The conversion of a protein from its native conformation to the pathogenic form is a critical event in the pathogenesis of several neurodegenerative disorders such as Alzheimer’ s (AD), Parkinson’ s, and Huntington’ s diseases, along with type II diabetic mellitus. Although there are several reports on the mechanism of protein aggregation, the actual conformation playing a part in the pathogenicity is yet unclear. Accordingly, the present study summarizes the early pathogenic conformation resulting in several protein aggregations. It is well-documented that a pre-molten globule (MG) structure appears at the early stages of some proteins. Pre-MG is one of the intermediate structures, which is formed during some protein unfolding processes. In addition, it is shown that the pre-molten structure is more flexible than the mature MG one and thus, protein easily rearranges to form amyloid fibrils in this conformation. Therefore, protein aggregation is halted by preventing the pre-MG structure. The strategy of protein aggregation prevention has profound implications in fighting the devastating disorder.

It is becoming increasingly recognized that biological membranes are primary targets for amyloid fibrils toxicity. In fact, interaction of amyloid fibrils with lipid bilayers alters the structure and properties of biomembrane and thereby interferes with membrane-bound proteins activity and their subcellular localization. In line with this concept, compounds that interfere with the amyloid fibrils to bind lipid bilayers may serve as therapeutic agents for the treatment of amyloid-associated disorders. Among the most studied are polyphenols, an important class of beneficial naturally-occurring antioxidative molecules that exert beneficial effects by their ability to interact with lipid bilayer and stabilize lipid membranes by decreasing membrane fluidity. In this study, we investigated the influence of mature Hen Egg White Lysozyme (HEWL) amyloid fibrils on the activity of the rat brain mitochondrial Hexokinase (HK). Moreover, the effect of naturally occurring polyphenol Resveratrol on the HEWL fibril-induced changes in HK activity was investigated. We found that the presence of fibrils gave rise to a reduction in HK activity in the both membrane-bound and solubilized forms, but the extent of reduction was much greater for membrane-bound enzyme than solubilized enzyme. However, pre-incubation of mitochondrial homogenates with 50 μM Resveratrol effectively hinder HK activity reduction induced by HEWL amyloid fibrils. Although the mechanisms by which Resveratrol inhibit HEWL fibril-induced reduction of HK are still unclear, we suggest that naturally occurring polyphenols could serve as scaffold for the design of more efficient inhibitors for amyloid fibril cytotoxicity.

Glycosaminoglycans (GAGs) such as heparin and heparan sulfate are frequently associated with extracellular and intracellular amyloid deposits in most amyloid diseases, and there is evidence to support their active role in amyloid fibril formation in some cases. However, it was not fully determined which mechanism, forces and moieties in GAG chains may be responsible for the observed effects and whether other non-sulfated GAGs like hyaluronic acid are also capable for a similar enhancement of fibril formation. In this work, the fibril formation of native and chemically modified lysozyme was investigated in the presence of a heparin and hyaluronic acid at pH 2 and 7 by using thioflavin T fluorometry to elucidate the role of electrostatic interactions and sulfate moiety in the fibrillogenesis. Lysozyme was modified by acetic anhydride and citraconic anhydride to convert lysine primary amine groups to the neutral and negative charged groups, respectively. Hyaluronic acid has no charge at pH 2 and suppresses lysozymes fibrillation, probably due to complex formation with undenatured states of proteins. At pH 7, both heparin and hyaluronic acid have negative charge and lysozymes normally do not show any tendency to aggregate. Moreover, the capability of hyaluronic acid in amyloid enhancement reveals that sulfate groups are not crucial for accelerating amyloidogenesis but the extent of acceleration is proportional to the number of negative charge. According to these findings, reconsideration in the development of future therapies based on glycosaminoglycans is proposed.

Objective: Several diseases which associated with accumulation of protein aggregation named fibrillar amyloid. Alpha synuclein protein (ASN) is present in brain and consists of protein plaques as a main part in lewy body diseases (including Parkinson's, Lewy body variant of Alzheimer's (LBV), and others). Wild type and mutated ASN can fibrillate in physiological condition.Materials and Method: Here we investigated the effect of dNTPs as natural small aromatic molecules on ASN fibrillation. Recombinant ASN protein was produced and fibrillate by agitation with fixed speed at 37°C. The fibrils were examined by ThT fluorescence, Congo red, CD, TEM and fluorescence image. Fibrils were cytotoxic for SK-N-MC cell. We explored their cytotoxicity by MTT, LDH, and Annexin assay. Results: Presence of fibrils and prefibrils in cell culture, enhanced cell death dramatically. The study showed that dNTPs have different effects on fibril formation. Adding dCTP and dTTP could inhibit fibrillation whereas dATP and dGTP had opposite effect. It seems that pyrimidines derivatives can interrupt fibril formation, but purine ones could not. Results were incredible by adding fibrils in present of dNTP to cell culture.Although adding dCTP and dTTP inhibit formation of mature fibril but, incubation with these dNTPs caused cell cytotoxicity even more than ASN fibril. While the aggregation types of ASN after adding dATP and dGTP had less dangerous effect on cell.Conclusion: It seems that addition of pyrimidines can produce more perilous type of prefibrils like oligomers. Purines not only induce mature fibrils but also make amorphous forms which have less serious effect on cell viability.

Timolol is a non-selective beta-adrenergic receptor antagonist administered for treating glaucoma, heart attacks and hypertension. In the present study, we set out to determine whether or not timolol can provoke cataract formation, thus the influence of timolol on the amyloid-type aggregation of crystallin was investigated. We then provided experimental evidence of crystallin aggregation and its induction by timolol using different spectroscopic measurements. Turbidimetric measurements as well as ThT fluorescence data indicated that timolol induce extent of crystallin amyloid formation. The kinetic of protein aggregation was also changed in presence of increasing concentrations of the drug suggesting that long-term drug administration may contribute to the development of cataract. Since the consequence of timolol-crystallin interaction has yet to be identified, additional data on it may help us to postpone amyloid cataract formation.