In Situ Preparation of Tannic Acid-Modified Poly(N-isopropylacrylamide) Hydrogel Coatings for Boosting Cell Response.

The improvement of the capability of poly(N-isopropylacrylamide) (PNIPAAm) hydrogel coating in cell adhesion and detachment is critical to efficiently prepare cell sheets applied in cellular therapies and tissue engineering. To enhance cell response on the surface, the amine group-modified PNIPAAm (PNIPAAm-APTES) nanohydrogels were synthesized and deposited spontaneously on tannic acid (TA)-modified polyethylene (PE) plates. Subsequently, TA was introduced onto PNIPAAm-APTES nanohydrogels to fabricate coatings composed of TA-modified PNIPAAm-APTES (PNIPAAm-APTES-TA). Characterization techniques, including TEM, SEM, XPS, and UV-Vis spectroscopy, confirmed the effective deposition of hydrogels of PNIPAAm as well as the morphologies, content of chemical bonding-TA, and stability of various coatings. Importantly, the porous hydrogel coatings exhibited superhydrophilicity at 20 °C and thermo-responsive behavior. The fluorescence measurement demonstrated that the coating's stability effectively regulated protein behavior, influencing cell response. Notably, cell response tests revealed that even without precise control over the chain length/thickness of PNIPAAm during synthesis, the coatings enhanced cell adhesion and detachment, facilitating efficient cell culture. This work represented a novel and facile approach to preparing bioactive PNIPAAm for cell culture.

Biflavones inhibit the fibrillation and cytotoxicity of the human islet amyloid polypeptide.

Biflavones are a kind of natural compound with a variety of biological activities, which have the capability of reversing diabetes and neurodegenerative diseases. The human islet amyloid polypeptide (hIAPP) is closely related to the pathological process of type II diabetes mellitus (T2DM). The development of new inhibitors is crucial to prevent hIAPP aggregation against T2DM. However, the influences of biflavones on hIAPP aggregation are unknown. In this work, we utilized a series of biophysical and biochemical techniques to seek the inhibitory effects of two biflavones on hIAPP fibril formation and their interaction mechanism. The biflavones namely amentoflavone (1), and bilobetin (2), distinctly prevented the self-assembly behavior of hIAPP, and depolymerized the aged aggregates to small oligomers and monomers. In addition, the two compounds displayed strong binding affinity to hIAPP mainly through hydrophobic and hydrogen bonding interactions, and the hydroxyl substitution in 1 was superior to the methoxy substitution in 2 at the same C8 position in impeding hIAPP aggregation. 1 and 2 also decreased hIAPP-induced cytotoxicity by reducing peptide oligomerization. This work offers useful data for understanding the roles of biflavones in hIAPP fibrillation and for the treatment of T2DM and other amyloidosis related diseases.

Triterpenoids impede the fibrillation and cytotoxicity of human islet amyloid polypeptide.

The inhibition of human islet amyloid polypeptide (hIAPP) deposition to block its toxicity is an important strategy for the prevention and treatment of type II diabetes mellitus (T2DM).Natural compounds with pharmacological properties and low toxicity can serve as a good point to discover potential inhibitors of protein misfolding, which may be useful for the treatment of various amyloidosis-related diseases. Previous studies have reported that triterpenoids, such as maslinic acid (MA) and momordicin I (MI), can modulate glucose metabolism partially by reducing insulin resistance. However, the internal antidiabetic mechanism of these triterpenoids remains unclear. In this study, we examined the inhibition and disaggregation of MAandits isomer MI on the fibrillation of hIAPP using various experimental and computational approaches. The assembly behaviors and peptide-induced cytotoxicity of hIAPP could be effectively resisted by MA and MI. Moreover, the interaction of the two triterpenoids with hIAPP displayed a spontaneous and exothermic process. Moreover, molecular dynamics simulation results of different peptides revealed that MA and MI could bind to Asn and other non-polar residues near the core C-terminal region and reduce the oligomerization of hIAPP. The binding affinity was predominantly contributed by hydrophobic, electrostatic and hydrogen bonding interactions. The present work provides valuable data for MA and MI to treat T2DM and amyloidosis-related diseases.

Procyanidine resists the fibril formation of human islet amyloid polypeptide.

Human islet amyloid polypeptide (hIAPP) is widely studied due to its close correlation with the pathogenic mechanism of type II diabetes mellitus (T2DM). Bioflavonoids have been used in the neurodegeneration and diabetes studies. However, the structure-activity relationship remains unclear in many of these compounds. In this work, we performed diverse biophysical and biochemical methods to explore the inhibition of procyanidine on hIAPP and compared with that on amyloid-ß (Aß) protein which is linked to Alzheimer's disease (AD). The procyanidine effectively inhibited the aggregation of hIAPP and Aß through hydrophobic and hydrogen bonding interactions, it dissolved the aged fibrils into nanoscale particles. The compound also ameliorated the cytotoxicity and the membrane leakage by reducing the peptide oligomerization. The procyanidine showed better binding affinity and inhibitory effects on peptide aggregation and upregulated the cell viability to hIAPP than to Aß, which could be a prospective inhibitor against hIAPP. This work also offered a possible strategy for T2DM and AD treatments.

Resistance of nepetin and its analogs on the fibril formation of human islet amyloid polypeptide.

The self-aggregation of human islet amyloid polypeptide (hIAPP) into toxic oligomers and fibrils is closely linked to the pathogenesis of type II diabetes mellitus. Inhibitors can resist hIAPP misfolding, and the resistance can be considered an alternative therapeutic strategy for this disease. Flavones have been applied in the field of diabetes research, however, the inhibition mechanism of many compounds on the fibril formation of related pathogenic peptides remains unclear. In this work, four flavones, namely, nepetin (1), genkwanin (2), luteolin (3), and apigenin (4), were used to impede the peptide aggregation of hIAPP and compared with that on Aß protein, which is correlated with Alzheimer's disease. Results indicated that the four flavones effectively inhibited the aggregation of the two peptides and mostly dispersed the mature fibrils to monomers. The interactions of flavones with the two peptides demonstrated a spontaneous and exothermic reaction through predominant hydrophobic and hydrogen bonding interactions. The binding affinities of 1 and 3 were stronger than those of 2 and 4 possibly because of the difference in the substituent groups of these molecules. These flavones could also decrease membrane leakage and upregulate cell viability by reducing the formation of toxic oligomers. Moreover, the performance of these flavones in terms of binding affinity, cellular viability, and decreased oligomerization was better on hIAPP than on Aß. This work offered valuable data about these flavones as prospective therapeutic agents against relevant diseases.

Tetracycline derivatives resist the assembly behavior of human islet amyloid polypeptide.

The misfolding of amyloid proteins is closely correlated with the pathogenesis of protein conformation-related diseases, such as Alzheimer's disease (AD), prion disease, and type 2 diabetes mellitus (T2DM). The deposition of human islet amyloid polypeptide (hIAPP) and amyloid-ß (Aß) protein is entangled in AD and diabetes mellitus. The development of potential inhibitors is a feasible therapeutic strategy to treat these diseases by resisting peptide aggregation. Doxycycline is a typical clinical antibiotic that has been utilized in neurodegenerative studies. However, the roles of tetracyclines in hIAPP aggregation remain unclear. Herein, we studied the inhibitory effects of three tetracycline derivatives, namely, minocycline hydrochloride (1), methacycline hydrochloride (2), and doxycycline (3), on the fibril formation and cytotoxicity of hIAPP and compared with that of Aß. The well-known 3 was selected and compared with 1 and 2. Tetracycline derivatives acted as effective inhibitors to reverse the self-assembly of hIAPP and Aß, and disaggregate the aged peptides fibrils into mostly monomers. Tetracycline derivatives also reduced the cytotoxicity induced by amyloid peptide oligomerization. Further molecular mechanism studies revealed hydrophobic and hydrogen bond interactions as the primary binding pattern between tetracycline derivatives and peptides. A good bioactivity against amyloidosis was demonstrated by three tetracyclines. This work provided a basis for using tetracycline antibiotics as potential inhibitors against hIAPP aggregation.

Regulation of Artemisinin and Its Derivatives on the Assembly Behavior and Cytotoxicity of Amyloid Polypeptides hIAPP and Aß.

The misfolding and aggregation of human islet amyloid polypeptide (hIAPP) and amyloid-ß (Aß) protein are closely associated with type 2 diabetes mellitus (T2DM) and Alzheimer's disease, respectively. Inhibitors of amyloid peptides include short peptides, aromatic organic molecules, nanoparticles, and even metal compounds. Sesquiterpenoid artemisinins are widely used in anti-malaria treatments, and they may modulate glucose homeostasis against diabetes. However, the antidiabetic mechanism of these compounds remains unclear. In this work, four compounds, namely, artemisinin (1), dihydroartemisinin (2), artesunate (3), and artemether (4), were exploited to inhibit the assembly behavior of hIAPP and compared with that of Aß. Although structurally distinct from other aromatic inhibitors of amyloid peptides, these sesquiterpenoids effectively altered the two peptides' fibril morphologies and disaggregated the mature fibrils mostly to the monomers. The interaction of artemisinins with the two peptides demonstrated a spontaneous, exothermic, and entropy-driven binding process predominantly through hydrophobic and hydrogen bonding interactions. Moreover, they reversed cytotoxicity and membrane leakage by reducing peptides' oligomerization. The results suggested that these compounds had better inhibition and disaggregation capability against hIAPP than against Aß. Furthermore, the effects of these compounds' structural modification on the amyloid fibril formation of the two peptides were observed. The molecular screening offered a new perspective for artemisinins as promising inhibitors against amyloidosis related diseases.

Assembly behavior of amylin fragment hIAPP19-37 regulated by Au(III) complexes.

Human islet amyloid polypeptide (hIAPP, amylin) may self-aggregate and rupture the membrane of ß cells, which is closely correlated with the pathogenesis of type 2 diabetes mellitus (T2DM). Hence, suppressing amyloidogenic hIAPP may be beneficial for the treatment of diabetes. As an important part of hIAPP, the fragment hIAPP19-37 was studied in this work to explore their disaggregation and cellular behavior regulation by some selected Au complexes, as follows: dichloro diethyl dithiocarbamate Au complex [AuCl2(DDTC)] (1), dichloro pyrrolidine dithiocarbamate Au complex [AuCl2(PDT)] (2), dichloro 4-4'-dimethyl-2,2'-bipyridyl Au(III) chloride [AuCl2(Me)2bpy]Cl (3), and dichloro 4-4-di-tert-butyl-2,2'-bipyridyl Au(III) chloride [AuCl2(t-Bu)2bpy]Cl (4). The peptide aggregation was observed and analyzed by fluorescence assay, atomic force microscopy (AFM), dynamic light scattering (DLS) and other methods. The assembly behaviors of hIAPP19-37 affected by the four Au complexes indicated that these complexes could effectively inhibit the fibrillation of the peptide and depolymerized the aged peptide into nanoscale particles. These Au compounds also remarkably reduced membrane leakage and cytotoxicity caused by peptide oligomers. An interaction study revealed that the complexes were predominantly bound with hIAPP19-37 through hydrophobic and electrostatic interactions, and metal coordination. The differences among various complexes were compared according to their binding affinity, inhibitory effect, and cellular behavior. Our study offers a potential path for the possible utilization of Au compounds as amyloidosis inhibitors.

Inhibitory effects of oxidovanadium complexes on the aggregation of human islet amyloid polypeptide and its fragments.

Human islet amyloid polypeptide (hIAPP) is synthesized by pancreatic ß-cells and co-secreted with insulin. Misfolding and amyloidosis of hIAPP induce ß-cell dysfunction in type II diabetes mellitus. Numerous small organic molecules and metal complexes act as inhibitors against amyloid-related diseases, justifying the need to explore the inhibitory mechanism of these compounds. In this work, three oxidovanadium complexes, namely, (NH4)[VO(O2)2(bipy)]·4H2O (1) (bipy = 2,2' bipyridine), bis(ethyl-maltolato, O,O)oxido-vanadium(IV) (2), and (bipyH2)H2[O{VO(O2)(bipy)}2]·5H2O (3), were synthesized and used to inhibit the aggregation of hIAPP and its fragments, namely, hIAPP19-37 and hIAPP20-29. Results revealed that shortening the peptide sequence decreased the aggregation capability of hIAPP fragments, and the oxidovanadium complexes inhibited the fibrillization of hIAPP better than its fragments. Interestingly, the binding of oxidovanadium complexes to hIAPP and its fragments presented a distinct thermodynamic behavior. Oxidovanadium complexes featured the disaggregation capability against hIAPP, better than against its fragments. These complexes also decreased the cytotoxicity caused by hIAPP and its fragments by reducing the production of oligomers. 3 may be a good hIAPP inhibitor based on its inhibition, disaggregation capability, and regulatory effect on peptide-induced cytotoxicity. Oxidovanadium complexes exhibit potential as metallodrugs against amyloidosis-related diseases.

Influence of methionine-ruthenium complex on the fibril formation of human islet amyloid polypeptide.

The abnormal aggregation and deposition of human islet amyloid polypeptide (hIAPP) are implicated in the pathogeny of type 2 diabetes mellitus (T2DM). Many aromatic ring-containing Ru complexes inhibit the aggregation of hIAPP. A new Ru complex Ru(bipy)(met)2·3H2O (1), where bipy is 2,2'-bipyridine and met is methionine, was synthesized and employed to resist the fibril formation of hIAPP and to promote the biocompatibility of metal complexes. Two polypyridyl Ru complexes, namely [Ru(bipy)3]Cl2(2) and Ru(bipy)2Cl2(3), were used for comparison. Results reveal that the three Ru complexes can inhibit hIAPP aggregation and depolymerize mature hIAPP fibrils. Interaction studies show that Ru complexes bind to hIAPP through metal coordination, hydrophobic interaction, and other intermolecular forces. The binding of the three compounds is spontaneous and exothermic. The compounds also rescue peptide-induced cytotoxicity to some extent. Similar to 3, the novel methionine-Ru complex 1 exhibits an enhanced inhibitory effect and binding affinity to hIAPP possibly because of the smaller steric hindrance and more profitable molecular configuration of 1 than those of 2. The newly designed amino acid-Ru complex may provide new insights into the treatment of T2DM and related amyloidosis diseases. Methionine-Ru complex effectively impedes the fibril formation of human islet amyloid polypeptide.

Regulation of heteronuclear Pt-Ru complexes on the fibril formation and cytotoxicity of human islet amyloid polypeptide.

The deposition of human islet amyloid polypeptide (hIAPP) is considered as a causative factor of type 2 diabetes mellitus (T2DM). Developing effective inhibitors against the fibril formation of hIAPP is a potential way to treat T2DM. Recent studies indicate that various metal complexes including homo-binuclear Ru complexes can inhibit hIAPP aggregation. Hetero-multinuclear PtRu metal complexes exhibit multiple bioactivities, but their roles in reversing amyloidosis remain unclear. In this work, we synthesized and identified a new hetero-binuclear PtRu metal complex Na{[RuCl4(DMSO-S)](bpy)[Pt(DMSO-S)Cl2]} (bpy: 4,4'-bipyridyl). We studied the inhibitory effect of the compound on hIAPP aggregation together with K{[RuCl4(DMSO-S)](pyz)[Pt (DMSO-S)Cl2]} (pyz: pyrazine) through diverse biophysical methods. Results showed that two PtRu metal complexes can remarkably reverse hIAPP aggregation and scatter the fibrils into nanoscale particles. Thermodynamic and spectrometric studies revealed that the binding of metal complexes with hIAPP was a spontaneous, enthalpy-driven process resulting from the predominant hydrophobic interaction and metal coordination. Two hetero-binuclear PtRu metal complexes showed stronger binding affinity and better inhibitory effects against peptide fibril formation than homo-binuclear Ru complexes and corresponding mononuclear Ru complexes. The compounds also regulated the peptide-induced cytotoxicity against Insulinoma ß-cells and significantly increased the cell viability. This work shed light on a potential strategy for designing hetero-multinuclear metal complexes against amyloidosis-related diseases.

Schiff base oxovanadium complexes resist the assembly behavior of human islet amyloid polypeptide.

The misfolding and fibrillation of human islet amyloid polypeptide (hIAPP) is related to the pathologic process of type II diabetes mellitus (T2DM). The inhibitors of hIAPP aggregation include aromatic organic molecules, short peptides, and metal complexes. Vanadium complexes have been applied for the treatment of diabetes since the 19th century. However, the antidiabetes mechanism remains unclear. In this work, we used four Schiff base oxidovanadium(IV) complexes, namely VO(bhbb)·H2O (1, and ligand 1 H2bhbb, 2-(5-bromo-2-hydroxylbenzylideneamino) benzoic acid), VO(nhbb)·H2O (2, and lignad 2 H2nhbb, 2-(5-nitro-2-hydroxylbenzylideneamino) benzoic acid), VO(cpmp)2 (3, and ligand 3 Hcpmp, 4-chloro-2-(phenylimino) methyl) phenol), and VO(bpmp)2 (4, and ligand 4 Hbpmp, 4-bromo- 2-(phenylmino) methyl) phenol) to inhibit the fibril formation of hIAPP and reduce peptide-induced cytotoxicity. Results indicated that the four Schiff base oxidovanadium complexes effectively impeded hIAPP aggregation and disaggregated mature fibrils into monomers or oligomers. These V complexes also decreased hIAPP-induced cytotoxicity. Among the four V complexes, 1 is a promising candidate metallodrug considering its inhibitory effect, disaggregation ability, regulation of peptide-induced cytotoxicity, and binding affinity to the peptide. Our research provides a new outlook for the design of oxidovanadium complexes as effective inhibitors of hIAPP against T2DM.

Regulation of the aggregation behavior of human islet amyloid polypeptide fragment by titanocene complexes.

The aggregation of human islet amyloid polypeptide (hIAPP) is associated with type II diabetes. The misfolding of hIAPP induces amyloid deposition and causes ß-cell dysfunction. Metal complexes are potential metallodrugs that may reverse the aggregation of amyloid peptides. hIAPP19-37 is a crucial fragment of the full-length hIAPP1-37 and contains typical aromatic residues and a core hydrophobic region. In this work, we studied the effects of titanocene complexes titanocene dichloride (1), titanocene salicylic acid complex (2), and titanocene methionine complex (3) on the aggregation behavior of hIAPP19-37. We also explored the possible interactions of these complexes with hIAPP19-37. Results demonstrated that the titanocene complexes could effectively inhibit the aggregation of hIAPP19-37. The complexes bound with hIAPP19-37 in a spontaneous and exothermic process through hydrophobic interaction. Moreover, complex 3 could significantly decrease the cytotoxicity of hIAPP19-37 and improve cell survival. These data provide a basis for the use of titanocene complexes as potential agents against amyloidosis.