Renoprotective effect of chronic adrenomedullin infusion in Dahl salt-sensitive rats

A multicenter, single-arm, phase II clinical trial of adrenomedullin in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy

Background

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), the most common form of hereditary cerebral small vessel disease (SVD), currently lacks disease-modifying treatments. Adrenomedullin (AM), a vasoactive peptide with angiogenic, vasodilatory, anti-inflammatory, and anti-oxidative properties, shows potential effects on the neuro-glial-vascular unit.

Objective

The AdrenoMedullin for CADASIL (AMCAD) study aims to assess the efficacy and safety of AM in patients with CADASIL.

Sample size

Overall, 60 patients will be recruited.

Methods

The AMCAD is a multicenter, investigator-initiated, single-arm phase II trial. Patients with a confirmed CADASIL diagnosis, based on NOTCH3 genetic testing, will receive an 8-h AM treatment (15 ng/kg/min) for 14 days following a baseline assessment (from day 1 to day 14). Follow-up evaluations will be performed on days 15, 28, 90, and 180.

Study outcomes

The primary endpoint is the cerebral blood flow change rate in the frontal cortex, evaluated using arterial spin labeling magnetic resonance imaging, from baseline to day 28. Summary statistics, 95% confidence intervals, and a one-sample t-test will be used for analysis.

Conclusion

The AMCAD study aims to represent the therapeutic potential of AM in patients with CADASIL, addressing an unmet medical need in this challenging condition.

Clinical Trial Registration

jRCT 2,051,210,117 (https://jrct.niph.go.jp/en-latest-detail/jRCT2051210117).

Use of proteomics to identify biomarkers associated with chronic kidney disease and long-term outcomes in patients with myocardial infarction

BACKGROUND

Patients with chronic kidney disease (CKD) have poor outcomes following myocardial infarction (MI). We performed an untargeted examination of 175 biomarkers to identify those with the strongest association with CKD and to examine the association of those biomarkers with long-term outcomes.

METHODS

A total of 175 different biomarkers from MI patients enrolled in the Swedish Web-System for Enhancement and Development of Evidence-Based Care in Heart Disease Evaluated According to Recommended Therapies (SWEDEHEART) registry were analysed either by a multiple reaction monitoring mass spectrometry assay or by a multiplex assay (proximity extension assay). Random forests statistical models were used to assess the predictor importance of biomarkers, CKD and outcomes.

RESULTS

A total of 1098 MI patients with a median estimated glomerular filtration rate of 85 mL min^-1 /1.73 m² were followed for a median of 3.2 years. The random forests analyses, without and with adjustment for differences in demography, comorbidities and severity of disease, identified six biomarkers (adrenomedullin, TNF receptor-1, adipocyte fatty acid-binding protein-4, TNF-related apoptosis-inducing ligand receptor 2, growth differentiation factor-15 and TNF receptor-2) to be strongly associated with CKD. All six biomarkers were also amongst the 15 strongest predictors for death, and four of them were amongst the strongest predictors of subsequent MI and heart failure hospitalization.

CONCLUSION

In patients with MI, a proteomic approach could identify six biomarkers that best predicted CKD. These biomarkers were also amongst the most important predictors of long-term outcomes. Thus, these biomarkers indicate underlying mechanisms that may contribute to the poor prognosis seen in patients with MI and CKD.

MicroRNA-Mediated Metabolic Reprograming in Renal Cancer

Metabolic reprogramming is one of the hallmarks of renal cell cancer (RCC). We hypothesized that altered metabolism of RCC cells results from dysregulation of microRNAs targeting metabolically relevant genes. Combined large-scale transcriptomic and metabolic analysis of RCC patients tissue samples revealed a group of microRNAs that contribute to metabolic reprogramming in RCC. miRNAs expressions correlated with their predicted target genes and with gas chromatography-mass spectrometry (GC-MS) metabolome profiles of RCC tumors. Assays performed in RCC-derived cell lines showed that miR-146a-5p and miR-155-5p targeted genes of PPP (the pentose phosphate pathway) (G6PD and TKT), the TCA (tricarboxylic acid cycle) cycle (SUCLG2), and arginine metabolism (GATM), respectively. miR-106b-5p and miR-122-5p regulated the NFAT5 osmoregulatory transcription factor. Altered expressions of G6PD, TKT, SUCLG2, GATM, miR-106b-5p, miR-155-5p, and miR-342-3p correlated with poor survival of RCC patients. miR-106b-5p, miR-146a-5p, and miR-342-3p stimulated proliferation of RCC cells. The analysis involving >6000 patients revealed that miR-34a-5p, miR-106b-5p, miR-146a-5p, and miR-155-5p are PanCancer metabomiRs possibly involved in global regulation of cancer metabolism. In conclusion, we found that microRNAs upregulated in renal cancer contribute to disturbed expression of key genes involved in the regulation of RCC metabolome. miR-146a-5p and miR-155-5p emerge as a key “metabomiRs” that target genes of crucial metabolic pathways (PPP (the pentose phosphate pathway), TCA cycle, and arginine metabolism).

Transcription Factor ETS-1 and Reactive Oxygen Species: Role in Vascular and Renal Injury

The E26 avian erythroblastosis virus transcription factor-1 (ETS-1) is a member of the ETS family and regulates the expression of a variety of genes including growth factors, chemokines and adhesion molecules. Although ETS-1 was discovered as an oncogene, several lines of research show that it is up-regulated by angiotensin II (Ang II) both in the vasculature and the glomerulus. While reactive oxygen species (ROS) are required for Ang II-induced ETS-1 expression, ETS-1 also regulates the expression of p47phox, which is one of the subunits of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and a major source of ROS in the kidney and vasculature. Thus, there appears to be a positive feedback between ETS-1 and ROS. ETS-1 is also upregulated in the kidneys of rats with salt-sensitive hypertension and plays a major role in the development of end-organ injury in this animal model. Activation of the renin angiotensin system is required for the increased ETS-1 expression in these rats, and blockade of ETS-1 or haplodeficiency reduces the severity of kidney injury in these rats. In summary, ETS-1 plays a major role in the development of vascular and renal injury and is a potential target for the development of novel therapeutic strategies to ameliorate end-organ injury in hypertension.

Epicardial-derived adrenomedullin drives cardiac hyperplasia during embryogenesis

BACKGROUND

Growth promoting signals from the epicardium are essential for driving myocardial proliferation during embryogenesis. In adults, these signals become reactivated following injury and promote angiogenesis and myocardial repair. Therefore, identification of such paracrine factors could lead to novel therapeutic strategies. The multi-functional peptide adrenomedullin (Adm 5 gene, AM 5 protein) is required for normal heart development. Moreover, elevated plasma AM following myocardial infarction offers beneficial cardioprotection and serves as a powerful diagnostic and prognostic indication of disease severity.

RESULTS

Here, we developed a new model of Adm overexpression by stabilizing the Adm mRNA through gene-targeted replacement of the endogenous 30 untranslated region. As expected, Admhi/hi mice express three-times more AM than controls in multiple tissues, including the heart. Despite normal blood pressures, Admhi/hi mice unexpectedly showed significantly enlarged hearts due to increased cardiac hyperplasia during development. The targeting vector was designed to allow for reversion to wild-type levels by means of Cre-mediated modification. Using this approach, we demonstrate that AM derived from the epicardium, but not the myocardium or cardiac fibroblast, is responsible for driving cardiomyocyte hyperplasia.

CONCLUSIONS

AM is produced by the epicardium and drives myocyte proliferation during development, thus representing a novel and clinically relevant factor potentially related to mechanisms of cardiac repair after injury.

Genomic structure of nucleotide diversity among Lyon rat models of metabolic syndrome

Background

The metabolic syndrome (MetS), a complex disorder involving hypertension, obesity, dyslipidemia and insulin resistance, is a major risk factor for heart disease, stroke, and diabetes. The Lyon Hypertensive (LH), Lyon Normotensive (LN) and Lyon Low-pressure (LL) rats are inbred strains simultaneously derived from a common outbred Sprague Dawley colony by selection for high, normal, and low blood pressure, respectively. Further studies found that LH is a MetS susceptible strain, while LN is resistant and LL has an intermediate phenotype. Whole genome sequencing determined that, while the strains are phenotypically divergent, they are nearly 98% similar at the nucleotide level. Using the sequence of the three strains, we applied an approach that harnesses the distribution of Observed Strain Differences (OSD), or nucleotide diversity, to distinguish genomic regions of identity-by-descent (IBD) from those with divergent ancestry between the three strains. This information was then used to fine-map QTL identified in a cross between LH and LN rats in order to identify candidate genes causing the phenotypes.

Results

We identified haplotypes that, in total, contain at least 95% of the identifiable polymorphisms between the Lyon strains that are likely of differing ancestral origin. By intersecting the identified haplotype blocks with Quantitative Trait Loci (QTL) previously identified in a cross between LH and LN strains, the candidate QTL regions have been narrowed by 78%. Because the genome sequence has been determined, we were further able to identify putative functional variants in genes that are candidates for causing the QTL.

Conclusions

Whole genome sequence analysis between the LH, LN, and LL strains identified the haplotype structure of these three strains and identified candidate genes with sequence variants predicted to affect gene function. This approach, merged with additional integrative genetics approaches, will likely lead to novel mechanisms underlying complex disease and provide new drug targets and therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-197) contains supplementary material, which is available to authorized users.

Angiotensin II blockade and renal protection

Current national guidelines have recommended the use of renin-angiotensin system inhibitors, including angiotensin II type 1 receptor blockers (ARBs), in preference to other antihypertensive agents for treating hypertensive patients with chronic kidney disease. However, the mechanisms underlying the renoprotective effects of ARBs are multiple and complex. Blood pressure reduction by systemic vasodilation with an ARB contributes to its beneficial effects in treating kidney disease. Furthermore, ARB-induced renal vasodilation results in an increase in renal blood flow, leading to improvement of renal ischemia and hypoxia. ARBs are also effective in reducing urinary albumin excretion through a reduction in intraglomerular pressure and the protection of glomerular endothelium and/or podocyte injuries. In addition to blocking angiotensin II-induced renal cell and tissue injuries, ARBs can decrease intrarenal angiotensin II levels by reducing proximal tubular angiotensinogen and production of collecting duct renin, as well as angiotensin II accumulation in the kidney. In this review, we will briefly summarize our current understanding of the pharmacological effects of an ARB in the kidney. We will also discuss the possible mechanisms responsible for the renoprotective effects of ARBs on type 2 diabetic nephropathy.

Age-dependent salt hypertension in Dahl rats: fifty years of research

Fifty years ago, Lewis K. Dahl has presented a new model of salt hypertension - salt-sensitive and salt-resistant Dahl rats. Twenty years later, John P. Rapp has published the first and so far the only comprehensive review on this rat model covering numerous aspects of pathophysiology and genetics of salt hypertension. When we summarized 25 years of our own research on Dahl/Rapp rats, we have realized the need to outline principal abnormalities of this model, to show their interactions at different levels of the organism and to highlight the ontogenetic aspects of salt hypertension development. Our attention was focused on some cellular aspects (cell membrane function, ion transport, cell calcium handling), intra- and extrarenal factors affecting renal function and/or renal injury, local and systemic effects of renin-angiotensin-aldosterone system, endothelial and smooth muscle changes responsible for abnormal vascular contraction or relaxation, altered balance between various vasoconstrictor and vasodilator systems in blood pressure maintenance as well as on the central nervous and peripheral mechanisms involved in the regulation of circulatory homeostasis. We also searched for the age-dependent impact of environmental and pharmacological interventions, which modify the development of high blood pressure and/or organ damage, if they influence the salt-sensitive organism in particular critical periods of development (developmental windows). Thus, severe self-sustaining salt hypertension in young Dahl rats is characterized by pronounced dysbalance between augmented sympathetic hyperactivity and relative nitric oxide deficiency, attenuated baroreflex as well as by a major increase of residual blood pressure indicating profound remodeling of resistance vessels. Salt hypertension development in young but not in adult Dahl rats can be attenuated by preventive increase of potassium or calcium intake. On the contrary, moderate salt hypertension in adult Dahl rats is attenuated by superoxide scavenging or endothelin-A receptor blockade which do not affect salt hypertension development in young animals.

The role of adrenomedullin in the renal NADPH oxidase and (pro)renin in diabetic mice

Adrenomedullin has an antioxidative action and protects organs in various diseases. To clarify the role of adrenomedullin in diabetic nephropathy, we investigated the NADPH oxidase expression, renin-secreting granular cell (GC) hyperplasia, and glomerular matrix expansion in the streptozotocin (STZ)-induced diabetic adrenomedullin gene knockout (AMKO) mice compared with the STZ-diabetic wild mice at 10 weeks. The NADPH oxidase p47phox expression and lipid peroxidation products were enhanced in the glomeruli of the diabetic mice compared with that observed in the controls in both wild and AMKO mice. These changes were more obvious in the AMKO mice than in the wild mice. Glomerular mesangial matrix expansion was more severe in the diabetic AMKO mice than in the diabetic wild mice and exhibited a positive correlation with the degree of lipid peroxidation products in the glomeruli. Proteinuria was significantly higher in the diabetic AMKO mice than in the diabetic wild mice. The GC hyperplasia score and the renal prorenin expression were significantly increased in the diabetic AMKO mice than in the diabetic wild mice, and a positive correlation was observed with the NADPH oxidase expression in the macula densa. The endogenous adrenomedullin gene exhibits an antioxidant action via the inhibition of NADPH oxidase probably by suppressing the local renin-angiotensin system.

Augmented intrarenal and urinary angiotensinogen in hypertension and chronic kidney disease

Activated intrarenal renin-angiotensin system plays a cardinal role in the pathogenesis of hypertension and chronic kidney disease. Angiotensinogen is the only known substrate for renin, which is the rate-limiting enzyme of the renin-angiotensin system. Because the levels of angiotensinogen are close to the Michaelis-Menten constant values for renin, angiotensinogen levels as well as renin levels can control the renin-angiotensin system activity, and thus, upregulation of angiotensinogen leads to an increase in the angiotensin II levels and ultimately increases blood pressure. Recent studies using experimental animal models have documented the involvement of angiotensinogen in the intrarenal renin-angiotensin system activation and development of hypertension. Enhanced intrarenal angiotensinogen mRNA and/or protein levels were observed in experimental models of hypertension and chronic kidney disease, supporting the important roles of angiotensinogen in the development and the progression of hypertension and chronic kidney disease. Urinary excretion rates of angiotensinogen provide a specific index of the intrarenal renin-angiotensin system status in angiotensin II-infused rats. Also, a direct quantitative method has been developed recently to measure urinary angiotensinogen using human angiotensinogen enzyme-linked immunosorbent assay. These data prompted us to measure urinary angiotensinogen in patients with hypertension and chronic kidney disease, and investigate correlations with clinical parameters. This short article will focus on the role of the augmented intrarenal angiotensinogen in the pathophysiology of hypertension and chronic kidney disease. In addition, the potential of urinary angiotensinogen as a novel biomarker of the intrarenal renin-angiotensin system status in hypertension and chronic kidney disease will be also discussed.

Effects of continuous intermedin infusion on blood pressure and hemodynamic function in spontaneously hypertensive rats

OBJECTIVE

To examine the effects of exogenously administered intermedin (IMD, adrenomedullin-2) on arterial blood pressure, cardiac function and the cardiovascular IMD receptor system in spontaneously hypertensive rats (SHRs) as well as to investigate the associated mechanisms.

METHODS

Thirteen week-old male rats were divided in Wistar Kyoto (WKY) group (n = 12), SHR group (n = 12), IMD group (SHRs infused with IMD 1-47 500 ng/kg per hour, n = 12), and ADM group (SHRs infused with adrenomedullin 500 ng/kg per hour, n = 12).

RESULTS

A two-week continuous administration of low dose IMD 1-47 via mini-osmotic pumps markedly reduced blood pressure, the maximal rates of increase and decrease of left-ventricle pressure development (LV ± dp/dt(max)), left ventricular systolic pressure and heart rate in SHRs. Furthermore, IMD also inhibited protein over-expression of cardiovascular IMD receptors, myocardial Receptor Activity-Modifying Proteins (RAMP1 and RAMP2), aortic RAMP1, RAMP2, RAMP3, and calcitonin receptor-like receptor (CRLR); suppressed up-regulation of aortic RAMP1, RAMP2, RAMP3 and CRLR gene expression; and markedly elevated the mRNA abundance of myocardial atrial natriuretic peptide (ANP) and myocardial brain natriuretic peptide (BNP). Additionally, IMD 1-47 administration in SHRs increased aortic cAMP concentration and reduced myocardial cAMP concentration.

CONCLUSION

These findings support the speculation that IMD, as a cardiovascular active peptide, is involved in blood pressure reduction and cardiac function amelioration during hypertension. The mechanism underlying this effect may involve IMD binding of a receptor complex formed by RAMPs and CRLR, and consequential regulation of cAMP levels and other cardiovascular active factors, such as ANP and BNP.

Adrenomedullin and cardiovascular diseases

The cardiovascular system is regulated by the autonomic nervous system, the renin-angiotensin-aldosterone system, nitric oxide (NO) and other factors including neuropeptides. Research in neurohumoral factors has led to the development of many cardiovascular drugs. Adrenomedullin (ADM), initially isolated from the adrenal gland, has diverse physiological and pathophysiological functions in the cardiovascular system. It is produced in many organs and tissues including the vasculature. ADM has numerous actions, including vasodilation, natriuresis, antiapoptosis and stimulation of NO production. It might play a protective role in various cardiovascular pathologies, and its plasma level is elevated in patients with hypertension and heart failure. Administration of ADM is a possible therapeutic approach for treating cardiovascular diseases. A number of studies have investigated the infusion of ADM in humans, which seems to be benficial in heart failure and myocardial infarction. Instead of ADM infusion, augmentation of its endogenous level is another possible strategy. Gene therapy is feasible in animal models, but its application in humans is limited. At present, the most promising clinical application of ADM is the use of the plasma level of mid-regional proadrenomedullin as a biomarker in cardiovascular diseases. It is a good marker of prognosis and survival in patients with coronary aretery disease or heart failure.

The renin-angiotensin system, adrenomedullins and urotensin II in the kidney: possible renoprotection via the kidney peptide systems

The incidence of chronic kidney disease, such as diabetic nephropathy, is increasing throughout the world. Many biologically active peptides play important roles in the kidney. The classical example is the renin-angiotensin system (RAS). Angiotensin II plays critical roles in the progression of chronic kidney disease through its vasoconstrictor action, stimulatory action on cell proliferation, and reactive oxygen-generating activity. A renin inhibitor, aliskiren, has recently been shown to be a clinically effective drug to reduce proteinuria in patients with diabetic nephropathy. (Pro)renin receptor, a specific receptor for renin and prorenin, was newly identified as a member of the RAS. When bound to prorenin, (pro)renin receptor activates the angiotensin I-generating activity of prorenin in the absence of cleavage of the prosegment, and directly stimulates the pathway of mitogen-activated protein kinase independently from the RAS. The kidney peptides that antagonize the intrarenal RAS may have renoprotective actions. Adrenomedullins, potent vasodilator peptides, have been shown to have renoprotective actions. On the other hand, urotensin II, a potent vasoconstrictor peptide, may promote the renal dysfunction in chronic kidney disease together with the renal RAS. Thus, in addition to the renin inhibitor and (pro)renin receptor, adrenomedullins and urotensin II may be novel targets to develop therapeutic strategies against chronic kidney disease.

Natriuretic peptide/natriuretic peptide receptor-A (NPR-A) system has inhibitory effects in renal fibrosis in mice

OBJECT

This study was designed to examine whether natriuretic peptide/natriuretic peptide receptor-A (NPR-A) system attenuates renal fibrosis in a unilateral ureteral obstruction (UUO) model and also examined the mechanism involved.

METHODS

Three groups were studied: untreated UUO in wild-type mice; untreated UUO in NPR-A KO mice; and ANP treated (0.05 microg/kg/min) UUO in wild-type mice. We measured histological and immunohistochemical findings (alpha-SMA and F4/80), tissue cGMP levels, various mRNA expression levels by real-time PCR analysis, and transcription factor levels (AP-1 and NF-kappaB) in renal tissue.

RESULTS

Compared with wild-type UUO mice, NPRA-KO UUO mice had abnormal morphological findings (fibrous area: +26%, alpha-SMA expression: +30%) with lower tissue cGMP levels and increases in the mRNA expression levels of TGF-beta, collagen I, collagen III, PAI-1, renin and angiotensinogen, whereas there were no differences in F4/80 positive cells or the mRNA expression levels of ICAM-1, osteopontin, or MCP-1 between the two groups. In contrast, ANP pre-treatment significantly improved morphological changes with increase of tissue cGMP levels and reduction in the mRNA expression level of TGF-beta, collagen I, collagen III, PAI-1, ICAM-1, osteopontin, MCP-1, renin, and angiotensinogen. NPRA-KO UUO mice had higher AP-1 levels than wild-type UUO mice and ANP pre-treatment reduced AP-1 and NF-kappaB activity.

CONCLUSION

The endogenous natriuretic peptide/NPR-A system may inhibit renal fibrosis partly via inhibition of the angiotensin/AP-1/TGF-beta/collagen pathway and exogenous ANP pre-treatment may inhibit it partly via both the angiotensin/AP-1/TGF-beta/collagen and NF-kappaB/inflammatory pathways.

Fasudil, a Rho-kinase inhibitor, reverses L-NAME exacerbated severe nephrosclerosis in spontaneously hypertensive rats

BACKGROUND

In this study, we tested the hypothesis that long-term Rho-kinase inhibition would reverse nitro-L-arginine methyl ester-exacerbated nephrosclerosis in spontaneously hypertensive rats and attempted to elucidate the mechanism involved.

METHODS

Five groups (each n = 8) were studied: untreated spontaneously hypertensive rats; nitro-L-arginine methyl ester (50 mg/l in drinking water, for 3 weeks)-treated spontaneously hypertensive rats; nitro-L-arginine methyl ester with fasudil (10 mg/kg/day)-treated spontaneously hypertensive rats; nitro-L-arginine methyl ester for 3 weeks followed by fasudil for 3 weeks-treated spontaneously hypertensive rats (same doses), and nitro-L-arginine methyl ester for 3 weeks followed by untreated for 3 weeks. We examined renal function, blood pressure, histological features, oxidative stress markers, and mRNA expression in the renal cortex.

RESULTS

Nitro-L-arginine methyl ester-treated spontaneously hypertensive rats had higher blood pressure, proteinuria, and serum creatinine and lower creatinine clearance, urinary NO3/NO2 ratio, and urinary cGMP excretion compared with control spontaneously hypertensive rats (all Ps < 0.05). Nitro-L-arginine methyl ester-treated spontaneously hypertensive rats also had increased free radical metabolites and abnormal morphological findings with increased nicotinamide adenine dinucleotide phosphate oxidase activity, phosphorylation of myosin phosphatase targeting subunit-1, and mRNA expression of RhoA, RhoB, RhoC, collagen I and III, transforming growth factor-beta, nicotinamide adenine dinucleotide phosphate subunit, endothelial nitric oxide synthase, plasminogen activator inhibitor, and intercellular adhesion molecule-1 in the renal cortex compared with control spontaneously hypertensive rats. Long-term co-treatment with fasudil slightly improved these indices, but most of them were not statistically significant. Late fasudil treatment significantly improved kidney function, morphological changes, and alterations of mRNA expression in the renal cortex, although late untreated controls did not show any improvement.

CONCLUSION

These results suggest that Rho-kinase inhibition partly reverses hypertensive glomerulosclerosis. The renoprotective effect of the Rho-kinase inhibitor may have multiple mechanisms including inhibition of extracellular matrix production, oxidative stress, adhesion molecule production, and antifibrinolysis.

Role of adrenomedullin system in lipid metabolism and its signaling mechanism in cultured adipocytes

We investigated the levels of adrenomedullin (AM) system during the process of preadipocyte differentiation and its role in lipid metabolism and cellular signaling mechanism in differentiated adipocytes. We cultured rat preadipocytes and measured the following during the process of differentiation: two molecular forms of AM in the culture medium using a specific immunoradiometric assay and gene expression of AM and its receptor component using RT-PCR analysis. In differentiated adipocytes, we measured the effects of AM on the intracellular cAMP level, lipolysis, glucose incorporation, and the protein levels. Two molecular forms of AM were secreted into the medium, and the AM-mature/AM-total ratio was increased after 6 days of differentiation. Cultured rat preadipocytes highly expressed the genes of AM and its receptor components at day 1, and they increased at day 10. Administration of AM to preadipocytes increased the number of Oil Red O-positive adipocytes and spectrophotometric absorbance of Oil Red O. AM dose dependently increased cAMP level and lipolysis, and its effect was blocked by CGRP(8-37). Isoproterenol increased lipolysis, and AM had additive effects on isoproterenol-induced lipolysis. KT5720 and U0126 significantly inhibited the AM-induced lipolysis, whereas KT5720, but not U0126, significantly inhibited the isoproterenol-induced lipolysis. AM increased glucose incorporation and its effect was blocked by wortmannin. Western blot analysis revealed that AM increased phospho PKA, ERK, and Akt. These results indicate that AM and its receptor component are highly expressed in cultured adipocytes and may play a role in lipid metabolism via a different signaling pathway.

The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease

In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.

Prevention of salt induced hypertension and fibrosis by angiotensin converting enzyme inhibitors in Dahl S rats

BACKGROUND AND PURPOSE

In Dahl S rats, high salt increases activity of the tissue renin-angiotensin-aldosterone system (RAAS) in the CNS, heart and kidneys. Here, we assessed the effects of chronic angiotensin converting enzyme (ACE) inhibition on salt-induced hypertension and cardiovascular and renal hypertrophy and fibrosis, relative to the extent of ACE blockade.

EXPERIMENTAL APPROACH

From 4.5 weeks of age, Dahl S rats received either the lipophilic ACE inhibitor trandolapril (1 or 5 mg kg(-1) day(-1)) or the hydrophilic ACE inhibitor lisinopril (10 or 50 mg kg(-1) day(-1)) and a high salt diet was started 0.5 week later. Treatments ended at 9 weeks of age.

KEY RESULTS

High salt diet markedly increased blood pressure (BP), decreased plasma angiotensin II and increased ACE binding densities in brain, heart, aorta and kidneys. Trandolapril and lisinopril prevented 50% of the increase in BP in light and dark period of the day. After the last doses, trandolapril decreased ACE densities by approximately 80% in brain nuclei and heart and lisinopril by approximately 60% in the brain and by approximately 70% in the heart. The two ACE inhibitors prevented right ventricular hypertrophy and attenuated left ventricular hypertrophy but did not affect renal hypertrophy caused by high salt. Both drugs prevented high salt-induced fibrosis in heart, kidney and aorta.

CONCLUSION AND IMPLICATION

As the ACE inhibitors could completely prevent tissue fibrosis and partially prevent tissue hypertrophy and hypertension, the tissue RAAS may play a critical role in salt-induced fibrosis, but a lesser role in the hypertrophy.

Inhibition of Rho-kinase attenuates nephrosclerosis and improves survival in salt-loaded spontaneously hypertensive stroke-prone rats

OBJECTIVES

We examined whether the Rho/Rho-kinase pathway is involved in the pathogenesis of nephrosclerosis in severely hypertensive rats and assessed the effects of long-term treatment with a Rho-kinase inhibitor, fasudil, on kidney function, histological findings, gene expressions, and survival. We also attempted to elucidate the mechanisms involved.

METHODS

We studied the following four groups: control Wistar-Kyoto rats (WKY), untreated salt-loaded spontaneously hypertensive stroke-prone rats (SHR-SP), low-dose fasudil (15 mg/kg per day)-treated SHR-SP, and high-dose fasudil (30 mg/kg per day)-treated SHR-SP. After 8 weeks' treatment, the effects of fasudil were examined.

RESULTS

Untreated SHR-SP were characterized by increased blood pressure without circadian variation, decreased kidney function, abnormal renal morphological findings, and increased messenger RNA expression levels of transforming growth factor beta, collagen I, collagen III, p40phox, p47phox, plasminogen activator inhibitor 1, and intracellular adhesion molecule 1 in the renal cortex, compared with WKY. Long-term high-dose fasudil treatment significantly improved renal function (serum creatinine -32%, creatine clearance +39%), proteinuria (-92%) and histological findings (glomerular injury score -57%, arteriolar injury score -55%, fibrous area -40%, ED-1-positive cells -43%) without changing blood pressure or circadian variation, compared with untreated SHR-SP. In addition, fasudil significantly improved increased mRNA expression levels in the renal cortex. Furthermore, high-dose fasudil significantly prolonged survival time compared with untreated SHR-SP (P < 0.01). Low-dose fasudil treatment improved these variables slightly, but did not affect most significantly.

CONCLUSION

The Rho/Rho-kinase pathway participates in the pathogenesis of nephrosclerosis in SHR-SP independently of blood pressure-lowering activity, partly by upregulation of the gene expressions of extracellular matrix, oxidative stress, adhesion molecules, and antifibrinolysis.

Adrenomedullin ameliorates lipopolysaccharide-induced acute lung injury in rats

Adrenomedullin (AM), an endogenous peptide, has been shown to have a variety of protective effects on the cardiovascular system. However, the effect of AM on acute lung injury remains unknown. Accordingly, we investigated whether AM infusion ameliorates lipopolysaccharide (LPS)-induced acute lung injury in rats. Rats were randomized to receive continuous intravenous infusion of AM (0.1 microg x kg(-1) x min(-1)) or vehicle through a microosmotic pump. The animals were intratracheally injected with either LPS (1 mg/kg) or saline. At 6 and 18 h after intratracheal instillation, we performed histological examination and bronchoalveolar lavage and assessed the lung wet/dry weight ratio as an index of acute lung injury. Then we measured the numbers of total cells and neutrophils and the levels of tumor necrosis factor (TNF)-alpha and cytokine-induced neutrophil chemoattractant (CINC) in bronchoalveolar lavage fluid (BALF). In addition, we evaluated BALF total protein and albumin levels as indexes of lung permeability. LPS instillation caused severe acute lung injury, as indicated by the histological findings and the lung wet/dry weight ratio. However, AM infusion attenuated these LPS-induced abnormalities. AM decreased the numbers of total cells and neutrophils and the levels of TNF-alpha and CINC in BALF. AM also reduced BALF total protein and albumin levels. In addition, AM significantly suppressed apoptosis of alveolar wall cells as indicated by cleaved caspase-3 staining. In conclusion, continuous infusion of AM ameliorated LPS-induced acute lung injury in rats. This beneficial effect of AM on acute lung injury may be mediated by inhibition of inflammation, hyperpermeability, and alveolar wall cell apoptosis.

Sanguinarine Downregulates AT1a Gene Expression in a Hypertensive Rat Model

We studied the in vivo effects of sanguinarine in a hypertensive rat model and its effects on AT1a mRNA expression in kidney tissues. Rats received daily for 14 d sanguinarine 0.1 mg/kg (SangL) and 0.3 mg/kg (SangH), losartan 1 mg/kg by weight (Los), or DMSO (Con). Blood pressures were monitored regularly and urine volume and sodium concentration was measured on days 0, 7, and 14. On day 15, animals were anesthetized (sodium thiopentane, 50 mg/kg), blood samples for aldosterone levels were taken, and kidneys were removed for AT1a mRNA expression. Los and SangH groups showed reduced AT1a mRNA expressions by 4.22- and 5.9-fold, respectively. In the SangL group it was reduced by 2.7-fold. Decreases in systolic blood pressures mirrored decreases in AT1a mRNA expressions in all groups. Los and SangH groups showed reductions in systolic blood pressure of 12.3% and 19.3%, respectively, whereas in the SangL group, it was reduced by 8.07%. Urine output in the Los group increased (228% mean increase from days 0-14), whereas sodium excretion decreased by 69.6% (mean decrease from days 0-14). In the SangL and SangH groups, urine volumes increased significantly by 108.3% and 115% (mean increase from days 0-14), respectively. Urinary sodium excretion increased significantly by 60.9% in the SangH group. We concluded that sanguinarine reduces blood pressure in the Dahl rat because of decreased AT1 receptor expression and reduced aldosterone levels. The action of losartan on increased urinary volume and decreased sodium excretion may be attributed to reduced vasopressin secretion.

Effects of Adrenomedullin on Cardiac Oxidative Stress and Collagen Accumulation in Aldosterone-Dependent Malignant Hypertensive Rats

We examined the effects of adrenomedullin on cardiac oxidative stress and collagen accumulation in aldosterone-dependent malignant hypertensive rats. Spontaneously hypertensive rats (SHRs) were treated with one of the following combinations for 4 weeks: tap water and vehicle [0.5% ethanol, subcutaneously (s.c.), n = 5], 1% NaCl in drinking water and vehicle (n = 8), 1% NaCl and aldosterone (0.75 microg/h s.c., n = 8), and 1% NaCl, aldosterone, and adrenomedullin (1.3 microg/kg/h s.c., n = 8). Systolic blood pressure (SBP) and left ventricular (LV) weight were higher in aldosterone-treated SHRs than vehicle- or vehicle/1% NaCl-treated SHRs. Thiobarbituric acid reactive substances (TBARS) levels and NADPH oxidase activity in LV tissues of aldosterone-treated SHRs were also higher than those of vehicle- or vehicle/1% NaCl-treated SHRs, and these changes were associated with increases in LV mRNA levels of p22phox, gp91phox, fibronectin, collagen types I and III, as well as collagen content. Treatment with adrenomedullin did not alter SBP or LV weight but attenuated aldosterone-induced increases in TBARS levels, NADPH oxidase activity, and mRNA levels of p22phox, gp91phox, fibronectin, collagen types I and III, as well as collagen content in LV tissues. These data suggest that NADPH oxidase-mediated reactive oxygen species production is involved in the pathogenesis of cardiac collagen accumulation in aldosterone-dependent malignant hypertensive rats and that the cardioprotective effects of adrenomedullin are mediated through the suppression of this pathway.

Increased Production of Adrenomedullin in Glomeruli from Anti-Glomerular Basement Membrane Glomerulonephritis Rats Treated with Methylprednisolone

BACKGROUND/AIMS

Adrenomedullin (AM) has anti-proliferative and apoptotic effects on mesangial cells (MCs). Both effects play an important role in the progression of glomerulonephritis (GN). Glucocorticoids are widely used for the treatment of GN; however, the relationship between AM regulation in MCs or glomeruli and glucocorticoid treatment has not been clarified.

METHODS

Using the cultured rat MCs, AM secretion induced by methylprednisolone (m-PSL), and MC proliferation and apoptosis caused by AM were examined. In addition, the role of AM receptor antagonist, AM(22-52), was also investigated. Then, we made an anti-glomerular basement membrane (GBM) GN rat model and compared the AM expression and production in each glomeruli obtained from the control or m-PSL-treated anti-GBM GN rats.

RESULTS

In the cultured rat MCs, AM secretion was increased by m-PSL. MC proliferation was inhibited, while MC apoptosis was increased by AM. MC apoptosis was inhibited by the addition of AM(22-52). M-PSL therapy ameliorated the progression of anti-GBM GN rats. AM expression and production were increased in the glomeruli from m-PSL-treated rats compared to the controls.

CONCLUSION

Considering the anti-proliferative and apoptotic effects of AM on MCs, increased AM in the glomeruli might participate in the improvement of glomerular lesions in anti-GBM GN rats treated with m-PSL.

Young Scholars Award Lecture: Intratubular angiotensinogen in hypertension and kidney diseases

Recent findings related to the renin-angiotensin system have provided a more elaborated understanding of the pathophysiology of hypertension and kidney diseases. These findings have led to unique concepts and issues regarding the intrarenal renin-angiotensin system. Angiotensinogen is the only known substrate for renin that is the rate-limiting enzyme of the renin-angiotensin system. Because the level of angiotensinogen in human beings is close to the Michaelis-Menten constant value for renin, changes in angiotensinogen levels can control the activity of the renin-angiotensin system, and its upregulation may lead to elevated angiotensin peptide levels and increases in blood pressure. Enhanced intrarenal angiotensinogen mRNA or protein levels or both have been observed in multiple models of hypertension including angiotensin II-dependent hypertensive rats, Dahl salt-sensitive hypertensive rats, and spontaneously hypertensive rats, as well as in kidney diseases including diabetic nephropathy, immunoglobulin A (IgA) nephropathy, and radiation nephropathy. Renal angiotensinogen is formed primarily in proximal tubular cells and is secreted into the tubular fluid. Urinary angiotensinogen excretion rates show a clear relationship to kidney angiotensin II contents and kidney angiotensinogen levels, suggesting that urinary angiotensinogen may serve as an index of the intrarenal renin-angiotensin system status. Establishment of concise and accurate methods to measure human angiotensinogen may allow clinical studies that would provide important information regarding the roles of intrarenal angiotensinogen in the development and progression of hypertension and kidney diseases.

Spironolactone preserves cardiac norepinephrine reuptake in salt-sensitive Dahl rats

An impairment of cardiac norepinephrine (NE) reuptake via the neuronal NE transporter (NET) enhances the effects of increased cardiac NE release in heart failure patients. Increasing evidence suggests that aldosterone and endothelins promote sympathetic overstimulation of failing hearts. Salt-sensitive Dahl rats (DS) fed a high-salt diet developed arterial hypertension and diastolic heart failure as well as elevated plasma levels of endothelin-1 and NE. Cardiac NE reuptake and NET-binding sites, as assessed by clearance of bolus-injected [(3)H]NE in isolated perfused rat hearts and [(3)H]mazindol binding, were reduced. Treatment of DS with the mineralocorticoid receptor antagonist spironolactone preserved the plasma levels of endothelin-1 and NE, cardiac NE reuptake, and myocardial NET density. Moreover, the ventricular function and survival of spironolactone-treated DS were significantly improved compared with untreated DS. The alpha(1)-inhibitor prazosin decreased blood pressure in DS similar to spironolactone treatment, but did not normalize the plasma levels of endothelin-1 and NE, NE reuptake, or ventricular function. In a heart failure-independent model, Wistar rats that were infused with aldosterone and fed a high-salt diet developed impaired cardiac NE reuptake. Treatment of these rats with the endothelin A receptor antagonist darusentan attenuated the impairment of NE reuptake. In conclusion, spironolactone preserves NET-dependent cardiac NE reuptake in salt-dependent heart failure. Evidence is provided that aldosterone inhibits NET function through an interaction with the endothelin system. Selective antagonism of the mineralocorticoid and/or the endothelin A receptor might represent therapeutic principles to prevent cardiac sympathetic overactivity in salt-dependent heart failure.

Long-term administration of rho-kinase inhibitor ameliorates renal damage in malignant hypertensive rats

We have shown recently that fasudil, a Rho-kinase inhibitor, has renoprotective effects in salt-sensitive hypertensive rats. We hypothesized that activation of Rho-kinase is involved in the pathogenesis of glomerulosclerosis in malignant hypertensive rats. To test this hypothesis, we studied the following 4 groups: control Wistar-Kyoto rats, untreated deoxycorticosterone-acetate salt spontaneously hypertensive rats (DOCA-SHR), low-dose fasudil-treated DOCA-SHR, and high-dose fasudil-treated DOCA-SHR. After 3 weeks of treatment, the effects of fasudil were examined. DOCA-SHR was characterized by increased blood pressure (BP); increased kidney weight; decreased renal function; increased proteinuria; abnormal histological findings; increased monocyte/macrophage infiltration; increased urinary 8-isoprostran levels; increased gene expression of collagen I, collagen III, transforming growth factor-beta, and reduced nicotinamide-adenine dinucleotide phosphate oxidase subunits (p40phox, p47phox, and p67phox); and decreased gene expression of endothelial NO synthase (eNOS) in the renal cortex as compared with Wistar-Kyoto rats. Long-term high-dose fasudil treatment significantly improved renal function and histological findings without changing BP, as compared with untreated DOCA-SHR. Interestingly, long-term fasudil treatment significantly decreased monocyte/macrophage infiltration and urinary 8-isoprostran excretion, in association with decreased mRNA levels of transforming growth factor-beta, collagen I, collagen III, and NADPH oxidase subunits (p40phox, p47phox, and p67phox), and increased mRNA levels of eNOS in the renal cortex. Long-term low-dose fasudil treatment tended to improve these variables slightly but did not affect most of them significantly. Our results suggest that long-term fasudil treatment provides renoprotective effects independent of BP-lowering activity. These renoprotective effects are associated with inhibition of extracellular matrix gene expression, monocyte/macrophage infiltration, oxidative stress, and upregulation of eNOS gene expression.

Pathophysiologic and therapeutic implications of adrenomedullin in cardiovascular disorders

Adrenomedullin (AM) is a vasodilator peptide that originally isolated from pheochromocytoma tissue. However, the mRNA is expressed in the normal adrenal gland, heart, kidney and blood vessels. The human AM gene is located in the short arm of chromosome 11 and is composed of 4 exons. There are 2 single nucleotide polymorphisms in introns 1 and 3, and the 3'-end of the AM gene is flanked by a microsatellite marker of cytosine-adenine repeats that is associated with an increased risk of developing hypertension and diabetic nephropathy. AM gene expression is promoted by various stimuli, including inflammation, hypoxia, oxidative stress, mechanical stress and activation of the renin-angiotensin and sympathetic nervous systems. The AM gene promoter region possessed binding site for several transcription factors, including nuclear factor for interleukin-6 expression (NF-IL6) and activator protein 2 (AP-2). Further, plasma AM levels are increased in patients with various cardiovascular diseases, including hypertension, heart failure and renal failure. These findings suggest that AM plays a role in the development of or response to cardiovascular disease. Indeed, experimental and clinical studies have demonstrated that systemic infusion of AM may have a therapeutic effect on myocardial infarction, heart failure and renal failure. Further, vasopeptidase inhibitors which augment the bioactivity of endogenous AM may benefit patients with hypertension and arteriosclerosis. Finally, the angiogenic and cytoprotective properties of AM may have utility in revascularization and infarcted myocardium and ischemic limbs. Because of the potential clinical benefits of AM, indications for use and optimal dosing strategies should be established.

Renoprotective effect of long-term combined treatment with adrenomedullin and omapatrilat in hypertensive rats

BACKGROUND

Previous studies demonstrated that adrenomedullin (AM) is metabolized by neutral endopeptidases and that the renal effect of AM is augmented by the inhibition of neutral endopeptidases. We have recently shown that the long-term administration of AM has renoprotective effects.

OBJECT

This study assessed the chronic renoprotective effects of AM combined with a vasopeptidase inhibitor in hypertensive rats and attempted to elucidate the mechanism involved.

METHODS

We studied the following four groups: control Dahl salt-resistant (DR) rats, untreated Dahl salt-sensitive (DS) rats, omapatrilat (35 mg/kg per day)-treated DS rats; and human AM (500 ng/h) plus omapatrilat-treated DS rats. After 7 weeks' treatment, blood pressure, renal function, neurohumoral factors, gene expression levels, and histological findings were examined.

RESULTS

DS rats were characterized by increased blood pressure, decreased renal function, abnormal histological findings, and increased gene expression of collagen I and III, transforming growth factor beta (TGF-beta), and NADPH oxidase subunits (p40phox, p47phox, and gp91phox) in the renal cortex compared with DR rats. Compared with DS rats, omapatrilat significantly decreased systolic blood pressure (-26 mmHg), improved renal function, histological findings, and messenger RNA expression levels of collagen I, collagen III, and TGF-beta. Combined treatment with omapatrilat and AM further improved renal function, histological findings, and mRNA expression levels of collagen I, collagen III, and TGF-beta, without a further reduction in blood pressure. Only combined treatment decreased mRNA levels of p40phox, p47phox, and gp91phox. There were no differences in plasma AM or atrial natriuretic peptide levels among three DS groups.

CONCLUSION

Our results suggest that combined treatment with omapatrilat and AM provides additional renoprotective effects independent of blood pressure-lowering activity partly via inhibition of gene expressions of oxidative stress and extracellular matrix.

Cardioprotective mechanisms of eplerenone on cardiac performance and remodeling in failing rat hearts

Aldosterone may play a pivotal role in the pathophysiology of heart failure. To elucidate the beneficial cardioprotective mechanism of eplerenone, a novel selective aldosterone blocker, we hypothesized that eplerenone stimulates endothelial NO synthase (eNOS) through Akt and inhibits inducible NO synthase (iNOS) via nuclear factor kappaB (NF-kappaB) after the development of oxidative stress and activation of the lectin-like, oxidized, low-density lipoprotein receptor 1 (LOX-1) pathway in Dahl salt-sensitive rats with heart failure. Eplerenone (10, 30, and 100 mg/kg per day) was given from the age of the left ventricular hypertrophy stage (11 weeks) to the failing stage (18 weeks) for 7 weeks. The left ventricular end-systolic pressure-volume relationship was evaluated using a conductance catheter. Decreased percentage of fractional shortening by echocardiography and end-systolic pressure-volume relationship in failing rats was significantly ameliorated by eplerenone. Downregulated eNOS expression, eNOS and Akt phosphorylation, and NOS activity in failing rats were increased by eplerenone. Upregulated expression of the mineralocorticoid receptor aldosterone synthase (CYP11B2); NAD(P)H oxidase p22phox, p47phox, gp91phox, iNOS, and LOX-1; and activated p65 NF-kappaB, protein kinase CbetaII, c-Src, p44/p42 extracellular signal-regulated kinase, and p70S6 kinase phosphorylation were inhibited by eplerenone. Eplerenone administration resulted in significant improvement of cardiac function and remodeling and upregulation of sarcoplasmic reticulum Ca(2+)-ATPase expression. These findings suggest that eplerenone may have significant therapeutic potential for heart failure, and these cardioprotective mechanisms of eplerenone may be mediated in part by stimulating eNOS through Akt and inhibiting iNOS via NF-kappaB after activation of the oxidative stress-LOX-1 pathway and signal transduction pathway.

Adrenomedullin reduces mesangial cell number and glomerular inflammation in experimental mesangioproliferative glomerulonephritis

BACKGROUND

Adrenomedullin (ADM) is a vasodilator peptide that is abundantly expressed in the kidney. ADM has antiproliferative effects on glomerular mesangial cells (MC) in vitro. Whether or not treatment with ADM can reduce MC proliferation in vivo [i.e., in mesangioproliferative glomerulonephritis (GN)] is unknown. We tested the hypothesis that ADM substitution reduces MC proliferation in GN.

METHODS

GN in rats was induced by injection of an anti-Thy-1.1 antibody. Rats received osmotic minipumps, which continuously delivered rat ADM (500 ng/hour, N = 11), or vehicle (N = 13) from day 3 to day 6 after GN induction. Rats were sacrificed 6 days after induction of GN. On kidney sections, cells staining positive for proliferating cell nuclear antigen, mesangial cells, monocytes, and apoptotic cells were counted. Parameters of inflammation and fibrosis were measured in renal cortex and sieved glomeruli by real-time polymerase chain reaction (PCR).

RESULTS

Systolic blood pressure, diuresis, albuminuria, creatinine clearance, microaneurysm formation, and mesangial matrix expansion were not influenced by ADM infusion. However, ADM treatment significantly reduced the number of MC, showed a tendency to reduce total glomerular cell proliferation, and significantly increased apoptosis. ADM-treated GN animals showed significantly less glomerular monocyte infiltration. ADM treatment normalized transforming growth factor (TGF)-beta1 mRNA expression and reduced monocyte chemoattractant protein-1 (MCP-1), osteopontin, plasminogen activator inhibitor-1 (PAI-1), collagen I, and collagen III mRNA expression significantly.

CONCLUSION

Exogenous ADM infusion reduces MC number and glomerular monocyte infiltration in the state of mesangial proliferation during acute experimental mesangioproliferative GN. These findings indicate that ADM can influence the course of mesangioproliferative GN.

A novel immunosuppressant FTY720 ameliorates proteinuria and alterations of intrarenal adrenomedullin in rats with autoimmune glomerulonephritis

FTY720 has been originally developed as a new immunosuppressive agent, which prolongs graft survival in organ transplantation. Adrenomedullin (AM) participates in the regulation of sodium homeostasis and has renoprotective effects. The possible involvement of renal AM in the pathophysiology of glomerulonephritis (GN) and the effect of FTY720 has been evaluated in rats. HgCl2 (1 mg/kg body weight) was inoculated subcutaneously 3 times/week for a total of 2 weeks. FTY720 (3 or 10 mg/kg) was inoculated subcutaneously daily. The proteinuria, urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion and serum total cholesterol levels were increased and serum albumin level was reduced in rats with HgCl2-induced GN compared with controls. FTY720 reduced proteinuria (3 mg/kg: -25%; 10 mg/kg: -41%), urinary NAG excretion (-11%; -52%) and total cholesterol level (-21%; -55%) in a dose-dependent manner. Renal AM level and its mRNA expression were increased in rats with GN compared with controls (Peptide Cortex: +69%; Medulla: +82%; mRNA Cortex: +25%). Interestingly, FTY720 additionally increased these levels (Peptide Cortex: +38%; Medulla: +39%; mRNA Cortex: +20%). Renal AM levels correlated with urinary NAG excretion and creatinine clearance. These results suggest that FTY720 suppresses the renal damage in rats with GN and renal AM may participate in the pathophysiology of GN and the renoprotective effects of FTY720.

Up-regulated synthesis of mature-type adrenomedullin in coronary circulation immediately after reperfusion in patients with anterior acute myocardial infarction

OBJECTIVE

Levels of adrenomedullin (AM), a potent vasodilatory peptide, have been shown to increase in the early stage of acute myocardial infarction (AMI). The purpose of this study was to determine whether coronary sinus-aortic step-up of mature forms of AM is accelerated in patients with AMI after reperfusion.

METHODS

The subjects were 29 consecutive patients with a first episode of anterior AMI and 10 normal controls. All patients with AMI underwent balloon reperfusion therapy within 24 h after symptom onset. Plasma levels of two molecular forms of AM (an active, mature form [AM-m] and an intermediate, inactive glycine-extended form [AM-Gly]) in the aorta and coronary sinus (CS) were measured by specific immunoradiometric assay after reperfusion.

RESULTS

Plasma levels of AM-m and AM-Gly in the aorta and CS were higher in AMI patients than in controls. CS-aortic step-up of AM-m, which is an index of myocardial production of AM-m, was significantly greater in AMI patients than in controls (1.7 +/- 1.4 vs. 0.4 +/- 0.3 pmol/L, P < 0.01). However, there was no significant difference in CS-aortic step-up of AM-Gly (P = 0.30). AMI patients with left ventricular dysfunction (n = 10) had a significantly higher CS-aortic AM-m step-up than AMI patients without left ventricular dysfunction (n = 19). AM-m in the aorta and CS negatively correlated with the left ventricular ejection fraction (r = -0.50, r = -0.48, P < 0.01).

CONCLUSIONS

Myocardial synthesis of AM-m is accelerated in patients with reperfused AMI, especially in patients with critical left ventricular dysfunction. Increased myocardial synthesis of active AM may protect against cardiac dysfunction, myocardial remodeling, or both after the onset of AMI.

The clinical relevance of adrenomedullin: a promising profile?

Adrenomedullin (AM) is a peptide that possesses potentially beneficial properties. Since the initial discovery of the peptide by Kitamura et al. in 1993, the literature has been awash with reports describing its novel mechanisms of action and huge potential as a therapeutic target. Strong evidence now exists that AM is able to act as an autocrine, paracrine, or endocrine mediator in a number of biologically significant functions, including the endothelial regulation of blood pressure, protection against organ damage in sepsis or hypoxia, and the control of blood volume through the regulation of thirst. Its early promise as a potential mediator/modulator of disease was not, however, entirely as a result of the discovery of physiological functions but due more to the observation of increasing levels measured in plasma in direct correlation with disease progression. In health, AM circulates at low picomolar concentrations in plasma in 2 forms, a mature 52-amino acid peptide and an immature 53-amino acid peptide. Plasma levels of AM have now been shown to be increased in a number of pathological states, including congestive heart failure, sepsis, essential hypertension, acute myocardial infarction, and renal impairment. These earliest associations have been further supplemented with evidence of a role for AM in other pathologies including, most intriguingly, cancer. In this review, we offer a timely review of our current knowledge on AM and give a detailed account of the putative role of AM in those clinical areas in which the best therapeutic opportunities might exist.

Haplotype-Based Case-Control Study Revealing an Association between the Adrenomedullin Gene and Proteinuria in Subjects with Essential Hypertension

Adrenomedullin (AM) has various physiological actions on the cardiovascular system, including vasodilatation, diuresis, natriuresis, inhibition of aldosterone secretion, and increases of the cardiac output, all of which cause hypotension. Since AM plays a role in the pathophysiology of vascular diseases, genes controlling AM might be involved in the development and etiology of essential hypertension (EH). However, there have been few studies examining the relationship between the AM gene and hypertension. The aims of this study were to genotype some of the genetic markers for the human AM gene in Japanese subjects, and via a haplotype-based case-control study, assess the association between and the AM gene and EH or its risk factors, such as hyperlipidemia, renal damage, and proteinuria. We genotyped 205 EH patients and 210 age-matched normotensive (NT) individuals for two single nucleotide polymorphisms of rs4399321, rs7944706 and a microsatellite polymorphism located approximately 5,400 base pairs downstream of the 3' end of the human AM gene. The overall distribution in each variant and haplotype did not significantly differ between the two groups. However, after dividing the groups into those subjects with and without proteinuria, the haplotype analysis revealed a positive association. In conclusion, a possible mutation linked to the haplotype may indicate a genetic predisposition for proteinuria in EH.

Alteration of renal adrenomedullin and its receptor system in the severely hypertensive rat: effect of diuretic

OBJECTIVE

We investigated the pathophysiological role of the renal adrenomedullin (AM) system, including the ligand, receptor, and amidating activity, in severe hypertensive rats.

METHOD

We studied three groups: control Wistar Kyoto rats (WKY), spontaneously hypertensive stroke-prone rats (SHR-SP), and diuretic-treated SHR-SP. We measured AM-mature, active form, and AM-total (active form+inactive form) in plasma and renal tissues, and mRNA levels of AM and AM receptor system components such as calcitonin receptor-like receptor (CRLR), receptor activity-modifying protein (RAMP) 2, and RAMP3 in renal tissues.

RESULTS

SHR-SP had higher blood pressure, plasma neurohumoral factors, and lower renal function than WKY. SHR-SP had higher AM-mature and AM-total levels in plasma and renal tissues than WKY. Although the plasma AM-mature/AM-total ratio was similar in the two groups, AM-mature/AM-total ratio in renal tissues was higher in SHR-SP than in WKY. In addition, mRNA levels of AM in the renal cortex and medulla and the mRNA levels of CRLR, RAMP2, and RAMP3 in the renal cortex were higher in SHR-SP than in WKY. Chronic diuretic treatment decreased blood pressure and improved kidney function and neurohumoral factors, with reductions in plasma and renal AM system.

CONCLUSION

Upregulation of circulating and renal AM system may modulate pathophysiology in SHR-SP.

Fasudil, a Rho-kinase inhibitor, attenuates glomerulosclerosis in Dahl salt-sensitive rats

OBJECTIVE

The present study was designed to clarify whether the Rho-Rho-kinase pathway is involved in the process of hypertensive glomerulosclerosis and to assess the therapeutic effect of fasudil, a specific Rho-kinase inhibitor.

METHOD AND RESULTS

Dahl salt-sensitive rats (DS) and Dahl salt-resistant rats (DR) were fed a high-salt diet at 6 weeks of age. Fasudil (30 mg/kg per day) was administered for 7 weeks to DS starting at the age of 11 weeks. After 7 weeks, untreated DS were characterized by decreased kidney function, increased proteinuria, abnormal morphological findings, increased adrenomedullin and atrial natriuretic peptide (ANP) levels, and increased renal messenger RNA expression of RhoB, Rho-kinasealpha, Rho-kinasebeta, collagen I and collagen III, and transforming growth factor-beta (TGF-beta) in the renal cortex compared with DR. Chronic fasudil treatment significantly improved renal function (serum creatinine, -26%; blood urea nitrogen, -41%; creatinine clearance, +42%), proteinuria (-24%) and histological findings (glomerular injury score, -49%; afferent arteriolar injury score, -17%) without changing blood pressure compared with untreated DS. Interestingly, long-term fasudil treatment decreased the plasma adrenomedullin (-25%) and ANP (-49%), but did not change the plasma renin or aldosterone. Furthermore, fasudil significantly decreased the messenger RNA expression of TGF-beta (-20%), collagen I (-23%), and collagen III (-24%) in the renal cortex. However, there were still significant differences in the aforementioned parameters between DR and fasudil-treated DS.

CONCLUSION

These results suggest that the Rho-Rho-kinase pathway may be partly responsible for the pathogenesis of hypertensive glomerulosclerosis independently of blood pressure in DS, and that chronic inhibition of the Rho-Rho-kinase pathway may be a new strategy for treating hypertensive nephrosclerosis.

Angiogenic effects of adrenomedullin in ischemia and tumor growth

Adrenomedullin (AM) is a novel vasodilating peptide involved in the regulation of circulatory homeostasis and implicated in the pathophysiology of cardiovascular disease. We tested the hypothesis that AM also possesses angiogenic properties. Using laser Doppler perfusion imaging, we found that AM stimulated recovery of blood flow to the affected limb in the mouse hind-limb ischemia model. AM exerted this effect in part by promoting expression of vascular endothelial growth factor (VEGF) in the ischemic limb, and immunostaining for CD31 showed the enhanced flow to reflect increased collateral capillary density. By enhancing tumor angiogenesis, AM also promoted the growth of subcutaneously transplanted sarcoma 180 tumor cells. However, heterozygotic AM knockout mice (AM+/-) showed significantly less blood flow recovery with less collateral capillary development and VEGF expression than their wild-type littermates. Similarly, mice treated with AM22-52, a competitive inhibitor of AM, showed reduced capillary development, and growth of sarcoma 180 tumors was inhibited in AM+/- and AM22-52-treated mice. Notably, administration of VEGF or AM rescued blood flow recovery and capillary formation in AM+/- and AM22-52-treated mice. In cocultures of endothelial cells and fibroblasts, AM enhanced VEGF-induced capillary formation, whereas in cultures of endothelial cells AM enhanced VEGF-induced Akt activation. These results show that AM possesses novel angiogenic properties mediated by its ability to enhance VEGF expression and Akt activity. This may make AM a useful therapeutic tool for relieving ischemia; conversely, inhibitors of AM could be useful for clinical management of tumor growth.

Betaxolol stimulates eNOS production associated with LOX-1 and VEGF in Dahl salt-sensitive rats

OBJECTIVE

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) and vascular endothelial growth factor (VEGF) may play key roles in atherosclerosis, and have been shown to regulate nitric oxide (NO) production. However, the molecular mechanisms by which betaxolol, a specific beta 1-antagonist, stimulates endothelial NO synthase (eNOS) expression associated with LOX-1 and VEGF are unclear. We hypothesized that in the left ventricle of Dahl salt-sensitive (DS) rats, betaxolol reduces production of LOX-1 by suppressing NAD(P)H oxidase p47phox expression; betaxolol stimulates eNOS production associated with expression of VEGF and LOX-1; and betaxolol inhibits adhesion molecule and signal transduction, which may be involved in cardiovascular remodeling.

METHODS

After 5 weeks of feeding an 8% NaCl diet to 6-week-old DS rats (i.e. at 11 weeks of age), a distinct stage of concentric left ventricular hypertrophy was noted. Betaxolol (0.9 mg/kg per day) was administered to 6-week-old DS rats for 5 weeks until the onset of left ventricular hypertrophy stage.

RESULTS

Decreased expression of eNOS and VEGF in DS rats was increased by betaxolol. Upregulated LOX-1, NAD(P)H oxidase p47phox, intercellular and vascular cell adhesion molecule-1 expression and phosphorylations of p38 mitogen-activated protein kinase and p65 nuclear factor-kappa B activity were inhibited by betaxolol. Betaxolol administration resulted in significant improvement of cardiovascular remodeling and suppression of transforming growth factor-beta 1 and type I collagen expression.

CONCLUSIONS

These results suggest that cardioprotective effects of betaxolol may stimulate eNOS production associated with VEGF and LOX-1, and inhibit adhesion molecule and signal transduction in DS rats.

Adrenomedullin modulates hemodynamic and cardiac effects of angiotensin II in conscious rats

We examined whether adrenomedullin, a vasoactive peptide expressed in the heart, modulates the increase in blood pressure, changes in systolic and diastolic function, and left ventricular hypertrophy produced by long-term administration of ANG II or norepinephrine in rats. Subcutaneous administration of adrenomedullin (1.5 μg·kg−1·h−1) for 1 wk inhibited the ANG II-induced (33.3 μg·kg−1·h−1 sc) increase in mean arterial pressure by 67% ( P < 0.001) but had no effect of norepinephrine-induced (300 μg·kg−1·h−1 sc) hypertension. Adrenomedullin enhanced the ANG II-induced improvement in systolic function, resulting in a further 9% increase ( P < 0.01) in the left ventricular ejection fraction and 19% increase ( P < 0.05) in the left ventricular fractional shortening measured by echocardiography, meanwhile norepinephrine-induced changes in systolic function were remained unaffected. Adrenomedullin had no effect on ANG II- or norepinephrine-induced left ventricular hypertrophy or expression of hypertrophy-associated genes, including contractile protein and natriuretic peptide genes. The present study shows that adrenomedullin selectively suppressed the increase in blood pressure and augmented the improvement of systolic function induced by ANG II. Because adrenomedullin had no effects on ANG II- and norepinephrine-induced left ventricular hypertrophy, circulating adrenomedullin appears to act mainly as a regulator of vascular tone and cardiac function.

Mycophenolate mofetil prevents autoimmune glomerulonephritis and alterations of intrarenal adrenomedullin in rats

We studied the effects of mycophenolate mofetil, a specific inhibitor of inosine monophosphate dehydrogenase, on the mercuric chloride induced autoimmune glomerulonephritis in Brown Norway rats and also on the renal contents of adrenomedullin. In the rats with autoimmune glomerulonephritis, plasma and renal tissue adrenomedullin levels were increased significantly. Coadministration of mycophenolate mofetil resulted in prevention of autoimmune glomerulonephritis and also in maintaining of plasma and renal tissue adrenomedullin levels at control levels. Adrenomedullin mRNA expressions in the renal cortex were also higher in the rats with autoimmune glomerulonephritis. Significant positive correlations were found between renal cortical adrenomedullin levels and urinary Na+ and N-acetyl-beta-D-glucosaminidase excretion. A significant negative correlation between renal cortical adrenomedullin levels and creatinine clearance was also found. These results suggest that mycophenolate mofetil suppresses the renal damage in rats with autoimmune glomerulonephritis and renal adrenomedullin may participate in the pathophysiology of autoimmune glomerulonephritis.

Effects of tempol on renal angiotensinogen production in Dahl salt-sensitive rats

We have recently reported that Dahl salt-sensitive rats (DS) on high salt diet (HS) have an inappropriate augmentation of intrarenal angiotensinogen. Recent studies also reported that the augmented superoxide anion formation plays important roles in this animal model of hypertension. This study was performed to address the hypothesis that an inappropriate augmentation of intrarenal angiotensinogen by HS is caused by the augmented reactive oxygen species. Male DS (200-220 g) were maintained on low salt diet LS (N = 7) or HS (N = 27) for 4 weeks. The HS group was subdivided into three subgroups to receive null (N = 12), superoxide dismutase mimetic, tempol (3 mmol/l, N = 8), or vasodilator, hydralazine (0.5 mmol/l, N = 7) in drinking water during the period. Systolic BP was significantly increased in the DS+HS group compared to the DS+LS group (184+/-7 mmHg vs. 107+/-5 at 4-week). Tempol or hydralazine treatment equivalently attenuated the hypertension (128+/-3 and 127+/-5 at 4-week, respectively). Urinary excretion of thiobarbituric acid reactive substances at 4-week was significantly increased in the DS+HS group compared to the DS+LS group (0.66+/-0.05 micromol/day vs. 0.14+/-0.01). Tempol treatment prevented this effect (0.24+/-0.04) but hydralazine treatment only partially prevented the effect (0.40+/-0.03). Kidney angiotensinogen levels, measured by Western blot analysis, were significantly increased in the DS+HS group compared to the DS+LS group (32+/-5 densitometric units vs. 21+/-1). Tempol (14+/-3) but not hydralazine (32+/-5) treatment prevented the intrarenal angiotensinogen augmentation. The evidence suggests that the enhanced intrarenal angiotensinogen in DS challenged with HS is associated with the augmented reactive oxygen species.

Protective effects of endogenous adrenomedullin on cardiac hypertrophy, fibrosis, and renal damage

BACKGROUND

Adrenomedullin (AM) is a novel vasodilating peptide thought to have important effects on cardiovascular function. The aim of this study was to assess the activity of endogenous AM in the cardiovascular system using AM knockout mice.

METHODS AND RESULTS

Mice heterozygous for an AM-null mutation (AM+/-) and their wild-type littermates were subjected to aortic constriction or angiotensin II (Ang II) infusion. The resultant cardiovascular stress led to increases in heart weight/body weight ratios, left ventricular wall thickness, and perivascular fibrosis, as well as expression of genes encoding angiotensinogen, ACE, transforming growth factor-beta, collagen type I, brain natriuretic peptide, and c-fos. In addition, renal damage characterized by decreased creatinine clearance with glomerular sclerosis was noted. In all cases, the effects were significantly more pronounced in AM+/- mice. Hearts from adult mice subjected to aortic constriction showed enhanced extracellular signal-regulated kinase (ERK) activation, as did cardiac myocytes from neonates treated acutely with Ang II. Again the effect was more pronounced in AM+/- mice, which showed increases in cardiac myocyte size, protein synthesis, and fibroblast proliferation. ERK activation was suppressed by protein kinase C inhibition to a greater degree in AM+/- myocytes. In addition, treatment of cardiac myocytes with recombinant AM suppressed Ang II-induced ERK activation via a protein kinase A-dependent pathway.

CONCLUSIONS

Endogenous AM exerts a protective effect against stress-induced cardiac hypertrophy via protein kinase C- and protein kinase A-dependent regulation of ERK activation. AM may thus represent a useful new tool for the treatment of cardiovascular disease.

Elevated BSC-1 and ROMK expression in Dahl salt-sensitive rat kidneys

This study compared the expression of enzymes and transport and channel proteins involved in the regulation of sodium reabsorption in the kidney of Dahl salt-sensitive (DS) and salt-resistant Brown-Norway (BN) and consomic rats (SS.BN13), in which chromosome 13 from the BN rat has been introgressed into the DS genetic background. The expression of the Na+/K+/2Cl- (BSC-1) cotransporter, Na+/H+ exchanger (NHE3), and Na+-K+-ATPase proteins were similar in the renal cortex of DS, BN, and SS.BN13 rats fed either a low-salt (0.1% NaCl) or a high-salt (8% NaCl) diet. The expression of the BSC-1 and the renal outer medullary K+ channel (ROMK) were higher, whereas the expression of the cytochrome P4504A proteins responsible for the formation of 20-hydroxyeicosatetraenoic (20-HETE) was lower in the outer medulla of the kidney of DS than in BN or SS.BN13 rats fed either a low-salt or a high-salt diet. In addition, the renal formation and excretion of 20-HETE was lower in DS than in BN and SS.BN13 rats. These results suggest that overexpression of ROMK and BSC-1 in the thick ascending limb combined with a deficiency in renal formation of 20-HETE may predispose Dahl S rats fed a high-salt diet to Na+ retention and hypertension.

Celiprolol activates eNOS through the PI3K-Akt pathway and inhibits VCAM-1 Via NF-kappaB induced by oxidative stress

Vascular cell adhesion molecule-1 (VCAM-1) and reactive oxygen species play critical roles in early atherogenesis, and nitric oxide (NO) is an important regulator of the cardiovascular system. Although celiprolol, a specific beta1-antagonist with weak beta2-agonistic action, stimulates endothelial nitric oxide synthase (eNOS) production, the mechanisms remain to be determined. Because it was recently reported that phosphatidylinositol 3-kinase (PI3K) and its downstream effector Akt are implicated in the activation of eNOS and that regulation of VCAM-1 expression is mediated via nuclear factor-kappaB (NF-kappaB), we hypothesized that celiprolol activates phosphorylation of eNOS through the PI3K-Akt signaling pathway; that celiprolol modulates VCAM-1 expression, which is associated with inhibiting NF-kappaB phosphorylation; and that celiprolol suppresses NAD(P)H oxidase p22phox, p47phox, gp91phox, and nox1 expression in the left ventricle of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. eNOS and Akt phosphorylation upregulated by celiprolol alone were suppressed by treatment with celiprolol plus wortmannin. Increased expression of VCAM-1, p22phox, p47phox, gp91phox, nox1, activated p65 NF-kappaB, c-Src, p44/p42 extracellular signal-regulated kinases, and their downstream effector p90 ribosomal S6 kinase phosphorylation in DOCA rats was inhibited by celiprolol. Celiprolol administration resulted in a significant improvement in cardiovascular remodeling and suppression of transforming growth factor-beta1 gene expression. In conclusion, celiprolol suppresses VCAM-1 expression because of inhibition of oxidative stress, NF-kappaB, and signal transduction, while increasing eNOS via stimulation of the PI3K-Akt signaling pathway and improving cardiovascular remodeling.