Peptide acylation by poly(alpha-hydroxy esters).
OBJECTIVE
Poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) microspheres were investigated concerning the possible acylation of incorporated peptides.


METHODS
Atrial natriuretic peptide (ANP) and salmon calcitonin (sCT) were encapsulated into PLA and PLGA microspheres. Peptide integrity was monitored by HPLC-MS analysis during microsphere degradation for four weeks. sCT fragmentation with endoproteinase Glu-C was used for identifying modified amino acids. Peptide stability in lactic acid solutions was investigated to elucidate possible mechanisms for preventing peptide acylation.


RESULTS
Both peptides were acylated by lactic and glycolic acid units inside degrading microspheres in a time-dependent manner. After 21 days, 60% ANP and 7% sCT inside PLA microspheres were acylated. Fragmentation of sCT with endoproteinase Glu-C revealed that besides the N-terminal amine group, lysine, tyrosine or serine are further possible targets to acylation. Stability studies of the peptides in lactic acid solutions suggest that oligomers are the major acylation source and that lower oligomer concentration and higher pH substantially decreased the reaction velocity.


CONCLUSIONS
The use of PLA and PLGA for drug delivery needs substantially more circumspection. As, according to FDA standards. the potential hazards of peptide acylation products need to be assessed, our findings may have significant implications for products already on the market. Techniques to minimize the acylation reaction are suggested.
Lucke
Andrea
A
Department of Pharmaceutical Technology, University of Regensburg, Germany.
Kiermaier
Josef
J
Göpferich
Achim
A
D000215:Acylation; D000595:Amino Acid Sequence; D009320:Atrial Natriuretic Factor / Q000737:chemistry; D002116:Calcitonin / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D004339:Drug Compounding; D016503:Drug Delivery Systems; D004355:Drug Stability; D004952:Esters / Q000737:chemistry*; D019344:Lactic Acid / Q000737:chemistry; D013058:Mass Spectrometry; D008863:Microspheres; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010455:Peptides / Q000737:chemistry*; D011091:Polyesters; D011100:Polyglycolic Acid / Q000737:chemistry; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry
D004952:Esters; D010455:Peptides; D011091:Polyesters; D011108:Polymers; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; C033616:poly(lactide); C028815:salmon calcitonin; D009320:Atrial Natriuretic Factor; D002116:Calcitonin