Fabrication and characterization of dual acting oleyl chitosan functionalised iron oxide/gold hybrid nanoparticles for MRI and CT imaging

Abstract

Bionanocomposites fabricated using metal nanoparticles serve a wide range of biomedical applications viz., site targeted drug delivery, imaging etc. Theranostics emerge as an important field of science, which focuses on the use of single entity for both disease diagnosis and treatment. The present work aimed at designing a multifunctional nanocomposite comprising of iron/gold hybrid nanoparticles, coated with oleyl chitosan and conjugated with methotrexate. The HR-TEM images revealed the spherical nature of the composite, while it's nontoxic and biocompatible property was proved by the MTT assay in NIH 3T3 cells and hemolysis assay. Though the VSM results exhibited the magnetic property, the MRI phantom images and X-ray contrast images demonstrated the potential of the composite to be used as contrast agent. Thus the prepared nanocomposite possess good cytocompatibility, magnetic property and also high X-ray attenuation, wherein it could serve as a novel platform for both MRI and CT diagnosis, as well as drug conjugation could aid in targeted drug delivery.

Introduction

Nanocomposites comprising of different components, have stirred great interest in the field of nanomedicine because of their diverse physicochemical properties. Nanoparticles are widely used for diagnostics and therapeutics owing to their unique capabilities and few side-effects. Due to this, recently nanoparticles are highly exploited for their theranostic potential as well, which aims at simultaneous detection and treatment of the disease using a single agent [1]. Among nanoparticles, superparamagnetic iron oxide nanoparticles (IONPs) offer high potential for several biomedical applications, such as magnetic resonance imaging (MRI), hyperthermia treatment, tissue engineering and as drug delivery systems, due to their biocompatibility, surface architecture and easy conjugation with targeting ligands [2,3].

Magnetic resonance imaging (MRI) is a potent, non-invasive, three dimensional technique used in disease diagnosis. It provides high spatial resolution with three-dimensional anatomic details devoid of instigating any harmful side effects in patients. The conventionally used gadolinium based contrast agents in MRI are reported to be toxic in nature and induces nephrogenic systemic fibrosis in patients with renal diseases [4]. Superparamagnetic iron oxide nanoparticles are used as T2 contrast agents in MRI owing to their better resolution than gadolinium based contrast agents [5]. However in many instances MRI alone doesn't work as the sole methodology of diagnosis, wherein the need of computed tomography (CT) arises. CT is also yet another diagnostic imaging modality which is non-invasive and exhibits fast scanning speed [6]. Among the noble metals (silver, gold and platinum), gold nanoparticles play a pivotal role in biomedical applications viz., in bioimaging, biosensors, diagnostics etc. The use of gold nanoparticles as a contrast agent for computed tomography (CT) is slowly gaining momentum owing to its remarkable properties including nonreactivity, high X-ray absorption coefficient, low cytotoxicity, tailored surface chemistry, excellent biocompatibility, and unique surface plasmon resonance [7]. Hence development of iron/gold hybrid nanoparticles could serve as dual modality contrast agents which could be used for both MRI and CT diagnosis [8,9].

Though the biomedical applications of IONPs are promising, their successful application depends on the surface modification of IONPs, because bare IONPs have poor colloidal stability and they are usually opsonised and sequestered by the reticuloendothelial system, especially by the Kupffer cells in the liver [10]. Hence, in order to overcome this limitation, stabilizers such as polyethylene glycol, dextran, chitosan etc. are used to enhance the dispersibility of nanoparticles in aqueous medium. Chitosan is a natural non-toxic biopolymer, derived from the partial deacetylation of chitin and it consists of repeating units of glucosamine and N-acetyl glucosamine. Its unique characteristics such as biocompatibility, biodegradability, rigid linear molecular structure etc. make it as an ideal candidate for medical applications [11]. Though chitosan is soluble in aqueous solution of acids, it doesn't have amphiphilic property. Hence surface modification of chitosan with long chain fatty acids viz., oleic acid, lineoleic acid, palmitic acid etc. can introduce hydrophobic groups into chitosan and form amphiphilic chitosan polymers. Chitosan conjugated with fatty acid moiety aids in the formation of nanomicelles in aqueous solution, with a hydrophobic core-hydrophilic shell structure. The hydrophobic core structure provides an amenable environment to load the drugs, while the shell structure offers colloidal stability of the particles [12,13].

There are several reports regarding the synthesis of iron oxide nanoparticles using inorganic sources, but this study reports the use of goat blood as the starting material for the synthesis of IONPs. The synthesised IONPs, if coupled with gold nanoparticles to form hybrid constructs, could be used for both MRI and CT diagnosis. In order to enhance the stability and dispersibility of the hybrid nanoparticles in aqueous medium, it will be encapsulated using oleyl chitosan. This functionalised hybrid nanoparticles will be conjugated with the anti-cancer drug methotrexate (MTX). Since, MTX is a folic acid analogue; it binds with the folate receptors expressed on tumor cells and inhibits dihydrofolate reductase, an enzyme critical for cell survival and division. Hence MTX displays dual function as targeting ligand and as a therapeutic agent [14].

Thus the objective of the current study is to synthesize a multifunctional nanocomposite comprising of iron/gold nanohybrid particles coated with oleyl chitosan and conjugated with methotrexate. This nanocomposite will be evaluated for its physico-chemical properties and biocompatibility in vitro. In addition the suitability of the nanocomposite for use in MRI and CT as contrast agent will also be determined.