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P Kristensen

Publications and source records attributed to P Kristensen.

At least 19 recordsLinked to original sources
PubMed2002

Role of mitochondria-rich cells for passive chloride transport, with a discussion of Ussing's contribution to our understanding of shunt pathways in epithelia.

A non-invasive method is applied for studying ion transport by single isolated epidermal mitochondria-rich (MR) cells. MR cells of toad skin (Bufo bufo) were prepared by trypsin (or pronase) treatment of the isolated epithelium bathed in Ca2+-free Ringer. Glass pipettes were pulled and heat- polished to obtain a tip of 2-4 mm with parallel walls and low tip resistances. The neck of an MR-cell was sucked into the tip of the pipette for being 'clamped mechanically' by the heat-polished glass wall. In this configuration the apical cell membrane faces the pipette solution while the major neck region and the cell body are in the electrically grounded bath. With Ringer in bath and pipette, transcellular voltage clamp currents were composed of an ohmic (I(leak)) and a dynamic (I(dynamic)) component. The dynamic component was studied by stepping the transcellular potential (Vp) from a holding value of +50 mV to the hyperpolarizing region (50 > Vp > or = -100 mV). The steady state I(dynamic)-Vp relationship was strongly outward rectified with I(dynamic) being practically zero for Vp > 0 mV. At Vp = -100 mV, MR cells isolated by trypsin or pronase generated a steady-state I(dynamic) of,-2.72 +/- 0.40 nA/cell (N = 21 MR cells). Continuous superfusion of the MR cell during recording increased the current to -7.99 +/- 1.48 nA/cell (N = 10 MR cells). The time course of the reversible activation of G(dynamic) varied among cells, but was usually sigmoid with T1/2 decreasing with Vp (-25 > or = Vp > or = -100 mV). T1/2 was in the order of 10 sec at Vp = -100 mV. The single-MR-cell currents recorded in this study are fully compatible with Cl- currents estimated by relating density of MR cells to transepithelial ICl or by measurements with the self-referencing ('vibrating') probe technique. In the discussion, Ussing's work on epithelial shunt pathways is considered. His thinking and experiments leading to his theory of isotonic transport in leaky epithelia is emphasized. It is our thesis that the understanding of the physiology of epithelia owes as much to Ussing's studies of shunt pathways as to his studies of the active sodium pathway.

Animals↗
PubMed2002

Single-chain antibody-based gene therapy: inhibition of tumor growth by in situ production of phage-derived human antibody fragments blocking functionally active sites of cell-associated matrices.

Experimental evidence suggests that blocking the interactions between endothelial cells and extracellular matrix (ECM) components may provide a potent and general strategy to inhibit tumor neovascularization. Based on these considerations, we have focused our efforts on laminin, component of the vascular basement membrane of every tumor-associated vessel, which serves an essential role in tube formation. We screened anti-laminin single-chain antibody fragments (scFv) derived from a human phage-display library and identified one that blocks the formation of capillary-like structures in vitro. This scFv inhibits angiogenesis in vivo in the chick embryo chorioallantoic membrane assay and prevents the establishment and growth of subcutaneous tumors in mice, either when administered as bolus protein therapy or when produced locally by gene-modified tumor cells. Our work represents the first demonstration of a direct in vivo therapeutic effect of a single-chain antibody secreted by gene-modified mammalian cells. These results open the way for a new antibody-based gene therapy strategy of cancer.

Animals↗
PubMed2002

Effects of leptin on arcuate pro-opiomelanocortin and cocaine-amphetamine-regulated transcript expression are independent of circulating levels of corticosterone.

In the hypothalamic arcuate nucleus, neurones that coexpress cocaine-amphetamine-regulated transcript (CART) and alpha-melanocyte-stimulating hormone [alpha-MSH; pro-opiomelanocortin (POMC) derived] peptides exert catabolic actions and are stimulated by leptin. However, leptin treatment also affects other circulating factors that influence hypothalamic gene expression. Notably, the hypercorticosteronaemia of ob/ob mice is lowered by leptin treatment. To examine the interaction between glucocorticoids and leptin on POMC/CART mRNA expression, an experiment combining leptin and adrenalectomy (ADX) in leptin deficient ob/ob mice was carried out. Obese ob/ob and lean littermate Ob/? mice were ADX or sham-operated. ADX mice received a pellet containing 25% corticosterone subcutaneously. Seven days postoperatively, mice were injected intraperitoneally for 5 days with either recombinant human leptin or vehicle. On the sixth day, the mice were decapitated and the brains removed and trunk blood was collected for corticosterone analysis. Plasma concentrations of corticosterone were elevated in all ob/ob groups compared to Ob/?. For both ob/ob and Ob/? groups, corticosterone concentrations exhibited a decline across groups: vehicle-sham>leptin-sham>ADX-vehicle>ADX-leptin. Leptin inhibited food intake and bodyweight in ob/ob-sham and ob/ob-ADX to a similar extent, whereas no effect of leptin was observed in Ob/? mice. Similarly, leptin caused an identical increase in arcuate POMC and CART mRNA expression in ob/ob-sham and ob/ob-ADX compared to vehicle. The present data support the view that leptin influences arcuate POMC and CART mRNA expression directly, and that the effect is not modulated by corticosterone across a wide range of circulating corticosterone concentrations.

Animals↗
PubMed2001

Comparison of the decameric structure of peroxiredoxin-II by transmission electron microscopy and X-ray crystallography.

The decameric human erythrocyte protein torin is identical to the thiol-specific antioxidant protein-II (TSA-II), also termed peroxiredoxin-II (Prx-II). Single particle analysis from electron micrographs of Prx-II molecules homogeneously orientated across holes in the presence of a thin film of ammonium molybdate and trehalose has facilitated the production of a >/=20 A 3-D reconstruction by angular reconstitution that emphasises the D5 symmetry of the ring-like decamer. The X-ray structure for Prx-II was fitted into the transmission electron microscopic reconstruction by molecular replacement. The surface-rendered transmission electron microscopy (TEM) reconstruction correlates well with the solvent-excluded surface of the X-ray structure of the Prx-II molecule. This provides confirmation that transmission electron microscopy of negatively stained specimens, despite limited resolution, has the potential to reveal a valid representation of surface features of protein molecules. 2-D crystallisation of the Prx-II protein on mica as part of a TEM study resulted in the formation of a p2 crystal form with parallel linear arrays of stacked rings. This latter 2-D form correlates well with that observed from the 2.7 A X-ray structure of Prx-II solved from a new orthorhombic 3-D crystal form.

Crystallography, X-Ray↗
PubMed2001

Prevalence of neuropsychiatric and mucous membrane irritation complaints among Palestinian shoe factory workers exposed to organic solvents and plastic compounds.

BACKGROUND: Long-term exposure to organic solvents is associated with neuropsychiatric and mucus membrane irritation. In developing countries, efforts to secure a good working environment are inadequate and protection against chemical exposures is often neglected. METHODS: In a cross-sectional survey, the prevalence of self-reported health complaints and the association with long-term exposure to solvents and plastic materials in the work environment was studied among 167 shoe-factory workers. Prevalences and adjusted prevalence ratios (PR)were calculated in Cox regression. 95% confidence intervals were estimated for PRs of adverse health effects. RESULTS: Overall, the workers reported high prevalences of neuropsychiatric and mucus membrane complaints: headache (65%), mental irritability (53%), tingling of limbs (46%), and sore eyes (43%). Cleaning work was associated with tingling of limbs (PR = 1.8, 1.0-3.2), sore eyes (PR = 1.9, 1.1-3.3), and breathing difficulty (PR = 2.0, 1.0-3.9); plastic work was associated with tingling of limbs (PR = 1.8, 1.2-2.9)and sore eyes (PR = 1.7, 1.1-2.7); and varnishing was associated with breathing difficulty (PR = 1.9, 1.1-3.5). CONCLUSIONS: The high prevalence of self-reported health complaints and the exposure-outcome association could be due to volatile organic solvents (dichloromethane, n-hexane)and plastic compounds (isocyanates and polyvinyl chloride). Absence of a satisfactory work environment is likely to contribute to high exposure levels.

Adolescent↗
PubMed2001

Calcium-dependent association of annexins with lipid bilayers modifies gramicidin A channel parameters.

In order to examine whether calcium-dependent binding of annexin to acidic phospholipids could change the lipid bilayer environment sufficiently to perturb channel-mediated transmembrane ion-transport, gramicidin A channel activity in planar lipid bilayers was investigated in the presence of calcium and annexins II, III or V. The experiments were performed with membranes consisting of phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine in 300 mM KCl solution buffered to pH 7.4 and with either 0.1 or 1 mM calcium added to the solution. Annexin (1 microM) was subsequently applied to the cis side of the membrane. All three annexins (II, III and V) when tested at 1 mM calcium decreased the gramicidin single-channel conductance. Annexins II and III increased the mean lifetime of the channels whereas annexin V seemed to have no influence on the mean lifetime. Since the lifetime of gramicidin A channels is a function of the rate constant for dissociation of the gramicidin dimer, which is dependent on the physical properties of the lipid phase, binding of annexins II and III seems to stabilize the gramicidin channel owing to a change of the bilayer structure.

Animals↗
PubMed2001

Generation and characterization of recombinant human antibodies specific for native laminin epitopes: potential application in cancer therapy.

Laminins are specific cellular regulators that directly and indirectly control activities such as cell attachment and migration, differentiation and polarity, proliferation and apoptosis, and protease expression. Considering the centrality of these issues to tumor progression, the generation of human-derived antibody fragments able to modulate laminin-regulated biological functions would allow the development of new strategies to improve treatment of cancer patients. In this report, we explore the use of phage display technology to isolate human anti-laminin antibody fragments. A library of single chain antibodies was selected using intact mouse laminin, and five different clones were identified. All the antibodies were specific for their cognate antigen, as revealed by lack of cross-reactivity with other components of the basement membranes. A more extensive characterization of the panel indicated that these antibodies recognize the native protein through conformational epitopes. All of them reduced tumor cell attachment to laminin, suggesting that domains of the laminin molecule that are recognized by these antibodies likely bind to cell-surface receptors. The antibody fragments bind to mouse, rat and human laminin. and show strong immunohistochemical reactivity with basement membranes in human and murine tissue sections. Their properties make them ideal candidates for in vivo applications.

Animals↗
PubMed2000

Identification of phage antibodies toward the Werner protein by selection on Western blots.

A procedure was established for selecting phage antibodies (phage-abs) from phage-displayed antibody repertoires by panning against proteins, separated by sodium dodecyl phosphate-polyacrylamide gel electrophoresis (SDS-PAGE) and electroblotted onto nitrocellulose membranes (Western blots). This immobilization strategy is applicable for secondary rounds of panning in selections against semipurified proteins, and directs the selection toward antibodies suitable as immunochemical reagents in Western blots. In model experiments, enrichment factors as high as 1.9x10(5) were obtained in a single round of panning. Furthermore, we demonstrate the application of this approach by selection of phage-abs recognizing the human Werner protein, which is defective in a premature aging syndrome.

Antibodies, Viral↗
PubMed2000

Implementing clinical guidelines in the treatment of diabetes mellitus in general practice. Evaluation of effort, process, and patient outcome related to implementation of a computer-based decision support system.

OBJECTIVES: To evaluate the implementation of clinical guidelines for diabetes mellitus in general practice with a specific computer-based clinical decision support system (CDSS) as part of the intervention. METHODS: Randomized study with health center as unit. General practice in Sør- and Nord-Trøndelag counties in Norway, 380,000 inhabitants. Seventeen health centers with 24 doctors and 499 patients with diabetes mellitus were in the intervention group and 12 health centers with 29 doctors and 535 patients were in the control group. Main outcome measures were group differences in fractions of patients without registrations (process evaluation) and mean group differences for the same variables (patient outcome evaluation). RESULTS: Statistically significant group differences were experienced for fractions of patients without registration of cigarette smoking (intervention group, 82.6%; control group 94.5%), body mass index (78.2% vs. 93.0%), and sufficient registrations for calculation of risk score for myocardial infarction (91.1% vs. 98.3%); all during 18 months. Large center variations were shown for all variables. The only statistically significant group difference was -2.3 mm Hg (95% CI, -3.8, -0.8) in diastolic blood pressure in favor of the intervention group. Statistically insignificant differences in favor of the intervention group were HbA1c, -0.1% (95% CI, -0.4, 0.1), systolic blood pressure, -1.2 mm Hg (95% CI, -4.4, 2.0). Statistically insignificant differences in favor of the control group were fractions of smokers, +3.0% (95% CI, -4.0, 10.0), body mass index, +0.3 kg/m2 (95% CI, -0.8, 1.4), risk score in female +0.1 (95% CI, -5.1, 5.2), and risk score in male +2.6 (95% CI, -14.2, 19.5). CONCLUSIONS: Implementation of clinical guidelines for diabetes mellitus in general practice, by means of a CDSS and several procedures for implementation, did not result in a clinically significant change in doctors' behavior or in patient outcome.

Aged↗
PubMed2000

Applying phage display technology in aging research.

Filamentous bacteriophage offers the possibility of linking genotype with phenotype in one genetic package. By creating a library of different proteins as fusion to one of the coat proteins of filamentous bacteriophage it becomes possible to isolate proteins based on their binding characteristics. Phage displayed libraries of varying formats, ranging from small peptides to antibody fragments, have been selected successfully for ligands toward a large panel of targets. These peptides and antibody fragments are applicable in analysis of the behaviour of certain proteins with respect to changes in biological processes such as aging, thus providing valuable tools for a general understanding of the aging process. Alternatively, display of antibody fragments or peptides on filamentous bacteriophage can be instrumental in the discovery of novel antigens as exemplified by selections on cell surfaces or on complex protein mixtures such as sera from aging individuals. Although phage display has been applied successfully in a large number of studies relating to cancer, viral infections and other biological processes, its application in the field of aging research is yet to be realised.

Aging↗
PubMed2000

Chronic intracerebroventricular administration of recombinant CART(42-89) peptide inhibits and causes weight loss in lean and obese Zucker (fa/fa) rats.

OBJECTIVE: Hypothalamic neuropeptide CART (cocaine-amphetamine-regulated transcript) is a leptin-dependent endogenous satiety factor in the rat, and single central injections of recombinant CART(42-89) lowers food intake in rats and mice. To assess the potential role of CART as a long-term regulator of food intake, we investigated the effects of continuous infusion of recombinant CART(42-89) on food consumption and body weight. RESEARCH METHODS AND PROCEDURES: Two doses of CART(42-89) were tested: 12 or 4.8 microg/d. Adult male, both lean (+/?) and Zucker (fa/fa) obese, rats were equipped with intracerebroventricular cannulae in the right lateral ventricle. The cannulae were connected to subcutaneously placed osmotic mini-pumps. Pumps were filled with either CART(42-89) or vehicle (50 mM phosphate-buffered saline, pH 7.4). The pumps delivered a continuous infusion of CART(42-89) or vehicle, and food intake and body weight were followed for 10 days (12 microg/d) or 7 days (4.8 microg/d). Animals given the low dose had the pump removed on Day 7, and from half of the group, trunk blood was collected after decapitation, whereas the other half of the group had their mini-pumps removed and were followed for another 7 days before being decapitated. RESULTS: Animals receiving the high doses displayed overt motor disturbances, whereas the low dose was devoid of such behavioral side effects. Both doses significantly lowered food intake with maximal effect on days 3 to 5 of the infusion period. The high dose of CART decreased body weight of normal animals to 85% of initial weight at days 3 to 5, whereas the weight of Zucker (fa/fa) obese rats dropped to 95% of the initial weight. In animals receiving 4.8 microg/d, moderate effects on body weight were seen between days 4 and 6 of the treatment period, but soon after termination of the treatment animals regained lost weight. To assess the biological activity of the contents of the osmotic mini-pumps, the pumps were removed from the subcutaneous implantation site, and 5 microL of their contents were injected intracerebroventricularly to naive animals kept on a restricted feeding schedule. The content of pumps from animals receiving 4.8 microg/d of CART(42-89) potently inhibited food intake, confirming full biological activity despite being kept for 7 days at body temperature. DISCUSSION: Due to obvious effects on motor behavior, it is impossible with certainty to conclude that the observed effects on feeding and body weight are primary interference with satiety centers or secondary to effects on locomotor pathways. Also, the present experiments suggest that hypothalamic appetite-regulating neurons are subject to pharmacological desensitization upon prolonged exposure to CART peptide. The underlying mechanism of such desensitization is as yet unknown.

Animals↗
PubMed2000

Central administration of cocaine-amphetamine-regulated transcript activates hypothalamic neuroendocrine neurons in the rat.

We have recently shown that intracerebroventricular (i.c.v.) administration of the hypothalamic neuropeptide cocaine-amphetamine-regulated transcript (CART) inhibits food intake and induces the expression of c-fos in several nuclei involved in the regulation of food intake. A high number of CART-induced c-Fos-positive nuclei in the paraventricular nucleus of the hypothalamus prompted us to examine the effect of i.c.v. recombinant CART-(42-89) on activation of CRH-, oxytocin-, and vasopressin-synthesizing neuroendocrine cells in the paraventricular nucleus (PVN). In addition, plasma levels of glucose were examined after central administration of CART-(42-89). Seventy-six male Wistar rats were fitted with i.c.v. cannulas and singly housed under 12-h light, 12-h dark conditions. One week postsurgery the animals were injected i.c.v. in the morning with 0.5 microg recombinant CART-(42-89) or saline. Trunk blood was collected by decapitation at 0 (baseline), 10, 20, 40, 60, 120, or 240 min. CART caused a strong increase in circulating corticosterone that was significantly different from saline at 20, 40, 60, and 120 min postinjection (P<0.05). Furthermore, CART caused a transient rise in plasma oxytocin levels (P<0.05 at 10 and 20 min postinjection), whereas plasma vasopressin levels were unaffected by i.c.v. CART. Animals injected i.c.v. with CART showed a rise in blood glucose levels 10 min postinjection (P<0.05). To examine whether the stimulatory effect of i.c.v. CART on corticosterone and oxytocin secretion is caused by activation of paraventricular nucleus/supraoptic nucleus (PVN/SON) neuroendocrine neurons, we used c-Fos as a marker of neuronal activity. Animals injected with CART showed a strong increase in c-Fos-immunoreactive nuclei in the PVN. Double immunohistochemistry revealed that a high (89+/-0.4%) number of CRH-immunoreactive neurons in the PVN contained c-Fos after CART i.c.v.. c-Fos expression was also observed in oxytocinergic cells (in both magnocellular and parvicellular PVN neurons as well as in the supraoptic nuclei) 120 min after CART administration, whereas none of the vasopressinergic neurons contained c-Fos. Triple immunofluorescence microscopy revealed that CART-immunoreactive fibers closely apposed c-Fos-positive CRH neurons, suggestive of a direct action of CART on PVN CRH neurons. In summary, i.c.v. CART activates central CRH neurons as well as both magnocellular (presumably neurohypophysial) and parvicellular (presumably descending) oxytocinergic neurons of the PVN. The effect of CART on CRH neurons most likely leads to corticosterone secretion from the adrenal gland, which may contribute to the inhibitory effects of CART on feeding behavior.

Animals↗
PubMed2000

Hormone-dependent cancer and adverse reproductive outcomes in farmers' families--effects of climatic conditions favoring fungal growth in grain.

OBJECTIVES: The impact of grain farming and climate on late-term abortion among female farmers, male genital birth defects among their sons, and hormone-dependent cancer among male and female farmers and their adult children was investigated. METHODS: National registers were cross-matched in Norway and 246,043 male and female farmers born in 1925-1971 were identified, as were their 264,262 children, born in 1952-1980, in agricultural censuses and in the population register. The subjects were followed in the Cancer Register through 1995. Farmers' births, conceived in 1973-1991, were identified, and the prevalences of late-term abortion in mothers and hypospadias and cryptorchidism in their sons at birth were examined. Exposure, defined as the combination of grain farming and categories of seasonal or cumulative warnings, was based on data in agricultural censuses and on local, seasonal, field fungal warnings. Estimated adjusted rate ratios or prevalence ratios served as the measures of association. RESULTS: Categories of high exposure were associated with reproductive outcomes and cancer among female farmers, the strongest occurring for late-term abortion (ratio 2.6, 95% confidence interval (95% CI) 1.6-4.3). Exposure associations for ovarian and breast cancer, and male genital defects, were more moderate. Endometrial cancer was associated with grain farming (ratio 2.0, 95% CI 1.4-2.8) across all levels of fungal warnings. Exposure associations for cancer were strongest for premenopausal, parous women. Exposure was not associated with cancer among male farmers or children. CONCLUSIONS: Climatic conditions favoring fungal growth in grain were associated with hormone-dependent adverse outcomes among female farmers; the results are consistent with hormonal effects of inhaled mycotoxins during pregnancy.

Abortion, Spontaneous↗
PubMed2000

Maternal reproductive history: a registry based comparison of previous pregnancy data derived from maternal recall and data obtained during the actual pregnancy.

OBJECTIVE: To compare the quality of data on previous pregnancies, based on maternal recall, to that of actual data in previous birth records, and to quantify to which extent recall based data bias results in epidemiologic studies on adverse reproductive outcomes. METHODS: Through linkage between agricultural censuses and the Medical Birth Registry, we identified 87,113 Norwegian female farmers with 174,764 single births in 1967-1991, including 533 late abortions (16-27 weeks). Data were linked into sibship records. In routine birth records, mothers provide information at each birth on previous fetal loss. Thus, we had information both based on recall and on the actual record. RESULTS: Among all mothers with a loss documented in previous records, 73.5% had a recall of previous loss (sensitivity), while 74.3% of all mothers reporting a previous loss also had a loss in previous sibship records (positive predictive value). Late abortion after a previous loss according to the sibship record was more frequent than after a previous loss based on maternal recall (18.3 vs. 10.8 per 1,000). There was a particular lack of recall for previous losses of short gestational age or when the current birth was a late abortion; both conditions tended to deflate the association between a previous and a current adverse outcome. Grain farming was associated with late abortion in mothers with previous loss in sibship records (odds ratio, 2.6) but not among mothers without previous loss (odds ratio, 1.0). When information on previous loss was based on maternal recall the odds ratios were 1.4 and 1.3, respectively. CONCLUSIONS: Consecutive sibship records give more valid information than data derived from maternal recall.

Abortion, Spontaneous↗
PubMed1999

Properties of thiol-specific anti-oxidant protein or calpromotin in solution.

We have isolated calpromotin, a protein reported abundant in human red cells and shown to be of significance for KCl transport. We show that calpromotin is identical to a radical scavenger protein, thiol-specific antioxidant protein (TSA). Calpromotin is known to exist partially as a large complex of identical subunits and partially as dimers probably held together by disulfide bridges. The stability of the high-molecular-weight form was studied by variations of pH and urea concentration. It is shown that the equilibrium between the large complex and the dimeric subunit is governed by the dissociation of a group with a pK value of about 7.5. Dissociation of the complex was also complete at 2.5 M urea, where no unfolding of the peptide chains was detectable.

Amino Acid Sequence↗