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Biomedical subjects

A Niendorf

Publications and source records attributed to A Niendorf.

At least 37 records · Page 2Linked to original sources
PubMed1995

Effects of pravastatin, a hydroxymethylglutaryl-CoA reductase inhibitor, on two human tumour cell lines.

Competitive inhibitors of 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase are currently used to treat patients with hypercholesterolaemia. These inhibitors affect not only cholesterol biosynthesis, but also the production of non-steroidal mevalonate derivatives, that are involved in a number of growth-regulatory processes. As a consequence, their potential use as anticancer drugs has been suggested. In order to examine long-term effects of this potential therapeutic approach, we cultivated the gastric carcinoma cell line, EPG85-257, and the breast tumour cell line, MDA-MB231, in the presence of increasing concentrations of the HMG-CoA reductase inhibitor, pravastatin. For both cell lines, this procedure led to the selection of resistant variants able to proliferate in more than 1000 microM inhibitor. By competitive reverse transcriptase/polymerase chain reaction assay (cRT-PCR), the expression of the mRNA for two key proteins of cellular cholesterol metabolism, HMG-CoA reductase and low-density lipoprotein (LDL) receptor, were analysed in sensitive and resistant cells. Despite similar growth rates, MDA-MB231 cells expressed approximately four times more HMG-CoA reductase mRNA than EPG85-257 cells and over 30 times more LDL receptor mRNA. Both mRNA species were coordinately regulated in the parental and in the pravastatin-resistant variant cells. Expression was highly stimulated (3- to 4-fold for the HMG-CoA reductase and 2- to 3-fold for the LDL receptor) in the resistant variants when cultured in lipoprotein-deficient medium in the presence of 1000 microM pravastatin. Immunocytological analysis of the expression of the HMG-CoA reductase and LDL receptor protein were in accordance with the data on specific mRNA expression obtained by cRT-PCR. Southern blot analysis revealed a 1.5-fold amplification of the HMG-CoA reductase gene in resistant MDA-MB231 cells, but not in the resistant EPG85-257 variant. Our data provide evidence for resistance mechanisms to pravastatin that are independent of the amplification of the HMG-CoA reductase gene. By analogy to the cell-culture models employed in this study, it is conceivable that similar mechanisms might occur in human tumour cells in vivo during long-term treatment with HMG-CoA reductase inhibitors. This might limit their application as chemotherapeutic anticancer agents.

Blotting, Southern↗
PubMed1995

Transfer of lipoprotein(a) and LDL into aortic intima in normal and in cholesterol-fed rabbits.

To study the relative atherogenic potential of lipoprotein(a) [Lp(a)], the transfer of Lp(a) and LDL into the arterial wall was compared in normal rabbits, cholesterol-fed rabbits, and normal rabbits in which the plasma concentration of Lp(a) before injection of labeled lipoproteins was increased by an intravenous mass injection of 45 mg Lp(a). Aorta was removed either 60 minutes or 180 minutes after intravenous injection of a mixed preparation of human 125I-Lp(a) and 131I-LDL; intimal clearance was calculated as radioactivity in aortic intima/inner media divided by the average concentration of the appropriate radioactivity in plasma and by the length of the exposure time. The intimal clearance of labeled Lp(a) and LDL in the aortic arch after 60 minutes of exposure was 87 +/- 9 and 47 +/- 7 nL.cm-2.h-1 (n = 9) in normal rabbits and 82 +/- 14 and 62 +/- 10 nL.cm-2.h-1 (n = 10) in cholesterol-fed rabbits; after 180 minutes of exposure, the intimal clearance of labeled Lp(a) and LDL was 62 +/- 14 and 84 +/- 21 nL.cm-2.h-1 (n = 6) and 30 +/- 6 and 47 +/- 12 nL.cm-2.h-1 (n = 4) in cholesterol-fed and Lp(a)-injected rabbits, respectively. Linear regression analysis showed positive associations between intimal clearance of the two lipoproteins in all four groups of rabbits in the aortic arch, the thoracic aorta, and the abdominal aorta. Aortic immunoreactivity of human apolipoprotein(a) was detected in the intima in association with fatty streak lesions, predominantly within the cytoplasm of foam cells. These results suggest that Lp(a) is transferred into the aortic intima by a mechanism similar to that for LDL and that Lp(a) can be taken up by intimal foam cells; however, Lp(a) and LDL may be metabolized differently upon entrance into the arterial wall.

Animals↗
PubMed1995

[In vitro and in vivo studies of a temporary absorbable dressing].

The major advantage of biodegradable synthetic wound dressings compared to other synthetic materials and biological tissue derivatives is avoidance of the necessity to change the dressing. The copolymer films used in this study were made of lactic and caproic acid. They pose no problems concerning immunology or transmission of diseases. Moreover, the substances released by degradation may possibly influence the process of wound healing. The material proved to be non-toxic and was used successfully as a carrier for cell culture with keratinocytes. The permeability for bacteria is determined by degradation. Evaluation of the bacteriological studies indicates secure protection against secondary contamination of the films for at least 15 days, however. Concerning application, dressing properties, wound healing and wound retraction, no disadvantages were found in comparison with the results of the competition's film Opsite. Based on these findings, the films are now used in a clinical study as a wound dressing for split-skin donor sites.

Animals↗
PubMed1994

[Quantitative analysis of mRNA expression of the LDL receptor and HMG-CoA reductase in bovine tissue with competitive RT-PCR].

The present study exemplifies the method of quantitative reverse transcriptase-polymerase chain reaction (cRT-PCR) by quantifying, in bovine tissues, the specific mRNAs for the two key proteins which regulate cellular cholesterol metabolism, the low density lipoprotein (LDL)-receptor and the 3-hydroxy-3-methylglutaryl-Coenzyme A (HMG-CoA) reductase. Our data reveal a broad range of expression for both mRNAs. The LDL-receptor mRNA expression was highest in the adrenal gland (6.7 x 10(4) molecules/micrograms cellular RNA) followed by the corpus luteum of the ovary, intermediate in the liver (8.6 x 10(2) molecules/micrograms cellular RNA) and not detectable in the large intestine. Expression of the HMG-CoA reductase almost paralleled LDL-receptor values. It was found to be highest in the ovary (6.1 x 10(6) molecules/micrograms cellular RNA) followed by the adrenal gland, intermediate in the liver (3.1 x 10(5) molecules/micrograms cellular RNA) and lowest in the large intestine (9.9 x 10(4) molecules/micrograms cellular RNA). These data are consistent with other reports concerning the quantitative analysis of the expression of both proteins as determined by other experimental approaches. Thus cRT-PCR is a valuable tool for the quantitative analysis of the LDL-receptor and the HMG-CoA reductase.

Adrenal Glands↗
PubMed1994

Rapid quantitation of mRNA species in ethidium bromide-stained gels of competitive RT-PCR products.

A rapid method for quantifying the low-abundant mRNAs of the low density lipoprotein receptor and the 3-hydroxy-3-methylglutaryl coenzyme A reductase by competitive polymerase chain reaction is presented. This approach requires neither special labeling nor blotting procedures. For each analysis, a defined amount of total cellular RNA is co-reverse transcribed and co-amplified with a titration series of in vitro synthesized competitor RNA that carries an internal deletion. The equivalence point, which defines the amount of specific RNA in the sample, can be scored in ethidium bromide-stained agarose or polyacrylamide gels of the reaction products. As an example, responses to pravastatin, a competitive inhibitor of the HMG-CoA reductase, in a human tumor cell line were analyzed with this new technique. As a control, the expression of the unregulated gene, glyceraldehyde-3-phosphate dehydrogenase was measured in parallel using the same methodology. The results obtained were compared with those obtained by conventional Northern blotting.

Base Sequence↗
PubMed1992

Elevated lipoprotein(a) levels in patients with acute myeloblastic leukaemia decrease after successful chemotherapeutic treatment.

Twenty-two patients with acute myeloblastic leukaemia (AML) were studied to investigate disease-associated changes in lipid metabolism. Lipoprotein (a) [Lp(a)] levels were found to be elevated at the time of diagnosis (median 23 mg/dl; 41% of patient group had levels greater than 25 mg/dl) and diminished after successful chemotherapeutic treatment in 9 of 10 cases, with a maximum decrease from 56 to 10 mg/dl. In contrast, reduced levels of total cholesterol, low density lipoprotein (LDL) and high density lipoprotein (HDL) (medians 137, 87 and 20 mg/dl, respectively) were observed at the time of diagnosis. Cholesterol and HDL levels increased in all 10 and LDL in 9 cases in which complete remission was achieved. These data suggest that the catabolism of LDL-cholesterol might be even more enhanced than assumed to date. Furthermore, it indicates that the Lp(a) level in acute myeloblastic leukaemia is influenced either directly or indirectly by the leukaemic blasts.

Adult↗
PubMed1991

Antiatherosclerotic effect of probucol in WHHL rabbits: are there plasma parameters to evaluate this effect?

Probucol has been used as a lipid-lowering agent for over 10 years. Lately it has been found that its antiatherogenic action is due mainly to its antioxidative capacity, in addition to its known lipid-lowering effect. To study the antioxidative capability of probucol and its influence on plaque development we used the animal model of the LDL-receptor-defective Watanabe heritable hyperlipidemic (WHHL) rabbit. In this study we measured all lipid values before and after probucol feeding and compared them with corresponding values in untreated controls. Probucol levels were determined, as were the physiological antioxidants alpha and gamma tocopherol (vitamin E). Thiobarbituric reactive substances were measured in plasma as a parameter for lipid peroxidation. In addition to the biochemical measurements the plaque area was analyzed macroscopically and microscopically to check the antiatherosclerotic effect and correlate it with the biochemical parameters. In four experiments we showed that probucol treatment in WHHL rabbits decreases the progression of atherosclerotic plaques by way of a combined lipid-lowering and antioxidative effect.

Animals↗
PubMed1990

Membrane vesicle formation due to acquired mitoxantrone resistance in human gastric carcinoma cell line EPG85-257.

A newly established gastric carcinoma cell line (EPG85-257P) exhibited a high sensitivity to mitoxantrone (DHAD) as determined by a monolayer proliferation assay. The concentration to inhibit cell growth to 50% of controls (IC50) was 0.0022 micrograms/ml culture medium. The cells were continuously incubated for more than 4 months in the presence of stepwise increased concentrations of DHAD, and the IC50 was increased to 0.41 micrograms/ml, i.e., 186.4-fold. This resistant variant was named EPG85-257RNOV. The EPG85-257RNOV cells became cross-resistant to Adriamycin with enhanced IC50 by 10.5-fold and to daunomycin with enhanced IC50 by 3.9-fold. No distinct resistance was observed to vinblastine, vincristine, and colchicine. Verapamil (10(-6), 4 X 10(-6) and 10(-5) M) and cyclosporin A (10(-6), 3 X 10(-6) and 10(-5) M) did not reverse DHAD resistance. As shown by immunocytochemistry (monoclonal antibodies: C219 and JSB-1) and Northern blot analysis, DHAD resistance was not associated with the appearance of the multidrug resistance (MDR)-associated (Mr 170,000) P-glycoprotein or the overexpression of P-glycoprotein mRNA. The data indicate a chemoresistance pattern unlike typical MDR (often called "atypical" MDR). The phenotypes of parent and resistant EPG85-257 cells were compared using interference contrast microscopy, electron microscopy, and immunocytochemistry. After DHAD application the following structural characteristics were found to be associated with emergence of resistance: (a) intensive formation of surface vesicles in the resistant variant. Such vesicles were almost absent in sensitive cells; (b) the vesicles contained the selecting DHAD which was visualized by its blue color; and (c) in electron microscopy the vesicles were formed by an inner and an outer double membrane, presumably derived from the plasmalemma. These observations suggest a complex cellular mechanism responsible for DHAD resistance which includes formation of membrane vesicles, vesicular drug binding, and drug compartmentalization.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1990

Immunocytochemical differential diagnosis of adrenocortical neoplasms using the monoclonal antibody D11.

The monoclonal antibody D11 is a valuable aid in the accurate typing of adrenal tumours as, in formalin-fixed, paraffin-embedding material, strong nuclear D11 positivity was observed only in adrenocortical cells in 190 neoplasms (including 100 adrenal tumours). This pattern was demonstrated for all zona glomerulosa cells in 27 normal adrenals and for the neoplastic cells of 15 adrenocortical adenomas derived from that zone, as judged from clinically evident hyperaldosteronism. Normal cells of zona fasciculata and reticularis also showed strong diffuse D11 immunostaining and the same nuclear plus cytoplasmic D11 reactivity was evident in 15 benign and malignant adrenocortical neoplasms derived from these zones, documented by hypercortisolism. Cytoplasmic and/or nuclear D11 staining made topohistogenetic typing possible in 15 non-functioning cortical tumours. D11 immunostaining gave negative results in 50 specimens containing normal, hyperplastic and neoplastic adrenomedullary cells. In addition, absence of D11 reactivity was recorded in 4 adrenal metastases of extra-adrenal carcinomas, 5 paragangliomas, 25 primary renal carcinomas and 59 of 60 primary thyroid carcinomas. D11 immunocytochemistry allows the accurate typing of benign and malignant adrenocortical neoplasms, irrespective of histology and function. With this method, primary adrenocortical tumours can be separated from carcinomas metastatic to the adrenal gland, including secondary tumours of similar phenotype (such as renal carcinomas). By exclusion, D11 negativity provides evidence of the medullary origin of primary adrenal tumours even in the absence of clinical, structural, histochemical and conventional immunohistochemical indicators of phaeochromocytoma.

Adenoma↗
PubMed1990

Morphological detection and quantification of lipoprotein(a) deposition in atheromatous lesions of human aorta and coronary arteries.

Lipoprotein(a), as an atherogenic particle, represents an independent risk factor for coronary heart disease. In the present study the morphological distribution of apoprotein (a) and apoprotein B within the arterial wall is described. Apoprotein B, a constituent of very low-density lipoprotein, low-density lipoprotein and lipoprotein(a) has previously been demonstrated in atheromatous lesions. Lipoprotein(a) possesses an additional protein, designated apoprotein (a). Autopsy material (n = 74) from the left coronary artery and from the thoracic aorta has been examined by means of immunohistochemistry and both apoprotein (a) and apoprotein B were detected, primarily associated with the extracellular matrix and accumulating in lesions in the arterial wall. The staining pattern for both antigens was almost always found to be congruent, suggesting that the detection of (a)-antigen has to be attributed at least in part to the presence of lipoprotein(a). It is concluded that both low-density lipoprotein and lipoprotein(a) have an important role in the pathogenesis of atherosclerosis.

Adolescent↗
PubMed1990

Lipoprotein(a) in the arterial wall.

We compared CHD patients with healthy blood donors to confirm the role of Lp(a) as an independent risk factor. More important, we performed biochemical and immunohistochemical studies to evaluate the potential mechanism by which Lp(a) causes CHD. We measured the Lp(a) concentration in comparison with other lipoprotein parameters in fresh human arterial wall biopsies and, in autopsy tissue, we localized apo (a) and apo B, as well as fibrin, with immunohistochemical methods in different vessel areas. Density gradient ultracentrifugation was used to analyse lipoprotein fractions isolated from human arterial wall. Lp(a) accumulates in the intima, preferentially in plaque areas, dependent on the serum Lp(a) level. Most of the Lp(a) can be located extracellularly, but apo(a) can also be detected in foam cells. A strong co-localization has been observed for apo(a) and apo B; only a few areas containing only apo B were detected. Moreover, a striking co-localization for apo(a) and fibrin was found. The possibilities for the pathways by which Lp(a) enters the arterial wall and accumulates extracellularly are discussed on the basis of the present data and recent data published by other groups.

Aorta↗
PubMed1990

[Leu-M1, CEA and intermediate filament proteins in histochemical differential diagnosis of malignant pleural mesothelioma].

The differential diagnosis "pleuramesothelioma" vs "metastatic adenocarcinoma" can mostly not be decided clearly by conventional histological methods in malignant pleuraneoplasias. Leu-M1 is employed in immunhistochemical diagnosis of lymphomas in Hodgkin's disease but it also reacts with adenocarcinoma cells. Pleuramesotheliomas are Leu-M1 negative. Intermediary filament proteins, CEA and Leu-M1 are important "markers" in the diagnosis of malignant pleuraneoplasias. 25 pleura biopsies of malignant pleura processes were subjected to immunhistochemical examination.

Adenocarcinoma↗
PubMed1989

[Individualization of chemotherapy through in vitro predictive determination of the cytostatic sensitivity of malignant tumors].

An in-vitro test was developed for predicting the efficacy of anti-tumour chemotherapy. Cell cultures were grown from freshly removed tumours and it was then demonstrated by DNA cytophotometry and immuno-cyto-chemistry whether the growing tumour cells corresponded to those of the original tumour cells. Several cytostatic agents were then tested for their efficacy of inhibiting growth at clinically customary dosage. Growing cell cultures were established in 306 of 413 submitted tumours (74%). They responded quite differently to the various drugs that were tried. The clinical course in 94 cases was observed for minimally four and a mean of eight months to obtain an in-vitro to in-vivo correlation of response, with 178 individual correlations. A discrepancy was recorded in 16% of cases, a false-positive in-vitro sensitivity result was 3.6 times more frequently associated with an in vivo resistance than the reverse. Concordance between test results and clinical tumour response occurred in 84%. The monolayer proliferation assay correctly indicated resistance in 93.8%, sensitivity in 72.8%.

Antineoplastic Agents↗