Chronic treatment with tocotrienol, an isoform of vitamin E, prevents intracerebroventricular streptozotocin-induced cognitive impairment and oxidative-nitrosative stress in rats

Tiwari V, Kuhad A, Bishnoi M, Chopra K.

Pharmacol Biochem Behav. 2009 Aug;93(2):183-9. Epub 2009 May 21.

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.

Purpose: To compare the antifibrotic effect of vitamin E isoforms α-,γ-, and δ-tocotrienol  on human Tenon’s fibroblasts (hTf) to the antimetabolite mitomycin C.

Methods: Antifbrotic effects of α- (40,60,80,100 and 120µM), γ- (10,20,330 and 40 µM) and δ–tocotrienol  (10,20,30 and 40 µM) on hTf cultures were evaluated by performing proliferation, migration and collagen synthesis assays. Whereas for vitamin E the exposure time was set to 7 days to mimic subconjunctival application, cultures were exposed only 5 min to mitomycin C 100µg/ml to mimic intraoperative administration. Cell morphology (phase contrast microscopy) as an assessment for cytotoxicity and cell density by measuring DNA content in a fluorometric assay to determine proliferation inhibition was performed on day 0,4, and 7. Migration ability and collagen synthesis of fibroblasts were measured.

Results: All tested tocotrienol isoforms were able to significantly inhibit hTf proliferation in a dose dependent manner (maximal inhibitory effect without relevant morphological changes at day 4 for α-tocotrienol 80µm with 36.7% and at day 7 for α-tocotrienol 80µM with 42.6% compared to control). Degenerative cell changes were observed in cultures with concentrations above 80µM for α- and above 30µM for γ- and δ-rocotrienol. The highest collagen synthesis inhibition has been found with 80µM α-tocotrienol (62.4%) and no significant inhibition for mitomycin C (2.5%). Migration ability was significantly reduced in cultures exposed to 80µM α- and 30µM γ-tocotrienol (inhibition of 82.2% and 79.5%, respectively, compared to control) and also after mitomycin C treatment (60.0%). Complete growth inhibition without significant degenerative cell changes could only be achieved with mitomycin C.

Conclusion: In vitro, all tested tocotrienol isoforms were able to inhibit proliferation, migration and collagen synthesis of human Tenon’s fibroblasts and therefore may have the potential as an anti-scarring agent in filtrating glaucoma surgery.

A novel mechanism of natural vitamin E tocotrienol activity: Involvement of ERbeta signal transduction

Comitato R, Nesaretnam K, Leoni G, Ambra R, Canali R, Bolli A, Marino M, Virgili F.

Am J Physiol Endocrinol Metab. 2009 Aug;297(2):E427-37.

Vitamin E is a generic term used to indicate all tocopherol (TOC) and tocotrienol (TT) derivates. In the last few years, several papers have shown that a TT-rich fraction (TTRF) extracted from palm oil inhibits proliferation and induces apoptosis in a large number of cancer cells. However, the molecular mechanism(s) involved in TT action is still unclear. In the present study, we proposed for the first time a novel mechanism for TT activity that involves estrogen receptor (ER) signaling. In silico simulations and in vitro binding analyses indicated a high affinity of TTs for ERbeta but not for ERalpha. In addition, in ERbeta-containing MDA-MB-231 breast cancer cells, we demonstrated that TTs increase the ERbeta translocation into the nucleus, which in turn activates estrogen-responsive genes (MIC-1, EGR-1 and cathepsin D), as demonstrated by cell preincubation with the ER inhibitor ICI-182,780. Finally, we observed that TT treatment is associated with alteration of cell morphology, DNA fragmentation, and caspase-3 activation. Altogether, these experiments elucidated the molecular mechanism underling gamma- and delta-TT effects.

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