Protective role of pravastatin in the pathogenesis of the metabolic syndrome

The metabolic syndrome is strongly associated with insulin resistance and consists of a constellation of factors such as hypertension and hyperlipidemia that raise the risk for cardiovascular diseases and diabetes mellitus. There is a growing body of evidence to show that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, statins, reduce cardiovascular-related morbidity and mortality in patients with or without coronary artery disease. Recent clinical observations argue for a simple strategy of considering routine statin therapy for patients with type 2 diabetes. Furthermore, statin therapy is also found to be effective in allowing LDL-cholesterol goal achievement in hypercholesterolemic high-risk patients with the metabolic syndrome. However, the effects of statins on the pathogenesis of the metabolic syndrome remain to be elucidated. Several types of statins are commercially available now. Among them, pravastatin is unique because it is the only statin that has been shown to have protective role against the development of diabetes in a large clinical trial. Moreover, a recent clinical study revealed that pravastatin treatment improved insulin sensitivity in 25 women with the metabolic syndrome with impaired glucose intolerance. These observations let us to speculate that pravastatin is a promising strategy for the treatment of hypercholesterolemic patients with the metabolic syndrome. It may improve the insulin sensitivity in these patients and subsequently prevent the development of type 2 diabetes. In this paper, we would like to propose the possible ways of testing our hypothesis as follows. (1) Does pravastatin treatment improve insulin resistance in patients of the metabolic syndrome or in insulin resistant hypertensive or obese patients? If the answers are yes, are these beneficial effects of pravastatin superior to those of other anti-hyperlipidemic statins with equihypolipidemic properties? (2) Does pravastatin treatment actually reduce the development of diabetes in these insulin resistant patients? At that time, does pravastatin treatment increase serum levels of adiponectin, a key adipokine with insulin-sensitizing property? How about the effects of pravastatin treatment on adipokines that could elicit insulin resistance such as tumor necrosis factor-alpha? These clinical studies will provide further information whether pravastatin treatment can improve insulin resistance and subsequently reduce the development of diabetes in insulin resistant patients with the metabolic syndrome.

Inhibition of intestinal cholesterol absorption by ezetimibe is a novel therapeutic target for fatty liver

Ezetimibe is a novel lipid-lowering agent that inhibits intestinal absorption of dietary and biliary cholesterol. The effects of ezetimibe on low-density lipoprotein (LDL)-cholesterol were found to generally consistent across all subgroups analyzed, including baseline lipid profile, hypertension, diabetes mellitus, and body mass index. Furthermore, recent clinical studies also revealed that co-administration of ezetimibe with on-going statins offered a well-tolerated and efficacious treatment to lower LDL-cholesterol levels in hypercholesterolemic patients with diabetes mellitus or the metabolic syndrome. Niemann-Pick C1 like 1 (NPC1L1) protein is recently found to be critical for intestinal cholesterol absorption, and is a target protein for ezetimibe. Human NPC1L1 protein is predominantly expressed in liver, whereas small intestine expression is only about 2-4% of that found in the liver. Thus, NPC1L1 does not function solely in the intestinal cholesterol absorption. Furthermore, loss of NPC1L1 expression has been shown to protect against diet-induced fatty liver. These observations let us to speculate that ezetimibe will become a new therapeutic approach for the treatment of non-alcoholic fatty liver, the hepatic manifestation of insulin resistant patients with the metabolic syndrome. In this paper, we would like to propose the possible ways of testing our hypothesis as follows. (1) Does ezetimibe treatment improve fatty liver in patients with hypercholesterolemia or the metabolic syndrome? If the answers are yes, are these beneficial effects of ezetimibe superior to those of other anti-hyperlipidemic resins with equihypolipidemic properties? (2) Does ezetimibe treatment improve insulin sensitivity in fatty liver patients with the metabolic syndrome? (3) How about the effects of ezetimibe treatment on serum levels of adiponectin, a key adipokine with insulin-sensitizing property? Large clinical trials will provide us with more definite information whether ezetimibe treatment can improve fatty liver and resultantly reduce the risk of progression of liver diseases in patients with the metabolic syndrome.

[Concomitant off-pump coronary artery bypass and left lower lobectomy for lung cancer with pneumoconiosis]

Surgical strategy for patients for lung cancer with coronary disease remains controversial. We performed concomitant off-pump coronary artery bypass grafting (off-pump CABG: OPCAB) and left lower lobectomy with ND 2a lymph nodes dissection for lung cancer with pneumoconiosis. After CABG, due to fixed adhesion of peribronchial lymph node, left lower lobectomy was hard to carry out. Postoperative management was done with much difficulty for massive sputum and pneumonia caused by chronic inflammatory lung disease. As a result, postoperative course has been uneventful for 2 years after operation. In the concomitant OPCAB and lung resection with chronic inflammatory lung disease, whether the synchronous or 2 periods operation was appropriate was still unknown. We think that careful pre- and intraoperative assessment for this disease is important.

Minodronate, a nitrogen-containing bisphosphonate, is a promising remedy for treating patients with diabetic retinopathy

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-their receptor (RAGE) interactions are involved in the development and progression of diabetic retinopathy. Bisphosphonates are potent inhibitors of bone resorption and are widely used drugs for the treatment of osteoporosis and osteolytic bone metastasis. Recently, farnesyl pyrophosphate synthase has been shown as a molecular target of nitrogen-containing bisphosphonates, and inhibition of post-translational prenylation of small molecular weight G proteins is likely involved in their anti-resorptive activity on osteoclasts. NADPH oxidase-derived reactive oxygen species (ROS) generation is required for the AGE-RAGE signaling in vascular wall cells, and small G protein Rac is a critical component of vascular NADPH oxidase complex. These observations let us to speculate that minodronate, a newly developed nitrogen-containing bisphosphonate, might be a promising remedy for treating patients with diabetic retinopathy by inhibiting the AGE-RAGE signaling pathways through suppression of ROS generation via inhibition of Rac prenylation. In this paper, we like to propose the possible ways of testing our hypotheses: (1) Does treatment with minodronate decrease the risk for the development and progression of diabetic retinopathy in osteoporotic patients? (2) If the answer is yes, is this beneficial effect of minodronate superior to that of other nitrogen-noncontaining bisphosphonates with equihypolipidemic properties? (3) Does minodronate treatment suppress NADPH oxidase-mediated ROS generation in retinas of diabetic animals? (4) Does treatment with pyridoxamine, a post-Amadori inhibitor of AGE formation, attenuate these beneficial effects of minodronate on diabetic retinopathy? These clinical and animal studies could clarify whether the use of minodronate is of benefit in patients with AGE-RAGE-related disorders such as diabetic retinopathy, even in the absence of osteoporosis.

Serum or cerebrospinal fluid levels of glyceraldehyde-derived advanced glycation end products (AGEs) may be a promising biomarker for early detection of Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in developed countries. AD is characterized pathologically by the presence of senile plaques and neurofibrillary tangles (NFTs), the major constituents of which are the amyloid beta protein (Abeta) and tau protein, respectively. Several epidemiological studies have reported moderately increased risks of AD in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end products (AGEs) progress. Recent understandings of this process have confirmed that AGEs - their receptor (RAGE) interactions may play a role in the pathogenesis of diabetic vascular complications and neurodegenerative disorders including AD. Indeed, it has been demonstrated that AGEs can be identified immunohistochemically to be present in both senile plaques and NFTs from patients with AD. Glycation of Abeta markedly enhances its aggregation in vitro, and the glycation of tau, in addition to hyperphosphorylation, appears to enhance the formation of paired helical filaments. Further, RAGE has been found a specific cell surface receptor for Abeta peptite, thus eliciting neuronal cell perturbation. The active participation of RAGE in the pathogenesis of AD has also been confirmed in RAGE-overexpressed transgenic mice. Moreover, we have recently found that glyceraldehyde-derived AGEs, one of the representative ligands for RAGE, exerted cytopathic effects on cultured neuronal cells and that neurotoxic effect of diabetic serum was completely blocked by neutralizing antibodies against glyceraldehydes-derived AGEs. These observations led us to hypothesize that serum or cerebrospinal fluid (CSF) levels of glyceraldehyde-derived AGEs could become a promising biomarker for early detection of AD. We also would like to propose the possible ways of testing our hypothesis. Are the concentrations of glyceraldehyde-derived AGEs in serum or CSF elevated early in the course of dementia? Are these levels correlated with disease severity and progression, especially in patients with diabetes? These clinical studies clarify whether use of serum or CSF levels of glyceraldehyde-derived AGEs as a biomarker for AD might enable more effective diagnosis and treatment of patients with this devastating disorder.

Possible participation of advanced glycation end products in the pathogenesis of colorectal cancer in diabetic patients

Colorectal cancer is a major public health problem, being the second most common cause of cancer in developed countries. Several epidemiological studies have reported moderately increased risks of colorectal cancer in diabetic patients compared with general population. However, the underlying molecular link between diabetes and colorectal cancer remains to be elucidated. 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-their receptor (RAGE) interactions are involved in the development of atherosclerosis and diabetic microangiopathy. AGEs-RAGE interactions stimulated the growth of human pancreatic cancer cells through the autocrine induction of platelet-derived growth factor-B. Furthermore, we have recently found that AGEs stimulated the growth and migration of cultured human melanoma cells and that anti-RAGE antibodies inhibited tumor formation and lung metastasis of melanoma cell xenografts and subsequently improved survival in athymic mice. These observations let us to hypothesize that AGEs could explain the molecular link between diabetes and colorectal cancer. In this paper, we would like to propose the possible ways of testing our hypotheses. Is elevation of serum AGE levels a risk factor for colorectal cancer in patients with diabetes? Does treatment with metformin, which has a potential effect on the inhibition of glycation reactions in vivo, decrease the risk for colorecetal cancer 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, reduce the risk for colorectal cancer as well? Furthermore, are increased levels of AGEs and RAGE in colorectal cancer associated with poor prognosis in patients with diabetes? These clinical studies could clarify whether the AGEs-RAGE interactions serve as a causal link between diabetes and colorectal cancer.

Potential utility of statins, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors in diabetic retinopathy

Diabetic retinopathy is a common and potentially devastating microvascular complication in diabetes and is a leading cause of acquired blindness among the people of occupational age. However, therapeutic options for the treatment of proliferative diabetic retinopathy, photocoagulation and vitrectomy, are limited by considerable side effects. Therefore, to develop novel therapeutic strategies that specifically target diabetic retinopathy is desired for patients with diabetes. 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-their receptor (RAGE) interactions are involved in the development and progression of diabetic retinopathy. Statins, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, have been recently shown to reduce the risk for cardiovascular events in diabetic patients with or without coronary artery disease. However, the efficacy of statin therapy for diabetic retinopathy is not fully investigated. We have recently found that protein prenylation is crucial for the AGE-RAGE signaling in microvascular endothelial cells. By blocking the protein prenylation, cerivastatin completely prevented the AGE-RAGE-elicited angiogenesis via suppression of vascular endothelial growth factor (VEGF). These observations let us to speculate that statins might be a promising remedy for treating patients with diabetic retinopathy by acting as a potential inhibitor of the AGE-RAGE signaling pathway in microvascular endothelial cells. In this paper, we would like to propose the possible ways of testing our hypotheses. (1) Does treatment with statins decrease the risk for the development and progression of diabetic retinopathy in patients with normocholesterolemia? (2) If the answer is yes, is this beneficial effect of statins superior to that of other cholesterol-lowering agents with equihypolipidemic properties? (3) Does statin treatment suppress retinal VEGF expression in diabetic patients? (4) Does treatment with pyridoxamine, a post-Amadori inhibitor of AGE formation, attenuate the beneficial effects of statins on diabetic retinopathy? These clinical studies could clarify whether the use of statins is of benefit in patients with AGE-RAGE-related disorders such as diabetic retinopathy, even in the absence of hypercholesterolemia.

Acarbose is a promising therapeutic strategy for the treatment of patients with nonalcoholic steatohepatitis (NASH)

The metabolic syndrome is strongly associated with insulin resistance and has been recognized as a cluster of risk factors for cardiovascular diseases such as visceral obesity, hypertension, and diabetes. There is a growing body of evidence to show that nonalcoholic steatohepatitis (NASH) is the hepatic manifestation of insulin resistant patients with the metabolic syndrome. Indeed, insulin resistance increases adipocyte lipolysis and subsequently elevates circulating free fatty acids, thus stimulating the accumulation of fatty acids in the liver (hepatic steatosis). Fatty acids elicit reactive oxygen species generation, thereby promoting disease progression to NASH by both lipid peroxidation and inflammatory cytokine production. Postprandial hyperglycemia, one of the characteristic features of insulin resistance, also induces oxidative stress generation, being involved in dysfunction of pancreatic beta cells and vascular wall cells in the metabolic syndrome. Recently, STOP-NIDDM trial revealed that acarbose (Glucobay), an alpha-glucosidase inhibitor, improved postprandial hyperglycemia and subsequently reduced the risk of development of type 2 diabetes and newly diagnosed hypertension in patients with impaired glucose tolerance. In this study, acarbose treatment was also found to reduce body mass index and waist circumference in these patients. Furthermore, a meta-analysis of seven long-term studies has also shown that intervention with acarbose improved triglyceride levels, body weight and systolic blood pressure and subsequently prevented myocardial infarction in type 2 diabetic patients. Since acarbose improves postprandial hyperglycemia by delaying the release of glucose from complex carbohydrates in the absence of an increase in insulin secretion, the beneficial aspects of acarbose could be ascribed to improvement of insulin sensitivity in these patients. Given the pathological link between NASH and insulin resistance, we would like to hypothesize here that acarbose may become a promising therapeutic strategy for the treatment of patients with NASH. Does acarbose treatment improve steatohepatitis histologically? Is the extent of histological improvement by acarbose parallel to that of insulin sensitivity in these patients? Large clinical trials will provide us with more definite information whether acarbose treatment can improve insulin sensitivity and resultantly reduce the risk of progression of liver diseases in patients with NASH.

Potential therapeutic implication of nifedipine, a dihydropyridine-based calcium antagonist, in advanced glycation end product (AGE)-related disorders

A non-enzymatic reaction between ketones or aldehydes and the amino groups of proteins contributes to the aging of proteins and to pathological complications of diabetes. Under hyperglycemic conditions in diabetes, this process begins with the conversion of reversible Schiff base adducts, and then to more stable, covalently-bound Amadori rearrangement products. Over a course of days to weeks, these early glycation products undergo further reactions and rearrangements to become irreversible crossed-linked, fluorescent protein derivatives termed advanced glycation end products (AGEs). Recent understanding of this process has confirmed that AGE-their receptor (RAGE) interaction-elicited oxidative stress generation was implicated in the pathogenesis of diabetic vascular complication, melanoma growth, expansion and metastasis. We have recently found that nifedipine, one of the most widely used dihydropyridine-based calcium antagonists (DHPs) for treatments of patients with angina pectoris and hypertension, inhibited RAGE overexpression in AGE-exposed endothelial cells by suppressing reactive oxygen species generation. Since RAGE is a signal-transducing receptor for AGEs and subsequently evokes inflammatory responses in various types of cells, thus eliciting angiogenesis and thrombogenesis, we hypothesize here that blockade of RAGE expression by nifedipine may have therapeutic potentials in treatment of patients with various AGE-related disorders. In this paper, we would like to propose the possible ways of testing our hypothesis. Does nifedipine treatment reduce the development and progression of diabetic vascular complications? If the answer is yes, is this beneficial effect of nifedipine superior than that of other DHPs with equihypotensive properties? Does nifedipine treatment decrease the incidence of melanoma and/or prolong the survival of patients with this devastating disorder? These prospective studies will provide further valuable information whether blockade by nifedipine of the AGE-RAGE signaling could be clinically relevant.

Role of insulin-sensitizing property of telmisartan, a commercially available angiotensin II type 1 receptor blocker in preventing the development of atrial fibrillation

Atrial fibrillation (Af) is the most common disorder of cardiac rhythm and is responsible for substantial morbidity and mortality in the general population. A recent community-based observational study revealed that diabetes and hypertension were associated with the development of Af. Since there is no definite evidence to show that type 1 diabetes is at increased risk for the development of Af, insulin resistance rather than hyperglycemia per se could explain the link between diabetes and Af. Several clinical trials suggest that the renin-angiotensin system (RAS) plays a pivotal role in the pathogenesis of insulin resistance. Indeed, interruption of the RAS with angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin II type 1 receptor blockers (ARBs) has been shown to prevent the onset of diabetes in hypertensive patients. Further, several experimental and clinical studies showed the beneficial role for the inhibition of the RAS in preventing Af as well. However, to what extent the insulin-sensitizing effects of ARBs could account for the prevention of Af remains to be clarified. Recently, telmisartan, an ARB, was found to act as a partial agonist of peroxisome proliferator-activated receptor-gamma (PPAR-gamma). PPAR-gamma influences the gene expression involved in carbohydrate metabolism. In animal study, telmisartan administration caused a significant attenuation of weight gain and reduced glucose, insulin, and triglyceride levels in rats fed a high-fat, high-carbohydrate diet, compared with treatments of losartan, another type of ARB. Furthermore, recently, some clinical papers also reported the insulin-sensitizing effects of telmisartan in hypertensive patients. In this paper, we would like to propose the possible ways of clarifying to what extent the insulin-sensitizing effects of ARBs could account for the prevention of Af. (1) Does telmisartan reduce the development of Af in insulin resistant hypertensive patients? (2) When adjusted for blood pressure, is the effect of telmisartan superior to other ARBs? (3) Does this beneficial effect of telmisartan correlate to its insulin-sensitizing properties? Ongoing clinical trial (ONTARGET) has been designed the efficacy of telmisartan with an ACEI, ramipril, alone or in combination. This randomized, double-blind, multicenter international studies will provide further information whether telmisartan can improve insulin resistance and subsequently reduce the development of Af in high-risk hypertensive patients.

Telmisartan is a promising cardiometabolic sartan due to its unique PPAR-gamma-inducing property

The metabolic syndrome is strongly associated with insulin resistance and consists of a constellation of factors such as hypertension and hyperlipidemia that raise the risk for cardiovascular diseases and diabetes mellitus. Indeed, hypertension occurs approximately twice as frequently in patients with diabetes compared with in non-diabetic controls. Conversely, hypertensive patients are more likely than normotensive persons to develop diabetes. In addition, up to 75% of CVD in diabetic patients can be attributed to hypertension. Therefore, the primary goals of treating hypertensive patients with insulin resistance are prevention of type 2 diabetes and cardiovascular events. Then, what is the optimal anti-hypertensive approach to target organ protection in these patients? Several clinical trials suggest that the renin-angiotensin system (RAS) plays a pivotal role in the pathogensis of insulin resistance and CVD in diabetes. Interruption of the RAS with angiotensin-coverting enzyme inhibitors (ACEIs) or angiotensin II type 1 receptor blockers (ARBs) has been shown to prevent the onset of diabetes in hypertensive patients and to reduce cardiovascular and renal disease progression in diabetic patients with hypertension. However, whether we should recommend ARBs for insulin resistant-hypertensive patients or type 2 diabetic patients without nephropathy due to its insulin-sensitizing property remains to be clarified. Recently, telmisartan, an ARB, was found to act as a patrtial agonist of peroxisome proliferator-activated receptor-gamma (PPAR-gamma). PPAR-gamma influences the gene expression involved in carbohydrate metabolism, and pioglitazone and rosiglitazone, ligands for PPAR-gamma, improve insulin resistance in diabetic patients. Furthermore, there is a growing body of evidence that activators of PPAR-gamma exert anti-inflammatory, anti-oxidative and anti-proliferative effects on vascular wall cells, thus decreasing the risks for atherosclerosis. We hypothesize here that due to its unique PPAR-gamma-modulating activity, telmisartan will become a promising 'cardiometabolic sartan', that targets both diabetes and CVD in hypertensive patients. In this paper, we would like to propose the possible ways of testing our hypothesis. Does telmisartan reduce the development of diabetes and CVD in insulin resistant patients pretreated with maximal doses of other ARBs? Does co-treatment with an activator of PPAR-gamma attenuate the effects of telmisartan in these patients? These clinical studies will provide further information whether the beneficial cardiometabolic actions of telmisartan could be ascribed to its PPAR-gamma-inducing property.

Clinical significance of serum CEA protein and CEA mRNA after resection of colorectal liver metastases

BACKGROUND

It is difficult to predict the recurrence of colorectal liver metastasis after curative hepatectomy. We investigated the relationship between subsequent metastasis and both CEA protein and CEA mRNA (TaqMan PCR) diachronic levels.

PATIENTS AND METHODS

The subjects were 30 patients with colorectal liver metastases. Serum CEA protein and CEA mRNA assays were performed every month after hepatectomy.

RESULTS

Metastasis recurred in 21 of the 30 patients. The CEA mRNA assay showed 26 cases with high (H) levels and 4 with low (L). Among the 15 patients whose protein levels were not elevated (NE group), 6 had recurrence; all 6 belonged to the mRNA H group. None of the 4 patients in the mRNA L group had recurrence. In the protein-elevated (E) group (DFI > 6 months) (n = 7), mRNA was elevated in 5 cases (71.4%) 6 months before recurrence, whereas protein was elevated in 1 case. The sensitivity, specificity and accuracy of CEA protein/mRNA for identifying recurrence were 71.4/100, 100/44.4, and 80/83.3%, respectively.

CONCLUSION

CEA mRNA is more sensitive than CEA protein in detecting recurrence. CEA mRNA may be useful for identifying high-risk groups or detecting recurrence at an early stage, when the CEA protein level is still low.

Alternative routes for the formation of glyceraldehyde-derived AGEs (TAGE) in vivo

The advanced stage of the glycation process (one of the post-translational modifications of proteins) leads to the formation of advanced glycation end-products (AGEs) and plays an important role in the pathogenesis of angiopathy in diabetic patients, and in Alzheimer's disease (AD). Recently we have provided direct immunochemical evidence for the existence of six distinct AGEs structures, designated AGEs-1 to -6, within the AGEs-modified proteins and peptides that circulate in the serum of diabetic patients. We found for the first time that glyceraldehyde-derived AGEs (AGE-2), which comprise main structure of TAGE (toxic AGEs), in the serum of diabetic patients have diverse biological activities on vascular wall cells and cortical neurons. These results suggest a causal role for AGE-2 in the pathogenesis of diabetic complications and AD in vivo. In AD brains, AGE-2 epitope was mainly present in the cytosol of neurons in the hippocampus and para-hipocampal gyrus. We propose three pathways for the in vivo formation of AGE-2 precursor, glyceraldehyde, by: (i) glycolytic pathway, (ii) polyol pathway, and (iii) fructose metabolic pathway. Glyceraldehyde can be transported or can leak passively across the plasma membrane. It can react non-enzymatically with proteins to lead to accelerated formation of AGE-2 at both intracellular and extracellular region.

TAGE (toxic AGEs) hypothesis in various chronic diseases

The advanced stage of the glycation process (one of the post-translational modifications of proteins) leads to the formation of advanced glycation end-products (AGEs) and plays an important role in the pathogenesis of angiopathy in diabetic patients, in aging, and in neurodegenerative diseases. However, it is still not clear which AGEs subtypes play a pathogenetic role and which of several AGEs receptor mediate AGEs effects on cells. We have provided direct immunochemical evidence for the existence of six distinct AGEs structures (AGEs-1 to -6) within the AGEs-modified proteins and peptides that circulate in the serum of diabetic patients. Recently we demonstrated for the first time that glyceraldehyde-derived AGEs (AGEs-2) and glycolaldehyde-derived AGEs (AGE-3) have diverse biological activities on vascular wall cells, mesangial cells, Schwann cells, malignant melanoma cells and cortical neurons. We also demonstrated for the first time that acetaldehyde (AA)-derived AGEs (AA-AGE) have cytotoxic activity on cortical neurons and the AA-AGE epitope was detected in human brain of alcoholics. These results indicate that of the various types of AGEs structures that can form in vivo, the toxic AGEs (TAGE) structures (AGEs 2, 3, and AA-AGE), but not non-toxic AGEs (N-carboxymethyllysine, pentosidine, pyrraline etc.) are likely to play an important role in the pathophysiological processes associated with AGEs formation.

Otsuka Long-Evans Tokushima fatty (OLETF) rat is not a suitable animal model for the study of angiopathic diabetic retinopathy

We have previously shown that the peak latency of oscillatory potential (OP), the earliest electroretinographic manifestation of diabetic retina, was prolonged in Otsuka Long-Evans Tokushima Fatty (OLETF) rat, a model of non-insulin-dependent diabetes. These observations suggest that retinal neuronal dysfunction revealed by the OP abnormality in the electroretinogram takes place prior to the angiopathic diabetic changes in this animal model. However whether acellular capillaries and pericyte ghosts, one of the histopathological hallmarks of early diabetic retinopathy in humans, could occur in OLETF rat remains to be elucidated. In the present study, we first prepared the retinal trypsin digests of OLETF and control Long-Evans Tokushima Otsuka (LETO) rats at 45 weeks old and then compared the number of acellular capillaries and pericyte ghosts in the retinas of OLETF rats with that in LETO rats. Blood glucose levels were higher in the OLETF rats than those in LETO rats. Retinal capillaries of OLETF rats were found to remain morphologically normal and pericyte ghosts were barely detectable. There was no difference in the number of acellular capillaries in the retinas between OLETF and LETO rats. The present study indicates that acellular capillaries and pericyte ghosts, the characteristic morphological changes in early diabetic retinopathy, are not accelerated in OLETF rats. Our data suggest that OLETF rat is not a suitable animal model for the study of angiopathic diabetic retinopathy.

Unique atheroprotective property of azelnidipine, a dihydropyridine-based calcium antagonist

Insulin resistance and central obesity are often associated with hypertension. The metabolic syndrome is a cluster of these common clinical disorders, and is related with an increased risk for cardiovascular diseases. A number of pro-inflammatory cytokines derived from adipose tissues have been thought to contribute to the development of insulin resistance and accelerated atherosclerosis. Among them, TNF-alpha has been most widely studied; it not only suppresses the insulin signaling, but also elicits vascular inflammation. Indeed, inhibition of TNF-alpha was found to improve insulin resistance in obese rats and reduce the progression of atherosclerosis in apolipoprotein E knockout mice, respectively. These observations demonstrate that TNF-alpha could play a central role in the pathogenesis of insulin resistance and accelerated atherosclerosis in the metabolic syndrome. Considering that the primary goals of treatment for hypertensive patients with the metabolic syndrome are prevention of the development of diabetes and cardiovascular events, anti-hypertensive drugs that have abilities to block the TNF-alpha signaling would be desirable as a first-line therapy for these patients. In the process of the search for such a unique anti-hypertensive drug, we have recently found that azelnidipine, a newly developed and commercially used long-acting dihydropyridine-based calcium antagonist (DHP), inhibited TNF-alpha-induced activator protein-1 activation and interleukin-8 expression in human umbilical vein endothelial cells by suppressing NADPH oxidase-mediated reactive oxygen species generation. The concentration of azelnidipine that was found effective in these in vitro-experiments is well within the therapeutic range. Since endothelial cells do not possess voltage-operated L-type calcium channels, these observations suggest that the beneficial effects of azelnidipine are not likely due to calcium channel blocking property, but due to its unique anti-oxidative ability. Furthermore, we have very recently found that serum levels of monocyte chemoattractant protein-1, a biomarker for subclinical atherosclerosis, were significantly decreased by the treatment of azelnidipine in patients with essential hypertension. In this paper, we would like to hypothesize that due to its unique TNF-alpha signal modulatory, anti-oxidative property, azelnidipine may be a promising DHP that targets diabetes and cardiovascular diseases in hypertensive patients with the metabolic syndrome.

Pericyte biology and diseases

Microvessels are composed of two types of cells: endothelial cells and pericytes. Pericytes are elongated cells of mesodermal origin that partially surround the endothelial cells of small vessels. As pericytes contain contractile muscle filaments on their endothelial cell side, they have long been regarded as just microvascular counterparts of smooth muscle cells, thus being implicated in the regulation of capillary tone. However recent understanding of pericyte biology suggests that pericytes play an important role in the maintenance of microvascular homeostasis. Indeed, loss or dysfunction of pericytes has been considered to play an active part in the pathogenesis of various types of disorders. In this study, we review the biology of pericytes and the pathological role of pericyte loss or dysfunction in various devastating disorders such as diabetic retinopathy, atherosclerosis and tumor angiogenesis

Azelnidipine, a dihydropyridine-based calcium antagonist, inhibits angiotensin II-induced oxidative stress generation and downregulation of pigment epithelium-derived factor mRNA levels in microvascular endothelial cells

We have previously shown that azelnidipine, a long-acting dihydropyridine-based calcium antagonist (DHP), inhibited tumor necrosis factor-alpha-induced endothelial cell (EC) activation through its antioxidative properties. However whether azelnidipine could also block the angiotensin II (Ang II)-signaling in ECs remains to be elucidated. Since Ang II-type 1 receptor interaction could contribute to exacerbation of diabetic retinopathy by downregulating pigment epithelium-derived factor (PEDF) gene expression in ECs, we examined here whether azelnidipine inhibited the Ang II-induced reactive oxygen species (ROS) generation and subsequent PEDF gene suppression in microvascular ECs. Azelnidipine, but not nitrendipine, the other popular DHFP completely inhibited the Ang II-induced ROS generation in ECs. Furthermore, azelnidipine, but not nitrendipine, was found to partially restore decreased PEDF mRNA levels in Ang II-exposed ECs. The present study suggests that azelnidipine could inhibit the Ang II-induced decrease in PEDF mRNA levels in ECs through its antioxidative properties. Upregulation of PEDF by azelnidipine may become a therapeutic target for the treatment of diabetic retinopathy associated with hypertension.

Inhibition by advanced glycation end products (AGEs) of pigment epithelium-derived factor (PEDF) gene expression in microvascular endothelial cells

Pigment epithelium-derived factor (PEDF) is a natural extracellular component of the retina with neuronal differentiating activity. Recently, decreased levels of PEDF in the mammalian eye have been shown to participate in the pathogenesis of diabetic retinopathy In addition, advanced glycation end products (AGEs), senescent macroprotein derivatives that form at an accelerated rate under diabetes, have also been implicated in the development and progression of diabetic retinopathy. However the role of AGEs in decreased levels of PEDF in the eye remains to be elucidated. In this study, we examined the effects of AGEs on PEDF gene expression in microvascular endothelial cells (ECs). Various types of immunochemically distinct AGEs, which were prepared in vitro by incubating bovine serum albumin with glucose, glyceraldehyde or glycolaldehyde, significantly decreased endothelial mRNA levels of PEDF Furthermore, H2O2 dose-dependently suppressed PEDF gene expression in ECs. Our present results suggest that AGEs could down-regulate mRNA levels of PEDF in ECs, probably via oxidative stress generation. The deleterious effects of AGEs on diabetic retinopathy could be due, at least in part, to their PEDF-inhibitory properties.

Olmesartan medoxomil, a newly developed angiotensin II type 1 receptor antagonist, protects against renal damage in advanced glycation end product (age)-injected rats

Diabetic nephropathy is a leading cause of end-stage renal disease in industrialized countries. Although the molecular mechanisms for the development and progression of diabetic nephropathy are not fully understood, the formation of advanced glycation end products (AGEs) and activation of the renin-angiotensin system (RAS) have been considered to be the main factors participating in the pathogenesis of diabetic nephropathy. However, functional cross-talk between AGEs and the RAS remains to be elucidated. In this study, we examined the effects of oral administration of olmesartan medoxomil, a newly developed angiotensin II type 1 receptor antagonist, on renal damage in AGE-treated rats. Administration of olmesartan medoxomil significantly inhibited the increase of systolic and diastolic blood pressure levels and urinary N-acetyl-beta-D-glucosaminidase activity in exogenously AGE-injected rats. Furthermore, olmesartan medoxomil treatment also prevented glomerulosclerosis in AGE-treated rats. These results indicate that exogenous AGE treatment could induce renal damage via the activation of the RAS. Our study suggests that olmesartan medoxomil could be a valuable drug for the treatment of diabetic nephropathy by blocking the deleterious effects of AGEs.

Molecular mechanisms for vascular injury in the metabolic syndrome

The metabolic syndrome is strongly associated with insulin resistance and has been recognized as a cluster of risk factors for cardiovascular diseases such as visceral obesity, hypertension, diabetes and dyslipidemia. Recently, insulin resistance in the absence of overt diabetes or the metabolic syndrome itself has been shown to be associated with endothelial dysfunction, one of the initial steps in the process of atherosclerosis. In the present article we review the molecular mechanisms by which the metabolic syndrome causes endothelial dysfunction and subsequently promotes atherosclerosis. We also discuss promising therapeutic strategies that specifically target the mechanisms responsible for vascular alterations in the metabolic syndrome.

Renoprotective effects of azelnidipine, a dihydropyridine-based calcium antagonist in advanced glycation end product (AGE)-injected rats

Diabetic nephropathy is a leading cause of end-stage renal disease in industrialized countries. Although the molecular mechanisms for the development and progression of diabetic nephropathy are not fully understood, the formation and accumulation of advanced glycation end products (AGEs) have been considered to play a major role in the pathogenesis of diabetic nephropathy. Hypertension is also an independent risk factor for the progression of diabetic nephropathy. However, functional cross-talk between AGEs and blood pressure and their involvement in diabetic nephropathy remain to be elucidated. In this study, we examined the effects of oral administration of azelnidipine, a commercially available dihydropyridine-based calcium antagonist, on renal injury in AGE-treated rats. Administration of azelnidipine inhibited the increase of systolic and diastolic blood pressure levels and urinary N-acetyl-beta-D-glucosaminidase activity in exogenously AGE-injected rats. Furthermore, azelnidipine treatment also prevented glomerulosclerosis in AGE-treated rats. These results indicate that renal damage in AGE-injected rats could be mediated, at least in part, by the elevation of blood pressure. Our present study suggests that azelnidipine would represent a valuable drug for the treatment of diabetic nephropathy by blocking the deleterious effects of AGEs.

Met72Thr polymorphism of pigment epithelium-derived factor gene and susceptibility to age-related macular degeneration

Age-related macular degeneration (ARMD) is the most common cause of acquired blindness among the people of occupational age. Although the pathogenesis of ARMD is not fully understood, several studies suggest a possible contribution of a genetic factor in the development and progression of ARMD. Pigment epithelium-derived factor (PEDF), a glycoprotein that belongs to the superfamily of serine protease inhibitors, was first purified from the conditioned media of human retinal pigment epithelial cells as a factor with potent neuronal differentiating activity in human retinoblastoma cells. Recently, PEDF has been shown to be a highly effective inhibitor of angiogenesis in cell culture and animal models. In addition, PEDF has been found in the vitreous, and its levels were decreased in angiogenic eye diseases, thus suggesting that a loss of PEDF in the eye is functionally important in the pathogenesis of ARMD. A functional amino acid change, a methionine to threonine polymorphism (Met72Thr polymorphism) at codon 72 in exon 3 (T/C polymorphism) of the PEDF gene, that results in the formation of BsstSI restriction site, has recently been identified. Since it is well known that a single nucleotide polymorphism and resultant amino acid change often alters the activity or expression level of the target protein, we would like to propose here a novel hypothesis that the Met72Thr polymorphism (T/C polymorphism) of PEDF gene may be a genetic marker for ARMD. Are genotype and allele frequencies of the Met72Thr polymorphism (T/C polymorphism) different between the patients with or without ARMD? Is this polymorphism associated with disease severity and progression? If the answer is yes, does this Met72Thr polymorphism regulate the vitreous levels of PEDF? These clinical studies could provide us with information whether this genetic variant of the PEDF gene could present an attractive candidate susceptibility gene for ARMD.