Kallikrein/K1, Kinins, and ACE/Kininase II in Homeostasis and in Disease Insight From Human and Experimental Genetic Studies, Therapeutic Implication

Abstract

Kallikrein-K1 is the main kinin-forming enzyme in organs in resting condition and in several pathological situations whereas angiotensin I-converting enzyme/kininase II (ACE) is the main kinin-inactivating enzyme in the circulation. Both ACE and K1 activity levels are genetic traits in man. Recent research based mainly on human genetic studies and study of genetically modified mice has documented the physiological role of K1 in the circulation, and also refined understanding of the role of ACE. Kallikrein-K1 is synthesized in arteries and involved in flow-induced vasodilatation. Endothelial ACE synthesis displays strong vessel and organ specificity modulating bioavailability of angiotensins and kinins locally. In pathological situations resulting from hemodynamic, ischemic, or metabolic insult to the cardiovascular system and the kidney K1 and kinins exert critical end-organ protective action and K1 deficiency results in severe worsening of the conditions, at least in the mouse. On the opposite, genetically high ACE level is associated with increased risk of developing ischemic and diabetic cardiac or renal diseases and worsened prognosis of these diseases. The association has been well-documented clinically while causality was established by ACE gene titration in mice. Studies suggest that reduced bioavailability of kinins is prominently involved in the detrimental effect of K1 deficiency or high ACE activity in diseases. Kinins are involved in the therapeutic effect of both ACE inhibitors and angiotensin II AT1 receptor blockers. Based on these findings, a new therapeutic hypothesis focused on selective pharmacological activation of kinin receptors has been launched. Proof of concept was obtained by using prototypic agonists in experimental ischemic and diabetic diseases in mice.

Keywords: Ischemic heart disease; angiotensin-converting enzyme; diabetic nephropathy; genetic human; genetic mouse models; kallikrein (tissue); kinins; vasodilation.

Figure 1

Schematic representation of the renin-angiotensin and kallikrein-kinin systems with physiological interrelation. ACE, angiotensin-converting enzyme/kininase II; NEP, neutral-endopeptidase; AP, aminopeptidase P; CPN, carboxypeptidase N.

Figure 2

Arterial dysfunction in K1 deficient mice and human subjects partially deficient in K1 activity. Upper graph: impairment of flow-induced vasodilatation in carotid artery of K1 deficient mice. Homozygote (TK^−/−) and heterozygote (TK^+/−) mice with inactivated K1 gene compared to littermate wild type animals (TK^+/+). ^*p < 0.05 compared to littermate TK^+/+. Note paradoxical vasoconstrictor response at low flow rate in TK^−/− and partial defective phenotype of TK^+/− mice (see text for discussion). Reproduced from Bergaya et al. (15). Lower panels: arterial dysfunction in subjects carrying the defective R53H mutation of K1 (heterozygote) and having roughly 50% K1 activity level of non-mutated, homozygous R53 subjects. Subjects were studied by vascular echotracking of brachial artery in basal condition, during hand ischemia and reactive hyperhemia and after nitroglycerin (GTN) administration. Study was repeated at contrasted dietary Na/K intake. Low Na-High K stimulates K1 synthesis in the kidney. Note increase in sheer stress (A) in R53H subjects with paradoxical reduction of arterial diameter (B). Reproduced from Azizi et al. (16). Observations in both man and mouse are indicative of endothelial dysfunction (see text).

Figure 3

Endothelial ACE distribution along the human and rat vascular tree. Endothelial ACE is heterogeneously distributed in humans (black line). Large arteries contain no or little ACE while maximal ACE content is observed in small muscular arteries and arterioles. Only a fraction of capillaries network contains ACE. Venules and veins contain no or little ACE except some muscular veins in upper and lower extremities. Exceptions to this general scheme are the renal circulation and the pulmonary capillary network (not shown, see text for discussion). In the rat (gray line) ACE is more homogeneously distributed in arteries and veins, while only a fraction of capillaries contains ACE, like in man. ACE is also dowregulated in renal arterioles (not shown). ^#Immunoreactivity (IR) shown is scored from 0 (no reactivity detectable) to 3 (maximal reactivity) and refers to defined mAb concentrations. ^§Localization of endothelial cells: (a) aorta ascendens, arcus aortae, aorta descendens/thoracalis/abdominalis; (b) a. brachiocephalica, a. pulmonalis, a. iliaca communis, a. carotis communis; (c) a. iliaca interna/externa, a. carotis interna/externa, a. subclavia; (d) truncus coeliacus, a. renalis, a. mesenterica sup./inf., a. axillaris, a. femoralis; (e) a. brachialis, a. poplitea, a. tibialis ant./posterior, a. ulnaris, a. radialis, a. peronea; (f) a. dorsalis pedis, a. digitalis plantaris/palmaris; (g) small peripheral arteries; (h) pre-arterioles, arterioles; (i) capillaries; (j) venules; (k) small peripheral veins; (l) v. digitalis plantaris, v. dorsalis pedis, v. saphena parva, v. saphena magna; (m) v. digitalis palmaris, v. tibialis, v. poplitea; (n) v. axillaris, v. femoralis, v. jugularis ext./int; (o) v. iliaca int./ext., v. subclavia; (p) v. iliaca communis, v. brachiocephalica, v. renalis; (q) v. cava sup./inf. Reproduced from Metzger et al. (7).

Figure 4

Loss of the cardioprotective effect of ischemic pre-conditioning in mice with an inactivated Klk1 gene or mice carrying a duplication of the ACE gene in cardiac ischemia-reperfusion. IS/AR: infarct size relative to area at risk. IR, ischemia-reperfusion; IPC, ischemic pre-conditioning followed by IR; WT, wild type; TK^−/−, K1 deficient mice; ACE1c, mice with a single ACE gene copy; ACE2c, mice with two ACE gene copies (wild type); ACE3c, mice with three ACE gene copies having roughly 140% ACE activity level of wild-type mice. Note also loss of cardioprotective effect of the ACE inhibitor Ramiprilat in K1 deficient mice. ^*p < 0.05, ^**p < 0.01 compared to IR; ^†p < 0.05 compared to littermate WT or ACE2c (WT). Adapted from Griol-Charhbili et al. (55) and Messadi et al. (56).

Figure 5

Aggravating effect of inactivating the KLK1 gene or duplicating the ACE gene on development of diabetic nephropathy in diabetic mice. Ordinate in both graphs: urinary albumin excretion. Upper graph, ACE gene titration; open symbols, non-diabetic mice; filled symbols, diabetic mice. Diamonds, one-copy mice; squares, two-copy mice (wild-type); circles, three-copy mice. ^*p < 0.05, ^**p < 0.01, ^***p < 0.001 compared to diabetic two-copy (WT) or one-copy mice. Lower graph: K1 gene inactivation. open bars control, non-diabetic mice; filled bars diabetic mice. ^***p < 0.001 compared to non-diabetic mice. ^##p < 0.01 compared to corresponding WT mice. Adapted from Bodin et al. (77) and Huang et al. (78).

Figure 6

Association of the ACE gene ID polymorphism with development of diabetic nephropathy in patients with type 1 diabetes. Graph shows cumulative incidence of renal events (progression from physiological to pathological microalbuminuria or from a given stage of nephropathy to a higher stage) according to ACE genotype. D allele is co-dominantly associated with higher ACE levels. Reproduced from Hadjadj et al. (97). This study documents the role of the genetic variation in ACE level in susceptibility to and progression of diabetic nephropathy. Same observation was made in other patient populations, before and after this study. See text and Marre et al. (93) through Hadjadj et al. (100).

Figure 7

Cardioprotective effect of a pharmacological kinin B1 receptor agonist in cardiac ischemia-reperfusion in diabetic mice. IS/AR, infarct size relative to area at risk; B1R ag, kinin B1 receptor agonist; B2R ag, kinin B2 receptor agonist; Ram, ramiprilat; IpostC, ischemic post-conditioning; SSR240612, kinin B1 receptor antagonist. Note resistance of the diabetic heart to cardioprotective treatments otherwise efficient in non-diabetic mice (Ram, B2R ag and IpostC). Reproduced from Potier et al. (114).