Concomitant Impairment in Endothelial Function and Neural Cardiovascular Regulation in Offspring of Type 2 Diabetic Subjects

Endothelial dysfunction and cardiovascular diseases: The role of human induced pluripotent stem cells and tissue engineering

Cardiovascular disease (CVD) remains to be the leading cause of death globally today and therefore the need for the development of novel therapies has become increasingly important in the cardiovascular field. The mechanism(s) behind the pathophysiology of CVD have been laboriously investigated in both stem cell and bioengineering laboratories. Scientific breakthroughs have paved the way to better mimic cell types of interest in recent years, with the ability to generate any cell type from reprogrammed human pluripotent stem cells. Mimicking the native extracellular matrix using both organic and inorganic biomaterials has allowed full organs to be recapitulated in vitro. In this paper, we will review techniques from both stem cell biology and bioengineering which have been fruitfully combined and have fueled advances in the cardiovascular disease field. We will provide a brief introduction to CVD, reviewing some of the recent studies as related to the role of endothelial cells and endothelial cell dysfunction. Recent advances and the techniques widely used in both bioengineering and stem cell biology will be discussed, providing a broad overview of the collaboration between these two fields and their overall impact on tissue engineering in the cardiovascular devices and implications for treatment of cardiovascular disease.

Evaluation of cardiac autonomic dysfunctions in children with type 1 diabetes mellitus

BACKGROUND

Cardiovascular autonomic neuropathy (CAN) is a serious complication of diabetes, impacting the autonomic nerves that regulate the heart and blood vessels. Timely recognition and treatment of CAN are crucial in averting the onset of cardiovascular complications. Both clinically apparent autonomic neuropathy and subclinical autonomic neuropathy, particularly CAN pose a significant risk of morbidity and mortality in children with type 1 diabetes mellitus (T1DM). Notably, CAN can progress silently before manifesting clinically. In our study, we assessed patients with poor metabolic control, without symptoms, following the ISPAD 2022 guideline. The objective is is to determine which parameters we can use to diagnose CAN in the subclinical period.

METHODS

Our study is a cross-sectional case-control study that includes 30 children diagnosed with T1DM exhibiting poor metabolic control (average HbA1c > 8.5% for at least 1 year) according to the ISPAD 2022 Consensus Guide. These patients, who are under the care of the pediatric diabetes clinic, underwent evaluation through four noninvasive autonomic tests: echocardiography, 24-h Holter ECG for heart rate variability (HRV), cardiopulmonary exercise test, and tilt table test.

RESULTS

The average age of the patients was 13.73 ± 1.96 years, the average diabetes duration was 8 ± 3.66 years, and the 1-year average HbA1c value was 11.34 ± 21%. In our asymptomatic and poorly metabolically controlled patient group, we found a decrease in HRV values, the presence of postural hypotension with the tilt table test, and a decrease in ventricular diastolic functions that are consistent with the presence of CAN. Despite CAN, the systolic functions of the ventricles were preserved, and the dimensions of the cardiac chambers and cardiopulmonary exercise test were normal.

CONCLUSIONS

CAN is a common complication of T1DM, often associated with the patient's age and poor glycemic control. HRV, active orthostatic tests, and the evaluation of diastolic dysfunctions play significant roles in the comprehensive assessment of CAN. These diagnostic measures are valuable tools in identifying autonomic dysfunction at an early stage, allowing for timely intervention and management to mitigate the impact of cardiovascular complications associated with T1DM.

Cardiac autonomic activity, endothelial function and physical fitness in type 2 diabetic patients

Objective: To investigate the association between cardiac autonomic activity, endothelial function, and physical fitness in patients with type 2 diabetes mellitus (T2DM). Methods: Twenty-seven patients with T2DM were studied, with a mean age of 57 ± 9 years and a mean disease duration of 7.4 ± 5 years. The assessment of physical fitness was performed using the Shuttle Walking Test (SWT), cardiac autonomic modulation by heart rate variability (HRV), and endothelial function was assessed by flow-mediated dilation (FMD) of the brachial artery through ultrasound imaging. Results: The main finding of this study was that some HRV indices (SDNN, RMSSD, and HF) were significantly correlated with endothelial function in individuals with T2DM, with R values between 0.51 and 0.57 (p < 0, 05), for all relationships. Additionally, an association was found between the distance covered in the SWT and the basal diameter of the brachial artery (R = 0.59; p = 0.01). Conclusion: Our data demonstrate that some HRV indices are associated with DMF, indicating an interaction between these two systems. Furthermore, our findings suggest a correlation between physical fitness and endothelial function in individuals with T2DM.

Acute ingestion of a high-fructose drink impairs vascular autonomic modulation and reflex control of blood pressure in first-degree relatives of diabetic patients

First-degree relatives of diabetes patients, despite being euglycemic, presented impaired BRS and exacerbation of sympathetic modulation after ingestion of a high fructose drink when challenged to orthostatic stress. This finding alerts the importance of early autonomic dysfunction even in clinically healthy people, especially in face of a stressful situation.

Diabetes Attenuates the Contribution of Endogenous Nitric Oxide but Not Nitroxyl to Endothelium Dependent Relaxation of Rat Carotid Arteries

Endothelial dysfunction is a major risk factor for several of the vascular complications of diabetes, including ischemic stroke. Nitroxyl (HNO), the one electron reduced and protonated form of nitric oxide (NO•), is resistant to scavenging by superoxide, but the role of HNO in diabetes mellitus associated endothelial dysfunction in the carotid artery remains unknown. Aim: To assess how diabetes affects the role of endogenous NO• and HNO in endothelium-dependent relaxation in rat isolated carotid arteries. Methods: Male Sprague Dawley rats were fed a high-fat-diet (HFD) for 2 weeks prior to administration of low dose streptozotocin (STZ; 35 mg/kg i. p./day) for 2 days. The HFD was continued for a further 12 weeks. Sham rats were fed standard chow and administered with citrate vehicle. After 14 weeks total, rats were anesthetized and carotid arteries collected to assess responses to the endothelium-dependent vasodilator, acetylcholine (ACh) by myography. The combination of calcium-activated potassium channel blockers, TRAM-34 (1 μmol/L) and apamin (1 μmol/L) was used to assess the contribution of endothelium-dependent hyperpolarization to relaxation. The corresponding contribution of NOS-derived nitrogen oxide species to relaxation was assessed using the combination of the NO• synthase inhibitor, L-NAME (200 μmol/L) and the soluble guanylate cyclase inhibitor ODQ (10 μmol/L). Lastly, L-cysteine (3 mmol/L), a selective HNO scavenger, and hydroxocobalamin (HXC; 100 μmol/L), a NO• scavenger, were used to distinguish between NO• and HNO-mediated relaxation. Results: At study end, diabetic rats exhibited significantly retarded body weight gain and elevated blood glucose levels compared to sham rats. The sensitivity and the maximal relaxation response to ACh was significantly impaired in carotid arteries from diabetic rats, indicating endothelial dysfunction. The vasorelaxation evoked by ACh was abolished by L-NAME plus ODQ, but not affected by the apamin plus TRAM-34 combination, indicating that NOS-derived nitrogen oxide species are the predominant endothelium-derived vasodilators in sham and diabetic rat carotid arteries. The maximum relaxation to ACh was significantly decreased by L-cysteine in both sham and diabetic rats, whereas HXC attenuated ACh-induced relaxation only in sham rats, suggesting that diabetes impaired the contribution of NO•, whereas HNO-mediated vasorelaxation remained intact. Conclusion: Both NO• and HNO contribute to endothelium-dependent relaxation in carotid arteries. In diabetes, NO•-mediated relaxation is impaired, whereas HNO-mediated relaxation was preserved. The potential for preserved HNO activity under pathological conditions that are associated with oxidative stress indicates that HNO donors may represent a viable therapeutic approach to the treatment of vascular dysfunction.

Endothelial dysfunction in normoglycaemic first-degree relatives of type 2 diabetes mellitus complicated with hyperuricaemia

OBJECTIVE

To reveal the effect of hyperuricaemia on endothelial function in normoglycaemic first-degree relatives of type 2 diabetes mellitus.

METHODS

In all, 40 first-degree relatives of type 2 diabetes mellitus with hyperuricaemia, 40 first-degree relatives of type 2 diabetes mellitus with normouricaemia and 35 healthy subjects without diabetic family history were recruited in this study. Anthropometric parameters as well as blood pressure, blood lipids, fasting blood glucose, fasting insulin, C-reactive protein, tumour necrosis factor-α and interleukin-6 were measured. Insulin resistance was assessed with homoeostasis model assessment index-insulin resistance index. To assess endothelial function, high-resolution ultrasonography was used for measuring flow- and nitroglycerine-mediated brachial artery vasodilation.

RESULTS

When compared with control, flow-mediated dilation was lower in first-degree relatives with or without hyperuricaemia (both p < 0.001). When compared with first-degree relative subjects with normouricaemia, there were lower flow-mediated dilation ( p < 0.001) and higher levels of uric acid ( p < 0.001), fasting blood glucose ( p < 0.001), C-reactive protein ( p = 0.001), tumour necrosis factor-α ( p < 0.001) and interleukin-6 ( p < 0.001) in first-degree relative subjects with hyperuricaemia. Flow-mediated dilation was found to be negatively related to uric acid ( r = -0.597, p < 0.001). Stepwise multiple regressions demonstrated that uric acid was a significant determinant of flow-mediated dilation independent of other variables in first-degree relatives of type 2 diabetes mellitus (β = -0.677, p < 0.001; confidence interval: -0.010 to -0.006).

CONCLUSION

Further endothelial dysfunction is found in normoglycaemic first-degree relatives of type 2 diabetes mellitus complicated with hyperuricaemia.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Alterations in perivascular innervation function in mesenteric arteries from offspring of diabetic rats

BACKGROUND AND PURPOSE

We have reported that exposure to a diabetic intrauterine environment during pregnancy increases blood pressure in adult offspring, but the mechanisms involved are not completely understood. This study was designed to analyse a possible role of perivascular sympathetic and nitrergic innervation in the superior mesenteric artery (SMA) in this effect.

EXPERIMENTAL APPROACH

Diabetes was induced in pregnant Wistar rats by a single injection of streptozotocin. Endothelium-denuded vascular rings from the offspring of control (O-CR) and diabetic rats (O-DR) were used. Vasomotor responses to electrical field stimulation (EFS), NA and the NO donor DEA-NO were studied. The expressions of neuronal NOS (nNOS) and phospho-nNOS (P-nNOS) and release of NA, ATP and NO were determined. Sympathetic and nitrergic nerve densities were analysed by immunofluorescence.

KEY RESULTS

Blood pressure was higher in O-DR animals. EFS-induced vasoconstriction was greater in O-DR animals. This response was decreased by phentolamine more in O-DR animals than their controls. L-NAME increased EFS-induced vasoconstriction more strongly in O-DR than in O-CR segments. Vasomotor responses to NA or DEA-NO were not modified. NA, ATP and NO release was increased in segments from O-DR. nNOS expression was not modified, whereas P-nNOS expression was increased in O-DR. Sympathetic and nitrergic nerve densities were similar in both experimental groups.

CONCLUSIONS AND IMPLICATIONS

The activity of sympathetic and nitrergic innervation is increased in SMA from O-DR animals. The net effect is an increase in EFS-induced contractions in these animals. These effects may contribute to the increased blood pressure observed in the offspring of diabetic rats.

Modulation of baroreflex function by rosiglitazone in prediabetic hyperglycemic rats

Baroreflex sensitivity (BRS) is abnormal in the prediabetic state. This study was conducted to determine effects of chronic rosiglitazone (RSG), an insulin sensitizer, on BRS in prediabetic hyperglycemic (PDH) rats induced by nicotinamide and streptozotocin. The fasting and postprandial blood glucose levels were 5.6-6.9 and 7.8-11.0 mmol/l, respectively. Rats were treated with RSG or saline for 12 weeks. BRS response to phenylephrine (PE-BRS) or sodium nitroprusside (NP-BRS) was determined by linear regression method. Cardiac sympathetic and parasympathetic influences were determined by autonomic blockades. In the saline-treated PDH rats, PE-BRS was enhanced early at week 4 and became greater at week 12. Abnormalities in NP-BRS and cardiac autonomic influences were found only after week 12. Four weeks of RSG treatment normalized blood glucose levels but not PE-BRS. All altered cardiovascular variables were completely restored by 12 weeks of RSG treatment. The correlation between BRS and blood glucose levels in saline-treated PDH rats was significant at week 12, but no correlation was found in RSG-treated rats. In conclusion, hyperglycemia, even in the prediabetic state, may play a role in BRS abnormalities. RSG treatment early in the prediabetic state may normalize BRS via cardiac autonomic modulation, besides its anti-hyperglycemic action.

Pioglitazone improves endothelial and adipose tissue dysfunction in pre-diabetic CAD subjects

OBJECTIVE

To investigate the effect of pioglitazone on endothelial and adipose tissue dysfunction in newly detected IGT patients with CAD.

METHODS AND DESIGN

Participants (n=25) were randomized to treatment with either placebo or pioglitazone (30 mg/day) for 12 weeks. Before and after treatment we evaluated endothelial function (flow-mediated dilation--FMD--of the brachial artery), circulating adipose and inflammatory markers (adiponectin isoforms, TNF-alpha, and high sensitivity-CRP), and insulin sensitivity (euglycemic hyperinsulinemic clamp).

RESULTS

No significant changes were observed in subjects (n=12) treated with placebo. By contrast, subjects (n=13) treated with pioglitazone had significant improvement in FMD (10.8±5.3 vs 13.3±3.6%, p<0.01), accompanied by increased high molecular weight adiponectin (HMW-Ad) (1.7±1.2 vs 4.8±3.6 μg/ml, p<0.05) and decreased TNF-alpha (4.3±1.9 vs 3.2±1.2 pg/ml, p<0.05) associated to an increased glucose disposal (4.8±1.9 vs 5.4±2.0 mg kg(-1) min(-1), p<0.05). A multiple regression analysis indicated that increasing of HMW-Ad after pioglitazone predicted increased FMD.

CONCLUSION

Pioglitazone significantly improves endothelial and adipose tissue dysfunction in pre-diabetic patients with CAD.

Early progression of the autonomic dysfunction observed in pediatric type 1 diabetes mellitus

To focus on early cardiac and vascular autonomic dysfunction that might complicate type 1 diabetes mellitus in children, we planned an observational, cross-sectional study in a population of 93 young patients, under insulin treatment, subdivided in 2 age subgroups (children: 11.5+/-0.4 years; adolescents: 19.3+/-0.2 years). Time and frequency domain analysis of RR interval and systolic arterial pressure variability provided quantitative indices of the sympatho-vagal balance regulating the heart period, of the gain of cardiac baroreflex, and of the sympathetic vasomotor control. Sixty-eight children of comparable age served as a reference group. At rest, systolic arterial pressure and the power of its low-frequency component were greater in patients than in controls, particularly in children (14.0+/-2.3 versus 3.1+/-0.3 mm Hg2). Moreover, baroreflex gain was significantly reduced in both subgroups of patients. Standing induced similar changes in the autonomic profiles of controls and patients. A repeat study after 1 year showed a progression in low-frequency oscillations of arterial pressure and a shift toward low frequency in RR variability. Data in young patients with type 1 diabetes mellitus show a significant increase in arterial pressure, a reduced gain of the baroreflex regulation of the heart period, and an increase of the low-frequency component of systolic arterial pressure variability, suggestive of simultaneous impairment of vagal cardiac control and increases of sympathetic vasomotor regulation. A repeat study after 1 year shows a further increase of sympathetic cardiac and vascular modulation, suggesting early progression of the autonomic dysfunction.

Could hypertension possibly be adaptive?

1. We believe that the ultimate goal of cardiovascular regulatory mechanisms is not the regulation of arterial blood pressure (BP), but the maintenance of tissue blood flows commensurate with metabolic requirements. Thus, elevated BP can potentially contribute to optimizing tissue blood flows under select circumstances; for example, when there are primary defects in autoregulation of tissue blood flows. 2. The hypothesis that a primary defect in autoregulation of tissue blood flows may be responsible for the development of hypertension is presented. It is argued that, in this context, at least part of the rise in BP may be reflexly driven by a 'metaboreflex', a homeostatic mechanism acting to regulate tissue blood flows. 3. We argue that in the context of primary defects in autoregulation of tissue blood flows, the ability to generate and sustain a hypertensive phenotype increases the lifespan of species (i.e. if it were not for this adaptive hypertensive phenotype, death due to circulatory failure would occur much earlier). 4. Experimental and clinical evidence that indirectly supports the hypothesis is reviewed briefly and a means for testing this hypothesis is suggested.

Prolonged head down bed rest-induced inactivity impairs tonic autonomic regulation while sparing oscillatory cardiovascular rhythms in healthy humans

BACKGROUND

Physical inactivity represents a major risk for cardiovascular disorders, such as hypertension, myocardial infarction or sudden death; however, underlying mechanisms are not clearly elucidated. Clinical and epidemiological investigations suggest, beyond molecular changes, the possibility of an induced impairment in autonomic cardiovascular regulation. However, this hypothesis has not been tested directly.

METHODS

Accordingly, we planned a study with noninvasive, minimally intrusive, techniques on healthy volunteers. Participants were maintained for 90 days strictly in bed, 24 h a day, in head-down (-6 degrees ) position (HDBR). Physical activity was thus virtually abolished for the entire period of HDBR. We examined efferent muscle sympathetic nerve activity, as a measure of vascular sympathetic control, baroreceptor reflex sensitivity, heart rate variability (assessing cardiovagal regulation), RR and systolic arterial pressure and low-frequency and high-frequency normalized components (as a window on central oscillatory regulation). Measures were obtained at rest and during simple maneuvers (moderate handgrip, lower body negative pressure and active standing) to assess potential changes in autonomic cardiovascular responsiveness to standard stimuli and the related oscillatory profiles.

RESULTS

HDBR transiently reduced muscle sympathetic nerve activity, RR, heart rate variability and baroreceptor reflex sensitivity late during HDBR or early during the recovery phase. Conversely, oscillatory profiles of RR and systolic arterial pressure variability were maintained throughout. Responsiveness to test stimuli was also largely maintained.

CONCLUSION

Prolonged inactivity as induced by HDBR in healthy volunteers reduces both cardiovagal and vascular sympathetic regulation, while largely maintaining peripheral responsiveness to standardized stimuli and sparing the functional structure of central oscillatory cardiovascular regulation.

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G(i) (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G(q) (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, exercise and dietary factors) and down-regulated (e.g. oxidative stress, smoking and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients.

Fish oil supplementation improves endothelial function in normoglycemic offspring of patients with type 2 diabetes

OBJECTIVE

Offspring of patients with type 2 diabetes (OPDs) exhibits endothelial dysfunction (ED) associated with a chronic inflammatory state. N-3 polyunsaturated fatty acids (n-3 PUFA) may have antioxidant and anti-inflammatory properties that are beneficial for cardiovascular and metabolic health. Therefore, in the present study, we tested the hypothesis that dietary supplementation with fish oil rich in n-3 PUFA may improve ED in otherwise healthy OPDs.

METHODS AND DESIGN

A double-blind, placebo-controlled trial was conducted with 50 OPDs. Participants were randomized to treatment with either placebo or n-3 PUFA (2g/day) for 12 weeks. Before and after treatment we evaluated endothelial function (using flow-mediated dilation (FMD) of the brachial artery), circulating inflammatory markers (adiponectin, TNF-alpha, and high sensitivity-CRP), and insulin resistance (QUICKI).

RESULTS

No significant changes were observed in study outcomes in subjects treated with placebo. By contrast, when compared with baseline values, subjects treated with n-3 PUFA had significant improvement in FMD (9.1+/-5.8% vs. 11.7+/-4.4%, p=0.02) that was accompanied by decreased plasma triglycerides (117+/-73mg/dl vs. 86+/-44mg/dl, p=0.001) and TNF-alpha levels (8.9+/-2.3pg/ml vs. 6.8+/-2.7pg/ml, p=0.001), and a trend towards increased plasma adiponectin levels (7.8+/-4.5microg/ml vs. 9.5+/-5.1microg/ml, p=0.09). When data were analyzed by multiple regression analysis, decreased TNF-alpha after treatment with n-3 PUFA predicted increased FMD.

CONCLUSION

Dietary supplementation with n-3 PUFA significantly improved endothelial function and reduced pro-inflammatory markers in OPDs. Thus, fish oil consumption may have beneficial cardiovascular and metabolic health effects in otherwise healthy subjects predisposed to diabetes and its vascular complications.

Impaired endothelial function and insulin action in first-degree relatives of patients with type 2 diabetes mellitus

First-degree relatives (FDR) of patients with type 2 diabetes mellitus are at increased risk of developing type 2 diabetes mellitus. We studied if endothelial dysfunction of the resistance vessels is present and may coexist with metabolic insulin resistance in FDR. Male FDR (n = 13; 26 +/- 1 years; body mass index, 25 +/- 1 kg m(2) [mean +/- SEM]) and matched control subjects (CON) (n = 22; 25 +/- 1 years; body mass index, 24 +/- 1 kg m(2)) were studied by hyperinsulinemic (40 mU min(-1)m(-2)) isoglycemic clamp combined with brachial arterial and deep venous catheterization of the forearm. Forearm blood flow (FBF) was measured by venous occlusion plethysmography upon stimulation with systemic hyperinsulinemia (291 +/- 11 pmol/L, pooled data from both groups) and upon intraarterial infusion of adenosine (ADN) and acetylcholine (ACH) +/- hyperinsulinemia. Forearm blood flow response to ADN and ACH was less in FDR vs CON (P < .05); systemic hyperinsulinemia added to the FBF effect of ADN in CON (P < .05) but not in FDR. In addition, FDR demonstrated impaired FBF to hyperinsulinemia (2.1 +/- 0.2 vs 4.0 +/- 0.6 mL 100 mL(-1) min(-1)) in FDR and CON, respectively (P < .05). Both M-value (5.0 +/- 0.7 vs 7.0 +/- 0.5 mg min(-1) kg(-1)) and forearm glucose clearance (0.6 +/- 0.1 vs 1.4 +/- 0.4 mL 100 mL(-1)min(-1)) were diminished in FDR compared with CON (all P < .05). FDR demonstrated endothelial dysfunction of the resistance vessels in addition to impaired insulin-stimulated increase in bulk flow. Moreover, FDR demonstrated whole-body insulin resistance as well as decreased basal and insulin-stimulated forearm glucose uptake. It remains to be established whether FDR also demonstrate impaired insulin-stimulated microvascular function.

Ethnic differences in heart rate: can these be explained by conventional cardiovascular risk factors?

OBJECTIVES

South Asians worldwide have an elevated risk of coronary heart disease (CHD), only partly explicable by a higher prevalence of diabetes. Diabetes and dysglycaemia are associated with increased heart rates and abnormal cardiac sympathovagal balance, and are predictive of increased coronary mortality. This study investigated ethnic differences in heart rate, sympathovagal balance, and baroreflex sensitivity (BRS) to establish if they were explained by dysglycaemia/insulin resistance.

METHODS

84 South Asian and 83 European men (age 45-85 yrs), half with established CHD and half without proven CHD, underwent metabolic profiling and assessment of mean RR interval, heart rate variablility (HRV) and BRS.

RESULTS

Mean resting RR interval was greater in Europeans than South Asians (1014 (149) ms vs. 936 (158) ms respectively, means (SD); P = 0.005). This corresponded to resting heart rates of 59.1 bpm for Europeans and 64.1 bpm for South Asians. No ethnic differences were detected in HRV or BRS. Insulin resistance, assessed by the homeostasis model of assessment of insulin resistance (HOMA-IR), correlated with mean RR interval (beta coefficient = -0.189, P = 0.04) and BRS (beta coefficient = -0.246, P = 0.006) and similar correlations were seen with fasting serum glucose. However, ethnic differences in mean RR interval persisted after adjustment for age, systolic BP, beta blocker use, and HOMA-IR.

INTERPRETATION

South Asian men have higher heart rates compared with European men. This difference was not explained by measures of insulin resistance or other risk factors. This may be indicative of altered sympathovagal balance, and contribute to the greater coronary disease risk in people of South Asian ethnicity.

Preserved heart rate variability in first-degree relatives of subjects with Type 2 diabetes mellitus without metabolic disorders

AIMS

To investigate the influence of a family history of Type 2 diabetes mellitus (T2DM) on resting heart rate variability in the absence of concomitant metabolic disorders.

METHODS

We studied 55 first-degree relatives (FDRs) of subjects with T2DM and 36 control subjects without any known family history of diabetes. FDRs were recruited from a University Hospital out-patient diabetes clinic. The protocol included: oral glucose tolerance test (30, 60, 90 and 120 min after ingestion of 75 g glucose) blood glucose, plasma insulin, cholesterol and subfractions, triglycerides, leptin and C-reactive protein. Heart rate variability (HRV) at rest was determined by spectral analysis of interbeat intervals recorded during 10 min in the supine position.

RESULTS

HRV was lower in FDRs compared with control subjects (P < 0.05). Multiple regression analysis identified cholesterol (P = 0.014) and triglycerides (P = 0.014) as significant independent predictors (model r = 0.40; P < 0.001) of HRV. Since FDRs had higher values for anthropometric and metabolic variables known to alter HRV, we performed an ancova adjusted for cholesterol and triglycerides and also another analysis in which the groups were comparable for anthropometric and metabolic characteristics. Comparison of FDRs and comparable control subjects revealed no significant difference in HRV (P > 0.05).

CONCLUSIONS

A family history of T2DM, in the absence of concomitant metabolic disorders, does not impair heart rate variability.

Relationships between heart rate variability, vascular function, and adiposity in children

OBJECTIVE

To examine the relationships and interactions between cardiovascular autonomic nervous system (cANS) function, adiposity, and vascular function in children of varying levels of adiposity.

METHODS

Participants were children (19 M, 17 F, age = 11.5 +/- 0.1 years) who had cANS function assessed via heart rate variability (HRV) methods during resting conditions. Vascular function was assessed with brachial artery flow-mediated dilation (FMD) and nitroglycerin-induced dilation. Spectral power of HRV was calculated for high frequency normalized units (HFnu; measure of PSNS activity) and low frequency:high frequency ratio (LF:HF; overall sympathovagal balance). A blood sample was drawn for measurement of fasting insulin, glucose, lipids, and C-reactive protein (CRP). Results were reported as mean +/- SEM.

RESULTS

FMD peak dilation was positively related to HFnu (r = 0.48, P = 0.01) and negatively related to LF:HF (r = -0.51, P = 0.01) indicating that reduced parasympathetic activity and states of dysfunctional sympathovagal balance were associated with decreased vascular function. After adjustment for confounding factors (insulin, CRP, age) and fat mass, the relationships between these measures of cANS and vascular function remained moderately strong and significant.

DISCUSSION

These data indicate a relationship between cANS and vascular function that is independent of fat mass, inflammation (CRP), and fasting insulin in children of varying levels of adiposity. These relationships and the mechanisms by which they exist require further study to allow for the identification of appropriate therapies for children with high levels of adiposity given the likelihood of them having concomitant cANS and vascular dysfunction.