Microbes and toll-like receptors in oral lichenoid disease and oral squamous cell carcinoma

Peter Rusanen

Research output: ThesisDoctoral ThesisCollection of Articles


Oral lichenoid disease (OLD) encompasses oral lichen planus (OLP) and oral lichenoid lesion (OLL), which are chronic T-cell-mediated mucocutaneus inflammatory disorders of unknown aetiology. Both OLP and OLL are classified as potentially malignant disorders. Although various antigens have been considered, it is not known what triggers the inflammatory response of T-cells. Suggested predisposing factors include stress, genetic factors, trauma, viral, fungal and bacterial infection. Oral squamous cell carcinoma (OSCC) is the most common malignant tumor in the oral cavity. It is a multifactorial disease with no single clearly recognizable cause. Chronic inflammation is one of the most important causes of OSCC. Chronic oral candidiasis has also been associated with oral carcinoma in several studies. It is still debatable whether microbial infections initiate cancer or is the preexisting cancer colonized by microbes secondarily. Acetaldehyde is the first metabolite of ethanol and it is carcinogenic. Acetaldehyde is also produced by microbes and poor oral hygiene increases acetaldehyde production. Recent studies of the oral microbial acetaldehyde production are mainly based on uncultured saliva samples. Saliva and mouth rinse samples are often used for general sampling but do not represent the microbes at a specific lesion or site. Toll-like receptors (TLRs) and nuclear factor-κB (NF-κB) signalling transduction pathway play important roles in the pathogenesis of several chronic inflammatory diseases. Tumour suppressor protein p53 regulates TLR expression. It was not known clearly what the optimal sampling site and method to study the microbial colonisation on mucosal lesions is and what impact specific microbial colonisation has on TLR expression. In addition, the immunohistochemical localisation of all TLRs in OLD was not established. Therefore, the aim of the first study was to investigate how the method and site of microbial sampling affect the discovery of Candida species on OSCC lesions. The objective of the second study was to develop a site-specific sampling method that would give quantitative results for samples from the oral mucosa. The aim of the third study was to explore lesion specific microbes and their ability to produce acetaldehyde in OSCC and OLD patients. Furthermore, the aim of the fourth study was to investigate the immunohistochemical staining and tissue localization of TLR1-10, p53 and NF-kB in mucosal biopsies from patients with OLD. In the first study, four different sampling methods in oral cancer patients were compared for culture of yeasts. In the second study, two site-specific sampling methods, filter paper and swab, were compared for microbiological analyses of the healthy oral mucosa. The filter paper sampling method was developed for the second study. In the third study, microbial samples from OSCC and OLD patients for microbiological analyses and acetaldehyde measurement were obtained using the filter paper sampling method. In the fourth study, oral mucosal biopsies from patients with OLD and from healthy controls were analysed for the expression of TLR1-10, NF-κB and p53 by immunohistochemistry. This work has demonstrated that after cancer treatment, the incidence of Candida albicans was found to be increased and a shift from C. albicans to other Candida species was found. The optimal sampling site for Candida in these patients was found to be the labial sulcus. Moreover, the filter paper sampling method was found to be an ideal technique for obtaining quantitative data from defined areas of the oral mucosa. Based on the filter paper sampling method, it was detected that the bacterial composition on OSCC and OLD lesions differed from that of the healthy appearing contralateral mucosa and from healthy controls. Candida colonization was higher in OSCC and OLD lesions and patients with Candida colonization produced significantly more frequently mutagenic amounts of acetaldehyde. The staining intensity of several TLRs was markedly stronger throughout the epithelium and in the basement membrane zone of OLD samples. Likewise, the staining for NF-κB and p53 were more intense in OLD samples compared to the control samples. We did not find any correlations between the microbial samples and the immunostaining of TLRs. In conclusion, this study showed that the composition of lesional microbes differs on OSCC and OLD lesions compared to the healthy appearing mucosa and to the healthy controls. Furthermore, the composition rather than the number of microbes is a significant factor that influences the production of carcinogenic level of acetaldehyde. Our results indicate that acetaldehyde and Candida colonisation may have an impact on TLR4 expression that may play a role in OSCC pathogenesis. The role of soluble TLR forms in the basement membrane zone calls for further studies.
Original languageEnglish
  • Richardson, Riina, Supervisor, External person
  • Marttila, Emilia, Supervisor
Place of PublicationHelsinki
Print ISBNs978-951-51-5856-7
Electronic ISBNs978-951-51-5857-4
Publication statusPublished - 2020
MoE publication typeG5 Doctoral dissertation (article)

Bibliographical note

M1 - 76 s. + liitteet

Fields of Science

  • Acetaldehyde
  • +microbiology
  • Candida
  • Candida albicans
  • Carcinoma, Squamous Cell
  • Ethanol
  • Lichen Planus, Oral
  • Mouth Mucosa
  • Mouth Neoplasms
  • Biopsy
  • NF-kappa B
  • Saliva
  • Toll-Like Receptors
  • Tumor Suppressor Protein p53
  • Mouth
  • Diagnostic Techniques and Procedures
  • Cigarette Smoking
  • Basement Membrane
  • 313 Dentistry

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