Effects of non-insulin dependent diabetes mellitus on the reactivity of human internal mammary artery and human saphenous vein

Vascular nitric oxide resistance in type 2 diabetes

Vascular nitric oxide (NO•) resistance, manifested by an impaired vasodilator function of NO• in both the macro- and microvessels, is a common state in type 2 diabetes (T2D) associated with developing cardiovascular events and death. Here, we summarize experimental and human evidence of vascular NO• resistance in T2D and discuss its underlying mechanisms. Human studies indicate a ~ 13-94% decrease in the endothelium (ET)-dependent vascular smooth muscle (VSM) relaxation and a 6-42% reduced response to NO• donors, i.e., sodium nitroprusside (SNP) and glyceryl trinitrate (GTN), in patients with T2D. A decreased vascular NO• production, NO• inactivation, and impaired responsiveness of VSM to NO• [occurred due to quenching NO• activity, desensitization of its receptor soluble guanylate cyclase (sGC), and/or impairment of its downstream pathway, cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG)] are the known mechanisms underlying the vascular NO• resistance in T2D. Hyperglycemia-induced overproduction of reactive oxygen species (ROS) and vascular insulin resistance are key players in this state. Therefore, upregulating vascular NO• availability, re-sensitizing or bypassing the non-responsive pathways to NO•, and targeting key vascular sources of ROS production may be clinically relevant pharmacological approaches to circumvent T2D-induced vascular NO• resistance.

Impact of type 2 diabetes on vascular reactivity to cGMP generators in human internal thoracic arteries

OBJECTIVE

The balance between nitric oxide (NO)-sensitive and -insensitive forms of soluble guanylate cyclase (sGC) has been demonstrated to be disrupted in certain lifestyle-related diseases. However, it remains unclear whether type 2 diabetes results in a shift of sGC to the NO-insensitive form. This study addressed this issue in the human blood vessel.

METHODS

Internal thoracic arteries were obtained from patients undergoing coronary artery bypass grafting. Helically cut strips of the arteries were suspended in organ chambers, and relaxant responses to nitroglycerin (NO-sensitive sGC stimulant) and BAY 60-2770 (NO-insensitive sGC stimulant) were assessed.

RESULTS

The patients were divided into two groups according to the presence of type 2 diabetes (HbA1c: 7.0±0.3%) or its absence (HbA1c: 5.6±0.1%). Nitroglycerin-induced relaxation was not different in the arteries obtained from type 2 diabetic and non-diabetic patients. In addition, the relaxant response to BAY 60-2770 in type 2 diabetics was comparable to that observed in non-diabetics. Although the patients enrolled often had vascular risk factors other than type 2 diabetes, the relaxant responses were still in the same range in a comparison based on the number of risk factors. However, in separate experiments, the relaxant response to nitroglycerin was attenuated by pre-incubation of the arteries with ODQ (sGC imbalance inducer), whereas the relaxant response to BAY-60-2770 was augmented.

CONCLUSIONS

These findings suggest that type 2 diabetes does not affect the balance between NO-sensitive and -insensitive sGC in human internal thoracic artery grafts.

Vascular dysfunction associated with type 2 diabetes and Alzheimer's disease: a potential etiological linkage

The endothelium performs a crucial role in maintaining vascular integrity leading to whole organ metabolic homeostasis. Endothelial dysfunction represents a key etiological factor leading to moderate to severe vasculopathies observed in both Type 2 diabetic and Alzheimer’s Disease (AD) patients. Accordingly, evidence-based epidemiological factors support a compelling hypothesis stating that metabolic rundown encountered in Type 2 diabetes engenders severe cerebral vascular insufficiencies that are causally linked to long term neural degenerative processes in AD. Of mechanistic importance, Type 2 diabetes engenders an immunologically mediated chronic pro-inflammatory state involving interactive deleterious effects of leukocyte-derived cytokines and endothelial-derived chemotactic agents leading to vascular and whole organ dysfunction. The long term negative consequences of vascular pro-inflammatory processes on the integrity of CNS basal forebrain neuronal populations mediating complex cognitive functions establish a striking temporal comorbidity of AD with Type 2 diabetes. Extensive biomedical evidence supports the pivotal multi-functional role of constitutive nitric oxide (NO) production and release as a critical vasodilatory, anti-inflammatory, and anti-oxidant, mechanism within the vascular endothelium. Within this context, we currently review the functional contributions of dysregulated endothelial NO expression to the etiology and persistence of Type 2 diabetes-related and co morbid AD-related vasculopathies. Additionally, we provide up-to-date perspectives on critical areas of AD research with special reference to common NO-related etiological factors linking Type 2 diabetes to the pathogenesis of AD.

Carbonyl stress in aging process: role of vitamins and phytochemicals as redox regulators

There is a growing scientific agreement that the cellular redox regulators such as antioxidants, particularly the natural polyphenolic forms, may help lower the incidence of some pathologies, including metabolic diseases like diabetes and diabesity, cardiovascular and neurodegenerative abnormalities, and certain cancers or even have anti-aging properties. The recent researches indicate that the degree of metabolic modulation and adaptation response of cells to reductants as well as oxidants establish their survival and homeostasis, which is linked with very critical balance in imbalances in cellular redox capacity and signaling, and that might be an answer the questions why some antioxidants or phytochemicals potentially could do more harm than good, or why some proteins lose their function by increase interactions with glyco- and lipo-oxidation mediates in the cells (carbonyl stress). Nonetheless, pursue of healthy aging has led the use of antioxidants as a means to disrupt age-associated physiological dysfunctions, dysregulated metabolic processes or prevention of many age-related diseases. Although it is still early to define their exact clinical benefits for treating age-related disease, a diet rich in polyphenolic or other forms of antioxidants does seem to offer hope in delaying the onset of age-related disorders. It is now clear that any deficiency in antioxidant vitamins, inadequate enzymatic antioxidant defenses can distinctive for many age-related disease, and protein carbonylation can used as an indicator of oxidative stress associated diseases and aging status. This review examines antioxidant compounds and plant polyphenols as redox regulators in health, disease and aging processes with hope that a better understanding of the many mechanisms involved with these distinct compounds, which may lead to better health and novel treatment approaches for age-related diseases.

Bilateral internal thoracic artery harvest and deep sternal wound infection in diabetic patients

BACKGROUND

Coronary artery bypass graft surgery is superior to percutaneous intervention in diabetic patients with multivessel disease. The use of bilateral internal thoracic arteries (BITA) may provide better long-term graft patency, but the risk of postoperative deep sternal wound infection has limited its use in diabetic patients. However, studies have reported conflicting results, and require systematic evaluation.

METHODS

MEDLINE, EMBASE, World of Science, and the Cochrane library were searched for randomized controlled trials and observational studies comparing the incidence of deep sternal wound infection in diabetic patients undergoing either left internal thoracic artery (LITA) or BITA harvest. We used random effect models to compare risk ratios within groups.

RESULTS

One randomized controlled trial and 10 observational studies (126,235 diabetic patients: 122,465 LITA, 3,770 BITA) met inclusion criteria. Deep sternal wound infection occurred in 3.1% and 1.6% for the BITA and LITA cohorts, respectively. The risk ratio for deep sternal wound infection development was 1.71 (1.37 to 2.14) for BITA compared with LITA. Patients who underwent skeletonized BITA harvest had a similar risk of deep sternal wound infection compared with LITA (0.9 [0.42 to 2.09]), although pedicled harvest demonstrated increased risk (1.77 [1.4 to 2.23]). Early mortality was comparable in the LITA cohort (2.5%) and the BITA cohort (2.3%; p = 0.8).

CONCLUSIONS

The risk of deep sternal wound infection can be minimized in diabetic patients undergoing coronary artery bypass graft surgery by performing ITA harvested in a skeletonized manner with meticulous attention to preserving sternal blood flow. Pedicled harvest is to be discouraged when utilizing both ITA owing to a significant increase in the risk of postoperative deep sternal wound infection.

D₂-receptor occupancy measurement of JNJ-37822681, a novel fast off-rate D₂-receptor antagonist, in healthy subjects using positron emission tomography: single dose versus steady state and dose selection

RATIONALE

JNJ-37822681 is a highly selective, fast dissociating dopamine D₂-receptor antagonist being developed for the treatment of schizophrenia. A single dose [¹¹C]raclopride positron emission tomography (PET) imaging study had yielded an estimated clinical dose range. Receptor occupancy at steady state was explored to test the validity of the single-dose estimates during chronic treatment.

OBJECTIVES

The aims of this study are to characterize single and multiple dose pharmacokinetics and obtain striatal D₂-receptor occupancies to predict doses for efficacy studies and assess the safety and tolerability of JNJ-37822681.

METHODS

An open-label single- and multiple-dose study with 10 mg JNJ-37822681 (twice daily for 13 doses) was performed in 12 healthy men. Twenty [¹¹C]raclopride PET scans (up to 60 h after the last dose) from 11 subjects were used to estimate D₂-receptor occupancy. A direct effect O (max) model was applied to explore the relationship between JNJ-37822681 plasma concentration and striatal D₂-receptor occupancy.

RESULTS

Steady state was reached after 4-5 days of twice daily dosing. JNJ-37822681 plasma concentrations of 3.17 to 63.0 ng/mL resulted in D₂ occupancies of 0 % to 62 %. The concentration leading to 50 % occupancy was 18.5 ng/mL (coefficient of variation 3.9 %) after single dose and 26.0 ng/mL (8.2 %) at steady state. JNJ-37822681 was well tolerated.

CONCLUSIONS

Receptor occupancy after single dose and at steady state differed for JNJ-37822681 and the robustness of the estimates at steady state will be tested in phase 2 studies. Dose predictions indicated that 10, 20, and 30 mg JNJ-37822681 twice daily could be suitable for these studies.

Glycoxidative stress and cardiovascular complications in experimentally-induced diabetes: effects of antioxidant treatment

Diabetes mellitus (DM) is a common metabolic disease, representing a serious risk factor for the development of cardiovascular complications, such as coronary heart disease, peripheral arterial disease and hypertension. Oxidative stress (OS), a feature of DM, is defined as an increase in the steady-state levels of reactive oxygen species (ROS) and may occur as a result of increased free radical generation and/or decreased anti-oxidant defense mechanisms. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage in DM, either through repeated acute changes in cellular glucose metabolism, or through long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs are formed by the Maillard process, a non-enzymatic reaction between ketone group of the glucose molecule or aldehydes and the amino groups of proteins that contributes to the aging of proteins and to the pathological complications of DM. In the presence of uncontrolled hyperglycemia, the increased formation of AGEs and lipid peroxidation products exacerbate intracellular OS and results in a loss of molecular integrity, disruption in cellular signaling and homeostasis, followed by inflammation and tissue injury such as endothelium dysfunction, arterial stiffening and microvascular complications. In addition to increased AGE production, there is also evidence of multiple pathways elevating ROS generation in DM, including; enhanced glucose auto-oxidation, increased mitochondrial superoxide production, protein kinase C-dependent activation of NADPH oxidase, uncoupled endothelial nitric oxide synthase (eNOS) activity, increased substrate flux through the polyol pathway and stimulation of eicosanoid metabolism. It is, therefore, not surprising that the correction of these variables can result in amelioration of diabetic cardiovascular abnormalities. A linking element between these phenomena is cellular redox imbalance due to glycoxidative stress (GOS). Thus, recent interest has focused on strategies to prevent, reverse or retard GOS in order to modify the natural history of diabetic cardiovascular abnormalities. This review will discuss the links between GOS and diabetes-induced cardiovascular disorders and the effect of antioxidant therapy on altering the development of cardiovascular complications in diabetic animal models.

Alteration of vascular reactivity in diabetic human mammary artery and the effects of thiazolidinediones

Vascular reactivity was investigated in endothelium-denuded human internal mammary artery (IMA) rings from type 2 diabetic patients. It was also investigated whether insulin sensitizer thiazolidinedione drugs, pioglitazone and rosiglitazone, can directly affect the reactivity of IMA. Using organ bath techniques, cumulative concentration-response curves to phenylephrine (PE), KCl, cromakalim (CRO) and sodium nitroprusside (SNP) were constructed in diabetic and non-diabetic IMA rings. Means of maximal responses (% Emax) and pEC50 values (sensitivity) were compared. Emax values and the sensitivity to PE and KCl were increased while KATP-channel-mediated relaxations were reduced significantly in diabetic rings compared with non-diabetic rings (n = 5–12, P < 0.05). No changes were observed for SNP responses (n = 5, P > 0.05). Incubations with pioglitazone (1 and 10 μM) and rosiglitazone (1 and 20 μM), for 30 min, did not affect KATP-channel-mediated relaxations (n = 5 each, P > 0.05). Pioglitazone partly inhibited pre-contractions of PE and KCl at 10 μM, rosiglitazone did not. Vascular dysfunction observed in diabetic IMA may be of specific importance since they are widely used as coronary bypass material. Thiazolidinedione drugs may not worsen arterial dilatation through KATP channels in ischaemic or hypoxic insults in diabetic patients who are prone to such conditions. Pioglitazone has vasorelaxant property in the grafts.

Saphenous Vein Grafts Display Poor Endothelium-Dependent and Endothelium-Independent Dilation—Implications for the Pathogenesis of Vein Graft Atherosclerosis

OBJECTIVE

As endothelial dysfunction has been implicated in the pathogenesis of late failure of saphenous vein grafts (SVG), we assessed endothelium-dependent and endothelium-independent vascular responses of SVG in humans.

METHODS

Subjects undergoing angiography after bypass grafting had selective infusions of acetylcholine (ACh, an endothelium-dependent dilator) and sodium-nitroprusside (SNP, an endothelium-independent dilator) into a non-obstructed vein graft. SVG diameters were measured by quantitative coronary angiography. Two matched groups of control subjects, with or without coronary artery disease (CAD), were studied after similar infusions into their femoral arteries.

RESULTS

We assessed 10 subjects with SVG, 8 controls with and 8 without CAD. SVG dilatation to high-dose ACh was 5+/-3%, similar to the femoral arteries of subjects with CAD (10+/-5%), but significantly less than the ACh-related arterial dilatation in the non-CAD group (16+/-2%, p=0.02). Similarly, dilatation of SVG after SNP infusion was 9+/-3%, which was not significantly different from the nitrate responses of femoral arteries in the CAD group (21+/-5%), but significantly poorer than in the non-CAD subjects (27+/-5%, p=0.02).

CONCLUSION

Saphenous vein bypass grafts display poor endothelium-dependent and endothelium-independent vascular responses in vivo, compared with healthy systemic arteries. This may contribute to the pathogenesis of accelerated atherosclerosis seen in SVG.

Diet-induced obesity and diabetes reduce coronary responses to nitric oxide due to reduced bioavailability in isolated mouse hearts

AIM

The aim of the present study was to examine nitric oxide (NO)-mediated coronary vascular responses in a mouse model of obesity and diabetes induced by a high-fat, high-carbohydrate diet. We hypothesized that endogenous NO bioavailability would be reduced in obese/diabetic mouse hearts due to enhanced superoxide anion production, and that coronary smooth muscle responses to exogenous NO would be reduced.

METHODS

Age-matched, male C57BL/6J mice were fed either a control diet or a high-fat, high-carbohydrate diet. After 15 weeks, the mice were anesthetized and their hearts were removed and perfused by the Langendorff method under constant flow conditions with an oxygenated buffer solution, and changes in coronary vascular resistance were quantified.

RESULTS

Mice fed the high-fat, high-carbohydrate diet became obese, hyperglycaemic and hyperinsulinaemic. Coronary vasoconstrictor responses to NO synthase inhibition by N(omega)-nitro-L-arginine methyl ester were reduced in obese/diabetic mice; normal responses were restored by pretreatment with the superoxide dismutase mimetic 2,2,6,6-tetramethyl-1-piperidinyloxy (Tempol). Coronary endothelium-independent vasodilation to the NO donor (+/-)-S-nitroso-N-acetylpenicillamine (SNAP) was reduced; however, 8-bromo-cyclic guanosine monophosphate (cGMP)-induced vasodilation was unchanged in obese/diabetic hearts.

CONCLUSIONS

These findings suggest that in a diet-induced mouse model of obesity and diabetes, NO bioavailability is reduced by increased superoxide NO scavenging leading to impaired NO-mediated vasodilation. Furthermore, the attenuation of SNAP-induced vasodilation may be due to increased reactive oxygen species scavenging of exogenous NO because normal vascular smooth muscle NO signalling is maintained as indicated by similar 8-bromo-cGMP responses in control and obese/diabetic hearts.

Compromised arterial function in human type 2 diabetic patients

Diabetes is associated with a perturbation of signaling pathways in vascular tissue, which causes vasomotor dysfunction such as hypertension and accelerated atherosclerosis. In the present study, the mechanisms of vasomotor dysfunction, Akt (Thr308 and Ser473) phosphorylation and expression of endothelial NO (nitric oxide) synthase, and inducible NO synthase were investigated in human diabetic internal mammary arteries. The phospho-Akt (Thr308) level in arteries from diabetic patients was reduced to about one-half of the level in nondiabetic patients, suggesting impaired insulin signaling in human diabetic vascular tissue. Augmented vasoconstriction was observed in diabetic arteries, due in part to deficiency of basal and stimulated NO production. This correlated with decreased endothelial NO synthase expression and activity in diabetic vessels. The sensitivity of diabetic vessels to the NO donor, sodium nitroprusside, was reduced as well, suggesting that NO breakdown and/or decreased sensitivity of smooth muscle to NO are also responsible for abnormal vasoconstriction. In addition, the abnormal vasoconstriction in diabetic vessels was not completely abolished in the presence of Nomega-nitro-L-arginine methyl ester, revealing that NO-independent mechanisms also contribute to vasomotor dysfunction in diabetes. In conclusion, diabetes downregulates the Akt-signaling pathway and compromises human arterial function through a decrease in NO availability as well as through NO-independent mechanisms.

Unfractioned Heparin Produces Vasodilatory Action on Human Internal Mammary Artery by Endothelium-Dependent Mechanisms

The aim of this study was to investigate whether unfractioned heparin produces a direct vasodilatory effect on the human internal mammary artery (IMA) and the possible underlying mechanisms. Samples of redundant IMA were obtained from 20 patients undergoing coronary artery bypass graft surgery, and concentration-response curves to unfractioned heparin were constructed. Unfractioned heparin (0.5-6 U/mL) caused a concentration-dependent relaxation in the endothelium-intact human IMA rings precontracted with phenylephrine (10(-6) M). Removal of endothelium significantly inhibited the responses of human IMA to unfractioned heparin (P < 0.05). Nomega-Nitro-L-arginine methyl ester (L-NAME, 10(-4) M), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10(-5) M) and L-NAME (10(-4) M) plus ODQ (10(-5) M) partially reduced unfractioned heparin-induced vasodilatory response in endothelium-intact rings, whereas indomethacin alone had no effect. The vasodilatory effect of unfractioned heparin was completely inhibited by 40 mM KCl in the presence of L-NAME, ODQ, and indomethacin. These results clearly demonstrated that unfractioned heparin causes a concentration-dependent vasodilatation in human internal mammary artery, and this action seems to be via endothelium-dependent mechanisms, including generation of nitric oxide and endothelium-derived hyperpolarizing factor.

Nitric oxide-sensitive soluble guanylyl cyclase activity is preserved in internal mammary artery of type 2 diabetic patients

Vascular reactivity to nitric oxide (NO) is mediated by NO-sensitive soluble guanylyl cyclase (sGC). Since a diminished activity of vascular sGC has been reported in an animal model of type 2 diabetes, the sGC activity was assayed in vitro in internal mammary artery specimens obtained during bypass surgery from patients with and without type 2 diabetes. The sensitivity of sGC to NO, which is dependent on Fe(2+)-containing heme, was measured in vitro using stimulation with diethylamine NONOate (DEA/NO). In addition, the novel cyclic guanosine monophosphate-elevating compound HMR-1766 was used to test the stimulation of the oxidized heme-Fe(3+)-containing form of sGC. Basal activity of sGC and its sensitivity to stimulation by DEA/NO and HMR-1766 were not different between control and type 2 diabetic patients: maximum stimulation by DEA/NO amounted to 475 +/- 67 and 418 +/- 59 pmol. mg(-1). min(-1) in control and type 2 diabetic patients, respectively. The maximum effects of HMR-1766 were 95 +/- 18 (control subjects) and 83 +/- 11 pmol. mg(-1). min(-1) (type 2 diabetic patients). Hypertension, hyperlipidemia, drug treatment with statins, ACE inhibitors, or nitrates had no effect on sGC activity. In conclusion, the present findings do not support the hypothesis that desensitization of sGC contributes to the pathogenesis of diabetic vascular dysfunction in humans.

Effect of exercise training on endothelium-derived nitric oxide function in humans

Vascular endothelial function is essential for maintenance of health of the vessel wall and for vasomotor control in both conduit and resistance vessels. These functions are due to the production of numerous autacoids, of which nitric oxide (NO) has been the most widely studied. Exercise training has been shown, in many animal and human studies, to augment endothelial, NO-dependent vasodilatation in both large and small vessels. The extent of the improvement in humans depends upon the muscle mass subjected to training; with forearm exercise, changes are restricted to the forearm vessels while lower body training can induce generalized benefit. Increased NO bioactivity with exercise training has been readily and consistently demonstrated in subjects with cardiovascular disease and risk factors, in whom antecedent endothelial dysfunction exists. These conditions may all be associated with increased oxygen free radicals which impact on NO synthase activity and with which NO reacts; repeated exercise and shear stress stimulation of NO bioactivity redresses this radical imbalance, hence leading to greater potential for autacoid bioavailability. Recent human studies also indicate that exercise training may improve endothelial function by up-regulating eNOS protein expression and phosphorylation. While improvement in NO vasodilator function has been less frequently found in healthy subjects, a higher level of training may lead to improvement. Regarding time course, studies indicate that short-term training increases NO bioactivity, which acts to homeostatically regulate the shear stress associated with exercise. Whilst the increase in NO bioactivity dissipates within weeks of training cessation, studies also indicate that if exercise is maintained, the short-term functional adaptation is succeeded by NO-dependent structural changes, leading to arterial remodelling and structural normalization of shear. Given the strong prognostic links between vascular structure, function and cardiovascular events, the implications of these findings are obvious, yet many unanswered questions remain, not only concerning the mechanisms responsible for NO bioactivity, the nature of the cellular effect and relevance of other autacoids, but also such practical questions as the optimal intensity, modality and volume of exercise training required in different populations.

Exercise and the nitric oxide vasodilator system

In the past two decades, normal endothelial function has been identified as integral to vascular health. The endothelium produces numerous vasodilator and vasoconstrictor compounds that regulate vascular tone; the vasodilator, nitric oxide (NO), has additional antiatherogenic properties, is probably the most important and best characterised mediator, and its intrinsic vasodilator function is commonly used as a surrogate index of endothelial function. Many conditions, including atherosclerosis, diabetes mellitus and even vascular risk factors, are associated with endothelial dysfunction, which, in turn, correlates with cardiovascular mortality. Furthermore, clinical benefit and improved endothelial function tend to be associated in response to interventions. Shear stress on endothelial cells is a potent stimulus for NO production. Although the role of endothelium-derived NO in acute exercise has not been fully resolved, exercise training involving repetitive bouts of exercise over weeks or months up-regulates endothelial NO bioactivity. Animal studies have found improved endothelium-dependent vasodilation after as few as 7 days of exercise. Consequent changes in vasodilator function appear to persist for several weeks but may regress with long-term training, perhaps reflecting progression to structural adaptation which may, however, have been partly endothelium-dependent. The increase in blood flow, and change in haemodynamics that occur during acute exercise may, therefore, provide a stimulus for both acute and chronic changes in vascular function. Substantial differences within species and within the vasculature appear to exist. In humans, exercise training improves endothelium-dependent vasodilator function, not only as a localised phenomenon in the active muscle group, but also as a systemic response when a relatively large mass of muscle is activated regularly during an exercise training programme. Individuals with initially impaired endothelial function at baseline appear to be more responsive to exercise training than healthy individuals; that is, it is more difficult to improve already normal vascular function. While improvement is reflected in increased NO bioactivity, the detail of mechanisms, for example the relative importance of up-regulation of mediators and antioxidant effects, is unclear. Optimum training schedules, possible sequential changes and the duration of benefit under various conditions also remain largely unresolved. In summary, epidemiological evidence strongly suggests that regular exercise confers beneficial effects on cardiovascular health. Shear stress-mediated improvement in endothelial function provides one plausible explanation for the cardioprotective benefits of exercise training.

Influence of type 2 diabetes on functional and structural properties of coronary artery bypass conduits

Recent studies have reported a high incidence of postoperative unfavorable cardiac-related events in patients with diabetes who underwent coronary artery bypass grafting (CABG). Structural and functional characteristics of CABG conduits, which have been shown to play an important role in patient outcome after myocardial revascularization, have not been fully investigated in diabetic subjects. Therefore, we sought to determine the influence of adult-onset diabetes on vasoreactivity and morphological profile of venous and arterial grafts. Of the 160 consecutive patients enrolled in the study, 90 were diagnosed with type 2 diabetes and 70 did not have diabetes (control group). All patients underwent evaluation of glucose control before surgery. Tissue specimens were collected from left internal thoracic artery (LITA) and saphenous vein (SV) grafts harvested during elective CABG. Functional tests were performed to assess contractile and vasodilative responses of bypass conduits. Histological evaluation was carried out to examine vessel wall structure. Univariate and multivariate analyses were performed to correlate the preoperative factors related to the control of the endocrine disorder with histological findings. Patient medical history and demographics did not differ between the groups. Diabetic patients showed significant microalbuminuria and higher plasma levels of C-peptide and GHb as compared with nondiabetic subjects. Functional tests of the LITA segments revealed no difference between groups with regard to contractile and vasodilative responses. In contrast, significant impairment in the endothelium-related vasodilation of the SV grafts was observed in diabetic subjects. Histological studies showed structural preservation of the arterial conduits in both groups. However, marked intimal abnormalities (also atherosclerotic calcified plaques) were detected in SV grafts harvested from diabetic patients. Logistic regression analysis showed that high levels of proteinuria and GHb were independent predictors of advanced structural degeneration of SV conduits. Treatment modality, duration of diabetes, and other demographic or metabolic factors were found to have no influence on the morphological characteristics of SV conduits. In conclusion, biological properties of LITA conduits for CABG were preserved in diabetic patients. However, these patients frequently showed impairment of the endothelium-dependent vasorelaxation and intimal degeneration of SV grafts. The extent of structural abnormalities of SV grafts was inversely correlated with the efficacy of the metabolic control of the endocrine disorder. Further studies are required to conclusively correlate preoperative SV graft abnormalities with postoperative conduit patency rate and the occurrence of adverse cardiac-related events in diabetic subjects.

Effect of dietary vitamin E supplementation on vascular reactivity of thoracic aorta in streptozotocin-diabetic rats

The present study evaluated the effect of dietary vitamin E supplementation (1,000 mg/kg chow) on the alterations in vascular reactivity of streptozotocin-diabetic aorta of Wistar rats. After 12 weeks of treatment, thoracic aortic rings of rats were mounted in organ baths and contractile responses to phenylephrine and 5-hydroxytryptamine and relaxant responses to acetylcholine, calcium ionophore and sodium nitroprusside were assessed. Plasma vitamin E concentration as measured by HPLC was markedly decreased in diabetic rats and increased with dietary vitamin E supplementation. Induction of diabetes significantly impaired endothelium-dependent relaxations to acetylcholine and calcium ionophore in aortic rings, but did not change endothelium-independent relaxation to sodium nitroprusside. Vitamin E significantly improved the impaired endothelium-dependent relaxations, further it decreased the enhanced contractile response to phenylephrine and 5-hydroxytryptamine in diabetic rings. The mechanical denudation of endothelium or the chemical inhibition of endothelium-dependent relaxation with N(omega)-nitro-L-arginine methyl ester (100 micromol/l) significantly increased phenylephrine contractility in control rings and the rings of diabetic rats treated with vitamin E; such a difference was not observed in diabetic rats fed with normal diet. Liver and lung malondialdehyde concentrations, as an index of lipid peroxidation, were increased in diabetic rats and significantly decreased with vitamin E supplementation. It is concluded that dietary supplementation of vitamin E improved endothelial dysfunction in insulin-dependent model of uncontrolled diabetes, probably decreasing membranal lipid peroxidation.

Vascular wall dysfunction in JCR:LA-cp rats: effects of age and insulin resistance

We tested the hypothesis that aging and insulin resistance interact to increase vascular dysfunction by comparing the function of isolated mesenteric resistance arteries in obese, insulin-resistant JCR:LA-cp rats and lean, insulin-sensitive rats of the same strain at 3, 6, 9, and 12 mo of age. The peak constrictor responses to norepinephrine, phenylephrine, and high potassium were elevated in arteries from obese rats. Responses to these agents increased with age in both obese and lean rats. An eicosanoid constrictor contributed substantially to vasoconstriction in the arteries from both lean and obese animals. Inhibition of nitric oxide synthase increased the vasoconstrictor response to norepinephrine in both obese and lean rats. This effect increased with age in lean rats only. Vascular relaxation in response to acetylcholine and sodium nitroprusside was impaired in the obese rats and did not alter with age. The results suggest that obese JCR:LA-cp rats have enhanced maximal constriction, which originates in the arterial smooth muscle and increases with age. There is evidence that the ability of the arteries to compensate for the enhanced contractility is impaired in obese rats, particularly with advanced age.

Vascular wall reactivity in conductance and resistance arteries: differential effects of insulin resistance

Insulin resistance is associated with an increased risk of cardiovascular disease that is probably related to abnormalities of vascular wall function. The JCR:LA-cp rat is a unique animal model of human vascular disease that exhibits a profound insulin resistance, vasculopathy, and cardiovascular disease, and allows study of the relationships between insulin resistance and vascular function. Conductance and resistance arteries serve different functions, thus vascular disease may affect these types of artery differently. Concentration-response curves to norepinephrine, phenylephrine, and acetylcholine were studied in conductance vessels (aortic rings) and resistance vessels (mesenteric arteries) from 12-week-old male obese and lean JCR:LA-cp rats. The aortic rings and mesenteric arteries from obese rats showed increased maximal response to phenylephrine compared with those from lean rats, whereas only the mesenteric arteries from obese rats showed increased maximal response to norepinephrine. In aortic rings, relaxation to acetylcholine was similar for both genotypes, but the mesenteric arteries of obese rats showed impaired relaxation to acetylcholine. We conclude that the sensitivity to vasoconstriction is enhanced in aortic rings and mesenteric arteries of obese male JCR:LA-cp rats, but endothelial function is impaired only in the mesenteric resistance arteries of these animals. Hence functional aberrations in the obese, insulin-resistant state are more pronounced in mesenteric resistance arteries than in a major conductance artery.

Does nitric oxide regulate smooth muscle cell proliferation? A critical appraisal

Smooth muscle proliferation is involved in the pathogenesis of atherosclerosis, restenosis after angioplasty and vein graft failure due to neointimal hyperplasia. Nitric oxide (NO) inhibits smooth muscle cell growth in vitro and experimental neointimal hyperplasia in vivo, suggesting a role for NO as a regulator of smooth muscle cell proliferation. NO is also involved in the control of numerous other vascular functions including platelet and inflammatory cell adhesion, vascular reactivity and endothelial permeability. This review critically examines the experimental and clinical evidence that supports a role for NO as a modulator of smooth muscle cell proliferation, with an emphasis on the multiple mechanisms by which NO acts on vascular lesions.

Oxidative stress and lipids in diabetes: a role in endothelium vasodilator dysfunction?

Endothelial dysfunction is a key feature of diabetes mellitus and is thought to be the major cause of vascular complications associated with the disease. The vascular endothelium demonstrates impaired synthesis of vasodilators and increased release of procoagulants and vasoconstrictors, defects which theoretically could explain the increased incidence of atherosclerosis and hypertension found within this patient group. The pathways mediating endothelial cell layer dysfunction are unknown, although many candidates have been proposed. This review concentrates on the hypothesis that increased oxidative stress combined with abnormal plasma lipid composition leads to reduced synthesis of endothelial vasodilators and hence endothelial dysfunction. Free radical generation is undoubtedly raised in diabetes but the evidence for decreased antioxidant status is debatable. The role of antioxidant and lipid-lowering therapy is considered, but few studies have directly investigated the effect of treatment on vascular function. Concern arises from individual studies of vitamin E in diabetic animals which have proved deleterious. Current literature implies that a combination therapy of vitamin E and vitamin C may be beneficial, but this needs to be investigated further in both animal and human diabetes.

Association of gestational diabetes with abnormal maternal vascular endothelial function

OBJECTIVE

To evaluate vascular endothelial function in isolated small arteries from women with gestational diabetes.

METHODS

Small subcutaneous arteries (mean luminal diameter approximately 250 microns) were dissected from biopsies obtained at caesarean section in 14 normotensive women with gestational diabetes and in 18 normotensive nondiabetic pregnant women. Vascular function was determined after mounting the arteries on a small vessel myograph.

RESULTS

Pre-constricted arteries from gestational diabetic pregnant women demonstrated poor relaxation to acetylcholine, an endothelium-dependent vasodilator (pEC50, mean [SE], 6.98 [0.10] vs normal pregnant, 7.28 [0.08], P < 0.03; % maximum relaxation, median [range], 88.2 [42.4-99.4] vs normal pregnant 94.2 [71.8-100.0], P < 0.01). In the presence of indomethacin relaxation to acetylcholine was similar in both groups suggesting a deficiency in dilator prostaglandin synthesis in the arteries from the diabetic women. The nitric oxide synthase inhibitor NG-monomethyl-L-arginine further reduced sensitivity of arteries to acetylcholine but to a similar degree in both normal pregnant and gestational diabetic women. Relaxation to sodium nitroprusside, an indicator of sensitivity of the vascular smooth muscle to nitric oxide, was similar in both groups.

CONCLUSIONS

Maternal vascular endothelial dysfunction may contribute to the increased incidence of cardiovascular disorders in women with gestational diabetes.