Modulation of microglial superoxide production by alpha-tocopherol in vitro: attenuation of p67(phox) translocation by a protein phosphatase-dependent pathway

Vitamin E research: Past, now and future

The early history of vitamin E from its discovery by Herbert M. Evans and Katharine J. S. Bishop in 1922 up to its chemical synthesis by Paul Karrer and coworkers in 1938 and the development of the concept that vitamin E acts as an antioxidant in vivo are recalled. Some more recent results shedding doubt on this hypothesis are reviewed. They comprise influence of vitamin E on enzyme activities, signaling cascades, gene expression and bio-membrane structure. The overall conclusion is that our knowledge of the vitamin's mechanism of action still remains fragmentary. The metabolism of tocopherols and tocotrienols is presented and discussed in respect to bioactivity of the metabolites, interference with drug metabolism and the future design of clinical trials. Some strategies are recommended how to reach the final goal: the identification of the primary vitamin E target(s) and the analysis of the downstream events up to the physiological phenomena.

Dual Inhibition of NOX2 and Receptor Tyrosine Kinase by BJ-1301 Enhances Anticancer Therapy Efficacy via Suppression of Autocrine-Stimulatory Factors in Lung Cancer

NADPH oxidase-derived reactive oxygen species (ROS) potentiate receptor tyrosine kinase (RTK) signaling, resulting in enhanced angiogenesis and tumor growth. In this study, we report that BJ-1301, a hybrid of pyridinol and alpha-tocopherol, exerts anticancer effects by dual inhibition of NADPH oxidase and RTK activities in endothelial and lung cancer cells. BJ-1301 suppresses ROS production by blocking translocation of NADPH oxidase cytosolic subunits to the cell membrane, thereby inhibiting activation. The potency of RTK inhibition by BJ-1301 was lower than that of sunitinib (a multi-RTK inhibitor), but the inhibition of downstream signaling pathways (e.g., ROS generation) and subsequent biological changes (e.g., NOX2 induction) by BJ-1301 was superior. Consistently, BJ-1301 inhibited cisplatin-resistant lung cancer cell proliferation more than sunitinib did. In xenograft chick or mouse tumor models, BJ-1301 inhibited lung tumor growth, to an extent greater than that of sunitinib or cisplatin. Treatments with BJ-1301 induced regression of tumor growth, potentially due to downregulation of autocrine-stimulatory ligands for RTKs, such as TGFα and stem cell factor, in tumor tissues. Taken together, the current study demonstrates that BJ-1301 is a promising anticancer drug for the treatment of lung cancer. Mol Cancer Ther; 16(10); 2144-56. ©2017 AACR.

Vitamin E neuroprotection against cisplatin ototoxicity: Preliminary results from a randomized, placebo-controlled trial

BACKGROUND

Few studies have investigated the effect of vitamin E in reducing the cisplatin (CDDP)-induced ototoxicity. This study evaluated vitamin E supplementation as a protecting agent against CDDP-induced ototoxicity.

METHODS

Patients who started CDDP were randomly assigned to receive vitamin E supplementation at 400 mg per day (group 1) or placebo (group 2). Audiograms and evoked brainstem responses were obtained at baseline, and after 1, 2, and 3 months.

RESULTS

Twenty-three patients affected by solid malignancies were enrolled (13 in group 1 and 10 in group 2). At 1 month, a significant hearing loss in group 2 at both 2000 HZ (right ear: p = .05; left ear: p = .04) and 8000 HZ (right ear: p = .04; left ear: p = .03) was detected when compared to baseline values. Audiograms did not show significant changes. At 1 month, evoked brainstem responses remained unchanged in both arms without significant differences between groups.

CONCLUSION

These preliminary findings confirm the neuroprotective properties of vitamin E against the CDDP-induced ototoxicity. © 2016 Wiley Periodicals, Inc. Head Neck 38: E2118-E2121, 2016.

Chronically active: activation of microglial proteolysis in ageing and neurodegeneration

One of the microglial cell functions is the removal of modified extracellular proteins in the brain. The connection between protein oxidation, proteolysis, and microglial activation is the topic of this review. The effect of various activation agents on microglial cells with regard to changes in substrate uptake, proteolytic capacity and degradation efficiency of different types of oxidized protein materials is reviewed. It is shown that different activation stimuli initiate substrate-specific modulation for uptake and proteolysis, influencing an array of factors including receptor expression, lysosomal pH, and proteasome subunit composition. Age-related alterations in activation and proteolytic capacity in microglial cells are also discussed. In ageing, proteolytic effectiveness is diminished, while microglial cells are chronically activated and lose the oxidative burst ability, possibly supporting a 'vicious circle' of macrophage-induced neurodegeneration.

NADPH oxidase as a therapeutic target for oxalate induced injury in kidneys

A major role of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family of enzymes is to catalyze the production of superoxides and other reactive oxygen species (ROS). These ROS, in turn, play a key role as messengers in cell signal transduction and cell cycling, but when they are produced in excess they can lead to oxidative stress (OS). Oxidative stress in the kidneys is now considered a major cause of renal injury and inflammation, giving rise to a variety of pathological disorders. In this review, we discuss the putative role of oxalate in producing oxidative stress via the production of reactive oxygen species by isoforms of NADPH oxidases expressed in different cellular locations of the kidneys. Most renal cells produce ROS, and recent data indicate a direct correlation between upregulated gene expressions of NADPH oxidase, ROS, and inflammation. Renal tissue expression of multiple NADPH oxidase isoforms most likely will impact the future use of different antioxidants and NADPH oxidase inhibitors to minimize OS and renal tissue injury in hyperoxaluria-induced kidney stone disease.

Ascorbate and α-tocopherol differentially modulate reactive oxygen species generation by neutrophils in response to FcγR and TLR agonists

Periodontitis, a ubiquitous chronic inflammatory disease, is associated with reduced antioxidant defences and neutrophil hyperactivity in terms of reactive oxygen species (ROS) generation. Its phenotype is thus characterized by oxidative stress. We have determined the effect of antioxidant micronutrients ascorbate and α-tocopherol on neutrophil ROS generation. Peripheral neutrophils from periodontally-healthy individuals ( n = 20) were challenged with phorbol myristate acetate, IgG-opsonised Staphylococcus aureus, Fusobacterium nucleatum or PBS in the presence and absence of micronutrients (50 µM). Total and extracellular ROS were measured by luminol and isoluminol chemiluminescence respectively. Total and extracellular unstimulated, baseline ROS generation was unaffected by α-tocopherol, but inhibited by ascorbate and a combination of both micronutrients. Fcγ-receptor (Fcγ-R)-stimulated total or extracellular ROS generation was not affected by the presence of individual micronutrients. However, the combination significantly reduced extracellular FcγR-stimulated ROS release. Neither micronutrient inhibited TLR-stimulated total ROS, but the combination caused inhibition. Ascorbate and the micronutrient combination, but not α-tocopherol, inhibited extracellular ROS release by TLR-stimulated cells. Such micronutrient effects in vivo could be beneficial in reducing collateral tissue damage in chronic inflammatory diseases, such as periodontitis, while retaining immune-mediated neutrophil function.

The NADPH oxidase family and its inhibitors

The classical nicotinamide adenine dinucleotide phosphate (NADPH) oxidase was originally detected in neutrophils as a multicomponent enzyme that catalyzes the generation of superoxide from oxygen and the reduced form of NADPH. This enzyme is composed of two membrane-bound subunits (p22phox and gp91phox), three cytosolic subunits (p67phox, p47phox, and p40phox) and a small G-protein Rac (Rac1 and Rac2). Recently, it has been demonstrated that there are several isoforms of nonphagocytic NADPH oxidase. Endothelial cells, vascular smooth muscle cells or adventitial fibroblasts possess multiple isoforms of this enzyme. The new homologs, along with gp91phox are now designated the Nox family of NADPH oxidases and are key sources of reactive oxygen species in the vasculature. Reactive oxygen species play a significant role in regulating endothelial function and vascular tone. However, besides the participation in the processes of physiological cell, these enzymes can also be the perpetrator of oxidative stress that causes endothelial dysfunction. This review summarizes the current state of knowledge of the structure and functions of NADPH oxidase and NADPH oxidase inhibitors in the treatment of disorders with endothelial damage.

Vitamin E isoforms directly bind PKCα and differentially regulate activation of PKCα

Vitamin E isoforms have opposing regulatory effects on leucocyte recruitment during inflammation. Furthermore, in vitro, vitamin E isoforms have opposing effects on leucocyte migration across endothelial cells by regulating VCAM (vascular cell-adhesion molecule)-1 activation of endothelial cell PKCα (protein kinase Cα). However, it is not known whether tocopherols directly regulate cofactor-dependent or oxidative activation of PKCα. We report in the present paper that cofactor-dependent activation of recombinant PKCα was increased by γ-tocopherol and was inhibited by α-tocopherol. Oxidative activation of PKCα was inhibited by α-tocopherol at a 10-fold lower concentration than γ-tocopherol. In binding studies, NBD (7-nitrobenz-2-oxa-1,3-diazole)-tagged α-tocopherol directly bound to full-length PKCα or the PKCα-C1a domain, but not PKCζ. NBD-tagged α-tocopherol binding to PKCα or the PKCα-C1a domain was blocked by diacylglycerol, α-tocopherol, γ-tocopherol and retinol, but not by cholesterol or PS (phosphatidylserine). Tocopherols enhanced PKCα-C2 domain binding to PS-containing lipid vesicles. In contrast, the PKCα-C2 domain did not bind to lipid vesicles containing tocopherol without PS. The PKCα-C1b domain did not bind to vesicles containing tocopherol and PS. In summary, α-tocopherol and γ-tocopherol bind the diacylglycerol-binding site on PKCα-C1a and can enhance PKCα-C2 binding to PS-containing vesicles. Thus the tocopherols can function as agonists or antagonists for differential regulation of PKCα.

Okadaic acid inhibits cell growth and photosynthetic electron transport in the alga Dunaliella tertiolecta

Okadaic acid (OA), which is produced by several dinoflagellate species, is a phycotoxin known to induce a decrease of biomass production in phytoplankton. However, the mechanisms of OA cytotoxicity are still unknown in microalgae. In this study, we exposed the green microalga Dunaliella tertiolecta to OA concentrations of 0.05 to 0.5 μM in order to evaluate its effects on cell division, reactive oxygen species production and photosynthetic electron transport. After 72 h of treatment under continuous illumination, OA concentrations higher than 0.10 μM decreased culture cell density, induced oxidative stress and inhibited photosystem II electron transport capacity. OA effect in D. tertiolecta was strongly light dependent since no oxidative stress was observed when D. tertiolecta was exposed to OA in the dark. In the absence of light, the effect of OA on culture cell density and photosystem II activity was also significantly reduced. Therefore, light appears to have a significant role in the toxicity of OA in microalgae. Our results indicate that the site of OA interaction on photosynthetic electron transport is likely to be at the level of the plastoquinone pool, which can lead to photo-oxidative stress when light absorbed by the light-harvesting complex of photosystem II cannot be dissipated via photochemical pathways. These findings allowed for a better understanding of the mechanisms of OA toxicity in microalgae.

alpha-Tocopherol enhances degranulation in RBL-2H3 mast cells

Based on the observation that 3 months alpha-tocopherol supplementation caused an up-regulation of the mRNA of vesicular transport proteins in livers of mice, the functional relevance was investigated in RBL-2H3 cells, a model for mast cell degranulation. In total, 24 h incubation with 100 muM alpha-tocopherol enhanced the basal and phorbol-12-myristyl-13-acetate/ionomycin-stimulated release of beta-hexosaminidase and cathepsin D as measured by enzymatic analysis as well as Western blotting and immunocytochemistry, respectively. beta-Tocopherol exerted the same effect, whereas alpha-tocopheryl phosphate and trolox were inactive, indicating that both the side chain and the 6-OH group at the chroman ring are essential for activation of degranulation. alpha-Tocopherol did not induce mRNA expression of soluble NSF-attachment protein receptor (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) proteins, such as N-ethylmaleimide sensitive fusion protein, complexin-2, SNAP23 or syntaxin-3, in the RBL-2H3 cell model. In view of the well known alpha-tocopherol-mediated activation of protein phosphatases, which regulate soluble NSF-attachment protein receptor activities by dephosphorylation, underlying mechanisms are discussed in terms of preventing oxidative inactivation of protein phosphatases and so far unknown functions in certain membrane domains.

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.

Vitamins C and E inhibit apoptosis of cultured human term placenta trophoblast

Preeclampsia can be lethal to both mother and baby. The prominent symptoms of this syndrome are hypertension, proteinuria and oedema, resulting from an exaggerated aseptic systemic inflammatory response, triggered by placental factors shed into the maternal circulation. Syncytiotrophoblast microparticles (STBM) are one possible factor, shed when the placenta is exposed to stressors such as hypoxia/reperfusion. These can disrupt mitochondria, triggering apoptosis and necrosis, placental pathologies which are increased in preeclampsia. We tested the effects of antioxidant vitamins C (50 microM) and E (50 microM) on trophoblast in culture, using term villous cytotrophoblast preparations. Following Percoll gradient centrifugation and MHC class I expressing cell depletion of placenta digests, syncytial fragments were removed using anti-placental alkaline phosphatase antibody. This yielded cytotrophoblasts of consistently high purity. EGF (10 ng/ml) stimulated syncytialisation and hCG and progesterone production. However, mitochondrial induced apoptosis (MIA) was evident 96h post-isolation, as mitochondrial membrane potential loss and caspase 9 and caspase 3 activation. ROCK-1 cleavage and syncytiotrophoblast particle shedding increased concurrently with apoptosis induction. Vitamins blocked MIA and syncytiotrophoblast particle shedding and significantly increased hCG (p<0.005) and progesterone (p<0.02) concentrations in culture supernatants, reflecting the increased survival rates. Although more cells survived in culture, syncytialisation rate (%) was significantly reduced (p<0.005). We conclude that vitamins C and E can significantly reduce mitochondrial damage generated following syncytialisation in vitro. However, further work is required to determine whether antioxidant vitamins interfere with normal fusion processes.

Tocopherols and tocotrienols in membranes: a critical review

The familiar role of tocols (tocopherols and tocotrienols) as lipid-soluble chain-terminating inhibitors of lipid peroxidation is currently in the midst of a reinterpretation. New biological activities have been described for tocols that apparently are not dependent on their well-established antioxidant behaviour. These activities could well be real, but there remain large gaps in our understanding of the behaviour of tocols in membranes, especially when it comes to the alpha-, beta-, gamma-, delta-chroman methylation patterns and the seemingly special nature of tocotrienols. It is inappropriate to make conclusions and develop models based on in vivo (or cell culture) results with reference to in vitro measurements of antioxidant activity. When present in biological membranes, tocols will experience a large variation in the local composition of phospholipids and the presence of neutral lipids such as cholesterol, both of which would be expected to change the efficiency of antioxidant action. It is likely that tocols are not homogeneously dispersed in a membrane, but it is still not known whether any specific combination of lipid head group and acyl chains are conferred special protection from peroxidation, nor do we currently appreciate the structural role that tocols play in membranes. Tocols may enhance curvature stress or counteract similar stresses generated by other lipids such as lysolipids. This review will outline what is known about the location and behaviour of tocols in phospholipid bilayers. We will draw mainly from the biophysical literature, but will attempt to extend the discussion to biologically relevant phenomena when appropriate. We hope that it will assist researchers when designing new experiments and when critically assessing the results, in turn providing a more thorough understanding of the biochemistry of tocols.

Vitamin E, antioxidant and nothing more

All of the naturally occurring vitamin E forms, as well as those of synthetic all-rac-alpha-tocopherol, have relatively similar antioxidant properties, so why does the body prefer alpha-tocopherol as its unique form of vitamin E? We propose the hypothesis that all of the observations concerning the in vivo mechanism of action of alpha-tocopherol result from its role as a potent lipid-soluble antioxidant. The purpose of this review then is to describe the evidence for alpha-tocopherol's in vivo function and to make the claim that alpha-tocopherol's major vitamin function, if not only function, is that of a peroxyl radical scavenger. The importance of this function is to maintain the integrity of long-chain polyunsaturated fatty acids in the membranes of cells and thus maintain their bioactivity. That is to say that these bioactive lipids are important signaling molecules and that changes in their amounts, or in their loss due to oxidation, are the key cellular events that are responded to by cells. The various signaling pathways that have been described by others to be under alpha-tocopherol regulation appear rather to be dependent on the oxidative stress of the cell or tissue under question. Moreover, it seems unlikely that these pathways are specifically under the control of alpha-tocopherol given that various antioxidants other than alpha-tocopherol and various oxidative stressors can manipulate their responses. Thus, virtually all of the variation and scope of vitamin E's biological activity can be seen and understood in the light of protection of polyunsaturated fatty acids and the membrane qualities (fluidity, phase separation, and lipid domains) that polyunsaturated fatty acids bring about.

Modulation of signal transduction by vitamin E

The ability of vitamin E to modulate signal transduction and gene expression has been observed in numerous studies; however, the detailed molecular mechanisms involved are often not clear. The eight natural vitamin E analogues and synthetic derivatives affect signal transduction with different potency, possibly reflecting their different ability to interact with specific proteins. Vitamin E modulates the activity of several enzymes involved in signal transduction, such as protein kinase C, protein kinase B, protein tyrosine kinases, 5-, 12-, and 15-lipoxygenases, cyclooxygenase-2, phospholipase A2, protein phosphatase 2A, protein tyrosine phosphatase, and diacylglycerol kinase. Activation of some these enzymes after stimulation of cell surface receptors with growth factors or cytokines can be normalized by vitamin E. At the molecular level, the translocation of several of these enzymes to the plasma membrane is affected by vitamin E, suggesting that the modulation of protein-membrane interactions may be a common theme for vitamin E action. In this review the main effects of vitamin E on enzymes involved in signal transduction are summarized and the possible mechanisms leading to enzyme modulation evaluated. The elucidation of the molecular and cellular events affected by vitamin E could reveal novel strategies and molecular targets for developing similarly acting compounds.

Anti-inflammatory properties of alpha- and gamma-tocopherol

Natural vitamin E consists of four different tocopherol and four different tocotrienol homologues (alpha,beta, gamma, delta) that all have antioxidant activity. However, recent data indicate that the different vitamin E homologues also have biological activity unrelated to their antioxidant activity. In this review, we discuss the anti-inflammatory properties of the two major forms of vitamin E, alpha-tocopherol (alphaT) and gamma-tocopherol (gammaT), and discuss the potential molecular mechanisms involved in these effects. While both tocopherols exhibit anti-inflammatory activity in vitro and in vivo, supplementation with mixed (gammaT-enriched) tocopherols seems to be more potent than supplementation with alphaT alone. This may explain the mostly negative outcomes of the recent large-scale interventional chronic disease prevention trials with alphaT only and thus warrants further investigation.

The microglial NADPH oxidase complex as a source of oxidative stress in Alzheimer's disease

Alzheimer's disease is the most common cause of dementia in the elderly, and manifests as progressive cognitive decline and profound neuronal loss. The principal neuropathological hallmarks of Alzheimer's disease are the senile plaques and the neurofibrillary tangles. The senile plaques are surrounded by activated microglia, which are largely responsible for the proinflammatory environment within the diseased brain. Microglia are the resident innate immune cells in the brain. In response to contact with fibrillar beta-amyloid, microglia secrete a diverse array of proinflammatory molecules. Evidence suggests that oxidative stress emanating from activated microglia contribute to the neuronal loss characteristic of this disease. The source of fibrillar beta-amyloid induced reactive oxygen species is primarily the microglial nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. The NADPH oxidase is a multicomponent enzyme complex that, upon activation, produces the highly reactive free radical superoxide. The cascade of intracellular signaling events leading to NADPH oxidase assembly and the subsequent release of superoxide in fibrillar beta-amyloid stimulated microglia has recently been elucidated. The induction of reactive oxygen species, as well as nitric oxide, from activated microglia can enhance the production of more potent free radicals such as peroxynitrite. The formation of peroxynitrite causes protein oxidation, lipid peroxidation and DNA damage, which ultimately lead to neuronal cell death. The elimination of beta-amyloid-induced oxidative damage through the inhibition of the NADPH oxidase represents an attractive therapeutic target for the treatment of Alzheimer's disease.

Protective effect of 1,2,4-benzenetriol on LPS-induced NO production by BV2 microglial cells

Hydroxyhydroquinone or 1,2,4-benzenetriol (BT) detected in the beverages has a structure that coincides with the water-soluble form of a sesame lignan, sesamol. We previously showed that sesame antioxidants had neuroprotective abilities due to their antioxidant properties and/or inducible nitric oxide synthase (iNOS) inhibition. However, studies show that BT can induce DNA damage through the generation of reactive oxygen species (ROS). Therefore, we were interested to investigate the neuroprotective effect of BT in vitro and in vivo. The results showed that instead of enhancing free radical generation, BT dose-dependently (10-100 microM) attenuated nitrite production, iNOS mRNA and protein expression in lipopolysaccharide (LPS)-stimulated murine BV-2 microglia. BT significantly reduced LPS-induced NF-kappaB and p38 MAPK activation. It also significantly reduced the generation of ROS in H2O2-induced BV-2 cells and in H2O2-cellfree conditions. The neuroprotective effect of BT was further demonstrated in the focal cerebral ischemia model of Sprague-Dawley rat. Taken together, the inhibition of LPS-induced nitrite production might be due to the suppression of NF-kappaB, p38 MAPK signal pathway and the ROS scavenging effect. These effects might help to protect neurons from the ischemic injury.

Oxidative and antioxidative potential of brain microglial cells

Microglial cells are the resident immune cells of the central nervous system. These cells defend the central nervous system against invading microorganisms and clear the debris from damaged cells. Upon activation, microglial cells produce a large number of neuroactive substances that include cytokines, proteases, and prostanoids. In addition, activated microglial cells release radicals, such as superoxide and nitric oxide, that are products of the enzymes NADPH oxidase and inducible nitric oxide synthase, respectively. Microglia-derived radicals, as well as their reactive reaction products hydrogen peroxide and peroxynitrite, have the potential to harm cells and have been implicated in contributing to oxidative damage and neuronal cell death in neurological diseases. For self-protection against oxidative damage, microglial cells are equipped with efficient antioxidative defense mechanisms. These cells contain glutathione in high concentrations, substantial activities of the antioxidative enzymes superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase, as well as NADPH-regenerating enzymes. Their good antioxidative potential protects microglial cells against oxidative damage that could impair important functions of these cells in defense and repair of the brain.

Inhibition of HMC-1 mast cell proliferation by vitamin E: involvement of the protein kinase B pathway

The effects of four natural tocopherols on the proliferation and signaling pathways were examined in the human mastocytoma cell line (HMC-1). The four tocopherols inhibited HMC-1 cell proliferation with different potency (delta > alpha = gamma > beta). Growth inhibition correlated with the reduction of PKB (protein kinase B) phosphorylation by the different tocopherols. The reduction of PKB phosphorylation led to a decrease of its activity, as judged from a parallel reduction of GSKalpha/beta phosphorylation. The translocation of PKB to the membrane, as a response to receptor stimulation by NGFbeta, is also prevented by treatment with tocopherols. In the presence of PKC or PP2A inhibitors, the reduction of PKB phosphorylation by tocopherols was still observed, thus excluding the direct involvement of these enzymes. Other pathways, such as the Ras-stimulated ERK1/2 (extracellular signal responsive kinase) pathway, were not affected by tocopherol treatment. The tocopherols did not significantly change oxidative stress in HMC-1 cells, suggesting that the observed effects are not the result of a general reduction of oxidative stress. Thus, the tocopherols interfere with PKB phosphorylation and reduce proliferation of HMC-1 cells, possibly by modulating either phosphatidylinositol 3-kinase, a kinase phosphorylating PKB (PDK1/2), or a phosphatase that dephosphorylates it. Inhibition of proliferation and PKB signaling in HMC-1 cells by vitamin E suggests a role in preventing diseases with mast cell involvement, such as allergies, atherosclerosis, and tumorigenesis.

The Potential Role of Neutrophils in Promoting the Metastatic Phenotype of Tumors Releasing Interleukin-8

In the last decade, several groups have shown a direct correlation between the inappropriate or ectopic release of interleukin (IL)-8 by tumor cells in vitro and their growth and metastatic potential using in vivo models of tumor growth. IL-8 is a potent neutrophil chemoattractant. Neutrophils, as "early responders" to wounds and infections, release enzymes to remodel the extracellular matrix of the tissues through which they migrate to reach the site of the wound or infection. It is proposed that the host's cellular response to IL-8 released by tumor cells enhances angiogenesis and contributes to tumor growth and progression. The activities released by the responding neutrophils could serve as enablers of tumor cell migration through the extracellular matrix, helping them enter the vasculature and journey to new, metastatic sites. The reactive oxygen species produced by neutrophilic oxidases to kill invading organisms have the potential to interact with tumor cells to attenuate their apoptotic cascade and increase their mutational rate. It is proposed that the increase in metastatic potential of tumors ectopically releasing IL-8 is, in part, attributable to their ability to attract neutrophils. Discussed here are possible mechanisms by which the neutrophils responding to ectopic IL-8 contribute to the in vivo growth, progression, and metastatic potential of tumor cells. Possible targets are also presented for the development of therapies to attenuate the effects of the ectopic IL-8 release by tumor cells.

Vitamin E reduces cisplatin ototoxicity

OBJECTIVES/HYPOTHESIS

Cisplatin ototoxicity is a major dose-limiting factor in the treatment of several neoplasms. Vitamin E, a slow-acting free radical scavenger, has been shown to ameliorate nephrotoxicity and endothelial cell damage in animals receiving cisplatin. The purpose of the study was to determine the effectiveness of vitamin E as an otoprotectant.

STUDY DESIGN

Prospective, randomized controlled trial in the rat model.

METHODS

Wistar rats (weight, 261-386 g) were sedated using 172.4 mg/kg intramuscular ketamine and 3.4 mg/kg xylazine. Baseline auditory brainstem response (ABR) testing was performed in response to clicks and 8-, 16-, and 32-kHz tone bursts. After auditory thresholds were determined, the animals received intraperitoneal drug administration according to one of three group classifications. Group 1 received 4 g/kg vitamin E followed after 30 minutes by 16 mg/kg cisplatin. Group 2 received 6 mL/kg soybean oil followed after 30 minutes by cisplatin. Group 3 received soybean oil followed after 30 minutes by 16 mL/kg saline. After 3 days' follow-up, ABR testing was performed and threshold changes were recorded. Cochleae were removed and processed for scanning electron microscopy after follow-up auditory testing was carried out.

RESULTS

Group 2 animals showed marked hearing loss with average threshold shifts of 28.75 +/- 2.3 dB for clicks, 30.0 +/- 1.9 dB at 8 kHz, 21.25 +/- 4.0 dB at 16 kHz, and 45.0 +/- 4.2 dB at 32 kHz. No significant loss was observed in group 3 with shifts of 2 +/- 1.3 dB, 3 +/-3.0 dB, -2.2 +/- 3.1 dB, and -1.1 +/- 4.0 dB for clicks and tone bursts at 8, 16, and 32 kHz, respectively. Significant protection was seen in group 1 animals compared with group 2 animals. In the former group, threshold shifts of 12.5 +/- 3.1 dB for clicks, 7.5 +/- 2.5 dB at 8 kHz, 5.0 +/- 3.3 dB at 16 kHz, and 24.4 +/- 5.6 dB at 32 kHz were observed. These findings were supported by the scanning electron microscope observations that severe outer hair cell destruction occurred in group 2 rats, whereas outer hair cells were preserved to a much greater extent in the cochleae of rats in group 1 that were pretreated with vitamin E.

CONCLUSION

Vitamin E appears to have a protective effect against cisplatin ototoxicity.

Uptake and transport of high-density lipoprotein (HDL) and HDL-associated alpha-tocopherol by an in vitro blood-brain barrier model

The present study aimed to investigate pathways that contribute to uptake and transcytosis of high-density lipoproteins (HDLs) and HDL-associated alpha-tocopherol (alpha TocH) across an in vitro model of the blood-brain barrier (BBB). In primary porcine brain capillary endothelial cells HDL-associated alpha TocH was taken up in 10-fold excess of HDL holoparticles, indicating efficient selective uptake, a pathway mediated by scavenger receptor class B, type I (SR-BI). SR-BI was present in caveolae of brain capillary endothelial cells and expressed almost exclusively at the apical membrane. Disruption of caveolae with methyl-beta-cyclodextrin (CDX) resulted in (mis)sorting of SR-BI to the basolateral membrane. Immunohistochemistry of porcine brain cryosections revealed SR-BI expression on brain capillary endothelial cells and presumably astrocytic endfeet. HDL-associated [(14)C]alpha TocH taken up by brain capillary endothelial cells was recovered in sucrose gradient fractions containing the majority of cellular caveolin-1, the major caveolae-associated protein. During mass transfer studies using alpha TocH-enriched HDL, approximately 50% of cellular alpha TocH was recovered with the bulk of cellular caveolin-1 and SR-BI. Efflux experiments revealed that a substantial amount of cell-associated [(14)C]alpha TocH could be mobilized into the culture medium. In addition, apical-to-basolateral transport of HDL holoparticles and HDL-associated alpha TocH was saturable. Results from the present study suggest that part of cerebral apolipoprotein A-I and alpha TocH originates from plasma HDL transcytosed across the BBB and that caveolae-located SR-BI facilitates selective uptake of HDL-associated alpha TocH at the BBB.

Vitamin E (alpha-tocopherol) attenuates cyclo-oxygenase 2 transcription and synthesis in immortalized murine BV-2 microglia

One of the immediate early microglial genes that are up-regulated in response to proinflammatory stimuli is cyclo-oxygenase 2 (COX-2). In the present study, we have investigated the effects of alpha-tocopherol (alpha TocH), an essential constituent of the nervous system, on the activation of COX-2 in lipopolysaccharide (LPS)-stimulated mouse BV-2 microglia. In unstimulated BV-2 cells, COX-2 mRNA and protein were almost undetectable but were strongly up-regulated in response to LPS. Activation of COX-2 protein synthesis in LPS-stimulated BV-2 cells involved activation of the extracellular-signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK) pathway and was sensitive to the protein kinase C (PKC) inhibitors staurosporine and chelerythrine, and the MAP kinase/ERK kinase 1/2 inhibitors PD98059 and U0126. Supplementation of BV-2 cells with alpha TocH before LPS stimulation resulted in pronounced up-regulation of protein phosphatase 2A (PP2A) activity, down-regulation of PKC activity, ERK1/2 phosphorylation and nuclear factor kappa B (NF kappa B) activation. As a result, COX-2 protein levels and prostaglandin E(2) production were significantly lower in alpha TocH-supplemented cells. The effects of alpha TocH on PKC activity could be reverted by calyculin A and okadaic acid, two PP inhibitors. In summary, our results suggest that alpha TocH activates microglial PP2A activity and thereby silences an LPS-activated PKC/ERK/NF kappa B signalling cascade resulting in significantly attenuated COX-2 protein synthesis. These in vitro results imply that alpha TocH could induce quiescence to pathways that are associated with acute or chronic inflammatory conditions in the central nervous system.

Silymarin protects dopaminergic neurons against lipopolysaccharide-induced neurotoxicity by inhibiting microglia activation

An inflammatory response in the central nervous system mediated by activation of microglia is a key event in the early stages of the development of neurodegenerative diseases. Silymarin is a polyphenolic flavanoid derived from milk thistle that has anti-inflammatory, cytoprotective and anticarcinogenic effects. In this study, we first investigated the neuroprotective effect of silymarin against lipopolysaccharide (LPS)-induced neurotoxicity in mesencephalic mixed neuron-glia cultures. The results showed that silymarin significantly inhibited the LPS-induced activation of microglia and the production of inflammatory mediators, such as tumour necrosis factor-alpha and nitric oxide (NO), and reduced the damage to dopaminergic neurons. Therefore, the inhibitory mechanisms of silymarin on microglia activation were studied further. The production of inducible nitric oxide synthase (iNOS) was studied in LPS-stimulated BV-2 cells as a model of microglia activation. Silymarin significantly reduced the LPS-induced nitrite, iNOS mRNA and protein levels in a dose-dependent manner. Moreover, LPS could induce the activation of p38 mitogen-activated protein kinase (MAPK) and c-jun N-terminal kinase but not extracellular signal-regulated kinase. The LPS-induced production of NO was inhibited by the selective p38 MAPK inhibitor SB203580. These results indicated that the p38 MAPK signalling pathway was involved in the LPS-induced NO production. However, the activation of p38 MAPK was not inhibited by silymarin. Nevertheless, silymarin could effectively reduce LPS-induced superoxide generation and nuclear factor kappaB (NF-kappaB) activation. It suggests that the inhibitory effect of silymarin on microglia activation is mediated through the inhibition of NF-kappaB activation.