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

ACE Phenotyping in Human Blood and Tissues: Revelation of ACE Outliers and Sex Differences in ACE Sialylation

Angiotensin-converting enzyme (ACE) metabolizes a number of important peptides participating in blood pressure regulation and vascular remodeling. Elevated ACE expression in tissues (which is generally reflected by blood ACE levels) is associated with an increased risk of cardiovascular diseases. Elevated blood ACE is also a marker for granulomatous diseases. Decreased blood ACE activity is becoming a new risk factor for Alzheimer's disease. We applied our novel approach-ACE phenotyping-to characterize pairs of tissues (lung, heart, lymph nodes) and serum ACE in 50 patients. ACE phenotyping includes (1) measurement of ACE activity with two substrates (ZPHL and HHL); (2) calculation of the ratio of hydrolysis of these substrates (ZPHL/HHL ratio); (3) determination of ACE immunoreactive protein levels using mAbs to ACE; and (4) ACE conformation with a set of mAbs to ACE. The ACE phenotyping approach in screening format with special attention to outliers, combined with analysis of sequencing data, allowed us to identify patient with a unique ACE phenotype related to decreased ability of inhibition of ACE activity by albumin, likely due to competition with high CCL18 in this patient for binding to ACE. We also confirmed recently discovered gender differences in sialylation of some glycosylation sites of ACE. ACE phenotyping is a promising new approach for the identification of ACE phenotype outliers with potential clinical significance, making it useful for screening in a personalized medicine approach.

Carriers of Heterozygous Loss-of-Function ACE Mutations Are at Risk for Alzheimer's Disease

We hypothesized that subjects with heterozygous loss-of-function (LoF) ACE mutations are at risk for Alzheimer's disease because amyloid Aβ42, a primary component of the protein aggregates that accumulate in the brains of AD patients, is cleaved by ACE (angiotensin I-converting enzyme). Thus, decreased ACE activity in the brain, either due to genetic mutation or the effects of ACE inhibitors, could be a risk factor for AD. To explore this hypothesis in the current study, existing SNP databases were analyzed for LoF ACE mutations using four predicting tools, including PolyPhen-2, and compared with the topology of known ACE mutations already associated with AD. The combined frequency of >400 of these LoF-damaging ACE mutations in the general population is quite significant-up to 5%-comparable to the frequency of AD in the population > 70 y.o., which indicates that the contribution of low ACE in the development of AD could be under appreciated. Our analysis suggests several mechanisms by which ACE mutations may be associated with Alzheimer's disease. Systematic analysis of blood ACE levels in patients with all ACE mutations is likely to have clinical significance because available sequencing data will help detect persons with increased risk of late-onset Alzheimer's disease. Patients with transport-deficient ACE mutations (about 20% of damaging ACE mutations) may benefit from preventive or therapeutic treatment with a combination of chemical and pharmacological (e.g., centrally acting ACE inhibitors) chaperones and proteosome inhibitors to restore impaired surface ACE expression, as was shown previously by our group for another transport-deficient ACE mutation-Q1069R.

The physiology of bilirubin: health and disease equilibrium

Bilirubin has several physiological functions, both beneficial and harmful. In addition to reactive oxygen species-scavenging activities, bilirubin has potent immunosuppressive effects associated with long-term pathophysiological sequelae. It has been recently recognized as a hormone with endocrine actions and interconnected effects on various cellular signaling pathways. Current studies show that bilirubin also decreases adiposity and prevents metabolic and cardiovascular diseases. All in all, the physiological importance of bilirubin is only now coming to light, and strategies for increasing plasma bilirubin levels to combat chronic diseases are starting to be considered. This review discusses the beneficial effects of increasing plasma bilirubin, incorporates emerging areas of bilirubin biology, and provides key concepts to advance the field.

Urinary ACE Phenotyping as a Research and Diagnostic Tool: Identification of Sex-Dependent ACE Immunoreactivity

BACKGROUND

Angiotensin-converting enzyme (ACE) is highly expressed in renal proximal tubules, but ACE activity/levels in the urine are at least 100-fold lower than in the blood. Decreased proximal tubular ACE has been associated with renal tubular damage in both animal models and clinical studies. Because ACE is shed into urine primarily from proximal tubule epithelial cells, its urinary ACE measurement may be useful as an index of tubular damage.

OBJECTIVE AND METHODOLOGY

We applied our novel approach-ACE phenotyping-to characterize urinary ACE in volunteer subjects. ACE phenotyping includes (1) determination of ACE activity using two substrates (ZPHL and HHL); (2) calculation of the ratio of hydrolysis of the two substrates (ZPHL/HHL ratio); (3) quantification of ACE immunoreactive protein levels; and (4) fine mapping of local ACE conformation with mAbs to ACE.

PRINCIPAL FINDINGS

In normal volunteers, urinary ACE activity was 140-fold less than in corresponding plasma/serum samples and did not differ between males and females. However, urinary ACE immunoreactivity (normalized binding of 25 mAbs to different epitopes) was strongly sex-dependent for the several mAbs tested, an observation likely explained by differences in tissue ACE glycosylation/sialylation between males and females. Urinary ACE phenotyping also allowed the identification of ACE outliers. In addition, daily variability of urinary ACE has potential utility as a feedback marker for dieting individuals pursuing weight loss.

CONCLUSIONS/SIGNIFICANCE

Urinary ACE phenotyping is a promising new approach with potential clinical significance to advance precision medicine screening techniques.

Petukhov P, Kurilova OV, Ilinsky VV, Trakhtman PE, Dadali EL, Samokhodskaya LM, Kamalov AA, Kost OA. Blood ACE Phenotyping for Personalized Medicine: Revelation of Patients with Conformationally Altered ACE

Background: The angiotensin-converting enzyme (ACE) metabolizes a number of important peptides participating in blood pressure regulation and vascular remodeling. Elevated blood ACE is a marker for granulomatous diseases and elevated ACE expression in tissues is associated with increased risk of cardiovascular diseases. Objective and Methodology: We applied a novel approach -ACE phenotyping-to find a reason for conformationally impaired ACE in the blood of one particular donor. Similar conformationally altered ACEs were detected previously in 2-4% of the healthy population and in up to 20% of patients with uremia, and were characterized by significant increase in the rate of angiotensin I hydrolysis. Principal findings: This donor has (1) significantly increased level of endogenous ACE inhibitor in plasma with MW less than 1000; (2) increased activity toward angiotensin I; (3) M71V mutation in ABCG2 (membrane transporter for more than 200 compounds, including bilirubin). We hypothesize that this patient may also have the decreased level of free bilirubin in plasma, which normally binds to the N domain of ACE. Analysis of the local conformation of ACE in plasma of patients with Gilbert and Crigler-Najjar syndromes allowed us to speculate that binding of mAbs 1G12 and 6A12 to plasma ACE could be a natural sensor for estimation of free bilirubin level in plasma. Totally, 235 human plasma/sera samples were screened for conformational changes in soluble ACE. Conclusions/Significance: ACE phenotyping of plasma samples allows us to identify individuals with conformationally altered ACE. This type of screening has clinical significance because this conformationally altered ACE could not only result in the enhancement of the level of angiotensin II but could also serve as an indicator of free bilirubin levels.

Reversal of aging-associated increase in myelopoiesis and expression of alarmins by angiotensin-(1-7)

Aging is associated with chronic systemic inflammation largely due to increased myelopoiesis, which in turn increases risk for vascular disease. We have previously shown evidence for the therapeutic potential of Angiotensin-(1-7) (Ang-(1-7)) in reversing vasoreparative dysfunction in aging. This study tested the hypothesis that ischemic vascular repair in aging by Ang-(1-7) involves attenuation of myelopoietic potential in the bone marrow and decreased mobilization of inflammatory cells. Young or Old male mice of age 3-4 and 22-24 months, respectively, received Ang-(1-7) (1 µg/kg/min, s.c.) for four weeks. Myelopoiesis was evaluated in the bone marrow (BM) cells by carrying out the colony forming unit (CFU-GM) assay followed by flow cytometry of monocyte-macrophages. Expression of pro-myelopoietic factors and alarmins in the hematopoietic progenitor-enriched BM cells was evaluated. Hindlimb ischemia (HLI) was induced by femoral ligation, and mobilization of monocytes into the blood stream was determined. Blood flow recovery was monitored by Laser Doppler imaging and infiltration of inflammatory cells was evaluated by immunohistochemistry. BM cells from Old mice generated a higher number of monocytes (Ly6G-CD11b+Ly6Chi) and M1 macrophages (Ly6ChiF4/80+) compared to that of Young, which was reversed by Ang-(1-7). Gene expression of selected myelopoietic factors, alarmins (S100A8, S100A9, S100A14 and HMGb1) and the receptor for alarmins, RAGE, was higher in the Old hematopoietic progenitor-enriched BM cells compared to the Young. Increased expressions of these factors were decreased by Ang-(1-7). Ischemia-induced mobilization of monocytes was higher in Old mice with decreased blood flow recovery and increased infiltration of monocyte-macrophages compared to the Young, all of which were reversed by Ang-(1-7). Enhanced ischemic vascular repair by Ang-(1-7) in aging is largely by decreasing the generation and recruitment of inflammatory monocyte-macrophages to the areas of ischemic injury. This is associated with decreased alarmin signaling in the BM-hematopoietic progenitor cells.

Association analysis and expression level of ace polymorphisms with egg-laying trait in Taihang chicken

The number of egg-laying is an important indicator of reproduction performance in poultry breeding. To investigate the relationship between the function of Angiotensin-converting enzyme (ACE) and egg-laying performance of Taihang chicken, the mRNA and protein expression and single nucleotide polymorphism (SNP) of ACE were detected. Analysis of ACE bioinformatics and association analysis of polymorphisms were then performed. The polymorphisms analysis of ACE showed that three SNP loci (g.5066812A>C, g.5080076G>A, and g.5072728A>G) were detected in 800 Taihang chickens with egg-laying records. Association analysis of egg-laying found that ACE g.5066812A>C mutation was significantly associated with the egg-laying performance of Taihang chickens (P < 0.05), and the individuals with the g.5066812A>C mutation showed significantly increasing egg-laying. The mRNA expression was significantly higher in individuals with the AA genotype mutation than those with the AC and CC genotypes (P < 0.01), and the expression of ACE protein levels was consistent with the mRNA expression. Bioinformatics analysis indicated that these mutations affected the secondary and tertiary structure of ACE. This study provides new insights into ACE affecting chicken egg production and some basis for improving the egg production rate of Taihang chickens.

Predictive potential of ACE phenotyping in extrapulmonary sarcoidosis

Elevated ACE expression in tissues (reflected by blood ACE levels) is associated with increased risk of cardiovascular diseases and is also a marker for granulomatous diseases. We developed a new approach for characterization of ACE status in the blood—ACE phenotyping and established normal values of ACE levels 50–150% of control pooled plasma. ACE phenotyping was performed in citrated plasma of 120 patients with known interstitial lung diseases. In the 1st set of 100 patients we found 22 patients with ACE levels > 150%; ACE phenotyping also objectively identified the presence of ACE inhibitors in the plasma of 15 patients. After excluding these patients and patient with ACE mutation that increases ACE shedding, 17 patients were identified as a suspicious for systemic sarcoidosis based on elevation of blood ACE (> 150% of mean). A new parameter that we have established–ACE immunoreactivity (with mAb 9B9)—allowed us to detect 22 patients with decreased values (< 80%) of this parameter, which may indicate the presence of ACE in the blood that originates from macrophages/dendritic cells of granulomas. In the remaining 20 patients, this new parameter (mAbs binding/activity ratio) was calculated using 3 mAbs (9B9, 3A5 and i1A8—having overlapping epitopes), and 8 patients were identified as having decreases in this parameter, thus increasing dramatically the sensitivity for detection of patients with systemic sarcoidosis. Whole body PET scan confirmed extrapulmonary granulomas in some patients with lower immunoreactivity towards anti-ACE mAbs. ACE phenotyping has novel potential to noninvasively detect patients with systemic sarcoidosis.

Cloaking the ACE2 receptor with salivary cationic proteins inhibits SARS-CoV-2 entry

Saliva contributes to the innate immune system, which suggests that it can prevent SARS-CoV-2 entry. We studied the ability of healthy salivary proteins to bind to angiotensin-converting enzyme 2 (ACE2) using biolayer interferometry and pull-down assays. Their effects on binding between the receptor-binding domain of the SARS-CoV-2 spike protein S1 (S1) and ACE2 were determined using an enzyme-linked immunosorbent assay. Saliva bound to ACE2 and disrupted the binding of S1 to ACE2 and four ACE2-binding salivary proteins were identified, including cationic histone H2A and neutrophil elastase, which inhibited the S1-ACE2 interaction. Calf thymus histone (ct-histone) also inhibited binding as effectively as histone H2A. The results of a cell-based infection assay indicated that ct-histone suppressed SARS-CoV-2 pseudoviral invasion into ACE2-expressing host cells. Manufactured polypeptides, such as ε-poly-L-lysine, also disrupted S1-ACE2 binding, indicating the importance of the cationic properties of salivary proteins in ACE2 binding. Overall, we demonstrated that positively-charged salivary proteins are a barrier against SARS-CoV-2 entry by cloaking the negatively-charged surface of ACE2, and provided a view that the cationic polypeptides represent a preventative and therapeutic treatment against COVID-19.

Sex differences in the lung ACE/ACE2 balance in hypertensive rats

The angiotensin-converting enzyme (ACE)/Angiotensin II (Ang II) and angiotensin-converting enzyme 2 (ACE2)/angiotensin-(1-7) (Ang-(1-7)) pathways are coexpressed in most tissues. The balance between these pathways determines, at least in part, whether tissue damage will occur in response to pathological stimuli. The present study tested the hypothesis that male sex and high blood pressure are associated with ACE/ACE2 imbalance in the lungs. Experiments were conducted in male and female Wistar rats and spontaneously hypertensive rats (SHRs). Lung ACE and ACE2 gene expression was also evaluated in normotensive and hypertensive humans using the Genotype-Tissue Expression (GTEx) project. Compared with Wistar rats and female SHRs, male SHRs displayed reduced lung ACE2 mRNA, ACE2 protein abundance and ACE2 activity, and increased Ang II concentration. Lung ACE mRNA levels were higher in male SHRs than in Wistar rats, whereas lung ACE protein abundance and activity were similar among the four groups of rats. Lung Ang-(1-7) concentration was higher in female than in male SHRs (89 ± 17 vs. 43 ± 2 pg/g, P<0.05). Lung ACE to ACE2 mRNA expression in hypertensive patients was significantly higher than that in normotensive subjects. Taken together, these results demonstrate that male hypertensive rats display imbalance between the ACE/Ang II and ACE2/Ang-(1-7) pathways in the lungs mainly attributable to ACE2 down-regulation. Further studies should be conducted to investigate whether this imbalance between ACE/ACE2 may promote and accelerate lung injury in respiratory infections, including coronavirus disease 2019 (COVID-19).

Phenotyping Angiotensin-Converting Enzyme in Blood: A Necessary Approach for Precision Medicine

BACKGROUND

Angiotensin-converting enzyme (ACE) metabolizes a number of important peptides participating in blood pressure regulation and vascular remodeling. Elevated ACE expression in tissues (which is generally reflected by ACE in blood) is associated with increased risk of cardiovascular diseases. Elevated ACE in blood is also a marker for granulomatous diseases.

METHODS

We applied our novel approach-ACE phenotyping-to characterize serum ACE in 300 unrelated patients and to establish normal values for ACE levels. ACE phenotyping includes (a) determination of ACE activity with 2 substrates (Z-Phe-His-Leu [ZPHL] and Hip-His-Leu [HHL]), (b) calculation of a ratio for hydrolysis of ZPHL and HHL, and (c) quantification of ACE immunoreactive protein levels and ACE conformation with a set of monoclonal antibodies (mAbs) to ACE.

RESULTS

Only a combination of ACE activity determination with 2 substrates and quantification of the amount of ACE immunoreactive protein with mAbs 1G12 and 9B9 allows for the unequivocal detection of the presence of ACE inhibitors in the blood. After excluding such subjects, we were able to establish normal values of ACE in healthy populations: 50%-150% from control pooled serum. This ACE phenotyping approach in screening format with special attention to outliers can also identify patients with various mutations in ACE and may help to identify the as yet unknown ACE secretase or other mechanistic details of precise regulation of ACE expression.

CONCLUSIONS

ACE phenotyping is a promising new approach with potential clinical significance to advance precision medicine screening techniques by establishing different risk groups based on ACE phenotype.

Development of a random forest model to classify sarcoidosis and tuberculosis

OBJECTIVE

To identify significant diagnostic factors and establish a predictive model for diagnosis of sarcoidosis and tuberculosis.

METHODS

This study included 252 patients (123 cases of lung sarcoidosis and 129 cases of lung tuberculosis) who underwent laboratory evaluation, including routine hematologic testing, serum immunology, blood coagulation, angiotensin-converting enzyme, and T lymphocyte subset. The factors that statistically different between the two groups were identified by an independent sample t test first, and then processed by the random forest model to distinguish two diseases with the classification function. Moreover, the diagnostic performance of the predictive random forest model was evaluated through the identification of individual contribution of various diagnostic factors conducted by the model.

RESULTS

The random forest model revealed a classification error rate of 24.9%. Among all of the statistically significant diagnostic factors, the individual factors with the greatest and second contribution were angiotensin-converting enzyme and prothrombin time, respectively. The area under the receiver operating characteristic (ROC) curve of the random forest prediction model was 0.915.

CONCLUSION

The random forest model can be used to distinguish between sarcoidosis and tuberculosis by incorporating statistically significant diagnostic factors, which is of potential clinical application value.

Epitope mapping of novel monoclonal antibodies to human angiotensin I-converting enzyme

Angiotensin I-converting enzyme (ACE, CD143) plays a crucial role in blood pressure regulation, vascular remodeling, and immunity. A wide spectrum of mAbs to different epitopes on the N and C domains of human ACE have been generated and used to study different aspects of ACE biology, including establishing a novel approach-conformational fingerprinting. Here we characterized a novel set of 14 mAbs, developed against human seminal fluid ACE. The epitopes for these novel mAbs were defined using recombinant ACE constructs with truncated N and C domains, species cross-reactivity, ACE mutagenesis, and competition with the previously mapped anti-ACE mAbs. Nine mAbs recognized regions on the N domain, and 5 mAbs-on the C domain of ACE. The epitopes for most of these novel mAbs partially overlap with epitopes mapped onto ACE by the previously generated mAbs, whereas mAb 8H1 recognized yet unmapped region on the C domain where three ACE mutations associated with Alzheimer's disease are localized and is a marker for ACE mutation T877M. mAb 2H4 could be considered as a specific marker for ACE in dendritic cells. This novel set of mAbs can identify even subtle changes in human ACE conformation caused by tissue-specific glycosylation of ACE or mutations, and can detect human somatic and testicular ACE in biological fluids and tissues. Furthermore, the high reactivity of these novel mAbs provides an opportunity to study changes in the pattern of ACE expression or glycosylation in different tissues, cells, and diseases, such as sarcoidosis and Alzheimer's disease.

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.

Tissue ACE phenotyping in lung cancer

Background

Pulmonary vascular endothelium is the main metabolic site for Angiotensin I-Converting Enzyme (ACE)-mediated degradation of several biologically-active peptides (angiotensin I, bradykinin, hemo-regulatory peptide Ac-SDKP). Primary lung cancer growth and lung cancer metastases decrease lung vascularity reflected by dramatic decreases in both lung and serum ACE activity. We performed precise ACE phenotyping in tissues from subjects with lung cancer.

Methodology

ACE phenotyping included: 1) ACE immunohistochemistry with specific and well-characterized monoclonal antibodies (mAbs) to ACE; 2) ACE activity measurement with two ACE substrates (HHL, ZPHL); 3) calculation of ACE substrates hydrolysis ratio (ZPHL/HHL ratio); 4) the pattern of mAbs binding to 17 different ACE epitopes to detect changes in ACE conformation induced by tumor growth (conformational ACE fingerprint).

Results

ACE immunostaining was dramatically decreased in lung cancer tissues confirmed by a 3-fold decrease in ACE activity. The conformational fingerprint of ACE from tumor lung tissues differed from normal lung (6/17 mAbs) and reflected primarily higher ACE sialylation. The increase in ZPHL/HHL ratio in lung cancer tissues was consistent with greater conformational changes of ACE. Limited analysis of the conformational ACE fingerprint in normal lung tissue and lung cancer tissue form the same patient suggested a remote effect of tumor tissue on ACE conformation and/or on “field cancerization” in a morphologically-normal lung tissues.

Conclusions/Significance

Local conformation of ACE is significantly altered in tumor lung tissues and may be detected by conformational fingerprinting of human ACE.

Tissue ACE phenotyping in prostate cancer

Epithelial cells of prostate express significant level of ACE and, as a result, seminal fluid has 50-fold more ACE than plasma. The substitution of highly specialized prostate epithelial cells by tumor cells results in dramatic decrease in ACE production in prostate tissues. We performed detailed characterization of ACE status in prostate tissues from patients with benign prostate hyperplasia (BPH) and prostate cancer (PC) using new approach- ACE phenotyping, that includes evaluation of: 1) ACE activity with two substrates (HHL and ZPHL); 2) the ratio of the rates of their hydrolysis (ZPHL/HHL ratio); 3) the ratio of immunoreactive ACE protein to ACE activity; 4) the pattern of mAbs binding to different epitopes on ACE – ACE conformational fingerprint - to reveal conformational changes in prostate ACE due to prostate pathology. ACE activity dramatically decreased and the ratio of immunoreactive ACE protein to ACE activity increased in PC tissues. The catalytic parameter, ZPHL/HHL ratio, increased in prostate tissues from all patients with PC, but was did not change for most |BPH patients. Nevertheless, prostate tissues of several patients diagnosed with BPH based on histology, also demonstrated decreased ACE activity and increased immunoreactive ACE protein/ACE activity and ZPHL/HHL ratios, that could be considered as more early indicators of prostate cancer development than routine histology. Thus, ACE phenotyping of prostate biopsies has a potential to be an effective approach for early diagnostics of prostate cancer or at least for differential diagnostics of BPH and PC.

Optimized angiotensin-converting enzyme activity assay for the accurate diagnosis of sarcoidosis

BACKGROUND

Serum angiotensin-converting enzyme (ACE) activity determination can aid the early diagnosis of sarcoidosis. We aimed to optimize a fluorescent kinetic assay for ACE activity by screening the confounding effects of endogenous ACE inhibitors and interfering factors. Genotype-dependent and genotype-independent reference values of ACE activity were established, and their diagnostic accuracies were validated in a clinical study.

METHODS

Internally quenched fluorescent substrate, Abz-FRK(Dnp)P-OH was used for ACE-activity measurements. A total of 201 healthy individuals and 59 presumably sarcoidotic patients were enrolled into this study. ACE activity and insertion/deletion (I/D) genotype of the ACE gene were determined.

RESULTS

Here we report that serum samples should be diluted at least 35-fold to eliminate the endogenous inhibitor effect of albumin. No significant interferences were detected: up to a triglyceride concentration of 16 mM, a hemoglobin concentration of 0.71 g/L and a bilirubin concentration of 150 μM. Genotype-dependent reference intervals were considered as 3.76-11.25 U/L, 5.22-11.59 U/L, 7.19-14.84 U/L for II, ID and DD genotypes, respectively. I/D genotype-independent reference interval was established as 4.85-13.79 U/L. An ACE activity value was considered positive for sarcoidosis when it exceeded the upper limit of the reference interval. The optimized assay with genotype-dependent reference ranges resulted in 42.5% sensitivity, 100% specificity, 100% positive predictive value and 32.4% negative predictive value in the clinical study, whereas the genotype-independent reference range proved to have inferior diagnostic efficiency.

CONCLUSIONS

An optimized fluorescent kinetic assay of serum ACE activity combined with ACE I/D genotype determination is an alternative to invasive biopsy for confirming the diagnosis of sarcoidosis in a significant percentage of patients.

Conformational fingerprint of blood and tissue ACEs: Personalized approach

Background

The pattern of binding of monoclonal antibodies (mAbs) to 18 epitopes on human angiotensin I-converting enzyme (ACE)–“conformational fingerprint of ACE”–is a sensitive marker of subtle conformational changes of ACE due to mutations, different glycosylation in various cells, the presence of ACE inhibitors and specific effectors, etc.

Methodology/Principal findings

We described in detail the methodology of the conformational fingerprinting of human blood and tissue ACEs that allows detecting differences in surface topography of ACE from different tissues, as well detecting inter-individual differences. Besides, we compared the sensitivity of the detection of ACE inhibitors in the patient’s plasma using conformational fingerprinting of ACE (with only 2 mAbs to ACE, 1G12 and 9B9) and already accepted kinetic assay and demonstrated that the mAbs-based assay is an order of magnitude more sensitive. This approach is also very effective in detection of known (like bilirubin and lysozyme) and still unknown ACE effectors/inhibitors which nature and set could vary in different tissues or different patients.

Conclusions/Significance

Phenotyping of ACE (and conformational fingerprinting of ACE as a part of this novel approach for characterization of ACE) in individuals really became informative and clinically relevant. Appreciation (and counting on) of inter-individual differences in ACE conformation and accompanying effectors make the application of this approach for future personalized medicine with ACE inhibitors more accurate. This (or similar) methodology can be applied to any enzyme/protein for which there is a number of mAbs to its different epitopes.

ACE phenotyping in Gaucher disease

BACKGROUND

Gaucher disease is characterized by the activation of splenic and hepatic macrophages, accompanied by dramatically increased levels of angiotensin-converting enzyme (ACE). To evaluate the source of the elevated blood ACE, we performed complete ACE phenotyping using blood, spleen and liver samples from patients with Gaucher disease and controls.

METHODS

ACE phenotyping included 1) immunohistochemical staining for ACE; 2) measuring ACE activity with two substrates (HHL and ZPHL); 3) calculating the ratio of the rates of substrate hydrolysis (ZPHL/HHL ratio); 4) assessing the conformational fingerprint of ACE by evaluating the pattern of binding of monoclonal antibodies to 16 different ACE epitopes.

RESULTS

We show that in patients with Gaucher disease, the dramatically increased levels of ACE originate from activated splenic and/or hepatic macrophages (Gaucher cells), and that both its conformational fingerprint and kinetic characteristics (ZPHL/HHL ratio) differ from controls and from patients with sarcoid granulomas. Furthermore, normal spleen was found to produce high levels of endogenous ACE inhibitors and a novel, tightly-bound 10-30 kDa ACE effector which is deficient in Gaucher spleen.

CONCLUSIONS

The conformation of ACE is tissue-specific. In Gaucher disease, ACE produced by activated splenic macrophages differs from that in hepatic macrophages, as well as from macrophages and dendritic cells in sarcoid granulomas. The observed differences are likely due to altered ACE glycosylation or sialylation in these diseased organs. The conformational differences in ACE may serve as a specific biomarker for Gaucher disease.

Conformational Fingerprinting Using Monoclonal Antibodies (on the Example of Angiotensin I-Converting Enzyme-ACE)

During the past 30 years my laboratory has generated 40+ monoclonal antibodies (mAbs) directed to structural and conformational epitopes on human ACE as well as ACE from rats, mice and other species. These mAbs were successfully used for detection and quantification of ACE by ELISA, Western blotting, flow cytometry and immunohistochemistry. In all these applications mainly single mAbs were used. We hypothesized that we can obtain a completely new kind of information about ACE structure and function if we use the whole set of mAbs directed to different epitopes on the ACE molecule. When we finished epitope mapping of all mAbs to ACE (and especially, those recognizing conformational epitopes), we realized that we had obtained a new tool to study ACE. First, we demonstrated that binding of some mAbs is very sensitive to local conformational changes on the ACE surface—due to local denaturation, inactivation, ACE inhibitor or mAbs binding or due to diseases. Second, we were able to detect, localize and characterize several human ACE mutations. And, finally, we established a new concept—conformational fingerprinting of ACE using mAbs that in turn allowed us to obtain evidence for tissue specificity of ACE, which has promising scientific and diagnostic perspectives. The initial goal for the generation of mAbs to ACE 30 years ago was obtaining mAbs to organ-specific endothelial cells, which could be used for organ-specific drug delivery. Our systematic work on characterization of mAbs to numerous epitopes on ACE during these years has lead not only to the generation of the most effective mAbs for specific drug/gene delivery into the lung capillaries, but also to the establishment of the concept of conformational fingerprinting of ACE, which in turn gives a theoretical base for the generation of mAbs, specific for ACE from different organs. We believe that this concept could be applicable for any glycoprotein against which there is a set of mAbs to different epitopes.

ACE phenotyping in human heart

Aims

Angiotensin-converting enzyme (ACE), which metabolizes many peptides and plays a key role in blood pressure regulation and vascular remodeling, is expressed as a type-1 membrane glycoprotein on the surface of different cells, including endothelial cells of the heart. We hypothesized that the local conformation and, therefore, the properties of heart ACE could differ from lung ACE due to different microenvironment in these organs.

Methods and results

We performed ACE phenotyping (ACE levels, conformation and kinetic characteristics) in the human heart and compared it with that in the lung. ACE activity in heart tissues was 10–15 lower than that in lung. Various ACE effectors, LMW endogenous ACE inhibitors and HMW ACE-binding partners, were shown to be present in both heart and lung tissues. “Conformational fingerprint” of heart ACE (i.e., the pattern of 17 mAbs binding to different epitopes on the ACE surface) significantly differed from that of lung ACE, which reflects differences in the local conformations of these ACEs, likely controlled by different ACE glycosylation in these organs. Substrate specificity and pH-optima of the heart and lung ACEs also differed. Moreover, even within heart the apparent ACE activities, the local ACE conformations, and the content of ACE inhibitors differ in atria and ventricles.

Conclusions

Significant differences in the local conformations and kinetic properties of heart and lung ACEs demonstrate tissue specificity of ACE and provide a structural base for the development of mAbs able to distinguish heart and lung ACEs as a potential blood test for predicting atrial fibrillation risk.

ACE Phenotyping as a Guide Toward Personalized Therapy With ACE Inhibitors

Background:

Angiotensin-converting enzyme (ACE) inhibitors (ACEI) are widely used in the management of cardiovascular diseases but with significant interindividual variability in the patient’s response.

Objectives:

To investigate whether interindividual variability in the response to ACE inhibitors is explained by the “ACE phenotype”—for example, variability in plasma ACE concentration, activity, and conformation and/or the degree of ACE inhibition in each individual.

Methods:

The ACE phenotype was determined in plasma of 14 patients with hypertension treated chronically for 4 weeks with 40 mg enalapril (E) or 20 mg E + 16 mg candesartan (EC) and in 20 patients with hypertension treated acutely with a single dose (20 mg) of E with or without pretreatment with hydrochlorothiazide. The ACE phenotyping included (1) plasma ACE concentration; (2) ACE activity (with 2 substrates: Hip-His-Leu and Z-Phe-His-Leu and calculation of their ratio); (3) detection of ACE inhibitors in patient’s blood (indicator of patient compliance) and the degree of ACE inhibition (ie, adherence); and (4) ACE conformation.

Results:

Enalapril reduced systolic and diastolic blood pressure in most patients; however, 20% of patients were considered nonresponders. Chronic treatment results in 40% increase in serum ACE concentrations, with the exception of 1 patient. There was a trend toward better response to ACEI among patients who had a higher plasma ACE concentration.

Conclusion:

Due to the fact that “20% of patients do not respond to ACEI by blood pressure drop,” the initial blood ACE level could not be a predictor of blood pressure reduction in an individual patient. However, ACE phenotyping provides important information about conformational and kinetic changes in ACE of individual patients, and this could be a reason for resistance to ACE inhibitors in some nonresponders.