Effects of angiotensin-converting enzyme inhibitor and angiotensin type 1 receptor antagonist in deoxycorticosterone acetate-salt hypertensive mice lacking Ren-2 gene

Epigenetics of Hypertensive Nephropathy

Hypertensive nephropathy (HN) is a leading cause of chronic kidney disease (CKD) and end-stage renal disease (ESRD), contributing to significant morbidity, mortality, and rising healthcare costs. In this review article, we explore the role of epigenetic mechanisms in HN progression and their potential therapeutic implications. We begin by examining key epigenetic modifications-DNA methylation, histone modifications, and non-coding RNAs-observed in kidney disease. Next, we discuss the underlying pathophysiology of HN and highlight current in vitro and in vivo models used to study the condition. Finally, we compare various types of HN-induced renal injury and their associated epigenetic mechanisms with those observed in other kidney injury models, drawing inferences on potential epigenetic therapies for HN. The information gathered in this work indicate that epigenetic mechanisms can drive the progression of HN by regulating key molecular signaling pathways involved in renal damage and fibrosis. The limitations of Renin-Angiotensin-Aldosterone System (RAAS) inhibitors underscore the need for alternative treatments targeting epigenetic pathways. This review emphasizes the importance of further research into the epigenetic regulation of HN to develop more effective therapies and preventive strategies. Identifying novel epigenetic markers could provide new therapeutic opportunities for managing CKD and reducing the burden of ESRD.

Ac-SDKP attenuates ER stress-stimulated collagen production in cardiac fibroblasts by inhibiting CHOP-mediated NF-κB expression

Inflammation and cardiac fibrosis are prevalent pathophysiologic conditions associated with hypertension, cardiac remodeling, and heart failure. Endoplasmic reticulum (ER) stress triggers the cells to activate unfolded protein responses (UPRs) and upregulate the ER stress chaperon, enzymes, and downstream transcription factors to restore normal ER function. The mechanisms that link ER stress-induced UPRs upregulation and NF-κB activation that results in cardiac inflammation and collagen production remain elusive. N-Acetyl-Ser-Asp-Lys-Pro (Ac-SDKP), a natural tetrapeptide that negatively regulates inflammation and fibrosis, has been reported. Whether it can inhibit ER stress-induced collagen production in cardiac fibroblasts remains unclear. Thus, we hypothesized that Ac-SDKP attenuates ER stress-stimulated collagen production in cardiac fibroblasts by inhibiting CHOP-mediated NF-κB expression. We aimed to study whether Ac-SDKP inhibits tunicamycin (TM)-induced ER stress signaling, NF-κB signaling, the release of inflammatory cytokine interleukin-6, and collagen production in human cardiac fibroblasts (HCFs). HCFs were pre-treated with Ac-SDKP (10 nM) and then stimulated with TM (0.25 μg/mL). We found that Ac-SDKP inhibits TM-induced collagen production by attenuating ER stress-induced UPRs upregulation and CHOP/NF-κB transcriptional signaling pathways. CHOP deletion by specific shRNA maintains the inhibitory effect of Ac-SDKP on NF-κB and type-1 collagen (Col-1) expression at both protein and mRNA levels. Attenuating ER stress-induced UPR sensor signaling by Ac-SDKP seems a promising therapeutic strategy to combat detrimental cardiac inflammation and fibrosis.

Drugs Interfering with Insulin Resistance and Their Influence on the Associated Hypermetabolic State in Severe Burns: A Narrative Review

It has become widely accepted that insulin resistance and glucose hypermetabolism can be linked to acute pathologies, such as burn injury, severe trauma, or sepsis. Severe burns can determine a significant increase in catabolism, having an important effect on glucose metabolism and on muscle protein metabolism. It is imperative to acknowledge that these alterations can lead to increased mortality through organ failure, even when the patients survive the initial trauma caused by the burn. By limiting the peripheral use of glucose with consequent hyperglycemia, insulin resistance determines compensatory increased levels of insulin in plasma. However, the significant alterations in cellular metabolism lead to a lack of response to insulin's anabolic functions, as well as to a decrease in its cytoprotective role. In the end, via pathological insulin signaling associated with increased liver gluconeogenesis, elevated levels of glucose are detected in the blood. Several cellular mechanisms have been incriminated in the development of insulin resistance in burns. In this context, the main aim of this review article is to summarize some of the drugs that might interfere with insulin resistance in burns, taking into consideration that such an approach can significantly improve the prognosis of the burned patient.

Hypotensive and antihypertensive effects of an aqueous extract from Guinep fruit (Melicoccus bijugatus Jacq) in rats

Melicoccus bijugatus Jacq (Mb) has been reported to have cardiovascular modulatory effects. In this study, we evaluated the antihypertensive effects and mechanism of action of Mb on N^G-Nitro-l-arginine Methyl Ester (l-NAME) and Deoxycorticosterone Acetate (DOCA) rat models. Aqueous extract of Mb fruit (100 mg/kg) was administered for 6 weeks to rats by gavage and blood pressure was recorded. Effects of the extract on vascular reactivity was evaluated using isolated organ baths, and tissues were collected for biochemical and histological analysis. The systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) were significantly (P < 0.05) reduced with extract (100 mg/kg) administration and treatment compared to the hypertensive models. Mb (100 µg/mL) reduced the vascular contractility induced by phenylephrine (PE), and caused a dose-dependent relaxation of PE-induced contraction of aortic vascular rings. The vasorelaxation properties seemed to be endothelium dependent, as well as nitric oxide (NO) and guanylyl cyclase, but not prostaglandin dependent. Histomicrograph of transverse sections of the ventricles from the Mb group did not show abnormalities. The extract significantly (P < 0.05) reduced an l-NAME induced elevation of cardiac output and Creatine Kinase Muscle-Brain (CKMB), but had no significant impact on the activities of arylamine N-acetyltransferase. In conclusion, Mb significantly decreased blood pressure in hypertensive models. The extract possesses the ability to induce endothelium dependent vasodilation, which is dependent on guanylyl cyclase but not prostaglandins.

Ameliorative effect of phosphodiesterase 4 and 5 inhibitors in deoxycorticosterone acetate-salt hypertensive uni-nephrectomized KKAy mice

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease (ESRD). Hypertension increases kidney stress, which deteriorates function, and leads to peripheral renal vascular resistance. Long-term hypoperfusion promotes interstitial fibrosis and glomerular sclerosis, resulting in nephrosclerosis. Although hypertension and DN are frequent ESRD complications, relevant animal models remain unavailable. We generated a deoxycorticosterone acetate (DOCA)-salt hypertensive uni-nephrectomized (UNx) KKA^y mouse model demonstrating hypertension, hyperglycemia, cardiac hypertrophy, kidney failure, increased urinary albumin creatinine ratio (UACR), and increased renal PDE4D and cardiac PDE5A mRNA levels. We hypothesized that the novel PDE4 selective inhibitor, compound A, and PDE5 inhibitor, sildenafil, exhibit nephroprotective, and cardioprotective effects in this new model. Compound A, sildenafil, and the angiotensin II receptor blocker, irbesartan, significantly reduced ventricular hypertrophy and pleural effusion volume. Meanwhile, compound A and sildenafil significantly suppressed the UACR, urinary kidney injury molecule-1, and monocyte chemoattractant protein-1 levels, as well as that of renal pro-fibrotic marker mRNAs, including collagen 1A1, fibronectin, and transforming growth factor-beta (TGF-β). Moreover, compound A significantly suppressed TGF-β-induced pro-fibrotic mRNA expression in vitro in all major kidney lesions, including within the glomerular mesangial region, podocytes, and epithelial region. Hence, PDE4 and PDE5 inhibitors may be promising treatments, in combination with irbesartan, for DN with hypertension as they demonstrate complementary mechanisms.

Knockout of TRPV1 Exacerbates Ischemia-reperfusion-induced Renal Inflammation and Injury in Obese Mice

BACKGROUND/AIM

Transient receptor potential vanilloid type 1 (TRPV1) has anti-inflammatory properties. The present study aimed to investigate the role of TRPV1 in renal inflammatory responses and tissue injury following renal ischemia-reperfusion (I/R) in diet-induced obese mice.

MATERIALS AND METHODS

TRPV1 knockout and wild type mice were fed a normal or western diet (WD) for 23 weeks and were then subjected to renal I/R injury.

RESULTS

TRPV1 knockout mice showed enhanced WD-induced renal macrophage infiltration and collagen deposition. Knocking out TRPV1 exacerbated renal I/R-induced increase of malondialdehyde, interleukin-6, monocyte chemoattractant protein-1, and NF-ĸB in obese mice. Similar results were observed in the expression of phosphorylated Smad1 and Smad2/3. Blockade of calcitonin gene-related peptide (CGRP) receptors with CGRP8-37 worsened the I/R-induced renal inflammation and injury.

CONCLUSION

Our data indicate that preserving TRPV1 expression and function may prevent renal I/R injury in obesity likely through alleviating inflammatory responses.

Intrarenal Renin Angiotensin System Imbalance During Postnatal Life Is Associated With Increased Microvascular Density in the Mature Kidney

Environmental stress during early life is an important factor that affects the postnatal renal development. We have previously shown that male rats exposed to maternal separation (MatSep), a model of early life stress, are normotensive but display a sex-specific reduced renal function and exacerbated angiotensin II (AngII)-mediated vascular responses as adults. Since optimal AngII levels during postnatal life are required for normal maturation of the kidney, this study was designed to investigate both short- and long-term effect of MatSep on (1) the renal vascular architecture and function, (2) the intrarenal renin-angiotensin system (RAS) components status, and (3) the genome-wide expression of genes in isolated renal vasculature. Renal tissue and plasma were collected from male rats at different postnatal days (P) for intrarenal RAS components mRNA and protein expression measurements at P2, 6, 10, 14, 21, and 90 and microCT analysis at P21 and 90. Although with similar body weight and renal mass trajectories from P2 to P90, MatSep rats displayed decreased renal filtration capacity at P90, while increased microvascular density at both P21 and P90 (p < 0.05). MatSep increased renal expression of renin, and angiotensin type 1 (AT1) and type 2 (AT2) receptors (p < 0.05), but reduced ACE2 mRNA expression and activity from P2-14 compared to controls. However, intrarenal levels of AngII peptide were reduced (p < 0.05) possible due to the increased degradation to AngIII by aminopeptidase A. In isolated renal vasculature from neonates, Enriched Biological Pathways functional clusters (EBPfc) from genes changed by MatSep reported to modulate extracellular structure organization, inflammation, and pro-angiogenic transcription factors. Our data suggest that male neonates exposed to MatSep could display permanent changes in the renal microvascular architecture in response to intrarenal RAS imbalance in the context of the atypical upregulation of angiogenic factors.

Depletion of cyclic-GMP levels and inhibition of cGMP-dependent protein kinase activate p21Cip1 /p27Kip1 pathways and lead to renal fibrosis and dysfunction

Cell-cycle regulatory proteins (p21^Cip1 /p27^Kip1 ) inhibit cyclin and cyclin-dependent kinase (CDK) complex that promotes fibrosis and hypertrophy. The present study examined the role of CDK blockers, p21^Cip1 /p27^Kip1 in the progression of renal fibrosis and dysfunction using Npr1 (encoding guanylyl cyclase/natriuretic peptide receptor-A, GC-A/NPRA) gene-knockout (0-copy; Npr1^-/- ), 2-copy (Npr1^+/+ ), and 4-copy (Npr1^++/++ ) mice treated with GC inhibitor, A71915 and cGMP-dependent protein kinase (cGK) inhibitor, (Rp-8-Br-cGMPS). A significant decrease in renal cGMP levels and cGK activity was observed in 0-copy mice and A71915- and Rp-treated 2-copy and 4-copy mice compared with controls. An increased phosphorylation of Erk1/2, p38, p21^Cip1 , and p27^Kip1 occurred in 0-copy and A71915-treated 2-copy and 4-copy mice, while Rp treatment caused minimal changes than controls. Pro-inflammatory (TNF-α, IL-6) and pro-fibrotic (TGF-β1) cytokines were significantly increased in plasma and kidneys of 0-copy and A71915-treated 2-copy mice, but to lesser extent in 4-copy mice. Progressive renal pathologies, including fibrosis, mesangial matrix expansion, and tubular hypertrophy were observed in 0-copy and A71915-treated 2-copy and 4-copy mice, but minimally occurred in Rp-treated mice compared with controls. These results indicate that Npr1 has pivotal roles in inhibiting renal fibrosis and hypertrophy and exerts protective effects involving cGMP/cGK axis by repressing CDK blockers p21^Cip1 and p27^Kip1 .

Evidence of Cardiovascular Calcification and Fibrosis in Pseudoxanthoma Elasticum Mouse Models Subjected to DOCA-Salt Hypertension

Pseudoxanthoma Elasticum (PXE) is a rare disorder characterized by fragmentation and progressive calcification of elastic fibres in connective tissues. Although arterial hypertension (AHT) has been reported in PXE patients, its impact on pathological manifestations has as yet been unexplored. We investigated the consequences of experimental AHT on Abcc6−/− PXE mouse models. Experimental AHT was induced by deoxycorticosterone acetate (DOCA-salt) in uni-nephrectomised mice. Blood pressure (BP) and vascular reactivity were monitored using tail-cuff plethysmography and myography respectively. Calcium content and fibrosis were assessed using colorimetry, Von Kossa and Sirius red staining respectively. The gene expression implicated in vascular biology was measured using quantitative polymerase chain reaction. DOCA-salt induced a matching rise in BP in Abcc6−/− and WT mice. Aortic ring contraction and relaxation in vitro were comparable. Calcium accumulated in the hearts of hypertensive Abcc6−/− mice along with significant fibrosis in the myocardium and aorta by contrast with the WT mice. In hypertensive Abcc6−/− mouse aortas, these results were corroborated by gene expression patterns favouring calcification, fibrosis and extracellular matrix remodelling. Abcc6 loss-of-function is associated with greater cardiovascular calcification and fibrosis in mice subjected to DOCA-Salt hypertension. These results suggest likely cardiovascular deterioration in PXE patients with AHT, necessitating diligent BP monitoring.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

Collecting Duct Renin Does Not Mediate DOCA-Salt Hypertension or Renal Injury

Collecting duct (CD)-derived renin is involved in the hypertensive response to chronic angiotensin-II (Ang-II) administration. However, whether CD renin is involved in Ang-II independent hypertension is currently unknown. To begin to examine this, 12 week old male and female CD-specific renin knock out (KO) mice and their littermate controls were subjected to uni-nephrectomy followed by 2 weeks of deoxycorticosterone acetate (DOCA) infusion combined with a high salt diet. Radiotelemetric blood pressure (BP) was similar between KO and control mice at baseline; BP increased in both groups to a similar degree throughout the 2 weeks of DOCA-salt treatment. Urinary albumin excretion and plasma blood urea nitrogen were comparable between the two groups after DOCA-salt treatment. Fibrosis as assessed by Masson’s Trichrome stain/Sirius Red stain and collagen-1 mRNA expression was similar between control and KO mice. Compared to baseline, DOCA-salt treatment decreased plasma renin concentration (PRC), urinary renin excretion and medullary renin mRNA expression in both floxed and CD renin KO mice with no detectable differences between the two groups. Further, in primary culture of rat inner medullary CD, aldosterone treatment did not change renin activity or total renin content. Taken together, these data suggest that CD derived renin does not play a role in DOCA-salt hypertension.

Non-Transgenic Mouse Models of Kidney Disease

Animal models are essential tools to understand the mechanisms underlying the development and progression of renal disease and to study potential therapeutic approaches. Recently, interventional models suitable to induce acute and chronic kidney disease in the mouse have become a focus of interest due to the wide availability of genetically engineered mouse lines. These models differ by their damaging mechanism (cell toxicity, immune mechanisms, surgical renal mass reduction, ischemia, hypertension, ureter obstruction etc.), functional and histomorphological phenotype and disease evolution. The susceptibility to a damaging mechanism often depends on strain and gender. The C57BL/6 strain, the most commonly used genetic background of transgenic mice, appears to be relatively resistant against developing glomerulosclerosis, proteinuria and hypertension. This review serves to provide a comprehensive overview of interventional mouse models of acute and chronic kidney disease.

Arrhythmogenic Remodeling in Murine Models of Deoxycorticosterone Acetate-Salt-Induced and 5/6-Subtotal Nephrectomy-Salt-Induced Cardiorenal Disease

BACKGROUND

Renal failure is associated with adverse cardiac remodeling and sudden cardiac death. The mechanism leading to enhanced arrhythmogenicity in the cardiorenal syndrome is unclear. The aim of this study was to characterize electrophysiological and tissue alterations correlated with enhanced arrhythmogenicity in two distinct mouse models of renal failure.

METHODS

Thirty-week-old 129Sv mice received a high-salt diet and deoxycorticosterone acetate (DOCA) for 8 weeks, followed by an additional period of high-salt diet for 27 weeks (DOCA-salt aged model). Adult CD-1 mice were submitted to 5/6-subtotal nephrectomy (SNx) and treated for 11 weeks with a high-salt diet (SNx-salt adult model). Vulnerability to arrhythmia as well as conduction velocities (CVs) of the hearts were determined ex vivo with epicardial mapping. Subsequently, the hearts were characterized for connexin 43 (Cx43) and fibrosis.

RESULTS

DOCA-salt and SNx-salt mice developed renal dysfunction characterized by albuminuria. Heart, lung and kidney weights were increased in DOCA-salt mice. Both DOCA-salt and SNx-salt mice were highly susceptible to ventricular arrhythmias. DOCA-salt mice had a significant decrease in both longitudinal and transversal CV in the left ventricle. Histological analysis revealed a significant reduction in Cx43 expression as well as an increase in interstitial fibrosis in both DOCA-salt and SNx-salt mice.

CONCLUSION

DOCA-salt and SNx-salt treatment induced renal dysfunction, which resulted in structural and electrical cardiac remodeling and enhanced arrhythmogenicity. The reduced Cx43 expression and increased fibrosis levels in these hearts are likely candidates for the formation of the arrhythmogenic substrate.

Renal protective effects of α-calcitonin gene-related peptide in deoxycorticosterone-salt hypertension

Deoxycorticosterone salt (DOC-salt) hypertension-induced renal damage is enhanced in α-calcitonin gene-related peptide (α-CGRP) knockout (KO) compared with wild-type (WT) mice. However, since the α-CGRP KO mice have a 15-20 mmHg higher baseline mean arterial pressure (MAP) than WT mice, they also have a higher MAP than WT mice throughout the course of DOC-salt hypertension. To determine the mechanism by which the absence of α-CGRP enhances hypertension-induced renal damage, DOC-salt hypertension was induced in telemetry probe implanted α-CGRP KO and WT mice. To equalize the blood pressure (BP) to that of DOC-salt WT mice, an additional group of DOC-salt α-CGRP KO mice was given 0.025% hydralazine to drink. The DOC-salt protocol increased the final MAP in α-CGRP KO mice to 155 ± 6 mmHg and in WT mice to 140 ± 5 mmHg. The MAP of the hydralazine-treated DOC-salt α-CGRP KO mice was 139 ± 6 mmHg. Urinary excretion of microalbumin and isoprostane, a marker for oxidative stress, was increased, and creatinine clearance was decreased in DOC-salt α-CGRP KO compared with DOC-salt WT mice. Equalization of the MAP in DOC-salt α-CGRP KO to that of DOC-salt WT mice did not significantly improve these parameters. Renal macrophage infiltration; desmin, a marker of podocyte damage; and the inflammatory cytokines TNF-α and IFN-γ and the chemokines monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1α (MIP-1α) were increased in DOC-salt α-CGRP KO mice and were not reduced by hydralazine treatment. However, BP equalization did improve the renal histopathological damage, as determined by light microscopy. Therefore, in DOC-salt hypertension in mice, the mechanism(s) of the renal protective effects of α-CGRP are both BP independent and BP dependent.

Renal protective effects of N-acetyl-Ser-Asp-Lys-Pro in deoxycorticosterone acetate-salt hypertensive mice

BACKGROUND

Hypertension-induced renal injury is characterized by inflammation, fibrosis and proteinuria. Previous studies have demonstrated that N-acetyl-Ser-Asp-Lys-Pro (Ac-SDKP) inhibits renal damage following diabetes mellitus and antiglomerular basement membrane nephritis. However, its effects on low-renin hypertensive nephropathy are not known. Thus, we hypothesized that Ac-SDKP has renal protective effects on deoxycorticosterone acetate (DOCA)-salt hypertensive mice, decreasing inflammatory cell infiltration, matrix deposition and albuminuria.

METHOD

We uninephrectomized 16-week-old C57BL/6J mice and treated them with either placebo, DCOA (10 mg/10 g body weight subcutaneous) and 1% sodium chloride with 0.2% potassium chloride in drinking water (DOCA-salt) or DOCA-salt with Ac-SDKP (800 μg/kg per day) for 12 weeks. We measured blood pressure, urine albumin, glomerular matrix, renal collagen content, monocyte/macrophage infiltration and glomerular nephrin expression.

RESULTS

Treatment with DOCA-salt significantly increased blood pressure (P < 0.01), which remained unaltered by Ac-SDKP. Ac-SDKP decreased DOCA-salt-induced renal collagen deposition, glomerular matrix expansion and monocyte/macrophage infiltration. Moreover, DOCA-salt-induced increase in albuminuria was normalized by Ac-SDKP (controls, 10.8 ± 1.7; DOCA-salt, 41 ± 5; DOCA-salt + Ac-SDKP, 13 ± 3 μg/10 g body weight per 24 h; P < 0.001, DOCA-salt vs. DOCA-salt + Ac-SDKP). Loss of nephrin reportedly causes excess urinary protein excretion; therefore, we determined whether Ac-SDKP inhibits proteinuria by restoring nephrin expression in the glomerulus of hypertensive mice. DOCA-salt significantly downregulated glomerular nephrin expression (controls, 37 ± 8; DOCA-salt, 10 ± 1.5% of glomerular area; P < 0.01), which was partially reversed by Ac-SDKP (23 ± 4.0% of glomerular area; P = 0.065, DOCA-salt vs. DOCA-salt + Ac-SDKP).

CONCLUSION

We concluded that Ac-SDKP prevents hypertension-induced inflammatory cell infiltration, collagen deposition, nephrin downregulation and albuminuria, which could lead to renoprotection in hypertensive mice.

Local angiotensin II aggravates cardiac remodeling in hypertension

Angiotensin II (ANG II) contributes to hypertension, cardiac hypertrophy, fibrosis, and dysfunction; however, it is difficult to separate the cardiac effect of ANG II from its hemodynamic action in vivo. To overcome the limitations, we used transgenic mice with cardiac-specific expression of a transgene fusion protein that releases ANG II from cardiomyocytes (Tg-ANG II) and treated them with deoxycorticosterone acetate (DOCA)-salt to suppress their systemic renin-angiotensin system. Using this unique model, we tested the hypothesis that cardiac ANG II, acting on the angiotensin type 1 receptor (AT(1)R), increases inflammation, oxidative stress, and apoptosis, accelerating cardiac hypertrophy and fibrosis. Male Tg-ANG II mice and their nontransgenic littermates (n-Tg) were uninephrectomized and divided into the following three groups: 1) vehicle-treated normotensive controls; 2) DOCA-salt; and 3) DOCA-salt + valsartan (AT(1)R blocker).Under basal conditions, systolic blood pressure (SBP) and cardiac phenotypes were similar between strains. In DOCA-salt hypertension, SBP increased similarly in both n-Tg and Tg-ANG II, and cardiac function did not differ between strains; however, Tg-ANG II had 1) greater ventricular hypertrophy as well as interstitial and perivascular fibrosis; 2) a higher number of deoxynucleotidyl-transferase-mediated dUTP nick end labeling-positive cells and infiltrating macrophages; 3) increased protein expression of NADPH oxidase 2 and transforming growth factor-β(1); and 4) downregulation of phosphatidylinositol 3-kinase (PI 3-kinase) and protein kinase B (Akt) phosphorylation. Valsartan partially reversed these effects in Tg-ANG II but not in n-Tg. We conclude that, when hemodynamic loading conditions remain unchanged, cardiac ANG II does not alter heart size or cardiac functions. However, in animals with hypertension, cardiac ANG II, acting via AT(1)R, enhances inflammation, oxidative stress, and cell death (most likely via downregulation of PI 3-kinase and Akt), contributing to cardiac hypertrophy and fibrosis.

Transient receptor potential vanilloid gene deletion exacerbates inflammation and atypical cardiac remodeling after myocardial infarction

The transient receptor potential vanilloid (TRPV1) channels expressed in sensory afferent fibers innervating the heart may be activated by protons or endovanilloids released during myocardial ischemia (MI), leading to angina. Although our previous in vitro data indicate that TRPV1 activation may preserve cardiac function after ischemia-reperfusion injury, the underlying mechanisms are largely unknown. To test the hypothesis that TRPV1 modulates inflammatory and early remodeling processes to prevent cardiac functional deterioration after myocardial infarction, TRPV1-null mutant (TRPV1(-/-)) and wild-type (WT) mice were subjected to left anterior descending coronary ligation or sham operation. The infarct size was greater in TRPV1(-/-) than in WT mice (P<0.001) 3 days after MI, and the mortality rate was higher in TRPV1(-/-) than in WT mice (P<0.05) 7 days after MI. The levels of plasma cardiac troponin I; cytokines, including tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6; chemokines, including monocyte chemoattractant protein-1 and macrophage inflammatory protein-2; and infiltration of inflammatory cells, including neutrophils, macrophages, and myofibroblasts; as well as collagen contents, were greater in TRPV1(-/-) than in WT mice (P<0.05) in the infarct area on days 3 and 7 after MI. Changes in left ventricular geometry led to increased end-systolic and -diastolic diameters and reduced contractile function in TRPV1(-/-) compared with WT mice. These data show that TRPV1 gene deletion results in excessive inflammation, disproportional left ventricular remodeling, and deteriorated cardiac function after MI, indicating that TRPV1 may prevent infarct expansion and cardiac injury by inhibiting inflammation and abnormal tissue remodeling.

Murine and rat cavernosal responses to endothelin-1 and urotensin-II Vasoactive Peptide Symposium

BACKGROUND: Endothelin-1 (ET-1) and urotensin-II (U-II) are the most potent constrictors of human vessels. Although the cavernosal tissue is higly responsive to ET-1, no information exists on the effects of U-II on cavernosal function. The aim of this study was to characterize ET-1 and U-II responses in corpora cavernosa from rats and mice. METHODS AND RESULTS: Male Wistar rats and C57/BL6 mice were used at 13 weeks. Cumulative concentration-response curves to ET-1, U-II and IRL-1620, an ET(B) agonist, were performed. ET-1 increased force generation in cavernosal strips from mice and rats, but no response to U-II was observed in the presence or absence of L-NAME, or in strips pre-stimulated with 20mM KCl. IRL-1620 did not induce cavernosal contraction even in presence of L-NAME, but induced a cavernosal relaxation which was greater in rats than mice. No relaxation responses to U-II were observed in cavernosal strips pre-contracted with phenylephrine. mRNA expression of ET-1, ET(A), ET(B) and U-II receptors, but not U-II was observed in cavernosal strips. CONCLUSION: ET-1, via ET(A) receptors activation, causes contractile responses in cavernosal strips from rats and mice whereas ET(B) receptor activation produces relaxation. Although the cavernosal tissue expresses U-II receptors, U-II does not induce contractile responses in corpora cavernosa from mice or rats.

Deletion of transient receptor potential vanilloid type 1 receptors exaggerates renal damage in deoxycorticosterone acetate-salt hypertension

To determine whether the transient receptor potential vanilloid type 1 (TRPV1) channel provides protection against hypertension-induced renal damage, hypertension was induced by uninephrectomy and by giving deoxycorticosterone acetate (DOCA)-salt in wild-type (WT) and TRPV1-null mutant (TRPV1-/-) mice. Mean arterial pressure, as determined by radiotelemetry, increased significantly and reached the peak 7 days after DOCA-salt treatment in both WT and TRPV1-/- mice. There was no difference in mean arterial pressure between the 2 strains at the baseline or at the peak that lasted for 4 treatment weeks. DOCA-salt treatment in both WT and TRPV1-/- mice led to increased urinary excretion of albumin and 8-isoprostane, glomerulosclerosis, renal cortical tubulointerstitial injury, tubulointerstitial fibrosis, increased number of tubular proliferating cell nuclear antigen-positive cells, and renal monocyte/macrophage infiltration, all of which were much more severe in DOCA-salt-treated TRPV1-/- compared with DOCA-salt-treated WT mice. Renal TRPV1 protein expression, but not the renal anandamide content, was elevated in DOCA-salt-treated WT compared with vehicle-treated WT mice. Renal anandamide levels were markedly elevated in DOCA-salt-treated TRPV1-/- but not in vehicle-treated TRPV1-/- mice. Thus, our data show that ablation of the TRPV1 gene exacerbates renal damage induced by DOCA-salt hypertension, indicating that TRPV1 may constitute a protective mechanism against end-organ damage induced by hypertension.

DOCA-salt treatment enhances responses to endothelin-1 in murine corpus cavernosum

The penis is kept in the flaccid state mainly via a tonic activity of norepinephrine and endothelins (ETs). ET-1 is important in salt-sensitive forms of hypertension. We hypothesized that cavernosal responses to ET-1 are enhanced in deoxycorticosterone acetate (DOCA)-salt mice and that blockade of ETA receptors prevents abnormal responses of the corpus cavernosum in DOCA-salt hypertension. Male C57BL/6 mice were unilaterally nephrectomized and treated for 5 weeks with both DOCA and water containing 1% NaCl and 0.2% KCl. Control mice were uninephrectomized and received tap water with no added salt. Animals received either the ETA antagonist atrasentan (5 mg x day(-1) x kg(-1) body weight) or vehicle. DOCA-salt mice displayed increased systolic blood pressure (SBP), and treatment with atrasentan decreased SBP in DOCA-salt mice. Contractile responses in cavernosal strips from DOCA-salt mice were enhanced by ET-1, phenylephrine, and electrical field stimulation (EFS) of adrenergic nerves, whereas relaxations were not altered by IRL-1620 (an ETB agonist), acetylcholine, sodium nitroprusside, and EFS of nonadrenergic noncholinergic nerves. PD59089 (an ERK1/2 inhibitor), but not Y-27632 (a Rho-kinase inhibitor), abolished enhanced contractions to ET-1 in cavernosum from DOCA-salt mice. Treatment of DOCA-salt mice with atrasentan did not normalize cavernosal responses. In summary, DOCA-salt treatment in mice enhances cavernosal reactivity to contractile, but not to relaxant, stimuli, via ET-1/ETA receptor-independent mechanisms.

Cardiac response to pressure overload in 129S1/SvImJ and C57BL/6J mice: temporal- and background-dependent development of concentric left ventricular hypertrophy

Left ventricular hypertrophy (LVH), a risk factor for cardiovascular morbidity and mortality, is commonly caused by essential hypertension. Three geometric patterns of LVH can be induced by hypertension: concentric remodeling, concentric hypertrophy, and eccentric hypertrophy. Clinical studies suggest that different underlying etiologies, genetic modifiers, and risk of mortality are associated with LVH geometric patterns. Since pressure overload-induced LVH can be modeled experimentally using transverse aortic constriction (TAC) and since C57BL/6J (B6) and 129S1/SvImJ (129S1) strains, which have different baseline cardiovascular phenotypes, are commonly used, we conducted serial echocardiographic studies to assess cardiac function up to 8 wk of post-TAC in male B6, 129S1, and B6129F1 (F1) mice. B6 mice had an earlier onset and more pronounced impairment in contractile function, with corresponding left and right ventricular dilatation, fibrosis, change in expression of hypertrophy marker, and increased liver weights at 5 wk of post-TAC. These observations suggest that B6 mice had eccentric hypertrophy with systolic dysfunction and right-sided heart failure. In contrast, we found that 129S1 and F1 mice delayed transition to decompensated heart failure, with 129S1 mice exhibiting preserved systolic function until 8 wk of post-TAC and relatively mild alterations in histology and markers of hypertrophy at 5 wk post-TAC. Consistent with concentric hypertrophy, our results show that these strains manifest different cardiac responses to pressure overload in a time-dependent manner and that genetic susceptibility to initial concentric hypertrophy is dominant to eccentric hypertrophy. These results also imply that genetic background differences can complicate interpretation of TAC studies when using mixed genetic backgrounds.

Role of N-acetyl-seryl-aspartyl-lysyl-proline in the antifibrotic and anti-inflammatory effects of the angiotensin-converting enzyme inhibitor captopril in hypertension

Angiotensin-converting enzyme inhibitors (ACEis) are known to have antifibrotic effects on the heart and kidney in both animal models and humans. N-acetyl-seryl-aspartyl-lysyl-proline is a natural inhibitor of proliferation of hematopoietic stem cells and a natural substrate of ACEi that was reported to prevent cardiac and renal fibrosis in vivo. However, it is not clear whether N-acetyl-seryl-aspartyl-lysyl-proline participates in the antifibrotic effects of ACEi. To clarify this issue, we used a model of aldosterone-salt-induced hypertension in rats treated with the ACEi captopril either alone or combined with an anti-N-acetyl-seryl-aspartyl-lysyl-proline monoclonal antibody. These hypertensive rats had the following: (1) left ventricular and renal hypertrophy, as well as increased collagen deposition in the left ventricular and the kidney; (2) glomerular matrix expansion; and (3) increased ED1-positive cells and enhanced phosphorylated-p42/44 mitogen-activated protein kinase in the left ventricle and kidney. The ACEi alone significantly lowered systolic blood pressure (P=0.008) with no effect on organ hypertrophy; it significantly lowered left ventricular collagen content, and this effect was blocked by the monoclonal antibody as confirmed by the histological data. As expected, the ACEi significantly decreased renal collagen deposition and glomerular matrix expansion, and these effects were attenuated by the monoclonal antibody. Likewise, the ACEi significantly decreased ED1-positive cells and inhibited p42/44 mitogen-activated protein kinase phosphorylation in the left ventricle and kidney, and these effects were blocked by the monoclonal antibody. We concluded that in aldosterone-salt-induced hypertension, the antifibrotic effect of ACEi on the heart and kidney, is partially mediated by N-acetyl-seryl-aspartyl-lysyl-proline, resulting in decreased inflammatory cell infiltration and p42/44 mitogen-activated protein kinase activation.

Vascular reactivity of mesenteric arteries and veins to endothelin-1 in a murine model of high blood pressure

We characterized vascular reactivity to endothelin-1 (ET-1) in mesenteric vessels from DOCA-salt hypertensive and SHAM control mice and assessed the effect that endothelial-derived vasodilators have on ET-1-induced vasoconstriction. Changes in the diameter of unpressurized small mesenteric arteries and veins (100- to 300-microm outside diameter) were measured in vitro using computer-assisted video microscopy. Veins were more sensitive than arteries to the contractile effects of ET-1. There was a decrease in arterial maximal responses (E(max)) compared to veins, this effect was larger in DOCA-salt arteries. The selective ET(B) receptor agonist, sarafotoxin 6c (S6c), contracted DOCA-salt and SHAM veins but did not contract arteries. The ET(B) receptor antagonist, BQ-788 (100 nM), but not the ET(A) receptor antagonist, BQ-610 (100 nM), blocked S6c responses. BQ-610 partially inhibited responses to ET-1 in mesenteric veins from DOCA-salt and SHAM mice while BQ-788 did not affect responses to ET-1. Co-administration of both antagonists inhibited responses to ET-1 to a greater extent than BQ-610 alone suggesting a possible functional interaction between ET(A) and ET(B) receptors. Responses to ET-1 in mesenteric arteries were completely inhibited by BQ-610 while BQ-788 did not affect arterial responses. Nitric oxide synthase inhibition potentiated ET-1 responses in veins from SHAM but not DOCA-salt mice. There was a prominent role for ET-mediated nitric oxide release in DOCA-salt but not SHAM arteries. In summary, these studies showed a differential regulation of ET-1 contractile mechanisms between murine mesenteric arteries and veins.

Dual angiotensin-converting enzyme/neutral endopeptidase inhibition on cardiac and renal fibrosis and inflammation in DOCA-salt hypertensive rats

OBJECTIVES

The relative roles of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) inhibition on cardiac and renal fibrosis in deoxycorticosterone acetate (DOCA)-salt hypertensive rats were studied.

METHODS

The ACE/NEP inhibitor omapatrilat (40 mg/kg per day), the ACE inhibitor enalapril (10 mg/kg per day) and the NEP inhibitor CGS 25462(100 mg/kg per day) were administrated for 3 weeks to DOCA rats. Collagen was stained with Sirius red, and mediators of inflammation were identified by immunolabeling (vascular cell adhesion molecule, nuclear factor-kappaB, infiltrating ED-1-positive macrophages and monocyte chemotactic protein-1) or by western blot (platelet-endothelial cell adhesion molecule-1).

RESULTS

Elevated systolic blood pressure of DOCA rats was significantly reduced (P < 0.05) by omapatrilat and CGS 25462. Omapatrilat and CGS 25462 significantly (P < 0.05) decreased interstitial collagen density in the left ventricle of DOCA rats compared with untreated DOCA rats. Enalapril only decreased the subepicardial collagen of DOCA rats. Omapatrilat significantly (P < 0.05) decreased renal mesangial collagen deposition in DOCA rats. Cardiac and renal expression of surface adhesion molecules, nuclear factor-kappaB, monocyte chemotactic protein and ED-1-positive cells were decreased in omapatrilat-treated DOCA rats compared with untreated DOCA rats. Enalapril and CGS 25462 did not alter mesangial collagen of DOCA rats.

CONCLUSIONS

Dual ACE/NEP inhibition was more effective than ACE or NEP inhibition in decreasing inflammatory mediators, and improving cardiac and renal fibrosis. This suggests a role for NEP inhibition added to blockade of the renin-angiotensin system that may explain the greater efficacy of omapatrilat.

Effects of AT1 receptor blockade on renal injury and mitogen-activated protein activity in Dahl salt-sensitive rats

BACKGROUND

The mitogen-activated protein kinase (MAPK) cascade is an important intracellular mediator of angiotensin II (Ang II)-induced cell growth and differentiation. Here, we examined the effect of angiotensin II type 1 receptor (AT1) receptor blockade on renal injury and MAPK activity in Dahl salt-sensitive (DS) rats.

METHODS

DS rats were maintained on a high (H: 8.0%NaCl, N= 8) or low (L: 0.3%NaCl, N= 7) salt diet, or H + candesartan cilexetil (10 to 15 mg/kg/day, N= 8). Urinary protein excretion (UproteinV), renal cortical collagen content, and glomerular injury (assessed by semiquantitative morphometric analysis) were determined after 4-week treatments. Plasma and kidney Ang II levels were measured by radioimmunoassay. Protein levels of AT1 and AT2 receptors in the renal cortical tissues were analyzed by Western-blotting analyses. MAPKs activities, including extracellular signal-regulated kinases (ERK)1/2, c-Jun NH2-terminal kinases (JNK), p38 MAPK, and Big-MAPK-1 (BMK1), were measured by Western-blotting analyses or in vitro kinase assays.

RESULTS

DS/H rats showed higher mean blood pressure (MBP), UproteinV, and renal cortical collagen content than DS/L rats. Increased ERK1/2, JNK, and BMK1 activities were observed in renal cortical tissues of DS/H rats (approximately 6.3-, 4.5-, and 2.5-fold, respectively), whereas p38 MAPK activity was unchanged. Plasma Ang II levels were significantly reduced in DS/H rats compared with DS/L rats, whereas kidney Ang II contents and AT1 receptor protein levels were similar. Candesartan did not alter MBP, but significantly reduced UproteinV and collagen content, and ameliorated progressive sclerotic and proliferative glomerular changes. Furthermore, candesartan decreased renal tissue Ang II contents (from 216 +/- 19 to 46 +/- 3 fmol/mL) and ERK1/2, JNK, and BMK1 activities (-45%, -60%, and -70%, respectively) in DS/H rats.

CONCLUSION

In DS hypertensive rats, some of the renoprotective effects of AT1 receptor blockade are accompanied by reductions in intrarenal Ang II contents and MAPK activity, which might not be mediated through arterial pressure changes.

Increased reactivity of murine mesenteric veins to adrenergic agonists: functional evidence supporting increased alpha1-adrenoceptor reserve in veins compared with arteries

These studies examined adrenergic reactivity of mesenteric arteries and veins from deoxycorticosterone acetate-salt (DOCA-salt) hypertensive and sham control mice. We measured constrictions in unpressurized arteries and veins by monitoring vessel diameter using computer-assisted video micros-copy in vitro. Veins were more sensitive than arteries to the constricting effects of norepinephrine (NE) and phenylephrine (PE), but the alpha2-agonists clonidine and UK 14,304 [5-bromo-6-(2-imidazolin-2-yl-amino)-quinoxaline] did not constrict arteries or veins. Reactivity was not altered in arteries or veins from DOCA-salt mice. We next investigated the mechanism of increased venous reactivity to NE and PE by studying desensitization to maximum concentrations of NE and PE. Sham arteries desensitized to NE and PE more than DOCA-salt arteries, whereas DOCA-salt and sham veins maintained 80% of the initial NE and PE constriction. To determine whether the increased reactivity and resistance to desensitization in veins was due to a greater alpha-adrenoceptor reserve, vessels were incubated with the alkylating agent phenoxybenzamine (PBZ; 0.3, 3, 10, and 30 nM). The NE-elicited initial constriction was reduced by PBZ (3, 10, and 30 nM) in sham but only by PBZ (30 nM) in DOCA-salt veins. All doses of PBZ blocked NE responses in sham and DOCA-salt arteries. These data suggest that mesenteric veins express more alpha1-adrenoceptors than arteries, accounting for greater reactivity and resistance to desensitization compared with arteries.

Blood pressure, cardiac, and renal responses to salt and deoxycorticosterone acetate in mice: role of Renin genes

Several studies have demonstrated that mice are polymorphic for the number of renin genes, with some inbred strains harboring one gene (Ren-1(c)) and other strains containing two genes (Ren-1(d) and Ren-2). In this study, the effects of 1% salt and deoxycorticosterone acetate (DOCA)/salt were investigated in one- and two-renin gene mice, for elucidation of the role of renin in the modulation of BP, cardiac, and renal responses to salt and DOCA. The results demonstrated that, under baseline conditions, mice with two renin genes exhibited 10-fold higher plasma renin activity, 100-fold higher plasma renin concentrations, elevated BP (which was angiotensin II-dependent), and an increased cardiac weight index, compared with one-renin gene mice (all P < 0.01). The presence of two renin genes markedly increased the BP, cardiac, and renal responses to salt. The number of renin genes also modulated the responses to DOCA/salt. In one-renin gene mice, DOCA/salt induced significant renal and cardiac hypertrophy (P < 0.01) even in the absence of any increase in BP. Treatment with losartan, an angiotensin II AT(1) receptor antagonist, decreased BP in two-renin gene mice but not in one-renin gene mice. However, losartan prevented the development of cardiac hypertrophy in both groups of mice. In conclusion, these data demonstrate that renin genes are important determinants of BP and of the responses to salt and DOCA in mice. The results confirm that the Ren-2 gene, which controls renin production mainly in the submaxillary gland, is physiologically active in mice and is not subject to the usual negative feedback control. Finally, these data provide further evidence that mineralocorticoids promote cardiac hypertrophy even in the absence of BP changes. This hypertrophic process is mediated in part by the activation of angiotensin II AT(1) receptors.

Reversible cardiac fibrosis and heart failure induced by conditional expression of an antisense mRNA of the mineralocorticoid receptor in cardiomyocytes

Cardiac failure is a common feature in the evolution of cardiac disease. Among the determinants of cardiac failure, the renin-angiotensin-aldosterone system has a central role, and antagonism of the mineralocorticoid receptor (MR) has been proposed as a therapeutic strategy. In this study, we questioned the role of the MR, not of aldosterone, on heart function, using an inducible and cardiac-specific transgenic mouse model. We have generated a conditional knock-down model by expressing solely in the heart an antisense mRNA directed against the murine MR, a transcription factor with unknown targets in cardiomyocytes. Within 2-3 mo, mice developed severe heart failure and cardiac fibrosis in the absence of hypertension or chronic hyperaldosteronism. Moreover, cardiac failure and fibrosis were fully reversible when MR antisense mRNA expression was subsequently suppressed.

Comparison of angiotensin-converting enzyme (ACE), neutral endopeptidase (NEP) and dual ACE/NEP inhibition on blood pressure and resistance arteries of deoxycorticosterone acetate-salt hypertensive rats

OBJECTIVES

Omapatrilat, an inhibitor of neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE), is an effective antihypertensive agent. Here, we studied the relative roles of NEP and ACE inhibition and their effect on resistance artery structure and function of deoxycorticosterone acetate (DOCA)-salt hypertensive rats.

METHODS

Omapatrilat (40 mg/kg per day), the NEP inhibitor CGS 25462 (CGS, 100 mg/kg per day) and the ACE inhibitor enalapril (10 mg/kg per day), were given for 3 weeks to DOCA-salt hypertensive rats. Effects on small mesenteric resistance arteries were studied on a pressurized myograph. Collagen deposition was evaluated by confocal microscopy.

RESULTS

Systolic blood pressure of DOCA-salt rats was significantly reduced (P < 0.05) by omapatrilat and CGS. Omapatrilat and CGS treatment increased lumen diameter and decreased media width and media/lumen ratio of small arteries of DOCA-salt rats (P < 0.05). Small artery relaxation responses to acetylcholine improved under omapatrilat or CGS treatment. The stress-strain curve shifted leftward in mesenteric arteries from DOCA-salt rats compared to control rats. Omapatrilat or CGS treatment resulted in a rightward shift, which was significantly different from that induced by enalapril. Omapatrilat and CGS decreased collagen deposition in the vessel wall of DOCA-salt rats. Enalapril had no effect on blood pressure, vascular structure, endothelial function or collagen deposition in the vessel wall of DOCA-salt rats.

CONCLUSIONS

Dual inhibition of ACE/NEP in DOCA-salt hypertensive rats resulted in potent anti-hypertensive effects, prevented vascular remodelling and improved endothelial function of resistance arteries. NEP inhibition is involved to a large extent in the effect of omapatrilat in DOCA-salt rats. These actions of omapatrilat may confer protection against end-organ damage characteristic of severe hypertension.