The effect of tocopheryl phosphates on atherosclerosis progression in rabbits fed with a high cholesterol diet

Modulation of CD36-mediated lipid accumulation and senescence by vitamin E analogs in monocytes and macrophages

The CD36/FAT scavenger receptor/fatty acids transporter regulates cellular lipid accumulation important for inflammation, atherosclerosis, lipotoxicity, and initiation of cellular senescence. Here we compared the regulatory effects of the vitamin E analogs alpha-tocopherol (αT), alpha-tocopheryl phosphate (αTP), and αTP/βCD (a nanocarrier complex between αTP and β-cyclodextrin [βCD]) and investigated their regulatory effects on lipid accumulation, phagocytosis, and senescence in THP-1 monocytes and macrophages. Both, αTP and αTP/βCD inhibited CD36 surface exposition stronger than αT leading to more pronounced CD36-mediated events such as inhibition of DiI-labeled oxLDL uptake, phagocytosis of fluorescent Staphylococcus aureus bioparticles, and cell proliferation. When compared to βCD, the complex of αTP/βCD extracted cholesterol from cellular membranes with higher efficiency and was associated with the delivery of αTP to the cells. Interestingly, both, αTP and more so αTP/βCD inhibited lysosomal senescence-associated beta-galactosidase (SA-β-gal) activity and increased lysosomal pH, suggesting CD36-mediated uptake into the endo-lysosomal phagocytic compartment. Accordingly, the observed pH increase was more pronounced with αTP/βCD in macrophages whereas no significant increase occurred with αT, alpha-tocopheryl acetate (αTA) or βCD. In contrast to αT and αTA, the αTP molecule is di-anionic at neutral pH, but upon moving into the acidic endo-lysosomal compartment becomes protonated and thus is acting as a base. Moreover, it is expected to be retained in lysosomes since it still carries one negative charge, similar to lysosomotropic drugs. Thus, treatment with αTP or αTP/βCD and/or inhibition of conversion of αTP to αT as it occurs in aged cells may counteract CD36-mediated overlapping inflammatory, senescent, and atherosclerotic events.

Reflections on a century of vitamin E research: Looking at the past with an eye on the future

The name vitamin E, was given by Barnett and Sure who suggested that the factor proposed by Evans and Bishop as substance "X," be termed vitamin "E" as the next vitamin after the A, B, C and D vitamins had been already described. The identification of vitamin E with a-tocopherol was made in 1936 by Evans' group. One year later β-tocopherol and 11 years later δ-tocopherol were isolated. Tocotrienol (named zetatocopherol) was first described in 1957 and later isolated in 1961. The antioxidant property of tocopherols was reported by Olcott and Emerson in 1937. Inherited vitamin E deficiency, AVED, characterized by a form of neuromyopathy was first described in 1981. The disease, was localized to chromosome 8q and found to be caused by a mutation of the a-TTP gene. The subsequent paragraphs are not a comprehensive review but only critical reflections on some important aspects of vitamin E research.

Reduction of senescence-associated beta-galactosidase activity by vitamin E in human fibroblasts depends on subjects' age and cell passage number

Cell senescence is due to the permanent cell cycle arrest that occurs as a result of the inherent limited replicative capacity toward the Hayflick limit (replicative senescence), or in response to various stressors (stress-induced premature senescence, SIPS). With the acquisition of the senescence-associated secretory phenotype (SASP), cells release several molecules (cytokines, proteases, lipids), and express the senescence-associated beta-galactosidase (SA-β-Gal). Here we tested whether vitamin E affects SA-β-Gal in an in vitro model of cell ageing. Skin fibroblasts from human subjects of different age (1, 13, 29, 59, and 88 years old) were cultured until they reached replicative senescence. At different passages (Passages 2, 9, 13, and 16), these cells were treated with vitamin E for 24 hr. Vitamin E reduced SA-β-Gal in all cells at passage 16, but at earlier passage numbers it reduced SA-β-Gal only in cells isolated from the oldest subjects. Therefore, short time treatment with vitamin E decreases SA-β-Gal in cells both from young and old subjects when reaching replicative senescence; but in cells isolated from older subjects, a decrease in SA-β-Gal by vitamin E occurs also at earlier passage numbers. The possible role of downregulation of CD36 by vitamin E, a scavenger receptor essential for initiation of senescence and SASP, is discussed.

Vitamin E: Regulatory role in the cardiovascular system

Cardiovascular disease (CVD) is one of the major causes of morbidity and mortality, all around the world. Vitamin E is an important nutrient influencing key cellular and molecular mechanisms as well as gene expression regulation centrally involved in the prevention of CVD. Cell culture and animal studies have focused on the identification of vitamin E regulated signaling pathways and involvement on inflammation, lipid homeostasis, and atherosclerotic plaque stability. While some of these vitamin E functions were verified in clinical trials, some of the positive effects were not translated into beneficial outcomes in epidemiological studies. In recent years, the physiological metabolites of vitamin E, including the liver derived (long- and short-chain) metabolites and phosphorylated (α-, γ-tocopheryl phosphate) forms, have also provided novel mechanistic insight into CVD regulation that expands beyond the vitamin E precursor. It is certain that this emerging insight into the molecular and cellular action of vitamin E will help to design further studies, either in animal models or clinical trials, on the reduction of risk for CVDs. This review focuses on vitamin E-mediated preventive cardiovascular effects and discusses novel insights into the biology and mechanism of action of vitamin E metabolites in CVD. © 2019 IUBMB Life, 71(4):507-515, 2019.

Effects of Selenium- and Chromium-Enriched Diets on Growth Performance, Lipid Profile, and Mineral Concentration in Different Tissues of Growing Rabbits

The aim of this study was to investigate the effect of dietary supplementation with different sources of selenium and/or organic chromium on the growth performance, digestibility, lipid profile, and mineral content of hair, liver, and fore and hind limb of growing rabbits. A total of 150 weanling New Zealand White (NZW) male rabbits were randomly allotted to six dietary treatment groups: (1) basal diet (control group), (2) basal diet + 0.6 mg sodium selenite/kg diet, (3) basal diet + 0.6 mg selenium yeast/kg diet, (4) basal diet + 0.3 mg sodium selenite/kg diet + 0.3 mg selenium yeast/kg diet, (5) basal diet + 0.6 mg chromium yeast/kg diet + 0.6 mg selenium yeast/kg diet, (6) basal diet + 0.6 mg chromium yeast/kg diet. Only the combination between inorganic and organic selenium led to significant improvement in body weight, body weight gain, and feed conversion ratio. Carcass traits were not different in all groups. Selenium (Se) and chromium (Cr) were deposited in the tissues of rabbits fed diets supplemented with Se and Cr, respectively. Blood serum in both of selenium- and chromium-supplemented groups showed declined total cholesterol, triglycerides, and low-density lipoprotein (LDL). Group supplemented with organic chromium showed higher high-density lipoprotein (HDL) than the other groups. It could be concluded that using a mixture of inorganic and organic Se has a positive effect on the growth performance of growing rabbits. Both Se and Cr have hypocholesterolemic effect. Both of Se and Cr can be deposited in the meat and other tissues of rabbits and that improves meat quality which positively reflects on human acceptance. The combination between inorganic (0.3 mg sodium selenite/kg diet) and organic selenium (0.6 mg selenium yeast/kg diet) improved growth performance traits of growing rabbits.

Vitamin E: Regulatory Role on Signal Transduction

Vitamin E modulates signal transduction pathways by several molecular mechanisms. As a hydrophobic molecule located mainly in membranes it contributes together with other lipids to the physical and structural characteristics such as membrane stability, curvature, fluidity, and the organization into microdomains (lipid rafts). By acting as the main lipid-soluble antioxidant, it protects other lipids such as mono- and poly-unsaturated fatty acids (MUFA and PUFA, respectively) against chemical reactions with reactive oxygen and nitrogen species (ROS and RNS, respectively) and prevents membrane destabilization and cellular dysfunction. In cells, vitamin E affects signaling in redox-dependent and redox-independent molecular mechanisms by influencing the activity of enzymes and receptors involved in modulating specific signal transduction and gene expression pathways. By protecting and preventing depletion of MUFA and PUFA it indirectly enables regulatory effects that are mediated by the numerous lipid mediators derived from these lipids. In recent years, some vitamin E metabolites have been observed to affect signal transduction and gene expression and their relevance for the regulatory function of vitamin E is beginning to be elucidated. In particular, the modulation of the CD36/FAT scavenger receptor/fatty acids transporter by vitamin E may influence many cellular signaling pathways relevant for lipid homeostasis, inflammation, survival/apoptosis, angiogenesis, tumorigenesis, neurodegeneration, and senescence. Thus, vitamin E has an important role in modulating signal transduction and gene expression pathways relevant for its uptake, distribution, metabolism, and molecular action that when impaired affect physiological and patho-physiological cellular functions relevant for the prevention of a number of diseases. © 2018 IUBMB Life, 71(4):456-478, 2019.

Grape seed proanthocyanidins protect against streptozotocin‑induced diabetic nephropathy by attenuating endoplasmic reticulum stress‑induced apoptosis

Diabetic nephropathy (DN) is by far the most common cause of end-stage renal disease (ESRD) in industrial countries, accounting for ~45% of all new ESRD cases in the United States. Grape seed proanthocyanidin extracts (GSPE) are powerful antioxidants, with an antioxidant ability 50-fold greater than that of vitamin E and 20-fold greater than that of vitamin C. The present study investigated whether GSPE can protect against streptozotocin (STZ)-induced DN and aimed to elucidate a possible mechanism. Male Sprague Dawley rats were randomly divided into three groups: Control group (N), diabetes mellitus group (DM) injected with 40 mg/kg STZ, and the GSPE treatment group (intragastric administration of 250 mg/kg/day GSPE for 16 weeks after diabetes was induced in the rats). Blood and kidney samples were collected after treatment. The renal pathological changes were determined with periodic acid-Schiff (PAS) staining, while the protein expression levels of glucose-regulated protein 78 (GRP78), phosphorylated-extracellular signal-regulated kinase (p-ERK) and Caspase-12 were determined by western blotting and immunohistochemical staining. Apoptosis was determined with a terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. Compared with the DM group, the GSPE group had no significant changes in the blood urea nitrogen (BUN) level and serum creatinine (Scr) level, but showed a significant decline in the renal index (RI) level and 24-h urinary albumin level (P<0.05). The histopathology results indicated very little pathological damage in the GSPE group. Compared with the DM group, the GSPE group had a significantly reduced number of TUNEL-positive cells (P<0.05), and the GSPE group had an obvious reduction in the protein expression of GRP78, p-ERK, and Caspase-12 (P<0.05). In this study, the results indicated that GSPE can protect renal function and attenuate endoplasmic reticulum stress-induced apoptosis via the Caspase-12 pathway in STZ-induced DN.

Vitamin E Phosphate Coating Stimulates Bone Deposition in Implant-related Infections in a Rat Model

BACKGROUND

Implant-related infections are associated with impaired bone healing and osseointegration. In vitro antiadhesive and antibacterial properties and in vivo antiinflammatory effects protecting against bone loss of various formulations of vitamin E have been demonstrated in animal models. However, to the best of our knowledge, no in vivo studies have demonstrated the synergistic activity of vitamin E in preventing bacterial adhesion to orthopaedic implants, thus supporting the bone-implant integration.

QUESTIONS/PURPOSES

The purpose of this study was to test whether a vitamin E phosphate coating on titanium implants may be able to reduce (1) the bacterial colonization of prosthetic implants and (2) bone resorption and osteomyelitis in a rat model of Staphylococcus aureus-induced implant-related infection.

METHODS

Twelve rats were bilaterally injected in the femurs with S aureus UAMS-1-Xen40 and implanted with uncoated or vitamin E phosphate-coated titanium Kirschner wires without local or systemic antibiotic prophylaxis. Eight rats represented the uninfected control group. A few hours after surgery, two control and three infected animals died as a result of unexpected complications. With the remaining rats, we assessed the presence of bacterial contamination with qualitative bioluminescence imaging and Gram-positive staining and with quantitative bacterial count. Bone changes in terms of resorption and osteomyelitis were quantitatively analyzed through micro-CT (bone mineral density) and semiquantitatively through histologic scoring systems.

RESULTS

Six weeks after implantation, we found only a mild decrease in bacterial count in coated versus uncoated implants (Ti versus controls: mean difference [MD], -3.705; 95% confidence interval [CI], -4.416 to -2.994; p < 0.001; TiVE versus controls: MD, -3.063; 95% CI, -3.672 to -2.454; p < 0.001), whereas micro-CT analysis showed a higher bone mineral density at the knee and femoral metaphysis in the vitamin E-treated group compared with uncoated implants (knee joint: MD, -11.88; 95% CI, -16.100 to -7.664; p < 0.001 and femoral metaphysis: MD, -19.87; 95% CI, -28.82 to -10.93; p < 0.001). We found decreased osteonecrosis (difference between medians, 1.5; 95% CI, 1-2; p < 0.002) in the infected group receiving the vitamin E-coated nails compared with the uncoated nails.

CONCLUSIONS

These preliminary findings indicate that vitamin E phosphate implant coatings can exert a protective effect on bone deposition in a highly contaminated animal model of implant-related infection.

CLINICAL RELEVANCE

The use of vitamin E coatings may open new perspectives for developing coatings that can limit septic loosening of infected implants with bacterial contamination. However, a deeper insight into the mechanism of action and the local release of vitamin E as a coating for orthopaedic implants is required to be used in clinics in the near future. Although this study cannot support the antimicrobial properties of vitamin E, promising results were obtained for bone-implant osseointegration. These preliminary results will require further in vivo investigations to optimize the host response in the presence of antibiotic prophylaxis.

Water-Soluble Vitamin E-Tocopheryl Phosphate

The hydrophobicity of vitamin E poses transport and metabolic challenges to regulate its bioavailability and to prevent its accumulation in lipid-rich tissues such as adipose tissue, brain, and liver. Water-soluble precursors of vitamin E (α-tocopherol, αT), such as its esters with acetate (αTA), succinate (αTS), or phosphate (αTP), have increased solubility in water and stability against reaction with free radicals, but they are rapidly converted during their uptake into the lipid-soluble vitamin E. Therefore, the bioavailability of these precursors as intact molecules is low; nevertheless, at least for αTS and αTP, the recent research has revealed unique regulatory effects on signal transduction and gene expression and the modulation of cellular events ranging from proliferation, survival/apoptosis, lipid uptake and metabolism, phagocytosis, long term potentiation, cell migration, telomere maintenance, and angiogenesis. Moreover, water-soluble derivatives of vitamin E including some based on αTP are increasingly used as components of nanocarriers for enhanced and targeted delivery of drugs and other molecules (vitamins, including αT and αTP itself, vitamin D3, carnosine, caffeine, docosahexaenoic acid (DHA), insulin) and cofactors such as coenzyme Q10. In this review, the chemical characteristics, transport, metabolic pathways, and molecular mechanisms of action of αTP in cells and tissues are summarized and put into perspective with its possible role in the prevention of a number of diseases.

A new lipid excipient, phosphorylated tocopherol mixture, TPM enhances the solubilisation and oral bioavailability of poorly water soluble CoQ10 in a lipid formulation

Phosphorylated tocopherols are a new class of lipid excipients that have demonstrated potential in pharmaceutical applications. Their ability to solubilise poorly water soluble drugs indicates their potential utility in improving bioavailability of drugs where solubility limits their bioavailability. In this study a commercial mixture of phosphorylated tocopherols, TPM was combined with medium chain triglyceride (MCT) as a formulation for CoQ₁₀, and in vitro and in vivo performance compared to the effect of addition of alternative tocopherol-based excipients. In in vitro digestion experiments, CoQ₁₀ was poorly solubilised in the digesting MCT as anticipated. Addition of TPM facilitated the enhanced solubilisation of CoQ₁₀ as did vitamin E TPGS (TPGS). Other tocopherol derivatives (tocopherol acetate, tocopherol) were less effective at solubilising the active during the digestion process. The trends in in vitro solubilisation were conserved in the in vivo bioavailability of CoQ₁₀ after oral administration to rats, with TPM and TPGS formulations providing approximately double the exposure of MCT alone, while the addition of the other tocopherol derivatives reduced the overall exposure. Collectively, the results indicate potential of TPM as a new solubilising excipient for use in oral drug delivery for poorly water soluble drugs.

Changes in Bioavailability of Omega-3 (DHA) through Alpha-Tocopheryl Phosphate Mixture (TPM) after Oral Administration in Rats

Benefits of Omega-3 Docosahexaenoic acid (DHA) supplements are hindered by their poor solubility and bioavailability. This study investigated the bioavailability of various formulations of Omega-3 and tocopheryl phosphate mixture (TPM), following oral administration in rats, and assessed whether TPM could improve the oral absorption of DHA. The rats were administered with a high (265.7 mg/kg) or low dose (88.6 mg/kg) of DHA. TPM was examined at 1:0.1 w/w (low TPM dose) and 1:0.5 w/w (high TPM dose). Over 24 h, the DHA plasma concentration followed a TPM dose-dependent relationship, reflected in the higher mean Cmax values (78.39 and 91.95 μg/mL) and AUC values (1396.60 and 1560.60) for the low and high TPM, respectively. The biggest difference between the low dose DHA control (LDCont) and TPM formulations was at 4 h after supplementation, where the low and high TPM showed a mean 20% (ns) and 50% (p < 0.05) increase in DHA plasma concentrations versus the control formulation. After correcting for baseline endogenous DHA, the mean plasma DHA at 4 h produced by the LD-HTPM was nearly double (90%) the LDC control (p = 0.057). This study demonstrated that co-administering omega-3 with TPM significantly increases the bioavailability of DHA in the plasma, suggesting potential use for commercially available TPM + DHA fortified products.

The effect of tocopheryl phosphates (TPM) on the development of atherosclerosis in apolipoprotein-E deficient mice

α-Tocopheryl phosphate (TP) is a naturally occurring form of vitamin E found in the body. In the present study we compared the ability of an α-TP mixture (TPM) against a standard vitamin E supplement, α-tocopherol acetate (TA) on the development of atherosclerotic lesions in ApoE-deficient mice. Mice were maintained on either a normal chow diet for 24 weeks (Normal Diet), vs a group in which the final 8 weeks of the 24-week period mice were placed on a high fat (21%), high cholesterol (0.15%) challenge diet (HFHC), to exacerbate atherosclerotic lesion development.. The difference in these two control groups established the extent of the diet-induced atherosclerotic lesion development. Mice in the various treatment groups received either TA (300 mg/kg chow) or TPM (6.7-200 mg/kg chow) for 24 weeks, with TPM treatment resulting in dose-dependent significant reductions in atherosclerotic lesion formation and plasma levels of pro-inflammatory cytokines. TA-treated mice, with the tocopherol equivalent TPM dose (200 mg/kg chow), showed no significant reduction in plasma lipid levels or evidence for aortic lesion regression. At this TPM equivalent TA dose, a 44% reduction in aortic lesion formation was observed. In addition, these TPM treated mice, also showed a marked reduction in aortic superoxide formation and decreased circulating plasma levels of known pro-inflammatory markers IL-6, MCP-1, IL-1β, IFN-γ and TNF-α. These findings indicate that TPM treatment slows progression of atherosclerotic lesions in ApoE-deficient mice with this effect potentially involving reduced oxidative stress and decreased inflammation.

In vitro comparison between α-tocopheryl acetate and α-tocopheryl phosphate against bacteria responsible of prosthetic and joint infections

Biofilm-related infections represent a recurrent problem in the orthopaedic setting. In recent years, great interest was directed towards the identification of novel molecules capable to interfere with pathogens adhesion and biofilm formation on implant surfaces. In this study, two stable forms of α-tocopherol, the hydrophobic acetate ester and the water-soluble phosphate ester, were tested in vitro as coating for titanium prosthesis. Antimicrobial activity against microorganisms responsible of prosthetic and joints infections was assessed by broth microdilution method. In addition, α-tocopherol esters were evaluated for both their ability to hamper bacterial adhesion to and biofilm formation on sandblasted titanium surfaces. Results showed that only α-tocopheryl phosphate displayed antimicrobial activity against the tested strains. Both esters were able to significantly interfere with bacterial adhesion and to prevent biofilm formation, especially by Staphylococcus aureus and Staphylococcus epidermidis. The activity of α-tocopheryl phosphate was greater than that of α-tocopheryl acetate. Alterations at membrane levels have been reported in literature and may be likely responsible for the interference on bacterial adhesion and biofilm formation shown by α-tocopherol esters. Although further studies are needed to better investigate the mechanisms of action and the spectrum of activity of α-tocopherol esters, these characteristics together with the positive effect on wound healing and immune response, make these molecules promising candidate for coating in order to prevent implant-associated infections.

α-Tocopheryl Phosphate Induces VEGF Expression via CD36/PI3Kγ in THP-1 Monocytes

The CD36 scavenger receptor binds several ligands and mediates ligand uptake and ligand-dependent signal transduction and gene expression, events that may involve CD36 internalization. Here we show that CD36 internalization in THP-1 monocytes is triggered by α-tocopherol (αT) and more strongly by α-tocopheryl phosphate (αTP) and EPC-K1, a phosphate diester of αTP and L-ascorbic acid. αTP-triggered CD36 internalization is prevented by the specific covalent inhibitor of selective lipid transport by CD36, sulfo-N-succinimidyl oleate (SSO). Moreover, SSO inhibited the CD36-mediated uptake of 14C-labelled αTP suggesting that αTP binding and internalization of CD36 is involved in cellular αTP uptake, whereas the uptake of αT was less affected. Similar to that, inhibition of selective lipid transport of the SR-BI scavenger receptor resulted mainly in reduction of αTP and not αT uptake. In contrast, uptake of αT was mainly inhibited by Dynasore, an inhibitor of clathrin-mediated endocytosis, suggesting that the differential regulatory effects of αTP and αT on signaling may be influenced by their different routes of uptake. Interestingly, αTP and EPC-K1 also reduced the neutral lipid content of THP-1 cells and the phagocytosis of fluorescent Staphylococcus aureus bioparticles. Moreover, induction of the vascular endothelial growth factor (VEGF) promoter activity by αTP occurred via CD36/PI3Kγ/Akt, as it could be inhibited by specific inhibitors of this pathway (SSO, Wortmannin, AS-605240). These results suggest that αTP activates PI3Kγ/Akt signaling leading to VEGF expression in monocytes after binding to and/or transport by CD36, a receptor known to modulate angiogenesis in response to amyloid beta, oxLDL, and thrombospondin. J. Cell. Biochem. 118: 1855-1867, 2017. © 2017 Wiley Periodicals, Inc.

Vitamin E: Emerging aspects and new directions

The discovery of vitamin E will have its 100th anniversary in 2022, but we still have more questions than answers regarding the biological functions and the essentiality of vitamin E for human health. Discovered as a factor essential for rat fertility and soon after characterized for its properties of fat-soluble antioxidant, vitamin E was identified to have signaling and gene regulation effects in the 1980s. In the same years the cytochrome P-450 dependent metabolism of vitamin E was characterized and a first series of studies on short-chain carboxyethyl metabolites in the 1990s paved the way to the hypothesis of a biological role for this metabolism alternative to vitamin E catabolism. In the last decade other physiological metabolites of vitamin E have been identified, such as α-tocopheryl phosphate and the long-chain metabolites formed by the ω-hydroxylase activity of cytochrome P-450. Recent findings are consistent with gene regulation and homeostatic roles of these metabolites in different experimental models, such as inflammatory, neuronal and hepatic cells, and in vivo in animal models of acute inflammation. Molecular mechanisms underlying these responses are under investigation in several laboratories and side-glances to research on other fat soluble vitamins may help to move faster in this direction. Other emerging aspects presented in this review paper include novel insights on the mechanisms of reduction of the cardiovascular risk, immunomodulation and antiallergic effects, neuroprotection properties in models of glutamate excitotoxicity and spino-cerebellar damage, hepatoprotection and prevention of liver toxicity by different causes and even therapeutic applications in non-alcoholic steatohepatitis. We here discuss these topics with the aim of stimulating the interest of the scientific community and further research activities that may help to celebrate this anniversary of vitamin E with an in-depth knowledge of its action as vitamin.

Subchronic Oral Toxicity Study of Mixed Tocopheryl Phosphates in Rats

Rats were fed diets containing 0%, 1 %, 3%, or 5% mixed tocopheryl phosphates for 90 days. No abnormal clinical signs related to treatment appeared. Some statistically significant changes in hematology and clinical chemistry parameters appeared, but the majority were not dose dependent, occurred in only one sex or group, and/or remained within the historical control range for this strain of rat. A statistically significant apparent reduction in blood protein was observed in animals treated with the tocopheryl phosphates, but further investigation showed that the test substance interfered with the protein assay. Repeat analysis using a method unaffected by plasma test substance levels showed no difference in plasma proteins among all groups. Gross necropsy revealed no abnormalities; reduced relative heart and epididymal weights were observed, but were not dose dependent and were considered incidental. Histopathological changes occurred only in the mesenteric lymph node and small intestine. Foreign material in a crystal-like form appeared in macrophages in both organs, and increased in a dose-related fashion. In the lymph node, sinus histiocytosis increased with dose, but the severity was similar between the control and low-dose groups. Foreign-body granulomatous inflammation, associated with Maltese cross birefringence of the crystals was seen in the mid- and high-dose animals, but not the low-dose group. Similarly, the small intestine showed increasing amounts of foreign material and inflammation in the mid- and high-dose but not in the 1 % diet. The 1 % diet (equivalent to 587 and 643 mg mixed tocopheryl phosphates/kg body weight/day for male and female rats, respectively) was considered the no observed adverse effect level.

Vitamins for enhancing plant resistance

This paper provides an overview on vitamins with inducing activities in plants, the molecular and cellular mechanisms implicated, and the hormonal signalling-network regulating this process. Moreover, it reports how vitamins might be part of the molecular events linked to induced resistance by the conventional elicitors. Induced resistance (IR), exploiting the plant innate-defense system is a sustainable strategy for plant disease control. In the last decade, vitamins have been proven to act as inducers of disease resistance, and these findings have received an important attention owing to their safety and cost effectiveness. Vitamins, including thiamine (TH, vitamin B1), riboflavin (RF, vitamin B2), menadione sodium bisulfite (MSB, vitamin K3), Para-aminobenzoic acid (PABA, vitamin Bx), and folic acid (FA, vitamin B9) provided an efficient protection against a wide range of pathogens through the modulation of specific host-defense facets. However, other vitamins, such as ascorbic acid (AA, vitamin C) and tocopherols (vitamin E), have been shown to be a part of the molecular mechanisms associated to IR. The present review is the first to summarize what vitamins are acting as inducers of disease resistance in plants and how could they be modulated by the conventional elicitors. Thus, this report provides an overview on the protective abilities of vitamins and the molecular and cellular mechanisms underlying their activities. Moreover, it describes the hormonal-signalling network regulating vitamin-signal transduction during IR. Finally, a biochemical model describing how vitamins are involved in the establishment of IR process is discussed.

Effect of a hypercholesterolemia as a starting factor on spinal degeneration in rabbits and role of Vitamin E (α-tocopherol)

Background:

To identify the role of the hypercholesterolemia as a starting factor in discovertebral degeneration that ultimately causes lower back pain, and investigate the role of Vitamin E in this process.

Methods:

The rabbits (n = 32) were divided into two broad experimental groups: A control group, and a hypercholesterolemia group, namely cholesterol, and cholesterol plus Vitamin E groups and they were fed sequentially for 4 or 8 weeks. Serum cholesterol and Vitamin E (α-tocopherol) levels were determined; vascular tissue was prepared for histopathological analyses and vertebra was decalcified for the study.

Results:

Cholesterol diet group resulted approximately 44-fold of increase plasma cholesterol levels over the 4-week control values. Additional supplementation with Vitamin E group induced a plasma cholesterol level increase of only 37-fold as compared to the control group. In the cholesterol groups, light microscope examination revealed atherosclerotic plaque in major arteries. However, in the cholesterol plus Vitamin E treatment groups, no lipid accumulation or foam cell formation was visible in the abdominal aorta and vertebral segmental artery. In histopathological examination, we found degenerative changes in the discovertebral unit in cholesterol treated groups.

Conclusion:

Hypercholesterolemia causes fat accumulation in the disc endplate and vertebral body that causes blood supply disturbances which might be a starting factor of discovertebral degeneration. This event was not reversed by the elimination of cholesterol from the diet. Vitamin E supplementation was not effective in reducing fat accumulation in vertebral bone marrow. As a result, we conclude that degeneration of the discovertebral unit is not related to atherosclerotic changes in the major blood vessels.

α-Tocopheryl Phosphate as a Bioactive Derivative of Vitamin E: A Review of the Literature

α-Tocopheryl phosphate (α-TP) is a naturally occurring derivative of α-tocopherol (α-T), one of the eight isoforms of vitamin E. α-TP is present at very low intracellular concentrations, traffics across plasma membranes, and affects many important cellular functions. In addition to being a signaling molecule, α-TP has also been shown to possess antioxidant and potentially antiatherosclerotic properties that are more potent than its parent compound (α-T). However, there is little published data on the clinical effects of α-TP supplements, the mechanisms involved in its metabolism and cellular function, and reliable methods for its determination in plasma.

Modulation of phosphorylation of tocopherol and phosphatidylinositol by hTAP1/SEC14L2-mediated lipid exchange

The vitamin E derivative, alpha-tocopheryl phosphate (αTP), is detectable in cultured cells, plasma and tissues in small amounts, suggesting the existence of enzyme(s) with α-tocopherol (αT) kinase activity. Here, we characterize the production of αTP from αT and [γ-32P]-ATP in primary human coronary artery smooth muscle cells (HCA-SMC) using separation by thin layer chromatography (TLC) and subsequent analysis by Ultra Performance Liquid Chromatography (UPLC). In addition to αT, although to a lower amount, also γT is phosphorylated. In THP-1 monocytes, γTP inhibits cell proliferation and reduces CD36 scavenger receptor expression more potently than αTP. Both αTP and γTP activate the promoter of the human vascular endothelial growth factor (VEGF) gene with similar potency, whereas αT and γT had no significant effect. The recombinant human tocopherol associated protein 1 (hTAP1, hSEC14L2) binds both αT and αTP and stimulates phosphorylation of αT possibly by facilitating its transport and presentation to a putative αT kinase. Recombinant hTAP1 reduces the in vitro activity of the phosphatidylinositol-3-kinase gamma (PI3Kγ) indicating the formation of a stalled/inactive hTAP1/PI3Kγ heterodimer. The addition of αT, βT, γT, δT or αTP differentially stimulates PI3Kγ, suggesting facilitated egress of sequestered PI from hTAP1 to the enzyme. It is suggested that the continuous competitive exchange of different lipophilic ligands in hTAPs with cell enzymes and membranes may be a way to make these lipophiles more accessible as substrates for enzymes and as components of specific membrane domains.

Evaluation of cardiovascular protective effect of different apple varieties - Correlation of response with composition

Epidemiological evidence supports the concept that diets rich in fruits and vegetables promote health and attenuate or delay the onset of cardiovascular disease (CVD). In particular, a reduced risk of CVD has been associated with apple consumption, probably due to the cholesterol-lowering effect of the main bioactive compounds, namely fibre and polyphenols. In this work, the effect of diet supplementation with 20% of three Portuguese apple cultivars (Bravo de Esmolfe, Malápio Serra and Golden), containing distinct phenolic and fibre concentrations, on serum lipid profile and oxLDL of male Wistar rats fed a cholesterol-enriched diet (2%) was evaluated. After 30 days, only Bravo de Esmolfe apple was able to decrease significantly serum levels of triglycerides, total and LDL cholesterol concentrations (reductions of 27.2%, 21.0% and 20.4%, respectively, in relation to the cholesterol-enriched diet group, P<0.05). The levels of oxLDL were also significantly improved with the consumption of this apple variety (reductions of 20.0% and 11.9%, in relation to the cholesterol-enriched diet group and control group, respectively, P>0.05) as well as with Malapio da Serra apple (reductions of 9.8% in relation to the cholesterol-enriched diet group, P<0.05). Correlation of the bioactive response with chemical composition showed that catechin, epicatechin, procyanidin B1 and β-carotene are the major phytocompounds responsible for the cholesterol lowering ability of apples. The antioxidant potential may have also contributed to this beneficial effect.

α-Tocopheryl phosphate--an activated form of vitamin E important for angiogenesis and vasculogenesis?

Vitamin E was originally discovered as a dietary factor essential for reproduction in rats. Since then, vitamin E has revealed many important molecular properties such as the scavenging of reactive oxygen and nitrogen species or the modulation of signal transduction and gene expression in antioxidant and nonantioxidant manners. A congenital disease, ataxia with vitamin E deficiency, which is characterized by impaired enrichment of α-tocopherol (αT) in plasma due to mutations in the α-tocopherol transfer protein gene, has been discovered. An effect of vitamin E on angiogenesis and vasculogenesis has been observed in several studies, and recently, it has been demonstrated in the placenta of pregnant ewes, possibly involving the stimulation of vascular endothelial growth factor (VEGF) expression. We recently observed that the phosphorylated form of αT, α-tocopheryl phosphate (αTP), increases the expression of VEGF. We propose that the stimulatory effect of αT on angiogenesis and vasculogenesis is potentiated by phosphorylation to αTP, which may act as a cofactor or active lipid mediator increasing VEGF expression. Increased VEGF expression and consequent enhanced angiogenesis and vasculogenesis induced by αTP may explain not only the essential roles of vitamin E on reproduction, but also its beneficial effects against pre-eclampsia, ischemia/reperfusion injury, and during wound healing. It may also serve as a survival factor for brain and muscle cells. The finding that αTP may regulate vasculogenesis may indicate potential, important pathophysiological implications.

α-Tocopheryl phosphate: uptake, hydrolysis, and antioxidant action in cultured cells and mouse

α-Tocopheryl phosphate (α-TP), a water-soluble analogue of α-tocopherol, is found in humans, animals, and plants. α-TP is resistant to both acid and alkaline hydrolysis and may exert its own function in this form in vivo. In this study, the uptake, hydrolysis, and antioxidant action of α-TP were measured using α-TP with a deuterated methyl group, CD(3), at position 5 of the chroman ring (α-TP(CD3)). The hydrolysis of α-TP(CD3) was followed by measuring α-tocopherol containing the CD(3) group, α-T(CD3), in comparison to unlabeled α-tocopherol, α-T(CH3). α-TP(CD3) was incubated with cultured cells, and the intracellular α-T(CD3) formed was measured with HPLC-ECD and GC-MS. α-TP(CD3) was also administered to mice for 4 weeks by mixing in the diet, and α-T(CD3) was measured in plasma, liver, brain, heart, and testis to compare with endogenous unlabeled α-T(CH3). It was found that α-TP(CD3) was taken in and hydrolyzed readily to α-T(CD3) in cultured cells and in mice. The hydrolysis of α-TP(CD3) in cell culture medium was not observed. α-TP protected primary cortical neuronal cells from glutamate-induced cytotoxicity, and α-TP given to mice reduced the levels of lipid peroxidation products in plasma and liver. These results suggest that α-TP is readily hydrolyzed in vivo to α-T, which acts as an antioxidant, and that α-TP may be used as a water-soluble α-T precursor in intravenous fluids, in eye drops, or as a dietary supplement.

Protective effects of vitamin E against hypercholesterolemia-induced age-related diseases

Hypercholesterolemia is a major risk factor for age-related diseases such as atherosclerosis and Alzheimer's disease (AD). Changes in human plasma cholesterol levels results from the interaction between multiple genetic and environmental factors. The accumulation of excess cholesterol in blood vessels leads to atherosclerosis. Many studies on this field show that differential expression of oxidative stress-related proteins, lipid metabolism-related enzymes, and receptors response to atherogenic diet. Additionally, excess brain cholesterol has been associated with increased formation and deposition of amyloid-β peptide from amyloid precursor protein which may contribute to the risk and pathogenesis of AD. To consider genetically, more than 50 genes have been reported to influence the risk of late-onset AD. Some of these genes might be also important in cholesterol metabolism and transport. Epidemiological studies have shown an association between high intake and high serum concentrations of antioxidant vitamins like vitamin E and lower rates of ischemic heart diseases. It has been known that vitamin E also inhibits smooth muscle cell proliferation by non-antioxidant mechanism. On the basis of the previous results, vitamin E has been accepted as an important protective factor against hypercholesterolemia-induced age-related diseases.

Hypercholesterolemia increases vasospasm resulting from basilar artery subarachnoid hemorrhage in rabbits which is attenuated by Vitamin E

BACKGROUND

Aneurysm rupture results in subarachnoid hemorrhage (SAH) with subsequent vasospasm in the cerebral and cerebellar major arteries. In recent years, there has been increasing evidence that hypercholesterolemia plays a role in the pathology of SAH. It is known that hypercholesterolemia is one of the major risk factors for the development of atherosclerosis. Among the factors that have been found to retard the development of atherosclerosis is the intake of a sufficient amount of Vitamin E. An inverse association between serum Vitamin E and coronary heart disease mortality has been demonstrated in epidemiologic studies. Therefore, we tested, in an established model of enhanced cholesterol feed in rabbits, the effects of hypercholesterolemia on vasospasm after SAH by using computed tomography (CT) angiograms of the rabbit basilar artery; in addition, we tested the effects of Vitamin E on these conditions, which have not been studied up to now.

METHODS

In this study rabbits were divided into 3 major groups: control, cholesterol fed, and cholesterol + Vitamin E fed. Hypercholesterolemia was induced by a 2% cholesterol-containing diet. Three rabbit groups were fed rabbit diet; one group was fed a diet that also contained 2% cholesterol and another group was fed a diet containing 2% cholesterol and they received i.m. injections of 50 mg/kg of Vitamin E. After 8 weeks, SAH was induced by the double-hemorrhage method and distilled water was injected into cisterna magna. Blood was taken to measure serum cholesterol and Vitamin E levels. Basilar artery samples were taken for microscopic examination. CT angiography and measurement of basilar artery diameter were performed at days 0 and 3 after SAH.

RESULTS

Two percent cholesterol diet supplementation for 8 weeks resulted in a significant increase in serum cholesterol levels. Light microscopic analysis of basilar artery of hypercholesterolemic rabbits showed disturbances in the subendothelial and medial layers, degeneration of elastic fibers in the medial layer from endothelial cell desquamation, and a reduction of waves in the endothelial layer. However, the cholesterol + Vitamin E group did not exhibit these changes. The mean diameter of the basilar artery after SAH induction in the cholesterol-treated group was decreased 47% compared with the mean diameter of the control group. This value was less affected in cholesterol + Vitamin E-treated rabbits, which decreased 18% compared with the mean diameter of the control group.

CONCLUSIONS

Hypercholesterolemia-related changes in the basilar artery aggravate vasospasm after SAH. Adding Vitamin E to cholesterol-treated rabbits decreased the degree of vasospasm following SAH in the rabbit basilar artery SAH model. We suggest that Vitamin E supplements and a low cholesterol diet may potentially diminish SAH complicated by vasospasm in high-risk patients.

Modulation of gene expression by α-tocopherol and α-tocopheryl phosphate in THP-1 monocytes

The natural vitamin E analog α-tocopheryl phosphate (αTP) modulates atherosclerotic and inflammatory events more efficiently than the unphosphorylated α-tocopherol (αT). To investigate the molecular mechanisms involved, we have measured plasma levels of αTP and compared the cellular effects of αT and αTP in THP-1 monocytes. THP-1 cell proliferation is slightly increased by αT, whereas it is inhibited by αTP. CD36 surface expression is inhibited by αTP within hours without requiring transport of αTP into cells, suggesting that αTP may bind to CD36 and/or trigger its internalization. As assessed by gene expression microarrays, more genes are regulated by αTP than by αT. Among a set of confirmed genes, the expression of vascular endothelial growth factor is induced by αTP as a result of activating protein kinase B (PKB/Akt) and is associated with increased levels of reactive oxygen species (ROS). Increased Akt(Ser473) phosphorylation and induction of ROS by αTP occur in a wortmannin-sensitive manner, indicating the involvement of phosphatidylinositol kinases. The induction of Akt(Ser473) phosphorylation and ROS production by αTP can be attenuated by αT. It is concluded that αTP and αT influence cell proliferation, ROS production, and Akt(Ser473) phosphorylation in an antagonistic manner, most probably by modulating phosphatidylinositol kinases.

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.

alpha-Tocopheryl phosphate--an active lipid mediator?

The vitamin E (alpha-tocopherol, alphaT) derivative, alpha-tocopheryl phosphate (alphaTP), is detectable in small amounts in plasma, tissues, and cultured cells. Studies done in vitro and in vivo suggest that alphaT can become phosphorylated and alphaTP dephosphorylated, suggesting the existence of enzyme(s) with alphaT kinase or alphaTP phosphatase activity, respectively. As a supplement in animal studies, alphaTP can reach plasma concentrations similar to alphaT and only a part is dephosphorylated; thus, alphaTP may act both as pro-vitamin E, but also as phosphorylated form of vitamin E with possibly novel regulatory activities. Many effects of alphaTP have been described: in the test tube alphaTP modulates the activity of several enzymes; in cell culture alphaTP affects proliferation, apoptosis, signal transduction, and gene expression; in animal studies alphaTP prevents atherosclerosis, ischemia/reperfusion injury, and induces hippocampal long-term potentiation. At the molecular level, alphaTP may act as a cofactor for enzymes, as an active lipid mediator similar to other phosphorylated lipids, or indirectly by altering membrane characteristics such as lipid rafts, fluidity, and curvature. In this review, the molecular and cellular activities of alphaTP are examined and the possible functions of alphaTP as a natural compound, cofactor and active lipid mediator involved in signal transduction and gene expression discussed.

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.

Vitamin E: the shrew waiting to be tamed

Vitamin E is the last of all vitamins whose essentiality is not yet understood. Its widely accepted role as a lipophilic antioxidant has been questioned, since proof of its in vivo relevance remained scarce. The influence of vitamin E on biomarkers of oxidative stress in vivo is inconsistent and metabolites of vitamin E having reacted as an antioxidant are hardly detectable. Novel functions of vitamin E include the regulation of enzymes, most of which are membrane bound or activated by membrane recruitment. Also, expression of genes responds to vitamin E. The search for a transcription factor common to all regulated genes failed so far and a receptor that specifically binds vitamin E has not yet been identified. According to microarray data, pathways preferentially affected by the vitamin E status are the inflammatory response and cellular traffic. A role of vitamin E in cellular trafficking could best explain the neurological symptoms seen in vitamin E deficiency. Emerging knowledge on vitamin E is compiled here with the perspective to unravel the molecular mechanisms that could more likely explain the essentiality of the vitamin than its ability to scavenge free radicals.

Synergy research: vitamins and secondary plant components in the maintenance of the redox-homeostasis and in cell signaling

The maintenance of the redox-homeostasis is an essential task of antioxidants. Reactive oxygen species (ROS) formed during oxidative stress can potentially damage the normal cellular functions and support pathological processes like atherosclerosis in vessels or malignant growth in other tissues, but also the aging process. However, recent findings link ROS also to cell survival and/or proliferation, which revolutionises the age-old dogmatic view of ROS being exclusively involved in cell damage and death. Low concentrations of hydrogenperoxide e.g. are involved in cell signaling and can activate mitogen-activated kinases (MAPK) to initiate cell growth. Nutritional antioxidants like vitamin C or E can promote endothelial cell growth, but can also inhibit growth of muscle cells, and influence MAPK. Thus, keeping the redox-homeostasis in a steady state especially in the context of tissue regeneration appears to be more important than previously known and seems to be a controlled synergistic action of antioxidants and ROS. The present review summarizes the properties and functions of ROS and nutritional antioxidants like the vitamins C and E, and polyphenols in redox-homeostasis. Their relevance in the treatment of various diseases is discussed in the context of a multitarget therapy with nutraceuticals and phytotherapeutic drugs.

Cardioprotection with alpha-tocopheryl phosphate: amelioration of myocardial ischemia reperfusion injury is linked with its ability to generate a survival signal through Akt activation

The emerging potential of alpha-tocopheryl phosphate, a phosphoric acid ester of alpha-tocopherol, in health benefits was tested gavaging this compound (5 mg/kg body wt) to a group of rats for a period of thirty days while the control rats were given water only. After thirty days, the rats were sacrificed, the hearts excised, and the isolated hearts were perfused by working mode. Both control and experimental hearts were subjected to 30-min global ischemia followed by 2 h of reperfusion. The tocopheryl phosphate fed rats exhibited significant cardioprotection as evidenced by improved ventricular performance and reduced myocardial infarct size and cardiomyocyte apoptosis. Supplementation with alpha-tocopheryl phosphate converted MAP kinase-induced death signal into a survival signal by enhancing anti-apoptotic p42/44 ERK kinase and p38 MAPKbeta and reducing pro-apoptotic proteins p38 MAPKalpha and JNK. In concert, the phosphorylation of pro-apoptotic c-Src was also reduced. Tocopheryl phosphate increased the DNA binding of the redox-sensitive transcription factor NFkappaB and potentiated the activation of anti-death protein Bcl-2 and survival signaling protein Akt. The results of this study demonstrated for the first time that tocopheryl phosphate could ameliorate myocardial ischemic reperfusion injury by converting ischemia/reperfusion-mediated death signal into a survival signal by modulating MAP kinase signaling.

Vitamin E: An overview of major research directions

During the last 90 years since the discovery of vitamin E, research has focused on different properties of this molecule, the focus often depending on the specific techniques and scientific knowledge present at each time. Originally discovered as a dietary factor essential for reproduction in rats, vitamin E has revealed in the meantime many more important molecular properties, such as the scavenging of reactive oxygen and nitrogen species with consequent prevention of oxidative damage associated with many diseases, or the modulation of signal transduction and gene expression in antioxidant and non-antioxidant manners. Research over the last 30 years has also resolved the biosynthesis and occurrence of vitamin E in plants, the proteins involved in the cellular uptake, tissue distribution and metabolism, and defined a congenital recessive neurological disease, ataxia with vitamin E deficiency (AVED), characterized by impaired enrichment of alpha-tocopherol in plasma as a result of mutations in the liver alpha-tocopherol transfer gene. This review is giving a brief introduction about vitamin E by following the major research directions since its discovery with a historical perspective.

Cellular, molecular and clinical aspects of vitamin E on atherosclerosis prevention

Randomised clinical trials and epidemiologic studies addressing the preventive effects of vitamin E supplementation against cardiovascular disease reported both positive and negative effects, and recent meta-analyses of the clinical studies were rather disappointing. In contrast to that, many animal studies clearly show a preventive action of vitamin E in several experimental settings, which can be explained by the molecular and cellular effects of vitamin E observed in cell cultures. This review is focusing on the molecular effects of vitamin E on the cells playing a role during atherosclerosis, in particular on the endothelial cells, vascular smooth muscle cells, monocytes/macrophages, T cells, and mast cells. Vitamin E may act by normalizing aberrant signal transduction and gene expression in antioxidant and non-antioxidant manners; in particular, over-expression of scavenger receptors and consequent foam cell formation can be prevented by vitamin E. In addition to that, the cellular effects of alpha-tocopheryl phosphate and of EPC-K1, a composite molecule between alpha-tocopheryl phosphate and l-ascorbic acid, are summarized.

Enhancement of intracellular gamma-tocopherol levels in cytokine-stimulated C3H 10T1/2 fibroblasts: relation to NO synthesis, isoprostane formation, and tocopherol oxidation

Background

Stimulation of C3H 10T1/2 murine fibroblasts with interferon-γ(IFN) and bacterial lipopolysaccharide (LPS) generates reactive oxygen and nitrogen species leading to DNA damage, lipid oxidation, and tocopherol oxidation. The tocopherols possess unique chemical and biological properties that suggest they have important roles related to intracellular defense against radical-mediated damage.

Results

Despite increased levels of reactive oxidants and decreased media tocopherol, cellular levels of γ-tocopherol, but not α-tocopherol, were observed to increase significantly when cells were treated with IFN/LPS. Inhibition of nitric oxide (NO) synthesis by a specific inhibitor of inducible NO synthase (iNOS) increased both intracellular α-tocopherol and γ-tocopherol concentrations, but did not significantly alter the reduction in media tocopherol levels caused by IFN/LPS treatment. Both exposure to exogenous NO and cellular synthesis of NO in cell culture increased media levels of 8-epi-prostaglandin F2α, a marker of oxidative lipid damage, whereas inhibition of endogenous NO synthesis reduced media 8-epi-prostaglandin F2α formation to control levels.

Conclusion

Elevated intracellular levels of γ-tocopherol in response to the cellular inflammatory state may indicate that it serves a unique role in minimizing cellular damage resulting from endogenous NO synthesis. Results of the current study suggest that NO is an important mediator of damage within the cell, as well as in the oxidation of both α- and γ-tocopherols. The paradoxical increase in cellular tocopherol associated with the induction of NO synthesis may indicate either enhanced cellular transport/decreased export for tocopherols or recruitment of free tocopherol from tocopherol storage molecules.

Molecular mechanism of alpha-tocopherol action

The inability of other antioxidants to substitute for alpha-tocopherol in a number of cellular reactions, the lack of a compensatory antioxidant response in the gene expression under conditions of alpha-tocopherol deficiency, the unique uptake of alpha-tocopherol relative to the other tocopherols and its slower catabolism, and the striking differences in the molecular function of the different tocopherols and tocotrienols, observed in vitro, unrelated to their antioxidant properties, are all data in support of a nonantioxidant molecular function of alpha-tocopherol. Furthermore, in vivo studies have also shown that alpha-tocopherol is not able, at physiological concentrations, to protect against oxidant-induced damage or prevent disease allegedly caused by oxidative damage. Alpha-tocopherol appears to act as a ligand of not yet identified specific proteins (receptors, transcription factors) capable of regulating signal transduction and gene expression.

Clinical pharmacology and therapeutic use of antioxidant vitamins

The clinical use of antioxidants has gained considerable interest during the last decade. It was suggested from epidemiological studies that diets high in fruits and vegetables might help decrease the risk of cardiovascular disease. Therefore, supplements of vitamins C and E were applied through protocols aimed to prevent diseases such as atherosclerosis, preeclampsia or hypertension, thought to be mediated by oxidative stress. Despite the biological properties of these vitamins could account for an effective protection, as shown by several clinical and experimental studies, their efficacy remains controversial in the light of some recent clinical trials and meta-analyses. However, the methodology of these studies, criteria for selection of patients, the uncertain extent of progression of the disease when initiating supplementation, the lack of mechanistic studies containing basic scientific aspects, such as the bioavailability, pharmacokinetic properties, and the nature of the antioxidant sources of vitamins, could account for the inconsistency of the various clinical trials and meta-analyses assessing the efficacy of these vitamins to prevent human diseases. This review presents a survey of the clinical use of antioxidant vitamins E and C, proposing study models based on the biological effects of these compounds likely to counteract the pathophysiological mechanisms able to explain the structural and functional organ damage.