Biomedical subjects

K Steiner

Publications and source records attributed to K Steiner.

At least 37 records · Page 2Linked to original sources

PubMed1996

In vivo evaluation of epidermal growth factor (EGF) receptor density on human tumor xenografts using radiolabeled EGF and anti-(EGF receptor) mAb 425.

In order to study the potential of non-invasive scintigraphic evaluation of the epidermal growth factor (EGF) receptor status in vivo, the biokinetics and tumor binding of 125I-EGF and anti-(EGF receptor) mAb 425 were investigated in nude mice bearing human tumor xenografts with different EGF-receptor densities as determined by a radioreceptor assay. The results demonstrated a tumor uptake for both substances depending on the receptor level. The EGF receptor status, however, was reflected slightly better by the binding of EGF to tumor tissue compared to the mAb. The rapid blood clearance of EGF with a plasma half-life of less than 1 min led to a tumor-to-blood ratio of approximately 3 within 6 h after injection in tumors with a high receptor expression. A similar ratio for the mAb was not obtained before day 6 after injection. The absolute concentration of EGF, however, was low compared to the mAb. Therefore, it can be concluded that the EGF receptor status as a target for (radio)immunotherapy can be evaluated in vivo with EGF labeled with a short-life positron-emitting radionuclide or with monoclonal antibodies to the EGF receptor or their fragments.

Animals↗

PubMed1996

Functional analysis of a relA/spoT gene homolog from Streptococcus equisimilis.

We examined the functional attributes of a gene encountered by sequencing the streptokinase gene region of Streptococcus equisimilis H46A. This gene, originally called rel, here termed relS. equisimilis, is homologous to two related Escherichia coli genes, spoT and relA, that function in the metabolism of guanosine 5',3'-polyphosphates [(p)ppGpp]. Studies with a variety of E. coli mutants led us to deduce that the highly expressed rel S. equisimilis gene encodes a strong (p)ppGppase and a weaker (p)ppGpp synthetic activity, much like the spoT gene, with a net effect favoring degradation and no complementation of the absence of the relA gene. We verified that the Rel S. equisimilis protein, purified from an E. coli relA spoT double mutant, catalyzed a manganese-activated (p)ppGpp 3'-pyrophosphohydrolase reaction similar to that of the SpoT enzyme. This Rel S. equisimilis protein preparation also weakly catalyzed a ribosome-independent synthesis of (p)ppGpp by an ATP to GTP 3'-pyrophosphoryltransferase reaction when degradation was restricted by the absence of manganese ions. An analogous activity has been deduced for the SpoT protein from genetic evidence. In addition, the Rel S. equisimilis protein displays immunological cross-reactivity with polyclonal antibodies specific for SpoT but not for RelA. Despite assignment of rel S. equisimilis gene function in E. coli as being similar to that of the native spoT gene, disruptions of rel S. equisimilis in S. equisimilis abolish the parental (p)ppGpp accumulation response to amino acid starvation in a manner expected for relA mutants rather than spoT mutants.

Cross Reactions↗

PubMed1995

Transcription termination of the streptokinase gene of Streptococcus equisimilis H46A: bidirectionality and efficiency in homologous and heterologous hosts.

In Streptococcus equisimilis H46A, a hypersymmetrical transcription terminator with bidirectional activity was localized between the translational termination codons of the streptokinase gene, skc, and the rel-orf1 genes. These two transcription units are oriented towards each other, and under normal conditions the skc mRNA level exceeds that of the rel-orf1 genes by a factor of at least 1000. Reporter vectors based on the promoterless cat gene were constructed by transcriptional fusion of skc to cat, such that the region between the two genes contained the terminator in skc orientation or in rel-orf1 orientation. Additionally, skc and cat were fused directly, with deletion of the terminator. The reporter vectors were designed to be capable of being studied either as multicopy plasmids in Escherichia coli or in single copy following integration, via skc, into the S. equisimilis chromosome. Chloramphenicol acetyl transferase (CAT) activity assays in conjunction with determination of chloramphenicol resistance levels and Northern hybridization analysis showed that the terminator is active in either host and orientation. However, termination efficiency was host dependent, with high terminator strength being observed in the homologous streptococcal background and appreciable readthrough occurring in E. coli. The extent of transcriptional readthrough was dependent upon terminator orientation, with termination being more efficient in rel-orf1 polarity. The results suggest that, in S. equisimilis, transcription of both skc and rel-orf1 is efficiently terminated by a common signal, and that these genes are largely protected from convergent transcription, which otherwise would seem to be particularly detrimental to the weakly expressed rel-orf1 genes.

Base Sequence↗

PubMed1995

Conservation of the organization of the streptokinase gene region among pathogenic streptococci.

Using ten gene-specific probes from the cloned and sequenced streptokinase gene (skc) region (8,931 bp) of Streptococcus equisimilis H46A, a human serogroup C strain, the conservation of these genes and their linkage relationships were studied by Southern hybridization in pathogenic streptococci differing taxonomically, serologically, in regard to their host range, and in the class of plasminogen activator produced. The results indicate that in S. pyogenes (strains A374, NZ131 and SF130/13) and a human group G strain (G19,908) both gene content and gene order as determined for H46A (dexB-abc-lrp-skc-orfl-rel) are preserved. The same is true of an equine S. equisimilis isolate (87-542-W), the streptokinase gene of which has been shown to hybridize detectably with skc, a result at variance with that obtained previously by others. In contrast, the chromosomal DNA of three S. uberis strains (0140J, C198, C216) of bovine origin, two of which produced a plasminogen activator different from streptokinase, hybridized only with dexB-, abc- and rel-specific probes, and the homologues of these genes appeared to lie close to each other. The maintenance of the organization of the streptokinase gene region in strains differing in overall chromosomal character suggests that this gene arrangement is of selective advantage.

Bacterial Proteins↗

PubMed1995

Pharmacokinetics of reshaped MAb 425 in three animal species.

The murine monoclonal antibody (MAb) 425 (mMAb 425) directed against the human EGFR (epidermal growth factor receptor) was reshaped (rMAb 425) in order to improve its therapeutical potential in humans. The pharmacokinetic properties of [125I]-mMAb and [125I]-rMAb 425 were compared in three animal species. Whereas the clearance curves of both antibodies decreased biphasically in rats and nude mice bearing human mammary carcinoma, a monophasic decline was observed in Cynomolgus monkeys. Plasma elimination half-lives of murine and reshaped MAb 425 were similar, short in the monkey (26 h for mMAb 425 and 31 h for rMAb 425) and long in rats (240 h for mMAb 425 and 225 h for rMAb 425). In xenografted nude mice however, the half-life of mMAb 425 (203 h) was about twice as long as that of rMAb 425 (124 h). The half-lives of intact rMAb 425 in the three species obtained by ELISA differed at most by a factor of two from those obtained by radioactivity measurements. Biodistribution studies of [125I]-rMAb 425 revealed a tumor/blood ratio of 1.2 on d 1 and 5.1 on d 18, respectively. Fifty-four and thirty-eight percent of the radioactive dose were excreted with urine in nude mice (within 12 d) and rats (within 11 d), respectively. Specific localization of [125I]-rMAb 425 in human mammary carcinoma xenografted to nude mice was demonstrated.

Animals↗

PubMed1995

Distribution of humanized MAb 425 (EMD 62,000) in rats and specific localization in tumor-bearing nude mice.

The murine MAb 425 (IgG2a) directed against human epidermal growth factor receptor is considered to have therapeutic potential in glioma patients. In order to circumvent immune response in clinical use, the MAb 425 was humanized by CDR-grafting (IgG1). We have studied the distribution of reshaped MAb 425 (EMD 62,000) in Wistar rats and the specific localization in female nude mice bearing human mamma carcinoma xenografts. The 125I-labelled MAb 425 was administered intravenously in a single dose (1 mg/kg) using unspecific human IgG1 antibody as control. The biodistribution was investigated both quantitatively and by whole-body autoradiography. The autoradiographs showed a selective uptake of radioactivity by the tumour tissue. 15 days after administration, radioactivity was bound exclusively to the tumour. Similar results were obtained with the murine monoclonal antibody. Quantitative studies exhibited a tumour-blood ratio of about 5. The study demonstrates that the humanized MAb 425 is selectively localized in human mamma carcinoma xenografted to athymic mice.

Animals↗

PubMed1995

The streptokinase gene: allelic variation, genomic environment and expression control.

The genes for streptokinase, the most important prokaryotic plasmingoen activator, exhibit allelic variation predominantly due to the polymorphism of an internal 220-base pair fragment that divides the phylogenetic tree of their products into two primary branches. Current molecular genetic research seeks functional correlates of the allelic variation, aims at analyzing the genomic environment of the streptokinase gene, skc, and focuses on understanding its expression. Of the six genes cloned and sequenced in the skc region of Streptococcus equisimilis H46A, skc is expressed most abundantly in a fashion that involves two overlapping core promoters and upstream sequences rich of AT tracts. Transcription of skc is terminated at a hypersymmetrical site that functions bidirectionally and prevents convergent transcription of the oppositely oriented skc and rel-orf1 genes whose mRNA abundance differs by a factor of at least three orders of magnitude.

Alleles↗

PubMed1993

Genetic organization of the streptokinase region of the Streptococcus equisimilis H46A chromosome.

The complete nucleotide sequences of four genes and one open reading frame (ORF1) adjacent to the streptokinase gene, skc, from Streptococcus equisimilis H46A were determined. These genes are encoded on the opposite DNA strand to skc and are arranged as follows: dexB-abc-lrp-skc-ORF1-rel. The dexB gene, coding for an alpha-glucosidase (M(r) 61,733), and abc, encoding an ABC transporter (M(r) 42,080), are similar to the dexB and msmK genes, respectively, from the multiple sugar metabolism operon of S. mutans. The lrp gene specifies a leucine-rich protein (M(r) 32,302) that has a leucine-zipper motif at its C-terminus. The function of the Lrp protein is not known but appeared to be detrimental when overexpressed in Escherichia coli. Although lrp appears not to be an essential gene, as judged by plasmid insertion mutagenesis, it is conserved in all streptococcal strains carrying a streptokinase gene. The rel gene showed significant homology to the E. coli relA and spoT genes involved in the stringent response to amino acid deprivation. Multiple alignment of the amino acid sequences of Rel (M(r) 83,913), RelA and SpoT revealed 59.4% homology of the primary structures. Northern hybridization analyses of the genes in the skc region showed skc to be transcribed most abundantly. In addition to transcripts for skc, monocistronic mRNAs were detected for all three genes divergently transcribed from skc. Although there was also some read-through transcription from lrp into abc, and from abc into dexB, the transcription pattern suggests a high degree of transcriptional and functional independence not only of skc but also abc and dexB. Prominent structural features in intergenic regions included a static DNA bending locus located upstream and a putative bidirectional transcription terminator downstream of skc.

Amino Acid Sequence↗

PubMed1992

Pharmacokinetics and first clinical experiences with an antihypertensive dopamine (DA2) agonist.

The pharmacokinetic properties and first clinical experiences with the antihypertensive dopamine (DA2) agonist, carmoxirole, are summarized. In man carmoxirole was rapidly absorbed. On oral administration the maximum plasma concentration was reached after 2-3 h. The drug was metabolized, mainly to an ester-type glucuronide, and was excreted (unchanged carmoxirole plus glucuronide) largely by the kidneys. The plasma half-life of the parent compound was 5.5 h. For the dose range tested (0.5 to 1.5 mg) the pharmacokinetics were linear. The drug was rapidly distributed in animals but only very small amounts penetrated the blood-brain barrier. Carmoxirole did not affect supine blood pressure in healthy subjects, but under the conditions of the Schellong's test some orthostatic reactions occurred with high doses. In patients the blood pressure was reduced for at least 8 h after single oral doses. On repeated administration for several weeks a relevant antihypertensive effect was still measurable 12 and 24 h after dose. The most frequently reported adverse events have been headache, dizziness, tiredness, nausea, and gastric disorders. These symptoms are considered to be mainly due to blood pressure reduction, as is frequently observed at the beginning of antihypertensive therapy. In patients the incidence of orthostatic reactions is appreciably lower than in healthy subjects, and in both change of position was sufficient to relieve the symptoms.

Administration, Oral↗

PubMed1990

The melanin binding of bisoprolol and its toxicological relevance.

Unexpectedly high accumulations of bisoprolol were detected in iris and ciliary body and in retina+choroid of beagles after 4 weeks of conjunctival and oral administration. This phenomenon gave reason to assume that these high concentrations in the pigmented structures of the eye might be related to melanin binding. According to literature a series of drugs, e.g. chloroquine, rifampicine, chlorpromazine, benzodiazepines, and also beta-adrenoceptor antagonists exhibit melanin-binding properties. By means of autoradiography it could be demonstrated in pigmented mice that after iv and po administration 14C-labelled bisoprolol was selectively bound to the melanin-containing parts of the eye, irrespective of the mode of administration. Since the melanin-bound radioactivity could be extracted from the eye of mice and was eliminated with a t1/2 of approx. 7 days, the melanin binding of bisoprolol is considered to be reversible. Other beta-blocking agents like timolol and befunolol used already for a long time in the therapy of glaucoma have been reported to bind specifically to the melanin of the eye, and show comparable long half-lives, similar to bisoprolol. Usually, autoradiographic studies on drug distribution are performed with albino animals. This leads to a lack of information on melanin binding and may result in misinterpretation concerning the retention of substances, especially in pigmented compartments of the eye. Therefore, in autoradiographic studies of new investigational drugs during preclinical development, one should use both pigmented and albino animals.

Adrenergic beta-Antagonists↗

PubMed1988

Risk factors for the development of chronic cyclosporine-nephrotoxicity.

Ninety CSA-treated kidney transplants recipients entered the study. The patients were allocated to three groups based on serum creatinine at 12 months and kidney biopsy findings: control group (serum creatinine less than 177 mumol/l), rejection group (verified by biopsy, serum creatinine greater than 177 mumol/l), nephrotoxicity group (verified by biopsy, serum creatinine greater than 177 mumol/l). Thirty variables were systematically evaluated. The following parameters had a predictive value for the development of chronic CSA-nephrotoxicity: number of CSA-induced episodes of acute deterioration of renal function, CSA trough level (day 0-30, day 31-90), number of unexplained episodes of acute deterioration of renal function, number of nephrotoxic drugs, number of rejection treatments, number of rejection episodes and primary poor renal function. The results indicate that all factors leading to acute renal failure, favor the development of CSA-nephrotoxicity.

Acute Kidney Injury↗

PubMed1986

Acute effects of desipramine and clomipramine on pituitary-adrenal axis in man.

Brain neurotransmitters play an essential role in central regulation of hypothalamic factors which stimulate or inhibit the secretion of pituitary hormones. Insight in this complex system might be obtained by analysing changes in pituitary and peripheral hormone secretion following the administration of neuroactive drugs which influence the action of neurotransmitters. Desipramine is well-known to inhibit presynaptic norepinephrine reuptake, clomipramine on the other hand interferes with the serotoninergic system. In 15 male volunteers, the effects of single-dose administration of each drug were studied in comparison to placebo. Basal concentrations of ACTH and cortisol, as well as the rise of both hormones following insulin-induced hypoglycemia, were studied. Basal cortisol values and the response to hypoglycemia were not affected by either pharmacon in this study. Slight differences could be seen in the ACTH responses, which were however not significant.

Adrenocorticotropic Hormone↗

PubMed1986

The mystery shopper: an anonymous review of your services.

Mystery shoppers can provide an unbiased report on the day-to-day functioning of hospital activities. For this study, six shoppers "used" various hospital services and reported their impressions through a questionnaire. The general findings may be applicable to many other well-run health care organizations.

Consumer Behavior↗

PubMed1984

Evidence for ACTH-unrelated mechanisms in the regulation of cortisol secretion in man.

In an attempt to elucidate the significance of ACTH independent mechanisms in the regulation of cortisol secretion in man, the dynamics of plasma ACTH and cortisol levels were studied in response to different stimuli. The cortisol response to small amounts of exogenous ACTH and to insulin induced hypoglycemia was preceded by an increase in ACTH levels appropriate to explain the increase in cortisol. In contrast, after administration of methamphetamine, there was an increase in cortisol levels in the absence of any changes in ACTH concentrations. Apparently, the methamphetamine induced cortisol secretion was not mediated by radioimmunoassayable ACTH. A diurnal rhythm was observed for the responses to hypoglycemia and to methamphetamine with larger cortisol responses in the evening as compared to the forenoon. These changes were not accompanied by parallel changes in the ACTH responses. From these differences, additional evidence is provided for the importance of ACTH independent mechanisms in the regulation of cortisol secretion.

Adrenal Cortex↗

PubMed1984

The metabolic effects of biosynthetic human proinsulin in individuals with type I diabetes.

To assess the significance of deficiency of circulating proinsulin in patients with type I diabetes mellitus, we studied the metabolic effects of biosynthetic human proinsulin in 24 patients. After withdrawing insulin, an infusion of proinsulin to physiological plasma levels did not prevent elevations of plasma glucose or beta-hydroxybutyrate. During steady state infusions of insulin and proinsulin, 13.7 times the steady state plasma level of proinsulin compared to insulin was required to maintain euglycemia. This finding indicates that proinsulin is approximately 7.3% as biologically active as insulin on a molar basis in maintaining glucose control. The MCRs of insulin and proinsulin during these steady state infusions were 12.5 +/- 2.2 (+/- SEM) and 2.62 +/- 0.33 ml/kg X min, respectively. After maintaining euglycemia overnight with an infusion of insulin or proinsulin and then acutely stopping these infusions, the rise in plasma glucose after proinsulin was delayed significantly compared to insulin, consistent with proinsulin's slower clearance. Further studies are necessary to determine whether biosynthetic human proinsulin has a specific role in the treatment of diabetes.

Blood Glucose↗

PubMed1983

[Computed tomography--basic principles and outlook for related procedures].

The computerized X-ray tomography uses for the information of the images besides a highly developed computer technology a special CT-algorithm, i.e. preprocessing of detected "projections", their "high-pass" convolution and back-projection. The diagnostic success of computerized X-ray tomography gave rise to the investigation of other carriers of information besides X-radiation for the production of cross-sectional pictures using CT reconstruction principles. Examples are: Emission-CT, Proton-CT, Nuclear Magnetic Resonance CT, Ultrasound-CT, Impedance-CT and Mikrowave-CT. This paper gives a review of such methods, their basis properties and an estimation of their capabilities for medical application. This discussion is opened by a summary of the basis CT principles.

Humans↗

PubMed1982

Sucralfate: pharmacokinetics, metabolism and selective binding to experimental gastric and duodenal ulcers in animals.

Pharmacokinetics, metabolism, and binding capability of a basic aluminium salt of sucrose octasulphate (sucralfate, Ulcogant) to ulcer lesions were investigated in Wistar rat, Beagle dog, Rhesus, and Cynomolgus monkey with 14C-labelled material. After i.v. injection in rats the 14C-radioactivity has a very short serum half-life of 1 h and is excreted almost completely by the kidneys. After oral administration only a very small portion of the dose is detectable in serum which is eliminated rapidly from the intravascular space. From the renal excretion data it is concluded that sucralfate is absorbed from the gastrointestinal tract of rat, Beagle dog, and Rhesus monkey only from 1% to 5% of the dose. The radioactive constituents in plasma, urine, and feces of rat and Cynomolgus monkey were analysed by HPLC. Both after i.v. and p.o. administration only unchanged substance could be detected. A possible binding of 14C-sucralfate to the ulcerated mucosa of stomach and duodenum was investigated in rats by histoautoradiography. The ulcers were induced by acetic acid. A selective accumulation of 14C-sucralfate in the area of the stomach ulcer could be demonstrated as long as 8 h after single p.o. administration. In the duodenum the autoradiographs showed a specific binding of 14C-sucralfate to the ulcerated mucosa at 1, 2, and 4 h after administration. Neither pretreatment with an H2-receptor antagonist nor simultaneous administration of an antacid influenced the binding of 14C-sucralfate. These results suggest that the mode of action of sucralfate is the formation of a protective layer which stops harmful agents like gastric juice and bile from further damaging the ulcerous lesions, thus ensuring an uninterrupted healing process. The very small extent of absorption and the rapid excretion from the organism minimize the risk of a systemic burden.

Aluminum↗

PubMed1976

[Pharmacokinetics of pramiverine in rats, dogs, and monkeys (author's transl)].

The pharmacokinetic properties of 4,4-diphenyl-N-isopropyl-cyclohexylamine-hydrochloride (pramiverine, Sistalgin) in Wistar rats, beagles, and rhesus monkeys are described. After i.v. injection of 14C-labelled pramiverine incorporation of radioactivity from the blood into organs and tissues is rapid. The radioactivity is eliminated from the blood with a half-life of 4-7 h in rats, 17-32 in dogs, and 8-26 h in rhesus monkeys. Unmetabolized pramiverine, in contrast, is eliminated much faster, the half-lives are 2 h in dogs and 3 h in rhesus monkeys. After oral administration maximum serum concentrations are reached after 4 h in rats and dogs and 2 h in rhesus monkeys. The drug undergoes a marked first-pass effect in the liver. In all species pramiverine is absorbed rapidly from the gastro-intestinal tract. Drug and/or metabolites are eliminated in rats and dogs predominantly with feces, in monkeys with urine, independent of the route of administration. During a 6 h interval, biliary elimination was found to be 50% after i.v. and 30% after oral administration. 90% of pramiverine present in the blood plasma is reversibly bound to proteins.

Administration, Oral↗