular production of LTB(4) regardless of different stimuli, consistent with its strong inhibition of the 5-LOX activity. These observations suggest that δT does not likely affect fMLP receptor-mediated signaling or store depletion-induced calcium entry. Instead, we found that δT prevented ionophore-caused cytoplasmic membrane disruption, which may account for its blocking of calcium influx. These activities by vitamin E forms and long-chain carboxychromanol provide potential molecular bases for the differential anti-inflammatory effects of vitamin E forms in vivo.

Analysis of vitamin E metabolites in biological specimen

Vitamin E is known as the most important lipid antioxidant and is widely used to prevent age-associated diseases. Despite increasing knowledge about human vitamin E metabolism, little is known to justify its widespread use. As meta-analyses revealed even harmful effects of high vitamin E doses, a profound understanding of vitamin E metabolism is mandatory. By recent advances in analytical methodology, new metabolites with distinct physicochemical and biological properties were discovered. This review covers current methods to analyze vitamin E metabolites in biological samples. Special emphasis is laid on analytical applications for the identification and quantification of metabolites with a modified hydroxychromanol ring or a truncated side chain.

Inhibition of inflammation and carcinogenesis in the lung and colon by tocopherols

Tocopherols, which exist in alpha, beta, gamma, and delta forms, are antioxidative nutrients also known as vitamin E. Although alpha-tocopherol (alpha-T) is the major form of vitamin E found in the blood and tissues, gamma- and delta-T have been suggested to have stronger anti-inflammatory activities. In the present study, using a tocopherol mixture that is rich in gamma-T (gamma-TmT, which contains 57%gamma-T), we demonstrated the inhibition of inflammation as well as of cancer formation and growth in the lung and colon in animal models. When given in the diet at 0.3%, gamma-TmT inhibited chemically induced lung tumorigenesis in the A/J mice as well as the growth of human lung cancer cell H1299 xenograft tumors. gamma-TmT also decreased the levels of 8-hydroxydeoxyguanosine, gamma-H2AX, and nitrotyrosine in tumors. More evident anti-inflammatory and cancer preventive activities of dietary gamma-TmT were demonstrated in mice treated with azoxymethane and dextran sulfate sodium. These results demonstrate the antioxidative, anti-inflammatory, and anticarcinogenic activities of tocopherols.

Tocotrienols, the vitamin E of the 21st century: its potential against cancer and other chronic diseases

Initially discovered in 1938 as a "fertility factor," vitamin E now refers to eight different isoforms that belong to two categories, four saturated analogues (α, β, γ, and δ) called tocopherols and four unsaturated analogues referred to as tocotrienols. While the tocopherols have been investigated extensively, little is known about the tocotrienols. Very limited studies suggest that both the molecular and therapeutic targets of the tocotrienols are distinct from those of the tocopherols. For instance, suppression of inflammatory transcription factor NF-κB, which is closely linked to tumorigenesis and inhibition of HMG-CoA reductase, mammalian DNA polymerases and certain protein tyrosine kinases, is unique to the tocotrienols. This review examines in detail the molecular targets of the tocotrienols and their roles in cancer, bone resorption, diabetes, and cardiovascular and neurological diseases at both preclinical and clinical levels. As disappointment with the therapeutic value of the tocopherols grows, the potential of these novel vitamin E analogues awaits further investigation.

Analysis of multiple metabolites of tocopherols and tocotrienols in mice and humans

Tocopherols and tocotrienols, collectively known as vitamin E, are essential antioxidant nutrients. The biological fates and metabolite profiles of the different forms are not clearly understood. The objective of this study is to simultaneously analyze the metabolites of different tocopherols and tocotrienols in mouse and human samples. Using HPLC/electrochemical detection and mass spectrometry, 18 tocopherol-derived and 24 tocotrienol-derived side-chain degradation metabolites were identified in fecal samples. Short-chain degradation metabolites, in particular gamma- and delta-carboxyethyl hydroxychromans (CEHCs) and carboxymethylbutyl hydroxychromans (CMBHCs) were detected in urine, serum, and liver samples, with tocopherols additionally detected in serum and liver samples. The metabolite profiles of tocotrienols and tocopherols were similar, but new tocotrienol metabolites with double bonds were identified. This is the first comprehensive report describing simultaneous analysis of different side-chain metabolites of tocopherols and tocotrienols in mice and humans. Urinary metabolites may serve as useful biomarkers for the nutritional assessment of vitamin E.

Cancer-preventive activities of tocopherols and tocotrienols

The cancer-preventive activity of vitamin E has been studied. Whereas some epidemiological studies have suggested a protective effect of vitamin E against cancer formation, many large-scale intervention studies with alpha-tocopherol (usually large doses) have not demonstrated a cancer-preventive effect. Studies on alpha-tocopherol in animal models also have not demonstrated robust cancer prevention effects. One possible explanation for the lack of demonstrable cancer-preventive effects is that high doses of alpha-tocopherol decrease the blood and tissue levels of delta-tocopherols. It has been suggested that gamma-tocopherol, due to its strong anti-inflammatory and other activities, may be the more effective form of vitamin E in cancer prevention. Our recent results have demonstrated that a gamma-tocopherol-rich mixture of tocopherols inhibits colon, prostate, mammary and lung tumorigenesis in animal models, suggesting that this mixture may have a high potential for applications in the prevention of human cancer. In this review, we discuss biochemical properties of tocopherols, results of possible cancer-preventive effects in humans and animal models and possible mechanisms involved in the inhibition of carcinogenesis. Based on this information, we propose that a gamma-tocopherol-rich mixture of tocopherols is a very promising cancer-preventive agent and warrants extensive future research.

Effects of vitamin E on the osteoblast differentiation

Vitamin E is thought to affect bone formation and bone remodeling. In this study, we investigated the effects of vitamin E (alpha-tocopherol and delta-tocopherol) on the osteoblasts isolated from rat calvariae. At 4 and 7 days (Day 4 and 7) after induction of osteoblastic differentiation, treatment of alpha-tocopherol (100 and 200 microM) and delta-tocopherol (2 and 20 microM) for 3 days significantly decreased alkaline phophatase activity of the cultured osteoblasts. At Day 14, however, no significant change was detected in ALP activity and expression of bone sialoprotein mRNA in the osteoblasts treated with alpha-tocopherol or delta-tocopherol for 3 days. Expression of osteocalcin mRNA was decreased by treatment of alpha-tocopherol (100 and 200 microM) and delta-tocopherol (2 and 20 microM) at Day 4 and 7. At Day 14, expression of osteocalcin mRNA was decreased only with treatment of 200 microM alpha-tocopherol. In addition, the noncalcified nodules were decreased by treatment of alpha-tocopherol (200 microM) and delta-tocopherol (20 microM) at Day 7. However, treatment of alpha-tocopherol and delta-tocopherol showed no significant change of formation of calcified nodules at Day 14. These results indicate that vitamin E inhibits differentiation of osteoblasts especially from early stage to osteoid-producing stage.

Present trends in vitamin E research

Nearly after one century of research and thousands of publications, the physiological function(s) of vitamin E remain unclear. Available evidence suggests a role in cell homeostasis that occurs through the modulation of specific signaling pathways and genes involved in proliferative, metabolic, inflammatory, and antioxidant pathways. Vitamin E presence in the human body is under close metabolic control so that only alpha-tocopherol and, to a lower extent, gamma-tocopherol are retained and delivered to tissues. Other vitamin E forms that are not retained in the body in significant amounts, exhibit responses in vitro that are different form those of alpha-tocopherol and may include tumor cell specific toxicity and apoptosis. These responses provide a therapeutic potential for these minor forms, either as such or metabolically modified, to produce bioactive metabolites. These cellular effects go beyond the properties of lipophilic antioxidant attributed to alpha-tocopherol particularly investigated for its alleged protective role in atherosclerosis or other oxidative stress conditions. Understanding signaling and gene expression effects of vitamin E could help assign a physiological role to this vitamin, which will be discussed in this review. Besides vitamin E signaling, attention will be given to tocotrienols as one of the emerging topics in vitamin E research and a critical re-examination of the most recent clinical trials will be provided together with the potential use of vitamin E in disease prevention and therapy.

In vitro stable isotope labeling for discovery of novel metabolites by liquid chromatography-mass spectrometry: Confirmation of gamma-tocopherol metabolism in human A549 cell

A general approach for discovering novel catabolic metabolites from a parent biocompound was developed and validated on the metabolism of gamma-tocopherol in human A549 cell. The method is based on LC-MS analysis of in vitro stable isotope-labeled metabolites and assumes that a parent compound and its metabolites share a common functional group that can be derivatized by well-documented reagents. In this method, two equal aliquots of extracted metabolites are separately derivatized with isotope-coded (heavy) and non-isotope-coded (light) form of derivatizing reagent, mixed at 1:1 ratio and analyzed using LC-MS. The metabolites with common functional group are then easily recognized by determination of a chromatographically co-eluted pair of isotopomers (MS doublet peaks) with similar peak intensities and mass difference corresponding to the mass difference between heavy and light form of derivatization reagent. The feasibility of this approach was demonstrated and validated by the identification of products of gamma-tocopherol catabolism in human A549 cell culture media using N-methyl-nicotinic acid N-hydroxysuccinimide ester (C1-NANHS) and N-methyl-d3-nicotinic acid N-hydroxysuccinimide ester (C1-d3-NANHS) derivatizing reagent. Overall four gamma-tocopherol metabolites were identified including 9'-COOH, 11'-COOH, 13'-COOH and 13'-OH. In addition, the developed LC-MS method can also be used for the fast and sensitive quantitative analysis of gamma-tocopherol and other forms of vitamin E related compounds.

Gamma-tocotrienol and gamma-tocopherol are primarily metabolized to conjugated 2-(beta-carboxyethyl)-6-hydroxy-2,7,8-trimethylchroman and sulfated long-chain carboxychromanols in rats

The metabolism of gamma-tocotrienol (gamma-TE) and gamma-tocopherol (gamma-T) was investigated in human A549 cells and in rats. Similar to gamma-T, A549 cells metabolized gamma-TE to sulfated 9'-, 11'-, and 13'-carboxychromanol and their unconjugated counterparts. After 72-h incubation with the cells, 90% of long-chain carboxychromanols in the culture media from gamma-TE, but <45% from gamma-T, were in the sulfated form. The formation of these metabolites was further investigated in rats gavaged by gamma-TE at 10 or 50 mg/kg, gamma-T at 10 mg/kg, or tocopherol-stripped corn oil in controls. Six hours after a single dosing, the supplemented rats had increased plasma concentrations of 13'-carboxychromanol and sulfated 9'-, 11'-, 13'-carboxychromanol, whereas none of these metabolites were detectable in the controls. Sulfated 11'-carboxychromanol was the most abundant long-chain metabolite in gamma-TE-supplemented rats. Sulfatase/glucuronidase hydrolysis revealed for the first time that >88% 2-(beta-carboxyethyl)-6-hydroxychroman (gamma-CEHC), the terminal beta-oxidation metabolite, was in the conjugated form in the plasma. In all groups, conjugated gamma-CEHC accounted for >75% of total metabolites, whereas free CEHC was a minor metabolite. At 10 mg/kg, the plasma concentrations of total metabolites from gamma-TE-supplemented rats were higher (P < 0.05) than those from gamma-T-fed rats. These results demonstrate that in rats, conjugation such as sulfation occurs parallel to beta-oxidation in the liver and is quantitatively important to vitamin E metabolism. Conjugated long-chain carboxychromanols may be novel excreted metabolites during supplementation. Our data also provide in vivo evidence that gamma-TE is more extensively metabolized than gamma-T.

Optimization of the enzymatic hydrolysis and analysis of plasma conjugated gamma-CEHC and sulfated long-chain carboxychromanols, metabolites of vitamin E

Natural forms of vitamin E are metabolized by omega-hydroxylation and beta-oxidation of the hydrophobic side chain to generate urinary-excreted 2-(beta-carboxyethyl)-6-hydroxychroman (CEHC) and CEHC conjugates (sulfate, glucuronide, or glucoside). We recently showed that sulfated long-chain carboxychromanols, the conjugated intermediate beta-oxidation products, are formed from tocopherols and tocotrienols in human cells and in rats. CEHC conjugates have been quantified after being converted to its unconjugated counterpart by sulfatase/glucuronidase. Although the enzymatic hydrolysis is critical for appropriate quantification of conjugated CEHC, it is not clear whether brief incubation of the plasma with sulfatases/glucuronidases results in complete deconjugation of conjugated CEHC. Here we show that quantitative hydrolysis of the conjugated vitamin E metabolites in the plasma requires an extraction procedure using methanol/hexane (2 ml/5 ml) and an overnight sulfatase/glucuronidase hydrolysis. Using this procedure, we demonstrate that conjugated gamma-CEHC and some sulfated long-chain carboxychromanols are fully deconjugated. In contrast, direct enzymatic hydrolysis of the whole plasma underestimates the conjugated metabolites by at least threefold. This protocol may be also useful for the analysis of other conjugated phenolic compounds in complicated biological matrices such as plasma.