Caffeine rapidly decreases potassium conductance of dissociated outer hair cells of guinea-pig cochlea

Association between caffeine intake from foods and beverages in the diet and hearing loss in United States adults

Background

Hearing loss (HL) is the third most prevalent condition, significantly affecting individuals and society. Recent research has explored the potential impact of nutrition, particularly caffeine intake, on HL. While some studies focus on coffee, caffeine intake should be assessed across all dietary sources. This study examines the association between dietary caffeine intake and HL.

Methods

Our cross-sectional study included 6,082 participants from the National Health and Nutrition Examination Survey (NHANES). Participants were divided into two groups based on their median caffeine intake: low and high. The study investigated two types of HL: speech-frequency hearing loss (SFHL) and high-frequency hearing loss (HFHL). Binary logistic regression analyzed the correlation between caffeine intake and HL, and a restricted cubic spline (RCS) model assessed potential non-linear associations. Subgroup analyses were also conducted.

Results

High caffeine intake was associated with significantly higher rates of SFHL and HFHL compared to low intake (SFHL: 15.4% vs. 10%, HFHL: 30.5% vs. 20.6%, both p < 0.001). Unadjusted logistic regression showed a higher likelihood of SFHL (OR[95%CI] = 1.65[1.41-1.92]) and HFHL (OR[95%CI] = 1.69[1.50-1.90]) in high caffeine consumers. After adjusting for confounders, high caffeine intake remained significantly associated with SFHL (OR[95%CI] = 1.35[1.09-1.66]) but not HFHL (OR[95%CI] = 1.14[0.96-1.35]). The RCS model indicated a linear increase in the risk of SFHL and HFHL with higher caffeine intake (non-linear p = 0.229 for SFHL, p = 0.894 for HFHL). Subgroup analysis revealed that increased caffeine intake was linked to higher SFHL and HFHL risks in participants under 65 years but not in those 65 years and older (SFHL: p for interaction = 0.002; HFHL: p for interaction <0.001).

Conclusion

Our study indicates a strong correlation between dietary caffeine intake and the risk of HL in American adults, particularly those under 65. High caffeine intake was linked to an increased risk of SFHL, but not HFHL, after adjusting for relevant variables.

The effect of coffee on contralateral suppression of transient evoked otoacoustic emissions

Background: Coffee is a popular non-alcoholic beverage consumed by humans across the world. It contains caffeine, which is a type of stimulant of the central nervous system. In the auditory system, it has a positive effect on auditory brainstem response and perception of speech in noise. Further, caffeine has an inhibitory effect in the cochlea, but studies have rarely investigated its effect on otoacoustic emissions (OAEs) in humans. OAEs are low-intensity sounds produced by the cochlea, which could be recorded in the ear canal. The present study was carried out to investigate the effect of coffee on transient evoked otoacoustic emission (TEOAE) and contralateral suppression of TEOAE. Method: A total of 52 young adults participated in the study. A cross-over study design was used for the present investigation. The TEOAE and contralateral suppression of TEOAE were recorded before and after consumption of coffee and milk. The contralateral suppression of TEOAE was measured by presenting white noise to the contralateral ear at 40, 50, and 60 dB sound pressure level (SPL). Results: The mean amplitude of TEOAE before and after consumption of coffee was similar in both ears. Further, the mean contralateral suppression of TEOAE was slightly larger after consumption of coffee in both ears. However, the mean difference was not significant in both the ears. Conclusions: Based on the findings of present study, coffee has no significant effect on the amplitude of TEOAE and contralateral suppression of TEOAE.

A comprehensive review of the effects of caffeine on the auditory and vestibular systems

Coffee, of which caffeine is a critical component, is probably the most frequently used psychoactive stimulant in the world. The effects of caffeine on the auditory and vestibular system have been investigated under normal and pathological conditions, such as acoustic trauma, ototoxicity, auditory neuropathy, and vestibular disorders, using various tests. Lower incidences of hearing loss and tinnitus have been reported in coffee consumers. The stimulatory effect of caffeine is represented by either a shorter latency or enhanced amplitude in electrophysiological tests of the auditory system. Furthermore, in the vestibular system, oculomotor testing revealed significant effects of caffeine, while other tests did not reveal any significant caffeine effects. It could be that caffeine improves transmission in the auditory and vestibular systems' central pathways. Importantly, the effects of caffeine seem to be dose-dependent. Also, inconsistent findings have been observed regarding caffeine's effects on the auditory and vestibular systems and related disorders. Overall, these findings suggest that caffeine does not strongly influence the peripheral auditory and vestibular systems. Instead, caffeine's effects seem to occur almost solely at the level of the central nervous system.

[Effects of the reduction of caffeine consumption on tinnitus perception]

INTRODUCTION

For many years, excessive caffeine consumption has been touted as an aggravating factor for tinnitus. The pathophysiology behind this effect is probably related to the blockage of adenosine receptors by the action of caffeine on the central nervous system.

OBJECTIVE

To evaluate the effects of reduction of coffee consumption on tinnitus sensation and to identify subgroups more prone to benefit from this therapeutic strategy.

STUDY DESIGN

Prospective.

METHODS

Twenty-six tinnitus patients who consumed at least 150 mL of coffee per day were selected. All were asked to reduce their coffee consumption. The Tinnitus Handicap Inventory (THI) questionnaire was completed by the patients before and after the reduction of coffee consumption, as well as a visual-analog scale (VAS) graduated from 1 to 10.

RESULTS

THI and VAS scores were significantly reduced (p<0.05). In the subgroups less than 60 years old, bilateral tinnitus and daily coffee consumption between 150 and 300 mL showed a significantly greater reduction of THI and VAS scores.

CONCLUSION

Patients under 60 years of age with bilateral tinnitus and daily coffee consumption between 150 and 300 mL are more prone to benefit from consumption reduction. Thirty-day observation periods may be helpful for a better therapeutical decision.

Dual regulation of the ATP-sensitive potassium channel by caffeine

ATP-sensitive potassium (K(ATP)) channels couple cellular metabolic status to changes in membrane electrical properties. Caffeine (1,2,7-trimethylxanthine) has been shown to inhibit several ion channels; however, how caffeine regulates K(ATP) channels was not well understood. By performing single-channel recordings in the cell-attached configuration, we found that bath application of caffeine significantly enhanced the currents of Kir6.2/SUR1 channels, a neuronal/pancreatic K(ATP) channel isoform, expressed in transfected human embryonic kidney (HEK)293 cells in a concentration-dependent manner. Application of nonselective and selective phosphodiesterase (PDE) inhibitors led to significant enhancement of Kir6.2/SUR1 channel currents. Moreover, the stimulatory action of caffeine was significantly attenuated by KT5823, a specific PKG inhibitor, and, to a weaker extent, by BAPTA/AM, a membrane-permeable Ca(2+) chelator, but not by H-89, a selective PKA inhibitor. Furthermore, the stimulatory effect was completely abrogated when KT5823 and BAPTA/AM were co-applied with caffeine. In contrast, the activity of Kir6.2/SUR1 channels was decreased rather than increased by caffeine in cell-free inside-out patches, while tetrameric Kir6.2LRKR368/369/370/371AAAA channels were suppressed regardless of patch configurations. Caffeine also enhanced the single-channel currents of recombinant Kir6.2/SUR2B channels, a nonvascular smooth muscle K(ATP) channel isoform, although the increase was smaller. Moreover, bidirectional effects of caffeine were reproduced on the K(ATP) channel present in the Cambridge rat insulinoma G1 (CRI-G1) cell line. Taken together, our data suggest that caffeine exerts dual regulation on the function of K(ATP) channels: an inhibitory regulation that acts directly on Kir6.2 or some closely associated regulatory protein(s), and a sulfonylurea receptor (SUR)-dependent stimulatory regulation that requires cGMP-PKG and intracellular Ca(2+)-dependent signaling.

Progressive deafness and altered cochlear innervation in knock-out mice lacking prosaposin

After a yeast two-hybrid screen identified prosaposin as a potential interacting protein with the nicotinic acetylcholine receptor (nAChR) subunit alpha10, studies were performed to characterize prosaposin in the normal rodent inner ear. Prosaposin demonstrates diffuse organ of Corti expression at birth, with gradual localization to the inner hair cells (IHCs) and its supporting cells, inner pillar cells, and synaptic region of the outer hair cells (OHCs) and Deiters' cells (DCs) by postnatal day 21 (P21). Microdissected OHC and DC quantitative reverse transcriptase-PCR and immunohistology localizes prosaposin mRNA to DCs and OHCs, and protein predominantly to the apex of the DCs. Subsequent studies in a prosaposin knock-out (KO) (-/-) mouse showed intact but slightly reduced hearing through P19, but deafness by P25 and reduced distortion product otoacoustic emissions from P15 onward. Beginning at P12, the prosaposin KO mice showed histologic organ of Corti changes including cellular hypertrophy in the region of the IHC and greater epithelial ridge, a loss of OHCs from cochlear apex, and vacuolization of OHCs. Immunofluorescence revealed exuberant overgrowth of auditory afferent neurites in the region of the IHCs and proliferation of auditory efferent neurites in the region of the tunnel of Corti. IHC recordings from these KO mice showed normal I-V curves and responses to applied acetylcholine. Together, these results suggest that prosaposin helps maintain normal innervation patterns to the organ of Corti. Furthermore, prosaposin's overlapping developmental expression pattern and binding capacity toward the nAChR alpha10 suggest that alpha10 may also play a role in this function.

Nicotinic acetylcholine receptor structure and function in the efferent auditory system

This article reviews and presents new data regarding the nicotinic acetylcholine receptor subunits alpha9 and alpha10. Although phylogentically ancient, these subunits have only recently been identified as critical components of the efferent auditory system and medial olivocochlear pathway. This pathway is important in auditory processing by modulating outer hair cell function to broadly tune the cochlea and improve signal detection in noise. Pharmacologic properties of the functionally expressed alpha9alpha10 receptor closely resemble the cholinergic response of outer hair cells. Molecular, immunohistochemical, and knockout mice studies have added further weight to the role this receptor plays in mediating the efferent auditory response. Alternate and complementary mechanisms of outer hair cell efferent activity might also be mediated through the nAChR alpha9alpha10, either through secondary calcium stores, second messengers, or direct protein-protein interactions. We investigated protein-protein interactions using a yeast-two-hybrid screen of the nAChR alpha10 intracellular loop against a rat cochlear cDNA library. Among the identified proteins was prosaposin, a precursor of saposins, which have been shown to act as neurotrophic factors in culture, can bind to a putative G0-coupled cell surface receptor, and may be involved in the prevention of cell death. This study and review suggest that nAChR alpha9alpha10 may represent a potential therapeutic target for a variety of ear disorders, including preventing or treating noise-induced hearing loss, or such debilitating disorders as vertigo or tinnitus.

Inhibition of human TREK-1 channels by caffeine and theophylline

Caffeine (1,3,7-trimethylxanthine) and theophylline (1,3-dimethylxanthine) are used for therapeutic purposes and can cause life-threatening convulsive seizures due to systemic toxicity. The mechanisms for the epileptogenicity of caffeine and theophylline are not clear. TWIK-related K(+) channels (TREK-1) are highly expressed in the human central nervous system and have a major role in the control of neuronal excitability by regulating the resting membrane potential. In view of their physiological significance, inhibition of TREK-1 channels may be implicated in caffeine- and theophylline-induced seizures. We thus investigated, using whole-cell patch-clamp technique, modulation of hTREK-1 channels expressed in Chinese hamster ovary (CHO) cells by caffeine and theophylline. Caffeine and theophylline produced reversible inhibition of TREK-1 channels in a concentration-dependent manner. The half-maximal inhibitory concentrations (IC(50)) for caffeine and theophylline were 377+/-54microM and 486+/-76microM, respectively. Caffeine and theophylline depolarized the membrane potential of CHO(TREK-1) cells in a reversible and concentration-dependent manner. Inhibition by caffeine (5mM) and theophylline (2mM) was attenuated in TREK-1 channels with mutation of the PKA consensus sequence at serine 348, suggesting the involvement of cAMP/PKA pathway in the inhibitory process. Inhibition of TREK-1 channels and consequent membrane depolarization may contribute to the convulsive seizures induced by toxic levels of caffeine and theophylline.

Caffeine and ryanodine demonstrate a role for the ryanodine receptor in the organ of Corti

The hypothesis that the release of Ca(2+) from ryanodine receptor activated Ca(2+) stores in vivo can affect the function of the cochlea was tested by examining the effects of caffeine (1-10 mM) and ryanodine (1-333 microM), two drugs that release Ca(2+) from these intracellular stores. The drugs were infused into the perilymph compartment of the guinea pig cochlea while sound (10 kHz) evoked cochlear potentials and distortion product otoacoustic emissions (DPOAEs; 2f(1)-f(2)=8 kHz, f(2)=12 kHz) were monitored. Caffeine significantly suppressed the compound action potential of the auditory nerve (CAP) at low intensity (56 dB SPL; 3.3 and 10 mM) and high intensity (92 dB SPL; 10 mM), increased N1 latency at high and low intensity (3 and 10 mM) and suppressed low intensity summating potential (SP; 10 mM) without an effect on high intensity SP. Ryanodine significantly suppressed the CAP at low intensity (100 and 333 microM) and at high intensity (333 microM), increased N1 latency at low intensity (33, 100 and 333 microM) and at high intensity (333 microM) and suppressed low intensity SP (100 and 333 microM) and increased high intensity SP (333 microM). The cochlear microphonic (CM) evoked by 10 kHz tone bursts was not affected by caffeine at high or low intensity, and ryanodine had no effect on it at low intensity but decreased it at high intensity (10, 33, 100 and 333 microM). In contrast, caffeine (10 mM) and ryanodine (33 and 100 microM) significantly increased CM evoked by l kHz tone bursts and recorded from the round window. Caffeine (10 mM) and ryanodine (100 microM) reversibly suppressed the cubic DPOAEs evoked by low intensity primaries. Overall, low intensity evoked responses were more sensitive and were suppressed to a greater extent by both drugs. This is consistent with the hypothesis that release of Ca(2+) from ryanodine receptor Ca(2+) stores, possibly in outer hair cells and supporting cells, affects the function of the cochlear amplifier.

Investigation of the role of intracellular Ca(2+) stores in generation of the muscarinic agonist-induced slow afterdepolarization (sADP) in guinea-pig olfactory cortical neurones in vitro

1. Intracellular recordings were made from guinea-pig olfactory cortical brain slice neurones to assess the possible role of intracellular Ca(2+) stores in the generation of the slow post-stimulus afterdepolarization (sADP) and its underlying tail current (I(ADP)), induced by muscarinic receptor activation. 2. Caffeine or theophylline (0.5 - 3 mM) reduced the amplitude of the I(ADP) (measured under 'hybrid' voltage clamp) induced in the presence of the muscarinic agonist oxotremorine-M (OXO-M, 10 microM) by up to 96%, without affecting membrane properties or muscarinic depolarization of these neurones. 3. The L-type Ca(2+) channel blocker nifedipine (1, 10 microM) also inhibited I(ADP) (by up to 46%), while ryanodine (10 microM) (a blocker of Ca(2+) release from internal stores) produced a small ( approximately 10%) reduction in I(ADP) amplitude; however, neither 10 microM dantrolene (another internal Ca(2+) release blocker) nor the intracellular Ca(2+) store re-uptake inhibitors thapsigargin (3 microM) or cyclopiazonic acid (CPA, 15 microM) affected I(ADP) amplitude. 4. IBMX (100 microM), a phosphodiesterase inhibitor, also had no effect on I(ADP). Furthermore, inhibition of I(ADP) by caffeine was not reversed by co-application of 100 microM adenosine. 5. Caffeine (3 mM) or nifedipine (10 microM) reduced the duration of presumed Ca(2+) spikes revealed by intracellular Cs(+) loading. When applied in combination, nifedipine and caffeine effects were occlusive, rather than additive, suggesting a common site of action on L-type calcium channels. 6. We conclude that Ca(2+)-induced Ca(2+) release (CICR) from internal stores does not contribute significantly to muscarinic I(ADP) generation in olfactory cortical neurones. However caffeine and theophylline, which enhance CICR in other systems, blocked I(ADP) induction. We suggest that this action might involve a combination of L-type voltage-gated Ca(2+) channel blockade, and a direct inhibitory action on the putative I(ADP) K(+) conductance.

Effects of potassium channel blockers on the acetylcholine-induced currents in dissociated outer hair cells of guinea pig cochlea

Much physiological evidence is available to show that acetylcholine (ACh) hyperpolarizes the outer hair cells (OHCs) of guinea pig cochlea and induces Ca2+-activated K+ currents. In this study, using the nystatin perforated patch-clamp technique, we investigated the effects of various K+ channel blockers on the ACh-induced currents (I[ACh]) in dissociated OHCs of guinea pig cochlea. The I(ACh) were inhibited by apamin in a concentration-dependent manner. The half-maximal inhibitory concentration for apamin on the ACh-induced response was 1.59 x 10(-9) M. Charybdotoxin and iberiotoxin had no inhibitory effect on the I(ACh) The inhibitory potency of the various K+ channel blockers on the I(ACh) was as follows: apamin >> quinine approximately quinidine approximately d-tubocurarine > tetraethylammonium chloride > 4-aminopyridine approximately Ba2+ > Cs2+. It is proposed that the Ca2+-activated K+ channels of mammalian cochlear OHCs should be classified as small conductance Ca2+-activated K+ (SK) channels according to their pharmacological properties.