Diagnostic aspects of angiotensin converting enzyme in pulmonary sarcoidosis

Angiotensin converting enzyme (ACE) has been measured in 102 biopsy-proven sarcoid patients, 70 patients diagnosed by clinical and radiological methods and 74 nonsarcoid patients as controls. The distributions of the various groups have been examined, and the effects of stage of disease, disease activity and prednisone treatment have been evaluated. Receiver operating characteristic (ROC) curves have been established for ACE, and the appropriateness of various statistical procedures is discussed. We have not discerned any effect of stage of sarcoidosis or of extent of disease activity on ACE values. The ROC curves suggest an upper limit of normal of about 50 U/L for our assay, and a sensitivity of 63% and specificity of 93%, yielding predictive values of 93% for a positive result and 74% for a negative result, with a likelihood ratio of 3.6. The results are discussed in the context of other work on ACE and in relation to the more invasive procedures of bronchoalveolar lavage and Gallium scan.     

Serum angiotensin converting enzyme activity in ex-smokers

A low activity of angiotensin converting enzyme (ACE) has been reported in people who smoke. To determine whether this low ACE activity would be reversible on cessation of smoking, we measured serum ACE activity in 107 healthy male volunteers. They included 27 active cigarette smokers, 28 non-smokers, 24 ex-smokers who had stopped smoking for less than 10 yr, and 28 ex-smokers who had stopped smoking for more than 10 yr. The mean value (±SD) of serum ACE in those who had stopped smoking for more than 10 yr was comparable to that of non-smokers: 23.2 ± 5.1 and 23.5 ± 4.5, respectively. ACE activity in smokers and the ex-smokers who had stopped smoking for less than 10 yr was significantly lower (17.8 ± 4.5 and 17.8 ± 3.9, respectively) than values obtained in non-smokers and the group who had not smoked for more than 10 yr (p < 0.001). These findings suggest that the effect of chronic smoking on the serum ACE activity may be reversible.     

Serum angiotensin converting enzyme activity in cigarette smokers

Low activity of angiotensin converting enzyme (ACE) has been reported in patients with smoking related diseases, such as chronic bronchitis, emphysaema and carcinoma of the lung [1] but this has not been reported in healthy, chronic smokers. Serum ACE was measured in 40 healthy cigarette smokers and in 42 healthy non-smokers. The mean value was significantly lower in the smokers. Hence a non-smokers. The mean value was significantly lower in the smokers. Hence a patient's smoking habits should be taken into consideration when assessing the significance of his serum ACE levels.     

A radioassay for angiotensin converting enzyme

Current methods for measuring angiotensin converting enzyme activity (EC 3.4.15.1, ACE) are somewhat cumbersome and have limited the general availability of the test. We describe here a simple four-step radioassay for ACE which uses the substrate 14C-Hippurate-L-Histidyl-L-Leucine and measures the product, 14C-Hippurate. We found that incubation at pH 7.0 (Hepes buffer) increased the sensitivity of the test by 50 percent when compared to results obtained with the pH 8.0 buffer normally used for ACE assays. A split sample comparison study between the radioassay and the spectrophotometric method showed good correlation (n = 47; mean, spectrophotometric, 26.0 U/mL; mean, radioassay, 26.1 U/mL; m = 0.86; b = 3.9; r = 0.868). We found that there was no significant difference between the spectrophotometric, kinetic and radioassay (Newman-Keuls multiple range test), but the liquid chromatographic method gave results significantly different from the other methods. The assay for ACE described here combines enhanced technical ease with the sensitivity of a radioassay.     

Serum angiotensin converting enzyme activity in patients with psoriasis

Serum angiotensin converting enzyme activity is frequently increased in patients with active sarcoidosis. In spite of a reported association between sarcoidosis and psoriasis, serum angiotensin converting enzyme activities have not been reported for patients with psoriasis. We found the mean (SD) angiotensin-converting enzyme activity for 51 healthy subjects was 18.6 (5.8) kU/l, but for 52 patients with psoriasis without coexisting sarcoidosis, it was 28.3 (6.7) kU/l. There is a significant difference between these means (p less than 0.01). Forty-two percent (22/52) of the psoriasis patients had an increased serum angiotensin converting activity. Other diseases sometimes associated with an increased serum angiotensin converting enzyme activity were excluded as possible causes of a elevated activity in our patients with psoriasis. We conclude that almost half of the patients with psoriasis will have an elevated serum angiotensin converting enzyme activity, even when coexisting sarcoidosis is absent.     

Serum angiotensin converting enzyme activity in human bronchial asthma.

Using hippuryl-L-histidyl-L-leucine as a substrate analog, serum angiotensin converting enzyme (ACE) was spectrophotometrically estimated in patients with bronchial asthma. There were significantly low activities of serum ACE in 115 patients with bronchial asthma irrespective of the presence or absence of acute attack. The activity of serum ACE was reduced more markedly in the chronic type of bronchial asthma than in the paroxysmal type.     

特发性肺纤维化患者血管紧张素转换酶基因多态性与其血清浓度的关系

目的探讨特发性肺纤维化(IPF)患者血管紧张素转换酶(ACE)基因多态性与其血清ACE浓度的关系。方法采用聚合酶链反应(PCR)技术检测ACE基因I/D多态性,应用ELISA法测定血清ACE的浓度。结果 IPF患者的血清ACE浓度与对照组比较明显降低,差异有统计学意义(P<0.05),其基因多态性与血清ACE水平有关,ACE水平由高到低依次为:II基因型、ID基因型、DD基因型。结论 ACE基因多态性是决定IPF患者血清ACE水平的重要因素。     

Improved micromethod for assay of serum angiotensin converting enzyme

We describe conditions for determining angiotensin converting enzyme (EC 3.4.15.1) in serum, by liquid chromatography. Serum (10 microL) is assayed with the artificial substrate hippuryl-glycyl-glycine (30 mmol/L) in a 50 mmol/L "HEPES" buffer solution with a high salt content (300 mmol of NaCl and 400 mmol of Na2SO4 per liter), at pH 8.0. The resulting enzymic activity is ninefold that of the currently popular spectrophotometric assay of Cushman and Cheung as modified by Lieberman (Am. J. Med. 59: 365-372, 1975). The hippuric acid end product is separated from the substrate by reversed-phase liquid chromatography and measured spectrophotometrically at 228 nm. o-Methyl hippuric acid is used as internal standard. The mean value for 100 normal control subjects was 317 (SD 96) nmol of hippuric acid released per milliliter of serum per minute. The enzyme activity is greater in newborns (p less than 0.05) and has a tendency to decrease with age. This partly automated method, which is optimized with regard to activity and detection, can be used in clinical routine.     

A simple spectrophotometric method for estimation of plasma angiotensin I converting enzyme activity.

The procedure described is rapid, fairly simple, and inexpensive. The method may easily be used even in a small clinical laboratory. This method, based on a specific reaction which gives a product, hippuric acid azlactone, which absorbs in the visible region, avoids the interference of reagents and solvents encountered in the UV spectrophotometric assay, in which hippuric acid is determined directly.     

Evaluation of a kinetic assay for angiotensin converting enzyme

We have verified the analytical reliability of a Sigma reagent kit, which is a modified method of Holmquist et al. (1) for the determination of angiotensin-converting enzyme (ACE) on the Abbott ABA-100 analyzer. The reaction was linear up to 160 U/L. Correlation with a radiometric method (Ventrex Laboratories) was good except for a negative constant bias and loss of linearity with the radiometric method at high levels. The reconstituted reagent was determined by atomic absorption spectroscopy to contain 5.6 mumol/L of zinc. An increase in zinc content up to 45.6 mumol/L had little or no effect on enzyme activities of preparations from three mammalian species: rabbit, guinea pig and human. Neither was ACE activity inhibited by preincubating each of two serum pools with any of four corticosteroids for up to 8 d. Enzyme activity in samples remained stable at 5 degrees C for 8 d.     

Characterization of a spectrophotometric assay for angiotensin converting enzyme

Although serum angiotensin converting enzyme (EC 3.4.15.1) activity has generally been shown to be increased in patients with sarcoidosis, considerable variation in the diagnostic usefulness of this test has been reported. We investigated the possibility that this variation may be the result of inhibition of the widely used spectrophotometric assay by various substances. We also prospectively examined the predictive value of measurements of this enzyme in serum from 100 patients being evaluated for sarcoidosis. The following did not significantly affect the results: storage at 4 or 25 degrees C for one week, hemoglobin, lipoproteins, or corticosteroid medications. Bilirubin, at concentrations of 20 mg/L of serum or move, significantly inhibited the assay. Sera with increased activity showed nonlinear reaction rates during the usual 60-min reaction interval, This was corrected by shortening the reaction time to 30 min. We found a predictive value of 88% when the serum angiotensin converting enzyme test was applied to the diagnosis of active sarcoidosis.     

Familial elevation of serum angiotensin converting enzyme

We report here a familial clustering of elevated serum angiotensin converting enzyme (ACE) levels. The patient is a 58-year-old Japanese female who had been in excellent health until age 45 when she developed an occlusion of the left central retinal vein. She was otherwise in excellent health, and no laboratory abnormality except a marked elevation of serum ACE level (625 nmol/min/ml; normal range; 22-40 nmol/min/ml of serum) was found. Her blood pressure was within normal limits (140/80 mmHg). There was no evidence for the diagnosis of sarcoidosis, Gaucher's disease, leprosy, hyperthyroidism, diabetic retinopathy, or liver disease. One of her two sisters also showed a marked increase in serum ACE activity (303 nmol/min/ml), and remarkably high levels of serum ACE (276 and 294 nmol/min/ml) were demonstrated in both sons of this sister. All the members of this family have been in excellent health. The serum ACE activity was activated by chloride and cobalt ions, and inhibited by EDTA, captopril and rabbit antiserum to purified human plasma ACE. Thus our study showed a familial clustering of elevated serum ACE in individuals who did not have conventional disease patterns associated with elevated serum ACE.     

Sensitive colorimetric assay for angiotensin converting enzyme in serum

A sensitive colorimetric procedure has been developed for the assay of angiotensin converting enzyme (EC 3.4.15.1) in serum. Serum (10 microL) is incubated for 30 min with hippuryl-glycyl-glycine as described earlier (Clin Chem 28: 1352-1355, 1982). After a Folin-Wu deproteinization, the liberated glycyl-glycine is derivatized with a borate-buffered (pH 9.3) trinitrobenzenesulfonate solution (60 mmol/L) to form trinitrophenyl-glycylglycine, the absorbance of which is read at 420 nm vs a serum blank. The linear range extends to an activity of more than 900 U/L of serum and the detection limit is less than 4 U/L. The mean activity for serum from 50 blood bank donors and 25 patients with active sarcoidosis was 281 (SD 77) and 693 (SD 81) U/L, respectively. The method demonstrates good precision (CVs less than 2.8%) and correlates well (r = .99) with results from a "high-pressure" liquid chromatographic procedure for determining hippuric acid. In addition, the proposed method is widely applicable, involving only commonly available apparatus.     

Inhibition of angiotensin converting enzyme activity in cultured endothelial cells by hypoxia.

Endothelial cells in tissue culture degrade bradykinin and convert angiotensin I to angiotensin II. These are both functions of a single dipeptidyl hydrolase, angiotensin converting enzyme. Monolayer cultures were prepared from human, rabbit, pig, and calf vessels. Angiotensin converting enzyme activity was assessed by adding either bradykinin or angiotensin I to the cells in culture flasks, and measuring residual peptide over time by radioimmunoassay. Peptide degradation was inhibited by the specific converting enzyme inhibitor, SQ 20881. The flasks were equilibrated with varying hypoxic gas mixtures: hypoxia rapidly (less than 2 min) decreased enzyme activity and room air restored it as rapidly. The extent to which activity was reduced was a direct function of PO2 (r = 0.93, P less than 0.001), and there was no enzyme activity below a PO2 of 30 mm Hg. Four preparations were studied with respect to decrease in enzyme activity by hypoxia: (a) intact cells in monolayer, (b) sonicated cells, (c) sonicated cells from which converting enzyme was partially dissolved by a detergent, and (d) purified converting enzyme. Hypoxia had progressively less of an inhibiting effect on the enzyme activity of the preparations as the degree of cell integrity decreased. Hypoxia inhibits angiotensin converting enzyme activity in cultured endothelial cells, but the effect of hypoxia is not on the enzyme per se, but appears to be a unique characteristic of the endothelial cell.     

血管紧张素转化酶(ACE)试剂盒的性能评价

目的自建血管紧张素转化酶检测系统的性能评价。方法依据临床和实验室标准化协会(CLSI)标准中EP5-A2,EP9-A文件的要求,采用全自动生化分析仪对九强公司的ACE试剂盒的精密度、线性、与比对试剂的相关性以及可报告范围等一些性能进行评价。结果自建系统血清ACE高低值的批内CV分别为6.87%和2.39%,批间CV分别为6.09%和1.81%,日间CV分别为8.00%和2.8%均在厂家提供的小于10%的范围内;线性结果R2=0.99;与比对试剂相关系数r=0.990 56,且平均偏倚为8.55%有良好的相关性;血清ACE检测试剂盒可报告范围为9.0U/L-600U/L。结论自建ACE检测系统各项性能可以满足临床应用的要求。     

Distribution of angiotensin converting enzyme in human tissues

Angiotensin converting enzyme (EC 3.4.15.1, dipeptidyl carboxypeptidase, ACE, Kininase II), the peptidase which transforms inactive decapeptide, angiotensin I, to the pressor octapeptide, angiotensin II, and which catalyses also the degradation of vasodilative nonapeptide bradykinin, was measured in 27 human tissue homogenates and physiological fluids. Two assays were used: one which measures the hydrolysis of the substrate hippuryl-glycyl-glycine, by means of high performance liquid chromatography and another, using a colorimetric assay measuring the cleaved glycyl-glycine after arylation with picrylsulfonic acid. All the tissues studied contained measurable converting enzyme activities which were inhibited by captopril (SQ 14.225) in low concentrations. High specific activities of converting enzyme were found in several tissues of the intestinal and urogenital tract, but the highest activity was found in benign prostatic hyperplasia. Normal prostate and prostatic adenocarcinoma have a much lower activity. Results obtained for human tissues are compared with those found in animals.