Intravascular Fluorocarbon-stabilized Microbubbles Protect Against Fatal Anemia in Rats

The impact of intravenous dodecafluoropentane on a murine model of acute lung injury

INTRODUCTION

Intravenous oxygen therapeutics present an appealing option for improving arterial oxygenation in patients with acute hypoxemic respiratory failure, while limiting iatrogenic injury from conventional respiratory management.

METHODS

We used an established two-hit murine model of acute lung injury (ARDS/VILI) to evaluate the effect of intravenous dodecafluoropentane (DDFPe) on oxygen saturation and bronchoalveolar lavage cell counts and protein levels. Twenty hours after challenge with intratracheal lipopolysaccharide, mice were intubated and ventilated with high tidal volumes (4 h) to produce acute lung injury. DDFPe (0.6 mL/kg) or saline was administered by IV bolus injection at the initiation of mechanical ventilation and again at 2 h. Oxygen saturation was measured every 15 min. Bronchoalveolar lavage was performed at the conclusion of the experiment.

RESULTS

The two-hit ARDS/VILI model produced substantial inflammatory acute lung injury reflected by markedly increased bronchoalveolar lavage (BAL) cell counts compared to BAL cell counts in spontaneous breathing controls (5.29 ± 1.50 × 10^-6 vs 0.74 ± 0.014 × 10^-6 cells/mL) Similarly, BAL protein levels were markedly elevated in ARDS/VILI-challenged mice compared with spontaneous breathing controls (1109.27 ± 223.80 vs 129.6 ± 9.75 ng/mL). We fit a linear mixed effects model that showed a significant difference in oxygen saturation over time between DDFPe-treated mice and saline-treated mice, with separation starting after the 2-h injection. DDFPe-treated ARDS/VILI-challenged mice also exhibited significant reductions in BAL cell counts but not in BAL protein.

CONCLUSION

DDFPe improves oxygen saturation in a murine model of ARDS/VILI injury with the potential for serving as an intravenous oxygen therapeutic.

Therapeutic oxygen delivery by perfluorocarbon-based colloids

After the protocol-related indecisive clinical trial of Oxygent, a perfluorooctylbromide/phospholipid nanoemulsion, in cardiac surgery, that often unduly assigned the observed untoward effects to the product, the development of perfluorocarbon (PFC)-based O₂ nanoemulsions ("blood substitutes") has come to a low. Yet, significant further demonstrations of PFC O₂-delivery efficacy have continuously been reported, such as relief of hypoxia after myocardial infarction or stroke; protection of vital organs during surgery; potentiation of O₂-dependent cancer therapies, including radio-, photodynamic-, chemo- and immunotherapies; regeneration of damaged nerve, bone or cartilage; preservation of organ grafts destined for transplantation; and control of gas supply in tissue engineering and biotechnological productions. PFC colloids capable of augmenting O₂ delivery include primarily injectable PFC nanoemulsions, microbubbles and phase-shift nanoemulsions. Careful selection of PFC and other colloid components is critical. The basics of O₂ delivery by PFC nanoemulsions will be briefly reminded. Improved knowledge of O₂ delivery mechanisms has been acquired. Advanced, size-adjustable O₂-delivering nanoemulsions have been designed that have extended room-temperature shelf-stability. Alternate O₂ delivery options are being investigated that rely on injectable PFC-stabilized microbubbles or phase-shift PFC nanoemulsions. The latter combine prolonged circulation in the vasculature, capacity for penetrating tumor tissues, and acute responsiveness to ultrasound and other external stimuli. Progress in microbubble and phase-shift emulsion engineering, control of phase-shift activation (vaporization), understanding and control of bubble/ultrasound/tissue interactions is discussed. Control of the phase-shift event and of microbubble size require utmost attention. Further PFC-based colloidal systems, including polymeric micelles, PFC-loaded organic or inorganic nanoparticles and scaffolds, have been devised that also carry substantial amounts of O₂. Local, on-demand O₂ delivery can be triggered by external stimuli, including focused ultrasound irradiation or tumor microenvironment. PFC colloid functionalization and targeting can help adjust their properties for specific indications, augment their efficacy, improve safety profiles, and expand the range of their indications. Many new medical and biotechnological applications involving fluorinated colloids are being assessed, including in the clinic. Further uses of PFC-based colloidal nanotherapeutics will be briefly mentioned that concern contrast diagnostic imaging, including molecular imaging and immune cell tracking; controlled delivery of therapeutic energy, as for noninvasive surgical ablation and sonothrombolysis; and delivery of drugs and genes, including across the blood-brain barrier. Even when the fluorinated colloids investigated are designed for other purposes than O₂ supply, they will inevitably also carry and deliver a certain amount of O₂, and may thus be considered for O₂ delivery or co-delivery applications. Conversely, O₂-carrying PFC nanoemulsions possess by nature a unique aptitude for ¹⁹F MR imaging, and hence, cell tracking, while PFC-stabilized microbubbles are ideal resonators for ultrasound contrast imaging and can undergo precise manipulation and on-demand destruction by ultrasound waves, thereby opening multiple theranostic opportunities.

Treatment of Swine Closed Head Injury with Perfluorocarbon NVX-428

Pre-hospital treatment of traumatic brain injury (TBI) with co-existing polytrauma is complicated by requirements for intravenous fluid volume vs. hypotensive resuscitation. A low volume, small particle-size-oxygen-carrier perfluorocarbon emulsion NVX-428 (dodecafluoropentane emulsion; 2% w/v) could improve brain tissue with minimal additional fluid volume. This study examined whether the oxygen-carrier NVX-428 shows safety and efficacy for pre-hospital treatment of TBI. Anesthetized swine underwent fluid percussion injury TBI and received 1 mL/kg IV NVX-428 (TBI-NVX) at 15 min (T15) or normal saline (no-treatment) (TBI-NON). Similarly, uninjured swine received NVX-428 (SHAM-NVX) or normal saline (SHAM-NON). Animals were monitored and measurements were taken for physiological and neurological parameters before euthanasia at the six-hour mark (T360). Histopathological analysis was performed on paraffin embedded tissues. Physiological, biochemical and blood gas parameters were not different, with the exception of a significant but transient increase in mean pulmonary artery pressure observed in the TBI-experimental group immediately after drug administration. There were no initial differences in brain oxygenation at baseline, but over time oxygen decreased ~50% in both TBI groups. Histological brain injury scores were similar between TBI-NVX and TBI-NON, although a number of subcategories (spongiosis-ischemic/dead neurons-hemorrhage-edema) in TBI-NVX had a tendency for lower scores. The cerebellum showed significantly lower spongiosis and ischemic/dead neuron injury scores and a lower number of Fluoro-Jade-B-positive cerebellar-Purkinje-cells after NVX-428 treatment compared to controls. NVX-428 may assist in mitigating secondary cellular brain damage.

Dodecafluoropentane Emulsion (DDFPE) as a Resuscitation Fluid for Treatment of Hemorrhagic Shock and Traumatic Brain Injury: A Review

Dodecafluoropentane emulsion (DDFPe) is a novel nanotechnology for oxygen delivery with therapeutic potential for hemorrhagic shock and/or traumatic brain injury (TBI). DDFPe demonstrates efficacy at smaller doses than previously tested perfluorocarbon oxygen therapeutics. This smaller dose potentially eliminates toxicities exhibited by previous oxygen therapeutics, whereas anti-inflammatory properties of DDFPe may alleviate damage from ischemia reperfusion injury. This minireview summarizes our progress in developing a battlefield-ready product to prevent combat death due to hemorrhagic shock and/or TBI. Preclinical studies, for both indications, show promising effects of DDFPe as a resuscitation fluid. DDFPe may become a part of the toolkit for tactical healthcare professionals in battlefield and domestic emergency medicine.

Albumin-derived perfluorocarbon-based artificial oxygen carriers can avoid hypoxic tissue damage in massive hemodilution

Artificial blood for clinical use is not yet available therefore, we previously developed artificial oxygen carriers (capsules) and showed their functionality in vitro and biocompatibility in vivo. Herein, we assessed the functionality of the capsules in vivo in a normovolemic hemodilution rat-model. We stepwise exchanged the blood of male Wistar-rats with medium either in the presence of capsules (treatment) or in their absence (control). We investigated tissue hypoxia thoroughly through online biomonitoring, determination of enzyme activity and pancreatic hormones in plasma, histochemical and immunohistochemical staining of small intestine, heart, liver and spleen as well as in situ hybridization of kidneys. After hemodilution, treated animals show higher arterial blood pressure and have a stable body temperature. Additionally, they show a more stable pH, a higher oxygen partial pressure (pO₂), and a lower carbon dioxide partial pressure (pCO₂). Interestingly, blood-glucose-levels drop severely in treated animals, presumably due to glucose consumption. Creatine kinase values in these animals are increased and isoenzyme analysis indicates the spleen as origin. Moreover, the small intestine of treated animals show reduced hypoxic injury compared to controls and the kidneys have reduced expression of the hypoxia-inducible erythropoietin mRNA. In conclusion, our capsules can prevent hypoxic tissue damage. The results provide a proof of concept for capsules as adequate erythrocyte substitute.

Use of Perfluorocarbon based Blood Substitute Perftoran in Correction of Hypoxia During Acute Anemia in Animals

The cause of acute and severe hypoxia of the organism is acute posthemorrhagic anemia. To eliminate posthemorrhagic anemia in animals, the perfluorocarbon blood substitute Perftoran (Russia) with a gas-transporting function was used. The aim of this study was to determine the clinical effectiveness of the perfluorocarbon based blood substitute Perftoran with a gas-carrying function in acute posthemorrhagic anemia in animals and reveal possible side effect of the blood substitute and remove them. In the study conducted in the Clinic of Veterinary Medicine of Pushchino Research Center (Russia) participated 20 cats of both sexes, who were admitted with internal bleeding as a result of injuries. The animals were divided into two groups: the control and the treatment groups (10 per group). All animals with anemia were examined according to the standard scheme: anamnesis vitae and anamnesis morbi, physical examination (basic methods of research were used), additional methods that were used: complete blood count (CBC) and biochemical analysis of blood (BA), microscopy of blood smears, abdominal ultrasonography. Based on the obtained results, we can conclude that the use of the gas-carrying substitute for donor blood Perftoran in the treatment group of animals with posthemorrhagic anemia, which resulted from polytrauma, eliminated tissue hypoxia; the treatment of the animals in the control group with standard solutions (by infusing Stabisol) without gas transport correction led to the development of persistent hypoxia, which persisted to the stage of reticulocyte crisis.

Imaging assessment of cardioprotection mediated by a dodecafluoropentane oxygen-carrier administered during myocardial infarction

INTRODUCTION

The objective of this study was to investigate the cardioprotective effects of a dodecafluoropentane (DDFP)-based perfluorocarbon emulsion (DDFPe) as an artificial carrier for oxygen delivery to ischemic myocardium, using ^99mTc-duramycin SPECT imaging.

METHODS

Rat hearts with Ischemia-reperfusion (I/R) was prepared by coronary ligation for 45-min followed by reperfusion. The feasibility of ^99mTc-duramycin in detecting myocardial I/R injury and its kinetic profile were first verified in the ischemic hearts with 2-h reperfusion (n = 6). DDFPe (0.6 mL/kg) was intravenously administered at 10 min after coronary ligation in fifteen rats and saline was given in thirteen rats as controls. ^99mTc-duramycin SPECT images were acquired in the DDFPe-treated hearts and saline controls at 2-h (DDFPe-2 h, n = 7 and Saline-2 h, n = 6) or 24-h (DDFPe-24 h, n = 8 and Saline-24 h, n = 7) of reperfusion.

RESULTS

SPECT images, showing "hot-spot" ^99mTc-duramycin uptake in the ischemic myocardium, exhibited significantly lower radioactive retention and smaller hot-spot size in the DDFPe-2 h and DDFPe-24 h hearts compared to controls. The infarcts in the Saline-24 h hearts extended significantly relative to measurements in the Saline-2 h. The extension of infarct size did not reach a statistical difference between the DDFPe-2 h and DDFPe-24 h hearts. Ex vivo measurement of ^99mTc-duramycin activity (%ID/g) was lower in the ischemic area of DDFPe-2 h and DDFPe-24 h than that of the Saline-2 h and Saline-24 h hearts (P < 0.05). The area of injured myocardium, delineated by the uptake of ^99mTc-duramycin, extended more substantially outside the infarct zone in the controls.

CONCLUSIONS

Significant reduction in myocardial I/R injury, as assessed by ^99mTc-duramycin cell death imaging and histopathological analysis, was induced by DDFPe treatment after acute myocardial ischemia. ^99mTc-duramycin imaging can reveal myocardial cell death in ischemic hearts and may provide a tool for the non-invasive assessment of cardioprotective interventions.

Perfluorocarbon NVX-108 increased cerebral oxygen tension after traumatic brain injury in rats

BACKGROUND

Hypoxia is a critical secondary injury mechanism in traumatic brain injury (TBI), and early intervention to alleviate post-TBI hypoxia may be beneficial. NVX-108, a dodecafluoropentane perfluorocarbon, was screened for its ability to increase brain tissue oxygen tension (PbtO2) when administered soon after TBI.

METHODS

Ketamine-acepromazine anesthetized rats ventilated with 40% oxygen underwent moderate controlled cortical impact (CCI)-TBI at time 0 (T0). Rats received either no treatment (NON, n=8) or 0.5 ml/kg intravenous (IV) NVX-108 (NVX, n=9) at T15 (15 min after TBI) and T75.

RESULTS

Baseline cortical PbtO2 was 28±3 mm Hg and CCI-TBI resulted in a 46±6% reduction in PbtO2 at T15 (P<0.001). Significant differences in time-group interactions (P=0.013) were found when comparing either absolute or percentage change of PbtO2 to post-injury (mixed-model ANOVA) suggesting that administration of NVX-108 increased PbtO2 above injury levels while it remained depressed in the NON group. Specifically in the NVX group, PbtO2 increased to a peak 143% of T15 (P=0.02) 60 min after completion of NVX-108 injection (T135). Systemic blood pressure was not different between the groups.

CONCLUSION

NVX-108 caused an increase in PbtO2 following CCI-TBI in rats and should be evaluated further as a possible immediate treatment for TBI.

On-demand drug delivery from local depots

Stimuli-responsive polymeric depots capable of on-demand release of therapeutics promise a substantial improvement in the treatment of many local diseases. These systems have the advantage of controlling local dosing so that payload is released at a time and with a dose chosen by a physician or patient, and the dose can be varied as disease progresses or healing occurs. Macroscale drug depot can be induced to release therapeutics through the action of physical stimuli such as ultrasound, electric and magnetic fields and light as well as through the addition of pharmacological stimuli such as nucleic acids and small molecules. In this review, we highlight recent advances in the development of polymeric systems engineered for releasing therapeutic molecules through physical and pharmacological stimulation.

Dodecafluoropentane emulsion elicits cardiac protection against myocardial infarction through an ATP-Sensitive K+ channel dependent mechanism

Purpose

Dodecafluoropentane emulsion (DDFPe) is a perfluorocarbon with high oxygen dissolving, transport, and delivery capacity that may offer the potential to limit ischemic injury prior to clinical reperfusion. Here we investigated the cardiac protective potential of DDFPe in a mouse model of myocardial infarction.

Methods

Myocardial infarction was initiated by permanent ligation of the left anterior descending (LAD) coronary artery. Mice were administered vehicle or 5-hydroxydecanoate (5-HD) intravenously 10 min before LAD occlusion followed by a single intravenous administration of vehicle or DDFPe immediately after occlusion. Heart tissue and serum samples were collected 24 after LAD occlusion for measurement of infarct size and cardiac troponin I (cTnI) levels, respectively.

Results

DDFPe treatment reduced infarct size by approximately 72 % (36.9 ± 4.2 % for vehicle vs 10.4 ± 2.3 % for DDFPe; p < 0.01; n = 6–8) at 24 h. Serum cTnI levels were similarly reduced by DDFPe (35.0 ± 4.6 ng/ml for vehicle vs 15.8 ± 1.6 ng/ml for DDFPe; p < 0.01; n = 6–8). Pretreatment with 5-HD, a mitochondrial ATP-sensitive potassium channel (mitoK_ATP) inhibitor, blocked the reduction in infarct size (29.2 ± 4.4 % for 5-HD vs 35.4 ± 7.4 % for 5-HD+DDFPe; p = 0.48; n = 6–8) and serum cTnI levels (27.4 ± 5.1 ng/ml for 5-HD vs 34.6 ± 5.3 ng/ml for 5-HD+DDFPe; p = 0.86; n = 6–8) by DDFPe.

Conclusion

Our data indicate a cardiac protective role of DDFPe that persists beyond its retention time in the body and is dependent on mitoK_ATP, an important mediator of ischemic preconditioning induced cardiac protection.

Dodecafluoropentane Emulsion (DDFPe) Decreases Stroke Size and Improves Neurological Scores in a Permanent Occlusion Rat Stroke Model

Background:

Dodecafluoropentane emulsion (DDFPe), given IV one hour after stroke, has been shown to greatly reduce the percent stroke volume (%SV) in rabbits. With repeated doses its effect continued for 24 hours.

Purpose:

Test DDFPe as neuroprotective agent in permanent occlusion rat stroke models in Sprague Dawley (SD) and Spontaneously Hypertensive Rats (SHR) measuring both %SV and neurological assessment scores (NAS).

Methods:

The male rats received either saline (control), or one or four doses (1x or 4x) of DDFPe (0.6ml/kg IV) one hour post stroke. Treatment groups were SD (n=26) (control, 1x and 4x; n=12, 7 and 7) and SHR (n=14) (control, 1x and 4x; n=7, 3 and 4). The 4x doses were given at 1.5 hour intervals. At six hours post stroke, the rats received a NAS using standard tests for balance, reflexes, and motor performance. Then rats were euthanized and brains removed for TTC evaluation of %SV.

Results:

For %SV analysis strain differences were not significant therefore strains were combined. DDFPe significantly decreased %SV in 1x and 4xDDFPe groups compared to control groups (2.59±1.81 and 0.98±0.88 vs. 9.24±6.06, p≤0.001 each; p≤0.0001 for the overall test for treatment effect). The 1x versus 4xDDFPe groups were not significantly different (p=0.40). In NAS analysis both strains showed significant improvement with 4xDDFPe therapy vs. controls, (SD: 5.00+2.45 vs. 9.36+3.56, p=0.01; SHR: 7.75+4.43 vs. 12.14+3.08, p=0.05). Differences between the 1x DDFPe group and controls were not significant (SD: 8.43+3.69; SHR: 9. 33+3.51).

Conclusion:

DDFPe treatment provides significant neuroprotection when assessed six hours post stroke.

Cardiovascular drug delivery with ultrasound and microbubbles

Microbubbles lower the threshold for cavitation of ultrasound and have multiple potential therapeutic applications in the cardiovascular system. One of the first therapeutic applications to enter into clinical trials has been microbubble-enhanced sonothrombolysis. Trials were conducted in acute ischemic stroke and clinical trials are currently underway for sonothrombolysis in treatment of acute myocardial infarction. Microbubbles can be targeted to epitopes expressed on endothelial cells and thrombi by incorporating targeting ligands onto the surface of the microbubbles. Targeted microbubbles have applications as molecular imaging contrast agents and also for drug and gene delivery. A number of groups have shown that ultrasound with microbubbles can be used for gene delivery yielding robust gene expression in the target tissue. Work has progressed to primate studies showing delivery of therapeutic genes to generate islet cells in the pancreas to potentially cure diabetes. Microbubbles also hold potential as oxygen therapeutics and have shown promising results as a neuroprotectant in an ischemic stroke model. Regulatory considerations impact the successful clinical development of therapeutic applications of microbubbles with ultrasound. This paper briefly reviews the field and suggests avenues for further development.

Nanoparticle oxygen delivery to the ischemic heart

Objective:

Currently there are no medications that can be administered to help deliver more oxygen to the myocardial region experiencing abnormal perfusion. The purpose of this study was to look at the nanoparticle dodecafluoropentane in an emulsion as an oxygen carrier. Using nanoparticles as an oxygen carrier is advantageous because they are able to carry oxygen past blockages that are obstructing red blood cells (6-8 µm) due to their smaller size (250 nm). With the reintroduction of oxygen to the ischemic muscle tissue, a reduced infarct size should be seen.

Methods:

Male C57BL/6J mice underwent left anterior descending artery (LAD) ligation using 8-0 monofilament nylon suture. Immediately after ligation of the LAD, the control group received a 200-µl intravenous injection of phosphate buffered saline (PBS). The treated group received a dose of 0.6 ml/kg of dodecafluoropentane diluted to a total volume of 200 µl in PBS. The mice were then allowed to recover from anesthesia and were sacrificed 24 hours after the time of ligation. After the mice were sacrificed, the heart was excised and placed at -20°C for 20 minutes. The heart was then sliced into 1-mm sections and stained with tetrazolium red to identify the infarcted area. The area of infarct and ventricle were then analyzed using ImageJ software.

Results:

The average area of infarct in comparison to the ventricle for the control mice was 29.3±0.04% compared to 11.7±0.02% for the dodecafluoropentane-treated mice.

Conclusion:

The use of dodecafluoropentane in this murine model of myocardial infarction showed a 60% reduction in infarct size (p<0.01). The possibility of using nanoparticles to deliver oxygen to hypoxic tissues has interesting implications and justifies further study.

Blood substitutes: evolution from noncarrying to oxygen- and gas-carrying fluids

The development of oxygen (O2)-carrying blood substitutes has evolved from the goal of replicating blood O2 transport properties to that of preserving microvascular and organ function, reducing the inherent or potential toxicity of the material used to carry O2, and treating pathologies initiated by anemia and hypoxia. Furthermore, the emphasis has shifted from blood replacement fluid to "O2 therapeutics" that restore tissue oxygenation to specific tissues regions. This review covers the different alternatives, potential and limitations of hemoglobin-based O2 carriers (HBOCs) and perfluorocarbon-based O2 carriers (PFCOCs), with emphasis on the physiologic conditions disturbed in the situation that they will be used. It describes how concepts learned from plasma expanders without O2-carrying capacity can be applied to maintain O2 delivery and summarizes the microvascular responses due to HBOCs and PFCOCs. This review also presents alternative applications of HBOCs and PFCOCs namely: 1) How HBOC O2 affinity can be engineered to target O2 delivery to hypoxic tissues; and 2) How the high gas solubility of PFCOCs provides new opportunities for carrying, dissolving, and delivering gases with biological activity. It is concluded that the development of current blood substitutes has amplified their applications horizon by devising therapeutic functions for O2 carriers requiring limited O2 delivery capacity restoration. Conversely, full, blood-like O2-carrying capacity reestablishment awaits the control of O2 carrier toxicity.

Progress in dodecafluoropentane emulsion as a neuroprotective agent in a rabbit stroke model

Dodecafluoropentane emulsion (DDFPe) in 250 nm nanodroplets seems to swell modestly to accept and carry large amounts of oxygen in the body at >29 °C. Small particle size allows oxygen delivery even into hypoxic tissue unreachable by erythrocytes. Using permanent cerebral embolic occlusion in rabbits, we assessed DDFPe dose response as a neuroprotectant at 7 and 24 h post-embolization without lysis of arterial obstructions and investigated blood pharmacokinetics. New Zealand White rabbits (N = 56) received cerebral angiography and embolic spheres (diameter = 700-900 μm) occluded middle and/or anterior cerebral arteries. Intravenous DDFPe dosing (2 % w/v emulsion) began at 60 min and repeated every 90 min until sacrifice at 7 or 24 h post-embolization. Seven-hour groups: (1) control (embolized without treatment, N = 6), and DDFPe treatment: (2) 0.1 ml/kg (N = 7), (3) 0.3 ml/kg (N = 9), (4) 0.6 ml/kg (N = 8). Twenty-four-hour groups: (5) control (N = 16), and DDFPe treatment: (6) 0.1 ml/kg (N = 10). Infarcts as percent of total brain volume were determined using vital stains on brain sections. Other alert normal rabbits (N = 8) received IV doses followed by rapid arterial blood sampling and GC-MS analysis. Percent infarct volume means significantly decreased for all DDFPe-treated groups compared with controls, p = <0.004 to <0.03. Blood DDFP (gas) half-life was 1.45 ± 0.17 min with R = 0.958. Mean blood clearance was 78.5 ± 24.9 ml/min/kg (mean ± SE). Intravenous DDFPe decreases ischemic stroke infarct volumes. Blood half-life values are very short. The much longer therapeutic effect, >90 min, suggests multiple compartments. Lowest effective dose and maximum effective therapy duration are not yet defined. Rapid development is warranted.

Theranostic oxygen delivery using ultrasound and microbubbles

Means to overcome tumor hypoxia have been the subject of clinical investigations since the 1960's; however these studies have yet to find a treatment which is widely accepted. It has been known for nearly a century that hypoxic cells are more resistant to radiotherapy than aerobic cells, and tumor hypoxia is a major factor leading to the resistance of tumors to radiation treatment as well as several cytotoxic agents. In this manuscript, the application of ultrasound combined with oxygen-carrier microbubbles is demonstrated as a method to locally increase dissolved oxygen. Microbubbles can also be imaged by ultrasound, thus providing the opportunity for image-guided oxygen delivery. Simulations of gas diffusion and microbubble gas exchange show that small amounts (down to 5 vol%) of a low-solubility osmotic gas can substantially increase microbubble persistence and therefore production rates and stability of oxygen-carrier microbubbles. Simulations also indicate that the lipid shell can be engineered with long-chain lipids to increase oxygen payload during in vivo transit. Experimental results demonstrate that the application of ultrasound to destroy the microbubbles significantly enhances the local oxygen release. We propose this technology as an application for ultrasound image-guided release of oxygen directly to hypoxic tissue, such as tumor sites to enhance radiotherapy.

Phase-change nanoparticles using highly volatile perfluorocarbons: toward a platform for extravascular ultrasound imaging

Recent efforts using perfluorocarbon (PFC) nanoparticles in conjunction with acoustic droplet vaporization has introduced the possibility of expanding the diagnostic and therapeutic capability of ultrasound contrast agents to beyond the vascular space. Our laboratories have developed phase-change nanoparticles (PCNs) from the highly volatile PFCs decafluorobutane (DFB, bp =-2 °C) and octafluoropropane (OFP, bp =-37 °C ) for acoustic droplet vaporization. Studies with commonly used clinical ultrasound scanners have demonstrated the ability to vaporize PCN emulsions with frequencies and mechanical indices that may significantly decrease tissue bioeffects. In addition, these contrast agents can be formulated to be stable at physiological temperatures and the perfluorocarbons can be mixed to modulate the balance between sensitivity to ultrasound and general stability. We herein discuss our recent efforts to develop finely-tuned diagnostic/molecular imaging agents for tissue interrogation. We discuss studies currently under investigation as well as potential diagnostic and therapeutic paradigms that may emerge as a result of formulating PCNs with low boiling point PFCs.

Oxygenated kidney preservation techniques

Improving preservation techniques to minimize injury is of particular importance in organs from marginal donors. Since the introduction of transplantation and routine use of hypothermic temperatures for kidney preservation, there has been much debate on whether it is necessary to add oxygen to support the low level of metabolism under these conditions. Supplementing the kidney with oxygen during hypothermic preservation is not common practice. However, there is evidence to support its application. Oxygen can be added by various techniques such as retrograde persufflation whereby filtered and humidified oxygen is bubbled through the vasculature; under hyperbaric conditions using specialized pressurized chambers; during hypothermic machine perfusion; with the addition of oxygen carriers; and under normothermic conditions. Evidence suggests that oxygenation is particularly beneficial in restoring cellular levels of adenosine triphosphate after kidneys have been subjected to warm or cold ischemic injury. However, under normal conditions, the benefits are less convincing, but the evidence is insufficient to draw any conclusions. This overview explores the ways in which oxygen can be administered during preservation in experimental and clinical models of kidney transplantation.

Dodecafluoropentane emulsion decreases infarct volume in a rabbit ischemic stroke model

PURPOSE

To assess the efficacy of dodecafluoropentane emulsion (DDFPe), a nanodroplet emulsion with significant oxygen transport potential, in decreasing infarct volume in an insoluble-emboli rabbit stroke model.

MATERIALS AND METHODS

New Zealand White rabbits (N = 64; weight, 5.1 ± 0.50 kg) underwent angiography and received embolic spheres in occluded internal carotid artery branches. Rabbits were randomly assigned to groups in 4-hour and 7-hour studies. Four-hour groups included control (n = 7, embolized without treatment) and DDFPe treatment 30 minutes before stroke (n = 7), at stroke onset (n = 8), and 30 minutes (n = 5), 1 hour (n = 7), 2 hours (n = 5), or 3 hours after stroke (n = 6). Seven-hour groups included control (n = 6) and DDFPe at 1 hour (n = 8) and 6 hours after stroke (n = 5). DDFPe dose was a 2% weight/volume intravenous injection (0.6 mL/kg) repeated every 90 minutes as time allowed. After euthanasia, infarct volume was determined by vital stains on brain sections.

RESULTS

At 4 hours, median infarct volume decreased for all DDFPe treatment times (pretreatment, 0.30% [P = .004]; onset, 0.20% [P = .004]; 30 min, 0.35% [P = .009]; 1 h, 0.30% [P = .01]; 2 h, 0.40% [P = .009]; and 3 h, 0.25% [P = .003]) compared with controls (3.20%). At 7 hours, median infarct volume decreased with treatment at 1 hour (0.25%; P = .007) but not at 6 hours (1.4%; P = .49) compared with controls (2.2%).

CONCLUSIONS

Intravenous DDFPe in an animal model decreases infarct volumes and protects brain tissue from ischemia, justifying further investigation.