Biomedical subjects

F Vanhoutte

Publications and source records attributed to F Vanhoutte.

7 recordsLinked to original sources

PubMed2005

Laser diffraction and image analysis as a supportive analytical tool in the pharmaceutical development of immediate release direct compression formulations.

Immediate release direct compression tablet formulations require a strict control of the particle characteristics (i.e. particle size (distribution) and shape) of both the active pharmaceutical ingredient (API) and the excipients. In this publication, the development of a dry dispersion laser diffraction (LD) method has been outlined. With this method, the chemical development of an API meant for the manufacturing of an immediate release direct compression tablet formulation can be supported. Comparison with static image analysis (SIA) and scanning electron microscopy (SEM) data often shows laser diffraction to generate different size data. However, since LD is fast and frequently shows an adequate precision over a wide particle size range, the technique is still considered as a valuable analytical tool in the screening of the particle size distribution of API batches. In the future, automated (static) image analysis and dynamic image analysis are believed to become more and more important, since these techniques will allow the fast analysis of large amounts of particles with a minimum intervention of the operator.

Chemistry, Pharmaceutical↗

PubMed1992

Alpha-oxidation of 3-methyl-substituted fatty acids in rat liver.

3-Methyl-substituted fatty acids are first oxidatively decarboxylated (alpha-oxidation) before they are degraded further via beta-oxidation. We synthesized [1-14C]phytanic and 3-[1-14C]methylmargaric acids in order to study their alpha-oxidation in isolated rat hepatocytes, rat liver homogenates and subcellular fractions. alpha-Oxidation was measured as the production of radioactive CO2. In isolated hepatocytes, maximal rates of alpha-oxidation amounted to 7 and 10 nmol/min x 10(8) cells with phytanic acid and 3-methylmargaric acid, respectively. At equimolar substrate concentrations, alpha-oxidation of branched fatty acids was approximately 10- to 15-fold slower than the beta-oxidation of the straight chain palmitate. In whole liver homogenates, rates of alpha-oxidation that equaled 60 to 70% of those observed in the hepatocytes were obtained. Optimum rates required O2, NADPH, Fe3+, and ATP. Fe3+ could be replaced by Fe2+ and ATP could be replaced by a number of other phosphorylated nucleosides and even inorganic phosphate without loss of activity. NADH could substitute for NADPH but not always with full restoration of activity. A variety of other cofactors and metal ions was either inhibitory or without effect. Scavengers of reactive oxygen species, known to be formed during the NADPH-dependent microsomal reduction of ferric-phosphate complexes, were without effect on alpha-oxidation. No evidence was found for the accumulation of NADPH-dependent or Fe(3+)-dependent reaction intermediates. Subcellular fractionation of liver homogenates demonstrated that alpha-oxidation was located predominantly, if not exclusively, in the endoplasmic reticulum. alpha-Oxidation, measured in microsomal fractions, was not inhibited by CO, cytochrome c, or ferricyanide, indicating that NADPH cytochrome P450 reductase and cytochrome P450 are not involved in alpha-oxidation. Our results indicate that, contrary to current belief, alpha-oxidation is catalyzed by the endoplasmic reticulum. The cofactor requirements suggest that alpha-oxidation involves the reduction of Fe3+ by electrons from NADPH and that it is stimulated by phosphate ions and nucleotides.

Animals↗

PubMed1991

Identification and purification of a peroxisomal branched chain fatty acyl-CoA oxidase.

Isoprenoid (branched) fatty acids such as pristanic acid can be degraded via beta-oxidation in peroxisomes. We synthesized 2-methylpalmitoyl-CoA as a model substrate in order to study the first step of the peroxisomal beta-oxidation of branched fatty acids, catalyzed by an acyl-CoA oxidase. 2-Methylpalmitoyl-CoA oxidase activity was found in rat liver homogenates. Subcellular fractionation demonstrated that the oxidase was confined to peroxisomes. 2-Methylpalmitoyl-CoA oxidase was also present in kidney and intestine. It was not induced in liver or in the extrahepatic tissues by treatment of rats with peroxisome proliferators or by feeding diets containing excess isoprenoids. The enzyme was partially purified together with palmitoyl-CoA oxidase and trihydroxycoprostanoyl-CoA oxidase by heat treatment and ammonium sulfate fractionation of liver extracts. The partially purified preparation was chromatographed on various columns. 2-Methylpalmitoyl-CoA oxidase could be separated from the inducible (by peroxisome proliferators) palmitoyl-CoA oxidase and from trihydroxycoprostanoyl-CoA oxidase, but it always coeluted with the noninducible palmitoyl-CoA oxidase, recently described by us (Schepers, L., Van Veldhoven, P. P., Casteels, M., Eyssen, H. J., and Mannaerts, G. P. (1990) J. Biol. Chem. 265, 5242-5246). 2-Methylpalmitoyl-CoA oxidase was purified to near homogeneity in three chromatographic steps (anion exchange, hydroxylapatite, and gel filtration). Its apparent molecular mass is approximately 415 kDa, and it consists of identical subunits of approximately 70 kDa. The enzyme oxidized 2-methylpalmitoyl-CoA twice as rapidly as palmitoyl-CoA and pristanoyl-CoA as rapidly as palmitoyl-CoA, so that it can be considered as a branched fatty acyl-CoA oxidase. Since pristanoyl-CoA is one of its naturally occurring substrates we propose to name this enzyme pristanoyl-CoA oxidase.

Animals↗

PubMed1991

Mitochondrial and peroxisomal beta oxidation of the branched chain fatty acid 2-methylpalmitate in rat liver.

A number of isoprenoids (e.g. pristanic acid and the side chains of fat soluble-vitamins) is degraded or shortened via beta oxidation. We synthesized 2-methyl-palmitate and 2-methyl[1-14C] palmitate as a model substrate for the study of the beta oxidation of branched (isoprenoid) fatty acids in rat liver. 2-Methylpalmitate was well oxidized by isolated hepatocytes and its oxidation was stimulated after treatment of the animals with a peroxisome proliferator. Subcellular fractionation of rat liver demonstrated that 2-methylpalmitate is activated to its CoA ester in endoplasmic reticulum, mitochondria, and peroxisomes and that mitochondria and peroxisomes are capable of beta-oxidizing 2-methylpalmitate. At low unbound 2-methylpalmitate concentrations and in the presence of competing straight chain fatty acids, a condition encountered in vivo, peroxisomal 2-methyl-palmitate oxidation was 2- to 4-fold more active than mitochondrial oxidation. Treatment of rats with a peroxisome proliferator markedly stimulated mitochondrial but only slightly peroxisomal 2-methylpalmitate oxidation. The same treatment dramatically induced palmitoyl-CoA oxidase but did not change 2-methyl-palmitoyl-CoA oxidase activity. Our results indicate 1) that in untreated rats peroxisomes contribute for an important part to the oxidation of 2-methylpalmitate; 2) that treatment with a peroxisome proliferator stimulates mainly the mitochondrial component of 2-methylpalmitate oxidation; and 3) that palmitoyl-CoA and 2-methylpalmitoyl-CoA are oxidized by different peroxisomal oxidases.

Acyl-CoA Oxidase↗

PubMed1991

Effects of the enantiomers of disopyramide and its major metabolite on the electrophysiological characteristics of the guinea-pig papillary muscle.

Disopyramide, a Class Ia antiarrhythmic drug, is clinically used as a racemic mixture; R(-)disopyramide and S(+)disopyramide. The major metabolite in man is desisopropyldisopyramide: R(-)desisopropyldisopyramide and S(+)desisopropyldisopyramide. The effects of the four compounds were compared on the electrophysiological characteristics of the guinea-pig papillary muscle using the standard microelectrode technique. At an external K+ concentration of 5.4 mmol/l and a stimulation frequency of 1 Hz, S(+)disopyramide (20 mumols/l) increased action potential duration (APD) by more than 18%, while it was diminished by 6% in the presence of R(-)disopyramide. Resting membrane potential amounted to -87.1 +/- 0.5 mV (n = 14) and -85.6 +/- 1.2 mV (n = 10), respectively. Also a small but significant difference in effect on the maximal rate of depolarization was observed, R(-)disopyramide being more potent, related with a slower recovery of the maximal rate of depolarization. The enantiomers of the metabolite appeared to be three times less potent than those of the parent drug in their effect on the maximal rate of depolarization. The characteristics of the enantiomers of the metabolite correlated with those of the parent drug: also the R(-)enantiomer was more potent in decreasing the maximal rate of depolarization and caused more shortening of the action potential than the S(+)enantiomer. Time constants for onset and recovery of/from rate dependent block of the maximal rate of depolarization were dependent upon the external K+ concentration, both for the enantiomers of the parent drug and those of the metabolite. Onset slowed down while recovery accelerated when external K+ was increased. Time constants were lower for the metabolite. When stimulation interval was shortened, the effect on the maximal rate of depolarisation increased. Only for the metabolite statistical significant stereoselective differences were observed at all stimulation intervals. The effects on the action potential duration were dependent upon stimulation interval; for all enantiomers the action potential duration tended to be relatively (% of control) higher at short stimulation intervals than at large stimulation intervals. The effect on the maximal rate of depolarization was also voltage dependent, but no significant differences were observed between the enantiomers, for the parent drug as well as for the metabolite.

Action Potentials↗

PubMed1991

Stereoselective effects of the enantiomers of bupivacaine on the electrophysiological properties of the guinea-pig papillary muscle.

1 Direct myocardial effects of the S(-)- and R(+)-enantiomers of bupivacaine were compared in the guinea-pig isolated papillary muscle by recording transmembrane action potentials with the standard microelectrode technique. 2 In 5.4 mM K+, at a stimulation rate of 1 Hz, the maximal rate of depolarization (Vmax) was reduced to 59.9 +/- 1.4% (n = 10) of control (mean +/- s.e.mean) in the presence of 10 microM R(+)-bupivacaine, and to 76.7 +/- 1.2% (n = 14) in the presence of the same concentration of S(-)-bupivacaine. This was mainly due to a difference in time constant at which block dissipated during the diastolic period. Recovery was slower in the presence of R(+)-bupivacaine. The slower recovery in the presence of R(+)-bupivacaine resulted also in a more pronounced frequency-dependent block of Vmax. 3 Time constants for recovery from use-dependent block became significantly faster for both enantiomers on hyperpolarization, while no significant change was observed at depolarization. At all membrane potentials recovery was slower in the presence of R(+)-bupivacaine. 4 The action potential duration (APD) was shortened to a greater extent in the presence of R(+)-bupivacaine over a large range of stimulation frequencies. 5 We conclude that S(-)-bupivacaine affects Vmax and APD in the guinea-pig papillary muscle less than the R(+)-enantiomer at different rates of stimulation and resting membrane potentials.

Action Potentials↗

PubMedDate not supplied

Effects of the enantiomers of flecainide on action potential characteristics in the guinea-pig papillary muscle.

The enantiomers of flecainide, a Class Ic antiarrhythmic agent, were tested in the guinea-pig papillary muscle using the standard microelectrode technique. In 5.4 mM external K+ and at a stimulation frequency of 1 Hz, significant differences were observed in the effect of the enantiomers on maximal rate of depolarization, action potential amplitude and action potential duration. Maximal rate of depolarization and action potential amplitude were more suppressed in the presence of (+)flecainide. Maximal rate of depolarization was reduced to 54.4 +/- 1.4% (n = 23) (mean +/- S.E.M.) of maximum in the presence of 7.2 microM (+)flecainide and to 60.5 +/- 1.1% (n = 24) in the presence of the same concentration of (-)flecainide. The stimulation interval used had a pronounced influence on maximal rate of depolarization for both enantiomers. At almost all stimulation intervals tested, block was larger for (+)flecainide than for (-)flecainide. When the stimulation interval was shortened from 10 sec to 0.25 sec, the maximal rate of depolarization was reduced from 89.8 +/- 0.8% (n = 13) to 37.4 +/- 2.3% (n = 10) of the control in the presence of 7.2 microM of (+)flecainide and from 91.7 +/- 0.8% (n = 14) to 44.9 +/- 1.6% (n = 12) when the same concentration of (-)flecainide was used. The effect on maximal rate of depolarization was also voltage-dependent. For both enantiomers, inactivation curves, recorded at a frequency of 0.6/min, were shifted to more negative potentials. There was no significant difference in magnitude of shift between the two enantiomers.

Action Potentials↗