Future therapeutic strategies for olfactory disorders: electrical stimulation, stem cell therapy, and transplantation of olfactory epithelium-an overview

Devices for the electrical stimulation of the olfactory system: A review

The loss of olfactory function has a profound impact on quality of life, affecting not only sensory perception but also memory, emotion, and overall well-being. Despite this, advancements in olfactory prostheses have lagged significantly behind those made for vision and hearing restoration. This review offers a comprehensive analysis of the current state of devices for electrical stimulation of the olfactory system. We begin by providing an overview of the olfactory system's structure and function, emphasizing the neural pathways involved in smell perception. Following this, we explore the key challenges associated with chronic implantation and electrical stimulation, material biocompatibility, inflammation risks, and ensuring long-term functionality and durability. A detailed analysis of existing neural stimulation devices-including ECoG, intracortical, and depth electrodes-is presented, assessing their potential for application in olfactory stimulation. We also discuss the limitations and pitfalls of current approaches and explore new emerging technologies aimed at overcoming these obstacles. A comprehensive literature review about the olfactory system electrical stimulation is reported, and results are analyzed to identify the most promising routes. Finally, the review highlights emerging technologies, ongoing research, and the ethical considerations associated with olfactory implants, along with future directions for developing more effective, safe, and durable solutions to restore the sense of smell for individuals with olfactory disorders.

The impact of COVID-19-related smell dysfunction on sexual and mental wellbeing: Data from a longitudinal sample

OBJECTIVE

Olfactory disorders are associated with poor sexual and mental wellbeing, but prior work mainly consists of retrospective and cross-sectional reports. The current study assessed their prospective associations.

METHODS

73 patients with COVID-19-associated olfactory dysfunction were recruited between 2021 and 2023 at a Smell Clinic in Dresden, Germany. Patients were assessed twice, about 6 months apart. On each occasion, patients' olfactory functioning (i.e., psychophysical tests and self-rated function) and sexual and mental wellbeing were measured (i.e., sexual frequency, sexual desire, wellbeing, anxiety symptoms, and depressive symptoms).

RESULTS

Within-person improvements in psychophysical olfactory functioning were associated with increased sexual frequency. In a subset of 51 people in stable romantic partnerships, improved psychophysical olfactory functioning predicted increased sexual frequency and increased sexual desire. No evidence emerged supporting an association between improvements in olfactory functioning and mental health or wellbeing outcomes CONCLUSIONS: A decline in sexual function may be an early reaction to olfactory dysfunction. Individuals with recent onset of olfactory disorders may benefit from sexual health support.

Altered PLCβ/IP3/Ca2+ Signaling Pathway Activated by GPRCs in Olfactory Neuronal Precursor Cells Derived from Patients Diagnosed with Schizophrenia

Background: Schizophrenia (SZ) is a multifactorial chronic psychiatric disorder with a worldwide prevalence of 1%. Altered expression of PLCβ occurs in SZ patients, suggesting alterations in the PLCβ/IP3/Ca2+ signaling pathway. This cascade regulates critical cellular processes in all cell types, including the neuronal lineage; however, there is scarce evidence regarding the functionality of this transduction signaling in neuronal cells derived from SZ patients. Objective: We evaluated the functionality of the PLCβ/IP3/Ca2+ pathway in olfactory neuronal precursor cells (hONPCs) obtained from SZ patients. Methods: Cryopreserved hONPCs isolated from SZ patients and healthy subjects (HS) were thawed. The cellular types in subcultures were corroborated by immunodetection of the multipotency and lineage markers SOX-2, Musashi-1, nestin, and β-III tubulin. The PLCβ/IP3/Ca2+ pathway was activated by GPCR (Gq) ligands (ATP, UTP, serotonin, and epinephrine). In addition, PLCβ and IP3R were directly stimulated by perfusing cells with the activators m-3M3FBS and ADA, respectively. Cytosolic Ca2+ was measured by microfluorometry and by Ca2+ imaging. The amount and subcellular distribution of the PLCβ1 and PLCβ3 isoforms were evaluated by confocal immunofluorescence. IP3 concentration was measured by ELISA. Results: The results show that the increase of cytosolic Ca2+ triggered by GPCR ligands or directly through either PLCβ or IP3R activation was significantly lower in SZ-derived hONPCs, regarding HS-derived cells. Moreover, the relative amount of the PLCβ1 and PLCβ3 isoforms and IP3 production stimulated with m-3M3FBS were reduced in SZ-derived cells. Conclusions: Our results suggest an overall functional impairment in the PLCβ/IP3/Ca2+ signaling pathway in SZ-derived hONPCs.

Tissue Engineering and Regenerative Medicine in the Field of Otorhinolaryngology

BACKGROUND

Otorhinolaryngology is a medical specialty that focuses on the clinical study and treatments of diseases within head and neck regions, specifically including the ear, nose, and throat (ENT), but excluding eyes and brain. These anatomical structures play significant roles in a person's daily life, including eating, speaking as well as facial appearance and expression, thus greatly impacting one's overall satisfaction and quality of life. Consequently, injuries to these regions can significantly impact a person's well-being, leading to extensive research in the field of tissue engineering and regenerative medicine over many years.

METHODS

This chapter provides an overview of the anatomical characteristics of otorhinolaryngologic tissues and explores the tissue engineering and regenerative medicine research in otology (ear), rhinology (nose), facial bone, larynx, and trachea.

RESULTS AND CONCLUSION

The integration of tissue engineering and regenerative medicine in otorhinolaryngology holds the promise of broadening the therapeutic choices for a wide range of conditions, ultimately improving quality of a patient's life.

The current possibilities of diagnosing and therapies for olfactory disorders

INTRODUCTION

Olfactory disorders significantly affect individuals, diminishing their capacity to detect dangers, appreciate flavors, and engage socially. Despite their considerable impact on quality of life, these disorders often receive less attention compared to other sensory impairments. This review emphasizes the importance of olfactory function and explores both traditional and innovative diagnostic and therapeutic approaches.

AREAS COVERED

This review comprehensively covers the pathophysiology, diagnostic challenges, and treatment options for olfactory disorders. It delves into the nuances of different disorders, such as anosmia and parosmia, and discusses the array of diagnostic tools from traditional sniff tests to advanced imaging techniques. The review also evaluates therapeutic strategies, from pharmacological treatments to emerging therapies like electrical stimulation and regenerative medicine, highlighting recent advances in the field.

EXPERT OPINION

Current insights suggest a growing recognition of the significance of olfactory disorders, driven by recent pandemics and advances in diagnostic and therapeutic technologies. Future perspectives indicate a promising direction toward more personalized medicine approaches and enhanced regenerative therapies. Continuous research and improved clinical awareness are critical for evolving the management strategies of olfactory impairments, potentially leading to better patient outcomes and quality of life enhancements.

Recovery rates and long-term olfactory dysfunction following COVID-19 infection

Objectives

Olfactory dysfunction is one of the most recognized symptoms of COVID-19, significantly impacting quality of life, particularly in cases where recovery is prolonged. This review aims to explore patterns of olfactory recovery post-COVID-19 infection, with particular focus on delayed recovery.

Data Sources

Published literature in the English language, including senior author's own work, online and social media platforms, and patients' anecdotal reports.

Method

A comprehensive review of the literature was undertaken by the authors with guidance from the senior author with expertise in the field of olfaction.

Results

Based on self-report, an estimated 95% of patients recover their olfactory function within 6 months post-COVID-19 infection. However, psychophysical testing detects higher rates of persistent olfactory dysfunction. Recovery has been found to continue for at least 2 years postinfection; negative prognostic indicators include severe olfactory loss in the acute phase, female sex, and older age. Variability in quantitative and qualitative disturbance in prolonged cases likely reflects both peripheral and central pathophysiological mechanisms. Limitations of many of the reviewed studies reflect lack of psychophysical testing and baseline olfactory assessment.

Conclusions

Post-COVID-19 olfactory dysfunction remains a significant health and psychosocial burden. Emerging evidence is improving awareness and knowledge among clinicians to better support patients through their olfactory rehabilitation, with hope of recovery after several months or years. Further research is needed to better understand the underlying pathogenesis of delayed recovery, identify at risk individuals earlier in the disease course, and develop therapeutic targets.

What do brain oscillations tell about the human sense of smell?

Brain activity may manifest itself as oscillations which are repetitive rhythms of neuronal firing. These local field potentials can be measured via intracranial electroencephalography (iEEG). This review focuses on iEEG used to map human brain structures involved in olfaction. After presenting the methodology of the review, a summary of the brain structures involved in olfaction is given, followed by a review of the literature on human olfactory oscillations in different contexts. A single case is provided as an illustration of the olfactory oscillations. Overall, the timing and sequence of oscillations found in the different structures of the olfactory system seem to play an important role for olfactory perception.