Changes in angiotensin-converting enzyme activity in lungs damaged by the pyrrolizidine alkaloid monocrotaline (original) (raw)
Related papers
British Journal of Pharmacology, 1993
Changes in the structural and functional integrity of endothelium have been recognized as relatively early features of delayed and progressive pulmonary vascular injury caused by the pyrrolizidine alkaloid, monocrotaline (MCT). Although a number of investigators have evaluated angiotensin-converting enzyme (ACE) activity in the lungs of rats treated with MCT, the exact nature of changes in activity of this enzyme and the role they may play in MCT pneumotoxicity remain controversial. 2 We examined the direct effects of monocrotaline pyrrole (MCTP), a toxic metabolite of MCT, on cultured endothelial cell ACE activity. Post-confluent monolayers of porcine or bovine pulmonary artery endothelial cells (PECs or BECs, respectively) were treated with a single administration of MCTP at time 0; then they were examined for their ability to degrade the synthetic peptide, [3H]-benzoyl-Phe-Ala-Pro. 3 In PECs, which are relatively insensitive to the direct cytolytic effects of MCTP, monolayer ACE activity was unchanged initially but gradually decreased within 4 days after treatment with a high concentration of MCTP (150 tLM). This decrease was transient, and PEC monolayer ACE activity returned to the control value by 10 days post treatment. 4 BEC monolayer ACE activity was also unchanged initially but rapidly declined within 4 days after MCTP treatment and remained depressed throughout the post treatment period. BECs were quite sensitive to the cytolytic effects of MCTP and the decline in ACE activity occurred coincident with the decrease in monolayer cellularity and appearance of marked cytotoxicity. 5 We conclude that high concentrations of MCTP decrease endothelial ACE activity. The decline in ACE activity is delayed and the magnitude and duration of the decrease corresponds to the degree of MCTP-induced cytotoxicity. This suggests that altered endothelial ACE activity is unlikely to be a direct effect of MCTP on the enzyme but may reflect the delayed cell injury which results from exposure to this compound.
Activation and pulmonary toxicity of pyrrolizidine alkaloids
Pharmacology & Therapeutics, 1990
Pyrrolizidine alkaloids unsaturated in the 1,2 position are hepatotoxins. Certain of them, such as monocrotaline, are also pneumotoxins, producing pulmonary arterial hypertension and right ventricular hypertrophy as a delayed response two weeks after administration. Pneumotoxicity is the result of hepatic metabolism, the lung itself being unable to bioactivate pyrrolizidine alkaloids. The changes produced in the lung following exposure to pneumotoxic pyrrolizidine alkaloids are reviewed, together with the factors and interventions which modify or influence these changes. In the main, the earliest changes are seen in vascular smooth muscle and in the interactions between smooth muscle and the endothelium. The search to identify the pneumotoxic metabolite is reviewed. It is generally accepted that pyrroles, or dehydroalkaloids, are responsible for the toxicity of pyrrolizidines. However, the primary pyrroles are intensely reactive, hydrolyzing and polymerizing within seconds in aqueous solution. Evidence for and against the pneumotoxin being a primary pyrrole or a stabilized secondary conversion product of a primary pyrrole is discussed. CONTENTS 1. Occurrence of Pyrrolizidine Alkaloids 2. Metabolic Activation of Pyrrolizidine Alkaloids and Structure-Activity Requirements 3. Cardiopulmonary Toxicity 3.1. Overview of pulmonary changes following pyrrolizidine exposure 3.1.1. Microvascular remodelling 3.2. Cause or consequence 4. Changes Produced in Lungs by Pyrrolizidines and Pyrroles 4.1. Biochemical changes 4.2. Structural changes 4.3. Changes in endothelial function 4.3.1. Monoamine transport 4.3.2. Angiotensin converting enzyme activity 4.3.3. Other endothelial activities 4.4. Platelets 4.5. Inflammation 4.6. Changes in smooth muscle function 4.7. Changes in endothelial-smooth muscle interactions 4.8. Summary of pulmonary actions of pyrrolizidines 5. Dose Relationships 6. Modification of Pyrrolizidine Toxicity 6.1. Collagenization 6.2. Hyperoxia 6.3. Angiotensin converting enzyme inhibitors 6.4. Drugs affecting arachidonate metabolism 6.5. Other interventions 7. What is the Pneumotoxic Metabolite? 7.1. Primary pyrroles 7.2. Secondary pyrroles 383 7.3. Other metabolites 383 7.4. Summary of findings on the identity of the pneumotoxic metabolite of monocrotaline 384 Acknowledgements 385 References 385
Induction of angiotensin-converting enzyme with the ACE inhibitory compound MK-421 in rat lung
European Journal of Pharmacology, 1982
Having observed that treatment of rats with captopril led to an increased ACE activity in serum and ACE concentration in lungs, we treated female Wistar Kyoto rats for 7 days with the esterified ACE inhibitor, MK-421 (I.0 mg/kg body weight per day), administered by Alzet osmotic minipump. Serum ACE activity decreased by 67% during MK-421 treatment when measured in non-dialyzed serum samples. Removal of the drug by dialysis unmasked a 280% increase of serum ACE activity. ACE concentration of crude lung homogenate increased 134% in MK-421-treated rats and ACE concentration in purified pulmonary plasma membranes increased by 34%. The increase of serum and lung ACE in MK-421-treated rats was similar to that seen in rats treated with captopril, and was probably due to induction of ACE biosynthesis. The mechanisms of this induction are unknown. Angiotensin converting enzyme MK-421 Enzyme induction Kininase 11 Pulmonary plasma membranes
Production of monoclonal antibodies to rat lung angiotensin-converting enzyme
Clinical Immunology and Immunopathology, 1984
Several monoclonal antibodies to rat lung angiotensin-converting enzyme (ACE) have been produced. The antibodies are of the IgG class, do not inhibit ACE catalytic activity, and do not cross-react with the human or bovine enzyme. They bind in a curvilinear fashion to lung capillary endothehum by immunofluorescence microscopy, and radiolabeled antibody localizes in lung and other organs after intravenous injection into living rats. Each antibody tested appears to bind preferentially to lung rather than kidney ACE by ELBA, a finding supported by weak or absent immunofluorescence of kidney slices in vitro. These antibodies may be used to probe structural differences between ACE in various tissues and, by quantitating changes in accumulation of radiolabeled antibody in experimental models of lung injury, should complement functional measurements in determining the presence of subtle and progressive endothelial damage.
Biochimica et biophysica acta, 1978
Antiontensin-converting enzyme (peptidyldipeptide hydrolase, EC 3.4.15.1) has been solubilized from canine pulmonary particles and purified to apparent homogeneity. A value of approx. 140000 was estimated for the molecular weight of the native and the reduced, denatured forms of the enzyme. No free NH2-terminal residue was detected by the dansylation procedure. Carbohydrate accounted for 17% of the weight of the enzyme, and the major residues were galactose, mannose and N-acetylglucosamine with smaller amounts of sialic acid and fucose. Removal of sialic acid residues with neuraminidase did not alter enzymatic activity. The enzyme contained one molar equivalent of zinc. Addition of this metal reversed stimulation and inhibition of activity observed in the presence of Co2+ and Mn2+, respectively. Immunologic homology of pure dog and rabbit enzymes was demonstrable with goat antisera. Fab fragments and intact IgG antibodies displayed similar inhibition dose vs. response curves with ho...
American Journal of Respiratory and Critical Care Medicine, 2009
Rationale: It has been proposed that an activated renin angiotensin system (RAS) causes an imbalance between the vasoconstrictive and vasodilator mechanisms involving the pulmonary circulation leading to the development of pulmonary hypertension (PH). Recent studies have indicated that angiotensin-converting enzyme 2 (ACE2), a member of the vasoprotective axis of the RAS, plays a regulatory role in lung pathophysiology, including pulmonary fibrosis and acute lung disease. Based on these observations, we propose the hypothesis that activation of endogenous ACE2 can shift the balance from the vasoconstrictive, proliferative axis (ACE-Ang II-AT1R) to the vasoprotective axis [ACE2-Ang-(1-7)-Mas] of the RAS, resulting in the prevention of PH. Objectives: We have taken advantage of a recently discovered synthetic activator of ACE2, XNT (1-[(2-dimethylamino) ethylamino]-4-(hydroxymethyl)-7-[(4-methylphenyl) sulfonyl oxy]-9Hxanthene-9-one), to study its effects on monocrotaline-induced PH in rats to support this hypothesis. Methods: The cardiopulmonary effects of XNT were evaluated in monocrotaline-induced PH rat model. Measurements and Main Results: A single subcutaneous treatment of monocrotaline in rats resulted in elevated right ventricular systolic pressure, right ventricular hypertrophy, increased pulmonary vessel wall thickness, and interstitial fibrosis. These changes were associated with increases in the mRNA levels of renin, ACE, angiotensinogen, AT1 receptors, and proinflammatory cytokines. All these features of PH were prevented in these monocrotaline-treated rats by chronic treatment with XNT. In addition, XNT caused an increase in the antiinflammatory cytokine, IL-10. Conclusions: These observations provide conceptual support that activation of ACE2 by a small molecule can be a therapeutically relevant approach for treating and controlling PH.
Bayero Journal of Pure and Applied Sciences, 2017
Angiotensin converting enzyme (ACE) was isolatedand partially purifiedfrom the lungs of Wistarrats (Rattusnorvegicus). The ACE was characterized and its amino acids composition determined.ACE was purified by ammonium sulphate precipitation, dialysis and ge chromatography. The activity of the enzyme was assayed by a spectrophotometric method, which involves monitoring the rate of production of hippuric acid from the hydrolysis of Hippuryl Histidyl-L-Leucine by ACE.Protein concentration wasassay optimum temperature and pH of the isolated enzyme were also determined. From the results, crude enzyme had a total activity of 0.12 U and a specific activity of 0.048U/mg of protein. Precipitation of protein increased the specific activity to 0.050U/mg at a recovery rate of 62%. Upon dialysis, the activity of the enzyme decreased from 0.074U to 0.038Uwhile specific activityalso increased. At this stage, only about 31% of the enzyme activity was retained over t crude. After gel filtration the specific activity of the enzyme increased to 0.087U/mg at a purification fold of 1.8 and a final recovery of 25%.The enzyme had an optimum pH and temperature of 7.0 and 40 0 C, respectively. The partially purified enzyme is havingseventeen amino acids:KHRDTSGPGACVMILYF. In conclusion, angiotensin-converting enzyme can be isolated from rat lungs, but the purification steps needs to be modified to obtain an enzyme with higher yield and assessable for research in developing countries.