Determining the mode of action of anti-mycobacterial C17 diyne natural products using expression profiling: evidence for fatty acid biosynthesis inhibition.

BACKGROUND: The treatment of microbial infections is becoming increasingly challenging because of limited therapeutic options and the growing number of pathogenic strains that are resistant to current antibiotics. There is an urgent need to identify molecules with novel modes of action to facilitate the development of new and more effective therapeutic agents. The anti-mycobacterial activity of the C17 diyne natural products falcarinol and panaxydol has been described previously; however, their mode of action remains largely undetermined in microbes. Gene expression profiling was therefore used to determine the transcriptomic response of Mycobacterium smegmatis upon treatment with falcarinol and panaxydol to better characterize the mode of action of these C17 diynes. RESULTS: Our analyses identified 704 and 907 transcripts that were differentially expressed in M. smegmatis after treatment with falcarinol and panaxydol respectively. Principal component analysis suggested that the C17 diynes exhibit a mode of action that is distinct to commonly used antimycobacterial drugs. Functional enrichment analysis and pathway enrichment analysis revealed that cell processes such as ectoine biosynthesis and cyclopropane-fatty-acyl-phospholipid synthesis were responsive to falcarinol and panaxydol treatment at the transcriptome level in M. smegmatis. The modes of action of the two C17 diynes were also predicted through Prediction of Activity Spectra of Substances (PASS). Based upon convergence of these three independent analyses, we hypothesize that the C17 diynes inhibit fatty acid biosynthesis, specifically phospholipid synthesis, in mycobacteria. CONCLUSION: Based on transcriptomic responses, it is suggested that the C17 diynes act differently than other anti-mycobacterial compounds in M. smegmatis, and do so by inhibiting phospholipid biosynthesis.

c-Src-mediated activation of Erk1/2 is a reaction of epithelial cells to carbon nanoparticle treatment and may be a target for a molecular preventive strategy.

Owing to their specific physico/chemical properties, engineered as well as environmental nanoparticles can induce pathogenic endpoints in humans. Earlier studies demonstrated that pure carbon nanoparticles induce cell signaling events at the level of membrane receptor activation in lung epithelial cells. As a possible link between receptor activation and subsequent MAP-kinase signaling, the involvement of Src family kinases was investigated in cell lines of organs potentially exposed to environmental nanoparticles. Human cells from bronchus, intestine, and skin (keratinocytes) as well as rat lung epithelial cells showed similar time patterns for the activation of mitogen-activated protein kinases Erk1/2 as well as Src family kinases (SFK) when treated with carbon nanoparticles. Moreover, c-Src was identified as an integral part of the signaling mediating the transfer of information from membrane receptors to members of the proliferative signaling cascade in lung epithelial cells. Pretreatment of cells with the compatible solute ectoine, which is known to stabilize macromolecules, reduced the nanoparticle specific phosphorylation of SFK. Together with earlier in vivo and in vitro data, this demonstrates that compatible solutes prevent nanoparticle-induced signaling steps at the level of membrane-coupled signaling.

Growth and dissemination of a newly-established murine B-cell lymphoma cell line is inhibited by multimeric YIGSR peptide.

B-cell lymphoma frequently shows simultaneous dissemination to multiple organs. It also occasionally involves bone and causes osteolytic lesions. To study the mechanisms responsible for this capacity of lymphoma cells to grow in different tissue microenvironments and search for effective therapeutic interventions for this hematological malignancy, we established a new murine B-cell lymphoma cell line named MH-95. The tumor disseminated to multiple organs including the lung, liver, kidney, spleen and lymph nodes within 2 weeks after subcutaneous inoculation in nude mice. In addition, the tumor also grew in bone and caused osteoclastic osteolytic lesions. Thus, this tumor model mimics the behavior in many ways of B-cell lymphoma in humans. We studied the role of laminin, a major component of the basement membrane, in this model, since although it has been implicated in solid tumor metastasis, little is known about the involvement of laminin in the growth of B-cell lymphoma in bone and other organs. Immunohistochemical examination showed strong laminin expression in the stroma of the primary subcutaneous tumor and tumors in the bone and other organs. Systemic administration of the antagonistic laminin peptide YIGSR decreased primary tumor growth and tumor cell deposit in the bone, liver and kidney. In addition, the peptide also decreased apparent neovascularization in the tumor, suggesting that the peptide suppressed angiogenesis presumably due to inhibition of laminin binding to its receptors. These results demonstrate that the MH-95 B-cell lymphoma cells express laminin and suggest that laminin plays a critical role in the growth and simultaneous dissemination of tumor cells to multiple organs, similar to what has been described in solid tumors. The results also suggest that suppression of angiogenesis through interfering with laminin actions may be a useful adjuvant therapy for B-cell lymphoma.

[Protective effect of tetrandrine on neuronal injury in cultured cortical neurons of rats].

The ability of tetrandrine (Tet), as a Ca2+ antagonist isolated from a traditional Chinese herb, to reduce cortical neuronal injury was quantitatively examined in cell cultures derived from fetal rats by measurement of lactate dehydrogenase (LDH) released to the extracellular bathing media. Cell cultures exposed to excitotoxins-glutamate (Glu), N-methyl-D-aspartate (NMDA), beta-N-oxalylamino-L-alanine(BOAA, on non-NMDA receptors) and beta-N-methylamino-L-alanine(BMAA, on NMDA receptors)-for 24 h showed widespread neuronal injury, which was substantially attenuated by addition of Tet 10(-7)-10(-6) mol.L-1 except to NMDA. Tet failed to protect neurons against NMDA. These results suggest that Tet has protective effect on fetal rat cortical neuronal injury induced by some excitotoxins in vitro. The mechanism of action was hypothesized that opening of Ca2+ channel in cellular membrane would not happen, because of inhibition of Na+ influx and membrane depolarization induced by Tet. As a result, cytosolic free Ca2+ overload and then neuroal injury were prevented or lightened.

Beta-N-methylamino-L-alanine in the presence of bicarbonate is an agonist at non-N-methyl-D-aspartate-type receptors.

Beta-N-Methylamino-L-alanine, a component of the neurotoxic Cycas circinalis plant, activates an ionic current which is antagonized by extracellular Ca2+ but not by the excitatory amino acid receptor antagonists D,L-2-amino-5-phosphonovalerate (10-100 microM) or 6-cyano-7-nitroquinoxaline-2,3-dione (1-10 microM). This current was reduced by 50% in 0.5 mM extracellular Ca2+ and 92% in 3.0 mM Ca2+ when compared to those recorded in 0.1 mM Ca2+. Addition of 10 or 20 mM NaHCO3 to beta-N-methylamino-L-alanine (500 microM) potentiated the currents 224% and 578%, respectively. Addition of NaHCO3 to the extracellular Ringers (pH 7.2) shifted the pH to 7.7 (10 mM) or 8.3 (20 mM). beta-N-Methylamino-L-alanine was potentiated by NaHCO3 at pH 7.2, 7.7 and 8.3, but the potentiation with NaHCO3 (20 mM) was larger at pH 8.3 (5.7-fold) compared to pH 7.2 (3-fold). NaHCO3 (20 mM) had no effect on quisqualate-, N-methyl-D-aspartate- or kainate-activated ionic currents. The beta-N-methylamino-L-alanine-NaHCO3-activated currents were reduced 49% by 1 microM and 80% by 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione suggesting an agonist action at non-N-methyl-D-aspartate-type receptors. Activity at N-methyl-D-aspartate receptors is unlikely since the beta-N-methylamino-L-alanine-NaHCO3 currents are not antagonized by D,L-2-amino-5-phosphonovalerate (10-100 microM), potentiated by addition of glycine (10 microM) or blocked by extracellular Mg2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific antagonism of excitotoxic action of 'uncommon' amino acids assayed in organotypic mouse cortical cultures.

Beta-N-Methylamino-L-alanine (BMAA) and beta-N-oxalylamino-L-alanine (BOAA) are chemically related excitant amino acids present in the seeds of Cycas circinalis and Lathyrus sativus, respectively. Consumption of these seeds has been linked to Guam amyotrophic lateral sclerosis (BMAA) and lathyrism (BOAA) (a form of primary lateral sclerosis). We report that the acute neuronotoxic actions of these amino acids are blocked selectively by specific glutamate receptor antagonists. Administration of BOAA and BMAA to neonatal mouse cortex explants (EC100 = 28 microM and 1.6 mM, respectively) rapidly induces postsynaptic vacuolation (PSV) and neuronal degeneration characterized by dark/shrunken (D/S) cells. BOAA-mediated neuronotoxic effects are attenuated in a concentration-dependent manner by cis-2,3-piperidine dicarboxylic acid (PDA), an antagonist of quisqualate (QA)-preferring and kainate (KA)-preferring glutamate receptors. PDA maximally protected against BOAA-induced PSV by 84% at 1 mM and D/S cells by 80% at 0.5 mM. BMAA-induced cellular changes were antagonized selectively in a concentration-dependent manner by 2-amino-7-phosphono-heptanoic acid (AP7), an N-methyl-D-aspartate (NMDA) glutamate-receptor antagonist. AP7 maximally protected against BMAA-induced PSV and D/S by 88% at 1.0 and 0.5 mM, respectively. These protective actions were selective and specific since AP7 failed to attenuate BOAA-induced alterations, and PDA was ineffective in ameliorating BMAA-induced changes. Other glutamate receptor antagonists (glutamic diethyl ester and streptomycin) failed to protect the explants from the destructive action of either toxin. Taken collectively, our data indicate that the acute neuronotoxic actions of BOAA and BMAA (or a metabolite) operate through different glutamate receptor species.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptides of 2-aminopimelic acid: antibacterial agents that inhibit diaminopimelic acid biosynthesis.

Succinyl-CoA:tetrahydrodipicolinate-N-succinyltransferase is a key enzyme in the biosynthesis of diaminopimelic acid (DAP), a component of the cell wall peptidoglycan of nearly all bacteria. This enzyme converts the cyclic precursor tetrahydrodipicolinic acid (THDPA) to a succinylated acyclic product. L-2-Aminopimelic acid (L-1), an acyclic analogue of THDPA, was found to be a good substrate for this enzyme and was shown to cause a buildup of THDPA in a cell-free enzyme system but was devoid of antibacterial activity. Incorporation of 1 into a di- or tripeptide yielded derivatives that exhibited antibacterial activity against a range of Gram-negative organisms. Of the five peptide derivatives tested, (L-2-aminopimelyl)-L-alanine (6) was the most potent. These peptides were shown to inhibit DAP production in intact resting cells. High levels (30 mM) of 2-aminopimelic acid were achieved in the cytoplasm of bacteria as a result of efficient uptake of the peptide derivatives through specific peptide transport systems followed, presumably, by cleavage by intracellular peptidases. Finally, the antibacterial activity of these peptides could be reversed by DAP or a DAP-containing peptide. These results demonstrate that the peptides containing L-2-aminopimelic acid exert their antibacterial action by inhibition of diaminopimelic acid biosynthesis.

Lathyrus excitotoxin: mechanism of neuronal excitation by L-2-oxalylamino-3-amino- and L-3-oxalylamino-2-amino-propionic acid.

Intracellular recordings were made in cultured neurones from foetal mouse spinal cord. The effects of applications of the neurotoxin, L-3-oxalylamino-2-amino-propionic acid (a constituent of the chickling pea, Lathyrus sativus) and its 2-oxalylamino isomer on membrane potential and conductance were examined in the presence of TTX and TEA and compared to those of other excitatory amino acids. Although both compounds produced membrane depolarization and an increase in input conductance, the 3-oxalylamino isomer (beta-ODAP) was approximately equal to 10 times more potent than the 2-oxalylamino isomer (alpha-ODAP). beta-ODAP caused a voltage-independent change in conductance, as compared to an apparent voltage-dependent decrease produced in the same neurons by L-aspartic acid (L-ASP). Although reversal potentials determined for beta-ODAP resembled those for alpha-ODAP and kainic acid, they were consistently and significantly lower than the reversal level for L-ASP. Although the receptor antagonist 2-amino-5-phosphonovaleric acid (APV) and the divalent cation Cd2+ did not alter the conductance increase evoked by beta-ODAP, they markedly depressed responses to L-ASP. Such differences suggest a mechanism of excitatory action for the neurotoxin, beta-ODAP, which does not involve a Ca2+-dependent mechanism and is quite different from that for L-ASP and N-methyl-D-aspartic acid, but similar to that of kainic and quisqualic acids.(ABSTRACT TRUNCATED AT 250 WORDS)