The angiotensin II type 2 receptor agonist Compound 21 is protective in experimental diabetes-associated atherosclerosis.

AIMS/HYPOTHESIS: Angiotensin II is well-recognised to be a key mediator in driving the pathological events of diabetes-associated atherosclerosis via signalling through its angiotensin II type 1 receptor (AT1R) subtype. However, its actions via the angiotensin II type 2 receptor (AT2R) subtype are still poorly understood. This study is the first to investigate the role of the novel selective AT2R agonist, Compound 21 (C21) in an experimental model of diabetes-associated atherosclerosis (DAA). METHODS: Streptozotocin-induced diabetic Apoe-knockout mice were treated with vehicle (0.1 mol/l citrate buffer), C21 (1 mg/kg per day), candesartan cilexetil (4 mg/kg per day) or C21 + candesartan cilexetil over a 20 week period. In vitro models of DAA using human aortic endothelial cells and monocyte cultures treated with C21 were also performed. At the end of the experiments, assessment of plaque content and markers of oxidative stress, inflammation and fibrosis were conducted. RESULTS: C21 treatment significantly attenuated aortic plaque deposition in a mouse model of DAA in vivo, in association with a decreased infiltration of macrophages and mediators of inflammation, oxidative stress and fibrosis. On the other hand, combination therapy with C21 and candesartan (AT1R antagonist) appeared to have a limited additive effect in attenuating the pathology of DAA when compared with either treatment alone. Similarly, C21 was found to confer profound anti-atherosclerotic actions at the in vitro level, particularly in the setting of hyperglycaemia. Strikingly, these atheroprotective actions of C21 were completely blocked by the AT2R antagonist PD123319. CONCLUSIONS/INTERPRETATION: Taken together, these findings provide novel mechanistic and potential therapeutic insights into C21 as a monotherapy agent against DAA.

Angiotensin II type 2 receptor (AT2R) in renal and cardiovascular disease.

Angiotensin II (Ang II) is well-considered to be the principal effector of the renin-angiotensin system (RAS), which binds with strong affinity to the angiotensin II type 1 (AT1R) and type 2 (AT2R) receptor subtype. However, activation of both receptors is likely to stimulate different signalling mechanisms/pathways and produce distinct biological responses. The haemodynamic and non-haemodynamic effects of Ang II, including its ability to regulate blood pressure, maintain water-electrolyte balance and promote vasoconstriction and cellular growth are well-documented to be mediated primarily by the AT1R. However, its biological and functional effects mediated through the AT2R subtype are still poorly understood. Recent studies have emphasized that activation of the AT2R regulates tissue and organ development and provides in certain context a potential counter-regulatory mechanism against AT1R-mediated actions. Thus, this review will focus on providing insights into the biological role of the AT2R, in particular its actions within the renal and cardiovascular system.

Role of bone-marrow- and non-bone-marrow-derived receptor for advanced glycation end-products (RAGE) in a mouse model of diabetes-associated atherosclerosis.

RAGE (receptor for advanced glycation end-products) is expressed on multiple cell types implicated in the progression of atherosclerosis and plays a role in DAA (diabetes-associated atherosclerosis). The aim of the present study was to determine the relative role of either BM (bone marrow)- or non-BM-derived RAGE in the pathogenesis of STZ (streptozotocin)-induced DAA. Male ApoE (apolipoprotein E)-null (ApoE-/-:RAGE+/+) and ApoE:RAGE-null (ApoE-/-:RAGE-/-) mice at 7 weeks of age were rendered diabetic with STZ. At 8 weeks of age, ApoE-/- and ApoE-/-:RAGE-/- control and diabetic mice received BM from either RAGE-null or RAGE-bearing mice, generating various chimaeras. After 10 and 20 weeks of diabetes, mice were killed and gene expression and atherosclerotic lesion formation were evaluated respectively. Deletion of RAGE in either the BM cells or non-BM cells both resulted in a significant attenuation in DAA, which was associated with reduced VCAM-1 (vascular cell adhesion molecule-1) expression and translated into reduced adhesion in vitro. In conclusion, the results of the present study highlight the importance of both BM- and non-BM-derived RAGE in attenuating the development of DAA.

The pleiotropic actions of rosuvastatin confer renal benefits in the diabetic Apo-E knockout mouse.

Diabetic nephropathy is a leading cause of end-stage renal disease. Statins may exert renoprotective effects independently of lipid-lowering properties. We investigated the pleiotropic effects of rosuvastatin on renal structure and function in streptozotocin diabetic apolipoprotein-E knockout (Apo-E(-/-)) mice, a model of progressive nephropathy in which dyslipidemia is resistant to statin treatment. These effects were compared with those observed with conventional renin-angiotensin system blockade (candesartan) or combined treatment. Nondiabetic and diabetic Apo-E(-/-) mice were randomized to no treatment or treatment with candesartan (2.5 mg/kg), rosuvastatin (5 mg/kg), or their combination per gavage for 20 wk. Urine and blood samples were collected for assessment of albuminuria, creatinine clearance, plasma lipids, glucose, and glycated hemoglobin. Renal sclerosis was analyzed on paraffin-embedded kidney sections stained with periodic acid-Schiff. Renal expression of collagen IV, fibronectin and advanced glycation end products (AGEs), receptor for advanced glycation and products (RAGE), NADPH oxidase 4 (NOX4), and nitrotyrosine was assessed by real-time PCR and/or immunohistochemistry. Diabetes-induced albuminuria was not affected by rosuvastatin and combination treatment but was prevented by candesartan. Diabetes resulted in increased creatinine clearance, which was not modified by the treatments. Rosuvastatin and/or candesartan prevented diabetes-associated renal extracellular matrix accumulation. Rosuvastatin reduced accumulation of AGEs and expression of RAGE, NOX4, and nitrotyrosine. In conclusion, in the diabetic Apo-E(-/-) mouse, rosuvastatin confers renal benefits that are independent of lipid lowering and equivalent or greater to those observed with candesartan. The combination treatment is not superior to monotherapies.

Disparate Effects of Diabetes and Hyperlipidemia on Experimental Kidney Disease.

It is well established that diabetes is the major cause of chronic kidney disease worldwide. Both hyperglycemia, and more recently, advanced glycation endproducts, have been shown to play critical roles in the development of kidney disease. Moreover, the renin-angiotensin system along with growth factors and cytokines have also been shown to contribute to the onset and progression of diabetic kidney disease; however, the role of lipids in this context is poorly characterized. The current study aimed to compare the effect of 20 weeks of streptozotocin-induced diabetes or western diet feeding on kidney disease in two different mouse strains, C57BL/6 mice and hyperlipidemic apolipoprotein (apo) E knockout (KO) mice. Mice were fed a chow diet (control), a western diet (21% fat, 0.15% cholesterol) or were induced with streptozotocin-diabetes (55 mg/kg/day for 5 days) then fed a chow diet and followed for 20 weeks. The induction of diabetes was associated with a 3-fold elevation in glycated hemoglobin and an increase in kidney to body weight ratio regardless of strain (p < 0.0001). ApoE deficiency significantly increased plasma cholesterol and triglyceride levels and feeding of a western diet exacerbated these effects. Despite this, urinary albumin excretion (UAE) was elevated in diabetic mice to a similar extent in both strains (p < 0.0001) but no effect was seen with a western diet in either strain. Diabetes was also associated with extracellular matrix accumulation in both strains, and western diet feeding to a lesser extent in apoE KO mice. Consistent with this, an increase in renal mRNA expression of the fibrotic marker, fibronectin, was observed in diabetic C57BL/6 mice (p < 0.0001). In summary, these studies demonstrate disparate effects of diabetes and hyperlipidemia on kidney injury, with features of the diabetic milieu other than lipids suggested to play a more prominent role in driving renal pathology.

Adverse effects of high glucose and free fatty acid on cardiomyocytes are mediated by connective tissue growth factor.

Diabetic cardiomyopathy is characterized by interstitial fibrosis and cardiomyocyte hypertrophy and apoptosis. Also known as CCN2, connective tissue growth factor (CTGF) is implicated in the fibrosis; however, whether it contributes to cardiomyocytes changes and adverse effects of high glucose and lipids on these cells remains unknown. Hearts from streptozotocin-induced diabetic rats had elevated CTGF and changes of pathological myocardial hypertrophy, fibrosis, and cardiomyocyte apoptosis. Rat H9c2 cardiomyocytes were then treated with recombinant human (rh)CTGF, high glucose, or the saturated free fatty acid palmitate. Each reagent induced cell hypertrophy, as indicated by the ratio of total protein to cell number, cell size, and gene expression of cardiac hypertrophy marker genes atrial natriuretic peptide (ANP), and alpha-skeletal actin. Each treatment also caused apoptosis measured by increased caspase3/7 activity, apoptotic cells by transferase-mediated dUTP nick end labeling (TUNEL) assay, and lower viable cell number. Further studies showed CTGF mRNA was rapidly induced by high glucose and palmitate in H9c2 cells and in mouse neonatal cardiomyocyte primary cultures. small interfering RNA against CTGF blocked the high glucose and palmitate induction of hypertrophy and apoptosis. In addition, these CTGF effects were through the tyrosine kinase A (TrkA) receptor with tyrosine kinase activity, which has previously been implicated in CTGF signaling: TrkA was phosphorylated by CTGF, and a specific TrkA blocker abrogated CTGF-induced effects on hypertrophy and apoptosis. For the first time in any system, fatty acid is newly identified as a regulator of CTGF, and this work implicates autocrine CTGF as a mediator of adverse effects of high glucose and fatty acids in cardiomyocytes.

Lack of the antioxidant enzyme glutathione peroxidase-1 accelerates atherosclerosis in diabetic apolipoprotein E-deficient mice.

BACKGROUND: Recent clinical studies have suggested a major protective role for the antioxidant enzyme glutathione peroxidase-1 (GPx1) in diabetes-associated atherosclerosis. We induced diabetes in mice deficient for both GPx1 and apolipoprotein E (ApoE) to determine whether this is merely an association or whether GPx1 has a direct effect on diabetes-associated atherosclerosis. METHODS AND RESULTS: ApoE-deficient (ApoE-/-) and ApoE/GPx1 double-knockout (ApoE-/- GPx1-/-) mice were made diabetic with streptozotocin and aortic lesion formation, and atherogenic pathways were assessed after 10 and 20 weeks of diabetes. Aortic proinflammatory and profibrotic markers were determined by both quantitative reverse-transcription polymerase chain reaction analysis after 10 weeks of diabetes and immunohistochemical analysis after 10 and 20 weeks of diabetes. Sham-injected nondiabetic counterparts served as controls. Atherosclerotic lesions within the aortic sinus region, as well as arch, thoracic, and abdominal lesions, were significantly increased in diabetic ApoE-/- GPx1-/- aortas compared with diabetic ApoE-/- aortas. This increase was accompanied by increased macrophages, alpha-smooth muscle actin, receptors for advanced glycation end products, and various proinflammatory (vascular cell adhesion molecule-1) and profibrotic (vascular endothelial growth factor and connective tissue growth factor) markers. Quantitative reverse-transcription polymerase chain reaction analysis showed increased expression of receptors for advanced glycation end products (RAGE), vascular cell adhesion molecule-1, vascular endothelial growth factor, and connective tissue growth factor. Nitrotyrosine levels were significantly increased in diabetic ApoE-/- GPx1-/- mouse aortas. These findings were observed despite upregulation of other antioxidants. CONCLUSIONS: Lack of functional GPx1 accelerates diabetes-associated atherosclerosis via upregulation of proinflammatory and profibrotic pathways in ApoE-/- mice. Our study provides evidence of a protective role for GPx1 and establishes GPx1 as an important antiatherogenic therapeutic target in patients with or at risk of diabetic macrovascular disease.

Diabetes Reduces Severity of Aortic Aneurysms Depending on the Presence of Cell Division Autoantigen 1 (CDA1).

Diabetes is a negative risk factor for aortic aneurysm, but the underlying explanation for this phenomenon is unknown. We have previously demonstrated that cell division autoantigen 1 (CDA1), which enhances transforming growth factor-ß signaling, is upregulated in diabetes. We hypothesized that CDA1 plays a key role in conferring the protective effect of diabetes against aortic aneurysms. Male wild-type, CDA1 knockout (KO), apolipoprotein E (ApoE) KO, and CDA1/ApoE double-KO (dKO) mice were rendered diabetic. Whereas aneurysms were not observed in diabetic ApoE KO and wild-type mice, 40% of diabetic dKO mice developed aortic aneurysms. These aneurysms were associated with attenuated aortic transforming growth factor-ß signaling, reduced expression of various collagens, and increased aortic macrophage infiltration and matrix metalloproteinase 12 expression. In the well-characterized model of angiotensin II-induced aneurysm formation, concomitant diabetes reduced fatal aortic rupture and attenuated suprarenal aortic expansion, changes not seen in dKO mice. Furthermore, aortic CDA1 expression was downregulated ∼70% within biopsies from human abdominal aortic aneurysms. The identification that diabetes is associated with upregulation of vascular CDA1 and that CDA1 deletion in diabetic mice promotes aneurysm formation provides evidence that CDA1 plays a role in diabetes to reduce susceptibility to aneurysm formation.

A 1,3-diacylglycerol-rich oil induces less atherosclerosis and lowers plasma cholesterol in diabetic apoE-deficient mice.

OBJECTIVE: Recent studies have demonstrated that 1,3-diacylglycerol (1,3-DAG) has several metabolic advantages over triacylglycerol (TAG) in humans and in animal models despite both oils having a similar fatty acid composition. In our current study, we have examined the effects of long-term feeding of a 1,3-DAG-rich oil on the dyslipidemia and atherosclerosis in the experimental model of the diabetic apolipoprotein E (apoE)-deficient mouse that develops accelerated atherosclerosis. METHODS AND RESULTS: Diets containing 1,3-DAG-rich oil or TAG oil were administered to control non-diabetic apoE-dificient and diabetic apoE-deficient mice for 20 weeks. In diabetic apoE-deficient mice, 1,3-DAG reduced the extent of atherosclerotic lesions in the aortic arch and thoracic aorta by 37 and 44%, respectively, compared to TAG. Further, in diabetic apoE-deficient mice, plasma total cholesterol and triglyceride levels were significantly lower in the 1,3-DAG-fed group than in the TAG-fed group. This occurred partially through an apparent reduction in the size of triglyceride-rich lipoproteins but not apparently by reducing the number of lipoprotein particles. By contrast the control non-diabetic apoE-deficient mice showed no differential responses to the type of oil at least over 20 weeks. CONCLUSIONS: We have demonstrated that dietary 1,3-DAG-rich oil reduced atherosclerosis in diabetic apoE-deficient mice, and was associated with reduction in plasma cholesterol especially within larger triglyceride-rich lipoproteins.

Rosiglitazone attenuates atherosclerosis in a model of insulin insufficiency independent of its metabolic effects.

OBJECTIVE: Recent studies have demonstrated a role for thiazolidinediones in attenuating atherosclerosis. However, these studies were performed in insulin-resistant animal models in association with reductions in insulin and glucose levels. To assess the vascular effects of thiazolidinediones, independent of their metabolic effects, we observed the effect of rosiglitazone on diabetes-associated atherosclerosis in a model of insulin insufficiency. METHODS AND RESULTS: Control and diabetic apolipoprotein E-deficient mice received rosiglitazone or placebo. Diabetic mice demonstrated a 3-fold increase in plaque area, which was attenuated by rosiglitazone. There was no significant difference in glucose, insulin, or cholesterol levels between treated and untreated diabetic animals. Rosiglitazone attenuated the increase in superoxide production observed in diabetic mice. A 4-fold increase in the reverse cholesterol transport marker ABCA1 was observed in treated diabetic mice. Rosiglitazone reduced angiotensin II receptor gene expression in control and diabetic mice, and macrophage accumulation was increased in diabetic mice compared with controls and was attenuated by rosiglitazone. CONCLUSIONS: These findings suggest peroxisome proliferator-activated receptor-gamma ligands such as rosiglitazone confer vascular protection independent of their effects on metabolic control. These antiatherosclerotic effects may have important clinical ramifications not only in insulin resistance/type 2 diabetes and also in type 1 diabetes.

Diabetes mellitus-associated atherosclerosis: mechanisms involved and potential for pharmacological invention.

While diabetes mellitus is most often associated with hypertension, dyslipidemia, and obesity, these factors do not fully account for the increased burden of cardiovascular disease in patients with the disease. This strengthens the need for comprehensive studies investigating the underlying mechanisms mediating diabetic cardiovascular disease and, more specifically, diabetes-associated atherosclerosis. In addition to the recognized metabolic abnormalities associated with diabetes mellitus, upregulation of putative pathological pathways such as advanced glycation end products, the renin-angiotensin system, oxidative stress, and increased expression of growth factors and cytokines have been shown to play a causal role in atherosclerotic plaque formation and may explain the increased risk of macrovascular complications. This review discusses the methods used to assess the development of atherosclerosis in the clinic as well as addressing novel biomarkers of atherosclerosis, such as low-density lipoprotein receptor-1. Experimental models of diabetes-associated atherosclerosis are discussed, such as the streptozocin-induced diabetic apolipoprotein E knockout mouse. Results of major clinical trials with inhibitors of putative atherosclerotic pathways are presented. Other topics covered include the role of HMG-CoA reductase inhibitors and fibric acid derivatives with respect to their lipid-altering ability, as well as their emerging pleiotropic anti-atherogenic actions; the effect of inhibiting the renin-angiotensin system by either ACE inhibition or angiotensin II receptor antagonism; the effect of glycemic control and, in particular, the promising role of thiazolidinediones with respect to their direct anti-atherogenic actions; and newly emerging mediators of diabetes-associated atherosclerosis, such as advanced glycation end products, vascular endothelial growth factor and platelet-derived growth factor. Overall, this review aims to highlight the observation that various pathways, both independently and in concert, appear to contribute toward the pathology of diabetes-associated atherosclerosis. Furthermore, it reflects the need for combination therapy to combat this disease.

Irbesartan but not amlodipine suppresses diabetes-associated atherosclerosis.

BACKGROUND: It remains controversial whether specific blockade of the renin-angiotensin system confers superior antiatherosclerotic effects over other antihypertensive agents in diabetes. Therefore, the aim of this study was to compare equihypotensive doses of the angiotensin II subtype 1 (AT1) receptor blocker irbesartan with the calcium antagonist amlodipine on diabetes-induced plaque formation in the apolipoprotein E (apoE)-null mouse and to explore molecular and cellular mechanisms linked to vascular protection. METHODS AND RESULTS: Diabetes was induced by injection of streptozotocin in 6-week-old apoE-null mice. Diabetic animals were randomized to no treatment, irbesartan, or amlodipine for 20 weeks. Diabetes was associated with an increase in plaque area and complexity in the aorta in association with a significant increase in aortic AT1 receptor expression, cellular proliferation, collagen content, macrophage- and alpha-smooth muscle actin-positive cell infiltration, as well as an increased expression of platelet-derived growth factor-B (PDGF-B), monocyte chemoattractant protein-1 (MCP-1), and vascular cell adhesion molecule-1 (VCAM-1). Irbesartan but not amlodipine treatment attenuated the development of atherosclerosis, collagen content, cellular proliferation, and macrophage infiltration as well as diabetes-induced AT1 receptor, PDGF-B, MCP-1, and VCAM-1 overexpression in the aorta despite similar blood pressure reductions by both treatments. CONCLUSIONS: Diabetes-associated atherosclerosis is ameliorated by AT1 receptor blockade but not by calcium channel antagonism, providing further evidence for the vascular renin-angiotensin system playing a pivotal role in the development and acceleration of atherosclerosis in diabetes.

Prevention of accelerated atherosclerosis by angiotensin-converting enzyme inhibition in diabetic apolipoprotein E-deficient mice.

BACKGROUND: Atherosclerosis is a major complication of diabetes, but the mechanisms by which diabetes promotes macrovascular disease have not been fully delineated. Although several animal studies have demonstrated that inhibition of ACE results in a decrease in the development of atherosclerotic lesions, information about the potential benefits of these agents on complex and advanced atherosclerotic lesions as observed in long-term diabetes is lacking. The aim of this study was to evaluate whether treatment with the ACE inhibitor perindopril affects diabetes-induced plaque formation in the apolipoprotein E (apoE)-deficient mouse. METHODS AND RESULTS: Diabetes was induced by injection of streptozotocin in 6-week-old apoE-deficient mice. Diabetic animals received treatment with perindopril (4 mg x kg(-1) x d(-1)) or no treatment for 20 weeks. Nondiabetic apoE-deficient mice were used as controls. Induction of diabetes was associated with a 4-fold increase in plaque area compared with nondiabetic animals. This accelerated atherosclerosis was associated with a significant increase in aortic ACE expression and activity and connective tissue growth factor and vascular cell adhesion molecule-1 expression. Perindopril treatment inhibited the development of atherosclerotic lesions and diabetes-induced ACE, connective tissue growth factor, and vascular cell adhesion molecule-1 overexpression in the aorta. CONCLUSIONS: The activation of the local renin-angiotensin system in the diabetic aorta and the reduction in atherosclerosis with ACE inhibitor treatment provides further evidence that the renin-angiotensin system plays a pivotal role in the development and acceleration of atherosclerosis in diabetes.

Advanced glycation end product interventions reduce diabetes-accelerated atherosclerosis.

Advanced glycation end product (AGE) formation may contribute to the progression of atherosclerosis, particularly in diabetes. The present study explored atherosclerosis in streptozotocin-induced diabetic apolipoprotein E-deficient (apoE-/-) mice that were randomized (n = 20) to receive for 20 weeks no treatment, the AGE cross-link breaker ALT-711, or the inhibitor of AGE formation aminoguanidine (AG). A sixfold increase in plaque area with diabetes was attenuated by 30% with ALT-711 and by 40% in AG-treated mice. Regional distribution of plaque demonstrated no reduction in plaque area or complexity within the aortic arch with treatment, in contrast to the thoracic and abdominal aortas, where significant attenuation was seen. Diabetes-associated accumulation of AGEs in aortas and plasma and decreases in skin collagen solubility were ameliorated by both treatments, in addition to reductions in the vascular receptor for AGE. Collagen-associated reductions in the AGEs carboxymethyllysine and carboxyethyllysine were identified with both treatments. Diabetes was also accompanied by aortic accumulation of total collagen, specifically collagens I, III, and IV, as well as increases in the profibrotic cytokines transforming growth factor-beta and connective tissue growth factor and in cellular alpha-smooth muscle actin. Attenuation of these changes was seen in both treated diabetic groups. ALT-711 and AG demonstrated the ability to reduce vascular AGE accumulation in addition to attenuating atherosclerosis in these diabetic mice.

Anti-atherosclerotic and renoprotective effects of combined angiotensin-converting enzyme and neutral endopeptidase inhibition in diabetic apolipoprotein E-knockout mice.

OBJECTIVE: To investigate the effects of the combined angiotensin-converting enzyme (ACE)/neutral endopeptidase (NEP) inhibitor omapatrilat on atherosclerosis and renal injury in a model of diabetes-associated accelerated atherosclerosis and renal injury. DESIGN: The study was performed using diabetic apolipoprotein E-knockout (apo E-KO) mice, a model combining hyperlipidemia and hyperglycemia, which leads to accelerated atherosclerosis and renal injury. METHODS: Diabetes was induced by the injection of streptozotocin in 6-week old apo E-KO mice. Diabetic animals received no treatment (n = 12) or treatment with the ACE/NEP inhibitor omapatrilat (30 mg/kg per day, via gavage, n = 12) or quinapril (10 mg/kg per day, in drinking water, n = 12) for 20 weeks. Non-diabetic apo E-KO mice (n = 12) served as controls. RESULTS: Omapatrilat reduced atherosclerosis and protected the mice from renal structural injury and albuminuria. The protective effects were associated with tissue inhibition of aortic and renal ACE and NEP as well as a significant reduction in blood pressure. Omapatrilat had similar anti-atherosclerotic effects compared with the ACE inhibitor quinapril in association with an almost complete inhibition of aortic ACE activity by both drugs. Omapatrilat conferred superior renoprotection in the diabetic apo E-KO mouse compared with quinapril in the context of greater renal ACE inhibition by omapatrilat than seen with quinapril, additional renal NEP inhibition and a modestly enhanced antihypertensive response. CONCLUSIONS: These studies demonstrate the anti-atherosclerotic and renoprotective effects of omapatrilat in diabetic apo E-KO mice, a model of accelerated atherosclerosis and renal injury. These effects were observed in association with the local inhibition of ACE and NEP at the tissue level in the aorta and kidney. These results suggest that the anti-atherosclerotic effect conferred by omapatrilat treatment in the diabetic apo E-KO mouse is predominantly mediated by its capacity to inhibit local vascular ACE. By contrast, in the kidney, local renal ACE and NEP inhibition and the superior antihypertensive effect of omapatrilat all contribute to the renoprotective effect conferred by omapatrilat treatment in the diabetic apo E-KO mouse.

Advanced glycation end products in diabetes-associated atherosclerosis and renal disease: interventional studies.

There is increasing evidence that advanced glycation end products (AGEs) and their interactions with various receptors (in particular, the receptor RAGE) play a pivotal role in the development and progression of diabetic macro- and microvascular complications. Several approaches have been used to inhibit tissue accumulation of AGEs in diabetes, including inhibitors of AGE formation such as aminoguanidine, ALT 946, and pyridoxamine-or putative cross-link breakers such as ALT 711. Alternative interventions have also included the administration of a soluble receptor for RAGE, sRAGE, thus capturing circulating AGEs and preventing them from binding to the cell-bound full-length receptor RAGE, thereby inhibiting the proinflammatory and profibrotic response following AGE-RAGE binding. In this review we summarize the evidence for such antiglycation therapies in retarding or delaying the development and progression of diabetes-associated atherosclerosis and renal disease while focusing on interventional strategies inhibiting AGE accumulation. In summary, all approaches have been shown to confer some degree of antiatherosclerotic and renoprotective effects, albeit to different degrees and by different mechanisms.

Imatinib attenuates diabetes-associated atherosclerosis.

OBJECTIVE: Diabetes is associated with accelerated atherosclerosis, the major factor contributing to increased mortality and morbidity in the diabetic population. The molecular mechanisms by which diabetes promotes atherosclerosis are not fully understood. Platelet-derived growth factor has been shown to play a major role in the pathology of vascular diseases, but whether it plays a role in atherosclerosis associated with diabetes remains unknown. The aims of this study were to assess whether platelet-derived growth factor-dependent pathways are involved in the development of diabetes-induced atherosclerosis and to determine the effects of platelet-derived growth factor receptor antagonism on this disorder. METHODS AND RESULTS: Diabetes was induced by injection of streptozotocin in 6-week-old apolipoprotein E knockout mice. Diabetic animals received treatment with a tyrosine kinase inhibitor that inhibits platelet-derived growth factor action, imatinib (STI-571, 10 mg/kg per day), or no treatment for 20 weeks. Nondiabetic apolipoprotein E knockout mice served as controls. Induction of diabetes was associated with a 5-fold increase in plaque area in association with an increase in aortic platelet-derived growth factor-B expression and platelet-derived growth factor-beta receptor phosphorylation as well as other prosclerotic and proinflammatory cytokines. Imatinib treatment prevented the development of atherosclerotic lesions and diabetes-induced inflammatory cytokine overexpression in the aorta. CONCLUSIONS: Tyrosine kinase inhibition with imatinib appears to be a novel therapeutic option to retard the development of atherosclerosis, specifically in the context of diabetes.

Diabetes induces Na/H exchange activity and hypertrophy of rat mesenteric but not basilar arteries.

Experimental hyperglycemia produces a marked hypertrophic response in rat mesenteric arteries, accompanied by activation of Na/H exchange (NHE) in medial smooth muscle. This study asked if other vascular beds are similarly affected by examining the hypertrophic and NHE response of the basilar artery. Sections of mesenteric and basilar arteries from adult rats were analysed by standard morphometric techniques at 1 and 3 weeks after streptozotocin injection. NHE activity was assessed as changes in intracellular pH in isolated intact vessels using concurrent myography and fluorescence spectroscopy. Mesenteric arteries showed a significant increase in lumenal (47%), medial (51%) and adventitial (17%) area. In contrast, these parameters were not increased in basilar arteries from the same set of animals. Maximal NHE activity was significantly increased at 1 week (24%) and 3 weeks (20%) in mesenteric arteries, but in basilar arteries there was no change in basal intracellular pH, maximal NHE activity or kinetic properties of the transporter. NHE plays a central role in vascular changes in diabetes. As the mesenteric hypertrophy is amenable to therapeutic intervention these findings add further to the potential of NHE as a therapeutic target for ameliorating vascular disease in diabetes.

A low-sodium diet potentiates the effects of losartan in type 2 diabetes.

OBJECTIVE: Diabetic subjects have a high prevalence of hypertension, increased total body exchangeable sodium levels, and an impaired ability to excrete a sodium load. This study assessed the effect of dietary sodium restriction on the efficacy of losartan in hypertensive subjects with type 2 diabetes and albumin excretion rates of 10-200 microg/min. RESEARCH DESIGN AND METHODS: In this study, 20 subjects were randomized to losartan 50 mg/day (n = 10) or placebo (n = 10). Drug therapy was given in two 4-week phases separated by a washout period. In the last 2 weeks of each phase, patients were assigned to low- or regular-sodium diets, in random order. In each phase, 24-h ambulatory blood pressure, urinary albumin-to-creatinine ratio (ACR), and renal hemodynamics were measured. RESULTS: Achieved urinary sodium on a low-sodium diet was 85 +/- 14 and 80 +/- 22 mmol/day in the losartan and placebo groups, respectively. In the losartan group, the additional blood pressure-lowering effects of a low-sodium diet compared with a regular-sodium diet for 24-h systolic, diastolic, and mean arterial blood pressures were 9.7 mmHg (95% confidence interval [CI], 2.2-17.2; P = 0.002), 5.5 mmHg (2.6-8.4; P = 0.002), and 7.3 mmHg (3.3- 11.3; P = 0.003), respectively. In the losartan group, the ACR decreased significantly on a low-sodium diet versus on a regular-sodium diet (-29% [CI -50.0 to -8.5%] vs. + 14% [-19.4 to 47.9%], respectively; P = 0.02). There was a strong correlation between fall in blood pressure and percent reduction in the ACR (r = 0.7, P = 0.02). In the placebo group, there were no significant changes in blood pressure or ACR between regular- and low-sodium diets. There were no significant changes in renal hemodynamics in either group. CONCLUSIONS: These data demonstrated that a low-sodium diet potentiates the antihypertensive and antiproteinuric effects of losartan in type 2 diabetes. The blood pressure reduction resulting from the addition of a low-sodium diet to losartan was of similar magnitude to that predicted from the addition of a second antihypertensive agent.

Mouse Models for Studying Diabetic Nephropathy.

Diabetic nephropathy (DN) is a term used to describe kidney damage cause by diabetes. With DN as one of the leading causes of end-stage renal disease worldwide, there is a strong need for appropriate animal models to study DN pathogenesis and develop therapeutic strategies. To date, most experiments are carried out in mouse models as opposed to other species for several reasons including lower cost, ease of handling, and easy manipulation of the mouse genome to generate transgenic and knockout animals. This unit provides detailed insights and technical knowledge in setting up one of the most widely used models of DN, the streptozotocin (STZ)-induced model. This model has been extensively exploited to study the mechanism of diabetic renal injury. The advantages and limitations of the STZ model and the availability of other genetic models of DN are also discussed.