Focus on increased serum angiotensin-converting enzyme level: From granulomatous diseases to genetic mutations

Angiotensin I-converting enzyme (ACE) is a well-known zinc-metallopeptidase that converts angiotensin I to the potent vasoconstrictor angiotensin II and degrades bradykinin, a powerful vasodilator, and as such plays a key role in the regulation of vascular tone and cardiac function. Increased circulating ACE (cACE) activity has been reported in multiple diseases, including but not limited to granulomatous disorders. Since 2001, genetic mutations leading to cACE elevation have also been described. This review takes advantage of the identification of a novel ACE mutation (25-IVS25 + 1G > A) in two Belgian pedigrees to summarize current knowledge about the differential diagnosis of cACE elevation, based on literature review and the experience of our centre. Furthermore, we propose a practical approach for the evaluation and management of patients with elevated cACE and discuss in which cases search for genetic mutations should be considered.

Increased circulatory RAS activity can be inhibited by statins in patients with hypercholesterolemia

OBJECTIVE

The objective of this paper is to investigate a profile on circulatory renin-angiotensin system (RAS) activity in hypercholesterolemic (HC) patients treated with statins.

METHODS

Eighteen primary HC patients and 18 sex- and age-matched healthy adults were included in this study as controls. Total cholesterol (TC), triglyceride (TG), LDL-C, blood glucose, angiotensin-converting enzyme (ACE) activity, and angiotensin II (Ang II) levels were measured before and four and eight weeks after beginning statin treatment in the HC group. Similar measurements were taken in the control group at baseline.

RESULTS

At baseline, TC, TG and LDL-C levels, as well as ACE activity and Ang II concentrations, were significantly higher in the HC group than in the control group. Based on the baseline data collection of 36 participants, there were significant positive correlations between ACE activity and TC (r = 0.54) or LDL-C (r = 0.51), and between Ang II level and TC (r = 0.34) or LDL-C (r = 0.27). TC, LDL-C, Ang II (35.46 ± 14.49 vs 71.10 ± 20.47 pg/ml, p < 0.05) levels and ACE activity (108.9 ± 51.9 vs 180.1 ± 71.3 U/L, p < 0.05) were decreased in HC patients eight weeks after starting statin treatment. In HC patients, RAS activity correlated positively with TC and LDL-C levels before and after treatment.

CONCLUSIONS

In HC patients, lowering serum cholesterol with statins is associated with decreased circulatory RAS activity.

Effect of long-term treatment with urocortin on the activity of somatic angiotensin-converting enzyme in spontaneously hypertensive rats

Our previous acute study on urocortin (Ucn) demonstrated that Ucn altered serum and tissue angiotensin-converting enzyme (ACE) activity in rats. Therefore, the present investigation was designed to explore the effect of long-term treatment with Ucn on somatic ACE (sACE) and other components of the renin–angiotensin system (RAS). After 8 weeks of intravenous administration of Ucn in spontaneously hypertensive rats (SHR), serum and tissue sACE, angiotensin II (Ang II), nitric oxide (NO), Ang-(1–7), and tissue chymase activities were evaluated. RT-PCR analysis was performed to determine the quantity of tissue sACE mRNA. Serum sACE activity was reduced by Ucn, although tissue sACE activity and tissue sACE mRNA were elevated. Chymase activity was observed to be enhanced by Ucn, whereas the ACE inhibitor enalapril failed to influence chymase. Serum and tissue Ang II activity was reduced, but NO and Ang-(1–7) production was increased in a concentration-dependent manner after Ucn treatment. Meanwhile, a significant decrease of the systolic blood pressure (SBP) was observed after the long-term Ucn administration, and there was a significant positive correlation (r2 = 0.6993) between serum ACE activity and SBP. Pretreatment with the corticotropin-releasing factor (CRF) blocker astressin and the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway blocker PD98059 abolished these effects of Ucn. Our findings further support the hypothesis that the changes of sACE activity and the production of other RAS components may play roles in the vasodilatory property of Ucn via the activation of the ERK1/2 pathway.

Comparison of angiotensin converting enzyme inhibition and angiotensin II receptor blockade for the prevention of experimental autoimmune myocarditis

The angiotensin converting enzyme inhibitor captopril prevents myosin-induced experimental autoimmune myocarditis. Captopril inhibits production of angiotensin II and increases bradykinin signaling, among other actions. To test whether captopril inhibits disease through blockade of angiotensin signaling, we tested the ability of losartan, an angiotensin II receptor blocker, to prevent myosin-induced myocarditis. A/J mice immunized with the heavy chain of cardiac myosin in complete Freund's adjuvant develop acute myocarditis by day 21 post-immunization, consisting of severe focal inflammation, necrosis and fibrosis. Administration of losartan (250 mg/L in the drinking water) or captopril (75 mg/L in the drinking water) significantly reduced inflammation, necrosis and fibrosis in myosin-immunized mice. The heart weights and the heart weight-to-body weight ratios were also significantly reduced in both treatment groups. However, whereas captopril reduced myosin-specific delayed-type hypersensitivity, losartan did not. Both captopril-treated mice and losartan-treated mice showed a decrease in myosin-specific autoantibody production. Because losartan treatment significantly reduced myocarditis, fibrosis and autoantibody production in EAM, it is likely that prevention of angiotensin II receptor stimulation is a major mechanism underlying the inhibition of myosin-induced myocarditis by captopril.

Effects of genistein on angiotensin-converting enzyme in rats

Genistein (4,5,7-trihydroxyisoflavone), a phytoestrogen with selective estrogen receptor modulator properties, has received a great deal of attention over the last few years because of its potentially preventive roles against cardiovascular diseases. However, the precise molecular mechanisms for this modulation are not fully elucidated. In this study, we investigated (both in vivo and in vitro) the relationship between genistein and the changes of angiotensin-converting enzyme (ACE) in rat aortic endothelial cells (RAECs), serum and tissue (aorta). ACE expression was assessed by the immunofluorescence and the reverse transcriptase-polymerase chain reaction (RT-PCR) assay. Serum and tissue ACE activity was detected with a commercial kit. Genistein exhibited a concentration-dependent inhibitory effect on the expression of ACE, particularly at higher concentrations (24.70+/-1.20 at 100microM, P<0.01, and 18.22+/-0.92 at 200microM, P<0.01 compared with the control group 50.49+/-5.19). The estrogen receptor blocker tamoxifen at 100microM attenuated this effect of genistein. The extracellular signal-regulated kinase 1/2 (ERK1/2) blocker PD98059 also markedly inhibited this effect. The observations in vivo were highly consistent with the data in RAECs. These results indicate that genistein inhibits the expression of ACE via estrogen receptor and subsequently ERK1/2 signaling pathway in RAECs. Our results suggest that the down-regulation of ACE with a consequent change in the circulating levels of angiotensin II (Ang II), vasorelaxant angiotensin-(1-7) [Ang-(1-7)] and bradykinin plays an important role in cardiovascular effects of genistein through the ERK1/2 pathway.

Effects of intravenous urocortin on angiotensin-converting enzyme in rats

We investigated the relationship between urocortin and the activity of angiotensin-converting enzyme (ACE), which plays a key role in producing the potent vasoconstrictor angiotensin II (Ang II). Urocortin was acutely and subchronically administered to Sprague-Dawley (SD) rats and then the serum and tissue (lung and aorta) ACE levels were evaluated. The tissue ACE mRNA was determined by using reverse transcription and polymerase chain reaction (RT-PCR) analysis. Immunofluorescence studies were also preformed to evaluate the effect of urocortin on ACE in cultured rat aortic endothelial cells (RAECs). Urocortin decreased the serum ACE level 1h after administration, whereas tissue ACE immunoreactivity and mRNA did not change. The prolonged administration of urocortin enhanced tissue ACE activity but the serum ACE level remained low. RT-PCR analysis showed that tissue ACE mRNA was elevated. Immunofluorescence studies also demonstrated an increase of ACE intensity in RAECs exposed to urocortin for 72 h. Corticotropin-releasing factor (CRF) receptor blocker, astressin, abolished the effects of urocortin. Extracellular signal-regulated kinase 1/2 (ERK1/2) pathway blocker, PD98059, also markedly inhibited these effects, suggesting urocortin affects the activity of ACE through the ERK1/2 pathway in rats. These findings support the changes in mean arterial pressure (MAP) following acute and subchronic injections of urocortin in previous studies. Thus, the changes of the ACE activity and its production of Ang II may play a role in the vasodilatory property of urocortin.

Evaluation of toxicity after one-months treatment with Bauhinia forficata decoction in streptozotocin-induced diabetic rats

Background

Previous experiments have shown that a decoction of Bauhinia forficata leaves reduces the changes in carbohydrate and protein metabolism that occur in rats with streptozotocin-induced diabetes. In the present investigation, the serum activities of enzymes known to be reliable toxicity markers were monitored in normal and streptozotocin-diabetic rats to discover whether the use of B. forficata decoction has toxic effects on liver, muscle or pancreas tissue or on renal microcirculation.

Methods

An experimental group of normal and streptozotocin-diabetic rats received an aqueous decoction of fresh B. forficata leaves (150 g/L) by mouth for 33 days while a control group of normal and diabetic rats received water for the same length of time. The serum activity of the toxicity markers lactate dehydrogenase, creatine kinase, amylase, angiotensin-converting enzyme and bilirubin were assayed before receiving B. forficata decoction and on day 19 and 33 of treatment.

Results

The toxicity markers in normal and diabetic rats were not altered by the diabetes itself nor by treatment with decoction. Whether or not they received B. forficata decoction the normal rats showed a significant increase in serum amylase activity during the experimental period while there was a tendency for the diabetic rats, both treated and untreated with decoction, to have lower serum amylase activities than the normal rats.

Conclusions

Administration of an aqueous decoction of B. forficata is a potential treatment for diabetes and does not produce toxic effects measurable with the enzyme markers used in our study.

Dietary weight loss decreases serum angiotensin-converting enzyme activity in obese adults

OBJECTIVE

To study the effect of dietary weight loss, postural change, and an oral glucose load on serum angiotensin-converting enzyme (ACE) activity in obese adults.

RESEARCH METHODS AND PROCEDURES

Sixteen obese adult men and women with a mean body mass index of 35.7 +/- 4.3 kg/m(2) were studied after 1 week on a maintenance energy lead-in diet and after 5 weeks on an identical but 40% reduced-energy diet provided by the General Clinical Research Center (GCRC). ACE activity was measured spectrophotometrically. Plasma renin activity and serum aldosterone were measured by radioimmunoassay.

RESULTS

All subjects lost weight, with a mean decrease in body weight of 7.0 +/- 2.1 kg or 6 +/- 3% of initial body weight (p < 0.00001). Systolic and diastolic blood pressure, supine plasma renin activity, and serum aldosterone levels decreased with weight loss (p < 0.05). Supine ACE activity decreased 23 +/- 12% with weight loss (p < 0.00001). Standing ACE activity, which was significantly higher than supine ACE activity before and after weight loss (p < 0.05), also decreased 18 +/- 17% with weight loss (p = 0.0007). A 75-g oral glucose load had no effect on serum ACE activity over a 3-hour period.

DISCUSSION

In obese adults, serum ACE activity declines with modest weight loss, increases with postural change, and is unaffected by an oral glucose load.

Dissociation between the circulating renin-angiotensin system and angiotensin II receptors in central losartan-induced hypertension

Losartan, an AT1 angiotensin II (ANG II) receptor non-peptide antagonist, induces an increase in mean arterial pressure (MAP) when injected intracerebroventricularly (icv) into rats. The present study investigated possible effector mechanisms of the increase in MAP induced by icv losartan in unanesthetized rats. Male Holtzman rats (280-300 g, N = 6/group) with a cannula implanted into the anterior ventral third ventricle received an icv injection of losartan (90 micro g/2 micro l) that induced a typical peak pressor response within 5 min. In one group of animals, this response to icv losartan was completely reduced from 18 +/- 1 to 4 +/- 2 mmHg by intravenous (iv) injection of losartan (2.5-10 mg/kg), and in another group, it was partially reduced from 18 +/- 3 to 11 +/- 2 mmHg by iv prazosin (0.1-1.0 mg/kg), an alpha1-adrenergic antagonist (P<0.05). Captopril (10 mg/kg), a converting enzyme inhibitor, injected iv in a third group inhibited the pressor response to icv losartan from 24 +/- 3 to 7 +/- 2 mmHg (P<0.05). Propranolol (10 mg/kg), a beta-adrenoceptor antagonist, injected iv in a fourth group did not alter the pressor response to icv losartan. Plasma renin activity and serum angiotensin-converting enzyme activity were not altered by icv losartan in other animals. The results suggest that the pressor effect of icv losartan depends on angiotensinergic and alpha1-adrenoceptor activation, but not on increased circulating ANG II.

Lack of antidiabetic effect of a Eugenia jambolana leaf decoction on rat streptozotocin diabetes

Streptozotocin-diabetic rats were treated for 17 days with a decoction of Eugenia jambolana (Myrtaceae) leaves (15%, w/v) as a substitute for water. Body weight, food and fluid intake, urine volume, glycemia, urinary glucose and urea were evaluated every 5 days. The animals were sacrificed by decapitation and blood samples collected for the determination of glycemia, serum cholesterol, HDL-cholesterol, triglycerides and angiotensin-converting enzyme. The weight of adipose and muscle tissues was also determined. There were no statistically significant differences between treated and untreated rats for any of the biochemical or physiological parameters. We conclude that, at least in this experimental model, Eugenia jambolana leaf decoction has no antidiabetic activity.