Biomedical subjects

S Armand

Publications and source records attributed to S Armand.

At least 19 recordsLinked to original sources

PubMed2006

Java project on periodontal diseases. The natural development of periodontitis: risk factors, risk predictors and risk determinants.

OBJECTIVE: To identify risk factors, risk predictors and risk determinants for onset and progression of periodontitis. MATERIAL AND METHODS: For this longitudinal, prospective study all subjects in the age range 15-25 years living in a village of approximately 2000 inhabitants at a tea estate on Western Java, Indonesia, were selected. Baseline examination was carried out in 1987 and follow-up examinations in 1994 and 2002. In 2002, 128 subjects could be retrieved from the original group of 255. Baseline examination included evaluation of plaque, bleeding on probing, calculus, pocket depth, attachment loss and presence of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, spirochetes and motile microorganisms. RESULTS: The mean attachment loss increased from 0.33 mm in 1987 to 0.72 mm in 1994 and 1.97 mm in 2002. Analysis identified the amount of subgingival calculus and subgingival presence of A. actinomycetemcomitans as risk factors, and age as a risk determinant, for the onset of disease. Regarding disease progression, the number of sites with a probing depth > or = 5 mm and the number of sites with recession were identified as risk predictors and male gender as a risk determinant. CONCLUSION: Screening of these parameters early in life could be helpful in the prevention of onset and progression of periodontal diseases.

Adolescent↗

PubMed2001

Influence of the aglycone region of the substrate binding cleft of Pseudomonas xylanase 10A on catalysis.

Pseudomonas cellulosa xylanase 10A (Pc Xyn10A) contains an extended substrate binding cleft comprising three glycone (-1 to -3) and four aglycone (+1 to +4) subsites and, typical of retaining glycoside hydrolases, exhibits transglycosylation activity at elevated substrate concentrations. In a previous study [Charnock, S. J., et al. (1997) J. Biol. Chem. 272, 2942-2951], it was demonstrated that the -2 subsite mutations E43A and N44A caused a 100-fold reduction in activity against xylooligosaccharides, but did not influence xylanase activity. This led to the proposal that the low activity of these mutants against xylooligosaccharides was due to nonproductive complex formation between these small substrates and the extended aglycone region of the active site. To test this hypothesis, key residues at the +2 (Asn182), +3 (Tyr255), and +4 (Tyr220) subsites were substituted for alanine, and the activity of the mutants against polysaccharides and oligosaccharides was evaluated. All the aglycone mutants exhibited greatly reduced or no transglycosylating activity, and the triple mutants, E43A/Y220A/Y255A and E43A/N182A/Y255A, had activity against xylotriose similar to that of E43A. The aglycone mutations caused an increase in both k(cat) and K(m) against xylan, with N182A/Y220A/Y255A and N182A/Y255A exhibiting 25- and 15-fold higher k(cat) values, respectively, than wild-type Pc Xyn10A. These data indicate that Glu43 plays a role in binding xylooligosaccharides, but not xylan, suggesting that the mechanisms by which Pc Xyn10A binds polysaccharides and oligosaccharides are distinct. The increased k(cat) of the mutants against xylan indicates that the aglycone region of wild-type Pc Xyn10A restricts the rate of catalysis by limiting diffusion of the cleaved substrate, generated at the completion of the k(2) step, out of the active site.

Alanine↗

PubMed2001

Untreated periodontal disease in Indonesian adolescents. Subgingival microbiota in relation to experienced progression of periodontitis.

BACKGROUND/AIMS: In an Indonesian population deprived of regular dental care, the experienced progression of disease between baseline (1987) and follow-up (1994) was investigated in relation to the composition of the subgingival microbiota at follow-up. At baseline the age ranged from 15 to 25 years. Clinical and microbiological evaluation was completed in 158 of the 167 subjects available at follow-up. METHODS: Plaque index (PI), pocket depth (PD), bleeding on probing (BOP), and attachment loss (AL) were scored at the approximal surfaces of all teeth and subgingival calculus on the approximal surfaces of the Ramfjord teeth only (number of sites with subgingival calculus: NSC). A pooled sample of the deepest pocket in each quadrant was evaluated using microbiological culture techniques. RESULTS: At baseline the mean values of the clinical parameters were AL=0.35 mm, PI=1.01, BOP=0.80 PD=3.25 mm and NSC=6.04 and at follow-up AL=0.75 mm, PI=1.16, BOP=1.19, PD=3.34 mm and NSC=5.85. All parameters except PD and NSC showed a statistically significant increase. At follow-up the prevalence of Actinobacillus actinomycetemcomitans was 40%, of Porphyromonas gingivalis 67%, of Prevotella intermedia 66%, of Fusobacterium nucleatum 79%, of Bacteroides forsythus 16%, of Campylobacter rectus 4%, and of P. micros 6%. No differences in clinical parameters were found between groups with or without these micro-organisms. In 129 subjects AL of > or =2 mm at > or =1 site was found. Logistic regression showed three significant odds-ratio's for experienced progressive periodontitis: Plaque index (12.2), gender (3.4) and Actinobacillus actinomycetemcomitans (2.9). CONCLUSIONS: The results of this retrospective study suggest that plaque is the most important parameter related to experienced disease progression, and that the presence of A. actinomycetemcomitans may be associated with increased chance of disease progression.

Adolescent↗

PubMed2000

The active site topology of Aspergillus niger endopolygalacturonase II as studied by site-directed mutagenesis.

Strictly conserved charged residues among polygalacturonases (Asp-180, Asp-201, Asp-202, His-223, Arg-256, and Lys-258) were subjected to site-directed mutagenesis in Aspergillus niger endopolygalacturonase II. Specific activity, product progression, and kinetic parameters (K(m) and V(max)) were determined on polygalacturonic acid for the purified mutated enzymes, and bond cleavage frequencies on oligogalacturonates were calculated. Depending on their specific activity, the mutated endopolygalacturonases II were grouped into three classes. The mutant enzymes displayed bond cleavage frequencies on penta- and/or hexagalacturonate different from the wild type endopolygalacturonase II. Based on the biochemical characterization of endopolygalacturonase II mutants together with the three-dimensional structure of the wild type enzyme, we suggest that the mutated residues are involved in either primarily substrate binding (Arg-256 and Lys-258) or maintaining the proper ionization state of a catalytic residue (His-223). The individual roles of Asp-180, Asp-201, and Asp-202 in catalysis are discussed. The active site topology is different from the one commonly found in inverting glycosyl hydrolases.

Aspergillus niger↗

PubMed2000

Untreated periodontal disease in Indonesian adolescents. Longitudinal clinical data and prospective clinical and microbiological risk assessment.

BACKGROUND, AIMS: In order to investigate the r le of various putative clinical and microbiological risk markers, a longitudinal study was initiated in a young population deprived of regular dental care. In 1987 all inhabitants in the age range 15-25 years living in a village with approximately 2,000 inhabitants at a tea estate on Western Java, Indonesia, were examined clinically and microbiologically. In total, 167 subjects of the original group of 255 adolescents were re-examined in 1994. The material presented in this paper describes the clinical periodontal condition at baseline (1987) and at follow-up (1994), 7 years later. Furthermore, the relationship between progression of the disease and baseline clinical and microbiological data was assessed. METHODS: Plaque index (PI), bleeding on probing (BOP), pocket depth (PD), and attachment loss (AL) were scored at the approximal surfaces of the vestibular aspects of all teeth. The number of approximal surfaces of the Ramfjord teeth showing subgingival calculus was recorded. At baseline, the dorsum of the tongue, the buccal gingiva in the upper jaw, the saliva and the deepest bleeding pocket without clinical loss of attachment were sampled for microbiological examination with phase contrast microscopy and indirect immunofluorescence. RESULTS: Mean values at baseline and at follow-up were PI: 1.01 and 1.15, BOP: 0.80 and 1.16, PD 3.26 mm and 3.32 mm, AL: 0.33 mm and 0.73 mm, respectively. All parameters except PD showed a statistically significant increase over the 7-year period. The prevalence of the studied bacteria irrespective of the sample site was: A. actinomycetemcomitans 53%, P. gingivalis 88%, P. intermedia 100%, spirochetes 89% and motile micro-organisms 100%. At the full mouth level, logistic regression showed significant odds ratios for progressive disease with age (1.15), subgingival calculus (1.20) and subgingival presence of A. actinomycetemcomitans (4.61). Presence of any of the selected micro-organisms on the mucous membranes was not related with progressive disease. In order to study local factors to explain local disease activity, each subject was characterized using the sampled pocket, which was the deepest bleeding pocket without LA at baseline, as a single response site per patient. In this constrained design, the main statistical factors associated with progressive disease were presence of motile micro-organisms and the plaque score. CONCLUSIONS: This study identified 3 main risk markers for disease progression at the full mouth level: age, amount of subgingival calculus and subgingival presence of A. actinomycetemcomitans.

Adolescent↗

PubMed2000

Histologic analysis of a fractured implant: a case report.

This study presents the histologic analysis of an implant retrieved 14 months after loading because of a fracture in the collar region. The implant (Biovent) was removed with part of the periimplant tissues, and the block was prepared using cutting and grinding equipment to obtain 3 sections approximately 30 microns thick. The examination evidenced a high degree of osseointegration, with a bone-to-implant contact of 74% +/- 13%. The lamellar bone was dense and in close relation with the hydroxyapatite coating of the implant. The connection between the 0.4-mm hydroxyapatite coating and the metal was always very tight. The thickness of the metal at the break point was assessed to be 1.6 mm. Besides the relative weakness of the metal at the neck of the implant, other possible causes of failure are discussed.

Biocompatible Materials↗

PubMed1999

1.68-A crystal structure of endopolygalacturonase II from Aspergillus niger and identification of active site residues by site-directed mutagenesis.

Polygalacturonases specifically hydrolyze polygalacturonate, a major constituent of plant cell wall pectin. To understand the catalytic mechanism and substrate and product specificity of these enzymes, we have solved the x-ray structure of endopolygalacturonase II of Aspergillus niger and we have carried out site-directed mutagenesis studies. The enzyme folds into a right-handed parallel beta-helix with 10 complete turns. The beta-helix is composed of four parallel beta-sheets, and has one very small alpha-helix near the N terminus, which shields the enzyme's hydrophobic core. Loop regions form a cleft on the exterior of the beta-helix. Site-directed mutagenesis of Asp(180), Asp(201), Asp(202), His(223), Arg(256), and Lys(258), which are located in this cleft, results in a severe reduction of activity, demonstrating that these residues are important for substrate binding and/or catalysis. The juxtaposition of the catalytic residues differs from that normally encountered in inverting glycosyl hydrolases. A comparison of the endopolygalacturonase II active site with that of the P22 tailspike rhamnosidase suggests that Asp(180) and Asp(202) activate the attacking nucleophilic water molecule, while Asp(201) protonates the glycosidic oxygen of the scissile bond.

Amino Acid Sequence↗

PubMed1999

Regulation of the transcription of genes encoding different virulence factors in Helicobacter pylori by free iron.

Since free iron possesses a poor solubility under physiologic conditions and thus becomes a limiting nutrient for growth, a shift from high- to low-iron environmental conditions is an important signal for bacteria to coordinate the regulation of gene expression. Here, we studied and compared the level of transcripts corresponding to the vacA (cytotoxin), ureA (urease), cagA (cytotoxin-associated antigen) and fur (ferric uptake regulator) genes of Helicobacter pylori, grown under iron-sufficient and iron-restricted conditions. A significant increase in the accumulation of vacA and fur transcripts was observed under iron-restricted conditions. This up-regulation by low levels of iron seems to be not directly regulated by Fur, and certainly requires other regulatory factors. No statistical difference was defined in the accumulation of cagA and ureA.

Antigens, Bacterial↗

PubMed1998

Meta-analysis of the efficacy of extradural clonidine to relieve postoperative pain: an impossible task.

Clonidine, an alpha2 adrenoceptor agonist, has anti-hypertensive and anti-nociceptive effects. It is commonly used in association with local anaesthetics and opioids to enhance the quality and duration of extradural analgesia in the postoperative period, and to decrease the incidence of side effects. As a sole analgesic, it has seldom been used to relieve postoperative pain. The dose of extradural clonidine to achieve good pain relief without deleterious side effects remains undetermined. In order to address this problem, we performed a computer search via two well-known databases, Medline and Excerpta Medica, covering the period from 1985 to September 1997. One hundred and fifty-nine articles were retrieved of which 38 dealt with extradural clonidine and postoperative pain. All but 16 studies suffered from serious design flaws, such as lack of controls and/or randomization, or inadequate statistical analysis. The data from these studies were difficult to interpret because of the tremendous variation in variables, especially dose of clonidine, level of extradural injection, time of administration, type of anaesthesia, type of surgery, and reference and rescue drugs. The simultaneous extradural use of local anaesthetics and opioids further hindered data interpretation, and precluded any meta-analysis. Proposals for a standard study design are made to help comparison between studies involving extradural clonidine and postoperative pain.

Adrenergic alpha-Agonists↗

PubMed1998

Untreated periodontal disease in Indonesian adolescents. Clinical and microbiological baseline data.

At present, several risk factors for the initiation and progression of periodontitis have been identified. In order to investigate the rôle of various potential clinical and microbiological risk factors and indicators, a longitudinal study was initiated in a young population deprived from regular dental care. The present communication describes the baseline cross-sectional data obtained in 1987 in terms of the clinical periodontal condition and prevalence of periodontal bacteria in the oral cavity. All inhabitants in the age range 15-25 years of a village with approximately 2000 inhabitants at a tea estate on Western Java, Indonesia, were examined clinically and microbiologically. In total, 255 adolescents, comprising 130 males and 125 females participated in the study. Samples for bacteriological examination were taken from the gingiva, the dorsum of the tongue, and the saliva. Plaque index, bleeding upon probing, pocket depth, and attachment loss (AL) were scored on the approximal surfaces from the vestibular aspect of all teeth as well as the mid-vestibular and mid-lingual aspects of the Ramfjord teeth. Calculus was scored only on the 4 surfaces of the Ramfjord teeth. Following the clinical measurements, the deepest bleeding pocket with no clinical loss of attachment was sampled for microbiological examination. In addition, in 37 subjects a deep bleeding (> or = 4 mm) with at least 4 mm of attachment loss was sampled. Moderate periodontitis (max. AL 3-4 mm) was found in 26% of the population, advanced periodontitis (max. AL > or = 5 mm) in 8%, whereas 66% of the population showed no or minor periodontitis (max. AL 0-2 mm). Actinobacillus actinomycetemcomitans was found in 57% of the population, Porphyromonas gingivalis in 87%, Prevotella intermedia and motile rods in all cases and spirochetes in 89%. P. gingivalis (66%), A. actinomycetemcomitans (37%) and spirochetes (63%) were, of all the sampled sites of the oral cavity, most frequently detected in pockets without attachment loss. Motile rods were most prevalent on the tongue and in the saliva (92% and 89%, respectively). A high prevalence of the investigated periodontal bacteria was detected both in the pockets without and with attachment loss. No significant association between the clinical periodontal parameters and the prevalence of the microorganisms was observed at a patient level. At a site level, both P. gingivalis and spirochetes were more prevalent in sites with attachment loss. The actual rôle of these putative periodontal pathogens may be elucidated more extensively, when longitudinal data on the present population become available.

Adolescent↗

PubMed1997

Serratia marcescens chitobiase is a retaining glycosidase utilizing substrate acetamido group participation.

The stereochemistry of the reaction catalysed by Serratia marcescens chitobiase was determined by HPLC separation of the anomers of N-acetylglucosamine produced during the hydrolysis of p-nitrophenyl N-acetyl-beta-d-glucosaminide (PNP-GlcNAc). In the early stages of the reaction, the beta-anomer was found to prevail, whereas the alpha-anomer dominated at mutarotation equilibrium. This established that chitobiase hydrolyses glycosidic bonds with overall retention of the anomeric configuration. Chitobiase-catalysed hydrolysis of PNP-GlcNAc was competitively inhibited by a series of chito-oligosaccharides (degree of polymerization 2-5) that were selectively de-N-acetylated at their non-reducing end. The results are in accord with the participation of the acetamido group at C-2 of the substrate in the catalytic mechanism of chitobiase and related enzymes.

Acetylation↗

PubMed1997

A bifunctionalized fluorogenic tetrasaccharide as a substrate to study cellulases.

Cellulases are usually classified as endoglucanases and cellobiohydrolases, but the heterogeneity of cellulose, in terms of particle size and crystallinity, has always represented a problem for the biochemical characterization of the enzymes. The synthesis of a bifunctionalized tetrasaccharide substrate suitable for measuring cellulase activity by resonance energy transfer is described. The substrate, which carries a 5-(2-aminoethylamino)-1-naphthalenesulfonate group on the non-reducing end and an indolethyl group on the reducing end, was prepared from beta-lactosyl fluoride and indolethyl beta-cellobioside by a chemoenzymatic approach using the transglycosylating activity of endoglucanase I of Humicola insolens as the key step. The bifunctionalized substrate has been used for the determination of the catalytic constants of H. insolens endoglucanase I and cellobiohydrolases I and II; this substrate could be of general use to measure the kinetic constants of cellulases able to act on oligomers of degree of polymerization <5. The data also provide evidence that cellobiohydrolases I and II are able to degrade an oligosaccharide substrate carrying non-carbohydrate substituents at both ends.

Carbohydrate Conformation↗

PubMed1996

Plant chitinases use two different hydrolytic mechanisms.

Bacterial, fungal, animal, and some plant chitinases form family 18 of glycosyl hydrolases. Most plant chitinases form the family 19. While some chitinases also have lysozyme activity, animal lysozymes belong to different families. For glycosyl hydrolases, two reaction mechanisms are possible, leading to either retention or inversion of the anomeric configuration. We analyzed by HPLC the stereochemical outcome of the hydrolysis catalyzed by cucumber and bean chitinases, belonging to families 18 and 19, respectively. Cucumber chitinase used the retaining mechanism as known for bacterial chitinases and hen egg white lysozyme for which the mechanism has been determined. In contrast, bean chitinase catalyzed the hydrolysis of chitooligosaccharides with overall inversion of anomeric configuration.

Catalysis↗

PubMed1996

Stereochemical course and reaction products of the action of beta-xylosidase from Thermoanaerobacterium saccharolyticum strain B6A-RI.

Beta-Xylosidases are grouped in families 39 and 43 of a general classification of glycosyl hydrolases based on amino acid sequence similarities. The Beta-xylosidase from Butyrivibrio fibrisolvens, which belongs to family 43, has been shown to operate by a molecular mechanism which results in the inversion of the anomeric configuration. Thermoanaerobacterium saccharolyticum B6A-RI Beta-xylosidase which belongs to family 39 was purified as a recombinant enzyme from Escherichia coli. The stereochemistry of the hydrolysis of p-nitrophenyl Beta-D-xylopyranoside was followed by 1H NMR. The spectrum recorded after 2 h hydrolysis showed a large signal centred at 4.47 ppm (J approximately 10 Hz) assignable to H1 of free Beta-xylose with a small amount of alpha-xylose (5.05 ppm, J approximately 3 Hz) attributable to mutarotation. This result indicates that T. saccharolyticum Beta-xylosidase operates with overall retention of the anomeric configuration. This result, with the lack of sequence similarity between the two families of Beta-xylosidases, suggests that these two families have major differences in their active-site geometries. Consistent with its retaining mechanism, Beta-xylosidase of T. saccharolyticum B6A-RI also displayed transglycosylating activity:reverse-phase HPLC showed approximately 30% conversion of p-nitrophenyl Beta-D-xylopyranoside into a number of higher nitrophenyl oligosaccharides after 5 min incubation with the enzyme. The structure of the most abundant oligosaccharides could be determined by total correlation spectroscopy NMR and showed that the enzyme can build Beta-1,4, Beta-1,3- and Beta-1,2-linked xylo-oligosaccharides.

Bacteria↗

PubMed1996

A modular family 19 chitinase found in the prokaryotic organism Streptomyces griseus HUT 6037.

The specificity of chitinase C-1 of Streptomyces griseus HUT 6037 for the hydrolysis of the beta-1,4-glycosidic linkages in partially acetylated chitosan is different from that of other microbial chitinases. In order to study the primary structure of this unique chitinase, the chiC gene specifying chitinase C-1 was cloned and its nucleotide sequence was determined. The gene encodes a polypeptide of 294 amino acids with a calculated size of 31.4 kDa. Comparison of the amino acid sequence of the deduced polypeptide with that of other proteins revealed a C-terminal catalytic domain displaying considerable sequence similarity to the catalytic domain of plant class I, II, and IV chitinases which form glycosyl hydrolase family 19. The N-terminal domain of the deduced polypeptide exhibits sequence similarity to substrate-binding domains of several microbial chitinases and cellulases but not to the chitin-binding domains of plant chitinases. The previously purified chitinase C-1 from S. griseus is suggested to be generated by proteolytic removal of the N-terminal chitin-binding domain and corresponds to the catalytic domain of the chitinase encoded by the chiC gene. High-performance liquid chromatography analysis of the hydrolysis products from N-acetyl chitotetraose revealed that chitinase C-1 catalyzes hydrolysis of the glycosidic bond with inversion of the anomeric configuration, in agreement with the previously reported inverting mechanism of plant class I chitinases. This is the first report of a family 19 chitinase found in an organism other than higher plants.

Amino Acid Sequence↗

PubMed1995

Stereochemistry of chitin hydrolysis by a plant chitinase/lysozyme and X-ray structure of a complex with allosamidin: evidence for substrate assisted catalysis.

The plant enzyme hevamine has both chitinase and lysozyme activity. HPLC analysis of the products of the hydrolysis of chitopentaose shows that hevamine acts with retention of the configuration, despite the absence of a nucleophilic or stabilizing carboxylate. To analyze the stabilization of a putative oxocarbonium ion intermediate, the X-ray structure of hevamine complexed with the inhibitor allosamidin was determined at 1.85 A resolution. This structure supports the role of Glu127 as a proton donor. The allosamizoline group binds in the center of the active site, mimicking a reaction intermediate in which a positive charge at C1 is stabilized intramolecularly by the carbonyl oxygen of the N-acetyl group at C2.

Acetylglucosamine↗

PubMed1994

Stereochemical course of the hydrolysis reaction catalyzed by chitinases A1 and D from Bacillus circulans WL-12.

Chitinases A1 and D were purified from the periplasmic proteins produced by Escherichia coli HB101 harbouring recombinant plasmids carrying respectively the chiA and chiD genes of Bacillus circulans WL-12. HPLC analysis indicated that during the hydrolysis of chitotriose, both chitinases initially produce N-acetylglucosamine and only one anomer of chitobiose. 1H NMR spectroscopy of the hydrolysis of chitotetraitol showed that this anomer corresponds to beta-chitobiose, demonstrating that chitinases A1 and D act by a molecular mechanism that retains the anomeric configuration. This mechanism is similar to that of lysozymes although both chitinases belong to a family of proteins sharing no demonstrable amino acid sequence similarity with lysozymes.

Bacillus↗

PubMed1993

The effect of sibling relationship on the periodontal condition.

The purpose of this investigation was to study clinically as well as microbiologically the effect of sibling relationship on the periodontal condition in a young population with a relatively high prevalence of periodontal disease and deprived from regular dental care. In this study, 23 family units consisting of 3 more siblings were evaluated. In all, 78 subjects aged 15 to 25 years were included in the study. The mean interproximal amount of loss of attachment in this population was 0.29 mm. The individual mean ranged from 0 to 1.27 mm. In 33% of the subjects, > or = 1 sites with a probing depth of 5 mm or more in conjunction with 2 mm of attachment loss were present. The results show a significant sibship effect for: plaque, calculus, loss of attachment, spirochetes on the tongue and in the pocket, Porphyromonas gingivalis on the gingiva and in the saliva and Prevotella intermedia in the saliva. These results support the hypothesis that periodontitis aggregates in families.

Adolescent↗