Histamine metabolism and transport are deranged in human keratinocytes in oral lichen planus.

BACKGROUND: Recent reports have indicated that nonimmune cells can produce low concentrations of histamine. This observation, together with the discovery of the high-affinity histamine H4 receptor (H4 R), has added additional layers of complexity to our understanding of histamine signalling. Human oral keratinocytes (HOKs) possess a uniform H4 R pattern, which is deranged in oral lichen planus (OLP). OBJECTIVES: To investigate histamine metabolism and transport in HOKs of healthy controls and patients with OLP. METHODS: Tissue sections and cultured primary HOKs were studied using immunostaining, quantitative real-time polymerase chain reaction and confocal microscopy. Histamine levels were analysed using high-performance liquid chromatography. RESULTS: l-histidine decarboxylase (HDC) and organic cation transporter (OCT)3 were increased in mRNA and protein levels in patients with OLP compared with controls. In contrast, histamine N-methyltransferase (HNMT) immunoreactivity was decreased in OLP. OCT1/OCT2 and diamine oxidase were not detectable in either tissue sections or in HOKs. Immunolocalization of HDC and OCT3 in HOKs revealed moderate-to-high expression within cytoplasm and cell boundaries. Stimulation with lipopolysaccharide (LPS) or interferon-γ upregulated HDC-gene transcript in HOKs, whereas this was downregulated with high histamine concentration and tumour necrosis factor-α. LPS induced a dose-dependent release of low histamine in HOKs, while high histamine concentration downregulated epithelial adhesion proteins. CONCLUSIONS: HOKs are histamine-producing cells. They release histamine via OCT3 channels in concentrations too low to activate the classical low-affinity H1 R and H2 R, but high enough to stimulate the high-affinity H4 R in autocrine and paracrine modes. The substantially deranged histamine metabolism and transport in OLP could, in part, contribute to the disease pathogenesis.

Infection and apoptosis associated with inflammation in periodontitis: An immunohistologic study.

OBJECTIVE: Evidence of increased apoptosis is observed in periodontitis and may be associated with destruction of the periodontal tissue caused by the increased cell death, with the release of danger signals and subsequent stimulation of the proinflammatory processes. However, the exact mechanisms associated with these processes remain unclear. This study aimed to investigate the presence of the periodontal pathogen Treponema denticola, apoptosis, high mobility group box 1 as a damage-associated molecular pattern, and several inflammatory markers in periodontitis and gingivitis subjects. MATERIALS AND METHODS: Soft tissue specimens from gingival tissues of periodontitis and gingivitis patients were used for immunohistochemical and immunofluorescence staining of T. denticola chymotrypsin-like proteinase (CTLP), apoptosis markers, high mobility group box 1, Toll-like receptor 4, inflammatory cell markers, and proinflammatory cytokines. RESULTS: Treponema denticola was detected in all periodontitis-affected tissues. This was associated with a significant increase in the number of apoptotic cells, including macrophages, alterations in the expression of high mobility group box 1 and its receptor, and increased levels of proinflammatory cytokines compared with gingivitis. CONCLUSIONS: In summary, the presence of T. denticola (especially its CTLP), apoptosis, high mobility group box 1, and inflammatory markers suggests their potential involvement in the pathogenesis of periodontitis.