Malathi Srivatsan

Copper nanoparticles exert size and concentration dependent toxicity on somatosensory neurons of rat.

Abstract Metal nanoparticles, due to their unique properties and important applications in optical, magnetic, thermal, electrical, sensor devices and cosmetics, are beginning to be widely manufactured and used. This new and rapidly growing field of technology warrants a thorough examination of the materials bio-compatibility and safety. Ultra-small particles may adversely affect living cells and organisms since they can easily penetrate the body through skin contact, inhalation and ingestion. Retrograde transport of copper nanoparticles from nerve endings on the skin can reach the somatosensory neurons in dorsal root ganglion (DRG). Since copper nanoparticles have industrial and healthcare applications, we determined the concentration and size-dependant effects of their exposure on survival of DRG neurons of rat in cell culture. The neurons were exposed to copper nanoparticles of increasing concentrations (10–100 μM) and sizes (40, 60 and 80 nm) for 24 h. Light microscopy, histochemical staining for copper, lactate dehydrogenase (LDH) assay for cell death, and MTS [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay for cell viability were performed to measure the resultant toxicity and cell survival. DRG neurons exposed to copper nanoparticles displayed vacuoles and detachment of some neurons from the substratum. Neurons also exhibited disrupted neurite network. LDH and MTS assays revealed that exposure to copper nanoparticles had significant toxic effect with all the sizes tested when compared to unexposed control cultures. Further analysis of the results showed that copper nanoparticles of smaller size and higher concentration exerted the maximum toxic effects. Rubeanic acid staining showed intracellular deposition of copper. These results demonstrate that copper nanoparticles are toxic in a size- and concentration-dependent manner to DRG neurons.

The effects of functional magnetic nanotubes with incorporated nerve growth factor in neuronal differentiation of PC12 cells

In this in vitro study the efficiency of magnetic nanotubes to bind with nerve growth factor (NGF) and the ability of NGF-incorporated magnetic nanotubes to release the bound NGF are investigated using rat pheochromocytoma cells (PC12 cells). It is found that functional magnetic nanotubes with NGF incorporation enabled the differentiation of PC12 cells into neurons exhibiting growth cones and neurite outgrowth. Microscope observations show that filopodia extending from neuron growth cones were in close proximity to the NGF-incorporated magnetic nanotubes, at times appearing to extend towards or into them. These results show that magnetic nanotubes can be used as a delivery vehicle for NGF and thus may be exploited in attempts to treat neurodegenerative disorders such as Parkinsons disease with neurotrophins. Further neurite outgrowth can be controlled by manipulating magnetic nanotubes with external magnetic fields, thus helping in directed regeneration.

Somatosensory neurons grown on functionalized carbon nanotube mats

We demonstrate that a functionalized carbon nanotube mat deposited on a track-etch membrane is a permissive substratum for somatosensory neurons from a dorsal root ganglion to grow in cell culture. The functional groups attached to the nanotube surface play an important role in assisting neurite extension during culture. Our scanning electron microcopy (SEM) study reveals intertwinement between the neurites and underlying functionalized carbon nanotubes which indicates their strong interaction at the nanoscale. The functional groups are considered to act as anchoring seeds which may enhance the adhesion of neurons as well as neurites, thus promoting neurite growth.

Nicotine Alters Nicotinic Receptor Subunit Levels Differently in Developing Mammalian Sympathetic Neurons

Abstract:  The subunit specific expression of nicotinic acetylcholine receptors (nAChRs) undergo changes in the superior cervical sympathetic ganglion (SCG) of rat pups during neonatal growth. Since nAChRs play a significant role in sympathetic transmission, and the effect of nicotine on the expression of nAChR subunits in neurons of neonatal SCG is not known, we determined the effects of nicotine on receptor profiles using primary cultures of SCG neurons of 1‐day‐old rat pups. Neurons in culture were exposed to 1 and 10 μM of nicotine in the presence and absence of nerve growth factor (NGF). After 24 h, protein from the control and experimental neuron cultures was analyzed for the presence of nAChR containing α7 and α3 subunits using subunit specific antibodies. Exposure to 1 μM of nicotine marginally increased α7 subunits only in the absence of NGF. However it increased the level of α3 subunits significantly by 18% and 33.6% in the presence and absence of NGF, respectively. Exposure to 10 μM of nicotine did not alter the levels of either of the subunits. Interestingly, when the neurons were pre‐exposed to α‐bungarotoxin (antagonist of α7 nAChR), exposure to 10 μM of nicotine resulted in significant increases not only in α7 nAChR (25.5%) but also in α3 nAChR (32.2%). These results show that exposure to nicotine alters the nAChR levels differently in the neonatal sympathetic neurons in a subunit specific manner and suggest that the level of α7 as well as α3 nAChR is linked to the functional status of α7 nAChR in these neurons.

Synthesis of hematite and maghemite nanotubes and study of their applications in neuroscience and drug delivery

This report discusses our work on synthesis of hematite and maghemite nanotubes, analysis of their biocompatibility with pheochromocytoma cells (PC12 cells), and study of their applications in the culture of dorsal root ganglion (DRG) neurons and the delivery of ibuprofen sodium salt (ISS) drug model. Two methods, template-assisted thermal decomposition method and hydrothermal method, were used for synthesizing hematite nanotubes, and maghemite nanotubes were obtained from the synthesized hematite nanotubes by thermal treatment. The crystalline, morphology and magnetic properties of the hematite and maghemite nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. The biocompatibility of the synthesized hematite nanotubes was confirmed by the survival and differentiation of PC12 cells in the presence of the hematite nanotubes coupled to nerve growth factor (NGF). To study the combined effects of the presence of magnetic nanotubes and external magnetic fields on neurite growth, laminin was coupled to hematite and maghemite nanotubes, and DRG neurons were cultured in the presence of the treated nanotubes with the application of external magnetic fields. It was found that neurons can better tolerate external magnetic fields when magnetic nanotubes were present. Close contacts between nanotubes and filopodia that were observed under SEM showed that the nanotubes and the growing neurites interacted readily. The drug loading and release capabilities of hematite nanotubes synthesized by hydrothermal method were tested by using ibuprofen sodium salt (ISS) as a drug model. Our experimental results indicate that hematite and maghemite nanotubes have good biocompatibility with neurons, could be used in regulating neurite growth, and are promising vehicles for drug delivery.

Magnetic Nanotubes Influence the Response of Dorsal Root Ganglion Neurons to Alternating Magnetic Fields

Magnetic nanotubes hold the potential for neuroscience applications because of the feasibility of controlling the orientation or movement of magnetic nanotubes and their ability to deliver chemicals or biomolecules by an external magnetic field, which can facilitate directed growth of neurites. Therefore, we sought to investigate the effects of laminin treated magnetic nanotubes and external alternating magnetic fields on the growth of dorsal root ganglion (DRG) neurons in cell culture. Magnetic nanotubes were synthesized by a hydrothermal method and characterized to confirm their hollow structure, the hematite and maghemite phases, and the magnetic properties. DRG neurons were cultured in the presence of laminin coupled magnetic nanotubes under alternating magnetic fields. Electron microscopy showed a close interaction between magnetic nanotubes and the growing neurites. Phase contrast microscopy revealed live growing neurons suggesting that the combination of the presence of magnetic nanotubes and the alternating magnetic field were tolerated by DRG neurons. The synergistic effects, from both laminin treated magnetic nanotubes and the applied magnetic field on the survival, growth, and electrical activities of the DRG neurons, are currently being investigated.

Magnetic nanotubes and their potential use in neuroscience applications

This paper presents our study on the synthesis and properties of magnetic nanotubes and their potential in neuroscience applications. Magnetic nanotubes were prepared by solution filtration through a template followed by thermal annealing and reduction. SEM and TEM were performed to characterize the as-prepared materials. To explore the potential use of magnetic nanotubes in neuroscience applications, we cultured neurons on iron oxide nanotube mats, and tested the effects of magnetic nanotubes on the growth of neurons. Based on our preliminary result, three original approaches for investigating and modulating neuron activities using magnetic nanotubes are proposed. The progress in this area of investigation could help to find better treatment for diseases in nervous systems in the future.

Synthesis of iron oxide nanotubes and their applications in neuroscience and drug delivery

This paper reports the synthesis of three types of iron oxide nanotubes, including hematite (α-Fe2O3), maghemite (γ-Fe2O3) and magnetite (Fe3O4), and their applications in neuroscience and drug delivery. Two methods, template-assisted thermal decomposition method and hydrothermal method, were used for synthesizing hematite nanotubes, and maghemite nanotubes were obtained from hematite nanotubes by thermal treatment. Template-assisted filtering method was used for synthesizing magnetite nanotubes from ferrofluid. The crystalline, morphology and magnetic properties of the synthesized iron oxide nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. The biocompatibility of the synthesized hematite nanotubes was confirmed by the survival and differentiation of PC12 cells in the presence of the hematite nanotubes coupled to nerve growth factor (NGF). The capacity of hematite nanotubes for coupling and leasing NGF was confirmed by cultivating PC12 cells in the presence of NGF-loaded hematite nanotubes. The drug loading and release capabilities of hematite nanotubes were tested by using ibuprofen sodium salt (ISS) as a drug model. Based on the experimental results presented in this paper, it can be concluded that iron oxide nanotubes have good biocompatibility with neurons, could be used in guding neurite growth, and are promising candidates for drug delivery.

Experimental Investigation of Magnetic Nanotubes in PC-12 Neuron Cells Culturing

This report discusses the effects of magnetic nanotubes on the differentiation and growth of neurons. The magnetic nanotubes used in this study are hematite nanotubes synthesized using template method, and their structural and magnetic properties have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). PC-12 cells are differentiated into neurons in the presence of magnetic nanotubes to confirm the biocompatibility and cytotoxic effects of magnetic nanotubes during the processes of neuron differentiation and neuronal growth. The morphological changes and synapse formation of neurons are investigated, and the contact effects of magnetic nanotubes on neurite (axon and dendrites) outgrowth are explored. This research allows us to understand the interaction between magnetic nanomaterials and neurons, and pave the way towards developing potential treatments using the magnetic nano tubes for neurodegenerative disorders and injuries to the nervous system in the future.

Tubular nanostructured materials for bioapplications

Tubular nanomaterials possess hollow structures as well as high aspect ratios. In addition to their unique physical and chemical properties induced by their nanoscale dimensions, their inner voids and outer surfaces make them ideal candidates for a number of biomedical applications. In this work, three types of tubular nanomaterials including carbon nanotubes, hematite nanotubes, and maghemite nanotubes, were synthesized by different chemical techniques. Their structural and crystalline properties were characterized. For potential bioapplications of tubular nanomaterials, experimental investigations were carried out to demonstrate the feasibility of using carbon nanotubes, hematite nanotubes, and maghemite nanotubes in glucose sensing, neuronal growth, and drug delivery, respectively. Preliminary results show the promise of tubular nanomaterials in future biomedical applications.