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Proton Oriented-“Smart Depot” for Responsive Release of Ca2+ to Inhibit Peptide Acylation in PLGA Microspheres

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Abstract

Purpose

The purpose of this study was to characterize and detail the mechanism of a smart Ca2+ release depot (Ca3(PO4)2) about its ability for sustainable inhibition on peptide acylation within PLGA microspheres.

Methods

The octreotide acetate release and acylation kinetics were analyzed by RP-HPLC. Changes of Ca2+ concentration and adsorption behavior were determined by a Calcium Colorimetric Assay Kit. The inner pH changes were delineated by a classic pH sensitive probe, Lysosensor yellow/ blue® dextran. Morphological changes of microspheres, adsorption between polymer and additive, transformation of Ca3(PO4)2 were characterized using SEM, FTIR and SSNMR separately.

Results

Before and after microspheres formulation, the property and effectiveness of Ca3(PO4)2 were investigated. Compared with a commonly used calcium salt (CaCl2), high encapsulation efficiency (96.56%) of Ca3(PO4)2 guarantees lasting effectiveness. In an increasingly acidic environment that simulated polymer degradation, the poorly water-soluble Ca3(PO4)2 could absorb protons and transform into the more and more soluble CaHPO4 and Ca(H2PO4)2 to produce sufficient Ca2+ according to severity of acylation. The corresponding Ca2+ produce capacity fully met the optimum inhibition requirement since the real-time adsorption sites (water-soluble carboxylic acids) inside the degrading microspheres were rare. A sustained retention of three switchable calcium salts and slow release of Ca2+ were observed during the microsphere incubation. FTIR results confirmed the long-term inhibition effect induced by Ca3(PO4)2 on the adsorption between drug and polymer.

Conclusions

With the presence of the smart Ca2+ depot (Ca3(PO4)2) in the microspheres, a sustainable and long-term inhibition of peptide acylation was achieved.

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Abbreviations

PLGA:

Poly(D,L-lactic-co-glycolic acid)

RP-HPLC:

Reversed phase high performance liquid chromatography

SEM:

Scanning Electron Microscopy

FTIR:

Fourier Transform Infrared Spectroscopy

SSNMR:

Solid State Nuclear Magnetic Resonance

PEG:

Polyethylene glycol

CMCS:

O-Carboxymethyl chitosan

Ca3(PO4)2 :

Calcium phosphate

CaHPO4 :

Calcium hydrophosphate

Ca(H2PO4)2 :

Calcium dihydrophosphate

CaCl2 :

Calcium chloride

Mw:

Molecular weight

PVA:

Poly (vinyl alcohol)

NaOH:

Sodium hydroxide

HCl:

Hydrochloric acid

TFA:

Trifluoroacetic acid

PBST:

Phosphate buffer solution (0.02 wt.% Tween 80)

HEPES:

2-[4-(2-Hydroxyethyl)-1-piperazinyl]ethanesulfonic acid

PLA:

Polylactic acid

PGA:

Polyglycolic acid

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Authors and Affiliations

  1. School of Pharmaceutical Science, Nanjing Tech University, No. 30 Puzhu South Road, Nanjing, 211816, China

    Jiwei Liu, Yan Xu, Yonglu Wang, Hao Ren, Kuntang Liu, Zhe Liu, He Huang & Xueming Li

  2. School of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, No. 30 Puzhu South Road, Nanjing, 211816, China

    Zhengjie Meng

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  1. Jiwei Liu
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  2. Yan Xu
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  3. Yonglu Wang
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  8. He Huang
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  9. Xueming Li
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Correspondence to He Huang or Xueming Li.

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Liu, J., Xu, Y., Wang, Y. et al. Proton Oriented-“Smart Depot” for Responsive Release of Ca2+ to Inhibit Peptide Acylation in PLGA Microspheres. Pharm Res 36, 119 (2019). https://doi.org/10.1007/s11095-019-2640-5

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