Lipid-Derived Aldehydes Accelerate Light Chain Amyloid and Amorphous Aggregation

Inhibitory Effects of Six Types of Tea on Aging and High-Fat Diet-Related Amyloid Formation Activities

Aging and lipid metabolism disorders promote the formation and accumulation of amyloid with β-sheet structure, closely related to cardiovascular disease, senile dementia, type 2 diabetes, and other senile degenerative diseases. In this study, five representative teas were selected from each of the six types of tea, and a total of 30 teas were selected to evaluate the inhibitory activities on the formation of aging-related amyloid in vitro. The results showed that the 30 teas had a significant inhibitory effect on the formation activity on aging-related amyloid at the protein level in vitro. Although the content of catechins is relatively low, black tea and dark tea still have significant antioxidant activity and inhibit the formation of amyloid. A high-fat diet established the model of lipid metabolism disorder in premature aging SAMP8 mice, and these mice were gavaged different tea water extracts. The results showed that different tea types have a significant inhibitory effect on the formation of β-amyloid and Aβ42 mediated by age-related lipid metabolism disorders, and the in vivo activity of fully fermented teas was better than that of green tea. The action mechanism was related to antioxidation, anti-inflammatory, and improving lipid metabolism.

Atherogenic oxoaldehyde of cholesterol induces innate immune response in monocytes and macrophages

Cholesterol oxidation product, 3β-hydroxy-5-oxo-5,6-secocholestan-6-al (cholesterol 5,6-secosterol, ChSeco or Atheronal-A), formed at inflammatory sites, has been shown to promote monocyte differentiation into macrophages and cause elevated expression of macrophage scavenger receptors. Since inflammation is a key event at all stages of atherosclerotic plaque formation, the pro-inflammatory actions of ChSeco in human THP-1 monocytes and mouse J774 macrophages were investigated in the present study by employing ELISA, qRT-PCR, and functional assays. An increase in the secretion of interleukin-8 and platelet-derived growth factor (PDGF) isoform AA and, to a limited extent, PDGF isoform BB was observed into the culture medium of THP-1 monocytes exposed to ChSeco. However, no changes were seen in the secretion of tumor necrosis factor-alpha. In J774 macrophages treated with ChSeco, there was an upregulation of gene expression of several pro-inflammatory cytokines and their receptors. Concomitantly, there was down-regulation of gene expression of interleukin-1ß, interleukin-10, and lymphotoxin-beta. An increase in the release of interleukin-18 and chemokine (C-C motif) ligand-20 from J774 macrophages (which corroborated well with their gene expression profiles) and increased binding of THP-1 monocytes to ChSeco-exposed human aortic endothelial cells were observed. The results of the present study, for the first time, demonstrate the pro-inflammatory action of ChSeco and suggest the underlying pro-atherogenic mechanisms. These could be mediated through enhanced monocyte recruitment into the sub-endothelial space and subsequent proliferation of smooth muscle cells under the influence of monocyte-derived PDGF.

Site-Specific Alkylation of the Islet Amyloid Polypeptide Accelerates Self-Assembly and Potentiates Perturbation of Lipid Membranes

The accumulation of insoluble amyloids in the pancreatic islets is a pathological hallmark of type II diabetes and correlates closely with the loss of β-cell mass. The predominant component of these amyloid deposits is the islet amyloid polypeptide (IAPP). The factors contributing to the conversion of IAPP from a monomeric bioactive peptide hormone into insoluble amyloid fibrils remain partially elusive. In this study, we investigated the effect of the oxidative non-enzymatic post-translational modification induced by the reactive metabolite 4-hydroxynonenal (HNE) on IAPP aggregation and cytotoxicity. Incubation of IAPP with exogenous HNE accelerated its self-assembly into β-sheet fibrils and led to the formation of a Michael adduct on the His-18 side chain. To model this covalent modification, the imidazole N(π) position of histidine was alkylated using a close analogue of HNE, the octyl chain. IAPP lipidated at His-18 showed a hastened random coil-to-β-sheet conformational conversion into fibrillar assemblies with a distinct morphology, a low level of binding to thioflavin T, and a high surface hydrophobicity. Introducing an octyl chain on His-18 enhanced the ability of the peptide to perturb synthetic lipid vesicles, to permeabilize the plasma membrane, and to induce the death of pancreatic β-cells. Alkylated IAPP triggered the self-assembly of unmodified IAPP by prompting primary nucleation and increased its capacity to perturb the plasma membrane, indicating that only a small proportion of the modified peptide is necessary to shift the balance toward the formation of proteotoxic species. This study underlines the importance of studying IAPP post-translational modifications induced by oxidative metabolites in the context of pancreatic amyloids.

Electrophilic oxysterols: generation, measurement and protein modification

Cholesterol is an essential component of mammalian plasma membranes. Alterations in sterol metabolism or oxidation have been linked to various pathological conditions, including cardiovascular diseases, cancer, and neurodegenerative disorders. Unsaturated sterols are vulnerable to oxidation induced by singlet oxygen and other reactive oxygen species. This process yields reactive sterol oxidation products, including hydroperoxides, epoxides as well as aldehydes. These oxysterols, in particular those with high electrophilicity, can modify nucleophilic sites in biomolecules and affect many cellular functions. Here, we review the generation and measurement of reactive sterol oxidation products with emphasis on cholesterol hydroperoxides and aldehyde derivatives (electrophilic oxysterols) and their effects on protein modifications.

Modification of proteins by reactive lipid oxidation products and biochemical effects of lipoxidation

Lipid oxidation results in the formation of many reactive products, such as small aldehydes, substituted alkenals, and cyclopentenone prostaglandins, which are all able to form covalent adducts with nucleophilic residues of proteins. This process is called lipoxidation, and the resulting adducts are called advanced lipoxidation end products (ALEs), by analogy with the formation of advanced glycoxidation end products from oxidized sugars. Modification of proteins by reactive oxidized lipids leads to structural changes such as increased β-sheet conformation, which tends to result in amyloid-like structures and oligomerization, or unfolding and aggregation. Reaction with catalytic cysteines is often responsible for the loss of enzymatic activity in lipoxidized proteins, although inhibition may also occur through conformational changes at more distant sites affecting substrate binding or regulation. On the other hand, a few proteins are activated by lipoxidation-induced oligomerization or interactions, leading to increased downstream signalling. At the cellular level, it is clear that some proteins are much more susceptible to lipoxidation than others. ALEs affect cell metabolism, protein-protein interactions, protein turnover via the proteasome, and cell viability. Evidence is building that they play roles in both physiological and pathological situations, and inhibiting ALE formation can have beneficial effects.

Understanding Mesangial Pathobiology in AL-Amyloidosis and Monoclonal Ig Light Chain Deposition Disease

Patients with plasma cell dyscrasias produce free abnormal monoclonal Ig light chains that circulate in the blood stream. Some of them, termed glomerulopathic light chains, interact with the mesangial cells and trigger, in a manner dependent of their structural and physicochemical properties, a sequence of pathological events that results in either light chain–derived (AL) amyloidosis (AL-Am) or light chain deposition disease (LCDD). The mesangial cells play a key role in the pathogenesis of both diseases. The interaction with the pathogenic light chain elicits specific cellular processes, which include apoptosis, phenotype transformation, and secretion of extracellular matrix components and metalloproteinases. Monoclonal light chains associated with AL-Am but not those producing LCDD are avidly endocytosed by mesangial cells and delivered to the mature lysosomal compartment where amyloid fibrils are formed. Light chains from patients with LCDD exert their pathogenic signaling effect at the cell surface of mesangial cells. These events are generic mesangial responses to a variety of adverse stimuli, and they are similar to those characterizing other more frequent glomerulopathies responsible for many cases of end-stage renal disease. The pathophysiologic events that have been elucidated allow to propose future therapeutic approaches aimed at preventing, stopping, ameliorating, or reversing the adverse effects resulting from the interactions between glomerulopathic light chains and mesangium.

Intensification of serum albumin amyloidogenesis by a glycation-peroxidation loop (GPL)

The interaction of reducing sugars with proteins leads to the formation of advanced glycation end products (AGE) and reactive oxidative species (ROS). ROS peroxidise free or membrane included unsaturated fatty acids, leading to generate reactive aldehydes as advanced lipid peroxidation end products (ALE). Aldehydes from lipid peroxidation (LPO) react with proteins to cause alteration of protein structure to exacerbate complication of diseases. Here we studied serum albumin glycation in the presence and absence of liposomes as a bio-membrane model to investigate protein structural changes using various techniques including intrinsic and extrinsic fluorescence spectroscopies and electron microscopy analysis. Accordingly, serum albumin glycation and fibrillation were accelerated and intensified in the presence of liposomes through a hypothesized glycation-peroxidation loop (GPL). Together, our results shed light on the necessity of reconsidering diabetic protein glycation to make it close to physiological conditions mimicry, more importantly, proteins structural change due to diabetic glycation is intensified in the proximity of cell membranes which probably potentiates programmed cell death distinct from apoptosis.

Effects of diets enriched in linoleic acid and its peroxidation products on brain fatty acids, oxylipins, and aldehydes in mice

BACKGROUND

Linoleic acid (LA) is abundant in modern industrialized diets. Oxidized LA metabolites (OXLAMs) and reactive aldehydes, such as 4-hydroxy-2-nonenal (4-HNE), are present in heated vegetable oils and can be endogenously synthesized following consumption of dietary LA. OXLAMs have been implicated in cerebellar degeneration in chicks; 4-HNE is linked to neurodegenerative conditions in mammals. It unknown whether increasing dietary LA or OXLAMs alters the levels of oxidized fatty acids (oxylipins), precursor fatty acids, or 4-HNE in mammalian brain.

OBJECTIVES

To determine the effects of increases in dietary OXLAMs and dietary LA, on levels of fatty acids, oxylipins, and 4-HNE in mouse brain tissues.

METHODS

Mice (n = 8 per group) were fed one of three controlled diets for 8 weeks: (1) a low LA diet, (2) a high LA diet, or (3) the low LA diet with added OXLAMs. Brain fatty acids, oxylipins, and 4-HNE were quantified in mouse cerebellum and cerebral cortex by gas chromatography-flame ionization detection, liquid chromatography-tandem mass spectrometry, and immunoblot, respectively.

RESULTS

Increasing dietary LA significantly increased omega-6 fatty acids, decreased omega-3 fatty acids, and increased OXLAMs in brain. Dietary OXLAMs had minimal effect on oxidized lipids but did decrease both omega-6 and omega-3 fatty acids. Neither dietary LA nor OXLAMs altered 4-HNE levels.

CONCLUSION

Brain fatty acids are modulated by both dietary LA and OXLAMs, while brain OXLAMs are regulated by endogenous synthesis from LA, rather than incorporation of preformed OXLAMs.

Biochemical properties of cholesterol aldehyde secosterol and its derivatives

Elevated levels of cholesterol aldehyde, 3β-hydroxy-5-oxo-5,6-secocholestan-6-al (secosterol-A, also called 5,6-secosterol), and its aldolization product (secosterol-B) have been detected in human atherosclerotic plaques and tissues samples of brains affected by neurodegeneration, such as Alzheimer’s disease and Lewy body dementia suggesting that increased formation of these compounds may be associated with inflammation-related diseases. Secosterol-A and secosterol-B, and also further oxidized products seco-A-COOH and seco-B-COOH induce several pro-inflammatory activities in vitro. Accumulating evidences demonstrate that the covalent bindings of these secosterols to target proteins seem to be critical to trigger their pro-inflammatory activities. One of the molecular mechanisms of protein adduct formations is that aldehydic function of secosterol-A and secosterol-B is reactive and form Schiff bases with ε- or N-terminal amino groups of proteins. In other cases, it is recently suggested that Michael acceptor moiety formed by the dehydration of not only secosterol-A and secosterol-B but also seco-A-COOH may react with nucleophilic site on target proteins. In this review, I summarize and provide an overview of formation mechanism of secosterols in in vitro and in vivo, patho- or physiological concentrations in biological and clinical samples, and molecular mechanisms of pro-inflammatory activities of secosterols.

Protein lipid modifications--More than just a greasy ballast

Covalent lipid modifications of proteins are crucial for regulation of cellular plasticity, since they affect the chemical and physical properties and therefore protein activity, localization, and stability. Most recently, lipid modifications on proteins are increasingly attracting important regulatory entities in diverse signaling events and diseases. In all cases, the lipid moiety of modified proteins is essential to allow water-soluble proteins to strongly interact with membranes or to induce structural changes in proteins that are critical for elemental processes such as respiration, transport, signal transduction, and motility. Until now, roughly about ten lipid modifications on different amino acid residues are described at the UniProtKB database and even well-known modifications are underrepresented. Thus, it is of fundamental importance to develop a better understanding of this emerging and so far under-investigated type of protein modification. Therefore, this review aims to give a comprehensive and detailed overview about enzymatic and nonenzymatic lipidation events, will report their role in cellular biology, discuss their relevancy for diseases, and describe so far available bioanalytical strategies to analyze this highly challenging type of modification.

Polyols (Glycerol and Ethylene glycol) mediated amorphous aggregate inhibition and secondary structure restoration of metalloproteinase-conalbumin (ovotransferrin)

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Conalbumin aggregates at 65 °C and denaturation occur at above this temperature.

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The nature of aggregates was identified as amorphous.

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The polyols inhibits the aggregation of conalbumin via protecting the secondary structure.

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Glycerol is found to be more protective than ethylene glycol.

Under physical or chemical stress, proteins tend to form aggregates either highly ordered (amyloid) or unordered (amorphous) causing many pathological disorders in human and loss of proteins functionality in both laboratory conditions and industries during production and storage at commercial level. We investigated the effect of increasing temperature on Conalbumin (CA) and induced aggregation at 65 °C. The enhanced Thioflavin T (ThT) and ANS (1-anilinonaphtalene 8-sulfonic acid) fluorescence intensity, show no shift on Congo red binding, additionally, transmission and scanning electron microscopy (TEM) (SEM) reveal amorphous morphology of the aggregate. Our investigation clearly demonstrated that polyols namely Glycerol (GL) and Ethylene glycol (EG) are so staunch to inhibit amorphous aggregates via restoring secondary conformation. Addition of polyols (15% GL and 35% EG) significantly decrease the turbidity, Rayleigh scattering ThT and ANS fluorescence intensity. The dynamic light scattering (DLS) data show that hydrodynamic radii (R_h) of the aggregates is ∼20 times higher than native CA while nearly similar for GL and EG protected CA due to condensation of core size with little difference.

Ozone-derived Oxysterols Affect Liver X Receptor (LXR) Signaling: A POTENTIAL ROLE FOR LIPID-PROTEIN ADDUCTS

When inhaled, ozone (O₃) interacts with cholesterols of airway epithelial cell membranes or the lung-lining fluid, generating chemically reactive oxysterols. The mechanism by which O₃-derived oxysterols affect molecular function is unknown. Our data show that in vitro exposure of human bronchial epithelial cells to O₃ results in the formation of oxysterols, epoxycholesterol-α and -β and secosterol A and B (Seco A and Seco B), in cell lysates and apical washes. Similarly, bronchoalveolar lavage fluid obtained from human volunteers exposed to O₃ contained elevated levels of these oxysterol species. As expected, O₃-derived oxysterols have a pro-inflammatory effect and increase NF-κB activity. Interestingly, expression of the cholesterol efflux pump ATP-binding cassette transporter 1 (ABCA1), which is regulated by activation of the liver X receptor (LXR), was suppressed in epithelial cells exposed to O₃ Additionally, exposure of LXR knock-out mice to O₃ enhanced pro-inflammatory cytokine production in the lung, suggesting LXR inhibits O₃-induced inflammation. Using alkynyl surrogates of O₃-derived oxysterols, our data demonstrate adduction of LXR with Seco A. Similarly, supplementation of epithelial cells with alkynyl-tagged cholesterol followed by O₃ exposure causes observable lipid-LXR adduct formation. Experiments using Seco A and the LXR agonist T0901317 (T09) showed reduced expression of ABCA1 as compared with stimulation with T0901317 alone, indicating that Seco A-LXR protein adduct formation inhibits LXR activation by traditional agonists. Overall, these data demonstrate that O₃-derived oxysterols have pro-inflammatory functions and form lipid-protein adducts with LXR, thus leading to suppressed cholesterol regulatory gene expression and providing a biochemical mechanism mediating O₃-derived formation of oxidized lipids in the airways and subsequent adverse health effects.

Rotenone Induces the Formation of 4-Hydroxynonenal Aggresomes. Role of ROS-Mediated Tubulin Hyperacetylation and Autophagic Flux Disruption

Oxidative stress causes cellular damage by (i) altering protein stability, (ii) impairing organelle function, or (iii) triggering the formation of 4-HNE protein aggregates. The catabolic process known as autophagy is an antioxidant cellular response aimed to counteract these stressful conditions. Therefore, autophagy might act as a cytoprotective response by removing impaired organelles and aggregated proteins. In the present study, we sought to understand the role of autophagy in the clearance of 4-HNE protein aggregates in ARPE-19 cells under rotenone exposure. Rotenone induced an overproduction of reactive oxygen species (ROS), which led to an accumulation of 4-HNE inclusions, and an increase in the number of autophagosomes. The latter resulted from a disturbed autophagic flux rather than an activation of the autophagic synthesis pathway. In compliance with this, rotenone treatment induced an increase in LC3-II while upstream autophagy markers such as Beclin- 1, Vsp34 or Atg5-Atg12, were decreased. Rotenone reduced the autophagosome-to-lysosome fusion step by increasing tubulin acetylation levels through a ROS-mediated pathway. Proof of this is the finding that the free radical scavenger, N-acetylcysteine, restored autophagy flux and reduced rotenone-induced tubulin hyperacetylation. Indeed, this dysfunctional autophagic response exacerbates cell death triggered by rotenone, since 3-methyladenine, an autophagy inhibitor, reduced cell mortality, while rapamycin, an inductor of autophagy, caused opposite effects. In summary, we shed new light on the mechanisms involved in the autophagic responses disrupted by oxidative stress, which take place in neurodegenerative diseases such as Huntington or Parkinson diseases, and age-related macular degeneration.

Assay of protein and peptide adducts of cholesterol ozonolysis products by hydrophobic and click enrichment methods

Cholesterol undergoes ozonolysis to afford a variety of oxysterol products, including cholesterol-5,6-epoxide (CholEp) and the isomeric aldehydes secosterol A (seco A) and secosterol B (seco B). These oxysterols display numerous important biological activities, including protein adduction; however, much remains to be learned about the identity of the reactive species and the range of proteins modified by these oxysterols. Here, we synthesized alkynyl derivatives of cholesterol-derived oxysterols and employed a straightforward detection method to establish secosterols A and B as the most protein-reactive of the oxysterols tested. Model adduction studies with an amino acid, peptides, and proteins provide evidence for the potential role of secosterol dehydration products in protein adduction. Hydrophobic separation methods—Folch extraction and solid phase extraction (SPE)—were successfully applied to enrich oxysterol-adducted peptide species, and LC-MS/MS analysis of a model peptide–seco adduct revealed a unique fragmentation pattern (neutral loss of 390 Da) for that species. Coupling a hydrophobic enrichment method with proteomic analysis utilizing characteristic fragmentation patterns facilitates the identification of secosterol-modified peptides and proteins in an adducted protein. More broadly, these improved enrichment methods may give insight into the role of oxysterols and ozone exposure in the pathogenesis of a variety of diseases, including atherosclerosis, Alzheimer’s disease, Parkinson’s disease, and asthma.

Probing lipid-protein adduction with alkynyl surrogates: application to Smith-Lemli-Opitz syndrome

Lipid modifications aid in regulating (and misregulating) protein function and localization. However, efficient methods to screen for a lipid's ability to modify proteins are not readily available. We present a strategy to identify protein-reactive lipids and apply it to a neurodevelopmental disorder, Smith-Lemli-Opitz syndrome (SLOS). Alkynyl surrogates were synthesized for polyunsaturated fatty acids, phospholipids, cholesterol, 7-dehydrocholesterol (7-DHC), and a 7-DHC-derived oxysterol. To probe for protein-reactive lipids, we used click chemistry to biotinylate the alkynyl tag and detected the lipid-adducted proteins with streptavidin Western blotting. In Neuro2a cells, the trend in amount of protein adduction followed known rates of lipid peroxidation (7-DHC >> arachidonic acid > linoleic acid >> cholesterol), with alkynyl-7-DHC producing the most adduction among alkynyl lipids. 7-DHC reductase-deficient cells, which cannot properly metabolize 7-DHC, exhibited significantly more alkynyl-7-DHC-protein adduction than control cells. Model studies demonstrated that a 7-DHC peroxidation product covalently modifies proteins. We hypothesize that 7-DHC generates electrophiles that can modify the proteome, contributing to SLOS's complex pathology. These probes and methods would allow for analysis of lipid-modified proteomes in SLOS and other disorders exhibiting 7-DHC accumulation. More broadly, the alkynyl lipid library would facilitate exploration of lipid peroxidation's role in specific biological processes in numerous diseases.

Occurrence of cytotoxic 9-oxononanoyl secosterol aldehydes in human low-density lipoprotein

The reaction products of three major cholesteryl esters, cholesteryl palmitate (C16:0-CE), cholesteryl oleate (C18:1-CE), and cholesteryl linoleate (C18:2-CE), present in human low-density lipoprotein (LDL) treated with ozone were isolated and characterized. In vitro ozonization of C16:0-CE was found to form the palmitoyl ester of secosterol-A (3β-hydroxy-5-oxo-5,6-secocholestan-6-al) and its aldolization product secosterol-B (3β-hydroxy-5β-hydroxy-B-norcholestane-6β-carboxaldehyde). On the other hand, when C18:1-CE and C18:2-CE were oxidized by ozone, the aldehyde 9-oxononanoyl cholesterol (9-ONC) was formed as a primary product, which was then further oxidized to form 9-oxononanoyl secosterol-A (9-ON-secoA) and 9-oxononanoyl secosterol-B (9-ON-secoB). The compounds 9-ON-secoA and -B, but not 9-ONC, were found to exhibit strong cytotoxicity against human leukemia HL-60 cells. An LC-ESI-MS/MS method was developed for the detection of these cholesteryl ester ozonolysis products by derivatizing them with dansyl hydrazine. Using this method, we found for the first time that low concentrations of 9-ON-secoA and -B, but not palmitoyl secosterols, were present in human LDL. These novel oxidized cholesterol esters, 9-ON-secoA and -B, probably play important roles in the pathogenesis of several inflammatory disorders such as cancer, diabetes, atherosclerosis, and neurodegenerative diseases.

New views on cellular uptake and trafficking of manufactured nanoparticles

Nanoparticles (NPs) are of similar size to typical cellular components and proteins, and can efficiently intrude living cells. A detailed understanding of the involved processes at the molecular level is important for developing NPs designed for selective uptake by specific cells, for example, for targeted drug delivery. In addition, this knowledge can greatly assist in the engineering of NPs that should not penetrate cells so as to avoid adverse health effects. In recent years, a wide variety of experiments have been performed to elucidate the mechanisms underlying cellular NP uptake. Here, we review some select recent studies, which are often based on fluorescence microscopy and sophisticated strategies for specific labelling of key cellular components. We address the role of the protein corona forming around NPs in biological environments, and describe recent work revealing active endocytosis mechanisms and pathways involved in their cellular uptake. Passive uptake is also discussed. The current state of knowledge is summarized, and we point to issues that still need to be addressed to further advance our understanding of cellular NP uptake.

In vitro aggregation behavior of a non-amyloidogenic λ light chain dimer deriving from U266 multiple myeloma cells

Excessive production of monoclonal light chains due to multiple myeloma can induce aggregation-related disorders, such as light chain amyloidosis (AL) and light chain deposition diseases (LCDD). In this work, we produce a non-amyloidogenic IgE λ light chain dimer from human mammalian cells U266, which originated from a patient suffering from multiple myeloma, and we investigate the effect of several physicochemical parameters on the in vitro stability of this protein. The dimer is stable in physiological conditions and aggregation is observed only when strong denaturating conditions are applied (acidic pH with salt at large concentration or heating at melting temperature T_m at pH 7.4). The produced aggregates are spherical, amorphous oligomers. Despite the larger β-sheet content of such oligomers with respect to the native state, they do not bind Congo Red or ThT. The impossibility to obtain fibrils from the light chain dimer suggests that the occurrence of amyloidosis in patients requires the presence of the light chain fragment in the monomer form, while dimer can form only amorphous oligomers or amorphous deposits. No aggregation is observed after denaturant addition at pH 7.4 or at pH 2.0 with low salt concentration, indicating that not a generic unfolding but specific conformational changes are necessary to trigger aggregation. A specific anion effect in increasing the aggregation rate at pH 2.0 is observed according to the following order: SO₄⁻≫Cl⁻>H₂PO₄⁻, confirming the peculiar role of sulfate in promoting protein aggregation. It is found that, at least for the investigated case, the mechanism of the sulfate effect is related to protein secondary structure changes induced by anion binding.

A chemical approach for cell-specific targeting of nanomaterials: small-molecule-initiated misfolding of nanoparticle corona proteins

A major challenge in nanomaterial science is to develop approaches that ensure that when administered in vivo, nanoparticles can be targeted to their requisite site of action. Herein we report the first approach that allows for cell-specific uptake of nanomaterials by a process involving reprogramming of the behavior of the ubiquitous protein corona of nanomaterials. Specifically, judicious surface modification of quantum dots with a small molecule that induces a protein-misfolding event in a component of the nanoparticle-associated protein corona renders the associated nanomaterials susceptible to cell-specific, receptor-mediated endocytosis. We see this chemical approach as a new and general method for exploiting the inescapable protein corona to target nanomaterials to specific cells.

Cholesterol secosterol aldehydes induce amyloidogenesis and dysfunction of wild-type tumor protein p53

Epidemiologic and clinical evidence points to an increased risk for cancer when coupled with chronic inflammation. However, the molecular mechanisms that underpin this interrelationship remain largely unresolved. Herein we show that the inflammation-derived cholesterol 5,6-secosterol aldehydes, atheronal-A (KA) and -B (ALD), but not the polyunsaturated fatty acid (PUFA)-derived aldehydes 4-hydroxynonenal (HNE) and 4-hydroxyhexenal (HHE), induce misfolding of wild-type p53 into an amyloidogenic form that binds thioflavin T and Congo red dyes but cannot bind to a consensus DNA sequence. Treatment of lung carcinoma cells with KA and ALD leads to a loss of function of extracted p53, as determined by the analysis of extracted nuclear protein and in activation of p21. Our results uncover a plausible chemical link between inflammation and cancer and expand the already pivotal role of p53 dysfunction and cancer risk.

Adduction of cholesterol 5,6-secosterol aldehyde to membrane-bound myelin basic protein exposes an immunodominant epitope

Myelin degradation in the central nervous system (CNS) is a clinical hallmark of multiple sclerosis (MS). A reduction in the net positive charge of myelin basic protein (MBP) via deimination of arginine to citrulline has been shown to correlate strongly with disease severity and has been linked to myelin instability and a defect that precedes neurodegeneration and leads to autoimmune attack. Recently, we have shown that lipid-derived aldehydes, such as cholesterol 5,6-secosterols atheronal A (1a) and atheronal B (1b), modulate the misfolding of certain proteins such as apolipoprotein B(100), β-amyloid, α-synuclein, and κ- and λ-antibody light chains in a process involving adduction of the hydrophobic aldehyde to lysine side chains, resulting in a decrease in the net positive charge of the protein. In this study, we show that the presence of either atheronal A (1a) or atheronal B (1b) in large unilamellar vesicles (cyt-LUVs) with the lipid composition found in the cytosolic myelin sheath and bovine MBP (bMBP) leads to an atheronal concentration-dependent increase in the surface exposure of the immunodominant epitope (V86-T98) as determined by antibody binding. Other structural changes in bMBP were also observed; specifically, 1a and 1b induce a decrease in the surface exposure of L36-P50 relative to control cyt-LUVs as measured both by antibody binding and by a reduction in the level of cathepsin D proteolysis of F42 and F43. Structure-activity relationship studies with analogues of 1a and 1b point to the aldehyde moiety of both compounds being critical to their effects on bMBP structure. The atheronals also cause a reduction in the size of the bMBP-cyt-LUV aggregates, as determined by fluorescence microscopy and dynamic light scattering. These results suggest that formation of an imine between inflammatory-derived aldehydes, which effectively reduces the cationic nature of MBP, can lead to structural changes in MBP and a decrease in myelin stability akin to deimination and as such may make a hitherto unknown contribution to the onset and progression of MS.

Transmission electron microscopy of amyloid fibrils

Transmission Electron Microscopy of negatively stained and cryo-prepared specimens allows amyloid fibrils to be visualised at high resolution in a dried or a hydrated state, and is an essential method for characterising the morphology of fibrils and pre-fibrillar species. We outline the key steps involved in the preparation and observation of samples using negative staining and cryo-electron preservation. We also discuss methods to measure fibril characteristics, such as fibril width, from electron micrographs.

Two disaccharides and trimethylamine N-oxide affect Abeta aggregation differently, but all attenuate oligomer-induced membrane permeability

Interaction between aggregates of amyloid beta protein (Abeta) and membranes has been hypothesized by many to be a key event in the mechanism of neurotoxicity associated with Alzheimer's disease (AD). Proposed membrane-related mechanisms of neurotoxicity include ion channel formation, membrane disruption, changes in membrane capacitance, and lipid membrane oxidation. Recently, osmolytes such as trehalose have been found to delay Abeta aggregation in vitro and reduce neurotoxicity. However, no direct measurements have separated the effects of osmolytes on Abeta aggregation versus membrane interactions. In this article, we tested the influence of trehalose, sucrose and trimethylamine-N-oxide (TMAO) on Abeta aggregation and fluorescent dye leakage induced by Abeta aggregates from liposomes. In the absence of lipid vesicles, trehalose and sucrose, but not TMAO, were found to delay Abeta aggregation. In contrast, all of the osmolytes significantly attenuated dye leakage. Dissolution of preformed Abeta aggregates was excluded as a possible mechanism of dye leakage attenuation by measurements of Congo red binding as well as hydrogen-deuterium exchange detected by mass spectrometry (HX-MS). However, the accelerated conversion of high order oligomers to fibril caused by vesicles did not take place if any of the three osmolytes presented. Instead, in the case of disaccharide, osmolytes were found to form adducts with Abeta, and change the dissociation dynamics of soluble oligomeric species. Both effects may have contributed to the observed osmolyte attenuation of dye leakage. These results suggest that disaccharides and TMAO may have very different effects on Abeta aggregation because of the different tendencies of the osmolytes to interact with the peptide backbone. However, the effects on Abeta membrane interaction may be due to much more general phenomena associated with osmolyte enhancement of Abeta oligomer stability and/or direct interaction of osmolyte with the membrane surface.

The ratio of cholesterol 5,6-secosterols formed from ozone and singlet oxygen offers insight into the oxidation of cholesterol in vivo

Ongoing efforts to unravel the origins of the cholesterol 5,6-secosterols (1a and 1b) in biological systems have revealed that the two known chemical routes to these oxysterols, ozonolysis of cholesterol (3) and Hock-cleavage of 5-alpha-hydroperoxycholesterol (4a), are distinguishable based upon the ratio of the hydrazone derivatives (2a and 2b) formed in each case and this ratio offers an insight into the chemical origin of the secosterols in vivo.