Near-Infrared Light-Induced Self-Powered Aptasensing Platform for Aflatoxin B1 Based on Upconversion Nanoparticles-Doped Bi2S3 Nanorods.

A light source plays a pivotal role in a photofuel cell (PFC)-based self-powered biosensor. Although a visible light source has been extensively employed to drive a PFC, it still has some drawbacks for biosensing due to its relatively high energy. Herein we constructed a PFC-based aptasensor using near-infrared (NIR) light as the irradiation source. To achieve an efficient absorption of the NIR light, NaYF4:Yb,Er upconversion nanoparticles (UCNPs) that could convert low-energy incident light into high-energy radiation were combined with Bi2S3 nanorods (UCNPs/Bi2S3) to serve as the photoactive materials. The PFC was comprised of a UCNPs/Bi2S3 photoanode and a Pt cathode, which could generate electrical output under NIR light irradiation to provide the self-powered sensing signal without the supply from an external power source. The aflatoxin B1 (AFB1) binding aptamer was immobilized on the photoanode to serve as the recognition element. The detection of AFB1 was based on the competition between the interaction of aptamer with AFB1 analyte and the hybridization of aptamer with Au nanoparticles-labeled DNA sequence (AuNPs-cDNA). Under optimum conditions, the proposed aptasensor presented good sensitivity and high specificity for AFB1 detection in the concentration range from 0.01 to 100 ng·mL-1, with a detection limit of 7.9 pg·mL-1. Moreover, the developed sensor was applied to an assay of AFB1 in flour samples with a desirable accuracy and precision.

Y12 nitration of human calcitonin (hCT): A promising strategy to produce non-aggregation bioactive hCT.

Irreversible aggregation can extremely limit the bioavailability and therapeutic activity of peptide-based drugs. There is therefore an urgent demand of effective strategy to control peptide aggregation. Recently, we found that tyrosine nitration at certain sites of peptide can effectively inhibit its aggregation. This minor modification may be an ideal strategy to the rational design of peptide-based drugs with low aggregation propensity yet without loss of bioactivity. Human calcitonin (hCT) is such a peptide hormone known for its hypocalcaemic effect but has limited pharmaceutical potential due to a high tendency to aggregate. In this study, by using multiple techniques including Fluorescence, TEM, Nu-PAGE and CD, we demonstrated that Y12 nitration of hCT would significantly inhibit its self-assembles, and we also found that this modification would not only reduce the cytotoxicity induced by peptide aggregation, but also had little effect on its potency. This finding may provide a novel strategy for clinically application of hCT instead of sCT.

Structure effect of water-soluble iron porphyrins on catalyzing protein tyrosine nitration in the presence of nitrite and hydrogen peroxide.

Water-soluble iron porphyrins, such as FeTPPS (5,10,15,20-tetrakis (4-sulfonatophenyl) porphyrinato iron (III)), FeTMPyP (5,10,15,20-tetrakis (N-methyl-4'-pyridyl) porphyrinato iron (III) chloride) and FeTBAP (5,10,15,20-tetrakis (4-benzoic acid) porphyrinato iron (III)), are highly active catalysts for peroxynitrite decomposition and thereby have been suggested as therapeutic agent for inflammatory diseases that implicate the involvement of nitrotyrosine formation. Here, we systemically investigated catalytic properties of FeTPPS, FeTMPyP and FeTBAP on protein nitration in the presence of hydrogen peroxide and nitrite. We showed that FeTPPS, FeTBAP and FeTMPyP all exhibited higher peroxidase activity in compared with hemin. As to protein nitration, the catalytic effect of FeTPPS and FeTBAP are effective in the presence of hydrogen peroxide and nitrite, while negligible BSA nitration was observed in the case of FeTMPyP. Moreover, the underlying mechanism of the oxidation of FeTPPS, FeTBAP and FeTMPyP was further studied. Collectively, our results suggest that, compound I and II species are involved in as the key intermediates in FeTMPyP/H2O2 system as similar as those in FeTPPS/H2O2 and FeTBAP/H2O2 system. As compared to weak antioxidants, TPPS and TBAP, however, TMPyP scavenges oxo-Fe (IV) intermediates of FeTMPyP at a faster rate by significant self-degradation; results in the shortest lifetimes of OFeIV-TMPyP and the lowest catalytic activity on oxidizing tyrosine and nitrite; and therefore, attributes to inactivation of FeTMPyP in protein nitration. In addition, association of FeTMPyP to BSA was found weak, while strong binding of FeTPPS and FeTBAP were observed. The weak binding keeps away of target residue of BSA from the center of FeTMPyP where the RNS is generated, which might be attributed as additional factors to the inactivation of FeTMPyP in protein nitration.

Nitration of hIAPP promotes its toxic oligomer formation and exacerbates its toxicity towards INS-1 cells.

Amyloid formation of human islet amyloid polypeptide (hIAPP) is one of the most common pathological features of type 2 diabetes (T2D). Increasing evidences have shown that the overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) play an important role in the development of the T2D. Interestingly, our previous studies indicated that heme could bind to hIAPP, and the complex might induce the nitration of tyrosine residue (Y37) of hIAPP in the presence of hydrogen peroxide and nitrite. However, it remains unclear about effect of the nitration on the implicated function of hIAPP in the development of T2D. In this study, fluorescent assays, transmission electron microscopy (TEM), atomic force microscope (AFM) were used to demonstrate that nitration of hIAPP significantly decreased its fibril formation. But the decreased fibril formation was not through the diminished aggregation of hIAPP monomer as suggested by the results of circular dichroism spectroscopy (CD) and gel electrophoresis assay. Surface-enhanced raman spectroscopy (SERS) indicated that nitration of hIAPP impaired the intermolecular hydrogen bonding. On the basis of these results, we hypothesize that nitration of hIAPP may block the intermolecular hydrogen bonding, leading to the inhibition of its fibril formation. In addition, cytotoxicity study of native and modified hIAPP was also performed on INS-1 cells, which revealed exacerbated toxicity of hIAPP by its nitration. The findings in this study that nitration of hIAPP promotes its oligomer formation and thus exacerbates its cytotoxicity suggests a possible link between the nitrite (or the sum of nitrite and nitrate) levels and T2D, and ameliorated nitration of hIAPP by diminishing nitrative stress might be a promising therapeutic strategy for T2D.

Tyrosine residues of bovine serum albumin play an important role in protecting SH-SY5Y cells against heme/H2O2/NO2--induced damage.

Serum albumin (SA) has been shown to act as a heme scavenger in hemolysis and can protect cell against the toxic effect of heme. However, the mechanism of SA in heme detoxification is not well understood. Interestingly, increasing studies indicate that heme/H2O2-dependent reaction is unlikely to be the principal cause of heme toxicity in excessive intravascular hemolysis conditions. Moreover, high levels of NO2- and NO3- were also found in patients with severe hemolytic diseases, which seem to involve in heme toxic effect as well. Therefore, we proposed that studying the protection mechanism of SA against the heme/H2O2/NO2--induced cytotoxicity may be more consistent with free heme-associated disorder pathologies. In this study, we tested the hypotheses that tyrosine residues of bovine serum albumin (BSA) play a prominent role in detoxifying heme in SH-SY5Y cells. Both BSA and tyrosine modified BSA (BSA-T) were used to explore this protective mechanism. Most of cellular injury (oxidative and nitrative damage) induced by heme/H2O2/NO2- were prevented by pretreatment with an equimolar concentration of BSA or BSA-T, and BSA was found more efficient than BSA-T. Meanwhile, BSA or BSA-T binding to heme is not accompanied by a decrease of heme's peroxidase activity. Collectively, these data suggest that the protecting effect of BSA against heme-induced damage in the intravascular hemolysis diseases is not accomplished by preventing the primary reactivity of heme with H2O2, but by trapping radical through special residues such as tyrosine to render other important protein less damaged.

Synthesis of a CdS-decorated Eu-MOF nanocomposite for the construction of a self-powered photoelectrochemical aptasensor.

A composite of CdS nanoparticles and a europium metal organic framework (Eu-MOF) (CdS/Eu-MOF) was synthesized. The unique properties of MOFs help to improve the photoelectrochemical (PEC) properties of CdS by reducing charge carrier recombination and utilizing a broader spectrum for light harvesting. Under visible light illumination, the photocurrent of the CdS/Eu-MOF composite modified electrode was about 2.5-fold higher than that of the CdS modified electrode. When an ampicillin (AMP)-binding aptamer was immobilized on the CdS/Eu-MOF modified electrode as a recognition element, a self-powered PEC aptasensor exhibiting a specific photocurrent response to AMP was constructed. Several experimental conditions such as the ratio of CdS to MOF, the coating amount of the CdS/Eu-MOF suspension and the concentration of the aptamer were studied. Under optimum conditions, the photocurrent of the developed sensor was linearly related to the logarithm AMP concentration in the range of 1 × 10-10 to 2 × 10-7 M, with a detection limit (3S/N) of 9.3 × 10-11 M. Moreover, this sensor exhibited excellent selectivity, good repeatability and desirable stability. It was successfully applied to the detection of AMP in lake water and milk samples.

Hemin-catalyzed biomimetic oxidative phenol-indole [3 + 2] reactions in aqueous media.

A hemin/H2O2 catalytic system for oxidative phenol-indole [3 + 2] coupling in aqueous solution has been developed, enabling benign synthesis of valuable benzofuroindolines under sustainable conditions. Mechanistic studies revealed the dual role of iron porphyrin responsible for both phenol oxidation and Lewis acid activation, which differs from the well-explored chemistry of hemin in carbene and nitrene insertion reactions. A preliminary experiment with cytochrome c showed that the turnover of iron porphyrin was amenable for a macromolecular setting with remarkable efficiency (ca. 13 300 TON).

Copper Binding Induces Nitration of NPY under Nitrative Stress: Complicating the Role of NPY in Alzheimer's Disease.

Neuropeptide Y (NPY) is a 36 amino acid peptide that regulates a multitude of physiological functions in the central nervous system and has been shown to be involved in Alzheimer's disease (AD). A change in copper homeostasis is a remarkable feature of AD, and the dysregulation may contribute to toxicity in neural cells. Moreover, it has been shown that copper could interact with many neuropeptides and result in catalyzing the production of reactive oxygen species, which may lead to peptide oxidation. Besides, copper could also catalyze protein tyrosine nitration under oxidative stress, and there are two tyrosine residues playing an important role in NPY. Therefore, it is also likely that copper has an action on NPY and potentially influences its functions through tyrosine nitration. In this paper, the studies of the interaction of copper with NPY and the copper-catalyzed NPY nitration were performed. The electrochemical techniques, UV-vis spectroscopy, mass spectrometry, and fluorescence titration, have been applied to show that copper can interact with NPY to form a Cu-NPY complex with a conditional dissociation constant of 0.021 µmol/L, and the binding promotes the generation of •OH. Dot blotting results reveal that NPY can be nitrated upon binding with copper under nitrative stress. Furthermore, liquid chromatography-mass spectrometry (LC-MS) identify that the tyrosine residues in NPY are all nitrated during the nitration process, which will cause the inactivation of NPY shown by our previous study. This study supports the hypothesis that copper has a close correlation with NPY and implicates the peptide in AD. These data may provide a new insight into understanding the pathology and pathogenesis of AD.

Hemin-Graphene Derivatives with Increased Peroxidase Activities Restrain Protein Tyrosine Nitration.

Protein tyrosine nitration is implicated in the occurrence and progression of pathological conditions involving free radical reactions. It is well recognized that hemin can catalyze protein tyrosine nitration in the presence of nitrite and hydrogen peroxide. Generally, the catalytic efficiency is positively correlated to its peroxidase activity. In this study, however, it is found that the efficiency of hemin in catalyzing protein tyrosine nitration is largely suppressed after functionalization with graphene derivatives, even though its peroxidase-like activity is more than quadrupled. Further studies show that the oxidation of tyrosine is still observed for these composites; dityrosine formation, however, is greatly inhibited. Furthermore, these composites also exhibit strong effects on the oxidation of nitrite into nitrate. Therefore, we propose a mechanism in which hemin-graphene derivatives facilitate the oxidation of tyrosine and nitrite to produce tyrosyl radicals and nitrogen dioxide radicals in the presence of hydrogen peroxide, but graphene interlayers serve as barriers that hinder radical-radical coupling reactions; consequently, protein tyrosine nitration is restrained. This property of hemin-graphene derivatives, by which they catalyze substrate oxidation but suppress radical-radical coupling reactions, shows their great potential in selective oxidation procedures for byproduct removal.

Interaction of glyceraldehyde-3-phosphate dehydrogenase and heme: The relevance of its biological function.

GAPDH was speculated to function as a transient trap to reduce the potential toxicity of free heme by a specific and reversible binding with heme. Up to now, there has been lack of studies focused on this effect. In this paper, the efficiency of GAPDH-heme complex on catalyzing protein carbonylation and nitration, the cross-linking of heme to protein formation, and cytotoxicity of GAPDH-heme were studied. It was found that the binding of GAPDH could inhibit H2O2-mediated degradation of heme. Peroxidase activity of GAPDH-heme complex was higher than that of free heme, but significantly lower than that of HSA-heme. Catalytic activity of heme corresponded complex toward tyrosine oxidation/nitration was decreased in the order of HSA-heme, heme and GAPDH-heme. GAPDH also inhibited heme-H2O2-NO2- induced protein carbonylation. No covalent bond was formed between heme and GAPDH after treated with H2O2. GAPDH was more effective than HSA on protecting cells against heme-NO2--H2O2 induced cytotoxicity. These results indicate that binding of GAPDH inhibits the activity of heme in catalyzing tyrosine nitration and protects the coexistent protein against oxidative damage, and the mechanism is different from that of HSA. This study may help clarifying the protective role of GAPDH acting as a chaperone in heme transfer to downstream areas.

Strong Inhibitory Effect of Heme on hIAPP Fibrillation.

The deposition of human islet amyloid polypeptide (hIAPP) within ß-cells is implicated in the etiology of type 2 diabetes mellitus (T2Dm). It was reported that heme could bind to hIAPP. We speculate that binding may affect the aggregation of hIAPP. In this study, UV-vis spectroscopy was used to detect the interaction pattern between the heme and hIAPP. ThT and Bis-ANS fluorescence assay, circular dichroism spectroscopy, gel electrophoresis assay, and transmission electron microscopy were employed to study the effect of heme on the aggregation of hIAPP. We found that heme dramatically inhibited hIAPP aggregation, even partially dismantled hIAPP aggregates by preventing its conformational changes. Moreover, a similar inhibitory effect was also observed on mutant hIAPP. In the compared group, the inhibitory effects of protoporphyrin on hIAPP and its mutants aggregation were weaker. Similarly, its effect on the dismantlement of the aggregates was also weaker. On the basis of these results, we revealed that the heme iron center was not required for the inhibitory effect on hIAPP but affected the binding affinity of heme to hIAPP. Besides Arg11 and His18, other hydrophobic residues of hIAPP may also play important roles in heme binding. Our results may help to develop an in-depth understanding of the interaction between heme and hIAPP, which would be helpful in designing new therapeutic strategies against T2Dm.

Nitration of Tyrosine Residue Y10 of Aß1-42 Significantly Inhibits Its Aggregation and Cytotoxicity.

Amyloid-ß plaques and oxidative stress are the major hallmarks of Alzheimer's disease. Our previous study found that the heme-Aß complex enhanced the catalytic effect of free heme on protein tyrosine nitration in the presence of hydrogen peroxide (H2O2) and nitrite (NO2-). Y10 in Aß could be the first target to be nitrated. We also found that nitration of Aß1-40 significantly decreased its aggregation. However, a contrary report showed that nitration of Aß1-42 by peroxynitrite enhanced its aggregation. To rule out the interference of peroxynitrite caused Aß oxidation, we used synthetic Y10 nitrated Aß1-42 to study the influence of Y10 nitration on Aß1-42's aggregation and cytotoxicity in this study. We confirmed that Aß1-42 could be nitrated in the presence of H2O2, NO2-, and heme by dot blotting. CD spectroscopy showed an increase of ß-sheet structure of Aß1-42 and its mutants. The thioflavin T (ThT) flourescence assay revealed that both nitration and chlorination significantly inhibited Aß1-42 fibril formation. TEM and AFM observations of Aß peptide aggregates further confirmed that Y10 modification inhibited Aß1-42 fibril formation. The cytotoxicity study of native and modified Aß peptides on SH-SY5Y cells revealed that nitration of Aß1-42 remarkably decreased the neurotoxicity of Aß1-42. On the basis of these results, we hypothesized that nitration of Y10 may block the π-π stacking interactions of Aß1-42 so that it inhibit its aggregation and neurotoxicity. More importantly, considerable evidence suggested that the levels of nitrite plus nitrate significantly decreased in the brain of AD patients. Thus, we believe that these findings would be helpful for further understanding the function of Aß in AD.

Triosephosphate isomerase tyrosine nitration induced by heme-NaNO2 -H2 O2 or peroxynitrite: Effects of different natural phenolic compounds.

Peroxynitrite and heme peroxidases (or heme)-H2 O2 -NaNO2 system are the two common ways to cause protein tyrosine nitration in vitro, but the effects of antioxidants on reducing these two pathways-induced protein nitration and oxidation are controversial. Both nitrating systems can dose-dependently induce triosephosphate isomerase (TIM) nitration, however, heme-H2 O2 -NaNO2 was less destructive to protein secondary structures and led to more nitrated tyrosine residue than 3-morpholinosydnonimine hydrochloride (SIN-1, a peroxynitrite donor). Both of desferrioxamine and catechin could inhibit TIM nitration induced by heme-H2 O2 -NaNO2 and SIN-1 and protein oxidation induced by SIN-1, but promoted heme-H2 O2 -NaNO2 -induced protein oxidation. Moreover, the antagonism of natural phenolic compounds on SIN-1-induced tyrosine nitration was consistent with their radical scavenging ability, but no similar consensus was found in heme-H2 O2 -NaNO2 -induced nitration. Our results indicated that peroxynitrite and heme-H2 O2 -NaNO2 -induced protein nitration was different, and the later one could be a better model for anti-nitration compounds screening.

Molecular extraction in single live cells by sneaking in and out magnetic nanomaterials.

Extraction of intracellular molecules is crucial to the study of cellular signal pathways. Disruption of the cellular membrane remains the established method to release intracellular contents, which inevitably terminates the time course of biological processes. Also, conventional laboratory extractions mostly use bulky materials that ignore the heterogeneity of each cell. In this work, we developed magnetized carbon nanotubes that can be sneaked into and out of cell bodies under a magnetic force. Using a testing model with overexpression of GFP, the nanotubes successfully transported the intracellular GFP out at the single-cell level. The confined nanoscale invasiveness did not change cell viability or proliferation. This study presents the proof of concept of a previously unidentified real-time and single-cell approach to investigate cellular biology, signal messengers, and therapeutic effects with nanomaterials.

Tyrosine residues play an important role in heme detoxification by serum albumin.

BACKGROUND: Serum albumin binds avidly to heme to form heme-serum albumin complex, also called methemalbumin, and this binding is thought to protect against the potentially toxic effects of heme. However, the mechanism of detoxification has not been fully elucidated. METHODS: SDS-PAGE and Western blot were used to determine the efficiency of methemalbumin on catalyzing protein carbonylation and nitration. HPLC was used to test the formation of heme to protein cross-linked methemalbumin. RESULTS: The peroxidase activity of heme increased upon human serum albumin (HSA) binding. Methemalbumin showed higher efficiency in catalyzing tyrosine oxidation than free heme in the presence of H2O2. Methemalbumin catalyzed self-nitration and significantly promoted the nitration of tyrosine in coexistent protein, but decreased the carbonylation of coexistent protein compared with heme. The heme to protein cross-linked form of methemalbumin suggested that HSA trapped the free radical accompanied by the formation of ferryl heme. When tyrosine residues in HSA were modified by iodination, HSA lost of protection effect on protein carbonylation. The low concentration of glutathione could effectively inhibit tyrosine nitration, but had no effect on protein carbonylation. CONCLUSION: HSA protects against the toxic effect of heme by transferring the free radical to tyrosine residues in HSA, therefore protecting surrounding proteins from irreversible oxidation, rather than by direct inhibiting the peroxidase activity. The increased tyrosine radicals can be reduced by endogenic antioxidants such as GSH. GENERAL SIGNIFICANCE: This investigation indicated the important role of tyrosine residues in heme detoxification by HSA and suggested a possible novel mechanism.

Key roles of Tyr 10 in Cu bound Aß complexes and its relevance to Alzheimer's disease.

Recent studies show that the accumulation of redox-active Cu mediates the aggregation of amyloid ß-peptide (Aß) and conspicuous oxidative damage to the brain in Alzheimer's disease (AD). However, the key roles for Tyr 10 in Aß-Cu(II) complex and its potential biological relevance to AD etiology under oxidative stress, were not stressed enough. Interestingly, our results indicated that Aß40 (not Aß16)-Cu(II) complex showed obviously enhanced peroxidase activity than free Cu(II). Although Tyr 10 was not the residue binding Cu(II), the mutation of Tyr 10 residue in Aß40 decreased the peroxidase activity of Aß40-Cu(II) complex, and the mutation of Tyr 10 could inhibit Aß40 aggregation. Under oxidative and nitrative stress conditions, the Aß-Cu(II) complex caused oxidation and nitration of the Aß Tyr 10 residue through peroxidase-like reactions, where the formation of Cu(I) and hydroxyl radical (OH) was proposed as a chemical mechanism. We also showed that, when Aß40 aggregates were bound to Cu(II), they retained peroxidase-like activity. Therefore, Tyr 10 residue is pivotal in Aß-Cu(II) complex and shows important relevance to oxidative stress, implicating the novel significance of Tyr 10 residue as well as Aß-Cu(II) complex in the pathology of AD.

Nitration of Y10 in Aß1-40: is it a compensatory reaction against oxidative/nitrative stress and Aß aggregation?

Amyloid ß peptide (Aß) aggregation is considered to be a crucial pathological biomarker of Alzheimer's disease (AD). It was found that Aß and heme can form an Aß-heme complex, which results in increased heme pseudoperoxidase activity. Recently, we found that increasing pseudoperoxidase activity induces elevated tyrosine nitration on Aß in the presence of nitrite and hydrogen peroxide. However, the nature of tyrosine nitration of Aß and its physiologic significance are still unknown. In this study, we revealed that Aß1-40 can be nitrated in vitro by binding to heme in the presence of nitrite and hydrogen peroxide. Moreover, we found that tyrosine nitration had little effect on Aß1-40's binding activity with heme. A TMB assay also revealed that the peroxidase activity of the heme-Aß1-40Y10(3N)T (tyrosine 10 was replaced with 3-nitrtotyrosine in Aß1-40) complex was moderately increased compared with that of the heme-Aß1-40 complex. Furthermore, Thioflavin T fluorescence and transmission electron microscopic characterization indicated that tyrosine nitration significantly decreased the aggregation of Aß1-40. In addition, a cytotoxicity test verified that wild-type Aß1-40 was more cytotoxic than that of Aß1-40Y10(3N)T. These results suggest that nitration of Aß1-40 might be an Aß detoxicant process and a compensatory reaction to nitrative stress. Our findings may lead to a detailed understanding of the function of Aß1-40 and may be helpful in preventing and curing AD.

Tyrosine nitration of glucagon impairs its function: Extending the role of heme in T2D pathogenesis.

New studies raise the possibility that the higher glucagon (GCG) level present in type 2 diabetes (T2D) is a compensatory mechanism to enhance ß-cell function, rather than induce dysregulated glucose homeostasis, due to an important role for GCG that acts directly within the pancreas on insulin secretion by intra-islet GCG signaling. However, in states of poorly controlled T2D, pancreatic α cell mass increases (overproduced GCG) in response to insufficient insulin secretion, indicating decreased local GCG activity. The reason for this decrease is not clear. Recent evidence has uncovered a new role of heme in cellular signal transduction, and its mechanism involves reversible binding of heme to proteins. Considering that protein tyrosine nitration in diabetic islets increases and glucose-stimulated insulin secretion (GSIS) decreases, we speculated that heme modulates GSIS by transient interaction with GCG and catalyzing its tyrosine nitration, and the tyrosine nitration may impair GCG activity, leading to loss of intra-islet GCG signaling and markedly impaired insulin secretion. Data presented here elucidate a novel role for heme in disrupting local GCG signaling in diabetes. Heme bound to GCG and induced GCG tyrosine nitration. Two tyrosine residues in GCG were both sensitive to the nitrating species. Further, GCG was also demonstrated to be a preferred target peptide for tyrosine nitration by co-incubation with BSA. Tyrosine nitration impaired GCG stimulated cAMP-dependent signaling in islet ß cells and decreased insulin release. Our results provided a new role of heme for impaired GSIS in the pathological process of diabetes.

Aß interacts with both the iron center and the porphyrin ring of heme: mechanism of heme's action on Aß aggregation and disaggregation.

Amyloid ß peptide (Aß) aggregation is a pathological hallmark of Alzheimer's disease (AD). Modulation of the self-assembly processes, therefore, is thought to be an attractive strategy for the prevention and treatment of AD. Interestingly, heme has been found to inhibit Aß aggregation and even dismantle Aß aggregates. However, the mechanism remains unresolved. Recent research has shown that heme binds preferentially to the His(13) residue of Aß with the iron center, while the hydrophobic domain of Aß is also able to bind to heme. Herein, absorption spectrometric, Thioflavin T fluorescence, and circular dichroism spectroscopic and transmission electron microscopic measurements revealed that the iron center is not required for the inhibition of Aß aggregation but do influence the binding affinity of heme toward Aß and the dismantlement rate and degree of the Aß aggregates. By studying the interaction of different truncated or mutated Aß peptides with heme or protoporphyrin, we further found that the porphyrin ring of heme is implicated to interact preferentially with the Phe(19) residue, facilitating the binding of heme to Aß and disturbing the interstrand aromatic interaction between the Phe residues, which is crucial for Aß fibrillation. These findings open new avenues in the understanding of the interaction between the heme and Aß and the pathways for modulation of Aß aggregation and disaggregation, which would be helpful in designing therapeutic strategies against AD.

Mussel inspired multifunctional bovine serum albumin (BSA) coatings loaded with Baicalein (BAI) to enhance osteogenesis and resist oxidative stress for potential application on implant.

Oxidative stress is associated with most traumatic or pathological bone defects, and seriously affects the effect of implantation. The construction of antioxidative and osteogenic coatings is of great significance to accelerate the bone regeneration of implants. In this study, baicalein (BAI), a nature flavonoid drug, was loaded in bovine serum albumin (BSA) by desolvent method to prepare BAI-BSA composite protein, and tannic acid (TA)/BAI-BSA coatings were further built via layer by layer self-assembly technology. BAI-BSA possesses good biocompatibility that showed no cytotoxicity to osteoblasts and erythrocytes, and helps to enhance the activity of alkaline phosphatase (ALP) and promote the formation of osteogenic mineralized calcium nodules. After assembled with TA, BAI-BSA coating significantly promoted cell adhesion and in vitro osteogenic mineralization of MC3T3-E1. Moreover, BAI drug loading improved the antioxidative function of BSA coatings effectively. The scavenging rates of (TA/BAI-BSA-10)4 for ABTS+• and DPPH• free radicals were 69.6 ± 16.1 % and 53.4 ± 2.4 %, respectively. At cellular level, the TA/BAI-BSA coating effectively inhibited the impact of oxidative stress on the oxidative damage of osteoblasts. The drug-loaded protein coatings possess both great antioxidative and osteogenic functions, which have important potential in the field of bone repair.