Biotechnology
(DM = 9 µm). La stabilité des liposomes a été évaluée par leur capacité à retenir la thiamine encapsulée. La moitié de la vitamine reste dans
les liposomes après 63 h de stockage en milieu tampon, alors que la moitié de la vitamine a fui après 3 h en présence d’eau de mer. Les liposomes
ont été enrobés par un dextrane greffé à du cholestérol. Un allongement
des temps de rétention, de 130 h et 18 h respectivement, est obtenu pour
les liposomes conservés dans un milieu tampon et dans l’eau de mer.
L’enrobage des liposomes par un polysaccharide améliore donc de manière
significative la rétention d’une vitamine hydrosoluble encapsulée.
Introduction
Liposomes, which consist in closed lipid structures dehmiting an aqueous
internal volume, may be used either as cell membrane models or as
potential carriers for biologically active substances (Lasic, 1993). Indeed,
they have already shown biocompatibility and biodegradability properties. However, their development as suitable artificial cliet is actually
poorly investigated although, due to their structure, they answer the
double purpose of lipid and hydrosoluble nutriment simultaneous delivery. Requirements for vitamins B1, B2 (Séguineau et al., 1996) and
polyunsaturated fatty acids (PUFAs) (Marty et al., 1992; Soudant et al.,
1996 a, b) have been pointed out for bivalve larvae. They are not always
satisfied by the phytoplanktonic food offered and supplementation may
be requested. Several attempts using liposomes as a part of the food
source for marine organisms are to be mentioned (Parker & Selivonchick,
1986; Hontaria et al., 1994; Ozkizilcik & Chu, 1994). Their major
drawback was their small size (200 nm), far from the optimal retention range of most marine organisms. However, larger liposomes can
be obtained by extrusion through filters and would be more convenient for nutrition. On the other hand, it is worth noting that most
studies focused on uptake and metabolism of lipid vesicles by larvae
or filter-feeding organisms but the liposome behaviour in sea water was
not fully understood. In particular, the osmotic shock due to the different osmolarities of sea water and the internal solution in the liposome
often leads to the leakage of the encapsulated compound. With the
aim of better handling the retention of hydrosoluble nutriments by
liposomes, encapsulation of vitamin B1 (thiamine) was performed, since
this vitamin is known to be of major importance for growth of scallop
larvae (Séguineau et al., 1996). Moreover, liposomes were based on
marine lipicls rich in PUFAs, in order to ensure a potential nutritional
supplementation in essential fatty acids. Liposome stability is presented
in terms of morphology and membrane permeability through thiamine
retention. The results present a comparison of the liposome behaviour
in buffer solution and in sea water. At last, in order to improve thiamine retention in sea water, liposome coating with a polysaccharide is
envisaged.
213
(DM = 9 µm). La stabilité des liposomes a été évaluée par leur capacité à retenir la thiamine encapsulée. La moitié de la vitamine reste dans
les liposomes après 63 h de stockage en milieu tampon, alors que la moitié de la vitamine a fui après 3 h en présence d’eau de mer. Les liposomes
ont été enrobés par un dextrane greffé à du cholestérol. Un allongement
des temps de rétention, de 130 h et 18 h respectivement, est obtenu pour
les liposomes conservés dans un milieu tampon et dans l’eau de mer.
L’enrobage des liposomes par un polysaccharide améliore donc de manière
significative la rétention d’une vitamine hydrosoluble encapsulée.
Introduction
Liposomes, which consist in closed lipid structures dehmiting an aqueous
internal volume, may be used either as cell membrane models or as
potential carriers for biologically active substances (Lasic, 1993). Indeed,
they have already shown biocompatibility and biodegradability properties. However, their development as suitable artificial cliet is actually
poorly investigated although, due to their structure, they answer the
double purpose of lipid and hydrosoluble nutriment simultaneous delivery. Requirements for vitamins B1, B2 (Séguineau et al., 1996) and
polyunsaturated fatty acids (PUFAs) (Marty et al., 1992; Soudant et al.,
1996 a, b) have been pointed out for bivalve larvae. They are not always
satisfied by the phytoplanktonic food offered and supplementation may
be requested. Several attempts using liposomes as a part of the food
source for marine organisms are to be mentioned (Parker & Selivonchick,
1986; Hontaria et al., 1994; Ozkizilcik & Chu, 1994). Their major
drawback was their small size (200 nm), far from the optimal retention range of most marine organisms. However, larger liposomes can
be obtained by extrusion through filters and would be more convenient for nutrition. On the other hand, it is worth noting that most
studies focused on uptake and metabolism of lipid vesicles by larvae
or filter-feeding organisms but the liposome behaviour in sea water was
not fully understood. In particular, the osmotic shock due to the different osmolarities of sea water and the internal solution in the liposome
often leads to the leakage of the encapsulated compound. With the
aim of better handling the retention of hydrosoluble nutriments by
liposomes, encapsulation of vitamin B1 (thiamine) was performed, since
this vitamin is known to be of major importance for growth of scallop
larvae (Séguineau et al., 1996). Moreover, liposomes were based on
marine lipicls rich in PUFAs, in order to ensure a potential nutritional
supplementation in essential fatty acids. Liposome stability is presented
in terms of morphology and membrane permeability through thiamine
retention. The results present a comparison of the liposome behaviour
in buffer solution and in sea water. At last, in order to improve thiamine retention in sea water, liposome coating with a polysaccharide is
envisaged.
213