www.bjorl.org
Brazilian
Journal
of
OTORHINOLARYNGOLOGY
ORIGINAL
ARTICLE
Ototoxicity
of
boric
acid
powder
in
a
rat
animal
model
夽
Murat
Salihoglu
a,∗,
Salim
Dogru
b,
Enver
Cesmeci
c,
Halil
Caliskan
d,
Onuralp
Kurt
e,
Zafer
Kuc
¸ukodaci
f,
Atila
Gungor
aaGATAHaydarpasaTrainingHospital,DepartmentofOtorhinolaryngology,Istanbul,Turkey bEfesOtolaryngologyBranchCenter,DepartmentofOtorhinolaryngology,Izmir,Turkey cDiyarbakirMilitaryHospital,DepartmentofOtorhinolaryngology,Diyarbakir,Turkey dEskisehirMilitaryHospital,DepartmentofOtorhinolaryngology,Eskisehir,Turkey eErzincanMilitaryHospital,DepartmentofOtorhinolaryngology,Erzincan,Turkey fGATAHaydarpas¸aTrainingHospital,DepartmentofPathology,Istanbul,Turkey
Received17August2016;accepted27March2017 Availableonline22April2017
KEYWORDS Boricacid; Ear; Otoacoustic emissions; Rats Abstract
Introduction:Boricacid,whichhasantisepticandacidicproperties,isusedtotreatexternal andmiddleearinfections.However,wehavenotfoundanyliteratureabouttheeffectofboric acidpowderonmiddleearmucosaandinnerear.
Objective:The purposeofthisstudyistoinvestigatepossibleototoxiceffectsofboricacid powderoncochlearouterhaircellfunctionandhistologicalchangesinmiddleearmucosaina ratanimalmodel.
Methods:Twenty healthy,matureWistaralbino ratswere usedinthisstudy.The ratswere dividedintotwogroups,GroupAandGroupB,eachofwhichconsistedof10rats.Initially,the animalsineachgroupunderwentdistortionproductotoacousticemissionstestingoftheirright andleftears.Afterthefirstdistortionproductotoacousticemissionstest,asurgicalmicroscope wasused tomakeasmallperforationinbothearsoftheratsineachgroup,andasecond distortionproductotoacousticemissionstestwasusedtomeasurebothearsinalloftherats. Boricacidpowderwasappliedtotherightmiddleearoftheratsusingtympanicmembrane perforation,andthedistortionproductotoacousticemissionsweremeasuredimmediatelyafter theboricacidpowderapplication.Thehistologicalchangesanddistortionproductotoacoustic emissionswereevaluatedthreedayslaterinGroupAand40dayslaterinGroupB.
Results:Nosignificantdifferenceswerefoundatallofthedistortionproductotoacoustic emis-sionsfrequencies.InGroupA,mildinflammationofthemiddleearmucosawasfoundonthe thirddayafterboricacidpowderapplication.InGroupB,boricacidpowdercausedmild inflam-matory changes onthe40th day, whichdeclinedover time.Those changes didnotlead to significantfibrosiswithinthemucosa.
夽 Pleasecitethisarticleas:SalihogluM,DogruS,CesmeciE,CaliskanH,KurtO,Kuc¸ukodaciZ,etal.Ototoxicityofboricacidpowderin aratanimalmodel.BrazJOtorhinolaryngol.2018;84:332---7.
∗Correspondingauthor.
E-mail:drmuratsali@gmail.com(M.Salihoglu).
PeerReviewundertheresponsibilityofAssociac¸ãoBrasileiradeOtorrinolaringologiaeCirurgiaCérvico-Facial. https://doi.org/10.1016/j.bjorl.2017.03.010
1808-8694/©2017Associac¸˜aoBrasileiradeOtorrinolaringologiaeCirurgiaC´ervico-Facial.PublishedbyElsevierEditoraLtda.Thisisanopen accessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).
Conclusion: Inrats,boricacidpowdercausesmildinflammationinmiddleearmucosaandit hasnoototoxiceffectsoncochlearouterhaircellfunctionintheinnerearofrats.
© 2017 Associac¸˜ao Brasileira de Otorrinolaringologia e Cirurgia C´ervico-Facial. Published by Elsevier Editora Ltda. This is an open access article under the CC BY license (http://
creativecommons.org/licenses/by/4.0/). PALAVRAS-CHAVE Ácidobórico; Ouvido; Emissões otoacústicas; Ratos
Ototoxicidadedeácidobóricoempóemummodeloanimalderato
Resumo
Introduc¸ão: Oácidobórico,quetempropriedadesantissépticaseácidas,éusadoparatratar infecc¸õesdeorelhaexternaemédia.Noentanto,nãoencontramosnenhumaliteraturasobre oefeitodoácidobóricoempósobreamucosadaorelhainternaedamucosadaorelhamédia.
Objetivo: Investigar possíveisefeitos ototóxicos do ácido bóricoem pósobre afunc¸ãodas célulasciliadasexternascoclearesealterac¸õeshistológicasnamucosadaorelhamédiaemum modeloanimalderato.
Método: VinteratosWistaralbinosmadurosesaudáveisforamutilizadosnesteestudo.Osratos foramdivididosemdoisgrupos,GrupoAeGrupoB,cadaumdosquaiscom10ratos. Inicial-mente,osanimaisdecadagrupoforamsubmetidosatestesdeemissõesotoacústicas---produto dedistorc¸ão,nasorelhasdireitaeesquerda.Apósoprimeirotestedeemissõesotoacústicas -produtodedistorc¸ão,utilizou-seummicroscópiocirúrgicoparafazerumapequenaperfurac¸ão emambasasorelhasdosratosemcadagrupo,eumsegundotestedeemissõesotoacústicas -produtodedistorc¸ãofoiutilizadoparamedireavaliarasorelhasemtodososratos.Oácido bóricoempófoiaplicadoorelhamédiadireitadosratosutilizandoperfurac¸ãodamembrana timpânicaeasemissõesotoacústicas-produtodedistorc¸ãoforammedidasimediatamenteapós aaplicac¸ãodeácidobóricoempó.Asalterac¸õeshistológicaseemissõesotoacústicas-produto dedistorc¸ãoforamavaliadastrêsdiasdepoisnoGrupoAe40diasdepoisnoGrupoB.
Resultados: Nãoforamencontradasdiferenc¸assignificativasemtodasasfrequênciasda emis-sõesotoacústicas-produtodedistorc¸ão.NoGrupoA,foiobservadaumaligeirainflamac¸ãoda mucosadaorelhamédianoterceirodiaapósaaplicac¸ãodeácidobóricoempó.NoGrupoB, oácidobóricoempócausoulevesalterac¸õesinflamatóriasapós40dias,quediminuíramao longodotempo.Essasalterac¸õesnãolevaramàfibrosesignificativadamucosa.
Conclusão:Emratos,oácidobóricoempócausainflamac¸ãolevenamucosadaorelhamédiae nãotemefeitosototóxicosnafunc¸ãodascélulasciliadasexternasdacócleanaorelhainterna. © 2017 Associac¸˜ao Brasileira de Otorrinolaringologia e Cirurgia C´ervico-Facial. Publicado por Elsevier Editora Ltda. Este ´e um artigo Open Access sob uma licenc¸a CC BY (http://
creativecommons.org/licenses/by/4.0/).
Introduction
In addition to commercially available drugs containing antibiotics and steroids, many topicalagents areused to treat ear diseases. Antiseptic and acidic ear drops are oftenusedincasesof middleearinflammation and infec-tion,whichaccompanyexternalearinfectionsandtympanic membrane perforations.1 Topical applications have some
advantages in otology.They provide a high concentration ofmedicationintheappliedregions,theyhaveless poten-tialtodevelopbacterialresistance,andtheydonotcause systemicside effectsin patients. Inspite of these advan-tages,afterapplication tothemiddleearcavity theycan passthroughtheroundwindowandtheycouldhaveadverse effectsonthecochlear andvestibularapparatus.2Studies
havedemonstratedtheototoxiceffectsof aminoglycoside groupmedicationssuchasgentamycin andstreptomycin.3
Inaddition,someantisepticsolutionshavebeenprovento haveototoxicpotential.4,5Duringtopicalmedication,
oto-toxicitycanbecausedeitherbytheactivesubstanceitself
orbythecarriersolution.Furthermore,theconcentrations oftheactivesubstanceandthecarriersolutionaffectthe ototoxicity.5
Boricacid(alsoknownasBoracic)isawhitecrystalline solidwiththemolecular formulaH3BO3. Itis a weakacid
found in nature (minerals, sea water, and fruits), and it canbeproducedbyreactingborateminerals withsulfuric acid.Boracichas varioususesasan insecticide, preserva-tive,lubricant,andindustrialagent.Medicinally,itisused asanantiseptic;forexample,itisdilutedasaneyewash, or it used totreat minor cuts and burns,acne, aphthous lesions,andulcerateddiphtherialesions,anditisusedto treatcasesinvolving flux,suchasgonorrheavaginitis,and cystitis.Itisalsousedtotreat fungalandbacterial infec-tionsin the external or middle ear.It hasbeen known to betoxicinhighdoses,especiallyininfants.Itisfrequently usedasa4%solutionpreparedwith70%alcoholordistilled water, and in pure powder form it is used as Boric Acid Powder(BAP).6,7BAPcontainsthehighestconcentrationof
theeffects of BAP on the inner andmiddle earhave not beenevaluated.Thispresentstudyinvestigatedthepossible ototoxiceffectsofBAPonthecochlearouterhaircell func-tion in rats by measuring Distortion Product Otoacoustic Emission (DPOAE) amplitudes. Histological changes within themiddleearmucosawerealsoevaluated.
Methods
Twentyhealthy, mature (16---20 month-old), Wistar albino rats(weighingbetween 250gand300g)wereusedinthis study.The experimental protocol was designed according to the Guide for the Care and Use of Laboratory Ani-malspublishedbytheNationalAcademicsPress.8Therats
were kept in separate cages in a room with 12h on/off lightcycles,simulatingthestandarddayandnightrhythm, atconstant temperature(20±2◦C)and humidity(55.5%). This study wasapproved by the EthicsCommittee onthe University Hospital (protocol number 58-2013). The rats were anesthetized with ketamine (75---90mg/kg, Ketalar, Pfizer,Istanbul,Turkey)andxylazine(5---8mg/kg,Rompun, Bayer,Leverkusen,Germany)throughintraperitoneal injec-tion. The depth of anesthesia was determined by pedal reflex,andadditionalanesthesiawasadministeredin half dose increments as required. The rats were euthanized withthiopentalsodium(200mg/kgPentothal;Abboth, Cam-poverdedi Aprilla, Italy)throughintraperitonealinjection underanesthesia.
The rats were divided into two groups, Group A and Group B, each consisting of 10 animals (five males, five females).Followingtheadministrationofgeneral anesthe-sia,we assessed theexternal earcanal andthe tympanic membrane of each ratusing a surgical microscope. None ofthe ratshadan earinfection oran earinjury.Initially, theanimalsineachgroupunderwentDPOAEtestinginthe rightandleftears.AfterthisfirstDPOAEtesting,asurgical microscopewasusedtomakeasmall(lessthanone-quarter ofthetympanicmembrane)perforationinbothearsofthe ratsin each group,and asecond DPOAE test wasusedto measureboth earsforalloftheratsineach group.Then, 35mg(0.1cc)BAP wasappliedtothe right middle earof theratsinbothgroupsviatympanicmembraneperforation usinga2.5ccsyringewitha22gaugeneedle.Afterthis pro-cedure,the middleearmucosa wasobservedthroughthe perforation usingmicroscope in ordertoensure that BAP inthemiddle earmucosa.DPOAEtestingwasrepeatedon therightearsoftheratsinbothgroups immediatelyafter theBAPapplication.HistologicalchangesandDPOAEswere evaluatedinbothearsthreedayslaterinGroupAandforty dayslaterinGroupB.ThehistologicalresultsandtheDPOAE measurementswere comparedbetweenthe rightand left ears,andbetweenbothgroups.
DPOAEthresholdswererecordedat2kHz,3kHz,4kHz, 6kHz, and 8kHz using a Madsen Capella cochlear emis-sionanalyzer,Noah3system(GNOtometricsA/S,Taastrup, Denmark). All measurements were carried out in a quiet room.Primary tones were emittedinto the sealed exter-nalearcanalsthroughanearphone. Theacousticstimulus that created the DPOAE signal consisted of two simulta-neous,continuous pure tonesat differentfrequencies: f1 andf2. Inthis study,we usedthestimulus parametersof
80dBSPL/70dBSPLwiththef2/f1ratioof1.22,andthen theamplitudeoftheDPOAEsignalwasanalyzed.Atotalof 1000acquisitionswereanalyzed.
Alloftheratsinbothgroupswereeuthanizedunder anes-thesiaforhistologicevaluation.Subsequently,thetemporal boneswereharvested,andthetympanicbullaswerequickly dissectedfromthetemporalbonesandpreparedfor micro-scopicexamination. Afterfixingin10%buffered formaline solutionfor48h,thespecimenswereplacedina10%nitric aciddecalcifyingsolutionfor oneday. Eachspecimenwas thenembeddedinparaffinandcutaccordingtothestandard histologictechnique(Leicamicrotome,Germany),andthen stained with trichrome, hematoxylin, and eosin. The tis-sueswereviewedwithamicroscope,andphotomicrographs were obtained.The histologic changeswere evaluatedby observingthemiddleearmucosatodeterminethe accumu-lationofinflammatorycells(polymorphonuclearleukocytes, macrophages,lymphocytes,giantcells,andothercells)and thepresenceoffibroblasticactivityandfibrosis.Thedegree ofthesechangeswasvisuallyassessedandgradedasfollows: absent(0),mild(1),moderate(2),orsevere(3).
The classificationof inflammation according to inflam-matory cell counts wasperformed at 200×magnification
and the counts were categorized as follows: mild
(<50cells/field),moderate(50---100cells/field),andsevere (>100cells/field).Ten200×magnificationareaswere exam-ined, and the average number of inflammatory cells was calculated.9 Fibroblasticactivity and fibrosis weregraded
according to the classificationusedby Dogru at al.10 The
histologicobservationswereperformedblindedbythesame pathologistwhoviewedeachslidetwice,andfive measure-mentswereperformedforeachspecimen.
Statisticalanalysis
Dataanalyses wereperformed using SPSS21.0 (Statistical PackageforSocialSciences,SPSSInc.,Chicago,IL).Thedata wereshownasthemean±standarddeviationforthe contin-uousvariables(DPOAE),andasthenumberofcasesforthe categoricalvariables(histologicobservations).When deter-mining whether or not thedata arenormally distributed, wehavefoundnon-normaldistribution.TheMann---Whitney
U test was used to compare between the right and left ears in all of the measured DPOAE frequencies in both groups. Wilcoxon rank-sum test wasused tocompare the DPOAEresults for theright ears(theBAP-appliedears) of the ratsin GroupB,measured threedifferent times(first day;beforeperforation,afterperforation,afterboricacid powderapplication,3rddayand40thday)throughout the study.Categorical variables (histologicobservations) were comparedbyFisher’sexacttest.Statisticalsignificancewas reservedforvalues(p<0.05).
Results
Noneoftheratsdiedduringthestudy.Thetympanic mem-branes of the rats were examined using otomicroscopy before euthanization. In Group A, iatrogenic perforations persistedinbothearsofalloftherats,andtherewereno signs ofinfection. InGroup B,the iatrogenicperforations in both ears were healedin of allof the rats. No
signifi-Table1 DistributionofDPOAEamplitudesfor2-,3-,4-,6-,and8kHzfrequencies intherightandleft earsoftheratsin GroupAandB(80DbSPL/70dBSPLstimuli).
DPOAE,mean±SD(GroupA/B)
Rightear Leftear p-Valuea
2kHz
Beforeperforation 12.08±0.98/12.35±1.16 12.18±1.10/12.38±0.90 0.70/0.91 Afterperforation 11.79±0.88/11.82±1.94 11.74±1.19/11.79±1.53 0.76/0.81
Afterboricacidpowder 11.49±1.12/11.21±1.70 ---/---
---/---3rdday 12.06±1.39/12.28±0.88 11.93±1.16/12.34±0.66 0.47/0.80
40thday ---/12.48±1.02 ---/12.17±1.10 ---/0.76
3kHz
Beforeperforation 23.75±1.87/23.72±1.32 23.23±1.40/23.62±1.72 0.57/0.88 Afterperforation 23.48±1.73/22.55±1.04 23.07±1.28/22.97±1.24 0.71/0.54
Afterboricacidpowder 23.27±2.11/23.09±1.50 ---/---
---/---3rdday 23.42±1.69/23.72±1.32 23.18±1.77/22.94±1.04 0.82/0.15
40thday ---/23.27±1.18 ---/22.99±1.84 ---/0.65
4kHz
Beforeperforation 26.28±1.51/26.18±1.88 26.17±2.05/26.08±2.14 0.94/0.53 Afterperforation 26.22±1.86/26.02±1.60 25.17±1.45/25.62±1.96 0.23/0.47
Afterboricacidpowder 25.97±1.74/25.94±1.95 ---/---
---/---3rdday 25.92±2.09/25.94±1.95 25.84±2.16/26.12±1.77 0.88/0.86
40thday ---/26.16±1.74 ---/26.06±1.82 ---/0.72
6kHz
Beforeperforation 32.87±2.27/33.76±2.21 32.70±1.75/33.50±1.93 0.79/0.92 Afterperforation 32.73±2.29/32.88±2.59 32.61±1.90/33.14±2.14 0.91/0.80
Afterboricacidpowder 32.41±1.96/32.68±2.06 ---/---
---/---3rdday 32.94±2.92/33.68±2.18 32.67±2.11/33.12±2.22 0.91/0.54
40thday ---/33.40±1.83 ---/33.47±2.80 ---/0.84
8kHz
Beforeperforation 37.96±3.37/38.23±2.81 38.09±3.13/38.53±30.0 1.00/0.80 Afterperforation 37.54±2.14/37.76±2.69 38.1±3.24/38.32±2.94 0.55/0.51
Afterboricacidpowder 37.44±2.63/37.25±4.25 ---/---
---/---3rdday 37.52±2.62/37.24±2.62 37.96±2.58/37.46±2.40 1.00/0.76
40thday ---/37.68±2.75 ---/37.59±2.62 ---/0.96
DPOAE,distortionproductotoacousticemission;SD,standarddeviation;SPL,soundpressurelevel.
a Mann---WhitneyUtest(p<0.05wasconsideredsignificant).
cantdifferenceswerefoundbetweentherightandleftears in all of the measured DPOAE frequencies in both groups (Table 1). When we compared the DPOAE results for the right ears (the BAP-applied ears) of the rats in Group B, measured threedifferent times(firstday;before perfora-tion,afterperforation,afterboricacidpowderapplication, 3rddayand40thday)throughoutthestudy,nostatistically significantdifferenceswerefound(Table2).
Histopathologic findings in Group A and Group B were as follows (Fig. 1). In Group A, a mild inflammatory cell increase was observed in both ears in eight rats and in theright earin tworats (p>0.05).In GroupB,therewas noinflammatorycellincrease ineightrats,buttherewas a mild inflammatory cellincrease in the right ear in two rats (p>0.05). In Group A, mild fibroblastic activity was observedintherightearinthreerats(p>0.05).InGroupB, mild fibroblastic activity wasobserved in the right earin onlyonerat(p>0.05).NofibrosiswasobservedinGroupA. Mildfibrosis wasobserved intheright earinthreeratsin
GroupB(p>0.05).Thehistologicchangesofthegroupsare summarizedinTable3.Therewasnostatisticalsignificant differenceinthehistologicfindingsbetweentherightand leftmiddleearmucosaoftheratsinbothgroups.
Discussion
Topical agents can beused alone or withsystemic medi-cationstotreatchronicmiddleearandexternal earcanal infections.11,12Manystudieshaveinvestigatedtheeffectsof
boricacidandother ototopicalsolutionsthathave similar characteristics.Ozcanetal.13reportedthata4%boricacid
solutionpreparedwith70%alcoholisaneffectiveand inex-pensivetreatmentoptionforotomycosisinadditiontolocal toiledofear.InastudyconductedbyMinjaetal.14aboric
acidsolutionpreparedwith70%alcoholwasreportedtobe effective andsafe in children diagnosedwith suppurative otitis media.Ozturkcan etal.6 investigatedthe effect of
Table2 Thecomparison(p-valuesa)ofDPOAEamplitudesfor2-,3-,4-,6-,and8kHzfrequenciesoftherightearsoftherats inGroupB. Comparison 2kHz 3kHz 4kHz 6kHz 8kHz I---II 0.73 0.07 0.76 0.36 0.72 I---III 0.09 0.37 0.54 0.28 0.51 I---IV 0.92 1.00 0.51 0.54 0.58 I---V 0.54 0.51 1.00 0.61 0.68 II---III 0.44 0.44 0.96 0.84 0.88 II---IV 0.51 0.07 0.57 0.44 0.59 II---V 0.41 0.20 0.88 0.51 0.88 III---IV 0.22 0.37 0.72 0.24 0.88 III---V 0.10 0.92 0.96 0.28 0.88 IV---V 0.41 0.51 0.48 0.44 0.80
I,firstday,beforeperforation;II,firstday,afterperforation;III,firstday,afterboricacidpowderapplication;IV,infollow-upon3rd day;V,infollow-upon40thday.
aWilcoxonrank-sumtest(p<0.05wasconsideredsignificant).
Table3 HistologicchangesafterBAPtreatmentintherightandleftearsinbothgroups.
Right/left Absent Mild Moderate Severe p-Valuec
Inflammatorycellsa ---/2 10/8 ---/--- ---/--- 0.47 Fibroblasticactivitya 7/10 3/--- ---/--- ---/--- 0.21 Fibrosisa ---/--- ---/--- ---/--- ---/--- ---Inflammatorycellsb 8/10 2/--- ---/--- ---/--- 0.14 Fibroblasticactivityb 9/10 1/--- ---/--- ---/--- 0.99 Fibrosisb 7/10 3/--- ---/--- ---/--- 0.21
a3rdday(GroupA). b 40thday(GroupB).
c Fisher’sexacttest(p<0.05wasconsideredsignificant).
boricacidsolutionsonAuditoryBrainstemResponses(ABR) inguineapigs.Theyreportedthata4%boricacidsolution preparedwith70%alcoholhasanototoxiceffect,whereas thesolution is saferif itis prepared withdistilledwater. Aktasetal.15investigatedtheototoxiceffectofboricacid
solutionpreparedwithdifferentconcentrationsof alcohol (60%and 40%) by performingABR on young albino guinea pigs.Theyreportedthata4%boricacidsolutionprepared with60%alcoholhadanegativeeffectonhearinginguinea pigs. They also found that an increase in the concentra-tionoftheboricacidsolutioncausedadditionalototoxicity. However,Ozdemir et al.16 demonstrated that the topical
applicationofboric acidinalcoholsolutionstothemiddle earofratswassafefortheinnerear.Intheirstudy, hear-ing wasevaluated usingDPOAE. In addition to boric acid solutions,Burow’ssolution,whichconsistsofdifferent con-centrationsofaluminumsubacetate,isfrequentlyusedasan antiseptic.Serinetal.17effectstudiedtheeffectsof4%and
13%Burow’ssolutionsonguineapighearingusingABR,and theyfoundnoototoxiceffectGultekinatal.1 investigated
theeffects of Castellani solution,which has antibacterial andantifungalproperties,andtheydidnotfindanyototoxic effectinratinnerearsusingDPOAE.
Previous studies have evaluated the ototoxicity of a 4%(4g/100mL)boric acidsolutionpreparedwithdistilled water or alcohol.6,13---16 However, we have not found any
previousstudies thathave examined theeffectofBAP on
middleearmucosaandtheinnerear.Anothercommonuse ofBAPistoinsufflateitintothewettympaniccavitiesand the external ear.We used 35mg pure formof BAP (100% concentration)whileotherstudies,mentionedabove,used 4%boricacidsolution.
Ototoxicityreferstotheinjurythatoccursintheinner earduetotheadministrationofmedicationsorchemicals resultinginsensorineuralhearingloss.1DPOAEstudieshave
been frequently usedto investigate ototoxicity. DPOAE is a noninvasive method for evaluating the outer hair cells, which produce Otoacoustic Emissions (OAEs).18 However,
OAEscan beaffected byfluid inthe middle earcavityor thepresenceofaperforationinthetympanicmembrane.19
When morethanhalfofthe tympanicmembraneis perfo-rated,OAEscannotbemeasuredduetoconductivehearing loss.20Therefore,inthispresentstudy,thetympanic
mem-braneswerepartiallyperforated(less thanone-quarterof thetympanicmembrane)withthehelpofapick,andBAP wasappliedusinga2.5ccsyringewitha22gaugeneedle.
In our study, no significant differences were observed betweentheDPOAElevelsoftheBAP-appliedandthe non-BAP-appliedearsatallfrequenciesinbothgroups.
Mildinflammationandfibroblasticactivityinthemiddle earmucosawereobservedthreedaysaftertheBAP applica-tioninGroupA.Wethoughtmildinflammation,detectedin GroupA,wasduetotraumaticeffectsofiatrogenic perfora-tion.Nofibrosiswasseenonthethirddayaftertreatmentin
Figure1 Mildinflammation(whitearrows),mildfibroblastic activity(blackarrows),andmildfibrosis(redarrow)inoneof theratsinGroupB(40days)(Trichrome400×).
GroupA.Histologicexaminationofthemiddleearmucosaon day40revealedthatBAPcausedmildinflammation,which declined overtimeinGroup B.Thosechangesledtomild fibrosisinthemucosaintherightearsofonlythreeratsin GroupB.
Conclusions
Inourstudy,we havedemonstratedthatBAP causedmild histologicchangesinmiddleearmucosainrats.Weutilized DPOAEtoinvestigateototoxiceffectsofBAPtotheratinner earandfoundthatBAPhasnoototoxiceffectsoncochlear outer hair cellfunction inthe innerear ofrats. Itis rea-sonable toutilize DPOAEto investigate theototoxicity of drugs.
Conflicts
of
interest
Theauthorsdeclarenoconflictsofinterest.
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