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K T Weber

Publications and source records attributed to K T Weber.

At least 55 records · Page 3Linked to original sources
PubMed1998

Inhibition of tissue repair by spironolactone: role of mineralocorticoids in fibrous tissue formation.

Mineralocorticoids have been implicated in promoting fibrous tissue formation in various organs. In the present study, we sought to address the potential contribution of mineralocorticoids to fibrous tissue formation using a skin pouch model which has proved valuable for the analysis of inflammatory and wound healing responses. Skin pouches were induced in rats by administration of a phorbol ester, croton oil (0.5 ml of a 1% solution). After 2 weeks, rats were killed and intact pouch tissue collected. Pouch weights of control and aldosterone-treated (0.75 microg/h via osmotic minipump) rats were similar (3.33 +/- 0.44 g vs. 3.70 +/- 0.28 g respectively). However, pouch weights were reduced by more than 50% in spironolactone-treated (25 mg/day powdered in food) animals (1.62 +/- 0.22 g and 1.27 +/- 0.23 g respectively in aldosterone and spironolactone alone groups). To ascertain the effects of different treatments on collagen accumulation, hydroxyproline concentration was measured. Compared with controls, hydroxyproline concentration was significantly reduced following spironolactone treatment (17.1 +/- 0.08 vs. 7.5 +/- 2.0 microg/mg dry wt, respectively, p < 0.01). This response to spironolactone was negated by coadministration of aldosterone (hydroxyproline concentration was 18.6 +/- 2.1 microg/mg dry wt). Following bilateral adrenalectomy, spironolactone reduced pouch weight and hydroxyproline concentration, which was not the case for adrenalectomy alone. Two week aldosterone administration in uninephrectomized rats on high salt diet was deemed ineffective in modulating pouch development (pouch wet wts were 3.48 +/- 0.4 g vs. 3.00 +/- 0.19 g in controls and aldosterone-treated rats, respectively). Mineralocorticoid receptor expression in pouch tissue was demonstrated by RT/PCR. Furthermore, NADP+-dependent 11beta-hydroxysteroid dehydrogenase 1 (11beta-HSD1) activity was detected in pouch tissue, together with lower levels of NAD+-dependent 11beta-HSD2. Spironolactone (p < 0.05) significantly reduced 11beta-HSD1 activity compared with controls. Thus, fibrous tissue possesses requisite components of MC action, and antagonism of mineralocorticoid receptors by spironolactone attenuates its formation. Pouch formation is under the influence of circulating MC and, we would like to propose, is also mediated through corticosteroids generated de novo at the site of tissue repair.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1998

Cardiac remodelling by fibrous tissue: role of local factors and circulating hormones.

Following myocardial infarction (MI), extensive fibrosis appears at and remote to the MI and is associated with diastolic dysfunction. Both circulating and tissue hormones contribute to the adverse structural remodelling of the myocardium and thereby influence the progressive nature of heart failure. In this review, factors contributing to the appearance of fibrous tissue will be considered, with special emphasis on the role of peptides produced within the diseased myocardium and on the circulating hormones of the renin-angiotensin-aldosterone system.

Aldosterone↗
PubMed1997

Antiparallel polypurine phosphorothioate oligonucleotides form stable triplexes with the rat alpha1(I) collagen gene promoter and inhibit transcription in cultured rat fibroblasts.

The rat alpha1(I) collagen promoter contains a unique polypurine-polypyrimidine sequence between -141 and -200 upstream of the transcription start site. The polypurine sequence from -171 to -200 (C2) is on the coding strand and the adjacent polypurine sequence from -141 to -170 (C1) is on the non-coding strand. Earlier we demonstrated triplex formation with a polypurine 30 nt parallel triplex-forming oligonucleotide (TFO) corresponding to C1 and inhibition of transcriptional activity of the rat alpha1(I) collagen promoter. In the present work we have tested triplex-forming abilities of shorter (18 nt) purine and pyrimidine TFOs in parallel and antiparallel orientation to the C1 purine sequence. Our results show that purine antiparallel TFOs formed triplexes with the highest binding affinities, while pyrimidine oligodeoxyribonucleotides (ODNs) did not show appreciable binding. Phosphorothioate modification of purine TFOs did not significantly reduce binding affinity. We also demonstrate that preformed triplexes are quite stable when precipitated with ethanol and resuspended in water. Further analysis was carried out using two purine phosphorothioate antiparallel TFOs, 158 APS and 164 APS, designed to bind to the promoter region from -141 to -158 and -147 to -164, respectively, which were found to form triplexes even under physiological conditions. DNase I footprinting experiments showed the ability of these TFOs to protect target sequences in the promoter region; both purine sequences (C1 and C2) were protected in the case of 158 APS. Transfection experiments using preformed triplexes with a reporter plasmid containing the collagen promoter sequence showed significant inhibition of transcription when compared with a control phosphorothioate ODN. The effect of 164 APS was greater than that of 158 APS. These results indicate that this triplex strategy could be used in the down-regulation of collagen synthesis in cultured cells and offer the potential to control fibrosis in vivo.

Animals↗
PubMed1997

What can we learn from exercise testing beyond the detection of myocardial ischemia?

Noninvasive cardiopulmonary exercise (CPX) testing has proven useful in the assessment of heart and lung disease, including cardiac and ventilatory reserves. CPX includes the monitoring of respiratory gas exchange, O2 uptake the CO2 production, together with minute ventilation and its components--tidal volume and respiratory rate--together with surveillance of electrocardiography and blood pressure during supervised, incremental exercise. Exercise responses in anaerobic threshold and/or maximal O2 uptake are used to grade functional capacity objectively and to predict cardiac reserve (exercise cardiac output), which grades the severity of chronic cardiac or circulatory failure. CPX also serves to distinguish primary cardiac from ventilatory-based exertional dyspnea.

Adult↗
PubMed1997

Cultured myofibroblasts generate angiotensin peptides de novo.

Scar tissue found at the site of myocardial infarction (MI) contains phenotypically transformed fibroblast-like cells termed myofibroblasts (myoFb). In injured cardiac tissue, autoradiography and immunolabeling have localized high density angiotensin (Ang) converting enzyme (ACE) and Ang II receptor binding to these cells, suggesting that they may regulate local concentrations of Ang II and transduce signals at this site. Ang II is known to modulate type I collagen gene expression of fibroblasts and myoFb, and to promote fibrous tissue contraction, each of which may contribute to tissue repair. It is unknown whether myoFb themselves generate Ang peptides de novo via expression of angiotensinogen (Ao), an aspartyl protease needed to convert Ao to Ang I, and ACE. We therefore isolated and cultured myoFb from 4-week-old scar tissue of the adult rat left ventricle with transmural MI. In cultured myoFb we found: (a) immunoreactive membrane-bound ACE, cytosolic cathepsin D (Cat-D), and AT, receptors by immunofluorescence and confocal microscopy, (b) mRNA expression for Ao, ACE, and Cat-D, but not renin, by reverse transcriptase-polymerase chain reaction, (c) production of Ang I and II in serum-free culture media; (d) absence of renin activity; (e) a time-dependent conversion of Ao to Ang I by myoFb cytosol, which was inhibited by pepstatin A, but not by renin inhibitor; and (f) significant increase in Ang II production (P < 0.05) by exogenous Ao and Ang I (10 nM), which was significantly blocked by lisinopril (0.1 microM: P < 0.05). Thus, cultured myoFb express requisite components and are able to generate Ang I and II de novo. In an autocrine and/or paracrine manner, Ang II may regulate myoFb collagen turnover and fibrous tissue contraction.

Angiotensin I↗
PubMed1997

Fibrous tissue and angiotensin II.

Myofibroblasts (myoFb) are cells responsible for fibrous tissue formation in injured systemic organs such as the heart. Cultured myoFb, obtained from rat cardiac scar tissue, express genes that encode components requisite for angiotensin (Ang) II generation, which in turn regulates myoFb collagen turnover in an autocrine/paracrine manner. In this study, we tested the hypothesis that these wound-healing fibroblast-like cells and locally generated Ang II are involved in other repairing tissue. To test this hypothesis, we used a granuloma pouch model, where a subcutaneous air sac is created followed by injection of croton oil. Pouch tissue was collected at days 4, 7, 14 and 21. The presence of myoFb was determined by immunohistochemical alpha-smooth muscle actin (alpha-SMA) labeling and collagen accumulation by picrosirius red staining. Angiotensin converting enzyme (ACE) and Ang II receptor binding were detected by in vitro quantitative autoradiography using 125I-351A and 125I[Sar1, Ile8]Ang II, respectively, while Ang II receptor subtype was defined by displacement studies using either an AT1 (losartan) or AT2 (PD123177) receptor antagonist. Cells expressing ACE were determined by immunohistochemistry. Ang II content in pouch tissue was measured by radioimmunoassay following HPLC separation while its capacity to generate Ang II was assessed in tissue bath, with and without exogenous Ang I or lisinopril, an ACE inhibitor. Collagen accumulation in pouch tissue was examined by determining hydroxyproline content in response to lisinopril, AT1 or AT2 receptor antagonists (losartan or PD123177). In pouch tissue, we found: (1) myoFb at day 4 which became more extensive at days 7, 14 and 21; (2) morphologic evidence of collagen deposition evident at day 4, which gradually became more extensive thereafter; (3) ACE and Ang II receptor binding was evident at day 4 and remained invariant on days 7, 14 and 21; (4) the predominant Ang II receptor subtype expressed was AT1; (5) myoFb express ACE and AT1 receptors; (6) picogram quantities of Ang II (per g tissue) was evident on days 7, 14 and 21; and (7) Ang II was generated from Ang I substrate. Lisinopril and losartan, but not PD123177, significantly attenuated pouch weight and accumulation of collagen. Thus, in this model of cutaneous repair, the appearance of myoFb is associated with Ang II generation that regulates fibrogenesis by AT1 receptor binding. Signals involved in the appearance of myoFb remain uncertain. Further studies are required to address the regulation of Ang II generation in pouch tissue of the rat.

Actins↗