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Biomedical subjects

H Peeters

Publications and source records attributed to H Peeters.

At least 19 recordsLinked to original sources
PubMed1992

[Mortality of cattle following feeding of moldy flower bulbs].

Five of eight meat cattle died suddenly without showing prior symptoms of disease. The sudden death occurred in connection with the feeding of mouldy tulip bulbs. A short review is given of the use of flower bulbs as cattle feed, the use of herbicides/fungicides in bulb cultivation, and the relevant legislation. Several toxicological aspects that should be taken into consideration when flower bulbs are used as cattle feed are discussed. Both the Central Veterinary Institute and the State Institute for Public Health and Environmental Hygiene showed, in experiments with mice, the presence of a toxin in extracts of the mouldy tulip bulbs. This toxin is probably produced by moulds present in the tulip bulbs. The death of the animals was probably caused by an as yet unidentified mycotoxin.

Animal Feed↗
PubMed1991

[The cat has not always done it. A case of alpha-chloralose poisoning in wild birds].

Neglected hens caused annoyance at a graveyard. Following veterinary advice, the authorities used alpha-chloralose-dressed feed in an attempt to sedate the animals, thus facilitating transport to a more suited place. However, the feed was also consumed by other birds. Moreover, the dosage alpha-chloralose appeared to be too high. Hence the resulting mortality struck both the hens and the wild birds. Obviously, alpha-chloralose should not be used for these applications.

Animals↗
PubMed1979

Influence of oral polyunsaturated and saturated phospholipid treatment on the lipid composition and fatty acid profile of chimpanzee lipoproteins.

The influence of treatment with polyunsaturated lecithin (EPL) and with saturated lecithin on the lipoprotein composition and fatty acid profile was investigated in 4 male chimpanzees. The animals were successively given 3 isocaloric diets containing the same amount of fat with a degree of saturation varying from 1 in the control diet to 0.2 in the diet enriched with polyunsaturated lecithin, to 4 in the diet enrich with saturated lecithin. The VLDL, LDL and HDL3 fractions were isolated by ultracentrifugal flotation; changes in their lipid and fatty acid composition were followed and their microviscosity was measured. The treatment with polyunsaturated lecithin increases the cholesterol esters and lysolecithin content in HDL3, presumably via activation of the enzyme LCAT. These modified HDL particles have a more fluid surface and a denser core and are susceptible to act as better cholesterol carriers. A complementary effect of this treatment is a decrease of the plasma triglycerides and VLDL concentration, an increase in the unsaturation ratio of the triglycerides which might take place via activation of triglyceride lipase. The saturated lecithin treatment increases the plasma VLDL and LDL concentrations and the triglyceride levels and increases mostly the saturation ratio of the cholesterol esters. These effects are likely to enhance the progression of atherosclerosis.

Administration, Oral↗
PubMed1978

A simple screening method for plasma lipids by thin-layer chromatography with flame ionization detection.

Thin-layer chromatography was carried out on glass rods coated with Silica gel (chromarod) and the fractions were detected with a flame ionization detector (FID). This system was applied to the fractionation and screening of plasma lipids. As the relative response of the flame ionization detector depends on the nature of the lipids, correction factors had to be introduced. These correction factors were derived from comparison of the results of the thin-layer chromatography with flame ionization detection with those obtained by conventional chemical analysis of the same sample. The coefficients of variation of the lipid profiles were comparable for both techniques. The absolute lipid concentration for the various fractions obtained by combination of the concentration of the total lipids with the relative lipid profile, correlate very well with the values obtained by conventional chemical analysis of the various lipids.

Cholesterol↗
PubMed1977

Ionization behaviour of native apolipoproteins and of their complexes with lecithin. 1. Calorimetric and potentiometric titration of the native apoA-I protein and of the apoA-I protein-dimyristoyl lecithin complex.

The ionization behaviour of native apoA-I protein is compare to that of its complex with synthetic dimyristoyl lecithin in studies using calorimetric, potentiometric and spectrophotometric titration. In the presence of phospholipids, 10 out of 21 lysines together with 22 acidic residues are masked in the complex. All tyrosines remain accessible to titration below pH 13. The apparent ionization enthalpy of the 11 lysine residues is not affected by the presence of phospholipids. These data are consistent with discrete binding sites located in the apoprotein helical segments as suggested by the model of Segrest et al. [FEBS Lett. 38, 247-253 (1974)]. A tentative localisation of lysine, arginine, aspartic acid and glutamic acid residues directly involved in phospholipid binding is suggested, assuming that such helical regions are involved in apoprotein-phospholipid association.

Amino Acid Sequence↗
PubMed1977

Ionization behaviour of native apolipoproteins and of their complexes with lecithin. 2. Potentiometric titration of the native apo-A-II, apoC-I, apoC-III proteins and of their complexes with dimyristoyl lecithin.

A comparison of the ionization behaviour of the human apoA-II, apoC-I, apoC-III proteins and of their complexes with dimyristoyl lecithin is based on potentiometric titration of the basic and acidic residues and spectrophotometric titration of the phenolic groups. Experimental data suggest that a number of lysine, arginine, aspartic acid and glutamic acid residues are masked in the complexes. For each of these amino acids and in all three proteins the number of masked residues is consistent with the content of those regions predicted to be involved in lipid binding by the model of Segrest et al. [FEBS Lett. 38, 247-253 (1974)]. These data taken together with the results of calorimetric and titration experiments with the apoA-I protein reported in the accompanying article [Rosseneu et al. (1977) Eur. J. Biochem. 79, 251-257] strongly support the general nature of the proposed model and further suggest that ionic interactions have some role in the formation of the dimyristoyl lecithin/apolipoprotein complexes.

Amino Acid Sequence↗
PubMed1977

Thermodynamics of lipid protein associations. Thermodynamics of helix formation in the association of high density apolipoprotein A-I (apoA-I) to dimyristoyl phosphatidylcholine.

The structure and phospholipid-binding properties of human plasma high density apolipoprotein A-I (apoA-I) has been studied at pH 7.4 and 3.1 by microcalorimetry, circular dichroism and density gradient ultracentrifugation. At pH values of 7.4 and 3.1, apoA-I binds to dimyristoyl phosphatidylcholine (DMPC) to form complexes of similar composition (molar ratio of DMPC/apoA-I of 100) and helical content (67%). At pH 7.4, the lipid-protein association is accompanied by an increase in helical content from 58 to 67% and an exothermic enthalpy of binding (deltaHB) of -90 kcal/mol apoA-I. At pH 3.1, the helical content of apoA-I is increased from 48 to 67% on binding to DMPC and the enthalpy of binding was -170 kcal/mol. We suggest that the difference in the enthalpies of binding (-80 kcal/mol) at pH 3.1 compared to 7.4 is due to the greater coil leads to helix transition at the lower pH.

Apolipoproteins↗
PubMed1977

Characterization of baboon plasma high-density lipoproteins and of their major apoproteins.

Baboon high-density lipoproteins (HDL) were isolated by preparative ultracentrifugation between d = 1.063 and 1.215 g/mL. The HDL contains 48.8% protein and a lipid distribution similar to human HDL. The phospholipid distribution shows a low sphingomyelin value (5.9%), and the fatty acid composition of HDL is comparable to the human data except for the 18:1/18:2 ratio as a result of a higher 18:1 content in the CE and a lower 18:2 concentration in the PL. The major HDL apoproteins isolated on diethylaminoethyl-cellulose had a mobility on sodium dodecyl sulfate--polyacrylamide gel electrophoresis and a molecular weight and an amino acid composition similar to human apoA-I. However, the amino acid sequence of the first 30 residues of baboon apoA-I differed from the human apoprotein in residues 15 and 21. Treatment of apoA-I with carboxypeptidase A indicated a carboxyl-terminal sequence of Leu-Ser-Thr-Gln. Baboon apoHDL contained monomeric apoA-II with the mobility of monomeric human apoA-II and a molecular weight of 8500. The amino acid composition differed from the human apoA-II by the presence of arginine and by the absence of half-cystine and isoleucine. The circular dichroic spectra of apoA-I and apoA-II demonstrated a higher helicity compared to the human apoproteins. Recombination studies by microcalorimetry of apoHDL with dimyristoylphosphatidylcholine (DMPC) indicated similarities in the thermodynamic binding properties of the HDL apoproteins from man and baboon. The maximal-binding enthalpies of DMPC to apoHDL, apoA-I, and apoA-II were lower for the baboon than for the human apoprotein.

Amino Acids↗
PubMed1977

Phospholipid binding and self-association of the major apoprotein of human and baboon high-density lipoproteins.

The purpose of this study was to establish a relationship between self-association and phospholipid binding of the human and the baboon apoA-I protein. The enthalpy changes on binding dimyristoyl lecithin and lysolecithin to either the human or the baboon native apoA-I protein were measured in a microcalorimeter. An endothermal process, most pronounced for the human apoprotein, was observed at low phospholipid levels. At higher phospholipid to protein ratios the binding was exothermal. Gel filtration experiments on Sephadex G-200 showed that the native apoprotein of both species consists of dimers and tetramers. The baboon native apoA-I protein contained a higher amount of dimers. After preincubation of the apoA-I protein with lysolecithin, the enthalpy changes measured on subsequent binding of dimyristoyl lecithin were shifted towards more exothermal values compared to the curve for the native apoprotein. The amplitude of this shift corresponds to that of the endothermal process observed on binding dimyristoyl lecithin to the native apoprotein. This process was attributed to a phospholipid-induced disaggregation of the apoA-I protein. Gel filtration data showed a decreased extent of aggregation in the apoA-I protein preincubated with lysolecithin. This sample consisted exclusively of dimers. Ultracentrifugal flotation of the complexes formed between the apoA-I protein, and respectively dimyristoyl lecithin and sphingomyelin indicated that preincubation with lysolecithin increased the extent of complex formation. These results suggest that the dimeric form of the apoA-I protein possesses the highest affinity for phospholipids. Any dissociation of higher polymers enhances the phospholipid-binding capacity of the human and the baboon apoA-I protein.

Animals↗
PubMed1977

Analysis of the proteins in sweat and urine by agarose-gel isotachophoresis.

A sensitive and practical method is described for the analysis of the proteins contained in human sweat and urine which does not require pre-concentration of the sample. Technical details are provided of the agarose-gel isotachophoresis and the proteinograms of normal and pathological urine samples, as well as proteinograms of human sweat. The method can also be applied as an electro-concentration system in a field-strength gradient. By means of this electro-concentration system, and in combination with immunodiffusion against monospecific antisera, a detection limit of albumin of 50 ng/ml has been obtained.

Albumins↗
PubMed1977

Five-component dielectric dispersion in bovine serum albumin solution.

Dielectric measurements were made on aqueous solutions of native BSA monomers at three concentrations and at about eighty separate frequencies in the range 0.03-800 MHz. All measurements were made at 25 degrees C on solutions of pH = 5.0, this being near the isoelectric point. The analysis shows the presence of a double component beta dispersion at frequencies below 10 MHz plus two delta dispersions with relaxation frequencies of around 15 MHz and 100 MHz. The origin at a molecular level of the beta and the higher frequency delta dispersion can be established with confidence but the remaining delta dispersion cannot be interpreted unambiguously. With the inclusion of the well known gamma dispersion at frequencies in excess of 1 GHz the measurements indicate the existence of five clearly separated dispersion regions. This is one more dispersion than previously suggested in the literature for a protein solution of this nature.

Electric Conductivity↗
PubMed1977

Effects of suloctidil on lipid metabolism in experimental animals.

A novel potent vasoactive agent, 1-(4-isopropyl-thiophenyl)-2-n-octylaminopropanol (suloctidil, Sulocton), lowers excess of plasma cholesterol and tends to normalize the plasma hyperbetalipoproteinemia of Rhesus monkeys fed a high-cholesterol, high-fat diet. The drug shows an inhibitory effect on the cholesterol biosynthesis in rat liver homogenates.

Animals↗
PubMed1976

Interaction of the apoproteins of very low density and high density lipoproteins with synthetic phospholipids.

The interaction of synthetic dimyristoyl phosphatidylcholine (lecithin) liposomes with isolated apoC-I and apoC-III proteins from very low density lipoproteins has been studied by microcalorimetry. Complex formation is a highly exothermal process characterized by a maximal enthalpy of -130 kcal/mol (-544 kJ) apoC-III-1 and -65 kcal/mol apoC-I proteins (-272 kJ). The complex composition determined after its isolation by ultracentrifugal flotation agrees with the value derived from the enthalpy binding curves. The binding of a constant amount of dimyristoyl lecithin to apoprotein mixtures containing various proportions of apoA-I and apoC-III failed to demonstrate the existence of any preferential association between the two apoproteins, in contrast with results obtained previously with apoA-I/apoA-II protein mixtures. Finally the various contributions to the enthalpy of binding such as that arising from an increase in apoprotein helicity have been evaluated. A classification of the apolipoproteins according to their lipid-binding affinity is proposed as: apoA-II congruent to apoC-III greater than apoC-I greater than apoA-I proteins.

Apolipoproteins↗
PubMed1976

Study of the lipid binding characteristics of the apolipoproteins from human high density lipoprotein. I. Electron microscopic and gel filtration studies with synthetic phosphatidylcholines.

The characteristics of the lipid - protein complex produced by the addition of the major apolipoproteins (apo AI and apo AII) of human high-density lipoprotein to synthetic phospholipids has been studied. Under the in vitro conditions utilized, apo AI binds to 1,2-dimyristoyl-sn-glycerophosphocholine and 1,2-dipalmitoyl-sn-glycerophosphocholine liposomes, but does not alter their morphologic characteristics. This binding occurs at temperatures above or below that of the transition (Tt) of the lipid bilayer. In contrast, apo AII spontaneously generates small, homogeneous disc-shaped lipid-protein complexes (50 X 10 a) from large phospholipid globules or from liposomes prepared with these lipids. This type of complex was only formed when the lipid/apo AII mixtures were warmed above the transition temperatures. The incorporation of apo AI into this small complex with apo AII may be greatly facilitated or inhibited depending on the sequence of addition of the various components. Under optimal circumstances, a maximum of 1 molecule of apo AI is incorporated with each molecule of apo A II into complexes with these two synthetic phospholipids.

Apoproteins↗
PubMed1976

Studies of the lipid binding characteristics of the apolipoproteins from human high density lipoprotein. II. Calorimetry of the binding of apo AI and apo AII with phospholipids.

The interactions of lysophosphatidylcholine and synthetic 1,2-dimyristoyl-sn-glycerophosphocholine (DMPC) liposomes with the isolated HDL-apolipoproteins, apo AI and apo AII, has been studied by microcalorimetry. Complex formation is a highly exothermal process characterized by a maximal enthalpy of about --200 kcal/mol of apoprotein when added to DMPC at 28 degrees C in 0.05 M sodium carbonate/bicarbonate buffer, pH 9.6. For the apo AI apoprotein, the binding consists of two processes, one endothermal occurring at low phospholipid/protein ratios and one exothermal predominant at higher phospholipid levels. The endothermal process has been attributed to a lipid-induced disaggregation of the apo AI while the exothermal process is similar to the binding of apo AII or apo HDL to phospholipids. The binding of a constant AI and apo AII, demonstrates the existence of a maximal association at a 1 : 1 molar ratio of the apolipoproteins. The sequential binding of DMPC to apo AI and apo AII suggests the existence of cooperativity between the two apoproteins in phospholipid binding as apo AII promotes the incorporation of apo AI into a protein-phospholipid complex.

Apoproteins↗
PubMed1976

The nonhuman primates as models for studying human atherosclerosis: studies on the chimpanzee, the baboon and the rhesus macacus.

There is no dearth of experimental techniques for producing the hyperlipoproteinemia resulting in atherosclerotic complications and for myocardial infarction in the non human primates. Most of the recent experiments which have given information of great value have been studied with relatively expensive animals for a long period of time up to 6-7 years. It is evident that no animal model perfectly duplicates the human disease or satisfies all desirable requirements. The chimpanzees, representatives of the New World monkeys, have circulating plasma lipoproteins identical to man in composition as well as in function. The results reported above indicate that the compositional changes of chimpanzee plasma lipoproteins in response to dietary changes reflect the appearance of type II and type IV hyperlipoproteinemia similar to the human disease. Moreover, there are more indications about the existence of genotype II a in the chimpanzee, and also on the influence of stress on the plasma lipids, so that the developed intimal lesions similar to the human pathology are in this sense multifactorially influenced. From a phylogenetic point of view the chimpanzee is closer to man than any other non human primate. Furthermore, the chimpanzee lipoproteins are useful models for understanding the relationship between function and structure of the plasma lipoproteins in health and disease. Baboon and rhesus monkeys show similar results, but more differences to the human lipoproteins in health and disease were observed. At present it appears that the most useful models of human atherosclerosis are those induced in the non human primates, especially in the chimpanzee.

Animals↗