Nanostructured Montmorillonite Clay for Controlling the Lipase

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Nanostructured Montmorillonite Clay for Controlling the LipaseMediated Digestion of Medium Chain Triglycerides Tahnee J. Dening,† Paul Joyce,‡ Shasha Rao,† Nicky Thomas,† and Clive A. Prestidge*,† †

School of Pharmacy and Medical Sciences, University of South Australia, City East Campus, Adelaide, South Australia 5001, Australia Future Industries Institute, University of South Australia, Mawson Lakes Campus, Mawson Lakes, South Australia 5095, Australia

‡

S Supporting Information *

ABSTRACT: Biocompatible lipid hybrid particles composed of montmorillonite and medium chain triglycerides were engineered for the first time by spray drying oil-in-water emulsions stabilized by montmorillonite platelets to form montmorillonite-lipid hybrid (MLH) microparticles containing up to 75% w/w lipid. In vitro lipolysis studies under simulated intestinal conditions indicated that the specific porous nanoarchitecture and surface chemistry of MLH particles significantly increased the rate (>10-fold) and extent of lipase-mediated digestion compared to that of coarse and homogenized submicrometer triglyceride emulsions. Proton nuclear magnetic resonance studies verified the rapid and enhanced production of fatty acids for MLH particles; these are electrostatically repelled by the negatively charged montmorillonite platelet faces and avoid the “interfacial poisoning” caused by incomplete digestion that retards lipid droplet digestion. MLH particles are a novel biomaterial and encapsulation system that optimize lipase enzyme efficiency and have excellent potential as a smart delivery system for lipophilic biomolecules owing to their exceptional physicochemical and biologically active properties. These particles can be readily fabricated with varying lipid loads and thus may be tailored to optimize the solubilization of specific bioactive molecules requiring reformulation. KEYWORDS: montmorillonite, clay, lipid-based formulation, lipid digestion, lipolysis, lipase, hybrid microparticles

1. INTRODUCTION Current estimates suggest that 40−70% of all newly discovered chemical entities suffer from low aqueous solubility and lipophilic character, resulting in significant oral delivery challenges.1,2 For such molecules, lipid-based formulations are one of the more promising formulation approaches for optimizing therapeutic potential.2 Despite the many apparent advantages of lipid-based formulations, including their solubility enhancing effects, ability to normalize pharmacokinetic profiles and high biocompatibility, their commercial application has been limited to date.1 Practical limitations such as physicochemical instability during storage and insufficient drug loading levels are largely responsible for the poor uptake of lipid-based formulations on a commercial scale.3,4 In light of this, solid-state lipid-based formulations have attracted extensive attention in recent times as a means of overcoming the limitations of traditional lipid-based formulations.3,5 Solidstate lipid-based formulations may be fabricated using © 2016 American Chemical Society

sophisticated lipid entrapment methods such as spray drying, thereby resulting in advanced nanostructured carrier systems formed by the controlled aggregation of carrier particles and lipid droplets.5,6 Such systems may offer significant advantages owing to their specific nanoarchitecture and its ability to influence lipid digestion and drug solubilization processes occurring in vivo.7 Hybrid particles whereby lipid is hosted within a porous carrier matrix can be specifically tailored to modulate the lipolysis kinetics of simple lipid emulsions and thus improve encapsulated drug solubilization and in vivo performance. By varying the characteristics of the carrier particles, such as particle size, porosity, and surface chemistry (hydrophobic/ hydrophilic nature and surface charge), it is possible to Received: October 25, 2016 Accepted: November 8, 2016 Published: November 8, 2016 32732

DOI: 10.1021/acsami.6b13599 ACS Appl. Mater. Interfaces 2016, 8, 32732−32742

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ACS Applied Materials & Interfaces

Laboratories (Australia). Soybean lecithin (containing >94% phosphatidylcholine and 0.05). A synergistic effect of lecithin and MMT in stabilizing the submicrometer emulsion and enhancing lipase enzyme action in the first phase of lipolysis likely exists to account for this phenomenon. When MMT was used as the sole submicrometer emulsion stabilizer (2% w/w relative to lipid content), lipid digestion occurred at a rate similar to that of the lecithin-stabilized submicrometer emulsion in the first phase. This can be attributed to the ability of MMT to form an effective Pickering emulsion (emulsion droplet size 317 ± 6 nm) with a large lipid surface area available for lipase enzymes to access. In the second and third phases of lipid digestion, significantly lower hydrolysis rate constants were observed for the MMT-stabilized emulsion such that lipid hydrolysis was no longer occurring in the third phase (i.e., k3 value of 0). The extent of lipid hydrolysis was also significantly reduced, whereby an Hmax value of only 65.4 ± 2.4% was achieved for the MMT-stabilized emulsion. It is hypothesized that MMT platelets inhibit lipase activity via mechanisms similar to those previously proposed for more commonly studied silica nanoparticles: (i) physical shielding of the oil−water droplet interface from lipase access and (ii) reducing the available lipid surface area for enzymatic digestion.7 Importantly, MMT platelets are significantly larger than silica nanoparticles and therefore display a more pronounced physical shielding effect on lipase enzyme action.18,19 Furthermore, positively charged areas on the surface of MMT platelets may strongly adsorb lipase molecules in their inactive, closed-lid orientation, as shown previously for hydrophobic porous silica.9,38 Accordingly, it can be inferred that MMT platelets have the potential to inhibit lipasemediated digestion of MCT lipids to a significantly greater extent than hydrophilic silica nanoparticles, even when used at very low concentrations. This effect may be exploited to facilitate the gastrointestinal solubilization of various lipophilic drugs that are susceptible to precipitation from lipid-based formulations during lipase-mediated digestion of triglyceride molecules, e.g. fenofibrate, halofantrine, and danazol.39−42 Interestingly, a recent in vivo study undertaken by Xu et al. demonstrated the potential of MMT as an antiobesity agent.43 Rats were fed either a normal diet (control group) or high-fat diet, and rats in the treatment group (high-fat diet plus MMT) were administered MMT at a dose of 1 g/kg body weight daily. At the end of the study, the high-fat diet plus MMT group weighed significantly less than the high-fat diet group, and the

Figure 5. Effect of hydrophilic MMT platelets on the digestion kinetics of a submicrometer MCT emulsion: submicrometer lecithin (6% w/w) stabilized emulsion (purple ■), submicrometer lecithin (6% w/w) and MMT (2% w/w) stabilized emulsion (green ◆), and submicrometer MMT (2% w/w) stabilized emulsion (blue ▲). Each value represents the mean ± SD (n = 3). For some points, the error bars are shorter than the height of the respective symbol.

Table 2. Kinetic Analysis Data for the Lipolysis of MCT Submicrometer Emulsions Stabilized by Lecithin and/or MMT Platelets Using Pseudo-First-Order Kineticsa hydrolysis rate constant, k (min−1) MMT (% w/w)

lecithin (% w/w)

0 2 2

6 6 0

phase I phase II phase III 6.96 15.1 7.08

1.84 0.43 0.10

0.02 0.01 0

extent of lipid hydrolysis after 60 min, Hmax 85.1 ± 1.0 81.9 ± 0.3 65.4 ± 2.4

a

MMT and lecithin percentage values are relative to MCT content (% w/w).

first, second, and third phases of lipolysis, respectively. As evidenced by these rate constants, the rate of lipid hydrolysis dramatically decreased as digestion proceeded such that the hydrolysis rate constant describing the third phase of lipolysis, k3, was lower than both rate constants describing digestion kinetics of a coarse MCT emulsion (Table 3). Following the initial rapid digestive phase, accumulation of interfacially active digestion products and the emulsifier lecithin, which is also known to interfere with lipase adsorption at the oil−water interface, promptly retarded the rate of lipid digestion such that Table 3. Kinetic Analysis Data for the Lipolysis of an MCT Coarse Emulsion and MLH Microparticle Formulations with Various Lipid Loads Using Pseudo-First-Order Kinetics hydrolysis rate constant, k (min−1 × 10−2) lipid formulation coarse emulsion MLH-2 MLH-3 MLH-4 MLH-5 MLH-8

phase I phase II phase III 0.09

0.03

1.13 1.05 1.08 1.08 1.65

1.13 0.51 0.56 0.22 0.19

extent of lipid hydrolysis after 60 min, Hmax 91.8 ± 2.7

0.06 0.06 0.07 0.04 0.01

100.7 100.7 102.7 95.2 81.9

± ± ± ± ±

0.7 2.0 0.9 0.4 3.8 32737


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better access to the oil−water interface for lipase enzymes.8 Interestingly, the k1 values for MLH microparticles were significantly decreased in comparison to those of the submicrometer MCT emulsion systems which exhibited k1 values in the range 6.96−15.1 min −1 . Two potential mechanisms related to the structure of spray dried microparticles may be responsible for this reduction in initial digestion kinetics compared with that of a bare submicrometer emulsion: (i) the aggregated nanostructure of MLH microparticles necessitates that lipase enzymes must diffuse into the pores of the particles to access encapsulated lipid, and (ii) the encapsulation of lipids within spray dried microparticles relies (in part) on the ability of the particles to redisperse effectively and expose internal lipid to lipase enzymes (Figure 7).8,33 Both mechanisms are related to the available surface area of the lipid substrate during the first phase of lipolysis. Despite the significant reduction in k1 values for MLH microparticles (compared with a submicrometer emulsion), the initial rate of lipid digestion is still considered rapid. Complete intestinal absorption of triglycerides is known to occur when 66% of FFA release has occurred from a lipid substrate; therefore, the time taken to reach approximately 60% lipid digestion (T60%) may be evaluated as a marker for in vivo performance.39,48 While T60% for the submicrometer emulsion occurred at 1 min, T60% for the MLH microparticles occurred between 2 and 3 min (4−5 min for MLH-5). Thus, MLH microparticles offer the ability to better control lipase-mediated lipid digestion and provide a more predictable performance while still providing a rapid rate of lipid digestion. While the initial rate of lipolysis was lower for MLH microparticles in comparison to that of a submicrometer emulsion, the extent of lipid digestion was significantly enhanced (p < 0.05). As shown in Figure 6, complete lipid digestion was demonstrated for the three MLH microparticle systems with lipid loads in the range of 42−60% w/w (i.e., MLH-2, MLH-3, and MLH-4). In contrast, the submicrometer emulsion reached only 85.1 ± 1.0% lipid hydrolysis after 60 min. This considerable difference in the extent of lipid digestion, despite the submicrometer emulsion demonstrating faster initial digestion kinetics, suggests that electrostatic charge repulsion between negatively charged MMT platelets and FFA molecules assists in the expulsion of FFA from MLH microparticles, thereby reducing interference of lipid digestion products on lipase action (Figure 7). Joyce et al. proposed a similar phenomenon to be responsible for an increased extent of lipid hydrolysis when lipid was loaded into porous silica particles compared with a submicrometer emulsion.38 When considering the lipolysis of MLH-5, the extent of lipid digestion was reduced in comparison to MLH-2, MLH-3, and MLH-4 systems with only 95.2 ± 0.4% lipid hydrolysis occurring after 60 min. In addition, the hydrolysis rate constants for the second and third phases of lipolysis, k2 and k3, respectively, were lower for MLH-5, indicating the rate of lipolysis was retarded when a higher lipid load was incorporated into MLH particles (Table 3). This may be explained 3-fold: (i) a significant difference in the rate and extent of redispersion of MLH-5 microparticles was observed in comparison to the MLH formulations with lower lipid loads. The increased particle size reduces the available lipid surface area for lipase enzymes, resulting in a lower rate and extent of lipid digestion, (ii) at this maximum achievable lipid load, there is increased blockage of the microparticle pores and reduced access of lipase to lipid, and (iii) for MLH-5, there is in excess of six times the

authors suggested MMT has the ability to adsorb dietary lipid and enhance fecal lipid excretion. However, these hypotheses as to the mechanism by which MMT reduces weight gain were not conclusively proven in this study. In addition to investigating the impact of MMT on lipid digestion kinetics for submicrometer emulsions, we also examined the ability of MMT to affect lipolysis of a coarse MCT emulsion (Supporting Information, Figure S1). At 2% w/w relative to lipid content, the presence of MMT platelets significantly inhibited lipid digestion kinetics. Rate constants decreased from 0.094 and 0.027 min−1 for the bare coarse emulsion to 0.087 and 0.011 min−1 for the MMT-stabilized coarse emulsion. This 1.1- and 2.4-fold reduction in the rate of lipid digestion for the first and second phases of lipolysis, respectively, also led to a significant decrease in the extent of lipolysis at 60 min (Hmax reduced from 91.8 ± 2.7 to 73.6 ± 3.2%) (p < 0.05). This in vitro data correlates with the clinical data presented by Xu et al. by demonstrating that MMT does influence lipid processing. Additional studies have demonstrated the potential of a protonated MMT (prepared by ion exchange) to reduce the in vitro solubilization and in vivo absorption of cholesterol,44−47 further indicating the massive potential of MMT for use in food and drug delivery science. Clearly, more studies that are mechanistic in nature are required to elucidate exactly how MMT affects lipid and lipid-like substance processing and absorption in vivo. 3.2.2. Spray Dried MLH Microparticles. Figure 6 depicts the lipid digestion profiles for the four developed MLH micro-

Figure 6. Lipase-mediated digestion kinetics of MLH microparticles and a MCT coarse emulsion: MLH-2 (orange ▲), MLH-3 (purple ■), MLH-4 (green ◆), MLH-5 (red ●), MLH-8 (black × ), and MCT coarse emulsion (blue ▲). Each value represents the mean ± SD (n = 3). For some points, the error bars are shorter than the height of the respective symbol.

particles with varying lipid loads as well as the MLH microparticles fabricated without lecithin. Triphasic kinetics described the hydrolysis of lipid encapsulated within MLH microparticles. In comparison to a coarse MCT emulsion, initial digestion kinetics were enhanced for all MLH microparticle systems. This was evidenced by an increase in the hydrolysis rate constant k1 from 0.09 min−1 for the coarse emulsion to within the range 1.05−1.13 min−1 for the hybrid microparticles (Table 3). This increase in the initial lipolysis kinetics for MLH microparticles (>10-fold) can be attributed to the significantly larger lipid surface area provided by the specific nanostructure of spray dried microparticles, thereby providing 32738


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Figure 7. Schematic representation of the potential concurrent processes occurring during the lipase-mediated digestion of MCT from MLH microparticles: (1) Lipase enzyme molecules must diffuse into the pores of MLH microparticles to access encapsulated lipid molecules. (2) MLH microparticles redisperse and disintegrate into smaller particles upon dilution and agitation in the gastrointestinal environment, exposing a greater surface area of lipid to lipase. (3) MCT molecules diffuse from the pores of MLH microparticles into the aqueous medium. (4) FFA released as a result of lipase-mediated digestion are expelled from MLH microparticles owing to electrostatic interactions with the negatively charged MMT platelet faces. In turn, there is a reduced interference of FFA on lipase-mediated lipid digestion.

Figure 8. Representative 1H NMR spectra of lipid extracts from the in vitro lipid digestion of MLH microparticles. Inset: changes to key spectra regions as a function of increasing lipolysis time.

MLH-5 to perform favorably in vivo for the optimized delivery of bioactive molecules. For the MLH microparticles fabricated without lecithin as an emulsifier (MLH-8), a significant reduction in the extent of lipid digestion over 60 min was demonstrated in comparison to the equivalent MLH microparticles fabricated using lecithin (MLH-2) (Figure 6). While Hmax for MLH-2 reached approximately 100%, Hmax was reduced to 81.9 ± 3.8% for MLH-8. This significant reduction in the extent of lipolysis may be attributed to the quality of the precursor emulsion because the MMT-stabilized emulsion had an increased droplet size in comparison to that of a lecithin-stabilized emulsion (317 ± 6

theoretical monolayer lipid coverage in the spray dried microparticles (Table 1). At such a high lipid load, the ability of the MMT platelet faces to expel FFA from the MLH microparticles via electrostatic repulsion is significantly reduced. As a result, FFA are more likely to remain at the oil−water interface and interfere with lipid digestion. Further, the reduced surface area of available lipids means fewer FFA molecules are required to saturate the oil−water interface and inhibit lipase enzyme.8 Despite this, it is worth noting that the extent of lipid digestion for MLH-5 was still more complete than the submicrometer emulsion after 60 min. Thus, we can expect 32739


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ACS Applied Materials & Interfaces versus 194 ± 1 nm). However, despite the reduction in the extent of digestion, the initial rate of lipolysis was increased for MLH-8 in comparison to that of MLH-2. This increased rate during the first phase of lipolysis is likely due to the absence of lecithin and its inhibitory effects on lipase-mediated digestion in MLH-8. 3.3. Quantification and Speciation of Lipolytic Products via 1H NMR Studies. To gain further insight into the lipolysis of MLH particles, 1H NMR studies were undertaken to elucidate the chemical nature of glycerides and FFA formed throughout digestion. A representative 1H NMR spectra is shown in Figure 8, demonstrating the key spectral changes that occur as lipolysis progresses. At t = 0 min, 1H NMR signals corresponding to protons supported by acyl groups and protons of the glyceryl backbone of triglycerides were evident for both the submicrometer emulsion and MLH2. The addition of pancreatic lipase resulted in a timedependent reduction in intensity or complete disappearance of the peaks corresponding to the glyceryl backbone of triglycerides and the appearance of peaks correlating to the glyceryl backbone of diglycerides and monoglycerides. The relative molar percentage of the lipolytic products, triglyceride, diglyceride, monoglyceride, and FFA during lipolysis studies with the submicrometer emulsion and MLH2 are presented in Figure 9. The evolution of lipolytic products

for both of these systems, as determined by 1H NMR analysis, correlated well with lipid hydrolysis data observed via NaOH titration. For the submicrometer emulsion, changes in the 1H NMR spectra revealed an 80.2% decrease in triglyceride molar concentration over 60 min, similar to the 85.1 ± 1.0% triglyceride digestion indicated by NaOH titration. Similarly, for MLH-2, the 5.6% triglycerides remaining after 60 min lipolysis correlates closely with the complete lipid digestion indicated by NaOH titration. Significant differences in the speciation of lipolysis products were observed between the submicrometer emulsion and MLH-2. A complex mixture of glycerides and FFA were released during the digestion of the submicrometer emulsion with approximately 19% triglycerides, 13% diglycerides, 8% monoglycerides, and 59% FFA present at the conclusion of the 60 min digestion period. In contrast, FFA were the principal lipolysis products released during the digestion of MLH-2. This data suggests that MLH particles are not only capable of increasing the rate and extent of lipid digestion but are also efficient at maximizing triglyceride hydrolysis. This effective release of FFA is likely to correlate with improved drug solubilization and absorption because FFA are incorporated within the solubilizing colloidal species of the gastrointestinal environment and further enhance the solubilization capacity of these vesicles for lipophilic bioactive molecules. The selfassembly structure of the amphiphilic digestion products is an important factor in determining drug solubilization and bioavailability of the lipid components and encapsulated molecules.49−52 Recently, Joyce et al. elucidated that the structure evolution of digestion products was dependent on the lipolysis kinetics and the relative concentration of FFA to glycerides.38 Subsequently, by controlling the FFA:glyceride ratio, it is possible to control the structure of colloidal phases formed by digestion products and hence manipulate the solubilization capacity of the solid-state lipid-based formulation. In the current study, significant differences were observed in the FFA:glyceride ratio of MLH microparticle digests compared to the submicrometer emulsion, whereby a FFA:glyceride ratio of 11.0 was measured for digestion of MLH microparticles compared to 1.5 for the submicrometer emulsion. This change in speciation and disposition of lipolysis products is hypothesized to have a dramatic effect on the solubilization and oral absorption of encapsulated lipophilic compounds. When the rate and extent of lipolysis and the resultant speciation of digestion products are controlled, MLH microparticles can be tailored to specific drug molecules to provide the best solubilization and absorption conditions in vivo.

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CONCLUSIONS Novel MLH microparticles were fabricated by spray drying simple oil-in-water emulsions stabilized by MMT. High lipid loads in excess of 70% w/w were achieved, and particles demonstrated effective redispersibility properties. MLH particles fabricated using lecithin as a coemulsifier demonstrated an improved lipid loading ability and physicochemical properties compared to those particles fabricated using MMT as the sole emulsifier. In comparison to submicrometer emulsions stabilized by soybean lecithin and/or MMT platelets, an increase in the rate and extent of lipid digestion was observed for MLH particles. This suggests the specific nanostructure of MLH particles plays a substantial role in influencing lipase enzyme activity, and this hypothesis was further verified by the results of 1H NMR studies. While a complex mixture of

Figure 9. Relative molar percentages of lipolytic products during in vitro lipolysis for (a) submicrometer emulsion and (b) MLH-2: triglycerides (blue ■), diglycerides (purple ◆), monoglycerides (green ▲), and free fatty acids (orange ●). Each value represents the mean ± SD (n = 3). For some points, the error bars are shorter than the height of the respective symbol. 32740


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(8) Joyce, P.; Tan, A.; Whitby, C. P.; Prestidge, C. A. The Role of Porous Nanostructure in Controlling Lipase-Mediated Digestion of Lipid Loaded into Silica Particles. Langmuir 2014, 30 (10), 2779−88. (9) Joyce, P.; Kempson, I.; Prestidge, C. A. Orientating Lipase Molecules Through Surface Chemical Control for Enhanced Activity: A QCM-D and ToF-SIMS Investigation. Colloids Surf., B 2016, 142, 173−181. (10) Aguzzi, C.; Cerezo, P.; Viseras, C.; Caramella, C. Use of Clays as Drug Delivery Systems: Possibilities and Limitations. Appl. Clay Sci. 2007, 36 (1−3), 22−36. (11) Sheskey, P. J.; Cook, W. G.; Cable, C. G. Handbook of Pharmaceutical Excipients; Pharmaceutical Press: London, 2014. (12) Joshi, G. V.; Kevadiya, B. D.; Patel, H. A.; Bajaj, H. C.; Jasra, R. V. Montmorillonite as a Drug Delivery System: Intercalation and In Vitro Release of Timolol Maleate. Int. J. Pharm. 2009, 374 (1−2), 53− 7. (13) Hou, D.; Hu, S.; Huang, Y.; Gui, R.; Zhang, L.; Tao, Q.; Zhang, C.; Tian, S.; Komarneni, S.; Ping, Q. Preparation and In Vitro Study of Lipid Nanoparticles Encapsulating Drug Loaded Montmorillonite for Ocular Delivery. Appl. Clay Sci. 2016, 119, 277−283. (14) Joshi, G. V.; Patel, H. A.; Kevadiya, B. D.; Bajaj, H. C. Montmorillonite Intercalated with Vitamin B1 as Drug Carrier. Appl. Clay Sci. 2009, 45 (4), 248−253. (15) Oh, Y. J.; Choi, G.; Choy, Y. B.; Park, J. W.; Park, J. H.; Lee, H. J.; Yoon, Y. J.; Chang, H. C.; Choy, J. H. AripiprazoleMontmorillonite: a New Organic-Inorganic Nanohybrid Material for Biomedical Applications. Chem. - Eur. J. 2013, 19 (15), 4869−75. (16) Lagaly, G.; Reese, M.; Abend, S. Smectites as Colloidal Stabilizers of Emulsions: I. Preparation and Properties of Emulsions with Smectites and Nonionic Surfactants. Appl. Clay Sci. 1999, 14 (1− 3), 83−103. (17) Lagaly, G.; Reese, M.; Abend, S. Smectites as Colloidal Stabilizers of Emulsions: II. Rheological Properties of Smectite-Laden Emulsions. Appl. Clay Sci. 1999, 14 (5−6), 279−298. (18) Guillot, S.; Bergaya, F.; de Azevedo, C.; Warmont, F.; Tranchant, J.-F. Internally Structured Pickering Emulsions Stabilized by Clay Mineral Particles. J. Colloid Interface Sci. 2009, 333 (2), 563− 569. (19) Abend, S.; Bonnke, N.; Gutschner, U.; Lagaly, G. Stabilization of Emulsions by Heterocoagulation of Clay Minerals and Layered Double Hydroxides. Colloid Polym. Sci. 1998, 276 (8), 730−737. (20) de Fuentes, I. E.; Viseras, C. A.; Ubiali, D.; Terreni, M.; Alcántara, A. R. Different Phyllosilicates as Supports for Lipase Immobilisation. J. Mol. Catal. B: Enzym. 2001, 11 (4−6), 657−663. (21) Reshmi, R.; Sugunan, S. Superior Activities of Lipase Immobilized on Pure and Hydrophobic Clay Supports: Characterization and Catalytic Activity Studies. J. Mol. Catal. B: Enzym. 2013, 97, 36−44. (22) Tzialla, A. A.; Pavlidis, I. V.; Felicissimo, M. P.; Rudolf, P.; Gournis, D.; Stamatis, H. Lipase Immobilization on Smectite Nanoclays: Characterization and Application to the Epoxidation of α-Pinene. Bioresour. Technol. 2010, 101 (6), 1587−1594. (23) Yeşiloğlu, Y. Utilization of Bentonite as a Support Material for Immobilization of Candida Rugosa Lipase. Process Biochem. 2005, 40 (6), 2155−2159. (24) Porter, C. J. H.; Williams, H. D.; Trevaskis, N. L. Recent Advances in Lipid-Based Formulation Technology. Pharm. Res. 2013, 30 (12), 2971−5. (25) Tan, A.; Simovic, S.; Davey, A. K.; Rades, T.; Prestidge, C. A. Silica-Lipid Hybrid (SLH) Microcapsules: a Novel Oral Delivery System for Poorly Soluble Drugs. J. Controlled Release 2009, 134 (1), 62−70. (26) Sek, L.; Porter, C. J. H.; Kaukonen, A. M.; Charman, W. N. Evaluation of the In-Vitro Digestion Profiles of Long and Medium Chain Glycerides and the Phase Behaviour of their Lipolytic Products. J. Pharm. Pharmacol. 2002, 54 (1), 29−41. (27) Sek, L.; Porter, C. J. H.; Charman, W. N. Characterisation and Quantification of Medium Chain and Long Chain Triglycerides and their In Vitro Digestion Products, by HPTLC Coupled with In Situ

glycerides and FFA was released during the digestion of a lecithin-stabilized submicrometer emulsion, 1H NMR spectra demonstrated FFA to be the predominant lipolytic product observed during the digestion of MLH particles. Owing to this ability to optimize the lipase-mediated digestion kinetics of MCT, biocompatible MLH microparticles demonstrate significant potential for optimizing oral drug delivery via enhanced drug solubilization from lipid-based formulations.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b13599. Lipid digestion kinetics for coarse MCT emulsions with and without MMT as a stabilizer (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; Tel.: +61 8 8302 3569; Fax: +61 8 8302 3683. ORCID

Clive A. Prestidge: 0000-0001-5401-7535 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The Australian Research Council (Discovery Grant Scheme, DP 120101065) is gratefully acknowledged for research funding and support. This work was performed (in part) at the South Australian node of the Australian National Fabrication Facility under the National Collaborative Research Infrastructure Strategy. Ms. Jessica Wojciechowski is acknowledged for her assistance in the calculation of kinetic data.

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REFERENCES

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Nanostructured Montmorillonite Clay for Controlling the Lipase

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