subject: Biodegradable Nanoparticles used as Diagnostic and Therapeutic tool [print this page] Introduction Introduction
Nanotechnology is wide field that concerns with the development of man made materials in 5-200nm size range (Faraji et al., 2009). Nanotechnology the word is derived from the Greek word nano meaning dwarf, applies to principles of all sciences and manufacture at molecular and submicron level. Albert franks defined nanotechnology as "The area of science and technology where the dimension and tolerances are in range of 0.1nm to 100nm" (Sahoo &Vinod, 2003).
Nanoparticles have different shape and composition. The physical and chemical properties of small sized particles are very different from those which posses by bulk form. The properties of large surface to volume ratio, enhanced particle aggregation depend on the type of surface modification, increased photoemission, high electrical conductivity, high heat conductivity and improved surface catalytic activity. The size of nanoparticles is in accordance with the size of biomolecules and organelles. This size compatibility allows one to one interaction between them. Because of these properties nanoparticles are widely used as diagnostic and therapeutic tool. Nanoparticles became the important because they can deliver the different drugs easily to the different part of body. (Azzay &. Mansour, 2008). Some time it is difficult for the nanoparticles to reach the CNS (central nervous tissue) because of uptake by reticuloendotheiel system (RES) (Y. E. L. Koo et al., 2006).
For the successfull drug delivery, material should be free from impurities and chemically inert. These polymers must be biodegradable and their resultant molecules must be biologically acceptable and can easily eliminate from the body. Different factor affect the biodegradation of nanopolymeric material like molecular structure chemical structure shape and molecular weight of material and different ionic groups present in the polymers (Rajini Sinha 2009).
Nanoparticles in drug delivery system not only target the drug to its site of action but also helpful to maintain the concentration of specific drug therapeutic level for sustained period of time. The delivery of drugs is maintained by the process nanoencapsulation. In which drug loaded particles are formed with diameter ranging from 1 to 1000nm. The nanoparticles may be of nanosphere and nanocapsules type. The structure of nanosphere is of matrix type. Drugs may be absorbed on surface or may be encapsulated within the particles. Nanocapsule has the vesicular system whose cavity is filled with drugs. This cavity has inner liquid core surrounded by a polymeric membrane. Different substances are usually dissolved in the inner core but they may be absorbed on the surface of capsule (Reis et al., 2006). The type of methods to prepare nanoparticles depends upon the nature of drug being used. Nanoparticles that are not recognized by the body system can be synthesized. Usually hydrophobic particles are recognized as the foreign particles and are rapidly taken up by the MPS (hans & Lowman et al., 2002). Generally, nanoparticles based in hydrophobic polymers provide an affinity to follicle-associated epithelia and also to absorptive enterocytes. The negatively charged poly (styrene) nanoparticles show only low affinity to intestinal tissues. While nanoparticles that are based on hydrophilic polymers and negatively charged, show strong bioadhesive properties and are absorbed by enterocytes (reis et al., 2006). In systemic circulation it is required that nanoparticles are modified in order to prevent the phagocytosis (hans & Lowman et al., 2002). These hydrophilic polymers coated nanoparticles are used to overcome the CNS barrier. Nanoparticles surface charges and increased hydrophilicity of the matrix material both affect the gastrointestinal uptake in a positive sense (reis et al., 2006). The mostly used hydrophilic polymer to coat the nanoparticles is poly ethylene glycol (PEG). This is nonionic polymer and exhibit good biocompatibility. PEG molecules used in different way to coat the nanoparticles including covalent bonding, mixing in during nanoparticles, or surface adsorption. The presence of PEG molecule also enhance the residence time in systemic circulation. These are not recognized as the foreign particles so are not taken up by the body. (Gref et al., 2000).
Different nanoparticles with their possible modification are described in the table. (Hans & Lowman, 2002).
Table 1: Representation of the polymers with their modifications
polymers Surface Modifications
PLGA Polyoxamine 908
PLGA Polyoxamer 407
PLGA Chitosan
PLGA-Mpeg mPEG
PLGA-PEG PEG
PLA PEG 6000
PLA-PEG PEG
PHDCA PEG
PECA PEG
PBCA PEG
These are biodegradable and biocompatible. Various types of the therapeutic agents can be encapsulated in these polymeric nanoparticles (NPs), like low molecular weight drugs, macromolecules such as protein, or plasmid DNA. Use of polymeric matrix prevents the degradation of drugs and are also helpful in control and release of drug ( Vasir& Vinod, 2007).
liposomes is another promising class of nano-sized vehicles that used in drug delivery. These vesicles prepared from lipids. It is used as potential drug carriers because it provides protection to drugs that contained in their core. However liposomes have some disadvantages like, a low encapsulation efficiency, poor storage stability, and rapid leakage of water-soluble drugs in blood. As such their ability to control the release of many drugs may not be good. Solid biodegradable nanoparticles have shown their advantage over liposomes because they have increased stability and the unique ability to create a controlled release (M.L Hans & A.M. Lowman 2002). The nanoparticles have the advantages over microparticles and liposomes.
Methods of preparation
The nanoparticles of different size and shape are prepared by the different methods and drug loading can be obtained by absorption, adsorption, encapsulation, and covalent linkage (Y.E.L. Koo et al., 2006)
Preparing of nanoparticles is based on two main methods polymerization reaction can be directly obtained from macromolecules. Nanoparticles from desolvation of macromolecules are either from synthetic or natural polymers. Polymerization reaction is of two types.
1. Emulsion polymerization.
2. Interfacial polymerization.
Emulsion polymerization
It is the fastest method for the preparation of nanoparticles. This is further classified into two categories, based on liquid phase it may be organic phase or it may be aqueous (Kreuter et al., 1990).
Continuous organic phase converts the monomer solution into an emulsion. As it was the first method for the preparation, here surfactants were used to prevent aggregation. It became less important because toxic organic solvents are required in early stages of polymerization (Ekman et al., 1978).
In aqueous continuous phase the monomer is dissolved in an aqueous solution and toxic surfactants or emulsifiers are not required. Polymerization starts when monomers are collide with initiator molecules that might be an ion and a free radical (Vauthier et al., 2003).
In this method hydrophilic drugs are entrapped by the nanoparticles, like ampicillin and doxorubicin. One example is poly (alkylcyanoacrylate) (PACA) that is biodegradable and not required irridation or chemical initiator for polymerization. Besides this insulin, growth factor and monoclonal antibodies can also be incorporated into PACA nanoparticles (Grislain et al., 1983).
Interfacial polymerization
In this method nanoparticles and suitable drug were dissolved in mixture of oil and ethanol. Then this solution was extruded into the aqueous solution through needle. Polymerization starts when the nanoparticles are in contact with initiating ions that are present in water. (Watnasirichaikul et at., 2000). There is no purification process so it is an acceptable excipient for oral administration (Allemann et at., 1998).
High efficiency drug encapsulation is achieved through interfacial polymerization technique (Couvreur et al., 2002). Polymers obtained by this method are produced in situ, and permit the poly membrane to follows the contours of inner phase emulsion. It is a difficult process and time consuming, and of organic solvent as an external phase which may create the toxicity. The examples are PECA poly isobutylcyanoacrylate and poly isohexylcyanoacrylate. (lenaerts et al., 1995). Different drugs are efficiently encapsulated in these polymers that include insulin, calcitonin, octreotide, darodipine, indomethacin, and photoactivatable cytotoxic compounds that are used in tumor therapy.
Nanoparticles can be obtained from the synthetic polymers because in polymerization of monomers different toxic substances were required for number of purposes. So get nanoparticles from synthetic polymers are safer. The methods are as follows.
Emulsification/ solvent evaporation.
Solvent displacement and interfacial deposition.
Emulsification/ solvent diffusion.
Salting out method.
Emulsification/ solvent evaporation
This technique has two steps. In the first step polymer solution is emulsified in an aqueous phase. In the second step the evaporation of solvent take place, and as the result polymer is precipitated as the nanospheres. The drugs are dissolved in to the organic solvent and this solution then dispersed into the nanodroplets by using the dispersing agent. The solvent is evaporated under the high temperature and pressure. The size of nanosphere is maintained by controlling some factors like stirring rate, amount of dispersing agent, viscosity of both phases and temperature of the reaction (Tice et al., 1985). A different emulsion is used in this method but best is oil/water emulsion. Polymers that are mostly used are PLA, PLGA, ethylceelulose (EC), cellulose acetate phthalate, poly (E-caprolactone) (PCL) and poly (h-hydroxybutyrate) (PHB). Albumin texanus toxoid testosterone loperamide prazinquantel cyclosporin A nucleic acid and indomethacin drugs that are mostly encapsulated (Reis et al., 2006).
Solvent displacement and interfacial deposition
Theses two methods are based on fact that polymer is dissolved in the organic internal phase which is then emulsified in to the aqueous external phase. Nanospheres and nanocapsules both are formed by the solvent displacement method while in case of interfacial deposition only nanocapsules are formed.
In solvent displacement polymers are precipitated from organic solution and organic solvent is diffused into the aqueous medium in presence and absence of surfactants. (Ganachaud et al., 2005). The polymer like PLA is dissolved into the solvent, which is usually water miscible. Then it is poured into aqueous solution that containing surfactant. Colloidal polymers are formed due to fast diffusion of solvent. Polymers are deposited at the interface between two solvents. Because of miscibility of solvent with aqueous phase this method is used for lipophilic drugs (Quintanar et al., 1998). Water soluble drugs are not encapsulated by this method. Various polymeric substances used including PLA, PLGA, PCL, poly (methyl vinyl ether-co-melic anhydride) (PVM/MA). To incorporate cyclosporine A this is well adaptive method because 98iciency is obtained (Reis et al., 2005).
Further the addition of polyanion like carboxymethyl cellulose (CMC) dextran sulfate or even the DNA to the polymers can generate the nanoparticles of different physicochemical properties that permit high drug encapsulation efficiency or greater stability in face of sheer forces ( Dailey et al., 2003).
Interfacial deposition produced nanocapsules. Basically this is emulsification/solidification technique. Addition of oil nature compound that show miscibility with solvent of polymer but don't mixed with the mixture. Between the dispersed oil droplets and aqueous phase polymers are deposited, to form the nanocapsules (Couvreur et al., 1995). Difference is that here dissolve polymers like PLA with drug in solvent mixture then it is poured in to the aqueous medium, hence nanoparticles are formed at the size of 230nm (Ammoury et al., 1990).
Emulsification/ solvent diffusion
In this technique polymer used for encapsulating material is dissolved in solvent that is partially water soluble such as propylene carbonate, then saturated with water to make initial thermodynamic equilibrium. To make precipitation of polymeric material it is essential to enhance the diffusion of solvent of dispersed phase with excess water, when the organic solvent is slightly miscible with water. Then polymer is emulsified in an aqueous solution that has the stabilizer, help the solvent to diffuse in external phase to formed nanospheres and nanocapsules.
This technique has several advantages including high encapsulating efficiency, there is no need for homogenization, ease of scale up, and there is a simple one process. But disadvantages are, high amount of water is need to be eliminated, water soluble drugs may leak into the aqueous external phase during emulsification, this tends to reduce encapsulating efficiency (Quintanar et al., 2005). Many nanoparticles are produced by this method, including mesotetra (hydroxyphenyl) porphyin-loaded PLGA (p-THPP) nanoparticles, doxorubicin-loaded PLGA nanoparticles, plasmid DNA loaded PLA nanoparticles, coumarin loaded PLA nanoparticles, inocynine, cyclosporine (Cy-A)-loaded gelatin and cyclosporine (Cy-A)-loaded sodium glycolate nanoparticles (Reiset al., 2006).
Salting out with synthetic polymer
Here in this technique water miscible solvent is separated by salting out effect. Basically it is modification of emulsification diffusion method. First dissolve polymer and drug both in solvent which can emulsify in the aqueous solution like acetone. The aqueous solution containing colloidal stabilizer such as polyvinylpyrrolidone or hydroxyethylcellulose, salting out agent including electrolytes, magnesium chloride, calcium chloride, and magnesium acetate, while non electrolyte is sucrose. To enhance the diffusion of acetone into the aqueous phase this oil/water emulsion is diluted with sufficient amount of water. Thus high diffusion of acetone permits the formation of nanosphere. At the end both salting out and solvent are eliminated by cross flow filtration (Quintanar et al., 1998).
In this process high temperature is not required, so heat sensitive substances can be easily prepared. Salting out can minimize stress to the substances that are encapsulated (Reis et at., 2005).
Diagnostic application
The performance has been done to improve diagnostic assay and to develop new strategies for efficient testing. Biodegradable nanoparticles promote in vitro diagnostic. Different nanoparticles have been modified for the diagnostic purpose, like gold nanoparticles, quantum dots, super paramagnetic nanoparticles etc. These nanoparticles can be conjugated with antibodies oligonucleotides for detection purposes. They have been used in immunoassay DNA diagnostic, cellular imaging, immunohistochemistry, to detect tumor, infectious diseases bioterrorism agents and neurological diseases. (Azzazy & mansour, 2008).
The nanoparticles are extensively used because they are incredibly sensitive to detect nanomolar concentration of any substances or any change. Nanoparticles can penetrate deep in to the tissue making possible to detect any defective tissue by florescent dye (Georgia institute of technology 2007).
Different nanoparticles are used for the diagnostic purpose like
Polymeric nanoparticles solid lipid particles
Liposomes gold nanoparticles
Layered double hydroxide particles iron oxide particles
Quantum dots superparamagnetic nanoparticles. (Faraji & Peter Wipf , 2009).
Some are explained below.
Gold nanoparticles
The gold nanoparticles have the size from 0.8 to 250 nm. They typically consist of thin gold shell that is surrounding a dielectric core referred to as the nanoshell (Azzazy & Mansour, 2009). The gold nanoparticles are prepared by gold salts in aqueous organic and mixed solvents. Commonly in this reaction chemical reduction of gold salts is involved (Faraji & P.Wipf, 2009).
For biodegradation purpose gold particle is coated with the PEG. Then this is more suitable for the diagnostic purpose. The plasmon interaction phenomenon permits gold nanoparticles used for the detection of biomolecules. Originally color of AuNP solution is red but when they come in contact with their target cells AuNPs shifts this color to detectable optical signal. AuNPs can be used to label DNA or proteins and also used in imaging, immunoassay, to detect the pathogens and other molecule for diagnostic purposes (Azzazy & Mansour, 2009).
Quantum dots
They are commonly known as nanocrystals with the size of 2-10nm. It consists of a core semiconductor and another shell semiconductor that has larger spectral band gap. This shell tends to increase photostability of QDs. They can be made biodegradable by silanization and coating with the polymers like PEG and PLA (Azzazy & Mansour, 2009).
With antibody-coated QDs within biodegradable polymeric nanospheres, It is designed so that it can undergoes endolysosomal to cytosolic translocation. When entering the cytosol, they undergo hydrolysis thus releasing the QD bioconjugates. This facilitates labeling of subcellular structures inside live cells without the requirement of cell fixation or membrane permeabilization (Ruan, et al., 2007).
When the QDs absorb the energy higher then the spectral band gap that is present on the shell semiconductor produced an excitation. When coming back to lower energy level it emitted the photon thus giving the strong fluorescence signal. This fluorescent signal can be detected by using different techniques like confocal microscopy, total internal reflection microscopy, fluorescence microscopy wide-field epifluorescence microscopy as well as fluorometry. They can be used as label in immunohistochemical processes immunoassay and cellular imaging (Azzazy & Mansour, 2009).
Superparamagnetic nanoparticles
They are made up of magnetic materials like iron, nickel, cobalt, or alloys of magnetic metals. They consist of core of iron oxide (magnetite Fe2O3, maghemite or other insoluble ferrites) coated with polymer Endorem (magnetite nanoparticles of 150 nm in diameter coated with dextran). For making them biodegradable they are coated with the PEG etc. superparamagnetic nanoparticles produce magnetic moment that is from the coupling of many atomic spins in the presence of magnetic field, so the nanoparticles can be used to capture the biomolecules, for interaction with these biomolecules surface is modified by different ligands (Jain et al., 2007; Bryant et al., 2007). They are used for multiplex immunoassay, and magnetic resonance imaging. These nanoparticulate contrast agents are being used for imaging of tissue for diagnostic applications. (Sanjeeb K. et al.,2003). Superparamagnetic iron oxide nanoparticles are used in MRI of Cardiovascular lesions illustrated by Smith et al., 2007.
The other diagnostic applications of some nanoparticles are detailed in following .(Hassan et al., 2009)
Nanoparticles
Quantum dots
They can be modified by conjugation with the monoclonal antibodies
When conjugated to genomic DNA.
QDs coated with Polyethylene glycol- conjugate to mannose. encapsulated with block copolymer,
In vivo imaging of the breast cancer cells expressing HER2 protein.
Detection of genomic aberrations of cancer genes by fluorescence in situ hybridization (FISH). Labeling of macrophages expressing mannose receptors. In vivo cancer imaging.
AuNPs
Conjugated with the EGFR
Conjugated with the HRPO enzyme and antibody PSA.
Used in diagnosis of oral cancer.
Molar level detection of PSA-anti chymotrypsin complex.
Superparamagnetic
Nanoparticles.
Iron oxide nanoparticles that are coated with the dextran conjugated with monoclonal antibody of CRP.
Nanoparticles immobilized on the polystyrene beads conjugated with target antibody.
Used in detection of whole blood CRP by magnetic permeability immunoassay.
Used to detect the model analytes by microfludic immnuassay.
Targeting the drug
The nanoparticle surface is also a very important in targeting drug delivery. Nanoparticles with no surface modification and negatively charged particles can be rapidly opsonized and cleared by the action of fixed macrophages. It is well known that the reticuloendothelial system is a major obstacle to target activly because of its ability to recognize these systems, and remove them from systemic circulation. Surface modification of this nanoparticulate system with hydrophilic polymers is the most common way to control the opsonization process and to improve the surface properties of the system (Soppimath et al., 2001). It can also performed coating modification with polymers example is the attachment of poly (ethylene glycol) (PEG) chains to biodegradable polymer such as poly (lactic acid) (PLA) and poly (lactic-co-glycolic acid) (PLGA). Thus the hydrophilic PEG chains allow the control of protein and peptide absorption and they can regulate the cell behavior at the polymer surface (Paryam et al., 2004; Prabha et al., 2004).
Surface modification play important role in the interaction trafficking and effect the efficiency of cytosolic drug delivery. These include the aspect of surface associated PVA that used to form the NPs remain associated with NPs and can alter the physical properties of the NPs. PVA can also effect the cellular uptake of NPs. Lower amount of the PVA show about 3fold higher cellular uptake in (VSMCs) vascular smooth muscle cells. PVA also affect the endosomal escape of NPs (paryam et al., 2002).
Thus to achieve the different surface properties the formulation of NPs have to changed, which can affect the cellular uptake and intracellular disposition of NPs (Vasir&Vinod , 2007).
Thus the properties like hydrophobicity, surface charge, and biodegradation profile of the nanoparticles, and the associated drug have appropriate molecular weight and charge that have the localization in the nanospheres by adsorption or incorporation have a great influence on the drug absorption, biodistribution pattern, and elimination (reis et al., 2006).
The delivery of the drug to the target tissue can be achieved primarily in two ways passive and active.
Passive Targeting
Passive targeting takes advantage of permeability of tumor tissue which in turn, can be easily accessible to toxic chemotherapeutic drugs. Some drugs can be administered as prodrugs which are term as inactive drugs; they can be exposed to tumor environment, and then become highly active. Passive targeting also used several invasive modalities to incorporate the delivery of drug to the tumor bed (Sinha et al., 2006). It is achieved by combining therapeutic agents to macromolecules that passively reaches target tissue through the enhanced permeation and retention (EPR) effect. (Sahoo & Vinod , 2003).
Active Targeting
In active targeting nanoparticles are conjugated with target moiety. Due to which drug is accumulated in target tissue. This condition is suitable to direct the nanoparticles to cell surface carbohydrate, receptors and antigens (Sinha et al., 2006). In active targeting the therapeutic agent is coupled with cell specific ligand (Sahoo &Vinod, 2003).
Mechanisms of cellular targeting
For therapeutic agents to target the specific tissue several obstacles are present in the form of membranes. Due to ineffective partitioning across the biological membrane therapeutic agents may become lost. Partition depend upon the polarity of molecule, if it is polar molecule then it can easily pass through biological membrane by the process of diffusion. Different metabolic process can effect the intracellular concentration and effectiveness of therapeutic agent that include endocytosis mechanisms, intracellular trafficking, release of therapeutic agent into the cytoplasm, and translucated at specific tissue .These problems are solved at the great extent with help of nanoparticles.
Nanoparticles are ingested into the cell by endocytosis processes. Which are of three types, phagocytosis, pinocytosis, and receptor mediated endocytosis. Nanoparticles have access to all type of cells. For this capability of nanoparticles they can be used as therapeutic agent to wide range of target cells (Kohane et al., 2006).
Cellular endocytosis
Receptor mediated endocytosis is widely used in the cellular targeting. The membrane has receptors which has the extra cellular binding and then create intracellular spaces. We have to functionalize nanoparticles with the specific ligands in accordance with the receptors on the surface of target tissue (Gao et al., 2005). The attachment permits different pathways, like internalization of ligands and its nanoparticles through which the nanoparticles enter into the cell (Faraji &Wipf, 2009). As illustrated in fig. no. 7
The drugs that has target to nucleus must crossing the nuclear membrane that provide another barrier to drug delivery. The molecules having the size of 40-45kDa and less than 100nm can easily pass the nuclear membrane by passive transport, while the other face cytosolic factors to cross the nuclear membrane. The nuclear localization signals interact with the cytoplasmic factors which can then permit the molecules to nucleus (Vasir & Vinod, 2007).
Oral drug delivery vehicles:
In most of therapies pharmacologically active drugs reach to target tissue with poor specificity. Conventional drug delivery methods that have been used included oral administration. There is disadvantage like when the drugs administered orally, rate of action of the drugs became slowdown due to exposure of drug particles to the metabolic pathways, therefor larger dose is required. Nanoparticles drug delivery method provides biodegradable polymers which are more efficient and less harmful and can overcome the problems associated with exposure of drug particles (Sinha et al., 2006).
In recent years, significant research has been done using nanoparticles as oral drug delivery vehicles. In this major application, the Peyer's patches in gut Associated lymphoid tissue (GALT) is involved in lymphatic uptake of the nanoparticles. Peyer's patches are characterized by M cells that overlie the lymphoid tissue and they have function of endocytosis and transport into intraepithelial spaces and adjacent lymphoid tissue. Nanoparticles bind the apical membrane of the M cells, then rapid internalization occur and a shuttling' to the lymphocytes (Florence et al., 1997).
The size and surface charge of the nanoparticles play important role for their uptake. There have been many reports as to the optimum size for Peyer's Patch uptakes ranging from less than 1mm to less than 5mm. Microparticles remain in the Peyer's patches while nanoparticles are released systemically. This application of nanoparticles in oral delivery holds tremendous promise for the development of oral vaccines and in cancer therapy (M.L. Hans & A.M. Lowman).
Therapy of different diseases
Biodegradable nanoparticles have used widely in medical field in therapy of different diseases ranging from cancer to infection (Faraji et al., 2009).
Different diseases described here, including
Neurological cancer.
Neurovascular diseases.
Neurodegenerative diseases.
Inflammatory Bowel disease.
Aerosol diseases.
Ophthalmic diseases.
Pulmonary tuberculosis.
Hepatitis B
Dental diseases
Orthopedic diseases
Cardiac diseases
1. Neurological cancer
The central nervous system offers great challenge for delivery off therapeutic agents due to blob brain barrier. The brain uptake is limited by this physical barrier (Faraji & P.Wipf et al., 2009).
Nanoparticles have emerged as the best vector for the brain delivery. That is able to overcome the blood brain barrier (Faraji et al., 2009). In cancer chemotherapy cytostatic drugs can damage both the normal and malignant tissue so such type of drug delivery is required that target tumor cells only. But the problem is that drug is lost through the rapid clearance and metabolism that's limits drug diffusion to the brain and other organ. The nanoparticles are modified to overcome the blood brain barrier. It is reported that poly-butylcyanoacrylate nanoparticle coated with the polysorbate 80, are efficient in transporting the drugs into the brain (Sahoo & Vinod, 2003).
Nanoparticles for chemotherapy
Several types of nanoparticles are used for anti cancer drug delivery system to the brain like
Solid lipid nanoparticles (SLNs)
Poly (butylcyanoacylate) (PBCA) nanoparticles.
polyacrylamide (PAA) nanoparticles.
PLGA nanoparticles.
PEG nanoparticles (Y.E.L Koo et al., 2006).
The drugs can be targeted in different conjugations with polymeric nanoparticles which are mentioned above. There are two conjugation systems like polymer drug conjugation and polymer-drug-ligand conjugate system.
Polymer drug conjugates
In the polymer drug conjugation, drugs are directly conjugated with polymers as mean of allowing the drug to accumulate at tumor site by enhanced permeability and retention effect. Several polymer drugs have been utilized (sinha et al., 2006). Like Abraxane (ABI-007) that is cremophore free, protein stabilized nanoparticle formulation of paclitaxel. This paclitaxel acts as anticancer agent and used in treatment of breast, lung, ovarian head and neck cancer (Crown et al., 2000). The side effects are fewer ABI-007 and it can deliver 50% higher dose of active agent paclitaxel (Sinha et al., 2006). Another is Genexol-PM polymeric micelle-loaded paclitaxel that is without the cremophor EL. It can deliver three times higher tolerated dose and also have the higher biodistribution in the various tissues. Its anticancer efficiency is higher than the taxol (kim et al., 2001).
Polymer drug ligand conjugates
In polymer drug conjugates higher specificity is not achieved. The development of ternary biomolecules can overcome this problem of nonspecific binding and permit cells to reach tumor cells only. The ternary complex is composed of three elements drug carrier, a drug and a ligand. To improve the tumor selectivity of polymeric drug carrier different ligands such as antibodies, cytokines, and homing peptides are used (Backer et al., 2001).
The anticancer drug doxorubicin was conjugated to HPMA and target ligand was galactosamin. Galactosamin has high affinity for binding to receptors on normal cell as well as on tumor cells. This conjugated drug accumulated at liver cells is more effective than the drug that is administered without any ligands (Seymour et al., 2002).
It is reported recently that ternary doxorubicin loaded poly (ethylene glycol) nanoparticles conjugated to cyclic RGD (Arg-Gly-Asp) has high affinity than its linear form (Cheng et al., 1994).
2. Neurovascular diseases
Different vascular diseases like atherosclerosis and hypertension are also detected and targeted with nanoparticles. Atherosclerosis is basically an inflammatory disease in which oxidized LDL particles are accumulated and triggering inflammation with the monocyte recruitment. Macrophages ingest these particles and convert them in foam cell. Then atherosclerosis plaque forms while lining of Blood vessels become activated and move inward. At the mean time the collagen deposition occurs and causes subendothelial inflammation after that plaque ruptures and tissue factors are easily accessible by circulating fibrinogen and platelets. Fibrin is produced during plaque rupture which is not only an indication but also form the growing vascular lesion. The rupture of plaque is dangerous event which causes the neurological stroke (Constantinides & Atheroscler, 2006).
Nanoparticles are used to target the fibrin imaging with MRI. This was declared by the Lanza group (Lanza, G. et al., 2001). Targeting ligand in form of antibody is highly specific for the cross linked fibrin. Antibody is conjugated with nanoparticles through the avidin biotin linkage (Lanza et al., 2002). The smooth muscle cells are incubated with the nanoparticles that are loaded with the paclitexal. When the nanoparticles are specifically bind, there is reduction in proliferation of smooth muscle cell (Lanza G.M, et al., 2004). Further it was reported that intravenous administration of nanoparticles loaded with antiangiogenesis agent like fumagilin, on the plaque's epitopes that is located on the vasa vasorum can inhibit the angiogenesis in cholesterol fed rabbits (Winter et al., 2004).
Alzheimer's diseases are the most common form of the dementia among American's over the age of 65 (Roney et al., 2005). In this disease there is irreversible damage to memory, thought, and language. For therapeutic purpose acetylcholineestrase inhibitors, cholinesterase inhibitors, antioxidants, amyloid--targeted drugs, nerve growth factors are used (Faraji et al., 2009). The primary factor in the Alzheimer's disease is oxidative stress triggered by different mechanism. In fact iron metabolism is involved in the oxidative stress because the patients show the elevated level of iron (Kennard,M L et al., 1996).
Besides that aluminum also show high concentration in the senile plaques and intraneuronal neurofibrillary within the brain of AD patients (Kong, S et al., 1992). It is thought that aluminum act as the synergy with iron to enhance the free radical damage because it is unable to participate in electron transfer reaction (Bondy, S C et al., 1998). The chelation of these metals can reduce the pathophysiological development of AD. A metal chelator desferrioxamine (DFO) have been used but it causes the toxicity and poorly absorbed by the gestrointedtinal tract, so rendering it futile in neurodegenerative disease therapy (Faraji et at., 2009).
Polymeric nanoparticles are widely used in the therapeutic purpose of AD. They can easily transport the drug across the blood brain barrier (Roneyet al.,2005). Nanoparticles may be designed such that it mimic the LDL, and have the ability to interact with the LDL receptors. These nanoparticles can mask the covalently bounded chelators and hence easily deliver across the BBB. In this way it can also minimize the toxiocity (Faraji et al., 2009).
The quinoline derivative like Clioquinol (CQ) is Cu/Zn chelator which is widely used in the treatment of AD. NMR studies showed that CQ can remove bond between Cu+2 and A plaques. Roney et al prepared NPs in conjugation with the CQ and used them in treatment of AD basically CQ was radioiodinated and then incorporated within PBCA nanoparticles. These nanoparticles are polymerized with the modified procedure of Kreuter et al., 1995.
Another metal chelator D-Penicillamine is used for the therapy of AD. Cui et al produced the nanoparticles in conjugation with the D-penicillamine to reverse the metal induced precipitation of the beta amyloid protein. It is demonstrated that NPs resolubilized the plaques under the reducing condition.
4. Inflammatory Bowel disease
The Inflammatory Bowel disease (IBD) is basically a group of inflammatory condition of colon and small intestine. IBD may cause the serious problems like delay in puberty or growth problems. The inflamed colon tissue demonstrates increased mucus production in area of ulceration as compared to healthy gut section (Lamprecht et al., 2001).
The two main type of IBD are Crohn's disease and ulcerative colitis. Crohn's disease occurs when ulcer developed due to inflammation in lining of intestine. Usually it occurs at lower part of the intestine where the joint of colon is present. The ulcerative colitis occurs when large intestine become inflamed and causes ulcer. The inflammation starts from rectum and may lead to whole large intestine (www.burnham.org). Many drug delivery systems have been utilized for the treatment of IBD (Rubinstein 1995). Different drugs are used in conjugation with the nanoparticles.
Tacrolimus nanoparticles are prepared from biodegradable PLGA. These are prepared by the oil/water emulsification-solvent method (Meissner et al., 2005). These nanoparticles have the potential for specific accumulation in inflamed tissue due to which the selectivity of local drug delivery is increased (Lamprecht et al., 2005).
There is selective drug release that is triggered by the luminal pH. It can prevent absorption of the premature drug during the flow, through the small intestine until target tissue is reached which in this case is ileal tissue. This makes high availability of tacrolimus in areas surrounding inflamed region. It also helps to lower the adverse effects (Meissner et al., 2005).
Another drug that is used in treatment of IBD is Rolipram which is an anti-inflammatory drug. It was incorporated with the poly lacticcoglycolic acid nanoparticles. The drug is delivered in the form of prodrug that lead to increase time period of drug and also decreases diarrhea which enhances elimination and lower drug releasing time (Hardy et al., 1998).
5. Aerosol disease
Different therapeutic agents are administrated to patients through aerosol inhalation. The nanoparticles being used to target these therapeutic drugs in different disease like asthma, cysic fibrosis, lung cancer, tuberculosis, and pulmonary hypertension (Dailey et al., 2003).
These carriers are formed in such a way that it can be able to incorporate into an aerosol form, it can stabilized itself from forces during the aerosolization, it can also able to target specific site, protect drugs against aggressive element in pulmonary tract, it can release drugs in predetermined manner, it should not contain any toxic additives, and degradable when applicable without producing toxic products (Edward et al., 2002). It was studied that polymer hydrophilicity was necessary to prevent the aggregation within the aerosolized fluid droplets during nebulization. It was also evident from different studies that only anionic formulation could be nebulized easily (Dailey et al., 2003).
To obtain these qualities the nanoparticles are formulated from hydrophilic poly lactic-co-glycolic (PLGA) derivatives. These derivatives are grafted onto poly vinyl alcohol backbone (3-dietylamino-1-propylamine) to form DEAPA-PVAL-g-PLGA nanoparticles which are highly suitable for pulmonary targeting. A drug named Rose Bengal (RB) is used in aerosol treatment effectively, as it is easily conjugates with the nanoparticles (Dailey et al., 2003).
6. Ophthalmic diseases
Biodegradable nanoparticles are used to overcome the solubility problems of poorly soluble drugs as well as for long acting injectable depot formulations and to target the specific drug to specific site. These drug loaded particles have applications in ophthalmic diseases like glaucoma, inflammations or infection of eye (Zimmer et al., 1995).
Many problems are associated with the ophthalmic drug delivery system. Conventional methods faces different factors like rapid tear turnover and resulting precorneal loss, induction of tear flow due to irritation caused by drug preparation. The dosage that actually penetrates is 1-3% which is not able to reach intraocular tissues (Kreuter et al., 1993). The nanoparticles used in ophthalmic diseases have been mainly prepared from synthetic polymers (poly alkyl cyanoacylates) through emulsion polymerization method (Zimmer et al., 1995). The elimination and distribution of drugs along with poly (hexyl) cyanoacylate nanoparticles in rabbits was studied by Wood et al., 1985.
A drug named Indium-oxine-labelled in conjugation with poly butyl cyanoacylate has the residence time of about 10min (Fitzgerald et al., 1987). Pilocarpine is most important drug for glaucoma therapy and can be incorporated in form of solid solution solid dispersion or it can be absorbed on to particle surface (Zimmer et al., 1995).
7. Pulmonary tuberculosis
Pulmonary tuberculosis is common form of the tuberculosis. Different methods are developed to deliver drug to lungs through the respiratory route. The inhaled therapy has advantages including direct drug delivery to the diseased organ, targeting the mycobacterium, harbouring macrophages, reducing risk of systemic toxicity and it can also improve patient's compliance. It is feasible to use nanoparticles as inhalable antitubercular drug carriers (Pandey & Khuller., 2005). Nanoparticles are prepared by PLG through double emulsification/solvent evaporation technique. Sizes of particles are maintained from 186 to 290nm. The drugs that are usually used to encapsulate in nanoparticles are rifampicin, isoniazid and pyrazinamid. It was also studied that high surface hydrophobic may cause particles aggregation during neubilization mainly on jet neubilizer. Nanoparticles are coated with PLG and stabilized by poly vinyl alcohol. Due to this modification nanoparticles possess hydrophilicity and hence aggregation is not a problem. (Panday & Khuller et al., 2005). In formulation of nanoparticles lectin was coupled with nanoparticles because lectin receptors are widely distributed in respiratory tract. (Dahad et al., 2001). Usually nebulization to guinea pig, therapeutic drug concentration was stabilized in the plasma for 6-15 days. It was studied that 46 conventional doses can minimized the five nebulized doses of PLG nanoparticles and only three doses with lectin PLG nanoparticles. (sharma et al., 2004).
8. Hepatitis B
Hepatitis B infection remains a problem for world however inject able vaccine is available that consists of recombinant hepatitis B surface antigen (HBsAg). Problem that most of vaccine recipient doesn't return booster doses thus efficacy of vaccination becomes limited. Several efforts have been used to develop nanoparticle mediated vaccine delivery systems that is prepared from biodegradable and biocompatible polymers. (Dhruba et al.)The most commonly used methods for preparation of antigen-encapsulated nanoparticles is solvent extraction or evaporation. (Gupta et al., 1997; O' hangen et al., 1993). These nanoparticles are administered both as oral vaccination and DNA- based vaccination.
Oral vaccination
The convenient way to administered drug or the vaccine is by oral route, because of high patient acceptability, compliance, ease of administration. The problem in this case is that by the harsh acidic condition of stomach mostly antigen is degraded in oral vaccination. (Gabor et al., 2002). The antigen are also poorly absorbed by gut- associated lymphoid tissue and leads to low efficacy, so large doses of antigen is required to obtained the sirable level of immunity comparable with systemic administration. (Gupta et al., 2006). In oder to overcome these problems nanoparticle carrier system are used whuch can effectively protect the antigen in gastrointestinal tract. It can also release the sustained antigen and can achieve the targeted antigen with the help of selective ligands. (jain et al., 2001 ;Lavelle et al., 2001). The nanoparticles are conjugated with the lectin in oder to increase the affinity towards antigen presenting cells of Peyer's patches. These lectin conjugated nanoparticles revealed four-fold increase in degree of interaction with the bovine submaxillary mucin (BSM) in vitro than the nonconjugated nanoparticles. Thus these nanoparticles have the potential to target the Peyer s patches.
DNA_based vaccination
The genetic approaches are another war to vaccine against hepatitis B infection especially for he chronic HBV. Long lasting humoral and cell-mediated immunity can be obtained by the DNA-based vaccination. (Oka et al., 2001). In the human clinical taril it is cleared that very high dose of DNA-based vaccine show the lower level of the immune responses as compared with the small animals. So it is necessary to improve the efficacy of DNA-based vaccine. He et al. (2005) produced PLGA nanoparticles in which plasmid DNA encoding HBV HBsAg by using the double emulsion solvent evaporation method. It was studied that these nanoparticles decreases the dose required to induce immune response.
9. Dental diseases
Nanoparticles are widely used in dental diseases. High quality dental care is provided to patients by using nanoparticles. Recent studies revealed that local anesthesia is induced by nanodentistry. In patients gingivae active analgesic dental nanorobotic particles could be instilled. These nanorobots when contecting with surface of crown, reach dentin then migrating into gingival sulcus and pass easily and painlessly to target site. On reaching dentin these nanorobots enter into dentinal tubule and proceed toward the pulp. This process is controlled by nanocomputers as directed by dentist. (Goracci et al.,1995; Dourda et al., 1994). Nanoparticles are also used to treat dental hypersensitivity. The nanorobots could selectively and painlessly occlued specific tubules within minutes, thus offering permanent cure t patients. (Freitas et al., 2000).
10. Orthopedic diseases
The musculoskeletal disoders are one of the major health concerns. In the treatment orthopedic implants used for internal fixing of the fractured bones, but this treatment have different problems, like implant failure. These implants are stiffer than cortical bones and removal of these implants require second operation. Efforts have been done to improve the qualities of the scaffold ideal. Scaffold for cell growth should be biocompatible, osteeoinductive, osteoconductive, integrative, porous, and mechanically compatible with native bones (Sahoo et al., 2007). Above mentioned treatment doesn't have all properties. While nanotechnology provide higher mechanical strength, enhanced bioactivity, and resorbability in improving quality of life of patients. Nanoparticles act as the effective constitute because bone is also made up of nanosized organic and mineral phases. Nanopolymers, carbon nanofibers and nanocomposites of ceramics show efficient deposition of calcium containing minerals on implants. (Webster et al., 2000). It is cleared that nanoparticles attract more protein towads their surface, because these particles has altered surface energetics and electron distributions as compared with conventional materials. Nanoparticles provide improved bonding between an implant and surrounding bones by increasing bone cell interaction hence improving orthopedic implant efficacy and minimizing patient's compliance problems (Sahoo et al., 2007).
11. Cardiovascular diseases
The cardiac diseases are most common cause of the mortality morbidity and disability. Various cardiac problems including atherosclerosis, myocardial infection, arrhythmias, ischemic heart disease, and restenosis (Kong et al., 2005). Although the oral and systemic administration are effective but appropriate therapeutic drug level didn't provided by them in target arteries for sufficient period of time. Nanotechnology based tool are the effective mean to treat the cardiovascular diseases. Nanotechnology is also helpful in designing atomic scale machines which are used for sensing, decision making and carrying out of intended purpose. (Sahoo et al., 2007). Nanotechnology based therapy is more effective because it can provide higher and prolonged drug levels in target tissues. It also doesn't cause systemic toxicity. (Panyam et al., 2003). Nanotechnology is also used in diagnosis and treatment of unstable plaques and in management of other cardiovascular problems like calcification of valves. Thus nanotechnology is used to achieve the localized and sustained arterial and cardiac drug therapy for prevention of cardiovascular diseases. (Sahoo et al., 2007).
Conclusion
Nanotechnology is wide field that is concerned with the development of man made materials in 5-200nm size range. The physical and chemical properties of small sized particles are very different from those which posses bulk form.They are also be used in the diagnostic and delivery purpose. For successfully drug delivery, material should be free from impurities and chemically inert. These polymers must be biodegradable and their resultant molecules must be biologically acceptable and can easily eliminate from the body.
Sometime it is difficult for nanoparticles to reach the CNS because of uptake by reticuloendotheliel system (RES). To overcome this problem and for prolonged plasma circulation time these nanoparticles are coated with hydrophilic polymers. The nanoparticles have advantages over microparticles and liposomes. The nanoparticles also have relatively high intracellular uptake as compared with microparticles. Their nature and charge properties influence on uptake by intertinal epithelia.
Different biodegradable nanoparticles,` which are prepared from the emulsification polymerization and interfacial polymerization are also used. Many other particles those are obtained from the synthetic polymers by the solvent displacement, solvent evaporation, and solvent diffusion and salting out methods. These nanoparticles can be conjugated with antibodies oligonucleotides for the detection purposes.
Surface modification play important role in interaction trafficking, effect and efficiency of cytosolic drug delivery. Thus to achieve different surface properties, the formulation of NPs are to be changed, which can affect cellular uptake and intracellular disposition of NPs. This application of nanoparticles in oral delivery holds tremendous promise for the development of oral vaccines and in therapy of different diseases.
Future aspects
Nanotechnologies will provide more medical benefits within next few years. The aim is to develop the nanoscale laboratory-based diagnostic and drug delivery platform devices. The National Cancer Institute has related programs, with the goal of producing nanometer scale multifunctional entities that can diagnose, deliver therapeutic agents, and monitor cancer treatment progress. These include design and engineering of targeted contrast agents that develop the resolution of cancer cells to single cell level, and nanodevices capable of addressing the biological and evolutionary diversity of the multiple cancer cells that make up a tumor within an individual. The future of nanomedicine will depend on rational design of nanomaterials and their consumption to recognize complex biological processes rather than forcing applications for some materials currently in vogue.
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Biodegradable Nanoparticles used as Diagnostic and Therapeutic tool
