Resveratrol: From Basic Science to the Clinic

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 compound in association with more specific target-oriented drugs.

Resveratrol: from basic studies to bedside

Plants produce a remarkable amount of low molecular mass natural products endowed with a large array of pivotal biological activities. Among these molecules, resveratrol (3,5,4'-trihydroxystilbene) has been identified as an important modulator of cell phenotype with a complex and pleiotropic mode of action. Extensive literature regarding its activity, mainly employing cellular models, suggests that this polyphenol controls cell proliferation, induces differentiation, and activates apoptosis and autophagy. The compound also modulates angiogenesis and inflammation. Similarly, studies on implanted cancers and chemical-induced tumors confirm the potential chemotherapeutical interest of the compound. Likewise, several reports clearly demonstrated, in animal models, that the compound might positively affect the development and evolution of chronic diseases including type 2 diabetes, obesity, coronary heart disease, metabolic syndrome, and neurogenerative pathologies. Finally, a number of investigations stated that the toxicity of the molecule is scarce. Despite these promising observations, few clinical trials have yet been performed to evaluate the effectiveness of the molecule both in prevention and treatment of human chronic disease. Preliminary findings therefore suggest the need for more extensive clinical investigations.

MCP-1 in psoriatic patients: effect of biological therapy

BACKGROUND

Monocyte chemoattractant protein-1 (MCP-1) is a chemokine locally and systemically augmented in psoriasis. A single nucleotide polymorphism in MCP-1 promoter region -2518A→G is associated with higher gene expression.

OBJECTIVE

The aim was to evaluate MCP-1 plasma level in psoriatic patients and to relate any association in plasmatic and cutaneous MCP-1 with clinical improvement due to biological drugs.

METHODS

Blood samples were obtained from: (i) 30 Caucasian patients with psoriasis and 10 controls, for determining MCP-1 plasma concentrations and -2518A→G polymorphism occurrence, (ii) 16 psoriatic patients treated by anti-tumor necrosis factor-α (TNF-α) adalimumab/etanercept or by anti-CD-11 efalizumab, before and after 2 months of treatment. Moreover, biopsies were performed on lesional skin of five patients treated with anti-TNF-α. MCP-1 plasma concentration and cutaneous expression were determined by ELISA and qRT-PCR.

RESULTS

MCP-1 plasma level was significantly increased in psoriatic patients. -2518A→G polymorphism was similarly distributed in patients and controls and unrelated to MCP-1 plasma level or to Psoriasis Area and Severity Index. All patients receiving biological drugs showed significant clinical improvement. Anti-TNF-α therapy moderately reduced MCP-1 plasma concentration and robustly decremented MCP-1 expression in lesional skin.

CONCLUSION

MCP-1 should be a potential local inflammatory marker in psoriatic patients to assess disease severity and anti-TNF-α treatment efficacy.

Protective effect of polyphenols from Glycyrrhiza glabra against oxidative stress in Caco-2 cells

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.

Impaired transmethylation potential in Parkinson's disease patients treated with L-Dopa

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.

Olive oil phenolic compounds inhibit homocysteine-induced endothelial cell adhesion regardless of their different antioxidant activity

In this study, we examine the effect of extra virgin olive oil phenolic compounds on homocysteine-induced endothelial dysfunction and whether the protective effects are related to their different scavenging activities. Structurally related compounds have been assayed for their ability to reduce homocysteine-induced monocyte adhesion as well as the cell surface expression of intercellular adhesion molecule-1 (ICAM-1) in EA.hy.926 cells. As well-known, among the selected phenolic compounds, hydroxytyrosol, homovanillyl alcohol, and the hydroxycinnamic acid derivatives caffeic and ferulic acid display high scavenging activities, while tyrosol and p-coumaric acid are poorly active. All of the tested compounds, approaching potential in vivo concentrations, significantly reduce homocysteine-induced cell adhesion and ICAM-1 expression. Interestingly, we report the first evidence that monophenols tyrosol and p-coumaric acid are selectively protective only in homocysteine-activated cells, while they are ineffective in reducing ICAM-1 expression induced by TNFalpha. Finally, we report the synergistic effect of o-diphenolic and monophenolic compounds.

Microsomal triglyceride transfer protein (MTP) -493G/T gene polymorphism contributes to fat liver accumulation in HCV genotype 3 infected patients

(A) A reduced activity of microsomal triglyceride transfer protein (MTP), a key enzyme of assembly/secretion of lipoproteins, is related to HCV steatosis. Host genetic background may influence development of steatosis. The aim of the study was to investigate the association between MTP-493 G/T gene polymorphism, fat liver accumulation and fibrosis progression in HCV infected patients. A total of 102 naïve patients with liver biopsy proven chronic hepatitis C were evaluated for MTP-493 G/T gene polymorphism, HCV RNA, HCV genotype, HOMA-IR, serum adiponectin, TNF-alpha and serum lipid levels. HCV genotype 3 infected patients carrying the T allele of the MTP gene polymorphism showed higher degree of steatosis than those carrying GG genotype (3.45 +/- 0.37 vs 1.30 +/- 0.45, respectively; P < 0.001). MTP'T' allele carriers also had higher HCV RNA serum levels (P < 0.01) and hepatic fibrosis (P < 0.001). Irrespective of MTP genotype, patients with HCV genotype 3 had lower levels of cholesterol, ApoB, HDL and LDL. In HCV genotype non-3 infected patients no parameters were associated with MTP gene polymorphism. In conclusion the presence of T allele of MTP-493G/T gene polymorphism predisposes patients infested with HCV genotype 3 to develop higher degree of fatty liver accumulation.

Protein isoaspartate methyltransferase prevents apoptosis induced by oxidative stress in endothelial cells: role of Bcl-Xl deamidation and methylation

Background

Natural proteins undergo in vivo spontaneous post-biosynthetic deamidation of specific asparagine residues with isoaspartyl formation. Deamidated-isomerized molecules are both structurally and functionally altered. The enzyme isoaspartyl protein carboxyl-O-methyltransferase (PCMT; EC 2.1.1.77) has peculiar substrate specificity towards these deamidated proteins. It catalyzes methyl esterification of the free α-carboxyl group at the isoaspartyl site, thus initiating the repair of these abnormal proteins through the conversion of the isopeptide bond into a normal α-peptide bond. Deamidation occurs slowly during cellular and molecular aging, being accelerated by physical-chemical stresses brought to the living cells. Previous evidence supports a role of protein deamidation in the acquisition of susceptibility to apoptosis. Aim of this work was to shed a light on the role of PCMT in apoptosis clarifying the relevant mechanism(s).

Methodology/Principal Findings

Endothelial cells transiently transfected with various constructs of PCMT, i.e. overexpressing wild type PCMT or negative dominants, were used to investigate the role of protein methylation during apoptosis induced by oxidative stress (H₂O₂; 0.1–0.5 mM range). Results show that A) Cells overexpressing “wild type” human PCMT were resistant to apoptosis, whereas overexpression of antisense PCMT induces high sensitivity to apoptosis even at low H₂O₂ concentrations. B) PCMT protective effect is specifically due to its methyltransferase activity rather than to any other non-enzymatic interactions. In fact negative dominants, overexpressing PCMT mutants devoid of catalytic activity do not prevent apoptosis. C) Cells transfected with antisense PCMT, or overexpressing a PCMT mutant, accumulate isoaspartyl-containing damaged proteins upon H₂O₂ treatment. Proteomics allowed the identification of proteins, which are both PCMT substrates and apoptosis effectors, whose deamidation occurs under oxidative stress conditions leading to programmed cell death. These proteins, including Hsp70, Hsp90, actin, and Bcl-xL, are recognized and methylated by PCMT, according to the general repair mechanism of this methyltransferase.

Conclusion/Significance

Apoptosis can be modulated by “on/off” switch partitioning the amount of specific protein effectors, which are either in their active (native) or inactive (deamidated) molecular forms. Deamidated proteins can also be functionally restored through methylation. Bcl-xL provides a case for the role of PCMT in the maintenance of functional stability of this antiapoptotic protein.

Histone deacetylase inhibitors upregulate p57Kip2 level by enhancing its expression through Sp1 transcription factor

Histone deacetylase inhibitors (HDACIs) represent a new class of targeted anticancer agents. Here, we evaluate the effects of butyrate (BuA) and other HDACIs on p57(Kip2), a cyclin-dependent kinase inhibitor (cki). We observed that inhibitors of class I/II histone deacetylases (HDACs), but not of class III HDACs, induce a remarkable accumulation of p57(Kip2) in several cells. The cki upregulation is associated with an increased gene expression that was not prevented by cycloheximide, indicating that HDACIs affect directly p57(Kip2) transcription. The characterization of p57(Kip2) promoter indicates that the first 165 bp are mostly involved in the BuA effects. Chromatin immunoprecipitation studies demonstrated that the BuA treatment causes the recruitment of Sp1 transcription factor. The Sp1 importance was confirmed by the reduction of BuA effects by mithramycin A (an Sp1 antagonist) and, most stringently, by Sp1 downregulation due to Sp1 siRNA. Moreover, both the treatments reduce the p57(Kip2) transcription in untreated cells, suggesting that Sp1 is required for the constitutive cki expression. Studies employing plasmids containing parts of the 165 bp of p57(Kip2) promoter indicate that the promoter region between -87 and -113 bp, which includes two putative Sp1 consensus sequences, plays a critical role in the response to HDACIs. Since this p57(Kip2) promoter region also embraces the consensus sequence for the transcriptional repressor chicken ovalbumin upstream promoter transcription factor-interacting protein 2 (CTIP2), we evaluated whether this factor is involved into the BuA effect. When CTIP2 was downregulated by a specific siRNA, we observed the enhancement of BuA activity on p57(Kip2) expression suggesting that CTIP2 might also be involved in HDACIs effects.

In vivo effect of the natural antioxidant hydroxytyrosol on cyclosporine nephrotoxicity in rats

BACKGROUND

Cyclosporine A (CsA) is the first-line immunosuppressant used in transplant patients and in auto- immune diseases. Nephrotoxicity is the major limitation of CsA use. Although the mechanisms of nephrotoxicity have not been completely defined, some evidence suggests that reactive oxygen species (ROS) play a causal role. The present study was designed to investigate in vivo effects of hydroxytyrosol (DOPET), a natural olive oil antioxidant, on oxidative stress, renal histology and haemodynamic alterations induced in rats by CsA treatment.

METHODS

Adult Sprague-Dawley rats were treated i.p. with CsA (15 mg/kg) alone or in combination with DOPET (20 mg/kg) for 3 weeks. At the end of the treatment, superoxide concentration within the cells of the abdominal aorta and renal artery was quantified from the oxidation of dihydroethidium (DHE) using fluorescence microscopic imaging analysis. In kidney tissues, lipid peroxidation was measured by thiobarbituric acid-reacting substances (TBARS) assay, glutathione level was assessed enzymatically and the expression of haem oxygenase-1 (HO-1) gene was evaluated by semiquantitative RT-PCR. Renal morphology was studied by classical histological techniques, while the glomerular filtration rate (GFR) was estimated by inulin clearance. Systemic blood pressure was monitored by the tail method and through the catheterization of the carotid artery.

RESULTS

CsA administration increased superoxide concentration both in the aorta and in the renal artery, while DOPET completely prevented this effect. Higher levels of TBARS, a significant decrease in GSH and an upregulation of HO-1 mRNA were observed in the kidneys of CsA-treated rats. DOPET treatment reversed quantitatively these effects. However, CsA-dependent changes in renal histology were only partially reversed by DOPET. Finally, CsA induced a severe reduction in GFR and a significant increase in both systolic and diastolic blood pressure; the DOPET treatment had no significant effect on these haemodynamic alterations.

CONCLUSION

The reported data indicate that effective DOPET protection from CsA-induced oxidative stress is associated with a mild effect on histological damages and does not affect the altered glomerular function and the hypertension, thus indicating that kidney injury by CsA is only in part dependent on oxidative stress.

Effect of reddening-ripening on the antioxidant activity of polyphenol extracts from cv. 'Annurca' apple fruits

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.

Accumulation of altered aspartyl residues in erythrocyte proteins from patients with Down's syndrome

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.

Homocysteine-induced endothelial cell adhesion is related to adenosine lowering and is not mediated byS-adenosylhomocysteine

Hyperhomocysteinemia is a cardiovascular risk factor and may contribute to the pathogenesis of atherosclerosis by altering endothelial functions. The mechanism of homocysteine-induced cell adhesion has been here investigated using EA.hy 926 cells. Homocysteine induces a stereospecific, time- and dose-dependent cell adhesion which is prevented by adenosine. The dramatic increase of S-adenosylhomocysteine induced by adenosine-2',3'-dialdehyde does not cause cell adhesion, indicating that no apparent relationship exists between this process and intracellular S-adenosylhomocysteine content. Homocysteine-induced cell adhesion is abolished by pre-treatment with adenosine-2',3'-dialdehyde, demonstrating that the adenosine depletion caused by reversal of S-adenosylhomocysteine hydrolase reaction is responsible for homocysteine-induced cell damage.

The first agmatine/cadaverine aminopropyl transferase: biochemical and structural characterization of an enzyme involved in polyamine biosynthesis in the hyperthermophilic archaeon Pyrococcus furiosus

We report here the characterization of the first agmatine/cadaverine aminopropyl transferase (ACAPT), the enzyme responsible for polyamine biosynthesis from an archaeon. The gene PF0127 encoding ACAPT in the hyperthermophile Pyrococcus furiosus was cloned and expressed in Escherichia coli, and the recombinant protein was purified to homogeneity. P. furiosus ACAPT is a homodimer of 65 kDa. The broad substrate specificity of the enzyme toward the amine acceptors is unique, as agmatine, 1,3-diaminopropane, putrescine, cadaverine, and sym-nor-spermidine all serve as substrates. While maximal catalytic activity was observed with cadaverine, agmatine was the preferred substrate on the basis of the k(cat)/K(m) value. P. furiosus ACAPT is thermoactive and thermostable with an apparent melting temperature of 108 degrees C that increases to 112 degrees C in the presence of cadaverine. Limited proteolysis indicated that the only proteolytic cleavage site is localized in the C-terminal region and that the C-terminal peptide is not necessary for the integrity of the active site. The crystal structure of the enzyme determined to 1.8-A resolution confirmed its dimeric nature and provided insight into the proteolytic analyses as well as into mechanisms of thermal stability. Analysis of the polyamine content of P. furiosus showed that spermidine, cadaverine, and sym-nor-spermidine are the major components, with small amounts of sym-nor-spermine and N-(3-aminopropyl)cadaverine (APC). This is the first report in Archaea of an unusual polyamine APC that is proposed to play a role in stress adaptation.

p27Kip1 metabolism: a fascinating labyrinth

The progression through the phases of cell division cycle is regulated by different cyclins and cyclin-dependent kinases (CDKs) complexes. Due to their key function, the activity of cyclin/CDK complexes is controlled by several mechanisms, including the inhibition by a number of proteins collectively defined CDK inhibitors or CKIs. Among the CKIs, p27Kip1 represents a protein of central activity for the control of several phenotypes, including proliferation, differentiation and malignant transformation. p27Kip1 belongs to the growing family of "natively unfolded," "intrinsically disordered" or "intrinsically unstructured" proteins. The disorder proteins present a very large number of possible conformations that, after the binding, converge to a well-defined structure with an extraordinary affinity for the target. As matter of fact, the absence of a pre-existing folding strongly facilitates p27Kip1 interaction with a number of targets. Until recently, p27Kip1 has been solely viewed as a nuclear protein with the function of modulating cyclin-CDK activity and hence, cell cycle progression. However, exhaustive studies have now demonstrated that the protein plays additional roles outside of the nucleus, including, particularly, the control of cell motility. Thus, the cellular localization is of fundamental importance in p27Kip1 function. Accordingly, at least two different mechanisms of degradation, occurring either in the nucleus or in the cytosol, have been observed. Convincing evidences have demonstrated that p27Kip1 is a phosphoprotein showing at least six to eight phosphorylatable residues. However, the precise functional roles of the phosphorylations and the identification of the kinases responsible for the post-synthetic modifications are still debated. In this brief review, we will report the Literature data that connect the post-synthetic modifications of p27Kip1 with its function, localization and metabolism. The picture that emerges demonstrates that several of the pieces of the CKI metabolism are still nebulous.

Biochemical and structural characterization of mammalian-like purine nucleoside phosphorylase from the Archaeon Pyrococcus furiosus

We report here the characterization of the first mammalian-like purine nucleoside phosphorylase from the hyperthermophilic archaeon Pyrococcus furiosus (PfPNP). The gene PF0853 encoding PfPNP was cloned and expressed in Escherichia coli and the recombinant protein was purified to homogeneity. PfPNP is a homohexamer of 180 kDa which shows a much higher similarity with 5'-deoxy-5'-methylthioadenosine phosphorylase (MTAP) than with purine nucleoside phosphorylase (PNP) family members. Like human PNP, PfPNP shows an absolute specificity for inosine and guanosine. PfPNP shares 50% identity with MTAP from P. furiosus (PfMTAP). The alignment of the protein sequences of PfPNP and PfMTAP indicates that only four residue changes are able to switch the specificity of PfPNP from a 6-oxo to a 6-amino purine nucleoside phosphorylase still maintaining the same overall active site organization. PfPNP is highly thermophilic with an optimum temperature of 120 degrees C and is characterized by extreme thermodynamic stability (T(m), 110 degrees C that increases to 120 degrees C in the presence of 100 mm phosphate), kinetic stability (100% residual activity after 4 h incubation at 100 degrees C), and remarkable SDS-resistance. Limited proteolysis indicated that the only proteolytic cleavage site is localized in the C-terminal region and that the C-terminal peptide is not necessary for the integrity of the active site. By integrating biochemical methodologies with mass spectrometry we assigned three pairs of intrasubunit disulfide bridges that play a role in the stability of the enzyme against thermal inactivation. The characterization of the thermal properties of the C254S/C256S mutant suggests that the CXC motif in the C-terminal region may also account for the extreme enzyme thermostability.

Retinoic acid induces p27Kip1 nuclear accumulation by modulating its phosphorylation

All-trans-retinoic acid (ATRA), the most biologically active metabolite of vitamin A, controls cell proliferation, apoptosis, and differentiation depending on the cellular context. These activities point to ATRA as a candidate for cancer therapy. A pivotal effect of the molecule is the modulation of p27Kip1, a cyclin-dependent kinase (CDK) inhibitor (CDKI). Here, we investigate the mechanisms by which ATRA regulates p27Kip1 level in LAN-5, a neuroblastoma cell line. When added to the cells, ATRA causes a rapid nuclear increase of p27Kip1, which clearly precedes growth arrest. The early buildup is not due to impairment of the CDKI degradation, in contrast to previous observations. Particularly, we did not detect the down-regulation of Skp2 and Cks1, two proteins involved in the nuclear ubiquitin-dependent p27Kip1 removal. Moreover, the morphogen does not impair the CDKI nuclear export and does not cause CDK2 relocalization. The characterization of CDKI isoforms by two-dimensional PAGE/immunoblotting showed that ATRA induces an early nuclear up-regulation of monophosphorylated p27Kip1. Immunologic studies established that this isoform corresponds to p27Kip1 phosphorylated on S10. The buildup of phospho(S10)p27Kip1 precedes the CDKI accumulation and increases its half-life. Finally, ATRA-treated nuclear LAN-5 extracts showed an enhanced capability of phosphorylating p27Kip1 on S10, thus explaining the nuclear up-regulation of the isoform. In conclusion, our data suggest a novel mechanism of ATRA antiproliferative activity, in which the morphogen rapidly up-regulates a nuclear kinase activity that phosphorylates p27Kip1 on S10. In turn, this event causes the stabilization of p27Kip1 and its accumulation in the nuclear compartment.

The N-terminal 11 amino acids of human erythrocyte band 3 are critical for aldolase binding and protein phosphorylation: implications for band 3 function

The 911 amino acid band 3 (SLC4A1) is the major intrinsic membrane protein of red cells and is the principal Cl-/HCO3- exchanger. The N-terminal cytoplasmic domain of band 3 anchors the spectrin-based membrane skeleton to the lipid bilayer through its interaction with ankyrin and also binds glycolytic enzymes and hemoglobin. We identified a son of a consanguineous marriage with severe anemia in association with marked deficiency of band 3 (12% +/- 4% of normal). Direct nucleotide sequencing of SLC4A1 gene demonstrated a single base substitution (T --> C) at position + 2 in the donor splice site of intron 2, resulting in the generation of a novel mutant protein. Biochemical characterization of the mutant protein showed that it lacked the first 11 N-terminal amino acids (band 3 Neapolis). The expression of the mutant protein resulted in the complete absence of membrane-bound aldolase, and the mutant band 3 could not be tyrosine phosphorylated. The ability of the malarial parasite P falciparum to invade these red cells was significantly decreased. The identification of a novel band 3 mutant and its structural and functional characterization enabled us to identify pivotal roles for the 11 N-terminal amino acids in several protein functions and, in turn, in red-cell physiology.

Von Hippel-Lindau-dependent polycythemia is endemic on the island of Ischia: identification of a novel cluster

Chuvash polycythemia (MIM 263400) is an autosomal recessive disorder characterized by a high hemoglobin level, relatively high serum erythropoietin, and early death. It results from a Von Hippel-Lindau (VHL) gene mutation (C598T) that causes increased HIF-1alpha activity and erythrocyte production in the face of normoxia. This polycythemia is endemic in Chuvashia, whereas its worldwide frequency is very low. We investigated the incidence of the Chuvash-type VHL mutation in Campania (South Italy) and identified 14 affected subjects (5 families). Twelve live on the island of Ischia (Bay of Naples). From analysis of the mutated allele, we found that the disease was more frequent on Ischia (0.070) than in Chuvashia (0.057). The haplotype of all patients matched that identified in the Chuvash cluster, thereby supporting the single-founder hypothesis. We also found that nonaffected heterozygotes had increased HIF-1alpha activity, which might confer a biochemical advantage for mutation maintenance. In conclusion, we have identified the first large cluster of Chuvash erythrocytosis outside Chuvashia, which suggests that this familial polycythemia might be endemic in other regions of the world.

Methylthioadenosine phosphorylase from the archaeon Pyrococcus furiosus. Mechanism of the reaction and assignment of disulfide bonds

The extremely heat-stable 5'-methylthioadenosine phosphorylase from the hyperthermophilic archaeon Pyrococcus furiosus was cloned, expressed to high levels in Escherichia coli, and purified to homogeneity by heat precipitation and affinity chromatography. The recombinant enzyme was subjected to a kinetic analysis including initial velocity and product inhibition studies. The reaction follows an ordered Bi-Bi mechanism and phosphate binding precedes nucleoside binding in the phosphorolytic direction. 5'-Methylthioadenosine phosphorylase from Pyrococcus furiosus is a hexameric protein with five cysteine residues per subunit. Analysis of the fragments obtained after digestion of the protein alkylated without previous reduction identified two intrasubunit disulfide bridges. The enzyme is very resistant to chemical denaturation and the transition midpoint for guanidinium chloride-induced unfolding was determined to be 3.0 M after 22 h incubation. This value decreases to 2.0 M in the presence of 30 mM dithiothreitol, furnishing evidence that disulfide bonds are needed for protein stability. The guanidinium chloride-induced unfolding is completely reversible as demonstrated by the analysis of the refolding process by activity assays, fluorescence measurements and SDS/PAGE. The finding of multiple disulfide bridges in 5'-methylthioadenosine phosphorylase from Pyrococcus furiosus argues strongly that disulfide bond formation may be a significant molecular strategy for stabilizing intracellular hyperthermophilic proteins.

Ex vivo expansion of bone marrow stromal cells by platelet-rich plasma: a promising strategy in maxillo-facial surgery

The aim of our study is to evaluate in vitro the response of bone marrow stromal cells (BMSCs) to platelet-rich plasma (PRP), in order to clarify the potential role of their combined use in a preclinical phase preceding BMSCs transplantation for bone repair and regeneration procedures. The incubation of BMSCs with PRP promoted a remarkable, dose- and time- dependent, growth stimulation, that was paralleled to a strong increase in the quantity of type I collagen and to a significant decrease in the activity of the early osteoblastic differentiation marker, alkaline phosphatase (AP). Once PRP was removed and osteogenic inducers were added, AP returned to levels comparable to the control, while the late phenotypic markers, osteocalcin and matrix calcification, were enhanced to higher levels than in controls. Our data demonstrate that PRP induces a remarkable ex vivo enrichment of BMSCs maintaining their differentiative potential. Thus PRP represents a valid preclinical tool for obtaining an effective, rapid and safe ex vivo expansion of BMSCs prior to their clinical utilization in bone engineering.

Hyperhomocysteinemia and the MTHFR C677T polymorphism promote steatosis and fibrosis in chronic hepatitis C patients

The factors and mechanisms implicated in the development of hepatitis C virus (HCV)-related steatosis are unknown. Hyperhomocysteinemia causes steatosis, and the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism induces hyperhomocysteinemia. We investigated the role of these factors in the development of HCV-related steatosis and in the progression of chronic hepatitis C (CHC). One hundred sixteen CHC patients were evaluated for HAI, fibrosis and steatosis grades, body mass index, HCV genotypes, HCV RNA levels, homocysteinemia, and the MTHFR C677T polymorphism. Hyperhomocysteinemia was associated with the TT genotype of MTHFR (r = 0.367; P = .001). Median values of homocysteine in the CC, CT, and TT genotypes of the MTHFR gene were 9.3, 12.2, and 18.6 micromol/L, respectively (P = .006). Steatosis correlated with the MTHFR polymorphism, homocysteinemia, HAI and fibrosis. Steatosis above 20% was significantly associated with fibrosis. Prevalence and high grade (>20%) of steatosis were 41% and 11% in CC, 61% and 49% in CT, and 79% and 64% in TT, respectively (P = .01). Relative risk of developing high levels of steatosis was 20 times higher for TT genotypes than CC genotypes. According to multivariate analysis, steatosis was independently associated with hyperhomocysteinemia (OR = 7.1), HAI (OR = 3.8), liver fibrosis (OR = 4.0), and HCV genotype 3 (OR = 4.6). On univariate analysis, fibrosis was associated with age, steatosis, MTHFR, homocysteinemia and HAI; however, on multivariate analysis, liver fibrosis was independently associated with age (P = .03), HAI (P = .0001), and steatosis (P = .007). In conclusion, a genetic background such as the MTHFR C677T polymorphism responsible for hyperhomocysteinemia plays a role in the development of higher degree of steatosis, which in turn accelerates the progression of liver fibrosis in CHC.

Diverse effects of natural antioxidants on cyclosporin cytotoxicity in rat renal tubular cells

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 muM 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-1 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.

A novel hyperthermostable 5′-deoxy-5′-methylthioadenosine phosphorylase from the archaeon Sulfolobus solfataricus

We report herein the first molecular characterization of 5'-deoxy-5'-methylthio-adenosine phosphorylase II from Sulfolobus solfataricus (SsMTAPII). The isolated gene of SsMTAPII was overexpressed in Escherichia coli BL21. Purified recombinant SsMTAPII is a homohexamer of 180 kDa with an extremely low Km (0.7 microm) for 5'-deoxy-5'-methylthioadenosine. The enzyme is highly thermophilic with an optimum temperature of 120 degrees C and extremely thermostable with an apparent Tm of 112 degrees C that increases in the presence of substrates. The enzyme is characterized by high kinetic stability and remarkable SDS resistance and is also resistant to guanidinium chloride-induced unfolding with a transition midpoint of 3.3 m after 22-h incubation. Limited proteolysis experiments indicated that the only one proteolytic cleavage site is localized in the C-terminal region and that the C-terminal peptide is necessary for the integrity of the active site. Moreover, the binding of 5'-deoxy-5'-methylthioadenosine induces a conformational transition that protected the enzyme against protease inactivation. By site-directed mutagenesis we demonstrated that Cys259, Cys261 and Cys262 play an important role in the enzyme stability since the mutants C259S/C261S and C262S show thermophilicity and thermostability features significantly lower than those of the wild-type enzyme. In order to get insight into the physiological role of SsMTAPII a comparative kinetic analysis with the homologous 5'-deoxy-5'-methylthioadenosine phosphorylase from Sulfolobus solfataricus (SsMTAP) was carried out. Finally, the alignment of the protein sequence of SsMTAPII with those of SsMTAP and human 5'-deoxy-5'-methylthioadenosine phosphorylase (hMTAP) shows several key residue changes that may account why SsMTAPII, unlike hMTAP, is able to recognize adenosine as substrate.

Olive oil hydroxytyrosol protects human erythrocytes against oxidative damages

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.

Oleuropein prevents oxidative myocardial injury induced by ischemia and reperfusion

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.

p21Cip1 gene expression is modulated by Egr1: a novel regulatory mechanism involved in the resveratrol antiproliferative effect

Epidemiological observations indicate that resveratrol, a natural antioxidant stilbene, exerts cardioprotective and chemopreventive effects. Moreover, the molecule induces in vitro cell growth inhibition and differentiation. Using human erythroleukemic K562 cells as model system, we demonstrated that resveratrol induces a remarkable gamma-globin synthesis, the erythroid differentiation being linked to impairment of cell proliferation, increased p21Cip1 expression and inhibition of cdk2 activity. The up-regulation of p21Cip1 transcription is prevented by cycloheximide, indicating the requirement of intermediate protein(s), which, in turn, regulate gene expression. The quantitative analysis of some transcription factors involved in the erythroid lineage, namely GATA-1, GATA-2, and Egr1, indicated that resveratrol selectively up-regulates Egr1 by an Erk1/2-dependent mechanism. The presence of an Egr1 consensus sequence in the p21Cip1 promoter suggested the hypothesis that this transcription factor directly regulates the expression of the cdk inhibitor. Transfection studies with deleted gene promoter constructs, as well as EMSA, pull-down, and chromatin immunoprecipitation experiments substantiated this view, demonstrating that Egr1 binds in vitro and in vivo to the identified consensus sequence of the p21Cip1 promoter. Moreover, an Egr1 phosphorothioate antisense hinders p21Cip1 accumulation and the antiproliferative effects of resveratrol. In conclusion, this is the first demonstration that Egr1 controls p21Cip1 expression by directly interacting with a specific sequence on its gene promoter. The identified regulatory mechanism also contributes to the clarification of the complex chemopreventive and antiproliferative properties of resveratrol.

Retinoic acid inhibits the growth of bone marrow mesenchymal stem cells and induces p27Kip1 and p16INK4A up-regulation

The importance of bone marrow mesenchymal stem cells in hemopoiesis has been definitely demonstrated. Thus, their impairment might cause profound alteration on production and maturation of blood cells. In the present paper, we investigated, for the first time, the effect of retinoic acid, an important antileukemic molecule, on the proliferation of primary cultures of human bone marrow mesenchymal stem cells. We demonstrated that retinoic acid, at a pharmacological concentration, hampers strongly the growth of the cells, without inducing osteoblastic differentiation. The analysis of cell division cycle machinery showed that the antiproliferative effect is associated with (i) the up-regulation of two cyclin-dependent kinase inhibitors, namely p27Kip1 and p16INK4A, and (ii) the down-regulation of cyclin-dependent kinase 2 activity and pRB phosphorylation. The reported findings represent novel insights into the antileukemic effects of the drug and contribute in clarifying the molecular mechanism of its pharmacological activity.

Purification and characterization of 5'-methylthioadenosine phosphorylase from the hyperthermophilic archaeon Pyrococcus furiosus: substrate specificity and primary structure analysis

5'-Methylthioadenosine phosphorylase (MTAP) was purified to homogeneity from the hyperthermophilic archaeon Pyrococcus furiosus. The protein is a homoexamer of 180 kDa. The enzyme is highly thermoactive, with an optimum temperature of 125 degrees C, and extremely thermostable, retaining 98% residual activity after 5 h at 100 degrees C and showing a half-life of 43 min at 130 degrees C. In the presence of 100 mM phosphate, the apparent T(m) (137 degrees C) increases to 139 degrees C. The enzyme is extremely stable to proteolytic cleavage and after incubation with protein denaturants, detergents, organic solvents, and salts even at high temperature. Thiol groups are not involved in the catalytic process, whereas disulfide bond(s) are present, since incubation with 0.8 M dithiothreitol significantly reduces the thermostability of the enzyme. N-Terminal sequence analysis of the purified enzyme is 100% identical to the predicted amino acid sequence of the gene PF0016 from the partially sequenced P. furiosus genome. The deduced amino acid sequence of the gene revealed a high degree of identity (52%) with human MTAP. Nevertheless, unlike human MTAP, MTAP from P. furiosus is not specific for 5'-methylthioadenosine, since it phosphorolytically cleaves adenosine, inosine, and guanosine. The calculated k(cat)/ K(m) values for 5'-methylthioadenosine and adenosine, about 20-fold higher than for inosine and guanosine, indicate that 6-amino purine nucleosides are preferred substrates of MTAP from P. furiosus. The structural features and the substrate specificity of MTAP from P. furiosus document that it represents a 5'-methylthioadenosine-metabolizing enzyme different from those previously characterized among Archaea, Bacteria, and Eukarya. The functional and structural relationships among MTAP from P. furiosus, human MTAP, and two putative MTAPs from P. furiosus and Sulfolobus solfataricus are discussed here for the first time.

Antioxidants induce different phenotypes by a distinct modulation of signal transduction

Antioxidants are known to exert a preventive activity against degenerative diseases. Here, we investigated the mechanism of action of three antioxidants: resveratrol, which causes differentiation of HL-60 cells, and hydroxytyrosol and pyrrolidine dithiocarbamate which, in the same model system, activate apoptosis. The expression profile of hydroxytyrosol-treated cells showed the up-regulation of several genes, including c-jun and egr1. Pyrrolidine dithiocarbamate activates both genes, while resveratrol increases uniquely egr1. A selective modulation of signalling pathway explained this finding. All antioxidants up-regulate Erk1/2, while only hydroxytyrosol and pyrrolidine dithiocarbamate activate c-Jun N-terminal kinase (JNK). Since JNK induces apoptosis by Bcl-2 phosphorylation, we investigated this event. Bcl-2 phosphorylation was increased by hydroxytyrosol and pyrrolidine dithiocarbamate and not by resveratrol. Our results indicate that the different phenotypical effects of antioxidants correlate with modulation of selective transduction pathways.

Protective effect of the phenolic fraction from virgin olive oils against oxidative stress in human cells

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.

Protein methylation as a marker of aspartate damage in glucose-6-phosphate dehydrogenase-deficient erythrocytes: role of oxidative stress

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.

Biocompatibility studies on biodegradable polyester-based composites of human osteoblasts: a preliminary screening

A series of biodegradable composites with natural hydroxyapatite, designed for possible use in orthopedics applications, were preliminarily screened for biocompatibility by employing primary cultures of human osteoblasts in a direct contact method. The cells were seeded at low density onto the materials under investigation and allowed to grow for 2 weeks. They then were analyzed for morphology, proliferation, viability, alkaline phosphatase activity (AP), osteocalcin (OC) production, and extracellular matrix mineralization. The results showed that all materials have good biocompatibility. Cell viability tests demonstrated that in all cases the values were comparable to the control, and the addition of hydroxyapatite always resulted in an enhancement of performance with respect to the plain polymer. AP and OC analysis confirmed that all composites allowed the expression of phenotypic markers. Scanning electron microscopy provided direct evidence of intense cell adhesion and proliferation on the tested materials.

Pharmacokinetics and metabolism of hydroxytyrosol, a natural antioxidant from olive oil

3,4-Dihydroxyphenylethanol (DOPET) is the major o-diphenol detectable in extra virgin olive oil, either in free or esterified form. Despite its relevant biological effects, mainly related to its antioxidant properties, little data have been reported so far on its toxicity and metabolism. The aim of the present work is to evaluate DOPET toxicity and to investigate its molecular pharmacokinetics by using the (14)C-labeled diphenol. When orally administered to rats, the molecule does not show appreciable toxicity up to 2 g/kg b.wt. To identify and quantify its metabolites, [(14)C]DOPET has been synthesized and intravenously injected in rats. The pharmacokinetic analysis indicates a fast and extensive uptake of the molecule by the organs and tissues investigated, with a preferential renal uptake. Moreover, 90% of the administered radioactivity is excreted in urine collected up to 5 h after injection, and about 5% is detectable in feces and gastrointestinal content. The characterization of the labeled metabolites, extracted from the organs and urine, has been performed by high-pressure liquid chromatography analysis. In all the investigated tissues, DOPET is enzymatically converted in four oxidized and/or methylated derivatives. Moreover, a significant fraction of total radioactivity is associated with the sulfo-conjugated forms, which also represent the major urinary excretion products. On the basis of the reported results, an intracellular metabolic pathway of exogenously administered DOPET, implying the involvement of catechol-O-methyltransferase, alcohol dehydrogenase, aldehyde dehydrogenase, and phenolsulfotransferase, has been proposed.

Metabolic consequences of hyperhomocysteinemia in uremia

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.

Genes modulated by histone acetylation as new effectors of butyrate activity

A wealth of evidence correlates the chemopreventive activity of a fiber-rich diet with the production of butyrate. In order to identify the genes transcriptionally modulated by the molecule, we analyzed the expression profile of butyrate-treated colon cancer cells by means of cDNA expression arrays. Moreover, the effect of trichostatin A, a specific histone deacetylase inhibitor, was studied. A superimposable group of 23 genes out of 588 investigated is modulated by both butyrate and trichostatin A. Among them, a major target was tob-1, a gene involved in the control of cell cycle. tob-1 is also up-regulated by butyrate in a neuroblastoma-derived cell line, and its overexpression in the colon cells caused growth arrest. Our findings represent an extensive analysis of genes modulated by butyrate and identify completely new effectors of its biological activities.

Plasma proteins containing damaged L-isoaspartyl residues are increased in uremia: implications for mechanism

BACKGROUND

Several 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.

METHODS

L-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.

RESULTS

The 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.

CONCLUSIONS

Plasma 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.

Diagnosis and follow-up of cystinuria: use of proton magnetic resonance spectroscopy

Proton Nuclear Magnetic Resonance (NMR) Spectroscopy of urine (as well as of other biological fluids) is a very powerful technique enabling multi-component analysis useful in both diagnosis and follow-up of a wide range of inherited metabolic diseases. Among these pathologies, cystinuria is characterised by accumulation in urine of four dibasic amino acids, namely lysine, arginine, ornithine and cystine; the last one, being only slightly water soluble, generates urolithiasis. The mentioned aminoacids can be detected in the urine NMR spectrum of cystinuric patients, the most abundant being the lysine (5 mM and over are often detected), whose typical signals become very high; arginine and ornithine are also usually detectable, although pathologic concentrations are lower (usually below 2mM). The proposed NMR technique is also suitable in monitoring the therapy with alpha-mercaptopropionylglycine (MPG), providing quantitation of several metabolites of interest in the follow-up of the pathology, like cystine, creatinine and citrate.

Hydroxytyrosol, a natural molecule occurring in olive oil, induces cytochrome c-dependent apoptosis

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.

Increased methyl esterification of altered aspartyl residues in erythrocyte membrane proteins in response to oxidative stress

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.

Transport mechanism and metabolism of olive oil hydroxytyrosol in Caco-2 cells

3,4-dihydroxyphenylethanol (hydroxytyrosol; DPE) is the major phenolic antioxidant present in extra virgin olive oil, either in a free or esterified form. Despite its relevant biological effects, no data are available on its bioavailability and metabolism. The aim of the present study is to examine the molecular mechanism of DPE intestinal transport, using differentiated Caco-2 cell monolayers as the model system. The kinetic data demonstrate that [(14)C]DPE transport occurs via a passive diffusion mechanism and is bidirectional; the calculated apparent permeability coefficient indicates that the molecule is quantitatively absorbed at the intestinal level. The only labelled DPE metabolite detectable in the culture medium by HPLC (10% conversion) is 3-hydroxy-4-methoxyphenylethanol, the product of catechol-O-methyltransferase; when DPE is assayed in vitro with the purified enzyme a K(m) value of 40 microM has been calculated.

Pyrrolidine dithiocarbamate induces apoptosis by a cytochrome c-dependent mechanism

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 microM 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.

Expression, purification, and characterization of recombinant S-adenosylhomocysteine hydrolase from the thermophilic archaeon Sulfolobus solfataricus

S-Adenosylhomocysteine hydrolase from Sulfolobus solfataricus was expressed in Escherichia coli by inserting the genomic fragment containing the gene encoding for S-adenosylhomocysteine hydrolase downstream the isopropyl-beta-d-thiogalactoside-inducible promoter of pTrc99A expression vector. An ATG positioned 25 bp upstream of the gene which is in frame with a stop codon was utilized as the initiation codon. This construct was used to transform E. coli RB791 and E. coli JM105 strains. The recombinant protein, purified by a fast and efficient two-step procedure (yield of 0.4 mg of enzyme per gram of cells), does not appear homogeneous on SDS-PAGE because of the presence of a protein contaminant corresponding to a "truncated" S-adenosylhomocysteine hydrolase subunit lacking the first 24 amino acid residues. The recombinant enzyme shows the same molecular mass, optimum temperature, and kinetic features of S-adenosylhomocysteine hydrolase isolated from S. solfataricus but it is less thermostable. To construct a vector which presents a correct distance between the ribosome-binding site and the start codon of S-adenosylhomocysteine hydrolase gene, a NcoI site was created at the translation initiation codon using site-directed mutagenesis. The expression of the homogeneous mutant S-adenosylhomocysteine hydrolase was achieved at high level (1.7 mg of mutant protein per gram of cells). The mutant S-adenosylhomocysteine hydrolase and the native one were indistinguishable in all physicochemical and kinetic properties including thermostability, indicating that the interactions involving the NH(2)-terminal sequence of the protein play a role in the thermal stability of S. solfataricus S-adenosylhomocysteine hydrolase.

p27Kip1 accumulation is associated with retinoic-induced neuroblastoma differentiation: evidence of a decreased proteasome-dependent degradation

Development of human neuroblastoma is due to an arrest in the differentiation program of neural crest sympathoadrenal progenitor cells. However, neuroblastomas, as well as their derived cell lines, maintain the potentiality of terminal differentiation. We investigated the molecular mechanisms by which retinoic acid, a molecule introduced in clinical trials for chemotherapy, induces differentiation in neuroblastoma cell lines. Our findings demonstrate that the retinoic acid-dependent growth arrest of LAN-5 neuroblastoma cell line is associated to a very large accumulation (>tenfold) of p27Kip1 protein, a cyclin-dependent kinase inhibitor; the protein binds and inhibits cyclin-dependent kinase 2, 4 and 6 activities, thus hampering pRb and p107 phosphorylation. p27Kip1 build-up was observable as an early phenomenon (12 - 24 h) after retinoic exposure and resulted in a time-dependent accumulation of high quantities of a free p27Kip1 form. Furthermore, retinoic treatment causes an increase of cyclin-dependent kinase 5 level and activity; however, immunoprecipitation studies proved the absence of interaction with p27kip1. No noticeable variation of other components of G1 phase cell cycle engine was observed. Pulse-chase experiments showed a remarkable elongation of p27Kip1 half-life in retinoic-treated LAN-5, while no enhancement of p27Kip1 gene expression and of the translational efficiency of its messenger RNA were demonstrated. In vivo degradation of p27Kip1 was sensitive to two highly specific proteasome inhibitors, LLnL and lactacystin, while the calpain inhibitor II ALLM and the cysteine protease inhibitor E64 did not modify the level of the protein. LLnL treatment caused a very rapid (2 h) build-up of the Cdk inhibitor content and the accumulation of higher molecular weight anti-p27Kip1 immunoreactive bands, which probably represent ubiquitinated forms of the protein. Finally, in vitro experiments demonstrated that extracts prepared from retinoic-treated LAN-5 cells degraded recombinant p27Kip1 at a rate remarkably slower than the untreated cells. Our results indicate that retinoic acid strongly increases p27Kip1 levels by down-regulating the ubiquitin-proteasome p27Kip1 degrading pathway.