Loss of bradykinin signaling does not accelerate the development of cardiac dysfunction in type 1 diabetic akita mice

Genetic Ablation and Pharmacological Blockade of Bradykinin B1 Receptor Unveiled a Detrimental Role for the Kinin System in Chagas Disease Cardiomyopathy

Chagas disease, the parasitic infection caused by Trypanosoma cruzi, afflicts about 6 million people in Latin America. Here, we investigated the hypothesis that T. cruzi may fuel heart parasitism by activating B1R, a G protein-coupled (brady) kinin receptor whose expression is upregulated in inflamed tissues. Studies in WT and B1R^-/- mice showed that T. cruzi DNA levels (15 days post infection-dpi) were sharply reduced in the transgenic heart. FACS analysis revealed that frequencies of proinflammatory neutrophils and monocytes were diminished in B1R^-/- hearts whereas CK-MB activity (60 dpi) was exclusively detected in B1R^+/+ sera. Since chronic myocarditis and heart fibrosis (90 dpi) were markedly attenuated in the transgenic mice, we sought to determine whether a pharmacological blockade of the des-Arg⁹-bradykinin (DABK)/B1R pathway might alleviate chagasic cardiomyopathy. Using C57BL/6 mice acutely infected by a myotropic T. cruzi strain (Colombian), we found that daily treatment (15-60 dpi) with R-954 (B1R antagonist) reduced heart parasitism and blunted cardiac injury. Extending R-954 treatment to the chronic phase (120-160 dpi), we verified that B1R targeting (i) decreased mortality indexes, (ii) mitigated chronic myocarditis, and (iii) ameliorated heart conduction disturbances. Collectively, our study suggests that a pharmacological blockade of the proinflammatory KKS/DABK/B1R pathway is cardioprotective in acute and chronic Chagas disease.

The kallikrein-kinin pathway as a mechanism for auto-control of brown adipose tissue activity

Brown adipose tissue (BAT) is known to secrete regulatory factors in response to thermogenic stimuli. Components of the BAT secretome may exert local effects that contribute to BAT recruitment and activation. Here, we found that a thermogenic stimulus leads to enhanced secretion of kininogen (Kng) by BAT, owing to induction of kininogen 2 (Kng2) gene expression. Noradrenergic, cAMP-mediated signals induce KNG2 expression and release in brown adipocytes. Conversely, the expression of kinin receptors, that are activated by the Kng products bradykinin and [Des-Arg9]-bradykinin, are repressed by thermogenic activation of BAT in vivo and of brown adipocytes in vitro. Loss-of-function models for Kng (the circulating-Kng-deficient BN/Ka rat) and bradykinin (pharmacological inhibition of kinin receptors, kinin receptor-null mice) signaling were coincident in showing abnormal overactivation of BAT. Studies in vitro indicated that Kng and bradykinin exert repressive effects on brown adipocyte thermogenic activity by interfering the PKA/p38 MAPK pathway of control of Ucp1 gene transcription, whereas impaired kinin receptor expression enhances it. Our findings identify the kallikrein–kinin system as a relevant component of BAT thermogenic regulation that provides auto-regulatory inhibitory signaling to BAT.

Brown adipose tissue, known produce heat by metabolizing fat, is also secretes molecules capable of communicating with other organs. Here the authors show that brown adipose tissue secretes kininogen, a component of heat system regulation, that provides auto-regulatory inhibitory signaling in brown adipose tissue.

Glucose transporter 4-deficient hearts develop maladaptive hypertrophy in response to physiological or pathological stresses

Pathological cardiac hypertrophy may be associated with reduced expression of glucose transporter 4 (GLUT4) in contrast to exercise-induced cardiac hypertrophy, where GLUT4 levels are increased. However, mice with cardiac-specific deletion of GLUT4 (G4H^-/-) have normal cardiac function in the unstressed state. This study tested the hypothesis that cardiac GLUT4 is required for myocardial adaptations to hemodynamic demands. G4H^-/- and control littermates were subjected to either a pathological model of left ventricular pressure overload [transverse aortic constriction (TAC)] or a physiological model of endurance exercise (swim training). As predicted after TAC, G4H^-/- mice developed significantly greater hypertrophy and more severe contractile dysfunction. Somewhat surprisingly, after exercise training, G4H^-/- mice developed increased fibrosis and apoptosis that was associated with dephosphorylation of the prosurvival kinase Akt in concert with an increase in protein levels of the upstream phosphatase protein phosphatase 2A (PP2A). Exercise has been shown to decrease levels of ceramide; G4H^-/- hearts failed to decrease myocardial ceramide in response to exercise. Furthermore, G4H^-/- hearts have reduced levels of the transcriptional coactivator peroxisome proliferator-activated receptor-γ coactivator-1, lower carnitine palmitoyl-transferase activity, and reduced hydroxyacyl-CoA dehydrogenase activity. These basal changes may also contribute to the impaired ability of G4H^-/- hearts to adapt to hemodynamic stresses. In conclusion, GLUT4 is required for the maintenance of cardiac structure and function in response to physiological or pathological processes that increase energy demands, in part through secondary changes in mitochondrial metabolism and cellular stress survival pathways such as Akt.NEW & NOTEWORTHY Glucose transporter 4 (GLUT4) is required for myocardial adaptations to exercise, and its absence accelerates heart dysfunction after pressure overload. The requirement for GLUT4 may extend beyond glucose uptake to include defects in mitochondrial metabolism and survival signaling pathways that develop in its absence. Therefore, GLUT4 is critical for responses to hemodynamic stresses.

Vascular endothelial dysfunction and pharmacological treatment

The endothelium exerts multiple actions involving regulation of vascular permeability and tone, coagulation and fibrinolysis, inflammatory and immunological reactions and cell growth. Alterations of one or more such actions may cause vascular endothelial dysfunction. Different risk factors such as hypercholesterolemia, homocystinemia, hyperglycemia, hypertension, smoking, inflammation, and aging contribute to the development of endothelial dysfunction. Mechanisms underlying endothelial dysfunction are multiple, including impaired endothelium-derived vasodilators, enhanced endothelium-derived vasoconstrictors, over production of reactive oxygen species and reactive nitrogen species, activation of inflammatory and immune reactions, and imbalance of coagulation and fibrinolysis. Endothelial dysfunction occurs in many cardiovascular diseases, which involves different mechanisms, depending on specific risk factors affecting the disease. Among these mechanisms, a reduction in nitric oxide (NO) bioavailability plays a central role in the development of endothelial dysfunction because NO exerts diverse physiological actions, including vasodilation, anti-inflammation, antiplatelet, antiproliferation and antimigration. Experimental and clinical studies have demonstrated that a variety of currently used or investigational drugs, such as angiotensin-converting enzyme inhibitors, angiotensin AT1 receptors blockers, angiotensin-(1-7), antioxidants, beta-blockers, calcium channel blockers, endothelial NO synthase enhancers, phosphodiesterase 5 inhibitors, sphingosine-1-phosphate and statins, exert endothelial protective effects. Due to the difference in mechanisms of action, these drugs need to be used according to specific mechanisms underlying endothelial dysfunction of the disease.

Antioxidant treatment normalizes mitochondrial energetics and myocardial insulin sensitivity independently of changes in systemic metabolic homeostasis in a mouse model of the metabolic syndrome

Cardiac dysfunction in obesity is associated with mitochondrial dysfunction, oxidative stress and altered insulin sensitivity. Whether oxidative stress directly contributes to myocardial insulin resistance remains to be determined. This study tested the hypothesis that ROS scavenging will improve mitochondrial function and insulin sensitivity in the hearts of rodent models with varying degrees of insulin resistance and hyperglycemia. The catalytic antioxidant MnTBAP was administered to the uncoupling protein-diphtheria toxin A (UCP-DTA) mouse model of insulin resistance (IR) and obesity, at early and late time points in the evolution of IR, and to db/db mice with severe obesity and type-two diabetes. Mitochondrial function was measured in saponin-permeabilized cardiac fibers. Aconitase activity and hydrogen peroxide emission were measured in isolated mitochondria. Insulin-stimulated glucose oxidation, glycolysis and fatty acid oxidation rates were measured in isolated working hearts, and 2-deoxyglucose uptake was measured in isolated cardiomyocytes. Four weeks of MnTBAP attenuated glucose intolerance in 13-week-old UCP-DTA mice but was without effect in 24-week-old UCP-DTA mice and in db/db mice. Despite the absence of improvement in the systemic metabolic milieu, MnTBAP reversed cardiac mitochondrial oxidative stress and improved mitochondrial bioenergetics by increasing ATP generation and reducing mitochondrial uncoupling in all models. MnTBAP also improved myocardial insulin mediated glucose metabolism in 13 and 24-week-old UCP-DTA mice. Pharmacological ROS scavenging improves myocardial energy metabolism and insulin responsiveness in obesity and type 2 diabetes via direct effects that might be independent of changes in systemic metabolism.

Genetic manipulation and genetic variation of the kallikrein-kinin system: impact on cardiovascular and renal diseases

Genetic manipulation of the kallikrein-kinin system (KKS) in mice, with either gain or loss of function, and study of human genetic variability in KKS components which has been well documented at the phenotypic and genomic level, have allowed recognizing the physiological role of KKS in health and in disease. This role has been especially documented in the cardiovascular system and the kidney. Kinins are produced at slow rate in most organs in resting condition and/or inactivated quickly. Yet the KKS is involved in arterial function and in renal tubular function. In several pathological situations, kinin production increases, kinin receptor synthesis is upregulated, and kinins play an important role, whether beneficial or detrimental, in disease outcome. In the setting of ischemic, diabetic or hemodynamic aggression, kinin release by tissue kallikrein protects against organ damage, through B2 and/or B1 bradykinin receptor activation, depending on organ and disease. This has been well documented for the ischemic or diabetic heart, kidney and skeletal muscle, where KKS activity reduces oxidative stress, limits necrosis or fibrosis and promotes angiogenesis. On the other hand, in some pathological situations where plasma prekallikrein is inappropriately activated, excess kinin release in local or systemic circulation is detrimental, through oedema or hypotension. Putative therapeutic application of these clinical and experimental findings through current pharmacological development is discussed in the chapter.

Antioxidant/oxidant status and cardiac function in bradykinin B(1)- and B(2)-receptor null mice

Kinin-vasoactive peptides activate two G-protein-coupled receptors (R), B(1)R (inducible) and B(2)R (constitutive). Their complex role in cardiovascular diseases could be related to differential actions on oxidative stress. This study investigated impacts of B(1)R or B(2)R gene deletion in mice on the cardiac function and plasma antioxidant and oxidant status. Echocardiography-Doppler was performed in B(1)R (B(1)R(-/-)) and B(2)R (B(2)R(-/-)) deficient and wild type (WT) adult male mice. No functional alteration was observed in B(2)R(-/-) hearts. B(1)R(-/-) mice had significantly lowered fractional shortening and increased isovolumetric contraction time. The diastolic E and A waves velocity ratio was similar in all mice groups. Thus B(1)R(-/-) mice provide a model of moderate systolic dysfunction, whereas B(2)R(-/-) mice displayed a normal cardiac phenotype. Plasma antioxidant capacity (ORAC) was significantly decreased in both B(1)R(-/-) and B(2)R(-/-) mice whereas the vitamin C levels were decreased in B(2)R(-/-) mice only. Plasma ascorbyl free radical was significantly higher in B(1)R(-/-) compared to WT and B(2)R(-/-) mice. Therefore, the oxidative stress index, ascorbyl free radical to vitamin C ratio, was increased in both B(1)R(-/-) and B(2)R(-/-) mice. Hence, B(1)R and B(2)R deficiency are associated with increased oxidative stress, but there is a differential imbalance between free radical production and antioxidant defense. The interrelationship between the differential B(1)R and B(2)R roles in oxidative stress and cardiovascular diseases remain to be investigated.

Targeting the 'Janus face' of the B2-bradykinin receptor

INTRODUCTION

Kinins are main active mediators of the kallikrein-kinin system (KKS) via bradykinin type 1 inducible (B1R) and type 2 constitutive (B2R) receptors. B2R mediates most physiological bradykinin (BK) responses, including vasodilation, natriuresis, NO, prostaglandins release.

AREAS COVERED

The article summarizes knowledge on kinins, B2R signaling and biological functions; highlights crosstalks between B2R and renin-angiotensin system (RAS). The double role (Janus face) in physiopathology, namely the beneficial protection of the endothelium, which forms the basis for the therapeutical utilization of B2 receptor agonists, on the one side, and the involvement of B2R in inflammation or infection diseases and in pain mechanisms, which justifies the use of B2R antagonists, on the other side, is extensively analyzed.

EXPERT OPINION

For decades, the B2R has been unconsciously activated during angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB) treatments. Whether direct B2R targeting with stable agonists could bring additional therapeutic benefit to RAS inhibition should be investigated. Efficacy, established in experimental models, should be confirmed by translational studies in cardiovascular pathologies, glaucoma, Duchenne cardiopathy and during brain cancer therapy. The other face of B2R is targeted by antagonists already approved to treat hereditary angioedema. The use of antagonists could be extended to other angioedema and efficacy tested against acute pain and inflammatory diseases.

Role of plasma kallikrein in diabetes and metabolism

Plasma kallikrein (PK) is a serine protease generated from plasma prekallikrein, an abundant circulating zymogen expressed by the Klkb1 gene. The physiological actions of PK have been primarily attributed to its production of bradykinin and activation of coagulation factor XII, which promotes inflammation and the intrinsic coagulation pathway. Recent genetic, molecular, and pharmacological studies of PK have provided further insight into its role in physiology and disease. Genetic analyses have revealed common Klkb1 variants that are association with blood metabolite levels, hypertension, and coagulation. Characterisation of animal models with Klkb1 deficiency and PK inhibition have demonstrated effects on inflammation, vascular function, blood pressure regulation, thrombosis, haemostasis, and metabolism. These reports have also identified a host of PK substrates and interactions, which suggest an expanded physiological role for this protease beyond the bradykinin system and coagulation. The review summarises the mechanisms that contribute to PK activation and its emerging role in diabetes and metabolism.

Involvement of enhanced cardiac sympathetic afferent reflex in sympathetic activation in early stage of diabetes

Cardiac sympathetic afferent reflex (CSAR) is involved in sympathetic activation. The present study was designed to investigate the contribution of enhanced CSAR to sympathetic activation in the early stage of diabetes and the involvement of AT1 receptors in the paraventricular nucleus (PVN). Diabetes was induced by a single intravenous injection of streptozotocin in rats. Acute experiments were carried out under anesthesia after 3 wk. The CSAR was evaluated by the responses of renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) to epicardial application of capsaicin or bradykinin. Sympathetic activity and CSAR were enhanced in diabetic rats. Plasma norepinephrine and angiotensin II were increased, but the transient receptor potential vanilloid 1 (TRPV1) in the left ventricle wall was not significantly increased in diabetic rats. Pericardial injection of resiniferatoxin to desensitize cardiac afferents or PVN microinjection of lidocaine attenuated the CSAR and decreased the RSNA and MAP in diabetic rats. The AT1 receptor expression in the PVN increased in diabetic rats. Angiotensin II in the PVN caused greater increases in the RSNA and MAP and enhancement in the CSAR in diabetic rats, which were abolished by the losartan pretreatment. Losartan decreased the RSNA and MAP and attenuated the CSAR in diabetic rats but not in control rats. These results indicate that the CSAR is enhanced in the early stage of diabetic rats, which contributes to the sympathetic activation. AT1 receptors in the PVN are involved in the enhanced CSAR in diabetic rats.

The kallikrein-kinin system and oxidative stress

PURPOSE OF REVIEW

The kallikrein-kinin system (KKS) constitutes a complex multienzyme cascade that produces several bioactive kinin peptides and their derivatives including bradykinin. In addition to the classical notion of the KKS as a potent vasodilator and a mediator of inflammatory responses, recent studies suggest a link between the KKS and oxidative stress. A number of established mouse models with altered levels of KKS components opened the way to evaluate precise functions of the KKS. Here we review recent findings on the role of the KKS in cardiovascular diseases and chronic kidney diseases, and discuss potential benefits of KKS activation in these diseases.

RECENT FINDINGS

Deletion of both B1R and B2R in a diabetic mouse model exacerbates its renal phenotypes, suggesting that the KKS exerts protective effects on diabetic nephropathy by suppressing oxidative stress, presumably via nitric oxide and prostaglandins.

SUMMARY

Accumulating evidence has highlighted the importance of the KKS as a protective system against oxidative stress and organ damage in the heart and kidney. The activation of the KKS by angiotensin I-converting enzyme inhibitors and vasopeptidase inhibitors is likely to be beneficial in senescence-associated cardiovascular diseases and chronic kidney diseases.

The kallikrein-kinin system in diabetic nephropathy

Diabetic nephropathy is the major cause of end-stage renal disease worldwide. Although the renin-angiotensin system has been implicated in the pathogenesis of diabetic nephropathy, angiotensin I-converting enzyme inhibitors have a beneficial effect on diabetic nephropathy independently of their effects on blood pressure and plasma angiotensin II levels. This suggests that the kallikrein-kinin system (KKS) is also involved in the disease. To study the role of the KKS in diabetic nephropathy, mice lacking either the bradykinin B1 receptor (B1R) or the bradykinin B2 receptor (B2R) have been commonly used. However, because absence of either receptor causes enhanced expression of the other, it is difficult to determine the precise functions of each receptor. This difficulty has recently been overcome by comparing mice lacking both receptors with mice lacking each receptor. Deletion of both B1R and B2R reduces nitric oxide (NO) production and aggravates renal diabetic phenotypes, relevant to either lack of B1R or B2R, demonstrating that both B1R and B2R exert protective effects on diabetic nephropathy presumably via NO. Here, we review previous epidemiological and experimental studies, and discuss novel insights regarding the therapeutic implications of the importance of the KKS in averting diabetic nephropathy.

Expression of slow skeletal TnI in adult mouse hearts confers metabolic protection to ischemia

Changes in metabolic and myofilament phenotypes coincide in developing hearts. Posttranslational modification of sarcomere proteins influences contractility, affecting the energetic cost of contraction. However, metabolic adaptations to sarcomeric phenotypes are not well understood, particularly during pathophysiological stress. This study explored metabolic adaptations to expression of the fetal, slow skeletal muscle troponin I (ssTnI). Hearts expressing ssTnI exhibited no significant ATP loss during 5 min of global ischemia, while non-transgenic littermates (NTG) showed continual ATP loss. At 7 min ischemia TG-ssTnI hearts retained 80±12% of ATP versus 49±6% in NTG (P<0.05). Hearts expressing ssTnI also had increased AMPK phosphorylation. The mechanism of ATP preservation was augmented glycolysis. Glycolytic end products (lactate and alanine) were 38% higher in TG-ssTnI than NTG at 2 min and 27% higher at 5 min. This additional glycolysis was supported exclusively by exogenous glucose, and not glycogen. Thus, expression of a fetal myofilament protein in adult mouse hearts induced elevated anaerobic ATP production during ischemia via metabolic adaptations consistent with the resistance to hypoxia of fetal hearts. The general findings hold important relevance to both our current understanding of the association between metabolic and contractile phenotypes and the potential for invoking cardioprotective mechanisms against ischemic stress. This article is part of a Special Issue entitled "Possible Editorial".