A lethal tetrad in diabetes: hyperglycemia, dyslipidemia, oxidative stress, and endothelial dysfunction

This paper addresses the consequences of diabetes and obesity, diseases that have become epidemic in our society, particularly in the past 20 years. Specifically, it summarizes current knowledge about some of the risk factors and mechanisms for the vascular complications of diabetes. These complications can be broadly divided into microvascular disease, such as diabetic retinopathy and diabetic nephropathy, and macrovascular disease, such as accelerated atherosclerosis, and they are the main cause for morbidity and premature mortality among diabetic patients. The roles of hyperglycemia, dyslipidemia and dyslipoproteinemia, oxidative stress, and endothelial dysfunction will be considered. Finally, the "treatment gap" will be addressed. This gap refers to our failure to achieve currently accepted goals to reduce established risk factors for complications in the clinical management of diabetic patients.

Vascular endothelial dysfunction in diabetic cardiomyopathy: pathogenesis and potential treatment targets

Cardiovascular complications account for significant morbidity and mortality in the diabetic population. Diabetic cardiomyopathy, a prominent cardiovascular complication, has been recognized as a microvascular disease that may lead to heart failure. Pathogenesis of diabetic cardiomyopathy involves vascular endothelial cell dysfunction, as well as myocyte necrosis. Clinical trials have identified hyperglycemia as the key determinant in the development of chronic diabetic complications. Sustained hyperglycemia induces several biochemical changes including increased non-enzymatic glycation, sorbitol-myoinositol-mediated changes, redox potential alterations, and protein kinase C (PKC) activation, all of which have been implicated in diabetic cardiomyopathy. Other contributing metabolic abnormalities may include defective glucose transport, increased myocyte fatty acid uptake, and dysmetabolism. These biochemical changes manifest as hemodynamic alterations and structural changes that include capillary basement membrane (BM) thickening, interstitial fibrosis, and myocyte hypertrophy and necrosis. Diabetes-mediated biochemical anomalies show cross-interaction and complex interplay culminating in the activation of several intracellular signaling molecules. Studies in both animal and human diabetes have shown alteration of several factors including vasoactive molecules that may be instrumental in mediating structural and functional deficits at both the early and the late stages of the disease. In this review, we will highlight some of the important vascular changes leading to diabetic cardiomyopathy and discuss the emerging potential therapeutic interventions.

Trans-arachidonic acids generated during nitrative stress induce a thrombospondin-1-dependent microvascular degeneration

Nitrative stress has an important role in microvascular degeneration leading to ischemia in conditions such as diabetic retinopathy and retinopathy of prematurity. Thus far, mediators of nitrative stress have been poorly characterized. We recently described that trans-arachidonic acids are major products of NO(2)(*)-mediated isomerization of arachidonic acid within the cell membrane, but their biological relevance is unknown. Here we show that trans-arachidonic acids are generated in a model of retinal microangiopathy in vivo in a NO(*)-dependent manner. They induce a selective time- and concentration-dependent apoptosis of microvascular endothelial cells in vitro, and result in retinal microvascular degeneration ex vivo and in vivo. These effects are mediated by an upregulation of the antiangiogenic factor thrombospondin-1, independently of classical arachidonic acid metabolism. Our findings provide new insight into the molecular mechanisms of nitrative stress in microvascular injury and suggest new therapeutic avenues in the management of disorders involving nitrative stress, such as ischemic retinopathies and encephalopathies.

Pathophysiological role of Amadori-glycated proteins in diabetic microangiopathy

Early and advanced nonenzymatic glycation of proteins are increased in diabetes. Although Amadori-glycated proteins are the major glycated modifications, most studies so far have focused on the role of advanced glycation end-products (AGEs) in diabetes-related vascular complications. It was only recently that the role of Amadori-glycated proteins has come under consideration. Here we review data that point to an important role of Amadori-modified glycated serum proteins in diabetic microangiopathy. Amadori-glycated albumin induces the activation of glomerular mesangial and endothelial cells to a phenotype that may be linked to the pathogenesis of diabetic microangiopathy, that is, by the stimulation of protein kinase C, activation of transforming growth factor beta, and the expression of extracellular matrix proteins. In type 1 diabetic patients, levels of Amadori-glycated proteins are independently associated with nephropathy and retinopathy. Reduction of Amadori-glycated albumin levels in diabetic animal models ameliorates the progression of nephropathy and retinopathy, indicating a causal role of Amadori-glycated proteins in the pathogenesis of diabetic nephropathy and retinopathy. Based on these data, inhibition of Amadori-glycated albumin may be a target for reduction of diabetic vascular complications.

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.

Cardiac structural and functional abnormalities in end stage renal disease patients with elevated cardiac troponin T

OBJECTIVES

To identify in a prospective observational study the cardiac structural and functional abnormalities and mortality in patients with end stage renal disease (ESRD) with a raised cardiac troponin T (cTnT) concentration.

METHODS

126 renal transplant candidates were studied over a two year period. Clinical, biochemical, echocardiographic, coronary angiographic, and dobutamine stress echocardiographic (DSE) data were examined in comparison with cTnT concentrations dichotomised at cut off concentrations of < 0.04 microg/l and < 0.10 microg/l.

RESULTS

Left ventricular (LV) size and filling pressure were significantly raised and LV systolic and diastolic function parameters significantly impaired in patients with raised cTnT, irrespective of the cut off concentration. The proportions of patients with diabetes and on dialysis were higher in both groups with raised cTnT. With a cut off cTnT concentration of 0.04 microg/l but not 0.10 microg/l, significantly more patients had severe coronary artery disease and a positive DSE result. The total ischaemic burden during DSE was similar in cTnT positive and negative patients, irrespective of the cut off concentration used. LV end systolic diameter index and E:Ea ratio were independent predictors of cTnT rises > or = 0.04 microg/l and > or = 0.10 microg/l, respectively. Diabetes was independently associated with cTnT at both cut off concentrations. Mortality was higher in all patients with raised cTnT.

CONCLUSIONS

Patients with ESRD with raised cTnT concentrations have increased mortality. Raised concentrations are strongly associated with diabetes, LV dilatation, and impaired LV systolic and diastolic function, but not with severe coronary artery disease.

Endothelin inhibition delays onset of hyperglycemia and associated vascular injury in type I diabetes: evidence for endothelin release by pancreatic islet beta-cells

This study investigated the role of endothelin-1 for hyperglycemia, vascular, and pancreatic injury in early type I diabetes in non-obese-diabetic (NOD) mice. Endothelium dependent relaxation to acetylcholine and vascular gene expression of endothelin converting enzyme (ECE) isoforms 1 and 2 were studied as indicators of vascular injury. Endothelial NO bioactivity in the aorta was reduced in diabetic NOD mice while vascular expression of ECE-1 and ECE-2 mRNA was increased compared with controls (all p<0.05). Vascular histology was normal in all animals. Unexpectedly, treatment of prediabetic NOD mice for 6 weeks with the orally active ET(A) receptor antagonist BSF461314 prevented onset of diabetes without affecting insulitis severity. ET(A) receptor blockade also restored abnormal endothelial NO bioactivity and reduced ECE-1 and ECE-2 gene expression in NOD mice to levels comparable with healthy controls (p<0.05). Moreover, secretion of endothelin-1 in a time-dependent fashion was observed by pancreatic islet beta-cells cultured in vitro. These data suggest a critical role for ET(A) receptor signaling in the development of autoimmune forms of diabetes and the early vascular injury associated with it.

Effect of in vitro glucose and diabetic hyperglycemia on mouse kidney protein synthesis: relevance to diabetic microangiopathy

To test the possible roles of diabetic hyperglycemia, we studied the in vitro effect of increasing glucose concentrations (5.0-27.5 mmol/L) on protein synthesis (PS) of the kidneys from "adult" male albino Swiss mice. In mouse kidney cortex slices, PS (3H-leucine incorporation into trichloroacetic acid-precipitable material), measured as cpm/mg protein/45 minutes, was already stimulated by 5.0 mmol/L of glucose (+24%, P < .05). At supraphysiologic glucose concentrations, PS was stimulated by 48% at 8.8 mmol/L of glucose and 31% at 13.6 mmol/L of glucose (P < .05, compared with the value observed at 5.0 mmol/L of glucose). However, the highest glucose levels (15.4 mmol/L and 27.5 mmol/L) were no longer effective. Other substrates (1.25 mmol/L or 6.26 mmol/L palmitic acid and 100 mcmol/L sorbitol) were without effect. Similar results were obtained when data were expressed as cpm/mg DNA/45 minutes. In contrast to adult mice, "young" mice showed the maximum stimulatory effect (+86%, P < .02), with a glucose concentration still in the nondiabetic range (6.6 mmol/L). However, in the "older" mice maximum stimulation was observed in the presence of high glucose concentrations (15.4 mmol/L and 27.5 mmol/L) with 52% (P < .02) and 26% (P < .05) increases, respectively, vs the value recorded at 5 mmol/L of glucose. With regard to the in vivo effect of diabetic hyperglycemia, the renal PS of 3-day streptozotocin diabetic mice was moderately increased, whereas the liver PS was markedly reduced. The effects of in vitro glucose and in vivo diabetic hyperglycemia, as modulated by both the concentration of glucose and the age, may lead to diabetic renal hypertrophy and the increased formation/accumulation of glycoproteins, thus contributing to microangiopathy.

Postprandial hypertriglyceridemia and oxidative stress in patients of type 2 diabetes mellitus with macrovascular complications

BACKGROUND

Oxidative stress has been implicated in vascular complications of diabetes mellitus (DM). This study aims to evaluate the relationship between postprandial hypertriglyceridemia (PP-HTG) and oxidative stress in Indian patients of type 2 DM with macrovascular complications.

METHODS

Plasma triglycerides (TG), thiobarbituric acid reactive substances (TBARS), erythrocyte reduced glutathione (GSH) and superoxide dismutase (SOD) were measured in fasting and postprandial (PP) state at 2, 4, 6 and 8 h after a high fat meal challenge in controls (Group I) and patients of type 2 DM without (Group II) and with macrovascular complications (Group III).

RESULTS

Postprandial TGs increased significantly in patients with type 2 DM, which showed an exaggerated response to high fat meal challenge in Group III as compared to Group II. Highest PP-TBARS were also observed in Group III which correlated positively with TG. However, GSH and SOD were lower in both groups of diabetics as compared to controls.

CONCLUSIONS

The magnitude of PP-HTG appears to be the major determinant of oxidative stress in type 2 DM, which along with a compromised antioxidant status may lead to endothelial dysfunction and macrovascular complications.

Proteinase-activated receptor-2 mediates arterial vasodilation in diabetes

OBJECTIVE

Proteinase-activated receptor-2 is widely expressed in vascular tissue and in highly vascularized organs in humans and other species. Its activation mainly causes endothelium-dependent vasorelaxation in vitro and hypotension in vivo. Here, using nonobese diabetic (NOD) mice at different disease stages, we have evaluated the role of PAR2 in the arterial vascular response during diabetes progression.

METHODS AND RESULTS

High (NOD-II; 20 to 500 mg/dL) or severe glycosuria (NOD-III; 500 to 1000 mg/dL) provokes a progressive reduction in the response to acetylcholine paralleled by an increase in the vasodilatory response to PAR2 stimulation. Western blot and quantitative real-time polymerase chain reaction (RT-PCR) studies showed that this effect is tied to an increased expression of PAR2 coupled to cyclooxygenase-2 expression. Pharmacological dissection performed with specific inhibitors confirmed the functional involvement of cyclooxygenase-2 in PAR2 vasodilatory effect. This vasodilatory response was confirmed to be dependent on expression of PAR2 in the smooth muscle component by immunohistochemistry studies performed on aorta isolated by both NOD-III and transgenic PAR2 mice.

CONCLUSIONS

Our data demonstrate an important role for PAR2 in modulating vascular arterial response in diabetes and suggest that this receptor could represent an useful therapeutic target.

Regulation of vascular genes by glucose

Endothelial dysfunction is an early sign of diabetic vascular disease. Due to their unique position at the border between blood and vascular tissue, endothelial cells (EC) are the first vascular cells to sensor humoral changes, and they are able to transmit the information about these changes to other vascular cell types by changing their gene expression profile and producing growth factors, cytokines, adhesion molecules, and other bioactive molecules. These signals alter vascular cell dynamics and interactions, vascular tone and result in inability of the vessel to maintain athrombogenic luminal surface and in alteration of vascular permeability. Although researchers have yet to uncover the precise mechanism(s) that leads to diabetic vascular disease, hyperglycemia has been identified as an independent risk factor for micro- and macrovascular complications. Elevated levels of glucose induce the expression of a variety of genes related to atherogenesis and angiogenesis regulation. However, most of our current knowledge about the molecular mechanisms used by glucose to regulate gene expression is based on studies that used cells with insulin-dependent glucose transport (hepatocytes, adipocytes). Such cells are significantly different than vascular cells, in which glucose uptake is mostly imparted by insulin-independent mechanisms. This review summarizes current information about the effects of hyperglycemia and elevated glucose in in vitro systems on vascular gene expression and molecular transcriptional and post-transcriptional mechanisms that may regulate the changes related to diabetic vascular complications.

Diabetic vascular complications: pathophysiology, biochemical basis and potential therapeutic strategy

Diabetic vascular complication is a leading cause of end-stage renal failure, acquired blindness, a variety of neuropathies and accelerated atherosclerosis, which could account for disabilities and high mortality rates in patients with diabetes. Recent large prospective clinical studies have shown that intensive glucose control reduces effectively microvascular complications among patients with diabetes, and insulin resistance and postprandial hyperglycemia seem to be involved in diabetic macrovascular complications. Chronic hyperglycemia is a major initiator of diabetic vascular complications. Indeed, high glucose, via various mechanisms such as increased production of advanced glycation end products, activation of protein kinase C, stimulation of the polyol pathway and enhanced reactive oxygen species generation, regulates vascular inflammation, altered gene expression of growth factors and cytokines, and platelet and macrophage activation, thus playing a central role in the development and progression of diabetic vascular complications. This article summarizes the molecular mechanisms of diabetic vascular complications and the potential therapeutic interventions that may prevent these disorders even in the presence of hyperglycemia, control of which is often difficult with current therapeutic options.

Type 2 Diabetic Mice Have Increased Arteriolar Tone and Blood Pressure

OBJECTIVE

Type 2 diabetes mellitus (T2-DM) is frequently associated with vascular dysfunction and elevated blood pressure, yet the underlying mechanisms are not completely understood. We hypothesized that in T2-DM, the regulation of peripheral vascular resistance is altered because of changes in local vasomotor mechanisms.

METHODS AND RESULTS

In mice with T2-DM (C57BL/KsJ-(db-)/db-), systolic and mean arterial pressures measured by the tail cuff method were significantly elevated compared with those of control (db+/db-) animals (db/db, 146+/-5 and 106+/-2 mm Hg versus control, 133+/-4 and 98+/-4 mm Hg, respectively; P<0.05). Total peripheral resistance, calculated from cardiac output values (measured by echocardiography) and mean arterial pressure were significantly elevated in db/db mice (db/db, 25+/-6 versus control, 15+/-1 mm Hg[middot]mL(-1)[middot]min(-1)). In isolated, pressurized gracilis muscle arterioles (diameter approximately 80 microm) from db/db mice, stepwise increases in intraluminal pressure (from 20 to 120 mm Hg) elicited a greater reduction in diameter than in control vessels at each pressure step (at 80 mm Hg, db/db, 66+/-4% versus control, 79+/-3%). The passive diameters of arterioles (obtained in Ca2+-free solution) and the calculated myogenic index were not significantly different in the 2 groups. The presence of the prostaglandin H2/thromboxane A2 receptor antagonist SQ29548 did not affect arteriolar diameters of control mice but reduced the enhanced arteriolar tone of db/db mice back to control levels (at 80 mm Hg, 80+/-4%). The inhibitor of cyclooxygenase-1 (COX-1), SC-560, did not affect the basal tone of arterioles, whereas NS-398, an inhibitor of COX-2, caused a significant shift in the arteriolar pressure-diameter curve of vessels from db/db mice (at 80 mm Hg, 76+/-3%) but not in those of control mice. Also, in aortas of db/db mice, expression of COX-2 was enhanced compared with controls.

CONCLUSIONS

Collectively, these findings suggest that in mice with T2-DM, the basal tone of skeletal muscle arterioles is increased because of an enhanced COX-2-dependent production of constrictor prostaglandins. These alterations in microvascular prostaglandin synthesis may contribute to the increase in peripheral resistance and blood pressure in T2-DM.

Vascular complications in diabetes mellitus: the role of endothelial dysfunction

The endothelium is a complex organ with a multitude of properties essential for control of vascular functions. Dysfunction of the vascular endothelium is regarded as an important factor in the pathogenesis of diabetic micro- and macro-angiopathy. Endothelial dysfunction in Type I and II diabetes complicated by micro- or macro-albuminuria is generalized in that it affects many aspects of endothelial function and occurs not only in the kidney. The close linkage between microalbuminuria and endothelial dysfunction in diabetes is an attractive explanation for the fact that microalbuminuria is a risk marker for atherothrombosis. In Type I diabetes, endothelial dysfunction precedes and may cause diabetic microangiopathy, but it is not clear whether endothelial dysfunction is a feature of the diabetic state itself. In Type II diabetes, endothelial function is impaired from the onset of the disease and is strongly related to adverse outcomes. It is not clear whether impaired endothelial function is caused by hyperglycaemia or by other factors. Impaired endothelial function is closely associated with and may contribute to insulin resistance regardless of the presence of diabetes. Endothelial dysfunction in diabetes originates from three main sources. Hyperglycaemia and its immediate biochemical sequelae directly alter endothelial function or influence endothelial cell functioning indirectly by the synthesis of growth factors, cytokines and vasoactive agents in other cells. Finally, the components of the metabolic syndrome can impair endothelial function.

Plasminogen activator inhibitor-1: a common denominator in obesity, diabetes and cardiovascular disease

A classical perspective of cardiovascular risk does not adequately account for all of the cardiovascular events associated with obesity and diabetes. The combination of hypertriglyceridemia, glucose intolerance and inflammation is linked with increased production of the primary inhibitor of endogenous thrombolysis, plasminogen activator inhibitor-1 (PAI-1). Recent data suggest that PAI-1 contributes directly to the complications of obesity, including type 2 diabetes, coronary arterial thrombi, and may even influence the accumulation of visceral fat. Therefore, direct inhibition of PAI-1 might not only provide a new therapeutic strategy for reducing cardiovascular risk, but may also have beneficial effects on obesity and insulin resistance.

Diabetes, glucose level, and risk of sudden cardiac death

AIMS

The prevalence of diabetes mellitus in industrialized countries is rapidly increasing, and diabetes is suspected to carry a particular high risk for sudden cardiac death (SCD).

METHODS AND RESULTS

We conducted a population-based case-control study at Group Health Cooperative. Cases (n=2040) experienced out-of-hospital cardiac arrest due to heart disease between 1980 and 1994. Controls (n=3800) were a stratified random sample of enrollees. Diabetes status was classified into four exclusive groups: (i) no diabetes, (ii) borderline, (iii) diabetes without microvascular disease (retinopathy or proteinuria), and (iv) diabetes with microvascular disease. When compared with no diabetes, we observed progressively higher risk of SCD associated with borderline diabetes [Odds ratio (OR)=1.24 (0.98-1.57)], diabetes without microvascular disease [OR=1.73 (1.28-2.34)], and diabetes with microvascular disease [OR=2.66 (1.84-3.85)], after adjustment for potential confounders (P-value for trend <0.001). Higher glucose levels were also associated with the risk of SCD both in the absence and in the presence of microvascular disease. However, subjects with microvascular complications but with glucose level <7.7 mmol/L were not at significant increased risk of SCD.

CONCLUSION

These results emphasize the role of diabetes as a strong risk factor for SCD and outline the importance of glucose level at every stage of diabetes severity.

Molecular Targets of Diabetic Cardiovascular Complications

Both the macro- and microvascular complications adversely affect the life quality of patients with diabetes and have been the leading cause of mortality and morbidity in this population. With the advancement of technologies in biomedical research, we have gained a great deal of understanding of the mechanisms underlying these complications. While euglycemic control still remains the best strategy, it is often difficult to maintain at a level that can completely prevent the vascular complications. Therefore, it is necessary to use the processes leading to vascular dysfunction as a framework for designing novel molecular therapeutic targets. Several of the mechanisms by which diabetes induces vascular complications include increased flux through the polyol pathway, increased oxidative stress, activation of protein kinase C (PKC), vascular inflammation, and abnormal expression and actions of cytokines in the vasculature. Many of the therapies that target these pathways have proven successful in experimental models of diabetic complications. However, clinical studies using these treatments have mainly yielded inconclusive results. The pathogenesis of diabetic vascular complications and results from animal studies and key clinical studies are reviewed here.

[Will the theory of metabolic memory change our therapeutic strategies in the face of type 2 diabetes?]

Many prospective studies have shown that tight glucose control reduces the risk of vascular complications in type 1 and type 2 diabetes. Besides, the intensive treatment group benefited from a preventive effect several years after the end of the study. In type 2 diabetes, the low glucose levels at the time of the diagnosis strongly correlate to the risk reduction of late complications. These various elements suggest the presence of a metabolic memory which would engage in very premature stages various pathways favoring the vascular development of diabetic complications. Our therapeutic strategy, based on thresholds of intervention favors the therapeutic slowness and strengthens negatively the metabolic memory. Therapeutic approach based on the tendencies to hyperglycemia could improve the prevention of the diabetic vascular complications.

Albumin excretion rate and cardiovascular risk: could the association be explained by early microvascular dysfunction?

Elevated albumin excretion rate (AER) independently predicts total and cardiovascular mortality in a variety of conditions, although the exact mechanisms are unknown. Laser Doppler fluximetry was used to study associations with risk factors and renal damage (AER calculated from a timed overnight urine collection) in 188 people without diabetes and 117 individuals with diabetes. Skin flow (flux) in response to arterial occlusion (ischemia) was measured. Three distinct patterns of postischemic peak flow were observed: 1) gradual rise to peak (normal), 2) nondominant early peak, and 3) dominant early peak. Those with a dominant early peak were more likely to have diabetes (P = 0.01), hypertension (P = 0.001), and obesity (P < 0.001) and had a higher AER (12.6 microg/min [95% CI 7.8-20.2] vs. 7.2 [5.5-9.5] nondominant early peak group and 3.7 [3.2-4.1] normal group; P < 0.001 for trend). This could not be accounted for by conventional cardiovascular risk factors (P < 0.001 after adjustment). A rapid peak flow response after ischemia is associated with an elevated AER and increased cardiovascular risk. This may represent shared mechanistic pathways and causative or con-sequential changes in the microvasculature and supports the hypothesis that microvascular dysfunction may contribute to large vessel pathophysiology.

Impaired revascularization in a mouse model of type 2 diabetes is associated with dysregulation of a complex angiogenic-regulatory network

OBJECTIVE

Diabetes is a risk factor for the development of cardiovascular diseases associated with impaired angiogenesis or increased endothelial cell apoptosis.

METHODS AND RESULTS

Here it is shown that angiogenic repair of ischemic hindlimbs was impaired in Lepr(db/db) mice, a leptin receptor-deficient model of diabetes, compared with wild-type (WT) C57BL/6 mice, as evaluated by laser Doppler flow and capillary density analyses. To identify molecular targets associated with this disease process, hindlimb cDNA expression profiles were created from adductor muscle of Lepr(db/db) and WT mice before and after hindlimb ischemia using Affymetrix GeneChip Mouse Expression Set microarrays. The expression patterns of numerous angiogenesis-related proteins were altered in Lepr(db/db) versus WT mice after ischemic injury. These transcripts included neuropilin-1, vascular endothelial growth factor-A, placental growth factor, elastin, and matrix metalloproteinases implicated in blood vessel growth and maintenance of vessel wall integrity.

CONCLUSIONS

These data illustrate that impaired ischemia-induced neovascularization in type 2 diabetes is associated with the dysregulation of a complex angiogenesis-regulatory network.

Progression of coronary artery calcium and occurrence of myocardial infarction in patients with and without diabetes mellitus

Progression of coronary artery calcium, a marker of atherosclerosis, can be slowed with statins, and continued progression of calcium is associated with an increased risk of myocardial infarction. However, it is not known whether statins are effective in slowing calcium progression in diabetes mellitus. In a retrospective study, we examined 1153 nondiabetic and 157 diabetic subjects who underwent sequential electron beam tomography scans at a minimum 1-year interval to assess progression of coronary calcium. A yearly score increase >15% was considered evidence of true progression. The use of statins and occurrence of myocardial infarction were recorded. There was no difference in baseline calcium score between diabetic and nondiabetic patients. Diabetic patients with no coronary calcium on the baseline scans developed it more often than nondiabetic subjects (42% versus 25%; P=0.046) during follow-up. Calcium progression was 33% greater in diabetic patients than nondiabetic subjects (P<0.001) if no statin therapy was provided and 17.7% greater when statins were used (P<0.001). Among the 49 subjects who experienced a myocardial infarction, the calcium score increased on average 20% more in diabetic than nondiabetic patients (P<0.001). In logistic models, diabetes mellitus and systemic hypertension were the best predictors of calcium progression (odds ratio, 3.1 and 1.9, respectively), whereas baseline calcium score percentile and statin therapy were the best predictors of infarction. These findings support the notion that diabetes mellitus causes accelerated atherosclerosis, even in the presence of statin therapy, and provide evidence that coronary calcium monitoring is an effective method to assess treatment efficacy.

Adenovirus-mediated overexpression of O-GlcNAcase improves contractile function in the diabetic heart

To examine whether excessive protein O-GlcNAcylation plays a role in the dysfunction of the diabetic heart, we delivered adenovirus expressing O-GlcNAcase (Adv-GCA) into the myocardium of STZ-induced diabetic mice. Our results indicated that excessive cellular O-GlcNAcylation exists in the diabetic heart, and that in vivo GCA overexpression reduces overall cellular O-GlcNAcylation. Myocytes isolated from diabetic hearts receiving Adv-GCA exhibited improved calcium transients with a significantly shortened T(decay) (P<0.01) and increased sarcoplasmic reticulum Ca2+ load (P<0.01). These myocytes also demonstrated improved contractility including a significant increase in +dL/dt and -dL/dt and greater fractional shortening as measured by edge detection (P<0.01). In isolated perfused hearts, developed pressure and -dP/dt were significantly improved in diabetic hearts receiving Adv-GCA (P<0.05). These hearts also exhibited a 40% increase in SERCA2a expression. Phospholamban protein expression was reduced 50%, but the phosphorylated form was increased 2-fold in the diabetic hearts receiving Adv-GCA. We conclude that excess O-GlcNAcylation in the diabetic heart contributes to cardiac dysfunction, and reducing this excess cellular O-GlcNAcylation has beneficial effects on calcium handling and diabetic cardiac function.

S-Adenosylmethionine and 5-Methyltetrahydrofolate Are Associated With Endothelial Function After Controlling for Confounding by Homocysteine

OBJECTIVE

To explore to what extent homocysteine, S-adenosylmethionine (SAM), S-adenosylhomocysteine, total folate, 5-methyltetrahydrofolate (5-MTHF), vitamin B12, and vitamin B6 are associated with endothelium-dependent, flow-mediated vasodilation (FMD), and whether these associations are stronger in individuals with diabetes or other cardiovascular risk factors.

METHODS AND RESULTS

In this population-based study of 608 elderly people, FMD and endothelium-independent nitroglycerin-mediated dilation (NMD) were ultrasonically estimated from the brachial artery (absolute change in diameter [mum]). High SAM and low 5-MTHF were significantly associated with high and low FMD, respectively (linear regression coefficient, [95% confidence interval]): 48.57 microm (21.16; 75.98) and -32.15 microm (-59.09; -5.20), but high homocysteine was not (-15.11 microm (-42.99; 12.78). High SAM and low 5-MTHF were also significantly associated with high and low NMD, respectively. NMD explained the association of 5-MTHF with FMD but not of SAM. No interactions were observed for diabetes or cardiovascular risk factors.

CONCLUSIONS

In this elderly population, both SAM and 5-MTHF are associated with endothelial and smooth muscle cell function. The effect of homocysteine on endothelial function is relatively small compared with SAM and 5-MTHF. The relative impact of SAM, 5-MTHF, and homocysteine, and the mechanisms through which these moieties may affect endothelial and smooth muscle cell function need clarification.