Dual Effect in the Mechanism of Action of Anti-Influenza Virus Amino Acid Analogues

In comparative research studies to clarify the mechanism governing the effects of anti-influenza amino acid analogues, it was established that amino acid analogues exhibit definite chemotherapeutic properties. They possess dual activity capable of inhibiting multiplication and pulmonary consolidation induced by influenza virus infection.     

Mechanism and Specificity of Action of Ribavirin

Ribavirin at a concentration of 30 mug/ml added immediately after infection completely inhibited influenza A/Port Chalmers/1/73 (H(3)N(2)) virus hemagglutinin production in infected MDCK cells. Under these conditions, host cell protein synthesis was inhibited by only 10 to 20%. Polyacrylamide gel electrophoresis of [(35)S]methionine-labeled material from virus-infected cultures confirmed that ribavirin inhibited viral but not host cell protein synthesis. In parallel experiments, actinomycin D also preferentially inhibited viral protein synthesis. The possibility that ribavirin inhibited viral protein synthesis as a result of general inhibition of ribonucleic acid synthesis was therefore examined. In uninfected cells, ribavirin at 30 mug/ml inhibited the incorporation of [(14)C]inosine or [(3)H]uridine into ribonucleic acid but stimulated the incorporation of [(3)H]guanosine. The effects noted are consistent with an inhibition of the host cell enzyme inosine 5'-monophosphate dehydrogenase. This suggestion is supported by the finding that addition of guanosine, but not inosine, to the culture medium substantially reversed the antiviral effect of ribavirin. There was no separation between the concentration of ribavirin causing inhibition of influenza A viral protein synthesis or inhibition of MDCK cell ribonucleic acid synthesis, suggesting that ribavirin is not specifically antiviral in this system but inhibits viral protein synthesis as a result of the general inhibition of ribonucleic acid synthesis.     

Androgen Receptor and Mechanism of Androgen Action

Androgen receptor is the intracellular protein that mediates biological actions of physiological androgens (testosterone and 5α-dihydrotestosterone). Androgen receptor belongs to a large family of ligand-dependent proteins whose function is to modulate expression of genes and gene networks in a cell-and tissue-specific manner. The present overview describes the structurally important domains of the receptor protein, and discusses several aspects in the structure-function relationship, using naturally occurring receptor mutants in androgen insensitfvity patients or experimental animals as examples. In addition, characteristics of androgen receptor expressed in a heterologous system are described, and their potential usefulness in specific molecular studies discussed.     

In Vivo Antimalarial Activity and Mechanisms of Action of 4-Nerolidylcatechol Derivatives

4-Nerolidylcatechol (1) is an abundant antiplasmodial metabolite that is isolated from Piper peltatum roots. O-Acylation or O-alkylation of compound 1 provides derivatives exhibiting improved stability and significant in vitro antiplasmodial activity. The aim of this work was to study the in vitro inhibition of hemozoin formation, inhibition of isoprenoid biosynthesis in Plasmodium falciparum cultures, and in vivo antimalarial activity of several 4-nerolidylcatechol derivatives. 1,2-O,O-Diacetyl-4-nerolidylcatechol (2) inhibited in vitro hemozoin formation by up to 50%. In metabolic labeling studies using [1-(n)-³H]geranylgeranyl pyrophosphate, diester 2 significantly inhibited the biosynthesis of isoprenoid metabolites ubiquinone 8, menaquinone 4, and dolichol 12 in cultures of P. falciparum 3D7. Similarly, 2-O-benzyl-4-nerolidylcatechol (3) significantly inhibited the biosynthesis of dolichol 12. P. falciparumin vitro protein synthesis was not affected by compounds 2 or 3. At oral doses of 50 mg per kg of body weight per day, compound 2 suppressed Plasmodium berghei NK65 in infected BALB/c mice by 44%. This in vivo result for derivative 2 represents marked improvement over that obtained previously for natural product 1. Compound 2 was not detected in mouse blood 1 h after oral ingestion or in mixtures with mouse blood/blood plasma in vitro. However, it was detected after in vitro contact with human blood or blood plasma. Derivatives of 4-nerolidylcatechol exhibit parasite-specific modes of action, such as inhibition of isoprenoid biosynthesis and inhibition of hemozoin formation, and they therefore merit further investigation for their antimalarial potential.     

Mechanism of Action of Indomethacin in Indomethacin-Responsive Headaches

Animal-assisted therapy is a complementary medicine intervention, typically utilizing dogs trained to be obedient, calm, and comforting. Several studies have reported significant pain relief after participating in therapy dog visits. Objective reports of reduced pain and pain-related symptoms are supported by studies measuring decreased catecholamines and increased endorphins in humans receiving friendly dog visits. Mirror neuron activity and disease-perception through olfactory ability in dogs may also play important roles in helping dogs connect with humans during therapeutic encounters. This review will explore a variety of possible theories that may explain the therapeutic benefits that occur during therapy dog visits.     

Mechanism of the Antiviral Action of 3-Methyleneoxindole

The biochemical basis underlying the antiviral action of 3-methyleneoxindole (MO), a plant metabolite, was examined in HeLa cells infected with poliovirus. In the presence of antiviral concentrations of MO, poliovirus-specific ribonucleic acid (RNA) synthesis can proceed normally, and the RNA synthesized under such conditions is infectious. It is suggested that the ability of MO to bind to ribosomes of HeLa cells may underlie the antiviral affect. Data are presented which indicate that poliovirus messenger RNA cannot attach to those ribosomes which already are bound to MO. Consequently, virus-specific polysomes cannot be recovered from infected cells treated with antiviral concentrations of MO. In contrast, antiviral concentrations of MO do not prevent the formation of polysomes in uninfected HeLa cells.     

Antimycobacterial Activity and Mechanism of Action of NAS-91

The antimalarial agents NAS-91 and NAS-21 were found to express potent antimycobacterial activity, NAS-91 being more active than NAS-21. They partially inhibited mycolic acid biosynthesis and profoundly altered oleic acid production. The development of a cell-free assay for Delta 9-desaturase activity allowed direct demonstration of the inhibition of oleic acid biosynthesis by these compounds.     

Studies on the Mechanism of Action of Nalidixic Acid

With three independent techniques (absorption spectrophotometry, measurement of the deoxyribonucleic acid [DNA] melting temperature, and equilibrium dialysis), no evidence has been found for the binding of nalidixic acid to purified DNA. Also, no evidence has been found to support the hypothesis that nalidixic acid is permanently modified to a new, active compound by the bacterial cell. By using an in vitro DNA replication system developed by Bonhoeffer and colleagues, soluble extracts from nalidixic acid-sensitive cells have been shown to confer nalidixic acid sensitivity on the DNA synthesis of lysates from nalidixic acid-resistant cells. The activity in the extracts is only present in sensitive cells and is nondialyzable and heat sensitive. Finally, two known nalidixic acid-resistant mutants of Escherichia coli, mapping at nal A and nal B, respectively, have been tested to determine whether either of them is a transport mutant. It has been shown that nal B(r) is a transport mutant whereas nal A(r) is not.     

Mechanism of Action of the Novel Aminomethylcycline Antibiotic Omadacycline

Omadacycline is a novel first-in-class aminomethylcycline with potent activity against important skin and pneumonia pathogens, including community-acquired methicillin-resistant Staphylococcus aureus (MRSA), β-hemolytic streptococci, penicillin-resistant Streptococcus pneumoniae, Haemophilus influenzae, and Legionella. In this work, the mechanism of action for omadacycline was further elucidated using a variety of models. Functional assays demonstrated that omadacycline is active against strains expressing the two main forms of tetracycline resistance (efflux and ribosomal protection). Macromolecular synthesis experiments confirmed that the primary effect of omadacycline is on bacterial protein synthesis, inhibiting protein synthesis with a potency greater than that of tetracycline. Biophysical studies with isolated ribosomes confirmed that the binding site for omadacycline is similar to that for tetracycline. In addition, unlike tetracycline, omadacycline is active in vitro in the presence of the ribosomal protection protein Tet(O).     

Mechanism of Action of 5-Nitrothiophenes against Mycobacterium tuberculosis

On using the streptomycin-starved 18b strain as a model for nonreplicating Mycobacterium tuberculosis, we identified a 5-nitrothiophene compound as highly active but not cytotoxic. Mutants resistant to 5-nitrothiophenes were found be cross-resistant to the nitroimidazole PA-824 and unable to produce the F₄₂₀ cofactor. Furthermore, 5-nitrothiophenes were shown to be activated by the F₄₂₀-dependent nitroreductase Ddn and to release nitric oxide, a mechanism of action identical to that described for nitroimidazoles.     

Mechanism of Action of Colchicine in the Treatment of Gout

Purpose

The aims of this article were to systematically review the literature about the mechanism of action of colchicine in the multimodal pathology of acute inflammation associated with gout and to consider the clinical utility of colchicine in other chronic inflammatory diseases.

Methods

The English-language literature on PubMed was searched for articles published between 1990 and October 2013, with a cross-reference to citations across all years. Relevant articles pertaining to the mechanism of action of colchicine and the clinical applications of colchicine in gout and other inflammatory conditions were identified and reviewed.

Findings

The molecular pathology of acute inflammation associated with gouty arthritis involves several concurrent pathways triggered by a variety of interactions between monosodium urate crystals and the surface of cells. Colchicine modulates multiple pro- and antiinflammatory pathways associated with gouty arthritis. Colchicine prevents microtubule assembly and thereby disrupts inflammasome activation, microtubule-based inflammatory cell chemotaxis, generation of leukotrienes and cytokines, and phagocytosis. Many of these cellular processes can be found in other diseases involving chronic inflammation. The multimodal mechanism of action of colchicine suggests potential efficacy of colchicine in other comorbid conditions associated with gout, such as osteoarthritis and cardiovascular disease.

Implications

Colchicine has multiple mechanisms of action that affect inflammatory processes and result in its utility for treating and preventing acute gout flare. Other chronic inflammatory diseases that invoke these molecular pathways may represent new therapeutic applications for colchicine.     

Mechanism of Action of EM 49, Membrane-Active Peptide Antibiotic

EM 49 (recently renamed octapeptin) is a membrane-active peptide antibiotic that has been reported to affect the structure of bacterial membranes (K. S. Rosenthal, P. E. Swanson, and D. R. Storm, Biochemistry 15:5783–5792, 1976). In this study, it is shown that the effects of EM 49 on bacterial metabolism are similar to those of uncouplers of oxidative phosphorylation. EM 49 stimulated bacterial respiration within a narrow concentration range corresponding to minimum inhibitory concentrations and inhibited respiration at concentrations comparable to minimum biocidal concentrations. In addition, the peptide increased membrane proton permeability and lowered the adenosine 5′-triphosphate pool size. Parallel studies done with the related antibiotic polymyxin B demonstrated that the two peptides differed considerably in their effects on bacterial respiration. In contrast to EM 49, polymyxin B did not stimulate respiration at any concentration. It is proposed that the primary action of EM 49 is to disrupt the selective ion permeability of the cytoplasmic membrane, thereby relaxing the membrane potential.     

Phosphonopeptides as Antibacterial Agents: Mechanism of Action of Alaphosphin

The novel antibacterial peptide mimetic alaphosphin (l-alanyl-l-1-aminoethylphosphonic acid) selectively inhibited peptidoglycan biosynthesis in both gram-negative and gram-positive bacteria. It induced accumulation of uridine diphosphate-N-acetyl-muramyl-tripeptide in gram-positive organisms and significantly reduced the intracellular pool levels of d-alanine. Alaphosphin was actively transported into bacterial cells by stereospecific peptide permeases and was subsequently hydrolyzed by intracellular aminopeptidases to yield l-1-aminoethylphosphonic acid. This alanine mimetic rapidly accumulated inside susceptible cells to yield a concentration which was 100- to 1,000-fold in excess of that of the precursor peptide in the surrounding medium. In the case of susceptible gram-negative organisms, it was shown that 1-aminoethylphosphonic acid was incorporated into a metabolite which was tentatively identified as uridine diphosphate-N-acetylmuramyl-aminoethylphosphonate. The primary intracellular target site of 1-aminoethylphosphonic acid was alanine racemase (EC 5.1.1.1), which was reversibly and competitively inhibited in the gram-negative organisms Escherichia coli and Pseudomonas aeruginosa and irreversibly inhibited in a time-dependent manner in the gram-positive organisms Staphylococcus aureus and Streptococcus faecalis. A secondary target site could be uridine diphosphate-N-acetylmuramyl-l-alanine synthetase [EC 6.3.2.8(b)]. The mechanism of action of alaphosphin may be regarded as involving at least three stages: (i) active transport by peptide permeases; (ii) intracellular peptidase cleavage; and (iii) action of l-1-aminoethylphosphonate on alanine racemase.     

Mechanism of Action of Colchicine in Acute Urate Crystal-Induced Arthritis

Phagocytosis of urate crystals by human or rabbit neutrophils induces the synthesis and release of a glycoprotein, the crystal-induced chemotactic factor (CCF), which is chemotactically active both in vitro and in vivo. It has been proposed that CCF is a prime mediator of the acute gouty attack. Colchicine has been shown to decrease the production and release of this factor in vitro. In these studies, colchicine, at nonleukopenic doses, is shown to abrogate the acute arthritis induced by monosodium urate crystals in rabbits, but to have no effect upon the arthritis induced by the injection of the purified cell-derived chemotactic factor. Serum colchicine levels were 0.48-0.58 muM at 30 min and 0.12-0.3 muM at 90 min after intravenous injection of 0.2 mg/kg colchicine. Peripheral blood polymorphonuclear leukocytes obtained from colchicine-treated animals migrated normally towards a chemotactic stimulus but failed to produce CCF after phagocytosis of monosodium urate crystals. The dialyzed synovial fluid from rabbits injected with microcrystalline sodium urate contained chemotactic activity that was not present when animals were also given intravenous colchicine or injected intra-articularly with the chemotactic factor formyl-methionyl-leucyl-phenylalanine. Furthermore, the synovial fluid from rabbits injected with microcrystalline sodium urate significantly decreased (125)I-CCF binding to neutrophils. The binding of (125)I-CCF to its neutrophil receptor was not significantly reduced by the synovial fluid of colchicine-treated rabbits nor by the synovial fluid of control rabbits injected with the chemotactic factor formyl-methionyl-leucyl-phenylalanine. Colchicine (10 and 0.1 muM) was shown to have no effect upon the binding of (125)I-CCF to its cell receptor.     

犬尿喹啉酸在肠易激综合征中的作用机制

肠易激综合征(irritable bowel syndrome,IBS) 是一种常见的肠道功能紊乱性疾病,以持续或间歇性腹痛及排便习惯改变为主要临床表现,常伴有焦虑、抑郁等精神症状,严重影响患者生活质量。目前,IBS的病因及发病机制尚不明确,现有研究表明IBS是由内脏感觉异常、肠道感染与炎症反应、肠道菌群失调、社会心理等多种因素共同作用的结果。近期研究表明IBS患者中存在肠道菌群-犬尿氨酸(kynurenine, KYN)代谢紊乱,且KYN代谢产物犬尿喹啉酸(kynurenic acid,KA)与炎症反应、疼痛刺激及心理症状相关,在IBS中可能起到抗炎、缓解疼痛等保护性作用,有望成为诊断和治疗IBS的新方法。本文就KYN代谢途径及其代谢产物KA在IBS中的作用机制作一综述,以期为临床相关专业人员提供参考和借鉴。     

Mechanism of Action for Respiratory Syncytial Virus Inhibitor RSV604

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infections in young children and other high-risk populations. RSV nucleoprotein (N) is essential for virus assembly and replication as part of the viral ribonucleoprotein (RNP) complex. RSV604 was a putative N inhibitor in phase 2 clinical trials whose molecular mechanism of action (MoA) was not well understood. This study investigated the cell line-dependent potency of RSV604 and demonstrated its direct binding to the N protein in vitro, providing the first evidence of direct target engagement for this class of inhibitors reported to date. The affinity of RSV604 N binding was not affected by RSV604 resistance mutations in the N protein. RSV604 engaged in two different MoAs in HeLa cells, inhibiting both RSV RNA synthesis and the infectivity of released virus. The lack of inhibition of viral RNA synthesis in some cell lines explained the cell-type-dependent potency of the inhibitor. RSV604 did not inhibit viral RNA synthesis in the RSV subgenomic replicon cells or in the cell-free RNP assay, suggesting that it might act prior to viral replication complex formation. RSV604 did not alter N protein localization in the infected cells. Taken together, these results provide new insights leading to an understanding of the MoAs of RSV604 and other similar N inhibitors.