Affinity Capillary Electrophoresis as a Tool To Characterize Molecularly Imprinted Nanogels in Solution.

In this work, an innovative and accurate affinity capillary electrophoresis (ACE) method was set up to monitor the complexation of aqueous MIP nanogels (NGs) with model cancer-related antigens. Using α2,6'- and α2,3'-sialyllactose as oversimplified cancer biomarker-mimicking templates, NGs were synthesized and characterized in terms of size, polydispersity, and overall charge. A stability study was also carried out in order to select the best storage conditions and to ensure product quality. After optimization of capillary electrophoresis conditions, injection of MIP NGs resulted in a single, sharp, and efficient peak. The mobility shift approach was applied to quantitatively estimate binding affinity, in this case resulting in an association constant of K ≈ 106 M-1. The optimized polymers further displayed a pronounced discrimination between the two sialylated sugars. The newly developed ACE protocol has the potential to become a very effective method for nonconstrained affinity screening of NG in solution, especially during the NG development phase and/or for a final accurate quantitation of the observed binding.

Rational Design of Highly Selective Sialyllactose-Imprinted Nanogels.

We describe a facile method to prepare water-compatible molecularly imprinted polymer nanogels (MIP NGs) as synthetic antibodies against target glycans. Three different phenylboronic acid (PBA) derivatives were explored as monomers for the synthesis of MIP NGs targeting either α2,6- or α2,3-sialyllactose, taken as oversimplified models of cancer-related sT and sTn antigens. Starting from commercially available 3-acrylamidophenylboronic acid, also its 2-substituted isomer and the 5-acrylamido-2-hydroxymethyl cyclic PBA monoester derivative were initially evaluated by NMR studies. Then, a small library of MIP NGs imprinted with the α2,6-linked template was synthesized and tested by mobility shift Affinity Capillary Electrophoresis (msACE), to rapidly assess an affinity ranking. Finally, the best monomer 2-acrylamido PBA was selected for the synthesis of polymers targeting both sialyllactoses. The resulting MIP NGs display an affinity constant≈106 M-1 and selectivity towards imprinted glycans. This general procedure could be applied to any non-modified carbohydrate template possessing a reducing end.

Modulation of Amyloid ß-Induced Microglia Activation and Neuronal Cell Death by Curcumin and Analogues.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is not restricted to the neuronal compartment but includes important interactions with immune cells, including microglia. Protein aggregates, common pathological hallmarks of AD, bind to pattern recognition receptors on microglia and trigger an inflammatory response, which contributes to disease progression and severity. In this context, curcumin is emerging as a potential drug candidate able to affect multiple key pathways implicated in AD, including neuroinflammation. Therefore, we studied the effect of curcumin and its structurally related analogues cur6 and cur16 on amyloid-ß (Aß)-induced microglia activation and neuronal cell death, as well as their effect on the modulation of Aß aggregation. Primary cortical microglia and neurons were exposed to two different populations of Aß42 oligomers (Aß42Os) where the oligomeric state had been assigned by capillary electrophoresis and ultrafiltration. When stimulated with high molecular weight Aß42Os, microglia released proinflammatory cytokines that led to early neuronal cell death. The studied compounds exerted an anti-inflammatory effect on high molecular weight Aß42O-stimulated microglia and possibly inhibited microglia-mediated neuronal cell toxicity. Furthermore, the tested compounds demonstrated antioligomeric activity during the process of in vitro Aß42 aggregation. These findings could be investigated further and used for the optimization of multipotent candidate molecules for AD treatment.

Capillary electrophoresis analysis of different variants of the amyloidogenic protein ß2 -microglobulin as a simple tool for misfolding and stability studies.

Free solution capillary electrophoresis with UV detection is here used to retrieve information on the conformational changes of wild-type ß2 -microglobulin and a series of naturally and artificially created variants known to have different stability and amyloidogenic potential. Under nondenaturing conditions, the resolution of at least two folding conformers at equilibrium is obtained and a third species is detected for the less stable isoforms. Partial denaturation by using chaotropic agents such as acetonitrile or trifluoroethanol reveals that the separated peaks are at equilibrium, as the presence of less structured species is either enhanced or induced at the expenses of the native form. Reproducible CE data allow to obtain an interesting semiquantitative correlation between the peak areas observed and the protein stability. Thermal unfolding over the range 25-42°C is induced inside the capillary for the two pathogenic proteins (wtß2 -microglobulin and D76N variant): the large differences observed upon small temperature variation draw attention on the robustness of analytical methods when dealing with proteins prone to misfolding and aggregation.

Targeting the multifaceted neurotoxicity of Alzheimer's disease by tailored functionalisation of the curcumin scaffold.

Simultaneous modulation of multifaceted toxicity arising from neuroinflammation, oxidative stress, and mitochondrial dysfunction represents a valuable therapeutic strategy to tackle Alzheimer's disease. Among the significant hallmarks of the disorder, Aß protein and its aggregation products are well-recognised triggers of the neurotoxic cascade. In this study, by tailored modification of the curcumin-based lead compound 1, we aimed at developing a small library of hybrid compounds targeting Aß protein oligomerisation and the consequent neurotoxic events. Interestingly, from in vitro studies, analogues 3 and 4, bearing a substituted triazole moiety, emerged as multifunctional agents able to counteract Aß aggregation, neuroinflammation and oxidative stress. In vivo proof-of-concept evaluations, performed in a Drosophila oxidative stress model, allowed us to identify compound 4 as a promising lead candidate.

Glucuronide directed molecularly imprinted solid-phase extraction: isolation of testosterone glucuronide from its parent drug in urine.

Two molecularly imprinted polymers (MIPs) that we recently described to be class-selective for glucuronides have been successfully exploited for the molecularly imprinted solid-phase extraction (MISPE) of testosterone glucuronide (TG) from its parent drug (T) in urine. Both sorbents targeted the glucuronate fragment but feature different functional groups for binding the carboxylate anion, MIP1, a neutral 1,3-diarylurea group, and MIP2, a cationic imidazolium functionality. MISPE-HPLC-UV methods developed using both sorbents allowed the extraction of TG from its parent compound in urine samples spiked at 150, 300 or 600 ng mL(-1) for TG and at 50 ng mL(-1) for T. By comparing the performance of the two sorbents it came out that MIP1 is a more suitable SPE packing than MIP2, since it isolated the glucuronide with a higher precision (RSD 2-5%, n = 3) and with an enhanced enrichment factor (EF = 4.2). On the basis of these results, the imprinted receptor MIP1 can be applied for the direct extraction of TG in doping and clinical analysis and to selectively capture any other relevant glucuronated metabolite avoiding tedious deconjugation steps prior to quantification.

CE can identify small molecules that selectively target soluble oligomers of amyloid beta protein and display antifibrillogenic activity.

Soluble and toxic oligomers of amyloid beta (A beta) protein have been identified as the true neurotoxic species involved in Alzheimer's disease and considering them as targets to inhibit A beta aggregation might have a therapeutic value. We previously set up a CE method that enables the separation and quantification of transient oligomers of A beta protein-containing 42 amino acids (A beta(1-42)) along the pathway leading to fibrils and we now demonstrate how this method can be successfully applied to examine the in vitro inhibitory effects of small molecules on A beta oligomerization. To this end, we investigated mitoxantrone and pixantrone, two well-known anticancer drugs, as well as suramin and a suramin-like compound. By using CE, it is here shown how mitoxantrone and pixantrone either reduce or block A beta(1-42) oligomerization, while Thioflavin T spectrofluorimetric assay and transmission electron microscopy demonstrate how these two compounds also display antifibrillogenic activity. Interestingly, in vitro cell viability experiments indicated that pixantrone significantly reduces A beta(1-42) neurotoxicity.

In vitro amyloid Abeta(1-42) peptide aggregation monitoring by asymmetrical flow field-flow fractionation with multi-angle light scattering detection.

Self-assembly of the 42-amino-acid-long amyloid peptide Abeta(1-42) into insoluble fibrillar deposits in the brain is a crucial event in the pathogenesis of Alzheimer's disease. The fibril deposition occurs through an aggregation process during which transient and metastable oligomeric intermediates are intrinsically difficult to be accurately monitored and characterised. In this work, the time-dependent Abeta(1-42) aggregation pattern is studied by asymmetrical flow field-flow fractionation with on-line multi-angle light scattering detection. This technique allows separating and obtaining information on the molar mass (M(r)) and size distribution of both the early-forming soluble aggregates and the late prefibrillar and fibrillar species, the latter having very high M(r). Preliminary results demonstrate that unique information on the dynamic aggregation process can be obtained, namely on the M(r) and size of the forming aggregates as well as on their formation kinetics.

Prenylated Curcumin Analogues as Multipotent Tools To Tackle Alzheimer's Disease.

Alzheimer's disease is likely to be caused by copathogenic factors including aggregation of Aß peptides into oligomers and fibrils, neuroinflammation, and oxidative stress. To date, no effective treatments are available, and because of the multifactorial nature of the disease, it emerges the need to act on different and simultaneous fronts. Despite the multiple biological activities ascribed to curcumin as neuroprotector, its poor bioavailability and toxicity limit the success in clinical outcomes. To tackle Alzheimer's disease on these aspects, the curcumin template was suitably modified and a small set of analogues was attained. In particular, derivative 1 turned out to be less toxic than curcumin. As evidenced by capillary electrophoresis and transmission electron microscopy studies, 1 proved to inhibit the formation of large toxic Aß oligomers, by shifting the equilibrium toward smaller nontoxic assemblies and to limit the formation of insoluble fibrils. These findings were supported by molecular docking and steered molecular dynamics simulations which confirmed the superior capacity of 1 to bind Aß structures of different complexity. Remarkably, 1 also showed in vitro anti-inflammatory and antioxidant properties. In summary, the curcumin-based analogue 1 emerged as multipotent compound worthy to be further investigated and exploited in the Alzheimer's disease multitarget context.

An integrated strategy to correlate aggregation state, structure and toxicity of Aß 1-42 oligomers.

Despite great efforts, it is not known which oligomeric population of amyloid beta (Aß) peptides is the main neurotoxic mediator in Alzheimer's disease. In vitro and in vivo experiments are challenging, mainly because of the high aggregation tendency of Aß (in particular of Aß 1-42 peptide), as well as because of the dynamic and non covalent nature of the prefibrillar aggregates. As a step forward in these studies, an analytical platform is here proposed for the identification and characterization of Aß 1-42 oligomeric populations resulting from three different sample preparation protocols. To preserve the transient nature of aggregates, capillary electrophoresis is employed for monitoring the oligomerization process in solution until fibril precipitation, which is probed by transmission electron microscopy. Based on characterization studies by ultrafiltration and SDS-PAGE/Western Blot, we find that low molecular weight oligomers build up over time and form bigger aggregates (> dodecamers) and that the kinetics strongly depends on sample preparations. The use of phosphate buffer results to be more aggregating, since trimers are the smallest species found in solution, whereas monomers and dimers are obtained by solubilizing Aß 1-42 in a basic mixture. For the first time, attenuated total reflection-Fourier transform infrared spectroscopy is used to assign secondary structure to the separated oligomers. Random coil and/or α-helix are most abundant in smaller species, whereas ß-sheet is the predominant conformation in bigger aggregates, which in turn are demonstrated to be responsible for Aß 1-42 toxicity.

Chromatographic comparison of bupivacaine imprinted polymers prepared in crushed monolith, microsphere, silica-based composite and capillary monolith formats.

A comprehensive comparison of five chromatographic stationary phases based on molecularly imprinted polymers is presented. Efficiency, imprinting factors, water compatibility and batch-to-batch reproducibility are discussed for crushed monolith, microspheres, two silica-based composites and capillary monoliths, all imprinted with the local anaesthetic bupivacaine. Synthesis protocol and chromatographic test conditions have been kept fixed within certain limits, in order to provide further insight into the strengths and weaknesses of the different formats. Excluding microparticles, all formats give satisfactory performance, especially in aqueous mobile phases. An assessment of batch-to-batch reproducibility in different mobile phases adds further value to this comparison study.

Evidence that the Human Innate Immune Peptide LL-37 may be a Binding Partner of Amyloid-ß and Inhibitor of Fibril Assembly.

BACKGROUND: Identifying physiologically relevant binding partners of amyloid-ß (Aß) that modulate in vivo fibril formation may yield new insights into Alzheimer's disease (AD) etiology. Human cathelicidin peptide, LL-37, is an innate immune effector and modulator, ubiquitous in human tissues and expressed in myriad cell types. OBJECTIVE: We present in vitro experimental evidence and discuss findings supporting a novel hypothesis that LL-37 binds to Aß42 and can modulate Aß fibril formation. METHODS: Specific interactions between LL-37 and Aß (with Aß in different aggregation states, assessed by capillary electrophoresis) were demonstrated by surface plasmon resonance imaging (SPRi). Morphological and structural changes were investigated by transmission electron microscopy (TEM) and circular dichroism (CD) spectroscopy. Neuroinflammatory and cytotoxic effects of LL-37 alone, Aß42 alone, and LL-37/Aß complexes were evaluated in human microglia and neuroblastoma cell lines (SH-SY5Y). RESULTS: SPRi shows binding specificity between LL-37 and Aß, while TEM shows that LL-37 inhibits Aß42 fibril formation, particularly Aß's ability to form long, straight fibrils characteristic of AD. CD reveals that LL-37 prevents Aß42 from adopting its typical ß-type secondary structure. Microglia-mediated toxicities of LL-37 and Aß42 to neurons are greatly attenuated when the two peptides are co-incubated prior to addition. We discuss the complementary biophysical characteristics and AD-related biological activities of these two peptides. CONCLUSION: Based on this body of evidence, we propose that LL-37 and Aß42 may be natural binding partners, which implies that balanced (or unbalanced) spatiotemporal expression of the two peptides could impact AD initiation and progression.

Interactions of charged ligands with beta(2)-microglobulin conformers in affinity capillary electrophoresis.

Alternative conformations of beta(2)-microglobulin (beta(2)m) are involved in its transformation from soluble monomeric precursor molecules to the insoluble polymeric material that constitutes beta(2)m amyloid. Accordingly, non-native conditions such as low pH or high ionic strength promote beta(2)m amyloid formation in vitro. The early events in these processes are not well known, partly because of the paucity of techniques available for the characterization of transient folding intermediates in proteins. We have used high-resolution separations in capillaries (capillary electrophoresis, CE) to resolve putative conformer fractions in native and structurally modified beta(2)m and to show the induction of alternatively folded beta(2)m under different experimental conditions. The conformer fractions are observed as distinct peaks in the separation profiles and thus it is possible to probe for the reactivity of these individual beta(2)m species with specific ligands that, upon binding, alter analyte mobility in affinity capillary electrophoresis experiments. Interactions were shown in this way for the negatively charged substances heparin, Congo red, and suramin, as well as for Cu(2+) ions. Marked differences in the binding behavior of the beta(2)m conformational variants compared with native beta(2)m could be demonstrated. This approach for conformer separation and binding characterization is a valuable starting point for the assessment of various ligand molecules, or analogues thereof, as agents capable of perturbing the mechanisms of fibril formation.

Variants of beta-microglobulin cleaved at lysine-58 retain the main conformational features of the native protein but are more conformationally heterogeneous and unstable at physiological temperature.

Cleavage of the small amyloidogenic protein beta2-microglobulin after lysine-58 renders it more prone to unfolding and aggregation. This is important for dialysis-related beta2-microglobulin amyloidosis, since elevated levels of cleaved beta2-microglobulin may be found in the circulation of dialysis patients. However, the solution structures of these cleaved beta2-microglobulin variants have not yet been assessed using single-residue techniques. We here use such methods to examine beta2-microglobulin cleaved after lysine-58 and the further processed variant (found in vivo) from which lysine-58 is removed. We find that the solution stability of both variants, especially of beta2-microglobulin from which lysine-58 is removed, is much reduced compared to wild-type beta2-microglobulin and is strongly dependent on temperature and protein concentration. 1H-NMR spectroscopy and amide hydrogen (1H/2H) exchange monitored by MS show that the overall three-dimensional structure of the variants is similar to that of wild-type beta2-microglobulin at subphysiological temperatures. However, deviations do occur, especially in the arrangement of the B, D and E beta-strands close to the D-E loop cleavage site at lysine-58, and the experiments suggest conformational heterogeneity of the two variants. Two-dimensional NMR spectroscopy indicates that this heterogeneity involves an equilibrium between the native-like fold and at least one conformational intermediate resembling intermediates found in other structurally altered beta2-microglobulin molecules. This is the first single-residue resolution study of a specific beta2-microglobulin variant that has been found circulating in dialysis patients. The instability and conformational heterogeneity of this variant suggest its involvement in beta2-microglobulin amyloidogenicity in vivo.

Evaluation of capillary electrophoresis-mass spectrometry for the analysis of the conformational heterogeneity of intact proteins using beta2-microglobulin as model compound.

In this work we explored the feasibility of different CE-ESI-MS set-ups for the analysis of conformational states of an intact protein. By using the same background electrolyte at quasi physiological conditions (50 mM ammonium bicarbonate, pH 7.4) a sequential optimization was carried out, initially by evaluating a sheath-liquid interface with both a single quadrupole (SQ) and a time-of-flight (TOF) mass spectrometer; then a sheathless interface coupled with high-resolution QTOF MS was considered. Beta2-microglobulin has been taken as a model, as it is an amyloidogenic protein and its conformational changes are strictly connected to the onset of a disease. The separation of two conformers at dynamic equilibrium is achieved all the way down to the MS detection. Notably, the equilibrium ratio of the protein conformers is maintained in the electrospray source after CE separation. Strengths and weaknesses of each optimized set-up are emphasized and their feasibility in unfolding studies is evaluated. In particular, ESI-TOF MS can assign protein forms that differ by 1 Da only and sheathless interfacing is best suited to preserve protein structure integrity. This demonstrates the CE-ESI-MS performance in terms of separation, detection and characterization of conformational species that co-populate a protein solution.

Lack of prolidase causes a bone phenotype both in human and in mouse.

The degradation of the main fibrillar collagens, collagens I and II, is a crucial process for skeletal development. The most abundant dipeptides generated from the catabolism of collagens contain proline and hydroxyproline. In humans, prolidase is the only enzyme able to hydrolyze dipeptides containing these amino acids at their C-terminal end, thus being a key player in collagen synthesis and turnover. Mutations in the prolidase gene cause prolidase deficiency (PD), a rare recessive disorder. Here we describe 12 PD patients, 9 of whom were molecularly characterized in this study. Following a retrospective analysis of all of them a skeletal phenotype associated with short stature, hypertelorism, nose abnormalities, microcephaly, osteopenia and genu valgum, independent of both the type of mutation and the presence of the mutant protein was identified. In order to understand the molecular basis of the bone phenotype associated with PD, we analyzed a recently identified mouse model for the disease, the dark-like (dal) mutant. The dal/dal mice showed a short snout, they were smaller than controls, their femurs were significantly shorter and pQCT and µCT analyses of long bones revealed compromised bone properties at the cortical and at the trabecular level in both male and female animals. The differences were more pronounce at 1 month being the most parameters normalized by 2 months of age. A delay in the formation of the second ossification center was evident at postnatal day 10. Our work reveals that reduced bone growth was due to impaired chondrocyte proliferation and increased apoptosis rate in the proliferative zone associated with reduced hyperthrophic zone height. These data suggest that lack of prolidase, a cytosolic enzyme involved in the final stage of protein catabolism, is required for normal skeletogenesis especially at early age when the requirement for collagen synthesis and degradation is the highest.

Pharmaceutical strategies against amyloidosis: old and new drugs in targeting a "protein misfolding disease".

The group of diseases caused by abnormalities of the process of protein folding and unfolding is rapidly growing and includes diseases caused by loss of function as well as diseases caused by gain of function of misfolded proteins. Amyloidoses are caused by gain of function of certain proteins that lose their native structure and self-assemble into toxic insoluble, extracellular fibrils. This process requires the contribution of multiple factors of which only a few are established, namely the conformational modification of the amyloidogenic protein, protein's post-translational modifications and the co-deposition of glycosaminoglicans and of serum amyloid P component. In parallel with the exponential growth of biochemical data regarding the key events of the fibrillogenic process, several reports have shown that small molecules, through the interaction with either the amyloidogenic proteins or with the common constituents, can modify the kinetics of formation of amyloid fibrils or can facilitate amyloid reabsorption. These small molecules can be classified on the basis of their protein target and mechanism of action, according to the following properties. 1) molecules that stabilize the amyloidogenic protein precursor 2) molecules that prevent fibrillogenesis by acting on partially folded intermediates of the folding process as well as on low molecular weight oligomers populating the initial phase of fibril formation 3) molecules that interact with mature amyloid fibrils and weaken their structural stability 4) molecules that displace fundamental co-factors of the amyloid deposits like glycosaminoglycans and serum amyloid P component and favor the dissolution of the fibrillar aggregate.

An enantioselective imprinted receptor for Z-glutamate exhibiting a binding induced color change.

Using 1-(4-styryl)-3-(3-nitrophenyl)urea as host monomer for the imprinting of Z-(D or L)-Glu, a polymeric receptor exhibiting strong enantioselectivity and a change in color intensity upon binding of the guest was obtained.

Approaches to imprinted stationary phases for affinity capillary electrochromatography.

The combination of two highly attractive technologies in analytical chemistry, namely molecular imprinting and capillary electrochromatography, is reviewed. Molecular imprinting represents an approach to incorporate affinity binding sites for one or a class of target molecules in network polymers whereas capillary electrochromatography is a technique that profits from the high separation efficiency of electrodriven separations and the high selectivity and capacity available with liquid chromatography. The review discusses and compares the various approaches taken, to combine these concepts aiming at robust, reproducible and easily available capillary-based affinity separation media.

Advanced glycation end products of beta2-microglobulin in uremic patients as determined by high resolution mass spectrometry.

By using a high resolution top-down and bottom-up approach we identified and characterized the AGEs of beta2-microglobulin (ß2-m) formed by incubating the protein in the presence of glucose and of the main reactive carbonyl species. Glucose induced glycation on the N-terminal residue, while glyoxal (GO) and methylglyoxal (MGO) covalently reacted with Arg3. Carboxymethyl (CM-R) and imidazolinone (R-GO) derivatives were identified in the case of GO and carboxyethyl arginine (CE-R) and methyl-imidazolinone (R-MGO) for MGO. Interestingly, α,ß-unsaturated aldehydes [4-hydroxy-2-nonenal (HNE); 4-oxo-2-nonenal (ONE); acrolein (ACR)] did not induce any covalent modifications up to 100µM. The different reactivity of ß2-m towards the different RCS was then rationalized by molecular modeling studies. The MS method was then applied to fully characterize the AGEs of ß2-m isolated from the urine of uremic subjects. CM-R, CE-R and R-MGO were easily identified on Arg3 and their relative abundance in respect to the native protein determined by a semi-quantitative approach. Overall, the AGEs content of urinary ß2-m ranged from 0.2 to 1% in uremic subjects. The results here reported offer novel insights and technical achievements for a potential biological role of AGEs-ß2-m in pathological conditions.