COMPARISON OF HOMOGENIZATION AND PRECIPITATION TECHNIQUES FOR PRODUCTION OF QUERCETIN NANOCRYSTALS

Transcription

1 COMPARISON OF HOMOGENIZATION AND PRECIPITATION TECHNIQUES FOR PRODUCTION OF QUERCETIN NANOCRYSTALS Mitali Kakran 1*, Nanda Gopal Sahoo 1, Lin Li 1, Rainer H. Müller 2 1 School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore Free University of Berlin, Department of Pharmacy, Biopharmaceutics and Nutricosmetics, Kelchstrass 31, Berlin, Germany ABSTRACT The aim of this study was to compare the production of nanocrystals of a poorly watersoluble antioxidant, quercetin, by top-down and bottom-up techniques. The top-down method used was high pressure homogenization (HPH) and bottom-up method of evaporative precipitation of nanosuspension (EPN) was used and the products from both these methods were compared. The particle size of the original drug was about 34 µm. The smallest average particle size obtained from HPH was 483 nm and after lyophilisation it was 575 nm, and from EPN it was 739 nm. The dissolution rate of the quercetin nanocrystals prepared by both the methods enhanced manifolds compared to the original quercetin. The antioxidant activities of the quercetin nanocrystals were better than the original drug. Our study demonstrated that both the methods can successfully prepare quercetin nanocrystals. HPH produced smaller crystals, which presented slightly better dissolution than those produced by the EPN. However, EPN is a simple process compared to the energy intensive HPH and is cost effective. Key words: Quercetin; Nanocrystals; High Pressure Homogenization; Evaporative Precipitation of Nanosuspension; Dissolution. INTRODUCTION The pharmaceutical compounds are characterized with respect to their aqueous solubility and intestinal permeability using a biopharmaceutics classification system (BCS), which divides drug compounds into four classes (Amidon et al, 1995). Class I drugs have high bioavailability and provide no challenge. Class IV drugs are pharmaceutical bricks which will never make it to the market. Class II and Class III drugs have a poor bioavailability because of their low solubility and their low membrane permeability, respectively. Quercetin (3, 3, 4, 5, 7-pentahydroxyflavone), shown in Fig. 1, is one of the most prominent dietary antioxidants. It has proven to exert potent chemopreventive actions and has demonstrated strong inhibition of breast, colon, lung, and ovarian cancer cell growth (Jagtap et al, 2009). In spite of this wide spectrum of pharmacological properties, its use in pharmaceutical field is still limited because of its poor bioavailability due to its poor solubility and fast metabolism. Besides quercetin, there are a number of newly developed drug molecules which exhibit poor water solubility and hence, fall under the category of class II drugs of the BCS. The 1

2 bioavailability of such class II drugs can be enhanced by improving their aqueous solubility and dissolution velocity. So, one of the most challenging tasks in drug development is to improve the solubility and dissolution rate of these drugs. Various methods to enhance solubility of poorly water-soluble drugs include formation of complexes (e.g. with β-cyclodextrin), solid dispersions, liposomes, emulsions, microemulsions etc. However, these methods are successful in some instances and are specific to drug candidates. An alternative universal approach, which can be applied to any drug, is to increase the particle surface area available for dissolution by reducing the particle size to nanoscale (Merisko-Liverside et al, 2003). Nanocrystals exhibit advantages like increased saturation solubility and dissolution velocity attributed to their higher surface area, and excellent adhesion to biological surfaces (Sahoo et al, 2008). This results in not only an improved bioavailability but also in the reduction of variation in bioavailability of these drugs. There are two key approaches to achieve the nanodimension namely, top down and bottom up. The commonly used top down methods are high pressure homogenization and pearl milling. The main bottom up technique is precipitation. Fig. 1. Chemical structure of quercetin, containing five characteristic hydroxyl groups. In the present study quercetin nanocrystals have been fabricated using the top-down technique of high pressure homogenization (HPH) and bottom-up technique of evaporative precipitation of nanosuspension (EPN). The two methods have been compared for the efficiency of production, the size and quality of the products obtained. MATERIALS AND METHODS Materials Quercetin was purchased from Sigma-Aldrich, Singapore. The stabilizer Tween 80 (polysorbate 80, Uniqema, Belgium) was used for this study. All the reagents used were of technical grade. Methods The quercetin nanosuspension (2% w/w) in Milli-Q water using Tween 80 as a stabilizer (0.5% w/w) was high pressure homogenized (HPH) using a Micron Lab40 (APV Deutschland GmbH, Unna, Germany) by premilling at increasing pressures (2 cycles at 300 bar, 2 cycles at 500 bar, 1 cycle at 1,000 bar) followed by 20 homogenization cycles at 1500 bar. Samples for characterization were collected after pre-milling, and after 1, 5, 2

3 10, 15 and 20 cycles of homogenization. The quercetin nanosuspension was dried by lyophilization at -80 o C using a freeze-drier (Martin Christ-α-1-2 LD freeze dry system) with 50 mbar vacuum for 24 h. The dried powder was stored in a desiccator. Quercetin nanocrystals were also prepared by the evaporative precipitation of nanosuspension (EPN) method. Original quercetin was dissolved in a good solvent (ethanol) and then nanocrystals were formed by quickly adding an antisolvent (hexane). Drug crystals in the nanosuspension were obtained by quick evaporation of the solvent and antisolvent, followed by vacuum drying. Parameters like drug concentration in solvent, and solvent to antisolvent ratio were varied during the process. Different drug concentrations (DC) used were 5-15 mg/ml and the solvent to antisolvent (SAS) ratios were varied from 1:5 to 1:25 (v/v). Characterization The mean particle size was measured using photon correlation spectroscopy (PCS) (Zetasizer Nano ZS, Malvern Instruments, Malvern, UK). The morphology of samples was observed using a scanning electron microscope (JSM-6390LA-SEM, Jeol Co., Japan). Differential scanning calorimetric (DSC) measurements were carried out using a TA DSC 200 thermal analyzer in a temperature range of o C at a heating rate of 10 o C/min in nitrogen gas. The melting point and heat of fusion were calculated using the DSC software. X-ray diffraction was studied using the Bruker AXS D8 Advance X- ray diffractometer with Cu Kα targets at a scanning rate of θ/s, applying 40 kv, 40 ma, to observe the crystallinity of samples. Solubility studies were performed with a shaker (InnovaTM 4230, New Brunswick Scientific Co., Inc., USA). Excess quercetin was added in 20 ml DI water and stored at 25 ± 0.01 o C. After 24 hours, suspensions were filtered and analyzed spectrometrically at 370 nm using a UV spectrometer (UV- 3101PC, Shimadzu). Experiments were carried out in triplicate, and solubility data were averaged. The in vitro dissolution of the quercetin nanocrystals samples as well as the original quercetin was determined using the paddle method (USP apparatus II, Vankel VK 7000 Dissolution Tester) in 900 ml of DI water. The paddle rotation was set at 100 rpm. The temperature was maintained at 37 ± 0.5 o C. The original quercetin and quercetin nanocrystals containing an equivalent 5 mg of quercetin were tested for their dissolution. The dissolved solution samples of 1 ml were collected at 15, 30, 45, 60, 90, 120 and 180 min of dissolution time. The dissolution test for each sample was performed in triplicate and the dissolution data was averaged. The concentration of drug was determined spectrometrically at 370 nm. The antioxidant activity was measured by the DPPH assay. DPPH (0.3 mm in methanol) was incubated (in darkness) with 2.0 ml of original quercetin and nanocrystals at concentrations of 25 and 50 µg/ml at 37 o C. After 30 minutes of incubation, the absorbance was measured at 518 nm using a Hitachi U-2000 spectrophotometer (Mensor et al, 2001). The percentage inhibition of the experimental samples was evaluated comparing the absorbance values of control and test samples. It was calculated using the formula: % of inhibition= [(Control OD -Test OD)/Control OD] 100 (1) where OD = Optical density. 3

4 RESULTS AND DISCUSSION Particle Size Analysis The average particle size of quercetin nanocrystals prepared by HPH and EPN are listed in Table 1. For HPH, the lowest mean particle size of the quercetin nanocrystals obtained after 20 homogenization cycles at 1500 bar was 483 nm. During homogenization, coarse suspension is passed under a high pressure through a very small homogenization gap, which leads to a high streaming velocity. In the homogenization gap, the dynamic pressure of the fluid increases with the simultaneous decrease in static pressure, which causes the water to boil at room temperature leading to the formation of gas bubbles, which implode when the suspension leaves the gap (called cavitation) and normal air pressure is reached again (Müller et al, 2001). The cavitation forces are high enough to disintegrate the microparticles to drug nanoparticles. The particle size of the drug obtained during the homogenization process depends primarily on the homogeneous pressure and the number of homogenization cycles. The microsuspension was first premilled to avoid blocking of the gap by larger particles and then the high pressure homogenization was carried out by 20 homogenization cycles at 1500 bar. From Table 1, it is clearly seen that the mean particle size decreased with an increase in homogenization cycles. Dried quercetin nanocrystals were prepared by lyophilization using a freeze dryer. All properties such as crystallinity, morphology, dissolution of the lyophilized quercetin nanocrystals were investigated. The PCS mean particle size of the lyophilized quercetin re-dispersed in water was 575 nm, which was slightly higher than that of the quercetin nanosuspension obtained from HPH. Tab. 1. The mean particle size (nm) for quercetin nanocrystals prepared. High Pressure Homogenization (HPH) Premilling 1 cycle 5 cycles 10 cycles 15 cycles 20 cycles Lyophilized Nanosuspension (after 20 cycles) Evaporative Precipitation of Nanosuspension (EPN) 10 mg/ml (DC) 5 mg/ml 15 mg/ml 1:5 (SAS) 1:15 (SAS) 1:25 (SAS) 1:25 (SAS) 1:25 (SAS) For the EPN prepared samples, it can be observed from Table 1 that increasing the solvent to antisolvent ratio and decreasing the drug concentration in solvent results in lower particle sizes. The effect of drug concentration can be explained by considering two factors: the amount of drug per unit volume of solvent and the influence of drug concentration on the viscosity (Galindo-Rodriguez et al, 2004). First, as a consequence of greater amount of drug per unit volume of the solvent, the solvent diffusing into the antisolvent phase carries more drug which aggregates and thus, forms larger particles. On the other hand, the viscosity of the drug solution increases with increasing concentration, which hinders the diffusion of drug molecules from the solution into the 4

5 antisolvent and thus, results in non-uniform supersaturation (Zhang et al, 2006). As a result, the drug particles are big in size and non-uniform. The effect of the solvent to antisolvent ratio can be explained on the basis that once the nuclei are formed, particle growth occurs simultaneously and for the subsequent growth a high solvent to antisolvent ratio increases the diffusion distance for growth species and consequently diffusion becomes the limiting factor for nuclei growth (Guozhong, 2003). For EPN process, the lowest drug concentration of 5 mg/ml and the highest solvent to antisolvent ratio of 1:25 (v/v) resulted in the smallest quercetin particles. SEM microphotographs of the original quercetin and its nanocrystals prepared by HPH and EPN are shown in Fig. 1. It is observed from Fig. 1 that the original quercetin exhibited lack of uniformity in size and were much larger (~34 µm) than those prepared by HPH and EPN. The morphology of particles prepared by HPH depends on that of the starting material. Original quercetin exhibited rod type morphology and HPH prepared nanocrystals showed needle type morphology, which were quite similar. In case of EPN, the morphology of the particles depends on the type of antisolvent being used. In our other study we found that when water was used as an antisolvent, quercetin particles were big, irregular and flake type (Kakran et al., 2011) but in case of benzene and hexane, the particle morphology was more needle type. To sum up, both HPH and EPN prepared quercetin nanocrystals presented similar morphology. (a) (b) (c) 5

6 Fig. 2. SEM photographs indicating clear reduction in particle size of querectin by many folds, (a) original quercetin, (b) lyophilized quercetin nanocrystals prepared by HPH, and (c) EPN prepared quercetin nanocrystals. DSC Analysis In order to understand the effect of the HPH, lyophilization and EPN process on the melting temperature and the melting enthalpy of quercetin, DSC was conducted. DSC thermograms of the original quercetin and its nanocrystals are shown in Fig. 2. The original quercetin used in this study had a sharp melting endothermic peak at 326 o C and a melting enthalpy of J/g. Lyophilized and EPN prepared nanocrystals showed melting points of 324 o C and 321 o C, respectively. The melting enthalpy of the lyophilized and EPN prepared nanocrystals (139.5 J/g and J/g, respectively) was comparatively lower than the original quercetin. The shifting of endothermic melting peak shifted to the lower temperature side and decreased melting enthalpy suggest that it can be due to the nano-size of the samples and/or the crystallinity of quercetin nanocrystals slightly decreased. Fig. 3. Differential scanning calorimetric (DSC) thermograms of (a) original quercetin, (b) lyophilized quercetin nanocrystals prepared by HPH, and (c) EPN prepared quercetin nanocrystals. X-Ray Diffraction Analysis The crystalline state of the samples was further evaluated by X-ray diffraction. Fig. 3 shows the X-ray diffraction patterns of the original quercetin, lyophilized and EPN prepared quercetin nanocrystals. The X-ray patterns of the quercetin powder in Fig. 3 (a) displayed the presence of numerous distinct peaks at 2θ of 5.54 o, o, o, o, o, o and o, which suggests the high crystalline form of the drug. The lyophilized and EPN prepared quercetin nanocrystals also showed the similar peaks but with slightly different peak intensities. This is probably the sign of nanometer scale quercetin crystals. Nanocrystallinity is known to cause such effect in the X-ray powder diffractograms. Hence, lyophilized and EPN prepared quercetin nanocrystals were in the crystalline state. We can also confirm the reason for the DSC results mainly to be the 6

7 nano-size of the samples and only slight decrease in crystallinity. There is some variation in the XRD patterns for the lyophilized and the EPN prepared quercetin nanocrystals, which can be attributed to the difference in the fabrication approaches for both. For HPH prepared nanocrystals, energy was applied by high pressure homogenization and it was followed by the freeze drying process; and for EPN prepared nanocrystals there was precipitation first, followed by the evaporation process. However, these processes did not transform quercetin into a fully amorphous state. It is well known that more amorphous substances show higher solubility than in the crystalline ones, but crystalline substances are physically more stable compared to the amorphous forms. As a substance in the amorphous state has a lower long-term stability and it might change to a more crystalline form (Carstensen, 2001), the drug nanocrystals in a crystalline form are more suitable to enhance its physical stability and dissolution velocity. Hence, quercetin nanocrystals prepared by both HPH and EPN are expected to show good physical stability. Fig. 4. Comparison of the X-ray diffractograms of (a) original quercetin, (b) lyophilized quercetin nanocrystals prepared by HPH, and (c) EPN prepared quercetin nanocrystals. Solubility and Dissolution Studies From Fig. 4(i), the solubility of original quercetin was extremely low being only 2.84 ± 0.03 µg/ml. There was the significant enhancement in the solubility of the nanocrystals produced by the two methods. This is because the saturation solubility increases with decreasing particle size below 1000 nm (Müller et al, 2001). Forming nanocrystals enhanced the saturation solubility of quercetin approximately 5.4 times to ± 1.94 µg/ml for the lyophilized quercetin nanocrystals prepared by HPH and 4.6 times to ± 1.32 µg/ml for EPN prepared ones. Fig. 4(ii) shows the dissolution profiles of original quercetin, lyophilized and EPN prepared quercetin nanocrystals. As seen from the dissolution profiles of the 3 samples in Fig. 4, only about 5% of the original quercetin dissolved within 180 minutes as compared to 75% of dissolution for the lyophilized quercetin nanocrystals. The EPN prepared quercetin nanocrystals exhibited 67% dissolution within the same time. These 7

8 results can be explained based on Noyes Whitney equation, which provides a general guideline as to how the dissolution rate of an insoluble drug improves (Noyes and Whitney, 1897). According to it the dissolution rate equation is expressed as: dc D A =. ( c S c x ) dt h (2) where dc/dt is the dissolution velocity, D is the diffusion coefficient of the drug, A is the surface area available for dissolution, h is the thickness of the diffusion boundary layer adjacent to the surface of the dissolving drug, c s is the saturation solubility, and c x the bulk concentration. According to this equation, the dissolution rate of a drug can be increased by reducing the particle size to increase the particles surface area (A). Therefore, nanosizing quercetin tremendously increased the exposed surface area of the drug crystals and hence, enhanced its dissolution rate. As a result, the quercetin nanocrystals prepared are expected to demonstrate a better bioavailability than the original drug powder. Furthermore, a comparison between the dissolution profiles of quercetin from different samples was made using the difference factor (f 1 ) and similarity factor (f 2 ) as below: f 2 f = 50 log n R T i= 1 i i 1 = n i= 1 R i 100 n [ 1+ (1/ n) R i Ti ] 100 i= 1 where i is the dissolution sample number, n is the number of dissolution times, R i and T i are the amounts dissolved of the reference drug and the test drug at each time point i. According to the FDA s guidelines, f 1 values lower than 15 (0-15) and f 2 values greater than 50 (50-100) indicate the similarity of the dissolution profiles (Costa and Lobo, 2001). It was observed that the dissolution profiles of the quercetin nanocrystals and original quercetin were not similar as f 1 values for all quercetin nanocrystals were very much higher than 15, whereas their f 2 values were lower than 50. However, dissolution profiles of the lyophilized and EPN prepared quercetin nanocrystals were very similar as the f 1 value was 11.5 (lower than 15) and the f 2 value was 78.5 (more than 50). (3) (4) (i) (ii) 8

9 Fig. 5. (i) Solubility study for (a) original quercetin, (b) lyophilized quercetin nanocrystals prepared by HPH, and (c) EPN prepared quercetin nanocrystals, at 25 ± 0.01 o C.; and (ii) dissolution profile of the same samples determined at 37 ± 0.5 o C by paddle method (USP apparatus II). DPPH free radical-scavenging assay DPPH is a free radical and stable at room temperature, which produces a deep violet solution in organic solvents. It is reduced in the presence of quercetin molecules, giving rise to uncoloured solutions. The use of DPPH provides an easy and rapid way to evaluate antioxidant properties of quercetin. Quercetin shows an antioxidative effect which is mainly due to its phenolic hydroxyl groups. These phenolic hydroxyl groups are able to donate the hydrogen to reduce the free radicals to prevent oxidation of lipids, proteins, and DNA (Heim et al, 2002). The free radical scavenging properties of the original quercetin and quercetin nanocrystals are shown in Fig. 5. The observed scavenging effect of quercetin on the DPPH radicals decreased in the following order: lyophilized nanocrystals > EPN prepared quercetin nanocrystals > original quercetin, which were 73.3%, 66.4% and 17.5% at the concentration of 50 mg/ml, respectively. From the dissolution studies, it was observed that the quercetin nanocrystals showed much higher dissolution than the original quercetin and hence, showed a higher free radical scavenging effect. The previous studies have also suggested that the nanoparticles systems of quercetin (Wu et al, 2008) and melatonin (Schaffazick et al, 2005) have improved antioxidant activity in vitro. Fig. 6. The antioxidant activities of (a) original quercetin, (b) lyophilized quercetin nanocrystals prepared by HPH, and (c) EPN prepared quercetin nanocrystals, measured by the DPPH assay. CONCLUSIONS This study demonstrated that both HPH and EPN methods can successfully prepare quercetin nanocrystals. Quercetin nanocrystals from both the methods were crystalline in nature and hence, expected to possess long term physical stability. HPH produced smaller crystals, which presented slightly better dissolution than those produced by the EPN. HPH also has the advantage that the drugs that are poorly water soluble in both 9

10 aqueous as well as organic media can be easily formulated into nanoparticulate suspensions. However, EPN is a simple process compared to the energy intensive HPH and is cost effective. To conclude, both these methods present an efficient means to obtain quercetin drug nanocrystals with higher dissolution in-vitro. Quercetin nanocrystals are expected to present higher bioavailability in-vivo, which will lead to a considerable dose reduction for patients. ACKNOWLEDGEMENT Authors acknowledge the financial support from SUG grant M , NTU, Singapore and Deutscher Akademischer Austauschdienst DAAD (PKZ: A/09/74578). REFERENCES Amidon, GL, Lennernas, H, Shah, VP & Crison, JR 1995, A theoretical basis for a biopharmaceutic drug classification: the correlation of in vitro drug product dissolution and in vivo bioavailability, Pharmaceutical Research, vol 12, pp Carstensen, JT 2001, Solid state stability, in: Carstenssen JT (Ed), Advanced pharmaceutical solids, Marcel Dekker Inc., New York. Costa, P & Lobo, JMS 2001, Modeling and comparison of dissolution profiles, European Journal of Pharmaceutical Sciences, vol 13, pp Galindo-Rodriguez, S, Allémann, E, Fessi, H & Doelker, E 2004, Physicochemical parameters associated with nanoparticle formation in the salting-out, emulsification-diffusion, and nanoprecipitation methods, Pharmaceutical Research, vol 21, pp Guozhong, C 2003, Nanostructures and nanomaterials: synthesis properties and applications, Imperial College Press, London, pp Heim, KE, Tagliaferro, AR & Bobilya, DJ 2002, Flavonoid antioxidants: chemistry, metabolism and structure activity relationships, Journal of Nutritional Biochemistry, vol 13, pp Jagtap, S, Meganathan, K, Wagh, V, Winkler, J, Hescheler, J & Sachinidis, A 2009, Chemoprotective mechanism of the natural compounds, epigallocatechin-3-ogallate, quercetin and curcumin against cancer and cardiovascular diseases, Current Medicinal Chemistry, vol 16, pp Kakran, M, Sahoo, NG & Li, L 2011, Dissolution Enhancement of Quercetin through Nanofabrication, Complexation, and Solid Dispersion, Colloids and Surfaces B, in press. Mensor, LL, Menezes, FS, Leitão, GG, Reis, AS, Santos, TC, Coube, CS & Leitão, SG 2001, Screening of brazilian plant extracts for antioxidant activity by the use of DPPH free radical method, Phytotherapy Research, vol 15, pp Merisko-Liverside, E, Liversidge, GG & Cooper, ER 2003, Nanosizing: a formulation approach for poorly-water-soluble compounds, European Journal of Pharmaceutical Sciences, vol 18, pp Müller, RH, Jacobs, C & Kayser, O 2001, Nanosuspensions as particulate drug formulations in therapy Rationale for Development and what we can expect for the future, Advanced Drug Delivery Reviews, vol 47, pp

11 Noyes, AA & Whitney, WR 1897, The rate of solution of solid substances in their own solutions, Journal of the American Chemical Society, vol 19, pp Sahoo, NG, Abbas, A & Li, CM 2008, Micro/Nanoparticle Design and Fabrication for Pharmaceutical Drug Preparation and Delivery Applications, Current Drug Therapy, vol 3, pp Schaffazick, SR, Pohlmann, AR, de Cordova, CA, Creczynski-Pasa, TB & Guterres, SS 2005, Protective properties of melatonin-loaded nanoparticles against lipid peroxidation, International Journal of Pharmaceutics, vol 289, pp Wu, TH, Yen, FL, Lin, LT, Tsai, TR, Lin, CC & Cham, TM 2008, Preparation, physicochemical characterization, and antioxidant effects of quercetin nanoparticles, International Journal of Pharmaceutics, vol 346, pp Zhang, JY, Shen, ZG, Zhong, J, Hu, TT, Chen, JF, Ma, ZQ & Yun, J 2006, Preparation of amorphous cefuroxime axetil nanoparticles by controlled nanoprecipitation method without surfactants, International Journal of Pharmaceutics, vol 323, pp BRIEF BIOGRAPHY OF PRESENTER Ms. Mitali Kakran (Singapore Airlines scholar) completed her B.Eng. in 2008 with First Class Honours from School of Chemical and Biomedical Engineering (SCBE), Nanyang Technological University (Singapore), majoring in Bioengineering. Presently she is pursuing her PhD in the School of Mechanical & Aerospace Engineering in Nanyang Technological University (Singapore) under the supervision of Assoc. Prof. Li Lin and Asst. Prof. Zaher Judeh since August Her current research activities include fabrication of micro- and nanoparticles of drugs for pharmaceutical applications, with the main aim to enhance the bioavailability of the drugs by improving their aqueous dissolution rate. 10