Assessment of chronic radiation proctopathy and radiofrequency ablation treatment follow-up with optical coherence tomography angiography: A pilot study

BACKGROUND

Chronic radiation proctopathy (CRP) occurs as a result of pelvic radiation therapy and is associated with formation of abnormal vasculature that may lead to persistent rectal bleeding. While incidence is declining due to refinement of radiation delivery techniques, CRP remains one of the major complications of pelvic radiation therapy and significantly affects patient quality of life. Radiofrequency ablation (RFA) is an emerging treatment modality for eradicating abnormal vasculature associated with CRP. However, questions remain regarding CRP pathophysiology and optimal disease management.

AIM

To study feasibility of optical coherence tomography angiography (OCTA) for investigating subsurface vascular alterations in CRP and response to RFA treatment.

METHODS

Two patients with normal rectum and 8 patients referred for, or undergoing endoscopic RFA treatment for CRP were imaged with a prototype ultrahigh-speed optical coherence tomography (OCT) system over 15 OCT/colonoscopy visits (2 normal patients, 5 RFA-naïve patients, 8 RFA-follow-up visits). OCT and OCTA was performed by placing the OCT catheter onto the dentate line and rectum without endoscopic guidance. OCTA enabled depth-resolved microvasculature imaging using motion contrast from flowing blood, without requiring injected dyes. OCTA features of normal and abnormal microvasculature were assessed in the mucosa and submucosa. Blinded reading of OCTA images was performed to assess the association of abnormal rectal microvasculature with CRP and RFA treatment, and rectal telangiectasia density endoscopic scoring.

RESULTS

OCTA/OCT images are intrinsically co-registered and enabled depth-resolved visualization of microvasculature in the mucosa and submucosa. OCTA visualized normal vascular patterns with regular honeycomb patterns vs abnormal vasculature with distorted honeycomb patterns and ectatic/tortuous microvasculature in the rectal mucosa. Normal arterioles and venules < 200 μm in diameter versus abnormal heterogenous enlarged arterioles and venules > 200 μm in diameter were visualized in the rectal submucosa. Abnormal mucosal vasculature occurred in 0 of 2 normal patients and 3 of 5 RFA-naïve patients, while abnormal submucosal vasculature occurred more often, in 1 of 2 normal patients and 5 of 5 RFA-naïve patients. After RFA treatment, vascular abnormalities decreased, with abnormal mucosal vasculature observed in 0 of 8 RFA-follow-up visits and abnormal submucosal vasculature observed in only and 2 of 8 RFA-follow-up visits.

CONCLUSION

OCTA visualizes depth-resolved microvascular abnormalities in CRP, allowing assessment of superficial features which are endoscopically visible as well as deeper vasculature which cannot be seen endoscopically. OCTA/OCT of the rectum can be performed in conjunction with, or independently from endoscopy. Further studies are warranted to investigate if OCTA/OCT can elucidate pathophysiology of CRP or improve management.

Inertial Cavitation Ultrasound with Microbubbles Improves Reperfusion Efficacy When Combined with Tissue Plasminogen Activator in an In Vitro Model of Microvascular Obstruction

We have previously reported that long-tone-burst, high-mechanical-index ultrasound (US) and microbubble (MB) therapy can restore perfusion in both in vitro and in vivo models of microvascular obstruction (MVO). Addition of MBs to US has been found to potentiate the efficacy of thrombolytics on large venous thrombi; however, the optimal US parameters for achieving microvascular reperfusion of MVO caused by microthrombi, when combined with tissue plasminogen activator (tPA), are unknown. We sought to elucidate the specific effects of US, with and without tPA, for effective reperfusion of MVO in an in vitro model using both venous and arterial microthrombi. Venous- and arterial-type microthrombi were infused onto a mesh with 40-μm pores to simulate MVO. Pulsed US (1 MHz) was delivered with inertial cavitation (IC) (1.0 MPa, 1000 cycles, 0.33 Hz) and stable cavitation (SC) US (0.23 MPa, 20% duty cycle, 0.33 Hz) regimes while MB suspension (2 × 106 MBs/mL) was infused. The efficacy of sonoreperfusion with these parameters was tested with and without tPA. Sonoreperfusion efficacy was significantly greater for IC + tPA compared with tPA alone, IC, SC and SC + tPA, suggesting lytic synergism between tPA and US for both venous- and arterial-type microthrombi. In contrast to our previous in vitro studies using 1.5 MPa at 5000 US cycles without tPA, the IC regime employed herein used 90% less US energy. These findings suggest an IC regime can be used with tPA synergistically to achieve a high degree of fibrinolysis for both thrombus types.

Fractionated abdominal irradiation induces intestinal microvascular changes in an in vivo model of radiotherapy-induced gut toxicity

PURPOSE

Radiotherapy-induced gut toxicity (RIGT) is associated with diarrhoea, pain and rectal bleeding and can occur as an acute or chronic toxicity. The microvasculature has been shown to be altered in the development of RIGT; however, the features are not yet characterized. We hypothesized that apoptosis of microvascular cells would occur early in the gastrointestinal tract following fractionated irradiation, followed by late microvascular changes, including sclerosis and telangiectasis.

METHODS

Female Dark Agouti rats were treated with a 6-week fractionated radiation schedule of 3 × 2.5 Gy doses per week localized to the abdomen. At 3, 6 and 15 weeks, the intestines were assessed for markers of acute and chronic injury including morphological changes, collagen deposition, apoptosis and proliferation.

RESULTS

Apoptosis of microvascular cells significantly increased at 6 and 15 weeks in the jejunum (p = 0.0026 and p = 0.0062, respectively) and at 6 and 15 weeks in the colon (p < 0.0001 and p = 0.0005, respectively) in rats receiving fractionated radiation to the abdomen. Histopathological changes of the colon microvasculature were also seen from week 3, including thickening of the lamina propria and dilated, thickened, telangiectatic vessels.

CONCLUSIONS

Findings of this study provide evidence of regional and timing-specific changes in the intestinal microvasculature in response to fractionated radiotherapy which may play a role in development of both acute and chronic RIGT.

Computational modelling of the cerebral cortical microvasculature: effect of x-ray microbeams versus broad beam irradiation

Microbeam Radiation Therapy is an innovative pre-clinical strategy which uses arrays of parallel, tens of micrometres wide kilo-voltage photon beams to treat tumours. These x-ray beams are typically generated on a synchrotron source. It was shown that these beam geometries allow exceptional normal tissue sparing from radiation damage while still being effective in tumour ablation. A final biological explanation for this enhanced therapeutic ratio has still not been found, some experimental data support an important role of the vasculature. In this work, the effect of microbeams on a normal microvascular network of the cerebral cortex was assessed in computer simulations and compared to the effect of homogeneous, seamless exposures at equal energy absorption. The anatomy of a cerebral microvascular network and the inflicted radiation damage were simulated to closely mimic experimental data using a novel probabilistic model of radiation damage to blood vessels. It was found that the spatial dose fractionation by microbeam arrays significantly decreased the vascular damage. The higher the peak-to-valley dose ratio, the more pronounced the sparing effect. Simulations of the radiation damage as a function of morphological parameters of the vascular network demonstrated that the distribution of blood vessel radii is a key parameter determining both the overall radiation damage of the vasculature and the dose-dependent differential effect of microbeam irradiation.

3D surface analysis of hippocampal microvasculature in the irradiated brain

Cranial irradiation used to control CNS malignancies can also disrupt the vasculature and impair neurotransmission and cognition. Here we describe two distinct methodologies for quantifying early and late radiation injury in CNS microvasculature. Intravascular fluorescently labeled lectin was used to visualize microvessels in the brain of the irradiated mouse 2 days post exposure and RECA-1 immunostaining was similarly used to visualize microvessels in the brain of the irradiated rat 1-month post exposure. Confocal microscopy, image deconvolution and 3-dimensional rendering methods were used to define vascular structure in a ∼4 × 10(7) μm(3) defined region of the brain. Quantitative analysis of these 3D images revealed that irradiation caused significant short- and long-term reductions in capillary density, diameter and volume. In mice, irradiation reduced mean vessel volume from 2,250 to 1,470 μm(3) and mean vessel diameter from 5.0 to 4.5 μm, resulting in significant reductions of 34% and 10%, in the hippocampus respectively. The number of vessel branch points and area was also found to also drop significantly in mice 2 days after irradiation. For rats, immunostaining revealed a significant, three-fold drop in capillary density 1 month after exposure compared to controls. Such radiation-induced disruption of the CNS microvasculature may be contributory if not causal to any number of neurocognitive side effects that manifest in cancer patients following cranial radiotherapy. This study demonstrates the utility of two distinct methodologies for quantifying these important adverse effects of radiotherapy. Environ. Mol. Mutagen. 57:341-349, 2016. © 2016 Wiley Periodicals, Inc.

Effects of chronic low-dose exposure to ionizing radiation on physician microvascular structure revealed by nail fold capillaroscopy

The aim of this study was to assess the long-term asymptomatic effects of low-dose radiation on microvascular structure among interventional physicians, whose hands are exposed to ionizing radiation during daily practice. The study, approved by the national ethics committee, included 186 radiation-exposed (surgeons, cardiologists, radiologists) and 35 unexposed physicians, all of whom had provided written consent. The subjects completed a questionnaire describing their current and past daily practice, from which tentative estimates of current and cumulative radiation exposure estimates were computed. Subject dermal microcirculation state was assessed by capillaroscopy of the nail fold of eight fingers (thumbs excluded) based on photographs. Two quantitative scores characterizing extravasation and morphological abnormalities based on seven semiquantitative indices were obtained from post hoc coding of the photographs by five capillaroscopists. These evaluations were randomized and blind to the exposure. The effect of the radiation exposure on both abnormality scores was modelled using multilevel proportional odds regression adjusted for potential confounders. The proportion of physicians for which the most frequent act is close to the radiation source was highest among surgeons, but with fewer weekly acts. The median duration of exposure was highest among radiologists and cardiologists. No exposure effect could be detected on the extravasation score. The morphological anomaly score increased significantly with duration of exposure and estimated cumulative exposure among surgeons and interventional radiologists, unlike cardiologists among whom no effect could be detected. It is concluded that the shown effects of chronic low-dose exposure to ionizing radiation on physician microvascular structure reveal the importance of increased exposure monitoring and prevention.

Ionizing radiation induces immediate protein acetylation changes in human cardiac microvascular endothelial cells

Reversible lysine acetylation is a highly regulated post-translational protein modification that is known to regulate several signaling pathways. However, little is known about the radiation-induced changes in the acetylome. In this study, we analyzed the acute post-translational acetylation changes in primary human cardiac microvascular endothelial cells 4 h after a gamma radiation dose of 2 Gy. The acetylated peptides were enriched using anti-acetyl conjugated agarose beads. A total of 54 proteins were found to be altered in their acetylation status, 23 of which were deacetylated and 31 acetylated. Pathway analyses showed three protein categories particularly affected by radiation-induced changes in the acetylation status: the proteins involved in the translation process, the proteins of stress response, and mitochondrial proteins. The activation of the canonical and non-canonical Wnt signaling pathways affecting actin cytoskeleton signaling and cell cycle progression was predicted. The protein expression levels of two nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases, sirtuin 1 and sirtuin 3, were significantly but transiently upregulated 4 but not 24 h after irradiation. The status of the p53 protein, a target of sirtuin 1, was found to be rapidly stabilized by acetylation after radiation exposure. These findings indicate that post-translational modification of proteins by acetylation and deacetylation is essentially affecting the radiation response of the endothelium.

New model for long-term investigations of cutaneous microcirculatory and inflammatory changes following irradiation

Radiotherapy is used for curative and palliative treatment. However, its negative effect on normal tissue is a limiting factor for the deliverable dose. Microcirculatory breakdown and prolonged inflammation in particular are major features of late side effects. The purpose of this study was to develop a reliable animal model that will allow a long-term in vivo analysis of microcirculation and inflammation following irradiation. A single dose of 90 Gy was delivered to the ears of hairless mice (n = 15). Intravital fluorescent microscopy was used to assess microcirculatory parameters and leukocyte behaviour. Values for the identical (control) areas were obtained before as well as during the following days, weeks and months following irradiation. The arteriolar and venular diameter increased up to Day 14, decreased during the following months, and increased again after one year. The red blood cell velocity increased up to 145% on Day 3, decreased on Day 7 to 115%, and stayed above baseline value the whole year. The integrity loss of the endothelium increased up to Day 7 and continued up to Day 75 after radiation. After one year, the oedema was at the baseline level. Leukocytes showed their maximal activity at one year after trauma. An increase was measured up to Day 25; the lowest values were measured at Day 40 post-irradiation, followed by a repeated increase. The present model allows a certain visualization of microcirculatory disturbances and inflammation over a period of months. This permits the possibility of long-term investigations of the underlying pathophysiology following irradiation, including possible drug interactions.

[Effects of small ionizing radiation doses on hemato-encephalic barrier permeability]

Goal and objectives of the study was comparative description and establishment of dose-time dependence of changes in permeability of the hemato-encephalic barrier (HEB) in phylogenetically different parts of the brain cortex, i.e. new (Fr2 and Cg3), old (hippocampal fields CA1-CA4 and dentate fascia) and paleocortex (piriform cortex) following exposure to 0.1; 0.2; 0.5 and 1 Gy of ionizing radiation (dose rate = 50 cGy). Dependence of microvessels permeability on dose, post-exposure time and cortex phylogenetic age was established. Changes in brain microvessels, in the phylogenetically young cortex in particular, produced by 0.5 Gy and 1 Gy remained uncompensated till the end of investigation. Pronounced changes persisted over the period of one year after radiation exposure; complete recovery was not observed even in the phylogenetically old cortex.

Whole brain radiation-induced vascular cognitive impairment: mechanisms and implications

Mild cognitive impairment is a well-documented consequence of whole brain radiation therapy (WBRT) that affects 40-50% of long-term brain tumor survivors. The exact mechanisms for the decline in cognitive function after WBRT remain elusive and no treatment or preventative measures are available for use in the clinic. Here, we review recent findings indicating how changes in the neurovascular unit may contribute to the impairments in learning and memory. In addition to affecting neuronal development, WBRT induces profound capillary rarefaction within the hippocampus - a region of the brain important for learning and memory. Therapeutic strategies such as hypoxia, which restore the capillary density, result in the rescue of cognitive function. In addition to decreasing vascular density, WBRT impairs vasculogenesis and/or angiogenesis, which may also contribute to radiation-induced cognitive decline. Further studies aimed at uncovering the specific mechanisms underlying these WBRT-induced changes in the cerebrovasculature are essential for developing therapies to mitigate the deleterious effects of WBRT on cognitive function.

External beam radiotherapy for head and neck cancers is associated with increased variability in retinal vascular oxygenation

BACKGROUND

Radiation retinopathy is a possible post-treatment complication of radiation therapy. The pathophysiologic mechanism is hypothesized to be microvascular in origin, but evidence is limited. In an effort to study retinal oxygenation in these patients, we herein evaluate the repeatability and variability of retinal oximetry measurements in subjects who had previously received radiation and make comparisons to a cohort of unirradiated subjects.

METHODS

Using retinal oximetry, a non-invasive imaging modality, we performed in vivo measurements of arteriole (SaO2) and venule SO2 (SvO2) in subjects (n = 9, 18 retinas) who had received incidental radiation to their retinas (≥ 45 Gy to one retina) and in healthy subjects (n = 20, 40 retinas). A total of 1367 SO2 observations on 593 vessels in 29 persons were analyzed to assess three sources of variance in vessel SO2: 1) variance in repeated measurements of the same vessel ("repeatability"), 2) variance in different vessels within the same subject ("within-subject variability"), and 3) variance between subjects ("between-subject variability").

RESULTS

Retinal oximetry measurements were highly repeatable in both irradiated patients and unirradiated subjects. The within-subject variability of SvO2 and SaO2 measurements constituted the highest component of variance in both groups and was significantly higher in venules vs. arterioles (relative effect size 1.8, p<0.001) and in irradiated subjects vs. unirradiated subjects (relative effect size 1.6, p<0.001).

CONCLUSIONS

Retinal oximetry is a highly repeatable technology and can be reliably used to study vascular oxygenation in irradiated subjects. Different vessels within the same subject exhibit a high degree of variability, suggesting that pooled analyses of multiple vessels are most likely to be informative of regional retinal oxygenation. Finally, irradiated subjects exhibited significantly higher within-subject variability in SO2 measurements, suggesting that radiation may cause regional alterations in retinal oxygen delivery and/or metabolism.

[Modeling of different degrees of microvessel laser-induced endothelium damage]

A comparative analysis of rat mesentery micro vascular reactions on thermal impact during radiation to the focused laser irradiation in UV and visible regions of spectrum is made. Local intravascular temperature rise during laser irradiation both impulse (lambda = 337 nm) and continuous (lambda = 532 nm) states causes thrombus formation. The thrombus development that determined by laser irradiation parameters gives a possibility to modulate different degrees of microvessel endothelium damage.

In vivo optical imaging of tumor and microvascular response to ionizing radiation

Radiotherapy is a widely used cancer treatment. However, understanding how ionizing radiation affects tumor cells and their vasculature, particularly at cellular, subcellular, genetic, and protein levels, has been limited by an inability to visualize the response of these interdependent components within solid tumors over time and in vivo. Here we describe a new preclinical experimental platform combining intravital multimodal optical microscopy for cellular-level longitudinal imaging, a small animal x-ray microirradiator for reproducible spatially-localized millimeter-scale irradiations, and laser-capture microdissection of ex vivo tissues for transcriptomic profiling. Using this platform, we have developed new methods that exploit the power of optically-enabled microscopic imaging techniques to reveal the important role of the tumor microvasculature in radiation response of tumors. Furthermore, we demonstrate the potential of this preclinical platform to study quantitatively--with cellular and sub-cellular details--the spatio-temporal dynamics of the biological response of solid tumors to ionizing radiation in vivo.

High-resolution in-vivo analysis of normal brain response to cranial irradiation

Radiation therapy (RT) is a widely accepted treatment strategy for many central nervous system (CNS) pathologies. However, despite recognized therapeutic success, significant negative consequences are associated with cranial irradiation (CR), which manifests months to years post-RT. The pathophysiology and molecular alterations that culminate in the long-term detrimental effects of CR are poorly understood, though it is thought that endothelial injury plays a pivotal role in triggering cranial injury. We therefore explored the contribution of bone marrow derived cells (BMDCs) in their capacity to repair and contribute to neo-vascularization following CR. Using high-resolution in vivo optical imaging we have studied, at single-cell resolution, the spatio-temporal response of BMDCs in normal brain following CR. We demonstrate that BMDCs are recruited specifically to the site of CR, in a radiation dose and temporal-spatial manner. We establish that BMDCs do not form endothelial cells but rather they differentiate predominantly into inflammatory cells and microglia. Most notably we provide evidence that more than 50% of the microglia in the irradiated region of the brain are not resident microglia but recruited from the bone marrow following CR. These results have invaluable therapeutic implications as BMDCs may be a primary therapeutic target to block acute and long-term inflammatory response following CR. Identifying the critical steps involved in the sustained recruitment and differentiation of BMDCs into microglia at the site of CR can provide new insights into the mechanisms of injury following CR offering potential therapeutic strategies to counteract the long-term adverse effects of CR.

Combined-modality radioimmunotherapy: synergistic effect of paclitaxel and additive effect of bevacizumab

INTRODUCTION

This study was undertaken to investigate the effect of paclitaxel and bevacizumab on the therapeutic efficacy of (90)Y-labeled B3 monoclonal antibody, directed against Le(y) antigen, for the treatment of Le(y)-positive A431 tumors implanted subcutaneously in the right hind flank of nude mice.

METHODS

When the tumor size reached ~200 mm(3), the mice received a single dose of intravenous (iv) (90)Y-labeled B3 (60 μCi/150 μg or 100 μCi/150 μg B3), intraperitoneal paclitaxel (40 mg/kg) or iv bevacizumab (5 mg/kg) for monotherapy. To investigate the effect of combined therapies on survival, the mice were treated with two or three agents in the following combinations: (90)Y-B3 on day 0 and paclitaxel on day 1; bevacizumab on -1 day and (90)Y-B3 on day 0; bevacizumab on -1 day and paclitaxel on day 1; bevacizumab, (90)Y-B3 and paclitaxel each at 1-day intervals. The mice with no treatment were used as a control. The tumor volume at 1000 mm(3) was used as a surrogate end point of survival.

RESULTS

Compared to control animals, paclitaxel delayed tumor growth with a significantly longer median survival time (P<.001), whereas bevacizumab alone showed a less pronounced effect on a median survival time (P=.18). (90)Y-B3 increased the median survival time in a dose-dependent manner (P<.05). The combined therapy of bevacizumab with paclitaxel produced a trend toward an increase of the median survival time compared to paclitaxel alone (P=.06), whereas bevacizumab combined with (90)Y-B3 showed a statistically insignificant increase in the median survival time compared to (90)Y-B3 alone (P=.25). The tumor sizes of all animals in these groups reached the surrogate end point of survival by day 35. In contrast, the combined therapy involving (90)Y-B3 with paclitaxel showed a striking synergistic effect in shrinking tumors and prolonging the survival time (P<.001); on day 120, three of nine mice (33%) and six of six mice (100%) were alive without tumor when treated with 60 μCi (90)Y-B3 and 100 μCi (90)Y-B3, respectively. The addition of bevacizumab treatment 1 day before the combined therapy of 60 μCi (90)Y-B3 with paclitaxel did not produce a statistically significant increase in survival when compared to the (90)Y-B3 with paclitaxel (P>.10). Fluorescence microscopy analysis indicated that paclitaxel increased, whereas bevacizumab decreased, the accumulation and penetration of Alexa Fluor 647-B3 into tumor microenvironment compared to the control (P<.05).

CONCLUSION

Our findings on the paclitaxel effect support a hypothesis that the increased tumor accumulation and penetration of (90)Y-B3 as well as the high radiosensitization of tumor cells by paclitaxel may be the major factors responsible for the synergistic effect of the combined therapy involving (90)Y-B3 with paclitaxel.

Phase II study of neoadjuvant bevacizumab and radiotherapy for resectable soft tissue sarcomas

PURPOSE

Numerous preclinical studies have demonstrated that angiogenesis inhibitors can increase the efficacy of radiotherapy (RT). We sought to examine the safety and efficacy of bevacizumab (BV) and RT in soft tissue sarcomas and explore biomarkers to help determine the treatment response.

METHODS AND MATERIALS

Patients with ≥5 cm, intermediate- or high-grade soft tissue sarcomas at significant risk of local recurrence received neoadjuvant BV alone followed by BV plus RT before surgical resection. Correlative science studies included analysis of the serial blood and tumor samples and serial perfusion computed tomography scans.

RESULTS

The 20 patients had a median tumor size of 8.25 cm, with 13 extremity, 1 trunk, and 6 retroperitoneal/pelvis tumors. The neoadjuvant treatment was well tolerated, with only 4 patients having Grade 3 toxicities (hypertension, liver function test elevation). BV plus RT resulted in ≥80% pathologic necrosis in 9 (45%) of 20 tumors, more than double the historical rate seen with RT alone. Three patients had a complete pathologic response. The median microvessel density decreased 53% after BV alone (p <.05). After combination therapy, the median tumor cell proliferation decreased by 73%, apoptosis increased 10.4-fold, and the blood flow, blood volume, and permeability surface area decreased by 62-72% (p <.05). Analysis of gene expression microarrays of untreated tumors identified a 24-gene signature for treatment response. The microvessel density and circulating progenitor cells at baseline and the reduction in microvessel density and plasma soluble c-KIT with BV therapy also correlated with a good pathologic response (p <.05). After a median follow-up of 20 months, only 1 patient had developed local recurrence.

CONCLUSIONS

The results from the present exploratory study indicated that BV increases the efficacy of RT against soft tissue sarcomas and might reduce the incidence of local recurrence. Thus, this regimen warrants additional investigation. Gene expression profiles and other tissue and circulating biomarkers showed promising correlations with treatment response.

Spatial frequency-based analysis of mean red blood cell speed in single microvessels: investigation of microvascular perfusion in rat cerebral cortex

Background

Our previous study has shown that prenatal exposure to X-ray irradiation causes cerebral hypo-perfusion during the postnatal development of central nervous system (CNS). However, the source of the hypo-perfusion and its impact on the CNS development remains unclear. The present study developed an automatic analysis method to determine the mean red blood cell (RBC) speed through single microvessels imaged with two-photon microscopy in the cerebral cortex of rats prenatally exposed to X-ray irradiation (1.5 Gy).

Methodology/Principal Findings

We obtained a mean RBC speed (0.9±0.6 mm/sec) that ranged from 0.2 to 4.4 mm/sec from 121 vessels in the radiation-exposed rats, which was about 40% lower than that of normal rats that were not exposed. These results were then compared with the conventional method for monitoring microvascular perfusion using the arteriovenous transit time (AVTT) determined by tracking fluorescent markers. A significant increase in the AVTT was observed in the exposed rats (1.9±0.6 sec) as compared to the age-matched non-exposed rats (1.2±0.3 sec). The results indicate that parenchyma capillary blood velocity in the exposed rats was approximately 37% lower than in non-exposed rats.

Conclusions/Significance

The algorithm presented is simple and robust relative to monitoring individual RBC speeds, which is superior in terms of noise tolerance and computation time. The demonstrative results show that the method developed in this study for determining the mean RBC speed in the spatial frequency domain was consistent with the conventional transit time method.

Noninvasive monitoring of radiation-induced early therapeutic response using high-resolution MR imaging and proton MR spectroscopy in VX2 carcinoma

The purpose of this study was to evaluate the usefulness of high-resolution MRI (HR-MRI) and proton MR spectroscopy ((1)H-MRS) for monitoring the early therapeutic response to radiotherapy. Twenty rabbits with VX2 carcinoma were divided into control (n = 8) and irradiation (n = 12) groups. The irradiation group underwent HR-MRI and (1)H-MRS using a microscopy coil at 1, 3, 7 or 14 days after irradiation. Rabbits in the control group were subjected to HR-MRI and (1)H-MRS at the same time intervals. All rabbits were killed after imaging and subjected to histopathologic examinations. The diameter of necrosis by HR-MRI was then compared to that on the gross specimens. The ratios of choline/creatine (Cho/Cr) and lactate/creatine (Lac/Cr) on the tumor and necrotic area detected by in vivo (1)H-MRS were compared between the control and irradiation groups, respectively. In addition, the ratios of Cho/Cr and Lac/Cr were compared between the tumor and necrotic area in each irradiation group. A significant correlation was found between the diameter of necrosis in each sequence of HR-MRI and that in the gross specimens (r = 0.84-0.91, p = 0.03- < 0.003). The ratios of Lac/Cr in the tumors of the irradiation groups were significantly higher than those in the control groups after 1 day and 3 days of irradiation (p = 0.04, and p = 0.02). Histological analysis showed necrosis and swelling of the endothelia of capillaries and arterioles at 1 day and 3 days after irradiation. It was suggested that HR-MRI and (1)H-MRS are useful methods for monitoring the early therapeutic response to radiotherapy.

Longitudinal, multimodal functional imaging of microvascular response to photothermal therapy

Although studies have shown that photothermal therapy can coagulate selectively abnormal vasculature, the ability of this method to achieve consistent, complete removal of the vasculature is questionable. We present the use of multimodal, wide-field functional imaging to study, in greater detail, the biological response to selective laser injury. Specifically, a single-platform instrument capable of coregistered fluorescence imaging and laser speckle imaging was utilized to monitor vascular endothelial growth factor gene expression and blood flow, respectively, in a transgenic rodent model. Collectively, the longitudinal, in vivo data collected with our instrument suggest that the biological response to selective laser injury involves early-stage redistribution of blood flow, followed by increased vascular endothelial growth factor promoter activity to stimulate pro-angiogenic events.

Effect of irradiation on microvascular endothelial cells of parotid glands in the miniature pig

PURPOSE

To evaluate the effect of irradiation on microvascular endothelial cells in miniature pig parotid glands.

METHODS AND MATERIALS

A single 25-Gy dose of irradiation (IR) was delivered to parotid glands of 6 miniature pigs. Three other animals served as non-IR controls. Local blood flow rate in glands was measured pre- and post-IR with an ultrasonic Doppler analyzer. Samples of parotid gland tissue were taken at 4 h, 24 h, 1 week, and 2 weeks after IR for microvascular density (MVD) analysis and sphingomyelinase (SMase) assay. Histopathology and immunohistochemical staining (anti-CD31 and anti-AQP1) were used to assess morphological changes. MVD was determined by calculating the number of CD31- or AQP1-stained cells per field. A terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) apoptosis assay was used to detect apoptotic cells. The activity of acid and neutral Mg(2+)-dependent SMase (ASMase and NSMase, respectively) was also assayed.

RESULTS

Local parotid gland blood flow rate decreased rapidly at 4 h post-IR and remained below control levels throughout the 14-day observation period. Parotid MVD also declined from 4 to 24 hours and remained below control levels thereafter. The activity levels of ASMase and NSMase in parotid glands increased rapidly from 4 to 24 h post-IR and then declined gradually. The frequency of detecting apoptotic nuclei in the glands followed similar kinetics.

CONCLUSIONS

Single-dose IR led to a significant reduction of MVD and local blood flow rate, indicating marked damage to microvascular endothelial cells in miniature pig parotid glands. The significant and rapid increases of ASMase and NSMase activity levels may be important in this IR-induced damage.

Development of a porcine delayed wound-healing model and its use in testing a novel cell-based therapy

PURPOSE

A delayed full-thickness wound-healing model was developed and used for examining the capacity of adipose-derived stem cells (ASCs), either alone or in platelet-rich fibrin gels, to promote healing.

METHODS AND MATERIALS

Four pigs received electron beam radiation to the dorsal skin surface. Five weeks after radiation, subcutaneous fat was harvested from nonirradiated areas and processed to yield ASCs. Two weeks later, 28 to 30 full-thickness 1.5-cm(2) wounds were made in irradiated and nonirradiated skin. Wounds were treated with either saline solution, ASCs in saline solution, platelet-rich plasma (PRP) fibrin gel, ASCs in PRP, or non-autologous green fluorescence protein-labeled ASCs.

RESULTS

The single radiation dose produced a significant loss of dermal microvasculature density (75%) by 7 weeks. There was a significant difference in the rate of healing between irradiated and nonirradiated skin treated with saline solution. The ASCs in PRP-treated wounds exhibited a significant 11.2% improvement in wound healing compared with saline solution. Enhancement was dependent on the combination of ASCs and PRP, because neither ASCs nor PRP alone had an effect.

CONCLUSIONS

We have created a model that simulates the clinically relevant late radiation effects of delayed wound healing. Using this model, we showed that a combination of ASCs and PRP improves the healing rates of perfusion-depleted tissues, possibly through enhancing local levels of growth factors.

[Peptidergic regulation of the pancreas function in the experimental model of rats with accelerated aging]

This study was devoted to the evaluation of morphofunctional alterations in the pancreas in the conditions of physiological and premature aging using the experimental model of irradiation-induced aging, and the possibility of peptidergic regulation of age-related alterations in the pancreas was also studied. Age-related alterations in the pancreas of old animals in the conditions of physiological aging were revealed in the form of dystrophic alterations of main cell populations, disordered microcirculatory vascular channels and reduced level of physiological regeneration of this organ. In the conditions of irradiation-induced premature aging the above mentioned manifestations of dystrophic alterations in the pancreas tissue were found to be more pronounced. Administration of tripeptide T-38 (Lys-Glu-Asp) to old irradiated animals activated the processes of post-irradiation reparative regeneration, thus restoring the disordered endocrine homeostasis in the pancreas.