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Biomedical subjects

T Christensen

Publications and source records attributed to T Christensen.

At least 55 records · Page 3Linked to original sources
PubMed1999

A distinct difference in clinical expression of two siblings with Aicardi-Goutières syndrome.

Two sibs with an encephalopathy, including intracerebral calcification and a white matter disease, are reported. In the younger sister, the cerebrospinal fluid showed chronic pleocytosis and clinically she strictly fits to the diagnosis of Aicardi-Goutières syndrome. Both sisters were affected by a spastic tetraplegia, truncal hypotonia and dystonic posturing, but the clinical course and the neuroradiological findings were milder in the older sister and she showed no cerebrospinal fluid pleocytosis. The present cases and recent reports of intrafamilial variability of Aicardi-Goutières syndrome may raise interesting aspects as to the limits and criteria of this syndrome.

Brain↗
PubMed1999

Effect of intravenous bilirubin infusion on biliary phospholipid secretion, hepatic P-glycoprotein expression, and biliary cytotoxicity in pigs.

BACKGROUND: Infusion of large intravenous bilirubin loads in bile acid-depleted pigs reduces P-glycoprotein-dependent biliary phospholipid secretion and increases the cytotoxicity of bile. The reasons for the diminution of biliary phospholipid secretion and the increase in biliary cytotoxicity are not known. This study was undertaken to determine whether the bilirubin-induced lowering of biliary phospholipid secretion is associated with alterations in hepatic P-glycoprotein (P-gp) expression and to determine why bilirubin infusions increase biliary cytotoxicity. METHODS: Hepatic bile was collected from bile acid-depleted pigs before and during intravenous bilirubin infusion. Hepatic P-gp expression was measured with protein blot analysis, using the P-gp-specific antibody C219. Biliary cytotoxicity was assayed against erythrocytes. The biliary phospholipid fatty acid profile was determined by means of gas chromatography. RESULTS: Bilirubin infusions lowered biliary phospholipid secretion by 69% without changing hepatic P-gp expression, suggesting that bilirubin infusions have an inhibitory effect on hepatic P-gp activity. Bilirubin infusions did not cause P-gp losses into bile. An unequivocal, proportional relationship (r2 = 0.80) pertained between cytotoxicity and the bile acid to phospholipid ratio in bile secreted before and during bilirubin infusion and in phosphatidylcholine-supplemented bile. Unconjugated bilirubin in bile did not contribute to biliary cytotoxicity. Biliary phospholipids were always phosphatidylcholine >> phosphatidylethanolamine, mainly of C16:0, 18:2 and C16:0, 18:1 fatty acid configuration. CONCLUSIONS: Intravenous bilirubin loads reduce biliary phospholipid secretion without changing hepatic P-gp expression. Bilirubin infusions increase biliary cytotoxicity by augmenting the biliary bile acid to phospholipid ratio.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed1999

Double-tracer autoradiographic study of protein synthesis and glucose consumption in rats with focal cerebral ischemia.

A double-tracer autoradiographic method for simultaneous measurement of regional glucose utilization (rCMRglc) and regional protein synthesis (PS) in consecutive brain sections is described and applied to study the metabolism of the ischemic penumbra 2 h after occlusion of the middle cerebral artery (MCAO) in rats. In halothane anesthesia, the left middle cerebral artery was permanently occluded. Two hours after MCAO an i.v. bolus injection of 14C-deoxyglucose and 3H-leucine was given and circulated for 45 min. Two sets of brain sections were processed for quantitative autoradiography. Neighboring brain sections exposed an X-ray film (3H-insensitive), and a 3H-sensitive for determination of rCMRglc and PS, respectively. Sections for PS determination were washed in trichloroacetic acid (TCA) prior to film exposure in order to remove 14C-deoxyglucose and unincorporated 3H-leucine. Regional rates of PS and glucose utilization were measured by densitometric image analysis. Normal rates of metabolism were defined as mean +/- 2 SD of values in the non-ischemic cortex. The volumes of ischemic cortex displaying normal rates of PS and glucose utilization, respectively, were measured. The cortical volume with normal PS was significantly less than that of normal rCMRglc: 142 (127-147) mm3 vs. 203 (184-206) mm3. Treatment with the glutamate antagonists MK-801 (1 mg kg-1) and NBQX (30 mg kg-1 x 2) did not significantly change this, although MK-801 tended to reduce the size of the metabolic penumbra calculated as the difference between ischemic cortex with reduced PS and ischemic cortex with reduced rCMRglc.

Animals↗
PubMed1999

The Arabidopsis FILAMENTOUS FLOWER gene is required for flower formation.

A screen for mutations affecting flower formation was carried out and several filamentous flower (fil) alleles were identified. In fil mutants, floral primordia occasionally give rise to pedicels lacking flowers at their ends. This defect is dramatically enhanced in fil rev double mutants, in which every floral primordium produces a flowerless pedicel. These data suggest that the FIL and REV genes are required for an early step of flower formation, possibly for the establishment of a flower-forming domain within the floral primordium. The FIL gene is also required for establishment of floral meristem identity and for flower development. During flower development, the FIL gene is required for floral organ formation in terms of the correct numbers and positions; correct spatial activity of the AGAMOUS, APETALA3, PISTILLATA and SUPERMAN genes; and floral organ development.

AGAMOUS Protein, Arabidopsis↗
PubMed1999

Another death due to ingestion of Nicotiana glauca.

Deaths attributed to ingestion of Nicotiana glauca are extremely rare. We report here a case where a 43-year-old man was found dead after apparently drinking a water extract of Nicotiana glauca. The primary alkaloid in the plant is anabasine. Toxicological analysis by capillary gas chromatography showed the deceased had a blood anabasine concentration of 2.2 mg/L. Clinically, the features of poisoning are nicotine-like and if death occurs it results from respiratory paralysis. The case further supports the view that, in the human, anabasine is considerably more toxic than nicotine.

Adult↗
PubMed1998

Thermodynamics of binding of heterobidentate ligands consisting of spacer-connected acarbose and beta-cyclodextrin to the catalytic and starch-binding domains of glucoamylase from Aspergillus niger shows that the catalytic and starch-binding sites are in close proximity in space.

The binding to glucoamylase 1 from Aspergillus niger (GA1) of a series of four synthetic heterobidentate ligands of acarbose and beta-cyclodextrin (beta-CD) linked together has been studied by isothermal titration calorimetry. GA1 consists of a catalytic and a starch-binding domain (SBD) connected by a heavily O-glycosylated linker region. Acarbose is a strong inhibitor of glucoamylase and binds exclusively in the catalytic site, while the cyclic starch mimic beta-CD binds exclusively to the two sites of SBD. No spacer or spacer arms of 14, 36, and 73 A in their extended conformations connect acarbose and beta-CD. These compounds were used as probes for bidentate ligand binding to both domains in order to estimate the distance between the catalytic site and the SBD binding site in solution. DeltaH of binding of the four heterobidentate ligands is within experimental uncertainty equal to the sum of DeltaH of binding of free acarbose and beta-CD, indicating ligand binding to both domains. However, the binding constants are 4-5 orders of magnitude smaller than for the binding of acarbose (K approximately 10(12) M-1), increasing with spacer length from 2 x 10(7) M-1 for no spacer to 1 x 10(8) M-1 for the 73 A spacer. Subsequent titrations with beta-CD of the glucoamylase-bidentate ligand complexes revealed that only one of the two binding sites of SBD was vacant. Further titrations with acarbose to these mixtures showed complete displacement of the acarbose moiety of the bidentate ligands from the catalytic sites. These experiments show that the bidentate ligands bind to both the catalytic domain and SBD. The weakening of the bidentate ligand binding compared to acarbose is a purely entropic effect point to steric hindrance between SBD and the beta-CD moiety. To test this, titrations of glucoamylase 2, a form containing the catalytic domain and the linker region but lacking SBD, with the bidentate ligands were carried out. The results were indistinguishable from the binding of free acarbose. Thus, the reduced affinity of the bidentate ligands observed with GA1 stems from interactions due to SBD. The results show that the catalytic and starch-binding sites are in close proximity in solution and thus indicate considerable flexibility of the linker region.

Acarbose↗
PubMed1998

[Effects of sunscreening agents and reactions with ultraviolet radiation].

The use of sunscreens is extensive. During the last few years there have been indications that UV radiation causes breakdown of the sunlight absorbing filters in the sunscreens, i.e. the sunscreens are not photostable. We describe briefly UV propagation in skin, the chemical and physical properties of sunscreens, and how these may react during UV irradiation. We have studied the stability of several sunscreens in vitro. The stability tests were performed by applying a thin film of the sunscreen preparation to the wall of a quartz window, irradiating it with a sun simulator, and measuring the absorbance with spectrophotometry before and during irradiation. The sunscreen agent studied most thoroughly was the UVB filter octyl methoxy cinnamate, but other UVA and UVB filters and some commercial products were also tested. Considerable breakdown of most filters was observed after doses of irradiation equivalent to moderate sun exposure. It can be questioned whether the breakdown products of sunscreens also possess other physical or biological properties. General practitioners should be able to advise their patients on sun protection and the proper use of sunscreens, considering the extensive use of sunscreens and the fact that sunbathing may be a health hazard.

Cinnamates↗
PubMed1998

[Quantification of iron level in the liver by MR imaging in patients treated for transfusion siderosis].

Patients with chronic blood transfusion requirements develop progressive iron overload, which is followed by organ damage in severe cases. Chemical determination of the liver iron concentration in liver biopsies is still regarded as the gold-standard for a precise determination of the degree of iron overload, but cannot be performed just for determination of the liver iron concentration alone due to the possible harmful side effects due to percutaneous liver biopsies. We have therefore validated a non-invasive MRI-technique based on the calculation of the ratio between the signal intensity (SIR) of the liver and skeletal muscle. We found a good correlation between the chemically determined liver iron concentration and the corresponding SIR-values (r2 = 0.98, p < 0.0001) low inter-day variation (2.9 +/- 2.7 mumol Fe/g) indicating that our non-invasive method is applicable for the determination of the liver iron concentration and may also be used for monitoring the efficacy of iron chelation by repeated measurements.

Biopsy↗
PubMed1998

Microglia and macrophages are major sources of locally produced transforming growth factor-beta1 after transient middle cerebral artery occlusion in rats.

The potentially neurotrophic cytokine transforming growth factor-beta1 (TGF-beta1) is locally expressed following human stroke and experimental ischemic lesions, but the cellular source(s) and profile of induction have so far not been established in experimental focal cerebral ischemia. This study presents the time course and a cellular localization of TGF-beta1 mRNA, visualized by in situ hybridization combined with immunohistochemical staining for microglia, macrophages, or astrocytes, on brain sections from adult spontaneously hypertensive rats subjected to transient proximal occlusion of their middle cerebral artery. Six hours after ischemia, an early and transient neuronal and microglial expression of TGF-beta1 mRNA was observed in the extraischemic cingulate and frontal cortices. Both early and protracted expression of TGF-beta1 mRNA in the caudate-putamen and neocortical infarcts and in the caudate-putamen penumbra colocalized with OX42/ED1-immunoreactive microglia and macrophages, whereas TGF-beta1 mRNA in the neocortical penumbra colocalized with OX42/ED1-immunoreactive cells of a microglial morphology. No astrocytes were double-labeled. The number of TGF-beta1 mRNA-expressing microglia and macrophages increased strongly during the first week. Thereafter, TGF-beta1 mRNA became increasingly restricted to the neocortical penumbra (3 weeks), and after 3 months it was confined to activated microglia in the anterior commissure. Our data establish activated microglia and macrophages as the major source of TGF-beta1 mRNA following experimental focal cerebral ischemia. Consequently, TGF-beta1-mediated functions may be exerted by microglia both in the early degenerative phase, and later in combination with blood-borne macrophages, in the remodeling and healing phase after focal cerebral ischemia.

Animals↗
PubMed1998

Isolation of a retrovirus from multiple sclerosis patients in self-generated Iodixanol gradients.

The use of Iodixanol, a relatively new iodinated gradient medium, is described for isolation of a retrovirus, which was harvested from the supernatant of lymphoid cell lines originating from patients with multiple sclerosis (MS). The virus is produced in low amounts and has been shown to be fragile, as manifested in a loss of surface glycoproteins when purified in other gradient media. The gradient fractions were analysed after centrifugation in Iodixanol by incorporation of 3H-UTP, reverse transcriptase (RT) assays and electron microscopy (EM) and it was found that Iodixanol does not cause the degree of damage to the particles observed previously. These more favourable conditions are probably due to low viscosity and almost iso-osmotic conditions even in high concentrations. Furthermore, these advantages go together with higher reproducibility in self-forming gradients, easier handling and shorter centrifugation time. Iodixanol can also be used for preparation of HTLV-1.

Cell Line↗
PubMed1998

The significance of Epstein-Barr virus seropositivity in multiple sclerosis patients?

The objective of this study was to evaluate and investigate the significance of the previously found 100% seropositivity toward Epstein-Barr virus (EBV) found in multiple sclerosis (MS) patients in contrast to healthy controls. Using a commercially available ELISA-test (Biotest), which differentiates infections with EBV into previous infections, primary infections, reactivated infections and no previous infection, we found 137 of 138 MS patients and 124 of 138 healthy controls seropositive. A primary infection in 4 of the 124 EBV seropositive healthy controls in contrast to no primary infections in the MS EBV seropositive group was significant (P=0.049652, Fishers exact test). This may be suggestive of a lack of primary infections in MS patients, and thus strengthens the idea that MS patients are infected with EBV before development of MS. Further studies are in progress to analyse whether EBV infection is a prerequisite for the development of this disease.

Adult↗
PubMed1998

A single subtype of Epstein-Barr virus in members of multiple sclerosis clusters.

OBJECTIVES: Epidemiological studies strongly indicate an infectious involvement in multiple sclerosis (MS). Epstein-Barr virus (EBV), to which all multiple sclerosis patients are seropositive, is also interesting from an epidemiological point of view. We have reported a cluster of MS patients with 8 members from a small Danish community called Fjelsø. To further evaluate the role of EBV in MS we have investigated the distribution of EBV subtypes in cluster members and in control cohorts. MATERIALS AND METHODS: Blood mononuclear cells were isolated from cluster members, unrelated MS patients, healthy controls, including healthy schoolmates to the Fjelsø cluster patients and finally from persons with autoimmune diseases in order to investigate the number of 39 bp repeats in the EBNA 6-coding region in the EBV seropositive individuals. RESULTS: We observed a preponderance of the subtype with 3 39 bp repeats in the EBNA 6-coding region both in the MS patients and the healthy controls. In the Fjels cluster all 8 cluster members were harbouring this subtype, which is significantly different from the finding in healthy controls (n = 16), which include 8 schoolmates to the cluster members and 8 randomly selected healthy persons (Fischer's exact test P = 0.0047), and also compared to all non-clustered individuals studied (P = 0.017). CONCLUSION: Infection with the same subtype of EBV links together the 8 persons from the Fjelsø cluster who later developed MS. This finding adds to the possibility that development of MS is linked to infection with EBV.

Adult↗
PubMed1998

Role of the regulatory gene areA of Aspergillus oryzae in nitrogen metabolism.

The areA gene of Aspergillus oryzae was cloned by cross-hybridization with the Aspergillus nidulans areA gene and was found to encode an 866-amino-acid protein that is very similar to other fungal nitrogen regulatory proteins. The A. oryzae areA gene can complement A. nidulans areA loss-of-function mutations. Functional analyses indicated that the N-terminal region of the A. oryzae AreA protein was dispensable for function and revealed a probable acidic activation domain in the protein. C-terminal truncation of the protein resulted in derepression of several nitrogen-controlled activities in A. nidulans, while deletions extending into the conserved GATA type zinc finger region abolished the activator function. The A. oryzae areA gene was inactivated by replacement with the A. oryzae pyrG gene. Strains containing the resulting areA deletion grew as well as the wild-type strain on glutamine but were unable to grow vigorously on other nitrogen sources, including ammonium. While A. oryzae exhibited reduced growth on 10 mM ammonium, the results of growth tests indicated that areA mutants of both A. oryzae and A. nidulans were affected in utilization of low concentrations of ammonium. The levels of the major nitrogen assimilatory enzymes, NADP-linked glutamate dehydrogenase (EC 1.4.1.4) and glutamine synthetase (EC 6.3.1.2), were determined. In both A. oryzae and A. nidulans areA mutants, the NADP-glutamate dehydrogenase levels were reduced, whereas the glutamine synthetase levels were not affected. These results suggest that the AreA protein may play an important role in the regulation of nitrogen assimilation in addition to its previously established regulatory role in nitrogen catabolism.

Amino Acid Sequence↗
PubMed1997

Some details of the reaction mechanism of glucoamylase from Aspergillus niger--kinetic and structural studies on Trp52-->Phe and Trp317-->Phe mutants.

Presteady and steady-state kinetic results on the interactions of a wild-type, and the mutant glucoamylases Trp52-->Phe and Trp317-->Phe, from Aspergillus niger with maltose, maltotriose and maltotetraose have been obtained and analyzed. The results are compared with previous ones on the mutants, Trp120-->Phe and Glu180-->Gln, and with results obtained from structure energy minimization calculations based on known three-dimensional structural data. All results are in accordance with a three-step reaction model involving two steps in the substrate binding and a rate-determining catalytic step. Trp317 and Glu180 belong to different subsites, but are placed on the same flank of the active site (beta-flank). The Trp317-->Phe and the Glu180-->Gln mutants show almost identical kinetic results: weakening of the substrate binding, mainly caused by changes in the second reaction step, and practically no change of the catalytic rate. Structure energy minimization calculations show that the same loss of Arg305 and Glu180 hydrogen bonds to the substrate occurs in the Michaelis complexes of each of these mutants. These results indicate that important interactions of the active site may be better understood from a consideration of its flanks rather than of its subsites. The results further indicate differences in the substrate binding mode of maltose and of longer substrates. Trp52 and Trp120 each interact with the catalytic acid, Glu179, and are placed on the flank (alpha-flank) of the active site opposite to Trp317, Arg305 and Glu180. Also the Trp52-->Phe and Trp120-->Phe mutants show kinetic results similar to each other. The catalytic rates are strongly reduced and the substrates are bound more strongly, mainly as a result of the formation of a more stable complex in the second reaction step. All together, the substrate binding mechanism seems to involve an initial enzyme-substrate complex, in which the beta-flank plays a minor role, except for maltose binding; this is followed by a conformational change, in which hydrogen bonds to Arg305 and Glu180 of the beta-flank are established and the correct alignment on the alpha-flank of Glu179, the general acid catalyst, governed by its flexible interactions with Trp52 and Trp120, occurs.

Aspergillus niger↗
PubMed1997

Microglial and macrophage reactions mark progressive changes and define the penumbra in the rat neocortex and striatum after transient middle cerebral artery occlusion.

Transient middle cerebral artery occlusion in rats leads to infarction of the lateral part of the striatum and adjacent neocortex, with selective neuronal necrosis in the bordering penumbral zones. Administration of glutamate, cytokine, and leukocyte antagonists have rescued mainly neocortical neurons, indicating differences in the degenerative processes. The aim of this study was, therefore, to describe the microglial/macrophage activation and polymorphonuclear leukocyte recruitment patterns and to correlate these with the ischemia-induced degenerative processes. The analysis showed significant differences in the characteristics and timing of the microglial/macrophage responses between the caudate putamen and neocortical infarct zones, the infarct zones and their associated penumbral zones, as well as between the striatal and the neocortical penumbral zone. Infiltrations with polymorphonuclear leukocytes into the infarct zones were limited and shortlasting and confined to the acutely degenerating striatum and piriform cortex. A delayed, massive infiltration with lipid phagocytes into the caudate putamen infarct markedly contrasted an early recruitment and activation of microglia/macrophages in the adjacent penumbra. Within the neocortex, a later onset of degeneration along the insular-parietal axis was marked by neuronal expression of heat shock protein and a progressive microglial activation with induction of the full repertoire of microglial activation markers, including a widespread microglial major histocompatibility complex (MHC) class II antigen expression. We interpret the present results as delineating two differentially progressing penumbral zones, which are likely to reflect differences in the underlying degenerative processes. Differences in the microglial/macrophage activation pattern attract special attention, as these cells may constitute specific targets for therapeutic intervention.

Animals↗