The Protective Effects of Taurine against Early Renal Injury in STZ-Induced Diabetic Rats,Correlated with Inhibition of Renal LOX-1-Mediated ICAM-1 Expression

Oxidative stress is a key cause in the development of diabetic nephropathy (DN). As a main receptor of oxidized low-density lipoprotein (oxLDL), LOX-1 plays an important role in the induction of leukocyte adhesion molecules, such as intercellular cell adhesion molecule-1 (ICAM-1). Taurine (TAU), a potent endogenous antioxidant, showed renoprotective effects in several model animals. This study was designed to determine the renoprotective effect and possible mechanism involved LOX-1 and ICAM-1 expression of taurine in early DN. Six-week-old male Wistar rats were divided into three groups: normal control (NC), diabetes mellitus (DM), and taurine-treated DM (DM+TAU). Diabetes was induced by streptozotocin (STZ, 60 mg/kg, i.p.). After the onset of diabetes, drinking water containing 1% taurine was given to rats in the DM+TAU group. After six weeks of treatment, blood glucose (BG), serum levels of creatinine (sCr) and BUN, and LOX-1 and ICAM-1 expression (protein and gene) in kidney cortices were estimated. Meanwhile, renal malondialdehyde (MDA) levels and glutathione peroxidase (GSH-Px) activities were examined as parameters of oxidative stress in diabetic rats. For DM+TAU rats, when compared with DM rats, the levels of serum BUN, sCr, and renal MDA were reduced, and the activities of renal GSH-Px were increased, but the BG levels were not influenced. Simultaneously, taurine attenuated histopathologic evidence of renal damages and reduced the overexpression of LOX-1 and ICAM-1 in kidney cortices of diabetic rats. In conclusion, taurine showed protective effects against early renal injury in diabetic rats. These renoprotective effects may be partly caused by suppression of oxLDL/LOX-1 system and subsequently ICAM-1 overexpression on renal cortex via its antioxidative property.     

Role of high glucose-induced nuclear factor-kappaB activation in monocyte chemoattractant protein-1 expression by mesangial cells

Although high glucose (HG) has been shown to induce nuclear factor-kappaB (NF-kappaB) activation in vascular cells, the upstream regulation and the biologic significance of NF-kappaB activation in diabetic renal injury are not clear. It was, therefore, examined if HG-induced generation of reactive oxygen species (ROS) and protein kinase C (PKC) activation are involved in NF-kappaB activation in mesangial cells (MC), and the role of NF-kappaB activation in HG-induced monocyte chemoattractant protein-1 (MCP-1) expression by MC was further investigated. Recent observations suggest that MCP-1 may play a role in the development and progression of diabetic nephropathy. HG rapidly induced NF-kappaB activation in MC as estimated by electrophoretic mobility shift assay. Supershift assay suggests that most of the binding activity arose from p50/p50 and p50/p65 dimers. Antioxidants, pyrrolidine dithiocarbamate, N-acetyl-L-cystein, and trolox effectively inhibited HG-induced NF-kappaB activation in MC. HG rapidly generated dichlorofluorescin-sensitive intracellular ROS in MC as measured by laser-scanning confocal microscopy. HG also activated PKC rapidly in MC. Inhibition of PKC effectively blocked HG-induced intracellular ROS generation and NF-kappaB activation in MC. HG increased MCP-1 mRNA expression by 1.9-fold and protein secretion by 1.6-fold that of control glucose in MC transfected with control vector but not in MC transfected with dominant negative mutant inhibitor of NF-kappaB (IkappaBalphaM). Inhibition of either PKC or ROS effectively blocked HG-induced, but not basal, MCP-1 protein secretion by MC transfected with control vector. Thus this study demonstrates that HG rapidly activates NF-kappaB in MC through PKC and ROS and suggests that HG-induced NF-kappaB activation in MC may play a role in diabetic renal injury through upregulation of MCP-1 mRNA and protein expression.     

LOX-1、VCAM-1在糖尿病肾病动脉粥样硬化大鼠中的表达及普罗布考的影响

目的 观察普罗布考（PL）对糖尿病肾病动脉粥样硬化大鼠模型肾脏及腹主动脉LOX-1、VCAM-1表达的干预,阐明PL减轻其肾脏及主动脉氧化应激的机制。方法 50只雄性SD大鼠随机分为正常对照组和模型组。对照组予以普通饮食,实验组给予高糖、高脂、高胆固醇饮食。8周后模型组予以腹腔注射链脲佐菌素（STZ）40mg/kg,将造模成功的大鼠随机分为糖尿病肾病组（DN组）和PL治疗组,PL组经口灌胃PL(500mg?kg-1?d-1)。第18周测鼠重,血糖及24h尿蛋白定量,处死大鼠抽取血液观察血清生化指标及SOD和MDA,取肾脏及腹主动脉行组织切片观察其病理改变,免疫组织化学法检测肾脏及腹主动脉内LOX-1、VCAM-1蛋白的表达,RT-PCR方法检测肾脏及腹主动脉内LOX-1、VCAM-1核酸的表达。结果 PL能减轻模型组大鼠蛋白尿,改善血清白蛋白,降低血清肌酐、尿素氮,降低甘油三酯、胆固醇及MDA;下调肾脏及腹主动脉LOX-1、VCAM-1蛋白及核酸的表达。结论 PL可减轻肾脏及主动脉的氧化应激,其机制可能与PL降低LOX-1、VCAM-1的表达相关,进而保护肾脏及主动脉内膜功能。     

Epstein-Barr virus latent membrane protein 1 activates nuclear factor-kappa B in human endothelial cells and inhibits apoptosis

BACKGROUND: Although vascular changes and transplant vasculopathy have been described with cytomegalovirus, the impact of Epstein-Barr virus (EBV) on the vascular endothelium of the transplanted allograft is largely unknown. We recently reported that EBV (+) patients taken off immunosuppressive medications for periods of time had a low incidence of chronic rejection. In another report, we noted that there was expression of the "protective" antiapoptotic factor Bcl-2 in the vascular endothelium of transplant allografts from EBV (+) patients. In this report, we determined the effect of latent EBV infection on endothelial cell activation and apoptosis. METHODS: Cultured human umbilical vein endothelial cells (HUVEC) were either infected with EBV or transduced with EBV latent membrane protein 1 and examined for apoptosis, nuclear factor (NF)-kappaB activation, and expression of chemokines, cytokines, and adhesion molecules. RESULTS: EBV infection and latent membrane protein 1 expression in HUVEC resulted in NF-kappaB activation and increased expression of the cytokines interleukin (IL)-1alpha, IL-1beta, and IL-6; the chemokines IL-8, monocyte chemotactic protein-1, and RANTES; and the adhesion molecules intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin. There was increased expression of the antiapoptotic genes A1, c-IAP2, and TRAF1; inhibition of caspase 3; and protection from apoptosis. CONCLUSIONS: Latent EBV in HUVEC results in constitutive NF-kappaB activation, protection from apoptosis, and increased basal expression of inflammatory factors. The in vivo effect of latent EBV in the vascular endothelium of the transplanted allograft and its resultant impact on transplant vasculopathy are the subject of further investigations in our laboratory.     

Mechanical stretch induces monocyte chemoattractant activity via an NF-kappaB-dependent monocyte chemoattractant protein-1-mediated pathway in human mesangial cells: inhibition by rosiglitazone

Hemodynamic abnormalities are important in the pathogenesis of the glomerular damage in diabetes. Glomerular macrophage infiltration driven by the chemokine monocyte chemoattractant protein-1 (MCP-1) is an early event in diabetic nephropathy. The thiazolidinedione rosiglitazone ameliorates albumin excretion rate in diabetic patients with microalbuminuria and has anti-inflammatory properties, raising the possibility of a relationship between its renoprotective and anti-inflammatory activity. Investigated was whether mesangial cell stretching, mimicking in vitro glomerular capillary hypertension, enhances MCP-1 expression and monocyte chemoattractant activity. The effect of the combination of stretch with high glucose on MCP-1 production was studied and, finally, the effect of rosiglitazone on these processes was assessed. Stretching of human mesangial cells significantly enhanced their monocyte chemoattractant activity. This effect was mediated by MCP-1 as it was paralleled by a significant rise in both MCP-1 mRNA and protein levels and was completely abolished by MCP-1 blockade. Combined exposure to both stretch and high glucose further increased MCP-1 production. Stretch activated the IkappaB-NF-kappaB pathway, and NF-kappaB inhibition, with the use of the specific inhibitor SN50, completely abolished stretch-induced MCP-1, indicating that stretch-induced MCP-1 was NF-kappaB dependent. The addition of rosiglitazone significantly diminished stretch-induced NF-kappaB activation, MCP-1 production, and monocyte chemotaxis. In conclusion, stretching of mesangial cells stimulates their monocyte chemoattractant activity via an NF-kappaB-mediated, MCP-1-dependent pathway, and this effect is prevented by rosiglitazone.     

Lectin-like oxidized low-density lipoprotein (LDL) receptor (LOX-1)-mediated pathway and vascular oxidative injury in older-age rat renal transplants

BACKGROUND: Older-age renal allografts are associated with inferior survival; however, the mechanisms are unclear. Reactive oxygen species participate in aging and in chronic vascular disease. We investigated how mediators of oxidative stress may increase allograft susceptibility to vascular injury. METHODS: We employed the low-responder allogeneic F344-to-Lew rat renal transplantation model. We used nonimmunosuppressed young (donors and recipients aged 12 weeks), old (donors and recipients aged 52 weeks), and old-to-young animal (donors aged 52 weeks and recipients aged 12 weeks) combinations. Grafts were transplanted after 2 hours cold preservation in University of Wisconsin solution and harvested 1, 2, 7 and 10 days later. Additionally, old animals receiving continuous 1.5 mg/kg cyclosporine (CyA) immunosuppression were included. Renal allograft pathology was scored according to Banff criteria. We studied intragraft vascular adhesion molecule-1 (VCAM-1), lectin-like oxidized low-density lipoprotein (LDL) receptor-1 (LOX-1), and hypochlorite-modified LDL expression as well as ED-1+ monocytes/macrophages and CD8+ lymphocyte infiltration. Intragraft in situ superoxide anion radical production was determined with dihydroethidium assay on cryosections. RESULTS: During the first 2 posttransplant days, old transplants demonstrated higher functional impairment and increased oxidative stress, while young transplant had higher ED-1+ monocytes/macrophage infiltration and VCAM-1 expression. The degree of VCAM-1 expression and ED-1+ monocytes/macrophage and CD8+ lymphocyte infiltration correlated at later time points directly with the transplant age. VCAM-1 and LOX-1 staining were localized predominantly on the endothelium of arterial vessels, shifting the distribution to vascular smooth muscle layer strongly dependent on donor age and the grade of vascular injury. LOX-1 staining colocalized with hypochlorite-modified epitopes in the media of injured arteries. We measured increased in situ superoxide anion radical production in corresponding areas. Immunosuppression with CyA had no protective effect on vascular injury and LOX-1 expression. CONCLUSION: Induction of LOX-1-related oxidation pathways and increased susceptibility to oxidative stress could play an important role in promoting vascular injury in old renal transplants independent of the recipient age.     

Role of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) in the development of hypertensive organ damage

Recently, a novel endothelial oxidized low-density lipoprotein (LDL) receptor, lectin-like oxidized LDL receptor (LOX)-1, has been identified by the expression cloning of cultured bovine aortic endothelial cells (BAEC). The experimental evidence has suggested that LOX-1 may contribute to the development of vascular injury. For example, LOX-1 is upregulated in aorta from hypertensive, diabetic, and hyperlipidemic model animals. Also, LOX-1 overexpression is observed in atherosclerotic regions and damaged kidneys. In hypertensive animals, not only antihypertensive drugs but also antioxidant agents suppress the LOX-1 overexpression. Peroxisome proliferator-activated receptor- (PPAR) activators inhibit cytokine-stimulated LOX-1 expression, possibly through their antioxidant effects, while, in contrast, LOX-1 generates reactive oxygen species (ROS). Therefore, ROS may play an important role in both the expression and function of LOX-1.     

Expression of LOX-1, an oxidized low-density lipoprotein receptor, in experimental hypertensive glomerulosclerosis

Oxidized low-density lipoprotein (OxLDL) has been implicated in atherosclerosis and glomerulosclerosis. LOX-1 is a recently identified OxLDL receptor that is abundantly expressed in vascular endothelial cells. The aim of the present study was to investigate LOX-1 expression in the kidneys of hypertensive rats. Dahl salt-sensitive (DS) and salt-resistant (DR) rats were fed a 0.3% or 8% NaCl diet. Some DS 8% rats were treated with manidipine or hydralazine. LOX-1 gene expression was markedly elevated in the kidneys and glomeruli of hypertensive DS 8% rats compared with those of normotensive DR and DS 0.3% rats. Prolonged salt loading further increased the renal LOX-1 expression in DS rats. The LOX-1 upregulation in DS 8% rats was accompanied by renal overexpression of transforming growth factor-beta 1 and type I collagen, impaired renal function, and histologic glomerulosclerotic changes, all of which were ameliorated by antihypertensive treatment. LOX-1 was indeed expressed in the glomeruli in vivo and in cultured glomerular cells in vitro. However, LOX-1 expression was elevated in the aorta but not the kidneys of spontaneously hypertensive rats, which exhibited hypertension but minor glomerulosclerotic changes. In conclusion, the LOX-1 upregulation in the kidney of DS 8% rats was parallel to glomerulosclerotic changes and renal dysfunction, suggesting a possible pathogenetic role for renal LOX-1 in the progression to hypertensive glomerulosclerosis.     

Oxidized low-density lipoprotein stimulates monocyte adhesion to glomerular endothelial cells.

BACKGROUND: Abnormalities in lipid and lipoprotein metabolism have been implicated in the pathogenesis of glomerulosclerosis. Atherogenic lipoproteins [for example, low-density lipoprotein (LDL) and oxidized LDL (ox-LDL)] have been shown to stimulate glomerular monocyte chemoattractants involved in monocyte infiltration. However, the role of LDL and ox-LDL in the early monocyte adhesion to glomerular endothelial cells (ECs) and associated intracellular signaling mechanisms are not clearly understood. METHODS: In this study, we examined the effect of LDL and ox-LDL on intracellular signaling mechanisms associated with monocyte adhesion to glomerular ECs and intercellular adhesion molecule-1 (ICAM-1) expression. RESULTS: Ox-LDL, but not LDL, stimulated EC ICAM-1 expression and monocyte adhesion. Ox-LDL elevated protein tyrosine kinase (PTK) activity, and the preincubation of ECs with specific PTK inhibitors blocked ox-LDL-induced ICAM-1 message and monocyte adhesion. Whereas experimental maneuvers that inhibit either protein kinase C activation (by PKC depletion or with inhibitors) or Gi-protein-mediated pathways (pertussis toxin sensitive) had no effect on ox-LDL-induced monocyte adhesion and ICAM-1 expression. cAMP-elevating compounds did not induce ICAM-1 or monocyte adhesion. CONCLUSIONS: The data indicate that ox-LDL, by stimulating monocyte adhesion to the glomerular endothelium, may regulate monocyte infiltration within the glomerulus, supporting an early pathobiological role for atherogenic lipoproteins in glomerular injury. The results suggest that the activation of specific PTK and associated signaling may, at least in part, play a critical role in ox-LDL-mediated endothelial-monocyte interaction-related events. The data suggest that the interventions aimed at modifying associated intracellular signaling events within the glomerulus may provide potential therapeutic modalities in monocyte/macrophage-mediated glomerular disease.     

Neuronatin: a new inflammation gene expressed on the aortic endothelium of diabetic mice

OBJECTIVE—Identification of arterial genes and pathways altered in obesity and diabetes.RESEARCH DESIGN AND METHODS—Aortic gene expression profiles of obese and diabetic db/db, high-fat diet–fed C57BL/6J, and control mice were obtained using mouse Affymetrix arrays. Neuronatin (Nnat) was selected for further analysis. To determine the function of Nnat, a recombinant adenovirus (Ad-Nnat) was used to overexpress the Nnat gene in primary endothelial cells and in the mouse aorta in vivo.RESULTS—Nnat, a gene of unknown vascular function, was upregulated in the aortas of db/db and high-fat diet–fed mice. Nnat gene expression was increased in db/db mouse aorta endothelial cells. Nnat protein was localized to aortic endothelium and was selectively increased in the endothelium of db/db mice. Infection of primary human aortic endothelial cells (HAECs) with Ad-Nnat increased expression of a panel of nuclear factor-κB (NF-κB)-regulated genes, including inflammatory cytokines, chemokines, and cell adhesion molecules. Infection of mouse carotid arteries in vivo with the Ad-Nnat increased expression of vascular cell adhesion molecule 1 protein. Nnat activation of NF-κB and inflammatory gene expression in HAECs was mediated through pathways distinct from tumor necrosis factor-α. Nnat expression stimulated p38, Jun NH₂-terminal kinase, extracellular signal–related kinase, and AKT kinase phosphorylation. Phosphatidylinositol 3-kinase and p38 inhibitors prevented Nnat-mediated activation of NF-κB–induced gene expression.CONCLUSIONS—Nnat expression is increased in endothelial cells of obese and diabetic mouse blood vessels. The effects of Nnat on inflammatory pathways in vitro and in vivo suggest a pathophysiological role of this new gene in diabetic vascular diseases.Epidemiological data has shown a strong association between diabetes and coronary heart disease (1,2). Although insulin-mediated improved glucose control reduced cardiovascular events in subjects with type 1 diabetes (3), less definitive information is available relating diabetes control and atherosclerosis prevention in type 2 diabetes. Recent findings suggest that hyperglycemia is associated with increased arterial wall inflammation (4) and increased expression of vascular inflammatory molecules, such as vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and E-Selectin (SELE) (5,6); nuclear factor-κB (NF-κB) activation (7,8); and inflammatory cytokine production. Fundamental understanding of the effects of diabetes on arterial genes and pathways may contribute to the discovery of new strategies for the treatment of diabetic vascular diseases beyond blood glucose control.Animal models of diabetes have been used to study the effects of hyperglycemia and insulin resistance at different stages of disease progression (9,10). We (11,12) and others (13,14) have demonstrated that mouse models of type 2 diabetes such as leptin receptor mutant db/db and diet-induced obesity mice have impaired vascular function. Kim et al. (15) demonstrated that high-fat diet feeding increases expression of markers of vascular inflammation in mouse thoracic aortas. Also, apolipoprotein E knockout db/db mice have increased VCAM-1 expression in aorta (16) and greater aortic sinus atherosclerosis (16,17). However, not all investigators have observed changes in expression of adhesion molecules in db/db mouse aortas (18).A number of studies have focused on the effects of diabetes on vascular cells. Endothelial cells isolated from db/db aortas have increased inflammatory cytokine and chemokine expression and more monocyte adhesion (19–21). The reasons for the altered biology of these cells is thought by many to be due to hyperglycemia; increased glucose concentrations induce interleukin (IL)-6, IL-8, and monocyte chemotactic protein-1 (MCP-1) secretion and adhesion molecule expression in endothelial cells. IL-6/IL-6Rα complex can induce an inflammatory phenotype in endothelial cells, promoting SELE, ICAM-1, and VCAM-1 expression and monocyte adhesion (21,22).In the current study, we performed gene expression profiling of aortas from two mouse models of type 2 diabetes to identify new genes and pathways that contribute to diabetic vascular diseases. We found that neuronatin (Nnat), a gene with unknown vascular function, was upregulated in the aortas of both db/db and high-fat diet–fed mice. Immunohistochemical studies localized Nnat to the vascular endothelium. To gain insight into the function of this molecule, the effects of adenovirus-induced Nnat expression in human aortic endothelial cells (HAECs) and mouse arteries were studied.     

Modification of tissue-factor mRNA and protein response to thrombin and interleukin 1 by high glucose in cultured human endothelial cells

Because diabetic vascular disease is accompanied by a state of hypercoagulability, manifested by increased thrombin activity and foci of intravascular coagulation, we investigated whether a specific procoagulant property of the endothelium--production and surface expression of tissue factor--is modified by elevated glucose concentrations. In unperturbed human vascular endothelial cells, tissue factor mRNA and expression of the functional protein were undetectable and were not induced by 10-12 days of exposure to 30 mM glucose. In thrombin-stimulated cultures, tissue-factor expression was related inversely to cellular density, with confluent cultures producing (per 10(5) cells) half the amount of tissue factor measured in sparse cultures. Cells exposed to high glucose and studied when cell number and thymidine incorporation were identical to control cells manifested increased tissue-factor mRNA level and functional protein production in response to thrombin (P = .002). This effect was not attributable to hypertonicity and was not observed after short exposure to high glucose. In contrast, the tissue-factor response to interleukin 1, a modulator of endothelial function in the context of host defense, was decreased in cells cultured in high glucose (P = .04). These findings indicate that exposure to high glucose can alter tissue-factor gene expression in perturbed vascular endothelium. The reciprocal effects of high glucose on the tissue-factor response to thrombin and interleukin 1 points to different pathways of tissue-factor stimulation by the two agents and suggests functional consequences pertinent to the increased thrombin activity and compromised host-defense mechanisms observed in diabetes.     

Role of protein kinase C on the expression of platelet-derived growth factor and endothelin-1 in the retina of diabetic rats and cultured retinal capillary pericytes

Increased expression of endothelin-1 (ET-1) is associated with diabetic retinopathy and vasculopathy, although the molecular explanation has not been defined. The effects of high glucose and protein kinase C (PKC) activation on platelet-derived growth factor (PDGF)-BB and of ET-1 expression in the retina of streptozotocin (STZ)-induced diabetic rats and bovine retinal pericytes (BRPC) were examined. In 4-week diabetic rats, PDGF-B and prepro-ET-1 (ppET-1) mRNA levels increased significantly by 2.8- and 1.9-fold, respectively, as quantified by RT-PCR. Treatment with PKC-beta isoform-specific inhibitor (LY333531) or insulin normalized retinal ET-1 and PDGF-B expression. In BRPC, high glucose levels increased ppET-1 and PDGF-B mRNA expression by 1.7- and 1.9-fold, respectively. The addition of PDGF-BB but not PDGF-AA increased expression of ppET-1 and vascular endothelial growth factor mRNA by 1.6- and 2.1-fold, respectively, with both inhibited by AG1296, a selective PDGF receptor kinase inhibitor. A general PKC inhibitor, GF109203X, suppressed PDGF-BB's induction of ET-1 mRNA. Thus, increased ET-1 expression in diabetic retina could be due to increased expression of PDGF-BB, mediated via PDGF-beta receptors in part by PKC activation. The novel demonstration of elevated expression of PDGF-B and its induction by PKC activation identifies a potential new molecular step in the pathogenesis of diabetic retinopathy.     

High glucose via peroxynitrite causes tyrosine nitration and inactivation of prostacyclin synthase that is associated with thromboxane/prostaglandin H(2) receptor-mediated apoptosis and adhesion molecule expression in cultured human aortic endothelial cells.

Loss of the modulatory role of the endothelium may be a critical initial factor in the development of diabetic vascular diseases. Exposure of human aortic endothelial cells (HAECs) to high glucose (30 or 44 mmol/l) for 7-10 days significantly increased the release of superoxide anion in response to the calcium ionophore A23187. Nitrate, a breakdown product of peroxynitrite (ONOO(-)), was substantially increased in parallel with a decline in cyclic guanosine monophosphate (GMP). Using immunochemical techniques and high-performance liquid chromatography, an increase in tyrosine nitration of prostacyclin (PGI(2)) synthase (PGIS) associated with a decrease in its activity was found in cells exposed to high glucose. Both the increase in tyrosine nitration and the decrease in PGIS activity were lessened by decreasing either nitric oxide or superoxide anion, suggesting that ONOO(-) was responsible. Furthermore, SQ29548, a thromboxane/prostaglandin (PG) H(2) (TP) receptor antagonist, significantly reduced the increased endothelial cell apoptosis and the expression of soluble intercellular adhesion molecule-1 that occurred in cells exposed to high glucose, without affecting the decrease in PGIS activity. Thus, exposure of HAECs to high glucose increases formation of ONOO(-), which causes tyrosine nitration and inhibition of PGIS. The shunting of arachidonic acid to the PGI(2) precursor PGH(2) or other eicosanoids likely results in TP receptor stimulation. These observations can explain several abnormalities in diabetes, including 1) increased free radicals, 2) decreased bioactivity of NO, 3) PGI(2) deficiency, and 4) increased vasoconstriction, endothelial apoptosis, and inflammation via TP receptor stimulation.