Angiotensin II and oxidative stress in Dahl Salt-sensitive rat with heart failure

Eucommia ulmoides (Tochu) and its extract geniposidic acid reduced blood pressure and improved renal hemodynamics

INTRODUCTION

Eucommia ulmoides leaves are used as Tochu tea, which has a blood pressure lowering effect of unknown mechanism.

PURPOSE AND METHODS

The effects of Tochu tea and its component, geniposidic acid, on blood pressure and renal hemodynamics were investigated in Dahl salt-sensitive (DS) rats received 1% saline solution from 4 weeks of age. At 9 weeks of age, 1% saline alone (DSHS), Tochu tea extract added 1% saline (DSHS+T), or geniposidic acid added 1% saline (DSHS+G) was administered for another 4 weeks. DS rats fed with tap water were used as controls (DSLS). At 13 weeks, the blood pressure, the renal plasma flow (RPF) and the renal NADPH oxidase, endothelial nitric oxide synthase (eNOS) were examined.

RESULTS

Blood pressure in DSHS rats was significantly increased in comparison to DSLS (144 vs. 196 mmHg, p < 0.01), and was significantly reduced in DSHS+T (158 mmHg) and DSHS+G (162 mmHg) rats. RPF in DSHS+T rats was significantly higher than in DSHS rats (p < 0.05). The expression of NADPH oxidase in DSHS rats was enhanced in comparison to DSLS rats; however, it was suppressed in DSHS+T and DSHS+G rats, and the NO production by eNOS was increased; thus, RPF was improved. The urinary Na excretion in DSHS rats was higher than that in DSLS rats; however it was further increased in DSHS+T rats without changes in the tubular Na transporters.

CONCLUSION

Tochu tea and geniposidic acid suppressed NADPH oxidase, increased eNOS, and improved blood pressure and renal hemodynamics.

Cardiorenal syndrome in heart failure with preserved ejection fraction-an under-recognized clinical entity

Cardiorenal syndrome (CRS) results from the complex and bidirectional interaction between the failing heart and the kidneys. Limited information exists about the pathophysiology and treatment options for worsening kidney function in the setting of heart failure with preserved ejection fraction (HFpEF). This review summarizes the salient pathophysiological pathways in CRS in patients with HFpEF, with emphasis on type 1 and type 2 phenotypes, and outlines diagnostic and therapeutic strategies that are applicable in this population. Elevated central venous and intra-abdominal pressure, left ventricular hypertrophy, LV strain, RAAS activation, oxidative injury, pulmonary hypertension, and RV dysfunction play key roles in the pathogenesis of CRS in the backdrop of HFpEF. The availability of biomarkers of renal and cardiac injury offer a new dimension in accurately diagnosing and quantifying end organ damage in CRS and will improve the accuracy of goal-directed therapies in this population. Novel targeted therapies such as the development of angiotensin/neprilysin inhibitors and sodium-glucose cotransporter-2 (SGLT-2) inhibitors offer new territory in realizing potential benefits in reduction of cardio-renal adverse outcomes in this population. Future studies focusing exclusively on renal outcomes in patients with HFpEF are crucial in delivering optimal therapies in this subset of patients.

Therapeutic Suppression of mTOR (Mammalian Target of Rapamycin) Signaling Prevents and Reverses Salt-Induced Hypertension and Kidney Injury in Dahl Salt-Sensitive Rats

mTOR (mammalian target of rapamycin) signaling has emerged as a key regulator in a wide range of cellular processes ranging from cell proliferation, immune responses, and electrolyte homeostasis. mTOR consists of 2 distinct protein complexes, mTORC1 (mTOR complex 1) and mTORC2 (mTOR complex 2) with distinct downstream signaling events. mTORC1 has been implicated in pathological conditions, such as cancer and type 2 diabetes mellitus in humans, and inhibition of this pathway with rapamycin has been shown to attenuate salt-induced hypertension in Dahl salt-sensitive rats. Several studies have found that the mTORC2 pathway is involved in the regulation of renal tubular sodium and potassium transport, but its role in hypertension has remained largely unexplored. In the present study, we, therefore, determined the effect of mTORC2 inhibition with compound PP242 on salt-induced hypertension and renal injury in salt-sensitive rats. We found that PP242 not only completely prevented but also reversed salt-induced hypertension and kidney injury in salt-sensitive rats. PP242 exhibited potent natriuretic actions, and chronic administration tended to produce a negative Na⁺ balance even during high-salt feeding. The results indicate that mTORC2 and the related downstream associated pathways play an important role in regulation of sodium balance and arterial pressure regulation in salt-sensitive rats. Therapeutic suppression of the mTORC2 pathway represents a novel pathway for the potential treatment of hypertension.

Association of Higher Advanced Oxidation Protein Products (AOPPs) Levels in Patients with Diabetic and Hypertensive Nephropathy

Background and Objectives: Diabetes mellitus (DM) and hypertension (HT) are characterized by cell damage caused by inflammatory and metabolic mechanisms induced by alteration in reduction-oxidative status. Serum advanced oxidation protein products (AOPP) are new markers of protein damage induced by oxidative stress. We evaluated serum levels of AOPP in a cohort of patients with DM and HT, with or without renal complications, compared with a control healthy population. Materials and Methods: The study group comprised of 62 patients with type 2 DM and 56 with HT. The 62 patients affected by DM were further distinguished in 24 subjects without renal impairment, 18 with diabetic nephropathy (DN), 20 with chronic kidney disease (CKD) stage 2–3 secondary to DN. The subgroup of 56 patients with primary HT comprised 26 subjects without renal complications and 30 with CKD (stage 2–3) secondary to HT. Thirty healthy controls, matched for age and sex, were recruited among blood donors. Results: Increased AOPP levels were found in DM patients compared with healthy subjects, although not significantly. This index was higher and more significant in patients with DN and CKD secondary to DN than in DM patients without nephropathy (p < 0.05) or controls (p < 0.0001). Patients with HT and with kidney impairment secondary to HT also had significantly higher AOPP serum levels than controls (p < 0.01 and p < 0.0001, respectively). There were no significant differences in mean AOPP levels among DM and HT patients. Conclusion: Our study showed that oxidative stress was higher in diabetic or hypertensive subjects than in healthy controls and, in particular, it appeared to be more severe in patients with renal complications. We suggest that the assessment of AOPP in diabetic and hypertensive patients may be important to predict the onset of renal failure and to open a new perspective on the adoption of antioxidant molecules to prevent CKD in those settings.

Dipeptidyl Peptidase 4 Inhibition Ameliorates Chronic Kidney Disease in a Model of Salt-Dependent Hypertension

Cardiovascular diseases frequently coexist with chronic kidney disease that constitutes a major determinant of outcome in patients with heart failure. Dysfunction of both organs is related to chronic inflammation, endothelial dysfunction, oxidative stress, and fibrosis. Widespread expression of serine protease DPP4 that degrades varieties of substrates suggests its involvement in numerous physiological processes. In this study, we tested the effects of selective DPP4 inhibition on the progression of renal disease in a nondiabetic model of hypertensive heart disease using Dahl salt-sensitive rats. Chronic DPP4 inhibition positively affected renal function with a significant reduction in albuminuria and serum creatinine. DPP4 inhibition attenuated the inflammatory component by reducing the expression of NF-κB, TNFα, IL-1β, IL-6, and MCP-1. Kidney macrophages expressed GLP-1R, and DPP4 inhibition promoted macrophage polarization toward the anti-inflammatory M2 phenotype. Finally, high degrees of NADPH oxidase 4 expression and oxidation of nucleic acids, lipids, and proteins were reduced upon DPP4 inhibition. Our study provides evidence of renoprotection by DPP4 inhibition in a nondiabetic hypertension-induced model of chronic cardiorenal syndrome, indicating that DPP4 pathway remains a valid object to study in the context of chronic multiorgan diseases.

Oxidative Stress and Cardiovascular Complications in Chronic Kidney Disease, the Impact of Anaemia

Patients with chronic kidney disease (CKD) have significant cardiovascular morbidity and mortality as a result of risk factors such as left ventricular hypertrophy (LVH), oxidative stress, and inflammation. The presence of anaemia in CKD further increases the risk of LVH and oxidative stress, thereby magnifying the deleterious consequence in uraemic cardiomyopathy (UCM), and aggravating progression to failure and increasing the risk of sudden cardiac death. This short review highlights the specific cardio-renal oxidative stress in CKD and provides an understanding of the pathophysiology and impact of uraemic toxins, inflammation, and anaemia on oxidative stress.

Reduced secretion of parathyroid hormone and hypocalcemia in systemic heterozygous ATP2B1-null hypertensive mice

The ATP2B1 gene is associated with hypertension. We previously reported that systemic heterozygous ATP2B1-null (ATP2B1^+/−) mice exhibited hypertension due to impaired endothelial nitric oxide synthase (eNOS) activity and decreased nitric oxide (NO) production. The ATP2B1 gene encodes plasma membrane calcium ATPase 1 (PMCA1), which has been thought to regulate only intracellular Ca²⁺ concentration. However, recently, it has been suggested that ATP2B1 works not only at cellular levels, but also throughout the entire body, including in the calcium metabolism, using small intestine-specific ATP2B1 knockout mice. To clarify the roles of ATP2B1 in the entire body and the effects of ATP2B1 on blood pressure, we examined the alterations of calcium related factors in ATP2B1^+/− mice. ATP2B1^+/− mice exhibited hypocalcemia. The expression of ATP2B1 in the kidney and small intestine decreased, and hypercalciuria was confirmed in ATP2B1^+/− mice. The intact-PTH levels were lower, and bone mineral density was increased in these mice. These results suggest that hypocalcemia is mainly a result of inhibited bone resorption without compensation by PTH secretion in the case of ATP2B1 knockout. Moreover, NO production may be affected by reduced PTH secretion, which may cause the increase in vascular contractility in these mice. The ATP2B1 gene is important for not only intra-cellular calcium regulation but also for calcium homeostasis and blood pressure control.

Role of the intrarenal renin-angiotensin system in the progression of renal disease

The intrarenal renin-angiotensin system (RAS) has many well-documented pathophysiologic functions in both blood pressure regulation and renal disease development. Angiotensin II (Ang II) is the major bioactive product of the RAS. It induces inflammation, renal cell growth, mitogenesis, apoptosis, migration, and differentiation. In addition, Ang II regulates the gene expression of bioactive substances and activates multiple intracellular signaling pathways that are involved in renal damage. Activation of the Ang II type 1 (AT1) receptor pathway results in the production of proinflammatory mediators, intracellular formation of reactive oxygen species, cell proliferation, and extracellular matrix synthesis, which in turn facilities renal injury. Involvement of angiotensinogen (AGT) in intrarenal RAS activation and development of renal disease has previously been reported. Moreover, studies have demonstrated that the urinary excretion rates of AGT provide a specific index of the intrarenal RAS status. Enhanced intrarenal AGT levels have been observed in experimental models of renal disease, supporting the concept that AGT plays an important role in the development and progression of renal disease. In this review, we focus on the role of intrarenal RAS activation in the pathophysiology of renal disease. Additionally, we explored the potential of urinary AGT as a novel biomarker of intrarenal RAS status in renal disease.

A high-salt diet enhances leukocyte adhesion in association with kidney injury in young Dahl salt-sensitive rats

Salt-sensitive hypertension is associated with severe organ damage. Generating oxygen radicals is an integral component of salt-induced kidney damage, and activated leukocytes are important in oxygen radical biosynthesis. We hypothesized that a high-salt diet causes the upregulation of immune-related mechanisms, thereby contributing to the susceptibility of Dahl salt-sensitive rats to hypertensive kidney damage. For verifying the hypothesis, we investigated leukocytes adhering to retinal vessels when Dahl salt-sensitive rats were challenged with a high-salt (8% NaCl) diet using acridine orange fluoroscopy and a scanning laser ophthalmoscope. The high-salt diet increased leukocyte adhesion after 3 days and was associated with a significant increase in mRNA biosynthesis of monocyte chemotactic protein-1 and intercellular adhesion molecule-1 (ICAM-1) -related molecules in the kidney. Losartan treatment did not affect increased leukocyte adhesion during the early, pre-hypertensive phase of high salt loading; however, losartan attenuated the adhesion of leukocytes during the hypertensive stage. Moreover, the inhibition of leukocyte adhesion in the pre-hypertensive stage by anti-CD18 antibodies decreased tethering of leukocytes and was associated with the attenuation of functional and morphological kidney damage without affecting blood pressure elevation. In conclusion, a high-salt challenge rapidly increased leukocyte adhesion through the over-expression of ICAM-1. Increased leukocyte adhesion in the pre-hypertensive stage is responsible for subsequent kidney damage in Dahl salt-sensitive rats. Immune system involvement may be a key component that initiates kidney damage in a genetic model of salt-induced hypertension.

Role of Renal Oxidative Stress in the Pathogenesis of the Cardiorenal Syndrome

Renal dysfunction and heart failure commonly co-exist; it is termed the cardiorenal syndrome (CRS). This combination of renal and cardiac impairment presents a substantial clinical challenge and is associated with adverse prognosis. The pathogenesis of the CRS is complex, including chronic activation of the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system, together with reduced renal perfusion. Chronic activation of the RAAS can impair mitochondrial function, and increase mitochondrial derived oxidative stress which in turn can lead to renal injury and sodium and water retention. For example, it has been shown that exogenous Ang II augments renal mitochondrial oxidative stress, reduces GFR and induces albuminuria in rats with heart failure. Administration of Ang II also augmented renal mitochondrial dysfunction in aged mice. Current treatments for CRS, including angiotensin-converting enzyme inhibitors, exert limited renal protection if any at all. Therefore, novel treatments particularly those that can target renal mechanisms downstream to chronic activation of the renal renin-angiotensin system are likely to exert renoprotection in the setting of CRS.

ROS production is increased in the kidney but not in the brain of Dahl rats with salt hypertension elicited in adulthood

Enhanced production of superoxide radicals by nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase in the brain and/or kidney of salt hypertensive Dahl rats has been proposed to participate in the pathogenesis of this form of experimental hypertension. Most information was obtained in young Dahl salt-sensitive (DS) rats subjected to high salt intake prior to sexual maturation. Therefore, the aim of our study was to investigate whether salt hypertension induced in adult DS rats is also accompanied with a more pronounced oxidative stress in the brain or kidney as compared to Dahl salt-resistant (DR) controls. NADPH oxidase activity as well as the content of thiobarbituric acid-reactive substances (TBARS) and conjugated dienes (oxidative index), which indicate a degree of lipid peroxidation, were evaluated in two brain regions (containing either hypothalamic paraventricular nucleus or rostral ventrolateral medulla) as well as in renal medulla and cortex. High salt intake induced hypertension in DS rats but did not modify blood pressure in DR rats. DS and DR rats did not differ in NADPH oxidase-dependent production of ROS, TBARS content or oxidative index in either part of the brain. In addition, high-salt diet did not change significantly any of these brain parameters. In contrast, the enhanced NADPH oxidase-mediated ROS production (without significant signs of increased lipid peroxidation) was detected in the renal medulla of salt hypertensive DS rats. Our findings suggest that there are no signs of enhanced oxidative stress in the brain of adult Dahl rats with salt hypertension induced in adulthood.

A local renal renin-angiotensin system activation via renal uptake of prorenin and angiotensinogen in diabetic rats

The mechanism of activation of local renal renin-angiotensin system (RAS) has not been clarified in diabetes mellitus (DM). We hypothesized that the local renal RAS will be activated via increased glomerular filtration and tubular uptake of prorenin and angiotensinogen in diabetic kidney with microalbuminuria. Streptozotocin (STZ)-induced DM and control rats were injected with human prorenin and subsequently with human angiotensinogen. Human prorenin uptake was increased in podocytes, proximal tubules, macula densa, and cortical collecting ducts of DM rats where prorenin receptor (PRR) was expressed. Co-immunoprecipitation of kidney homogenates in DM rats revealed binding of human prorenin to the PRR and to megalin. The renal uptake of human angiotensinogen was increased in DM rats at the same nephron sites as prorenin. Angiotensin-converting enzyme was increased in podocytes, but decreased in the proximal tubules in DM rats, which may have contributed to unchanged renal levels of angiotensin despite increased angiotensinogen. The systolic blood pressure increased more after the injection of 20 μg of angiotensinogen in DM rats than in controls, accompanied by an increased uptake of human angiotensinogen in the vascular endothelium. In conclusion, endocytic uptake of prorenin and angiotensinogen in the kidney and vasculature in DM rats was contributed to increased tissue RAS and their pressor response to angiotensinogen.

Diagnosis and management of acute heart failure

Acute heart failure (AHF) is a life threatening clinical syndrome with a progressively increasing incidence in general population. Turkey is a country with a high cardiovascular mortality and recent national statistics show that the population structure has turned to an 'aged' population.As a consequence, AHF has become one of the main reasons of admission to cardiology clinics. This consensus report summarizes clinical and prognostic classification of AHF, its worldwide and national epidemiology, diagnostic work-up, principles of approach in emergency department,intensive care unit and ward, treatment in different clinical scenarios and approach in special conditions and how to plan hospital discharge.

Depressor effect of chymase inhibitor in mice with high salt-induced moderate hypertension

The aim of the present study was to determine whether long-term high salt intake in the drinking water induces hypertension in wild-type (WT) mice and whether a chymase inhibitor or other antihypertensive drugs could reverse the increase of blood pressure. Eight-week-old male WT mice were supplied with drinking water containing 2% salt for 12 wk (high-salt group) or high-salt drinking water plus an oral chymase inhibitor (TPC-806) at four different doses (25, 50, 75, or 100 mg/kg), captopril (75 mg/kg), losartan (100 mg/kg), hydrochlorothiazide (3 mg/kg), eplerenone (200 mg/kg), or amlodipine (6 mg/kg). Control groups were given normal water with or without the chymase inhibitor. Blood pressure and heart rate gradually showed a significant increase in the high-salt group, whereas a dose-dependent depressor effect of the chymase inhibitor was observed. There was also partial improvement of hypertension in the losartan- and eplerenone-treated groups but not in the captopril-, hydrochlorothiazide-, and amlodipine-treated groups. A high salt load significantly increased chymase-dependent ANG II-forming activity in the alimentary tract. In addition, the relative contribution of chymase to ANG II formation, but not actual average activity, showed a significant increase in skin and skeletal muscle, whereas angiotensin-converting enzyme-dependent ANG II-forming activity and its relative contribution were reduced by high salt intake. Plasma and urinary renin-angiotensin system components were significantly increased in the high-salt group but were significantly suppressed in the chymase inhibitor-treated group. In conclusion, 2% salt water drinking for 12 wk caused moderate hypertension and activated the renin-angiotensin system in WT mice. A chymase inhibitor suppressed both the elevation of blood pressure and heart rate, indicating a definite involvement of chymase in salt-sensitive hypertension.

The Dahl salt-sensitive rat is a spontaneous model of superimposed preeclampsia

The mechanisms of the pathogenesis of preeclampsia, a leading cause of maternal morbidity and death worldwide, are poorly understood in part due to a lack of spontaneous animal models of the disease. We hypothesized that the Dahl salt-sensitive (S) rat, a genetic model of hypertension and kidney disease, is a spontaneous model of superimposed preeclampsia. The Dahl S was compared with the Sprague-Dawley (SD) rat, a strain with a well-characterized normal pregnancy, and the spontaneously hypertensive rat (SHR), a genetic model of hypertension that does not experience a preeclamptic phenotype despite preexisting hypertension. Mean arterial pressure (MAP, measured via telemetry) was elevated in the Dahl S and SHR before pregnancy, but hypertension was exacerbated during pregnancy only in Dahl S. In contrast, SD and SHR exhibited significant reductions in MAP consistent with normal pregnancy. Dahl S rats exhibited a severe increase in urinary protein excretion, glomerulomegaly, increased placental hypoxia, increased plasma soluble fms-like tyrosine kinase-1 (sFlt-1), and increased placental production of tumor necrosis factor-α (TNF-α). The Dahl S did not exhibit the expected decrease in uterine artery resistance during late pregnancy in contrast to the SD and SHR. Dahl S pups and litter sizes were smaller than in the SD. The Dahl S phenotype is consistent with many of the characteristics observed in human superimposed preeclampsia, and we propose that the Dahl S should be considered further as a spontaneous model to improve our understanding of the pathogenesis of superimposed preeclampsia and to identify and test new therapeutic targets for its treatment.

Protective effects of N-acetylcysteine against monosodium glutamate-induced astrocytic cell death

Monosodium glutamate (MSG) is a flavor enhancer, largely used in the food industry and it was reported to have excitotoxic effects. Higher amounts of MSG consumption have been related with increased risk of many diseases, including Chinese restaurant syndrome and metabolic syndromes in human. This study investigated the protective effects of N-acetylcysteine (NAC) on MSG-induced cytotoxicity in C6 astrocytic cells. MSG (20 mM)-induced reactive oxygen species (ROS) generation and apoptotic cell death were significantly attenuated by NAC (500 μM) pretreatment. NAC effectively inhibited the MSG-induced mitochondrial membrane potential (MMP) loss and intracellular reduced glutathione (GSH) depletion. In addition, NAC significantly attenuated MSG-induced endoplasmic reticulum (ER) stress markers, such as XBP1 splicing and CHOP, PERK, and GRP78 up-regulation. Furthermore, NAC prevented the changes of MSG-induced Bcl-2 expression level. These results suggest that NAC can protect C6 astrocytic cells against MSG-induced oxidative stress, mitochondrial dysfunction, and ER stress.

The physiological role of reversible methionine oxidation

Sulfur-containing amino acids such as cysteine and methionine are particularly vulnerable to oxidation. Oxidation of cysteine and methionine in their free amino acid form renders them unavailable for metabolic processes while their oxidation in the protein-bound state is a common post-translational modification in all organisms and usually alters the function of the protein. In the majority of cases, oxidation causes inactivation of proteins. Yet, an increasing number of examples have been described where reversible cysteine oxidation is part of a sophisticated mechanism to control protein function based on the redox state of the protein. While for methionine the dogma is still that its oxidation inhibits protein function, reversible methionine oxidation is now being recognized as a powerful means of triggering protein activity. This mode of regulation involves oxidation of methionine to methionine sulfoxide leading to activated protein function, and inactivation is accomplished by reduction of methionine sulfoxide back to methionine catalyzed by methionine sulfoxide reductases. Given the similarity to thiol-based redox-regulation of protein function, methionine oxidation is now established as a novel mode of redox-regulation of protein function. This article is part of a Special Issue entitled: Thiol-Based Redox Processes.

Reactive oxygen species in vascular biology: role in arterial hypertension

The cellular metabolism of oxygen generates potentially deleterious reactive oxygen species, including superoxide anion, hydrogen peroxide and hydroxyl radical. Under normal physiologic conditions, the rate and magnitude of oxidant formation is balanced by the rate of oxidant elimination. However, an imbalance between pro-oxidants and antioxidants results in oxidative stress, which is the pathogenic outcome of the overproduction of oxidants that overwhelms the cellular antioxidant capacity. There is growing evidence that increased oxidative stress and associated oxidative damage are mediators of vascular injury in cardiovascular pathologies, including hypertension, atherosclerosis and ischemia-reperfusion. This development has evoked considerable interest because of the possibilities that therapies targeted against reactive oxygen intermediates by decreasing the generation of reactive oxygen species and/or by increasing availability of antioxidants may be useful in minimizing vascular injury. This review focuses on the vascular actions of reactive oxygen species, the role of oxidative stress in vascular damage in hypertension and the therapeutic potential of modulating oxygen radical bioavailability in hypertension. In particular, the following topics will be highlighted: chemistry and sources of reactive oxygen species, antioxidant defense mechanisms, signaling events mediated by reactive oxygen species, role of reactive oxygen species in hypertension and the putative therapeutic role of antioxidants in cardiovascular disease.

Pathogenesis of chronic cardiorenal syndrome: is there a role for oxidative stress?

Cardiorenal syndrome is a frequently encountered clinical condition when the dysfunction of either the heart or kidneys amplifies the failure progression of the other organ. Complex biochemical, hormonal and hemodynamic mechanisms underlie the development of cardiorenal syndrome. Both in vitro and experimental studies have identified several dysregulated pathways in heart failure and in chronic kidney disease that lead to increased oxidative stress. A decrease in mitochondrial oxidative metabolism has been reported in cardiomyocytes during heart failure. This is balanced by a compensatory increase in glucose uptake and glycolysis with consequent decrease in myocardial ATP content. In the kidneys, both NADPH oxidase and mitochondrial metabolism are important sources of TGF-β1-induced cellular ROS. NOX-dependent oxidative activation of transcription factors such as NF-kB and c-jun leads to increased expression of renal target genes (phospholipaseA2, MCP-1 and CSF-1, COX-2), thus contributing to renal interstitial fibrosis and inflammation. In the present article, we postulate that, besides contributing to both cardiac and renal dysfunction, increased oxidative stress may also play a crucial role in cardiorenal syndrome development and progression. In particular, an imbalance between the renin-angiotensin-aldosterone system, the sympathetic nervous system, and inflammation may favour cardiorenal syndrome through an excessive oxidative stress production. This article also discusses novel therapeutic strategies for their potential use in the treatment of patients affected by cardiorenal syndrome.

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.

Association between renal vasculature changes and generalized atherosclerosis: an autopsy survey

AIM

To examine the association between renal vasculature changes and generalized atherosclerosis using autopsy cases.

METHODS

We histologically examined 107 autopsy patients(mean age, 68.4 years; 64% men; 81% non-CVD) to investigate the association between renal vasculature changes and generalized atherosclerosis. We measured the intima/media(I/M) ratio for the renal, intrarenal and systemic arteries(coronary, cerebral, common carotid and common iliac), calculated the rates of arteriolar hyalinization and global glomerulosclerosis and evaluated the frequency of advanced lesions(AHA classification ≥IV) in the systemic arteries.

RESULTS

The I/M ratios of the renal and intrarenal arteries and the rate of global glomerulosclerosis increased with age, while the rates of arteriolar hyalinization and global glomerulosclerosis were associated with diabetes and hypertension(all p＜0.05). The I/M ratio of the coronary artery was independently associated with the rate of global glomerulosclerosis(p＜0.05). The frequency of advanced atherosclerotic lesions in the coronary and cerebral arteries was also correlated with the I/M ratio of the renal artery and rates of arteriolar hyalinization and global glomerulosclerosis(all p＜0.05). The frequency of advanced lesions in the cerebral and common carotid arteries was independently associated with the I/M ratio of the renal artery and the rate of renal arteriolar hyalinization(odds ratio(OR) with [95% confidence interval]; 5.09 [1.15-27.9] and 4.11 [1.38-13.9], respectively).

CONCLUSIONS

The results of this study demonstrated that pathological changes in four portions of the renal vasculature differ. Renal vasculature changes except the intrarenal arteries were significantly associated with those observed in the cerebral, common carotid and coronary arteries.

Rutin and quercetin show greater efficacy than nifedipin in ameliorating hemodynamic, redox, and metabolite imbalances in sodium chloride-induced hypertensive rats

Rutin and quercetin were investigated for their effects on blood pressure and antioxidant defense system of rats fed with 8% sodium chloride-supplemented diet (high salt diet) for 6 weeks. Animals fed with high salt diet demonstrated an increase in systolic, diastolic, pulse, and mean arterial blood pressures (p < 0.05) as well as lipid peroxidation but decreases in the activities of antioxidant enzymes compared with control group. Groups post-treated with rutin and quercetin for 2 weeks showed significant reversals in the values of these indices compared with the group fed with only the high salt diet but not post-treated. The high salt diet also led to significant increase in serum glucose, urea, creatinine, triglycerides, low-density-lipoprotein, and total cholesterol concentrations. Treatment with rutin and quercetin ameliorated the effects of high salt diet on these biochemical indices. The reference standard, nifedipin was less effective than rutin and quercetin. The results of this study highlight the risk of high salt consumption on cardiovascular health and the potent antioxidant and antihypertensive property of rutin and quercetin.

Redox signaling is an early event in the pathogenesis of renovascular hypertension

Activation of the renin-angiotensin-aldosterone system plays a critical role in the development of chronic renal damage in patients with renovascular hypertension. Although angiotensin II (Ang II) promotes oxidative stress, inflammation, and fibrosis, it is not known how these pathways intersect to produce chronic renal damage. We tested the hypothesis that renal parenchymal cells are subjected to oxidant stress early in the development of RVH and produce signals that promote influx of inflammatory cells, which may then propagate chronic renal injury. We established a reproducible murine model of RVH by placing a tetrafluoroethylene cuff on the right renal artery. Three days after cuff placement, renal tissue demonstrates no histologic abnormalities despite up regulation of both pro- and anti-oxidant genes. Mild renal atrophy was observed after seven days and was associated with induction of Tnfα and influx of CD3⁺ T cells and F4/80⁺ macrophages. By 28 days, kidneys developed severe renal atrophy with interstitial inflammation and fibrosis, despite normalization of plasma renin activity. Based on these considerations, we propose that renal parenchymal cells initiate a progressive cascade of events leading to oxidative stress, interstitial inflammation, renal fibrosis, and atrophy.

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.

Combination therapy with an angiotensin-converting-enzyme inhibitor and an angiotensin II receptor antagonist ameliorates microinflammation and oxidative stress in patients with diabetic nephropathy

Aims/Introduction

Recent studies have pointed to the effectiveness of combination therapy with an angiotensin‐converting‐enzyme inhibitor (ACEI) and an angiotensin receptor blocker (ARB) for diabetic nephropathy. However, some controversy over this combination treatment remains and the mechanisms underlying its renoprotective effects have not been fully clarified. Therefore, we compared the renoprotective effects of imidapril (ACEI) and losartan (ARB) combination therapy with losartan monotherapy in patients with diabetic nephropathy. We also compared the anti‐inflammatory and anti‐oxidative stress effects of these two treatments.

Materials and Methods

A total of 32 Japanese patients with type 2 diabetes and nephropathy were enrolled. Patients were randomized to either 100 mg/day losartan (n = 16) or 50 mg/day losartan plus 5 mg/day imidapril (n = 16). We evaluated clinical parameters, serum concentrations of high‐sensitivity C‐reactive protein (hs‐CRP), soluble intercellular adhesion molecule‐1 (sICAM‐1), interleukin‐18 (IL‐18) and monocyte chemotactic protein‐1 (MCP‐1), and the urinary concentrations of IL‐18, MCP‐1 and 8‐hydroxy‐2′‐deoxyguanosine (8‐OHdG) at 24 and 48 weeks after starting treatment.

Results

Blood pressure was not significantly different between the two groups. The serum levels of hs‐CRP, sICAM‐1 and IL‐18, as well as urinary excretion of albumin, IL‐18 and 8‐OHdG decreased significantly in the combination therapy group at 48 weeks. The percent decreases in serum IL‐18 concentrations and urinary IL‐18 and 8‐OHdG were significantly greater in the combination therapy group than in the monotherapy group.

Conclusions

Combination therapy with an ACEI and an ARB could be beneficial for treating diabetic nephropathy through its anti‐inflammatory and anti‐oxidative stress effects.

Ramipril attenuates lipid peroxidation and cardiac fibrosis in an experimental model of rheumatoid arthritis

INTRODUCTION

Recent studies revealed that co-morbidity and mortality due to cardiovascular disease are increased in patients with rheumatoid arthritis (RA) but little is known about factors involved in these manifestations. This study aimed at characterizing the impact of arthritis on oxidative stress status and tissue fibrosis in the heart of rats with adjuvant-induced arthritis (AIA).

METHODS

AIA was induced with complete Freund's adjuvant in female Lewis rats. Animals were treated by oral administration of vehicle or angiotensin-converting enzyme inhibitor ramipril (10 mg/kg/day) for 28 days, beginning 1 day after arthritis induction. Isolated adult cardiomyocytes were exposed to 10 μM 4-hydroxynonenal (HNE) for 24 hours in the presence or absence of 10 μM ramipril.

RESULTS

Compared to controls, AIA rats showed significant 55 and 30% increase of 4-HNE/protein adducts in serum and left ventricular (LV) tissues, respectively. Cardiac mitochondrial NADP+-isocitrate dehydrogenase (mNADP-ICDH) activity decreased by 25% in AIA rats without any changes in its protein and mRNA expression. The loss of mNADP-ICDH activity was correlated with enhanced accumulation of HNE/mNADP-ICDH adducts as well as with decrease of glutathione and NADPH. Angiotensin II type 1 receptor (AT1R) expression and tissue fibrosis were induced in LV tissues from AIA rats. In isolated cardiomyocytes, HNE significantly decreased mNADP-ICDH activity and enhanced type I collagen and connective tissue growth factor expression. The oral administration of ramipril significantly reduced HNE and AT1R levels and restored mNADP-ICDH activity and redox status in LV tissues of AIA rats. The protective effects of this drug were also evident from the decrease in arthritis scoring and inflammatory markers.

CONCLUSION

Collectively, our findings disclosed that AIA induced oxidative stress and fibrosis in the heart. The fact that ramipril attenuates inflammation, oxidative stress and tissue fibrosis may provide a novel strategy to prevent heart diseases in RA.

Diuretics in heart failure: practical considerations

This review discusses the role of diuretics in heart failure by focusing on different classifications and mechanisms of action. Pharmacodynamic and pharmacokinetic properties of diuretics are elucidated. The predominant discussion highlights the use of loop diuretics, which are the most commonly used drugs in heart failure. Different methods of using this therapy in different settings along with a comprehensive review of the side-effect profile are highlighted. Special situations necessitating adjustment and the phenomenon of diuretic resistance are explained.

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.

Oxidative stress-mediated effects of angiotensin II in the cardiovascular system

Angiotensin II (Ang II), an endogenous peptide hormone, plays critical roles in the pathophysiological modulation of cardiovascular functions. Ang II is the principle effector of the renin-angiotensin system for maintaining homeostasis in the cardiovascular system, as well as a potent stimulator of NAD(P)H oxidase, which is the major source and primary trigger for reactive oxygen species (ROS) generation in various tissues. Recent accumulating evidence has demonstrated the importance of oxidative stress in Ang II-induced heart diseases. Here, we review the recent progress in the study on oxidative stress-mediated effects of Ang II in the cardiovascular system. In particular, the involvement of Ang II-induced ROS generation in arrhythmias, cell death/heart failure, ischemia/reperfusion injury, cardiac hypertrophy and hypertension are discussed. Ca²⁺/calmodulin-dependent protein kinase II is an important molecule linking Ang II, ROS and cardiovascular pathological conditions.

Early apoptosis in different models of cardiac hypertrophy induced by high renin-angiotensin system activity involves CaMKII

The objective of this study was to establish whether 1) hyperactivity of renin-angiotensin-aldosterone system (RAAS) produces apoptosis in early stages of cardiac disease; and 2) Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) is involved in these apoptotic events. Two models of hypertrophy were used at an early stage of cardiac disease: spontaneously hypertensive rats (SHR) and isoproterenol-treated rats (Iso-rats). At 4 mo, SHR showed blood pressure, aldosterone serum levels, used as RAAS activity index, and left ventricular mass index, used as hypertrophy index, above control values by 84.2 ± 2.6 mmHg, 211.2 ± 25.8%, and 8.6 ± 1.1 mg/mm, respectively. There was also an increase in apoptotis (Bax-to-Bcl-2 ratio and terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling positive cells) associated with an enhancement of CaMKII activity with respect to age-matched controls (phosphorylated-CaMKII, 98.7 ± 14.1 above control). Similar results were observed in 4-mo-old Iso-rats. Cardiac function studied by echocardiography remained unaltered in all groups. Enalapril treatment significantly prevented hypertrophy, apoptosis, and CaMKII activity. Moreover, intracellular Ca(2+) handling in isolated myocytes was similar between SHR, Iso-rats, and their aged-matched controls. However, SHR and Iso-rats showed a significant increase in superoxide anion generation (lucigenin) and lipid peroxidation (thiobarbituric acid reactive substance). In transgenic mice with targeted cardiomyocyte expression of a CaMKII inhibitory peptide (AC3-I) or a scrambled control peptide (AC3-C), Iso treatment increased thiobarbituric acid reactive substance in both strains, whereas it increased CaMKII activity and apoptosis only in AC3-C mice. Endogenous increases in RAAS activity induce ROS and CaMKII-dependent apoptosis in vivo. CaMKII activation could not be associated with intracellular Ca(2+) increments and was directly related to the increase in oxidative stress.

Heart angiotensin II-induced cardiomyocyte hypertrophy suppresses coronary angiogenesis and progresses diabetic cardiomyopathy

To examine whether and how heart ANG II influences the coordination between cardiomyocyte hypertrophy and coronary angiogenesis and contributes to the pathogenesis of diabetic cardiomyopathy, we used Spontaneously Diabetic Torii (SDT) rats treated without and with olmesartan medoxomil (an ANG II receptor blocker). In SDT rats, left ventricular (LV) ANG II, but not circulating ANG II, increased at 8 and 16 wk after diabetes onset. SDT rats developed LV hypertrophy and diastolic dysfunction at 8 wk, followed by LV systolic dysfunction at 16 wk, without hypertension. The SDT rat LV exhibited cardiomyocyte hypertrophy and increased hypoxia-inducible factor-1α expression at 8 wk and to a greater degree at 16 wk and interstitial fibrosis at 16 wk only. In SDT rats, coronary angiogenesis increased with enhanced capillary proliferation and upregulation of the angiogenic factor VEGF at 8 wk but decreased VEGF with enhanced capillary apoptosis and suppressed capillary proliferation despite the upregulation of VEGF at 16 wk. In SDT rats, the phosphorylation of VEGF receptor-2 increased at 8 wk alone, whereas the expression of the antiangiogenic factor thrombospondin-1 increased at 16 wk alone. All these events, except for hyperglycemia or blood pressure, were reversed by olmesartan medoxomil. These results suggest that LV ANG II in SDT rats at 8 and 16 wk induces cardiomyocyte hypertrophy without affecting hyperglycemia or blood pressure, which promotes and suppresses coronary angiogenesis, respectively, via VEGF and thrombospondin-1 produced from hypertrophied cardiomyocytes under chronic hypoxia. Thrombospondin-1 may play an important role in the progression of diabetic cardiomyopathy in this model.

Secreted klotho and chronic kidney disease

Soluble Klotho (sKl) in the circulation can be generated directly by alterative splicing of the Klotho transcript or the extracellular domain of membrane Klotho can be released from membrane-anchored Klotho on the cell surface. Unlike membrane Klotho which functions as a coreceptor for fibroblast growth factor-23 (FGF23), sKl, acts as hormonal factor and plays important roles in anti-aging, anti-oxidation, modulation of ion transport, and Wnt signaling. Emerging evidence reveals that Klotho deficiency is an early biomarker for chronic kidney diseases as well as a pathogenic factor. Klotho deficiency is associated with progression and chronic complications in chronic kidney disease including vascular calcification, cardiac hypertrophy, and secondary hyperparathyroidism. In multiple experimental models, replacement of sKl, or manipulated up-regulation of endogenous Klotho protect the kidney from renal insults, preserve kidney function, and suppress renal fibrosis, in chronic kidney disease. Klotho is a highly promising candidate on the horizon as an early biomarker, and as a novel therapeutic agent for chronic kidney disease.

CaMKII in the cardiovascular system: sensing redox states

The multifunctional Ca(2+)- and calmodulin-dependent protein kinase II (CaMKII) is now recognized to play a central role in pathological events in the cardiovascular system. CaMKII has diverse downstream targets that promote vascular disease, heart failure, and arrhythmias, so improved understanding of CaMKII signaling has the potential to lead to new therapies for cardiovascular disease. CaMKII is a multimeric serine-threonine kinase that is initially activated by binding calcified calmodulin (Ca(2+)/CaM). Under conditions of sustained exposure to elevated Ca(2+)/CaM, CaMKII transitions into a Ca(2+)/CaM-autonomous enzyme by two distinct but parallel processes. Autophosphorylation of threonine-287 in the CaMKII regulatory domain "traps" CaMKII into an open configuration even after Ca(2+)/CaM unbinding. More recently, our group identified a pair of methionines (281/282) in the CaMKII regulatory domain that undergo a partially reversible oxidation which, like autophosphorylation, prevents CaMKII from inactivating after Ca(2+)/CaM unbinding. Here we review roles of CaMKII in cardiovascular disease with an eye to understanding how CaMKII may act as a transduction signal to connect pro-oxidant conditions into specific downstream pathological effects that are relevant to rare and common forms of cardiovascular disease.

Selective Rac1 inhibition protects renal tubular epithelial cells from oxalate-induced NADPH oxidase-mediated oxidative cell injury

Oxalate-induced oxidative cell injury is one of the major mechanisms implicated in calcium oxalate nucleation, aggregation and growth of kidney stones. We previously demonstrated that oxalate-induced NADPH oxidase-derived free radicals play a significant role in renal injury. Since NADPH oxidase activation requires several regulatory proteins, the primary goal of this study was to characterize the role of Rac GTPase in oxalate-induced NADPH oxidase-mediated oxidative injury in renal epithelial cells. Our results show that oxalate significantly increased membrane translocation of Rac1 and NADPH oxidase activity of renal epithelial cells in a time-dependent manner. We found that NSC23766, a selective inhibitor of Rac1, blocked oxalate-induced membrane translocation of Rac1 and NADPH oxidase activity. In the absence of Rac1 inhibitor, oxalate exposure significantly increased hydrogen peroxide formation and LDH release in renal epithelial cells. In contrast, Rac1 inhibitor pretreatment, significantly decreased oxalate-induced hydrogen peroxide production and LDH release. Furthermore, PKC α and δ inhibitor, oxalate exposure did not increase Rac1 protein translocation, suggesting that PKC resides upstream from Rac1 in the pathway that regulates NADPH oxidase. In conclusion, our data demonstrate for the first time that Rac1-dependent activation of NADPH oxidase might be a crucial mechanism responsible for oxalate-induced oxidative renal cell injury. These findings suggest that Rac1 signaling plays a key role in oxalate-induced renal injury, and may serve as a potential therapeutic target to prevent calcium oxalate crystal deposition in stone formers and reduce recurrence.

Salt-induced hemodynamic regulation mediated by nitric oxide

Excess daily salt intake impairs vasodilatation and enhances vasoconstriction, resulting in reduction of regional blood flow and elevation of blood pressure in healthy individuals and hypertensive patients with either salt sensitivity or not tested for salt sensitivity or not evaluated for salt sensitivity. The mechanism may involve decreased production of nitric oxide via endothelial nitric oxide synthase (eNOS), impaired bioavailability of nitric oxide, and elevated plasma levels of asymmetric dimethylarginine (ADMA). Experimental animals, irrespective of salt sensitivity, although less extensive in those with salt-resistance, fed a high-salt diet have deteriorated endothelial functions; the mechanisms involved include an impairment of eNOS activation, a decrease in eNOS expression, and an increase in oxidative stress and ADMA. The imbalance of interactions between nitric oxide and angiotensin II is also involved in salt sensitivity. Deficiency of nitric oxide formed via neuronal NOS and inducible NOS may contribute to salt-induced hypertension. Reduced daily salt intake, therefore, would be the most rational prophylactic measure against the development of hypertension.

Strategies for the prevention of contrast-induced acute kidney injury

PURPOSE OF REVIEW

The intravascular administration of iodinated contrast media for diagnostic imaging is a common cause of acute kidney injury and a leading cause of iatrogenic renal disease. The purpose of this review is to describe the principal risk factors for contrast-induced acute kidney injury and to summarize recent data describing the efficacy of various preventive interventions for this condition.

RECENT FINDINGS

Whereas earlier studies suggested that certain low-osmolal contrast agents including iohexol and ioxaglate are more nephrotoxic than iso-osmolal iodixanol, recent clinical trials and meta-analyses comparing other low-osmolal contrast agents with iodixanol have found little difference in risk. The provision of prophylactic renal replacement therapy does not ameliorate the risk of contrast-induced acute kidney injury, and likely poses undue risk. Despite some research supporting a benefit of atrial natriuretic peptide, statins, and prostaglandin analogs, additional data from large, adequately powered studies are needed before these agents can be recommended. N-Acetylcysteine and isotonic intravenous bicarbonate have been investigated intensely, yet the data on these interventions are conflicting due to methodological limitations in past studies.

SUMMARY

Prevention of contrast-induced acute kidney injury involves the identification of high-risk patients, consideration of alternative imaging procedures that do not involve the administration of iodinated contrast, and integration of the cumulative data available on preventive interventions in high-risk patients.

Reactive oxygen species and the pathogenesis of radiocontrast-induced nephropathy

Experimental findings in vitro and in vivo illustrate enhanced hypoxia and the formation of reactive oxygen species (ROS) within the kidney following the administration of iodinated contrast media, which may play a role in the development of contrast media-induced nephropathy. Clinical studies indeed support this possibility, suggesting a protective effect of ROS scavenging or reduced ROS formation with the administration of N-acetyl cysteine and bicarbonate infusion, respectively. Furthermore, most risk factors, predisposing to contrast-induced nephropathy are prone to enhanced renal parenchymal hypoxia and ROS formation. In this review, the association of renal hypoxia and ROS-mediated injury is outlined. Generated during contrast-induced renal parenchymal hypoxia, ROS may exert direct tubular and vascular endothelial injury and might further intensify renal parenchymal hypoxia by virtue of endothelial dysfunction and dysregulation of tubular transport. Preventive strategies conceivably should include inhibition of ROS generation or ROS scavenging.

Therapeutic strategies for heart failure in cardiorenal syndromes

Cardiorenal syndromes are disorders of the heart and kidneys whereby acute or long-term dysfunction in one organ may induce acute or long-term dysfunction of the other. The management of cardiovascular diseases and risk factors may influence, in a beneficial or harmful way, kidney function and progression of kidney injury. In this review, we assess therapeutic strategies and discuss treatment options for the management of patients with heart failure with decreased kidney function and highlight the need for future high-quality studies in patients with coexisting heart and kidney disease.

Ramipril mitigates radiation-induced impairment of neurogenesis in the rat dentate gyrus

BACKGROUND

Sublethal doses of whole brain irradiation (WBI) are commonly administered therapeutically and frequently result in late delayed radiation injuries, manifesting as severe and irreversible cognitive impairment. Neural progenitors within the subgranular zone (SGZ) of the dentate gyrus are among the most radiosensitive cell types in the adult brain and are known to participate in hippocampal plasticity and normal cognitive function. These progenitors and the specialized SZG microenvironment required for neuronal differentiation are the source of neurogenic potential in the adult dentate gyrus, and provide a continuous supply of immature neurons which may then migrate into the adjacent granule cell layer to become mature granule cell neurons. The extreme radiosensitivity of these progenitors and the SGZ microenvironment suggests the hippocampus as a prime target for radiation-induced cognitive impairment. The brain renin-angiotensin system (RAS) has previously been implicated as a potent modulator of neurogenesis within the SGZ and selective RAS inhibitors have been implicated as mitigators of radiation brain injury. Here we investigate the angiotensin converting enzyme (ACE) inhibitor, ramipril, as a mitigator of radiation injury in this context.

METHODS

Adult male Fisher 344 rats received WBI at doses of 10 Gy and 15 Gy. Ramipril was administered beginning 24 hours post-WBI and maintained continuously for 12 weeks.

RESULTS

Ramipril produced small but significant reductions in the deleterious effects of radiation on progenitor proliferation and neuronal differentiation in the rat dentate gyrus following 10 Gy-WBI, but was not effective following 15 Gy-WBI. Ramipril also reduced the basal rate of neurogenesis within the SGZ in unirradiated control rats.

CONCLUSIONS

Our results indicate that chronic ACE inhibition with ramipril, initiated 24 hours post-irradiation, may reduce apoptosis among SGZ progenitors and/or inflammatory disruption of neurogenic signaling within SGZ microenvironment, and suggest that angiotensin II may participate in maintaining the basal rate of granule cell neurogenesis.

Silent Partner in Blood Vessel Homeostasis? Pervasive Role of Nitric Oxide in Vascular Disease

The endothelium generates powerful mediators that regulate blood flow, temper inflammation and maintain a homeostatic environment to prevent both the initiation and progression of vascular disease. Nitric oxide (NO) is arguably the single most influential molecule in terms of dictating blood vessel homeostasis. In addition to direct effects associated with altered NO production (e.g. vasoconstriction, excessive inflammation, endothelial dysfunction), NO is a critical modulator of vaso-relevant pathways including cyclooxygenase (COX)-derived prostaglandin production and angiotensin II generation by the renin-angiotensin system. Furthermore, NO may influence the selectivity of COX-2 inhibitors and ultimately contribute to controversies associated with the use of these drugs. Consistent with a central role for NO in vascular disease, disruptions in the production and bioavailability of NO have been linked to hypertension, diabetes, hypercholesterolemia, obesity, aging, and smoking. The ability of the vessel wall to control disease-associated oxidative stress may be the most critical determinant in maintaining homeostatic levels of NO and subsequently the prospect of stroke, myocardial infarction and other CV abnormalities. To this end, investigation of mechanisms that alter the balance of protective mediators, including pathways that are indirectly modified by NO, is critical to the development of effective therapy in the treatment of CV disease.

Thiol antioxidants regulate angiotensin II AT1 and arginine vasopressin V1 receptor functions differently in vascular smooth muscle cells

BACKGROUND

We compared the effects of the sulfhydryl-containing (thiol) antioxidant dithiothreitol (DTT), which disrupts disulfide bonds, on cell signaling through angiotensin II (AngII) Type 1 receptors (AT1Rs) and arginine vasopressin (AVP) V1 receptors (V1Rs). The AT1R contains two extracellular disulfides bonds but its ligand contains none, whereas the V1R contains no extracellular disufides bonds but its ligand contains 1.

METHODS

We measured radioligand binding, intracellular calcium responses, and extracellular signal-regulated kinase phosphorylation in cultured rat aortic vascular smooth muscle cells and alterations in urine osmolality in intact rats.

RESULTS

Preincubation of cells with DTT, a maneuver designed to target receptor disulfides, resulted in concentration-dependent decreases in specific (125)I-AngII binding to AT1Rs and acute angiotensin-stimulated intracellular calcium mobilization but no decreases in specific (125)I-AVP binding to V1Rs or AVP-stimulated intracellular calcium mobilization. In contrast, preincubation of the ligands with DTT followed by acute exposure to the cells, a maneuver designed to target ligand disulfides, blunted calcium mobilization to AVP robustly but to AngII only minimally. In intact rats, the increase in urine osmolality caused by subcutaneous injection with the AVP analogue desmopressin was significantly diminished when the analogue was preincubated with an excess of DTT.

CONCLUSION

DTT inhibits cell signaling to AngII AT1Rs and AVP V1Rs, at least in part through disruption of disulfide linkages, but the pattern of response depends upon whether disulfides of ligand or receptor are targeted.