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Biomedical subjects

H Schmitz

Publications and source records attributed to H Schmitz.

At least 37 records · Page 2Linked to original sources
PubMed2001

Antibodies to Lassa virus Z protein and nucleoprotein co-occur in human sera from Lassa fever endemic regions.

It is not known whether the small 11-kDa Z protein of Lassa virus is immunogenic during human Lassa virus infection. To obtain evidence for the existence of an antibody response and to test the suitability of these antibodies for serosurveys, sera from Lassa fever endemic regions (Guinea and Nigeria, n = 75) were tested for co-reactivity to Z protein and nucleoprotein (NP). Sera from a non-endemic region (Uganda, n = 50) served as a specificity control. Z protein and NP were expressed in Escherichia coli, affinity-purified, and used as antigen in Western blot. Indirect immunofluorescence (IIF) with Lassa virus-infected cells was performed for comparison. Due to high unspecific reactivity of the African sera, Western blot testing was performed with a 1:1,000 serum dilution. Under these conditions, none of the control sera but 12% of the sera from endemic regions co-reacted with both Z protein and NP. Reactivity to Z protein was significantly associated with NP reactivity (P < 10(-6)). NP and Z protein-specific antibodies were co-detected in 33% of the IIF-positive sera and in 5% of the IIF-negative sera (P = 0.001). These data provide evidence for appearance of antibodies to Z protein and NP following Lassa virus infection. A recombinant blot for detection of both antibody specificities seems to be specific but less sensitive than IIF.

Antibodies, Viral↗
PubMed2001

Sensitivity threshold and response characteristics of infrared detection in the beetle Melanophila acuminata (Coleoptera: Buprestidae).

The minimum detection threshold of the infrared sensitive beetle, Melanophila acuminata, was measured with a helium-neon laser that emitted light at a wavelength of 3.39 microm. Extracellular recordings were taken both at the pit organ responsible for detection and at the interganglionic connectives in the thorax of the beetle. At the pit organ, generator and action potentials from single neurons were measured with a sharpened tungsten electrode. At the connectives that linked the fused second meso-/metathoracic and prothoracic ganglia, compound action potentials were measured with a tungsten hook electrode that encircled the connective. The latter recordings confirmed conveyance of infrared information through specific pathways to rostrally-situated sites in the nervous system of the beetle. The 50% probability irradiance threshold at which action potentials were elicited from the receptor and connectives occurred at 17.3 and 14.6 mW/cm(2), respectively. In addition to sensitivity threshold, several other characteristics of the response were quantified including dependence of generator potential latency, generator potential duration, spike frequency, and spike latency on irradiance, dependence of response strength (spike count) on exposure time, and flicker fusion frequency. The ability to detect infrared radiation is rare in nature, and these results provide valuable information necessary to understand this unique sensitivity.

Action Potentials↗
PubMed2001

Ultramicrostructure and microthermomechanics of biological IR detectors: materials properties from a biomimetic perspective.

Microstructural organization of the biological infrared (IR) receptors was studied to elucidate their materials properties useful for prospective biomimetic design of artificial IR sensors from organic/polymeric materials. The IR receptors in Melanophila acuminata beetles were studied with ultrahigh-resolution scanning probe microscopy (SPM) in a range of temperatures. By application of micromechanical mapping and thermal stage, we made attempts to reveal the micromechanical and thermomechanical properties of the cuticular apparatus of the IR sensillum. The main component of the cuticular apparatus is an internal endocuticular sphere with a diameter of about 15-20 microm. Highly ordered multilayered organization of the lamellated peripheral mantle of the sphere was confirmed and characterized. We observed that the interlayer spacing of this microstructure varied along the circumference and decreased to 300 nm in the vertex of the sphere. We demonstrated that the microlayered structure is composed of nanolayers with very different micromechanical properties and thermal behaviors. Thermal expansion of the outer mantle was observed, and the local thermal expansion coefficient under given preparation conditions was estimated to be below 1.5 x 10(-4) grad(-1).

Animals↗
PubMed2001

Loss of N-linked glycans in the V3-loop region of gp120 is correlated to an enhanced infectivity of HIV-1.

We describe mutants of human immunodeficiency virus type-1 (HIV-1) strain NL4-3, which are lacking the thirteenth, fifteenth, or seventeenth sites for N-linked glycosylation (g13, g15, g17) of the envelope protein gp120. All three sites are located within the hypervariable V3 loop region of gp120. Those mutants lacking carbohydrates g15 or combinations of g15/g17 showed markedly higher infectivity for GHOST cells (human osteosarcoma cells) expressing CXCR4 (GHOST-X4), compared to the fully glycosylated NL4-3 wild type virus. In addition, these mutants could also infect cells which exhibits low background expression of CXCR4, corresponding to <10% of that observed for GHOST-X4 cells. In addition to the enhanced infectivity observed, mutants lacking g15 and g17 showed increased resistance to inhibition by SDF-1, the natural ligand of CXCR4. Thus, loss of the oligosaccharides g15 and g17 in the V3 region of gp120 markedly influences CXCR4-specific infection.

Amino Acid Sequence↗
PubMed2001

Purification and characterization of West Nile virus nucleoside triphosphatase (NTPase)/helicase: evidence for dissociation of the NTPase and helicase activities of the enzyme.

The nucleoside triphosphatase (NTPase)/helicase associated with nonstructural protein 3 of West Nile (WN) virus was purified from cell culture medium harvested from virus-infected Vero cells. The purification procedure included sequential chromatography on Superdex-200 and Reactive Red 120 columns, followed by a concentration step on an Ultrogel hydroxyapatite column. The nature of the purified protein was confirmed by immunoblot analysis using a WN virus-positive antiserum, determination of its NH(2) terminus by microsequencing, and a binding assay with 5'-[(14)C]fluorosulfonylbenzoyladenosine. Under optimized reaction conditions the enzyme catalyzed the hydrolysis of ATP and the unwinding of the DNA duplex with k(cat) values of 133 and 5.5 x 10(-3) s(-1), respectively. Characterization of the NTPase activity of the WN virus enzyme revealed that optimum conditions with respect to the Mg(2+) requirement and the monovalent salt or polynucleotide response differed from those of other flavivirus NTPases. Initial kinetic studies demonstrated that the inhibition (or activation) of ATPase activity by ribavirin-5'-triphosphate is not directly related to changes in the helicase activity of the enzyme. Further analysis using guanine and O(6)-benzoylguanine derivatives revealed that the ATPase activity of WN virus NTPase/helicase may be modulated, i.e., increased or reduced, with no effect on the helicase activity of the enzyme. On the other hand the helicase activity could be modulated without changing the ATPase activity. Our observations show that the number of ATP hydrolysis events per unwinding cycle is not a constant value.

Acid Anhydride Hydrolases↗
PubMed2001

A double-blind trial of perindopril and nitrendipine in incipient diabetic nephropathy.

UNLABELLED: We conducted a randomised, double-blind multicentre trial to compare the efficacy of the inhibitor of the angiotensin-converting enzyme (ACE) perindopril (P) with nitrendipine (N) in incipient diabetic nephropathy. METHODS: Forty-six patients with insulin-treated diabetes mellitus and mild-to-moderate hypertension and stable microalbuminuria were examined. P 4 or 8 mg once daily was compared to N 20 or 40 mg once daily; an optional open combination treatment with indapamide 2.5 mg once daily was given when needed. Main outcome measures were urinary albumin excretion rate, creatinine clearance and isotopic clearance measurements after 12 months. RESULTS: Baseline characteristics (blood pressure, HbA1, renal function) were highly comparable between groups. No serious adverse events occurred during the study period. Blood pressure was controlled (<140/90 mmHg) in all patients except for one in each group who dropped out. At the end of the study, albumin excretion rate was stabilized in both groups (P: 72% of baseline, N: 108%, NS). There were no significant differences found in radiometric clearance measurements. Creatinine clearance rose in patients treated with P by 10.0 ml/min on average, while it decreased by 9.8 m/min under N treatment (group effect: p<0.05). CONCLUSIONS: In this head-to-head comparison, P and N were effective in stabilising most parameters of renal function in incipient diabetic nephropathy.

Adolescent↗
PubMed2001

Inhibition of the helicase activity of HCV NTPase/helicase by 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide-5 '-triphosphate (ribavirin-TP).

In the presented study the ribavirin-TP--an established inhibitor of the NTPase activity of the superfamily NTPase/helicases II--was investigated as an inhibitor of the unwinding activity of the hepatitis C virus (HCV) NTPase/helicase. The kinetics of the reaction revealed that ribavirin-TP reduces the turnover number of the helicase reaction by a mechanism that does not correspond to that of the inhibition of the NTPase activity. Our results suggest that derivatives of ribavirin-TP with enhanced stability towards hydrolytic attack may be effective inhibitors of the enzyme.

Acid Anhydride Hydrolases↗
PubMed2000

Enhanced replication contributes to enrichment of hepatitis B virus with a deletion in the core gene.

Accumulation in immunosuppressed patients of hepatitis B virus (HBV) with a deletion in the C gene is associated with severe liver disease. The aim of this study was to determine the phenotype of such genomes in vitro. Four C gene fragments with different types of deletions were inserted in the context of a wild-type genome and tested by transfection into HuH7 cells. The deletions did not influence mRNA and surface protein levels. Truncated C gene translation products were expressed only from variants with in-frame deletions, whereas full-length polymerase was expressed from all variants at a similar or higher level than in wild-type virus. None of the variants was competent for autonomous replication; however, they produced 2- to 4.5-fold more progeny DNA than wild-type HBV when sufficiently complemented with wild-type core protein. Similarly, when variant and wild-type DNA were cotransfected in different ratios, the variants produced 2- to 5-fold more progeny DNA relative to the wild-type; this enrichment required the expression of the viral polymerase in cis. The mechanism of enrichment depended on the percentage of variant in the transfected DNA mixture. When the transfected DNA contained a small percentage of variant, enhanced replication of the variant accompanied by no or little suppression of wild-type replication was seen. Accordingly, overall production of progeny virus was slightly increased. At a high percentage of variant DNA, replication of both variant and wild-type decreased, probably due to a shortage of wild-type core protein. In conclusion, emergence of C gene deletion variants in vivo may be due to enhanced replication mediated at the level of encapsidation or reverse transcription. If the variants constitute a small part of the ccc DNA, they can be fully trans-complemented by wild-type virus which may increase the overall virus production.

Cells, Cultured↗
PubMed2000

The ability of Rhodnius prolixus (Hemiptera; Reduviidae) to approach a thermal source solely by its infrared radiation.

The ability of the haematophagous bug Rhodnius prolixus to approach a pure IR source only by its long-wave infrared radiation (IR) was investigated. To exclude any heated air from reaching the bug a cooled IR-transmitting window was placed between the IR-source (a Peltierelement heated to 35 degrees C) and the bug. Starved bugs were tested under invisible short-wave IR illumination (lambda<1 µm) in order to exclude also any visual cues. The number of bugs approaching the IR-source was significantly increased compared to the controls in which the IR-source was turned off (chi(2)-test, P<0.01). Our results show that Rhodnius prolixus can use infrared stimuli to find a host.

Journal Article↗
PubMed2000

[The Marjolin's ulcer": a malignant and rarely complication after burn trauma of the upper extremity - a case report].

The,Marjolin's ulcer" is a malignant lesion which is developed especially at chronic wounds after burn trauma. The latency from primary trauma to the malignant transformation is about 30 years. The lesion is more aggressive than other squamous cell carcinomas. We report on the combined radiation and surgical therapy of an 65-year-old patient with this lesion on the right hand and regional lymph node metastases. The extensive tissue defect after wide excision was reconstructed with a reversal radial forearm flap.

Aged↗
PubMed2000

A new type of infrared organ in the Australian "fire-beetle" Merimna atrata (Coleoptera: Buprestidae).

The Australian buprestid beetle Merimna atrata (Coleoptera: Buprestidae) approaches forest fires because its larvae develop in freshly burnt wood. So far nothing is known about possible sensory systems enabling the beetles to detect fires and to cope with the thermal environment close to the flames. We found that M. atrata has two pairs of infrared (IR) organs on the ventrolateral sides of the abdomen. Each IR organ consists of a specialized IR-absorbing area which is innervated by one thermosensitive multipolar neuron. The primary dendritic branches ramify into more than 800 closely packed terminal endings which contain a large number of mitochondria. We called the special morphology of the dendritic region a terminal dendritic mass. The type of IR receptor found in M. atrata is unique in insects and can best be compared with the IR organs of boid snakes.

Abdomen↗
PubMed2000

Responses of the infrared sensilla of Melanophila acuminata (Coleoptera: Buprestidae) to monochromatic infrared stimulation.

The pit organs of the beetle Melanophila acuminata were stimulated with monochromatic infrared radiation using a continuous wave CO overtone infrared laser. Best sensitivity was in the wavelength range 2.8-3.5 micron. In this range a stimulus intensity of 14.7 mW cm(-2) was sufficient to generate single action potentials. At a wavelength of 5 microm receptor performance significantly decreased. An increase in stimulus intensity caused a decrease in response latency and an increase in the number of action potentials elicited. At a given wavelength (3.4 microm) the dynamic amplitude range of action potential responses covered 12 dB. At high stimulus intensities (94.2 mW cm(-2)) a stimulus duration of 4 ms was sufficient to generate one to two action potentials and a stimulus duration of 60 ms already caused response saturation (with up to nine action potentials). In a repetitive stimulus regime distinct receptor potentials were visible up to a frequency of 600 Hz.

Action Potentials↗
PubMed2000

Isolation and partial characterization of dengue virus type 2 and 4 strains from dengue fever and dengue haemorrhagic fever patients from Mindanao, Republic of the Philippines.

OBJECTIVE: Isolation of dengue virus from dengue fever and dengue haemorrhagic fever cases from Mindanao, Republic of the Philippines. METHODS: 12 patients with clinically suspected dengue fever (DF) or dengue haemorrhagic fever (DHF) presenting in four regional hospitals between August and September 1995 on Minadano were enrolled in the study. Dengue virus was isolated by inoculation of Vero/E6 or C6/36 cells with patient serum. IgM antibodies were measured using a commercial test system. Up to 454 bp of the capsid region and 240 bp of the E/NS1 gene junction of different viral isolates were sequenced and phylogenetically analyzed. RESULTS: Virus could be isolated from seven patients, five isolates were typed as dengue virus type 2 and two as dengue virus type 4 by immunostaining with monoclonal antibodies or by RT/PCR. Phylogenetic analysis confirmed a close relationship of the dengue virus type 2 isolates with viruses isolated in the Philippines in 1983 and 1988. CONCLUSION: As observed in studies from other parts of South East Asia, dengue virus type 2 was readily isolated from dengue haemorrhagic fever cases. Dengue virus type 2 and 4 circulate in Mindanao, Philippines, with dengue type 2 being responsible for most of our severe DF or DHF cases.

Child↗
PubMed2000

Epithelial barrier defects in HT-29/B6 colonic cell monolayers induced by tumor necrosis factor-alpha.

The barrier function of intestinal epithelia relies upon the continuity of the enterocyte monolayer and intact tight junctions. After incubation with tumor necrosis factor-alpha TNF-alpha, however, the number of strands that form the tight junctions decreases, and apoptosis is induced in intestinal epithelial cells. These morphological changes lead to a rise of transepithelial ion permeability, because the paracellular ion permeability increases and leaks associated with sites of apoptosis increase by number and magnitude. Thus apoptosis and degradation of tight junctions contribute to the increased permeability observed after exposure to TNF-alpha. These mechanisms explain clinical manifestations in the inflamed intestinal wall containing cytokine-secreting macrophages--for example, leak flux diarrhea and invasion of bacterial enterotoxins.

Apoptosis↗
PubMed2000

Enhanced expression of iNOS in inflamed colons of IL-2-deficient mice does not impair colonic epithelial barrier function.

On the basis of recently observed high levels of iNOS expression that correlated with intestinal inflammation in interleukin-2-deficient [IL-2(-/-)] mice, it was postulated that nitric oxide may damage colonic epithelial cells or impair intestinal epithelial barrier function. This damage may result in an increased permeability of the colonic epithelium leading to high antigenic exposure of the intestinal immune system, which may perpetuate chronic inflammation. Our data demonstrate that high expression of iNOS in IL-2(-/-) mice is correlated with the length/weight ratio (L/W ratio), a widely accepted marker for intestinal inflammation. However, no reduction of epithelial resistance was observed, as would be expected in case of a damaged, leaky epithelium. Our results suggest that enhanced formation of NO in IL-2(-/-) mice does not cause impairment of epithelial barrier function.

Animals↗
PubMed2000

Mechanisms of epithelial barrier impairment in HIV infection.

Diarrhea and malabsorption due to intestinal dysfunction are common symptoms in HIV infection. The pathophysiologic mechanisms of these alterations are often not known, and the role of HIV per se is still controversially discussed. We measured the epithelial transport and barrier function by means of a miniaturized Ussing chamber system in the duodenum of HIV-infected patients in different disease stages, determined by the CD4 cell count in the serum as well as symptoms in patients with and without diarrhea. We could show that diarrhea induced by HIV per se is caused by a leak flux mechanism due to impaired epithelial barrier function. Antisecretory therapy does not seem to be useful in these patients, because we did not find increased active ion secretion. Along the course of the HIV infection, the epithelial transport and barrier function varies with HIV disease stage (expressed by CD4 cell status). In addition, an in vitro model was studied to characterize the effect of HIV-infected human immune cells on the epithelial barrier function using the human colonic epithelial cell line HT-29/B6. HIV infection of human immune cells induced an increase in cytokine release--for example, TNF-alpha, IL-1 beta, IFN-alpha, and IFN-gamma--downregulating the epithelial barrier function of the human colonic epithelial cell line HT-29/B6. Taken together we postulate a specific stage-dependent cytokine pattern released from HIV-infected immune cells in the mucosa, which, corresponding to the HIV disease stage, is responsible for the variation in epithelial function.

Biopsy↗