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Biomedical subjects

Angelo Azzi

Publications and source records attributed to Angelo Azzi.

At least 19 recordsLinked to original sources
PubMed2005

Role of peroxisome proliferator-activated receptor gamma in amyloid precursor protein processing and amyloid beta-mediated cell death.

Recent data indicate that PPARgamma (peroxisome proliferator-activated receptor gamma) could be involved in the modulation of the amyloid cascade causing Alzheimer's disease. In the present study we show that PPARgamma overexpression in cultured cells dramatically reduced Abeta (amyloid-beta) secretion, affecting the expression of the APP (Abeta precursor protein) at a post-transcriptional level. APP down-regulation did not involve the pathway of the secretases and correlated with a significant induction of APP ubiquitination. Additionally, we demonstrate that PPARgamma was able to protect the cells from H(2)O(2)-induced necrosis by decreasing Abeta secretion. Taken together, our results indicate a novel mechanism at the basis of the neuroprotection shown by PPARgamma agonists and an additional pathogenic role for Abeta accumulation.

Alzheimer Disease↗
PubMed2005

Vitamin E inhibits CD36 scavenger receptor expression in hypercholesterolemic rabbits.

A numerous studies suggest that Vitamin E has a preventive role in atherosclerosis, although the mechanism of action still remains unclear. CD36, a member of the scavenger receptor family is centrally involved in the uptake of oxidized low density proteins (oxLDLs) from bloodstream. During the atherosclerotic process, the lipid cargo of oxLDL accumulates in macrophages and smooth muscle cells, inducing their pathological conversion to foam cells. In the present study, we investigate the role of Vitamin E on CD36 expression in an in vivo model. Atherosclerosis was induced by a 2% cholesterol containing Vitamin E poor diet. Three groups of six rabbits each were studied. The first group (control) was fed on Vitamin E poor diet. The second group was fed with Vitamin E poor diet containing 2% cholesterol and the rabbits in the third group were fed with Vitamin E poor diet containing 2% cholesterol and received injections of 50 mg/kg of Vitamin E i.m. After 4 weeks, aortas were removed and analysed by light microscopy for atherosclerotic lesions. Aortic samples were analysed for CD36 mRNA expression. The aortas of cholesterol-fed rabbits showed typical atherosclerotic lesions, detected by macroscopic and microscopic examination, and exhibited an increase in CD36 mRNA expression. Vitamin E fully prevented cholesterol induced atherosclerotic lesions and the induction of CD36 mRNA expression. The effects observed at the level of CD36 scavenger receptor expression in vivo suggest an involvement of reduced foam cell formation in the protective effect of Vitamin E against atherosclerosis.

Animals↗
PubMed2005

Tocotrienol inhibits proliferation of human Tenon's fibroblasts in vitro: a comparative study with vitamin E forms and mitomycin C.

PURPOSE: To evaluate the potential of the vitamin E compound alpha-tocotrienol as antifibrotic agent in vitro. METHODS: Using human Tenon's capsule fibroblast cultures, the antiproliferative and cytotoxic effects of the different vitamin E forms alpha-tocopherol, alpha-tocopheryl acetate, alpha-tocopheryl succinate and alpha-tocotrienol were compared with those of mitomycin C. To mimic subconjunctival and regular oral application in vivo, exposure time of serum-stimulated and serum-restimulated fibroblasts (SF and RF, respectively) to vitamin E forms was set at 6 days. Cultures were only exposed for 5 min to mitomycin C due to its known acute toxicity and to mimic the short-time intraoperative administration. Proliferation (expressed as % of control) was determined by DNA content quantification on days 2, 4 and 6, whereas cytotoxicity was assessed by cell morphology and glucose 6-phosphate dehydrogenase (G6PD) release after 24 h. RESULTS: alpha-Tocopherol and alpha-tocopheryl acetate stimulated growth of SF, but not RF. Reduction of fibroblast content by alpha-tocopheryl succinate was accompanied by increased G6PD release and necrosis. Contrary to alpha-tocopheryl succinate, 50 microM or repeatedly 20 microM of alpha-tocotrienol significantly inhibited proliferation without causing cellular toxicity (maximal effect: 46.8%). RF were more sensitive to this effect than SF. Mitomycin C 100-400 microg/ml showed a stronger antiproliferative effect than alpha-tocotrienol (maximal effect: 13.8%). Morphologic characteristics of apoptosis were more commonly found under treatment with mitomycin C. CONCLUSIONS: Of the vitamin E forms tested, only alpha-tocotrienol significantly inhibited growth at non-toxic concentrations. In this in vitro study, antiproliferative effects of mitomycin C were stronger than those of alpha-tocotrienol.

Aged↗
PubMed2005

CD36 overexpression in ritonavir-treated THP-1 cells is reversed by alpha-tocopherol.

Therapies with antiretroviral protease inhibitors (ARPI) are correlated with a higher risk for dyslipidemia, hypercholesterolemia, and atherosclerosis. The original aim of this study was to establish whether alpha-tocopherol can reduce CD36 scavenger receptor overexpression occurring after treatment of monocytes with the ARPI ritonavir. We show here that treatment of THP-1 monocytes with ritonavir increases total protein and surface expression of CD36; however, only weak changes are observed at the mRNA level, suggesting that CD36 overexpression occurs mainly at the posttranscriptional level. Concentrations of ritonavir that upregulate CD36 expression inhibit proteasome activity in THP-1 cells, indicating a possible regulatory role of the proteasome in CD36 overexpression. Similar to ritonavir, the proteasome inhibitor ALLN increases the CD36 surface expression on THP-1 cells. alpha-Tocopherol efficiently normalizes CD36 protein overexpression after ritonavir treatment and reduces oxLDL uptake. Furthermore, in THP-1 monocytes, alpha-tocopherol reverses the proteasome activity inhibited by ritonavir. This study indicates that an increased CD36 protein expression in THP-1 monocytes induced by ritonavir can be normalized by alpha-tocopherol. CD36 overexpression is caused by inhibition of proteasome activity by ritonavir, which is efficiently restored by alpha-tocopherol.

Base Sequence↗
PubMed2005

Recombinant SEC14-like proteins (TAP) possess GTPase activity.

The three human SEC14-like proteins TAP1, TAP2, and TAP3 were expressed in Escherichia coli and purified by means of an amino-terminal His-tag. The recombinant TAP proteins bound alpha-, beta-, gamma-, and delta-tocopherol, certain phospholipids, and squalene. Intriguingly, the TAP proteins showed considerable GTPase activity that was comparable to that of small GTP-binding proteins of the Rab family. Although the TAP proteins contain important motifs to provide GTPase activity, the surrounding secondary structure markedly differed from common G-protein domains. However, these motifs are located in close proximity in the TAP structure and may therefore form an active site for GTP-binding and hydrolysis.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2005

On the existence of cellular tocopheryl phosphate, its synthesis, degradation and cellular roles: a hypothesis.

The finding that alpha-tocopheryl phosphate is present in cells in small amounts, that it can be synthesized and hydrolyzed supports the hypothesis that alpha-tocopheryl phosphate might be a signaling molecule. The possible pathways needed for the synthesis, hydrolysis and signaling are considered in this hypothesis as well the possible extension of this reaction to additional molecules such as tocopherols and tocotrienols. A possible mechanism of action of other tocopherol esters (succinate and maleate) is also hypothesized.

Cell Physiological Phenomena↗
PubMed2005

Vitamins E and C are safe across a broad range of intakes.

A robust database shows that dietary supplements of vitamins E and C are safe for the general population. Because these nutrients supply antioxidant and other functions for homeostasis and protection against free radical damage, supplementation has been intensively studied. Because of perceived benefits, many persons consume quantities of vitamins E and C well above the recommended dietary allowances. As safety guidance, tolerable upper intake levels have been established by the Food and Nutrition Board, Institute of Medicine, at 1000 mg for vitamin E and 2000 mg for vitamin C in adults. Many clinical trials with these vitamins have involved subjects with various diseases, and no consistent pattern of adverse effects has occurred at any intake. Numerous studies of vitamin C supplementation have provided no pattern of evidence to support concerns about safety other than occasional gastrointestinal upset or mild diarrhea resulting from the osmotic effects of unabsorbed quantities of vitamin C. Evidence of bleeding effects and other potential adverse effects of high vitamin E intakes in humans is not convincing. Evidence of adverse effects of vitamin C that result from its effects on iron absorption and metabolism has not been confirmed in clinical trials. Thus, we conclude from clinical trial evidence that vitamin E supplements appear safe for most adults in amounts </=1600 IU (1073 mg RRR-alpha-tocopherol or the molar equivalent of its esters) and that vitamin C supplements of </=2000 mg/d are safe for most adults.

Antioxidants↗
PubMed2004

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.

Apoptosis↗
PubMed2004

Modulation of cell proliferation and gene expression by alpha-tocopheryl phosphates: relevance to atherosclerosis and inflammation.

The effect of a mixture of alpha-tocopheryl phosphate and di-alpha-tocopheryl phosphate (TPm) was studied in vitro on two cell lines, RASMC (from rat aortic smooth muscle) and human THP-1 monocytic leukaemia cells. Inhibition of cell proliferation by TPm was shown in both lines and occurred with TPm at concentrations lower than those at which alpha-tocopherol was equally inhibitory. TPm led in non-stimulated THP-1 cells to inhibition of CD36 mRNA and protein expression, to inhibition of oxidized low density lipoprotein surface binding and oxLDL uptake. In non-stimulated THP-1 cells, alpha-tocopherol had only very weak effects on these events. Contrary to alpha-tocopherol, TPm was cytotoxic to THP-1 cells at high concentrations. Thus, TPm is able to inhibit the major aggravating elements involved in the progression of atherosclerosis. The higher potency of TPm may be due to a better uptake of the molecule and to its intracellular hydrolysis, providing more alpha-tocopherol to sensitive sites. Alternatively, a direct effect of the phosphate ester on specific cell targets may be considered.

Animals↗
PubMed2004

CD36 overexpression in human brain correlates with beta-amyloid deposition but not with Alzheimer's disease.

Scavenger receptors recently have been related to Alzheimer's disease, although it is still unclear whether they contribute to the pathogenesis of the disease or reflect an inflammatory response to the deposition of amyloid beta-protein (Abeta). In this study we demonstrate that CD36, a class B scavenger receptor, is highly expressed in the cerebral cortex of Alzheimer's disease patients and cognitively normal aged subjects with diffuse amyloid plaques compared with age-matched amyloid-free control brains. Moreover, in vitro experiments indicated that Abeta is able to induce CD36 expression in neuronal cells after 24 h treatment. The interaction between CD36 and Abeta has been reported to trigger oxidant production by macrophages and microglia. In line with this observation, we found an increased presence of nitrated proteins in brains showing Abeta loads and CD36 overexpression, independent of the occurrence of Alzheimer's disease pathologic features.

Aged↗
PubMed2004

The effect of alpha- and gamma-tocopherol and their carboxyethyl hydroxychroman metabolites on prostate cancer cell proliferation.

It is known that gamma-tocopherol inhibits human prostate cancer cell proliferation via down-regulation of cyclin-related signalling but tocopherol and tocotrienol metabolites with a shortened phytyl chain, carboxyethyl hydroxychromans, were not previously investigated as anti-proliferative agents. In this study, the effect of the two main tocopherols, namely, alpha-tocopherol and gamma-tocopherol, and their corresponding metabolites (alpha- and gamma-carboxyethyl hydroxychromans) was studied on proliferation and cyclin D1 expression of the prostate cancer cell line PC-3. The hydrosoluble vitamin E analogues Trolox and alpha-tocopherol succinate were also tested. The most effective inhibitors of PC-3 proliferation were gamma-tocopherol and gamma-carboxyethyl hydroxychroman. Their effect was discernable at 1 microM and reached a plateau at concentrations > or = 10 microM with maximal inhibition values ranging between 70 and 82%. alpha-Tocopherol, alpha-carboxyethyl hydroxychroman, and the analogue Trolox were much less effective; a weak effect was observed for concentrations < or = 10 microM and a maximal inhibition of less than 45% was found at 50 microM concentration. PC-3 cells showed higher inhibition, particularly by the gamma derivatives, than HTB-82 and HECV cells. Tocopherols and carboxyethyl hydroxychromans exerted an inhibitory effect on cyclin D1 expression parallel to the retardation of cell growth. gamma-Carboxyethyl hydroxychroman and gamma-tocopherol showed effects also upstream of the cyclin modulation. Furthermore, the inhibition of cyclin D1 expression by gamma-carboxyethyl hydroxychroman was competed for by alpha-carboxyethyl hydroxychroman. In conclusion, this study shows that carboxyethyl hydroxychroman metabolites are as effective as their vitamin precursors to inhibit PC-3 growth by specific down-regulation of cyclin expression, with the gamma forms being the most effective ones. Although the inhibition of PC-3 cell growth and diminution of cyclin expression are clearly visible, more subtle mechanistic effects of tocopherols and their corresponding carboxyethyl hydroxychroman metabolites deserve further investigations.

Antioxidants↗
PubMed2004

Free radical biology - terminology and critical thinking.

What is an antioxidant? Can one, at a cellular level, speak of direct and indirect antioxidants? Can oxidative stress be quantified and characterized? What are the oxidant species that may have regulatory functions in a cell? Since the above concepts have become of frequent use in all Journals, it may be appropriate if some critical thinking outlined in this review could become available to a broad public.

Animals↗
PubMed2004

The role of alpha-tocopherol in preventing disease.

A role of oxidative stress in atherosclerosis lies on experimental results carried out in vitro and in animal models. In humans, the supplementation with the antioxidant vitamin E has given in some cases supportive results and in others no effects. From in vitro studies, a large amount of data has shown that alpha-tocopherol (the major component of vitamin E) regulates key events in the cellular pathogenesis of atherosclerosis. We first described the inhibition of protein kinase C (PKC) activity by alpha-tocopherol to be at the basis of the vascular smooth muscle cell growth inhibition by this compound. Subsequently, PKC was recognized to be the target of alpha-tocopherol in different cell types, including monocytes, macrophages, neutrophils, fibroblasts and mesangial cells. Inhibiting the activity of protein kinase C by alpha-tocopherol results in different events in different cell types: inhibition of platelet aggregation, of nitric oxide production in endothelial cells, of superoxide production in neutrophils and macrophages as well as impairment of smooth muscle cell proliferation. Adhesion molecule expression and inflammatory cell cytokine production are also influenced by alpha-tocopherol. Scavenger receptors, particularly important in the formation of atherosclerotic foam cells, are also modulated by alpha-tocopherol. The oxidized LDL scavenger receptors SR-A and CD36 are down regulated at the transcriptional level by alpha-tocopherol. The relevance of CD36 expression in the onset of atherosclerosis has been indicated by the protection against atherosclerosis by CD36 knockout mice. In conclusion, the effect of alpha-tocopherol against atherosclerosis is not due only to the prevention of LDL oxidation but also to the down regulation of the scavenger receptor CD36 and to the inhibition of PKC activity.

Animals↗
PubMed2004

Vitamin E mediates cell signaling and regulation of gene expression.

alpha-Tocopherol modulates two major signal transduction pathways centered on protein kinase C and phosphatidylinositol 3-kinase. Changes in the activity of these key kinases are associated with changes in cell proliferation, platelet aggregation, and NADPH-oxidase activation. Several genes are also regulated by tocopherols partly because of the effects of tocopherol on these two kinases, but also independently of them. These genes can be divided in five groups: Group 1. Genes that are involved in the uptake and degradation of tocopherols: alpha-tocopherol transfer protein, cytochrome P450 (CYP3A), gamma-glutamyl-cysteine synthetase heavy subunit, and glutathione-S-transferase. Group 2. Genes that are implicated with lipid uptake and atherosclerosis: CD36, SR-BI, and SR-AI/II. Group 3. Genes that are involved in the modulation of extracellular proteins: tropomyosin, collagen-alpha-1, MMP-1, MMP-19, and connective tissue growth factor. Group 4. Genes that are connected to adhesion and inflammation: E-selectin, ICAM-1 integrins, glycoprotein IIb, IL-2, IL-4, IL-1b, and transforming growth factor-beta (TGF-beta). Group 5. Genes implicated in cell signaling and cell cycle regulation: PPAR-gamma, cyclin D1, cyclin E, Bcl2-L1, p27, CD95 (APO-1/Fas ligand), and 5a-steroid reductase type 1. The transcription of p27, Bcl2, alpha-tocopherol transfer protein, cytochrome P450 (CYP3A), gamma-glutamyl-cysteine sythetase heavy subunit, tropomyosin, IL-2, and CTGF appears to be upregulated by one or more tocopherols. All the other listed genes are downregulated. Gene regulation by tocopherols has been associated with protein kinase C because of its deactivation by alpha-tocopherol and its contribution in the regulation of a number of transcription factors (NF-kappaB, AP1). A direct participation of the pregnane X receptor (PXR) / retinoid X receptor (RXR) has been also shown. The antioxidant-responsive element (ARE) and the TGF-beta-responsive element (TGF-beta-RE) appear in some cases to be implicated as well.

Absorption↗
PubMed2004

Modulation of cell proliferation and gene expression by alpha-tocopheryl phosphates: relevance to atherosclerosis and inflammation.

The effect of a mixture of alpha-tocopheryl phosphate plus di-alpha-tocopheryl phosphate (TPm) was studied in vitro on two cell lines, RASMC (from rat aortic smooth muscle) and human THP-1 monocytic leukemia cells. Inhibition of cell proliferation by TPm was shown in both lines and occurred with TPm at concentrations lower than those at which alpha-tocopherol was equally inhibitory. TPm led in nonstimulated THP-1 cells to inhibition of CD36 mRNA and protein expression, to inhibition of oxidized low-density lipoprotein surface binding and oxLDL uptake. In nonstimulated THP-1 cells, alpha-tocopherol had only very weak effects on these events.

Animals↗
PubMed2004

Regulation of gene expression by alpha-tocopherol.

Several genes are regulated by tocopherols which can be categorized, based on their function, into five groups: genes that are involved in the uptake and degradation of tocopherols (Group 1) include alpha-tocopherol transfer protein (alpha-TTP) and cytochrome P450 (CYP3A); genes that are associated with lipid uptake and atherosclerosis (Group 2) include CD36, SR-BI and SR-AI/II. Genes that modulate the expression of extracellular proteins (Group 3) include tropomyosin, collagen(alpha1), MMP-1, MMP-19 and connective tissue growth factor (CTGF). Genes that are related to inflammation, cell adhesion and platelet aggregation (Group 4) include E-selectin, ICAM-1, integrins, glycoprotein IIb, II-2, IL-4 and IL-beta. Group 5 comprises genes coding for proteins involved in cell signaling and cell cycle regulation and consists of PPAR-gamma, cyclin D1, cyclin E, Bcl2-L1, p27 and CD95 (Apo-1/Fas ligand). The expression of P27, Bcl2, alpha-TTP, CYP3A, tropomyosin, II-2, PPAR-gamma, and CTGF appears to be up-regulated by one or more tocopherols whereas all other listed genes are down-regulated. Several mechanisms may underlie tocopherol-dependent gene regulation. In some cases protein kinase C has been implicated due to its deactivation by alpha-tocopherol and its participation in the regulation of a number of transcription factors (NF-kappaB, AP-1). In other cases a direct involvement of PXR/RXR has been documented. The antioxidant responsive element (ARE) appears in some cases to be involved as well as the transforming growth factor beta responsive element (TGF-beta-RE). This heterogeneity of mediators of tocopherol action suggests the need of a common element that could be a receptor or a co-receptor, able to interact with tocopherol and with transcription factors directed toward specific regions of promoter sequences of sensitive genes. Here we review recent results of the search for molecular mechanisms underpinning the central signaling mechanism.

Animals↗