Discovery of hyaluronidase inhibitors from natural products and their mechanistic characterization under DMSO-perturbed assay conditions

Toward an Improved Triterpene 3-O-Glucuronidation: The Systematic Determination of the Relative Reactivities of Glucuronyl Donors and Acceptors

3-O-β-Glucuronide triterpenes are plant-derived compounds. Some of them have been used as herbal medicine and in pharmaceuticals, such as chikusetsu saponins and Quillaja saponins. However, the demand for these materials has remained largely a challenge owing to their natural scarcity and low-yielding purification process. Therefore, a chemical triterpene 3-O-glucuronidation was conducted in this study to alleviate the surging demand on natural source. Various glucuronyl imidate donors and oleanane-type triterpene acceptors were synthesized, and the relative reactivity values (RRV) and acceptor nucleophilic constants (Aka) were systematically measured to study their influence on glucuronidation yield. As a result, applying donors in higher RRV value generally improved the production of 3-O-glucuronide triterpenes. Meanwhile, a bulky pivaloyl group was an ideal 2-O-protection to provide β-selectivity and prevented side reactions, including orthoester formation and acyl-transfer reaction. Collectively, a positive correlation was observed between reactive donors/acceptors and improved glucuronidation yields. These findings offered insights on the influence of donors' and acceptors' reactivities on 3-O-β-glucuronide triterpenes synthesis, and this knowledge would help to access saponins of interest to address future needs.

The Effects of Sorbus aucuparia L. Fruit Extracts on Oxidative/Nitrative Modifications of Human Fibrinogen, Impact on Enzymatic Properties of Thrombin, and Hyaluronidase Activity In Vitro

Sorbus aucuparia L. fruits (rowanberries) are food products with acknowledged nutritional value, high phenolic content, and traditional application in diabetes. In this study, the effects of rowanberry extracts (phytochemically standardised, i.a., by LC-MS/MS) on some aspects of plasma haemostasis and vascular conditions were evaluated in vitro as possible mechanisms connected with cardiovascular complications of diabetes. The analyses of structural modifications of human fibrinogen under oxidative stress conditions (C-ELISA, SDS-PAGE and Western blot) revealed that the extracts (at a concentration of 1-5 µg/mL) considerably reduced the nitration of tyrosine residues and formation of high-molecular-weight aggregates. Moreover, they inhibited the enzymatic activity of thrombin (both amidolytic and proteolytic). Additionally, some promising outcomes might be expected regarding endothelial functions from the extracts ability to inhibit hyaluronidase. Parallel experiments on model polyphenols and correlation studies formed the basis for determining the contribution of different compounds, including hydroxycinnamic acid derivatives, flavonols, and low- or high-molecular-weight flavan-3-ols derivatives (proanthocyanidins), to the observed effects. The possible synergistic activity of individual constituents was also noticed. These results broaden the knowledge on the biological activity of rowanberries, partly confirming their health-promoting properties, and indicating that their functional applications might be promising.

Water-Based Extraction of Bioactive Principles from Blackcurrant Leaves and Chrysanthellum americanum: A Comparative Study

The water-based extraction of bioactive components from flavonoid-rich medicinal plants is a key step that should be better investigated. This is especially true when dealing with easy-to-use home-made conditions of extractions, which are known to be a bottleneck in the course for a better control and optimization of the daily uptake of active components from medicinal plants. In this work, the water-based extraction of Blackcurrant (Ribes nigrum) leaves (BC) and Chrysanthellum americanum (CA), known to have complementary pharmacological properties, was studied and compared with a previous work performed on the extraction of Hawthorn (Crataegus, HAW). Various extraction modes in water (infusion, percolation, maceration, ultrasounds, microwaves) were compared for the extraction of bioactive principles contained in BC and CA in terms of extraction yield, of amount of flavonoids, phenolic compounds, and proanthocyanidin oligomers, and of UHPLC profiles of the extracted compounds. The qualitative and quantitative aspects of the extraction, in addition to the kinetic of extraction, were studied. The optimized easy-to-use-at-home extraction protocol developed for HAW was found very efficient to easily extract bioactive components from BC and CA plants. UHPLC-ESI-MS and high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were also implemented to get more qualitative information on the specific and common chemical compositions of the three plants (including HAW). Their antihyaluronidase, antioxidant, and antihypertensive activities were also determined and compared, demonstrating similar activities as the reference compound for some of these plants.

Mechanistic Insights into a DMSO-Perturbing Inhibitory Assay of Hyaluronidase

A hyaluronic acid-degrading enzyme (hyaluronidase; HAase) is involved in tumor growth and inflammation, and consequently, HAase inhibitors have received recent attention as potential pharmaceuticals. Previous studies have discovered a wide range of inhibitors; however, unfortunately, most of them are dissimilar to the original ligand hyaluronic acid, and their mode of inhibition remains ambiguous or seems promiscuous. This situation presents an urgent need for readily available and highly reliable assay systems identifying the promiscuous inhibitory properties of HAase inhibitors. We have previously proposed a unique method to identify promiscuous nonspecific binding inhibitors of HAase by using the DMSO-perturbing effect. Here, to obtain mechanistic insights into the DMSO-perturbing assay, we studied the addition effect of 11 water-compatible chemicals on HAase inhibitory assay. Intriguingly, the perturbing property was found to be highly specific to DMSO. Furthermore, kinetic analyses described characteristic description of the perturbing property of DMSO: DMSO displayed entropy-driven interactions with HAase, whereas nonperturbing agents such as ethanol and urea exhibited enthalpy-driven interactions. The enthalpy-driven tight interactions of ethanol and urea with HAase would lead to the irreversible denaturation of the enzymes, while the entropy-driven weak interactions caused structural and catalytic perturbation, generating nonproductive but nondenatured states of enzymes, that are key species of the perturbation assay. With these mechanistic understandings in hand, the present assay will enable rapid and reliable identification of HAase inhibitors with certain pharmaceutical potential.

Bioassay-Guided Isolation, Metabolic Profiling, and Docking Studies of Hyaluronidase Inhibitors from Ravenala madagascariensis

Hyaluronidase enzyme (HAase) has a role in the dissolution or disintegration of hyaluronic acid (HA) and in maintaining the heathy state of skin. Bioassay-guided fractionation of Ravenala madagascariensis (Sonn.) organ extracts (leaf, flower, stem, and root) testing for hyaluronidase inhibition was performed followed by metabolic profiling using LC–HRMS. Additionally, a hyaluronidase docking study was achieved using Molecular Operating Environment (MOE). Results showed that the crude hydroalcoholic (70% EtOH) extract of the leaves as well as its n-butanol (n-BuOH) partition showed higher HAase activity with 64.3% inhibition. Metabolic analysis of R. madagascariensis resulted in the identification of 19 phenolic compounds ranging from different chemical classes (flavone glycosides, flavonol glycosides, and flavanol aglycones). Bioassay-guided purification of the leaf n-BuOH partition led to the isolation of seven compounds that were identified as narcissin, rutin, epiafzelechin, epicatechin, isorhamnetin 7-O-glucoside, kaempferol, and isorhamnetin-7-O-rutinoside. The docking study showed that narcissin, rutin, and quercetin 3-O-glucoside all interact with HAase through hydrogen bonding with the Asp111, Gln271, and/or Glu113 residues. Our results highlight Ravenala madagascariensis and its flavonoids as promising hyaluronidase inhibitors in natural cosmetology preparations for skin care.

Comparative Effectiveness of Different Interventions of Perivascular Hyaluronidase

BACKGROUND

Soft-tissue necrosis caused by vascular compromise is a frequent and troublesome complication of hyaluronic acid filler injection. Hyaluronidase has been proposed as a treatment for this condition. This study aimed to determine the effective dose and administration interval of hyaluronidase injection in a skin necrosis animal model.

METHODS

New Zealand rabbits were used to simulate the hyaluronic acid-associated vascular occlusion model. Hyaluronic acid filler (0.1 ml) was injected into the central auricular artery to create an occlusion. Three rabbit auricular flaps were injected with 500 IU of hyaluronidase once (group A) and three flaps each were injected at 15-minute intervals with 250 IU of hyaluronidase twice (group B), 125 IU of hyaluronidase four times (group C), 100 IU of hyaluronidase five times (group D), and 75 IU of hyaluronidase seven times (group E), all at 24 hours after occlusion. No intervention was administered after occlusion in the control group. Flap fluorescence angiography was performed immediately after hyaluronidase injection and on postoperative days 2, 4, and 7. Flap necrotic areas were analyzed.

RESULTS

All control and experimental flaps demonstrated total occlusion after hyaluronic acid injection. The average total survival rate (positive area/total area ×100 percent) of control flaps was 37.61 percent. For experimental groups, the average total survival rates were 74.83 percent, 81.49 percent, 88.26 percent, 56.48 percent, and 60.69 percent in groups A through E, respectively.

CONCLUSION

A better prognosis can be obtained by administering repeated doses rather than a single high dose of hyaluronidase.

Early identification of promiscuous attributes of aldose reductase inhibitors using a DMSO-perturbation assay

Aldose reductase (AR) inhibitors are used clinically to treat long-term diabetic complications. Previous studies reported a series of AR inhibitory candidates, but unfortunately the mode of inhibition was poorly described due mainly to the lack of readily available methods for evaluating the specificity. The present study examined the AR inhibitory effects of novel synthetic hydantoins and their structural relatives, some of which were obtained from chemically engineered extracts of natural plants, and discovered several novel AR inhibitors with moderate inhibitory activity. The identified inhibitors were then subjected to a two-step mechanistic characterization using a detergent-addition assay and our novel dimethyl sulfoxide (DMSO)-perturbation assay. The detergent-addition assay revealed aggregation-based inhibitors, and the subsequent DMSO-perturbation assay identified nonspecific binding inhibitors. Thus, the present study demonstrates the usefulness of the DMSO-perturbation screen for identifying nonspecific binding characteristics of AR inhibitors.

DMSO-Perturbing Assay for Identifying Promiscuous Enzyme Inhibitors

In search for enzyme inhibitors, we often encounter "promiscuous" enzyme inhibitors exhibiting nonspecific binding property toward enzyme active site. Therefore, inhibitory candidates should be mechanistically characterized as early as possible in discovery processes. However, there remains a lack of highly reliable and readily available methodology to evaluate specificity of initial hits inhibitors. The present study developed and established a novel DMSO-perturbing assay to identify promiscuous enzyme inhibitors. The assay successfully identified nonspecific binding inhibitors with a broad scope, typically by the attenuation of inhibitory activity by the influence of DMSO-addition. This attenuation would be attributed to the nonspecific binding property of inhibitors toward both productive and nonproductive (nondenatured) states of enzymes in perturbation solution. This working hypothesis was supported by spectroscopic analyses of enzyme conformations and analyses of solvent effects on perturbation. Overall, these results provided a novel concept of the DMSO-perturbing assay.

Computational advances in combating colloidal aggregation in drug discovery

Small molecule effectors are essential for drug discovery. Specific molecular recognition, reversible binding and dose-dependency are usually key requirements to ensure utility of a novel chemical entity. However, artefactual frequent-hitter and assay interference compounds may divert lead optimization and screening programmes towards attrition-prone chemical matter. Colloidal aggregates are the prime source of false positive readouts, either through protein sequestration or protein-scaffold mimicry. Nevertheless, assessment of colloidal aggregation remains somewhat overlooked and under-appreciated. In this Review, we discuss the impact of aggregation in drug discovery by analysing select examples from the literature and publicly-available datasets. We also examine and comment on technologies used to experimentally identify these potentially problematic entities. We focus on evidence-based computational filters and machine learning algorithms that may be swiftly deployed to flag chemical matter and mitigate the impact of aggregates in discovery programmes. We highlight the tools that can be used to scrutinize libraries, and identify and eliminate these problematic compounds.

Affinity adsorption of bovine hyaluronidase with ligands targeting to active site

Four affinity ligands were designed from 6-chloromethyluracil and 2-aminobenzimidazole and simulated for the interaction with bovine hyaluronidase-1. Regarding sequence alignment, bovine hyaluronidase-1 precursor showed circa 83.6% similarity with human hyaluronidase-1. Regarding structural modeling and molecular docking, bovine hyaluronidase-1 interacted with ligands in the active site. Using epichlorohydrin, 1,3-propanediamine and cyanuric chloride as spacers, 6-chloromethyluracil and 2-aminobenzimidazole were composed to Sepharose beads. The modified Sepharose beads were then subjected to adsorption analysis with bovine hyaluronidase. After one step of affinity adsorption, the samples extracted from bovine testes were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis and activity assay. As calculated, the densities of four ligands on sorbents (entitled as L-1, L-2, L-3 and L-4) were 37.7 ± 2.3, 36.4 ± 3.2, 42.4 ± 4.2 and 33.7 ± 2.3 μmol/g wet gel; the theoretical maximum adsorption (Q_max) of bovine hyaluronidase on the four sorbents were 63.6 ± 1.6, 72.0 ± 0.7, 111.0 ± 4.1 and 121.7 ± 2.3 mg/g wet gel, respectively; the dissociation constants (K_d) of the four sorbents were 18.5 ± 0.8, 48.1 ± 4.3, 35.0 ± 3.0, 40.6 ± 2.7 μg/g wet gel, respectively. After optimization, the proteins captured by sorbents attaching 2-aminobenzimidazole based ligands (L-3 and L-4) revealed the main single band at approximately 50 kDa, and the purities were about 85.2 and 96.4%; the bioactivity recoveries were 83.5 and 89.4%. In addition, the bands on SDS-PAGE gel were also extracted and confirmed with linear trap quadropole mass spectrometry (LTQ-MS) analysis.