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Biomedical subjects

D Constantin

Publications and source records attributed to D Constantin.

15 recordsLinked to original sources
PubMed2005

Electric field unbinding of solid-supported lipid multilayers.

We studied by X-ray reflectivity the behaviour of fully hydrated solid-supported lipid multilayers under the influence of a transverse electric field, under conditions routinely used in the electroformation process. The kinetics of sample loss (unbinding) was measured as a function of the amplitude and frequency of the applied field by monitoring the integrated intensity of the Bragg peaks. We also performed a time-resolved analysis of the intensity of the first Bragg peak and characterized the final state of the sample.

Binding Sites↗
PubMed2004

A detrimental role for nitric oxide synthase-2 in the pathology resulting from acute cerebral injury.

Nitric oxide (NO) synthesized from the inducible isoform of nitric oxide synthase (NOS-2) has been suggested to play both beneficial and deleterious roles in various neuropathologies. To define the role of nitric oxide in traumatic brain injury, we subjected male mice lacking a functional NOS-2 gene (NOS-2-/-) and their wild-type littermates (NOS-2+/+) to mild or severe aseptic cryogenic cerebral injury. Expression of NOS-2 mRNA and protein was observed in NOS-2+/+ animals following injury. Lesion volume (as measured by histology and brain imaging) and neurological outcome (using motor and cognitive behavioral paradigms) were assessed at various times after injury. While magnetic resonance imaging revealed the extent of edema of the 2 genotypes to be similar, histology showed a reduced (32%) lesion volume in severely injured NOS-2-/- compared with NOS-2+/+ mice. In addition, NOS-2-/- mice showed significant improvements in both contralateral sensorimotor deficits (grid test: p = 0.011) and cognitive function (Morris water maze: p = 0.009) after severe injury compared to their wild-type littermates. This indicates that lesion volume is reduced and neurological recovery is improved after acute traumatic injury in mice lacking a functional NOS-2 gene, and strongly suggests that the post-trauma production of NO from this source contributes to neuropathology.

Acute Disease↗
PubMed2003

Solid-supported lipid multilayers: structure factor and fluctuations.

We present a theoretical description of the thermal fluctuations in a solid-supported stack of lipid bilayers, for the case of vanishing surface tension gamma = 0 and in the framework of continuous smectic elasticity. The model is successfully used to model the reflectivity profile of a thin (16 bilayers) DMPC sample under applied osmotic pressure and the diffuse scattering from a thick (800 bilayers) stack. We compare our model to previously existing theories.

Computer Simulation↗
PubMed2001

Regulation of interleukin-8 gene expression after phagocytosis of zymosan by human monocytic cells.

Monocyte phagocytosis of pathogens or inflammatory debris leads to chemokine secretion and heralds the influx of leukocytes to the site of injury. Persistent chemokine secretion can lead to tissue damage. However, the mechanisms by which phagocytosis regulates chemokine synthesis remain poorly understood. As a first step, we have studied regulation of interleukin (IL) 8 gene expression after interaction with zymosan or latex. IL-8 secretion was consistently one- or twofold higher after incubation with zymosan than with latex. Nuclear factor (NF) kappaB translocation to the nucleus was induced by zymosan but not latex, indicating that its translocation is dependent on the nature of the phagocytic stimulus. NFkappaB activation coincided with IkappaBalpha degradation but had no effect on processing of NFkappaB1/p105, the precursor of the NFkappaB protein p50. The NFkappaB inhibitor gliotoxin abrogated zymosan-induced IL-8 synthesis in peripheral blood monocytes, further demonstrating that the induction of IL-8 mRNA by zymosan is NFkappaB dependent. SB203580 inhibition of the p38 mitogen-activated protein kinase (MAPK) pathway significantly decreased zymosan-induced IL-8 mRNA accumulation. Inhibitors of protein kinases A and C or tyrosine kinases had no significant effect on zymosan-induced IL-8 synthesis. These data indicate that p38 MAPK and NFkappaB are critical in controlling zymosan-induced IL-8 secretion.

Cell Line↗
PubMed2000

Diffusion coefficients in a lamellar lyotropic phase: evidence for defects connecting the surfactant structure

We measure diffusion coefficients in the lamellar phase of the nonionic binary system C(12)EO(6)/H(2)O using fluorescence recovery after photobleaching. The diffusion coefficient across the lamellae shows an abrupt increase upon approaching the lamellar-isotropic phase transition. We interpret this feature in terms of defects connecting the surfactant structure. An estimation of the defect density and of the variation in defect energy close to the transition is given in terms of a simple model.

Journal Article↗
PubMed1996

Uroporphyria induced by 5-aminolaevulinic acid alone in Ahrd SWR mice.

In mice, depression of hepatic uroporphyrinogen decarboxylase (UROD) leading to porphyrin accumulation (uroporphyria) occurs with chlorinated ligands of the aryl hydrocarbon (AH) receptor especially after iron overload. However, in the absence of chlorinated ligands, iron itself will eventually cause uroporphyria, but this response is not associated with the Ahr genotype. These effects are potentiated by administration of the haem precursor 5-aminolaevulinate (ALA). The aim of this study was to investigate the effects of ALA alone. Prolonged administration of 2 mg ALA/mL in the drinking water to SWR mice also led to decarboxylase insufficiency (11% of control) and uroporphyria by 8 weeks, whereas DBA/2 mice did not show reduced enzyme activity. Both strains are considered AH nonresponsive and analysis of the Ahr gene using restriction fragment length polymorphism was consistent with SWR, like DBA/2, possessing the Ahrd allele. Exposure of isolated hepatocytes to ALA (150-500 microM) for up to 48 hr showed a significant accumulation of both uroporphyrin and coproporphyrin in the medium, which for uroporphyrin particularly was significantly greater with SWR than with DBA/2 cells. Basal in vivo CYP1A2 activity, measured as microsomal methoxyresorufin dealkylation, was significantly greater in SWR than in DBA/2 mice (1.3-fold), but it was unclear whether this was sufficient to explain the marked difference in sensitivities of the two strains. Despite SWR mice being AH nonresponsive, uroporphyria and decarboxylase depression after an initial iron overload and ALA for 3 weeks were greatly potentiated by a single dose (100 mg/kg) of hexachlorobenzene (a weak AH ligand). The results demonstrate that there is a genetic difference in mice independent of the Ahr genotype and response to iron, which influences the susceptibility to ALA-induced uroporphyria. Thus chemicals, iron and ALA can act independently, but also together, to cause porphyria in susceptible individuals.

Aminolevulinic Acid↗
PubMed1996

Age-related differences in the metabolism of sulphite to sulphate and in the identification of sulphur trioxide radical in human polymorphonuclear leukocytes.

Sulphite oxidation and sulphur trioxide radical formation were studied in polymorphonuclear leukocytes (PMNs) isolated from healthy young, old and centenarian donors and from patients with Down's syndrome. The sulphur radical formation measured by electron spin resonance spectroscopy-spin trapping (EPR-ST) was correlated with the activity of sulphite oxidase and with the rate of sulphite oxidation to sulphate by PMNs. Sulphite metabolism was studied both in resting, and phorbol myristate acetate (PMA) stimulated freshly isolated cells. The rate of sulphur trioxide radical formation was demonstrated by use of the spin trapping agent 5,5-dimethyl-1-pyroline-1-oxide (DMPO) with subsequent formation of an adduct. The intensity of adduct formation was most intense in cells with low sulphite oxidase activity, while a mixture of the adduct and of DMPO hydroxyl radical was mainly observed in cells with high sulphite oxidase activity. Furthermore, experiments carried out on purified sulphite oxidase showed that in the presence of sulphite the enzyme could also give rise to a DMPO-OH adduct. Sulphite oxidase activity in cells isolated from healthy young and old donors was positive correlated with both rates of sulphur trioxide radical formation and sulphite oxidation to sulphate, respectively. However, sulphite oxidase activity in cells isolated from centenarians and patients with Down's syndrome seems to loose partly its rate of oxidising sulphite to sulphate. The intensity of the sulphur centred radical adduct increased in the two latter groups of population and the radical observed was predominantly sulphur trioxide radical.

Aging↗
PubMed1995

Studies on the effect of sulfite on benzo[a]pyrene-7,8-dihydrodiol activation to reactive intermediates in human polymorphonuclear leukocytes.

Sodium sulfite, a hydrolysis product of the environmental pollutant sulfur dioxide increased the activation of (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) to the (+)-anti-enantiomer of trans-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) in phorbol myristate acetate (PMA)-stimulated human polymorphonuclear leukocytes (PMNs). This effect was potentiated in the presence of DMSO. No significant effect of sulfite on BP-7,8-diol activation was observed in resting leukocytes. As revealed by the 32P-postlabelling technique the dominant adduct in both intracellular DNA and to DNA added to the leukocytes was (+)-anti-BPDE bound to the exocyclic nitrogen of deoxyguanosine. The mechanism underlying the stimulatory effect of sulfite on diol epoxide production and increased DNA-binding probably involves one-electron oxidation of sulfite to a sulfur trioxide radical anion and subsequent reaction with molecular oxygen to form the corresponding peroxyl radical. This step obviously requires PMA-initiated oxidative burst and thus, production of superoxide radical anions (O2-.).

Biotransformation↗
PubMed1995

Synergy of iron in the toxicity and carcinogenicity of polychlorinated biphenyls (PCBs) and related chemicals.

In Ah-responsive C57BL/10ScSn mice a single dose of iron significantly potentiated the property of the polychlorinated biphenyl (PCB) mixture Aroclor 1254 to induce porphyria by inhibition at the uroporphyrinogen decarboxylase stage of hepatic haem biosynthesis. The induction of liver tumors and other lesions were also enhanced markedly by iron overload suggesting a link between porphyria and cancer. The cellular, molecular and biochemical processes involved have been investigated in attempts to explain these phenomena by an iron-catalysed 'oxidative stress' mechanism.

Animals↗
PubMed1994

Nitrite-stimulated DNA-binding of carcinogenic diol epoxides from benzo[a]pyrene-7,8-dihydrodiol in human polymorphonuclear leukocytes.

Human polymorphonuclear leukocytes (PMNs) previously treated with 12-O-tetradecanoyl phorbolmyristate-13-acetate (PMA) to initiate the oxidative burst activate (-)-trans-7,8-dihydroxy-7,8- dihydrobenzo[a]pyrene [(-)-BP-7,8-diol)] to DNA-binding intermediates. The 32P-postlabelling technique and HPLC-analysis of enzyme-digested DNA were employed for identification of DNA-adducts following incubation of (-)-BP-7,8-diol in PMNs. The results are consistent with the formation of (+)-anti-BPDE, the ultimate carcinogen of BP, bound via trans-addition of the C-10 position in the diol epoxide molecule to the exocyclic nitrogen of deoxyguanosine (BPDE-N2-dG adduct). Addition of nitrite, the major aqueous dissolution product of NO2, stimulated the formation of (+)-anti-BPDE and subsequent binding to both nuclear DNA in PMNs (about twofold) and to DNA present outside the cells (two- to fourfold). Preliminary experiments suggest that nitrite stimulates the metabolism of (-)-BP-7,8-diol by direct interaction with myeloperoxidase and hydrogen peroxide. Consistent with previous work by us and others, the covalent binding of (+)-anti-BDPE to extracellular targets demonstrate that these reactive products, expected to be formed intracellularly, can be released from the leukocytes. Measurement of hydroxyl radical-induced DNA damage by estimating the formation of 8-hydroxydeoxyguanosine (8-OH-dG) in resting PMNs revealed low amounts of adducts (1 adduct/10(6) dG-1 adduct/10(5) dG). Pretreating the cells with PMA or PMA in conjunction with nitrite had no significant effect on 8-OH-dG adduct formation.

Biotransformation↗
PubMed1994

Alternative pathways of sulfite oxidation in human polymorphonuclear leukocytes.

Sodium sulfite is metabolized by human polymorphonuclear leukocytes by two alternative pathways, one enzymatic route dependent on sulfite oxidase and one non-enzymatic which involves intermediate formation of sulfur trioxide anion radicals. Initiation of the oxidative burst by phorbol myristate acetate significantly stimulates sulfate formation through the second pathway. The activity of sulfite oxidase in polymorphonuclear leukocytes varies greatly among individuals, a variation consistent with the suggested polymorphic distribution of sulfite oxidase in the human population.

Chromatography, High Pressure Liquid↗
PubMed1994

Stimulatory effects of sulfur and nitrogen oxides on carcinogen activation in human polymorphonuclear leukocytes.

The occurrence of inflammatory processes and of cancer in the human respiratory tract is intimately associated. One of the major factors in this is probably the recruitment of and stimulated activity of polymorphonuclear leukocytes (PML) in conjunction with the ability of these cells to convert various carcinogens to their ultimate active metabolites. In this study, we demonstrate that nitrite and sulfite, the major dissolution products of the environmental pollutants nitrogen dioxide and sulfur dioxide in water enhance the metabolic activation of trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-dihydrodiol), the proximal carcinogen of benzo[a]pyrene, to trans-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) and tetraols, the corresponding hydrolysis products, in human PML prestimulated with 12-O-tetradecanoylphorbol-13-acetate. Nitrite was more efficient than sulfite in stimulating the formation of reactive intermediates of BP-7,8-dihydrodiol in PML that covalently bind to extracellular DNA and, in particular, to intracellular proteins. The mechanism by which sulfite stimulates the metabolism of BP-7,8-dihydrodiol most probably involves the intermediate formation of a sulfur trioxide radical anion (SO3.-) the subsequent formation of the corresponding sulfur peroxyl radical anion (.OOSO3-) in the presence of oxygen. The mechanism underlying the stimulatory action of nitrite is less clear but the major pathway seems to involve myeloperoxidase. These results offer an explanation for the increased incidence of lung cancer in cigarette smokers living in urban areas. The major glutathione transferase (GST) isoenzyme in human PML is GST P1-1, a Pi-class form. The GST activity of PML was found to be inversely correlated with the extent of binding of BP-7,8-dihydrodiol products to exogenous DNA. These results suggest that individuals exhibiting high GST-activity in the PML may be better protected against the type of carcinogenic dealt with in this study.

Biotransformation↗
PubMed1991

Sodium nitrite-stimulated metabolic activation of benzo[a]pyrene 7,8-dihydrodiol in human polymorphonuclear leukocytes.

Sodium nitrite was shown to enhance the metabolism of trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) to 7/8,9,10- and 7,10/8,9-tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene (tetraols) in phorbol myristate acetate (PMA)-stimulated polymorphonuclear leukocytes (PMNs). The production of these tetraols implicates the intermediate formation of the corresponding trans-7,8-dihydroxy-9,10-epoxy-7,8-9,10-tetrahydrobenzo[a]pyrene (anti-BPDE). A 2- to 3-fold increase in the tetraol yield was observed in the presence of nitrite in excess of 1 mM. Sodium azide, an inhibitor of myeloperoxidase and catalase, reduced the nitrite-stimulated metabolism of BP-7,8-diol in PMA-activated leukocytes. Diphenylene iodonium sulphate, a NADPH-oxidase inhibitor, lowered the production of tetraols in PMA-stimulated leukocytes both in the absence and presence of nitrite. Additionally, nitrite markedly enhanced the covalent binding of metabolites derived from [3H](-)-BP-7,8-diol to leukocyte proteins as well as to DNA present extracellularly. The nitrite-stimulated covalent binding to both proteins and DNA was inhibited by the presence of sodium azide. The mechanism underlying the effect of nitrite on the metabolism of BP-7,8-diol to reactive intermediates in PMA-activated human polymorphonuclear leukocytes is not known. However, the results are compatible with a peroxidase-dependent mechanism although other possible pathways may contribute to the enhanced rate of metabolism.

Biotransformation↗