Effects of Losartan and Enalapril at Different Doses on Cardiac and Renal Interstitial Matrix in Spontaneously Hypertensive Rats

Inflammatory cell phenotypes in AAAs: their role and potential as targets for therapy

Abdominal aortic aneurysms (AAAs) are characterized by chronic inflammatory cell infiltration. AAA is typically an asymptomatic disease and caused ≈15 000 deaths annually in the United States. Previous studies have examined both human and murine aortic tissue for the presence of various inflammatory cell types. Studies show that in both human and experimental AAAs, prominent inflammatory cell infiltration, such as CD4(+) T cells and macrophages, occurs in the damaged aortic wall. These cells have the ability to undergo phenotypic modulation based on microenvironmental cues, potentially influencing disease progression. Proinflammatory CD4(+) T cells and classically activated macrophages dominate the landscape of aortic infiltrates. The skew to proinflammatory phenotypes alters disease progression and plays a role in causing chronic inflammation. The local cytokine production and presence of inflammatory mediators, such as extracellular matrix breakdown products, influence the uneven balance of the inflammatory infiltrate phenotypes. Understanding and developing new strategies that target the proinflammatory phenotype could provide useful therapeutic targets for a disease with no current pharmacological intervention.

The effect of chemotherapy for malignancy on the natural history of aortic aneurysm

OBJECTIVE

Surgical dogma holds that chemotherapy increases the risk of aneurysm growth and rupture. We sought to determine the effect of cytotoxic chemotherapy on the growth of aortic aneurysms.

METHODS

All patients undergoing chemotherapy for malignancy with coexisting aortic aneurysms at our institution between 2000 and 2011 were identified. Review of electronic medical records and rereview of serial cross-sectional imaging was performed. An additional cohort of patients undergoing aneurysm surveillance during the same period was identified, and demographic and anatomic variables were collected. Planned analysis included descriptive analysis, change in aneurysm diameter over time, and association of growth or need for intervention with type of chemotherapy and type of malignancy.

RESULTS

Between 2000 and 2011, 125 patients at our institution had a concurrent diagnosis of aortic aneurysm and malignancy requiring cytotoxic chemotherapy. Cross-sectional imaging was available for 91 patients. The predominant malignancy type was lung cancer (34 of 91 [38%]), followed by lymphoma (21 of 91 [23%]) and colorectal cancer (10 of 91 [11%]). Most aneurysms were infrarenal (53 of 91 [58%]). Most patients were treated with more than one class of chemotherapeutic agent over 267 days (interquartile range [IQR], 144-469 days), and most had at least one cycle of alkylating agents (73 of 91), in addition to antimetabolites (42 of 91) and plant alkaloids/terpenoids (40 of 92). Chemotherapy regimens included steroids in 84 patients (92%). The baseline aneurysm diameter was 41.4 mm (IQR, 34.9-51.3 mm) for patients who received chemotherapeutic agents and 46.0 mm (IQR, 40-52 mm) for those who did not. Eight of the 91 patients (9%) underwent aneurysm repair during chemotherapy, but only two required urgent repair due to aneurysm rupture. The rate of aneurysm growth per year for patients who did and did not receive chemotherapy was similar at 2.3 mm vs 2.4 mm (P = .69).

CONCLUSIONS

In 91 patients over 10 years at our institution, chemotherapy did not increase aneurysm growth compared with patients not undergoing treatment for malignancy.

Medical therapy of thoracic aortic aneurysms

Thoracic aortic aneurysm is a major health problem with multiple etiologies and potentially devastating consequences. Currently, no large randomized trial has shown that medical therapy can significantly slow or halt the progressive dilatation that eventually leads to dissection and rupture. A recent study that suggested that angiotensin receptor blocking agents slow the development of aneurysm dilatation in Marfan syndrome has revived interest in medical interventions to improve outcomes for patients with aortic aneurysm. In this article, we review the available data on established medical therapies and investigational medical therapies for thoracic aortic aneurysms.

THE AUTODIGESTION HYPOTHESIS AND RECEPTOR CLEAVAGE IN DIABETES AND HYPERTENSION

One of the key features of cardiovascular complications, such as hypertension or diabetes, is that they often appear at the same time in the same individual together with other forms of co-morbidities. While clinically a recognized phenomenon, no molecular mechanism for such co-morbidities has received universal acceptance. We propose a new hypothesis that provides a molecular basis for co-morbidities in hypertension due to unchecked proteolytic activity and receptor destruction. Testing of the hypothesis in the spontaneously hypertensive rat reveals an unchecked matrix metalloproteinase and serine protease activity in plasma and on several cardiovascular and parenchymal cells. The elevated proteolytic activity causes extracellular cleavage of multiple receptor types, such that cleavage of one receptor type leads to loss of the function carried out by this receptor. Proteolytic cleavage of the extracellular domain of the β(2) adrenergic receptor in arteries and arterioles causes vasoconstriction and elevation of the central blood pressure while cleavage of the extracellular domain of the insulin receptor leads to insulin resistance and lack of transmembrane glucose transport. A diverse set of cell dysfunctions in the spontaneously hypertensive rat are accompanied by cleavage of the membrane receptors that are involved in these functions. Chronic inhibition of the unchecked protease activity in the spontaneously hypertensive rat serves to restore the extracellular receptor density and alleviates the corresponding cell dysfunctions. The mild unchecked proteolytic activity in the spontaneously hypertensive rat points towards a chronic autodigestion process as a contributor to the end organ injury encountered in this rat strain. The presence of various soluble receptors, which consist of extracellular fragments of membrane receptors, in the plasma of hypertensive and diabetic patients suggest that the autodigestion process may also be present in man.

Effects of Melatonin and Pycnogenol on Small Artery Structure and Function in Spontaneously Hypertensive Rats

It was suggested that oxidative stress has a key role in the development of endothelial dysfunction, as well as microvascular structural alterations. Therefore, we have investigated 2 substances with antioxidant properties: melatonin and Pycnogenol. We treated 7 spontaneously hypertensive rats (SHRs) with melatonin and 7 with Pycnogenol for 6 weeks. We compared results obtained with those observed in 7 SHRs and 7 Wistar-Kyoto normotensive control rats kept untreated. Mesenteric small resistance arteries were dissected and mounted on a wire myograph, and a concentration-response curve to acetylcholine was performed. Aortic contents of metalloproteinase 2, Bax, inducible NO synthase, and cyclooxygenase 2 were evaluated, together with the aortic content of total collagen and collagen subtypes and apoptosis rate. A small reduction in systolic blood pressure was observed. A significant improvement in mesenteric small resistance artery structure and endothelial function was observed in rats treated with Pycnogenol and melatonin. Total aortic collagen content was significantly greater in untreated SHRs compared with Wistar-Kyoto control rats, whereas a full normalization was observed in treated rats. Apoptosis rate was increased in the aortas of untreated SHRs compared with Wistar-Kyoto control rats; an even more pronounced increase was observed in treated rats. Bax and metalloproteinase 2 expressions changed accordingly. Cyclooxygenase 2 and inducible NO synthase were more expressed in the aortas of untreated SHRs compared with Wistar-Kyoto control rats; this pattern was normalized by both treatments. In conclusion, our data suggest that treatment with Pycnogenol and melatonin may protect the vasculature, partly independent of blood pressure reduction, probably through their antioxidant effects.

A New Hypothesis for Insulin Resistance in Hypertension Due to Receptor Cleavage

BACKGROUND: One of the most important unresolved issues in diabetes is the mechanism for the attenuated response to insulin, i.e. insulin resistance. AIMS AND METHODS: We hypothesize that the mechanism for the insulin resistance is due to uncontrolled protease activity in the plasma, on endothelial cells and in the tissue parenchyma. To examine this hypothesis we use of microzymographic techniques in the microcirculation, plasma zymography, and receptor labeling techniques with antibodies against an extracellular domain of the insulin receptor α. RESULTS: The spontaneously hypertensive rat has an enhanced proteolytic activity and significant cleavage of the receptor with attenuated glucose transport. We present evidence for insulin receptor cleavage in a high fat diet and a transgenic model of diabetes. CONCLUSION: These results suggest that cleavage of the extracellular domain of the insulin receptor, a situation that interferes with the ability for insulin to bind and provide an intracellular signal for glucose transport, may be involved in insulin resistance.

Effects of olmesartan and enalapril at low or high doses on cardiac, renal and vascular interstitial matrix in spontaneously hypertensive rats

We have evaluated the effects of different doses of an angiotensin-converting enzyme (ACE) inhibitor, enalapril (ENA) and of an angiotensin II type 1 receptor blocker olmesartan (OLM), on extracellular matrix of the heart, kidney, aorta and mesenteric artery of spontaneously hypertensive rats (SHR). Forty SHR and eight Wistar-Kyoto controls (WKY) were included in the study. Eight SHR were treated with high-dose OLM 15 mg/kg per day, eight with high-dose ENA 25 mg/kg per day, eight with low-dose OLM 1 mg/kg per day and eight with low-dose ENA (2 mg/kg per day). Eight SHR and eight WKY were kept untreated as controls. Treatment was from age 4 to 12 weeks. Systolic blood pressure (SBP) was measured non-invasively every week. The left ventricular weight to body weight (RLVM) was measured, and the cardiac, aortic and glomerular interstitial collagen content was evaluated using Sirius red staining and image analysis. Mesenteric small arteries were dissected and mounted on a micromyograph, and the media:lumen ratio (M/L) was calculated. Collagen subtypes were evaluated by polarized light microscopy. The SHR treated with high-dose OLM or ENA showed a normalization of SBP. The RLVM was significantly increased in untreated SHR compared with untreated WKY, whereas significantly lower values were observed in the groups of SHR treated with high-dose OLM or ENA. A significant increase in cardiac and glomerular collagen content was observed in untreated SHR. Both high- or low-dose OLM and ENA normalized collagen content in the heart and the kidney. Both high-dose OLM and high-dose ENA normalized M/L ratio; however, OLM proved to be more effective than ENA in normalizing collagen pattern. In fact, aortic collagen content was normalized by both high-dose and low-dose OLM, but only by high-dose ENA. In conclusion, both OLM and ENA were significantly and equally effective in the prevention of cardiac and renal damage in SHR, whereas OLM was more effective than ENA in terms of effects on vascular extracellular matrix.

Medical management of small abdominal aortic aneurysms

Abdominal aortic aneurysm is a common condition that may be lethal when it is unrecognized. Current guidelines suggest repair as the aneurysm diameter reaches 5.0 to 5.5 cm. Most aortic aneurysms are detected incidentally when imaging is done for other purposes or through screening programs. Ninety percent of these aneurysms are below the threshold for intervention at the time of detection. A number of studies have sought to determine factors that lead to progression of aneurysmal disease that might be amenable to intervention during this period of observation. We review these studies and make recommendations for the medical management of small abdominal aortic aneurysms. On the basis of our current knowledge of the causes of aneurysm, a number of approaches have been proposed to prevent progression of aneurysmal disease. These include hemodynamic management, inhibition of inflammation, and protease inhibition. The American College of Cardiology/American Heart Association clinical practice guidelines rules of evidence have helped to define strength of evidence to support these approaches. Level A evidence (from large randomized trials) is available to indicate that observation of small aneurysms in men is safe up to a size of 5.5 cm and that propranolol does not inhibit aneurysm expansion. Level B evidence (from small randomized trials) suggests that roxithromycin or doxycycline will decrease the rate of aneurysm expansion. A number of studies agree that tobacco use is associated with an increased rate of aneurysm expansion. Level B and C evidence is available to suggest that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) may inhibit aneurysm expansion. There are animal data but no human data demonstrating that angiotensin-converting enzyme inhibitors or losartan, an angiotensin receptor blocker, will decrease the rate of AAA expansion. A pharmacological agent without important side effects that inhibited aneurysm expansion could change current approaches to aneurysm treatment. Additional studies are needed to clarify the potential role of doxycycline, roxithromycin, and statin therapy in the progression of aneurysmal disease.

Disease-associated changes in the expression of ion channels, ion receptors, ion exchangers and Ca(2+)-handling proteins in heart hypertrophy

The molecular pathology of cardiac hypertrophy is multifactorial with transcript regulation of ion channels, ion exchangers and Ca(2+)-handling proteins being speculative. We therefore investigated disease-associated changes in gene expression of various ion channels and their receptors as well as ion exchangers, cytoskeletal proteins and Ca(2+)-handling proteins in normotensive and spontaneously hypertensive (SHR) rats. We also compared experimental findings with results from hypertrophic human hearts, previously published (Borlak, J., and Thum, T., 2003. Hallmarks of ion channel gene expression in end-stage heart failure. FASEB J. 17, 1592-1608). We observed significant (P < 0.05) induction in transcript level of ATP-driven ion exchangers (Atp1A1, NCX-1, SERCA2a), ion channels (L-type Ca(2+)-channel, K(ir)3.4, Na(v)1.5) and RyR-2 in hypertrophic hearts, while gene expression was repressed in diseased human hearts. Further, the genes coding for calreticulin and calmodulin, PMCA 1 and 4 as well as alpha-skeletal actin were significantly (P < 0.05) changed in hypertrophic human heart, but were unchanged in hypertrophic left ventricles of the rat heart. Notably, transcript level of alpha- and beta-MHC, calsequestrin, K(ir)6.1 (in the right ventricle only), phospholamban as well as troponin T were repressed in both diseased human and rat hearts. Our study enabled an identification of disease-associated candidate genes. Their regulation is likely to be the result of an imbalance between pressure load/stretch force and vascular tonus and the observed changes may provide a rational for the rhythm disturbances observed in patients with cardiac hypertrophy.

The protective effect of caffeic acid phenethyl ester against cyclosporine A-induced cardiotoxicity in rats

Cyclosporine A (CsA) is the immunosuppressor, which is most frequently used in transplant surgery and in the treatment of autoimmune diseases. Oxidative stress has been considered as one of the possible mechanisms of CsA-induced cardiotoxicity. The present investigation examines the ability of caffeic acid phenethyl ester (CAPE), which is an active component of propolis extracts, as a natural antioxidant to protect against CsA-induced oxidative stress and cardiotoxicity. CsA cardiotoxicity was induced by subcutaneous injection of CsA at a dose of 15 mg/kg/body weight daily for 21 days in rats. Cardiotoxicity was evaluated by morphological and biochemical studies. CsA treated rats showed degenerative changes with cardiac fibrosis localized around the fibers. These latters were disorganised and the network was disappeared. The ROS production was increased whereas cytochrome-c-oxidase decreased. The expression and levels of matrix metalloproteinase 2 (MMP2) were increased whereas those of its inhibitor were downregulated. CAPE subcutaneous administration (15 micromol/kg/day) improved cardiac cytoarchitecture, decreased the levels and the expression of MMP2, and increased those of TIMP2 proteins. Moreover, it increased cytochrome-c-oxidase activity and decreased ROS production. These results suggest that CAPE could have protective effect against CsA-induced cardiotoxicity.

Enhanced angiotensin II-mediated effects in fibroblasts of patients with familial hypercholesterolemia

OBJECTIVE

Familial hypercholesterolemia (FH) is characterized by a high incidence of coronary heart disease. Evidence suggests an important role for angiotensin II (AngII) in the fibrotic response to tissue injury, and in promoting myocardial hypertrophy via paracrine mechanisms mediated by fibroblasts. We sought to determine whether AngII promotes proliferative and pro-atherogenic responses in FH patients.

METHODS

We used primary fibroblasts -- from five patients with heterozygous FH and five control subjects (C) -- to study AngII-induced cell growth, intracellular calcium fluxes, and expression/release of matrix components and pro-inflammatory peptides [transforming growth factor-beta1 (TGFbeta1) and endothelin-1 (ET-1)] and metalloproteinases involved in plaque remodeling and vulnerability.

RESULTS

AngII stimulated cell replication (5.1 +/- 0.03 versus 3.2 +/- 0.04 cells/50 cells per well, P < 0.001), and induced a larger increase in intracellular calcium content in FH cells than in C cells, in a dose-dependent fashion (mean difference = 76 nmol/l, P < 0.001). Similarly, TGFbeta1 and ET-1 expression and release were potentiated (after 24-h incubation with 1 micromol/l AngII: TGFbeta1 was 190 +/- 12 in C and 376 +/- 9 pg/ml per 10(6) cells in FH, and ET-1 was 93 +/- 5 in C and 192 +/- 7 pmol/ml per 10(6) cells in FH; P < 0.001 for both). AngII-induced release of the metalloproteinases MMP-1 and MMP-2 was also increased in FH versus C cells (0.52 +/- 0.04 versus 0.36 +/- 0.05 and 24 +/- 4 versus 13 +/- 3 ng/mg protein with 1 micromol/l AngII). These enhanced responses were likely due to an increased angiotensin receptor 1 (AT1) expression in cells from FH patients induced by AngII, and were prevented by pretreating cells with the selective AT1 antagonist irbesartan.

CONCLUSIONS

These findings show that some AngII-mediated pathways are enhanced in FH subjects irrespective of the presence of low-density lipoprotein (LDL), thus contributing to the development and progression of atherosclerosis in these patients.

Human-antigen R (HuR) expression in hypertension: downregulation of the mRNA stabilizing protein HuR in genetic hypertension

In aged spontaneously hypertensive rats (SHR), vasorelaxant responses to NO are attenuated compared with normotensive control rats (Wistar-Kyoto [WKY]) because of a decreased expression of the important NO receptor soluble guanylyl cyclase (sGC). Because the expression of sGC subunits alpha1 and beta1 is controlled at the post-transcriptional level by the mRNA-binding protein human-antigen R (HuR), we now assessed whether or not altered expression of HuR could account for downregulation of sGCalpha1 and sGCbeta1 in genetic hypertension. The expression of HuR (and sGCalpha1 and sGCbeta1) in aortas from aged SHR was significantly decreased at the mRNA and protein level compared with age-matched WKY rats, whereas expression of HuR was not different in prehypertensive young (2 months of age) SHR and age-matched WKY rats. The mRNA-binding activity of HuR in native aortic protein extracts from aged SHR was markedly reduced compared with normotensive WKY rats, as detected by RNA electrophoretic mobility shift analysis, using biotin-labeled adenine and uracil (AU)-rich element (ARE)-containing RNA probes from the 3'-untranslated region of sGCalpha1 and sGCbeta1. In contrast, ARE-binding activity was not different between prehypertensive young SHR and young WKY rats. In vitro RNA degradation assays using the same AU-rich sGC mRNA probes revealed an accelerated sGCalpha1 and sGCbeta1 mRNA decay in the presence of native protein extract from hypertensive SHR, which was less rapid with aortic protein from normotensive WKY rats. These findings suggest that in this animal model of genetic hypertension, the reduced expression of sGC subunits is mediated by downregulation of the sGC mRNA-stabilizing protein HuR.

Chemopreventive effect of five drugs on renal interstitial fibrosis induced by an aristolochic acid-containing Chinese herb in rats

BACKGROUND/AIMS

This study focuses on the chemopreventive effect of five drugs on renal interstitial fibrosis induced by an aristolochic acid-containing Chinese herb Mu-Tong.

METHODS

Renal interstitial fibrosis was induced in rats by administration of the Mu-Tong solution intragastrically for 6 weeks, and 36 rats were randomly divided into six groups: (1) Mu-Tong, (2) Mu-Tong + captopril, (3) Mu-Tong + losartan, (4) Mu-Tong + simvastatin, (5) Mu-Tong + spironolactone, and (6) Mu-Tong + diammonium glycyrrhizinate. Blood biochemistry and extracellular matrix were detected at weeks 0, 2, 4, and 6. At the end of week 6, kidney tissue of all groups was evaluated with special Masson staining for the degree of renal fibrosis as well as regular histopathology.

RESULTS

Mu-Tong caused progressive elevation of blood urea nitrogen, creatinine, hyaluronic acid, procollagen type III, and laminin. All five drugs suppressed elevation of blood biochemistry and extracellular matrix to some degree, but only the simvastatin group showed a significantly reduced percentage of positive Masson staining area in renal section compared to the Mu-Tong group (p < 0.05).

CONCLUSIONS

Our study indicates that Mu-Tong induces a similar kidney injury with general characteristics in patients with renal interstitial fibrosis. All five different drugs have suppressive effects on Mu-Tong-induced renal function damage, and in particular, simvastatin shows a protective effect on development of Mu-Tong-induced renal interstitial fibrosis to a certain degree.