Inclusion Complexes of Non-Steroidal Anti-Inflammatory Drugs with Cyclodextrins: A Systematic Review

Abstract

Non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most widely used classes of medicines in the treatment of inflammation, fever, and pain. However, evidence has demonstrated that these drugs can induce significant toxicity. In the search for innovative strategies to overcome NSAID-related problems, the incorporation of drugs into cyclodextrins (CDs) has demonstrated promising results. This study aims to review the impact of cyclodextrin incorporation on the biopharmaceutical and pharmacological properties of non-steroidal anti-inflammatory drugs. A systematic search for papers published between 2010 and 2020 was carried out using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol and the following search terms: “Complexation”; AND “Cyclodextrin”; AND “non-steroidal anti-inflammatory drug”. A total of 24 different NSAIDs, 12 types of CDs, and 60 distinct inclusion complexes were identified, with meloxicam and β-CD appearing in most studies. The results of the present review suggest that CDs are drug delivery systems capable of improving the pharmacological and biopharmaceutical properties of non-steroidal anti-inflammatory drugs.

1. Introduction

Inflammation is the body's response to tissue damage, which aims to restore the integrity of the injured tissue through different mechanisms of induction, regulation, and resolution. Regardless of the aggressor stimulus, this response is essential for the restoration of homeostasis and, therefore, plays an important physiological role [1,2].

While inflammation is essential for the host defense against pathogens, it frequently occurs in the absence of infection, a phenomenon known as sterile inflammation [3,4]. Accordingly, despite the existence of efficient control mechanisms, failures in the resolution of inflammation often occur, which contributes significantly to the pathogenesis of several chronic diseases [5,6]. In these cases, the inflammatory response is the main cause of tissue injury and disease progression, besides contributing to the severity of other comorbidities [7,8].

The classical therapeutic strategies for inflammatory diseases are mostly based on the use of anti-inflammatory drugs that act by either inhibiting the production of pro-inflammatory mediators or preventing the recruitment and activation of leukocytes at the inflammatory site [9,10]. In this context, non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most widely used drug classes in the treatment of inflammation, fever, and pain. The mechanism of action underlying the anti-inflammatory, antipyretic, and analgesic effects of NSAIDs involves the inhibition of cyclooxygenases (COXs), enzymes that are critically responsible for the synthesis of prostaglandins, thromboxanes, and other prostanoids [11,12]. Prostaglandin E₂ (PGE₂) is produced in a wide variety of tissues, playing crucial roles in vasodilation and hyperalgesia in addition to interacting with pro-inflammatory cytokines that generate fever [13,14]. Thus, the mechanism of action of NSAIDs results in the inhibition of key clinical signs such as redness, warmth, pain, and swelling [2].

While non-selective NSAIDs inhibit both COX-1 and COX-2 isoforms, selective NSAIDs were developed to preferentially inhibit COX-2, which was expected to potentiate anti-inflammatory effects and reduce adverse effects. However, accumulating evidence has demonstrated that these drugs can induce significant toxicity [15]. Therefore, the development of innovative, safe, and effective anti-inflammatory drugs remains challenging [16].

In the search for innovative strategies to overcome NSAID-related problems, nanotechnology-based formulations have been developed to improve the pharmacokinetic properties of drugs as well as their interaction with their molecular targets. In this context, the incorporation of drugs into cyclodextrins represented a revolution in drug delivery systems [17,18].

Cyclodextrins (CDs) are cyclic oligosaccharides formed by α-D-glucopyranose units linked by α-1.4 bonds, which contain a hydrophobic central cavity and a hydrophilic outer surface [19]. They are classified according to the number of glucopyranose units in α-CD, β-CD, or γ-CD as they present six, seven, and eight units, respectively. They may be presented as derivatives such as hydroxypropyl, methyl, di-methyl, sulfobutyl, and carboxymethyl CDs [20].

Among CDs, β-CD presents the lowest water solubility, and despite presenting some intake restrictions [21], it is the most used CD mainly due to its easy production and lower price [19]. The characteristics of α-CD, β-CD, and γ-CD are summarized in Table 1.

Considering the importance of inclusion complexes in drug development, this study aims to review the impact of cyclodextrin incorporation on the biopharmaceutical and pharmacological properties of non-steroidal anti-inflammatory drugs. 2. Methods

The present study is a systematic review conducted in four scientific databases (Pubmed, Medline, Scopus, and EMBASE) according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol [22], using the following search terms: "Complexation"; AND "Cyclodextrin"; AND "Non-steroidal anti-inflammatory drug".

This search included all original articles addressing the impact of CD complexation on the biopharmaceutical and pharmacological effects of NSAIDs, published in the last decade (from 2010/01/01 to 2020/02/05, followed date of this study). The following inclusion criteria were adopted: (1) articles investigating inclusion complexes containing at least one CD and one NSAID in the same formulation; (2) articles analyzing the impact of the complexation on parameters directly related to the biological effects of the complexed NSAID; (3) articles with an analysis conducted in vivo, in vitro, ex vivo, in silico, or during clinical research. The exclusion criteria were the following: (1) studies demonstrating physicochemical characterization without pharmacological correlations; (2) studies investigating drugs with an NSAID-like mechanism of action without approval by drug regulatory agencies. Articles randomly found during the theoretical reference search which met the inclusion criteria were also included in the results.

Following the search on the selected databases and considering the randomly found articles, a total of 644 studies (Figure 1) were used for abstract reading, after which 553 articles were excluded as they did not meet the inclusion criteria. After full-text reading of the manuscripts, another 11 articles were excluded, totaling 80 articles selected to compose this review. The authors, type of inclusion complex, and main findings of these articles are summarized in Table 2. The Jeffrey Amazing Statistics Program (JASP) software version 0.9.2 for MacBook Pro 2010 [23] (Jasp Team, 2020) was used to determine the frequency of inclusion complexes, cyclodextrins, and NSAIDs reported in the studies. The data are expressed in pie charts (Figure 2) and the descriptive analysis is shown in the Supplementary Materials.

3. Results

A detailed analysis of the studies selected in the present review is shown in Table 2, while the analysis of frequency represented in pie charts is shown in Figure 2, and the descriptive analysis is detailed in the Supplementary Materials. We identified a total of 24 different NSAIDs used in inclusion complexes with cyclodextrins, including meloxicam (n = 11; 12.94%), diclofenac (n = 8; 9.41%), flurbiprofen (n = 8; 9.41%), ibuprofen (n = 7; 8.23%), piroxicam (n = 7; 8.23%), aceclofenac (n = 6; 7.05%), and oxaprozin (n = 6; 7.05%) as the most frequently complexed drugs. Regarding the type of CD, from a total of 12 different molecules, β-CD (40%) and HP-β-CD (34.78%) were the cyclodextrins most used in the obtention of inclusion complexes with NSAIDs. According to the present frequency analysis, 60 distinct inclusion complexes were obtained and studied from the combination of the NSAIDs and CDs described above, including meloxicam/β-CD (n = 9; 7.82 %), piroxicam/β-CD (n = 7; 6.08), flurbiprofen/HP-β-CD (n = 6; 5.21%), ibuprofen/β-CD (n = 4; 3.47%), oxaprozin/Rme-β-CD (n = 4; 3.47%), and piroxicam/HP-β-CD (n = 4; 3.47%) as the most frequent inclusion complexes in the selected studies.

4. Discussion

In a worldwide context, significant concern has arisen regarding the efficacy and safety of the currently available anti-inflammatory drugs [103]. There have been specific conditions in which they are either not effective or can cause significant side effects [104,105]. Therefore, strategies aiming to improve the safety and efficacy of NSAIDs, such as CD preparations, have a cornerstone impact on anti-inflammatory therapy.

Consistent evidence has demonstrated that cyclodextrins can form complexes with both organic and inorganic compounds and, therefore, have become widely used in the food, pharmaceutical, and cosmetic industries. These molecules can be used as functional excipients able to prevent volatility, increase stability, solubility, and membrane permeation, and improve organoleptic characteristics of many molecules [106,107]. Importantly, evidence has demonstrated that CDs are promising drug delivery systems for several drugs, improving their physicochemical and biopharmaceutical properties, increasing their bioavailability, and reducing toxicity, which has a significant impact on the pharmacological effects of both synthetic and naturally occurring compounds [108].

The three-dimensional conformation of glucopyranose units in the CD macrocyclic structures places the hydrophobic carbon backbones facing the inner part of the cone, providing the hydrophobic characteristic of the cavity. This structural arrangement determines the application of CDs as host structures to form inclusion complexes with diverse poorly water-soluble molecules such as NSAIDs [109]. Additionally, structural changes in the CD structure by the substitution of chemical groups (such as acetyl, hydroxypropyl, dimethyl, and sulphate) have a significant impact on solubility and drug-release properties of the delivery system [110].

In this study, β-CD was the most frequently used native cyclodextrin, while hydroxypropyl β-CD was the principal synthetic CD derivative addressed in the manuscripts, which is probably due to the easy production and low cost of this naturally occurring molecule. However, compared to α- and γ-CDs, β-CD has the lowest solubility, and its acceptable daily intake is up to a dose of 5 mg/kg/day [21]. Thus, although CDs are generally recognized as safe, exposure to higher doses of β-CD can lead to toxicity, as highlighted in the study by Kontogiannidou et al. [96], which attributed the loss of superficial cell layers of porcine buccal mucosa to β-CD and its synthetic derivatives. According to Ishiguro et al. [50], the cytotoxicity (hemolytic activity) of flurbiprofen-2-HB-CD inclusion complexes with different degrees of substitution depends on the degree of substitution. Moreover, consistent evidence has demonstrated the safety of the use of β-CD-based formulations both in vitro [51] and in vivo [36]. Importantly, a study by Rescifina et al. [34] in 2019 demonstrated that the complexation of celecoxib with SBE-β-CD significantly increased the cytotoxic activity of this NSAID, in addition to potentiating the cytotoxicity of gemcitabine, demonstrating enhanced anti-cancer activity.

The development of pharmacological effects depends on adequate drug concentration reaching the aimed tissue. Plasma and other aqueous fluids perfuse most tissues in the body; thus, solubilization in aqueous fluids is often required for drug effectiveness [111]. In contrast, to be absorbed from the application site to the blood or to other tissues, the active compound needs to leave the aqueous phase and permeate lipidic membranes [112] (Lennernas, 2014), and therefore, a balance between lipophilicity and hydrophilicity is desirable for a drug candidate [113]. Thereby, solubility and permeability are considered as key aspects to achieve adequate drug bioavailability and pharmacological effect [114].

Following this principle, several studies included in the present review used cyclodextrins (especially β-CD and HP-β-CD) to improve the water solubility and increase the bioavailability of NSAIDs such as aceclofenac [29], meloxicam [80], flurbiprofen [54], diclofenac [37], and lornoxicam. It is worth mentioning that increased solubility was associated with improved bioavailability [37,54] and anti-inflammatory activity [70]. In general, NSAIDs are acidic lipophilic compounds characterized by the presence of an aromatic ring bearing an acidic moiety and can differ in their lipophilicities based on their aryl structure and substituents. For instance, the Log P (octanol-water partition coefficient) values for sodium diclofenac, ibuprofen, piroxicam, and paracetamol are 4.51, 3.97, 1.8, and 0.31, respectively [115]. Sodium diclofenac, ibuprofen, and piroxicam are classified as class II drugs and paracetamol as class III according to the Biopharmaceutics Classification System [116,117]. Considering that most NSAID preparations aim for systemic distribution, the development of pharmaceutical formulations based on CD inclusion complexes may be a promising strategy to reverse their low solubility [117,118].

The local or topical administration of drugs in the skin or other membranes is an interesting alternative to the oral route, decreasing systemic side effects and avoiding first-pass metabolism [119]. Topical and transdermal drug administration may show advantages compared to oral administration, especially when a regional effect is expected due the possibility of drug application close to the action site, e.g., deeper skin layers, muscles, and blood vessels [120]. In this context, many studies have investigated the effect of CD complexation (in both binary and ternary systems) on the permeation properties of NSAIDs such as aceclofenac [28], diclofenac [40,41], celecoxib [19], and nepafenac [86]. Regarding formulations designed for ocular administration, aqueous solubility in biological fluid as well as lipophilicity to ensure the membrane permeation are also required characteristics to achieved pharmacological effects [121]. Abdelkader and colleagues [40] showed that α-CD, β-CD, γ-CD, and HP-β-CD had little effect on the ocular permeability of diclofenac, although the toxicity of this drug was significantly reduced by association with γ-CD and HP-β-CD. On the other hand, celecoxib/γ-CD/Rme-β-CD [19] and nepafenac/HP-β-CD [86] showed excellent corneal permeability, resulting in increased drug concentration in the cornea, sclera, and retina, demonstrating the relevance of cyclodextrins as drug delivery systems in ocular formulations.

Cyclodextrin-complexed drugs have demonstrated improved pharmacokinetics aspects, resulting in greater efficacy and safety [108]. In a study by Dahiya and collaborators [25], the incorporation of HP-β-cyclodextrin provided a more rapid onset of pharmacological effects of aceclofenac in comparison to the market formulation and pure drug. Importantly, a clinical study using a diclofenac-HP-β-CD formulation in patients with mild or moderate renal insufficiency or mild hepatic impairment indicated its safe use without the requirement of dose adjustment [39]. Moreover, evidence has indicated that β-CD, HP-β-CD, and SBE-β-CD can be successfully used to improve the pharmacokinetic profile of flurbiprofen, indicating that they are promising delivery systems for poorly soluble drugs [52,55]. An interesting approach has been investigated by Hartlieb et al. (2017). A pharmaceutical preparation of ibuprofen-MOF-CD exhibited similar in vivo bioavailability and uptake in blood plasma as pure ibuprofen. However, the complexed samples showed a significant increase in the blood half-life of ibuprofen when compared to the pure drug, pointing out that the pharmacokinetic aspect improvement may change according to the pharmaceutical preparation. Their results suggested that ibuprofen-MOF-CD may be an effective delivery vehicle able to produce extended analgesic effects. Another interesting use of CDs to avoid drug passage through the blood-brain barrier has been described by Wang et al. [122].

To evaluate the effectiveness of cyclodextrins in improving the pharmacological effects of NSAIDs, several studies investigated the anti-inflammatory and analgesic properties of different NSAID-CD inclusion complexes, as these drugs have fundamental importance in the management of inflammation and pain. On the other hand, these drugs can present significant side effects, such as increased cardiovascular risk and stimulation of gastric ulcer formation [121]. Grecu and collaborators [68] demonstrated that ketoprofen/β-CD complex presented a stronger anti-inflammatory activity than ketoprofen pure in rat models of paw edema and peritonitis. Similar findings were obtained by Auda [88], Alshehri et al. [123], and Ammar et al. [70] using inclusion complexes of nimesulide-Me-β-CD, flufenamic acid-β-CD, and lornoxicam-β-CD/lornoxicam-HP-β-CD, respectively. The impact of CD incorporation on the anti-inflammatory effects of NSAIDs has been further demonstrated in vitro and was associated with inhibition of inflammatory mediator production [32,83].

According to Singh et al. [47], etoricoxib, a selective COX-2 inhibitor, presented increased solubility and enhanced analgesic activity upon complexation with β-CD and HP-β-CD, exhibiting maximum analgesic effects when complexed to HP-β-CD. The incorporation of meloxicam [77] or aceclofenac [30] to β-CD was found to significantly improve the biopharmaceutical properties and potentiate the analgesic and anti-inflammatory effects of these NSAIDs in vivo. Accordingly, a clinical study demonstrated that piroxicam had its analgesic activity potentiated by incorporation with β-CD [99]. Furthermore, evidence has indicated that this complexation may result in significantly reduced ulcerogenic potential [95]. This finding is corroborated with studies addressing the ulcerogenic potential of NSAIDs complexed with cyclodextrins, which showed that complexation with either β-CD or HP-β-CD significantly reduced gastric ulcer formation in rats treated with indomethacin or piroxicam, as shown in Table 2. Additionally, a clinical study conducted by Gan et al. [38] demonstrated the cardiovascular safety of intravenous HP-β-CD-diclofenac. On the other hand, β-CD significantly enhanced the solubility of sulindac but had no protective effect against gastric ulcer formation in rats [101]. The authors discuss that the reported non-effect is related to sulindac itself, which is characterized by its greater ability for gastrointestinal adhesion and high accumulation that can induce gastric ulcer [101].

Cyclodextrin-based inclusion complexes have proven their usefulness to improve the stability [124] and taste of oral pharmaceutical forms, resulting in improved patient compliance in addition to contributing to the biopharmaceutical properties of oral drugs [107]. Accordingly, this study showed that incorporation of cyclodextrins (such as α-, β-, γ-, and HP-β-CD) had a positive impact on the stability of NSAIDs [24,28,102] as well as demonstrated the potential to be used as taste-masking excipients [26,42,69,72].

The use of CDs can be limited depending on the drug structure and the CD structure and size. The guest molecules need to interact by non-covalent bonding and fit totally or partially within the CD cavity. The main aspects to ensure proper complexation are related to the chemical structure and physicochemical properties of the guest and host molecules [31,45]. Several studies have used NSAID-CD inclusion complexes as part of ternary and quaternary systems in association with a wide variety of compounds and nanoparticles (e.g., liposomes, chitosan, L-arginine, and poly (lactic-co-glycolic acid) (PLGA)) to achieve additional improvement of the physicochemical, biopharmaceutical, and pharmacological properties. It has been shown that water-soluble polymers such as PLGA, polyethylene glycol (PEG), and HP-methylcellulose, among others, can reduce CD mobility and increase the complex solubility [31,43,45,48,51,61,82,90,92].

Sherje et al. achieved a relevant increase in the solubility of etodolac using a ternary system with HP-β-CD and L-arginine. It has been described that basic amino acids such as L-arginine can complex with the drug and the CD by hydrogen bonding, electrostatic interactions, and salt formation. The amphiphilic characteristic of L-arginine allows the structure to interact its hydrophobic region with the hydrophobic portion of HP-β-CD, resulting in a supramolecular ternary complex [45,71]. The findings of the present systematic review indicate that ternary and quaternary systems may contribute to the effectiveness of some NSAID-CD complexes by promoting better complexation, solubility, and a more controlled drug release.

5. Conclusions The results from this review suggest that cyclodextrins, including 2-HB-CD, DiMe-β-CD, EPI-CM-β-CD, EPI-β-CD, HP-β-CD, Me-β-CD, Rme-β-CD, SBE-β-CD, TA-β-CD, α-CD, β-CD, and γ-CD, can be successfully employed in the obtention of inclusion complexes with NSAIDs such as meloxicam, diclofenac, and flurbiprofen, the most frequently complexed drugs. While the effectiveness of different cyclodextrins in improving the biopharmaceutical and pharmacological properties of NSAIDs depends on both the complexed drug and the type of CD, an overall analysis of the studies included in the present review showed that drug characteristics, including solubility, stability, taste, toxicity, and bioavailability, in addition to the expected anti-inflammatory and analgesic activity were found to be improved upon complexation with molecules such as β-CD and HP-β-CD, the most frequently used CDs. In conclusion, the findings of the present systematic review suggest that cyclodextrins are promising drug delivery systems capable of improving the pharmacological and biopharmaceutical properties of non-steroidal anti-inflammatory drugs.