Variation of intrarenal angiotensin II and angiotensin II receptors by acute renal ischemia in the aged rat

Extracellular matrix roles in cardiorenal fibrosis: Potential therapeutic targets for CVD and CKD in the elderly

Whereas hypertension, diabetes, and dyslipidemia are age-related risk factors for cardiovascular disease (CVD) and chronic kidney disease (CKD), aging alone is an independent risk factor. With advancing age, the heart and kidney gradually but significantly undergo inflammation and subsequent fibrosis, which eventually results in an irreversible decline in organ physiology. Through cardiorenal network interactions, cardiac dysfunction leads to and responds to renal injury, and both facilitate aging effects. Thus, a comprehensive strategy is needed to evaluate the cardiorenal aging network. Common hallmarks shared across systems include extracellular matrix (ECM) accumulation, along with upregulation of matrix metalloproteinases (MMPs) including MMP-9. The wide range of MMP-9 substrates, including ECM components and inflammatory cytokines, implicates MMP-9 in a variety of pathological and age-related processes. In particular, there is strong evidence that inflammatory cell-derived MMP-9 exacerbates cardiorenal aging. This review explores the potential therapeutic targets against CVD and CKD in the elderly, focusing on ECM and MMP roles.

Sodium-pump gene-expression, protein abundance and enzyme activity in isolated nephron segments of the aging rat kidney

Aging is associated with alteration in renal tubular functions, including sodium handling and concentrating ability. Na-K-ATPase plays a key role in driving tubular transport, and we hypothesized that decreased concentrating ability of the aging kidney is due in part to downregulation of Na-K-ATPase. In this study, we evaluated Na and K balance, aldosterone levels, and Na-K-ATPase gene expression, protein abundance, and activity in aging rat kidney. Na-K-ATPase activity (assayed microfluorometrically), mRNA (RT-PCR), and protein abundance (immunoblotting) were quantitated in the following isolated nephron segments: PCT, PST, MTAL, DCT, and CCD from 2, 8, 15, and 24 month-old-rats. In the course of aging, creatinine clearance decreased from 0.48 ± 0.02 mL/min/100 g BW to 0.28 ± 0.06 (P < 0.001) and aldosterone decreased from 23.6 ± 0.8 ng/dL to 13.2 ± 0.6 (P < 0.001). Serum Na⁺ and K⁺ increased by 4.0% and 22.5%, respectively. Na-K-ATPase activity, mRNA, and protein abundance of the α₁ subunit displayed similar trends in all assayed segments; increasing in PCT and PST; decreasing in MTAL and DCT; increasing in CCD: in PCT they increased by 40%, 75%, and 250%, respectively; while in PST they increased by 80%, 50%, and 100%, respectively (P < 0.001). In MTAL they declined by 36%, 24%, and 34%, respectively, and in DCT by 38%, 59%, and 60%, respectively (P < 0.001). They were higher in CCD by 110%, 115%, and 246%, respectively (P < 0.001). Rats maintained Na/K balance; however with a steady state elevated serum K⁺. These results reveal quantitative changes in axial distribution of Na-K-ATPase at the level of gene expression, protein abundance, and activity in the nephrons of aging animals and may explain, in part, the pathophysiology of the senescent kidney.

Aged rats are susceptible to nephrotoxicity induced by iodinated contrast media

OBJECTIVE

The objective of this study is to evaluate the effect and mechanism of aging on iodinated-contrast-media-induced nephropathy in male rats.

METHODS

Twenty-four healthy male rats were initially divided into 12-month-old and 24-month-old age groups (adult and older age groups, respectively; n = 12/group); subsequently, each age group was randomly divided into saline control (NS) and contrast media (CM) groups (n = 6/group). CM (76% diatrizoate, 10 mL/kg b.w.) was given through the caudal vein. Urinary creatinine (Ucr) and serum creatinine (Scr) were detected by an automatic biochemical analyzer. The activities of renal malondialdehyde (MDA), superoxide dismutase (SOD), angiotensin-converting enzyme (ACE), angiotensin II (Ang II), and reduced form of nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) were determined by spectrophotometric assays with commercially available kits according to the manufacturers' protocols. Renal histological changes were observed by hematoxylin and eosin staining and scored semiquantitatively.

RESULTS

In diatrizoate-injected aged rats, Scr, the activities of ACE, Ang II, MDA, and NADPH oxidase in renal tissues were significantly increased (p < 0.01). The histologic scores were higher in the aged animals with CM treatment than those of control or adult rats (p < 0.01). There was an increasing trend but no significant statistical difference in renal ACE, Ang II, MDA, and NADPH oxidase or histologic scores in adult CM-injected rats compared with control animals (p > 0.05).

CONCLUSIONS

Older age is an aggravating factor of iodinated-contrast-media-induced nephropathy in male rats. Oxidative stress and the renin-angiotensin system (RAS) may play an important role in nephrotoxicity induced by iodinated contrast media, especially in aged male rats.

Kidney aging--inevitable or preventable?

The aging process affects all organs, including the kidneys. As part of this process, progressive scarring and a measurable decline in renal function occur in most people over time. The improved understanding of the processes that can lead to and/or hasten scarring and loss of renal function over time parallels advances in our understanding of the aging process. Clinical factors, including hypertension, diabetes mellitus, obesity, abnormal lipid levels and vitamin D deficiency, have been associated with increasing renal sclerosis with age. In addition, tissue factors such as angiotensin II, advanced glycation end products, oxidative stress and Klotho are associated with renal aging. These associations and possible interventions, including the control of blood pressure, blood sugar, weight, diet and calorie restriction might make renal aging more preventable than inevitable.

Positron-Emission Tomography Imaging of the Angiotensin II Subtype 1 Receptor in Swine Renal Artery Stenosis

The angiotensin II subtype 1 receptor (AT 1 R) has been linked to the development and progression of renovascular hypertension. In this study we applied a pig model of renovascular hypertension to investigate the AT 1 R in vivo with positron-emission tomography (PET) and in vitro with quantitative autoradiography. AT 1 R PET measurements were performed with the radioligand [ 11 C]KR31173 in 11 control pigs and in 13 pigs with hemodynamically significant renal artery stenosis; 4 were treated with lisinopril for 2 weeks before PET imaging. The radioligand impulse response function was calculated by deconvolution analysis of the renal time-activity curves. Radioligand binding was quantified by the 80-minute retention of the impulse response function. Median values and interquartile ranges were used to illustrate group statistics. Radioligand retention was significantly increased ( P =0.044) in hypoperfused kidneys of untreated (0.225; range: 0.150 to 0.373) and lisinopril-treated (0.237; range:0.224 to 0.272) animals compared with controls (0.142; range:0.096 to 0.156). Increased binding of [ 11 C]KR31173 documented by PET in vivo was confirmed by in vitro autoradiography. Both in vivo and in vitro binding measurements showed that the effect of renal artery stenosis on the AT 1 R was not abolished by lisinopril treatment. These studies provide insight into kidney biology as the first in vivo/in vitro experimental evidence about AT 1 R regulation in response to reduced perfusion of the kidney. The findings support the concept of introducing AT 1 R PET as a diagnostic biomarker of renovascular disease.

Future Direction of Renal Positron Emission Tomography

Positron emission tomography (PET) is perfectly suited for quantitative imaging of the kidneys, and the recent improvements in detector technology, computer hardware, and image processing software add to its appeal. Multiple positron emitting radioisotopes can be used for renal imaging. Some, including carbon-11, nitrogen-13, and oxygen-15, can be used at institutions with an on-site cyclotron. Other radioisotopes that may be even more useful in a clinical setting are those that either can be obtained from radionuclide generators (rubidium-82, copper-62) or have a sufficiently long half-life for transportation (fluorine-18). The clinical use of functional renal PET studies (blood flow, glomerular filtration rate) has been slow, in part because of the success of concurrent technologies, including single-photon emission computed tomography (SPECT) and planar gamma camera imaging. Renal blood flow studies can be performed with O-15-labeled water, N-13-labeled ammonia, rubidium-82, and copper-labeled PTSM. With these tracers, renal blood flow can be quantified using a modified microsphere kinetic model. Glomerular filtration can be imaged and quantified with gallium-68 EDTA or cobalt-55 EDTA. Measurements of renal blood flow with PET have potential applications in renovascular disease, in transplant rejection or acute tubular necrosis, in drug-induced nephropathies, ureteral obstruction, before and after revascularization, and before and after the placement of ureteral stents. The most important clinical application for imaging glomerular function with PET would be renovascular hypertension. Molecular imaging of the kidneys with PET is rather limited. At present, research is focused on the investigation of metabolism (acetate), membrane transporters (organic cation and anion transporters, pepT1 and pepT2, GLUT, SGLT), enzymes (ACE), and receptors (AT1R). Because many nephrological and urological disorders are initiated at the molecular and organelle levels and may remain localized at their origin for an extended period of time, new disease-specific molecular probes for PET studies of the kidneys need to be developed. Future applications of molecular renal imaging are likely to involve studies of tissue hypoxia and apoptosis in renovascular renal disease, renal cancer, and obstructive nephropathy, monitoring the molecular signatures of atherosclerotic plaques, measuring endothelial dysfunction and response to balloon revascularization and restenosis, molecular assessment of the nephrotoxic effects of cyclosporine, anticancer drugs, and radiation therapy. New radioligands will enhance the staging and follow-up of renal and prostate cancer. Methods will be developed for investigation of the kinetics of drug-delivery systems and delivery and deposition of prodrugs, reporter gene technology, delivery of gene therapy (nuclear and mitochondrial), assessment of the delivery of cellular, viral, and nonviral vectors (liposomes, polycations, fusion proteins, electroporation, hematopoietic stems cells). Of particular importance will be investigations of stem cell kinetics, including local presence, bloodborne migration, activation, seeding, and its role in renal remodeling (psychological, pathological, and therapy induced). Methods also could be established for investigating the role of receptors and oncoproteins in cellular proliferation, apoptosis, tubular atrophy, and interstitial fibrosis; monitoring ras gene targeting in kidney diseases, assessing cell therapy devices (bioartificial filters, renal tubule assist devices, and bioarticial kidneys), and targeting of signal transduction moleculas with growth factors and cytokines. These potential new approaches are, at best, in an experimental stage, and more research will be needed for their implementation.

Altered cardiovascular responses to chronic angiotensin II infusion in aged rats

In this work we determined by telemetry the cardiovascular effects produced by Ang II infusion on blood pressure (BP) and heart rate (HR) in aged rats. Male Wistar aged (48-52 weeks) and young (12 weeks) rats were used. Ang II (6 microg/h, young, n=6; aged, n=6) or vehicle (0.9% NaCl 1 microl/h, young, n=4; aged, n=5) were infused subcutaneously for 7 days, using osmotic mini-pump. The basal diurnal and nocturnal BP values were higher in aged rats (day: 98+/-0.3 mm Hg, night: 104+/-0.4 mm Hg) than in the young rats (day: 92+/-0.2 mm Hg, night: 99+/-0.2 mm Hg). In contrast, the basal diurnal and nocturnal HR values were significantly smaller in the aged rats. Ang II infusion produced a greater increase in the diurnal BP in the aged rats (Delta MAP=37+/-1.8 mm Hg) compared to the young ones (Delta MAP=30+/-3.5 mm Hg). In contrast, the nocturnal MAP increase was similar in both groups (young rats; Delta MAP=22+/-3.0 mm Hg, aged rats; Delta MAP=24+/-2.6 mm Hg). During Ang II infusion HR decreased transiently in the young rats. An opposite trend was observed in the aged rats. Ang II infusion also inverted the BP circadian rhythm, in both groups. No changes in HR circadian rhythm were observed. These differences suggest that the aging process alters in a different way Ang II-sensitive neural pathways involved in the control of autonomic activity.

The mechanism of increased renal susceptibility to toxic substances in the elderly. Part I. The role of increased vasoconstriction

The mechanisms of increased susceptibility to nephrotoxins in aging are complex and incompletely understood. It is very important to try to increase our knowledge of them because adults become increasingly vulnerable to nephrotoxic substances, as they grow older. In addition, the percentage of elderly people will increase markedly in the near future, at least in the developed countries. Drugs such as diuretics, laxatives, NSAIDs, aminoglycosides and other nephrotoxic antibiotics, and converting enzyme inhibitors are used a lot by aging people and can produce severe renal problems. Beside drugs, the clinical use of radiocontrast agents also rises in older patients. It seems that the main mechanism of the increased renal susceptibility to toxic substances in the elderly is a disbalance between vasoconstrictor and vasodilator factors (in favor of vasoconstrictor ones). Increased propensity to vasoconstriction (to Ang II, ET and PAF), as well as increased levels of oxidatively modified biomolecules in the elderly, may enhance susceptibility of old kidney to toxic substances. In addition, all mechanisms that influence both mesangial and fibroblast cell proliferation and over-production of extracellular matrix might also be involved in the processes that make the old kidney prone to drug-induced chronic toxic injury.

Changes in angiotensin II receptors in dopamine-rich regions of the mouse brain with age and ethanol consumption

The density of angiotensin II (Ang II) receptors was determined in three dopaminergic nerve terminal-rich brain regions (caudate putamen, nucleus accumbens, and ventral pallidum) of mice that were given either water (control) or 20% w/v ethanol (EtOH) to drink for either 2-8 weeks (young) or 46 weeks (old). The receptors were labeled with 125I-sarcosine1, isoleucine8 angiotensin II (125I-SI Ang II) and measured by quantitative densitometric image analysis (receptor autoradiography) or by saturation binding assays on homogenates of these brain regions. The selective AT2 receptor subtype antagonist PD 123319 (10 microM) was used to inhibit 125I-SI Ang II binding to AT2 receptors to determine AT1 receptor density in brain sections. In young control mice the density of Ang II receptor binding sites in the caudate putamen was 407+/-26 fmol/g, in the nucleus accumbens the density was 346+/-27 fmol/g, and in the ventral pallidum the density was 317+/-27 fmol/g. Less than 5% of specific 125I-SI Ang II binding was displaced by PD 123319, suggesting that nearly all of the Ang II receptors in these brain regions were the AT1 subtype. The Bmax in homogenates of these three regions in young control mice was 11.0+/-2.1 fmol/mg protein. The KD was 0.49+/-0.13. Ang II receptors in old mouse brains were decreased, respectively, by 32%, 35% and 30% in the caudate putamen, nucleus accumbens and ventral pallidum (p<0.001). Ang II receptors were slightly, but not significantly increased in both young and old EtOH-consuming mice.