Stephanie Dinkelmann

A SYSTEM ESTABLISHING COMPATIBILITY PROFILES FOR ARTIFICIAL OXYGEN CARRIERS AND OTHER SUBSTANCES

Worldwide, great efforts are being made to develop a clinically useful artificial oxygen carrier. Toxicological and immunological compatibility is generally tested using animal experiments but inflammatory parameters in particular show large species-specific differences. Therefore, we developed an in vitro system using human components to establish a compatibility profile of unknown compounds. The test system comprises induction of hemolysis, activation of complement (C3a), induction/suppression of cytokine production, influence on cell proliferation, direct toxicity on peripheral leukocytes, and phagocytosis of the material under test and of microbes. The test system will be described, along with results of various perfluorocarbon emulsions. When testing lecithin-based perfluorodecalin (PFD) emulsions, and comparing them to Pluronic-based PFD emulsions, we could show that Pluronic-based emulsions were virtually untoxic to peripheral human leukocytes. They neither inhibited cell proliferation nor caused any hemolysis, but caused mild to moderate inhibition of endotoxin-induced cytokine production. At the same time, lecithin-based PFD emulsion caused substantial cytotoxicity in phagocytic cells like monocytes (60–100% after 24 h incubation) and granulocytes (10–20% after 24 h incubation). They also suppressed endotoxin-induced cytokine production in monocytes to more than 98% and inhibited cell proliferation of an endothelial (ECV 304) and a monocytic cell line (MonoMac6) to more than 95%.

Semifluorinated symmetrical diethers for intraocular use: synthesis, characterization, and in vitro biocompatibility.

Semifluorinated symmetrical diethers were synthesized using the William ether synthesis. These diethers should have similar properties to perfluorocarbons as are chemical inertness and high oxygen solubility, but in contrast a considerably lower density. With their lower density the damaging of the choroidal tissue of the eye observed with perfluorocarbons should be avoided. The synthesized diethers are inert compounds being stable against nucleophiles, oxidiziers and strong bases. Their density is in the range of 1.1–1.2 g/cm3. Besides the physical and chemical tests we conducted several in vitro biocompatibility tests. The tests comprised induction of hemolysis, the generation of C3a complement, the influence on the production of interleukin1β, the influence on cell proliferation of a Raji and a Hela cell line (3H-Thymidine uptake) and finally the direct cytotoxic effect on these cell lines. All tested symmetrical diethers were positive in one or more tests and can be expected to be incompatible in vivo. Especially the “short” semifluorinated diethers [(CF3CH2O)2(CH2)3–6] showed a nearly total inhibition of cell proliferation or interleukin1β release. Further variation of the compounds will be necessary to generate better biocompatible derivates.

A MODEL OF STEPWISE ISOVOLAEMIC BLOOD EXCHANGE IN ANAESTHETISED, SPONTANEOUSLY BREATHING RATS TO EVALUATE THE OXYGEN TRANSPORT EFFICIENCY OF ARTIFICIAL OXYGEN CARRIERS

Our research pursues the production of hypo-oncotic artificial oxygen carriers, based on artificial covalently cross-linked hyperpolymeric mammalian haemoglobins. To evaluate their in vivo efficiency in oxygen delivery to the tissue we developed a small animal model of stepwise isovolaemic blood exchange in anaesthetised, spontaneously breathing rats. With the aid of a two-way respiratory micro valve for small animals the overall oxygen uptake by the tissue of the animal can be determined. Measurements of oxygen contents in arterial and mixed venous blood and of some further blood parameters together with known oxygen-binding characteristics of artificial and native oxygen carriers, permits the determination of the way the two oxygen carriers contribute to the overall oxygen uptake. These so-called partial oxygen netto transport rates (i.e. partial oxygen uptakes), related to the corresponding intravascular mass flow of the transporters, are characteristic measures of the efficiency of the oxygen transporter, the so-called oxygen transport quality. Other biological indicators for an adequate oxygen supply are oxygen-dependent changes of ventilation, cardiac output, heart rate, and systemic vascular resistance. The performance of artificial oxygen carriers is elucidated by a comparison with experimental results from the analogous treatment of rats with non oxygen-transporting plasma expanders.