Chronic alcohol consumption produces a painful peripheral neuropathy for which there is no reliable successful therapy, which is mainly due to lack of understanding of its pathobiology. Alcoholic neuropathy is characterized by spontaneous burning pain, hyperalgesia (an exaggerated pain in response to painful stimuli) and allodynia (a pain evoked by normally innocuous stimuli). Chronic alcohol intake is known to decrease the nociceptive threshold with increased oxidative-nitrosative stress and release of proinflammatory cytokines coupled with activation of protein kinase C. The aim of the present study is to investigate the effect of both isoforms of vitamin E, alpha-tocopherol (100mg/kg; oral gavage) and tocotrienol (50, 100 and 200mg/kg; oral gavage) against alcohol-induced neuropathic pain in rats. Male Wistar rats, were administered 35% v/v ethanol (10 g/kg; oral gavage) for 10 weeks, and were treated with alpha-tocopherol and tocotrienol for the same duration. Ethanol-treated animals showed a significant decrease in nociceptive threshold as evident from decreased tail flick latency (thermal hyperalgesia) and decreased paw-withdrawal threshold in Randall-Sellito test (mechanical hyperalgesia) and von-Frey hair test (mechanical allodynia) along with the reduction in nerve glutathione and superoxide dismutase levels. TNF-alpha and IL-1beta levels were also significantly increased in both serum and sciatic nerve of ethanol-treated rats. Treatment with alpha-tocopherol and tocotrienol for 10 weeks significantly improved all the above-stated functional and biochemical deficits in a dose-dependent manner with more potent effects observed with tocotrienol. The study demonstrates the effectiveness of tocotrienol in attenuation of alcoholic neuropathy.

Intracerebroventricular (ICV) streptozotocin (STZ) has been shown to cause cognitive impairment, which is associated with increased oxidative stress in the brain of rats. In the present study, we investigated the effect of both the isoforms of vitamin E, alpha-tocopherol and tocotrienol against ICV STZ-induced cognitive impairment and oxidative-nitrosative stress in rats. Adult male Wistar rats were injected with ICV STZ (3 mg/kg) bilaterally. The learning and memory behavior was assessed using Morris water maze and elevated plus maze. The rats were sacrificed on day 21 and parameters of oxidative stress, nitrite levels and acetylcholinesterase activity were measured in brain homogenate. alpha-Tocopherol as well astocotrienol treated groups showed significantly less cognitive impairment in both the behavioral paradigms but the effect was more potent withtocotrienol. Both isoforms of vitamin E effectively attenuated the reduction in glutathione and catalase and reduced the malonaldehyde, nitrite as well as cholinesterase activity in the brains of ICV STZ rats in a dose dependent manner. The study demonstrates the effectiveness of vitamin E isoforms, of which tocotrienol being more potent in preventing the cognitive deficits caused by ICV STZ in rats and suggests its potential in the treatment of neurodegenerative diseases such as Alzheimer’s disease.

Besides acting as potent free radical scavengers, tocopherols and tocotrienols have been known to have non-antioxidant properties such as the involvement of alpha-tocopherol (alphaT) in PKC pathway and the anti-cancer properties of gamma-tocotrienol (gammaT3). This study aims to elucidate whether protective effects shown by alphaT and gammaT3 in H(2)O(2)-induced neuron cultures have anti-apoptotic or pro-apoptotic tendency toward the initiation of neuronal apoptosis. H(2)O(2) is used to induce apoptosis in primary cerebellar neuron cultures which is attenuated by pretreatment of alphaT or gammaT3 at concentrations < or =10 microM. Similar to our previous work, gammaT3 was found to be neurotoxic at concentrations > or =100 microM, whereas alphaT showed no neurotoxicity. Cellular uptake of gammaT3 was higher than that of alphaT. Treating cells simultaneously with either gammaT3 or alphaT and with then H(2)O(2) led to higher expression of Bax and Bcl-2 than in neurons exposed to H(2)O(2) alone. Analysis of Bcl-2/Bax ratio as ‘survival index’ showed that both pretreatment of gammaT3 and alphaT followed by H(2)O(2) increase the ‘survival index’ of Bcl-2/Bax ratio compared to H(2)O(2)-treated cells, while treatment of gammaT3 alone decrease the ratio compared to unchanged Bcl2/Bax ratio of similar treatment with alphaT alone. Similar treatment of gammaT3 decreased p53 expression and activates p38 MAPK phosphorylation, whereas alphaT did not alter its expression compared to H(2)O(2)-treated cells. Treating neurons with only gammaT3 or alphaT increased the expression of Bax, Bcl-2, p53, and p38 MAPK compared to control with gammaT3 exerting stronger expression for proteins involved than alphaT. In conclusion, low doses of gammaT3 and alphaT confer neuroprotection to H(2)O(2)-treated neurons via their antioxidant mechanism but gammaT3 has stronger pro-apoptosis tendency than alphaT by activating molecules involved in the neuronal apoptotic pathway in the absence of H(2)O(2).

Familial dysautonomia (FD) is an inherited, fatal, neurodegenerative disorder manifested by autonomic/hypertensive crises and cardiac instability. Patients produce little IKAP, the gene product of the affected mutated gene, and have low levels of monoamine oxidase A (MAO A), whose reduced presence appears to result in an increased accumulation of biogenic amines, which is a trigger for hypertensive crises. As ingestion of tocotrienols elevates IKAP and MAO A in FD patients, we examined their impact on the frequency of hypertensive crises and cardiac function. After 3 to 4 months of tocotrienol ingestion, approximately 80% of patients reported a significant (> or = 50%) decrease in the number of crises. In a smaller group of patients, a postexercise increase in heart rate and a decrease in the QT interval were observed in the majority of participants. Based on these findings, we hypothesize that tocotrienol therapy will improve the long-term clinical outlook and survival of individuals with FD.

Excessive free radical formation has been implicated as one of the causative factors in neurotoxic damage associated with variety of metals, including methylmercury (MeHg). Although the mechanisms associated with MeHg-dependent neurotoxicity remains are unclear, it is known that MeHg leads to neurotoxicity in cerebellar granule cells (CGCs). In vitro exposure of murine CGC primary cultures to MeHg resulted in time- and concentration-dependent cell death. The present study was designed to assess the effect of fat-soluble antioxidant tocopherols and tocotrienols (unsaturated vitamin E) on MeHg-induced neurotoxicity using cultured CGCs. Significant protection from MeHg-induced neuronal cell death was observed with both tocopherols and tocotrienols. Moreover, we observed that tocotrienols are multi-fold more potent than tocopherols in protecting CGCs against MeHg neurotoxicity. At micromolar concentration, tocotrienols, but not tocopherols, showed complete protection by an antioxidant mechanism. Similarly, tocopherols and tocotrienols showed a protective effect on CGCs migration against MeHg-toxicity. These results suggested that oxidative events may contribute to MeHg toxicity in isolated cerebellar granule neurons, and that tocotrienols are potent supplements for pharmacological protection of the developing brain exposed to MeHg.

The natural vitamin E tocotrienols possess properties not shared by tocopherols. Nanomolar alpha-tocotrienol, not alpha-tocopherol, is potently neuroprotective. On a concentration basis, this finding represents the most potent of all biological functions exhibited by any natural vitamin E molecule. We sought to dissect the antioxidant-independent and -dependent neuroprotective properties of alpha-tocotrienol by using two different triggers of neurotoxicity, homocysteic acid (HCA) and linoleic acid. Both HCA and linoleic acid caused neurotoxicity with comparable features, such as increased ratio of oxidized to reduced glutathione GSSG/GSH, raised intracellular calcium concentration and compromised mitochondrial membrane potential. Mechanisms underlying HCA-induced neurodegeneration were comparable to those in the path implicated in glutamate-induced neurotoxicity. Inducible activation of c-Src and 12-lipoxygenase (12-Lox) represented early events in that pathway. Overexpression of active c-Src or 12-Lox sensitized cells to HCA-induced death. Nanomolar alpha-tocotrienol was protective. Knock-down of c-Src or 12-Lox attenuated HCA-induced neurotoxicity. Oxidative stress represented a late event in HCA-induced death. The observation that micromolar, but not nanomolar, alpha-tocotrienol functions as an antioxidant was verified in a model involving linoleic acid-induced oxidative stress and cell death. Oral supplementation of alpha-tocotrienol to humans results in a peak plasma concentration of 3 microm. Thus, oral alpha-tocotrienol may be neuroprotective by antioxidant-independent as well as antioxidant-dependent mechanisms.

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Oxidative stress is thought to be one of the factors that cause neurodegeneration and that this can be inhibited by antioxidants. Since astrocytes support the survival of central nervous system (CNS) neurons, we compared the effect of alpha-tocopherol and gamma-tocotrienol in minimizing the cytotoxic damage induced by H₂O₂, a pro-oxidant. Primary astrocyte cultures were pretreated with either alpha-tocopherol or gamma-tocotrienol for 1 h before incubation with 100 microM H₂O₂ for 24 h. Cell viability was then assessed using the MTS assay while apoptosis was determined using a commercial ELISA kit as well as by fluorescent staining of live and apoptotic cells. The uptake of alpha-tocopherol and gamma-tocotrienol by astrocytes were also determined using HPLC. Results showed that gamma-tocotrienol is toxic at concentrations >200 microM but protects against H₂O₂ induced cell loss and apoptosis in a dose dependent manner up to 100 microM. alpha-Tocopherol was not cytotoxic in the concentration range tested (up to 750 microM), reduced apoptosis to the same degree as that of gamma-tocotrienol but was less effective in maintaining the viable cell number. Since the uptake of alpha-tocopherol and gamma-tocotrienol by astrocytes is similar, this may reflect the roles of these 2 vitamin E subfamilies in inhibiting apoptosis and stimulating proliferation in astrocytes.

Familial dysautonomia (FD), a recessive neurodegenerative disease, is caused by mutations in the IKBKAP gene that result in the production of nonfunctional IKAP protein. Manifestations of FD include autonomic crises characterized by hypertension, tachycardia, diaphoresis, and vomiting. Elevated plasma levels of norepinephrine (NE) and dopamine observed during autonomic crises and an exaggerated hypertensive response to low doses of NE prompted an examination of monoamine oxidase (MAO) levels, key isoenzymes responsible for degrading biogenic and dietary monoamines, in individuals with FD. Fetal tissue homozygous for the common FD-causing mutation and peripheral blood cells of individuals with FD have reduced MAO A mRNA levels. FD-derived cells, stimulated with tocotrienols or EGCG to produce increased levels of functional IKAP, express increased amounts of MAO A mRNA transcript and protein. Administration of tocotrienol to individuals with FD results in increased expression of both functional IKAP and MAO A transcripts in their peripheral blood cells. These findings provide new insight into the pathophysiology of FD and demonstrate the value of therapeutic approaches designed to elevate cellular levels of functional IKAP and MAO A.