Silver nanoparticle embedded copper oxide as an efficient core-shell for the catalytic reduction of 4-nitrophenol and antibacterial activity improvement.

A facile and eco-friendly method was developed to prepare a microporous CuO@Ag0 core-shell with high catalytic and antibacterial activities. Scanning and transmission electron microscopy revealed a preponderance of nearly spherical 50 nm particles with slight structure compaction. Comparison of the hysteresis loops confirmed the structure compaction after AgNP incorporation, and a significant decrease of the specific surface area from 55.31 m2 g-1 for CuO to 8.03 m2 g-1 for CuO@Ag0 was noticed. A kinetic study of 4-nitrophenol (4-NP) reduction into 4-aminophenol (4-AP) with sodium borohydride revealed a first order reaction that produces total conversion in less than 18 minutes. CuO@Ag0 also exhibited appreciable antibacterial activity against Staphylococcus aureus. The antibacterial effects were found to strongly depend on the size, contact surface, morphology and chemical composition of the catalyst particles. The addition of Ag0-NPs produced more reactive oxygen species in the bacteria medium. These results open promising prospects for its potential applications as a low cost catalyst in wastewater treatment and antibacterial agent in cosmetics.

Comparative study of 7 fluorescent pseudomonad clinical isolates.

There is some debate about the potential survival of Pseudomonas fluorescens at temperatures above 37 degrees C and its consequences for infectious potential, owing to the heterogeneity of clinical strains. Seven clinical strains growing at 37 degrees C or more were submitted for polyphasic identification; 2 were identified as Pseudomonas mosselii and 4 were precisely characterized as P. fluorescens bv. I or II. The binding indexes on glial cells of the strains identified as P. fluorescens bv. I and P. mosselii were compared with that of a reference psychrotrophic strain, P. fluorescens MF37 (bv. V). Clinical P. fluorescens had a similar adherence potential range than strain MF37. Conversely, the binding indexes for P. mosselii strains were 3 times greater than that for strain MF37. These data, and those obtained by comparing the cytotoxic activities of P. fluorescens clinical strains, suggest the existence of different virulence mechanisms, leading either to a low infectious form or to a microorganism with cytotoxic activity in the same range as that of P. mosselii or even Pseudomonas aeruginosa.

In vitro thrombogenicity investigation of new water-dispersible polyurethane anionomers bearing carboxylate groups.

New segmented polyurethane (PU) anionomers based on hydroxytelechelic polybutadiene were synthesized via an aqueous dispersion process. Incorporation of carboxylic groups was achieved using thioacids of different length. Surface properties were investigated by mean of water absorption analysis and static contact-angle measurements using water, diiodomethane, formamide and ethylene glycol. Blood compatibility of the PUs was evaluated by in vitro adhesion assays using 111In-radiolabeled platelet-rich plasma and [125I]fibrinogen. Morphology of the adhered platelets was examined by scanning electron microscopy (SEM). Results were compared to two biomedical-grade PUs, namely Pellethane and Tecoflex. Insertion of carboxylic groups increased surface hydrophilicity and limited water uptake ( < 8% for an ion content of 5% by weight). Surface energy of all synthesized PUs was between 40 and 45 mJ/m2. Platelet adhesion and fibrinogen adsorption on the PU anionomer surfaces were affected as a function to the increase of graft length; thiopropionic was the most haemocompatible, followed by thiosuccinic and then thioglycolic acid. SEM analyses of all ionic PU samples exhibited low platelet adhesion to surfaces with no morphological modification. In conclusion, increased hydrophily, dynamic mobility and charge repulsion are synergistic key factors for enhanced haemocompatibility.

Sequential activation of constitutive and inducible nitric oxide synthase (NOS) in rat cerebellar granule neurons by pseudomonas fluorescens and invasive behaviour of the bacteria.

Previous studies have shown that Pseudomonas fluorescens and its lipopolysaccharide (LPS) exert dose-related cytotoxic effects on neurons and glial cells. In the present work, we investigated the time course effect of P. fluorescens MF37 and its LPS on cultured rat cerebellar granule neurons. The kinetics of binding of P. fluorescens to cerebellar granule neurons is rapid and reaches a mean of 3 bacteria/cell after 5 h. As demonstrated by measurement of the concentration of nitrite in the culture medium, P. fluorescens induces a rapid stimulation (3 h) of the nitric oxide synthase (NOS) activity of the cells. In contrast, LPS extracted from P. fluorescens requires a long lag phase (24 h) before observation of an activation of NOS. Measurement of the membrane resting potential of granule neurons showed that within 3 h of incubation there was no difference of effect between the action of P. fluorescens and that of its endotoxin. Two complementary approaches allowed to demonstrate that P. fluorescens MF37 presents a rapid invasive behaviour suggesting a mobilisation of calcium in its early steps of action. The present study reveals that P. fluorescens induces the sequential activation of a constitutive calcium-dependent NOS and that of an inducible NOS activated by LPS. Our results also suggest that in P. fluorescens cytotoxicity and invasion are not mutually exclusive events.

Aldosterone increases T-type calcium currents in human adrenocarcinoma (H295R) cells by inducing channel expression.

In adrenal glomerulosa cells, low-threshold voltage-activated (T-type) calcium channels are known to play a crucial role in coupling physiological variations of extracellular potassium to aldosterone biosynthesis. On the other hand, aldosterone itself has been recently shown to regulate Ca(2+) currents in its target cells. In the present study, we have investigated the effect of aldosterone on Ca(2+) channels of the steroidogenic human adrenocarcinoma cell line, using both electrophysiological and molecular techniques. Cell incubation with aldosterone (1 microM) for 24 h increased by 39% the density of T-type calcium currents, as assessed with the patch clamp technique. This effect of aldosterone was not related to a modification of T channel activation and inactivation properties. In contrast, L-type calcium currents remained unaffected by aldosterone treatment. The mineralocorticoid receptor antagonist, spironolactone, blunted the aldosterone-induced increase in T-type calcium current. By RT-PCR, we detected in human adrenocarcinoma cells the presence of mRNA coding for the alpha(1) subunits of three different calcium channels: the alpha(1)H isoform of T channels and the alpha(1)C and alpha(1)D isoforms of the L channels. The presence of mRNA coding for the mineralocorticoid receptor was also found in these cells. Aldosterone treatment induced a 36% increase of mRNA coding for alpha(1)H, as assessed by real-time PCR. This aldosterone-evoked stimulation of mRNA expression was maximal at 24-48 h and reversed by spironolactone, suggesting a receptor-mediated genomic effect of aldosterone. Pregnenolone production in response to KCl stimulation was increased after aldosterone treatment, in parallel to T channel expression, confirming the essential role of these channels in the steroidogenic response to potassium. Taken together, these data indicate that, in human adrenocarcinoma cells, aldosterone increases, through an autocrine pathway, the expression of T-type calcium channels and therefore modifies the ability of these cells to respond to steroidogenic agonists.

The effect of the endozepine triakontatetraneuropeptide on corticosteroid secretion by the frog adrenal gland is mediated by activation of adenylyl cyclase and calcium influx through T-type calcium channels.

We have recently found that, in the frog adrenal gland, endozepines are present in chromaffin cells and we have shown that the triakontatetraneuropeptide TTN is a potent stimulator of corticosteroid secretion in vitro. In the present study, we have investigated the transduction mechanisms mediating the corticotropic effect of TTN on adrenocortical cells. Incubation of adrenal explants with graded concentrations of TTN induced a dose-dependent increase in cAMP formation, but did not affect polyphosphoinositide metabolism. Pretreatment of adrenal cells with the protein kinase A inhibitor H-89 markedly reduced the stimulatory effect of TTN on corticosterone and aldosterone secretion by perifused cells, whereas the phospholipase C inhibitor U-73122 did not affect the TTN-evoked stimulation of corticosteroid output. Incubation of adrenal cells with cholera toxin abolished the stimulatory effect of TTN on steroid secretion. Administration of a brief pulse of TTN (10(-6) M) in the vicinity of cultured adrenocortical cells induced a robust increase in the concentration of intracellular calcium ([Ca2+]i). Repeated pulses of TTN resulted in a gradual attenuation of the responses, indicating the existence of a desensitization phenomenon. Incubation of the cells with the T-type calcium channel blocker mibefradil significantly reduced the TTN-evoked [Ca2+]i increase, whereas the L-type calcium channel blocker nifedipine and the N-type calcium channel blocker omega-conotoxin GVIA had no effect. Incubation of adrenal cells with H-89 markedly reduced the stimulatory effect of TTN on [Ca2+]i. The involvement of calcium in steroid secretion induced by TTN has also been investigated. Administration of mibefradil significantly reduced the TTN-evoked stimulation of steroid production, whereas nifedipine was devoid of effect. Taken together, these data indicate that in frog adrenocortical cells, the endozepine TTN stimulates cAMP formation and calcium entry through T-type calcium channels. The effects of TTN on the adenylyl cyclase/protein kinase A pathway and calcium influx both contribute to the stimulatory action of the peptide on corticosteroid secretion.

Mechanism of action of endothelins on adrenocortical cells.

Endothelins (ETs) play a pivotal role in the control of various endocrine and neuroendocrine tissues. In this review, we discuss the involvement of ETs as possible regulators of steroid secretion and we describe the mechanism of action of ETs on adrenocortical cells. The occurrence of ETs has been demonstrated in the human, porcine and rat adrenal gland. In humans, immunohistochemical and biochemical techniques have reported that ETs are localized exclusively in the cortex but the presence of ETs has also been detected in pheochromocytomas. In vitro studies have shown that ETs stimulate aldosterone secretion by adrenal tissues in various mammalian and amphibian animal models. The receptor subtype involved in the corticotropic action of ETs clearly differs among the various vertebrate species studied. In rat, the effect of ETs is mediated through an ET(B) receptor subtype while, in frog, an ET(A) receptor is implicated in the stimulatory action of ETs. In human adrenocortical cells, both ET(A) and ET(B) receptor subtypes are involved in the corticotropic effect of ETs. Activation of adrenal receptors causes an elevation of inositol trisphosphates associated with an increase in cytosolic calcium concentration. In addition, ETs induce an elevation of prostaglandin E2 (PGE2) and prostacyclin PGI2 production in the adrenal tissue, indicating that prostanoids may act as second messengers of ETs. It thus appears that ETs present in the adrenal gland may act as paracrine factors to stimulate the secretory activity of adrenocortical cells.

Effect of the triakontatetraneuropeptide (TTN) on corticosteroid secretion by the frog adrenal gland.

Diazepam-binding inhibitor (DBI) was initially isolated from the rat brain as a result of its ability to compete with benzodiazepines for their receptors. Immunohistochemical studies have recently shown the presence of peripheral-type benzodiazepine receptor (PBR)- and DBI-like immunoreactivity in the frog adrenal gland. The aim of the present study was to investigate the effect of two biologically active DBI-derived peptides, the triakontatetraneuropeptide [TTN; DBI(17-50)] and the octadecaneuropeptide [ODN; DBI(33-50)], on corticosteroid secretion by frog adrenocortical cells. Exposure of frog adrenal explants to graded concentrations of TTN (3.16 x 10(-8) to 3.16 x 10(-6) M) induced a dose-related increase in corticosterone and aldosterone secretion. In contrast, ODN did not modify corticosteroid output. When repeated pulses of TTN (10(-6) M) were administered at 2-h intervals, the response of the adrenal explants to the second dose of TTN was markedly reduced, suggesting the existence of a desensitization phenomenon. Exposure of dispersed adrenal cells to TTN also induced a marked stimulation of corticosteroid secretion, indicating that TTN acts directly on adrenocortical cells. The central-type benzodiazepine receptor (CBR) agonist, clonazepam, did not stimulate corticosteroid secretion and the CBR antagonist, flumazenil, did not block the stimulatory action of TTN. Similarly, the PBR agonist, Ro5-4864, did not mimic the stimulatory effect of TTN and the PBR antagonist, flunitrazepam, did not affect the stimulatory action of TTN. The present study provides the first evidence for a stimulatory effect of TTN on intact adrenocortical cells. The receptor mediating the corticotropic action of TTN is not related to central- or peripheral-type benzodiazepine receptors. Our data suggest that TTN, released by chromaffin cells, may act as a paracrine factor regulating the activity of adrenocortical cells.

Localization of diazepam-binding inhibitor-related peptides and peripheral type benzodiazepine receptors in the frog adrenal gland.

The adrenal gland of mammals contains high concentrations of peripheral-type benzodiazepine receptors (PBR) and diazepam-binding inhibitor (DBI), a polypeptide which acts as an endogenous ligand for PBR. The aim of the present study was to investigate the localization of DBI and PBR in the adrenal gland of the frog Rana ridibunda. Reverse transcription followed by polymerase chain reaction with specific primers for the frog DBI cDNA showed the presence of DBI mRNA in frog adrenal gland extracts. The cellular distribution of DBI and PBR was investigated using an antiserum against the octadecaneuropeptide DBI [33-50] (ODN) and antibodies against the 18-kDa isoquinoline binding protein subunit of PBR (IBP), respectively. ODN-like immunoreactivity was found in chromaffin cells and in Stilling s cells, but not in adrenocortical cells. IBP-like immunoreactivity was observed in chromaffin cells, in Stilling s cells and in a small proportion (11%) of steroid-secreting cells. The ODN- and IBP-immunoreactive materials were homogeneously distributed in the cytoplasm of chromaffin cells and concentrated at the periphery of large cytoplasmic vesicles in Stilling s cells. The proportion of ODN-positive Stilling s cells showed marked circannual variations with a maximum in July. Similarly, the proportion of IBP-positive Stilling s cells was 17 times higher in July than in December. These results indicate that, in the frog adrenal gland, DBI-related peptides and PBR are simultaneously expressed in chromaffin cells and Stilling s cells, suggesting that endogenous ligands for PBR may play a physiological role in the control of adrenal cell activity.

In vitro study of the effect of urotensin II on corticosteroid secretion in the frog Rana ridibunda.

Urotensin II is a cyclic dodecapeptide that was originally isolated from the fish urophysis, the terminus of a neurosecretory system located in the caudal area of the spinal cord. We have recently isolated and characterized urotensin II in the brain of a tetrapod, the frog Rana ridibunda. Recent reports, suggesting that urotensin II may stimulate cortisol secretion in fish, prompted us to investigate the possible effects of fish and frog urotensin II on corticosteroid secretion in amphibians. Exposure of perifused frog adrenal slices to goby (Gillichthys mirabilis) urophysis extracts induced a marked stimulation of corticosterone and aldosterone secretion. In contrast, at concentrations ranging from 10(-10) to 10(-6) M, synthetic goby urotensin II had no effect on corticosteroid production. Similarly, infusion of synthetic frog urotensin II (10(-10) to 10(-6) M) did not modify the spontaneous release of corticosterone and aldosterone. In addition, frog urotensin II had no effect on ACTH- and angiotensin II-induced secretion of corticosteroids. These results show that in frog, urotensin II does not modulate spontaneous and ACTH- or angiotensin II-evoked adrenal steroidogenesis.