Zinc inhibition of electron transfer: mechanism of beta receptor inhibition?

Zinc has been shown to inhibit β-receptor activation of adenylate cyclase at a post receptor site. We have postulated that the β-receptor is one of several receptors activated by reduction, followed by transmembrane elector transfer accelerated by GTP. GTP accelerates electron transfer in a model system and this accelerated electron transfer is inhibited by zinc. This could explain the mechanism of the post receptor inhibition by zinc of the adenylate cyclase stimulation which follows β-receptor activation.     

Growth inhibition of pathogenic yeast isolates by α-difluoromethylornithine: An inhibition of ornithine decarboxylase

A large body of evidence exists suggesting that polyamines can play essential roles in cellular growth and differentiation. We examined the ability of -difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, the major rate-limiting enzyme in polyamine biosynthesis, to inhibit the growth of Candida albicans, C. tropicalis, and C. parapsilosis. Substantial growth-inhibition was observed for all three species at DFMO concentrations ranging from 1 to 100 mM. C. tropicalis was significantly more susceptible to DFMO than C. albicans or C. parapsilosis. Depletion of cellular polyamine pools was seen in all 3 species following exposure to DFMO and polyamine depletion enhanced the susceptibility of the organisms to DFMO. The action of DFMO was specifically antagonized by exogenous polyamines. These data suggest that polyamines are important in the growth of Candida spp. and that inhibitors of polyamine biosynthesis may be useful as antifungal agents.     

Carnosine-synthetase inhibition by β-alanine analogues

A number of β-alanine analogues were tested for their ability to inhibit carnosine-synthetase from rat and chick skeletal muscle. Of the analogues tested, 3-aminopropanesulfonic acid (APS) was the most effective inhibitor of enzyme from either source. 5-Aminovaleric acid (5-AV) also inhibited the enzyme from rat, but did not inhibit the enzyme from chick. 2-Aminoethylphosphonic acid and o-phosphoethanolamine had a small amount of inhibitory activity on both rat and chick enzymes, while 3-aminopropanephosphonic acid, aminooxyacetic acid and nipecotic acid had a small amount of inhibitory activity on the rat enzyme only. None of the analogues tested acted as substrates for either enzyme under our conditions. Kinetic data indicated that the inhibition by APS was competitive with respect to β-alanine for both rat and chick enzymes. Inhibition of the rat enzyme by 5-AV was non-competitive with respect to β-alanine for both rat and chick enzymes. Inhibition of the rat enzyme by 5-AV was noncompetitive with respect to β-alanine. APS and 5-AV were also shown to inhibit carnosine-synthetase from rat brain and heart. Chronic injections of either APS or 5-AV failed to produce significant changes in carnosine levels in rat skeletal muscle or brain; however preliminary results indicate that APS injections may produce a lowering of carnosine levels in rat heart.     

TrxR1 inhibition overcomes both hypoxia-induced and acquired bortezomib resistance in multiple myeloma through NF-кβ inhibition

Multiple myeloma (MM) is a B-cell malignancy characterized by an accumulation of abnormal clonal plasma cells in the bone marrow. Introduction of the proteasome-inhibitor bortezomib has improved MM prognosis and survival; however hypoxia-induced or acquired bortezomib resistance remains a clinical problem. This study highlighted the role of thioredoxin reductase 1 (TrxR1) in the hypoxia-induced and acquired bortezomib resistance in MM. Higher TrxR1 gene expression correlated with high-risk disease, adverse overall survival, and poor prognosis in myeloma patients. We demonstrated that hypoxia induced bortezomib resistance in myeloma cells and increased TrxR1 protein levels. Inhibition of TrxR1 using auranofin overcame hypoxia-induced bortezomib resistance and restored the sensitivity of hypoxic-myeloma cells to bortezomib. Hypoxia increased NF-кβ subunit p65 nuclear protein levels and TrxR1 inhibition decreased hypoxia-induced NF-кβ p65 protein levels in the nucleus and reduced the expression of NF-кβ-regulated genes. In addition, higher TrxR1 protein levels were observed in bortezomib-resistant myeloma cells compared to the naïve cells, and its inhibition using either auranofin or TrxR1-specific siRNAs reversed bortezomib resistance. TrxR1 inhibition reduced p65 mRNA and protein expression in bortezomib-resistant myeloma cells, and also decreased the expression of NF-кβ-regulated anti-apoptotic and proliferative genes. Thus, TrxR1 inhibition overcomes both hypoxia-induced and acquired bortezomib resistance by inhibiting the NF-кβ signaling pathway. Our findings demonstrate that elevated TrxR1 levels correlate with the acquisition of bortezomib resistance in MM. We propose considering TrxR1-inhibiting drugs, such as auranofin, either for single agent or combination therapy to circumvent bortezomib-resistance and improve survival outcomes of MM patients.     

Does inhibition balance excitation in neocortex?

The distribution of inhibitory and excitatory synapses on neocortical neurons is at odds with a simple view that cortical functioning can persist by maintaining a balance between inhibitory and excitatory drives. Pyramidal cells can potentially be shut down by very powerful proximal inhibitory synapses, despite these accounting for perhaps less than 1% of their total number of synaptic inputs. Interneurons in contrast are dominated by excitatory inputs. These may be powerful enough to effect an apparent depolarizing block at the soma. In this extreme case though, models suggest that action potentials are generated down the axon, and the cells behave like integrate-and-fire neurons. We discuss possible network implications of these modelling studies.     

Contact inhibition of what? An analytical review

Quite a number of phenomena having to do with cells' influences upon one another's movements have come to be regarded as expressions of “contact inhibition.” However, no single, central mechanism has been shown to underlie them all. Consequently, the term “contact inhibition” should not be used without operational modifiers. Inhibitions of individual cell movements imputed to be mediated by cell-cell contacts include inhibition of overlapping (which results in monolayering), of colony expansion, of cell speed (nuclear translocation), of ruffling, of orthogonal movement (proposed to explain spontaneous parallel alignment of cells), and of neighbor exchanges. The six inhibitions listed above are operationally distinct, and only two (overlapping and colony expansion) are known to result from a common mechanism. A seventh phenomenon, so-called “contact inhibition of cell division” (more operationally termed postconfluence inhibition of cell division) is in a separate category and is not considered here. Evidence eliminating action-at-a-distance is available only for the first three, and hence only these should at present be termed contact inhibitions. Inhibition of neighbor exchanges is yet hypothetical; at its extreme, it would immobilize cells in a confluent monolayer, but such immobilization has been found not to occur. Contact inhibition of overlapping, the most studied of the six, is not displayed by invasive cells with respect to normal cells; invasive tumor cells overlap freely upon normal cells, although not necessarily upon one another. Contact inhibition of overlapping, and its loss by invasive cells, can readily be interpreted, by means of the differential adhesion hypothesis, as consequences of cell-type-specific differences in cell-cell and cell-substratum “strengths of adhesion.” These strengths of adhesion are formulated as specific interfacial free energies, which are the only parameters of cellular adhesiveness that have been rigorously shown to determine equilibrium configurations of cell populations.     

Cerebellar cortex: computation by extrasynaptic inhibition?

In the cerebellar cortex, inhibitory inputs to granule cells exhibit prominent tonic and spillover components resulting from the activation of extrasynaptic receptors. A recent study shows how extrasynaptic inhibition affects information flow through cerebellar cortex.     

How many carbonic anhydrase inhibition mechanisms exist?

Six genetic families of the enzyme carbonic anhydrase (CA, EC 4.2.1.1) were described to date. Inhibition of CAs has pharmacologic applications in the field of antiglaucoma, anticonvulsant, anticancer, and anti-infective agents. New classes of CA inhibitors (CAIs) were described in the last decade with enzyme inhibition mechanisms differing considerably from the classical inhibitors of the sulfonamide or anion type. Five different CA inhibition mechanisms are known: (i) the zinc binders coordinate to the catalytically crucial Zn(II) ion from the enzyme active site, with the metal in tetrahedral or trigonal bipyramidal geometries. Sulfonamides and their isosters, most anions, dithiocarbamates and their isosters, carboxylates, and hydroxamates bind in this way; (ii) inhibitors that anchor to the zinc-coordinated water molecule/hydroxide ion (phenols, carboxylates, polyamines, 2-thioxocoumarins, sulfocoumarins); (iii) inhibitors which occlude the entrance to the active site cavity (coumarins and their isosters), this binding site coinciding with that where CA activators bind; (iv) compounds which bind out of the active site cavity (a carboxylic acid derivative was seen to inhibit CA in this manner), and (v) compounds for which the inhibition mechanism is not known, among which the secondary/tertiary sulfonamides as well as imatinib/nilotinib are the most investigated examples. As CAIs are used clinically in many pathologies, with a sulfonamide inhibitor (SLC-0111) in Phase I clinical trials for the management of metastatic solid tumors, this review updates the recent findings in the field which may be useful for a structure-based drug design approach of more selective/potent modulators of the activity of these enzymes.     

Human tumour-induced inhibition of interferon action in vitro: Reversal of inhibition by β-carotene (pro-vitamin A)

Summary Inhibitors of human interferon action that might be relevant to tumour resistance or escape mechanisms were investigated in a macrophage system. The effects of IFN on macrophage Fc receptor expression were inhibited by three preparations: (1) a low-molecular-weight component of normal autologous serum; (2) a low-molecular-weight component of carcinoma supernatant; and (3) physiological concentrations of retinol and retinoic acid. Since human carcinoma tissue contains abnormally high levels of retinoic acid-binding protein, the possibility that a tumour-associated retinoid contributes to tumour-induced inhibition in vitro was investigated. Inhibition of IFN action in vitro by retinoic acid (vitamin A acid) was found to be reversed by -carotene (pro-vitamin A). When tested in the tumour system -carotene also reversed inhibition by the human-carcinoma-derived signal. These data are consistent with the view that at least one of the tumour-derived signals inhibitory towards IFN is a tumour-associated retinoid, although firm evidence for this must await further physicochemical characterization of the inhibitory signal(s). The present data clearly show, nevertheless, that human tumour-induced inhibition of IFN in vitro can be reversed by the pro-vitamin -carotene.     

Human tumour-induced inhibition of interferon action in vitro: Reversal of inhibition by β-carotene (pro-vitamin A)

Inhibitors of human interferon action that might be relevant to tumour resistance or escape mechanisms were investigated in a macrophage system. The effects of IFN on macrophage Fc gamma receptor expression were inhibited by three preparations: (1) a low-molecular-weight component of normal autologous serum; (2) a low-molecular-weight component of carcinoma supernatant; and (3) physiological concentrations of retinol and retinoic acid. Since human carcinoma tissue contains abnormally high levels of retinoic acid-binding protein, the possibility that a tumour-associated retinoid contributes to tumour-induced inhibition in vitro was investigated. Inhibition of IFN action in vitro by retinoic acid (vitamin A acid) was found to be reversed by beta-carotene (pro-vitamin A). When tested in the tumour system beta-carotene also reversed inhibition by the human-carcinoma-derived signal. These data are consistent with the view that at least one of the tumour-derived signals inhibitory towards IFN is a tumour-associated retinoid, although firm evidence for this must await further physicochemical characterization of the inhibitory signal(s). The present data clearly show, nevertheless, that human tumour-induced inhibition of IFN in vitro can be reversed by the pro-vitamin beta-carotene.     

Notch inhibition promotes fetal liver stem/progenitor cells differentiation into hepatocytes via the inhibition of HNF-1β

In a previous study, the Notch pathway inhibited with N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (also called DAPT) was shown to promote the differentiation of fetal liver stem/progenitor cells (FLSPCs) into hepatocytes and to impair cholangiocyte differentiation. The precise mechanism for this, however, was not elucidated. Two mechanisms are possible: Notch inhibition might directly up-regulate hepatocyte differentiation via HGF (hepatocyte growth factor) and HNF (hepatocyte nuclear factor)-4α or might impair cholangiocyte differentiation thereby indirectly rendering hepatocyte differentiation as the dominant state. In this study, HGF and HNF expression was detected after the Notch pathway was inhibited. Although our initial investigation indicated that the inhibition of Notch induced hepatocyte differentiation with an efficiency similar to the induction via HGF, the results of this study demonstrate that Notch inhibition does not induce significant up-regulation of HGF or HNF-4α in FLSPCs. This suggests that Notch inhibition induces hepatocyte differentiation without the influence of HGF or HNF-4α. Moreover, significant down-regulation of HNF-1β was observed, presumably dependent on an impairment of cholangiocyte differentiation. To confirm this presumption, HNF-1β was blocked in FLSPCs and was followed by hepatocyte differentiation. The expression of markers of mature cholangiocyte was impaired and hepatocyte markers were elevated significantly. The data thus demonstrate that the inhibition of cholangiocyte differentiation spontaneously induces hepatocyte differentiation and further suggest that hepatocyte differentiation from FLSPCs occurs at the expense of the impairment of cholangiocyte differentiation, probably being enhanced partially via HNF-1β down-regulation or Notch inhibition.     

In vitro evaluation of single- and multi-strain probiotics: Inter-species inhibition between probiotic strains, and inhibition of pathogens

Many studies comparing the effects of single- and multi-strain probiotics on pathogen inhibition compare treatments with different concentrations. They also do not examine the possibility of inhibition between probiotic strains with a mixture. We tested the ability of 14 single-species probiotics to inhibit each other using a cross-streak assay, and agar spot test. We then tested the ability of 15 single-species probiotics and 5 probiotic mixtures to inhibit Clostridium difficile, Escherichia coli and S. typhimurium, using the agar spot test. Testing was done with mixtures created in two ways: one group contained component species incubated together, the other group of mixtures was made using component species which had been incubated separately, equalised to equal optical density, and then mixed in equal volumes. Inhibition was observed for all combinations of probiotics, suggesting that when used as such there may be inhibition between probiotics, potentially reducing efficacy of the mixture. Significant inter-species variation was seen against each pathogen. When single species were tested against mixtures, the multi-species preparations displayed significantly (p < 0.05 or less) greater inhibition of pathogens in 12 out of 24 cases. Despite evidence that probiotic species will inhibit each other when incubated together in vitro, in many cases a probiotic mixture was more effective at inhibiting pathogens than its component species when tested at approximately equal concentrations of biomass. This suggests that using a probiotic mixture might be more effective at reducing gastrointestinal infections, and that creating a mixture using species with different effects against different pathogens may have a broader spectrum of action that a single provided by a single strain.     

Endocannabinoids: losing inhibition to increase learning capacity?

Recent work has implicated endocannabinoids in various forms of synaptic plasticity. In this issue of Neuron, Chevaleyre and Castillo describe a new mechanism whereby a CB1 receptor-mediated LTD of inhibitory synaptic transmission facilitates the subsequent induction of LTP in a narrow band of synapses surrounding a region of potentiated synapses.     

Is vasohibin-1 for more than angiogenesis inhibition?

Angiogenesis, a formation of neo-vessels from pre-existing ones, is regulated by the local balance between its stimulators and inhibitors. Vasohibin-1 (VASH1) was originally identified as an endothelium-derived vascular endothelial growth factor (VEGF)-inducible angiogenesis inhibitor that acts in a negative feedback manner. The expression of VASH1 has been shown in endothelial cells (ECs) in both physiological and pathological conditions associated with angiogenesis. However, recent reports indicate that VASH1 is expressed not only in ECs but also in other cell types including haematopoietic cells. The function of VASH1 may not be restricted to angiogenesis inhibition.     

“Glial inhibition” of memory in Alzheimer's disease

<正>Two recent studies on Nature Medicine and Nature Communications reported the unusual roles of astrocytes in the brain,that is,release gamma-aminobutyric acid(GABA)and impair hippocampal memory in Alzheimer’s disease(AD).AD represents one common form of neurodegenerative diseases,and is characterized by progressive dementia.The pathological feature of an AD brain includes the appearance     

Is there more to GABA than synaptic inhibition?

In the mature brain, GABA (gamma-aminobutyric acid) functions primarily as an inhibitory neurotransmitter. But it can also act as a trophic factor during nervous system development to influence events such as proliferation, migration, differentiation, synapse maturation and cell death. GABA mediates these processes by the activation of traditional ionotropic and metabotropic receptors, and probably by both synaptic and non-synaptic mechanisms. However, the functional properties of GABA receptor signalling in the immature brain are significantly different from, and in some ways opposite to, those found in the adult brain. The unique features of the early-appearing GABA signalling systems might help to explain how GABA acts as a developmental signal.     

Rapamycin promotes β-amyloid production via ADAM-10 inhibition

Rapamycin is a well known immunosuppressant drug for rejection prevention in organ transplantation. Numerous clinical trials using rapamycin analogs, involving both children and adults with various disorders are currently ongoing worldwide. Most recently, rapamycin gained much attention for what appears to be life-span extending properties when administered to mice. The risk for Alzheimer disease (AD) is strongly and positively correlated with advancing age and is characterized by deposition of β-amyloid peptides (Aβ) as senile plaques in the brain. We report that rapamycin (2.5 μM), significantly increases Aβ generation in murine neuron-like cells (N2a) transfected with the human “Swedish” mutant amyloid precursor protein (APP). In concert with these observations, we found rapamycin significantly decreases the neuroprotective amino-terminal APP (amyloid precursor protein) cleavage product, soluble APP-α (sAPP-α) while increasing production of the β-carboxyl-terminal fragment of APP (β-CTF). These cleavage events are associated with decreased activation of a disintegrin and metallopeptidase domain-10 (ADAM-10), an important candidate α-secretase which opposes Aβ generation. To validate these findings in vivo, we intraperitoneal (i.p.) injected Tg2576 Aβ-overproducing transgenic mice with rapamycin (3 mg/kg/day) for 2 weeks. We found increased Aβ levels associated with decreased sAPP-α at an average rapamycin plasma concentration of 169.7 ± 23.5 ng/mL by high performance liquid chromatography (HPLC). These data suggest that although rapamycin may increase the lifespan in some mouse models, it may not decrease the risk for age-associated neurodegenerative disorders such as AD.     

Synthesis and α-glucosidase inhibition activity of dihydroxy pyrrolidines

A new series of Deacetylsarmentamide A and B derivatives, amides and sulfonamides of 3,4-dihydroxypyrrolidines as α-glucosidase inhibitors were designed and synthesized. The biological screening test against α-glucosidase showed that some of these compounds have the positive inhibitory activity against α-glucosidase. Saturated aliphatic amides were more potent than the olefinic amides. Among all the compounds, 5o/6o having polar –NH₂ group, 10f/11f having polar –OH group on phenyl ring displayed 3–4-fold more potent than the standard drugs. Acarbose, Voglibose and Miglitol were used as standard references. The promising compounds 6i, 5o, 6o, 10a, 11a, 10f and 11f have been identified. Molecular docking simulations were done for compounds to identify important binding modes responsible for inhibition activity of α-glucosidase.