Biomedical subjects
Publications and source records attributed to M Pourtois.
G. Vanbelle, President of the Flemish Dental Association, interviews professor M. Pourtois of the Free University of Brussels on various topics. Are discussed the free market mechanisms, permanent education, quality assurance, policy of editing scientific articles, subvention of dental schools, evidence based medicine, ethics and empathy for the patient.
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NADH: hypothiocyanite oxidoreductase (NHOR) activity, found in some oral Streptococci, is postulated to protect these microorganisms against salivary peroxidase-produced hypothiocyanite. NHOR, however, has not been purified so far. The purification of NHOR from crude extracts of Streptococcus sanguis NCTC 7863 strain (by ultrafiltration and anion-exchange chromatography) revealed one fraction of 125 +/- kDa. However, SDS-PAGE electrophoresis provided a single protein of 21.1 +/- 1.2 kDa. This last discovery suggests that NHOR enzyme is a hexameric complex having six subunits.
The physiological variations of fibrinolytic activity (FA) in saliva were investigated in a population of 149 healthy volunteers including 12 pregnant women. An increase in FA could be observed with increasing age. Marked variations were observed during daytime with a peak value early in the morning. Higher FA values were observed in males as compared with females in the 20-39 yr age group. A clear decrease in FA was observed during pregnancy. A significant correlation existed between FA and suspended epithelial cell concentration, which seemed responsible for most of the physiological FA variations. It was concluded that age, sex, pregnancy, and the time of the day are important for salivary FA and should be taken into account in any study on salivary FA related to physiological or pathological processes.
Fluoride-mediated inhibition of peroxidase potential activity in human saliva was investigated using NaF, NH4F, CaF2, Na2PO3F (MFP), SnF2 and TiF4. At pH 5.5 and for a 20 mM F concentration, the inhibition percentages increased from 2% for MFP and 5% for CaF2 to 61% for NaF and 65% for NH4F, while a 100% inhibition was observed at 10 mM for TiF4 and at 5 mM for SnF2. The inhibition was enhanced at acid pH and removed at pH 7. The inhibition could be attributed to ionized F-, except for SnF2 and TiF4, in which part of the inhibition could be imputed to the cations.
The balance of NADH oxidation by neutrophil lysates in the presence and in the absence of peroxidase/H2O/halide systems, pointed out a NADH oxidation excess when these hypohalite generators were actually present. This unexplained NADH consumption could not be attributed to a direct oxidation by hypohalites nor by the lysate self. Using OCI- as substrate, the NADH oxidation excess ranged from 52 to 99 mU/ml at pH 7.40 and from 446 to 1346 mU/ml at pH 6.00 (N = 6). Similar results were also found while using hypoiodous and hypothiocyanous compounds at pH 7.40 but not at pH 5.50. The authors discuss different hypotheses to explain this phenomenon and accordingly elaborate on the possible consequences of neutrophils degranulation in the oral tissues during inflammation processes.
The effect of the human recombinant myeloperoxidase (recMPO) system on the viability of Candida albicans blastospores was determined. Cells were incubated in the presence of the enzyme, H2O2, and various substrates. In optimal conditions, 100% mortality was reached with only 41 mU of recMPO per ml, confirming its powerful candidicidal activity.
This study describes a method aimed at measuring the bacterial ATP content of dental plaques formed on a polyester support attached on tooth surfaces in the oral cavity. It reports on the variations in ATP content in 3 days old plaques of a well-defined surfaces with or without the use of 0.2% chlorhexidine mouth-wash twice daily. The results, expressed in bacterial equivalents, show a reduction of dental plaque metabolism after 3 days of chlorhexidine rinses to 19.5% of its value in the control tests without mouth-washes. Bacterial metabolism represented 6.05 bacterial equivalents per mm2 in the control group versus 1.18 equivalents in the chlorhexidine test group.
The oral flora is under the control of both immunity and non specific defense factors. The immunity factors are mostly represented by polymorphonuclears immunoglobulins Non specific defense factors include lysozyme lactoferrin high molecular weight proteins, such as mucins fibronectin and beta 2 microglobulin histidine rich proteins cystatins salivary amylases salivary peroxidase system.
Fluoride (F-) inhibition of peroxidase activity in whole saliva and of recombinant human myeloperoxidase was investigated using thiocyanate (SCN-) and chloride (Cl-) as substrates. At pH 5.5, SCN(-)-linked activity in whole saliva reduced to < 40% of its initial value at F- concentration of 20 mM, while Cl- linked activity was maintained at 90% of its initial value for the same F-concentration. Based on this Cl(-)-linked activity, the contribution of natural MP to the SCN(-)-linked activity in whole saliva can be calculated. This shows a total inhibition of SCN- dependent activity of salivary peroxidase (SP) for F-concentrations > 10 mM. At a 20 mM F-concentration, recombinant MP activity reduced to 66% of its initial value with SCN-, against 88% for Cl- as substrate. This inhibition of the SCN- linked SP activity is enhanced at acid pH for a F-concentration of 20 mM: 26% residual activity at pH 5 for whole saliva + SCN-against 93% for whole saliva + Cl-; 61% for recombinant MP + SCN- and 88% for MP + Cl-. Calculated activities for SP alone showed a total inhibition at pH 5, while the inhibition was absent at pH 6.5. F-inhibition in whole saliva could also be suppressed by the addition of hydrogen peroxide.
The susceptibility of Capnocytophaga ochracea, Eikenella corrodens, Eubacterium yurii, Fusobacterium nucleatum, Peptostreptococcus micros, Prevotella intermedia, Selenomonas sputigena, Wolinella recta to hypothiocyanite (OSCN-) produced by the lactoperoxidase system was tested. Results showed a decrease of bacterial survival rate after OSCN- exposure, with an intra- and inter-species variability from 0 to 95% for C. ochracea, 34-100% for E. corrodens, 0-83% for E. yurii, 1-15% for F. nucleatum, 8-61% for P. micros, 0-100% for P. intermedia, 0-44% for S. sputigena and 0-8% for W. recta. The survival rate did not correlate with the NADH/OSCN- oxidoreductase activity present in the lysed bacteria (r = -0.3248; N = 15; NS).
Filtration or centrifugation are two methods frequently used to clarify human whole saliva. This study compares both the drop in peroxidase activity following filtration (49.3% +/- 16.4%; N = 12) or centrifugation (33.6% +/- 15.9%; N = 6) and the drop in total protein concentration after filtration (33.9% +/- 13.4%) and centrifugation (23.6% +/- 8.7%). After filtration, the loss was not only due to retention of the large particle-bound fraction but also to adsorption on the filter membranes. This adsorption could be inhibited by a previous dilution of saliva in a citrate buffer, which also gave rise to active subunits with a molecular weight less than or equal to 100 kDa.
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HIV aliquots, from a supernatant of ARV-4 cell line, were mixed with an equal volume of a OSCN.generating glucose-glucose oxidase + thiocyanate-lacteroperoxidase solution, and then pre-incubated at 37 degrees C for periods of 30 secs to one hour. These mixtures were then inoculated into cultures of phytohaemagglutinin-stimulated lymphocytes. Viral growth was monitored with an ELISA quantitating the specific p24 protein either in the culture cells or in the supernatant. In control experiments, the virus produced both intra- and extra-cellular p24. In the controls, concentration of p24 per 10(6) lymphocytes grew rapidly. By contrast, HIV that was pretreated with the OSCN generating system for 30 sec., produced very little p24, and no detectable amount of this protein could be found after 2 min. pre-treatment.
HSV1 suspensions were pre-incubated in a lactoperoxidase thiocyanate oxidizing system before inoculation in MRC5 fibroblast cultures. This pre-treatment could either delay or even abolish the HSV1 cytopathic potentiality. The effect was found to be time-dependent.
Growth control of anaerobes in the oral cavity, is secured--among other means--by: 1) phagocytosis of opsonized bacteria; 2) synthesis of hypothiocyanite by the salivary peroxidase system. The former may be inhibited by bacterial acid byproducts. As for the salivary hypothiocyanite, it proved itself able of hindering in vitro the growth of bacterial strains known as customary periodontal pathogens. Its possible effectiveness in vivo remains however hypothetical in the case of deep gingival pockets according to the poor diffusion there of salivary components.
Risk assessment methods do not refer to the dynamical processes at the back of observed values of parameters, when relating an effect to one evaluation of doses, or bio-indicator values to external contamination levels. This results in decreasing responses of the human organism as a function of increasing exposure levels. On the contrary, the ecotoxicological approach, applied to the case of lead, shows that a first order kinetics holds until blood lead of 80 micrograms/dl blood, either for the relation between tooth and blood lead, or for this between blood lead and the flux of lead absorbed daily (micrograms/day). Then, the max. admissible concentrations for various sources of Pb should be lowered strongly, for maintaining the Pb body burden below limit values. The method is proposed for application to a series of other pollutants, and for risk reevaluation.
Rapidly progressive periodontal disease was found in three patients belonging to three different generations of the same family. Beyond the clinical inspection, blood examination allowed measurements of the luminol enhanced biochemiluminescence from the circulating PMN leukocytes. Abnormally low values were recorded in the affected individuals (75, 84 and 138 mVolts per 10(6) cells) whereas a sample of healthy individuals exhibited photonic values from 240 up to 910 mVolts per 10(6) cells. These abnormal values, however, were not constantly recorded. They gave way to higher PMN activity indices after the patients had been treated either by antibiotics, scaling, debridement or classical pocket cleaning.