Administration of the tris salt of alpha-tocopheryl hemisuccinate inactivates CYP2E1, enhances microsomal alpha-tocopherol levels and protects against carbon tetrachloride-induced hepatotoxicity

α-Tocopheryl succinate-suppressed development of cerebral malaria in mice

α-Tocopheryl succinate (α-TOS), a derivative of vitamin E, is synthesized by esterification of α-tocopherol. It has been reported that α-TOS inhibits the mitochondrial complex II resulting in generation of reactive oxygen species, which triggers selective apoptosis in a large number of cancer cells, while it appears largely non-toxic towards normal cells. Plasmodium parasites are well known to have high sensitivity to oxidative stress. Thus, α-TOS is suspected to impact Plasmodium parasites by oxidative stress. In this study, to ascertain whether α-TOS is an appropriate candidate for an anti-malarial drug, C57BL/6J mice were infected with P. yoelii 17XL and P. berghei ANKA, a lethal strain of rodent malaria and experimental cerebral malaria (ECM), and treated with several concentrations of α-TOS by intraperitoneal administration on 1, 3, 5, and 7 days post infection (dpi). In addition, the permeability of the blood brain barrier (BBB) was examined by Evans blue staining in ECM on 7 dpi. As a result of α-TOS treatment, parasitemia was decreased and survival rate was significantly increased in mice infected with both parasites. Furthermore, the intensity of Evans blue staining on brains taken from α-TOS-treated mice was weaker than that of untreated mice. This means that α-TOS might inhibit the breakdown of BBB and progress of cerebral malaria. These findings indicate that vitamin E derivatives like α-TOS might be a potential candidate for treatment drugs against malaria.

Dietary lycopene and tomato extract supplementations inhibit nonalcoholic steatohepatitis-promoted hepatocarcinogenesis in rats

Epidemiological and experimental studies provide supportive evidence that lycopene (LY), a major carotenoid from tomatoes and tomato products, may act as a chemopreventive agent against certain types of cancers. We recently showed that high-fat diet (HFD)-induced nonalcoholic steatohepatitis (NASH) promoted diethylnitrosamine (DEN)-initiated hepatocarcinogenesis in a rat model. Using this model, we investigated the efficacy of an equivalent dosage of dietary LY from either a pure compound or a tomato extract (TE) against NASH-promoted hepatocarcinogenesis. Six groups of rats were injected with DEN and then fed either Lieber-DeCarli control diet or HFD with or without LY or TE for 6 weeks. Results showed that both LY and TE supplementations significantly decreased the number of altered hepatic foci expressing the placental form of glutathione S-transferase in the livers of HFD-fed rats. This was associated with significantly lower proliferating cell nuclear antigen positive hepatocytes and cyclinD1 protein, as well as decreased activation of extracellular signal-regulated kinase and nuclear NF-kappaB. Although both LY and TE supplementations reduced HFD-induced lipid peroxidation in the livers, we observed significantly decreased cytochrome P450 2E1, inflammatory foci and mRNA expression of proinflammatory cytokines (TNF-alpha, IL-1beta and IL-12) in the HFD+TE fed group but increased nuclear NF-E2-related factor-2 and heme oxygenase-1 proteins in the HFD+LY fed group, relative to HFD feeding alone. These data indicate that LY and TE can inhibit NASH-promoted hepatocarcinogenesis mainly as a result of reduced oxidative stress, which could be fulfilled through different mechanisms.

Vitamin E supplementation does not prevent ethanol-reduced hepatic retinoic acid levels in rats

Chronic, excessive ethanol intake can increase retinoic acid (RA) catabolism by inducing cytochrome P450 2E1 (CYP2E1). Vitamin E (VE) is an antioxidant implicated in CYP2E1 inhibition. In the current study, we hypothesized that VE supplementation inhibits CYP2E1 and decreases RA catabolism, thereby preventing ethanol-induced hepatocyte hyperproliferation. For 1 month, 4 groups of Sprague-Dawley rats were fed a Lieber-DeCarli liquid ethanol (36% of the total energy) diet as follows: either ethanol alone (Alc group) or ethanol in combination with 0.1 mg/kg body weight of all-trans-RA (Alc + RA group), 2 mg/kg body weight of VE (Alc + VE group), or both together (Alc + RA + VE group). Control rats were pair-fed a liquid diet with an isocaloric amount of maltodextrin instead of ethanol. The ethanol-fed groups had 3-fold higher hepatic CYP2E1 levels, 50% lower hepatic RA levels, and significantly increased hepatocyte proliferation when compared with the controls. The ethanol-fed rats given VE had more than 4-fold higher hepatic VE concentrations than the ethanol-fed rats without VE, but this did not prevent ethanol induction of CYP2E1, lower hepatic retinoid levels, or hepatocellular hyperproliferation. Furthermore, VE supplementation could not prevent RA catabolism in liver microsomal fractions of the ethanol-fed rats in vitro. These results show that VE supplementation can neither inhibit ethanol-induced changes in RA catabolism nor prevent ethanol-induced hepatocyte hyperproliferation in the rat liver.

Synergic effects of α-tocopherol and β-carotene on tert-butylhydroperoxide-induced HepG2 cell injury

Oxidative stress produced by the dietary or chemical substrates is one of the major causes of liver cell injury. In this study, we compared the effects of two dietary antioxidants, α-tocopherol (α-T) and β-carotene (β-C) against tert-butyl hydroperxide (tBHP)-induced oxidative stress in human hepatoma HepG2 cells. Cell proliferation, lipid peroxidation (LPO), cellular lactate dehydrogenase (LDH), [3H]-aflatoxin B1(AFB1)-DNA adduct formation, and cytochrome P450 2E1 (CYP2E1) expression were determined after antioxidants were added to the tBHP-stressed cells. When compared to an ethanol-based control, all biomarkers for the cell damage were significantly increased by treatments. Treatments of β-C or the combination of two antioxidants at 50 ppm for 48 h enhanced cell proliferation ( P < 0.05) compared to tBHP control. The antioxidative and cytoprotective actions of α-T and β-C, alone or in combination, were associated with modulation of microsomal CYP2E1 expression, corresponding to the regulation of LPO production ( P < 0.0001). Our results indicate that α-T and β-C may contribute differently to protection of cellular membrane disruption in CYP2E1-expressing HepG2 cells. Moreover, the combination of α-T and β-C appears to impel the greater protection of pathogenic processes of oxidative stress in liver.

Free radical scavenging and hepatoprotective actions ofQuercus alienaacorn extract against CCl4-induced liver

In the present study, we investigated the protective effect of Quercus aliena acorn extracts against CCl4-induced hepatotoxicity in rats, and the mechanism underlying the protective effects. Aqueous extracts of Quercus aliena acorn had higher superoxide radical scavenging activity than other types of extracts. The Quercus aliena acorn extracts displayed dose-dependent superoxide radical scavenging activity (IC50 = 4.92 microg/ml), as assayed by the electron spin resonance (ESR) spin-trapping technique. Pretreatment with Quercus aliena acorn extracts reduced the increase in serum aspartate aminotransferase (AST) and serum alanine aminotransferase (ALT) levels. The hepatoprotective action was confirmed by histological observation. The aqueous extracts reversed CCl4-induced liver injury and had an antioxidant action in assays of FeCl2- ascorbic acid induced lipid peroxidation in rats. Expression of cytochrome P450 2E1 (CYP2E1) mRNA, as measured by RT-PCR, was significantly decreased in the livers of Quercus aliena acorn-pretreated rats compared with the livers of the control group. These results suggest that the hepatoprotective effects of Quercus aliena acorn extract are related to its antioxidative activity and effect on the expression of CYP2E1.

Lipid peroxidation induced by carbon tetrachloride and its inhibition by antioxidant as evaluated by an oxidative stress marker, HODE

We have recently proposed total hydroxyoctadecadienoic acid (HODE) as a biomarker for oxidative stress in vivo. The biological samples such as plasma, urine, and tissues were first reduced and then saponified to convert the oxidation products of linoleate to HODE. In the present study, this method was applied to measure the oxidative damage induced by the administration of carbon tetrachloride to mice and also to evaluate the capacity of antioxidant to inhibit the above damage. alpha-Tocopherol transfer protein knock out (alpha-TTP-/-) mice were used to evaluate antioxidant effect in the absence of alpha-tocopherol. The intraperitoneal administration of carbon tetrachloride to mice induced the increase in HODE in liver and plasma, which was followed by an increase in plasma glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT). F2-isoprostanes, another prevailing biomarker, were also increased similarly, but their concentration was approximately two to three orders of magnitude smaller than that of HODE. The lipophilic antioxidants such as gamma-tocopherol, gamma-tocotrienol and 2,3-dihydro-5-hydroxy-4,6-di-tert-butyl-2,2-dipentylbenzofuran (BO-653) were effective in suppressing the formation of HODE.

Preventive Treatment with Vitamin E Alleviates the Poisoning Effects of Carbon Tetrachloride in Cattle

Fifteen yearling steers were used to study the preventive effect of vitamin E on the protection against free radicals produced by carbon tetrachloride (CCl4). The animals were randomly divided in three equal groups and treated as follows: group A--previously injected (i.m.) with 15 IU/kg BW on the 15th and second day before the trial and drenched with 0.05 ml/kg BW CCl4; group B--only drenched with the same dose of CCl4; group C--drenched with a placebo. Food intake was recorded and blood samples collected daily for 8 days after the CCl4 drenching to compare the activity of aspartate aminotransferase (AST), gamma-glutamyltransferase (gamma-GT) and the levels of erythrocyte reduced glutathione (GSH) and serum malonyldialdehyde (MDA). Food intake was reduced in group B for the first 3 days (P < 0.05); higher activities of AST and gamma-GT were observed in the poisoned groups, nevertheless the overall values were lower in the group A than B (P < 0.02); only the group A reached the basal values of AST at the seventh day; higher levels of GSH and MDA were recorded in the poisoned cattle indicating the generation of free radicals. It was concluded that the preventive use of Vitamin E lessened the damage in hepatic tissue caused by the free radicals and prevented the anorexia caused by CCl4.

α-Tocopheryl Succinate Inhibits Malignant Mesothelioma byDisrupting the Fibroblast Growth Factor Autocrine Loop

We have studied the potential effect against human malignant mesotheliomas (MM) of alpha-tocopheryl succinate (alpha-TOS), a redox-silent vitamin E analog with strong pro-apoptotic and anti-cancer activity. alpha-TOS at sub-apoptotic levels inhibited proliferation of MM cell lines, while being nontoxic to nonmalignant mesothelial cells. Because MM cells are typified by a highly metastatic phenotype, we investigated the effect of alpha-TOS on genes playing a major role in MM progression. Of these, alpha-TOS down regulated fibroblast growth factor (FGF)-1 and, in particular, FGF-2 on the transcriptional level in MM cells, and this was not observed in their nonmalignant counterparts. FGF-2 short interfering RNA suppressed proliferation of MM cells. Down-regulation of FGF-2 was likely because of inhibition of the egr-1 transcription activity that was decreased in MM cells via oxidative stress induced by alpha-TOS, as evidenced by EPR spectroscopy, whereas nonmalignant cells did not show this response. Treatment of MM cells with egr-1 short interfering RNA suppressed proliferation, which was overridden by exogenously added recombinant FGF-1 and, in particular, FGF-2. An analog of coenzyme Q targeted to mitochondria and superoxide dismutase overrode inhibition of MM cell proliferation by alpha-TOS as well as alpha-TOS-induced inhibition of egr-1-dependent transactivation. Finally, alpha-TOS significantly suppressed experimental MM in immunocompromised mice. Our data suggest that alpha-TOS suppresses MM cell proliferation by disrupting the FGF-FGF receptor autocrine signaling loop by generating oxidative stress and point to the agent as a selective drug against thus far fatal mesotheliomas.

Pharmacokinetics and tissue distribution ofd-alpha-tocopheryl succinate formulations following intravenous administration in the rat

Unlike d-alpha tocopherol (T), d-alpha tocopheryl succinate (TS) has the unique ability to selectively kill tumor cells while protecting normal tissue from toxic oxidative stress. The pharmacokinetics of TS and the serum and tissue disposition of TS were studied in male Sprague-Dawley rats to delineate formulation dependent disposition between TS administered as the Tris salt (TS-T) (a liposomal formulation) or as the free acid (TS-FA) dissolved in polyethylene glycol (PEG) 400. The pharmacokinetics of TS was studied after single intravenous (i.v.) equimolar doses of 124 mg/kg TS-T and 100 mg/kg of TS-FA. Serial blood samples were collected via a catheter inserted into the right jugular vein and serum samples were analysed for TS and T levels using a reverse phase HPLC method. Terminal tissue samples were also collected at 24 and 48 h. After an acute i.v. dose of TS-T, serum AUC, t(1/2), Cl and V(d) of TS were 2601.0 +/- 351.7 microg h/ml, 9.98 +/- 1.02 h, 0.049 +/- 0. 0073 l/h/kg and 0.7 +/- 0.14 l/kg (mean +/- SD), respectively. The acute i.v. administration of TS-FA (PEG formulation) yielded results similar to those observed for TS-T, with a serum AUC, t(1/2), Cl and V(d) of 2553.3 +/- 166.4 microg h/ml, 9.83 +/- 0.86 h, 0.039 +/- 0.0027 l/h/kg and 0.56 +/- 0.09 l/kg (mean +/- SD), respectively. Distribution into tissues and a low Cl was apparent, with the highest concentrations of TS in the liver and lung, regardless of formulation. As expected, baseline endogenous concentrations of T were present in both groups, with a net increase in T levels, occurring as TS was hydrolysed to T, which slowly peaked in serum between 7-8 h post-dose. Intravenous TS administration, regardless of formulation, also resulted in significant T accumulation in all tissues examined, which was especially abundant in the liver and lung. Likewise, there was a lack of significant effect of formulation on the pharmacokinetics and tissue distribution of TS. The only significant formulation difference was a small but significant increase in serum T and liver T levels in the TS in PEG formulation group. These results indicate that TS may be especially useful for the targeted delivery of T and TS to the lung and liver for anti-oxidant and anti-cancer activity.

Vitamin E succinate and cancer treatment: a vitamin E prototype for selective antitumour activity

Great hope has been given to micronutrients as anticancer agents, since they present natural compounds with beneficial effects for normal cells and tissues. One of these is vitamin E (VE), an antioxidant and an essential component of biological membranes and circulating lipoproteins. In spite of a number of epidemiological and intervention studies, little or no correlation between VE intake and incidence of cancer has been found. Recent reports have identified a redox-silent analogue of VE, alpha-tocopheryl succinate (alpha-TOS), as a potent anticancer agent with a unique structure and pharmacokinetics in vivo. alpha-TOS is highly selective for malignant cells, inducing them into apoptotic death largely via the mitochondrial route. The molecule of alpha-TOS may be modified so that analogues with higher activity are generated. Finally, alpha-TOS and similar agents are metabolised to VE, thereby yielding a compound with a secondary beneficial activity. Thus, alpha-TOS epitomises a group of novel compounds that hold substantial promise as future anticancer drugs. The reasons for this optimistic notion are discussed in the following paragraphs.

Alpha-tocopheryl succinate epitomizes a compound with a shift in biological activity due to pro-vitamin-to-vitamin conversion

With the advent of the third millennium, a number of pathologies have been eradicated or taken under control. However, the incidences, of cancer and atherosclerosis, the two most common causes of death in developed countries, have increased or, in some instances, only stagnated. Therefore there has been an intensive search for agents effective against such life-threatening conditions. Accordingly, the potential anti-atherogenic activity of vitamin E analogs has been studied extensively. Interestingly, recent reports strongly suggest that certain vitamin E analogs, represented in particular by alpha-tocopheryl succinate (alpha-TOS), also possess anti-neoplastic activity. In this communication, we review our current understanding of the molecular basis for these double effects of alpha-TOS and propose a testable hypothesis, according to which this semi-synthetic analog exerts both anti-atherogenic and anti-neoplastic activities. We propose that the prevalence of each activity depends on the actual form of the vitamin E analog. That is, the conversion of the pro-vitamin E form, alpha-TOS, to the corresponding vitamin form, alpha-tocopherol, makes this anti-neoplastic agent active against inflammatory diseases like atherosclerosis.

Vitamin E analogues as inducers of apoptosis: implications for their potential antineoplastic role

Recent evidence suggests that vitamin E and its analogues, which have been used for many years as antioxidants, may not only protect cells from free radical damage but also induce apoptotic cell death in various cell types. While alpha-tocopherol (alpha-TOH) is mainly known as an anti-apoptotic agent, its redox-silent analogues either have no influence on cell survival (alpha-tocopheryl acetate, alpha-TOA), or induce apoptosis (alpha-tocopheryl succinate, alpha-TOS). Although precise mechanisms of apoptosis induction by alpha-TOS remain to be elucidated, there is evidence that this process involves both the antiproliferative and membrane destabilising activities of the agent. Alpha-TOS has been shown to induce apoptosis in malignant cell lines but not, in general, in normal cells, and to inhibit tumorigenesis in vivo. These features suggest that this semi-synthetic analogue of vitamin E could be a promising antineoplastic agent.

Mitochondrial electron transport inhibitors cause lipid peroxidation-dependent and -independent cell death: protective role of antioxidants

Mitochondrial electron transport inhibitors induced two distinct pathways for acute cell death: lipid peroxidation-dependent and -independent in isolated rat hepatocytes. The toxic effects of mitochondrial complex I and II inhibitors, rotenone (ROT) and thenoyltrifluoroacetone (TTFA), respectively, were dependent on oxidative stress and lipid peroxidation, while cell death induced by inhibitors of complexes III and IV, antimycin A (AA) and cyanide (CN), respectively, was caused by MMP collapse and loss of cellular ATP. Accordingly, cellular and mitochondrial antioxidant depletion or supplementation, in general, resulted in a dramatic potentiation or prevention, respectively, of toxic injury induced by complex I and II inhibitors, with little or no effect on complex III and IV inhibitor-induced toxicity. ROT-induced oxidative stress was prevented by the addition of d-alpha-tocopheryl succinate (TS) but surprisingly TS did not afford hepatocytes protection against TTFA-induced oxidative damage. TS treatment prevented ROT-induced mitochondrial lipid hydroperoxide formation but had no effect on the loss of mitochondrial GSH or cellular ATP, suggesting a mitochondrial lipid peroxidation-mediated mechanism for ROT-induced acute cell death. In contrast, only fructose treatment provided excellent cytoprotection against AA- and CN-induced toxicity. Our findings indicate that complex III and IV inhibitors cause a rapid and severe depletion of cellular ATP content resulting in acute cell death that is dependent on cellular energy impairment but not lipid peroxidation. In contrast, inhibitors of mitochondrial complex I or II moderately deplete cellular ATP levels and thus cause acute cell death via a lipid peroxidation pathway.

The protection of Vitamin E and selenium against carbon tetrachloride-induced genotoxicity in ovine peripheral blood lymphocytes

The protective effect of Vitamin E and selenium was studied for the possibility of decreasing the chromosome aberrations (CA), micronuclei (MN) and sister chromatid exchanges (SCE) induced by carbon tetrachloride (CCl(4)) in ovine peripheral lymphocytes cultured in vitro. The cultures of lymphocytes from two healthy lambs were treated with carbon tetrachloride at concentrations of 2, 4, 8, and 16 microg/ml for the last 48 h of cultivation and subsequently with the same doses of CCl(4) and Vitamin E and selenium. A possible metabolic modification in carbon tetrachloride genotoxicity was detected with the application of S9 fraction for 2h. No positive clastogenic effect of CCl(4), and subsequently no protective effect of either antioxidant was obtained in the CA assay. In the MN assay for 48 h, an increase and, respectively, a decrease in the frequency of MN was found in cultures treated with CCl(4) alone and in cultures treated concurrently with CCl(4), Vitamin E and selenium at concentrations of 8 and 16 microg/ml (P<0.001 and P<0.01). High statistical significance was achieved in SCE assay after the treatment of ovine peripheral lymphocytes with CCl(4) at all concentrations tested (P<0.001), except the lowest dose. A significant decrease in SCEs was obtained in cultures treated simultaneously with CCl(4), Vitamin E and selenium (P<0.001). The highest dose (16 microg/ml) was also shown to improve the cell-cycle kinetics in comparison with corresponding unprotected dose (P<0.01). Insufficient confirmation of the genotoxicity of CCl(4) and the protective effect of the antioxidants, respectively were seen in cultures with metabolic activation.