Myocardial-directed overexpression of the human beta(1)-adrenergic receptor in transgenic mice.

The beta(1)-adrenergic receptor (AR) is the dominant subtype in non-failing and failing myocardium. beta(1)-AR signaling, by the endogenous neurotransmitter norepinephrine, is central to the regulation of myocardial contractility. In heart failure, the beta(1)-AR undergoes subtype-selective downregulation which may protect against the increased cardiac adrenergic drive associated with this pathophysiological state. To examine the hypothesis that chronically increased beta(1)-AR mediated signaling has adverse myocardial effects, transgenic mice overexpressing the human beta(1)-AR in a cardiac-selective context were produced, utilizing an alpha-myosin heavy chain (MHC) promoter. In these mice, beta(1)-AR protein abundance was approximately 24-46-fold (1-2 pmol/mg protein) that of wild-type mice. Histopathological examination of young (4 months old) and old (approximately 9 months old) transgenic mouse hearts consistently demonstrated large areas of interstitial replacement fibrosis, marked myocyte hypertrophy and myofibrilar disarray. In addition, increased expression of the pre-apoptotic marker, Bax, was observed coincident with regions of fibrosis accompanied by an increased apoptotic index, as measured by TUNEL assay. Older non-transgenic mice exhibited a slight tendency towards a decreased fractional shortening, whereas older beta(1)-AR transgenic mice had a marked reduction in fractional shortening (%FS approximately 30) as determined by echocardiography. Additionally, older beta(1)-AR transgenic mice had an increased left ventricular chamber size. In summary, cardiac-directed overexpression of the human beta(1)-AR in transgenic mice leads to a significant histopathological phenotype with no apparent functional consequence in younger mice and a variable degree of cardiac dysfunction in older animals. This model system may ultimately prove useful for investigating the biological basis of adrenergically-mediated myocardial damage in humans.

Angiotensin-1 converting enzyme polymorphisms in chronic beryllium disease.

To test the hypothesis that the angiotensin converting enzyme (ACE) genotype is associated with chronic beryllium disease (CBD) and disease severity, we studied 50 cases of CBD and compared their ACE genotype to that of two different control groups, consisting of: (1) 50 participants from a beryllium machining facility; and (2) 50 participants from a non-beryllium-associated workplace. We found no statistically significant difference in the frequency of the I or D allele or of the DD genotype among cases of CBD and either control group. The odds ratio (OR) for the CBD DD genotype as compared with the non-DD genotype was 1.58 (95% confidence interval [CI]: 0.68 to 3.66, p = 0.12) for the beryllium-exposed control group, and 1.09 (95% CI: 0.48 to 2.46, p = 0.56) for the non-beryllium-exposed controls. We found an association between serum ACE activity and the ACE genotype, with DD cases having the highest median serum ACE activity (p = 0.005). We evaluated the beryllium lymphocyte proliferation test (BeLPT), bronchoalveolar lavage (BAL) cell components, chest radiography, pulmonary function test results, and exercise physiology in our CBD cases. No statistically significant associations with these disease markers were found for the CBD cases with the DD genotype. Although the difference was not statistically significant, the DD cases had a shorter median duration of exposure to beryllium before diagnosis of CBD, and tended to have a weaker response in their blood and BAL BeLPT than did the non-DD cases. These findings may indicate that the ACE genotype is important in the immune response to beryllium and in progression to beryllium disease.

Angiotensin-converting enzyme gene polymorphism in non-insulin dependent diabetes mellitus and its relationship with diabetic nephropathy.

Previous studies have shown that the angiotensin-converting enzyme (ACE) gene polymorphism is associated with an increased risk of vascular disease in non-diabetic patients. The present study was conducted on 509 NIDDM patients who underwent a screening test to determine their ACE genotype for the Appropriate Blood Pressure Control in Diabetes (ABCD) Trial. Various baseline indices were correlated with the three ACE polymorphisms. The genotype was determined through polymerase chain reaction amplification of the angiotensin-converting enzyme polymorphism. The univariate relationship between the presence of the DD genotype with nephropathy as measured by urinary albumin excretion (UAE), and a history coronary artery disease (CAD) was then examined. Finally, a multiple model for each UAE and CAD was created so as to determine the independent effects of the presence of the DD genotype on each diabetic complication. Univariately, the presence of the DD genotype was associated with diabetic nephropathy. Furthermore, in a multiple model predicting diabetic nephropathy, the presence of the DD genotype was independently associated with diabetic nephropathy (odds ratio = 2.8, 95% confidence interval 1.4 to 5.5) but not CAD. Thus, the ACE DD genotype in 509 non-Hispanic white NIDDM patients in a metropolitan area in the U.S. was independently associated with the presence of diabetic nephropathy and, therefore, may be potentially used as a marker for NIDDM patients at risk for developing diabetic nephropathy.

Selective downregulation of the angiotensin II AT1-receptor subtype in failing human ventricular myocardium.

BACKGROUND: The regulation of angiotensin II receptors and the two major subtypes (AT1 and AT2) in chronically failing human ventricular myocardium has not been previously examined. METHODS AND RESULTS: Angiotensin II receptors were measured by saturation binding of 125I-[Sar1,Ile8]angiotensin II in crude membranes from nonfailing (n = 19) and failing human left ventricles with idiopathic dilated cardiomyopathy (IDC; n = 31) or ischemic cardiomyopathy (ISC; n = 21) and membranes from a limited number of right ventricles in each category. The AT1 and AT2 fractions were determined by use of an AT1-selective antagonist, losartan. beta-Adrenergic receptors were also measured by binding of 125I-iodocyanopindolol with the beta 1 and beta 2 fractions determined by use of a beta 1-selective antagonist, CGP20712A, AT1 but not AT2 density was significantly decreased in the combined (IDC + ISC) failing left ventricles (nonfailing: AT1 4.66 +/- 0.48, AT2 2.73 +/- 0.39; failing: AT1 3.20 +/- 0.29, AT2 2.70 +/- 0.33 fmol/mg protein; mean +/- SE). The decrease in AT1 density was greater in the IDC than in the ISC left ventricles (IDC: 2.73 +/- 0.40, P < .01; ISC: 3.89 +/- 0.39 fmol/mg protein, P = NS versus nonfailing). beta 1 but not beta 2 density was decreased in the failing left ventricles. AT1 density was correlated with beta 1 density in all left ventricles (r = .43). AT1 density was also decreased in IDC right ventricles. In situ reverse transcription-polymerase chain reaction in sections of nonfailing and failing ventricles indicated that AT1 mRNA was present in both myocytes and nonmyocytes. CONCLUSIONS: AT1 receptors are selectively downregulated in failing human ventricles, similar to the selective downregulation of beta 1 receptors. The relative lack of AT1 downregulation in ISC hearts may be related to differences in the degree of ventricular dysfunction.

The role of genetic variants in angiotensin I converting enzyme, angiotensinogen and the angiotensin II type-1 receptor in the pathophysiology of heart muscle disease.

The cardiac vasculature and myocardium contain components of the renin-angiotensin system (RAS), which may regulate local growth and cellular function. Alterations in the expression or action of these components, which include angiotensin converting enzyme (ACE), angiotensinogen, and angiotensin II type-1 receptors, may contribute to the development of disease, such as hypertension, left ventricular hypertrophy, myocardial infarction, and end-stage heart failure. ACE is one RAS component found to have genetic variants associated with cardiovascular disease. Molecular variants in any of the RAS components may affect signalling pathways, possibly increasing the risk of heart failure. In addition, variants may exacerbate the deleterious effects of altered RAS expression on cardiac function. Genetic variation in RAS components may affect therapy with ACE inhibitors and receptor-blocking agents. Although at present there is no compelling reason to target molecular variations for treatment, a new era in selective pharmacological therapy for cardiovascular disease may be imminent.

Angiotensin II formation in the intact human heart. Predominance of the angiotensin-converting enzyme pathway.

It has been proposed that the contribution of myocardial tissue angiotensin converting enzyme (ACE) to angiotensin II (Ang II) formation in the human heart is low compared with non-ACE pathways. However, little is known about the actual in vivo contribution of these pathways to Ang II formation in the human heart. To examine angiotensin II formation in the intact human heart, we administered intracoronary 123I-labeled angiotensin I (Ang I) with and without intracoronary enalaprilat to orthotopic heart transplant recipients. The fractional conversion of Ang I to Ang II, calculated after separation of angiotensin peptides by HPLC, was 0.415 +/- 0.104 (n = 5, mean +/- SD). Enalaprilat reduced fractional conversion by 89%, to a value of 0.044 +/- 0.053 (n = 4, P = 0.002). In a separate study of explanted hearts, a newly developed in vitro Ang II-forming assay was used to examine cardiac tissue ACE activity independent of circulating components. ACE activity in solubilized left ventricular membrane preparations from failing hearts was 49.6 +/- 5.3 fmol 125I-Ang II formed per minute per milligram of protein (n = 8, +/- SE), and 35.9 +/- 4.8 fmol/min/mg from nonfailing human hearts (n = 7, P = 0.08). In the presence of 1 microM enalaprilat, ACE activity was reduced by 85%, to 7.3 +/- 1.4 fmol/min/mg in the failing group and to 4.6 +/- 1.3 fmol/min/mg in the nonfailing group (P < 0.001). We conclude that the predominant pathway for angiotensin II formation in the human heart is through ACE.

Importance of angiotensin-converting enzyme in pulmonary hypertension.

Angiotensin II causes pulmonary vasoconstriction in man and in animals, and angiotensin-converting enzyme (ACE) inhibitors have prevented the development of chronic pulmonary hypertension in animals models. Angiotensin II may contribute to lung vascular remodeling in pulmonary hypertensive disease, since cilazapril, an inhibitor of ACE, reduces pulmonary vascular medical thickening in chronically hypoxic rats with established pulmonary hypertension. Furthermore, the ACE DD genotype, which has been associated with increased circulating and tissue ACE activity, has been associated with left ventricular hypertrophy in human hypertensive disorders. The ACE DD genotype may also 'permit' a greater hypertrophic adaptation of the pressure-over-loaded right ventricle. In fact, we have shown that pulmonary hypertension patients with maintained cardiac output and less right-heart failure fall into the group with the DD genotype and that patients with a low cardiac output and more severe right-heart failure fall into the group with the non-DD genotype, supporting the hypothesis. We assessed cardiopulmonary hemodynamics in patients with primary (unexplained) pulmonary hypertension and segregated the patients based on their ACE genotype. For similar mean pulmonary artery pressures in the DD and non-DD groups, the cardiac output was substantially lower in the patients with the non-DD genotype, whereas the values for mean right atrial pressure and pulmonary vascular resistance were double when compared with the DD group. Our data show that the ACE DD genotype is prevalent in patients with severe pulmonary hypertension and is a marker of maintained right ventricular function.

Reduced beta 1 receptor messenger RNA abundance in the failing human heart.

Heart failure in humans is characterized by alterations in myocardial adrenergic signal transduction, the most prominent of which is down-regulation of beta 1-adrenergic receptors. We tested the hypothesis that down-regulation of beta 1-adrenergic receptors in the failing human heart is related to decreased steady-state levels of beta 1 receptor mRNA. Due to the extremely low abundance of beta 1 receptor mRNA, measurements were possible only by quantitative polymerase chain reaction (QPCR) or by RNase protection methods. Because the beta 1 receptor gene is intronless and beta 1 receptor mRNA abundance is low, QPCR yielded genomic amplification in total RNA, and mRNA measurements had to be performed in poly (A)(+)-enriched RNA. By QPCR the concentration of beta 1 receptor mRNA varied from 0.34 to 7.8 x 10(7) molecules/microgram poly(A)(+)-enriched RNA, and the assay was sensitive to 16.7 zeptomol. Using 100-mg aliquots of left ventricular myocardium obtained from organ donors (nonfailing ventricles, n = 12) or heart transplant recipients (failing ventricles, n = 13), the respective beta 1 mRNA levels measured by QPCR were 4.2 +/- 0.7 x 10(7)/micrograms vs. 2.10 +/- 0.3 x 10(7)/micrograms (P = 0.006). In these same nonfailing and failing left ventricles the respective beta 1-adrenergic receptor densities were 67.9 +/- 6.9 fmol/mg vs. 29.6 +/- 3.5 fmol/mg (P = 0.0001). Decreased mRNA abundance in the failing ventricles was confirmed by RNase protection assays in total RNA, which also demonstrated a 50% reduction in beta 1 message abundance. We conclude that down-regulation of beta 1 receptor mRNA contributes to down-regulation of beta 1 adrenergic receptors in the failing human heart.

Angiotensin-converting enzyme DD genotype in patients with ischaemic or idiopathic dilated cardiomyopathy.

Polymorphism in the angiotensin-converting enzyme (ACE) gene has been shown to correlate with circulating ACE concentrations, and also to be an independent risk factor for the development of myocardial infarction, particularly in men thought to be at low risk by standard criteria. We determined the genotypes of individuals with end-stage heart failure due to either ischaemic dilated cardiomyopathy (102) or idiopathic dilated cardiomyopathy (112) and compared these to organ donors with normally functioning hearts (79). Genotypes were determined by the polymerase chain reaction with oligonucleotide primers flanking the polymorphic region in intron 16 of the ACE gene to amplify template DNA isolated from patients. Compared with the DD frequency in the control population, the frequency of the ACE DD genotype was 48% higher in individuals with idiopathic dilated cardiomyopathy (p = 0.008) and 63% higher in subjects with ischaemic cardiomyopathy (p = 0.008), suggesting that an ACE gene variant may contribute to the pathogenesis of both types of cardiomyopathy.

Structure of the rat gonadotropin releasing hormone (rGnRH) gene promoter and functional analysis in hypothalamic cells.

The gonadotropin releasing hormone (GnRH) gene encodes a protein which plays a critical role in mammalian reproductive physiology. Its expression is predominantly restricted to the hypothalamus although it has also been described in the placenta. To begin to determine the promoter elements important for tissue specific expression and to examine the mechanisms of developmental and hormonal regulation of the rat GnRH (rGnRH) gene, we cloned the rGnRH gene from a rat liver genomic DNA library. The nucleotide sequence of greater than 3 kb of 5'-flanking region was determined. The transcriptional initiation site in rat hypothalamic tissue and a mouse hypothalamic cell line were mapped by primer extension analysis and found to be different. In addition, transient transfection studies demonstrated that multiple regions of the distal promoter are important for tissue specific and basal promoter activity in hypothalamic cells. Furthermore, in these cells a potent activation region resides between -3026 and -1031 bp and suppressor region between -1031 and -903 bp upstream of the transcriptional start site. We conclude that different portions of the 5'-flanking region, which are activating and suppressing in nature, are critical for hypothalamic expression of the rGnRH gene.

Lipoprotein lipase gene expression in rat adipocytes is regulated by isoproterenol and insulin through different mechanisms.

Lipoprotein lipase (LPL) is highly regulated by catecholamines and insulin in adipocytes. Isoproterenol, a beta-adrenergic agonist, decreases LPL enzyme activity, whereas insulin increases LPL activity. We have isolated an 868-basepair rat LPL cDNA clone to assess hormone-mediated changes in LPL steady state mRNA levels and LPL gene transcription rates in adipocytes. Northern blot analysis of isoproterenol-treated (10(-6) M) adipocytes showed that LPL steady state mRNA decreased by 15 min. Nuclear run-on transcription assays in isoproterenol-treated cells indicated that LPL gene transcription was also decreased at 15 min compared to that in control cells. Conversely, insulin (6.7 x 10(-8) M) mediated an increase in LPL steady state mRNA in treated adipocytes, yet LPL gene transcription was not different from that in control cells. Thus, the isoproterenol-mediated decrease in LPL enzyme activity and steady state mRNA levels in adipocytes is associated with decreases in LPL gene transcription. Insulin, which does not affect LPL gene transcription, increases LPL enzyme activity and steady state mRNA levels. The effect of insulin on LPL mRNA is probably due to insulin-induced changes in mRNA stability.

Comparison of immunoreactive gonadotropin-releasing hormone and human chorionic gonadotropin in term placentas from normal women and those with insulin-dependent and gestational diabetes.

We measured prohormone gonadotropin-releasing hormone (high-molecular-weight gonadotropin-releasing hormone), gonadotropin-releasing hormone and human chorionic gonadotropin concentrations in term placentas from normal women and those with insulin-dependent and gestational diabetes. The placental immunoreactive gonadotropin-releasing hormone levels were significantly higher in normal tissues than in tissues from insulin-dependent and gestational diabetes (p less than 0.01). When compared with diabetic placental extracts, normal tissue also had more stored prohormone immunoreactive gonadotropin-releasing hormone. Whereas there were no consistent differences in placental human chorionic gonadotropin concentrations in normal tissues and tissues from insulin-dependent and gestational diabetes, there was a significant correlation between gonadotropin-releasing hormone and human chorionic gonadotropin concentrations in normal samples (r = 0.57, p less than 0.05), which was abolished when the diabetic tissue was included in the analysis. These data suggest that differences in high-molecular-weight gonadotropin-releasing hormone and gonadotropin-releasing hormone concentrations in term placentas from normal versus diabetic mothers may be due to enhanced processing of the prohormone and increased release of the decapeptide in diabetic pregnancy.