Mild maternal iron deficiency anemia induces DPOAE suppression and cochlear hair cell apoptosis by caspase activation in young guinea pigs

Iron deficiency at birth and risk of hidden hearing loss in infants modification by socioeconomic status: mother-newborn cohort in Shenyang, China

OBJECTIVE

The diagnosis of hidden hearing loss (HHL) in calm state has not yet been determined, while the nutritional status is not involved in its pathogenic risk factors. In utero iron deficiency (ID) may delay auditory neural maturation in infants. We evaluated the association between ID and HHL as well as the modification effect of socioeconomic status (SES) on this association in newborns.

STUDY DESIGN

We included 859 mother-newborns from the baseline of this observational northeast cohort. Data on exposure assessment included iron status [maternal hemoglobin (Hb) and neonatal heel prick serum ferritin (SF)] and SES (occupation, education and income). Auditory neural maturation was reflected by auditory brainstem response (ABR) testing and electrocochleography (ECochG).

RESULTS

Iron status and SES were independently and jointly associated with the prediction of neonatal HHL by logistic and linear regression model. The mediation effects were performed by Process. ID increased absolute latency wave V, interpeak latency (IPL) III-V, and summting potentials (SP) /action potentials (AP), which were combined as HHL. Low SES showed the highest risk of HHL and the highest levels of related parameters in ID newborns. Moreover, after Corona Virus Disease 2019 (COVID-19) were positive, preschool children who experience ID in neonatal period were more likely to suffer from otitis media with effusion (OME). High SES also showed similar risk effects.

CONCLUSION

Both low and high SES may strengthen the risk of ID on neonatal HHL in Northeast China.

A review of the auditory-gut-brain axis

Hearing loss places a substantial burden on medical resources across the world and impacts quality of life for those affected. Further, it can occur peripherally and/or centrally. With many possible causes of hearing loss, there is scope for investigating the underlying mechanisms involved. Various signaling pathways connecting gut microbes and the brain (the gut-brain axis) have been identified and well established in a variety of diseases and disorders. However, the role of these pathways in providing links to other parts of the body has not been explored in much depth. Therefore, the aim of this review is to explore potential underlying mechanisms that connect the auditory system to the gut-brain axis. Using select keywords in PubMed, and additional hand-searching in google scholar, relevant studies were identified. In this review we summarize the key players in the auditory-gut-brain axis under four subheadings: anatomical, extracellular, immune and dietary. Firstly, we identify important anatomical structures in the auditory-gut-brain axis, particularly highlighting a direct connection provided by the vagus nerve. Leading on from this we discuss several extracellular signaling pathways which might connect the ear, gut and brain. A link is established between inflammatory responses in the ear and gut microbiome-altering interventions, highlighting a contribution of the immune system. Finally, we discuss the contribution of diet to the auditory-gut-brain axis. Based on the reviewed literature, we propose numerous possible key players connecting the auditory system to the gut-brain axis. In the future, a more thorough investigation of these key players in animal models and human research may provide insight and assist in developing effective interventions for treating hearing loss.

Distortion product otoacoustic emissions in newborn babies with and without late-term maternal iron deficiency anaemia

Background

Studies on animals have demonstrated that maternal iron deficiency anaemia (IDA) could result in decreased cochlear sensory hair cells and reduced amplitudes of distortion-product otoacoustic emissions (DPOAEs) of young guinea pigs. Thus, it is essential to study the functioning of cochlear hair cells using DPOAEs in human newborn babies with maternal IDA. The current study explores maternal IDA's effect on DPOAEs in newborn babies.

Method

A total of 110 newborn babies with gestational age ≥34 weeks were considered and a 'between-subjects' design was used. The participants were divided into 3 groups- "Normal" (61 babies without maternal IDA), "Mild" (28 babies with mild maternal IDA) and "Moderate" (21 babies with moderate maternal IDA). The cord blood was collected and the DPOAEs were recorded for each baby for a range of frequencies (1 k - 8 kHz) and a range of intensities (70-40 dB SPL in 10 dB steps).

Results

The analysis of both DP-gram and DP input-output (I/O) function showed that there was no significant difference (p > 0.05) across the normal, mild, and moderate groups in the overall presence of DPOAEs as well as the amplitude across frequencies or intensities (70-40 dB SPL). Also, the overall correlation of RBC indices with DPOAE amplitude across frequencies as well as the slope of the I/O function showed no relationship.

Conclusion

The current study concludes that there is no effect of late-term maternal IDA on the DPOAEs of newborn babies.

The effect of increase in blood glucose level on hearing loss

OBJECTIVE

Previous studies have shown that hearing function is also vulnerable to the effects of diabetes mellitus which can be shown by brainstem auditory evoked potential and distortion product otoacoustic emission recordings. This study aimed to investigate the changes of brainstem auditory evoked potential and distortion product otoacoustic emission in hyperglycemia and whether there is a relationship between reactive oxygen substances production and hearing deterioration in the rat model.

METHODS

25 streptozotocin induced diabetic rats were divided into three groups: control, high blood glucose, and diabetes mellitus. Brainstem auditory evoked potential and distortion product otoacoustic emission were recorded, and thiobarbituric acid reactive substances levels were measured in the brainstem tissue.

RESULTS

At 8 kHz, the latencies of I, II, III, IV, and V brainstem auditory evoked potential waves in high blood glucose and diabetes mellitus groups were elongated, at 16 kHz, only these wave latencies of the diabetes mellitus group were prolonged compared with the control group. A significant decrease was also found in distortion product otoacoustic emission amplitudes at 4, 6, 8, and 10 kHz in the high blood glucose and diabetes mellitus groups compared to the control group. There was a significant increase in thiobarbituric acid reactive substances values due to the increase in blood glucose levels in the high blood glucose and diabetes mellitus groups compared to the control group.

CONCLUSION

These results suggested that high blood glucose levels may cause hearing impairment not only in the diabetic state but also in the period of hyperglycemia before the onset of manifest diabetes mellitus and reactive oxygen substances may play an important role in the pathophysiology of diabetes mellitus. We suggest that regulating high glucose levels even before the onset of manifest diabetes mellitus may prevent hazardous effects on hearing function.

LEVEL OF EVIDENCE

Level 3.

Outer hair cell functioning in infants with iron deficiency anemia

BACKGROUND

Distortion product otoacoustic emissions (DPOAE) in infants with Iron Deficiency Anemia (IDA) helps in understanding the cochlear status especially the functioning of outer hair cells.

OBJECTIVES

To analyze the presence of DPOAE across frequencies and DP amplitude in infants with and without IDA.

METHOD

DPOAE were recorded on 40 infants with IDA and 40 infants without IDA in the age range of 6-24 months. Cubic DPOAEs (2f1-f2) were measured at six f2 frequencies (1500 Hz, 2000 Hz, 3000 Hz, 4500 Hz, 6000 Hz & 8000 Hz) with primary tone stimulus of intensity L1 equal to 65 dBSPL and L2 equal to 55 dBSPL. Immittance audiometry was performed using 226 Hz probe tone prior to DPOAE recording to ascertain normal middle ear functioning.

RESULTS

DPOAEs were present in all infants with and without IDA across frequencies tested. DP amplitude across the frequencies did not show any statistically significant difference (p < 0.05) between anemic and non-anemic groups. There was no statistically significant difference observed when both the groups were compared in terms of gender and age.

CONCLUSION

The study indicated that reduced iron levels does not have any influence on outer hair cell functioning as there were no changes observed in the DPOAE amplitude levels between infants with IDA and infants without IDA. Iron status does not seem to have a direct effect on outer hair cell functioning in infants. However, fine structure DPOAEs can reveal even more precise changes (if any) that are caused due to iron deficiency.

Interplay between Nutrition and Hearing Loss: State of Art

Hearing loss has been recently ranked as the fifth leading cause of years lived with disability, ahead of many other chronic diseases such as diabetes, dementia, or chronic obstructive pulmonary disease. Moreover, according to the World Health Organization, moderate-to-profound hearing loss affects about 466 million people worldwide. Its incidence varies in each population segment, affecting approximately 10% of children and increasing to 30% of the population over 65 years. However, hearing loss receives still very limited research funding and public awareness. This sensory impairment is caused by genetic and environmental factors, and among the latter, the nutritional status has acquired relevance due its association to hearing loss detected in recent epidemiological studies. Several experimental models have proved that the onset and progression of hearing loss are closely linked to the availability of nutrients and their metabolism. Here, we have reviewed studies focused on nutrient effects on auditory function. These studies support the potential of nutritional therapy for the protection against hearing loss progression, which is especially relevant to the aging process and related quality of life.

Auditory brainstem response in full-term neonates born to mothers with iron deficiency anemia: relation to disease severity

Background: Iron is crucial for fetal brain development; however, there are insufficient data regarding the effects of maternal iron deficiency anemia (IDA) on auditory neural maturation.Aim: We evaluated the effect of maternal IDA on auditory brainstem response (ABR) in full-term neonates.Methods: Out of 223 pregnant women, 50 were diagnosed as having IDA and 50 healthy mothers were enrolled as controls. ABR test was done for the studied neonates within 48 hours after birth and at 3 months.Results: We found that hemoglobin and iron profile were lower in neonates born to anemic mothers compared with controls. Of 100 neonates screened for ABR, 25 failed the test (all of them were born to anemic mothers). The majority of neonates who failed the screening ABR test (88%) had latent iron deficiency (cord blood ferritin 11-75 µg/L). After 3 months, 85 neonates underwent diagnostic ABR test which revealed significantly prolonged interpeak latencies I-III, III-V, and I-V among neonates born to IDA mothers compared with the control group. Within the IDA group, all interpeak latencies were more prolonged in neonates with latent iron deficiency and in those born to mothers with serum ferritin <15 µg/L. Logistic regression analysis showed that maternal hemoglobin and mean corpuscular volume could predict neonatal ABR results.Conclusions: IDA during late pregnancy adversely affects cord blood iron and hearing status. ABR results are closely related to the severity of maternal and neonatal iron status. Antenatal screening of pregnant mothers is needed to improve fetal iron status and prevent abnormal auditory maturation.

Lycium barbarum polysaccharides attenuates N-methy-N-nitrosourea-induced photoreceptor cell apoptosis in rats through regulation of poly (ADP-ribose) polymerase and caspase expression

ETHNOPHARMACOLOGICAL RELEVANCE

Lycium barbarum L., popularly known as "Goji berry", a classic of Traditional Chinese Medicine has long been used to treat ocular diseases and cardiovascular diseases. Recently, the photoreceptor cell protection of Lycium barbarum polysaccharides (LBP), a water extract from Lycium barbarum L. has received more attention. The present study was designed to investigate the effect of LBP on N-methyl-N-nitrosourea (MNU)-induced photoreceptor cell apoptosis, and the involvement of the poly (ADP-ribose) polymerase (PARP) and caspase.

MATERIALS AND METHODS

Photoreceptor cell injury was induced in male Sprague-Dawley rats by an intraperitoneal injection of MNU 60mg/kg. Seven days prior to MNU injection, LBP were intragastrical administered daily, rats were sacrificed at 24h and 7 days after MNU injection. Retinal morphologies, photoreceptor cells apoptosis, and protein expression were evaluated at 24h and 7 days after MNU injection.

RESULTS

Morphologically, the outer nuclear layer was well preserved in the LBP-treated rat retinas throughout the experimental period. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-digoxigenin nick-end labeling (TUNEL) assays showed that LBP could significantly suppress the loss of photoreceptor cells, as determined by the photoreceptor cell ratio at the central retina 24h and 7 days after MNU administration. Western-blot analysis demonstrated the expression levels of procaspase-9, -7, -3 and cleaved caspase-9, -7, -3 were upregulated, and PARP were downregulated both 24h and 7 days after MNU injection. LBP treatment significantly decreased protein levels of procaspase and cleaved caspase, increased the level of PARP and cleaved PARP on 24h and 7 days.

CONCLUSIONS

LBP inhibits MNU-induced rat photoreceptor cell apoptosis and protects retinal structure via the regulation of the expressions of PARP and caspase.

Low Iron Diet Increases Susceptibility to Noise-Induced Hearing Loss in Young Rats

We evaluated the role of iron deficiency (ID) without anemia on hearing function and cochlear pathophysiology of young rats before and after noise exposure. We used rats at developmental stages as an animal model to induce ID without anemia by dietary iron restriction. We have established this dietary restriction model in the rat that should enable us to study the effects of iron deficiency in the absence of severe anemia on hearing and ribbon synapses. Hearing function was measured on Postnatal Day (PND) 21 after induction of ID using auditory brainstem response (ABR). Then, the young rats were exposed to loud noise on PND 21. After noise exposure, hearing function was again measured. We observed the morphology of ribbon synapses, hair cells and spiral ganglion cells (SGCs), and assessed the expression of myosin VIIa, vesicular glutamate transporter 3 and prestin in the cochlea. ID without anemia did not elevate ABR threshold shifts, but reduced ABR wave I peak amplitude of young rats. At 70, 80, and 90 dB SPL, amplitudes of wave I (3.11 ± 0.96 µV, 3.52 ± 1.31 µV, and 4.37 ± 1.08 µV, respectively) in pups from the ID group were decreased compared to the control (5.92 ± 1.67 µV, 6.53 ± 1.70 µV, and 6.90 ± 1.76 µV, respectively) (p < 0.05). Moreover, ID without anemia did not impair the morphology hair cells and SGCs, but decreased the number of ribbon synapses. Before noise exposure, the mean number of ribbon synapses per inner hair cell (IHC) was significantly lower in the ID group (8.44 ± 1.21) compared to that seen in the control (13.08 ± 1.36) (p < 0.05). In addition, the numbers of ribbon synapses per IHC of young rats in the control (ID group) were 6.61 ± 1.59, 3.07 ± 0.83, 5.85 ± 1.63 and 12.25 ± 1.97 (3.75 ± 1.45, 2.03 ± 1.08, 3.81 ± 1.70 and 4.01 ± 1.65) at 1, 4, 7 and 14 days after noise exposure, respectively. Moreover, ABR thresholds at 4 and 8 kHz in young rats from the ID group were significantly elevated at 7 and 14 days after noise exposure compared to control (p < 0.05). The average number of young rat SGCs from the ID group were significantly decreased in the basal turn of the cochlea compared to the control (p < 0.05). Therefore, ID without anemia delayed the recovery from noise-induced hearing loss and ribbon synapses damage, increased SGCs loss, and upregulated prestin after noise exposure. Thus, the cochleae in rat pups with ID without anemia were potentially susceptible to loud noise exposure, and this deficit may be attributed to the reduction of ribbon synapses and SGCs.