Intravenous administration of human mesenchymal stem cells after noise- or drug-induced hearing loss in rats

Stem Cell-Based Therapies for Auditory Hair Cell Regeneration in the Treatment of Hearing Loss

The incidence and prevalence of hearing loss is increasing globally at an accelerated pace. Hair cells represent the sensory receptors of auditory and vestibular systems. Hair cell absence, loss or degeneration due to congenital diseases, trauma, toxicity, infection or advancing age, results in disabling hearing loss. Regenerative medicine approaches consisting in stem cell-based hair cell rescue or regeneration, gene therapy, as well as cell and tissue engineering are expected to dramatically improve the therapeutic arsenal available for addressing hearing loss. Current strategies that are using different stem cell types to rescue or to induce hair cell proliferation and regeneration are presented. Gene and cell therapy methods that modulates transdifferentiation of surrounding cell types into hair cells are presented, together with their specific advantages and limitations. Several modalities for improving therapeutic targeting to the inner ear such as nanoparticle-mediated cell and gene delivery are introduced. Further steps in building more relevant high-throughput models for testing novel drugs and advanced therapies are proposed as a modality to accelerate translation to clinical settings.

The Protective Effects of Human Embryonic Stem Cell-Derived Mesenchymal Stem Cells in Noise-Induced Hearing Loss of Rats

A few prior animal studies have suggested the transplantation or protective effects of mesenchymal stem cells (MSCs) in noise-induced hearing loss. This study intended to evaluate the fates of administered MSCs in the inner ears and the otoprotective effects of MSCs in the noise-induced hearing loss of rats. Human embryonic stem cell-derived MSCs (ES-MSCs) were systematically administered via the tail vein in adult rats. Eight-week-old Sprague-Dawley rats were randomly allocated to the control (n = 8), ES-MSC (n = 4), noise (n = 8), and ES-MSC+noise (n = 10) groups. In ES-MSC and ES-MSC+noise rats, 5 × 105 ES-MSCs were injected via the tail vein. In noise and ES-MSC+noise rats, broadband noise with 115 dB SPL was exposed for 3 h daily for 5 days. The hearing levels were measured using auditory brainstem response (ABR) at 4, 8, 16, and 32 kHz. Cochlear histology was examined using H&E staining and cochlear whole mount immunofluorescence. The presence of human DNA was examined using Sry PCR, and the presence of human cytoplasmic protein was examined using STEM121 immunofluorescence staining. The protein expression levels of heat shock protein 70 (HSP70), apoptosis-inducing factor (AIF), poly (ADP-ribose) (PAR), PAR polymerase (PARP), caspase 3, and cleaved caspase 3 were estimated. The ES-MSC rats did not show changes in ABR thresholds following the administration of ES-MSCs. The ES-MSC+ noise rats demonstrated lower ABR thresholds at 4, 8, and 16 kHz than the noise rats. Cochlear spiral ganglial cells and outer hair cells were more preserved in the ES-MSC+ noise rats than in the noise rats. The Sry PCR bands were highly detected in lung tissue and less in cochlear tissue of ES-MSC+noise rats. Only a few STEM121-positivities were observed in the spiral ganglial cell area of ES-MSC and ES-MSC+noise rats. The protein levels of AIF, PAR, PARP, caspase 3, and cleaved caspase 3 were lower in the ES-MSC+noise rats than in the noise rats. The systemic injection of ES-MSCs preserved hearing levels and attenuated parthanatos and apoptosis in rats with noise-induced hearing loss. In addition, a tiny number of transplanted ES-MSCs were observed in the spiral ganglial areas.

Mechanism and Prevention of Spiral Ganglion Neuron Degeneration in the Cochlea

Sensorineural hearing loss (SNHL) is one of the most prevalent sensory deficits in humans, and approximately 360 million people worldwide are affected. The current treatment option for severe to profound hearing loss is cochlear implantation (CI), but its treatment efficacy is related to the survival of spiral ganglion neurons (SGNs). SGNs are the primary sensory neurons, transmitting complex acoustic information from hair cells to second-order sensory neurons in the cochlear nucleus. In mammals, SGNs have very limited regeneration ability, and SGN loss causes irreversible hearing loss. In most cases of SNHL, SGN damage is the dominant pathogenesis, and it could be caused by noise exposure, ototoxic drugs, hereditary defects, presbycusis, etc. Tremendous efforts have been made to identify novel treatments to prevent or reverse the damage to SGNs, including gene therapy and stem cell therapy. This review summarizes the major causes and the corresponding mechanisms of SGN loss and the current protection strategies, especially gene therapy and stem cell therapy, to promote the development of new therapeutic methods.

Achievements and Challenges in Transplantation of Mesenchymal Stem Cells in Otorhinolaryngology

Otorhinolaryngology enrolls head and neck surgery in various tissues such as ear, nose, and throat (ENT) that govern different activities such as hearing, breathing, smelling, production of vocal sounds, the balance, deglutition, facial animation, air filtration and humidification, and articulation during speech, while absence of these functions can lead to high morbidity and even mortality. Conventional therapies for head and neck damaged tissues include grafts, transplants, and artificial materials, but grafts have limited availability and cause morbidity in the donor site. To improve these limitations, regenerative medicine, as a novel and rapidly growing field, has opened a new therapeutic window in otorhinolaryngology by using cell transplantation to target the healing and replacement of injured tissues. There is a high risk of rejection and tumor formation for transplantation of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs); mesenchymal stem cells (MSCs) lack these drawbacks. They have easy expansion and antiapoptotic properties with a wide range of healing and aesthetic functions that make them a novel candidate in otorhinolaryngology for craniofacial defects and diseases and hold immense promise for bone tissue healing; even the tissue sources and types of MSCs, the method of cell introduction and their preparation quality can influence the final outcome in the injured tissue. In this review, we demonstrated the anti-inflammatory and immunomodulatory properties of MSCs, from different sources, to be safely used for cell-based therapies in otorhinolaryngology, while their achievements and challenges have been described too.

Therapeutic Application of Mesenchymal Stem Cells for Cochlear Regeneration

Hearing loss is one of the major worldwide health problems that seriously affects human social and cognitive development. In the auditory system, three components outer ear, middle ear and inner ear are essential for the hearing mechanism. In the inner ear, sensory hair cells and ganglion neuronal cells are the essential supporters for hearing mechanism. Damage to these cells can be caused by long-term exposure of excessive noise, ototoxic drugs (aminoglycosides), ear tumors, infections, heredity and aging. Since mammalian cochlear hair cells do not regenerate naturally, some therapeutic interventions may be required to replace the damaged or lost cells. Cochlear implants and hearing aids are the temporary solutions for people suffering from severe hearing loss. The current discoveries in gene therapy may provide a deeper understanding in essential genes for the inner ear regeneration. Stem cell migration, survival and differentiation to supporting cells, cochlear hair cells and spiral ganglion neurons are the important foundation in understanding stem cell therapy. Moreover, mesenchymal stem cells (MSCs) from different sources (bone marrow, umbilical cord, adipose tissue and placenta) could be used in inner ear therapy. Transplanted MSCs in the inner ear can recruit homing factors at the damaged sites to induce transdifferentiation into inner hair cells and ganglion neurons or regeneration of sensory hair cells, thus enhancing the cochlear function. This review summarizes the potential application of mesenchymal stem cells in hearing restoration and combining stem cell and molecular therapeutic strategies can also be used in the recovery of cochlear function.

Cell Transplantation to Restore Lost Auditory Nerve Function is a Realistic Clinical Opportunity

Hearing is one of our most important means of communication. Disabling hearing loss (DHL) is a long-standing, unmet problem in medicine, and in many elderly people, it leads to social isolation, depression, and even dementia. Traditionally, major efforts to cure DHL have focused on hair cells (HCs). However, the auditory nerve is also important because it transmits electrical signals generated by HCs to the brainstem. Its function is critical for the success of cochlear implants as well as for future therapies for HC regeneration. Over the past two decades, cell transplantation has emerged as a promising therapeutic option for restoring lost auditory nerve function, and two independent studies on animal models show that cell transplantation can lead to functional recovery. In this article, we consider the approaches most likely to achieve success in the clinic. We conclude that the structure and biochemical integrity of the auditory nerve is critical and that it is important to preserve the remaining neural scaffold, and in particular the glial scar, for the functional integration of donor cells. To exploit the natural, autologous cell scaffold and to minimize the deleterious effects of surgery, donor cells can be placed relatively easily on the surface of the nerve endoscopically. In this context, the selection of donor cells is a critical issue. Nevertheless, there is now a very realistic possibility for clinical application of cell transplantation for several different types of hearing loss.

Application of Mesenchymal Stem Cell Therapy and Inner Ear Regeneration for Hearing Loss: A Review

Inner and middle ear disorders are the leading cause of hearing loss, and are said to be among the greatest risk factors of dementia. The use of regenerative medicine for the treatment of inner ear disorders may offer a potential alternative to cochlear implants for hearing recovery. In this paper, we reviewed recent research and clinical applications in middle and inner ear regeneration and cell therapy. Recently, the mechanism of inner ear regeneration has gradually been elucidated. "Inner ear stem cells," which may be considered the precursors of various cells in the inner ear, have been discovered in the cochlea and vestibule. Research indicates that cells such as hair cells, neurons, and spiral ligaments may form promising targets for inner ear regenerative therapies by the transplantation of stem cells, including mesenchymal stem cells. In addition, it is necessary to develop tests for the clinical monitoring of cell transplantation. Real-time imaging techniques and hearing rehabilitation techniques are also being investigated, and cell therapy has found clinical application in cochlear implant techniques.

Mesenchymal stem cells for sensorineural hearing loss: a systematic review of preclinical studies

Sensorineural hearing loss (SNHL) is the most common form of hearing loss that is routinely treated with hearing aids or cochlear implants. Advances in regenerative medicine have now led to animal studies examining the possibility of restoring injured hair cells with mesenchymal stem/stromal cell (MSC) administration. We conducted a systematic review and meta-analysis to collate the existing preclinical literature evaluating MSCs as a treatment for SNHL and quantify the effect of MSCs on functional hearing. Our protocol was published online on CAMARADES. Searches were conducted in four medical databases by two independent investigators. Twelve studies met inclusion and were evaluated for risk of bias using SYRCLE. Rodent models were commonly used (n = 8, 66%), while auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE) were the most frequent measures assessing hearing loss. MSCs were derived from multiple tissue sources, including bone marrow, adipose tissue, and umbilical cord blood and the dose ranged from 4 × 10³ to 1 × 10⁷ cells. Treatment with MSCs resulted in an improvement in ABR and DPOAE (mean difference-15.22, + 9.10, respectively). Despite high heterogeneity and multiple "unclear" domains in the risk of bias, this review provides evidence that MSCs may have a beneficial effect in hearing function.

Mesenchymal stem cells for sensorineural hearing loss: protocol for a systematic review of preclinical studies

BACKGROUND

Sensorineural hearing loss (SNHL) is the most common form of hearing impairment and is characterized by a loss of receptor hair cells and/or spiral ganglion neurons. Regenerative stem cell therapy could potentially restore normal hearing and slow the progression of hearing loss in patients. Preclinical animal studies have demonstrated that mesenchymal stem cells (MSCs) could be a promising new therapy for this condition. These findings have prompted investigators to begin human clinical trials to assess the safety and efficacy of MSCs for the treatment of SNHL. The objective of the proposed systematic review is to examine the efficacy of MSCs as a therapy for SNHL in animal models.

METHODS

We will include preclinical animal studies of SNHL in which MSCs are administered, and outcomes are compared against MSC-naïve controls. The primary outcome will include audiologic tests that are routinely used in experimental studies of hearing loss, such as auditory brainstem response (ABR) and distortion product otoacoustic emissions testing (DPOAE). Secondary outcomes will include histology, microscopy, gene protein expression, and behavioral responses of animals. Electronic searches of MEDLINE via PubMed, Scopus, ScienceDirect, and Cumulative Index to Nursing and Allied Health Literature (CINAHL) will be performed. Search results will be screened independently and in duplicate. Data from eligible studies will be extracted, pooled, and analyzed using random effects models. Risk of bias and publication bias will be assessed using the Systematic Review Center for Laboratory Animal Experimentation (SYRCLE) risk of bias tool and Funnel Plots/Egger's regression tests, respectively.

DISCUSSION

This systematic review will provide a summary of the efficacy of MSC therapy in animal models of SNHL, utilizing functional hearing assessment as a primary outcome. Findings from this review are important because they can elucidate research gaps that should be addressed in future preclinical studies and in turn can be translated into clinical studies.

SYSTEMATIC REVIEW REGISTRATION

CAMARADES ( http://www.dcn.ed.ac.uk/camarades/ ).

Harderian gland-derived stem cells as a cytotherapy in a guinea pig model of carboplatin-induced hearing loss

BACKGROUND

Stem cells therapy of hearing loss is a challenging field due to lacking self-regenerative capacity of cochlea. Harderian gland of guinea pigs was thought to harbour a unique type of progenitors which could restore the damaged cochlear tissues.

THE AIM

of this study was to isolate Harderian gland derived stem cells (HG-SCs) and investigate their efficacy in restoring the damaged cochlear tissue in carboplatin-induced hearing loss.

METHODOLOGY

Sixty female and 10 male pigmented guinea pigs were used; the male animals were HG-SCs donors, while the females were assigned into 3 groups; control, hearing loss (HL) and HG-SC-treated groups. Auditory reflexes were assessed throughout the study. The animals were euthanized 35 days after HG-SCs transplantation, the cochleae were extracted and processed for assessment by light microscope and scanning electron microscope. Morphometric assessment of stria vascularis thickness, hair cells and spiral ganglia neuronal number and optical density of TLR4 expression were done.

RESULTS

The isolated HG-SCs had the same morphological and phenotypical character as mesenchymal stem cells. HL group revealed destruction of organ of Corti, stria vascularis and spiral ganglion with decreased morphometric parameters. Restoration of both cochlear structure and function was observed in HG-SC-treated group along with a significant increase in IHCs, OHCs numbers, stria vascularis thickness and spiral ganglionic cell count to be close to the values of control group.

CONCLUSION

The isolated HG-SCs were proved to restore structure and function of cochlea in guinea pig model of hearing loss.

Biological therapies in otology

Hearing loss is present in millions of people worldwide. Current treatment for patients with severe to profound hearing loss consists of cochlear implantation. Providing the cochlear nerve is intact, patients generally benefit greatly from this intervention, frequently achieving significant improvements in speech comprehension. There are, however, some cases where current technology does not provide patients with adequate benefit. Ongoing research in cell transplantation and gene therapy promises to lead to new developments that will improve the function of cochlear implants. Translation of these experimental approaches is presently at an early stage. This review focuses on the application of biological therapies in severe hearing loss and discusses some of the barriers to translating basic scientific research into clinical reality. We emphasize the application of these novel therapies to cochlear implantation.

The olfactory mucosa: a potential source of stem cells for hearing regeneration

The olfactory mucosa contains cells that enable it to generate new neurons and other supporting cells throughout life, allowing it to replace cells of the mucosa that have been damaged by exposure to various insults. In this article, we discuss the different types of stem cell found within the olfactory mucosa and their properties. In particular, the mesenchymal-like cells found within the lamina propria will be reviewed in detail. In addition, we discuss potential applications of olfactory-derived stem cells toward hearing regeneration secondary to either inner hair cell loss or primary or secondary auditory nerve degeneration.

Challenges in Cell-Based Therapies for the Treatment of Hearing Loss

Hearing loss in mammals is an irreversible process caused by degeneration of the hair cells of the inner ear. Current therapies for hearing loss include hearing aids and cochlear implants that provide substantial benefits to most patients, but also have several shortcomings. There is great interest in the development of regenerative therapies to treat deafness in the future. Cell-based therapies, based either on adult, multipotent stem, or other types of pluripotent cells, offer promise for generating differentiated cell types to replace lost or damaged hair cells of the inner ear. In this review, we focus on the methods proposed and avenues for research that seem the most promising for stem cell-based auditory sensory cell regeneration, from work collected over the past 15 years.

Human mesenchymal stromal cell therapy for damaged cochlea repair in nod-scid mice deafened with kanamycin

BACKGROUND

Kanamycin, mainly used in the treatment of drug-resistant-tuberculosis, is known to cause irreversible hearing loss. Using the xeno-transplant model, we compared both in vitro and in vivo characteristics of human mesenchymal stromal cells (MSCs) derived from adult tissues, bone marrow (BM-MSCs) and adipose tissue (ADSCs). These tissues were selected for their availability, in vitro multipotency and regenerative potential in vivo in kanamycin-deafened nod-scid mice.

METHODS

MSCs were isolated from informed donors and expanded ex vivo. We evaluated their proliferation capacity in vitro using the hexosaminidase assay, the phenotypic profile using flow-cytometry of a panel of surface antigens, the osteogenic potential using alkaline phosphatase activity and the adipogenic potential using oil-red-O staining. MSCs were intravenously injected in deafened mice and cochleae, liver, spleen and kidney were sampled 7 and 30 days after transplantation. The dissected organs were analyzed using lectin histochemistry, immunohistochemistry, polymerase chain reaction (PCR) and dual color fluorescence in situ hybridization (DC-FISH).

RESULTS

MSCs showed similar in vitro characteristics, but ADSCs appeared to be more efficient after prolonged expansion. Both cell types engrafted in the cochlea of damaged mice, inducing regeneration of the damaged sensory structures. Several hybrid cells were detected in engrafted tissues.

DISCUSSION

BM-MSCs and ADSCs showed in vitro characteristics suitable for tissue regeneration and fused with resident cells in engrafted tissues. The data suggest that paracrine effect is the prevalent mechanism inducing tissue recovery. Overall, BM-MSCs and ADSCs appear to be valuable tools in regenerative medicine for hearing loss recovery.

Advances in translational inner ear stem cell research

Stem cell research is expanding our understanding of developmental biology as well as promising the development of new therapies for a range of different diseases. Within hearing research, the use of stem cells has focused mainly on cell replacement. Stem cells however have a broad range of other potential applications that are just beginning to be explored in the ear. Mesenchymal stem cells are an adult derived stem cell population that have been shown to produce growth factors, modulate the immune system and can differentiate into a wide variety of tissue types. Potential advantages of mesenchymal/adult stem cells are that they have no ethical constraints on their use. However, appropriate regulatory oversight seems necessary in order to protect patients from side effects. Disadvantages may be the lack of efficacy in many preclinical studies. But if proven safe and efficacious, they are easily translatable to clinical trials. The current review will focus on the potential application on mesenchymal stem cells for the treatment of inner ear disorders.

[Biological therapies in otology. German version]

Millions of people worldwide suffer from hearing loss. Current treatment for patients with severe to profound hearing loss consists of cochlear implants. Providing the cochlear nerve is intact, patients generally benefit enormously from this intervention, frequently achieving significant improvements in speech comprehension. There are, however, some cases where current technology does not provide patients with adequate benefit. New therapeutic concepts based on cell transplantation and gene therapy are developing rapidly, at least in the research sector. Compared to the wealth of basic research available in this area, translation of these new experimental approaches into clinical application is presently at a very early stage. The current review focuses on translatable treatment concepts and discusses the barriers that need to be overcome in order to translate basic scientific research into clinical reality. Furthermore, the first examples of clinical application of biological therapies in severe hearing loss are presented, particularly in connection with cochlear implants.

Biohybrid cochlear implants in human neurosensory restoration

BACKGROUND

The success of cochlear implantation may be further improved by minimizing implantation trauma. The physical trauma of implantation and subsequent immunological sequelae can affect residual hearing and the viability of the spiral ganglion. An ideal electrode should therefore decrease post-implantation trauma and provide support to the residual spiral ganglion population. Combining a flexible electrode with cells producing and releasing protective factors could present a potential means to achieve this. Mononuclear cells obtained from bone marrow (BM-MNC) consist of mesenchymal and hematopoietic progenitor cells. They possess the innate capacity to induce repair of traumatized tissue and to modulate immunological reactions.

METHODS

Human bone marrow was obtained from the patients that received treatment with biohybrid electrodes. Autologous mononuclear cells were isolated from bone marrow (BM-MNC) by centrifugation using the Regenlab™ THT-centrifugation tubes. Isolated BM-MNC were characterised using flow cytometry. In addition, the release of cytokines was analysed and their biological effect tested on spiral ganglion neurons isolated from neonatal rats. Fibrin adhesive (Tisseal™) was used for the coating of silicone-based cochlear implant electrode arrays for human use in order to generate biohybrid electrodes. Toxicity of the fibrin adhesive and influence on insertion, as well on the cell coating, was investigated. Furthermore, biohybrid electrodes were implanted in three patients.

RESULTS

Human BM-MNC release cytokines, chemokines, and growth factors that exert anti-inflammatory and neuroprotective effects. Using fibrin adhesive as a carrier for BM-MNC, a simple and effective cell coating procedure for cochlear implant electrodes was developed that can be utilised on-site in the operating room for the generation of biohybrid electrodes for intracochlear cell-based drug delivery. A safety study demonstrated the feasibility of autologous progenitor cell transplantation in humans as an adjuvant to cochlear implantation for neurosensory restoration.

CONCLUSION

This is the first report of the use of autologous cell transplantation to the human inner ear. Due to the simplicity of this procedure, we hope to initiate its widespread utilization in various fields.

Modulation of physical environment makes placental mesenchymal stromal cells suitable for therapy

Low level of oxygen at the site of injury is likely to affect the viability and proliferation of the transplanted mesenchymal stromal cells (MSCs). Hence there is a need to understand the effect of the physical environment on transplanted stromal cells. Therefore, we have studied the effect of the duration of hypoxic exposure alone or in combination with normoxia on placenta derived mesenchymal stem cell (PDMSCs). PDMSCs and bone marrow MSCs (BMMSCs) were analysed under four different culture conditions, exposure to direct normoxia (N), direct hypoxia (H) and intermittent normoxia followed by hypoxia (NH) and intermittent hypoxia followed by normoxia (HN). The effect on morphology, proliferation, metabolic activity by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide) and viability by 7AAD (7-amino-actinomycin D) were assayed, along with markers for MSCs and HLADR. No change in morphology, marker expression or HLADR was detected in N, H, NH or HN. An increase in proliferation rate, decrease in population doubling-time (PDT) and a relative increase in metabolic activity was strongly noted in the order: NH, N/HN and H. No significant difference was observed in the viability between N, H, NH or HN. A similar pattern was also observed in BMMSCS, indicating comparable suitability of PDMSCs in therapeutic applications. Thus we conclude that intermittent exposure to normoxia prior to hypoxic exposure is a better option than direct exposure to hypoxia. This may have clinical relevance in that they probably mirror the in vivo scenario of systemic delivery (NH) of cells as opposed to local delivery (H), thereby suggesting that systemic delivery is better than local delivery.

Postnatal development, maturation and aging in the mouse cochlea and their effects on hair cell regeneration

The organ of Corti in the mammalian inner ear is comprised of mechanosensory hair cells (HCs) and nonsensory supporting cells (SCs), both of which are believed to be terminally post-mitotic beyond late embryonic ages. Consequently, regeneration of HCs and SCs does not occur naturally in the adult mammalian cochlea, though recent evidence suggests that these cells may not be completely or irreversibly quiescent at earlier postnatal ages. Furthermore, regenerative processes can be induced by genetic and pharmacological manipulations, but, more and more reports suggest that regenerative potential declines as the organ of Corti continues to age. In numerous mammalian systems, such effects of aging on regenerative potential are well established. However, in the cochlea, the problem of regeneration has not been traditionally viewed as one of aging. This is an important consideration as current models are unable to elicit widespread regeneration or full recovery of function at adult ages yet regenerative therapies will need to be developed specifically for adult populations. Still, the advent of gene targeting and other genetic manipulations has established mice as critically important models for the study of cochlear development and HC regeneration and suggests that auditory HC regeneration in adult mammals may indeed be possible. Thus, this review will focus on the pursuit of regeneration in the postnatal and adult mouse cochlea and highlight processes that occur during postnatal development, maturation, and aging that could contribute to an age-related decline in regenerative potential. Second, we will draw upon the wealth of knowledge pertaining to age related senescence in tissues outside of the ear to synthesize new insights and potentially guide future research aimed at promoting HC regeneration in the adult cochlea.