Influence of diabetes mellitus on coronary collateral flow: an answer to an old controversy

Microvascular Complications Are Associated With Coronary Collateralization in Type 2 Diabetes and Chronic Occlusion

CONTEXT

Coronary collateral (CC) vessel development appears to be protective with regard to adverse cardiovascular events and survival in patients with coronary chronic total occlusion (CTO). The influence of type 2 diabetes mellitus (T2DM) on CC growth has been controversial. In particular, the role of diabetic microvascular complications (DMC) in determining coronary collateralization has not been elucidated.

OBJECTIVE

To investigate whether patients with DMC presented differences in CC vessel presence and grading as compared with patients without DMC.

METHODS

We conducted a single-center observational study, including consecutive T2DM patients, without previous cardiovascular history, undergoing a clinically indicated coronary angiography for chronic coronary syndrome (CCS) and angiographic evidence of at least one CTO. Patients were subdivided into 2 study groups according to the presence/absence of at least one DMC (neuropathy, nephropathy, or retinopathy). The presence and grading of angiographically visible CC development from the patent vessels to the occluded artery were assessed using the Rentrop classification.

RESULTS

We enrolled 157 patients (mean age 68.6 ± 9.8 years; 120 [76.4%] men). Patients with DMC (75 [47.8%]) had a higher prevalence of CC (69 [92.0%] vs 62 [75.6%], P = .006) and high-grade CC (55 [73.3%] vs 39 [47.6%], P = .001) compared with those without, and we found a positive association between the number of DMC in each patient and the prevalence of high-grade CC.

CONCLUSION

Among T2DM patients with coronary CTO, the presence of DMC was associated with a high CC development.

Correlation of serum Vascular Endothelial growth factor (VEGF) and cardiovascular risk factors on collateral formation in patients with acute coronary artery syndrome

Coronary collaterals serve as an alternative source of blood flow in obstructive coronary heart disease. Coronary collateral development by releasing various angiogenic growth factors, including vascular endothelial growth factor-A (VEGF-A). Cardiovascular risk factors strongly associated with coronary artery disease include age, sex, elevated serum cholesterol, disturbed carbohydrate metabolism, and elevated blood pressure. A better understanding of the effects of these cardiovascular risk factors and serum VEGF-A level on collateral recruitment is necessary for a better prognosis in coronary artery diseases and new insight for further therapeutic promotion of coronary collaterals.220 consecutive patients undergoing coronary angiography with a mean age of 61 ± 9.83 were selected for the analysis. Two millilitres of blood were taken from the patients for analysis. The blood serum VEGF concentration was quantified via the ELISA method. Angiograms and other clinical reports were collected. Significant coronary artery disease was diagnosed in those with ≥ 70% of stenosis in at least one of the coronary arteries. The angiographic and clinical data were documented. The collateral grading was done according to the Rentrop Scoring system. The serum vascular endothelial growth factor level was correlated with the collateral score and cardiovascular risk factors like age, sex, type ll diabetes, blood pressure, and cholesterol level. An increase in the level of the collateral score was noted with an increase in the level of VEGF in blood serum. A significant association was founded between serum VEGF level and cardiovascular risk factors on collateral formation in patients with diabetes and hypertension. This article is protected by copyright. All rights reserved.

Indicators and predictors of in-hospital mortality and survival in patients with ventricular septal rupture

Background

Ventricular septal rupture (VSR), a mechanical complication of myocardial infarction (MI), usually presents with rapid clinical deterioration with acute heart failure or cardiogenic shock. VSR may occur within 24 h to several days after MI and can occur in both anterior and inferior wall MI. Although guidelines recommend emergent surgery, this is associated with a high mortality rate of up to 40%. Intra-aortic balloon pump (IABP) and extracorporeal membrane oxygenation (ECMO) stabilize patients in preparation for angiography and surgery. Delayed surgery allows better septal repair in scarring tissue but also carries the risk of rupture extension and death while waiting. Percutaneous closure of the defect with appropriately designed devices results in better survival in the subacute phase.

Aims

To study the indicators and predictors of VSR in the current era of primary percutaneous coronary interventions and mechanical circulatory support.

Methods

Of total of 34,681 patients presenting with MI, the incidence of VSR was 0.45%. We sought to evaluate the predictors of survival and death in VSR. Coronary angiography (CAG) was performed, hemodynamic support provided to unstable patients, and consenting patients were referred to definitive therapy, either surgery or percutaneous device closure. The previously postulated hypotheses of triple vessel disease (TVD), diabetes mellitus (DM), and concentric left ventricular hypertrophy (LVH) due to Hypertension (HTN) being protective against VSR were explored.

Results

Of the 169 patients with VSR, we found that the group that survived was mostly men and the mean age was 61.5 years; this was in contrast to the non-survivors, who were mainly women, and the mean age was 65.2 years (p = 0.025); higher Killip Class was 111-1V (p = 0.001), lower LVEF (p = 0.010), apical VSR and LV aneurysm (p = 0.015 and p = 0.002, respectively) were predictors of death. 48 patients underwent CAG, with single vessel disease (SVD) with lower-grade Rentrop collateral flow being most common in the death group. 25 patients were subjected to definitive therapy with surgical patch closure or percutaneous device closure. The patients who died were older by approximately 7 years. The risk factors for coronary artery disease, such as HTN, diabetes, and smoking, were not statistically different between the two groups.

Conclusion

Prevention of myocardial infarction is more important than managing a VSR, which carries a high mortality despite advanced mechanical support and definitive interventional therapy such as emergent surgery and percutaneous device closure.

Clinical and Angiographic Prophesy of Hemodynamic Status in Patients with Acute Anterior Wall ST-Segment-Elevation Myocardial Infarction and Totally Occluded Left Anterior Descending Artery

Background

Left anterior descending artery (LAD) is the most common occluded vessel in a patient presenting with acute anterior wall ST-segment elevated myocardial infarction (STEMI). Acute occlusion of LAD usually results in hemodynamic compromise. However, some patients maintain hemodynamic stability despite its proximal occlusion. As the factors associated with hemodynamic status in such patients are poorly understood, our study sought to determine the clinical and angiographic parameters associated with hemodynamic stability in these patients.

Methods

In this prospective observational study, 60 consecutive patients of acute anterior wall STEMI with completely occluded LAD on coronary angiography were included. Various clinical and angiographic parameters associated with hemodynamic status were evaluated.

Results

Of the 60 patients, 30 patients each were included in the hemodynamically stable (group I) and hemodynamically unstable group (group II). The mean age of the patients in group I and group II was 51.07±13.78 years and 55.47±11.69 years, respectively. The hemodynamically unstable group had a significantly higher number of patients with diabetes mellitus, elevated Troponin T level, and lower left ventricular ejection fraction as compared to the stable group (p<0.05). In contrast, 11 (36.7%) patients in the hemodynamically stable group had rich collaterals compared to 4 (13.3%) patients in the hemodynamically unstable group. The difference was statistically significant (p=0.037).

Conclusion

The present study showed that the presence of diabetes, severe LV systolic dysfunction, elevated Troponin-T level, and poor collaterals were associated with hemodynamic instability, whereas the presence of better collaterals predicted hemodynamic stability in patients presenting with anterior wall STEMI and total LAD occlusion.

Visceral fat index: a novel predictor for coronary collateral circulation

Objective This study was designed to investigate the role of visceral adiposity along with other clinical parameters in predicting poor coronary collateral circulation (CCC) among patients with severe obstructive coronary artery disease (CAD). Subjects and methods A total of 135 patients with severe obstructive CAD and good (n = 70) or poor (n = 65) CCC were included. Data on angiographically detected CCC, the quality criteria for CCC (Rentrop scores) and visceral fat index (VFI) obtained via bioelectrical impedance were compared between good and poor CCC groups. Independent predictors of poor CCC, the correlation between VFI and Rentrop score and the role of VFI in the identification of CCC were analyzed. Results A significant negative correlation was noted between VFI and Rentrop scores (r = -0.668, < 0.001). The presence of hypertension (OR 4.244, 95% CI 1.184 to 15.211, p = 0.026) and higher VFI (OR 1.955, 95% CI 1.342 to 2.848, p < 0.001) were shown to be independent predictors of an increased risk for poor CCC. ROC analysis revealed a VFI > 9 (AUC [area under the curve] (95% CI): 0.898 (0.834-0.943), p < 0.0001) to be a potential predictor of poor CCC with a sensitivity of 95.38% and specificity of 85.71%. Conclusion In conclusion, our findings revealed comorbid hypertension and higher VFI to significantly predict the risk of poor CCC in patients with severe obstructive CAD.

Blood Group Types O and Non-O Are Associated With Coronary Collateral Circulation Development

Blood group types are associated with coronary artery disease. However, data are scarce about the impact of blood group types on coronary collateral circulation. In this study, we aimed to investigate the relationship between the blood group types and coronary collateral circulation. Two hundred and twelve patients who underwent coronary angiography in our department and had a stenosis of ≥ 90% in at least one major epicardial vessel were included in our study. Collateral degree was graded according to Rentrop-Cohen classification. After grading, patients were divided into poor coronary collateral circulation (Rentrop grade 0 and 1) and good coronary collateral circulation (Rentrop 2 and 3) groups. The ABO blood type of all participants was determined. The incidence rates of O blood group type were significantly higher in the good coronary collateral group compared to the poor collateral group (37.9% vs 17.1%, P < .001). The O type blood group was an independent predictor of good coronary collateral circulation (odds ratio = 1.83, 95% confidence interval = 1.56-6.18, P = .015). Coronary collateral circulation is associated with blood group types. The O blood group predicts good coronary collateral development among patients with coronary artery disease.

Impact of Admission Blood Glucose on Coronary Collateral Flow in Patients with ST-Elevation Myocardial Infarction

In patients with acute myocardial infarction, glucose metabolism is altered and acute hyperglycemia on admission is common regardless of diabetes status. The development of coronary collateral is heterogeneous among individuals with coronary artery disease. In this study, we aimed to investigate whether glucose value on admission is associated with collateral flow in ST-elevation myocardial infarction (STEMI) patients. We retrospectively evaluated 190 consecutive patients with a diagnosis of first STEMI within 12 hours of onset of chest pain. Coronary collateral development was graded according to Rentrop classification. Rentrop 0-1 was graded as poor collateral development, and Rentrop 2-3 was graded as good collateral development. Admission glucose was measured and compared between two groups. Mean admission glucose level was 173.0 ± 80.1 mg/dl in study population. Forty-five (23.7%) patients had good collateral development, and 145 (76.3%) patients had poor collateral development. There were no statistically significant differences in demographic characteristics between two groups. Three-vessel disease was more common in patients with good collateral development (p=0.026). Mean admission glucose level was higher in patients with poor collateral than good collateral (180.6 ± 84.9 mg/dl versus 148.7 ± 56.6 mg/dl, resp., p=0.008). In univariate analysis, higher admission glucose was associated with poor collateral development, but multivariate logistic regression analysis revealed a borderline result (odds ratio 0.994, 95% CI 0.989-1.000, p=0.049). Our results suggest that elevated glucose on admission may have a role in the attenuation of coronary collateral blood flow in acute myocardial infarction. Further studies are needed to validate our results.

Coronary collateralization shows sex and racial-ethnic differences in obstructive artery disease patients

Background

Coronary collateral circulation protects cardiac tissues from myocardial infarction damage and decreases sudden cardiac death. So far, it is unclear how coronary collateralization varies by race-ethnicity groups and by sex.

Methods

We assessed 868 patients with obstructive CAD. Patients were assessed for collateral grades based on Rentrop grading system, as well as other covariates. DNA samples were genotyped using the Affymetrix 6.0 genotyping array. To evaluate genetic contributions to collaterals, we performed admixture mapping using logistic regression with estimated local and global ancestry.

Results

Overall, 53% of participants had collaterals. We found difference between sex and racial-ethnic groups. Men had higher rates of collaterals than women (P-value = 0.000175). White Hispanics/Latinos showed overall higher rates of collaterals than African Americans and non-Hispanic Whites (59%, 50% and 48%, respectively, P-value = 0.017), and especially higher rates in grade 1 and grade 3 collateralization than the other two populations (P-value = 0.0257). Admixture mapping showed Native American ancestry was associated with the presence of collaterals at a region on chromosome 17 (chr17:35,243,142-41,251,931, β = 0.55, P-value = 0.000127). African ancestry also showed association with collaterals at a different region on chromosome 17 (chr17: 32,266,966-34,463,323, β = 0.38, P-value = 0.00072).

Conclusions

In our study, collateralization showed sex and racial-ethnic differences in obstructive CAD patients. We identified two regions on chromosome 17 that were likely to harbor genetic variations that influenced collateralization.

The relationship between fasting blood glucose variability and coronary artery collateral formation in type 2 diabetes patients with coronary artery disease

BACKGROUND

Coronary collaterals are an alternative source of blood supply to ischemic myocardium. Well-developed coronary collateral arteries in patients with coronary artery disease (CAD) limit the size of acute myocardial infarction and improves survival. The aim of this study was to investigate the relationship between glycemic variability and coronary collateral formation in patients with type 2 diabetes mellitus and CAD.

METHODS

Consecutive patients undergoing percutaneous coronary intervention or coronary artery bypass grafting procedures were studied. Multivariate logistic regression models were used to examine the association between coronary artery collateral formation graded by Rentrope classification and glycemic variability, measured by coefficient variation of fasting blood glucose.

RESULTS

In our study, we retrospectively enrolled 300 patients, of whom 239 were diabetic (age: 70.1±11.9, 56% men) and 61 were nondiabetic (age: 71.5±11.5, 72% men). Diabetic patients were further stratified as follows: those with poor coronary collateral artery development (n=171, age: 69.7±12.4, 55% men) and those with good coronary collateral artery development (n=68, age 71.1±10.8, 59% men) according to the Rentrope classification. Our findings did not show association between glycemic variability and coronary collateral vessels development after controlling for potential confounders (odds ratio: 2.51; 95% confidence interval: 0.57-11.03; P=0.22). The culprit lesion (≥75% stenosis) in the left anterior descending artery and the right coronary artery was more frequent in the good collateral group compared with the poor collateral group (66 vs. 50%, P=0.02; 63 vs. 45%, P=0.01 respectively).

CONCLUSION

Glycemic variability is not associated with coronary collateral artery formation in patients with type 2 diabetes mellitus and CAD.

Cardiovascular risk factors cause premature rarefaction of the collateral circulation and greater ischemic tissue injury

RATIONALE

Collaterals lessen tissue injury in occlusive disease. However, aging causes progressive decline in their number and smaller diameters in those that remain (collateral rarefaction), beginning at 16 months of age in mice (i.e., middle age), and worse ischemic injury-effects that are accelerated in even 3-month-old eNOS(-/-) mice. These findings have found indirect support in recent human studies.

OBJECTIVE

We sought to determine whether other cardiovascular risk factors (CVRFs) associated with endothelial dysfunction cause collateral rarefaction, investigate possible mechanisms, and test strategies for prevention.

METHODS AND RESULTS

Mice with nine different models of CVRFs of 4-12 months of age were assessed for number and diameter of native collaterals in skeletal muscle and brain and for collateral-dependent perfusion and ischemic injury after arterial occlusion. Hypertension caused collateral rarefaction whose severity increased with duration and level of hypertension, accompanied by greater hindlimb ischemia and cerebral infarct volume. Chronic treatment of wild-type mice with L-N (G)-nitro-arginine methylester caused similar rarefaction and worse ischemic injury which were not prevented by lowering arterial pressure with hydralazine. Metabolic syndrome, hypercholesterolemia, diabetes mellitus, and obesity also caused collateral rarefaction. Neither chronic statin treatment nor exercise training lessened hypertension-induced rarefaction.

CONCLUSION

Chronic CVRF presence caused collateral rarefaction and worse ischemic injury, even at relatively young ages. Rarefaction was associated with increased proliferation rate of collateral endothelial cells, effects that may promote accelerated endothelial cell senescence.

The association of plasma vitamin A and E levels with coronary collateral circulation

OBJECTIVE

To investigate if plasma levels of vitamin A and E have an association with coronary collateral development.

METHODS

A total of 189 patients who underwent coronary angiography and had total occlusion in at least one major epicardial coronary artery were enrolled in the study. To classify coronary collateral circulation (CCC), the Rentrop scoring system was used. Patients were classified as having poor CCC (Rentrop grades 0-1) or good CCC (Rentrop grades 2-3), and all patients were also screened for hypertension, hypercholesterolemia, diabetes, and smoking history.

RESULTS

There were no differences in plasma vitamin A and E levels between the two groups (vitamin A: 2.37 ± 0.65 vs. 2.35 ± 0.78, p = 0.253; vitamin E: 47.1 ± 12.8 vs. 44.6 ± 15.1, p = 0.082), and plasma vitamin A and E levels were not associated with CCC. Serum high-sensitivity C-reactive protein (hs-CRP) levels were significantly higher in patients with poor CCC (4.68 ± 2.52 vs. 3.89 ± 1.78, p = 0.001). The higher frequency of diabetes and higher serum hs-CRP levels were found to be an independent predictor for poor CCC (odds ratio = 2.44, p = 0.006; odds ratio = 1.24, p = 0.007, respectively). And a higher frequency of total occluded RCA was found to be a positive predictor for good CCC (odds ratio = 2.36, p = 0.06) in a multivariate logistic regression analysis.

CONCLUSIONS

We found that serum hs-CRP levels, presence of diabetes, and total occlusion of RCA have an effect on coronary collateral development. We found no correlation between plasma vitamin A and E levels and CCC.

Coronary Collateral Circulation and Cardiovascular Risk Factors: Is There a Paradox?

We sought to determine the association of major cardiovascular risk factors and other comorbidities with the presence or absence of coronary collateral (CC) circulation. All electronic medical records from 2010 to 2011 were retrospectively reviewed. A total of 563 patients were divided into 2 groups: CC present (180) and CC absent (383). Smoking (P = .012, odds ratio [OR] 1.58), hypercholesterolemia (P = .001, OR 2.21), and hypertension (P = .034, OR 1.75) were associated with the presence of CC. Increasing body mass index (BMI, P = .001) and decreasing estimated glomerular filtration rate (eGFR, P = .042) were associated with the absence of CC. On multivariable linear regression analysis, hypercholesterolemia (P = .001, OR 2.28), BMI (P = .012, OR 0.77), and eGFR (P = .001, OR 0.70) were found to be independently associated with CC. Our findings will help predict patient populations more likely to have presence or absence of CC circulation.

Exercise training and peripheral arterial disease

Peripheral arterial disease (PAD) is a common vascular disease that reduces blood flow capacity to the legs of patients. PAD leads to exercise intolerance that can progress in severity to greatly limit mobility, and in advanced cases leads to frank ischemia with pain at rest. It is estimated that 12 to 15 million people in the United States are diagnosed with PAD, with a much larger population that is undiagnosed. The presence of PAD predicts a 50% to 1500% increase in morbidity and mortality, depending on severity. Treatment of patients with PAD is limited to modification of cardiovascular disease risk factors, pharmacological intervention, surgery, and exercise therapy. Extended exercise programs that involve walking approximately five times per week, at a significant intensity that requires frequent rest periods, are most significant. Preclinical studies and virtually all clinical trials demonstrate the benefits of exercise therapy, including improved walking tolerance, modified inflammatory/hemostatic markers, enhanced vasoresponsiveness, adaptations within the limb (angiogenesis, arteriogenesis, and mitochondrial synthesis) that enhance oxygen delivery and metabolic responses, potentially delayed progression of the disease, enhanced quality of life indices, and extended longevity. A synthesis is provided as to how these adaptations can develop in the context of our current state of knowledge and events known to be orchestrated by exercise. The benefits are so compelling that exercise prescription should be an essential option presented to patients with PAD in the absence of contraindications. Obviously, selecting for a lifestyle pattern that includes enhanced physical activity prior to the advance of PAD limitations is the most desirable and beneficial.

Plasma chemokine levels are associated with the presence and extent of angiographic coronary collaterals in chronic ischemic heart disease

BACKGROUND

In patients with chronic ischemic heart disease (IHD), the presence and extent of spontaneously visible coronary collaterals are powerful determinants of clinical outcome. There is marked heterogeneity in the recruitment of coronary collaterals amongst patients with similar degrees of coronary artery stenoses, but the biological basis of this heterogeneity is not known. Chemokines are potent mediators of vascular remodeling in diverse biological settings. Their role in coronary collateralization has not been investigated. We sought to determine whether plasma levels of angiogenic and angiostatic chemokines are associated with of the presence and extent of coronary collaterals in patients with chronic IHD.

METHODOLOGY/PRINCIPAL FINDINGS

We measured plasma concentrations of angiogenic and angiostatic chemokine ligands in 156 consecutive subjects undergoing coronary angiography with at least one ≥90% coronary stenosis and determined the presence and extent of spontaneously visible coronary collaterals using the Rentrop scoring system. Eighty-eight subjects (56%) had evidence of coronary collaterals. In a multivariable regression model, the concentration of the angiogenic ligands CXCL5, CXCL8 and CXCL12, hyperlipidemia, and an occluded artery were associated with the presence of collaterals; conversely, the concentration of the angiostatic ligand CXCL11, interferon-γ, hypertension and diabetes were associated with the absence of collaterals (ROC area 0.91). When analyzed according to extent of collateralization, higher Rentrop scores were significantly associated with increased concentration of the angiogenic ligand CXCL1 (p<0.0001), and decreased concentrations of angiostatic ligands CXCL9 (p<0.0001), CXCL10 (p = 0.002), and CXCL11 (p = 0.0002), and interferon-γ (p = 0.0004).

CONCLUSIONS/SIGNIFICANCE

Plasma chemokine concentrations are associated with the presence and extent of spontaneously visible coronary artery collaterals and may be mechanistically involved in their recruitment.

Poor coronary collateral vessel development in patients with mild to moderate renal insufficiency

BACKGROUND

The development of coronary collaterals is crucial to survival through acute ischemia. Mild to moderate loss of renal function has been suggested to play a role in this event, but evidential data are scarce. The aim of this study was to investigate the relationship between mild to moderate renal insufficiency and coronary collateral development in patients with chronic total coronary artery occlusion.

METHODS AND RESULTS

A total of 83 patients with mild to moderate loss of renal function (30 mL/min/1.73 m(2) ≤ eGFR < 90 mL/min/1.73 m(2)) with chronic total coronary artery occlusion were included in our study. The collateral circulation was graded according to Rentrop classification and the function of collateral circulation was graded according to Werner collateral connection (CC) grades. Compared to patients with good collateral circulation (Rentrop = 2,3), eGFR was found to be lower in those patients with poor coronary collateral circulation (Rentrop = 0,1) (63.30 ± 10.51 vs. 54.13 ± 10.56, P = 0.02). eGFR was also found to be lower in poorly functioning coronary collateral circulation (CC = 0,1) than in efficiently functioning coronary collateral circulation (CC = 2) (55.22 ± 9.98 vs. 66.28 ± 9.16, P = 0.03). Multiple logistic regression analysis showed that low eGFR was independently associated with poor coronary collateral circulation (Rentrop = 0,1, 95% CI, 0.09-1.09, P = 0.044) and poor function of coronary collateral circulation (CC = 0,1, 95% CI, 0.02-0.17, P = 0.02).

CONCLUSIONS

Lower eGFR is associated with poorer coronary collateral vessel development in patients experiencing mild to moderate renal insufficiency. Moreover, eGFR represents an independent factor affecting coronary collateral vessel development.

Cardiovascular risk factors and collateral artery formation

Arterial lumen narrowing and vascular occlusion is the actual cause of morbidity and mortality in atherosclerotic disease. Collateral artery formation (arteriogenesis) refers to an active remodelling of non-functional vascular anastomoses to functional collateral arteries, capable to bypass the site of obstruction and preserve the tissue that is jeopardized by ischaemia. Hemodynamic forces such as shear stress and wall stress play a pivotal role in collateral artery formation, accompanied by the expression of various cytokines and invasion of circulating leucocytes. Arteriogenesis hence represents an important compensatory mechanism for atherosclerotic vessel occlusion. As arteriogenesis mostly occurs when lumen narrowing by atherosclerotic plaques takes place, presence of cardiovascular risk factors (e.g. hypertension, hypercholesterolaemia and diabetes) is highly likely. Risk factors for atherosclerotic disease affect collateral artery growth directly and indirectly by altering hemodynamic forces or influencing cellular function and proliferation. Adequate collateralization varies significantly among atherosclerotic patients, some profit from the presence of extensive collateral networks, whereas others do not. Cardiovascular risk factors could increase the risk of adverse cardiovascular events in certain patients because of the reduced protection through an alternative vascular network. Likewise, drugs primarily thought to control cardiovascular risk factors might contribute or counteract collateral artery growth. This review summarizes current knowledge on the influence of cardiovascular risk factors and the effects of cardiovascular medication on the development of collateral vessels in experimental and clinical studies.

Paradoxically enhanced heart tolerance to ischaemia in type 1 diabetes and role of increased osmolarity

There is considerable controversy regarding the tolerance of diabetic hearts to ischaemia and the underlying mechanisms responsible for the increased heart tolerance to ischamia remain uncertain. In the present study, we observed, in vitro, type 1 diabetic heart responses to ischaemia and reperfusion at different degrees of hyperglycaemia. In addition, the possible role of increased osmolarity in cardioprotection due to hyperglycaemia was evaluated. Hearts from 3 week streptozocin-induced diabetic rats were isolated and perfused in a Langendorff apparatus and subjected to 30 min ischaemia and 30 min reperfusion. Cardiac function and the electrocardiogram were recorded. Myocardial content of osmolarity associated heat shock protein (hsp) 90, heme oxygenase (HO)-1 and anti-oxidant enzymes were determined in diabetic or hyperosmotic solution-perfused hearts using western blot. The hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG; 2 x 10(-7) mol/L) or the nitric oxide synthase (NOS) inhibitor Nomega-nitro-L-arginine methyl ester (1 x 10(-5) mol/L) was added to the perfusate to observe the effects of hsp90 inhibition and hsp90-associated endothelial NOS on ischaemic responses of diabetic hearts. Compared with normal control rats, diabetic hearts with severe hyperglycaemia (blood glucose > 20 mmol/L) showed markedly improved postischaemic heart function with fewer reperfusion arrhythmias. Mild hyperglycaemia (< 12 mmol/L) exhibited no significant cardioprotection. Elevated expression of hsp90 accompanied the enhanced resistance to ischaemia in diabetic hearts, which was abrogated by 17-AAG. In the presence of the NOS inhibitor, heart function was preserved, whereas reperfusion arrhythmias were increased in diabetes. Diabetic hearts also had markedly elevated HO-1 and catalase, with no significant change in superoxide dismutase. Hyperosmotic perfusion with glucose or mannitol also increased myocardial hsp90 and catalase. The present findings reveal that heart resistance to ischaemia is increased in short-term type 1 diabetes with severe hyperglycaemia. Elevated osmolarity caused by significant hyperglycaemia may contribute to the enhanced myocardial activity against oxidative injury during ischaemia and reperfusion.