Upregulation of cannabinoid receptor gene expression in oral tissues subjected to hyposalivation and periodontitis

Abstract

Cannabinoid receptors (CBr) 1 and 2 (CB1r and CB2r) are present in periodontal tissues and salivary glands and play a significant role in the pathogenesis of oral diseases. Aim: To study the gene expression of CB1r and CB2r in gingival tissue and submandibular glands (SMG) of rats subjected to experimental periodontitis (EP) and/or hyposalivation (H), and discuss their possible implication in oral health. Material and methods: Rats were divided into controls, rats with EP induced by application of lipopolysaccharide (1 mg/ml), rats with H induced by bilateral submandibulectomy, and rats with both EP and H. Alveolar bone loss was measured with a digital caliper, mRNA expression of CBr and bone parameters were determined by endpoint RT-PCR, PGE₂ glandular content was assessed by radioimmunoassay, and stimulated salivary secretion was collected and weighed. Results: CB1r and CB2r mRNA in gingival tissue were upregulated in groups EP, H and EP+H as compared  to controls (CB1r (AU): C 0.27±0.06^A, EP 0.46±0.05^B, H 0.51±0.08^B, EP+H 0,49±0,1^B; CB2r (AU): C 0.38±0.04^A, EP 1.22±0.08^B, H 0.98±0.06^C, EP+H 1,041±0,1^BC). Groups EP, H and EP+H showed alveolar bone loss as opposed to controls, while only groups EP and EP+H evidenced RANKL/OPG imbalance measured in the dental attachment tissue. Likewise, CB1r and CB2r mRNA in SMG showed upregulation in group EP as compared to controls (CB1r (AU): C 0.52±0.09A, EP 0.95±0.13B; CB2 (AU): C 0.23±0.12^A, EP 1.48±0.22^B). In group EP, salivary secretion was lower and the content of PGE2 (inhibitory mediator of said function) was higher than in controls. Conclusion: The upregulation of CB2r in oral tissues under the pathophysiological conditions studied suggests that they participate actively in the response to oral diseases.