Interdomain Interactions Modulate the Active Site Dynamics of Human Inducible Nitric Oxide Synthase.

Nitric oxide synthase (NOS) is a homodimeric flavohemoprotein responsible for catalyzing the oxidation of l-arginine (l-Arg) to citrulline and nitric oxide. Electrons are supplied for the reaction via interdomain electron transfer between an N-terminal heme-containing oxygenase domain and a FMN-containing (sub)domain of a C-terminal reductase domain. Extensive attention has focused on elucidating how conformational dynamics regulate electron transfer between the domains. Here we investigate the impact of the interdomain FMN-heme interaction on the heme active site dynamics of inducible NOS (iNOS). Steady state linear and time-resolved two-dimensional infrared (2D IR) spectroscopy was applied to probe a CO ligand at the heme within the oxygenase domain for full-length and truncated or mutated constructs of human iNOS. Whereas the linear IR spectra of the CO ligand were identical among the constructs, 2D IR spectroscopy revealed variation in the frequency dynamics. The wild-type constructs that can properly form the FMN/oxygenase docked state due to the presence of both the FMN and oxygenase domains showed slower dynamics than the oxygenase domain alone. Introduction of the mutation (E546N) predicted to perturb electrostatic interactions between the domains resulted in measured dynamics intermediate between those for the full-length and individual oxygenase domain, consistent with perturbation to the docked/undocked equilibrium. These results indicate that docking of the FMN domain to the oxygenase domain not only brings the FMN cofactor within electron transfer distance of the heme domain but also modulates the dynamics sensed by the CO ligand within the active site in a way expected to promote efficient electron transfer.

Screening and Identification of Potential iNOS Inhibitors to Curtail Cervical Cancer Progression: an In Silico Drug Repurposing Approach.

Cervical cancer is the second most common cause of cancer deaths in women worldwide and remains the main reason of mortality among women of reproductive age in developing countries. Nitric oxide is involved in several physiological functions inclusive of inflammatory and immune responses. However, the function of NO in tumor biology is debatable. The inducible NOS (iNOS/NOS2) isoform is the one responsible to maintain the levels of NO, and it exhibits pleotropic effects in various cancers with concentration-dependent pro- and anti-tumor effects. iNOS triggers angiogenesis and endothelial cell migration in tumors by regulating the levels of vascular endothelial growth factor (VEGF). In drug discovery, drug repurposing involves investigations of approved drug candidates to treat various other diseases. In this study, we used anti-cancer drugs and small molecules to target iNOS and identify a potential selective iNOS inhibitor. The structures of ligands were geometrically optimized and energy minimized using Hyperchem software. Molecular docking was performed using Molegro virtual docker, and ligands were selected based on MolDock score, Rerank score, and H-bonding energy. In the study shown, venetoclax compound demonstrated excellent binding affinity to iNOS protein. This compound exhibited the lowest MolDock score and Rerank score with better H-bonding energy to iNOS. The binding efficacy of venetoclax was analyzed by performing molecular docking and molecular dynamic simulations. Multiple parameters were used to analyze the simulation trajectory, like root mean square deviation (RMSD), radius of gyration (Rg), and hydrogen bond interactions. Based on the results, venetoclax emerges to be a promising potential iNOS inhibitor to curtail cervical cancer progression.

Potential of Ageratum conyzoides in Inhibiting Nitric Oxide Synthase.

<b>Background and Objective:</b> Inflammation occurs <i>via</i> several mechanisms, one of which includes the production of Nitric Oxide (NO) catalyzed by inducible nitric oxide synthase (iNOS), which is inhibited selectively by isothioureas. <i>Ageratum conyzoides</i> L. has shown activity in reducing pain and inflammation, although the molecular mechanism had not been undertaken. The objectives of this work were (1) to study the mechanism of anti-inflammatory activity of <i>A. conyzoides</i> through inhibition of iNOS, (2) to correlate the iNOS inhibitory activity of the plant with the total flavonoid content of the plants and (3) to identify the flavonol synthase (FLS), an enzyme that catalyzes the production of quercetin. <b>Materials and Methods:</b> The inhibitory activity against iNOS was assayed by <i>in vitro</i> method. The total flavonoids (calculated as quercetin) of <i>A. conyzoides</i> were determined by fluorometry. The protein extraction of the leaves was carried out by employing Laing and Christeller's (2004) method, followed with SDS-PAGE. <b>Results:</b> The inhibitory activity (IC₅₀) of ethanol extract and ethyl acetate fraction of <i>A. conyzoides</i> against iNOS was 92.05 and 4.78 µg mL¹, respectively. Pearson correlation analysis resulted in 0.548 (ethanol extract) and 0.696 (ethyl acetate fraction). The total flavonoids (calculated as quercetin) contained in the ethanol extract and ethyl acetate fraction of <i>A. conyzoides</i> were 0.71 and 7.65%, respectively. The FLS in <i>A. conyzoides</i> leaves was identified at 31 kDa. <b>Conclusion:</b> <i>A. </i>c<i>onyzoides</i> L. is potential in inhibiting iNOS due to quercetin contained in the leaves. This report will add a scientific insight of <i>A. conyzoides</i> for biological sciences.

Structural basis for the regulation of inducible nitric oxide synthase by the SPRY domain-containing SOCS box protein SPSB2, an E3 ubiquitin ligase.

Relatively high concentration of nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) in response to a variety of stimuli is a source of reactive nitrogen species, an important weapon of host innate immune defense. The SPRY domain-containing SOCS box protein 2 (SPSB2) is an E3 ubiquitin ligase that regulates the lifetime of iNOS. SPSB2 interacts with the N-terminal region of iNOS via a binding site on the SPRY domain of SPSB2, and recruits an E3 ubiquitin ligase complex to polyubiquitinate iNOS, leading to its proteasomal degradation. Although critical residues for the SPSB2-iNOS interaction have been identified, structural basis for the interaction remains to be explicitly determined. In this study, we have determined a crystal structure of the N-terminal region of iNOS in complex with the SPRY domain of SPSB2 at 1.24 Å resolution. We have resolved the roles of some flanking residues, whose contribution to the SPSB2-iNOS interaction was structurally unclear previously. Furthermore, we have evaluated the effects of SPSB2 inhibitors on NO production using transient transfection and cell-penetrating peptide approaches, and found that such inhibitors can elevate NO production in RAW264.7 macrophages. These results thus provide a useful basis for the development of potent SPSB2 inhibitors as well as recruiting ligands for proteolysis targeting chimera (PROTAC) design.

Multiple in vitro biological effects of phenolic compounds from Terminalia chebula var. tomentella.

ETHNOPHARMACOLOGICAL RELEVANCE: Terminalia chebula (TC), a well-known Indian Ayurvedic medicine introduced into China in the Sui and Tang Dynasties, has been recorded and used medicinally as Fructus Chebulae, together with its variety tomentella (TCT) in the Chinese Pharmacopoeia. They have been also used commonly for the treatment of diabetes mellitus by Tibetan medicine. AIM OF THE STUDY: To investigate the main bioactive and therapeutic principles in the fruits of TCT, based on the extensive evaluation of their anti-inflammatory and hypoglycemic activities. MATERIALS AND METHODS: The TCT fresh fruits were analyzed by HPLC and separated further by column chromatography and preparative HPLC. The isolated compounds were identified by extensive spectroscopic analyses, including 1D/2D NMR, MS, UV, IR and ECD. Anti-inflammatory activity was evaluated by inhibition of NO production in RAW264.7 cells. The specific iNOS (PDB ID: 3E7G) structure was prepared by Discovery Studio 4.0, and the molecular docking simulation was performed on GOLD (version 5.2.2). Hypoglycemic activity was measured using the substrate solution of 4-nitrophenyl-α-d-glucopyranoside enzyme and buffer solution. RESULTS: The HPLC analysis method of polyphenols in the fruits of TCT was established, and 13 main chromatographic peaks were identified, including six hydrolyzable tannins (2, 4-7, 10-11), three simple phenols (12-14), and one oleanane pentacyclic triterpene, arjungenin. Extensive chromatographic separation of TCT fresh fruits yielded 14 compounds, including one new natural hydrolyzable tannin, 2,3-(S)-HHDP-6-O-galloyl-d-glucose (1). The known compounds were identified as 10 hydrolyzable tannins (2-11) and three simple phenols (12-14). Compounds 10 (IC50 = 36.43 ± 0.21 µM), 11 (IC50 = 42.28 ± 0.09 µM) displayed stronger NO inhibitory activity than the positive control L-NMMA (IC50 = 42.34 ± 0.66 µM), while 2, 4, and 9 showed moderate inhibitory activity against NO production. Further molecular docking simulation of specific iNOS on 10 and 11, as well as five previously isolated lignans 15-19 showed that there were no obvious rules between docking results and the in vitro NO inhibitory activity for hydrolyzable tannins (10 and 11), while the mechanism of anti-inflammatory activity for lignans was related to the substitution of conjugated aldehyde groups. Moreover, most of the hydrolyzable tannins (1-2, 4-5, 9-11) and simple phenol (12) displayed stronger inhibitory effects on α-glucosidase than the positive control, quercetin (IC50 = 6.118 ± 0.071 µM), with IC50 values ranging from 0.079 to 16.494 µM. Among these bioactive isolates, the hydrolyzable tannins 2, 4-5, and 9-11, and simple phenol 12 are major chemical components in TCT fruit. CONCLUSIONS: The results showed that lignans and hydrolyzed tannins are the main active ingredients of TCT fruits, responsible for the traditional treatment of sore throat and cough. Moreover, hydrolyzed tannins and simple phenolic compounds with potential hypoglycemic activity are closely related to the ethno-pharmacological uses of TCT fruits on diabetes in Tibetan medicine.

4-Sulfonyloxy/alkoxy benzoxazolone derivatives with high anti-inflammatory activities: Synthesis, biological evaluation, and mechanims of action via p38/ERK-NF-κB/iNOS pathway.

In an effort to discover new agents with high anti-inflammatory activity, 22 new 4-sulfonyloxy/alkoxy benzoxazolone derivatives were synthesized, characterized, and evaluated for their anti-inflammatory activities against lipopolysaccharide (LPS)-induced nitric oxide (NO) production and TNF-α expression in RAW 264.7 cells in vitro. Most of these compounds displayed greater inhibitory ability against NO production than the lead compound 4-o-methyl-benzenesulfonyl benzoxazolone, and the most active compound 2h exhibited the strongest inhibitory activity against NO, IL-1ß, and IL-6 production with IC50 values 17.67, 20.07, and 8.61 µΜ, respectively. The effects of 2h were comparable or stronger than those of the positive control celecoxib. Compound 2h also displayed higher activity in vivo than celecoxib in a mouse model of xylene-induced ear edema, based on their inhibitory rates of 42.69% and 30.87%, respectively. Further molecular analysis revealed that compound 2h significantly reduced the iNOS levels in cell supernatant and suppressed the protein expression of iNOS, p-p38, p-ERK, and nuclear NF-κB. The results indicated that the anti-inflammatory effect of 2h might be realized through the regulation of ERK- and p38-mediated mitogen-activated protein kinase (MAPK)-NF-κB/iNOS signaling, thereby reducing the excessive release of NO, IL-1ß, and IL-6. Our findings demonstrated that compound 2h, a new benzoxazolone derivative, could inhibit activation of the MAPK-NF-κB/iNOS pathway, supporting its potential as a novel anti-inflammatory agent.

Bioactive sesquiterpene derivatives from mangrove endophytic fungus Phomopsis sp. SYSU-QYP-23: Structures and nitric oxide inhibitory activities.

Eight new sesquiterpene derivatives (2, 4-6 and 10-13), along with five known analogues were isolated from the mangrove endophytic fungus Phomopsis sp. SYSU-QYP-23. Their structures of new compounds were established by spectroscopic methods, and the absolute configurations were confirmed by single-crystal X-ray diffraction analysis and comparison of the experimental ECD spectra. The absolute configuration of the side chain in 1 was first defined by modified Mosher's method. Compounds 1-7 showed potent inhibitory activities against nitric oxide (NO) production in lipopolysaccharides (LPS) induced RAW 264.7 cells with IC50 values ranging from 8.6 to 14.5 µM. The molecular docking results implied that the bioactive sesquiterpenes may directly bind with targeting residues in the active cavity of iNOS protein.

N-Glycosylation at Asn695 might suppress inducible nitric oxide synthase activity by disturbing electron transfer.

Inducible nitric oxide synthase (iNOS) plays critical roles in the inflammatory response and host defense. Previous research on iNOS regulation mainly focused on its gene expression level, and much less is known about the regulation of iNOS function by N-glycosylation. In this study, we report for the first time that iNOS is N-glycosylated in vitro and in vivo. Mass spectrometry studies identified Asn695 as an N-glycosylation site of murine iNOS. Mutating Asn695 to Gln695 yields an iNOS that exhibits greater enzyme activity. The essence of nitric oxide synthase catalytic reaction is electron transfer process, which involves a series of conformational changes, and the linker between the flavin mononucleotide-binding domain and the flavin adenine dinucleotide-binding domain plays vital roles in the conformational changes. Asn695 is part of the linker, so we speculated that attachment of N-glycan to the Asn695 residue might inhibit activity by disturbing electron transfer. Indeed, our NADPH consumption results demonstrated that N-glycosylated iNOS consumes NADPH more slowly. Taken together, our results indicate that iNOS is N-glycosylated at its Asn695 residue and N-glycosylation of Asn695 might suppress iNOS activity by disturbing electron transfer.

An isoform-specific pivot modulates the electron transfer between the flavin mononucleotide and heme centers in inducible nitric oxide synthase.

Intraprotein interdomain electron transfer (IET) between the flavin mononucleotide (FMN) and heme centers is an obligatory step in nitric oxide synthase (NOS) enzymes. An isoform-specific pivotal region near Leu406 in the heme domain of human inducible NOS (iNOS) was proposed to mediate the FMN-heme domain-domain alignment (J Inorg Biochem 153:186-196, 2015). The FMN-heme IET rate is a measure of the interdomain FMN/heme complex formation. In this work, the FMN-heme IET kinetics in the wild type (wt) human iNOS oxygenase/FMN (oxyFMN) construct were directly measured by laser flash photolysis with added synthetic peptide related to the pivotal region, in comparison with the wt construct alone. The IET rates were decreased by the iNOS HKL peptide in a dose-saturable fashion, and the inhibitory effect was abolished by a single L406 → E mutation in the peptide. A similar trend in change of the NO synthesis activity of wt iNOS holoenzyme by the peptides was observed. These data, along with the kinetics and modeling results for the L406T and L406F mutant oxyFMN proteins, indicated that the Leu406 residue modulates the FMN-heme IET through hydrophobic interactions. Moreover, the IET rates were analyzed for the wt iNOS oxyFMN protein in the presence of nNOS or eNOS-derived peptide related to the equivalent pivotal heme domain site. These results together indicate that the isoform-specific pivotal region at the heme domain specifically interacts with the conserved FMN domain surface, to facilitate proper interdomain docking for the FMN-heme IET in NOS.

DNA-based fluorescent probes of NOS2 activity in live brains.

Innate immune cells destroy pathogens within a transient organelle called the phagosome. When pathogen-associated molecular patterns (PAMPs) displayed on the pathogen are recognized by Toll-like receptors (TLRs) on the host cell, it activates inducible nitric oxide synthase (NOS2) which instantly fills the phagosome with nitric oxide (NO) to clear the pathogen. Selected pathogens avoid activating NOS2 by concealing key PAMPs from their cognate TLRs. Thus, the ability to map NOS2 activity triggered by PAMPs can reveal critical mechanisms underlying pathogen susceptibility. Here, we describe DNA-based probes that ratiometrically report phagosomal and endosomal NO, and can be molecularly programmed to display precise stoichiometries of any desired PAMP. By mapping phagosomal NO produced in microglia of live zebrafish brains, we found that single-stranded RNA of bacterial origin acts as a PAMP and activates NOS2 by engaging TLR-7. This technology can be applied to study PAMP-TLR interactions in diverse organisms.

A novel pyrazole-containing selenium compound modulates the oxidative and nitrergic pathways to reverse the depression-pain syndrome in mice.

Bearing in mind that pain and major depressive disorder (MDD) often share biological pathways, this condition is classified as depression-pain syndrome. Mounting evidence suggests that oxidative stress is implicated in the pathophysiology of this syndrome. The development of effective pharmacological interventions for the depression-pain syndrome is of particular importance as clinical treatments for this comorbidity have shown limited efficacy. Therefore, the present study aimed to evaluate whether the 3,5-dimethyl-1-phenyl-4-(phenylselanyl)-1H-pyrazole (SePy) was able to reverse the depression-pain syndrome induced by intracerebroventricular (i.c.v) streptozotocin (STZ) in mice and the possible modulation of oxidative and nitrergic pathways in its effect. The treatment with SePy (1 and 10 mg/kg) administered intragastrically (i.g.) reversed the increased immobility time in the tail suspension test, decreased grooming time in the splash test, latency time to nociceptive response in the hot plate test, and the response frequency of Von Frey hair (VFH) stimulation induced by STZ (0.2 mg/4 µl/per mouse). Additionally, SePy (10 mg/kg, i.g.) reversed STZ-induced alterations in the levels of reactive oxygen species, nitric oxide, and lipid peroxidation and the superoxide dismutase and catalase activities in the prefrontal cortices (PFC) and hippocampi (HC) of mice. Treatment with SePy (10 mg/kg, i.g.) also reversed the STZ-induced increased expression of inducible nitric oxide synthase (iNOS) and glycogen synthase kinase 3 beta (GSK3ß) in the PFC and HC. An additional molecular docking investigation found that SePy binds to the active site of iNOS and GSK3ß. Altogether, these results indicate that the antidepressant-like effect of SePy is accompanied by decreased hyperalgesia and mechanical allodynia, which were associated with its antioxidant effect.

Imperatorin suppresses IL-1ß-induced iNOS expression via inhibiting ERK-MAPK/AP1 signaling in primary human OA chondrocytes.

Joint inflammation is a key player in the pathogenesis of osteoarthritis (OA). Imperatorin, a plant-derived small molecule has been reported to have anti-inflammatory properties; however, its effect on chondrocytes is not known. Here, we investigated the effects of Imperatorin on interleukin-1ß (IL-1ß) induced expression of inducible nitric oxide synthase (iNOS) and nitric oxide production in primary human OA chondrocytes and cartilage explants culture under pathological conditions and explored the associated signaling pathways. We pretreated chondrocytes or explants with Imperatorin (50 µM) followed by IL-1ß (1 ng/ml), and the culture supernatant was used to determine the levels of nitrite production by Griess assay and chondrocytes were harvested to prepare cell lysate or RNA for gene expression analysis of iNOS by Western blot or qPCR and in explants by immunohistochemistry (IHC). Pretreatment of primary chondrocytes and cartilage explants with Imperatorin suppressed IL-1ß induced expression of iNOS and NO production. Imperatorin blocked the IL-1ß-induced phosphorylation of ERK-MAPK/AP1 signaling pathway to suppress iNOS expression. The role of ERK in the regulation of iNOS expression was verified by using ERK inhibitor. Interestingly, we also found that Imperatorin binds to iNOS protein and inhibits its activity in vitro. Our data demonstrated that Imperatorin possess strong anti-inflammatory activity and may be developed as a therapeutic agent for the management of OA.

Macrocyclic Modalities Combining Peptide Epitopes and Natural Product Fragments.

"Hot loop" protein segments have variable structure and conformation and contribute crucially to protein-protein interactions. We describe a new hot loop mimicking modality, termed PepNats, in which natural product (NP)-inspired structures are incorporated as conformation-determining and -restricting structural elements into macrocyclic hot loop-derived peptides. Macrocyclic PepNats representing hot loops of inducible nitric oxide synthase (iNOS) and human agouti-related protein (AGRP) were synthesized on solid support employing macrocyclization by imine formation and subsequent stereoselective 1,3-dipolar cycloaddition as key steps. PepNats derived from the iNOS DINNN hot loop and the AGRP RFF hot spot sequence yielded novel and potent ligands of the SPRY domain-containing SOCS box protein 2 (SPSB2) that binds to iNOS, and selective ligands for AGRP-binding melanocortin (MC) receptors. NP-inspired fragment absolute configuration determines the conformation of the peptide part responsible for binding. These results demonstrate that combination of NP-inspired scaffolds with peptidic epitopes enables identification of novel hot loop mimics with conformationally constrained and biologically relevant structure.

Novel Coupled Molecules from Active Structural Motifs of Synthetic and Natural Origin as Immunosuppressants.

INTRODUCTION: Nitric oxide (NO) is an important mediator in the pathogenesis and control of immune system-related disorders and its levels are modulated by inducible NO synthase (iNOS). Oxidative stress is another pathological indication in majority of autoimmune disorders. The present study aims at the development of coupled molecules via selection of pharmacophores for both immunomodulatory and antioxidant activities through iNOS inhibition. METHODS: Variedly substituted coumarin moieties are coupled with naturally occurring phenols through an amide linkage and were predicted for activities using computer-based program PASS. The compounds predicted to have dual activities were synthesized. Docking studies were carried out against iNOS (PDB 1R35) and compounds having good docking score were evaluated for immunomodulatory and antioxidant activities. RESULTS: The synthesized compounds were found to be pure and were obtained in good yields. Compounds with maximum docking score (YR1a, YR2e, YR2c and YR4e) were selected for evaluation by in vitro models. Compounds YR2e and YR2c markedly inhibited the reduction of NBT dye and showed maximum % iNOS inhibition. In DPPH assay, compound YR4e was observed as the most potent antioxidant (EC50 0.33 µM/mL). Based on these studies, compounds YR2e and YR2c were selected for haemagglutination test. Compound YR2e was observed as the most active immunosuppressant with maximal inhibitory ability of iNOS and NBT reduction and lower HAT value of 3.5. CONCLUSION: Compound YR2e can be utilized as a pharmacological agent in the prevention or treatment of immunomodulatory diseases such as tumors, rheumatoid arthritis, ulcerative colitis, organ transplant and other autoimmune disorders.

Inducible nitric oxide synthase: Regulation, structure, and inhibition.

A considerable number of human diseases have an inflammatory component, and a key mediator of immune activation and inflammation is inducible nitric oxide synthase (iNOS), which produces nitric oxide (NO) from l-arginine. Overexpressed or dysregulated iNOS has been implicated in numerous pathologies including sepsis, cancer, neurodegeneration, and various types of pain. Extensive knowledge has been accumulated about the roles iNOS plays in different tissues and organs. Additionally, X-ray crystal and cryogenic electron microscopy structures have shed new insights on the structure and regulation of this enzyme. Many potent iNOS inhibitors with high selectivity over related NOS isoforms, neuronal NOS, and endothelial NOS, have been discovered, and these drugs have shown promise in animal models of endotoxemia, inflammatory and neuropathic pain, arthritis, and other disorders. A major issue in iNOS inhibitor development is that promising results in animal studies have not translated to humans; there are no iNOS inhibitors approved for human use. In addition to assay limitations, both the dual modalities of iNOS and NO in disease states (ie, protective vs harmful effects) and the different roles and localizations of NOS isoforms create challenges for therapeutic intervention. This review summarizes the structure, function, and regulation of iNOS, with focus on the development of iNOS inhibitors (historical and recent). A better understanding of iNOS' complex functions is necessary before specific drug candidates can be identified for classical indications such as sepsis, heart failure, and pain; however, newer promising indications for iNOS inhibition, such as depression, neurodegenerative disorders, and epilepsy, have been discovered.

Inhibitory Effects of Myrtucommuacetalone 1 (MCA-1) from Myrtus communis on Inflammatory Response in Mouse Macrophages.

(1) Introduction: Reactive oxygen species (ROS) and nitric oxide (NO) are key signaling molecules that play important roles in the progression of inflammatory disorders. The objective of this study was to explore the use of myrtucommuacetalone-1 (MCA-1), as a novel compound of natural origin and a potential anti-inflammatory agent. (2) Methodology: The anti-inflammatory potential of MCA-1, which was isolated from Myrthus communis Linn, was determined by assaying superoxide, hydrogen peroxide, and nitric oxide production in macrophages. Furthermore, the effects of the compound were analyzed via phosphorylation and translocation of the transcription factor NF kappa B, which is a key regulator of iNOS activation. The effect of MCA-1 on the inducible nitric oxide synthase (iNOS) enzyme was also examined using in silico docking studies. The anticancer potential for MCA-1 was evaluated with an MTT cytotoxic assay. (3) Results: In stimulated macrophages, MCA-1 inhibited superoxide production by 48%, hydrogen peroxide by 53%, and nitric oxide (NO) with an IC50 of <1 µg/mL. MCA-1 also showed a very strong binding pattern within the active site of the inducible nitric oxide synthase enzyme. Furthermore, 25 µg/mL of MCA-1 inhibited inducible nitric oxide synthase expression and abolished transcription factor (NFκB) phosphorylation and translocation to the nucleus. Cytotoxicity analyses of MCA-1 on 3T3 mouse fibroblasts, CC1 liver cell line, J774.2, macrophages and MDBK bovine kidney epithelial cell, yielded IC50 values of 6.53 ± 1.2, 4.6 ± 0.7, 5 ± 0.8, and 4.6 ± 0.7, µg/mL, respectively. (4) Conclusion: Our results suggest that MCA-1, a major phloroglucinol-type compound, shows strong anti-inflammatory activity and has a potential to be a leading therapeutic agent in the future.

Crystal structure of the SPRY domain of human SPSB2 in the apo state.

The SPRY domain-containing SOCS box protein 2 (SPSB2) is one of four mammalian SPSB proteins that are characterized by a C-terminal SOCS box and a central SPRY/B30.2 domain. SPSB2 interacts with inducible nitric oxide synthase (iNOS) via the SPRY domain and polyubiquitinates iNOS, resulting in its proteasomal degradation. Inhibitors that can disrupt SPSB2-iNOS interaction and augment NO production may serve as novel anti-infective and anticancer agents. The previously determined murine SPSB2 structure may not reflect the true apo conformation of the iNOS-binding site. Here, the crystal structure of human SPSB2 SPRY domain in the apo state is reported at a resolution of 1.9 Å. Comparison of the apo and ligand-bound structures reveals that the iNOS-binding site is highly preformed and that major conformational changes do not occur upon ligand binding. Moreover, the C-terminal His6 tag of the recombinant protein binds to a shallow pocket adjacent to the iNOS-binding site on a crystallographically related SPSB2 molecule. These findings may help in structure-based and fragment-based SPSB2 inhibitor design in the future.

Bioactive Diterpenoids from the Stems of Euphorbia antiquorum.

A total of 18 diterpenoids, including 10 new analogues (1-10), were isolated from Euphorbia antiquorum. The structures were characterized by spectroscopic techniques, and circular dichroism data analysis was adopted to confirm the absolute configurations of 1-10. Compounds 1-9 were classified as ent-atisane diterpenoids, and 10 was assigned as an ent-kaurane diterpenoid. The biological evaluation of nitric oxide (NO) production inhibition was conducted, and all of these isolates showed the property of inhibiting NO generation in lipopolysaccharide-induced BV-2 cells. Further research on molecular docking disclosed the affinities between the diterpenoids obtained and inducible nitric oxide synthase.

The protective efficacy of soursop fruit extract against hepatic injury associated with acetaminophen exposure is mediated through antioxidant, anti-inflammatory, and anti-apoptotic activities.

In the current report, we examined the potential beneficial role of soursop fruit extract (SSFE) on liver injury induced by a single paracetamol (APAP) overdose (2000 mg/kg). Thirty-five Wistar albino rats were randomly divided into five groups as follows: control, SSFE, APAP, SSFE+APAP, and silymarin (SIL)+APAP. APAP intoxication was found to elevate alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and total bilirubin levels. Moreover, it increased the levels of malondialdehyde, nitrites, and nitrates and depleted glutathione, superoxide dismutase, catalase, glutathione reductase, and glutathione peroxidase. APAP intoxication inactivated the nuclear factor erythroid 2-related factor 2 (Nrf2) defense pathway and upregulated the expression of heme oxygenase-1 (HO-1). APAP administration enhanced the activation of nuclear factor-kappa B (NF-κB), the elevation of tumor necrosis factor-alpha and interleukin 1-beta levels, and the upregulation of inducible nitric oxide synthase mRNA expression. In addition, APAP activated the overexpression of Bax protein, increased release of cytochrome c, and the downregulation of Bcl-2 protein. Finally, APAP-induced overexpression of transforming growth factor-beta (TGF-ß) further suggested enhanced liver damage. On the other hand, SSFE pretreatment attenuated these biochemical, molecular, and histopathological alterations in the liver, which might be partially due to the regulation of hepatic Nrf2/HO-1 and downregulation of NF-κB and TGF-ß.

Mechanism and regulation of ferrous heme-nitric oxide (NO) oxidation in NO synthases.

Nitric oxide (NO) synthases (NOSs) catalyze the formation of NO from l-arginine. We have shown previously that the NOS enzyme catalytic cycle involves a large number of reactions but can be characterized by a global model with three main rate-limiting steps. These are the rate of heme reduction by the flavin domain (kr ), of dissociation of NO from the ferric heme-NO complex (kd ), and of oxidation of the ferrous heme-NO complex (kox). The reaction of oxygen with the ferrous heme-NO species is part of a futile cycle that does not directly contribute to NO synthesis but allows a population of inactive enzyme molecules to return to the catalytic cycle, and thus, enables a steady-state NO synthesis rate. Previously, we have reported that this reaction does involve the reaction of oxygen with the NO-bound ferrous heme complex, but the mechanistic details of the reaction, that could proceed via either an inner-sphere or an outer-sphere mechanism, remained unclear. Here, we present additional experiments with neuronal NOS (nNOS) and inducible NOS (iNOS) variants (nNOS W409F and iNOS K82A and V346I) and computational methods to study how changes in heme access and electronics affect the reaction. Our results support an inner-sphere mechanism and indicate that the particular heme-thiolate environment of the NOS enzymes can stabilize an N-bound FeIII-N(O)OO- intermediate species and thereby catalyze this reaction, which otherwise is not observed or favorable in proteins like globins that contain a histidine-coordinated heme.