PubMed · 14135209
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L G ABBOTT. 1964. WARTS.. https://pubmed.ncbi.nlm.nih.gov/14135209/
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Poly(ethylene glycol)--poly(D,L-lactide) (PEG-PDLLA) block copolymers were prepared by anionic ring-opening polymerization, resulting in block sizes effectively controlled by initial monomer/initiator ratios and low molecular weight distributions (<1.12). A pyrene derivative (1-pyrenyl carbonyl cyanide--Py) was conjugated to the end of the hydrophobic block (PDLLA) in a quantitative manner, with coupling efficiencies >95%. The so-obtained PEG-PDLLA-Py copolymers displayed fluorescent properties that were associated with the pyrene monomers, when placed in good solvents for both the hydrophilic and hydrophobic blocks. When placed in selective solvents, these copolymers self-assembled into micelles in the 30-nm range, also with low particle size distributions (<0.09), within which Py could be readily entrapped in the hydrophobic PDLLA core. Py entrapment resulted in the formation of excimers, as evident from fluorescence measurements. Observation of excimer formation/dissociation further conveyed information on the physicochemical properties of the core. Thermal characterization of these systems showed that an increase in the temperature resulted in changes in the properties of excimer fluorescence, an occurrence attributed to a higher mobility of the otherwise glassy PDLLA. This, in turn, greatly affected the inter-molecular distance between pyrene molecules, a crucial factor for excimer formation. The glass transition of the PDLLA block, approximately 38 degrees C, defined the onset for increasing chain mobility and whence excimer dissociation. Excimer fluorescence appeared to be time-dependent. Based on these observations, chain exchange processes were clearly evidenced through the time-dependent dissociation of excimers into unimers, a process that was influenced by changes in temperature.
This paper deals with the preparation and characterization of monomethoxypoly(ethylene oxide)-poly(lactic acid) (MPEO-PLA) nanoparticles containing protein C, a plasma inhibitor which regulates the mechanism of blood coagulation. Protein C was entrapped in MPEO-PLA nanoparticles using the double emulsion method. The influence of MPEO-PLA copolymers on the different parameters was evaluated: characteristics of protein C-loaded nanoparticles, in vitro release of the protein, evolution of the particle size with incubation time and MPEO release. The nanoparticle size does not depend on copolymer characteristics (MPEO and/or PLA block molecular weight). On the other hand, the efficiency of protein C entrapment is affected by the copolymer characteristics. The burst effect during the protein C release is increased with the hydrophilic character of the copolymer. Moreover, protein C adsorption on the particle surface during its release may be related to MPEO release. Only 25% of the released protein C is active, which clearly illustrates that it is altered during its encapsulation. The optimization of the experimental parameters which disturbed entrapped protein C activity, i.e. sonication time and organic solvent was investigated and has led to a preservation of protein C activity. Then, to optimize its entrapment efficiency, a blend PLA/MPEO-PLA (25/75) was used to prepare nanoparticles. This blend limited burst effect of protein C and its adsorption. However, protein C is only partially released which implicates further investigation for a potential therapeutic use.
The addition of bovine serum albumin (BSA) to a solution of lactate and alanine resulted in the disappearance of the 1H-NMR resonances from lactate but not alanine. As temperature is increased lactate becomes increasingly NMR visible and after heating above 65 degreesC and cooling to 25 degreesC lactate binding is reduced. With a concentration of 0.2 mM BSA, there was a linear relationship between NMR visible lactate versus total lactate over a range of lactate concentrations of 0.2-35 mM (slope 0.384+/-0.003) indicating that approx. 60% of the added lactate is not visible in the 1H-NMR spectrum. With a 0.1 mM BSA solution, however, the slope was markedly higher indicating that under these conditions only 25-30% of the lactate was NMR invisible. The results from this study indicate that decreased NMR visibility of lactate in proteinaceous solutions is due to non-specific binding which is dependent on the tertiary structure of the protein. This has important implications not only for the interpretation of in vivo 1H-NMR experiments but also for 13C, and 14C studies of metabolism.