[Show abstract][Hide abstract]ABSTRACT: Lycopene beta-cyclase (tlcy-b) tomatoes, obtained by modulating carotenogenesis via genetic engineering, contain a large amount of beta-carotene, as clearly visible by their intense orange colour. In the present study we have subjected tlcy-b tomatoes to an in vitro simulated digestion and analysed the effects of digestate on cell proliferation. To this aim we used HT-29 human colon adenocarcinoma cells, grown in monolayers, as a model. Digested tomatoes were diluted (20 ml, 50 ml and 100 ml/l) in culture medium and added to the cells for different incubation times (24 h, 48 h and 72 h). Inhibition of cell growth by tomato digestate was dose-dependent and resulted from an arrest of cell cycle progression at the G0/G1 and G2/M phase and by apoptosis induction. A down-regulation of cyclin D1, Bcl-2 and Bcl-xl expression was observed. We also found that heat treatment of samples before digestion enhanced beta-carotene release and therefore cell growth inhibition. To induce with purified beta-carotene solubilised in tetrahydrofuran the same cell growth inhibition obtained with the tomato digestate, a higher amount of the carotenoid was necessary, suggesting that beta-carotene micellarised during digestion is utilised more efficiently by the cells, but also that other tomato molecules, reasonably made available during digestion, may be present and cooperate with beta-carotene in promoting cell growth arrest.
Full-text · Article · Jul 2009 · The British journal of nutrition
[Show abstract][Hide abstract]ABSTRACT: Transthyretin (TTR), a homotetrameric protein of 54 kDa, is one of the carriers of thyroid hormone and, as a macromolecular complex with retinol-binding protein 4(RBP4), is involved in the transport of vitamin A in blood, preventing kidney glomerular filtration of the small, 21 kDa RBP4. TTR cDNA has been cloned in many vertebrates (man, rat, chicken, etc.) and more recently also in several teleost fishes. Fish TTR shows a strong homology with the same protein of other vertebrates, with similar monomer-monomer and dimer-dimer interfaces and a conserved tetrameric structure. RBP4 was also isolated from several teleosts and characterized. The expression of the two proteins was investigated during embryonic development and in adult tissues. TTR is expressed in adult fish liver and is therefore present in their serum, even though RBP4 and TTR have never been detected in the blood as a complex. The lack of RBP4-TTR complex formation in fish has been explained, since the residues specifically involved in the interaction between the two proteins in mammals are different from the corresponding residues in fish.
[Show abstract][Hide abstract]ABSTRACT: Epidemiological studies have suggested a correlation between consumption of carotenoid-rich food and incidence of chronic diseases. In this review chemical structure, bioavailability and mechanisms of action of carotenoids most represented in human diet, mainly beta-carotene and lycopene, are reported, with focus on results obtained with cells in culture.
No preview · Article · Dec 2007 · Mini Reviews in Medicinal Chemistry
[Show abstract][Hide abstract]ABSTRACT: In the present study, we utilised an in vitro digestion procedure to deliver molecules contained in tomatoes to cultured cells and to analyse potential mechanisms underlying the antitumoural effects of tomatoes reported in the literature. Ripe tomatoes underwent in vitro simulated digestion and the aqueous fraction obtained was delivered to HT-29 and HCT-116 colon adenocarcinoma cells. The amount of lycopene released during digestion and transferred to the aqueous fraction during digestion was 10-fold lower than that present in tomato homogenate before digestion. The carotenoid was accumulated by colon adenocarcinoma cells in a dose-dependent manner after the addition of tomato digestate (20-100 ml/l) for 24 h. Tomato digestate inhibited the growth of HT-29 and HCT-116 cells in a dose-dependent manner. Growth inhibition resulted from an arrest of cell cycle progression at the G0/G1 phase and by apoptosis induction. A down regulation of cyclin D1, Bcl-2 and Bcl-xL expression was also observed, without apparent changes in p53, p21, p27 and Bax. In conclusion, the present data demonstrate that the in vitro digestion procedure represents a useful approach to supply tomato to colon cultured cells. Moreover, we have shown that tomato digestate is able to inhibit the growth of colon cancer cells by modulating the expression of regulators of the cell cycle and apoptosis.
Full-text · Article · Nov 2007 · British Journal Of Nutrition
[Show abstract][Hide abstract]ABSTRACT: Retinoid transport is well characterized in many vertebrates, while it is still largely unexplored in fish. To study the transport and utilization of vitamin A in these organisms, we have isolated from a carp liver cDNA library retinol-binding protein, its plasma carrier. The primary structure of carp retinol-binding protein is very conserved, but presents unique features compared to those of the correspondent proteins isolated and characterized so far in other species: it has an uncleavable signal peptide and two N-glycosylation sites in the NH(2)-terminal region of the protein that are glycosylated in vivo. In this paper, we have investigated the function of the carbohydrate chains, by constructing three mutants deprived of the first, the second or both carbohydrates. The results of transient transfection of wild type and mutant retinol-binding protein in Cos cells followed by Western blotting and immunofluorescence analysis have shown that the absence of both carbohydrate moieties blocks secretion, while the presence of one carbohydrate group leads to an inefficient secretion. Experiments of carp RBP mRNA in vitro translation in a reticulocyte cell-free system in the presence of microsomes have demonstrated that N-glycosylation is necessary for efficient translocation across the endoplasmic reticulum membranes. Moreover, when Cos cells were transiently transfected with wild type and mutant retinol-binding protein (aa 1-67)-green fluorescent protein fusion constructs and semi-permeabilized with streptolysin O, immunofluorescence analysis with anti-green fluorescent protein antibody revealed that the double mutant is exposed to the cytosol, thus confirming the importance of glycan moieties in the translocation process.
No preview · Article · Aug 2005 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract]ABSTRACT: Ceruloplasmin, a blue copper oxidase circulating in serum of all vertebrates, is a glycoprotein synthesized mainly in hepatocytes and secreted into plasma with six tightly bound atoms of copper per molecule. Many aspects of the mechanisms by which synthesis and secretion of this protein are regulated by copper are still not known. In HepG2 hepatocarcinoma cells this fine regulation is not maintained; we have then utilized Met-murine-hepatocytes (MMH), isolated from the liver of transgenic mice expressing a truncated form of c-Met (hepatocyte growth factor receptor), that are immortalized but not transformed. Copper deficiency was induced by treatment of cells with bathocuproine disulphonate. Experiments of metabolic labeling with 35S-methionine-cysteine and of Western blotting followed by immunostaining, demonstrated that maturation and secretion of ceruloplasmin but not its synthesis are affected by copper availability. In this paper we have shown that in copper deficiency ceruloplasmin accumulates in a pre-Golgi compartment, in which the protein is still in a Endo H sensitive form, and where presumably copper binding to the apo-protein takes place. Moreover, we found that treatment of copper-deficient cells with the proteasomal inhibitor lactacycstin leads to immature ceruloplasmin accumulation in the cell. We have optimized conditions to induce in vitro copper deficiency and found that MMH-D3 cells represent a suitable model to study in detail the molecular mechanism of copper-regulated ceruloplasmin synthesis, secretion and degradation.
No preview · Article · Feb 2005 · Cellular and molecular biology (Noisy-le-Grand, France)
[Show abstract][Hide abstract]ABSTRACT: There is evidence that organic food often contains relatively high amounts of natural toxic compounds produced by fungi or plants, whereas corresponding conventional food tends to contain more synthetic toxins such as pesticide residues, but only a few studies have evaluated the impact of their consumption on health. This study proposes a novel approach to evaluate the potential health risk of organic compared to conventional food consumption, that is, the assay of sensitive markers of cell function in vulnerable conditions. The markers utilized were intestinal and splenic lymphocyte proliferative capacity and liver acute-phase reaction, both responding to the presence of toxins. The vulnerable conditions in which body defenses can be less efficient were weaning and protein-energy malnutrition. This study reports the results of a pilot experiment on one sample of eight varieties of organically and conventionally grown wheat. Weaned rats were assigned to two groups fed conventional (CV) or organic (ORG) wheat for 30 days. Each group was divided in two subgroups of well-nourished (WN) or protein-energy-malnourished (PEM) rats. For each rat, the lymphocyte proliferation was assayed by [(3)H]thymidine incorporation after stimulation of cells with a mitogen, in a culture medium containing either commercial fetal calf serum (FCS) or the corresponding rat serum (RS) to mimic the in vivo proliferative response. The acute-phase proteins (albumin, transthyretin, transferrin, ceruloplasmin, retinol-binding protein) were measured in plasma by Western blotting and immunostaining with specific antibodies. The proliferative response of lymphocytes cultured with FCS and the amount of acute-phase proteins of rats fed the ORG wheat sample, either WN or PEM, did not differ from those of rats fed the CV wheat sample. However, the proliferative response of lymphocytes cultured with RS was inhibited in PEM-CV compared with PEM-ORG. The content of mycotoxins was highest in the organic sample, and therefore the immunotoxic effect was probably due to other contaminants in the CV wheat. In conclusion, these results indicate that the conventional wheat sample tested represented a higher risk for lymphocyte function than the wheat sample organically grown, at least in vulnerable conditions.
Full-text · Article · Jan 2005 · Journal of Agricultural and Food Chemistry
[Show abstract][Hide abstract]ABSTRACT: Retinol-binding protein (RBP) is the specific plasma carrier of retinol, encharged of the vitamin transport from the liver to target cells. Ligand binding influences the RBP affinity for transthyretin (TTR), a homotetrameric protein involved in the RBP/TTR circulating complex, and the secretion rate of RBP. In fact, in vitamin A deficiency, the RBP release from the hepatocytes dramatically decreases and the protein accumulates in the cells, until retinol is available again. The mechanism is still not clear and new cellular models are needed to understand in detail how the soluble RBP can be retained inside the cell. In fish, a vitamin A transport system similar to that of higher vertebrates is emerging, although with significant differences.
Full-text · Article · Jan 2004 · Molecular Aspects of Medicine
[Show abstract][Hide abstract]ABSTRACT: The retinol/retinol-binding protein/transthyretin complex, that carries and delivers hydrophobic retinol molecules to target cells, is assembled in the hepatocyte endoplasmic reticulum. In this paper, we review data related to events that lead to the formation of this complex, including transthyretin oligomerization and retinol-binding protein secretion. Our studies on transthyretin oligomerization have demonstrated that cleavage of signal peptide and the environment of endoplasmic reticulum influence transthyretin oligomerization. In vitro, mutated transthyretin without signal sequence fails to form dimers, while wild-type transthyretin is translocated into the microsomes where it forms dimers and small amounts of tetramers. In vivo, tetramers were detected in HepG2 cells but not in transfected Cos cells, suggesting that tissue-specific factors affect tetramer stability. In vitamin A deficiency, retinol-binding protein secretion is blocked and the protein accumulates in the endoplasmic reticulum, from where it is promptly released after retinol repletion. We use MMH cells to identify factors involved in complex formation, retention and secretion, the crucial steps to understand the molecular mechanisms underlying vitamin A homeostasis. In parallel, studies on vitamin A transport in fish are in progress; retinol-binding protein and transthyretin have already been characterized in different fish species.
No preview · Article · Jan 2003 · Clinical Chemistry and Laboratory Medicine
[Show abstract][Hide abstract]ABSTRACT: Vitamin A alcohol and its precursors carotenoids are introduced in the organism with the diet, transported to the liver and from there as retinol to target tissues by a specific carrier, the retinol-binding protein (RBP). RBP, isolated and characterized in many vertebrates, shows very high homology among the species investigated; however, very little is known in fish. In the present work RBP cDNA isolated from a carp liver library was transcribed and translated in vitro and the corresponding protein characterized. Carp RBP amino acid sequence and tertiary structure are highly conserved, but the protein shows two peculiar and unique characteristics: the signal sequence is not processed by the ER signal peptidase and two N-glycosylations are present at the N-terminus portion of the protein. It was also demonstrated that RBP glycosylation is not a feature common to all teleosts. Transfection experiments show that the green fluorescent protein (GFP) can be directed into the secretory pathway by the carp RBP N-terminal region, both in fish and in mammal cells, demonstrating that the sequence, although not processed, is recognized as a secretory signal in different species. Results obtained from different investigators indicated that in fish plasma RBP circulates without interacting with transthyretin (TTR) or other proteins, suggesting that the complex with TTR, whose postulated function is to hamper easy kidney filtration of circulating RBP, has evolved later in the evolutionary scale. This hypothesis is reinforced by the finding that carp RBP, as well as trout and other lower vertebrates in which circulating complex has never been demonstrated, lacks a short C-terminal sequence that seems to be involved in RBP-TTR interaction. In carp, carbohydrates could be involved in the control of protein filtration through the kidney glomeruli. Moreover, experiments of carp RBP expression in Cos-1 cells and in the yeast Saccharomyces cerevisiae show that glycosylation is necessary for protein secretion; in particular, additional in vitro experiments have shown it is involved in protein translocation through ER membranes.
[Show abstract][Hide abstract]ABSTRACT: Retinol transport and metabolism have been well characterized in mammals; however, very little is known in fish. To study the mechanism by which fish retinol-binding protein (RBP) is able to remain in plasma besides its small molecular size, we isolated RBP cDNA from a carp liver cDNA library. Comparison of the deduced amino acid sequence with that of known vertebrate RBPs showed that carp RBP has high homology to the other cloned vertebrate RBPs, but it lacks the COOH-terminal tetrapeptide, RNL(S)L, which is most likely involved in the interaction with transthyretin in mammalian RBPs. In addition, the primary structure of carp RBP contains two consensus N-linked glycosylation sites that represent a unique feature. We have obtained experimental evidence, by in vitro and in vivo expression experiments, that both sites are indeed glycosylated. We have also characterized the protein as a complex type N-linked glycoprotein by lectin binding assay, neuraminidase and endoglycosidase H and F digestion. Inhibition of glycosylation by tunicamycin treatment of transfected cells caused a great reduction of RBP secretion. Since kidney filtration of anionic proteins is less than half that of neutral protein of the same size, this finding strongly suggests that the amount of carp RBP filtration through kidney glomeruli may be reduced by a glycosylation-dependent increase in the molecular size and negative charge of the protein. A second unique feature of carp RBP as secretory protein is the presence of a nonconserved NH(2)-terminal hydrophobic domain, which functions as an insertion signal but is not cleaved cotranslationally and remains in the secreted RBP.
No preview · Article · May 2001 · Journal of Biological Chemistry
[Show abstract][Hide abstract]ABSTRACT: The untransformed stable cell line Met murine hepatocytes (MMH), generated from liver explants of transgenic mice expressing a constitutively active truncated form of the human hepatocyte growth factor receptor (cyto-Met), represents an innovative tool for in vitro studies of liver function. In the present report, we show that the MMH-D3 line isolated from the liver of a 3-day-old mouse is a useful model to investigate the regulation of the synthesis and secretion of retinol-binding protein (RBP) by retinol (vitamin A alcohol). Experiments with Northern blot hybridization, metabolic labeling of cellular proteins followed by immunoprecipitation, and Western blot analysis demonstrated that, similarly to the in vivo situation, in MMH-D3 cells the presence of retinol does not affect transcriptional and translational rate of the RBP gene but is essential for regulating the secretion rate of the protein. Unlike HepG2 human hepatocarcinoma cells used thus far in studies of retinoid metabolism, including the synthesis and secretion of RBP, vitamin A deficiency causes, in MMH-D3 cells, the inhibiton of RBP secretion and the protein accumulation in the cell, whereas retinol repletion promptly results in RBP secretion. This model will be very useful in future studies on vitamin A distribution in the organism.
No preview · Article · Oct 1999 · Journal of Cellular Physiology
[Show abstract][Hide abstract]ABSTRACT: The oligomerization of transthyretin has been studied in vitro and in vivo. The results showed that wild-type transthyretin synthesized in vitro in the absence of microsomes did not form dimers and tetramers, but in the presence of microsomes the mature transthyretin which had been translocated into the microsomal lumen formed dimers and a small amount of tetramers which could be detected only by using a cross-linking reagent. Efficiency of tetramer formation depends upon the source of microsomes; in fact the amount of tetramer formed in liver microsomes was much higher than that in pancreas microsomes. Transthyretin synthesized in HepG2 cells appeared after SDS-PAGE analysis in mostly tetrameric form, while that synthesized in transfected COS-1 cells appeared mainly as dimers. Brefeldin A treatment and pulse-chase experiments in HepG2 cells showed that transthyretin tetramer was formed in the endoplasmic reticulum. These results strongly indicate that transthyretin tetramer is formed most efficiently in the endoplasmic reticulum lumen of hepatocytes. Transthyretin without the signal peptide [S(-)] and transthyretin with a mutation that prevents processing of the signal peptide Msc failed to form dimers and tetramers in vitro. In the transfected COS-1 cells, however, S(-) transthyretin did form dimers while Msc transthyretin failed to oligomerize. These results show that the cleavage of the signal peptide and some cellular factors are required for transthyretin oligomerization.
No preview · Article · Sep 1998 · Experimental Cell Research
[Show abstract][Hide abstract]ABSTRACT: We have previously reported that the induction of Vitamin A deficiency results in a threefold decrease in the hepatic expression of cellular retinol binding protein I (CRBP I) mRNA in vivo and that the treatment of intestinal cell lines in vitro with retinoids leads to the induction of CRBP I transcription. In the present paper we extend the analysis to retinoid-dependent gene expression in the testicular epithelium in vivo and in the intestinal cell line FRIC B. In rat testis excess Vitamin A results in the reduced production of mature spermatozoa and in the premature release of immature germ cells in the lumen, while Vitamin A deficiency leads to almost complete degeneration of the germinal epithelium. We show reduced level of expression of CRBP I mRNA in vitamin A deficient testis. Retinoid treatment of cultured intestinal cells, which induces a reorganization of the actin cytoskeleton, has no effect on the expression of the differentiation induced gene Dri 42. The results show that even though unable to trigger by themselves the differentiation process, retinoids exert a direct effect on the expression of specific genes.
No preview · Article · Feb 1998 · Zeitschrift für Ernährungswissenschaft