Reduced expression of angiotensin I-converting enzyme in caveolin-1 knockout mouse lungs

Reduced lung capillary expression of angiotensin I-converting enzyme (ACE), a key enzyme in cardiovascular pathophysiology, and of caveolin-1, an important regulator of endothelial cell signalling, has been demonstrated in various models of pulmonary arterial hypertension (PAH). We addressed the relationship between PAH and ACE expression in caveolin-1 knockout mice (Cav1(-/-)), which have moderate PAH. Tissue ACE activity was reduced by 50% in lungs from 3-month-old Cav1(-/-) mice compared to wild type (WT). A similar reduction in lung endothelial ACE expression was observed by measuring the lung uptake of (125)I-labeled monoclonal anti-ACE antibody and by quantitative immunohistochemistry. These alterations in ACE are limited to capillary segments of the pulmonary circulation. Functionally, the increase in pulmonary artery pressure (PAP) in response to ACE conversion of angiotensin I to angiotensin II in isolated, perfused mouse lungs was reduced significantly in Cav1(-/-) mice compared to WT. Thus, these complementary approaches demonstrate the dependence of lung microvascular endothelial cell ACE protein expression on caveolin-1 expression and underscore the vital role of caveolin-1-regulated pulmonary vascular homeostasis on endothelial ACE expression and activity. In summary, we have revealed a novel role of caveolin-1 in the regulation of ACE expression in pulmonary capillary endothelial cells. Further understanding of the mechanism by which reduced caveolin-1 expression leads altered pulmonary vascular development, PAH, and reduced ACE expression may have important clinical implications in patients with these severe lung diseases.

Selective rat lung endothelial targeting with a new set of monoclonal antibodies to angiotensin I-converting enzyme

We demonstrated previously that monoclonal antibody (mAb) 9B9 to angiotensin-converting enzyme (ACE) accumulates selectively in the rat lung after systemic injection and thus is a powerful tool for immunotargeting therapeutic agents/genes to the lung microvasculature. Bearing in mind the tremendous research and therapeutic potential of lung immunotargeting via ACE, we generated a novel set of mAbs to rat ACE in order to enhance the repertoire of mAbs suitable for targeting drugs/genes to the rat lung. Five new mAbs recognizing different epitopes on rat ACE were examined for their efficacy to bind rat ACE both in vitro and in vivo. Gene delivery into cultured rat lung endothelial cells increased 30-50-fold after coating modified adenoviruses (containing Ig-binding domain) with mAbs to rat ACE. Radiolabeled mAbs specifically accumulated in the lung after systemic injection. mAb 1A2, 4H3 and 2E1 demonstrated the highest efficacy of lung uptake-around 50% of injected dose per gram of tissue; for mAb 1A2, the selectivity of lung uptake (ratio of lung to blood radioactivity) was 205. The effect of the mAbs on ACE shedding was epitope-specific: injection of mAb 1A2 and 4H3 did not change lung ACE activity, whereas injection of mAb 2E1 and 9B9 decreased rat lung ACE activity by 20%. None of the tested mAbs inhibited ACE activity in vitro. A new set of mAbs to rat ACE demonstrated highly efficient and selective lung accumulation and thus have the potential for targeting drugs/genes to the pulmonary vasculature in different rat models of lung diseases.

Isoflurane, but Not Sevoflurane, Increases Transendothelial Albumin Permeability in the Isolated Rat Lung

Background

Caveolae mediated transendothelial transport of albumin has recently been shown to be the primary mechanism regulating microvascular endothelial albumin permeability. The authors investigated the effects of isoflurane and sevoflurane on pulmonary endothelial albumin permeability and assessed the potential role of the caveolae scaffold protein, caveolin-1, in these effects.

Methods

Isolated rat lungs and cultured rat lung microvessel endothelial cells (RLMVECs) were exposed to 1.0 or 2.0 minimum alveolar concentration (MAC) isoflurane or sevoflurane for 30 min. I-albumin permeability-surface area product and capillary filtration coefficient were determined in the isolated lungs. In RLMVECs, uptake and transendothelial transport of I-albumin were measured in the absence and presence of pretreatment with 2 mm methyl-beta-cyclodextrin, a caveolae-disrupting agent. Uptake of fluorescent-labeled albumin, as well as phosphorylation of Src kinase and caveolin-1, was also determined. In Y14F-caveolin-1 mutant (nonphosphorylatable) expressing RLMVECs, uptake of I-albumin and phosphorylation of caveolin-1 were evaluated.

Results

In the isolated lungs, 2.0 MAC isoflurane increased I-albumin permeability-surface area product by 48% without affecting capillary filtration coefficient. In RLMVECs, isoflurane more than doubled the uptake of I-albumin and caused a 54% increase in the transendothelial transport of I-albumin. These effects were blocked by pretreatment with methyl-beta-cyclodextrin. The isoflurane-induced increase in uptake of I-albumin in wild-type RLMVECs was abolished in the Y14F-caveolin-1 mutant expressing cells. Isoflurane also caused a twofold increase in Src and caveolin-1 phosphorylation. Neither 1.0 MAC isoflurane nor 1.0 or 2.0 MAC sevoflurane affected any index of albumin transport or phosphorylation of caveolin-1.

Conclusion

Isoflurane, but not sevoflurane, increased lung transendothelial albumin permeability through enhancement of caveolae-mediated albumin uptake and transport in the isolated lung. This effect may involve an enhanced phosphorylation of caveolin-1.

Monoclonal antibodies to native mouse angiotensin-converting enzyme (CD143): ACE expression quantification, lung endothelial cell targeting and gene delivery

We demonstrated previously that the monoclonal antibody 9B9 to angiotensin-converting enzyme (ACE), which accumulates very selectively into the rat lung after systemic injection, is a powerful tool for immunotargeting of therapeutic agents or genes to the rat lung vascular bed. Bearing in mind a high research and therapeutic potential of lung targeting via ACE, we obtained a new set of rat monoclonal antibodies to different epitopes of mouse ACE in order to expand this approach to mice. Nine new monoclonal antibodies, recognizing epitopes on the N- and C-domains of catalytically active mouse ACE, were obtained and examined for their efficacy to bind ACE both in vitro and in vivo. This set of monoclonal antibodies was proved to be useful for ACE quantification (by flow cytometry and cell enzyme-linked immunosorbent assay) on the surface of different mouse ACE-expressing cells: endothelial cells, monocytes, macrophages, dendritic cells and spermatozoa. Moreover, gene delivery into mouse ACE-expressing cells using adenoviruses increased 40-fold after redirecting of these viruses to ACE (by coating these viruses with anti-ACE monoclonal antibodies). Radiolabelled (I(125)) monoclonal antibodies specifically accumulated in the mouse lung after systemic injection. Monoclonal antibodies 3G8.17, 4B10.5 and 4B10.17 demonstrated the highest level of lung uptake, 40-50% of injected dose, and high selectivity of lung uptake. Influence of monoclonal antibodies on ACE shedding was negligible, except monoclonal antibody 1D10.11. None of the tested monoclonal antibodies inhibited ACE activity in vitro. In conclusion, a new set of rat monoclonal antibodies to mouse ACE was obtained suitable to study ACE biology in mice and for ACE expression quantification on mouse cells in particular. These monoclonal antibodies also demonstrated highly efficient and selective lung accumulation and thus has the potential for targeting drugs/genes to the pulmonary vasculature in different mouse models of human lung diseases, including numerous knockout models.

Propofol attenuates lung endothelial injury induced by ischemia-reperfusion and oxidative stress

Lung dysfunction after cardiopulmonary bypass and lung transplantation results from oxidant-mediated cellular damage. Previously, we observed the shedding of angiotensin-converting enzyme (ACE) from the endothelial cell surface to be a more sensitive and earlier marker of oxidative lung endothelial injury than lung wet-to-dry weight ratio. The aim of this study was to evaluate the potential of the anesthetic propofol, which has antioxidant properties, to prevent oxidative lung injury by measuring ACE shedding. ACE release from isolated perfused rat lungs increased significantly after ischemia-reperfusion (I/R). Propofol significantly decreased I/R-induced ACE release by 23.4% (P < 0.05). Perfusion with 0.75 mM H(2)O(2) also caused ACE release from the lung microvasculature, which was similarly attenuated by propofol. The protective effect of propofol on H(2)O(2)-induced ACE shedding was confirmed in vitro using Chinese Hamster Ovary cells overexpressing human ACE. Thus, propofol can attenuate oxidative injury of the pulmonary endothelium as detected by ACE shedding in I/R and H(2)O(2) models of acute lung injury.

Clinical biochemistry of epilepsy. I. Nature of the disease and a review of the chemical findings in epilepsy

In idiopathic or generalized epilepsy, serum glucose and cholesterol concentrations tend to be low, especially just before the seizure. Glucose tolerance curves are abnormal and variable. The electrolyte balance is disturbed, and epileptics tend to go readily into alkalosis. Serum [Na+] is usually unaffected, but [K+] is normal to low between attacks and increases during and after the seizure. Serum [Cl-] is usually high just before the seizure. Epileptics are generally mildly hypocalcemic, especially in the period before the seizure. Serum urea and nonprotein nitrogen values are low between paroxysms but increase after the seizure. Serum protein concentration is usually normal. Stress, which releases epinephrine and corticotropin, results in high serum citrate concentration, which probably contributes to decreased serum [Ca2+] just before a seizure. In the healthy individual, any increase in serum citrate is accompanied by increasing [Ca2+]. In the rabbit, convulsions can be induced with corticotropin, a result of increased serum citrate concentration coupled with a decrease in [Ca2+]. The net result is severe hypo-ionic-calcemia. A similar phenomenon has been reported in a few humans. Administration of insulin causes serum citrate concentrations to decrease. Apparently, the dynamic system that controls glucose and lipid metabolism, and thus electrolyte balance, through the hormones epinephrine, corticotropin, insulin, glucagon, calcitonin, and parathormone, is abnormal in the epileptic.

Clinical biochemistry of epilepsy. I. Nature of the disease and a review of the chemical findings in epilepsy

In idiopathic or generalized epilepsy, serum glucose and cholesterol concentrations tend to be low, especially just before the seizure. Glucose tolerance curves are abnormal and variable. The electrolyte balance is disturbed, and epileptics tend to go readily into alkalosis. Serum [Na+] is usually unaffected, but [K+] is normal to low between attacks and increases during and after the seizure. Serum [Cl-] is usually high just before the seizure. Epileptics are generally mildly hypocalcemic, especially in the period before the seizure. Serum urea and nonprotein nitrogen values are low between paroxysms but increase after the seizure. Serum protein concentration is usually normal. Stress, which releases epinephrine and corticotropin, results in high serum citrate concentration, which probably contributes to decreased serum [Ca2+] just before a seizure. In the healthy individual, any increase in serum citrate is accompanied by increasing [Ca2+]. In the rabbit, convulsions can be induced with corticotropin, a result of increased serum citrate concentration coupled with a decrease in [Ca2+]. The net result is severe hypo-ionic-calcemia. A similar phenomenon has been reported in a few humans. Administration of insulin causes serum citrate concentrations to decrease. Apparently, the dynamic system that controls glucose and lipid metabolism, and thus electrolyte balance, through the hormones epinephrine, corticotropin, insulin, glucagon, calcitonin, and parathormone, is abnormal in the epileptic.

Clinical biochemistry of epilepsy. II. Observations on two types of epileptiform convulsions induced in rabbits with corticotropin

We propose than an alarm mechanism is operative in animals, designed to regulate neuromuscular irritability by regulating [Ca2+]. Epinephrine or corticotropin (ACTH), injected intramuscularly into animals, causes a hypercitricemia, resulting in decreased [Ca2+]. This increases muscular excitability to facilitate escape. To avoid over reaction, [Cl-] is shifted into the plasma without a concomitant shift of Na+, thus generating an acidosis and an increase in ionization of Ca. Plasma pH, pCO2, total CO2, and [K+] decrease, and [Mg2+] increases. The acidosis, decrease in K+, and increase in [Mg2+] serve to counteract the effect of the decrease in [Ca2+], to protect against tetany. In the rabbit the hypercitricemia observed upon ACTH administration is accompained by a severe hypocalcemia and drop in blood pressure, resluting in tetanic convulsions. This seems to indicate calcitonin release, independent of the hypercitricemia. Thyroidectomized rabbits show only mild hypocalcemia when given ACTH, but develop a severe acidosis and typical grand mal epileptiform seizures. Administration of ACTH and then calcitonin to the goat, an animal resistant to the effects of ACTH alone, simulates the effect observed in the rabbit with respect to changes in blood components and blood pressure. Changes in the blood in the goat and rabbit resemble those in humans before an epileptic seizure. alpha-Melanotropin, containing a portion of the ACTH sequence, reacts in a manner similar to ACTH but more rapidly.

Clinical biochemistry of epilepsy. II. Observations on two types of epileptiform convulsions induced in rabbits with corticotropin

We propose than an alarm mechanism is operative in animals, designed to regulate neuromuscular irritability by regulating [Ca2+]. Epinephrine or corticotropin (ACTH), injected intramuscularly into animals, causes a hypercitricemia, resulting in decreased [Ca2+]. This increases muscular excitability to facilitate escape. To avoid over reaction, [Cl-] is shifted into the plasma without a concomitant shift of Na+, thus generating an acidosis and an increase in ionization of Ca. Plasma pH, pCO2, total CO2, and [K+] decrease, and [Mg2+] increases. The acidosis, decrease in K+, and increase in [Mg2+] serve to counteract the effect of the decrease in [Ca2+], to protect against tetany. In the rabbit the hypercitricemia observed upon ACTH administration is accompained by a severe hypocalcemia and drop in blood pressure, resluting in tetanic convulsions. This seems to indicate calcitonin release, independent of the hypercitricemia. Thyroidectomized rabbits show only mild hypocalcemia when given ACTH, but develop a severe acidosis and typical grand mal epileptiform seizures. Administration of ACTH and then calcitonin to the goat, an animal resistant to the effects of ACTH alone, simulates the effect observed in the rabbit with respect to changes in blood components and blood pressure. Changes in the blood in the goat and rabbit resemble those in humans before an epileptic seizure. alpha-Melanotropin, containing a portion of the ACTH sequence, reacts in a manner similar to ACTH but more rapidly.