Oral treatment with SRP299 (killed Mycobacterium vaccae) inhibits experimental periodontal disease in Wistar rats

Objective: Mycobacterium vaccae injected subcutaneously was previously shown to prevent and treat ligature-induced periodontal disease (PD) in Wistar rats (Breivik & Rook 2000, 2002). Since mycobacteria are readily taken up via Peyer's patches in the intestine, we have now tested the ability of oral SRP299 (killed M. vaccae) to prevent ligature-enhanced PD in Wistar rats, and to modulate the accompanying cytokine and corticosterone responses. Material and Methods: A single oral dose of SRP299 (1 mg) was given 14 days before the application of ligatures. PD was assessed when the ligatures had been in place for 56 days. Results: Oral SRP299 reduced bone loss (p=0.036, X-ray; p=0.061, histometry) and fibre loss, both on the ligatured (p=0.0047) and control (p=0.005) sides, and also reduced the level of TNF-alpha (p=0.0137) and corticosterone (p=0.048) induced by intraperitoneal endotoxin lipopolysaccharide (LPS). Conclusions: SRP299 administered by the oral route diminishes ligature-induced bone and fibre loss in this model. This effect may be attributable to the known ability of SRP299 to evoke regulatory T cells, although the mechanism could not be investigated in this study. Treated rats also had less excitable hypothalamo-pituitary-adrenal (HPA) axes. HPA axis overactivity is a known risk factor in human PD. Trials of SRP299 in human PD are now justified.