Enhancement of transdermal apomorphine delivery with a diester prodrug strategy

Clinical trial evaluating apomorphine oromucosal solution in Parkinson's disease patients

Apomorphine, used to treat OFF episodes in patients with Parkinson's disease (PD), is typically administered via subcutaneous injections. Administration of an oromucosal solution could offer a non-invasive and user-friendly alternative. This two-part clinical study evaluated the safety, tolerability, pharmacokinetics (PK), and dose proportionality of a novel apomorphine hydrochloride oromucosal solution, as well as its relative bioavailability to subcutaneous apomorphine injection and apomorphine sublingual film. In part A of the study, 12 patients with PD received 2 mg oromucosal apomorphine (4% weight/volume) and 2 mg subcutaneous apomorphine in a randomized order, followed by 4 and 8 mg oromucosal apomorphine. In part B of the study, 13 patients with PD received 7 mg oromucosal apomorphine (7% weight/volume) and 30 mg sublingual apomorphine in a randomized order, followed by 14 mg oromucosal apomorphine. Washout between dose administrations in both study parts was at least 2 days. Safety, tolerability, and PK were assessed pre- and post-dose. Both study parts showed that oromucosal apomorphine was generally well-tolerated. Observed side effects were typical for apomorphine administration and included asymptomatic orthostatic hypotension, yawning, fatigue, and somnolence. Oromucosal apomorphine exposure increased with dose, although less than dose proportional. The mean (SD) maximum exposure reached with 14 mg oromucosal apomorphine was 753.0 (298.6) ng*min/mL (area under the plasma concentration-time curve from zero to infinity) and 8.0 (3.3) ng/mL (maximum plasma concentration). This was comparable to exposure reached after 2 mg subcutaneous apomorphine and approximately half of the exposure observed with 30 mg sublingual apomorphine. In summary, clinically relevant plasma concentrations could be reached in PD patients without tolerability issues.

Fabrication and Characterization of Dissolving Microneedles for Transdermal Drug Delivery of Apomorphine Hydrochloride in Parkinson's Disease

PURPOSE

We fabricated and characterized polyvinyl alcohol (PVA)-based dissolving microneedles (MNs) for transdermal drug delivery of apomorphine hydrochloride (APO), which is used in treating the wearing-off phenomenon observed in Parkinson's disease.

METHODS

We fabricated MN arrays with 11 × 11 needles of four different lengths (300, 600, 900, and 1200 μm) by micromolding. The APO-loaded dissolving MNs were characterized in terms of their physicochemical and functional properties. We also compared the pharmacokinetic parameters after drug administration using MNs with those after subcutaneous injection by analyzing the blood concentration of APO in rats.

RESULTS

PVA-based dissolving MNs longer than 600 μm could effectively puncture the stratum corneum of the rat skin with penetrability of approximately one-third of the needle length. Although APO is known to have chemical stability issues in aqueous solutions, the drug content in APO-loaded MNs was retained at 25°C for 12 weeks. The concentration of APO after the administration of APO-loaded 600-μm MNs that dissolved completely in skin within 60 min was 81%. The absorption of 200-μg APO delivered by MNs showed a Tmax of 20 min, Cmax of 76 ng/mL, and AUC0-120 min of 2,829 ng・min/mL, compared with a Tmax of 5 min, Cmax of 126 ng/mL, and AUC0-120 min of 3,224 ng・min/mL for subcutaneous injection. The bioavailability in terms of AUC0-120 min of APO delivered by MNs was 88%.

CONCLUSION

APO-loaded dissolving MNs can deliver APO via skin into the systemic circulation with rapid absorption and high bioavailability.

Lornoxicam-Loaded Chitosan-Decorated Nanoemulsion: Preparation and In Vitro Evaluation for Enhanced Transdermal Delivery

Nanoemulsions are promising drug delivery systems for the administration of poorly soluble drugs like lornoxicam (LRX) by oral or parenteral routes. Such formulations work perfectly for transdermal delivery of lornoxicam-type drugs. It has also been established that formulating such a delivery system is highly dependent on the presence, type, and concentration of excipients taking part in the formulation. The inherent characteristics of nanoemulsion (NE), i.e., smaller globule size and excipient nature, facilitate the drug's passage through skin. The current study was aimed at the development of an NE-based formulation of LRX to improve the drug solubility in vitro as well as to enhance drug skin permeation to promote therapeutic outcome in appropriate time. Spontaneous self-emulsification technique was utilized to develop optimized LRX-encapsulated NE-based formulations. ATR-FTIR spectra of the pure drug and various formulations did not show any interaction between the drug and various formulation excipients showing compatibility. Globule size for stable formulations ranged between 63-168 nm. These formulations were characterized for viscosity, surface tension, pH, drug encapsulation efficiency, in vitro drug release, and drug skin permeation studies. Chitosan-decorated optimized NE formulation of LRX showed about 58.82% cumulative drug release, showing an anomalous non-Fickian diffusion mechanism of drug release. Drug encapsulation efficiency, in vitro drug release, and skin permeation studies exhibited promising results. An appreciable drug entrapment efficiency was exhibited by optimized NE formulations LRX-6, 71.91 ± 3.17% and C-LRX, 65.25 ± 4.89%. Permeability parameters like enhancement ratio (Er), permeability constant (Kp), and steady state flux (Jss) showed higher values and exhibited good results based on formulation type. The selected promising formulation type "LRX-6" showed significantly different results as compared to other formulations (LRX-4, 5, and 7). The skin permeation property of the LRX-6 formulation was compared to similar chitosan-based formulations and was found to have better skin permeation results than chitosan-based formulations. This study clearly exhibited that an LRX-containing NE-based formulation can be formulated to form a stable drug delivery system. Such formulations are promising in terms of physicochemical characteristics, improved solubility, and high skin permeation potential.

Lipophilic Conjugates of Drugs: A Tool to Improve Drug Pharmacokinetic and Therapeutic Profiles

Lipophilic conjugates (LCs) of small molecule drugs have been used widely in clinical and pre-clinical studies to achieve a number of pharmacokinetic and therapeutic benefits. For example, lipophilic derivatives of drugs are employed in several long acting injectable products to provide sustained drug exposure for hormone replacement therapy and to treat conditions such as neuropsychiatric diseases. LCs can also be used to modulate drug metabolism, and to enhance drug permeation across membranes, either by increasing lipophilicity to enhance passive diffusion or by increasing protein-mediated active transport. Furthermore, such conjugation strategies have been employed to promote drug association with endogenous macromolecular carriers (e.g. albumin and lipoproteins), and this in turn results in altered drug distribution and pharmacokinetic profiles, where the changes can be 'general' (e.g. prolonged plasma half-life) or 'specific' (e.g. enhanced delivery to specific tissues in parallel with the macromolecular carriers). Another utility of LCs is to enhance the encapsulation of drugs within engineered nanoscale drug delivery systems, in order to best take advantage of the targeting and pharmacokinetic benefits of nanomedicines. The current review provides a summary of the mechanisms by which lipophilic conjugates, including in combination with delivery vehicles, can be used to control drug delivery, distribution and therapeutic profiles. The article is structured into sections which highlight a specific benefit of LCs and then demonstrate this benefit with case studies. The review attempts to provide a toolbox to assist researchers to design and optimise drug candidates, including consideration of drug-formulation compatibility.

On-Demand Therapy for OFF Episodes in Parkinson's Disease

Levodopa is the most effective therapy for Parkinson's disease; however, chronic treatment is associated with the development of OFF episodes, in which there is a return of parkinsonian features following a dose of levodopa and prior to the onset of benefit from the subsequent dose. OFF episodes can be a major source of disability for PD patients and frequently result in depression, apathy and an unwillingness to participate in social activities. Most currently available medical and surgical therapies are designed to reduce total daily OFF time but do not provide a rapid and reliable "on-demand" therapy for individual OFF episodes. Indeed, responses to individual doses of levodopa during an acute OFF episode are unreliable, frequently leading to partial-ON, delayed-ON, or no-ON responses even at different times in the same patient. There are now 3 therapies that are available for the on-demand treatment of OFF episodes; subcutaneous injection of apomorphine, sublingual apomorphine film, and inhaled levodopa. The first has not enjoyed widespread use in the PD community, whereas the latter 2 therapies have only recently been approved. This review will consider the currently available on-demand therapies and their potential advantages and disadvantages. © 2021 International Parkinson and Movement Disorder Society.

Importance of Nanoparticles for the Delivery of Antiparkinsonian Drugs

Parkinson's disease (PD) affects around ten million people worldwide and is considered the second most prevalent neurodegenerative disease after Alzheimer's disease. In addition, there is a higher risk incidence in the elderly population. The main PD hallmarks include the loss of dopaminergic neurons and the development of Lewy bodies. Unfortunately, motor symptoms only start to appear when around 50-70% of dopaminergic neurons have already been lost. This particularly poses a huge challenge for early diagnosis and therapeutic effectiveness. Actually, pharmaceutical therapy is able to relief motor symptoms, but as the disease progresses motor complications and severe side-effects start to appear. In this review, we explore the research conducted so far in order to repurpose drugs for PD with the use of nanodelivery systems, alternative administration routes, and nanotheranostics. Overall, studies have demonstrated great potential for these nanosystems to target the brain, improve drug pharmacokinetic profile, and decrease side-effects.

Advancing skin delivery of α-tocopherol and γ-tocotrienol for dermatitis treatment via nanotechnology and microwave technology

This study investigated combination nanocarrier and microwave system for α-tocopherol and γ-tocotrienol delivery against dermatitis, without skin thinning effect of steroids. The vitamin E was formulated into water-rich/water-poor nanoemulsions, and had their droplet size, zeta potential, morphology, therapeutic content, encapsulation efficiency and release, in vitro skin therapeutics/nanoemulsion penetration, retention and permeation profiles, and in vivo pharmacodynamics characteristics examined, with skin pre-treated by precision microwave when applicable. The nanoemulsions had droplet sizes <150 nm and negative zeta potential values. The skin pre-treatment by microwave (1 mW/3985 MHz) promoted therapeutics accumulation in epidermis through enhancing nanoemulsion penetration into skin. The combination nano- and microwave technologies fluidized skin lipid and protein domains with epidermal microstructures being fluidized to a greater extent than dermis, allowing a relatively high epidermal-to-dermal nanoemulsion distribution. Microwave of lower or higher than 3985 MHz brought about lower skin therapeutics/nanoemulsion accumulation due to insufficient lipid/protein domain fluidization or microwave-skin interaction limiting at skin surfaces only. Using water-rich nanoemulsion with higher therapeutic release and skin pre-treatment with 3985 MHz microwave, dermatitis was alleviated in vivo without skin thinning of standard steroid. The use of combination microwave and nanotechnology promotes vitamin delivery and translates to positive dermatitis treatment outcome that warrants future investigation.

Drug/Vehicle Impacts and Formulation Centered Stratagems for Enhanced Transdermal Drug Permeation, Controlled Release and Safety: Unparalleled Past and Recent Innovations-An Overview

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Transdermal drug delivery systems (TDDS) are one of the fascinating unconventional drug delivery systems offering plentiful advantages of which patient compliance is of paramount importance. However, as a matter of fact, the transdermal delivery of drug molecules is absolutely a tedious job which is precisely influenced by a number of factors including penetration barrier properties of the skin, drug characteristics formulation allied issues, etc. Over the years, innumerable tremendous efforts have been made in transporting the drugs through the skin into the systemic circulation by noteworthy tactics. This paper discusses such revolutionary formulation based techniques that have been endeavored in achieving the enhanced skin permeation of drugs, controlled release, and safety.

Challenges and trends in apomorphine drug delivery systems for the treatment of Parkinson's disease

Parkinson's disease (PD) is a chronic debilitating disease affecting approximately 1% of the population over the age of 60. The severity of PD is correlated to the degree of dopaminergic neuronal loss. Apomorphine has a similar chemical structure as the neurotransmitter dopamine and has been used for the treatment of advanced PD patients. In PD patients, apomorphine is normally administered subcutaneously with frequent injections because of the compound's extensive hepatic first-pass metabolism. There is, hence, a large unmet need for alternative administrative routes for apomorphine to improve patient compliance. The present review focuses on the research and development of alternative delivery of apomorphine, aiming to highlight the potential of non-invasive apomorphine therapy in PD, such as sublingual delivery and transdermal delivery.

Nanoemulsion as pharmaceutical carrier for dermal and transdermal drug delivery: Formulation development, stability issues, basic considerations and applications

The use of nanoemulsion in augmenting dermal and transdermal effectiveness of drugs has now well established. The development of nanoemulsion based semisolid dosage forms is an active area of present research. However, thickening or liquid-to-semisolid conversion of the nanoemulsions provides opportunities to the formulation scientist to explore novel means of solving instability issues during transformation. Extending knowledge about the explicit role of nature/magnitude of zeta potential, types of emulsifiers and selection of appropriate semisolid bases could place these versatile carriers from laboratory to industrial scale. This article reviews the progressive advancement in the delivery of medicament via nanoemulsion with special reference to the dermal and transdermal administration. It is attempted to explore the most suitable semi solid dosage form for the particular type of nanoemulsion (o/w, w/o and others) and effect of particle size and zeta potential on the delivery of drugs through dermal or transdermal route. Finally, this review also highlights the basic principles and fundamental considerations of nanoemulsion manufacture, application of nanoemulsion based semisolid dosage forms in the dermal/transdermal administration and basic considerations during the nanoemulsion absorption into and through skin.

A prodrug approach to enhance azelaic acid percutaneous availability

Azelaic acid is a dicarboxylic acid compound used in treatment of acne vulgaris. However, high concentration (ca 20%) is needed to guarantee the drug availability in the skin. The latter increases the incidence of side effects such as local irritation. The prodrug strategy to enhance azelaic acid diffusion through skin was not reported before. Thus, a lipophilic prodrug of azelaic acid (diethyl azelate [DEA]) was synthesized and investigated to improve percutaneous availability of azelaic acid, with a subsequent full physical, chemical, and biological characterization. Expectedly, DEA exhibited a significant increase in diffusion compared to azelaic acid through silicone membrane. In contrast, the diffusion results through human stratum corneum (SC) displayed weaker permeation for DEA with expected retention in the SC. Therefore, a desorption study of DEA from SC was conducted to examine the reservoir behavior in SC. Results showed an evidence of sustained release behavior of DEA from SC. Consequently, enhancement of keratolytic effect is expected due to azelaic acid produced from enzymatic conversion of DEA released from SC.

Methylation and Esterification of Magnolol for Ameliorating Cutaneous Targeting and Therapeutic Index by Topical Application

PURPOSE

As a continuing effort to elucidate the impact of structure modification upon cutaneous absorption behavior, we attempted to assess the skin permeation of magnolol by methylation and acetylation.

METHODS

Diacetylmagnolol and 2-O-acetyl-2'-O-methylmagnolol (AMM) were designed and synthesized in this study. The anti-inflammatory activity against stimulated neutrophils and keratinocytes was evaluated to check the bioactivity of the analogues. In vitro skin absorption was investigated using nude mouse and pig skin models at both equimolar and saturated doses.

RESULTS

Magnolol generally showed the strongest anti-inflammatory potential, followed by diacetylmagnolol and AMM. The antibacterial activity was observed for magnolol and diacetylmagnolol but not AMM. Diacetylmagnolol and AMM could be partly hydrolyzed to magnolol and 2-O-methylmagnolol after entering the skin. The hydrolysis rate of diacetylmagnolol was faster than that of AMM. The lipophilicity played a crucial role in cutaneous absorption, with AMM exhibiting the highest skin deposition. AMM accumulation within nude mouse skin was about 2.5-fold greater than that of magnolol and diacetylmagnolol. On the other hand, the transdermal penetration across the skin was lessened by methylation and esterification. This led to a superior skin targeting of AMM. Although the pharmacological activity of AMM was low, the high skin uptake and bioconversion into 2-O-methylmagnolol in the skin contributed to a greater therapeutic index (TI, skin deposition x inflammatory inhibition percentage) compared to the others. The accumulation of AMM in the hair follicles was 77.12 nmol/cm(2), which was significantly greater than that with magnolol (44.84 nmol/cm(2)) and diacetylmagnolol (26.96 nmol/cm(2)). The synthetic analogues were tolerable to the nude mouse skin.

CONCLUSIONS

Based on the experimental results, we may suggest topically applied AMM as a potent and safe candidate for the treatment of cutaneous inflammation.

Prodrugs for transdermal drug delivery - trends and challenges

Prodrugs continue to attract significant interest in the transdermal drug delivery field. These moieties can confer favorable physicochemical properties on transdermal drug delivery candidates. Alkyl chain lengthening, pegylation are some of the strategies used for prodrug synthesis. It is usually important to optimize partition coefficient, water and oil solubilities of drugs. In this review, progress made in the field of prodrugs for percutaneous penetration is highlighted and the challenges discussed.

Prodrug strategies for enhancing the percutaneous absorption of drugs

The transdermal application of drugs has attracted increasing interest over the last decade or so, due to the advantages it offers, compared to other delivery methods. The development of an efficient means of transdermal delivery can increase drug concentrations, while reducing their systemic distribution, thereby avoiding certain limitations of oral administration. The efficient barrier function of the skin, however, limits the use of most drugs as transdermal agents. This limitation has led to the development of various strategies to enhance drug-skin permeation, including the use of penetration enhancers. This method unfortunately has certain proven disadvantages, such as the increased absorption of unwanted components, besides the drug, which may induce skin damage and irritancy. The prodrug approach to increase the skin’s permeability to drugs represents a very promising alternative to penetration enhancers. The concept involves the chemical modification of a drug into a bioreversible entity that changes both its pharmaceutical and pharmacokinetic characteristics to enhance its delivery through the skin. In this review; we report on the in vitro attempts and successes over the last decade by using the prodrug strategy for the percutaneous delivery of pharmacological molecules.

The risk of hydroquinone and sunscreen over-absorption via photodamaged skin is not greater in senescent skin as compared to young skin: nude mouse as an animal model

Intrinsic aging and photoaging modify skin structure and components, which subsequently change percutaneous absorption of topically applied permeants. The purpose of this study was to systematically evaluate drug/sunscreen permeation via young and senescent skin irradiated by ultraviolet (UV) light. Both young and senescent nude mice were subjected to UVA (10 J/cm(2)) and/or UVB radiation (175 mJ/cm(2)). Physiological parameters, immunohistology, and immunoblotting were employed to examine the aged skin. Hydroquinone and sunscreen permeation was determined by in vitro Franz cell. In vivo skin absorption was documented using a hydrophilic dye, rhodamine 123 (log P=-0.4), as a permeant. UVA exposure induced cyclooxygenase (COX)-2 and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) upregulation. Epidermal tight junction (TJ) were degraded by UVA. UVB increased transepidermal water loss (TEWL) from 13 to 24 g/m(2)/h. Hyperplasia and inflammation, but not loss of TJ, were also observed in UVB-treated skin. UVA+UVB- and UVA-irradiated skin demonstrated similar changes in histology and biomarkers. UVA+UVB or UVA exposure increased hydroquinone flux five-fold. A negligible alteration of hydroquinone permeation was shown with UVB exposure. Hydroquinone exhibited a lower penetration through senescent skin than young skin. Both UVA and UVB produced enhancement of oxybenzone flux and skin uptake. However, the amount of increase was less than that of hydroquinone delivery. Photoaging did not augment skin absorption of sunscreens with higher lipophilicity, including avobenzone and ZnO. Exposure to UVA generally increased follicular entrance of these permeants, which showed two- to three-fold greater follicular uptake compared to the untreated group. Photoaging had less impact on drug/sunscreen absorption with more lipophilic permeants. Percutaneous absorption did not increase in skin subjected to both intrinsic and extrinsic aging.

Lasers as an approach for promoting drug delivery via skin

INTRODUCTION

Using lasers can be an effective drug permeation-enhancement approach for facilitating drug delivery into or across the skin. The controlled disruption and ablation of the stratum corneum (SC), the predominant barrier for drug delivery, is achieved by the use of lasers. The possible mechanisms of laser-assisted drug permeation are the direct ablation of the skin barrier, optical breakdown by a photomechanical wave and a photothermal effect. It has been demonstrated that ablative approaches for enhancing drug transport provide some advantages, including increased bioavailability, fast treatment time, quick recovery of SC integrity and the fact that skin surface contact is not needed. In recent years, the concept of using laser techniques to treat the skin has attracted increasing attention.

AREAS COVERED

This review describes recent developments in using nonablative and ablative lasers for drug absorption enhancement. This review systematically introduces the concepts and enhancement mechanisms of lasers, highlighting the potential of this technique for greatly increasing drug absorption via the skin. Lasers with different wavelengths and types are employed to increase drug permeation. These include the ruby laser, the erbium:yttrium-gallium-garnet laser, the neodymium-doped yttrium-aluminum-garnet laser and the CO2 laser. Fractional modality is a novel concept for promoting topical/transdermal drug delivery. The laser is useful in enhancing the permeation of a wide variety of permeants, such as small-molecule drugs, macromolecules and nanoparticles.

EXPERT OPINION

This potential use of the laser affords a new treatment for topical/transdermal application with significant efficacy. Further studies using a large group of humans or patients are needed to confirm and clarify the findings in animal studies. Although the laser fluence or output energy used for enhancing drug absorption is much lower than for treatment of skin disorders and rejuvenation, the safety of using lasers is still an issue. Caution should be used in optimizing the feasible conditions of the lasers in balancing the effectiveness of permeation enhancement and skin damage.

Impact of ester promoieties on transdermal delivery of ketorolac

Different types of ketorolac ester prodrugs incorporating tert-butyl (KT), benzyl (KB), heptyl (KH), and diketorolac heptyl (DKH) promoieties were synthesized for the comparison of percutaneous penetration. The prodrugs were characterized according to their melting point, capacity factor, lipophilicity, solubility in 30% ethanol/buffer, enzymatic hydrolysis, in vitro skin permeation, hair follicle accumulation, and in vivo skin tolerance. Interactions between the prodrugs and esterases were predicted by molecular docking. Both equimolar suspensions and saturated solutions in 30% ethanol/pH 7.4 buffer were employed as the applied dose. All of the prodrugs exhibited a lower melting point than ketorolac. The lipophilicity increased in the following order: ketorolac < KT < KB < KH < DKH. The prodrugs were rapidly hydrolyzed to the parent drug in esterase medium, skin homogenate, and plasma, with KT and KB exhibiting higher degradation rates. KT exhibited the highest skin permeation, followed by KB. The flux of KT and KB exceeded that of ketorolac by 2.5-fold and twofold, respectively. KH and DKH did not improve ketorolac permeation but exhibited a sustained release behavior. KT and KH revealed selective absorption into follicles and a threefold greater follicular uptake compared with ketorolac. KB, KH, and DKH slightly but significantly increased transepidermal water loss (TEWL) after consecutive administration for 7 days, whereas ketorolac and KT exhibited no influence on TEWL. According to the experimental results, it can be concluded that an optimal balance between lipophilicity and aqueous solubility is important in the design of a successful prodrug. The acceptable skin tolerance for safe application is also an important consideration.

Noninvasive delivery of siRNA and plasmid DNA into skin by fractional ablation: erbium:YAG laser versus CO₂ laser

The present study was conducted to evaluate the impacts of fractional erbium (Er):YAG and CO2 lasers on skin permeation of small interfering (si)RNA and plasmid (p)DNA vectors. In vitro skin delivery was determined with a Franz diffusion cell. In vivo absorption was investigated by observing fluorescence and confocal microscopic imaging. Fractional laser-mediated ablation of the skin resulted in significant enhancement of dextran and siRNA penetration. Respective fluxes of dextran (10 kDa) and siRNA, which had similar molecular size, with Er:YAG laser irradiation at 5 J/cm(2) were 56- and 11-fold superior to that of intact skin. The respective permeation extents of dextran and siRNA by the CO2 laser at 4 mJ/400 spots were 42- and 12-fold greater than that of untreated skin. Fluorescence and confocal images showed increased fluorescence intensities and penetration depths of siRNA and pDNA delivery. According to an examination of the follicular permeant amount and fluorescence microscopy, hair follicles were important deposition areas for fractional laser-assisted delivery, with the Er:YAG modality revealing higher follicular siRNA selectivity than the CO2 modality. This is the first report of siRNA and pDNA penetrating the skin with a sufficient amount and depth with the assistance of fractional lasers.

Designing prodrugs for the treatment of Parkinson's disease

INTRODUCTION

Current Parkinson's disease (PD) therapy is essentially symptomatic, and l-Dopa (LD), is the treatment of choice in more advanced stages of the disease. However, motor complications often develop after long-term treatment, and at this point physicians usually prescribe adjuvant therapy with other classes of antiparkinsonian drugs, including dopamine (DA) agonists, catechol-O-methyl transferase (COMT) or monoamine oxidase (MAO)-B inhibitors. In order to improve bioavailability, the prodrug approach appeared to be the most promising, and some antiparkinsonian prodrugs have been prepared in an effort to solve these problems.

AREAS COVERED

This review discusses the evidence of progress in PD therapy, mainly focused on prodrug approach for treatment of this neurological disorder. Several derivatives were studied with the aim of enhancing its chemical stability, water or lipid solubility, as well as diminishing the susceptibility to enzymatic degradation. Chemical structures mainly related to LD, DA and dopaminergic agonists are also reviewed in this paper.

EXPERT OPINION

In order to strengthen the pharmacological activity of antiparkinsonian drugs, enhancing their penetration of the blood-brain barrier (BBB), different approaches are possible. Among these, the prodrug approach appeared to be the most promising, and many prodrugs have been prepared in an effort to optimize physicochemical characteristics. In addition, novel therapeutic strategies based on formulations linking dopaminergic drugs with neuroprotective agents, increasing LD striatal levels and offering sustained release of the drug without any fluctuation of brain concentration, offer promising avenues for development of other effective new treatments for PD.

Combined strategies of apomorphine diester prodrugs and nanostructured lipid carriers for efficient brain targeting

Our aim is to develop nanostructured lipid carriers (NLCs) for loading the apomorphine diester prodrugs, diacetyl apomorphine (DAA) and diisobutyryl apomorphine (DIA), into the brain. NLCs were prepared using sesame oil/cetyl palmitate as the lipid matrices. Experiments were performed with the objective of evaluating the physicochemical characteristics, drug release, safety and brain-targeting efficacy of the NLCs. The size of regular NLCs (N-NLCs) was 214 nm. The addition of Forestall (FE) and polyethylene glycol (PEG) to the NLCs (P-NLCs) increased the particle diameter to 250 nm. The zeta potentials of N-NLCs and P-NLCs were respectively shown to be - 21 and 48 mV. Diester prodrugs were more lipophilic and more chemically stable than the parent apomorphine. The hydrolysis study indicated that the prodrugs underwent bioconversion in plasma and brain extract, with DAA exhibiting faster degradation than DIA. Sustained release was achieved through the synergistic effect of integrating strategies of prodrugs and NLCs, with the longer carbon chain showing the slower release (DIA < DAA). None of the NLCs tested here exhibited a toxicity problem according to the examination of neutrophil lactate dehydrogenase (LDH) release and hemolysis. Results of a bioimaging study in mice showed that P-NLCs largely accumulated in the brain. The distribution duration of the fluorescent dye in the brain region was also prolonged by the nanocarriers.