Microvascular function: a potential link between salt sensitivity, insulin resistance and hypertension

Diabetic Peripheral Neuropathy Associated with Foot Ulcer: One of a Kind

Significance: Diabetic peripheral neuropathy (DPN) associated with a diabetic foot ulcer (DFU) is likely to be complicated with critical factors such as biofilm infection and compromised skin barrier function of the diabetic skin. Repaired skin with a history of biofilm infection is known to be compromised in barrier function. Loss of barrier function is also observed in the oxidative stress affected diabetic and aged skin. Recent Advances: Loss of barrier function makes the skin prone to biofilm infection and cellulitis, which contributes to chronic inflammation and vasculopathy. Hyperglycemia favors biofilm formation as glucose lowering led to reduction in biofilm development. While vasculopathy limits oxygen supply, the O2 cost of inflammation is high increasing hypoxia severity. Critical Issues: The host nervous system can be inhabited by bacteria. Because electrical impulses are a part of microbial physiology, polymicrobial colonization of the host's neural circuit is likely to influence transmission of action potential. The identification of perineural apatite in diabetic patients with peripheral neuropathy suggests bacterial involvement. DPN starts in both feet at the same time. Future Directions: Pair-matched studies of DPN in the foot affected with DFU (i.e., DFU-DPN) compared with DPN in the without ulcer, and intact skin barrier function, are likely to provide critical insight that would help inform effective care strategies. This review characterizes DFU-DPN from a translational science point of view presenting a new paradigm that recognizes the current literature in the context of factors that are unique to DFU-DPN.

Skin microvascular function, as assessed with laser speckle contrast imaging, is impaired in untreated essential and masked hypertension

Skin microcirculation has been proposed as a model of generalized microvascular function. Laser speckle contrast imaging (LSCI) is a novel, noninvasive method to assess skin microvascular function (SMF). To date, SMF data in hypertension are conflicting, and no study with LSCI exists. In addition, the application of LSCI in masked hypertension is scarce. We assessed SMF with LSCI coupled with postocclusive reactive hyperemia (PORH) in patients with newly diagnosed untreated essential hypertension (UHT) and masked hypertension (MH) compared to healthy normotensive (NT) individuals. We enrolled consecutive UHT and MH patients and NT individuals matched for age, sex, body mass index, and smoking status. All participants underwent SMF assessment by LSCI coupled with PORH (PeriCam PSI system, Perimed, Sweden). Correlation analyses were performed between SMF and common cardiovascular risk factors and BP parameters. In total, 70 UHT patients, 20 MH patients and 40 NT individuals were enrolled. UHT and MH patients exhibited significantly impaired SMF compared to NT individuals (UHT patients: base-to-peak flux (p < 0.001)), PORH amplitude (p < 0.001); MH patients: base-to-peak flux (p = 0.013), PORH amplitude (p = 0.022). MH patients did not differ compared to UHT patients. SMF was negatively associated with office, ambulatory and central BP. SMF was negatively associated with blood lipids and smoking. Hypertensive status was the single most important predictor of SMF. UHT and MH patients exhibit impaired SMF compared to NT individuals. MH patients did not differ compared to UHT patients. SMF is negatively associated with BP and cardiovascular risk factors. LSCI could be implemented as a useful tool to investigate SMF in hypertension.

β-blockade prevents coronary macro- and microvascular dysfunction induced by a high salt diet and insulin resistance in the Goto-Kakizaki rat

A high salt intake exacerbates insulin resistance, evoking hypertension due to systemic perivascular inflammation, oxidative-nitrosative stress and endothelial dysfunction. Angiotensin-converting enzyme inhibitor (ACEi) and angiotensin receptor blockers (ARBs) have been shown to abolish inflammation and redox stress but only partially restore endothelial function in mesenteric vessels. We investigated whether sympatho-adrenal overactivation evokes coronary vascular dysfunction when a high salt intake is combined with insulin resistance in male Goto-Kakizaki (GK) and Wistar rats treated with two different classes of β-blocker or vehicle, utilising synchrotron-based microangiography in vivo. Further, we examined if chronic carvedilol (CAR) treatment preserves nitric oxide (NO)-mediated coronary dilation more than metoprolol (MET). A high salt diet (6% NaCl w/w) exacerbated coronary microvessel endothelial dysfunction and NO-resistance in vehicle-treated GK rats while Wistar rats showed modest impairment. Microvascular dysfunction was associated with elevated expression of myocardial endothelin, inducible NO synthase (NOS) protein and 3-nitrotyrosine (3-NT). Both CAR and MET reduced basal coronary perfusion but restored microvessel endothelium-dependent and -independent dilation indicating a role for sympatho-adrenal overactivation in vehicle-treated rats. While MET treatment reduced myocardial nitrates, only MET treatment completely restored microvessel dilation to dobutamine (DOB) stimulation in the absence of NO and prostanoids (combined inhibition), indicating that MET restored the coronary flow reserve attributable to endothelium-derived hyperpolarisation (EDH). In conclusion, sympatho-adrenal overactivation caused by high salt intake and insulin resistance evoked coronary microvessel endothelial dysfunction and diminished NO sensitivity, which were restored by MET and CAR treatment in spite of ongoing inflammation and oxidative-nitrosative stress presumably caused by uninhibited renin-angiotensin-aldosterone system (RAAS) overactivation.

Glucocorticoids affect metabolic but not muscle microvascular insulin sensitivity following high versus low salt intake

BACKGROUNDSalt-sensitive hypertension is often accompanied by insulin resistance in obese individuals, but the underlying mechanisms are obscure. Microvascular function is known to affect both salt sensitivity of blood pressure and metabolic insulin sensitivity. We hypothesized that excessive salt intake increases blood pressure and decreases insulin-mediated glucose disposal, at least in part by impairing insulin-mediated muscle microvascular recruitment (IMMR).METHODSIn 20 lean and 20 abdominally obese individuals, we assessed mean arterial pressure (MAP; 24-hour ambulatory blood pressure measurements), insulin-mediated whole-body glucose disposal (M/I value; hyperinsulinemic-euglycemic clamp technique), IMMR (contrast-enhanced ultrasound), osmolyte and water balance, and excretion of mineralocorticoids, glucocorticoids, and amino and organic acids after a low- and high-salt diet during 7 days in a randomized, double-blind, crossover design.RESULTSOn a low-, as compared with a high-salt, intake, MAP was lower, M/I value was lower, and IMMR was greater in both lean and abdominally obese individuals. In addition, natural logarithm IMMR was inversely associated with MAP in lean participants on a low-salt diet only. On a high-salt diet, free water clearance decreased, and excretion of glucocorticoids and of amino acids involved in the urea cycle increased.CONCLUSIONOur findings imply that hemodynamic and metabolic changes resulting from alterations in salt intake are not necessarily associated. Moreover, they are consistent with the concept that a high-salt intake increases muscle glucose uptake as a response to high salt-induced, glucocorticoid-driven muscle catabolism to stimulate urea production and thereby renal water conservation.TRIAL REGISTRATIONClinicalTrials.gov, NCT02068781.

Tuberculoid leprosy: An in vivo microvascular evaluation of cutaneous lesions

Tuberculoid leprosy (TT) is characterized by cutaneous lesions called plaques. Although microvascular ultrastructure of TT patients’ skin is well-documented, little is known about functional aspects of their microcirculation. We aimed, for the first time, to evaluate, in vivo, the microcirculation of TT cutaneous lesions. Seven TT patients, males, under treatment were included in the study. The spectral analysis of frequency components of flowmotion (endothelial, sympathetic, myogenic, cardiac and respiratory) was performed using laser Doppler flowmetry (LDF). Endothelial dependent and independent vasodilatations were assessed by LDF associated to acetylcholine (ACh) and sodium nitroprusside (SNP) iontophoresis, respectively. Vessel density (VD), perfused vessel density (PVD), proportion of perfused vessels (PPV%), microvascular flow index (MFI) and flow heterogeneity index (FHI), reflecting tissue perfusion and oxygenation, were evaluated through sidestream dark field (SDF) imaging. All microvascular analysis were performed in TT lesions and in healthy skin in the contralateral limb of the same patient, used as control skin. VD, PVD and PPV% and MFI were significantly lower in the cutaneous lesion compared to contralateral healthy skin. The contribution of different frequency components of flowmotion, endothelial dependent and independent vasodilatations and FHI were not statistically different between control skin and cutaneous lesion. Our results suggest that TT cutaneous lesions have a significant impairment of tissue perfusion, which may aggravate peripheral nerve degeneration caused by Mycobacterium leprae infection.

Microvascular function in non-dippers: Potential involvement of the salt sensitivity biomarker, marinobufagenin-The African-PREDICT study

Suppressed nighttime blood pressure dipping is associated with salt sensitivity and may increase the hemodynamic load on the microvasculature. The mechanism remains unknown whereby salt sensitivity may increase the cardiovascular risk of non-dippers. Marinobufagenin, a novel steroidal biomarker, is associated with salt sensitivity and other cardiovascular risk factors independent of blood pressure. The authors investigated whether microvascular function in non-dippers is associated with marinobufagenin. The authors included 220 dippers and 154 non-dippers (aged 20-30 years) from the African-PREDICT study, with complete 24-hour urinary marinobufagenin and sodium data. The authors determined dipping status using 24-hour blood pressure monitoring and defined nighttime non-dipping <10%. The authors measured microvascular reactivity as retinal artery dilation in response to light flicker provocation. Young healthy non-dippers and dippers presented with similar peak retinal artery dilation, urinary sodium, and MBG excretion (P > .05). However, only in non-dippers did peak retinal artery dilation relate negatively to marinobufagenin excretion after single (r = -0.20; P = .012), partial (r = -0.23; P = .004), and multivariate-adjusted regression analyses (Adj. R²  = 0.34; β = -0.26; P < .001). The authors also noted a relationship between peak artery dilation and estimated salt intake (Adj. R²  = 0.30; β = -0.14; P = .051), but it was lost upon inclusion of marinobufagenin (Adj. R²  = 0.33; β = -0.015; P = .86). No relationship between microvascular reactivity and marinobufagenin was evident in dippers (P = .77). Marinobufagenin, representing salt sensitivity, may be involved in early microvascular functional changes in young non-dippers and thus contributes to the development of hypertension and cardiovascular disease later in life.

Negative regulation of eNOS-NO signaling by over-SUMOylation of PPARγ contributes to insulin resistance and dysfunction of vascular endothelium in rats

SUMOylation of peroxisome proliferator-activated receptor gamma (PPAR γ) plays important regulatory role in its transcriptional activity. Our recent studies in vitro found that over-SUMOylation of PPARγ, like high glucose and high fat (HG/HF), induced endothelial insulin resistance (IR). However, whether such an event occurs in rats remains unclear. Therefore, our study aimed at investigating whether PPARγ over-SUMOylation could mimic high sucrose/fat diet (HFD) to induce endothelial IR and dysfunction and explored its underlying mechanisms. Normal chow-fed rats were intravenously infected with adenoviruses carrying the wild type cDNAs encoding PPARγ, SUMO1 and PIAS1 (protein inhibitor of activated STAT1). HFD-fed rats were regarded as a positive control. Body physical and biochemical parameters, glucose tolerance and vessel function were detected. The expression and SUMOylation levels of PPARγ were measured by western blotting and co-immunoprecipitation. Our results showed that like HFD, PPARγ over-SUMOylation induced endothelial IR and dysfunction via a negative regulation of eNOS-NO pathway. More importantly, we found that PPARγ over-SUMOylation induced endogenous SUMOylation cascade and exacerbated endothelial IR and dysfunction.The findings will deepen the understanding on PPARγ SUMOylation-regulating insulin signaling network and offer a potential target for prevention and cure of diabetic vascular complications.

Microvascular Dysfunction and Hyperglycemia: A Vicious Cycle With Widespread Consequences

Microvascular and metabolic physiology are tightly linked. This Perspective reviews evidence that 1) the relationship between hyperglycemia and microvascular dysfunction (MVD) is bidirectional and constitutes a vicious cycle; 2) MVD in diabetes affects many, if not all, organs, which may play a role in diabetes-associated comorbidities such as depression and cognitive impairment; and 3) MVD precedes, and contributes to, hyperglycemia in type 2 diabetes (T2D) through impairment of insulin-mediated glucose disposal and, possibly, insulin secretion. Obesity and adverse early-life exposures are important drivers of MVD. MVD can be improved through weight loss (in obesity) and through exercise. Pharmacological interventions to improve MVD are an active area of investigation.

Associations of lifestyle factors (smoking, alcohol consumption, diet and physical activity) with type 2 diabetes among American adults from National Health and Nutrition Examination Survey (NHANES) 2005-2014

BACKGROUND

Over the long term, unhealthy lifestyles can lead to many health problems, especially type 2 diabetes (T2D). The aim of the present study was to determine associations between lifestyle factors (smoking, alcohol consumption, physical activity, and diet) and T2D in American adults (aged ≥20 years) in a nationally representative sample.

METHODS

Data for 12 987 American adults participating in the National Health and Nutrition Examination Survey 2005-2014 were evaluated. Weighted multiple logistic regression models were used to examine associations between the four lifestyle factors and T2D after adjusting for demographics and socioeconomic status (SES). Prevalence trends for T2D were examined using Cochran-Armitage tests.

RESULTS

There was a significant increasing prevalence trend for T2D among American adults. Smokers and individuals consuming >12 alcoholic drinks in the past year were less likely to report having T2D than non-smokers (odds ratio [OR] 0.41; 95% confidence interval [CI] 0.35-0.48) and those consuming <12 alcoholic drinks (OR 0.46; 95% CI 0.39-0.55). Participants with light physical activity have a greater likelihood of having T2D than those engaging in vigorous physical activity (OR 5.72; 95% CI 4.30-7.60). Individuals consuming a poor diet were more likely to report having T2D than those eating an excellent diet (OR 1.18; 95% CI 1.02-1.41). All these relationships remained significant after adjustment for demographics and SES.

CONCLUSION

All four lifestyle factors were significantly associated with T2D among American adults. The findings of the present study provide useful information for healthcare providers that may help them promote specific lifestyle modifications.

Cutaneous and renal vasodilatory response to local pressure application: A comparative study in mice

BACKGROUND AND AIM

We have reported a novel relationship involving mechanical stimulation and vasodilation in rodent and human skin, referred to as pressure-induced vasodilation (PIV). It is unknown whether this mechanism exists in kidney and reflects the microcirculation in deep organs. Therefore, we compared the skin and kidney PIV to determine whether their changes were similar.

METHODS

In anesthetized mice fed a normal salt-diet, laser Doppler flux (LDF) signals were measured when an increase in local pressure was applied to the surface of the head skin with the rate of 2.2Pa/s (1mmHg/min) and to the left kidney with a rate of 4.4Pa/s (2mmHg/min). The mechanism underlying renal PIV was also investigated. The skin and kidney PIV were also compared during salt load (4% NaCl diet).

RESULTS

The kidney had higher baseline LDF and vascular conductance compared to those of the skin. Pressure application increased the LDF in the kidney as well as in the skin with a comparable maximal magnitude (about 25% from baseline value), despite different kinetics of PIV evolution. As we previously reported in the skin, the kidney PIV response was mediated by the activation of transient receptor potential vanilloid type 1 channels, the release of calcitonin gene-related peptide, and the participation of prostaglandins and nitric oxide. In the absence of hypertension, high salt intake abolished the cutaneous PIV response and markedly impaired the renal one.

CONCLUSION

PIV response in the mouse kidney results from a neuro-vascular interaction. Despite some differences between the skin and the kidney PIV, the similarities in their response and signaling mechanisms suggest that the cutaneous microcirculation could reflect, in part, the microcirculation of the renal cortex.

Structural and functional changes in the microcirculation of lepromatous leprosy patients - Observation using orthogonal polarization spectral imaging and laser Doppler flowmetry iontophoresis

Leprosy is a chronic granulomatous infection of skin and peripheral nerves caused by Mycobacterium leprae and is considered the main infectious cause of disability worldwide. Despite the several studies regarding leprosy, little is known about its effects on microvascular structure and function in vivo. Thus, we have aimed to compare skin capillary structure and functional density, cutaneous vasomotion (spontaneous oscillations of arteriolar diameter), which ensures optimal blood flow distribution to skin capillaries) and cutaneous microvascular blood flow and reactivity between ten men with lepromatous leprosy (without any other comorbidity) and ten age- and gender-matched healthy controls. Orthogonal polarization spectral imaging was used to evaluate skin capillary morphology and functional density and laser Doppler flowmetry to evaluate blood flow, vasomotion and spectral analysis of flowmotion (oscillations of blood flow generated by vasomotion) and microvascular reactivity, in response to iontophoresis of acetylcholine and sodium nitroprusside. The contribution of different frequency components of flowmotion (endothelial, neurogenic, myogenic, respiratory and cardiac) was not statistically different between groups. However, endothelial-dependent and -independent vasodilatations elicited by acetylcholine and sodium nitroprusside iontophoresis, respectively, were significantly reduced in lepromatous leprosy patients compared to controls, characterizing the existence of microvascular dysfunction. These patients also presented a significant increase in the number of capillaries with morphological abnormalities and in the diameters of the dermal papilla and capillary bulk when compared to controls. Our results suggest that lepromatous leprosy causes severe microvascular dysfunction and significant alterations in capillary structure. These structural and functional changes are probably induced by exposure of the microvascular bed to chronic inflammation evoked by the Mycobacterium leprae.

Compliance with dietary guidelines affects capillary recruitment in healthy middle-aged men and women

PURPOSE

Healthy microcirculation is important to maintain the health of tissues and organs, most notably the heart, kidney and retina. Single components of the diet such as salt, lipids and polyphenols may influence microcirculation, but the effects of dietary patterns that are consistent with current dietary guidelines are uncertain. It was hypothesized that compliance to UK dietary guidelines would have a favourable effect on skin capillary density/recruitment compared with a traditional British diet (control diet).

METHODS

A 12-week randomized controlled trial in men and women aged 40-70 years was used to test whether skin microcirculation, measured by skin video-capillaroscopy on the dorsum of the finger, influenced functional capillary density (number of capillaries perfused under basal conditions), structural capillary density (number of anatomical capillaries perfused during finger cuff inflation) and capillary recruitment (percentage difference between structural and functional capillary density).

RESULTS

Microvascular measures were available for 137 subjects out of the 165 participants randomized to treatment. There was evidence of compliance to the dietary intervention, and participants randomized to follow dietary guidelines showed significant falls in resting supine systolic, diastolic and mean arterial pressure of 3.5, 2.6 and 2.9 mmHg compared to the control diet. There was no evidence of differences in capillary density, but capillary recruitment was 3.5 % (95 % CI 0.2, 6.9) greater (P = 0.04) on dietary guidelines compared with control.

CONCLUSIONS

Adherence to dietary guidelines may help maintain a healthy microcirculation in middle-aged men and women. This study is registered at www.isrctn.com as ISRCTN92382106.

Capillary Rarefaction Associates with Albuminuria: The Maastricht Study

Albuminuria may be a biomarker of generalized (i.e., microvascular and macrovascular) endothelial dysfunction. According to this concept, endothelial dysfunction of the renal microcirculation causes albuminuria by increasing glomerular capillary wall permeability and intraglomerular pressure, the latter eventually leading to glomerular capillary dropout (rarefaction) and further increases in intraglomerular pressure. However, direct evidence for an association between capillary rarefaction and albuminuria is lacking. Therefore, we examined the cross-sectional association between the recruitment of capillaries after arterial occlusion (capillary density during postocclusive peak reactive hyperemia) and during venous occlusion (venous congestion), as assessed with skin capillaroscopy, and albuminuria in 741 participants of the Maastricht Study, including 211 participants with type 2 diabetes. Overall, 57 participants had albuminuria, which was defined as a urinary albumin excretion ≥30 mg/24 h. After adjustment for potential confounders, participants in the lowest tertile of skin capillary recruitment during postocclusive peak reactive hyperemia had an odds ratio for albuminuria of 2.27 (95% confidence interval, 1.07 to 4.80) compared with those in the highest tertile. Similarly, a comparison between the lowest and the highest tertiles of capillary recruitment during venous congestion yielded an odds ratio of 2.89 (95% confidence interval, 1.27 to 6.61) for participants in the lowest tertile. In conclusion, lower capillary density of the skin microcirculation independently associated with albuminuria, providing direct support for a role of capillary rarefaction in the pathogenesis of albuminuria.

Physical exercise restores microvascular function in obese rats with metabolic syndrome

BACKGROUND

Obesity and metabolic syndrome are related to systemic functional microvascular alterations, including a significant reduction in microvessel density. The aim of this study was to investigate the effects of exercise training on functional capillary density in the skeletal muscle and skin of obese rats with metabolic syndrome.

METHODS

We used male Wistar-Kyoto rats that had been fed a standard commercial diet (CON) or high-fat diet (HFD) for 32 weeks. Animals receiving the HFD were randomly divided into sedentary (HFD+SED) and training groups (HFD+TR) at the 20(th) week. After 12 weeks of aerobic treadmill training, the maximal oxygen uptake (VO2max); hemodynamic, biochemical, and anthropometric parameters; and functional capillary density were assessed. In addition, a maximal exercise test was performed.

RESULTS

Exercise training increased the VO2max (69 ± 3 mL/kg per min) and exercise tolerance (30 ± 1 min) compared with the HFD+SED (41 ± 6 mL/kg per min, P < 0.05 and 16 ± 1 min, P < 0.001) and with the CON (52 ± 7 mL/kg per min and 18 ± 1 min, P < 0.05) groups. The HFD+TR group also showed reduced retroperitoneal fat (0.03 ± 0.00 vs. 0.05 ± 0.00 gram/gram, P < 0.001), epididymal fat (0.01 ± 0.00 vs. 0.02 ± 0.00 gram/gram, P < 0.001), and systolic blood pressure (127 ± 2 vs. 150 ± 2 mmHg, P<0.001). The HFD+TR group also demonstrated improved glucose tolerance, as evaluated by an intraperitoneal glucose tolerance test, fasting plasma glucose levels (5.0 ± 0.1 vs. 6.4 ± 0.2 mmol/L, P<0.001) and fasting plasma insulin levels (26.5 ± 2.3 vs. 38.9 ± 3.7 μIU/mL, P < 0.05). Glucose tolerance did not differ between HFD+TR and CON groups. Exercise training also increased the number of spontaneously perfused capillaries in the skeletal muscle (252 ± 9 vs. 207 ± 9 capillaries/mm(2)) of the training group compared with that in the sedentary animals (260 ± 15 capillaries/mm(2)).

CONCLUSIONS

These results demonstrate that exercise training reverses capillary rarefaction in our experimental model of metabolic syndrome and obesity.

L-NAME iontophoresis: a tool to assess NO-mediated vasoreactivity during thermal hyperemic vasodilation in humans

BACKGROUND

Decreased endothelial Nitric oxide (NO) bioavailability is one of the earliest events of endothelial dysfunction. Assessment of microvascular blood flow using a Laser Doppler Imager during local noninvasive administration of L-N-Arginine-Methyl-Ester (L-NAME) by skin iontophoresis may help discriminate the relative contributions of NO and non-NO pathways during a skin thermal hyperemic test.

METHODS

In healthy nonsmokers, the effects of thermal vasodilation and sodium nitroprusside-mediated vasodilation were tested on skin pretreated with 0.9% saline solution, 2% L-NAME iontophoresis (n = 12), or intradermal injection of 25 nmol L-NAME (n = 10). The effects of L-NAME iontophoresis were also measured in a group of smokers (n = 10).

RESULTS

L-NAME iontophoresis and intradermal injection of L-NAME decreased the skin response to local heating to a similar degree (-41% ± 4% vs. -44% ± 6%). L-NAME iontophoresis site-to-site and day-to-day coefficients of correlation were 0.83 and 0.76, respectively (P < 0.01). The site-to-site and day-to-day coefficients of correlation of L-NAME injection were lower than those of iontophoresis at 0.66 (P < 0.05) and 0.12, respectively (P = not significant). Sodium nitroprusside-induced skin hyperemia was not affected by L-NAME administration. L-NAME iontophoresis-mediated inhibition of skin thermal hyperemia was greater in smokers than in nonsmokers (P < 0.05).

CONCLUSIONS

Laser Doppler Imager assessment of skin thermal hyperemia after L-NAME iontophoresis provides a reproducible and selective bedside method of qualitatively analyzing the contribution of the NO pathway to microvascular vasomotor function.

Acute exposure to diesel exhaust impairs nitric oxide-mediated endothelial vasomotor function by increasing endothelial oxidative stress

Exposure to diesel exhaust was recently identified as an important cardiovascular risk factor, but whether it impairs nitric oxide (NO)-mediated endothelial function and increases production of reactive oxygen species (ROS) in endothelial cells is not known. We tested these hypotheses in a randomized, controlled, crossover study in healthy male volunteers exposed to ambient and polluted air (n=12). The effects of skin microvascular hyperemic provocative tests, including local heating and iontophoresis of acetylcholine and sodium nitroprusside, were assessed using a laser Doppler imager. Before local heating, skin was pretreated by iontophoresis of either a specific NO-synthase inhibitor (L-N-arginine-methyl-ester) or a saline solution (Control). ROS production was measured by chemiluminescence using the lucigenin technique in human umbilical vein endothelial cells preincubated with serum from 5 of the subjects. Exposure to diesel exhaust reduced acetylcholine-induced vasodilation (P<0.01) but did not affect vasodilation with sodium nitroprusside. Moreover, the acetylcholine/sodium nitroprusside vasodilation ratio decreased from 1.51 ± 0.1 to 1.06 ± 0.07 (P<0.01) and was correlated to inhaled particulate matter 2.5 (r=-0.55; P<0.01). NO-mediated skin thermal vasodilatation decreased from 466 ± 264% to 29 ± 123% (P<0.05). ROS production was increased after polluted air exposure (P<0.01) and was correlated with the total amount of inhaled particulate matter <2.5 μm (PM2.5). In healthy subjects, acute experimental exposure to diesel exhaust impaired NO-mediated endothelial vasomotor function and promoted ROS generation in endothelial cells. Increased PM2.5 inhalation enhances microvascular dysfunction and ROS production.

Microvascular dysfunction: a potential mechanism in the pathogenesis of obesity-associated insulin resistance and hypertension

The intertwined epidemics of obesity and related disorders such as hypertension, insulin resistance, type 2 diabetes, and subsequent cardiovascular disease pose a major public health challenge. To meet this challenge, we must understand the interplay between adipose tissue and the vasculature. Microvascular dysfunction is important not only in the development of obesity-related target-organ damage but also in the development of cardiovascular risk factors such as hypertension and insulin resistance. The present review examines the role of microvascular dysfunction as an explanation for the associations among obesity, hypertension, and impaired insulin-mediated glucose disposal. We also discuss communicative pathways from adipose tissue to the microcirculation.

Evaluation of systemic microvascular endothelial function using laser speckle contrast imaging

OBJECTIVE

The aim of this study was to compare cutaneous microvascular function in young healthy subjects (n=50) with that of cardiometabolic diseased patients (n=50) using laser speckle contrast imaging (LSCI) coupled with transdermal iontophoretic delivery of acetylcholine (ACh) and post-occlusive reactive hyperemia (PORH).

METHODS

Cutaneous blood flow was assessed in the forearm using LSCI at rest, during PORH and during iontophoresis of ACh with increasing anodal currents of 30, 60, 90, 120, 150 and 180 μA during 10-second intervals spaced 1 min apart.

RESULTS

Endothelium-dependent skin microvascular vasodilator responses induced by both ACh and PORH were significantly reduced in cardiometabolic diseased patients compared to healthy subjects. Vasodilator responses induced by ACh were significantly higher in young women than in young men. Iontophoresis charges up to 1.5 mC do not induce nonspecific effects on skin microvascular flux.

CONCLUSION

LSCI appears to be a promising noninvasive technique for evaluating systemic microvascular endothelial function.

Matsuda-DeFronzo insulin sensitivity index is a better predictor than HOMA-IR of hypertension in Japanese: the Tanno-Sobetsu study

Here we examined whether the Matsuda-DeFronzo insulin sensitivity index (ISI-M) is more efficient than the homeostasis model assessment of insulin resistance (HOMA-IR) for assessing risk of hypertension. Cross-sectional and longitudinal analyses were conducted using normotensive subjects who were selected among 1399 subjects in the Tanno-Sobetsu cohort. In the cross-sectional analysis (n=740), blood pressure (BP) level was correlated with HOMA-IR and with ISI-M, but correlation coefficients indicate a tighter correlation with ISI-M. Multiple linear regression analysis adjusted by age, sex, body mass index (BMI) and serum triglyceride level (TG) showed contribution of ISI-M and fasting plasma glucose, but not of HOMA-IR. In the longitudinal analysis (n=607), 241 subjects (39.7%) developed hypertension during a 10-year follow-up period, and multiple logistic regression indicated that age, TG, systolic BP and ISI-M, but not HOMA-IR, were associated with development of hypertension. In subjects <60 years old, odds ratio of new-onset hypertension was higher in the low ISI-M group (ISI-M, less than the median) than in the high ISI-M group for any tertile of BMI. In conclusion, ISI-M is a better predictor of hypertension than is HOMA-IR. Non-hepatic IR may be a determinant, which is independent of TG, BP level and BMI, of the development of hypertension.

Repeatability of the evaluation of systemic microvascular endothelial function using laser doppler perfusion monitoring: clinical and statistical implications

OBJECTIVE

An awareness of the repeatability of biological measures is required to properly design and calculate sample sizes for longitudinal interventional studies. We investigated the day-to-day repeatability of measures of systemic microvascular reactivity using laser Doppler perfusion monitoring.

METHODS

We performed laser Doppler perfusion monitoring in combination with skin iontophoresis using acetylcholine and sodium nitroprusside as well as post-occlusive reactive and thermal hyperemia twice within two weeks. The repeatability was assessed by calculating the within-subject standard deviations, limits of agreement, typical errors and intra-class correlation coefficients between days 1 and 2. The ratio of the within-subject standard deviation to the mean values obtained on days 1 and 2 (within-subject standard deviation/GM) was used to determine the condition with the best repeatability.

RESULTS

Twenty-four healthy subjects, aged 24.6 ± 3.8 years, were recruited. The area under the curve of the vasodilatory response to post-occlusive reactivity showed marked variability (within-subject standard deviation/GM = 0.83), while the area under the curve for acetylcholine exhibited less variability (within-subject standard deviation/ GM = 0.52) and was comparable to the responses to sodium nitroprusside and thermal treatment (within-subject standard deviations/GM of 0.67 and 0.56, respectively). The area under the blood flow/time curve for vasodilation during acetylcholine administration required the smallest sample sizes, the area under the blood flow/time curve during post-occlusive reactivity required the largest sample sizes, and the area under the blood flow/time curves of vasodilation induced by sodium nitroprusside and thermal treatment required intermediate sizes.

CONCLUSIONS

In view of the importance of random error related to the day-to-day repeatability of laser Doppler perfusion monitoring, we propose an original and robust statistical methodology for use in designing prospective clinical studies.

Reduction in skin microvascular density and changes in vessel morphology in patients treated with sunitinib

Hypertension is a common side effect in cancer patients treated with inhibitors of vascular endothelial growth factor/vascular endothelial growth factor receptor-2 signaling and may represent a marker of clinical benefit. Functional rarefaction (a decrease in perfused microvessels) or structural rarefaction (a reduction in anatomic capillary density) may play an important role in the development of hypertension. We investigated whether sunitinib caused impairment of microvascular function and/or reduction of capillary density in patients with metastatic renal cell cancer (mRCC). Sixteen mRCC patients were treated with sunitinib (50 mg/day). Assessments of 24-h ambulatory blood pressure, microvascular endothelial function by laser Doppler fluxmetry, and capillary density by capillary microscopy were performed at baseline and days 14 and 28. Median blood pressure had increased on day 14 (systolic 10 mmHg, P<0.01 and diastolic blood pressure 8 mmHg, P<0.01). Capillary density had decreased from 69 to 61 capillaries/mm (P<0.01). This decrease was related to the increase in systolic and diastolic blood pressure (r=-0.57, P<0.05 and r=-0.68, P<0.01, respectively). A more pronounced decrease in capillary density was associated with increased visibility of the subpapillary plexus (P=0.041). Preliminary findings indicated that median progression-free survival was significantly prolonged in patients with a greater than 6 capillaries/mm decrease in density as compared with patients with a less pronounced decrease (P=0.044). In conclusion, reduction in skin capillary density is associated with a rise in blood pressure during sunitinib therapy and, by itself, might be useful as a predictive marker of clinical outcome.

Age-related change in endothelial and microvessel function and therapeutic consequences

As the absolute numbers and proportion of older adults increases across most of the developed world, a greater understanding of the aetiopathogenic mechanisms of the increased vascular risk and their therapeutic implications becomes essential to all clinicians assessing and managing the geriatric patient. The role of endothelial function and the microcirculation is increasingly recognized in the maintenance of adequate perfusion, and their dysfunction is thought to be an early and potentially reversible mechanism by which age acts to increase cardiovascular risk.

Here we review evidence that altered microvascular function appears before other recognized predictors of vascular disease, and progresses from childhood to late adult life, preceding fulminant atherosclerotic or arteriosclerotic disease. Low birth-weight babies have reduced endothelial function in skin microvessels at 3 months, and by age ten brachial artery endothelial function is reduced in comparison with normal birth-weight babies. In overweight/obese adolescent children with clustering of traditional cardiovascular disease risk factors, endothelial function is lower compared with normal weight children and this appears to persist into early adulthood. Adult ageing is associated with impaired microvessel endothelial function and an increase in capillary blood pressure, independent of brachial artery blood pressure. Biological and lifestyle factors that influence microvessel function include body fat and visceral adiposity, sex hormone status, diet and physical activity.

Exploration of the therapeutic implications for management of endothelial dysfunction remains in embryonic state. The use of ACE-inhibitors, angiotensin receptor blockers and direct renin inhibitors in patients with evidence of microvascular damage such as retinopathy and microalbuminuria has been established; however, in the general older population the benefit has yet to be established. Therefore current recommendations are to screen for microvascular damage and if present target treatments after control of other vascular risk factors such as hypertension.

Associations of metabolic factors, especially serum retinol-binding protein 4 (RBP4), with blood pressure in Japanese--the Tanno and Sobetsu study

Excess secretion of various adipocyte-derived molecules has been linked with insulin resistance, obesity, diabetes, inflammation, atherosclerosis, and cardiovascular disease. Retinol-binding protein 4 (RBP4), one of the new adipocytokine, is recently reported to provide a link between insulin resistance and features of metabolic factors. Hypertension is one of the most influential risk factors among cardiovascular disease. We examined the relationship between systolic blood pressure (BP) levels and metabolic factors including homeostasis model assessment of insulin resistance (HOMA-R), high sensitivity c-reactive protein (hs-CRP), adiponectin, and RBP4. The subjects were 153 men aged 59 ± 14 years and 224 women aged 57 ± 14 years who had undergone medical check-ups in rural communities in 2007. Systolic BP was positively correlated with HOMA-R, hs-CRP and RBP4 but not with adiponectin in women. There was a positive significant relationship between serum RBP4 levels and blood pressure in women, but such a relationship was not found in men. Serum RBP4 levels were not correlated with HOMA-R in either men or women. Serum RBP4 levels negatively were correlated with estimated glomerular filtration rate (eGFR) in women but not in men. Multiple regression analysis revealed that serum RBP4 levels significantly were related to systolic BP independently of age, sex, body mass index (BMI), total cholesterol levels and eGFR. Our study showed that increased levels of RBP4 as well as HOMA-R and hs-CRP in women were significantly associated with increased levels of systolic BP.

Human endothelial function and microvascular ageing

Age is a primary risk factor for cardiovascular disease, and this is an increasingly important public health concern because of an increase in the absolute number and proportion of the population at an older age in many countries. A key component of cardiovascular ageing is reduced function of the vascular endothelium, and this probably contributes to the impaired microvessel function observed with ageing in multiple vascular beds. In turn, impaired microvessel function is thought to contribute to the pathophysiology of cardiovascular and metabolic diseases. Here we review evidence that the first signs of altered endothelial and microvessel function can appear in childhood and at all stages of the human lifespan; low-birth-weight babies have reduced endothelial function in skin microvessels at 3 months, and by age 10 years their brachial artery endothelial function is reduced in comparison with normal-birth-weight babies. In overweight/obese adolescent children with clustering of traditional cardiovascular disease risk factors, endothelial function is reduced compared with normal-weight children, and this appears to persist into early adulthood. Adult ageing is associated with impaired microvessel endothelial function and an increase in capillary blood pressure. Biological and lifestyle factors that influence microvessel function include body fat and visceral adiposity, sex hormone status, diet and physical activity. The mechanisms underlying age-associated changes in microvessel function are uncertain but may involve alterations in nitric oxide, prostanoid, endothelium-derived hyperpolarizing factor(s) and endothelin-1 pathways.

Birth weight relates to salt sensitivity of blood pressure in healthy adults

The association between birth weight and blood pressure is well established but at present unexplained. According to the Borst-Guyton concept, chronic hypertension can occur only with a shift in the renal pressure-natriuresis relationship resulting in increased salt sensitivity of blood pressure. We assessed salt sensitivity of blood pressure in a group of 27 healthy adults whose birth weight was available. Birth weight was ascertained from birth certificates or announcements. Salt sensitivity of blood pressure was determined as difference in mean arterial pressure (MAP) between a 1-week high-salt ( approximately 235 mmol NaCl/d) versus low-salt diet ( approximately 55 mmol NaCl/d). Creatinine clearance was estimated according to the formula of Cockcroft and Gault. Birth weight was negatively associated with salt sensitivity of blood pressure (r=-0.60, P=0.002). The creatinine clearance was positively associated with birth weight (r=0.53; P=0.008) but did not influence the association between birth weight and salt sensitivity of blood pressure. Birth weight is associated with salt sensitivity of blood pressure, and this may play a role in the maintenance of elevated blood pressure in individuals with a low birth weight.

Hypertension and microvascular remodelling

In the present review, microvascular remodelling refers to alterations in the structure of resistance vessels contributing to elevated systemic vascular resistance in hypertension. We start with some historical aspects, underscoring the importance of Folkow's contribution made half a century ago. We then move to some basic concepts on the biomechanics of blood vessels, and explicit the definitions proposed by Mulvany for specific forms of remodelling, especially inward eutrophic and inward hypertrophic. The available evidence for the existence of remodelled resistance vessels in hypertension comes next, with relatively more weight given to human, in comparison with animal data. Mechanisms are discussed. The impact of antihypertensive drug treatment on remodelling is described, again with emphasis on human data. Some details are given on the three studies to date which point to remodelling of subcutaneous resistance arteries as an independent predictor of cardiovascular risk in hypertensive patients. We terminate by considering the potential role of remodelling in the pathogenesis of end-organ damage and in the perpetuation of hypertension.

Salt, the kidneys, and arterial hypertension

The kidneys play a major role in the regulation of the salt balance and thereby regulate blood pressure. Salt sensitivity is acquired or genetically-induced and is noted in about 50% of patients with essential hypertension. This property leads to a high cardiovascular risk. In this situation, the benefit of salt restriction is significant, and this dietary change should be associated with a high potassium intake. In patients treated by antihypertensive drugs, salt restriction improves the blood pressure control, which can permit a reduction of the number of drugs required to achieve a normal blood pressure. The recommended maximal salt intake should not exceed 6 grams/day (NaCl). Because most dietary salt comes from processed foods, the help of the food industry is crucial for a long-term compliance with a reduced salt intake, which could yield an additional important benefit in the reduction of cardiovascular risk.