Merlin N.J.*, Shaji Selvin, Sukesh T.N.
Ezhuthachan College of Pharmaceutical Sciences, Marayamuttom, Neyyattinkara, Thiruvananthapuram, Kerala
Nanotechnology is the science that deals with the processes that occur at molecular level. Nanotechnology is a multidisciplinary field, convergence of basic sciences and applied disciplines like biophysics, molecular biology, and bioengineering. It has created powerful impact in various fields of medicine including cardiology, ophthalmology, endocrinology, oncology, pulmonology, immunology etc., and to highly specialized areas like gene delivery, brain targeting, tumor targeting, and oral vaccine formulations. Nanotechnology provides intelligent systems, devices and materials for better pharmaceutical applications.
Nanotechnology is defined as the engineering of functional systems at the molecular scale. Nonomaterials are important sources for the development of nanotechnology and its application. Nanoparticle research is currently an area of intense scientific research, due to wide variety of potential applications in biomedical, optical and electronic fields. Nanoparticles for therapeutic purpose are made by forming nanocrystals or drug-polymer complexes. They have successfully removed many bottlenecks related to drug/gene delivery in the biological systems. Current trends in this field include functionalizing these nanoparticles by using polyethylene glycol (PEG) to increase circulation, which makes them stable in blood serum against the effect of enzyme nucleases to enhance immunological cross reaction. Due to its fine size, nanoparticles are easily taken up by the cells and once into target tissue or cell, they allow controlled release of entrapped drugs.
Nanoparticles are small enough to move easily inside the body. There are different routes followed to target the drug/ gene-encapsulated nanoparticles to the target cell/ tissue. Route of administration plays a significant role because not all drug/ gene encapsulated nanoparticles can simply cross the mucosal surface and biological membranes. They can be easily denaturized and cleared rapidly in the liver. A drug delivered in gastrointestinal tract faces many problems like acid induced hydrolysis in stomach enzymatic degradation, acid base variations in the intestines and bacterial fermentation in colon.
Therefore the best route followed to avoid all such problems is the preoral route. Liposomes, micelles, dendrimers are best for pulmonary delivery via aerosols, metered dose inhalers and nebulisers. Trans tissue and local delivery systems favour hydrogels as drug delivery carries as they produce elevated pharmacological effects and minimize toxicity associated with systemic administration. Cell based delivery that is gene transducted through through oral mucosal epithelial cell (OMEC) implanted sheet and device directed delivery with rechargeable drug infusion device that can be attached to the resected site.
Pharmaceutical nanotechnology’ embraces applications of nanoscience to pharmacy as nanomaterials, and as devices like drug delivery, diagnostic, imaging and biosensor.
Types of nanoparticle:
It is a linear polysaccharide composed of B-(1-4) linked D-glucosamine (deacylated unit) and N- aetyl –D-glucosamine (acetylated unit) and act as bioadhesives, which helps them to penetrate nasal mucosa and brain endothelium. They can be administered orally and are stable in acidic and neutral solution.
They are spherical vesicles with a phospholipids bilayer membrane ranging from size nm to m and are used to deliver drugs or genetic materials into a cell. In some cases, liposomes fuse to form bigger liposomes. To avoid such a condition phospholipids liposomes are mixed with charged nanoparticles i.e. carboxylated modified polystyrene, sonicated to mix at low volume fraction so as to produce particle stabilized liposomes that repel one another and do not fuse.
Hydrogels are 3D hydrophilic components that swell in aqueous media, have cross linkages which makes them an insoluble polymeric network facilitating regulated drug release. The latest technology involved in hydrogels includes molecular imprinting based drug delivery involving rate programmed drug delivery, activation modulated drug delivery and feedback regulated drug delivery. Water soluble cytotoxic agents are encapsulated in hydrogels to target tumours so as to minimize toxicity to reticuloendothelial systems. Hydrogels can be used for selective local delivery of drugs.
Quantum dots are bright hot stable fluorescent nanocrystals. They exhibit extensive range of size and composition and can transform the colour of light i.e from blue to near infra red by altering the size and composition. This property allows them to be used as invivo tags for localizing tumours.
Polyplexus are assemblies that are formed between nucleic acid and polycations. They are widely used in therapeutics like gene transfer protocols since they mimic the properties of proteins.
Nanobodies are derived from heavy chain antibodies that are found naturally in camels. It is used in psoriasis, solid tumour and Alzeimers disease. Nanobodies have unparallel stability and can be delivered in variety of ways, thus overcoming the delivery issues associated with full sized antibodies, which can be delivered by injection.
Nanospores are integrated into artificially constructed encapsulated cells of silicon wafers. These pores allow small molecules like glucose, O2 and insulin to pan, however they prevent large immune system molecule like immunoglobulin to leave the cell.
Gold nanoparticles are the metal of choice because gold remains unioxidised at the nanoparticulate size. Gold remains its nanoparticle property to produce great contrast in optical images. Gold particles can be used for imaging cancer, monitoring blood flow, mapping blood vessels and allow for 3D imaging.
Dendrimers are nanostructured materials, which are tree shaped, have a branching system starting out from a central core. It has potential therapeutic applications as the group of atoms that form its outer boundary consist of meaner molecular groups that can act as hooks and therefore can attach onto molecules like DNA. They act as effective therapeutic agents because they can insert DNA into the cell without triggering a immune system response. Dendrimers are used as invitro diagnostics for heart muscle damage, drug delivery, targeting tumour cells.
Carbon nanotubes are used to deliver therapeutic molecules and micro structures to targeted cells and organs in a safe manner, which generates a low immunogenic response and is generally low in toxicity. Two types of CNTs are used in biomedical applications. The first is a SWNT, or Single Walled Nano Tube consisting of a single sheet of carbon benzene rings wrapped into the shape of a cylinder. The second is MWNT or Multi Walled Nano Tubes, which is similar to SWNT, but contains multiple concentric layers of carbon sheets.
Fullerenes are natural hollow spheres, one nanometer in diameter made up of 60 carbon atoms. They are powerful antioxidants, reaching readily and at a high rate with free radicals and are often the cause of cell damage or cell death.
Nanomedicine is the application of nanotechnology in health care, offers promising possibilities to improve medical diagnosis, therapy and follow up care leading to an affordable higher quality of life for everyone. It exploits the improved and novel physical, chemical and biological properties of materials at the nanometer scale.
Medical uses of nanomedicals:
Nanomedical approaches in drug delivery system aims in improving the bioavailability of the drug i.e maximizing bioavailability both at specific places in the body and over a period of time and is achieved by molecular targeting using nanoengineered devices. Lipid or polymer-based nanoparticles are designed to improve the pharmacological and therapeutic properties of drugs. The nanoparticles have unusual properties which can improve drug delivery where larger particles are cleared from the body and the cells take up the nanoparticles because of their size.
Nanotechnology and Cancer Treatment:
Cancer: Cancer is caused by damage of genes which control the growth and division of cells. Genes carry the instructions for basic functions of cells. Cancerous cell need blood supply to grow. A hormone like molecule causes nearby blood vessel to grow towards the cell to supply the oxygen and other nutrients. Cancer can be cured by rectifying the damaging mechanism of the genes or by stopping the blood supply to the cells or by destroying it. Detection/diagnose is possible by confirming the growth of the cells. One nanometer (nm) is one billionth, or 10–9 of a meter. For comparison, typical carbon-carbon bond lengths, or the spacing between these atoms in a molecule, are in the range 0.12 - 0.15 nm, and a DNA double helix has a diameter around 2 nm. On the other hand, the smallest cellular life forms, the bacteria of the genus Mycoplasma, are around 200 nm in length. Many of the cells are of the dimensions of micro meter. These provide the possibility of nanoparticles entering the cells and detect/treat the molecular changes that occur due to cancerous causes, in small percentage of cells. Therefore, the necessary tools must be extremely sensitive. Scientists and researchers hope that nanotechnology can be used to create therapeutic agents that target specific cells and deliver the toxin in a controlled, time-release manner. The basic aim is to create single agents that are able to both detect cancer and deliver treatment. The nanoparticles will circulate through the body, detect cancer-associated molecular changes, assist with imaging release a therapeutic agent and then monitor the effectiveness of the intervention.
Nano-particles (NP) are of a few of nm and the cells are of the size of few microns. So NP can enter inside the cells and can access the DNA molecules/Genes and, there is a possibility that the defect in the genes can be detected. DNA molecules can be detected in their incipient stage. This could be possible in vivo or in vitro. It will be shown latter that NP does show potential of cancer detection in its incipient stage.
Certain nano particles can be designed to absorb preferentially certain wave length of radiation and gets heated. Such a NP if enters in the cancerous cell will burn it if irradiated by suitable wavelength radiation. This is the kind of, analogue of radiation therapy. As mentioned before, nanotechnology can be used to create therapeutic agents that target specific cells and deliver toxin to kill them. The NP will circulate through the body, detect cancer associated molecular changes, assist with imaging release a therapeutic agent and then monitor the effectiveness of the intervention.
Tools of Nanotechnology:
Some of the tools of nanotechnology having applications in cancer detection and treatment are the following:
(i) Cantilevers: Tiny bars anchored at one end can be engineered to bind to molecules associated with cancer. These molecules may bind to altered DNA proteins that are present in certain types of cancer. This will change the surface tension and cause the cantilevers to bend. By monitoring the bending of cantilevers, it would be possible to tell whether the cancer molecules are present and hence detect early molecular events in the development of cancer.
(ii) Nanopores: Nanopores (holes) allow DNA to pass through one strand at a time and hence DNA sequencing can be made more efficient. Thus the shape and electrical properties of each base on the strand can be monitored. As these properties are unique for each of the four bases that make up the genetic code, the passage of DNA through a nanopore can be used to decipher the encoded information, including errors in the code known to be associated with cancer.
(iii) Nanotubes: Nanotubes aresmaller than Nano pores. Nanotubes and carbon rods, about half the diameter of a molecule of DNA, will also help identify DNA changes associated with cancer. It helps to exactly pin point location of the changes. Mutated regions associated with cancer are first tagged with bulky molecules. Using a nano tube tip, resembling the needle on a record player, the physical shape of the DNA can be traced. A computer translates this information into topographical map. The bulky molecules identify the regions on the map where mutations are present. Since the location of mutations can influence the effects they have on a cell, these techniques will be important in predicting disease.
(iv) Quantum Dots (QD): These are tiny crystals that glow when these are stimulated by ultraviolet light. The latex beads filled with these crystals when stimulated by light, the colors they emit act as dyes that light up the sequence of interest. By combining different sized quantum dotes within a single bead, probes can be created that release a distinct spectrum of various colors and intensities of lights, serving as sort of spectral bar code.
(v) Nanoshells (NS): These are another recent invention. NS are miniscule beads coated with gold. By manipulating the thickness of the layers making up the NS, the beads can be designed that absorb specific wavelength of light. The most useful nanoshells are those that absorb near infrared light that can easily penetrate several centimeters in human tissues. Absorption of light by nanoshells creates an intense heat that is lethal to cells. Nanoshells can be linked to antibodies that recognize cancer cells. In laboratory cultures, the heat generated by the light-absorbing nanoshells has successfully killed tumor cells while leaving neighbouring cells intact.
(vi) Dendrimer: A number of nanoparticles that will facilitate drug delivery are being developed. One such molecule that has potential to link treatment with detection and diagnostic is known as dendrimer. These have branching shape which gives them vast amounts of surface area to which therapeutic agents or other biologically active molecules can be attached. A single dendrimer can carry/ translates this information into topographical map. A single dendrimer can carry a molecule that recognizes cancer cells, a therapeutic agent to kill those cells and a molecule that recognizes the signals of cell death. It is hoped that dendrimers can be manipulated to release their contents only in the presence of certain trigger molecules associated with cancer. Following drug releases, the dendrimers may also report back whether they are successfully killing their targets.
The technologies mentioned above are in the various stages of discovery and development. Some of the technologies like quantum dots, nano pores and other devices may be available for detection and diagnosis and for clinical use within next ten years.1
NANOTECHNOLOGY- IN HIV/AIDS THERAPY:
HIV primarily infects vital cells in the human immune system such as helper T cells (specifically CD4+ T cells), macrophages, and dendritic cells. HIV infection leads to low levels of CD4+ T cells through three main mechanisms: firstly, direct viral killing of infected cells; secondly, increased rates of apoptosis in infected cells; and thirdly, killing of infected CD4+ cells by CD8 cytotoxic lymphocytes that recognizes infected cells. When CD4+ T cell numbers decline below a critical level, cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections. Eventually most HIV-infected individuals develop AIDS. These individuals mostly die from opportunistic infections or malignancies associated with the progressive failure of the immune system Treatment with anti-retroviral increases the life expectancy of people infected with HIV. Without antiretroviral therapy, death normally occurs within a year. Nanoparticles are stable, solid colloidal particles consisting of macromolecules materials and ranging in size from 10 to 1000nm. Drugs can be absorbed on the particle surface or can be entrapped or dissolved in the particle matrix. Nanoparticles are known to accumulate in the tissue because of phagocytosis by MO/Mac2. Thus using nanotechnology, engineering researchers have developed a small but powerful device capable of enhancing the targeted delivery of drugs to treat life-threatening illnesses3.
Use in Therapy:
Endothelium is an important target for drug or gene therapy because of its important role in the biological system. In the case of AIDS, the macrophages of the RES represent one of the most important therapeutic targets. In addition to the CD4 +T lymphocytes, these cells play a decisive role as a reservoir for the human immunodeficiency virus (HIV), apart from having a function in the pathogenesis of the disease, cells of the macrophage lineage are vectors for the transmission of HIV. So a fully effective anti-HIV therapy must reach Mo/Mac in addition to other cells. Nanoparticles could be used for localizing therapeutic agents or gene into endothelial cells. Nanoparticles localized in the endothelium could provide prolonged drug effects because of their sustained release characteristics, and also could protect the encapsulated agent from enzymatic degradation 4. Nanoparticles can be well targeted to organs like brain and placenta. Targeting drug to placenta also helps in stopping transmission of disease to fetus. Using Nanoparticles as drug carriers systems can improve the delivery of antiviral agents to the mononuclear phagocyte system, enhancing the activity of drug for the treatment of HIV infection. By using Polyhexylcyanoacrylate Nanoparticles loaded with either the human immunodeficiency virus (HIV) protease inhibitor saquinavir or the nucleoside analog zalcitabine were prepared by emulsion polymerization and tested for antiviral activity in primary human monocytes/macrophages in vitro. Both nanoparticulate formulations led to a dose-dependent reduction of HIV type 1 antigen production 5. Another investigation shows the possibilities of targeting anti viral drugs such as AZT to macrophages using nanoparticles as colloidal drug carriers. In the first series of experiments the body distribution of 14C-labelled AZT bound to nanoparticles and a similarly prepared control solution with unbound AZT were studied in rats after I.V. injection. In a second series of experiments polysorbate 80 coated nanoparticles and a solution of AZT was bound to nanoparticles using the surfactant bis (2-ethylhexyl) sulphosuccinate sodium (DOSS). AZT concentrations were up to 18 times higher in organs belonging to the RES if the drug was bound to nanoparticles compared with unbound AZT. Thus this allows dose reduction 6.Modified form of nanoparticles, solid lipid nanoparticles (SLNs) as carrier for delivery of lipophillic prodrugs 3’-azido-3’deoxythimidinepalmitate of zalcitabine. Solid lipid nanoparticles were prepared using trilaurin as the SLNs solid core and a mixture of neutral and negatively charged phospholipids and coated with PEG. To produce SLNS with a polyethylene glycol coating, PEG was incorporated in SLNS using dipalmitoyl phosphatidyl ethanolamine-N-[poly(ethyleneglycol 2000](PEPEG). 3%-azido-3%deoxythymidinepalmitate(AZT-P)with [3H]-AZT-P as tracer were synthesized and incorporated in SLNS. Biodistribution studies were performed in mice using free AZT-P, AZT-P incorporated in SLNS or AZT-P incorporated in PE-PEG coated SLNS (SLN-PE-PEG).SLNs as a drug carrier increases the bioavailability of incorporated AZT-P, and then the pharmacokinetic behavior of the incorporated drug can be modified by changing the surface characteristics of SLNs by using the amphiphilic solvation enhancer. Unlike the solution, nanoparticles did concentrate AZT very efficiently in the intestinal mucosa, as well as in the Peyer's patches, and could simultaneously control the release of free AZT. Concentration in Peyer's patches was 4 times higher for nanoparticles, compared with the control solution. Nanoparticles have been shown to be efficient in concentrating AZT in the intestinal epithelium and gut-associated lymphoid tissues, supporting the view that these particles may represent a promising carrier to treat specifically the GI reservoir of HIV.
Use in diagnosis:
Nanotechnology is now being used by the scientists in U.S. for detecting viruses of diseases like HIV in not more than one minute. The new technique measures frequency changes of a near infrared laser as viral RNA or DNA is scattered by it. The frequency changes are as discrete as fingerprints of each individual. While this phenomenon is an established one, previous endeavor of using spectroscopy to detect viruses failed due to the inherent weakness of the signal produced. However a way of significant amplification of the signal is via nano rods. The factors of enhancement are extraordinary and this method is cheap, reproducible and simple to implement. Nanometre-sized quantum dots can be made to tag biological molecules for the recognition of proteins that point out disease status. However, this technique doesn’t have shortcomings, which are associated with regular organic dyes used to mark cells. Quantum dots could ultimately be used in clinical analytic tests to rapidly spot molecules linked with cancer cells and HIV/AIDS. This has the greatest advantage to developing countries; where over 95% of new HIV infections occurred in last few years.
Use in Prophalaxis:
As it is well said that prevention is better that cure, so for a condition as lethal as AIDS scientists are on their way for prophylaxis. The team of engineers at the Yale university found a new method that may help stop HIV infection. The method delivers short interfering RNAs into vaginal cells using nanoparticles. The short interfering RNAs repress specific HIV genes and stop the virus reproducing in humanized mice siRNAs when transferred to cells using lipids as carriers are expensive and toxic. In answer approach scientists pack thousand of siRNAs into nanosized biodegradable and biocompatible plastics which are already approved for medical use. Such nanoparticles are incorporated in vaginal gel and applied by women before sex, helps preventing infection .Testing is on with the monkey version of HIV but still there is a long way to go. Nanotechnology-based vaccines for HIV are also in the work.
Nanoscience and nanotechnologies are truly interdisciplinary, interlacing together physics, chemistry and biology. Materials that exist in nanospace are not only smaller but have entirely different physical and chemical properties than their macro versions. Nanotechnologies have enabled the development of entirely new drugs and altered the properties of already marketed drugs to create potentially safer, more directed and effective pharmaceuticals.
The whole process of nanotechnological development can take decades, and it is often evolutionary rather than revolutionary. Nanotechnology offers important new tools and is expected to have a great impact on many areas in medical technologies. It provides extra ordinary opportunities not only to improve materials and medical devices and technologies, but have profound influence on disease prevention efforts because it offers innovative tools for understanding the cell as well as the difference between normal and abnormal cells.
Nanomedicine, with safety, ethical and social issues addressed, will have extra ordinary and far reaching implications for the medical profession, for the definition of disease, for the diagnosis and treatment of medical condition and ultimately for the improvement and extension of natural biological structures and function. The main advantage of nanomedicine on quality of life and on cost for health care is earlier detection of a disease, leading to less severe and costly therapeutic demands and an improved clinical result.
The authors thank Shri. T. G. Hari Kumar, General Secretary, Ezhuthachan College of Pharmaceutical Sciences, Marayamuttom for providing the necessary facilities.
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Received on 27.04.2011 Accepted on 26.05.2011
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