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Red fluorescent dyes are usually charged, lipophilic molecules with relatively high molecular weight, which tend to localize in specific intracellular locations, e. g., a cyanine dye Cy5 is biased towards mitochondria. They are often used as markers of biomolecules including nucleic acids and proteins. Since the molecular weight of the dyes is much smaller than that of the biomolecules, the labelling has a negligible effect on the properties of the biomolecules. In contrast, conjugation of the dyes to low molecular weight (pro)drugs can dramatically alter their properties. For example, conjugates of Cy5 with lysosome‐targeting aminoferrocenes accumulate in mitochondria and exhibit no intracellular effects characteristic for the parent (pro)drugs. Herein we tested several neutral and negatively charged dyes for labelling lysosome‐targeting aminoferrocenes 7 and 8 as well as a non‐targeted control 3. We found that a BODIPY derivative BDP‐TR exhibits the desired unbiased properties: the conjugation does not disturb the intracellular localization of the (pro)drugs, their mode of action, and cancer cell specificity. We used the conjugates to clarify the mechanism of action of the aminoferrocenes. In particular, we identified new intermediates, explained why lysosome‐targeting aminoferrocenes are more potent than their non‐targeted counterparts, and evaluated their distribution in vivo. [ABSTRACT FROM AUTHOR]

Specific proteins found in food sources tend to aggregate into fibrils under heat treatment; studying these aggregation processes and developing tools to control protein heat‐induced aggregation is an active area of research. Phthalocyanine complexes are known to exhibit antiprionic and anti‐fibrillogenic activity. Thus, the anti‐fibrillogenic effect of a series of Zr phthalocyanines with different out‐of‐plane coordinated ligands, namely positively charged (PcZrLys2), negatively charged (PcZrCitr2), and group able to form disulfide bridges (PcZrS2), on the heat‐induced aggregation of such proteins as BLG, insulin, and lysozyme was studied. The inhibition of reaction activity up to about 90% was observed in the presence of these compounds for all proteins. The effective concentration of the inhibitor was calculated for the compound with the highest activity (PcZrS2) to be 10.6 ± 3.6 and 7.3 ± 1.2 μM/L, respectively. Fluorescence spectroscopy studies demonstrated similar binding constants of three phthalocyanines binding with BLG globule. This is consistent with the results of molecular dynamics simulation, which imply the interaction of the globule with the tetrapyrrole macrocycle of phthalocyanine, leading to the globule stabilization. At the same time, TEM shows that in the presence of phthalocyanine PcZrS2, thinner and longer fibrils were formed compared to control in all three proteins (BLG, insulin, and lysozyme). Thus, we can conclude that phthalocyanine PcZrS2 affects the amyloid aggregation's general mechanism, which is typical for proteins of different structures. Therefore, the phthalocyanine PcZrS2 is proposed as an anti‐amyloidogenic agent suppressing heat‐induced aggregation of proteins of different structures, making it potentially suitable for application in the food industry. [ABSTRACT FROM AUTHOR]

Amyloid fibrils are widely studied both as target in conformational disorders and as basis for the development of protein-based functional materials. The three Zr phthalocyanines bearing dehydroacetic acid residue (PcZr(L1)2) and its condensed derivatives (PcZr(L2)2 and PcZr(L3)2) as out-of-plane ligands were synthesized and their influence on insulin fibril formation was studied by amyloid-sensitive fluorescent dye based assay, scanning electron microscopy, fluorescent and absorption spectroscopies. The presence of Zr phthalocyanines was shown to modify the fibril formation. The morphology of fibrils formed in the presence of the Zr phthalocyanines differs from that of free insulin and depends on the structure of out-of-plane ligands. It is shown that free insulin mostly forms fibril clusters with the length of about 0.3–2.1 μm. The presence of Zr phthalocyanines leads to the formation of individual 0.4–2.8 μm-long fibrils with a reduced tendency to lateral aggregation and cluster formation (PcZr(L1)2), shorter 0.2–1.5 μm-long fibrils with the tendency to lateral aggregation without clusters (PcZr(L2)2), and fibril-like 0.2–1.0 μm-long structures (PcZr(L3)2). The strongest influence on fibrils morphology made by PcZr(L3)2 could be explained by the additional stacking of phenyl moiety of the ligand with aromatic amino acids in protein. The evidences of binding of studied Zr phthalocyanines to mature fibrils were shown by absorption spectroscopy (for PcZr(L1)2 and PcZr(L2)2) and fluorescent spectroscopy (for PcZr(L3)2). These complexes could be potentially used as external tools allowing the development of functional materials on protein fibrils basis. [ABSTRACT FROM AUTHOR]

The self-association of proteins into insoluble filamentous aggregates – amyloid fibrils – is associated with a range of protein deposition disorders. With the aim of developing fluorescent probes sensitive to amyloid aggregates, a new series of derivatives of (2Z,5Z,7E)-6-hydroxy-2-(alkylamino)-8-arylocta-2,5,7-trien-4-one dyes was synthesized. These dyes are less sensitive to native amyloidogenic proteins, such as insulin or lysozyme, while they have the ability to exhibit a pronounced fluorescence response in the presence of amyloid fibrils of these proteins depending on the structure of the dye tail groups. The dyes associated with the fibrils show green-yellow emission (495–540 nm) and rather large Stokes shift values (68–125 nm). Upon binding to the fibrils, the fluorescence quantum yields of the dyes could increase by a hundred times up to 0.18–0.47, and the fluorescence intensity decay time strongly enhances up to 0.9–1.3 ns. These features make ketoenoles attractive as probes for the detection of amyloid fibrils; besides, the efficiency of these dyes for real-time monitoring of the kinetics of protein aggregation is shown. The best sensing properties were shown by dyes 2 and 9 bearing short amino tail groups (correspondingly 2-methoxyethyl and 2-hydroxyethyl) and a 4-substituted phenyl moiety at the other end of the ketoenole backbone. [ABSTRACT FROM AUTHOR]

The applicability of surface-enhanced Raman scattering (SERS) on silver nanoparticles for characterization of interaction between the phthalocyanine molecule and amyloid fibril was studied using the axially coordinated Hf phthalocyanine dichloride and fibrils of amyloidogenic protein insulin. The SERS spectra of the phthalocyanine were obtained; the analytical enhancement factor was estimated to be in the range from 4 to 6 × 104. An intensity enhancement in its SERS spectra caused by the presence of fibrillar insulin was observed. Deviation of this enhancement with the change of fibrillar insulin concentration was manifested. [ABSTRACT FROM AUTHOR]

Abstract: The activity of the boron cluster ‐ closo‐borates in protein amyloid fibrillization was first studied. For this, we explored the effect of dianionic compound [B12H12]2− on aggregation of amyloidogenic protein insulin by the circular dichroism spectroscopy, amyloid‐sensitive fluorescent dye based assay and transmission electron microscopy. It was shown that the presence of closo‐borate during fibrillization reaction speeds up the loss of the protein α‐helical structure. This effect of dianionic compound on protein fibrillization process is concentration‐dependent. Closo‐borate at low concentration (10 mM) enhances the intensity of insulin fibrillization, while at higher concentration (50 mM, 100 mM) fluorescent assay showed the decrease of this intensity. The morphology of fibrils formed in the presence of the boron dianion differs from that of free insulin, namely they are less branched and have the bigger diameter. Besides, closo‐borate‐induced fibrils have strong proneness to stick together forming large aggregated clots. [ABSTRACT FROM AUTHOR]

Amyloid fibrils are insoluble protein aggregates whose accumulation in cells and tissues is connected with a range of pathological diseases. We studied the impact of 2 metal complexes (axially coordinated Hf phthalocyanine and iron (II) clathrochelate) on aggregation of insulin and lysozyme. For both proteins, the host-guest interaction with these compounds changes the kinetics of fibrillization and affects the morphology of final aggregates. The Hf phthalocyanine is a very efficient inhibitor of insulin fibrillization; in its presence, only very low amounts of fibrils with the diameters of 0.8 to 5 nm and spherical aggregates were found. Effective concentration of fibrillization inhibition (IC50) was estimated to be 0.11 ± 0.04 μM. The clathrochelate induced the formation of thin fibrils with the diameters of 0.8 to 2.5 nm; IC50 was estimated as 20 ± 9 μM. The lysozyme fibrillization remained quite intensive in the presence of the studied compounds; they induced the formation of long filaments (the length up to 2.5 μm, the diameters of 1.5-3.5 nm). These fibrils noticeably differed from those of free lysozyme short linear species (the diameters of 3-5 nm, the length up to 0.6 μm). Thinning and elongation of fibrils suggest that the metal complexes bind mainly to the grooves of protofilaments; this hinders the stacking of early aggregates or protofilaments together but does not hinder their growth. The image of the fibril separated into 2 protofilaments allows suggesting that the fibril formation occurs via the growth of the parallel protofilaments with their subsequent twisting in the fibril. The changes of the lysozyme intrinsic fluorescence indicate that both metal complexes interact with the protein during the stage of the fibrillar seeds formation. [ABSTRACT FROM AUTHOR]

The effect of various N,N ′-substituents in the molecule of benzothiazole trimethine cyanine dye on its ability to sense the amyloid aggregates of protein was studied. The dyes are low fluorescent when free and in the presence of monomeric proteins, but their emission intensity sharply increases in complexes with aggregated insulin and lysozyme, with the fluorescence quantum yield reaching up to 0.42. The dyes carrying butyl, hydroxyalkyl, and phenylalkyl groups as N,N ′-substituents possess the increased fluorescent sensitivity to fibrillar lysozyme, whereas the ones carrying quaternary amino groups are preferably sensitive to fibrillar insulin. This fluorescent sensitivity preference provided by the N,N ′-functional groups could be explained by the interaction between these groups and protein side chains. The strongest fluorescent response (up to 70 times) and the same sensitivity to aggregates of both proteins were exhibited by the dye D-51 carrying N -sulfoalkyl group. The studied cyanines allow the detection of fibrillar aggregates in the wide range up to 0.8 to 300 μg/ml and permit monitoring the protein aggregation kinetics with high reproducibility. The modification of trimethine cyanine dyes by functional substituents in N,N ′-positions is suggested as a tool for the design of fluorescent molecules with the enhanced fluorescent sensitivity to the fibrillar aggregates of proteins. [ABSTRACT FROM AUTHOR]

Amyloid fibrils are rigid β‐pleated protein aggregates that are connected with series of harmful diseases and at the same time are promising as base for novel nanomaterials. Thus, design of compounds able to inhibit or redirect those aggregates formation is important both for the biomedical aims and for nanotechnology applications. Here, we studied the effect of tetraphenylporphyrins (metal free, their Cu and Pd complexes, and those functionalized by carboxy and amino groups on periphery) on insulin amyloid self‐assembling. The strongest impact on insulin aggregation was demonstrated by a metal‐free porphyrin bearing four carboxy groups. This compound strongly suppresses insulin aggregation (about 88% reduction in amyloid‐sensitive probe emission) inducing formation of fibrils with the length close to this of free insulin (1.7 ± 0.6 μm as compared with 1.4 ± 0.4 μm, respectively) with an essentially reduced tendency to lateral aggregation. Contrarily, the presence of tetraphenylporphyrin containing four amino groups only slightly affects fibrils' morphology and makes weaker impact on insulin aggregation yield (about 44% reduction). This is explained by the ability of aromatic carboxy groups of 5,10,15,20‐(tetra‐4‐carboxyphenyl)porphyrin to interact with complementary protein‐binding groups and thus stabilize the supramolecular complex. For 5,10,15,20‐(tetra‐4‐aminophenyl)porphyrin, full protonation takes place in acidic medium of protein aggregation reaction; this results in the high positive charge of TPPN4 (equal or close to +6) and hence higher contribution of coulombic repulsion to interaction of TPPN4 with insulin. One more possible mechanism of the lower inhibition effect of TPPN4 as compared with TPPC4 could be the more restricted possibility of the former as compared with the latter to form H bonds with insulin groups. It was also shown that metal‐free, Pd‐containing, and Cu‐containing tetraphenylporphyrins without peripheral substituents make almost the same impact on the protein self‐assembling. We suppose this to be due to coordination saturation of these metal atoms. [ABSTRACT FROM AUTHOR]

We have studied spectral-luminescent properties of the monomethine cyanine dyes both in their free states and in the presence of either double-stranded deoxyribonucleic acids (dsDNAs) or single-stranded ribonucleic acids (RNAs). The dyes possess low fluorescence intensity in an unbound state, which is increased up to 479 times in the presence of the nucleic acids. In the presence of RNAs, the fluorescence intensity increase was stronger than that observed in the presence of dsDNA. Next, we have performed staining of live and fixed cells by all prepared dyes. The dyes proved to be cell and nuclear membrane permeant. They are photostable and brightly stain RNA-containing organelles in both live and fixed cells. The colocalization confirmed the specific nucleoli staining with anti-Ki-67 antibodies. The RNA digestion experiment has confirmed the selectivity of the dyes toward intracellular RNA. Based on the obtained results, we can conclude that the investigated monomethine cyanine dyes are useful fluorescent probes for the visualization of intracellular RNA and RNA-containing organelles such as nucleoli by using fluorescence microscopy., (Creative Commons Attribution license.)