Brazilin Inhibits Prostatic Acidic Phosphatase Fibrillogenesis and Decreases its Cytotoxicity

Sappanwood-derived polyphenolic antidote of amyloidal toxins achieved detoxification via inhibition/reversion of amyloidal fibrillation

The formidable virulence of methicillin-resistant staphylococcus aureus (MRSA) have thrown great challenges to biomedicine, which mainly derives from their autocrine phenol-soluble modulins (PSMs) toxins, especially the most toxic member termed phenol-soluble modulins α3 (PSMα3). PSMα3 cytotoxicity is attributed to its amyloidal fibrillation and subsequent formation of cross-α sheet fibrils. Inspired by the multiple biological activity of Sappanwood, herein, we adopted brazilin, a natural polyphenolic compound originated from Caesalpinia sappan, as a potential antidote of PSMα3 toxins, and attempted to prove that the regulation of PSMα3 fibrillation was an effective alexipharmic way for MRSA infections. In vitro results revealed that brazilin suppressed PSMα3 fibrillation and disassembled preformed amyloidal fibrils in a dose-dependent manner, in which molar ratio (brazilin: PSMα3) of efficient inhibition and disassembly were both 1:1. These desired regulations dominated by brazilin benefited from its bonding to core fibrils-forming residues of PSMα3 monomers urged by hydrogen bonding and pi-pi stacking, and such binding modes facilitated brazilin-mediated inhibition or disruption of interactions between neighboring PSMα3 monomers. In this context, these inhibited and disassembled PSMα3 assemblies could not easily insert into cell membrane and subsequent penetration, and thus alleviating the membrane disruption, cytoplasmic leakage, and reactive oxygen species (ROS) generation in normal cells. As such, brazilin dramatically decreased the cytotoxicity borne by toxic PSMα3 fibrils. In addition, in vivo experiments affirmed that brazilin relieved the toxicity of PSMα3 toxins and thus promoted the skin wound healing of mice. This study provides a new antidote of PSMα3 toxins, and also confirms the feasibility of the assembly-regulation strategy in development of antidotes against supramolecular fibrillation-dependent toxins.

Dual concentration-dependent effect of ascorbic acid on PAP(248-286) amyloid formation and SEVI-mediated HIV infection

Human semen contains various amyloidogenic peptides derived from Prostatic Acid Phosphatase (PAP) and Semenogelin proteins that are capable of enhancing HIV-1 infection when assembled into fibrils. The best characterized among them is a 39 amino acid peptide PAP(248–286), which forms amyloid fibrils termed SEVI (semen-derived enhancer of viral infection) that increase the infectivity of HIV-1 by orders of magnitude. Inhibiting amyloid formation by PAP(248–286) may mitigate the sexual transmission of HIV-1. Several vitamins have been shown to reduce the aggregation of amyloids such as Aβ, α-Synuclein, and Tau, which are associated with neurodegenerative diseases. Since ascorbic acid (AA, vitamin C) is the most abundant vitamin in semen with average concentrations of 0.4 mM, we here examined how AA affects PAP(248–286) aggregation in vitro. Using ThT binding assays, transmission electron microscopy, and circular dichroism spectroscopy, a dual and concentration-dependent behavior of AA in modulating PAP(248–286) fibril formation was observed. We found that low molar ratios of AA:PAP(248–286) promoted whereas high molar ratios inhibited PAP(248–286) fibril formation. Accordingly, PAP(248–286) aggregated in the presence of low amounts of AA enhanced HIV-1 infection, whereas excess amounts of AA during aggregation reduced the infectivity enhancing effect in cell culture. Collectively, this work provides a biophysical insight into the effect of AA, an important seminal component, on SEVI fibrillation which might impact amyloid formation kinetics, thereby modulating the biological activity of semen amyloids.

Human semen contains various amyloidogenic peptides derived from Prostatic Acid Phosphatase (PAP) and Semenogelin proteins that are capable of enhancing HIV-1 infection when assembled into fibrils.

Brazilin Inhibits α-Synuclein Fibrillogenesis, Disrupts Mature Fibrils, and Protects against Amyloid-Induced Cytotoxicity

The inhibitory effect of brazilin against α-synuclein (α-syn) fibrillogenesis, disruption effect against mature fibrils, and the following cytotoxicity were examined by systematical biochemical, biophysical, cellular biological, and molecular simulation experiments. It is found that brazilin inhibited α-syn fibrillogenesis and disrupted the performed fibrils with a concentration-dependent manner. Moreover, cellular experimental data showed that brazilin effectively reduced the cytotoxicity induced by α-syn aggregates. Finally, molecular dynamics simulations were performed to explore the interactions between brazilin and α-syn pentamer. It is found that brazilin directly interacts with α-syn pentamer, and the hydrophobic interactions are favorable for brazilin binding with the α-syn pentamer, while the electrostatic part provides adverse effects. Three binding regions were identified to inhibit α-syn fibrillogenesis or disrupt the preformed aggregates. Furthermore, six important residues (i.e., G51, V52, A53, E61, V66, and K80) of α-syn were also identified. We expected that brazilin is an effective agent against α-syn fibrillogenesis and associated cytotoxicity.

Inhibitory Effect of Naphthoquinone-Tryptophan Hybrid towards Aggregation of PAP f39 Semen Amyloid

PAP_248–286, a 39 amino acid peptide fragment, derived from the prostatic acid phosphatase secreted in human semen, forms amyloid fibrils and facilitates the attachment of retroviruses to host cells that results in the enhancement of viral infection. Therefore, the inhibition of amyloid formation by PAP_248–286 (termed PAP f39) may likely reduce HIV transmission in AIDS. In this study, we show that the naphthoquinone tryptophan (NQTrp) hybrid molecule significantly inhibited PAP f39 aggregation in vitro in a dose-dependent manner as observed from the ThT assay, ANS assay, and transmission electron microscopy imaging. We found that even at a sub-molar concentration of 20:1 [PAP f39:NQTrp], NQTrp could reduce >50% amyloid formation. NQTrp inhibition of PAP f39 aggregation resulted in non-toxic intermediate species as determined by the vesicle leakage assay. Isothermal titration calorimetry and molecular docking revealed that the binding of NQTrp and PAP f39 is spontaneous, and NQTrp predominantly interacts with the polar and charged residues of the peptide by forming hydrogen bonds and hydrophobic contacts with a strong binding energy. Collectively, these findings indicate that NQTrp holds significant potential as a small molecule inhibitor of semen amyloids.

Inhibition of protein misfolding and aggregation by natural phenolic compounds

Protein misfolding and aggregation into fibrillar deposits is a common feature of a large group of degenerative diseases affecting the central nervous system or peripheral organs, termed protein misfolding disorders (PMDs). Despite their established toxic nature, clinical trials aiming to reduce misfolded aggregates have been unsuccessful in treating or curing PMDs. An interesting possibility for disease intervention is the regular intake of natural food or herbal extracts, which contain active molecules that inhibit aggregation or induce the disassembly of misfolded aggregates. Among natural compounds, phenolic molecules are of particular interest, since most have dual activity as amyloid aggregation inhibitors and antioxidants. In this article, we review many phenolic natural compounds which have been reported in diverse model systems to have the potential to delay or prevent the development of various PMDs, including Alzheimer's and Parkinson's diseases, prion diseases, amyotrophic lateral sclerosis, systemic amyloidosis, and type 2 diabetes. The lower toxicity of natural compounds compared to synthetic chemical molecules suggest that they could serve as a good starting point to discover protein misfolding inhibitors that might be useful for the treatment of various incurable diseases.

Structure, function and antagonism of semen amyloids

Amyloid fibrils are linear polypeptide aggregates with a cross-β structure. These fibrils are best known for their association with neurodegenerative diseases, such as Alzheimer's or Parkinson's, but they may also be used by living organisms as functional units, e.g. in the synthesis of melanin or in the formation of bacterial biofilms. About a decade ago, in a search for semen factors that modulate infection by HIV-1 (a sexually transmitted virus and the causative agent of the acquired immune deficiency syndrome (AIDS)), it was demonstrated that semen harbors amyloid fibrils capable of markedly increasing HIV infection rates. This discovery not only created novel opportunities to prevent sexual HIV-1 transmission but also stimulated research to unravel the natural role of these factors. We discuss here the identification of these intriguing structures, their molecular properties, and their effects on both sexually transmitted diseases and reproductive health. Moreover, we review strategies to antagonize semen amyloid to prevent sexual transmission of viruses.

Bifunctionality of Iminodiacetic Acid-Modified Lysozyme on Inhibiting Zn2+-Mediated Amyloid β-Protein Aggregation

Aggregation of amyloid β-proteins (Aβ) mediated by metal ions such as Zn²⁺ has been suggested to be implicated in the progression of Alzheimer's disease (AD). Hence, development of bifunctional agents capable of inhibiting Aβ aggregation and modulating metal-Aβ species is an effective strategy for the treatment of AD. In this work, we modified iminodiacetic acid (IDA) onto human lysozyme (hLys) surface to create an inhibitor of Zn²⁺-mediated Aβ aggregation and cytotoxicity. The IDA-modified hLys (IDA-hLys) retained the stability and biocompatibility of native hLys. Extensive biophysical and biological analyses indicated that IDA-hLys significantly attenuated Zn²⁺-mediated Aβ aggregation and cytotoxicity due to its strong binding affinity for Zn²⁺, whereas native hLys showed little effect. Stopped-flow fluorescence spectroscopy showed that IDA-hLys could protect Aβ from Zn²⁺-induced aggregation and rapidly depolymerize Zn²⁺-Aβ aggregates. The research indicates that IDA-hLys is a bifunctional agent capable of inhibiting Aβ fibrillization and modulating Zn²⁺-mediated Aβ aggregation and cytotoxicity as a strong Zn²⁺ chelator.

Semen-derived amyloidogenic peptides-Key players of HIV infection

Misfolding and amyloid aggregation of intrinsically disordered proteins (IDPs) are implicated in a variety of diseases. Studies have shown that membrane plays important roles on the formation of intermediate structures of IDPs that can initiate (and/or speed-up) amyloid aggregation to form fibers. The process of amyloid aggregation also disrupts membrane to cause cell death in amyloid diseases like Alzheimer's disease and type-2 diabetes. On the other hand, recent studies reported the membrane fusion properties of amyloid fibers. Remarkably, amyloid-fibril formation by short peptide fragments of highly abundant prostatic acidic-phosphatase (PAP) in human semen and are capable of boosting the rate of HIV infection up to 400,000-fold during sexual contact. Unlike the least toxic fully matured fibers of most amyloid proteins, the semen-derived enhancer of virus infection (SEVI) amyloid-fibrils of PAP peptide fragments are highly potent in rendering the maximum rate of HIV infection. This unusual property of amyloid fibers has witnessed increasing number of studies on the biophysical aspects of fiber formation and fiber-membrane interactions. NMR studies have reported a highly disordered partial helical structure in a membrane environment for the intrinsically disordered PAP peptide that promotes the fusion of the viral membrane with that of host cells. The purpose of this review article is to unify and integrate biophysical and immunological research reported in the previous studies on SEVI. Specifically, amyloid aggregation, dramatic HIV infection enhancing properties, membrane fusion properties, high resolution NMR structure, and approaches to eliminate the enhancement of HIV infection of SEVI peptides are discussed.