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.

Inhibition of amyloid peptide fibril formation by gold-sulfur complexes.

Amyloid-related diseases are characterized by protein conformational change and amyloid fibril deposition. Metal complexes are potential inhibitors of amyloidosis. Nitrogen-coordinated gold complexes have been used to disaggregate prion neuropeptide (PrP106-126) and human islet amyloid polypeptide (hIAPP). However, the roles of metal complexes in peptide fibril formation and related bioactivity require further exploration. In this work, we investigated the interactions of amyloid peptides PrP106-126 and hIAPP with two tetracoordinated gold-sulfur complexes, namely, dichloro diethyl dithiocarbamate gold complex and dichloro pyrrolidine dithiocarbamate gold complex. We also determined the effects of these complexes on peptide-induced cytotoxicity. Thioflavin T assay, morphological characterization, and particle size analysis indicated that the two gold-sulfur complexes effectively inhibited the fibrillation of the amyloid peptides, which led to the formation of nanoscale particles. The complexes reduced the cytotoxicity induced by the amyloid peptides. Intrinsic fluorescence, nuclear magnetic resonance, and mass spectrometry revealed that the complexes interacted with PrP106-126 and hIAPP via metal coordination and hydrophobic interaction, which improved the inhibition and binding of the two gold-sulfur compounds. Our study provided new insights into the use of tetracoordinated gold-sulfur complexes as drug candidates against protein conformational disorders.

Disaggregation of human islet amyloid polypeptide fibril formation by ruthenium polypyridyl complexes.

The toxicity of amyloid proteins is associated with many degenerative and systematic diseases. The aggregation of human islet amyloid polypeptide may induce pancreatic ß-cell death, which is linked to type II diabetes. Ruthenium complexes are inhibitors of various proteins and potential anticancer metallodrugs, which can also be used to disaggregate amyloid proteins. This work reported that several ruthenium polypyridyl complexes remarkably affected the peptide aggregation by predominant hydrophobic interaction and metal coordination, as reflected by thermodynamic parameters and mass spectrometry analysis. Morphology and particle size analysis showed that the amyloid fibrils were disaggregated from long fibrils into small nano particles. Addition of these complexes also decreased the cytotoxicity induced by the peptide. The results indicated that ruthenium polypyridyl complexes may be potential metallodrugs to treat amyloidosis.