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Biomedical subjects

A Boersma

Publications and source records attributed to A Boersma.

At least 37 records · Page 2Linked to original sources
PubMed1994

Analysis by electrospray mass spectrometry of glycopeptides from the in vitro O-glycosylation reaction using human mucin motif peptide.

A mucin-motif peptide in the one-letter code T T T P S P P M T T P I T P P A, representative of the human intestinal mucin tandem repeat sequence (MUC2), containing several threonine residues in clusters, was used as an acceptor substrate to investigate the effect of peptide structure on the activity of crude preparation of human gastric UDP-GalNAc:polypeptide N-acetyl galactosaminyltransferases. High-performance liquid chromatography was performed to separate the different products of the in vitro O-glycosylated reaction. The electrospray mass spectrometry was used to identify the different masses (m/z) of these products. Although the m/z of glycopeptide(s) could be higher than the detection limits of the spectrometer, an accurate study of the doubly charged ions allowed us to demonstrate the linkage of more than two sugars. Hence, the peptide MUC2 will accept at least four carbohydrate residues but the exact substituted positions should be confirmed by further sequence determination.

Amino Acid Sequence↗
PubMed1993

Hypogonadism induced by African trypanosomes in humans and animals.

1. The clinical syndromes of the African trypanosomiasis (also called sleeping sickness in humans) are defined. The basic knowledge on the hypothalamo-anterior pituitary-gonad axis functions is briefly recalled. 2. Hypogonadism caused by the trypanosomes both in men and in women as well as in male and female animals are extensively reviewed in publications over the last two decades as well as on our own very recent works which provided new insights on the physiopathology of the gonadal disorders.

Animals↗
PubMed1993

Experimental "chronic" African trypanosomiasis: endocrine dysfunctions generated by parasitic components released during the tryptanolytic phase in rats.

The disorders of the gonadotropic axis have been studied during the course of a "chronic" african trypanosomiasis induced experimentally in rats inoculated by the variant Trypanosoma brucei brucei AnTat 1.1.E. The levels of serum and pituitary LH as well as serum testosterone and corticosterone have been determined, during the infestation, at a particular period of the circadian cycle, in regard to the parasitemia variations. In addition, the inoculation of trypanosomal component fractions [obtained by concanavalin-A sepharose chromatography (conA-components)], has been performed in an attempt to define more exactly the nature of factor(s) producing the hypotestosteronemia in rats. This work evidenced that the hormonal parameter levels were predominantly decreased at the trypanolytic phase during the evolution of the disease. The action towards the hypothalamo-pituitary gonadal axis was attributed not only to peculiar trypanosomal enzyme(s) [a serine, thiol-dependent, cation sensitive endoprotease with a post-proline cleaving activity (purified from unretained conA fraction)], but also to protein and/or glycoprotein factor(s) released by the trypanosomes (components with affinity to the lectin).

Animals↗
PubMed1993

Unusual cleavage of peptidic hormones generated by trypanosome enzymes released in infested rat serum.

Gonad and thyroid dysfunctions are often observed in human and experimental models during african trypanosomiasis. The enzymatic activity of components released by the trypanosomes towards peptide hormones (e.g. GnRH, TRH) have consequently been studied. The incubation products of GnRH by (i) healthy or infested rat serum: (ii) trypanosomal components released by using a specific procedure; (iii) infested and normal rat brain extracts have been analysed by RP-HPLC fractionation. The peptide cleavage has been assessed by determination of either the amino acid compositions or relative molecular weight (by FAB mass spectrometry) of the different resolved HPLC fractions. Different protease inhibitors and a reducing agent have also been tested and a serine, cation-sensitive, thiol-dependent endopeptidase activity has been predominantly identified to be released by the trypanosomes in host circulation. It has been shown that the peptidase activity(ies) is(are) able to: (i) degrade the peptide hormones (GnRH, TRH) considered as important neuromodulators and neurotransmitters; (ii) generate an unusual N-terminal tetrapeptide (GnRH1-4) appearing to be still active towards the gonadal hypothalamo-pituitary axis.

Amino Acid Sequence↗
PubMed1992

Estradiol, progesterone and testosterone exposures affect the atrial natriuretic peptide gene expression in vivo in rats.

To clarify the effects of sex hormones on the expression of atrial natriuretic peptide (ANP), ovariectomized and intact female rats were subcutaneously injected with estradiol, progesterone, a mixture of them or olive oil solvent; castrated and untouched male rats were subcutaneously injected with estradiol, testosterone or olive oil, once a day for 7 days. The relative rANP-mRNA contents of rat atrial were measured by molecular hybridization. rANP-cDNA was labeled with 32P as a probe. The results revealed that estradiol and progesterone increased ANP gene expression. Furthermore their effects were associated with administration dose of these hormones and it was shown that they are probably coordinated. The physiological amounts of estradiol and progesterone may maintain suitable levels of rANP-mRNA and androgen may also increase the ANP gene expression in vivo. These experiments suggested that female sex hormone may have a dual purpose in fluid balance.

Animals↗
PubMed1992

Decrease of testosterone level during an experimental African trypanosomiasis: involvement of a testicular LH receptor desensitization.

To investigate gonadal disorders and changes of the testicular receptors occurring during the sleeping sickness disease (African trypanosomiasis), an experimental model was developed with 10-month-old rats infested by bloodstream forms of two variants of Trypanosoma brucei brucei (AnTat 1.1 A and AnTat 1.8). At the acute phase, three days after inoculation, the animals were sacrificed for estimating the serum levels of LH and testosterone and the number of testicular LH receptors. Considering a possible intervention of the stress during the infestation and to improve our investigations on gonadal imbalance related to trypanosomasis, levels of additional parameters [corticosterone, glucose and transaminases (glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase)] were determined. Stimulation testing with hCG was likewise assessed in infested rats to analyse the testicular testosterone response to gonadotropin. A significant decrease was demonstrated for serum LH and testosterone levels in the infested rats, as well as the loss of: (i) the testicular responsiveness to exogenous gonadotropin; (ii) the number of testicular LH receptors. Moreover, the remaining testicular receptors of infested rats showed an increase in their equilibrium association constant (Ka). Our study suggests that dysfunction of Leydig cells occurring during African trypanosomiasis is in part related to stress induced by the presence of the parasites.

Acute-Phase Reaction↗
PubMed1992

[Glycoprotein hormones, glycosylation and biological activity].

Glycoprotein hormones LH, FSH, TSH and hCG are heterodimeric molecules: each contains two subunits, a common alpha and a unique beta subunit. Each subunit bears one or two Asparagine linked carbohydrate moieties which have a biantennary complex-type or hybrid-type structure. Different technical methods as deglycosylation or molecular biology techniques have been used to study the role of carbohydrate residues in hormonal bioactivity. The carbohydrate chains are not directly involved in receptor binding events but their mechanisms of action is not fully understood. Two hypotheses are frequently emphasised: a conformational role or an involvement in the coupling of the receptor-adenylate cyclase system. At the post receptor level carbohydrate chains modulate the bioactivity in two ways: a global regulation following an all-or-none mode and slight one. The removal of the carbohydrate moieties leads to a loss of the in vitro hormonal activity. The results observed are dependent of the deglycosylation techniques and the bioactivity tests used. Hormone's deglycosylation reduces their capacity of production of cAMP and, to a lesser extent, their steroidogenic power. Deglycosylated hormones are antagonists to negative hormones although deglycosylated hCG has some agonist properties in vivo. Microheterogeneity of the glycoprotein hormones is due to slight variations in sialic acid and/or sulfate content. Glycoprotein hormones exist as several isoforms which differ in biological potency. Alkaline isoforms (less sialylated ones) are the most biologically active in vitro but have a short half live in vivo; acid isoforms are less active in vitro but have a longer circulatory half live. The polymorphism of glycoprotein hormones is a highly regulated process.(ABSTRACT TRUNCATED AT 250 WORDS)

Chorionic Gonadotropin↗
PubMed1991

The effects of streptozotocin induced diabetes mellitus and fish oil compound on gene expression of atrial natriuretic peptide in rat.

1. Adult male Wistar rats were injected with streptozotocin (STZ: 55 mg/kg) for inducing diabetes. Then blood and atria for RNA extraction were withdrawn from rats treated 3 and 11 weeks previously with STZ respectively. Atrial total RNA were extracted with cold phenol method. The ANP mRNA contents were determined using Dot blot hybridization technique with alpha-32-P-labelled r-prepro ANP cDNA probe. 2. Plasma glucose was increased and plasma immunoreactive insulin was lowered in rats at 3 and 11 weeks after injection of STZ. ANP gene expression in diabetic rats was depressed. ANP mRNA contents in rats treated 3 and 11 weeks with STZ were 86.4% and 31.7% of that of control rats. 3. Three weeks after treatment of STZ, the rats were gastrically perfused with FOC (Fish Oil Compound) (0.355 ml/kg) once a day successively until 11 weeks. This treatment induces lower blood pressure in rats. ANP gene expression in FOC group was apparently recovered which had been decreased because of the effect of diabetes mellitus.

Animals↗
PubMed1990

Gonadotropic dysfunction produced by Trypanosoma brucei brucei in the rat.

Hormonal disorders have been frequently observed in humans and animals infected with tsetse-transmitted (African) trypanosomes. We studied the pituitary gonadal axis (plasma concentrations of testosterone, luteinizing hormone (LH), follicle stimulating hormone (FSH) and the pituitary gonadotropin (LH, FSH) concentrations) in rats as an experimental model infected with an acute stock of Trypanosoma brucei brucei (AnTat 1.1A). The same investigations in vivo were carried out with rats inoculated by trypanosomal preparations: surface coat components slowly released at pH 5.5 and the parasitic cellular pellet. The releasing procedure as firstly described by Baltz et al. (1976) was performed in the presence or the absence of protease inhibitors. We noted a testicular hypogonadism produced by the acute infection with the decrease of the testosterone level and an increase of the pituitary LH concentration, although the other circulating FSH and LH hormone levels were stable. The injection of the trypanosomal pellet, obtained in the presence of antiproteases, generated a similar clinical hormonal picture: decrease of testosterone level; increase in pituitary LH, FSH content; absence of significant variation of circulating FSH and LH rates. When the trypanosomal pellet was prepared in absence of antiproteases the circulating gonadostimuline levels were significantly decreased. In the same conditions (absence of antiproteases) the trypanosomal supernatant pH 5.5 induced the decrease of the testosterone and plasma LH levels. These results suggested that component(s) from trypanosomes generated hormonal perturbations.

Acute Disease↗
PubMed1990

[Macroprolactinemia in a child].

An hyperprolactinemia, with basal serum prolactin levels ranging from 41 to 135 ng/ml was found to be coincidentally associated with psychosocial dwarfism in a 11 year-old boy. Sephadex G 100 exclusion chromatography showed that the predominating form of immunoreactive prolactin levels ranging from 41 to 135 ng/ml was found to be weight, differing from the regular occurrence of a 22 kilodalton major variant. Prolactin levels increased under TRH (increments between 29 and 76%) but were not blunted by bromocriptine at a dose of 2.5 mg/day. This so-called macroprolactinemia syndrome should be searched for whenever a discrepancy is noted between clinical symptoms and blood prolactin levels.

Adolescent↗
PubMed1989

Reversed phase HPLC of different membrane-bound variant surface glycoprotein preparations from Trypanosoma brucei brucei.

The chromatographic behaviour of the membrane-attached variant surface glycoprotein (mfVSG) of bloodstream forms of Trypanosoma brucei brucei AnTat 1.1 A preparations were studied by reversed phase high performance liquid chromatography (RP-HPLC). Among the different preparation procedures used, only the trifluoroacetic acid extraction gave a mfVSG preparation which was eluted from the RP-HPLC column. As well as for the soluble variant surface glycoprotein (sVSG) it was found that different mfVSG forms were eluted at different organic solvent concentrations from the RP-HPLC column. In addition, in preliminary studies, we have attempted to characterize the factors responsible for the trypanosome surface coat assembly. Using chromatographic techniques (RP-HPLC and thin layer chromatography), the results suggest a close relationship between the content of lipid-containing species and the heterogeneity of mfVSG preparation.

Animals↗
PubMed1989

Gonadotropic axis and Trypanosoma brucei gambiense infection.

A gonad endocrine survey on 46 Congolese patients (15 women and 31 men) with parasitologically confirmed trypanosomiasis found amenorrhoea in 60% of the women and impotence in 70% of the men. The basic gonad endocrine examination showed a decrease in oestradiol levels in about 65% of the women. Both amenorrhoea and low oestrogen levels were observed in the second phase (P2) of the disease, but low oestrogen levels were sometimes noted in the first phase of the disease (P1). In the men, about 50% of the cases (P2) showed a decrease in testosterone. However, as in the women, the variation of testosterone was also observed in the first phase (P1). A static and dynamic examination of the hypothalamic-pituitary-gonadal axis was undertaken in order to investigate the origin of these hypogonadisms. A supra - or extra-hypophyseal origin is discussed.

Adolescent↗
PubMed1988

Trypanosoma brucei brucei: variability in the association of some variant surface glycoproteins.

In our isolation procedure, the surface antigens of the variants AnTat 1.1 and 1.10 (Trypanosoma brucei brucei) are essentially obtained as a disulfide-linked dimer while the AnTat 1.8 surface antigen is found as a mixture of monomer and disulfide-linked dimer. This observation may be related to the localization of the cysteine residues in the protein sequences. In the purification procedure using concanavalin-A Sepharose chromatography, besides the VSG elution by methyl-alpha-D-mannopyranoside, a quantitative elution of still bound VSG may be obtained by the addition of beta-mercaptoethanol to methyl-alpha-D-mannopyrannoside in the elution buffer. The surface antigen of the variant AnTat 1.1 was examined for molecular form at several different times during the release procedure. The disulfide-linked dimer could be observed within 30 min of the surface coat release, indicating its presence within the parasite.

Animals↗
PubMed1988

[Endocrine function and African trypanosomiasis. Evaluation of 79 cases].

Although the high frequency of hypogonadism was found during the sleeping sickness, the physiological properties of the gonads have been poorly studied. We reported here the exploration of the gonadotropic axis in 79 patients infected by Trypanosoma brucei gambiense. It has been noted a decrease in oestradiol for 50% of women, in testosterone levels for 50% of men whereas no decrease of pituitary gonadotropins (FSH and LH) was found. The results of the gonad adenohypophyseal tests suggested that the dysfunction may be of central origin. The studies of thyreotropic axis were also examined: a decrease in T3 and FT3 (free fraction) even though T4 was normal. The specific relationship between hypogonadism and trypanosomal infection is discussed in this report.

Adolescent↗
PubMed1987

Heterogeneity in high performance liquid chromatography of a variant surface glycoprotein of Trypanosoma brucei.

High performance liquid chromatography (HPLC) procedures have been used to analyze a preparation of the variant surface glycoprotein AnTat 1.1A of Trypanosoma brucei. The native preparation gives several peaks with a high reproducibility both by reverse-phase (RP-) and gel permeation (GP-) HPLC. Under RP-HPLC conditions, nine fractions are fully resolved. The RP-HPLC fractions migrate with the same molecular weight VSG band on polyacrylamide slab gel electrophoresis and no significant differences are observed in amino acid composition among these fractions. The RP-HPLC resolution is found to be related to the ability of the VSG to polymerize as shown using GP-HPLC. These results suggest the existence of a microheterogeneity of the AnTat 1.1A VSG preparation in relation to post-translational modification of the VSG molecule.

Animals↗
PubMed1987

Isolation and characterization of human urinary colony-stimulating factor.

CSF-1 was isolated from a large volume of human normal urine (10,000 l), using the following 5 stages of purification: concentration by dialysis, silica gel adsorption, hydrophobic chromatography on phenyl-Sepharose CL-6B, fast protein liquid chromatography (FPLC) and finally preparative electrophoresis on polyacrylamide gels. We have isolated 8 mg of purified CSF-1 which migrated as a single band under non-reducing conditions in SDS-PAGE (staining with Coomassie Blue and the sensitive silver techniques). But in the presence of dithiothreitol, the SDS-PAGE pattern revealed a minor second band with a molecular mass of 50,000 Da. CSF-1 was purified 100,000-fold and has a specific activity of 2.16 X 10(7) units/mg protein. Its apparent molecular mass is 57,000 Da with an isoelectric point, pI = 5.8-6.0. The amino-acid composition is reported and compared with that of murine CSF-1. The carbohydrate content (sialic acid, sulphate groups, N-acetylglucosamine, N-acetylgalactosamine) was also determined, and it shows that CSF is a glycoprotein.

Amino Acids↗
PubMed1986

Analysis of free porphyrins in biological samples by high performance liquid chromatography.

High performance liquid chromatography has been used to separate and analyse the different free porphyrins in biological materials. The selective determination of uroporphyrin, coproporphyrin, protoporphyrin and hepta, hexa, pentacarboxylic porphyrins, the sensitive and quantitative fluorescence detection contribute to the clinical diagnosis of porphyria.

Chromatography, High Pressure Liquid↗