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Biomedical subjects

M Hoebeke

Publications and source records attributed to M Hoebeke.

16 recordsLinked to original sources
PubMed1998

The antibiotic ceftazidime is a singlet oxygen quencher as demonstrated by ultra-weak chemiluminescence and by inhibition of AAP consumption.

We demonstrated that the cephalosporin antibiotic ceftazidime (CAZ) deactivated singlet oxygen (1O2). We then studied the mechanisms of the CAZ effects on the ultra weak chemiluminescence (uwCL) associated with the energy decay of 1O2 generated by the Mallet reaction (H2O2 + HOCl --> HCl + H2O + 1O2), and on the anthracene-9,10-dipropionic acid (AAP) consumption by 1O2 generated by irradiation of Rose Bengal (RB). The uwCL generated by the Mallet reaction was amplified (6.2 times) by CAZ. The use of red and blue filters, which absorb radiation below 610 nm and between 470 and 700 nm respectively, demonstrated that CAZ increased the uwCL by a radiation emission at wavelengths shorter than the 633 and 704 nm wavelength emissions of 1O2. CAZ was excited by scavenging the energy excess of 1O2, which so returned to its fundamental state, while CAZ deactivated with light emission between 430-480 nm. CAZ also inhibited in a dose-dependent manner the consumption of AAP by 1O2 generated by the irradiation of RB. The protection of AAP by 5 x 10(-3) M CAZ was equivalent to that of 10(-3) M histidine and 3 X 10(-6) M sodium azide. This process of 1O2 deactivation will be useful in diseases characterized by an excessive PMN activation with a release of activated oxygen species.

Anthracenes↗
PubMed1997

Electron spin resonance evidence of the generation of superoxide anion, hydroxyl radical and singlet oxygen during the photohemolysis of human erythrocytes with bacteriochlorin a.

Photodynamic therapy with bacteriochlorin a (BCA) as sensitizer induces damage to red blood cells in vivo. To assess the extent of the contributuion of reactive oxygen species (ROS) and to determine a possible reaction mechanism, competition experiments with assorted ROS quenching or/and enhancing agents were performed in human erythrocytes as model system and in phosphate buffer. In the erythrocyte experiments, a 2% suspension was incubated with BCA for 1 h, washed with phosphate-buffered saline, resuspended and subsequently illuminated with a diode laser using a fluence rate of 2.65 mW/cm2. Potassium leakage and hemolysis were light and BCA dose dependent. Adding tryptophan (3.3 mM), azide (1 mM) or histidine (10 mM) to the erythrocyte suspension before illumination delayed the onset of K-leakage and hemolysis suggesting a type II mechanism. The D2O did not affect K-leakage nor photohemolysis. Adding mannitol (13.3 mM) or glycerol (300 nM) also caused a delay in the onset of K-leakage and hemolysis, suggesting the involvement of radicals. In phosphate buffer experiments, it was shown using electron spin resonance (ESR) associated with spin-trapping techniques that BCA is able to generate O2-. and OH. radicals without production of aqueous electron. Visible or UV irradiation of the dye in the presence of the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) gave an ESR spectrum characteristic of the DMPO-hydroxyl radical spin adduct DMPO-OH. Addition of ethanol or sodium formate produced supplementary hyperfine splittings due to the respective CH3CHOH. and CO2-. radical adducts, indicating the presence of free OH.. Production of DMPO-OH was partly inhibited by superoxide dismutase (SOD), catalase and desferrioxamine, suggesting that the iron-catalyzed decomposition of H2O2 was partly involved in the formation of one part of the observed OH.. The complementary inhibition of DMPO-OH production by azide and 9,10-anthracenedipropionic acid (ADPA) was consistent with 1O2 production by BCA followed by reaction of 1O2 with DMPO and decay of the intermediate complex to form DMPO-OH and free OH.. All our results seem to indicate that BCA is a 50%/50% type 1/type 2 sensitizer in buffered aqueous solutions and confirmed that the dye-induced hemolysis of erythrocytes was cell caused by a mixed type 1/type 2 mechanism.

Cyclic N-Oxides↗
PubMed1995

The importance of liposomes as models and tools in the understanding of photosensitization mechanisms.

The various applications of liposomes in understanding photosensitization are described in this paper, with particular emphasis on the various kinds of information that these models allow to obtain in phototherapy. Liposomes are simple vesicles in which an aqueous phase is enclosed by a phospholipidic membrane. They are suitable models mimicking specific situations occurring in vivo and they allow study of the influence of physicochemical, photobiological and biochemical factors on the uptake of photosensitizers by tissues, their mechanisms of action and the subsequent photoinduced tumor necrosis. Moreover, solubilization of the sensitizer into the bilayer seems to improve its tumoral selectivity and its photodynamic efficiency.

Animals↗
PubMed1995

Endonasal dacryocystorhinostomy: indications, technique and results.

Dacryocystorhinostomy (DCR) allows an obstructed lachrymal drainage system to be drained into the nasal fossa. Since the development of endonasal microsurgical techniques, the endonasal approach presents itself as an alternative choice to the conventional external approach. It is far less traumatic, yet as efficacious as the conventional approach, and avoids the need for a skin incision and the disruption of the medial canthal structures. Twenty-six patients suffering from lachrymal system obstruction underwent 28 endonasal dacryocystorhinostomies under microscopical (n = 25) or endoscopic control (n = 3). Pre-operative assessment included clinical symptoms (sac swelling, purulent secretions, epiphora) and outflow obstruction on X-rays (conventional dacryocystography and/or subtraction macrodacryocystography). Post-operatively, 23 DCR were free of symptoms. Two presented occasional epiphora and three were unsuccessful. The presence of pre-operative purulent secretions was significantly correlated with post-operative success and with lachrymal sac patency, which is also confirmed by X-ray examination (p<0.001). Thus in cases of purulent secretion with epiphora, X-ray examination is redundant and may be avoided. On the contrary, when epiphora is an isolated symptom, X-rays must be performed in order to determine where the obstruction is located and to provide information on lachrymal sac morphology.

Adolescent↗
PubMed1995

[Effect of local medications on intraocular pressure control following trabeculectomy].

Longterm administration of topical antiglaucoma therapies had been indicated to be a serious risk for failure of trabeculectomy through inducing a subclinical inflammation of conjunctival tissues and stimulating secondary fibroblastic proliferation. Our study had 3 main aims: (1) to check if this pejorative effect is present in our population of glaucomatous patients, (2) in order to improve the rate of surgical success in theoretically high risk patients (duration of topical treatment longer than 36 months), to determine the usefulness of the following actions: suppression of beta blocking agents 8 days before surgery, suppression of miotics and eventual topical administration of fluorometholone one month before surgery. (3) to correlate the observed clinical results to the cellular profile of preoperative conjunctival biopsies. We presented in a first step the results of a retrospective analysis including 88 trabeculectomies performed between January '93 and April '95 in 62 GCAO patients older than 40 years and without any previous ocular surgery. The mean age of patients was 66,8 years (41 to 87 years). Patients were classified into "complete success", "qualified success" and "failures" according to the "target" IOP was or was not reached in the last examination. Mean follow up was 5,8 months (1 to 26 months). The second prospective part of our study included 20 trabeculectomies performed in 16 patients we chose according to the nature, the duration of the preoperative topical therapy and the preoperative eventual preparation of the conjunctiva. This study also included a semiquantitative count of the different conjunctival cellular colonies in peroperative biopsies. Mean follow up of this study was 2,3 months (1 to 5 months). 31 "complete success", 52 "qualified success" and 5 "failure" were observed in the retrospective study. The reduction of IOP following trabeculectomy was statistically significant at all examinations (mean IOP in the last examination: 14,9 +/- 4,3 mmHg) but the level of success was not significantly different according to the nature, (mono against polytherapy), the duration of preoperative medical topical treatment, as well as the preoperative actions in order to improve the operative success in high risk patients. Preliminary results of our second prospective study did not yet show any failure and did not exhibit any clear correlation between the counts of the different cellular colonies and the level of operative success on one hand and the different topical therapies in the other hand. The results and limitations of this study were compared to those of the literature.

Adrenergic beta-Antagonists↗
PubMed1994

Quenching of merocyanine 540 triplet state by nitroxyl radicals in liposomal systems: a laser flash photolysis study.

Laser flash photolysis experiments were undertaken to investigate the interaction between stearic acid nitroxide spin probes and photoexcited merocyanine 540 (MC540) in dimyristoyl-L-alpha-phosphatidylcholine liposomes (membrane model). The measurements of the paramagnetic signal decay kinetics of four different spin-labelled stearic acids (n-DSA) show that the direct interaction between the dye and the probe is affected by the position of the nitroxyl group along the carbon chain. Laser flash photolysis results reveal a significant decrease in the MC540 triplet lifetime in the presence of n-DSA, the effect depending on the depth at which the nitroxyl moiety is localized in the bilayer. Previous results on the rate of disappearance of the electron spin resonance (ESR) nitroxide signal on continuous photolysis of the same systems do not show the same dependence on the localization of the nitroxyl moiety in the liposome. Although the MC540 triplet state seems to be implicated in the reaction process, the results suggest that ESR and laser flash experiments demonstrate two different kinds of mechanism.

Dimyristoylphosphatidylcholine↗
PubMed1993

Destruction of stearic acid nitroxyl radicals mediated by photoexcited merocyanine 540 in liposomal and micellar systems.

Fatty acid spin labels have been included into liposomes and micelles, in order to study the photochemical behavior of merocyanine 540 toward nitroxyl radicals situated at various depths in the bilayer or the surfactant layer. Visible illumination of the dye, either free in ethanol or bound to liposomes or micelles, leads to the reduction of the electron spin resonance signal of the label. The efficiency of the interaction between merocyanine 540 and spin labels depends on the depth at which the nitroxyl moiety is localized in the micelle or vesicle. Fluorescence measurements indicate that the first excited singlet state of merocyanine 540 is not directly implicated in the reaction mechanism. Flash photolysis experiments conducted in aqueous solutions of hexadecyltrimethylammonium bromide micelles show that the presence of nitroxyl radical decreases the rate constant of triplet decay in a concentration-dependent fashion. The corresponding quenching rate constant (kq) is determined for the different spin labels. The kq values and the reduction rates of ESR signal show the same dependence on the localization of the nitroxyl moiety in the micelles.

Cetrimonium↗
PubMed1993

HIV-1 promoter activation following an oxidative stress mediated by singlet oxygen.

Various biological processes, such as photosensitization or inflammatory reactions, can generate singlet oxygen (1O2) as one of the major oxidative species. Because this oxidant can be generated either extracellularly or intracellularly, it can cause severe damage to various biological macromolecules, even to those deeply embedded inside the cells such as DNA. Sublethal biological modifications induced by different DNA-damaging agents can promote various cellular responses initiated by the activation of various cellular genes and certain heterologous viruses. Since 1O2 fulfils essential prerequisites for a genotoxic substance, we have examined the effects of an oxidative stress, mediated by this species, on cells harbouring a heterologous promoter-leader sequence derived from the human immunodeficiency virus type 1 (HIV-1). Our results demonstrate that HIV-1 long terminal repeat (LTR), integrated into the cellular DNA of epithelial cells, can be transactivated following an oxidative stress mediated by 1O2. In addition, using HIV-1 latently infected promonocytes or lymphocytes, it can be shown that virus reactivation can be induced through a sublethal dose of 1O2 generated intracellularly. An extracellular generation of 1O2 can promote a substantial lethal effect without HIV-1 reactivation. These data may be relevant to the understanding of the events converting a latent infection into a productive one and to the appearance of the acquired immune deficiency syndrome.

Cell Survival↗
PubMed1991

Photosensitized production of singlet oxygen by merocyanine 540 bound to liposomes.

The production of singlet oxygen by merocyanine 540 was studied in dimyristoyl-phosphatidylcholine liposomes using two singlet oxygen probes: 9,10-anthracenedipropionic acid (water soluble) and 9,10-dimethylanthracene (liposoluble). Upper and lower limits of singlet oxygen quantum yield for bound merocyanine 540 were determined to be 0.055 and 0.015 respectively. The diffusion characteristics of singlet oxygen were examined using the isotropic enhancement effect of D2O and the inhibitory effect of sodium azide. It was shown that 1O2 spent more than 87% of its lifetime in a vesicle environment. When the singlet-reacting substrate and the dye were both located in the bilayer, approximately 40% of the singlet oxygen remained in the liposomes where it was originally generated.

Dimyristoylphosphatidylcholine↗
PubMed1991

[Microsurgical approach to the lacrimal ducts. Technical aspects--indications--reasons for failure].

The dacryocystorhinostomy is an operation that connects directly the lacrymal sac to the nasal cavity. In 1904, Toti described the external approach but one had to wait until the development of the sinus surgery to have a new interest in the endonasal approach. It appears to be a safe, efficacious and a less traumatizing procedure preserving the lacrymal function without skin incision. It allows a procedure in a non-scarred field. A good relationship between the ENT and the ophthalmologist is required.

Child, Preschool↗
PubMed1990

Triplet yield of merocyanine 540 in water is wavelength dependent.

Monomers and aggregates of Merocyanine 540 (MC540) in water are able to photoisomerize. The shape of the photoisomer absorption spectrum is very similar to that of the ground state. Triplet state of MC540 in water has been produced by energy transfer from triplet anthracene and displays a broad absorption spectrum between 600 and 700 nm. The triplet state may also be produced by direct excitation of MC540 with UV light. However, when the dye is excited by visible light, no triplet state absorbance in the red could be detected so that the triplet yield of MC540 in water seems to be excitation wavelength dependent.

Kinetics↗
PubMed1988

Singlet oxygen production and photoisomerization: two competitive processes for merocyanine 540 irradiated with visible light.

The quantum yields of singlet oxygen production by merocyanine 540 have been measured during visible light irradiation performed in methanol and ethanol. These appear to be one hundred times smaller than the quantum yield for rose bengal measured under the same conditions. Flash photolysis experiments demonstrate the ability of merocyanine 540 molecules to isomerize under visible light irradiation: the isomerization quantum yields are about 0.65 in both ethanol and methanol. This information combined with the fluorescence quantum yield data account for the low values for singlet oxygen production.

Isomerism↗