Is oxidative stress involved in the hepatic inflammatory response to apical periodontitis? A comparative study in normal and hyperlipidaemic rat.

AIM: The aim of the study was to explore the involvement of oxidative stress (OS) in the hepatic inflammation induced by apical periodontitis (AP). Periapical, systemic and hepatic reaction to AP under hyperlipidaemia was also investigated.

METHODOLOGY: A total of 16 male Sprague-Dawley rats were fed with a hyperlipidaemic diet (HD) whereas another 16 rats with a normal diet (ND). After 9 weeks, the first molars of the right maxilla and mandible of 8 HD and 8 ND rats were exposed to induce AP (ND, ND + AP, HD and HD + AP group). After 5 weeks, rats were euthanized, the haematological tissue was collected directly from the heart, and serum levels of inflammatory cytokines were measured. Liver tissue was analysed by haematoxylin-eosin and Masson staining, and reverse transcription-polymerase chain reaction (RT-PCR) was performed to detect mRNA expression of inflammatory cytokines. Serum, periapical, and hepatic OS parameters including total oxidant status (TOS), total antioxidant capacity (TAOC) and oxidative stress index (OSI) were measured by enzyme-linked immunosorbent assay (ELISA). The area of AP lesion in the right maxilla or mandible was radiographically assessed. Student's t-test was performed on the periapical data. A one-way analysis of variance and the Kruskal-Wallis test were analysed for others.

RESULTS

The HD + AP group had a larger AP lesion in the maxilla, compared with the ND + AP group (p < .05). The ND + AP group presented higher serum interleukin (IL)-18, IL-1β, TOS, OSI levels, lower serum TOAC levels, higher hepatic tumour necrosis factor (TNF)-α mRNA expression and higher hepatic TOS, and OSI levels, compared with the ND group (p < .05). The HD + AP group had lower serum IL-4 level, higher serum IL-1β level, and higher hepatic IL-6 and transforming growth factor (TGF) -β1 mRNA expression, compared with the HD group (p < .05).

CONCLUSIONS

Apical periodontitis could activate systemic and liver inflammation by promoting serum IL-18, 1L-1β, TOS and OSI expression, enhancing hepatic TOS and OSI expression and inhibiting serum TOAC expression. AP under hyperlipidaemia led to more profound periapical bone destruction in the maxilla and elicit systemic and liver inflammatory responses through elevating serum levels of IL-1β, descending serum IL-4 level and improving hepatic IL-6 and TGF-β1 expression.