Discovery of xanthine oxidase inhibitors from a complex mixture using an online, restricted-access material coupled with column-switching liquid chromatography with a diode-array detection system

Agents for the Treatment of Gout: Current Advances and Future Perspectives

Gout is characterized by hyperuricemia and the deposition of monosodium urate (MSU) crystals around joints. Despite the availability of several drugs on the market, its treatment remains challenging owing to the notable side effects, such as hepatorenal toxicity and cardiovascular complications, that are associated with most existing agents. This perspective aims to summarize the current research progress in the development of antigout agents, particularly focusing on xanthine oxidase (XO) and urate anion transporter 1 (URAT1) inhibitors from a medicinal chemistry viewpoint and their preliminary structure-activity relationships (SARs). This perspective provides valuable insights and theoretical guidance to medicinal chemists for the discovery of antigout agents with novel chemical structures, better efficiency, and lower toxicity.

Screening of Tyrosinase, Xanthine Oxidase, and α-Glucosidase Inhibitors from Polygoni Cuspidati Rhizoma et Radix by Ultrafiltration and HPLC Analysis

Polygoni Cuspidati Rhizoma et Radix (PCR), the rhizome and root of Polygonum cuspidatum Sieb. et Zucc., has been used as an herbal medicine for a long time. In this study, the ultrafiltration combined with high performance liquid chromatography (UF-HPLC) method was developed to screen tyrosinase (TYR), α-glucosidase (α-GLU), and xanthine oxidase (XOD) inhibitors from PCR. Firstly, the inhibitory activity of 50% methanol PCR extract on TYR, α-GLU, XOD, and acetylcholinesterase (ACHE) was tested. The extract showed a good inhibition on the enzymes, except for ACHE. Therefore, UF-HPLC experiments were carried out to screen TYR, α-GLU, and XOD inhibitors from PCR extract. Seven potential bioactive components were discovered, including methylgallate (1), 1,6-di-O-galloyl-D-glucose (2), polydatin-4'-O-D-glucoside (3), resveratrol-4'-O-D-glucoside (4), polydatin (5), malonyl glucoside resveratrol (6), and resveratrol-5-O-D-glucoside (7). Most of them were found as enzyme inhibitors from PCR for the first time, except polydatin (5), which had been reported as an α-GLUI in PCR in the literature. Finally, molecular docking analysis was applied to validate the interactions of these seven potential active components with the enzymes. Compounds 1-7 were proven as TYR inhibitors, compounds 2, 4-7 were identified as XOD inhibitors, and compounds 4-6 were confirmed as α-GLU inhibitors. In short, the current study provides a good reference for the screening of enzyme inhibitors through UF-HPLC, and provides scientific data for future studies of PCR.

Unraveling the mystery of efficacy in Chinese medicine formula: New approaches and technologies for research on pharmacodynamic substances

Traditional Chinese medicine (TCM) is the key to unlock treasures of Chinese civilization. TCM and its compound play a beneficial role in medical activities to cure diseases, especially in major public health events such as novel coronavirus epidemics across the globe. The chemical composition in Chinese medicine formula is complex and diverse, but their effective substances resemble "mystery boxes". Revealing their active ingredients and their mechanisms of action has become focal point and difficulty of research for herbalists. Although the existing research methods are numerous and constantly updated iteratively, there is remain a lack of prospective reviews. Hence, this paper provides a comprehensive account of existing new approaches and technologies based on previous studies with an in vitro to in vivo perspective. In addition, the bottlenecks of studies on Chinese medicine formula effective substances are also revealed. Especially, we look ahead to new perspectives, technologies and applications for its future development. This work reviews based on new perspectives to open horizons for the future research. Consequently, herbal compounding pharmaceutical substances study should carry on the essence of TCM while pursuing innovations in the field.

Collision-Induced Affinity Selection Mass Spectrometry for Identification of Ligands

Hyphenated mass spectrometry has been used to identify ligands binding to proteins. It involves mixing protein and compounds, separation of protein-ligand complexes from unbound compounds, dissociation of the protein-ligand complex, separation to remove protein, and injection of the supernatant into a mass spectrometer to observe the ligand. Here we report collision-induced affinity selection mass spectrometry (CIAS-MS), which allows separation and dissociation inside the instrument. The quadrupole was used to select the ligand-protein complex and allow unbound molecules to be exhausted to vacuum. Collision-induced dissociation (CID) dissociated the protein-ligand complex, and the ion guide and resonance frequency were used to selectively detect the ligand. A known SARS-CoV-2 Nsp9 ligand, oridonin, was successfully detected when it was mixed with Nsp9. We provide proof-of-concept data that the CIAS-MS method can be used to identify binding ligands for any purified protein.

Natural Compound Library Screening Identifies Oroxin A for the Treatment of Myocardial Ischemia/Reperfusion Injury

Myocardial ischemia/reperfusion injury (MI/RI) is a serious pathophysiological process relating to cardiovascular disease. Oroxin A (OA) is a natural flavonoid glycoside with various biological activities. However, its effect on the pathophysiological process of MI/RI has not yet been reported. The aim of this study was to determine whether OA could alleviate MI/RI induced inflammation and pyroptosis in vivo and in vitro, providing a novel therapeutic regimen for the treatment of MI/RI. A high-throughput drug screening strategy was employed to test 2,661 natural compound libraries that can alleviate MI/RI in vivo and in vitro. The rat model of MI/RI was established by ligating the left anterior descending (LAD) coronary artery. H9c2 cells were subjected to oxygen-glucose deprivation/reperfusion (OGD/R) to simulate MI/RI. The results show that OA is able to significantly inhibit apoptosis, pyroptosis and the inflammation response (TNF-α, IL-6, IL-8, IL-10, IL-1β, IL-18) in vivo and in vitro, and reduce the release of myocardial enzymes (cTnI, cTnT, CK-MB, LDH, AST). In the rat MI/RI model, OA can not only improve cardiac function and reduce inflammatory cell infiltration but also reduce myocardial infarct size. The results revealed that OA is an effective remedy against MI/RI as it reduces the inflammatory response and inhibits pyroptosis. This may provide a new therapeutic target for the clinical treatment of MI/RI.

Comprehensive screening and separation of cyclooxygenase-2 inhibitors from Pterocephalus hookeri by affinity solid-phase extraction coupled with preparative high-performance liquid chromatography

Pterocephalus hookeri, a classical Tibetan herb, is mainly used to treat rheumatoid arthritis (RA) and contains various constituents potentially with cyclooxygenase-2 (COX-2) selective inhibition. A novel strategy for screening and target separating COX-2 inhibitors from the extracts of P. hookeri based on affinity solid-phase extraction (ASPE) column combined with preparative high-performance liquid chromatography (pre-HPLC) was successfully developed. The potential COX-2 inhibitors of P. hookeri were screened and recognized by the ASPE-HPLC system, which strategy is to analyze the compounds isolated by the ASPE column. Then, the active compounds were targeted separated by pre-HPLC according to real-time chromatograms. The control drugs celecoxib and glipizide were analyzed to verify the specificity and accuracy of the developed method. As a result, two pure compounds with COX-2 binding affinities were successfully separated from P. hookeri. They were characterized as swertisin and scopoletin using ¹H- and ¹³C NMR spectroscopy, and the in vitro COX-2 inhibitory activities were verified. Compounds with COX-2 inhibitory activities could be screened and targeted separated from crude extracts by this strategy, which indicated that the proposed method was feasible, robust and effective for rapid separation of COX-2 inhibitors from natural products.

Baicalein alleviates hyperuricemia by promoting uric acid excretion and inhibiting xanthine oxidase

BACKGROUND

Insufficient renal urate excretion and/or overproduction of uric acid (UA) are the dominant causes of hyperuricemia. Baicalein (BAL) is widely distributed in dietary plants and has extensive biological activities, including antioxidative, anti-inflammatory and antihypertensive activities.

PURPOSE

To investigate the anti-hyperuricemic effects of BAL and the underlying mechanisms in vitro and in vivo.

METHODS

We investigated the inhibitory effects of BAL on GLUT9 and URAT1 in vitro through electrophysiological experiments and ¹⁴C-urate uptake assays. To evaluate the impact of BAL on serum and urine UA, the expression of GLUT9 and URAT1, and the activity of xanthine oxidase (XOD), we developed a mouse hyperuricemia model by potassium oxonate (PO) injection. Molecular docking analysis based on homology modeling was performed to explain the predominant efficacy of BAL compared with the other test compounds.

RESULTS

BAL dose-dependently inhibited GLUT9 and URAT1 in a noncompetitive manner with IC₅₀ values of 30.17 ± 8.68 μM and 31.56 ± 1.37 μM, respectively. BAL (200 mg/kg) significantly decreased serum UA and enhanced renal urate excretion in PO-induced hyperuricemic mice. Moreover, the expression of GLUT9 and URAT1 in the kidney was downregulated, and XOD activity in the serum and liver was suppressed. The docking analysis revealed that BAL potently interacted with Trp336, Asp462, Tyr71 and Gln328 of GLUT9 and Ser35 and Phe241 of URAT1.

CONCLUSION

These results indicated that BAL exerts potent antihyperuricemic efects through renal UA excretal promotion and serum UA production. Thus, we propose that BAL may be a promising treatment for the prevention of hyperuricemia owing to its multitargeted inhibitory activity.

Host-guest interaction of cucurbit[8]uril with oroxin A and its effect on the properties of oroxin A

In this study, we investigated the host-guest interactions between oroxin A (OA) and cucurbit[8]uril (Q[8]) using 1H NMR, MS, UV-vis and IR spectroscopy. The results showed that OA and Q[8] formed an inclusion compound (OA@Q[8]) with a molar ratio of 1:1 and a binding constant of 1.299 × 107 L·mol-1. In addition, the effect of Q[8] on the properties of OA was investigated through comparative experiments. The solubility of OA in water increased 22.47-fold when the concentration of Q[8] was 1 × 10-4 mol·L-1. Q[8] hardly affected the antioxidant capacity of OA, while the cumulative release of OA in gastric juice increased 2.3-fold after forming the inclusion compound with Q[8].

Recent applications of immobilized biomaterials in herbal analysis

Immobilization of biomaterials developed rapidly due to the great promise in improving their stability, activity and even selectivity. In this review, the immobilization strategies of biomaterials, including physical adsorption, encapsulation, covalent attachment, cross-linking and affinity linkage, were briefly introduced. Then, the major emphasis was focused on the reported various types of immobilized biomaterials, including proteins, enzymes, cell membrane and artificial membrane, living cells, carbohydrates and bacteria, used in the herbal analysis for bioactive compound screening, drug-target interaction evaluation and chiral separation. In addition, a series of carrier materials applied in biomaterials immobilization, such as magnetic nanoparticles, metal-organic frameworks, silica capillary column, cellulose filter paper, cell membrane chromatography, immobilized artificial membrane chromatography and hollow fiber, were also discussed. Perspectives on further applications of immobilized biomaterials in herbal analysis were finally presented.

Screening techniques for the identification of bioactive compounds in natural products

Natural products (NPs) have a long history of clinical use and are rich source of bioactive compounds. The development of tools and techniques for identifying and analyzing NP bioactive compounds to ensure their quality and discover new drugs is thus very important and still in demand. Screening techniques have proven highly useful for screening and analyzing active components in complex mixtures, which rely on cell culture, dialysis, ultrafiltration, chromatographic methods and target molecule immobilization, using biological targets to identify the active compounds. The recent progress in biological screening techniques in the field of natural products is reviewed here. This includes a review on the strategy and application of the screening methods, their detailed description and discussion of their existing limitations of the different models along with prospective in future development of screening techniques.

Oroxin A from Oroxylum indicum prevents the progression from prediabetes to diabetes in streptozotocin and high-fat diet induced mice

BACKGROUND

Oroxylum indicum (L.) Kurz (Bignoniaceae) has been widely used for the treatment of respiratory infections and gastrointestinal disorders. Our previous study showed that an ethanol-water O. indicum seed extract (OISE), when combined with acarbose, reduced the risk of diabetes by 75% and effectively prevented the associated complications. Oroxin A, a major component of OISE, can activate PPARγ and inhibit α-glucosidase and it represents a promising candidate for diabetes intervention.

PURPOSE

The aim of this study is to investigate the effect of oroxin A from O. indicum on the progression of prediabetes to diabetes and the underlying mechanisms in streptozotocin and high-fat-diet induced prediabetic mice.

METHODS

Oroxin A was purified from OISE and its PPARγ transcriptional activation was determined in vitro and in vivo. The prediabetic mice were established by high-fat diet and streptozotocin, which was followed by treatment with oroxin A. The effect of oroxin A was determined by analysis of the lipid profiles, oxidative stress, hepatic function and histology. The mechanism of oroxin A was also investigated.

RESULTS

Oroxin A is a compound with low toxicity that has reduced the relative risk of progression from prediabetes to diabetes by 66.7% without inducing weight gain or hepatotoxicity. Oroxin A also improved the complications of prediabetes, such as lipid metabolism dysfunction and liver injury. Results of mechanism studies suggested that oroxin A is a partial PPARγ agonist that can activate PPARγ transcriptional activation in vitro and in vivo. Oroxin A also exhibited an inhibitory activity against α-glucosidase and an antioxidant capacity.

CONCLUSION

Oroxin A prevents the progression from prediabetes to diabetes through a multi-pathway intervention mechanism.

Xanthine oxidase inhibitors beyond allopurinol and febuxostat; an overview and selection of potential leads based on in silico calculated physico-chemical properties, predicted pharmacokinetics and toxicity

Xanthine oxidase (XO), a versatile metalloflavoprotein enzyme, catalyzes the oxidative hydroxylation of hypoxanthine and xanthine to uric acid in purine catabolism while simultaneously producing reactive oxygen species. Both lead to the gout-causing hyperuricemia and oxidative damage of the tissues where overactivity of XO is present. Over the past years, significant progress and efforts towards the discovery and development of new XO inhibitors have been made and we believe that not only experts in the field, but also general readership would benefit from a review that addresses this topic. Accordingly, the aim of this article was to overview and select the most potent recently reported XO inhibitors and to compare their structures, mechanisms of action, potency and effectiveness of their inhibitory activity, in silico calculated physico-chemical properties as well as predicted pharmacokinetics and toxicity. Derivatives of imidazole, 1,3-thiazole and pyrimidine proved to be more potent than febuxostat while also displaying/possessing favorable predicted physico-chemical, pharmacokinetic and toxicological properties. Although being structurally similar to febuxostat, these optimized inhibitors bear some structural freshness and could be adopted as hits for hit-to-lead development and further evaluation by in vivo studies towards novel drug candidates, and represent valuable model structures for design of novel XO inhibitors.

Oroxylum indicum (L.) Kurz, an important Asian traditional medicine: from traditional uses to scientific data for its commercial exploitation

ETHNOPHARMACOLOGICAL RELEVANCE

Oroxylum indicum\ (L.) Kurz has been used for centuries as a traditional medicine in Asia in ethnomedicinal systems for the prevention and treatment of several diseases, such as jaundice, arthritic and rheumatic problems, gastric ulcers, tumors, respiratory diseases, diabetes, and diarrhea and dysentery, among others. The present review provides scientific evidence supporting the therapeutic potency of the plant for ethnomedicinal uses and identifies gaps for future research to facilitate commercial exploitation.

METHODS

This review is based on available information on traditional uses and phytochemical, pharmacological, clinical and toxicity data for Oroxylum indicum that was collected from electronic (SciFinder, PubMed, Science Direct, and ACS, among others) and library searches.

KEY FINDING

A variety of traditional medicinal uses of Oroxylum indicum in different Southeast and South Asian countries have been reported in books describing the uses of these plants. Phytochemical investigations of the different parts of the plant resulted in identification of approximately 111 compounds, among which flavonoids, naphthalenoids and cyclohexylethanoids are the predominant groups. The crude extracts and their isolates exhibit a wide spectrum of in vitro and in vivo pharmacological activities involving antimicrobial, anti-inflammatory, anti-arthritic, anticancer, anti-ulcer, hepatoprotective, antidiabetic, antidiarrheal and antioxidant activities. Flavonoids are the major constituents of all parts of the plant. From a toxicity perspective, only aqueous and ethanolic extracts of stem bark, root bark and fruits have been assessed and found to be safe. The major flavonoids of the stem bark, such as baicalein, chrysin and oroxylin A, were reported for the first time as natural flavonoids with potent inhibitory activity against endoprotease enzymes and proprotein convertases, which play a key role in the growth of cancer and in viral and bacterial infections. Flavonoids are the active components of bioactive extracts. Several Ayurvedic medicines have been formulated either singly using this plant or along with other herbs for the treatment of different diseases.

CONCLUSIONS

Pharmacological results have supported some traditional medicinal uses of Oroxylum indicum. Several extracts and their isolates have been reported to exhibit interesting pharmacological properties. These components could be useful as sources of modern medicines following future detailed studies to elucidate their underlying mechanisms, toxicity, synergistic effects and clinical trials. Attention should also be focused on pharmacological studies investigating the traditional uses of the plant, which have not been yet addressed, as well as clinical studies investigating commercial Ayurvedic medicines and other ethnomedicinal preparations in human subjects based on this plant to confirm the safety and quality of the preparations.

Development of a Concise Synthetic Approach to Access Oroxin A

A novel environment-friendly method to access bioactive oroxin A through a one-pot/two-step process from naturally abundant and inexpensive baicalin is described. The procedure presented here has several advantages including clean, one-pot, synthetic ease, and large-scale feasibility. This work also provides a model strategy for rapid and diverse access to natural molecules sharing the common skeleton of this family.