The necessity for the coating of perfluorodecalin-filled poly(lactide-co-glycolide) microcapsules in the presence of physiological cholate concentrations: Tetronic-908 as an exemplary polymeric surfactant.

Recently, we demonstrated that biodegradable poly(lactide-co-glycolide) (PLGA) micro- and nanocapsules with a liquid content of perfluorodecalin are principally useful for the development of artificial oxygen carriers. In order to solve a decisive and well-known problem with PLGA microcapsules, i.e. the spontaneous agglomeration of the capsules after depletion of the emulsifying agent (i.e. cholate), coating with the ABA block copolymer, Tetronic-908 was studied. After Tetronic-908 treatment at concentrations that were harmless to cultured cells, the clustering of the microcapsules was prevented, the adsorption of opsonins was decreased and the attachment to cells was inhibited, but the oxygen transport capacity of PLGA microcapsules was even increased. The present data clearly show that perfluorodecalin-filled PLGA microcapsules must be coated before decreasing the emulsifying agent cholate to physiological concentrations, in order to develop a solution that has the capabilities to function as a potential artificial oxygen carrier suspension.

NAD(H) enhances the Cu(II)-mediated inactivation of lactate dehydrogenase by increasing the accessibility of sulfhydryl groups.

Copper ions are known to inactivate a variety of enzymes, and lactate dehydrogenase (LDH) is exceptionally sensitive to the presence of this metal. We now found that NADH strongly enhances the Cu(II)-mediated loss of LDH activity. Surprisingly, NADH was not oxidized in this process and also NAD+ promoted the Cu(II)-dependent inactivation of LDH. Catalase only partly protected the enzyme, whereas hypoxia even enhanced LDH inactivation. NAD(H) accelerated sulfhydryl (SH) group oxidation of LDH by 5,5-dithio-bis(2-nitrobenzoic acid) (DTNB), and, vice versa, LDH-mediated Cu(II) reduction. LDH activity was preserved by thiol donators and pyruvate and partially preserved by lactate and oxamate. Our results suggest that reactive oxygen species (ROS) are of minor importance for the inactivation of LDH induced by Cu(II)/NADH. We propose that conformational changes of the enzymes' active sites induced by NAD(H)-binding increase the accessibility of active sites' cysteine residues to Cu(II) thereby accelerating their oxidation and, consequently, loss of catalytic activity.