Modeling of oxygen transport in blood-perfluorocarbon emulsion mixtures: Part II: tissue oxygenation

Quality by design approach identifies critical parameters driving oxygen delivery performance in vitro for perfluorocarbon based artificial oxygen carriers

Perfluorocarbons (PFCs) exhibiting high solubility for oxygen are attractive materials as artificial oxygen carriers (AOC), an alternative to whole blood or Haemoglobin-based oxygen carriers (HBOCs). PFC-based AOCs, however, met clinical translation roadblocks due to product quality control challenges. To overcome these issues, we present an adaptation of Quality by Design (QbD) practices to optimization of PFC nanoemulsions (PFC-NEs) as AOCs. QbD elements including quality risk management, design of experiments (DoE), and multivariate data analysis facilitated the identification of composition and process parameters that strongly impacted PFC colloidal stability and oxygen transport function. Resulting quantitative relationships indicated a composition-driven tradeoff between stability and oxygen transport. It was found that PFC content was most predictive of in vitro oxygen release, but the PFC type (perfluoro-15-crown-5-ether, PCE or perfluorooctyl bromide, PFOB) had no effect on oxygen release. Furthermore, we found, under constant processing conditions, all PFC-NEs, comprised of varied PFC and hydrocarbon content, exhibited narrow droplet size range (100–150 nm) and narrow size distribution. Representative PFOB-NE maintained colloidal attributes upon manufacturing on larger scale (100 mL). QbD approach offers unique insights into PFC AOC performance, which will overcome current product development challenges and accelerate clinical translation.

Optimization of perfluoro nano-scale emulsions: the importance of particle size for enhanced oxygen transfer in biomedical applications

Nano-scale emulsification has long been utilized by the food and cosmetics industry to maximize material delivery through increased surface area to volume ratios. More recently, these methods have been employed in the area of biomedical research to enhance and control the delivery of desired agents, as in perfluorocarbon emulsions for oxygen delivery. In this work, we evaluate critical factors for the optimization of PFC emulsions for use in cell-based applications. Cytotoxicity screening revealed minimal cytotoxicity of components, with the exception of one perfluorocarbon utilized for emulsion manufacture, perfluorooctylbromide (PFOB), and specific w% limitations of PEG-based surfactants utilized. We optimized the manufacture of stable nano-scale emulsions via evaluation of: component materials, emulsification time and pressure, and resulting particle size and temporal stability. The initial emulsion size was greatly dependent upon the emulsion surfactant tested, with pluronics providing the smallest size. Temporal stability of the nano-scale emulsions was directly related to the perfluorocarbon utilized, with perfluorotributylamine, FC-43, providing a highly stable emulsion, while perfluorodecalin, PFD, coalesced over time. The oxygen mass transfer, or diffusive permeability, of the resulting emulsions was also characterized. Our studies found particle size to be the critical factor affecting oxygen mass transfer, as increased micelle size resulted in reduced oxygen diffusion. Overall, this work demonstrates the importance of accurate characterization of emulsification parameters in order to generate stable, reproducible emulsions with the desired bio-delivery properties.

19F MRI oximetry: simulation of perfluorocarbon distribution impact

In (19)F MRI oximetry, a method used to image tumour hypoxia, perfluorocarbons serve as oxygenation markers. The goal of this study is to evaluate the impact of perfluorocarbon distribution and concentration in (19)F MRI oximetry through a computer simulation. The simulation studies the correspondence between (19)F measured (pO(FNMR)(2)) and actual tissue oxygen tension (pO(2)) for several tissue perfluorocarbon distributions. For this, a Krogh tissue model is implemented which incorporates the presence of perfluorocarbons in blood and tissue. That is, in tissue the perfluorocarbons are distributed homogeneously according to Gaussian diffusion profiles, or the perfluorocarbons are concentrated in the capillary wall. Using these distributions, the oxygen tension in the simulation volume is calculated. The simulated mean oxygen tension is then compared with pO(FNMR)(2), the (19)F MRI-based measure of pO(2) and with pO(0)(2), pO(2) in the absence of perfluorocarbons. The agreement between pO(FNMR)(2) and actual pO(2) is influenced by vascular density and perfluorocarbon distribution. The presence of perfluorocarbons generally gives rise to a pO(2) increase in tissue. This effect is enhanced when perfluorocarbons are also present in blood. Only the homogeneous perfluorocarbon distribution in tissue with no perfluorocarbons in blood guarantees small deviations of pO(FNMR)(2) from pO(2). Hence, perfluorocarbon distribution in tissue and blood has a serious impact on the reliability of (19)F MRI-based measures of oxygen tension. In addition, the presence of perfluorocarbons influences the actual oxygen tension. This finding may be of great importance for further development of (19)F MRI oximetry.

Modified haemoglobins and perfluorocarbons

After decades of research activities and product improvements in the field of artificial oxygen carriers based on either haemoglobin modifications or perfluorocarbon emulsions, these products have reached a critical stage of their development. Varieties of haemoglobin-based oxygen carriers and perfluorocarbon emulsions are under current clinical investigation. Although the clinical availability of artificial oxygen carriers may result in profound changes of fluid resuscitation from haemorrhage, the transfusion of human blood components as an integral part of medical trauma management will not be replaced. However, a rapid and effective restoration of tissue oxygenation by the use of artificial oxygen carriers in the treatment of severe haemorrhage may bridge time delays until stored and cross-matched human packed red cells are available. Whether artificial oxygen carriers could provide additional clinical benefits by sustaining tissue oxygenation even under conditions of a disturbed macro- or microcirculation is the subject of current investigations. Therefore, the application of safe and effective artificial oxygen carriers would not only be restricted to the treatment of severe haemorrhage, but additional therapeutic indications of artificial oxygen carriers in emergency medicine, trauma anaesthesia and other medical specialities would emerge.

Biochemistry, physiology, and complications of blood doping: facts and speculation

Competition is a natural part of human nature. Techniques and substances employed to enhance athletic performance and to achieve unfair success in sport have a long history, and there has been little knowledge or acceptance of potential harmful effects. Among doping practices, blood doping has become an integral part of endurance sport disciplines over the past decade. The definition of blood doping includes methods or substances administered for non-medical reasons to healthy athletes for improving aerobic performance. It includes all means aimed at producing an increased or more efficient mechanism of oxygen transport and delivery to peripheral tissues and muscles. The aim of this review is to discuss the biochemistry, physiology, and complications of blood doping and to provide an update on current antidoping policies.

Perfluorocarbon Emulsion Improves Cerebral Oxygenation and Mitochondrial Function after Fluid Percussion Brain Injury in Rats

OBJECTIVE

Cerebral ischemia is a common secondary sequela of traumatic brain injury (TBI). Experimental models of stroke have demonstrated reductions in ischemia after perfluorocarbon (PFC) administration; however, there are no published reports of PFC efficacy after TBI. The current study analyzed the effect of the PFC emulsion Oxygent (AF0144; Alliance Pharmaceutical Corp., San Diego, CA) on cerebral oxygenation, mitochondrial redox potential, and free radical formation after lateral fluid percussion injury.

METHODS

After fluid percussion injury, five 2.25 ml/kg doses of PFC or saline were administered to rats breathing 100% O(2), and oxygen tension was recorded. In a second experiment, a single bolus (11.25 ml/kg) of PFC or saline was given after injury, and redox potential and free radical formation were measured at 1 or 4 hours with Alamar blue dye and dihydrorhodamine 123, respectively.

RESULTS

Cerebral oxygen tension was significantly increased in both injured and sham animals treated with 11.25 ml/kg of PFC as compared with saline (P < 0.05). Likewise, PFC significantly increased mitochondrial redox potential as compared with saline at 4 hours after injury (P < 0.01). Mitochondrial peroxynitrite and peroxide production also increased with the administration of PFC (P < 0.05).

CONCLUSION

The current study demonstrates that a PFC emulsion can significantly increase cerebral oxygenation after TBI and enhance mitochondrial function at 4 hours after injury as compared with saline. This study demonstrates a new therapeutic potential for PFC to enhance cerebral oxygenation and aerobic metabolism after TBI. However, the increased free radical formation with high-dose PFCs suggests the need for further studies combining PFCs with free radical scavengers.

Engineering blood: synthetic substitutes from fluorinated compounds

Concerns about blood safety and the logistical problems associated with conventional transfusion have fuelled the search for effective alternatives (so-called blood substitutes). Such materials include hemoglobin derivatives and those based on synthetic, highly fluorinated, inert organic compounds called perfluorochemicals (PFCs). PFCs dissolve large volumes of oxygen and other gases, are unreactive in the body, and are excreted primarily as a vapor by exhalation. Liquid PFCs are immiscible with blood and other body fluids, but can be injected safely into the bloodstream as submicron emulsions. Emulsified PFCs have been evaluated in clinical trials as temporary, intravascular tissue-oxygenating fluids. One such emulsion, a commercial perflubron-based, phospholipid-stabilized formulation, is in advanced clinical trials as an alternative to transfusing donated (allogeneic) blood during surgery. Basic and clinical studies have shown that this emulsion can adequately maintain tissue oxygenation during acute blood loss with no abnormal hemodynamic changes. The use of PFC emulsions as an efficacious, short-term transfusion alternative underpins the longer term objective of producing a totally synthetic, bioengineered blood substitute.

[Cardiovascular effects of doping]

Cardiovascular effects of doping drugs are numerous, with different mechanisms: vasoconstriction of amphetamines, erythropoietin and cocaine; sodium water retention of anabolic steroids and corticosteroids; elevation in blood viscosity of erythropoietin, perflurocarbon emulsion, recombinant hemoglobin and anabolic steroids; sympathetic nervous system activation of amphetamines, beta 2 agonists and clenbuterol; lipids profile disorder of anabolic steroids. Physical activity consequences, particularly bradycardia and dehydration, are worsening. Thrombosis and arrythmogenic effects, with possibility of sudden death, are the severe immediate events. Hypertension and coronary diseases are medium-term effects; acute myocardial infarction is frequent. Heart failure can be secondary to cardiac muscle direct fibrosis, like with anabolic steroids. These cardiovascular effects are serious and it is necessary to early detect the doping drugs use in sporstmen; all prescribing physician should be aware of existing drugs and their clinical events.