Elevated Angiotensin I-converting Enzyme Research Articles

Novel ACE mutations mimicking sarcoidosis by increasing blood ACE levels

An elevated blood angiotensin I-converting enzyme (ACE) supports diagnosis of sarcoidosis and Gaucher disease. However, some ACE mutations increase ACE shedding, and patients with these mutations are therefore at risk of being incorrectly diagnosed with sarcoidosis because of elevated serum ACE levels. We applied a novel approach called "ACE phenotyping" to identify possible ACE mutations in 3 pulmonary clinic patients that had suspected sarcoidosis based on elevated blood ACE levels. Conformational fingerprinting of ACE indicated that these mutations may be localized in the stalk region of the protein and these were confirmed by whole exome sequencing. Index patient 1 (IP1) had a mutation (P1199L) that had been previously identified, while the other 2 patients had novel ACE mutations. IP2 had 2 mutations, T887M and N1196K (eliminating a putative glycosylation site), while IP3 had a stop codon mutation Q1124X (eliminating the transmembrane anchor). We also performed a comprehensive analysis of the existing database of all ACE mutations to estimate the proportion of mutations increasing ACE shedding. The frequency of ACE mutations resulting in increased blood ACE levels may be much higher than previously estimated. ACE phenotyping, together with whole exome sequencing, is a diagnostic approach that could prevent unnecessary invasive and/or costly diagnostic procedures, or potentially harmful treatment for patients misdiagnosed on the basis of elevated blood ACE levels.

Lysozyme and bilirubin bind to ACE and regulate its conformation and shedding.

Angiotensin I-converting enzyme (ACE) hydrolyzes numerous peptides and is a critical participant in blood pressure regulation and vascular remodeling. Elevated tissue ACE levels are associated with increased risk for cardiovascular and respiratory disorders. Blood ACE concentrations are determined by proteolytic cleavage of ACE from the endothelial cell surface, a process that remains incompletely understood. In this study, we identified a novel ACE gene mutation (Arg532Trp substitution in the N domain of somatic ACE) that increases blood ACE activity 7-fold and interrogated the mechanism by which this mutation significantly increases blood ACE levels. We hypothesized that this ACE mutation disrupts the binding site for blood components which may stabilize ACE conformation and diminish ACE shedding. We identified the ACE-binding protein in the blood as lysozyme and also a Low Molecular Weight (LMW) ACE effector, bilirubin, which act in concert to regulate ACE conformation and thereby influence ACE shedding. These results provide mechanistic insight into the elevated blood level of ACE observed in patients on ACE inhibitor therapy and elevated blood lysozyme and ACE levels in sarcoidosis patients.

Angiotensin I-converting enzyme inhibitory activity and hypocholesterolemic effect of some fermented tropical legumes in streptozotocin-induced diabetic rats

Cardiovascular disease (CVD) is the common cause of morbidity and mortality in diabetes. Any antidiabetic management strategy should therefore include the control of CVD risk factors. Thus, this study describes the effect of fermented legume condiment-supplemented diets on lung angiotensin I-converting enzyme (ACE) and lipid profile in streptozotocin (STZ)-induced diabetic rats. Adult male Wistar rats were used for the study and diabetes was induced in them by a single intraperitoneal injection of STZ (35 mg/kg b.w.). After the diabetic status had been confirmed, the animals were randomly divided into six groups consisting of six animals each and were fed with diets supplemented with fermented Bambara groundnut, locust bean, and soybean. The study lasted for 14 days after which the plasma was analyzed for the lipid profile and the rats’ lungs were assayed for ACE activity. Elevated ACE activity, plasma total cholesterol, triglyceride, and LDL-cholesterol showed significant (P < 0.05) reduction in the rats treated with fermented legume condiment-supplemented diets, with a concomitant increase in plasma HDL-cholesterol as compared with the diabetic control. This study therefore concludes that fermented legume condiment-supplemented diets could attenuate diabetes-induced dyslipidemia, a major coronary disease risk factor, in experimental rats. This health benefit of the condiment diets could be associated with their ACE inhibitory and antihypercholesterolemic properties. However, the diet supplemented with fermented locust bean condiment appeared to be the most potent.

A Novel Splice-Site Mutation in Angiotensin I-Converting Enzyme (ACE) Gene, c.3691+1G&gt;A (IVS25+1G&gt;A), Causes a Dramatic Increase in Circulating ACE through Deletion of the Transmembrane Anchor

BackgroundAngiotensin-converting enzyme (ACE) (EC 4.15.1) metabolizes many biologically active peptides and plays a key role in blood pressure regulation and vascular remodeling. Elevated ACE levels are associated with different cardiovascular and respiratory diseases.Methods and ResultsTwo Belgian families with a 8-16-fold increase in blood ACE level were incidentally identified. A novel heterozygous splice site mutation of intron 25 - IVS25+1G>A (c.3691+1G>A) - cosegregating with elevated plasma ACE was identified in both pedigrees. Messenger RNA analysis revealed that the mutation led to the retention of intron 25 and Premature Termination Codon generation. Subjects harboring the mutation were mostly normotensive, had no left ventricular hypertrophy or cardiovascular disease. The levels of renin-angiotensin-aldosterone system components in the mutated cases and wild-type controls were similar, both at baseline and after 50 mg captopril. Compared with non-affected members, quantification of ACE surface expression and shedding using flow cytometry assay of dendritic cells derived from peripheral blood monocytes of affected members, demonstrated a 50% decrease and 3-fold increase, respectively. Together with a dramatic increase in circulating ACE levels, these findings argue in favor of deletion of transmembrane anchor, leading to direct secretion of ACE out of cells.ConclusionsWe describe a novel mutation of the ACE gene associated with a major familial elevation of circulating ACE, without evidence of activation of the renin-angiotensin system, target organ damage or cardiovascular complications. These data are consistent with the hypothesis that membrane-bound ACE, rather than circulating ACE, is responsible for Angiotensin II generation and its cardiovascular consequences.

An Angiotensin I-Converting Enzyme Mutation (Y465D) Causes a Dramatic Increase in Blood ACE via Accelerated ACE Shedding

BackgroundAngiotensin I-converting enzyme (ACE) metabolizes a range of peptidic substrates and plays a key role in blood pressure regulation and vascular remodeling. Thus, elevated ACE levels may be associated with an increased risk for different cardiovascular or respiratory diseases. Previously, a striking familial elevation in blood ACE was explained by mutations in the ACE juxtamembrane region that enhanced the cleavage-secretion process. Recently, we found a family whose affected members had a 6-fold increase in blood ACE and a Tyr465Asp (Y465D) substitution, distal to the stalk region, in the N domain of ACE.Methodology/Principal FindingsHEK and CHO cells expressing mutant (Tyr465Asp) ACE demonstrate a 3- and 8-fold increase, respectively, in the rate of ACE shedding compared to wild-type ACE. Conformational fingerprinting of mutant ACE demonstrated dramatic changes in ACE conformation in several different epitopes of ACE. Cell ELISA carried out on CHO-ACE cells also demonstrated significant changes in local ACE conformation, particularly proximal to the stalk region. However, the cleavage site of the mutant ACE - between Arg1203 and Ser1204 - was the same as that of WT ACE. The Y465D substitution is localized in the interface of the N-domain dimer (from the crystal structure) and abolishes a hydrogen bond between Tyr465 in one monomer and Asp462 in another.Conclusions/SignificanceThe Y465D substitution results in dramatic increase in the rate of ACE shedding and is associated with significant local conformational changes in ACE. These changes could result in increased ACE dimerization and accessibility of the stalk region or the entire sACE, thus increasing the rate of cleavage by the putative ACE secretase (sheddase).

Conformational Fingerprinting of the Angiotensin I-Converting Enzyme (ACE). 1. Application in Sarcoidosis

Fine epitope mapping of monoclonal antibodies (mAbs) to 16 epitopes on human angiotensin I-converting enzyme (ACE) revealed that the epitopes of all mAbs contained putative glycosylation sites. ACE glycosylation is both cell- and tissue-specific and, therefore, the local conformation of ACE produced by different cells could be also unique. The pattern of ACE binding by a set of mAbs to 16 epitopes of human ACE - "conformational fingerprint of ACE" - is the most sensitive marker of ACE conformation and could be cell- and tissue-specific. The recognition of ACEs by mAbs to ACE was estimated using an immune-capture enzymatic plate precipitation assay. Precipitation patterns of soluble recombinant ACE released from Chinese hamster ovary (CHO)-ACE cells was influenced by conditions that alter ACE glycosylation. This pattern was also strongly cell type specific. Patients with sarcoidosis exhibited conformational fingerprints of tissue ACE (lungs and lymph nodes), as well as blood ACE, which were distinct from controls. Conformational fingerprinting of ACE may detect ACE originated from the cells other than endothelial cells in the blood and when combined with elevated blood ACE levels in patients with sarcoidosis may potentially reflect extrapulmonary sarcoidosis involvement (bone marrow, spleen, liver). If proven true, this would serve as a biomarker of enormous potential clinical significance.

Angiotensin I-Converting Enzyme: A Pathogenetic Role in Diabetic Renal Damage?

The renin-angiotensin aldosterone system (RAAS) is well-established to be involved in diabetic nephropathy. Several abnormalities in the RAAS have been described in diabetes mellitus, including an abnormal aldosterone to renin ratio, elevated angiotensin I-converting enzyme (ACE) levels, and altered angiotensin II sensitivity. Whereas the renoprotective properties of ACE-inhibition in diabetic nephropathy have been demonstrated more than a decade ago, somewhat surprisingly, the role of ACE-activity in the pathogenesis of diabetic nephropathy is not well established. This paper addresses the possible functional impact of genetic and environmental increased in ACE activity in the pathogenesis of diabetic renal damage, in the context of the various other abnormalities in the RAAS in diabetes. Human and experimental data on circulating and tissue ACE in diabetes are reviewed, as well as the associations of ACE with angiotensin I conversion, with pathophysiological responses, and with renal end organ damage. New data from our laboratory provide evidence for interaction between genetical regulation of ACE activity by the ACE (I/D) genotype and diabetes as an environmental factor. Moreover, for functional effects of the elevated ACE activity in terms of increased conversion of angiotensin I to angiotensin II. The effects of enhanced generation of angiotensin II are modulated by the angiotensin II-subtype I receptor (AT1R). Altered AT1R sensitivity has been reported in diabetes that may further modu-late the eventual effects of elevated ACE. Epidemiological data on the association of genetically elevated ACE activity with diabetic nephropathy provide support for a pathogenetic role of elevated ACE activity in diabetic nephropathy. Together, the data suggest that differences in ACE expression and activity, resulting from both genetic and environmental factors and their interaction can modulate the pathogenesis of diabetic nephropathy. Unravelling the nature of this interaction, with focus on modifiable environmental factors, may help to ameliorate the risk for nephropathy in diabetes.

Localization of a Small Genomic Region Associated with Elevated ACE

Defining the relationship between multiple polymorphisms in a small genomic region and an underlying quantitative trait locus (QTL) represents a major challenge in human genetics. Pedigree analyses have shown that angiotensin I-converting enzyme (ACE) levels are influenced by a QTL located within or close to the ACE gene and most likely resides in the 3' region of this locus. We genotyped seven polymorphisms spanning 13 kb in the 3' end of ACE in 159 Afro-Caribbean subjects to evaluate the linkage disequilibrium between these sites and to narrow the genomic region associated with an elevated ACE level using a cladistic analysis. The linkage disequilibrium measurement D' and a haplotype tree revealed three distinct haplotype segments, presumably because of recombination. The value of the linkage disequilibrium parameter p(excess) was highest for site 22982, which is located in the middle segment. A series of nested, cladistic analyses confirmed that the other two regions are unlikely to be the ACE-linked QTL and that the variant resides in the middle region. Analyses of the same polymorphisms in 98 unrelated Europeans in the Monitoring Trends and Determinants in Cardiovascular Diseases (MONICA) study resulted in fewer haplotypes than were observed among the Afro-Caribbean subjects, suggesting that populations with greater genetic diversity may be especially informative for fine-scale mapping.

Effects of trandolapril on cardiac angiotensin I converting enzyme activity in rats with chronic heart failure following myocardial infarction.

The effects of long-term treatment with a novel angiotensin I converting enzyme (ACE) inhibitor, trandolapril, on ACE activity and cardiac function in rats with chronic heart failure (CHF) were examined and compared with those of captopril and enalapril. Left coronary artery ligation of rats resulted in decreases in mean arterial pressure, left ventricular systolic pressure, dP/dt, cardiac output and stroke volume indices, and increases in left ventricular end-diastolic pressure and systemic vascular resistance 12 weeks after the operation. A significant increase in ACE activity of the myocardium, but not that of serum or other tissues, was detected in the CHF rat 12 weeks after the operation. Oral treatment with ACE inhibitors (10 mg/kg/day captopril, 10 mg/kg/day enalapril or 3 mg/kg/day trandolapril) from the 2nd to 12th week, attenuated the changes in cardiac output and stroke volume indices, left ventricular end-diastolic pressure and systemic vascular resistance of the CHF rat. Treatment also attenuated the increase in the cardiac. ACE activity of CHF rats. A close relationship between the decrease in cardiac output index and the increase in cardiac ACE activity was detected. The results suggest that trandolapril, like other ACE inhibitors, exerts a beneficial effect on cardiac function in the CHF rat and that one of the mechanisms for this effect is attenuation of elevated cardiac ACE activity.

Elevated serum angiotensin I converting enzyme activity in type I, insulin-dependent diabetic subjects with persistent microalbuminuria

Angiotensin I-converting enzyme (ACE), which is synthesized by vascular endothelial cells, is sometimes elevated in diabetic subjects. To determine whether serum ACE is elevated in subjects at high risk of malignant microangiopathy, serum ACE activity in 34 normotensive, type 1 insulin-dependent diabetic subjects with persistent microalbuminuria (30–300 mg/24 h) was compared with that in 30 normotensive, normoalbuminuric type 1 diabetic subjects of the same age [37±15 (mean ±SD) vs 38±14 years], sex (21 M/13 F vs 15 M/15 F), stage of retinopathy (14 vs 16 nil/11 vs 7 background/6 vs 4 preproliferative/3 vs 3 proliferative) and HbA1c (7.7±1.9 vs 8.2±1.0%). Serum ACE activity of diabetic subjects was also compared with 120 age and sex related healthy controls. Serum ACE activity was higher in subjects with microalbuminuria than in those with normoalbuminuria (406±114 vs 359±97 IU/l;P=0.03), or in controls (307±95 IU/l;P=0.0001). Normoalbuminuric subjects also had higher ACE activity than controls (P=0.02). Serum ACE activity was not related to diabetes duration (r=0.01; NS), HbA1c (r=0.05; NS), or stage of retinopathy in diabetic subjects (r=0.06; NS), while stage of retinopathy was related to age (r=0.42;P=0.003) and to diabetes duration (r=0.74;P=0.0001) in these subjects. Elevated ACE activity occurs in type 1 diabetic subjects, especially in those with microalbuminuria. This may give early indication of lesions in vascular endothelial cells.