BioNanoSci. (2013) 3:102–111 DOI 10.1007/s12668-013-0084-7
Nanocarriers as Promising Drug Vehicles for the Management of Tuberculosis Anil K. Sharma & Raman Kumar & Bhawna Nishal & Oisik Das
Published online: 12 April 2013 # Springer Science+Business Media New York 2013
Abstract Nanoscience is emerging as a new era of technology advancement which has promoted our ability to understand scientific developments at nanoscale. The nanoparticle-based drug delivery systems have been implicated in the treatment of a variety of diseases especially the ones caused by intracellular pathogens. Therapeutic failures and antibiotic resistance developed by the notorious pathogenic bacteria like Mycobacterium tuberculosis have prompted researchers to develop novel ways to counter drug resistance, to shorten the treatment duration, and more importantly to reduce drug interactions with antiretroviral therapies. The pharmaceutical technologists of today are focusing more on improving the effectiveness of the drug by specifically targeting the sources and reservoirs of infections. The nanotechnology has the potential to develop more effective and compliant medicines. Current review discusses about various challenges faced in the development of effective nano-based tuberculosis therapies and overviews various state-of-art technologies being developed interms of nano-based drug delivery systems for encapsulation and sustained release of antituberculosis drugs. Keywords Nanotechnology . Nanomedicine . Nanoparticles . Tuberculosis . Emulsions . Nanosuspensions . Liposomes . Polylactide-co-glycolide microparticles (PLG) . Niosomes . Dendrimers
A. K. Sharma (*) : R. Kumar : B. Nishal : O. Das Department of Biotechnology, M.M.E.C., Maharishi Markandeshwar University, Mullana, Ambala 133203, India e-mail:
[email protected]
1 Introduction Nanotechnology has recently emerged as a highly sophisticated and advanced technology leading us to understand scientific developments at a nanoscale referring to the size range of atoms, molecules and macromolecules having unique or superior physicochemical properties [1]. It is possible nowadays to treat some dreadful diseases such as tuberculosis and AIDS with the advent of this new technology using nanoparticles as drug delivery systems. However, repeated therapeutic failures and emergence of multidrug resistance strains especially in case of TB and human immunodeficiency virus (HIV) have prompted researchers to develop novel ways to counter drug resistance, to shorten the treatment duration, and more importantly to reduce drug interactions with antiretroviral therapies. Despite having an effective chemotherapeutic regimen for tuberculosis, still the treatment schedule is cumbersome and poses many problems such as hepatotoxicity, patient noncompliance, and requirement of administering multiple antitubercular drugs. Therapeutic failures and antibiotic resistance developed by Mycobacterium tuberculosis and HIV have prompted researchers to develop novel ways to counter drug-resistance, to shorten the treatment duration, and more importantly to reduce drug interactions with antiretroviral therapies. The pharmaceutical technologists of today are focusing more on improving the effectiveness of the drug by specifically targeting the sources and reservoirs of infections. The nanotechnology has the potential to develop more effective and compliant medicines. Current review discusses about various challenges faced in the development of effective nano-based tuberculosis therapy and overviews various state-of-art technologies being developed in-terms of nano-based drug delivery systems for encapsulation and sustained release of anti-TB drugs.
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1.1 Nanotechnology: Challenges Posed by Pathogens The incidence of tuberculosis caused by M. tuberculosis and other respiratory diseases and infections is increasing worldwide. The treatment of these ailments has been proved to be a challenging task. Moreover, the development of resistance to currently available drugs due to successful adaptation of the pathogen has been a major factor for their control failure [2–4]. Tuberculosis is a major threat to human life and has been rated as the world’s leading cause of mortality. According to the WHO estimates, approximately one third of the global population is infected with tuberculosis [5]. Current treatment for tuberculosis involves the daily administration of four oral antibiotics including isoniazid (INH), rifampicin (RIF), pyrazinamide (PZA), and ethambutol, for a period of 6 months or more which not only gave rise to many side effects but also resulted in the increase in prevalence of multi-drug resistant tuberculosis. Multi-drug-resistant tuberculosis is resistant to isoniazid and rifampicin, two of the firstline anti-TB drugs [4]. Extremely drug resistant (XDR-TB) strains have also been reported recently from South Africa and other parts of the world, with high prevalence in HIV-positive individuals. XDR-TB is resistant to both first and second line of anti-TB drugs [6]. The question is how to manage this deadly disease as antimycobacterial chemotherapy is a difficult and laborious one and take up long duration for treatments. Also drugs efficiency to reach targets are pretty low not enough to induce antimycobacterial effect. Toxicity of these antimycobacterial drugs is another issue to be dealt with. Another pathogen, Streptococcus pneumoniae has been found to be resistant to most of the antibiotics used to treat pneumonia including cephalosporins, penicillin, macrolides, doxycycline, trimethoprim–sulfamethoxazole, etc. Poor therapeutic outcomes because of patient noncompliance to prescribed medication which may be as a result of inadequate modes of drug administration pose a great challenge for the scientific community [7, 8]. Nanotechnology science has been a kind of boon to current pharmacology. Today it is possible to design drug delivery carriers/systems able to target phagocytic cells infected by intracellular pathogens, such as mycobacteria. Nanotechnology-based delivery systems offer a broad range of opportunities for improving the diagnosis and therapy for various diseases, an area which is gaining momentum and subsequently holds a particular promise.
2 Nanotechnology in the Treatment of Tuberculosis Oral or injectable antibiotics are basically used for the treatment of various diseases caused by intracellular pathogens. Combinatorial therapy has been employed in case of M. tuberculosis and S. pneumoniae. However, poor bioavailability and higher doses for longer duration of the
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treatment required to maintain therapeutic levels are some of the potential challenges for therapeutic intervention of these diseases. Considering the above facts in terms of increased incidence of multidrug resistant strains as a result of incorrect dosage regimen, toxicity, side effects, etc., there is a strong urge to develop novel ways of delivering the therapeutic compounds to the specific target [9]. Polymer-based antitubercular drug delivery systems have been reported to have many advantages in terms of their bioavailability, least dosage frequency, direct drug targeting, etc. Two kinds of polymers have been thoroughly investigated for the nano-encapsulation of active agents including synthetic and natural polymers. Synthetic polymers comprise of poly-esters and poly-acids while oligomers such as alginate, starch, and chitosan found abundant in nature belong to the natural polymer category. There are varieties of methods being developed now for the nano-based delivery of drugs such as nano-emulsions, nanosuspensions, polymeric and nonpolymeric particles, etc. 2.1 Emulsions Spontaneously generated oil-in-water dispersions of sizes between10 and 100 nm which can be produced in large amounts have been used for delivery and enhanced uptake by the cells of the phagocytic system [10, 11] and lipoprotein receptors in the liver after oral administration [12]. The first-line drug for tuberculosis, rifampicin, was developed as an oil–water emulsion [13] for intra-venous administration using excipients such as Sefsol 218 as the oil phase, Tween 80 as the surfactant, Tween 85 as the co-surfactant, and saline water as an aqueous phase. The entrapment efficiency achieved was over 99 % along with excellent homogeneity and sustained release. Thus, overall it appears that these nano-emulsions can be effectively used for drug delivery as they are thermodynamically stable and can be sterilized by filtration [14, 15]. 2.2 Nanosuspensions Pure drug is stabilized with surfactants resulting in a colloidal dispersion. To improve the solubility of the drugs, the average size of the drug particles is reduced to nanosizes by grinding or top milling. This process facilitates strong solute–solute interactions with high melting points and improved water and lipid solubility [16], though milling or grinding might alter the physical state of the drug and stability as well [17, 18]. Studies were conducted to optimize the pharmacotherapy of tuberculosis for which clofazimine nanosuspension has been developed to overcome low solubility and toxicity problems [15, 19]. Clofazimine-loaded liposomes displayed reasonably good stability, half life, and overall clinical effectiveness. Efforts have been made to produce submicronic particles of controlled size for injectables and aerosolizable drug delivery systems [20, 21].
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2.3 Liposomes Like Vesicles or Niosomes Charged phospholipids (stearyl amine and dicethylphosphate, etc.) and nonionic surfactants (monoalkyl or dialkyl polyoxyethylene ether) formed as a result of cholesterol hydration lead to formation of liposomes like vesicles called niosomes [22]. These niosomes have many advantages over liposomes such as they are more stable, less difficulties in scaling up, and low-cost production. Both hydrophilic and lipophilic drugs could be accommodated in these vesicles. Efforts were made to adjust the carrier size for efficient delivery of rifampicin-loaded niosomes along with the surfactants (Span 20, 40, 60, 80, 85) to the lungs [23, 24]. The slower drug release depended largely upon the lipophilic nature of the surfactant, and higher drug concentrations were achieved on the targets through intra-peritoneal route of administration in comparison to intra-venous route [25]. There was a significant increase in accumulation of the rifampicin-loaded niosomes observed in the lungs after intra-tracheal administration as well. 2.4 Polymeric and Nonpolymeric Particles They are being extensively used delivery carriers for drug solubilization, stability, and specific targeting [26–28]. High stability, ease of administration by various routes, and loading of hydrophilic and hydrophobic drugs have made these particles as one of the most popular approaches for drug encapsulation [15]. In the past few years, several biodegradable and biocompatible adjuvants such as immunostimulatory complexes such as biopolymers have been developed boosting the host response without any side effects (Fig. 1). Microparticles based on biodegradable polymers such as polyglycolic acid, polylactic acid (PLA), and their copolymers such as poly-DL-lactide-coglycolide (PLG) have gained much attention as carriers of Fig. 1 Poly-DL-lactide-coglycolide
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antigen (Fig. 1). These PLG microparticles are the primary candidates for the development as adjuvants as they have been used in humans for years as controlled release delivery systems and as suture materials. The adjuvant effect was achieved through the encapsulation of antigen into PLG microparticles. For the prolonged circulation in the blood stream and to prevent recognition by the host immune response, the surface was modified with highly hydrophilic chains (e.g., polyethylene glycol) for antituberculosis drug delivery. To overcome the nonbiodegradability problem, anti-TB drugs have now been encapsulated within biodegradable PLG microspheres [27, 29, 30]. In TB-infected mice, five oral doses in PLG microparticles administered over 7 weeks significantly eliminated the pathogen from different organs [30]. The same group also produced successfully the anti-TB drug-loaded alginate nanoparticles by means of ionotropic gelation. Alginate nanoparticles are known for being inexpensive and free of organic solvents providing advantages over other conventional methods. Some of the reported polymeric and nonpolymeric materials and their use as effective drug carriers have been shown in Table 1 and Fig. 1. More recently, Semete et al. [31] proposed that PLGA nanocarriers could be a safer way to deliver antitubercular drugs at the target as they did not find any significant pathological alteration or tissue damage in different organs of BALB/C mice after oral administration of double emulsion PLGA nanoparticles. 2.5 Polymeric Nanocarriers or Micelles Amphiphilic polymers in water as a result of self assembly give rise to the polymeric micelles. Micellar shell is formed as a result of exposure of hydrophilic blocks to the aqueous medium facilitating the solubilization of amphiphile in water and stabilizing the aggregate. On the other hand, hydrophobic blocks form the inner micellar core which facilitates the
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Table 1 Some of the reported antituberculosis drug delivery systems Formulation
Drug
Action
PLGA nanoparticles in porous material
Rifampicin
Poly(butyl-2-cyanoacrylate) nanoparticles Wheat germ agglutinin-coated PLGA nanoparticles PLG microparticles (porous, nonporous, hardened) Microparticles employing PLG
Moxifloxacin Rifampicin
Strong therapeutic efficacy, high encapsulation efficiency, [33] prolonged plasma drug levels, greater dispersibility Enhanced in vitro and in vivo therapeutic efficacy of the drug [34, 35] Increased bioavailability, prolonged plasma drug levels [33]
Nanoparticles employing PLG Single PLGA polymer implant prepared from PLGA Implant prepared from PLGA Aerosolized liposomes using egg-PC and Chol-based liposomes) Nebulized solid lipid nanoparticles from nanocrystalline lipid suspensions in water Alginate micro- and nanoparticles Spherical micelles (PLA-modified chitosan oligomers) Micelle forming poly(ethylene glycol)–poly (aspartic acid) conjugate Dendrimeric nanocarriers r-Cyclodextrin (r-CD) and hydroxypropyl cyclodextrins (HP-rCD)
INH
Prolonged sustained drug release, prolonged plasma drug concentrations RIF, INH, PYZ, ETB Sustained drug release, high entrapment efficiency, prolonged drug levels in circulation (greater than 72 h) RIF, INH, PYZ Total clearance of TB bacilli after 5 oral treatments INH, PYZ Sustained drug levels (up to 8 weeks),significant clearance of tubercle bacilli INH Prolonged drug concentrations in plasma and serum (∼9 weeks) RIF High concentration of the drug in the target organ (e.g., lung)
References
[36] [37] [30] [38] [39] [40]
RIF, INH, PYZ
Better therapeutic efficacy in Guinea pigs
[41]
RIF, INH RIF
Effective and sustained drug release Sustained release of the drug (in vitro)
[42] [43]
INH, PZA, RIF
Sustained drug release and 6-fold increase in anti-TB activity
[44–46]
RIF
Improved selective uptake of drug-loaded nanocarriers by macrophages, increased drug entrapment Greater solubility and chemical stability, strong interaction of the drug with HP-rCD
[47, 48]
RIF
solubilization of poorly water-soluble drugs [32] and protection from chemical and biological degradation. They have been made more lipophilic which enhanced the penetration of the drug into the pathogen and antibacterial activity against Mycobacterium. Some of the micelle-forming prodrugs have been mentioned below (see Table 1). Despite having some leaky character of these micelle-forming prodrug-like materials, they have shown a sustained release of anti-TB drugs and enhanced therapeutic efficacy against tuberculosis as well.
[49]
monosialogangliosides–distearylphophatidylethanolamine– poly(ethylene glycol) 2000 were used for the targeted delivery of anti-TB drugs to the lung. There was a significant accumulation of the nanocarriers in the lungs suggestive of their potential use in targeted drug delivery [53]. The liposomeencapsulated drugs have also been shown to significantly reduce the bacterial load as compared to the free drug [15] improving the antimycobacterial activity and reducing the toxicity as well. Pyrazinamide- and rifabutin-containing liposomes are some of the recent examples representing the great potential and versatility of these nanocarriers (see Table 1).
2.6 Liposomes 2.7 Dendrimers and Cyclodextrins They are nano- to micro-sized vesicles comprising a phospholipid bilayer that surrounds an aqueous core which are very efficient in entrapment and encapsulation of the drugs. In order to prolong the sustainability and circulation time of the drug, these liposomes are usually PEGylated. Klemens et al. [50] reported for the first time that incorporating gentamicin into liposomes, there was a significant reduction in the mycobacterial count in the liver and spleen of a mouse model of disseminated Mycobacterium avium complex infection. Similar studies with liposome encapsulated second-line antibiotics produced comparable results [51, 52]. Lung-specific stealth liposomes composed of phosphatidylcholine, dicetyl-phosphate, O-steroyl amylopectin, cholesterol, and
They are hyper-branched, three-dimensional, low molecular weight macromolecules. Polyamidoamines were the first of its kind of dendrimers [54]. Despite limited research on these molecules, they are also attractive candidates for the encapsulation and delivery of antituberculosis agents [15]. Cyclodextrins represent another category of these dendrimers which enhance the pulmonary bioavailability of insoluble drugs and are highly biocompatible with very less adverse effects [55]. When complexed with anti-TB drugs, these complexes may lead to a sustained and controlled release of the drugs, resulting in an enhanced therapeutic efficacy against experimental tuberculosis.
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Despite having so many advantages with the polymeric particles, there are some limitations as well such as for implantable polymeric systems, one needs surgical maneuvers and a specific delivery device requiring critical supervision. High cost, painful procedures, and use of organic solvents in the emulsion-based techniques are some other disadvantages to be resolved in future. Dendrimers being a new class of polymeric materials are highly branched, mono-disperse macromolecules. A dendrimer is typically symmetric around the core and often adopts a spherical three-dimensional morphology. Dendrimers are a highly branched type of nanoparticle that can target specific cells based on the molecular “hooks” on the ends of the polymers that make up their outer surface. There are two basic structural types: One is the globular structure with a central core from which polymer branches radiate; the second type has no central core and consists simply of a series of highly branched polymers. The structure of these materials has a great impact on their physical and chemical properties. Dendrimers offer advantages including a lower polydispersity index, multiple sites of attachment, and a controllable, welldefined size and structure that can be easily modified to change the chemical properties of the system. 2.7.1 Dendrimers: Targeted and Controlled Release Drug Delivery Dendrimers have attracted attention as possible drug carriers because of their unique properties, namely their welldefined three-dimensional structure, the availability of many functional surface groups, their low polydispersity, and their ability to mimic (Table 2). These are particularly attractive as they offer a high drug-loading capacity. Drug molecules can be loaded both in the interior of the dendrimers as well as attached to the surface groups. Dendrimers can function
as drug carriers either by encapsulating drugs within the dendritic structure or by interacting with drugs at their terminal functional groups via electrostatic or covalent bonds (prodrug). Thus, the major methods of dendrimer drug delivery are encapsulation of drugs and dendrimer– drug conjugates. Encapsulation of drugs uses the steric bulk of the exterior of the dendrimer or interactions between the dendrimer and the drug inside the dendrimer. Dendrimer– drug conjugates have the drug attached to the exterior of the dendrimer. Most of these conjugates are prodrugs and are inactive or have decreased activity relative to the free drug. The properties of dendrimers are dominated by the functional groups on the molecular surface; however, there are examples of dendrimers with internal functionality [56–58]. Dendritic encapsulation of functional molecules allows for the isolation of the active site, a structure that mimics that of active sites in biomaterials [59, 60]. Also, it is possible to make dendrimers water soluble, unlike most polymers, by functionalizing their outer shell with charged species or other hydrophilic groups. Other controllable properties of dendrimers include toxicity, crystallinity, tecto-dendrimer formation, and chirality. Approaches for delivering unaltered natural products using polymeric carriers is of widespread interest; dendrimers have been explored for the encapsulation of hydrophobic compounds and for the delivery of anticancer drugs. In other way, we can state that there are three methods for using dendrimers in drug delivery: First, the drug is covalently attached to the periphery of the dendrimer to form dendrimer prodrugs; second, the drug is coordinated to the outer functional groups via ionic interactions; or third, the dendrimer acts as a unimolecular micelle by encapsulating a pharmaceutical through the formation of a dendrimer–drug supramolecular assembly [61]. The use of dendrimers as drug carriers by encapsulating hydrophobic drugs is a potential method for
Table 2 Properties of dendrimer and linear polymers Sr. no.
Property
Dendrimers
Linear polymers
1 2 3 4 5 6
Structure Synthesis Structural control Architecture Shape Crystallanity
7 8 9 10 11 12
Aqueous solubility Nonpolar solubility Viscosity Reactivity Compressibility Polydispersity
Compact, globular Careful and stepwise growth Very high Regular Spherical Noncrystalline, amorphous materials–lower glass temperatures High High Nonlinear relationship with molecular weight High Low Monodisperse
Not compact Single-step polycondensation Low Irregular Random coil Semicrystalline/crystalline materials–higher glass temperatures Low Low Linear relation with molecular weight Low High Polydisperse
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delivering highly active pharmaceutical compounds that may not be in clinical use due to their limited water solubility and resulting suboptimal pharmacokinetics. Dendrimers have been widely explored for controlled delivery of antiretroviral bioactives [62]. The inherent antiretroviral activity of dendrimers enhances their efficacy as carriers for antiretroviral drugs [63, 64]. The dendrimer enhances both the uptake and retention of compounds within cancer cells, a finding that was not anticipated at the onset of studies. The encapsulation increases with dendrimer generation, and this method may be useful to entrap drugs with a relatively high therapeutic dose. The ability of dendrimer drug carriers to show higher cytotoxicity toward carcinoma cells than free anticancer drugs shows promise for targeted drug delivery even though further examination of the targeted release is required. While other carriers were developed, additional research in the field focused on improving the dendrimer structure to make the drug carriers more biocompatible. Also, the majority of drugs available in pharmaceutical industry are hydrophobic in nature, and this property in particular creates major formulation problems. This drawback of drugs can be ameliorated by dendrimeric scaffolding, which can be used to encapsulate as well as to solubilize the drugs because of the capability of such scaffolds to participate in extensive hydrogen bonding with water. Applications of dendrimers typically involve conjugating other chemical species to the dendrimer surface that can function as detecting agents (such as a dye molecule), affinity ligands, targeting components, radioligands, imaging agents, or pharmaceutically active compounds. Dendrimers have very strong potential for these applications because their structure can lead to multivalent systems. In other words, one dendrimer molecule has hundreds of possible sites to couple to an active species. Dendrimers can also be used as a solubilizing agent. Dendrimers with hydrophobic core and hydrophilic periphery have shown to exhibit micelle-like behavior and have container properties in solution [65]. 2.7.2 Dendrimers as Nanodrugs in Gene Delivery Poly(lysine) dendrimers modified with sulfonated naphthyl groups have been found to be useful as antiviral drugs against the herpes simplex virus can potentially prevent/reduce transmission of HIV. This multivalency is of particular importance for biomedical applications. The multiple interactions between surface amines and nucleic acid phosphates are also important for the formation of dendrimers and DNA complexes. Dendrimers’ solubility is strongly influenced by the nature of surface groups. The ability to deliver pieces of DNA to the required parts of a cell includes many challenges. Current research is being
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focused to find ways to use dendrimers to traffic genes into cells without damaging or deactivating the DNA. To maintain the activity of DNA during dehydration, the dendrimer/DNA complexes were encapsulated in a water-soluble polymer and then deposited on or sandwiched in functional polymer films with a fast degradation rate to mediate gene transfection. Based on this method, PAMAM dendrimer/DNA complexes were used to encapsulate functional biodegradable polymer films for substrate-mediated gene delivery. Research has shown that the fast degrading functional polymer has great potential for localized transfection [66, 67]. The studies based on dendritic polymer also open up new avenues of research into the further development of drug–dendrimer complexes specific for a cancer and/or targeted organ system. The encouraging results provide further impetus to design, synthesize, and evaluate dendritic polymers for use in basic drug delivery studies.
3 Targeted Delivery and Strategies Local delivery of the nanocarrier encapsulated drug to the lungs by inhalation is one of the attractive routes of administration adopted by the researchers. Similarly, spray drying has been employed as one of the methods for targeting to specific organs with nanoparticles of natural origin (e.g., gelatin) and synthetic (e.g., polybutylcyanoacrylate) polymers [68]. Other modifications such as encapsulation of the nanoparticles in the mannitol have shown significant improvement for in vivo uptake of the drug by the alveolar macrophages in rat lungs as compared to rifampicincontaining PLG microspheres, providing an interesting platform toward selective delivery of drugs to the respiratory system. Mannose-coated liposomes and mannose concentrations on the cell surface increased the cellular uptake as well making them very effective to specifically deliver the drugs to the target [15]. Effectiveness of pulmonary drug delivery using nanoparticles has been demonstrated in number of studies [42]. Sharma et al. [69] discovered that nebulized antituberculosis drugs encapsulated in wheat germ agglutinin-functionalized PLG nanoparticles and in solid lipid nanoparticles [42] were very effective in eliminating mycobacteria from lungs and spleen. During intravenous administration, the nanoparticles follow the route of other foreign particulates including intracellular microbes such as Mycobacterium, Brucella, Listeria, Salmonella, etc. So the macrophages harboring these pathogens represent one of the targets for delivery of antimicrobial agents. Most of the in vitro reports so far support the potential for development of nanoparticlebased antituberculosis drugs through this macrophage targeting strategy. Other advantages of intravenous administration of the nanoparticles include the passive drug
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delivery to inflammatory sites where the endothelium becomes permeable due to pathologic processes. Nanoparticle-based formulation has been further demonstrated by effective subcutaneous treatment of mice infected with M. tuberculosis [70]. A single dose of PLG nanoparticles along with rifampicin, isoniazid, and pyrazinamide maintained therapeutic drug levels in lungs and spleen for more than 5 weeks and produced a kind of sterilizing effect in the above organs of the infected mice along with a sustained release for longer duration. More recently, UK Cystic Fibrosis Gene Therapy Consortium reported the use of magnetic particles with either the therapeutic gene or a reporter gene attached to them. Strong high gradient magnet is employed to pull the nanoparticles into contact with the cells to target the airway epithelium [8]. Further efforts are underway to develop an oscillating magnet array system which will introduce energy and a lateral component to advance the movement and interaction of particles with the epithelial cells and simultaneously improving the in vivo transfection efficiency of DNA delivery of this system.
4 Future Perspectives and Challenges Ahead Global challenges and scientific progress in diagnosing various diseases caused by intracellular pathogens such as tuberculosis have prompted researchers to understand the etiology of these diseases at the nano scale. Early detection, diagnosis, treatment, and prevention of tuberculosis have been made much simpler with the advent of this nanoscience as it has an immense potential to empower a local response to challenges apart from being cost-effective and very promising alternative [71]. Nanoparticle-based gene therapy and drug delivery hold a great promise for the sound management of diseases in terms of improved drug bioavailability and reduced dosing frequency, though it is extremely important to investigate the toxic effects of these nanoparticles for which we need to know the chemistry, size, and other physical properties of these particles. It is now possible to visualize nanoparticle once they are administered along with the desired gene and measure gene expression as well [72]. Also the nanoparticles along with the reporter gene can be traced so that one can track DNA complexes in vivo and simultaneously determining the dosage administration. However, we still need to determine a system which is sensitive enough to measure a range of gene expression levels for in vivo imaging and also targeting the nanoparticles to specific/diseased cell types [14, 73, 74]. Future holds up in designing of drug-delivery systems or formulations which can resolve all the limitations of tuberculosis drug therapy and making them affordable to all patients. Several antitubercular drugs encapsulated in natural or synthetic carrier-based controlled release formulations have
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been explored and nanoparticles appeared to be the best in terms of therapeutic efficacy. It is hoped that future research would focus on developing vector-based delivery systems which can combine colloidal carriers such as large payloads of drug with active targeting to the infection sites improving the efficacy and practicability of the nanoparticle-based formulations. Understanding the fate of nanocarriers and their polymeric constituents along with elimination of any residual organic solvents is a must for dealing with any toxicological issues associated with these nanoformulations [75]. Commercialization of this nanoparticle-based technology may unleash a spectrum of human health hazards that can only be speculated without any detailed understanding of the toxic nature of nanoparticles. Pharmacokinetic and toxicological studies are mandatory before large scale industrial production and widespread use of these carriers. Toxicity screening, reporting, and hazard identification of engineered nanomaterials [76] have been initiated by agencies such as US Environmental Protection Agency, International Life Sciences Institute research foundation, etc. Many studies have reported association between ultra-fine particles (UFP) exposure and morbidity in elderly and immunocompromised individuals. The reason to suspect is justified as UFPs are very similar in characteristic features to nanoparticles. Nanoparticle delivery looks promising as a key mediator not only against drug-susceptible but also against drugresistance tuberculosis. It holds the power to reduce the dosage burden on the patients, but simultaneously, this technology is likely to face many challenges especially this (TB) being a poor man’s disease. Lots of health gaps need to be filled along with sustained global efforts in order to overcome tuberculosis. Many biological and physiological barriers seem to pose a great challenge to this technology as the particles cannot reach to the needed areas in the secondary lymphoid organs [77]. Issues of nebulization, injectables, or inhalable routes of administration require thorough medical supervision which are playing the role of a deterrent in the way of this technology. There is an urgency to have safety guidelines for the nanotechnology industry including manufacturing, monitoring exposures of the workers, ambient release of the nanoparticles, and risk assessment for promoting this wonderful technology at a commercial scale and for many medicinal applications.
5 Summary and Conclusions Due to scarcity of anti-TB drug candidates in the pipeline and with the emergence of drug resistance tuberculosis cases exponentially, the scientific community today has to look for plausible alternatives. Nano-based drug formulations have been quite effective not only in extending the retention time of the drug but also reducing the toxicity and increasing the
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half-life of the drug which has further revolutionized the field of pharmacotherapy. Increasing incidence of multidrug resistant strains has made scientists to develop novel ways of delivering the therapeutic compounds to the specific target, and many such delivery systems for example nano-emulsions, nanosuspensions, polymeric and nonpolymeric particles, liposomes, niosomes and dendrimers, etc. have been developed in the recent past overcoming many of the shortcomings of the delivery of conventional drugs. In vivo tracking of DNA complexes via bioluminescent imaging along with determining when the next dose is to be administered has been made possible with the advent of nanoscience. Targeting nanoparticles to specific tissues/diseased cell types and to measure the range of gene-expression levels are some of the major challenges to be tackled in future. Nanoparticle drug delivery and gene therapy hold a great potential though few toxicological aspects needs to be looked very carefully before commercializing this technology for medical and industrial applications.
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