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Biomedical subjects

A Jensen

Publications and source records attributed to A Jensen.

At least 55 records · Page 3Linked to original sources
PubMed2000

Lipopolysaccharides do not alter metabolic disturbances in hippocampal slices of fetal guinea pigs after oxygen-glucose deprivation.

The aim of the present study was to clarify whether endotoxins [lipopolysaccharides (LPS)] have a toxic effect on fetal brain tissue after cerebral ischemia, while excluding their effect on the cardiovascular system. Experiments were therefore performed on hippocampal slices prepared from mature fetal guinea pigs. In particular, we studied the influence of LPS on nitric oxide production, energy metabolism, and protein synthesis after oxygen-glucose deprivation (OGD). Incubating hippocampal slices in LPS (4 mg/L) for as long as 12 h did not alter cGMP tissue concentrations significantly. However, 10 min after OGD of 40-min duration, cGMP tissue concentrations were substantially increased in relation to controls, and this increase was almost completely blocked by the application of 100 microM N:(omega)-nitro-L-arginine, indicating that nitric oxide synthase was activated after OGD in fetal brain tissue. Again, LPS did not have any effect on cGMP tissue concentrations after OGD. Furthermore, addition of LPS altered neither protein synthesis nor energy metabolism measured 12 h after OGD. We therefore conclude that, apart from their well-known influence on the cardiovascular system, LPS do not alter metabolic disturbances in hippocampal slices of fetal guinea pigs 12 h after OGD. A direct toxic effect of LPS on immature brain tissue within this interval does not therefore seem to be very likely. However, delayed activation of LPS-sensitive pathways that may be involved in cell death, or damage limited to a small subgroup of cells such as oligodendrocyte progenitors, cannot be fully excluded.

Adenosine Triphosphate↗
PubMed1999

Dynamics of fetal circulatory responses to hypoxia and asphyxia.

This review will focus on the dynamic changes of the fetal circulation, the distribution of organ blood flow during normoxemia, and that during hypoxia and asphyxia caused by various experimental perturbations. Furthermore, the relation between oxygen delivery and tissue metabolism during oxygen lack as well as evidence to support a new concept will be presented along with the principal cardiovascular mechanisms involved. Finally, blood flow and oxygen delivery to the principal fetal organ will be examined and discussed in relation to organ function. The fetal circulatory response to hypoxaemia and asphyxia is a rapid centralization of blood flow in favour of the brain, heart, and adrenals and at the expense of almost all peripheral organs, particularly of the lungs, carcass, skin and scalp. This response is qualitatively similar but quantitatively different under various experimental conditions. However, at the nadir of severe acute asphyxia the circulatory centralization cannot be maintained. Then there is circulatory de-centralization, and the fetus will experience severe brain damage if not expire unless immediate resuscitation occurs. Future work in this field will have to concentrate on the important questions, what factors determine this collapse of circulatory compensating mechanisms in the fetus, how does it relate to neuronal damage, and how can the fetal brain be pharmacologically protected against the adverse effects of asphyxia?

Asphyxia Neonatorum↗
PubMed1999

Cognitive abilities in children with congenital muscular dystrophy: correlation with brain MRI and merosin status.

The aim of the study was to evaluate whether children with merosin-positive or merosin-deficient congenital muscular dystrophy (CMD) show any cognitive impairment and whether this is related to brain abnormalities on magnetic resonance imaging (MRI). Twenty-two patients (age range: 5.8-15.3 years) were assessed by the Wechsler Intelligence Scales. Twelve were merosin-positive and ten merosin-deficient. One child had severe mental retardation and could not be tested. The full scale IQ in the remaining 21 ranged from 51 to 134, the verbal IQ ranged from 78 to 136 and the performance from 51 to 136. Of the twelve children with normal merosin one had a mild delay (IQ < 75) and two were borderline (IQ 75-95). Of the ten children with merosin-deficiency, one showed severe mental retardation and could not be tested, one showed a mild delay and two had borderline results. While the children with merosin deficiency with the typical diffuse white matter changes on MRI had normal scores, the children who in addition had cerebellar hypoplasia had lower performance IQ. The child with cortical dysplasia had severe mental retardation. Our results suggest that the spectrum of cognitive abilities in CMD is very wide even within genetically homogeneous conditions.

Adolescent↗
PubMed1998

Influence of Alcohol on the Behavior of Sodium Dodecylsulfate Micelles.

The effect of medium chain alcohol molecules on the size and shape of sodium dodecylsulfate micelles, and on the self-diffusion coefficient of the surfactant and alcohol, has been investigated by means of small angle neutron scattering (SANS), and Fourier transform pulsed field gradient spin echo (FT-PGSE) nuclear magnetic resonance measurements. All measurements were done in D2O containing a sodium chloride concentration of 0.4 mol/kg, and a surfactant concentration of 0.04 mol/kg. The alcohols used were 1-propanol, 1-butanol, and 1-pentanol. The data obtained from the different techniques agrees qualitatively. The results show that propanol successively breaks down the micelles while pentanol brings about a structural change toward large wormlike aggregates. Butanol shows a highly complex behavior on the structure of the micelles and can decrease and increase the size of the aggregates, depending on the added alcohol concentration range. All analyzed solutions show a distribution of the alcohol between the aqueous bulk solution and the palisade layer of the micelles, resulting in an increased "hydration" of D2O in the micellar surface. Moreover, the structural changes of the micelles indicate that butanol and pentanol solubilize in the micellar core in the high molality range, near the end of the solubility limit. Propanol is apparently too hydrophilic to do so. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

Metabolic disturbances in hippocampal slices of fetal guinea pigs during and after oxygen-glucose deprivation: is nitric oxide involved?

The aim of this study was to investigate the role of nitric oxide in metabolic disturbances induced in brain tissue of fetal guinea pigs by oxygen-glucose deprivation. Experiments were performed on hippocampal slices so as to exclude the effects of nitric oxide on the cardiovascular system. Metabolic disturbances were assessed by measuring changes in energy metabolism and protein synthesis after different periods of oxygen-glucose deprivation (OGD). Ten min after OGD of 40 min duration, the concentration of cGMP in tissue slices rose from 1.35 +/- 0.38 to 18.6 +/- 1.04 pmol/mg protein (P < 0.05). This rise was almost completely inhibited by the addition of 100 microM N-nitro-L-arginine (NNLA), indicating that NO-synthase was strongly activated after OGD in fetal brain tissue. However, addition of NNLA improved neither protein synthesis nor energy metabolism measured 12 h after OGD. Thus, nitric oxide does not appear to contribute directly to processes leading to metabolic disturbances induced by transient ischemia in immature brain tissue.

Adenosine Triphosphate↗
PubMed1998

Epidermal-growth-factor receptor correlates negatively with cell density in cervical squamous epithelium and is down-regulated in cancers of the human uterus.

The role of the epidermal-growth-factor receptor (EGFR) in cervical cancer is controversial, due to technical difficulties in localizing or in quantifying EGFR by homogenate assays or immunohistochemistry. Our autoradiographic approach, in combination with morphometry, allowed cell-type-specific quantification of EGFR, leading to the following observations: (i) In normal cervical epithelium, EGFR levels per cell were high in non-dividing squamous cells of the upper layers of normal epithelium, where a mitogenic function of these EGFRs can be excluded. (ii) In contrast to earlier findings in tissue homogenates, but consistent with our observation in normal cervical epithelium that cells of the proliferating strata (basal and parabasal cells) express intermediate and comparatively reduced levels of EGFR per cell, cervical cancers displayed a significant reduction both of specific EGF binding and of EGFR levels per cell as compared with normal epithelium. (iii) A significant negative correlation of cell density and EGFR number per cell was obtained. In normal cervical epithelium, cervical intra-epithelial neoplasia and invasive cervical cancer (p = 0.002). This negative correlation was most evident in normal epithelium, where large changes of cell density occur within one slide (p < 0.001). (iv) Specific EGF-binding was also significantly reduced in endometrial cancers when compared with normal endometrium. It is proposed that in uterine tissues low or intermediate levels of EGFR do not exclude their function as mediators of cell proliferation.

Autoradiography↗
PubMed1998

Effect of mild hypothermia during and after transient in vitro ischemia on metabolic disturbances in hippocampal slices at different stages of development

In the present study the neuroprotective effect of mild hypothermia (decrease of temperature from 37degreesC to 33degreesC) during and after transient ischemia in brain tissue at different stages of development was tested in vitro by measuring energy metabolism, glutamate release and protein biosynthesis rate (PSR) in hippocampal slices. Slices were taken from immature (E40) and mature (E60) guinea pig fetuses and adult guinea pigs. The slices were exposed to ischemia-like conditions (oxygen/glucose deprivation, OGD) for periods of between 10 to 40 min followed by a 2-h or 12-h recovery phase. During OGD, mild hypothermia slowed down the depletion of energy stores only in slices from immature fetuses, but had no effect on slices prepared from mature fetuses and adult animals. Hypothermia also reduced glutamate release significantly during oxygen/glucose deprivation. Lowering temperature to 33degreesC had no effect on energy metabolism and only a minor effect on PSR of slices from mature fetuses and adult animals subjected to 2 h of recovery. However, 12 h after OGD PSR was markedly improved by mild hypothermia in slices from mature animals and in slices from adults that had been exposed to OGD for only 20 or 30 min. The inhibition of PSR was more severe in the slices from adults than in those from mature fetuses subjected to the same duration of OGD. Age- and temperature-related differences in glutamate release during OGD did not fully agree with corresponding disparities in the values for PSR obtained 12 h after OGD. These results indicate that the neuroprotective effect of mild hypothermia was not mediated by a temperature-dependent retardation of the depletion of energy stores during OGD. Age-related disparities in the vulnerability of the brain to ischemia and the neuroprotective efficiency of mild hypothermia appear to be only partially reflected by the varying levels of glutamate release during ischemia but best reflected by the extent of PSR inhibition. It is concluded that mild hypothermia may be a suitable therapeutical intervention for the suppression of hypoxic-ischemic cell damage during birth.

Journal Article↗
PubMed1998

Effect of mild hypothermia during and after transient in vitro ischemia on metabolic disturbances in hippocampal slices at different stages of development.

In the present study the neuroprotective effect of mild hypothermia (decrease of temperature from 37 degrees C to 33 degrees C) during and after transient ischemia in brain tissue at different stages of development was tested in vitro by measuring energy metabolism, glutamate release and protein biosynthesis rate (PSR) in hippocampal slices. Slices were taken from immature (E40) and mature (E60) guinea pig fetuses and adult guinea pigs. The slices were exposed to ischemia-like conditions (oxygen/glucose deprivation, OGD) for periods of between 10 to 40 min followed by a 2-h or 12-h recovery phase. During OGD, mild hypothermia slowed down the depletion of energy stores only in slices from immature fetuses, but had no effect on slices prepared from mature fetuses and adult animals. Hypothermia also reduced glutamate release significantly during oxygen/glucose deprivation. Lowering temperature to 33 degrees C had no effect on energy metabolism and only a minor effect on PSR of slices from mature fetuses and adult animals subjected to 2 h of recovery. However, 12 h after OGD PSR was markedly improved by mild hypothermia in slices from mature animals and in slices from adults that had been exposed to OGD for only 20 or 30 min. The inhibition of PSR was more severe in the slices from adults than in those from mature fetuses subjected to the same duration of OGD. Age- and temperature-related differences in glutamate release during OGD did not fully agree with corresponding disparities in the values for PSR obtained 12 h after OGD. These results indicate that the neuroprotective effect of mild hypothermia was not mediated by a temperature-dependent retardation of the depletion of energy stores during OGD. Age-related disparities in the vulnerability of the brain to ischemia and the neuroprotective efficiency of mild hypothermia appear to be only partially reflected by the varying levels of glutamate release during ischemia but best reflected by the extent of PSR inhibition. It is concluded that mild hypothermia may be a suitable therapeutical intervention for the suppression of hypoxic-ischemic cell damage during birth.

Adenine↗
PubMed1998

HIV-1 rev nuclear export signal binding peptides isolated by phage display.

The human immunodeficiency virus type 1 (HIV-1) Rev protein is absolutely essential in the viral replication cycle, where it induces the production of viral structural proteins. Rev functions in part by inducing the nuclear export of incompletely spliced mRNA species specified by the presence of an RNA element, the Rev response element (RRE). Several proteins implicated in RNA processing and nucleo-cytoplasmic transport have been shown to interact with Rev, however, their exact roles remain unknown. To map potential protein recognition sites within the Rev structure, we have screened a phage library, displaying random 15-mer peptides, and isolated clones exhibiting similar sequences that specifically interact with Rev. The binding sites on Rev of the corresponding synthetic peptides were characterised by protein footprinting, involving partial proteolysis of radioactively end-labelled Rev protein. Two of the peptides produced a significant footprint within the nuclear export signal of Rev, raising the possibility that they mimic the binding of cellular protein factors implicated in nuclear export.

Amino Acid Sequence↗
PubMed1998

Low-dose flunarizine does not affect short-term fetal circulatory responses to acute asphyxia in sheep near term.

Asphyxia is one of the major causes of perinatal brain damage and neuronal cell loss, which may result in psychomotor deficits during later development. It has been shown previously that the immature brain can be protected from ischemic injury by flunarizine, a class IV calcium antagonist. However, cardiovascular side-effects of flunarizine, when applied at the dosages used in those studies, have been reported. Recently, the present authors were able to demonstrate that even by injecting flunarizine at a far lower dosage (1 mg kg-1 estimated bodyweight) neuronal cell damage, caused by occlusion of both carotid arteries for 30 min, can be reduced in fetal sheep near term. The aim of the present study was, therefore, to examine whether low-dose flunarizine affects fetal cardiovascular responses to acute asphyxia in sheep near term. Ten fetal sheep were chronically instrumented at a mean gestational age of 132 +/- 1 days (term is at 147 days). Fetuses from the study group received a bolus injection of flunarizine (1 mg kg-1 estimated fetal weight) 60 min before asphyxia, whereas the solvent was administered to the fetuses from the control group. Organ blood flows, physiological variables and plasma concentrations of catecholamines were measured before, during and after a single occlusion of uterine blood flow for 2 min (i.e. at 0, 1, 2, 3, 4, and 30 min). Before asphyxia, the distribution of combined ventricular output and physiological variables, as well as concentrations of catecholamines, in fetuses from the control group were in the normal range for chronically prepared fetal sheep near term. During acute asphyxia there was a redistribution of cardiac output towards the central organs accompanied by a pronounced bradycardia and a rapid increase in arterial blood pressure. After asphyxia circulatory centralization did not resolve quite as rapidly as it developed, but was almost completely recovered at 30 min after the insult. There were nearly no differences in the time course of physiological and cardiovascular variables measured before, during and after acute intrauterine asphyxia between the control and study groups. From the present study it was concluded that low-dose flunarizine does not affect short-term fetal circulatory responses to acute asphyxia in sheep near term.

Adrenal Glands↗
PubMed1998

Low dose flunarizine protects the fetal brain from ischemic injury in sheep.

Flunarizine, a calcium channel blocker, reduced cerebral damage caused by hypoxic-ischemic insults in neonatal rats and in fetal sheep near term. However, the high dose regimen used in these studies produced cardiovascular side effects that might have counteracted the neuroprotective properties of flunarizine. Therefore, the neuroprotective effect was tested in a low dose protocol (1 mg/kg estimated body weight). Twelve fetal sheep near term were instrumented chronically. Six fetuses were pretreated with 1 mg of flunarizine per kg of estimated body weight 1 h before ischemia, whereas the remainder (n=6) received solvent. Cerebral ischemia was induced by occluding both carotid arteries for 30 min. To exclude the possibility that the neuroprotective effects of flunarizine were caused by cerebrovascular alterations we measured cerebral blood flow by injecting radiolabeled microspheres before (-1 h), during (3 min and 27 min) and after (40 min, 3 h, and 72 h) cerebral ischemia. At the end of the experiment (72 h) the ewe was given a lethal dose of sodium pentobarbitone and saturated potassium chloride i.v., and the fetal brain was perfused with formalin. Neuronal cell damage was assessed in various brain structures by light microscopy after cresyl violet/fuchsin staining using a scoring system: 1, 0-5% damage; 2, 5-50% damage; 3, 50-95% damage; 4, 95-99% damage; and 5, 100% damage. In 10 other fetal sheep effects of low dose flunarizine on circulatory centralization caused by acute asphyxia could be excluded. In the treated group neuronal cell damage was reduced significantly in many cerebral areas to varying degrees (range for control group, 1.03-2.14 versus range for treated group, 1.00-1.13; p < 0.05 to p < 0.001, respectively). There were only minor differences in blood flow to the various brain structures between groups. We conclude that pretreatment with low dose flunarizine protects the brain of fetal sheep near term from ischemic injury. This neuroprotective effect is not mediated by changes in cerebral blood flow. We further conclude that low dose flunarizine may be clinically useful as a treatment providing fetal neuroprotection, particularly because the fetal cardiovascular side effects are minimal.

Animals↗
PubMed1997

Comparison of the physiologically equivalent proteins cytochrome c6 and plastocyanin on the basis of their electrostatic potentials. Tryptophan 63 in cytochrome c6 may be isofunctional with tyrosine 83 in plastocyanin.

The blue copper protein plastocyanin and the heme protein cytochrome c6 differ in composition and in structure but perform the same function in the photosynthetic electron-transport chain. We compare these two proteins on the basis of their electrostatic potentials in order to understand the structural basis of their functional equivalence. In the first approach, we use a monopole-dipole approximation of the electrostatic potentials to superimpose the proteins. The resulting alignment suggests that Tyr51 in cytochrome c6 corresponds to Tyr83 in plastocyanin. But since Tyr51 is not conserved in all known cytochrome c6 sequences, a physiological role of this residue is questionable. In a more sophisticated approach, we applied the recently-developed Fame (flexible alignment of molecule ensembles) algorithm, in which molecules are superimposed by optimizing the similarity of their electrostatic potentials with respect to the relative orientation of the molecules. On the basis of the Fame alignments of plastocyanin and cytochrome c6, we analyze the docking and the electron-transfer reactions of these two proteins with its physiological reaction partner cytochrome f. We derive functional analogies for individual amino acids in possible electron-transfer paths in the interprotein redox reactions. We identify two surface patches in cytochrome c6 that may be involved in electron-transfer paths. The hydrophobic patch with the exposed heme edge in cytochrome c6 may be equivalent to the hydrophobic patch with His87 in plastocyanin, whereas Trp63 in cytochrome c6 may be equivalent to Tyr83 in plastocyanin. An aromatic amino acid is present at the position of Trp63 in all known cytochrome c6 sequences. The electronic coupling between the heme and the copper site on the one side and several potentially important amino acid residues on the other is analyzed by the Pathways method. We have proposed recently that Lys65 of cytochrome f and Tyr83 of plastocyanin form a cation-pi system, which may be involved in a two-step mechanism of the electron-transfer reaction between these two proteins from higher plants. Now we corroborate this proposal by analyzing available amino acid sequences.

Algorithms↗
PubMed1997

Probing the structure of HIV-1 Rev by protein footprinting of multiple monoclonal antibody-binding sites.

Human immunodeficiency virus type 1 (HIV-1) Rev is a small RNA-binding protein which is essential for viral replication. To investigate the structure of Rev we have mapped the binding sites of a panel of monoclonal antibodies (mAb) by protein footprinting and identified a mAb protecting amino acids within both the N- and C-terminal parts of Rev. Our mapping results support a previously proposed structure (Auer et al., Biochemistry, 33 (1994) 2988-2996) predicting that a helix-loop-helix motif in Rev brings the termini of the protein into proximity. Furthermore, we demonstrate that the binding sites mapped by protein footprinting are in agreement with conventional epitope mapping results and that this technique provides an advantageous strategy for mapping discontinuous sites.

Antibodies, Monoclonal↗
PubMed1997

mRNA expression of ligands of the epidermal-growth-factor-receptor in the uterus.

Six different ligands of the epidermal-growth-factor receptor (EGFR) have been identified in the past. In some cervical squamous-cell carcinomas, an increased amount of proteins binding to the EGFR has been reported. In order to identify the mRNA of EGFR ligands (EGFRL), which might be overexpressed in cervical and endometrial cancers, we performed semi-quantitative reverse-transcription/polymerase chain reactions (RT-PCR) for all 6 EGFRL in RNA extracts of normal and malignant tissue samples of the human uterus. PCR products from RNA extracts of 83 patients were quantitated relative to the housekeeping gene and internal standard pyruvate dehydrogenase by analyzing the PCR kinetics of product synthesis. In extracts of normal cervix, the level of mRNA expression of the EGFRL was significantly higher than in endometrium. No significant difference was detected between normal cervix and cervical carcinomas. However, both in cervical and in endometrial cancers, mRNA expression was non-parametrically distributed and in some cervical cancers overexpression of transforming growth factor alpha (TGF-alpha), amphiregulin or EGF was observed. In endometrial cancers, mRNA levels of all EGFRL were higher than in normal endometrium. This increase was significant (p < 0.005) for TGF-alpha and amphiregulin. Thus, TGF-alpha mRNA is overexpressed in approximately 10% of cervical cancers and in the majority of endometrial cancers. Since TGF-alpha anti-sense therapy might represent a future strategy in such cancers, we also determined the absolute level of TGF-alpha mRNA expression by quantitative PCR using a cloned standard.

Cloning, Molecular↗
PubMed1997

No effect of glutamate on metabolic disturbances in hippocampal slices of mature fetal guinea pigs after transient in vitro ischemia.

The involvement of glutamate in the development of cerebral metabolic disturbances in mature fetuses after transient ischemia was studied using a hippocampal slice model. We investigated the effects of exogenously applied glutamate or glutamate antagonists on the recovery of energy metabolism and protein synthesis rate (PSR) in hippocampal slices of mature guinea pigs after in vitro ischemia. The slices were incubated in a thermostatically controlled flow-through chamber and gassed with carbogen (95% O2/5% CO2). In vitro ischemia was induced by transferring the slices to an aglycemic, artificial cerebrospinal fluid (aCSF) equilibrated with 95% N2/5% CO2. In a first set of experiments slices were exposed to 10 mM glutamate during a 20-40 min period of in vitro ischemia. In a second set slices were incubated in aCSF containing MK-801 (100 microM) or kynurenic acid (0.5 mM) 30 min before, during and 2 h after in vitro ischemia. After a 12 h recovery phase, the concentrations of adenylates in the slices were measured by HPLC after extraction with perchloric acid. PSR was calculated from the rate of incorporation of [14C]leucine into tissue proteins. Neither glutamate nor glutamate antagonists had any effect on the postischemic recovery of energy metabolism and PSR when applied during in vitro ischemia. It is therefore concluded that glutamate does not play a major role in the development of metabolic disturbances in hippocampal slices from mature guinea pig fetuses subjected to transient in vitro ischemia.

Adenosine Triphosphate↗