Combination therapy with nateglinide and vildagliptin improves postprandial metabolic derangements in Zucker fatty rats

Postprandial metabolic derangements are one of the risk factors of cardiovascular disease in humans. Insulin resistance and/or impaired early-phase insulin secretion are major determinants of postprandial metabolic derangements. In this study, we investigated the potential utility of combination therapy with vildagliptin, a dipeptidyl peptidase IV (DPP-IV) inhibitor and nateglinide, a rapid-onset/short-duration insulinotropic agent, for the treatment of postprandial metabolic derangements in Zucker Fatty (ZF) rats, an animal model of obesity with insulin resistance. ZF rats fed twice daily with or without high fat diet (HFD) were given vehicle, 50 mg/kg of nateglinide, 10 mg/kg of vildagliptin, or both for 6 weeks. Combination therapy with nateglinide and vildagliptin for 2 weeks ameliorated postprandial hyperglycemia, hypertriglyceridemia, and elevation of free fatty acid in ZF rats fed with HFD. 6-week treatment with nateglinide and vildagliptin not only increased hepatic levels of phosphorylated forkhead box protein 1A (FOXO1A), but also reduced triglyceride contents in the liver. Combination therapy also prevented the loss of pancreatic islet mass in ZF rats fed with HFD. These observations demonstrate that combination therapy with nateglinide and vildagliptin may improve postprandial metabolic derangements probably by ameliorating early phase of insulin secretion and hepatic insulin resistance, respectively, in ZF rats fed with HFD. Since combination therapy with nateglinide and vildagliptin restored the decrease in pancreatic beta cell mass, our present findings suggest that combination therapy could be a promising therapeutic strategy for postprandial dysmetabolism associated with obese and insulin resistance.

Branched-chain amino acids and pigment epithelium-derived factor: novel therapeutic agents for hepatitis c virus-associated insulin resistance

Recent clinical studies have shown that patients with chronic liver disease are insulin resistant. Of all etiologies of chronic liver disease including non-alcoholic fatty liver disease, the one that causes the most sever insulin resistance is hepatitis C virus (HCV) infection. Since insulin resistance promotes inflammatory and fibrogenic reactions in the liver, thus leading to the development of liver cirrhosis and hepatocellular carcinoma (HCC) in patients with HCV infection, amelioration of insulin sensitivity may inhibit the progression of HCV-associated liver disease, and could improve the survival of these patients. HCV directly causes insulin resistance through HCV core protein-elicited proteasomal degradation of insulin receptor substrates and subsequent inactivation of intracellular insulin signaling molecules such as Akt. Furthermore, tumor necrosis factor-alpha (TNF-alpha) and/or triglyceride accumulation-induced nuclear factor-kappaB (NF-kappaB) activation in the liver is shown to play a role in insulin resistance in patients with HCV-related chronic liver disease as well. We, along with others, have recently found that branched-chain amino acids (BCAAs) and pigment epithelium-derived factor (PEDF) could improve the HCV-associated insulin resistance via suppression of NF-kappaB and preservation of insulin signaling pathway. In this review, we discuss the mechanisms for the actions of BCAAs and PEDF, and their clinical implications in insulin resistance of chronic liver disease in patients with HCV infection. We also discuss here which chemical structures could contribute to insulin-sensitization in patients with HCV infection.

Possible link of food-derived advanced glycation end products (AGEs) to the development of diabetes

China Da Qing diabetes prevention study has recently shown that group-based lifestyle interventions over six years can prevent or delay the development of diabetes in patients with impaired glucose tolerance (IGT) for up to 14 years after the active intervention. These findings suggest the sustained beneficial effects of lifestyle interventions to prevent diabetes in at-risk patients for diabetes. Therefore, the clinical study suggests that so-called 'metabolic memory' is involved in the development of diabetes. Potential mechanisms for propagating this 'metabolic memory' are the non-enzymatic glycation of proteins. The formation and accumulation of advanced glycation end products (AGEs) have been known to progress at an accelerated rate under diabetes, and there is accumulating evidence that AGEs play a role in the development of diabetes by inducing islet beta cell damage and/or insulin resistance. Further, there are several animal studies to suggest that dietary AGEs are involved in insulin resistance, visceral obesity and the development of diabetes. These findings led us to speculate that the long-term beneficial influence of early lifestyle interventions on the development of diabetes could be ascribed, at least in part, to their inhibitory effects on AGEs. That is, intake of food-derived AGEs may be suppressed in the lifestyle intervention group, which could reduce the risk for the development of diabetes in high-risk patients with IGT. Therefore, it is an interesting issue to clarify whether food-derived AGEs are actually restricted during the active intervention period and if circulating or tissue AGE levels at the closure of the China Da Qing diabetes prevention study could predict the risk for the development of diabetes 14 years after the trial. This additional, clinical investigation may provide us more information about whether restriction of food-derived AGEs is beneficial for the prevention of the development of diabetes in high-risk patients and may be a novel therapeutic target to prevent diabetes and its related complications.

Pigment epithelium-derived factor (PEDF) ameliorates advanced glycation end product (AGE)-induced hepatic insulin resistance in vitro by suppressing Rac-1 activation

Advanced glycation end products (AGEs) could be implicated in insulin resistance. However, the molecular mechanisms underlying this are not fully understood. Since pigment epithelium-derived factor (PEDF) blocks the AGE-signaling pathways, we examined here whether and how PEDF improves insulin resistance in AGE-exposed hepatoma cells, Hep3B cells. Proteins were extracted from Hep3B cells, immunoprecipitated with or without insulin receptor substrate-1 (IRS-1) antibodies, and subjected to Western blot analysis. Glycogen synthesis was measured using [ (14)C]-d-glucose. AGE induced Rac-1 activation and increased phosphorylation of IRS-1 at serine-307 residues, JNK, c-JUN, and IkappaB kinase in association with decreased IkappaB levels in Hep3B cells. PEDF or overexpression of dominant negative Rac-1 blocked these effects of AGE on Hep3B cells. Further, AGEs decreased tyrosine phosphorylation of IRS-1, and subsequently reduced the association of p85 subunit of phosphatidylinositol 3-kinase with IRS-1 and glycogen synthesis in insulin-exposed Hep3B cells, all of which were inhibited by PEDF. Our present study suggests that PEDF could improve the AGE-elicited insulin resistance in Hep3B cells by inhibiting JNK- and IkappaB kinase-dependent serine phosphorylation of IRS-1 via suppression of Rac-1 activation. PEDF may play a protective role against hepatic insulin resistance in diabetes.

Possible involvement of tobacco-derived advanced glycation end products (AGEs) in an increased risk for developing cancers and cardiovascular disease in former smokers

Tobacco smoking is one of the strongest risk factors for various disorders such as lung cancers and cardiovascular disease (CVD). Further, former smokers remain at an increased risk for developing lung cancers and CVD even years after they stop smoking. These observation suggest that expression levels of some of the genes related to tobacco smoking may not return to levels similar to never smokers and could be permanently altered despite prolonged smoking cessation, thereby being involved in the development of lung cancers and CVD. The modification, aggregation, and deposition of proteins are a prominent part of many pathological processes and can play a direct role in tissue damage. Advanced glycation end products (AGEs) have been shown to play a role in the development of many of the pathological sequelae of aging and diabetes such as CVD and cancer growth and metastasis. Moreover, there are several papers to show that tobacco smoke is a source of toxic reactive glycation products. Further, recent epidemiological and prospective data have supported the concept of 'metabolic memory', a long-term influence of previous hyperglycemia on the development of CVD in diabetes. Potential mechanism for propagating this 'memory' is considered to be the non-enzymatic glycation of proteins because the process of formation and accumulation of AGEs are most compatible with the theory. Therefore, it is conceivable that tobacco-derived AGEs are also involved in the increased risk for developing cancers and CVD in former smokers. In this paper, we would like to propose the possible ways of testing our hypotheses. Are tissue levels of AGEs still higher in former smokers, compared with age-, sex- and other confounders-matched non-smokers? If the answer is yes, are the tissue levels of AGEs following smoking cessation decreased? If we examine the effects of smoking cessation as a function of years since quitting, is the extent of decrease in tissue AGEs levels parallel to that of risk reduction for developing cancers and CVD? Further, are genes that are permanently altered despite prolonged smoking cessation identical to those that regulated by AGEs? These investigations could clarify whether tobacco-derived AGEs are involved in sustained tissue injury in former smokers.

Telmisartan, an Angiotensin II Type 1 Receptor Blocker, Inhibits Advanced Glycation End-product (AGE)-elicited Hepatic Insulin Resistance via Peroxisome Proliferator-activated Receptor-γ Activation

This study examined whether telmisartan, a unique angiotensin II type 1 receptor blocker (ARB) with peroxisome proliferator-activated receptor-γ (PPAR-γ)-modulating activity, improved insulin resistance in advanced glycation end-product (AGE)-exposed human hepatoma (Hep3B) cells. AGE increased phosphorylation of insulin receptor substrate-1 (IRS-1) at serine-307 residues in Hep3B cells. It also decreased tyrosine phosphorylation of IRS-1 and, subsequently, reduced the association of the p85 subunit of phosphatidylinositol 3-kinase with IRS-1 and glycogen synthesis in insulin-exposed Hep3B cells, all of which were inhibited by telmisartan. The insulin-sensitizing properties of telmisartan in AGE-exposed Hep3B cells were significantly blocked by GW9662, an inhibitor of PPAR-γ. Candesartan, another ARB, did not affect AGEs-induced serine phosphorylation of IRS-1 at serine-307 residues in Hep3B cells. Our study suggests that telmisartan could improve AGE-elicited insulin resistance in Hep3B cells by inhibiting serine phosphorylation of IRS-1, at least in part, via activation of PPAR-γ. Telmisartan may play a protective role against hepatic insulin resistance in diabetes.

Aqueous humour levels of asymmetric dimethylarginine (ADMA) are correlated with pigment epithelium-derived factor (PEDF) in patients with uveitis

The association between the aqueous humour levels of asymmetric dimethylarginine (ADMA) and pigment epithelium-derived factor (PEDF) was evaluated. Aqueous humour levels of ADMA and PEDF were measured by high-performance liquid chromatography and enzyme-linked immunosorbent assay, respectively, in 31 uveitis samples and nine cataract control samples. Aqueous humour ADMA and PEDF levels were significantly higher in infectious and non-infectious uveitis patients than in controls (0.67+/-0.04 nmol/ml and 0.55+/-0.03 nmol/ml versus 0.43+/-0.04 nmol/ml for ADMA; 8.22+/-1.45 microg/ml and 5.22+/-0.95 microg/ml versus 1.32+/-0.22 microg/ml for PEDF). A significant positive correlation between ADMA and PEDF levels in aqueous humour was found in control and uveitis patients. These results demonstrated that the aqueous humour level of ADMA is correlated with PEDF in humans and suggest that both ADMA and PEDF in aqueous humour may be elevated in response to inflammation in uveitis.

Bay w 9798, a dihydropyridine structurally related to nifedipine with no calcium channel-blocking properties, inhibits tumour necrosis factor-alpha-induced vascular cell adhesion molecule-1 expression in endothelial cells by suppressing reactive oxygen species generation

Dihydropyridine-based calcium antagonists (DHPs) are widely used to treat hypertension. We have previously shown that nifedipine, one of the most popular DHPs, blocks tumour necrosis factor-alpha (TNF-alpha)-induced monocyte chemoattractant protein-1 as well as vascular cell adhesion molecule-1 (VCAM-1) expression in endothelial cells by suppressing reactive oxygen species generation (ROS). The molecular mechanism is still to be elucidated, however, because endothelial cells do not possess voltage-operated L-type calcium channels. The aim of this study was to determine in TNF-alpha-exposed human umbilical vein endothelial cells (HUVECs) whether and how Bay w 9798, a dihydropyridine structurally related to nifedipine with no calcium antagonistic properties, may suppress VCAM-1 expression, a key molecule which mediates the adhesion of monocytes to vasculature in the early stages of atherosclerosis. In HUVECs, 10 ng/ml TNF-alpha for 4 h stimulated ROS generation and subsequently upregulated VCAM-1 mRNA levels, both of which were dose-dependently blocked by Bay w 9798. The results demonstrated that Bay w 9798 inhibited VCAM-1 expression in TNF-alpha-exposed cells by suppressing ROS generation. They suggest that the anti-inflammatory and anti-oxidative properties of nifedipine and Bay w 9798 may be ascribed to the dihydropyridine structure, which is common to both molecules and has no calcium antagonistic ability.

Potential utility of combination therapy with nateglinide and telmisartan for metabolic derangements in Zucker Fatty rats

The metabolic syndrome is strongly associated with insulin resistance and has been recognized as a cluster of risk factors for cardiovascular disease. Insulin resistance and/or impaired early-phase insulin secretion are major determinants of postprandial hyperglycemia. In this study, we investigated the potential utility of combination therapy with telmisartan, an angiotensin II receptor blocker and nateglinide, a rapid-onset/short-duration insulinotropic agent, for the treatment of postprandial hyperglycemia and metabolic derangements in Zucker Fatty (ZF) rats. ZF rats fed twice daily were given vehicle, 50 mg/kg of nateglinide, 5 mg/kg of telmisartan, or both for 6 weeks. Combination therapy with nateglinide and telmisartan for 2 weeks ameliorated postprandial hyperglycemia in ZF rats fed twice daily. Furthermore, 6-week treatment with nateglinide and telmisartan not only decreased fasting plasma insulin, triglycerides, and free fatty acid levels, but also improved the responses of blood glucose to insulin and subsequently reduced the decremental glucose areas under the curve in the ZF rats. Combination therapy also restored the decrease of plasma adiponectin levels in the ZF rats. Monotherapy with nateglinide or telmisartan alone didnot significantly improve these metabolic parameters. These observations demonstrate that combination therapy with nateglinide and telmisartan may improve the metabolic derangements by ameliorating early phase of insulin secretion as well as insulin resistance in ZF rats fed twice daily. Our present findings suggest that the combination therapy with nateglinide and telmisartan could be a promising therapeutic strategy for the treatment of the metabolic syndrome.

Serum level of advanced glycation end-products (AGEs) is an independent determinant of plasminogen activator inhibitor-1 (PAI-1) in nondiabetic general population

Glucose can react nonenzymatically with amino groups of proteins to form senescent macroprotein derivatives termed advanced glycation end-products (AGEs). Recently, AGEs have been shown to play an important role in atherosclerosis even in nondiabetic subjects. However, the molecular mechanism underlying this is not fully understood. We have now investigated whether serum AGE level was an independent determinant of plasminogen activator inhibitor-1 (PAI-1), a major physiological inhibitor of fibrinolysis, in nondiabetic general population. One-hundred and eighty-six nondiabetic Japanese subjects underwent a complete history and physical examination, determination of blood chemistries, PAI-1, and AGEs. Uni- and multivariate analyses were applied for the determinants of PAI-1 levels. The average PAI-1 levels were 29.7+/-23.8 ng/ml in males and 21.8+/-17.1 ng/ml in females, respectively. Univariate regression analysis showed that PAI-1 levels were associated with age (inversely, p=0.003), male (p=0.003), body mass index (BMI) (p<0.001), HDL-cholesterol (inversely, p<0.001), triglycerides (p<0.001), fasting plasma glucose (p<0.001), insulin (p<0.001), uric acids (p<0.001), AGEs (p=0.037), and alcohol intake (p<0.001). By the use of multiple regression analyses, BMI (p<0.001), male (p=0.003), fasting plasma glucose (p=0.005), age (inversely, p=0.017), and AGEs (p=0.034) remained significant. The present study is the first demonstration that serum AGE level was one of the independent determinants of PAI-1 in nondiabetic general population. The AGE-associated thrombogenic abnormality may be involved in atherogenesis in nondiabetic subjects.

Pigment Epithelium-derived Factor Inhibits Vascular Endothelial Growth Factor-induced Vascular Hyperpermeability Both In Vitro and In Vivo

Administration of pigment epithelium-derived factor (PEDF) inhibits advanced glycation end products-elicited retinal vascular hyperpermeability, as well as cold injury-induced brain oedema in rats. However, the underlying molecular mechanism by which PEDF blocks the hyperpermeability in vivo is not fully understood. This study investigated whether PEDF could inhibit vascular endothelial growth factor (VEGF)-induced vascular hyperpermeability both in vitro and in vivo. The Miles assay revealed that, after intradermal injection of VEGF in nude mice, simultaneous administration of PEDF inhibited vascular hyperpermeability in a dose-dependent manner. The in vitro permeability assay also showed that PEDF blocked the VEGF-induced barrier dysfunction in endothelial cells. These results demonstrated that PEDF could inhibit the VEGF-induced vascular hyperpermeability both in vitro and in vivo, and suggest that PEGF may be suitable to be considered as a novel therapeutic agent for various vasopermeable disorders in which VEGF is involved.

Telmisartan, an angiotensin II type 1 receptor blocker, inhibits advanced glycation end-product (AGE)-induced monocyte chemoattractant protein-1 expression in mesangial cells through downregulation of receptor for AGEs via peroxisome proliferator-activated receptor-gamma activation

Interaction between advanced glycation end-products (AGEs) and their receptor (RAGE) plays a central role in diabetic nephropathy pathogenesis. Pathophysiological crosstalk between the AGEs-RAGE system and angiotensin II (Ang II) is also involved in this disease. This study investigated the role of proliferator-activated receptor-gamma (PPAR-gamma)-modulating activity on inhibition of monocyte chemoattractant protein (MCP-1) expression. Telmisartan, an Ang II type 1 receptor blocker, downregulated RAGE mRNA and inhibited superoxide generation and MCP-1 gene expression in mesangial cells; these processes were blocked by GW9662, a PPAR-gamma inhibitor. Candesartan, an Ang II type 1 receptor blocker, did not suppress AGEs-induced superoxide generation. Telmisartan and the antioxidant, N-acetylcysteine, completely inhibited AGEs-induced MCP-1 overproduction by mesangial cells. These results suggest that telmisartan inhibits AGEs-signalling to MCP-1 expression in mesangial cells by downregulating RAGE gene expression and subsequent oxidative stress generation via PPAR-gamma activation. This study has demonstrated a unique benefit of telmisartan in that it may function as an anti-inflammatory agent against AGEs via PPAR-gamma activation and may play a protective role in diabetic nephropathy.

Increased expression of HLA-DR and CD86 in nasal epithelial cells in allergic rhinitics: antigen presentation to T cells and up-regulation by diesel exhaust particles

BACKGROUND

A proportion of nasal epithelial cells (NEC) in patients with allergic rhinitis (AR) are known to express the major histocompatibility complex Class II molecule (HLA-DR).

OBJECTIVE

We hypothesized that NEC may play a role in antigen presentation to T cells. To elucidate the possible role of NEC in antigen presentation, we examined the expression of HLA-DR, CD80 and CD86 in NEC, their regulation by cytokines and the capacity of NEC to induce antigen-specific proliferation of T cells.

METHODS

We examined the expression of HLA-DR, CD80 and CD86 in nasal epithelial scrapings of patients with seasonal allergic rhinitis (SAR) to Japanese cedar pollen pre-season and in-season, by immunohistochemistry. Next, we examined the effect of IL-1beta, TNF-alpha, (IFN-gamma), IL-4 alpha, IL-13 and diesel exhaust particles (DEP) on the HLA-DR, CD80 and CD86 expression in cultured nasal epithelial cells (CNEC), by flow cytometry. Further, we analysed the capacity of mite antigen (Der f II)-pulsed mitomycin-C-treated CNEC to induce proliferation of autologous T cells from patients with perennial allergic rhinitis.

RESULTS

NEC constitutively expressed HLA-DR and CD86, but not CD80. The expression of HLA-DR and CD86 in NEC was significantly increased in-season, in patients with SAR as compared with that of pre-season. While IFN-gamma up-regulated the expression of HLA-DR, IL-1beta and TNF-alpha up-regulated the expression of CD86 in CNEC. Furthermore, in the presence of mite antigen, CNEC induced the proliferation of autologous peripheral blood T lymphocytes. Anti-CD86 and anti-HLA-DR monoclonal antibody but not anti-CD80 inhibited the epithelial cell-induced T cell proliferation. Stimulation with a combination of DEP and mite antigen significantly up-regulated HLA-DR and CD86 expression in CNEC.

CONCLUSIONS

These studies suggest that NEC in patients with AR may play a role in antigen presentation through the enhanced expression of HLA-DR and CD86. Furthermore, these results suggest the possibility that DEP may enhance the antigen-presenting function of CNEC.

Hydrogen peroxide stimulates pigment epithelium-derived factor gene and protein expression in the human hepatocyte cell line OUMS-29

Pigment epithelium-derived factor (PEDF) may have a protective role in atherosclerosis and is associated with the presence of components of the metabolic syndrome. Since oxidative stress has been postulated to play an important role in the pathogenesis of vascular injury in the metabolic syndrome, this study investigated the effects of hydrogen peroxide (H2O2) on PEDF in the immortalized human hepatocyte cell line OUMS-29. PEDF gene expression was measured using quantitative real-time reverse transcription-polymerase chain reaction and PEDF protein expression was analysed by Western blot. H2O2 upregulated PEDF mRNA levels and increased PEDF protein production in OUMS-29 cells in time- and dose-dependent manners. The anti-oxidant N-acetylcysteine significantly blocked H2O2-induced PEDF overexpression in OUMS-29 cells. These results suggest that hepatic PEDF levels may be elevated to counteract the effects of oxidative stress. H2O2-induced PEDF overproduction in the liver may act as a negative feedback system against vascular damage in the metabolic syndrome.

Aqueous humor levels of asymmetric dimethylarginine (ADMA) are positively associated with monocyte chemoattractant protein-1 (MCP-1) in patients with uveitis

BACKGROUND/AIMS

The aim of the study was to evaluate whether aqueous humor levels of asymmetric dimethylarginine (ADMA) are associated with monocyte chemoattractant protein-1 (MCP-1).

METHODS

Aqueous humor levels of ADMA and MCP-1 were measured by high-performance liquid chromatography (HPLC) and ELISA, respectively, in 31 uveitis samples and nine cataract control samples.

RESULTS

Aqueous humor ADMA and MCP-1 levels were significantly higher in infectious or non-infectious uveitis patients than in controls (0.67+/-0.04 nmol/ml vs 0.55+/-0.03 nmol/ml vs 0.43+/-0. 04 nmol/ml (p<0.01) and 29.0+/-11.3 ng/ml vs 4.5+/-1.2 ng/ml vs 0.47+/-0.1 ng/ml (p<0.01), respectively). A positive correlation between ADMA and MCP-1 levels in aqueous humor was found in control and uveitis patients (r = 0.33, p<0.05).

CONCLUSION

The results demonstrated that aqueous humor levels of ADMA were positively associated with MCP-1 in humans. Our present observations suggest that aqueous humor levels of ADMA may be a novel biomarker of inflammation in uveitis.

Novel therapeutic targets for diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal failure, which could account for disabilities and high mortality rates in patients with diabetes. Diabetic nephropathy seems to occur as a result of an interaction between metabolic and hemodynamic factors, which activate common pathways that lead to renal damage. Recent large prospective clinical studies have shown that intensive glucose control reduces microvascular complications effectively among patients with diabetes, and the renin-angiotensin system (RAS) is also an important target for both metabolic and hemodynamic derangements in diabetic nephropathy. High glucose, via various mechanisms such as increased production of oxidative stress and advanced glycation end products (AGEs), activation of the RAS and protein kinase C (PKC), and stimulation of the polyol pathway, elicits vascular inflammation and alters gene expression of growth factors and cytokines, thereby it might be involved in the development and progression of diabetic nephropathy. Therefore, to develop novel therapeutic strategies that specifically target these metabolic and hemodynamic derangements is desired for patients with diabetic nephropathy. In this review, we discuss the molecular mechanisms of diabetic nephropathy and review the promising therapeutic targets for this devastating disorder.

Azelnidipine, a new long-acting calcium-channel blocker, inhibits tumour necrosis factor-alpha-induced monocyte chemoattractant protein-1 expression in endothelial cells

Dihydropyridine-based calcium antagonists are among the most widely used drugs for the treatment of hypertension. Since azelnidipine is a highly lipid-soluble dihydropyridine-based calcium antagonist with high vascular affinity, it is conceivable that azelnidipine could play a protective role against atherosclerosis. The aim of this study was to determine whether azelnidipine could suppress the expression of monocyte chemoattractant protein-1, a principal chemokine which mediates the recruitment of monocytes to the vasculature, in tumour necrosis factor (TNF)-alpha-exposed human umbilical vein endothelial cells. TNF-alpha, at a concentration of 10 ng/ml, upregulated monocyte chemoattractant protein-1 mRNA levels about seven-fold. Azelnidipine, 10 nmol/l, was found to inhibit the TNF-alpha-induced upregulation of monocyte chemoattractant protein-1 mRNA levels in human umbilical vein endothelial cells significantly. Furthermore, azelnidipine suppressed TNF-alpha-induced monocyte chemoattractant protein-1 production by human umbilical vein endothelial cells. This study demonstrates a novel beneficial aspect of azelnidipine, whereby azelnidipine could play a protective role against atherosclerosis by suppressing monocyte chemoattractant protein-1 overexpression in endothelial cells.

Oral administration of AST-120 (Kremezin) is a promising therapeutic strategy for advanced glycation end product (AGE)-related disorders

The pathological role of the non-enzymatic modification of proteins by reducing sugars has become increasingly evident in various disorders. It is now well established that early glycation products undergo progressive modification over time in vivo to the formation of irreversible cross-links, after which these molecules are termed "AGEs (advanced glycation end products)". AGEs have been implicated in the development of many of the pathological sequelae of diabetes and aging, such as diabetic microangiopathy, ischemic heart disease and neurodegenerative diseases. Recently, digested food-derived AGEs are also found to play an important role in the pathogenesis of AGE-related disorders. Diet is a major environmental source of pro-inflammatory AGEs. Indeed, restriction of dietary glycotoxins decreases excessive AGE levels and subsequently reduces the inflammatory responses in patients with diabetes. These observations suggest that inhibition of absorption of dietary AGEs may be a novel target for therapeutic intervention in the above-mentioned AGE-related disorders. AST-120 (Kremezin) is an oral adsorbent that attenuates the progression of chronic renal failure (CRF) by removing uremic toxins. We have recently found that AST-120 binds to carboxymethyllysine (CML), one of the well-characterized, digested food-derived AGEs in vitro and that administration of AST-120 decreases serum levels of AGEs in non-diabetic CRF patients. These findings suggest that digested food-derived AGEs such as CML may be a novel molecular target for oral adsorbent AST-120 and that AST-120 could exert beneficial effects on CRF patients by adsorbing diet-derived AGEs and subsequently decreasing serum AGE levels. If our speculation is correct, AST-120 may have therapeutic potentials for the treatment of patients with various AGE-related disorders as well. In this paper, we would like to propose the possible ways of testing our hypotheses. Does the long-term treatment of AST-120 decrease serum and tissue levels of AGEs in diabetic patients? Does this treatment also reduce the risk for the development and progression of diabetic vascular complications such as diabetic retinopathy or ischemic heart disease? If the answers are yes, do the serum and/or tissue levels of AGEs after AST-120 treatment predict its beneficial effects on diabetic vascular complications? How about the effects of AST-120 on Alzheimer's disease, another AGE-related neurodegenerative disorder? Does the treatment of AST-120 reduce the risk for Alzheimer's disease and/or improve the cognitive impairment of patients with this disorder? These prospective studies will provide further valuable information whether the inhibition of absorption of dietary AGEs by AST-120 could be clinically relevant.

Revival of nifedipine, a dihydropyridine-based calcium blocker

A recent analysis by the Blood Pressure Lowering Treatment Trialists' Collaboration revealed that any commonly-used blood pressure (BP)-lowering regimen reduced the risk of total major cardiovascular events, and larger reductions in BP produced larger reductions in the risk. These observations suggest that most of the differences among treatment regimens in their effects on cardiovascular outcomes could be explained by the differences in achieved BP level. However, it may also be true that some treatment regimen is superior or inferior to others with regard to the risk reduction of cardiovascular events. Indeed, the data from dihydropyridine-based calcium antagonist (DHP) trails are consistent in that they could not protect against new-onset heart failure or progression of renal disease in patients with left-ventricular systolic dysfunction or overt proteinuria, respectively. However, a multicenter, randomized, placebo-controlled, double-blind ACTION trial, which compared the effect of long-acting nifedipine or placebo on mortality and cardiovascular morbidity in patients with stable angina, revealed that nifedipine reduced the risk for new-onset overt heart failure by 29%. Further, an open-label, randomized prospective J-MIND trial, which compared the effect of long-acting nifedipine or enalapril, an angiotensin-converting enzyme inhibitor on onset and progression of nephropathy in hypertensive patients with type 2 diabetes, showed that long-acting nifedipine had an equipotent reoprotective effect on diabetic nephropathy. In this paper, we would like to propose our hypothesis that nifedipine may be unique and superior in its effects on heart failure and proteinuria compared with various DHPs. For ensuring our hypothesis, the following clinical issues would be addressed. Does nifedipine treatment alone decrease the progression of renal disease with overt proteinuria? If these answers are yes, are these beneficial effects of nifedipine superior to that of other DHPs with equihypotensive properties? Does nifedipine treatment also reduce oxidative stress markers? Are these unique effects of nifedipine correlated with its anti-oxidative properties? These prospective studies will provide further valuable information whether nifedipine may be a preferred DHP to achieve BP goals in hypertensive patients with systolic dysfunction or overt proteinuria.

Prevention of diabetic vascular calcification by nifedipine, a dihydropyridine-based calcium channel blocker

Vascular calcification is a common feature in advanced atherosclerosis and also a predictor of future cardiovascular events such as unstable angina and myocardial infarction, especially in diabetes. There is a growing body of evidence that advanced glycation end products (AGEs), senescent macroprotein derivatives formed at an accelerated rate in diabetes, exist within atherosclerotic lesions, thereby being implicated in the pathogenesis of accelerated atherosclerosis in diabetes. Indeed, we have previously shown that AGE - their receptor (RAGE) interaction could induce angiogenesis through autocrine production of vascular endothelial growth factor, suggesting its role for plaque formation and enlargement in diabetes. Furthermore, we have found that AGEs have the ability to induce the osteoblatic differentiation of pericytes, thus contributing to the development of vascular calcification as well. These observations suggest that the inhibition of AGE formation or blockade of the downstream signaling of RAGE may be a novel therapeutic target for the inhibition of vascular calcification in diabetic atherosclerosis. Since we, along with others, have shown that nifedipine inhibits glycation of low-density lipoprotein in vitro and blocks the AGE-induced RAGE expression in endothelial cells through its anti-oxidative properties, nifedipine could inhibit vascular calcification by blocking the AGE formation or the downstream signaling in diabetes. In this paper, we would like to propose the possible ways of testing our hypothesis. Does nifedipine treatment slow down the progression of coronary calcification in diabetic patients? If the answer is yes, is this beneficial effect of nifedipine superior to that of other DHPs with equihypotensive properties? Does nifedipine treatment decrease expression levels of AGEs and RAGE in diabetic atherosclerosis? Is the unique effect of nifedipine on vascular calcification correlated with its AGE or RAGE-suppressing properties? These prospective studies will provide further valuable information whether nifedipine could prevent vascular calcification in diabetic atherosclerosis by blockade the AGE-RAGE signaling in vascular wall cells.

A possible involvement of crosstalk between advanced glycation end products (AGEs) and asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor in accelerated atherosclerosis in diabetes

Endothelial dysfunction due to reduced bioavailability of nitric oxide (NO) is an early step in the course of atherosclerotic cardiovascular disease (CVD). NO is synthesized from L-arginine via the action of NO synthase (NOS), which is known to be blocked by endogenous L-arginine analogues such as asymmetric dimethylarginine (ADMA). ADMA is a naturally occurring amino acid found in plasma and various types of tissues. Recently, it has been demonstrated that plasma levels of ADMA are elevated in patients with diabetes. It has also been reported that elevated plasma levels of ADMA are associated with increased risks of nonfatal stroke and myocardial infarction in patients with early diabetic nephropathy. These findings suggest that the elevated ADMA in diabetes could contribute to acceleration of atherosclerosis in this population. In diabetes mellitus, the formation and accumulation of advanced glycation end products (AGEs) progress. There is a growing body of evidence to show that AGEs are involved in the development and progression of atherosclerosis in patients with diabetes. Since ADMA is mainly metabolized by dimethylarginine dimethylaminohydrolase (DDAH), it is conceivable that the impairment of DDAH actions by AGEs could be one possible molecular mechanism of the ADMA elevation in diabetic patients. In this paper, we would like to propose the possible ways of testing our hypotheses. Does treatment with metformin, which has a potential effect on the inhibition of glycation reactions in vivo, decrease the levels of ADMA in diabetic patients? If the answer is yes, is this beneficial effect of metformin superior to that of other anti-diabetic agents with equihypoglycemic properties? Does treatment with pyridoxamine, a post-Amadori inhibitor (so-called Amadorins) of AGE formation, also reduce the levels of ADMA and subsequently improve endothelial dysfunction in diabetic patients? Are the ADMA-lowering effects of these agents associated with an increase of DDAH expression and/or activity in endothelial cells? These clinical studies could clarify whether AGEs are involved in the elevation of ADMA in patients with diabetes via suppression of DDAH expression and/or activity, thus providing a novel molecular mechanism for accelerated atherosclerosis in diabetes.

Telmisartan inhibits AGE-induced C-reactive protein production through downregulation of the receptor for AGE via peroxisome proliferator-activated receptor-gamma activation

AIMS/HYPOTHESIS

C-reactive protein (CRP), an acute-phase reactant produced mainly by the liver, is elevated in diabetes, thus contributing to the development and progression of atherosclerosis. However, the molecular mechanism underlying the elevation of CRP in diabetes is not fully understood. Since a crosstalk between AGE and angiotensin II (Ang II) has been proposed in the pathogenesis of accelerated atherosclerosis in diabetes, we examined here whether and how telmisartan, a unique Ang II type 1 receptor blocker (ARB) with peroxisome proliferator-activated receptor-gamma (PPAR-gamma)-modulating activity, could inhibit AGE-induced CRP expression in a human hepatoma cell line, Hep3B cells.

METHODS

Protein levels of the receptor for AGE (RAGE) were analysed by western blots. Gene expression was analysed by quantitative real-time RT-PCR. CRP released into the medium was measured with ELISA. Intracellular formation of reactive oxygen species (ROS) was measured using the fluorescent probe CM-H(2)DCFDA.

RESULTS

Telmisartan, but not candesartan, another ARB, downregulated RAGE mRNA levels in a dose-dependent manner. Telmisartan decreased basal as well as AGE-induced RAGE protein expression in Hep3B cells. Furthermore, telmisartan dose-dependently inhibited AGE-induced ROS generation and subsequent CRP gene and protein induction in Hep3B cells. GW9662, an inhibitor of PPAR-gamma, blocked the inhibitory effects of telmisartan on RAGE expression and its downstream signalling in Hep3B cells.

CONCLUSIONS/INTERPRETATION

Our present study indicates a unique beneficial aspect of telmisartan: it may work as an anti-inflammatory agent against AGE by suppressing RAGE expression via PPAR-gamma activation in the liver and may play a protective role in vascular injury in diabetes.