Transdermal delivery of bisphosphonates using dissolving and hydrogel-forming microarray patches: Potential for enhanced treatment of osteoporosis

As of 2023, more than 200 million people worldwide are living with osteoporosis. Oral bisphosphonates (BPs) are the primary treatment but can cause gastrointestinal (GI) side effects, reducing patient compliance. Microarray (MAP) technology has the potential to overcome GI irritation by facilitating the transdermal delivery of BPs. This study examines the delivery of alendronic acid (ALN) and risedronate sodium (RDN) using dissolving and hydrogel-forming MAPs for osteoporosis treatment. In vivo testing on osteoporotic female Sprague Dawley rats demonstrated the efficacy of MAPs, showing significant improvements in mean serum and bone alkaline phosphatase levels, bone volume, and porosity compared to untreated bilateral ovariectomy (OVX) controls. Specifically, MAP treatment increased mean bone volume to 55.04 ± 2.25 % versus 47.16 ± 1.71 % in OVX controls and reduced porosity to 44.30 ± 2.97 % versus 52.84 ± 1.70 % in the distal epiphysis of the femur. In the distal metaphysis, bone volume increased to 43.32 ± 3.24 % in MAP-treated rats compared to 24.31 ± 3.21 % in OVX controls, while porosity decreased to 55.39 ± 5.81 % versus 75.69 ± 3.21 % in OVX controls. This proof-of-concept study indicates that MAP technology has the potential to be a novel, patient-friendly alternative for weekly osteoporosis management.

Highlights

• Risedronate sodium (RDN) and alendronic acid (ALN) were formulated into dissolving (D-MAPs) and hydrogel-forming microarray patches (HF-MAPs), to investigate the transdermal delivery of the two bisphosphonates (BPs).
• These MAPs were tested ex vivo before subjecting to an in vivo pharmacodynamic study employing an osteoporotic female Sprague Dawley rat model.
• Therapeutic efficacy of formulated MAPs was assessed in terms of alkaline phosphatase (ALP) levels, Calcium/Phosphorus (Ca/P) ratios, and bone microarchitecture, i.e. bone volume (BV/TV %), porosity (%), trabecular thickness (Tb.th), separation (Tb.sp) and number (Tb.N).
• All MAPs investigated, proved their potential as a novel, alternative treatment option for patients living with osteoporosis.

Introduction

Osteoporosis is the most common bone disease in humans, worldwide, representing a major public health problem. It is characterised by low bone mass and density and a disruption in bone microarchitecture, all of which result in a decrease in bone strength and subsequent increased risk of fractures (Porter and Varacallo, 2024;Sozen et al., 2017). Globally, osteoporosis causes more than 9 million fractures, according to latest figures, released in 2023. In the UK alone, over 3 million people are estimated to have osteoporosis with at least 500,000 fragility fractures reported to occur each year (NICE, 2019). The economic burden of osteoporosis fractures is significant, costing in and around $17.9 and £4 billion per year in the US and UK, respectively (Clynes et al., 2020).

Osteoporosis is often referred to as a ‘silent disease’ due to absence of symptoms, and is most commonly diagnosed when fractures occur due to disease severity (Cosman et al., 2014, de Oliveira et al., 2022). Post-menopausal osteoporosis develops as a result of decreased levels of oestrogen, directly affecting the bone remodelling process. Vitamin D and calcium deficiencies may also contribute to bone loss, as can long-term glucocorticoid treatment, or certain autoimmune diseases (Mirza and Canalis, 2015). The most commonly used diagnostic test for osteoporosis is bone densitometry, using a Dual Energy X-ray Absorptiometry (DEXA) scanner, outlined by the World Health Organisation (WHO) as the gold standard for bone mineral density measurements (Leslie et al., 2006). Based on bone density measurements, management of the disease and associated bone loss, will primarily involve non-pharmacological, lifestyle changes, such as smoking cessation, reduced alcohol intake and healthy exercise. Pharmacological interventions involve the use of bisphosphonates (BPs), as first-line treatment agents, for all patients diagnosed with the disease. Alendronic acid (ALN) and risedronate sodium (RDN), specifically, are the two most commonly prescribed agents, at doses of either 10 mg and 5 mg daily, respectively, or, more commonly, 70 mg and 35 mg weekly. Alternatively, raloxifene, hormone replacement therapy or denosumab can be used (Zhu and March 2022). All of the above treatment options, ultimately work by reducing the rate of bone turnover (Drake et al., 2008). Parathyroid hormones can be used as anabolic therapies which stimulate bone formation (NICE, 2019).

BPs exert their effects by inhibiting osteoclast activation and thus prevent bone resorption, ultimately slowing down bone loss, improving bone mineral density (BMD) and reducing a patient’s risk of fractures (Zhu and March 2022). Interestingly, modification of the generic BP structure has significant effects on the potency and thus effective concentration of the drugs needed for antiresorptive activity. Potency may, in fact, be increased 10–10,000 fold in nitrogen-containing BPs, such as RDN and ALN, relative to the non-nitrogen-containing ones (Coxon et al., 2005). BPs have also been reported to selective target sites of active resorption high metabolic activity, such as trabecular regions of diseased bone tissue. Their distribution across the skeleton is thus varied.

All oral BPs have been reported as having low and variable bioavailabilities, due to their hydrophilic nature. Co-administration of the compounds with calcium or magnesium-containing foods may further hinder their intestinal absorption. Depending on the BP used, concentration and pH values, plasma and serum protein-binding may vary from 5-90 %. Gastrointestinal (GI) adverse effects are the most commonly reported reason for patient intolerance or non-compliance to oral BP treatments. Patients are counselled on administration of oral preparations, highlighting the importance of taking the dose on an empty stomach, with a full glass of water and standing or sitting upright for at least 30 min’ post dose (NICE, 2019). Other side-effects associated with BP use are: osteonecrosis of the jaw (ONJ), atrial fibrillation, atypical femoral fractures, hypocalcaemia and vitamin D deficiency.

Most commonly prescribed marketed oral preparations of BPs, are thus commonly linked to oesophageal irritation, and ulceration, as discussed above. The mechanism by which bisphosphonates cause gastric damage, however, has not fully been established, with a variety of different explanations reported in the literature (Lichtenberger et al., 2000). It has been suggested that BPs may replace hydrophobic, acid-resistant phospholipids found on the gastric mucosal barrier, due to structural similarities. The weakening of this barrier therefore causes erosions and ulceration to the oesophagus, which may lead to undesired complications if left undetected (Peter et al., 1998, Vestergaard et al., 2010, Yamamoto et al., 2019). Intravenous (IV) preparations may cause flu-like symptoms as well as pain and inflammation at the site of action. Transdermal delivery of BPs, is an attractive alternative to the oral and IV routes, but has only recently been investigated for the delivery of RDN and ALN, either via transdermal gels, or with the aid of microneedle (MN) technology (Gyanewali et al., 2021, Katsumi et al., 2017, Kusamori et al., 2010, Naito et al., 2019).

MN technology involves the use of micron-scale needle projections, which, when inserted into the skin, penetrate through its outermost layers, creating microconduits for enhanced permeation of a variety of different compounds (Alkilani et al., 2015, Donnelly et al., 2012, Ramadon et al., 2021). MNs are pain-free and overcome issues relating to needle phobia. Multiple MNs are usually attached to a baseplate, forming a microarray patch (MAP), offering a more supportive platform for application to the skin. There are five different types of MNs, namely, solid, coated, hollow, dissolving and hydrogel-forming (Alkilani et al., 2015, Tuan-Mahmood et al., 2013). Dissolving MAPs (D-MAPs) consist of aqueous blends of biocompatible polymers loaded with the active drug. Upon application to the skin surface, the polymers dissolve, delivering the drug into the dermal region of skin for uptake by the microcirculation (Ramadon et al., 2021). Hydrogel-forming MAPs (HF-MAPs) consist of a drug-free, crosslinked hydrogel network as the MAP, which upon contact with interstitial fluid in the outer layers of skin, starts to swell, creating pores for controlled drug diffusion and permeation (Donnelly et al., 2012). The drug is incorporated into a separate reservoir layer, placed on top of the array, which dissolves, as MNs start to swell, thus allowing drug molecules to move through the swollen network and into the skin. Both MAP types are good candidates for self-administration and cannot be reused, so eliminate the risk of transmission of blood borne diseases. Additionally, HF-MAPs have the ability to control or sustain the release of compounds, by modifying polymer composition and/or the degree of crosslinking, to alter swelling kinetics and thus rates of diffusion and permeation (Garland et al., 2011).

Katsumi et al. (2012), investigated the use of D-MAPs for the transdermal delivery of ALN, both in vitro and in vivo. Recently, Sultana et al. (2023) reported the use of D-MAPs for the delivery of RDN nanotransferosomes in vitro. To date, there have not been any reports of the use of HF-MAPs for the transdermal delivery of BPs.

The overall aim of the study was to assess the treatment efficacy of BPs, specifically RDN and ALN, delivered transdermally, using MN technology, for the management of osteoporosis, compared to oral control treatments. The use of HF-MAPs, in particular, for the transdermal delivery of BPs within this study, is investigated for the first time. To test this hypothesis, an in vivo pharmacodynamic study was designed, using an osteoporotic female Sprague Dawley rat model.

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Materials

Poly(vinyl alcohol) (PVA) 31–50 kDa, PVA 85–124 kDa, acetonitrile (ACN) (suitable for HPLC, gradient grade, ≥ 99.9 %), trehalose dihydrate, gelatin, poly(ethylene glycol) (PEG) 10,000, O- phthalaldehyde (OPA), N-acetylcysteine (NAC), formaldehyde solution 37 %, and sodium acetate were purchased from Sigma-Aldrich (Dorset, UK). Poly(vinyl pyrrolidone) (PVP) 58 kDa, marketed as Plasdone™ k29/32 was obtained from Ashland (Wilmington, DE, USA). Gantrez® S-97 was provided by Ashland (Worcestershire, UK). Anhydrous citric acid was purchased from BDH laboratory supplies (Poole, Dorset, England). RDN was purchased from Cangzhou Enke Pharma-tech Co., ltd. and ALN from Tokyo Chemical Industry UK ltd, Oxford, UK. For the neonatal porcine skin used in vitro, stillborn piglets were obtained from a local farm immediately after birth and excised skin was stored at − 20 °C until further use.

Anastasia Ripolin, Fabiana Volpe-Zanutto, Akmal H. Sabri, Victor Augusto Benedicto dos Santos, Sidney R. Figueroba, Arthur A.C. Bezerra, Brendo Vinicius Rodrigues Louredo, Pablo Agustin Vargas, Mary B. McGuckin, Aaron R.J. Hutton, Eneko Larrañeta, Michelle Franz-Montan, Ryan F. Donnelly, Transdermal delivery of bisphosphonates using dissolving and hydrogel-forming microarray patches: Potential for enhanced treatment of osteoporosis, International Journal of Pharmaceutics, Volume 665, 2024, 124642, ISSN 0378-5173, https://doi.org/10.1016/j.ijpharm.2024.124642.

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