SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A series of xanthone 1,4-dihydropyridine derivatives bearing a 2,3-lactone ring and a 2-acetoxymethyl group were prepared. The compounds were evaluated for inotropic, chronotropic and calcium antagonist properties. The introduction of a 2,3-lactone ring improved the negative inotropic activity and selectivity.
Ten male Wistar rats were divided into two groups. The experimental rats were injected with subconvulsive dosage of coriaria lactone (1 mg/kg) intramuscularly every 3.5 days to induce kindling seizures. The controls were injected with normal saline. Cerebral motor cortex of kindling rats was taken at the time between seizures and layer V was compared morphologically with that of the control. The number of neurons and neuroglias was counted from light micrographs. The numerical density and length fraction of boutons on the surface of pyramidal somata were measured from electron micrographs with MIAS 300 type image analyser. The number of synapses in neuropil was counted directly and the areal fraction of various constitute in neuropil was measured stereologically from EM photos. In the experimental rats, the number of neurons remained unchanged and the numerical density and length fraction of boutons on the surface of pyramidal somata showed no change, either. The number of synapses (or presynaptic terminals) decreased significantly in neuropil, but the areal fraction of synaptic terminals had no change and the areal fraction of dendrites and unmyelinated fibers decreased. The areal fraction of myelinated fibers increased significantly. The number of neuroglias and the areal fraction of neuroglial processes increased significantly in the experimental rats. The data suggest that the major morphological changes are manifested as a decline in the pyramidal dendritic components, especially dendritic spines, and the axons with its terminals from superficial neurons in motor cortex layer V of the kindling rats induced by coriaria lactone, besides the neurogliosis which is similar to that occurring in other long-term seizures.
Many plants and flowers can cause dermatitis in florists, growers, and others working in the industry. In the United States, Alstromeria, also called Peruvian Lily, has frequently been reported to cause hand eczema in floral workers. This interesting report details sesquiterpene lactone allergy in the occupational setting. Fortunately, in this case, it seems that resolution of the dermatitis was achieved fairly rapidly by avoiding the occupational situation. Unfortunately, for many of our patients with airborne compositae dermatitis, there is no way to avoid the allergen; therefore, many of these individuals develop severe, chronic recalcitrant dermatitis requiring aggressive therapy. Diagnosis of this condition is not always easy, as it appears that the sesquiterpene lactone mix allergen that we have commercially available misses a number of cases, at least in the United States. Better characterization of the allergens involved and better supply of allergenic extracts for testing is critical to improve our diagnostic ability.
A quantitative, specific, and sensitive method for the determination of N-acylhomoserine lactones (HSLs - a group of bacterial semiochemicals) in the form of their hydrolysis products (N-acylhomoserines, HSs) is presented. Real samples were analyzed by capillary zone electrophoresis-mass spectrometry (CZE-MS) after alkaline lactonolysis and extraction by mixed-mode anion-exchange solid-phase extraction. The presented cleanup significantly speeds up the HSL extraction procedure, strongly reduces sample consumption, and is more selective compared to the commonly used liquid/liquid extraction. Completeness of the hydrolysis reaction was examined by nuclear magnetic resonance spectroscopy. This CZE-MS method complements recently published capillary separation techniques (nano liquid chromatography-MS, partial-filling micellar electrokinetic chromatography-MS, gas chromatography-MS) and provides a possibility to differentiate quantitatively between the homoserines (as naturally occurring degradation products) besides the intact homoserine lactones. The method was found to be quantitative down to a concentration of 0.05 microg/mL (limit of quantification), while the limit of detection was determined with 0.01 microg/mL - sufficient for the analysis of culture supernatants.
GD3 is the ganglioside most abundantly expressed on the cell surface of human melanoma, and treatment with a murine MAb recognizing GD3 has induced major responses in a small proportion of patients with melanoma. We have therefore attempted to induce production of GD3 antibodies in melanoma patients by active immunization. We found, however, that vaccination with GD3-expressing melanoma cells or purified GD3 does not result in antibody production. We describe here attempts to overcome the poor immunogenicity of GD3 in patients with melanoma by chemical modification. GD3 lactones, GD3 amide and GD3 gangliosidol were synthesized, and the humoral immune response to these derivatives was analyzed. Immunization of melanoma patients with these GD3 derivatives resulted in production of IgM antibodies and, in the case of GD3 amide, also of IgG antibodies. The antibodies to the GD3 derivatives did not cross-react with GD3. This is in contrast to observations in the mouse, where GD3 lactone I induced antibodies that showed cross-reactivity with GD3. Thus, the human immune response was specifically directed toward the modified epitope, rather than to the native structure.
The determination of the absolute configuration of chiral molecules is an important aspect of molecular stereochemistry. Vibrational circular dichroism (VCD) is the extension of electronic CD into the infrared region where fundamental vibrational transitions occur. VCD has a number of advantages over all previous methods of absolute configuration assignment. The absolute configuration and predominant solution-state conformation in CDCl(3) of the chiral lactone, 5-formyl-cis,cis-1,3,5-trimethyl-3-hydroxymethylcyclohexane-1-carboxylic acid lactone, 1, obtained by the comparison of measured and calculated VCD spectra, are reported. It is found that (-)-1 corresponds to the absolute configuration (1S,3S,5R)-1.
In our previous studies (Refs. 1 and 2), it was shown that protein tyrosine kinase (PTK) inhibitors, radicicol and herbimycin A, inhibit the expression of the mitogen-inducible cyclooxygenase (COX-2) and proinflammatory cytokines. Radicicol and herbimycin A possess polarized double bonds which can conjugate sulphydryl groups of proteins. Parthenolide, the predominant sesquiterpene lactone in European feverfew (Tanacetum parthenium), contains alpha-methylene-gamma-lactone (MGL) and an epoxide in its structure. These moieties can interact with biological nucleophiles such as a sulfhydryl group. Parthenolide inhibited the expression of COX-2 and proinflammatory cytokines (TNF alpha and IL-1) in lipopolysaccharide (LPS)-stimulated macrophages. The structure-function relationship indicates that the MGL moiety confers the inhibitory effect. Parthenolide suppressed LPS-stimulated protein tyrosine phosphorylation in the murine macrophage cell line (RAW 264.7). This suppression was correlated with its inhibitory effect on the expression of COX-2 and the cytokines. Among tyrosine phosphorylated proteins, mitogen-activated protein kinases (MAPKs) exhibited the most dramatic inhibition.
The aerobic bacterial degradation of chloroaromatic compounds often involves chlorosubstituted catechols as central intermediates. They are converted to 3-oxoadipate in a series of reactions similar to that for catechol catabolism and therefore designated as modified ortho-cleavage pathway. Among the enzymes of this catabolic route, the chlorocatechol 1,2-dioxygenases are known to have a relaxed substrate specificity. In contrast, several chloromuconate cycloisomerases are more specific, and the dienelactone hydrolases of chlorocatechol catabolic pathways do not even convert the corresponding intermediate of catechol degradation, 3-oxoadipate enol-lactone. While the sequences of chlorocatechol 1,2-dioxygenases and chloromuconate cycloisomerases are very similar to those of catechol 1,2-dioxygenases and muconate cycloisomerases, respectively, the relationship between dienelactone hydrolases and 3-oxoadipate enol-lactone hydrolases is more distant. They seem to share an alpha/beta hydrolase fold, but the sequences comprising the fold are quite dissimilar. Therefore, for chlorocatechol catabolism, dienelactone hydrolases might have been recruited from some other, preexisting pathway. Their relationship to dienelactone (hydrolases identified in 4-fluorobenzoate utilizing strains of Alcaligenes and Burkholderia (Pseudomonas) cepacia is investigated). Sequence evidence suggests that the chlorocatechol catabolic operons of the plasmids pJP4, pAC27, and pP51 have been derived from a common precursor. The latter seems to have evolved for the purpose of halocatechol catabolism, and may be considerably older than the chemical industry.
Molecular modelling of brefeldin A and its derivatives shows that the presence of a rigid and planar lactone ring conformation is necessary for cytotoxic and anti-fungal activity. Cytotoxic compounds had lactone ring torsion angles of -28.77 +/- 6.13 degrees, while non-cytotoxic compounds had torsion angles of -88.25 +/- 14.6 degrees.
Homoserine lactone (HSL) is a ubiquitous product of metabolism. It is generated by all known biota during the editing of certain mischarged aminoacyl-tRNA reactions, and is also released as a product of quorum signal degradation by bacterial species expressing acyl-HSL acylases. Little is known about its environmental fate over long or short periods of time. The mammalian enzyme paraoxonase, which has no known homologs in bacteria, has been reported to degrade HSL via a lactonase mechanism. Certain strains of Variovorax and Arthrobacter utilize HSL as a sole source of nitrogen, but not as a sole source of carbon or energy. In this study, the enrichment and isolation of four strains of soil bacteria capable of utilizing HSL as a carbon and energy source are described. Phylogenetic analysis of these isolates indicates that three are distinct members of the genus Arthrobacter, whereas the fourth clusters within the non-clinical Burkholderia. The optimal pH for growth of the isolates ranged from 6.0 to 6.5, at which their HSL-dependent doubling times ranged from 1.4 to 4 h. The biodegradation of HSL by these 4 isolates far outpaced its chemical decay. HSL degradation by soil bacteria has implications for the consortial mineralization of acyl-homoserine lactones by bacteria associated with quorum sensing populations.
N-Acylated homoserine lactones (AHLs) are produced by Gram-negative bacteria as communication signals and are frequently studied as mediators of the "quorum sensing" response of bacterial communities. Several reports have recently been published on the identification of AHLs from different species and attempts have been made to study their role in natural habitats, for example the surface of plant roots in the rhizosphere. In this article, different analytical methods, including bacterial biosensors and chromatographic techniques, are reviewed. A concept for assignment of the structures of AHLs is also presented. The retention behaviour of derivatives of AHLs containing beta-keto or hydroxyl groups and/or double bonds has been evaluated in relation to the separation behaviour of AHLs with saturated and unsubstituted alkanoyl chains. Samples have also been analysed by high resolution mass spectrometry (Fourier-transform ion-cyclotron-resonance mass spectrometry, FTICR-MS), nano liquid chromatography-electrospray ionization ion trap mass spectrometry (nano-LC-MS) and by the aid of a biosensor. The results obtained from ultra performance liquid chromatography (UPLC), FTICR-MS, nano-LC-MS, and bioassays have been compared to attempt structural characterisation of AHL without chemical synthesis of analytical standards. The method was used to identify the major AHL compound produced by the rhizosphere bacterium Acidovorax sp. N35 as N-(3-hydroxydecanoyl)homoserine lactone.
Quorum sensing enables bacteria to regulate expression of certain genes according to population density. N-acyl homoserine lactone (AHL)-based quorum sensing is known to be widespread among gram-negative bacteria. Several bacterial whole-cell biosensors for AHL detection have been developed and some were used in in situ studies of AHL production. From these studies our knowledge of the significance of quorum sensing in various environments has been improved. However, very little is known about production of AHLs in soil environments. In the present study, an approach for detecting AHL production in bulk soil was developed. A whole-cell biosensor based on the regulatory region of the lux-operon from Vibrio fischeri fused to gfp was constructed, resulting in a luxR-PluxI-gfpmut3*-fusion in the high copy plasmid, pAHL-GFP. Escherichia coli MC4100 harboring pAHL-GFP responded to the AHL-compound N-octanoyl homoserine lactone (OHL) by expressing green fluorescence. In situ application of E. coli MC4100/pAHL-GFP was tested by adding OHL in different concentrations to sterile soil microcosms. E. coli MC4100/pAHL-GFP were incubated in the soil microcosms and extracted by an improved Nycodenz-extraction method optimized for flow cytometry. The presence of induced cells was then verified by single-cell analysis by flow cytometry. OHL concentrations between 0.5 and 50 nmol per g soil were detected. When introducing the AHL-producing Serratia liquefaciens to soil microcosms, expression of green fluorescent protein was induced in E. coli MC4100/pAHL-GFP. Thereby, the ability of this strain to detect excretion of AHLs by S. liquefaciens in sterile soil was shown. The use of an improved extraction method and a whole-cell biosensor combined with flow cytometry analysis proved to be promising tools in future studies of AHL production by microbial populations in soil environments.
A method is described which is suitable for protection of all free hydroxyl groups of a glycosphingolipid under conditions which will not cleave ester linkages, including inner ester linkages characteristic of ganglioside lactones. The protecting methoxyethoxymethyl group is stable in alkaline media, surviving permethylation procedures which introduce a methyl ether at all sites previously acylated. Hydrolysis, reduction, and acetylation then yield alditol acetate derivatives which can be analyzed by conventional GC-MS to locate the methyl ether groups. The method is used to locate the inner esterification site of GM3 lactone.
alpha-Methylene-gamma-butyrolactone (MBL), which can be described as the cyclic analog of methyl methacrylate, exhibits greater reactivity in free radical polymerizations than conventional methacrylate monomers. Unfilled resin formulations composed of Bis-GMA/MBL or Bis-GMA/TEGDMA/MBL were light-cured. The effect of the more reactive methylene lactone monomer on mechanical properties and the degree of conversion of the polymers was examined. The infrared absorption bands for the carbon-carbon double bonds of MBL and the methacrylate monomers are well resolved and allow the conversion of each component to be calculated individually. The incorporation of a small amount of MBL (5 w/o) to Bis-GMA significantly increased the conversion; however, additional MBL (10 to 30 w/o) did not further increase the Bis-GMA conversion level. This appears to indicate an incompatibility between MBL and the bulky Bis-GMA monomer. Addition of 10 w/o MBL to Bis-GMA/TEGDMA (7:3) resulted in a cured resin with 71% methacrylate and 75% overall conversion efficiencies compared with the 57% conversion of the control formulation. The diametral tensile and the transverse strengths were approximately 10% greater for the MBL resin compared with the Bis-GMA/TEGDMA control; however, these differences were not statistically significant. The synthesis and polymerization of several substituted methylene lactones was also studied.
As a primary antioxidant, ascorbic acid (AA) provides beneficial effects for vascular health mitigating oxidative stress and endothelial dysfunction. However, the association of intracellular AA with NO production occurring inside the endothelial cells remains unclear. In the present study, we addressed this issue by increasing intracellular AA directly through de novo synthesis. To restore AA synthesis pathway, bovine aortic endothelial cells were transfected with the plasmid vector encoding L-gulono-1,4-lactone oxidase (GULO, EC 1.1.3.8), the missing enzyme converting L-gulono-1,4-lactone (GUL) to AA. Functional expression of GULO was verified by Western blotting and in vitro enzyme activity assay. GULO expression alone did not lead to AA synthesis but the supply of GUL resulted in a marked increase of intracellular AA. When the cells were stimulated with calcium ionophore, A23187, NO production was more active in the GULO-expressing cells supplied with GUL, in comparison with the cells without GULO expression or without GUL supply, indicating that intracellular AA regulated NO production. Enhancement of NO production by intracellular AA was further verified in aortic endothelial cells obtained from eNOS knockout mice that were cotransfected with eNOS and GULO constructs. GULO-dependent AA synthesis also elevated intracellular tetrahydrobiopterin content, implicating that this essential cofactor of endothelial nitric oxide synthase (eNOS) might mediate the AA effect. The present study strongly suggests that intracellular AA plays critical roles in vascular physiology through enhancing endothelial NO production.
The mode of action of ivermectin (IVM) in nematodes appears to be the opening of inhibitory ion channels, including the glutamate-gated chloride channel (GluCl). Recently, it has been shown that IVM binds with high affinity to a Haemonchus contortus GluCl subunit (HcGluCla) expressed in COS-7 cells, and this binding is potentiated in the presence of glutamate. To gain further insight into the potentiation of macrocyclic lactone anthlemintics we have screened various glutamatergic and nonglutamatergic ligands for their ability to enhance [ 3H ] IVM binding to HcGluCla. Of the ligands tested, only glutamate and ibotenate potentiated [ 3H ] IVM binding. Interestingly, these ligands have also been shown to open the HcGluCla channel expressed in Xenopus oocytes. We examined the effect of ibotenate on macrocyclic lactone binding in more detail and found that it caused a 7-fold enhancement in [ 3H ] IVM binding affinity and a 4-fold increase in [ 3H ] MOX binding affinity. In in vivo efficacy studies, ibotenate (up to 2mg/kg) had no anthelmintic activity against H. contortus in gerbils. When 1mg/kg ibotenate was used in combination with IVM, IVM efficacy increased by 15% ( P=0.048 ). These results demonstrate that a GluCl agonist enhances IVM activity and provides further information on the mode of action of ivermectin in parasitic nematodes.
Pseudomonas aeruginosa is a gram-negative bacterium that causes serious illnesses, particularly in immunocompromised individuals, often with a fatal outcome. The finding that the acylated homoserine lactone quorum sensing (QS) system controls the production of virulence factors in P. aeruginosa makes this system a possible target for antimicrobial therapy. It has been suggested that an N-(3-oxododecanoyl)-homoserine lactone (3O-C12-HSL) antagonist, a QS blocker (QSB), would interfere efficiently with the quorum sensing system in P. aeruginosa and thus reduce the virulence of this pathogen. In this work, a mathematical model of the QS system in P. aeruginosa has been developed. The model was used to virtually add 3O-C12-HSL antagonists that differed in their affinity for the receptor protein and for their ability to mediate degradation of the receptor. The model suggests that very small differences in these parameters for different 3O-C12-HSL antagonists can greatly affect the success of QSB based inhibition of the QS system in P. aeruginosa. Most importantly, it is proposed that the ability of the 3O-C12-HSL antagonist to mediate degradation of LasR is the core parameter for successful QSB based inhibition of the QS system in P. aeruginosa. Finally, this study demonstrates that QSBs can shift the system to a low steady state, corresponding to an uninduced state and thus, suggests that the use of 3O-C12-HSL antagonists may constitute a promising therapeutic approach against P. aeruginosa involved infections.
In an effort to find novel semisynthetic macrolides with extended antibacterial spectrum and improved activity we prepared a series of compounds based on commercially available clarithromycin, a potent and safe antimicrobial agent of outstanding clinical and commercial interest. According to the literature, improvement of antibacterial activity of erythromycin type antibiotics can be achieved by introduction of fused heterocycles such as cyclic carbonates or carbamates at positions 11 and 12 (such as in telithromycin). In the course of the work presented here, a similar, hitherto unprecedented set of compounds bearing a five-membered lactone ring fused to positions 11 and 12 was prepared based on carbon-carbon bond formation via intramolecular Michael addition of a [(hetero)arylalkylthio]acetic acid ester enolate to an alpha,beta-unsaturated ketone as the key step. Some of the ketolide compounds described in this paper were highly active against a representative set of erythromycin sensitive and erythromycin resistant test strains. The best compound showed a similar antimicrobial spectrum and comparable activity in vitro as well as in vivo as telithromycin. Furthermore, some physicochemical properties of these compounds were determined and are presented here. On the basis of these results, the novel ketolide lactones presented in this paper emerged as valuable lead compounds with comparable properties as the commercial ketolide antibacterial telithromycin (Ketek).