Truong, Pham-Quynh-Huong
(2023)
A comparison of capsaicin and menthol as trigeminal modulators of salivary composition for use in oral care applications.
MRes thesis, University of Nottingham.
Abstract
Part A:
The human oral cavity contains 700 types of bacteria. Gram-negative anaerobe bacteria are associated biofilm formation and oral malodour due to their abundance and metabolism producing volatile sulfur compounds. Human saliva contains Mucin, Proline-Rich Proteins (PRPs), Alpha-Amylase (α-Amylase), Cystatins, Histatins, and Statherin, which contribute to lubricate mouth, protect mucosal integrity and against microorganisms, and digest food. Due to their ability to stimulate the saliva and also have antibacterial activities. In this review, we investigate how menthol and capsaicin affect the salivary flow, oral protein composition, and also their effect on these oral bacteria. Following the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, we conducted a literature search using Google Scholar from 1980 to 2023 in English form. The search query was based on the question "How do trigeminal modulators including capsaicin and menthol affect salivary flow, salivary protein composition, and oral microbiomes?" A total of twenty-seven articles were selected for analysis. The results showed that capsaicin still increased the saliva flow at 1 ppm, 5 ppm, 0.005M, 3x10-5M, and 0.3nM concentrations after the first minute of stimulation and then decreased after two minutes. In contrast, menthol did not change the saliva flow at 0.05M and 250 ppm doses and slightly changed the flow at 500 ppm only during the first minute. Regarding protein composition and its changes, MUC5B (above 188kDa), MUC7 (~150kDa), α-Amylase (50-60kDa), PRPs (40-50kDa), Cystatin (~14kDa), Statherin (~6kDa) were identified on 12% SDS-PAGE. Menthol did not increase protein content at 250 ppm and 0.05M whereas 500 ppm menthol increased slightly protein content and significantly increased cystatin S (P < 0.05). Capsaicin slightly increased protein content and significantly increased protein compositions, except MUC5B at 1 ppm and 0.05M. Regarding antibacterial activity measured by MBC and MIC methods, menthol decreased the growth of Bacteroides, P. gingivalis, and F. nucleatum, while capsaicin also decreased the abundance of Bacteroides, P. gingivalis and increased Bacteroides. In conclusion, based on their characteristics, menthol and capsaicin at some concentrations are potential ingredients for oral care applications.
Part B:
Menthol and capsaicin, derived from peppermint and chili, exhibit bioactive attributes that could enhance oral antibacterial defences and alleviate halitosis. This study examined the effect of menthol and capsaicin on the properties of the oral cavity such as their effect on bacterial growth (mainly Bacteroides, Prevotella, Lactobacillus, Streptococcus spp), saliva flow rate, interactions with salivary proteins and oral malodour. Employing viable cell counts, SDS-PAGE, AUC, GC-MS, the effect of menthol and capsaicin on the saliva properties of a healthy woman was investigated. Generally, capsaicin exerted a stronger effect than menthol. Although not statistically significant within the sample population, both menthol and capsaicin reduced bacterial counts and odour compounds, with some exceptions in-vivo. However, capsaicin exhibited no significant odour compound reduction in the in-vitro experiment. Both menthol and capsaicin increased saliva flow rates and altered the salivary protein composition. Interestingly, menthol prompted a significant salivary secretion within the initial two-minute, whereas capsaicin significantly continued to build up the saliva flow during the 10-minute experimental time. SDS-PAGE revealed five main salivary proteins, corresponding to MUC(s) (above 188kDa), MUC7 (150kDa), α-Amylase (50-62kDa), PRPs (16-50kDa), and Cystatin (10-14kDa). SV-AUC highlighted two distinct populations at ~1.8S and ~4.2S, correlating with previous reports. Although the analysis indicated no significant differences in the total salivary concentration, some lower molecular weight compounds such as PRPs and Cystatins were significantly affected upon stimulation with the two trigeminal compounds (P > 0.05). A thorough clinical trial would therefore be recommended to confirm the effects observed in this proof of concept study.
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