Promising Natural Compounds against Flavivirus Proteases: Citrus Flavonoids Hesperetin and Hesperidin

High-throughput MALDI-MSI metabolite analysis of plant tissue microarrays

A novel metabolomics analysis technique, termed matrix-assisted laser desorption/ionization mass spectrometry imaging-based plant tissue microarray (MALDI-MSI-PTMA), was successfully developed for high-throughput metabolite detection and imaging from plant tissues. This technique completely overcomes the disadvantage that metabolites cannot be accessible on an intact plant tissue due to the limitations of the special structures of plant cells (e.g. epicuticular wax, cuticle and cell wall) through homogenization of plant tissues, preparation of PTMA moulds and matrix spraying of PTMA sections. Our study shows several properties of MALDI-MSI-PTMA, including no need of sample separation and enrichment, high-throughput metabolite detection and imaging (>1000 samples per day), high-stability mass spectrometry data acquisition and imaging reconstruction and high reproducibility of data. This novel technique was successfully used to quickly evaluate the effects of two plant growth regulator treatments (i.e. 6-benzylaminopurine and N-phenyl-N'-1,2,3-thiadiazol-5-ylurea) on endogenous metabolite expression in plant tissue culture specimens of Dracocephalum rupestre Hance (D. rupestre). Intra-day and inter-day evaluations indicated that the metabolite data detected on PTMA sections had good reproducibility and stability. A total of 312 metabolite ion signals in leaves tissues of D. rupestre were detected, of which 228 metabolite ion signals were identified, they were composed of 122 primary metabolites, 90 secondary metabolites and 16 identified metabolites of unknown classification. The results demonstrated the advantages of MALDI-MSI-PTMA technique for enhancing the overall detection ability of metabolites in plant tissues, indicating that MALDI-MSI-PTMA has the potential to become a powerful routine practice for high-throughput metabolite study in plant science.

Computer-aided identification of dengue virus NS2B/NS3 protease inhibitors: an integrated molecular modelling approach for screening of phytochemicals

Globally, dengue (DENV) fever has appeared as the most widespread vector-borne disease, affecting more than 100 million individuals annually. No approved anti-DENV therapy or preventive vaccine is available yet. DENV NS3 protein is associated with protease activity and is essential for viral replication process within the host cell. NS2B is linked with NS3 protein as a cofactor. Hence, NS3/NS2B is a potential druggable target for developing inhibitors against dengue virus. In the present study, a dataset of Beta vulgaris L.-based natural compounds was developed. Virtual ligand screening of 30 phytochemicals was carried out to find novel inhibitors against the NS2B/NS3 protein. Spatial affinity, drug-likeness, and binding behaviors of selected phytochemicals were analyzed. Post-simulation analysis, including Principal Component Analysis (PCA), MMGBSA, and Co-relation analysis, was also performed to provide deep insight for elucidating protein-ligand complexes. This computer-aided screening scrutinized four potent phytochemicals, including betavulgaroside II, vitexin xyloside, epicatechin, and isovitexin2-O-xyloside inhibitors exhibiting optimal binding with viral NS3/NS2B protein. Our study brings novel scaffolds against DENV NS2B/NS3 of serotype-2 to act as lead molecules for further biological optimization. In future, this study will prompt the exploration and development of adjuvant anti-DENV therapy based on natural compounds.Communicated by Ramaswamy H. Sarma.

Pharmacologic Comparison of High-Dose Hesperetin and Quercetin on MDCK II Cell Viability, Tight Junction Integrity, and Cell Shape

The modulation of tight junction (TJ) integrity with small molecules is important for drug delivery. High-dose baicalin (BLI), baicalein (BLE), quercetin (QUE), and hesperetin (HST) have been shown to open TJs in Madin-Darby canine kidney (MDCK) II cells, but the mechanisms for HST and QUE remain unclear. In this study, we compared the effects of HST and QUE on cell proliferation, morphological changes, and TJ integrity. HST and QUE were found to have opposing effects on the MDCK II cell viability, promotion, and suppression, respectively. Only QUE, but not HST, induced a morphological change in MDCK II into a slenderer cell shape. Both HST and QUE downregulated the subcellular localization of claudin (CLD)-2. However, only QUE, but not HST, downregulated CLD-2 expression. Conversely, only HST was shown to directly bind to the first PDZ domain of ZO-1, a key molecule to promote TJ biogenesis. The TGFβ pathway partially contributed to the HST-induced cell proliferation, since SB431541 ameliorated the effect. In contrast, the MEK pathway was not involved by both the flavonoids, since U0126 did not revert their TJ-opening effect. The results offer insight for using HST or QUE as naturally occurring absorption enhancers through the paracellular route.

The Importance of Epigallocatechin as a Scaffold for Drug Development against Flaviviruses

Arboviruses such as Dengue, yellow fever, West Nile, and Zika are flaviviruses vector-borne RNA viruses transmitted biologically among vertebrate hosts by blood-taking vectors. Many flaviviruses are associated with neurological, viscerotropic, and hemorrhagic diseases, posing significant health and socioeconomic concerns as they adapt to new environments. Licensed drugs against them are currently unavailable, so searching for effective antiviral molecules is still necessary. Epigallocatechin molecules, a green tea polyphenol, have shown great virucidal potential against flaviviruses, including DENV, WNV, and ZIKV. The interaction of EGCG with the viral envelope protein and viral protease, mainly identified by computational studies, describes the interaction of these molecules with viral proteins; however, how the viral NS2B/NS3 protease interacts with epigallocatechin molecules is not yet fully deciphered. Consequently, we tested the antiviral potential of two epigallocatechin molecules (EGC and EGCG) and their derivative (AcEGCG) against DENV, YFV, WNV, and ZIKV NS2B/NS3 protease. Thus, we assayed the effect of the molecules and found that a mixture of the molecules EGC (competitive) and EGCG (noncompetitive) inhibited the virus protease of YFV, WNV, and ZIKV more effectively with IC50 values of 1.17 ± 0.2 µM, 0.58 ± 0.07 µM, and 0.57 ± 0.05 µM, respectively. As these molecules fundamentally differ in their inhibitory mode and chemical structure, our finding may open a new line for developing more effective allosteric/active site inhibitors to combat flaviviruses infection.

Dietary citrus flavonoid extract improves lactational performance through modulating rumen microbiome and metabolites in dairy cows

The effects of dietary supplementation with citrus flavonoid extract (CFE) on milk performance, rumen fermentation, rumen microbiome, rumen metabolome, and serum antioxidant indexes were evaluated. Eight multiparous lactating cows were allocated to a replicated 4 × 4 Latin square with 25-d periods consisting of 20 d of adaptation and 5 d of sampling. Experimental treatments included a control diet (CON) and CON supplemented with 50 g d^-1 (CFE50), 100 g d^-1 (CFE100), and 150 g d^-1 (CFE150). Feeding CFE to dairy cows increased milk production and milk lactose. Milk somatic cell count linearly reduced with increasing CFE amount. Supplementing CFE linearly increased the ruminal concentrations of total volatile fatty acids, acetate, propionate, butyrate, and microbial crude protein. Ruminal lipopolysaccharide linearly decreased with increasing CFE amount. Compared with CON, CFE150 cows exhibited a greater abundance of Firmicutes and a low abundance of Bacteroidetes. Cellulolytic bacteria (genera Ruminococcus, Clostridium, and Butyrivibrio) and carbohydrate metabolism were enriched in the CFE150 cows. For archaea and viruses, major methanogens (genera Methanobacterium and Methanosarcina) and phylum Uroviricota were inhibited in the CFE150 cows. Compared with CON, the ruminal concentrations of tyrosine, proline, pyruvate, glucose, and glucose-6-phosphate were higher in the CFE150 cows. The metabolites of citrus flavonoids, such as hippuric acid, hesperetin, and naringenin, were increased in the CFE150 cows. Supplementing CFE significantly improved the antioxidant capacity of the dairy cows. This study highlighted that dietary supplementation with CFE led to significant changes in the rumen microbial composition and metabolites, and consequently resulted in an improved lactational performance of dairy cows.

Recent advances in natural products as potential inhibitors of dengue virus with a special emphasis on NS2b/NS3 protease

Dengue virus (DENV) is an arbovirus widespread through tropical and subtropical areas. It is transmitted to humans through Aedes mosquitoes. Infections with DENV can lead to a series of complications, including dengue fever, dengue haemorrhagic fever, or dengue shock syndrome, which might manifest through secondary infections because of a vulnerable immune system. To date, only one tetravalent DENV vaccine is approved to be administered to children whom have been previously DENV-infected and between 9 and 16 years of age. One of the key targets in discovering DENV antiviral agents is the NS2b/NS3 protease. This protease is a crucial enzyme complex for the proteolytic and cleavage activities of the translated polyprotein during DENV life cycle. Several studies were conducted to discover potential antivirals from natural sources or synthetic compounds and peptides. In this review, we describe the recent studies from the past five years dealing with isolated natural products as potential inhibitors of DENV with a greater focus on inhibiting the NS2b/NS3 protease. This review describes recent discoveries in anti-DENV potential of isolated phytochemicals belonging to different groups including fatty acids, glucosides, terpenes and terpenoids, flavonoids, phenolics, chalcones, acetamides, and peptides. Curcumin, quercetin, and myricetin were found to act as non-competitive inhibitors for the NS2b/NS3 protease enzyme. In some studies, the molecular targets of some of these compounds are yet to be identified using in-silico and in-vitro approaches. So far, none of the isolated natural products was tested clinically for the management of DENV infections. The discussed studies demonstrate that natural products are a rich source of potential anti-DENV compounds. However, not all of these compounds were studied for their kinetic molecular mechanism and type of inhibition. In-silico studies provided an ample number of phytochemical hits to be tested experimentally as DENV protease inhibitors. In conclusion, derivatives of these natural products can be designed and synthesised, which could enhance their specificity and efficacy towards the protease. Other sources of natural products, such as fungi, bacterial toxins, marine organisms, and animals, should also be explored towards discovering more potential and effective DENV NS2b/NS3 protease inhibitors.

Riboflavin, a Potent Neuroprotective Vitamin: Focus on Flavivirus and Alphavirus Proteases

Several neurotropic viruses are members of the flavivirus and alphavirus families. Infections caused by these viruses may cause long-term neurological sequelae in humans. The continuous emergence of infections caused by viruses around the world, such as the chikungunya virus (CHIKV) (Alphavirus genus), the zika virus (ZIKV) and the yellow fever virus (YFV) (both of the Flavivirus genus), warrants the development of new strategies to combat them. Our study demonstrates the inhibitory potential of the water-soluble vitamin riboflavin against NS2B/NS3pro of ZIKV and YFV and nsP2pro of CHIKV. Riboflavin presents a competitive inhibition mode with IC50 values in the medium µM range of 79.4 ± 5.0 µM for ZIKV NS2B/NS3pro and 45.7 ± 2.9 μM for YFV NS2B/NS3pro. Against CHIKV nsP2pro, the vitamin showed a very strong effect (93 ± 5.7 nM). The determined dissociation constants (KD) are significantly below the threshold value of 30 µM. The ligand binding increases the thermal stability between 4 °C and 8 °C. Unexpectedly, riboflavin showed inhibiting activity against another viral protein; the molecule was also able to inhibit the viral entry of CHIKV. Molecular dynamics simulations indicated great stability of riboflavin in the protease active site, which validates the repurposing of riboflavin as a promising molecule in drug development against the viruses presented here.