Exploration of Isoquinoline Alkaloids as Potential Inhibitors against Human Islet Amyloid Polypeptide

Inhibitory mechanism of lithospermic acid on the fibrillation of type 2 diabetes associated islet amyloid polypeptide

The abnormal fibrillation of a 37-residue peptide hormone human islet amyloid polypeptide (hIAPP) is linked with type 2 diabetes (T2D). Pang et al. depicted a prominent role of lithospermic acid (LA) in blocking hIAPP fibrillation and alleviating the hIAPP aggregates-induced cytotoxicity. LA is a polyphenolic compound present in extra virgin olive oil with therapeutic properties. Despite its notable inhibitory effect on hIAPP fibrillation, the inhibition mechanism remains unclear. Here, molecular dynamics (MD) simulations have been utilized to shed light on the putative binding mechanism and inhibitory mechanism of LA against hIAPP fibrillation. The molecular docking predicted favourable binding (-7.1 kcal/mol) of LA with hIAPP. Interestingly, LA increases the helix content in hIAPP and blocks the conformational transition to the aggregation-competent conformations. The conformational clustering and hydrogen bond analyses depicted that LA formed hydrogen bonds with Asn21 of hIAPP, which play an important role in hIAPP aggregation. LA binds favourably to hIAPP (ΔGbinding = -49.62 ± 3.34 kcal/mol) with a major contribution from the van der Waals interactions. The MD simulations highlighted that LA dramatically interfered with the intrapeptide interactions and inhibited sampling of aggregation-competent β-sheet conformations in hIAPP via hydrogen bonds through its hydroxyl groups, van der Waals interactions with hIAPP residues, thus blocking hIAPP aggregation to β-sheet rich cytotoxic fibrillar aggregates. The MD simulations illuminated specific interactions between hIAPP and LA, which will benefit in developing new chemical entities against hIAPP fibrillation.

Effect and mechanism of oritavancin on hIAPP amyloid formation

Amyloidosis of the human islet amyloid polypeptide (hIAPP) is closely related to the pathogenesis of type 2 diabetes (T2D) and serves as both a diagnostic hallmark and a key therapeutic target for T2D. In this study, we discovered that oritavancin (Ori), a glycopeptide antibiotic primarily prescribed for Gram-positive bacterial infections, can dose-dependently inhibit recombinant hIAPP (rhIAPP) amyloid formation. Ori specifically inhibited rhIAPP amyloid formation at the initial nucleation stage but didn't affect mature rhIAPP fibrils. As a result, Ori reduced amyloidosis of rhIAPP induced pancreatic NIT-1 cell apoptosis and reactive oxygen species (ROS) release. Based on the results from studies involving antibiotic homologues of Ori and its acid hydrolysates, we demonstrated that both the N-(4-chlorobiphenyl) methyl group (CBP) and glycopeptide backbone were necessary for inhibiting rhIAPP amyloid formation. The mechanism behind Ori on rhIAPP amyloid formation lies in the direct interaction of the two molecules identified by ESI-MS and molecular docking assays. Consequently, this research not only lays the groundwork for developing novel therapeutic approaches for T2D but also presents the opportunity to repurpose Ori as a treatment option.

Peroxynitrite scavenger FeTPPS binds with hCT to effectively inhibit its amyloid aggregation

Human calcitonin (hCT) is an endogenous polypeptide commonly employed in treating bone resorption-related illnesses, but its clinical application is limited due to its high aggregation tendency. Metalloporphyrins are effective in suppressing amyloid fibrillation, positioning them as potential drug candidates for amyloidogenic disorders like Alzheimer's and type 2 diabetes. In this work, we investigated the effects of Fe(III) meso-tetra(4-sulfonatophenyl)porphine chloride (FeTPPS), a highly efficient ONOO- decomposition catalyst, on hCT aggregation. Our findings reveal that FeTPPS effectively precludes hCT fibrillation by stabilizing the monomers and delaying the structural transition from α-helix bundles to β-sheet-rich aggregates. The macrocyclic ring of FeTPPS plays a significant role in disrupting hCT self-associations. Among various porphyrin analogs, those with an iron center and negatively charged peripheral substituents exhibit a stronger inhibitory effect on hCT aggregation. Spectroscopic analyses and computational simulations indicate that FeTPPS binds to hCT's core aggregation region via complexation with His20 in a 1 : 1 molar ratio. Hydrophobic interaction, hydrogen bonding, and π-π stacking with the residues involving Tyr12, Phe19, and Ala26 also contribute to the interactions. Collectively, our study provides a promising approach for developing novel hCT drug formulations and offers theoretical guidance for designing metalloporphyrin-based inhibitors for various amyloidosis conditions.

Biologically active isoquinoline alkaloids covering 2019-2022

Isoquinoline alkaloids are an important class of natural products that are abundant in the plant kingdom and exhibit a wide range of structural diversity and biological activities. With the deepening of research in recent years, more and more isoquinoline alkaloids have been isolated and identified and proved to contain a variety of biological activities and pharmacological effects. In this review, we introduce the research progress of isoquinoline alkaloids from 2019 to 2022, mainly in the part of biological activities, including antitumor, antimicrobial, antidiabetic, antiviral, anti-inflammatory, antioxidant, neuroprotective, hepatoprotective, analgesic, and other activities. This study provides a clear direction for the rational development and utilization of isoquinoline alkaloids, suggesting that these alkaloids have great potential in the field of drug research.

Indenoquinoxaline-phenylacrylohydrazide hybrids as promising drug candidates for the treatment of type 2 diabetes: In vitro and in silico evaluation of enzyme inhibition and antioxidant activity

Existing drugs that are being used to treat type-2 diabetes mellitus are associated with several side effects; thus, exploring potential drug candidates is still an utter need these days. Hybrids of indenoquinoxaline and hydrazide have never been explored as antidiabetic agents. In this study, a series of new indenoquinoxaline-phenylacrylohydrazide hybrids (1-30) were synthesized, structurally characterized, and evaluated for α-amylase and α-glucosidase inhibitory activities, as well as for their antioxidant properties. All scaffolds exhibited varying degrees of inhibitory activity against both enzymes, with IC50 values ranging from 2.34 to 61.12 μM for α-amylase and 0.42 to 54.72 μM for α-glucosidase. Particularly, compounds 10, 16, 17, 18, 24, and 25 demonstrated the highest efficacy in inhibiting α-amylase, while compounds 6, 7, 8, 10, 12, 14, 13, 16, 17, 18, 24, and 25 were the most effective α-glucosidase inhibitors, compared to standard acarbose. Moreover, most of these compounds displayed substantial antioxidant potential compared to standard butylated hydroxytoluene (BHT). Kinetics studies revealed competitive inhibition modes by compounds. Furthermore, a comprehensive in silico study and toxicity prediction were also conducted, further validating these analogs as potential drug candidates. The structured compounds demonstrated enhanced profiles, underscoring their potential as primary candidates in drug discovery.

Hypoglycemic Effects and Quality Marker Screening of Dendrobium nobile Lindl. at Different Growth Years

(1) Background: The effect of Dendrobium nobile Lindl. (D. nobile) on hyperglycemic syndrome has only been recently known for several years. Materials of D. nobile were always collected from the plants cultivated in various growth ages. However, regarding the efficacy of D. nobile on hyperglycemic syndrome, it was still unknown as to which cultivation age would be selected. On the other hand, with the lack of quality markers, it is difficult to control the quality of D. nobile to treat hyperglycemic syndrome. (2) Methods: The effects of D. nobile cultivated at year 1 and year 3 were checked on alloxan-induced diabetic mice while their body weight, diet, water intake, and urinary output were monitored. Moreover, levels of glycosylated serum protein and insulin were measured using Elisa kits. The constituents of D. nobile were identified and analyzed by using UPLC-Q/trap. Quality markers were screened out by integrating the data from UPLC-Q/trap into a network pharmacology model. (3) Results: The D. nobile cultivated at both year 1 and year 3 showed a significant effect on hyperglycemic syndrome at the high dosage level; however, regarding the significant level, D. nobile from year 1 showed the better effect. In D. nobile, most of the metabolites were identified as alkaloids and sesquiterpene glycosides. Alkaloids, represented by dendrobine, were enriched in D. nobile from year 1, while sesquiterpene glycosides were enriched in D. nobile from year 3. Twenty one metabolites were differentially expressed between D. nobile from year 1 and year 3. The aforementioned 21 metabolites were enriched to 34 therapeutic targets directly related to diabetes. (4) Conclusions: Regarding the therapy for hyperglycemic syndrome, D. nobile cultivated at year 1 was more recommended than that at year 3. Alkaloids were recommended to be used as markers to control the quality of D. nobile for hyperglycemic syndrome treatment.

Roles of Apigenin and Nepetin in the Assembly Behavior and Cytotoxicity of Prion Neuropeptide PrP106-126

Development of potential inhibitors to prevent prion protein (PrP) fibrillation is a therapeutic strategy for prion diseases. The prion neuropeptide PrP106-126, a research model of abnormal PrP (PrPSc), presents similar physicochemical and biochemical characters to PrPSc, which is also a target of potential inhibitors against prion deposition. Many flavones have antioxidant, anti-inflammatory, and antibacterial properties, and they are applied in treating prion disorder and other amyloidosis as well. However, the inhibition mechanism of flavones on PrP106-126 fibrillation is still unclear. In the current work, apigenin and nepetin were used to suppress the aggregation of PrP106-126 and to alleviate the peptide-induced cytotoxicity. The results showed that apigenin and nepetin impeded the fibril formation of PrP106-126 and depolymerized the preformed fibrils. They were bound to PrP106-126 predominantly by hydrophobic and hydrogen bonding interactions. In addition, both flavones upregulated cell viability and decreased membrane leakage through reducing peptide oligomerization. The differences in inhibition and cell protection between the two small molecules were presumably attributed to the substitution of hydroxyl and methoxy groups in nepetin, which demonstrated the significant structure-function relationship of flavones with prion neuropeptide and the prospect of flavonoids as drug candidates against prion diseases.

New trends in the practical use of isoquinoline alkaloids as potential drugs applicated in infectious and non-infectious diseases

In the last years, traditional natural products have been the center of attention for the scientific community and exploration of their therapeutic abilities is proceeding permanently. Isoquinoline alkaloids have always attracted scientific interest due to either their positive or negative effects on human organism. The present review describes research on isoquinoline alkaloids isolated from different plant species. Alkaloids are one of the most important classes of plant derived compounds among these isoquinoline alkaloids possess varied biological activities such as anticancer, antineurodegenerative diseases, antidiabetic, antiinflammatory, antimicrobial, and many others. The use of plants against different disorders is entrenched in traditional medicine around the globe. Recent progress in modern therapeutics has stimulated the use of natural products worldwide for various ailments and diseases. The review provides a collection of information on the capabilities of some isoquinoline alkaloids, its potential for the treatment of various diseases and is designed to be a guide for future research on different biologically active isoquinoline alkaloids and plant species containing them. The authors are aware that they were not able to cover the whole area of the topic related to biological activity of isoquinoline alkaloids. This review is intended to suggest directions for further research and can also help other researchers in future studies.

β-Carboline Alkaloids Resist the Aggregation and Cytotoxicity of Human Islet Amyloid Polypeptide

β-Carboline alkaloids have a variety of pharmacological activities, such as antitumor, antibiosis and antidiabetes. Harmine and harmol are two structurally similar β-carbolines that occur in many medicinal plants. In this work, we chose harmine and harmol to impede the amyloid fibril formation of human islet amyloid polypeptide (hIAPP) associated with type 2 diabetes mellitus (T2DM), by a series of physicochemical and biochemical methods. The results indicate that harmine and harmol effectively prevent peptide fibril formation and alleviate toxic oligomer species. In addition, both small molecules exhibit strong binding affinities with hIAPP mainly through hydrophobic and hydrogen bonding interactions, thus reducing the cytotoxicity induced by hIAPP. Their distinct binding pattern with hIAPP is closely linked to the molecular configuration of the two small molecules, affecting their ability to impede peptide aggregation. The study is of great significance for the application and development of β-carboline alkaloids against T2DM.

Rh(III)-Catalyzed Reaction of 4-Diazoisochroman-3-imines with (2-Formylaryl)boronic Acids To Access a Straightforward Construction of 5H-Isochromeno[3,4-c]isoquinolines

An Rh(III)-catalyzed one-pot synthesis of 5H-isochromeno[3,4-c]isoquinolines from readily available 4-diazoisochroman-3-imines and (2-formylphenyl)boronic acids is reported. The cascade annulation involves a Rh(III)-catalyzed cross-coupling and an intramolecular nucleophilic addition-elimination process. A series of biologically important 5H-isochromeno[3,4-c]isoquinolines were obtained in good to excellent yields. The method can be extended to synthesize 7H-isochromeno[3,4-b]thieno[3,2-d]pyridines and 7H-isochromeno[3,4-b]thieno[2,3-d]pyridines from the corresponding heteroaryl boronic acids.

Anti-α-Glucosidase, SAR Analysis, and Mechanism Investigation of Indolo[1,2-b]isoquinoline Derivatives

To find potential α-glucosidase inhibitors, indolo[1,2-b]isoquinoline derivatives (1-20) were screened for their α-glucosidase inhibitory effects. All derivatives presented potential α-glucosidase inhibitory effects with IC₅₀ values of 3.44 ± 0.36~41.24 ± 0.26 μM compared to the positive control acarbose (IC₅₀ value: 640.57 ± 5.13 μM). In particular, compound 11 displayed the strongest anti-α-glucosidase activity, being ~186 times stronger than acarbose. Kinetic studies found that compounds 9, 11, 13, 18, and 19 were all reversible mix-type inhibitors. The 3D fluorescence spectra and CD spectra results revealed that the interaction between compounds 9, 11, 13, 18, and 19 and α-glucosidase changed the conformational changes of α-glucosidase. Molecular docking and molecular dynamics simulation results indicated the interaction between compounds and α-glucosidase. In addition, cell cytotoxicity and drug-like properties of compound 11 were also investigated.

Inhibitory effects of sesquiterpene lactones on the aggregation and cytotoxicity of prion neuropeptide

The misfolding and conformational transformation of prion protein (PrP) are crucial to the progression of prion diseases. Screening for available natural inhibitors against prion proteins can contribute to the rational design and development of new anti-prion drugs and therapeutic strategies. The prion neuropeptide, PrP106-126 is commonly used as a model peptide of the abnormal PrP^Sc, and a number of potential inhibitors were explored against the amyloid fibril formation of PrP106-126. The well-known sesquiterpene lactone, artemisinin, shows diverse biological functions in anti-malarial, anti-cancer and lowering glucose. However, its inhibitory effect on PrP106-126 fibrillation is unclear. In this work, we selected two sesquiterpene lactones, artemisinin (1) and artesunate (2), to explore their roles in PrP106-126 aggregation by a series of physicochemical and biochemical methods. The results demonstrated that 1 and 2 could effectively impede the formation of amyloid fibrils and remodel the preformed fibrils. The binding of the small molecules to PrP106-126 was dominated by electrostatic, hydrophobic and hydrogen bonding interactions. In addition, both compounds exhibited neuroprotective effects by reducing peptide oligomerization. 2 showed better inhibition and regulation on peptide aggregation and cellular viability than 1 due to its specific succinate modification. Our study provides the information of sesquiterpene lactones to prevent PrP fibril formation and other related amyloidosis.

Chiral 8-Amino-5,6,7,8-tetrahydroquinoline Derivatives in Metal Catalysts for the Asymmetric Transfer Hydrogenation of 1-Aryl Substituted-3,4-dihydroisoquinolines as Alkaloids Precursors

Chiral diamines based on an 8-amino-5,6,7,8-tetrahydroquinoline backbone, known as CAMPY (L1), or the 2-methyl substituted analogue Me-CAMPY (L2) were employed as novel ligands in Cp* metal complexes for the ATH of a series of substituted dihydroisoquinolines (DHIQs), known for being key intermediates in the synthesis of biologically active alkaloids. Different metal-based complexes were evaluated in this kind of reaction, rhodium catalysts, C3 and C4, proving most effective both in terms of reactivity and enantioselectivity. Although modest enantiomeric excess values were obtained (up to 69% ee in the case of substrate I), a satisfactory quantitative conversion was successfully fulfilled even in the case of the most demanding hindered substrates when La(OTf)₃ was used as beneficial additive, opening up the possibility for a rational design of novel chiral catalysts alternatives to the Noyori-Ikariya (arene)Ru(II)/TsDPEN catalyst.

Illustrating the Effect of Small Molecules Derived from Natural Resources on Amyloid Peptides

The onset of amyloidogenic diseases is associated with the misfolding and aggregation of proteins. Despite extensive research, no effective therapeutics are yet available to treat these chronic degenerative diseases. Targeting the aggregation of disease-specific proteins is regarded as a promising new approach to treat these diseases. In the past few years, rapid progress in this field has been made in vitro, in vivo, and in silico to generate potential drug candidates, ranging from small molecules to polymers to nanoparticles. Small molecular probes, mostly those derived from natural sources, have been of particular interest among amyloid inhibitors. Here, we summarize some of the most important natural small molecular probes which can inhibit the aggregation of Aβ, hIAPP, and α-syn peptides and discuss how their binding efficacy and preference for the peptides vary with their structure and conformation. This provides a comprehensive idea of the crucial factors which should be incorporated into the future design of novel drug candidates useful for the treatment of amyloid diseases.

Gold Nanoclusters Enhance the Efficacy of the Polymer-Based Chaperone in Restoring and Maintaining the Native Conformation of Human Islet Amyloid Polypeptide

The misfolding and un-natural fibrillation of proteins/peptides are associated with many conformation diseases, such as human islet amyloid polypeptide (hIAPP) in type 2 diabetes (T2D). Inspired by molecular chaperones maintaining protein homeostasis in vivo, many polymer-based artificial chaperones were introduced to regulate protein/peptide folding and fibrillation. However, the pure polymer chaperones prefer to agglomerate into large-size micelles in the physiological environment and thus lose their chaperone functions, which greatly restricts the application of polymer-based chaperones. Here, we designed and prepared a core-shell artificial chaperone based on a dozen poly-(N-isopropylacrylamide-co-N-acryloyl-O-methylated-l-arginine) (PNAMR) anchored on a gold-nanocluster (AuNC) core. The introduction of the AuNC core significantly reduced the size and enhanced the efficacy and stability of polymer-based artificial chaperones. The PNAMR@AuNCs, with a diameter of 2.5 ± 0.5 nm, demonstrated exceptional ability in maintaining the natively unfolded conformation of protein away from the misfolding and the following fibrillation by directly binding to the natively unfolded monomolecular hIAPP and hence in preventing their conversion into toxic oligomers. More excitingly, the PNAMR@AuNCs were able to restore the natural unfolded conformation of hIAPP via dissolving the β-sheet-rich hIAPP fibrils. Considering the uniform molecular mechanism of protein misfolding and fibrillation in conformation disorders, this finding provides a generic therapeutic strategy for neurodegenerative diseases and other conformation diseases by using PNAMR@AuNC artificial chaperones to restore and maintain the native conformation of amyloid proteins.

Disparate Effect of Hybrid Peptidomimetics Containing Isomers of Aminobenzoic Acid on hIAPP Aggregation

The abnormal misfolding of human islet amyloid polypeptide (hIAPP) in pancreatic β-cells is implicated in the progression of type II diabetes (T2D). With the prevalence of T2D increasing worldwide, preventing the aggregation of hIAPP has been recognized as a promising therapeutic strategy to control this disease. Recently, a class of novel conformationally restricted β-sheet breaker hybrid peptidomimetics (BSBHps) was found to demonstrate efficient inhibitory ability toward amyloid formation of hIAPP. One (Ile26) or more (Gly24 and Ile26) residues in these six-membered peptide sequences, which have been extracted from the amyloidogenic core of hIAPP, N₂₂FGAIL₂₇, are substituted by three different isomers of the conformationally restricted aromatic amino acid, i.e., aminobenzoic acid (β, γ, and δ), to generate these BSBHps. The presence of the nonproteinogenic aminobenzoic acid moiety renders the BSBHps to be more stable toward proteolytic degradation. The different isomeric BSBHps exhibit contrasting influence on the self-assembly of hIAPP. The BSBHps containing β- and γ-aminobenzoic acid can sufficiently prevent hIAPP aggregation, but those with the δ-aminobenzoic group stabilize the β-sheet-rich aggregate of hIAPP. The difference in the angle between the amino and carboxyl groups in the isomers of the aminobenzoic moiety causes the BSBHps to attain discrete conformation and hence leads to variation in their binding preference with hIAPP and ultimately their inhibitory potency. This guides the pathway for the dissimilar effect of BSBHps on peptide aggregation and, therefore, provides insights into the design considerations for novel drugs against T2D.