D-alpha-tocopheryl succinate (vitamin E) enhances radiation-induced chromosomal damage levels in human cancer cells, but reduces it in normal cells

Discovery of Alpha-Tocopheryl Succinate as a Cancer Treatment Agent Led to the Development of Methods to Potentially Improve the Efficacy of Cancer Therapy

The discovery of alpha-tocopheryl succinate (alpha-TS) as a cancer therapeutic agent markedly stimulated research with or without tumor therapeutic agents on cancer cells and normal cells. Results showed that alpha-TS treatment induced apoptosis in cancer cells and enhanced the apoptotic effects of tumor therapeutic agents on tumor cells in a synergistic manner without affecting the growth of normal cells. Liposomal alpha-TS was more effective than alpha-TS. Some tumors are difficult to treat with chemotherapeutic agents while some become resistant of such treatment. Using a nanotechnology technique, it was demonstrated that alpha-TS conjugated with a chemotherapeutic agent enhanced the levels of apoptosis and restored the sensitivity of tumor cells to that chemotherapeutic agent. The mechanisms of action of alpha-TS alone or in combination with therapeutic agents include the following: (a) inhibition of the expression of oncogenes C-myc and H-ras; (b) alterations in the levels of expression of numerous genes; (c) activation of caspases; (d) inhibition of angiogenesis; (e) destabilization of mitochondria and lysosomes; (f) inhibition of production of production of prostaglandin E2 (PGE2) and PGE2-mediated pro-inflammatory responses; (g) reduction of survivin signaling pathway; and (h) reduction of CD47 expression on the tumor cell surface causing enhancement of phagocytic activity of macrophages leading to engulfment of tumor cells. Despite impressive results in cell culture and in animal models, no studies with alpha-TS alone or in combination with cancer therapeutic agents in human cancer resistant to these therapies have been performed.

Low to moderate adherence to 2018 diet and physical exercise recommendations of the World Cancer Research Fund/American Institute for Cancer Research is associated with prooxidant biochemical profile in women undergoing adjuvant breast cancer treatment

Adequate adherence to the 2018 diet and exercise recommendations of the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) can possibly result in less oxidative stress, lower risk to chemo- and radiotoxicity, lower risk of relapse, and increased quality of life in breast cancer survivors. This observational study aims to investigate the influence of adherence to updated recommendations of the WCRF/AICR on oxidative stress biomarkers in women with breast cancer undergoing adjuvant treatment (AT). We hypothesized that adherence to WCRF/AICR recommendations is inversely related to oxidative damage biomarkers and directly associated with antioxidant status. Women (n = 78) were evaluated before (T0) and after AT. After collecting anthropometric, physical activity, and food consumption data, a standardized score of adherence to WCRF/AICR recommendations was applied. The sample was divided into low-medium adherence and high adherence groups. Blood samples were collected at both timepoints for oxidative stress biomarkers analysis. Multiple linear regression analyzes were applied to verify associations between WCRF/AICR score and biomarkers. We found that low-medium adherence to WCRF/AICR recommendations at T0 affected lower levels of reduced glutathione (P= .003) and higher levels of lipid hydroperoxides (P= .002) and plasma carbonylated proteins (P= .001) after AT. The WCRF/AICR score at T0 was inversely associated with changes in plasma carbonylated protein concentrations after AT (adjusted β = -0.359; P= .01). Our findings suggest that high WCRF/AICR score before and during AT may provide greater stability of antioxidant capacity and protection against exacerbated oxidative stress.

Phytochemicals: A potential next generation agent for radioprotection

BACKGROUND

Radiation hazards are accountable for extensive damage in the biological system and acts as a public health burden. Owing to the rapid increasing in radiation technology, both Ionizing radiation (IR) from natural and man made source poses detrimental outcome to public health. IR releases free radicals which induces oxidative stress and deleterious biological damage by modulating radiation induced signalling intermediates. The efficacy of existing therapeutic approach and treatment strategy are limited owing to their toxicity and associated side effects. Indian system of traditional medicine is enriched with prospective phytochemicals with potential radioprotection ability.

PURPOSE

The present review elucidated and summarized the potential role of plant derived novel chemical compound with prospective radioprotective potential.

METHOD

So far as the traditional system of Indian medicine is concerned, plant kingdom is enriched with potential bioactive molecules with diverse pharmacological activities. We reviewed several compounds mostly secondary metabolites from plant origin using various search engines.

RESULTS

Both compounds from land plants and marine source exhibited antioxidant antiinflammatory, free radical scavenging ability. These compounds have tremendous potential in fine-tuning of several signalling intermediates, which are actively participated in the progression and development of a pathological condition associated with radiation stress.

CONCLUSION

Development and explore of an operational radioprotective agent from originated from plant source that can be used as a novel molecular tool to eliminate the widespread damage caused by space exploration, ionizing radiation, nuclear war and radiotherapy has been significantly appreciated. Through extensive literature search we highlighted several compounds from both land plant and marine origin can be implemented for a better therapeutic potential against radiation induced injury. Furthermore, extensive clinical trials must be carried out in near future for better therapeutic modality and clinical efficacy.

Promising role of filgrastim and α-tocopherol succinate in amelioration of gastrointestinal acute radiation syndrome (GI-ARS) in mice

The protective role of α-tocopherol succinate (α-TCS) and the therapeutic efficacy of filgrastim were investigated in gastrointestinal acute radiation syndrome (GI-ARS) induced following 10 Gy whole-body γ-irradiation. Mice were randomly allocated into 5 groups: [1] normal-control, [2] irradiated-control, [3] subcutaneous (s.c.) injection of filgrastim (5 μg/kg/day) for 4 consecutive days given 1 h post-irradiation, [4] s.c. injection with α-TCS (400 mg/kg) 1 day prior to irradiation, [5] s.c. injection with α-TCS (400 mg/kg) 1 day prior to irradiation and filgrastim (5 μg/kg/day) for 4 consecutive days 1 h post-irradiation. Histopathological analysis, serum citrulline level, intestinal interleukin-1β (IL-1β), reduced glutathione (GSH), and malondialdehyde (MDA) contents as well as myeloperoxidase (MPO) activity were measured. Intestinal caspase-3, p53, cyclooxygenase-2 (COX-2), and inducible nitric oxide synthase (iNOS) immunopositivity were examined. In irradiated-control, MDA increased (249%) and GSH decreased (25%) compared to normal and were unaffected by filgrastim. α-TCS alone significantly reduced MDA (84.5%) and normalized GSH. The combination significantly reduced MDA (59%) and dramatically increased GSH (1573%), pointing to a possible synergistic action. In irradiated-control, MPO and IL-1β significantly increased (111% and 613%, respectively) compared to normal-control and both were significantly decreased in all treated groups. Compared to normal-control, citrulline significantly declined (68%) in irradiated-control; a significant elevation was achieved by treatments with α-TCS alone or combined with filgrastim (88% and 94%, respectively). The combination therapy significantly decreased the degree of irradiation-induced injury of the epithelium and cellular infiltration and showed the lowest histopathological scoring compared to the other groups (p ≤ 0.05). In irradiated-control, immune-reactive expressions of iNOS, COX-2, caspase-3, and p53 were remarkable (18.62%, 34.27%, 31.19%, and 27.44%, respectively) and after combination therapy were reduced (1.04%, 22.39%, 8.76%, and 4.91%, respectively). The current findings represent a first-hand strategy in dealing with GI-ARS with a potential preference to using a combined therapy of filgrastim and α-TCS.

Antioxidants in the Treatment of Cancer

Several clinical trials have produced conflicting results regarding the benefit of antioxidants in cancer therapy thus questioning the incorporation of these substances in standard treatment regimens. Vitamins E and C, selenium, carotenoids, lycopene, soy products, and green tea extract are a few substances with antioxidant properties that have been studied in detail. This article reviews the results generated over the last 20 years through in vitro and in vivo studies in various types of cancers and stages of cancer treatment. Despite the commercial popularity and the multitude of studies examining antioxidant therapy, the true role of antioxidants is yet to be determined, requiring further investigation into its propagative, causal, or protective nature.

TP53 alteration determines the combinational cytotoxic effect of doxorubicin and an antioxidant NAC

The anticancer effect of doxorubicin is closely related to the generation of reactive oxygen species. On the contrary, doxorubicin-induced reactive oxygen species induces heart failure, a critical side effect of doxorubicin. Antioxidant supplementation has been proposed to reduce the side effects. However, the use of antioxidants may hamper the anticancer effect of doxorubicin. In this study, doxorubicin-induced reactive oxygen species was shown to differentially affect cancer cells based on their TP53 genetic status; doxorubicin-induced apoptosis was attenuated by an antioxidant, N-acetylcysteine, in TP53 wild cells; however, N-acetylcysteine caused a synergistic increase in the apoptosis rate in TP53-altered cells. N-acetylcysteine prevented phosphorylation of P53 protein that had been induced by doxorubicin. However, N-acetylcysteine increased the cleavage of poly (ADP-ribose) polymerase in the presence of doxorubicin. Synergy score of 26 patient-derived cells were evaluated after the combination treatment of doxorubicin and N-acetylcysteine. The synergy score was significantly higher in TP53-altered group compared with those in TP53 wild group. In conclusion, TP53 genetic alteration is a critical factor that determines the use of antioxidant supplements during doxorubicin treatment.

Ameliorative efficacy of bioencapsulated Chironomous larvae with Shilajit on Zebrafish (Danio rerio) exposed to Ionizing radiation

Using Zebrafish (Danio rerio) as a model organism, we evaluated the radioprotective and antioxidant effects of the Indian traditional medicine Shilajit exposed to X-Ray. The Zebrafish were divided into three experimental groups and control group, each group containing ten fish. The three experimental fish groups, group I, group II and group III were fed with 3, 5 and 7ppm shilajit encapsulated Chironomous larvae and group IV served as a control fed with non- encapsulated larvae. After 60 days of feeding trial, fish were irradiated with X-Ray at a single acute dose of 1Gy. 72h of post-irradiation, each experimental fish were observed for its morphological, behavioral, clinical symptoms, antioxidant levels and DNA damage were evaluated. Among the experimental groups 5ppm shilajit encapsulated Chironomous larvae fed fish group shows the most significant radioprotective effects compared with control and other experimental fish groups. The present study indicates that shilajit have significant radioprotective and antioxidant enhancing capability. The humus substance of shilajit may be the factor responsible to react with radiation-derived or radiation related reactive species on zebrafish.

Vitamin E Analogs as Radiation Response Modifiers

The potentially life-threatening effects of total body ionizing radiation exposure have been known for more than a century. Despite considerable advances in our understanding of the effects of radiation over the past six decades, efforts to identify effective radiation countermeasures for use in case of a radiological/nuclear emergency have been largely unsuccessful. Vitamin E is known to have antioxidant properties capable of scavenging free radicals, which have critical roles in radiation injuries. Tocopherols and tocotrienols, vitamin E analogs together known as tocols, have shown promise as radioprotectors. Although the pivotal mechanisms of action of tocols have long been thought to be their antioxidant properties and free radical scavenging activities, other alternative mechanisms have been proposed to drive their activity as radioprotectors. Here we provide a brief overview of the effects of ionizing radiation, the mechanistic mediators of radiation-induced damage, and the need for radiation countermeasures. We further outline the role for, efficacy of, and mechanisms of action of tocols as radioprotectors, and we compare and contrast their efficacy and mode of action with that of another well-studied chemical radioprotector, amifostine.

Molecular dynamics guided design of tocoflexol: a new radioprotectant tocotrienol with enhanced bioavailability

There is a pressing need to develop safe and effective radioprotector/radiomitigator agents for use in accidental or terrorist-initiated radiological emergencies. Naturally occurring vitamin E family constituents, termed tocols, that include the tocotrienols, are known to have radiation-protection properties. These agents, which work through multiple mechanisms, are promising radioprotectant agents having minimal toxicity. Although α-tocopherol (AT) is the most commonly studied form of vitamin E, the tocotrienols are more potent than AT in providing radioprotection and radiomitigation. Unfortunately, despite their very significant radioprotectant activity, tocotrienols have very short plasma half-lives and require dosing at very high levels to achieve necessary therapeutic benefits. Thus, it would be highly desirable to develop new vitamin E analogues with improved pharmacokinetic properties, specifically increased elimination half-life and increased area under the plasma level versus time curve. The short elimination half-life of the tocotrienols is related to their low affinity for the α-tocopherol transfer protein (ATTP), the protein responsible for maintaining the plasma level of the tocols. Tocotrienols have less affinity for ATTP than does AT, and thus have a longer residence time in the liver, putting them at higher risk for metabolism and biliary excretion. We hypothesized that the low-binding affinity of tocotrienols to ATTP is due to the relatively more rigid tail structure of the tocotrienols in comparison with that of the tocopherols. Therefore, compounds with a more flexible tail would have better binding to ATTP and consequently would have longer elimination half-life and, consequently, an increased exposure to drug, as measured by area under the plasma drug level versus time curve (AUC). This represents an enhanced residence of drug in the systemic circulation. Based on this hypothesis, we developed a new class of vitamin E analogues, the tocoflexols, which maintain the superior bioactivity of the tocotrienols with the potential to achieve the longer half-life and larger AUC of the tocopherols.

Vitamin E: tocopherols and tocotrienols as potential radiation countermeasures

Despite the potential devastating health consequences of intense total-body irradiation, and the decades of research, there still remains a dearth of safe and effective radiation countermeasures for emergency, radiological/nuclear contingencies that have been fully approved and sanctioned for use by the US FDA. Vitamin E is a well-known antioxidant, effective in scavenging free radicals generated by radiation exposure. Vitamin E analogs, collectively known as tocols, have been subject to active investigation for a long time as radioprotectors in patients undergoing radiotherapy and in the context of possible radiation accidents or terrorism scenarios. Eight major isoforms comprise the tocol group: four tocopherols and four tocotrienols. A number of these agents and their derivatives are being investigated actively as radiation countermeasures using animal models, and several appear promising. Although the tocols are well recognized as potent antioxidants and are generally thought to mediate radioprotection through 'free radical quenching', recent studies have suggested several alternative mechanisms: most notably, an 'indirect effect' of tocols in eliciting specific species of radioprotective growth factors/cytokines such as granulocyte colony-stimulating factor (G-CSF). The radioprotective efficacy of at least two tocols has been abrogated using a neutralizing antibody of G-CSF. Based on encouraging results of radioprotective efficacy, laboratory testing of γ-tocotrienol has moved from a small rodent model to a large nonhuman primate model for preclinical evaluation. In this brief review we identify and discuss selected tocols and their derivatives currently under development as radiation countermeasures, and attempt to describe in some detail their in vivo efficacy.

Baicalein Triggers Mitochondria-Mediated Apoptosis and Enhances the Antileukemic Effect of Vincristine in Childhood Acute Lymphoblastic Leukemia CCRF-CEM Cells

Acute lymphoblastic leukemia (ALL) accounts for approximately 75% of childhood leukemia, and chemotherapy remains the mainstay therapy. Baicalein is an active flavonoid used in traditional Chinese medicine and has recently been found to have anticancer, anti-inflammatory, and antiallergic properties. This study aims to investigate the molecular apoptotic mechanisms of baicalein in CCRF-CEM leukemic cells and to evaluate the combined therapeutic efficacy of baicalein with several commonly used chemotherapeutic drugs in CCRF-CEM cells. Our results demonstrate that baicalein induces mitochondria-dependent cleavage of caspases-9 and -3 and PARP with concomitant decreases in IAP family proteins, survivin, and XIAP. Furthermore, our results present for the first time that baicalein triggers a convergence of the intrinsic and extrinsic apoptotic pathways via the death receptor-caspase 8-tBid signaling cascade in CCRF-CEM cells. In addition, we also present for the first time that the combination of baicalein and vincristine results in a synergistic therapeutic efficacy. Overall, this combination strategy is recommended for future clinical trials in the treatment of pediatric leukemia owing to baicalein's beneficial effects in alleviating the vomiting, nausea, and skin rashes caused by chemotherapy.

Role of vitamin E-acetate on cisplatin induced genotoxicity: An in vivo analysis

Vitamin E has generated immense interest because of its potential of being an antioxidant, a neuroprotector, and a protector against atherosclerosis, carcinogenesis and cardiovascular disease. However, the prooxidant chemistry of vitamin E cannot be ignored since it is related to the generation of peroxyl radicals. In the present study, 125, 250 and 500 mg/kg of vitamin E-acetate (VE) administered intraperitoneally (i.p.) to Balb/C mice significantly induced 6%, 8% and 11.33% (control value=2.33%) of chromosome aberrations (CA) and 0.88%, 1.39% and 1.81% (control value=0.61%) of micronucleus (MN), following 24 hour of treatment in the bone marrow cells. In the germ cells, VE did not induce any sperm head abnormality (SHA) after 35 days of exposure. Most importantly, it has been observed that pre-treatment with VE significantly reduces CA, MN, and SHA induction by chemotherapeutic drug cisplatin (CIS). Our findings suggest that lone treatment with VE induce genotoxicity in somatic cells after 24 and 48 hours of exposure but not in germ cells after 35 days of exposure, whereas pre-treatment with VE reduces CIS induced genotoxicity as well as cytotoxicity. There exists a thin line of difference on the behavioral transition of VE when acting alone and when acting with a drug.

Induction of DNA damage and caspase-independent programmed cell death by vitamin E

Vitamin E comprises 8 functionally unique isoforms and may be a suitable candidate for the adjuvant treatment of prostate cancer. In this study, we examined the ability of 2 vitamin E isoforms [α-tocotrienol (γ-TT) and δ-tocotrienol (δ-TT)] and 4 synthetic derivatives [γ- and δ-tocotrienol succinate (γ-TS, δ-TS), α-tocopheryl polyethylene glycol succinate (TPGS), and α-tocopheryl polyethylene glycol ether (TPGS-e)] of vitamin E to induce cell death in AR- (DU145 and PC-3) and AR+ (LNCaP) prostate cancer cell lines. Our results show that δ-TT and TPGS-e are the most effective isoform and synthetic derivative, respectively, of all compounds examined. Overall, the results of our study suggest that isoforms and synthetic derivatives of vitamin E have the potency to trigger both caspase-dependent and -independent DNA damage and dominant caspase-independent programmed cell death. The capacity of vitamin E to trigger caspase-independent programmed cell death suggests that it may be useful in the chemotherapy of prostate cancer since it may prevent the tumor resistance commonly associated with the use of classical chemotherapeutic agents that trigger caspase-dependent programmed cell death.

Dl-α-tocopherol enhances the herbicide 1,1'-dimetyl-4,4'-bipyridium dichloride (paraquat, PQ) genotoxicity in cultured anuran leukocytes

This cytogenetic and pharmacological study attempts to clarify genotoxicity-enhancement-effect of dl-α-tocopherol (one form of vitamin E) in combination with the herbicide 1,1'-dimetyl-4,4'-bipyridium dichloride (paraquat, PQ) on cultured anuran leukocytes using the superoxide dismutase-mimic Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin (Mn(III)TMpyP), the hydrogen peroxide-scavenger catalase and the electron donor nicotinamide adenine dinucleotido phosphate (NADPH). PQ only was found to induce structural chromosomal damage in cultured anuran leukocytes in a dose-dependent manner. PQ plus NADPH, which served as positive control, enhanced the genotoxic effect of PQ. Dl-α-tocopherol only did not induce any structural chromosomal damage in the leukocytes. PQ plus dl-α-tocopherol, however, enhanced the genotoxic effect of PQ. PQ plus Mn(III)TMpyP, PQ plus catalase and PQ plus Mn(III)TMpyP plus catalse suppressed the genotoxic effect of PQ. Furthermore, PQ plus dl-α-tocopherol-enhanced chromosomal damage was also inhibited by Mn(III)TMpyP plus catalase. These results suggest that dl-α-tocopherol in combination with PQ functions as an electron donor to PQ.

Mechanisms underlying the radioprotective properties of γ-tocotrienol: comparative gene expression profiling in tocol-treated endothelial cells

Among the eight naturally occurring vitamin E analogs, γ-tocotrienol (GT3) is a particularly potent radioprophylactic agent in vivo. Moreover, GT3 protects endothelial cells from radiation injury not only by virtue of its antioxidant properties but also by inhibition of 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase and by improving the availability of the nitric oxide synthase cofactor tetrahydrobiopterin. Nevertheless, the precise mechanisms underlying the superior radioprotective properties of GT3 compared with other tocols are not known. This study, therefore, examined the differences in gene expression profiles between GT3 and its tocopherol counterpart, γ-tocopherol, as well as between GT3 and α-tocopherol in human endothelial cells. Cells were treated with vehicle or the appropriate tocol for 24 h, after which total RNA was isolated and genome-wide gene expression profiles were obtained using the Illumina platform. GT3 was far more potent in inducing gene-expression changes than α-tocopherol or γ-tocopherol. In particular, GT3 induced multiple changes in pathways known to be of importance in the cellular response to radiation exposure. Affected GO functional clusters included response to oxidative stress, response to DNA damage stimuli, cell cycle phase, regulation of cell death, regulation of cell proliferation, hematopoiesis, and blood vessel development. These results form the basis for further studies to determine the exact importance of differentially affected GO functional clusters in endothelial radioprotection by GT3.

Tocopherol succinate: modulation of antioxidant enzymes and oncogene expression, and hematopoietic recovery

PURPOSE

A class of naturally occurring isoforms of tocopherol (tocols) was shown to have varying degrees of protection when administered before radiation exposure. We recently demonstrated that α-tocopherol succinate (TS) is a potential radiation prophylactic agent. Our objective in this study was to further investigate the mechanism of action of TS in mice exposed to (60)Co γ-radiation.

METHODS AND MATERIALS

We evaluated the effects of TS on expression of antioxidant enzymes and oncogenes by quantitative RT-PCR in bone marrow cells of (60)Co γ-irradiated mice. Further, we tested the ability of TS to rescue and repopulate hematopoietic stem cells by analyzing bone marrow cellularity and spleen colony forming unit in spleen of TS-injected and irradiated mice.

RESULTS

Our results demonstrate that TS modulated the expression of antioxidant enzymes and inhibited expression of oncogenes in irradiated mice at different time points. TS also increased colony forming unit-spleen numbers and bone marrow cellularity in irradiated mice.

CONCLUSIONS

Results provide additional support for the observed radioprotective efficacy of TS and insight into mechanisms.

DNA damage in cultured skin microvascular endothelial cells exposed to gamma rays and treated by the combination pentoxifylline and α-tocopherol

PURPOSE

This in vitro study aims at evaluating the effect of the combination of pentoxifylline (PTX) and trolox (Tx), the water-soluble analogue of alpha-tocopherol, on the oxidative state and DNA damage in dermal microvascular endothelial cells exposed to doses up to 10 Gy of ionizing radiation.

MATERIALS AND METHODS

Confluent primary cultures of dermal endothelial cells were gamma irradiated at 3 and 10 Gy, and 0.5 mM of both drugs, PTX and Tx, was added either before (15 min) or after (30 min or 24 h) irradiation. Reactive oxygen species (ROS), measured by the dichlorodihydrofluorescein diacetate assay, and DNA damage, assessed by the comet and micronucleus assays, were measured at different times after exposure (0 - 21 days).

RESULTS

The PTX/Tx treatment decreased the early and delayed peak of ROS production by a factor of 2.8 in 10 Gy-irradiated cells immediately after irradiation and the basal level by a factor of 2 in non-irradiated control cells. Moreover, the level of DNA strand breaks, as measured by the comet assay, was shown to be reduced by half immediately after irradiation when the PTX/Tx treatment was added 15 min before irradiation. However, unexpectedly, it was decreased to a similar extent when the drugs were added 30 min after radiation exposure. This reduction was accompanied by a 2.2- and 3.6-fold higher yield in the micronuclei (MN) frequency observed on days 10 and 14 post-irradiation, respectively.

CONCLUSION

These results suggest that oxidative stress and DNA damage induced in dermal microvascular endothelial cells by radiation can be modulated by early PTX/Tx treatment. These drugs acted not only as radical scavengers, but they were also responsible for the increased MN frequency in 10 Gy-irradiated cells. Thus, these drugs may cause a possible interference with DNA repair processes.

Antioxidants and Other Micronutrients in Complementary Oncology

Many patients being treated for cancer use micronutrient supplements, with the intention to complement their cancer treatment or help them cope with the therapy- and disease-associated side effects. The majority are adding antioxidants without the knowledge of the treating physician. There are many concerns that antioxidants might decrease the effectiveness of chemotherapy, but increasing evidence suggests a benefit when antioxidants are added to conventional cytotoxic therapies. However, it is imperative that physicians explore the use of antioxidant and other micronutrient supplements with their cancer patients and educate them about potentially negative as well as potentially beneficial effects.

Vitamin E and cancer: An insight into the anticancer activities of vitamin E isomers and analogs

Current observations in the literature suggest that vitamin E may be a suitable candidate for the adjuvant treatment of cancer. Even though historically most research focused on alpha-tocopherol, more recent evidence suggests that the other isomers of vitamin E (beta-, gamma- and delta-tocopherols and alpha-, beta-, gamma- and delta-tocotrienols) differ in their proapoptotic potencies. The main focus of this communication is the current understanding of the molecular mechanisms regulated by vitamin E isomers and their analogs during the induction of apoptosis. This review highlights that the mitochondria are the major target for the induction of apoptosis by vitamin E isomers and analogs and that the various signaling pathways regulated by these agents are likely to contribute towards maximizing the intrinsic pathway of apoptosis triggered initially by the mitochondria. Overall, the presentation of recent studies from the literature in this communication allows the drawing of the following important conclusions: (i) no direct link exists between the antioxidant activity of each isomer/derivative and proapoptotic potency, (ii) tocotrienols are more effective proapoptotic agents than tocopherols, (iii) synthetic modifications of the naturally occurring compounds may improve their apoptotic potency and (iv) vitamin E isomers and derivatives regulate caspase-independent pathways of apoptosis. The latter combined with the evidence presented in this review regarding the additive or synergistic anticarcinogenic effects obtained when vitamin E analogs are used in combination with other cancer chemotherapeutic agents, supports further research to design the most promising vitamin E derivatives and clinically test them in adjuvant chemotherapeutic treatments.

The vitamin E analog tocopherol succinate strongly inhibits gap junctional intercellular communication in rat liver epithelial cells (IAR203)

Vitamin E is a scavenger molecule trapping free radicals in biological membranes. However, it has also been shown to elicit the formation of reactive oxygen species and apoptosis in cancer cells. In this study, we tested the ability of alpha-tocopherol, tocopherol acetate, tocopherol phosphate and tocopherol succinate (TS) to modulate gap junctional intercellular communication in the rat liver epithelial cell line IAR203, as measured by the transfer of Lucifer yellow. While alpha-tocopherol, tocopherol acetate and tocopherol phosphate moderately reduced the dye transfer, TS at 10 and 25 microM strongly inhibited it, probably via the induction of the hypophosphorylation of connexin 43. Our results show that, besides their interesting antioxidant properties, vitamin E analogs, especially TS, can exert adverse effects on gap junctional intercellular communication, which could explain their controversial effects in carcinogenesis.

Modulation of gamma-ray-induced apoptosis in human peripheral blood leukocytes by famotidine and vitamin C

To study the radioprotective effects of vitamin C and famotidine against radiation-induced apoptosis in human peripheral blood leukocytes, peripheral blood was obtained from six healthy volunteers including three males and three females. Twelve microlitres of blood sample diluted in 1 ml complete RPMI-1640 medium was irradiated with various doses of gamma-rays (4, 8 and 12 Gy) in the presence or absence of various doses of vitamin C and famotidine. After 48 and 72 h incubation in a 37 degrees C CO(2) incubator, neutral comet assay was performed for all samples. At least 1000 cells were analyzed for each sample for presence of apoptosis. Data were statistically evaluated using Mann-Whitney non-parametric and ANOVA tests. Results show a significant increase in apoptosis induction following gamma-irradiation with a dose dependent manner compared to controls (p<0.001). Presence of famotidine at 200 microg/ml produced a significant protective effect against radiation-induced apoptosis for various doses of radiation. Similar effects were observed for vitamin C at much lower doses (10 microg/ml). Dose reduction factor (DRF) calculated for famotidine treatment was about 1.5, and above 2 for vitamin C treatment. These results suggest that both vitamin C and famotidine suppresses radiation-induced apoptosis when used with various doses of gamma-irradiation (4-12 Gy) probably via *OH radical scavenging and an intracellular antioxidation mechanism.

Mechanism of apoptosis with the involvement of calpain and caspase cascades in human malignant neuroblastoma SH-SY5Y cells exposed to flavonoids

Neuroblastoma is the most common extracranial solid tumor in children causing death at pre-school age, as no cure has yet been developed. We investigated the proteolytic mechanisms for apoptosis in human malignant (N-type) neuroblastoma SH-SY5Y cells following exposure to flavonoids such as apigenin (APG), (-)-epigallocatechin (EGC), (-)-epigallocatechin-3-gallate (EGCG) and genistein (GST). We found decrease in viability of SH-SY5Y cells with an increase in dose of APG, EGC, EGCG and GST. Predominantly apoptosis occurred following exposure of SH-SY5Y cells to 50 microM APG, 50 microM EGC, 50 microM EGCG and 100 microM GST for 24 hr. Apoptosis was associated with increases in intracellular free [Ca(2+)] and Bax:Bcl-2 ratio, mitochondrial release of cytochrome c and activation of caspase-9, calpain and caspase-3. Induction of apoptosis with APG and GST showed activation of caspase-12 as well. Activation of caspase-3 could cleave the inhibitor-of-caspase-activated DNase (ICAD) to release and translocate caspase-3-activated DNase (CAD) to the nucleus. Activation of caspase-8 cleaved Bid to truncated Bid (tBid) in cells treated with EGC and EGCG. EGC and EGCG induced apoptosis with caspase-8 activation and mitochondria-mediated pathway, whereas APG and GST caused apoptosis via an increase in intracellular free [Ca(2+)] with calpain activation and mitochondria-mediated pathway. Activation of different proteases for cell death was confirmed using caspase-8 inhibitor II, calpeptin (calpain inhibitor), caspase-9 inhibitor I and caspase-3 inhibitor IV. Thus, plant-derived flavonoids cause cell death with activation of proteolytic activities of calpain and caspases in SH-SY5Y cells, and therefore serve as potential therapeutic agents for controlling the growth of neuroblastoma.

Vitamin E and L-carnitine, separately or in combination, in the prevention of radiation-induced oral mucositis and myelosuppression: a controlled study in a rat model

The aim of this study was to determine the effects of vitamin E (VE) and L-carnitine (LC) supplementation, separately or in combination, on radiation-induced oral mucositis and myelosuppression. Group 1 received no treatment (control). Group 2 received 15 Gray of 60Co gamma irradiation as a single dose to total cranium (IR). Group 3, 4, and 5 received irradiation plus 40 mg/kg/day VE (IR+VE) or 200 mg/kg/day LC (IR+LC) or in combination (IR+VE+LC) respectively. Clinically and histopathologically, assessments of mucosal reactions were performed by two independent experts in Radiation Oncology and Pathology, respectively. Hematologic analyses and antioxidant enzyme evaluations were also performed. Irradiation significantly increased oral mucositis, and decreased thrombocyte and White Blood Cell counts. A significant increase in malondialdehyde (MDA) levels and decrease in superoxide dismutase (SOD) and catalase (CAT) activities in plasma were found in the IR group. VE and LC administration, separately, plus irradiation significantly delayed the starting day, and reduced the severity of, oral mucositis. This administration also reduced a fall in the numbers of thrombocyte and WBC caused by irradiation, and decreased the MDA level, and increased the activity of SOD and CAT enzymes in the plasma. VE and LC, in combination, plus irradiation did not provide a superior radioprotection against radiation-induced toxicities.

Rationale for using multiple antioxidants in protecting humans against low doses of ionizing radiation

Health risks of low doses of ionizing radiation (10 cGy or less) may not be accurately estimated in humans by epidemiological study or mathematical modelling because of several inherent confounding factors including environmental, dietary and biological variables that cannot be accounted for in any radio-epidemiological study. In addition, the expression of radiation-induced damage in humans not only depends upon total dose, dose rate, linear energy transfer (LET), and fractionation and protraction of total doses, but also on repair mechanisms, bystander effects, and exposure to chemical carcinogens, tumour promoters and other toxins. It also depends upon the levels of anti-carcinogenic and anti-tumour promoting agents. Low doses of ionizing radiation should not be considered insignificant with regard to increasing the incidence of somatic mutations (neoplastic and non-neoplastic diseases) and heritable mutations in humans owing to its interaction with other toxins that can enhance damage produced by irradiation. It is very prudent to continue to support the well-established radiobiological concept that no radiation dose can be considered completely safe, and that all efforts must be made to reduce both the radiation dose and biological damage, no matter how small that damage might be, without sacrificing the benefits of radiation. Based on the results of many scientific experiments, formulations containing multiple antioxidants for biological protection against radiation damage in humans can be developed, and this strategy together with the existing physical concept of radiation protection, should further reduce potential risks of low doses of ionizing radiation in humans.

Randomized trial of antioxidant vitamins to prevent acute adverse effects of radiation therapy in head and neck cancer patients

PURPOSE

Many cancer patients take antioxidant vitamin supplements with the hope of improving the outcome of conventional therapies and of reducing the adverse effects of these treatments. A randomized trial was conducted to determine whether supplementation with antioxidant vitamins could reduce the occurrence and severity of acute adverse effects of radiation therapy and improve quality of life without compromising treatment efficacy.

PATIENTS AND METHODS

We conducted a randomized, double-blind, placebo-controlled trial among 540 head and neck cancer patients treated with radiation therapy. Patients were randomly assigned into two arms. The supplementation with alpha-tocopherol (400 IU/d) and beta-carotene (30 mg/d) or placebos was administered during radiation therapy and for 3 years thereafter. During the course of the trial, supplementation with beta-carotene was discontinued because of ethical concerns.

RESULTS

Patients randomly assigned in the supplement arm tended to have less severe acute adverse effects during radiation therapy (odds ratio [OR], 0.72; 95% CI, 0.52 to 1.02). The reduction was statistically significant when the supplementation combined alpha-tocopherol and beta-carotene for adverse effects to the larynx (OR, 0.38; 95% CI, 0.21 to 0.71) and overall at any site (OR, 0.38; 95% CI, 0.20 to 0.74). Quality of life was not improved by the supplementation. The rate of local recurrence of the head and neck tumor tended to be higher in the supplement arm of the trial (hazard ratio, 1.37; 95% CI, 0.93 to 2.02).

CONCLUSION

Supplementation with high doses of alpha-tocopherol and beta-carotene during radiation therapy could reduce the severity of treatment adverse effects. However, this trial suggests that use of high doses of antioxidants as adjuvant therapy might compromise radiation treatment efficacy.

Radical mediators and mitogen-activated protein kinase signaling in oxygen-dependent radiosensitivity of human tumor cell lines

Oxygen enhancement of tumor radiosensitivity is attributed to DNA damage by reactive oxygen species. The mechanism remains unclear but may involve mitochondria as major sources of oxygen and nitrogen radicals as well as central effectors of energy homeostasis and apoptosis. Here we used dihydrorhodamine and 2',7'-dichlorodihydrofluorescein to compare mitochondrial and total cell generation, respectively, of reactive oxygen or nitrogen species in cells irradiated at 5 Gy. Irradiation in the presence of oxygen selectively stimulated mitochondrial radical production in HeLa and MeWo cells, but in MCF7 cells radical production was more generalized. In all three cell lines oxygen impaired cell proliferation as measured by resazurin reduction 7 days after irradiation. Antioxidants N-acetylcysteine, ascorbic acid, and melatonin largely prevented dye oxidation during normoxic irradiation yet had no effect on oxygen-dependent irradiation injury. However, NO synthase inhibitor N(G)-monomethyl-L-arginine protected HeLa and MCF7 though not MeWo cells, consistent with their different levels of constitutive NO generation. SB203580 inhibition of p38 MAPK appreciably protected HeLa and marginally protected MCF7 cells against oxygen-dependent irradiation injury, while the less specific JNK/SAPK inhibitor SP600125 and ERK inhibitor U0126 had no effect. None of the inhibitors affected MeWo radiosensitivity. Therefore oxygen-enhanced radiosensitivity in these tumor cell lines does not depend on extensive production of oxygen radicals and is cell-type dependent. NO mediates oxygen-dependent injury in HeLa and MCF7 cells, by p38-dependent and MAPK-independent mechanisms, respectively. In MeWo cells this oxygen-enhanced radiosensitivity is independent of both NO and MAPK signaling.

Modulation of DNA Damage by Pentoxifylline and α-Tocopherol in Skin Fibroblasts Exposed to Gamma Rays

Previous in vivo studies showed the combination pentoxifylline (PTX) and alpha-tocopherol was highly efficient in reducing late radiation-induced skin damage. The present work aimed at investigating the molecular and cellular mechanisms involved in the effects of this combination. Primary cultures of confluent dermal fibroblasts were gamma-irradiated in the presence of PTX and trolox (Tx), the water-soluble analogue of alpha-tocopherol. Drugs were added either before or after radiation exposure and were maintained over time. Their antioxidant capacity and their effect on radiation-induced ROS production was assessed together with cell viability and clonogenicity. DNA damage formation was assessed by the alkaline comet assay and by the micronucleus (MN) test. Cell cycle distribution was also determined. The combination of PTX/ Tx was shown to reduce both immediate and late ROS formation observed in cells after irradiation. Surprisingly, decrease in DNA strand breaks measured by the comet assay was observed any time drugs were added. In addition, the micronucleus test revealed that for cells irradiated with 10 Gy, a late significant increase in MN formation occurred. The combination of PTX/Tx was shown to be antioxidant and to decrease radiation-induced ROS production. The observed effects on DNA damage at any time the drugs were added suggest that PTX/Tx could interfere with the DNA repair process.

Multiple dietary antioxidants enhance the efficacy of standard and experimental cancer therapies and decrease their toxicity

Cancer patients can be divided into 3 groups: those receiving standard or experimental therapy, those who have become unresponsive to these therapies, and those in remission at risk for recurrence or a second new cancer. While impressive progress in standard cancer therapy has been made, the value of this therapy in the management of solid tumors may have reached a plateau. At present, there is no strategy to reduce the risk of recurrence of the primary tumors or of a second cancer among survivors. Patients unresponsive to standard or experimental therapies have little option except for poor quality of life for the remainder of life. Therefore, additional approaches should be developed to improve the efficacy of current management of cancer. In this review, the author proposes that an active nutritional protocol that includes high doses of multiple dietary antioxidants and their derivatives (vitamin C, alpha-tocopheryl succinate, and natural beta-carotene), but not endogenously made antioxidants (glutathione- and antioxidant enzyme-elevating agents), when administered as an adjunct to radiation therapy, chemotherapy, or experimental therapy, may improve its efficacy by increasing tumor response and decreasing toxicity. This nutritional protocol can also be used when patients become unresponsive to standard therapy or experimental therapy to improve quality of life and possibly increase the survival time. The authors also propose that after completion of standard therapy and/or experimental therapy, a maintenance nutritional protocol that contains lower doses of antioxidants and their derivatives, together with modification in diet and lifestyle, may reduce the risk of recurrence of the original tumor and development of a second cancer among survivors. Experimental data and limited human studies suggest that use of these nutritional approaches may improve oncologic outcomes and decrease toxicity. This review also discusses the reasons for the current debates regarding the use of antioxidants during radiation or chemotherapy.

Micronutrients and Cancer Therapy

The effect of micronutrient supplementation on the effectiveness of cancer chemotherapeutic agents is reviewed, and the efficacy of antioxidants, folic acid, and other vitamins and minerals is discussed. Although some micronutrients show promise in enhancing the cytotoxicity of anticancer agents in vitro, caution should be exercised in recommending micronutrient supplementation for cancer patients receiving chemotherapeutic drugs. To date, few well-controlled clinical trials have been conducted to evaluate the efficacy of micronutrients in promoting the sensitivity of tumors to chemotherapeutic agents.

Role of reactive oxygen species in the induction of apoptosis by ?-tocopheryl succinate

Alpha-tocopheryl succinate (TOS), a vitamin E analog, is a promising anticancer agent due to its abilities to inhibit proliferation and to induce apoptosis in a variety of human malignant cell lines, while being relatively less active toward normal cells. However, the molecular mechanisms underlying the apoptotic effects of TOS are not precisely understood. Reports that TOS can generate reactive oxygen species (ROS) prompted us to investigate the role of ROS in TOS-induced apoptosis in cancer cells. We found that the human lung cancer A549 and H460 cell lines were much more sensitive to TOS-induced apoptosis than the human glioblastoma T98G and U87MG cell lines. Our data suggested that the differential TOS sensitivity was not caused by differences in the uptake and retention of TOS between TOS-sensitive and -resistant cancer cells. The differential ability of cancer cells to generate ROS in response to TOS appears to be an important factor in determining the susceptibility of cells to TOS-induced apoptosis. Our results further suggest that TOS-induced generation of ROS is involved in caspase-independent apoptosis. Taken together, our findings suggest an important role of ROS generation in TOS-induced, caspase-independent apoptosis of cancer cells.

Alpha-tocopheryl succinate, the most effective form of vitamin E for adjuvant cancer treatment: a review

In 1982, it was established that alpha-tocopheryl succinate (alpha-TS) was the most effective form of vitamin E in comparison to alpha-tocopherol, alpha-tocopheryl acetate and alpha-tocopheryl nicotinate in inducing differentiation, inhibition of proliferation and apoptosis in cancer cells, depending upon its concentration. During the last two decades, several studies have confirmed this observation in rodent and human cancer cells in culture and in vivo (animal model). The most exciting aspect of this alpha-TS effect is that it does not affect the proliferation of most normal cells. In spite of several studies published on the anti-cancer properties of alpha-TS, the value of this form of vitamin E has not drawn significant attention from researchers and clinicians. Therefore, a critical review on the potential role of alpha-TS in the management of cancer is needed. In addition, such a review can also provide in-depth analysis of existing literature on this subject. alpha-TS treatment causes extensive alterations in gene expression; however, only some can be attributed to differentiation, inhibition of proliferation and apoptosis. alpha-TS also enhances the growth-inhibitory effect of ionizing radiation, hyperthermia, some chemotherapeutic agents and biological response modifiers on tumor cells, while protecting normal cells against some of their adverse effects. Thus, alpha-TS alone or in combination with dietary micronutrients can be useful as an adjunct to standard cancer therapy by increasing tumor response and possibly decreasing some of the toxicities to normal cells.

Pros and cons of antioxidant use during radiation therapy

Radiation therapy is one of the major treatment modalities in the management of human cancer. While impressive progress like more accurate dosimetry and more precise methods of radiation targeting to tumor tissue has been made, the value of radiation therapy in tumor control may have reached a plateau. At present, two opposing hypotheses regarding the use of antioxidants during radiation therapy have been proposed. One hypothesis states that supplementation with high doses of multiple micronutrients including high dose dietary antioxidants (vitamins C and E, and carotenoids) may improve the efficacy of radiation therapy by increasing tumor response and decreasing some of its toxicity on normal cells. The other hypothesis suggests that antioxidants (dietary or endogenously made) should not be used during radiation therapy, because they would protect cancer cells against radiation damage. Each of these hypotheses is based on different conceptual frameworks that are derived from results obtained from specific experimental designs, and thus, each may be correct within its parameters. The question arises whether any of these concepts and experimental designs can be used during radiation therapy to improve the management of human cancer by this modality. This review has analyzed published data that are used in support of each hypothesis, and has revealed that the current controversies can be resolved, if the results obtained from one experimental design are not extrapolated to the other. This review has also discussed the scientific rationale for a micronutrient protocol that includes high doses of dietary antioxidants (vitamin C, vitamin E succinate and natural beta-carotene) which can be used adjunctively with radiation therapy.

Scientific rationale for using high-dose multiple micronutrients as an adjunct to standard and experimental cancer therapies

We have hypothesized that high-dose multiple micronutrients, including antioxidants, as an adjunct to standard (radiation therapy and chemotherapy) or experimental therapy (hyperthermia and immunotherapy), may improve the efficacy of cancer therapy by increasing tumor response and decreasing toxicity. Several in vitro studies and some in vivo investigations support this hypothesis. A second hypothesis is that antioxidants may interfere with the efficacy of radiation therapy and chemotherapy. This hypothesis is based on the concept that antioxidants will destroy free radicals that are generated during therapy, thereby protecting cancer cells against death. None of the published data on the effect of antioxidants in combination with radiation or chemotherapeutic agents on tumor cells supports the second hypothesis. Scientific rationale in support of a micronutrient protocol to be used as an adjunct to standard or experimental cancer therapy is presented.