DISTINCT AND INTERACTIVE EFFECTS OF LIPOPOLYSACCHARIDES FROM PORPHYROMONAS GINGIVALIS AND ESCHERICHIA COLI ON MOUSE NOVELTY-INDUCED HYPERLOCOMOTION, BLOOD CYTOKINE LEVELS AND TLR4-RELATED PROCESSES

Abstract Background Lipopolysaccharide (LPS), a constituent of the Gram-negative bacterial cell wall, activates Toll-like receptors (TLRs). Porphyromonas gingivalis (Pg) is implicated in the progression of periodontal disease. When mice are exposed to a novel environment they exhibit hyperlocomotion, which can be inhibited by the systemic administration of LPS derived from Escherichia coli (Ec-LPS). However, it remains unknown whether Pg-LPS affects novelty-induced locomotion. Aims & Objectives We conducted an open field test to assess the effects of Pg-LPS and compared them to those of Ec-LPS. We also investigated the influence of systemic Pg-LPS and Ec-LPS administration on blood IL-6, TNF-alpha and IL-10 levels, as they may be involved in changes in locomotion. We used the TLR4 antagonist TAK-242 to examine TLR4 involvement. Given the potential of Pg-LPS to block TLR4 in vitro, we analysed its effects on Ec-LPS-induced behavioural and biochemical changes. Methods Male ddY mice weighing 20-25 g were used. Compounds were administered intraperitoneally. In the open field test, each mouse underwent habituation in a sawdust-covered plastic cage before being transferred to a larger Plexiglas box without sawdust. Locomotion in the novel environment was recorded via video and total distance traveled was determined automatically. We also assessed exploration of the central vs peripheral zones as an index of anxiety potentially induced by systemic LPS administration. For the measurement of blood cytokine levels, blood samples were obtained from the submandibular vein using a disposable lancet. Approximately 0.5 ml of blood was rapidly collected without total anaesthesia. Serum IL-6, TNF-alpha and IL-10 levels were quantified with bead-based Multi-Plex kits. Results Ec-LPS at 840 µg/kg, but not Pg-LPS at 100, 500 or 840 µg/kg, suppressed novelty-induced locomotion and this effect was blocked by TAK-242 (3.0 mg/kg). Ec-LPS treatment inhibited locomotion in both the central and peripheral zones of the open field. Ec-LPS elevated blood IL- 6 and IL-10 levels, an effect that was antagonised by TAK-242 (3.0 mg/kg), while TNF-alpha levels were unaffected. Pg-LPS at 100, 500, and 840 µg/kg did not alter blood IL-6, TNF-alpha or IL-10 levels. Additionally, Pg-LPS at 500 µg/kg inhibited the Ec-LPS-induced increase in blood IL-10 levels but had no effect on IL-6 or TNF-alpha levels. Discussion & Conclusion These results suggest that TLR4 stimulation mediates the inhibition of novel environment-induced locomotion in mice following systemic administration of Ec-LPS, while also increasing blood IL-6 and IL-10 levels. In contrast, Pg-LPS did not produce these effects. This study provides in vivo evidence that Pg-LPS can inhibit TLR4-mediated increases in blood IL-10 levels. Ec-LPS- induced inhibition of novelty-induced locomotor activity in mice is likely mediated by increases in blood IL-6 rather than TNF-alpha or IL-10. This conclusion is supported by the observation that TAK-242, but not Pg-LPS, counteracted the effect of Ec-LPS on mouse locomotion, corresponding to changes in blood IL-6 levels.