Kodlipet Dharmashankar

Vascular Endothelial Function and Hypertension: Insights and Directions

Hypertension contributes significantly to worldwide cardiovascular morbidity and mortality. Hypertension appears to have a complex association with endothelial dysfunction, a phenotypical alteration of the vascular endothelium that precedes the development of adverse cardiovascular events and portends future cardiovascular risk. This review concentrates on recent findings with respect to the mechanisms of hypertension-associated endothelial dysfunction, the interrelationship between these two entities, and the relationship of the efficacy of antihypertensive therapies to improvements in vascular homeostasis beyond blood pressure reduction. Current evidence suggests that hypertension and endothelial dysfunction are integrally related with respect to pathophysiologic mechanisms. Future studies will need to identify the key connections between hypertension and endothelial dysfunction to allow novel interventions to be designed and promulgated.

Acute Exposure to Low Glucose Rapidly Induces Endothelial Dysfunction and Mitochondrial Oxidative Stress Role for AMP Kinase

Objective—Hypoglycemia is associated with increased mortality. The reasons for this remain unclear, and the effects of low glucose exposure on vascular endothelial function remain largely unknown. We endeavored to determine the effects of low glucose on endothelial cells and intact human arterioles. Methods and Results—We exposed human umbilical vein endothelial cells to low glucose conditions in a clinically relevant range (40–70 mg/dL) and found rapid and marked reductions in nitric oxide (NO) bioavailability (P<0.001). This was associated with concomitantly increased mitochondrial superoxide production (P<0.001) and NO-dependent mitochondrial hyperpolarization (P<0.001). Reduced NO bioavailability was rapid and attributable to reduced endothelial nitric oxide synthase activity and destruction of NO. Low glucose rapidly activated AMP kinase, but physiological activation failed to restore NO bioavailability. Pharmacological AMP kinase activation led to phosphorylation of endothelial nitric oxide synthases Ser633 activation site, reversing the adverse effects of low glucose. This protective effect was prevented by L-NG-Nitroarginine methyl ester. Intact human arterioles exposed to low glucose demonstrated marked endothelial dysfunction, which was prevented by either metformin or TEMPOL. Conclusion—Our data suggest that moderate low glucose exposure rapidly impairs NO bioavailability and endothelial function in the human endothelium and that pharmacological AMP kinase activation inhibit this effect in an NO-dependent manner.

Adverse Alterations in Mitochondrial Function Contribute to Type 2 Diabetes Mellitus–Related Endothelial Dysfunction in Humans

Objective—Mitochondrial dysfunction plays a key pathophysiological role in type 2 diabetes mellitus (T2DM). Data delineating relationships between mitochondrial and endothelial dysfunction in humans with T2DM are lacking. Methods and Results—In 122 human subjects (60 with T2DM, 62 without T2DM), we measured endothelial function by brachial artery ultrasound (flow mediated dilation) and digital pulse amplitude tonometery. Endothelial function in arterioles isolated from gluteal subcutaneous adipose was measured by videomicroscopy. In arterioles and mononuclear cells, we measured inner mitochondrial membrane potential (&Dgr;&psgr;m), mitochondrial mass, and mitochondrial superoxide production using fluorophores. Endothelial function was impaired in T2DM subjects versus control subjects. &Dgr;&psgr;m magnitude was larger and mitochondrial mass was lower in arterioles and mononuclear cells in T2DM. Mononuclear mitochondrial mass correlated with flow-mediated dilation and pulse amplitude tonometery (&rgr;=0.38 and 0.33, P=0.001 and 0.02, respectively), and mononuclear mitochondrial superoxide production inversely correlated with flow-mediated dilation (&rgr;=−0.58, P=0.03). Low doses of 2 different mitochondrial uncoupling agents (carbonyl cyanide m-chlorophenyl hydrazone and 2,4-dinitrophenol) that reduce &Dgr;&psgr;m magnitude and a mitochondrial-targeted antioxidant (MitoTEMPOL) improved endothelial function and reduced mitochondrial superoxide levels in T2DM arterioles. Conclusion—Mitochondrial dysfunction may play a central role in the impairment of endothelial dysfunction in T2DM.

Acute Exertion Elicits a H2O2-Dependent Vasodilator Mechanism in the Microvasculature of Exercise-Trained but not Sedentary Adults

Brachial artery flow–mediated vasodilation in exercise-trained (ET) individuals is maintained after a single bout of heavy resistance exercise compared with sedentary individuals. The purpose of this study was to determine whether vasodilation is also maintained in the microcirculation of ET individuals. A total of 51 sedentary and ET individuals underwent gluteal subcutaneous fat biopsy before and after performing a single bout of leg press exercise. Adipose arterioles were cannulated in an organ bath, and vasodilation to acetylcholine was assessed±the endothelial nitric oxide inhibitorL-NG-nitroarginine methyl ester, the cyclooxygenase inhibitor indomethacin, or the hydrogen peroxide scavenger polyethylene glycol catalase. Separate vessels (isolated from the same groups) were exposed to an intraluminal pressure of 150 mm Hg for 30 minutes to mimic the pressor response, which occurs with isometric exercise. Vasodilation to acetylcholine was reduced in microvessels from sedentary subjects after either a single weight lifting session or exposure to increased intraluminal pressure, whereas microvessels from ET individuals maintained acetylcholine-mediated vasodilation. Before weight lifting, vasodilation of microvessels from ET individuals was reduced in the presence of L-NG-nitroarginine methyl ester and indomethacin. After weight lifting or exposure to increased intraluminal pressure, polyethylene glycol catalase significantly reduced vasodilation, whereas L-NG-nitroarginine methyl ester and indomethacin had no effect. These results indicate that (1) endothelium-dependent vasodilation in the microvasculature is maintained after heavy resistance exercise in ET individuals but not in sedentary subjects and that (2) high pressure alone or during weight lifting may induce a mechanistic switch in the microvasculature to favor hydrogen peroxide as the vasoactive mediator of dilation.

Relative Importance of Step Count, Intensity, and Duration on Physical Activity's Impact on Vascular Structure and Function in Previously Sedentary Older Adults

Background Age‐related endothelial dysfunction and vascular stiffening are associated with increased cardiovascular (CV) risk. Many groups have encouraged goals of ≥10 000 steps/day or ≥30 min/day of moderate intensity physical activity (MPA) to reduce age‐related CV risk. The impact of MPA on the vasculature of older adults remains unclear. Methods and Results We randomized 114 sedentary older adults ages ≥50 to 12 weeks of either no intervention (group 1), a pedometer‐only intervention (group 2), or a pedometer with an interactive website employing strategies to increase the adoption of habitual physical activity (PA, group 3). Endothelial function by brachial flow‐mediated dilation (FMD%), vascular stiffness by tonometry, step‐count by pedometer, and PA intensity/distribution by accelerometer were measured. Step‐count increased in groups 2 (5136±1554 to 9596±3907, P<0.001) and 3 (5474±1512 to 8167±3111, P<0.001) but not in group 1 (4931±1667 to 5410±2410). Both groups 2 and 3 increased MPA ≥30 min/day. Only group 3 increased MPA in continuous bouts of ≥10 minutes (P<0.001) and improved FMD% (P=0.001). Neither achievement of ≥10 000 steps/day nor ≥30 min/day of MPA resulted in improved FMD%. However, achieving ≥20 min/day in MPA bouts resulted in improved FMD%. No changes in vascular stiffness were observed. Conclusions MPA reverses age‐related endothelial dysfunction, but may require MPA to be performed in bouts of ≥10 minutes duration for ≥20 min/day to be effective. Commonly encouraged PA goals do not guarantee improved endothelial function and may not be as effective in reducing CV risk. Clinical Trial Registration URL: Clinicaltrials.gov. Unique identifier: NCT‐01212978.

Nitric Oxide Synthase-Dependent Vasodilation of Human Subcutaneous Arterioles Correlates With Noninvasive Measurements of Endothelial Function

BACKGROUND Noninvasive measurements of endothelial function predict future adverse cardiovascular events, but offer limited opportunities for mechanistic insights into phenotypic observations. Subcutaneous adipose arterioles, accessible through minimally invasive methods, provide an opportunity for complimentary mechanistic studies. Limited data relating subcutaneous arteriolar endothelial function, cardiovascular risk factors, and noninvasive measurements of endothelial function currently exist. METHODS Forty-four subjects underwent noninvasive studies of endothelial function (brachial reactivity (flow-mediated dilation (FMD) and digital pulse arterial tonometry (PAT)) and measurements of endothelial-dependent vasodilation of gluteal subcutaneous arterioles to acetylcholine. Arteriolar endothelial function was measured (i) percent vasodilation to maximal acetylcholine dose (10(-5) mol/l) and (ii) total area under the curve (AUC) for the entire acetylcholine dose-response curve (total AUC-acetylcholine (Ach), doses 10(-10)-10(-5) mol/l). RESULTS Acetylcholine responses were almost completely nitric oxide (NO) dependent. Total AUC-Ach predicted FMD and PAT, but maximal acetylcholine vasodilation was not associated with these measures. A history of hypertension, diabetes, smoking, and low-density lipoprotein cholesterol levels were independent predictors of total AUC-Ach. In regression models, total AUC-Ach independently predicted FMD. CONCLUSIONS Acetylcholine vasodilator responses in human gluteal subcutaneous arterioles are NO synthase dependent and correlate with cardiac risk factors and in vivo measures of endothelial function. These data suggest subcutaneous arterioles offer an opportunity for translational studies of mechanisms of modulating NO bioavailability relevant to in vivo endothelial function measures.

Moderate obesity and endothelial dysfunction in humans: influence of gender and systemic inflammation

Our objective was to determine whether moderate obesity (Body Mass Index [BMI] ≥ 30 kg/m²) is associated with impaired conduit and microvascular endothelial function, and whether men or women are more susceptible to impairment of endothelial function related to moderate obesity. Forty‐one middle aged, nondiabetic moderately obese (BMI 34.7 ± 4.0 kg/m2) and nonobese (BMI 24.3 ± 2.6 kg/m2) subjects of both sexes underwent noninvasive studies of endothelial function (brachial reactivity) and measurements of endothelial‐dependent vasodilation of gluteal subcutaneous arterioles to acetylcholine (Ach). Endothelium‐dependent vasodilation to Ach was decreased in the moderately obese compared with the nonobese (P < 0.001). Stratified analysis based on sex showed impairment of arteriolar endothelial function in women BMI ≥ 30 kg/m2 (P = 0.02), but not men. There was no difference between in vivo endothelial function flow‐mediated dilation (FMD%) by BMI category. Sex‐specific analysis showed FMD% was lower in women with BMI ≥ 30 kg/m2 compared to those with BMI < 30 kg/m2 (P = 0.02). No differences were seen in men based on BMI category (P = 0.18). In women, high sensitivity C‐reactive protein (hsCRP) correlated with BMI (ρ = 0.68, P = 0.006). Moderate obesity is associated with impaired resistance arteriolar endothelial function. This is more prominent in women than men and is associated with systemic inflammation.

Associations of Reducing Sedentary Time With Vascular Function and Insulin Sensitivity in Older Sedentary Adults

BACKGROUND We previously reported increased moderate-intensity (3-6 metabolic equivalents (METs)) physical activity (PA) reverses aging-associated vascular endothelial dysfunction, a surrogate marker of cardiovascular risk. Whether reductions in sedentary time alone contribute to this improvement is unknown. METHODS Data from 96 adults (aged ≥50 years) enrolled in a randomized control trial evaluating a 12-week intervention to increase PA in sedentary individuals were analyzed. Amount and intensity of activity were measured pre- and post-intervention by step count and accelerometry. Subjects were divided into 3 categories based on change in sedentary activity (<1. 5 METs): (i) ≥5% reduction in sedentary time, (ii) 0-4.99% reduction, and (iii) increase sedentary time. Vascular endothelial function was measured by brachial artery flow-mediated dilation (FMD%) pre- and post-intervention. RESULTS Sedentary time decreased overall (P = 0.001), with a 101-minute decrease in category 1 (N = 27, P < 0.001), a 42-minute decrease in category 2 (N = 29, P = 0.003), and a 44-minute increase in category 3 (N = 40, P = 0.02). While FMD% increased in the entire study population (P = 0.008) over 12 weeks, no differences were observed between the categories (P = 0.73). In category 1, FMD% improvement was associated achievement of ≥20 minutes/day of moderate intensity PA in bouts ≥ 10 minutes in length. CONCLUSIONS Reductions of up to 100 minutes of sedentary time per day over 12 weeks was not significantly associated with improved vascular endothelial function in older adults. FMD% was significantly higher among those with lower sedentary behavior and concomitant moderate-intensity PA of ≥20 minutes/day in bouts.

Mineralocorticoid exposure and receptor activity modulate microvascular endothelial function in African Americans with and without hypertension

Prior work suggests blood pressure in African Americans is more sensitive to the effects of aldosterone than in Caucasians. This mechanism may relate to a negative response of the vascular endothelium to aldosterone, including reduced glucose-6-phosphate dehydrogenase (G6PD) activity. Thirty-three African Americans (11 hypertensives, 22 controls) without evidence of diabetes or metabolic syndrome completed the protocol. The protocol included measurement of in vivo microvascular endothelial function by digital pulse arterial tonometry and ex vivo measurement of endothelial function by videomicroscopy of arterioles obtained from these same subjects with and without exposure to aldosterone or spironolactone. Systemic and arteriolar G6PD activities were also measured. In vivo and ex vivo microvascular endothelial function were impaired in African Americans with hypertension. One-hour exposure with aldosterone impaired endothelium-dependent vasodilation in arterioles from normotensive subjects, while 1 hour of spironolactone exposure reversed endothelial dysfunction in arterioles from hypertensive subjects. G6PD activity was impaired in hypertensive arterioles. Aldosterone-related endothelial dysfunction may be responsible for at least a portion of the greater blood pressure sensitivity to aldosterone in African Americans. This may be in part related to vascular suppression of G6PD activity.

The impact of moderate intensity physical activity on cardiac structure and performance in older sedentary adults

Background Sedentary aging leads to adverse changes in vascular function and cardiac performance. We published improvements in vascular function with moderate intensity physical activity (PA) in continuous bouts. Whether moderate intensity PA also impacts cardiac structure and cardiovascular performance of the aging left ventricle (LV) is unknown. Methods We recruited and analyzed results from 102 sedentary older adults ages ≥ 50 from a randomized controlled trial with 3 study groups: control (group 1), a pedometer-only intervention (group 2), or a pedometer with an interactive website employing strategies to increase habitual physical activity (PA, group 3) for 12 weeks. Transthoracic echocardiograms were performed prior to and following the 12 week intervention period to assess cardiac morphology, left ventricular (LV) systolic performance, LV diastolic function, and arterial and LV ventricular elastance. Step count and PA intensity/distribution were measured by a pedometer and an accelerometer. Results We found no significant changes in cardiac morphology. Further, we found no improvement in the aforementioned cardiac functional parameters. Comparing those who achieved the following benchmarks to those who did not showed no significant changes in cardiac structure or performance: 1) 10,000 steps/day, 2) ≥ 30 min/day of moderate intensity physical activity, or 3) moderate intensity PA in bouts ≥ 10 min for ≥ 20 min/day Conclusions In sedentary older adults, increasing moderate intensity PA to currently recommended levels does not result in favorable changes in LV morphology or performance over 12 weeks. More prolonged exposure, higher PA intensity, or earlier initiation of PA may be necessary to see benefits.