Release of angiotensin converting enzyme by the lung after Pseudomonas bacteremia in sheep

A Low-Protein Diet Enhances Angiotensin II Production in the Lung of Pregnant Rats but not Nonpregnant Rats

Pulmonary angiotensin II production is enhanced in pregnant rats fed a low-protein (LP) diet. Here we assessed if LP diet induces elevations in angiotensin II production in nonpregnant rats and whether Ace expression and ACE activity in lungs are increased. Nonpregnant rats were fed a normal (CT) or LP diet for 8, 12, or 17 days and timed pregnant rats fed for 17 days from Day 3 of pregnancy. Plasma angiotensin II, expressions of Ace and Ace2, and activities of these proteins in lungs, kidneys, and plasma were measured. These parameters were compared among nonpregnant rats or between nonpregnant and pregnant rats fed different diets. Major findings are as follows: (1) plasma angiotensin II levels were slightly higher in the LP than CT group on Days 8 and 12 in nonpregnant rats; (2) expression of Ace and Ace2 and abundance and activities of ACE and ACE2 in lungs, kidneys, and plasma of nonpregnant rats were unchanged by LP diet except for minor changes; (3) the abundance and activities of ACE in lungs of pregnant rats fed LP diet were greater than nonpregnant rats, while those of ACE2 were decreased. These results indicate that LP diet-induced increase in pulmonary angiotensin II production depends on pregnancy.

LPS-induced effects on angiotensin I-converting enzyme expression and shedding in human pulmonary microvascular endothelial cells

Angiotensin I-converting enzyme (kininase II, ACE, and CD143) availability is a determinant of local angiotensin and kinin concentrations and their physiological actions. Until now, it is unclear whether the decrease of pulmonary ACE activity in sepsis-described in clinical studies-is due to an enzyme compensatory downregulation (reduced ACE-mRNA expression) to shedding of ACE or endothelial damage. To address these questions, ACE distribution under septic conditions was studied in vitro by treating pulmonary microvascular endothelial cells (HPMEC) and human umbilical vein endothelial cells (HUVEC) with lipopolysaccharide from Escherichia coli (LPS). Primary isolated HUVEC and HPMEC were compared by detecting ACE activity, membrane-bound ACE, as well as shedding and mRNA production of ACE with and without LPS (1 ng/ml-1 μg/ml). ACE mRNA expression was detected by real-time PCR, and shedded ACE was measured in cell culture supernatant by ELISA. Additionally, membrane-bound protein expression was investigated by immunohistochemistry in situ. In septic ARDS, the distribution of ACE protein was significantly reduced in all lung endothelial cells (p<0.001). After stimulation with LPS, cultivated HPMEC showed more markedly than HUVEC, a concentration-dependent reduction of ACE protein expression compared to the respective untreated controls. Real-time PCR demonstrated a reduced ACE mRNA expression after LPS stimulation, predominantly in HPMEC. Specifically, in HPMEC, a concentration-dependent increase of shedded ACE was shown 24 h after LPS treatment. HPMEC cultures are an apt model for the investigation of pulmonary ACE expression in sepsis. This study suggests that reduced pulmonary microvascular endothelial ACE expression in septic ARDS is caused by two processes: (initial) increased shedding of ACE accompanied by a compensatory downregulation of ACE-mRNA and membrane-bound protein expression.

Gestational protein restriction increases angiotensin II production in rat lung

Gestational protein restriction (PR) alters the renin-angiotensin system in uterine arteries and placentas and elevates plasma levels of angiotensin II in pregnant rats. To date, how PR increases maternal plasma levels of angiotensin II remains unknown. In this study, we hypothesize that the expression and/or the activity of angiotensin I converting enzyme (peptidyl-dipeptidase A) 1 (ACE) in lungs, but not kidneys and blood, largely contribute to elevated plasma angiotensin II levels in pregnant rats subject to gestational PR. Time-scheduled pregnant Sprague-Dawley rats were fed a normal or low-protein diet from Day 3 of pregnancy until euthanized at Day 19 or 22. Expressions of Ace and Ace2 (angiotens in I converting enzyme [peptidyl-dipeptidase A] 2) in lungs and kidneys from pregnant rats by quantitative real-time PCR and Western blotting, and the activities of these proteins in lungs, kidneys, and plasma, were measured. The mRNA levels of Ace and Ace2 in lungs were elevated by PR at both Days 19 and 22 of pregnancy. The abundance of ACE protein in lungs was increased, but ACE2 protein was decreased, by PR. The activities of ACE, but not ACE2, in lungs were increased by PR. PR did not change expressions of Ace and Ace2, the activities of both ACE and ACE2 in kidneys, and the abundance and activity of plasma ACE. These findings suggest that maternal lungs contribute to the elevated plasma levels of angiotensin II by increasing both the expression and the activity of ACE in response to gestational PR.

Prognostic role of serum ACE activity on outcome of type 2 diabetic patients on chronic ambulatory peritoneal dialysis

Overexpression of the renin-angiotensin system is important in the pathogenesis of macroangiopathy (MA). Patients with diabetes with end-stage renal failure have elevated serum angiotensin-converting enzyme (ACE) activity compared with their nonuremic counterparts. Because their major cause of death is MA, the significance of serum ACE activity on outcome of this group of patients is studied. We performed a prospective cohort study of 49 patients with type 2 diabetes on continuous ambulatory peritoneal dialysis (CAPD) therapy. Baseline serum ACE activity was determined by a modified spectrophotometric method and followed up at a median of 34 months. The prevalence of MA (defined as ischemic heart disease, sudden cardiac arrest, stroke, or peripheral vascular disease) and all-cause mortality rates were studied. Risk for MA is associated with serum ACE activity (median with MA, 69.0 U/L [range, 46.0 to 100.1 U/L] versus without MA, 57.2 U/L [range, 36.3 to 81.0 U/L]; P = 0.02). At the end of follow-up, 48% of patients (24 of 49 patients) died, 70% of MA. The group that died had increased baseline serum ACE activity (nonsurvivors, 65.0 U/L [range, 33.5 to 100.0 U/L] versus survivors, 49.4 U/L [range, 36.4 to 86.5 U/L]; P < 0.05) and MA rates (nonsurvivors, 77% versus survivors, 36%; P < 0.01). Cox regression analysis performed with age, sex, mean blood pressure, body mass index, metabolic control, Kt/V, residual renal function, serum albumin level, and ACE activity showed that baseline serum ACE activity (P = 0.033) is an independent predictor for mortality in patients with type 2 diabetes on CAPD therapy. Among patients with type 2 diabetes on CAPD therapy, serum ACE activity is associated with risk for MA and is an independent predictor for mortality. Whether ACE inhibition will have a beneficial effect on the outcome of these patients needs further investigation.

Effect of acute administration of bleomycin on lung fluid balance in sheep

This study examined the effects of acute administration of bleomycin (BLM) on lung liquid and protein exchange in anesthetized sheep prepared with caudal mediastinal lung lymph fistulas. Six sheep received BLM (15 U IV) after a baseline period, while seven others were given BLM after a steady state was obtained following elevation of left atrial pressure (PLA), a procedure intended to minimize changes in pulmonary microvascular surface area and produce high lung lymph flow (QL). Plasma and lung lymph angiotensin converting enzyme (ACE) activities were measured in order to independently assess the effects of BLM on pulmonary endothelial integrity. QL rose significantly in all animals following BLM. The ratio of lymph to plasma protein concentration (CL/CP) did not change in the group given BLM alone, and fell continuously during the period of PLA elevation after BLM in that group. Plasma and lung lymph ACE activities were unchanged following BLM administration in either group. The ultrastructure of the gas-exchanging region of lungs from animals in each group was examined by transmission electron microscopy. The data suggest that acute administration of a low dose of BLM does not increase pulmonary microvascular permeability, but may induce an increase in perfused pulmonary microvascular surface area responsible for increased QL.

Elevated lactate dehydrogenase values in patients with Pneumocystis carinii pneumonia

We investigated the source of elevated serum lactate dehydrogenase (LDH) levels in seven patients with Pneumocystis carinii pneumonia (PCP) by analyzing blood and bronchoalveolar lavage (BAL) albumin (ALB) and LDH, with isoenzyme fractionation. Four patients with non-PCP lung disease served as control subjects. In PCP patients, BAL LDH was sixfold higher, and BAL ALB, fourfold higher than in the non-PCP patients. The increased LDH/ALB in BAL as compared to serum, in addition to a BAL isoenzyme pattern characteristic of lung, suggest that BAL LDH arises from a pulmonary source. We postulate that the high correlation observed between BAL and serum LDH (r = 0.93, p less than 0.001) reflects backflow of pulmonary-derived LDH into the blood through an alveolocapillary membrane (ACM) compromised by PCP. Furthermore, a comparison of BAL LDH/ALB for each isoenzyme with the same serum ratio showed less backflow for the cationic isoenzymes. The ACM appears to sieve proteins on an electrical basis which may account for the LDH isomorphic pattern observed in the serum of PCP patients.

The effect of indomethacin on plasma and lung lymph angiotensin converting enzyme activity in sheep

The effect of indomethacin (INDO), an inhibitor of prostaglandin (PG) cyclooxygenase, on pulmonary vascular permeability is unclear. We measured angiotensin converting enzyme (ACE) activity in plasma and lung lymph in order to evaluate pulmonary endothelial integrity. Eighteen sheep, anesthetized and acutely prepared for the collection lung lymph, were used in the study. Four animals (Group I) served as sham controls and were not subjected to experimental intervention. In order to minimize changes in pulmonary microvascular surface area (PMSA), left atrial blood pressure (Pla) was elevated (12-20 Torr) following the baseline period in animals in the three experimental groups. Group II (n = 4) was subjected to increased Pla only in order to assess the effects of that maneuver alone on experimental parameters. Group III (n = 3) received an infusion of buffered vehicle only during a four hour period of elevated Pla, and, thus served as a vehicle control for Group IV (n = 7) which received INDO for the same period of increased Pla. Pulmonary blood pressures, cardiac output (CO), lung lymph flow (Ql) and the ratio of lymph to plasma protein concentration (L/P) were measured in all experiments in order to independently assess changes in lung vascular permeability. While ACE activity in plasma and lymph fell in each experimental group, average ACE experimental values were unchanged from corresponding baseline values. Increased Pla caused a characteristic increase in Ql and fall in L/P in each of the experimental groups. We conclude that INDO does not alter lung fluid and protein balance by a process which involves increased pulmonary vascular permeability secondary to a loss of endothelial integrity.

Pulmonary microvascular injury induced by Pseudomonas aeruginosa cytotoxin in isolated rabbit lungs

The effects of Pseudomonas aeruginosa cytotoxin on the pulmonary microvasculature were studied in blood-free, perfused, isolated rabbit lungs. Cytotoxin was administered to the recirculating Krebs Henseleit albumin (1%) buffer during two consecutive 30-min-perfusion phases (phases 1 and 2) at a concentration of 13 micrograms/ml, followed by a third perfusion phase (phase 3) without toxin. After perfusion phases 2 and 3, the capillary filtration coefficient (Kf,c) and vascular compliance were determined gravimetrically from two-step microvascular pressure increments under zero-flow conditions. Cytotoxin caused a continuous release of K+ and lactate dehydrogenase, which started within the first 5 min and amounted to about 50% of the total lung cellular K+ and 5 to 7% of the total lactate dehydrogenase by the end of the experiment. The toxin caused the continuous generation of prostaglandin I2, which was detectable in the perfusates of all perfusion phases at maximum values five times above the control values and which was measured in the bronchoalveolar lavage fluid at the end of the experiment. Thromboxane generation in toxin-treated lungs did not significantly exceed that of control lungs or of lungs with mechanically induced edema. Cytotoxin caused a gradual increase in pulmonary vascular resistance, to maximum values 2.5 times above the control, starting within 1 min; the increase was partially reversible after washout of the toxin. After a lag period of 20 to 30 min, the lungs gained weight, amounting to a mean gain of 9.1 g at the end of the experiments. After perfusion phases 2 and 3, an almost fourfold increase in Kf,c, which was not reversible after washout of the toxin, was measured, whereas the values of vascular compliance were not altered. We conclude that pseudomonal cytotoxin may be an important factor in the pathogenesis of prolonged microvascular injury, encountered in states of P. aeruginosa sepsis or acute lung failure with secondarily acquired P. aeruginosa pneumonia.

Elevated serum D-arabinitol levels in patients with sarcoidosis

D-Arabinitol has been found in the serum of patients with candidiasis in an incidence varying from 38 to 82%. While screening serum by gas chromatography for the presence of this sugar, we observed elevated concentrations in several patients with sarcoidosis. In an attempt to determine the significance of this chance observation, we tested serum from additional patients with sarcoidosis along with serum from patients with other clinical conditions known to be associated with elevated D-arabinitol levels. Of 53 patients with sarcoidosis, 27 (51%) had elevated concentrations of this compound. Only one of these patients had decreased renal function (creatinine, 2.5 mg/dl). We were unable to correlate elevated values with extent of the disease. Although the significance of this finding is not clear, it may represent a clue to the pathogenesis of sarcoidosis.

Effects of lipopolysaccharide on human endothelial cells in culture

Lipopolysaccharide (LPS) in concentrations up to 10 micrograms/ml did not induce detectable direct cytotoxicity in human umbilical vein, pulmonary artery, or pulmonary vein endothelial cells. By contrast, significant cytotoxicity was observed in bovine aortic endothelial cells exposed to LPS 0.01 micrograms/ml. Transmission electron microscopy of human umbilical vein cells exposed to LPS 10 micrograms/ml for 4 days revealed no significant ultrastructural abnormalities compared to control cells. Whereas human umbilical vein endothelial cell cytotoxicity was observed when neutrophils were stimulated with phorbol myristate acetate, LPS-stimulated neutrophils did not induce significant cytotoxicity even in the presence of fresh human serum as a complement source. Moreover, human umbilical vein endothelial cell factor VIII-antigen and fibronectin release, angiotensin-converting enzyme activity, and PGI2 release were unaffected by a 24-hour exposure to LPS. Cytotoxicity, however, was produced when human umbilical vein endothelial cells were coincubated with LPS and cycloheximide. The proliferation of human umbilical vein endothelial cells was also inhibited after prolonged, continuous exposure to LPS 10 micrograms/ml. We conclude that LPS with or without complement or neutrophils does not induce significant human endothelial cell lysis or detachment. Moreover, brief exposure to LPS has minimal, direct effect on several functions of human endothelial cells in vitro.