Introduction

Hearing disorders are associated with certain changes in the physical functioning of the hearing system and affect one’s ability to process sounds. These disorders cause difficulty establishing communication with others. Hearing losses are divided into three types, namely conductive, sensorineural, and mixed [1,2], and may cause other disorders such as earache and tinnitus and therefore exacerbate the associated problems of the patients.

Earache

Earache is one of the most common ear disorders [3-5]. If ear anatomy is pathologically involved, earache is referred to as primary, and if the surrounding organs are pathologically involved, it is referred to as referred earache. In children, primary earache is more common while adults are more likely to develop referred earache [6]. In differential diagnosis between primary and referred earache, description and physical examination play a determinative role. Primary earache can be due to acute or chronic otitis media, external otitis, mastoid diseases, Eustachian tube dysfunction, cerumen impaction, ear inflammation, trauma to the ear, or tumoral lesions [7-9] that are easily diagnosed by clinical symptoms. In some cases, however, para-clinical tests such as radiography and audiogram tests are required [3,5,10-12]. Although the causes of primary earache can be benign and selflimiting, ear tumors, metastatic tumors, or primary tumors in the surrounding organs can present with earache [13-15]

Tinnitus

Tinnitus is one of the most common ear, nose, and throat disorders with an estimated 14.2% prevalence in adults. Tinnitus is considered irritating and a serious issue in 3-5% of the patients [16]. Tinnitus is a complicated and multifactorial disorder; although certain factors such as stress and anxiety, exposure to loud noises, antiinflammatory drugs, antibiotics, and sedatives are definite causes of tinnitus in some cases, the definite cause of this disease cannot be detected in other cases [17]. Holistic and novel approaches and therapies to treat tinnitus, which cause few side effects, are constantly being sought out. In many cases, there is no standard treatment for tinnitus. Anti-depressants seem to reduce tinnitus yet with numerous side effects. Current treatments for tinnitus include the use of hearing aids, voice therapy, environmental sound enrichment, adjuvant therapies, vasodilators using corticosteroids, anticonvulsants, antispasmodics, lidocaine, and benzodiazepines [18]. Cinnarizine is an anti-histamine used to treat tinnitus, however, the use of high doses of cinnarizine causes vasodilation. In addition to pharmacological treatments, phytotherapy may be used to treat tinnitus.

Despite recent developments in modern medicine, there are still no standard treatments for hearing loss. These disorders have fueled research to discover new therapeutic approaches. In this regard, there has been a renewed interest in the approaches of traditional medicine and phytotherapy. Medicinal plants and their derivatives have been studied using scientific approaches in vitro, in vivo, and ultimately in clinical trials so that more efficient therapeutic approaches and drugs can be discovered [19-26]. Indeed, in any region across the world, local people use different medicinal plants and approaches to treat diseases, most of which have not yet been scientifically investigated and confirmed [27-39]. Because ethnobotanical evidence is mostly unwritten or has been reported in textbooks only in the language of a specific country, researchers abroad do not have access to such information and cannot be aware of newly identified drugs. It is important to publicize this valuable information to identify and review the traditional uses of medicinal plants in different regions of the world to prevent and treat several diseases. This can help researchers discover new therapeutic approaches and develop more effective drugs. This review was conducted to report medicinal plants occurring in different regions of Iran and used for ear disorders (especially earache and tinnitus) in this country with reference to articles on ethnobotany and textbooks on Iranian traditional medicine and herbal drugs.

Material and Methods

Scientific databases Directory of Open Access Journals (DOAJ), Google Scholar, PubMed, LISTA (EBSCO), Embase, and Web of Science were searched using relevant search terms to retrieve eligible publications on traditional medicine and medicinal plants to treat ear diseases. In addition, a library search was conducted to examine less widely accessible textbooks on Iranian traditional medicine and medicinal plants to collect relevant evidence.

Results and Discussion

According to this review, it was established that the people in Khorasan, Kerman, Hormozgan, Fars, Kohghiluyeh va BoyerAhmad, Kermanshah, West Azerbaijan, Semnan, Khuzestan, and Isfahan provinces regularly used medicinal plants to treatment earache and tinnitus in Iran. The study revealed that species belonging to sixteen families were used for the treatment of earache and tinnitus in Iran by the people of these provinces (Tables 1 and 2). The data also showed that the members of families Asteraceae and Lamiaceae were the most commonly used plants to treat earache. Four medical plants consisting of Panax ginseng, Melissa officinalis, Allium cepa, and Ginkgo biloba (Table 2) were frequently reported to be used for the treatment of tinnitus by the people of different regions of Iran. Leaves were the most frequently used parts of the plants, including herbal preparations, followed by the flower and roots, fruits, and seeds. Boiling the plant was the most commonly used method of preparation to use these plants to treat earache and tinnitus [40-50].

Table 1. The list of medicinal plants used to treat earache in Iran.

Table 2. The list of medicinal plants used to treat tinnitus in Iran.

Our library search showed that Iranian’s use certain plants, according to traditional medicine, to treat earache and tinnitus. For example, Calendula officinalis or Calendula persica is used as an independent preparation to treat earache in Iran. Origanum majorana is dissolved in olive oil and Carum carvi juice and the resulting solution is used to treat earache. Pulverized olive leaf is mixed with honey and is applied into the ear, as an ointment, to treat ear infection [51,52]. Allium sativum can exert therapeutic effects on otitis media. To achieve this purpose, Allium sativum wrapped up in a small piece of clean cloth is applied into the ear to relieve otitis media. To reduce tinnitus, Amygdalus communis oil is dropped, alongside Matricaria recutita juice, into the ear. To reduce tinnitus, first, Origanum majorana is boiled and then its juice is mixed with olive oil; the resulting solution is poured into the ear. Allium cepa juice is dropped into the ear to reduce tinnitus [51-53].

In Iran, people use various medicinal plants for the prevention and treatment of earache and tinnitus. However, the effects of most of these plants have not been investigated and confirmed in animal models and clinical trials. In other regions of the world, especially in East Asia, some medicinal plants are used for the treatment of hearing disorders and their effects have been investigated. For example, Gushen Pianas a Chinese medicinal herb is effective in the treatment of sensorineural deafness and tinnitus. Zhai et al. indicated that the effect of Gushen Pianis is due to splenonephric hypofunction and phlegm-accumulation stasis [54]. Radix astragali has been used for the treatment of deafness for hundreds of years in Chinese medicine history. The investigators have shown that R. astragali can effectively reduce cisplatin ototoxicity through inhibiting apoptosis of hair cells [55]. In addition, R. astralgi reduces the acoustic trauma by inhibiting the down-regulation of cx26, and Potassium Voltage-Gated Channel Subfamily Q Member 1 (KCNQ1) through inhibiting ROS production [56]. Reactive oxygen species (ROS) are produced when the ear is under pathological condition. ROS are negative regulators of gap-junction channels such as cx26, reducing intercellular coupling in many systems. Noise-induced hearing loss was reported to be associated with inhibition of cx26 and KCNQ1 by increasing ROS production. R. astralgi can also effectively reduce cisplatin ototoxicity through the inhibition of apoptosis of hair cells [56,57]. In addition, the potential protective effects of astragalosides have been demonstrated against cisplatin-induced oxidative stress in the guinea pig cochlea. Astragaloside IV inhibited the activity of inducible nitric oxide synthase (iNOS) and nitrotyrosine in the cochlea exposed to impulse noise, leading to decrease in outer hair cells (OHCs) with stereocilia loss and minor auditory brainstem response (ABR) threshold shifts [58]. Astragaloside IV can inhibit iNOS to protect the ear from the impulse noise. Another possible mechanism is that astragaloside IV directly scavenges ROS [59]. In addition, astragaloside IV can decrease noise induced hearing loss (NIHL) by inhibiting the apoptosis of cochlear cells through the suppression of ROS [58]. It was also reported that carboxy alkyl esters of Uncaria tomentosa can induce otoprotection by increasing potential antioxidant activities [60]. A study indicated that Korean red ginseng (KRG) ameliorated acute 3-nitropropionic acidinduced cochlear damage in mice. In an animal model of acute cochlear dysfunction induced by intratympanic administration of 3-NP, the hearing impairment was found to be dose-dependent, and that functional changes were well matched with the histological changes. KRG ameliorates the cochlear damage induced by 3-NP in the acute stage through suppression of degeneration of fibrocytes in lateral walls and spiral ganglion cells [61]. A clinical trial in Japan indicated that Wu-Ling-Sanas, a popular anti-lithic chinese herbal formula, in combination with an oral steroid was significantly more effective than the diuretic alone, Wu-Lin-San alone, or the steroiddiuretic combination [62].

Conclusion

In Iran, medicinal plants and herbal drugs are more popular among people because they are cheap with fewer side effects compared with synthesis drugs, but when the patients go to clinics for their diseases, physicians prescribe the synthesis drugs for the diseases such as earache and tinnitus because their effects have been confirmed scientifically and their therapeutic responses work quickly. This study has shown the important role of Iranian medicinal plants in the treatment of earache and tinnitus in some regions of Iran. Phytochemical and pharmacological studies with such plants are needed to confirm their anti-earache and tinnitus activities. The use of medicinal plants and their derivatives results in reduction in the overall prevalence of earache probably due to inhibition of ROS production, and iNOS and antiinflammatory activities. Thus, the extract of the above mentioned plants, or their purified derivatives, are valuable extracts to be considered in the treatment of earache and tinnitus, and should be investigated more extensively in clinical trials.

Conflict of interest

We declare that there is no any conflict of interests for this publication.

Ethical consideration

Ethical issues (including plagiarism, data fabrication, double publication) have been completely observed by the authors.

Funding/Support

None

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