The receptor RAGE as a progression factor amplifying arachidonate-dependent inflammatory and proteolytic response in human atherosclerotic plaques: role of glycemic control

The RAGE axis and endothelial dysfunction: maladaptive roles in the diabetic vasculature and beyond

Receptor for advanced glycation end product (RAGE) is a member of the immunoglobulin superfamily of cell surface molecules. The ligand-RAGE axis is emerging as a central mechanism linked to vascular injury and atherosclerosis in diabetes and in euglycemia. The repertoire of RAGE ligands, including advanced glycation end products, S100/calgranulins, high-mobility group box 1, amyloid-beta peptide, and Mac-1, transcends RAGE biology from specifically the science of diabetic complications to central aspects of the inflammatory response and oxidative stress. Experiments in cell culture and in vivo support the notion that interaction of RAGE ligands with RAGE activates key signal transduction pathways that modulate fundamental cellular properties, thereby leading to vascular and inflammatory cell perturbation. These considerations support the premise that the ligand-RAGE axis may be an important target for therapeutic intervention in cardiovascular disease and, fundamentally, in initiation and amplification of inflammatory responses.

The RAGE Gly82Ser polymorphism is not associated with cardiovascular disease in the Framingham offspring study

The receptor for advanced glycation end-products (RAGE) is expressed to enhance degrees in human atherosclerotic plaques and co-localizes with inflammatory and pro-oxidant mediators in the vulnerable regions of the plaque. Previous studies highlighted a number of variants in the gene encoding the receptor, including a Gly to Ser substitution at amino acid 82 within the ligand-binding domain of RAGE. The Ser82 allele enhanced ligand-binding affinity and increased ligand-stimulated generation of inflammatory mediators in transfected cells and human monocytes compared to the common RAGE Gly82 allele. Thus it was logical to test the hypothesis that increased prevalence of the Gly82Ser polymorphism was associated with cardiovascular events in the Framingham offspring study (n=1632). Our analyses revealed that the Gly82Ser RAGE polymorphism did not demonstrate any association with the incidence of cardiovascular disease in diabetic or non-diabetic subjects (Gly82 96%, Ser82 4%). Analysis of specific manifestations of cardiovascular disease, including coronary heart disease (CHD), cardiovascular disease (CVD), myocardial infarction (MI) and ischemic disease (ISD) revealed no association with RAGE genotype. Further studies are required on other more prevalent genetic variants of RAGE and cardiovascular disease.

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.

Role of astrocytic S100β in behavioral hypersensitivity in rodent models of neuropathic pain

S100beta is a calcium-binding peptide produced mainly by astrocytes that exerts paracrine and autocrine effects on neurons and glia. We have previously shown that S100beta is markedly elevated at the mRNA level in the spinal cord following peripheral inflammation, intraplantar administration of complete Freund's adjuvant in the rat. The purpose of the present study was to further investigate the role of astrocytic S100beta in mediating behavioral hypersensitivity in rodent models of persistent pain. First, we assessed the lumbar spinal cord expression of S100beta at the mRNA and protein level using real-time RT-PCR, Western blot and immunohistochemistry analysis following L5 spinal nerve transection in rats, a rodent model of neuropathic pain. Second, we assessed behavioral hypersensitivity (mechanical allodynia) in wild type and genetically modified mice lacking or overexpressing S100beta following L5 spinal nerve transection. Third, we assessed the expression level of S100beta protein in the CD1 wild type mice after nerve injury. We report that lumbar spinal S100beta mRNA steadily increased from days 4-28 after nerve injury. S100beta protein in the lumbar spinal cord was significantly increased in both rats and mice at day 14 following nerve injury as compared with sham control groups. S100beta genetically deficient mice displayed significantly increased tactile thresholds (reduced response to non-noxious stimuli) after nerve injury as compared with the wild type group. S100beta overexpressing mice displayed significantly decreased tactile threshold responses (enhanced response to non-noxious stimuli). Together, these results from both series of experiments using a peripheral nerve injury model in two different species implicate the involvement of glial-derived S100beta in the pathophysiology of neuropathic pain.

Oxidized-1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine induces vascular endothelial superoxide production: implication of NADPH oxidase

Modified low-density lipoprotein (LDL) induces reactive oxygen species (ROS) production by vascular cells. It is unknown if specific oxidized components in these LDL particles such as oxidized-1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (ox-PAPC) can stimulate ROS production. Bovine aortic endothelial cells (BAEC) were incubated with ox-PAPC (50 microg/ml). At 4 h, ox-PAPC significantly enhanced the rate of O2- production. Pretreatment of BAEC in glucose-free Dulbecco's modified Eagle's medium plus 10 mM 2-deoxyglucose (2-DOG), the latter being an antimetabolite that blocks NADPH production by the pentose shunt, significantly reduced the rate of O2- production. The intensity of NAD(P)H autofluorescence decreased by 28 +/- 12% in BAEC incubated with ox-PAPC compared to untreated cells, with a further decrease in the presence of 2-DOG. Ox-PAPC also increased Nox4 mRNA expression by 2.4-fold +/- 0.1 while pretreatment of BAEC with the small interfering RNA (siNox4) attenuated Nox4 RNA expression. Ox-PAPC further reduced the level of glutathione while pretreatment with apocynin (100 microM) restored the GSH level (control = 22.54 +/- 0.23, GSH = 18.06 +/- 0.98, apocynin = 22.55 +/- 0.60, ox-PAPC + apocynin = 21.17 +/- 0.36 nmol/10(6) cells). Treatment with ox-PAPC also increased MMP-2 mRNA expression accompanied by a 1.5-fold increase in MMP-2 activity. Ox-PAPC induced vascular endothelial OO2-(.) production that appears to be mediated largely by NADPH oxidase activity.

Matrix metalloproteinases of epithelial origin in facial sebum of patients with acne and their regulation by isotretinoin

Acne vulgaris is a skin disorder of the sebaceous follicles, involving hyperkeratinization and perifollicular inflammation. Matrix metalloproteinases (MMP) have a predominant role in inflammatory matrix remodeling and hyperproliferative skin disorders. We investigated the expression of MMP and tissue inhibitors of MMP (TIMP) in facial sebum specimens from acne patients, before and after treatment with isotretinoin. Gelatin zymography and Western-blot analysis revealed that sebum contains proMMP-9, which was decreased following per os or topical treatment with isotretinoin and in parallel to the clinical improvement of acne. Sebum also contains MMP-1, MMP-13, TIMP-1, and TIMP-2, as assessed by ELISA and western blot, but only MMP-13 was decreased following treatment with isotretinoin. The origin of MMP and TIMP in sebum is attributed to keratinocytes and sebocytes, since we found that HaCaT keratinocytes in culture secrete proMMP-2, proMMP-9, MMP-1, MMP-13, TIMP-1, and TIMP-2. SZ95 sebocytes in culture secreted proMMP-2 and proMMP-9, which was also confirmed by microarray analysis. Isotretinoin inhibited the arachidonic acid-induced secretion and mRNA expression of proMMP-2 and -9 in both cell types and of MMP-13 in HaCaT keratinocytes. These data indicate that MMP and TIMP of epithelial origin may be involved in acne pathogenesis, and that isotretinoin-induced reduction in MMP-9 and -13 may contribute to the therapeutic effects of the agent in acne.

Diabetic vascular disease: it's all the RAGE

The major consequence of long-term diabetes is the increased incidence of disease of the vasculature. Of the underlying mechanisms leading to disease, the accumulation of advanced glycation end products (AGEs), resulting from the associated hyperglycemia, is the most convincing. Interaction of AGEs with their receptor, RAGE, activates numerous signaling pathways leading to activation of proinflammatory and procoagulatory genes. Studies in rodent models of macro- and microvascular disease have demonstrated that blockade of RAGE can prevent development of disease. These observations highlight RAGE as a therapeutic target for treatment of diabetic vascular disease.

Receptor for advanced glycation end products and its ligands: a journey from the complications of diabetes to its pathogenesis

Many studies have suggested that the expression of RAGE (receptor for advanced glycation end products) is upregulated in human tissues susceptible to the long-term complications of diabetes. From the kidneys to the macrovessels of the aorta, RAGE expression is upregulated in a diverse array of cell types, from glomerular epithelial cells (podocytes) to endothelial cells, vascular smooth muscle cells, and inflammatory mononuclear phagocytes and lymphocytes. Although RAGE was first described as a receptor for advanced glycation end products (AGEs), the key finding that RAGE was also a signaling receptor for proinflammatory S100/calgranulins and amphoterin, led to the premise that even in euglycemia, ligand-RAGE interaction propagated inflammatory mechanisms linked to chronic cellular perturbation and tissue injury. Indeed, such considerations suggested that RAGE might even participate in the pathogenesis of type 1 diabetes. Our studies have shown that pharmacological and/or genetic deletion/mutation of the receptor attenuates the development of hyperglycemia in NOD mice; in mice with myriad complications of diabetes, interruption of ligand-RAGE interaction prevents or delays the chronic complications of the disease in both macro- and microvessel structures. Taken together, these findings suggest that RAGE is "at the right place and time" to contribute to the pathogenesis of diabetes and it complications. Studies are in progress to test the premise that antagonism of this interaction is a logical strategy for the prevention and treatment of diabetes.

Thromboxane, prostacyclin and isoprostanes: therapeutic targets in atherogenesis

Atherosclerosis is a chronic disease of the vasculature that is influenced by multiple factors that involve a complex interplay between some components of the blood and the arterial wall. Inflammation and oxidative stress have key roles in atherogenesis. The production of F2-isoprostanes (F2-IPs), thromboxane A2 (TxA2) and prostacyclin (PGI2) increases in atherosclerosis, and recent studies show that pharmacological modulation of their biosynthesis and biological activities are important therapeutic targets for managing atherosclerosis. In this review, we highlight recent breakthroughs in the roles of F2-IPs, TxA2 and PGI2 in atherogenesis, and identify pertinent therapeutic targets.

Plasma level of endogenous secretory RAGE is associated with components of the metabolic syndrome and atherosclerosis

OBJECTIVE

Advanced glycation endproducts, AGEs, and its specific receptor, RAGE, are involved in diabetic vascular complications. Endogenous secretory RAGE, esRAGE, has been identified as an alternatively spliced form of RAGE, and shown to act as a decoy receptor for AGE. Here, we measured plasma esRAGE level with a recently developed enzyme-linked immunosorbent assay (ELISA) and examined its association with atherosclerosis in age- and gender-matched 203 type 2 diabetic and 134 nondiabetic subjects.

METHODS AND RESULTS

Plasma esRAGE was inversely associated with carotid or femoral atherosclerosis, as quantitatively measured as intimal-medial thickness (IMT) by arterial ultrasound. Stepwise regression analyses revealed that plasma esRAGE was the third strongest and independent factor associated with carotid IMT, following age and systolic blood pressure. Plasma esRAGE was significantly lower in diabetic patients (0.176+/-0.092 ng/mL) than nondiabetic controls (0.253+/-0.111). Of note, in all, diabetic or nondiabetic group, plasma esRAGE was significantly and inversely correlated with components of the metabolic syndrome including body mass index, blood pressure, triglyceride, HbA1c, or an insulin resistance index. Stepwise regression analyses showed that body mass index or insulin resistance index was the major factor determining plasma esRAGE in all, nondiabetic or diabetic population.

CONCLUSIONS

esRAGE is a novel and potential protective factor for the metabolic syndrome and atherosclerosis.

Advanced glycosylation end products might promote atherosclerosis through inducing the immune maturation of dendritic cells

OBJECTIVE

Both advanced glycosylation end products (AGEs) and dendritic cells (DCs) have been shown to play a causative role in atherosclerosis. However, whether they function interactively in the process remains uncertain. We therefore studied the effects of AGE-bovine serum albumin (AGE-BSA) on the maturation of DCs and the expressions of scavenger receptor-A (SR-A) and receptor for AGEs (RAGE) on DCs.

METHODS AND RESULTS

AGE-BSA induced DCs maturation accompanied with increased expressions of CD1a, CD40, CD80, CD83, CD86, and MHC class II. The capacity of DCs to stimulate T-cell proliferation and secretion of cytokines (interferon [IFN], IFN-gamma, interleukin [IL]-10 and IL-12) was also enhanced by AGE-BSA. AGE-BSA significantly upregulated SR-A and RAGE expression on DCs and the upregulation was abolished by inhibition of mitogen-activated protein (MAP) kinase Jnk, but not by that of Erk and p38 MAP kinase. AGE-BSA-induced expression of CD83 and secretion of IL-12 were partly inhibited by either an anti-RAGE neutralizing antibody or a Jnk inhibitor.

CONCLUSIONS

AGE-BSA induces maturation of DCs and augmented their capacity to stimulate T-cell proliferation and cytokine secretions possibly through upregulation of RAGE and SR-A, which at least in part through Jnk. These findings might explain in part the interactive roles of AGEs and DCs in the processes of atherosclerosis.

Novel determinants of plaque instability

Arachidonic acid metabolism plays an important role in acute ischemic syndromes affecting the coronary or cerebrovascular territory, as reflected by biochemical measurements of eicosanoid biosynthesis and the results of inhibitor trials in these settings. Two cyclooxygenase (COX)-isozymes have been characterized, COX-1 and COX-2, that differ in terms of regulatory mechanisms of expression, tissue distribution, substrate specificity, preferential coupling to upstream and downstream enzymes and susceptibility to inhibition by the extremely heterogeneous class of COX-inhibitors. While the role of platelet COX-1 in acute coronary syndromes and ischemic stroke is firmly established through approximately 20 years of thromboxane metabolite measurements and aspirin trials, the role of COX-2 expression and inhibition in atherothrombosis is substantially uncertain, because the enzyme was first characterized in 1991 and selective COX-2 inhibitors became commercially available only in 1998. In this review, we discuss the pattern of expression of COX-2 in the cellular players of atherothrombosis, its role as a determinant of plaque 'vulnerability,' and the clinical consequences of COX-2 inhibition. Recent studies from our group suggest that variable expression of upstream and downstream enzymes in the prostanoid biosynthetic cascade may represent important determinants of the functional consequences of COX-2 expression and inhibition in different clinical settings.

Bridging advanced glycation end product, receptor for advanced glycation end product and nitric oxide with hormonal replacement/estrogen therapy in healthy versus diabetic postmenopausal women: A perspective

Cardiovascular diseases (CVD) are the most significant cause of death in postmenopausal women. The loss of estrogen biosynthesis with advanced age is suggested as one of the major causes of higher CVD in postmenopausal women. While some studies show beneficial effects of estrogen therapy (ET)/hormonal replacement therapy (HRT) in the cardiovascular system of healthy postmenopausal women, similar studies in diabetic counterparts contradict these findings. In particular, ET/HRT in diabetic postmenopausal women results in a seemingly detrimental effect on the cardiovascular system. In this review, the comparative role of estrogens is discussed in the context of CVD in both healthy and diabetic postmenopausal women in regard to the synthesis or expression of proinflammatory molecules like advanced glycation end products (AGEs), receptor for advanced glycation end products (RAGEs), inducible nitric oxide synthases (iNOS) and the anti-inflammatory endothelial nitric oxide synthases (eNOS). The interaction of AGE-RAGE signaling with molecular nitric oxide (NO) may determine the level of reactive oxygen species (ROS) and influence the overall redox status of the vascular microenvironment that may further determine the ultimate outcome of the effects of estrogens on the CVD in healthy versus diabetic women.

Monocyte adhesion to xenogeneic endothelium during laminar flow is dependent on alpha-Gal-mediated monocyte activation

Monocytes are the predominant inflammatory cell recruited to xenografts and participate in delayed xenograft rejection. In contrast to allogeneic leukocytes that require up-regulation of endothelial adhesion molecules to adhere and emigrate into effector tissues, we demonstrate that human monocytes adhere rapidly to unstimulated xenogeneic endothelial cells. The major xenoantigen galactosealpha(1,3)galactosebeta(1,4)GlcNAc-R (alpha-gal) is abundantly expressed on xenogeneic endothelium. We have identified a putative receptor for alpha-gal on human monocytes that is a member of the C-type family of lectin receptors. Monocyte arrest under physiological flow conditions is regulated by alpha-gal, because cleavage or blockade results in a dramatic reduction in monocyte adhesion. Recruitment of human monocytes to unactivated xenogeneic endothelial cells requires both alpha(4) and beta(2) integrins on the monocyte; binding of alpha-gal to monocytes results in rapid activation of beta(2), but not alpha(4), integrins. Thus, activation of monocyte beta(2) integrins by alpha-gal expressed on xenogeneic endothelium provides a mechanism that may explain the dramatic accumulation of monocytes in vivo.

Prostaglandin E synthase in the pathophysiology of arthritis

Prostaglandin E synthase (PGES) is a recently identified terminal enzyme that acts downstream of cyclooxygenase and catalyzes the conversion of prostaglandin (PG) H2 to PGE2. At least three isozymes have been cloned so far, which are called membrane-associated PGES (mPGES)-1, mPGES-2, and cytosolic PGES. Among them, mPGES-1 is induced by various inflammatory stimuli in some cells and tissues. Induction of mPGES-1 in the component of articular tissues of patients with rheumatoid arthritis and osteoarthritis has been demonstrated in vitro. Recent studies using adjuvant induced arthritis model have shown the increase of mPGES-1 expression resulted in the increase of PGE2 production at the sites of inflammation. In addition, reports of mPGES-1-deficient mice clearly suggest the role of mPGES-1 in the process of chronic inflammation such as collagen-induced arthritis and collagen antibody induced arthritis in vivo. Thus, recent in vitro and in vivo findings suggest that mPGES-1 may be a novel therapeutic target for arthritis. This paper introduces recent advances in research about the role of PGES in the pathophysiology of arthritis.

Assessing risk across the spectrum of patients with the metabolic syndrome

The metabolic syndrome represents a constellation of interrelated risk factors that identify individuals at increased risk for the development of type 2 diabetes mellitus and cardiovascular events. Currently, the major cardiovascular risk factors and validated risk-assessment tools do not adequately account for the increased cardiovascular risk that accompanies the metabolic syndrome. In prospective population studies, cardiovascular risk assessment in individuals with the metabolic syndrome is improved by measures of low-density lipoprotein (LDL) particle number, C-reactive protein, and plasminogen activator inhibitor-1 levels. Although adiponectin and soluble tumor necrosis factor receptor-2 may be more integrally involved in insulin resistance, the studies with these biomarkers are less extensive. Risk assessment models for patients with the metabolic syndrome should consider inclusion of LDL particle number, inflammatory markers, and levels of plasminogen activator inhibitor-1.

Association Between 5-Lipoxygenase Expression and Plaque Instability in Humans

OBJECTIVE

The participation of 5-lipoxygenase (5-LO) in the development of atherosclerosis has been suggested by recent studies. However, a role for 5-LO as a modulator of atherosclerotic plaque instability has not been previously reported in humans. Thus, the aims of this study was to analyze the expression of 5-LO in human carotid plaques and to investigate the mechanism by which this enzyme could lead to plaque instability and rupture.

METHODS AND RESULTS

We obtained atherosclerotic plaques from 60 patients undergoing carotid endarterectomy. We divided the plaques into symptomatic and symptomatic according to clinical evidence of plaque instability. Clinical evidence of plaque instability was provided by the assessment of recent ischemic symptoms attributable to the stenosis and by the presence of ipsilateral cerebral lesion(s) determined by computed tomography. Plaques were analyzed for CD68+ macrophages, CD3+ T cells, alpha-actin+ smooth muscle cells, 5-LO, cyclooxygenase 2, matrix metalloproteinase (MMP)-2, and MMP-9 by immunohistochemical, immunoblotting, and densitometric analyses. MMP activity was assessed by zymography. Leukotriene (LT) B4 and collagen were quantified by ELISA and Sirius red polarization, respectively. The percentage of macrophage-rich and T-cell-rich areas was larger in symptomatic compared with asymptomatic patients (25+/-6% versus 8+/-4%, P<0.0001, and 74+/-17 versus 18+/-4 cell/mm2, P<0.003). 5-LO expression was higher in symptomatic compared with asymptomatic plaques (24+/-4% versus 6+/-3%, P<0.0001) and was associated with increased MMP-2 and MMP-9 expression (27+/-4% versus 7+/-3%, P<0.0001, and 29+/-5% versus 8+/-2%, P<0.0001) and activity and with decreased collagen content (6.9+/-2.4% versus 17.8+/-3.1%, P<0.01). Immunofluorescence showed that 5-LO and MMPs colocalize in activated macrophages. Notably, higher 5-LO in symptomatic plaques correlated with increased LTB4 production (18.15+/-3.56 versus 11.27+/-3.04 ng/g tissue, P<0.0001).

CONCLUSIONS

The expression of 5-LO is elevated in symptomatic compared with asymptomatic plaques and is associated with acute ischemic syndromes, possibly through the generation of LTB4, subsequent MMP biosynthesis, and plaque rupture.

The role of reactive oxygen species in TNFα-dependent expression of the receptor for advanced glycation end products in human umbilical vein endothelial cells

Engagement of the receptor for advanced glycation end products (RAGE) by its signal transduction ligands is implicated in the development and progression of atherosclerosis. TNFalpha, a proinflammatory cytokine, is a potent inducer of RAGE expression in endothelial cells. In the present study, we demonstrate that reactive oxygen species (ROS) generated by TNFalpha stimulated human umbilical vein endothelial cells (HUVECs) induce RAGE expression. The complex III of mitochondrial respiratory chain appears to be the primary source of ROS. The gp91phox subunit of NADPH oxidase appears to be the source of ROS that induces TNFalpha-dependent mitochondrial ROS generation and subsequent RAGE expression. We also demonstrate that the ROS-mediated RAGE induction occurs via activation of NF-kappaB, a proinflammatory transcription factor. Thus, stimulation of HUVECs by TNFalpha evokes the following sequence of events: stimulation of NADPH oxidase --> generation of ROS --> activation of the mitochondrial respiratory chain --> stimulation of NF-kappaB activity --> induction of RAGE expression.

Matrix metalloproteinases and diabetic vascular complications

Diabetes mellitus (DM) is associated with an increased incidence of cardiovascular events and microvascular complications. These complications contribute to the morbidity and mortality associated with DM. There is increasing evidence supporting a role for matrix metalloproteinases (MMPs) and their inhibitors (tissue inhibitors of matrix metalloproteinases - TIMPs) in the atherosclerotic process. However, the relationship between MMPs/TIMPs and diabetic angiopathy is less well defined. Hyperglycemia directly or indirectly (eg, via oxidative stress or advanced glycation products) increases MMP expression and activity. These changes are associated with histologic alterations in large vessels. On the other hand, low proteolytic activity of MMPs contributes to diabetic nephropathy. Within atherosclerotic plaques an imbalance between MMPs and TIMPs may induce matrix degradation, resulting in an increased risk of plaque rupture. Furthermore, because MMPs enhance blood coagulability, MMPs and TIMPs may play a role in acute thrombotic occlusion of vessels and consequent cardiovascular events. Some drugs can inhibit MMP activity. However, the precise mechanisms involved are still not defined. Further research is required to demonstrate the causative relationship between MMPs/TIMPs and diabetic atherosclerosis. It also remains to be established if the long-term administration of MMP inhibitors can prevent acute cardiovascular events.

Monocytes promote natural killer cell interferon gamma production in response to the endogenous danger signal HMGB1

Substantial attention has been paid to the role of the toll-like receptor (TLR) ligands of late and their role in regulating the innate immune response. They serve as exogenous danger signals important in informing and driving the distal adaptive immune response to pathogens. Less clear has been the role of the nominal endogenous danger signals released and recognized in stressed cells following genotoxic or metabolic stress as occurs in progressively growing tumors. HMGB1 (high-mobility group B1) is a nuclear protein well characterized for its ability to modify DNA access to transcriptional proteins that is released from necrotic cells as well as secreted through the endosomal route from hematopoietic cells, serving as a late mediator of sepsis. It interacts with high-affinity RAGE (receptor for advanced glycation end products) and TLR2 receptors. Here we show that HMGB1 enhances interferon gamma release from macrophage (but not dendritic cell)-stimulated NK cells. This is effective only when coupled with other pro-inflammatory cytokines particularly with IL-2 in combination with IL-1 or IL-12. We have used this information to suggest that HMGB1, which also promotes epithelial migration and proliferation, drives repair in the absence or inhibition of other factors but enhances inflammation in their presence. The implications for tumorigenesis and tumor progression are quite important as they may be for other states of chronic inflammation.

Differential effect of estrogen receptor alpha and beta agonists on the receptor for advanced glycation end product expression in human microvascular endothelial cells

Estrogens are known to induce the expression of the receptor for advanced glycation end products (RAGE). In the current investigation, we examined the effect of three estrogens with different potency for specific estrogen receptors (ER) on RAGE expression in human microvascular endothelial cells (HMEC-1). Of the three estrogens tested, ethinyl estradiol (EE), an estrogen receptor alpha (ERalpha) agonist, was the strongest inducer of RAGE expression in HMEC-1. By comparison, 17-epiestriol, an estrogen receptor beta (ERbeta) agonist and 17-beta-E2, an ER agonist that is almost equally potent for ERalpha and ERbeta were less effective in stimulating RAGE expression. We then determined whether the prooxidative and proinflammatory transcription factors Sp1 or NF-kappaB were downstream modulators of ER-agonists that mediate RAGE expression. The results implicated Sp1 but not NF-kappaB in estrogen-dependent RAGE expression. We further demonstrated that ERalpha but not ERbeta was responsible for the estrogen-mediated Sp1 activation. In summary, the present investigation demonstrates that a direct interaction of EE-ERalpha-Sp1 plays a central role in estrogen-induced RAGE expression in HMEC-1.

Advanced glycation end products and RAGE: a common thread in aging, diabetes, neurodegeneration, and inflammation

The products of nonenzymatic glycation and oxidation of proteins and lipids, the advanced glycation end products (AGEs), accumulate in a wide variety of environments. AGEs may be generated rapidly or over long times stimulated by a range of distinct triggering mechanisms, thereby accounting for their roles in multiple settings and disease states. A critical property of AGEs is their ability to activate receptor for advanced glycation end products (RAGE), a signal transduction receptor of the immunoglobulin superfamily. It is our hypothesis that due to such interaction, AGEs impart a potent impact in tissues, stimulating processes linked to inflammation and its consequences. We hypothesize that AGEs cause perturbation in a diverse group of diseases, such as diabetes, inflammation, neurodegeneration, and aging. Thus, we propose that targeting this pathway may represent a logical step in the prevention/treatment of the sequelae of these disorders.

Insulin alters nuclear factor-κB and peroxisome proliferator-activated receptor-γ protein expression induced by glycated bovine serum albumin in vascular smooth-muscle cells

In both type 2 diabetes and insulin-resistance syndromes, hyperglycemia and advanced glycation end products (AGEs) activate the transcription factor nuclear factor-kappaB (NF-kappaB) through a mechanism that partly involves the generation of reactive oxygen species (ROS). The contribution of hyperinsulinemia in this sequence has not been completely elucidated. In this work we investigated the actions of insulin and PPAR-gamma on the stimulation by AGEs of NF-kappaB protein expression in cultured aortic vascular smooth-muscle cells (VSMCs) from non-insulin-dependent diabetic rats and nondiabetic rats. The expression of proteins was evaluated with the use of Western immunoblotting. Incubations (24 hours) of VSMCs with 10 to 100 microg/mL glycated bovine serum albumin (AGE- BSA) increased NF-kappaB protein expression in both models. PPAR-gamma protein expression was only enhanced at concentrations of 500 to 1000 microg/mL (AGE-BSA). In the presence of insulin (10-100 nmol/L), the stimulation of NF-kappaB protein expression by AGE-BSA (100 microg/mL) was decreased, whereas the expression of PPAR-gamma, protein was enhanced. 15-Deoxyprostaglandin J2, a direct activator of PPAR-gamma, decreased AGE-BSA-stimulated NF-kappaB expression. These findings suggest that insulin decreases the incidence of alterations in VSMCs induced by AGEs through the reduction of NF-kappaB and an increase in PPAR-gamma protein expression (as far as the model could be extrapolated to in vivo situations). These data may help justify current therapeutic approaches involving the use of insulin and PPAR-gamma agonists.

Atorvastatin reduces the plasma lipids and oxidative stress but did not reverse the inhibition of prostacyclin generation by aortas in streptozotocin diabetic rats

The effect of atorvastatin (Lipitor) on diabetes-induced changes in plasma lipids, oxidative stress and the ability of aortic tissues to generate prostacyclin was studied in streptozotocin diabetic rats. In diabetic rats, plasma total cholesterol, triglycerides and serum glucose significantly increased compared to nondiabetic rats. Atorvastatin administration to diabetic rats did not affect hyperglycemia but significantly reduced plasma total cholesterol and triglycerides compared to diabetic rats. The oxidative stress markers urinary isoprostane, liver thiobarbituric acid reactive substances (TBARS) and plasma protein carbonyl content significantly increased in diabetic rats compared to nondiabetic rats. Atorvastatin admnistration to diabetic rats significantly reduced oxidative stress levels compared to diabetic rats, but urinary isoprostane and liver TBARS remained significantly higher than nondiabetic rats. Prostacyclin (PGI(2)) generation by aortic tissues significantly decreased in diabetic rats compared to nondiabetic rats. Atorvastatin administration to diabetic rats did not reverse that inhibition. These results were discussed in the light of the possible effects of hyperglycemia and statins on NAD(P)H-oxidase and cyclooxygenase-2 activities and the genetic difference between rats and other mammals regarding the level of vascular superoxide dismutase (SOD) activity.

Plasma levels of soluble receptor for advanced glycation end products and coronary artery disease in nondiabetic men

OBJECTIVE

The receptor for advanced glycation end products (RAGE) is a cell surface receptor whose signaling pathway has been implicated in atherogenesis. RAGE has an endogenous secretory receptor form, called soluble RAGE (sRAGE), that could exert antiatherogenic effects by acting as a decoy. We sought to determine whether a decreased plasma level of sRAGE could be independently associated with the prevalence of coronary artery disease (CAD) in nondiabetic men.

METHODS AND RESULTS

Plasma levels of sRAGE were determined in 328 nondiabetic male patients with angiographically proved CAD and in 328 age-matched healthy controls. The concentration of sRAGE in plasma was significantly lower (P<0.0001) in CAD cases [median (interquartile range): 966 (658-1372) pg/mL] than in control subjects [1335 (936-1954) pg/mL]. In logistic regression analysis, the multivariate-adjusted odds ratio for the presence of CAD was 6.719 (95% confidence interval, 3.773 to 11.964; P<0.0001) when the lowest quartile of the sRAGE level was compared with the highest quartile.

CONCLUSIONS

Our findings indicate that low levels of sRAGE in plasma are independently associated with the presence of CAD in nondiabetic men and suggest that sRAGE is one of the clinically important molecules associated with atherosclerosis.

Protein glycation: a firm link to endothelial cell dysfunction

The advanced glycation end products (AGEs) are a heterogeneous class of molecules, including the following main subgroups: bis(lysyl)imidazolium cross-links, hydroimidazolones, 3-deoxyglucosone derivatives, and monolysyl adducts. AGEs are increased in diabetes, renal failure, and aging. Microvascular lesions correlate with the accumulation of AGEs, as demonstrated in diabetic retinopathy or renal glomerulosclerosis. On endothelial cells, ligation of receptor for AGE (RAGE) by AGEs induces the expression of cell adhesion molecules, tissue factor, cytokines such as interleukin-6, and monocyte chemoattractant protein-1. A chief means by which AGEs via RAGE exert their effects is by generation of reactive oxygen species, at least in part via stimulation of NADPH oxidase. Diabetes-associated vascular dysfunction in vivo can be prevented by blockade of RAGE. Thus, agents that limit AGE formation, increase the catabolism of these species, or antagonize their binding to RAGE may provide new targets for vascular protection in diabetes.

Splice variants of the receptor for advanced glycosylation end products (RAGE) in human brain

Previous studies indicate that the receptor for advanced glycosylation end products (RAGE) plays an important role in multiple pathological processes, including Alzheimer's disease. Currently there are three established isoforms of the RAGE receptor, with each isoform generated as the result of alternative splicing. It is presently unclear which of the RAGE isoforms are normally expressed in the human brain, nor has it been determined if additional RAGE isoforms exist in the human brain. In the present study we demonstrate for the first time that each of the three established RAGE isoforms, as well as three previously unidentified RAGE splicing variants, are normally expressed in the human brain. These data suggest that RAGE may have multiple functions in the human brain, mediated by the individual or coordinated efforts of the different RAGE isoforms, with alternative splicing generating individual RAGE isoforms that specifically interact with the various ligands present in the brain.

Roles of thromboxane A(2) and prostacyclin in the development of atherosclerosis in apoE-deficient mice

Production of thromboxane (TX) A2 and PG I2/prostacyclin (PGI2) is increased in patients with atherosclerosis. However, their roles in atherogenesis have not been critically defined. To examine this issue, we cross-bred atherosclerosis-prone apoE-deficient mice with mice deficient in either the TXA receptor (TP) or the PGI receptor (IP). Although they showed levels of serum cholesterol and triglyceride similar to those of apoE-deficient mice, apoE-/-TP-/- mice exhibited a significant delay in atherogenesis, and apoE-/-IP-/- mice exhibited a significant acceleration in atherogenesis compared with mice deficient in apoE alone. The plaques in apoE-/-IP-/- mice showed partial endothelial disruption and exhibited enhanced expression of ICAM-1 and decreased expression of platelet endothelial cell adhesion molecule 1 (PECAM-1) in the overlying endothelial cells compared with those of apoE-/-TP-/- mice. Platelet activation with thrombin ex vivo revealed higher and lower sensitivity for surface P-selectin expression in platelets of apoE-/-IP-/- and apoE-/-TP-/- mice, respectively, than in those of apoE-/- mice. Intravital microscopy of the common carotid artery revealed a significantly greater number of leukocytes rolling on the vessel walls in apoE-/-IP-/- mice than in either apoE-/-TP-/- or apoE-/- mice. We conclude that TXA2 promotes and PGI2 prevents the initiation and progression of atherogenesis through control of platelet activation and leukocyte-endothelial cell interaction.

Activation of nuclear factor-kappaB by hyperglycemia in vascular smooth muscle cells is regulated by aldose reductase

Activation of the polyol pathway has been linked to the development of secondary diabetic complications. However, the underlying molecular mechanisms remain unclear. To probe the contribution of this pathway, we examined whether inhibition of aldose reductase, which catalyzes the first step of the pathway, affects hyperglycemia-induced activation of the inflammatory transcription factor nuclear factor (NF)-kappaB. Treatment of vascular smooth muscle cells with the aldose reductase inhibitors tolrestat and sorbinil prevented high-glucose-induced protein kinase C (PKC) activation, nuclear translocation of NF-kappaB, phosphorylation of IKK, and the increase in the expression of intracellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and aldose reductase. High-glucose-induced NF-kappaB activation was also prevented by the PKC inhibitors chelerythrine and calphostin C. Ablation of aldose reductase by small interference RNA (siRNA) prevented high-glucose-induced NF-kappaB and AP-1 activation but did not affect the activity of SP-1 or OCT-1. Stimulation with iso-osmotic mannitol activated NF-kappaB and increased the expression of aldose reductase but not ICAM-1 and VCAM-1. Treatment with aldose reductase inhibitors or aldose reductase siRNA did not affect mannitol-induced NF-kappaB or AP-1 activation. Administration of tolrestat (15 mg . kg(-1) . day(-1)) decreased the abundance of activated NF-kappaB in balloon-injured carotid arteries of diabetic rats. Collectively, these results suggest that inhibition of aldose reductase, which prevents PKC-dependent nonosmotic NF-kappaB activation, may be a useful approach for treating vascular inflammation caused by diabetes.

Cigarette suppresses the expression of P4Halpha and vascular collagen production

OBJECTIVE

Collagen plays a major role in arterial wall remodeling, aneurysm formation, and atherosclerotic cap stability. Smokers often have weakened arterial walls associating with aneurysm and thinned atherosclerotic plaque caps leading to rupture and acute coronary syndromes. We hypothesize that these detrimental effects on arterial wall by tobacco are partially mediated by disturbed collagen metabolism.

METHODS AND RESULTS

We first investigated the effect of cigarette smoke extracts (CSE) on prolyl-4-hydroxylase (P4H) expression and collagen production in human aortic endothelial cells (HAECs) and human coronary artery smooth muscle cells (HCSMCs). After exposure to 0.01-U CSE for 24 h, expression of P4Halpha-a rate limiting subunit of P4H enzyme responsible for the formation of 4-hydroxyproline in mature functional collagen, was significantly down-regulated according to Western blotting and quantitative RT-PCR (HAEC p < 0.01 and HCSMC p < 0.001) when treated by CSE. The decreased P4Halpha expression was corresponded with reduced cellular collagen levels (HAEC p < 0.001 and HCSMC p < 0.001). We also found that one of the cigarette components benzo(a)pyrene exerted similar effect as CSE, but not nicotine or acrolein. We further examined P4H expression in a few human atherosclerotic abdominal aortas. These in vivo data demonstrated that smokers had thinner atherosclerotic cap thickness and lower levels of P4Halpha and collagen.

CONCLUSIONS

Our study suggests that cigarette may interfere with one of the key enzymes in arterial wall collagen metabolism, which may be responsible for thin fibrous cap in atherosclerotic lesion, impaired arterial wall extensibility, and increased likelihood of aneurysm in smokers.

Increased Expression of Transforming Growth Factor-β1 as a Stabilizing Factor in Human Atherosclerotic Plaques

BACKGROUND AND PURPOSE

Transforming growth factor-beta (TGF-beta) is a growth factor/cytokine involved in vascular remodeling and atherogenesis. Recent studies in apolipoprotein E-deficient mice have demonstrated a pivotal role of TGF-beta in the maintenance of the balance between inflammation and fibrosis in atherosclerotic plaques. Furthermore, inhibition of TGF-beta signaling has been shown to accelerate plaque formation and its progression toward an unstable phenotype in mice. However, if this mechanism is operative also in humans is still unknown. The aim of this study was to characterize the expression of TGF-beta1 in human carotid plaque and to correlate it with the extent of inflammatory infiltration and collagen content with the clinical signs of plaque instability.

METHODS

Plaques were obtained from patients undergoing carotid endoarterectomy and divided into symptomatic and asymptomatic according to clinical evidence of recent transient ischemic attack or stroke. Plaques were analyzed for TGF-beta1 expression by Immunocytochemistry, Western, and Northern blotting analysis. Immunocytochemistry was used to identify CD68+ macrophages, CD3 T lymphocytes, HLA-DR+ cells, and alpha-smooth muscle cells. Procollagen and interstitial collagen content were analyzed by immunohistochemistry and Sirius Red staining, respectively.

RESULTS

Plaque TGF-beta1 mRNA was increased up to 3-fold in asymptomatic as compared with symptomatic plaques. Plaques from asymptomatic group had fewer (P<0.0001) macrophages and T lymphocytes compared with symptomatic plaques. TGF-beta1 gene was transcriptionally active as demonstrated by increased (P<0.0001) TGF-beta1 protein expression in asymptomatic plaques. Immunohistochemistry showed that TGF-beta was mainly expressed in plaque shoulder and was associated with a comparable increase (P<0.0001) in plaque procollagen and collagen content.

CONCLUSIONS

In conclusion, this study demonstrates the higher expression of TGF-beta1 in human asymptomatic lesions and provides evidence that TGF-beta1 may play an important role in the process of plaque stabilization.

Increased expression of the DNA-binding cytokine HMGB1 in human atherosclerotic lesions: role of activated macrophages and cytokines

OBJECTIVE

Atherosclerosis is a chronic inflammatory response of the arterial wall to injury. High-mobility group box 1 (HMGB1) is a DNA-binding protein, which on release from cells exhibits potent inflammatory actions. We examined its expression in atherosclerotic lesions and regulation by cytokines.

METHODS AND RESULTS

In atherosclerotic lesions, HMGB1 protein is expressed by endothelial cells, some intimal smooth muscle cells, and macrophages. As atherosclerosis develops and progresses from fatty streaks to fibrofatty lesion, the number of HMGB1-producing macrophages increases markedly. Studies using the THP-1 cell line indicated that HMGB1 mRNA expression could be markedly upregulated by inflammatory cytokines, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and also transforming growth factor (TGF)-beta. IFN-gamma, TNF-alpha, TWEAK, and TGF-beta induced an intracellular redistribution of HMGB1 and stimulated secretion by THP-1 cells and human blood monocytes. Inhibitors of MEK1/MEK2, protein kinase C, and PI-3/Akt, which inhibit lysosomal degranulation and mRNA translation, attenuated cytokine-induced HMGB1 secretion.

CONCLUSIONS

Macrophage is the major cell type responsible for HMGB1 production in human atherosclerotic lesions. Inflammatory cytokines and TGF-beta increase HMGB1 expression and secretion by monocyte/macrophages. HMGB1 appears to be a common mediator of inflammation induced by inflammatory cytokines and is likely to contribute to lesion progression and chronic inflammation.

Advanced glycation end product cross-linking: pathophysiologic role and therapeutic target in cardiovascular disease

Advanced glycation end products (AGEs) form by a nonenzymatic reaction between reducing sugars and biological proteins. These stable compounds accumulate slowly throughout the life span and contribute to structural and physiologic changes in the cardiovascular system such as increased vascular and myocardial stiffness, endothelial dysfunction, altered vascular injury responses, and atherosclerotic plaque formation. Mechanisms underlying these alterations include AGE cross-linking of collagen and AGE interactions with circulating proteins and AGE receptors. The clinical manifestations of AGE accrual-isolated systolic hypertension, endothelial and diastolic dysfunction, and atherosclerosis-underscore their role in increased cardiovascular risk associated with aging as well as diabetes and hypertension, conditions that enhance AGE formation. New pharmacologic agents that prevent AGE, break cross-links, or block AGE receptors reduce vascular and myocardial stiffness, inhibit atherosclerotic plaque formation, and improve endothelial function. These agents promise to reduce the risk of isolated systolic hypertension, diastolic dysfunction, and diabetes, and thus, heart failure.

Metabolic syndrome: an appraisal of the pro-inflammatory and procoagulant status

Inflammation and hypercoagulability predispose to atherothrombosis and seem to be important features of the metabolic syndrome. The most convincing evidence is the association with increased levels of C-reactive protein. The hemostatic abnormality that has been most consistently associated with insulin resistance is an elevated plasminogen activator inhibitor-1 level. In contrast, markers of hypercoagulability have been associated inconsistently with hyperinsulinemia and glucose intolerance. Fibrinogen clusters with inflammatory factors, which suggests involvement of adipose tissue-generated inflammatory cytokines. Elevated von Willebrand's factor and factor VIII levels aggregate with indicators of endothelial injury,whereas vitamin K-dependent coagulation proteins correlate with triglyceride levels.

Lipid inflammatory mediators in diabetic vascular disease

Type 2 diabetes is associated with significantly accelerated rates of macrovascular complications such as atherosclerosis. Emerging evidence now indicates that atherosclerosis is an inflammatory disease and that certain inflammatory markers may be key predictors of diabetic atherosclerosis. Proinflammatory cytokines and cellular adhesion molecules expressed by vascular and blood cells during stimulation by growth factors and cytokines seem to play major roles in the pathophysiology of atherosclerosis and diabetic vascular complications. However, more recently, data suggest that inflammatory responses can also be elicited by smaller oxidized lipids that are components of atherogenic oxidized low-density lipoprotein or products of phospholipase activation and arachidonic acid metabolism. These include oxidized lipids of the lipoxygenase and cyclooxygenase pathways of arachidonic acid and linoleic acid metabolism. These lipids have potent growth, vasoactive, chemotactic, oxidative, and proinflammatory properties in vascular smooth muscle cells, endothelial cells, and monocytes. Cellular and animal models indicate that these enzymes are induced under diabetic conditions, have proatherogenic effects, and also mediate the actions of growth factors and cytokines. This review highlights the roles of the inflammatory cyclooxygenase and 12/15-lipoxygenase pathways in the pathogenesis of diabetic vascular disease. Evidence suggests that inflammatory responses in the vasculature can be elicited by small oxidized lipids that are components of oxidized low-density lipoprotein or products of the lipoxygenase and cyclooxygenase pathways of arachidonic and linoleic acid metabolism. This review evaluates these inflammatory and proatherogenic pathways in the pathogenesis of diabetic vascular disease.

Balance between PGD synthase and PGE synthase is a major determinant of atherosclerotic plaque instability in humans

OBJECTIVE

Inducible cyclooxygenase (COX-2) catalyzes the first step in prostanoid biosynthesis and is considered a proinflammatory enzyme. COX-2 and type 1 inducible PGE synthase (mPGES-1) have a role in metalloproteinase (MMP) release leading to plaque rupture. In contrast, lipocalin-type PGD synthase (L-PGDS) has been shown to exert antiinflammatory actions. Thus, in this study we investigated whether a shift from a PGDS-oriented to a PGES-oriented profile in arachidonate metabolism leads to inflammatory activation in rupture-prone plaque macrophages.

METHODS AND RESULTS

Atherosclerotic plaques were obtained from 60 patients who underwent carotid endarterectomy, symptomatic (n=30) and asymptomatic (n=30) according to evidence of recent transient ischemic attack or stroke. Plaques were analyzed for COX-2, mPGES-1, L-PGDS, PPARgamma, IkappaBalpha, NF-kappaB, and MMP-9 by immunocytochemistry, Western blot, reverse-transcriptase polymerase chain reaction, enzyme immunoassay, and zymography. Prostaglandin E2 (PGE2) pathway was significantly prevalent in symptomatic plaques, whereas PGD2 pathway was overexpressed in asymptomatic ones, associated with NF-kappaB inactivation and MMP-9 suppression. In vitro COX-2 inhibition in monocytes was associated with reduced MMP-9 release only when PGD2 pathway overcame PGE2 pathway.

CONCLUSIONS

These results suggest that COX-2 may have proinflammatory and antiinflammatory properties as a function of expression of downstream PGH2 isomerases, and that the switch from L-PGDS to mPGES-1 in plaque macrophages is associated with cerebral ischemic syndromes, possibly through MMP-induced plaque rupture.

RAGE axis: Animal models and novel insights into the vascular complications of diabetes

Receptor for AGE (RAGE) is a multi-ligand member of the immunoglobulin superfamily of cell surface molecules. Engagement of RAGE by its signal transduction ligands evokes inflammatory cell infiltration and activation in the vessel wall. In diabetes, when fueled by oxidant stress, hyperglycemia, and superimposed stresses such as hyperlipidemia or acute balloon/endothelial denuding arterial injury, the ligand-RAGE axis amplifies vascular stress and accelerates atherosclerosis and neointimal expansion. In this brief synopsis, we review the use of rodent models to test these concepts. Taken together, our findings support the premise that RAGE is an amplification step in vascular inflammation and acceleration of atherosclerosis. Future studies must rigorously test the potential impact of RAGE blockade in human subjects; such trials are on the horizon.

RAGE and its ligands: a lasting memory in diabetic complications?

The complications of diabetes are myriad and represent a rising cause of morbidity and mortality, particularly in the Western world. The update of the Diabetes Control and Clinical Trials Group/Epidemiology of Diabetes Interventions and Complications Research Group (DCCT/EDIC) suggested that previous strict control of hyperglycaemia was associated with reduced carotid atherosclerosis compared to conventional treatment, even after levels of glycosylated haemoglobin between the two treatment groups became indistinguishable. These intriguing findings prompt the key question, why does the blood vessel 'remember'? This review focuses on the hypothesis that the ligand/RAGE axis contributes importantly to glycaemic 'memory'. Studies in rodent models of diabetes suggest that blockade or genetic modification of RAGE suppress diabetes-associated progression of atherosclerosis, exaggerated neointimal expansion consequent to acute arterial injury, and cardiac dysfunction. We propose that therapeutic RAGE blockade will intercept maladaptive diabetes-associated memory in the vessel wall and provide cardiovascular protection in diabetes.

Glycation, inflammation, and RAGE: a scaffold for the macrovascular complications of diabetes and beyond

The cardiovascular complications of diabetes represent the leading cause of morbidity and mortality in affected subjects. The impact of hyperglycemia may be both direct and indirect: indirect consequences of elevated blood glucose lead to generation of advanced glycation endproducts, the products of nonenzymatic glycation/oxidation of proteins/lipids that accumulate in the vessel wall, and are signal transduction ligands for Receptor for AGE (RAGE). Although enhanced in diabetes, AGE accumulation also occurs in euglycemia and aging, albeit to lower degrees, driven by oxidant stress and inflammation. In hyperglycemia, production of 3-deoxyglucosone, at least in part via the polyol pathway, provides an amplification loop to sustain AGE generation, oxidant stress, and vascular activation. Furthermore, recruitment of inflammatory cells bearing S100/calgranulins, also ligands for RAGE, augments vascular dysfunction. We hypothesize that activation of RAGE is a final common pathway that transduces signals from these diverse biochemical and molecular species, leading to cardiovascular perturbation. Ultimately, these pathways synergize to construct a scaffold on which the complications of diabetes in the vasculature and heart may be built. We propose that antagonism of RAGE will provide a unique means to dismantle this scaffold and, thereby, suppress initiation/progression of vascular disease and cardiac dysfunction that accompany diabetes and aging.

Microsomal prostaglandin E synthase-1 is overexpressed in inflammatory bowel disease. Evidence for involvement of the transcription factor Egr-1

Microsomal prostaglandin E synthase-1 (mPGES-1) catalyzes the conversion of cyclooxygenase-derived prostaglandin (PG) H(2) to PGE(2). Increased amounts of mPGES-1 were detected in inflamed intestinal mucosa from patients with inflammatory bowel disease (IBD). Treatment with tumor necrosis factor (TNF)-alpha stimulated mPGES-1 transcription in human colonocytes, resulting in increased amounts of mPGES-1 mRNA and protein. The inductive effect of TNF-alpha localized to the GC box region of the mPGES-1 promoter. Binding of Egr-1 to the GC box region of the mPGES-1 promoter was enhanced by treatment with TNF-alpha. Notably, increased Egr-1 expression and binding activity were also detected in inflamed mucosa from IBD patients. Treatment with TNF-alpha induced the activities of phosphatidylcholine-phospholipase C (PC-PLC) and protein kinase (PK) C and enhanced NO production. A pharmacological approach was used to implicate PC-PLC --> PKC --> NO signaling as being important for the induction of mPGES-1 by TNF-alpha. TNF-alpha also enhanced guanylate cyclase activity and inhibitors of guanylate cyclase activity blocked the induction of mPGES-1 by TNF-alpha. YC-1, an activator of guanylate cyclase, induced mPGES-1. Overexpressing a dominant negative form of PKG blocked TNF-alpha-mediated stimulation of the mPGES-1 promoter. Taken together, these results suggest that overexpression of mPGES-1 in IBD is the result of Egr-1-mediated activation of transcription. Moreover, TNF-alpha induced mPGES-1 by stimulating PC-PLC --> PKC --> NO --> cGMP --> PKG signal transduction pathway.

Molecular mechanisms of high glucose-induced cyclooxygenase-2 expression in monocytes

The cyclooxygenase (COX)-2 enzyme has been implicated in the pathogenesis of several inflammatory diseases. However, its role in diabetic vascular disease is unclear. In this study, we evaluated the hypothesis that diabetic conditions can induce COX-2 in monocytes. High glucose treatment of THP-1 monocytic cells led to a significant three- to fivefold induction of COX-2 mRNA and protein expression but not COX-1 mRNA. High glucose-induced COX-2 mRNA was blocked by inhibitors of nuclear factor-kappaB (NF-kappaB), protein kinase C, and p38 mitogen-activated protein kinase. In addition, an antioxidant and inhibitors of mitochondrial superoxide, NADPH oxidase, and glucose metabolism to glucosamine also blocked high glucose-induced COX-2 expression to varying degrees. High glucose significantly increased transcription from a human COX-2 promoter-luciferase construct (twofold, P < 0.001). Promoter deletion analyses and inhibition of transcription by NF-kappaB superrepressor and cAMP-responsive element binding (CREB) mutants confirmed the involvement of NF-kappaB and CREB transcription factors in high glucose-induced COX-2 regulation. In addition, isolated peripheral blood monocytes from type 1 and type 2 diabetic patients had high levels of COX-2 mRNA, whereas those from normal volunteers showed no expression. These results show that high glucose and diabetes can augment inflammatory responses by upregulating COX-2 via multiple signaling pathways, leading to monocyte activation relevant to the pathogenesis of diabetes complications.

Cyclooxygenase-2 Expression and Inhibition in Atherothrombosis

Arachidonic acid metabolism plays an important role in acute ischemic syndromes affecting the coronary or cerebrovascular territory, as reflected by biochemical measurements of eicosanoid biosynthesis and the results of inhibitor trials in these settings. Two cyclooxygenase (COX)-isozymes have been characterized, COX-1 and COX-2, that differ in terms of regulatory mechanisms of expression, tissue distribution, substrate specificity, preferential coupling to upstream and downstream enzymes, and susceptibility to inhibition by the extremely heterogeneous class of COX-inhibitors. Although the role of platelet COX-1 in acute coronary syndromes and ischemic stroke is firmly established through ≈20 years of thromboxane metabolite measurements and aspirin trials, the role of COX-2 expression and inhibition in atherothrombosis is substantially uncertain, because the enzyme was first characterized in 1991 and selective COX-2 inhibitors became commercially available only in 1998. In this review, we discuss the pattern of expression of COX-2 in the cellular players of atherothrombosis, its role as a determinant of plaque “vulnerability,” and the clinical consequences of COX-2 inhibition. Recent studies from our group suggest that variable expression of upstream and downstream enzymes in the prostanoid biosynthetic cascade may represent important determinants of the functional consequences of COX-2 expression and inhibition in different clinical settings.