Effects of endothelin or angiotensin II receptor blockade on diabetes in the transgenic (mRen-2)27 rat

Four-week inhibition of the renin-angiotensin system in spontaneously hypertensive rats results in persistently lower blood pressure with reduced kidney renin and changes in expression of relevant gene networks

AIMS

Prevention of human hypertension is an important challenge and has been achieved in experimental models. Brief treatment with renin-angiotensin system (RAS) inhibitors permanently reduces the genetic hypertension of the spontaneously hypertensive rat (SHR). The kidney is involved in this fascinating phenomenon, but relevant changes in gene expression are unknown.

METHODS AND RESULTS

In SHR, we studied the effect of treatment between 10 and 14 weeks of age with the angiotensin receptor blocker, losartan, or the angiotensin-converting enzyme inhibitor, perindopril [with controls for non-specific effects of lowering blood pressure (BP)], on differential RNA expression, DNA methylation, and renin immunolabelling in the kidney at 20 weeks of age. RNA sequencing revealed a six-fold increase in renin gene (Ren) expression during losartan treatment (P < 0.0001). Six weeks after losartan, arterial pressure remained lower (P = 0.006), yet kidney Ren showed reduced expression by 23% after losartan (P = 0.03) and by 43% after perindopril (P = 1.4 × 10-6) associated with increased DNA methylation (P = 0.04). Immunolabelling confirmed reduced cortical renin after earlier RAS blockade (P = 0.002). RNA sequencing identified differential expression of mRNAs, miRNAs, and lncRNAs with evidence of networking and co-regulation. These included 13 candidate genes (Grhl1, Ammecr1l, Hs6st1, Nfil3, Fam221a, Lmo4, Adamts1, Cish, Hif3a, Bcl6, Rad54l2, Adap1, Dok4), the miRNA miR-145-3p, and the lncRNA AC115371. Gene ontogeny analyses revealed that these networks were enriched with genes relevant to BP, RAS, and the kidneys.

CONCLUSION

Early RAS inhibition in SHR resets genetic pathways and networks resulting in a legacy of reduced Ren expression and BP persisting for a minimum of 6 weeks.

Glucose and Blood Pressure-Dependent Pathways-The Progression of Diabetic Kidney Disease

The major clinical associations with the progression of diabetic kidney disease (DKD) are glycemic control and systemic hypertension. Recent studies have continued to emphasize vasoactive hormone pathways including aldosterone and endothelin which suggest a key role for vasoconstrictor pathways in promoting renal damage in diabetes. The role of glucose per se remains difficult to define in DKD but appears to involve key intermediates including reactive oxygen species (ROS) and dicarbonyls such as methylglyoxal which activate intracellular pathways to promote fibrosis and inflammation in the kidney. Recent studies have identified a novel molecular interaction between hemodynamic and metabolic pathways which could lead to new treatments for DKD. This should lead to a further improvement in the outlook of DKD building on positive results from RAAS blockade and more recently newer classes of glucose-lowering agents such as SGLT2 inhibitors and GLP1 receptor agonists.

Intravitreal administration of endothelin type A receptor or endothelin type B receptor antagonists attenuates hypertensive and diabetic retinopathy in rats

Hypertension is an independent risk factor for diabetic retinopathy, yet anti-hypertensive medications such as blockade of angiotensin II do not completely protect against vision-threatening vascular disease. We hypothesized that the potent vasoactive factor, endothelin (ET), is up-regulated in diabetic retinopathy and antagonism of the ET type A receptor (ETRA) or ET type B receptor (ETRB) ameliorates retinal vascular leakage independently of any blood pressure lowering effects. Spontaneously hypertensive rats (SHR) and their normotensive and genetic controls, Wistar Kyoto rats, were randomized to become diabetic or non-diabetic and studied for 8 weeks. Rats were further randomized to receive by intravitreal injection the ETRA antagonist, BQ123, the ETRB antagonist, BQ788, or vehicle, 5 days after the induction of streptozotocin diabetes and 4 weeks later. The treatments had no effect on systolic blood pressure which remained elevated in SHR. ET-1, ET-2, ETRA and ETRB were expressed in retina and retinal pigment epithelium (RPE)/choroid and increased by hypertension or diabetes. BQ123 reduced ET-1 and ET-2 expression in retina and RPE/choroid, while BQ788 had a similar effect but did not influence the mRNA levels of ET-1 in retina. Retinal vascular leakage and Müller cell stress as well as vascular endothelial growth factor (VEGF) expression in retina and RPE/choroid, were increased by hypertension or diabetes and there was an additive effect of these conditions. Treatment with BQ123 or BQ788 effectively reduced these events as well as the elevated levels of inflammatory factors in the retina. Our findings indicate that local ET systems exist in the retina and RPE/choroid that are up-regulated by hypertension and diabetes. The ability of locally delivered ET receptor antagonists to supress these overactive ET systems and reduce retinal vascular leakage and VEGF in the presence of hypertension indicate the potential of these approaches for the treatment of diabetic retinopathy.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

RAS and sex differences in diabetic nephropathy

The incidence and progression of kidney diseases are influenced by sex. The renin-angiotensin system (RAS) is an important regulator of cardiovascular and renal function. Sex differences in the renal response to RAS blockade have been demonstrated. Circulating and renal RAS has been shown to be altered in type 1 and type 2 diabetes; this enzymatic cascade plays a critical role in the development of diabetic nephropathy (DN). Angiotensin converting enzyme (ACE) and ACE2 are differentially regulated depending on its localization within the diabetic kidney. Furthermore, clinical and experimental studies have shown that circulating levels of sex hormones are clearly modulated in the context of diabetes, suggesting that sex-dependent RAS regulation may be also be affected in these individuals. The effect of sex hormones on circulating and renal RAS may be involved in the sex differences observed in DN progression. In this paper we will review the influence of sex hormones on RAS expression and its relation to diabetic kidney disease. A better understanding of the sex dimorphism on RAS might provide a new approach for diabetic kidney disease treatment.

The role of Krüppel-like factor 4 in transforming growth factor-β-induced inflammatory and fibrotic responses in human proximal tubule cells

Krüppel-like factor 4 (KLF4) is known to mitigate inflammation in several cell types. Using human proximal tubule cells, the present study aimed to investigate the role of KLF4 in regulating transforming growth factor (TGF)-β₁ induced inflammatory and fibrotic responses. Human kidney proximal tubular cells were exposed to high glucose, or TGF-β₁ and KLF4 expressions were determined. Cells were then transfected with empty vector or KLF4 and exposed to 2-ng/mL TGF-β₁ for up to 72 h. Inflammatory proteins (macrophage migration inhibitory factor and monocyte chemoattractant protein-1) and pro-fibrotic proteins (fibronectin and collagen IV) were measured after 72 h by enzyme-linked immunosorbent assay and western blot, respectively. To determine the relevance to in vivo models of chronic kidney disease, KLF4 protein expression in streptozotocin-induced diabetic mice was determined. Krüppel-like factor 4 messenger RNA (mRNA) levels were significantly reduced in high glucose-treated human kidney proximal tubular cells. High glucose increased TGF-β₁ mRNA expression, which significantly increased migration inhibitory factor and monocyte chemoattractant protein-1 protein secretion. Transforming growth factor-β₁ significantly increased fibronectin and collagen IV protein expression. The overexpression of KLF4 significantly reduced TGF-β-mediated increases in migration inhibitory factor and monocyte chemoattractant protein-1 but had no effect on TGF-β-mediated fibronectin and collagen IV mRNA and protein expression. The levels of KLF4 mRNA were significantly reduced in the diabetic kidney, and diabetic animals had a significant reduction in renal tubular expression of KLF4 proteins. This data suggest that KLF4 reduces inflammation induced by TGF-β₁, suggesting a therapeutic role for KLF4 in diabetic nephropathy.

Role of endothelin receptor antagonist; bosentan in cisplatin-induced nephrotoxicity in ovariectomized estradiol treated rats

Background: Endothelin-1 (ET-1) is a vasoconstrictor peptide that mediates cell proliferation, fibrosis, and inflammation. ET-1 has 2 receptors A and B.

Objectives: The present study investigated whether administration of ET-1 receptor type A antagonist leads to protect cisplatin (CP) induced nephrotoxicity in ovariectomized-estradiol (Es) treated rats.

Materials and Methods: Thirty-six ovariectomized Wistar rats were divided into 6 groups. Group 1 received CP (2.5 mg/kg/day) for one week. Groups 2 and 3 received 2 different doses of Es (0.25 and 0.5 mg/kg/week) for 3 weeks, but CP was started in the third week. Group 4 was treated as group 1, but bosentan (BOS, 30 mg/kg/day) was also added. Groups 5 and 6 treated similar to groups 2 and 3 but CP and BOS were added in the third week. At the end of the experiment, blood samples were obtained, and the animals were sacrificed for histopathological investigation of kidney tissue.

Results: The serum levels of creatinine (Cr) and blood urea nitrogen (BUN) increased by CP; however, BOS significantly elevated the BUN and Cr levels that were increased by CP administration (P < 0.05). Co-treatment of Es, BOS, and CP decreased the serum levels of BUN, Cr, and malondialdehyde (MDA) when compared with the group treated with BOS plus CP (P < 0.05). Such finding was obtained for kidney tissue damage score (KTDS). As expected, Es significantly increased uterus weight (P < 0.05). The groups were not significantly different in terms of serum and kidney nitrite, kidney weight (KW), and bodyweight

Conclusions: According to our findings, BOS could not protect renal functions against CP-induced nephrotoxicity. In contrast, Es alone or accompanied with BOS could protect the kidney against CP-induced nephrotoxicity via reduction of BUN, Cr, and KTDS.

Twenty years after ACEIs and ARBs: emerging treatment strategies for diabetic nephropathy

Diabetic nephropathy (DN) is a serious complication of both type 1 and type 2 diabetes mellitus. The disease is now the most common cause of end-stage kidney disease (ESKD) in developed countries, and both the incidence and prevalence of diabetes mellitus is increasing worldwide. Current treatments are directed at controlling hyperglycemia and hypertension, as well as blockade of the renin angiotensin system with angiotensin-converting enzyme inhibitors (ACEIs), and angiotensin receptor blockers. Despite these therapies, DN progresses to ESKD in many patients. As a result, much interest is focused on developing new therapies. It has been over two decades since ACEIs were shown to have beneficial effects in DN independent of their blood pressure-lowering actions. Since that time, our understanding of disease mechanisms in DN has evolved. In this review, we summarize major cell signaling pathways implicated in the pathogenesis of diabetic kidney disease, as well as emerging treatment strategies. The goal is to identify promising targets that might be translated into therapies for the treatment of patients with diabetic kidney disease.

Endothelin Blockade in Diabetic Kidney Disease

Diabetic kidney disease (DKD) remains the most common cause of chronic kidney disease and multiple therapeutic agents, primarily targeted at the renin-angiotensin system, have been assessed. Their only partial effectiveness in slowing down progression to end-stage renal disease, points out an evident need for additional effective therapies. In the context of diabetes, endothelin-1 (ET-1) has been implicated in vasoconstriction, renal injury, mesangial proliferation, glomerulosclerosis, fibrosis and inflammation, largely through activation of its endothelin A (ET_A) receptor. Therefore, endothelin receptor antagonists have been proposed as potential drug targets. In experimental models of DKD, endothelin receptor antagonists have been described to improve renal injury and fibrosis, whereas clinical trials in DKD patients have shown an antiproteinuric effect. Currently, its renoprotective effect in a long-time clinical trial is being tested. This review focuses on the localization of endothelin receptors (ET_A and ET_B) within the kidney, as well as the ET-1 functions through them. In addition, we summarize the therapeutic benefit of endothelin receptor antagonists in experimental and human studies and the adverse effects that have been described.

Renal protection by low dose irbesartan in diabetic nephropathy is paralleled by a reduction of inflammation, not of endoplasmic reticulum stress

Diabetes can disrupt endoplasmic reticulum (ER) homeostasis which leads to ER stress. ER stress-induced renal apoptosis seems to be involved in the development of diabetic nephropathy. The present study was designed to investigate the contribution of reduced ER stress to the beneficial effects of an angiotensin receptor blocker. Insulin-dependent diabetes mellitus was induced by streptozotocin injections to hypertensive mRen2-transgenic rats. After 2weeks animals were treated with 0.7mg/kg/day irbesartan. Blood glucose, blood pressure and protein excretion were assessed. Expression of ER stress markers was measured by real-time PCR. Immunohistochemistry was performed to detect markers of ER stress, renal damage and infiltrating cells. Glomerulosclerosis and apoptosis were evaluated. Diabetic mRen2-transgenic rats developed renal injury with proteinuria, tubulointerstitial cell proliferation as well as glomerulosclerosis and podocyte injury. Moreover, an increase in inflammation, podocyte ER stress and apoptosis was detected. Irbesartan somewhat lowered blood pressure and reduced proteinuria, tubulointerstitial cell proliferation and glomerulosclerosis. Podocyte damage was ameliorated but markers of ER stress (calnexin, grp78) and apoptosis were not reduced by irbesartan. On the other hand, inflammatory cell infiltration in the tubulointerstitium and the glomerulus was significantly attenuated. We conclude that irbesartan reduced renal damage even in a very low dose. The beneficial effects of low dose irbesartan were paralleled by a reduction of blood pressure and inflammation but not by a reduction of ER stress and apoptosis. Thus, sustained endoplasmic reticulum stress in the kidney does not necessarily lead to increased inflammation and tubulointerstitial or glomerular injury.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Aliskiren reduces vascular pathology in diabetic retinopathy and oxygen-induced retinopathy in the transgenic (mRen-2)27 rat

AIM/HYPOTHESIS

We examined whether the renin inhibitor, aliskiren, provides similar or greater protection than ACE inhibition from non-proliferative diabetic retinopathy and from the proliferative neoangiogenesis of oxygen-induced retinopathy.

METHODS

Transgenic (mRen-2)27 rats, which overexpress mouse renin and angiotensin in extra-renal tissues, were studied. For diabetic studies, non-diabetic, diabetic (streptozotocin, 55 mg/kg), diabetic + aliskiren (10 mg kg(-1) day(-1), pump), or diabetic + lisinopril (10 mg kg(-1) day(-1), drinking water) rats were evaluated over 16 weeks. For oxygen-induced retinopathy studies, rats were exposed to 80% oxygen (22 h/day) from postnatal days 0 to 11, and then room air from postnatal days 12 to 18. Aliskiren (10 or 30 mg kg(-1) day(-1), pump) or lisinopril (10 mg kg(-1) day(-1), drinking water) was administered during retinopathy development between postnatal days 12 and 18.

RESULTS

Systolic BP in diabetic (mRen-2)27 rats was reduced with 10 mg kg(-1) day(-1) aliskiren, but only lisinopril normalised systolic blood pressure. In diabetic (mRen-2)27 rats, 10 mg kg(-1) day(-1) aliskiren and lisinopril reduced retinal acellular capillaries and leucostasis to non-diabetic levels. In oxygen-induced retinopathy, neoangiogenesis and retinal inflammation (leucostasis, ED-1 immunolabelling) were partially reduced by 10 mg kg(-1) day(-1) aliskiren and normalised by 30 mg kg(-1) day(-1) aliskiren, whereas lisinopril normalised neoangiogenesis and reduced leucostasis and ED-1 immunolabelling. Aliskiren and lisinopril normalised retinal vascular endothelial growth factor expression; however, only aliskiren reduced intercellular adhesion molecule-1 to control levels.

CONCLUSIONS/INTERPRETATION

Aliskiren provided similar or greater retinal protection than ACE inhibition and may be a potential treatment for diabetic retinopathy.

Animal models of retinal disease

Diseases of the retina are the leading causes of blindness in the industrialized world. The recognition that animals develop retinal diseases with similar traits to humans has led to not only a dramatic improvement in our understanding of the pathogenesis of retinal disease but also provided a means for testing possible treatment regimes and successful gene therapy trials. With the advent of genetic and molecular biological tools, the association between specific gene mutations and retinal signs has been made. Animals carrying natural mutations usually in one gene now provide well-established models for a host of inherited retinal diseases, including retinitis pigmentosa, Leber congenital amaurosis, inherited macular degeneration, and optic nerve diseases. In addition, the development of transgenic technologies has provided a means by which to study the effects of these and novel induced mutations on retinal structure and function. Despite these advances, there is a paucity of suitable animal models for complex diseases, including age-related macular degeneration (AMD) and diabetic retinopathy, largely because these diseases are not caused by single gene defects, but involve complex genetics and/or exacerbation through environmental factors, epigenetic, or other modes of genetic influence. In this review, we outline in detail the available animal models for inherited retinal diseases and how this information has furthered our understanding of retinal diseases. We also examine how transgenic technologies have helped to develop our understanding of the role of isolated genes or pathways in complex diseases like AMD, diabetes, and glaucoma.

Angiotensin-converting enzyme (ACE) 2 overexpression ameliorates glomerular injury in a rat model of diabetic nephropathy: a comparison with ACE inhibition

The reduced expression of angiotensin-converting enzyme (ACE) 2 in the kidneys of animal models and patients with diabetes suggests ACE2 involvement in diabetic nephrology. To explore the renoprotective effects of ACE2 overexpression, ACE inhibition (ACEI) or both on diabetic nephropathy and the potential mechanisms involved, 50 Wistar rats were randomly divided into a normal group that received an injection of sodium citrate buffer and a diabetic model group that received an injection of 60 mg/kg streptozotocin. Eight wks after streptozotocin injection, the diabetic rats were divided into no treatment group, adenoviral (Ad)-ACE2 group, Ad-green flurescent protein (GFP) group, ACEI group receiving benazepril and Ad-ACE2 + ACEI group. Four wks after treatment, physical, biochemical, and renal functional and morphological parameters were measured. An experiment in cultured glomerular mesangial cells was performed to examine the effects of ACE2 on cellular proliferation, oxidative stress and collagen IV synthesis. In comparison with the Ad-GFP group, the Ad-ACE2 group exhibited reduced systolic blood pressure, urinary albumin excretion, creatinine clearance, glomeruli sclerosis index and renal malondialdehyde level; downregulated transforming growth factor (TGF)-β1, vascular endothelial growth factor (VEGF) and collagen IV protein expression; and increased renal superoxide dismutase activity. Ad-ACE2 and ACEI had similar effects, whereas combined use of Ad-ACE2 and ACEI offered no additional benefits. ACE2 transfection attenuated angiotensin (Ang) II-induced glomerular mesangial cell proliferation, oxidative stress and collagen IV protein synthesis. In conclusion, ACE2 exerts a renoprotective effect similar to that of ACEI treatment. Decreased renal Ang II, increased renal Ang-(1-7) levels, and inhibited oxidative stress were the possible mechanisms involved.

Tranilast attenuates the up-regulation of thioredoxin-interacting protein and oxidative stress in an experimental model of diabetic nephropathy

BACKGROUND

Diabetic nephropathy is the leading cause of kidney failure in the developed world. Tranilast has been reported to not only act as an anti-inflammatory and anti-fibrotic compound, but it also exerts anti-oxidative stress effects in diabetic nephropathy. Thioredoxin-interacting protein (Txnip) is the endogenous inhibitor of the anti-oxidant thioredoxin and is highly up-regulated in diabetic nephropathy, leading to oxidative stress and fibrosis. In this study, we aimed to investigate whether tranilast exerts its anti-oxidant properties through the inhibition of Txnip.

METHODS

Heterozygous Ren-2 rats were rendered diabetic with streptozotocin. Another group of rats were injected with citrate buffer alone and treated as non-diabetic controls. After 6 weeks of diabetes, diabetic rats were divided into two groups: one group gavaged with tranilast at 200 mg/kg/day and another group with vehicle.

RESULTS

Diabetic rats had a significant increase in albuminuria, tubulointerstitial fibrosis, peritubular collagen IV accumulation, reactive oxygen species (ROS) and macrophage infiltration (all P < 0.05). These changes were associated with an increase in Txnip mRNA and protein expression in the tubules and glomeruli of diabetic kidney. Treatment with tranilast for 4 weeks significantly attenuated Txnip up-regulation in diabetic rats and this was associated with a reduction in ROS, fibrosis and macrophage infiltration (all P < 0.05).

CONCLUSIONS

This is the first study to demonstrate that tranilast not only has anti-inflammatory and anti-fibrotic effects as previously reported but also attenuates the up-regulation of Txnip and oxidative stress in diabetic nephropathy.

Angiotensin II mediates epithelial-to-mesenchymal transformation in tubular cells by ANG 1-7/MAS-1-dependent pathways

Epithelial-to-mesenchymal transformation (EMT) of tubular cells into a myofibroblastic phenotype is an important mediator of renal scarring in chronic nephropathy. This study examines the role of the renin-angiotensin system (RAS) in this process. NRK-52E cells were exposed to angiotensin (ANG) II and ANG 1-7 in the presence or absence of inhibitors and agonists of RAS signaling. EMT was assessed at 3 days by expression of alpha-smooth muscle actin (alpha-SMA) and E-cadherin and the induction of a myofibroblastic phenotype. Expression of fibrogenic growth factors and matrix proteins was assessed by RT-PCR and immunofluorescence microscopy. To confirm findings in vivo, rats were also infused with ANG 1-7 (24 microg*kg(-1)*h(-1)) or saline via an osmotic minipump for 10 days, and renal fibrogenesis was then assessed. Treatment of NRK-52E cells with ANG II induced characteristic changes of EMT. Selective blockade of the AT(1) receptor or the AT(2) receptor failed to inhibit ANG II-induced EMT. However, blockade of the ANG 1-7 receptor, Mas-1, was able to prevent ANG II-dependent EMT. To confirm these findings, both ANG 1-7 and the selective Mas receptor agonist, AVE-0991, were able to induce NRK-52E cells in a dose-dependent manner. Exposing cells to recombinant ACE2 was also able to induce EMT. In addition, an infusion of ANG 1-7 induced the tubular expression of alpha-SMA and the expression of matrix proteins in the kidney. ANG II is a potent stimulus for EMT, but not through conventional pathways. This study points to the possible limitations of conventional RAS blockade, which not only fails to antagonize this pathway, but also may enhance it via augmenting the synthesis of ANG 1-7.

The renin-angiotensin system in retinal health and disease: Its influence on neurons, glia and the vasculature

Renin-Angiotensin System is classically recognized for its role in the control of systemic blood pressure. However, the retina is recognized to have all the components necessary for angiotensin II formation, suggestive of a role for Angiotensin II in the retina that is independent of the systemic circulation. The most well described effects of Angiotensin II are on the retinal vasculature, with roles in vasoconstriction and angiogenesis. However, it is now emerging that Angiotensin II has roles in modulation of retinal function, possibly in regulating GABAergic amacrine cells. In addition, Angiotensin II is likely to have effects on glia. Angiotensin II has also been implicated in retinal vascular diseases such as Retinopathy of Prematurity and diabetic retinopathty, and more recently actions in choroidal neovascularizaiton and glaucoma have also emerged. The mechanisms by which Angiotensin II promotes angiogensis in retinal vascular diseases is indicative of the complexity of the RAS and the variety of cell types that it effects. Indeed, these diseases are not purely characterized by direct effects of Angiotensin II on the vasculature. In retinopathy of prematurity, for example, blockade of AT1 receptors prevents pathological angiogenesis, but also promotes revascularization of avascular regions of the retina. The primary site of action of Angiotensin II in this disease may be on retinal glia, rather than the vasculature. Indeed, blockade of AT1 receptors prevents glial loss and promotes the re-establishment of normal vessel growth. Blockade of RAS as a treatment for preventing the incidence and progression of diabetic retinopathy has also emerged based on a series of studies in animal models showing that blockade of the RAS prevents the development of a variety of vascular and neuronal deficits in this disease. Importantly these effects may be independent of actions on systemic blood pressure. This has culminated recently with the completion of several large multi-centre clinical trials that showed that blockade of the RAS may be of benefit in some at risk patients with diabetes. With the emergence of novel compounds targeting different aspects of the RAS even more effective ways of blocking the RAS may be possible in the future.

New Insights into Hyperglycemia-induced Molecular Changes in Microvascular Cells

Hyperglycemia is the most prevalent characteristic of diabetes and plays a central role in mediating adverse effects on vascular cells during the progression of diabetic vascular complications. In diabetic microangiopathy, hyperglycemia induces biochemical and molecular changes in microvascular cells that ultimately progress to retinal, renal, and neural complications and extends to other complications, including advanced periodontal disease. In this review, we describe changes involving basement membrane thickening, tissue remodeling, gap junctions, inflammation, cytokines, and transcription factors, and their effects on the pathogenesis of diabetic microvascular complications. The majority of the changes described relate to retinal microangiopathy, since ultrastructural, structural, and biochemical alterations have been well-characterized in this tissue.

Role of Kruppel-like factor 6 in transforming growth factor-beta1-induced epithelial-mesenchymal transition of proximal tubule cells

Krüppel-like factor 6 (KLF6) is a DNA-binding protein containing a triple zinc-fingered motif and plays a key role in the regulation of cell proliferation, differentiation, and development. More recently it has been implicated in hepatic fibrosis via its binding to the transforming growth factor (TGF)-beta control element. In the kidney, epithelial-mesenchymal transition (EMT) is a major contributor to the pathogenesis of renal fibrosis, with TGF-beta1 being a key mediator of EMT. The present study aimed to determine the role of KLF6 and TGF-beta1 in EMT in proximal tubule cells. To determine the relevance in clinical disease, KLF6 was measured in kidneys of streptozotocin-induced diabetic Ren-2 rats and in cells exposed to high (30 mM) glucose. TGF-beta1 was confirmed to induce EMT by morphological change, loss of E-cadherin, and gain in vimentin expression. KLF6 mRNA expression was concomitantly measured. To determine the role of KLF6 in EMT, the above markers of EMT were determined in KLF6-silenced (small interfering RNA) and KLF6-overexpressing proximal tubule cells. KLF6 overexpression significantly promoted a phenotype consistent with EMT. High glucose induced KLF6 in proximal tubule cells (P < 0.05). This increase in KLF6 in response to high glucose was TGF-beta1 mediated. In an in vivo model of diabetic nephropathy KLF6 increased at week 8 (P < 0.05). KLF6 plays a permissive role in TGF-beta1-induced EMT in proximal tubule cells. Its upregulation in in vivo models of diabetic nephropathy suggests it as a potential therapeutic target.

Reversal of proteinuric renal disease and the emerging role of endothelin

Proteinuria is a major long-term clinical consequence of diabetes and hypertension, conditions that lead to progressive loss of functional renal tissue and, ultimately, end-stage renal disease. Proteinuria is also a strong predictor of cardiovascular events. Convincing preclinical and clinical evidence exists that proteinuria and the underlying glomerulosclerosis are reversible processes. This Review outlines the mechanisms involved in the development of glomerulosclerosis--particularly those responsible for podocyte injury--with an emphasis on the potential capacity of endothelin receptor blockade to reverse this process. There is strong evidence that endothelin-1, a peptide with growth-promoting and vasoconstricting properties, has a central role in the pathogenesis of proteinuria and glomerulosclerosis, which is mediated via activation of the ET(A) receptor. Several antiproteinuric drugs, including angiotensin-converting-enzyme inhibitors, angiotensin receptor antagonists, statins and certain calcium channel blockers, inhibit the formation of endothelin-1. Preclinical studies have demonstrated that endothelin receptor antagonists can reverse proteinuric renal disease and glomerulosclerosis, and preliminary studies in humans with renal disease have shown that these drugs have remarkable antiproteinuric effects that are additive to those of standard antiproteinuric therapy. Additional clinical studies are needed.

The differential regulation of Smad7 in kidney tubule cells by connective tissue growth factor and transforming growth factor-beta1

AIMS

Smad7 is an inhibitory Smad that regulates transforming growth factor-beta (TGF-beta) signaling. Connective tissue growth factor (CTGF) is recognized as a potent downstream mediator of the fibrogenic effects of TGF-beta1. SMAD binding sites have been identified in both TGF-beta and CTGF promoters. The effect of CTGF on Smad7 expression and its role in the regulation of Smad7 induced by TGF-beta1 in renal tubular cells is unknown.

METHODS

Human model of proximal tubular cells (HK-2 cells) was used and confirmed using a diabetic rat model. RT-PCR was performed to measure Smad7, TGF-beta1 and Smad2 and ELISA was performed to measure active TGF-beta1. CTGF or TGF-beta1 was silenced in HK-2 cells using siRNA methodology.

RESULTS

TGF-beta1 induced Smad7 in a time-dependent manner, peaking at 30 min (P<0.0005) but sustained up to 24 hrs (p<0.005). Conversely, CTGF reduced Smad7, which was maximal at 24 hrs (p<0.05). This was supported by our in vivo data demonstrating that CTGF protein significantly increased while Smad7 mRNA level was reduced in a diabetic rat model. The basal expression level of Smad7 decreased in TGF-beta1 silenced cells compared to cells transfected with non-specific siRNA (p<0.0005). The basal expression level of Smad7 increased in CTGF silenced cells (p<0.05), which was increased by TGF-beta1 (p<0.005). Both mRNA and protein levels of TGF-beta1 decreased in CTGF silenced cells (p<0.05 and p<0.005 respectively) accompanied by reduction in Smad2 mRNA level in CTGF silenced cells.

CONCLUSIONS

Smad7 is induced rapidly by TGF-beta1 limiting the response to TGF-beta1. CTGF likely plays a key role in promoting TGF-beta1 activity by decreasing the availability of Smad7 and increasing Smad2.

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.

High glucose-induced thioredoxin-interacting protein in renal proximal tubule cells is independent of transforming growth factor-beta1

Hyperglycemia is a causative factor in the pathogenesis of diabetic nephropathy. Here, we demonstrate the transcriptional profiles of the human proximal tubule cell line (HK-2 cells) exposed to high glucose using cDNA microarray analysis. Thioredoxin-interacting protein (Txnip) was the gene most significantly increased among 10 strongly up-regulated and 15 down-regulated genes. Txnip, heat shock proteins 70 and 90, chemokine (C-C motif) ligand 20, and matrix metalloproteinase-7 were chosen for verification of gene expression. Real-time reverse transcriptase-polymerase chain reaction confirmed the mRNA expression levels of these five genes, consistent with microarray analysis. The increased protein expression of Txnip, CCL20, and MMP7 were also verified by Western blotting and enzyme-linked immunosorbent assay. Increased expression of Txnip and of nitrotyrosine, as a marker of oxidative stress, were confirmed in vivo in diabetic Ren-2 rats. Subsequent studies focused on the dependence of Txnip expression on up-regulation of transforming growth factor (TGF)-beta1 under high-glucose conditions. Overexpression of Txnip and up-regulation of Txnip promoter activity were observed in cells in which the TGF-beta1 gene was silenced in HK-2 cells using short interfering RNA technology. High glucose further increased both Txnip expression and its promoter activity in TGF-beta1 silenced cells compared with wild-type cells exposed to high glucose, suggesting that high glucose induced Txnip through a TGF-beta1-indepen-dent pathway.

AT1 antagonist modulates activin-like kinase 5 and TGF-beta receptor II in the developing kidney

Previous studies by our group have demonstrated that angiotensin-converting enzyme (ACE) inhibition in the developing kidney modulates transforming growth factor-beta receptors. Blocking of angiotensin II (ANG II) mainly through angiotensin II type 1 receptor (AT1) has been implicated in mediating this ACE inhibition. The present study was designed to investigate the effects of an AT1 antagonist, losartan, on transforming growth factor-beta1 (TGF-beta1), TGF-beta receptor I [TbetaRI, activin-like kinase (ALK)-1, ALK-5], TGF-beta receptor II (TbetaRII), and alpha-smooth muscle actin (alpha-SMA) expression in the developing kidney. Newborn rat pups were treated with losartan (30 mg/kg per day) or normal saline for 7 days. Kidneys were removed for immunohistochemistry, reverse transcription polymerase chain reaction (PCR), and Western blotting of TGF-beta1, ALK-1, ALK-5, TbetaRII, and alpha-SMA. Renal ALK-5 and TbetaRII protein expressions in the losartan-treated group were found to be significantly increased (P<0.05), whereas TGF-beta1, ALK-1, and alpha-SMA protein expressions were not changed by losartan treatment. The losartan-treated group also showed significantly increased mean tubular diameter and interstitial area of the kidney (P<0.05). These results suggest that AT1 inhibition in the developing kidney impairs renal growth and development and modulates the expression of ALK-5 and TbetaRII.

Hypertension and diabetes: role of the renin-angiotensin system

Hypertension is often associated clinically with diabetes as part of the insulin-resistance syndrome or as a manifestation of renal disease. Elevated systemic blood pressure accelerates micro- and macrovascular complications in diabetes. Vasoactive hormone pathways including the renin-angiotensin-aldosterone system (RAAS) appear to play a pivotal role in the pathogenesis and progression of diabetic complications and possible diabetes itself. Recent studies have increased our understanding of the complexity of the RAAS with identification of new components of this cascade including angiotensin-converting enzyme 2 and a putative renin receptor. Agents that interrupt the RAAS confer end-organ protection in diabetes via hemodynamic and non-hemodynamic mechanisms. Trials are investigating the possible role of RAAS blockade in the prevention of type 2 diabetes.

Involvement of the Pancreatic Renin-Angiotensin System in Insulin Resistance and the Metabolic Syndrome

The cardiometabolic syndrome consists of several major components: hypertension, hyperinsulinemia, hyperlipidemia, and hyperglycemia. Central to this syndrome are insulin resistance and generation of reactive oxygen species; these features are particularly prominent in patients with type 2 diabetes mellitus. In this context, large clinical trials have shown that blockade of the renin-angiotensin system (RAS) is protective against type 2 diabetes. In spite of these solid clinical data, the mechanistic pathways by which RAS blockade achieves these protective effects have yet to be resolved. A recently identified local pancreatic islet RAS has, however, been implicated in this regard. Furthermore, RAS blockade was recently shown to enhance islet blood flow, oxygen tension, and insulin biosynthesis, thus improving beta-cell function and glucose tolerance. Meanwhile, RAS activation may also influence islet cell inflammatory responses, apoptosis, fibrosis, and superoxide anion production. This RAS-associated oxidative stress can induce islet cell dysfunction in the pancreas and insulin resistance in peripheral tissues.

Emerging drugs for diabetic nephropathy

There is an increasing number of patients with diabetes mellitus in many countries. Diabetic kidney disease, one of its microvascular complications, is also increasing markedly and has become a major cause of end stage renal disease worldwide. Intervention for preventing and delaying the development and progression of diabetic kidney disease is not only a medical concern, but also a social issue. Despite extensive efforts, however, medical interventions thus far are not effective enough to prevent the progression of the disease and the development of end stage renal disease. This justifies attempts to develop novel therapeutic approaches for diabetic nephropathy. Recent insights on its pathogenesis and progression have suggested new targets for the specific treatment of this disease. They include aldosterone, aldose reductase, arachidonic acid metabolites, growth factors, advanced glycosylation end-products, peroxisome proliferator-activated receptors and endothelin. Several other biochemical mediators have been targeted in experimental animal models with the goal to prevent diabetic nephropathy progression, but translation to clinics of these experimental achievements are still limited or lacking.

Diabetic Endothelin B Receptor–Deficient Rats Develop Severe Hypertension and Progressive Renal Failure

The endothelin (ET) system has been implicated in the pathogenesis of diabetic nephropathy. The role of the ET-B receptor (ETBR) is still unclear. The effect of ETBR deficiency on the progression of diabetic nephropathy in a streptozotocin model was analyzed in four groups: (1) Homozygous ETBR-deficient (ETBRd) diabetic rats, (2) ETBRd rats, (3) diabetic controls, and (4) wild-type controls. BP and kidney function were measured for 10 wk, followed by biochemical and histologic analysis of the kidneys. The study demonstrates that ETBRd diabetic rats on a normal-sodium diet develop severe hypertension, albuminuria, and a mild reduction of creatinine clearance. The strong BP rise seems not to be caused by activation of the renin-angiotensin-aldosterone system or by suppression of the nitric oxide system. Elevated plasma ET-1, possibly reflecting a reduced ETBR-dependent clearance, seems to cause the severe hypertension via the ETA receptor. The results do not support the hypothesis that a reduction of ETBR activity inhibits the progression of diabetic nephropathy. The study demonstrates for the first time that the combination of diabetes and ETBR deficiency causes severe low-renin hypertension with progressive renal failure.

Renal expression and localization of the facilitative glucose transporters GLUT1 and GLUT12 in animal models of hypertension and diabetic nephropathy

Renal tubular glucose reabsorption is mediated by facilitative glucose transporter (GLUT) proteins and energy-dependent sodium glucose luminal transporters. Glucose transport in the diabetic kidney is upregulated and has been implicated in the pathogenesis of progressive diabetic nephropathy. Hyperglycemia, hypertension, and activation of the renin-angiotensin system are believed important in the development of the disease. The present study examines the renal expression of the facilitative glucose transporters GLUT1 and GLUT12 in rat models of diabetic nephropathy. Sprague-Dawley and transgenic (mRen-2)27 rats received either streptozotocin-induced diabetes or vehicle. GLUT12 expression and localization were determined by immunohistochemistry, immunoblotting, in situ hybridization, and confocal immunofluorescence. GLUT1 immunolabeling was detected on the basolateral membrane throughout the nephron. GLUT12 was localized to the distal tubules and collecting ducts. A significant increase in GLUT12 immunolabeling was measured in Ren-2 controls and Ren-2 diabetic animals compared with Sprague-Dawley controls. GLUT12 expression was higher in Ren-2 diabetic compared with Sprague-Dawley diabetic rats. Long-term diabetes resulted in significant increases in GLUT1 levels in the renal proximal tubules and expression was higher in Ren-2 diabetic than Sprague-Dawley diabetic rats. GLUT12 protein was localized to the cytoplasm and to the apical membrane of human and rat distal tubules and collecting ducts. The apical localization of GLUT12 in the distal tubules and collecting ducts suggests that it could contribute to additional glucose reabsorption in the late nephron. Levels of both GLUT1 and GLUT12 are elevated in animal models of hypertension and diabetic nephropathy.

Association between endothelin-1 and collagen deposition in db/db diabetic mouse kidneys

Endothelin-1 has been implicated in diabetic kidney injury, but there are few firm data establishing the temporal and spatial expression of kidney endothelin-1 in diabetes. We performed an immunohistochemical and histopathological analysis to determine endothelin-1 peptide expression in the kidneys of diabetic db/db mice and non-diabetic db/m controls. Diabetic mice were studied at 8 weeks, before histological damage is evident, and again at 16 weeks, when significant glomerular injury has occurred. Urinary endothelin-1 was 6.2- and 3.6-fold higher in 8- and 16-week diabetic mice compared to age-matched controls (P<0.01 db/db vs. db/m). Compared to non-diabetic kidneys, immunoreactive endothelin-1 was first elevated 2.5-fold (P=0.02) in the tubulointerstitial compartment at 8-week and remained high (3.8-fold, P<0.01) at 16 weeks. In contrast, glomerular endothelin-1 was elevated 3.2-fold (P=0.03) only in 16-week diabetic mice. Glomerular and tubulointerstitial endothelin-1 were unchanged in 8- and 16-week non-diabetic mice. Elevated endothelin-1 in diabetic mice associated temporally and spatially with collagen deposition, especially in the tubulointerstitial compartment. The localization of kidney endothelin-1 is consistent with a role for this peptide in renal fibrogenesis. These results also highlight the potential role of ET-1 in the pathogenesis of early tubulointerstitial changes in diabetes.

Angiotensin and diabetic retinopathy

Diabetic retinopathy develops in patients with both type 1 and type 2 diabetes and is the major cause of vision loss and blindness in the working population. In diabetes, damage to the retina occurs in the vasculature, neurons and glia resulting in pathological angiogenesis, vascular leakage and a loss in retinal function. The renin-angiotensin system is a causative factor in diabetic microvascular complications inducing a variety of tissue responses including vasoconstriction, inflammation, oxidative stress, cell hypertrophy and proliferation, angiogenesis and fibrosis. All components of the renin-angiotensin system including the angiotensin type 1 and angiotensin type 2 receptors have been identified in the retina of humans and rodents. There is evidence from both clinical and experimental models of diabetic retinopathy and hypoxic-induced retinal angiogenesis that the renin-angiotensin system is up-regulated. In these situations, retinal dysfunction has been linked to angiotensin-mediated induction of growth factors including vascular endothelial growth factor, platelet-derived growth factor and connective tissue growth factor. Evidence to date indicates that blockade of the renin-angiotensin system can confer retinoprotection in experimental models of diabetic retinopathy and ischemic retinopathy. This review examines the role of the renin-angiotensin system in diabetic retinopathy and the potential of its blockade as a treatment strategy for this vision-threatening disease.

Reduction of urinary connective tissue growth factor by Losartan in type 1 patients with diabetic nephropathy

BACKGROUND

Connective tissue growth factor (CTGF) is an important profibrotic cytokine implicated in development of diabetic glomerulosclerosis. Urinary CTGF is reported to be significantly increased in patients with diabetic nephropathy. The present study aimed to investigate the short- and long term effects of angiotensin II receptor blockade by Losartan on urinary CTGF levels in hypertensive type 1 diabetic patients with diabetic nephropathy.

METHODS

Seventy-one hypertensive type 1 diabetic patients with diabetic nephropathy were included in the study. After a washout period of 4 weeks, the patients received Losartan 50 mg, 100 mg, and 150 mg once daily in treatment periods each lasting 2 months. Thereafter, patients were followed prospectively during treatment with Losartan 100 mg o.d. with a total mean follow-up time of 36 months. At baseline, after 2, 4, and 6 months and then biannually, urinary and plasma CTGF levels [enzyme linked immunosorbent assay (ELISA) fibroGen], albuminuria (Turbidimetry), glomerular filtration rate (GFR) [51-creatinine ethylenediaminetetraacetic acid ((51)Cr-EDTA plasma clearance)] and 24 hours blood pressure (TM2420)) were determined.

RESULTS

Baseline levels of urinary and plasma CTGF were 7076 (5708 to 8770) ng/24 hours [geometric mean (95% CI)] and 12.7 (7.3) ng/mL [mean (SD)], respectively. Albuminuria, GFR, and arterial blood pressure at baseline were 1152 (937 to 1416) mg/24 hours, 88 (24) mL/min/1.73 m(2), and 153/80 (17/9) mm Hg, respectively. Losartan significantly reduced urinary CTGF by 21% (9 to 31) (95% CI) initially (P < 0.05 vs. baseline), with no further reduction after increasing dose. The sustained reduction in urinary CTGF was 22% (12 to 32) (P < 0.05 vs. baseline). Rate of decline in GFR during the study was 3.2 (-1.6 to 15.9) mL/min/year [median (range)]. Reduction in urinary CTGF was correlated with a lower rate of decline in GFR (r= 0.23, P= 0.05). Plasma CTGF remained unchanged throughout the study.

CONCLUSION

Our 3-year study demonstrates that Losartan persistently reduces urinary CTGF excretion, which is associated with a slower rate of decline in GFR.

The renin-angiotensin-aldosterone system, glucose metabolism and diabetes

In diabetes mellitus (DM), the circulating renin-angiotensin system (RAS) is suppressed, but the renal tissue RAS is activated. Hyperglycemia increases tissue angiotensin II (Ang II), which induces oxidative stress, endothelial damage and disease pathology including vasoconstriction, thrombosis, inflammation and vascular remodeling. In early DM, the type 1 Ang II (AT(1)) receptor is upregulated but the type 2 Ang II (AT(2)) receptor is downregulated. This imbalance can predispose the individual to tissue damage. Hyperglycemia also increases the production of aldosterone, which has an unknown contribution to tissue damage. The insulin resistance state is associated with upregulation of the AT(1) receptor and an increase in oxygen free radicals in endothelial tissue caused by activation of NAD(P)H oxidase. Treatment with an AT(1) receptor blocker normalizes oxidase activity and improves endothelial function. An understanding of the tissue renin-angiotensin-aldosterone system, which is a crucial factor in the progression of tissue damage in DM, is imperative for protection against tissue damage in this chronic disease.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Cardiorenal protective effects of vasopeptidase inhibition with omapatrilat in hypertensive transgenic (mREN-2)27 rats

Vasopeptidase inhibitors simultaneously inhibit both angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP). The aim of this study was to determine the cardiorenal effects of the vasopeptidase inhibitor omapatrilat in the transgenic m(Ren-2)27 rat which exhibits fulminant hypertension and severe organ pathology. At 6 weeks of age, male Ren-2 rats were randomized to receive no treatment (N = 10), the ACE inhibitor fosinopril 10 mg/kg/day (N = 10), or omapatrilat 10 mg/kg/day (N = 10) or 40 mg/kg/day (N = 10) by daily gavage for 24 weeks. Various cardiorenal functional and structural parameters were assessed. Compared to controls, all treatment groups reduced hypertension in control Ren-2 rats, with both doses of omapatrilat reducing systolic blood pressure significantly more than fosinopril (control, 178 +/- 3 mmHg; fosinopril 10 mg/kg/day, 130 +/- 4 mmHg; omapatrilat 10 mg/kg/day, 110 +/- 3 mmHg; omapatrilat 40 mg/kg/day, 91 +/- 3 mmHg). Omapatrilat dose-dependently reduced cardiac hypertrophy, caused a greater inhibition of renal ACE than fosinopril, and was the only treatment to inhibit renal NEP. Attenuation of albuminuria, glomerulosclerosis and cardiorenal fibrosis occurred to a similar degree with omapatrilat and fosinopril. Omapatrilat confers cardiorenal protection in the hypertensive Ren-2 rat. Although inhibition of tissue NEP may contribute to the superior blood pressure reduction by omapatrilat, overall, the results are consistent with the central role that angiotensin II plays in renal and cardiac fibrosis in this model of hypertension.

Abnormal Vasoconstrictor Responses to Angiotensin II and Noradrenaline in Isolated Small Arteries From Patients With Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy (CADASIL)

Background and Purpose— Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is characterized by ultrastructural abnormalities in small cerebral and systemic vessels. We assessed vasomotor function in systemic small arteries in CADASIL.

Methods— We studied 10 CADASIL patients and 10 control subjects. Resistance arteries isolated from gluteal biopsies were mounted on small-vessel myographs, and concentration responses were determined for vasoconstrictors (noradrenaline, angiotensin II, and endothelin-I) and vasodilators (acetylcholine, bradykinin, spermine-NONOate, and nifedipine). Maximum data are shown as percent potassium contraction.

Results— There was reduced potency for noradrenaline in CADASIL (CADASIL [38 arteries]: EC 50 , 240 nmol/L; control subjects [27 arteries]: EC 50 , 100 nmol/L; 2-way analysis of variance, F=9.76, P =0.002). Maximum response to angiotensin II was greater in CADASIL (120±8% versus 97±5% in control subjects; F=4.28, P =0.043). Tachyphylaxis to angiotensin II occurred in all control subjects studied but in only 3 of 9 CADASIL subjects ( P =0.011, Fisher’s exact test). Vasodilation was similar in CADASIL patients compared with control subjects for endothelium-dependent dilators (acetylcholine and bradykinin) and endothelium-independent dilators (spermine-NONOate and nifedipine).

Conclusions— These results suggest a selective systemic microvascular vasoconstrictor abnormality in CADASIL in noradrenaline and angiotensin II pathways that is not explained by vasodilator impairment in endothelium or vascular smooth muscle. This could have important implications for prophylaxis and treatment of CADASIL.

Improved islet morphology after blockade of the renin- angiotensin system in the ZDF rat

The renin-angiotensin system (RAS) has an important role in the endocrine pancreas. Although angiotensin II has significant effects on cell proliferation and apoptosis, the contribution of the RAS to changes in islet structure and function associated with type 2 diabetes is yet to be defined. This study examined the specific effects of RAS blockade on islet structure and function in diabetes. Thirty-six male Zucker diabetic fatty (ZDF) rats, 10 weeks of age, were randomized to receive the angiotensin-converting enzyme inhibitor perindopril (8 mg/l in drinking water; n = 12), irbesartan (15 mg/kg via gavage; n = 12), or no treatment (n = 12) for 10 weeks. Results were compared with lean littermates (ZL) (n = 12) studied concurrently. ZDF rats had increased intra-islet expression of components of the RAS correlating with increased intraislet fibrosis, apoptosis, and oxidative stress. Disordered islet architecture, seen in ZDF rats, was attenuated after treatment with perindopril or irbesartan. Islet fibrogenesis was also diminished, as measured by picrosirius staining and expression of collagens I and IV. Gene expression of transforming growth factor-beta1 was increased in the ZDF pancreas (ZL, 1.0 +/- 0.1; ZDF, 2.0 +/- 0.3; P < 0.05) and reduced after blockade of the RAS (ZDF + P, 1.3 +/- 0.2; ZDF + I, 1.5 +/- 0.1; vs. ZDF, both P < 0.05). Improvements in structural parameters were also associated with functional improvements in first-phase insulin secretion. These findings provide a possible mechanism for the reduced incidence of new-onset diabetes that has been observed in clinical trials of RAS blockade.

Fas-induced apoptosis is a feature of progressive diabetic nephropathy in transgenic (mRen-2)27 rats: Attenuation with renin-angiotensin blockade

BACKGROUND AND AIM

Tubular atrophy is a major feature of most renal diseases and is closely associated with the loss of renal function. The present study sought to investigate whether Fas/FasL-induced tubular epithelial cell apoptosis was a feature of experimental diabetic nephropathy. The effects of renoprotective therapy with blockade of the renin-angiotensin (RAS) system were also examined.

METHOD

Six-week-old female Ren-2 rats were injected with streptozotocin and maintained diabetic for 12 weeks. Further groups of diabetic rats were treated with the angiotensin-converting enzyme inhibitor, perindopril, for 12 weeks.

RESULTS

Widespread apoptosis, identified by using mediated Terminal dUTP nick-end labelling (TUNEL) staining was noted in the tubules of diabetic Ren-2 rats. These changes were associated with an increase in both Fas mRNA and Fas L (ligand) within the tubules (P < 0.01). Treatment of diabetic Ren-2 rats with perindopril (6 mg/kg per day) reduced the apoptosis to control levels and was associated with a reduction in Fas mRNA and Fas L protein (P < 0.05).

CONCLUSION

In conclusion, Fas/Fas L-induced tubular apoptosis is a feature of diabetic Ren-2 rats and is attenuated by the blockade of the RAS.

Progression and regression in renal vascular and glomerular fibrosis

End-stage renal disease (ESRD) is characterized by the development of fibrotic lesions in the glomerular, interstitial and vascular compartments. Renal fibrogenesis, a common complication of diabetes and hypertension, is a complex dynamic process involving several players such as inflammatory agents, cytokines, vasoactive agents and enzymes participating in extracellular matrix assembly, anchoring or degradation. The only available treatment today against chronic renal failure is dialysis or kidney transplantation, making thus ESRD one of the most expensive diseases to treat on a per-patient basis. An emerging challenge for clinicians, maybe the nephrologist's Holy Grail in the 21st century, is to stop definitively the decline of renal function and, if possible, to achieve regression of renal fibrosis and restoration of renal structure. Over the last 5 years, different approaches have been tested in experimental models of nephropathy with variable degree of success. In this review, we will focus on the mechanisms of the hypertension-associated fibrosis and the few recent studies that gave promising results for a therapeutic intervention.

Kidney function during and after withdrawal of long-term irbesartan treatment in patients with type 2 diabetes and microalbuminuria

OBJECTIVE

Irbesartan is renoprotective in patients with type 2 diabetes and microalbuminuria. Whether the observed reduction in microalbuminuria is reversible (hemodynamic) or persistent (glomerular structural/biochemical normalization) after prolonged antihypertensive treatment is unknown. Therefore, the present substudy of the Irbesartan in Patients with Type 2 Diabetes and Microalbuminuria Study (IRMA-2) investigated the reversibility of kidney function changes after withdrawal of 2 years' antihypertensive treatment.

RESEARCH DESIGN AND METHODS

The substudy included 133 hypertensive type 2 diabetic patients with persistent microalbuminuria in IRMA-2, randomized to double-masked treatment with either placebo, irbesartan 150 mg, or irbesartan 300 mg o.d. for 2 years. Arterial blood pressure, overnight urinary albumin excretion rate, and glomerular filtration rate (GFR) were determined repeatedly.

RESULTS

Baseline characteristics were similar in the placebo, irbesartan 150-mg, and irbesartan 300-mg groups. At the end of the study, mean arterial blood pressure (MABP) was similarly lowered to 105 +/- 2 (mean +/- SE), 103 +/- 2, and 102 +/- 2 mmHg, respectively (P < 0.05 versus baseline), and urinary albumin excretion rate reduced by 8% (-16 to 27) (NS), 34% (95% CI 8-53), and 60% (46-70) (P < 0.05). Rates of decline in GFR were 1.3 +/- 0.7, 1.2 +/- 0.7, and 1.0 +/- 0.8 ml. min(-1). 1.73 m(-2) per month, respectively, during the initial 3 months of the study and 0.3 +/- 0.1, 0.3 +/- 0.1, and 0.4 +/- 0.1 ml. min(-1). 1.73 m(-2) per month in the remaining study period. One month after withdrawal of all antihypertensive medication, MABP remained unchanged in the placebo group, 105 +/- 2 mmHg, but increased significantly in the irbesartan groups, to 109 +/- 2 and 108 +/- 2 mmHg, respectively. Compared with baseline, urinary albumin excretion rate was increased by 14% (-17 to 54) in the placebo group and by 11% (-26 to 65) in the irbesartan 150-mg group but was persistently reduced by 47% (24-73) in the irbesartan 300-mg group (P < 0.05). GFR levels increased to baseline values in the placebo group and approached initial levels in irbesartan groups.

CONCLUSIONS

Persistent reduction of microalbuminuria after withdrawal of all antihypertensive treatment suggests that high-dose irbesartan treatment confers long-term renoprotective effects.

Hypertension in the (mRen-2)27 Rat Is Not Explained by Enhanced Kinetics of Transgenic Ren-2 Renin

Enhanced efficiency of the reaction between transgenic Ren-2 mouse renin and endogenous rat angiotensinogen has been suggested as 1 mechanism that contributes to the accelerated hypertension and increased tissue angiotensin of the (mRen-2)27 transgenic rat. This was tested in a study conducted at pH 7.4 in vitro that compared the kinetic constants of purified mouse Ren-2 and rat renin (each at 100, 75, 50, and 25 pmol/L) reacting with physiologic concentrations of rat angiotensinogen (0 to 4 μmol/L). Under these conditions, the kinetic constants for Ren-2 ( K m , 1.8 μmol/L; K cat , 0.07/s; and K cat / K m , 0.04 L · μmol −1 · s −1 ) were not different from rat renin. However, Ren-2 renin acting on its homologous mouse angiotensinogen was confirmed as being much slower. We conclude that hypertension in the Ren-2 rat is not related to renin kinetics. Other mechanisms are considered, with reference to human essential hypertension.

Renal damage in the SHR/N-cp type 2 diabetes model: comparison of an angiotensin-converting enzyme inhibitor and endothelin receptor blocker

SUMMARY

The pathomechanisms that cause renal damage in diabetes have not been completely clarified. Treatment with angiotensin-converting enzyme inhibitors (ACE-i) is highly effective but fails to completely prevent end-stage renal disease. The effects of ET(A)-receptor blockers (ET(A)-RB) on renal damage are controversial and have rarely been investigated in type 2 diabetes. We compared the influence of the selective ET(A)-RB LU135252 and the ACE-i Trandolapril on renal structure in the SHR/N-cp rat model of type 2 diabetes. Three-month-old male SHR/N-cp rats were left untreated or received daily either Trandolapril or LU135252. The experiment was terminated after 6 months. The glomerulosclerosis index; tubulointerstitial damage index; and glomerular geometry, glomerular cell number, and capillary density were investigated. Proliferating cell nuclear antigen and desmin expression of podocytes, renal mRNA expression of endothelin (ET-1) and transforming growth factor-beta, blood pressure, and urine albumin excretion were measured. The glomerulosclerosis index was significantly higher in untreated diabetic animals than in the groups that were treated with ACE-i and ET(A)-RB. There were analogous changes in tubulointerstitial damage index. Treatment with either substance comparably lowered urinary albumin excretion in diabetic SHR/N-cp. Podocyte and endothelial cell numbers per glomerulus decreased in untreated diabetic animals; this was prevented by the ACE-i but not by the ET(A)-RB. Glomerular capillary length density was lower in SHR/N-cp, and this was normalized by ACE-i only. Increased expression of desmin and proliferating cell nuclear antigen expression of podocytes in the SHR/N-cp was abrogated by ACE-i but not by ET(A)-RB. Treatment with ACE-i or ET(A)-receptor antagonist resulted in less structural and functional alterations, but the ET(A)-RB was inferior to the ACE-i. This is particularly the case for podocyte changes pointing to angiotensin II-dependent pathomechanisms.

Direct actions of urotensin II on the heart: implications for cardiac fibrosis and hypertrophy

Urotensin II (UII) is a somatostatin-like peptide recently identified as a potent vasoconstrictor. In this study, we examined whether UII promotes cardiac remodeling through nonhemodynamic effects on the myocardium. In a rat model of heart failure after myocardial infarction (MI), increased UII peptide and UII receptor protein expression was observed in both infarct and noninfarct regions of the left ventricle compared with sham. Moreover, post-MI remodeling was associated with a significant 75% increase in UII receptor gene expression in the heart (P<0.05 versus sham controls), with this increase noted in both regions of the left ventricle. In vitro, UII (10-7 mol/L) stimulation of neonatal cardiac fibroblasts increased the level of mRNA transcripts for procollagens alpha1(I), alpha1(III), and fibronectin by 139+/-15% (P<0.01), 59+/-5% (P<0.05), and 141+/-14% (P<0.01), respectively, with a concomitant 23+/-2% increase in collagen peptide synthesis as determined by 3H-proline incorporation (P<0.01). UII had no effect on cellular hypertrophy, as determined by changes in total protein content in isolated neonatal cardiomyocytes. However, expression of recombinant rat UII receptor in neonatal cardiomyocytes resulted in significant UII-dependent activation of hypertrophic signaling as demonstrated by increased total protein content (unstimulated, 122.4+/-4.0 microg/well; rat UII, 147.6+/-7.0 microg/well; P<0.01) and activation of the hypertrophic phenotype through Galpha(q)- and Ras-dependent pathways. These results indicate that, in addition to potent hemodynamic effects, UII may be implicated in myocardial fibrogenesis through increased collagen synthesis by cardiac fibroblasts and may also be an important determinant of pathological cardiac hypertrophy in conditions characterized by UII receptor upregulation.