Search

In the present article, we have investigated the antioxidant properties of methanolic liquorice polyphenol extracts (LPE(s)). Polyphenol extraction was performed with 60% and 100% methanol. Analysis of LPE(s) by thin-layer chromatography revealed that a higher amount of polyphenols was recovered by extraction with 60% methanol. Antioxidant activity measurement of the reducing power, scavenging effect on 2,2'-diphenyl-1-picrylhydrazyl free radical, and hydrogen peroxide scavenging capability have been taken as the parameters for assessment of antioxidant potential of LPE(s). Results have been compared with both natural and synthetic antioxidants. All experimental data have indicated that LPE(s) possess strong antioxidant power proportional to their o-diphenolic and total polyphenolic content, independently from the assay used. Therefore, the LPE(s) antioxidant property was examined against the cytotoxic effects of reactive oxygen species in human colon carcinoma cells. Pretreatment of Caco-2 cells with liquorice polyphenolic extracts provided a remarkable protection against oxidative damage induced by H(2)O(2). The highest oxidative stress protection (72% of cell vitality) was measured in cells pretreated with 0.54 mM polyphenols. This effect seems to be associated to the antioxidant activity of liquorice polyphenolic compounds. Our data suggest that polyphenols from Glycyrrhiza glabra could exert a beneficial action in the prevention of intestinal pathologies related to production of reactive oxygen species.

Spontaneous protein deamidation of labile Asn residues, generating L-isoaspartates and D-aspartates, is associated with cell aging and is enhanced by an oxidative microenvironment; to minimize the damage, the isoaspartate residues can be 'repaired' by a specific L-isoaspartate (D-aspartate) protein O-methyltransferase (PIMT). As both premature aging and chronic oxidative stress are typical features of Down's syndrome (DS), we tested the hypothesis that deamidated proteins may build up in trisomic patients. Blood samples were obtained from children with karyotypically confirmed full trisomy 21 and from age-matched healthy controls. Using recombinant PIMT as a probe, we demonstrated a dramatic rise of L-isoaspartates in erythrocyte membrane proteins from DS patients. The content of D-aspartate was also significantly increased. The integrity of the repair system was checked by evaluating methionine transport, PIMT specific activity, and intracellular concentrations of adenosylmethionine and adenosylhomocysteine. The overall methylation pathway was directly monitored by incubating fresh red blood cells with methyl-labeled methionine; a three-fold increase of protein methyl esters was detected in trisomic children. Deamidated species include ankyrin, band 4.1, band 4.2 and the integral membrane protein band 3; ankyrin and band 4.1 were significantly hypermethylated in DS. When DS red blood cells were subjected to oxidative treatment in vitro, the increase of protein deamidation paralleled lipid peroxidation and free radical generation. We observed a similar pattern in Epstein-Barr virus B-lymphocytes from trisomic patients. In conclusion, our findings support the hypothesis that protein instability at asparagine sites is a biochemical feature of DS, presumably depending upon the oxidative microenvironment. The possible pathophysiological implications are discussed.

Eukaryotic protein carboxyl methyltransferase catalyzes a two-substrates reaction in which the methyl group of S-adenosylmethionine is transferred to the free carboxyl group of D-aspartyl and L-isoaspartyl-containing peptide or protein substrates. It has been previously shown that at least three binding sites are required for the interaction of adenosylmethionine with the enzyme and/or the protein substrate [Oliva A., Galletti P., Zappia V., Paik W. K. & Kim S. (1980) Eur. J. Biochem. 104, 595–602], while very little is know concerning the structural requirements of the protein substrate. In this study several synthetic tripeptides were selected in order to elucidate the structural requirements of the methyl-accepting substrates. The results obtained with this series of peptides suggested that: (1) three residues appear to be the minimal length, so far identified, required for a productive enzyme-substrate interaction, several dipeptides being ineffective as substrates [McFadden P. N. & Clarke S. (1986) J. Biol. Chem. 261, 11 503–11 511]; (2) the isoaspartyl residue is not recognized unless its α-amino group is involved in a carboamide bond; (3) an hydrogen atom on the amide linkage following the isoaspartyl residue is essential for both recognition and catalysis; (4) oligopeptides containing both D-aspartyl and D-isoaspartyl residues are not recognized by this methyltransferase. On the basis of these results, interaction sites between the peptide substrate and the enzyme molecule have been proposed. This paper also reports the first application of fast-atom-bombardment mass spectrometry to the detection of the products of the enzymatic methyl esterification reaction. By this soft ionization technique, the methylesterified peptides as well as the corresponding cyclic imides generated during the spontaneous demethylation process have been identified.

Plasma proteins in hemodialysis patients display a significant increase in deamidated/isomerized Asx (asparagine and aspartic acid) content, a marker of protein fatigue damage. This has been linked to the toxic effects of hyperhomocysteinemia in uremic erythrocytes; however, treatment aimed at abating homocysteine levels did not lead to significant reductions in plasma protein damage. The hypothesis that lack of reduction in protein damage could be due to protein increased intrinsic instability, as result of interference with the uremic milieu rather than to hyperhomocysteinemia, was put forward. The deamidated/isomerized Asx content of normal plasma incubated with several uremic toxins for 24 h, 72 h, and 7 d was measured, identifying a group of toxins that were able to elicit this kind of damage. Uremic toxins were also incubated with purified human albumin, and dose-response experiments with the two most toxic agents in terms of protein damage (guanidine and guanidinopropionic acid) were carried out. The effect of the hemodialysis procedure on protein damage was evaluated. For investigating also the consequences of these alterations, human albumin was treated in vitro to produce an increase in deamidated/isomerized Asx residues, and the effects of albumin deamidation on protein binding were evaluated. Among the uremic toxins that are able to elicit protein damage, guanidine produced a dose-dependent increase in protein damage. No difference was found after a hemodialysis session. Deamidated albumin shows normal binding capacity to warfarin, salicylic acid, or diazepam but reduced binding to homocysteine. In conclusion, uremic toxins, especially guanidine, display an ability to induce significant protein damage, which can in turn have functional consequences. Plasma proteins in hemodialysis patients display a significant increase in deamidated/isomerized Asx (asparagine and aspartic acid) content, a marker of protein fatigue damage. This has been linked to the toxic effects of hyperhomocysteinemia in uremic erythrocytes; however, treatment aimed at abating homocysteine levels did not lead to significant reductions in plasma protein damage. The hypothesis that lack of reduction in protein damage could be due to protein increased intrinsic instability, as result of interference with the uremic milieu rather than to hyperhomocysteinemia, was put forward. The deamidated/isomerized Asx content of normal plasma incubated with several uremic toxins for 24 h, 72 h, and 7 d was measured, identifying a group of toxins that were able to elicit this kind of damage. Uremic toxins were also incubated with purified human albumin, and dose-response experiments with the two most toxic agents in terms of protein damage (guanidine and guanidinopropionic acid) were carried out. The effect of the hemodialysis procedure on protein damage was evaluated. For investigating also the consequences of these alterations, human albumin was treated in vitro to produce an increase in deamidated/isomerized Asx residues, and the effects of albumin deamidation on protein binding were evaluated. Among the uremic toxins that are able to elicit protein damage, guanidine produced a dose-dependent increase in protein damage. No difference was found after a hemodialysis session. Deamidated albumin shows normal binding capacity to warfarin, salicylic acid, or diazepam but reduced binding to homocysteine. In conclusion, uremic toxins, especially guanidine, display an ability to induce significant protein damage, which can in turn have functional consequences. Copyright & 2004 by the American Society of Nephrology.

The ‘Mediterranean’ variant of glucose-6-phosphate dehydrogenase (G6PD) deficiency is due to the C563CT point mutation, leading to replacement of Ser with Phe at position 188, resulting in acute haemolysis triggered by oxidants. Previous work has shown increased formation of altered aspartate residues in membrane proteins during cell ageing and in response to oxidative stress in normal erythrocytes. These abnormal residues are specifically recognized by the repair enzyme l-isoaspartate (d-aspartate) protein O-methyltransferase (PCMT; EC 2.1.1.77). The aim of this work was to study the possible involvement of protein aspartate damage in the mechanism linking the G6PD defect and erythrocyte injury, through oxidative stress. Patients affected by G6PD deficiency (Mediterranean variant) were selected. In situ methylation assays were performed by incubating intact erythrocytes in the presence of methyl-labelled methionine. Altered aspartate residues were detected in membrane proteins by methyl ester quantification. We present here evidence that, in G6PD-deficient erythrocytes, damaged residues are significantly increased in membrane proteins, in parallel with the decay of pyruvate kinase activity, used as a cell age marker. Erythrocytes from patients were subjected to oxidative stress in vitro, by treatment with t-butylhydroperoxide, monitored by a rise in concentration of both methaemoglobin and thiobarbituric acid-reactive substances. l-Isoaspartate residues increased dramatically in G6PD-deficient erythrocytes in response to such treatment, compared with baseline conditions. The increased susceptibility of G6PD-deficient erythrocytes to membrane protein aspartate damage in response to oxidative stress suggests the involvement of protein deamidation/isomerization in the mechanisms of cell injury and haemolysis.

Plasma proteins containing damaged L-isoaspartyl residues are increased in uremia: Implications for mechanism.BackgroundSeveral alterations of protein structure and function have been reported in uremia. Impairment of a transmethylation-dependent protein repair mechanism possibly related to a derangement in homocysteine metabolism is also present in this condition, causing erythrocyte membrane protein damage. Homocysteine may affect proteins via the accumulation of its parent compound S-adenosylhomocysteine (AdoHcy), a powerful in vivo methyltransferase inhibitor. However, since plasma homocysteine is mostly protein bound, a direct influence on protein structures cannot be ruled out. We measured the levels of L-isoaspartyl residues in plasma proteins of uremic patients on hemodialysis. These damaged residues are markers of molecular age, which accumulate when transmethylation-dependent protein repair is inhibited and/or protein instability is increased.MethodsL-isoaspartyl residues in plasma proteins were quantitated using human recombinant protein carboxyl methyl transferase (PCMT). Plasma concentrations of homocysteine metabolites were also measured under different experimental conditions in hemodialysis patients.ResultsThe concentration of damaged plasma proteins was increased almost twofold compared to control (controls 147.83 ± 17.75, uremics 282.80 ± 26.40 pmol of incorporated methyl groups/mg protein, P < 0.003). The major protein involved comigrated with serum albumin. Although hyperhomocysteinemia caused a redistribution of thiols bound to plasma proteins, this mechanism did not significantly contribute to the increase in isoaspartyl residues. The S-adenosylmethionine (AdoMet)/AdoHcy concentration ratio, an indicator of the flux of methyl group transfer, was altered. This ratio was partially corrected by folate treatment (0.385 ± 0.046 vs. 0.682 ± 0.115, P < 0.01), but protein L-isoaspartate content was not.ConclusionsPlasma protein damage, as determined by protein L-isoaspartyl content, is increased in uremia. This alteration is to be ascribed to an increased protein structural instability, rather than the effect of hyperhomocysteinemia.

Segmented poly(ether–ester–amide)s (PEEAs) were obtained from sebacoyl chloride (SEB), α,ω-hydroxyl terminated poly( l , l -lactide) (PLLA) or PLLA–PEG–PLLA macromers and the hydrophilic diamines 4,7,10-trioxa-1,13-tridecanediamine ( 1 ) and 3,6,9,12,15-pentoxa-1,17-heptadecanediamine ( 2 ) or diamide–diamines derived from 1 and 2 by inserting Gly-Phe or Gly-Val-Phe sequences. The molar ratio macromer/SEB/diamine was 1/2/1. The PEEAs were characterized by i.r. and 1 H n.m.r spectroscopy and S.E.C. They are soluble in polar organic solvents and insoluble in water, but show equilibrium water absorptions up to 21.0% by wt. All PEEAs are semicrystalline, as shown by d.s.c. and WAXS techniques, with T m s ranging from 110 to 135°C. D.s.c. and d.m.t.a. showed a single T g in the temperature range 31–53°C. Evidence of microphase separation was obtained only for aminoacids containing PEEAs by t.e.m.. Biocompatibily was assessed for selected polymers checking the viability and growth of Caco-2 cells on polymer films.

Protein-L-isoaspartate (D-aspartate) O-methyltransferase (PCMT; EC 2. 1.1.77) catalyses the methyl esterification of the free alpha-carboxyl group of abnormal L-isoaspartyl residues, which occur spontaneously in protein and peptide substrates as a consequence of molecular ageing. The biological function of this transmethylation reaction is related to the repair or degradation of age-damaged proteins. Methyl ester formation in erythrocyte membrane proteins has also been used as a marker reaction to tag these abnormal residues and to monitor their increase associated with erythrocyte ageing diseases, such as hereditary spherocytosis, or cell stress (thermal or osmotic) conditions. The study shows that levels of L-isoaspartyl residues rise in membrane proteins of human erythrocytes exposed to oxidative stress, induced by t-butyl hydroperoxide or H2O2. The increase in malondialdehyde content confirmed that the cell membrane is a primary target of oxidative alterations. A parallel rise in the methaemoglobin content indicates that proteins are heavily affected by the molecular alterations induced by oxidative treatments in erythrocytes. Antioxidants largely prevented the increase in membrane protein methylation, underscoring the specificity of the effect. Conversely, we found that PCMT activity, consistent with its repair function, remained remarkably stable under oxidative conditions, while damaged membrane protein substrates increased significantly. The latter include ankyrin, band 4.1 and 4.2, and the integral membrane protein band 3 (the anion exchanger). The main target was found to be particularly protein 4.1, a crucial element in the maintenance of membrane-cytoskeleton network stability. We conclude that the increased formation/exposure of L-isoaspartyl residues is one of the major structural alterations occurring in erythrocyte membrane proteins as a result of an oxidative stress event. In the light of these and previous findings, the occurrence of isoaspartyl sites in membrane proteins as a key event in erythrocyte spleen conditioning and hemocatheresis is proposed.

Hydroxytyrosol, the major representative phenolic compound of virgin olive oil, is a dietary component. Its possible protective effect on hydrogen peroxide (H(2)O(2))-induced oxidative alterations was investigated in human erythrocytes. Cells were pretreated with micromolar hydroxytyrosol concentrations and then exposed to H(2)O(2) over different time intervals. Subsequently, erythrocytes were analyzed for oxidative hemolysis and lipid peroxidation. Our data demonstrate that hydroxytyrosol prevents both oxidative alterations, therefore, providing protection against peroxide-induced cytotoxicity in erythrocytes. The effect of oxidative stress on erythrocyte membrane transport systems, as well as the protective role of hydroxytyrosol, also were investigated in conditions of nonhemolytic mild H(2)O(2) treatment. Under these experimental conditions, a marked decrease in the energy-dependent methionine and leucine transport is observable; this alteration is quantitatively prevented by hydroxytyrosol pretreatment. On the other hand, the energy-independent glucose transport is not affected by the oxidative treatment. The reported data give new experimental support to the hypothesis of a protective role played by nonvitamin antioxidant components of virgin olive oil on oxidative stress in human systems.

Resveratrol (3,5,4′-trihydroxystilbene) is a naturally occurring phytoalexin, found in grapes and wine, which has been reported to exert a variety of important pharmacological effects. We have investigated the activity of resveratrol on proliferation and differentiation of the promyelocitic cell line HL-60. A concentration as low as 30 μM causes a complete arrest of proliferation and a rapid induction of differentiation towards a myelo-monocytic phenotype. Analyses by flow cytometry showed the absence of the G2/M peak and the accumulation of cells in G1 and S phases. Moreover, at the concentrations employed, a very low amount of apoptotic cells was evidenced. A detailed biochemical analysis demonstrated that the G1 phase of the cell division cycle engine was completely unmodified by resveratrol addition, thus indicating that the G1 → S transition occurs normally. Conversely, after only 24 h treatment, a significant increase of cyclins A and E could be observed along with the accumulation of cdc2 in the inactive phosphorylated form. These data demonstrate that resveratrol causes a complete and reversible cell cycle arrest at the S phase checkpoint.

We investigated the injurious effects of reactive oxygen metabolites on the intestinal epithelium and the possible protective role played by two olive oil phenolic compounds, (3,4-dihydroxyphenyl)ethanol and (p-hydroxyphenyl)ethanol, using the Caco-2 human cell line. We induced oxidative stress in the apical compartment, either by the addition of 10 mmol/L H2O2 or by the action of 10 U/L xanthine oxidase in the presence of xanthine (250 micromol/L); after the incubation, we evaluated the cellular and molecular alterations. Both treatments produced significant decreases in Caco-2 viability as assessed by the neutral red assay. Furthermore, we observed a significant increase in malondialdehyde intracellular concentration and paracellular inulin transport, indicating the occurrence of lipid peroxidation and monolayer permeability changes, respectively. The H2O2-induced alterations were completely prevented by preincubating Caco-2 cells with (3,4-dihydroxyphenyl)ethanol (250 micromol/L); when the oxidative stress was induced by xanthine oxidase, complete protection was obtained at a concentration of polyphenol as small as 100 micromol/L. In contrast, (p-hydroxyphenyl)ethanol was ineffective up to a concentration of 500 micromol/L. Our data demonstrate that (3,4-dihydroxyphenyl)ethanol can act as a biological antioxidant in a cell culture experimental model and that the ortho-dihydroxy moiety of the molecule is essential for antioxidant activity. This study suggests that dietary intake of olive oil polyphenols may lower the risk of reactive oxygen metabolite-mediated diseases such as some gastrointestinal diseases and atherosclerosis.

Spontaneous protein deamidation of labile asparagines (Asn), generating abnormal l-isoaspartyl residues (IsoAsp), is associated with cell aging and enhanced by an oxidative microenvironment. The presence of isopeptide bonds impairs protein structure/function. To minimize the damage, IsoAsp can be "repaired" by the protein l-isoaspartyl/d-aspartyl O-methyltransferase (PIMT) and S-adenosylmethionine (AdoMet) is the methyl donor of this reaction. PIMT is a repair enzyme that initiates the conversion of l-isoAsp (or d-Asp) residues to l-Asp residues. Amyotrophic lateral sclerosis (ALS) is a severe neurodegenerative disease principally affecting motor neurons. The condition of oxidative stress reported in familial and sporadic forms of ALS prompted us to investigate Asn deamidation in ALS tissue. Erythrocytes (RBCs) were selected as a model system since they are unable to replace damaged proteins and protein methylesterification is virtually the only AdoMet-consuming reaction operating in these cells. Our data show that, in vitro assay, abnormal IsoAsp residues were significantly higher in ALS patients erythrocyte membrane proteins with an increased methyl accepting capability relative to controls (p

The sulphonium compound S -adenosylmethionine (AdoMet) plays a central role in many metabolic reactions of cellular metabolism, acting both as a propylamine donor in the biosynthesis of polyamines as well as a methyl donor in the transmethylation reactions. Moreover, AdoMet is a key intermediate of the transsulphuration pathway by which methionine is converted into cysteine, a precursor of glutathione. The aim of this study was to investigate the methionine and AdoMet metabolism in bovine lenses cultured in the presence of labelled methionine, upon treatment with H 2 O 2 , as the experimental model for studying the molecular mechanisms responsible for the onset of senile cataract. The results reveal that one of the earliest changes following an oxidative stress is a severe impairment of protein synthesis. As far as the synthesis of AdoMet is concerned, a small but significant decrease in the conversion of labelled methionine into AdoMet occurs in treated lenses compared to the controls. In order to verify if the decreased AdoMet synthesis would lead in turn to alterations of methyl transfer reactions, we examined changes in the levels of various macromolecular methylations, such as protein methyl esterification and phospholipid methylation. The data clearly indicate that both the synthesis of AdoMet and the methyl transfer reactions could be significantly affected in eye lens upon an oxidative stress, suggesting that these alterations could be one of the biochemical events related to the ethiology of senile cataract. Finally, the question of whether or not H 2 O 2 -induced alterations of methionine and AdoMet metabolism could, in turn, affect some closely related metabolism, such as glutathione-associated reactions, is also discussed.

Spontaneous protein deamidation of labile asparagines (Asn), generating abnormal isoaspartyl residues (IsoAsp), is associated with cell aging and enhanced by an oxidative microenvironment. The presence of isopeptide bonds impairs protein structure/function and can trigger autoimmune responses. To minimize the damage, IsoAsp can be “repaired” by a specific l-isoaspartate-(d-aspartate)-protein-O-methyltransferase. The condition of chronic oxidative stress reported in psoriatic patients, and the potential etiological role of unknown self-antigens, prompted us to investigate Asn deamidation in psoriatic tissues. Erythrocytes (RBC) were selected as the model system since, lacking protein synthesis apparatus, they are unable to replace damaged proteins. Blood samples were obtained from 36 patients and 34 controls. l-isoAsp content was highly increased in RBC membrane proteins from psoriatic patients. Deamidated species included ankyrin, band 4.1, band 4.2 and the integral membrane protein band 3. A functional analysis demonstrated that this result was unrelated to a reduced efficiency of the S-adenosylmethionine-dependent repair system suggesting an increased protein instability at Asn sites, responsible for IsoAsp accumulation in psoriatic patients.

The enzyme protein carboxyl methyltransferase type II has been recently shown to play a crucial role in the repair of damaged proteins. S-adenosylmethionine (AdoMet) is the methyl donor of the reaction, and its demethylated product, S-adenosylhomocysteine (AdoHcy), is the natural inhibitor of this reaction, as well as of most AdoMet-dependent methylations. We examined erythrocyte membrane protein methyl esterification in chronic renal failure (CRF) patients on conservative treatment or hemodialyzed to detect possible alterations of the methylation pattern, in a condition where a state of disrupted red blood cell function is present. We observed a significant reduction in membrane protein methyl esterification in both groups, compared to control. The decrease was particularly evident for cytoskeletal component ankyrin, which is known to be involved in membrane stability and integrity. Moreover, we observed a severalfold rise in AdoHcy levels, while AdoMet concentration was comparable to that detected in the control, resulting in a lower [AdoMet]/[AdoHcy] ratio (P < 0.001). Our findings show an impairment of this posttranslational modification of proteins, associated with high AdoHcy intracellular concentration in CRF. The data are consistent with the notion that, in CRF, structural damages accumulate in erythrocyte membrane proteins, and are not adequately repaired.

Plants continuously produce an extraordinary variety of biologically active low-molecular-mass compounds. Among them, resveratrol (3,5,4'-trihydroxystilbene) is endowed with significant positive activities by protecting against cardiovascular diseases and preventing the development and progression of atherosclerosis. Furthermore, the molecule significantly ameliorates glucose homeostasis in obese mice. These beneficial effects have driven considerable interest towards resveratrol molecular activities, and intensive efforts for the identification of the stilbene targets have been made. The molecule shows a pleiotropic mode of action. Particularly, its cellular targets are crucial for cell proliferation and differentiation, apoptosis, antioxidant defence and mitochondrial energy production. The complexity of resveratrol activities might account for its effectiveness in ameliorating multifactorial processes, including the onset and/or progression of several degenerative diseases such as myocardial infarction, atherosclerosis and type 2 diabetes. This article reports the actions of resveratrol on cardiovascular diseases and the molecular bases of its activity. We also discuss recent data on the effect of resveratrol on glucose homeostasis and obesity. Finally, the relevance of the stilbene use in the development of new pharmacological strategies is evaluated.

Publisher Summary Olive oil represents the typical lipidic source of the Mediterranean diet that has been associated with a low incidence of several pathologies, including cardiovascular diseases and neurological disorders. The beneficial properties of olive oil have been mainly attributed to its high content of monounsaturated oleic acid; however, in recent years converging evidence indicates that the non-glyceride fraction of olive oil, rich in vitamin and non-vitamin antioxidants including polyphenols, significantly contributes to its benefits on human health. Hydroxytyrosol (3,4-dihydroxyphenylethanol; DOPET) is the main ortho-diphenolic compound of olive oil and is mainly responsible for the antioxidant properties of this nutrient. Indeed, it has been shown to function as an efficient scavenger of peroxyl radicals in several biological systems and contributes to increase the shelf life of the oil, preventing its auto-oxidation. DOPET inhibits in vitro low-density lipoprotein oxidation and modulates the oxidative/antioxidative balance in plasma. Experiments in the present study demonstrate that DOPET, which effectively permeates cell membranes via passive diffusion, counteracts the cytotoxic effects of reactive oxygen species (ROS) in various human systems. Preincubation of intestinal Caco-2 cells with DOPET prevents the typical damages of oxidative stress. Similarly, this polyphenol exerts a protective effect against the H 2 O 2 -induced oxidative hemolysis and lipid peroxidation in red blood cells.

Hyperhomocysteinaemia was reported in patients with Parkinson's disease (PD) treated with l-Dopa. The increase in plasma concentration of this sulfur compound arises from the massive methylation of the drug operated by the enzyme catechol-O-methyltransferase (COMT), which acts as a powerful sink of methyl groups. The contemporary occurrence of C677T polymorphism in homozygosity, leading to a temperature-labile variant of the MTHFR enzyme, induces an even more marked increase in tHcy. Here we show that l-Dopa administration in hyperhomocysteinemic PD patients is able to lower intracellular concentration of S-Adenosylmethionine (AdoMet) in erythrocytes (RBC), while the occurrence of hyperhomocysteinaemia causes a significant increase in S-Adenosylhomocysteine (AdoHcy) level. In patients with PD treated with l-Dopa and hyperhomocysteinemic, the remarkable decrease in AdoMet and the concurrent increase in AdoHcy concentration both contribute to significantly lower the transmethylation potential ([AdoMet]/[AdoHcy]), a useful index of the effectiveness of methyl group transfer by methyltransferases. This decrease could indeed contribute to partly attenuate, through a self-limiting kinetic mechanism, the tendency of developing drug resistance, partly mediated in these patients by COMT upregulation. Our results also support the conclusion that COMT inhibitors (entacapone or tolcapone), when administered in PD patients treated with l-Dopa, may potentiate the endogenous AdoHcy-dependent COMT inhibition mechanism already operative in a variable fashion.

Apple is among the most consumed fruits worldwide, and several studies suggest that apple polyphenols could play a role in the prevention of degenerative diseases. 'Annurca' apple fruit undergoes, after harvest, a typical reddening treatment to turn the apples' skin red, and it is noted for its high firmness. This paper reports the effect of reddening-ripening treatment on polyphenol concentration and antioxidant activity of both peel and flesh extracts. The in vitro antioxidant properties have been compared with the protective effect against the cytotoxic effects of reactive oxygen species using Caco-2 cells as model system. Pretreatment of cells with different polyphenolic apple extracts provides a remarkable protection against oxidative damage. This effect seems to be associated with the antioxidant activity of 'Annurca' apple polyphenolic compounds. The flesh has antioxidant properties comparable to those possessed by the peel. Neither the reddening nor the fruit conservation causes changes in the antioxidant properties possessed by this apple variety. The data indicate that polyphenolic compounds in 'Annurca' apples are relatively stable in the peel and also in the flesh; therefore, the health benefits of polyphenols should be maintained during long-term storage. Finally, a diet rich in apple antioxidants could exert a beneficial effect in the prevention of intestinal pathologies related to the production of reactive oxygen species.

Plants produce an extraordinary array of low molecular mass natural products endowed with biological activity. Among these molecules, resveratrol (3,5,4’-trihydroxystilbene) has been identified as an inhibitor of carcinogenesis with a pleiotropic mode of action. Extensive literature on its anticancer activity, performed in cellular models, suggests a potential antiproliferative and apoptogenic use of the stilbene. Similarly, studies on implanted cancers and chemical-induced tumors confirm a potential chemotherapeutical interest of the compound. Moreover, recent intriguing studies have demonstrated, in mice, that the negative effects (insulin resistance and hyperglycemia) of a high-fat diet might be prevented by resveratrol treatment. Despite these promising observations, only few clinical trials have been performed on the compound due to the scarce interest of pharmaceutical industry. We suggest that resveratrol might be considered an interesting anticancer compound in association with more specific target-oriented drugs.

Exposure to nickel and chromium, and their compounds, has been associated with adverse health effects. These metals are two human carcinogens whose pathogenesis involves active extracellular matrix degradation and remodelling. In this work we have compared the effects of in vitro exposure to nickel and chromium of a keratinocyte cell line (HaCat). The modulation of matrix metalloproteinase genes was used as biomarker of chemical damage. Confluent cells were constantly exposed to subtoxic chromium and nickel concentrations (10 −5 and 10 −7 M) up to 72 h. Total RNA was extracted and specific matrix metalloproteinase, and inhibitor, gene expression was analyzed by RT-PCR. Moreover, cell cycle alterations were evaluated by flow cytometry. Nickel and chromium showed different results, with an upregulation of MMP-2 mRNA production in nickel-treated cells while chromium exposure down-regulated MMP-2 mRNA production. This result could be correlated to the precocious (6 h) over-expression of tissue inhibitor-1 (TIMP-1) mRNA in chromium-treated cells. Cell cycle analysis showed and increase of cells with 4N DNA. These results could be explained as a survival response of cells that escape metal induced apoptosis through the anti-apoptotic effects of TIMP-1. These cells that encompass the genotoxic insult may have a selective proliferation advantage, and therefore represent the precursor pool from which degenerating variants may emerge. To study if the chemical damage was reversible, subconfluent cells were stimulated only for 24 h, then the medium was replaced without metal. Cells were able to recover from nickel exposure, showing only weak alterations in specific mRNA expression and cell cycle alteration respect to control. Chromium-induced damage was irreversible. Our results demonstrated that there is an association between metal toxicity and expression of MMPs and their inhibitors. These biomarkers could be potentially useful to elaborate a prediction model of chemical toxicity.

Background. As is well known, the use of the immunosuppressive drug cyclosporin A (CsA) is partially restricted by its nephrotoxic effects, which include early changes in haemodynamics followed by irreversible injuries to the renal tubules. Although the mechanisms responsible for these side effects are poorly understood, an involvement of reactive oxygen species (ROS) has been suggested. In this study, we selected three natural antioxidants, resveratrol, hydroxytyrosol and vitamin E, on the basis of their scavenging capabilities, and tested their protective effects against CsA toxicity.Methods. Immortalized rat tubular cells (RPTc) were used as the model system. Cell viability was checked with trypan blue assay, and free radical formation was measured using the fluorescent probe 2,7-dichlorofluorescein (DCF). We evaluated several oxidative stress parameters, including phospholipid peroxidation products, glutathione levels and oxygenase expression.Results. Incubation of RPTc with 25 mu M CsA induced a significant decrease in cell viability paralleled by intracellular ROS formation and alterations in lipid peroxidation. There was also an imbalance of glutathione redox state as well as upregulation of heme oxygenase-1 (HO-1). The three antioxidants, at micromolar concentration, quantitatively prevented the ROS-activated DCF fluorescent signal and membrane lipid peroxidation. Both hydroxytyrosol and resveratrol strengthened the CsA induction of HO-I expression. Moreover, vitamin E and resveratrol counteracted CsA-induced changes in the glutathione redox state via different mechanisms, whereas hydroxytyrosol was completely ineffective. Similarly, CsA-dependent nephrotoxicity was prevented by vitamin E, while resveratrol only exerted partial protection, and hydroxytyrosol showed no protective effects.Conclusion. Our results indicate that the diverse cytoprotective effects of the antioxidants tested in these studies were not directly related to their scavenging capabilities. These findings confirm a key role for glutathione in protecting cells from CsA-induced adverse effects and do not support a direct link between CsA-mediated ROS generation and adverse renal effects.

Previous studies showed that long-wave ultraviolet (UVA) radiation induces severe skin damage through the generation of reactive oxygen species and the depletion of endogenous antioxidant systems. Recent results from our laboratory indicate a dramatic increase of both lipid peroxidation products (TBARS) and abnormal L-isoaspartyl residues, marker of protein damage, in UVA-irradiated human melanoma cells. In this study, the effects of hydroxytyrosol (DOPET), the major antioxidant compound present in olive oil, on UVA-induced cell damages, have been investigated, using a human melanoma cell line (M14) as a model system. In UVA-irradiated M14 cells, a protective effect of DOPET in preventing the uprise of typical markers of oxidative stress, such as TBARS and 2'7'-dichlorofluorescein (DCF) fluorescence intensity, was observed. In addition, DOPET prevents the increase of altered L-isoAsp residues induced by UVA irradiation. These protective effects are dose dependent, reaching the maximum at 400 microM DOPET. At higher concentrations, DOPET causes an arrest of M14 cell proliferation and acts as a proapoptotic stimulus by activating caspase-3 activity. In the investigated model system, DOPET is quantitatively converted into its methylated derivative, endowed with a radical scavenging ability comparable to that of its parent compound. These findings are in line with the hypothesis that the oxidative stress plays a major role in mediating the UVA-induced protein damage. Results suggest that DOPET may exerts differential effects on melanoma cells according to the dose employed and this must always be taken into account when olive oil-derived large consumer products, including cosmetics and functional foods, are employed.

The potential protective effects of oleuropein, a dietary antioxidant of olive oil, has been investigated in the isolated rat heart. The organs were subjected to 30 minutes of no-flow global ischemia and then reperfused. At different time intervals, the coronary effluent was collected and assayed for creatine kinase activity as well as for reduced and oxidized glutathione. In addition, the extent of lipid peroxidation was evaluated by measuring thiobarbituric acid reactive substance concentration in cardiac muscle. Pretreatment with 20 microg/g oleuropein before ischemia resulted in a significant decrease in creatine kinase and reduced glutathione release in the perfusate. The protective effect of oleuropein against the post-ischemic oxidative burst was investigated by measuring the release, in the coronary effluent, of oxidized glutathione, a sensitive marker of heart’s exposure to oxidative stress. Reflow in ischemic hearts was accompanied by a prompt release of oxidized glutathione; in ischemic hearts pretreated with oleuropein, this release was significantly reduced. Membrane lipid peroxidation was also prevented by oleuropein. The reported data provide the first experimental evidence of a direct cardioprotective effect of oleuropein in the acute events that follow coronary occlusion, likely because of its antioxidant properties. This finding strengthens the hypothesis that the nutritional benefit of olive oil in the prevention of coronary heart disease can be also related to the high content of oleuropein and its derivatives. Moreover, our data, together with the well documented antithrombotic and antiatherogenic activity of olive oil polyphenols, indicate these antioxidants as possible therapeutic tools for the pharmacological treatment of coronary heart disease as well as in the case of cardiac surgery, including transplantation.

This paper reports the protective effect of the phenolic fraction extracted from extra virgin olive oils (OOPEs) against the cytotoxic effects of reactive oxygen species in human erythrocytes and Caco-2 cells, employed as model systems. Pretreatment of cells with various OOPEs, indeed, provides a remarkable protection against oxidative damages: this effect was strictly dependent on the o-diphenolic content of the extracts. Moreover, the protective effects observable in cellular systems were compared with in vitro antioxidant properties, measured by using the FRAP (ferric reducing/antioxidant power) assay; the reducing ability of OOPEs strictly parallels their o-phenolic content. The linear relationship demonstrated between biological effects and antioxidant capacity measured by the FRAP assay allows us to propose the use of this rapid colorimetric method in assessing and certifying the antioxidant power of extra virgin olive oil.

An elevated blood level of homocysteine (Hcy), a sulfur amino acid, is associated with increased cardiovascular risk. Hcy is generated from S-adenosylhomocysteine (AdoHcy), the demethylated product of S-adenosylmethionine (AdoMet) in transmethylation reactions. AdoHcy is a competitive inhibitor of AdoMet-dependent methyltransferases. AdoHcy accumulation is prevented by rapid metabolism of its products. Chronic renal failure (CRF) is almost constantly associated with hyperhomocysteinemia. It has been shown that: (1) AdoHcy concentration is significantly increased and the AdoMet-AdoHcy ratio is reduced in erythrocytes of patients with CRF; (2) erythrocyte membrane protein methyl esterification, catalyzed by the enzyme protein l-isoaspartyl O-methyltransferase (PCMT; EC 2.1.1.77), is reduced in CRF; PCMT catalyzes a repair reaction involved in the conversion of an isopeptide bond (detrimental to protein structure and function) into a normal peptide bond; (3) d-aspartate residues, a side product of protein methylation and repair, are significantly reduced in erythrocyte membrane proteins of patients with CRF; and (4) folate treatment significantly reduces plasma Hcy levels and improves AdoMet-AdoHcy ratios. Stable isotope studies recently confirmed that the rate of methyl transfer reactions is significantly reduced in uremia. Additional evidence, obtained by independent groups, is consistent with this interpretation. We recently found increased isoaspartyl content of circulating plasma protein levels, particularly albumin, which was only partially reduced after folate treatment, in uremia. This kind of molecular damage possibly is caused by protein increased intrinsic instability as a result of interference with the uremic milieu. In conclusion, Hcy is an uremic toxin involved in protein molecular damage through the inhibition of methylation reactions and protein PCMT-mediated repair. © 2001 by the National Kidney Foundation, Inc.

It has been reported that UVA effects are partly mediated by production of reactive oxygen species. Moreover, oxidative stress increases protein damage, involving the occurrence of isoaspartyl residues, a product of protein deamidation/isomerization reactions. This work was undertaken in order to study the effects of UVA irradiation, mediated by oxidation, on sensitive protein targets. Melanoma cells exposed to UVA rays have been chosen as a model for monitoring the occurrence of L-isoaspartyl sites. A dramatic increase of these abnormal residues, specifically recognized and methylated by the enzyme L-isoaspartate(D-aspartate) O-methyltransferase (PCMT; EC 2.1.1.77), can be detected after exposure of M14 cells to raising doses of UVA. The effect of UVA on NO and TBARS accumulation, as well as on DNA fragmentation, has also been investigated. NO formation parallels the increase in isoaspartyl formation, while lipid peroxidation occurs only at the highest UVA doses. No DNA fragmentation has been detected under the employed experimental conditions. These results, as a whole, indicate that protein damages are one of the early events on UVA-induced cell injury. The endogenous activity of PCMT remains remarkably stable under UVA treatment, suggesting that this enzyme might play a crucial role in the repair and/or disposal of damaged proteins in UVA-irradiated cells.

2-(3,4-Dihydroxyphenyl)ethanol (DPE), a naturally occurring phenolic antioxidant molecule found in olive oil, has been reported to exert several biological and pharmacological activities. We studied the effect of this compound on the proliferation and survival of HL60 cell line. Concentrations from 50 to 100 microM DPE, comparable to its olive oil content, caused a complete arrest of HL60 cell proliferation and the induction of apoptosis. This was demonstrated by flow cytometric analyses, poly(ADP-ribose) polymerase cleavage, and caspase 3 activation. The apoptotic effect requires the presence of two ortho-hydroxyl groups on the phenyl ring, since tyrosol, 2-(4-hydroxyphenyl)ethanol, did not induce either cell growth arrest or apoptosis. DPE-dependent apoptosis is associated with an early release of cytochrome c from mitochondria which precedes caspase 8 activation, thus ruling out the engagement of cell death receptors in the apoptotic process. 2-(3,4-Dihydroxyphenyl)ethanol induced cell death in quiescent and differentiated HL60 cells, as well as in resting and activated peripheral blood lymphocytes, while did not cause cell death in two colorectal cell lines (HT-29 and CaCo2). These results suggest that DPE down-regulates the immunological response, thus explaining the well-known antinflammatory and chemopreventive effects of olive oil at the intestinal level.

Pyrrolidine dithiocarbamate (PDTC) is a synthetic antioxidant molecule, which has been recently proposed as an antitumoral agent on the basis of its capability of inducing apoptosis. We investigated the effect of PDTC on the proliferation and survival of the promyelocitic cell line HL-60. Concentration as low as 10 μM of PDTC induces a significant reduction of the growth rate and the contemporaneous activation of the apoptotic process. Programmed cell death was demonstrated by biochemical analyses, including the activation of procaspase 3 and the cleavage of poly(ADP-ribose) polymerase (PARP). PDTC-dependent apoptosis was associated with an early release of cytochrome c from mitochondria, while the involvement of pathways due to cell death receptors engagement was ruled out by detailed time-course analyses of caspases 3 and 8 activation. Moreover, no up-regulation of p21 CIP1 level, a pivotal cyclin-dependent kinase inhibitor, occurred at PDTC concentration able to induce apoptosis. Finally, in vitro incubation of purified mitochondria with PDTC demonstrated that the molecule is directly able to induce cytochrome c release from the intermembrane space, thus confirming that mitochondria are a primary cellular target of the molecule.

Most large observational studies available today establish that moderate hyperhomocysteinemia, either genetically or nutritionally determined, is an independent risk factor for myocardial infarction, stroke, and thromboembolic disease. This is also true for chronic renal failure patients, who exhibit a high prevalence of hyperhomocysteinemia (85–100%), which reaches high plasma concentrations (20–40 µM, while control values range between 8 and 12 µM−). After a renal transplant, homocysteine levels decrease, but tend to be higher than normal. The cause of hyperhomocysteinemia in renal failure is still obscure, since recent data have questioned the previous notion that a net homocysteine renal extraction and/or excretion take place in man. No matter the cause of its increase, the sulfur amino acid homocysteine is thought to induce an increment in cardiovascular risk through three basic biochemical mechanisms: (1) homocysteine oxidation, with H2O2 generation; (2) hypomethylation through S-adenosylhomocysteine accumulation, and (3) protein acylation by homocysteine thiolactone. The final result is membrane protein damage, endothelial damage, and endothelial cell growth inhibition, among other effects. Hyperhomocysteinemia, in general, is susceptible of therapeutic intervention with the vitamins involved in its metabolism. Depending on the cause, vitamin B6, vitamin B12, betaine, and/or folic acid can be effectively utilized. Chronic renal failure patients benefit from folic acid in high dosage: 1–2 mg are usually not effective (‘relative folate resistance’), while 5–15 mg reduce homocysteine levels to a ‘normative’ range (M) in a substantial group of patients. Good results are also obtained in transplant patients, best with a combination of folic and vitamin B6. The results of the interventional trials focusing on the possible reduction in cardiovascular risk after homocysteine-lowering therapy, both in the general population and in end-stage renal disease, are expected soon, as well as the genetic and biochemical studies in suitable models, with the aim to clarify the cause-effect link suggested by the numerous observational and basic science studies.

A number of epidemiological studies indicate that dietary factors may influence the development of some types of cancer and degenerative pathologies, including cardiovascular diseases and cataract. In this respect, it is well documented that daily consumption of fruits and vegetables is associated with a lowered risk of these diseases.1 Polyphenols are bioactive substances that are widely distributed in the vegetable kingdom2,3 and therefore are present in high concentrations in typical components of the Mediterranean diet, such as fruit, vegetables, red wine, and olive oil. The aim of this article is to overview the most recent data on the nutritional value of the phenolic fraction of virgin olive oil in the ongoing studies on its beneficial effects on human health.

Protein L-isoaspartate (D-aspartate) O-methyltransferase (PCMT) is a ubiquitous enzyme with substrate specificity toward proteins and peptides containing altered aspartyl residues. These are generated from the spontaneous deamidation of normal L-asparaginyl residues and/or isomerization of L-aspartyl residues. Such degradation reactions occur both in vivo and in purified protein molecules. Because of its peculiar substrate specificity, PCMT has been proposed as a tool for identifying and characterizing the L-isoaspartyl-containing byproducts of natural and recombinant proteins. Data presented here show the usefulness of PCMT for the identification of these altered residues in food proteins and the occurrence of these at detectable levels in several proteins from various animal sources. In addition, we noted that ovalbumin, either as a purified protein or in the whole chicken egg, becomes a better substrate for this enzyme during prolonged storage, thus indicating a progressive accumulation of the altered amino acid residues over time. The protective effects of trehalose against the occurrence of such specific protein damage in ovalbumin stored for several days were also assessed. Protein L-isoaspartate (D-aspartate) O-methyltransferase (PCMT) is a ubiquitous enzyme with substrate specificity toward proteins and peptides containing altered aspartyl residues. These are generated from the spontaneous deamidation of normal L-asparaginyl residues and/or isomerization of L-aspartyl residues. Such degradation reactions occur both in vivo and in purified protein molecules. Because of its peculiar substrate specificity, PCMT has been proposed as a tool for identifying and characterizing the L-isoaspartyl-containing byproducts of natural and recombinant proteins. Data presented here show the usefulness of PCMT for the identification of these altered residues in food proteins and the occurence of these at detectable levels in several proteins from various various animal sources. In addition, we noted that ovalbumin, either as a purified protein or in the whole chicken egg, becomes a better substrate for this enzyme during prolonged storage, thus indicating a progressive accumulation of the altered amino acid residues over time. The protective effects of trehalose against the occurence of such specific protein damage in ovalbumin stored for several days were also assessed.

Based on quantitative analysis of red cell membrane proteins, hereditary spherocytosis (HS) can be divided into two main groups including isolated or ankyrin combined spectrin deficiency and band 3 reduction. Protein methyl esterification catalysed by protein carboxyl methyl-transferase (PCMT type II; EC 2.1.1.77) is a post-biosynthetic modification which is involved in the metabolism of damaged membrane proteins. We utilized the evaluation of erythrocyte membrane protein methyl esterification as a marker of cytoskeletal disarray in seven HS subjects with spectrin reduction and in seven patients with HS due to band 3 deficiency. Our results support the notion that band 3 deficient erythrocytes are not affected by an extensive cytoskeletal derangement. On the contrary, we found a remarkable increase of membrane methylation in the unsplenectomized, spectrin-deficient. HS patients, suggesting a striking membrane skeleton disarray. This phenomenon was not observed in the spectrin-deficient red cells of splenectomized patients. Therefore in spectrin deficient erythrocytes the induction of cytoskeletal damage, specifically recognized by PCMT type II, could be one of the splenic steps producing conditioned spherocytes.

Mechanism of erythrocyte accumulation of methylation inhibitor S-adenosylhomocysteine in uremia. We have recently demonstrated that methyl esterification of erythrocyte membrane proteins, a reaction involved in recognition and repair of specifically damaged proteins, is impaired in uremia. This is accompanied by a significant increase in intracellular S-adenosylhomocysteine (AdoHcy), a potent inhibitor of methyltransferases. AdoHcy accumulation is normally prevented by its enzymatic hydrolysis to homocysteine (Hey) and adenosine, a reversible reaction catalyzed by AdoHcy hydrolase. To assess the contribution that Hey offers in the elevation of AdoHcy, we measured plasma and red blood cell Hey, AdoHcy, adenosine, and S-adenosylmethionine (AdoMet) intracellular concentrations, as well as RBC AdoHcy hydrolase specific activity, in standard hemodialysis patients and normal subjects. Plasma and red blood cell Hey levels are significantly higher in the dialysis group, and are positively correlated to AdoHcy levels. Adenosine and AdoMet levels, and AdoHcy hydrolase specific activity are not significantly different between the two groups. The enzymatic formation of labeled AdoHcy from Hey and tracer adenosine appears to be significantly increased, in vitro, in erythrocytes from both control and uremic patients, when 50 µM Hey (concentration comparable to plasma levels actually found in vivo in uremic patients) is added to the incubation medium. When erythrocytes from uremic patients are incubated in vitro in absence of Hey, a significant reduction of intracellular AdoHcy is observed with time compared to identical samples incubated in presence of 50 µM Hey, with a T1/2 of approximately 270 minutes. The results allow us to conclude that plasma and red cell Hey levels actually found in uremia can be effectively responsible for the intracellular accumulation of the toxic compound AdoHcy.

Protein carboxyl methyltransferase of type II selectively recognizes L‐isoaspartyl and D‐aspartyl residues spontaneously occurring in proteins and peptide substrates. Membrane protein methylation levels increase with erythrocyte aging in circulation, in parallel with the spontaneous formation of abnormal aspartyl sites, due to protein intrinsic instability. We found that enzymic methyl esterification of erythrocyte membrane proteins in hereditary spherocytosis, a model of cytoskeletal disarray, is significantly increased compared to normal red blood cells. This cannot be explained by an increase in mean age of spherocytes, which are on the contrary significantly younger than control cells. No differences in cytosolic methyltransferase specific activity, as well as in the intracellular concentrations of the methyl donor adenosylmethionine and/or of the methylation inhibitor adenosylhomocysteine were observed. We identified bands 2.1, 4.1 and 4.2 as the main targets for increased methylation, whose levels were correlated with the degree of spectrin deficiency associated with this anemia. Our findings indicate that membrane‐protein methyl esterification represents a marker of membrane structural alteration in vivo in spherocytosis. We hypothesize that either an increased accessibility of methylation sites normally not available to the methyltransferase, or accelerated formation of methyl‐accepting sites in membrane proteins are present in spherocytosis. Copyright © 1995, Wiley Blackwell. All rights reserved

Summary The enzymatic methyl esterification of proteins, catalyzed by the enzyme S-adenosylmethlonine: protein carboxyl-O-methyl transferase (PCMT), has been investigated in two age-related fractions of bovine lenses. The eukaryotic PCMT methyl esterifies peptides and proteins containing altered aspartyl residues, such as D-aspartyls and L-isoaspartyls, which can arise from the age-dependent deamidation of tabile Asn residues. When intact bovine lenses were incubated in a cell culture medium under physiological conditions (pH 7.4, 37°C), in the presence of L-(methyl-14C)methionine, the in vivo precursor of the methyl donor substrate S-adenosylmethionine (AdoMet), a significant decrease in the level of protein methyl esterification was observed in the oldest cell fraction compared to the youngest one; in contrast, the in vitro activity of PCMT does not change during cell aging. It has also been demonstrated that the cell aging in the lens is accompanied by a reduction of the AdoMet synthetase activity and, consequently, of the endogenous level of the methyl donor AdoMet. Furthermore, the activity of the enzyme S-adenosylhomocysteine (AdoHcy) hydrolase, which cleaves the methylation inhibitor AdoHcy, also appears dramatically reduced in the oldest cells, probably leading to an increase in the AdoHcy cellular level. Finally, the possible correlation between the decrease in the efficiency of the overall methyl esterification process during aging and the accumulation of aberrant forms of proteins observed in aged tissues is also discussed.

A pharmacokinetic analysis of CDPcholine has been carried out treating either rats or dogs by oral administration with the double labelled molecule. [ methyl - 14 C,5- 3 H]CDPcholine represents a useful tool to test the structural integrity of this compound during the transmembrane transport and to follow the metabolic fate of cytidine and choline fragments. Furthermore, the identification of the labelled metabolites of the exogenously administered CDPcholine in the various organs allows us to draw inferences about its pharmacological mechanism(s). These studies appear of great interest in view of the extensive therapeutic use of the molecule in the treatment of several CNS pathologies including traumatic brain injury. The results of this work can be summarized as follows. (a) The molecule is rapidly cleaved at the level of the pyrophosphate bridge and a fast uptake of the hydrolytic products occurs. (b) The metabolism of the molecule is characterized by a differential utilization of the two moieties by the various organs. Liver is the most active organ utilizing in CDPcholine with a preferential uptake of the choline fragment. (c) The [ 3 H]cytidine moiety, in all the organs examined, appears to be incorporated into the nucleic acid fraction via the cytidine nucleotide pool. The [ 14 C]choline moiety is in part converted into betaine, which in turn acts as methyl donor to homocysteine, yielding [ 14 C]methionine, subsequently incorporated into proteins. The time-dependent increase in the labelling of phospholipids is indicative of a recycling of choline methyl groups via CDPcholine and/or S -adenosylmethionine. (d) The uptake of CDPcholine by the brain is relatively low; however, a good metabolic utilization of the drug can be observed. The salvage of the choline moeity in de novo phospholipid biosynthesis is indeed highly operative in this organ.

A rapid, sensitive and specific high-performance liquid chromatographic method for the simultaneous separation of natural adenosyl-sulphur compounds has been developed. The compounds were separated by using the strong cation-exchange resin Partisil 10 SCX with isocratic elution. The adenosyl-compounds were monitored by an ultraviolet detector operating at 254 nm. Sensitivity was greater than 50 pmoles for all compounds tested and standard curves were found to be linear for concentrations of up to 50 nmoles. The method can be applied to biological samples for the estimation of S-adenosyl- l -methionine, S-adenosyl- l -homocysteine and S-adenosyl-(5′)-3-methylthiopropylamine and for measurement of enzyme activities involving the above-mentioned compounds.

Membrane proteins from human erythrocytes were methylated with purified protein methylase II (S-adenosylmethionine:protein-carboxyl O-methyltransferase, EC.2.1.1.24). The methylated proteins were analyzed by dodecyl sulfate/polyacrylamide gel electrophoresis. Monomeric and dimeric glycophorin A (NaIO4/Schiff-2 and NaIO4/Schiff-1 positive bands) and 'band 4.5' were identified as two major classes of methyl-acceptor polypeptides for protein methylase II. In rabbit erythrocyte membrane where glycophorin A is absent, 'band 4.5' was the only major methyl-acceptor protein component. Extracted and purified glycophorin A from human erythrocytes was also found to be an excellent substrate for protein methylase II with a Km of 35.7 microM. The role of erythrocyte membrane protein methylation is discussed with regard to membrane function.

Kinetic properties of protein methylase II (S-adenosylmethionine:protein-carboxyl methyltrans- ferase, EC 2.1.1.24), which methylates the free carboxyl groups of protein substrates, were studied with various analogs and derivatives of S-adenosyl-l-methionine (AdoMet) and S-adenosyl-l- homocysteine (AdoHcy), using corticotropin as methyl-accepting polypeptide. Experiments with methyl-labelled structural analogs of AdoMet showed that the replacement of the amino groups of AdoMet by hydroxyl groups, as well as the removal of the carboxyl group, results in a loss of methylating ability of the molecule. Deaminated and decarboxylated derivatives were also inactive as inhibitors. Among the sulfonium analogs tested, only S-adenosyl-l- (2-amino-4-carboxymethylthio)butyric acid exerted a significant inhibition. AdoHcy, the demethylated product of AdoMet, exerts a competitive inhibition on the reaction (Ki= 0.65 μM); the probable regulatory role of this inhibition will be discussed. The removal of the adenine amino group of the thioether resulted in a loss of the inhibitory effect. Experiments with the D-isomer of AdoHcy showed the relevance of the steric configuration of the α-carbon in the binding to the enzyme protein. 5′-Methylthioadenosine, a metabolic product of AdoMet, in- hibited competitively the reaction (Ki= 41 μM) while 5′-methylthioadenosine derivatives, such as n-butylthioadenosine, isobutylthioadenosine and thioethanoladenosine, failed to exert any in- hibition. Three synthetic polypeptides differing in amino acid composition and in chain length have also been tested as methyl-acceptor substrates and as inhibitors for the reaction. Only the copolymer of l-glutamic acid and l-tyrosine [poly(Glul1.16, Tyrl)] (Mr= 22600) exerts a relevant non-com- petitive inhibition, while none of the tested synthetic polypeptides is active as substrate.

Double-labelled [methyl-14C,5-3H]CDPcholine has been synthesized and subjected to a pharmacokinetic analysis in several biological systems. In transport experiments with intact human erythrocytes no incorporation of radioactivity is observable. On the other hand the results obtained with perfused rat liver suggest a rapid cleavage of the pyrophosphate bridge of the molecule, followed by a rapid uptake of the hydrolytic products. The plasma half-lives of intravenously injected CDPcholine and of its metabolites have been evaluated within 60 sec range. Renal and fecal excretion of the injected radioactivity is negligible: only 2.5% of administered 14C- and 6.5% of the 3H- is excreted up to 48 hr after administration. Liver and kidney are the major CDPcholine metabolizing organs, characterized by a fast and extensive uptake of choline metabolites, followed by a slow release; conversely the rate of uptake of both 3H and 14C-labelled moieties by rat brain is significantly slower, reaching a steady-state level after 10 hr. The characterization of the labelled compounds detectable in the investigated organs provides some insights on the metabolism of the drug: the 3H-cytidine moiety in all the examined organs appears to be incorporated into the nucleic acid fraction via the cytidine nucleotide pool; the [14C]choline moiety of the molecule is in part converted, at the mitochondrial level, into betaine which accounts for about 60% of the total 14C-radioactivity associated with liver and kidney 30 min after administration; [14C]betaine in turn acts as methyl donor to homocysteine yielding [14C]methionine subsequently incorporated into proteins; the time dependent increase in labelled phospholipids is indicative of a recycling of the choline methyl-groups in this lipid fraction via CDPcholine and/or S-adenosylmethionine; the rather extensive amount of labelled methionine detectable in brain probably arises from its uptake from the blood stream, since the enzyme catalyzing the conversion of betaine into methionine is lacking in brain.

1. 1. Evidence of the presence of a pyridoxal-5-phosphatc-dependcnt omithinc decarboxylase in human prostate gland is reported. 2. 2. Thiols are required for enzyme activity, which is inhibited by sulphydryl reagents. 3. 3. The p H curve exhibits an optimum p 7.0 and a reproducible shoulder at pH 8.o. 4. 4. The apparent Km for the substrate is o-13 mM. Putrcscine is a competitive inhibitor, with an apparent K t of 4-3 mM.

Methyl esterification of erythrocyte membrane proteins have been demonstrated by incubating the isolated membrane with purified protein methylase II (S-adenosyl-methionine:protein-carboxyl O-methyltransferase, EC 2.1.1.24) and S-adenosyl-L-[methyl-14C]methionine. Methyl esterification of membrane-bound proteins occurred selectively to proteins corresponding to bands 3 (mol wt 97 000), 4 (mol wt 75 000), and 4.5 (mol wt 48 000) [designated according to Steck, T. L. (1974), J. Cell Biol. 62, 1] as identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Mild alkali treated depleted vesicles which lacked bands 1, 2, 5, and 6 had a higher methyl accepting capacity; 500 pmol of methyl groups/mg of depleted vesicle proteins vs. 200 pmol of methyl groups/mg of intact membrane proteins. Alkali-extractable membrane components were not methylated.

The enzyme S-adenosylmethionine: protein carboxyl-O-methyltransfe-rase (PCMT) was first identified in 1965 by Axelrod and Daly as “methanol forming “ enzyme, since it was thought to catalyze the hydrolysis of S-adenosylmethionine (AdoMet) yielding methanol and S-adenosylhomocysteine (AdoHcy) (1). A few years later Liss et al. (2) and Kim and Paik (3) described an AdoMet-dependent methyl transferase which methylates free carboxyl groups in protein substrates and leads to the formation of unstable methyl esters. The two enzymes shared methanol as a common end product and were found to be identical on the basis of their properties and tissue distribution (4). During the following fifteen years the enzyme was purified from eukaryotic and prokaryotic sources, extensively characterized, and a number of different regulatory roles have been attributed to it, as reviewed by Paik and Kim in 1980 (5). However, in eukaryotes none of the hypothesized regulatory functions has been unequivocally demonstrated. More recently the eukaryotic and prokaryotic enzymes were found to differ in terms of methylation site, substrate specificity and functional role (6,7); therefore a new systematic name and classification number have been assigned to the eukaryotic PCMT. This enzyme indeed has been shown to recognize and selectively modify proteins at D-aspartyl and L-isoaspartyl residue levels (6,7).

The effect of Ca2+ loading, induced by the ionophore A23187, on methyl esterification of membrane proteins (i.e. bands 2.1, 3, 4.1 and 4.5) has been investigated in intact human erythrocytes. When the cells were incubated with l-[methyl-3H]methionine, 40 μM CaCl2 and 10 μM A23187 induce a 50% inhibition of membrane protein methyl esterification. This effect is selectively due to the increased intracellular Ca2+ concentration, as it is antagonized by 10 μM EGTA, and other divalent cations such as Mn2+ do not exert any inhibition. In order to clarify the mechanism(s) of the reported inhibition, the various events involved in the methyl esterification process in vivo were analyzed. 1 l-Methionine uptake as well as protein methylase II activity are not directly affected by altered intracellular Ca2+ concentrations. Conversely in the Ca2+-loaded erythrocytes the conversion of [3H]methionine into [3H]AdoMet, catalyzed by AdoMet synthetase, decreases up to 25%. 3 When the undialyzed erythrocyte cytosolic fraction is assayed in vitro for AdoMet synthetase the activity of the enzyme from the CaCl2/A23187-treated erythrocytes is significantly lower than the control, up to 5 μM ATP. This result suggests that in the Ca2+-loaded erythrocytes the ATP intracellular concentration is significantly lowered. 4 The direct evaluation of ATP intracellular concentration, by HPLC, confirms a significant drop of ATP level, as a consequence of the Ca2+ loading. 5 The removal of Ca2+ from the cells quantitatively restores both the AdoMet synthesis and the methyl esterification levels. The possible role of altered ATP intracellular concentrations as a regulatory factor in the AdoMet-dependent reactions as well as in post-translational protein methylation related to the ageing process is also discussed.

The enzymatic carboxyl methyl esterification of erythrocyte membrane proteins has been investigated in three different age-related fractions of human erythrocytes. When erythrocytes of different mean age, separated by density gradient centrifugation, were incubated under physiological conditions (pH 7.4, 37°C) in the presence of l-[methyl-3H]methionine, the precursor in vivo of the methyl donor S-adenosylmethionine, a fourfold increase in membrane-protein carboxyl methylation was observed in the oldest cells compared with the youngest ones. The identification of methylated species, based on comigration of radioactivity with proteins stained with Coomassie blue, analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis, shows, in all cell fractions, a pattern similar to that reported for unfractionated erythrocytes. However in the membrane of the oldest erythrocytes the increase in methylation of the cytoskeletal proteins, bands 2.1 and 4.1, appears to be significantly more marked compared with that observed in the other methylated polypeptides. Furthermore the turnover rate of incorporated [3H]methyl groups in the membrane proteins of the oldest cells markedly increases during cell ageing. Particularly in band 4.1 the age-related increase in methyl esterification is accompanied by a significant reduction of the half-life of methyl esters. The activity of cytoplasmic protein methylase II does not change during cell ageing, while the isolated ghosts from erythrocytes of different age show an age-related increased ability to act as methyl-accepting substrates, when incubated in presence of purified protein methylase II and methyl-labelled S-adenosylmethionine, therefore the relevance of membrane structure in determining membrane protein methylation levels can be postulated. Finally the possible correlation of this posttranslational protein modification with erythrocyte ageing is discussed.