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Biomedical subjects

I Schumacher

Publications and source records attributed to I Schumacher.

11 recordsLinked to original sources
PubMed1999

Butyrylcholinesterase formulated in liposomes.

Exogenous cholinesterases have the potential to take part in defence against organophosphate toxins, by acting as scavenger systems. Postulating that formulation in liposomes could enhance the toxin-scavenging potential of these enzymes, we have initiated studies of such formulations and are reporting here our first steps, exploring butyrylcholinesterase (BChE) in multilamellar liposomes composed of phosphatidylcholine. We started by developing an essential research tool: a multisample, sensitive and rapid enzyme-activity assay, based on the Ellman reaction, that could be performed directly on liposome-containing samples. Using an ELISA reader equipped to follow time-dependant absorbency changes, 10 min sufficed to assay 96 samples simultaneously. Next, several key properties of liposome-formulated BChE were explored and the major findings were: (i) the encapsulated enzyme was found to retain its activity. (ii) Enzyme activity was found to increase (at constant enzyme concentration) in the presence of the lipid, in a lipid-concentration-dependant manner. Through data analysis it was possible to attribute this effect to changes in k(cat). (iii) Good, reproducible, encapsulation efficiencies (for macromolecules) in the range of 30% were obtained at liposome concentrations of 100 mM lipid. (iv) Free BChE was completely susceptible to proteolysis under conditions mimicking enzymically-hostile biological environments, whereas > or = 60% of the liposome-formulated BChE was protected, found to be inaccessible to the proteolytic enzymes. (v) Short-term exposures of free and liposome-encapsulated BChE to the inhibitor paraoxon, generated significant losses in enzyme activity. Residual activities of both BChE formulations dropped considerably over the paraoxon concentration range of 0.02-0.11 microM, down to 3 and 11% for free and liposome-encapsulated enzyme respectively. These data are a clear indication that the encapsulated BChE was accessible to the inhibitor, indicating that such liposomal formulations have the potential to perform as the desired scavenger systems.

Butyrylcholinesterase↗
PubMed1997

Liposome-encapsulated ampicillin: physicochemical and antibacterial properties.

The objectives of this study were to develop high-performance liquid chromatography (HPLC) and antibacterial assays for ampicillin encapsulated in multilamellar liposomes (MLV) and investigate the physicochemical and antibacterial properties of ampicillin-liposome systems. The major findings were fourfold. First, ammonium acetate (0.575%) in methanol:water (450:550; v/v), adjusted to pH 7.2, was suitable as the mobile phase for the HPLC determinations of ampicillin in both aqueous and liposomal systems. This mobile phase also provided (alone or with additional methanol) complete dissolution of liposomal assay samples in a precolumn treatment that made all of the encapsulated drug available for chromatography. Multiple samples were assayed without any technical limitations. Second, the growth-inhibition antibacterial assay developed, which used the USP test organism Micrococcus Luteus and paper disks, was quantitative for both free and liposome-encapsulated ampicillin. Third, the physicochemical properties of encapsulated ampicillin include encapsulation efficiencies of 10 to 50% for liposome concentrations in the range 10-200 mM (lipid), and a single rate constant to sufficiently and quantitatively describe the diffusion of encapsulated ampicillin, with half-lives in the range of 40 h. Fourth, the biological properties include the first direct evidence that encapsulated ampicillin retains full biological activity; that is, liposome-encapsulated ampicillin was active against extracellular bacterial colonies of Micrococcus luteus. Furthermore, encapsulation enhanced ampicillin stability. For example, free ampicillin in an aqueous solution that was stored for 5 weeks at 4 degrees C lost 50% of its initial activity, whereas liposome-encapsulated ampicillin (freed from unencapsulated drug) stored under the same conditions lost only 17% of its initial activity. The findings of this study, provide strong support for ampicillin-liposome formulations as valid dosage forms for this drug that are worthy of further experimental evaluations.

Ampicillin↗
PubMed1988

[40 years biliary surgery at the surgical clinic of the Charité].

Evaluation of 4,374 bile operations performed between 1945 and 1984 revealed drop in lethality from 4.0 to 0.8 per cent. The average age distribution of patients who had undergone surgery from 1945 to 1954 was identical with that for the period between 1975 and 1984. Case histories were probably shortened owing to earlier diagnosis. The rate of choledochotomy dropped from 11.5 per cent (1945 to 1954) to 7.9 per cent (1975 to 1984). The rates of choledochotomy and surgical papillotomy declined, ever since endoscopic papillotomy had been introduced more than ten years ago. Endoscopic lithotripsy and shock-wave lithotripsy are new approaches to cholelithotherapy.

Adolescent↗
PubMed1986

Enolase isoenzymes as tumour markers.

alpha- and gamma-enolase isoenzyme substance concentrations were measured in serum and plasma from healthy subjects and from 174 patients with different solid tumours. While alpha-enolase was found to be increased in the plasma of patients with tumours of quite different origin, gamma-enolase apparently reflected malignancies of the neuroendocrine system. Before the beginning of the cytotoxic therapy gamma-enolase was increased above the upper limit of the reference range (10 micrograms/l) in 27/27 patients (100%) suffering from small cell lung cancer. Most patients with squamous cell carcinoma of the lung or with prostatic cancer exhibited normal gamma-enolase, while both tumour types produced high plasma substance concentrations of the alpha-isoenzymes of enolase.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1981

[Plasma level of etidocaine within the first two hours after axillary plexus block in healthy adults and patients with renal insufficiency (author's transl)].

The plasma level of etidocaine was studied within the first two hours of axillary block in 7 patients with renal insufficiency and 7 healthy adults. After 15-20 min the maximum of plasma concentration was found in the group with renal failure and after 30-45 min in the healthy adults. 30 min after the block the plasma level was 1,26 +/- 0,62 mug/ml in the ill patients and only 0,73 +/- 0,31 in the normal group. Using a mathematical model the ratio of permeation into the blood is significantly higher in the group with renal failure than in the healthy adults. The main reason for these results seems to be the acidosis, which is often combined with renal insufficiency. The meaning of these results for regional anaesthesia in patients like these is discussed.

Acetanilides↗