Candidosis management:antifungal, cytotoxic andimmunomodulatory properties of tea treeoil and its derivative components

QR Microbiology;RK Dentistry

Milligan, Steven George ; Ramage, Gordon

University:University of Glasgow

Department:School of Medicine, Dentistry & Nursing

关键词: tea tree oil, terpinen-4-ol, oral candidosis, antifungal, cytotoxicity, immunomodulation, candida biofilm;   

Others  :  http://theses.gla.ac.uk/2282/1/2010milliganmsc.pdf

来源: University of Glasgow

【 摘 要 】

Oropharyngeal candidosis (OPC) is a common opportunistic yeast infection inelderly and immuno-compromised populations, caused by Candida albicans andother Candida spp. forming biofilms on the oral epithelium or artificial denturesurfaces. Oral thrush (pseudomembranous candidosis) is the most common typeof OPC occurring when a biofilm grows on oral mucosal surfaces, while growthon dentures commonly causes denture stomatitis in denture-wearers. OPCcauses significant morbidity with symptoms including inflammation, pain, burning,eating difficulties and alteration of taste sensation. Conventional antifungaltreatments have limited success due to biofilm resistance mechanisms, withrecurring infections promoting development of azole resistance. Other problemswith current antifungal drugs include toxicity, drug interactions and unpleasanttaste. Therefore, alternative methods for prophylactic or therapeutic managementof Candida spp. biofilms are desirable.This study aimed firstly to evaluate the efficacy of tea tree oil (TTO) and itsderivatives against biofilms formed by a clinically-diverse panel of C. albicansisolates; and secondly to assess the toxicological effects of TTO exposure usinga clinically relevant oral cell line. Thirdly, this study aimed to further investigatepreviously reported anti-inflammatory effects of TTO.TTO is a complex mixture of essential oils; however, individual components ofTTO are commercially available. TTO has broad spectrum antimicrobial activityand TTO oral products are currently available. However, evidence for antifungalefficacy is limited and there are concerns regarding safety of long-term use ofTTO products.The data presented demonstrate TTO and its derivatives are effective antifungalagents. Minimal inhibitory concentrations (MIC) of TTO and seven componentswere determined for planktonic C. albicans cells (PMIC) using the standard CLSIdilution technique. The PMIC50 value for TTO was 0.5%, with lower values for twocomponents - 0.25% for both terpinen-4-ol (T4-ol) and α-terpineol. Growth of all100 strains was inhibited by 1% TTO, 0.5% terpinen-4-ol and 0.5% α-terpineol. Apilot study found no decrease in TTO sensitivity with multiple TTO exposure.Sessile susceptibilities (SMFC) were determined using a metabolic assay onC. albicans cells after 24 h treatment of pre-formed biofilms, to determine themost effective anti-biofilm components. T4-ol and α-terpineol were potent biofilminhibitors, which could inhibit biofilm metabolism by 50% at PMIC50concentrations (SMFC50 = 0.25%), exhibiting significantly greater anti-biofilmactivity than TTO (SMFC50 = 1%). Strains isolated from different patient groupshad similar biofilm susceptibilities. Other components tested had little effect onbiofilm metabolism (SMFC50 of 2% to >4%). Shorter treatments modelling a‘mouthwash’ exposure time produced moderate inhibition (50%) of pre-formedbiofilm metabolism after 2 min in 1% α-terpineol, while longer exposures with 1%T4-ol (15 min) and 2% TTO (60 min) were required to give this level of inhibition.A time-dependent treatment effect for TTO and the single components was alsoseen at these concentrations, with longer exposures giving better inhibition ofbiofilm metabolism.Inhibition of biofilm formation and morphogenesis was also investigated to defineeffective components, concentrations and exposure times for prophylactic use.Presence of TTO, T4-ol or α-terpineol could prevent morphogenesis ofC. albicans, and therefore block biofilm formation, if present within 2 hours ofadherence of cells to a surface. One hour treatments with PMIC50 levels of TTO(0.5%) or the 2 components (0.25%) could effectively prevent biofilm formation.Pre-coating a plastic well with 1% TTO prior to inoculation resulted in stronginhibition (>50%) of biofilm formation.Cellular cytotoxicity studies demonstrated that antifungal concentrations of TTOand T4-ol were cytotoxic to human cells in vitro. Investigations using a humanoral epithelial cell line (OKF6-TERT2) and primary oral fibroblasts indicated that 2min exposures to TTO and T4-ol showed cytotoxic effects at 0.25%, comparablewith 0.12% chlorhexidine, with 0.125% TTO / T4-ol being non-toxic. Previouslyreported immunomodulatory effects were investigated using non-toxicconcentrations of TTO / T4-ol (0.125%). The cytokine response of oral epithelialcells following TTO / T4-ol treatment was monitored using quantitative PCR,protein arrays and an IL-8 ELISA. TTO did not exhibit any clearimmunomodulatory effects, but T4-ol pre-treatment of zymosan-activated cellsresulted in reduced IL-8 protein in ELISA assays, indicating a potential to reduceinflammation. Although inflammation is a major symptom of OPC infections, it isalso an important part of the host response to control the yeast pathogen. Ananti-inflammatory agent may help to control candidosis symptoms, but may causeproblems in controlling the infection.These studies demonstrate that T4-ol could be suitable for use in prophylacticoral hygiene products such as mouthrinses and denture cleansers, and also as anovel treatment for established OPC infections. The use of T4-ol, a singlecomponent from TTO, has advantages over the complete essential oil in terms ofproduct safety and consistency. Preclinical and clinical trials of mouthwashes ordenture cleansers, containing the range of T4-ol concentrations (0.125 - 0.5%)investigated in these studies, would be required to validate the clinical use ofsuch a product.In conclusion, TTO-derived mouthwashes and denture cleansers may offer botha suitable alternative to conventional azole treatment of OPC and also a safeprophylactic alternative for inhibiting microbial biofilms, as they exhibit potentantifungal activity.