Biomedical subjects

M Pina

Publications and source records attributed to M Pina.

11 recordsLinked to original sources

PubMed2004

Toward the synthesis of pyroglutamate lauroyl ester: biocatalysis versus chemical catalysis.

The synthesis of dodecyl pyroglutamate (or pyroglutamate lauroyl ester) was achieved in a two-step process involving a pyroglutamic acid alkyl ester intermediate. The reaction was carried out either by lipase or by chemical catalysis using ion exchange resin. Among the various tested lipases, the one from Candida antarctica B gave the best results allowing 73% formation of the desired ester after 6 h. Comparing the efficiency of this latter lipase with the one of Amberlyst IR120H resin in catalyzing this reaction, the biocatalyst gave a molar yield of pyroglutamate lauroyl ester of 79% compared to 69% when using the ion exchange resin starting with 1.04 mmol substrate in each case.

Catalysis↗

PubMed2003

Acyl migration incidence on accuracy of a triacylglycerol regioanalysis--a theoretical evaluation.

We will consider the Grignard chemical deacylation to study the regioanalysis of triacylglycerols (TAGs). Using a given TAG structure, a cross-contamination model is developed and used for evaluating the incidence of the acyl migration and its influence on the accuracy of a regiospecific analysis of the molecule. Despite unavoidable isomerization, the newly formed alpha,beta-diacylglycerols are considered as most representative of the original TAG composition. In this paper, we present evidence that in conditions of limited acyl migration, the regiospecific distribution could more accurately be determined from the alpha-monoacylglycerol rather than through calculations based on the alpha,beta-diacylglycerols fraction.

Acylation↗

PubMed2002

Physical properties of chitosan pellets produced by extrusion-spheronisation: influence of formulation variables.

Pellets comprising chitosan, cellulose microcrystalline, povidone, filler excipient and diclofenac sodium as model drug were prepared by extrusion-spheronisation. The effects of chitosan load (zero, 0%, low, 4% and high, 16% levels), type of filler (lactose, tribasic calcium phosphate and beta-cyclodextrin) and composition of the binding liquid (ethanol/water mixtures 20 and 50%) on physical characteristics of pellets were evaluated. A three-factor factorial design was employed in the study. Analysis of variance (ANOVA) indicated that single factors had significant effect on the physical characteristics of the pellets. The type of filler followed by polymer load markedly affected the density. The type of binding liquid had negligible effect on the shape and surface roughness of the pellets. Increase in the chitosan load resulted in pellets of lower porosity values. This could be attributed to the binding capacity of chitosan and povidone leading to more compacted structures. Chitosan load and type of filler had significant influence on the surface roughness. The surface of pellets became rougher as the chitosan load increased, however, there was no significant difference between zero and low contents of chitosan. Pellets prepared using tribasic calcium phosphate showed a smoother surface when compared with formulations including lactose or beta-cyclodextrin. Chitosan was useful to provide pellets of acceptable physical characteristics when employing an alcohol/water mixture 50% (v/v) as binding liquid for the extrusion-spheronisation process.

Analysis of Variance↗

PubMed2002

A direct method for regiospecific analysis of TAG using alpha-MAG.

An analytical procedure was developed for regiodistribution analysis of TAG using alpha-MAG prepared by an ethyl magnesium bromide deacylation. In the present communication, the deacylation procedure is shown to lead to representative alpha-MAG, allowing the composition of the native TAG in the alpha-position to be determined directly. The composition in the beta-position can then be estimated from the composition of the alpha-MAG and TAG according to the formula 3 x TAG - 2 x alpha-MAG. The estimates are superior to those obtained using the alpha,beta-DAG and Brockerhoff calculations as they come closer to the theoretical value and have smaller SD. The present procedure, first demonstrated on a synthetic TAG, was then successfully applied to the analysis of borage oil, milkfat, and tuna oil.

Acylation↗

PubMed1999

Direct detection of Helicobacter pylori resistance to macrolides by a polymerase chain reaction/DNA enzyme immunoassay in gastric biopsy specimens.

BACKGROUND: The increasing use of macrolides especially in the treatment of Helicobacter pylori infection has led to an increase in resistant strains. The resistance of H pylori to macrolides, especially clarithromycin, is one of the major causes of eradication failure. In H pylori, clarithromycin resistance is due to point mutations localised in domain V of 23S rRNA. AIM: To develop a molecular technique based on amplification of a relevant fragment of the 23S rRNA and colorimetric hybridisation in liquid phase to detect directly in biopsy specimens the type of mutation associated with resistance of H pylori to clarithromycin. METHODS: Gastric biopsy samples from 61 patients were submitted to this test. The results were compared with standard methods (determination of minimal inhibition concentration, polymerase chain reaction/restriction fragment length polymorphism, and/or DNA sequencing) in order to evaluate the test and to define the cut off values, specificity, and sensitivity. RESULTS: The 14 biopsy samples in which H pylori was not detected did not give a positive result in any assay, and the 14 samples harbouring strains susceptible to clarithromycin gave a positive result with the wild type probe as expected. The 33 biopsy specimens containing resistant strains always gave a positive signal with one of the probes detecting resistant organisms, but in eight cases they also reacted with the wild type probe, indicating that a mixture of resistant and susceptible organisms was present. CONCLUSION: The importance of this new assay is that it allows the detection of multiple genotypes corresponding to either heterogeneous genotypes or mixed infections. Moreover, it allows in a single step not only the detection of H pylori but also the determination of its susceptibility to clarithromycin directly in biopsy specimens without the need for culture.

Anti-Bacterial Agents↗

PubMed1998

Detection of point mutations associated with resistance of Helicobacter pylori to clarithromycin by hybridization in liquid phase.

When the standard procedure for determining antibiotic susceptibility of bacteria is used, the results are delayed, especially for bacteria that grow slowly, such as Helicobacter pylori. Treatment for this bacterium may involve clarithromycin, a compound for which resistance has been associated with point mutations on the 23S rRNA gene. This resistance is currently found in organisms isolated from 0 to 15% of patients and jeopardizes the success of the treatment. We have designed a test involving amplification and colorimetric hybridization in the liquid phase to detect the mutation at the molecular level. First, four reference strains, including the wild type and three strains with the mutations A2143C, A2143G, and A2144G, were used to optimize the method. Amplification was carried out with primers previously published. The amplified products were added to probe-coated microtiter wells. A DNA enzyme immunoassay was used to detect the hybrids. The optimal conditions of the hybridization were defined for each probe. Nineteen H. pylori strains resistant to clarithromycin and 22 susceptible according to phenotypic data were submitted to restriction with BsaI and BbsI, and part of the 23S rRNA gene was sequenced in order to determine the mutation involved for the resistant strains. The new assay showed a complete correlation with the reference methods, except for one strain. Cross-hybridizations as well as application of the reaction to other bacteria did not lead to optical densities higher than the cutoff values chosen with the receiving operating characteristic curve. This method can be easily standardized and gives a result within a day. Its application directly to the biopsy specimens or infected gastric juice is planned in the future.

Anti-Bacterial Agents↗

PubMed1997

Chemoenzymatic synthesis of glucose fatty esters.

D-Glucose fatty esters at C-6 were obtained by chemoenzymatic synthesis involving 1,2-O-cyclohexylidene-alpha-D-glucofuranose (1) followed by hydrolysis of the cyclohexylidene protecting group. The enzymatic esterification of 1 was performed with fatty acids of variable chain lengths (C8:0 to C18:0). The kinetic of the reaction was studied for each fatty acid and the structure of the octanoyl ester was determined by 1H and 13C NMR spectroscopy.

Esters↗

PubMed1997

Fluctuations in GAD65 antibodies after clinical diagnosis of IDDM in young children.

OBJECTIVE: To investigate whether the presence of GAD antibodies at onset of IDDM correlates to a more aggressive rate of beta-cell destruction after clinical onset. RESEARCH DESIGN AND METHODS: We studied GAD antibodies at onset of disease, after 1 year, and after 6 years in 33 consecutively referred children (mean age 8.08, range 1.7-16.3). In a subset of 11 patients, GAD antibodies were studied very frequently. The correlation between GAD antibodies and clinical parameters, including glycosylated hemoglobin, residual insulin secretion, and insulin dosage, was evaluated. RESULTS: GAD antibody titers were highly variable. Four patients became GAD antibody positive weeks to years after clinical onset. Other patients switched between testing positive and negative for GAD antibodies shortly after clinical onset. No correlation was found between the presence of GAD antibodies and the rate of beta-cell destruction, but patients with high GAD antibody indexes at onset had significantly higher glycosylated hemoglobin levels. CONCLUSIONS: GAD antibodies at clinical onset do not predict the rate of beta-cell destruction in young children with newly diagnosed IDDM. The highly variable GAD antibody levels suggest variation of the autoimmune process.

Autoantibodies↗

PubMed1996

Determination of pregastric lipase specificity in young ruminants.

The combined hydrolysis of a chiral triglyceride clearly defined on these three positions and of its racemic equivalent reveals all sorts of lipase specificities: regioselectivity, typoselectivity and stereospecificity. This article describes a study of the pregastric lipases of young ruminants (kid, calf, lamb), whose specificity is still somewhat ambiguous. The use of a chiral triglyceride in which position sn 1 was occupied by a short-chain fatty acid showed that these lipases had dual specificity, i.e. a combination of typoselectivity with respect to short-chain fatty acids and sn3 stereospecificity. A comparison between the performance of the lipase of young animals and the fatty acid composition and distribution in the mother's milk suggests that the degree of dual specificity in these enzymes is related to the characteristics of the mother's milk.

Animals↗

PubMed1993

Compound PCA-4248 interferes with bronchopulmonary anaphylaxis and with in vitro hyperresponsiveness to platelet-activating factor.

The intravenous (i.v.) or oral administration of the platelet-activating factor (PAF) antagonist, PCA-4248, to guinea-pigs blocked selectively the bronchoconstriction induced by PAF, as well as the accompanying thrombocytopenia and leucopenia. In addition, PCA-4248 i.v. or intratracheal (i.t.) administration blocked the bronchoconstriction caused by the i.t. instillation of PAF. As in the case of other PAF antagonists, bronchoconstriction caused by the i.t. instillation of antigen was only inhibited by PCA-4248 in guinea-pigs that did not receive a booster injection of antigen during sensitization whereas the booster injection of antigen made anaphylactic bronchoconstriction resistant to the compound. In vitro, when lungs from non-sensitized guinea-pigs were perfused with Krebs-bovine serum albumin (BSA) solution supplemented with PCA-4248, bronchoconstriction and the formation of thromboxane A2 by PAF were blocked. In this in vitro model of perfused lungs, active sensitization with a booster injection of antigen leads to bronchopulmonary hyperresponsiveness to PAF and failure of other PAF antagonists to inhibit the effects of PAF itself. Surprisingly, in lungs isolated from actively sensitized and boosted guinea-pigs, PCA-4248 blocked the effects of PAF, indicating that this compound possesses additional original properties in this model.

Anaphylaxis↗

PubMed1987

An improved method for the colorimetric assay of lipase activity using an optically clear medium.

Lipase activity can be spectrophometrically measured in an optically clear medium using long chain fatty thioesters of 1-mercapto-2,3-propanediol or 2-mercaptoethanol as substrates. With hexamethylphosphoric triamide solutions of these thiosubstrates, the Michaëlis-Menten constants of lipase from Rhizopus arrhizus were determined. The effects of calcium chloride and of bovine serum albumin on the enzyme activity were established.

Colorimetry↗