Effects of the angiotensin-converting enzyme inhibitor perindopril on endothelial injury and hemostasis in rabbit endotoxic shock

Tan

Journal of Biological Chemistry

et al. 2008

Kinin B1 receptor (B1R) expression is induced by injury or inflammatory mediators, and its signaling produces both beneficial and deleterious effects. Kinins cleaved from kininogen are agonists of the B2R and must be processed by a carboxypeptidase to generate B1R agonists des-Arg 9 -bradykinin or desArg 10 Carboxypeptidase M (CPM) 2 was discovered as a glycosylphosphatidylinositol (GPI)-anchored membrane protein with B-type carboxypeptidase activity (1-3) and is a member of the "regulatory" or carboxypeptidase N/E subfamily of metallocarboxypeptidases (4 -8) based on its cDNA sequence (9), genomic structure (10), and x-ray crystal structure (11). The overall structure of CPM is composed of a 295-residue N-terminal catalytic domain, followed by an 86-residue conical ␤-sandwich (transthyretin-like domain) and a unique 25-residue extension to which the GPI anchor is post-translationally attached (11).CPM cleaves only C-terminal Arg or Lys residues, and some of its endogenous substrates include bradykinin, anaphylatoxins C3a, C4a, and C5a, Arg-or Lys-enkephalins, epidermal growth factor, and hemoglobin (2, 7, 12, 13). CPM preferentially cleaves C-terminal Arg as exemplified by the kinetics with Arg 6 -Met 5 -enkephalin (K m ϭ 46 M, k cat ϭ 934 min Ϫ1 ) versus Lys 6 -Met 5 -enkephalin (K m ϭ 375 M, k cat ϭ 663 min Ϫ1 ) (2). Bradykinin exhibits the lowest K m (16 M) of any CPM substrate tested (2), a concentration that is still much higher than the typical physiological concentration of this peptide in the nanomolar range. However, peptidases in vivo typically work at substrate concentrations far below the K m as exemplified by angiotensin I-converting enzyme (ACE), which has the same relatively high K m (16 M) with angiotensin I (14), a major physiological substrate. The development of ACE inhibitors as effective agents for treating hypertension and cardiovascular diseases was based in large part on the critical role of this enzyme in converting angiotensin I to II in vivo (15).The kinin peptides bradykinin and kallidin (Lys-bradykinin) are generated by the proteolytic action of plasma or tissue kallikrein on high or low molecular weight kininogen (16,17). Removal of the C-terminal Arg from bradykinin or kallidin inactivates these peptides as agonists of the constitutively expressed B2 receptor (B2R) (16,17). However, this conversion is a required processing step to generate desArg 9 -bradykinin or des-Arg 10 -kallidin (16, 18), metabolites that have a variety of biological activities mediated by specific activation of a different B1 receptor (B1R) whose expression is induced by inflammatory mediators (19,20). Thus, CPM acts as a cell surface processing enzyme to generate des-Arg-kinin agonists for the B1R, and without this catalytic conversion, B1R signaling could not occur. This is of potential importance in inflammatory or pathological responses. For example, B1R activation stimulates extracellular signal-regulated kinase phosphorylation, prostaglandin production (20), and inducible nitric-oxide synthase-mediate...

Section: Discussionmentioning

confidence: 99%

Carboxypeptidase M and Kinin B1 Receptors Interact to Facilitate Efficient B1 Signaling from B2 Agonists

Tan

Journal of Biological Chemistry

et al. 2008

“…Angiotensin-converting enzyme (ACE) inhibitors had been shown to improve endothelium-dependent vasodilation via a NO-dependent mechanism in a rabbit model of endotoxin shock (59) . However, no effect could be seen in endothelial histological injury or tissue factor expression in this same model.…”

Section: Vasodilatorsmentioning

confidence: 99%

Microcirculatory assessment in daily clinical practice - not yet ready but not too far!

Salgado

Favory

Backer

2010

Einstein (São Paulo)

Shock is characterized by an alteration in tissue perfusion that may lead to tissue hypoxia. Recent guidelines recommend aggressive and early resuscitation therapy, but mortality rate is still unacceptably high. Unfortunately, traditional clinical surrogates used to guide resuscitation therapy poorly correlate with microcirculatory blood flow, a key determinant of tissue perfusion. New techniques that directly assess microcirculatory perfusion at the bedside have emerged as a complement to traditional macrohemodynamic parameters. These techniques have been supported by several studies showing microcirculatory alterations in different clinical settings. In addition, these microcirculatory alterations are related with outcome and persist regardless of arterial pressure normalization, being a better predictor of organ dysfunction and mortality than global hemodynamic and laboratory parameters. These findings allowed the concept of "microcirculatory-goal directed therapy", which is now in its preliminary phase, as the impact of many interventions still needs to be assessed. Finally, microcirculation assessment has also been explored in other medical fields such as perioperative, systemic arterial hypertension, heart failure, and hyperviscosity syndromes. In this review, we shortly present the characteristics of microcirculation and the main determinants of capillary blood flow, and we discuss advantages and limitations of some recently available techniques to evaluate microcirculation at the bedside, and how they could be useful for the general clinician in daily practice.Keywords: Shock; Resuscitation; Microcirculation/pathophysiology; Hemodynamics/physiology; Multiple organ failure/pathophysiology; Prognosis ReSUMOO choque é caracterizado por uma alteração na perfusão tecidual que pode levar à hipóxia tecidual. Diretrizes recentes recomendam uma terapia de ressuscitação hemodinâmica precoce e agressiva nos estados de choque, mas a taxa de mortalidade ainda é inaceitavelmente alta. Os parâmetros clínicos habituais usados para orientar a terapia de reanimação correlacionam-se mal com o fluxo sanguíneo capilar, um determinante essencial da perfusão tecidual. Novas técnicas que avaliam diretamente a perfusão da microcirculação à beira do leito surgem como um complemento aos parâmetros macro-hemodinâmicos tradicionais. Estas técnicas foram testadas em vários estudos que mostraram alterações microcirculatórias em diferentes situações clínicas de choque. Além disso, estas alterações microcirculatórias estão relacionadas ao prognóstico, e persistem independentemente da normalização da pressão arterial, sendo um melhor preditor de disfunção orgânica e mortalidade do que os parâmetros hemodinâmicos globais e laboratoriais. Estes achados permitiram lançar o conceito de "terapia dirigida por parâmetros microcirculatórios", atualmente em fase preliminar, uma vez que o impacto de muitas intervenções ainda precisa ser avaliado. Finalmente, a avaliação da microcirculação também foi explorada em outras áreas que não o choq...

“…In animals, angiotensin-converting enzyme (ACE) inhibitors have been shown to improve splanchnic perfusion (21)(22)(23)(24), to decrease bacterial translocation (25) and to improve survival (26) in various types of shock. Moreover, enalaprilat enhanced gut perfusion measured by gastric tonometry in critically injured trauma patients (27) and improved endothelial function in septic patients (28).…”

Section: Introductionmentioning

confidence: 96%

Systemic and regional hemodynamic effects of enalaprilat infusion in experimental normotensive sepsis

Rahal¹,

Garrido²,

Cruz³

et al. 2006

Braz J Med Biol Res

Angiotensin-converting enzyme inhibitors have been shown to improve splanchnic perfusion in distinct shock states. We hypothesized that enalaprilat potentiates the benefits of early fluid resuscitation in severe experimental sepsis, particularly in the splanchnic region. Anesthetized and mechanically ventilated mongrel dogs received an intravenous infusion of live Escherichia coli over a period of 30 min. Thereafter, two interventions were performed: fluid infusion (normal saline, 32 mL/kg over 30 min) and enalaprilat infusion (0.02 mg kg -1 min -1 for 60 min) in randomized groups. The following groups were studied: controls (fluid infusion, N = 4), E1 (enalaprilat infusion followed by fluid infusion, N = 5) and E2 (fluid infusion followed by enalaprilat infusion, N = 5). All animals were observed for a 120 min after bacterial infusion. Mean arterial pressure, cardiac output (CO), portal vein blood flow (PVBF), systemic and regional oxygen-derived variables, and lactate levels were measured. Rapid and progressive reductions in CO and PVBF were induced by the infusion of live bacteria, while minor changes were observed in mean arterial pressure. Systemic and regional territories showed a significant increase in oxygen extraction and lactate levels. Widening venous-arterial and portal-arterial pCO 2 gradients were also detected. Fluid replacement promoted transient benefits in CO and PVBF. Enalaprilat after fluid resuscitation did not affect systemic or regional hemodynamic variables. We conclude that in this model of normotensive sepsis inhibition of angiotensin-converting enzyme did not interfere with the course of systemic or regional hemodynamic and oxygen-derived variables.