Glucocorticoid induction of angiotensin converting enzyme

Angiotensin converting enzyme (ACE) converts angiotensin I (Angio I) to angiotensin II (Angio II) and inactivates bradykinin (BK).Glucocorticoids in the physiological range increase ACE in rabbit alveolar macrophages and bovine endothelial cells in culture. Since Angio I and BK are cleaved by ACE catalysis during passage through the pulmonary vasculature we have studied the steroid modulation of ACE in the rat lung.The conversion of Angio I to Angio II by isolated lungs from normal or adrenalectomized male Wistar rats has been evaluated.The initial conversion of Angio I to Angio II in lungs from normal rats was about 60%. In contrast the initial converting activity in lungs from adrenalectomized rats was about 30%.In both groups the converting activity progressively decreased. After 3 h it was about 30% in normal lungs and virtually undetectable in lungs from adrenalectomized rats.Dexamethasone infusion (1 g/ml) prevented the decrease in ACE activity observed in normal lungs and induced a gradual enhancement of converting activity in lungs from adrenalectomized animals up to the control level. The effect of dexamethasone was abolished by simultaneous infusion of cycloheximide (1 g/ml).These results demonstrate that glucocorticoids induce ACE synthesis in the rat lung.By this induction glucocorticoids promote the increase of both Angio II formation and BK degradation. Thus ACE induction may represent a possible mechanism whereby glucocorticoids might control vascular tone and permeability according to the general mode of action of steroid hormones.     

Investigations into the concept of a threshold for topoisomerase inhibitor-induced clastogenicity

Although the application of the concept of a threshold to risk assessment is widespread, there remains little experimental evidence for the existence of thresholds for genotoxic compounds, other than aneugens. The clastogenicity of topoisomerase inhibitors is believed to result from the transient stabilization of the topoisomerase enzyme with DNA during the catalytic cycle. This leads to the formation of a stabilized cleavage complex, which, in turn, may result in the formation of a DNA strand break. This indirect mechanism of clastogenicity is the basis for the concept of threshold for this class of drug. Using micronucleus induction in L5178Y mouse lymphoma cells as a genotoxic end-point, a three pronged approach was used to examine whether the concept of a threshold for clastogenicity could be demonstrated for topoisomerase type II inhibitors in vitro. This involved (i) the study of mechanism (TARDIS assay), (ii) hypothesis testing versus estimation (i.e. scoring up to 10,000 cells/treatment at concentrations immediately above and below the NOEL for micronucleus induction) and (iii) statistical modelling of the concentration-response curves for micronucleus induction. Several topoisomerase type II inhibitors were investigated with varying clastogenic potencies (etoposide = doxorubicin < genistein < ciprofloxacin). Pragmatic thresholds for clastogenicity in L5178Y cells were defined at 0.00236 microg/ml for etoposide, 0.00151 microg/ml for doxorubicin, 1 microg/ml for genistein and 50 microg/ml for ciprofloxacin. In addition, it was demonstrated that etoposide-induced clastogenicity was concentration and time dependent. These results, along with mechanistic data showing that all of the compounds induced concentration-dependent increases in the formation of topoisomerase II stabilized cleavage complexes, provide a weight of evidence to support a threshold concept for clastogenicity with topoisomerase II poisons.     

Glucocorticoid receptors in lymphocytes and stability of kidney graft function

The glucocorticoid receptors in lymphocytes of patients treated with glucocorticoids aftert kidney transplantation have been studied in order to determine whether abnormalities in corticosteroid binding and trans-activation of steroid-receptor complexes, i. e., their translocation into nuclei, may contribute to the resistance of patients to glucocorticoid therapy. The patients were divided into two groups, according to graft stability: patients with stable graft function and those with chronic allograft rejection. The study revealed changes in both level and binding affinity of glucocorticoid receptors in peripheral blood lymphocytes from patients with chronic graft rejection, compared with control level, as well as with values of patients with stable graft function. These data indicate that sensitivity to glucocorticoids depends, at least in part, on the alterations of glucocorticoid receptors. The receptor translocation into nuclei indicates that unknown post-receptor events might also be involved in glucocorticoid resistance that seriously impair successive glucocorticoid therapy after organ transplantation. Further examination of glucocorticoid receptors in cases of organ transplantation seems warranted. Received: 21 March 2001 / Accepted: 14 December 2001     

Old antihypertensives as novel antineoplastics: angiotensin-I-converting enzyme inhibitors and angiotensin II type 1 receptor antagonists

Angiogenesis, cellular growth and invasion of a cancer cell are attractive targets for new treatment strategies of malignancies in recent years. The evidences are accumulating that ACE inhibitors and angiotensin II type 1 antagonists could be novel anti-angiogenic, anti-invasive, and even anti-growth agents against neoplastic tissues: The renin-angiotensin system promotes angiogenesis directly or indirectly and growth of neoplastic cell. Some tumors carry angiotensin II type 1 receptors. Angiotensin II antagonists and angiotensin-I-converting enzyme inhibitors have shown some anti-neoplastic actions. Angiotensin II receptor blocker losartan antagonises platelets, which are thought to modulate via vascular endothelial growth factor. They may even protect the patient from the major toxicity of chemotherapy and/or radiotherapy, myelotoxicity, enabling us to give higher doses and end up with higher success rate. We believe that these agents can be useful on clinical grounds and suggest their incorporation into clinical studies.     

A case of losartan induced angioedema

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARB) target the renin-angiotensin system and are used in the management of hypertension. Both classes of drugs have similar side effects. ARBs are considered to be much better tolerated than ACE inhibitors with lesser incidence of side effects. Angioedema is a very rare side effect associated with ACE inhibitors (ACEI) and even rarer so with ARBs. The cause for angioedema in ACE inhibitors is said to be the rise in bradykinin levels. It has been postulated that angiotensin II receptor activates the bradykinin-prostaglandin-nitric oxide cascade, resulting in bradykinin-mediated side effects of ARBs such as angioedema, but the true mechanism remains largely unknown. We present here a rare case of late onset angioedema associated with losartan (an ARB) in a female patient. She had been started on an ARB as a first line treatment for uncomplicated mild to moderate hypertension. She had no prior exposure to ACE inhibitors and did not have any other significant medical history. Though rare angioedema is a serious recognized side effect of ARB therapy and the patients started on them should be warned to look for the early signs so as to take corrective action.     

Steroid Metabolism and Immunity

The glucocorticoids are generally regarded as immunosuppressants. In reality they are immunoregulatory, with both positive and negative effects on the immune system. The effects of glucocorticoids in any given tissue cannot easily be related to the early morning plasma cortisol level. The diurnal rhythm, which in normal people results in occupation of the glucocorticoid receptors in T lymphocytes for about half the 24-hour cycle, is also important. Moreover, the effects within each tissue depend upon the metabolism, both systemically and within each tissue, of the glucocorticoids themselves and of other steroids derived from dehydroepiandrosterone sulphate that have antiglucocorticoid properties. These points highlight numerous potential targets for novel therapies, including: the regulation of the glucocorticoid/dehydroepiandrosterone balance;regulation of the diurnal rhythm;development of inhibitors of enzymes that metabolise glucocorticoids or dehydroepiandrosterone in different tissues; anduse of novel combinations of glucocorticoid and antiglucocorticoid (dehydroepiandrosterone) metabolites that have properties unlike those of either steroid used alone.     

Captopril increases the intensity of monocyte infection by Trypanosoma cruzi and induces human T helper type 17 cells

The anti-hypertensive drug captopril is used commonly to reduce blood pressure of patients with severe forms of Chagas disease, a cardiomyopathy caused by chronic infection with the intracellular protozoan Trypanosoma cruzi. Captopril acts by inhibiting angiotensin-converting enzyme (ACE), the vasopressor metallopeptidase that generates angiotensin II and promotes the degradation of bradykinin (BK). Recent studies in mice models of Chagas disease indicated that captopril can potentiate the T helper type 1 (Th1)-directing natural adjuvant property of BK. Equipped with kinin-releasing cysteine proteases, T. cruzi trypomastigotes were shown previously to invade non-professional phagocytic cells, such as human endothelial cells and murine cardiomyocytes, through the signalling of G protein-coupled bradykinin receptors (B(2) KR). Monocytes are also parasitized by T. cruzi and these cells are known to be important for the host immune response during infection. Here we showed that captopril increases the intensity of T. cruzi infection of human monocytes in vitro. The increased parasitism was accompanied by up-regulated expression of ACE in human monocytes. While T. cruzi infection increased the expression of interleukin (IL)-10 by monocytes significantly, compared to uninfected cells, T. cruzi infection in association with captopril down-modulated IL-10 expression by the monocytes. Surprisingly, studies with peripheral blood mononuclear cells revealed that addition of the ACE inhibitor in association with T. cruzi increased expression of IL-17 by CD4(+) T cells in a B(2) KR-dependent manner. Collectively, our results suggest that captopril might interfere with host-parasite equilibrium by enhancing infection of monocytes, decreasing the expression of the modulatory cytokine IL-10, while guiding development of the proinflammatory Th17 subset.     

Suppression of growth of PHA-stimulated human lymphocytes by a novel steroid (RU 28 362) lacking the 21-OH group

RU 28 362 is a novel synthetic steroid (lacking the 21-OH group) which reacts exclusively with the glucocorticoid receptor. It is therefore chemically different from the other natural and synthetic glucocorticoids in common use which also bind to a lesser extent to receptors for other classes of steroids. Aspects of the immunosuppressive effect of RU 28 362 were studied by comparing its suppressive effects on PHA-stimulated growth of human lymphocytes with those of hydrocortisone, betamethasone and the inactive analogue, 21-deoxyhydrocortisone. RU 28 362 was more potent than either hydrocortisone or betamethasone, but all three glucocorticoids had a parallel dose-response curve in suppression of the increase in cell volume that occurs with activation during the first day in culture. In studies on the time of appearance and density of IL-2 receptors during the first 3 days in culture, RU 28 362 was also somewhat more inhibitory and had a steeper dose-response curve than hydrocortisone or betamethasone. RU 28 362 was much more inhibitory and had a steeper dose-response curve than either hydrocortisone or betamethasone in inhibiting [3H]-TdR incorporation by 3-day PHA stimulated cultures. 21-deoxyhydrocortisone did not inhibit any aspect of PHA-stimulated lymphocyte growth.     

The clinical use of glucocorticoids

Glucocorticoids are potent anti-inflammatory agents and their administration results in a wide range of effects on inflammatory and immunologically mediated disease processes. The precise mechanisms by which glucocorticoids impair the human immune response are unknown. Intracytoplasmic glucocorticoids specific receptors are important in the specificity of glucocorticoid actions. Glucocorticoid administration results in neutrophillia, monocytopenia, lymphopenia, and eosinopenia. A principle mechanism whereby glucocorticoids limit inflammation is by limiting the access of leukocytes, particularly neutrophils, to inflammatory sites. Neutrophil function is relatively refractory while monocyte and T-cell function is more easily impaired. A variety of glucocorticoid preparations are available for use, and appreciation of their relative potency and plasma half-lives is essential for designing therapeutic regimens. High doses and frequent administration of glucocorticoids are necessary in order to induce a remission in patients with flagrantly active disease. Once a remission is induced, the glucocorticoid regimen should be adjusted to attain maximal therapeutic benefit with minimal adverse effects. Alternate day dosage regimens can often be used to maintain a remission.     

Distinct roles for angiotensin-converting enzyme 2 and carboxypeptidase A in the processing of angiotensins within the murine heart

Angiotensin-converting enzyme 2 (ACE2), a homologue of angiotensin-converting enzyme (ACE), converts angiotensin (Ang) I to Ang(1-9) and Ang II to Ang(1-7), but does not directly process Ang I to Ang II. Cardiac function is compromised in ACE2 null mice; however, the importance of ACE2 in the processing of angiotensin peptides within the murine heart is not known. We determined the metabolism of angiotensins in wild-type (WT), ACE (ACE(-/-)) and ACE2 null mice (ACE2(-/-)). Angiotensin II was converted almost exclusively to Ang(1-7) in the cardiac membranes of WT and ACE(-/-) strains, although generation of Ang(1-7) was greater in the ACE(-/-) mice (27.4 +/- 4.1 versus 17.5 +/- 3.2 nmol(-1) mg h(-1) for WT). The ACE2 inhibitor MLN4760 significantly attenuated Ang II metabolism and the subsequent formation of Ang(1-7) in both strains. In the ACE2(-/-) hearts, Ang II metabolism and the generation of Ang(1-7) were significantly attenuated; however, the ACE2 inhibitor reduced the residual Ang(1-7)-forming activity in this strain. Angiotensin I was primarily converted to Ang(1-9) (WT, 28.9 +/- 3.1 nmol(-1) mg h(-1); ACE(-/-), 49.8 +/- 5.3 nmol(-1) mg h(-1); and ACE2(-/-), 35.9 +/- 5.4 nmol(-1) mg h(-1)) and to smaller quantities of Ang(1-7) and Ang II. Although the ACE2 inhibitor had no effect on Ang(1-9) formation, the carboxypeptidase A inhibitor benzylsuccinate essentially abolished the formation of Ang(1-9) and increased the levels of Ang I in cardiac membranes. In conclusion, our studies in the murine heart suggest that ACE2 is the primary pathway for the metabolism of Ang II and the subsequent formation of Ang(1-7), a peptide that, in contrast to Ang II, exhibits both antifibrotic and antiproliferative actions.     

Activation of the hypothalamo-hypophyseal-adrenocortical system as an important gastroprotective component of the stress reaction

This article presents an analysis of data providing evidence of the important contribution of the hypothalamo-hypophyseal-adrenocortical system (HHACS) to the processes maintaining the integrity of the gastric mucosa. According to these data, glucocorticoid hormones produced during stress-induced activation of the HHACS are gastroprotective hormones rather than ulcerogenic factors, as is widely believed. The gastroprotective influence of glucocorticoids has been demonstrated on exposure to ulcerogenic stimuli of different modalities. The gastroprotective action of glucocorticoid hormones is mediated via type II glucocorticoid receptors and may be associated with the maintenance of the blood glucose level, their calming effects on pathogenetic factors, and their favorable effects on protective factors for the gastric mucosa. Glucocorticoid hormones can compensate for the absence of the gastroprotective action of prostaglandins, nitric oxide, and capsaicin-sensitive neurons. The data lead to the conclusion that activation of the HHACS is an important gastroprotective component of the stress reaction. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 92, No. 2, pp. 249–261, February, 2006.     

Role of losartan therapy in the management of diabetic hypertension

The management of diabetic hypertension requires meticulous selection of agents in the antihypertension armamentorium. There may be several associated factors to be considered while treating a hypertensive diabetic. These include hyperglycemia, dyslipidemia, proteinuria, left ventricular hypertrophy and heart failure to name a few. Losartan is the first of a new class of agents in the list of antihypertensive drugs. By its selective angiotension II receptor (subtype AT1) blocking action it is postulated to bring about a more complete inhibition of the renin-angiotensin system. Thus, it might produce all the benefits of angiotensin converting enzyme (ACE) inhibitor therapy with the freedom from cough so commonly seen with the use of ACE inhibitors. This review attempts to analyze the possible benefits of losartan therapy in diabetes.     

Inactivation of Crithidia fasciculata carbamoyl phosphate synthetase II by the antitumor drug acivicin

In Crithidia fasciculata, carbamoyl phosphate synthetase II, which catalyses the first step of de novo pyrimidine biosynthesis, was separated from aspartate carbamoyltransferase by ammonium sulfate fractionation. The antitumor drug acivicin competitively inhibited the synthetase II activity with respect to L-glutamine, yielding an apparent Ki of 2 microM. In the absence of L-glutamine, acivicin resulted in a selective, time-dependent inactivation of L-glutamine-dependent activity of the enzyme, with an inactivation constant (Kinact) of 100 microM and a minimum inactivation half-time (T) of 0.2 min. L-Glutamine protected the enzyme from inactivation. These results are consistent with a postulate that acivicin is an active site-directed affinity analogue of L-glutamine, achieving irreversible inactivation. The inactivated enzyme retained ammonia-dependent activity. Acivicin stimulated the ammonia-dependent activity by increasing the Vmax value of the enzyme; apparent Km values for ammonia and MgATP were not affected. Differential action of acivicin on the Crithidia and mammalian synthetase II is discussed.     

Direct effects of the angiotensin-converting enzyme inhibitor ramiprilat on adult rat ventricular cardiomyocytes

Aim: Angiotensin‐converting enzyme (ACE) inhibitors like ramiprilat bind to ACE expressed on the cell surface of endothelial cells and induce cell‐specific signalling including the activation of activator protein (AP)‐1. The present study addressed the question whether ramiprilat exerts a similar effect on adult ventricular cardiomyocytes, i.e. activates the AP‐1 or modifies contractile performance. It was further aimed to decide whether such effects depend on bradykinin receptors or whether they are directly mediated via ACE. Methods: Adult rat ventricular cardiomyocytes were isolated and cultured. mRNA expression of ACE was investigated by RT‐PCR, AP‐1 activation by gel mobility shift assays, and cardiac contractile performance by electrical pacing of isolated cells and analysis of cell shortening via a line‐camera. Results: Cardiomyocytes stably express ACE. Ramiprilat increased maximal contraction velocity and shortened the time‐to‐peak of contraction. In contrast to effects evoked by bradykinin, such effects caused by ramiprilat were not attenuated by HOE 140, a bradykinin‐receptor antagonist. These effects were also not attenuated in the presence of l ‐nitro‐arginine, used to mimic bradykinin‐dependent signalling. In cardiomyocytes, bradykinin but not ramiprilat activated AP‐1. Ramiprilat activates AP‐1 in endothelial cells that are known to respond to ramiprilat in this way. Conclusion: Ramiprilat exerts direct, bradykinin‐receptor independent effects on cardiomyocytes that improve cellular function without a corresponding effect on AP‐1 activation or induction of AP‐1 dependent effects. This newly described effect of ramiprilat may contribute to the protective effects seen by application of ACE inhibitors.     

Cyclooxygenase-2 and the renal renin-angiotensin system

In the kidney, cyclooxygenase-2 (COX-2) is expressed in the macula densa/cTALH and medullary interstitial cells. The macula densa is involved in regulating afferent arteriolar tone and renin release by sensing alterations in luminal chloride via changes in the rate of Na(+)/K(+)/2Cl(-) cotransport, and administration of non-specific cyclooxygenase inhibitors will blunt increases in renin release mediated by macula densa sensing of decreases in luminal NaCl. High renin states [salt deficiency, angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blockers, diuretic administration or experimental renovascular hypertension] are associated with increased macula densa/cTALH COX-2 expression. Furthermore, there is evidence that angiotensin II and/or aldosterone may inhibit COX-2 expression. In AT1 receptor knockout mice, COX-2 expression is increased similar to increases with ACE inhibitors or AT1 receptor blockers. Direct administration of angiotensin II inhibits macula densa COX-2 expression. Previous studies demonstrated that alterations in intraluminal chloride concentration are the signal for macula densa regulation of tubuloglomerular feedback and renin secretion, with high chloride stimulating tubuloglomerular feedback and low chloride stimulating renin release. When cultured cTALH or macula densa cells were incubated in media with selective substitution of chloride ions, COX-2 expression and prostaglandin production were significantly increased. A variety of studies have indicated a role for COX-2 in the macula densa mediation of renin release. In isolated perfused glomerular preparations, renin release induced by macula densa perfusion with a low chloride solution was inhibited by a COX-2 inhibitor but not a COX-1 inhibitor. In vivo studies in rats indicated that increased renin release in response to low-salt diet, ACE inhibitor, loop diuretics or aortic coarctation could be inhibited by administration of COX-2-selective inhibitors. In mice with genetic deletion of COX-2, ACE inhibitors or low-salt diet failed to increase renal renin expression, although renin significantly increased in wild type mice. In contrast, in COX-1 null mice there were no significant differences in either the basal or ACE inhibitor-stimulated level of renal renin activity from plasma or renal tissue compared with wild type mice. In summary, there is increasing evidence that COX-2 expression in the macula densa and surrounding cortical thick ascending limb cells is regulated by angiotensin II and is a modulator of renal renin production. These interactions of COX-2 derived prostaglandins and the renin-angiotensin system may underlie physiological and pathophysiological regulation of renal function.     

Altered epithelial cell proportions in the fetal lung of glucocorticoid receptor null mice

Glucocorticoids provide important signals for maturation of the fetal lung and antenatal glucocorticoids are used to reduce the respiratory insufficiency suffered by preterm infants. To further understand the role of glucocorticoids in fetal lung maturation, we have analyzed mice with a targeted null mutation for the glucocorticoid receptor (GR) gene, which severely retards lung development. The lungs of fetal GR-null mice have increased lung weight and DNA content, are condensed and hypercellular, with reduced septal thinning leading to a 6-fold increase in the airway to capillary diffusion distance. In fetal GR-null mice, mRNA levels of the type II epithelial cell surfactant protein genes A and C were reduced by approximately 50%. Analysis of epithelial cell types by electron microscopy revealed that the proportions of type II cells were increased by approximately 30%, whereas the proportions of type-I cells were markedly reduced (by approximately 50%). Similarly, we found a 50% reduction in mRNA levels for T1alpha and aquaporin-5, two type I cell-specific markers, and a 20% reduction in aquaporin-1 mRNA levels. This demonstrates that during murine embryonic development, receptor-mediated glucocorticoid signaling facilitates the differentiation of epithelial cells into type I cells, but is not obligatory for type II cell differentiation.     

The ACE-DD genotype is associated with endothelial dysfunction in postmenopausal women

OBJECTIVE: To evaluate the effects of the angiotensin-converting enzyme (ACE) insertion/deletion (I/D), the angiotensinogen M235T and the angiotensin II type 1 receptor A1166C polymorphisms, and hormone therapy used on endothelial function in postmenopausal women without manifestation of coronary artery disease. DESIGN: Sixty-four postmenopausal women (42 hormone therapy users and 22 hormone therapy nonusers) without clinical manifestation of coronary artery disease were evaluated using external vascular ultrasonography to measure endothelium-dependent (hyperemic response, flow-mediated dilatation) and -independent (nitroglycerin) dilatation. Genotypes were determined by polymerase chain reaction amplification. RESULTS: Women with the ACE-DD genotype displayed a lower flow-mediated dilatation compared to those with the ACE-II genotype (8.4% +/- 3.9% vs 12.6% +/- 5.4%, P = 0.04). Endothelial function was not associated with the angiotensinogen M235T and anglotensin II type 1 receptor A1166C polymorphisms. ACE polymorphism seems to modulate endothelial function among postmenopausal women without hormone therapy (8.2% +/- 5.1% vs 18.4% +/- 5.9% for the DD and the II genotype, respectively, P = 0.02). However, in hormone therapy users, flow-mediated dilatation was similar according to the ACE genotypes. CONCLUSIONS: Our findings suggest that ACE-I/D polymorphism is related to endothelial dysfunction in postmenopausal women. Furthermore, a potential interaction between estrogen users and ACE polymorphism on endothelial function may be present.     

2型糖尿病血管紧张素转换酶基因与隐性心肌缺血的关系

目的　为了探讨2型糖尿病(diabetes mellitus,DM)患者血管紧张素转换酶(angiotensinconverting enzyme,ACE)基因与运动诱发的隐性心肌缺血(exercise- induced silent myocardial ischemia,SI)的关系。方法　选择静息心电图正常的2型DM患者10 8例和5 0名健康人。采用踏车运动试验进行筛选SI。应用PCR技术检测ACE基因。结果　(1)对照组及2型DM组ACE基因型及等位基因频率分布相似(P>0 .0 5 )。与非SI组比较,SI组ACE D等位基因频率明显增高(χ2 =4 .5 0 1,P<0 .0 5 ) ,两组ACE基因型频率分布相似(P>0 .0 5 )。(2 ) 2型DM患者不同ACE基因型组间临床特征及血脂水平相似(P>0 .0 5 )。(3) 2型DM患者DD型SI发生率为6 8.2 % ,明显高于II基因型组的39.5 % (χ2 =4 .5 93,P<0 .0 5 )。结论　ACE D等位基因增高2型DM患者并发SI的危险性。