Brain enzymes resistance

Numerous modifications of in vitro culture systems have been developed for the estimation of BBB transfer [52]. Culture systems in use are either primary cultures of brain microvessel endothelial cells (BMEC) or immortalized endothelial cell hues. BMEC may be grown in co-culture with astrocytes or in astrocyte-conditioned medium. Astrocyte-derived factors increase the tightness of the barrier as measured by transendothelial electrical resistance (TEER) and by the permeability of hydrophUic markers such as sucrose. They also up-regulate the expression of BBB-enriched enzymes such as y-glutamyl transpeptidase (y-GTP) and alkaline phosphatase. A setup of the in vitro technique in a transwell system for transport studies is depicted in Figure 2.5. 

Additional information <1, 3, 6, 18, 20, 21, 24> (<1, 3, 6> comparison of various enzymes of variou.s sources [37] <18, 20, 21> enzymes from marine fishes are less thermostable than that of carp, the latter being more labile than the rabbit enzyme [42] <24> shark muscle isozyme marginally more resistant to temperature inactivation than brain isozyme [46]) [37, 42, 46]... 

D-Ala-deltorphin-I and -II transverse the blood brain barrier in vivo and in vitro [51]. Recently, D-Ala-deltorphin-II was identified as a transport substrate of organic anion transporting polypeptides (Oatp/OATP), a family of polyspecific membrane transporters, strongly expressed at the rat and human blood brain barrier [52]. Modified analogues of these peptides were synthesized to improve their transit across the blood brain barrier [48,49,53]. Because they resist enzyme degradation and can cross endothelial barriers into the CNS, the deltorphins meet the criteria for peptides with potential for systemic administration. 

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