Search

The discovery of vitamin E will have its 100th anniversary in 2022, but we still have more questions than answers regarding the biological functions and the essentiality of vitamin E for human health. Discovered as a factor essential for rat fertility and soon after characterized for its properties of fat-soluble antioxidant, vitamin E was identified to have signaling and gene regulation effects in the 1980s. In the same years the cytochrome P-450 dependent metabolism of vitamin E was characterized and a first series of studies on short-chain carboxyethyl metabolites in the 1990s paved the way to the hypothesis of a biological role for this metabolism alternative to vitamin E catabolism. In the last decade other physiological metabolites of vitamin E have been identified, such as α-tocopheryl phosphate and the long-chain metabolites formed by the ω-hydroxylase activity of cytochrome P-450. Recent findings are consistent with gene regulation and homeostatic roles of these metabolites in different experimental models, such as inflammatory, neuronal and hepatic cells, and in vivo in animal models of acute inflammation. Molecular mechanisms underlying these responses are under investigation in several laboratories and side-glances to research on other fat soluble vitamins may help to move faster in this direction. Other emerging aspects presented in this review paper include novel insights on the mechanisms of reduction of the cardiovascular risk, immunomodulation and antiallergic effects, neuroprotection properties in models of glutamate excitotoxicity and spino-cerebellar damage, hepatoprotection and prevention of liver toxicity by different causes and even therapeutic applications in non-alcoholic steatohepatitis. We here discuss these topics with the aim of stimulating the interest of the scientific community and further research activities that may help to celebrate this anniversary of vitamin E with an in-depth knowledge of its action as vitamin.

Atherosclerosis and associated cardiovascular complications such as stroke and myocardial infarction are major causes of morbidity and mortality. We have previously reported a significant increase in mRNA levels of the scavenger receptor CD36 in aortae of cholesterol-fed rabbits and shown that vitamin E treatment attenuated increased CD36 mRNA expression. In the present study, we further investigated the redox signaling pathways associated with protection against atherogenesis induced by high dietary cholesterol and correlated these with CD36 expression and the effects of vitamin E supplementation in a rabbit model. Male albino rabbits were assigned to either a control group fed with a low vitamin E diet alone or a test group fed with a low vitamin E diet containing 2% cholesterol in the absence or presence of daily intramuscular injections of vitamin E (50 mg/kg). To elucidate the mechanisms by which vitamin E supplementation alters the effects of hypercholesterolemia in rabbit aortae, we measured peroxisome proliferator-activated receptor γ (PPARγ), ATP-binding cassette transporter A1 (ABCA1), and matrix metalloproteinase-1 (MMP-1) mRNA levels by quantitative RT-PCR and the expression of MMP-1, nuclear factor-erythroid 2-related factor 2 (Nrf2), and glutathione S-transferase α (GSTα) protein by immunoblotting. The increased MMP-1 and decreased GSTα expression observed suggests that a cholesterol-rich diet contributes to the development of atherosclerosis, whereas vitamin E supplementation affords protection by decreasing MMP-1 and increasing PPARγ, GSTα, and ABCA1 levels in aortae of rabbits fed a cholesterol-rich diet. Notably, protein expression of Nrf2, the antioxidant transcription factor, was increased in both the cholesterol-fed and the vitamin E-supplemented groups. Although Nrf2 activation can promote CD36-mediated cholesterol uptake by macrophages, the increased induction of Nrf2-mediated antioxidant genes is likely to contribute to decreased lesion progression. Thus, our study demonstrates that Nrf2 can mediate both pro- and antiatherosclerotic effects.

Oxidative stress is an inevitable process in the nucleus, especially in antitumor chemotherapy, and adaptation by defense mechanisms seems to be one element in the development of long-term resistance to many chemotherapeutic drugs. In this study, a potential chromatin repair mechanism during oxidative stress was investigated in HT22 cells. The 20S proteasome has been shown to be largely responsible for the degradation of oxidatively modified histone proteins in the nucleus. Poly(ADP-ribosyl)ation reactions also play an important role in DNA repair as a consequence of oxidative damage and single-strand breaks. Such a reaction may occur also with the 20S proteasome-with a known increase in enzymatic activity-and also with histones-reducing their proteolytic susceptibility as shown for the first time here. After hydrogen peroxide treatment of HT22 cells, degradation of the model peptide substrate suc-LLVY-MCA and degradation of oxidized histones by nuclear proteasome increased. During the removal of protein carbonyls, single-strand breaks and 8-hydroxy-2'-deoxyguanosine, proteasome, and poly(ADP-ribose) polymerase-1 enzymes were shown to play tightly interacting roles. Our results following the repair of oxidative damage show the proteolytic activation of proteasome concerning poly(ADP-ribosyl)ation together with a decline in poly(ADP-ribosyl)ation of oxidized histones, leading to a selective recognition of oxidatively modified histones. (C) 2009 Elsevier Inc. All rights reserved.

The role of ER in the proper synthesis and correct folding of protein, to establish the homeostasis of organism, is well documented by various studies. Following excessive oxidative stress, the accumulation of unfolded/misfolded proteins increase in the lumen of ER which blocks the inhibitory effect of GRP78 on UPR regulatory proteins; IRE1, PERK and ATF6. It is clear that ER stress mediated UPR is a potent inducer of proteasomal and autophagic activities which serves as a degradation process for maintaining stress tolerance, limited damage and viability under stress conditions. Interestingly, aberrantly activation of autophagy can result in destroying major portions of the cytosol and organelles, which will lead to autophagic death of cardiac myocytes, and development of cardiac failure. In the present study Grp78, Grp94, pIRE1, pPERK, derlin-1, proteasome β5 subunit, VCP, beclin-1 and LC3-II, well known markers of ER stress, proteasomal and autophagic activities, are investigated in the heart tissue of rabbits. Furthermore, autophagic activity in heart tissue is observed in hypercholesterolemic vs control rabbits by electron microscopy. Additionally, colocalization studies of mitochondria and p62 in cryo sections of heart tissue were applied to understand the levels of mitochondria degradation by autophagy.

Proper synthesis and correct folding of proteins in endoplasmic reticulum (ER) is important for the proper function of many organs including heart. Cardiovascular diseases (CVDs) are the leading cause of death, with highest mortality and morbidity rates worldwide. High blood cholesterol levels are well recognized as a risk factor for atherosclerosis and the development of CVDs such as heart failure. Globally, high blood cholesterol levels are estimated to cause 56% of ischemic heart disease and 18% of strokes, which equals to 4.4 million deaths per year. Elevated oxLDL levels have significant roles in the induction of reactive oxygen species, unfolded/misfolded proteins and oxidative/ER stress related changes. Although autophagy plays a beneficial role in cellular homeostasis, excessive autophagy might be expected to lead to cellular destruction by high degrading rate of proteins and organelles such as mitochondria and ER. Heart failure, as a result of the disturbed unfolded protein response mediated cardiomyocyte death leads to many cardiovascular disorders. The role of apoptosis and necrosis in development of CVDs, especially heart failure, has been well documented. Recent evidence suggests the potential role of another cell death mechanism, autophagy, in loss of cardiomyocytes. In our study, protein levels of well-known ER stress markers (Grp78, Grp94, pIRE1, pPERK), autophagic activity markers (beclin-1, LC3-II), and apoptotic activity markers (bax, caspase 3), are investigated in the heart of hypercholesterolemic rabbits. Furthermore, autophagic activity in heart is also observed in hypercholesterolemic rabbits by electron microscopy along with apoptotic cell death by TUNEL. Additionally, colocalization studies of mitochondria and p62 in cryosections of heart tissue were applied by confocal microscopy. Our animal model showed that hypercholesterolemia mediated ER stress activation triggers autophagy/mitophagy, which might cause cell death of cardiomyocytes by organel depletion in juxtanuclear area, pathophysiological setting of autophagic cardiomyocyte death in heart failure needs to be further studied. Supported by Marmara University Research Funds SAG-A-130612-0202 and SAG-C-DRP-130515-0164.

Proteasomal degradation is crucial to prevent the accumulation of cellular damage. The removal of the damage is a required process for healthy organisms to keep the integrity while in cancer cells this situation may induce drug resistance. Regarding chemotherapy for the cancer treatment, degradation mechanisms such as proteasomal system and autophagy have been focused recently and proteasomal inhibition in cancer cells have been shown to induce autophagy. This induced pathway may prevent the cancer cells from death or can cause autophagic cell death which is an important reason for chemotherapy resistance. There are many preclinic studies to improve the results and on the other hand heat shock proteins are accepted to be protective which may bring new approach. In our laboratory, several cancer cell lines have been tested from different aspects of proteasomal activity. HCT116 colon cancer cell line was used to test the role of HSP70 and proteasome inhibition on autophagic cell death. In this direction, heat shock treatment has been applied to the cells which is also an applied process for cancer patients. Cell viability, proteasome activity, degradation of long-lived proteins, and the expressions of HSP70, LC3, beclin1, caspase 9 and PARP have been analysed. Additionally, mouse hippocampal cell line is used to test the proteasomal activity in relation to heat shock proteins which highlighted another important point for the chemothrapy resistance with antioxidant gene expressions. Different breast cancer cell lines have also confirmed the role of proteasomal degradation in the failure of chemotherapy. Supported by TUBITAK COST-CM1001-110S281 and TUBITAK 212T156

Hypercholesterolemia is the major risk factor for the development of atherosclerosis and vitamin E is suggested to have a preventive role in this process (1), although the mechanism of action still remains unclear.The ubiquitin-proteasome system (UPS) may in?uence atherosclerosis by affecting disease-relevant cellular processes such as apoptosis, proliferation, and differentiation, or by affecting cellular stress responses and/or adaptive phenomena, such as ER stress, in?ammation, and redox homeostasis (2). NF-E2-related factor 2 (Nrf2) is a transcription factor that controls the expression of phase II detoxi?cation and antioxidant genes. Nrf2 signaling has additionally been shown to upregulate the expression of the proteasome catalytic subunits (3). In the present study, we investigated the role of Nrf2 pathway on oxidative and ER stress conditions induced by cholesterol diet and the effects of vitamin E on related signaling pathways in in vivo model of atherosclerosis. All experimental procedures were approved by the Marmara University Ethics Committee. Twenty-one male albino rabbits (23 months old) were assigned randomly to four groups fed for 8 weeks: (i) vitamin E deficient diet, (ii) vitamin E deficient diet containing 2% cholesterol, and (iii) vitamin E deficient diet containing 2% cholesterol with daily intramuscular injections of vitamin E (50mg/kg), (iv) vitamin E deficient diet with daily intramuscular injections of vitamin E (50mg/kg). In order to elucidate in vivo role of oxidative stress and ER stress in cardiovascular system of hypercholesterolemic rabbits, we investigated serum levels of cholesterol, MDA and vitamin E and Nrf2, GST-1, GRP78, GRP94, PERK, IRE1 protein levels and the proteasomal activity in aortic tissues will be discussed.

Colon carcinoma is the third among the cancer related deaths. The role of pro-apoptotic Bax protein on the resveratrol related apoptosis, mitochondrial membrane potential and signal pathways has not been identified in colon carcinoma cells. In this direction, HCT-116 bax positive and HCT-116 negative cell lines were utilized to detect the apoptotic effect and I?B, MEK1 and STAT 3 signal transduction pathways of resveratrol. The impact on the cell viability and IC50 value of resveratrol has been determined via WST-1 viability assay. The ratio of apoptosis has been evaluated via flow cytometry following Annexin V/Propidium iodide (PI) double staining. Changes in the mitochondrial membrane potential have been analyzed by flow cytometry and JC-1 fluorometric staining. IkB, MEK1 and STAT3 molecules were measured by Enspire device. Data showed the IC50 value for resveratrol as 50M. According to the flow cytometry, apoptosis ratio has been determined as 29.65% in the experimental group of bax positive cells, as 13.98% in the experimental group of bax negative cells. Changes in the membrane potential has been established as 8.62% in the experimental group of bax positive cells, as 97.98% in the experimental group of bax negative cells. When the obtained data from Enspire device was reviewed; bax positive cells I?B phosphorylations were found as as 5.22 for experimental groups; MEK1 phosphorylations were found as and as 1.15 for experimental groups; STAT 3 phosphorylations were found as and as 2.52 for experimental groups. In HCT-116 bax negative cells, I?B phosphorylation were and 2.71 in experimental groups; MEK1 phosphorylation were 1.18 in experimental groups; STAT 3 phosphorylation were 1.54 in experimental groups. Our data show that Bax protein plays role in the apoptotic effect of resveratrol by altering mitochondrial membrane potential and mitochondrial membrane permeability, signal transduction and the absence of Bax increase the sensitivity of HCT-116 colon carcinoma cells to apoptosis.

Proteasomal degradation of oxidized proteins is a crucial mechanism to prevent the accumulation of cellular damage. The removal of the damage is generally a required process for healthy organisms to keep the integrity while in cancer cells the situation may be different. In normal conditions, cancer cells have higher proteasome activity compared to normal cells. During cancer treatment, cellular damage by chemotherapy is an expected process to be able to kill the tumor cells. And the accumulation of this damage accompanied by the decrease in protein repair and removal systems may increase the efficacy of the cancer therapy. Heat shock proteins (Hsp) as molecular chaperones are involved in the folding, activation and assembly of a variety of proteins. Among these Hsp40, Hsp70 and Hsp90 are believed to act as a chaperone system to regulate the proteasomal degradation. In this study, we tested the role of heat stress response on the proteasomal degradation of oxidized proteins. We used two different cell lines to observe the difference in normal and tumor cells. First the effect of heat stress (42°C, 1h) were tested in terms of protein oxidation tested by protein carbonyl formation and proteasomal degradation. The results were extremely different in normal fibroblast cells and hippocampal tumor cells. In the same direction, the expressions of Hsp40, Hsp70 and Hsp90 were affected in a different manner in two cell lines, will be discussed in detail. Supported by TUBITAK COST-CM1001-110S281.