Determination of physiological, taxonomic, and molecular characteristics of a cultivable arsenic-resistant bacterial community

A collection of 219 bacterial arsenic-resistant isolates was constituted from neutral arsenic mine drainage sediments. Isolates were grown aerobically or anaerobically during 21 days on solid DR2A medium using agar or gelan gum as gelling agent, with 7 mM As(III) or 20 mM As(V) as selective pressure. Interestingly, the sum of the different incubation conditions used (arsenic form, gelling agent, oxygen pressure) results in an overall increase of the isolate diversity. Isolated strains mainly belonged to Proteobacteria (63%), Actinobacteria (25%), and Bacteroidetes (10%). The most representative genera were Pseudomonas (20%), Acinetobacter (8%), and Serratia (15%) among the Proteobacteria; Rhodococcus (13%) and Microbacterium (5%) among Actinobacteria; and Flavobacterium (13%) among the Bacteroidetes. Isolates were screened for the presence of arsenic-related genes (arsB, ACR3(1), ACR3(2), aioA, arsM, and arrA). In this way, 106 ACR3(1)-, 74 arsB-, 22 aioA-, 14 ACR3(2)-, and one arsM-positive PCR products were obtained and sequenced. Analysis of isolate sensitivity toward metalloids (arsenite, arsenate, and antimonite) revealed correlations between taxonomy, sensitivity, and genotype. Antimonite sensitivity correlated with the presence of ACR3(1) mainly present in Bacteroidetes and Actinobacteria, and arsenite or antimonite resistance correlated with arsB gene presence. The presence of either aioA gene or several different arsenite carrier genes did not ensure a high level of arsenic resistance in the tested conditions.

S18616, a highly potent spiroimidazoline agonist at alpha(2)-adrenoceptors: II. Influence on monoaminergic transmission, motor function, and anxiety in comparison with dexmedetomidine and clonidine

The alpha(2)-adrenoceptor (AR) agonist, S18616 ((S)-spiro[(1-oxa-2-amino-3-azacyclopent-2-ene)-4,2'-(8'-chloro-1' , 2',3',4'-tetrahydronaphthalene)] accompanying article), suppressed electrical activity of adrenergic neurons in the locus ceruleus, an action reversed by the alpha(2)-AR antagonist, idazoxan, which itself enhanced their firing rate. Electrical activity of serotonergic neurons in the dorsal raphe nucleus was similarly suppressed, an action likewise blocked by idazoxan, which did not, itself, influence firing. In freely moving rats, S18616 decreased extracellular levels of norepinephrine (NE), serotonin (5-HT), and dopamine (DA) in frontal cortex and hippocampus. The selective alpha(2)- versus alpha(1)-AR antagonists, atipamezole and BRL-44408 (a preferential alpha(2A)-AR antagonist), elevated levels of NE and DA but not 5-HT. In their presence, the influence of S18616 on frontocortical levels of NE, DA, and 5-HT was blocked. In contrast, prazosin, a selective alpha(1)- versus alpha(2)-AR antagonist (which also preferentially blocks alpha(2B/2C)-ARs) dose dependently decreased levels of 5-HT, but not NE and DA, and failed to modify the actions of S18616. Ultrasonic vocalizations elicited by rats in an aversive environment were inhibited by S18616, which also suppressed aggressive and marble-burying behaviors in mice. Furthermore, S18616 (biphasically) enhanced punished responses in the Vogel conflict test and active social interaction tests in rats. At higher doses, S18616 displayed sedative/hypnotic properties. Both anxiolytic and motor actions of S18616 were inhibited by atipamezole and BRL-44408 but not prazosin. Dexmedetomidine mimicked the actions of S18616 at higher doses except for more potent sedative/hypnotic properties. Clonidine also mimicked S18616, but only at markedly higher doses. In conclusion, via activation of alpha(2)-ARs, S18616 potently inhibits corticolimbic adrenergic, serotonergic, and (frontocortical) dopaminergic transmission in parallel with the expression of its anxiolytic and sedative properties.

S18616, a highly potent, spiroimidazoline agonist at alpha(2)-adrenoceptors: I. Receptor profile, antinociceptive and hypothermic actions in comparison with dexmedetomidine and clonidine

S18616 ((S)-spiro[(1-oxa-2-amino-3-azacyclopent-2-ene)-4, 2'-(8'-chloro-1',2',3',4'-tetrahydronaphthalene)]) displayed high affinity at native rat alpha(2)-adrenoceptors (AR)s (pK(i), 9.8), native human (h)alpha(2A)-ARs (9.6), and cloned halpha(2A)- (9.5), halpha(2B)- (9.2), and halpha(2C)- (9.0) ARs. It showed 40-fold lower affinity for halpha(1A)-ARs (8.4) and >/=100-fold lower affinity for rat alpha(1)-ARs (7.1), halpha(1B)-ARs (7.7), halpha(1D)-ARs (7.6), imidazoline(1) (7.4), and imidazoline(2) (7.4) sites and >100-fold lower affinity for all other (>50) sites. At halpha(2A)-ARs, in guanosine-5'-O-(3-[(35)S]thio)triphosphate binding studies, S18616 was a potent (partial) agonist: log effective concentration (pEC(50)), 9.3/maximal effect, 51%. This observation was corroborated employing a halpha(2A)-Gi1alpha fusion protein/GTPase assay (9.0/40%) in which the actions of S18616 were blocked by pertussis toxin. Employing guanosine-5'-O-(3-[(35)S]thio)triphosphate binding assays, S18616 was also a partial agonist at halpha(2C)-ARs (8.2/63%) but a full agonist (8.4/124%) at halpha(2B)-ARs. At halpha(2A)-, halpha(2B)-, and halpha(2C)-ARs, the selective alpha(2)-AR antagonist, atipamezole, abolished the actions of S18616: pK(b) values of 9.1, 9. 1, and 9.4, respectively. As determined by depletion of membrane-bound [(3)H]phosphatidyl inositols, S18616 behaved as a (less potent) agonist (7.8/79%) at halpha(1A)-ARs, an action abolished by prazosin (pK(b), 8.9). Reflecting alpha(2)-AR agonist properties, S18616 potently (>/=1 microg/kg, s.c.) and dose dependently elicited hypothermia and antinociception (nine diverse models) in rodents. These actions were dose dependently inhibited by chemically diverse alpha(2)- versus alpha(1)-AR antagonists, atipamezole, idazoxan, RX821,002, and BRL44418 (a preferential alpha(2A)-AR ligand). In contrast, the actions of S18616 were unaffected by the alpha(1)-AR antagonists, ARC239 and prazosin (which preferentially block alpha(2B/2C)- versus alpha(2A)-ARs). Although the affinity of dexmedetomidine at alpha(2)-ARs was lower than S18616; it displayed a similar receptor and functional profile. Clonidine displayed lower efficacy than S18616, was substantially less potent, and had marked affinity for imidazoline(1) sites and alpha(1)-ARs. In conclusion, S18616 is a novel, selective, and highly potent agonist at alpha(2)-ARs.

Effect of chronic treatment with the inducible nitric oxide synthase inhibitor N-iminoethyl-L-lysine or with L-arginine on progression of coronary and aortic atherosclerosis in hypercholesterolemic rabbits

BACKGROUND

We examined the implications of iNOS in atherosclerosis progression using the selective inducible NO synthase (iNOS) inhibitor N:-iminoethyl-L-lysine (L-NIL) in hypercholesterolemic rabbits.

METHODS AND RESULTS

Nine rabbits were fed a 0.3% cholesterol diet for 24 weeks (Baseline group); 25 animals were maintained on the diet and treated for 12 extra weeks with L-NIL (5 mg x kg(-1) x d(-1), L-NIL group, n=8), vehicle (Saline group, n=9), or L-arginine (2.25%, L-Arg group, n=8). In abdominal aortas of Saline rabbits, the lesions (53.7+/-5.7%, Baseline) increased to 75.0+/-5.0% (P:<0.05) but remained unaltered in the L-NIL group (63. 4+/-6.6%). Similar results were obtained for the intima/media ratio in thoracic aortas. In coronary arteries, the intima/media ratio was comparable in Baseline (0.68+/-0.18) and Saline (0.96+/-0.19) rabbits but decreased to 0.34+/-0.19 (P:<0.05) in L-NIL rabbits. L-Arginine had beneficial effects only in abdominal aortas. An increased thoracic aorta collagen content was found in Saline and L-Arg but not in L-NIL rabbits. In thoracic aortas of the Saline group, acetylcholine caused modest relaxations that slightly increased by L-arginine but not by L-NIL. Relaxations to nitroglycerin were ameliorated by L-NIL.

CONCLUSIONS

This is the first study showing that chronic treatment with an iNOS inhibitor, L-NIL, limits progression of preexisting atherosclerosis in hypercholesterolemic rabbits. Increased intimal collagen accumulation may participate in iNOS-induced atherosclerosis progression.

Design, synthesis and structure-activity relationships of novel strychnine-insensitive glycine receptor ligands

The in vitro activities of 3-hydroxy-imidazolidin-4-one derivatives demonstrated very restricted structure-activity relationships at the strychnine-insensitive glycine site of the NMDA receptor. The most active compound (3a) was completely unsubstituted and exhibited affinity and efficacy similar to that of D-cycloserine, the prototypical partial agonist at this site.

Synthesis of 1,2-diacyl-3-nicotinoyl glycerol derivatives and evaluation of their acute effects on plasma lipids in the rat

Nicotinic acid (CAS 59-67-6) is the only hypolipidemic agent whose activity has been shown both on atherosclerotic lesions and on long term mortality. Unfortunately, its use is hindered by the frequent occurrence ( > 70%) of adverse reactions (i.e. cutaneous rash, pruritus and, most significantly, flush). New prodrugs of nicotinic acid have been prepared by the use of diacylglycerol esters. In the rat, after acute oral administration of these products, a significant decrease of the free fatty acid plasma levels was obtained without the dramatic increase in nicotinic acid plasma levels observed after the oral administration of an equimolecular dose of nicotinic acid. The most interesting ester, S 16961 ((d,l)-1,2-dipalmitoyl-3-nicotinoyl glycerol, CAS 160555-46-4) is undergoing clinical trials.

Inhibition of amine oxidase activity by derivatives that recognize imidazoline I2 sites

Nonadrenergic imidazoline binding sites (imidazoline I2 sites) have been described to be colocated with monoamine oxidase (MAO) in the mitochondrial fraction of various cell types. In the present work, the authors considered whether this colocation could be associated with a functional interplay. In rat liver membranes, [3H]-idazoxan binding to I2 receptors was competed for by naphazoline and idazoxan, which also shared a high affinity for alpha-2 adrenoceptors (alpha-2 ARs). The chemicals 2-n-heptylimidazoline (S 15430), 1-methyl-5-n-heptylimidazole (S 15674), 2-benzofuran-2-yl-imidazoline (RX 801077) and 2-(1,3-benzodioxanyl)-2-imidazoline (RX 821029) exhibited higher affinity for I2 receptors than for alpha-2 ARs. The most selective agent was S 15430 with a 150-fold higher affinity for liver I2 receptors than for adipocyte alpha-2 ARs. Moreover, [3H]-idazoxan binding was also competed for by several MAO inhibitors (MAOI) that are not imidazoline or guanidinium derivatives such as tranylcypromine, harmaline, clorgiline and pargyline. Rat liver MAO activity was not only inhibited by MAOIs but also by some imidazoline derivatives: cirazoline, naphazoline, S 15674, RX 801077 and RX 821029. Idazoxan had no effect on MAO activity; it neither inhibited MAO nor prevented the inhibition induced by other imidazolines or MAOIs. This suggested that the ligand recognition site of I2 receptors was distinct from the MAOI target site. Furthermore, some imidazolines inhibited the activity of bovine plasma amine oxidase, an enzyme that does not possess the same cofactor as MAO and is insensitive to harmaline or pargyline.(ABSTRACT TRUNCATED AT 250 WORDS)

[3H]-idazoxan binding to rabbit cerebral cortex recognises multiple imidazoline I2-type receptors: pharmacological characterization and relationship to monoamine oxidase

1. In rabbit cerebral cortical homogenates, saturation analysis of [3H]-idazoxan, an alpha 2-adrenoceptor antagonist, revealed high affinity binding to a single site with high density. Competition experiments demonstrated that the [3H]-idazoxan recognition site was insensitive to the catecholamines, adrenaline and noradrenaline and possessed a low affinity for the alpha 2- and alpha 1-adrenoceptor antagonists, rauwolscine, yohimbine and prazosin, suggesting that the site was not an adrenoceptor. Mapping [3H]-idazoxan binding sites in the forebrain of rabbits by autoradiography, showed high densities of I2 sites in the medial preoptic area and in the stria terminalis. Moderate binding was found in caudate nucleus, putamen, cerebral cortex and hippocampus. 2. The imidazolines cirazoline, naphazoline, guanabenz and BRL44408 along with amiloride, which is structurally related to the imidazolines, all had high affinity for the [3H]-idazoxan site, suggesting that the site was related to the I2 imidazoline-recognition site described by other groups. However, the imidazolines, clonidine and UK-14,304 and the structurally related rilmenidine all had a low affinity for the binding site, showing that [3H]-idazoxan was not binding to the I1 imidazoline-recognition site found in rat, bovine and human medulla oblongata. 3. Naphazoline, guanabenz, clonidine and amiloride competition studies had Hill slopes which were significantly different from unity (P < 0.01) and computer analysis showed that the [3H]-idazoxan binding data could be best fitted to a model which considers binding to two sites (P < 0.01). One site has a high affinity for idazoxan, cirazoline, naphazoline, guanabenz and amiloride and a moderate affinity for BRL44408 and clonidine (70% of binding) and the second site (30% of binding) has a high affinity for idazoxan and cirazoline, but a lower affinity for naphazoline, guanabenz, amiloride,BRL44408 and clonidine.4. Experiments using [3H]-RX821002, in contrast to [3H]-idazoxan, clearly demonstrated the presence ofa single type of alpha2-adrenoceptor in rabbit cortex with a pharmacological profile which is similar to the alpha2A-adrenoceptor possessing a high affinity for yohimbine, rauwolscine, BRL44408 and oxymetazoline,but a lower affinity for prazosin.5. The monoamine oxidase inhibitors, clorgyline, pargyline and deprenyl had at least a ten fold lower affinity at the rabbirt cortex I2 site as compared to their known affinity at monoamine oxidase suggesting that the I2 site is not related to the active site of the enzyme, monoamine oxidase. In addition, the peripheral benzodiazepine ligands, PK-11195 or Ro 5-4864 both had very low affinities at the I2 site in rabbit cortex suggesting that the [3H]-idazoxan binding was not to the peripheral benzodiazepine binding site.

Competitive inhibition by NBQX of kainate/AMPA receptor currents and excitatory synaptic potentials: importance of 6-nitro substitution

We evaluated the inhibitory potencies at excitatory amino acid receptors of 2,3-dihydroxy-7-sulfamoyl-benzo[f]quinoxaline (BQX) and its 6-nitro derivative, NBQX. Currents activated by kainate or (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) in two-electrode voltage-clamp recordings of Xenopus oocytes injected with rat cortex mRNA were inhibited by BQX and NBQX: the apparent Ki values versus kainate were 14 microM and 78 nM, respectively, and versus AMPA were 23 microM and 63 nM, respectively. Thus, to a degree even more marked than with other quinoxalinedione derivatives, 6-nitro substitution of BQX to yield NBQX increases potency (200-fold) at the non-NMDA ionotropic receptor, but does not confer selectivity for kainate or AMPA. Schild analysis of the NBQX inhibition of the kainate and AMPA currents yielded pA2 values of 7.17 +/- 0.05 and 7.05 +/- 0.10, respectively, and slopes near unity confirming the competitive nature of the inhibition. Neither BQX nor NBQX significantly inhibited the current activated by glycine plus NMDA. The selectivity ratio of NBQX (greater than 5000-fold) is by far the greatest of any quinoxalinedione derivative antagonist of the kainate/AMPA receptor. BQX and NBQX also inhibited the excitatory postsynaptic field potentials mediated by kainate/AMPA receptors in the CA1 region of hippocampal slices after stimulation of the Schaffer collateral-commissural pathways with IC50 values of 130 and 0.90 microM, respectively. The 10-fold differences between the IC50 values in hippocampal slices and the Ki values in Xenopus oocytes correlate closely with data for other quinoxalinedione derivative antagonists.

Quinoxaline derivatives: structure-activity relationships and physiological implications of inhibition of N-methyl-D-aspartate and non-N-methyl-D-aspartate receptor-mediated currents and synaptic potentials

The inhibitory potencies at excitatory amino acid (EAA) receptors of 11 quinoxaline derivatives were evaluated in two-electrode voltage-clamp recordings of Xenopus oocytes injected with rat cortex mRNA. Currents activated by kainate or (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) in Xenopus oocytes were inhibited competitively by all the quinoxaline derivatives, with apparent Ki values ranging from 0.27 to 300 microM against kainate and from 0.25 to 137 microM against AMPA. An excellent correlation was observed between inhibitory potencies of the quinoxaline derivatives against kainate and AMPA currents, in support of the contention that in this preparation these two agonists act at a single site. All 11 quinoxaline derivatives also inhibited current activated by the combination of glycine and N-methyl-D-aspartate (NMDA), apparently acting at the glycine site, and did so over a narrower range of apparent Ki values (0.37-8.1 microM). The correlation between the quinoxalines' kainate/AMPA potencies and their glycine/NMDA potencies was relatively weak. Thus, the quinoxaline derivatives were all good antagonists of glycine/NMDA currents and displayed a greater range of potencies against kainate and AMPA. The inhibitory effects of the six quinoxaline derivatives most potent in the Xenopus oocyte experiments were also tested against the excitatory postsynaptic field potential (EPSFP) recorded in the pyramidal cell dendritic field of the CA1 region of hippocampal slices after stimulation of the Schaffer collateral-commissural pathways. In slices superfused with "normal" medium (containing 1 mM Mg2+), in which the EPSFP is mediated primarily by non-NMDA receptors, IC50 values correlated closely with the Ki values against kainate/AMPA obtained in oocyte experiments but were approximately 8-fold higher. Similarly, in slices superfused with nominally Mg(2+)-free medium, in which the EPSFP is amplified due to a relief of the Mg2+ block of NMDA receptors, IC50 values correlated closely with the Ki values against glycine/NMDA obtained in oocyte experiments but were 60-fold higher. This comparison of results from the two experimental systems lends further support to the argument that hippocampal synaptic transmission is mediated postsynaptically by kainate/AMPA-type and NMDA/glycine-type EAA receptors that are pharmacologically indistinguishable from those expressed in mRNA-injected Xenopus oocytes. Furthermore, it suggests that EAA receptors in situ may be nearly saturated by high local concentrations of the endogenous ligands, a condition that would contribute substantially to the apparent non-NMDA receptor selectivity of certain quinoxaline derivatives.

Anticonvulsant activity of milacemide

The anticonvulsant activity of a new drug, milacemide (2-(pentylamino)-acetamide), has been studied in animal models of convulsions like those induced by bicuculline, pentylenetetrazol, picrotoxin, strychnine, inhibitors of GABA synthesis as 3-mercaptopropionic acid, allylglycine, isoniazid and thiosemicarbazide and electroshock. Milacemide is particularly effective in inhibiting the convulsions induced by bicuculline. The ED50 is 5.7 mg/kg by oral route and the activity lasts for more than 48 hr. It is less active against pentylenetetrazol and only marginally active against electroshock. It has not be found active against the other types of convulsions. Milacemide has a low toxicity (LD50: 2585 mg/kg in the mouse) and alters the behaviour of mouse, rat and monkey, only at high doses (greater than or equal to 1000 mg/kg). Milacemide seems to be specially free of sedative potential.