Understanding hormone and hormone therapies' impact on the auditory system

Advances in the Study of Etiology and Molecular Mechanisms of Sensorineural Hearing Loss

Sensorineural hearing loss (SNHL), a multifactorial progressive disorder, results from a complex interplay of genetic and environmental factors, with its underlying mechanisms remaining unclear. Several pathological factors are believed to contribute to SNHL, including genetic factors, ion homeostasis, cell apoptosis, immune inflammatory responses, oxidative stress, hormones, metabolic syndrome, human cytomegalovirus infection, mitochondrial damage, and impaired autophagy. These factors collectively interact and play significant roles in the onset and progression of SNHL. The present review offers a comprehensive overview of the various factors that contribute to SNHL, emphasizes recent developments in understanding its etiology, and explores relevant preventive and intervention measures.

Bone-turnover biomarkers as potential prognostic factors in sudden sensorineural hearing loss: A prospective cohort study

Objectives

This study aims to explore the relationship between bone-turnover biomarkers and the recovery of SSNHL to provide clues for further improvements in etiological research and predictors.

Methods

The medical history, hearing thresholds, biomarkers of bone-turnover, and related hormones of 117 SSNHL patients were collected prospectively between August 2018 and December 2021. Linear correlation and logistic regression models were applied to examine the association between bone-turnover biomarkers and the prognosis of SSNHL.

Results

Age, the incidence of vertigo, pure tone average of the impaired frequencies (PTAimpairedfre), and the levels of bone turnover [including alkaline phosphatase (ALP), β-carboxy terminal crosslinked telopeptide of type 1 collagen (β-CTX), and N-terminal-midfragment of osteocalcin (N-MID)] were higher in the nonresponders than responders (P < 0.05). Logistic regression showed that the age (OR = 1.035, P = 0.027), time to treatment (OR = 1.157, P = 0.038), PTAimpairedfre (OR = 1.031, P = 0.008), and β-CTX (OR = 1.004, P = 0.001) were independent risk factors for the prognosis of SSNHL. In the women SSNHL subgroup, age, postmenopause percentage, PTAimpairedfre, the activity of ALP, levels of β-CTX, and N-MID were significantly higher in the nonresponders than the responders (P < 0.05). Compared to the men SSNHL subgroup, β-CTX has a higher correlation coefficient and predictive efficiency in the women SSNHL subgroup, and logistic regression showed that β-CTX (OR = 1.004, P = 0.004) was an independent risk factor for the women SSNHL.

Conclusions

Bone-turnover biomarkers are risk factors for poor prognosis in SSNHL, especially β-CTX. The differences were significant in women SSNHL, which may be related to the rapid regression of estrogen after menopause that leads to the occurrence of osteoporosis with a high conversion rate.

Insulin-like Growth Factor 1 Signaling in Mammalian Hearing

Insulin-like growth factor 1 (IGF-1) is a peptide hormone belonging to the insulin family of proteins. Almost all of the biological effects of IGF-1 are mediated through binding to its high-affinity tyrosine kinase receptor (IGF1R), a transmembrane receptor belonging to the insulin receptor family. Factors, receptors and IGF-binding proteins form the IGF system, which has multiple roles in mammalian development, adult tissue homeostasis, and aging. Consequently, mutations in genes of the IGF system, including downstream intracellular targets, underlie multiple common pathologies and are associated with multiple rare human diseases. Here we review the contribution of the IGF system to our understanding of the molecular and genetic basis of human hearing loss by describing, (i) the expression patterns of the IGF system in the mammalian inner ear; (ii) downstream signaling of IGF-1 in the hearing organ; (iii) mouse mutations in the IGF system, including upstream regulators and downstream targets of IGF-1 that inform cochlear pathophysiology; and (iv) human mutations in these genes causing hearing loss.

[Hormonal influence on hearing]

BACKGROUND

Hearing loss leads to impairments in communication, social interactions, and cognitive functions. This renders early treatment particularly important. A causal therapy is not yet available. Human and animal studies have shown that certain hormones can have a positive effect on hearing.

OBJECTIVE

This review provides an overview of the effects of various hormones on hearing and describes the potential benefit for future therapeutic approaches.

MATERIALS AND METHODS

A systematic literature review of reviews dealing with the effects of various hormones on hearing in humans and animals published in PubMed between 2015 and 2020 was conducted.

RESULTS

Hormones may mediate antiapoptotic effects on structure-relevant cells of the cochlea and auditory pathway, and may influence hair cell functionality or the electrolyte balance of the endo- and perilymph. Current research focuses on glucocorticoids; the mineral corticoid aldosterone; the sex hormones estrogen, progesterone, and testosterone; the growth hormones GH (growth hormone) and IGF‑1 (insulin-like growth factor 1); thyroid hormones; and insulin. Study results are still inconsistent at this time, but various hormones appear to represent a possible future treatment option for acute hearing loss. Long-term hormone treatment, which would be necessary particularly in the case of age-related hearing loss, does not currently represent a sensible course of action due to the side effect profile of the systemic treatment/lack of practicable topical application options.

CONCLUSION

The mode of action of hormones is complex. Whether they can be used in the future for individualized treatment of patients with acute hearing impairment requires further investigation.

Age-related hearing loss: Why we need to think about sex as a biological variable

It has long been known that age-related hearing loss (ARHL) is more common, more severe, and with an earlier onset in men compared to women. Even in the absence of confounding factors such as noise exposure, these sexdifferences in susceptibility to ARHL remain. In the last decade, insight into the pleiotrophic nature by which estrogen signaling can impact multiple signaling mechanisms to mediate downstream changes in gene expression and/or elicit rapid changes in cellular function has rapidly gathered pace, and a role for estrogen signaling in the biological pathways that confer neuroprotection is becoming undeniable. Here I review the evidence why we need to consider sex as a biological variable (SABV) when investigating the etiology of ARHL. Loss of auditory function with aging is frequency-specific and modulated by SABV. Evidence also suggests that differences in cochlear physiology between women and men are already present from birth. Understanding the molecular basis of these sex differences in ARHL will accelerate the development of precision medicine therapies for ARHL.