Two-Photon Image Tracking of Neural Stem Cells via Iridium Complexes Encapsulated in Polymeric Nanospheres

Nanotechnology-Assisted Cell Tracking

The usefulness of nanoparticles (NPs) in the diagnostic and/or therapeutic sector is derived from their aptitude for navigating intra- and extracellular barriers successfully and to be spatiotemporally targeted. In this context, the optimization of NP delivery platforms is technologically related to the exploitation of the mechanisms involved in the NP–cell interaction. This review provides a detailed overview of the available technologies focusing on cell–NP interaction/detection by describing their applications in the fields of cancer and regenerative medicine. Specifically, a literature survey has been performed to analyze the key nanocarrier-impacting elements, such as NP typology and functionalization, the ability to tune cell interaction mechanisms under in vitro and in vivo conditions by framing, and at the same time, the imaging devices supporting NP delivery assessment, and consideration of their specificity and sensitivity. Although the large amount of literature information on the designs and applications of cell membrane-coated NPs has reached the extent at which it could be considered a mature branch of nanomedicine ready to be translated to the clinic, the technology applied to the biomimetic functionalization strategy of the design of NPs for directing cell labelling and intracellular retention appears less advanced. These approaches, if properly scaled up, will present diverse biomedical applications and make a positive impact on human health.

Tracking Neural Stem Cells in vivo: Achievements and Limitations

Neural stem cell (NSC) therapies are developing rapidly and have been proposed as a treatment option for various neurological diseases, such as stroke, Parkinson's disease and multiple sclerosis. However, monitoring transplanted NSCs, exploring their location and migration, and evaluating their efficacy and safety have all become serious and important issues. Two main problems in tracking NSCs have been noted: labeling them for visibility and imaging them. Direct labeling and reporter gene labeling are the two main methods for labeling stem cells. Magnetic resonance imaging and nuclear imaging, including positron emission tomography, single-photon emission computed tomography, and optical imaging, are the most commonly used imaging techniques. Each has its strengths and weaknesses. Thus, multimodal imaging, which combines two or more imaging methods to complement the advantages and disadvantages of each, has garnered increased attention. Advances in image fusion and nanotechnology, as well as the exploration of new tracers and new imaging modalities have substantially facilitated the development of NSC tracking technology. However, the safety issues related to tracking and long-term tracking of cell viability are still challenges. In this review, we discuss the merits and defects of different labeling and imaging methods, as well as recent advances, challenges and prospects in NSC tracking.

The GDF11 Promotes Nerve Regeneration After Sciatic Nerve Injury in Adult Rats by Promoting Axon Growth and Inhibiting Neuronal Apoptosis

Introduction: Sciatic nerve injury is a common injury of the nervous system. Stem cell-based therapies, drug-based therapies and rehabilitation physiotherapy therapies are currently available, but their limited therapeutic efficacy limits their use. Here, we aimed to explore a novel lentiviral-based gene therapeutic strategy and to elaborate its mechanism.

Materials and Methods: Recombinant GDF11 protein was used for the in vitro treatment of dorsal root ganglion (DRG) cells. Lentivirus was used to construct a vector system for the in vivo expression of GDF11. The nerve conduction function was detected using action-evoked potentials at different time periods, and the regulatory effect of nerves on target organs was detected by weighing the gastrocnemius muscle. Immunofluorescence of NF200 and S100 was used to show the regeneration of the sciatic nerve, and myelin and Nissl staining were performed to observe the pathological features of the tissue. Western was used to validate signaling pathways. The expression of related genes was observed by qPCR and Western blotting, and cell apoptosis was detected by flow cytometry.

Result: GDF11 promotes the axonal growth of DRG cells and inhibits DGR cell apoptosis in vitro. GDF11 acts by activating the Smad pathway. GDF11 promotes the recovery of damaged sciatic nerve function in rats, the regeneration of damaged sciatic nerves in rats, and myelin regeneration of damaged sciatic nerves in rats. GDF11 also exerts a protective effect on neuronal cells in rats.

Conclusion: Based on the present study, we conclude that GDF11 promotes axonal growth and inhibits DRG cell apoptosis in vitro through the Smad pathway, and lentivirus-mediated GDF11 overexpression in vivo can promote the recovery of sciatic nerves after transection by promoting axonal growth and inhibiting neuronal apoptosis in the spinal cord.

Promising Applications of Nanoparticles in the Treatment of Hearing Loss

Hearing loss is one of the most common disabilities affecting both children and adults worldwide. However, traditional treatment of hearing loss has some limitations, particularly in terms of drug delivery system as well as diagnosis of ear imaging. The blood–labyrinth barrier (BLB), the barrier between the vasculature and fluids of the inner ear, restricts entry of most blood-borne compounds into inner ear tissues. Nanoparticles (NPs) have been demonstrated to have high biocompatibility, good degradation, and simple synthesis in the process of diagnosis and treatment, which are promising for medical applications in hearing loss. Although previous studies have shown that NPs have promising applications in the field of inner ear diseases, there is still a gap between biological research and clinical application. In this paper, we aim to summarize developments and challenges of NPs in diagnostics and treatment of hearing loss in recent years. This review may be useful to raise otology researchers’ awareness of effect of NPs on hearing diagnosis and treatment.

Atrial Natriuretic Peptide Promotes Neurite Outgrowth and Survival of Cochlear Spiral Ganglion Neurons in vitro Through NPR-A/cGMP/PKG Signaling

Sensorineural hearing loss (SNHL) is a dominant public health issue affecting millions of people around the globe, which is correlated with the irreversible deterioration of the hair cells and spiral ganglion neurons (SGNs) within the cochlea. Strategies using bioactive molecules that regulate neurite regeneration and neuronal survival to reestablish connections between auditory epithelium or implanted electrodes and SGN neurites would become attractive therapeutic candidates for SNHL. As an intracellular second messenger, cyclic guanosine-3’,5’-monophosphate (cGMP) can be synthesized through activation of particulate guanylate cyclase-coupled natriuretic peptide receptors (NPRs) by natriuretic peptides, which in turn modulates multiple aspects of neuronal functions including neuronal development and neuronal survival. As a cardiac-derived hormone, atrial natriuretic peptide (ANP), and its specific receptors (NPR-A and NPR-C) are broadly expressed in the nervous system where they might be involved in the maintenance of diverse neural functions. Despite former literatures and our reports indicating the existence of ANP and its receptors within the inner ear, particularly in the spiral ganglion, their potential regulatory mechanisms underlying functional properties of auditory neurons are still incompletely understood. Our recently published investigation revealed that ANP could promote the neurite outgrowth of SGNs by activating NPR-A/cGMP/PKG cascade in a dose-dependent manner. In the present research, the influence of ANP and its receptor-mediated downstream signaling pathways on neurite outgrowth, neurite attraction, and neuronal survival of SGNs in vitro was evaluated by employing cultures of organotypic explant and dissociated neuron from postnatal rats. Our data indicated that ANP could support and attract neurite outgrowth of SGNs and possess a high capacity to improve neuronal survival of SGNs against glutamate-induced excitotoxicity by triggering the NPR-A/cGMP/PKG pathway. The neuroregenerative and neuroprotective effects of ANP/NPRA/cGMP/PKG-dependent signaling on SGNs would represent an attractive therapeutic candidate for hearing impairment.

Iridium(III) Sensitisers and Energy Upconversion: The Influence of Ligand Structure upon TTA-UC Performance

Six substituted ligands based upon 2-(naphthalen-1-yl)quinoline-4-carboxylate and 2-(naphthalen-2-yl)quinoline-4-carboxylate have been synthesised in two steps from a range of commercially available isatin derivatives. These species are shown to be effective cyclometallating ligands for Ir^III , yielding complexes of the form [Ir(C^N)₂ (bipy)]PF₆ (where C^N=cyclometallating ligand; bipy=2,2'-bipyridine). X-ray crystallographic studies on three examples demonstrate that the complexes adopt a distorted octahedral geometry wherein a cis-C,C and trans-N,N coordination mode is observed. Intraligand torsional distortions are evident in all cases. The Ir^III complexes display photoluminescence in the red part of the visible region (668-693 nm), which is modestly tuneable through the ligand structure. The triplet lifetimes of the complexes are clearly influenced by the precise structure of the ligand in each case. Supporting computational (DFT) studies suggest that the differences in observed triplet lifetime are likely due to differing admixtures of ligand-centred versus MLCT character instilled by the facets of the ligand structure. Triplet-triplet annihilation upconversion (TTA-UC) measurements demonstrate that the complexes based upon the 1-naphthyl derived ligands are viable photosensitisers with upconversion quantum efficiencies of 1.6-6.7 %.

Tracking mesenchymal stem cells with Ir(III) complex-encapsulated nanospheres in cranium defect with postmenopausal osteoporosis

Osteoporosis (OP) is a significant public health problem with associated fragility fractures, thereby causing large bone defects and difficulty in self-repair. The introduction of human mesenchymal stem cells (hMSCs) is the most promising platform in bone tissue engineering for OP therapy, which induces less side effects than conventional medication. However, the safety and efficiency of the cell-based OP therapy requires the ability to monitor the cell's outcome and biodistribution after cell transplantation. Therefore, we designed an in vivo system to track hMSCs in real time and simultaneously attempted to obtain a significant therapeutic effect during the bone repair process. In this study, we synthesized Ir(III) complex, followed by encapsulation with biodegradable methoxy-poly(ethylene glycol) poly(lactic-co-glycolic acid) nanospheres through double emulsions strategy. The Ir(III) complex nanospheres did not affect hMSC proliferation, stemness, and differentiation and realized highly efficient and long-term cellular labeling for at least 25 days in vivo. The optimal transplantation conditions were also determined first by injecting a gradient number of labeled hMSCs percutaneously into the cranial defect of the nude mouse model. Next, we applied this method to ovariectomy-induced OP mice. Results showed long-term optical imaging with high fluorescence intensity and computed tomography (CT) scanning with significantly increased bone formation between the osteoporotic and sham-operated bones. During the tracking process, two mice from each group were sacrificed at two representative time points to examine the bony defect bridging via micro-CT morphometric analyses. Our data showed remarkable promise for efficient hMSC tracking and encouraging treatment in bioimaging-guided OP stem cell therapy.

Atrial Natriuretic Peptide Improves Neurite Outgrowth from Spiral Ganglion Neurons In Vitro through a cGMP-Dependent Manner

The spiral ganglion neurons (SGNs) are the primary afferent neurons in the spiral ganglion (SG), while their degeneration or loss would cause sensorineural hearing loss. As a cardiac-derived hormone, atrial natriuretic peptide (ANP) plays a critical role in cardiovascular homeostasis through binding to its functional receptors (NPR-A and NPR-C). ANP and its receptors are widely expressed in the mammalian nervous system where they could be implicated in the regulation of multiple neural functions. Although previous studies have provided direct evidence for the presence of ANP and its functional receptors in the inner ear, their presence within the cochlear SG and their regulatory roles during auditory neurotransmission and development remain largely unknown. Based on our previous findings, we investigated the expression patterns of ANP and its receptors in the cochlear SG and dissociated SGNs and determined the influence of ANP on neurite outgrowth in vitro by using organotypic SG explants and dissociated SGN cultures from postnatal rats. We have demonstrated that ANP and its receptors are expressed in neurons within the cochlear SG of postnatal rat, while ANP may promote neurite outgrowth of SGNs via the NPR-A/cGMP/PKG pathway in a dose-dependent manner. These results indicate that ANP would play a role in normal neuritogenesis of SGN during cochlear development and represents a potential therapeutic candidate to enhance regeneration and regrowth of SGN neurites.

Stem Cell-Based Therapeutic Approaches to Restore Sensorineural Hearing Loss in Mammals

The hair cells that reside in the cochlear sensory epithelium are the fundamental sensory structures responsible for understanding the mechanical sound waves evoked in the environment. The intense damage to these sensory structures may result in permanent hearing loss. The present strategies to rehabilitate the hearing function include either hearing aids or cochlear implants that may recover the hearing capability of deaf patients to a limited extent. Therefore, much attention has been paid on developing regenerative therapies to regenerate/replace the lost hair cells to treat the damaged cochlear sensory epithelium. The stem cell therapy is a promising approach to develop the functional hair cells and neuronal cells from endogenous and exogenous stem cell pool to recover hearing loss. In this review, we specifically discuss the potential of different kinds of stem cells that hold the potential to restore sensorineural hearing loss in mammals and comprehensively explain the current therapeutic applications of stem cells in both the human and mouse inner ear to regenerate/replace the lost hair cells and spiral ganglion neurons.

Spectroscopic and Theoretical Investigation of Color Tuning in Deep-Red Luminescent Iridium(III) Complexes

A series of heteroleptic, neutral iridium(III) complexes of the form [Ir(L)2(N^O)] (where L = cyclometalated 2,3-disubstituted quinoxaline and N^O = ancillary picolinate or pyrazinoate) are described in terms of their synthesis and spectroscopic properties, with supporting computational analyses providing additional insight into the electronic properties. The 10 [Ir(L)2(N^O)] complexes were characterized using a range of analytical techniques (including 1H, 13C, and 19F NMR and IR spectroscopies and mass spectrometry). One of the examples was structurally characterized using X-ray diffraction. The redox properties were determined using cyclic voltammetry, and the electronic properties were investigated using UV-vis, time-resolved luminescence, and transient absorption spectroscopies. The complexes are phosphorescent in the red region of the visible spectrum (λem = 633-680 nm), with lifetimes typically of hundreds of nanoseconds and quantum yields ca. 5% in aerated chloroform. A combination of spectroscopic and computational analyses suggests that the long-wavelength absorption and emission properties of these complexes are strongly characterized by a combination of spin-forbidden metal-to-ligand charge-transfer and quinoxaline-centered transitions. The emission wavelength in these complexes can thus be controlled in two ways: first, substitution of the cyclometalating quinoxaline ligand can perturb both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital levels (LUMO, Cl atoms on the ligand induce the largest bathochromic shift), and second, the choice of the ancillary ligand can influence the HOMO energy (pyrazinoate stabilizes the HOMO, inducing hypsochromic shifts).

A Review of The Lesser-Studied Microemulsion-Based Synthesis Methodologies Used for Preparing Nanoparticle Systems of The Noble Metals, Os, Re, Ir and Rh

This review focuses on the recent advances in the lesser-studied microemulsion synthesis methodologies of the following noble metal colloid systems (i.e., Os, Re, Ir, and Rh) using either a normal or reverse micelle templating system. The aim is to demonstrate the utility and potential of using this microemulsion-based approach to synthesize these noble metal nanoparticle systems. Firstly, some fundamentals and important factors of the microemulsion synthesis methodology are introduced. Afterward, a review of the investigations on the microemulsion syntheses of Os, Re, Ir, and Rh nanoparticle (NP) systems (in all forms, viz., metallic, oxide, mixed-metal, and discrete molecular complexes) is presented for work published in the last ten years. The chosen noble metals are traditionally very reactive in nanosized dimensions and have a strong tendency to aggregate when prepared via other methods. Also, the particle size and particle size distribution of these colloids can have a significant impact on their catalytic performance. It is shown that the microemulsion approach has the capability to better stabilize these metal colloids and can control the size of the synthesized NPs. This generally leads to smaller particles and higher catalytic activity when they are tested in applications.