Dhana Lakshmi P. et al. / International Journal of Biopharmaceutics. 2012; 3(2): International Journal of Biopharmaceutics

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1 70 e- ISSN Print ISSN International Journal of Biopharmaceutics Journal homepage: IJB SOLID LIPID NANOPARTICLE SYSTEMS FOR DELIVERY OF DRUGS TO THE BRAIN Dhana Lakshmi. P*, Rahul Nair, Chakrapani. M, Venkatkrishnakiran. P *Sree Vidyanikethan College of Pharmacy, A. Rangampet, Tirupati, Andhra Pradesh , India. ABSTRACT The Solid lipid nanoparticles (SLNs) of hydrophilic drug Gabapentin is partial seizures drug are developed and the entrapment efficiency of drug in the SLN has been improved. The hydrophilic drugs were delivered to the brain was very difficult because of poor penetration across the BBB, efflux of drugs from the brain by p- glycoprotein. The hydrophilic drug is the problem associated with the incorporation in to SLN. The SLNs were prepared by ethanol injection method using tristearin and phospholipon 80 H. Different combinations of tween 80 concentrations and varied sonication time were used to prepare SNLs. The two operating variables such as sonication time and tween 80 concentrations were found to have significant effect on particle size, entrapment efficiency of SLN but not on the drug release. The prepared SLNs were characterized for surface morphology by SEM analysis, entrapment efficiency, zeta potential, FTIR, DSC, invitro diffusion studies. The prepared SLNs were spherical in shape and possess mean average size of 159.2nm. As the preparation of SLN suffer from the drawback of poor incorporation of hydrophilic drugs, the present work is focused to assess the various formulations and process parameters to enhance the incorporation of Gabapentin into SLNs. The SLN could be alternate delivery system for administering molecules into the brain with prolonged drug release profiles and better therapeutic effect can be achieved for the treatment of seizures. Keywords: Solid lipid Nanoparticles, Gabapentin, Entrapment efficiency, in vitro diffusion. INTRODUCTION Polymeric and lipid based sub-micron sized carrier systems such as SLNs have attained a great deal of interest during the past decades (Westesen K et al., 1996; Krutika Khanderao Sawant and Shamsunder S. Dodiya, 2008). The SLNs possess a lipid core matrix in the nanometer range stabilized by a layer of surfactants. The SLNs were novel delivery system to reach the therapeutic drug level in the brain, as drug carriers with high loading capacity and small particle size, which bypass the reticulo endothelial system (RES), are Corresponding Author Dhana Lakshmi. P dhanalakshmi.0009@gmail.com considered as suitable delivery system (Bummer PM, 2004; Muller RH and Keck CM, 2004; Begley DJ, 2004; Wang JX et al., 2002). They have been used as ideally suited drug delivery systems for the proteins, vaccines and other drugs for controlled release compared to other colloidal drug delivery systems. Their ability to penetrate through several anatomical barriers, sustained release of their contents, and their nanometer size range makes the implementation of SLN as successful drug delivery systems (Mukherjee S et al., 2010). The SLNs has the potential to carry both lipophilic and hydrophilic drugs (Fundaro A et al., 2000; Chen D et al., 2001; Reddy JS and Venkateshwarlu V, 2004). SLNs combine the advantages of both polymeric nanoparticles and liposome s such as possibility of controlled drug release and drug targeting, increased drug stability, incorporation of lipophilic and hydrophilic drugs etc. SLN production

2 71 techniques include High shear homogenization, ultrasound, high pressure homogenization, hot homogenization, cold homogenization, solvent emulsification and evaporation etc. Lipidic carriers used to prepare SLNs can be highly purified lipids such as tristearin or pripalmitin, hard fats such as stearic acid or behenic acid, waxes such as cetyl palmitate and acylglycerol mixtures such as compritol or glyceryl monostearate (Goto M et al., 2005). For the lipophilic drugs SLNs serves as potential drug delivery but aqueous solubility of the drug serves as a limiting factor for its absorption. Although both hydrophilic and lipophilic drugs can be incorporated in to SLNs loding of hydrophilic drugs is a great challenge as the drug has maximum tendency to partition in the water during the preparation process. Gabapentin is a hydrophilic drug which is effective drug for the treatment of partial seizures. The Gabapentin mechanism is not clearly known but there is evidence that it promotes GABA (Gamma Amino Butyric Acid) release. Gabapentin is an amino acid, an analog of GABA that is effective against partial seizurs. It do not act directly on GABA receptors, they may, however, modify the synaptic or non-synaptic release of GABA. An increase in brain GABA concentration is observed in patients receiving gabapentin. Gabapentin is transported into the brain by the L-amino acid transported. Gabapentin is a biopharmaceutical classification system class III drug (high solubility and low permeability) having an aqueous solubility of approximately 10mg/ml. the drug is characterized by a short half-life ranging from 5 to 7 h. Gabapentin has rapid Absorption. Absorbed in part by the L-amino acid transport system, which is a carriermediated, saturable transport system; as the dose increases, bioavailability decreases. Food has a slight effect on the rate and extent of absorption of gabapentin (14% increases in AUC) (Safal Jain et al., 2010). The objective of the present study was to adopt a simple approach of SLNs systems for delivery of Gabapentin to the brain. Two formulation variables Tween 80 concentration and sonication time were studied to optimize the formulation for maximum entrapment efficiency (EE). In addition to EE, the particle size and Drug release were also considered as response using design expert software. The other characterizations such as zeta potential, SEM, FTIR, and DSC were carried out to determine the lipid nature size of prepared formulation etc. MATERIALS AND METHODS Materials Gabapentin was gift sample from Aurobindo pharma Ltd. (Hyderabad, India). Phospholipon R 80 H was a gift sample from Lipoid (Ludwigshafen, Germany). Tristearin was procured from TCI chemicals (India) Private Ltd. All other reagents used in this study were of analytical grade. METHOD OF PREPARATION OF SLN DESPERSION Preparation of gabapentin loaded SLN and the process of optimization Gabapentin, a hydrophilic drug has been used in the present investigation to determine the process variables effecting the incorporation of hydrophilic drugs in to SLN. In the present Study a simple approach for the fabrication of SLN of the basic molecule Gabapentin was adopted. Two formulation variables such as tween 80 concentration (as stabilizer) and sonication time were studied to optimize the formulation for maximum entrapment efficiency (EE). In addition to EE, the particle size and % drug release were also considered as response using Design expert software. Further, the optimized operating parameters were employed for the fabrication of Gabapentin SLN. Nine different concentrations of tween 80 and sonication time to determine the effect of surfactant and sonication time on the potency of the SLNs. The variable parameters used during formulation development are given in table. No.1 Table 1. Variables used in the formulation development S.No Formulation F1 F2 F3 F4 F5 Tween 80 Con.(ml) Sonication time (min) S.No Formulation F6 F7 F8 F9 Tween 80 Con.(ml) Sonication time (min) Preparation of SLNs The SLNs were prepared by modified solvent injection method. Briefly, tristearin, phospholipon 80 H and drug Gabapentin were dissolved in ethanol in a definite ratio and warmed to 70±2 C. Tween 80 in a definite amount was dissolved in PBS solution (P H 7.4) to prepare aqueous phase. The organic phase, i.e. alcoholic solution containing lipid mixture, was added solution (70±2 C) with the help of a hypodermic needle (Safal Jain et al., 2010). Stir the mixture was then sonicated for varying time periods to obtain nanoparticles with optimum size. Fourier transformed infrared (FTIR) spectroscopic analysis Fourier transform infrared (FT-IR) spectra of the samples were obtained in the range of 450 to 4000cm - 1.

3 72 IR spectral analysis of pure Gabapentin, tristearin, phospholipon 80 H, physical mixture of Gabapentin with tristearin, phospholipon 80 H and Gabapentin SLN formulation were carried out. The peaks and pattern produced by the pure drug were compared with physical mixture and formulation. Scanning electron microscopy (SEM) Scanning electron microscopy (SEM) was conducted to characterize the surface morphology of the SLNs. The samples were mounted on alumina stubs using double adhesive tape, coated with gold in HUS- 5GB Vaccum evaporator, and then the sample was observed in Hitachi S-3000N SEM at an acceleration voltage of 10KV and a magnification of 5000X. Differential scanning colorimetry (DSC) Differential Scanning Calorimetry (DSC) analysis was performed using Netzsch DSC 200PC (Netzsche, Selb, Germany). The instrument was calibrated with indium (calibration standard, >99.999%) for melting point and heat of fusion. A heating rate of 100C/min was employed in the range of C. Analysis was performed under nitrogen purge (20 ml/min). The samples were weighted into standard aluminium pans and an empty pan was used as reference. Particle size determination The average particle size, polydispersity index and zeta potential of the lipid particulate dispersions were determined using a Zetasizer (DTS Ver.4.10, Malvern Instruments, UK). The sample of dispersion was diluted to 1:9 v/v with double distilled water to ensure that the light scattering intensity was within the instrument s sensitivity range. Double distilled water was filtered through 0.45 μm membrane filters (Pall Life sciences, Mumbai, India) prior to particle size determination. Determination of Entrapment Efficiency (EE) The EE was determined by analyzing the free drug content in the supernatant obtained after centrifuging the SLN suspension in high speed centrifuge at rpm for 30 min at 30 C using Remi cooling centrifuge (Mumbai, India). The EE was calculated as follows: In vitro drug release Drug release from the formulations was studied in vitro using dialysis membrane (Himedia, India molecular cut-off point 3500 Da; Gupta et al. 2005). Membrane was soaked in double-distilled Water for 12 h before mounting in a diffusion cell. SLN suspension (1 ml) free from any unentrapped drug was placed in dialysis tube, which was suspended in a beaker containing 20mL PBS (ph 7.4) containing 50% v/v ethanol. The contents of the beaker were stirred using a magnetic stirrer at 37±20C. Samples were withdrawn periodically and replaced with the same volume of fresh elution solution to keep the volume in the receptor compartment constant. The samples were analysed for drug content using UVvisible spectrophotometry. Drug Release Kinetics Different kinetic models such as zero order (cumulative amount of drug released vs. time), First order (log cumulative percentage of drug remaining vs. time), Higuchi model (cumulative percentage of drug released vs. square root of time), korsmeyer-peppas model and Hixson crowell model were applied to interpret the drug release kinetics from the formulations. Based on the highest regression values (R 2 ) for correlation coefficients for formulations, the best fit model was decided. Table 2. Composition of various SLNs formulations Formulation Gabapentin Tristearin Phospslipon Tween Sonication 80H 80 time F-1 50mg 50mg 50mg 0.5ml 6 min F-2 50mg 50mg 50mg 0.5ml 12 min F-3 50mg 50mg 50mg 0.5ml 15 min F-4 50mg 50mg 50mg 1ml 6 min F-5 50mg 50mg 50mg 1ml 12 min F-6 50mg 50mg 50mg 1ml 15min F-7 50mg 50mg 50mg 1.5ml 6min F-8 50mg 50mg 50mg 1.5ml 12min F-9 50mg 50mg 50mg 1.5ml 15min

4 73 RESULTS AND DISCUSSION SLNs with a narrow size distribution were prepared by modified solvent injection method using tristearin as a solid lipid. The small and uniform sized SLNs can be prepared by this method without using any sophisticated instruments. The SEM study revealed that most of the SLNs were fairly spherical in shape, the surface of the particle showed a characteristic smoothness, and that the particle size was in the nanometric range, as depicted in Figure 1. IR spectroscopic studies were conducted to determine possible drug: lipid interactions. IR spectra of pure drug Gabapentin, tristearin, phospholipon 80 H and physical mixture of Gabapentin with tristearin and phospholipon 80 H were obtained and shown in figure 2. The characteristic peaks of Gabapentin and lipids were present in the physical mixture, thus indicating that there is no significant evidence of chemical interaction between drug and lipid, which confirms the stability of drug. The major peaks alkyl C-H stretch at 2930cm-1, alkynyl C=C stretch at 2150cm-1, aromatic C=C bend at 1614cm-1, aromatic C-H stretch at 708 cm-1 which were present in drug gabapentin are also present in physical mixture which indicates that there is no interaction between Gabapentin and the solid lipid. Figure 3 reveals the thermal behaviors of the pure components Gabapentin, tristearin, phospholipon 80 H, together with the thermal behavior of the final SLNs prepared and the melting point peaks were tabulated in table.no.3. The DSC curve of pure drug Gabapentin exhibits a sharp endothermic peak at C. The thermograms of Phospholipon 80 H and tristearin displayed broad endothermic peaks at 83 and 77.5 C. On the other hand, the SLNs thermogram displayed complete disappearance of characteristic peak of Gabapentin; a fact that the drug was molecularly dispersed within the lipid matrix. That was accompanied by the formation of a new endothermic peak at C. The SLNs were characterized for average particle size, polydispersity index (PDI), zeta potential and percentage drug entrapment efficiency. The particles of size range to 189.1nm were obtained for Gabapentin loaded SLNs. Zeta potential of various Gabapentin loaded SLNs varies from -4.0 to -7.7 and polydispersity index was found to be between 0.206to (table. No.4). Despite of the low zeta potential the prepared SLNs were stable. Figure 1. SEM image of Gabapentin loaded SLNs Table 3. DSC data of pure components, physical mixture and SLN formulation S.No. Sample Melting peak Gabapentin Phospholipon 80 H Tristearin Gabapentin physical mixture Gabapentin SLN formulation C 83.0 C 77.5 C C C

5 74 Figure 2. Overlaid FTIR graphs Figure 3. Overlaid DSC thermograms

6 75 Table 4. Average particle size, zeta potential and PDI of Gabapentin loaded SLN formulations Formulation Average particle Polydispersity size(nm) index Zeta potential F-1 F-2 F-3 F-4 F-5 F-6 F-7 F-8 F Table 5. Total drug content and entrapment efficiency of Gabapentin loaded SLN formulations S.No. Formulation Total drug content (mg) Entrapment efficiency 1. F % 2. F % 3. F % 4. F % 5. F % 6. F % 7. F % 8. F % 9. F % Table 6. % Drug release data of Gabapentin loaded SLNs formulation Time (hrs) % Drug Release F-1 F-2 F-3 F-4 F-5 F-6 F-7 F-8 F Figure 4. Average particle size of formulation F-5

7 76 Figure 5. % Drug release graph of different SLN Formulations Table 7. Drug release kinetic data of Gabapentin loaded SLN formulations F-1 F-2 F-3 F-4 F-5 F-6 F-7 F-8 F-9 Zero R order model K First R order - - K model Higuchi R matrix model K Peppas R model K Hixson R crowell model K CONCLUSION SLN are a new and innovative therapeutic delivery system for administering molecules into the brain with the concept of surface modification among the traditional colloidal carrier system, it will have an advantage over the conventional invasive methods of drug delivery to the brain. Gabapentin, a hydrophilic drug was successfully incorporated into SLNs by modified solvent injection method. The formulated Gabapentin loaded SLNs were in nanometric range with spherical structure. The release of drug from SLNs best-fitted Higuchi equation and the possible mechanisms for the drug release might be diffusion of the drug from the matrix and matrix erosion resulting from degradation of lipids. This experiment confirmed the evidence that solvent injection technique was a simple, available and effective method to prepare SLNs loading hydrophilic drugs. ACKNOWLEDGMENT The authors wish to thank the management and faculty in department of pharmaceutics, Sree Vidyanikethan College of Pharmacy for providing the necessary facilities for carrying out the research work and Lipoid (Ludwigshafen, Germany) for providing Phospholipon 80 H. REFERENCES Begley DJ. Delivery of therapeutic agents to the central nervous system: the problems and the possibilities. Pharm. Ther. 2004; 104 (1): Bummer PM. Physical chemical considerations of lipid based oral drug delivery-solid lipid nanoparticles. Crit.Rev.Ther. Drug Carr. Syst. 21, 2004; 21: Chen D, Yang I, Liang W, Zhang Q. In vitro and in vivo study of two types of long circulating solid lipid nanoparticles containg paclitaxel. Chem. Pharm. Bull. 2001; 49:

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