A few words on the location of ACE. It is present on all endothelial cells but in highest concentration in the pulmonary circulation from where hence it is believed to give origin to the Ang II seen in circulation
Liver produced angiotensinogenReninattatches to prorenin receptor
The far from optimal pharmacokinetic properties of aliskiren (2 – 7% bioavailability)39 and a ceiling dose of 300 mg daily (due to gastrointestinal irritation) invite novel agents in this class to the pipelinesHRP also useful as Antiapoptitic hence anti cancer
ACE inhibitor–induced elevation in Ang I facilitates its hydrolysis by other peptidases that is where chymases play a role.
Although ACE may be isolated from plasma, it pri-marily exists within tissues located on the endotheliumof all blood vessels as well as in the parenchyma of the heart, kidneys, brain, and adrenal glands . ACE isanchored to the plasma membrane of these cells, and therefore may be accurately referred to as tissue ACE
Renin and angio-tensinogen (AOGEN) are mostly taken up from the plasma or formed locally. Mast cell production of human heart chy-mase may present an alternative path-way. ANG II synthesis occurs extracellu-larly and acts on cell-speciﬁc receptors on different cell types such as cardiomy-ocytes and ﬁbroblasts. unable to ﬁnd proof for local mRNA expression in the literature. evidence for the presence of renin protein in the heart attributed to uptake from the circulation (134) either due to nonspeciﬁc uptake (diffu-sion) into the cellular interstitium (144, 315, 542) or through the actions of speciﬁc functional binding sites or receptor for prorenin and renin . This suggests that cardiac ANG II generation by circulating renin occurs predominantly on the cell surface (315, 603). Thus, ACE in-hibitors may prevent cardiac enlargement and remod-eling by reducing myocyte apoptosis. Systolic function, however, is largely unaffected by AII which is responsible for diastolic dysfunction and inc lvedp
Indeed, ACE expression is reported to be higher in ruptured plaques than in fibrosclerotic plaques, and in the former, ACE is highly expressed in macrophages accumulated around the attenuated fibrous cap. Such findings indicate that the presence of ACE within lesions, atheroma-tous plaques, and ruptured plaques contributes greatly to thefurther progression of atherosclerosis.2
PC could promote PKCε-induced activation of ALDH2, which would then remove toxic aldehydes known to degranulate mast cells, such as acetaldehyde and 4-hydroxynonenal (4-HNE), formed by lipid peroxidation.13–15 Our study outlines a novel protective anti-RAS effect of IPC; we find that the sequential activation of adenosine A2b- and A3-receptors,PKCε and ALDH2 in cardiac mast cells diminishes the release of renin elicited by I/R and thus, curtails ANG II- and NE-induced arrhythmias.proteinkinase C (PKC), PKCεisoform
Figure 6 Model explaining the changes in cardiac renin – angio-tensin – aldosterone system parameters and norepinephrine content following left ventricular assist device (LVAD) implan-tation. Concomitant angiotensin-converting enzyme inhibitor (ACE-I) treatment will keep renin levels high and, in combination with the blockade of ACE, prevent the rise in cardiac angiotensin II post-LVAD. Moreover, these drugs, when given both before and after LVAD implantation, are unlikely to alter aldosterone.See text for explanation Left ventricular assist device-induced LV unloading inﬂuences the RAAS signiﬁcantly: although it decreases renal renin release (and thus, presumably, the plasma levels of Ang II and aldosterone), it allows cardiac angiotensin generation to increase. The lattermost likely relates to the rate-limiting quantities of angiotensinogen in cardiac tissue (Figure 6). A decrease in circulating aldosterone (the main source of cardiac aldosterone) would explain why cardiac aldosterone decreased in parallel with cardiac renin. However, cardiac norepinephrine increased seven-fold, possibly due to the rise in Ang II generated at cardiac tissue sites. Both ago-nists are likely determinants of the increased myocardial ﬁbrosis and stiffness following LVAD support. Importantly, the use of an ACE-I not only prevented the increase in angiotensin II and norepi-nephrine, but also ameliorated myocardial ﬁbrosis and stiffness.12 Nevertheless, it did not result in a complete recovery of ventricu-lar function. As these beneﬁcial effects occurred in the absence of a change in cardiac aldosterone, additional improvement might be expected by applying mineralocorticoid receptor antagonists in addition to ACE-Is during LVAD support. Obviously, this con-clusion should be viewed with care, given the low patient number investigated in this study. Additionally, b -blockers mightfurther suppress sympathetic activity. It is interesting to note, however, that both ACE-Is and mineralocorticoid receptor antag-onist therapy were employed (in addition to other agents) by Birks et al.5 in their series of patients, which resulted in a 70% rate of myocardial recovery allowing LVAD explantation. Additional studies should prospectively test the contribution of these various drugs to myocardial recovery during prolonged mechanicalunloading by LVADs.
Proximal tubular cells as an example of a local RAAS. Tubular cells could generate AngII in nanomolarconcentra-tions and secrete into the tubular fluid as well as the interstitial space. Furthermore, tubular cells secrete intact angiotensinogen into the tubular fluid. Cells also could take renin and angio-tensinogen up from the circulation, indicating a close interac-tion with the systemic RAAS. Although proximal tubular cells have ACE in their brush border membranes, it is controversial whether intracellular ACE contributes to AngIIformation.decreased progression of diabetic nephropathy ap-pears to occur through a mechanism that is independent of blood pressure reduction.
increases reduced nicotinamide-adenine dinucleotide-dependent oxidase On the other hand, bradykinincan stimulate the synthesis of plasminogenactivator.Thus, by synthesizing AII and degrading bradykinin,ACE regulates vascular ﬁbrinolytic balance in favor of thrombosis. These data raise the possibility that reductions in AII and increases in bradykinin may contribute to the vasculo-protective effects of ACE inhibitors by way of tiltingthe vascular ﬁbrinolytic balance in favor of ﬁbrinolysis. Patients who had received ramipril within 24-hours ofthe onset of symptoms had lower levels of both PAI-1 antigen and PAI-1 activity than patients who receivedplacebo; therefore, intervention in the local RAS has important effects on the regulation of vascular ﬁbri-nolysis and may represent an additional mechanism through which high tissue-afﬁnity ACE inhibitors ex-ert their vasculoprotective effects
obese women are reported to have higher circulating angiotensinogen, renin, aldosterone, and ACE levels than lean women. ACE inhibitor and an AT1 receptor antagonist were found to reduce adipocyte size and to increase insulin sensitivity in Sprague-Dawley rats fed a fructose-rich diet.23 The increase in insulin sensitivity alsofits with a recent report that in subjects with essential hypertension and insulin resistance, RAS blockade witheither an ACE inhibitor or an AT1 antagonist increased the secretion of the insulin-sensitizing adipokineadiponectin.
Two possible ways of ANG II generation within the CNS are discussed: 1) volume transmission: extracellulargeneration of angiotensin peptides, acting as neurohormones; and 2) wiring transmission: uptake of angiotensinogen by neurons and forma-tion of peptides within the neuron. ANG II acts as neurotransmitter or cotransmitter (528).
Renin, synthesized and secreted by theca cells, leads to local ANG production. Two possible ways in which ANGII may modulate atresia in ovaries has been suggested: 1) ANG II is acting on the AT2 receptor within the same follicle by an autocrine mechanism leading to apoptosis and atresia; and 2) ANG II is secreted by preovulatory follicles causing apoptosis in adjacent atretic follicles (paracrine mechanism). Follicular ﬂuid contains high levels of renin andANG II.
Location of ANG II forming pathways in Leydig cells. Expression of the alternative testicular isoform of ACE(tACE) in germ cells. RAS in the epididymis: intraluminal and intracellular gener-ation of ANG II in the epididymis. Paracrine and autocrine secretion of ANG II is mediated via the AT1 receptor. AT2 receptors may modulatebasal cell proliferation and differentiation. tACE may play an important part in local modulation of fertility, but its exact role is unclear. [Adapted from Zhao et al. (808).]
quinaprilat had a far longer tissue dissocia-tion rate than either lisinopril or enalaprilat
Indeed, this under-standing of the balance between local NO and AII leads one to consider the therapeutic potential of intervening in AII-induced endothelial dysfunction with ACE in-hibitors that have a high afﬁnity for tissue ACE.Both enalapril and quinapril inhibited plasma ACE to the same degree, and both inhibitors produced similar re-ductions in blood pressure. Quinapril, however, caused a signiﬁcantly greater inhibition of AII induced vasocon-striction than enalapril, whose effect was not different from placebo . In phase one of the QUO VADIS study(effects of QUinapril On Vascular Ace and Determi-nants of Ischemia) patients with CAD and scheduled for coronary artery bypass graft (CABG) surgery were randomized to either captopril or quinapril. Althoughboth agents had comparable and signiﬁcant effects on blood pressure reduction compared to placebo, onlyquinaprilsigniﬁcantly inhibited the vascular conversion of AI to AII . Thus, the relative ability of high tissue-afﬁnity ACE inhibitors to inhibit the de novo produc-tion of AII and enhance NO bioactivity may be clinically signiﬁcant
DD50, ACE inhibitor concentration required for 50% displacemen t of bound radiolig and. Adapted from Ferrari (2004) 29by permission of LLS
perindopril and ramipril were the only ACE inhibitors tested to signiﬁcantly reducethe apoptotic rate . bradykinin has a strong anti-apoptotic action, whereasangiotensin is pro-apoptotic.therefore increased affinity for bradykinin helps
All three trials in stabble CAD or in those with high risk he experimental and clinical research thus far pre-sented substantiate the importance of tissue ACE,locally elaborated AII, and the therapeutic potentialof tissue ACE inhibition. Possible support for thisparadigm may be found in the HOPE study . HOPEwas designed to test the hypothesis that ramipril, a hightissue-afﬁnity ACE inhibitor, could retard the progres-sion of ischemic heart disease, reduce the risk of stroke,and prevent complications related to diabetes in a broadrange of patients who were at high risk for cardiovas-cular events but who did not have left ventricular dysfunction or heart failure. HOPE randomized 9,297 high-risk patients to ramipril, vitamin E, or placebo for 5years of follow-up. The primary study endpoint was acomposite of cardiovascular death, MI, or stroke; sec-ondary measures included congestive heart failure, hos-pitalization, revascularization procedures, and a num-ber of diabetes-related endpoints. Patients who wereat least 55 years old included those with a history ofCAD, stroke, peripheral vascular disease, or diabetes,plus at least one other cardiovascular risk factor.The combined heart attack rate, stroke, and car-diovascular death rate among atients treated withramipril was 14% versus that of 18% in the placebogroup ( P < 0. 001), and represents an overall riskreduction of 22%. Moreover, the continuing divergence in results between those patients who received ramipriland those who received placebo suggests that longer-term treatment may yield even better results .When analyzed individually, the relative risk for cardio-vascular death was reduced by 25%. There was a 20%risk reduction for nonfatal MI, and a 32% risk reduc-tion for stroke. The risk of death from any cause wasreduced by 16% that of those patients who receivedplacebo ( P = 0.006).There were also important risk reductions in thesecondary outcome measures most notably amongdiabetics. Patients who were treated with ramipril ex-perienced a signiﬁcant reduction in diabetes-related complications and remarkably, the rate of newly diag-nosed diabetes was reduced by nearly one third. Theinvestigators attribute most of the long-term clinicalbeneﬁt observed in HOPE to a vasculoprotectiveef-fect, rather than to blood pressure reduction, whichwas only modest. The results of this study are excep-tional, and support the long-held hypothesis that tissueACE inhibition provides important clinical beneﬁtsina wide range of patients. The results of two similar on-going large-scale trials (PEACE and EUROPA) withthe ACE inhibitors trandolapril and perindopril (re-spectively), and two trials evaluating quinapril in pa-tients with CAD and consequent ischemia (QUASAR, which excludes patients who have undergone CABGwithin 6 months of enrollment and IMAGINE, a follow-up study to QUO VADIS, which will treat patients upto 24 months post-CABG), may ultimately conﬁrmtheHOPEﬁndings and the overall therapeutic value of tis-sue ACE inhibition.
Siragy HM et al. J Clin Invest.1996;97:1978–1982. Siragy HM et al. J Clin Invest. 1997;100:264–269. Siragy HM et al. Hypertension. 1999;33:1247–1242. Siragy HM et al. Proc Nat Acad Sci. 1999;96:6506–6510. Siragy HM et al. Hypertension. 2000;35:1074–1077.ARBs increase Ang II levels several-fold above baseline byuncoupling a negative-feedback loop. Increased levels of circulating Ang II result in unopposedstimulation of the AT2 receptors. AT2 receptor stimulation may be harmful under certaincircumstances through mediation of growth promotion, fibrosis, and hypertrophy, as well asproatherogenic and proinflammatory effects [34,35]. Ang II may promote plaque rupture byaugmenting matrix metalloproteinase-1 in an AT2-dependent fashion and by preventinggrowth of vascular smooth muscle cells with reduced collagen deposition and additionalcellular apoptosis within advanced plaques . These data raise the possibility that ARBsmay promote plaque vulnerability and propensity to rupture. Indeed, the reduction in incidenceof both MI and cardiovascular death seen with ACE inhibitors is significantly greater than thatachieved by ARBs in patients [37–39]. However, new trials ONTARGET/TRANSCEND(ONgoingTelmisartan Alone and in combination with Ramipril Global Endpoint Trial/Telmisartan Randomized AssessmeNt Study in ACEiNtolerant subjects with cardiovascularDisease) report that ARBs give results comparable to ACE inhibitors with respect to MI andcardiovascular death.The increased risk of MI which was thought to be associated with ARBs has been discarded after ONTARGET but none the less ACEI have an edge and it may be due blockage of tissue ras
mitogen-activated protein kinases (MAPKs) The ACE homologue ACE2 metabolisesAngII to An g1-7, decreasing AngII and increasing An g1-7, w hich counter ac tsAngIIactivityviatheMas receptor.However,ACE2alsoconvertsAngItoAng1-9,apoorly char ac terised p eptide which can be fur therconver ted to Ang1-7 v ia ACE. Ang1-9 stimulates bradykinin re lease in endothelium and h as antihy p er t rophic ac tions in the hear t, att r ibuted to its being a comp etitive inhibitor of ACE, leading to decreased AngII, r ather than increased Ang1-7. he AT 1 R antagonist losar tan blocked An gII-induce d, but n ot vasopressin-induce d, hy p er t rophy. Lo sar t an did n ot block the antihy p er t rophiceffects of Ang1-9, or An g1-7 on vasopressin-stimulated card io-myocytes. T he Ma s a ntagonist A 779 efﬁcientlyblocke d t he antihy p er t rophiceffec t s of Ang1-7, w ithout a ffec ting An g1-9.
N Engl J Med 1998;339:1285–1292.
atrial (ANP) and brain-derived (or B-type [BNP]) natriuretic peptides that are produced principally in the cardiac atria and myocardium, respectively. Secretion of ANP and BNP is increased in response to mechanical strain of heart muscle. C-type natriuretic peptide, found in thekidney, heart, lung, and vascular endothelium, is released in response to shear stress.2 Natriuretic peptides have direct vasodilator effects; inhibit renin, aldosterone, and endothelin secretion; reduce sympathetic activity; and may also reduce smooth muscle proliferation and reduce cardiac fibrosis.increase peptide levels by inhibiting metabolism may be negated by reduced natriuretic peptide secretion caused by a diuresis- and natriuresis-induced reduction in cardiac filling pressures.
The variable effect of NEP inhibition on blood pressure and systemic vascular resistance is likely to be a response to the increased levels of the many different vasoactive peptides metabolized by NEP. increased of levels of vasodilator natriuretic and kinin peptides, NEP inhibition may increase levels of the vasocon-strictorsAng II and endothelin, and reduce levels of the vasodilator Ang-(1-7).Major concern is angioedema of the combination as high as 4 times more
Lesser incidence of angioedema was seen with there use in HF than in hypertension as ssen in OVERTURE and OCTAVE respectively . This is because of tolerance to or resisitance to kinins seen in HFMost of the combinations at a particular dose produce more of ace inhibition, cause nep inhibition for less time, hence beneficial effects seen in trials are doughtfuland inconclusive.
The BP reduction after spironolactone is conferred similarly in hypertensives with and without primary aldosteronism (thoughhere higher dose is required), independently of ethnicity and urinary aldosterone excretion and it occurs within weeks and persists indeﬁnitely.Aldosterone increases the effect of AngII, induces ROS, and acceleration of the AngII-induced activation of mitogen-activated protein kinases
partially block T-type voltage-dependent calcium channels in addition to the blockade of L-type voltage-dependent calcium channel. Therofore, the dihydropyridinestructure might be exploited to design non-steroid compounds with dual aldosterone antagonism + L-type voltage-dependent calcium channelblockade Voltage-dependent Ca channels are classified into several subtypes based on the isoform of their α1 subunits. Traditional Ca channels blockers (CCBs), including nifedipine and amlodip-ine, act predominantly on L-type Ca channelswhereas novel CCBs such as efonidipine, beni-dipine and azelnidipine inhibit both L-type and T-type Ca channels. Cilnidipine blocks L-type and N-type Ca channels. divergent actions on renal microves-sels.L-type CCBs preferentially dilate afferent arterioles, L-/T-type and L-/N-type CCBs potently dilate afferent and efferent arterioles.
However, the development of LCI699 was stopped in the 2nd quarter of 2010 in favour of seeking more speciﬁc inhibitors
Dysregulation of the rennin–angiotensin–aldosterone system (RAAS) may contribute to thepathogenesis of atherosclerosis. Angiotensin II binds to angiotensin II type I receptor (AT1R)resulting in enzymatic production of oxygen-derived free radicals. This leads to dissociationof inhibitory factor, IκB with subsequent activation of NF-κB that stimulates expression ofproinflammatory genes, chemokines, and cytokines. Cross-talk between hyperlipidemia and RAAS at multiple steps is illustrated here. This may help to explain why combined therapywithstatins, peroxisome proliferators-activated receptors (PPARs), and RAAS blockade haveadditive beneficial effects on endothelial dysfunction and insulin resistance when comparedwithmonotherapies in patients with cardiovascular risk factors. Modified from Dr. Koh [1,4,5,6].NF-B, an impor-tantproinflammatory transcription factor. NF-B–medi-ated transcription of chemokines, including monocyteche-moattractant protein-1, RANTES, and other chemokines, then isresponsible for renal tissue infiltration with leukocytes
TISSUE RENIN ANGIOTENSIN SYSTEM
Newer Concepts in RAAS:Tissue, and Cardiac RAAS Dr Amarpal Singh Gulati Asst. Prof. Dept. of Cardiology Nizam’s Institute of medical Sciences
Deﬁnition“The renin-angiotensin system (RAS) is apeptidergic system with endocrinecharacteristics.”
How the RAAS Was Seen in the Past•Substrate : Angiotensinogen, an α-glycoprotein,released from the liver•In the circulation, enzyme renin, secreted from theII “main effector” Circulating Angjuxtaglomerular apparatus of the kidney forms thedecapeptide angiotensin (ANG) I. Involved in •global regulation of sympathetic•ANG I is then activated to the octapeptide ANG II byangiotensin converting enzyme (ACE), a activity •Regulation of blood pressuremembrane-bound metalloproteinase, which is •Fluid and electrolyte balancepredominantly expressed in high concentrations onthe surface of endothelial cells in the pulmonarycirculation.•ANG II, considered the main effector peptide of theRAS, which acts on speciﬁc receptors on vascularsmooth muscle cells to induce vasoconstriction or,by stimulating the release of aldosterone from theadrenal cortex. Vascular Disease Prevention, 2009, 6, 65-74
POSITIVE FEEDBACK EXISTS BETWEEN DISEASE PROCESSES IN THE CARDIORENAL CONTINUUM HTN RAAS activity Ang II Oxidative stress/ Vasoconstriction IGT DM risk CVD risk GFR SCr Glomerular pressure •Atherosclerosis •cardiac hypertrophy •fibrosis, Glomerular sclerosis MAU UAER •nephropathy of diabetic and nondiabetic etiology. Macro- CKD albuminuria proteinuria Predicts stroke, Technical Advances ESRD CHD, CVD risk 1. molecular biologyCHD=coronary heart disease; IGT=impaired glucose tolerance; UAER=urinary albumin excretion rate rat 2. Availability of transgenic and knock-out models CHD=coronary heart disease; IGT=impaired glucose tolerance; UAER=urinary albumin excretion rate with altered expression of RAS components.Kopyt NP. JAOA. 2005;105:207–15. 4 Kopyt NP. JAOA. 2005;105:207–15.
• Circulating Ang II levels tend to increase in patients taking ACE inhibitors over long periods.• “ACE is not the only enzyme implicated in the generation of Ang II”
Interplay of recently discovered components of the renin – angiotensin – aldosterone system. Alternative pathways of ANG II formation Concept of “local” or “tissue” renin angiotensin systems Additional truncated peptides (1-9) & (1-7) Different ANG receptors and signal transduction pathwaysEuropean Heart Journal (2011) 32, 2739–2747
•Prorenin can be activated by •Proteolytic :Endopeptidases/trypsin/cathepsin B or •Nonproteolytic :low pH• Three receptors •Mannose-6-phosphate receptor (M6P) •Endothelial cells •Clearance mechanism •Prorenin binding protein •Cardiac cells •Local tissue RAAS •45-kDa membrane protein binding both prorenin and renin •Angiotensin independent effects •Cofactor in increase production of Ang I •Activation of •promyelocytic zinc ﬁnger (PLZF) •protein-phosphatidylinositol-3-kinase •mitogen-activated protein kinases (MAPKs) •localized in the mesangium (kidney) and in the subendothelium of renal, uterine, and cardiac blood vessels
Newer Theraupeutic Targets “1” •Direct renin inhibitors DRI’s •like aliskiren •attenuate the plasma renin activity which is increased by ACE inhibition or AT1R blockade •High renin levels cause ‘escape’ from renin inhibition •Do not prevent binding of renin to the (P)RR. •A handling region peptide (HRP) inhibiting the binding of prorenin to (P)RR, •completely abolished diabetic nephropathy in AT1R knockout mice “2” •Reduced cardiac ﬁbrosis in stroke-prone Spontaneously Angiotensin Hypertensive Rats Independent •reduced cardiac hypertrophy and ﬁbrosis Effects •HRP were only effective in low-renin conditions Ichihara A et al. Hypert ens Res 2010;33:177 – 180 Susic D et al. Am J Physiol Heart Circ Physiol 2008;295:H1117 – H1121.
cleavage of the COOH-terminal dipeptide Angiotensin converting enzyme ACE independent enzyme activity • chymases, • In circulation – high substrate speciﬁcity – Cellular localization largely restricted to mast cells – Normally remains inactivated • Locally expressed – Selective chymase inhibitors used in animal models •Mediate > 80% of AngII formation in • carboxypeptidases, the heart and >60% in the vessels • cathepsin G •Not inhibited by ACE inhibitors • tonin. •Upregulation during pathologic conditions causing increased local Ang • neprylisin II generation •Also form Alternative cleavage products
White bars : nondiabetic controls (control) Black bars : streptozotocin (STZ)- induced diabetic hamsters (STZ) Hatched bars : STZ hamsters rendered normoglycemic by continuous intraperitoneal insulin infusion (STZ CIPII).Quantiﬁcation of hamster chymase and ACE mRNA in the kidney by real-time PCR.Results are shown as a percentage of controls.
ACE (dipeptidyl-carboxypeptidase) subtypes• Two distinct forms of ACE • Two active sites – Somatic form on the endothelial – N-terminal domain cells(lung, smooth muscle cells, • Ang 1-7 cleavage monocytes, T lymphocytes, and – C-terminal domain adipocytes) • Responsible for Ang I conversion – Germinal form (testis) • Selective C domain inhibition is • glycosylphosphatidylinositol (GPI) sufficient to prevent Ang I–induced hydrolase activity not inhibited by ACE vasoconstriction inhibitors • Both sites required for degradation of • capacitation, formation of the sperm bradykinin membrane, located on the 1. endothelium of all blood vessels• Two types of Existence 2. In the parenchyma of the – At the cell surface (ectoenzymes) heart, kidneys, brain, and adrenal hydrolyzing circulating peptides glands. 2. Also in non- – Soluble form (plasma ACE) after action endothelial cells such as of ACE secretase macrophage • lungs have traditionally been considered to be an integral part of the circulating RAS • 10% of total ACE • Risk factor for coronary stent restenosis, CAD, MI and post MI LV dilation Anchored to the plasma membrane
“Local” or “tissue” renin angiotensin systems• RAS components in “unlikely” places – such as the “kidney enzyme” renin in the brain – Local expression of angiotensinogen, renin, renin-binding protein, ACE, chymase, as well as Ang II receptors and secretion of Ang II.• “Tissue-based synthesis of ANG II” – Angiotensin and renin messenger RNA (mRNA) has been discovered in 12 different extrahepatic tissues of rats, strongly suggesting that there is local synthesis of angiotensinogen and renin• Local synthesis or Uptake from the circulation• Clinical relevance : “Dissociating from the class effect”
• Both Local and systemic actions of the RAS integrate and cause ANG- mediated effects Though• An independent function of local RAS (for example, in the brain, inside the blood-brain barrier as well as in testis/ovary/bonemarrow and so on)• Local RAAS at the cellular level – Paracrine – Autocrine effects • cell growth, proliferation, and metabolism – Intracellular or intracrine RAS sffects • ANG binding in the cell nucleus
The renin-angiotensin system (RAS) in the heart. •Contractility •Chronotropy •Hypertrophy •Apoptosis •Fibrosis Inducers of ACE 1. Vol or press overload 2. Wall stress 3. CHF 4. MI 5. aging endothelium Physiol Rev • VOL 86 • JULY 2006
•Van Kats et al. used infusions of radiolabeled ANG I and ANG II peptides in pigs andmeasured plasma and tissue levels of endogenous as well as the radiolabeledpeptides.•>90% of cardiac ANG I is synthesized locally in the heart•>75% of cardiac ANG II is synthesized locally, most of it using local ANG I generationas a basis.•Concept of a cardiacClinically,dependent only on the extremely of 1) RAS is not ACE inhibitors are local synthesisangiotensinogen and renin. in the treatment of cardiac disease; efﬁcient ACE independent pathways•Tissue ACE is regarded as the vital rate limiting enzyme in the local elaboration ofAII 2) Most of the ANG II generatedin intact cardiac are particularly important by disease states such as cardiac blood vessels can heartblocked by ACE hypertrophy and be failure inhibitors;•. Even partial inhibition of cardiac ACE has been shown to contribute to the e.g,beneﬁcial effects associatedACE expression is higher in with ACE inhibitors in patients with heart failure,hypertension, or coronary artery disease as well as in ruptured plaque 3) Expression of human heart chymase is highly the macrophages around compartmentalized and mostly restricted to ruptured plaque mast cells
Activation of a local renin-angiotensin system (RAS) in heart IPC •~50,000 mast cells/g human heart tissue in close proximity to vessels and nerves • Density further increases in heart failure, ischemic cardiomyopathy and experimental infarct models Circulation. 2010 August 24; 122(8): 771–781
RAS after LVAD European Heart Journal (2009) 30, 805–812
Local RASS in Kidney Proximal tubular cell 1. Unlike heart Ang II is required for normal renal development 2. Activated by •Hyperglycemia •Proteinuria •Renal injury •Reduction in calcitriol 3. ACEI’s do not significantly reduce intrarenal AngII production which is regionally4. Never the less, antihypertensive therapy with compart-mentalized and inACE inhibitors, successfully ameliorates proteinuria endosomessuggesting beneﬁcial effects independent ofreductions in blood pressure.5. Also decreases risk associated with death,dialysis, increased creatinine, and transplantation Wolf G et al. Nephron Physiol 93: 3–13, 2003
Tissue ACE and the Vasculature• Endothelial cells cover 700 m2 and weigh 1 • Locally produced AII is responsible for to 1.5 kg in a 70-kg individual endothelial dysfunction.• Vascular homeostasis • Local renin production as well as – relaxation and contraction; endothelial ACE upregulation occurs in – thrombogenesis and ﬁbrinolysis; response to injury – platelet activation and inhibition; – Hypercholesterolemia, – Cellular growth stimulation and inhibition. – smoking, – hypertension,• The vascular wall is the effector organ for the – aging, hormonal or plasma RAS – Diabetes• The substrate mRNA levels are abundantly • Expression of ACE is further modulated expressed in periadventitial fat cells by – steroids, – calcium ionophores,• Renin uptake also takes place via unspeciﬁed – growth factors binding sites on endothelial cells or speciﬁc prorenin/renin receptors – Clearance mechanism as well as pathological
Tissue ACE and Endothelial Dysfunction• Ang II ↑ NADPH+, producing superoxide anion and hydrogen peroxide that inactivate NO The reduction of tissue AngII• Oxidative stress also activates the transcription of factor NF-κ B that induces the expression of increased and NO bioavailability may underlie genes controlling cytokine formation and leukocyte adhesion to the vessel wall the mechanisms by which• ACE degrades and inactivates bradykinin, inhibitors exert their ACE hence vasoconstriction and inflammation vasculoprotective effects. – ↓ NO and other endothelial derived vasodilators – ↑ vascular smooth muscle cell growth and migration – ↑ expression of VCAM-1 & monocyte chemoattractant protein-1 – ↓ plasminogen activator• AngII also stimulates the production of endothelin-1 (potent vasoconstrictor) and plasminogen activator inhibitor-1 (PAI-1)
Balloon angioplasty induced endothelial dysfunction• Percutaneous transluminal coronary angioplasty (PTCA) injury in humans results in upregulation of ACE at sites of active repair• After pretreatment with perindopril, there was a reduced neointima formation after balloon injury of rabbit carotid artery• Trial on Reversing Endothelial Dysfunction (TREND) – CAD patients • normotensive, • had no heart failure, Free of RAS activation • no major lipid abnormalities; – randomized to placebo or quinapril and followed for 6 months – quinapril experienced signiﬁcant improvement in endothelial response over those patients who had received placebo ( P = 0. 002). Ohishi M et al.Circulation 96: 3328 –3337, 1997 Circulation 1996;94:258–265.
RAAS: BENEFICIAL EFFECTS OF INHIBITION ON THE CVS AND KIDNEY Cardiovascular system (CVS) Kidney • ↓ Elevated BP • ↓ Sodium and water reabsorption • ↓ Vascular smooth muscle cell • ↓ Proteinuria growth • ↓ Glomerular and tubulointerstitial fibrosis • ↓ LVH • Stabilization of renal function in CKD • Prevents LV remodeling after MI • Prevents HF after MI • ↓ Sympathetic NS activity • Stabilization of atherosclerotic plaque • Normalization of endothelial function • ↑ Fibrinolytic systemLVH=left ventricular hypertrophy; NS=nervous systemCowie MR. In Cardiovascular Medicine. Eds: Willerson JT, et al. 2007.
Other organs/systems• Skin• Digestive organs• Sensory organs• Lymphatic tissue• Bone marrow• Adipose tissue
Pharmokinetics of Angiotensin-Converting Enzyme Inhibitors• 2-methylpropranolol-L-proline moiety is common (active site)• Functional group :Adherence to the zinc component of the active site of ACE (potency dependent on strength of binding) quinaprilat =benazeprilat > 1. carboxyl-containing ramiprilat > perindoprilat > 2. Sulphydryl containing lisino-pril > enalaprilat > fosinoprilat > captopril 3. phosphoryl-containing• Drug lipophilicity – tissue penetration – differences in clinical effect ? Clin. Cardiol. Vol. 28, December 2005
Issues• Lipophilicity (α ACEI activity) • Tolerability• Potency • Prodrugs• Bioavailability •Hemodynamic effects: well proven as in trials of • Plasma levels CHF/MI• bradykinin selectivity and potentiation • intermediary metabolism• effects on endothelial-cell apoptosis •Local vasculoprotective effects: CAD / • half-lives endothelial dysfunction, validated 1st by HOPE• Co-morbidity • Elimination• Evidence based • durations of action OR • trough:peak plasma concentration relationships •Peripheral drug effects e.g decreasing afterload • Design •CardiacDemographics as in CHF (as seen in aorta • drug effects clipped model ) • Prostaglandins & free radicle scavanger
Major morbidity – mortality studies of angiotensin-convertingenzyme inhibitors across the continuum of cardiovascular disease
Relative tissue afﬁnity of various angiotensin-converting enzyme inhibitors Relative selectivity of angiotensin-converting enzyme (ACE) inhibitors for bradykinin vs.Ferrari R et al.Dialogues Cardiovasc Med 2004; 9 :71 –89Ceconi C et al.Eur J Pharmaco l 2007; 577 :1– 6. angiotensin I binding sites on ACE
Effects of ACE Inhibitor administration on Decreasing lipopolysaccharide (LPS)-induced endothelial apoptosis in rat aorta Ceconi C et al.Cardiovasc Drugs Ther 2007; 21 :423 – 429.
•↓LDL BANFF •Statins•High-resolution usg used for brachial art ﬂow mediatedvasodilation (FMD) before & after 8 wks of treatment. Quinapril is known to decrease vol overload •relatively lower- hypertrophy compared to enalapril•CAD pts had impaired FMD compared to pts without CAD. risk pt population.•Among the antihypertensive agents tested (quinapril, enalapril,losartan, amlodipine), only quinapril signiﬁcantly Circulation 1995;91:16–19.improved FMD . Am J Physiol 1997;273:H641–H646J Am Coll Cardiol 2000;35:60–66.78]. •Quinapril Ische-mic Event Trial (QUIET) •CAD without left ventricular dysfunction •quinapril failed to reduce cardiovascular events overall •Subset with increased concentration of LDL cholesterol improvement seen. •High tissue affinity alone cannot determine the effectiveness of an ACE inhibitor in preventing cardiovascular events though it is an important component •Other pharmacologic and structural characteristics of ACE inhibitors result in differences in effectiveness. •Perindopril or ramipril is likely to be a better therapeutic option than certain other ACE inhibitors in the setting of stable CAD.
RAAS Blockade with ARB; ACEI and ARB : Is there difference? Ang II Ang IIThe Blood Pressure Lowering Treatment Trialists’ Collaboration— •meta-regression analyses of 26 large-scale trials AT1 AT2 •Almost 150 000 patients with hypertension or ↑ CVD risk X •ACE inhibitors and ARBs produced Bradykinin similar BP-dependent decreases in NOS the risks of major coronary heart disease (CHD) events, such as stroke and heart failure NO •However, ACE inhibitors, but not ARBs, had effects beyond BP lowering cGMP •(9%) of ACE inhibitor efﬁcacy in reducing CHD risk was attributed to Proliferation BP-independent effects( P =0.002) Antiproliferation Vasodilation Vasoconstriction J Hype rtens 2007; 25 :951 –958.
Angiotensin 1 -9 (Ang1-9) & Ang1-7• Ang 1-9 – reduces AngII – increases Ang1-7 levels ACE 2 – Stimulates bradykinin release •Novel enzyme similar to ACE, called angiotensin- converting enzyme 2 (ACE2) – Directly binds the AT 2R •Removes the COOH-terminal amino acid phenylalanine and has 400-fold less affinity to Ang I than to Ang II• Ang1-7 blocks the des-Arg(9)-bradykinin •ACE2 can cleave effects of AngII via the G protein-coupledACE inhibitors •Insensitive to receptor Mas
•AT2R •Mas •Inhibits MAPKs, activates •Promotes Akt NO/cGMP and phospho- phosphorylation,NO lipase A2 pathways release. •Stimulation with a •Stimulation with non- synthetic peptide peptide agonist, induced vasorelaxation, compound 21, improved reduced BP in myocardial function in spontaneously rats with myocardial hypertensive rats (SHR) infarction independently and showed of BP effects, along with anti-inﬂammatory action antiarrhythmic effects. and NF-k B inhibitionFunke-Kaiser H et al. J Renin Angiotensin Aldosterone Syst 2010;11:7 – 17 Savergnini SQ et al.Hyp ertension 2010;56:112 – 120
Cardiac ACE2/Ang-(1–7)/Mas Axis • Protective role of ACE2 in the heart • Vascular endothelial cells( including kidney, lung & small intestine), cardiomyocytes, fibroblasts & myofibroblasts • ACEi, ARBs, and aldosterone receptor blockers, increase ACE2 activity/ expression Ang II • Ang-(1–7) causes vasodilation in forearm circulation of normotensive subjects and patients with essential hypertension but no significant effect in the same vascular territory in ACEi-treated patients • Activation of Endogenous ACE2 (XNT) causes a dose-dependent hypotensive effect in normotensive and hypertensive rats but no significant effect in response to the administration of Ang II or Losartan With XNT Without XNTInternational Journal of HypertensionVolume 2012 (2012), Article ID 147825, 13 pagesdoi:10.1155/2012/147825
Metabolism of bradykinin [BK-1-9] Kinins •Vasodilators •Promote diuresisRemoval of two C- •Natriuresisterminal dipeptides •Cardioprotective actions •Prevention of cardiac hypertrophy •Reduction in infarct size •Regulate coronary vascular tone and BP •Contribute to the vasodilation in heart failure •Doppler imaging used to measure radial artery blood •Captopril + bradykinin receptor antagonist HOE140 •High levelsﬂowkinin peptides produce of effects of •high tissue-afﬁnity ACE inhibitor (quinaprilat) given to both normotensive and hypertensive subjects •inflammation •HOE140, •HOE140 •Angioedema •Combination. •reduced the hypotensive effect of captopril, •Quinaprilat increased ﬂow nearly 50% over baseline, Contribute/Support/Mediate •renal hemodynamic response to captopril was not changed, the cardiac effects of ACEI •HOE140 decreased ﬂow from baseline by 33%. •response of plasma renin activity to captopril was signiﬁcantly altered •Coadministration yielded results similar to those N Engl J Med 1998;339:1285–1292. obtained with the B2 antagonist alone Hypertension. 2003;41:383-389 Circulation 1997;95:1115–1118.
ACE & NEP• ACE and NEP are 2 membrane-bound zinc- containing metallopeptidases involved in the ACE NEP metabolism of a variety of biological peptides Angiotensin (Ang) I Natriuretic peptides. Ang-(1-7) Ang I Kinin peptides bradykinin Ang II• Tissue distribution and kallidin – The vascular endothelium Kinin peptides Chemotactic peptide – smooth muscle cells Enkephalins Substance P – cardiac myocytes Neurotensin Adrenomedullin – fibroblasts, P Substance Endothelin – Brush border of proximal tubule cells of the kidney, LH–releasing hormone Chemotactic peptide – BrainHemoregulatory peptide N- Enkephalins, and the Amyloid acetyl-Ser-Asp-Lys-Pro peptide. Erdos Eget al. FASEB J. 1989;3:145–151. Ferrario CM et al.Hypertension. 1997;30:535–541.
Effects of ACE Inhibition ACE Independent pathways↑Renin Hypertension. 2003;41:383-389.
Vasopeptidase Inhibitors: Dual ACE/NEP Inhibition by a Single Molecule OCTAVE IMPRESS OVERTURE•Major concerns were •Angioedema •upto 4 times •Particularly in HTN rather in HF •More of ACE inhibition rather than NEP inhibition
•Angiotensin type 1 receptor (AT1R) •mediates most of the Ang II effectsLower Affinity •Trigerrs aldosterone release •Telmisartan or losartan with its metabolite XP 3179, might offer even more metabolic protection as they have peroxisome proliferator- activated receptor-γ activating properties. •AT4R : predominantly in kidney (endothelial cells and tubules) Kappert K et al.Hypertension 2009;54:738 – 743. J Physiol 589.4 (2011) pp 939–951
Aldosterone receptor antagonists • Aldosterone is generated in many tissues besides the adrenal cortex and is involved in endothelial dysfunction, inflammation, proteinuria, and fibrosis •Blockade of mineralocorticoid receptors presumably is beneficial even in situations with high AngII, because of common signal transduction pathwaysSpironolactone Eplerenone•Reduce BP (Resistant hypertension) •Selective for MR•Diminish urine protein excretion •200 mg b.i.d. required to achieve BP•Confer CV gain in heart failure apparently reduction comparable with 50 mgindependently of volume alterations spironolactone b.i.d.•Reduces the apnoea-hypopnea index in patientswith OSA Nishizaka MK et al. Am J Hypertens 2003;16:925 – 930. Sica DA et al. J Clin Hypertens (Greenwich) 2011;13:65 – 69.
Non-steroid generation of MRAs . Nimodipine WO2005097118; DE102005034267Dietz JD et al. Hyp ertension 2008;51:742 – 748.Arhancet GB et al. J Med Chem 2010;53:4300 – 4304.
Aldosterone synthase inhibitors •Fadrozole • Aromatase inhibitor or its dextroenantiomer (FAD286) •Reduces mortality, cardiac hypertrophy, albuminuria, cell inﬁltration, and matrix deposition in the kidney in double transgenic renin rats (dTGR) •Both FAD286 and MRAs comparably reduced hypertrophy and interstitial ﬁbrosis of the kidney and heart induced by Ang II and a high-salt intake •No profound effect on BP •LCI699 •Reduced 24 h-ambulatory systolic BP by - 4.1 mmHg after 4 weeks of treatment •Suppressed supine plasma aldosterone concentrations •ACTH concentrations were also elevated though cortisol remained same Fiebeler A et al. Circulation 2005;111:3087 – 3094. Amar L etal.Hyperte nsion 2010;56:831 – 838
Cross-talk between statin and RAAS Cross-talk between PPARs and RAAS •Hypercholesterolemia is associated with AT1-receptor upregulation and increased O2- production secondary to an activation of vascular NADPH oxidase. •Pioglitazone inhibits gp91phox expression, and attenuatsed toxic peroxynitrite (ONOO-) formation•Statins, thiazolidinediones (PPARγ agonists) and RAAS blockade may have additivebeneficial effects on endothelial function, insulin resistance, and atherosclerosis•Telmisartan and losartan also have additional inbuilt PPARγ agonist activity Koh KK et al. Int J Cardiol 2009;132:297–9. [PubMed: 19136168] Vascular Disease Prevention, 2009, 6, 65-74
Ac-SDKP (N-acetyl-seryl-aspartyl-lysyl-proline)• The breakdown of Ac-SDKP can be blocked by ACE inhibitor treatment resulting in an increase of its plasma levels• Measurement of Ac-SDKP could be a marker for the clinical efﬁciency of ACE inhibition• N-acetyl-Ser-Asp-Lys-Pro (Ac-SDKP), is a hematopoetic factor (acts on the cell cycle and prevents the activation of pluripotent stem cells)• Increased levels of Ac-SDKP have recently been associated with anemia in heart failure patients treated with ACE inhibitors Van der Meer P et al.Circulation 112: 1743–1747, 2005.
ACE Inhibitor and ARB Effects “Independent of the RAAS”• ACE inhibitors as well as AT1 receptor blockers can influence cellular functions independent of inhibition of the RAAS. – ACE inhibitors block the hydrolysis of Ac-SDKP • Hence inhibition of fibrosis, reduction of inflammatory cell infiltration – Ramiprilat and perindoprilat increase CK2-mediated phosphorylation of serine1270 and increase the activity of N-terminal kinase in endothelial cells (↑NO) • Hence mediate cellular function by “outside-in” signaling directly through ACE – The PPAR-γ activating properties of certain sartanes (molecular structure of the specific sartanes) Peng H et al. Circulation 112: 2436 –2445, 2005 Fleming I et al. Curr Opin Neph-rol Hypertens 15: 8 –13, 2006
Conclusion• With overexpression of RAS components or inhibition of others, the RAS becomes a mediator of pathophysiological stimuli: – Most importantly “progression of atherosclerosis in multiple organs”• The search for new members/components / pathways still continues.• It offers new and promising drug targets
Conclusion• The concept of tissue RAS, should not be considered as an opposing or alternative but rather as a complimentary or integrated functional concept of ANG formation and function.• The plasma RAS : Acute “response unit”• Tissue RAS : Subacute and chronic modulation• Tissue ACE inhibition results in vasculoprotection beyond blood pressure reduction alone
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