Effect of angiotensin II type 2 receptor blockade on mitogen activated protein kinases during myocardial ischemia-reperfusion

Rosa rugosa flavonoids alleviate myocardial ischemia reperfusion injury in mice by suppressing JNK and p38 MAPK

OBJECTIVE

Although Rosa rugosa has been applied for preventing coronary artery disease, the pharmacological mechanism is little explored. In this study, the effects and mechanisms of Rosa rugosa flavonoids (RRF) on myocardial ischemia reperfusion injury (MIRI) were investigated.

METHODS

Mice were pretreated by intragastric administration of 600 mg/kg RRF for 7 days. Then MIRI was induced by 45 minutes coronary artery ligation and 3 hours reperfusion. Myocardial infarct size (MIS) and histopathology, activities of myocardial enzymes, and effects of RRF on inflammation and apoptosis were evaluated.

RESULTS

Pretreating the mice with RRF significantly reduced MIS and inhibited activity of plasma myocardial enzymes. Activity of the enzymes associated with anti-oxidation, SOD, and TEAC, and mRNA expression of NOX2 were significantly elevated. RRF pretreatment significantly decreased the translocation of p65 from the cytoplasm into the nucleus and reduced the expression of the pro-inflammatory cytokines, IL-6 and IL-1β. RRF pretreatment also significantly prevented the expression of caspase-3 and Bax, and increased the expression of Bcl-2. And RRF inhibited the phosphorylation of JNK and p38 MAPK.

CONCLUSIONS

RRF significantly inhibited MIRI through anti-oxidative, anti-inflammatory, and anti-apoptosis effects, and mechanisms were associated with its inhibition on phosphorylation of JNK and p38 MAPK.

Chronic Losartan Treatment Up-Regulates AT1R and Increases the Heart Vulnerability to Acute Onset of Ischemia and Reperfusion Injury in Male Rats

Inhibition of angiotensin II type 1 receptor (AT1R) is an important therapy in the management of hypertension, particularly in the immediate post-myocardial infarction period. Yet, the role of AT1R in the acute onset of myocardial ischemia and reperfusion injury still remains controversial. Thus, the present study determined the effects of chronic losartan treatment on heart ischemia and reperfusion injury in rats. Losartan (10 mg/kg/day) was administered to six-month-old male rats via an osmotic pump for 14 days and hearts were then isolated and were subjected to ischemia and reperfusion injury in a Langendorff preparation. Losartan significantly decreased mean arterial blood pressure. However, heart weight, left ventricle to body weight ratio and baseline cardiac function were not significantly altered by the losartan treatment. Of interest, chronic in vivo losartan treatment significantly increased ischemia-induced myocardial injury and decreased post-ischemic recovery of left ventricular function. This was associated with significant increases in AT1R and PKCδ expression in the left ventricle. In contrast, AT2R and PKCε were not altered. Furthermore, losartan treatment significantly increased microRNA (miR)-1, -15b, -92a, -133a, -133b, -210, and -499 expression but decreased miR-21 in the left ventricle. Of importance, addition of losartan to isolated heart preparations blocked the effect of increased ischemic-injury induced by in vivo chronic losartan treatment. The results demonstrate that chronic losartan treatment up-regulates AT1R/PKCδ and alters miR expression patterns in the heart, leading to increased cardiac vulnerability to ischemia and reperfusion injury.

Identification of the Vasoconstriction-Inhibiting Factor (VIF), a Potent Endogenous Cofactor of Angiotensin II Acting on the Angiotensin II Type 2 Receptor

BACKGROUND

The renin-angiotensin system and especially the angiotensin peptides play a central role in blood pressure regulation. Here, we hypothesize that an as-yet unknown peptide is involved in the action of angiotensin II modulating the vasoregulatory effects as a cofactor.

METHODS AND RESULTS

The peptide with vasodilatory properties was isolated from adrenal glands chromatographically. The effects of this peptide were evaluated in vitro and in vivo, and the receptor affinity was analyzed. The plasma concentration in humans was quantified in patients with chronic kidney disease, patients with heart failure, and healthy control subjects. The amino acid sequence of the peptide from bovine adrenal glands was HSSYEDELSEVL EKPNDQAE PKEVTEEVSSKDAAE, which is a degradation product of chromogranin A. The sequence of the peptide isolated from human plasma was HSGFEDELSEVLENQSSQAELKEAVEEPSSKDVME. Both peptides diminished significantly the vasoconstrictive effect of angiotensin II in vitro. Therefore, we named the peptide vasoconstriction-inhibiting factor (VIF). The vasoregulatory effects of VIF are mediated by the angiotensin II type 2 receptor. VIF impairs angiotensin II-induced phosphorylation of the p38 mitogen-activated protein kinase pathway but not of extracellular-regulated kinase 1/2. The vasodilatory effects were confirmed in vivo. The plasma concentration was significantly increased in renal patients and patients with heart failure.

CONCLUSIONS

VIF is a vasoregulatory peptide that modulates the vasoconstrictive effects of angiotensin II by acting on the angiotensin II type 2 receptor. It is likely that the increase in VIF may serve as a counterregulatory effect to defend against hypertension. The identification of this target may help us to understand the pathophysiology of renal and heart failure and may form a basis for the development of new strategies for the prevention and treatment of cardiovascular disease.

Renal Development and Blood Pressure in Offspring from Dams Submitted to High-Sodium Intake during Pregnancy and Lactation

Exposure to an adverse environment in utero appears to programme physiology and metabolism permanently, with long-term consequences for health of the fetus or offspring. It was observed that the offspring from dams submitted to high-sodium intake during pregnancy present disturbances in renal development and in blood pressure. These alterations were associated with lower plasma levels of angiotensin II (AII) and changes in renal AII receptor I (AT₁) and mitogen-activated protein kinase (MAPK) expressions during post natal kidney development. Clinical and experimental evidence show that the renin-angiotensin system (RAS) participates in renal development. Many effects of AII are mediated through MAPK pathways. Extracellular signal-regulated protein kinases (ERKs) play a pivotal role in cellular proliferation and differentiation. In conclusion, high-sodium intake during pregnancy and lactation can provoke disturbances in renal development in offspring leading to functional and structural alterations that persist in adult life. These changes can be related at least in part with the decrease in RAS activity considering that this system has an important role in renal development.

Role of Mitogen-Activated Protein Kinases in Myocardial Ischemia-Reperfusion Injury during Heart Transplantation

In solid organ transplantation, ischemia/reperfusion (IR) injury during organ procurement, storage and reperfusion is an unavoidable detrimental event for the graft, as it amplifies graft inflammation and rejection. Intracellular mitogen-activated protein kinase (MAPK) signaling pathways regulate inflammation and cell survival during IR injury. The four best-characterized MAPK subfamilies are the c-Jun NH2-terminal kinase (JNK), extracellular signal- regulated kinase-1/2 (ERK1/2), p38 MAPK, and big MAPK-1 (BMK1/ERK5). Here, we review the role of MAPK activation during myocardial IR injury as it occurs during heart transplantation. Most of our current knowledge regarding MAPK activation and cardioprotection comes from studies of preconditioning and postconditioning in nontransplanted hearts. JNK and p38 MAPK activation contributes to myocardial IR injury after prolonged hypothermic storage. p38 MAPK inhibition improves cardiac function after cold storage, rewarming and reperfusion. Small-molecule p38 MAPK inhibitors have been tested clinically in patients with chronic inflammatory diseases, but not in transplanted patients, so far. Organ transplantation offers the opportunity of starting a preconditioning treatment before organ procurement or during cold storage, thus modulating early events in IR injury. Future studies will need to evaluate combined strategies including p38 MAPK and/or JNK inhibition, ERK1/2 activation, pre- or postconditioning protocols, new storage solutions, and gentle reperfusion.

MAPK and angiotensin II receptor in kidney of newborn rats from losartan-treated dams

Several lines of evidence suggest that angiotensin II (A-II) participates in the postnatal development of the kidney in rats. Many effects of A-II are mediated by mitogen-activated protein kinase (MAPK) pathways. This study investigated the influence that treatment with losartan during lactation has on MAPKs and on A-II receptor types 1 (AT(1)) and 2 (AT(2)) expression in the renal cortices of the offspring of dams exposed to losartan during lactation. In addition, we evaluated the relationship between such expression and changes in renal function and structure. Rat pups from dams receiving 2% sucrose or losartan diluted in 2% sucrose (40 mg/dl) during lactation were killed 30 days after birth, and the kidneys were removed for histological, immunohistochemical, and Western blot analysis. AT(1) and AT(2) receptors and p-p38, c-Jun N-terminal kinases (p-JNK) and extracellular signal-regulated protein kinases (p-ERK) expression were evaluated using Western blot analysis. The study-group rats presented an increase in AT(2) receptor and MAPK expression. In addition, these rats also presented lower glomerular filtration rate (GFR), greater albuminuria, and changes in renal structure. In conclusion, newborn rats from dams exposed to losartan during lactation presented changes in renal structure and function, which were associated with AT(2) receptor and MAPK expression in the kidneys.

Aminopyridine-based c-Jun N-terminal kinase inhibitors with cellular activity and minimal cross-kinase activity

The c-Jun N-terminal kinases (JNK-1, -2, and -3) are members of the mitogen activated protein (MAP) kinase family of enzymes. They are activated in response to certain cytokines, as well as by cellular stresses including chemotoxins, peroxides, and irradiation. They have been implicated in the pathology of a variety of different diseases with an inflammatory component including asthma, stroke, Alzheimer's disease, and type 2 diabetes mellitus. In this work, high-throughput screening identified a JNK inhibitor with an excellent kinase selectivity profile. Using X-ray crystallography and biochemical screening to guide our lead optimization, we prepared compounds with inhibitory potencies in the low-double-digit nanomolar range, activity in whole cells, and pharmacokinetics suitable for in vivo use. The new compounds were over 1,000-fold selective for JNK-1 and -2 over other MAP kinases including ERK2, p38alpha, and p38delta and showed little inhibitory activity against a panel of 74 kinases.

Angiotensin II subtype AT1 and AT2 receptors regulate microvascular hydraulic permeability via cAMP and cGMP

INTRODUCTION

Angiotensin II receptor subtypes (AT1 and AT2) have been shown to modulate microvascular fluid leak. However, their intracellular signal transduction pathways have not been elucidated. We hypothesized that AT1 activation exerts its permeability-increasing effect by provoking cGMP synthesis and inducing cAMP degradation and that AT2 activation decreases fluid leak by stimulating cAMP synthesis and enhancing cGMP degradation.

METHODS

Using a microcannulation technique, hydraulic permeability (Lp) was measured in rat mesenteric venules. The messenger signal transduction of ATI was studied during continuous perfusion with the AT1 agonist, Sar1 plus either 1) a cGMP synthesis inhibitor, LY83583, or 2) an inhibitor of cAMP degradation, Rolipram. Likewise, AT2 signal transduction was studied with the AT2 agonist, CGP42112A, plus either 1) a cAMP synthesis inhibitor, dideoxyadenosine, or 2) an inhibitor of cGMP degradation, Zaprinast. Lp values are represented as mean +/- SEM x 10(-7) cm/s/cm H2O. For each group n = 6.

RESULTS

Inhibition of cGMP synthesis blunted the permeability-increasing effect of AT1 agonism and decreased the peak Lp from 4.91 +/- 0.25 to 2.30 +/- 0.10 (P < 0.001). Inhibition of cAMP degradation also reduced the effect of AT1 agonism on peak L(p) from 2.25 +/- 0.22 to 1.30 +/- 0.13 (P < 0.001). Meanwhile, cAMP synthesis inhibition completely blocked the permeability-decreasing effect of AT2 agonism during which Lp increased from a baseline of 0.92 +/- 0.08 to a peak of 4.38 +/- 0.20 (P < 0.001). During inhibition of cGMP degradation, AT2 activation was able to decrease peak Lp from 2.26 +/- 0.15 to 1.46 +/- 0.05 (P < 0.001).

CONCLUSIONS

When cGMP synthesis and cAMP degradation were inhibited, the effect on fluid leak by AT1 activation was blunted. Inhibition of cAMP synthesis completely blocked the effect of AT2 activation on fluid leak, while AT2 activation continued to decrease fluid leak despite inhibition of cGMP degradation. The AT1 receptor appears to increase fluid leak by stimulating both cGMP synthesis and cAMP degradation, while the AT2 receptor decreases fluid leak by stimulating cAMP synthesis, but not cGMP degradation.