Effects of perfluorocarbon emulsions on microvascular blood flow and oxygen transport in a model of severe arterial gas embolism

Hepatic venous gas secondary to pulmonary barotrauma: rat model study

Intrahepatic gas (IHG) is commonly observed during early postmortem examinations of humans with upper or lower airway obstructions. We conducted a study to test the hypothesis that intrapulmonary gas could retrogradely spread to the hepatic vein following pulmonary barotrauma (PB). To establish a rat model of pulmonary barotrauma, we utilized a controllable pressure-vacuum pump to apply airway pressure (40, 60, or 80 mmHg). The rats were dissected directly at the end of the experiment, and histological analysis was performed through microscopic examination of the rats. Additionally, the rats were ventilated with meglumine diatrizoate under pressures of 160 and 250 mmHg to observe the signal dynamic diffusion using X-ray fluoroscopy examination. Rats exhibited classical changes associated with PB, such as alveolar rupture, pulmonary interstitial emphysema, and hemorrhage, as well as IHG characterized by the presence of gas in the hepatic vein and hepatic sinusoids. Air emboli were not observed in the liver in any of the 40 mmHg groups. However, they were observed in the liver in the 60 and 80 mmHg groups, the amount and size of air emboli in the 80 mmHg group were greater than those in the 60 mmHg group (p < 0.05). The 80 mmHg group presented radial grape-like bubbles in the centrilobular portion of the liver accompanied by congestion in the peripheral region of the hepatic lobule. X-ray fluoroscopy examination revealed a gradual enhancement of dynamic contrast medium signals from the lung to the inferior vena cava and then to the liver. Our findings indicate that pulmonary barotrauma can lead to the retrograde spread of intrapulmonary gas to the hepatic vein. When it is clear that no decomposition of the body has occurred, the presence of IHG serves as a novel indicator for the diagnosis of obstructive pulmonary disease or obstruction in the upper or lower airway.

Oxygen therapy alternatives in COVID-19: From classical to nanomedicine

Around 10-15% of COVID-19 patients affected by the Delta and the Omicron variants exhibit acute respiratory insufficiency and require intensive care unit admission to receive advanced respiratory support. However, the current ventilation methods display several limitations, including lung injury, dysphagia, respiratory muscle atrophy, and hemorrhage. Furthermore, most of the ventilatory techniques currently offered require highly trained professionals and oxygen cylinders, which may attain short supply owing to the high demand and misuse. Therefore, the search for new alternatives for oxygen therapeutics has become extremely important for maintaining gas exchange in patients affected by COVID-19. This review highlights and suggest new alternatives based on micro and nanostructures capable of supplying oxygen and/or enabling hematosis during moderate or acute COVID-19 cases.

Perfluorocarbons cause thrombocytopenia, changes in RBC morphology and death in a baboon model of systemic inflammation

A perfluorocarbon (PFC) investigated for treatment of traumatic brain injury (TBI) delivers oxygen to support brain function, but causes transient thrombocytopenia. TBI can cause acute inflammation with resulting thrombocytopenia; an interaction between the PFC effects and TBI inflammation might exacerbate thrombocytopenia. Therefore, PFC effects on platelet (PLT) function and hemostasis in a lipopolysaccharide (LPS) model of inflammation in the baboon were studied. Animals were randomized to receive saline ±LPS, and ± one of two doses of PFC. PLT count, transmission electron microscopy, and microparticle populations were quantified at baseline (BL) and at 2, 24, 48, 72, and 96 hours; hemostatic parameters for aggregometry and for blood clotting were measured at baseline (BL) and days 3 and 4. Injection of vehicle and LPS caused thrombocytopenia within hours; PFCs caused delayed thrombocytopenia beginning 48 hours post-infusion. LPS+PFC produced a more prolonged PLT decline and decreased clot strength. LPS+PFC increased ADP-stimulated aggregation, but PFC alone did not. Microparticle abundance was greatest in the LPS+PFC groups. LPS+PFC caused diffuse microvascular hemorrhage and death in 2 of 5 baboons in the low dose LPS-PFC group and 2 of 2 in the high dose LPS-PFC group. Necropsy and histology suggested death was caused by shock associated with hemorrhage in multiple organs. Abnormal morphology of platelets and red blood cells were notable for PFC inclusions. In summary, PFC infusion caused clinically significant thrombocytopenia and exacerbated LPS-induced platelet activation. The interaction between these effects resulted in decreased hemostatic capacity, diffuse bleeding, shock and death.

Perfluorocarbons therapeutics in modern cancer nanotechnology for hypoxia-induced anti-tumor therapy

With an estimated failure rate of about 90%, immunotherapies that are intended for the treatment of solid tumors have caused an anomalous rise in the mortality rate over the past decades. It is apparent that resistance towards such therapies primarily occurs due to elevated levels of HIF-1 (Hypoxia-induced factor) in tumor cells, which are caused by disrupted microcirculation and diffusion mechanisms. With the advent of nanotechnology, several innovative advances were brought to the fore; and, one such promising direction is the use of perfluorocarbon nanoparticles in the management of solid tumors. Perfluorocarbon nanoparticles enhance the response of hypoxia-based agents (HBAs) within the tumor cells and have been found to augment the entry of HBAs into the tumor micro-environment. The heightened penetration of HBAs causes chronic hypoxia, thus aiding in the process of cell quiescence. In addition, this technology has also been applied in photodynamic therapy, where oxygen self-enriched photosensitizers loaded perfluorocarbon nanoparticles are employed. The resulting processes initiate a cascade, depleting tumour oxygen and turning it into a reactive oxygen species eventually to destroy the tumour cell. This review elaborates on the multiple applications of nanotechnology based perfluorocarbon formulations that are being currently employed in the treatment of tumour hypoxia.

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.

Perfluorocarbon as an adjuvant for tumor anti-angiogenic therapy: Relevance to hypoxia and HIF-1

Lack of vascularization results in increased demand for oxygen and creates a defined feature of the tumor microenvironment known as tumor hypoxia. It is well established that in response to hypoxia, hypoxia-inducible factor-1 α (HIF-1α) is induced which is an important factor in angiogenesis, invasion and metastasis. In turn, HIF-1α regulates the expression of angiogenic factors, such as vascular endothelial growth factor (VEGF). Ascribed to abnormal characteristics of tumor angiogenic networks, antiangiogenic therapy approaches can even worsen the hypoxic condition and can create cancer cells with stemness features. Hence oxygen delivery via perfluorocarbon (PFC) to hypoxic sites seems to result in unstable HIF expression and consequent inactivation of angiogenesis cascade and metastasis and therefore, inhibition of cancer cells stemness.

Oxygen therapeutic agents to target hypoxia in cancer treatment

Solid tumors have abnormal microcirculation that limits oxygen delivery and leads to a hypoxic tumor microenvironment. Tumor hypoxia stabilizes the transcription factor HIF-1α that can trigger immunosuppression through A2A adenosine receptors which prevents immune attack on tumors. In addition, success of chemotherapy and radiation therapy appears to be dependent on oxygen levels. Two main pharmaceutical classes of agents (hemoglobin based and perfluorocarbon man-made carbon oils) have been tested in tumor models as enhanced oxygen therapeutics. This article will review how these agents function as well as examine work to date with both drug classes.

Mini-review: Perfluorocarbons, Oxygen Transport, and Microcirculation in Low Flow States: in Vivo and in Vitro Studies

The in vivo study of microvascular oxygen transport requires accurate and challenging measurements of several mass transfer parameters. Although recommended, blood flow and oxygenation are typically not measured in many studies where treatments for ischemia are tested. Therefore, the aim of this communication is to briefly review cardinal aspects of oxygen transport, and the effects of perfluorocarbon (PFC) treatment on blood flow and oxygenation based mostly on studies performed in our laboratory. As physiologically relevant events in oxygen transport take place at the microvascular level, we implemented the phosphorescence quenching technique coupled with noninvasive intravital videomicroscopy for quantitative evaluation of these events in vivo. Rodent experimental models and various approaches have been used to induce ischemia, including hemorrhage, micro- and macroembolism, and microvessel occlusion. Measurements show decrease in microvascular blood flow as well as intravascular and tissue oxygen partial pressure (PO2) after these procedures. To minimize or reverse the effects of ischemia and hypoxia, artificial oxygen carriers such as different PFCs were tested. Well-defined endpoints such as blood flow and tissue PO2 were measured because they have significant effect on tissue survival and outcome. In several cases, enhancement of flow and oxygenation could be demonstrated. Similar results were found in vitro: PFC emulsion mixed with blood (from healthy donors and sickle cell disease patients) enhanced oxygen transport. In summary, PFCs may provide beneficial effects in these models by mechanisms at the microvascular level including facilitated diffusion and bubble reabsorption leading to improved blood flow and oxygenation.

A characterization of ABL-101 as a potential tracer for clinical fluorine-19 MRI

The two main challenges that prevent the translation of fluorine-19 (¹⁹ F) MRI for inflammation monitoring or cell tracking into clinical practice are (i) the relatively low signal-to-noise ratio generated by the injected perfluorocarbon (PFC), which necessitates long scan times, and (ii) the need for regulatory approval and a high biocompatibility of PFCs that are also suitable for MRI. ABL-101, an emulsion of perfluoro(t-butylcyclohexane), is a third-generation PFC that is already used in clinical trials, but has not yet been used for ¹⁹ F MRI. The objective of this study was therefore to assess the performance of ABL-101 as a ¹⁹ F MRI tracer. At magnetic field strengths of 3, 9.4 and 14.1 T, the CF₃ groups of ABL-101 generated a large well-separated singlet with T₂ /T₁ ratios of >0.27, >0.14 and > 0.05, respectively. All relaxation times decreased with the increase in magnetic field strength. The detection limit of ABL-101 in a 0.25 mm³ voxel at 3 T, 37°C and with a 3-minute acquisition time was 7.21mM. After intravenous injection, the clearance half-lives of the ABL-101 ¹⁹ F MR signal in mouse (n = 3) spleen and liver were 6.85 ± 0.45 and 3.20 ± 0.35 days, respectively. These results demonstrate that ABL-101 has ¹⁹ F MR characteristics that are similar to those of PFCs developed specifically for MRI, while it has clearance half-lives similar to PFCs that have previously been used in large doses in non-MRI clinical trials. Overall, ABL-101 is thus a very promising candidate tracer for future clinical trials that use ¹⁹ F MRI for cell tracking or the monitoring of inflammation.

Fluorocapsules allow in vivo monitoring of the mechanical stability of encapsulated islet cell transplants

Clinical trials that have used encapsulated islet cell therapy have been few and overall disappointing. This is due in part to the lack of suitable methods to monitor the integrity vs. rupture of transplanted microcapsules over time. Fluorocapsules were synthesized by embedding emulsions of perfluoro-15-crown-5-ether (PFC), a bioinert compound detectable by 19F MRI, into dual-alginate layer, Ba2+-gelled alginate microcapsules. Fluorocapsules were spherical with an apparent smooth surface and an average diameter of 428 ± 52 μm. After transplantation into mice, the 19F MRI signal of capsules remained stable for up to 90 days, corresponding to the total number of intact fluorocapsules. When single-alginate layer capsules were ruptured with alginate lyase, the 19F MRI signal dissipated within 4 days. For fluoroencapsulated luciferase-expressing mouse βTC6 insulinoma cells implanted into autoimmune NOD/ShiLtJ mice and subjected to alginate-lyase induced capsule rupture in vivo, the 19F MRI signal decreased sharply over time along with a decrease in bioluminescence imaging signal used as a measure of cell viability in vivo. These results indicate that maintenance of capsule integrity is essential for preserving transplanted cell survival, where a decrease in 19F MRI signal may serve as a predictive imaging surrogate biomarker for impending failure of encapsulated islet cell therapy.

Pharmaceutical design and development of perfluorocarbon nanocolloids for oxygen delivery in regenerative medicine

Perfluorocarbons (PFCs) have been investigated as oxygen carriers for several decades in varied biomedical applications. PFCs are chemically and biologically inert, temperature and storage stable, pose low to no infectious risk, can be commercially manufactured, and have well established gas transport properties. In this review, we highlight design and development strategies for their successful application in regenerative medicine, transplantation and organ preservation. Effective tissue preservation strategies are key to improving outcomes of extremity salvage and organ transplantation. Maintaining tissue integrity requires adequate oxygenation to support aerobic metabolism. The use of whole blood for oxygen delivery is fraught with limitations of poor shelf stability, infectious risk, religious exclusions and product shortages. Other agents also face clinical challenges in their implementation. As a solution, we discuss new ways of designing and developing PFC-based artificial oxygen carriers by implementing modern pharmaceutical quality by design and scale up manufacturing methodologies.