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L Diomede

Publications and source records attributed to L Diomede.

At least 19 recordsLinked to original sources
PubMed2001

1,5-Benzodiazepine tricyclic derivatives exerting anti-inflammatory effects in mice by inhibiting interleukin-6 and prostaglandinE(2)production.

The 1,4- and the 1,5-benzodiazepines (BDZ) are commonly used as anxiolytic and anticonvulsive drugs. It has been suggested that they influence, particularly through stimulation of peripheral BDZ receptors, some immune cell properties such as pro-inflammatory cytokine production. The availability of a new class of [1,2,4]triazolo[4,3-a][1,5]benzodiazepine derivatives (compounds IV), endowed with anti-inflammatory and/or analgesic properties but no anti-pentylenetetrazole activity, prompted us to investigate in more detail the anti-inflammatory properties of three selected compounds IV (N,N-dimethyl-1-phenyl-4H-[1,2,4]triazolo[4,3-a][1,5]benz- odiazepin-5-amine; N,N-dibutyl-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepin-5-amine; 1-methyl-N,N-dimethyl-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepin-5-amine) and one structurally related compound (1-phenyl-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepin-5(6H)-one). These BDZ derivatives have lost their affinity for the central and peripheral BDZ receptors. The in vivo effect on leukocyte migration of these compounds was investigated by using the mouse air-pouch model of local inflammation. Compounds A and B, significantly inhibited the carrageenan-induced leukocyte recruitment in a dose-dependent manner starting from the dose of 50 mgkg(-1), whereas compound C was effective only at the higher dose of 100 mgkg(-1). Compound D did not exert such effects at any of the doses considered. The effect of compounds A, B and C on leukocyte recruitment was paralleled by a significant inhibition of interleukin-6 and prostaglandin E(2)production in the exudate, similarly to indomethacin, and by a partial reduction of vascular permeability. These features may be relevant for the design and development of innovative anti-inflammatory molecules among the 4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepin-5-amine derivatives.

Analgesics↗
PubMed2001

In vivo anti-inflammatory effect of statins is mediated by nonsterol mevalonate products.

This study set out to clarify whether the inhibition of sterol or nonsterol derivatives arising from mevalonate biotransformation plays a major role in the in vivo anti-inflammatory action of statins. Hepatic synthesis of all these derivatives was inhibited in mice by administered statins, whereas squalestatin inhibited only sterol derivatives. Using a short-term treatment schedule, we found that statins reduced the hepatic activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase without affecting blood cholesterol. This treatment inhibited lipopolysaccharide- and carrageenan-induced pouch leukocyte recruitment and the exudate production of interleukin-6, monocyte chemotactic protein-1, and RANTES. Coadministration of mevalonate reversed the effect of statin on leukocyte recruitment. The inhibition of sterol synthesis by squalestatin did not have any anti-inflammatory effect, indicating that the biosynthesis of nonsterol compounds arising from mevalonate is crucial for the in vivo regulation of cytokine and chemokine production by statins. Their inhibition by statins may account for the reported anti-inflammatory effects of these drugs and may provide a biochemical basis for the recently reported effects of statins in the prevention of cardiovascular disease and mortality.

Animals↗
PubMed2000

Inhibition of HMG-CoA reductase activity by hypercholesterolaemia reduces leukocyte recruitment and MCP-1 production.

To clarify the relationship between cholesterol homeostasis and inflammation we studied the effect of hypercholesterolaemia on in vivo cytokine production and leukocyte migration, in a murine model of local inflammation. Hypercholesterolaemia reduced of 40% the leukocyte recruitment by inhibiting interleukin-6 and monocyte chemotactic protein-1 production in the pouch exudate, without affecting vascular permeability or leukocytes motility.

Animals↗
PubMed2000

L-asparagine depletion and L-asparaginase activity in children with acute lymphoblastic leukemia receiving i.m. or i.v. Erwinia C. or E. coli L-asparaginase as first exposure.

PURPOSE: The present study was aimed at investigating L-asparaginase (L-ASE) activity (in plasma) and L-asparagine (L-ASN) depletion (in plasma and CSF) in children with newly diagnosed acute lymphoblastic leukemia (ALL) exposed for the first time to different L-ASE products. PATIENTS AND METHODS: During the induction treatment of the AIEOP ALL 95 study, 62 patients were treated with either Erwinase (n = 15), or E. coli medac (n = 47) L-ASE products, given either i.m. or i.v., at the standard dosage of 10,000 IU/m2, q 3 days x 8 (first exposure). RESULTS: Plasma and CSF L-ASN trough levels were undetectable in all cases, including those with L-ASE trough activity < 50 mU/ml. L-ASE trough activity during the administration of medac was however significantly higher when compared with that of Erwinase. CONCLUSIONS: L-ASN depletion after a first exposure to standard doses of Erwinase or medac is obtained in virtually all patients. No differences are seen between the I.M. or I.V. administration routes but the medac product is associated with a significantly higher enzyme activity in respect of Erwinase. L-ASN levels may be undetectable also in patients with L-ASE trough activity levels < 50 mU/ml, challenging the current opinion that an activity level of 100 mU/ml is needed to obtain L-ASN depletion.

Antineoplastic Agents↗
PubMed2000

Inhibition of monocyte chemotactic protein-1 synthesis by statins.

The beneficial effects of statins on the reduction of cardiovascular events has been partly attributed to their anti-inflammatory properties. In the complex of the different pathogenetic events leading to atherosclerosis, recent data suggest a central role of monocyte chemotactic protein-1 (MCP-1), because mice knock-out for MCP-1 or its receptor CC-chemokine receptor 2 were considerably resistant to plaque formation. In this study we investigated the effect of different statins on in vitro and in vivo production of MCP-1. Lovastatin and simvastatin caused a dose-dependent inhibition of MCP-1 production in peripheral blood mononuclear cells exposed to lipopolysaccharide or inactivated Streptococcus hemoliticus and in human endothelial cells exposed to interleukin-1beta. The addition of mevalonate overrode the inhibitory effect of statins indicating that mevalonate-derived products are important for chemokine production. The in vivo anti-inflammatory effect of statins was investigated using the mouse air-pouch model of local inflammation. Lovastatin and pravastatin were orally administered to mice according to a treatment schedule that significantly inhibited the hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activity without affecting total blood cholesterol. At the dose of 10 mg/kg, lovastatin and pravastatin reduced by approximately 50% the lipopolysaccharide-induced leukocytes recruitment and the exudate MCP-1 production. In conclusion, statins, by inhibiting mevalonate-derived products, reduced both in vitro and in vivo the production of chemokines involved in leukocyte migration, and this effect is unrelated to their cholesterol-lowering action.

Cells, Cultured↗
PubMed1999

Oleamide-mediated sleep induction does not depend on perturbation of membrane homeoviscosity.

To verify whether the sleep-inducing properties of oleamide were related to its ability to perturb membrane homeoviscosity, affecting 5-HT(2A) receptors, we compared the effects of oleamide and oleic acid, the latter lacking both the sleep-inducing effect and the action on 5-HT(2A) receptors. In binding studies the two compounds did not directly interact with rat brain cortex 5-HT(2A) receptors, nor did they increase the affinity of a 5-HT(2A) agonist, either in vitro or ex vivo. They had similar fluidizing effects, in vitro at high concentrations (>/=10 microM), and ex vivo after a dose of 100 mg/kg, and they reduced locomotor activity with similar potency. There thus appears to be no causal relationship between the fluidizing effects of oleamide and its sleep-inducing properties.

Animals↗
PubMed1999

Alteration of SREBP activation in liver of trisomy 21 fetuses.

We previously reported that trisomy 21 (T21) fetuses have an intrinsic lipid metabolism abnormality resulting in higher serum cholesterol levels than their matched controls. In an attempt to clarify the biochemical basis of this derangement we analyzed the liver cholesterol levels and activation of the sterol regulatory element binding proteins SREBP-1 and SREBP-2. We report here for the first time that SREBP-1 and SREBP-2 are present in human fetal liver and their activation follows a different regulatory pattern. Moreover T21 fetuses show a peculiar pattern of SREBP activation which, at variance from control fetuses, involves sterol-independent maturation of SREBP-1. Multiple defects accompanied the lipid derangement in T21, resulting in high circulating and tissue cholesterol. This may serve as an early biochemical marker of an unknown, possibly genetically determined mechanism, whose consequence on lipid homeostasis during postnatal and adult life is still not understood.

Blotting, Western↗
PubMed1999

Hypericum perforatum L. extract does not inhibit 5-HT transporter in rat brain cortex.

The hydroalcoholic extract of Hypericum perforatum L. is an effective antidepressant, although its mechanism of action is still unknown. It inhibits the synaptosomal uptake of serotonin (5-HT), dopamine and noradrenaline, suggesting a biochemical mechanism similar to the synthetic standard antidepressants. In the present study, further investigating this hypothesis, we confirmed that a hydromethanolic extract of H. perforatum inhibited [3H]5-HT accumulation in rat brain cortical synaptosomes with an IC50 value of 7.9 microg/ml. The IC50 of pure hyperforin was 1.8 microg/ml, so the activity of the total extract is not related only to its hyperforin content (<5%). This inhibitory effect, however, is not due to a direct interaction with, and blockade of, the 5-HT transporters since the extract, like hyperforin, did not inhibit [3H]citalopram binding (IC50 > 100 microg/ml and 10 microg/ml, respectively). We also found that 3-10 microg/ml of the extract, or 0.3-1 microg/ml hyperforin, induced marked tritium release from superfused synaptosomes previously loaded with [3H]5-HT. The releasing effect of the extract resembles the releasing effect of a reserpine-like compound (Ro 04-1284), i.e. it was slightly delayed and was 5-HT carrier- and calcium-independent. These data suggest that the hydromethanolic extract of H. peforatum, similarly to Ro 04-1284, rapidly depletes storage vesicles, raising the cytoplasmic concentration of 5-HT, and this increase is presumably responsible for the apparent inhibition of [3H]5-HT uptake. Therefore, our in vitro data do not confirm that the hydromethanolic extract of H. perforatum acts as a classical 5-HT uptake inhibitor but indicate reserpine-like properties. However, the concentrations of the active component(s) effective in vitro as reserpine-like agent(s) (i.e. corresponding to > or =3 microg/ml of the hydromethanolic extract) do not seem to be achieved in the brain after pharmacologically effective doses of the extract, as indicated by the finding that there were no significant changes of rat brain 5-HT and 5-hydroxyindoleacetic acid levels after a schedule of treatment (3 x 300 mg/kgday, orally) active in an animal model predictive of antidepressant-like activity. These data also suggest that the antidepressant effect of H. perforatum extracts is unlikely to be associated with interaction with GABA, benzodiazepine and 5-HT1 receptors since, in receptor binding studies, we found IC50 values higher than 5 microg/ml. Therefore other, still unknown, mechanisms are possibly involved in H. perforatum antidepressant effects.

Animals↗
PubMed1998

Rapid solid-phase extraction method for automated gas chromatographic-mass spectrometric determination of nicotine in plasma.

The aim of this study was to develop a simple, rapid and sensitive assay of nicotine in plasma for automated gas chromatographic-mass spectrometric analysis. Biological samples were extracted using pre-packed Extrelut-1 columns with 5 ml of ethyl acetate. Quantitative analysis was done using deuterium-labelled nicotine as internal standard. The limit of quantitation was 0.5 ng in 1-ml plasma samples. Precision was ranging from 13.3% to 1.64% (R.S.D.) depending on the concentration, while the deviation was 4.16%. This method has been used for determination of nicotine bioavailability from new, low-dosage, nicotine chewing gum strips.

Adult↗
PubMed1998

Kupffer cell depletion partially prevents hepatic heme oxygenase 1 messenger RNA accumulation in systemic inflammation in mice: role of interleukin 1beta.

The heme oxygenase 1 (HO-1) gene is rapidly activated in the liver after lipopolysaccharide (LPS) treatment. Ninety minutes after LPS treatment (0.1 mg/kg, intraperitoneally) hepatic HO-1 messenger RNA (mRNA) of mice was 40 times the control value. To investigate the hepatic cellular source of the increased HO-1 transcript, we treated mice with LPS and galactosamine (700 mg/kg, intraperitoneally), a selective transcriptional inhibitor of hepatocytes. Galactosamine prevented the LPS-mediated increase of HO-1 mRNA in the liver, indicating that hepatocytes are the main cell type in which HO-1 mRNA accumulates after LPS treatment. We then tested in vitro and in vivo the hypothesis that LPS-mediated hepatic accumulation of HO-1 mRNA is caused by intercellular communication between Kupffer cells and hepatocytes. Isolated rat hepatocytes showed an increase in HO-1 mRNA compared with controls after 90 minutes of exposure to a LPS stimulated Kupffer cell-conditioned medium. This suggests that soluble mediators from Kupffer cells were responsible for this effect. To study the role of Kupffer cells in vivo, we treated mice with Kupffer cell-inactivating or -depleting agents and LPS. Gadolinium chloride and liposome-encapsulated dichloromethylene diphosphonate lowered LPS-mediated HO-1 mRNA accumulation (by about 50%); in these groups hepatic levels of interleukin (IL)-1beta were decreased, by more than 75%. Methylpalmitate hardly affected hepatic HO-1 mRNA accumulation or IL-1beta content after LPS treatment. There was no relationship between HO-1 mRNA and serum TNF or IL-6 levels. These results suggest that LPS-mediated hepatic HO-1 mRNA accumulation is a hepatocyte response partly caused by soluble mediators, particularly IL-1beta, released from Kupffer cells.

Animals↗
PubMed1997

A neurotoxic and gliotrophic fragment of the prion protein increases plasma membrane microviscosity.

Prion-related encephalopathies are characterized by astrogliosis and nerve cell degeneration and loss. These lesions might be the consequence of an interaction between the abnormal isoform of the cellular prion protein that accumulates in nervous tissue and the plasma membranes. Previously we found that a synthetic peptide, homologous to residues 106-126 of the human prion protein, is fibrillogenic and toxic to neurons and trophic to astrocytes in vitro. This study dealt with the ability of the peptide to interact with membranes. Accordingly, we compared PrP 106-126 with different synthetic PrP peptides (PrP 89-106, PrP 127-147, a peptide with a scrambled sequences of 106-126, and PrP 106-126 amidated at the C-terminus) as to the ability to increase the microviscosity of artificial and natural membranes. The first three had no effect on nerve and glial cells in vitro, whereas the amidated peptide caused neuronal death. Using a fluorescent probe that becomes incorporated into the hydrocarbon core of the lipid bilayer and records the lipid fluidity, we found PrP 106-126 able to increase significantly the membrane microviscosity of liposomes and of all cell lines investigated. This phenomenon was associated with the distribution of the peptide over the cell surface, but not with changes in the membrane lipid or protein content, or with membrane lipid phase transitions. Accordingly, we deduced that increased membrane microviscosity was unrelated to changes in the membrane native components and was the result of increased lipid density following PrP 106-126 embedding into the lipid bilayer. No control peptides had comparable effects on the membrane microviscosity, except PrP 106-126 amidated at the C-terminus. Since the latter was as neurotoxic, but not as fibrillogenic, as PrP 106-126, we argued that the ability of PrP 106-126 to increase membrane microviscosity was unrelated to the propensity of the peptide to raise fibrils. Rather, it could be connected with the primary structure of PrP 106-126, characterized by two opposing regions, one hydrophilic and the other hydrophobic, that enabled the peptide to interact with the lipid bilayer. Based on these findings, we speculated that the glial and nerve cell involvement occurring in prion-related encephalopathies might be caused by the interaction with the plasma membrane of a PrP 106-126-like fragment or of the sequence spanning residues 106-126 of the abnormal isoform of the prion protein.

Amino Acid Sequence↗
PubMed1996

Activation effects of a prion protein fragment [PrP-(106-126)] on human leucocytes.

Prion-related encephalopathies are characterized by the intracerebral accumulation of an abnormal isoform of the cellular prion protein (PrPC) named scrapie prion protein (PrPSc). The pathological forms of this protein and its cellular precursor are not only expressed in the brain but also, at lower concentrations, in peripheral tissues. We recently showed that a synthetic peptide corresponding to residues 106-126 [PrP-(106-126)] of the human PrP is toxic to neurons and trophic to astrocytes in vitro. Our experiments were aimed at verifying whether PrP-(106-126) and other peptides corresponding to fragments of the amyloid protein purified from brains of patients with Gerstmann-Sträussler-Scheinker disease-namely PrP-(89-106), PrP-(106-114), PrP-(127-147)-were capable of stimulating circulating leucocytes. Native PrP expression in human lymphocytes, monocytes and neutrophils was first confirmed using PCR amplification of total RNA, after reverse transcription, and immunoblot analysis of cell extracts with anti-PrP antibodies. PrP-(106-126), but not the other peptides, increased membrane microviscosity, intracellular Ca2+ concentration and cell migration in circulating leucocytes, and O2-. production in monocytes and neutrophils. Membrane microviscosity was determined by the fluorescence polarization technique, using diphenylhexatriene as a probe, 300 s after the addition of PrP-(106-126) to the cell suspension in the concentration range 5-50 microM. The increase in intracellular Ca2+ elicited by PrP-(106-126) was dose-dependent in the range 5-500 microM. PrP-(106-126) stimulated O2-. production in monocytes and neutrophils in a dose- (10-300 microM) and time-(5-30 min) dependent manner in the presence of 10 microM dihydrocytochalasin B. Both the increase in Ca2+ concentration and the O2-. production were partially sensitive to pertussis toxin. PrP-(106-126) stimulated leucocyte migration in a dose-dependent (30-300 microM) manner and, at the highest concentration used, this migration was comparable with that elicited by 2.5 nM interleukin 8 or 10 nM fMet-Leu-Phe peptide.

Actins↗
PubMed1996

Potentials of liposomes in diagnosis and treatment of pulmonary metastases: an experimental study in the rat.

OBJECTIVE: The ultimate goal of the therapy of lung metastases is to destroy all malignant cells while sparing normal ones. Liposomes represent a novel approach for the selective transport of tracers and therapeutic agents to cancer cells because of their flexibility, low toxicity, wide range of possible variants, simplicity to make, and because agents can be entrapped in them in their native states in large amounts. We have studied the biodistribution of "Stealth" liposomes in the experimental model of lung metastases in the rat. METHODS: The secondaries were induced by i.v. injection 20. 10(6) cancer cells (DHD/K12/TRb line) in BD-IX rats. The study of the liposome biodistribution in the rat was carried out by the use of unilamellar liposomes with homogeneous size distribution (0.1 microns), the liposomes were labeled with Cholesteryl-Bodipy. The rats were sacrificed at scheduled times after the injection; blood, urine, metastatic and healthy lung, colon, liver and spleen were analysed by a microcytofluorimetric examination. RESULTS: Liposomes prolonged the circulation time of Cholesteryl-Bodipy. Only spleen and lung metastases exhibited an accretion of fluorescent liposomes. CONCLUSIONS: The biodistribution of such formulation of liposomes in rats with lung metastases, may be of considerable importance in diagnosis and therapy of the secondaries, for increasing the concentration of tracers and therapeutic agents in tumor tissue while minimizing the likelihood of aspecific distribution and toxicity to non target tissue.

Adenocarcinoma↗
PubMed1996

Placental transfer of valproic acid after liposome encapsulation during in vitro human placenta perfusion.

Valproic acid (VPA) is an antiepileptic drug that crosses the placenta freely. Because its use in pregnancy is associated with an increased incidence of fetal malformation and toxic effects, this study was designed to check whether the placental transfer of VPA entrapped in liposomes was reduced. VPA was encapsulated in dehydrated-rehydrated liposomes prepared with equimolar concentrations of phosphatidylcholine, cholesterol and alpha-tocopherol. Liposomes were analyzed for their physicochemical characteristics, their stability and percentage of encapsulation of VPA. A system of dual perfusion of an isolated lobule of term human placenta was used. Six placentas were perfused with liposome-VPA and six with free VPA for 180 min using recirculating maternal and fetal circuits. The rate of transfer and time to reach equilibrium of VPA was similar in placentas perfused with free VPA and with liposome-encapsulated VPA. Liposomes significantly reduced VPA transplacental transfer and placental uptake. This was confirmed by FMM at equilibrium, that was 0.548 +/- 0.058 in free VPA and 0.393 +/- 0.075 in liposome-VPA. The ratio of fetal to maternal concentrations at equilibrium was 0.90 +/- 0.10 in controls and 0.66 +/- 0.13 in liposome-VPA. The amount of VPA recovered in fetal circulation and in placental tissue were 28 +/- 4 and 7 +/- 3% in controls and 19 +/- 4 and 3 +/- 2% in liposome-VPA. In conclusion, our data indicate that encapsulating VPA in liposomes significantly reduces the fetal amount and exposure, and further in vitro and in vivo investigations are needed to optimize the use of liposomes, particularly in pregnancy.

Anticonvulsants↗
PubMed1995

Phosphatidic acid and lysophosphatidic acid induce haptotactic migration of human monocytes.

The present study was aimed at defining the chemotactic activity of phosphatidic acid, which is rapidly produced by phagocytes in response to chemotactic agonists. Exogenously added phosphatidic acid induced human monocyte directional migration across polycarbonate filters with an efficacy (number of cell migrated) comparable to that of "classical" chemotactic factors. In lipid specificity studies, activity of phosphatidic acid decreased with increasing acyl chain length but was restored by introducing unsaturation in the acyl chain with the most active form being the natural occurring 18:0,20:4-phosphatidic acid. Lysophosphatidic acid was also active in inducing monocyte migration. No other phospholipid and lysophospholipid tested was effective in this response. Monocyte migration was regulated by a gradient of phosphatidic acid and lysophosphatidic acid bound to the polycarbonate filter, in the absence of detectable soluble chemoattractant. Migration was also observed if phospholipids were bound to fibronectin-coated polycarbonate filters. Thus, phosphatidic acid and lysophosphatidic acid, similarly to other physiological chemoattractants (e.g. C5a and interleukin-8), induce cell migration by an haptotactic mechanism. Phosphatidic acid caused a rapid increase of filamentous actin and, at higher concentrations, induced a rise of intracellular calcium concentration. Monocyte migration to phosphatidic acid and lysophosphatidic acid, but not to diacylglycerol, was inhibited in a concentration-dependent manner by Bordetella pertussis toxin, while cholera toxin was ineffective. In the chemotactic assay, phosphatidic acid and lysophosphatidic acid induced a complete homologous desensitization and only partially cross-desensitized one with each other, or with diacyl-glycerol and monocyte chemotactic protein-1. Suramine inhibited monocyte chemotaxis with a different efficiency phosphatidic acid > lysophosphatidic acid" diacyl-glycerol On the contrary, monocyte chemotactic protein-1-induced chemotaxis was not affected by the drug. Collectively, these data show that phosphatidic acid induces haptotactic migration of monocytes that is at least in part receptor-mediated. These results support a role for phosphatidic acid and lysophosphatidic acid in the regulation of leukocyte accumulation into tissues.

Actins↗
PubMed1994

The induction of apoptosis is a common feature of the cytotoxic action of ether-linked glycerophospholipids in human leukemic cells.

The ability of 2 recent ether-lipid derivatives, aza-phospholipids BN52205 and BN52211, to induce apoptosis in different leukemia cell lines was investigated using I-octadecyl-2-methyl-rac-glycero-3- phosphocholine (ET-18-OCH3) as a positive control. HL60, K562, Molt-4 and U937 cells were exposed for 24 hr to 20 microM of drug. The 2 aza-derivatives were as cytotoxic as ET-18-OCH3: BN52205 and BN52211 selectively induced apoptotic death in HL60, Molt-4 and U937 cells, but not in the K562-resistant cell line. Around 50% of DNA was fragmented in HL60 cells after exposure to the aza-derivatives, and 34% and 20% of DNA was fragmented in Molt-4 and U937 cells respectively. Similar results were obtained when cells were exposed to ET-18-OCH3. Our data confirm that ether lipids induce apoptosis in a variety of human leukemic cells, providing a possible explanation for their selectivity and mechanism of action.

Antineoplastic Agents↗
PubMed1994

Conformational polymorphism of the amyloidogenic and neurotoxic peptide homologous to residues 106-126 of the prion protein.

Prion-related encephalopathies are characterized by cerebral accumulation of a post-translationally modified form of the cellular prion protein (PrPC), designated PrPSc. Evidence suggests that the conversion from PrPC to PrPSc involves changes in the secondary structure leading to an increase in beta-sheet content. We have previously shown that a synthetic peptide homologous to residues 106-126 of human PrP, belonging to a predicted alpha-helical domain, exhibits a beta-sheet conformation, forms amyloid-like fibrils, and is neurotoxic in vitro. The present study investigated how different chemicophysical conditions such as pH and ionic strength or a membrane-like environment influenced the secondary structure of this peptide. PrP 106-126 exhibited a predominantly beta-sheet structure in 200 mM phosphate buffer, pH 5.0, but a combination of beta-sheet and random coil structure in 200 mM phosphate buffer, pH 7.0, or in deionized water. The addition of trifluoroethanol (50% final concentration) to solutions of peptide in deionized water induced the appearance of an alpha-helical secondary structure, but did not modify the beta-sheet conformation of the peptide dissolved in 200 mM phosphate buffer, pH 5.0. In the presence of micelles formed by a 5% solution of sodium dodecyl sulfate, PrP 106-126 showed a high content of alpha-helix. When the peptide was dissolved in 5 mM phosphate buffer, pH 7.4, and incubated with liposomes, it changed from a prevalently random coil structure to a beta-sheet conformation. The environment-dependent conformational polymorphism of PrP 106-126 and its marked tendency to form stable beta-sheet structures at acidic pH could account for the shift from alpha-helix to beta-sheet associated with the conversion of PrPC to PrPSc, which occurs most likely in the endosomal-lysosomal compartment.

Amino Acid Sequence↗