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Gamma Irradiation of Active Self-Healing PLGA Microspheres for Efficient Aqueous Encapsulation of Vaccine Antigens

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ABSTRACT

Purpose

To investigate the effect of γ-irradiation of poly(lactic-co-glycolic acid) (PLGA)/Al(OH)3/0 or 5 wt% diethyl phthalate (DEP) microspheres for active self-healing encapsulation of vaccine antigens.

Methods

Microspheres were irradiated with 60Co at 2.5 and 1.8 MRad and 0.37 and 0.20 MRad/h. Encapsulation of tetanus toxoid (TT) was achieved by mixing Al(OH)3-PLGA microspheres with TT solution at 10–38°C. Electron paramagnetic resonance (EPR) spectroscopy was used to examine free radical formation. Glass transition temperature (Tg) and molecular weight of PLGA was measured by differential scanning calorimetry and gel permeation chromatography, respectively. Loading and release of TT were examined by modified Bradford, amino acid analysis, and ELISA assays.

Results

EPR spectroscopy results indicated absence of free radicals in PLGA microspheres after γ-irradiation. Antigen-sorbing capacity, encapsulation efficiency, and Tg of the polymer were also not adversely affected. When DEP-loaded microspheres were irradiated at 0.2 MRad/h, some PLGA pores healed during irradiation and PLGA healing during encapsulation was suppressed. The molecular weight of PLGA was slightly reduced when DEP-loaded microspheres were irradiated at the same dose rate. At the 0.37 MRad/h dose rate, these trends were not observed and the full immunoreactivity of TT was preserved during encapsulation and 1-month release. Gamma irradiation slightly increased TT initial burst release. The small increase in total irradiation dose from 1.8 to 2.5 MRad had insignificant effect on the polymer and microspheres properties analyzed.

Conclusions

Gamma irradiation is a plausible approach to provide a terminally sterilized, self-healing encapsulation PLGA excipient for vaccine delivery.

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Abbreviations

AAA:

amino acid analysis

Active SM:

active self-microencapsulating

Al(OH)3 :

aluminum hydroxide adjuvant

BSA:

bovine serum albumin

DEP:

diethyl phthalate

DSC:

differential scanning calorimetry

EDTA:

ethylenediaminetetraacetic acid

ELISA:

enzyme-linked immunosorbent assay

EPR:

electron paramagnetic resonance

FMOC:

9-fluoromethyl-chloroformate

GPC:

gel permeation chromatography

HCl:

hydrochloric acid

ISO:

international organization for standardization

M w :

weight-average molecular weight

OPA:

o-phthalaldehyde

PBB:

phosphate buffered saline + 0.5% bovine serum albumin + 0.05% Brij® 35

PBS:

phosphate buffered saline

PBST:

phosphate buffered saline + 0.02% Tween 80

PLGA:

poly(lactic-co-glycolic acid)

PNPP:

(p-nitrophenyl phosphate, disodium salt) liquid substrate

PTFE filter:

hydrophobic fluoropore filter

PVA:

poly(vinyl alcohol)

SEM:

scanning electron microscopy

Tg :

glass transition temperature

THF:

tetrahydrofuran

TT:

tetanus toxoid

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ACKNOWLEDGMENTS AND DISCLOSURES

This study was funded by NIH R01 HL 68345 and R21 EB 08873. We greatly appreciate Mrs. Shobha Churi (Dept. of Pharmacy Practice, JSS University, Mysore, India) and Dr. Manjunatha (Registrar, JSS University, Mysore, India) for their help in receiving TT sample from Serum Institute of India. We thank Dr. Rajesh Gupta, FDA, for sending Equine tetanus antitoxin sample and helpful discussion.

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  1. Department of Pharmaceutical Sciences and the Biointerfaces Institute, University of Michigan, NCRC, 2800 Plymouth Road, Ann Arbor, Michigan, 48109, USA

    Kashappa-Goud H. Desai, Samer Kadous & Steven P. Schwendeman

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  1. Kashappa-Goud H. Desai
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  2. Samer Kadous
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  3. Steven P. Schwendeman
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Correspondence to Steven P. Schwendeman.

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Desai, KG.H., Kadous, S. & Schwendeman, S.P. Gamma Irradiation of Active Self-Healing PLGA Microspheres for Efficient Aqueous Encapsulation of Vaccine Antigens. Pharm Res 30, 1768–1778 (2013). https://doi.org/10.1007/s11095-013-1019-2

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