Effect of probiotic root canal irrigation on macrophage polarization in rat periapical lesions

The aim of this study was to evaluate the effect of the probiotic Bifidobacterium animalis subsp. lactis HN019 as a root canal irrigant on the polarization of macrophages into M1 and M2 subtypes in periapical lesions induced in rats, using immunohistochemical analysis. Forty-eight adult male Wistar Hannover rats were divided into six groups: Group I (4 animals/8 teeth): sound teeth; Group II (4 animals/4 teeth): 2.5% sodium hypochlorite as the irrigation solution (3 days); Group III (4 animals/4 teeth): probiotic solution as the irrigant (3 days); Group IV (12 animals/24 teeth per period): periapical lesions without irrigation (7, 21, and 42 days); Group V (12 animals/24 teeth per period): 2.5% sodium hypochlorite irrigation (7, 21, and 42 days); Group VI (12 animals/24 teeth per period): probiotic irrigation (7, 21, and 42 days). The animals were euthanized following the experimental periods. Immunohistochemical analysis was performed using NOS2 and CD163 markers for the M1 and M2 subtypes, respectively. The findings showed no significant differences in NOS2 and CD163 expression across the experimental periods (3, 7, 21, and 42 days) or between the irrigated groups, except at 42 days, when NOS2 expression was higher in the probiotic-treated group than in the control group. The probiotic Bifidobacterium animalis subsp. lactis HN019 demonstrated the potential to modulate the immune-inflammatory response in periapical lesions by increasing NOS2 expression 42 days after pulp exposure.