Role of angiotensin II in diabetic nephropathy

Inflammatory cytokines as predictive markers for early detection and progression of diabetic nephropathy

Diabetic nephropathy is a major complication of diabetes mellitus and the leading cause of end-stage renal disease. Both hyperglycemia and hypertension (systemic and/or intraglomerular) are established causal factors for diabetic nephropathy. Nonetheless, there is growing evidence that activated innate immunity and inflammation are also contributing factors to the pathogenesis of diabetic nephropathy. This notion is based on increasing evidence indicating that both cytokines-chemokines and pro-fibrotic growth factors are important players in the progression of diabetic nephropathy, effectively accelerating and exacerbating inflammatory and fibrotic processes leading to end-stage renal disease. In this review, we focus on several predominant cytokines-chemokines as potential predictive markers for diabetic nephropathy. These cytokines-chemokines may also be helpful as biomarkers to monitor the progression of the disease and the impact of interventional modalities aimed at halting eventual manifestation of end-stage renal disease in diabetic patients.

Advanced glycation end products, oxidative stress and diabetic nephropathy

About 246 million people worldwide have diabetes in 2007. The global figure of people with diabetes is projected to increase to 370 million in 2030. As the prevalence of diabetes has risen to epidemic proportions worldwide, diabetic nephropathy has become one of the most challenging health problems. Therapeutic options such as strict blood glucose and blood pressure controls are effective for preventing diabetic nephropathy, but are far from satisfactory, and the number of diabetic patients on end-stage renal disease is still increasing. Therefore, a novel therapeutic strategy that could halt the progression of diabetic nephropathy should be developed. There is accumulating evidence that advanced glycation end products (AGEs), senescent macroprotein derivatives formed at an accelerated rate under diabetes, play a role in diabetic nephropathy via oxidative stress generation. In this paper, we review the pathophysiological role of AGEs and their receptor (RAGE)-oxidative stress system in diabetic nephropathy.

Mechanism of VEGF expression by high glucose in proximal tubule epithelial cells

Angiotensin II (Ang II) and vascular endothelial growth factor (VEGF) are important mediators of kidney injury in diabetes. VEGF expression is increased in proximal tubules of mice with type 1 diabetes. In mouse proximal tubular epithelial cells (MCT) cultured with 30 mM glucose (HG) for 24h, VEGF expression is increased at the protein and the mRNA level, suggesting a transcriptional mechanism. HG stimulation of VEGF synthesis is prevented by captopril, an inhibitor of angiotensin-converting enzyme, and, by losartan, a specific antagonist of angiotensin type 1 receptor (AT1), suggesting that VEGF synthesis is mediated by Ang II. Synthesis of angiotensinogen (AGT), a precursor of angiotensin II, is increased in MCTs cultured in HG. Although synthesis of renin and ACE is not affected by HG, their activity is increased in the conditioned medium. Concentrations of Ang I and Ang II are also increased in conditioned medium from HG-treated MCTs and captopril prevents increased Ang II, but not Ang I, synthesis. Finally, AT1 is activated in MCTs treated with HG, and its activation is prevented by captopril and losartan. The ERK pathway is activated by HG within minutes of stimulation and lasting for up to 24h. The initial phase of ERK activation is due to HG itself and leads to AGT upregulation and the sustained phase is mediated for the most part by Ang II-activated AT1 receptor and leads to increased VEGF synthesis. These data show that: (1) HG increases AGT synthesis and activation of renin and ACE by MCTs, leading to local production of Ang I and Ang II. (2) Ang II activates endogenous AT1 and stimulates synthesis of VEGF. (3) HG activation of ERK starts within minutes and lasts for up to 24h. Early ERK activation is involved in AGT upregulation and sustained ERK activation, mediated via AT1, is responsible for VEGF synthesis. In conclusion, our study shows that MCTs express an endogenous renin-angiotensin system that is activated by high glucose to stimulate the synthesis of VEGF, through activation of the ERK pathway.

Cinnamaldehyde impairs high glucose-induced hypertrophy in renal interstitial fibroblasts

Cinnamaldehyde is a major and a bioactive compound isolated from the leaves of Cinnamomum osmophloeum kaneh. To explore whether cinnamaldehyde was linked to altered high glucose (HG)-mediated renal tubulointerstitial fibrosis in diabetic nephropathy (DN), the molecular mechanisms of cinnamaldehyde responsible for inhibition of HG-induced hypertrophy in renal interstitial fibroblasts were examined. We found that cinnamaldehyde caused inhibition of HG-induced cellular mitogenesis rather than cell death by either necrosis or apoptosis. There were no changes in caspase 3 activity, cleaved poly(ADP-ribose) polymerase (PARP) protein expression, and mitochondrial cytochrome c release in HG or cinnamaldehyde treatments in these cells. HG-induced extracellular signal-regulated kinase (ERK)/c-Jun N-terminal kinase (JNK)/p38 mitogen-activated protein kinase (MAPK) (but not the Janus kinase 2/signal transducers and activators of transcription) activation was markedly blocked by cinnamaldehyde. The ability of cinnamaldehyde to inhibit HG-induced hypertrophy was verified by the observation that it significantly decreased cell size, cellular hypertrophy index, and protein levels of collagen IV, fibronectin, and alpha-smooth muscle actin (alpha-SMA). The results obtained in this study suggest that cinnamaldehyde treatment of renal interstitial fibroblasts that have been stimulated by HG reduces their ability to proliferate and hypertrophy through mechanisms that may be dependent on inactivation of the ERK/JNK/p38 MAPK pathway.

Increased urinary angiotensinogen is precedent to increased urinary albumin in patients with type 1 diabetes

BACKGROUND

We previously reported that kidney and urinary angiotensinogen levels were significantly increased before the development of diabetic nephropathy in diabetic rats. To address this system in humans, we have developed an enzyme-linked immunosorbent assay for human angiotensinogen and reported that urinary excretion of angiotensinogen levels is enhanced in patients with chronic kidney disease, including patients with type 2 diabetes. On the basis of these findings, this study was performed to demonstrate that urinary angiotensinogen levels increased before the onset of microalbuminuria and that urinary angiotensinogen can be an early biomarker of intrarenal renin-angiotensin system status in normoalbuminuric patients with type 1 diabetes compared with age- and sex-matched control subjects.

METHODS

The study included 28 patients with type 1 diabetes and 21 control subjects. No subject received renin-angiotensin system blockades. Random spot urine samples as well as blood samples were obtained and analyzed.

RESULTS

Urinary albumin:creatinine ratio or urinary protein:creatinine ratio did not increase in patients compared with control subjects, suggesting that these patients were in their premicroalbuminuric phase of diabetic nephropathy. However, the urinary angiotensinogen:creatinine ratio was significantly higher in patients than in control subjects (12.1 +/- 3.2 microg/g versus 4.2 +/- 0.7 microg/g). Importantly, an increase in plasma angiotensinogen levels was not observed (26.3 +/- 1.3 microg/mL versus 29.5 +/- 3.3 microg/mL).

CONCLUSIONS

Thus, in patients, an increase in urinary angiotensinogen levels is observed, and this increase is precedent to an increase in urinary albumin levels, suggesting that urinary angiotensinogen may function as an early marker of diabetic nephropathy.

The endothelin receptor antagonist avosentan ameliorates nephropathy and atherosclerosis in diabetic apolipoprotein E knockout mice

AIMS/HYPOTHESIS

There is convincing evidence that the endothelin system contributes to diabetic nephropathy and cardiovascular disease. This study aimed to assess the effects of the non-peptidergic endothelin receptor A (ETA) antagonist avosentan in a mouse model of accelerated diabetic nephropathy and atherosclerosis in comparison with the ACE inhibitor, quinapril.

METHODS

Apolipoprotein E (Apoe) knockout (KO) mice (n = 20 per group, five groups) were randomised to the following groups: non-diabetic controls and streptozotocin-induced diabetic animals gavaged daily for 20 weeks with placebo, avosentan (high dose: 30 mg/kg, or low dose: 10 mg/kg) or quinapril (given in drinking water, 30 mg/kg).

RESULTS

BP was unchanged by avosentan treatment but decreased with quinapril treatment. Diabetes-associated albuminuria was significantly attenuated by high-dose avosentan after 10 and 20 weeks of treatment. Diabetic animals showed a decreased creatinine clearance, which was normalised by avosentan treatment. In diabetic mice, high-dose avosentan treatment significantly attenuated the glomerulosclerosis index, mesangial matrix accumulation, glomerular accumulation of the matrix proteins collagen IV, and renal expression of genes encoding connective tissue growth factor, vascular endothelial growth factor, transforming growth factor beta and nuclear factor kappaB (p65 subunit). Furthermore, high-dose avosentan treatment was also associated with reduced expression of the genes for ETA, ETB and angiotensin receptor 1. The renoprotective effects of avosentan were comparable or superior to those observed with quinapril. High-dose avosentan also significantly attenuated diabetes-associated aortic atherosclerosis in Apoe KO mice and reduced macrophage infiltration and aortic nitrotyrosine expression.

CONCLUSIONS/INTERPRETATION

This study demonstrates that ETA blockade with avosentan may provide an alternate therapeutic strategy for the treatment of diabetic micro- and macrovascular complications.

A longitudinal study of kidney structure and function in adults

BACKGROUND

Although kidney size is commonly measured in patients with chronic kidney disease (CKD), its relationship with kidney function is poorly understood. We conducted this longitudinal study to better understand the relationship between kidney size and function.

METHODS

We retrospectively studied 178 kidneys measured by ultrasound in 93 patients with CKD who did not have autosomal polycystic kidney disease. Renal function was measured using estimated glomerular filtration rate (GFR). A mixed model that accounted for repeated measurements or nested observations was used for statistical analysis.

RESULTS

In cross-sectional analyses, the following independent variables emerged as predictors of kidney size: estimated GFR along with its squared term, height, age and interactions of each of these two independent variables with aetiology of CKD. In longitudinal analyses over a median follow-up of 3.7 years, after accounting for predictors of baseline kidney size such as aetiology, height and estimated GFR, we found that kidney atrophy occurred at a rate of 0.072 cm/year (SD 0.016, P = 0.007). This atrophy was 'blunted' with declining GFR. Each 1 mL/min/1.73 m(2)/year greater decline in eGFR abrogated kidney atrophy by 0.015 cm/year (P = 0.024).

CONCLUSION

Although in cross-sectional surveys kidney size is directly related to function, the longitudinal relationship between form and function is inverted. Since the rate of change in GFR determines kidney atrophy, we conclude that kidney size is a determinant of renal prognosis.

Do resident renal mast cells play a role in the pathogenesis of diabetic nephropathy?

Diabetic nephropathy is associated with high morbidity and mortality and the prevalence of this disease is continuously increasing world wide. Though, the major risk factors like hyperglycemia and hypertension play a pivotal role in the pathogenesis of diabetic nephropathy, the etiology of this insidious disorder is not well understood. Mast cells are pluripotent bone marrow derived cells that play a key role in inflammation. Degranulation of mast cells releases various mediators including inflammatory cytokines, endothelins, growth factors, and proteolytic enzymes. Infiltration of mast cells has been noted to occur in renal diseases. In addition, the renal density of mast cells is significantly increased in diabetic patients with nephropathy. It remains unclear whether resident renal mast cells derived mediators play a role in the pathogenesis of diabetic nephropathy. Recent studies suggest the involvement of renal mast cell infiltration and degranulation in diabetic nephropathy. The present review focuses on the role of resident renal mast cells in diabetic nephropathy.

[Molecular bases of diabetic nephropathy]

The determinant of the diabetic nephropathy is hyperglycemia, but hypertension and other genetic factors are also involved. Glomerulus is the focus of the injury, where mesangial cell proliferation and extracellular matrix occur because of the increase of the intra- and extracellular glucose concentration and overexpression of GLUT1. Sequentially, there are increases in the flow by the poliol pathway, oxidative stress, increased intracellular production of advanced glycation end products (AGEs), activation of the PKC pathway, increase of the activity of the hexosamine pathway, and activation of TGF-beta1. High glucose concentrations also increase angiotensin II (AII) levels. Therefore, glucose and AII exert similar effects in inducing extracellular matrix formation in the mesangial cells, using similar transductional signal, which increases TGF-beta1 levels. In this review we focus in the effect of glucose and AII in the mesangial cells in causing the events related to the genesis of diabetic nephropathy. The alterations in the signal pathways discussed in this review give support to the observational studies and clinical assays, where metabolic and antihypertensive controls obtained with angiotensin-converting inhibitors have shown important and additive effect in the prevention of the beginning and progression of diabetic nephropathy. New therapeutic strategies directed to the described intracellular events may give future additional benefits.

Urinary angiotensinogen as a novel biomarker of the intrarenal renin-angiotensin system status in hypertensive patients

We reported previously that urinary angiotensinogen (UAGT) levels provide a specific index of the intrarenal renin-angiotensin system (RAS) status in angiotensin II-dependent hypertensive rats. To study this system in humans, we recently developed a human angiotensinogen ELISA. To test the hypothesis that UAGT is increased in hypertensive patients, we recruited 110 adults. Four subjects with estimated glomerular filtration levels <30 mL/min per 1.73 m(2) were excluded because previous studies have already shown that UAGT is highly correlated with estimated glomerular filtration in this stage of chronic kidney disease. Consequently, 106 paired samples of urine and plasma were analyzed from 70 hypertensive patients (39 treated with RAS blockers [angiotensin-converting enzyme inhibitors or angiotensin II type 1 receptor blockers; systolic blood pressure: 139+/-3 mm Hg] and 31 not treated with RAS blockers [systolic blood pressure: 151+/-4 mm Hg]) and 36 normotensive subjects (systolic blood pressure: 122+/-2 mm Hg). UAGT, normalized by urinary concentrations of creatinine, were not correlated with race, gender, age, height, body weight, body mass index, fractional excretion of sodium, plasma angiotensinogen levels, or estimated glomerular filtration. However, UAGT/urinary concentration of creatinine was significantly positively correlated with systolic blood pressure, diastolic blood pressure, urinary albumin:creatinine ratio (r=0.5994), and urinary protein:creatinine ratio (r=0.4597). UAGT/urinary concentration of creatinine was significantly greater in hypertensive patients not treated with RAS blockers (25.00+/-4.96 microg/g) compared with normotensive subjects (13.70+/-2.33 microg/g). Importantly, patients treated with RAS blockers exhibited a marked attenuation of this augmentation (13.26+/-2.60 microg/g). These data indicate that UAGT is increased in hypertensive patients, and treatment with RAS blockers suppresses UAGT, suggesting that the efficacy of RAS blockade to reduce the intrarenal RAS activity can be assessed by measurements of UAGT.

Novel mechanisms of protein synthesis in diabetic nephropathy--role of mRNA translation

Ambient protein levels are affected by both synthesis and degradation. Synthesis of a protein is regulated by transcription and messenger RNA (mRNA) translation. Translation has emerged as an important site of regulation of protein expression during development and disease. It is under the control of distinct factors that regulate initiation, elongation and termination phases. Regulation of translation occurs via signaling reactions, guanosine diphosphate-guanosine triphosphate binding and by participation of non-coding RNA species such as microRNA. Recent work has revealed an important role for translation in hypertrophy, matrix protein synthesis, elaboration of growth factors in in vivo and in vitro models of diabetic nephropathy. Studies of translation dysregulation in diabetic nephropathy have enabled identification of novel therapeutic targets. Translation of mRNA is a fertile field for exploration in investigation of kidney disease.

ACE-dependent and chymase-dependent angiotensin II generation in normal and glucose-stimulated human mesangial cells

High glucose (HG) increases angiotensin II (AngII) generation in mesangial cells (MC). Chymase, an alternative AngII-generating enzyme, is upregulated in the glomeruli of diabetic kidneys. In this study, we examined AngII synthesis by human MC via angiotensin-converting enzyme (ACE)-dependent and chymase-dependent pathways under normal glucose (NG, 5 mM) and HG (30 mM) conditions. NG cells expressed ACE and chymase mRNA. Under NG conditions the chymase inhibitor chymostatin reduced AngII levels in cell lysates and in the culture medium, and the ACE inhibitor captopril had no effect. HG induced a 3-fold increase in chymase mRNA and protein but not in ACE mRNA; however, HG induced a 10-fold increase in intracellular ACE activity. The increase in AngII generation induced by HG was found in the cell lysate but not in the culture medium. The rise in intracellular AngII was not prevented by captopril or by chymostatin. Moreover, captopril inhibited extracellular ACE activity but failed to block intracellular ACE activity; these results suggested that captopril was unable to reach intra-cellular ACE. Losartan did not change the intracellular AngII content in either NG or HG conditions, and this lack of change suggested that the increase in AngII was due to intracellular generation. Together these results suggest that chymase may be active in human MC and that both ACE and chymase are involved in increased AngII generation during the HG stimulus by different mechanisms, including an upregulation of chymase mRNA and a rise in intracellular ACE activity, favoring the generation and accumulation of intracellular AngII.

Angiotensin II- and glucose-stimulated extracellular matrix production: mediation by the insulin-like growth factor (IGF) axis in a murine mesangial cell line

In diabetic nephropathy, glomerular mesangial cells exhibit aberrant anabolic activity that includes excessive production of extracellular matrix (ECM) proteins, leading to crowding of filtration surface areas and possible renal failure. In the present study, a murine mesangial cell line (MES-13 cells) was studied to determine the roles of the renin-angiotensin system (RAS) and the insulin-like growth factor (IGF) axis in the anabolic response to elevated glucose levels. Culture of MES-13 cells in medium containing supra-physiological glucose concentrations (>5.5 mmol/l) resulted in increased production of ECM proteins including laminin, fibronectin, and heparan sulfate proteoglycan with concurrent increases in IGF-binding protein (IGFBP)-2 production. These responses were blocked by the angiotensin receptor antagonists saralasin and losartan, while exogenous angiotensin II (Ang II) treatment directly stimulated increases in ECM and IGFBP-2. In all experiments, IGFBP-2 levels were correlated with anabolic activity implicating IGFBP-2 as a possible mediator in cellular responses to high glucose and Ang II. Such mediation appears to involve IGFBP-2 modulation of IGF-I signaling, since all responses to high glucose or Ang II were blocked by immuno-neutralization of IGF-I. These data suggest alterations in the IGF axis as key mechanisms underlying nephropathic responses of mesangial cells to Ang II and high glucose.

Products of 12/15-lipoxygenase upregulate the angiotensin II receptor

Angiotensin II and its type 1 receptor (AT1R) play important roles in the pathogenesis of renal disease and diabetic nephropathy. The 12/15-lipoxygenase pathway of arachidonate metabolism and its lipid products have also been implicated in diabetic nephropathy. However, it is unclear whether 12/15-lipoxygenase regulates expression of AT1R. In cultured rat mesangial cells, we found that the 12/15-lipoxygenase product 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) increased AT1R mRNA and protein expression, primarily by stabilizing AT1R mRNA. Pretreatment with 12(S)-HETE also amplified the signaling effects of angiotensin II, likely due to the increased AT1R expression. Levels of AT1R protein expression decreased when 12/15-lipoxygenase was knocked down with specific short hairpin RNA (shRNA) compared with control cells. Similarly, levels of the AT1 receptor, but not the AT2 receptor, were significantly lower in mesangial cells and glomeruli derived from 12/15-lipoxygenase knockout mice compared with control mice. Reciprocally, stable overexpression of 12/15-lipoxygenase increased AT1R expression in cultured mesangial cells. In vivo, modified siRNA targeting 12/15-lipoxygenase reduced glomerular AT1R expression in a diabetic mouse model. Interestingly, angiotensin II induced greater levels of 12/15-lipoxygenase, TGF-beta1, and fibronectin (FN) in AT1R-overexpressing mesangial cells compared with control cells. Therefore, oxidized lipids generated by the 12/15-lipoxygenase-mediated metabolism of arachidonic acid can enhance AT1R expression in mesangial cells and augment the profibrotic effects of angiotensin II.

An association between metabolic syndrome and the estimated glomerular filtration rate

OBJECTIVE

Metabolic syndrome (MetS) is a major public health problem. However, few studies have examined the significance of MetS as a risk factor for the development of chronic kidney disease (CKD) in the general Japanese population.

METHODS

Study participants without a clinical history of stroke, transient ischemic attack, myocardial infarction, angina, or renal failure (1,158 men, aged 61+/-15 years and 1,606 women, aged 63+/-12 years) were recruited from a single community. We examined the cross-sectional relationship between MetS and renal function as evaluated by estimated glomerular filtration rate (eGFR).

RESULTS

The presence of MetS was consistently associated with reduced eGFR, with the level of reduction proportional to the number of MetS components present. Multiple linear regression analysis using eGFR as an objective variable showed that BMI, DBP, antihypertensive drug use, high-density lipoprotein cholesterol, antilipidemic drug use and fasting blood glucose, which were components of MetS, were significantly and independently associated with eGFR, in addition to age and low-density lipoprotein cholesterol. Individuals with MetS showed a multivariate-adjusted odds ratio of 1.53 (95% confidence interval, 1.10-2.13) for CKD compared to those without MetS.

CONCLUSIONS

MetS was significantly associated with decreased eGFR in the general population.

Dynamic blood pressure load and nephropathy in the ZSF1 (fa/facp) model of type 2 diabetes

Diabetes and increased blood pressure (BP) are believed to interact synergistically in the pathogenesis and progression of diabetic nephropathy. The present studies were performed to examine if there were differences in BP load and/or protective renal autoregulatory capacity between the obese diabetic Zucker fatty /spontaneously hypertensive heart failure F1 hybrid (ZSF1) ( fa/ facp) rats and their lean controls. By ∼26 wk of age, ZSF1 ( n = 13) but not their lean controls ( n = 16) had developed substantial proteinuria (180 ± 19 vs. 16 ± 1.4 mg/24 h) and glomerulosclerosis (19 ± 2.4 vs. 0.6 ± 0.2%; P < 0.001). However, average ambient systolic BP by radiotelemetry (12–26 wk of age) was modestly lower in ZSF1 than in lean controls (130 ± 1.4 vs. 137 ± 1.7 mmHg, P < 0.002), although the 24-h BP power spectra showed a mild increase at frequencies <0.1 Hz in the ZSF1. Autoregulatory capacity under anesthesia in response to step changes in perfusion pressure between 100 and 140 mmHg was similarly well preserved in both ZSF1 and lean controls at 16–18 wk of age [autoregulatory indexes (AI) <0.1]. Similarly, differences were not observed for dynamic autoregulation in conscious rats [transfer functions between BP (input) and renal blood flow (output) using chronic Transonic flow probes]. Collectively, these data indicate that the pathogenesis of nephropathy in the ZSF1 model of type 2 diabetic nephropathy is largely independent of differences in systemic BP and/or its potential renal transmission. However, these data do not exclude the possibility that the diabetic milieu may alter the glomerular capillaries in the ZSF1, such that there is an enhanced local susceptibility to injury with even normal glomerular pressures.

Mice with enhanced macrophage angiotensin-converting enzyme are resistant to melanoma

Angiotensin-converting enzyme (ACE) is a peptidase responsible for the cleavage of angiotensin I and several other peptides. Here, gene targeting was used to switch control of the ACE locus from the endogenous promoter to the macrophage-specific c-fms promoter. Challenge of these mice, called ACE 10/10, with the aggressive mouse melanoma cell line B16 showed that they are remarkably resistant to tumor growth. Tumor resistance was seen after challenge with different melanoma cell lines and in mice with different genetic backgrounds. Histological study of the tumors that did grow in ACE 10/10 mice showed an enhanced inflammatory response. ACE 10/10 mice had increased numbers of tumor epitope-specific CD8(+) T cells after challenge with melanoma or lymphoma. ACE 10/10 macrophages showed increased production of interleukin-12 and nitric oxide but reduced interleukin-10. Engraftment of wild-type mice with ACE 10/10 bone marrow transferred B16 tumor resistance. Injection of B16 tumors with ACE 10/10 macrophages also reduced tumor growth. ACE 10/10 mice may define a new means of enhancing the immune response, which may be potentially useful in several human clinical situations.

Enhanced TGF-beta/Smad signaling in the early stage of diabetic nephropathy is independent of the AT1a receptor

BACKGROUND

Angiotensin II (AII) and transforming growth factor-beta (TGF-beta) are closely involved in the pathogenesis of diabetic nephropathy (DN). AII is known to induce TGF-beta production in resident renal cells, including glomerular mesangial cells and tubular epithelial cells. TGF-beta receptor types I and II (TGF-betaRI, II) are up-regulated in the diabetic kidney. The aim of this study was to clarify the role of AII in the regulation of the TGF-beta system in the early stage of DN using AII type1a receptor-deficient(AT1a(-/-)) mice.

METHODS

We investigated the expression of TGF-beta1, TGF-betaRI, II, and Smad signaling in AT1a(-/-) mice with streptozotocin (STZ)-induced DN. Mice were killed 10 and 20 days after the induction of hyperglycemia. The expression of TGF-beta receptors was analyzed by immunohistochemical staining and reverse transcriptase-polymerase chain reaction (RT-PCR). TGF-beta-specific Smad signaling was analyzed by electrophoretic mobility shift assay and Western blotting.

RESULTS

The expression of both TGF-betaRI and RII was up-regulated in the glomerular tufts and vasculature in diabetic AT1a(+/+) mice kidney by immunohistochemistry. RT-PCR revealed that mRNAs for TGF-betaRI and RII were also up-regulated. Smad2 and 4 protein levels were reduced in the renal cortex after the induction of diabetes, with an increase of Smad 3/4 complex in the nucleus. The expression of TGF-beta receptors increased in both diabetic AT1a(-/-) and AT1a(+/+) mice. Smad signaling in AT1a(-/-) mice was also enhanced.

CONCLUSIONS

Our results suggest that the complete blockade of the AT1a-mediated pathway has a minimal effect on the enhanced TGF-beta/Smad signaling in the early stage of DN, at least in the AT1a(-/-) model.

Activation of the renin-angiotensin system within podocytes in diabetes

The autocrine and paracrine activation of the renin-angiotensin system (RAS) within cells of the kidney plays a role in the overall pathophysiology of the renal disease due to diabetes. In this study, we focus on components of the RAS in the podocyte as these cells are important in the pathogenesis of glomerulosclerosis and proteinuria. Immortalized mouse podocytes were exposed to media containing normal glucose (NG) or high glucose (HG) for in vitro studies. In vivo studies utilized kidney tissue obtained from rats treated for 3 months with streptozotocin to induce diabetes. Angiotensinogen (AGT) and the angiotensin II (AII) type 1 receptor mRNA and protein were significantly increased in the podocytes cultured under the high glucose conditions. Both angiotensins I and II levels were significantly higher in cell lysates and the conditioned media of cells grown in high glucose. There were no differences in renin activity, angiotensin-converting enzyme level, or AII type 2 receptor level. Glomerular AGT and AII type 1 receptor assessed by means of immunohistochemistry were increased in diabetic rats compared with the control rats. Other measured components of the RAS within the glomeruli were not different. We suggest that increased AGT, an attendant increase in AII and increased AII type 1 receptor in podocytes experiencing diabetic conditions play an important role in the pathogenesis of diabetic nephropathy.

Urinary albumin excretion and the renin-angiotensin system in cardiovascular risk management

Microalbuminuria has been shown to be a strong predictor of cardiovascular morbidity and mortality in diabetic and hypertensive patients, but also in the general population. Moreover, several reports suggest that reduction of urinary albumin excretion (UAE) is associated with improvement of cardiovascular prognosis. Reduction of UAE can be achieved by lowering arterial blood pressure, but blockers of the renin-angiotensin system (RAS) with their specific renal actions have demonstrated to be able to reduce UAE more than might be expected from reduction of blood pressure alone. Consequently, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers may also provide superior cardiovascular protection, especially in subjects with higher levels of albuminuria, but evidence is still scarce. The ability of both angiotensin-converting enzyme inhibitors and angiotensin receptor blockers to reduce UAE and provide cardiovascular protection suggests that the RAS may play a central role. New developments in this area include the use of aldosterone antagonists in albuminuric/proteinuric subjects, and the development of oral renin inhibitors. Combinations of the aforementioned drugs may have the ability to fully block the RAS, potentially avoiding all detrimental effects of this hormonal cascade. However, combination therapy is expected to also increase the incidence of side effects, such as hyperkalaemia and acute renal insufficiency. The current knowledge of microalbuminuria represents the proverbial tip of the iceberg, and future studies should focus on the underlying pathophysiological mechanism of urinary albumin excretion in relation to cardiovascular protection. Only then can a better understanding of the problem be achieved and the optimal pharmacological approach be ascertained.

Combinational effect of genes for the renin-angiotensin system in conferring susceptibility to diabetic nephropathy

To elucidate the role of the renin-angiotensin system (RAS) in diabetic nephropathy, we examined the association between diabetic nephropathy in a large cohort of Japanese type 2 diabetic patients and polymorphisms within the genes that encode angiotensin-converting enzyme (ACE), angiotensinogen (AGT) and angiotensin II receptor type 1 (AGTR1). Single nucleotide polymorphisms (SNPs) within these genes were genotyped using invader assay in 747 nephropathy cases and 557 control subjects. Eight SNPs within the ACE gene were significantly associated with diabetic nephropathy (P<0.05), including five SNPs in almost complete linkage disequilibrium to the insertion/deletion polymorphism in the 16th intron (P=0.01, odds ratio =1.34, 95% CI 1.07-1.69). Three SNPs within the AGT, including M235T and one SNP in the AGTR1, were also significantly associated with nephropathy (M235T P=0.01, odds ratio =0.74, 95% CI 0.59-0.94). In addition, we found that the allelic mRNA expression corresponding to the 235M allele was significantly higher than that for the 235T allele in normal kidney tissues. Furthermore, we found a significant additional effect of these three genes by a step-wise logistic regression analysis (final empirical P value =0.00005). We concluded that RAS gene polymorphisms may contribute to the susceptibility to diabetic nephropathy in type 2 diabetes.

Combined AGE inhibition and ACEi decreases the progression of established diabetic nephropathy in B6 db/db mice

The accumulation of advanced glycation end products (AGE) is a key factor in diabetic nephropathy (DN). Pyridoxamine inhibits AGE formation and protects against type I DN. Herein we tested: (1) whether C57BL6 db/db mice as a model of established type II DN resembled patients treated with drugs which inhibit angiotensin II action; (2) whether pyridoxamine was effective as a single therapy; and (3) whether pyridoxamine would add to the benefit of angiotensin-converting enzyme inhibition (ACEi) by enalapril. In first set of experiments mice were treated with ACEi (benazepril) and an angiotensin II receptor blocker (valsartan) combination for 16 weeks after the onset of diabetes. In second group, mice with established DN were treated with pyridoxamine for 8 weeks. In a third set, mice with established DN were treated with pyridoxamine and enalapril combination for 16 weeks. Benazepril and valsartan combination partially prevented the development and progression of DN. Pyridoxamine treatment, as single therapy, decreased the progression of albuminuria and glomerular lesions. The combination of pyridoxamine with enalapril reduced both mortality and the progression of DN. In conclusion, (1) C57 BL6 db/db mice are a model of progressive type II DN; (2) The combination of pyridoxamine with enalapril decreased progression of type 2 DN and overall mortality. Thus, pyridoxamine could be a valuable adjunct to the current treatment of established type II DN.

High glucose increases extracellular matrix production in pancreatic stellate cells by activating the renin-angiotensin system

Pancreatic stellate cells (PSCs) are involved in pancreatic inflammation and fibrosis. Recent studies have shown that blocking the renin-angiotensin system (RAS) attenuates pancreatic inflammation and fibrosis. However, there are few data about the direct effects of high glucose on extracellular matrix (ECM) protein synthesis and angiotensin II (Ang II) induction in PSCs. PSCs were isolated from male Sprague-Dawley rats and cultured in medium containing 5.5 mM (LG group) or 27 mM D-glucose (HG group). Levels of Ang II and transforming growth factor-beta (TGF-beta) in culture media were measured and Ang II-positive cells were counted. We used real-time polymerase chain reaction (PCR) to detect Ang II receptor expression and Western blot analysis for the expression of ECM proteins such as connective-tissue growth factor (CTGF) and collagen type IV. Cells were also treated with an Ang II-receptor antagonist (candesartan, 10 microM) or angiotensin-converting enzyme (ACE) inhibitor (ramiprilat, 100 nM). Thymidine uptake by PSCs increased fourfold with high glucose treatment. Ang II levels and the proportion of Ang II-positive PSCs were significantly increased after 6 h under high-glucose conditions. TGF-beta concentrations also increased significantly with high glucose. After 72 h, the expression of CTGF and collagen type IV proteins in high-glucose cultures increased significantly and this increase was effectively attenuated by the candesartan or the ramiprilat. All together, high glucose induced PSCs proliferation and ECM protein synthesis, and these effects were attenuated by an Ang II-receptor antagonist. The data suggest that pancreatic inflammation and fibrosis aggravated by hyperglycemia, and Ang II play an important role in this pathogenesis.

Angiotensin II antagonists: clinical experience in the treatment of hypertension, prevention of cardiovascular outcomes and renal protection in diabetic nephropathy and proteinuria

Angiotensin II antagonists (AIIAs) were introduced to treat hypertension about 10 years ago. During this period they were evaluated not only in terms of efficacy and safety but also in several large studies with clinical outcomes. They are efficacious in all clinical forms of hypertension and are effective also in all ethnic groups. Cardiovascular and renal protection in proteinuric diabetic nephropathy beyond blood pressure reduction was proved in major clinical studies: Losartan Intervention For Endpoint reduction in hypertension study (LIFE), Reduction of Endpoint in Non-Insulin dependent Diabetes Mellitus with the AII Antagonist Losartan (RENAAL) and Irbesartan Type 2 Diabetic Nephropathy Trial (IDNT). Their blood pressure independent protective effect is also mentioned by the blockade of AT1 receptor. As a class AIIs have a tolerability profile similar to placebo.

Cross-talk between angiotensin II and glucagon receptor signaling mediates phosphorylation of mitogen-activated protein kinases ERK 1/2 in rat glomerular mesangial cells

We have recently shown that the pancreatic hormone glucagon-induced phosphorylation of mitogen-activated protein (MAP) kinase ERK 1/2 as well as growth and proliferation of rat glomerular mesangial cells (MCs) via activation of cAMP-dependent protein kinase A (PKA)- and phospholipase C (PLC)/Ca2+-mediated signaling pathways. Since circulating glucagon and tissue angiotensin II (Ang II) levels are inappropriately elevated in type 2 diabetes, we tested the hypothesis that glucagon induces phosphorylation of ERK 1/2 in MCs by interacting with Ang II receptor signaling. Stimulation of MCs by glucagon (10 nM) induced a marked increase in intracellular [Ca2+]i that was abolished by [Des-His1, Glu9]-glucagon (1 microM), a selective glucagon receptor antagonist. Both glucagon and Ang II-induced ERK 1/2 phosphorylation (glucagon: 214+/-14%; Ang II: 174+/-16%; p<0.001 versus control), and these responses were inhibited by the AT1 receptor blocker losartan (glucagon + losartan: 77+/-14%; Ang II + losartan: 84+/-18%; p<0.01 versus glucagon or Ang II) and the AT2 receptor blocker PD 123319 (glucagon + PD: 78+/-7%; Ang II + PD: 87+/-7%; p<0.01 versus glucagon or Ang II). Inhibition of cAMP-dependent PKA with H89 (1 microM) or PLC with U73122 (1 microM) also markedly attenuated the phosphorylation of ERK 1/2 induced by glucagon (glucagon + U73122: 109+/-15%; glucagon + H89: 113+/-16%; p<0.01 versus glucagon) or Ang II (Ang II + U73122: 111+/-13%; Ang II + H89: 86+/-10%; p<0.01 versus Ang II). Wortmannin (1 microM), a selective PI 3-kinase inhibitor, also blocked glucagon- or Ang II-induced ERK 1/2 phosphorylation. These results suggest that AT1 receptor-activated cAMP-dependent PKA, PLC and PI 3-kinase signaling is involved in glucagon-induced MAP kinase ERK 1/2 phosphorylation in MCs. The inhibitory effect of PD 123319 on glucagon-induced ERK 1/2 phosphorylation further suggests that AT2 receptors also play a similar role in this response.

Long-term blockade of angiotensin AT1 receptors increases survival of obese Zucker rats

Despite the well-documented effect of irbesartan, an angiotensin AT1 receptor antagonist, on diabetic nephropathy, its effect on mortality related to multiple metabolic risk factors is unknown. To address this question, obese fa/fa Zucker rats were submitted to a 13-month treatment by irbesartan (30 mg/kg/day p.o.). Vehicle-treated obese fa/fa Zucker rats exhibited an important mortality (72%), which was markedly reduced by irbesartan (22%, P<0.05). Mortality in control lean fa/+ rats attained 12%. Irbesartan diminished the elevation in urinary protein excretion, plasma creatinine and urea nitrogen levels, and reduced the extent of glomerular and tubulo-interstitial lesions together with a reduction of urinary monocyte chemoattractant protein-1 excretion in fa/fa Zucker rats. Irbesartan treatment prevented the rise in plasma total cholesterol, triglycerides and glucose levels, and partially corrected low-density lipoprotein/high-density lipoprotein (LDL/HDL) cholesterol ratio in fa/fa Zucker rats. Therefore, prolonged irbesartan treatment preserves renal function and metabolic profile, and substantially increases survival in obese fa/fa Zucker rats.

Blockade of the renin-angiotensin-aldosterone system: a key therapeutic strategy to reduce renal and cardiovascular events in patients with diabetes

Diabetes (particularly type 2 diabetes) represents a global health problem of epidemic proportions. Individuals with diabetes are not only more likely to develop hypertension, dyslipidemia, and obesity, but are also at a significantly higher risk for coronary heart disease, peripheral vascular disease, and stroke. Angiotensin II plays a key pathophysiological role in the progression of diabetic renal disease, and blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors (ACEi) or angiotensin II antagonists has therefore become an important therapeutic strategy to reduce renal and cardiovascular events in patients with diabetes. Several studies have demonstrated the effects of angiotensin II antagonists on the reduction of albuminuria and the progression of renal disease from microalbuminuria to macroalbuminuria. More importantly, several endpoint trials have shown that the antiproteinuric effects of losartan and irbesartan translate into cardiovascular and renoprotective benefits beyond blood pressure lowering, thereby delaying the need for dialysis or kidney transplantation by several years. These and other studies indicate that angiotensin II antagonists not only improve survival and quality of life of patients with diabetic nephropathy, but also have the potential to reduce the substantial healthcare burden associated with managing these patients. ACEi also appear to exert similar beneficial effects in diabetic patients, but whether clinically significant differences in renoprotection or mortality exist between angiotensin II antagonists and ACEi in patients with type 2 diabetes remains to be fully investigated in appropriate head-to-head studies.

Preventing microalbuminuria in patients with diabetes: rationale and design of the Randomised Olmesartan and Diabetes Microalbuminuria Prevention (ROADMAP) study

Diabetic nephropathy has developed into a worldwide epidemic and is responsible for the majority of end-stage renal disease in most countries. Antihypertensive treatment slows the progression of the disease. In addition, blockade of the renin-angiotensin system reduces the degree of albuminuria and angiotensin II receptor blockers (ARBs) have been shown to delay the progression from microalbuminuria to overt proteinuria in patients with diabetes. However, few studies have examined whether the initial stage of diabetic nephropathy (i.e. the development of microalbuminuria) in patients with type 2 diabetes can be slowed or prevented by ARB treatment. The Randomised Olmesartan And Diabetes MicroAlbuminuria Prevention (ROADMAP) study is a placebo-controlled, multicentre, double-blind, parallel group study investigating the effect of the ARB, olmesartan medoxomil, on the incidence of microalbuminuria. A total of 4400 type 2 diabetes patients with normoalbuminuria will be randomized to treatment with 40 mg of olmesartan medoxomil once daily or placebo. Goal blood pressure will be 130/80 mmHg. The primary endpoint of the study is the occurrence of microalbuminuria. In ROADMAP, we will also assess as secondary endpoints the effects of olmesartan on fatal and non-fatal cardiovascular events in patients with diabetes. In addition, within subgroups of the ROADMAP patients, the effects of olmesartan on retinopathy and other microvascular circulations will be analysed. The study is expected to last a median of 5 years. The ROADMAP study will answer the question whether an ARB can prevent or delay the onset of microalbuminuria and whether this translates into protection against cardiovascular events and renal disease.

Role of altered renal lipid metabolism and the sterol regulatory element binding proteins in the pathogenesis of age-related renal disease

BACKGROUND

There are well-known changes in age-related renal function and structure, including glomerulosclerosis and decline in glomerular filtration rate (GFR). The purpose of this study was to identify a potential role for lipids in mediating age-related renal disease.

METHODS

Mice of five different age groups (3, 6, 12, 19, and 23 months old) were studied.

RESULTS

We have found that in C57BL/6 mice there was a progressive increase in age-related glomerulosclerosis [increase in periodic acid-Schiff (PAS) staining and accumulation of extracellular matrix proteins including type IV collagen and fibronectin], increased glomerular basement thickness and podocyte width and effacement, and increased proteinuria. These changes were associated with age-related increase in lipid accumulation as determined by increased Oil Red O staining in kidney sections. Biochemical analysis indicated that these lipid deposits corresponded to significant increases in renal triglyceride and cholesterol content. We have also found significant age-related increases in the nuclear transcription factors, sterol regulatory element-binding proteins (SREBP-1 and SREBP-2), protein abundance and increased expression or activity of their target enzymes that play an important role in lipid synthesis.

CONCLUSION

Our results indicated that there was an age-related increase in renal expression of SREBP-1 and SREBP-2 with resultant increases in lipid synthesis and triglyceride and cholesterol accumulation in the kidney. Because we have previously shown that increased expression of SREBPs in the kidney per se results in glomerulosclerosis and proteinuria, our data suggested that increased SREBPs' expression resulting in increased renal lipid accumulation may play an important role in age-related nephropathy.

The renin-angiotensin system and its blockade in diabetic renal and cardiovascular disease

Diabetic nephropathy, the most common cause of end-stage renal disease in the United States, is also associated with increased cardiovascular mortality. The renin-angiotensin-aldosterone system (RAAS) plays a central role in the development and progression of kidney disease and cardiovascular disease. Randomized, controlled trials have demonstrated renoprotection with the use of angiotensin receptor blockers (ARBs) in type 2 and angiotensin-converting enzyme inhibitors (ACEIs) in type 1 diabetes. More recent studies have demonstrated similar cardiovascular benefits with the use of ARBs compared with ACEIs. The combination of the two classes of RAAS blockers has been investigated in large studies of patients with heart failure and after myocardial infarction, and a few small studies of patients with diabetic nephropathy. In this review, we summarized the results of the studies on the benefits of ARBs, ACEIs, and their combination in patients with diabetic nephropathy or cardiovascular diseases.

Therapeutic potential of angiostatin in diabetic nephropathy

Angiostatin is a proteolytic fragment of plasminogen and a potent angiogenic inhibitor. Previous studies have shown that angiostatin inhibits retinal neovascularization and reduces retinal vascular permeability in diabetic retinopathy. Here, it is reported for the first time that angiostatin is also implicated in diabetic nephropathy (DN). Angiostatin levels are dramatically decreased in the kidney of streptozotocin-induced diabetic rats. Consistently, diabetic kidneys also showed decreased expression and proteolytic activities of matrix metalloproteinase-2, an enzyme that releases angiostatin from plasminogen. Adenovirus-mediated delivery of angiostatin significantly alleviated albuminuria and attenuated the glomerular hypertrophy in diabetic rats. Moreover, angiostatin treatment downregulated the expression of vascular endothelial growth factor and TGF-beta1, two major pathogenic factors of DN, in diabetic kidneys. In cultured human mesangial cells, angiostatin blocked the overexpression of vascular endothelial growth factor and TGF-beta1 that were induced by high glucose while increasing the levels of pigment epithelium-derived factor, an endogenous inhibitor of DN. Moreover, angiostatin effectively inhibited the high-glucose-and TGF-beta1-induced overproduction of proinflammatory factors and extracellular matrix proteins via blockade of the Smad signaling pathway. These findings suggest that the decrease of angiostatin levels in diabetic kidney may contribute to the pathologic changes such as inflammation and fibrosis in DN. Therefore, angiostatin has therapeutic potential in DN as a result of its anti-inflammatory and antifibrosis activities.

Angiotensin II antagonists--therapeutic benefits spanning the cardiovascular disease continuum from hypertension to heart failure and diabetic nephropathy

BACKGROUND

The cardiovascular benefits of angiotensin II antagonists (AIIAs) have been evaluated not only in terms of their ability to lower blood pressure but also on their ability to prevent strokes, cardiac events, and target organ damage. This review summarizes the body of evidence-based data demonstrating the efficacy of AIIAs across the spectrum of cardiovascular disease.

METHODS

A PubMed/MEDLINE search of English-language articles (1990 to September 2005) was used to identify articles describing clinical studies, particularly outcome trials, or mechanisms of therapeutic action pertinent to the therapy of cardiovascular disease or nephropathy.

FINDINGS

The antihypertensive efficacy of AIIAs is apparent across a wide spectrum of hypertensive patients, including black and Asian patients and patients with isolated systolic hypertension. More importantly, large outcome-based studies have demonstrated the efficacy of AIIAs across the continuum of cardiovascular disease, including hypertension, heart failure, post-myocardial infarction, and diabetic nephropathy. The Losartan Intervention For Endpoint reduction in hypertension study (LIFE), Reduction of Endpoints in Non-insulin-dependent Diabetes Mellitus with the AII Antagonist Losartan (RENAAL), and the Irbesartan Type 2 Diabetic Nephropathy Trial (IDNT) indicate that AIIAs confer cardiovascular and renal protective effects beyond their ability to lower blood pressure. These bloodpressure independent protective benefits of AIIAs may arise not only by blocking the deleterious effects of AII mediated via the AT1-receptor but may also be due to beneficial molecule-specific effects. As a class, AIIAs are well tolerated with an overall adverse event profile generally comparable to placebo and superior to that typically seen with calcium channel blockers, ACE inhibitors, diuretics, and beta-blockers.

CONCLUSIONS

By utilizing the body of clinical trial evidence as a guide to rational prescribing of AIIAs, practitioners can expect to deliver clinical benefits to their patients in terms of survival, prognosis, and quality of life.

Frequency of angiotensin-converting enzyme gene polymorphism in Turkish type 2 diabetic patients

We aimed to investigate the angiotensin-converting enzyme (ACE) gene polymorphism, ACE activity and their associations with diabetic complications in Turkish patients with type 2 diabetes mellitus. A total of 143 patients and 133 controls were screened for ACE gene I/D polymorphism by using polymerase chain reaction. Serum ACE activities were determined spectrophotometrically. There was no significant difference in the distribution of ACE I/D genotypes between patients and controls. The patients with DD genotype had a higher ACE activity than those with ID and II. Hypertensive diabetic patients with DD genotype had higher ACE activities than those with ID and II. There was no significant difference in the distribution of ACE I/D genotypes between patients with and without nephropathy, retinopathy and hypertension except for patients with and without neuropathy. In patients with DD genotype, creatinine clearance correlated with duration of diabetes. The grade of retinopathy was correlated with duration of diabetes in DD and ID genotypes. The highest ACE activity was measured in hypertensive diabetics with DD genotype. ID genotype was suggested to be a risk factor and II was suggested to be protective for diabetic neuropathy. The DD and ID genotypes might be a predictor for the development of retinopathy in relation to duration of diabetes.

Preventing end stage renal disease in diabetic patients--genetic aspect (part I)

Diabetic nephropathy is a major cause of diabetes- related morbidity and mortality; however the clinical course of the disease and the renal prognosis is highly variable among individuals. The current review will discuss the genetic influence on the development of end stage renal disease (ESRD) in diabetic patients and potential improvements to the current treatment strategy to slow the loss of kidney function in these patients. In this first part, the growing evidence that glucose-induced activation of the intra-renal and systemic renin-angiotensin systems plays an essential role in processes leading to destruction of renal function is summarised. Genetic variations, especially the angiotensin-converting enzyme (ACE)/ID polymorphisms in the gene coding for ACE, are involved in activation of the renin-angiotensin system and seem to influence the clinical course of diabetic nephropathy during treatment with ACE inhibitors. In addition, this polymorphism may interact with other polymorphisms within the renin-angiotensin system, leading to high risk of ESRD. As new genetic approaches and methods develop, further understanding of diabetic nephropathy will evolve and genotyping will help prevent ESRD in diabetic patients.

Effects of irbesartan on intracellular antioxidant enzyme expression and activity in adolescents and young adults with early diabetic angiopathy

OBJECTIVE

Defective intracellular antioxidant enzyme production (IAP) has been demonstrated in adults with diabetic nephropathy. The objective of this study was to evaluate the effects of irbesartan, an angiotensin II receptor antagonist, on IAP in adolescents and young adults with type 1 diabetes and early signs of retinopathy and nephropathy.

RESEARCH DESIGN AND METHODS

This prospective, matched case-control study was conducted between November 2001 and December 2002 among 14 type 1 diabetic patients with early signs of angiopathy (ages 14-21 years), 11 type 1 diabetic patients without angiopathy (ages 12-22 years), and 10 healthy volunteers (ages 16-22 years). Skin fibroblasts were obtained by skin biopsies from the anterior part of the forearm and cultured in Dulbecco's modified Eagle's medium. The activity and mRNA expression of CuZn superoxide dismutase (CuZnSOD), Mn superoxide dismutase (MnSOD), catalase (CAT), and glutathione peroxidase (GPX) were measured before and after 6 months of treatment with irbesartan (150 mg/day); on both occasions, antioxidant enzyme activity was evaluated at different glucose concentrations (5 and 22 mmol/l).

RESULTS

At a normal glucose concentration (5 mmol/l), the activity and mRNA expression of CuZnSOD (0.50 +/- 0.21 units/mg protein, 4.4 +/- 1.5 mRNA/glyceraldehyde-3-phosphate dehydrogenase), MnSOD (0.26 +/- 0.04 units/mg protein, 0.08 +/- 0.07 mRNA), CAT (0.32 +/- 0.08 units/mg protein, 4.8 +/- 1.3 mRNA), and GPX (0.53 +/- 0.09 units/mg protein, 2.2 +/- 0.9 mRNA) were not different among the three groups (only values of diabetic subjects with angiopathy are shown). At high glucose concentrations, the activity and mRNA expression of CuZnSOD increased similarly in all groups (diabetic subjects with angiopathy: 0.93 +/- 0.26 units/mg protein, 9.4 +/- 2.1 mRNA); that of CAT and GPX increased in only control subjects and diabetic subjects without angiopathy (diabetic subjects with angiopathy: 0.33 +/- 0.09 units/mg protein and 5.0 +/- 1.4 mRNA; 0.54 +/- 0.10 units/mg protein and 2.3 +/- 1.0 mRNA, respectively). MnSOD did not change in any group. Treatment with irbesartan in adolescents with diabetic angiopathy was able to restore CAT and GPX activity and mRNA expression after exposure to high glucose concentrations. Markers of oxidative stress (serum malondialdehyde, fluorescent products of lipid peroxidation, monocyte chemoattractant protein-1, and 8-isoprostanes prostaglandin F(2alpha)) were significantly reduced after treatment with irbesartan.

CONCLUSIONS

Adolescents and young adults with early signs of diabetic angiopathy have defective intracellular antioxidant enzyme production and activity. Treatment with irbesartan can substantially improve the activity and production of these enzymes in skin fibroblasts.

In vivo imaging of oxidative stress in the kidney of diabetic mice and its normalization by angiotensin II type 1 receptor blocker

This study was undertaken to evaluate oxidative stress in the kidney of diabetic mice by electron spin resonance (ESR) imaging technique. Oxidative stress in the kidney was evaluated as organ-specific reducing activity with the signal decay rates of carbamoyl-PROXYL probe using ESR imaging. The signal decay rates were significantly faster in corresponding image pixels of the kidneys of streptozotocin-induced diabetic mice than in those of controls. This technique further demonstrated that administration of angiotensin II type 1 receptor blocker (ARB), olmesartan (5 mg/kg), completely restored the signal decay rates in the diabetic kidneys to control values. In conclusion, this study provided for the first time the in vivo evidence for increased oxidative stress in the kidneys of diabetic mice and its normalization by ARB as evaluated by ESR imaging. This technique would be useful as a means of further elucidating the role of oxidative stress in diabetic nephropathy.

Increased urinary TGF-beta1 and cortical renal GLUT1 and GLUT2 levels: additive effects of hypertension and diabetes

BACKGROUND/AIM

Diabetes and mesangial stretch caused by hypertension increase mesangial matrix deposition which is induced by local production of transforming growth factor beta 1 (TGF-beta1). Both conditions are associated with cortical GLUT1 overexpression. We evaluated the effect of genetically determined hypertension and its association with diabetes on urinary TGF-beta1 and cortical GLUT1 and GLUT2 expression.

METHODS

We studied Wistar-Kyoto rats (controls, C) and spontaneously hypertensive rats (SHR), weighing approximately 210 g, 30 days after the injection of streptozotocin (diabetic, D) or citrate buffer (10 C, 9 SHR, 12 C-D and 15 SHR-D). Twenty-four-hour urine was collected for glucose, albumin, and TGF-beta1 determinations. Catheters were implanted into the femoral artery to measure the arterial blood pressure in conscious animals 1 day later. Then GLUT1 and GLUT2 protein levels (Western blotting) in renal cortex and medulla were evaluated.

RESULTS

The cortical GLUT1 levels were 5, 2, and 7 times higher in SHR, C-D, and SHR-D groups versus C group (p < 0.05); the GLUT2 contents were 1.5, 1.8, and 2.3 times higher in SHR, C-D and SHR-D groups versus C group (p < 0.05). The urinary TGF-beta1 level was elevated by diabetes and diabetes and hypertension, but not by hypertension alone: 1.39 +/- 0.2, 2.34 +/- 0.6, 18.2 +/- 3.2, and 28.8 +/- 7.6 ng/24 h, respectively, in C, SHR, C-D, and SHR-D groups (p < 0.05).

CONCLUSIONS

Diabetes, hypertension, and especially their association increase the renal cortical GLUT1 and GLUT2 levels. The magnitude of GLUT1 overexpression caused by hypertension is higher than that induced by diabetes alone. The impact on urinary TGF-beta1 occurs when diabetes and hypertension are associated, suggesting an effect that is triggered in the presence of GLUT1 overexpression and hyperglycemia.

Effect of High Glucose on Superoxide in Human Mesangial Cells: Role of Angiotensin II

BACKGROUND/AIMS

Reactive oxygen species, and especially superoxide (O2*),have been implicated in diabetic nephropathy. O2* accumulation in cells is dependent on O2* production (by NADH/NADPH oxidase) as well as scavenging by superoxide dismutase (SOD) activity. This study was designed to investigate the effects of high glucose (HG) on O2* accumulation and SOD activity in human mesangial cells (HMC) and to determine if these effects are mediated by angiotensin II (Ang II).

METHODS

HMC were incubated in media containing 10 mM glucose (control, C), 30 mM glucose (HG), 10 mM glucose + either 20 mM 2-deoxy-D-glucose (2-DG) or 20 mM mannitol (high mannitol, HM) (osmotic controls), or Ang II (10(-5) M). Ang II action was antagonized by employing 10(-4) M of Ang II receptor antagonists (losartan or irbesartan) or 10(-4) M of NADH/NADPH oxidase inhibitors [diphenyleneiodonium chloride (DPI) or apocynin]. Superoxide and total SOD activity were assayed using chemiluminescence of lucigenin.

RESULTS

Incubation of HMC in HG resulted in a 1.6-fold increase in Ang I (p < 0.05) and a 1.4-fold increase in Ang II levels (p < 0.05) in cell lysates. These changes were accompanied by a >2-fold increase in O2* accumulation (p < 0.01), which was inhibited by losartan and irbesartan. Exogenous Ang II increased net O2* accumulation by 2.7-fold (p < 0.01), which was normalized by losartan and irbesartan. DPI and apocynin blocked the HG and Ang II-induced increases in O2* (p < 0.01). HG but not exogenous Ang II inhibited total SOD activity by 30%, which was not affected by losartan.

CONCLUSION

High glucose increases O2* accumulation in HMC primarily by increasing its production via the Ang II-NADH/NADPH oxidase system.

Translational regulation of vascular endothelial growth factor expression in renal epithelial cells by angiotensin II

ANG II regulates growth factor expression in the kidney. We investigated whether ANG II regulated vascular endothelial growth factor (VEGF) synthesis in proximal tubular epithelial (MCT) cells. ANG II (1 nM) increased VEGF protein expression within 5 min, the effect lasting for 30 min. There was no change in VEGF mRNA levels or mRNA stability, and transcription inhibitors did not affect ANG II-induced VEGF expression. Regulation of VEGF translation was investigated. Polyribosomal analysis revealed selective enrichment of heavy ribosomes (polysomes) with VEGF mRNA transcripts compared with light ribosomes in ANG II-treated cells, although distribution of GAPDH was unaltered. In vitro translation of total RNA from polysomal fractions showed selective increase in VEGF protein synthesis in ANG II-treated cells. Preincubation with LY-294002, a PI 3-kinase inhibitor, or expression of dominant-negative Akt prevented ANG II-stimulated increase in VEGF translation. ANG II increased phosphorylation of eukaryotic initiation factor 4E and its binding protein 4E-BP1, critical events that regulate the initiation phase of protein translation. ANG II failed to increase VEGF mRNA translation in cells stably expressing the phosphorylation mutant of 4E-BP1. Our data illustrate that a rapid increase in VEGF protein expression by ANG II is regulated at the initiation phase of translation of VEGF mRNA in renal epithelial cells. Regulation of VEGF translation by ANG II represents a novel pathway of renal response to injury.

Angiotensin II receptor blocker inhibits p27Kip1 expression in glucose-stimulated podocytes and in diabetic glomeruli

BACKGROUND

Diabetic nephropathy is characterized by glomerular and tubular hypertrophy, and angiotensin II receptor blockers (ARBs) are known to prevent renal hypertrophy in diabetic patients.

METHODS

To determine the effect of ARB on podocyte p27(Kip1) mRNA and protein expression, podocytes were exposed to 5.6 mmol/L normal glucose or 25 mmol/L high glucose with or without ARB, 10(-7) mol/L L-158,809. For animal studies, streptozotocin-induced diabetic rats were left untreated or were treated with 1 mg/kg/day L-158,809 for 3 months (diabetes mellitus + ARB). Competitive reverse transcription-polymerase chain reaction (RT-PCR), Western blot, immunohistochemistry, and morphometric analyses were performed.

RESULTS

p27(Kip1) mRNA and protein expression in podocytes exposed to high glucose and in 3-month diabetic glomeruli were significantly increased (P < 0.01). High glucose significantly increased angiotensin II levels both in cell lysates and in media compared with normal glucose (P < 0.05) and exogenous angiotensin II also increased p27(Kip1) mRNA and protein expression in podocytes. L-158,809 treatment in podocytes inhibited the increase in p27(Kip1) mRNA expression by 84%, and protein expression by 89% (P < 0.05). p27(Kip1) mRNA and protein expression in diabetic + ARB glomeruli were also significantly reduced by 78% and 85%, respectively, compared with diabetic glomeruli (P < 0.01). ARB treatment also significantly ameliorated increased glomerular p27(Kip1) expression in diabetes mellitus as assessed by immunohistochemistry (P < 0.01). The increase in glomerular volume in diabetes mellitus was also inhibited by 81% with ARB treatment (P < 0.05).

CONCLUSION

p27(Kip1) mRNA and protein expression were increased in diabetic glomeruli as well as in high glucose-stimulated podocytes, and this increment in p27(Kip1) expression was ameliorated by ARB treatment. These findings indicate that ARB treatment has an additional effect on preventing renal hypertrophy in diabetes mellitus.

Do angiotensin II antagonists provide benefits beyond blood pressure reduction?

Hypertension is a powerful risk factor for cardiovascular (CV) morbidity and mortality; therefore, blood pressure (BP) lowering plays a central role in reducing the cardiovascular complications of hypertension, including stroke. Recent outcomes studies--Losartan Intervention For Endpoint reduction in hypertension, Reduction of Endpoints in Non-insulin-dependent Diabetes Mellitus with the Angiotensin II Antagonist Losartan, and the Irbesartan Type 2 Diabetic Nephropathy Trial--suggest that some angiotensin II antagonists are associated with CV and renal effects beyond their ability to lower BP in patients with hypertension or diabetic nephropathy and may play a role in the prevention of new-onset type 2 diabetes. Angiotensin II antagonists are associated with a wide variety of vascular, cardiac, and renal effects, as well as molecule-specific effects independent of those induced by the angiotensin-I receptor. These actions may offer a mechanistic explanation for the outcome benefits observed in patients with hypertension or diabetic nephropathy. Angiotensin-converting enzyme inhibitors and calcium-channel blockers may also have effects that are not completely explained by differences in the antihypertensive response to these agents, but the evidence is less robust. Collectively, these findings suggest that management of patients with hypertension, with or without diabetes or renal disease, should no longer be viewed as simply a matter of correcting elevated BP. Antihypertensive agents that possess CV benefits beyond their BP-reducing effects should be used to prevent the development of end-organ damage.

Renin-angiotensin system blockade prevents the increase in plasma transforming growth factor beta 1, and reduces proteinuria and kidney hypertrophy in the streptozotocin-diabetic rat

INTRODUCTION

Combination therapy with angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) is used to improve renal outcome achieved by monotherapy in diabetic patients. In addition, interference with the renin-angiotensin system (RAS) reduced expression and excretion of transforming growth factor beta 1 (TGF-beta 1) in diabetic nephropathy. The aim of this study was to investigate the effects of interrupting the RAS by ACE inhibitor (ACE-I) or ARB monotherapy or by combination therapy on proteinuria, kidney hypertrophy and plasma TGF-beta 1 in diabetic rats.

MATERIALS AND METHODS

Forty-one male Wistar rats were allocated to five groups: 1 = control rats, 2 = diabetic rats (streptozotocin [STZ] 55 mg/kg), 3 = diabetic rats as above receiving enalapril (20 mg/kg/day), 4 = diabetic rats receiving losartan (80 mg/kg/day), 5 = diabetic rats receiving both losartan and enalapril. The study lasted 60 days.

RESULTS

Urinary protein excretion, kidney weight, serum ACE activity and plasma TGF-beta1 increased significantly in untreated diabetic rats compared with controls. Administration of losartan, enalapril, or both for 60 days prevented these changes. Furthermore, combined therapy for 30 days normalised urinary protein excretion, while monotherapy did not. Losartan inhibited serum ACE activity both in vivo and in vitro. Plasma TGF-beta 1 levels were positively correlated with blood glucose levels (r=0.4059) and with urinary protein excretion (r=0.3558).

CONCLUSIONS

Combination therapy with losartan and enalapril was more effective than monotherapy with either drug in achieving an early antiproteinuric response. Long-term treatment with losartan was as effective as the combined treatment, possibly due to a dual inhibitory effect on the RAS. The antiproteinuric effect may be related, in part, to reduced TGF-beta 1.

A novel mechanism for angiotensin II formation in streptozotocin-diabetic rat glomeruli

Recent evidence suggests that the intrarenal renin-angiotensin system (RAS) may play an important role in the development of glomerular changes associated with diabetic nephropathy. In this study, the glomerular RAS was examined in male Sprague-Dawley rats made diabetic with streptozotocin (STZ), and the findings compared with those obtained in control nondiabetic rats. In diabetic rat glomerular extracts, angiotensinogen and angiotensin II (ANG II) levels were increased significantly by 2.2- and 1.9-fold, respectively, compared with nondiabetic controls. No significant differences in ANG I and angiotensin-converting enzyme (ACE) levels were observed between these groups. The HPLC analysis of the glomerular extracts demonstrated that exogenous ANG I was converted into various ANG peptides including ANG II, ANG1-9, and ANG1-7. A significant increase in formation of ANG II from exogenous ANG I was observed in STZ rats compared with control rats. Preincubation of glomerular extracts with captopril resulted in a 20-30% decrease in ANG II conversion from exogenous ANG I in diabetic and control rats. The possible role of ANG1-9 in formation of ANG II was examined by HPLC. Exogenous ANG1-9 in glomerular extracts was converted into ANG II, this conversion being significantly higher in STZ rats than in control rats. These findings provide new information that ANG1-9 is produced in rat glomerular extracts, can be converted to ANG II, and that this conversion is also stimulated in diabetic rat glomeruli. Thus this study demonstrates that in diabetic rats, glomerular ANG II levels are increased due to an increase in angiotensinogen and an increase in the formation of ANG II.

Renoprotective effect of benazepril on diabetic nephropathy mediated by P42/44MAPK

The effects of benazepril on P42/44MAPK, angiotensin II expression in renal tissue and renal pathological change of the experimental diabetic rats were assessed and the possible mechanism of benazepril's renoprotective effect was explored. Adult male Wistar rats, 11-12 weeks age, weighing initially 160 to 200 g were randomly allocated into 2 groups: control group (A, n = 6) and experimental group (n = 12). Diabetic rats in experimental group were rendered diabetic by intraperitoneal injection of Streptozotocin (60 mg/kg body weight), and randomly subdivided into B group (diabetic control) and C group (diabetic rats treated with benazepril, 6 mg/kg every day). Studies were performed 8 weeks after induction of diabetes. Twenty-four h urine of every rat was collected to detect urine creatinine. Serum glucose concentration and serum creatinine were determined by collecting blood samples from the inferior vena cava. Body and kidney weight were recorded. Creatinine clearance (Ccr) and ratio of kidney weight to body weight were calculated. Plasma and renal tissue angiotensin II concentration was assayed by radioimmunoassay (RIA). The phospo-p44/42MAPK protein expression was detected by Western-blot. The results showed that benazepril had no significant effect on the blood glucose level in diabetic rats in two experimental groups. Ccr and ratio of kidney weight to body weight were increased in group B (P < 0.01) as compared with normal rats at the end of the 8th week. At the end of the 8th week, Ccr in group C was lower than that in group B (P < 0.01). The ratio of kidney weight to body weight in group C was lower than that in group B at the 8th week. There were glomeruli hypertrophy and slight or moderate mesangium proliferation in diabetic rats, while there was fragmentally proliferative mesangium in group C at the end of the 8th week. Renal tissue angiotensin II concentration was significantly increased in group B, while benazepril could significantly decrease the concentration of angiotensin II in renal tissue. The expression of the phospo-p44/42MAPK protein in group B was increased as compared with group A, while it was decreased in group C as compared with group B. P42/ 44MAPK pathway participated in the pathogenesis of diabetic nephropathy. Benazepril can eliminate high filtration of glomeruli, decrease proteinuria, and eliminate renal hypertrophy as well as renal destruction. Renoprotective effect of benazepril in diabetic rats may be partly related to the inhibition of angiotensin II -P42/44MAPK pathway.

Transcription factor decoy for AP-1 reduces mesangial cell proliferation and extracellular matrix production in vitro and in vivo

Diabetic nephropathy is characterized by an expansion of glomerular mesangium, caused by mesangial cell proliferation and excessive accumulation of extracellular matrix (ECM) proteins, which eventually leads to glomerulosclerosis and renal failure. Activator protein-1 (AP-1), a transcription factor, is implicated in the transcriptional regulation of a wide range of genes participating in cell proliferation and ECM production. This investigation was undertaken to test the hypothesis that AP-1 plays an important role in ECM gene expression, and to develop a molecular therapeutic strategy based on decoy oligodeoxynucleotides (ODN). In this report, we show that transfection with AP-1 decoy ODN strongly inhibits high glucose- and angiotensin II-induced cell proliferation and expression of ECM genes in cultured mesangial cells in vitro. Administration of AP-1 decoy ODN into streptozotocin-induced diabetic rat kidney in vivo using the hemagglutinating virus of Japan (HVJ)-liposome method virtually abolished TGF-beta1 and plasminogen activator inhibitor-1 expression. Our results collectively indicate that AP-1 activation is crucial for mesangial cell proliferation and ECM production in response to high glucose and angiotensin II. Moreover, use of stable AP-1 decoy ODN combined with the highly effective HVJ-liposome method provides a novel potential molecular therapeutic strategy for the prevention of diabetic nephropathy.