Bilirubin-induced neurotoxic and ototoxic effects in rat cochlear and vestibular organotypic cultures

The pyroptosis mechanism of ototoxicity caused by unconjugated bilirubin in neonatal hyperbilirubinemia

When activated by unconjugated bilirubin (UCB), inflammatory mediators such as IL - 18 and TNF contribute to the neurotoxicity and ototoxicity observed in severe neonatal hyperbilirubinemia. However, in cell and molecular level, the regulation and mechanism of UCB-induced ototoxicity are remained unclear. In this study, 7-day-old mammary rats were exposed to various concentrations of UCB to imitate the infant auditory damage. The auditory brainstem response result (ABR) indicated severe hearing loss, which occurred with increasing concentration. Morphological analysis of organotypic cochlear cultures treated with different concentrations of UCB indicated that auditory nerve fibers (ANF) were demyelinated and the density of spiral ganglion neurons (SGN) were decreased. In addition, HEI-OC1 cells treated with different concentrations of UCB showed severe necrosis by Flow Cytometry. The morphologic feature of pyroptosis has been observed by scanning electronic microscope. Cleaved Caspase-1, GSDMD and NLRP3 expression were significantly increased in cochlear explants with UCB-induced. To further clarify the molecular mechanism of UCB-induced inner ear cell pyroptosis, specific inhibitors of pyroptosis were applied, the protein associated with pyrotosis such as Cleaved Caspase-1, GSDMD, ASC, IL-18 and NLRP3 were significantly lower than the group with UCB alone. All the data above indicated that ERK /NLRP3/GSDMD signaling pathway involved in UCB-induced ototoxicity.

Protective effect of anakinra on audiovestibular function in a murine model of endolymphatic hydrops

Introduction

Ménière's disease (MD), a common disease in the inner ear, is characterized by an increase in endolymph in the cochlear duct and vestibular labyrinth. The pathophysiology of the condition appears to be the immune response. Studies have shown that basal levels of the IL-1β increased in some MD patients.

Methods

Here, we used a murine model of endolymphatic hydrops (EH) to study the effect of anakinra on auditory and vestibular function. Mice were intraperitoneal injected with anakinra or saline before LPS by postauricular injection. Weight and disease severity were measured, histologic changes in auditory were assessed, and inflammation state was evaluated.

Results

We found that anakinra therapy reduced LPS-induced EH, alleviated LPS-induced hearing loss and vestibular dysfunction, and inhibited the expression of the inflammatory cytokines and macrophage infiltration in the cochlea of mice. We further demonstrated that anakinra ameliorated the disorganization and degeneration of myelin sheath, and reduced the neuron damage in cochlea of EH mice.

Discussion

Consequently, anakinra contributes to a promising therapeutic approach to MD, by restricting EH, alleviating auditory and vestibular function, inhibiting inflammation of the inner ear and protecting the cochlear nerve. Further investigations are needed to assess the potential therapeutic benefits of anakinra in patients with MD.

Animal Kernicterus Models: Progress and Challenges

Kernicterus is a leading cause of neonatal death throughout the world, especially in low-middle-income countries. It is developed by an unconjugated hyperbilirubinemia in the blood and brain tissue, triggering pathological processes that spawn neurotoxicity and neurodegeneration. However, the biological mechanism (s) of bilirubin-induced neurotoxicity and Kernicterus development remain to be well elucidated. Likewise, a practical therapeutic approach for human Kernicterus has yet to be found. Undoubtedly, animal models of Kernicterus can be helpful in the identification of underlying biological processes of hyperbilirubinemia evolution to Kernicterus, as well as the evaluation of various treatments efficacy in preclinical studies. More importantly, establishing an animal model that can mimic the Kernicterus and its behavioral, neuro-histological, and hematological manifestations is a severe priority in preclinical studies. So far, several Kernicterus animal models have been established that could partially mimic one or more clinical and paraclinical signs of human Kernicterus. The present study aimed to review all methods modeling Kernicterus with a focus on their potentials and shortcomings and subsequently provide the optimal methods for an ideal Kernicterus animal model.

Inhibitory Effects of Bilirubin on Colonization and Migration of A431 and SK-MEL-3 Skin Cancer Cells Compared with Human Dermal Fibroblasts (HDF)

This study evaluated the inhibitory effects of bilirubin on colony formation and cell migration of melanoma and non-melanoma skin cancer cell lines SK-MEL-3 and A431, compared with normal human dermal fibroblasts (HDF). The IC₅₀ obtained from the MTT assay was 125, 100, and 75 μM bilirubin for HDF, A431, and SK-MEL-3 cells, respectively. The colony formation and cell migration of cancer cells, treated with 100 μM bilirubin, were reduced significantly (p < 0.05). Bilirubin decreased cell adhesion and inhibited cell colonization via inducing apoptosis and cell death. Also by interaction with migration main factors, bilirubin caused inhibition the cell migration.

Association between Hyperbilirubinemia and Hearing Screen Failure in the Neonatal Intensive Care Unit in Infants Born Preterm

OBJECTIVE

To characterize the association between hyperbilirubinemia and a failed newborn hearing screen in infants born at 22-32 weeks of gestation.

STUDY DESIGN

We included infants with gestational ages of 22-32 weeks who were discharged from neonatal intensive care units in the US from 2002 to 2017 with available newborn hearing screen results obtained after 34 weeks postmenstrual age. We excluded infants with severe birth asphyxia or craniofacial abnormalities. We identified 95 672 infants from 313 neonatal intensive care units. We used multivariable logistic regression to examine the association between maximum total bilirubin at <21 days postnatal age with failed hearing screen, adjusting for important demographic and clinical risk factors.

RESULTS

The median gestational age and birth weight were 30 weeks (IQR, 28-32 weeks) and 1330 g (IQR, 1010-1630 g), respectively. The median maximum total bilirubin was 8.3 mg/dL (IQR, 6.7-10.0 mg/dL), and 5275 infants (6%) failed their newborn hearing screen. On adjusted analysis, each 1 mg/dL increase in maximum total bilirubin was associated with a small, but significant, increase in odds of a failed hearing screen (OR, 1.03; 95% CI, 1.02-1.04).

CONCLUSIONS

An increased maximum total bilirubin level was independently associated with hearing screen failure. Further prospective studies are needed to understand whether this increased risk of hearing screen failure translates to increased risk of hearing loss.

Molecular Physiology and Pathophysiology of Bilirubin Handling by the Blood, Liver, Intestine, and Brain in the Newborn

Bilirubin is the end product of heme catabolism formed during a process that involves oxidation-reduction reactions and conserves iron body stores. Unconjugated hyperbilirubinemia is common in newborn infants, but rare later in life. The basic physiology of bilirubin metabolism, such as production, transport, and excretion, has been well described. However, in the neonate, numerous variables related to nutrition, ethnicity, and genetic variants at several metabolic steps may be superimposed on the normal physiological hyperbilirubinemia that occurs in the first week of life and results in bilirubin levels that may be toxic to the brain. Bilirubin exists in several isomeric forms that differ in their polarities and is considered a physiologically important antioxidant. Here we review the chemistry of the bilirubin molecule and its metabolism in the body with a particular focus on the processes that impact the newborn infant, and how differences relative to older children and adults contribute to the risk of developing both acute and long-term neurological sequelae in the newborn infant. The final section deals with the interplay between the brain and bilirubin and its entry, clearance, and accumulation. We conclude with a discussion of the current state of knowledge regarding the mechanism(s) of bilirubin neurotoxicity.

A prospective observational study to investigate the correlation analysis between neonatal hyperbilirubinemia and deafness gene: Study protocol clinical trial (SPIRIT compliant)

INTRODUCTION

There are many studies on the relationship between serum levels of hyperbilirubinemia and hearing impairment. However, the mechanism of hyperbilirubinemia on auditory impairment is not clear.

METHODS AND ANALYSIS

A total of 1000 children with hyperbilirubinemia who are mainly indirectly elevated bilirubin in the full-term neonatal ward of Xiamen Children's Hospital from March 2020 to September 2020 will be enrolled. Using second-generation high-throughput sequencing technology, 127 deaf-related genes were sequenced from the collected samples. At the same time, physical audiometry was performed on the selected persons and audiometry data were recorded.

DISCUSSION

In this study, we will combine gene sequencing with clinical indications of hyperbilirubinemia to find the loci suitable for high-frequency pathogenic deafness related to hyperbilirubinemia, so as to provide early guidance for deafness gene screening in children with hyperbilirubinemia.

TRIAL REGISTRATION

Chinese Clinical trial registry: ChiCTR2000030075.

Review of bilirubin neurotoxicity I: molecular biology and neuropathology of disease

Despite the availability of successful prevention strategies to prevent excessive hyperbilirubinemia, the neurological sequelae of bilirubin neurotoxicity (BNTx) still occur throughout the world. Kernicterus, encephalopathy due to BNTx, is now understood to be a spectrum of severity and phenotypes known as kernicterus spectrum disorder (KSD). A better understanding of the selective neuropathology and molecular biology of BNTx and using consistent clinical definitions of KSDs as outcome measure can lead to more accurately predicting the risk and causes of BNTx and KSDs. In Part I of our two-part review, we will summarize current and recent advances in the understanding of the selective neuropathology and molecular biology of the disease. Herein we emphasize the role of unbound, free unconjugated bilirubin as well as genetic contributions to the susceptibility BNTx and the development of KSDs. In Part II, we focus on current and possible novel methods to prevent BNTx and ABE and treat ABE and KSDs.