Microvascular Flow Rate Research Articles

Repeated passive heat treatment increases muscle tissue capillarization, but does not affect postprandial muscle protein synthesis rates in healthy older adults.

Prolonged passive heat treatment (PHT) has been suggested to trigger skeletal muscle adaptations that may improve muscle maintenance in older individuals. To assess the effects of PHT on skeletal muscle tissue capillarization, perfusion capacity, protein synthesis rates, hypertrophy and leg strength, 14 older adults (9males, 5 females; 73 ± 6years) underwent 8weeks of PHT (infrared sauna: 3× per week, 45min at ∼60°C). Before and after PHT we collected muscle biopsies to assess skeletal muscle capillarization and fibre cross-sectional area (CSA). Basal and postprandial muscle tissue perfusion kinetics and protein synthesis rates were assessed using contrast-enhanced ultrasound and primed continuous l-[ring-13C6]phenylalanine infusions, respectively. One-repetition maximum (1RM) leg strength and vastus lateralis muscle CSA were assessed. Type I and type II muscle fibre capillarization strongly increased following PHT (capillary-to-fibre perimeter exchange index: +31 ± 18 and +33 ± 30%, respectively; P<0.001). No changes were observed in basal (0.24 ± 0.27 vs. 0.18 ± 0.11 AU; P=0.266) or postprandial (0.20 ± 0.12 vs. 0.18 ± 0.14 AU; P=0.717) microvascular blood flow following PHT. Basal (0.048 ± 0.014 vs. 0.051 ± 0.019%/h; P=0.630) and postprandial (0.041 ± 0.012 vs. 0.051 ± 0.024%/h; P=0.199) muscle protein synthesis rates did not change in response to prolonged PHT. Furthermore, no changes in vastus lateralis muscle CSA (15.3 ± 4.6 vs. 15.2 ± 4.6 cm2; P=0.768) or 1RM leg strength (46 ± 12 vs. 47 ± 12 kg; P=0.087) were observed over time. In conclusion, prolonged PHT increases muscle tissue capillarization but this does not improve muscle microvascular blood flow or increase muscle protein synthesis rates in healthy, older adults. Prolonged PHT does not induce skeletal muscle hypertrophy or increase leg strength in healthy, older adults. KEY POINTS: Repeated exposure to heat has been suggested to trigger skeletal muscle adaptive responses. We investigated the effect of 8weeks of whole-body passive heat treatment (PHT; infrared sauna: 3× per week for 45min at ∼60°C) on skeletal muscle tissue capillarization, perfusion capacity, basal, and postprandial muscle protein synthesis rates, muscle (fibre) hypertrophy, and leg strength in healthy, older adults. Prolonged PHT increases muscle tissue capillarization, but this does not improve muscle microvascular blood flow or increase muscle protein synthesis rates. Despite increases in muscle tissue capillarization, prolonged PHT does not suffice to induce skeletal muscle hypertrophy or increase leg strength in healthy, older adults.

Ultrasound super-resolution imaging for the assessment of renal allograft dysfunction: A pilot study

BackgroundThe purpose of this study was to examine the feasibility and practical application of ultrasound (US) super-resolution imaging (SRI) in evaluating microvasculature and measuring renal allograft function. MethodsSixteen consecutive patients who received kidney transplants were prospectively enrolled. The patients were assigned as: normal allograft function (n = 6), and allograft malfunction (n = 10). Localizing each potential contrast signal resulted in super-resolution images (SRI). SRI was utilized to assess micro-vessel density (MVD) and microvascular flow rate, whereas contrast-enhanced (CE) US images were statistically processed to get the time to peak (TTP) and peak intensity. Logistic regression was utilized to evaluate their relationship. ResultsUS SRI may be utilized effectively on allografts to show microvasculature with significantly higher resolution than typical color Doppler flow and CEUS pictures. In the multivariate analysis, MVD and TTP were significant US markers of renal allograft failure (p = 0.031 and p = 0.045). The combination of MVD and TTP produced an AUC of 0.783 (p < 0.05) for allograft dysfunction. ConclusionsSRI can accurately portray the microvasculature of renal allografts, while MVD and TTP are appropriate US markers for assessing renal allograft failure.

Microcirculation, endothelium and glycocalyx changes associated with the use of milrinone in children with septic shock.

The goal of fluid resuscitation and the use of inotropes in septic shock has traditionally focused on improving blood pressure and cardiac output, without considering the microcirculatory changes. Reaching macrocirculatory goals but with persistent microcirculatory abnormalities (hemodynamic incoherence) in septic shock has been associated with greater organ dysfunction and mortality. The objective of this study was to evaluate the microcirculation (flow and capillary density) and endothelial glycocalyx changes associated with the use of milrinone in children with septic shock, as well as their relationship with clinical variables and organ dysfunction. A prospective cohort study from February 2022 to January 2023 at a university hospital (Fundación Cardioinfantil-Instituto de Cardiología). Sublingual video microscopy was used to evaluate capillary density, microvascular flow rates and perfused boundary region (PBR-inverse parameter of glycocalyx thickness-abnormal if >2.0 microns). The primary outcome was the association between microcirculation and endothelial glycocalyx changes related to the use of milrinone. A total of 140 children with a median age of two years [interquartile range (IQR) 0.58-12.1] were included. About 57.9% (81/140) of the patients received milrinone infusions. Twenty-four hours after receiving milrinone, the patients maintained functional capillary density (P<0.01) and capillary recruitment capacity (P=0.04) with no changes in capillary blood volume versus those who did not receive milrinone. Children under two years old who received milrinone had better 4-6-micron capillary density than older children [odds ratio (OR) 0.33; 95% confidence interval (95% CI): 0.12-0.89; P=0.02] and less endothelial glycocalyx degradation [adjusted OR (aOR) 0.34 95% CI: 0.11-0.99; P=0.04]. These changes persisted despite elevated ferritin (aOR 0.41; 95% CI: 0.18-0.93; P=0.03). Prolonged capillary refill and elevated lactate were correlated with microcirculation changes in both groups. The patients who died had the highest PBR levels (P=0.04). Children with septic shock who receive milrinone infusions have microcirculation changes compared with those who do not receive them. The group that received milrinone was found to maintain functional capillary density and capillary recruitment capacity and have less endothelial glycocalyx degradation 24 hours after administration. These changes were present despite the inflammatory response and were more significant in those under two years of age.

Effect of Ultrasound Pulse Length on Sonoreperfusion Therapy.

In recent years, long- and short-pulse ultrasound (US)-targeted microbubble cavitation (UTMC) has been found to increase perfusion in healthy and ischemic skeletal muscle, in pre-clinical animal models of microvascular obstruction and in the myocardium of patients presenting with acute myocardial infarction. There is evidence that the observed microvascular vasodilation is driven by the nitric oxide pathway and purinergic signaling, but the time course of the response and the dependency on US pulse length are not well elucidated. Because our prior data supported that sonoreperfusion efficacy is enhanced by long-pulse US versus short-pulse US, in this study, we sought to compare long-pulse (5000 cycles) and short-pulse (500×10 cycles) US at a pressure of 1.5 MPa with an equivalent total number of acoustical cycles, hence constant acoustic energy, and at the same frequency (1 MHz), in a rodent hind limb model with and without microvascular obstruction (MVO). In quantifying perfusion using burst replenishment contrast-enhanced US imaging, we made three findings: (i) Long and short pulses result in different vasodilation kinetics in an intact hind limb model. The long pulse causes an initial spasmic reduction in flow that spontaneously resolved at 4 min, followed by sustained higher flow rates (approximately twofold) compared with baseline, starting 10 min after therapy (p < 0.05). The short pulse caused a short-lived approximately twofold increase in flow rate that peaked at 4 min (p < 0.05), but without the initial spasm. (ii) The sustained increased response with the long pulse is not simply reactive hyperemia. (iii) Both pulses are effective in reperfusion of MVO in our hindlimb model by restoring blood volume, but only the long pulse caused an increase in flow rate after treatment ii, compared with MVO (p < 0.05). Histological analysis of hind limb muscle post-UTMC with either pulse configuration indicates no evidence of tissue damage or hemorrhage. Our findings indicate that the microbubble oscillation induces vasodilation, and therapeutic efficacy for the treatment of MVO can be tuned by varying pulse length; relative to short-pulse US, longer pulses drive greater microbubble cavitation and more rapid microvascular flow rate restoration after MVO, warranting further optimization of the pulse length for sonoreperfusion therapy.

Abstract 14673: The Effect of Increasing the Ultrasound Pulse Length on Sonoreperfusion Therapy

Background: In recent years, long and short pulse ultrasound (US)-targeted microbubble cavitation (UTMC) has been shown to increase perfusion in healthy and ischemic skeletal muscle, in pre-clinical animal models of microvascular obstruction, and in the myocardium of patients presenting with acute myocardial infarction, and microvascular vasodilation played an important role in its efficacy. Our prior preliminary data suggested that long pulse US confers enhanced sonoreperfusion efficacy compared to short pulse US. Objective: In this study, we sought to definitively compare acoustic energy matched, long (5000 cycles) and short pulse (500 х 10 cycles, separated by 100 μs intervals) US (pressure of 1.5 MPa with an equivalent total number of acoustical cycles and at the same frequency (1 MHz)), in a rodent hindlimb model, with and without microvascular obstruction (MVO). Results: By quantifying perfusion using burst replenishment contrast enhanced US imaging, we found that: (1) long and short pulses result in different vasodilation kinetics in an intact hindlimb model. The long pulse causes an initial reduction in flow due to microvascular spasm that spontaneously resolved at 4-min, followed by sustained higher flow rates (~2-folds) compared to baseline, starting 10 min after therapy ( p &lt;0.05). The short pulse caused a short-lived ~2-fold increase in flow rate that peaked at 4-min ( p &lt;0.05), but without the initial microvascular spasm; (2) the sustained increase in perfusion during long pulse is not simply reactive hyperemia; and (3) both pulses are effective in reperfusion of MVO in our hindlimb model by restoring blood volume, but only the long pulse caused an increase in flow rate after treatment 2, compared to MVO ( p &lt;0.05). Histological analysis post UTMC with either pulse configuration indicates no evidence of tissue damage or hemorrhage. Conclusions: Our findings demonstrate that the microbubble oscillation induces vasodilation and therapeutic efficacy for the treatment of MVO can be tuned by varying pulse length; relative to short pulse US, longer pulses drive greater microbubble cavitation and more rapid microvascular flow rate restoration after MVO, warranting further optimization of the pulse length for sonoreperfusion therapy.

Ultrasound super-resolution imaging for differential diagnosis of breast masses.

Ultrasound imaging has been widely used in breast cancer screening. Recently, ultrasound super-resolution imaging (SRI) has shown the capability to break the diffraction limit to display microvasculature. However, the application of SRI on differential diagnosis of breast masses remains unknown. Therefore, this study aims to evaluate the feasibility and clinical value of SRI for visualizing microvasculature and differential diagnosis of breast masses. B mode, color-Doppler flow imaging (CDFI) and contrast-enhanced ultrasound (CEUS) images of 46 patients were collected respectively. SRI were generated by localizations of each possible contrast signals. Micro-vessel density (MVD) and microvascular flow rate (MFR) were calculated from SRI and time to peak (TTP), peak intensity (PI) and area under the curve (AUC) were obtained by quantitative analysis of CEUS images respectively. Pathological results were considered as the gold standard. Independent chi-square test and multivariate logistic regression analysis were performed using these parameters to examine the correlation. The results showed that SRI technique could be successfully applied on breast masses and display microvasculature at a significantly higher resolution than the conventional CDFI and CEUS images. The results showed that the PI, AUC, MVD and MFR of malignant breast masses were significantly higher than those of benign breast masses, while TTP was significantly lower than that of benign breast masses. Among all five parameters, MVD showed the highest positive correlation with the malignancy of breast masses. SRI is able to successfully display the microvasculature of breast masses. Compared with CDFI and CEUS, SRI can provide additional morphological and functional information for breast masses. MVD has a great potential in assisting the differential diagnosis of breast masses as an important imaging marker.

Ultrasound super-resolution imaging for the differential diagnosis of thyroid nodules: A pilot study.

Ultrasound imaging provides a fast and safe examination of thyroid nodules. Recently, the introduction of super-resolution imaging technique shows the capability of breaking the Ultrasound diffraction limit in imaging the micro-vessels. The aim of this study was to evaluate its feasibility and value for the differentiation of thyroid nodules. In this study, B-mode, contrast-enhanced ultrasound, and color Doppler flow imaging examinations were performed on thyroid nodules in 24 patients. Super-resolution imaging was performed to visualize the microvasculature with finer details. Microvascular flow rate (MFR) and micro-vessel density (MVD) within thyroid nodules were computed. The MFR and MVD were used to differentiate the benign and malignant thyroid nodules with pathological results as a gold standard. Super-resolution imaging (SRI) technique can be successfully applied on human thyroid nodules to visualize the microvasculature with finer details and obtain the useful clinical information MVD and MFR to help differential diagnosis. The results suggested that the mean value of the MFR within benign thyroid nodule was 16.76 ± 6.82 mm/s whereas that within malignant thyroid was 9.86 ± 4.54 mm/s. The mean value of the MVD within benign thyroid was 0.78 while the value for malignant thyroid region was 0.59. MFR and MVD within the benign thyroid nodules were significantly higher than those within the malignant thyroid nodules respectively (p < 0.01). This study demonstrates the feasibility of ultrasound super-resolution imaging to show micro-vessels of human thyroid nodules via a clinical ultrasound platform. The important imaging markers, such as MVD and MFR, can be derived from SRI to provide more useful clinical information. It has the potential to be a new tool for aiding differential diagnosis of thyroid nodules.

INOCA affects more than the coronaries

Abstract Background Ischaemia with normal coronary arteries (INOCA) may result in disabling symptoms and has an association with adverse long-term prognosis. The diagnosis of INOCA necessitates invasive coronary angiography to perform a physiological evaluation of microvascular function. The conjunctiva has a readily assessable microvascular network in which physiological parameters can be evaluated. We compared conjunctival haemodynamics in patients with and without coronary microvascular disease (MVD) to assess if systemic microvascular dysfunction was present in this coronary artery disease sub-group. Methods In this study, we recruited patients undergoing invasive coronary angiography for the investigation of angina or angina equivalent symptoms. All patients had physiologically insignificant epicardial disease (FFR≥0.80) and underwent a physiological evaluation of coronary microvascular function. We compared a group with evidence of coronary MVD (IMR≥25 or CFR&amp;lt;2.0); to a group of controls without MVD (IMR&amp;lt;25 and CFR≥2.0). The conjunctival microvasculature was imaged using a previously validated combination of a smartphone and slit-lamp biomicroscope. The conjunctival vasculature was assessed using a semi-automated process of vessel diameter measurement and erythrocyte tracking to obtain haemodynamic parameters of microvascular function. Results A total of 111 patients were included (43 MVD and 68 controls). There were no differences in baseline demographics, co-morbidities, epicardial coronary disease severity or regular pharmacological therapies between the groups. Mean coronary flow reserve (CFR) was lower and mean index of microcirculatory resistance (IMR) higher in the MVD cohort (CFR 2.5±1.3 vs 5.2±2.5, p&amp;lt;0.001 and IMR 28.4±11.8 vs 13.7±5.0, p&amp;lt;0.001). A total of 2295 conjunctival vessels were analysed. The mean number of vessels per patient was 21.0±12.8 (3.2±3.5 arterioles and 14.8±10.8 venules). Significant reductions in axial/cross-sectional velocity, wall shear rate and wall shear stress were observed in the MVD cohort. Table 1 demonstrates a comparison of conjunctival physiological parameters between the groups. The most marked differences were observed in conjunctival arterioles. Due to the heterogenous size distribution of microvessels, arterioles were categorised into 2 diameter sub-groups (10–25 μm and 25–40 μm) for analysis (Table 2). Conclusion The reductions in microvascular blood flow velocity and rate that form the basis for the diagnosis of coronary microvascular dysfunction can be observed non-invasively in the bulbar conjunctiva microcirculation. Conjunctival vascular imaging may have utility as a non-invasive imaging modality to both diagnose microvascular dysfunction and augment conventional cardiovascular risk stratification. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): Belfast Trust Heart Trust Fund and Northern Ireland Chest Heart and Stroke

Coronary Flow Assessment Using 3-Dimensional Ultrafast Ultrasound Localization Microscopy

BackgroundDirect assessment of the coronary microcirculation has long been hampered by the limited spatial and temporal resolutions of cardiac imaging modalities. ObjectivesThe purpose of this study was to demonstrate 3-dimensional (3D) coronary ultrasound localization microscopy (CorULM) of the whole heart beyond the acoustic diffraction limit (<20 μm resolution) at ultrafast frame rate (>1000 images/s). MethodsCorULM was performed in isolated beating rat hearts (N = 6) with ultrasound contrast agents (Sonovue, Bracco), using an ultrasonic matrix transducer connected to a high channel–count ultrafast electronics. We assessed the 3D coronary microvascular anatomy, flow velocity, and flow rate of beating hearts under normal conditions, during vasodilator adenosine infusion, and during coronary occlusion. The coronary vasculature was compared with micro-computed tomography performed on the fixed heart. In vivo transthoracic CorULM was eventually assessed on anaesthetized rats (N = 3). ResultsCorULM enables the 3D visualization of the coronary vasculature in beating hearts at a scale down to microvascular structures (<20 μm resolution). Absolute flow velocity estimates range from 10 mm/s in tiny arterioles up to more than 300 mm/s in large arteries. Fitting to a power law, the flow rate–radius relationship provides an exponent of 2.61 (r2 = 0.96; P < 0.001), which is consistent with theoretical predictions and experimental validations of scaling laws in vascular trees. A 2-fold increase of the microvascular coronary flow rate is found in response to adenosine, which is in good agreement with the overall perfusion flow rate measured in the aorta (control measurement) that increased from 8.80 ± 1.03 mL/min to 16.54 ± 2.35 mL/min (P < 0.001). The feasibility of CorULM was demonstrated in vivo for N = 3 rats. ConclusionsCorULM provides unprecedented insights into the anatomy and function of coronary arteries at the microvasculature level in beating hearts. This new technology is highly translational and has the potential to become a major tool for the clinical investigation of the coronary microcirculation.

Dynamic diagnosis of early gastric cancer with microvascular blood flow rate using magnifying endoscopy (with video): A pilot study.

Background and AimMagnifying endoscopy (ME) diagnostic algorithm for early gastric cancer (EGC) relies on qualitative features such as microvascular (MV) architecture and microsurface structure; however, it is a “static” diagnostic algorithm that uses still images. ME can visualize red blood cell flow within subepithelial microvessels in real time. Here, we evaluated the utility of using the MV blood flow rate in combination with ME for the diagnosis of EGC as a retrospective study.MethodsPatients with differentiated‐type EGC (n = 10) or patchy redness (n = 10) underwent ME with blue laser imaging. The mean MV blood flow rates of EGC, patchy redness, and background mucosa were calculated by the mean movement distance of one tagging red blood cell using split images of ME with blue laser imaging videos. We compared the mean MV blood flow rate between EGC, patchy redness, and background mucosa and also calculated the MV blood flow imaging ratio (inside lesion/background mucosa) between EGC and patchy redness.ResultsMean MV blood flow rate was significantly lower in EGC (1481 μm/s; range 1057–1762) than in patchy redness (3859 μm/s; 2435–5899) or background mucosa (4140.6 μm/s; 2820–6247) (P < 0.01). The MV blood flow imaging ratio was significantly lower in EGC (0.39; 0.27–0.62) than in patchy redness (0.90; 0.78–1.1) (P < 0.01).ConclusionsDynamic diagnosis with MV blood flow rate using ME may be useful for the differential diagnosis of EGC and patchy redness. Endoscopic assessment of dynamic processes within the gastric mucosa may facilitate the diagnosis of EGC.

Vaso-Occlusion in Sickle Cell Disease: Is Autonomic Dysregulation of the Microvasculature the Trigger?

Sickle cell disease (SCD) is an inherited hemoglobinopathy characterized by polymerization of hemoglobin S upon deoxygenation that results in the formation of rigid sickled-shaped red blood cells that can occlude the microvasculature, which leads to sudden onsets of pain. The severity of vaso-occlusive crises (VOC) is quite variable among patients, which is not fully explained by their genetic and biological profiles. The mechanism that initiates the transition from steady state to VOC remains unknown, as is the role of clinically reported triggers such as stress, cold and pain. The rate of hemoglobin S polymerization after deoxygenation is an important determinant of vaso-occlusion. Similarly, the microvascular blood flow rate plays a critical role as fast-moving red blood cells are better able to escape the microvasculature before polymerization of deoxy-hemoglobin S causes the red cells to become rigid and lodge in small vessels. The role of the autonomic nervous system (ANS) activity in VOC initiation and propagation has been underestimated considering that the ANS is the major regulator of microvascular blood flow and that most triggers of VOC can alter the autonomic balance. Here, we will briefly review the evidence supporting the presence of ANS dysfunction in SCD, its implications in the onset of VOC, and how differences in autonomic vasoreactivity might potentially contribute to variability in VOC severity.

1219 Usefulness of Blood Flow Rate of Subepithelial Microvessels in Gastric Mucosa Using Magnifying Endoscopy in the Stomach

INTRODUCTION: Magnifying endoscopy simple diagnostic algorithm for early gastric cancer (MESDA-G) is used for qualitative diagnosis based on irregular microvascular architecture and micro-surface structure, but it is a static diagnostic algorithm using still images. On the other hand, magnifying endoscopy (ME) visualizes subepithelial microvascular red blood cell (RBC) flow in real time, but there has been no study focusing on the usefulness of microvascular blood flow in the diagnosis of early gastric cancer. We therefore evaluated microvascular blood flow using ME in the diagnosis of early gastric cancer. METHODS: Patients with early gastric cancer (EGC, n = 5) or patchy redness (PR, n = 5) underwent ME with blue light imaging (M-BLI, EG-L600ZW7, Fujifilm) at our hospital. A scale in 1-mm increments was visualized at 100× (3 frames) to 135× (4 frames) magnifications prior to examination, and gastric subepithelial microvascular blood flow in lesions and background mucosa videoed using M-BLI. Images were split into 30 frames/sec, and the mean blood flow rate was calculated by the mean movement distance of one tagging RBC. The blood flow rates in EGC, PR and background mucosa were compared between them. The ratio of blood flow rate (inside lesion/background mucosa) was compared between EGC and PR. RESULTS: EGC characteristics were as follows: mean age, 74.6 ± 7.8 years; male/female ratio, 2:3; previous history (hypertension: 1); Helicobacter pylori infection (current: 3, eradicated: 2); location (M: 4, L: 1); macroscopic type (IIa: 3, IIc: 2); histology (well- [n = 4] and moderately differentiated [n = 1] adenocarcinoma); and invasion depth (all M). PR characteristics were as follows: mean age, 68.2 ± 10 years; male/female ratio, 4:1; previous history (hypertension: 3); H. pylori infection (eradicated: 5); location (M: 2, L: 4). The mean blood flow rate was significantly slower in EGC (1881.4 μm/s; range 1406–2344) vs. PR (4162.6 μm/s; 3281–4688) or background mucosa (4265.7 μm/s; 3750–5156) (P &lt; 0.01). The ratio of blood flow rate (inside lesion/background mucosa) was significantly lower in EGC (0.46; 0.38–0.50) than in PR (0.94; 0.88–1.10; P &lt; 0.01). CONCLUSION: Early gastric cancer was associated with a significantly slower gastric subepithelial microvascular flow rate compared to patchy redness and background mucosa. Gastric subepithelial microvascular flow using magnifying endoscopy in real time may enable physiological diagnosis of early gastric cancer.

Novel Noninvasive Assessment of Microvascular Structure and Function in Humans.

Optical coherence tomography (OCT) is a novel high-resolution imaging technique capable of visualizing in vivo structures at a resolution of ~10 μm. We have developed specialized OCT-based approaches that quantify diameter, speed, and flow rate in human cutaneous microvessels. In this study, we hypothesized that OCT-based microvascular assessments would possess comparable levels of reliability when compared with those derived using conventional laser Doppler flowmetry (LDF). Speckle decorrelation images (OCT) and red blood cell flux (LDF) measures were collected from adjacent forearm skin locations on 2 d (48 h apart), at baseline, and after a 30-min rapid local heating protocol (30°C-44°C) in eight healthy young individuals. OCT postprocessing quantified cutaneous microvascular diameter, speed, flow rate, and density (vessel recruitment) within a region of interest, and data were compared between days. Forearm skin LDF (13 ± 4 to 182 ± 31 AU, P < 0.05) and OCT-derived diameter (41.8 ± 6.6 vs 64.5 ± 6.9 μm), speed (68.4 ± 9.5 vs 89.0 ± 7.3 μm·s), flow rate (145.0 ± 60.6 vs 485 ± 132 pL·s), and density (9.9% ± 4.9% vs 45.4% ± 5.9%) increased in response to local heating. The average OCT-derived microvascular flow response (pL·s) to heating (234% increase) was lower (P < 0.05) than the LDF-derived change (AU) (1360% increase). Pearson correlation was significant for between-day local heating responses in terms of OCT flow (r = 0.93, P < 0.01), but not LDF (P = 0.49). Bland-Altman analysis revealed that between-day baseline OCT-derived flow rates were less variable than LDF-derived flux. Our findings indicate that OCT, which directly visualizes human microvessels, not only allows microvascular quantification of diameter, speed, flow rate, and vessel recruitment but also provides outputs that are highly reproducible. OCT is a promising novel approach that enables a comprehensive assessment of cutaneous microvascular structure and function in humans.

Phenomenon of Endothelial Antibody Capture: Principles and Potential for Locoregional Targeting of Hepatic Tumors.

The systemic drug circulation represents a source of adverse effects during tumor targeting. We studied the binding efficacy of endothelium-specific antibodies after a very short contact with an antigen target, along with assessing the intravascular capture and targeting potential of these antibodies after locoregional injection. Fast-binding anti-CD 146 (clone ME-9F1) and anti-CD31 (clone 390) antibodies were selected based on histological analysis of their binding activity. The efficacy of antibody capture by hepatic endothelium under different conditions was analyzed using an isolated liver perfusion model. The local enrichment of R-phycoerythrin and 125 I-conjugated antibody was studied in vivo in two hepatic tumor models using biodistribution, scintigraphic imaging, and fluorescence microscopy. Upon injection into the tumor-feeding artery, the antibody was immediately captured in the microvasculature during the first passage. At doses not exceeding the saturation level of endothelial epitopes, the capture efficacy was almost 90%. We showed that the efficacy of endothelial capture is controlled by factors such as antibody affinity, number of binding sites on the endothelium, and microvascular flow rate. The targeting potential of endothelial capture was experimentally proven in vivo using scintigraphic imaging and biodistribution analysis after locoregional intra-arterial injection of 125 I-labeled antibodies in hepatic tumor models. Conclusion: The unique phenomenon of endothelial capture can broadly prevent systemic circulation of the antibody or antibody-drug conjugates applied by intravascular injection and may have specific relevance for targeting of hepatic tumors.

Dynamic contrast enhanced MRI detects changes in vascular transport rate constants following treatment with thermally-sensitive liposomal doxorubicin

Temperature-sensitive liposomal formulations of chemotherapeutics, such as doxorubicin, can achieve locally high drug concentrations within a tumor and tumor vasculature while maintaining low systemic toxicity. Further, doxorubicin delivery by temperature-sensitive liposomes can reliably cure local cancer in mouse models. Histological sections of treated tumors have detected red blood cell extravasation within tumors treated with temperature-sensitive doxorubicin and ultrasound hyperthermia. We hypothesize that the local release of drug into the tumor vasculature and resulting high drug concentration can alter vascular transport rate constants along with having direct tumoricidal effects. Dynamic contrast enhanced MRI (DCE-MRI) coupled with a pharmacokinetic model can detect and quantify changes in such vascular transport rate constants. Here, we set out to determine whether changes in rate constants resulting from intravascular drug release were detectable by MRI. We found that the accumulation of gadoteridol was enhanced in tumors treated with temperature-sensitive liposomal doxorubicin and ultrasound hyperthermia. While the initial uptake rate of the small molecule tracer was slower (k1=0.0478±0.011s−1 versus 0.116±0.047s−1) in treated compared to untreated tumors, the tracer was retained after treatment due to a larger reduction in the rate of clearance (k2=0.291±0.030s−1 versus 0.747±0.24s−1). While DCE-MRI assesses a combination of blood flow and permeability, ultrasound imaging of microvascular flow rate is sensitive only to changes in vascular flow rate; based on this technique, blood flow was not significantly altered 30min after treatment. In summary, DCE-MRI provides a means to detect changes that are associated with treatment by thermally-activated particles and such changes can be exploited to enhance local delivery.

Clonal Variants of Plasmodium falciparum Exhibit a Narrow Range of Rolling Velocities to Host Receptor CD36 under Dynamic Flow Conditions

Cytoadhesion of Plasmodium falciparum parasitized red blood cells (pRBCs) has been implicated in the virulence of malaria infection. Cytoadhesive interactions are mediated by the protein family of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1). The PfEMP1 family is under strong antibody and binding selection, resulting in extensive sequence and size variation of the extracellular domains. Here, we investigated cytoadhesion of pRBCs to CD36, a common receptor of P. falciparum field isolates, under dynamic flow conditions. Isogeneic parasites, predominantly expressing single PfEMP1 variants, were evaluated for binding to recombinant CD36 under dynamic flow conditions using microfluidic devices. We tested if PfEMP1 size (number of extracellular domains) or sequence variation affected the pRBC-CD36 interaction. Our analysis showed that clonal parasite variants varied ∼5-fold in CD36 rolling velocity despite extensive PfEMP1 sequence polymorphism. In addition, adherent pRBCs exhibited a characteristic hysteresis in rolling velocity at microvascular flow rates, which was accompanied by changes in pRBC shape and may represent important adaptations that favor stable binding.

Microvascular biodistribution of L19-SIP in angiogenesis targeting strategies

IntroductionVarious strategies using L19-mediated fibronectin targeting have become useful clinical tools in anti-tumour therapy and diagnostics. The aim of our study was to characterise the microvascular biodistribution and binding process during tumour angiogenesis and after anti-angiogenic therapy. Materials and methodsSF126 glioma and F9 teratocarcinoma cells were implanted into dorsal skin fold chambers (SF126: n=4; F9: n=6). Using fluorescence and confocal intravital microscopy the biodistribution process was assessed at t=0h, t=4h and t=24h after intravenous application of Cy3-L19-SIP. Sunitinib treatment was applied for six days and microscopy was performed 2 and 6days after treatment initiation. Analysed parameters included: vascular and interstitial binding, preferential binding sites of L19-SIP, microvascular blood flow rate, microvascular permeability. Histological analysis included CD31 and DAPI. ResultsL19-SIP showed a specific and time-dependent neovascular binding with a secondary extravasation process reaching optimal vascular/interstitial binding ratio 4hours after iv administration (F9: L19-SIP: vascular binding: 74.6±14.5; interstitial binding: 46.8±12.1; control vascular: 22,2±16.6). Angiogenic sprouts were preferred binding sites (F9: L19-SIP: 188±15.5; RTV: 90.6±13.5). Anti-angiogenic therapy increased microvascular hemodynamics (SF126: Su: 106.6±13.3μl/sec; Untreated: 19.7±9.1μl/sec) and induced increased L19-SIP accumulation (SF 126: t24; Su: 92.6±2.7; Untreated: 71.9±5.9) in therapy resistant tumour vessels. ConclusionL19-SIP shows a time and blood-flow dependent microvascular biodistribution process with angiogenic sprouts as preferential binding sites followed by secondary extravasation of the antibody. Microvascular biodistribution is enhanced in anti-angiogenic-therapy resistant tumour vessels.

Photosensibilité du lupus érythémateux

Photosensitivity is one of the ARA diagnostic criteria of systemic lupus erythematosus. Sun exposure can also induce extracutaneous manifestations of the disease. Photosensitivity may be difficult to prove by history taking in lupus patients, as the delay between sun exposure and the onset of specific skin lesions is rather long. Photo-induction of lupus can occur by ultraviolet A (UVA) radiation in the shadow or behind window glass, so that the relationship between radiation exposure and exacerbation of the disease may not seem obvious to the patient. Phototesting procedures for lupus erythematosus have been described, but they are not used in routine practice. Both UVB and UVA play a role in the pathogenesis of lupus erythematosus: in the epidermis they induce DNA damage, they expose nuclear antigens and photo-induced neo-antigens at the cell surface, they lead to an accumulation of apoptotic material, and they induce several pro-inflammatory cytokines. In the dermis, UV radiation triggers skin infiltration by inflammatory cells by modulation of microvascular flow rates and by upregulation of white blood cell migration from dermal capillaries to the skin. Photodistribution of skin lesions and a delay of their onset of more than 48 hours after sun exposure are clinical hallmarks of cutaneous lupus erythematosus that are usually completed by histological confirmation. Photoprotection is essential in the treatment of lupus patients: it comprises sun avoidance suitable for both UVB and UVA radiation, protective clothing, and topical broad-spectrum filters.

Lipid-Shelled Vehicles: Engineering for Ultrasound Molecular Imaging and Drug Delivery

Ultrasound pressure waves can map the location of lipid-stabilized gas micro-bubbles after their intravenous administration in the body, facilitating an estimate of vascular density and microvascular flow rate. Microbubbles are currently approved by the Food and Drug Administration as ultrasound contrast agents for visualizing opacification of the left ventricle in echocardiography. However, the interaction of ultrasound waves with intravenously-injected lipid-shelled particles, including both liposomes and microbubbles, is a far richer field. Particles can be designed for molecular imaging and loaded with drugs or genes; the mechanical and thermal properties of ultrasound can then effect localized drug release. In this Account, we provide an overview of the engineering of lipid-shelled microbubbles (typical diameter 1000-10 000 nm) and liposomes (typical diameter 65-120 nm) for ultrasound-based applications in molecular imaging and drug delivery. The chemistries of the shell and core can be optimized to enhance stability, circulation persistence, drug loading and release, targeting to and fusion with the cell membrane, and therapeutic biological effects. To assess the biodistribution and pharmacokinetics of these particles, we incorporated positron emission tomography (PET) radioisotopes on the shell. The radionuclide (18)F (half-life approximately 2 h) was covalently coupled to a dipalmitoyl lipid, followed by integration of the labeled lipid into the shell, facilitating short-term analysis of particle pharmacokinetics and metabolism of the lipid molecule. Alternately, labeling a formed particle with (64)Cu (half-life 12.7 h), after prior covalent incorporation of a copper-chelating moiety onto the lipid shell, permits pharmacokinetic study of particles over several days. Stability and persistence in circulation of both liposomes and microbubbles are enhanced by long acyl chains and a poly(ethylene glycol) coating. Vascular targeting has been demonstrated with both nano- and microdiameter particles. Targeting affinity of the microbubble can be modulated by burying the ligand within a polymer brush layer; the application of ultrasound then reveals the ligand, enabling specific targeting of only the insonified region. Microbubbles and liposomes require different strategies for both drug loading and release. Microbubble loading is inhibited by the gas core and enhanced by layer-by-layer construction or conjugation of drug-entrapped particles to the surface. Liposome loading is typically internal and is enhanced by drug-specific loading techniques. Drug release from a microbubble results from the oscillation of the gas core diameter produced by the sound wave, whereas that from a liposome is enhanced by heat produced from the local absorption of acoustic energy within the tissue microenvironment. Biological effects induced by ultrasound, such as changes in cell membrane and vascular permeability, can enhance drug delivery. In particular, as microbubbles oscillate near a vessel wall, shock waves or liquid jets enhance drug transport. Mild heating induced by ultrasound, either before or after injection of the drug, facilitates the transport of liposomes from blood vessels to the tissue interstitium, thus increasing drug accumulation in the target region. Lipid-shelled vehicles offer many opportunities for chemists and engineers; ultrasound-based applications beyond the few currently in common use will undoubtedly soon multiply as molecular construction techniques are further refined.

Soluble Thrombomodulin Protects Ischemic Kidneys

Altered coagulation and inflammation contribute to the pathogenesis of ischemic renal injury. Thrombomodulin is a necessary factor in the anticoagulant protein C pathway and has inherent anti-inflammatory properties. We studied the effect of soluble thrombomodulin (sTM) in a hypoperfusion model of ischemic kidney injury. To markedly reduce infrarenal aortic blood flow and femoral arterial pressures, we clamped the suprarenal aorta of rats, occluding them 90%, for 60 min. Reversible acute kidney injury (AKI) occurred at 24 h in rats subjected to hypoperfusion. Histologic analysis at 24 h revealed acute tubular necrosis (ATN), and intravital two-photon microscopy showed flow abnormalities in the microvasculature and defects of endothelial permeability. Pretreatment with rat sTM markedly reduced both I-R-induced renal dysfunction and tubular histologic injury scores. sTM also significantly improved microvascular erythrocyte flow rates, reduced microvascular endothelial leukocyte rolling and attachment, and minimized endothelial permeability to infused fluorescence dextrans, assessed by intravital quantitative multiphoton microscopy. Furthermore, sTM administered 2 h after reperfusion protected against ischemia-induced renal dysfunction at 24 h and improved survival. By using an sTM variant, we also determined that the protective effects of sTM were independent of its ability to generate activated protein C. These data suggest that sTM may have therapeutic potential for ischemic AKI.