Primary aldosteronism: From genesis to genetics

The fact that a debate concerning the unexpectedly high prevalence of normokalaemic primary aldosteronism (PAL) attracted a large audience at the 2002 Scientific Meeting of the International Society of Hypertension makes it timely to address this issue. The affirmative case argues that PAL is the most common potentially curable and specifically treatable form of hypertension, itself the most common chronic disorder in Western societies, with significant morbidity and mortality, consuming large proportions of health budgets. Recent discoveries about the genetics of aldosterone production and of its unexpectedly broad effects on the cardiovascular system need to be placed in clinical context.

mRNA differential display of 2-amino-1-methyl-6-phenylinlidazo[4,5-b]pyridine-induced rat mammary gland tumors

The mRNA differential display technique was used to compare mRNAs between normal mammary gland and turner-derived epithelial cells from female Sprague-Dawley rat mammary gland tumors induced by the heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and promoted by a high-fat diet (23.5% corn oil). Two genes, beta-casein and transferrin, were identified as differentially expressed. The expression of these genes was examined across a bank of rat mammary gland tumors derived from animals on a low-fat diet (5% corn oil) or the high-fat diet. Carcinomas had over a 10- and 50-fold lower expression of beta-casein and transferrin, respectively than normal mammary gland. In addition, carcinomas from animals on the high-fat diet showed on average a 5-fold higher expression of beta-casein, and transferrin than carcinomas from animals on the low-fat diet. The results indicate the process of mammary gland tumorigenesis alters the expression of certain genes in the mammary gland, and that the level of dietary fat further modulates the expression of these genes.

alpha-Conotoxin ImI inhibits the alpha-bungarotoxin-resistant nicotinic response in bovine adrenal chromaffin cells

The activity of alpha-conotoxin (alpha-CTX) lml, from the vermivorous marine snail Conus imperialis, has been studied on mammalian nicotinic receptors on bovine chromaffin cells and at the rat neuromuscular junction. Synthetic alpha-CTX lml was a potent inhibitor of the neuronal[ nicotinic response in bovine adrenal chromaffin cells (IC50 = 2.5 mu M, log IC50 = 0.4 +/- 0.07), showing competitive inhibition of nicotine-evoked catecholamine secretion. (alpha-CTX lml also inhibited nicotine-evoked Ca-45(2+) uptake but not Ca-45(2+) uptake stimulated by 56 mM Kr. In contrast, alpha-CTX lml had no effect at the neuromuscular junction over the concentration range 1-20 mu M. Bovine chromaffin cells are known to contain the alpha 3 beta 4, alpha 7, and (possibly) alpha 3 beta 4 alpha 5 subtypes. However, the secretory response of bovine chromaffin cells is not inhibited by alpha-bungarotoxin, indicating that alpha 7 nicotinic receptors are not involved. We propose that alpha-CTX lml interacts selectively with the functional (alpha 3 beta 4 or alpha 3 beta 4 alpha 5) nicotinic acetylcholine receptor to inhibit the neuronal-type nicotinic response in bovine chromaffin cells.

Characterization of peroxisome proliferator-activated receptor alpha in normal rat mammary gland and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced mammary gland tumors from rats fed high and low fat diets

Normal Sprague-Dau ley rat mammary gland epithelial cells and mammary gland carcinomas induced by 2-amino-1 -methyl-6-phenylimidazo[4,5-b]pyridine, a carcinogen found in the diet, were examined for the expression of peroxisome proliferator-activated receptor alpha (PPAR alpha). PPAR alpha mRNA and protein was detected in normal and tumor tissue by reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry. By quantitative RT-PCR, carcinomas had a 12-fold higher expression than control mammary glands, a statistically significant difference. PPAR alpha expression was examined in carcinomas and normal tissues from rats on high fat (23.5/% corn oil) and low fat (5% corn oil) diets. Although neither carcinomas, nor control tissues showed statistically significant differences between the two diet groups, PPAR alpha expression was the highest in carcinomas from rats on the high fat diet. The expression of PPAR alpha in normal mammary gland and its significant elevation in mammary gland carcinomas raises the possibility of its involvement in mammary gland physiology and pathophysiology. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserved.

Sporadic and familial pheochromocytomas are associated with loss of at least two discrete intervals on chromosome 1p

Pheochromocytomas are tumors of the adrenal medulla originating in the chromaffin cells derived from the neural crest. Ten % of these tumors are associated with the familial cancer syndromes multiple endocrine neoplasia type 2, von Hippel-Lindau disease (VHL), and rarely, neurofibromatosis type 1, in which germ-line mutations have been identified in RET, VHL, and NF1, respectively. In both the sporadic and familial forms of pheochromocytoma, allelic loss at 1p, 3p, 17p, and 22q has been reported, yet the molecular pathogenesis of these tumors is largely unknown. Allelic loss at chromosome 1p has also been reported in other endocrine tumors, such as medullary thyroid cancer and tumors of the parathyroid gland, as well as in tumors of neural crest origin including neuroblastoma and malignant melanoma, In this study, we performed fine structure mapping of deletions at chromosome 1p in familial and sporadic pheochromocytomas to identify discrete regions likely housing tumor suppressor genes involved in the development of these tumors. Ten microsatellite markers spanning a region of similar to 70 cM (Ipter to 1p34.3) were used to screen 20 pheochromocytomas from 19 unrelated patients for loss of heterozygosity (LOH). LOH was detected at five or more loci in 8 of 13 (61%)sporadic samples and at five or more loci in four of five (80%) tumor samples from patients with multiple endocrine neoplasia type 2. No LOH at 1p was detected in pheochromocytomas from two VHL patients, Analysis of the combined sporadic and familial tumor data suggested three possible regions of common somatic loss, designated as PCI (D1S243 to D1S244), PC2 (D1S228 to D1S507), and PC3 (D1S507 toward the centromere). We propose that chromosome Ip may be the site of at least three putative tumor suppressor loci involved in the tumorigenesis of pheochromocytomas. At least one of these loci, PC2 spanning an interval of <3.8 cM, is Likely to have a broader role in the development of endocrine malignancies.

Insertion/deletion polymorphism of the angiotensin converting enzyme gene and loss of the insertion allele in aldosterone-producing adenoma

The genetic mechanisms responsible for the formation of adrenocortical adenomas which autonomously produce aldosterone are largely unknown, The adrenal renin-angiotensin system has been implicated in the pathophysiology of these tumours, Angiotensin-converting enzyme (ACE) catalyses the generation of angiotensin II, and the insertion/deletion (I/D) polymorphism of the ACE gene regulates up to 50% of plasma and cellular ACE variability in humans. We therefore examined the genotypic and allelic frequency distributions of the ACE gene I/D polymorphism in 55 patients with aldosterone-producing adenoma, APA, (angiotensin-unresponsive APA n = 28, angiotensin-responsive APA n = 27), and 80 control subjects with no family history of hypertension, We also compared the ACE gene I/D polymorphism allelic pattern in matched tumour and peripheral blood DNA in the 55 patients with APA, The frequency of the D allele was 0.518 and 0.512 and the I allele was 0.482 and 0.488 in the APA and control subjects respectively, Genotypic and allelic frequency analysis found no significant differences between the groups, Examination of the matched tumour and peripheral blood DNA samples revealed the loss of the insertion allele in four of the 25 patients who were heterozygous for the ACE I/D genotype. The I/D polymorphism of the ACE gene does not appear to contribute to the biochemical and phenotypic characteristics of APA, however, the deletion of the insertion allele of the ACE gene I/D polymorphism in 16% of aldosterone-producing adenomas may represent the loss of a tumour suppressor gene/s or other genes on chromosome 17q which may contribute to tumorigenesis in APA.

Dorsal and ventral medullary catecholamine cell groups contribute differentially to systemic interleukin-1 beta-induced hypothalamic pituitary adrenal axis responses

Medial parvocellular paraventricular corticotropin-releasing hormone (mPVN CRH) cells are critical in generating hypothalamic-pituitary-adrenal (HPA) axis responses to systemic interleukin-1 beta (IL-1 beta). However, although it is understood that catecholamine inputs are important in initiating mPVN CRH cell responses to IL-1 beta, the contributions of distinct brainstem catecholamine cell groups are not known. We examined the role of nucleus tractus solitarius (NTS) and ventrolateral medulla (VLM) catecholamine cells in the activation of mPVN CRH, hypothalamic oxytocin (OT) and central amygdala cells in response to IL-1 beta (1 mug/kg, i.a.). Immunolabelling for the expression of c-fos was used as a marker of neuronal activation in combination with appropriate cytoplasmic phenotypic markers. First we confirmed that PVN 6-hydroxydopamine lesions, which selectively depleted catecholaminergic terminals, significantly reduced IL-1 beta -induced mPVN CRH cell activation. The contribution of VLM (A1/C1 cells) versus NTS (A2 cells) catecholamine cells to mPVN CRH cell responses was then examined by placing ibotenic acid lesions in either the VLM or NTS. The precise positioning of these lesions was guided by prior retrograde tracing studies in which we mapped the location of IL-1 beta -activated VLM and NTS cells that project to the mPVN. Both VLM and NTS lesions reduced the mPVN CRH and OT cell responses to IL-1 beta. Unlike VLM lesions, NTS lesions also suppressed the recruitment of central amygdala neurons. These studies provide novel evidence that both the NTS and VLM catecholamine cells have important, but differential, contributions to the generation of IL-1 beta -induced HPA axis responses. Copyright (C) 2001 S. Karger AG, Basel.

Role of circumventricular organs in pro-inflammatory cytokine-induced activation of the hypothalamic-pituitary-adrenal axis

1. The past 15 years has seen the emergence of a new field of neuroscience research based primarily on how the immune system and the central nervous system can interact. A notable example of this interaction occurs when peripheral inflammation, infection or tissue injury activates the hypothalamic- pituitary-adrenal axis (HPA). 2. During such assaults, immune cells release the pro- inflammatory cytokines interleukin (IL)-1, IL-6 and tumour necrosis factor-alpha into the general circulation. 3. These cytokines are believed to act as mediators for HPA axis activation. However, physical limitations of cytokines impede their movement across the blood-brain barrier and, consequently, it has been unclear as to precisely how and where IL-1beta signals cross into the brain to trigger HPA axis activation. 4. Evidence from recent anatomical and functional studies suggests two neuronal networks may be involved in triggering HPA axis activity in response to circulating cytokines. These are catecholamine cells of the medulla oblongata and the circumventricular organs (CVO). 5. The present paper examines the role of CVO in generating HPA axis responses to pro-inflammatory cytokines and culminates with a proposed model based on cytokine signalling primarily involving the area postrema and catecholamine cells in the ventrolateral and dorsal medulla.

Immunization with tumor-associated epitopes fused to an endoplasmic reticulum translocation signal sequence affords protection against tumors with down-regulated expression of MHC and peptide transporters

Treatment of human cancers with an inherent antigen-processing defect due to a loss of peptide transporters (TAP-1 and TAP-2) and/or MHC class I antigen expression remains a considerable challenge. There is now an increasing realization that tumor cells with down-regulated expression of TAP and/or MHC class I antigens display strong resistance to cytotoxic T lymphocyte (CTL)mediated immune control, and often fail to respond to the conventional immunotherapeutic protocols based on active immunization with tumor-associated epitopes (TAE) or adoptive transfer of tumor-specific T cells, In the present study, we describe a novel approach based on immunization with either genetically modified tumor cells or naked DNA vectors encoding TAE fused to an endoplasmic reticulum (ER) signal sequence (ER-TAE) which affords protection against challenge by melanoma cells with down-regulated expression of TAP-1/2 and MHC class I antigens. In contrast, animals immunized with a vaccine based on TAE alone showed no protection against tumor challenge. Although MHC-peptide tetramer analysis showed a similar frequency of antigen-specific CTL in both ER-TAE- and TAE-immunized mice, functional analysis revealed that CTL activated following immunization with ER-TAE displayed significantly higher avidity for TAE when compared to animals immunized with the TAE alone, These observations provide a new strategy in anti-cancer vaccine design that allows activation of a highly effective and well-defined CTL response against tumors with down-regulated expression of TAP and MHC class I antigens.

Reliability of the input-output properties of the cortico-spinal pathway obtained from transcranial magnetic and electrical stimulation

The purpose of this experiment was to assess the test-retest reliability of input-output parameters of the cortico-spinal pathway derived from transcranial magnetic (TMS) and electrical (TES) stimulation at rest and during muscle contraction. Motor evoked potentials (MEPs) were recorded from the first dorsal interosseous muscle of eight individuals on three separate days. The intensity of TMS at rest was varied from 5% below threshold to the maximal output of the stimulator. During trials in which the muscle was active, TMS and TES intensities were selected that elicited MEPs of between 150 and 300 X at rest. MEPs were evoked while the participants exerted torques up to 50% of their maximum capacity. The relationship between MEP size and stimulus intensity at rest was sigmoidal (R-2 = 0.97). Intra-class correlation coefficients (ICC) ranged between 0.47 and 0.81 for the parameters of the sigmoid function. For the active trials, the slope and intercept of regression equations of MEP size on level of background contraction were obtained more reliably for TES (ICC = 0.63 and 0.78, respectively) than for TMS (ICC = 0.50 and 0.53, respectively), These results suggest that input-output parameters of the cortico-spinal pathway may be reliably obtained via transcranial stimulation during longitudinal investigations of cortico-spinal plasticity. (C) 2001 Elsevier Science B.V. All rights reserved.