The diabetic vasculature: physiological mechanisms of dysfunction and influence of aerobic exercise training in animal models

Evaluation of coronary function in female rats with severe type 1 diabetes: Effects of combined treatment with insulin and pyridoxamine

BACKGROUND

This study aimed to evaluate the coronary function, myocardium, and epicardial adipose tissue (EAT) in female rats with severe type 1 diabetes and the effects of combined treatment with insulin and pyridoxamine (AGEs inhibitor).

METHODS

Female Wistar rats were divided into groups: control (CTR, n = 13), type 1 diabetes (DM1, n = 12), type 1 diabetes treated with insulin (DM1 + INS, n = 11), and type 1 diabetes treated with insulin and pyridoxamine (DM1 + INS + PDX, n = 14). The vascular responsiveness was performed in the septal coronary artery and the protein expressions of AGE, RAGE, GPER, NF-kB was evaluated in the left ventricle (LV), as well as the reactive oxygen species (ROS) was measured in LV and in EAT. We analyzed plasma levels of glucose, estradiol, Nε-carboxymethylisine (CML), thiobarbituric acid reactive substances (TBARS), catalase (CAT), and superoxide dismutase (SOD).

RESULTS

The maximal responses to ACh were reduced in the DM1 compared with the CTR group, accompanied by an increase in circulating glucose, CML, and TBARS. Additionally, the expression of NF-kB in LV and generation of ROS in the presence of MnTMPyP (SOD mimetic) were increased in the DM1 group compared with CTR. Only the combined treatment was effective for fully re-establish ACh relaxation response, NF-kB protein expression, ROS generation, and increased SOD activity in the DM1 + INS + PDX group.

CONCLUSION

The reduction of the endothelium-dependent relaxation response in the septal coronary artery of female rats with severe type 1 diabetes was normalized with the combined treatment with insulin and pyridoxamine, associated with reduced inflammation and oxidative stress in the myocardium and increased circulating antioxidant activity.

Development and validation of a nomogram to predict the risk of peripheral artery disease in patients with type 2 diabetes mellitus

OBJECTIVE

To develop and validate a nomogram for predicting the risk of peripheral artery disease (PAD) in patients with type 2 diabetes mellitus (T2DM) and assess its clinical application value.

METHODS

Clinical data were retrospectively collected from 474 patients with T2DM at the Air Force Medical Center between January 2019 and April 2022. The patients were divided into training and validation sets using the random number table method in a ratio of 7:3. Multivariate logistic regression analysis was performed to identify the independent risk factors for PAD in patients with T2DM. A nomogram prediction model was developed based on the independent risk factors. The predictive efficacy of the prediction model was evaluated using the consistency index (C-index), area under the curve (AUC), receiver operating characteristic (ROC) curve, Hosmer-Lemeshow (HL) test, and calibration curve analysis. Additionally, decision curve analysis (DCA) was performed to evaluate the prediction model's performance during clinical application.

RESULTS

Age, disease duration, blood urea nitrogen (BUN), and hemoglobin (P<0.05) were observed as independent risk factors for PAD in patients with T2DM. The C-index and the AUC were 0.765 (95% CI: 0.711-0.819) and 0.716 (95% CI: 0.619-0.813) for the training and validation sets, respectively, indicating that the model had good discriminatory power. The calibration curves showed good agreement between the predicted and actual probabilities for both the training and validation sets. In addition, the P-values of the HL test for the training and validation sets were 0.205 and 0.414, respectively, indicating that the model was well-calibrated. Finally, the DCA curve indicated that the model had good clinical utility.

CONCLUSION

A simple nomogram based on three independent factors-duration of diabetes, BUN, and hemoglobin levels-may help clinicians predict the risk of developing PAD in patients with T2DM.

Ginsenoside Rb1 Ameliorates Diabetic Arterial Stiffening via AMPK Pathway

Background and Purpose: Macrovascular complication of diabetes mellitus, characterized by increased aortic stiffness, is a major cause leading to many adverse clinical outcomes. It has been reported that ginsenoside Rb1 (Rb1) can improve glucose tolerance, enhance insulin activity, and restore the impaired endothelial functions in animal models. The aim of this study was to explore whether Rb1 could alleviate the pathophysiological process of arterial stiffening in diabetes and its potential mechanisms. Experimental Approach: Diabetes was induced in male C57BL/6 mice by administration of streptozotocin. These mice were randomly selected for treatment with Rb1 (10-60 mg/kg, i. p.) once daily for 8 weeks. Aortic stiffness was assessed using ultrasound and measurement of blood pressure and relaxant responses in the aortic rings. Mechanisms of Rb1 treatment were studied in MOVAS-1 VSMCs cultured in a high-glucose medium. Key Results: Rb1 improved DM-induced arterial stiffening and the impaired aortic compliance and endothelium-dependent vasodilation. Rb1 ameliorated DM-induced aortic remodeling characterized by collagen deposition and elastic fibers disorder. MMP2, MMP9, and TGFβ1/Smad2/3 pathways were involved in this process. In addition, Rb1-mediated improvement of arterial stiffness was partly achieved via inhibiting oxidative stress in DM mice, involving regulating NADPH oxidase. Finally, Rb1 could blunt the inhibition effects of DM on AMPK phosphorylation. Conclusion and Implications: Rb1 may represent a novel prevention strategy to alleviate collagen deposition and degradation to prevent diabetic macroangiopathy and diabetes-related complications.

The risk trajectory of different cardiovascular morbidities associated with chronic kidney disease among patients with newly diagnosed diabetes mellitus: a propensity score-matched cohort analysis

Background

Chronic kidney disease (CKD) introduces an increased cardiovascular risk among patients with diabetes mellitus (DM). The risk and tempo of cardiovascular diseases may differ depending upon their type. Whether CKD differentially influences the risk of developing each cardiovascular morbidity in patients with newly diagnosed DM remains unexplored.

Methods

We identified patients with incident DM from the Longitudinal Cohort of Diabetes Patients (LCDP) cohort (n = 429,616), and uncovered those developing CKD after DM and their propensity score-matched counterparts without. After follow-up, we examined the cardiovascular morbidity-free rates of patients with and without CKD after DM, followed by Cox proportional hazard regression analyses. We further evaluated the cumulative risk of developing each outcome consecutively during the study period.

Results

From LCDP, we identified 55,961 diabetic patients with CKD and matched controls without CKD. After 4.2 years, patients with incident DM and CKD afterward had a significantly higher risk of mortality (hazard ratio [HR] 1.1, 95% confidence interval [CI] 1.06–1.14), heart failure (HF) (HR 1.282, 95% CI 1.19–1.38), acute myocardial infarction (AMI) (HR 1.16, 95% CI 1.04–1.3), and peripheral vascular disease (PVD) (HR 1.277, 95% CI 1.08–1.52) compared to those without CKD. The CKD-associated risk of mortality, HF and AMI became significant soon after DM occurred and remained significant throughout follow-up, while the risk of PVD conferred by CKD did not emerge until 4 years later. The CKD-associated risk of ischemic, hemorrhagic stroke and atrial fibrillation remained insignificant.

Conclusions

The cardiovascular risk profile among incident DM patients differs depending on disease type. These findings can facilitate the selection of an optimal strategy for early cardiovascular care for newly diagnosed diabetic patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-021-01279-6.

Endothelium-Dependent Hyperpolarization (EDH) in Diabetes: Mechanistic Insights and Therapeutic Implications

Diabetes mellitus is one of the major risk factors for cardiovascular disease and is an important health issue worldwide. Long-term diabetes causes endothelial dysfunction, which in turn leads to diabetic vascular complications. Endothelium-derived nitric oxide is a major vasodilator in large-size vessels, and the hyperpolarization of vascular smooth muscle cells mediated by the endothelium plays a central role in agonist-mediated and flow-mediated vasodilation in resistance-size vessels. Although the mechanisms underlying diabetic vascular complications are multifactorial and complex, impairment of endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells would contribute at least partly to the initiation and progression of microvascular complications of diabetes. In this review, we present the current knowledge about the pathophysiology and underlying mechanisms of impaired EDH in diabetes in animals and humans. We also discuss potential therapeutic approaches aimed at the prevention and restoration of EDH in diabetes.

The usefulness of short-term high-fat/high salt diet as a model of metabolic syndrome in mice

Diabetic cardiomyopathy (DC) describes diabetes-associated changes in the structure and function of myocardium that are not directly linked to other factors such as hypertension. Currently there are some models of DC; however, they take a large time period to mimic key features. In the present study, we investigated the effects of a short-term high-fat/high salt diet (HFHS) treatment on myocardial function and structure, and vascular reactivity in C57BL/6 male mice. After 14 weeks HFHS induced hypertension (MAP = 144.95 ± 16.13 vs 92.90 ± 18.95 mm Hg), low glucose tolerance (AUC = 1049.01 ± 74.79 vs 710.50 ± 52.57 a.u.), decreased insulin sensitivity (AUC = 429.83 ± 35.22 vs 313.67 ± 19.55 a.u.) and increased adiposity (epididymal fat weight 0.96 ± 0.10 vs 0.59 ± 0.06 OW/BW × 10²), aspects present in metabolic syndrome. Cardiac evaluation showed diastolic dysfunction (E/A ratio = 1.20 vs 1.90 u.a.) and cardiomyocyte hypertrophy (cardiomyocyte area = 502.82 ± 31.46 vs 385.58 ± 22.11 μm²). Lastly, vascular reactivity was impaired with higher contractile response (136.10 ± 3.49 vs 120.37 ± 5.43%) and lower response to endothelium-dependent vasorelaxation (74.01 ± 4.35 vs 104.84 ± 3.57%). In addition, the diet was able to induce an inward coronary remodeling (vascular total area: SCNS 6185 ± 800.6 vs HFHS 4085 ± 213.7 μm²). Therefore, we conclude that HFHS short-term treatment was able to induce metabolic syndrome-like state, cardiomyopathy and vascular injury working as an important tool to study cardiometabolic diseases.

Coronary microvascular disease as an early culprit in the pathophysiology of diabetes and metabolic syndrome

Metabolic syndrome (MetS) is a group of cardio-metabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia; these are also a combination of independent coronary artery disease (CAD) risk factors. Alarmingly, the prevalence of MetS risk factors are increasing and a leading cause for mortality. In the vasculature, complications from MetS and type 2 diabetes (T2D) can be divided into microvascular (retinopathy and nephropathy) and macrovascular (cardiovascular diseases and erectile dysfunction). In addition to vascular and endothelial dysfunction, vascular remodeling and stiffness are also hallmarks of cardiovascular disease (CVD), and well-characterized vascular changes that are observed in the early stages of hypertension, T2D, and obesity [1-3]. In the heart, the link between obstructive atherosclerosis of coronary macrovessels and myocardial ischemia (MI) is well established. However, recent studies show that abnormalities in the coronary microcirculation are associated with functional and structural changes in coronary microvessels (classically defined as being ≤150-200μm internal diameter), which may cause or contribute to MI even in the absence of obstractive CAD. This suggests a prognostic value of an abnormal coronary microcirculation as an early sub-clinical culprit in the pathogenesis and progression of heart disease in T2D and MetS. The aim of this review is to summarize recent studies investigating the coronary microvascular remodeling in an early pre-atherosclerotic phase of MetS and T2D, and to explore potential mechanisms associated with the timing of coronary microvascular remodeling relative to that of the macrovasculature.

Blocking 5-HT2 receptor restores cardiovascular disorders in type 1 experimental diabetes

This study aimed to determine whether the serotonergic modulation, through selective 5-HT₂ receptor blockade, restores cardiovascular disturbances in type 1 diabetic rats. Diabetes was induced by alloxan (150 mg/kg, s.c.) and maintained for 4 weeks. 5-HT₂ receptor was blocked by sarpogrelate (30 mg/kg.day; 14 days; p.o.). Systolic blood pressure (SBP), heart rate (HR), glycaemia and body weight (BW) were monitored periodically. Animals were sacrificed at the end of the study and the heart, right kidney and thoracic aorta were removed; plasma samples were also obtained. Left ventricular hypertrophy index (LVH) and renal hypertrophy index (RH) were determined. Vascular function was studied in aorta rings; additionally, superoxide anion (O₂•⁻) production (by lucigenin-enhanced chemiluminescence) and lipid peroxidation (by thiobarbituric acid reactive substances assay) were measured. Neither alloxan nor sarpogrelate treatments altered HR, LVH or endothelium-independent relaxation. SBP, glycaemia, BW, RH, O₂•⁻ production and lipid peroxidation were significantly altered in diabetic animals compared with controls. Sarpogrelate treatment considerably decreased SBP, RH, O₂•⁻ production and lipid peroxidation. Endothelium-dependent relaxation was severely reduced in diabetic animal aortas compared to controls; sarpogrelate treatment markedly improved it. Our outcomes show that selectively blocking 5-HT₂ receptors has beneficial effects on impaired cardiovascular parameters in diabetes.

Redifferentiation of expanded human islet β cells by inhibition of ARX

Ex-vivo expansion of adult human islet β cells has been evaluated for generation of abundant insulin-producing cells for transplantation; however, lineage-tracing has demonstrated that this process results in β-cell dedifferentiation. Redifferentiation of β-cell-derived (BCD) cells can be achieved using a combination of soluble factors termed Redifferentiation Cocktail (RC); however, this treatment leads to redifferentiation of only a fraction of BCD cells. This study aimed at improving redifferentiation efficiency by affecting the balance of islet progenitor-cell transcription factors activated by RC treatment. Specifically, RC treatment induces the transcription factors PAX4 and ARX, which play key roles in directing pancreas endocrine progenitor cells into the β/δ or α/PP developmental pathways, respectively. Misactivation of ARX in RC-treated BCD cells may inhibit their redifferentiation into β cells. Blocking ARX expression by shRNA elevated insulin mRNA levels 12.8-fold, and more than doubled the number of insulin-positive BCD cells. ARX inhibition in expanded α-cell-derived cells treated with RC did not cause their transdifferentiation into insulin-producing cells. The combination of RC and ARX shRNA treatment may facilitate the generation of abundant insulin-producing cells for transplantation into patients with type 1 diabetes.

Effects of non-supervised low intensity aerobic excise training on the microvascular endothelial function of patients with type 1 diabetes: a non-pharmacological interventional study

Background

The aim of the present study was to evaluate changes in microvascular density and reactivity in patients with type 1 diabetes (T1D) resulting from low intensity chronic exercise training.

Methods

This study included 22 (34 ± 7 years) consecutive outpatients with T1D and disease duration > 6 years. We used intravital video-microscopy to measure basal skin capillary density and capillary recruitment using post-occlusive reactive hyperemia (PORH) in the dorsum of the fingers. Endothelium-dependent and -independent vasodilation of the skin microcirculation was evaluated in the forearm with a laser Doppler flow monitoring (LDF) system in combination with acetylcholine and sodium nitroprusside iontophoresis, PORH and local thermal hyperemia.

Results

The basal mean capillary density (MCD) after exercise training was significantly higher than before exercise (134 ± 25 vs. 119 ± 19 capillaries/mm², respectively; P = 0.0013). MCD during PORH was also higher after exercise (140 ± 26 vs. 121 ± 24 capillaries/mm², respectively; P < 0.0001). Endothelium-dependent capillary recruitment during PORH was also significantly higher after exercise (140 ± 26 vs. 134 ± 25 capillaries/mm², respectively; P < 0.0012). There were no significant changes in skin microvascular reactivity after exercise as investigated using LDF.

Conclusions

Our results showed that low intensity aerobic exercise, performed four times per week for 12 weeks by patients with T1D, induces significant increases in microvascular density and endothelial-dependent capillary reactivity.

Trial registration

ClinicalTrials.gov NCT02441504. Registered 7 May 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s12872-016-0191-9) contains supplementary material, which is available to authorized users.

Tribbles 3: A potential player in diabetic aortic remodelling

Tribbles 3, whose expression is up-regulated by insulin resistance, was confirmed to be involved in diabetic cardiomyopathy in our previous study. However, it is not known whether Tribbles 3 has a role on conduit arteries such as the aorta in diabetes. Type 2 diabetic rat model was induced by high-fat diet and low-dose streptozotocin. We evaluated the characteristics of diabetic rats by serial ultrasonography and histopathologic analyses of aortic wall architecture. Diabetic rats displayed increased aortic medial thickness, excessive collagen deposition, diminished elastic fibres and reduced vascular compliance together with Tribbles 3 overexpression. To further investigate the role of Tribbles 3 in aortic remodelling, we used Tribbles 3 gene silencing in vivo 12 weeks after onset of diabetes. Silence of Tribbles 3 significantly reversed pathological aortic remodelling without blood pressure modification. In Tribbles 3-small interfering RNA group, medial thickness and perivascular fibrosis were markedly decreased; moreover, there were prominent reductions in collagen content and collagen/elastin ratio, resulting in an improved arterial compliance. Additionally, with Tribbles 3 silencing, the diminished phosphorylation of PI3K/Akt was restored, and increased activation of MKK4/JNK was decreased. Silence of Tribbles 3 is potent in mediating reversal of aortic remodelling, implicating that Tribbles 3 is proposed to be a potential therapeutic target for vascular complication in diabetes.

Implication of pattern-recognition receptors in cardiovascular diseases

SIGNIFICANCE

Pattern-recognition receptors (PRRs) are a family of receptors that are used to detect pathogen-associated molecular patterns or damage-associated molecular patterns, which initiate immune responses to resolve infections and repair damaged tissues. Abnormalities in PRR activation will unavoidably lead to excessive inflammation.

RECENT ADVANCES

Although multiple pathophysiological processes are involved in cardiovascular disease, recent studies have highlighted the importance of innate PRRs, in particular, Toll-like receptors and nucleotide-binding oligomerization domain-like receptors, in mediating inflammatory responses and cardiovascular function.

CRITICAL ISSUES

The functional roles and regulatory mechanisms of PRRs in cardiovascular diseases are still largely unknown. In particular, controversies exist on the certainty of these detrimental or beneficial effects of some PRRs in different diseased states or different experimental animal models.

FUTURE DIRECTIONS

Considering that the molecular mechanisms for individual PRR to regulate cellular function are complex and multiple PRRs are activated simultaneously or synergistically, a better understanding of the function of individual PRRs and the interplay of PRRs will provide unexpected opportunities to develop new therapies for cardiovascular disease by modulation of an innate immune system.

Hyperglycemia has no effect on development of restenosis after percutaneous transluminal angioplasty (PTA) in a diabetic rabbit model

It is well known that hyperglycemia is a trigger of atherosclerosis in patients with diabetes mellitus. However, the role of hyperglycemia in restenosis remains unclear. In this study, we investigated the effects of hyperglycemia on restenosis. Stenosis was evaluated in two sets of diabetic rabbit models: i) diabetic restenosis versus nondiabetic restenosis and ii) diabetic atherosclerosis versus nondiabetic atherosclerosis. Our results indicated that there was no difference in rates of stenosis between the diabetic and the nondiabetic groups in restenosis rabbit models. However, the incidence of stenosis was significantly higher in the diabetic atherosclerosis group compared with the nondiabetic atherosclerosis group. Similarly, the intima-media thickness and cell proliferation rate were significantly increased in the diabetic atherosclerosis group compared with the nondiabetic atherosclerosis group, but there was no difference between the diabetic restenosis and the nondiabetic restenosis groups. Our results indicate that hyperglycemia is an independent risk factor for atherosclerosis, but it has no evident effect on restenosis. These findings indicate that the processes of atherosclerosis and restenosis may involve different pathological mechanisms.

Cardiovascular control during exercise in type 2 diabetes mellitus

Controlled studies of male and female subjects with type 2 diabetes mellitus (DM) of short duration (~3-5 years) show that DM reduces peak VO2 (L·min(-1) and mL·kg(-1)·min(-1)) by an average of 12-15% and induces a greater slowing of the dynamic response of pulmonary VO2 during submaximal exercise. These effects occur in individuals less than 60 years of age but are reduced or absent in older males and are consistently associated with significant increases in the exercise pressor response despite normal resting blood pressure. This exaggerated pressor response, evidence of exertional hypertension in DM, is manifest during moderate submaximal exercise and coincides with a more constrained vasodilation in contracting muscles. Maximum vasodilation during contractions involving single muscle groups is reduced by DM, and the dynamic response of vasodilation during submaximal contractions is slowed. Such vascular constraint most likely contributes to exertional hypertension, impairs dynamic and peak VO2 responses, and reduces exercise tolerance. There is a need to establish the effect of DM on dynamic aspects of vascular control in skeletal muscle during whole-body exercise and to clarify contributions of altered cardiovascular control and increased arterial stiffness to exertional hypertension.