POTENTIAL OF HERBAL MEDICINE IN ASIA FOR ORAL CANDIDIASIS THERAPY: A SYSTEMATIC REVIEW

The objective of this review was to provide antifungal recommendations for Oral Candidiasis (OC) derived from herbal medicine based on the research results of the last 5 y. This systematic review was conducted according to Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines using the PubMed and Science Direct databases with studies published between 2016 and 2021. The review was conducted on 13 studies, in vitro and clinical trial. A total of 41 species of plants have studied its antifungal effects on Candida albicans. The Minimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (MFC) varied in the range of 0.098 µl/ml to 125 µl/ml for different types of plants and Candida samples, while the mean inhibition zone (ZOI) was 11 mm. The most recommended herbal medicine for the development of antifungal drugs for oral candidiasis therapy were Nigella sativa, Lawsonia inermis, and Zingiber officinale.


INTRODUCTION
Oral candidiasis (OC), commonly referred to as "thrush" includes infections of the tongue and other oral mucosal sites and is characterized by fungal overgrowth that invades the superficial tissues. C. albicans is the main causative agent of OC, accounting for up to 95% of cases. The tongue dorsum is the initiation point of infection for the majority of the clinical forms of OC. Predisposing factors for candidiasis are the use of broad-spectrum antibiotics, immunosuppressive agents, installation of medical devices and Nasogastric tube (NGT), as well as decreased immunity related to human immunodeficiency virus (HIV) infection [1].
The pharmacological treatment of candidiasis can be distinguished between topical or systemic antifungal [2]. Antifungal agents comprise three main classes: polyenes, azoles, and echinocandins [1]. More than 200 polyene antifungals have been discovered, some of which are most commonly used in antifungal therapy, such as amphotericin B, nystatin, and natamycin. Polyenes were the first broad-spectrum antifungal drugs on the market and still used to treat a variety of fungal infections after 70 y [3]. The side effects of polyene antifungals are high toxicity, including fever, nausea and vomiting, nephrotoxicity, liver toxicity, and interactions with coadministered drugs. Another crucial problem is the increasing drug resistance that invalidates the clinical treatments [4].
Some of the side effects of existing antifungal agents and the need for cost-effective treatments to manage oral candidiasis have prompted the search for new alternatives in this field. Natural agents have emerged as sources of bioactive molecules with potential therapeutic applications in the medical and dental fields in recent years. Among them, plant extracts are considered a group of natural compounds that are highly desirable in the prevention and treatment of oral candidiasis [5]. Many studies have shown that plant extracts such as Coriandrum sativum [5], Hypericum hircinum [4], Chrysobalanus icaco [6], Ononis spinosa [7], Ricinus communis [8], and Gymnema sylvestre [9] have the potential as antifungal and inhibit the growth of Candida albicans. Medicinal plant extracts and selected active fractions have been investigated and have low cytotoxicity in human cells [5].
The large number of plant species that tested for antifungal activity in previous studies make it difficult to obtain an overview of the subject and their interpretation. In this context, the authors aimed to perform a systematic review of the literature on in vitro studies and clinical trials of medicinal plants that have anti-Candida potential, based on the research conducted in the last 5 y. Clinically, this systematic review aims to provide antifungal recommendations for OC derived from herbal medicine.

Method
This systematic review was carried out in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines [10]. The themes in this study were arranged according to Population, Intervention, Comparison, and Outcome (PICO) [11]  , and keywords used in the Science Direct database was: (("oral candidiasis") AND ("herbal medicine" OR "plant medicine")). Another inclusion criteria was medicinal plants in Asia which were adapted from the purpose of this systematic review.
Articles were initially screened based on the title and abstract according to the scope. A manual hand-searching of the reference lists of relevant studies was also performed. The quality of the research methodology of the selected articles was assessed for risk of bias using "Risk of Bias Assessment of Non-randomized Studies (RoBANS)" tools [12]. RoBANS was chosen because it is most suitable for assessing the quality of non-randomized studies and observational studies. Furthermore, all articles that are judged to be of good quality are reviewed with thematic analysis, which is grouped by theme according to the purpose of writing. In terms of  Fig. 1 shows a complete process flowchart of article identification, screening, and eligibility assessment according to the inclusion criteria that have been determined. A total of 568 articles were obtained from the database Medline via PubMed and 412 articles from the database Science Direct. A total of 555 articles from Medline via PubMed and 410 articles from ScienceDirect were excluded because they did not meet the inclusion criteria using the filters in the database system. One of the 13 articles is known to be a duplication so that it is removed and remains 12 articles. Then we obtained another 1 article with manual hand searching, so the total articles that will be reviewed qualitatively are 13 articles.

Fig. 1: Flowchart of the systematic article search process with PRISMA guidelines [10]
Assessment of the risk of bias for selected articles was performed using RoBANS. There are 6 assessment points as shown in table 1. The risk of bias assessment shows that all of these articles have a low risk of bias or have a high quality, so they can be reviewed systematically.
Candida albicans were used in the in vitro studies using ATCC 10231 in 5 studies, whilst ATCC 66027, SC 5314, and ATCC 14053 each in 1 study. ATCC and SC cell cultures are easy to control as desired by environmental physicochemistry and inexpensive [26]. In addition, there are 4 in vitro studies using cell cultures taken from the oral mucosa and removable dentures of patients with oral candidiasis. This clinical trial study was followed by 22 patients with a diagnosis of denture stomatitis and 11 patients given conventional therapy as positive controls. Nigella sativa is the most tested plant, which is commonly found in South and Southwest Asia. The part of the plant used is the seeds which are commonly called black cumin seeds. The extract has been explored and had antifungal properties. Thymoquinone is the main ingredient in N. sativa, which is a monoterpenoid [18,19,23]. The mechanism of action of monoterpenoids on N. sativa inhibit calcineurin signaling, affect cell surface integrity (cell walls and cell membranes), yeast to hyphae transition, biofilm formation, cell cycle arrest in S phase and mitochondrial dysfunction [27].
Other active plant compounds are phenolic compounds contained in Lawsonia inermis [17,21], and Zingiber officinale [15,21]. Phenolic compounds act by damaging cell walls, inhibiting the isocitrate lyase enzyme activity, disrupting plasma membrane dimorphism inhibition, in vitro immunoregulatory, effect on monocytes against C. albicans and against biofilms [28]. The mechanism of action of these polyphenol compounds and monoterpenoids is similar to the mechanism of action of Nystatin which has been established in the treatment of Oral candidiasis. Nystatin induces membrane permeability by forming complexes with ergosterol located in fungal membranes, leading to intracellular leakage and cell death [3].
Of all the articles reviewed, there were several plants that were of concern to the author. There were 3 articles that explored the potential of the Nigella sativa plant. The in vitro study of Nigella sativa plants showed that it can prevent the adhesion of Candida albicans and have a good antifungal potency [18,19,23]. In addition, there are also two studies conducted on Lawsonia inermis (henna nail) plant. The inhibition of L. inermis against C. albicans was very good with ZOI of 15±0.5 mm and 10±0.22 mm [17,21]. Finally, there were also two articles that discussed the antifungal potential of Zingiber officinale (ginger). It also said it has good inhibition and anti-biofilm formation activities against C. albicans with the MIC of 0.625 ml/ml and ZOI of 16±0.12 mm [2,21]. Apart to these three plants, each of the other plants was only carried out once, or did not have good antifungal activity. The secondary metabolites that play a role in the antifungal activity of these plants are monoterpenoids and/or polyphenolic/phenolic compounds. So that these three plants, Nigella sativa, Lawsonia inermis, and Zingiber officinale, are recommended to be researched by using clinical trial design as an antifungal alternative for oral candidiasis therapy.

CONCLUSION
The most recommended herbal medicine for the development of antifungal drugs for Oral candidiasis therapy were Nigella sativa, Lawsonia inermis, and Zingiber officinale.