Promotion of olfactory receptor neuron differentiation of olfactory neuroepithelial cells by using chitosan solution

Mechanism of Anosmia Caused by Symptoms of COVID-19 and Emerging Treatments

The occurrence of anosmia, the loss or change in sense of smell, is one of the most common symptoms of COVID-19 experienced by almost 53% of those affected. Several hypotheses explain the mechanism of anosmia in patients suffering from COVID-19. This study aims to review the related mechanisms and answer the questions regarding COVID-19-related anosmia as well as propose a new strategy for treatment of long-term anosmia as a result of COVID-19 infection. This paper covers all of the studies investigating olfactory disorders following COVID-19 infection and explains the possible reasons for the correlated anosmia, including olfactory cleft syndrome, local inflammation in the nasal epithelium, early apoptosis of olfactory cells, changes in olfactory cilia and odor transmission, damage to microglial cells, effect on olfactory bulbs, epithelial olfactory injury, and impairment of olfactory neurons and stem cells. The key questions that arise in this field have been discussed, such as why prevalent anosmia is varied among the age categories and among sexes and the correlation of anosmia with mild or severe COVID-19 infection. The angiotensin-converting enzyme 2 receptor is a significant player in the mechanism of anosmia in COVID-19 patients. Based on current studies, a novel approach to treat long-COVID-19 with ongoing anosmia has been proposed. The fields of smart drug delivery, tissue engineering, and cell therapy provide a hypothesized strategy that can minimize the side effects of current treatments and support efficient recovery of the olfactory system.

Regeneration of olfactory neuroepithelium in 3-methylindole-induced anosmic rats treated with intranasal chitosan

Olfactory dysfunction significantly impairs the life quality of patients but without effective treatments to date. The previous report has demonstrated that chitosan mediates the differentiation of olfactory receptor neurons (ORNs) through insulin-like growth factors and insulin-like growth factor binding protein-2 axis in an in vitro model. However, whether chitosan can further treat olfactory dysfunction in vivo remains unexplored. This study aims to evaluate the therapeutic effect of chitosan on a 3-methylindole-induced anosmic rat model. Intraperitoneal injection of 3-methylindole is performed to induce anosmia in rats. Experimental results demonstrate that the food-finding duration after chitosan treatment gradually decrease to around 80 s, and both the olfactory neuroepithelium (ON) thickness and mature ORNs (expressing olfactory marker protein) are significantly restored. Furthermore, proliferating cells (expressing bromodeoxyuridine) are mainly co-expressed with immature ORNs (expressing βIII tubulin) below the intermediate layer of the ON in the chitosan-treated group on day 28 following 3-methylindole treatment. Conversely, proliferating cells are scattered over the ON, and co-localized with immature ORNs and sustentacular cells (expressing keratin 18) in the sham group, and even immature ORNs go into apoptosis (expressing DNA fragmentation and cleaved caspase-3), possibly causing incomplete regeneration. Consequently, chitosan regenerates the ON by regulating olfactory neural homeostasis and reducing ORN apoptosis, and serves as a potential therapeutic intervention for olfactory dysfunction in the future.

Regulation of chitosan-mediated differentiation of human olfactory receptor neurons by insulin-like growth factor binding protein-2

Olfaction is normally taken for granted in our lives, not only assisting us to escape from dangers, but also increasing our quality of life. Although olfactory neuroepithelium (ON) can reconstitute its olfactory receptor neurons (ORNs) after injury, no adequate treatment for olfactory loss has yet emerged. The present study investigates the role of glycosaminoglycans (GAGs) in modulating olfactory neuronal homeostasis and elucidates the regulatory mechanism. This work isolates and cultures human olfactory neuroepithelial cells (HONCs) with various GAGs for 7 days, and find that chitosan promotes ORN maturation, expressing olfactory marker protein (OMP) and its functional components. Growth factor protein array, ELISA and western blot analysis reveal that insulin-like growth factor binding protein 2 (IGFBP2) shows a higher level in chitosan-treated HONCs than in controls. Biological activity of insulin-like growth factor-1 (IGF-1), IGF-2 and IGF-1 receptor (IGF1R) is further investigated. Experimental results indicate that IGF-1 and IGF-2 enhance the growth of immature ORNs, expressing βIII tubulin, but decrease mature ORNs. Instead, down-regulation of phosphorylated IGF1R lifts the OMP expression, and lowers the βIII tubulin expression, by incubation with the phosphorylated inhibitor of IGF1R, OSI-906. Finally, the effect of chitosan on ORN maturity is antagonized by concurrently adding IGFBP2 protease, matrix metallopeptidase-1. Overall, our data demonstrate that chitosan promotes ORN differentiation by raising the level of IGFBP2 to sequestrate the IGFs-IGF1R signaling. STATEMENT OF SIGNIFICANCE: Olfactory dysfunction serves as a crucial alarm in neurodegenerative diseases, and one of its causes is lacking of sufficient mature olfactory receptor neurons to detect odorants in the air. However, the clinical treatment for olfactory dysfunction is still controversial. Chitosan is the natural linear polysaccharide and exists in rat olfactory neuroepithelium. Previously, chitosan has been demonstrated to mediate the differentiation of olfactory receptor neurons in an in vitro rat model, but the mechanism is unknown. The study aims to evaluate the role and mechanism of chitosan in an in vitro human olfactory neurons model. Overall, these results reveal that chitosan is a potential agent for treating olfactory disorder by the maintenance of olfactory neural homeostasis. This is the first report to demonstrate that chitosan promotes differentiation of olfactory receptor neurons through increasing IGFBP2 to sequestrate the IGFs-IGF1R.

Chitosan-hyaluronan: promotion of mucociliary differentiation of respiratory epithelial cells and development of olfactory receptor neurons

Developing a biomaterial that promotes regeneration of both respiratory epithelium (RE) and olfactory neuroepithelium (ON) improves the surgical outcome of endoscopic sinus surgery. Although chitosan (CS) inhibits mucociliary differentiation of RE, it has been reported to regenerate ON. In addition, hyaluronic acid (HA) has been demonstrated to promote regeneration of RE. Whether the composite CS + HA would simultaneously benefit RE and ON remains unexplored. Human nasal respiratory epithelial cells (RECs) and olfactory neuroepithelial cells (ONCs) are respectively obtained from the RE and the ON. They are cultured in vitro and divided into groups undergoing four treatments, control, CS, HA, and CS + HA and assessed by scanning electron microscope, immunocytochemistry, and Western blots following indicated growth conditions. RECs keep polygonal morphology with mucociliary differentiation in the CS + HA group. The levels of E-cadherin, zonula occludens-1, mucin 5AC, and forkhead box protein J1 are significantly higher in the CS + HA group than in the CS alone group. In addition, ONCs express lower cytokeratin 18 (CK18) and higher olfactory marker protein (OMP) in the CS + HA group than in HA alone group. ONCs express more signal transduction apparatuses, adenylate cyclase 3, in CS and CS + HA groups than in HA and controls. Chitosan-hyaluronan plays a part in promoting differentiation of ORNs and facilitating mucociliary differentiation of RECs. This composite is a promising biomaterial for the sinonasal application.