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Biomedical subjects

M Böhm

Publications and source records attributed to M Böhm.

At least 271 records · Page 15Linked to original sources
PubMed1996

The hypertensive Ren-2 transgenic rat TGR (mREN2)27 in hypertension research. Characteristics and functional aspects.

Primary human hypertension is a polygenic disorder. It is the prevalent cause of cardiovascular disease leading to cardiac failure, stroke, chronic renal failure and, ultimately to death. Several genes are involved in cardiovascular control mechanisms and their genetics are complex. Experimental models which are well defined are needed to clarify the role of individual genes. The generation of the hypertensive transgenic rat line TGR (mREN2)27 bearing the murine Ren-2 gene cloned from the DBA/2J mouse strain provides a monogenic model of hypertension in which the genetic basis (the additional renin gene) is known. These rats develop severe hypertension, which reaches 200 mm Hg and higher at 8 weeks of age in the heterozygous animal. Homozygous rats develop even higher blood pressures than heterozygous animals, which is paralleled by a higher mortality rate in homozygous rats. Animals develop pathomorphologic alterations which are characteristic for systemic hypertension. The transgenic rats are characterized by unchanged or even suppressed concentrations of active renin, angiotensin I (ANG I), ANG II, and angiotensinogen compared to transgene-negative littermates. In contrast, plasma levels of inactive renin (prorenin) are much higher in TGR (mREN)27 rats than in control animals. In the kidneys, renin is suppressed, probably mediated through negative feedback inhibition, in other tissues, especially in the adrenal gland, murine Ren-2 mRNA is expressed at very high levels. The cascade of pathophysiologic events which finally lead to hypertension is not fully understood in this rat model. Treatment with ACE inhibitors or angiotensin II receptor antagonists such as losartan is extremely efficient, which could mean that hypertension in this model is mediated through ANG II. Since the the renin-angiotensin system (RAS) in the kidneys is suppressed, other ANG II generating sites must be considered. This favors the concept of extrarenal RASs in this model.

Animals↗
PubMed1996

Heterotrimeric G proteins in heart disease.

Heterotrimeric G proteins couple many types of cell surface receptors to intracellular effectors such as enzymes or ion channels. In the mammalian heart, G protein-mediated signalling pathways are involved in the regulation of contractile force, heart rate, conduction velocity, and relaxation. In the first part of this review we summarize some important structural and functional features of receptors, G proteins, and effectors with special focus on the heart. In the second part, we review the current knowledge about alterations of G protein-mediated signalling in heart disease such as myocardial hypertrophy and heart failure.

Animals↗
PubMed1996

Growth regulatory proteins that repress differentiation markers in melanocytes also downregulate the transcription factor microphthalmia.

Expression of basic fibroblast growth factor cDNA or dominantly acting oncogenes, e.g., E1A, in immortalized mouse melanocytes leads to autonomous growth in vitro, depigmentation, and in the case of the oncogenes, tumorigenesis. Because downregulation of pigmentation is a common event in human metastatic melanoma cells grown in culture, we determined the molecular basis of depigmentation in a mouse melanocyte model system. We tested the effect of E1A mutants deficient in their ability to neutralize several regulatory proteins and determined changes in melanogenic gene expression. We identified Microphthalmia as the affected, downregulated transcription factor in melanocytes rendered amelanotic by E1A, basic fibroblast growth factor, or the oncogenes ras or neu, and in an amelanotic cell variant of Cloudman S91 mouse melanoma. Against expectations, sequestration of p300, a transcriptional adaptor that mediates responses to cyclic adenosine monophosphate, was not required for the full transforming effects of E1A. Our results suggest that in addition to controlling tyrosinase (albino locus) and tyrosinase-related protein 1 (TR-P1/gp75/brown locus), both known to possess the DNA consensus site for binding the Microphthalmia protein, this transcription factor also controls other melanocyte-specific genes such as pink-eyed dilution and Pmel 17 (silver), but not tyrosinase-related protein 2 (slaty locus). Furthermore, these findings show that microphthalmia is downregulated not only by experimentally introduced dominantly acting oncogenes but also by the aberrant expression of basic fibroblast growth factor and by spontaneous tumorigenic transformation.

Animals↗
PubMed1996

Investigation of the negative inotropic effects of 17 beta-oestradiol in human isolated myocardial tissues.

1. The aim of the present study was to evaluate the effects of 17 beta-oestradiol in human myocardium. The effects of 17 beta-oestradiol, progesterone and testosterone on force of contraction were investigated in electrically driven isolated atrial trabeculae and ventricular papillary muscles from human hearts in the presence and absence of Bay K 8644, a calcium channel agonist. In addition, the effects of 17 beta-oestradiol, progesterone and testosterone on binding of [3H]-PN 200 110 were assessed in membranes prepared from human ventricular myocardium. 2. 17 beta-Oestradiol elicited a negative inotropic effect in atrial (IC50: 7.1 mumol 1(-1), confidence interval 3.8 to 13.4, n = 3) and ventricular preparations (IC50: 4.6 mumol 1(-1)), confidence interval 2.2 to 9.4, n = 3) as compared with solvent controls. There was no significant difference (P > 0.05) of IC50 values in the absence and presence of isoprenaline (0.0 mumol 1(-1)) in atrial (IC50: 10.8 mumol 1(-1), confidence interval 9.1 to 12.9, n = 6) and ventricular preparations (IC50: 9.4 mumol 1(-1), confidence interval 7.3 to 11.9, n = 8). 3. 17 beta-Oestradiol at 30 mumol 1(-1) induced a significant rightward shift of the concentration-response curves for the positive inotropic effect of Bay K 8644 in atrial preparations (EC50: 0.13 mumol 1(-1), confidence interval 0.08 to 0.19, n = 6; EC50 with 17 beta-oestradiol: 0.58 mumol 1(-1), confidence interval 0.33 to 0.83, n = 6, P < 0.05) and ventricular preparations (EC50: 0.07 mumol 1(-1), confidence interval 0.04 to 0.11, n = 8; EC50 with 17 beta-oestradiol: 0.3 mumol 1(-1), confidence interval 0.18 to 0.49, n = 8, P < 0.05). Testosterone, progesterone at 30 mumol 1(-1) and the solvent control had no significant effect on the concentration-response curves to Bay K 8644. 4. In membranes prepared from human ventricular myocardium the effect of 17 beta-oestradiol on binding of [3H]-PN 200 110, an antagonist at the 1,4 dihydropyridine binding site, was not different from that observed with progesterone, testosterone or solvent controls. 5. In myocardial membranes no specific oestrogen receptors were demonstrated by [3H]-oestradiol binding studies. 6. Thus, the calcium antagonistic property of 17 beta-oestradiol cannot be attributed to a direct interaction with 1, 4 dihydropyridine binding sites.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1996

Interleukin-7. Biology and implications for dermatology.

In recent years, it has become apparent that IL-7, originally characterized as a growth factor for pre-B lymphocytes, also has important implications for the skin. Keratinocytes have been shown to produce IL-7. which in turn can elicit a variety of biological responses on several cell types residing in the skin. IL-7 has been demonstrated to augment the cytolytic activity of cytotoxic T cells (CTL) and natural killer (NK) cells against various neoplastic targets including melanoma cells. Proliferation and long-term survival of murine dendritic epidermal T lymphocytes (DETC) in vitro is supported by IL-7. IL-7 also induces secretion of inflammatory cytokines by monocytes/macrophages and renders these cells to become tumoricidal against melanoma cells. Normal and malignant melanocytes respond to IL-7 with increased expression of intercellular adhesion molecule (ICAM-1). In addition, IL-7 has been shown to act as growth factor for Sezary cells, suggesting a role of keratinocyte-derived IL-7 in the pathogenesis of cutaneous T cell lymphoma. Because of the potent in vitro immunomodulatory effects of IL-7 which have been confirmed in mouse tumor models, IL-7 may become a valuable additional agent to immunotherapeutical regimens currently studied in patients with advanced melanoma. This review summarizes our present knowledge about the molecular and immunological properties of IL7 with emphasis on the effects of that cytokine within the cutaneous compartment and the potential clinical utility in dermatology.

Animals↗
PubMed1996

Physiological characterization of the hypertensive transgenic rat TGR(mREN2)27.

Transgenic techniques represent powerful tools for the study of gene-related mechanisms of diseases such as hypertension, which results from a complex interaction between genetic and environmental factors. The renin-angiotensin system, a biochemical cascade in which renin functions as the key enzyme in the formation of the effector peptide angiotensin II, plays a major role in the regulation of blood pressure. The renin gene, therefore, represents an important candidate gene for hypertension. Because rats are more suited than mice for a number of experimental settings often employed in cardiovascular research, we modified the transgenic technique to generate the transgenic rat strain TGR(mREN2)27 harboring the murine Ren-2 gene. These transgenic rats develop fulminant hypertension at an early age despite low levels of renin in plasma and kidney. In addition, high expression of the transgene in a number of extrarenal tissues is associated with increased local formation of angiotensin II. Thus the TGR(mREN2)27 rat represents a model of hypertension with a defined genetic background. Studies on the transgenic rat may not only provide new insights into pathophysiological mechanisms of hypertension in this animal model but also offer the unique possibility to investigate the function and regulation of renin-angiotensin systems in extrarenal tissues. The aim of this review is to compile the knowledge that has been accumulated to date on this transgenic rat and to discuss possible mechanisms responsible for its hypertensive phenotype.

Animals↗
PubMed1996

Permanent inhibition of angiotensinogen synthesis by antisense RNA expression.

The renin-angiotensin system plays a pivotal role in blood pressure regulation. Recent molecular biological findings led to the new concept that in addition to the classic endocrine system, local tissue systems may also play an important role in cardiovascular diseases such as hypertension. In particular, the brain renin-angiotensin system was shown to influence the central control of blood pressure and is thought to contribute to the hypertensive phenotype of genetically hypertensive rat models. To identify the physiological role of these local systems, we established an antisense strategy to downregulate the expression of the precursor hormone angiotensinogen (AOGEN) in cell culture, which can also be used to establish transgenic rat lines. Plasmids encoding an RNA sequence complementary to the rat AOGEN mRNA under control of different viral and tissue-specific promoters were constructed and transfected into an AOGEN-expressing cell line. A competitive reverse transcription-polymerase chain reaction method was established for the quantification of AOGEN mRNA. Depending on the level of antisense RNA, the expression of the AOGEN gene was reduced down to 22% of control levels. Furthermore, the secretion of AOGEN protein was totally abolished. These results clearly demonstrate that the antisense constructs used are functional in reducing the AOGEN gene expression in vivo and can be used for the production of transgenic rats.

Angiotensinogen↗
PubMed1996

Microsatellite instability and loss of heterozygosity at the hMLH1 locus on chromosome 3p21 occur in a subset of nonsmall cell lung carcinomas.

Microsatellite alterations observed in tumor specimens may reflect genomic instability due to defective mismatch repair genes. To investigate whether this occurs in human nonsmall cell lung carcinomas we have analyzed microsatellite instability at 5 marker loci and loss of heterozygosity (LOH) at the hMLH1 locus on chromosome 3p21 using the polymerase chain reaction. Of a total of 49 nonsmall cell lung carcinomas examined, 43% (13 of 30 informative cases) showed LOH at 3p21 and 29% (14 of 49) exhibited microsatellite instability at one or multiple loci. LOH of the mismatch repair gene hMLH1 at 3p21 occurred in 82% (9 of 11 informative cases) of the tumors with microsatellite instability. This suggests that defects in the mismatch repair gene hMLH1 at 3p21 may be involved in microsatellite instability and tumorigenesis of a subset of nonsmall cell lung carcinomas. However, in those nonsmall cell lung carcinomas without microsatellite instability LOH at 3p21 probably involved another tumor suppressor gene(s) in this chromosomal region.

Carcinoma, Non-Small-Cell Lung↗
PubMed1996

Enantioselective inotropic actions of the Na+-channel activators BDF 9148, BDF 9196 and BDF 9167 in human failing and nonfailing myocardium.

Our study investigated the inotropic effect of the novel Na+-channel activator BDF 9148 and its enantiomeres [S(-)BDF 9169, R(+)BDF 9167] in human failing [New York Heart Association Class (NYHA IV) heart transplants, n = 15] and nonfailing myocardium (NF, donor hearts, n = 5). We studied the effect of BDF 9148 (BDF, 0.03-10 micromol/liter) and of its enantiomeres [S(-) BDF 9196; R(+)BDF 9167] on isometric force of contraction (1 Hz) as well as on the force-frequency-relationship (0.5-3 Hz) in electrically driven (37 degrees C) left ventricular papillary muscle strips, BDF and S-BDF, but not R-BDF, increased force of contraction in a dose-dependent manner in NYHA IV and NF. The effectiveness of BDF, S-BDF and Ca2+ (15 mmol/liter) to increase force of contraction was similar in human nonfailing and failing myocardium. The potency of BDF and S-BDF to increase force of contraction was significantly higher in NYHA IV compared to NF. Carbachol (1 mmol/liter) did not affect the positive inotropic response of the studied compounds. In the presence of 3 micromol/liter BDF or S-BDF force of contraction increased after an increase in stimulation frequency only from 0.5 to 1 Hz in NYHA IV and human nonfailing myocardium. At frequencies above 1 Hz the force-frequency-relationship was negative in human nonfailing myocardium and NYHA IV in the presence of high concentrations of BDF or S-BDF. These results suggest that the racemic Na+-channel activator BDF 9148 and the S(-) BDF-enantiomere, but not the R(+) BDF-enantiomere, are effective to increase force development maximally in NYHA IV and in nonfailing myocardium. Human failing myocardium exerts an enhanced sensitivity toward the Na+-channel activator BDF 9148 and its S(-) enantiomere to increase force of contraction when compared to nonfailing tissue. As Na+-channel activators increase force in a frequency-dependent mode of action the force-frequency-relationship may depend on the intracellular Ca2+- and Na+- homeostasis.

Azetidines↗
PubMed1996

[Altered calcium homeostasis in chronic heart failure].

Intracellular calcium homoeostasis is greatly altered in heart failure. This does not seem to be due to altered calcium influx through L-type calcium channels but rather due to altered calcium uptake mechanisms of the sarcoplasmic reticulum. Recently, a negative force-frequency behaviour of the human myocardium has been detected in hearts from patients with severe heart failure. In the myocardium from these patients, SR-Ca(2+)-ATPase activity was decreased. The same defect has been reported in human isolated cardiac myocytes. A disturbed calcium release from the SR may also contribute to this finding of the inverse force-frequency-relationship in the failing myocardium. The altered intracellular calcium handling is connected with the diastolic and systolic failure of the myocardium. Mg++ and Na(+)-channel modulators are able to restore the positive force-frequency-relationship even in severely failing myocardium.

Calcium↗
PubMed1996

[Therapy of chronic heart failure with beta-receptor blockers].

The elevated plasma norepinephrine concentrations closely correlate to the poor prognosis in heart failure. Inhibition of myocardial norepinephrine effects on the heart by beta-blocker treatment are reported to improve left ventricular ejection fraction and to a lesser extent exercise tolerance. The mechanisms are a restoration of beta-adrenergic signal transduction, an increase of contractile reserve and a protection from toxic catecholamine effects. Bradycardic effects improve energetic situation of the failing heart and directly reduce neuroendocrine activation (plasma norepinephrine concentrations, renin activity). Randomized studies have shown a good clinical effectiveness with carvedilol, metoprolol, bucindolol, and bisoprolol in combination with cardiac glycosides, diuretics and ACE inhibitors. Improvement of survival has been shown for carvedilol and bisoprolol and possibly for metoprolol in dilated cardiomyopathy. In ischemic cardiomyopathy, carvedilol appears to be effective to improve prognosis. Therapy has to be started at very low concentrations of the beta-blocker and the patients must be followed up closely. The beta-blocker therapy is evidenced on pathophysiological research findings and could prove to be useful as additional component of the standard therapy of heart failure when the issue of improvement of survival is solved by future studies.

Adrenergic beta-Antagonists↗
PubMed1995

Effects of angiotensin II and angiotensin-converting enzyme inhibitors on human myocardium.

Human myocardial angiotensin II receptors and the angiotensin AT1 and AT2 receptor subtypes were characterised using the partial angiotensin II receptor agonist [125I][Sar1,IIe8]angiotensin II and the selective antagonists losartan (2-n-butyl-4-chloro-5-hydroxymethyl-1-[2'((1H-tetrazol-5-yl)biphen yl-4-yl)- methyl]imidazole) and PD 123177 (1-[(4-amino-3-methylphenyl)methyl]-5-(diphenyl-acetyl)- 4,5,6,7-tetrahydro-1H-imidazol[4,5-c]pyridine-6-carboxylic acid). The density of angiotensin II receptors was higher in atrial than in ventricular myocardium. Angiotensin AT2 receptors were predominant in atria and ventricles (80-85% of total angiotensin II receptors). Only in isolated, electrically driven atrial trabeculae but not in ventricular preparations, angiotensin II did produce a concentration-dependent positive inotropic effect, which was antagonized exclusively by the angiotensin AT1 receptor antagonist losartan and which amounted to about 20% of the positive inotropic effect of milrinone and isoprenaline. The application of the angiotensin-converting enzyme inhibitors captopril, enalaprilat and ramiprilat had no inotropic effect in either tissue. It is concluded that angiotensin AT1 receptors exclusively mediate direct positive inotropic effects in atrial myocardium. Since angiotensin-converting enzyme inhibitors do not produce any inotropic effect, tonic regulation of basal force of contraction by angiotensin II does not occur.

Adolescent↗
PubMed1995

Unchanged protein levels of SERCA II and phospholamban but reduced Ca2+ uptake and Ca(2+)-ATPase activity of cardiac sarcoplasmic reticulum from dilated cardiomyopathy patients compared with patients with nonfailing hearts.

BACKGROUND: The aim of the present study was to investigate whether Ca2+ uptake into the sarcoplasmic reticulum (SR) is altered in failing human myocardium resulting from dilated cardiomyopathy. METHODS AND RESULTS: Ca(2+)-ATPase (SERCA II) activity and Ca(2+)-dependent 45Ca2+ uptake (oxalate supported, steady state) in isolated vesicles from the SR (VSR) and in crude membrane preparations (CSR) (free Ca2+, 0.01 to 100 mumol/L) from nonfailing (donor hearts, n = 13) and terminally failing (heart transplants, dilated cardiomyopathy, n = 17) human myocardium were studied. In the same hearts, protein levels (Western blot analysis) and mRNA levels (Northern blot analysis) of SERCA II and phospholamban were measured. Increasing concentrations of Ca2+ were followed by an increased Ca(2+)-ATPase activity and Ca2+ uptake. Ca2+ uptake activity and Ca(2+)-ATPase activity in CSR preparations from failing myocardium were significantly reduced compared with nonfailing hearts (Ca(2+)-ATPase, 163 +/- 8 and 125 +/- 7 nmol ATP/mg protein per minute for nonfailing tissue and failing tissue in New York Heart Association [NYHA] class IV, respectively; Ca2+ uptake, 7.1 +/- 0.8 and 3.5 +/- 0.3 nmol/mg protein per minute in CSR from nonfailing and NYHA class IV hearts, respectively P < .05). In contrast, no significant difference was measured in VSR. In the same preparations (CSR and VSR), both SERCA II and phospholamban levels (Western blot technique with monoclonal antibodies) were unchanged in failing compared with nonfailing tissue. mRNA expression relative to GAPDH mRNA for SERCA IIa and for phospholamban was significantly reduced in failing human myocardium (P < .05). CONCLUSIONS: These findings provide evidence that in failing human myocardium caused by dilated cardiomyopathy, protein levels of SERCA II and phospholamban are unchanged even though mRNA levels for SERCA II and phospholamban and the SERCA II function are reduced compared with nonfailing myocardium.

Adenosine Triphosphatases↗
PubMed1995

Dose-dependent dissociation of ACE-inhibitor effects on blood pressure, cardiac hypertrophy, and beta-adrenergic signal transduction.

BACKGROUND: Dose-dependent effects of ACE inhibitors on blood pressure, cardiac hypertrophy, and beta-adrenergic signal transduction were examined in an animal model with beta-adrenergic desensitization, which has been identified in failing hearts and in hypertensive cardiac hypertrophy. It is unknown whether beneficial ACE-inhibitor effects are due to an unloading of the failing heart or a reduction of neuroendocrine activation with beta-adrenergic resensitization. METHODS AND RESULTS: Low-dose (LD, 1 mg/kg) and high-dose (HD, 25 mg/kg) fosinopril treatment was performed in spontaneously hypertensive rats (SHR) and control (WKY) rats. Myocardial norepinephrine concentrations, adenylyl cyclase activity, beta-adrenergic receptors (radioligand binding), Gs alpha (functional reconstitution), and Gi alpha (pertussis toxin labeling) were determined. Ventricular weights and blood pressures were measured. HD but not LD reduced blood pressure and left ventricular weights in SHR. Isoprenaline- and guanylylim-idodiphosphate-stimulated adenylyl cyclase activities as well as beta 1-adrenergic receptors were reduced in SHR. The catalyst and Gs alpha were unchanged, but Gi alpha and norepinephrine concentrations were increased. Both LD and HD treatments restored beta-adrenergic alteration. CONCLUSIONS: LD treatment with ACE inhibitors restored beta-adrenergic signal transduction defects independently of regression of cardiac hypertrophy. This could contribute to the effects of ACE inhibitors in patients, who are often treated with nonhypotensive doses.

Adenylyl Cyclases↗