Perfluorocarbon-based oxygen carriers: from physics to physiology.

Developing biocompatible, synthetic oxygen carriers is a consistently challenging task that researchers have been pursuing for decades. Perfluorocarbons (PFC) are fascinating compounds with a huge capacity to dissolve gases, where the respiratory gases are of special interest for current investigations. Although largely chemically and biologically inert, pure PFCs are not suitable for injection into the vascular system. Extensive research created stable PFC nano-emulsions that avoid (i) fast clearance from the blood and (ii) long organ retention time, which leads to undesired transient side effects. PFC-based oxygen carriers (PFOCs) show a variety of application fields, which are worthwhile to investigate. To understand the difficulties that challenge researchers in creating formulations for clinical applications, this review provides the physical background of PFCs' properties and then illuminates the reasons for instabilities of PFC emulsions. By linking the unique properties of PFCs and PFOCs to physiology, it elaborates on the response, processing and dysregulation, which the body experiences through intravascular PFOCs. Thereby the reader will receive a scientific and easily comprehensible overview why PFOCs are precious tools for so many diverse application areas from cancer therapeutics to blood substitutes up to organ preservation and diving disease.

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.

When the Brain Yearns for Oxygen.

Nearly 30 years ago hypoxia-inducible factor (HIF) was described as a protein complex bound to regulatory DNA sequences termed hypoxia response elements because HIF binding induced transcription of the erythropoietin gene under hypoxia. However, it soon became clear that HIF is part of a ubiquitous cellular oxygen sensing system, which ensures finely tuned control of HIF abundance and activity in dependence of the cellular oxygen tension. For their discoveries of how cells sense and adapt to oxygen availability Gregg L. Semenza, William G. Kaelin Jr. and Sir Peter J. Ratcliffe received the Nobel Prize in Physiology or Medicine 2019. The Nobel laureates' pioneering work on cellular oxygen sensing has unraveled that HIF has numerous target genes reflecting its multiple functions in cellular metabolism and adaptation to different levels of oxygen. Importantly, HIF is also crucial for the development of the nervous system. HIF has an influence on different neural cell types regarding neurogenesis, maturation and apoptosis. Furthermore, HIF is involved in pathophysiological processes of the brain like stroke and Alzheimer's disease resulting in the development of HIF-related therapeutic approaches.

Artificial Oxygen Carriers-Past, Present, and Future-a Review of the Most Innovative and Clinically Relevant Concepts.

Blood transfusions are a daily practice in hospitals. Since these products are limited in availability and have various, harmful side effects, researchers have pursued the goal to develop artificial blood components for about 40 years. Development of oxygen therapeutics and stem cells are more recent goals. Medline (https://www.ncbi.nlm.nih.gov/pubmed/?holding=ideudelib), ClinicalTrials.gov (https://clinicaltrials.gov), EU Clinical Trials Register (https://www.clinicaltrialsregister.eu), and Australian New Zealand Clinical Trials Registry (http://www.anzctr.org.au) were searched up to July 2018 using search terms related to artificial blood products in order to identify new and ongoing research over the last 5 years. However, for products that are already well known and important to or relevant in gaining a better understanding of this field of research, the reader is punctually referred to some important articles published over 5 years ago. This review includes not only clinically relevant substances such as heme-oxygenating carriers, perfluorocarbon-based oxygen carriers, stem cells, and organ conservation, but also includes interesting preclinically advanced compounds depicting the pipeline of potential new products. In- depth insights into specific benefits and limitations of each substance, including the biochemical and physiologic background are included. "Fancy" ideas such as iron-based substances, O2 microbubbles, cyclodextranes, or lugworms are also elucidated. To conclude, this systematic up-to-date review includes all actual achievements and ongoing clinical trials in the field of artificial blood products to pursue the dream of artificial oxygen carrier supply. Research is on the right track, but the task is demanding and challenging.

Functionality of albumin-derived perfluorocarbon-based artificial oxygen carriers in the Langendorff-heart †.

The aim of this study was to prove whether albumin-derived perfluorocarbon-based nanoparticles (capsules) can operate as a novel artificial oxygen carrier in a rat Langendorff-heart perfusion model. Hearts perfused with capsules showed increased left ventricular pressure and rate pressure product compared to hearts perfused with pure Krebs-Henseleit (KH)-buffer. The capsules prevented the myocardium from functional fail when in their absence a noxious ischemia was observed. Capsules did not change rheological properties of KH-buffer and could repeatedly reload with oxygen. This albumin-derived perfluorocarbon-based artificial oxygen carrier preserved the function of rat hearts due to the transport of oxygen in a satisfactory manner. Because of these positive results, the functionality of the applied capsules should be verified in living animals.

Albumin-derived perfluorocarbon-based artificial oxygen carriers: A physico-chemical characterization and first in vivo evaluation of biocompatibility.

Until today, artificial oxygen carriers have not been reached satisfactory quality for routine clinical treatments. To bridge this gap, we designed albumin-derived perfluorocarbon-based nanoparticles as novel artificial oxygen carriers and evaluated their physico-chemical and pharmacological performance. Our albumin-derived perfluorocarbon-based nanoparticles (capsules), composed of an albumin shell and a perfluorodecalin core, were synthesized using ultrasonics. Their subsequent analysis by physico-chemical methods such as scanning electron-, laser scanning- and dark field microscopy as well as dynamic light scattering revealed spherically-shaped, nano-sized particles, that were colloidally stable when dispersed in 5% human serum albumin solution. Furthermore, they provided a remarkable maximum oxygen capacity, determined with a respirometer, reflecting a higher oxygen transport capacity than the competitor Perftoran®. Intravenous administration to healthy rats was well tolerated. Undesirable effects on either mean arterial blood pressure, hepatic microcirculation (determined by in vivo microscopy) or any deposit of capsules in organs, except the spleen, were not observed. Some minor, dose-dependent effects on tissue damage (release of cellular enzymes, alterations of spleen's micro-architecture) were detected. As our promising albumin-derived perfluorocarbon-based nanoparticles fulfilled decisive physico-chemical demands of an artificial oxygen carrier while lacking severe side-effects after in vivo administration they should be advanced to functionally focused in vivo testing conditions.

Perfluorodecalin-Filled Poly(n-butyl-cyanoacrylate) Nanocapsules as Potential Artificial Oxygen Carriers: Preclinical Safety and Biocompatibility.

With regard to the development of artificial blood substitutes, perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules are already discussed for the use as artificial oxygen carriers. The aim of the present study was to thoroughly investigate the preclinical safety and biocompatibility of the perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules prepared by interfacial polymerization. Nanocapsules were assessed for physical and microbial stability. Subsequent to intravenous infusion to anesthetized rats, effects on systemic parameters, microcirculation, circulatory in vivo half-life, acid base/metabolic status, organ damage and biodistribution were evaluated using inter alia 19F-NMR spectroscopy and in vivo microscopy. Perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules displayed physical and microbial stability over a period of 4 weeks and the circulatory in vivo half-life was t1/2 = 30 min. In general, all animals tolerated intravenous infusion of the prepared nanocapsules, even though several side-effects occurred. As a consequence of nanocapsule infusion, a transient decrease in mean arterial blood pressure, impairment of hepatic microcirculation, organ/tissue damage of liver, spleen and small intestine, as well as an elevation of plasma enzyme activities such as lactate dehydrogenase, creatine kinase and aspartate aminotransferase could be observed. The assessment of the distribution pattern revealed nanocapsule accumulation in spleen, kidney and small intestine. Perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules conformed to basic requirements of drugs under preclinical development but further improvement is needed to establish these nanocapsules as novel artificial oxygen carriers.

Artificial oxygen carriers based on perfluorodecalin-filled poly(n-butyl-cyanoacrylate) nanocapsules.

Poly(n-butyl-cyanoacrylate)-nanocapsules filled by perfluorodecalin (PFD) are proposed as potential oxygen carriers for blood substitute. The capsule dispersion is prepared via interfacial polymerisation from a PFD emulsion in water which in turn is generated by spontaneous phase separation. The resulting dispersion is capable of carrying approximately 10% of its own volume of gaseous oxygen, which is approximately half of the capacity of human blood. The volumes of the organic solvents and water are varied within a wide range, connected to a change of the capsule radius between 200 and 400 nm. The principal suitability of the capsule dispersion for intravenous application is proven in first physiological experiments. A total amount of 10 ml/kg body weight has been infused into rats, with the dispersion supernatant and a normal saline solution as controls. After the infusion of nanocapsules, the blood pressure as well as the heart rate remains constant on a normal level.

Safety of poly (ethylene glycol)-coated perfluorodecalin-filled poly (lactide-co-glycolide) microcapsules following intravenous administration of high amounts in rats.

The host response against foreign materials designates the biocompatibility of intravenously administered microcapsules and thus, widely affects their potential for subsequent clinical use as artificial oxygen/drug carriers. Therefore, body distribution and systemic parameters, as well as markers of inflammation and indicators of organ damage were carefully evaluated after administration of short-chained poly (vinyl alcohol, (PVA)) solution or poly (ethylene glycol (PEG))-shielded perfluorodecalin-filled poly (d,l-lactide-co-glycolide, PFD-filled PLGA) microcapsules into Wistar rats. Whereas PVA infusion was well tolerated, all animals survived the selected dose of 1247 mg microcapsules/kg body weight but showed marked toxicity (increased enzyme activities, rising pro-inflammatory cytokines and complement factors) and developed a mild metabolic acidosis. The observed hypotension emerging immediately after start of capsule infusion was transient and mean arterial blood pressure restored to baseline within 70 min. Microcapsules accumulated in spleen and liver (but not in other organs) and partly occluded hepatic microcirculation reducing sinusoidal perfusion rate by about 20%. Intravenous infusion of high amounts of PFD-filled PLGA microcapsules was tolerated temporarily but associated with severe side effects such as hypotension and organ damage. Short-chained PVA displays excellent biocompatibility and thus, can be utilized as emulsifier for the preparation of drug carriers designed for intravenous use.

Acid-base and electrolyte status during normovolemic hemodilution with succinylated gelatin or HES-containing volume replacement solutions in rats.

BACKGROUND: In the past, several studies have compared different colloidal replacement solutions, whereby the focus was usually on the respective colloid. We therefore systematically studied the influence of the carrier solution's composition of five approved colloidal volume replacement solutions (Gelafundin, Gelafusal, Geloplasma, Voluven and Volulyte) on acid-base as well as electrolyte status during and following acute severe normovolemic hemodilution. The solutions differed in the colloid used (succinylated gelatin vs. HES) and in the presence and concentration of metabolizable anions as well as in their electrolyte composition. METHODS: Anesthetized Wistar rats were subjected to a stepwise normovolemic hemodilution with one of the solutions until a final hematocrit of 10%. Subsequent to dilution (162 min), animals were observed for an additional period (150 min). During dilution and observation time blood gas analyses were performed eight times in total. Additionally, in the Voluven and Volulyte groups as well as in 6 Gelafundin animals, electrolyte concentrations, glucose, pH and succinylated gelatin were measured in urine and histopathological evaluation of the kidney was performed. RESULTS: All animals survived without any indications of injury. Although the employed solutions differed in their respective composition, comparable results in all plasma acid-base and electrolyte parameters studied were obtained. Plasma pH increased from approximately 7.28 to 7.39, the plasma K(+) concentration decreased from circa 5.20 mM to 4.80-3.90 mM and the plasma Cl(-) concentration rose from approximately 105 mM to 111-120 mM. Urinary analysis revealed increased excretion of K(+), H(+) and Cl(-). CONCLUSIONS: The present data suggest that the carrier solution's composition with regard to metabolizable anions as well as K(+), Ca(2+) only has a minor impact on acid-base and electrolyte status after application of succinylated gelatin or HES-containing colloidal volume replacement solutions.

Long-circulating poly(ethylene glycol)-coated poly(lactid-co-glycolid) microcapsules as potential carriers for intravenously administered drugs.

The intrinsic advantages of microcapsules with regard to nanocapsules as intravenous drug carrier systems are still not fully exploited. Especially, in clinical situations where a long-term drug release within the vascular system is desired, if large amounts of drug have to be administered or if capillary leakage occurs, long-circulating microparticles may display a superior alternative to nanoparticles. Here, microcapsules were synthesised and parameters such as in vitro tendency of agglomeration, protein adsorption and in vivo performance were investigated. Biocompatible poly(ethylene glycol) (PEG)-coated poly(DL-lactide-co-glycolide) (PLGA) as wall material, solid and perfluorodecalin (PFD)-filled PEG-PLGA microcapsules (1.5 µm diameter) were manufactured by using a modified solvent evaporation method with either 1% poly(vinyl alcohol) (PVA) or 1.5% cholate as emulsifying agents. Compared to microcapsules manufactured with cholate, the protein adsorption (albumin and IgG) was clearly decreased and agglomeration of capsules was prevented, when PVA was used. The intravenous administration of these microcapsules, both solid and PFD-filled, in rats was successful and exhibited a circulatory half-life of about 1 h. Our data clearly demonstrate that PEG-PLGA microcapsules, manufactured by using PVA, are suitable biocompatible, long-circulating drug carriers, applicable for intravenous administration.

Nerve growth factor and brain-derived neurotrophic factor but not granulocyte colony-stimulating factor, nimodipine and dizocilpine, require ATP for neuroprotective activity after oxygen-glucose deprivation of primary neurons.

In previous work, we have demonstrated by radiolabeling, mass spectrometry and site-directed mutagenesis that nerve growth factor (NGF) as well as brain-derived neurotrophic factor (BDNF) and fibroblast growth factor 2 (FGF2) are capable of ATP-binding and that this binding appears to be essential for their neuroprotective activity. In this study, we attempted to shed some light on the question whether ATP is a general prerequisite for neuroprotection. Therefore, we used the non-ATP-binding granulocyte colony-stimulating factor (GCSF), the calcium antagonist nimodipine and the NMDA antagonist dizocilpine to find out whether they need ATP for neuroprotection comparable to NGF and BDNF. However, ATP was not necessary for the neuroprotective effects of GCSF, nimodipine and dizocilpine on primary cultures of rat cortical neurons damaged by oxygen-glucose deprivation whereas neuroprotection was demonstrable for NGF and BDNF only when ATP was present in the culture medium at a concentration higher than ca. 0.4nmol/l. In circular dichroism studies ATP caused changes of the secondary structure of NGF but not of GCSF. Taken together, we suggest that ATP is not a general prerequisite for neuroprotectivity but some growth factors like NGF and BDNF can stimulate their receptors only if they have bound ATP.

Binding of ATP to vascular endothelial growth factor isoform VEGF-A165 is essential for inducing proliferation of human umbilical vein endothelial cells.

BACKGROUND: ATP binding is essential for the bioactivity of several growth factors including nerve growth factor, fibroblast growth factor-2 and brain-derived neurotrophic factor. Vascular endothelial growth factor isoform 165 (VEGF-A(165)) induces the proliferation of human umbilical vein endothelial cells, however a dependence on ATP-binding is currently unknown. The aim of the present study was to determine if ATP binding is essential for the bioactivity of VEGF-A(165). RESULTS: We found evidence that ATP binding to VEGF-A(165) induced a conformational change in the secondary structure of the growth factor. This binding appears to be significant at the biological level, as we found evidence that nanomolar levels of ATP (4-8 nm) are required for the VEGF-A(165)-induced proliferation of human umbilical vein endothelial cells. At these levels, purinergic signaling by ATP via P2 receptors can be excluded. Addition of alkaline phosphate to cell culture lowered the ATP concentration in the cell culture medium to 1.8 nM and inhibited cell proliferation. CONCLUSIONS: We propose that proliferation of endothelial cells is induced by a VEGF-A(165)-ATP complex, rather than VEGF-A(165) alone.