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H Sinn

Publications and source records attributed to H Sinn.

At least 19 recordsLinked to original sources
PubMed1992

Differentiation of binding sites on reconstituted hepatic scavenger receptors using oxidized low-density lipoprotein.

Reduced hepatic membrane receptors for acetylated low-density lipoprotein (acetyl-LDL) and maleylated BSA (Mal-BSA) with apparent molecular masses of 35 kDa, 85 kDa and 15 kDa have been extracted from rat liver and separated by affinity chromatography as described by us previously [Ottnad, Via, Sinn, Freidrich, Ziegler & Dresel (1990) Biochem. J. 265, 689-698]. Binding of these three reduced scavenger receptors to oxidatively modified LDL has been now examined. Competition studies with receptor-phosphatidylcholine complexes and 131I-acetyl-LDL and 131I-Mal-BSA as ligands were conducted. Mal-BSA, acetyl-LDL and fully oxidized LDL were used as competitors, and differentiated in the three receptors three types of binding site: a class I binding site for acetyl-LDL, Mal-BSA and fully oxidized LDL; a class II binding site recognizing only 131I-Mal-BSA and class III binding sites recognizing 131I-Mal-BSA and fully oxidized LDL. The results of competition studies with mildly oxidized LDL and polyadenylic acid demonstrated that the binding sites might be even more heterogenous. Thus there is evidence that the reconstituted receptors either have several binding sites for each of the various ligands or are functionally different, despite the fact that they do not differ in their apparent molecular masses.

Albumins↗
PubMed1992

Design of compounds having enhanced tumour uptake, using serum albumin as a carrier--Part II. In vivo studies.

In the present in vivo study the uptake kinetics of radioiodinated albumin were determined in normal organs, and tumours of rats using sequential scintigraphy. Rat serum (RSA) was radioiodinated either directly at a tyrosine residue (d-RSA), or indirectly at a residualizing marker tagged to the albumin (rm-RSA). These labelling procedures did not alter the kinetics of labelled albumin, as shown by blood disappearance curves. Directly labelled albumin was shown to have tumour uptake. Residualizing markers like tyramine-cellobiose (TCB), tyramine-deoxysorbitol (TDS) and aminonaphthaltyrimide-deoxysorbitol (ANTDS) are metabolically inert. After the intracellular degradation of the albumin carrier the TCB-, TDS- and ATNDS-residues accumulate in the lysosomes, particularly those of tumour cells. It was able to be demonstrated that residualizing-marker tagged albumin-bound radioactivity was five times higher after 72 h than the tumour radioactivity after use of directly labelled RSA. These data found support when whole-body retention of directly labelled RSA, and residualizing marker-RSAs, were determined. After 72 h, 60% of 131I bound to RSA directly had been excreted, compared to only 25% of the activity attached indirectly to RSA with a residualizing marker. Whole-body autoradiography of rats injected with directly labelled RSA, or residualizing marker-RSA, support these results. Most of the radioactivity of directly labelled RSA was excreted within 24 h, whereas labelled residualizing marker-RSAs were also stored in tumour and liver tissue. ANTDS bound to RSA allows fluorescence microscopy. Cryosections of tumours from rats preinjected 10 min and 24 h with ANTDS-RSA before dissection, demonstrated that the fluorescence is localized on and in tumour cells. This indicates that cellular uptake of the marker takes place. Fluorescence was not observed in muscle tissue. This appears to suggest that the albumin uptake is greater in tumours than in normal tissue, and that it is metabolized in the tumour cells.

Animals↗
PubMed1992

Hepatic uptake of a modified low molecular weight heparin in rats.

Fractionated and unfractionated heparins are widely used as antithrombotic agents. Because of their heterogeneous composition, it is difficult to study the pharmacokinetics of these drugs. We now report on a new method for labeling low molecular weight heparins with 131I by binding tyramine to the anhydromannose end of the molecules. We examined the pharmacokinetics of the compound by intravenous injection of 131I-tyramine-heparin into Wistar rats. About 18% of the activity was found in the liver, whereas 33% was detected in urine. Biological activity in terms of Factor Xa inhibition was measurable. Since evidence from cell culture experiments implies that reticuloendothelial cell system receptors might be involved in heparin metabolism, maleylated BSA, a substance known to block scavenger receptors, was injected before the radiolabeled heparin compound. The liver uptake was reduced from 17.4 to 4.8%. Injection of unfractionated heparin before tracer application caused a considerable increase in urine excretion of the tracer substance. To our knowledge, this is the first report that liver uptake of heparins is linked to scavenger receptor mediated mechanisms in vivo. This interaction of heparins with scavenger receptors might play an important role in the biology of the vessel wall.

Animals↗
PubMed1992

Scavenging of lipid peroxidation products from oxidizing LDL by albumin alters the plasma half-life of a fraction of oxidized LDL particles.

We analyse LDL oxidation in vitro in the presence of copper (II) ions and differentiate a lag phase and a rapid peroxidation phase. We demonstrate that a physiological concentration of albumin does not alter the kinetics of the dienes in the oxidizing LDL but reduces the fluorescence of the oxidizing LDL and alters the biological properties of oxidized LDL. We find in rats after intravenous administration of oxidized LDL, that it is rapidly cleared from the circulating blood. The presence of albumin during the peroxidation phase, however, reduces the fraction of oxidized LDL with rapid blood clearance. We propose that some lipid peroxidation products formed in oxidizing LDL are hydrophilic enough to diffuse into the aqueous buffer from where they react either with the epsilon-amino-groups of apolipoprotein B or albumin. Effective scavengers for these hydrophilic endproducts of the LDL oxidation pathways such as albumin might reduce modification of the LDL and might be useful to reduce its atherogenicity.

Animals↗
PubMed1990

Binding characteristics of reduced hepatic receptors for acetylated low-density lipoprotein and maleylated bovine serum albumin.

The binding characteristics of reduced hepatic membrane proteins for acetylated low-density lipoprotein (acetyl-LDL) and maleylated bovine serum albumin (Mal-BSA) have been examined. Two receptor activities were extracted from hepatic membranes in the presence of octyl beta-D-glucoside and beta-mercaptoethanol, and were separated by chromatography on Mal-BSA-Sepharose 4B. The receptors were revealed by ligand blotting. The active binding proteins had apparent molecular masses of 35 and 15 kDa in SDS/polyacrylamide gels. Equilibrium studies with protein-phosphatidylcholine complexes indicated that the reduced 35 kDa protein expresses two binding sites for Mal-BSA and one for acetyl-LDL, whereas the 15 kDa protein-phosphatidylcholine complex binds 131I-Mal-BSA and 131I-acetyl-LDL with a 4:1 stoichiometry. 131I-Mal-BSA binding was linear with both proteins, with a Kd of 4.8 nM at the 35 kDa protein and a Kd of 5.6 nM at the 15 kDa protein. The 35 kDa protein displayed saturable binding of 131I-acetyl-LDL with a Kd of 5 nM; the 15 kDa binding protein bound 131I-acetyl-LDL with a Kd of 2.3 nM. A 85 kDa protein was obtained by Mal-BSA-Sepharose chromatography when the hepatic membranes had been solubilized with Triton X-100 in presence of GSH/GSSG. This protein displayed saturable 131I-Mal-BSA binding with a Kd of 30 nM and 131I-acetyl-LDL binding with a Kd of 6.5 nM. The 131I-Mal-BSA binding capacity was four times higher than that of 131I-acetyl-LDL. Competition studies with the 35 kDa, 15 kDa and 85 kDa proteins binding Mal-BSA, acetyl-LDL, formylated albumin and polyanionic competitors provide evidence for the existence of more than one class of binding sites at the reduced binding proteins.

Acetylation↗
PubMed1990

[Improved intraoperative leak control in cytostatic drug isolation perfusion of tumors of the extremities].

The success of extremity perfusion and the protection from systemic side effects largely depend upon the prevention of systemic drug leakage from the extremity circulation. The use of autologous 111-Indium labelled erythrocytes for leakage control allows a continuous exact surveillance and timely correction of the tourniquet position in case a major leak should occur. A total of 97 patients were studied. In 6 patients (= 6%) the perfusion had to be discontinued within the first 30 min due to an uncorrectable leak of greater than 20%. In 31 patients (= 32%), a major leak could be reduced by manipulation of the tourniquet. No systemic side-effects could be observed in any of our patients. Applying leakage control by means of 111-Indium labelled erythrocytes extremity perfusion has proved to be a safe procedure in patients with high risk or recurrent malignant melanoma and soft tissue sarcoma.

Adolescent↗
PubMed1990

Tumour targeting with antibody-coupled liposomes: failure to achieve accumulation in xenografts and spontaneous liver metastases.

The potential of small unilamellar liposomes coupled to anti-tumour monoclonal antibodies (immunoliposomes) to accumulate in solid tumour tissue was tested in two systems, i.e. a human malignant melanoma xenografted into nude mice and a syngeneic murine lymphoma ESb.Mp exhibiting spontaneous metastasis to the liver. Both monoclonal antibodies tested were partly released from immunoliposomes within a few hours, thus generating a seemingly constant level of circulating antibody. Nevertheless it was possible to follow the biodistribution of intact immunoliposomes by virtue of a radioiodine label incorporated into the lipid moiety. It was found that in both tumor systems, though they differed with respect to the size of lesions and maybe also to the vascular architecture of surrounding tissue, immunoliposome uptake was virtually nil. The blockade of uptake into solid tumour tissue was caused by the limited availability of immunoliposomes due to their moderate stability, but especially by the inability of the particulate carrier to extravasate.

Animals↗
PubMed1990

Design of compounds having an enhanced tumour uptake, using serum albumin as a carrier. Part I.

The search for a radioiodinated "cumulative" protein label, stored within cells following intracellular protein degradation, suggested that plasma protein turnover of tumours might be of use. While earlier investigators were primarily interested in metabolism and utilization of plasma proteins by tumours, we tried to utilize the tumour protein turnover to channel radioiodine labelled compounds, covalently bound to serum albumin, into neoplastic tissues. To identify those parameters which influence the tumour uptake and storage, we investigated a series of compounds having different chemical and physicochemical properties. Unbound, small molecular weight compounds were rapidly eliminated from the circulatory system. They had a prolonged biological half life if linked to serum albumin (SA), especially when derivatized with deoxysorbitol. Parallel with the prolongation of the biological half-life we noted a remarkable increase in tumour uptake, which was not accompanied by increased liver activity. Furthermore, without thyroid blockade, we failed to detect significant radioiodine uptake in this organ after 24 or 72 h. This is due to the particular coupling mechanism, which may be relevant for other (radio)iodinated pharmaceuticals used in medicine. Glucose and aromatic amines, as well as aromatic aldehydes and glucamine react to form deoxysorbitol derivates, which then have similar biokinetics after linkage to serum albumin. This indicates that a new approach in tumour detection and possibly in tumour therapy may be possible when SA is used as a carrier molecule, using the described labelling procedure.

Animals↗
PubMed1990

Synthesis of positively charged phthalocyanines and their activity in the photodynamic therapy of cancer cells.

Positively charged zinc containing or metal free phthalocyanines 6a-c and 7a-c were prepared via a three step procedure starting from 4-nitrophthalonitrile. The phthalocyanines contain alkyl chains of different length in order to influence the hydrophilic vs lipophilic character of the compounds. The partition between a hydrophilic (water) and lipophilic (octanol-1) phase was determined, and the photoredox activities were investigated. Initial results on the photodynamic activity of these compounds were compared with those of Dougherty's Photofrin II on different malignant and non-malignant cell lines (XP 29MAmal, CX1, HeLa, S180 and NO17). Positively charged phthalocyanines in vitro showed a higher photodynamic activity than Photofrin II.

Animals↗
PubMed1989

Stability in biological fluids and clearance of immunoliposomes.

The in vivo and in vitro stability of liposomes having covalently bound monoclonal antibodies (MAB) connected to their surface via a disulfide bridge (about 6 anti-melanoma MAB-molecules per liposome) in tissue fluids was investigated. These immunoliposomes were composed of equimolar amounts of hydrogenated soybean lecithin and cholesterol and had a mean diameter of 113 nm. The protein-lipid binding, change of vesicle size and the release of encapsulated carboxyfluorescein (CF) were estimated. After i.v. injection into mice, an initial protein cleavage of 21% occurred within 30 min p.a., followed by a slow elimination of intact MAB-liposomes from blood circulation (t50 = 2.2 h). These liposomes had a similar elimination rate as protein-free liposomes. The in vitro results after incubation of MAB-liposomes in blood, plasma, serum and tissue fluid were very similar with regard to the protein-lipid cleavage, but the time dependence was different. The CF-release in vitro was slower (about 1.5%/d) than the protein cleavage; the vesicle size of MAB-liposomes increased substantially in contrast to protein-free liposomes in serum during 4 days.

Animals↗
PubMed1988

Evidence in liver for a disulphide-linked scavenger receptor containing a binding site for acetylated low-density lipoprotein and maleylated bovine serum albumin.

Membranes from rat liver were analysed under reducing conditions. The components of the soluble membranes responsible for the binding of acetylated low density lipoprotein (acetyl-LDL) and maleylated bovine serum albumin (Mal-BSA) were chromatographed on a polyethyleneimine-cellulose column and subsequently separated by gel electrophoresis. For both ligands a major binding protein (Mr = 35,000) was revealed by ligand blotting. A minor protein (Mr greater than 67,000) exhibited little binding. The Scatchard plot of the 131I-Mal-BSA binding data of the 35 kDa protein was linear, with a Kd of 17.3 nM. High concentrations of acetyl-LDL competed for half of the 131I-Mal-BSA binding. Excessive Mal-BSA competed for all the visible acetyl-LDL binding. The findings indicate the existence, in the reduced hepatic membrane, of a 35 kDa protein that has two binding sites for 131I-Mal-BSA and one binding site for acetyl-LDL.

Albumins↗
PubMed1987

Binding of acetylated low density lipoprotein and maleylated bovine serum albumin to the rat liver: one or two receptors?

The liver is the major organ involved in clearance of acetylated low density lipoprotein (acetyl-LDL) and maleylated serum albumin (Mal-BSA). Quantitative analysis of the hepatic uptake by sequential scintigraphy in rats shows that the hepatic uptake capacity for Mal-BSA is at least 15 times larger than for acetyl-LDL particles. A membrane-associated M approximately 250,000 daltons hepatic receptor for acetyl-LDL and Mal-BSA was 1450-fold purified from total membrane by Triton X-114 solubilization, chromatography on polyethylenimine cellulose and gel filtration. This receptor incorporated into liposomes displayed a saturable binding of [131I]Mal-BSA with a dissociation constant Kd = 15 nM and to [131I]acetyl-LDL with a dissociation constant Kd = 0.9 nM. The binding of both ligands was sensitive to poly(vinyl sulfate). The purified scavenger receptor system has a binding capacity for [131I]Mal-BSA 20 times larger than for [131I]acetyl-LDL. This is similar to the maximal removal capacity of the rat liver for both ligands in vivo. Binding studies with Mal-BSA, acetyl-LDL and anti-idiotypic receptor antibodies as competitors for [131I]Mal-BSA and [131I]acetyl-LDL binding demonstrate that [131I]Mal-BSA and [131I]acetyl-LDL compete for a common binding site. However, not all of the Mal-BSA binding sites are capable of interacting with acetyl-LDL.

Albumins↗
PubMed1986

123I-N-isopropyl-amphetamine single photon emission computed tomography as a brain imaging technique in dementia.

Because of its binding to specific cerebral amine receptor sites 123I-N-isopropyl-amphetamine (IMP) tracer activity can be used as a measure for the regional cerebral blood flow (rCBF) in the human brain. In 21 psychiatric in-patients an IMP perfusion study was performed using a rotating gamma camera system. The findings at single photon emission computed tomography (SPECT) were compared with different clinical parameters including conventional transmission computed tomography. In SPECT, two different patterns of decrease in IMP uptake could be identified. In patients with a history of cerebrovascular disease SPECT showed asymmetrical, multifocal microcirculatory defects without preference for either hemisphere. In patients with suggested Alzheimer type dementia the perfusion deficits involved the gray and white matter of the parieto-occipital lobes in a bilaterally symmetrical mode with variable extension. Thus, by using IMP-SPECT, it was possible to define the underlying pathologic condition in dementia.

Adult↗
PubMed1985

Visualization of the hepatic low-density lipoprotein receptor in rats by sequential scintiscans.

The usefulness of a gamma camera system for external imaging of the degradation sites of low-density lipoprotein (LDL) is demonstrated in rats. [131I]LDL was injected intravenously in normal rats and rats pretreated with 17 alpha-ethinyl estradiol for LDL receptor induction. Distribution of the radioligand was followed for 20 min, for perfusion control [131I]albumin was administered. Rats pretreated with 17 alpha-ethinyl estradiol showed a marked increase in the LDL uptake by the liver, which was not competed by the preinjection of physiological amounts of unlabelled LDL. It is concluded that the injection of small amounts of [131I]LDL is sufficient to image the hepatic LDL receptor and that the endogenous LDL does not compete effectively at physiological LDL levels.

Animals↗
PubMed1985

Characterization of binding sites for acetylated low density lipoprotein in the rat liver in vivo and in vitro.

Acetylated low density lipoprotein (acetyl-LDL) binding to hepatic membrane proteins of rats was analysed in vitro by ligand blotting. Specific binding could be demonstrated to two hepatic proteins with an apparent mol. wt. of 250 kd and 220 kd. Polyanionic competitors and maleylated bovine serum albumin inhibited the binding of acetyl-LDL effectively. To determine the sites of the catabolism of acetyl-LDL, [131I]-acetyl-LDL was injected intravenously into control rats and rats pre-treated with the known competitors of the acetyl-LDL binding. Distribution of the radiolabelled acetyl-LDL was followed by a scintillation camera. Six minutes after injection, the radioactivity was concentrated in the liver. The competitors and unlabelled acetyl-LDL but not native LDL reduced the hepatic uptake of [131I]acetyl-LDL dramatically. Thus, the sensitivity of the 220- and 250-kd membrane binding sites to the competitors for the acetyl-LDL binding resembled that of the hepatic compartment in vivo. Finally, an application of scintigraphy with radiolabelled low density lipoproteins for diagnostic evaluation of tumor compartments is presented.

Animals↗
PubMed1985

11C-butanol for imaging of the blood-flow distribution in tumor-bearing animals.

1-11C-n-Butanol produced semiautomatically using a cyclotron was employed to investigate the whole-body distribution and kinetics of the label of this compound. Following the administration of 11C-butanol into the aorta of two dogs, more than 80% of the activity was cleared from the blood within 1 min. The activity distribution mirrored the cardiac output distribution as determined using 121I microspheres. Within 25 min p.i., a significant release of decay-corrected activity was only observed for the liver, spleen, and kidneys. Muscle and whole-body activity showed constant levels during this period. In 45 tumor transplants from rats, the dynamic behavior of the label was studied. The tissue retention of activity following injection into the a. femoralis was approximately 100% during the 1st 15 s for both tumor and muscle (n = 6). The activity release by tumors during the 1st 10 min after intra-aortic injection was 18% +/- 4.5% (n = 39; decay corrected). In five different tumor lines (n = 10), the initial 11C-butanol uptake was related to that of muscle, and the results were correlated with the tumor-to-muscle retention of 121I-microspheres (r = 0.89). In 17 tumors, the correlation between 11C-butanol uptake and the washout rate of 133Xe resulted in a correlation coefficient of 0.96. Tumor-to-muscle uptake ratios could be equally determined using intra-aortic and intravenous injection, as evaluated by intraindividual comparison in 12 rats (y = 0.01 + 0.98x; r = 0.98). 11C-Butanol appears to be an appropriate radiotracer for the assessment of blood supply to malignant tumors relative to muscle.

1-Butanol↗
PubMed1984

N-13 L-glutamate uptake in malignancy: its relationship to blood flow.

Studies on glutamate uptake, with special reference to perfusion, were carried out in 35 rats, each bearing one of five different tumor transplants; also in 15 rats after bone fracture, and in three rabbits. Single-pass extraction of N-13 glutamate was 85-93% in the VX2 tumor of the rabbit and in muscle. Bone fracture in rats caused a threefold increase of tracer uptake 2 days after the event. In tumor transplants, the tumor-to-muscle uptake ratio reached a maximum immediately following injection of the tracer. Comparing N-13 glutamate uptake with the retention of 1-121 microspheres, identical tumor-to-muscle ratios were found for three out of five tumor lines. Comparing the uptake with that of C-11 butanol (ten rats), a close correlation was observed throughout the range of tumor lines. The results suggested that glutamate uptake by malignant tumors is related to blood flow. In nine patients with malignant or benign lesions tumor-to-muscle uptake of N-13 glutamate and TI-201 showed a linear correlation close to identity.

Adolescent↗