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Biomedical subjects

John W Funder

Publications and source records attributed to John W Funder.

At least 37 records · Page 2Linked to original sources
PubMed2004

Eplerenone, but not steroid withdrawal, reverses cardiac fibrosis in deoxycorticosterone/salt-treated rats.

Aldosterone has been thought to act primarily on epithelia to regulate fluid and electrolyte homeostasis. Mineralocorticoid receptors (MR), however, are also expressed in nonepithelial tissues, such as the heart and vascular smooth muscle. Recently, pathophysiological effects of nonepithelial MR activation by aldosterone have been demonstrated in the context of inappropriate mineralocorticoid levels for salt status, including coronary vascular inflammation and cardiac fibrosis. These effects are mostly prevented by the concomitant administration of MR antagonists, but to date, no equivalent studies have determined whether MR blockade can reverse established inflammation and fibrosis. Uninephrectomized rats maintained on 0.9% NaCl solution to drink were treated as follows: group 1 served as controls; group 2 received deoxycorticosterone (DOC; 20 mg/wk) for 4 wk until death, and group 3 received DOC for 8 wk. Group 4 received DOC for 4 wk and no steroid from wk 5-8; group 5 received DOC for 8 wk and eplerenone in their chow during wk 5-8. DOC progressively raised cardiac collagen accumulation at 4 and 8 wk. Rats given DOC for 4 wk and killed at 8 wk showed levels of fibrosis identical to those in animals killed at 4 wk, i.e. persistently elevated above control values. Rats given DOC for 8 wk and eplerenone for the second half of the period showed cardiac collagen levels indistinguishable from control values. Values for inflammatory marker and NAD(P)H oxidase subunit expression in coronary vessels showed a similar pattern of response, with minor variation. Thus, MR antagonists do not only prevent cardiac fibrosis, but also reverse cardiac fibrosis once it is established. In addition, the continuing vascular inflammatory response and fibrosis after DOC withdrawal (group 4) support a role for activation of vascular MR by endogenous glucocorticoids in the context of tissue damage and generation of reactive oxygen species.

Animals↗
PubMed2004

Towards selectively modulating mineralocorticoid receptor function: lessons from other systems.

Although there is clinical utility in blocking mineralocorticoid receptor (MR) action, the usefulness of available MR antagonists is limited because of cross-reactivity with the androgen and progesterone receptors (spironolactone) or possibly by low affinity for MR (eplerenone). MR binds aldosterone and physiologic glucocorticoids, such as cortisol, which both can act as MR agonists in epithelial tissues. However, in preliminary studies aldosterone and cortisol appear to induce different conformations in non-epithelial tissues; in the cardiomyocyte, cortisol usually acts as an MR antagonist, whereas in vascular smooth muscle cortisol mimics aldosterone actions if it can access MR, just as it does in the kidney. Thus, there are needs for improved MR antagonists with higher selectivity and potency and, if possible, for compounds that lock MR into specific desirable conformations. Efforts are underway to modulate selectively the action of many nuclear receptors, and insights from one nuclear receptor may be applicable to others given the similarities in structure and function. We have used traditional approaches aided by X-ray crystallography to obtain several classes of selective ligands that modulate thyroid receptor (TR) action. We describe the properties of these selective TR modulators here, and discuss the possibility that similar approaches to ligand design may yield MR interacting compounds with improved specificity and, possibly, tissue specificity.

Aldosterone↗
PubMed2004

Aldosterone, mineralocorticoid receptors and vascular inflammation.

For the past 50 years, the physiological action of aldosterone was considered to be on epithelial tissues to maintain fluid and electrolyte homeostasis. Recently, a nonepithelial, pathophysiologic, proinflammatory role for aldosterone has been inferred from studies on mineralocorticoid/salt administration, with or without mineralocorticoid receptor (MR) blockade, in experimental animals, and from clinical studies such as RALES and EPHESUS. More recently still, it has become clear that the pathophysiologic trigger for the vascular inflammatory response observed is not necessarily aldosterone per se, but inappropriate activation of vascular wall MR. MR can be inappropriately activated by aldosterone in the context of an inappropriate salt status, or by glucocorticoids in the context of tissue damage. The studies supporting this latter conclusion, and the novel mechanisms proposed to support this concept, are details in the text to follow.

Aldosterone↗
PubMed2004

Dehydroepiandrosterone increases endothelial cell proliferation in vitro and improves endothelial function in vivo by mechanisms independent of androgen and estrogen receptors.

Dehydroepiandrosterone (DHEA) may be beneficial in cardiovascular health, but mechanisms of DHEA action in the cardiovascular system are unclear. We have therefore 1) determined DHEA effects on the proliferation of cultured endothelial cells (EC), 2) compared effects of DHEA with estradiol (E) and testosterone (T), and 3) examined DHEA effects on subcellular messengers. We have in addition examined effects of DHEA (100 mg/d, 3 months) in 36 healthy postmenopausal women on blood pressure, lipids, and endothelial function, assessed noninvasively in large vessels by flow-mediated dilation of the brachial artery during reactive hyperemia, and in small vessels by laser Doppler velocimetry with iontophoresis of acetylcholine. DHEA, E, and T all increased EC proliferation; the effect of E was abolished by the estrogen receptor antagonist ICI 182,780, and that of T was abolished by the androgen receptor antagonist flutamide; neither blocked the effect of DHEA. In vitro, DHEA increased EC expression of endothelial nitric oxide synthase and activity of extracellular signal-regulated kinase 1/2. In vivo, DHEA increased flow-mediated dilation and laser Doppler velocimetry and reduced total plasma cholesterol. Thus, DHEA increases EC proliferation in vitro by mechanism(s) independently of either androgen receptor or estrogen receptor and in vivo enhances large and small vessel EC function in postmenopausal women.

Adult↗
PubMed2003

Rapid, nongenomic effects of aldosterone in the heart mediated by epsilon protein kinase C.

Aldosterone elevates Na+/K+/2Cl- cotransporter activity in rabbit cardiomyocytes within 15 min, an effect blocked by K-canrenoate and thus putatively mineralocorticoid receptor mediated. Increased cotransporter activity raises intracellular [Na+] sufficient to produce a secondary increase in Na+-K+ pump activity; when this increase in intracellular [Na+] is prevented, a rapid effect of aldosterone to lower pump activity is seen. Addition of transcription inhibitor actinomycin D did not change basal or aldosterone-induced lowered pump activity, indicating a direct, nongenomic action of aldosterone. We examined a possible role for protein kinase C (PKC) in the rapid nongenomic effects of aldosterone. Single ventricular myocytes and pipette solutions containing 10 mm intracellular [Na+] were used in patch clamp studies to measure Na+-K+ pump activity. Aldosterone lowered pump current, an effect abolished by epsilon PKC (epsilonPKC) inhibition but neither alphaPKC nor scrambled epsilonPKC; addition of epsilonPKC activator peptide mimicked the rapid aldosterone effect. In rabbits chronically infused with aldosterone, the lowered pump current in cardiomyocytes was acutely (< or =15 min) restored by epsilonPKC inhibition. These studies show that rapid effects of aldosterone on Na+-K+ pump activity are nongenomic and specifically epsilonPKC mediated; in addition, such effects may be prolonged (7 d) and long-lived ( approximately 4 h isolated cardiomyocyte preparation time). The rapid, prolonged, long-lived effects can be rapidly (< or =15 min) reversed by epsilonPKC blockade, suggesting a hitherto unrecognized complexity of aldosterone action in the heart and perhaps by extension other tissues.

Aldosterone↗
PubMed2003

Transgenic model of aldosterone-driven cardiac hypertrophy and heart failure.

Aldosterone classically promotes unidirectional transepithelial sodium transport, thereby regulating blood volume and blood pressure. Recently, both clinical and experimental studies have suggested additional, direct roles for aldosterone in the cardiovascular system. To evaluate aldosterone activation of cardiomyocyte mineralocorticoid receptors, transgenic mice overexpressing 11beta-hydroxysteroid dehydrogenase type 2 in cardiomyocytes were generated using the mouse alpha-myosin heavy chain promoter. This enzyme converts glucocorticoids to receptor-inactive metabolites, allowing aldosterone occupancy of cardiomyocyte mineralocorticoid receptors. Transgenic mice were normotensive but spontaneously developed cardiac hypertrophy, fibrosis, and heart failure and died prematurely on a normal salt diet. Eplerenone, a selective aldosterone blocker, ameliorated this phenotype. These studies confirm the deleterious consequences of inappropriate activation of cardiomyocyte mineralocorticoid receptors by aldosterone and reveal a tonic inhibitory role of glucocorticoids in preventing such outcomes under physiological conditions. In addition, these data support the hypothesis that aldosterone blockade may provide additional therapeutic benefit in the treatment of heart failure.

11-beta-Hydroxysteroid Dehydrogenase Type 2↗
PubMed2003

Early inflammatory responses in experimental cardiac hypertrophy and fibrosis: effects of 11 beta-hydroxysteroid dehydrogenase inactivation.

In epithelial tissues such as kidney, mineralocorticoid receptors (MR) are protected against glucocorticoid occupancy by the enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) type 2. If the enzyme is congenitally inactive, or blocked by carbenoxolone, physiologic glucocorticoids act as MR agonists in such tissues. In most nonepithelial tissues, including cardiomyocytes, 11 beta HSD2 is expressed at minimal levels; in these tissues physiologic glucocorticoids act as MR antagonists, with the basis for this tissue selectivity currently unknown. Vascular smooth muscle cells (VSMC) express MR and 11 beta HSD1/2, with 11 beta HSD1 reported to show uncharacteristic oxidase activity, so that VSMC thus constitute a potential physiologic aldosterone target tissue. Because mineralocorticoid/salt administration triggers marked inflammatory responses in coronary vasculature, we reasoned that VSMC (like epithelial) MR may be activated by glucocorticoids if the protective enzyme is blocked. We thus gave uninephrectomized rats 0.9% NaCl solution to drink, and deoxycorticosterone (DOC, as a single 20 mg sc dose) or carbenoxolone (CBX, 2.5 mg/d in the drinking solution). Both DOC and CBX increased systolic blood pressure, heart, and kidney weight, and expression of cyclooxygenase 2, ED-1-positive macrophages, and osteopontin, with effects of both DOC and CBX blocked by the selective MR antagonist eplerenone. These findings suggest that local glucocorticoid excess, reflecting lower VSMC 11 beta HSD1/2 activity may mimic systemic mineralocorticoid excess, and play a direct etiologic role in coronary vascular inflammatory responses under circumstances of a high salt intake.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed2003

Mechanism of cortisol/progesterone antagonism in the regulation of 15-hydroxyprostaglandin dehydrogenase activity and messenger ribonucleic acid levels in human chorion and placental trophoblast cells at term.

Prostaglandin dehydrogenase (PGDH) metabolizes prostaglandins (PGs) to render them inactive. We reported previously that cortisol (F) decreases and progesterone (P(4)) maintains PGDH activity/expression in human chorion and placenta. Furthermore, we have shown that F and P(4) compete for regulation of PGDH. We hypothesized that P(4) maintains PGDH activity through interaction with the glucocorticoid receptor (GR) and that elevations in F compete with P(4) at the GR, resulting in a decrease in PGDH at term. By immunohistochemistry and Western blotting analysis, we localized immunoreactive GR and progesterone receptor (PR) to chorion and placental trophoblast cells. We treated chorion and placental trophoblast cells in culture with F, dexamethasone (DEX), beta-methasone, P(4), trilostane (a 3 beta-hydroxysteroid dehydrogenase inhibitor), medroxyprogesterone acetate (MPA), and/or 21-hydroxy-6,19-oxidopregn-4-ene-3,20-dione (21OH-6OP; a GR antagonist). By RIA and Northern blotting analysis, all glucocorticoids (GCs) decreased PGDH activity/expression. Coincubation with 21OH-6OP reversed GC inhibition of PGDH; MPA, but not P(4), treatment stimulated PGDH activity. Trilostane inhibited PGDH activity, and coincubation with P(4) or MPA reversed trilostane inhibition of PGDH. Treatment with trilostane, P(4), 21OH-6OP, or MPA plus 21OH-6OP reversed P(4) and MPA up-regulation of PGDH activity. Our findings suggest that F inhibition and P(4) stimulation of PGDH may be mediated by PR, but also via the GR, in chorion and placenta.

Cells, Cultured↗
PubMed2003

A compound heterozygote case of type II aldosterone synthase deficiency.

An infant with failure to thrive, persistent hyponatremia and episodic vomiting and diarrhea was admitted to hospital at 9 months of age, and the diagnosis of type II aldosterone synthase deficiency was confirmed by plasma and urinary steroid determinations. The entire coding sequence of the aldosterone synthase gene (CYP11B2) was determined (both strands) in the affected infant, an unaffected sibling, and both parents. An exon 3 mutation (C554T, leading to amino acid T185I) was found in the father and both siblings, and an exon 9 mutation (A1492G, leading to T498A) was found in the affected infant and the mother. Expression of the mutant sequences in COS cells showed steroidogenic patterns typical of aldosterone synthase type II deficiency, including very low levels of aldosterone synthesis (< or =0.5% of wild-type enzyme) consistent with the low aldosterone levels in the patient's plasma. Both mutations in this compound heterozygote localize to the beta 3-sheet in the cytochrome P450 enzyme structure, as does the previously characterized R181W mutation. This region of the enzyme is not part of the putative structural core, but mutations to this region suggest that it is important for conferring the unique ability of aldosterone synthase to catalyze efficient oxygenation of the C(18) carbon of steroid substrates.

Alleles↗
PubMed2003

The role of mineralocorticoid receptor antagonists in the treatment of cardiac failure.

In most countries the last two decades have seen a very substantial rise in the prevalence of heart failure, and in a majority of patients hypertension is both an antecedent condition and a contributing cause. Heart failure is also a major cause of hospital admissions; its amelioration and, as far as possible, prevention is therefore important in terms not only of morbidity and premature mortality for the individual patient, but also containment of healthcare costs. Over the past 5 years, mineralocorticoid receptor (MR) antagonists have been used in two major outcome trials (the Randomized Aldactone Evaluation Study [RALES] with spironolactone, and the Eplerenone Post-AMI Heart Failure Efficacy and Survival Study [EPHESUS]), in severe (New York Heart Association class III) and post-myocardial infarct heart failure, respectively. Experimental studies have largely focused, however, on various animal models of hypertension; on the basis of a portfolio of clinical studies on the efficacy of eplerenone, administered either alone and in combination as an antihypertensive agent, the novel MR antagonist was approved by the FDA for the treatment of hypertension, though it has yet to be launched. In this review, the two major outcome studies (RALES, EPHESUS) are discussed in the context of the new biology of aldosterone action. The relevance to heart failure of current experimental studies, largely on vascular protection, will also be discussed.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed2002

Telomerase activation causes vascular smooth muscle cell proliferation in genetic hypertension.

Although abnormal cell growth in arterial vessel walls underpins vascular remodeling in high blood pressure, the molecular basis of the abnormality in hypertension has not been fully defined. Here, we report that in the aorta of spontaneously hypertensive rats, telomerase is selectively activated and telomeres are lengthened, in vivo and in vitro. Down-regulation of telomerase, the ribonucleoprotein complex responsible for the maintenance and elongation of telomeres (the ends of chromosomes) arrests the increased proliferation of spontaneously hypertensive rat vascular smooth muscle cells and induces apoptosis. This apoptosis is reversible by overexpressing telomerase and is prevented by increasing p53 tumor suppressor protein expression and worsened by lowering p53. Telomerase activation, telomere maintenance, and the p53 checkpoint appear to be critical for increased vascular smooth muscle proliferation, thus they represent potential novel therapeutic targets in hypertension.

Animals↗
PubMed2002

Mineralocorticoid receptors and pathophysiological roles for aldosterone in the cardiovascular system.

For almost 40 years since its discovery in 1953, the mineralocorticoid hormone, aldosterone, was considered to affect blood volume, and thus blood pressure, by its action to retain sodium at epithelial tissues. Over the past decade, direct effects of aldosterone on the heart and blood vessels, and on the cerebral control of blood pressure, have been established in experimental animals. Simultaneously, the incidence of primary aldosteronism in essential hypertension is now acknowledged to be 10-20%, rather than <or= 1%, underscoring a previously unrecognized role for aldosterone in hypertension. The 30% improvement in mortality (and 35% in morbidity) seen in the RALES trial with the addition of low-dose spironolactone to best practice therapy in moderate to severe heart failure, similarly points to an unrecognized role for aldosterone in the pathophysiology of heart failure. Currently, both experimental and clinical studies are directed towards establishing the mechanisms involved in these pathophysiological effects of aldosterone in the cardiovascular system, and of the role of mineralocorticoid receptor antagonists in offsetting or blocking such effects. A brief account of the current state of these mechanisms in at a cellular and tissue level forms the basis of this review.

Aldosterone↗