Characterization of two distinct mechanisms for induction of apoptosis in human vascular endothelial cells.

Tissue homeostasis is fundamentally influenced by the functional integrity and state of endothelial cells. Survival and death of endothelial cells are encountered in cardiovascular disease and may, moreover, affect and determine the development of atherosclerosis and restenosis following intracoronary therapeutical interventions. Apoptosis was studied in cultured human umbilical vein endothelial cells (HUVEC) to investigate the regulation of endothelial cell death following serum/growth factor depletion as well as incubation with actinomycin-D. Apoptosis was verified by DNA fragmentation and quantified by fluorescence activated cell sorting (FACS) analysis after TdT-mediated deoxyuridine-triphosphate nick end-labeling (TUNEL). An ELISA was used for detecting intracytoplasmatic nucleosomes. Untreated HUVEC showed 16+/-6% TUNEL positive cells after 24 hours as analyzed by FACS. Serum/growth factor depletion increased apoptosis by 79+/-7%, while 50 ng/ml of the pro-apoptotic drug actinomycin-D induced comparable effects (72+/-11%). Apoptosis by serum/ growth factor depletion could be blocked completely by the anti-apoptotic agent cycloheximide (2 microg/ml), but was ineffective in blocking actinomycin-D-induced apoptosis. Pyrrolidine dithiocarbamate (PDTC) also acted as an anti-apoptotic agent by blocking apoptosis induced by actinomycin-D, but had no effect on apoptosis induced by factor depletion. Thus, two independent mechanisms for regulation of apoptosis are suggested to be present in human vascular endothelial cells.

Human cardiac microvascular and macrovascular endothelial cells respond differently to oxidatively modified LDL.

Oxidation of low density lipoproteins (LDL) is considered a key event in the pathogenesis of atherosclerotic lesions. Disturbed generation of coagulatory and anticoagulatory factors by endothelial cells contributes to thrombosis and the progression of atherosclerosis in coronary arteries. In this study, the effects of native LDL (n-LDL) and oxidized LDL (ox-LDL) on human coronary endothelial cells were measured. The reaction of coronary endothelial cells to LDL were compared with those of cardiac microvascular endothelial cells grown under comparable conditions. LDL was isolated by ultracentrifugation and copper oxidized. The degree of oxidation was expressed as malondialdehyd (MDA) equivalents and was 0.78+/-0.14 nM MDA/mg LDL for native LDL and 13.63+/-1.18 nmol MDA/mg LDL for ox-LDL. Basal secretion of t-PA and PAI-1 activity were higher in macrovascular endothelial cells. Incubation of n-LDL in concentrations ranging from 3 to 100 microM/ml LDL-protein did not change t-PA-secretion, PAI-1 activity or procoagulant activity in both cell types. Ox-LDL (3 to 100 microM/ml LDL protein) decreased t-PA secretion in a concentration dependent manner from 30.9+/-1.7 to 13.7+/-30 ng/ml per 24 h per 10(6) cells (P < 0.01), increased PAI-1 antigen from 2772+/-587 to 4441+/-766 ng/ml per 24 h per 10(6) cells (P < 0.05) as well as PAI-1 activity from 34+/-6 to 55+/-9 AU/ml per 24 h per 10(6) cells (P < 0.05) in macrovascular endothelial cells but had only minor effects on microvascular endothelial cells. Procoagulant activity measured as coagulation time, similarly increased only in macrovascular endothelial cells from 197+/-6 to 76+/-6 s/24 h per 10(6) cells (P < 0.05). The effect on PAI-1 secretion showed a dependency to the degree of oxidation and could be completely blocked by the antioxidant probucol. The angiotensin converting enzyme (ACE), which represents an endothelial enzyme not related to coagulation, remained unchanged during incubation with ox-LDL. Basal ACE activity was higher in microvascular endothelial cells. The higher susceptibility of macrovascular endothelial cells to ox-LDL may partially determine the localization of thrombus formation and the development of atherosclerotic plaques in hyperlipidemic patients.

Reversal of multidrug resistance by novel cyclosporin A analogues and the cyclopeptolide SDZ 214-103 biosynthesized in vitro.

It was shown that cyclopeptolide SDZ 214-103 (10 microM) is more active in rhodamine-123 accumulation in actinomycin-D-resistant human lymphoma cells CCRF/ACTD400 than cyclosporin A (10 microM), but equipotent in the doxorubicin-resistant Friend erythroleukemia cell line F4-6/ADR. In F4-6/ADR cells, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay showed comparable cytotoxic effects of doxorubicin at various concentrations in the presence of SDZ 214-103 and cyclosporin A. For the other novel cyclosporin A analogues minor multidrug-resistance-modulating potency was demonstrated. At equipotent modulating doses of verapamil (10 microM) and cyclosporin A (10 microM) in the MTT assay regarding doxorubicin cytotoxicity, cyclosporin A was efficient in the rhodamine-123-uptake assay while verapamil was not active when identical incubation times were used.

Induction of differentiation in Friend-erythroleukemia cells by aclacinomycin A: early transient decrease in c-myc and c-myb mRNA levels.

Chemical inducers of the differentiation are known to cause an early transient decrease in c-myc and c-myb mRNA levels in Friend erythroleukemia cells preceding the down-regulation of c-myc and c-myb expression in the course of irreversible terminal differentiation. We therefore investigated the early effect of the potent differentiation-inducing anthracycline antitumor antibiotic, aclacinomycin A, on the c-myc and c-myb mRNA levels in the Friend cell line, F4-6, using Northern blot analysis. Aclacinomycin A induced a rapid decrease in the levels of c-myc and c-myb transcripts within 0.5-1 h and 2-3 h, respectively. The time course of decline in c-myc and c-myb expression was similar to that observed with dimethylsulfoxide or after transcription blockage brought about by a high concentration of actinomycin D. By 12 to 18 h after aclacinomycin A exposure, the c-myc and c-myb mRNA levels had returned to about pretreatment levels. When the cells were treated with adriamycin, an anthracycline that reduces cell proliferation in F4-6 cells without increasing differentiation, an early decrease in c-myc and c-myb expression was not observed. These results suggest that the transient decrease in c-myc and c-myb mRNA levels in F4-6 cells may be an early differentiation-related biochemical effect of aclacinomycin A.

Structure-activity relationship between anthracycline-induced differentiation and inhibition of glycoprotein synthesis in Friend erythroleukemia cells.

The effect of adriamycin, daunomycin, N,N-dimethyladriamycin, N,N-dimethyldaunomycin, pyrromycin, marcellomycin, and aclacinomycin A on erythroid differentiation and glycoprotein synthesis in Friend erythroleukemia cells, clone F4-6 was investigated. Whereas N-dimethylated natural anthracyclines, pyrromycin, marcellomycin, and aclacinomycin A stimulated erythroid differentiation (induction of hemoglobin synthesis), this was not seen with adriamycin, daunomycin and their N-dimethylated derivatives. The incorporation of 3H-mannose in glycoprotein was inhibited by the N-alkylated natural anthracyclines at a concentration at which they induced erythroid differentiation. N,N-Dimethyladriamycin and N,N-dimethyldaunomycin only inhibited 3H-mannose incorporation into glycoprotein at cytotoxic concentrations. However, adriamycin and daunomycin did not inhibit glycoprotein synthesis, even at high cytotoxic concentrations. Aclacinomycin A decreased the incorporation of 3H-mannose into proteins earlier than the incorporation into dolichol-linked oligosaccharide intermediates. Tunicamycin, a specific inhibitor of glycoprotein synthesis, failed to stimulate differentiation in Friend erythroleukemia cells. These results indicate a structure-specific induction of the differentiation and inhibition of glycoprotein synthesis in Friend cells by N-alkylated anthracyclines. The inhibition of glycoprotein synthesis may be involved in the induction of differentiation by N-alkylated anthracyclines, but it cannot be the only target for the differentiation-inducing effect of these substances.

Recombinant hemopoietic growth factors. Molecular cloning and potential therapeutic applications.

In analogy with data obtained from other mammalian species it appears that the majority of physiologically relevant human hemopoietic growth factors (e.g. erythropoietin and colony stimulating factors) has been characterized in biological systems, defined by biochemical methods and manufactured by molecular cloning of the corresponding genetic elements and expression in suitable biological systems. A review of the present situation of production of recombinant hemopoietic growth factors is presented and potential therapeutic applications of these factors will be discussed. In addition some preliminary clinical results, due to the medical application of recombinant hemopoietic growth factors, will be described.

Inhibition of amino acid uptake and incorporation into proteins in Friend erythroleukemia cells by the anthracycline antitumor antibiotic aclacinomycin A.

Treatment of Friend erythroleukemia cells with aclacinomycin A caused a concomitant inhibition of the uptake of 14C-alpha-aminoisobutyric acid (AIB) and of the incorporation of 3H-alanine into proteins. The decrease in amino acid uptake and incorporation into proteins was dose-dependent and reached a maximum of 60% within 3 hours at the concentration of aclacinomycin A, 200 ng/ml. A comparison of the effect on protein incorporation of 3H-alanine and cell proliferation by various anthracycline antitumor antibiotics in a concentration range of 50-200 ng/ml revealed that two other N-alkylated anthracyclines, pyrromycin and marcellomycin, are also potent inhibitors of the incorporation of amino acids into proteins. Inhibition of amino acid incorporation into proteins correlated well with the reduction of cell number at a later time. In contrast, adriamycin and daunomycin inhibited the incorporation of 3H-alanine into proteins only weakly, although these substances were highly active at inhibiting cell proliferation. Studies with an inhibitor of RNA synthesis, actinomycin D, suggest that the concomitant inhibition of amino acid uptake and incorporation into proteins observed with aclacinomycin A is not due to a reduced RNA synthesis. In addition, aclacinomycin A, up to a concentration of 10 micrograms/ml, did not inhibit protein synthesis in a cell-free translational system from rabbit reticulocytes. These results indicate that the reduction of amino acid incorporation into proteins after treatment of Friend erythroleukemia cells with aclacinomycin A may be due to a reduced uptake of amino acids. Inhibition of the transport of 14C-AIB may be indicative for an interaction of aclacinomycin A with the plasma membrane.

Induction of erythroid differentiation by the anthracycline antitumor antibiotic pyrromycin.

The oligosaccharide-anthracyclines, aclacinomycin A, marcellomycin and musettamycin, are potent inducers of erythroid differentiation in hemopoietic cells lines of rodent and human origin. The present studies revealed that pyrromycin, a closely related monosaccharide-anthracycline, induced erythroid differentiation in Friend leukemia cells and in the human leukemia cell line K 562. Pyrromycin, marcellomycin and musettamycin, which possess an identical aglycone structure containing a Cl-hydroxyl group, exhibited relatively low optimal inductive concentrations. In contrast, the optimal inductive concentration of aclacinomycin A, which lacks the Cl-hydroxyl group, was markedly higher, i.e., the differentiation inducing capacity was lower. It should be noted, however, that the yield of differentiated cells following treatment with the monosaccharide-anthracycline pyrromycin was distinctly lower than that after treatment with the oligo-saccharide-anthracyclines, aclacinomycin A, marcellomycin or musettamycin. Thus, our data indicate that the efficacy of anthracyclines to induce erythroid differentiation is related to a) the presence of a Cl-hydroxyl group in the aglycone and b) the presence of an oligosaccharide side chain.

Induction of chromosomal aberrations by the anthracycline antitumor antibiotics N,N-dimethyldaunomycin and aclacinomycin A.

The clastogenic effect of the anthracycline antitumor antibiotics, N,N-dimethyldaunomycin and aclarcinomycin A, was studied in a murine hemopoietic cell line (Friend leukemia cells). A dose-dependent increase in chromatid lesions, i.e., achromatic lesions, chromatid breaks, chromatid deletions and triradial or quandriradial chromosomal exchange fiqures, was found. It appears that the clastogenicity of N,N-dimethyldaunomycin and aclacinomycin A is lower than that of the classic anthracycline, daunomycin, which is also a potent mutagen and carcinogen. The data demonstrate that the capacity of chemicals to induce point mutations and chromosomal aberrations may not necessarily be correlated: aclacinomycin A is devoid of mutagenic activity in bacterial (Salmonella typh.) and mammalian cell (HGPRT) mutagenesis assays, and is non-carcinogenic in rats. Nevertheless, it was now found to possess clastogenic activity.

Erythroid differentiation and the Na+,K+-pump in ouabain-sensitive and ouabain-resistant Friend erythroleukemia cell lines.

The selection and biochemical characterization of ouabain-resistant erythroleukemia cell lines are described. Treatment of ouabain-resistant Friend erythroleukemia cell (FLC) lines with 1 mM ouabain demonstrated a reduced ouabain-sensitive 86Rb+-uptake after Na+-preloading in comparison with ouabain-sensitive cells. The ouabain- and diuretic (piretanide)-insensitive component of the 86Rb+-uptake (residual influx) was significantly enhanced in the ouabain-resistant FLC clones. Measurements of the Na+,K+-ATPase activity (E.C. 3.6.1.3) in plasma membrane preparations of the ouabain-resistant FLC clone B6/2 indicated that a ouabain-resistant Na+,K+-ATPase activity of about 20% of the total enzyme activity existed in the presence of 1 mM ouabain. Further experiments showed that the Na+,K+-ion-gradient in ouabain-resistant B6/2 cells was unaffected by ouabain exposure whereas the gradient collapsed in wild type 12 N cells. Another property of the ouabain-resistant cell lines was a decrease of the 86Rb+-uptake due to the Na+,K+, 2Cl(-)-cotransport system measured as piretanide-sensitive 86Rb+-uptake. The data on ion transport mechanisms in QuaR and QuaS FLC are discussed with respect to mutagen-induced and spontaneous cellular ouabain resistance. In addition, the role of altered ion transport mechanisms is considered for induced erythroid differentiation.

Evaluation of nongenotoxic and genotoxic factors modulating the frequency of micronucleated erythrocytes in the peripheral blood of mice.

The hematological micronucleus test is regarded as an indicator of the clastogenic effect of chemicals and acute cytogenetic damage. The test can be carried out in red blood cells of the bone marrow and of the spleen, as well as in peripheral erythrocytes. We have determined the precise background values of micronucleated red blood cells for the peripheral blood of BALB/c, DBA/2, and NMRI mice. Bleeding, phenylhydrazine-induced hemolysis, and splenectomy generated an increase of micronucleated erythrocytes in the peripheral blood of mice. Our data thus demonstrate that such factors should be taken into consideration when the micronucleus test is used for screening the genotoxic potential of chemicals. Furthermore, the micronucleus-inducing effect of cyclophosphamide was studied in normal and splenectomized mice and, in addition, a comparison of the sensitivity of the micronucleus test was carried out in peripheral blood and bone marrow after cyclophosphamide treatment. Our data demonstrate that the kinetics of micronucleus formation were similar in normal and in splenectomized mice in which the micronucleus levels had returned to normal. The comparison of micronucleus formation in bone marrow and peripheral blood after cyclophosphamide treatment revealed the generation of similar quantities of micronucleated red blood cells in both tissues. The physiological mechanisms of micronucleus formation and removal and the potential role of chemically induced spleen damage during this process are discussed; the usefulness of the peripheral micronucleus test as a simple, rapid, and animal-saving modification of the standard bone marrow test is evaluated.

Induction of erythroid differentiation by the anthracycline antitumor antibiotics, aclacinomycin A, musettamycin and marcellomycin.

The oligosaccharide anthracycline aclacinomycin A is of considerable clinical interest since, in comparison to adriamycin and daunomycin, the compound exhibits reduced cardiac toxicity and is devoid of mutagenicity/carcinogenicity. In addition, induction of differentiation in the human promyelocytic leukemia cell line HL 60 and possibly in one case of human acute myeloblastic leukemia by aclacinomycin A has been observed. Our data indicate that aclacinomycin A and related compounds, such as musettamycin and marcellomycin, are extremely potent inducers of differentiation in mouse (Friend leukemia cells, clone F4-6), rat (rat erythroleukemia, clone D5A1), and human erythroid cell lines (K 562 cell line) and that the relative inductive potency of marcellomycin and musettamycin, in general, is higher than that of aclacinomycin A. This potency difference may be due to the presence of a Cl-hydroxyl group in the aglycone of the marcellomycin and musettamycin molecule. Thus, oligosaccharide anthracyclines are a new class of inducers of erythroid differentiation. The high potency of these compounds, the possibility to study structure-activity relationships relative to their inductive potency and the fact that they induce erythroid differentiation in cells of different species as well as granulocytic differentiation in human cells should facilitate the study of basic mechanisms of hemopoietic differentiation. In addition, the therapeutical significance of these anthracycline effects should be investigated by studying, comparatively, the differentiation-inducing and antitumor effects of these compounds in primary leukemic cell cultures from patients.

Evaluation of nongenotoxic and genotoxic factors modulating the frequency of micronucleated erythrocytes in the peripheral blood of mice.

The hematological micronucleus test is regarded as an indicator of the clastogenic effect of chemicals and acute cytogenetic damage. The test can be carried out in red blood cells of the bone marrow and of the spleen, as well as in peripheral erythrocytes. We have determined the precise background values of micronucleated red blood cells for the peripheral blood of BALB/c, DBA/2, and NMRI mice. Bleeding, phenylhydrazine-induced hemolysis, and splenectomy generated an increase of micronucleated erythrocytes in the peripheral blood of mice. Our data thus demonstrate that such factors should be taken into consideration when the micronucleus test is used for screening the genotoxic potential of chemicals. Furthermore, the micronucleus-inducing effect of cyclophosphamide was studied in normal and splenectomized mice and, in addition, a comparison of the sensitivity of the micronucleus test was carried out in peripheral blood and bone marrow after cyclophosphamide treatment. Our data demonstrate that the kinetics of micronucleus formation were similar in normal and in splenectomized mice in which the micronucleus levels had returned to normal. The comparison of micronucleus formation in bone marrow and peripheral blood after cyclophosphamide treatment revealed the generation of similar quantities of micronucleated red blood cells in both tissues. The physiological mechanisms of micronucleus formation and removal and the potential role of chemically induced spleen damage during this process are discussed; the usefulness of the peripheral micronucleus test as a simple, rapid, and animal-saving modification of the standard bone marrow test is evaluated.

Formation of DNA-adducts and induction of DNA-crosslinks and chromosomal aberrations by the new potent anthracycline antitumor antibiotics: morpholinodaunomycin, cyanomorpholinodaunomycin and cyanomorpholinoadriamycin.

The DNA-interaction of three newly developed semisynthetic anthracyclines with high antitumor potency MoDNM3, CNMoDNM, and CNMoADM, was investigated. When primary rat hepatocytes were incubated with tritium labeled MoDNM and CNMoDNM and their DNA was purified and enzymatically hydrolized, the formation of DNA-adducts could be demonstrated by the HPLC chromatography of the resulting mononucleoside mixtures. The parent compound, daunomycin (DNM), also formed covalent adducts with hepatocyte DNA, but to a lesser extent. These findings correlate well with earlier observations that MoDNM and CNMoDNM are potent inducers of DNA-repair in primary rat hepatocytes, whereas DNM is only weakly active in this regard. Alkaline elution studies were performed with L 1210 mouse leukemia cells and V79 Chinese hamster fibroblasts. The cyanomorpholinyl derivatives showed dose-dependent DNA crosslinking activities in both cell lines at concentrations greater than or equal to 5 nMol/l. The formation of crosslinks began a few minutes after treatment of the cells and reached a maximum after 1 hr. In contrast, MoDNM, at concentrations of up to 10 muMol/l, had only a limited capacity to induce single strand breaks in L 1210 cells but did not induce DNA-crosslinks. In addition, chromosomal aberrations (chromatid breaks and translocations) were induced by the treatment of Friend and L 1210 leukemia cells with CNMoADM at concentrations between 0.07-0.6 nMol/l. At higher doses, chromosome clumping was observed. These results indicate that the high capacity of MoDNM, CNMoDNM and CNMoADM to induce DNA repair in primary rat hepatocytes is due to the formation of covalent adducts with DNA. The cyanomorpholino compounds have alkylating capacities also in cell lines such as L 1210 and V79, whereas MoDNM requires rat hepatocytes for activation. The ready formation of DNA crosslinks and chromosomal aberrations could be responsible for the high cytotoxicity of these compounds.

DNA-mediated gene transfer in Friend leukemia cells by cotransfection of simian virus 40 DNA with herpes simplex virus thymidine kinase DNA.

Thymidine kinase-negative Friend leukemia cells were cotransfected with simian virus 40 (SV40) DNA and thymidine kinase gene DNA of herpes simplex virus type 1. The transfected thymidine kinase-positive cells were selected in HAT medium, and SV40 T-antigen expression was observed over many months in cells cultured under selective conditions, and after adaptation to normal growth medium under nonselective conditions. It was shown by Southern blot hybridization that SV40 DNA was integrated in multiple copies in the chromosomal DNA of several clones. All SV40 DNA-containing Friend leukemia cell clones analyzed were able to undergo induced erythroid differentiation. Induced cultures still expressed SV40 T-antigen to the same extent that untreated control cultures did.

Co-expression of mouse and rat haemoglobins in interspecific hybrids of mouse and at erythroleukemia cells.

A modified technique for cell fusion with lysolecithin-lipid emulsions was used to generate hybrid erythroleukemia cell lines from Friend leukemia mouse cells (FLC) and chemically transformed rat erythroleukemia cells. Chromosome analysis of the hybrid cells showed the presence of both parental genomes even after long culture periods. The hybrids were still able to undergo erythroid differentiation after dimethylsulphoxide (DMSO) stimulation. Analysis of the globin chains from the DMSO-stimulated cells showed that both the rat and the mouse erythroid phenotypes were expressed. This demonstrates the compatibility of the regulatory genetic elements for the control of erythroid differentiation in cell hybrids of erythroleukemic populations from different species.

Normal and Friend virus specific cell compartments in Friend leukemia characterized by their sensitivity to actinomycin D in vivo.

DBA/2 mice were infected with the polycythemia inducing Friend Virus (F-MuLV-P) and treated with different doses of Actinomycin D (Act D) when the whole erythroid cell system, as measured by the CFU-E technique with and without addition of erythropoietin (Ep), had been transformed into Ep-independence. During and after this therapy the different stem cell pools CFU-S, CFU-C, BFU-E and CFU-E (with and without Ep) were studied and their sensitivity to Act D in bone marrow and spleen was compared to that of normal mice, recently published by other authors. There seemed to be no difference in the Act D sensitivity between normal erythropoiesis and Ep-independent erythropoiesis caused by F-MuLV-P. Furthermore a cell called ICPC (infectious centers producing cell) was studied. This cell system, detected by spleen colony formation due to high local virus production in an unirradiated host, proved to be Act D sensitive in the spleen but not in the marrow. When the erythroid cell system regenerated after Act D chemotherapy, all erythroid colony growth was Ep-independent. This means that Act D did not induce normal erythropoiesis as seen with hydroxyurea treatment.

Characterization of early leukemic cells in spleen and bone marrow of Friend virus infected mice.

Nonidentity of leukemic cell populations of DBA/w mice (TCFU and CRVEI) early after Friend Visus infection has been demonstrated for spleen by different growth kinetics of these cell populations during leukemogenesis and for spleen and bone marrow of DBA/w mice by the velocity sedimentation technique. In addition the velocity sedimentation data indicate a heterogeneity of the TCFU population. Stem cell analysis of TCFU and CFUS derived spleen colonies showed that TCFU colonies contain significantly more CFUEI than the surrounding tissue. The erythroid nature of TCFU colonies is confirmed by the almost complete absence of CFUC from these colonies as compared to CFUS derived spleen colonies.