Physcion inhibition of CYP2C9, 2D6 and 3A4 in human liver microsomes

CONTEXT

The effect of the active ingredients in traditional Chinese medicines on the activity of cytochrome P450 enzymes (CYP450s) is a critical factor that should be considered in TCM prescriptions. Physcion, the major active ingredient of Rheum spp. (Polygonaceae), possesses wide pharmacological activities.

OBJECTIVES

The effect of physcion on CYP450 activity was investigated to provide a theoretical basis for use.

MATERIALS AND METHODS

The experiments were conducted in pooled human liver microsomes (HLMs). The activity of CYP450 isoforms was evaluated with corresponding substrates and probe reactions. Blank HLMs were set as negative controls, and typical inhibitors were employed as positive controls. The inhibition model was fitted with Lineweaver Burk plots. The concentration (0, 2.5, 5, 10, 25, 50 and 100 μM physcion) and time-dependent (0, 5, 10, 15 and 30 min) effects of physcion were also assessed.

RESULTS

Physcion suppressed CYP2C9, 2D6 and 3A4 in a concentration-dependent manner with IC50 values of 7.44, 17.84 and 13.50 μM, respectively. The inhibition of CYP2C9 and 2D6 was competitive with the Ki values of 3.69 and 8.66 μM, respectively. The inhibition of CYP3A4 was non-competitive with a Ki value of 6.70 μM. Additionally, only the inhibition of CYP3A4 was time-dependent with the KI and Kinact parameters of 3.10 μM-1 and 0.049 min-1, respectively.

CONCLUSIONS

The inhibition of CYP450s by physcion should be considered in its clinical prescription, and the study design can be employed to evaluate the interaction of CYP450s with other herbs.

Rehmannioside A inhibits the activity of CYP3A4, 2C9 and 2D6 in vitro

To assess the effect of Rehmannioside A on CYP450s activity and to estimate its inhibitory properties.The effect of Rehmannioside A on the activity of major CYP450s in human liver microsomes (HLMs) was assessed with the corresponding substrates and marker reactions, and compared with a blank control and the respective inhibitors. Suppression of CYP3A4, 2C9 and 2D6 was assessed by the dose-dependent assay and fitted with non-competitive or competitive inhibition models. The inhibition of CYP3A4 was determined in a time-dependent manner.Rehmannioside A suppressed the activity of CYP3A4, 2C9, and 2D6 with IC50 values of 10.08, 12.62, and 16.43 μM, respectively. Suppression of CYP3A4 was fitted to a non-competitive model with Ki value of 5.08 μM, whereas CYP2C9 and 2D6 were fitted to a competitive model with Ki values of 6.25 and 8.14 μM. Additionally, the inhibitory effect on CYP3A4 was time-dependent with KI value of 8.47 μM-1 and a Kinact of 0.048 min-1.In vitro suppression of CYP3A, 2C9 and 2D6 by Rehmannioside A indicated that Rehmannioside A or its source herbs may interact with drugs metabolised by these CYP450s, which could guide the clinical application.

ADMET and Solubility Analysis of New 5-Nitroisatine-Based Inhibitors of CDK2 Enzymes

The development of new substances with the ability to interact with a biological target is only the first stage in the process of the creation of new drugs. The 5-nitroisatin derivatives considered in this study are new inhibitors of cyclin-dependent kinase 2 (CDK2) intended for anticancer therapy. The research, carried out based on the ADMET (absorption, distribution, metabolism, excretion, toxicity) methods, allowed a basic assessment of the physicochemical parameters of the tested drugs to be made. The collected data clearly showed the good oral absorption, membrane permeability, and bioavailability of the tested substances. The analysis of the metabolite activity and toxicity of the tested drugs did not show any critical hazards in terms of the toxicity of the tested substances. The substances' low solubility in water meant that extended studies tested compounds were required, which helped to select solvents with a high dissolving capacity of the examined substances, such as DMSO or NMP. The use of aqueous binary mixtures based on these two solvents allowed a relatively high solubility with significantly reduced toxicity and environmental index compared to pure solvents to be maintained, which is important in the context of the search for green solvents for pharmaceutical use.

Selective inhibitory effects of suberosin on CYP1A2 in human liver microsomes

Suberosin is a natural phytoconstituent isolated from Citropsis articulata, especially employed for its anticoagulant properties. Although metabolic studies assessing suberosin have been conducted, it is possible interactions with drugs and food have not yet been investigated. In the present study, we analyzed the selective inhibitory effects of suberosin on cytochrome P450 (CYP) enzymes using a cocktail probe assay. Various concentrations of suberosin (0-50 μM) were incubated with isoform-specific CYP probes in human liver microsomes (HLMs). We found that suberosin significantly inhibited CYP1A2-catalyzed phenacetin O-deethylation, exhibiting IC50 values of 9.39 ± 2.05 and 3.07 ± 0.45 μM with and without preincubation in the presence of β-NADPH, respectively. Moreover, suberosin showed concentration-dependent, but not time-dependent, CYP1A2 inhibition in HLMs, indicating that suberosin acts as a substrate and reversible CYP1A2 inhibitor. Using a Lineweaver-Burk plot, we found that suberosin competitively inhibited CYP1A2-catalyzed phenacetin O-deethylation. Furthermore, suberosin showed similar inhibitory effects on recombinant human CYP1A1 and 1A2. In conclusion, suberosin may elicit herb-drug interactions by selectively inhibiting CYP1A2 during the concurrent administration of drugs that act as CYP1A2 substrates.

Mechanistic insights into the inhibition of human placental glutathione S-transferase P1-1 by abscisic and gibberellic acids: An integrated experimental and computational study

The interactions of the classic phytohormones gibberellic acid (gibberellin A3 , GA3 ) and abscisic acid (dormin, ABA), which antagonistically regulate several developmental processes and stress responses in higher plants, with human placental glutathione S-transferase P1-1 (hpGSTP1-1), an enzyme that plays a role in endo- or xenobiotic detoxification and regulation of cell survival and apoptosis, were investigated. The inhibitory potencies of ABA and GA3 against hpGSTP1, as well as the types of inhibition and the kinetic parameters, were determined by making use of both enzyme kinetic graphs and SPSS nonlinear regression models. The structural basis for the interaction between hpGSTP1-1 and phytohormones was predicted with the aid of molecular docking simulations. The IC50 values of ABA and GA3 were 5.3 and 5.0 mM, respectively. Both phytohormones inhibited hpGSTP1-1 in competitive manner with respect to the cosubstrates GSH and CDNB. When ABA was the inhibitor at [CDNB]f -[GSH]v and at [GSH]f -[CDNB]v , Vm , Km , and Ki values were statistically estimated to be 205 ± 16 μmol/min-mg protein, 1.32 ± 0.18 mM, 1.95 ± 0.25 mM and 175 ± 6 μmol/min-mg protein, 0.85 ± 0.06 mM, 1.85 ± 0.16 mM, respectively. On the other hand, the kinetic parameters Vm , Km , and Ki obtained with GA3 at [CDNB]f -[GSH]v and at [GSH]f -[CDNB]v were found to be 303 ± 14 μmol/min-mg protein, 1.77 ± 0.13 mM, 3.38 ± 0.26 mM and 249 ± 7 μmol/min-mg protein, 1.43 ± 0.07 mM, 2.89 ± 0.19 mM, respectively. Both phytohormones had the potential to engage in hydrogen-bonding and electrostatic interactions with the key residues that line the G- and H-sites of the enzyme's catalytic center. Inhibitory actions of ABA/GA3 on hpGSTP1-1 may guide medicinal chemists through the structure-based design of novel antineoplastic agents. It should be noted, however, that the same interactions may also render fetuses vulnerable to the potentially toxic effects of xenobiotics and noxious endobiotics.

Synthesis of 4-hydroxy-L-proline derivatives as new non-classical inhibitors of human carbonic anhydrase II activity: an in vitro study

Carbonic anhydrase (CA) is a zinc metalloenzyme that facilitates the rapid conversion of water and carbon dioxide into proton and bicarbonate ion. CA isozymes have been broadly studied in many pathological/physiological processes. In the current research, a series of 4-hydroxy-L-proline derivatives were designed and chemically synthetized, and interaction of these carboxylic acid-based compounds with hCA II were evaluated. Results indicated that different derivatives had different potencies on hCAII inhibitory activity and among them, compounds 3 b and 3c had the lowest IC50 and Kd values than 4-hydroxy-L-proline and other derivatives and therefore had the most affinity to the hCA II enzyme. As a result, compounds 3 b and 3c were chosen for additional testing in this research. The Kinetic data demonstrated that 3 b and 3c inhibit the hCA II esterase activity in a linear competitive way, with Ki values in the low micromolar range. Fluorescence tests showed that the hCA II surface hydrophobicity is diminished in the presence of compounds 3 b and 3c, as confirmed by the decrease in ANS binding to hCA II in their presence. Docking results revealed that 3 b and 3c had more binding energy than 4-hydroxy-L-proline. Furthermore, these compounds could occupy the active site of hCA II, where they would interact with critical amino acid residues via non-covalent forces to inhibit hCA II. Overall, the strengthening of inhibitory activity and the binding power of these carboxylic acid derivatives (3 b and 3c) for the hCA II makes these compounds interesting for designing novel hCA II inhibitors.Communicated by Ramaswamy H. Sarma.

4'-Deoxypyridoxine disrupts vitamin B6 homeostasis in Escherichia coli K12 through combined inhibition of cumulative B6 uptake and PLP-dependent enzyme activity

Pyridoxal 5'-phosphate (PLP) is the active form of vitamin B₆ and a cofactor for many essential metabolic processes such as amino acid biosynthesis and one carbon metabolism. 4'-deoxypyridoxine (4dPN) is a long known B₆ antimetabolite but its mechanism of action was not totally clear. By exploring different conditions in which PLP metabolism is affected in the model organism Escherichia coli K12, we showed that 4dPN cannot be used as a source of vitamin B₆ as previously claimed and that it is toxic in several conditions where vitamin B₆ homeostasis is affected, such as in a B₆ auxotroph or in a mutant lacking the recently discovered PLP homeostasis gene, yggS. In addition, we found that 4dPN sensitivity is likely the result of multiple modes of toxicity, including inhibition of PLP-dependent enzyme activity by 4'-deoxypyridoxine phosphate (4dPNP) and inhibition of cumulative pyridoxine (PN) uptake. These toxicities are largely dependent on the phosphorylation of 4dPN by pyridoxal kinase (PdxK).

Alpinetin suppresses CYP3A4, 2C9, and 2E1 activity in vitro

CONTEXT

Alpinetin, the major active constitutes of Alpinia katsumata Hayata (Zingiberaceae), has been demonstrated to possess the activity of anti-breast cancer. Cytochrome P450 enzymes (CYP450s) plays vital roles in the biotransformation of various drugs.

OBJECTIVE

To assess the effect of alpinetin on the activity of CYP450s and estimate the inhibition characteristics.

MATERIALS AND METHODS

The activity of CYP450s was evaluated in pooled human liver microsomes with corresponding substrates and marker reactions. The effect of alpinetin was compared with blank control (negative control) and corresponding inhibitors (positive control). The dose-dependent and time-dependent experiments were conducted in the presence of 0, 2.5, 5, 10, 25, 50, and 100 μM alpinetin and incubated for 0, 5, 10, 15, and 30 min.

RESULTS

Alpinetin suppressed CYP3A4, 2C9, and 2E1 activity. All the inhibitions were significantly influenced by alpinetin contration with the IC₅₀ values of 8.23 μM (CYP3A4), 12.64 μM (CYP2C9), and 10.97 μM (CYP2E1), respectively. The inhibition of CYP3A4 was fitted with the non-competitive model with a Ki value of 4.09 μM and was time-dependent with KI and Kinact values of 4.67 min and 0.041 μM^-1, respectively. While CYP2C9 and 2E1 were inhibited by alpinetin competitively with Ki values of 6.42 (CYP2C9) and 5.40 μM (CYP2E1), respectively, in a time-independent manner.

DISCUSSION AND CONCLUSION

The in vitro inhibitory effect of alpineticn on CYP3A, 2C9, and 2E1 implied the potential interaction of alpinetin or its origin herbs with the drugs metabolised by those CYP450s, which needs further in vivo validation.

Mechanism of Pyrazine Formation Intervened by Oxidized Methionines during Thermal Degradation of the Methionine-Glucose Amadori Compound

Methionine (Met) oxidation was observed during thermal degradation of methionine/glucose-derived Amadori rearrangement product (MG-ARP). The effects of oxidized methionine products, methionine sulfoxide (MetSO) and methionine sulfone (MetSO₂), on pyrazine yields of the MG-ARP model were investigated. The pyrazine contents in the MG-ARP/Met and MG-ARP/MetSO models were found lower compared to those in the MG-ARP/MetSO₂ model, and the inefficiency of pyrazine formation in the MG-ARP/Met model was proposed due to the fact that Met oxidation competitively inhibited the oxidation of dihydropyrazines for pyrazine formation in spite of relatively high methylglyoxal (MGO) content. The models of MGO mixed with Met, MetSO, or MetSO₂ were established for further investigation of the mechanism for the involvement of Met oxidation in pyrazine formation. It was observed that the aldolization or carbonyl-amine reaction of MetSO with MGO was another important reason for the inhibition of pyrazine formation, except for the competitive inhibition of oxidative formation of MetSO on dihydropyrazine oxidation, and the adduct of MGO-MetSO was identified by MS/MS. These results also accounted for the phenomenon of low pyrazine yields but high yields of long-chain substituted pyrazines, which were converted from dihydropyrazines with the aldehyde involvement.

Phosphatidic acid suppresses autophagy through competitive inhibition by binding GAPC (glyceraldehyde-3-phosphate dehydrogenase) and PGK (phosphoglycerate kinase) proteins

Macroautophagy/autophagy is a finely-regulated process in which cytoplasm encapsulated within transient organelles termed autophagosomes is delivered to lysosomes or vacuoles for degradation. Phospholipids, particularly phosphatidic acid (PA) that functions as a second messenger, play crucial and differential roles in autophagosome formation; however, the underlying mechanism remains largely unknown. Here we demonstrated that PA inhibits autophagy through competitive inhibition of the formation of ATG3 (autophagy-related)-ATG8e and ATG6-VPS34 (vacuolar protein sorting 34) complexes. PA bound to GAPC (glyceraldehyde-3-phosphate dehydrogenase) or PGK (phosphoglycerate kinase) and promoted their interaction with ATG3 or ATG6, which further attenuated the interactions of ATG3-ATG8e or ATG6-VPS34, respectively. Structural and mutational analyses revealed the mechanism of PA binding with GAPCs and PGK3, and that GAPCs or ATG8e competitively interacted with ATG3, and PGK3 or VPS34 competitively interacted with ATG6, at the same binding interface. These results elucidate the molecular mechanism of how PA inhibits autophagy through binding GAPC or PGK3 proteins and expand the understanding of the functional mode of PA, demonstrating the importance of phospholipids in plant autophagy and providing a new perspective for autophagy regulation by phospholipids.Abbreviation: ATG: autophagy-related; BiFC: bimolecular fluorescence complementation; co-IP: co-immunoprecipitation; Con A: concanamycin A; ER: endoplasmic reticulum; EZ: elongation zone; FRET-FLIM: fluorescence resonance energy transfer with fluorescence lifetime imaging microscopy; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GST: glutathione S-transferase; MDC: monodansylcadaverine; MZ: meristem zone; PA: phosphatidic acid; PAS: phagophore assembly site; PC: phosphatidylcholine; PE: phosphatidylethanolamine; PGK3: phosphoglycerate kinase; PtdIns3K: phosphatidylinositol 3-kinase; PLD: phospholipase D; TEM: transmission electron microscopy; TOR: target of rapamycin; VPS34: vacuolar protein sorting 34; WT: wild type; Y2H: yeast two-hybrid.

Liquorice Extract and 18β-Glycyrrhetinic Acid Protect Against Experimental Pyrrolizidine Alkaloid-Induced Hepatotoxicity in Rats Through Inhibiting Cytochrome P450-Mediated Metabolic Activation

Misuse of pyrrolizidine alkaloid (PA)-containing plants or consumption of PA-contaminated foodstuffs causes numerous poisoning cases in humans yearly, while effective therapeutic strategies are still limited. PA-induced liver injury was initiated by cytochrome P450 (CYP)-mediated metabolic activation and subsequent formation of adducts with cellular proteins. Liquorice, a hepato-protective herbal medicine, is commonly used concurrently with PA-containing herbs in many compound traditional Chinese medicine formulas, and no PA-poisoning cases have been reported with this combination. The present study aimed to investigate hepato-protective effects of liquorice aqueous extract (EX) and 18β-glycyrrhetinic acid (GA, the primary bioactive constituent of liquorice) against PA-induced hepatotoxicity and the underlying mechanism. Histopathological and biochemical analysis demonstrated that both single- and multiple-treatment of EX (500 mg/kg) or GA (50 mg/kg) significantly attenuated liver damage caused by retrorsine (RTS, a representative hepatotoxic PA). The formation of pyrrole-protein adducts was significantly reduced by single- (30.3% reduction in liver; 50.8% reduction in plasma) and multiple- (32.5% reduction in liver; 56.5% reduction in plasma) treatment of GA in rats. Single- and multiple-treatment of EX also decreased the formation of pyrrole-protein adducts, with 30.2 and 31.1% reduction in rat liver and 51.8 and 53.1% reduction in rat plasma, respectively. In addition, in vitro metabolism assay with rat liver microsomes demonstrated that GA reduced the formation of metabolic activation-derived pyrrole-glutathione conjugate in a dose-dependent manner with the estimated IC₅₀ value of 5.07 µM. Further mechanism study showed that GA inhibited activities of CYPs, especially CYP3A1, the major CYP isoform responsible for the metabolic activation of RTS in rats. Enzymatic kinetic study revealed a competitive inhibition of rat CYP3A1 by GA. In conclusion, our findings demonstrated that both EX and GA exhibited significant hepato-protective effects against RTS-induced hepatotoxicity, mainly through the competitive inhibition of CYP-mediated metabolic activation of RTS.

Inhibitory effect of ascorbate on tryptophan 2,3-dioxygenase

Tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) catalyze the same reaction, oxidative cleavage of L-tryptophan (L-Trp) to N-formyl-kynurenine. In both enzymes, the ferric (FeIII) form is inactive, and ascorbate (Asc) is frequently used as a reductant in in vitro assays to activate the enzymes by reducing the heme iron. Recently, it has been reported that Asc activates IDO2 by acting as a reductant, however, it is also a competitive inhibitor of the enzyme. Here, the effect of Asc on human TDO (hTDO) is investigated. Similar to its interaction with IDO2, Asc acts as both a reductant and a competitive inhibitor of hTDO in the absence of catalase, and its inhibitory effect was enhanced by the addition of H2O2. Interestingly, however, no inhibitory effect of Asc was observed in the presence of catalase. TDO is known to be activated by H2O2 and a ferryl-oxo (FeIV=O) intermediate (Compound II) is generated during the activation process. The observation that Asc acts as a competitive inhibitor of hTDO only in the absence of catalase can be explained by assuming that the target of Asc is Compound II. Asc seems to compete with L-Trp in an unusual manner.

Novel proteinase inhibitor from the hemolymph of soybean pest Anticarsia gemmatalis (lepidóptera: Noctuidae): Structural modeling and enzymatic kinetic

New approaches are needed to reduce risks to the environment and natural enemies and to avoid or delay the onset of insecticide resistance. The use of insecticides based on proteinase inhibitors of hemolymph is an alternative for the control of Lepidoptera pests primarily by having low toxicity and short persistence in the environment. Thus, in this study, we describe the purification process and identification of protease inhibitors from hemolymph Anticarsia gemmatalis and their activities against trypsin enzymes. Furthermore, the three-dimensional (3D) structure of the inhibitor and binding mode to trypsin enzymes was determined, and the stability of the inhibitory activity in several pHs and temperature values was evaluated. The inhibitor was characterized as a serpin family inhibitor and named A. gemmatalis hemolymph serpin inhibitor (AHSI), with an approximate mass of 38 ± 2 kDa, highly stable to temperature and pH variations, and with inhibitory capacity on bovine trypsin and gut trypsin of A. gemmatalis demonstrated by calculated Ki values and affinity energy through molecular docking, being a reversible competitive inhibitor that binds to the active site of trypsin-like enzymes. We conclude that the AHSI inhibitor identified from the hemolymph of the soybean pest A. gemmatalis preserves the original structure of the serpin family with a good overall stereochemical quality confirmed from molecular modeling. The docking analysis showed that the reactive site of the inhibitor is in contact with the catalytic cavity of the trypsin with high-affinity energy.

How alternative splicing changes the properties of plant proteins

Most plant primary transcripts undergo alternative splicing (AS), and its impact on protein diversity is a subject of intensive investigation. Several studies have uncovered various mechanisms of how particular protein splice isoforms operate. However, the common principles behind the AS effects on protein function in plants have rarely been surveyed. Here, on the selected examples, we highlight diverse tissue expression patterns, subcellular localization, enzymatic activities, abilities to bind other molecules and other relevant features. We describe how the protein isoforms mutually interact to underline their intriguing roles in altering the functionality of protein complexes. Moreover, we also discuss the known cases when these interactions have been placed inside the autoregulatory loops. This review is particularly intended for plant cell and developmental biologists who would like to gain inspiration on how the splice variants encoded by their genes of interest may coordinately work.

Corrigendum: Crystal Structure of the Chloroplastic Glutamine Phosphoribosylpyrophosphate Amidotransferase GPRAT2 From Arabidopsis thaliana

[This corrects the article DOI: 10.3389/fpls.2020.00157.].

Molecular Determinants and Pharmacological Analysis for a Class of Competitive Non-transported Bicyclic Inhibitors of the Betaine/GABA Transporter BGT1

The betaine/GABA transporter 1 (BGT1) is a member of the GABA transporter (GAT) family with still elusive function, largely due to a lack of potent and selective tool compounds. Based on modeling, we here present the design, synthesis and pharmacological evaluation of five novel conformationally restricted cyclic GABA analogs related to the previously reported highly potent and selective BGT1 inhibitor (1S,2S,5R)-5-aminobicyclo[3.1.0]hexane-2-carboxylic acid (bicyclo-GABA). Using [³H]GABA radioligand uptake assays at the four human GATs recombinantly expressed in mammalian cell lines, we identified bicyclo-GABA and its N-methylated analog (2) as the most potent and selective BGT1 inhibitors. Additional pharmacological characterization in a fluorescence-based membrane potential assay showed that bicyclo-GABA and 2 are competitive inhibitors, not substrates, at BGT1, which was validated by a Schild analysis for bicyclo-GABA (pK_B value of 6.4). To further elaborate on the selectivity profile both compounds were tested at recombinant α₁β₂γ₂ GABA_A receptors. Whereas bicyclo-GABA showed low micromolar agonistic activity, the N-methylated 2 was completely devoid of activity at GABA_A receptors. To further reveal the binding mode of bicyclo-GABA and 2 binding hypotheses of the compounds were obtained from in silico-guided mutagenesis studies followed by pharmacological evaluation at selected BGT1 mutants. This identified the non-conserved BGT1 residues Q299 and E52 as the molecular determinants driving BGT1 activity and selectivity. The binding mode of bicyclo-GABA was further validated by the introduction of activity into the corresponding GAT3 mutant L314Q (38 times potency increase cf. wildtype). Altogether, our data reveal the molecular determinants for the activity of bicyclic GABA analogs, that despite their small size act as competitive inhibitors of BGT1. These compounds may serve as valuable tools to selectively and potently target BGT1 in order to decipher its elusive pharmacological role in the brain and periphery such as the liver and kidneys.

Selection of Atoxigenic Aspergillus flavus for Potential Use in Aflatoxin Prevention in Shandong Province, China

Aspergillus flavus is a common filamentous fungus widely present in the soil, air, and in crops. This facultative pathogen of both animals and plants produces aflatoxins, a group of mycotoxins with strong teratogenic and carcinogenic properties. Peanuts are highly susceptible to aflatoxin contamination and consumption of contaminated peanuts poses serious threats to the health of humans and domestic animals. Currently, the competitive displacement of aflatoxin-producers from agricultural environments by atoxigenic A. flavus is the most effective method of preventing crop aflatoxin contamination. In the current study, 47 isolates of A. flavus collected from peanut samples originating in Shandong Province were characterized with molecular methods and for aflatoxin-producing ability in laboratory studies. Isolates PA04 and PA10 were found to be atoxigenic members of the L strains morphotype. When co-inoculated with A. flavus NRRL3357 at ratios of 1:10, 1:1, and 10:1 (PA04/PA10: NRRL3357), both atoxigenic strains were able to reduce aflatoxin B₁ (AFB₁) levels, on both culture media and peanut kernels, by up to 90%. The extent to which atoxigenic strains reduced contamination was correlated with the inoculation ratio. Abilities to compete of PA04 and PA10 were also independently verified against local aflatoxin-producer PA37. The results suggest that the two identified atoxigenic strains are good candidates for active ingredients of biocontrol products for the prevention of aflatoxin contamination of peanuts in Shandong Province.

Mechanism of protein tyrosine phosphatase 1B inhibition by theaflavanoside IV isolated from methanolic extract of tea (Camellia sinensis) seed shells

Camellia sinensis (tea) seeds have been identified as potential sources of nutraceutical compounds. In this study, caffeine and theaflavanoside IV were annotated as the most abundant phytochemicals in the seed shells of C. sinensis. Both compound displayed potent inhibitions against protein tyrosine phosphatase 1B (PTP1B) with IC₅₀ values of 37.9 ± 3.5 and 8.7 ± 1.1 µM, respectively. In the kinetic study, caffeine inhibited PTP1B with mixed type I mode, which prefers to bind to free enzyme. Theaflavanoside IV showed competitive and reversible simple slow-binding inhibition [k₃ = 0.1 µM^-1·min^-1, k₄ = 0.002 min^-1, K_i^app = 0.0002 µM]. This is the first report on PTP1B-inhibitory activity of these compounds and their action mechanisms. These results suggest their potential in the development of antidiabetic agents.

The Kinetic and Analytical Aspects of Enzyme Competitive Inhibition: Sensing of Tyrosinase Inhibitors

An amperometric biosensor based on tyrosinase, immobilized onto a carbon black paste electrode using glutaraldehyde and BSA was constructed to detect competitive inhibitors. Three inhibitors were used in this study: benzoic acid, sodium azide, and kojic acid, and the obtained values for fifty percent of inhibition (IC50) were 119 µM, 1480 µM, and 30 µM, respectively. The type of inhibition can also be determined from the curve of the degree of inhibition by considering the shift of the inhibition curves. Amperometric experiments were performed with a biosensor polarized at the potential -0.15 V vs. Ag/AgCl and using 0.1 M phosphate buffer (pH 6.8) as an electrolyte. Under optimized conditions, the proposed biosensor showed a linear amperometric response toward catechol detection from 0.5 µM to 38 µM with a detection limit of 0.35 µM (S/N = 3), and its sensitivity was 66.5 mA M-1 cm-2. Moreover, the biosensor exhibited a good storage stability. Conversely, a novel graphical plot for the determination of reversible competitive inhibition was represented for free tyrosinase. The graph consisted of plotting the half-time reaction (t1/2) as a function of the inhibitor concentration at various substrate concentrations. This innovative method relevance was demonstrated in the case of kojic acid using a colorimetric bioassay relying on tyrosinase inhibition. The results showed that the t1/2 provides an extended linear range of tyrosinase inhibitors.

Non-microRNA binding competitively inhibits LIN28 regulation

RNA binding protein (RBP) expression is finite. For RBPs that are vastly outnumbered by their potential target sites, a simple competition for binding can set the magnitude of post-transcriptional control. Here, we show that LIN28, best known for its direct regulation of let-7 miRNA biogenesis, is also indirectly regulated by its widespread binding of non-miRNA transcripts. Approximately 99% of LIN28 binding sites are found on non-miRNA transcripts, like protein coding and ribosomal RNAs. These sites are bound specifically and strongly, but they do not appear to mediate direct post-transcriptional regulation. Instead, non-miRNA sites act to sequester LIN28 protein and effectively change its functional availability, thus impeding the regulation of let-7 in cells. Together, these data show that the binding properties of the transcriptome broadly influence the ability of an RBP to mediate changes in RNA metabolism and gene expression.

Transient Competitive Inhibition Bypasses the Binding Site Barrier to Improve Tumor Penetration of Trastuzumab and Enhance T-DM1 Efficacy

Poor penetration of mAbs in solid tumors is explained, in part, by the binding site barrier hypothesis. Following extravasation, mAbs rapidly bind cellular antigens, leading to the observation that, at subsaturating doses, therapeutic antibody in solid tumors localizes around tumor vasculature. Here we report a unique strategy to overcome the binding site barrier through transient competitive inhibition of antibody-antigen binding. The anti-trastuzumab single domain antibody 1HE was identified through in vitro binding assays as a model inhibitor. Coadministration of 1HE did not alter the plasma pharmacokinetics of trastuzumab or ado-trastuzumab emtansine (T-DM1) in vivo. Administration of 1HE alone was rapidly eliminated with a terminal plasma half-life of 1.2 hours, while coadministrations of 1HE with trastuzumab had a terminal half-life of 56 hours. In mice harboring SKOV3 xenografts, coadministration of 1HE with trastuzumab led to significant increases in both penetration of trastuzumab from vasculature and the percentage of tumor area that stained positive for trastuzumab. 1HE coadministered with a single dose of T-DM1 to NCI-N87 xenograft-bearing mice significantly enhanced T-DM1 efficacy, increasing median survival. These results support the hypothesis that transient competitive inhibition can improve therapeutic antibody distribution in solid tumors and enhance antibody efficacy. SIGNIFICANCE: This study describes the development of a transient competitive inhibition strategy that enhances the tumor penetration and efficacy of anticancer antibodies.See related commentary by van Dongen, p. 3956.

4-O-galloylalbiflorin inhibits the activity of CYP3A, 2C9, and 2D in human liver microsomes

The effect of 4-O-galloylalbiflorin on the activity of cytochrome P450 enzymes (CYP450s) is an important factor that may induce drug-drug interaction.The effect of 4-O-galloylalbiflorin on the activity of CYP450s was evaluated in the presence of 0, 2.5, 5, 10, 25, 50, and 100 μM 4-O-galloylalbiflorin in pooled human liver microsomes. The inhibition model and corresponding parameters were assessed b fitting with Lineweaver-Burk plots. The time-dependent study was performed with the incubation time of 0, 5, 10, 15, and 30 min.4-O-galloylalbiflorin significantly inhibited the activity of CYP3A, 2C9, and 2 D in a concentration-dependent manner with the IC50 values of 8.2, 13, and 11 μM, respectively. The inhibition of CYP3A was found to be non-competitive and time-dependent with the Ki value of 4.0 μM and the KI/Kinact value of 2.2/0.030 (μM·min). The inhibition of CYP2C9 and 2 D was not affected by the incubation time but was found to be competitive with the Ki values of 6.7 and 6.6 μM, respectively.The inhibitory effect of 4-O-galloylalbiflorin on the activity of CYP3A, 2C9, and 2 D implying the potential drug-drug interaction between 4-O-galloylalbiflorin and the drugs metabolized by these CYP450s.

Enhancement of angiogenin inhibition by polyphenol-capped gold nanoparticles

Angiogenin (Ang), is a ribonucleolytic protein that is associated with angiogenesis, the formation of blood vessels. The involvement of Ang in vascularisation makes it a potential target for the identification of compounds that have the potential to inhibit the process. The compounds may be assessed for their ability to inhibit the ribonucleolytic activity of the protein and subsequently blood vessel formation, a crucial requirement for tumor formation. We report an inhibition of the ribonucleolytic activity of Ang with the gallate containing green tea polyphenols, ECG and EGCG that exhibits an increased efficacy upon forming polyphenol-capped gold nanoparticles (ECG-AuNPs and EGCG-AuNPs). The extent of inhibition was confirmed using an agarose gel-based assay followed by fluorescence titration studies that indicated a hundred fold stronger binding of polyphenol-capped gold nanoparticles (GTP-AuNPs) compared to the bare polyphenols. Interestingly, we found a change in the mode of inhibition from a noncompetitive type to a competitive mode of inhibition in case of the GTP-AuNPs, which is in agreement with the 'n' values obtained from the fluorescence quenching studies. The effect on angiogenesis has also been assessed by the chorioallantoic membrane (CAM) assay. We find an increase in the inhibition potency of GTP-AuNPs that could find applications in the development of anti-angiogenic compounds.

Excess histone H3 is a competitive Chk1 inhibitor that controls cell-cycle remodeling in the early Drosophila embryo

The DNA damage checkpoint is crucial to protect genome integrity.^1,2 However, the early embryos of many metazoans sacrifice this safeguard to allow for rapid cleavage divisions that are required for speedy development. At the mid-blastula transition (MBT), embryos switch from rapid cleavage divisions to slower, patterned divisions with the addition of gap phases and acquisition of DNA damage checkpoints. The timing of the MBT is dependent on the nuclear-to-cytoplasmic (N/C ratio)^3-7 and the activation of the checkpoint kinase, Chk1.^8-17 How Chk1 activity is coupled to the N/C ratio has remained poorly understood. Here, we show that dynamic changes in histone H3 availability in response to the increasing N/C ratio control Chk1 activity and thus time the MBT in the Drosophila embryo. We show that excess H3 in the early cycles interferes with cell-cycle slowing independent of chromatin incorporation. We find that the N-terminal tail of H3 acts as a competitive inhibitor of Chk1 in vitro and reduces Chk1 activity in vivo. Using a H3-tail mutant that has reduced Chk1 inhibitor activity, we show that the amount of available Chk1 sites in the H3 pool controls the dynamics of cell-cycle progression. Mathematical modeling quantitatively supports a mechanism where titration of H3 during early cleavage cycles regulates Chk1-dependent cell-cycle slowing. This study defines Chk1 regulation by H3 as a key mechanism that coordinates cell-cycle remodeling with developmental progression.

Assessing the Mechanism of Fluoxetine-Mediated CYP2D6 Inhibition

Fluoxetine is still one of the most widely used antidepressants in the world. The drug is extensively metabolized by several cytochrome P450 (CYP450) enzymes and subjected to a myriad of CYP450-mediated drug interactions. In a multidrug regimen, preemptive mitigation of drug-drug interactions requires knowledge of fluoxetine actions on these CYP450 enzymes. The major metabolic pathway of fluoxetine leading to the formation of its active metabolite, norfluoxetine, is mediated by CYP2D6. Fluoxetine and norfluoxetine are strong affinity substrates of CYP2D6 and can inhibit, potentially through various mechanisms, the metabolism of other sensitive CYP2D6 substrates. Remarkably, fluoxetine-mediated CYP2D6 inhibition subsides long after fluoxetine first passes through the liver and even remains long after the discontinuation of the drug. Herein, we review pharmacokinetic and pharmacogenetic information to help us understand the mechanisms underlying the prolonged inhibition of CYP2D6 following fluoxetine administration. We propose that long-term inhibition of CYP2D6 is likely a result of competitive inhibition. This is due to strong affinity binding of fluoxetine and norfluoxetine to the enzyme and unbound fluoxetine and norfluoxetine levels circulating in the blood for a long period of time because of their long elimination half-life. Additionally, we describe that fluoxetine is a CYP2C9 substrate and a mechanism-based inhibitor of CYP2C19.

Structure of 3-mercaptopropionic acid dioxygenase with a substrate analog reveals bidentate substrate binding at the iron center

Thiol dioxygenases are a subset of nonheme iron oxygenases that catalyze the formation of sulfinic acids from sulfhydryl-containing substrates and dioxygen. Among this class, cysteine dioxygenases (CDOs) and 3-mercaptopropionic acid dioxygenases (3MDOs) are the best characterized, and the mode of substrate binding for CDOs is well understood. However, the manner in which 3-mercaptopropionic acid (3MPA) coordinates to the nonheme iron site in 3MDO remains a matter of debate. A model for bidentate 3MPA coordination at the 3MDO Fe-site has been proposed on the basis of computational docking, whereas steady-state kinetics and EPR spectroscopic measurements suggest a thiolate-only coordination of the substrate. To address this gap in knowledge, we determined the structure of Azobacter vinelandii 3MDO (Av3MDO) in complex with the substrate analog and competitive inhibitor, 3-hydroxypropionic acid (3HPA). The structure together with DFT computational modeling demonstrates that 3HPA and 3MPA associate with iron as chelate complexes with the substrate-carboxylate group forming an additional interaction with Arg168 and the thiol bound at the same position as in CDO. A chloride ligand was bound to iron in the coordination site assigned as the O2-binding site. Supporting HYSCORE spectroscopic experiments were performed on the (3MPA/NO)-bound Av3MDO iron nitrosyl (S = 3/2) site. In combination with spectroscopic simulations and optimized DFT models, this work provides an experimentally verified model of the Av3MDO enzyme-substrate complex, effectively resolving a debate in the literature regarding the preferred substrate-binding denticity. These results elegantly explain the observed 3MDO substrate specificity, but leave unanswered questions regarding the mechanism of substrate-gated reactivity with dioxygen.

Organoids to Study Intestinal Nutrient Transport, Drug Uptake and Metabolism - Update to the Human Model and Expansion of Applications

Intestinal transport and sensing processes and their interconnection to metabolism are relevant to pathologies such as malabsorption syndromes, inflammatory diseases, obesity and type 2 diabetes. Constituting a highly selective barrier, intestinal epithelial cells absorb, metabolize, and release nutrients into the circulation, hence serving as gatekeeper of nutrient availability and metabolic health for the whole organism. Next to nutrient transport and sensing functions, intestinal transporters including peptide transporter 1 (PEPT1) are involved in the absorption of drugs and prodrugs, including certain inhibitors of angiotensin-converting enzyme, protease inhibitors, antivirals, and peptidomimetics like β-lactam antibiotics. Here, we verify the applicability of 3D organoids for in vitro investigation of intestinal biochemical processes related to transport and metabolism of nutrients and drugs. Establishing a variety of methodologies including illustration of transporter-mediated nutrient and drug uptake and metabolomics approaches, we highlight intestinal organoids as robust and reliable tool in this field of research. Currently used in vitro models to study intestinal nutrient absorption, drug transport and enterocyte metabolism, such as Caco-2 cells or rodent explant models are of limited value due to their cancer and non-human origin, respectively. Particularly species differences result in poorly correlative data and findings obtained in these models cannot be extrapolated reliably to humans, as indicated by high failure rates in drug development pipelines. In contrast, human intestinal organoids represent a superior model of the intestinal epithelium and might help to implement the 3Rs (Reduction, Refinement and Replacement) principle in basic science as well as the preclinical and regulatory setup.

Mechanisms of CYP450 Inhibition: Understanding Drug-Drug Interactions Due to Mechanism-Based Inhibition in Clinical Practice

In an ageing society, polypharmacy has become a major public health and economic issue. Overuse of medications, especially in patients with chronic diseases, carries major health risks. One common consequence of polypharmacy is the increased emergence of adverse drug events, mainly from drug–drug interactions. The majority of currently available drugs are metabolized by CYP450 enzymes. Interactions due to shared CYP450-mediated metabolic pathways for two or more drugs are frequent, especially through reversible or irreversible CYP450 inhibition. The magnitude of these interactions depends on several factors, including varying affinity and concentration of substrates, time delay between the administration of the drugs, and mechanisms of CYP450 inhibition. Various types of CYP450 inhibition (competitive, non-competitive, mechanism-based) have been observed clinically, and interactions of these types require a distinct clinical management strategy. This review focuses on mechanism-based inhibition, which occurs when a substrate forms a reactive intermediate, creating a stable enzyme–intermediate complex that irreversibly reduces enzyme activity. This type of inhibition can cause interactions with drugs such as omeprazole, paroxetine, macrolide antibiotics, or mirabegron. A good understanding of mechanism-based inhibition and proper clinical management is needed by clinicians when such drugs are prescribed. It is important to recognize mechanism-based inhibition since it cannot be prevented by separating the time of administration of the interacting drugs. Here, we provide a comprehensive overview of the different types of mechanism-based inhibition, along with illustrative examples of how mechanism-based inhibition might affect prescribing and clinical behaviors.

MAp34 Regulates the Non-specific Cell Immunity of Monocytes/Macrophages and Inhibits the Lectin Pathway of Complement Activation in a Teleost Fish

The lectin pathway of the complement system is one of the main components of innate immunity, which plays a pivotal role in the defense against infectious microorganisms and maintains immune homeostasis. However, its control mechanisms remain unclear in teleost fish. In this study, we described the identification and functional characterization of a mannose-binding lectin associated protein MAp34 (OnMAp34) from Nile tilapia (Oreochromis niloticus) at molecular, cellular, and protein levels. The open reading frame (ORF) of OnMAp34 is 918 bp of nucleotide sequence encoding a polypeptide of 305 amino acids. The deduced amino acid sequence has three characteristic structures, including two C1r/C1s-Uegf-BMP domains (CUB) and one epidermal growth factor domain (EGF). Expression analysis revealed that the OnMAp34 was highly expressed in the liver and widely existed in other examined tissues. In addition, the mRNA and protein expression levels of OnMAp34 were remarkably altered upon infection with Streptococcus agalactiae and Aeromonas hydrophila in vivo and in vitro. Further, we found that the OnMAp34 could participate in the non-specific cellular immune defense, including the regulation of inflammation, migration, and enhancement of phagocytosis of monocytes/macrophages. Moreover, the OnMAp34 could compete with OnMASPs to combine OnMBL and inhibit the lectin pathway of complement activation. Overall, our results provide new insights into the understanding of MAp34 as a potent regulator in the lectin complement pathway and non-specific cell immunity in an early vertebrate.

Epstein-Barr virus is a promoter of lymphoma cell metastasis

It is well-known that Epstein-Barr virus (EBV) is the promoter of cell tumourigenesis. We found that EBV is also a promoter of lymphoma cell dissemination, because we found the typical morphopathological phenomenon of cell adhesion, which confirmed that the adhesion of tumour cells was higher than that of normal cells. We also observed that tumour cells disrupted the dynamic pathological changes of vascular endothelial cells, and this made it clear that the rate of tumour cell metastasis was directly proportional to the degree of EBV infection. Furthermore, when we discovered exosomes, it was considered that this was associated with cancer stem cells, suggesting the formation of a microenvironment before tumour cell metastasis. In addition, competitive inhibition was found in cell adhesion, indicating the breakthrough point of preventing tumour cell metastasis, which has clinical reference value for tumour immunotherapy.

The Effect of Cellular Coenzyme Q10 Deficiency on Lysosomal Acidification

Coenzyme Q₁₀ (CoQ₁₀) deficiency currently represents the only treatable mitochondrial disorder, however, little is known about how it may affect other organelles. The lysosome has been found to have a large concentration of CoQ₁₀ localised at its membrane; additionally, it has been suggested that it plays a role in the normal acidification of the lysosomal lumen. As a result, in this study we assessed the effect of CoQ₁₀ deficiency on lysosomal acidification. In order to investigate this, a neuronal cell model of CoQ₁₀ deficiency was established via the treatment of SH-SY5Y cells with para-aminobenzoic acid (PABA). This method works through the competitive inhibition of the CoQ₁₀ biosynthetic pathway enzyme, CoQ₂. A single 1 mM (5 days) treatment with PABA resulted in a decrease of up to 58% in cellular CoQ₁₀ (p < 0.05). It was found that this resulted in a significant decrease in fluorescence of both the LysoSensor (23%) and LysoTracker (35%) probes used to measure lysosomal pH (p < 0.05). It was found that subsequent treatment with CoQ₁₀ (5 µM, 3 days) was able to restore cellular CoQ₁₀ concentration (p < 0.005), which was associated with an increase in fluorescence from both probes to around 90% of controls (p < 0.05), suggesting a restoration of lysosomal pH. This study provides insights into the association between lysosomal pH and cellular CoQ₁₀ status and the possibility that a deficit in the status of this isoprenoid may result in an impairment of lysosomal acidification.

Origanum essential oils reduce the level of melanin in B16-F1 melanocytes

BACKGROUND

Hyperpigmentation disorders are considered signs of skin aging and are aesthetically unpleasant. Most active ingredients used against hyperpigmentation disorders predominantly target tyrosinase activity.

OBJECTIVES

To study the effect of two Origanum essential oils on the melanogenic activity of B16-F1 murine melanocytes. The main component of these oils, carvacrol, was also investigated and a model for anti-melanogenic activity is proposed.

MATERIALS AND METHODS

B16-F1 melanocytes were exposed to different concentrations of essential oils and carvacrol. The level of tyrosinase and melanin was determined using spectrophotometric measurements.

RESULTS

Essential oils of Origanum syriacum and Origanum ehrenbergii led to a significant 14% and 17% reduction in melanin level at 40 μg mL^-1, respectively. However, neither demonstrated a significant effect on the level of intracellular tyrosinase. The same effects were found for carvacrol which led to a 30% reduction in melanin at 45 μg mL^-1.

CONCLUSION

Our results indicate that the oils studied are anti-melanogenic. We propose a mechanism, similar to that for hydroquinone, whereby carvacrol functions as a competitive inhibitor of tyrosinase, thus inhibiting oxidation of tyrosine and causing a deregulation of melanogenesis.

Bakkenolides and Caffeoylquinic Acids from the Aerial Portion of Petasites japonicus and Their Bacterial Neuraminidase Inhibition Ability

Petasites japonicus have been used since a long time in folk medicine to treat diseases including plague, pestilential fever, allergy, and inflammation in East Asia and European countries. Bioactive compounds that may prevent and treat infectious diseases are identified based on their ability to inhibit bacterial neuraminidase (NA). We aimed to isolate and identify bioactive compounds from leaves and stems of P. japonicas (PJA) and elucidate their mechanisms of NA inhibition. Key bioactive compounds of PJA responsible for NA inhibition were isolated using column chromatography, their chemical structures revealed using ¹ H NMR, ¹³ C NMR, DEPT, and HMBC, and identified to be bakkenolide B (1), bakkenolide D (2), 1,5-di-O-caffeoylquinic acid (3), and 5-O-caffeoylquinic acid (4). Of these, 3 exhibited the most potent NA inhibitory activity (IC₅₀ = 2.3 ± 0.4 μM). Enzyme kinetic studies revealed that 3 and 4 were competitive inhibitors, whereas 2 exhibited non-competitive inhibition. Furthermore, a molecular docking simulation revealed the binding affinity of these compounds to NA and their mechanism of inhibition. Negative-binding energies indicated high proximity of these compounds to the active site and allosteric sites of NA. Therefore, PJA has the potential to be further developed as an antibacterial agent for use against diseases associated with NA.

Crystal Structure of the Chloroplastic Glutamine Phosphoribosylpyrophosphate Amidotransferase GPRAT2 From Arabidopsis thaliana

Chloroplastic glutamine phosphoribosylpyrophosphate amidotransferase (GPRATase) catalyzes the first committed step of de novo purine biosynthesis in Arabidopsis thaliana, and DAS734 is a direct and specific inhibitor of AtGPRAT, with phytotoxic effects similar to the leaf beaching phenotypes of known AtGPRAT genetic mutants, especially cia1 and atd2. However, the structure of AtGPRAT and the inhibition mode of DAS734 still remain poorly understood. In this study, we solved the structure of AtGPRAT2, which revealed structural differences between AtGPRAT2 and bacterial enzymes. Kinetics assay demonstrated that DAS734 behaves as a competitive inhibitor for the substrate phosphoribosyl pyrophosphate (PRPP) of AtGPRAT2. Docking studies showed that DAS734 forms electrostatic interactions with R264 and hydrophobic interactions with several residues, which was verified by binding assays. Collectively, our study provides important insights into the inhibition mechanism of DAS734 to AtGPRAT2 and sheds light on future studies into further development of more potent herbicides targeting Arabidopsis GPRATases.

Competitive Inhibitory Effect of Calcium Polypeptides on Cd Enrichment of Brassia campestris L

Most cadmium-polluted farmland and land surrounding mining areas are difficult to repair and control, seriously threatening the food safety of the crops planted in these regions. As an essential element for plant growth, calcium plays an important role in stress-resistance regulation. In this study, Brassia campestris L. was used as the experimental material and polluted soil with cadmium was used as the experimental soil sample, to explore the competition inhibition of calcium polypeptide application on the absorption of Cd²⁺ by Brassia campestris L. in the growth process, as well as the effect of calcium application on the growth. Results showed that the application of calcium polypeptides significantly promoted the growth of Brassia campestris L. Calcium polypeptides could be used as high-quality fertilizer, alleviating the effect of Cd²⁺ stress on the growth of Brassia campestris L., and promoting the absorption of K⁺, Ca²⁺, and other nutrients by Brassia campestris L. Under different calcium polypeptide application conditions, the effective state of Cd²⁺ in the soil showed less significant difference, indicating that the calcium polypeptide had weak or limited passivation effects on Cd²⁺. There was a significantly negative correlation between Cd concentration in Brassia campestris L. and calcium application (r = −0.99, p < 0.01) when calcium polypeptide was over-applied, which indicates that the inhibition effect of Cd²⁺ absorption on Brassia campestris L. is mainly through competitive inhibition rather than passivation. The results showed that calcium polypeptide has dual functions on the competitive inhibition of heavy metals and a good fertilizer effect, providing a new technology for in situ remediation of heavy-metal pollution, and a new approach for the treatment of cadmium-contaminated farmland and surrounding mining land.

A mechanistic modelling approach for the determination of the mechanisms of inhibition by cyclosporine on the uptake and metabolism of atorvastatin in rat hepatocytes using a high throughput uptake method

Determine the inhibition mechanism through which cyclosporine inhibits the uptake and metabolism of atorvastatin in fresh rat hepatocytes using mechanistic models applied to data generated using a high throughput oil spin method.Atorvastatin was incubated in fresh rat hepatocytes (0.05-150 nmol/ml) with or without 20 min pre-incubation with 10 nmol/ml cyclosporine and sampled over 0.25-60 min using a high throughput oil spin method. Micro-rate constant and macro-rate constant mechanistic models were ranked based on goodness of fit values.The best fitting model to the data was a micro-rate constant mechanistic model including non-competitive inhibition of uptake and competitive inhibition of metabolism by cyclosporine (Model 2). The association rate constant for atorvastatin was 150-fold greater than the dissociation rate constant and 10-fold greater than the translocation into the cell. The association and dissociation rate constants for cyclosporine were 7-fold smaller and 10-fold greater, respectively, than atorvastatin. The simulated atorvastatin-transporter-cyclosporine complex derived using the micro-rate constant parameter estimates increased in line with the incubation concentration of atorvastatin.The increased amount of data generated with the high throughput oil spin method, combined with a micro-rate constant mechanistic model helps to explain the inhibition of uptake by cyclosporine following pre-incubation.

Crosstalk of Cellulose and Mannan Perception Pathways Leads to Inhibition of Cellulase Production in Several Filamentous Fungi

In fungi, the production of enzymes for polysaccharide degradation is controlled by complex signaling networks. Previously, these networks were studied in response to simple sugars or single polysaccharides. Here, we tackled for the first time the molecular interplay between two seemingly unrelated perception pathways: those for cellulose and the hemicellulose (gluco)mannan. We identified a so far unknown competitive inhibition between the respective degradation products acting as signaling molecules. Competition was detected both at the level of the uptake and intracellularly, upstream of the main transcriptional regulator CLR-2. Our findings provide novel insights into the molecular communication between perception pathways. Also, they present possible targets for the improvement of industrial strains for higher cellulase production through the engineering of mannan insensitivity.

It is essential for microbes to acquire information about their environment. Fungi use soluble degradation products of plant cell wall components to understand the substrate composition they grow on. Individual perception pathways have been well described. However, the interconnections between pathways remain poorly understood. In the present work, we provide evidence of crosstalk between the perception pathways for cellulose and the hemicellulose mannan being conserved in several filamentous fungi and leading to the inhibition of cellulase expression. We used the functional genomics tools available for Neurospora crassa to investigate this overlap at the molecular level. Crosstalk and competitive inhibition could be identified both during uptake by cellodextrin transporters and intracellularly. Importantly, the overlap is independent of CRE-1-mediated catabolite repression. These results provide novel insights into the regulatory networks of lignocellulolytic fungi and will contribute to the rational optimization of fungal enzyme production for efficient plant biomass depolymerization and utilization.

Coumarins and P450s, Studies Reported to-Date

Cytochrome P450 enzymes (CYPs) are important phase I enzymes involved in the metabolism of endogenous and xenobiotic compounds mainly through mono-oxygenation reactions into more polar and easier to excrete species. In addition to their role in detoxification, they play important roles in the biosynthesis of endogenous compounds and the bioactivation of xenobiotics. Coumarins, phytochemicals abundant in food and commonly used in fragrances and cosmetics, have been shown to interact with P450 enzymes as substrates and/or inhibitors. In this review, these interactions and their significance in pharmacology and toxicology are discussed in detail.

Co-metabolic degradation of naphthalene and pyrene by acclimated strain and competitive inhibition kinetics

A dominant strain named Ochrobactrum sp. was isolated from soils contaminated with coal tar. The batch experiments were carried out to study the co-metabolic degradation of pyrene by Ochrobactrum MB-2 with naphthalene as the main substrate and the effects of several significant parameters such as naphthalene concentration, pH and temperature on removal efficiency were explored. The results showed that Ochrobactrum MB-2 effectively degraded naphthalene and that the addition of naphthalene favored the degradation of pyrene. The maximum elimination efficiency of naphthalene (10 mg L^-1) and pyrene (1 mg L^-1) was achieved at pH 7 and 25 °C, and the corresponding values were 99 and 41%, respectively. A competitive inhibition model based on the Michaelis-Menten equation was used to characterize the inhibitory effect of pyrene on naphthalene degradation. The values of the half-saturation coefficient for naphthalene (K_S) and dissociation constant of enzyme-inhibitor complex (K_C) were determined to be 4.93 and 1.38 mg L^-1, respectively.

Resveratroloside Alleviates Postprandial Hyperglycemia in Diabetic Mice by Competitively Inhibiting α-Glucosidase

The regulation of postprandial blood glucose (PBG) levels is an effective therapeutic method to treat diabetes and prevent diabetes-related complications. Resveratroloside is a monoglucosylated form of stilbene that is present in red wine, grapes, and several traditional medicinal plants. In our study, the effect of resveratroloside on reducing PBG was studied in vitro and in vivo. In comparison to the starch treatment alone, the oral administration of resveratroloside-starch complexes significantly inhibited the PBG increase in a dose-dependent pattern in normal and diabetic mice. The PBG level treated with resveratrol (30 mg/kg) was not lower than that of resveratroloside. Further analyses demonstrated that resveratroloside strongly and effectively inhibited α-glucosidase, with an 50% inhibitory concentration value of 22.9 ± 0.17 μM, and its inhibition was significantly stronger than those of acarbose and resveratrol (264 ± 3.27 and 108 ± 2.13 μM). Moreover, a competitive inhibition mechanism of resveratroloside on α-glucosidase was determined by enzyme kinetic assays and molecular docking experiments. The molecular docking of resveratroloside with α-glucosidase demostrated the competitive inhibitory effect of resveratroloside, which occupies the catalytic site and forms strong hydrogen bonds with the residues of α-glucosidase. Resveratrol was also determined to be a competitive inhibition mechanism on α-glucosidase by enzyme kinetic assays and molecular docking experiments. This study suggested that resveratroloside had the ability to regulate PBG levels and can be considered a potential agent for the treatment of diabetes mellitus.

Asprellcosides B of Ilex asprella Inhibits Influenza A Virus Infection by Blocking the Hemagglutinin- Mediated Membrane Fusion

Ilex asprella is routinely used in China as a traditional medicinal herb to treat influenza (Flu). However, its specific antiviral activity and underlying molecular mechanism have not yet been determined. In this study, we sought to determine the antiviral activity and mechanism of Asprellcosides B, an active component extracted from Ilex asprella, and used against the influenza A virus cell culture. We also performed a computer-assisted structural modeling analysis and carried out surface plasmon resonance (SPR) experiments in the hope of determining the viral target of Asprellcosides B. Results from our studies show that Asprellcosides B reduced virus replication by up to 63% with an IC50 of about 9 μM. It also decreased the low pH-induced and virus-mediated hemolysis by 71% in vitro. Molecular docking simulation analysis suggested a possible binding of Asprellcosides B to the hemagglutinin (HA), which was confirmed by a surface plasmon resonance (SPR) assay. Altogether, our findings demonstrate that Asprellcosides B inhibits the influenza A virus, through a specific binding to the HA, resulting in the blockade of the HA-mediated membrane fusion.

GAPDH with NAD+-binding site mutation competitively inhibits the wild-type and affects glucose metabolism in cancer

BACKGROUND

Rapid utilization of glucose is a metabolic signature of majority of cancers, hence enzymes of the glycolytic pathway remain attractive therapeutic targets. Recent reports have shown that targeting the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an abundant, ubiquitous multifunctional protein frequently upregulated in cancer, affects cancer progression. Here, we report that a catalytically-deficient mutant-GAPDH competitively inhibits the wild-type, and disrupts glucose metabolism in cancer cells.

METHODS

Using site-directed mutagenesis, the human GAPDH clone was mutated at one of the NAD⁺-binding sites, (i.e.) arginine (R13) and isoleucine (I14) to glutamine (Q13) and phenylalanine (F14), respectively. The inhibitory role of the mutant-GAPDH, and its effect on energy metabolism and cancer phenotype was determined using in vitro and in vivo models of cancer.

RESULTS

The enzymatically-dysfunctional mutant-GAPDH competitively inhibited the wild-type GAPDH in a cell-free system. In cancer cells, ectopic expression of the mutant-GAPDH, but not the wild-type, inhibited the glycolytic capacity of cellular-GAPDH, and led to the induction of metabolic stress accompanied by a sharp decline in glucose-uptake. Furthermore, expression of mutant-GAPDH affected cancer growth in vitro and in vivo. Mechanistically, structural analysis by bioinformatics revealed that the mutations at the NAD⁺-binding site altered the solvent-accessibility that perhaps affected the functionality of mutant-GAPDH.

CONCLUSION

Mutant-GAPDH affects the enzymatic function of cellular-GAPDH and disrupts energy metabolism.

GENERAL SIGNIFICANCE

Our findings demonstrate that a minimal mutation at the NAD⁺-binding site is sufficient to generate a competitive but dysfunctional GAPDH, and its ectopic expression inhibits the wild-type to disrupt glycolysis.

Assessment of Three-Drug Combination Pharmacodynamic Interactions in Pancreatic Cancer Cells

The pharmacodynamic interactions among trifluoperazine (TFP), gemcitabine (GEM), and paclitaxel (PTX) were assessed in pancreatic cancer cells (PANC-1). The phenothiazine TFP was chosen for its potential activity on cancer stem cells, while GEM and PTX cause apoptosis. Effects of each drug alone and in various combinations on cell growth inhibition of PANC-1 cells were studied in vitro to determine the drug-specific parameters and assess the nature of drug interactions. Joint inhibition (JI) and competitive inhibition (CI) equations were applied with a ψ interaction term. TFP fully inhibited growth of cells (I_max = 1) with an IC₅₀ = 9887 nM. Near-maximum inhibition was achieved for GEM (I_max = 0.825) and PTX (I_max= 0.844) with an IC₅₀ = 17.4 nM for GEM and IC₅₀ = 7.08 nM for PTX. Estimates of an interaction term ψ revealed that the combination of TFP-GEM was apparently synergistic; close to additivity, the combination TFP-PTX was antagonistic. The interaction of GEM-PTX was additive, and TFP-GEM-PTX was synergistic but close to additive. The combination of TFP IC₆₀-GEM IC₆₀-PTX IC₆₀ seemed optimal in producing inhibition of PANC-1 cells with an inhibitory effect of 82.1-90.2%. The addition of ψ terms to traditional interaction equations allows assessment of the degree of perturbation of assumed mechanisms.

Molecular principles for heparin oligosaccharide-based inhibition of neutrophil elastase in cystic fibrosis

Cystic fibrosis (CF) is a multifactorial disease in which dysfunction of protease-antiprotease balance plays a key role. The current CF therapy relies on dornase α, hypertonic saline, and antibiotics and does not address the high neutrophil elastase (NE) activity observed in the lung and sputum of CF patients. Our hypothesis is that variants of heparin, which potently inhibit NE but are not anticoagulant, would help restore the protease-antiprotease balance in CF. To realize this concept, we studied molecular principles governing the effectiveness of different heparins, especially 2-O,3-O-desulfated heparin (ODSH), in the presence of sputum components and therapeutic agents. Using sputa from CF patients and an NE activity assay, we found that heparins are ineffective if used in the absence of dornase. This is true even when mucolytics, such as DTT or N-acetylcysteine, were used. Computational modeling suggested that ODSH and DNA compete for binding to an overlapping allosteric site on NE, which reduces the anti-NE potential of ODSH. NE inhibition of both DNA and ODSH is chain length-dependent, but ODSH chains exhibit higher potency per unit residue length. Likewise, ODSH chains exhibit higher NE inhibition potential compared with DNA chains in the presence of saline. These studies suggest fundamental differences in DNA and ODSH recognition and inhibition of NE despite engaging overlapping sites and offer unique insights into molecular principles that could be used in developing antiprotease agents in the presence of current treatments, such as dornase and hypertonic saline.

Unraveling the Enzymatic Activity of Oxygenated Carbon Nanotubes and Their Application in the Treatment of Bacterial Infections

Carbon nanotubes (CNTs) and their derivatives have emerged as a series of efficient biocatalysts to mimic the function of natural enzymes in recent years. However, the unsatisfiable enzymatic efficiency usually limits their practical usage ranging from materials science to biotechnology. Here, for the first time, we present the synthesis of several oxygenated-group-enriched carbon nanotubes (o-CNTs) via a facile but green approach, as well as their usage as high-performance peroxidase mimics for biocatalytic reaction. Exhaustive characterizations of the enzymatic activity of o-CNTs have been provided by exploring the accurate effect of various oxygenated groups on their surface including carbonyl, carboxyl, and hydroxyl groups. Because of the "competitive inhibition" effect among all of these oxygenated groups, the catalytic efficiency of o-CNTs is significantly enhanced by weakening the presence of noncatalytic sites. Furthermore, the admirable enzymatic activity of these o-CNTs has been successfully applied in the treatment of bacterial infections, and the results of both in vitro and in vivo nanozyme-mediated bacterial clearance clearly demonstrate the feasibility of o-CNTs as robust peroxidase mimics to effectively decrease the bacterial viability under physiological conditions. We believe that the present study will not only facilitate the construction of novel efficient nanozymes by rationally adjusting the degree of the "competitive inhibition" effect, but also broaden the biological usage of o-CNT-based nanomaterials via their satisfactory enzymatic activity.

Structural basis for tumor necrosis factor blockade with the therapeutic antibody golimumab

Tumor necrosis factor α (TNFα) is a proinflammatory cytokine, and elevated levels of TNFα in serum are associated with various autoimmune diseases, including rheumatoid arthritis (RA), ankylosing spondylitis (AS), Crohn's disease (CD), psoriasis, and systemic lupus erythaematosus. TNFα performs its pleiotropic functions by binding to two structurally distinct transmembrane receptors, TNF receptor (TNFR) 1 and TNFR2. Antibody-based therapeutic strategies that block excessive TNFα signaling have been shown to be effective in suppressing such harmful inflammatory conditions. Golimumab (Simponi®) is an FDA-approved fully human monoclonal antibody targeting TNFα that has been widely used for the treatment of RA, AS, and CD. However, the structural basis underlying the inhibitory action of golimumab remains unclear. Here, we report the crystal structure of the Fv fragment of golimumab in complex with TNFα at a resolution of 2.73 Å. The resolved structure reveals that golimumab binds to a distinct epitope on TNFα that does not overlap with the binding residues of TNFR2. Golimumab exerts its inhibitory effect by preventing binding of TNFR1 and TNFR2 to TNFα by steric hindrance. Golimumab does not induce conformational changes in TNFα that could affect receptor binding. This mode of action is specific to golimumab among the four anti-TNFα therapeutic antibodies currently approved for clinical use.

Erythritol Attenuates Postprandial Blood Glucose by Inhibiting α-Glucosidase

Diabetes mellitus (DM) is a serious metabolic disorder, where impaired postprandial blood glucose regulation often leads to severe health complications. The natural chemical erythritol is a C4 polyol approved by the U.S. Food and Drug Administration for use as a sweetener. Here, we examined a potential role for erythritol in the control of postprandial blood glucose levels in DM. An anti-postprandial hyperglycemia effect upon erythritol administration (500 mg kg^-1) was demonstrated in alloxan-induced DM model mice by monitoring changes in blood glucose after intragastric administration of drugs and starch. We also found that erythritol most likely exerts its anti-postprandial hyperglycemic activities by inhibiting α-glucosidase in a competitive manner. This was supported by enzyme activity assays and molecular modeling experiments. In the latter experiments, it was possible to successfully dock erythritol into the catalytic pocket of α-glucosidase, with the resultant interaction likely driven by electrostatic interactions involving Asp215, Asp69, and Arg446 residues. This study suggests that erythritol may not only serve as a glucose substitute but also be a useful agent in the treatment of DM to help manage postprandial blood glucose levels.

Molecular Insights into Function and Competitive Inhibition of Pseudomonas aeruginosa Multiple Virulence Factor Regulator

New approaches to antimicrobial drug discovery are urgently needed to combat intractable infections caused by multidrug-resistant (MDR) bacteria. Multiple virulence factor regulator (MvfR or PqsR), a Pseudomonas aeruginosa quorum sensing transcription factor, regulates functions important in both acute and persistent infections. Recently identified non-ligand-based benzamine-benzimidazole (BB) inhibitors of MvfR suppress both acute and persistent P. aeruginosa infections in mice without perturbing bacterial growth. Here, we elucidate the crystal structure of the MvfR ligand binding domain (LBD) in complex with one potent BB inhibitor, M64. Structural analysis indicated that M64 binds, like native ligands, to the MvfR hydrophobic cavity. A hydrogen bond and pi interaction were found to be important for MvfR-M64 affinity. Surface plasmon resonance analysis demonstrated that M64 is a competitive inhibitor of MvfR. Moreover, a protein engineering approach revealed that Gln194 and Tyr258 are critical for the interaction between MvfR and M64. Random mutagenesis of the full-length MvfR protein identified a single-amino-acid substitution, I68F, at a DNA binding linker domain that confers M64 insensitivity. In the presence of M64, I68F but not the wild-type (WT) MvfR protein retained DNA binding ability. Our findings strongly suggest that M64 promotes conformational change at the DNA binding domain of MvfR and that the I68F mutation may compensate for this change, indicating allosteric inhibition. This work provides critical new insights into the molecular mechanism of MvfR function and inhibition that could aid in the optimization of anti-MvfR compounds and improve our understanding of MvfR regulation.

Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that causes serious acute, persistent, and relapsing infections. New approaches to antimicrobial drug discovery are urgently needed to combat intractable infections caused by this pathogen. The Pseudomonas aeruginosa quorum sensing transcription factor MvfR regulates functions important in both acute and persistent infections. We used recently identified inhibitors of MvfR to perform structural studies and reveal important insights that would benefit the optimization of anti-MvfR compounds. Altogether, the results reported here provide critical detailed mechanistic insights into the function of MvfR domains that may benefit the optimization of the chemical, pharmacological, and safety properties of MvfR antagonist series.

Targeting the β-clamp in Helicobacter pylori with FDA-approved drugs reveals micromolar inhibition by diflunisal

The β-clamp is the processivity-promoting factor for most of the enzymes in prokaryotic DNA replication; hence, it is a crucial drug target. In the present study, we investigated the β-clamp from Helicobacter pylori, aiming to seek potential drug molecules against this gastric-cancer-causing bacterium. An in silico screening of Food and Drug Administration (FDA) approved drugs against the H. pylori β-clamp, followed by its in vitro inhibition using a surface competition approach, yielded the drug diflunisal as a positive initial hit. Diflunisal inhibits the growth of H. pylori in the micromolar range. We determined the structure of diflunisal in complex with the β-clamp to show that the drug binds at subsite I, which is a protein-protein interaction site. Successful identification of FDA-approved molecules against H. pylori may lead to better and faster drug development.

Competitive Inhibition Mechanism of Acetylcholinesterase without Catalytic Active Site Interaction: Study on Functionalized C60 Nanoparticles via in Vitro and in Silico Assays

Acetylcholinesterase (AChE) activity regulation by chemical agents or, potentially, nanomaterials is important for both toxicology and pharmacology. Competitive inhibition via direct catalytic active sites (CAS) binding or noncompetitive inhibition through interference with substrate and product entering and exiting has been recognized previously as an AChE-inhibition mechanism for bespoke nanomaterials. The competitive inhibition by peripheral anionic site (PAS) interaction without CAS binding remains unexplored. Here, we proposed and verified the occurrence of a presumed competitive inhibition of AChE without CAS binding for hydrophobically functionalized C₆₀ nanoparticles (NPs) by employing both experimental and computational methods. The kinetic inhibition analysis distinguished six competitive inhibitors, probably targeting the PAS, from the pristine and hydrophilically modified C₆₀ NPs. A simple quantitative nanostructure-activity relationship (QNAR) model relating the pocket accessible length of substituent to inhibition capacity was then established to reveal how the geometry of the surface group decides the NP difference in AChE inhibition. Molecular docking identified the PAS as the potential binding site interacting with the NPs via a T-shaped plug-in mode. Specifically, the fullerene core covered the enzyme gorge as a lid through π-π stacking with Tyr72 and Trp286 in the PAS, while the hydrophobic ligands on the fullerene surface inserted into the AChE active site to provide further stability for the complexes. The modeling predicted that inhibition would be severely compromised by Tyr72 and Trp286 deletions, and the subsequent site-directed mutagenesis experiments proved this prediction. Our results demonstrate AChE competitive inhibition of NPs without CAS participation to gain further understanding of both the neurotoxicity and the curative effect of NPs.