Preparation of budesonide-loaded porous PLGA microparticles and their therapeutic efficacy in a murine asthma model

Abstract

Inhaling corticosteroids, such as budesonide (BD), is the most common treatment for asthma. However, frequent steroid administration is associated with many side effects. We hypothesized that porous microparticles containing BD could provide an effective treatment method for asthma, as the sustained delivery of corticosteroid and a reduced number of doses could be achieved using porous polymeric microparticles. Porous microparticles were prepared from poly(lactic-co-glycolic acid) (PLGA) by a water-in-oil-in-water double emulsion method with ammonium bicarbonate as the porogen. Varying the porogen concentration controlled the morphology, particle size, and pore size of the PLGA microparticles, with particle size and pore size increasing as the porogen concentration increased. The BD loading efficiency in the porous PLGA microparticles was about 60%, and BD was released from the porous microparticles in a sustained manner for 24 h in vitro. Lung uptake efficiency of the porous PLGA microparticles in mice was significantly higher than that of non-porous PLGA microparticles. Budesonide-loaded porous PLGA microparticles were delivered to asthmatic mice, and the numbers of inflammatory cells in bronchoalveolar lavage (BAL) fluid and tissue sections were significantly reduced when the drug was administrated every 3 days. We also found significantly reduced bronchial hyperresponsiveness of asthmatic mice after treatment with budesonide-loaded porous PLGA microparticles. This approach to controlling the porous structure of polymeric microparticles, as well as the release behavior of drugs from the microparticles, could have useful applications in the pulmonary delivery of many therapeutic drugs.

Introduction

Asthma is a chronic airway disease caused by a complex interaction of environmental and genetic factors, which induces airway inflammation to cause wheezing, chest tightness and cough [1]. According to the latest World Health Organization estimates, about 300 million people suffer from asthma, and the prevalence of asthma has increased by 75% since 1994 [2]. The most common treatment method for asthma includes the use of controller medications such as corticosteroids, as they have excellent anti-inflammatory effects and efficiently inhibit a variety of inflammatory responses that evoke airway hyperresponsiveness. Corticosteroids, which can reduce the number of inflammatory cells and protect blood vessels from leaking fluid into the airway tissues, can be administered in three ways, including inhalation via a metered dose inhaler (MDI) or dry powder inhaler, oral administration of a tablet, and injection of a liquid form [3]. However, despite the excellent therapeutic effects of these treatments, their use has been limited due to systemic side effects such as adrenocortical suppression, Cushing's syndrome and osteoporosis [4], [5].

Budesonide (BD) is a glucocorticoid with high anti-inflammatory activity and low systemic effects due to high receptor affinity, airway selectivity, and rapid diversion [6], [7], [8]. This drug is a potential candidate for the treatment of asthma, allergic rhinitis, and inflammatory bowel disease through inhalation. In addition, it has been known to prevent lung tumors [9]. Inhaled BD is widely used for the management of asthma with a daily dose of 160–640 μg based on severity. However long-term use, as well as frequent BD administration, may generate many unwanted side effects such as growth suppression, skin thinning, reduced bone mineral density, and cataract [10].

Pulmonary drug delivery is an alternative for the systemic delivery of therapeutic drugs, as it has many advantages over oral delivery and injection [11], [12]. For example, when a drug is administered via a pulmonary route, absorption of the drug is very effective due to high solute permeability and the large surface area of the lungs. It has been reported that many drugs such as insulin, calcitonin, lysozyme, and deslorelin can be delivered via a pulmonary route [13], [14]. Recently, dry powder inhaler (DPI) technology was found to be efficient for pulmonary drug delivery, but it requires a thorough characterization of the drug powder, including the determination of particle size, density, morphology, and surface area [15].

Polymeric micro- or nanoparticles have been frequently used as a pulmonary delivery vehicle for therapeutic drugs due to their many advantages, including the controlled release of encapsulated drugs and easy administration in a minimally invasive manner. However, there are difficulties associated with the use of small microparticles (1–5 μm in diameter) and nanoparticles for effective pulmonary drug delivery because these particles are susceptible to alveolar macrophage removal and mucociliary clearance in the lungs. In contrast, large microparticles (10–20 μm in diameter) with a low density (i.e., high porosity) are suitable for deep lung delivery, as they are protected from alveolar macrophage clearance due to their large size [16]. Poly(d,l-lactide-co-glycolide) (PLGA) has been widely used for fabrication of particulate systems [17], [18], [19], [20], including porous microparticles [21], [22], [23]. However, few studies have reported the mechanism of porous microparticles containing glucocorticoid as a long acting agent for asthma treatment when delivered via a pulmonary route.

In this study, porous PLGA microparticles containing BD were prepared by a water-in-oil-in-water (w/o/w) double emulsion method using ammonium bicarbonate as the porogen. Characteristics of the porous PLGA microparticles, including particle size, pore size, density, porosity, drug loading efficiency, and in vitro release behavior, were investigated. In addition, the therapeutic efficacy of the BD-loaded porous PLGA particles was tested in a murine asthma model.