Oropharyngeal candidiasis is a serious clinical dilemma within the immunosuppressed and elderly population, commonly caused by Candida albicans species. The ability of C. albicans to infect the epithelial cells is mediated by the dimorphic switching to virulent hyphae form while expressing different virulence patterns to facilitates cell invasion. The cellular immune response to Candida infection is mediated by toll-like receptors, which signals the recruitment of neutrophils to the infection site by the release of chemokines/cytokines (IL-8/IL-6). Current research suggests that the non-neurogenic cholinergic system has an immune regulating/antibiofilm functions facilitated by muscarinic receptors found on epithelial keratinocytes and Candida species, respectively. This study aimed firstly to evaluate the immune modulating effect of a general muscarinic receptor agonist, pilocarpine hydrochloride (PHCL) against C. albicans infection, using TR146 cell lines as an in vitro model of oral epithelium. Secondly, to determine the antibiofilm/antimetabolic effect of PHCL on 22 clinical Candida isolates.
Three concentrations of PHCL (1 mM, 5 mM, and 25 mM) with/without C. albicans (SC5315) were used to treat monolayers of epithelial cells (TR146) in two-time intervals (4h and 24h). Enzyme-linked immunosorbent assay and real-time PCR were used to determine the effect of C. albicans and PHCL on expression of Interleukin-6 and interleukin-8 by TR146 epithelial cells. The antibiofilm and antimetabolic effects of 25 mM PHCL on 22 clinical Candida isolates after 24 h were determined using crystal violet and XTT assays, respectively.
A dose-dependent inhibition of IL-6 and IL-8 expression occurred in cells stimulated with C. albicans and PHCL. PHCL at 25 mM induced a significant reduction in the biofilm biomass of most of the clinical Candida isolates after treatment, while induced a significant metabolic inhibitory effect against high biofilm forming isolates only compared to control.
In conclusion, PHCL represents a promising therapeutic alternative to conventional antifungals. However, further studies should consider the role of each muscarinic receptor for a more selective antifungal effect.