C Cecutti

A Novelli

I Rico

A Lattes

The synthesis of a novel microemulsion system composed a fluorinated oil C g F 17 -cH z -CH=CH-C 4 H g with a biocompatible drogenated surfactant, Montanox 80, is described.

of hy -

Investigation of the solubility of oxygen in these microe mulsions showed that they absoi-bed more oxygen than Fluosol-DA, currently used as an oxygen transporter in biological systems. Oxygen absorption was comparable to that of blood.

Light scattering studies showed that these systems are com posed of small-sized aggregates which should, in principle, be compatible with blood. The toxicity of the oil c 8 F 17 -cH 2 -CH=CH c 4 H 9 was tested after intraperitoneal injection in rats. No toxic effects were observed at doses up to 5 g/kg.

This study opens new perspectives for the development of oxygen-transporting compounds for biomedical applications.

INTRODUCTION

The supply of human blood for transfusion and other medi cal applications is now faced with new exigencies of biocompati bility and sterility, as well as those inherent in the econo mics of the collection and storage of samples. Recent concern with AIDS bas highlighted the well recognized problem of viral contamination of blood,especially that due ta viral hepatitis.

Th e c hoi ce of a synthetic blood substitute depends to a large exten t on the particular requirement : 1) co nserva tion of blood volume can be achieved using solu tions of plasm a expanders 2) pres ervation of ionic balance, for which solutions of electrolyte s are often adequate 3) transport and distribution of oxygen, and elimination of carbon dioxide;

The third function is a more difficult but nonetheless vi tal requirement, and forms the subject of this report.

Blood is a complex liquid containing a large number of com ponents serving different functions, of which the most impor tant is the dissolution of respiratory gases. Various formula tions can be envisaged which satisfy : a number of these require ments, although in each case gas exchange must not be iff ipaired.

This latter consideration is so important that gas exchange needs to be optimized even at the expense of other capacities which can usually be provided by additional components of the mixture.

Respiratory gases can be dissolved in 1) artifical solutions of hemoglobin

2) solutions of fluorocarbons

Commercially available preparations are in fact based on the latter approacb. Perfluorinated derivatives combined with a suitable oncotic agent are currently used as blood substitutes.

Emulsions of perfluorinated compounds have now been tested in several hundreds of subjects throughout the world (1-3).

The essential qualities of fluorocarbons (1,4,5) are high capacity to dissolve gases, e-specially oxygen and carbon dioxide low toxicity resulting from the rapid elimination of the unrne tabolized substance from the organism.

The capacity to dissolve gases is explained by the lack of structure of perfluorinaged liquids. They appear to contain ca- One way round this probl.em is to use microemulsions. They have the tri�le advantage of forming spontaneously, remaining stable for months or years, and have a range of particle sizes which are, compatible with blood.

How�ver, the formation of microemulsions (like emulsions) cornes UJ?:, against problems due to the structure of the perfluori nated derivatives themselves. A microemulsion contains three es senti�l compori.ent-s (6) : water -surfactant -oil (in this ca se a perfluorill.ated c"Ompound).

The intrinsic hydrophobicity of perfluorinated deriVati ves h:i:.rtders microemulsification, due to the phenomenon of segre gation between perhydrogenated and perfluorinated chains (i;à). Attempts to make these two components mutually compatible ban be. div, ided into two main strategies, based on i) structural modification of the perfluorinated derivatives, or ii) selection of the surfactant For the completely fluorinated compounds, various structu res have been tested, including amines, ethers, cyclanes, ole fins, etc ... The various studies have shown that the presence of a functional group or heteroatom generally leads to slower elimination from the organism with a corresponding increase in toxicity. This is particularly marked for the amines. The best , derfv � --tiv es tbus appear to be represented b y . alkanes, cyclanes or :.01€.fins (1) • The structure of the • surfactant is also crucial for produc tion of suitable microemulsions. Much research is devoted to this aspect, especially on the synthesis of surfactants which are compatible with perfluorinated alkanes and alkenes lacking heteroatoms.

In view of the problems due to segregation between hydro carbon and•perfluorinated chains, reSear-ch bas concentrated on perfluorinated surfactants (5,9).

However, amphiphilic molecules of this type will inevita bly present the same disadvantages as the perfluorinated oils.

In all cases, they are compounds with a polar head (ionic or not) and a perfluorinated tail. These surfactants are elimina ted slowly from the organism, often being degraded to taxie fluoride ions. Much effort is now being put into the develop ment of non-toxic fluorinated surfactants. This approach can be summarized as •:

The • development of biocompatible fluorinated surfactants ta microemulsify perfluorinated oils.

In view of thè above mentioned considerations, we felt that this approach was fraught with difficulties, and we opted for an approach which can be summàrized as :

The adaptation of the oil to a known bioCompatible surfac tant. This is effectively the converse of the first approach.

At present, only hydrogenated non-ionic surfactants (ampho teric) have been found to be biocompatible. We thus decided to synthesize and test mix. ed oils sufficiently fluorinated to dis solve gas and be eliminated rapidly, but sufficiently hydrogena ted to enable them to be microemulsified using biocompatible hy drogenated sur. factants.

METHODS AND RESULTS

SyntheSis of mixed oils

The mixed oils synthesized were of general formula R F - From the various compounds synthesized, the mixed oil C a F1 7 CH 2 -CH=CH-C4H9 produced in 74% yield was tested. This com pound was found to be a good gas solvent. Determination of oxy gen solubility using the Clark electrode showed that it dissol ved 43 ml of oxygen per 100 ml. This is comparable to that of F decalin (the oil employed in Fluosol DA).

Microemulsification of the mixed oil c 8 F 17 -CH 2 -CH=CH-C4H9 Various hydrogenated surfactants were tested in order to produce rnicroemulsions with this oil. We optimized an aqueous system with c 8 r 17 -cH 2 -CH=CH-C 4 H9 as oil, and the biocompatible surfactant, Montanox 80 (see Fig_. 1). This surfactant is used in the formulation of vaccines by the Institut Pasteur (Paris, France) (1 2 ).

The diagram in Figure 1 shows the microernulsion zone at 37°C (body temperature ) . The rnicroemulsions are of the oil-in water type, which are well suited for use as blood substitutes, since they are readily diluted in blood after intravenous admi- Properties of the microemulsions Measurement of viscosity and light scattering at 37 °C de monstrated that the microemulsions were of the oil-in-water ty pe, and were composed of small-sized aggregates (mean diaw.. 50 -60 A). Aggregates of this size do not, in principle, favor for� mation of emboli after injection into the general circulation.

The values of viscosity, and oxygen solubility measured with the Clark electrode are presented in Table I.

DISCUSSION

All the microemulsions tested dissolved more FLuosol DA (11 ml 02/100 ml). Oxygen sol_ ubility was to that o f blood (20,6 ml 0 2 ;100 ml). oxygen thàn comµarable It should be emphasized that the theoretical values ' of oxygen solubility (given the amount of oil in the microèffiulsion) are much lower than the measured values. The excess sol,ubility was around 500%, This would tend to indicate that the structu re of the microemulsions (existence of micellar cages) increa ses their capacity to dissolve gas. This phenomenon bas been ob served, although to a lesser extent (around 200%) ,for perhydro genated oils [START_REF] Berthod | Microemulsion systems[END_REF]. It should also be noted that the presence of a fluorinated oil is required to observe this phe'nomenon of so lubilization. Corresponding micellar solutions (without oil) on ly took up small amounts of oxygen (around 6 ml/100 ml) �imi lar to that observed for water (3 ml/100 ml).

Preliminary toxicological studies in the rat after inttape ritoneal administration have demonstrated the lack of toxicity of these systems [START_REF] Cecutti | [END_REF]. Further trials are in progress using intravenous administration.

  vities. whLch can trap oxygen and carbon diàxide. llowever, fluorirt ated com p ounds cannot be used in the pu r e state, the. y need to be formulat:ed as emulsion• s. A sùspension of per� and fine particles of fluorocarbon, c.an l)e pt'oduced with the aid of a sui table surfact ant. At present, the cqmmerciall y-available systems of this ty pe are based on Fl1J,O$:Ol DA (an emulsion of perfl_uorodecalin and Pluronic F 68:th� l�tter is a copolymer of ethylene and propyle ne oxide with a_ molecular weight of 8,350) (2,3). However, thé se emulsions lack lon g t• erm stability, and must be kept refrige rated.

CH 2 -

 2 CH=CH-R H .A rnethod for synthesizing compounds of this type deve loped in this laboratory enabled the balance between the fluori nated and hydrogenated parts to be altered at will(l0,11) : (C 6 H 5 ) 3P + RpCH 2 cH 2 I -----(C6Hs)3P + CH 2 CH 2 Rp, 1-� Rp-CH 2 -CH-CH-R H + (C6H5)P-O (R p -C2F5, C 4 F9, C6F l 3• C s F 17 , C 10 F 21 )

Fig. 1 .

 1 Fig. 1 .-Phase diagr am of the syste m a 2 o -Monta nox 80 -c 8 F 17 -CH 2 -CH-C H-C 4 H9

  used for these experiments. It is a good gas solvent, and it could be readily formulated to be com patible with blood by the addition of salts. No hem ? lysis has been observed in the use of these formulations. These results demonstrate the feasibility of production of microemulsions using fluorinated oils and hydrogenated, biocom patible surfactants. Such systems could be employed as blood substitutes. An immedtate application WQuld be in the formula tion of culture media.