Effects of oil palm tocotrienol rich fraction on the viability and morphology of astrocytes injured with glutamate

Abstract

Tocotrienol-rich fraction (TRF) is an extract of palm oil that consists of 25% α-tocopherol and 75% tocotrienols. TRF was shown to possess antioxidant, anti-inflammatory, anticancer, neuroprotective and cholesterol-lowering activities. Glutamate is the major mediator of excitatory signals in the mammalian central nervous system. Extreme amounts of glutamate in the extracellular spaces can lead to numerous neurodegenerative diseases. Hence, the efficacy of oil palm TRF and α-tocopherol in protecting astrocytes against glutamate-induced cell death was studied. Specifically, the effectiveness of pre-or post-treatment of TRF and αtocopherol upon glutamate excitotoxicity was determined by evaluating cell viability and morphology of astrocytes. Cell viability was measured using MTT assay while cell morphology was monitored under fluorescent microscope using the acridine orange/propidium iodide (AO/PI) assay. Exposure to 230 mM glutamate significantly reduced cell viability to 50% in both the pre-and post-treatment studies; however, pre-and post-treatment with TRF and α-tocopherol attenuated the cytotoxic effect of glutamate. Compared to glutamate-injured astrocytes, pre-treatment with 100, 200 and 300 ng/ml TRF significantly improved cell viability following glutamate injury to 86.6%, 86.7% and 93.9%, respectively (p < 0.05). On the contrary, high concentrations of α-tocopherol promote cell death. This study shows that TRF not only provide a better protection against glutamate toxicity (pre-treatment), but was also able to reverse the lipid peroxidation resulting from glutamate insults (post-treatment). The present results demonstrate that TRF, but not αtocopherol, protected the astrocytes against glutamate-induced cell death, indicating its neuro-protective potential.

Vitamins D and E Stimulate the PI3K-AKT Signalling Pathway in Insulin-Resistant SK-N-SH Neuronal Cells

“…Vitamin D may modulate insulin sensitivity because a functional vitamin D receptor (VDR) element has been identified in the promoter region of the insulin receptor, suggesting that vitamin D regulates insulin transcription through genomic interactions [15]. Vitamin E is a fat-soluble compound with antioxidant properties that exist in eight forms in nature (alpha-, beta-, gamma- and delta-tocopherol and alpha-, beta-, gamma- and delta- tocotrienol) each with its own biological properties [16]. The difference between tocopherol and tocotrienol is that they have different number and position of methyl groups attached to the aromatic ring [17].…”

“…Currently, there is an increase of interests on tocotrienol rich fraction (TRF) from palm oil. TRF consist of 25% of alpha-tocopherol (α-TCP) and 75% of tocotrienol [16]. Hence, vitamin E in the form of tocotrienol-rich fraction (TRF) may also boost insulin sensitivity and decrease diabetes risk by quenching free radicals and simultaneously reducing oxidative stress in the body [21].…”

Safety and Neuroprotective Efficacy of Palm Oil and Tocotrienol-Rich Fraction from Palm Oil: A Systematic Review

“…Both pre-treatment and post-treatment with TRF protected the integrity of cell membranes [28]; however, the underlying molecular mechanism was not evaluated. Conversely, the effect of TRF was not as effective in astrocytes as in neurons [26]. Accordingly, further in vivo studies should be conducted to elucidate the antioxidant, antiapoptotic and antinecrotic effects of TRF on neuronal and neuroglial cells of animals, or even in vitro studies using human neuronal and neuroglial cell lines.…”

“…On the other hand, 300 mg/mL of TRF significantly attenuated lipid peroxidation in the same cells [28]. Similarly, a 30-min post-treatment with 100, 200 or 300 ng/mL of TRF neither recovered the cellular viability nor produced antioxidant activity in human astrocytes cell line (CRL-2020 cells) challenged with glutamate neurotoxin for 24 h, but was able to attenuate lipid peroxidation and exerted antiapoptotic and antinecrotic activities [26]. •L-buthionine (S,R)-sulfoximine or L-buthionine (S,R)-sulfoximine +arachidonic acid neurotoxicity for 24 h using immature primary cortical neurons of Sprague-Dawley rats (17th day of gestation)…”

“…However, a five-minute pre-treatment with 100, 200 or 300 ng/mL of TRF neither enhanced cellular viability nor modulated the redox status in a human astrocytes cell line (CRL-2020 cells) against a 24-h challenge with glutamate neurotoxin. Conversely, 200 and 300 ng/mL of TRF attenuated lipid peroxidation and reduced the percentages of apoptotic and necrotic cells [26], (Table 6).…”